东天山哈尔里克地区晚石炭世淡色花岗岩成因及其地质意义  

Petrogenesis and Geological Implications of Late Carboniferous Leucogranites in Harlik Area,Eastern Tianshan

作　　者：朱小辉[1,2,3] 朱涛[1] 张欣[1] 奚任刚 孟勇[1] 王凯[1] Zhu Xiaohui;Zhu Tao;Zhang Xin;Xi Rengang;Meng Yong;Wang Kai(Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits,Ministry of Natural Resources Xi'an Center of Geological Survey,China Geological Survey,Xi'an 710054,China;State Key Laboratory of Continental Dynamics,Northwest University,Xi'an 710069,China;Department of Geology,Northwest University,Xi'an 710069,China)

机构地区：[1]中国地质调查局西安地质调查中心,自然资源部岩浆作用成矿与找矿重点实验室,陕西西安710054 [2]西北大学大陆动力学国家重点实验室,陕西西安710069 [3]西北大学地质学系,陕西西安710069

出　　处：《地球科学》2018年第12期4443-4458,共16页Earth Science

基　　金：国家自然科学基金项目(No.41402051);中国地质调查局工作项目(Nos.1212012110000026,DD20179395)

摘　　要：淡色花岗岩对深入理解造山带构造演化具有重要意义.哈尔里克山南麓小铺地区出露多种类型的淡色花岗岩脉,包括黑云母花岗岩、二云母花岗岩、含电气石花岗岩以及含石榴石花岗岩.岩石地球化学研究显示这些淡色花岗岩整体具有高硅(SiO2=73.22%~75.12%)、铝(Al2O3=13.59%~14.49%)、碱(ALK=7.11%~9.67%),低钛(TiO2=0.01%~0.14%)、铁(TFeO=0.26%~1.37%)、镁(MgO=0.09%~0.46%)、钙(CaO=0.46%~1.92%)的特点,属于弱过铝质钙碱性-钾玄岩系列岩石.其中黑云母花岗岩具有较高的CaO/Na2O比值(0.46~0.47)和低的Rb/Sr比值(0.31~0.33),指示其为砂质源岩经黑云母脱水熔融形成;二云母花岗岩和含电气石花岗岩具有较低的CaO/Na2O比值(0.11~0.31)和高的Rb/Sr比值(1.41~3.75),为泥质源岩经白云母脱水熔融形成;含石榴石花岗岩具有强烈的Eu负异常以及“海鸥状”稀土配分模式,为高分异型花岗岩.小铺淡色花岗岩初始岩浆温度较低(T=637~744℃),结合其野外地质特征,认为其形成可能与深部物质的折返、造山带的伸展垮塌有关.利用LA-ICP-MS微区原位锆石U-Pb定年获得黑云母花岗岩的形成时代为308.5±2.2Ma,含电气石花岗岩的形成时代为307.8±2.3Ma,二者在误差范围内近乎一致,指示哈尔里克地区在晚石炭世末处于伸展构造背景.The leucogranite provides key insights into the tectonic evolution of orogenic belt. Petrology, geochemistry and geochronology results show that there are four types of leucogranites in the Xiaopu area in the southern piedmont of the Harlik area, eastern Tianshan, including the biotite leucogranite, two-mica leucogranite, tourmaline-bearing leucogranite and garnet-bearing leucogranite. These leucogranites are rich in silica (SiO2=73.22%-75.12%), aluminium (Al2O3=13.59%- 14.49% ), alkali(ALK=7.11%-9.67%), but low in titanium (TiO2=0.01%-0.14%), iron(TFeO=0.26%-1.37%), magnesium (MgO=0.09%-0.46%) and calcium (CaO=0.46%-1.92%), which belong to the calc-alkaline to shoshonite peraluminous granite. The high CaO/Na2O (0.46-0.47) and low Rb/Sr (0.31-0.33) ratios of the biotite leucogranite imply that it was formed by the biotite dehydration of greywacke, whereas the low CaO/Na2O (0.11- 0.31) and high Rb/Sr (1.41-3.75) ratios indicate that the two-mica and tourmaline-bearing leucogranites were formed by the muscovite dehydration of meta-pelitic-arenaceous sedimentary rocks, and the strong negative Eu anomalies and “seagull forms” REE patterns reveal that the garnet-bearing leucogranite belongs to highly fractionated granite. Considered the geological features and low initial temperature (T=637-644℃), the Xiaopu leucogranites were probably formed related to the exhumation of deep material, or extensional collapse of the orogen. Zircon U-Pb results show that the formation ages of biotite and tourmaline-bearing leucogranites are 308.5±2.2Ma and 307.8±2.3 Ma, respectively. Combining with the previous data, it is suggested that the Harlik area was in extensional tectonic setting in the Late Carboniferous.

关 键 词：锆石U-PB定年 淡色花岗岩 后碰撞 哈尔里克 地球化学 

分 类 号：P59[天文地球—地球化学]