Structural dynamic analysis of the Dabashan foreland arc structure belt and basin-mountain system Introduction
The Dabashan tectonic belt is situated at the northern margin of thecentral Yangtze block，which is dividied into two parts by the Chengkou Fangxian fault zone. It’s foreland is a large-scale, southwestward-concaving arc-shaped thrust-fold belt,belonging to the transition zone between Sichuan basin and Qinling Mountains orogenic belt. In recently years, the study of the tectonic evolution of Dabashan foreland arc structure belt and basin-mountain system has been the focus of many geologists, due to its special oroclinal structure and gas/oil potential (Dong et al., 2005, 2006, 2013; Liu et al., 2006; E.C.Wang et al., 2006; Z.C. Wang et al., 2006; Shi et al., 2007, 2012a;Hu et al., 2008, 2009, 2012; Pei et al., 2009; Wu et al., 2009; Zhang and Dong, 2009; Zhang et al., 2010; Q.S. Li et al., 2011).
Previous studies have made a lot of acheievements in the structural styles, geometric formation models and tectonic evolution of the Dabashan foreland arc structure belt (He et al., 1997, 1999; Zhang et al., 2001, 2010;Dong et al., 2005, 2006, 2008, 2011; Li et al., 2006; Liu et al., 2006;E.C. Wang et al., 2006; Shi et al., 2007, 2012a; Tan et al., 2007; Hu et al., 2009, 2012). He (1997,1999) proposed the “dextral shearing strike slip mechanism” by structural analysis and balanced section reconstruction, which considered that the Daba Mountains underwent stretched in early Paleozoic, structural inversion in middle three Triassic , structural thrust in middle three Triassic and early Jurassic. Zhang et al (2001)considered that Daba Mountain is an intracontinental orogenic process on the basis of collision and suture between North China and Southern China plates, and has experienced multi-stage tectonic deformation. Li (2005) determined the stress direction and stress value of Northeast Sichuan by acoustic emission, and considered that there are two tectonic movements before and after the deposition of the Shaxi formation. Liu et al (2005) considered that the multi phase stress field is dominated by different periods and different terranes according to the analysis of the stress field in the Shanxi section of the Daba Mountain. Liu et al. (2006) and Li (2006) put forward a "multi-level slip forward" model through structural style, basin filling characteristics and deformation mechanism analysis. Shi et al. (2007) analyzed the superimposed deformation of the Shanxi segment of the Daba Mountain, and established two tectonic stress fields: the late Trassic-early Jurassic south-north extrusion and late Jurassic-early Cretaceous near East-West extrusion. Dong (2008) considered that besides the very development of thrust nappe structure, the Dabashan superimposed folds were also very developed, and the early NE-SW trending folds have been modified to form NW-SE superposed folds. Hu et al.(2008) inferred that the mian suture may pass through the Daba arc according to the analysis of the Devonian Carboniferous carbonate strata developed in the high Sichuan block of the northwest end of the Daba arc. According to the structural analysis and 40Ar-30Ar, Shi(2011) determined the three tectonic events of the Daba Mountain: Late Jurassic Early Cretaceous in N-S to NNE-SSE extrusion; Late Jurassic Early Cretaceous NE-SW extrusion, shortening as 150km, slippage in the 10-12km depth, forming the present Dabashan tectonic pattern; Late Cretaceous Paleogene near ENE-WSW/NE-SW tension . Based on detailed analysis of the two compressional structures of the Daba Mountain, Hu et al.(2012) determined the tectonic stress direction, time limit and dynamic background.
However, owing to lacking of detailed structural analysis and paleomagnetic combination，there are still much disagreement highlighted in the tectonic evolution models of the Dabashan orocline, e
