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New Paleomagnetic Results From Middle Jurassic Limestones of the Qiangtang Terrane, Tibet: Constraints on the Evolution of the Bangong‐Nujiang Ocean
Author(s) -
Cao Yong,
Sun Zhiming,
Li Haibing,
Pei Junling,
Liu Dongliang,
Zhang Lei,
Ye Xiaozhou,
Zheng Yong,
He Xiangli,
Ge Chenglong,
Jiang Wan
Publication year - 2019
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/2017tc004842
Subject(s) - terrane , paleomagnetism , geology , paleontology , cretaceous , fibrous joint , permian , gondwana , palaeogeography , tectonics , medicine , structural basin , volcanism , anatomy
To constrain the relationship between the Qiangtang and Lhasa terranes and the evolution of the Bangong‐Nujiang Ocean (BNO), we carried out a paleomagnetic investigation of the Middle Jurassic limestone from the Shuanghu region in the southern Qiangtang terrane. Stepwise thermal demagnetization succeeded in isolating high‐temperature characteristic directions by either principal component or great circle fitting analyses. The site‐mean direction of the 13 sampling sites was Dg = 334.7°, Ig = 51.2°, kg = 27.9, α 95 = 8.0° (in geographic coordinates) and Ds = 245.2°, Is = 54.1°, ks = 113.9, α 95 = 3.9° (in stratigraphic coordinates). The paleomagnetic data passed both fold and reversal tests. Both rock magnetic and petrographic investigations suggest a primary magnetization. The paleomagnetic results imply that the paleolatitude of the Qiangtang terrane was 34.6 ± 4.6°N (reference site: 32.7°N, 89.4°E) in the Middle Jurassic. Combined with previous reliable paleomagnetic results, it is suggested that the Qiangtang terrane was situated at a stable paleolatitudinal position and did not undergo obvious N‐S displacement between the Late Triassic and the Middle Jurassic. Comparison with the paleomagnetic results available for the Lhasa terrane implies that the width of the BNO was 2,600 ± 710 km (23.4° ± 6.4°) during the Middle Jurassic. The BNO expanded from the Early to Middle Triassic, reached its maximum width in the Late Triassic, and then shrank until it closed by the Cretaceous.