Paleomagnetism and Ar-Ar Geochronology of Cretaceous Volcanic Rocks in the Middle Lhasa Terrane, China and Tectonic Implications
详细信息
- 责任者：Tang Xiangde (State Key Laboratory of Lithospheric Evolution ; Institute of Geology and Geophysics ; Chinese Academy of Sciences ; Beijing 100029 ; China) ; Huang Baochun
- 刊名：Chinese Journal of Geophysics
- 出版年：2013
- 卷期：56(1)
- 关键词：火山岩 ; volcanic rocks ; 氩—氩计时 ; Ar-Ar dating ; 西藏 ; Tibet
- 页码：p.136-149
- 图表：illus., 2 tables, 51 refs.
- 分类号：0801
- issnNo：ISSN0001-5733
- isbnNo：CN11-2074/P
摘要
In order to better understand Cretaceous to Paleogene paleogeography of the Lhasa terrane,180 drill core samples at 18 sites were collected from Linzizong volcanic rocks near the Coqên town in the middle Lhasa terrane for paleomagnetic studies.Detailed rock magnetic analyses reveal fine-grained ferrimagnetic magnetite as remanence carrier,whilst stepwise thermal and alternating field demagnetizations isolate a high temperature or high field characteristic remanent magnetization(ChRM) from the majority of the sampled rocks.We interpret this characteristic remanence as primary one in the light of a positive fold test result.The ChRM has a tilt-corrected site-mean direction of D=16.2°,I=17.7° with α 95=5.6°,and a corresponding paleopole at 63.1°N,224.6°E with A95=5.1°.On the other hand,the Ar-Ar dating on three rock samples show that the collected Linzizong volcanic rocks have a geochronological age ranging from ~99 to 93 Ma,which is much older than those outcropped in the Linzhou Basin,eastern part of the Lhasa terrane.Then both geochronological and paleomagnetic results reported here indicate a paleolatitude of 8.5°±6.9°N in the Northern Hemisphere for the middle part of the Lhasa terrane during the Late Cretaceous,which is well compatible with those estimated from the Early Paleogene Dianzhong and Nianbo formations in the Linzhou Basin,further indicating that the southernmost margin of the Eurasian continent might have a low paleolatitude of ~10°N in the Northern Hemisphere during the Late Cretaceous and Paleocene times.Together with recently published paleomagnetic results for the Paleocene Tethyan Himalayan marine sediments,the low paleolatitudes for Late Cretaceous and Paleocene Lhasa terrane support the view that the initial contact between India and Asia should be no later than～60.5 Ma.In addition,our results indicate also that at least ~1900 km collision-induced crustal shortening should have occurred between the Lhasa terrene and Siberia given that the Eurasian continent behaves as a single rigid plate during the Cenozoic.