Article

Tuff beds in Kurnool subbasin, southern India and implications for felsic volcanism in Proterozoic intracratonic basins

Geological Studies Unit, Indian Statistical Institute, Kolkata 700108, India
Geoscience Frontiers 03/2012; DOI: 10.1016/j.gsf.2012.01.002

ABSTRACT A first report on tuff beds from the Owk Shale in the Proterozoic Kurnool sub-basin in southern India is presented. The rhyolitic to rhodacitic tuffs, overlying shelfal limestones formed at depths below storm wave base, have rheomorphic features indicative of viscoplastic flow, and geochem-ical signatures of rhyolitic to rhyodacitic unwelded to welded tuffs, similar to those described from other Proterozoic intracratonic basins like Vindhyan and Chhattisgarh basins in India. Fragmentary nature of altered glass with perlitic cracks and local admixture with intrabasinal sediments suggest phreatomag-matic reactions. The widespread and repeated occurrences of felsic tuffs in these basins, possibly derived from low degree melting of continental crust, suggest intermittent tectonothermal instability which likely influenced basinal topography and cyclic development of the carbonate platforms. ª 2011, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.

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    ABSTRACT: Abstract: Felsic tuff beds with some presumed sedimentary components were reported from the Owk Shale (Kurnool Group; bearing Neoproterozoic fossils) in the upper part of the sedimentary succession in the Cuddapah basin in India by Saha and Tripathy (2012a). Our optical and SEM petrographic study of three thin sections, however, indicates that the parent samples are sandy mudstones with variable amounts of a felsic volcaniclastic component. New highquality U-Pb (SHRIMP and LA-MC-ICPMS) ages of 133 detrital zircon grains from a sample show that one grain is ca. 1880 Ma, one grain is ca. 3300 Ma, and the ages of the remaining 131 grains fall between 2690 Ma and 2429 Ma, the population averaging 2522 ± 36 Ma. The data indicate that the zircons are detrital grains derived from the ca. 2.5 Ga granitic/gneissic/greenstone basement of the Dharwar cratons that also host minor older Archean enclaves. The single 1880 Ma grain could have come from a ca. 1.9 Ga LIP. In the absence of any younger magmatic zircon, the absolute age of the Owk Shale remains elusive.
    Journal of the Geological Society of India 01/2013; 82:207-216. · 0.57 Impact Factor
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    ABSTRACT: The sedimentary basins are often influenced by adjoining mobile belts as is the case of the Proterozoic Cuddapah basin in southern India, lying in proximity of the Eastern Ghats granulite belt (EGB) and the Southern granulite terrain (SGT). Two major faults – Gani–Kalva and Kona faults – in the western part of the Cuddapah basin have been examined in this work to comment on the changes in paleostress conditions affecting the basin evolution punctuated by several stages of extensional and compressional regimes in the time interval 1.9–0.5 Ga. The tensor solutions were obtained for the mesoscale faults and fault striae using the improved Right Dihedron method followed by the Rotational Optimization method (TENSOR, Delvaux and Sperner, 2003). Combining the paleostress field reconstruction and other struc-tural/stratigraphic attributes we propose a possible scenario of punctuated evolution of the Cuddapah basin and its inversion. The stress regimes are tentatively correlated with multiple stages of basin opening and deformation of basin in-fill, representing the pre-Grenvillian through the Pan-African orogeny. The paleostress conditions derived from various stratigraphic horizons provide an opportunity to comment on the changes in tectonic stresses including several stages of extensional and compressive regimes in the Cuddapah basin. The tensor solutions were obtained for the mesoscale faults and fault striae in the neighborhood of above two fault lines using the improved Right Dihedron method followed by the Rotational Optimiza-tion method (TENSOR, Delvaux and Sperner, 2003). The most prominent stress states recorded around the two fault lines can be classified into those affecting (1) the Paleoproterozoic lower Cuddapah succes-sions, (2) the younger Kurnool Group and (3) both the groups. Integrating the stress states of the fault-slip analysis obtained from different unconformity bounded rock groups of lower Cuddapah and other geo-logic data, we suggest extensional to transtensive/pure strike-slip regime to be active during the first phase of basin opening and c. 1.89 Ga mafic igneous activity. Late compressional to transpressive/pure strike-slip regimes are well recorded from the younger Kurnool Group, representing late Neoproterozoic deformations. The tensor solutions from different unconformity bound stratigraphic horizons constrain different states of deformation. We relate the extensional to transtensive/pure strike-slip regimes from lower Cuddapah successions to the ongoing basin opening events and the associated Palaeoproterozoic igneous activities. The late Neoproterozoic to early Paleozoic compressional to transpressive/strike-slip regime present the possible effects of compressional activities happening around the cratonic margin. The present analysis lends further support to the idea that estimation of paleostress states from fault-slip data even in regions of relatively weak deformation in continental interior are important while assessing influence of plate margin stresses on the continental interior.
    Precambrian Research 09/2013; 235:107-130. · 4.44 Impact Factor

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