Diffuse Deformation in the SE Tibetan Plateau: New Insights From Geodetic Observations

Abstract

The southeastern Tibetan Plateau is a key component in the India-Eurasia collision zone, which is characterized by spatially prevalent strike-slip fault systems with devastating earthquakes. However, slip rates on some of these faults are still poorly constrained, hindering an understanding of kinematic and dynamic processes in this region. We analyze contemporary crustal deformation in the SE Tibetan Plateau based on the latest, dense geodetic observations. Slip rates on a set of dextral NW/NNW-striking faults are determined using a 3-D elastic half-space dislocation model. Our results show that boundary faults such as the Red River and Lancangjiang faults yield dextral slip rates ranging from 1 to 3 mm/a, similar to those of other small-scale sub-parallel faults such as the Chuxiong, Qujiang, and Wuliangshan faults. Additionally, sinistral slip of the Xiaojiang fault may have partly transferred to transpressional slip on the Qujiang, Jianshui, and central Red River faults, which increase seismicity on these faults. New seismic relocation results, geodetic measurements, and existing structural observations show the geometry of this dextral fault system at the depth, which may be restricted above or within the rheologically weak mid-lower crust rather than cutting into the mantle. Results confirm that the SE Tibetan Plateau is characterized by ongoing diffuse deformation between the Sagaing and Xianshuihe-Xiaojiang faults. Driven by the northward advance of the eastern Himalayan syntaxis and southward crustal extrusion, distributed right-lateral movements occurred along the NW/NNW-striking fault system.

Initiation of Clockwise Rotation and Eastward Transport of Southeastern Tibet Inferred from Deflected Fault Traces and GPS Observations

“…50 Ma, the style of deformation changed since 10-15 Ma. Although the thick crust beneath the Tibetan Plateau resulted from Late Cretaceous and Cenozoic horizontal shortening both before and since India collided with Eurasia (e.g., Kapp and DeCelles, 2019), both fault plane solutions of earthquakes and GPS measurements show that normal faulting, E-W extension, and crustal thinning characterize the latest active deformation within the plateau (e.g., Armijo et al, 1986;Elliott et al, 2010;Gan et al, 2007;Ge et al, 2015;Li et al, 2020;Molnar and Chen, 1983;Molnar and Lyon-Caen, 1989;Molnar and Tapponnier, 1978;Ni and York, 1978;Shen et al, 2005;Wang et al, 2001;Zhang et al, 2004). Detailed studies of individual grabens throughout Tibet suggest that the widespread normal faulting began since ca.…”

“…East of the highest part of the plateau, GPS velocities show a clockwise rotation and eastward transport of the southeastern plateau, around the Eastern Himalayan Syntaxis (e.g., Gan et al, 2007;Li et al, 2020;Wang et al, 2001;Zhang et al, 2004). The smoothly varying velocity field southeast of Tibet raises the question of when did that pattern of deformation begin and did it occur concurrently with the onset of normal faulting in central and southern Tibet.…”

Meso-cenozoic tectonic evolution of the ziyun-luodian fault in SW China

“…D 3 sinistral strike-slip faulting may have occurred in the late Cenozoic because (Figure 9): 1) subvertical fault planes, subhorizontal striations, and geomorphic features (such as linear valleys and fault scarps) are present in the fault zone, indicating strike-slip movement. Combined with crosscutting relationship, sinistral shearing represents another deformation episode which is distinct from the early sinistral transpression featured by shortening structures and NW-or SE-plunging striations; 2) to the southwest of the ZLF, several large-scale fault zones were developed sub-parallelly in Yunnan, such as the Ailaoshan-Red River, Chuxiong-Qujiang, Wuliangshan, and Lancang-Genma faults (e.g., Wang et al, 2014, Wang et al, 2022Li et al, 2020). Published structural analysis and geochronologic data indicate that sinistral strike-slip shearing may have occurred along these faults in the early Oligocene to early Miocene (e.g., Leloup et al, 2001;Liu et al, 2012;Zhang et al, 2014;Wang et al, 2016, Wang et al, 2022.…”

Strain Transformation Adjacent to the West Qinling Orogen: Implications for the Growth of the Northeastern Tibetan Plateau

“…Contemporary GPS observations identify two significant expansion passages blocked by the Sichuan Basin: 1) the southeastward extrusion around the eastern Himalaya Syntaxis (EHS) despite its dynamic mechanisms and 2) the north-/east-/ northeast-ward growth (Zhang et al, 2004;Gan et al, 2007;Wang & Shen, 2020). Unlike the clear extrusion in the southeastern Tibetan Plateau (Bai et al, 2010;Bao et al, 2015;Li et al, 2020;Wang & Shen, 2020), the expansion passage and strain pattern are still under debate within the northeastern Tibetan Plateau. There are two leading models to explain the expansion and deformation pattern of the northeastern Tibetan Plateau.…”