Magma Source and Tectonic Setting of the Porphyritic Alkaline Basalts in the Silurian Taohekou Formation,
详细信息
- 责任者：Xiang Zhongjin (Institute of Geology ; Chinese Academy of Geological Sciences ; Beijing 100037 ; China) ; Yan Quanren
- 刊名：Acta Petrologica Sinica
- 出版年：2010
- 卷期：26(4)
- 关键词：碱性玄武岩 ; alkali basalts ; 单斜辉石 ; clinopyroxene ; 岩石地球化学 ; lithogeochemistry ; 大巴山 ; Daba Mountains
- 页码：p.1116-1133
- 图表：illus., 5 tables, 54 refs.
- 分类号：0801
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
There are four different types of basalts lithofacies in the Silurian Taohekou Formation, including coarse porphyritic basalts, fine porphyritic basalts, amygdaloidal basalts and pillow basalts. All of them are classified to alkaline basalts, and show similar geochemistry features. The basalts are characterized by lower Si, strong differentiation between LREE and HREE, and higher Ti, LILE (including Th, Rb, Ba) and LREE. The REE distribution patterns and trace elements spider diagram of these basalts are the same as the ocean island basalt(OIB). Almost all of the phenocrysts are sahlite or diopside, and their REE and trace elements distribution patterns display good conformity to the basalts’. This implicates that all the basalts are cognate, may be derived from a same primary magma. The depth of host magma chamber which calculated from equilibrium temperatures and pressures between clinopyroxene and melt isn’t shallower than 67.65 km, which indicates that primary magma originated at mantle. During the upward transporting, magma stagnated and then crystallized at three depth intervals, 39.93～67.65 km, 14.52～20.46 km and 4.62～9.24 km. Coarse porphyritie basalts are rich in phlogopite, which supports that magma source underwent metasomatism by incompatible element-rich melts at mantle. The geochemical feature of clinopyroxene and whole rocks, combining with the volcanic-sedimentary succession suggest that the alkaline basalts in the Silurian Taohekou Formation produced within oceanic plate.