青海省东昆仑五龙沟地区加里东期、印支期花岗岩成因及构造意义与控矿意义研究

发布时间：2018-03-23 07:03

本文选题：Hf同位素　切入点：锆石U-Pb定年　出处：《吉林大学》2016年硕士论文　论文类型：学位论文

【摘要】：东昆仑造山带可以分为东昆北带、东昆中带和东昆南带三个次级构造单元。五龙沟地区就位于东昆中带中东段。沿着东昆中断裂和东昆南断裂发育两条蛇绿岩带,一般认为其分别代表了原特提斯洋和古特提斯洋的存在。五龙沟地区以大面积花岗岩、多个造山型金矿床和矽卡岩型铜多金属矿点发育为特征。通过对五龙沟地区的五龙沟花岗闪长岩、小垭口花岗岩和猴头沟二长花岗岩开展岩石地球化学分析和LA-ICP-MS锆石U-Pb定年研究,表明猴头沟二长花岗岩的206Pb/238U加权平均年龄值为(419.0±1.9)Ma;该花岗岩富Si O2、K2O、贫Al2O3、贫Sr、富Y和Yb,具有强烈的负铕异常,Rb、Th、U、La、Ce、Nd相对富集,Nb、Ta高场强不相容元素亏损,Ba、Sr、P、Ti强烈亏损,为典型的造山后A2型花岗岩;由此表明原特提斯洋在东昆仑地区的最晚闭合时限应该不晚于晚志留世末期(~419Ma),而不是前人认为的早泥盆世。获得原被认为属于新元古代的五龙沟花岗闪长岩样品的206Pb/238U加权平均年龄值分别为247±2、248±1和249±1Ma;该花岗闪长岩为准铝质花岗岩,铝的饱和指数为0.90~0.96,低Fe2O3T/Mg O比值,低Zr+Nb+Ce+Y含量,表明其属于I型岛弧花岗岩;获得原被认为属于新元古代的小垭口花岗岩样品的206Pb/238U加权平均年龄值为246±3 Ma;该花岗岩高铝质其铝的饱和指数为1.02~1.03,(La/Yb)N值为16.98~25.07,Sr/Y比值为17.68~28.77,重稀土含量亏损(Yb=1.10×10-6~2.00×10-6)和贫Y(13.00×10-6~21.10×10-6),表明其为类埃达克岩。综上分析表面五龙沟的花岗闪长岩和小垭口的花岗岩产生于早印支期东昆仑断裂带和巴颜喀拉-松潘甘孜造山带之间古特提斯洋板片向北部俯冲的过程。猴头沟二长花岗岩中锆石的Hf同位素结果显示,锆石εHf(t)值为0.2~5.1,对应二阶段模式年龄(TDM2)为1066~1371Ma,推测花岗岩源区来自中元古代镁铁质下地壳部分熔融。五龙沟花岗闪长岩中锆石εHf(t)值为-2.9~+3.9,对应的二阶段模式年龄(TDM2)为997~1436Ma;小垭口花岗岩的锆石εHf(t)值为-7.8~+3.2,对应的二阶段模式年龄(TDM2)为1047~1735Ma;由此推测这些三叠纪岩浆均来源于镁铁质中元古代下地壳部分熔融,但是五龙沟花岗闪长质岩浆遭受老地壳的同化混染作用要比小垭口花岗质岩浆强烈。
[Abstract]:The East Kunlun orogenic belt can be divided into three sub-tectonic units: the East Kunming North Belt, the East Kunming Middle Belt and the East Kunn South Belt. The Wulonggou area is located in the middle and eastern part of the East Kunming Middle Belt. Two ophiolite belts are developed along the Dongkunzhong fault and the East Kunnan fault. It is generally considered that it represents the existence of the original Tethys Ocean and the PaleoTethys Ocean, respectively. The Wulonggou area is a large area of granite. The development of multiple orogenic gold deposits and skarn copper polymetallic ore sites is characterized by the analysis of the Wulonggou granodiorite in the Wulonggou area. The Xiaoyakou granite and the Erzhigou granite have been studied by geochemistry and LA-ICP-MS zircon U-Pb dating. The results show that the weighted average age of 206Pb/238U of Ertougou monzogranite is 419.0 卤1.9 Ma.The granite is rich in Sio _ 2 K _ 2O, Al _ 2O _ 3, Sr, Y and Yb, and has a strong negative EU ~ (3 +) anomaly. It is a typical post-orogenic A2 type granite. This indicates that the last time limit for the closure of the original Tethys in the East Kunlun region should not be later than the late Silurian end of the late Silurian, rather than the early Devonian considered by previous generations. Samples of the granodiorite considered to belong to the Neoproterozoic era were obtained. The weighted average age of 206Pb/238U is 247 卤2248 卤1 and 249 卤1 Ma.The granodiorite is quasi-aluminous granite. The saturation index of aluminum is 0.90 ~ 0.96, the ratio of Fe2O3T/Mg to O is low, and the content of Zr NB ce Y is low, which indicates that it belongs to I-type island arc granite. The weighted average age of Xiaoyakou granite considered to belong to Neoproterozoic is 246 卤3 Ma.The saturation index of aluminum in the granite is 1.02U 1.03G / YbN = 16.980.07% Sr-r-Y ratio is 17.68nb 28.77, Yb 1.10 脳 10-6U 2.00 脳 10-6) and poor Yb1.00 脳 10-621.10 脳 10-6), indicating that the content of Yb1.10 脳 10-62.00 脳 10-621.10 脳 10 ~ (-6) and Yb1.10 脳 10-621.10 脳 10 ~ (-6). The granodiorite on the surface of Wulonggou and the granite at Xiaoya pass are derived from the early Indosinian East Kunlun fault zone and the Bayankara-Songpan Ganzi orogenic belt. The paleotertes plate subducts to the north. The HF isotopic results of zircon in the Ertougou monzogranite show that, The zircon 蔚 Hft1 (corresponding to TDM2) is 1066 / 1371Ma. it is inferred that the source region of the granite originated from partial melting of the lower crust of Mesoproterozoic magnesite. The zircon 蔚 Hftt of the granodiorite in the Wulonggou granodiorite is -2.9 ~ 3.9 and the corresponding two-stage model age is TDM2). The zircon 蔚 Hft2 of the Xiaoyakou granite is -7.8 ~ 3.2and the corresponding two-stage model age (TDM2) is 104747 / 1735Ma. it is assumed that these Triassic magmas all originated from the partial melting of the lower Proterozoic crust of the Mesoproterozoic. But Wulonggou granodiorite magma suffered from assimilation mixing of the old crust is stronger than Xiao-Yakou granitic magma.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P588.121;P612

【相似文献】