Abstract
The Sichuan basin is the main part of the middle-upper Yangtze block, which has been experienced a long-term tectonic evolution since Archean. The Yangtze block was regarded as a stable block until the collision with the Cathaysia block in late Neoproterozoic. A new deep seismic reflection profile conducted in the eastern Sichuan fold belt (ESFB) discovered a serials of south-dipping reflectors shown from lower crust to the mantle imply a frozen subduction zone within the Yangtze block. In order to prove the speculation, we also obtain the middle-lower crustal gravity anomalies by removing the gravity anomalies induced by the sedimentary rocks and the mantle beneath the Moho, which shows the mid-lower crustal structure of the Sichuan basin can be divided into eastern and western parts. Combined with the geochronology and Aeromagnetic anomalies, we speculated the Yangtze block was amalgamated by the West Sichuan and East Sichuan blocks separated by the Huayin-Chongqing line. The frozen subduction zone subsequently shifted to a shear zone accommodated the lower crustal shortening when the decollement at the base of the Nanhua system functioned in the upper plate.
Highlights
Deep seismic profiling images the frozen subduction zone within the continental lithosphere, including the first discovery of the Paleoproterozoic subduction-related structure in the Svecofennian orogen (1.89 Ga) (BABEL Working Group 1990), the oldest relict suture associated with subduction (2.69 Ga) (Calvert et al 1995), and other relict plate convergence, subduction or accretion (Cook et al 1999; Juhlin et al 2002; Warner et al 1996; White et al 2000; Yuan et al 2003)
One of the two main units of South China continent that was amalgamated by Yangtze and Cathaysia blocks at ca. 0.82 Ga (Charvet 2013; Zhao and Cawood 2012), has the Archean basement outcropped in northwestern and southwestern parts and George dam area (Greentree and Li 2008; Qiu et al 2000; Wu et al 2012), Yangtze block was thought to be a stable block since the early Precambrian, the Sm-Nd dating and geochemical research of the Yangtze block unraveled the distinctive difference features between the northern and the southern part (Wu et al 2012), which inspired the debate of the Yangtze block as a stable unit
The Yangtze block was amalgamated, acted as the lower basement after the upper deformed basement was formed by the consolidation of the Lengjiaxi and Banxi Groups in Neoproterozoic, the sedimentary cover deposited on the top of the double basement
Summary
Deep seismic profiling images the frozen subduction zone within the continental lithosphere, including the first discovery of the Paleoproterozoic subduction-related structure in the Svecofennian orogen (1.89 Ga) (BABEL Working Group 1990), the oldest relict suture associated with subduction (2.69 Ga) (Calvert et al 1995), and other relict plate convergence, subduction or accretion (Cook et al 1999; Juhlin et al 2002; Warner et al 1996; White et al 2000; Yuan et al 2003). One of the two main units of South China continent that was amalgamated by Yangtze and Cathaysia blocks at ca. From October 2010 to May 2011, we acquire a 550 km deep seismic reflection profile from the sub-project of Deep Exploration in China (SinoProbe02), with high-quality to Earthq Sci (2016) 29(2):
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