Precambrian geology

Precambrian geology

1. Precambrian GeologyPrecambrian Geology

2. The Precambrian lasted for more than 4 billion The Precambrian lasted for more than 4 billion
years!years!
This large time span is difficult for humans to This large time span is difficult for humans to
comprehendcomprehend
Suppose that a 24-hour clock represented Suppose that a 24-hour clock represented
all 4.6 billion years of geologic timeall 4.6 billion years of geologic time
then the Precambrian would be then the Precambrian would be
slightly more than 21 hours long, slightly more than 21 hours long,
constituting about 88% of all geologic timeconstituting about 88% of all geologic time
PrecambrianPrecambrian

3. 88% of 88% of
geologic timegeologic time
Precambrian Time SpanPrecambrian Time Span

4. The term The term PrecambrianPrecambrian is informal is informal
but widely used, referring to both time and rocksbut widely used, referring to both time and rocks
The Precambrian includes The Precambrian includes
time from Earth’s origin 4.6 billion years ago time from Earth’s origin 4.6 billion years ago
to the beginning of the Phanerozoic Eon to the beginning of the Phanerozoic Eon
542 million years ago542 million years ago
It encompasses It encompasses
all rocks older than Cambrian-age rocksall rocks older than Cambrian-age rocks
No rocks are known for the first No rocks are known for the first
640 million years of geologic time640 million years of geologic time
The oldest known rocks on Earth The oldest known rocks on Earth
are 3.96 billion years oldare 3.96 billion years old
PrecambrianPrecambrian

5. The earliest record of geologic time The earliest record of geologic time
preserved in rocks is difficult to interpret preserved in rocks is difficult to interpret
because many Precambrian rocks have been because many Precambrian rocks have been
altered by metamorphismaltered by metamorphism
complexly deformedcomplexly deformed
buried deep beneath younger rocksburied deep beneath younger rocks
fossils are rare, andfossils are rare, and
the few fossils present are of little use in stratigraphythe few fossils present are of little use in stratigraphy
Subdivisions of the Precambrian Subdivisions of the Precambrian
have been difficult to establishhave been difficult to establish
Two eons for the Precambrian Two eons for the Precambrian
are the are the ArcheanArchean and and ProterozoicProterozoic
Rocks Difficult to InterpretRocks Difficult to Interpret

6. Shortly after accretion, Earth was Shortly after accretion, Earth was
a rapidly rotating, hot, barren, waterless planeta rapidly rotating, hot, barren, waterless planet
bombarded by comets and meteoritesbombarded by comets and meteorites
with no continents, intense cosmic radiation with no continents, intense cosmic radiation
and widespread volcanismand widespread volcanism
Hot, Barren, Waterless Early EarthHot, Barren, Waterless Early Earth
about 4.6 billion years agoabout 4.6 billion years ago

7. Key Events of Precambrian timeKey Events of Precambrian time
Acasta Gneiss is dated at
3.96 bya. It is near Yellowknife Lake , NWT Canada
Zircons possibly a bit older in Australia

8. Global Evolution: The First Five Global Evolution: The First Five
Billion YearsBillion Years
Global Evolution: The First Five Billion YearsGlobal Evolution: The First Five Billion Years
The National Academy of Sciences says that it is the role of science to provide The National Academy of Sciences says that it is the role of science to provide
plausible(probable) natural explanations of natural phenomena. plausible(probable) natural explanations of natural phenomena.
The ultimate question for Earth System History is: How did a giant cloud of cold The ultimate question for Earth System History is: How did a giant cloud of cold
dilute gas and dust evolve into astronauts in a spacecraft orbiting a planet orbiting a dilute gas and dust evolve into astronauts in a spacecraft orbiting a planet orbiting a
star?star?
The short answer is when energy flows, complexity grows.The short answer is when energy flows, complexity grows.
The fact is that the solid Earth, hydrosphere, atmosphere, and biosphere have The fact is that the solid Earth, hydrosphere, atmosphere, and biosphere have
undergone nearly undergone nearly
five billion years of physical, chemical, and/or biological evolution because of the five billion years of physical, chemical, and/or biological evolution because of the
flows of energy and/or matter into and/or out of these systems, a process that is flows of energy and/or matter into and/or out of these systems, a process that is
called global evolution. called global evolution.
Each section addresses the structures, functions, composition, interactions and flows Each section addresses the structures, functions, composition, interactions and flows
of energy and matter,and origin and evolution of a complex natural system.of energy and matter,and origin and evolution of a complex natural system.

9. The Structure and Evolution of theThe Structure and Evolution of the
Hydrosphere, Atmosphere, and GeobiosphereHydrosphere, Atmosphere, and Geobiosphere
How did a giant cloud of cold dilute gas and How did a giant cloud of cold dilute gas and
dust evolve into astronauts in a spacecraft dust evolve into astronauts in a spacecraft
orbiting a planet orbiting a star? orbiting a planet orbiting a star?
The short answer is when energy flows, The short answer is when energy flows,
complexity grows.complexity grows.

10. The Structure and Evolution of theThe Structure and Evolution of the
Hydrosphere, Atmosphere, and GeobiosphereHydrosphere, Atmosphere, and Geobiosphere

11. Earth’s early atmosphere and hydrosphere Earth’s early atmosphere and hydrosphere
were quite different than they are nowwere quite different than they are now
They also played an important role They also played an important role
in the development of the biospherein the development of the biosphere
Today’s atmosphere is mostly Today’s atmosphere is mostly
nitrogen (Nnitrogen (N
22))
abundant free oxygen (Oabundant free oxygen (O
22),),
or oxygen not combined with other elements or oxygen not combined with other elements
such as in carbon dioxide (COsuch as in carbon dioxide (CO
22))
water vapor (Hwater vapor (H
22O)O)
small amounts of other gases, like ozone (Osmall amounts of other gases, like ozone (O
33))
which is common enough in the upper atmosphere which is common enough in the upper atmosphere
to block most of the Sun’s ultraviolet radiationto block most of the Sun’s ultraviolet radiation
Evalution of Atmosphere and Evalution of Atmosphere and
HydrosphereHydrosphere

12. Earth’s very early atmosphere was probably Earth’s very early atmosphere was probably
composed of composed of
hydrogen and helium, hydrogen and helium,
the most abundant gases in the universethe most abundant gases in the universe
If so, it would have quickly been lost into space If so, it would have quickly been lost into space
because Earth’s gravity is insufficient to retain thembecause Earth’s gravity is insufficient to retain them
because Earth had no magnetic field until its core because Earth had no magnetic field until its core
formed (magnetosphere)formed (magnetosphere)
Without a magnetic field, Without a magnetic field,
the solar wind would have swept away the solar wind would have swept away
any atmospheric gasesany atmospheric gases
Earth’s Very Early AtmosphereEarth’s Very Early Atmosphere

13. Nonvariable gasesNonvariable gases
NitrogenNitrogenNN
2278.08%78.08%
OxygenOxygenOO
2220.9520.95
ArgonArgon ArAr 0.93 0.93
NeonNeon NeNe 0.002 0.002
OthersOthers 0.001 0.001
in percentage by volumein percentage by volume
Present-day Present-day
Atmosphere CompositionAtmosphere Composition
Variable gasesVariable gases
Water vaporWater vaporHH
22OO0.1 to 4.00.1 to 4.0
Carbon dioxideCarbon dioxideCOCO
220.0380.038
OzoneOzone OO
330.0000060.000006
Other gasesOther gases TraceTrace
Particulates Particulates normally normally
tracetrace

14. Once a magnetosphere was Once a magnetosphere was
present present
Atmosphere began Atmosphere began
accumulating as a result of accumulating as a result of
outgassingoutgassing
released during volcanismreleased during volcanism
Water vapor Water vapor
is the most common is the most common
volcanic gas todayvolcanic gas today
but volcanoes also emit but volcanoes also emit
carbon dioxide, sulfur carbon dioxide, sulfur
dioxide, dioxide,
OutgassingOutgassing
carbon monoxide, sulfur, carbon monoxide, sulfur,
hydrogen, chlorine, and nitrogenhydrogen, chlorine, and nitrogen

15. Archean volcanoes probably Archean volcanoes probably
emitted the same gases, emitted the same gases,
and thus an atmosphere developedand thus an atmosphere developed
but one lacking free oxygen and an ozone layerbut one lacking free oxygen and an ozone layer
It was rich in carbon dioxide, It was rich in carbon dioxide,
and gases reacting in this early atmosphere and gases reacting in this early atmosphere
probably formed probably formed
ammonia (NHammonia (NH
33))
methane (CHmethane (CH
44))
This early atmosphere persisted This early atmosphere persisted
throughout the Archeanthroughout the Archean
Archean AtmosphereArchean Atmosphere

16. The atmosphere was chemically reducing The atmosphere was chemically reducing
rather than an oxidizing onerather than an oxidizing one
Some of the evidence for this conclusion Some of the evidence for this conclusion
comes from detrital deposits comes from detrital deposits
containing minerals that oxidize rapidly containing minerals that oxidize rapidly
in the presence of oxygenin the presence of oxygen
pyrite (FeSpyrite (FeS
22))
But oxidized iron becomes But oxidized iron becomes
increasingly common in Proterozoic rocksincreasingly common in Proterozoic rocks
indicating that at least some free oxygen indicating that at least some free oxygen
was present thenwas present then
Evidence for an Evidence for an
Oxygen-Free AtmosphereOxygen-Free Atmosphere

17. Ratio of radiogenic heat production in the past to Ratio of radiogenic heat production in the past to
the presentthe present
Decreasing HeatDecreasing Heat
The width of The width of
the colored the colored
band indicates band indicates
variations in variations in
ratios from ratios from
different different
modelsmodels
Heat production Heat production
4 billion years 4 billion years
ago was 3 to ago was 3 to
6 times as great 6 times as great
as it is nowas it is now
With less heat With less heat
outgassing outgassing
decreaseddecreased

18. Layers of the Present Layers of the Present
AtmosphereAtmosphere

19. HydrosphereHydrosphere
All water at or near the surface of the earthAll water at or near the surface of the earth
Water is constantly recycled (groundwater, Water is constantly recycled (groundwater,
glaciers, oceans, freshwater etc)glaciers, oceans, freshwater etc)

20. HydrosphereHydrosphere

21. The BiosphereThe Biosphere
The biosphere is the “life zone” of the Earth, and includes all
living organisms (including humans), and all organic matter that has not
yet decomposed.
• The biosphere is structured into a hierarchy known as the food chain
(all life is dependant on the first tier – mainly the primary producers that
are capable of photosynthesis).
• Energy and mass is transferred from one level of the food chain to the
next.

22. BiosphereBiosphere

23. Evalution of lithosphereEvalution of lithosphere
First continental crustFirst continental crust
Density differences allow subduction of
mafic rocks. Further partial melting and
fractionation makes higher silica melt that
won’t subduct
Water out
Komatiite partially melts, Basalt gets
to surface, piles up. The stack sinks,
partially melts when pressure high
enough. Fractionation makes
increasingly silica-rich magmas
First
Then:
At high temperatures, only Olivine and Ca-Plagioclase crystallize “Komatiite”

24. Archean: Growth of the early continentsArchean: Growth of the early continents
Magmatism from Subduction Zones causes thickening

25. Growth of the early continentsGrowth of the early continents
Island Arcs and other terranes accrete as
intervening ocean crust is subducted
Little Archean ocean crust survives: most subducted
But silica-rich continental crust too buoyant to subduct.

26. Growth of the early continentsGrowth of the early continents
Sediments extend continental materials seaward
Quartz sand
becomes SS or
quartzite, too
buoyant to
subduct

27. Judging from the oldest known rocks on Earth, Judging from the oldest known rocks on Earth,
the 3.96-billion-year-old Acasta Gneiss in Canada the 3.96-billion-year-old Acasta Gneiss in Canada
and other rocks in Montana and Greenlandand other rocks in Montana and Greenland
some continental crust had evolved by early Archean some continental crust had evolved by early Archean
timetime
Sedimentary rocks in Australia contain detrital Sedimentary rocks in Australia contain detrital
zircons (ZrSiOzircons (ZrSiO
44) dated at 4.4 billion years old) dated at 4.4 billion years old
so source rocks at least that old existedso source rocks at least that old existed
These rocks indicted that some kind These rocks indicted that some kind
of Eoarchean crust was certainly present, of Eoarchean crust was certainly present,
but its distribution is unknownbut its distribution is unknown
Oldest RocksOldest Rocks

28. Early Archean crust was probably thin Early Archean crust was probably thin
and made up of ultramafic rockand made up of ultramafic rock
igneous rock with less than 45% silicaigneous rock with less than 45% silica
This ultramafic crust was disrupted This ultramafic crust was disrupted
by upwelling mafic magma at ridges, by upwelling mafic magma at ridges,
and the first island arcs formed at subduction zonesand the first island arcs formed at subduction zones
Early Archean continental crust may have formed Early Archean continental crust may have formed
by collisions between island arcsby collisions between island arcs
as silica-rich materials were metamorphosed. as silica-rich materials were metamorphosed.
Larger groups of merged island arcsLarger groups of merged island arcs
protocontinentsprotocontinents
grew faster by accretion along their marginsgrew faster by accretion along their margins
Early Archean CrustEarly Archean Crust

29. Origin of Continental CrustOrigin of Continental Crust
Andesitic Andesitic
island arcs island arcs
form by form by
subduction subduction
and partial and partial
melting of melting of
oceanic oceanic
crustcrust
The island The island
arc collides arc collides
with anotherwith another

30. Continents consist of rocks Continents consist of rocks
with composition similar to that of granitewith composition similar to that of granite
Continental crust is thicker Continental crust is thicker
and less dense than oceanic crust and less dense than oceanic crust
which is made up of basalt and gabbrowhich is made up of basalt and gabbro
Precambrian shieldsPrecambrian shields
consist of vast areas of exposed ancient rocks consist of vast areas of exposed ancient rocks
and are found on all continentsand are found on all continents
Outward from the shields are broad Outward from the shields are broad platformsplatforms
of buried Precambrian rocks of buried Precambrian rocks
that underlie much of each continentthat underlie much of each continent
Continental FoundationsContinental Foundations

31. Distribution of Precambrian RocksDistribution of Precambrian Rocks
Areas of Areas of
exposed exposed
Precam-Precam-
brian rocks brian rocks
constitute constitute
the shieldsthe shields
Platforms Platforms
consist of consist of
buried Pre-buried Pre-
cambrian cambrian
rocksrocks
Shields and adjoining platforms make up cratonsShields and adjoining platforms make up cratons

32. CRYOSPHERECRYOSPHERE
What is cryosphere?What is cryosphere?
Cryo (frozen), a component of Cryo (frozen), a component of
the earththe earth’s climate system ’s climate system
comprised of water in its solid comprised of water in its solid
state. It consists of state. It consists of
glaciers & ice sheets, glaciers & ice sheets,
snow, snow,
permafrost (continuous and permafrost (continuous and
discontinuous) discontinuous)
sea ice (perennial and seasonal).sea ice (perennial and seasonal).
Largest fresh water reservoir on earthLargest fresh water reservoir on earth

33. Cryospheric component Area (% of earth surface) Mass (10
3

kg/m
2
)
Antarctic ice sheet 2.7 53
Greenland ice sheet 0.35 5
Alpine glaciers 0.01 0.2
Sea-ice (in season of maximal extent) 7 0.01
Seasonal snow cover 9 <0.01
Permafrost 5 1
What can we infer from ice mass listed above?What can we infer from ice mass listed above?
Surface area: 5.1X10Surface area: 5.1X10
1 41 4
m m
22
, total land area: 1.45X10, total land area: 1.45X10
1 41 4
m m
22
1010
33
kg/m kg/m
22
: equivalent to depth of liquid water in meter per unit : equivalent to depth of liquid water in meter per unit
area.area.
If Antarctic ice sheet melted, it would create 53 m If Antarctic ice sheet melted, it would create 53 m
deep water layer over entire earth.deep water layer over entire earth.
How much would sea-level rise?How much would sea-level rise?
76M = 53mX5.1/(5.1-1.45)

34. Role in climate system:Role in climate system:
Largest fresh water storage:Largest fresh water storage:
Influence sea-level riseInfluence sea-level rise
Water resourcesWater resources
Influence ocean circulationInfluence ocean circulation
Regular earthRegular earth’s albedo change, ’s albedo change,
Reduce turbulent transport of heat, water and Reduce turbulent transport of heat, water and
momentummomentum
Change ocean buoyancy flux, S and TChange ocean buoyancy flux, S and T
Glacial runoff from Antarctic is a major source of Glacial runoff from Antarctic is a major source of
fresh water for southern ocean.fresh water for southern ocean.
Regular regional-global climateRegular regional-global climate

35. How do we estimate water in snow and ice?How do we estimate water in snow and ice?
Snow (ice) equivalent depth: snow is porous and its Snow (ice) equivalent depth: snow is porous and its
porosity depends on temperature and age of the porosity depends on temperature and age of the
snow. A measure of liquid water contained in snow snow. A measure of liquid water contained in snow
is water equivalent depth, his water equivalent depth, h
mm::
hh
mm==rr
ss//rr
ww·h·h
ss
rr
ss,,rr
ww: density of the snow and water, respectively.: density of the snow and water, respectively.
hh
ss: depth of the snow/ice layer: depth of the snow/ice layer
hh
mm: The depth of water that will resulted from complete melt of : The depth of water that will resulted from complete melt of
snow/ice.snow/ice.
Snow relative density, Snow relative density, rr
ss//rr
ww ranges from 0.15-0.4 ranges from 0.15-0.4

37. Snow/ice albedo (whiteness):Snow/ice albedo (whiteness):
Albedo: ratio of the reflected vs. incident Albedo: ratio of the reflected vs. incident
radiative flux. It is a function of wavelength.radiative flux. It is a function of wavelength.
Surface Typical Albedo
Fresh asphalt 0.04
Conifer forest (Summer) 0.08, 0.09 to 0.15
Worn asphalt 0.12
Deciduous trees 0.15 to 0.18
Bare soil 0.17
Green grass 0.25
Desert sand 0.40
New concrete 0.55
Fresh snow 0.80–0.90

38. Snow:Snow:
Distribution and Distribution and
variations:variations:
Seasonal snow covers Seasonal snow covers
~12.5% of the global ~12.5% of the global
surface, mainly in high surface, mainly in high
latitudes and high latitudes and high
altitudes;altitudes;
Snow cover varies Snow cover varies
strongly (50%), seasonally strongly (50%), seasonally
(8-16.5%), weekly, (8-16.5%), weekly,
interannually, decadally; interannually, decadally;

39. Glacier:Glacier:
when snow/ice deposit reaches 50 m, pressure compaction when snow/ice deposit reaches 50 m, pressure compaction
and melt-freeze cycles cause ice and melt-freeze cycles cause ice rr=550 kgm=550 kgm
-3-3
, i.e., firn. As , i.e., firn. As
firn firn rr increases to 820 kgm increases to 820 kgm
-3-3
, air no longer can circulate , air no longer can circulate
within ice and glacier ice forms. within ice and glacier ice forms.
As the thickness of glacier ice continues to increase and As the thickness of glacier ice continues to increase and
pressure at the base of the glacier increase, melting at the pressure at the base of the glacier increase, melting at the
glacier base occurs. Glacier behavior as a 3D lattice, and glacier base occurs. Glacier behavior as a 3D lattice, and
deform and slip along slop of underlying topography at deform and slip along slop of underlying topography at
speed upto to 1-10 km/yr.speed upto to 1-10 km/yr.

40. Antarctic Ice Sheet:Antarctic Ice Sheet:
Creep rate: near zero at the divides Creep rate: near zero at the divides
of the ice sheet, and >10 m/yr at the of the ice sheet, and >10 m/yr at the
periphery; Why?periphery; Why?
Creep rate is especially high in the Creep rate is especially high in the
W. Antarctic.W. Antarctic.
Collapse of W. Antarctic can cause Collapse of W. Antarctic can cause
abrupt sea-level rise.abrupt sea-level rise.
Satellite image of the Antarctic ice sheet
and the rate of creep of the ice (m/yr) on
a logarithmic scale.
P
S

41. Greenland Ice Sheet:Greenland Ice Sheet:
Lower latitudes and smaller than Lower latitudes and smaller than
the Antarctic ice sheet,the Antarctic ice sheet,
S. Greenland is highly vulnerable S. Greenland is highly vulnerable
to climate change because to climate change because
summer temperature reaches summer temperature reaches
melting point (-5C).melting point (-5C).
IV

42. Alpine glaciers:Alpine glaciers:
Alpine glaciers, smaller ice sheets, Alpine glaciers, smaller ice sheets,
can exist at any latitudes although can exist at any latitudes although
their altitudes increase from < 1 km their altitudes increase from < 1 km
in high latitudes to 4-6 km in in high latitudes to 4-6 km in
tropics; tropics; Why?Why?
Alpine glacier retreat has been Alpine glacier retreat has been
observed globally.observed globally.
Air T
T to form
glacier for
given P
P

43. Permafrost: Permafrost:
The top few meters of soil thaws during The top few meters of soil thaws during
summer and freezes in winter. summer and freezes in winter.
Below a few meters, the soil temperature Below a few meters, the soil temperature
remains constant around 0˚C. It would remains constant around 0˚C. It would
takes hundreds of years for the permafrost takes hundreds of years for the permafrost
to adjust to air temperature;to adjust to air temperature;
Carbon locked up in the permafrost > Carbon locked up in the permafrost >
carbon stored in global vegetation.carbon stored in global vegetation.

44. Sea Ice:Sea Ice:
Sea ice in arctic covers maximumly 3% of the earth Sea ice in arctic covers maximumly 3% of the earth
and in Antarctic covers maximumly 4% of the earthand in Antarctic covers maximumly 4% of the earth’ ’
surface, and about 1-3 m thick (not much mass, 0.01 surface, and about 1-3 m thick (not much mass, 0.01
m)m)
Sea ice cover in Antarctic varies seasonally from 2 to Sea ice cover in Antarctic varies seasonally from 2 to
14 X1014 X10
1212
m m
22
, and in Arctic varies from 4 - 11 X10, and in Arctic varies from 4 - 11 X10
1212

mm
22
..
Why does sea ice varies more in Antarctic than in Why does sea ice varies more in Antarctic than in
Arctic?Arctic?

45. Formation of sea ice transition and Formation of sea ice transition and
columnar zonescolumnar zones
Formation of sea ice release heat and salt below. Formation of sea ice release heat and salt below.
Because heat transfer is faster than salt transfer, Because heat transfer is faster than salt transfer,
act temperature below sea ice can be lower than act temperature below sea ice can be lower than
freezing temperature, i.e., supercooling.freezing temperature, i.e., supercooling.
Supercooling leads to downward growth of Supercooling leads to downward growth of
platelets into brine layer, brine trapped between platelets into brine layer, brine trapped between
platelets form long and narrow brine pockets. platelets form long and narrow brine pockets.

46. Sea ice is a fractal field comprised of ice Sea ice is a fractal field comprised of ice
floes.floes.
A new pack of ice is formed by freezing A new pack of ice is formed by freezing
of water in newly formed leads in region of water in newly formed leads in region
where wind drag pack ice away from where wind drag pack ice away from
shore; after reach 1 m thick, it is formed shore; after reach 1 m thick, it is formed
by collisions of ice floes;by collisions of ice floes;
Sea ice moves with transpolar drift Sea ice moves with transpolar drift
stream.stream.
leads
floes
Floes streaming southward off the east
coast of Greenland
Fridtjof Nansen
(1861-1930)

47. SummarySummary
What is cryosphere?What is cryosphere?
Cryo (frozen), a component of the earthCryo (frozen), a component of the earth’s climate system comprised ’s climate system comprised
of water in its solid state. It consists of of water in its solid state. It consists of
glaciers & ice sheets, glaciers & ice sheets,
snow, snow,
permafrost (continuous and discontinuous) permafrost (continuous and discontinuous)
sea ice (perennial and seasonal).sea ice (perennial and seasonal).
What is the distribution of different components of cryosphere?What is the distribution of different components of cryosphere?
Largest mass in Antarctic and Greenland, 58 m deep of water globally if they Largest mass in Antarctic and Greenland, 58 m deep of water globally if they
melt completely;melt completely;
Sea ice and land snow cover 8-16% of the earthSea ice and land snow cover 8-16% of the earth’s surface’s surface
Greenland and W. Antarctic ice sheet, Arctic sea ice and alpine glaciers have Greenland and W. Antarctic ice sheet, Arctic sea ice and alpine glaciers have
retreated rapidly in recent decades.retreated rapidly in recent decades.
What is the roles of cryosphere in climate system?What is the roles of cryosphere in climate system?
Largest storage of global surface fresh waterLargest storage of global surface fresh water
Contribute to the thermal inertial of the earthContribute to the thermal inertial of the earth’s climate ’s climate
Contribute to albedo of the earthContribute to albedo of the earth
Controls fresh water flux in the polar region, thus influence oceanic Controls fresh water flux in the polar region, thus influence oceanic
thermohaline circulation;thermohaline circulation;
Store more carbon than that by global vegetationStore more carbon than that by global vegetation

48. A shield and platform make up a A shield and platform make up a craton,craton,
a continent’s ancient nucleusa continent’s ancient nucleus
Along the margins of cratons, Along the margins of cratons,
more continental crust was added more continental crust was added
as the continents took their present sizes and shapesas the continents took their present sizes and shapes
Both Archean and Proterozoic rocks Both Archean and Proterozoic rocks
are present in cratons and show evidence ofare present in cratons and show evidence of
episodes of deformation accompanied by episodes of deformation accompanied by
metamorphism, igneous activity, metamorphism, igneous activity,
and mountain buildingand mountain building
Cratons have experienced little deformation Cratons have experienced little deformation
since the Precambriansince the Precambrian
CratonsCratons

49. Certainly several small cratons Certainly several small cratons
existed during the Archean existed during the Archean
and grew by periodic continental accretionand grew by periodic continental accretion
during the rest of that eonduring the rest of that eon
They amalgamated into a larger unit They amalgamated into a larger unit
during the Proterozoicduring the Proterozoic
By the end of the Archean, By the end of the Archean,
30-40% of the present volume 30-40% of the present volume
of continental crust existedof continental crust existed
The Origin of CratonsThe Origin of Cratons

50. Cratons in Indian ShieldCratons in Indian Shield
Gorur Gneiss, Mysore
Biligirirangan Granulite

51. Rift ValleysRift Valleys
A rift valley is a linear-shaped lowland A rift valley is a linear-shaped lowland
between several highlands or mountain between several highlands or mountain
ranges created by the action of a ranges created by the action of a
geologic rift or fault. This action is geologic rift or fault. This action is
manifest as crustal extension, a manifest as crustal extension, a
spreading apart of the surface, which is spreading apart of the surface, which is
subsequently further deepened by the subsequently further deepened by the
forces of erosion. forces of erosion.
When the tensional forces are strong When the tensional forces are strong
enough to cause the plate to split apart, enough to cause the plate to split apart,
it will do so such that a center block will it will do so such that a center block will
drop down relative to its flanking drop down relative to its flanking
blocks, forming a graben.blocks, forming a graben.

52. This creates the nearly parallel steeply dipping walls. This This creates the nearly parallel steeply dipping walls. This
feature is the beginning of the rift valley. As this process feature is the beginning of the rift valley. As this process
continues, the valley widens, until it becomes a large basin, continues, the valley widens, until it becomes a large basin,
that fills with sediment from the rift walls and the surrounding that fills with sediment from the rift walls and the surrounding
area. area.
 Rifts can occur at all elevations, from the sea floor to plateaus Rifts can occur at all elevations, from the sea floor to plateaus
and mountain ranges. and mountain ranges.
They can occur in continental crust or in oceanic crust. Rift They can occur in continental crust or in oceanic crust. Rift
valleys are often associated with a number of adjoining valleys are often associated with a number of adjoining
subsidiary or co-extensive valleys, which are typically subsidiary or co-extensive valleys, which are typically
considered part of the principal rift valley geologically.considered part of the principal rift valley geologically.

53. Narmada Rift ValleyNarmada Rift Valley
The Narmada also called the Rewa, is a river in central India and the fifth longest The Narmada also called the Rewa, is a river in central India and the fifth longest
river in the Indian subcontinent. It is the third longest river that flows entirely river in the Indian subcontinent. It is the third longest river that flows entirely
within India, after the Godavari and the Krishna. within India, after the Godavari and the Krishna.
It forms the traditional boundary between North India and South India and flows It forms the traditional boundary between North India and South India and flows
westwards over a length of 1,312 km (815.2 mi) before draining through the Gulf of westwards over a length of 1,312 km (815.2 mi) before draining through the Gulf of
Khambhat into the Arabian Sea, 30 km (18.6 mi) west of Bharuch city of Gujarat.Khambhat into the Arabian Sea, 30 km (18.6 mi) west of Bharuch city of Gujarat.

54. It is one of only three major rivers in peninsular India that run from east to It is one of only three major rivers in peninsular India that run from east to
west (longest west flowing river), along with the Tapti River and the Mahi west (longest west flowing river), along with the Tapti River and the Mahi
River. It is the one of the rivers in India that flows in a rift valley,flowing west River. It is the one of the rivers in India that flows in a rift valley,flowing west
between the Satpura and Vindhya ranges. between the Satpura and Vindhya ranges.
The Narmada basin, hemmed between Vindya and Satpura ranges, extends The Narmada basin, hemmed between Vindya and Satpura ranges, extends
over an area of 98,796 km2 (38,145.3 sq mi) and lies between east longitudes over an area of 98,796 km2 (38,145.3 sq mi) and lies between east longitudes
72 degrees 32' to 81 degrees 45' and north latitudes 21 degrees 20‘ to 23 72 degrees 32' to 81 degrees 45' and north latitudes 21 degrees 20‘ to 23
degrees 45' lying on the northern extremity of the Deccan Plateau. degrees 45' lying on the northern extremity of the Deccan Plateau.
The basin covers large areas in the states of Madhya Pradesh (86%), Gujarat The basin covers large areas in the states of Madhya Pradesh (86%), Gujarat
(14%) and a comparatively smaller area (2%) in Maharashtra. In the river (14%) and a comparatively smaller area (2%) in Maharashtra. In the river
course of 1,312 km (815.2 mi) explained above, there are 41 tributaries, out of course of 1,312 km (815.2 mi) explained above, there are 41 tributaries, out of
which 22 are from the Satpuda range and the rest on the right bank are from which 22 are from the Satpuda range and the rest on the right bank are from
the Vindhya range.the Vindhya range.
 Dhupgarh (1,350m), near Pachmarhi is the highest point of the Narmada Dhupgarh (1,350m), near Pachmarhi is the highest point of the Narmada
basin.basin.
The other rivers which flows through rift valley include Damodar River in The other rivers which flows through rift valley include Damodar River in
Chota Nagpur Plateau & Tapti.Chota Nagpur Plateau & Tapti.

55. GeologyGeology
The Narmada Valley is a graben, a layered block of the Earth's crust that dropped down The Narmada Valley is a graben, a layered block of the Earth's crust that dropped down
relative to the blocks on either side due to ancient spreading of the Earth's crust. Two relative to the blocks on either side due to ancient spreading of the Earth's crust. Two
normal faults, known as the Narmada North fault and Narmada South fault, parallel to normal faults, known as the Narmada North fault and Narmada South fault, parallel to
the river's course, and mark the boundary between the Narmada block and the Vindhya the river's course, and mark the boundary between the Narmada block and the Vindhya
and Satpura blocks or Horsts which rose relative to the Narmada Graben.and Satpura blocks or Horsts which rose relative to the Narmada Graben.
 The Narmada's watershed includes the northern slopes of the Satpuras, and the steep The Narmada's watershed includes the northern slopes of the Satpuras, and the steep
southern slope of the Vindhyas, but not the Vindhyan tableland, the streams from southern slope of the Vindhyas, but not the Vindhyan tableland, the streams from
which flow into the Ganges and Yamuna. which flow into the Ganges and Yamuna.
The Narmada valley is considered extremely important for palaeontological studies in The Narmada valley is considered extremely important for palaeontological studies in
India. Several dinosaur fossils have been found in the area including Titanosaurus India. Several dinosaur fossils have been found in the area including Titanosaurus
indicus found in 1877 by Richard Lydekker and the recently discovered Rajasaurus indicus found in 1877 by Richard Lydekker and the recently discovered Rajasaurus
narmadensis.narmadensis.

56. Mahanadi Rift ValleyMahanadi Rift Valley
The Mahanadi basin at the eastern margin of India
is arcuate in shape with an onshore part (Mahanadi
delta) that extends from longitudes 85°E to 87°E
and latitudes 19.5°N to 21°N and has a complex
geological setup. Most of the area in the delta is
covered with recent alluvium with few places
having exposed Archean/Precambrian igneous and
metamorphic rocks of the Eastern Ghat orogeney
towards the northwest. These rocks are disposed in
the form of detached hillocks striking in ENE-
WSW direction bordering the Mahanadi delta
(Behera et al., 2004). The exposed rocks comprise
mainly of Gondwana (lower Triassic to upper
Carboniferous), laterites (Pliocene to Pleistocene),
granites/gneisses (Archean), khondalites
(Precambrian metamorphic rocks), and
charnockites/anorthosites (Precambrian igneous
rocks). Fuloria (1994) has suggested the presence
of a Gondwana graben and reports extensive
volcanism along the rift zones of the delta. Until
the Jurassic, it was an intra-continental pull-apart
basin and became pericratonic after the breakup of
the Gondwana.

57. Godhavari Rift ValleyGodhavari Rift Valley
The Godavari basin is divided into three parts namely
Godavari-Pranhita, Chintalapudi, and coastal sub-basins.
The Godavari-Pranhita sub-basin, located northwest of
the Mailaram basement ``high'', depicts the characteristics
of a half graben. The maximum thickness of the
Gondwana sediments in this part is approximately 7.5
km. The gravity ``highs'' along the shoulders and inside
the basin around Chinnur are interpreted as subsurface
mass excesses along the Moho and within the crust. The
Chinnur ``high'' in the centre of the basin probably
represents a remanence of the arial doming characterizing
the rift valleys. The Chintalapudi basin is bounded by the
Mailaram ``high'' and the coastal fault towards the south.
This part of the basin has faulted margins on both the
sides as indicated by sharp gradients in the Bouguer
anomaly with 3.0 km of sediments in the central part and
associated mass excesses along the Moho and the
shoulders suggesting it to be a full graben. The
development of this full graben in this region alone is
probably constrained by the deep faults on all four sides.
The boundary faults defining these sub-basins, the
shoulder ``highs'' and the transverse Mailaram ``high'' are
still associated with occasional seismic activity suggesting
some neo-tectonic adjustments along them. 

58. Cambay Rift ValleyCambay Rift Valley
The Cambay Basin is located in Gujarat
State, on the western margin of India.
The basin lies predominantly onshore,
with only the southwestern corner
offshore in the Gulf of Cambay. The
Cambay basin is rich petroleum province,
with active exploration history. The basin
is a narrow elongated, intra-cratonic rift
basin of late Cretaceous age and contains
different sub-basins with varying
sediment fills.
The origin of the Cambay and other basins on the western margin of India are
related to the break up of the Gondwana super-continent in the Late-Triassic
to Early-Jurassic (215 m.y.a.). As India drifted away from Africa and
Madagascar, rift grabens began to form on the west coast of India. As a result
of movement, the boundary faults of the grabens were initiated through
reactivation of Pre-Cambrian faulting.

59. Kutchch Rift ValleyKutchch Rift Valley

60. Cratons of the Indian ShieldCratons of the Indian Shield
The Indian shield is made up of a mosaic of Precambrian The Indian shield is made up of a mosaic of Precambrian
metamorphic terrains that exhibit low to high-grade crystalline metamorphic terrains that exhibit low to high-grade crystalline
rocks in the age range of 3.6–2.6 Ga. rocks in the age range of 3.6–2.6 Ga.
These terrains, constituting the continental crust, attained These terrains, constituting the continental crust, attained
tectonic stability for prolonged period (since Precambrian time) tectonic stability for prolonged period (since Precambrian time)
and are designated cratons.The cratons are flanked by a fold belt, and are designated cratons.The cratons are flanked by a fold belt,
with or without a discernible suture or shear zone, suggesting with or without a discernible suture or shear zone, suggesting
that the cratons, as crustal blocks or microplates, moved against that the cratons, as crustal blocks or microplates, moved against
each other and collided to generate these fold belts. each other and collided to generate these fold belts.
Alternatively, these cratons could be the result of fragmentation Alternatively, these cratons could be the result of fragmentation
of a large craton that constituted the Indian shield.of a large craton that constituted the Indian shield.

61. Cratons of the Indian ShieldCratons of the Indian Shield
These six cratons shows different geological characteristics. we enquire into These six cratons shows different geological characteristics. we enquire into
the age, composition, and structural architecture of these cratonic masses to the age, composition, and structural architecture of these cratonic masses to
which the fold belts had accreted. which the fold belts had accreted.
In general, the cratons are dominated by granite and metamorphic rocks, In general, the cratons are dominated by granite and metamorphic rocks,
mainly gneisses, which imply a series of intense mountain making episodes mainly gneisses, which imply a series of intense mountain making episodes
(deformation and metamorphism) in the Precambrian time before the stable (deformation and metamorphism) in the Precambrian time before the stable
conditions set in. A common feature of these cratonic regions is the conditions set in. A common feature of these cratonic regions is the
occurrence of greenstone-gneiss association, as found in other Archaean occurrence of greenstone-gneiss association, as found in other Archaean
cratons of the world.cratons of the world.
 Geochronological data have disclosed that rocks, especially the grey tonalitic Geochronological data have disclosed that rocks, especially the grey tonalitic
gneisses, range in age from 3.4 to 2.6 Ga old, which may be taken to indicate gneisses, range in age from 3.4 to 2.6 Ga old, which may be taken to indicate
that all these regions contain continental nucleus. Another feature of these that all these regions contain continental nucleus. Another feature of these
cratons is that they are often bordered by a shear zone or a major fault system cratons is that they are often bordered by a shear zone or a major fault system
and the intervening fold belt is composed of metamorphosed, deformed and the intervening fold belt is composed of metamorphosed, deformed
Proterozoic rocks. Proterozoic rocks.

62. Cratons of the Indian ShieldCratons of the Indian Shield
This implies that the stable Archaean cratons subdivided by This implies that the stable Archaean cratons subdivided by
mobile belts or fold belts had split or rifted during the mobile belts or fold belts had split or rifted during the
Proterozoic and the resulting basin was wholly ensialic, with no Proterozoic and the resulting basin was wholly ensialic, with no
rock associations that could be equated with ancient ocean rock associations that could be equated with ancient ocean
basins. basins.
In most fold belts, one observes that gneiss-amphibolite-In most fold belts, one observes that gneiss-amphibolite-
migmatites are exposed as the dominant cratonic rocks, migmatites are exposed as the dominant cratonic rocks,
suggesting that the supracrustals sequences rested upon the suggesting that the supracrustals sequences rested upon the
Archaean gneissic rocks of the cratons and that both basement Archaean gneissic rocks of the cratons and that both basement
and cover rocks were deformed and recrystallized in the and cover rocks were deformed and recrystallized in the
subsequent orogeny.subsequent orogeny.

63. Cratons of Indian ShieldCratons of Indian Shield
Cratonic blocks are described with respect to their geology, Cratonic blocks are described with respect to their geology,
geochronology, and structural characteristics :geochronology, and structural characteristics :
(1) Dharwar Craton (also called Karnataka Craton) in the south(1) Dharwar Craton (also called Karnataka Craton) in the south
(2) Bastar Craton (also called Bastar-Bhandara Craton) in the central (2) Bastar Craton (also called Bastar-Bhandara Craton) in the central
partpart
(3) Singhbhum Craton (also called Singhbhum-Orissa Craton) in the (3) Singhbhum Craton (also called Singhbhum-Orissa Craton) in the
northeastnortheast
(4) Chhotanagpur Gneiss Complex in eastern India(4) Chhotanagpur Gneiss Complex in eastern India
(5) Rajasthan (Aravalli-Bundelkhand) Craton in the north(5) Rajasthan (Aravalli-Bundelkhand) Craton in the north
(6) Meghalaya Craton in east Indian shield(6) Meghalaya Craton in east Indian shield

64. CRATONS IN PENINSULAR INDIAN
SHIELD
Aravalli
Bundelkhand
Singhbhum
Bastar
Dharwar
EGMB
SGT

65. Aravalli (Rajasthan) CratonAravalli (Rajasthan) Craton
The Aravalli Rajasthan Craton (AC) is a collage of two cratonic blocks: The Aravalli Rajasthan Craton (AC) is a collage of two cratonic blocks:
(1) The Banded Gneissic Complex-Berach granite (BGC), and (1) The Banded Gneissic Complex-Berach granite (BGC), and
(2) the Bundelkhand Granite massif (BKC). (2) the Bundelkhand Granite massif (BKC).
Therefore AC is in fact a large Rajasthan-Bundelkhand craton These two Therefore AC is in fact a large Rajasthan-Bundelkhand craton These two
cratonic blocks are separated by a vast tract of cover rocks, besides the cratonic blocks are separated by a vast tract of cover rocks, besides the
occurrence of the occurrence of the Great Boundary Fault Great Boundary Fault at the eastern limit of the BGC at the eastern limit of the BGC
block, making the correlation between the two cratonic areas difficult block, making the correlation between the two cratonic areas difficult
However, the two blocks have a common lithology that includes gneisses, However, the two blocks have a common lithology that includes gneisses,
migmatites, metavolcanic and metasedimentary rocks and a number of migmatites, metavolcanic and metasedimentary rocks and a number of
granitic intrusions. Both the BBC (i.e. Banded Gneissic Complex-Bearch granitic intrusions. Both the BBC (i.e. Banded Gneissic Complex-Bearch
Granite) and the BKGC (i.e. Bundelkhand Granite Complex) blocks (unitedly Granite) and the BKGC (i.e. Bundelkhand Granite Complex) blocks (unitedly
designated Rajasthan Craton, AC) have been affected by similar designated Rajasthan Craton, AC) have been affected by similar
deformational events.deformational events.
The two blocks also share same geodynamic settings in Proterozoic as The two blocks also share same geodynamic settings in Proterozoic as
revealed by geochemistry of their mafic magmatic rocks (Mondal and Ahmad, revealed by geochemistry of their mafic magmatic rocks (Mondal and Ahmad,
2001) and same geochronological ages2001) and same geochronological ages

66. Geological map of Aravalli CratonGeological map of Aravalli Craton
Simplified geological map of Rajasthan
craton (after Heron, 1953 and GSI, 1969),
made up of Banded Gneissic Complex
(BGC), Berach Granite and other
Archaean granitoids. Granulite outcrops
are in the BGC terrain and in the
metasediments of the Delhi Super group
Blank area occupied by Proterozoic fold
belts and sand cover. Abbreviations: BL =
Bhilwara, BW = Beawar, N = Nathdwara,
M = Mangalwar. Inset shows the location
of BBC (Banded gneissic complex-Berach
Granite) and BKC (Bundelkhand) cratonic
blocks that together constitute what is
here termed the Rajasthan (-Bundelkhand)
Craton, abbreviated RC.

67. Evolution of Aravalli Craton with summary of eventsEvolution of Aravalli Craton with summary of events
Modified after Sharma
(1999)

68. Geological Settings of Aravalli CratonGeological Settings of Aravalli Craton
The BGC including the Berach Granite occupies a large tract in the Mewar The BGC including the Berach Granite occupies a large tract in the Mewar
plains (Udaipur region) of south and east Rajasthan. It is skirted on the west plains (Udaipur region) of south and east Rajasthan. It is skirted on the west
and southwest by Proterozoic fold belts of Aravalli and Delhi Supergroups. and southwest by Proterozoic fold belts of Aravalli and Delhi Supergroups.
The eastern boundary of this cratonic region is demarcated by the Vindhyan The eastern boundary of this cratonic region is demarcated by the Vindhyan
platform sediments and southern boundary is covered by Deccan Trap (Fig. platform sediments and southern boundary is covered by Deccan Trap (Fig.
2.8). The BGC cratonic region is dominantly gneissic to migmatitic with 2.8). The BGC cratonic region is dominantly gneissic to migmatitic with
amphibolites and metasediments of amphibolite facies, intruded by Late amphibolites and metasediments of amphibolite facies, intruded by Late
Archaean granites (Untala, Gingla, Berach etc.) and rare ultramafics. Archaean granites (Untala, Gingla, Berach etc.) and rare ultramafics.
Amongst the gneissic rocks, grey coloured biotite gneisses are dominant with Amongst the gneissic rocks, grey coloured biotite gneisses are dominant with
leucocratic bands as a result of which the name Banded Gneissic Complex is leucocratic bands as a result of which the name Banded Gneissic Complex is
appropriately given by Gupta (1934) and Heron (1953). One can observe a appropriately given by Gupta (1934) and Heron (1953). One can observe a
gradational contact between the biotite gneiss (quartz-feldspar-biotite ± gradational contact between the biotite gneiss (quartz-feldspar-biotite ±
hornblende ± garnet) to leucogranite (quartz-feldspar) with gradual hornblende ± garnet) to leucogranite (quartz-feldspar) with gradual
obliteration of gneissic foliation. obliteration of gneissic foliation.
At certain places, faint relics of gneissic foliation are seen within dominantly At certain places, faint relics of gneissic foliation are seen within dominantly
massive granitoid.massive granitoid.

70. Bundelkhand Craton
Geology: The Bundelkhand craton lies to the
east of the Aravalli–Delhi Fold Belt. The most
conspicuous feature of the region is the
Bundelkhand Igneous Complex that intrudes
enclaves of schists, gneisses, banded iron
formations, mafic volcanic rocks and
quartzites.
Geochronology: Ages of the enclaves are not
known, but there are a few ages on the granites
that intrude them. The Bundelkhand granite is
dated to 2492±10Ma and is therefore
contemporaneous with the intrusion of the
Berach Granite in the Aravalli craton dated
2500Ma numerous mafic dykes of unknown
∼
age intrude the Bundelkhand Igneous Complex.
suggests that most of the mafic dikes were
emplaced in two phases, one at 2.15 Ga and the
second at 2.0 Ga based on the 40Ar/39Ar age
determination of the dolerite dykes.

71. Singhbum cratonSinghbum craton
The Singhbum craton (SBC) is also called Singhbhum-The Singhbum craton (SBC) is also called Singhbhum-
Orissa craton in eastern India. It is made of Archaean Orissa craton in eastern India. It is made of Archaean
rocks that are exposed in an area of 40,000 km2 in
∼
rocks that are exposed in an area of 40,000 km2 in
∼
Singhbhum district of Jharkhand (formerly Bihar) and Singhbhum district of Jharkhand (formerly Bihar) and
northern part of the State of Orissa. northern part of the State of Orissa.
The craton is bordered by Chhotanagpur Gneissic The craton is bordered by Chhotanagpur Gneissic
Complex to the north, Eastern Ghats mobile belt to the Complex to the north, Eastern Ghats mobile belt to the
southeast, Bastar craton to the southwest, and alluvium southeast, Bastar craton to the southwest, and alluvium
to the east. Much of the geological information about to the east. Much of the geological information about
Singhbhum craton (SC) or Singhbhum Granite Singhbhum craton (SC) or Singhbhum Granite
Complex (SGC) is due to Saha (1994). The following Complex (SGC) is due to Saha (1994). The following
rock-suite constitute the Singhbhum cratonrock-suite constitute the Singhbhum craton

72. Singhbum cratonSinghbum craton
Location and Geological map of Singhbhum
(-Orissa) craton comprising Archaean rocks
of Older Metamorphic Group (1) and Older
Metamorphic Tonalite Gneiss (2),
Singhbhum Granite Group (SBG) with three
phases (I, II, & III) of emplacement, and
Iron-Ore Group (IOG) made up of: 1 –
lavas and ultramafics, 2 – shale-tuff and
phyllite, 3 – BHJ, BHQ, sandstone and
conglomerate. Abbreviations: C =
Chakradharpur, D = Daiteri, K = Koira,
SSZ = Singhbhum shear zone.(1) =
Singhbhum Granite, (2) = Bonai Granite, 3
= Mayurbhanj Granite

73. General geologic settingsGeneral geologic settings
The basement of the Singhbhum metasedimentary rocks can be traced in a The basement of the Singhbhum metasedimentary rocks can be traced in a
broadly elliptical pattern of granitoids, with patches of TTG rock assembly, broadly elliptical pattern of granitoids, with patches of TTG rock assembly,
surrounded by metasediments and metavolcanics of Greenstone Belt surrounded by metasediments and metavolcanics of Greenstone Belt
association. association.
Most of the intrusive rock area is occupied by the Singhbhum granodiorite, Most of the intrusive rock area is occupied by the Singhbhum granodiorite,
dated at 3.1 Ga, and crosscut in rectangular pattern by voluminous dated at 3.1 Ga, and crosscut in rectangular pattern by voluminous
Neoarchaean mafic and ultramafic dike swarms. Neoarchaean mafic and ultramafic dike swarms.
An ancient core to the Singhbhum rocks is built by the relatively small An ancient core to the Singhbhum rocks is built by the relatively small
remnant of the Olderremnant of the Older
Metamorphic Group (OMG) and Older Metamorphic Tonalite Gneis Metamorphic Group (OMG) and Older Metamorphic Tonalite Gneis
(OMTG) rocks, dated between 3.4 and 3.5 Ga and metamorphosed to (OMTG) rocks, dated between 3.4 and 3.5 Ga and metamorphosed to
amhibolite facies. amhibolite facies.
The Singhbhum granodiorite is intrusive into these old rocks and to younger, The Singhbhum granodiorite is intrusive into these old rocks and to younger,
mid Archaean metasediments, at upper greenschist facies, including iron mid Archaean metasediments, at upper greenschist facies, including iron
formations, schists and metaquartzites and siliciclastics of the Iron Ore formations, schists and metaquartzites and siliciclastics of the Iron Ore
Group (IOG).Group (IOG).

74. MAHANADI GRABEN/TECTONIC ZONE IN CONTACT
WITH SINGHBHUM CRATON
GODAVARI GRABEN/GRANULITE BELTS
IN CONTACT WITH
DHARWAR CRATON
TECTONIC ZONE,
GRANULITE BELT IN
CONTACT WITH
EGMB
TECTONIC/GRANULITE
CONTACT WITH SMB
OF CITZ
TECTONIC
CONTACT
WITH
SAKOLI FOLD BELT
C I T Z
SMB
SFB
BASTAR CRATON- MARGINAL FEATURES
Bastar Craton

75. Bastar cratonBastar craton
The Bastar craton (BC) is also called Bastar-Bhandara craton. It lies to ENE The Bastar craton (BC) is also called Bastar-Bhandara craton. It lies to ENE
of the Dharwar craton (DC), separated from the latter by the Godavari rift. of the Dharwar craton (DC), separated from the latter by the Godavari rift.
Located to the south of the Central Indian Tectonic Zone (CITZ) the Bastar Located to the south of the Central Indian Tectonic Zone (CITZ) the Bastar
craton is limited by three prominent rifts, namely the Godavari rift in the SW, craton is limited by three prominent rifts, namely the Godavari rift in the SW,
the Narmada rift in the NW and the Mahanadi rift in the NE.the Narmada rift in the NW and the Mahanadi rift in the NE.
Its southeastern boundary is marked by the Eastern Ghats front. The western Its southeastern boundary is marked by the Eastern Ghats front. The western
limit of the Eastern Ghats mobile belt overlying the Bastar craton is limit of the Eastern Ghats mobile belt overlying the Bastar craton is
demarcated by a shear zone, which in fact is a terrain boundary shear zone demarcated by a shear zone, which in fact is a terrain boundary shear zone
(Bandyopadhyay et al., 1995).(Bandyopadhyay et al., 1995).
The Bastar craton is essentially formed of orthogneisses with enclaves of The Bastar craton is essentially formed of orthogneisses with enclaves of
amphibolites, vestiges of banded TTG gneisses of 3.5–3.0 Ga, and low- to amphibolites, vestiges of banded TTG gneisses of 3.5–3.0 Ga, and low- to
high-grade metasediments as supracrustals.high-grade metasediments as supracrustals.
The gneiss/migmatites and amphibolites, constituting the early crustal The gneiss/migmatites and amphibolites, constituting the early crustal
componentscomponents
of the Bastar craton, are grouped under the of the Bastar craton, are grouped under the Amgaon gneiss that resembles Amgaon gneiss that resembles the the
Peninsular Gneiss Complex of the Dharwar craton. It ranges in composition Peninsular Gneiss Complex of the Dharwar craton. It ranges in composition
from tonalite to adamellite. Amgaon gneisses occur in the north of Bastar from tonalite to adamellite. Amgaon gneisses occur in the north of Bastar
craton and south of Central Indian Shear zone (CIS).craton and south of Central Indian Shear zone (CIS).

77. Bastar cratonBastar craton
In In Bastar craton the gneisses are classified into 5 types. These are: the Bastar craton the gneisses are classified into 5 types. These are: the
Sukma Sukma granitic gneiss (Group 1), Barsur migmatitic gneiss granitic gneiss (Group 1), Barsur migmatitic gneiss
(Group 2), leucocratic granite (Group 3) occurring as plutons (Group 2), leucocratic granite (Group 3) occurring as plutons
with migmatitic gneiss, pegmatoidal or very coarse granite with migmatitic gneiss, pegmatoidal or very coarse granite
(Group 4), and fine-grained granite (Group 5) occurring amidst (Group 4), and fine-grained granite (Group 5) occurring amidst
the Sukma gneisses. the Sukma gneisses.
The gneisses of Groups 1 and 2 are chemically and The gneisses of Groups 1 and 2 are chemically and
mineralogically similar to the Archaean TTG, while the gneisses mineralogically similar to the Archaean TTG, while the gneisses
of Groups 3, 4 and 5 are of granitic nature.of Groups 3, 4 and 5 are of granitic nature.
In the Bastar craton, three Archaean supracrustal units are In the Bastar craton, three Archaean supracrustal units are
recognized. First is Sukma metamorphic suite consisting of recognized. First is Sukma metamorphic suite consisting of
quartzites, metapelites, calc-silicate rocks, and BIF with quartzites, metapelites, calc-silicate rocks, and BIF with
associated metabasalt and ultramafic rocks.associated metabasalt and ultramafic rocks.

78. Bastar cratonBastar craton
Second is Bengpal Group which is also characterized by the similar Second is Bengpal Group which is also characterized by the similar
rock association as that of the Sukma unit. Hence, no distinction rock association as that of the Sukma unit. Hence, no distinction
can be made between the two groups except that the Sukma suite can be made between the two groups except that the Sukma suite
shows a higher grade of metamorphism characterized by shows a higher grade of metamorphism characterized by
cordierite-sillimanite in the metapelites.cordierite-sillimanite in the metapelites.
Third Group, the Bailadila Group is seen to overlie them. This Third Group, the Bailadila Group is seen to overlie them. This
Group contains BIF,grunerite-quartzite, and white quartzites.Group contains BIF,grunerite-quartzite, and white quartzites.

80. Bastar cratonBastar craton
Central Indian fold belts and cratons.
(a)Location of central Indian fold belts.
(b)Geological setting of Bastar Craton in relation to
adjacent cratons and Central Indian Tectonic Zone
(CITZ).
Abbreviations:
BC=Bastar Craton,
CGGC=Chhotangapur Granite Gneiss Complex,
CIS=Central Indian shear zone,
DC = Dharwar craton,
SBC=Singhbhum craton,
SONA ZONE = Son-Narmada Lineament zone
bounded by Son-Narmada North Fault (SNNF) and Son-
Narmada South Fault (SNSF).
(c) Simplified geological map (bottom sketch) shows
the CITZ sandwiched between Bastar craton in the
south and Bundelkhand craton in the north.
The four localities of granulites described in the Satpura
fold belt are:
BBG = Bhandara-Balaghat granulite,
BRG = Bilaspur-Raipur granulite,
MG = Makrohar granulite, and
RKG = Ramakona-Katangi granulite

81. Evolution of Southwestern margin
of the Bastar Craton
Bastar Craton = 1.9 Ga
Did Kondagaon Granulite Belt evolve
\earlier (intrusive granites 2.4-2.6 Ga)
Bhopalpatnam belt evolved between
1.9-1.6 Ga
But lithologies from 3.5 Ga older
Supracrustals can be traced onto the
Bhopalpatnam Belt
So only thrust and granulite metamorphic
Imprint at 1.9-1.6 Ga?

82. SUMMARY OF EVOLUTION OF BASTAR CRATON
4.0-3.5 Thick silicic crust, TTG type Did Trondhjemite dominate?
Early Supracrustals probably in several time episodes
Mesoarchaean Granulite facies rocks?
3.5-2.7 Early Supracrustals and Granite magmatism, history not clear
2.7-2.0 Early Neoarchaean Superior type BIF belts
Kondagaon Granulites
Late Neoarchaean Kotri- Dongargarh
1.9 Ga Chandenar-Tulsidongar Belt Intracratonic tectonomagmatism
Mafic Dyke Swarms
1.9-1.6 Ga Bhopalpatnam Granulite Belt evolves
1.6 Ga to 600 Ma Rift basins evolve
Final amalgamation of terrane components by this time?
New Cretaceous - Kimberlites and Deccan Trap dykes

83. Dharwar CratonDharwar Craton
•The Dharwar craton in Karnataka witnessed
Widespread development of greenstones
during the Meso- and Neo-Archaean. The
major greenstone belts in the Karnataka
craton have been designated with local
names from west to east as Kudremukh,
Bababudan, Shimoga, Chitradurga, Sandur,
Ramgiri-Hungund, Hutti-Kolar, Raichur,
Narayanpet-Gadwal, Khammam and Nellore.
• Dharwar supergroup and divided into
Bababudan and Chitradurga. There is no
unconformity between Bababudan and
Chitradurga groups. The Chitradurga group
is made up of mafic-ultramafic volcanic
rocks, BIF, BMF, arenites, phyllites,
stromatolitic carbonates, carbon phyllites,
polymictic and oligomictic conglomerates,
greywacke, felsic volcanics, bimodal
volcanics intruded by granitoids and dykes.

84. Map of Western and Eastern Dharwar Craton

85. 
Western Dharwar Craton is occupied by vast
areas of Peninsular Gneiss along with two
prominent super belts of Bababudan- Western
Ghats-Shimoga and Chitradurga-Gadag belonging
to the Dharwar Super group.
 Younger granites (~2600 Ma) like
Chitradurga, Hosadurga, Arsikere and Banavara
occur as isolated plutons in the gneissic country.
 The Chitradurga-Gadag superbelt belt
covering an area of 6000sq.km.
 The latter includes the Bababuddan and
Chitradurga Group which is exposed in central part
of the terrain exposed in a curvilinear belt broadly
oriented by NNW-NNE.
WESTERN DHARWAR CRATON

86. EASTERN DHARWAR CRATON
 Eastern Dharwar Craton has three major lithological
types: Greenstone belts, TTG and Granitoids. They are
preserved as linear arcuate Belts with limited width
dismembered, truncated and punctuated by different types
of granitoids of variable ages but mostly 2.6-2.5 Ga. Old K-
granites and tonolites.
 These granitoids form the most prominent rock
complex of the Eastern Dharwar Craton and have yielded
examples are Kolar, Hutti, Ramgiri-Hungund and Gadwal.
There are other small greenstone belts such as Khammam.
 All these greenstone belts have been truncated by
major transcurrent shear zone which behaved as plumbing
systems for the flow of hydrothermal fluids responsible for
gold mineralization. The eastern margin of these belts
appears to be Accretionary planes.

87. Closepet GraniteClosepet Granite
The Closepet granite appears to be an excellent case-study, showing all parts of a typical
granitic body:
(1)the roots, where magma is generated, interacts with the basement and evolves;
(2)the magma chamber and transfer zone, where magma moves upwards;
(3)the intrusions with feeder dykes. This makes the Closepet Granite an outstanding
"natural laboratory“ to study magmatic processes operating in a granitic body. It's also a
unique example where the hypothesis on formation and evolution of granitic intrusions can
be tested directly on the field, rather than through indirect methods.
Some problems, however, remain to be assessed regarding the origin of the Closepet
Granite.
One is the problem of the size: even if the processes operating are the same all along the
Closepet Granite, such a huge body probably needs several feeding zones, or even a
continuous band of magma input zones, even if the subsequent evolution is similar all
along the granite.
A second question is the unique nature of the Closepet granite within the Dharwar craton:
even if granitic bodies are common in the area none of them reaches the same size, nor
displays the same degree of crust-mantle interaction.
The source of both the large quantity of observed magma, and the considerable amount of
heat needed remains unknown. This calls for further investigations on the geodynamical
setting and evolution of the Late Archaean Dharwar Craton.

89. Archean Formation of granite greenstone beltsArchean Formation of granite greenstone belts
•Early continents formed by collision of felsic proto-continents.
•Greenstone belts represent volcanic rocks and sediments that accumulated
along and above subduction zones and then were sutured to the protocontinents during collisions.
•Protocontinents small, rapid convection breaks them up

90. CHITRADURGA SUPER GROUP
1.Chitradurga Schist belt
2.Gadag Schist belt
3.Javanahalli Schist belt
4.Chikkanayakana Halli Schsit belt
5.Kunigal schist belt
6.Karighatta Schist belt

91. Chitradurga Schist belt

92. The Chitradurga schist belt extends over a strike length of about 460 km from
Gadag in the north to Srirangapatnam in the south. The lithounits of this
schist belt comprise metavolcanic rocks- both metabasalts and meta acid
volcanics and metasedimentaries comprising graywacke-argillite suite of rocks
and banded iron formation. There is a well known sulphide belt extending
from Yerahalli in the south to Honnemaradi in the north over a strike length
of 40 km hosting sulphides like pyrite, pyrrhotite, arsenopyrite, chalcopyrite,
galena, sphalerite, etc. Parallel to this sulphide belt and sometimes closely
intermixed with this sulphide belt gold mineralisation is also encountered. In
this sulphide belt considerable silver mineralisation is also noticed.
Geologically, this mineralisation simulates mesothermal type of copper-silver-
gold-lead-zinc deposit. At present, exploration for gold in this schist belt is in
progress in the G.R. Halli-C.K. Halli and Honnemaradi area. In addition,
further investigation is in progress in Ajjanahalli and Bellara areas. The details
of the above prospects are furnished in a tabular formt.
Chitradurga Schist belt

93. Gadag schist belt

94. The Gadag schist belt consists of a 2000m thick pile of meta-volcanics and meta-
sediments and a banded iron-formation . The structural disposition of the belt is the
result of an overall E-W compressional regime with uplift and diaperism of the sialic
basement within which the N-S trending Archaean shear systems have caused buckling
and refolding of earlier fold belts, making all the linear elements parallel to the direction
of shear. The underlying gneisses as well as the younger Closepet granite have a similar
trend.
Gadag schist belt is drawn out in the form of a 400 km long narrow N-S to NW-SE
belt with a convexity towards the east. The eastern margin of the schist belt is a major
thrust contact marked by a strong mylonitic zone believed to represent the line of
suture marking the junction of the Archaean nucleus lying to the west and the
comparatively younger gneiss complex to the east. Deep seismic sounding carried
across the schist belt shows a major fault dipping to the east along the eastern margin
of the schist belt. Followed south- ward, the schist belt splits into several narrow belts
inter-layered with gneisses. While the geological nature and the inter- relationship of
the volcano-sedimentary rocks of the supracrustals sequences help in understanding
the tectono-sedimentary environments of deposition, there are no results of detailed
geophysical studies reported so far over the schist belts of the carton.

95. Javanahalli Schist belt
Rock types:
Dolerite
Quartz vein
Augen Gneiss
Migmatite Gneiss
Fuchsite Quartzite
Ultramafic rock
B M Q
Amphibolite
Calc silicate
Paragneiss

96. Nuggihalli Schist belt, Hassan district

97. Sulphide mineralisation (pyrite with subordinate pyrrhotite and chalcopyrite)
associated with titaniferous magnetite bands is seen near Nuggihalli.
In the Tagadur area, sulphide mineralisation (pyrite, pyrrhotite,
pentlandite and cubanite) is seen in gabbro and titaniferous magnetite bands.
Nuggihalli Schist Belt is a narrow arcuate belt (60 km x 12 km) extending
from Arsikere in the north to Kempinkote in south. It occurs as a mega
enclave within the granite gneisses of the Western Dharwar Craton.
Chromite first reported from the serpentinite , was established as segregates
of the fractionated melt and the serpentinite was an altered product of
original dunite - peridotite of a layered complex. Anomalous values of PGE
(approx. 258 ppb of Pt and 43 ppb of Pd) along with significant amount of
gold and copper have been reported from this belt although the PGE values
reported are of semiquantitative in nature.
The Nuggihalli schist belt comprises metavolcanics (hornblende schist and
amphibolite) surrounded by Peninsular gneisses and granites with associated
quartz veins and pegmatites of post-Dharwar age. These formations are
intruded by an ultramafic complex consisting serpentinite, talctremolite
schist (pyroxenite), olivine dolerite titaniferous magnetite veins and
chromite veins.

98. KUNIGAL SCHIST BELTKUNIGAL SCHIST BELT

99. HOLENARSIPUR SCHIST BELTHOLENARSIPUR SCHIST BELT

100. HOLENARSIPUR SCHIST BELTHOLENARSIPUR SCHIST BELT
The Holenarasipur schist belt is one of the most critical, complicated and The Holenarasipur schist belt is one of the most critical, complicated and
oldest (3.2-3.5 by) supracrustal belts in the Dharwar craton of India. Two oldest (3.2-3.5 by) supracrustal belts in the Dharwar craton of India. Two
lithostratigraphic groups, the Sargur and Dharwar, are separated by an angular lithostratigraphic groups, the Sargur and Dharwar, are separated by an angular
unconformity. The Sargur group starts with a basic-ultrabasic base which is unconformity. The Sargur group starts with a basic-ultrabasic base which is
overlain by metasediments of various compositions, whereas the Dharwar overlain by metasediments of various compositions, whereas the Dharwar
group develops upward from a basal conglomerate into a sequence of group develops upward from a basal conglomerate into a sequence of
amphibolites, quartzites and banded magnetite quartzites. amphibolites, quartzites and banded magnetite quartzites.
The Dharwar belt as a whole is metamorphosed to an amphibolite facies The Dharwar belt as a whole is metamorphosed to an amphibolite facies
grade, but the Sargur group shows a higher grade (kyanite zone). Recumbent, grade, but the Sargur group shows a higher grade (kyanite zone). Recumbent,
isoclinal, doubly plunging folds are common, but a regional northward plunge isoclinal, doubly plunging folds are common, but a regional northward plunge
is dominant. is dominant.
Unlike the Dharwars there is no conglomerate at the base or anywhere in the Unlike the Dharwars there is no conglomerate at the base or anywhere in the
succession of the Sargur group. The meta-ultramafics/mafics of the Sargur succession of the Sargur group. The meta-ultramafics/mafics of the Sargur
group are in places interbedded with fuchsite quartzite and show deformed group are in places interbedded with fuchsite quartzite and show deformed
pillow lavas and microspinifex textures. Their composition is similar to pillow lavas and microspinifex textures. Their composition is similar to
peridotitic, pyroxenitic and basaltic komatiites.peridotitic, pyroxenitic and basaltic komatiites.

102. Bababudan Group- Western ghats
Shimoga schist & ChikmagalurIron formations
Archean
Meta volcanics
Meta basalts
Basement gniess
Quartzites
Younger Granites &
dyke rocks

103. Sandur schist belt- Iron formations
Proterozoic BIF’s
Granites
Amphibolite/chlorite
Schist belt
Pegmatites
Kolar Schist belt
Archean Granites
Neo archean Amphibolites
Meta volcanics
Chlorite schist belt
Quartzites
Basement gneisses

105. Hutti Maski schist belt
Pegmatites
Younger dykes
Meta sediments
Quartzties
Amphibolite schist
Chlorite schist
Meta volcanics
Basement gneiss

106. Mobile belts are elongated areas of mountain Mobile belts are elongated areas of mountain
building activity – “orogenic activity”building activity – “orogenic activity”
along the margins of continents along the margins of continents
where sediments are deposited in the where sediments are deposited in the
relatively shallow waters of the continental relatively shallow waters of the continental
shelf shelf
and the deeper waters at the base of the and the deeper waters at the base of the
continental slopecontinental slope
During plate convergence along these margins, During plate convergence along these margins,
the sediments are deformed the sediments are deformed
and intruded by magmaand intruded by magma
creating mountain rangescreating mountain ranges
Mobile BeltsMobile Belts

107. Mobile BeltsMobile Belts
Orogenic (Gr. Orogenic (Gr. Oros means mountain and genic means birth) belts or orogens Oros means mountain and genic means birth) belts or orogens
are are some of the most prominent tectonic features of continents. some of the most prominent tectonic features of continents.
These terms are, however, not synonymous to Mountain belt These terms are, however, not synonymous to Mountain belt
which is a geographic term referring to areas of high and rugged which is a geographic term referring to areas of high and rugged
topography. Surely, topography. Surely, mountain belts are also orogenic belts but mountain belts are also orogenic belts but
not all orogenic belts are mountainsnot all orogenic belts are mountains. orogenic belts, also called . orogenic belts, also called
mobile belts, are termed fold belts because they are made up of mobile belts, are termed fold belts because they are made up of
rocks that show large-scale folds, and faults/thrusts and rocks that show large-scale folds, and faults/thrusts and
metamorphism with evidence of melting or high mobility in the metamorphism with evidence of melting or high mobility in the
core region during orogenesis. These belts are characteristically core region during orogenesis. These belts are characteristically
formed of (a) thick sequences of shallow water sandstones, formed of (a) thick sequences of shallow water sandstones,
limestones and shales deposited on continental crust and (b) limestones and shales deposited on continental crust and (b)
deep-water trubidites and pelagic sediments, commonly with deep-water trubidites and pelagic sediments, commonly with
volcanoclastic sediments and volcanic rocks. volcanoclastic sediments and volcanic rocks.

108. Mobile BeltsMobile Belts
Typical mobile belts, rather fold belts as titled here, have rocks Typical mobile belts, rather fold belts as titled here, have rocks
that were deformed and metamorphosed to varying degrees and that were deformed and metamorphosed to varying degrees and
intruded by plutonic bodies of granitic compositions. Some fold intruded by plutonic bodies of granitic compositions. Some fold
belts are also characterized by extensive thrust faulting and by belts are also characterized by extensive thrust faulting and by
movements along large transcurrent fault zones. Even movements along large transcurrent fault zones. Even
extensional deformation may be found in such belts. Most belts extensional deformation may be found in such belts. Most belts
show a linear central region of thick multiply deformed and show a linear central region of thick multiply deformed and
metamorphosed rocks bordered by continental margins, but metamorphosed rocks bordered by continental margins, but
some belts are also having oceanic margin on one side.some belts are also having oceanic margin on one side.

109. Mobile BeltsMobile Belts
AFB AFB Aravalli Fold BeltAravalli Fold Belt
Delhi FB Delhi FB Delhi Fold BeltDelhi Fold Belt
DFB DFB Dongargarh Fold BeltDongargarh Fold Belt
EGMB EGMB Eastern Ghats Mobile BeltEastern Ghats Mobile Belt
MFB MFB Mahakoshal Fold BeltMahakoshal Fold Belt
PMB PMB Pandyan Mobile BeltPandyan Mobile Belt
Satpura FB Satpura FB Satpura Fold BeltSatpura Fold Belt
SFB SFB Singhbhum Fold BeltSinghbhum Fold Belt
SKFB SSKFB S akoli Fold Beltakoli Fold Belt

110. Pandyan Mobile BeltPandyan Mobile Belt
Pandyan Mobile Belt (PMB) is the name given by Pandyan Mobile Belt (PMB) is the name given by
Ramakrishnan (1993, 1988) to the Southern Granulite Ramakrishnan (1993, 1988) to the Southern Granulite
Terrain (SGT) situated to the south of the E-W Terrain (SGT) situated to the south of the E-W
trending Palghat-Cauvery Shear Zone (PCSZ) .The trending Palghat-Cauvery Shear Zone (PCSZ) .The
name Pandyan is adopted after the legendary dynasty name Pandyan is adopted after the legendary dynasty
that ruled this part of South India in the historical past. that ruled this part of South India in the historical past.
Interestingly, the SGT has been defined variously by Interestingly, the SGT has been defined variously by
different workers. According to Fermor (1936), this different workers. According to Fermor (1936), this
terrain is a part of the large “Charnockite Province” terrain is a part of the large “Charnockite Province”
located to the south of the orthopyroxene-in (Opx-in) located to the south of the orthopyroxene-in (Opx-in)
isograd, delineated along a line straddling the join isograd, delineated along a line straddling the join
Mangalore-Mysore-Bangalore-Chennai (Pichamuthu, Mangalore-Mysore-Bangalore-Chennai (Pichamuthu,
1965). 1965).

111. The Pandyan mobile belt (PMB), according to Ramakrishnan (1993), The Pandyan mobile belt (PMB), according to Ramakrishnan (1993),
is the geological domain between the PCSZ in the north and the is the geological domain between the PCSZ in the north and the
AKSZ in the south. Impressed by swirling structural pattern in the AKSZ in the south. Impressed by swirling structural pattern in the
Madurai Block, Similar to Limpopo belt in South Africa, and by the Madurai Block, Similar to Limpopo belt in South Africa, and by the
general occurrence of fold belts either at the peripehery of a general occurrence of fold belts either at the peripehery of a
continent or sandwiched between two continents, Ramakrishnan continent or sandwiched between two continents, Ramakrishnan
carved out his Pandyan mobile belt from the segmented Southern carved out his Pandyan mobile belt from the segmented Southern
Granulite Terrain. A few years later, Ramakrishnan (2003) enlarged Granulite Terrain. A few years later, Ramakrishnan (2003) enlarged
the domain of his mobile belt and included areas of granulites on the domain of his mobile belt and included areas of granulites on
both n orth and south margins of his initially proposed Pandyan both n orth and south margins of his initially proposed Pandyan
mobile belt, perhaps on the consideration of meaningful mobile belt, perhaps on the consideration of meaningful
geochronological data available over almost entire SGT. geochronological data available over almost entire SGT.
Ramaskrishnan also incorporated the granulite region north of the Ramaskrishnan also incorporated the granulite region north of the
MBSZ.MBSZ.

112. Simplified Geological map of the southern India
(after GSI and ISRO, 1994), showing the
major geological domains, the Western Dharwar
Craton (WDC), Eastern Dharwar Craton (EDC),
and Southern Granulite Terrain (SGT) along
with the Cauveri Shear Zone System (CSZ).
Abbreviations: AKSZ = Achankovil Shear Zone;
AH = Anamalai Hills; AT = Attur; BS =
Bhavani Shear zone; BL = Bangalore; BR
=Biligirirangan; CHS = Chitradurga Shear Zone;
CG = Coorg;
CM = Coimbatore; EDC = East Dharwar
Craton; K = Kabbaldurga; KL = Kolar; KKB =
Kerala Khondalite Belt;MS = Moyar Shear zone;
N = Nilgiri; OT= Ooty; PCSZ = Palgahat Shear
Zone; PL = Pollachi; PMB = Pandyan Mobile
Belt; SGT = Southern Granulite Terrain; SH =
Shevaroy Hills; WDC = West Dharwar Craton;
GR-Am = Isograd between Greenschist and
Amphibolite Facies; Am-Gt = Isograd between
Amphibolite and Granulite Facies; TZ =
Transition Zone of amphibolite and granulite
facies. Inset shows various identified crustal block

113. A variety of mineral deposits are of Archean-ageA variety of mineral deposits are of Archean-age
but gold is the most commonly associated,but gold is the most commonly associated,
although it is also found although it is also found
in Proterozoic and Phanerozoic rocksin Proterozoic and Phanerozoic rocks
This soft yellow metal is prized for jewelry, This soft yellow metal is prized for jewelry,
but it is or has been used as a monetary standard, but it is or has been used as a monetary standard,
in glass making, electric circuitry, and chemical industryin glass making, electric circuitry, and chemical industry
About half the world’s gold since 1886 About half the world’s gold since 1886
has come from Archean and Proterozoic rocks has come from Archean and Proterozoic rocks
in South Africain South Africa
Gold mines also exist in Archean rocks Gold mines also exist in Archean rocks
of the Superior craton in Canadaof the Superior craton in Canada
Archean Mineral ResourcesArchean Mineral Resources

114. Archean sulfide deposits of Archean sulfide deposits of
zinc, zinc,
copper copper
and nickel and nickel
occur in Australia, Zimbabwe, occur in Australia, Zimbabwe,
and in the Abitibi greenstone belt and in the Abitibi greenstone belt
in Ontario, Canadain Ontario, Canada
Some, at least, formed as mineral deposits Some, at least, formed as mineral deposits
next to hydrothermal vents on the seafloor, next to hydrothermal vents on the seafloor,
much as they do now around black smokersmuch as they do now around black smokers
Archean Sulfide DepositsArchean Sulfide Deposits

115. About 1/4 of Earth’s chrome reserves About 1/4 of Earth’s chrome reserves
are in Archean rocks, especially in Zimbabweare in Archean rocks, especially in Zimbabwe
These ore deposits are found in These ore deposits are found in
the volcanic units of greenstone beltsthe volcanic units of greenstone belts
where they appear to have formed where they appear to have formed
when crystals settled and became concentrated when crystals settled and became concentrated
in the lower parts of plutons in the lower parts of plutons
such as mafic and ultramafic sillssuch as mafic and ultramafic sills
Chrome is needed in the steel industryChrome is needed in the steel industry
The United States has very few chrome deposits The United States has very few chrome deposits
so must import most of what it usesso must import most of what it uses
ChromeChrome

116. One chrome deposit in the United States One chrome deposit in the United States
is in the Stillwater Complex in Montanais in the Stillwater Complex in Montana
Low-grade ores were mined there during war Low-grade ores were mined there during war
times, times,
but they were simply stockpiled but they were simply stockpiled
and never refined for chromeand never refined for chrome
These rocks also contain platinum, These rocks also contain platinum,
a precious metal, that is used a precious metal, that is used
in the automotive industry in catalytic convertersin the automotive industry in catalytic converters
in the chemical industryin the chemical industry
for cancer chemotherapyfor cancer chemotherapy
Chrome and PlatinumChrome and Platinum

117. Banded Iron formations are sedimentary rocks Banded Iron formations are sedimentary rocks
consisting of alternating layers consisting of alternating layers
of silica (chert) and iron mineralsof silica (chert) and iron minerals
About 6% of the world’s About 6% of the world’s
banded iron formations were deposited banded iron formations were deposited
during the Archean Eonduring the Archean Eon
Although Archean iron ores Although Archean iron ores
are mined in some areas are mined in some areas
they are neither as thick they are neither as thick
nor as extensive as those of the Proterozoic Eon, nor as extensive as those of the Proterozoic Eon,
which constitute the world’s major source of ironwhich constitute the world’s major source of iron
IronIron

118. PegmatitesPegmatites are very coarsely crystalline igneous are very coarsely crystalline igneous
rocks, rocks,
commonly associated with granite plutons commonly associated with granite plutons
Some Archean pegmatites, Some Archean pegmatites,
such in the Herb Lake district in Manitoba, Canada, such in the Herb Lake district in Manitoba, Canada,
and Rhodesian Province in Africa, and Rhodesian Province in Africa,
contain valuable mineralscontain valuable minerals
In addition to minerals of gem quality, In addition to minerals of gem quality,
Archean pegmatites contain minerals mined Archean pegmatites contain minerals mined
for lithium, beryllium, rubidium, and cesiumfor lithium, beryllium, rubidium, and cesium
PegmatitesPegmatites

119. Archean To Proterozoic Sedimentary Archean To Proterozoic Sedimentary
RocksRocks
• Archean
•4 bya: mostly deep water clastic deposits such as mudstones and muddy sandstones.
–high concentration of eroded volcanic minerals (Sandstones called Graywackes).
• 3 bya: absence of shallow water shelf carbonates.
–increasing chert.
– low oxygen levels, free iron was much more common in the Archean.
–Iron formed “chemical sinks” that consumed much of the early planetary oxygen.
–Formed banded ironstones, commonly with interbedded chert.
•Proterozoic – 2 bya Carbonates* become important
- Non-marine sediments turn red – iron is oxidized by the oxygen in AIR

120. • “Purana Basins”.
• Cratonic or Epicratonic basins.
• Platform Basins.
• Witness to the story of early crustal evolution.
• Useful for global comparison with similar basins.
• Importantly, these basins unveil the prelude to the
cambrian explosion of life.
• Occupies 20% of the area of the Precambrian of the
Peninsular India.
Proterozoic Sedimentary Proterozoic Sedimentary
BasinsBasins

121. Purana basins of Peninsular India within different Purana basins of Peninsular India within different
cratonscratons

122. Proterozoic sedimentary basins are divided into 2 types
based on age:
(a).Paleoproterozoic basins:
1.Bijawar and Sonrai basins Bundelkhand
and Harda Inlier craton
2.Gwalior basin
3.Abujhmar basin Bastar craton
4.Papaghni sub-basin Dharwar craton
[Cuddapah basin]

123. (b).(b).Meso-Neoproterozoic basins
11. Vindhyan basin Bundhekhand craton
2. Chhattisgarh basin
3. Khariar basin
4. (a)Ampani basin,
(b)Keskal, Singanpar Bastar craton
and Chedrapal outliers
5. Indravathi basin
6. Sabari[Sukma] basin
7. Pranhita-Godavari basin b/n Bastar and Dharwar
cratons
8. Cuddapah basin
9. Kaladgi basin Dharwar craton
10. Bhima basin

124. Palaeoproterozoic Basins
1.Bijawar Basin- trends ENE-WSW for about 100km with a
width of 4 to 20km from Ken River in the east to sonari in the
west. Sandwiched b/n Bundelkhand granite and Vindhyan
sediments.
2.Sonari Basin- 28km long and 5km wide, E-W trending situated
to the west of the ‘type’ Bijawar basin.
3.Harda Inlier- it exposed at Harda within the-Vindhyan
succession and Deccan Trap of Narmada valley.
4.Gwalior Basin- extends E-W for 80km with a width of
25km,near Gwalior to the north of Bundelkhand granite,almost
200km N-W of Bijawar basin.
5.Abujhmar Basin- named for ‘abujh mar’ or ‘unknown hills’
in the remote bansal region, covers an area of 3000sq.
km
6.Papaghni sub-basin : This sub-basin is described under
Cuddapah basin.

125. Meso-Neoproterozoic Basins
1.Vindhyan basin
Largest single Purana basin, spectacular, sickle shaped, ENE
trending, situated on Bundelkhand craton.
Includes 4 groups: (d). Bhander group (1300-1500m)
(c). Rewa group(100-300m)
(b). Kaimur group(400m)
(a). Semri group (3000-4000m)
Major structure is synclinorium with the axis curving along the
middle of the sickle-shaped basin.
Recent robust dating has fixed the beginning of Vindhyan
sedimentation around 1600-1720 Ma.
Life: Stromatolites are abundant in Vindhayan record but they
have long time range and hence have only limited correlative
value.

126. Geologic map of the Vindhyan basin, central India.

127. 2.Chhattisgarh basin
Larget Purana basin in Bastar craton, covering an area
of about 36000 sq. km is situated on the northern edge
of Bastar craton.
Lithostatigraphy:
(c). Raipur Group[1900m]
(b). Chandrapur Group[400m]
(a). Singhora Group[400m]
Lithology: Felspathic arenite, arkose, basal
conglomerate, sandstone, dolomite shale, limestone.
Evidence of life- Microbiota include prokaryotic
cyanobacteria, unidentified algal remains and
acritarchs.

128. Generalised geological map of Chhattisgarh basin(after Das et Generalised geological map of Chhattisgarh basin(after Das et
al.1992)al.1992)

129. 3.Khariar Basin3.Khariar Basin
It is an irregular, oval-shaped basin occupying It is an irregular, oval-shaped basin occupying
the N-S trending Nawagarh-Khariar plateau.the N-S trending Nawagarh-Khariar plateau.
Covering an area of 1500sq.km and containing Covering an area of 1500sq.km and containing
1000m thick sediments.1000m thick sediments.
Sediments are called as Sediments are called as Pairi GroupPairi Group(600-1000m)(600-1000m)
Stromatolites indicate Lower to Upper Riphean Stromatolites indicate Lower to Upper Riphean
age, but no radiometric data are available.age, but no radiometric data are available.

130. Occupying an area of 220 sq.km on a small plateau
south of Khariar near Ampani consists of a 280m thick
sandstone – shale sequence.
The sediments are domed up around hornblend
granodiorite at Khaligarh,which is thought to be
intrusive.
5.Indravati Basin
Irregular rhomboid basin covering an area of 900 sq.km
and containing orthoquartzite-shale-carbonate sequence
of about 500m thick on the average.
Cement grade Limestone and dolomite are important
economic minerals.
4.Ampani Basin

131. 6.Sabari Basin
A triangular basin of 700 sq.km
Sabari group consists of a basal conglomerate and thick-
bedded ortho-quartzite, overlain by a cream to grey
coloured limestone and followed by purple to grey shale.
7. Pranhita-Godavari Basin
Occurs in two parallel NW-SE trending sub-basins,
situated at the junction of Dharwar and Bastar cratons.
Developed after amalgamation of the cratons in
Palaeoproterozoic.

132. The western sub-basin is called the Pakhal belt and the
eastern sub-basin as the Albaka belt.
The P-G basin is extends for a length of ~400km with
width of ~100km.
Includes the width of ~40km for Godavari graben of
Gondwana sediments occurring in the middle and
separating the two sub-basins.
The aggregate thickness of the sediments of the P-G basin
is estimated at about 6000m.
Divided into 4 major groups, namely Mallampalli, Mulug,
Penganga and Sullavai separated by 3 unconformities.

133. 8.Cuddapah Basin
Crescent shaped,easterly concave and N-S trending,covers
an area of 44000 sq.km in the east-central part of Dharwar
craton.
Characterised by quartzite-carbonate-shale cycles having an
aggregate thickness i.e estimated b/n 6 to 12km.
The western half of the basin is undeformed and consists
of 4 sub-basins: the Papaghni, Kurnool, Srisailam and Palnad.
Life-Stromatolites are abounding,carbonaceous
microfossils like Tawuia, Chuaria, trace fossils, calcareous
algae indicate Neoproterozoic age.

134. Cuddapah Basin in Eastern Dharwar Cuddapah Basin in Eastern Dharwar
Craton Craton

135. 9.Kaladgi Basin
E-W trending irregular basin,covers an area 8300sq.km
The older succession of Kaladgi basin is called the
Bagalkot Group that correspond to the Cuddapah
supergroup
The upper succession is called the Badami Group i.e the
possible equivalent of Kurnool Group.
Bagalkot Group is divided into the lower Lokpur
Subgroup and the upper Simikeri subgroup.
Life - Bagalkot Group contains microstromatolites
suggest early Riphean age, Badami Group also contains
acritarchs & trace fossils that suggest Vendian age.

136. 10.Bhima basin
Irregular,NE trending,consisting dominantly of limestone
covers an area of 5200sq.km,situated to the northwest of
Cuddapah basin and northeast of Kaladgi basin.
Aggregate thickness of sediments is about 270m.
Well known for its large reserves of limestone and the newly
discovered uranium occurrence near Gogi.
Sediments are practically horizontal, but disturbed along
transverse faults.

137. Bhima basin Dharwar craton(after Kale and Bhima basin Dharwar craton(after Kale and
Peshwa,1991)Peshwa,1991)

138. Economic mineral deposits Economic mineral deposits
Diamond- Vindhyan and Kurnool formationsDiamond- Vindhyan and Kurnool formations
Pyrite- the Bijaigarh shales of the Lower KaimursPyrite- the Bijaigarh shales of the Lower Kaimurs
Coal- Semris and Kaimurs groupCoal- Semris and Kaimurs group
Lime stone- in the Sone Valley in Bihar and U.P., in Rewa, in Lime stone- in the Sone Valley in Bihar and U.P., in Rewa, in
Jabalpur, in Guntur and in the Bhima Valley in Hyderabad Jabalpur, in Guntur and in the Bhima Valley in Hyderabad
Building and decorative stones- Lower Vindhyan and Lower Building and decorative stones- Lower Vindhyan and Lower
Bhander stages, limestones of the Palnad regionBhander stages, limestones of the Palnad region
Glass Sand- Some Vindhyan sandstones near Allahabad, U.P Glass Sand- Some Vindhyan sandstones near Allahabad, U.P

139. Life during PrecambrianLife during Precambrian
The Precambrian fossil record is poorer than that for the succeeding Phanerozoic, and The Precambrian fossil record is poorer than that for the succeeding Phanerozoic, and
those fossils present (e.g. stromatolites) are of limited biostratigraphy biostratigraphic those fossils present (e.g. stromatolites) are of limited biostratigraphy biostratigraphic
use.use.
This is because many Precambrian rocks are heavily metamorphic rock This is because many Precambrian rocks are heavily metamorphic rock
metamorphosed, obscuring their origins, while others have either been destroyed by metamorphosed, obscuring their origins, while others have either been destroyed by
erosion, or remain deeply buried beneath Phanerozoic strataerosion, or remain deeply buried beneath Phanerozoic strata
The oldest fossil evidence of complex life comes from the Lantian formation, at least The oldest fossil evidence of complex life comes from the Lantian formation, at least
580 million years ago. A quite diverse collection of soft-bodied forms is known from a 580 million years ago. A quite diverse collection of soft-bodied forms is known from a
variety of locations worldwide between 542 and 600 Ma. These are referred to as variety of locations worldwide between 542 and 600 Ma. These are referred to as
Ediacaran biota Ediacaran or Vendian biota. Hard-shelled creatures appeared toward Ediacaran biota Ediacaran or Vendian biota. Hard-shelled creatures appeared toward
the end of that time span. By the middle of the later Cambrian period a very diverse the end of that time span. By the middle of the later Cambrian period a very diverse
fauna is recorded in the Burgess shale, including some which may represent stem fauna is recorded in the Burgess shale, including some which may represent stem
groups of modern taxa. The rapid radiation of lifeforms during the early Cambrian is groups of modern taxa. The rapid radiation of lifeforms during the early Cambrian is
called the Cambrian explosion of life.While land seems to have been devoid of plants called the Cambrian explosion of life.While land seems to have been devoid of plants
and animals, cyanobacteria and other microbes formed prokaryotic mats that covered and animals, cyanobacteria and other microbes formed prokaryotic mats that covered
terrestrial areas. terrestrial areas.

140. The first organisms were members The first organisms were members
of the kingdom Monera of the kingdom Monera
consisting of bacteria and archaea, consisting of bacteria and archaea,
both of which consist of both of which consist of prokaryotic cellsprokaryotic cells, ,
cells that lack an internal, membrane-bounded nucleus cells that lack an internal, membrane-bounded nucleus
and other structuresand other structures
Prior to the 1950s, scientists assumed that life Prior to the 1950s, scientists assumed that life
must have had a long early historymust have had a long early history
but the fossil record offered little to support this ideabut the fossil record offered little to support this idea
The Precambrian, once called The Precambrian, once called Azoic Azoic
(“without life”), seemed devoid of life(“without life”), seemed devoid of life
Oldest Known OrganismsOldest Known Organisms

141. Charles Walcott (early 1900s) described structures Charles Walcott (early 1900s) described structures
from the Paleoproterozoic Gunflint Iron Formation of Ontario, from the Paleoproterozoic Gunflint Iron Formation of Ontario,
Canada Canada
that he proposed represented reefs constructed by that he proposed represented reefs constructed by
algaealgae
Oldest Know OrganismsOldest Know Organisms
•Now called
stromatolites,
–not until 1954 were
they shown
–to be products of
organic activity
Present-day stromatolites (Shark Bay, Australia)

142. Different types of stromatolites include Different types of stromatolites include
irregular mats, columns, and columns linked by matsirregular mats, columns, and columns linked by mats
StromatolitesStromatolites

143. Present-day stromatolites form and grow Present-day stromatolites form and grow
as sediment grains are trapped as sediment grains are trapped
on sticky mats on sticky mats
of photosynthesizing cyanobacteriaof photosynthesizing cyanobacteria
although now they are restricted although now they are restricted
to environments where snails cannot liveto environments where snails cannot live
The oldest known undisputed stromatolites The oldest known undisputed stromatolites
are found in rocks in South Africa are found in rocks in South Africa
that are 3.0 billion years oldthat are 3.0 billion years old
but probable ones are also known but probable ones are also known
from the Warrawoona Group in Australia from the Warrawoona Group in Australia
which is 3.3 to 3.5 billion years oldwhich is 3.3 to 3.5 billion years old
StromatolitesStromatolites

144. Chemical evidence in rocks 3.85 billion years old Chemical evidence in rocks 3.85 billion years old
in Greenland indicate life was perhaps present thenin Greenland indicate life was perhaps present then
The oldest known cyanobacteria The oldest known cyanobacteria
were photosynthesizing organismswere photosynthesizing organisms
but photosynthesis is a complex metabolic process but photosynthesis is a complex metabolic process
A simpler type of metabolism A simpler type of metabolism
must have preceded itmust have preceded it
No fossils are known of these earliest organismsNo fossils are known of these earliest organisms
Other Evidence of Early LifeOther Evidence of Early Life

145. The earliest organisms must have resembled The earliest organisms must have resembled
tiny tiny anaerobicanaerobic bacteria bacteria
meaning they required no oxygenmeaning they required no oxygen
They must have totally depended They must have totally depended
on an external source of nutrientson an external source of nutrients
that is, they were that is, they were heterotrophicheterotrophic
as opposed to as opposed to autotrophicautotrophic organisms organisms
that make their own nutrients, as in photosynthesisthat make their own nutrients, as in photosynthesis
They all had They all had prokaryotic cellsprokaryotic cells
Earliest OrganismsEarliest Organisms

146. The earliest organisms, then, The earliest organisms, then,
were anaerobic, heterotrophic prokaryoteswere anaerobic, heterotrophic prokaryotes
Their nutrient source was most likely Their nutrient source was most likely
adenosine triphosphate (ATP) adenosine triphosphate (ATP)
from their environmentfrom their environment
which was used to drivewhich was used to drive
the energy-requiring reactions in cellsthe energy-requiring reactions in cells
ATP can easily be synthesizedATP can easily be synthesized
from simple gases and phosphatefrom simple gases and phosphate
so it was available so it was available
in the early Earth environmentin the early Earth environment
Earliest OrganismsEarliest Organisms

147. Proterozoic Fossil RecordProterozoic Fossil Record
EukaryotesEukaryotes (large cells with nuclei and organelles) (large cells with nuclei and organelles)
appeared by Mesoproterozoic time. Appeared by appeared by Mesoproterozoic time. Appeared by
1.6 by to 1.4 by. Increased in abundance about 1.4 1.6 by to 1.4 by. Increased in abundance about 1.4
by ago. by ago.
Potential for sexual reproduction and increasing Potential for sexual reproduction and increasing
variation (evolution)variation (evolution)

148. AcritarchsAcritarchs are single-celled are single-celled
spherical, organic-walled spherical, organic-walled
microfossils. microfossils.
Not known what sort of Not known what sort of
organism they were, but they organism they were, but they
may have been phytoplankton. may have been phytoplankton.
First appeared 1.6 by ago. First appeared 1.6 by ago.
Maximum diversity and Maximum diversity and
abundance 850 my ago. They abundance 850 my ago. They
declined steadily during the declined steadily during the
Neoproterozoic glaciation, and Neoproterozoic glaciation, and
few remained by 675 my ago. few remained by 675 my ago.
Useful for correlation in Useful for correlation in
Proterozoic strata.Proterozoic strata.
AcritarchsAcritarchs

149. Origin of Eukaryotes Origin of Eukaryotes
EukaryotesEukaryotes are thought to have arisen from an are thought to have arisen from an
originally endosymbiotic relationship between two or originally endosymbiotic relationship between two or
more prokaryotic cells. more prokaryotic cells.
Symbiosis - two or more organisms living together, Symbiosis - two or more organisms living together,
where each organism usually derives some benefit where each organism usually derives some benefit
froom the relationship. froom the relationship.
Endosymbiosis - One organism lives inside the other, Endosymbiosis - One organism lives inside the other,
e. g. bacteria in stomachs of cattle. e. g. bacteria in stomachs of cattle.

150. Origin of Eukaryotes Origin of Eukaryotes
Organelles (Mitochondria, plastids) were once free living Organelles (Mitochondria, plastids) were once free living
bacteria, that entered or were engulfed by another bacteria, that entered or were engulfed by another
prokaryote. Eventually, relationship became mutually prokaryote. Eventually, relationship became mutually
beneficial. beneficial.
E. g. host cell provided proto-mitochondrion (primitive E. g. host cell provided proto-mitochondrion (primitive
oxidizing bacteria) with plenty of food, mitochondrion oxidizing bacteria) with plenty of food, mitochondrion
performed oxidation and released energy for a bacterium that performed oxidation and released energy for a bacterium that
previously could only ferment. Eventually proto-mitochondrion previously could only ferment. Eventually proto-mitochondrion
gives up trying to reproduce. gives up trying to reproduce.
E.g. host cell waste products (carbon dioxide etc.) used by a E.g. host cell waste products (carbon dioxide etc.) used by a
cyanobacterium (proto-plastid) to photosynthesize. Plastid leaks cyanobacterium (proto-plastid) to photosynthesize. Plastid leaks
energy to host cell. Eventually gives up reproducing on its own.energy to host cell. Eventually gives up reproducing on its own.

151. Precambrian–Cambrian Precambrian–Cambrian
boundaryboundary
The Precambrian–Cambrian boundary problem The Precambrian–Cambrian boundary problem
is being studied in an areno-argillaceous is being studied in an areno-argillaceous
sequence in the Kashmir and Spiti Valley, sequence in the Kashmir and Spiti Valley,
Northwest Himalaya, India. In Kashmir, a rich Northwest Himalaya, India. In Kashmir, a rich
and diversified microbiota – cryptarchs and and diversified microbiota – cryptarchs and
algae of the Late Precambrian, and low Lower algae of the Late Precambrian, and low Lower
Cambrian trace fossils are recorded. In the Spiti Cambrian trace fossils are recorded. In the Spiti
Valley, the yield of microbiota is poor and the Valley, the yield of microbiota is poor and the
trace fossils are late Lower Cambrian.trace fossils are late Lower Cambrian.

152. Microfossils and Precambrian-Cambrian boundary stratigraphy at Maldeota, Lesser HimalayaMicrofossils and Precambrian-Cambrian boundary stratigraphy at Maldeota, Lesser Himalaya

153. Precambrian–Cambrian boundary;Precambrian–Cambrian boundary;
Lesser HimalayaLesser Himalaya
The affinity of the Ediacaran fossil The affinity of the Ediacaran fossil Shaanxilithes ningqiangensisShaanxilithes ningqiangensis and putatively  and putatively
related forms has long been enigmatic; over the past few decades, related forms has long been enigmatic; over the past few decades,
interpretations ranging from trace fossils to algae to metazoans of uncertain interpretations ranging from trace fossils to algae to metazoans of uncertain
phylogenetic placement have been proposed. Combined morphological and phylogenetic placement have been proposed. Combined morphological and
geochemical evidence from a new occurrence of geochemical evidence from a new occurrence of SS.. ningqiangensis ningqiangensis in the Krol  in the Krol
and Tal groups of the Lesser Himalaya of India indicates and Tal groups of the Lesser Himalaya of India indicates
that that SS.. ningqiangensis ningqiangensis is not a trace fossil, but rather an organic-walled tubular  is not a trace fossil, but rather an organic-walled tubular
body fossil of unknown taxonomic affinity.body fossil of unknown taxonomic affinity.
Specimens consist of compressed organic cylindrical structures, characterized Specimens consist of compressed organic cylindrical structures, characterized
by extended, overlapping or fragmented iterated units. Where specimens by extended, overlapping or fragmented iterated units. Where specimens
intersect, overlapping rather than branching or intraplanar crossing is intersect, overlapping rather than branching or intraplanar crossing is
observed. Lithologic comparisons and sequence stratigraphic data all suggest observed. Lithologic comparisons and sequence stratigraphic data all suggest
a late Ediacaran age for the uppermost Krol Group and basalmost Tal Groupa late Ediacaran age for the uppermost Krol Group and basalmost Tal Group

154. Plate tectonic activity has operated Plate tectonic activity has operated
since the early Proterozoic (or perhaps late Archean)since the early Proterozoic (or perhaps late Archean)
Most geologists are convinced Most geologists are convinced
that some kind of plate tectonic activity that some kind of plate tectonic activity
took place during the Archean as welltook place during the Archean as well
but it differed in detail from todaybut it differed in detail from today
Plates must have moved faster Plates must have moved faster
with more residual heat from Earth’s origin with more residual heat from Earth’s origin
and more radiogenic heat, and more radiogenic heat,
and magma was generated more rapidlyand magma was generated more rapidly
Archean Plate TectonicsArchean Plate Tectonics

155. As a result of the rapid movement of plates, As a result of the rapid movement of plates,
continents grew more rapidly along their margins continents grew more rapidly along their margins
a process called continental accretiona process called continental accretion
as plates collided with island arcs and other platesas plates collided with island arcs and other plates
Also, ultramafic extrusive igneous rocks,Also, ultramafic extrusive igneous rocks,
komitiites,komitiites,
were more common were more common
Archean Plate TectonicsArchean Plate Tectonics

156. The exposed part of the craton in North The exposed part of the craton in North
America is the America is the Canadian shieldCanadian shield
which occupies most of northeastern Canadawhich occupies most of northeastern Canada
a large part of Greenlanda large part of Greenland
parts of the Lake Superior region parts of the Lake Superior region
in Minnesota, Wisconsin, and Michiganin Minnesota, Wisconsin, and Michigan
and the Adirondack Mountains of New Yorkand the Adirondack Mountains of New York
Its topography is subdued, Its topography is subdued,
with numerous lakes and exposed Archean with numerous lakes and exposed Archean
and Proterozoic rocks thinly covered and Proterozoic rocks thinly covered
in places by Pleistocene glacial depositsin places by Pleistocene glacial deposits
Canadian ShieldCanadian Shield

157. Outcrop of Archean gneiss in the Canadian Outcrop of Archean gneiss in the Canadian
Shield in Ontario, CanadaShield in Ontario, Canada
Canadian Shield RocksCanadian Shield Rocks

158. Archean Brahma Schist in the deeply eroded Archean Brahma Schist in the deeply eroded
parts of the Grand Canyon, Arizonaparts of the Grand Canyon, Arizona
Archean Rocks Beyond the ShieldArchean Rocks Beyond the Shield