Characteristics of Volcanic Rocks from Late Permian to Early Triassic in Ailaoshan Tectono-Magmatic Belt and Implications for Tectonic Settings
详细信息
- 责任者：Liu Cui (Graduate University ; Chinese Academy of Sciences ; Beijing 100049 ; China) ; Deng Jinfu
- 刊名：Acta Petrologica Sinica
- 出版年：2011
- 卷期：27(12)
- 关键词：粗安岩 ; trachyandesite ; 玄武岩 ; basalts ; 哀牢山 ; Ailao Mountains
- 页码：p.3590-3602
- 图表：6 illus., 2 tables, 34 refs.
- 分类号：0801
- 出版序号：20122306
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
This paper studies the volcanic rocks of Yaxuanqiao, Maoheshan and Lvchun in Ailaoshan tectono-magmatic belt, Yunnan Province, SW China. Yaxuanqiao volcanic rocks mainly composed of Mugearite-basalts with minor andesites formed in Late Permian. Analysis suggested that Yaxuanqiao igneous rocks belong to arc-type igneous rocks in Late Permian. Zircon SHRIMP U-Pb dating of Maoheshan basalt gave an age of (249±1.6) Ma, i.e., Early Triassic. These rocks are sub-alkaline albite basalts, belonging to low-potassic calc-alkaline series. Combined with previous studies, the paper suggests that Ailaoshan Ocean had opened since Late Devonian and probably been spreading between Carboniferous and Early Permian(?). But in Late Permian the Ailaoshan ocean had begun to subduct to form initial arc of Yaxuanqiao to the west of the Ailaoshan. In Early Triassic (249±1.6) Ma, Maoheshan basalts, characterized by both arc and MORB, formed as a part of Ailaoshan ophiolites. It may suggest that the Ailaoshan ocean basin had been shrunk, or converted to intra-arc or back-arc basins of supra-subduction zones. Thus the evolution of the Ailaoshan ocean went into the late stage, and in some area, such as Lvchun area, it became a transitional setting from matured arc to continent-continent collision (247.3±1.8) Ma. All those mentioned above support the conclusion that the Ailaoshan ocean had closed in Late Triassic, which also coincides with the fact that Yiwanshui Group of Late Triassic unconformably overlied the Ailaoshan Shuanggou ophiolites.