滇西耿马大山三叠纪花岗岩的地球化学、锆石U-Pb年代学及其意义

发布时间：2018-03-16 21:43

本文选题：岩石地球化学　切入点：锆石U-Pb年龄　出处：《昆明理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：滇西保山地块东缘与昌宁-孟连结合带之间的漕涧-耿马-西盟-孟连一线出露有一系列的三叠纪二长花岗岩,构成一条长约500km的花岗岩带,主要岩体包括漕涧铁厂岩体、昌宁薅坝地岩体、永德云岭岩体、耿马大山岩体及孟连勐阿岩体。虽然在规模上远不及昌宁-孟连结合带东侧的碧罗雪山-临沧花岗岩带,但同样记录了昌宁-孟连洋盆关闭后的弧-陆碰撞造山作用过程及相关的成矿地质作用。本文以其中的耿马大山岩体为研究对象,通过详细的野外地质调查,从岩石地层、地球化学特征及年代学数据来解析耿马大山花岗岩的侵位时代、成因类型和物质来源,为全面认识耿马大山花岗岩的岩石成因和构造背景以及与临沧花岗岩之间的联系提供新的见解。耿马大山岩体位于昌宁-孟连结合带西侧的保山地块之耿马被动边缘上,是由三叠纪的花岗闪长岩-二长花岗岩与古近纪的闪长玢岩-花岗闪长斑岩-二长花岗岩组成的复式花岗岩基。研究结果表明,三叠世花岗岩具有高硅ω(Si02)为65.54%～70.04%,富钾(K20/Na2O)=1.26～3.58(平均为 1.94),贫钙ω(CaO)=0.86%～3.57%,全碱含量较低(alk=4.04%～7.69%),A/CNK为0.95～1.70,平均为1.1731.1,具有高钾钙碱性过铝质-强过铝质花岗岩的特征。岩石富集大离子亲石元素,亏损高场强元素,稀土总量为214.26×10-6～276.06×10-6(平均 241.81×10-6),LREE/HREE 比值介于 7.39～10.27,平均为8.93,(La/Yb)N为6.63～13.44,具有明显的轻重稀土分馏;(La/Sm)N为3.51～4.31,轻稀土分异明显;δEu为0.50～0.68,平均为0.58,稀土元素球粒陨石标准化配分曲线为明显的右倾型,并显示中等程度的负铕异常。LA-ICP-MS锆石的U-Pb定年结果显示,耿马大山花岗岩的结晶年龄大致集中在225-239Ma,表明该岩体侵位于中-晚三叠世。在ACF图解和Si02-Zr判别图中显示耿马大山花岗岩为S型花岗岩,其源岩为富含长石的碎屑岩。在Nb-Y和Rb-Y+Nd及Hf-Rb/30-Ta×3的构造环境判别图解中具有后碰撞花岗岩的环境。综合以上岩石地球化学特征、锆石定年结果及区域地质背景分析,耿马大山三叠纪花岗岩是弧(陆)-陆碰撞过程中深部洋壳的反向俯冲导致地幔物质上涌熔融中、下地壳,形成以中、下地壳物质组分为主,伴随有少量地幔物质组分参与的壳幔混合型花岗质岩浆;形成的构造背景可能为古特提斯洋关闭后,弧-陆碰撞过程中深部洋壳向西的反向俯冲作用所导致。
[Abstract]:Between the eastern margin of Baoshan block and Changning Menglian junction belt in western Yunnan, a series of Triassic granitic granites appeared on the line between Caojian, Gengma, Ximengmeng and Menglian, forming a granite belt about 500 km long. The main rock mass includes the Caojian Tiechang rock body. The Changning Huabadi, Yongde Yunling, Gengma Dashan and Menglian Menga rock bodies are far smaller in size than the Bello Snow Mountain Lincang granite belt east of the Changning-Menglian joint belt. However, the orogenic processes of arc-land collision and related ore-forming geological processes after the closure of the Changning-Menglian ocean basin were also recorded. Geochemical characteristics and chronological data are used to analyze the emplacement age, genetic type and material source of Gengma Dashan granite. It provides a new understanding of the petrogenesis and tectonic setting of Gengma Dashan granite and its relationship with Lincang granite. Gengma Dashan granite is located on the Gengma passive edge of Baoshan block in the west of Changning-Menglian junction belt. It is a composite granite base composed of granodiorite-dicorite granodiorite and Paleogene diorite porphyry granodiorite monzomorphic granodiorite granodiorite monzogranite. The Triassic granites have a high silicon content 蠅 -Si _ (02) = 65.54 / 70.04, potassium rich K ~ (20 / Na _ 2O) = 1.263.58 (mean = 1.94, Ca ~ (2 +)) ~ (0.86) = 3.57, the total alkali content is lower than 7.69A / C _ (CNK) = 0.955.69 ~ (1.70) with an average of 1.1731.1a, which is characterized by high potassium calc-alkaline peraluminous and strong peraluminous granites. The rocks are enriched with large ionophile elements. Loss of high field strength elements, The total amount of rare earth is 214.26 脳 10-6 / 276.06 脳 10-6 (average 241.81 脳 10-6 / L REE / hree = 7.39 / 10.27, mean = 8.93% / YbN = 6.63 / YbN = 6.63 / 13.44), and the light rare earths are significantly different from each other, the 未 EU is 0.50 ~ 0.68, the average is 0.58, and the standardized distribution curve of chondrites is obviously right-tilted. The U-Pb dating results of zircon from LA-ICP-MS show that the negative europium anomaly is moderate. The crystallization age of Gengma Dashan granite is about 225-239 Ma, which indicates that the intrusion occurred in the middle and late Triassic. The ACF diagram and Si02-Zr discriminant diagram show that Gengma Dashan granite is S-type granite. The source rocks are clastic rocks rich in feldspar. In the tectonic environment discriminant diagrams of Nb-Y, Rb-Y ND and Hf-Rb/30-Ta 脳 3, there is a post-collision granite environment. The geochemistry of the above rocks, zircon dating results and regional geological background are analyzed. Gengma Dashan Triassic granites were formed mainly in the middle and lower crust by reverse subduction of deep oceanic crust in the process of arc-continental collision, which resulted in the upwelling and melting of mantle material. The crustal and mantle mixed granitic magma is accompanied by a small amount of mantle material components, and the tectonic setting may be caused by the reverse subduction of the deep oceanic crust westward during the arc-continent collision after the closure of the PaleoTethys ocean.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P597.3;P588.121

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