摘要
基于内蒙古朝克乌拉地区开展的1∶5万区域地质调查工作,发现一期以辉长岩为主的基性岩浆活动。研究表明:朝克乌拉地区辉长岩锆石U-Pb年龄为142.6±0.5 Ma、145.1±2.1 Ma,显示岩石为晚侏罗世—早白垩世产物。辉长岩为拉斑系列岩石,具有低硅、低钛、贫碱且高钠低钾特点,分异作用极弱,Eu异常不明显,微量元素Ba、Ta、Sr、Hf富集,Rb、Th、Nb、P亏损。辉长岩岩石地球化学显示其岩浆源区为亏损尖晶石二辉橄榄岩地幔发生30%以上的部分熔融形成,存在流体影响的地球化学特征。岩浆在演化过程中存在一定程度的分离结晶作用,地壳混染作用极其微弱。通过与贺根山蛇绿岩配套岩系的类比,结合研究区古生代至中生代构造背景和贺根山缝合带壳幔电性结构全面分析,推断晚侏罗世—早白垩世辉长岩具有的岛弧印记特征为贺根山洋发育时期古岛弧环境的反映,辉长岩只是伸展背景下幔源岩浆沿深大断裂上涌作用的产物。
Objectives:Based on the 1∶50,000 regional geological survey carried out in the Chaokewula area of Inner Mongolia,a basic magmatic activity dominated by gabbro was discovered.The purpose of this study is to explore the formation age,petrogenesis and geological significance of gabbro.Methods:Taking the gabbro as the research object,we carried out the isotopic age determination and rock geochemical testing.Results:Our study demonstrates that the ages of the gabbro zircons U-Pb in the Chaokewula area are 142.62±0.51 Ma and 145.1±2.1 Ma,indicating that the rock is a product of the Late Jurassic to Early Cretaceous.Gabbro is a series of tholeiite rocks,characterized by low silicon,low titanium,lean alkali,high sodium and low potassium.Its differentiation is extremely weak.The Eu anomalies are not obvious,and trace elements Ba,Ta,Sr,and Hf are enriched,and Rb,Th,Nb,and P are deficient.Conclusions:The rock geochemistry shows that the source area of gabbro magma is depleted spinel Lherzolite,which is formed by partial melting of more than 30%of the mantle,and characterized by fluid-influenced geochemistry.There is a certain degree of separation and crystallization of magma during its evolution,and the crustal mixing is very weak.Through analogy with the supporting rock series of ophiolite in Hegen Mountain,and the combination of Paleozoic to Mesozoic tectonic background in the study area and the comprehensive analysis of hegenshan back-arc suture zone crust—mantle electrical structure,we concluded that the island arc imprinting characteristics of Late Jurassic—Early Cretaceous gabbro are the reflection of the ancient island arc environment developed during the Hegenshan Ocean period,and gabbro is only the product of mantle-derived magma upwelling along deep and large faults under extensional background.
作者
郭喜运
GUO Xiyun(Shanxi Mineral Resources Survey and Monitoring Center,Taiyuan,030024)
出处
《地质论评》
CAS
CSCD
北大核心
2021年第3期787-802,共16页
Geological Review
基金
中国地质调查局地质矿产调查项目(编号:1212011220447)的成果。
关键词
辉长岩
锆石U-PB年龄
地球化学
岛弧
贺根山
内蒙古
大兴安岭
gabbro
zircon U-Pb age
geochemistry
island arc
Hegen Mountain
Inner Mongolia
Great Hinggan Mountains
