Geochronology, Geochemistry and Petrogenesis of the Bamco Andesites from the Northern
详细信息
- 责任者：Chen Yue (State Key Laboratory of Geological Processes and Mineral Resources ; School of Earth Science and Mineral Resources ; China University of Geosciences ; Beijing 100083 ; China) ; Zhu Dicheng
- 刊名：Acta Petrologica Sinica
- 出版年：2010
- 卷期：26(7)
- 关键词：安山岩 ; andesite ; 铀—铅计时 ; U-Pb dating ; 冈底斯山 ; Gangdise Range
- 页码：p.2193-2206
- 图表：8 illus., 3 tables, 63 refs.
- 分类号：0801
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
The authors report the petrological,zircon LA-ICPMS U-Pb dating, whole-rcok geochemical, and zircon Hf isotopic data for andesites from eastern Bamco, northern Gangdese. One Bamco andesite sample was dated to be 122.1±0.9 Ma. The samples are porphyric, with dominant plagioclase, hornblende phenocrysts, together with minor pyroxene, biotite phenocrysts. They have SiO2 of 58.65%~60.16%, total alkalis（K2O+Na2O）of 5.25%~5.52%, K2O of 2.67%~2.81%, TiO2 of 0.61%0.72%, MgO of 2.78%3.10%, with Mg numbers of 45~48, and K2O/Na2O>1. The Bamco andesites are enriched in Rb, Th, U, K and Pb, and depleted in Ba, Nb, Ta, P and Ti, indicative of arc-related rocks. The andesite samples have higher εNd（t）values（-9.3~-9.8）, higher zircon εHf（t）values（-4.6~-0.3）, and lower initial 87Sr/86Sr ratios（0.710 2~0.710 3）relative to melts derived from mature continental crust in the Gangdese（e.g., Ningzhong Early Jurassic strongly peraluminous granite）. The ancient Nd model ages（1.61~1.76 Ga）and zircon Hf mantle model ages（795~965 Ma）suggest an origin of ancient lithosphere mantle for their generation. Data indicate that the Bamco andesites are high-K calc-alkaline, and were emplaced at a transitional setting from continental arc to syn-collisional setting. The Bamco andesites may be the products of magma mixing between ancient lithosphere mantle-derived melts and crust-derived felsic melts resulting from rising asthenosphere material following slab rollback. Such a slab can be correlated with the Bangong-Nujiang Ocean seafloor that has been subducted southward towards beneath the Gangdese Belt.