滇西腾冲—保山地块岩浆作用研究及其构造意义

发布时间：2018-03-01 01:13

本文关键词： 滇西腾冲地块保山地块花岗岩类岩石学地球化学　出处：《中国地质大学(北京)》2016年博士论文　论文类型：学位论文

【摘要】：腾冲、保山地块是滇西特提斯构造带的重要组成部分,保山地块早古生代岩浆侵位活动主要集中在447~452 Ma和480~490 Ma两期,中-新生代花岗岩类侵位年龄为83~85Ma和60~66 Ma;腾冲地块中-新生代花岗岩类侵位年龄为115~118Ma、67~74 Ma和51~55 Ma。保山地块的岩石类型主要为二长花岗岩和正长花岗岩,富硅,K2O/Na2O比值均大于1,Al2O3含量较高,铝饱和指数A/CNK均大于1.1,标准矿物计算结果中均含有刚玉分子且含量都大于1%,为高钾钙碱性过铝质花岗岩;腾冲地块的岩石类型主要为花岗闪长岩、二长花岗岩和花岗岩,全碱含量高,绝大多数属于高钾钙碱性和钾玄岩系列,部分表现高分异钙碱性特征。保山地块的岩石总体上都富集Rb、K等大离子亲石元素和Pb,相对亏损高场强元素。平河岩基和赧洒岩株,具有明显的轻稀土富集,重稀土亏损的特征,球粒陨石标准化配分曲线显示明显的负Eu异常,而松坡、平达、勐堆三个淡色花岗岩株的稀土元素总量都比较低,(La/Yb)N比值较低,稀土元素分配曲线呈“雁式”平缓样式,体现A型花岗岩的特征。中-新生代岩体轻/重稀土分馏强烈,但岩浆结晶分异作用不同,两者与S型花岗岩接近。腾冲地块中-新生代岩石大部分具明显的轻/重稀土分馏,部分具“雁式”A型花岗岩特征,可能与岩石本身分异程度较高有关。保山地块锆石Hf同位素组成比较均一,εHf(t)均为负值,范围集中在-2.1~-12.4,对应的地壳模式年龄集中在1.6~2.2 Ga,推断其为古老地壳部分熔融的产物。腾冲地块不同时代岩石的εHf(t)变化范围较大,变化范围在-13.1~8.8之间,对应的地幔/地壳模式年龄变化范围在0.41~1.76 Ga之间,推断其来源于中上地壳并伴随有不同程度幔源物质的加入。由于与拉萨地体在时代、地球化学性质和构造记录方面的可对比性,腾冲、保山地块很可能与拉萨地体一样裂离自澳大利亚边缘,可能与古地理上位于澳大利亚北缘一侧的拉萨地体和古地理上位于印度大陆北缘一侧的特提斯喜马拉雅、安多、南羌塘一样,可能代表了面向原特提斯洋一侧的早古生代岩浆弧的一部分。
[Abstract]:The Tengchong and Baoshan massifs are an important part of the Tethys tectonic belt in western Yunnan. The early Paleozoic magmatic emplacement activities of the Baoshan massif are mainly concentrated in the two periods of 447 ~ 452 Ma and 480 ~ 490 Ma. The Mesozoic and Cenozoic granitic emplacement ages are 83 ~ 85 Ma and 60 ~ 66 Ma, respectively, while the Meso-Cenozoic granitic emplacement ages of the Tengchong block are 115 ~ (118) Ma ~ 67 ~ 74 Ma and 51 ~ 55 Ma. The rock types of Baoshan block are mainly monzogranite and syenite. The ratio of K _ 2O _ 2O to Na _ 2O _ 2O is higher than 1% Al _ 2O _ 3, and the Al saturation index A / C _ (K) is higher than 1.1. The standard mineral calculation results all contain corundum molecules and the contents are more than 1%, which are high potassium calc-alkaline peraluminous granites. The rock types of the Tengchong block are mainly granodiorite, monzogranite and granite, and the total alkali content is high, most of them belong to the high-potassium calc-alkaline and potash series. The rocks of Baoshan massif are generally enriched in RbGK and Pb, and are relatively depleted of high field strength elements. The Pinghe rock base and blushing rock plant have obvious characteristics of light rare earth enrichment and heavy rare earth depletion. The normalized distribution curve of chondrites showed obvious negative EU anomalies, while the total amount of rare earth elements in Songpo, Pingda and Mengdui pale granite strains were all relatively low, and the ratio of La- / Yb-N was lower, and the REE distribution curve showed a "geese" flat pattern. The characteristics of A-type granites are reflected. The light / heavy rare earth fractionation of Meso-Cenozoic rocks is strong, but the crystallization differentiation of magma is different, which is close to that of S-type granite. Most of the Meso-Cenozoic rocks in the Tengchong block have obvious light / heavy rare earth fractionation. Some of them are characterized by "Yan" A-type granite, which may be related to the higher degree of differentiation of the rocks themselves. The zircon HF isotopic composition of Baoshan block is relatively uniform, and 蔚 Hftis is negative. The range is -2.1 ~ 12.4, and the corresponding crustal model age is 1.6 ~ 2.2 Ga, which is inferred to be the product of partial melting of the ancient crust. The variation range of the rocks of the Tengchong block in different ages is larger, ranging from -13.1 to 8.8. The corresponding mantle / crustal model ages range from 0.41 to 1.76 Ga. It is inferred that the mantle / crust model originated from the upper and middle crust and was accompanied by the addition of mantle material to different degrees. In terms of geochemical properties and tectonic records, the Tengchong and Baoshan massif are likely to be split from the Australian margin just like the Lhasa terrane. Probably the same as the Lhasa terrane on the northern edge of Australia and the Tethys Himalayas, Ando and southern Qiangtang on the northern edge of the Indian continent. It may represent part of the early Paleozoic magmatic arc facing the side of the original Tethys Ocean.
【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】：2016
【分类号】：P588.1;P542

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