Paleomagnetism of the Upper Cretaceous red-beds from the eastern edge of the Lhasa Terrane: New constraints on the onset of the India-Eurasia collision and latitudinal crustal shortening in southern Eurasia

摘要

The Late Cretaceous location of the Lhasa Terrane is important for constraining the onset of India-Eurasia collision. However, the Late Cretaceous paleolatitude of the Lhasa Terrane is controversial. A primary magnetic component was isolated between 580 degrees C and 695 degrees C from Upper Cretaceous Jingzhushan Formation red-beds in the Dingqing area, in the northeastern edge of the Lhasa Terrane, Tibetan Plateau. The tilt-corrected site-mean direction is D-s/I-s = 0.9 degrees/24.3 degrees, k = 46.8, alpha(95) = 5.6 degrees, corresponding to a pole of Plat./Plon. = 71.4 degrees/273.1 degrees, with A(95) = 5.2 degrees. The anisotropy-based inclination shallowing test of Hodych and Buchan (1994) demonstrates that inclination bias is not present in the Jingzhushan Formation. The Cretaceous and Paleogene poles of the Lhasa Terrane were filtered strictly based on the inclination shallowing test of red-beds and potential remagnetization of volcanic rocks. The summarized poles show that the Lhasa Terrane was situated at a paleolatitude of 13.2 degrees +/- 8.6 degrees N in the Early Cretaceous, 10.8 degrees +/- 6.7 degrees N in the Late Cretaceous and 15.2 degrees +/- 5.0 degrees N in the Paleogene (reference point: 29.0 degrees N, 87.5 degrees E). The Late Cretaceous paleolatitude of the Lhasa Terrane (10.8 degrees +/- 6.7 degrees N) represented the southern margin of Eurasia prior to the collision of India-Eurasia. Comparisons with the Late Cretaceous to Paleogene poles of the Tethyan Himalaya, and the 60 Ma reference pole of East Asia indicate that the initial collision of India-Eurasia occurred at the paleolatitude of 10.8 degrees +/- 6.7 degrees N, since 60.5 +/- 1.5 Ma (reference point: 29.0 degrees N, 87.5 degrees E), and subsequently similar to 1300 +/- 910 km post-collision latitudinal crustal convergence occurred across the Tibet. The vast majority of post-collision crustal convergence was accommodated by the Cenozoic folding and thrust faulting across south Eurasia. (C) 2017 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.