梵净山群上碎屑岩系沉积地质特征与构造古地理格局

发布时间：2018-04-12 17:34

本文选题：梵净山群 + 地层序列　；参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：江南造山带是上扬子陆块与华夏陆块间的地壳缝合带,主体为一北东东—南西西向延展的新元古代变质岩带。梵净山群发育于江南造山带的西北端,主体出露于黔东北的梵净山地区,主要为一套陆源碎屑岩、浅变质火山岩岩系,角度不整合于下江群之下。本文综合运用沉积地质学、岩石大地构造学、构造地层学等理论、方法,重点研究以铜厂组为代表的梵净山群上碎屑岩系的沉积地质特征,并结合火山岩系的大地构造属性探讨了梵净山群上碎屑岩系的原型盆地及构造古地理格局,主要取得以下新的进展:1.恢复了梵净山群的地层序列,查明其主体为灰色中厚层变质砂岩、粉砂岩及变凝灰砂岩及绢云千枚岩、板岩,以及多层中、基性火山岩等。2.野外实测了铜厂组、洼溪组中、粗粒浊积砂岩中发育的小型斜层理,经水平校正,前积层的倾向玫瑰花图解分析显示,黔东北梵净山群上亚群的浊积碎屑岩系古流向总体指向北、北东,证明其物源来自南方,它们源源不断的向北提供碎屑物质。3.铜厂组及洼溪组粗砂岩骨架颗粒统计分析及骨架颗粒成分三角图解显示,梵净山群上碎屑岩系沉积地层的物源为火山岛弧。4.野外采集了回香坪组中的具典型枕状构造的玄武岩及安山质集块火山岩样品。样品的全岩地球化学特征分析结果表明,其形成的构造环境为活动大陆边缘,形成于弧后伸展。5.综合以上研究成果,结合与庐山地区筲箕洼组以及星子岩群玄武岩进行相同构造环境图解判别的对比,推测梵净山群上碎屑岩系板块构造环境应为弧后伸展盆地,即边缘海。再结合前人研究成果,分析判断梵净山群与出露于桂北及黔南地区的四堡群相对应,形成完整的弧盆系统。进而推论梵净山群上部碎屑岩系沉积期间,江南造山带为一西太平洋型俯冲造山带或西太平洋型活动大陆边缘。
[Abstract]:The Jiangnan orogenic belt is a crustal suture zone between the upper Yangtze and Cathaysian blocks, and the main body is a Neoproterozoic metamorphic belt extending from north to west to west to west.The Fanjingshan Group is developed at the northwest end of the Jiangnan orogenic belt, and its main body is the Fanjingshan area in the northeast of Guizhou, which is mainly composed of a set of continental clastic rocks and shallow metamorphic volcanic rock series, and the angle is unconformity under the Lower Yangtze Group.Based on the theories of sedimentary geology, lithotectonics and tectonostratigraphy, this paper focuses on the sedimentary geological characteristics of the upper clastic rock series of the Fanjingshan Group, represented by the Tongchang formation.The prototype basin and tectonic paleogeographic pattern of the upper clastic rock series of the Fanjingshan Group are discussed based on the geotectonic attributes of the volcanic rock series.The stratigraphic sequence of the Fanjingshan Group is restored, and the main bodies are found to be grey medium thick metamorphic sandstone, siltstone and metagglutinite sandstone and sericite phyllite, slate, and multilayer, basic volcanic rocks, etc.The small diagonal bedding developed in the coarse turbidite sandstone in Tongchang formation, Waxi formation and in the Tongchang formation was measured in the field.The turbidite clastic rocks of the upper subgroup of the Fanjingshan group in northeastern Guizhou generally point to the north and the north to the east, which proves that their provenance comes from the south, and they continue to supply the clastic material .3to the north.Statistical analysis of coarse sandstone skeleton particles and triangular diagram of skeleton grain composition in Tongchang and Waxi formations show that the source of sedimentary strata of upper clastic rock series in Fanjingshan group is volcanic island arc .4.Samples of basalt and Anshan mass volcanic rocks with typical pillow structure in Huixiangping formation were collected in the field.The analysis of the geochemical characteristics of the whole rock shows that the tectonic environment is active continental margin and formed in the back-arc extension of .5.Based on the above research results and the comparison of the same tectonic environmental diagrams with the Shaojiwa formation and the basalt of the Xingzi group in Lushan area, it is inferred that the tectonic environment of the upper clastic rock series of the Fanjingshan group should be a back-arc extensional basin, that is, the marginal sea.Combined with the previous research results, it is analyzed and judged that the Fanjingshan group corresponds to the Sibao group exposed in northern Guangxi and southern Guizhou to form a complete arc basin system.It is inferred that during the depositional period of the upper clastic rock series in the upper part of the Fanjingshan Group, the Jiangnan orogenic belt is a west Pacific subduction orogenic belt or a western Pacific active continental margin.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P548;P512.2

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