Longriba fault zone in eastern Tibet: An important tectonic boundary marking the westernmost edge of the Yangtze block

Abstract

AbstractGlobal Positioning System (GPS) measurements across eastern Tibet reveal a sharp velocity gradient zone located about 150 km west of the Longmen Shan frontal thrust zone, where eastward block motion of Tibet decreases from ~12 mm/yr to ~3 mm/yr over a distance of less than 10 km. In order to investigate the tectonic cause for this rapid change in GPS velocity, together with systematic review on the available geological and geophysical data in easternmost Tibet, we provide new constraints on the tectonic feature of the Longriba fault zone from Advanced Land Observing Satellite Phased Array type L‐band Synthetic Aperture Radar data. We propose that the NE striking Longriba fault zone is the key structure responsible for the observed sharp gradient in GPS velocities. In addition, the evidence indicates that the Longriba fault zone, instead of the Longmen Shan fault zone, marks the westernmost edge of the Yangtze crustal block. Given the irregular western margin of the Yangtze block, the Longriba fault zone represents part of the actual tectonic boundary between the Songpan‐Ganzi terrane and the Yangtze block. The newly identified western edge of the Yangtze block implies a paleocontinent‐ocean boundary at depth. This boundary was a potential weak zone and may have been exploited during the formation of the Longriba fault zone. The results of this paper should advance our understanding of the tectonic relationship between the Songpan‐Ganzi terrane and Yangtze block and provide additional constraints for studies of the geodynamic response of eastern Tibet to the ongoing India‐Eurasia collision.