A new Triassic shortening-extrusion tectonic model for Central-Eastern Asia: Structural, geochronological and paleomagnetic investigations in the Xilamulun Fault (North China)

Abstract

International audienceAt the northern margin of the North China Block (NCB), the Xilamulun Fault (XMF) is a key belt to decipher the tectonic evolution of Central-Eastern Asia, as it records the Paleozoic final closure of the Paleo-Asian Ocean, and localizes a Late Triassic intracontinental deformation. In this study, structural analysis, 40Ar–39Ar dating, and paleomagnetic studies were performed to investigate the kinematics of the XMF and to further discuss its Triassic geodynamic significance in the Central-Eastern Asia framework after the Paleozoic Central Asian Orogenic evolution. The structural analyses reveal two phases of ductile deformation. The first one (D1), which displays N-verging and E–W trending folds, is related to the Early Paleozoic collisional event between the NCB and the Songliao–Hunshandake Block (SHB). The second phase (D2) displays a high-angle foliation and a pervasive sub-horizontal E–W stretching lineation with kinematic criteria indicative of dextral strike–slip shearing. The 40Ar–39Ar dating on mylonitic granite places the main shearing event around 227–209 Ma. This D2 shearing is coeval with that of the dextral strike–slip Bayan Obo–Chifeng Fault (BCF) and the Chicheng–Fengning–Longhua Fault to the south, which together constitute a dextral shearing fault system on the northern margin of the NCB during the Late Triassic. The paleomagnetic study performed on the Middle Permian Guangxingyuan pluton, located between the XMF and BCF, documents a local clockwise rotation of this pluton with respect to the NCB and SHB. Our multidisciplinary study suggests an NNW–SSE shortening and strike–slip shearing dominated tectonic setting on the northern margin of the NCB during the Late Triassic. Combining the contemporaneous dextral strike–slip movements of the XMF and BCF in northern China and the sinistral strike–slip movement of East Gobi Fault (EGF) in southeastern Mongolia with the large-scale tectonic framework, a Late Triassic NNW–SSE shortening-eastward extrusion tectonic model for Central-Eastern Asia is firstly proposed. The NNW–SSE shortening results in the eastward extrusion of the continental wedge bounded by the BCF and EGF, which is accommodated by the different kinematic patterns of the southern (XMF and BCF) and northwestern (EGF) bounding faults. This shortening-extrusion tectonic framework is tentatively interpreted as the result of the far field forces associated with three Late Triassic lithosphere-scale convergences in East Asia: i) northward intracontinental subduction between the NCB and South China Block, ii) collision of the Qiangtang Block with the Qaidam Block, and iii) southward subduction of the Mongol–Okhotsk Ocean beneath the Mongolia Block

Permian Paleogeography of the Eastern CAOB: Paleomagnetic Constraints From Volcanic Rocks in Central Eastern Inner Mongolia, NE China

“…The Kungurian (~280‐Ma) pole from the SXB shows declination differences of Δ D = 69.9° ± 6.4° and 61.9° ± 7.3° with respect to the Late Carboniferous and Late Permian poles from the SXB. These changes are associated with Late Triassic dextral strike‐slip movements of the NMNCB and the accompanying shortening‐eastward extrusion of central eastern Asia (P. Zhao et al, ).…”

“…changes are associated with Late Triassic dextral strike-slip movements of the NMNCB and the accompanying shortening-eastward extrusion of central eastern Asia (P. Zhao et al, 2015).…”

Macro‐and Microstructural, Textural Fabrics and Deformation Mechanism of Calcite Mylonites from Xar Moron‐Changchun Dextral Shear Zone, Northeast China

“…Lots of A-type granites which implying a post-collision intraplate tectonic setting also have been found in Late Triassic as an EW trending (e.g., Han et al, 2015Han et al, , 2017Song et al, 2018;Zhang and Zhai, 2010). Moreover, several muscovite 40 Ar/ 39 Ar ages from mylonite and granitic gneiss along the Xar Moron-Changchun Fault have been published with consistent ages of 209-221 Ma (Ma, 2009;Zhao et al, 2015;Zhang L et al, 2009;Zhang S H et al, 2009Zhang S H et al, , 2010. Lastly, undeformed Early Cretaceous granites intrude the older rocks along the fault zone, especially the O-S rocks and the Late Permian series (Figs.…”

“…After the end of the CAOB formation that resulted in the amalgamation and compression of the NCC, Tarim Craton, SIB and several intervening microcontinents, intra -continental strike-slip faults are the prominent tectonic features of Central-Eastern Asia during the Early Mesozoic (Lamb et al, 1999;Johnson, 2004;Webb and Johnson, 2006;Webb et al, 2010;Zhao et al, 2013Zhao et al, , 2015Zhai et al, 2004;Zhang et al, 2013;Heumann et al, 2014). The strike-slip faults can be ascribed to the consequence of several tectonic events, such as the southward subduction of the Mongol-Okhotsk Ocean (Meng, 2003;Zorin, 1999;Enkin et al, 1992;Cogné et al, 2005;Liang et al, 2019), the northwestern subduction of Paleo-Pacific plate , and the far-field effects of the north-directed continental subduction between the NCC-South China Block (SCB) (Rowley et al, 1997;Liu et al, 2006;Meng and Zhang, 1999;Zhang et al, 2013).…”

“…The E-W trending dextral strike-slip Xar Moron-Changchun shear zone, which was coeval with magmatic intrusions (Zhang S H et al, 2012;Wang et al, 2013), formed just in this shortening regime. The main activity age has been constrained to the Late Triassic (Ma, 2009;Wang et al, 2013;Zhao et al, 2015). This E-W large-scale strike-slip movement is a consequence of the eastward extrusion of the of XMOB , and results from far-field forces associated with Late Triassic convergence domain .…”