Petrology, geochemistry and tectonic settings of the mafic dikes and sills associated with the evolution of the Proterozoic Cuddapah Basin of south India

Abstract

In this article we summarize the petrological, geochemical and tectonic processes involved in the evolution of the Proterozoic intracratonic Cuddapah basin. We use new and available ages of Cuddapah igneous rocks, together with field, stratigraphic, geophysical and other criteria, to arrive at a plausible model for the timing of these processes during basin evolution. We present petrological and geochronological evidence of dike emplacement along preferred lineament directions around the basin in response to stresses, which may have been responsible for the evolution of the basin itself. Basaltic dike intrusion started on the south Indian shield around 2400 Ma and continued throughout the Cuddapah basin evolution and sedimentation. A deep mantle perturbation, currently manifested by a lopolithic cupola-like intrusion under the southwestern part of the basin, may have occurred at the onset of basin evolution and played an important role in its development. Paleomagnetic, gravity and geochronological evidence indicates that it was a constant thermal source responsible for dike and sill emplacement between 1500 and 1200 Ma both inside and outside the basin. Lineament reactivation in the NW-SE and NE-SW directions, in response to the mantle perturbation, intensified between 1400 and 1200 Ma, leading to the emplacement of several cross cutting dikes. Fe-Mg partition coefficients of olivine and augite and Ca-Na partition coefficient of plagioclase, calculated from the composition of these minerals and bulk composition of their host rocks, indicate that the dikes outside the Cuddapah basin are cumulates. The contemporary dikes may be related by fractional crystallization as indicated by a positive correlation between their plagioclase Ca# (atomic Ca/[Ca+Na]) and augite Mg# (atomic Mg/[Mg+Fe]). A few NW-SE and NE-SW cross cutting dikes of the period between 1400 and 1200 Ma, preserve petrographic evidence of episodic magmatic intrusive activity along preferred directions. Petrological reasoning indicates that a magmatic liquid reacted with a set of cross cutting dikes, intruding into one that was already solidified and altering the composition of the magma that produced the other dike. The Cuddapah basin tholeiites may be related by fractional crystallization at 5 kb and 1019-1154 • C, which occurred in the lopolithic cupola near the southwestern margin of the basin. Xenolith bearing picrites, which occur near the periphery of the cupola, originated by the accumulation of xenoliths in the tholeiites. This is indicated by the composition of the olivine in the xenoliths (Fo 78.7−81.9), which are closely similar to calculated olivine compositions (Fo 77.8−78.3) in equilibrium with the tholeiites under the same P-T conditions. It is inferred that fractionation in the cupola resulted in crystals settling on its walls. Hence, the xenolith-bearing sills occur at the periphery of the lopolithic body.

Precambrian crustal evolution of Peninsular India: A 3.0 billion year odyssey

“…Chatterjee and Bhattacharji (2001) report a 40 Ar-39 40 age of 1879 ± 5 Ma for the mafic dyke that is coeval with the 1882 Ma U-Pb age on the Pulivendla Sill by French et al (2008). Unpublished paleomagnetic data from the $1.9 Ga Bastar dykes are identical to the Cuddapah traps volcanic (Clark, 1982).…”

“…Two competing hypotheses for the initiation of basinal subsidence and deposition were forwarded. Chatterjee and Bhattacharji (2001) propose that the basin was formed due to a mantle induced thermal trigger. Evidence for this comes from the presence of a large subsurface mafic body in the southwestern portion of the basin that provided episodic magmatism to form the abundant dykes and lava flows in and around the basin.…”

India's changing place in global Proterozoic reconstructions: A review of geochronologic constraints and paleomagnetic poles from the Dharwar, Bundelkhand and Marwar cratons

“…Radiometric data on these doleritic dykes suggest at least three major episodes of dyke emplacement in the region that occurred at 1.9-1.7, 1.4-1.3 and 1.2-1.0 Ga (Murthy et al, 1987;Padmakumari and Dayal, 1987;Mallikarjuna Rao et al, 1995;Chatterji and Bhattacharji, 2001). A high precision baddeleyite age of 1885.4 ± 3.1 Ma for the Pullivendla mafic sill from the Cuddapah basin has been interpreted to coincide with the widespread ∼1.9 Ga basaltic magmatism occurred in the widely separated Large Igneous Provinces (French et al, 2008).…”

SHRIMP U–Pb zircon provenance of the Sullavai Group of Pranhita–Godavari Basin and Bairenkonda Quartzite of Cuddapah Basin, with implications for the Southern Indian Proterozoic tectonic architecture

“…A lower limit to the onset of deposition is provided by ~2.2 Ga ages for dolerite dyke swarms that intrude the EDC lithologies but not the overlying Cuddapah formations. The Vempalle lavas, sills and dykes have been dated between 1879 and 1899 Ma (Chatterjee and Bhattacharji, 2001;Anand et al, 2003). An upper age constraint of ~1400 Ma for the Cuddapah deposition is provided by the ages for lamproite dykes intrusive to Cumbum shale, between 1354 and 1418 Ma (Anil Kumar et al, 2001, Chalapathi Rao et al, 1996.…”

“…Malani Vempalle lava and dolerite intrusive Chatterjee and Bhattacharji, 2001;Anand et al, 2003 Dykes in E Dharwar French et al, 2008, Meert et al, 20102300-2200 Intrusive granites in the Godavari granulites Rajesham et al, 1993 Bangalore and Mahabubnagar Dyke Swarm. French et al, 2008, Meert et al, 2010~ 2500 Closepet granite and equivalents, East Dharwar Granite Gneiss Friend and Nutman, 1991, Jayananda et al, 2008, Meert et al, 20102700-2500 Granulites in PG Valley Rajesham et al, 1993 Dharwar Batholith (East Dharwar) Friend and Nutman, 1991, Nutman et al, 1996, Chadwick et al, 2000 3400-3000…”