An assembly of the Indian Shield at c. 1.0 Ga and shearing at c. 876-784 Ma in Eastern India: Insights from contrasting P-T paths, and burial and exhumation rates of metapelitic granulites

Recent studies indicate that the Indian Shield formed contemporaneously but separately from Rodinia in Late Mesoproterozoic-Early Neoproterozoic. However, assembly of the eastern Indian Shield is poorly constrained. The dominant WSW-ENE- similar to 1.0 Ga foliation in Central Indian Tectonic Zone (CITZ) including Chotanagpur Gneissic Complex (CGC) in Eastern India indicates a north-south collision between the Northern and Southern Indian Blocks (NIB and SIB). But in northeastern CGC, the dominant foliation is north-south and parallel to the Eastern Indian Tectonic Zone (EITZ), a linear N-S to NNE-SSW belt associated with sinistral shearing at similar to 876-784 Ma along the eastern margin of CGC, in Elan Bank of Kerguelen Plateau, and possibly in East Antarctica. The youngest dates in the metapelitic granulites from EITZ and NE-CGC ( > 13 km west of EITZ) are similar to 876-784 Ma and similar to 1.0 Ga, respectively. But monazite crystallization depends on bulk composition, and it is unclear whether the N-S foliation in NE-CGC metapelites originated at similar to 1.0 Ga or similar to 876-784 Ma. Pseudosection analysis in the MnO-CaO-Na2O-K2O-FeO-MgO-Al2O3-SiO2-H2O-P2O5-Y2O3-Ce2O3-F system shows contrasting PT paths for the metapelites of NE-CGC (clockwise with < 7 kbar/700 degrees C to similar to 14 kbar/825 degrees C prograde conditions) and EITZ (counterclockwise with 8.93 kbar/794 degrees C to 8.80 kbar/809 degrees C prograde conditions, loading to 10.22 kbar/777 degrees C, and isothermal decompression to 6.83 kbar/787 degrees C). Furthermore, garnet diffusion modeling indicates that the burial rate (3.5-8.4 km/Ma) was similar to the exhumation rate (2.2-7.2 km/Ma) in NE-CGC, whereas exhumation (15-27 km/Ma) was similar to 8-25 times faster than burial (1.1-2.0 km/Ma) in EITZ. The N-S foliation in NE-CGC is a manifestation of a similar to 1.0 Ga collision between the CGC and Dinajpur Block along the EITZ, and is similar to the N-S trend in the NIB-Marwar Block collision zone in northwestern India. Evidently, SIB collided northward with NIB, NIB collided westward with Marwar Block, and Dinajpur Block collided westward with NIB simultaneously at similar to 1.0 Ga. The EITZ was reactivated by sinistral shearing at similar to 876-784 Ma, when the Dinajpur Block moved northward. In Cretaceous, dextral strike-slip movement on the E-W Dauki Fault split the Dinajpur Block into its present configuration. The northern parts of NIB and Dinajpur Block collided with Asia in Cenozoic during Himalayan Orogeny.