Weak and vanishing upper mantle discontinuities generated by large-scale lithospheric delamination in the Longmenshan area, China

Chuansong He

doi:10.1038/s41598-021-01061-4

Abstract

A large amount of high-quality teleseismic data is used for common conversion point (CCP) stacking of receiver functions in the Longmenshan area and near-by region. The results show that a large-scale high-velocity anomaly (LHVA) or lithospheric delamination can modify the structure of upper mantle discontinuities or weaken the phase boundary of olivine, which is a very important finding and can be used to assess stagnant slabs in the mantle transition zone globally. The deepening region of the 660 km discontinuity beneath the Songpan-Ganzi terrane identified in this study might be generated by the LHVA.

Highlights

A large amount of high-quality teleseismic data is used for common conversion point (CCP) stacking of receiver functions in the Longmenshan area and near-by region
GPS studies have reported that crustal materials move eastward from the Tibetan Plateau into the Longmenshan area in the C enozoic[8], but they are obstructed by the rigid crust and lithosphere of the Yangtze Block or the Sichuan Basin[9,10]
A previous tomographic study suggested that the assembly and collision among the North China, Yangtze and Qiangtang terranes during the Indosinian period in the Mesozoic or the northward subduction and amalgamation of the Indian plate during the Cenozoic resulted in delamination of the lithospheric structure in the Longmenshan area in the mantle transition zone (MTZ)[11], which might facilitate the eastern extrusion of the Tibetan Plateau[12] as well as ductile crustal thickening[13,14]

Summary

Introduction

A large amount of high-quality teleseismic data is used for common conversion point (CCP) stacking of receiver functions in the Longmenshan area and near-by region. A previous tomographic study suggested that the assembly and collision among the North China, Yangtze and Qiangtang terranes during the Indosinian period in the Mesozoic or the northward subduction and amalgamation of the Indian plate during the Cenozoic resulted in delamination of the lithospheric structure in the Longmenshan area in the mantle transition zone (MTZ)[11], which might facilitate the eastern extrusion of the Tibetan Plateau[12] as well as ductile crustal thickening[13,14]. I collected a large amount of high-quality teleseismic data (Fig. 1, left panel), carried out common conversion point (CCP) stacking of receiver functions and imaged the structure of the MTZ.

Results

Conclusion