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

Abstract

Global 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.

The Longriqu fault zone, eastern Tibetan Plateau: Segmentation and Holocene behavior

“…Guo et al . [] suggest that both structures formed when the eastern edge of the Yangtze craton, which lies underneath from the LFS to the Sichuan basin, was a passive margin [e.g., Roger et al ., ; Harrowfield and Wilson , ]. The Longmen Shan and the LFS were inverted during the closure of the Songpan Garze basin (Middle Triassic) [ Roger et al ., ; Pullen et al ., ; Guo et al ., ].…”

“…The Longmen Shan and the LFS are important active structures of the eastern Tibet that find their origin during the Paleozoic Era [ Guo et al ., ] (Figure ). Guo et al .…”

“…[] suggest that both structures formed when the eastern edge of the Yangtze craton, which lies underneath from the LFS to the Sichuan basin, was a passive margin [e.g., Roger et al ., ; Harrowfield and Wilson , ]. The Longmen Shan and the LFS were inverted during the closure of the Songpan Garze basin (Middle Triassic) [ Roger et al ., ; Pullen et al ., ; Guo et al ., ]. The Longmen Shan, which represents a topographic boundary between the Sichuan basin (500 m above sea level (asl)) and the Tibetan plateau (~4000 m asl), is composed of three main transpressive NE trending faults: the Wenchuan, Beichuan, and Guanxian faults, accommodating most of the convergence between the basin and the plateau (Figure ).…”

Relationship between the regional tectonic activity and crustal structure in the eastern Tibetan plateau discovered by gravity anomaly

“…Red lines are the locations of faults. QHNS Qinghainanshan fault, GHNS Gonghenanshan fault, LJS Lajishan fault, JSS Jishishan fault, KLF Kunlun fault, DBWDF Diebu-Bailongjiang fault, XREF Xiarier fault, TZF Tazang fault, AWCF Awancang fault, LRBF Longriba fault zone, XSF Xueshan fault, MJF Minjiang fault, HYF Haiyuan fault, QCF Qinchuan fault, LMSFZ Longmenshan fault zone, GZYSF Garze-Yunshu fault, XSHF Xianshuihe fault, XJF Xiaojiang fault (Modified from Tapponnier et al 2001;He and Chéry 2008;Yuan et al 2013;Ren et al 2013;Guo et al 2015) a whole and focused on the regional crustal feature in a map view to determine the lateral contact relationship between crustal structure and tectonic activity.…”

Preface to special issue on relationship between continental tectonics and the seismic activities of China, research techniques and methods

“…Meanwhile, owing to coeval subduction in the north and southwest, the Songpan-Garze remnant ocean experienced northeast-southwestward crustal shortening and, therefore, southeast-directed thrusting (e.g., Reid et al 2005;Roger et al 2011). Consequently, western margin of the Yangtze block, which was originally the passive margin prior to thrusting, was inverted to be the active margin (Guo et al 2013(Guo et al , 2014(Guo et al , 2015aXu et al 2016). Contemporaneously, the Longmenshan thrust belt adjacent to the western Sichuan basin was initiated as a result of resistance from the rigid basement of the Yangtze hinterland (Burchifel et al 1995).…”