Crustal anisotropy study in the central Qilian Mountains: Evidence from teleseismic P wave receiver functions

doi:10.13745/j.esf.sf.2022.4.23

Abstract

Abstract:

The Tibetan Plateau uplift is driven by the collision between the Indian and Eurasian plates. Its growth and evolution, especially the mechanism of its outward expansion, is still controversial. At the forefront of its northeastward expansion lies the Qilian Mountains, whose crustal structure and anisotropy are of great significance for understanding the northward growth of the Tibetan Plateau. The central Qilian Mountains on the northeastern margin of the Tibetan Plateau experienced strong crustal compressional deformation. Existing studies have described phenomenons of non-coupling non-uniform deformations of crust and upper mantle, while understanding the deformation mechanism has become a frontier scientific issue. Previous anisotropy researches in this region mostly relied on seismic network data using large station spacing, however, which could not reflect the fine changes in the crustal anisotropy across the mountain range. To solve this problem, this study used the stacking method based on a dense linear seismic array to obtain the lateral variation of the crustal thickness, Poisson’s ratio and crustal anisotropy. The crust was found to be at its thickest in the Central Qilian and northern South Qilian, while the average Poisson’s ratio was the lowest in these areas, indicating loss of mafic lower crust and shortening of felsic upper-middle crust during crustal thickening. In addition, the Poisson’s ratio of felsic component did not support the existence of crustal flow in this region. In the interior of the mountain range, the fast polarization directions (FPDs) of the crust followed the direction of crustal outward expansion and were nearly perpendicular to the FPDs of the upper mantle, suggesting the crust-mantle deformation might be decoupled. In southern South Qilian and southern North Qilian where the crust is thinner, FPDs were parallel to the strike of the ancient suture, indicating the Early Paleozoic tectonic frame still had an impact on the shortening and uplifting of the Qilian Mountains.

Key words: Qilian Mountain, crustal anisotropy, receiver function, stacking

CLC Number:

P631.4
P542

ZHOU Pengzhe, GAO Rui, YE Zhuo. Crustal anisotropy study in the central Qilian Mountains: Evidence from teleseismic P wave receiver functions[J]. Earth Science Frontiers, 2022, 29(4): 265-277.

Figures/Tables 7

Fig.1 Topographic map of the study area showing major tectonic feature and distribution of stations. Modified after [40-41].

Fig.2 H-κ-c stacking results on station QL17

Fig.3 Histograms of the errors (standard deviation) of crustal thickness and velocity ratio before (grey) and after (white) harmonic corrections

Fig.4 The variation of crustal thickness with altitude

Fig.5 The variation of crustal velocity ratio with altitude

Fig.6 Splitting parameters obtained by harmonic fitting of PS converted wave. Modified after [18,36-37,57-58].

Fig.7 The correlation analysis of the crustal thickness and Poisson’s ratio

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