Crustal and Upper Mantle Attenuation Structure Beneath the Southeastern Tibetan Plateau and Its Implications on Plateau Outgrowth

Abstract

AbstractThe eastern Tibetan Plateau (TP) is crucial to the exploration of plateau outgrowth mechanisms. Teleseismic attenuation may provide constraints on anelasticity in the lithosphere‐asthenosphere system and may therefore improve the understanding of plateau outgrowth and material extrusion. This study use dense array data across the eastern TP to measure relative attenuation from teleseismic P‐wave phases. These observations are then used to invert a 2D relative attenuation map and a 3D Qp−1 model. Weak attenuation is observed beneath the Sichuan Basin and most of the Dianzhong Block at depths of both 0–100 km and 100–200 km (Qp−1 < 0.003). Strong attenuation is observed beneath the eastern TP and southwestern Dianzhong Block at depths of 0–100 km (Qp−1 ∼ 0.01–0.13), but underneath the eastern TP only at depths of 100–200 km (Qp−1 ∼ 0.013–0.015). These results suggest a cratonic lithosphere underneath the Dianzhong Block similar to that beneath the Sichuan Basin. We assume that this is the cooled lithosphere remnant of the Permian Emeishan plume. In contrast, strong attenuation beneath the eastern TP would indicate a thick lower crust and asthenosphere with intense heating. The boundary between strong and weak attenuation lies close to the Longmenshan‐Xiaojinhe faults. We infer that the materials extruded eastward from the eastern TP cross this boundary into the southwestern Dianzhong Block in the lower crust, but stop at this boundary in the asthenosphere.