Lithospheric structure across the northeastern margin of the Tibetan Plateau: Implications for the plateau's lateral growth

We constructed a high‐resolution 3‐D Vs model of the northern Ordos block and its surrounding areas by surface wave tomography, which reveals significant intracratonic heterogeneities. In the western Ordos, the lithosphere thickness is ~200 km with shear velocities comparable to the high velocities of other Archean cratons worldwide. However, the lithosphere thins gradually toward the east and Vs drops by 2–3% in the uppermost mantle beneath the eastern Ordos, coincident with the high surface heat flow (~68 mW/m2 in average) there. This observation suggests that the thick, cratonic keel is only locally preserved beneath the western Ordos, and the eastern part of the Ordos seems to undergo local rejuvenation. At greater depths (>180 km), a low‐velocity channel is observed beneath the high‐velocity keel of the Ordos. Beneath the Datong volcanoes, a low‐velocity anomaly is observed, dipping westward with depth and closely following the slope of the lithosphere beneath the northern Ordos. This prominent low velocity is connected with the low‐velocity zone beneath the northern Ordos, which is further connected with the low‐velocity zone beneath the northeastern Tibetan Plateau (NET). We propose that the asthenosphere beneath the NET flows toward the northern Ordos in response to the continuous northward convergence of the Indian‐Eurasian continents, and the asthenosphere flows upward following the eastward thinning lithosphere which leads to decompression partial melting, which migrates upward to feed the Datong volcanoes. The significant variations of the lithospheric thickness of the Ordos block may control the distribution of the asthenospheric flow.

Section: Discussionmentioning

confidence: 99%

Lithospheric Structure of the Northern Ordos From Ambient Noise and Teleseismic Surface Wave Tomography

Guo

Chen

et al. 2018

“…The western part is marked by a thick crust; the eastern part possesses a thin crust (Figure ). The western Alxa block exhibits a thin lithosphere [ Shen et al ., ] with a low V s value in the lithospheric mantle (Figures g and h); in contrast, thick lithosphere [ Shen et al ., ] with a high velocity (Figures g and h) in the lithospheric mantle is present beneath the eastern Alxa block and Ordos block. The significant lateral variation in lithospheric structure indicates that the western part may have been modified as a result of the far‐field effect of the India‐Asia collision, whereas the eastern part appears to have been less influenced.…”

Section: Discussionmentioning

confidence: 99%

“…The Alxa block and the Ordos block, which are traditionally considered to be parts of the western North China Craton (NCC), have resisted the northeastward expansion of the Tibetan Plateau [ Chang et al ., ; Shen et al ., ]. Whether or not these two blocks have been modified is a subject of debate.…”

Section: Introductionmentioning

confidence: 99%

Three‐dimensional lithospheric S wave velocity model of the NE Tibetan Plateau and western North China Craton

Xingchen

Ding

et al. 2017

We present a new 3‐D lithospheric Vs model for the NE Tibetan Plateau (NETP) and the western North China Craton (NCC). First, high‐frequency receiver functions (RFs) were inverted using the neighborhood algorithm to estimate the sedimentary structure beneath each station. Then a 3D Vs model with unprecedented resolution was constructed by jointly inverting RFs and Rayleigh wave dispersions. A low‐velocity sedimentary layer with thicknesses varying from 2 to 10 km is present in the Yinchuan‐Hetao graben, Ordos block, and western Alxa block. Velocities from the middle‐lower crust to the uppermost mantle are generally high in the Ordos block and low in the Alxa block, indicating that the Alxa block is not part of the NCC. The thickened crust in southwestern Ordos block and western Alxa block suggests that they have been modified. Two crustal low‐velocity zones (LVZs) were detected beneath the Kunlun Fault (KF) zone and western Qilian Terrane (QLT). The origin of the LVZ beneath the KF zone may be the combined effect of shear heating, localized asthenosphere upwelling, and crustal radioactivity. The LVZ in the western QLT, representing an early stage of the LVZ that has developed in the KF zone, acts as a decollement to decouple the deformation between the upper and lower crust and plays a key role in seismogenesis. We propose that the crustal deformation beneath the NETP is accommodated by a combination of shear motion, thickening of the upper‐middle crust, and removal of lower crust.

“…Whether or not the Tibetan Plateau will grow into these bounding blocks depends on the strength of the mantle lithosphere of these blocks. Seismological results indicate that the mantle lithosphere of the Alashan and Ordos blocks is largely intact, blocking the Tibetan Plateau as deep walls (Bao et al, ; Shen et al, ). However, between the Alashan and the Ordos blocks, the mantle lithosphere seems reworked to be similar to that under the Tibetan Plateau (Z. Guo & Chen, ; Shen et al, ), and crustal deformation associated with the Tibetan orogeny has expanded northeastward, beyond the Haiyuan Fault, commonly regarded as the boundary fault (Zheng, Zhang, Ge et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…Blue dashed lines show the Moho changes along the profiles (data from Etopo1: doi:10.7289/V5C8276M). LAB is based on data from (a) Zhao et al (), (b) Hu et al () and Z. Zhang, Yuan, et al (), (c) Shen et al (), and (d) Ye et al ().…”

Section: Introductionmentioning

confidence: 99%

Rheological Control of Lateral Growth of the Tibetan Plateau: Numerical Results

Sun

Liu

2018

Self Cite

The collision and continued convergence between the Indian and Eurasian plates in the past ~50 million years has raised the Tibetan Plateau, but whether or not, and how, the plateau has grown laterally remain controversial. Here we show that useful insights can be gained by studying lithospheric deformation across the frontal margins of the Tibetan Plateau. Crossing its northern and eastern sides where the plateau is bounded by the Tarim and Sichuan blocks, the topographic slope is steep and crustal deformation is localized near the margins of the plateau, whereas across northeastern Tibetan Plateau the topographic slope is gentle and crustal deformation is diffuse over a broad transition zone. Using a suite of two-dimensional visco-plastic finite element models, we reproduced the major features of the two types of plateau margins with different rheological contrasts between the Tibetan Plateau and the bounding Asian blocks. Our results suggest that the bounding Asian blocks with a strong mantle lithosphere, such as the Tarim and the Sichuan basins, have restricted the lateral growth of the Tibetan Plateau, although limited lateral expansion of the plateau can occur where the upper crust of these bounding blocks are relatively weak. Major lateral growth of the Tibetan Plateau mainly occurred northeastward, where numerous terranes with relatively weak mantle lithosphere are readily deformed and incorporated into the Tibetan Plateau. This growth-front has reached the strong Alashan and Ordos blocks. Further lateral growth of the Tibetan Plateau depends on whether or not the Tibetan tectonics can weaken the mantle lithosphere of these Asian blocks.