鲁西金岭地区含矿闪长岩体成因:来自锆石U-Pb年代学和地球化学证据

鲁西金岭闪长岩位于华北克拉通东南部,主要由辉石闪长岩-黑云母闪长岩组成。LA-ICP-MS锆石U-Pb定年测定闪长岩侵位年龄为(129.17±0.96)和(130.15±0.65)Ma,属于早白垩世岩浆活动的产物。闪长岩SiO2和K_2O的质量分数较低,MgO、Na_2O、Fe_2O_3、MgO和Al_2O_3的质量分数较高,Mg#为58.00~70.00。Na_2O/K_2O为1.08~2.96,相对富钠高铝,其里特曼指数为1.95~2.96,具有钙碱性系列的岩浆演化趋势。金岭闪长岩w(Ni)为99.00×10~(-6)~237.00×10~(-6),w(Cr)为270.00×10~(-6)~600.00×10~(-6),w(Co)为19.00×10~(-6)~44.00×10~(-6),表明其具有幔源岩浆的属性。稀土元素球粒陨石标准化曲线表明样品具有富集轻稀土元素(LREE),亏损重稀土元素(HREE)以及弱Eu(δEu为0.91~1.12)异常的特征。所有样品富集大离子亲石元素(Ba、K、Sr)和高场强元素Nd,亏损高场强元素Rb、Nb、Ta、Zr。样品中约2.5Ga古老锆石的存在证明岩浆源区受到古老下地壳物质的混染作用。鲁西金岭地区闪长岩应形成于太平洋板块俯冲后后撤引起的伸展环境,其岩浆源区是富集地幔起源的基性岩浆底侵华北古老下地壳并与下地壳熔融形成的壳源酸性岩浆混合过程的产物。

Petrogenesis of Ore-Bearing Dioritic Pluton in Jinling Area in Western Shandong: Evidence from Zircon U-Pb Chronology and Petro-Geochemistry

The Jinling dioritic pluton in west Shandong is mainly composed of pyroxene diorite and biotite diorite.The zircon U-Pb dating results reveal that the dioritic pluton was emplaced in Early Cretaceous(129.17±0.96) Ma and (130.15 ± 0.65)Ma.The major element data show that the diorites contain low contents of SiO2,K2O,and high contents of Na2O,Fe2O3,MgO,Mg# and Al2O3.The Na2O/K2O ratios range from 1.08 to 2.96.The diorites are enriched relatively in sodium and alumina.The diorites have calc-alkaline characteristics according to the Ritttman index(1.95-2.96).The contents of Ni、Cr、Co are 99.00 × 10-6-237.00 × 10-6,270.00 × 10-6-600.00 × 10-6,19.00 × 10-6-44.00 × 10-6 respectively,similar to the contents of mantle magma.The chondrite standardized REE curves show that they are enriched in light REE,and depleted of heavy REE with weak Eu anomaly (0.91-1.12).The diorites are enriched in large ion lithophile element (LILE) Ba,K,Sr,and high field strength elements (HFSE) Nd,while depleted of high field strength elements (HFSE) Rb,Nb,Ta,and Zr.The residual ancient zircons (～2.5 Ga) in the sample (N1) indicate a mix of ancient lower crust occurred in the source area.The Jinling pluton might be formed under a lithospheric extension related to the rollback of the subducted Pacific plate,and the magma was the mixing product of the siliceous crust melted through underplating of basaltic magma,and the mantle enriched basaltic magma.