Meso-Neoproterozoic mid-crustal metamorphic record from the Ajmer–Shrinagar section, Rajasthan, India and its implication to the assembly of the Greater Indian Landmass during the Grenvillian-age orogenesis
Sankar Bose, Pritha Seth, Nilanjan Dasgupta, 2017. "Meso-Neoproterozoic mid-crustal metamorphic record from the Ajmer–Shrinagar section, Rajasthan, India and its implication to the assembly of the Greater Indian Landmass during the Grenvillian-age orogenesis", Crustal Evolution of India and Antarctica: The Supercontinent Connection, N. C. Pant, S. Dasgupta
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The Shrinagar–Ajmer section of the South Delhi Fold Belt exposes a package of medium-grade metasedimentary rocks intruded by synkinematic granite, and the entire package was thrust on top of the basement gneisses occurring further east. The metamorphic history is best developed in the staurolite schist that shows an overall increase in modal abundance of staurolite towards the east. Textural analyses, garnet zoning profiles, thermobarometric data and phase equilibria analyses show an increase in metamorphic pressure and temperature, reaching peak conditions of 592 ± 12°C and 7.7 ± 0.11 kbar. In situ monazite dating of a staurolite schist sample yields a pooled age of 980 ± 22 Ma, which is assumed to be close to the age of the peak metamorphism. The Shrinagar granite was possibly emplaced close to the orogeny occurring at approximately 980 Ma and deformed by later events. The style and timing of metamorphism in the Shrinagar–Ajmer section match with the granulite-facies reworking of the basement rocks of the Aravalli–Delhi Mobile Belt. We envisage that the Grenvillian-age orogeny with its characteristic collisional style involved deep- to mid-crustal sections of the Aravalli–Delhi Mobile Belt. Our results further indicate that the Greater Indian Landmass was assembled during the formation of the supercontinent Rodinia.
Supplementary material: Electron microprobe data of the garnet used for chemical zoning in Figure 5 are available at https://doi.org/10.6084/m9.figshare.c.3738335
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The Proterozoic aeon involved at least three major continental readjustments. India and Antarctica appear in most models of supercontinent reconstructions, but their relative position has been the subject of debate. High-resolution petrological and geochronological data, especially from the Proterozoic mobile belts, provide the principal means of resolving this issue. The ice-covered nature of Antarctica allows only limited access to the rocks, and then only in coastal tracts, so detailed studies in more accessible Proterozoic terrains in India assume added significance.
This volume, a follow-up to the XII International Symposium on Antarctic Earth Science, Goa (a SCAR symposium), provides new data from selected locations in east Antarctica (Enderby Land and Dronning Maud Land) and from India, including the Eastern Ghats Mobile Belt (EGMB), Chota Nagpur Gneissic Complex, the Khasi Hills and the Aravalli–Delhi Mobile Belt. The presented geochronological data, constrained by petrological studies, are expected to provide new insights, especially into the EGMB–east Antarctica connection and the rate of continental readjustments in the post-Rodinia break-up.