Pati, and three co-authors, concluded in 2008 that the Dhala structure formed in Archean crystalline basement of the Bundelkhand craton in the Central Indian Shield was previously called the “Mohar Cauldron” by Jain et al. (2001), Srivastava et al. (2002), and Srivastava and Nambiar (2003). The presence of shock metamorphic features, such as PDFs, ballen-textured quartz, coesite, and checkerboard feldspar in melt breccia confirms the impact origin of the Dhala structure.
Isolated outcrops of impact melt breccia could represent remnants of an originally much wider sheet complex of impact melt breccia. The possibility is entertained that these patchy outcrops are connected below surface, and possibly forms (or formed) a sheet-like layer above the monomict breccia of the interior of the structure.
The Dhala impact structure has an apparent minimum diameter of about 11 km, as indicated by the currently accessible exposures of monomict impact breccia. As a large
part of the area is covered by alluvium, the present measured diameter possibly represents a minimum estimate. The structure represents the eroded remnant of the largest impact structure currently known from the Indian subcontinent, and in fact from the wider region between the Middle East and southeastern Asia. Preliminary geochemical analysis showed that impact melt rock and granitic basement have similar compositions, in accordance with the petrographic finding that granitoid clastic material forms the overwhelming proportion of the clast content of the melt breccia. Thus, it is unlikely that a major supracrustal component of the target region has not been sampled by us.
No meteoritic component has so far been detected in the melt breccia, but further geochemical work is in progress. The age of the Dhala structure is so far only loosely
constrained by the ages of the impacted basement (mafic dykes) of >2.1 Ga and of the overlying supracrustals of the Vindhyan Supergroup at <1.6 Ga.
Managed & Built by I2M Consulting, LLC | © 2010-
