Sources of continental magmatism adjacent to the late Archean Kolar Suture Zone,south India: distinct isotopic and elemental signatures of two late Archean magmatic series |
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| Authors: | E J Krogstad G N Hanson V Rajamani |
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| Institution: | (1) Department of Earth and Space Sciences, State University of New York, Stony Brook, NY 11794-2100 USA, US;(2) School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110 067 India, IN |
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| Abstract: | Conspicuous Nd, Sr and Pb isotopic differences exist between the Archean gneiss terranes adjoining the suture at the Kolar
Schist Belt, south India. These gneisses, which are the deformed equivalents of plutonic and volcanic rocks, have known or
inferred igneous ages of 2630 to 2530 Ma. Initial isotopic ratios of Nd, Sr and Pb suggest that metaplutonic gneisses west
of the Kolar Schist Belt were emplaced into, and variably contaminated by, an evolved continental crust that formed prior
to 3200 Ma. Felsic metaigneous gneisses that occur as slivers on the western margin of the schist belt have an isotopic character
similar to that of the metaplutonic rocks on the same side of the Kolar Schist Belt. On the east side of the Kolar Schist
Belt the isotopic evidence suggests that the 2530 Ma granitic gneisses were not derived from or contaminated by an older continental
crust. Their source probably evolved with a Nd isotopic composition similar to that of typical Archean mantle, but became
light rare earth element enriched after 2900 to 2700 Ma. The inferred tectonic setting for the west side of the Kolar Schist
Belt is an Andean continental magmatic arc. For the east side of the Kolar Schist Belt, a possible Phanerozoic analog is an
evolved island arc, such as Japan.
Received: 24 June 1994/Accepted: 9 January 1995 |
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