Abstract

The first-order configuration of the Himalayan orogen is defined by the northward motion of the Indian Plate, whether directly "underplating" under the Tibetan crust or "subducting" beneath a mantle wedge. Our 3D S-wave receiver-functions newly reveal orogen-perpendicular tearing or warping of the Indian Plate. West of 90°E, the southern limit of the Tibetan lithosphere-asthenosphere boundary is at the Indian crustal front, ~100-km north of the Yarlung-Zangbo suture, implying an underplating of the intact Indian lithosphere beneath Tibet. Further east, the delaminated Indian lithospheric mantle during its gravitationally-induced rollback is separated from the Indian crust by an interposed asthenospheric wedge. The nascent Tibetan lithosphere and its subjacent thin asthenosphere continue ~100 km south of the Yarlung-Zangbo suture. This contrast in lithospheric structures across the Yadong-Gulu and Cona-Sangri rifts at 90-92°E, in 2 agreement with helium isotopic anomalies and deep seismicity, requires the subducting Indian Plate be warped or torn.