Extensive Early Neoproterozoic high-grade metamorphism in North Chotanagpur Gneissic Complex of the Central Indian Tectonic Zone

Abstract

The Indian Shield was assembled through a Proterozoic collision between the northern and southern Indian continental blocks along the ENE–WSW Central Indian Tectonic Zone (CITZ). Chemical dating of monazite, xenotime and uraninite, and thermobarometric analysis are carried out to determine the spatial extent and assess the significance of Early Neoproterozoic high-grade metamorphism in the northern sector of the Chotanagpur Gneissic Complex (CGC), a Proterozoic belt of granite and granitic gneiss in the eastern part of CITZ. In northwest CGC, xenotime in granitic gneiss crystallized at 975 ± 67 Ma along foliation that developed at high metamorphic temperatures (788–861 °C). Thus Grenvillian metamorphism in northwest CGC may be correlated with the high-grade Grenvillian metamorphic terranes in northeast and north–central CGC, and similar terrane in central India. In the area northwest of the NE–SW boundary fault of CGC, monazite crystallized at 1697 ± 17 Ma in porphyritic granite that lacks < 1.6 Ga thermal imprint. Thus the Grenvillian metamorphic front did not extend across the boundary of the CGC. Furthermore, the lithological association of granite and country schist/phyllite, and the timing of granite intrusion are similar to those in the Son–Narmada Graben, a major ENE–WSW lineament comprising the northern part of CITZ in central India. Therefore, the graben most probably extends in a northeasterly direction along the NE–SW boundary of the CGC. In the northeastern corner of the CGC, a 768 ± 11 Ma age of uraninite in biotite–gneiss may be related to mid-Neoproterozoic high-grade metamorphism along the eastern margin of the CGC. Pervasive high-grade Grenvillian metamorphism in the entire northern sector of the CGC may be related to a terminal Grenvillian assembly of the Indian Shield in the Rodinia supercontinent.