Crustal thicknesses and Poisson's ratios in the eastern Tibetan Plateau and their tectonic implications

Abstract

[1] Crustal thicknesses and Poisson's ratios in the eastern Tibetan Plateau were estimated using the H-k stacking method on teleseismic receiver functions. The data came mainly from the regional seismic networks in 2006 show that the crust thickens from east to west, with a thickness difference of ∼30 km. A sharp change of crustal thickness from 41.5 to 52.5 km is observed across the Longmen Shan. Crustal thickness predictions based on the Airy-type isostasy are consistent with the estimations from H-k stacking, implying that the topography is approximately compensated. The study area can be divided into three parts according to the Poisson's ratios: (1) the northern Songpan-Garze terrane and the western Qinling orogenic belt with low ratios (n ≤ 0.26); (2) the southern Songpan-Garze terrane, the Sanjiang fold system, and the Sichuan Basin with high-to-intermediate ratios (0.27 ≤ n < 0.30); and (3) the southwestern Yangtze platform with low to intermediate ratios (n ≤ 0.27). Joint interpretation of the low average V p values from deep seismic sounding profiles and the low V p /V s ratios from receiver function analysis favors the presence of felsic crust rather than significant volumes of partial melts in the northern Songpan-Garze terrane and the western Qinling orogenic belt. The junction of the Longmen Shan fault zone, the Xianshuihe fault zone, and the Anninghe fault zone has an ultrahigh Poisson's ratio (n ≥ 0.30), which could be considered as an evidence of local partial melt. We propose that the eastward movement of upper and middle crustal material in the southern Songpan-Garze terrane is obstructed by the more rigid Sichuan Basin, resulting in strain accumulation along the Longmen Shan fault zone.

Crustal imaging of the Northwest Himalaya and its foredeep region from teleseismic events

“…Mechie and Kind (2013) correlated the crustal Poisson ratio with the crustal age contemporary to our study region of the tertiary period. We obtained lower to intermediate Poisson ratios (0.253À0.287) for the Indo-Gangetic Plain which is more or less similar to that of the Tarim and Sichuan basins with an average Poisson ratio of 0.270 (Wang et al 2010).…”

Crustal stress field in Yunnan: implication for crust-mantle coupling

“…1 Earthq Sci (2016) 1989) model. Seismic tomography shows important extensive low-velocity zones in the upper mantle under Yunnan which are proposed as back-arc spreading due to the subduction of the Indian or Burman Plate (e.g., Ni et al 1989;Li et al 2008;Lei et al 2009;Wang et al 2010;Wei et al 2012;Huang et al 2015b). There is possible asthenospheric flow from SE Tibet to eastern China (e.g., Li et al 2008;Lei et al 2014;Huang et al 2015b, c) that may probably help the lithosphere of the Indochina and South China blocks above it move southeastward (e.g., Tapponnier et al 1982Tapponnier et al , 2001.…”

Crustal structure of Hubei Province of China from teleseismic receiver functions: Evidence for lower crust delamination

“…1 and 4). Most previous studies of crustal structure of continental China found that crustal thicknesses correlate with surface elevations, indicating that the crust is in Airy-type isostasy (Wang et al, 2010(Wang et al, , 2014Zhang et al, 2011). While it is common for long-wavelength topographic highs to be supported by crustal roots, short-wavelength topography can usually be supported by the strength of lithosphere.…”