Location of the Lhasa terrane in the Late Cretaceous and its implications for crustal deformation

Abstract

The Cenozoic crustal deformation of the Asian continent is constrained by the location of its southern margin in the Late Cretaceous, which is, however, affected by potential remagnetization and inclination shallowing of redbeds in the Linzhou Basin. Our paleomagnetic results from the Shexing Formation redbeds in the Late Cretaceous yield a mean paleo-inclination of ~21.5°, consistent with the recalculation of previous data. Rock-magnetic, paleomagnetic and petrographic analyses indicate that the redbeds have recorded the original paleomagnetic field and have not suffered from significant inclination shallowing. The paleopole from 70 redbeds sites is at 71.8°N, 281.5°E with A 95 = 2.6°, yielding a paleolatitude of ~12.0 ± 2.6°N at ~70–91 Ma for the Linzhou Basin. This result indicates a latitudinal convergence of 1264 ± 477 km north of the sampling area within Asia since the Late Cretaceous. Combined with previous data, our results show that the southern margin of Asia was at ~11–15°N in the Late Cretaceous, aligning in a WNW-ESE direction, which is similar to its present-day orientation. A review of available data shows that the sharp bending of the southern margin of Asia around the eastern Himalayan syntaxis (EHS) is probably due to different crustal movement patterns around the EHS. The shape of the southern margin of Asia determines the arc-shaped orientation of Himalayan orogen. • The Shexing Formation redbeds have recorded the prefold magnetizatioin. • The southern margin of Asia was oriented in a WNW-ESE direction at ~12°N. • Different movement around the eastern Himalayan syntaxis make a sharp turn. • The southern margin of Asian plays a primary role in shaping the Himalayan orogen.