Palaeomagnetic data about southern Tibet (Xizang) — I. The Cretaceous formations of the Lhasa block |
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Authors: | Michel Westphal Jean-Pierre Pozzi Yao Xiu Zhou Li Sheng Xing Xian Yao Chen |
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Institution: | Institut de Physique du Globe de Strasbourg, 5 rue Descartes, F-67084 Strasbourg, Cedex, France; Institut de Physique du Globe de Paris, 4 place Jussieu, F- 75230 Paris 05, France; Chinese Academy of Geological Sciences, Bai Wan Zhuang Road, Beijing, People's Republic of China |
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Abstract: | Summary. A palaeomagnetic study of Middle to late Cretaceous redbeds from Linzhou basin (Lhasa block), north of the Yarlung Zangbo suture zone, gives a stable palaeomagnetic direction of magnetization with a positive fold-test: six sites, 57 samples, D = 333°, I = 38°, k = 78, α95= 8°, pole 64°N, 348°E. We discuss the problem of a possible remagnetization but consider that this direction of magnetization gives a good approximation for the palaeolatitude of the Lhasa block during Middle to late Cretaceous time. Results from more recent Tibetan formations are also presented: late Cretaceous to Palaeocene sediments and volcanics give a lower palaeolatitude of 10° N and but more recent andesites have emplaced about 30°N, close to the present-day latitude. An interpretation is proposed whereby the Lhasa block, which was a part of Asia in the early Cretaceous, has undergone first a southward motion accompanied by an anticlockwise rotation and then, after the Palaeocene, a northward motion under the constraint of the colliding India. |
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