摘要
辽宁兴城新立屯地区岩浆杂岩主要由4种不同的岩石单元组成,分别为似斑状黑云母二长花岗岩,中细粒石英闪长岩,花岗细晶岩和花岗伟晶岩,前两者分布广泛且为研究区的主要岩石单元,后两者则呈脉状侵入到前两者中。应用LA-ICP-MS锆石U-Pb定年方法,测得似斑状黑云母二长花岗岩,中细粒石英闪长岩及花岗细晶岩的年龄分别为2 496±18 Ma,2 490±19 Ma,2 479±29 Ma,形成于古元古代早期。结合野外地质特征,侵位顺序由早到晚依次为:似斑状黑云母二长花岗岩,中细粒石英闪长岩,花岗细晶岩,花岗伟晶岩。岩石地球化学特征显示,新立屯地区岩浆杂岩主量元素方面具高硅(SiO2=61.38%~74.99%),富碱(Na2O+K2O=6.86%~9.41%),富Mg#(56~70)特征;A/CNK=0.91~1.18,属准铝质-过铝质岩石;微量元素方面,相对富集轻稀土元素,亏损重稀土元素,具有Eu异常(δEu=0.50~0.96);富集大离子亲石元素,亏损高场强元素;锆石Lu-Hf同位素特征εHf(t)值为-1.12^+6.13;TDM2(Hf)介于2 594~2 937 Ma,显示该套岩浆杂岩可能为地幔物质加入新生地壳再造的产物。
Magmatic complex in Xinlitun of Liaoning is mainly composed of four different kinds of rocks,including biotite monzogranite,medium-fine quartz diorite,granite aplite and granite pegmatite. The later two presented as fine veins intruding into the former two which are the main rock units and widely distributed. LA-ICP-MS zircons U-Pb dating yielded three concordant ages of 2 496 ± 18 Ma for biotite monzogranite,2 490 ± 19 Ma for medium-fine quartz diorite and 2 479 ± 29 Ma for granite aplite,indicating the instrusive time is Early Paleoproterozoic. Combined with their contact relationships in the field,the authors infer that biotite monzogranite intruded firstly,then medium-fine quartz diorite,granite aplite in turn and granite pegmatite at last. The major elements show that magmatic complex in Xinlitun has high Si（ Si O2= 61. 38% - 74. 99%）,high Alkali（ Na2 O ＋ K2 O =6. 86% - 9. 41%）,high Mg#（ 56 - 70） and A/CNK ratios range from 0. 91 to 1. 18,and it belongs to metaluminous-peralumous rock. Besides,the REE patterns are characterized by the enrichment of LREEs,depletion of HREEs and distinct negative Eu anomalies（ δEu = 0. 50 - 0. 96） in chondrite- normalized REE diagram. The rocks are also enriched in large lithophile elements（ LILE）,depleted in high field strength elements（ HFSE）.Combined with the results of zircon Lu-Hf isotope（ εHf（ t） =- 1. 12 - ﹢ 6. 13,TDM2（ Hf） = 2 594 - 2 937 Ma）,we can draw the conclusion that magmatic complex is the product of mantle material,which are contaminated by juvenile crust.
出处
《世界地质》
CAS
2015年第3期571-589,共19页
World Geology
基金
国土资源部公益性行业科研专项经费项目(201011083)
