Mantle deformation patterns and signatures of rift, beneath Eastern Ghats Mobile Belt

Abstract

The Eastern Ghats Mobile Belt (EGMB) and the adjacent Archaean Singhbhum and Bastar craton contact collisional sutures zones in southeastern India are investigated for seismic anisotropic signatures. The EGMB-craton contact boundary is a witness to the episode of rifting related to the breakup of super-continent Columbia, followed by reassembly and breakup of Rodinia, and eventual episode of collision of eastern India with Antarctica during the Pan-African age. With the intent to capture signatures of the collision, 22 broadband seismic stations were installed along two distinct profiles covering cratons and Eastern Ghats contact boundaries. Shear wave splitting analysis using core refracted phases, SKS, SKKS and PKS, waveforms resulted in 202 high-quality measurements, with variation in delay times (δt) from 0.4 s to 2.0 s, and predominant NE trend for the fast polarization directions (FPDs). The anisotropic parameters along the two profiles depict the influence of two dominant mechanisms. First, Absolute Plate Motion (APM) related strain where mantle drag at the base of lithosphere combined with other plate driving forces creates a NE dominance of fast-axis orientations in the direction of the Indian plate motion. Second, fossil anisotropy of the lithospheric origin, as fast axis is not completely in the direction of the Indian plate motion, specially across Rengali Province and Mahanadi Rift basin. Fast-axis orientations parallel to the surface geological features indicate large-scale pervasive deformation related to the collision and rifting episodes of India and East Antarctica. The composite stacked FPDs and δt in the Rengali domain is manifestation of the NE trend of the Indian Plate motion, combined with the WNW–ESE to E–W oriented fabrics associated to the EGMB-cratons contact shear zones. The Mahanadi Rift has a predominance of the rift parallel signatures due to the ancient preserved fabrics, which correlates the Mahanadi Rift with the Lambert Rift of East Antarctica, and is of key importance in plate-tectonic reconstructions.