Resumen

LI, Jun et al. Deep physical structure and geotectonic implications of the eastern margin of the Qinghai-Tibet Plateau. Earth Sci. Res. J. [online]. 2016, vol.20, n.4, pp.A1-A8. ISSN 1794-6190.  https://doi.org/10.15446/esrj.v20n4.61632.

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 magneto telluric 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.

Palabras clave : Eastern margin of Qinghai-Tibet Plateau; Bouguer gravity; Long period magnetotellurics; Crustal fluid; Apparent density.

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