Affiliation:
1. 1 Centre for Earth Ocean & Atmospheric Sciences University of Hyderabad Hyderabad 500 046 India uohyd.ac.in
2. 2 Department of Earth and Environmental Sciences IISER Bhopal Bhopal India iiserb.ac.in
3. 3 Laboratoire Magmas et Volcans Observatoire de Physique du Globe de Clermont-Ferrand Universite Clermont Auvergne IRD CNRS UMR 6524 6 Avenue Blaise Pascal 63178 Aubière France ird.fr
4. 4 CSIR-National Geophysical Research Institute Uppal Road Hyderabad 500 007 India ngri.org.in
Abstract
Abstract
A widely spaced Neoarchean shear zone network traverses the granite-greenstone terrains of the Western Dharwar craton (WDC). The NNW-SSE trending Balehonnur shear zone traverses the largest part of the preserved tilted Archean crustal ensemble in the Western Dharwar craton (WDC) from the amphibolite-granulite transition in the south to greenschist facies in the north and eventually concealed under Deccan lava flows. Published tectonic fabrics data and kinematic analysis, with our data reveal a sinistral sense of shearing that effectuate greenstone sequences, Tonalite-Trondhjemite-Granodiorite Gneisses (TTG), and Koppa granite as reflected in variable deformation and strain localization. A profound increase of strain towards the core of the shear zone in the ca. 2610 Ma Koppa granite is marked by a transition from weak foliation outside the shear zone through the development of C-S structures and C-prime fabrics, mylonite to ultramylonite. The mineral assemblages in the Koppa granite and adjoining greenstone indicate near peak P-T conditions of 1.2 Gpa, 775-800°C following a slow cooling path of 1.0 GPa and 650°C. Field-based tectonic fabrics data together with U-Pb zircon ages reveal that the Koppa granite emplaced along the contact zone of Shimoga-Bababudan basin ca. 2610 Ma, coinciding with the emplacement of ca. 2600 Ma Arsikere-Banavara, Pandavpura, and Chitradurga granites further east which mark the stabilization of WDC. Significant variation in major element oxide (SiO2 = 56-69 wt.%) together with high content of incompatible elements (REE, Nb, Zr, and Y) and high zircon crystallization temperatures (~1000°C) of Koppa granite suggests derivation by partial melting of composite sources involving enriched uppermost mantle and lower crust. The development of widely spaced shear zones is probably linked to the assembly of eastern and western blocks through westward convergence of hot oceanic lithosphere against already cratonized thick colder western block leading to the development of strain heterogeneities between greenstone and TTGs due to their different mineral assemblages leading to rheological contrast in the cratonic lithologies.
Funder
IISER Bhopal
Shyama Prasad Mukherjee Fellowship
Dr. D.S. Kothari Post-doctoral Fellowship
French Research Agency
LabEx ClerVolc
DST Inspire Fellowship
DST-FIST
Cited by
2 articles.
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