北山磁海辉绿岩型铁矿区基性杂岩锆石U-Pb年代学及岩石成因

Zircon U-Pb Geochronology and Genesis Study on the Mafic Complex from Diabase-Type Iron Deposit in Cihai,Beishan Area[KH*2/3D]

磁海辉绿岩型铁矿位于塔里木北缘北山裂谷带,主要岩石类型为辉绿岩,岩石具有较高的Mg#(55.7～70.1)、中铝Al2O3(13.75～14.65)特征,Na2O/K2O(1.79～14.04)变化较大,整体属于钙碱性系列(K2O/Na2O=0.07～0.56,FeO/MgO=0.77～1.46)。稀土元素方面,磁海辉绿岩具有较高的稀土元素质量分数和δEu异常特征[w(∑REE)=88.01×10-6～213.07×10-6,δEu=0.63～1.44],球粒陨石标准化稀土元素配分模式为缓右倾型[(La/Yb)N=1.32～3.87,(La/Sm)N=1.05～2.17,(Gd/Yb)N=1.12～1.58],微量元素上选择性富集大离子亲石元素(Rb、K),亏损高场强元素(Nb、Ta)。岩浆演化过程中斜长石和单斜辉石的分离结晶作用是岩浆演化的主要机制,同时伴有较为明显的地壳混染作用。LA-ICP-MS锆石U-Pb年代学指示该辉绿岩形成于约291.9Ma,构造环境分析表明磁海辉绿岩为板内拉张环境的产物。

The diabase type of Cihai ore deposit is located in the Beishan rift belt,Xinjiang Province.The main rock type is diabase with high Mg#（55.7-70.1）,middle aluminum value Al2O3（13.75-14.65）,variate Na2O/K2O value（1.79-14.04）,which belongs to calc-alkali rocks（K2O/Na2O=0.07-0.56;FeO/MgO=0.77-1.46）.The rocks have a high total REE（∑REE=88.01×10-6-213.07×10-6） and the Eu anomaly feature（δEu=0.63-1.44）.Their chondrite-normalized REE pattern displays a slight rightleaning flat pattern [（La/Yb）N=1.32-3.87];（La/Sm）N=1.05-2.17;（Gd/Yb）N=1.12-1.58）.Primitive mantle-normalized trace element abundances is enriched in LILE（Rb,K） and depleted in HFSE（Nb,Ta）.Fractional crystallization of plagioclase and clinopyroxene is the main mechanism for magma evolution,and meanwhile accompany with obvious crustal contamination.The LA-ICP-MS zircon U-Pb dating indicates that the Cihai diabase was formed at 291.9 Ma and was produced under the intracontinental extensional environment.