Hales Discontinuity in the Southern Indian Continental Lithosphere: Seismological and Petrological Models

摘要

We model the depth and V-s structure of the Hales discontinuity (H-D) beneath Eastern Dharwar Craton (EDC) and Southern Granulite Terrain (SGT) using P wave receiver function (P-RF) analysis and joint inversion with Rayleigh wave phase velocity dispersion. We calculate P-RFs at higher frequency (f(max) = 0.46 Hz), compared to previous studies, to show that the H-D P-to-S converted phase (P(h)s) is distinct from crustal reverberations. P(h)s at stations Hyderabad (HYB) and Gauribidanur (GBA), in the EDC, arrive at similar to 11.5 s and similar to 12 s, respectively. From joint inversion, the H-D is modeled at 107 5 km and 113 4 km depth, with similar to 3% and similar to 4% V-s increase, beneath HYB and GBA, respectively. For station Kodaikanal (KOD), in SGT, the P(h)s destructively interferes with the negative midcrustal reverberation at most ray-parameters, which explains its apparent absence in previous studies. We isolated P-RFs where P(h)s is distinct at similar to 11 s and model it at 102 3 km depth. Common conversion point stack profiles constructed by depth migrating P-RFs through the V-s model show an undulatory nature of the H-D. From data of mantle xenoliths (Wajrakarur kimberlite field), we calculate V-s of mantle peridotite and eclogite, using published bulk rock compositions. At the H-D depth and temperature derived from Indian shield geotherm, we observed a good match to the V-s structure of the H-D. Our results support the geodynamic model of the H-D being an interface of paleosubducted eclogitic oceanic crust embedded within the upper mantle peridotite. Global observations of mantle reflectors within the continental lithosphere, at depths similar to H-D, have been related to relict subduction and independently support our model.