Crust and upper mantle structure beneath western China from P wave travel time tomography

Abstract

Three‐dimensional velocity images of the crust and upper mantle beneath western China are obtained through seismic tomography by using P wave arrival times of local/regional and teleseismic events recorded in Chinese and Kyrgyzstan seismic networks. At shallow depths, most mountain belts and tectonically elevated areas are imaged as higher velocities, relative to adjacent sediment‐filled basins and foreland depressions with lower velocities. At mid‐lower crust depths, the Kyrgyz Tian Shan is underlain by lower velocity material and a distinct low‐velocity zone in the south‐north direction is observed between the eastern and western parts of the Chinese Tian Shan. The Moho of the southern Tarim basin has a greater depth over 50 km in front of the western Kun Lun, compared to the northern and western Tarim basin. Lateral heterogeneity within the upper mantle is apparent at depths from 71 to 571 km. The uppermost mantle beneath the Kyrgyz Tian Shan, Altay, Qi Lian, and eastern Kun Lun is characterized by low‐velocity material that is probably related to the upwelling of hot mantle. The lithospheric thickness varies from 120 to 170 km beneath the Chinese Tian Shan and northern Tibetan Plateau to 200–250 km beneath the Tarim basin. Deep coupling pattern of the Chinese Tian Shan with adjacent provinces can be classified into the embedding, detaching and sinking, and underthrusting of lithospheric roots. In addition, the lithosphere of the northern edge of the Tibetan Plateau seems to be thickened, in contrast to the central part of the northern plateau. North dipping low velocities exist in the upper mantle between the Tibetan Plateau and provinces to its north, which might indicate mantle flow from the Tibetan Plateau toward surrounding areas, but it has been blocked by the thick Tarim lithosphere.

The Early Permian Tarim Large Igneous Province: Main characteristics and a plume incubation model

“…From this study it is clear that the present-day lithosphere beneath Tarim is relatively thick, ranging from 150 to 200 km. A similarly thick lithosphere beneath the Tarim Basin is also revealed by seismic tomography (Lei and Zhao, 2007;Xu et al, 2002) and by a receiver function analysis of S-to-P converted waves at the boundary between the lithosphere and asthenosphere (Kumar et al, 2005). Using the teleseismic data collected from digital seismograms, Lei and Zhao (2007) showed that the Cenozoic sediments of the Tarim Basin are characterized by some low Vp, low Vs and high Poisson anomalies, whereas at greater depths high Vp, high Vs and low s anomalies dominate, indicating the relatively strong craton-like structure.…”

“…However, there is little evidence that significant stretching has occurred in the Tarim since the Paleozoic. A low extension rate is also suggested by the presence of N 150 km thick lithosphere beneath this basin (Lei and Zhao, 2007;Priestley and McKenzie, 2006;Xu et al, 2002). Lithospheric extension therefore cannot be the principal trigger of melting of the mantle in Tarim.…”

“…In fact, the relatively long time span of magmatism, pre-volcanic crustal uplift and intrusion of alkalic magmas of the Tarim LIP are more consistent with a plume incubation model , in which the lithosphere contributed both directly and indirectly to the formation and evolution of the province. It is likely that the relatively thick lithosphere (N150 km) presently beneath Tarim (Lei and Zhao, 2007;Priestley and McKenzie, 2006;Xu et al, 2002) may have existed in the Permian and prevented the convecting asthenosphere/plume from decompression melting. As proposed for the Parana-Etendeka and Karoo LIPs, the generation of the first two episodes of magmatism in the Tarim LIP can be accounted for by a plume heating model, in which melting of enriched components in the lithospheric mantle is due to conductive and advection heating by upwelling mantle plume (Gibson et al, 2006).…”

Crustal Velocity Structure of the Northeastern Tibetan Plateau from Ambient Noise Surface-Wave Tomography and Its Tectonic Implications

“…The shear-wave velocity in each layer with fixed thickness is taken as the inversion parameter, and P-wave velocity and density are calculated from shear-wave velocity with empirical formulas. The shear-wave velocity and Moho depth in the initial models are referred to the deep seismic sounding profiles (Xu et al, 2002;Zhao et al, 2004;S. Li et al, 2006), tomography results (Huang et al, 2003;Wang et al, 2003Wang et al, , 2007Maceira et al, 2005), and receiver functions (Pan and Niu, 2011; Ⓔ Fig.…”

Depth determination of the Moho interface beneath the Tibetan plateau and other areas of China

“…Although CRUST 2.0 (Bassin et al, 2000) was compiled by tomographic inversion, there are too few deep seismic soundings (DSSs) from which refraction data are obtained to provide detailed models for the areas with DSS data. Regional P-wave travel-time tomography by Liu et al (1990) and Xu et al (2002) showed the crustal and upper mantle structure beneath China over a large scale. Detailed crustal structures are not shown in these models.…”