辽东宽甸东北沟钼矿二长花岗岩年代学、地球化学及Hf同位素特征

Chronology, geochemistry and Hf Isotope of monzonitic granite from the Dongbeigou molydbenum deposit in Kuandian, Liaoning Province

东北沟钼矿是辽宁宽甸地区近些年发现的大型隐爆角砾岩型钼矿床。文章首次对东北沟钼矿床赋矿围岩二长花岗岩进行LA-MC-ICP-MS锆石U-Pb定年,主量元素、微量元素和Hf同位素地球化学研究,锆石U-Pb定年结果表明,二长花岗岩形成年龄为(129.4±0.3)Ma(MSWD=0.83),为燕山期构造岩浆活动产物。地球化学成分上,岩石具有富硅(SiO_2=62.21%~83.21%)、高钾(K_2O/Na_2O=3.35~20.27)和富碱(K_2O+Na_2O=5.82%~12.23%)的特点,属于钾玄岩系列。岩石富集轻稀土元素(LREE/HREE=10.26~24.21),亏损重稀土元素,具有弱负铕异常(δEu=0.63~1.07),富集大离子亲石元素(如K、Rb、Pb)和不相容元素(如Th、U)的特征,相对亏损高场强元素(如Nb、Ta、P、Ti)。锆石Hf同位素分析结果表明,东北沟钼矿二长花岗岩的ε_(Hf)(t)值为介于-12.4^-8.5,二阶段模式年龄(t_(DM2))介于442~1610 Ma,反映岩浆源区可能来源于中元古界古老地壳的再熔融。结合区域构造演化,成岩成矿构造背景为早白垩世古太平洋板块向欧亚之下俯冲,岩石圈减薄的构造环境。

The Dongbeigou molybdenum deposit is a newly discovered large-sized cryptoexplosive breccia molybdenum deposit inKuandian, Liaoning Province. In this study, the authors first carried out a comprehensive study including zircon U- Pb dating,petrogeochemical investigation and Hf isotope analysis of the monzonitic granite related to the Dongbeigou molybdenum deposit.LA-ICP-MS zircon U-Pb chronology indicates that the monzonitic granite was emplaced at (129.4±0.3) Ma. Geochemically, the monzonitic granite has rich silicon (SiO2=62.21%-83.21%), high potassium (K2O/Na2O=3.35-20.27), and rich alkali (K2O + Na2O=5.82%-12.23%), belonging to shoshonite series peraluminous granite and characterized by LREE enrichment, HREE depletion, andweak negative Eu anomaly (δ Eu=0.63-1.07). The monzonitic granite is enriched in LILEs such as K, Rb and Pb, and depleted inHFSEs such as Nb, Ta, P and Ti. According to zircon Hf isotope analyses, the εHf(t) values of monzonitic granite are -12.4 - -8.5,and two-stage model ages (tDM2) vary from 442 Ma to 1610 Ma. These characteristics suggest that the primary magma was derivedfrom the remelting of the Mesoproterozoic crustal materials. In combination with metallogenic geological background, the authorshold that the monzonitic granite and the Dongbeigou molybdenum deposit were developed from the subduction of the Pacific Platebeneath Eurasia associated with Cretaceous lithospheric thinning.