ChatGPT "Granitoids" includes diverse felsic intrusive rocks

"Granitoids" (sensu lato): loosely applied to a wide range of felsic plutonic rocks

1. Granitic Rocks
(Chapter 18)
Image: http://www.yosemite.ca.us/library/granite_crags/yosemite_watercolors.html

2. Granitoids
Image source: Winter, 2001
"Granitoids" (sensu lato): loosely applied to a wide range
of felsic plutonic rocks
1)Most granitoids of significant volume
occur in areas where the continental
crust has been thickened by orogeny,
either continental arc subduction or
collision of sialic masses.
Many granites, however, may post-
date the thickening event by tens of
millions of years.
A few broad generalizations:

3. Granitoids
Image source: Winter, 2001
"Granitoids" (sensu lato): loosely applied to a wide range
of felsic plutonic rocks
2) Because the crust is solid in its normal state, a thermal
disturbance is required to form granitoids
3) Most granitoids are derived by crustal anatexis, but
that the mantle may also be involved as a source of heat
for crustal anatexis, or a source of melt.
A few broad generalizations:

4. Granitoids
Image source: Darrell Henry
Petrographic characteristics of granitoid rocks
medium-to-coarsed grained rocks -
reflect slow cooling a volatiles.
•dominated by plagioclase
(generally first), quartz and K-
feldspar
•Hornblende (brown to green) and
biotite are the chief mafic minerals,
and Al-in-hornblende
geobarometer can yield P of
crystallization.
•Muscovite may be present as melt
phase or are a secondary mineral.
•Cpx may be found in the more
mafic granitoids
Common minor minerals: apatite, zircon,
magnetite, ilmenite, monazite, titanite,
tourmaline, allanite, fluorite and pyrite

5. Granitoids
Image source: From Paterson et al. (1992),
Trans. Royal. Soc. Edinburgh. 83, 459-471.
Also Geol. Soc. Amer. Spec. Paper, 272, 459-
471.
Petrographic characteristics of granitoid rocks
Backscattered electron image of a zircon
from the Strontian Granite, Scotland.
The grain has a rounded, un-zoned core
(dark) that is an inherited high-
temperature non-melted crystal from
the pre-granite source.
The core is surrounded by a zoned
epitaxial igneous overgrowth rim,
crystallized from the cooling granite.

6. Granitoids
Textures in granitoid rocks
Image source: John Winter, 2001
At relatively low P
H2O, a single
feldspar will crystallize and
then undergo further
exsolution (a, b) [hypersolvus]
At relatively high
P
H2O, two
feldspars will
crystallize with
possible further
exsolution of
each phase (c)
[subsolvus]

7. Granitoids
Myrmekitepatch that appears to be replacing microcline.Faint twins in the
myrmekite clearly shows that the probably quartz "worms" are in a plagioclase
matrix. image source: Kurt Hollocher
Petrographic characteristics of granitoid rocks
Myrmekites
•intergrowth of dendritic
quartz and plagioclase at K-
feldspar/plagioclase interface
•texture likely related to
subsolidus deformation

8. Granitoids
Petrographic characteristics of granitoid rocksTable 18-1. The Various Types of Enclaves
Name Nature Margin Shape Features
Xenolith piece of countrysharp toangularcontact metamorphic
rocks gradualto ovoidtexture and minerals
Xenocryst isolated foreignsharp angular corroded
crystal reaction rim
Surmicaceous residue of meltingsharp,lenticularmetamorphic texture
Enclave (restite) biotite rim micas, Al-rich minerals
Schlieren disrupted enclavegradualoblatecoplanar orientation
Felsic Micro- disrupted sharp toovoid fine-granied
granular Enclavefine-grained margingradual igneous texture
Mafic Micro- Blob of coevalmostly ovoid fine-granied
granular Enclavemafic magma sharp igneous texture
Cumulate Enclave disrupted mostly ovoid coarse-grained
(Autolith) cumulate gradual cumulate texture
After Didier and Barbarin (1991, p. 20).

9. Granitoids
Granitoid Chemistry Al
2O
3
K
2O
CaO
Al
2O
3
K
2O
CaO
Al
2O
3
CaO
biotite
muscovite
cordierite
andalusite
garnet
pyroxene
hornblende
biotite
aegirine
riebeckite
arfvedsonite
Peraluminous Metaluminous Peralkaline
moles
Na
2O
Na
2O
K
2O
Na
2O
CaO
•Composition of
granitoid controlled by
composition of
source, pressure,
temperature, degree of
partial melting, and
the nature of
differentiation.
•most commonly calc-
alkaline
•variable aluminum
saturation that
generally depends on
the source of melting
Image source: John Winter, 2001

10. Granitoids
Granitoid Chemistry
The fact that most
granitoids plot near the
low P ternary minimum
melts are most
consistent with melting
of a quartzofeldspathic
crustal parent.
Note the effects of
increasing pressure and
the An, B, and F
contents on the position
of the thermal minima.
Image source: John Winter, 2001

11. Granitoids
Granitoid Chemistry
•MORB-normalized spider
diagrams for the analyses in
Table 18-2
•The subduction zone
granitoids display the typical
decoupling of the LIL/HFS
elements.
•The plagiogranite is more
similar to patterns associated
with MORBs.
Image source: John Winter, 2001

12. Granitoids
Crustal melting (anatexis)
two possible ways to produce melts
H2O-saturated melting-produces minor
amounts of melt due to small amounts of
trapped water
Dehydration melting–fluid from breakdown of
hydrous minerals: e.g.
Mu + Pl + Qtz = Kfs + Al-sil + Melt
or
Bt + Pl + Al-sil + Qtz = Kfs + Grt + Melt
if produced melts are <30% the melt generally
stays with the source to produce a migmatite.
initiated due to increase in mantle-produced heat or thickened crust.
Migmatite from the Hellroaring
Plateau in the Beartooth Mtns
(MT) with felsic granitoid melt
and restite of quartz +
plagioclase + K-feldspar +
biotite + garnet + sillimanite.
Image source: Darrell Henry

13. Granitoids
Crustal melting (anatexis)
(a)Simplified P-T phase
diagram for melting of
aluminous quartzofeldspathic
materials and
(b) quantity of melt generated
during the melting of
muscovite-biotite-bearing
crustal source rocks
Shaded areas in (a) indicate
melt generation.

14. Granitoids
Classifications of Granitoids –(genetic classification)
•I-type granitoids(igneous source) -partial melts of
mantle-derived mafic rocks (underplated basaltic
melts?); contain abundant hornblende and magnetiteTable 18-3. The S-I-A-M Classification of Granitoids
TypeSiO
2K
2O/Na
2OCa, SrA/(C+N+K)*Fe
3+
/Fe
2+
Cr, Ni
18
O
87
Sr/
86
Sr Misc Petrogenesis
M 46-70% low high low low low< 9‰< 0.705Low Rb, Th, USubduction zone
Low LIL and HFS or ocean-intraplate
Mantle-derived
I53-76% low high inlow: metal-moderatelow< 9‰< 0.705high LIL/HFSSubduction zone
maficuminous to med. Rb, Th, U Infracrustal
rocksperaluminous hornblende Mafic to intermed.
magnetite igneous source
S65-74% high low high low high> 9‰> 0.707variable LIL/HFSSubduction zone
high Rb, Th, U
metaluminous biotite, cordieriteSupracrustal
Als, Grt, Ilmenitesedimentary source
A high Na
2O low var var low var var low LIL/HFS Anorogenic
 77% high peralkaline high Fe/Mg Stable craton
high Ga/Al Rift zone
High REE, Zr
High F, Cl
* molar Al
2O
3/(CaO+Na
2O+K
2O) Data from White and Chappell (1983), Clarke (1992), Whalen (1985)

15. Granitoids
Classifications of Granitoids –(genetic classification)
•S-type granitoids(sedimentary source) -partial melts of
aluminous sedimentary rocks; w/ Al-rich minerals (Al-
silicates; cordierite, garnet), biotite (brown) and ilmenite Table 18-3. The S-I-A-M Classification of Granitoids
TypeSiO
2K
2O/Na
2OCa, SrA/(C+N+K)*Fe
3+
/Fe
2+
Cr, Ni
18
O
87
Sr/
86
Sr Misc Petrogenesis
M 46-70% low high low low low< 9‰< 0.705Low Rb, Th, USubduction zone
Low LIL and HFS or ocean-intraplate
Mantle-derived
I53-76% low high inlow: metal-moderatelow< 9‰< 0.705high LIL/HFSSubduction zone
maficuminous to med. Rb, Th, U Infracrustal
rocksperaluminous hornblende Mafic to intermed.
magnetite igneous source
S65-74% high low high low high> 9‰> 0.707variable LIL/HFSSubduction zone
high Rb, Th, U
metaluminous biotite, cordieriteSupracrustal
Als, Grt, Ilmenitesedimentary source
A high Na
2O low var var low var var low LIL/HFS Anorogenic
 77% high peralkaline high Fe/Mg Stable craton
high Ga/Al Rift zone
High REE, Zr
High F, Cl
* molar Al
2O
3/(CaO+Na
2O+K
2O) Data from White and Chappell (1983), Clarke (1992), Whalen (1985)

16. Granitoids
Classifications of Granitoids –(genetic classification)
•M-type granitoids(direct mantle source) -e.g.
plagiogranites in ophiolites
•A-type granitoids(on anorogenicsettings) -peralkaline
melts in rifts Table 18-3. The S-I-A-M Classification of Granitoids
TypeSiO
2K
2O/Na
2OCa, SrA/(C+N+K)*Fe
3+
/Fe
2+
Cr, Ni
18
O
87
Sr/
86
Sr Misc Petrogenesis
M 46-70% low high low low low< 9‰< 0.705Low Rb, Th, USubduction zone
Low LIL and HFS or ocean-intraplate
Mantle-derived
I53-76% low high inlow: metal-moderatelow< 9‰< 0.705high LIL/HFSSubduction zone
maficuminous to med. Rb, Th, U Infracrustal
rocksperaluminous hornblende Mafic to intermed.
magnetite igneous source
S65-74% high low high low high> 9‰> 0.707variable LIL/HFSSubduction zone
high Rb, Th, U
metaluminous biotite, cordieriteSupracrustal
Als, Grt, Ilmenitesedimentary source
A high Na
2O low var var low var var low LIL/HFS Anorogenic
 77% high peralkaline high Fe/Mg Stable craton
high Ga/Al Rift zone
High REE, Zr
High F, Cl
* molar Al
2O
3/(CaO+Na
2O+K
2O) Data from White and Chappell (1983), Clarke (1992), Whalen (1985)

17. Granitoids
Classifications of Granitoids (tectonic setting)

18. Granitoids
Classifications of Granitoids (tectonic setting)