U-Pb Ages and Sr, Pb and Nd Isotope Data for Gneisses near the Kolar Schist Belt: Evidence for the Juxtaposition of Discrete Archean Terranes
Abstract
Uranium-lead ages and Sr, Pb, and Nd isotopic data for gneisses near the Kolar Schist Belt and their interpretation as evidence for the juxtaposition of discrete Archean terranes were presented. The granodioritic Kambha gneiss east of the schist belt has a zircon age of 2532 + or - 3 Ma and mantle-like initial Sr, Pb, and Nd isotopic ratios. Therefore these gneisses are thought to represent new crust added to the craton in the latest Archean. By contrast, more mafic Dod gneisses and leucocratic Dosa gneisses west of the schist belt (2632 + or - 7 and 2610 + or - 10 Ma) show evidence for contamination of their magmatic precursors (LREE-enriched mantle-derived for the Dod gneisses) by older (greater than 3.2 Ga) continental crust. Fragments of this older crust may be present as granitic and tonalitic inclusions in the 2.6-Ga gneisses and in shear zones. The antiquity of these fragments is supported by their Nd, Sr, and Pb isotopic compositions and by 2.8 to greater than 3.2 Ga zircon cores.
- Publication:
-
Workshop on the Deep Continental Crust of South India
- Pub Date:
- 1988
- Bibcode:
- 1988dcc..work...84K
- Keywords:
-
- Geochronology;
- Gneiss;
- Isotopes;
- Minerals;
- Precambrian Period;
- Radioactive Age Determination;
- Schist;
- Cores;
- Cratons;
- Crusts;
- Fragments;
- Granite;
- Inclusions;
- Terrain;
- Geophysics