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S. S. Iyer ¹, A. Choudhuri ², U. G. Cordani ³

Affiliations
1 Departmento de Processos Especiais, Instituto de Pesquisas Energeticas e Nucleares-IPEN/CNEN/SP Cidade Universitaria-Caixa Postal 11049-Pinheiros Sao Paulo, BR
2 Departamento de Metalogenese e Geoquimica Aplicada. Instituto de Geociencias, Universidade de Campinas Caixa Postal 6152-Campinas, BR
3 Instituto de Geociencias-Geochronology Research Center, Universidade de Sao Paulo, Sao Paulo, BR

Abstract

An attempt to assemble the available data on the granulite facies rocks spread around Brazil is made with a view to discuss their geological setting, geochronological evolution, petrographic and geochemical evolution. The isotopic ages of the granulites fall into different groups ranging from Archaean to Late Proterozoic. The geotectonic evolution of these rock types is discussed in terms of their being either fragments of geochemically differentiated lower crustal layers or eroded segments of modern Cordilleran (Himalayan) type collision belts. The geochemical feature of the rock types demonstrates the non-systematic fractionation of trace elements.

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M. Santosh ¹, P. K. Thampi ¹, S. S. Iyer ², Marina B. A. Vasconcellos ²

Affiliations
1 Centre for Earth Science Studies, P. B. 2235, Sasthamangalam, Trivandrum 695010, IN
2 Departmento de Processos Especiais-MEC, Institute de Resquisas Energ. e Nucleares, Caixa Postal 11049-Butanta, Sao Paulo, BR

Abstract

Rare earth element abundance in carbonatite associated with the 740 Ma old alkaline complex of Munnar is reported. High values of La (up to 232 ppm) and Ce (up to 261 ppm), moderate Sm (upto 11 ppm), with low Tb (up to 1.1 ppm), Yb (upto 3 ppm) and Lu (up to 0.6 ppm) are observed, comparable with similar values for carbonatites from other regions. The chondrite normalised patterns exhibit a steep slope from LREE to HREE, with (La/Lu)_cn ranging upto 191. A genetic model involving CO₂ degassing from the mantIe and ion exchange reactions with deep crustal rocks is envisaged, with the carbonatites probably representing a late immiscible fraction that separated from a polymerized alkali silicate melt. REE geochemistry of the carbonatite substantiates the view of a Late Precambrian alkaline magmatic regime in this part of the Indian Shield.

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