Secular evolution of continental crust: recorded from massif-type charnockites of Eastern Ghats belt, India

Samarendra Bhattacharya,Ashwini Kumar Chaudhary

doi:10.4236/ns.2010.210134

Samarendra Bhattacharya, Ashwini Kumar Chaudhary

Open Access

https://doi.org/10.4236/ns.2010.210134

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Abstract

It is reasonably well established that the Earth has substantially cooled from the Archean to the pre-sent and hence the sites, rates and pro- cesses of crust formation must have changed through geo-logic time. Archean and Proterozoic granitic rocks are the principal record of such changes. Massif-type charnockites in the Eastern Ghats granulite belt, India, of Archean and Proterozoic ages mirror the changing conditions and/or processes of continental crust for- mation. Though both can be explained by dehydration melting of mafic rocks, the conditions differ. Potasium and rubidium rich Proterozoic charnockites have significant negative Eu ano- maly indicating melting at shallow depths in the stability field of plagioclase. In contrast, sodium and strontium rich Archean charnockites with less LREE enrichment and less depletion in Eu indicate melting at greater depths in the stability field of garnet or amphibole.

Highlights

The continental crust comprising byouant quartzofeldspathic materials are difficult to destroy by subduction and can be considered as the principal record of crustal evolution through geologic time
There remains considerable debate on the processes of crust formation in the Archean compared to those operating in the later period, significant differences in key geochemical features have been documented between Archean and later granitic rocks [3,4,5]
TTG suites of Archean greenstone belts are taken as the Archean continental crust, while large varieties of Proterozoic granitic plutons represent the Proterozoic continental crust

Summary

INTRODUCTION

The continental crust comprising byouant quartzofeldspathic materials are difficult to destroy by subduction and can be considered as the principal record of crustal evolution through geologic time. Considering charnockite-massifs as products of partial melting in the deep crust under granulite facies conditions, U-Pb ages of zircons in them can be taken as representing this deep crustal anatexis, while the Nd-model ages could provide the mantle-derivation ages of their protoliths. In this communiqué, we present selected geochemical and isotopic data for two sets of massif-type charnockites of the Eastern Ghats belt, of Archean and Proterozoic ages respectively.

GEOLOGICAL SETTING

GEOCHEMICAL SIGNATURES

ISOTOPIC SIGNATURES

DISCUSSIONS

Findings

CONCLUSIONS