Geophysical evidence for marine prolongation of the Palghat-Cauvery shear system into the offshore Cauvery basin, Eastern continental margin of India

Abstract

The Precambrian basement shear zones played a major role in developing offshore structures that are zones of weakness along the eastern continental margin of India. A compilation and analysis of various geophysical datasets, particularly magnetic, gravity, seismicity and seismic reflection data support a clear geometric connection between the shear zones and offshore structures. The presence of shear zones within the crystalline basement in the continental domain and oceanic domain is demarcated primarily by prominent magnetic lineation. We identified three major magnetic lineaments in the offshore Cauvery basin, which correspond to the Plaghat Cauvery shear system (PCSS) of Southern Granulite terrain (SGT). The faults interpreted in the seismic sections are correlated to the extension of PCSS and indicate the location of reactivation of the shear zones which give rise to considerable intraplate seismicity. The geophysical crustal model shows deep crustal-scale faults associated with the marine prolongation of PCSS. The shear zone extended structures in the offshore might have formed at the breakup stage at the onset of rifting and might be extending up to the continent-ocean transition zone (COTZ). The PCSS partly seems to accommodate the stress created by the northward push of Indian plate against the Asian plate. It is also possible that the shear zone might have extended to the nearby land mass that marks it as one of the principal component in Gondwana reconstruction.