摘要
新疆克拉玛依中基性岩墙群出现在后碰撞花岗岩(锆石U-Pb年龄约为300～320Ma)及其下石炭统火山岩-硅质岩围岩之中,空间分布受区域构造裂隙控制,总体走向以280°～300°为主,K-Ar表观年龄为241.3～271.5Ma。岩墙群属于亚碱性系列,根据岩性和Mg#的不同,可分为辉绿岩岩墙、高Mg#闪长玢岩岩墙和低Mg#(石英)闪长玢岩岩墙等三组。主元素、稀土元素和其他微量元素等资料表明,形成岩墙群的岩浆起源于亏损地幔,由部分熔融作用形成的原始玄武质岩浆在侵位过程中发生了分离结晶作用,但同时还受到同化混染作用的影响,致使克拉玛依岩墙群具有较典型的AFC过程的成因特征。克拉玛依岩墙群形成于新疆北部后碰撞伸展构造环境,是幔源岩浆活动的产物,因而可以作为地壳垂向生长的标志之一。
A great number of basic-intermediate dykes occur in the Karamay region,n orthern Xinjiang.The Karamay dyke swarm emplaces in the postcollisional granites with the zir con U-Pb ages of 300to 320Ma and the Lower Carboniferous volcanic and siliceous rocks.The distribution of t he swarm is strictly controlled by extensional fractures,mainly with a striking of280°～300°,and the K-Ar ages are in th e range of 241.3to 271.5Ma.The Karamay dyke swarm is principally co mposed of fine-grained diabase and d ioritic prophyrite,with SiO 2 of 51.32%～63.87%and Na 2 O +K 2 O of 3.86%～6.15%,belonging to the su balkaline series.Out of 14samples,11samples have the magnesium numbers犤Mg # =100×Mg /(Mg +Fe 2+ ),assuming Fe 2 O 3 /FeO =0.15犦in the range of 53to64,and the magnesium numbers of the r emaining vary from 36to 43.Accordin gly,dioritic prophyrite could be subdivided into two groups:high-Mg # and low-Mg # .The Karamay dyke swarm is characterized by enrichment in K,Rb,Ba,Sr,Zr,Hf,U,Pb and LREE,and r elative depletion in Nb and Th.The petrographic,geochemical and geochronological evidences indica te that the dykes were produced by a pr ocess of assimilation and fractional crystallization during the emplace ment of depleted mantle-derived magma into the middle-upper crust.During late Paleozoic,northern Xinjiang was in a postcollisional setting and was ch aracterized by significant additio n of mantle-derived magmas and their differentiates to the crust.The Karama y dyke swarm is indicative of the vertical growth of continental crust.
出处
《地球化学》
CAS
CSCD
北大核心
2004年第6期574-584,共11页
Geochimica
基金
国家重点基础研究发展规划项目(2001CB409802)
