Deep physical structure and geotectonic implications of the eastern margin of the Qinghai–Tibet Plateau

Abstract

The eastern margin of the Qinghai-Tibet Plateau (QTP) is the focus of studies on eastward lateral extrusion of the latter's crustal material. This study aims to explore the structural response of the QTP's eastern crust-mantle to the extrusion, and the basis for the latter's geological structure. Data on the long-period magnetotelluric sounding of cross-tectonic units and Bouguer gravity were used to determine the physical structure of the crust-mantle at the plateau's eastern margin. The findings are as follows: (i) the apparent density structure indicates the large presence of a low-density material in the middle-lower crusts of the Songpan and Sichuan-Yunnan blocks at the QTP's eastern margin. On the other hand, the Yangtze cratonic block (Sichuan Basin) contains a material with a significantly higher density. To the west of the Longmenshan-Panxi tectonic zones, and along the lower crust at 40-50 km depth, is an obvious low-density zone aligned in a northeast-southwest orientation. (ii) The electrical structural model spanning Songpan block-Longmenshan tectonic zone-Yangtze block reveals three distinct electrical structural units along the cross-section bounded by the Longmenshan tectonic zone. The first is the Songpan block, which has high and low resistivity at the superficial layer and middle-lower crusts, respectively. Next is the Yangtze craton, which has a low and relatively higher resistivity at the superficial layer and middle-lower crusts, respectively. The third is the Longmenshan transitional tectonic zone, whose shallow layer and deep structure are characterized by an electrical structure with a thrust nappe towards the east, and a high-conductivity material extending to the lithospheric mantle, respectively. (iii) The apparent density and electrical structures indicate that the Panxi tectonic zone has a weakened structure in the lower crust; and (iv) physical properties of the QTP's deep structure show that its eastern margin may contain a middle-lower crustal fluid material with the attributes of high conductivity and low density. Its distribution is interrelated to the uplift mechanism and deep seismogenic activities at the QTP's eastern margin. El margen oriental del altiplano Qinghai-Tíbet (QTP, del inglés Qinghai-Tibet Plateau) es el área de la extrusión lateral hacia el Este de material cortical. Este trabajo se enfoca en explorar la respuesta estructural de las capas superiores en el altiplano y las bases para su estructuracón geológica. Se utilizó información magnetotelúria y anomalías de Bouguer para determinar la respuesta geofísica de las capas superiores en el margen occidental del altiplano. Dentro de los principales resultados se tiene: (i) la distribución de la densidad aparente indica la presencia de material de baja densidad en las capas medias y bajas de los bloques Songpan y Sichuan-Yunnan en el Este del QTP. Por otro lado, el bloque cratónico Yangtze (en la cuenca Sichuan) contiene material con una mayor densidad. Al oeste de las zonas tectónicas Longmeshan-Panxi, y a lo largo...

The Coupling Relationship between the Uplift of Longmen Shan and the Subsidence of Foreland Basin, Sichuan, China

“…In the Cenozoic, it reflected the massive movement of block and overall uplifting along the large boundary strike-slip fault; it was stable inside the block, but tectonic shortening was absent. In this period, the Longmen Shan demonstrated obvious tectonic shortening and uplifting; the tectonic shortening was confined in the Longmen Shan, being local shortening (Li et al, 2006;Densmore et al, 2007). The restoration of the Longmen Shan crustal shortening by using the technology of structure balanced section reveals that the minimum crustal shortening rate of the Longmen Shan occurred since the Pliocene (4 Ma), which was about 2 mm/a (Fig.…”

“…The Longmen Shan is an independent intra-continental orogenic belt. It develops the Maowen fault in the back margin, which is a detachment fault (ETD, Xu Zhiqin et al, 2007) or shear zone (Li et al, 2006), the Beichuan fault in the central region, which is a thrust with dextral slip fault, and the Pengguan fault in the front margin, which is a thrust with dextral slip fault (Li et al, 2006;Densmore et al, 2007). In the present-day Longmen Shan area, the horizontal movement rate is quite small (the movement rate of GPS is about 1-3 mm/a, Zhang et al, 2004), and the rate of vertical uplifting is also very small about 0.3-0.4 mm/a (Li Yong et al, 1994).…”

“…The distal edge (close to foreland slope in the craton) has small thickness (about 1000 m) and low subsidence rate (about 0.05 mm/a), overlapping the forebulge (Kaijiang-Luzhou uplift) in the east. The forebulge is well developed, and the uplifting and denudation are intensive (Li Yong et al, 1995, 2006. In its east part, the back-bugle basin is developed ( Fig.…”

“…2 389 ACTA GEOLOGICA SINICA (English Edition) http://www.geojournals.cn/dzxben/ch/index.aspx http://mc.manuscriptcentral.com/ags wedge-shaped foreland basin in the early stage, and the coupling mechanism between crustal isostatic rebound and tabular foreland basin in the late stage. With consideration to the unique features of the Jurassic foreland basin, and based on the Burbank model (1992), Li Yong et al (1994, 1998, 2006, 2013 proposed the coupling mechanism of crustal shortening, crustal isostatic rebound of the Longmen Shan and the foreland basin, and indicated that crustal shortening and crustal isostatic rebound of the Longmen Shan were different dynamic mechanisms driving the formation and evolution of the foreland basin. The Longmen Shan was once in two states, i.e.…”

“…The tectonic shortening of the present-day Longmen Shan was confined between the back margin fault and the front margin fault, which presented as limited crustal shortening (Li et al, 2006;Densmore et al, 2007). The back margin fault is shown as a large detachment fault or shear zone (Xu Zhiqin et al, 2007), and divides the Longmen Shan and the Tibetan Plateau into two geological bodies (the Sichuan-Qinghai block or the Songpan-Garzê fold belt).…”