摘要
胶东地区发育大规模早白垩世壳幔混合源花岗岩类,但一直未发现与花岗岩类相关的独立的幔源侵入体,给深入理解早白垩世壳幔演化带来了困惑。胶东的柳林庄和夏河城岩体以往被认为是三叠纪闪长岩类,本文在详细的野外地质工作基础上,通过年代学、岩石地球化学、同位素地球化学分析,发现这2个岩体为早白垩世高镁闪长岩。样品的SiO 2含量在53.29%~62.54%之间,MgO含量为3.60%~8.10%,Mg#主要介于0.47~0.68之间;富集Ba、Rb、K等大离子亲石元素,亏损Nb、Ta、Zr等高场强元素;初始87 Sr/86 Sr值为0.7082~0.7083,与地幔平均值接近;εNd(t=113Ma)值很低(-20.5^-16.8),与胶东地区的基性脉岩同位素组成一致。2个岩体相比而言,柳林庄岩体富K2O、Fe2O3^T,REE、LILE、HFSE含量较高,而MgO、Ni和Cr含量偏低。3件样品的锆石LA-ICP-MS U-Pb同位素加权平均年龄值分别为120.1±1.6Ma、118.3±1.7Ma和122.3±4.0Ma,与壳幔混合源的伟德山型花岗岩及胶东金矿的成岩、成矿时代一致,指示他们形成于统一的地球动力学背景。高镁闪长岩的地球化学特征介于高镁埃达克岩与赞岐岩及埃达克岩与Piip型高镁安山岩之间,指示其形成于古太平洋板块俯冲的地幔楔环境,为富集岩石圈地幔部分熔融的产物。夏河城岩体的岩浆直接来源于含角闪石的富集岩石圈地幔源区,而柳林庄岩体岩浆源区为含金云母的岩石圈地幔并且在岩浆上侵过程中混染了部分地壳物质。
A large number of Early Crataceous granitoids with crust-mantle mixed source were reported in the Jiaodong Peninsula,however,mantle-derived plutons have not been reported so far.In this paper,we present new data from the Liulinzhuang and Xiahecheng plutons in the Jiaodong area.These two plutons were previously taken as Triassic diorites,however,based on detailed field work,lithogeochemistry together with geochronology and isotopic geochemistry analyses,we proposed that they were formed in the Early Cretaceous with high-Mg diorite affinity.The SiO 2 contents of the collected samples vary from 53.29%to 62.54%,MgO from 3.60%to 8.10%,and Mg^# mainly between 0.47 and 0.68.They are characterized by enrichments of Ba,Rb and K,and depletions of Nb,Ta and Zr,together with the initial 87 Sr/86 Sr values of 0.7082~0.7083,which are similar to the values of the mantle.TheirεNd(t=113Ma)values are very low(-20.5^-16.8),which is similar to mafic dykes in the Jiaodong Peninsula.Compared with the Xiahecheng pluton,samples from the Liulinzhuang pluton are rich in K 2 O,Fe2O3^T,REE,LILE and HFSE,but low in MgO,Ni and Cr.LA-ICPMS U-Pb zircon data from three samples yield weighted mean ages of 120.1±1.6Ma,118.3±1.7Ma and 122.3±4.0Ma,respectively.These ages are similar to that of the Weideshan type granitoid and the ages of gold deposits in Jiaodong Peninsula.Therefore,we propose that they were formed in a unified geodynamic setting.In addition,geochemical characteristics of the high-Mg diorites in the Jiaodong Peninsula are similar to the high-Mg adakitic and sanukite,closer to Piip type high-Mg andesite,indicating that the high-Mg diorites are most likely formed in a mantle wedge due to the subduction of the Pacific Plate.So,the primary magma of the high-Mg diorites in the Jiaodong Peninsula was derived from partial melting of the enriched lithospheric mantle.In details,the Xiahecheng pluton was formed as the amphibole-rich enriched mantle,whereas the Liulinzhuang pluton was most likely formed as phlogopite-rich mantle and modified by the ancient lower crustal materials.
作者
宋明春
李杰
周建波
宋英昕
李世勇
王斌
丁正江
张照录
SONG MingChun;LI Jie;ZHOU JianBo;SONG YingXin;LI ShiYong;WANG Bin;DING ZhengJiang;ZHANG ZhaoLu(Shandong Provincial No6 Exploration Institute of Geology and Mineral Resources,Weihai 264209,China;Key Laboratory of Gold Mineralization Processes and Resources Utilization Subordinated to the Ministry of Nature and Resources,Jinan 250013,China;School of Resources,Hebei GEO University,Shijiazhuang 050031,China;College of Earth Sciences,Jilin University,Changchun 130061,China;Shandong Institute of Geophysical and Geochemical Exploration,Jinan 250013,China;Shandong Provincial Bureau of Geology&Mineral Resources,Jinan 250013,China;College of Resources and Environmental Engineering,Shandong University of Technology,Zibo 255000,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2020年第1期279-296,共18页
Acta Petrologica Sinica
基金
山东省自然科学基金项目(ZR2016DM01)
山东省重点研发计划(2017CXGC1604)
山东省泰山学者建设工程专项经费(ts201511076)
山东省地矿局科研项目(KY2016011、KY201014)联合资助
关键词
高镁闪长岩
早白垩世
幔源侵入岩
锆石U-PB年龄
胶东
High-Mg diorites
The Early Cretaceous
Mantle-derived pluton
Zircon U-Pb age
Jiaodong Peninsula
