Late Paleozoic paleomagnetism of South Mongolia: Exploring relationships between Siberia, Mongolia and North China

摘要

The tectonic evolution of a large region that includes South Siberia, Mongolia and North China is still a matter of fierce debate. This is due, at least in part, to the contentious proposals detailing the kinematics of the major tectonic units in that area. One solution to the problem is the acquisition of better defined paleomagnetic data for the various players in the system. We carried out a paleomagnetic study of Early Carboniferous subduction-related volcanic rocks of the Trans-Altai zone in South Mongolia and successfully isolated a pre-folding and presumably primary component from 22 sites. A critical analysis of Late Paleozoic paleomagnetic data from Mongolia revealed several problematic data sets, while the paleolatitudes derived from more reliable studies agreed well with the expected values for Siberia and were consistently different from those for the North China block. We also found that Late Paleozoic declinations from Mongolia are rotated counterclockwise through various angles with respect to Siberia. In addition, those rotations are widespread in both Inner Mongolia and the North China block. In this paper, we put forward some testable hypotheses and propose a preliminary paleogeographic scheme of the region: 1) Consistent difference in Late Paleozoic paleolatitudes between Siberia and Mongolia on the one hand and the North China block on the other, is largely due to strong inclination shallowing in paleomagnetic data for the latter area, where most data are from sedimentary rocks. 2) Widespread counterclockwise rotations in Mongolia, Inner Mongolia and North China may be accounted for by a wide zone of sinistral transpression that was active in the Early Mesozoic. 3) In the Early Mesozoic, the Mongol-Okhotsk Ocean was much narrower than is usually assumed; 4) There was no large-scale oroclinal bending between Siberia and North China in the Permian-Early Mesozoic. (C) 2016 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.