贵州独山地区二叠纪—三叠纪凝灰岩地球化学特征及其地质意义

本文对右江盆地北缘晚二叠世大隆组、早三叠世罗楼组中的凝灰岩夹层开展地质分析研究。镜下岩石学鉴定显示其为一套玻屑、晶屑凝灰岩;而其主量元素特征分析表明属流纹质、安山质凝灰岩,具高硅、高铝、高钾特征。结合稀土元素球粒陨石标准化分布型式图及微量元素原始地幔标准化蛛网图形态特征,Y、Nb、Rb、La、Pb及Ce等稀土、微量元素的比值特征,认为凝灰岩的岩浆来源与该时期发生在凭祥一带的中—酸性火山弧活动密切相关。构造背景属于古特提斯洋向北往华南陆块之下俯冲时,形成活动大陆边缘岛弧,弧后陆壳发生伸展活动形成右江盆地。岩浆来源于洋壳俯冲发生部分熔融,且尚未与地幔发生作用,在上升过程中与陆壳物质发生混染,由火山弧的活动喷发而来。

Geochemical Characteristics and Its Geological Significance of Tuff in Dias-Triassic in Dushan Area, Guizhou

Comprehensive geochemical analyses were conducted on the interbedded tuff collected from Late Permian Dalong Formation to Early Triassic Luolou Formation. The samples are rhyolitic and andesitic tuff, characterized by high contents of SiO₂, Al₂O₃ and K₂O with vitroclastic texture. According to the REE pattern and trace elements spider diagram, the source has a close connection with volcanic arc within Pingxiang area. Active continental margin arc was formed while the Paleo-tethys Ocean subduction towards to the South China Block. Then Youjiang basin was formed after continental crust extension. It indicates that the source material was partly melted by oceanic crust subduction, contaminated with continental crust materials during the rising process.