This document summarizes the Archean crustal building process. It describes how early Archean crust formed from successive volcanic eruptions that deposited greenstone belts in synclinorial basins. As the greenstone belts thickened due to continued volcanic activity and accretion, melting produced tonalite-trondhjemite-granodiorite (TTG) batholiths. Further thickening led to emplacement of potash-rich granites and the process of charnockitization around 2.6 billion years ago. The Archean crust evolved through alternating sequences of greenstone belt formation, TTG emergence, and granite intrusion driven by volcanism, melting, and mantle degassing over time.
The term "trap" has been used in geology since 1785–95 for rock formations. It is derived from the Swedish word for stairs (trapp , trappa) and refers to the step-like hills forming the landscape of the region.
The plateau: also called a high plain or tableland, is an area of highland, usually consisting of relatively flat terrain. A plateau is an elevated land. It is a flat-topped table standing above the surrounding area. A plateau may have one or more sides with steep slopes.
LIP – Large Igneous provinces. (Province = Area / Region)
DVP - The Deccan Volcanic Province is one of the Earth’s giant continental flood basalts and has a total exposed area of about half a million square kilometers in Maharashtra, Madhya Pradesh, Gujrat and some part of Andhra Pradesh. Deccan trap has maximum thickness 3400m in western ghat and its thickness goes decrease toward east side. At Amrakantat on east its thickness is just 160m. Geographical distribution is between latitudes 16° - 24° N and longitudes 70° - 77° E.
Kutch is an East-west Oriented pericraton Rift basin Situated between Nagar Parkar Fault in North and Kathiawar Uplift in South.
Here we will discuss Geology and its Sequence Stratigraphy.
The term "trap" has been used in geology since 1785–95 for rock formations. It is derived from the Swedish word for stairs (trapp , trappa) and refers to the step-like hills forming the landscape of the region.
The plateau: also called a high plain or tableland, is an area of highland, usually consisting of relatively flat terrain. A plateau is an elevated land. It is a flat-topped table standing above the surrounding area. A plateau may have one or more sides with steep slopes.
LIP – Large Igneous provinces. (Province = Area / Region)
DVP - The Deccan Volcanic Province is one of the Earth’s giant continental flood basalts and has a total exposed area of about half a million square kilometers in Maharashtra, Madhya Pradesh, Gujrat and some part of Andhra Pradesh. Deccan trap has maximum thickness 3400m in western ghat and its thickness goes decrease toward east side. At Amrakantat on east its thickness is just 160m. Geographical distribution is between latitudes 16° - 24° N and longitudes 70° - 77° E.
Kutch is an East-west Oriented pericraton Rift basin Situated between Nagar Parkar Fault in North and Kathiawar Uplift in South.
Here we will discuss Geology and its Sequence Stratigraphy.
Komattite
Named after the Komati River in South Africa.
first described by Morris and Richard (twins) for ultramafic units in the Barberton Greenstone belt of South Africa.
Mostly of komatiite are Archean age
distributed in the Archaean shield areas.
Also a few are Proterozoic and Phanerozoic.
In all ages komatiites are highly magnesium.
Mostly a volcanic rock; occasionally intrusive.
Mafic rocks were identified as extrusive because of their volcanic textures and structures, and they seem to have been accepted as a normal component of Archean volcanic successions, Abitibi in Canada.
The ultramafic rocks were interpreted as intrusive which are founded as sills and dykes, Barberton in South Africa.
Spinifex texture-typical of Komatiites:
Minerals are formed by changes in chemical energy in systems which contain one fluid or vapor phase. In nature, minerals are formed by crystallisation or precipitation from concentrated solutions. These solutions are called as ore-bearing fluids. Ore-bearing fluids are characterised by high concentration of certain metallic or other elements.
Fluids are the most effective agents for the transport of material in the mantle and the Earth's crust.
Metallogenic Epoch and Province
Metallogenetic Epochs
Metallogenetic epochs, as defined above, are specific periods characterised by formation of large number of mineral deposits. It does not mean that all the mineral deposits formed during a definite metallogenetic epochs. In India the chief metallogenetic epochs were:
1. Precambrian
2. Late Palaeozoic
3. Late Mesozoic to Early Tertiary
Komattite
Named after the Komati River in South Africa.
first described by Morris and Richard (twins) for ultramafic units in the Barberton Greenstone belt of South Africa.
Mostly of komatiite are Archean age
distributed in the Archaean shield areas.
Also a few are Proterozoic and Phanerozoic.
In all ages komatiites are highly magnesium.
Mostly a volcanic rock; occasionally intrusive.
Mafic rocks were identified as extrusive because of their volcanic textures and structures, and they seem to have been accepted as a normal component of Archean volcanic successions, Abitibi in Canada.
The ultramafic rocks were interpreted as intrusive which are founded as sills and dykes, Barberton in South Africa.
Spinifex texture-typical of Komatiites:
Minerals are formed by changes in chemical energy in systems which contain one fluid or vapor phase. In nature, minerals are formed by crystallisation or precipitation from concentrated solutions. These solutions are called as ore-bearing fluids. Ore-bearing fluids are characterised by high concentration of certain metallic or other elements.
Fluids are the most effective agents for the transport of material in the mantle and the Earth's crust.
Metallogenic Epoch and Province
Metallogenetic Epochs
Metallogenetic epochs, as defined above, are specific periods characterised by formation of large number of mineral deposits. It does not mean that all the mineral deposits formed during a definite metallogenetic epochs. In India the chief metallogenetic epochs were:
1. Precambrian
2. Late Palaeozoic
3. Late Mesozoic to Early Tertiary
The earliest (Precambrian) history of the earth's crustDhanBahadurkhatri
The duration of the Precambrian era and the earliest known state of the crust, Development of Archean Cratons, the Precambrian shield rocks, Paleogeography during Precambrian, and Precambrian glaciations.
2015 Broken Hill Resources Investment Symposium - Geological Survey of New So...Symposium
"Uncovering the Curnamona and Surround: A New South Wales Perspective."
Phil Gilmore, Senior Geoscientist, Geological Survey of New South Wales.
Technical presentation at 2015 Broken Hill Resources Investment symposium.
TABLE OF CONTENT
>Introduction
>General Morphology of Subduction Zone
>Ocean Trenches
>Back Arc Basins
>Accretionary Prism
>Variation in Zones Characteristics
>Structure of Zones from Earthquakes
>Thermal Structure of Down-going Slab
>Gravity Anomalies
>Volcanic and Plutonic Activity
>Metamorphism at convergent boundaries
Kutch Basin Sequence Stratigraphy.
Kutch is an east-west oriented pericratonic basin comprising of rocks ranging from Mesozoic to Cenozoic.
Kutch Basin experienced various phases of marine Transgression and Regression throughout its Geological History.
for More Information email at ravgou39@gmail.com
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
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Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
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The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
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2. CONTENTS
1. What before archean ?
2. What is archean ?
3. Examples of archean rocks.
4. How did these nuclei evolve ?
5. Greenstone belt classification
6. Events involved in archean crust building process
7. References
3. WHAT BEFORE ARCHEAN ?
• Before Archean, Hadean eon (4.5-4.0 Ga) is there.
• There’s hardly any proof left that indicates about Hadean except few.
• So how do we come to know about the hadean eon ?
• Indicated by the zircon.
• Zircon – oldest terrestrial material on the earth.
• Two evidences indicating about the Hadean Eon –
1. Zircon in metamorphosed sandstone in the Jack Hill, Australia- 4.404±0.008By.
2. Acasta Gneiss in Slave Craton, Canada – 4.031± 0.003By.
4. WHAT IS ARCHEAN ?
• A time period in the Geological Time Scale.
• Archean ranges from 4.0 to 2.5 By.
• Archean Eon consists of 4 Eras:
1. Eoarchean Era- 4.0 to 3.6 By.
2. Paleoarchean Era- 3.6 to 3.2 By.
3. Mesoarchean Era- 3.2 to 2.8 By.
4. Neoarchean Era- 2.8 to 2.5 By.
Source:- From the geological time scale v
6.0
5. EXAMPLES OF ARCHEAN ROCKS
• Most continental crusts have the basement- archean.
• Crust building processes- liquid earth to solid earth.
• Study the rock types – tectonics operated in the Archean.
• Some examples of the Archean rocks:
1. In India, Gorur Gneiss in dharwar craton- 3.4-3.6by, some also in bastar craton,
singhbhum craton, etc.
2. Barberton hills, Kaapvaal craton in Africa – around 3.6 by.
3. Yilgarn (2.8by) and Pilbara (3.8-2.83by) cratons in Australia.
4. Baltic (3.1by) Craton in Russia.
5. Hudson Craton in Canada.
6. THESE ARE SOME INDIAN EXAMPLES OF THE
ARCHEAN ROCKS.
Source:- Simplified geological map of India showing
the Archaean cratons, Proterozoic mobile belts,
sedimentary basins and major Precambrian metallic
resources, modified after Ramakrishnan &
Vaidyanadhan (2008) and Sharma (2009). Available
radiometric ages in the Aravalli– Bundelkhand (a,
Weidenbeck & Goswami (1994), Roy & Kröner
(1996), Weidenbeck et al. (1996); b, Mondal et al.
(2002)) and Bastar (c) Rajesh et al. (2009) cratons
and the SSZ (d, Pal & Rhede (2013)) are also
indicated in boxes. ADFB, Aravalli Delhi Fold Belt;
CB, Cuddapah Basin; CGC, Chotanagpur Gneissic
Complex; CHB, Chhattisgarh Basin; CSZ; Chitradurga
Shear Zone; EDC, Eastern Dharwar Craton; IB,
Indravati Basin; MB, mobile belts; NSMB, North
Singhbhum Mobile Belt; PCSZ, Palghat–Cauvery
Shear Zone; SSZ, Singhbhum Shear Zone; VB,
Vindhyan Basin; WDC, Western Dharwar Craton.
4 cratons collectively called as archean
nuclei.
7. HOW DID THESE NUCLEI EVOLVE ?
• To explain the evolution (crustal building process) of archean – dharwar craton.
• Look in the dharwar craton- mostly igneous rocks- mostly basalt, mafic and
ultramafic rocks abundantly present- spinifex texture predominates.
• No sedimentary rock of archean age would be found in the dharwar craton- no
thick crust.
• To understand it, know about some rocks:- Peninsular Gneiss, TTG, Greenstone-
schist belt, Batholithic granite and charnockites.
• Before that let’s look at the map of dharwar craton-
8. Greenstone-Schist Belt- zones of
metamorphosed mafic and ultramafic
volcanic rocks. Only found in archean
times.
Peninsular Gneiss- actually TTG. Lots of
migmatites.
TTG- stands for Tonalite Trondhjemite
Gneiss which is simply plag-rich Granite.
Batholithic Granite- Granite which is in
batholithic form. Usually it is K-rich
granite.
Charnockite- opx bearing granite.
Cross section from EDC to CG- GB
synclinorium in nature.
9. GREENSTONE BELT CLASSIFICATION
• Greenstone belts – synclinorium in nature, both sides bounded by fractures, floating
in the PG and have conglomerates.
• On the basis of this, greenstone belts are classified into
WDC EDC
Chitradurga group (2700Ma)
BIF, greywacke, Mn-bearing, Felsic volcanics
CONGLOMERATE BEDS
Bababudhan group (3600Ma)
Metabasalt, Gabbro, Basic and ultrabasic rocks,
komatites, BIF
KOLAR GROUP- Champion Gneiss (felsic gneiss,
metabasalt, bimodal volcanics, komatites,
greywackes.
CONGLOMERATE BEDS
Peninsular Gneiss (3000Ma)
Sargur group
Ultramafic-mafic layered intrusives, komatites, BIF,
Quartzite(fuchistic) and Marble
Gorur Gneiss (TTG) (3400Ma)
10. EVENTS INVOLVED IN ARCHEAN CRUST BUILDING
PROCESS
1. Formation of Greenstone Belt
2. Development of Greenstone Belt
3. Emergence of TTG
4. Emplacement of potash rich Granite
5. Mantle degassing
6. Charnokitisation.
11. GREENSTONE BELT FORMATION
• First solidified crust formed around the earth in 4.0 By and Very thin- 3-5km – Primordial
crust. Composition- basaltic.
• This crust not preserved that much except in few places – earth very hot ~6000ºC.
• Molten mantle started to appear on the surfaces through various fractures in the crust.
• In the archean time, earth- very unstable, lots of volcanism happening back then.
• Everyday fracturing of the crust happening, hot molten lava came out and floods over the
surface – solidifies the flooded basalt- again fracturing happen- again flooding happened-
again solidified – so on.
• In this way, one flow after another flow came rapidly- in rapid succession they added up.
• Gradually, cooling happened of the top layers but the below layer still hot – sagging
happened- forms synclinorium and the layers called greenstone belt.
• Synclinorium floating in the primordial crust.
• In this way formation of greenstone belt happened.
12. DEVELOPMENT OF GREENSTONE BELT
• As we see, synclinorium type greenstone belt formed.
• Entire crust marked by many such depressions over the PC.
• Archean unstable- fracturing happened near these depressions- again flooding happened
but this time unable to make flood due to these depression and then settled into these
depressions.
• In this way, successive phase of greenstone eruptions took place and seat over the
previously formed layers.
• In another way greenstone belt can also form-
Fracturing can happen within the synclinorium and greenstone came out from this fracture
and seat over the previously formed greenstone belt.
• These depressions hold water- sediments like chert, greywacke, limestone and BIF formed.
• Similarly in the dharwar craton,
Sargur developed in 3.4 by followed by bababudhan in 3.0 by and lastly formed chitradurga
in 2.9 by.
• Younger greenstone belts- more sedimentary dominant and the older greenstone belts-
more komatiite dominant.
13. EMERGENCE OF TTG
• Each stages of fracturing produces new greenstone belt- added up and becoming
thick. This is called the accretion of greenstone belt. (5km to15km)
• Thickening of the crust induced melting of the basal part of the greenstone belt.
• This produced the Granite known as TTG which come in batholithic form.
• This TTG may undergo fracturing (following the fundamental fractures)and form
greenstone over the TTG.
• TTG become base for the younger Greenstone belt. That’s what we are seeing today
in the form of Gorur gneiss.
• Then the succession would look like this-
Greenstone belt- TTG- Greenstone belt- TTG- Greenstone belt-so on- Closepet
granite + dharwar granite+…….
• That’s why Archean tectonics are also known as Greenstone- TTG tectonics.
14. EMPLACEMENT OF POTASH GRANITE
• Along with GS belt melting, TTG- start melting to form Potash rich granite in 2.6By.
• 2.6By- mark the emplacement of potash-rich Granite.
CHARNOKITISATION
• All fractures sealed – granitic emplacement.
• Mantle degassing- process in which mantle fumes and volatile-enrich(CO2) layer
forms below the 15km crust.
• CO2 metasomatism- CO2 removes water from system and replace itself.
• H2O replaced by the CO2 transforming the hornblende and biotite into opx and
thus charnokite formed.
• Formation of charnokite- charnokitization.
• Released water – TTG- more potash granite.
• 2.7-2.5 – rapid crustal growth.
15. REFERENCES
• Geology of India, volume 1 by M. Ramakrishnan and R. Vaidyanandhan
• https://www.youtube.com/playlist?list=PLRFsXLaFH0Z_pN1Lnm1WTet3G31L2OqSg