摘要
辽东王家堡子地区出露大量古元古代花岗质岩石,前人将其统称为花岗质混杂岩。通过详细的野外地质调查和室内综合研究,将该套花岗质混杂岩解体为条痕状黑云母二长花岗岩和片麻状黑云母二长花岗岩两类。岩石地球化学分析结果显示二者具有一致的地球化学特征。均显示高SiO_2、富K_2O、贫Al_2O_3的特征,K_2O/Na_2O=0.64～2.14,TiO_2含量为0.16%～0.3%,MnO、MgO、CaO和P_2O_5的含量较低,铝指数A/CNK集中分布在1.06～1.1之间,A/NK在1.50～1.62之间,均属于过铝质高钾钙碱性系列;微量元素显示强烈亏损Nb、Ti、Ta等高场强元素,富集Rb、U、K等大离子亲石元素,具有明显的负Eu异常,具有A型花岗岩的特征。条痕状黑云母二长花岗岩大部分锆石为具有清晰振荡环带的岩浆锆石,LA-ICP-MS锆石U-Pb年龄为2188±13Ma,代表该岩石的岩浆结晶年龄。片麻状黑云母二长花岗岩大部分锆石具有明显的变质增生边,部分核部锆石具有清晰的振荡环带,LA-ICP-MS锆石U-Pb测年获得核部年龄为2214±16Ma,代表该岩石的岩浆结晶年龄;增生边年龄为1905±13Ma,应代表该岩石的变质年龄。条痕状黑云母二长花岗岩和片麻状黑云母二长花岗岩的Hf同位素模式年龄分别为2387～2584Ma和2474～2641Ma,平均地壳模式年龄分别为2495～2808Ma和2633～2868Ma,大于岩石形成年龄,暗示研究区古元古代花岗岩源区主要为太古宙基底,混有少量古元古代新生地壳。结合前人报道的埃达克质花岗闪长岩的形成环境,认为胶-辽-吉古元古代造山/活动带早期经历了2.2～2.15Ga的拉伸裂解过程和2.0Ga左右俯冲挤压的构造演化过程。
Paleoproterozoic granites are widely distributed in the Wangjiapuzi area of eastern Liaoning Province. In the past, some granitic plutons were considered as granitic melange in this area. In this paper, the authors divided the granitic melange into two types, i.e., striate biotite monzogranites and gneissic biotite monzogranites, on the basis of comprehensive studies of field observation, petrography, geochemistry and isotope chronology. The results of geochemical analysis show that the two components are homogeneous, having uniform geochemical characteristics. They all show high SiO2\, rich K2 O and poor Al2 O3 features, with K2 O/Na2 O being 0.64~2.14. Their TiO2 values are between 0.16% and 0.3%, with lower MnO, MgO, CaO and P2 O5 content. The saturation index A/CNK is between 1.06 and 1.1, and A/NK is between 1.50 and 1.62, which suggests that the granodiorites should belong to the peraluminum calcium alkaline series. Some trace elements show that high field strength elements such as Nb, Ti, Ta are strongly depleted, with an obvious anomaly of negative Eu. All the geochemical characteristics suggest that they should belong to Atype granites.The most zircon grains of striate biotite monzogranites show clear oscillating zoning structures, and LA-ICP-MS zircon U-Pb weighted mean age is 2188±13 Ma(MSWD=0.49), with the age of magma crystallization representing the age of the rock.The most zircons of gneissic biotite monzogranites show obvious metamorphic edge, zircons from the part of the nucleus show clear oscillating zoning structures. LA-ICP-MS nucleus zircon U-Pb weighted mean age is 2214±16 Ma(MSWD=1.01), with the age of magma crystallization representing the age of the rock. LA-ICP-MS edge zircon U-Pb weighted mean age is 1905±13 Ma(MSWD=4.5), representing the age of metamorphic rock. The model ages of these two types of granites obtained from Hf isotope are respectively 2387~2584 Ma and 2474~2641 Ma,the average of the crustal pattern is 2495~2808 Ma and 2633~2868 Ma,older than the age of rock formation.
作者
杨仲杰
王伟
赵岩
周永恒
张璟
孙守亮
刘长纯
YANG Zhongjie;WANG Wei;ZHAO Yan;ZHOU Yongheng;ZHANG Jing;SUN Shouliang;LIU Changchun(Geological and Mineral Survey Institute of Liaoning Province, Shenyang 110031, Liaoning, China;No. 103 Geological Party, Nonferrous Geological Bureau for Liaoning Province, Dandong 118008, Liaoning, China;Geological and Mineral Resources Institute of Shenyang, Shenyang 110034, Liaoning, China)
出处
《地质通报》
CAS
CSCD
北大核心
2019年第4期603-618,共16页
Geological Bulletin of China
基金
中国地质调查局项目<辽东-吉南成矿带永吉-凤城地区地质矿产调查>(编号:DD20160049)
