HR: 1340h
AN: V33B-1397    [Abstracts]
TI: Permian Large Volume Basalt In Tarim Basin Of China And Its Geological Implication
AU: * Li, Z
EM: zilongli@zju.edu.cn
AF: Zhejiang University, 38 Zheda Rd., Xihu District, Hangzhou, 310027, China
AU: * Li, Z
EM: zilongli@zju.edu.cn
AF: Harvard University, 20 Oxford St., Cambridge, 02138, United States
AU: Chen, H
EM: hlchen@zju.edu.cn
AF: Zhejiang University, 38 Zheda Rd., Xihu District, Hangzhou, 310027, China
AU: Yang, S
EM: yjsy-ysf@zju.edu.cn
AF: Zhejiang University, 38 Zheda Rd., Xihu District, Hangzhou, 310027, China
AU: Langmuir, C H
EM: langmuir@eps.harvard.edu
AF: Harvard University, 20 Oxford St., Cambridge, 02138, United States
AU: Chen, Z
EM: zchen@fas.harvard.edu
AF: Harvard University, 20 Oxford St., Cambridge, 02138, United States
AU: Jia, C
EM: czjia@petrochina.com.cn
AF: PetroChina, 16 Andelu, Dongcheng District, Beijing, 100011, China
AU: Wei, G
EM: weiguoqi@163.com
AF: PetroChina, 16 Andelu, Dongcheng District, Beijing, 100011, China
AU: Dong, C
EM: dcw@mail.hz.zj.cn
AF: Zhejiang University, 38 Zheda Rd., Xihu District, Hangzhou, 310027, China
AB: The Tarim basin is the biggest sedimentary basin in China with an area of 560,000 km², and is surrounded by the Tianshan, Kunlun and Altun orogenic belts. It consists mainly of Precambrian basement and Phanerozoic stratum, and has recorded a magmatic history at ages ranging from 2500 Ma to 270 Ma. Based on geological studies and oil-gas surveys, the total area covered by the Permian basic igneous rocks is estimated to be more than 200,000 km². The Permian rocks are mainly composed of basalts, with a maximum thickness of ca. 600m, and diabases, and some occurrences of basaltic andesites and ultramafic rocks. The field survey and drilling core data show that the Tarim basin has experienced a major tectonothermal event in the Permian, with strong imprints in the central and western parts of the basin. An important unanswered question is whether the Tarim Permian magmatism is associated with the Permian mafic magmatic events from the surrounding regions, such as the 258 Ma Emeishan large igneous province (ELIP) in SW China. The goals of this study are to constrain precisely the time of formation of the Tarim Permian basalts using ⁴⁰Ar-³⁹Ar ages, and to discuss its origin using geochemical and isotopic tools. Using our new ⁴⁰Ar-³⁹Ar dating combined with other age data and the paleontological and sedimentary evidences, we estimate a time interval for the Permian basalt formation ranging from 280 to 290 Ma. In detail, distinct ages have been obtained for the different units, i.e. 290 Ma and 282 Ma for Kupukuziman (lower section) and Kaipaizilaike (upper section) basalts, respectively. Our study reveals that the different rock suites belonging to the Permian volcanic suites represent an igneous activity which spanned for about 10 Ma ranging from 280 to 290 Ma. We suggest that the timing of these rocks is intimately related to a lastly widespread and large thermo-tectonic event in the Tarim basin. The Permian basalts and diabases have compositions of tholeiite and alkali basalt series, and display high K, Rb, Ba, Th, LILE and LREE concentrations with no Nb-Ta anomalies. The basalts from the Yigan section of NW Tarim have initial ¹⁴³Nd/¹⁴⁴Nd of 0.5120-0.5122, initial ⁸⁷Sr/⁸⁶Sr of 0.7068-0.7077, ²⁰⁶Pb/²⁰⁴Pb of 17.90-18.05, ²⁰⁷Pb/²⁰⁴Pb of 15.52-15.53, and ²⁰⁸Pb/²⁰⁴Pb of 38.33-38.73. The trace element contents and Sr-Nd-Pb isotopic ratios suggest that the basalts are derived from partial melting under an extensional setting of an enriched mantle reservoir, likely related to a mantle plume as explained below. In addition, the trace element contents and Sr-Nd-Pb isotopic ratios are similar to those of the ELIP, suggesting a genetic linkage between them. Based on the new data from the Tarim event, a genetic link between the Tarim basalt (285 Ma) and ELIP (258 Ma) is that the existence of two short magmatic pulses at 285 and 258 Ma may indicate two discrete events in the source region, and two discrete plume/LIP events originated as discrete plumes arising from the deep mantle.
DE: 1033 Intra-plate processes (3615, 8415)
DE: 1037 Magma genesis and partial melting (3619)
DE: 1038 Mantle processes (3621)
DE: 3619 Magma genesis and partial melting (1037)
DE: 8415 Intra-plate processes (1033, 3615)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting