滇西地区户撒盆地上新世沉积特征及物源分析

发布时间：2018-06-09 03:54

本文选题：滇西地区 + 户撒盆地　；参考：《中国地质大学(北京)》2017年博士论文

【摘要】：本文以滇西地区户撒盆地上新世芒棒组为研究对象,通过系统收集区域地质、遥感、物探、水文等基础研究资料,结合钻井岩心以及周缘露头观察、采样测试,开展对户撒盆地盆地基底、沉积特征、沉积物源及砂岩型铀成矿背景等研究,得到以下几点认识:(1)滇西户撒盆地周缘出露花岗岩,锆石U-Pb同位素年龄为49.28±0.66 Ma,属始新世。花岗岩具较高SiO_2(67.86%~72.04%),较高全碱(Na_2O+K_2O=7.62%~8.64%),高K_2O/Na_2O比值(1.53~3.09),富集Rb、Th、U、K、P、Nd、Sm等大离子亲石元素,亏损Nb、Ta、Zr、Hf、Ti等高场强元素,LREE/HREE比值为8.57~10.81,(La/Yb)N为10.34~14.35,轻、重稀土元素分馏明显,弱Eu异常(δEu=0.31~0.58)等特征。FeO*/MgO-10-4×Ga/Al图解、(K_2O+Na_2O)/CaO-(Zr+Nb+Ce+Y)图解和Sr、Ba、Eu、La、Yb元素特征指示盆地基底为弱分异花岗岩。铝饱和指数(A/CNK=1.00~1.14)、P_2O_5-SiO_2图解、Th(Y)-Rb图解表明盆地基底为I型花岗岩。Ni-Mg~#、Mg~#-SiO_2判别图解结合区域地质特征推测户撒盆地盆地基底为早期幔源物质侵入到地壳底部形成初生地壳,在后期热事件作用下,以古老基底地壳为主和初生地壳为辅的混合地壳部分熔融形成,与印度-欧亚大陆俯冲碰撞相关,是印度-欧亚大陆由碰撞期过渡为碰撞后伸展期的岩浆活动响应,碰撞结束时间在49 Ma之前。(2)户撒盆地上新世芒棒组根据岩性特征分为5段,新近发现的砂岩型铀矿异常层位主要位于芒棒组第一段、第二段、第三段,部分为芒棒组第四段、第五段。系统收集前人沉积相研究成果,结合野外剖面详尽观察以及42口(煤田钻孔36口,新近施工6口)钻孔资料得出:户撒盆地芒棒组第一段-第三段沉积类型为冲积扇、辫状河三角洲、扇三角洲、湖相等四种,可细分为10种亚相。冲击扇相岩性以土黄色、灰黄色厚层块状砾岩为主,夹含砾砂岩、粉砂岩,相带展布窄,以中部曼统-万明小寨和小寨-皇阁寺为典型。辫状河三角洲相带发育较齐全,其中辫状河三角洲前缘亚相最为发育,各相带均沿盆地北东-南西方向在缓坡带展布,相带展布窄。辫状河三角洲平原岩性以土黄色、灰黄色砾岩、细砂岩为主,夹含砾粗砂岩、泥岩,发育厚层褐煤,见底冲刷构造;辫状河三角洲前缘亚相岩性以灰色、灰绿色含砾粗砂岩、细砂岩为主,夹炭质泥岩、泥岩及煤线,见水平层理、交错层理、波状层理及底冲刷构造;前辫状河三角洲亚相岩性主要为灰色、灰绿色细砂岩、粉砂岩、泥岩为主,见水平层理、逆序层理。扇三角洲相展布不全,尤其前扇三角洲不甚发育,各相带沿盆地北东-南西方向在陡坡带展布,相带窄。扇三角洲平原亚相岩性主要为灰黄色、土黄色砾岩、含砾粗砂岩为主,夹少量粉砂岩;扇三角洲前缘亚相岩性主要为灰色、灰绿色含砾粗砂岩、中砂岩为主,夹细砂岩、粉砂岩、泥岩、煤线薄层,见底冲刷构造;前扇三角洲亚相岩性主要为灰色、灰绿色细砂岩为主,夹泥岩薄层,见水平层理。滨浅湖相岩性主要为灰绿色、灰白色泥岩组成,见水平层理,以芒困-曼板一带最为发育。缓坡带物源主要来自盆地北西方向,以发育辫状河三角洲相和冲积扇相为主;陡坡带物源来自南东方向,以扇三角洲相为主;中部凹陷带为来自北西和南东双物源,以发育滨浅湖相为主。户撒盆地缓坡带辫状河三角洲相展布较广,具“泥-砂-泥”结构,有利于后期含铀含氧水顺层侵入形成砂岩型铀矿,该盆地已发现砂岩型铀矿矿化显示位于该相带。(3)户撒盆地芒棒组新近发现有砂岩型铀矿成矿显示,碎屑沉积岩源岩及其风化作用是控制砂岩型铀矿成矿物质(U)来源的重要影响因素,泥岩地球化学特征可用于研究碎屑沉积岩源岩及其风化作用。δCe-δEu、δCe-∑REE、δCe-(Dy/Sm)N以及A-CN-K图解表明:芒棒组第三段泥岩地球化学组成较少受成岩作用影响,泥岩地球化学组成较好的保存了其物源和风化作用信息。δEu、Th/Sc、Al_2O_3/TiO_2、以及K_2O-Rb、Co/Th-La/Sc、La/Yb-∑REE、La-Th-Sc图解得出:芒棒组第三段碎屑沉积岩物源主要为周缘花岗岩,少量为高黎贡山群变质岩。综合ICV、SiO_2/Al_2O_3及区域构造演化和沉积相特征得出:芒棒组第三段碎屑沉积岩为活动构造环境下再循环沉积物的快速沉积产物。Rb/Sr、Fe/Mn、CIA、CIW、PIA分析表明:芒棒组第三段碎屑沉积岩源岩经历了强烈化学风化作用。户撒盆地芒棒组碎屑沉积岩源岩主要为始新世花岗岩,少量为高黎贡山群变质岩,花岗岩U含量较高,为砂岩型铀矿成矿的良好铀源;另一方面,物源区经历了强烈化学风化作用,化学风化作用越强U溶解迁移越多,砂岩型铀矿容矿层富集U相应增大;因此沉积物源为花岗岩且经历强烈化学风化作用可为砂岩型铀矿成矿提供充足铀源。(4)沉积环境及沉积期古气候制约着碎屑沉积岩还原介质含量以及含铀含氧水能否下渗,推移,是砂岩型铀矿能否成矿的影响因素之一。通过对芒棒组第二段泥岩进行地球化学组成分析,明确了其古盐度、古气候以及氧化还原环境。δCe-δEu、δCe-∑REE以及δCe-(Dy/Sm)N图解表明:样品地球化学组成受成岩作用影响较小,较完整保存了环境信息。Cl、B、Sr、B/Ga、Sr/Ba、Sr/Ca及B-Ga-Ra图解分析得出:芒棒组第二段为淡水沉积。Rb/Sr、Mg/Ca、Fe/Mn、SiO_2/Al_2O_3、(La/Yb)N等比值说明:芒棒组第二段古气候为温暖潮湿环境,温暖、潮湿环境下形成的含煤碎屑岩建造还原介质充足,是砂岩型铀矿良好的容矿空间。Ce/Ce*、Eu/Eu*、V/Cr、V/Sc、Ce/La、V/(V+Ni)、V/(V+Cr)等比值研究得出:户撒盆地芒棒组第二段沉积水体总体为还原环境,部分过渡为氧化-还原环境。氧化环境下周源剥蚀区U元素剥蚀带走,顺层侵入早期还原环境形成的含煤碎屑岩建造富集成矿,因此沉积水体由还原环境向氧化-还原环境的转化有助于形成砂岩型铀矿。(5)户撒盆地芒棒组第二段砂岩地球化学分析表明:砂岩主要为长石砂岩和杂砂岩,少量为页岩;矿物成分主要为石英、钾长石、斜长石和伊利石等;REE配分模式曲线一致,LREE/HREE=9.75~15.91,平均13.24,(La/Yb)N=13.06~26.41,平均19.21,轻稀土元素相对重稀土元素明显富集,稀土元素分馏明显。SiO_2/Al_2O_3=2.06~6.01,平均4.60,ICV=0.54~1.09,平均0.86,结合沉积特征表明:样品为被动构造环境下沉积物的再循环而成,而非强烈风化作用过程中形成的第一次旋回沉积物。Th/U=5.44%~12.10%,平均8.48%,CIA矫正均值为69,反映了温暖、湿润条件下的中等化学风化作用。A-CN-K判别图说明交代作用降低了CIA值、且样品源岩钾长石比斜长石含量高。Th/Sc=4.43~25.35,平均8.18,Rb-K_2O图解、Co/Th-La/Sc图解和La/Yb-∑REE图解表明样品物源为花岗岩。TiO_2-(Fe2O3T+MgO)、Al_2O_3/(Cao+Na_2O)-(Fe2O3T+MgO)、La-Th-Sc以及(K_2O/Na_2O)-SiO_2构造判别图解表明:侏罗世-早白垩世花岗岩形成于被动大陆边缘环境,与中特提斯洋在晚侏罗世-早白垩世已经打开且长期稳定相对应。户撒盆地为沿早期户撒走滑-挤压断裂拉张沉积形成,接受周缘侏罗世-早白垩世和始新世花岗岩沉积。上述研究成果和认识不仅有助于了解滇西地区小型山间盆地基底、沉积环境、沉积物源及沉积古气候特征,而且还为该区域砂岩型铀矿下一步找矿勘察工作提供指导。
[Abstract]:In this paper , the characteristics of the basement , sedimentary characteristics , sediment source and sandstone - type uranium ore - forming background are studied by means of systematic collection of basic research data such as regional geology , remote sensing , geophysical prospecting , hydrology and so on . The results are as follows : ( 1 ) The REE / HREE ratio is 49.28 卤 0.66 Ma , and the REE / HREE ratio is 10.34 - 14.35 , and the characteristics of REE / HREE are 10.34 - 14.35 , and the characteristics of REE / HREE are 10.34 - 14.35 , and the characteristics of REE / HREE are as follows : ( 1 ) The REE / HREE ratio is 8.57 ~ 10.81 , the REE fractionation is low , the weak Eu anomalies ( 未Eu = 0.31 ~ 0.58 ) , and the characteristics of Sr , Ba , Eu , La and Yb indicate that the basement of the basin is weakly - differentiated granite . The saturation index of Al ( A / CNK = 1.00 ~ 1.14 ) , P _ 2O _ 5 - SiO _ 2 is illustrated . Th ( Y ) - Rb diagram shows that the basement of the basin is type I granite . The basement of the basin is inferred from the regional geological characteristics . The basement of the basin is formed by the intrusion of the early mantle source material into the crust at the bottom of the crust . Under the action of late thermal events , the crust of the old basement and the mixed crust of the primary crust are melted and formed . It is related to the subduction of the India - Eurasia continental crust . It is the magmatic activity response of the Indo - Eurasia continent from the collision period to the post - collision extension period . The end time of the collision is before 49 Ma . The sedimentary facies of braided river delta are mainly gray , gray - yellow conglomerate and fine sandstone . The sub - facies lithology of the fan delta plain is mainly gray , gray and green , mainly gray , gray - green and coarse sandstone , with a small amount of silty sandstone . The sub - facies lithology of the fan delta is mainly gray , gray - green fine sandstone , mudstone and coal - line thin layer , and it is mainly composed of gray - green fine sandstone , mudstone and coal - line thin layer . ( 3 ) The formation of sandstone - type uranium deposits is newly discovered in the Munro Formation in the Hushai Basin . The clastic sedimentary rock source rocks and their weathering functions are the important factors controlling the source rocks of sandstone - type uranium deposits . ( 4 ) The sedimentary environment and the ancient climate restrict the contents of the reducing media of clastic sedimentary rocks and whether the uranium - containing oxygen - containing water can be infiltrated and advanced , which is one of the factors affecting the formation of sandstone - type uranium deposits . ( 5 ) The analysis of sandstone in the second section of the Mangrod Formation in the Husa Basin indicates that the sandstone is mainly of feldspar sandstone and complex sandstone , and the small amount is shale ; the mineral composition is mainly quartz , potash feldspar , orthite and Illite etc . The REE distribution pattern curve is consistent , LREE / HREE = 9.75 - 15.91 , average 13.24 , ( La / Yb ) N = 13.06 - 26.41 , average 19.21 , and the average value of the light rare earth element is 9.75 - 15.91 , average 19.21 , and the average value of the light rare - earth element is 4.43 - 25.35 , the average is 8.18 ;
【学位授予单位】：中国地质大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P619.14;P534.622

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