Insights into crustal architecture and tectonics across Palghat Cauvery Shear Zone, India from combined analysis of gravity and magnetic data

Abstract

The Palghat Cauvery Shear Zone (PCSZ), which dissects the Southern Granulite Terrane (SGT), evoked much attention for last two-three decades as it offers an enticing opportunity to understand Precambrian tectonics. Many studies suggest that it is a suture zone or a terrane boundary, but tectonic evolution is mainly derived from structural and geochronological evidences. The present gravity-magnetic study provides insight into both shallow and deeper crustal architecture and addresses the issues related to validation/modification of the existing tectonic realm. A total of 3,650 gravity and magnetic measurements were made covering 8,640 km 2 area, represented by high-grade metamorphic rocks and acid intrusives of Archean to Neoproterozoic age. Representative rock samples were also collected for determination of petrophysical properties (density and susceptibility) which have augmented the understanding of gravity-magnetic signature. The gravity anomaly map and subsequent modelling suggest an occurrence of a high-density batholith at mid-crustal level at the central part of the area. The magnetic anomaly map reveals that ENE-WSW trending linear magnetic low zone is coincident with a residual gravity high, which probably indicates the fossil of an oceanic crust. The horizontal gradient of gravity-magnetic data reveals the shallow crust, which is bounded by Palghat Cauvery Shear Zone (PCSZ) and Dharapuram Shear Zone (DSZ), and separates two terranes in terms of density and susceptibilities. The study suggests N-S verging compressional tectonics had led to closure of an ocean, imprints of which is well manifested in gravity and magnetic maps.

Gravity-magnetic appraisal of the southern part of the Cauvery Basin, Eastern Continental Margin of India (ECMI): evidence of a volcanic rifted margin

“…The spectral analysis and subsequent wavelength filtering of the gravity and magnetic anomaly are useful for separating anomalies resulting from shallow causative sources and deeper causative sources (Telford et al, 1990;Ganguli et al, 2020Ganguli et al, , 2022. The radially averaged power spectrums (Spector and Grant, 1970;Blakely R. J., 1996;Ganguli et al, 2021, Teknik et al, 2023 were generated for both the gravity and magnetic data (Figure 5). The radially averaged power spectrum of the gravity data shows three density interfaces at 13.3 km, 5.5 km, and 1.6 km.…”