Combined paleomagnetic and geochronological study on Cretaceous strata of the Qiangtang terrane, central Tibet

A combined paleomagnetic and geochronological investigation has been performed on Cretaceous rocks in southern Qiangtang terrane (32.5 degrees N, 84.3 degrees E), near Gerze, central Tibetan Plateau. A total of 14 sites of volcanic rocks and 22 sites of red beds have been sampled. Our new U-Pb geochronologic study of zircons dates the volcanic rocks at 103.8 +/- 0.46 Ma (Early Cretaceous) while the red beds belong to the Late Cretaceous. Rock magnetic experiments suggest that magnetite and hematite are the main magnetic carriers. After removing a low temperature component of viscous magnetic remanence, stable characteristic remanent magnetization (ChRM) was isolated successfully from all the sites by stepwise thermal demagnetization. The tilt-corrected mean direction from the 14 lava sites is D = 348.0 degrees, I = 47.3 degrees, k = 51.0, a(95) = 5.6 degrees, corresponding to a paleopole at 79.3 degrees N, 339.8 degrees E, A(95) = 5.7 degrees and yielding a paleolatitude of 29.3 degrees +/- 5.7 degrees N for the study area. The ChRM directions isolated from the volcanic rocks pass a fold test at 95% confidence, suggesting a primary origin. The volcanic data appear to have effectively averaged out secular variation as indicated by both geological evidence and results from analyzing the virtual geomagnetic pole (VGP) scatter. The mean inclination from the Late Cretaceous red beds, however, is 13.1 degrees shallower than that of the similar to 100 Ma volcanic rocks. After performing an elongation/inclination analysis on 174 samples of the red beds, a mean inclination of 47.9 degrees with 95% confidence limits between 41.9 degrees and 54.3 degrees is obtained, which is consistent with the mean inclination of the volcanic rocks. The site-mean direction of the Late Cretaceous red beds after tiltcorrection and inclination shallowing correction is D = 312.6 degrees, I = 47.7 degrees, k = 109.7, a(95) = 3.0 degrees, N = 22 sites, corresponding to a paleopole at 49.2 degrees N, 1.9 degrees E, A(95) = 3.2 degrees (yielding a paleolatitude of 28.7 degrees +/- 3.2 degrees N for the study area). The ChRM of the red beds also passes a fold test at 99% confidence, indicating a primary origin. Comparing the paleolatitude of the Qiangtang terrane with the stable Asia, there is no significant difference between our sampling location in the southern Qiangtang terrane and the stable Asia during similar to 100Ma and Late Cretaceous. Our results together with the high quality data previously published suggest that an similar to 550 km N-S convergence between the Qiangtang and Lhasa terranes happened after similar to 100 Ma. Comparison of themean directions with expected directions from the stable Asia indicates that the Gerze area had experienced a significant counterclockwise rotation after similar to 100 Ma, which is most likely caused by the India-Asia collision. (C) 2015 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.