Petrology

Petrology
Definition of a rock, petrology. Classification of rocks-Geological classification of rocks. Rock Cycle. Classification of igneous Forms, structures and textures of igneous rocks. Classification of sedimentary rocks, and its structures and textures. Classification of metamorphic rocks, its structures and textures.
Megascopic Study of Granite, Dolerite, Basalt, Pegmatite, Charnockite, Sandstone, Shale, Limestone, Gneiss, Schist, Quartzite, Marble and Slate.

1. UNIT - 3 PETROLOGY Bindusara TS Assistant Professor Civil Engineering Department Sreenidhi Institute of Science and Technology, Hyderabad

2. UNIT - 3 PETROLOGY Eng- Geo [6K473]-Unit1 2

3. Define Petrology Petrology means “ STUDY OF ROCKS” Petro = Rock Logy = Study The branch of geology deals with the various aspects of rocks such as, Origin, Association, Occurrence, Mineral composition, Chemical composition, Texture, Structure, Physical properties of rocks. Eng- Geo [6K473]-Unit1 3 PETROLOGY

4. Define Rock Rock or stone  is a natural substance, a solid   aggregate of one or more  minerals combined together in an orderly manner. Petrography deals with the descriptive part of rocks. Petrogeny deals with the mode of formation of rocks. Eng- Geo [6K473]-Unit1 4 PETROLOGY

5. Classification of Rocks Eng- Geo [6K473]-Unit1 5 PETROLOGY

6. Igneous Rock Igneous rocks are the primary rocks, which are formed due to cooling and solidification of magma. Magma is a hot viscous, siliceous melt, containing water vapour and gases . Magma comes out from the greater depth below the earth surface, such magma is called LAVA. Eng- Geo [6K473]-Unit1 6 PETROLOGY

7. Classification of Igneous Rock Eng- Geo [6K473]-Unit1 7 PETROLOGY

8. Igneous Rock Intrusive igneous rocks Intrusive igneous rocks are formed from magma that cools and solidifies within the crust of a planet, surrounded by pre-existing rock (called country rock ). T he magma cools slowly and, as a result, these rocks are coarse-grained . The mineral grains in such rocks can generally be identified with the naked eye. Eng- Geo [6K473]-Unit1 8 PETROLOGY

9. Eng- Geo [6K473]-Unit1 9 Intrusive Igneous Rock Diorite Granite

10. Eng- Geo [6K473]-Unit1 10 Intrusive Igneous Rock Gabbro Pegmatite

11. Classification of Igneous Rock Eng- Geo [6K473]-Unit1 11 PETROLOGY

12. Igneous Rock Intrusive igneous rocks Hypabasel Rock These Rocks are formed at intermediate depth generally up to 2 km below the earth surface and exhibits mixed characteristics of volcanic and plutonic. Eng- Geo [6K473]-Unit1 12 PETROLOGY

13. Eng- Geo [6K473]-Unit1 13 Intrusive Igneous Rock Hypabasel Rock Diorite

14. Igneous Rock Intrusive igneous rocks Plutonic Rock These Rocks are formed at considerable depth generally up to 7-10 km below the earth surface. Because of very slow rate of cooling at these depth coarse grained rocks are formed. Eng- Geo [6K473]-Unit1 14 PETROLOGY

15. Eng- Geo [6K473]-Unit1 15 Intrusive Igneous Rock Plutonic Rocks Gabbro Pegmatite

16. Eng- Geo [6K473]-Unit1 16 Intrusive Igneous Rock Plutonic Rocks Gabbro Hypabasel Rock Diorite

17. Igneous Rock Extrusive igneous rocks It is also called as volcanic rocks. These rocks are formed due to cooling and solidification of magma at the crust surface. The magma, which is brought to the surface through fissures or volcanic eruptions, solidifies at a faster rate . Hence such rocks are smooth, crystalline and fine-grained . Eng- Geo [6K473]-Unit1 17 PETROLOGY

18. Igneous Rock Extrusive igneous rocks Volcanic Rocks These rocks are formed due to cooling and solidification of lava erupted from volcanoes. since lava cools down very fast rate. The grain size of the crystal formed in these rock is fine . Eng- Geo [6K473]-Unit1 18 PETROLOGY

19. Eng- Geo [6K473]-Unit1 19 Extrusive Igneous Rock Volcanic Rock Volcanic Rock

20. Eng- Geo [6K473]-Unit1 20 Extrusive Igneous Rock Volcanic Rock Basalt

21. Eng- Geo [6K473]-Unit1 21 Igneous Rock Basalt Diorite

22. Classification of Rocks Eng- Geo [6K473]-Unit1 22 PETROLOGY

23. Sedimentary Rock Sedimentary rocks are those, which are formed by the accumulation, compaction and consolidation of sediments. The sediments are the particles produced from the disintegration of pre-existing rocks (Igneous/metamorphic rocks ) through the process of transportation and deposition by various natural agencies like wind, water and glaciers . Eng- Geo [6K473]-Unit1 23 PETROLOGY

24. Sedimentary Rock Eng- Geo [6K473]-Unit1 24 PETROLOGY

25. Sedimentary Rock Eng- Geo [6K473]-Unit1 25 PETROLOGY

26. Eng- Geo [6K473]-Unit1 26 Sedimentary Rock Sand Stone Conglomerate

27. Eng- Geo [6K473]-Unit1 27 Sedimentary Rock shale Lime stone

28. Sedimentary Rock Clastic deposit rock They are mechanically formed rocks. These are formed due to the process of weathering, erosion, transportation and deposition of pre-existing rocks . Rudaceous rocks - If the grain size are more than 2 mm in dia, Arenaceous rocks- If the grain size is in between 1 and 2 mm. Argillaceous rocks- If the size of the particle is < 1mm in dia, Eng- Geo [6K473]-Unit1 28 PETROLOGY

29. Eng- Geo [6K473]-Unit1 29 Sedimentary Rock Clastic Deposit [ Rudaceous rocks ] Conglomerate Breccia

30. Eng- Geo [6K473]-Unit1 30 Sedimentary Rock Clastic Deposit [ Arenaceous rocks ] Quartz Sand stone Gri t

31. Eng- Geo [6K473]-Unit1 31 Sedimentary Rock Clastic Deposit [ Argillaceous rocks ] Shale and Mud stone

32. Sedimentary Rock Chemical deposit rock They are formed by precipitation, evaporation or crystallization from natural aqueous solution. When water is rich in dissolved salt evaporates and left behind minerals. (Halite) Limestone can form when calcite minerals dissolved in lakes, sea and underground water comes out of solution and form crystal. Eng- Geo [6K473]-Unit1 32 PETROLOGY

33. Eng- Geo [6K473]-Unit1 33 Sedimentary Rock Chemical Deposit Lime Stone Halite

34. Sedimentary Rock Organic deposit rock Sedimentary rocks which are formed exclusively from remains of organisms like plant / animals deposited in a thick layer. Eng- Geo [6K473]-Unit1 34 PETROLOGY

35. Eng- Geo [6K473]-Unit1 35

36. Eng- Geo [6K473]-Unit1 36 Sedimentary Rock Chemical Deposit Coal Lignite

37. Classification of Rocks Eng- Geo [6K473]-Unit1 37 PETROLOGY

38. Metamorphic Rock The word "Metamorphism" comes from the Greek: Meta = change , Morph = form , so metamorphism means to change form. Metamorphic rocks are those rocks that are formed as a result of transformation that takes place in the pre-existing rocks (Igneous/sedimentary rocks). When the pre-existing rocks are subjected to higher temperature, pressure and chemically active liquids and gases, the minerals present in the original rocks changes to new environmental condition. Eng- Geo [6K473]-Unit1 38 PETROLOGY

39. Eng- Geo [6K473]-Unit1 39 Metamorphic Rock Slate Slate

40. Eng- Geo [6K473]-Unit1 40 Metamorphic Rock Gneiss Gneiss

41. Metamorphic Rock Foliated W hen pressure squeezes the flat or elongate minerals within a rock so they become aligned. These rocks develop a  platy  or sheet-like structure that reflects the direction that pressure was applied in.  Slate ,  schist , and  gneiss   are all foliated metamorphic rocks. Eng- Geo [6K473]-Unit1 41 PETROLOGY

42. Eng- Geo [6K473]-Unit1 42 Metamorphic Rock Foliated Rock Slate Schist

43. Metamorphic Rock Non Foliated Non foliated metamorphic rocks are formed around igneous intrusions where the temperatures are high but the pressures are relatively low and equal in all directions  Eng- Geo [6K473]-Unit1 43 PETROLOGY

44. Eng- Geo [6K473]-Unit1 44 Metamorphic Rock Non Foliated Rock White Marble Marble

45. Eng- Geo [6K473]-Unit1 45 Metamorphic Rock

46. Classification of Rocks Eng- Geo [6K473]-Unit1 46 PETROLOGY

47. Physical Classification Stratified rocks These rocks are having layered structure . They possess planes of stratification or cleavage. They can be easily split along these planes. Sand stones, lime stones, slate etc . Eng- Geo [6K473]-Unit1 47 PETROLOGY

48. Eng- Geo [6K473]-Unit1 48 Physical Classification of Rocks Stratified Rocks

49. Physical Classification Un-stratified rocks These rocks are not stratified. They possess crystalline and compact grains . They cannot be split in to thin slab. Granite , trap, marble etc. are the examples of this type of rocks. Eng- Geo [6K473]-Unit1 49 PETROLOGY

50. Eng- Geo [6K473]-Unit1 50 Physical Classification of Rocks Un Stratified Rocks Granite Marble

51. Physical Classification Foliated Rocks These rocks have a tendency to split along a definite direction only. The direction need not be parallel to each other as in case of stratified rocks. This type of structure is very common in case of metamorphic rocks. Eng- Geo [6K473]-Unit1 51 PETROLOGY

52. Eng- Geo [6K473]-Unit1 52 Physical Classification of Rocks Foliated Rocks

53. Chemical Classification Siliceous rocks These rocks which have silica as the main constituent. The silica in the free state is called sand and in combined state is silicate. Examples:  Granite, Quartzite, Sandstone etc. Eng- Geo [6K473]-Unit1 53 PETROLOGY

54. Chemical Classification Argillaceous rocks   These rocks which have clay or alumina as the main constituent. Examples:  Kaolin, Laterite, Slate etc . Eng- Geo [6K473]-Unit1 54 PETROLOGY

55. Chemical Classification Calcareous rocks   These rocks which have calcium carbonate or lime as their leading constituent. These rocks are readily acted upon by even  dilute HCl . Examples:  Limestone and Marble. Eng- Geo [6K473]-Unit1 55 PETROLOGY

56. Forms of Igneous Rock Eng- Geo [6K473]-Unit1 56 PETROLOGY

57. Forms of Igneous Rock Concordant intrusive bodies T he magma intrusion is parallel to the structure of the country rock, they are called ‘Concordant intrusive bodies Eng- Geo [6K473]-Unit1 57 PETROLOGY

58. Forms of Igneous Rock Concordant intrusive bodies Sill It is a concordant intrusive igneous bodies. Sills are formed due to the penetration of magma into bedding planes of enclosing sedimentary rock. Their spreading capacity is mainly depends upon viscosity of magma, its temperature and the weight of overlaying rocks. The thickness varies from few centimetres to several kilometres. Eng- Geo [6K473]-Unit1 58 PETROLOGY

59. Eng- Geo [6K473]-Unit1 59 PETROLOGY Sill

60. Forms of Igneous Rock Concordant intrusive bodies Phacolith When thick sedimentary strata are folded, along the crust and trough, some empty space occurs. These spaces are readily occupied if magmatic intrusion get access to them. On solidification these appear as lens shaped across the axial plane. Eng- Geo [6K473]-Unit1 60 PETROLOGY

61. Eng- Geo [6K473]-Unit1 61 PETROLOGY Phacolith

62. Forms of Igneous Rock Concordant intrusive bodies Lopolith This is basin or saucer shaped concordant intrusive igneous body of enormous size. Its top is nearly flat and bottom is convex downward bowl-like bodies, which are sagged downwards due to the weight of the intruded magma. Eng- Geo [6K473]-Unit1 62 PETROLOGY

63. Eng- Geo [6K473]-Unit1 63 PETROLOGY Lopolith

64. Forms of Igneous Rock Concordant intrusive bodies Laccolith This is a mushroom like concordant intrusive igneous bodies. It is nearly flat bottom but it is convex upward i.e. dome shaped. When viscous magma is injected along the bedding plane, as it cannot spread easily, it pushes up the overlaying rocks and piles up more at the place. Eng - Geo [6K473]-Unit1 64 PETROLOGY

65. Forms of Igneous Rock Concordant intrusive bodies Laccolith Eng - Geo [6K473]-Unit1 65 PETROLOGY

66. Eng- Geo [6K473]-Unit1 66 PETROLOGY Laccolith

67. Forms of Igneous Rock Discordant intrusive bodies Batholith These are the largest known discordant intrusive igneous bodies mainly occurring in mountain ranges. Batholiths have side sloping away from each other which makes them larger and larger downwards and they have extended to very great depths covering several kilometres. Eng- Geo [6K473]-Unit1 67 PETROLOGY

68. Eng- Geo [6K473]-Unit1 68 PETROLOGY Batholith

69. Forms of Igneous Rock Discordant intrusive bodies Dyke Dykes are discordant igneous body of more or less tabular shape and exhibit a cross –cutting relationship with the country rocks they occur commonly n the forms of wall like masses of exactly or nearly vertical attitude. If the rocks constituting the dyke are hard and compact, they can resist weathering and Erosional process. Eng- Geo [6K473]-Unit1 69 PETROLOGY

70. Eng- Geo [6K473]-Unit1 70 PETROLOGY Dyke

71. Eng- Geo [6K473]-Unit1 71 PETROLOGY Dyke

72. Forms of Igneous Rock Discordant intrusive bodies Volcanic neck The vents of quiet volcanoes have become sealed with the igneous intrusions and is called volcanic necks/plugs. These forms may be circular, semi circular or irregular and in varying diameter. Eng - Geo [6K473]-Unit1 72 PETROLOGY

73. Eng- Geo [6K473]-Unit1 73 PETROLOGY Volcanic neck

74. Structure Structure are physical features associated with the rocks. They are primary in nature they occurs along with the formation of rocks Structure contribute the strength and weakness of the rock. Structure helps to distinguishing features of rock group. Structure reveals the mode of formation. Eng- Geo [6K473]-Unit1 74 PETROLOGY

75. Structure of Igneous Rock Vesicular Structure Structure is porous in nature. Commonly observed in Volcanic rocks. Magma is a mixture of rock melts and volatiles, (Gases). The gases present in the magma are lighter and escape into atmosphere. Empty cavity of various sizes and shapes are formed on surface. These cavity called Vesicles. Eng- Geo [6K473]-Unit1 75 PETROLOGY

76. Structure of Igneous Rock Vesicular Structure Eng- Geo [6K473]-Unit1 76 PETROLOGY

77. Structure of Igneous Rock Amygdaloidal Structure The empty vesicles in the vesicular structure are filled by surface water or under ground water or sediments. The in filled cavity are called Amygdales. When empty cavities are filled with amygdales that structure is called Amygdaloidal Structure Eng- Geo [6K473]-Unit1 77 PETROLOGY

78. Structure of Igneous Rock Amygdaloidal Structure Eng- Geo [6K473]-Unit1 78 PETROLOGY

79. Structure of Igneous Rock Columnar Structure The volcanic igneous rock appears to be made up of numerous parallel polygon prismatic column bundled together. This results of the contraction of lava during cooling. Eng- Geo [6K473]-Unit1 79 PETROLOGY

80. Structure of Igneous Rock Columnar Structure Eng- Geo [6K473]-Unit1 80 PETROLOGY

81. Structure of Igneous Rock Sheet Structure The rocks appears to be made up of a number of sheets, because of the development of nearly horizontal crack . Plutonic rocks are formed at a great depth which means under the great pressures. When erosion takes place in the over laying strata gradually dis appear ultimately exposing of plutonic rock in the form sheet. Eng- Geo [6K473]-Unit1 81 PETROLOGY

82. Structure of Igneous Rock Sheet Structure Eng- Geo [6K473]-Unit1 82 PETROLOGY

83. Structure of Igneous Rock Flow Structure These structures are linear and nearly parallel features occurring in volcanic rocks which develops as a consequence of the flow of lava. Eng- Geo [6K473]-Unit1 83 PETROLOGY

84. Structure of Igneous Rock Flow Structure Eng- Geo [6K473]-Unit1 84 PETROLOGY

85. Structure of Igneous Rock Pillow Structure The Volcanic igneous body appears as a pile of numerous overlapping pillows. It occurs only in soda rich basalt rock. The pillows are generally interconnected vesicular and glassy tops. Eng- Geo [6K473]-Unit1 85 PETROLOGY

86. Structure of Igneous Rock Pillow Structure Eng- Geo [6K473]-Unit1 86 PETROLOGY

87. Textures of Igneous Rock Texture mainly refers to Mutual relationship with constituent minerals of rocks in addition to crystallinity, granularity and shape of minerals in the rocks. Eng- Geo [6K473]-Unit1 87 PETROLOGY

88. Textures of Igneous Rock Equigranular Texture In this type, the mineral grains are all of approximately same size. This is because all the minerals are simultaneously get consolidated. Ex: Granite, Basalt Eng- Geo [6K473]-Unit1 88 PETROLOGY

89. Textures of Igneous Rock Equigranular Texture Eng - Geo [6K473]-Unit1 89 PETROLOGY Granite Basalt

90. Textures of Igneous Rock In Equigranular Texture In this type, the mineral grains show marked difference in their grain size. This is because different mineral grains consolidate at different level and hence different minerals exhibit different sizes . Ex: Syenite Eng- Geo [6K473]-Unit1 90 PETROLOGY

91. Textures of Igneous Rock In Equigranular Texture Eng - Geo [6K473]-Unit1 91 PETROLOGY Syenite Basalt

92. Textures of Igneous Rock Porphyritic texture It is a type of inequigranular texture, where tabular or large sized minerals called phenocrysts are fully embedded within the fine grained minerals known as matrix Ex : Syenite Porphyry Eng- Geo [6K473]-Unit1 92 PETROLOGY

93. Textures of Igneous Rock Porphyritic texture Eng - Geo [6K473]-Unit1 93 PETROLOGY

94. Textures of Igneous Rock Poikilitic texture: This is the converse of porphyritic texture, which is characterized by the presence of fine grained crystals within the body of large sized crystals. Ex: Peridotite Eng- Geo [6K473]-Unit1 94 PETROLOGY

95. Textures of Igneous Rock Poikilitic texture Eng - Geo [6K473]-Unit1 95 PETROLOGY

96. Textures of Igneous Rock Ophitic texture This is similar to porphyritic texture, which shows the phenocrysts are partially embedded within the matrix . This is observed in dolerite rock whose lath shaped of mineral Augite enclosed within small Plagioclase mineral. Ex : Dolerite Eng- Geo [6K473]-Unit1 96 PETROLOGY

97. Textures of Igneous Rock Ophitic texture Eng - Geo [6K473]-Unit1 97 PETROLOGY

98. Textures of Igneous Rock Pegmatitic / intergrowth texture Two or more minerals crystallize simultaneously in a limited space. Here one crystal intrudes another. An alternate bands of dark and light coloured minerals are seen (quartz and feldspar ). Ex : Pegmatite Eng- Geo [6K473]-Unit1 98 PETROLOGY

99. Textures of Igneous Rock Pegmatitic / Intergrowth texture Eng - Geo [6K473]-Unit1 99 PETROLOGY

100. Textures of Igneous Rock Vesicular Texture Most lavas are heavily charged with gas which escapes as soon as it comes in contact with Earth’s atmosphere. The escape of these gases leads to the formation of different sizes / shapes of holes in the cooled volcanic rocks. Eng- Geo [6K473]-Unit1 100 PETROLOGY

101. Textures of Igneous Rock Vesicular Texture Eng - Geo [6K473]-Unit1 101 PETROLOGY

102. Structure of Sedimentary Rock Stratification and Lamination The sedimentary rocks are bedded in nature. A bed is called stratum and a number of beds are called Strata. A bed is generally homogeneous in composition, texture and colour . These are called Bedding planes. The different layers of beds may vary in grain size, mineral composition, colour, texture etc., depending upon the environment and formation. This feature is called stratification. Eng- Geo [6K473]-Unit1 102 PETROLOGY

103. Structure of Sedimentary Rock Stratification and Lamination Eng- Geo [6K473]-Unit1 103 PETROLOGY

104. Structure of Sedimentary Rock Graded Bedding In some beds at the bottom, there will be bigger particles and very fine particles at the top. There is a gradual decrease in the size of the particles from bottom to top. This phenomenon is called Graded bedding. Here individual layer is said to be graded with different particle size. Eng- Geo [6K473]-Unit1 104 PETROLOGY

105. Structure of Sedimentary Rock Graded Bedding Eng- Geo [6K473]-Unit1 105 PETROLOGY

106. Structure of Sedimentary Rock Current Bedding Generally , the sedimentary beds are parallel to one another. Some times the beds are deposited slightly inclined to the major bedding plane because of change in the velocity and direction of flow of stream. This structure is known as Current Bedding. Eng- Geo [6K473]-Unit1 106 PETROLOGY

107. Structure of Sedimentary Rock Current Bedding Eng- Geo [6K473]-Unit1 107 PETROLOGY

108. Structure of Sedimentary Rock Ripple Marks This is a minor structure in sedimentary rocks formed due to mechanical origin. They are the undulations structure formed on the surface of loose sediments due to action of wind in a shallow water body. It is also called wave marks. If the ripple marks are formed by stagnant water then the feature will be symmetrical and if they are formed by moving water then they are asymmetrical . Eng- Geo [6K473]-Unit1 108 PETROLOGY

109. Structure of Sedimentary Rock Ripple Marks Eng- Geo [6K473]-Unit1 109 PETROLOGY

110. Structure of Sedimentary Rock Mud Cracks These are common structural features of fine grained sedimentary rocks. The development of mud cracks is because of the drying of huge masses of fine grained sediments under sub-aerial condition. It is also called Sun cracks since they are formed due to the effect of solar heat. Eng- Geo [6K473]-Unit1 110 PETROLOGY

111. Structure of Sedimentary Rock Mud Cracks Eng- Geo [6K473]-Unit1 111 PETROLOGY

112. Structure of Sedimentary Rock ‘Tracks and Trails, Rain Prints The movement of organisms on the surface of loose sediments develops a marking or impression and is called ‘tracks and trails’. On the other hand ‘Rain prints’ are formed on the top surface of loose sediments due to impact of ‘drops’ of rainwater. Eng- Geo [6K473]-Unit1 112 PETROLOGY

113. Structure of Sedimentary Rock Tracks and Trails, Rain Prints Eng- Geo [6K473]-Unit1 113 PETROLOGY

114. Texture of Sedimentary Rock Clastic T exture G rains do not interlock but rather are piled together and cemented. Boundaries of individual grains may be another grain, cement or empty pore space. Overall rock is generally porous and not very dense. Because Clastic are only cemented together, grains are relatively easy to “scrape off" using a rock hammer point or metal nail. Eng- Geo [6K473]-Unit1 114 PETROLOGY

115. Texture of Sedimentary Rock Clastic Texture Eng- Geo [6K473]-Unit1 115 PETROLOGY

116. Texture of Sedimentary Rock Microclastic texture This texture is the same as the Clastic texture except that the clasts are not visible to the eye. Because the grains are invisible, examining the ease in which grains (silt or clay) may be knocked off is the best test to perform. Eng- Geo [6K473]-Unit1 116 PETROLOGY

117. Texture of Sedimentary Rock Microclastic texture Eng- Geo [6K473]-Unit1 117 PETROLOGY

118. Texture of Sedimentary Rock Bioclastic texture The texture is similar to Clastic texture except that all of the clasts or grains are fossils. Eng- Geo [6K473]-Unit1 118 PETROLOGY

119. Texture of Sedimentary Rock Bioclastic texture Eng- Geo [6K473]-Unit1 119 PETROLOGY

120. Texture of Sedimentary Rock Crystalline texture Crystals are visible and form an interlocking network. Unlike igneous crystalline textures, however, sedimentary crystalline textures are typically formed from one mineral throughout the entire rock. Eng- Geo [6K473]-Unit1 120 PETROLOGY

121. Texture of Sedimentary Rock Crystalline texture Eng- Geo [6K473]-Unit1 121 PETROLOGY

122. Texture of Sedimentary Rock Microcrystalline texture N o crystals are visible but the rock is composed of interlocking microscopic crystals. Such rocks are dense and typically nonporous. Microcrystalline rocks break with a characteristic Conchoidal fracture. That is, the broken surface may smooth concentric lines resembling the inside of an oyster shell or broken glass. Eng- Geo [6K473]-Unit1 122 PETROLOGY

123. Texture of Sedimentary Rock Microcrystalline texture Eng- Geo [6K473]-Unit1 123 PETROLOGY

124. Eng- Geo [6K473]-Unit1 124 PETROLOGY Structure of Metamorphic Rock

125. Structure of Metamorphic Rock Porphyroclastic Structure It is produced under stress and in absence of high temperature, where by rocks are subjected to shearing and fragmentation. Only the durable mineral partly survive the crushing force and the less durable ones are powdered . Thus, when resistant minerals and rock fragments stand out in a pseudo porphyritic manner in the finer materials, it is known as ' porphyroclastic ’ structure. Eng- Geo [6K473]-Unit1 125 PETROLOGY

126. Structure of Metamorphic Rock Porphyroclastic Structure Eng- Geo [6K473]-Unit1 126 PETROLOGY

127. Structure of Metamorphic Rock Maculose structure It is produced by thermal metamorphism of argillaceous rocks like shale. Here, larger crystals of cordierite and biotite are sometimes well developed giving a spotted appearance to the rocks. The well developed crystals are known as ' porphyroblasts ' with increasing degree of metamorphism, the spotted slates pass into extremely fine grained granular rock known as Hornfels. Eng- Geo [6K473]-Unit1 127 PETROLOGY

128. Structure of Metamorphic Rock Maculose structure Eng- Geo [6K473]-Unit1 128 PETROLOGY

129. Structure of Metamorphic Rock Schistose structure Here the platy or flaky minerals like the micas and other Inequidimensional minerals show a preferred orientation along parallel planes , under the effect of the stress dominating during metamorphism. The longer directions are parallel to the direction of maximum stress. Schistosity is the property or tendency of a foliated rock, whereby it can be readily split along foliation plane. Eng- Geo [6K473]-Unit1 129 PETROLOGY

130. Structure of Metamorphic Rock Schistose structure Eng- Geo [6K473]-Unit1 130 PETROLOGY

131. Structure of Metamorphic Rock Granulose structure This is found in the rocks composed of equidimensional minerals like quartz, feldspar and pyroxenes. They are formed by the recrystallization of pre-existing rocks, under uniform pressure and great heat. The typical texture is coarsely granoblastic. These structures are also known as Quartzite's and marbles are typical examples of this structure . Eng- Geo [6K473]-Unit1 131 PETROLOGY

132. Structure of Metamorphic Rock Granulose structure Eng- Geo [6K473]-Unit1 132 PETROLOGY

133. Structure of Metamorphic Rock Gneissose structure It is a banded structure due to alter nation of schistose (dark coloured) and granulose (light coloured) bands and is produced by highest grade of metamorphism, typically by regional metamorphism. The bands differ from are another in colour, texture and mineral composition. Gneisses typically show this type of structure, hence the name . Eng- Geo [6K473]-Unit1 133 PETROLOGY

134. Structure of Metamorphic Rock Gneissose structure Eng- Geo [6K473]-Unit1 134 PETROLOGY

135. Texture of Metamorphic Rock Gneissose structure It is a banded structure due to alter nation of schistose (dark coloured) and granulose (light coloured) bands and is produced by highest grade of metamorphism, typically by regional metamorphism. The bands differ from ore another in colour, texture and mineral composition. Gneisses typically show this type of structure, hence the name . Eng- Geo [6K473]-Unit1 135 PETROLOGY

136. Structure of Metamorphic Rock Gneissose structure Eng- Geo [6K473]-Unit1 136 PETROLOGY

137. ROCK CYCLE Eng- Geo [6K473]-Unit1 137 PETROLOGY

138. Crystallization M A G MA I G N E OU S

139. IGNEOUS Plutonic Crystalliza M A G MA

140. Volcanic IGNEOUS Plutonic Crystallization M A G MA

141. M A G MA U pl i f t Volcanic IGNEOUS Plutonic Crystallization W ea t h er i n g

142. M A G MA U pl i f t Volcanic IGNEOUS Plutonic Crystallization W ea t h er i n g S E D IM E N T

143. Volcanic S E D IM E N T IGNEOUS Plutonic C rys t a lli z Uplift SE D I M E N T A R Y ation MAGMA W ea t h er i n g Erosion T r a n s po rt Deposition

144. M A G MA Volcanic IGNEOUS S E D IM E N T SE D I M E N T A R Y U pl i f t Plutonic Crystallization W ea t h er i n g Erosion T r a n s po rt Deposition

145. M A G MA Volcanic IGNEOUS Plutonic S E D IM E N T SE D I M E N T A R Y M E T A M O R P H I C U pl i f t Bur ial Increased P&T Crystallization W ea t h er i n g Erosion T r a n s po rt Deposition

146. M A G MA Volcanic IGNEOUS Plutonic S E D IM E N T SE D I M E N T A R Y M E T A M O R P H I C U pl i f t Bur ial Increased P&T M e lti n g Crystallization W ea t h er i n g Erosion T r a n s po rt Deposition Can you see any shortcuts?

147. M A G MA Volcanic IGNEOUS Plutonic S E D IM E N T SE D I M E N T A R Y M E T A M O R P H I C U pl i f t Bur ial Increased P&T M e lti n g Crystallization W ea t h er i n g Erosion T r a n s po rt Deposition

148. • • • • • • The rock cycle demonstrates the relationships among the three major rock groups It is powered by the interior heat of the Earth As well as earth’s momentum and… The energy from the sun It involves processes on the Earth’s surface as well as the Earth’s interior It connects the “hydrologic cycle” with the “tectonic cycle”. In Conclusion…

149. M A G MA Volcanic IGNEOUS Plutonic S E D IM E N T SE D I M E N T A R Y M E T A M O R P H I C U pl i f t Bur ial Increased P&T M e lti n g Crystallization W ea t h er i n g Erosion T r a n s po rt Deposition