Match the following structural trends with their regional orientation :(a) Dharwar Trend(1) ENE - WSW(b) Satpura Trend(2) NW - SE(c) Aravali Trend(3) NE - SW

The correct matching is (a) - 2, (b) - 1, (c) - 3.The Dharwar trend, seen in the schist belts of Karnataka, runs NNW-SSE, the NW-SE direction.The Satpura trend, followed by the Satpura range and the Central Indian Tectonic Zone, runs ENE-WSW.The Aravalli trend, followed by the Aravalli range of Rajasthan, runs NE-SW.Option B swaps the Dharwar and Satpura trends; option C gives Aravalli the NW-SE trend that belongs to Dharwar; option D reverses the whole set.

Precambrian Geology Questions and Answers

Q: The Mesoproterozoic rift-valleys, Mahandi and Pranhita-Godavari are equated with Lambert rift of Antarctica and Unita rift of North America is supposed to be indicative of :

They are taken as indicative of the Fragmentation of Columbia.Columbia (also called Nuna) was the supercontinent assembled around 2.0-1.8 billion years ago, which broke up during the Mesoproterozoic, roughly 1.5-1.2 billion years ago. Rift valleys of Mesoproterozoic age that can be matched across India, Antarctica and North America fit that break-up.The other options have the wrong ages. Pannotia existed briefly around 600-550 million years ago, the collision of East and West Gondwana belongs to the Pan-African events at about the same time, and the fragmentation of Gondwana took place in the Mesozoic. None of them is Mesoproterozoic.

Q: The oldest life form recorded anywhere in world are ......................

Of the options, the oldest life forms are the stromatolites of the Barberton Greenstone Belt of South Africa.The Barberton Greenstone Belt contains some of the best preserved early Archaean rocks, and its cherts and carbonates carry stromatolites and microfossils over 3.3 billion years old, among the oldest accepted traces of life anywhere. (Some claims from Western Australia and Greenland are older, but they are not among the options.)The other options are far younger: Vindhyan stromatolites and trace fossils are Proterozoic, the Jhamarkotra stromatolites of the Aravalli Group are Palaeoproterozoic (about 2 billion years), and the Karewa beds of Kashmir are Plio-Pleistocene.

Q: Correctly match the regional stratigraphic sequence of the Western Dharwar Craton :AB(a) Sargur Group(1) 3.3 - 3.4 Ga(b) Gorur gneiss(2) 3.3 - 3.1 Ga(c) Closepet granite(3) 2.5 - 26 Ga

The correct match is a-2, b-1, c-3.In the Western Dharwar Craton the Gorur gneiss is among the oldest basement rocks, dated to about 3.3-3.4 Ga (b-1). The Sargur Group supracrustal rocks, the oldest greenstone sequence, are dated to about 3.3-3.1 Ga (a-2). The Closepet granite, the large intrusion that separates the western and eastern parts of the craton, was emplaced at about 2.5-2.6 Ga, printed in the option as '2.5 - 26 Ga' (c-3).The other codes either make the Sargur Group older than the Gorur gneiss or give the late Archaean Closepet granite an early Archaean age.

Q: Arrange the following formations into a north to south cross-section trend occurring within Central Indian Tectonic Zone :(a) Son-Narmada South fault(b) Sausar group(c) Mahakoshar group(d) Betul group

The key's north-to-south order is (c)-(a)-(d)-(b): Mahakoshal group, Son-Narmada South Fault, Betul group, Sausar group.The Central Indian Tectonic Zone is bounded by the Son-Narmada North Fault and the Central Indian Shear. From north to south it contains the Mahakoshal belt (printed 'Mahakoshar'), lying between the Son-Narmada North and South Faults; the Son-Narmada South Fault; the Betul belt to its south; and the Sausar Group in the southern part of the zone, next to the Central Indian Shear and the Bastar craton.The other orders place the Sausar Group north of Betul or the fault north of the Mahakoshal belt, which reverses parts of this arrangement.

Q: Which of the following Eon characterizes the more tonalitic batholiths, more biomodal volcanic suites and the komatites ?

These features characterise the Archean eon.Archean crust (4.0 to 2.5 billion years ago) is dominated by granite-greenstone terrains. The granitoids are mostly tonalite-trondhjemite-granodiorite (TTG) batholiths, the greenstone belts contain bimodal volcanic suites of basalt and felsic volcanics, and komatiites, ultramafic lavas erupted at very high temperatures, are almost confined to the Archean because the mantle was then hotter.Phanerozoic and Proterozoic crust has more potassic granites and almost no komatiites, and the Mesozoic is an era within the Phanerozoic, not an eon.

Q: Banded iron formations in the Archaean greenstone belts are best witness for :

Banded iron formations are best witness for the shift from anoxic to oxygenated environments.Iron dissolves as ferrous iron only in water without free oxygen. BIFs record an ocean that carried large amounts of dissolved iron, which was precipitated as ferric oxides wherever oxygen, produced by early photosynthesisers, became available. Their abundance in the Archaean and early Proterozoic, and their near disappearance after about 1.8 Ga, track the oxygenation of the ocean and atmosphere.The other options are too general. BIFs are sedimentary rocks deposited in basins and often found on cratons, but those facts are true of many rocks. What makes BIFs distinctive is the redox change they record, not basin development or weathering processes.

Q: The Palghat-Cauvery shear zone comprises :

The keyed answer is charnockite interbanded with khondalites.The Palghat-Cauvery shear zone, which separates the Dharwar craton from the Madurai block in south India, cuts through high-grade granulite-facies terrain. Its dominant rocks are charnockites and hornblende-biotite gneisses, interlayered with metasedimentary garnet-sillimanite (khondalitic) gneisses and quartzites, the association that option A names.Tonalite-trondhjemite-granodiorite gneisses with dolerite dykes and greenstone belts are the typical low-grade associations of the Dharwar craton to the north. Anorthosite bodies such as Sittampundi do occur in the zone, but an association that leaves out the charnockites does not describe it.

Q: The Yilgarn shield and Pilbara shield comprises significant part of the older cratonic shields of the continent :

The Yilgarn and Pilbara cratons are in Australia.Both are Archaean cratons in Western Australia. The Pilbara contains some of the oldest well-preserved crust and early evidence of life, about 3.5 Ga, and the larger Yilgarn, about 3.0-2.6 Ga, hosts major gold and nickel deposits, including those around Kalgoorlie.Africa's Archaean nuclei are the Kaapvaal and Zimbabwe cratons, South America's the Amazonian and Sao Francisco, and Canada's the Superior and Slave, so the other continents are wrong.

Q: Despite being older, the Aravali rocks from the type area are lower grade than the juxtaposed Delhi metasediments :

The key explains it as the two units were temporally apart then accreted.In normal burial the older, deeper rocks are of equal or higher grade than younger rocks above them. If the older Aravalli rocks are of lower grade than the Delhi rocks beside them, the two cannot have been metamorphosed together in a single sequence. They must have been metamorphosed at different times or places and then brought together later by tectonic juxtaposition.Option A would not explain an older unit ending up lower in grade at one place, option C invokes lava flows for which there is no basis in a regional metamorphic belt, and option D contradicts the stem, which says the Aravallis are older.

The Mesoproterozoic rift-valleys, Mahandi and Pranhita-Godavari are equated with Lambert rift of Antarctica and Unita rift of North America is supposed to be indicative of :

A.Fragmentation of Columbia
B.Fragmentation of Pannotia
C.Fragmentation of East and West Gondwana
D.Collision of East & West Gondwana

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: A

They are taken as indicative of the Fragmentation of Columbia.

Columbia (also called Nuna) was the supercontinent assembled around 2.0-1.8 billion years ago, which broke up during the Mesoproterozoic, roughly 1.5-1.2 billion years ago. Rift valleys of Mesoproterozoic age that can be matched across India, Antarctica and North America fit that break-up.

The other options have the wrong ages. Pannotia existed briefly around 600-550 million years ago, the collision of East and West Gondwana belongs to the Pan-African events at about the same time, and the fragmentation of Gondwana took place in the Mesozoic. None of them is Mesoproterozoic.

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The oldest life form recorded anywhere in world are ......................

A.Trace fossils and stromatolites from Vindhyan rocks of middle proterozoic age
B.stromatolites from South African Greenstone belt of + 3.3 billion year age from Barbartan Greenstone belt.
C.Trace fossils from Karewa beds of Kashmir
D.Stromatolites from Jhamarkotra dolomites of Aravalli Group.

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: B

Of the options, the oldest life forms are the stromatolites of the Barberton Greenstone Belt of South Africa.

The Barberton Greenstone Belt contains some of the best preserved early Archaean rocks, and its cherts and carbonates carry stromatolites and microfossils over 3.3 billion years old, among the oldest accepted traces of life anywhere. (Some claims from Western Australia and Greenland are older, but they are not among the options.)

The other options are far younger: Vindhyan stromatolites and trace fossils are Proterozoic, the Jhamarkotra stromatolites of the Aravalli Group are Palaeoproterozoic (about 2 billion years), and the Karewa beds of Kashmir are Plio-Pleistocene.

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Correctly match the regional stratigraphic sequence of the Western Dharwar Craton :

A	B
(a) Sargur Group	(1) 3.3 - 3.4 Ga
(b) Gorur gneiss	(2) 3.3 - 3.1 Ga
(c) Closepet granite	(3) 2.5 - 26 Ga

A.a-2, b-1, c-3
B.a-1, b-2, c-3
C.a-1, b-3, c-2
D.a-2, b-3, c-1

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: A

The correct match is a-2, b-1, c-3.

In the Western Dharwar Craton the Gorur gneiss is among the oldest basement rocks, dated to about 3.3-3.4 Ga (b-1). The Sargur Group supracrustal rocks, the oldest greenstone sequence, are dated to about 3.3-3.1 Ga (a-2). The Closepet granite, the large intrusion that separates the western and eastern parts of the craton, was emplaced at about 2.5-2.6 Ga, printed in the option as '2.5 - 26 Ga' (c-3).

The other codes either make the Sargur Group older than the Gorur gneiss or give the late Archaean Closepet granite an early Archaean age.

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Arrange the following formations into a north to south cross-section trend occurring within Central Indian Tectonic Zone :

(a) Son-Narmada South fault
(b) Sausar group
(c) Mahakoshar group
(d) Betul group

A.(a)-(b)-(c)-(d)
B.(a)-(c)-(b)-(d)
C.(d)-(b)-(a)-(c)
D.(c)-(a)-(d)-(b)

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: D

The key's north-to-south order is (c)-(a)-(d)-(b): Mahakoshal group, Son-Narmada South Fault, Betul group, Sausar group.

The Central Indian Tectonic Zone is bounded by the Son-Narmada North Fault and the Central Indian Shear. From north to south it contains the Mahakoshal belt (printed 'Mahakoshar'), lying between the Son-Narmada North and South Faults; the Son-Narmada South Fault; the Betul belt to its south; and the Sausar Group in the southern part of the zone, next to the Central Indian Shear and the Bastar craton.

The other orders place the Sausar Group north of Betul or the fault north of the Mahakoshal belt, which reverses parts of this arrangement.

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Which of the following Eon characterizes the more tonalitic batholiths, more biomodal volcanic suites and the komatites ?

A.Phanerozoic
B.Proterozoic
C.Archean
D.Mesozoic

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: C

These features characterise the Archean eon.

Archean crust (4.0 to 2.5 billion years ago) is dominated by granite-greenstone terrains. The granitoids are mostly tonalite-trondhjemite-granodiorite (TTG) batholiths, the greenstone belts contain bimodal volcanic suites of basalt and felsic volcanics, and komatiites, ultramafic lavas erupted at very high temperatures, are almost confined to the Archean because the mantle was then hotter.

Phanerozoic and Proterozoic crust has more potassic granites and almost no komatiites, and the Mesozoic is an era within the Phanerozoic, not an eon.

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Banded iron formations in the Archaean greenstone belts are best witness for :

A.Archaean sedimentary basin development
B.Shift from anoxic to oxygenated environments
C.Archaean cratons
D.Archaean weathering process

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: B

Banded iron formations are best witness for the shift from anoxic to oxygenated environments.

Iron dissolves as ferrous iron only in water without free oxygen. BIFs record an ocean that carried large amounts of dissolved iron, which was precipitated as ferric oxides wherever oxygen, produced by early photosynthesisers, became available. Their abundance in the Archaean and early Proterozoic, and their near disappearance after about 1.8 Ga, track the oxygenation of the ocean and atmosphere.

The other options are too general. BIFs are sedimentary rocks deposited in basins and often found on cratons, but those facts are true of many rocks. What makes BIFs distinctive is the redox change they record, not basin development or weathering processes.

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The Palghat-Cauvery shear zone comprises :

A.Charnokite interbanded with khondalites
B.TTG with dolerites
C.Greenstone belts
D.Khondalites interbanded with Anorthosites

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: A

The keyed answer is charnockite interbanded with khondalites.

The Palghat-Cauvery shear zone, which separates the Dharwar craton from the Madurai block in south India, cuts through high-grade granulite-facies terrain. Its dominant rocks are charnockites and hornblende-biotite gneisses, interlayered with metasedimentary garnet-sillimanite (khondalitic) gneisses and quartzites, the association that option A names.

Tonalite-trondhjemite-granodiorite gneisses with dolerite dykes and greenstone belts are the typical low-grade associations of the Dharwar craton to the north. Anorthosite bodies such as Sittampundi do occur in the zone, but an association that leaves out the charnockites does not describe it.

Discuss in Forum

Match the following structural trends with their regional orientation :

(a) Dharwar Trend	(1) ENE - WSW
(b) Satpura Trend	(2) NW - SE
(c) Aravali Trend	(3) NE - SW

A.(a) - 2, (b) - 1, (c) - 3
B.(a) - 1, (b) - 2, (c) - 3
C.(a) - 2, (b) - 1, (c) - 2
D.(a) - 3, (b) - 2, (c) - 1

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: A

The correct matching is (a) - 2, (b) - 1, (c) - 3.

The Dharwar trend, seen in the schist belts of Karnataka, runs NNW-SSE, the NW-SE direction.
The Satpura trend, followed by the Satpura range and the Central Indian Tectonic Zone, runs ENE-WSW.
The Aravalli trend, followed by the Aravalli range of Rajasthan, runs NE-SW.

Option B swaps the Dharwar and Satpura trends; option C gives Aravalli the NW-SE trend that belongs to Dharwar; option D reverses the whole set.

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The Yilgarn shield and Pilbara shield comprises significant part of the older cratonic shields of the continent :

A.Australia
B.Africa
C.South America
D.Canada

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: A

The Yilgarn and Pilbara cratons are in Australia.

Both are Archaean cratons in Western Australia. The Pilbara contains some of the oldest well-preserved crust and early evidence of life, about 3.5 Ga, and the larger Yilgarn, about 3.0-2.6 Ga, hosts major gold and nickel deposits, including those around Kalgoorlie.

Africa's Archaean nuclei are the Kaapvaal and Zimbabwe cratons, South America's the Amazonian and Sao Francisco, and Canada's the Superior and Slave, so the other continents are wrong.

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10.

Despite being older, the Aravali rocks from the type area are lower grade than the juxtaposed Delhi metasediments :

A.The two units experienced different metamorphism at same place
B.The two units were temporally apart then accreted
C.Delhi experience thermal metamorphism due to Lava flow
D.The Aravalis deposited latter than Delhi

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: B

The key explains it as the two units were temporally apart then accreted.

In normal burial the older, deeper rocks are of equal or higher grade than younger rocks above them. If the older Aravalli rocks are of lower grade than the Delhi rocks beside them, the two cannot have been metamorphosed together in a single sequence. They must have been metamorphosed at different times or places and then brought together later by tectonic juxtaposition.

Option A would not explain an older unit ending up lower in grade at one place, option C invokes lava flows for which there is no basis in a regional metamorphic belt, and option D contradicts the stem, which says the Aravallis are older.

Precambrian Geology Questions and Answers

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