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高校地质学报 ›› 2020, Vol. 26 ›› Issue (6): 639-655.DOI: 10.16108/j.issn1006-7493.2019060

• 岩石·矿物·地球化学 • 上一篇    下一篇

右江盆地中三叠世碎屑岩地球化学特征及其物源分析∶以贵州册亨地区为例

陈 兴,彭成龙*,陈建书,吴开彬,张德明,王文明,龚桂源,邓贵标,骆 珊   

  1. 贵州省地质调查院,贵阳 550081
  • 出版日期:2020-12-20 发布日期:2021-01-05

Geochemistry and Provenance of the Middle Triassic Clastic Rocks in the Youjiang Basin, Ceheng, Guizhou

CHEN Xing,PENG Chenglong*,CHEN Jianshu,WU Kaibin,ZHANG Deming,WANG Wenming,#br# GONG Guiyuan,DENG Guibiao,LUO Shan   

  1. Guizhou Geological Survey, Guiyang 550081, China
  • Online:2020-12-20 Published:2021-01-05

摘要: 右江盆地中三叠世充填了一套巨厚的复理石沉积,岩性为细砂岩、粉砂岩、泥岩及其过渡岩石,其独特的沉积特征颇受国内外地质学界关注,但目前对该套碎屑岩的物源尚有争议。文章通过对册亨地区中三叠世碎屑岩开展详细的岩石学和地球化学分析,结果显示:碎屑岩成分成熟度与结构成熟度都较低,具近源沉积特征。SiO2(平均为58.49%)含量较低,变化范围较大,说明石英含量较低;Al2O3(平均为12.46%)含量较高,说明粘土矿物及长石含量较高;Al2O3/SiO2的比值平均为0.22,与杂砂岩(0.20~0.23)一致,说明碎屑岩成熟度较差,亦具近源沉积特征;CaO(平均为7.83%)含量较高,说明含碳酸盐类物质较多。微量元素表现为富集Rb、Th、La、Nd、Hf和Pb以及相对亏损P、Ti、Sr、Nb和Ta的特点,稀土元素具有ΣREE变化范围大,轻稀土富集,Eu亏损的特点。主量、微量和稀土元素分析表明,碎屑岩的源岩以长英质岩石为主,并有少量中性岩及石英质沉积岩的混入;源区构造背景以大陆岛弧为主,兼有被动大陆边缘及活动大陆边缘特
征。化学蚀变指数(CIA)值为53.93~74.80,均值为65.12。通过CIA以及Th/U比值,表明碎屑岩源区主要经历了中等化学风化作用。

关键词: 右江盆地, 册亨, 中三叠世, 物源, 构造背景

Abstract: Owing to the unique sedimentary characteristics, the Youjiang Basin has attracted considerable attention from numerous geologists. The Middle Triassic of the Youjiang Basin was filled with a set of thick flysch sediments, which are predominantly fine-grained sandstones, siltstones, mudstones and transition rocks. However, there are still controversies about the provenance of the clastic rocks. In this paper, detailed petrological and geochemical analyses of the Middle Triassic clastic rocks in Ceheng have been carried out. Results show that the clastic rocks are featured by low compositional maturity and textural maturity, which reflects a proximal sedimentation. The content of SiO2 (average=58.49%) is low with a wide range of variation, which indicates that the quartz contents are relatively low. The high content of Al2O3 (average=12.46%) indicates the high contents of clay minerals and feldspars. The average ratio of Al2O3/SiO2 is 0.22, which is consistent with the graywacke (0.20~0.23), indicating that the clastic rocks are low in maturity and also have proximal sedimentary characteristics. The high content of CaO (average 7.83%) indicates more carbonates. The trace elements are characterized by the enrichment of Rb, Th, La, Nd, Hf and Pb,
but relatively depleted in P, Ti, Sr, Nb and Ta. Rare earth elements are featured by large variation range of ΣREE, enrichment of light rare earth elements and Eu depletion. Analysis of major, trace and rare earth elements reveals that the source rocks of clastic rocks are mainly felsic rocks, with a little mixture of intermediate rocks and quartzose sedimentary rocks. The tectonic setting of the source area is dominated by continental island arc, and partially passive continental margins and active continental margins. The chemical index of alteration (CIA) is 53.93~74.80 (average=65.12). The CIA and Th/U ratios indicate that the source area of clastic rocks mainly experienced moderate chemical weathering.

Key words: Youjiang Basin, Ceheng, Middle Triassic, provenance, tectonic setting

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