Depositional history and provenance of cratonic “Purana” basins in southern India: A multipronged geochronology approach to the Proterozoic Kaladgi and Bhima basins

Abstract

Peninsular India is a collage of Archaean cratonic domains separated by Proterozoic mobile belts. A number of cratonic basins, known as “Purana basins” in the Indian literature, formed in different parts of the Indian Peninsula during extensional tectonic events, from Paleoproterozoic through Neoproterozoic times. In this contribution, we present a diversity of new geochronological data for different units within the Kaladgi and the Bhima basins, which overlie the western and eastern Dharwar cratons, respectively. The new geochronology data are discussed in terms of depositional history and provenance of these poorly understood Proterozoic intracratonic basins. For the Kaladgi Group, a U–Pb baddeleyite age of 1,861 ± 4 Ma obtained for a dolerite dyke intruding the Yendigere Formation is used to constrain the minimum age of deposition of the lower Kaladgi Group. This result demonstrates that this part of the succession is comparable in age to the Papaghni Group of the Cuddapah Basin, heralding onset of Purana sedimentation at ~1,900 Ma. The detrital zircon populations from the clastic rocks of the Kaladgi and Bhima basins show unique and distinct age patterns indicating different source of sediments for these two basins. Palaeocurrent analysis indicates a change in provenance from south or southeast to west or northwest between the Kaladgi and Bhima clastic sedimentation. New U–Th–Pb and Rb–Sr radiometric dates of limestones and glauconite‐bearing sandstones of the Bhima Group (Bhima Basin) and the Badami Group (Kaladgi Basin) indicate deposition at around 800–900 Ma, suggesting contemporaneity for the two successions. Thus, the unconformity between the Kaladgi Group and the overlying Badami Group represents a time gap of up to 1,000 Myr. These new results demonstrate the complex multistage burial and unroofing history of the Archaean Dharwar Craton throughout the Proterozoic, with important implications for exploration of metal deposits and diamonds in Peninsular India.

Reply to the comments by Pillai, S. P., George, B. G., Ray, J. S., and Kale, V. S., (GJ‐19‐0112) on Paper: “Depositional history and provenance of cratonic “Purana” basins in southern India: A multipronged geochronology approach to the Proterozoic Kaladgi and Bhima basins” by Joy et al., 2018

“… Comment 1 We recognize that multiple (sometimes conflicting) stratigraphic terms are used in the Kaladgi Basin, but it was not the aim of Joy et al () to attempt a resolution of such problems. We have followed the stratigraphic division adopted in the latest Geological Survey of India geological map accompanying GSI Memoir 129 (Jayaprakash, ) and have retained the stratigraphy and nomenclature as used in Saha, Patranabis‐Deb, and Collins ().…”

“…We apologize for that error from our side. Comment 2 The focus of the Joy et al () paper is to present new and comprehensive geochronological data for the Kaladgi and Bhima basins using multiple isotope systematics. Thus, the lithological and petrographic descriptions were kept to a minimum and have been generalized in the text.…”

“… Comment 4 Figures 6 and 7 are perfectly legible in the online version. Table 1 in Joy et al () omits longitude values for some sample locations, and a supplementary data table is provided with this reply (Table ). Figures 6 and 7 are not intended to find the locations of the samples, as they were provided in Table 1.…”

“…The Bhima Basin limestone samples were more reactive and were thus treated briefly with cold 2M HNO 3 . Trace element data for the carbonate fractions (not published in Joy et al, , for space reasons) show some hallmarks of marine carbonates, such as mild Ce depletion, high LREE/HFSE, low Rb/Sr, high Ca, and low Ti. In obviously complex open systems such as these limestones, this was considered encouraging, and the HNO 3 extracts were thus used for the Pb‐Sr isotope work.…”

“…The 2.5 Ga source has been discussed in section 7.1.2. Joy et al () do not advocate absence of Closepet Granite age zircons in the Kaladgi Group clastic rocks. As correctly pointed out by the critique, the detrital zircons spread from 2,300 to 2,700 Ma.…”