滇西龙陵象达—平达地区中—新生代花岗岩地球化学特征及其构造意义

发布时间：2018-09-03 17:26

【摘要】：龙陵县象达-平达地区位于滇西古特提斯构造域的东段,是冈瓦纳大陆与欧亚陆块南缘相碰撞的结合部,对研究古特提斯造山作用和寻找有色金属矿产有重要意义。本文以出露于象达-平达地区的中-新生代花岗岩为研究主体,对其岩石学、地球化学特征进行比较细致的研究,结合岩石年代学、区域地质学、岩石大地构造学等方面的研究探讨花岗岩的成因与构造环境,获得的主要结论概括如下：(1)研究区出露的中-新生代花岗岩主要有三期：分布在象达乡的侏罗纪花岗岩；分布在象达东边和平达乡两侧的白垩纪花岗岩；分布在勐堆北部地区的古近纪花岗岩。(2)三期花岗岩均具有“富铝-钠、高镁-钾”的特点。属强过铝花岗岩,具有高钾钙碱性岩的特点；稀土元素总量较高；轻、重稀土元素的分馏较为强烈。侏罗纪花岗岩与张旗等(2006)所称的高Sr低Yb花岗岩(埃达克岩)相同；而白垩纪和古近纪花岗岩在Sr-Yb图解中落入低Sr低Yb到极低Sr高Yb花岗岩区。(3)三期花岗岩主要落在Pearce (1994)重新定义的Post-COLG(即后碰撞花岗岩),与Hf-Rb-Ta图解的投影结论较吻合。(4)侏罗纪花岗岩具有钾质C型埃达克岩特征,可能形成于加厚地壳开始减薄及地壳从挤压向拉张伸展转换的环境；为下地壳内的底侵玄武岩在榴辉岩相的部分熔融产物；白垩纪和古近纪花岗岩可能是在正常地壳厚度下差异性深度上的部分熔融产生的,也可能是区域拉张环境下的减薄地壳部分熔融的产物。(5)结合近年来完成的地质资料分析,怒江-昌宁-孟连结合带以西广泛出露的晚中生代花岗岩总体上具有连续演化的趋势,特别是在Sr-Yb图解中表现更为清晰：蚌渺岩体属高Sr低Yb型花岗岩,腾冲微地块东缘的中侏罗世花岗岩主要为低Sr低Yb型花岗岩,早白垩世花岗岩的低Sr高Yb型花岗岩,晚白垩世花岗岩主要属极低Sr高Yb型花岗岩,少数为低Sr高Yb型；可能反映了后碰撞→后造山构造背景的演化过程中岩浆源区逐渐向上迁移、压力环境逐渐降低的过程。
[Abstract]:The Xiangda-Pingda area of Longling County is located in the eastern part of the PaleoTethys tectonic domain in western Yunnan. It is the confluence of the southern margin of Gondwana continent and Eurasian continental block, which is of great significance to the study of the Paleotesian orogeny and the exploration of non-ferrous metal minerals. In this paper, the Mesozoic and Cenozoic granites exposed in Xiangda Pingda area are taken as the main body of study. The petrology and geochemistry of granites are studied in detail, combined with petrochronology and regional geology. The main conclusions are summarized as follows: (1) the Meso-Cenozoic granites in the study area mainly have three periods: Jurassic granites distributed in Xiangda Township; Cretaceous granites distributed in the east of Xiangda and Pingda Township, and Paleogene granites in northern Mengdui. (2) the third stage granites have the characteristics of "rich aluminum-sodium and high magnesia-potassium". It is a strong peraluminous granite with the characteristics of high potassium calc-alkaline rock, high rare earth elements and strong fractionation of light and heavy rare earth elements. Jurassic granite is the same as Zhangqi et al. (2006) called high Sr low Yb granite (Adakite); The Cretaceous and Paleogene granites fell into the low Sr low Yb to very low Sr high Yb granite areas in the Sr-Yb diagram. (3) the third stage granites mainly fall in the Post-COLG (post-collision granite) redefined by Pearce (1994), which is consistent with the projection results of the Hf-Rb-Ta diagram. (4) Jurassic granites are characterized by K-C type adakite. It may be formed in the environment where the thickened crust begins to thinning and the crust is transformed from compression to extensional extension, which is the partial melting product of the underthrust basalt in the lower crust in the eclogite facies. The Cretaceous and Paleogene granites may have resulted from partial melting at different depths under normal crustal thickness, or may be the product of partial melting of thinned crust in a regional extensional environment. (5) Analysis of geological data completed in recent years. The late Mesozoic granites, widely exposed to the west of the Nujiang Changning Menglian junction belt, have a general trend of continuous evolution, especially in the Sr-Yb diagram. The oysterian granites belong to high Sr low Yb type granites. The middle Jurassic granites in the eastern margin of the Tengchong microblock are mainly low Sr low Yb type granites, the early Cretaceous granites are low Sr high Yb type granites, the late Cretaceous granites are mainly very low Sr high Yb type granites, and a few are low Sr high Yb type granites. It may reflect the gradual upward migration of magmatic source region and the decrease of pressure environment during the evolution of post-collision and post-collision orogenic tectonic setting.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.121

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