Timing and sources of late Archean magmatism, Kolar area, south India: Implications for Archean tectonics
The N-S trending 80 km long by 4-8 km wide Kolar Schist Belt in the Achean Dharwar craton of south India is bounded on its east and west by gneiss terranes. The contacts between the schist belt and surrounding gneisses are tectonic, rather than intrusive or unconformable. On the west side of the schist belt, monzodioritic to granitic gneisses have U-Pb zircon ages of 2631 +6.5/{minus}6 Ma, 2610 +10/{minus}10 Ma, and 2551 +3/{minus}3 Ma. The U-Pb sphene ages of these orthogneisses are between 2553 and 2551 Ma. Later granitic intrusions have U-Pb sphene and garnet ages as young as 2400 Ma. Gneisses occurring as tectonic and magmatic inclusions in the area contain zircons older than 3140 Ma. The dominant gneiss unit on the east side of the schist belt has a U-Pb zircon age of 2532 +3.5/{minus}3Ma; U-Pb sphene ages east of the belt range from 2520 to 2500 Ma. The last major shearing episode, probably represented by Pb-Pb K-feldspar-whole rock ages on both sides of the schist belt, and by an {sup 40}Ar/{sup 39}Ar muscovite plateau age from sheared gneisses, occurred between 2520 and 2420 Ma. Pb, Nd and Sr initial ratios for the western gneisses suggest that their parent magmas were mantle-derived, but were contaminated by continental crust older than 3200 Ma. Nd, Sr and Pb initial ratios for the eastern gneisses show no evidence of older continental crust either having contaminated the magmas, or acting as part of the source materials. The Kolar Schist Belt is interpreted as the site of a latest Archean or earliest Proterozoic (2520 to 2420 Ma) suture zone where newly generated continental crust on the east was tectonically accreted to the margin of an older (3400 to 2550 Ma) continental nucleus to the west.
- Research Organization:
- State Univ. of New York, Stony Brook, NY (USA)
- OSTI ID:
- 7164484
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580000* -- Geosciences
ACTINIDES
AGE ESTIMATION
ALKALINE EARTH ISOTOPES
ARGON 39
ARGON 40
ARGON ISOTOPES
ASIA
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CONTINENTAL CRUST
DEVELOPING COUNTRIES
EARTH CRUST
ELEMENTS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGIC DEPOSITS
GNEISSES
GRANITES
IGNEOUS ROCKS
INDIA
INTRUSION
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
LEAD
LEAD ISOTOPES
LIGHT NUCLEI
MAGMATISM
METALS
METAMORPHIC ROCKS
MINERALS
NEODYMIUM ISOTOPES
NUCLEI
ORIGIN
OXYGEN COMPOUNDS
PLUTONIC ROCKS
RADIOISOTOPES
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
STABLE ISOTOPES
STRONTIUM ISOTOPES
TECTONICS
TRANSITION ELEMENT COMPOUNDS
URANIUM
YEARS LIVING RADIOISOTOPES
ZIRCON
ZIRCONIUM COMPOUNDS
ZIRCONIUM SILICATES