中祁连西段肃北白石头沟辉长岩年代学、地球化学特征及地质意义  

Chronology and Geochemistry of Gabbro in Baishitougou area,the Western Segment of Central Qilian and Its Geological Implications

作　　者：杨国林 任文秀[2] 李军 王文佳 丁仨平 梁明宏[2] Yang Guolin;Ren Wenxiu;Li Jun;Wang Wenjia;Ding Sanping;Liang Minghong(BaiLie School of Petroleum Engineering,Lanzhou City University,Lanzhou,Gansu,730070,China;Gansu Geological Survey Institute,Lanzhou,Gansu,730000,China;College of Geography and Environmental Engineering,Lanzhou City University,Lanzhou,Gansu,730070,China)

机构地区：[1]兰州城市学院培黎石油工程学院,甘肃兰州730070 [2]甘肃省地质调查院,甘肃兰州730000 [3]兰州城市学院地理与环境工程学院,甘肃兰州730070

出　　处：《新疆地质》2022年第2期268-274,共7页Xinjiang Geology

基　　金：甘肃省自然科学基金项目(20JR5RA039);甘肃省区域地质调查片区总结与服务产品开发项目(12120113013500);兰州城市学院博士科研启动基金项目(LZCU-BS2018-11)共同资助。

摘　　要：为厘清白石头沟辉长岩体形成时代、成因及构造环境,对该岩体开展LA-ICP-MS锆石U-Pb同位素测年和地球化学特征分析。结果显示,岩体锆石^(206)Pb/^(238)U同位素加权平均年龄为(300.8±3.5)Ma,时代为晚石炭世。肃北地区白石头沟辉长岩之锆石在CL图像呈条痕状吸收,Th/U比值较高,为0.30~2.97,为典型岩浆成因锆石。辉长岩具较低的SiO2含量(48.01%~49.32%)、较高的Al2O3(16.90%~17.42%)和CaO含量(8.19%~9.71%);稀土总量较高,ΣREE=129.77×10^(-6)~145.53×10^(-6),具弱的Eu负异常,δEu=0.79,LREE/HREE=6.25~8.03,轻重稀土元素分馏相对明显,(La/Yb)_(N)=9.36~12.55,稀土元素分布模式呈右倾型。在微量元素蛛网图上,相对富集大离子亲石元素(LILE)Rb,Ba,Sr,亏损高场强元素(HFSE)Th,Nb,Ta,Ce,Zr,Hf。结合区域构造演化历史,表明肃北地区晚石炭世辉长岩体可能形成于板内伸展构造环境。In order to clarify the formation age,genesis and tectonic setting of the Baishitougou gabbro,LA-ICP-MS zircon U-Pb isotopic dating and geochemical characteristics were analyzed.The results show that the zircon ^(206)Pb/^(238)U iso-topeweighted mean age is 300.8±3.5Ma,which is at the turn of the Late Carboniferous.The selected zircons of pluton exhibit striped absorption in cathodoluminescence(CL)images,and have high Th/U ratios(0.30~2.97),implying a mag-matic origin.Gabbro in Baishitougou,Subei area has low content of SiO2(48.01%~49.32%),high content of Al2O3(16.90%~17.42%)and CaO(8.19%~9.71%).And have high REE(ΣREE=129.77×10^(-6)~145.53×10^(-6)),with slightly Eu anomalies(δEu=0.79),LREE/HREE=6.25~8.03,enrichment in LREE and relatively depletion in HREE[(La/Yb)_(N)=9.36~12.55].The rare earth element distribution patterns display as right-leaning.The trace element spider diagrams showed that they are enriched in LILE(Rb,Ba and Sr),moderately depleted of HFSE(Th,Nb,Ta,Ce,Zr and Hf).Combining with the tectonic implications,the Late Carboniferous gabbro was formed in intraplate extensional tectonic setting.

关 键 词：中祁连 肃北 辉长岩 SHRIMP锆石U-PB定年 晚石炭世 

分 类 号：P588.124[天文地球—岩石学]