Paleomagnetic results from the Early Cretaceous Zenong Group volcanic rocks, Cuoqin, Tibet, and their paleogeographic implications

Abstract

A paleomagnetic study has been carried out on the Early Cretaceous Zenong Group volcanic rocks (ca. 110–130Ma) near Cuoqin town in the central Lhasa terrane. Stepwise thermal demagnetization up to 680°C isolated a stable high-temperature component (HTC) including antipodal dual polarities. The HTC directions passed both a fold test at 99% confidence and a reversal test at 95% confidence, suggesting a primary origin. The tilt-corrected average direction for 18 sites is D=327.0°, I=35.7°, κ=59.3°, α95=4.5°, which corresponds to a paleopole at 58.2° N, 341.9° E (A95=4.6°), yielding a paleolatitude of 19.8°±4.6° N for the study area. Our results, combined with previous paleomagnetic data, suggest that southern Tibet was at a mean paleolatitude of 20° N during the Cretaceous and Paleogene. When compared with the apparent polar wander paths of Asia, the difference suggests that only ca. 870km north–south crustal shortening has accumulated between the Lhasa terrane and stable Asia since ca. 110Ma. When comparing the paleolatitudes of the Lhasa terrane and India, the results indicate that the width of the Neotethys was 6720±690km during the Early Cretaceous.