Crust and uppermost mantle structure beneath the north and south china collision zone by joint inversion of receiver functions and ambient noise tomography

Abstract:

The collision zone between the North China Block (NCB) and the South China Block (SCB) is one of the most important tectonic boundaries in the eastern part of China. There are several characteristics in this collision zone, including the exposure of high pressure and ultrahigh pressure metamorphic (HPM/UHPM) rocks. However, the detail structure under this collision zone is still uclear. In this work we try to obtain high resolution and reliable crustal and uppermost mantle structure in this collision zone. We process continuous ambient noise data collected from ~300 stations of Chinese provincial networks operating during 2010 and 2013 to extract inter-station surface wave dispersion curves. Then we generate Rayleigh wave group and phase velocity maps at 5-60 sec periods. In order to improve the precision of Moho depth and shear wave structure, we further collect teleseismic data to calculate receiver functions for all of the stations, and do a joint inversion with receiver function and surface wave dispersion curves to construct a 3D isotropic Vsv model. The 3D Vsv model reveals detailed crustal and uppermost mantle velocity structures which help to decipher the tectonic mechanisms of the SCB and NCB collision zone.

Two belts with thin Moho thickness are observed: one belt starts from south part of the Yangtze block and extends to Sulu Basin along the Tancheng-Lujiang Fault (TLF), the other one starts from the south part of Yangtze block and extends to the west part of the eastern North China Craton. There is a dramatic crustal thickness gradient along the North-South gravity Lineament (NSGL), which means that the NSGL is the consequence of the variation of crustal thickness. The shear wave velocity structure of the Qinling-Dabie orogen (QDO) is different from the surrounding NCB and SCB, there is a deep rooted high velocity anomaly in east end of the QDO this region, which may be the residuals of the exhumation of the UHPM rocks. The upper mantle velocity under the Subei Basin is much lower than that of Sulu Belt and the west side of TLF, which may be resulted from the thinning of the lithosphere in the east side of TLF, arguing for significant extension of the Subei Basin during the collision process of the NCB and the SCB blocks.