Regional variability in the thermal structure of Tibetan Lithosphere

Abstract

<p>We present a thermal model- of lithospheric thickness and surface heat flow in Tibet and adjacent regions (74-110<sup>o</sup> E, 26-42<sup>o</sup> N) based on topography and seismic Moho. We interpret strong heterogeneity in lithospheric thermal structure to be caused by longitudinal variations in the northern extent of the subducting Indian plate, southward subduction of the Asian plate beneath central Tibet, and possible preservation of fragmented Tethyan paleo-slabs. Cratonic-type cold and thick lithosphere (200-240 km) with a predicted surface heat flow of 40-50 mW/m<sup>2</sup> typifies the Tarim Craton, the northwest Yangtze Craton, and most of the Lhasa Block that is likely refrigerated by underthrusting Indian lithosphere. We identify a ‘North Tibet anomaly’ (at 84-92<sup>o </sup>E, 33-38<sup>o </sup>N) with thin (<80 km) lithosphere and high surface heat flow (>80-100 mW/m<sup>2</sup>) in a region with anomalous seismic Sn and Pn propagation. We interpret this anomaly as the result of removal of lithospheric mantle and asthenospheric upwelling at the junction of the Indian and Asian slabs with opposite subduction polarities. Other parts of Tibet typically have intermediate lithosphere thickness of 120-160 km and a surface heat flow of 45-60 mW/m<sup>2</sup>, with patchy anomalies in eastern Tibet.</p>