Dynamics of Early Neoproterozoic accretion, west-central India: II ~1.65 Ga HT-LP and ~0.95 Ga LT-HP metamorphism in Godhra-Chhota Udepur, and a tectonic model for Early Neoproterozoic accretion

Abstract

The n/nne-striking aravalli delhi fold belt (adfb) and the e-striking central indian tectonic zone (citz) converge at the godhra-chhota udepur (gc) sector, west-central india. Analyses of mesoscale deformation structures and metamorphic phase equilibria in the basement and supracrustal rocks are integrated with geochronological-geochemical data (accompanying article) to address the dynamics of the early neoproterozoic citz-adfb accretion. In the gc sector, ~1.65 ga granulite facies anatectic gneisses, ~2.5 ga and 1.03–1.02 ga granitoids, and greenschist to amphibolite facies allochthonous supracrustal rocks constitute a tectonic mélange (d2 deformation). The lithodemic units are traversed by networks of w/wnw-striking steep-dipping transpressional shear zones with sinistral kinematics (d3). The shallow-dipping mélange with top-to-the south kinematics is intruded by post-d2 to syn-d3 0.95–0.93 ga granitoids. Mn-nckfmash p-t pseudosection analyses of the anatectic gneisses with pre-d2 garnet + cordierite-bearing leucosomes suggest the rocks evolved along a clockwise p-t path in the range of 5–6 kbar and 680–720 °c. By contrast, the early neoproterozoic (0.95–0.93 ga) chlorite + phengite (si up to 3.32 apfu) + clinozoisite + quartz ± biotite ± garnet schists in the mélange attained pre/syn-d2 peak metamorphic conditions (10–12 kbar, 450–500 °c). Nckfmash pseudosection analyses of the ~0.95 ga phengite-bearing schists indicate the supracrustal rocks evolved along a high-p, low-t clockwise path; phengite-poor micas defining the d3 fabric (si up to 3.04 apfu) attest to post-peak decompression in the schists. The ~2.5 ga adfb granites accreted with the ~1.65 ga ht-lp anatectic gneisses, ~1.03 ga granites, and the ~0.95 ga lt-hp supracrustal rocks of the citz during d2 thrusting. The crustal convergence continued with the emplacement of post-d2 0.95–0.93 ga granitoids that culminated with the nucleation of w/wnw-striking d3 transpressional shear zones. This broad contemporaneity among felsic plutonism, lt-hp metamorphism in the supracrustal rocks, and the d2-d3 shortening are interpreted to be the result of a switch in subduction polarity between 1.03 and 0.93 ga during oblique adfb-citz convergence. © 2022 elsevier b.v.