THE CENTRAL INDIAN TECTONIC ZONE (CITZ): A PROTEROZOIC ENIGMA IN SUPERCONTINENT ASSEMBLY

Paul Hoffman (1988) addressed the sequence of collisional events that resulted in the assembly of Laurentia. The individual Archean nuclei of Laurentia are connected by a series of orogenic belts that resulted in the coalescence of the core of the continent by ~1.7 Ga. The initial premise was confirmed, at least in part, by comprehensive studies of well-dated paleomagnetic poles. Although the size of Peninsular India is considerably smaller than Laurentia, India is dissected by a number of mobile belts that mark the edges of Archean nuclei. Interpreting the deformational history within these mobile belts is difficult because each has experienced multi-phase tectonism and geochronological data are sparse. The Dharwar and Bastar cratons are geographically separated by the Prahnita-Godavari Rift (PG), the Singhbhum and Bastar cratons by the Mahanadi Rift (MR) and the Bastar/Singhbhum and Bundelkhand/Aravalli cratons are separated by the Central Indian Tectonic Zone (CITZ). The MR is filled with Carboniferous-Triassic Gondwana rift sediments. Limited geochronology on basement metamorphic rocks indicate that the region was active during the ~1.0-0.9 Ga orogenic cycle, but there are also remnants of much older reworked Archean material. The Prahnita-Godavari Rift basin is filled with Proterozoic and Phanerozoic sedimentary rocks bordered to the north by the Bhopalpatnam granulite belt (BPG) and the south by the Karimnagar granulite belts (KGB). The BPG granulites yield ages of 1.6 and 1.0 Ga and led to a proposal that the 1.6 Ga metamorphism in the BPG developed during Bastar-Dharwar collision. The Central Indian Tectonic Zone (CITZ) traverses Peninsular India from East to West and is thought to demarcate a major boundary between the Northern Indian Block (NIB; Aravalli Bundelkhand) and South Indian Block (SIB: Dharwar, Bastar and Singhbhum). The CITZ is a polymetamorphic terrane with key ages of 2.5, 1.6 and 1.0 Ga. Stein et al. (2004) maintain that the younger ages (1.6 and 1.0 Ga) reflect re-working of material within an older 2.5 Ga suture. Other authors find the model problematic and argue for a ~1.6 Ga collision between the SIB and the NIB or the Bastar-Bundelkhand cratons. There are also models that favor a much younger Stenian-Tonian aged (~1.1-0.88 Ga) collisions between the NIB, the SIB and the Marwar Block to form ‘Greater India’.