胶东地区西石棚单元似斑状二长花岗岩的地球化学特征及其重建

Geochemical Characteristics and Reconstruction of Porphyritic Monzonitic Granite in Xishipeng Unit in Jiaodong Area

郭家岭序列侵入岩主要分布在胶东半岛西北部,是胶东地区金矿床的主要控矿围岩,提高该序列岩石演化研究程度,有助于指导该地区金矿找矿。通过对郭家岭序列各单元岩体进行野外地质调查研究,在莱州三山岛、龙口冯家—前迟家等地区,均发现原西石棚单元似斑状粗中粒含角闪黑云二长花岗岩。其具有高的SiO2(69.06%~72.01%)、全碱(Na2O+K2O=7.69%~8.58%)、Ba(>1573×10^-6)、Sr(>765×10^-6)、(La/Yb)N(>28.56)、Sr/Y(>116)、LILE/HFSE,低的Al2O3(14.76%~15.53%)、MgO(0.32%~1.16%)、Y(<8.31×10^-6)、Yb(<0.65×10^-6),相对平坦的HREE,无明显的铕异常,以及明显亏损Nb,Ta,P,Ti等高场强元素;锆石LA-ICP-MS定年结果为127±2Ma。研究表明,似斑状粗中粒含角闪黑云二长花岗岩与郭家岭序列花岗岩具有相似的主量元素组成及稀土和微量元素分布模式,属于郭家岭序列花岗岩。该文认为应该在郭家岭序列中恢复西石棚单元似斑状粗中粒含角闪黑云二长花岗岩,置于罗家单元之下。

Intrusive rocks in Guojialing sequence is mainly located in the northwestern Jiaodong Peninsula. It is the main ore-controlled surrounding rock of gold deposits in Jiaodong Peninsula. Increasing the research degree of rock evolution in Guojialing sequence will help guide gold prospecting in this area. Based on field geological investigation of the rock masses in Guojialing sequence, coarse and medium grained porphyritic amphibole biotite monzogranite in Xishipeng unit have been found in Sanshandao island of Laizhou city and Fengjia-Qianchijia area of Longkou city. The contents of SiO 2 (69.06%~72.01%), total alkalis(Na 2O+K 2O=7.69%~8.58%), Ba(>1573×10^-6 ), Sr(>765×10^-6 ),(La/Yb)N (>28.56), Sr/Y(>116) and LILE /HFSE are high, the contents of Al 2O 3(14.76%~15.53%), MgO(0.32%~1.16%), Y(<8.31×10^-6 ) and Yb(<0.65×10^-6 ) are low, HREE is relatively smooth, and no obvious Eu anomaly. The rocks are characterized by prominent depletion of Nb, Ta, P, Ti. The LA-ICP-MS zircon dating result is (127±2)Ma. It is showed that the porphyritic coarse and medium grained amphibolite-bearing monzonitic granite is similar to granites in Guojialing sequence in the composition of major elements and the distribution pattern of rare earth and trace elements. It belongs to the Guojialing sequence granite. It is suggested that the porphyritic coarse and medium grained amphibolite-bearing biotite monzonitic granite of Xishipeng unit should be restored in Guojialing sequence and placed under Luojia unit.