- 责任者：Yan Han (State Key Laboratory of Geological Processes and Mineral Resources ; School of Earth Sciences and Mineral Resources ; China University of Geosciences ; Beijing 100083 ; China) ; Zhao Zhidan
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(11)
- 关键词：白榴岩 ; leucitite ; 斑岩 ; porphyry ; 铀—铅计时 ; U-Pb dating ; 西藏 ; Tibet
- 页码：p.3731-3744
- 图表：6 illus., 2 tables, 42 refs.
- 分类号：0801
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
The petrology, geochemistry, and U-Pb geochronology of the Yangbajain leucite porphyry cellected from Rongniduo, in the Dangxung-Yangbajain rift （graben） in southern Tibet were studied. The leucite samples are porphyritic texture, with megacrysts of leucite （as large as 4cm to 6cm） and other small minerals （plagioclase, pyroxene and olivine）. They are basaltic-like （SiO2 = 52% - 54% ）, high alkalis （K20 ＋ Na20 =9. 8% - 12. 3% ）, potassic rocks, which belongs to tephriphonolite in TAS diagram. The rocks are enriched in light rare earth element [ （La/Yb） N = 19 -20], with slightly Eu nagetive anormaly （SEu =0. 68 -0. 77）. They show enrichment in large-ion lithophile dements （LILEs, Rb, Th, and U）, depleted in high field strength elements （HFSEs, Nb, Ta, P, and Ti）, and depleted in MgO, and other compatible dements （ Cr, Co and Ni）. This suggests that the rocks are not generated directly from mantle. And the rocks also show depleted in Sr-Nd isotopic, combined with other characteristics that containing olivine and pyroxene and basaltic-like （SiOz = 52% -54% ）, indicating that they did not result from partial melting of mantle directly, but they inherit the characteristics of the depleted mantle sources, and fractional crystallization occurred thereafter. The Yangbajain leucite porphyry and Linzizong volcanic rocks are from different magma sources, magmatic evolutionary relationships do not exist between them. The zircon dating shows the rocks crystallized at the age of 8. 2 - 15.4Ma （ weighted average age is 10. 9 ± 1.6Ma）, which provides a powerful evidence for the timing of the Dangxung-Yangbajain rift （graben）.