Did the Paleo‐Asian Ocean between North China Block and Mongolia Block exist during the late Paleozoic? First paleomagnetic evidence from central‐eastern Inner Mongolia, China

Abstract

[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.

Sedimentological and geochronological constraints on the Carboniferous evolution of central Inner Mongolia, southeastern Central Asian Orogenic Belt: Inland sea deposition in a post-orogenic setting

“…Our sedimentological analyses and depositional setting interpretations are consistent with both the paleontological Xin et al, 2011) and the paleomagnetic data in this region (Pruner, 1987;Chen et al, 1997;Li et al, 2012;Zhao et al, 2013).…”

“…Recently, paleomagnetic studies were carried out on the Devonian-Permian strata of Hunshandake Block, showing that this block was located at the northern margin of NCC since the Late Devonian . These blocks were accreted to the northern margin of NCC, and formed a large continental block before the Late Devonian Zhao et al, 2013).…”

Further paleomagnetic results from the ~ 155 Ma Tiaojishan Formation, Yanshan Belt, North China, and their implications for the tectonic evolution of the Mongol–Okhotsk suture

“…Geological and geophysical evidence may demonstrate that the Mongolia block (MOB) and the NCB had merged into a single entity ("MOB-NCB") by the Late Permian or Triassic (Xiao et al, 2003;Xu et al, 2013;Zhao et al, 2013;. However, the paleomagnetic results presented here for the Tiaojishan Fm are in serious conflict with some of those obtained from the MOB Gilder and Courtillot, 1997;Gilder et al, 1999;Fig.…”

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

“…Central-Eastern Asia experienced an important tectonic transition from the completion of the Paleozoic accretion between the NCB and the Mongolian Block (Xiao et al, 2003;Johnson et al, 2008;Xu et al, 2013;Zhao et al, 2013) to the Late Mesozoic intracontinental extension (Meng, 2003;Daoudene et al, 2012). Hence, the Triassic period is a key to decipher the tectonic transition and the evolution of Central-Eastern Asia.…”

“…Magnetic mineralogical investigation and stepwise demagnetization were carried out at the Laboratoire de Magnétisme des Roches d'Orléans (LMRO) and the Laboratoire de Paleomagnétisme of Institut de Physique du Globe de Paris (IPGP) at Saint Maur (France). The detailed experiment procedures and data analysis processes can be found in Zhao et al (2013).…”