新疆伊犁盆地南缘侏罗系物源分析及盆山关系研究

发布时间：2018-08-25 19:42

【摘要】：伊犁盆地位于西天山造山带西南缘,侏罗系发育一套巨厚的陆源碎屑沉积岩,它记录了西天山的造山作用与伊犁盆地的沉积充填演化历史。对该套碎屑岩物源的系统研究可以清楚揭示西天山与伊犁盆地的盆山关系,为深入研究中生代中亚造山带西段的成盆-成山作用提供借鉴。同时,伊犁盆地是我国重要的砂岩型铀矿富集盆地,侏罗系是其主要赋矿层位。针对砂岩型铀矿的勘探,明确赋铀砂体成因,查明碎屑物来源,进而准确评估蚀源区岩石供铀能力具有极其重要的生产实践意义。基于此,本论文依托对伊犁盆地南缘露头的调查和典型剖面的精细测量,结合收集到的盆地内钻井岩心和测井资料,以沉积学、高分辨层序地层学、构造地质学、沉积地球化学等理论为指导,通过大量的岩石薄片的鉴定、岩屑和稳定轻矿物的统计,并结合野外古流向的测量和室内全岩元素地球化学、碎屑锆石年代学及微量元素地球化学、阴极发光等多种测试手段,对伊犁盆地侏罗系碎屑岩岩石学特征、高分辨层序格架内的古地理展布、碎屑物质来源、碎屑岩物源区母岩成分及形成时大地构造背景、盆地充填沉积特征与周缘造山带耦合关系进行了系统而深入的研究。伊犁盆地南缘侏罗系主要为中粗粒硅质岩屑砂岩、中粗粒岩屑石英砂岩及杂砂岩,分选中等-较差,大多数颗粒磨圆度呈次圆状-次菱角状,颗粒间主要为杂基充填,部分砂岩为钙质胶结,颗粒支撑,孔隙式胶结。碎屑颗粒中岩屑含量约占23-65%,石英约为32-74%,长石含量约为2-10%。砂岩成分和结构成熟度均较低,显示其近物源堆积的特征。伊犁盆地南缘侏罗系砂岩中岩屑主要为硅质岩岩屑、粉砂岩岩屑、泥岩岩屑,流纹岩、花岗岩等中酸性火成岩岩屑次之,另含少量石英岩岩屑;碎屑石英颗粒主要为单晶石英,大多数呈非波状消光特征,多晶石英颗粒边界呈平直线状接触,阴极发光显示蓝色或蓝紫光;长石含量少,且以来源于中酸性火山岩区的微斜长石等钾长石为主,少见中基性斜长石。碎屑颗粒组分特征表明物源区母岩来源于火山岩源区,砂岩碎屑组分Dickinson图解投点则显示该套碎屑岩形成于再旋回造山带环境,元素地球化学特征显示其母岩为大陆岛弧背景下长英质岩石,碎屑锆石年代学特征表明八道湾组碎屑岩来源于早中二叠世和石炭纪的岩石,三工河组和西山窑组主要来自石炭纪岩石,且随着时代越新,来自泥盆纪和志留纪物源贡献越大,表明侏罗纪时期物源区剥蚀具有揭顶特征。据此可知,伊犁盆地侏罗纪碎屑来源于再旋回造山带环境,物源区母岩主要形成于石炭纪大陆岛弧环境下中酸性火山-沉积岩系。伊犁盆地南缘侏罗纪时期主要发育扇三角洲-湖泊-辫状河三角洲-河流相沉积体系,其中八道湾组主要为扇三角洲沉积,三工河组主要为浅湖-半深湖沉积,西山窑组主要为辫状河三角洲沉积,头屯河组主要为河流相沉积。古植物叶片化石主要呈宽大平直特征,泥岩表现较强的Na、Ca和Sr亏损,且泥岩化学风化指数值(CIA)高达85~91,表明侏罗纪碎屑岩沉积时期为温暖、潮湿古气候环境。自晚泥盆世末期到晚石炭世,受古南天山洋向北俯冲作用的影响,在伊犁-中天山地块南缘发育大量大陆岛弧环境火山岩。晚石炭世末期,伊犁-中天山地块与塔里木地块碰撞,南天山造山带进入后碰撞演化阶段,并形成大量火山-碎屑岩。在早侏罗世早期,受盆地南缘快速隆升的影响,石炭纪-二叠纪火山-沉积岩地层被再次抬升遭受剥蚀,此时山体与盆地落差较大,坡度陡,粗粒碎屑物快速充填盆地,形成了八道湾组扇三角洲沉积;早侏罗世末期,湖盆迅速扩张,湖平面上升,沉积物供给量不足,形成了三工河组湖泊相沉积;中侏罗世后,受前期山体不断被剥蚀和盆地不断被充填的双重影响,山体与盆地相对高程差不断减少,湖平面不断萎缩,直至消失,形成了西山窑组辫状河三角洲沉积和头屯河组河流相沉积。总之,伊犁盆地南缘在侏罗纪沉积时期表现为明显的填平补齐的准平原化特征。
[Abstract]:The Yili basin is located in the southwestern margin of the western Tianshan orogenic belt. A set of thick terrigenous clastic sedimentary rocks developed in the Jurassic system, which records the orogeny of the western Tianshan Mountains and the history of sedimentary filling and evolution of the Yili basin. Meanwhile, Yili Basin is an important sandstone-type uranium enrichment basin in China, and Jurassic is its main ore-bearing horizon. It is very important to clarify the genesis of uranium-bearing sand bodies, ascertain the source of clastic materials and accurately evaluate the uranium-supplying capacity of rocks in the source area for sandstone-type uranium exploration. Based on the investigation of outcrop in the southern margin of Yili Basin and the fine measurement of typical section, the paper combines the collected drilling core and logging data in the basin, guided by the theories of sedimentology, high-resolution sequence stratigraphy, structural geology and sedimentary geochemistry, and identifies a large number of thin sections of rocks and rocks. Based on the statistics of clastic and stable light minerals, combined with field paleocurrent measurements and indoor whole-rock element geochemistry, detrital zircon chronology and trace element geochemistry, and cathodoluminescence measurements, the petrological characteristics of the Jurassic clastic rocks in the Yili Basin, paleogeographic distribution within the framework of high-resolution sequence, source of clastic materials, and clastic materials were studied. The compositions of parent rocks and the tectonic setting at the time of their formation, the coupling relationship between basin filling and sedimentary characteristics and the surrounding orogenic belts have been studied systematically and deeply. The clastic grains contain about 23-65% lithic debris, 32-74% quartz and 2-10% feldspar. The compositions and structures of the sandstones are low maturity, showing the characteristics of near provenance accumulation. The Jurassic sandstones in the southern margin of Yili Basin are sandstones. The intermediate debris is mainly siliceous, siltstone, mudstone, rhyolite, granite and other intermediate-acidic igneous rock debris, followed by a small amount of quartz rock debris; the detrital quartz particles are mainly monocrystalline quartz, most of them are non-wavy extinction characteristics, the boundary of polycrystalline quartz particles is flat linear contact, cathodoluminescence shows blue or blue violet. Light and feldspar content is low, and micro-plagioclase and other K-feldspar from intermediate-acidic volcanic rocks are dominant, but medium-basic plagioclase is rare. Characteristic of clastic grain composition indicates that source rocks originate from volcanic source area, while the Dickinson plot of sandstone clastic component shows that the clastic rocks were formed in the environment of recycle orogenic belt and the elements are geochemical. The clastic zircon chronology indicates that the clastic rocks of the Badaowan Formation originated from the Early-Middle Permian and Carboniferous rocks, and the Sangonghe Formation and Xishanyao Formation mainly originated from the Carboniferous rocks. With the development of the age, the contribution of the Devonian and Silurian provenances increased, indicating the Jurassic. It can be concluded that the Jurassic clastic rocks in Yili Basin originated from the environment of the recycling orogenic belt, and the parent rocks in the provenance area were mainly formed in the intermediate-acid volcanic-sedimentary rocks under the Carboniferous continental island arc environment. The fan delta-lake-braided River delta-fluvial facies were mainly developed in the southern margin of Yili Basin during the Jurassic. The Badaowan Formation is mainly fan-delta deposit, the Sangonghe Formation is mainly shallow-semi-deep Lake deposit, the Xishanyao Formation is mainly Braided River Delta deposit, and the Toutunhe Formation is mainly fluvial deposit. The values (CIA) are as high as 85-91, indicating that the Jurassic clastic rocks were deposited in a warm, humid paleoclimate. From the late Devonian to the Late Carboniferous, a large number of continental island-arc volcanic rocks were developed in the southern margin of the Ili-Zhongtianshan block due to the northward subduction of the Paleo-South Tianshan Ocean. In the early Early Jurassic, the Carboniferous-Permian volcanic-sedimentary strata were uplifted and eroded again under the influence of rapid uplift in the southern margin of the basin. At this time, the difference between the mountain and the basin was large, the slope was steep, and coarse-grained clastic materials filled the basin rapidly. The fan delta deposits of Badaowan Formation were formed; in the late Early Jurassic, the lake basin expanded rapidly, the lake level rose, and the sediment supply was insufficient, forming the lacustrine deposits of Sangonghe Formation; after the Middle Jurassic, the relative elevation difference between the mountain and the basin decreased and the lake level did not change because of the double effects of the erosion of the mountain body and the filling of the basin. The braided river delta deposits of Xishanyao Formation and fluvial deposits of Toutunhe Formation were formed by faulting and shrinking until disappearance.
【学位授予单位】：成都理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P619.14

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