石柱复向斜及周缘下志留统砂岩碎屑组分特征及其构造意义

Lower Silurian sandstones in the Shizhu synclinorium and its periphery, Chongqing:Compositional variations and tectonic significance

关键词:  石柱复向斜  下志留统  碎屑组分分析  物源  扬子板块

Key words:  Shizhu synclinorium  Lower Silurian  compositional analysis  source area  Yangtze plate

摘要:

通过系统研究石柱复向斜露头和钻井剖面的砂岩薄片,统计分析了下志留统龙马溪组、小河坝组、韩家店组砂岩碎屑组分特征,在此基础上,进行了砂岩多碎屑的Dickinson图解分析,对物源区类型和板块构造背景进行了分析。研究结果表明,研究区下志留统主要物源区的板块构造位置为被动大陆边缘,总体上看,研究区下志留砂岩的成熟度和稳定度很高,反应本区距物源区具有相当远的距离,陆源碎屑经过较为充分的搬运;龙马溪组砂岩主要来自稳定克拉通和再旋回造山带,小河坝组砂岩主要来自稳定克拉通,韩家店组砂岩主要来自再旋回造山带,反映华南板块和扬子板块的拼接除奥陶纪末期的初次碰撞外,早志留世均呈现出幕式、蠕动式的非刚性拼接特点。

Abstract:

According to the thin section examination of the field outcrops and drilled holes, the present paper focuses on the statistical analysis of the detrital compositions, source area types and plate tectonic settings of the Lower Silurian sandstones in the Shizhu synclinorium and its periphery, Chongqing. Tectonically, the Silurian sandstones are mainly derived from the passive continental margins. The high maturity and stability of the Silurian sandstones suggest a very long distance of the study area from the source areas. The absence of typical volcanic arcs and subduction zones as source areas shows that no volcanic arcs and subduction zones were formed during the amalgamation of the Cathaysian land and Yangtze plate. The provenances include the stable craton and recycled orogen for the Longmaxi Formation sandstones;stable craton for the Xiaoheba Formation sandstones, and recycled orogen for the Hanjiadian Formation sandstones. The amalgamation of the Cathaysian land and Yangtze plate displayed characteristic episodic and creep patterns during the Early Silurian.