The Xing'an-Inner Mongolia Orogenic Belt (XIMOB) exposed in the eastern section of the Central Asian Orogenic Belt (CAOB) is generally thought to have resulted from closure of the Paleo-Asian ocean [Şengör et al., 1993]. However, the current hot debate is focused on whether the orogen formed through continuous subduction and accretion over a prolonged period of time until the closure of the Paleo-Asian ocean at the Early Triassic [Xiao et al., 2003], or through the subduction of the Paleo-Asian ocean and related collision in the Early-Mid Devonian [Xu et al., 2013], and the tectonic setting in the Late Paleozoic to Mesozoic has been a pivotal issue. In order to establish the tectonic framework and orogenic processes of XIMOB, systemic researches of petrology, geochemistry, phase equilibria and zircon geochronology were carried on the metamorphic rocks in the central Inner Mongolia, such as the Xilingol complex and the low-grade metamorphism in the Carboniferous to Permian sequences along the Solonker suture zone [Dong et al., 1986]. The results suggest that the Xilingol complex is characterized by clockwise P-T evolution with T max condition of 770-790 °C for a pressure of 5-6 kbar, being in typical hightemperature and low-pressure (HT-LP) type; and the low-grade metamorphism along the Solonker suture zone is characterized by clockwise P-T paths with the peak P-T conditions of metabasite and mica-schist being intermediate and low P/T series respectively.

For citation : Hou H., Gao R., Kröner A., Zhang X., Zhang S., 2017. Discussion on the relationship between deep seismic reflection patterns and tectonic units of the eastern part of the Central Asian

[1] The tectonic evolution of the Paleo-Asian Ocean between the North China Block (NCB) and the Mongolia Block (MOB) is a contentious issue, and geodynamic models remain speculative. In an effort to puzzle out this controversy, a paleomagnetic study was carried out on the Silurian to Permian formations in central-eastern Inner Mongolia (China). More than 680 sedimentary and volcanic samples were collected from 86 sites. We have established titanium-poor magnetite and hematite as the principal magnetic carriers. Anisotropy of the magnetic susceptibility measurements demonstrate negligible deformation of the majority of study rocks with sedimentary fabrics. From primary magnetizations, a Late Devonian and a Permian pole are calculated for Inner Mongolia Block (IMB) at l = 46.8 N, j = 349.1 E, dp = 14.6, dm = 27.3 with N = 3 and l = 48.7 N, j = 3.7 E, dp = 5.2 , dm = 9.1 with N = 6, respectively. Two stages of secondary magnetization are also identified probably due to Early Permian and Early Cretaceous magmatic events. As preliminary results, the comparison of our new paleomagnetic poles with available data from NCB, MOB, and Siberia indicates that (1) the paleolatitudes of IMB, NCB, and MOB are consistent between Late Devonian and Permian, suggesting pre-Late Devonian closure of the Paleo-Asian Ocean and further evaluation of these three blocks as a single entity and (2) post-Permian intracontinental deformation was significant and characterized by block rotations, which are due to strike-slip faulting within the welded NCB-IMB-MOB block.