Crustal Density and Susceptibility Structure beneath Achankovil Shear Zone, India

Abstract

The Southern Granulite Terrain (SGT) is a large tract of exposed Archean continental crust, divided into the Madurai Block (MB), Trivandrum Block (TB), and Nagercoil Block (NB). These crustal domains are linked with the NW-SE trending Achankovil Shear Zone (AKSZ). We combine gravity and magnetic data with previously published ground observations and geochronological data to re-evaluate the crustal architecture, evolution of the AKSZ, and possible extension of AKSZ into Madagascar. Analyses indicate that the long wavelength trends of the magnetic anomalies originate at ~20 km depth of different SGT blocks. These observations are corroborated with the gravity as well as computed gravity gradient anomalies. The presence of khondalite outcrops in Trivandrum Block implies that high magnetization crust is the main source of positive magnetic anomalies. Such magnetic anomalies advocate that SGT preserves the remanent of Archean crustal blocks in South India, a part due to variation in thermal and geochemical processes. The AKSZ, TB, and MB exhibit contrasting magnetic crustal signatures. The joint modeling results reveal a three-layered crustal configuration with varying Moho ranging from 41 to 34 km in NE to SW, respectively. It is also noted that AKSZ is a narrow and deep structure near to the Western Ghats Escarpment while it is wide and shallow in the far-east, which implies that the evolution of the Western Ghats is a late geological event.

Estimation of Moho Depth Beneath Southern Indian Shield by Inverting Gravity Anomalies Constrained by Seismic Data

“…In contrast, Trivandrum and Nagercoil blocks have crustal evolutionary and metamorphic records restricted to Proterozoic (T. V. Kumar et al., 2017). Madurai block is separated from the Trivandrum and Nagercoil block to the south by the tabular Achankovil shear zone (AKSZ) (Prasad et al., 2021; Rajesh & Chetty, 2006). In contrast, the Madurai block constitutes two major internal shear zones named the Suruli (Dev, Sorcar, et al., 2022), and Karur‐Kambam‐Painav‐Trichur Shear Zone (Ghosh et al., 2004; Plavsa et al., 2012).…”

Crustal and Lithospheric Variations along the Western Passive Continental Margin of the Indian Peninsula

“…From gravity studies, crustal thickness following range: SGT (35-44 km), EDC (32-38 km), WDC (40-52 km), DVP (30-50 km), and along the WPCM (38-53 km); [25,[45][46][47][48][49]. Various seismic and receiver function analyses: SGT (36-46 km), EDC (31-38 km), WDC (40-60 km), DVP (30-54 km), and along the WPCM (37-45 km); [26,29,[50][51][52][53][54][55][56].…”