北大巴山花栎村镁铁质岩地球化学、年代学及其构造环境制约  

Geochemistry and geohronology of Hualicun mafic rocks in North Daba Mountain and tectonic control

作　　者：许光[1,2] 王坤明 王宗起[3] 张英利[3] 王刚[3] 武昱东[3] XU Guang;WANG Kunming;WANG Zongqi;ZHANG Yingli;WANG Gang;WU Yudong(School of Earth Sciences and Mineral Resources,China University of Geosciences,Beijing 100083,China;China Geological Survey,Beijing 100037,China;MNR Key Laboratory of Metallogeny and Mineral Assessment/Institute of Mineral Resources,CAGS,Beijing 100037,China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]中国地质调查局,北京100037 [3]中国地质科学院矿产资源研究所/自然资源部成矿作用与资源评价重点实验室,北京100037

出　　处：《地质通报》2018年第7期1279-1290,共12页Geological Bulletin of China

基　　金：国家自然科学基金项目<陕西紫阳镁铁质岩墙群矿物学;同位素地球化学特征及其对岩浆源区环境的指示>(批准号:41602061);中国地质科学院基本科研业务费项目<我国青藏高原周缘三叠系中锂等能源金属的成矿机制研究>(编号:JYYWF201814)

摘　　要：北大巴山岚皋花栎村镁铁质岩为一套辉绿岩、辉长辉绿岩、辉绿玢岩和辉长岩组合,主要组成矿物为单斜辉石、长石,副矿物主要为铁钛氧化物等。镁铁质岩地球化学特征表现为高TiO_2(2.26%~7.30%)、TFe_2O_3(11.17%~17.0%)、较低的MgO(2.96%~5.52%)及较高的全碱含量(K_2O+Na_2O=3.07%~6.76%),属于典型的碱性辉长岩系列,Mg~#值(36~42)较高,表明岩体来源于高度演化的岩浆。微量元素特征显示富集大离子亲石元素Ba、Pb,稀土元素配分曲线显示明显的轻稀土元素富集特征(La_N/Yb_N=9.34~13.05),微量和稀土元素综合显示似洋岛玄武岩的地球化学特征。花栎村镁铁质岩LA-ICP-MS锆石年龄为436.9±2.4Ma,与相邻地区岩体形成年代一致,综合限定北大巴山地区岩浆活动时代为早志留世。岩体表现为EMⅠ、EMⅡ和少量HIMU的混和富集地幔源区特征及地幔柱源区特征,地幔动力学分析表明,早志留世或之前北大巴山地区可能存在一期与俯冲相关的弧后拉张作用导致下部岩浆上涌侵位,最终完成该区岩浆作用。Hualicun mafic rocks are exposed in Langao County, Shaanxi Province. They are dominated by diabase-porphyrite, gabbro-diabase, diabase, and gabbro. The main minerals are clionopyroxene and plagioclase, and the accessory minerals are Fe-Ti oxides. Major elements show high TiO2 （2.26%~7.30%）, high TFe2O3 （11.17%~17.0%）, low MgO （2.96%~5.52%）, and high alkaline content（K2O＋Na2O=3.07%~6.76%）, thus belonging to alkaline gabbro series. Mg# （36~42） of Hualicun mafic rocks suggest that they possibly originated from an extremely evolved magma. Primitive mantle-normalized multi-element patterns show enrichment of Ba and Pb for large ion lithophile elements, and depletion of K. Chondrite-normalized REE patterns display LREE enrichment （LaN/YbN=9.34~13.05）, and normalized patterns for trace elements and REE similar to features of typical OIB. Detailed LA-ICPMS zircon U-Pb dating yielded emplacement ages of 436.9±2.4Ma, corresponding to the age of regional mafic rock and indicating that regional magma occurred in early Silurian. The enriched mantle characteristics for Hualicun mafic rocks suggest that mafic rocks in the North Daba Mountain were derived from a mixture of EMⅠ, EMⅡ and a small amount of HIMU components. Furthermore, the mantle geodynamic analysis of Hualicun mafic rocks that occurred in the Silurian or earlier period indicates an extension related to subduction and uplift of magma.

关 键 词：花栎村镁铁质岩 LA-ICP-MS锆石U-PB年龄 地球化学 构造环境 

分 类 号：P588.1[天文地球—岩石学] P597.3[天文地球—地质学]