Insights into the Tibetan Plateau

A model showing an extrusion-styled growth of the Tibetan Plateau toward the northeast, bounded by the left-lateral ATF to the northwest and the dominantly right-lateral central and northern LFZ to the southeast. We suggest that this mode of plateau growth started at ca. 40 Ma. Bold red arrows symbolize directions of the extrusion-style growth of the Tibetan Plateau. Thin blue arrows show generalized GPS measurements of present-day crustal motions [Zhang et al., 2004]. Thin violet arrows represent observed cumulative postseismic surface displacements during the first 7 years after the Wenchuan earthquake [Diao et al., 2018]. Ages indicate the estimated timing of dominant plateau uplift for a given region, bounded by red dashed lines [Richardson et al., 2008]. Rates of relative motion along the margins of the Tibetan Plateau are from Bendick et al. [2000] and Li et al. [2011]. Purple numbers on contour lines are depths in kilometers of the Cenozoic foreland basin deposits in both the southwestern Sichuan Basin and southern Tarim Basin [Wang et al., 2006]. MIN, Min Mountains; Qilian, Qilian Mountains; DA, Danba anticline.

Figure showing contrasting structure, topography and behaviors between the southern and the central-northern LFZ. (a) Subdivision of crustal blocks in the eastern Tibetan Plateau (after Burchfiel et al. [2008]) and positions of the two lithospheric block diagrams as in (b). Focal solutions of the M7.9 Wenchuan earthquake (W) and aftershocks (orange dots), and that of the the M6.7 Ya’an event (Y), are shown. D – Danba Block; SP – Songpan Block; XS – Xue Shan Block (after Burchfiel et al. [2008], Xu et al. [2008] and Guo et al. [2013]). (b) A 3D tectonic model for the eastern margin of Tibet along the LFZ. The 895 earthquake events of magnitude > 3.5 ruptured within ~100 km of transects L and LL (positions shown in (a)) between August 1933 and April 2015 (http://earthquake.usgs.gov/earthquakes/search/) are projected onto the two transects. The purple dot line marks the boundary between the Danba and Songpan crustal blocks – note the contrasting topography on the two sides of this boundary fault. Major faults are constrained by earthquake distribution and published seismic profiles [Robert et al., 2010a, 2010b; Guo et al., 2013]. (c) A schematic diagram illustrating a twisted fault plane along the LFZ (after Shen et al. [2009]) driven by different block motion directions along the eastern margin of the Tibetan Plateau, with the hypocenter of the M7.9 Wenchuan earthquake (W) located near the twisting zone. The thrust plane in southern LFZ is within the crust, whereas in central and northern LFZ the increasingly more strike-slip fault cuts through the lithosphere.