Magma source and tectonic setting of the porphyritic alkaline basalts in the Silurian Taohekou Formation, North Daba Mountain: Constraints from the geochemical features of pyroxene phenocrysts and whole rocks.

作者：Xiang ZhongJin^*; Yan QuanRen; Yan Zhen; Wang ZongQi; Wang Tao; Zhang YingLi; Qin XiaoFeng

来源：Acta Petrologica Sinica, 2010, 26(4): 1116-1132.

• Clinopyroxene phenocryst
• Porphyritic alkaline basalts
• Silurian Taohekou Formation
• North Dabs Mountain

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 67.65km, which indicates that primary magma originated at mantle. During the upward transporting, magma stagnated and then crystallized at three depth intervals, 39.93 similar to 67.65km, 14.52 similar to 20.46km and 4.62 similar to 9.24km. Coarse porphyritic 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.

• 出版日期2010-4
• 单位中国地质科学院矿产资源研究所