Paleomagnetism of Carboniferous sediments in the Hexi corridor: its origin and tectonic implications

Abstract

We report paleomagnetic results for Carboniferous rocks from the eastern part of the Hexi Corridor, which we have demonstrated to be the western extension of the North China block (NCB). The characteristic high-temperature remanence component (B-component) exhibits predominantly reverse polarity, and is generally separable by thermal demagnetization temperature steps between 350 and 580°C. This B-component can also be isolated by alternating fields (AFs) cleaning at a peak value of 20–30 mT using a hybrid thermal–AF demagnetization method. The B-component shows a positive fold test at the 95% confidence level, indicating that it was acquired before Late Triassic to Early Jurassic folding. We interpret the B-component to be of primary origin acquired during the Carboniferous. The corresponding pole positions are at 14.0°E, 10.5°N, α95=6.2° for the Early-Middle Carboniferous (late Visean to Namurian) and at 10.2°E, 33.3°N, α95=16.7° for the Late Carboniferous (Stephanian). The preliminary Late Carboniferous pole is in agreement with that for the NCB, supporting earlier claims that the Hexi Corridor has been the western extension of the NCB since the Ordovician. On the other hand, these two Carboniferous paleopoles are distinct from the coeval ones for Inner Mongolia, Outer Mongolia, South China, Tarim and stable Europe at greater than 95% confidence, suggesting that these continental blocks could not have been connected in their present configuration during Carboniferous time. The significant difference in paleolatitude between the NCB and Australian part of Gondwanaland according to the two new Hexi Corridor poles indicates that they had drifted apart by the late Visean.