Magmatism in Western Cuddapahs: The Mafic Sills and Lava Flows of Vempalle and Tadpatri Formations

Abstract

The western part of Cuddapah basin has been considered as a foreland to the fold-thrust belt represented by eastern Nallamalais and Nellore schist belt. The igneous activities, in the form of lava flows and sills, in western Cuddapahs have been a subject of controversy since tectonogenetic models ranging from a mantle plume to lithospheric extension have been suggested. The present work covers a detailed study of the mafic sills and lava flows of Vempalle and Tadpatri formations in western Cuddapahs, which earlier workers have also noted. A detailed field and laboratory work in this study brings out, for the first time, five distinct petrographic and geochemical varieties of sills. Geochemical studies also suggest that the different sill types have originated from varying degrees of partial melting of a metasomatized sub-crustal lithospheric mantle, the metasomatism of source being attributed to older Archaean convergent settings/greenstone belts that the basin unconformably overlies. The possible contribution of any small plume is only heating and doming of overlying mantle that induced incipient crustal rifting. Our geochemical studies on the lava flows of Vempalle Formation also suggest that the magma was derived from small degree of partial melting of spinel-garnet peridotite mantle in a rift setting.

Platinum group element geochemistry and whole‐rock systematics of the Vempalle sills, Cuddapah Basin, India: Implications on sulphur saturation history, mantle processes, and tectonic setting

“…Within the Vempalle Formation, the mafic magmatic rocks are associated with stromatolitic carbonates, cherts, and shales that are suggested to be deposited in a shallow marine environment (Khelen et al, ). Geochemical and geochronological studies on the extrusive and intrusive mafic rocks exposed in the Vempalle Formation have been reported by few earlier workers (Anand, Gibson, Subbarao, Kelley, & Dickin, ; Chakraborty, Mukhopadhyay, & Pankaj, ; Dhanakumar et al, 2018; French, Heaman, Chacko, & Srivastava, ; Sheppard et al, ). In this paper, we document the PGE geochemistry along with major and trace elements systematics of mafic sills from the Vempalle Formation to evaluate their sulphur saturation history, source heterogeneity, and tectonic setting.…”

Cuddapah Basin, India: A Collage of Proterozoic Subbasins and Terranes

“…Several dolerite sills and basaltic lava flows are present within the Tadpatri Formation (Chakraborty et al, 2016). Chilled margins of the dolerite and contact metamorphic effect in the host carbonates are commonly seen.…”

“…Suspected volcaniclastics interbedded within the Nallamalai Group and volcanogenic cherts in the limestones of Kurnool Group are potential exceptions to this statement, awaiting confirmation from future studies. Chakraborty et al (2016) had attributed partial melting of spinel -garnet peridotite for Vempalle lava flows. Singh et al (2018) studied six basaltic lava flows from the Vempalle Formation.…”

“…They suggested sulphur-saturated nature of magmas in a riftcontrolled intraplate setting associated with an oceancontinent transition zone for the emplacement of these lava flows based on PGE chemistry. Chakraborty et al (2016) distinguished five varieties of sills intruding the Tadpatri Formation based on petrographic and geochemical studies. They inferred that the mafic sills of Tadpatri Formation are derived from small scale localized melting of the contaminated mantle in a rift setting.…”

Petrology and geochemistry of mafic dyke and sills in Cumbum Formation, of the Proterozoic Nallamalai fold belt, Rajampet area, Andhra Pradesh, India

“…Tadpatri sills are relatively unaltered in nature, consists of olivine, pyroxene, phlogopite and some spinel. The lower part of the sills shows cumulate texture with fresh olivine, while the upper part of 1 2 3 4 5 6 7 8 9 10 11 12 Standard NIM-S GSR-2 JSL-1 GSR-5 JA-2 GSR-7 SARM-50 NIM-P JB-3 JGb-2 GSI-SA-1 GSR-3 (Chakraborty et al 2016).…”