摘要
摘要:四川盆地华蓥山玄武岩出露于茅口组顶部，夹于龙潭组底部的杂色泥岩、页岩之间，岩性为灰黑色粗玄岩，底部致密块状，顶部见气孔—杏仁状构造。TAS图解显示玄武岩属于碱性与偏碱性过渡带上的拉斑玄武岩系列，TiO₂含量介于2.92%～3.63%之间，Ti/Y值为465～567，属于高钛玄武岩（HT）。岩石LREE/HREE=3.25～3.96，轻稀土略富集，具有右倾平滑型稀土分配模式。华蓥山玄武岩与云南宾川，贵州赫章等地峨眉山玄武岩的地球化学特征相似，反映了相同的幔源性质。结合野外地质特征，认为华蓥山玄武岩应属峨眉地幔柱的一部分，是沿着华蓥山基底断裂发生裂隙式喷发的产物。研究区的高钛玄武岩Ce/Yb介于22.65～27.93，与前人报道的高钛玄武岩Ce/Yb比值范围基本一致，处于石榴石稳定区与尖晶石稳定区的过渡带，Th/Ta、Nb/U、La/Ta等比值反映出岩石受壳源物质的混染程度很低，可能是地幔柱轴部的产物。
关键词: 峨眉山大火成岩省/
地球化学/
地幔柱/
华蓥山/
高钛玄武岩

Abstract:Huayingshan basalt was overlain the top of Middle Permian Maokou Formation, and intruded into the black, greyish green and dark purple shales and mudstones in the bottom of Upper Permian Longtan Formation in Huangkongcao outcrop, Sichuan Basin. The rock type is mainly composed of gray-black dolerite. There are numerous vesicles and amygdaloids at the top of Huayingshan basalt, but not found any of them in the bottom. The TAS diagram shows that Huayingshan basalt belongs to the transitional series tholeiite between alkaline and subalkaline. The content of TiO₂ varies from 2.92%~3.63%, and the ratio of Ti/Y varies from 465~567 which reflects typical features of high-Ti basalt(HT). The ratios of LREE/HREE in Huayingshan basalt range between 3.25 and 3.96, slightly rich in light rare earth elements (LREE), presenting a right-leaning smooth trends in REE patterns. The geochemical characteristics of Huayingshan basalt are similar to those of Emeishan basalt in Binchuan area and Hezhang area, indicating an origin of mantle plume and the same mantle source. Moreover, the geological position of Huayingshan basalt in Huangkongcao outcrop is consistent with regional record of the eruption of Emeishan basalt in Southwest China. Therefore, Huayingshan basalt is believed to be a part of Emeishan mantle plume. The Ce/Yb of Huayingshan basalt is between 22.65 and 27.93, which is resembled with the Ce/Yb ratio range of high-Ti basalt (HT) reported by other regions. The data points of basalt in(Tb/Yb)_N-(La/Sm)_N diagram fall on the boundary of garnet stabilization zone and spinel stabilization zone. Ratios of Th/Ta, Nb/U and La/Ta reflect a relative low mixing degree with crust materials, indicating that Huayingshan basalt was possibly sourced from the axis of mantle plume.
Key words:ELIP/
Geochemistry/
Mantle plume/
Huayingshan/
HT basalt



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