文章摘要
张志强,彭青松,祝新友,黄行凯,徐巧,马腾瀚.大兴安岭中南段桦杆子沟岩体地球化学特征、锆石Hf同位素及地质意义[J].矿产勘查,2017,8(6):937-947
大兴安岭中南段桦杆子沟岩体地球化学特征、锆石Hf同位素及地质意义
Geochemical characteristics of Huaganzigou pluton,isotopic characteristics of zircon Hf and their geological significance in central and southern section of the Da Hinggan Mountains
投稿时间:2017-09-13  
DOI:
中文关键词: 大兴安岭中南段  地球化学  Hf同位素  花岗岩
英文关键词: geochemical characteristics, Hf isotope, granite pluton, central and southern section of the Da Hinggan Mountains
基金项目:中国地质调查局国家二级项目内蒙古赤峰有色金属基地综合地质调查(编号:DD20160072)资助。
作者单位
张志强 中国地质大学北京地球科学与资源学院,北京 100083 
彭青松 北京矿产地质研究院,北京 100012 
祝新友 北京矿产地质研究院,北京 100012 
黄行凯 北京矿产地质研究院,北京 100012 
徐巧 北京矿产地质研究院,北京 100012 
马腾瀚 中国地质大学北京地球科学与资源学院,北京 100083 
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中文摘要:
      大兴安岭中南段晚中生代岩浆活动剧烈,其岩浆物源及伸展构造成因一直存在争议。桦杆子沟岩体呈复式岩基产出,主要分为二长花岗岩与黑云母花岗岩组成的正常花岗岩单元和闪长质包体及其寄主岩等构成的基性岩浆单元。两类岩石主量元素相似,具高硅(67.71%~76.62%)、富碱(7.92%~9.10%),低CaO(0.37%~0.50%)、MgO(0.19%~0.34%)的特征,属高钾钙碱性系列;闪长质包体及其寄主岩相对富CaO(1.98%~2.39%),MgO (1.17%~1.23%),同属高钾钙碱性系列;ACNK值介于0.98~1.06之间,为准铝质—弱过铝质岩石。岩石相对富集轻稀土,(La/Yb)N为1.97~8.18,在球粒陨石标准化稀土配分图解中呈缓右倾海鸥型,具有较为明显的负铕异常(δEu为0.01~0.40)。两类岩石微量元素组成显示岩石富集Rb、U、Th、Zr、Hf等元素,强烈亏损Sr、Ba、Ti、P等元素,为高分异I型花岗岩。岩石具有高正的εHf(t)值(+3.7~+8.7)和年轻的二阶段Hf模式年龄(408~731 Ma),表明这些花岗岩源区主要为年轻地壳物质,并有幔源物质的混入。在蒙古—鄂霍茨克洋闭合导致陆壳碰撞的地球动力背景下,由基性的幔源岩浆携带大量的热量上涌至新元古界的下地壳,诱发下地壳岩石(变杂砂岩)部分熔融,并与幔源熔体(角闪岩相部分熔融)混合形成母岩浆,最终上涌侵位形成了以桦杆子沟为代表的复式岩体。
英文摘要:
      The late Mesozoic magmatic activity in the central and southern part of the Da Hinggan Mountains is intense, and there has been controversial in aspects of the magmatic source and extensional tectonics . The petrographic, geochemical and isotopic characteristics of Lu-Hf of the Huaganzigou pluton in Balinzuoqi area, Inner Mongolia, are first studied in this paper. The Huaganzigou pluton occurred as complex bathylith,it is divided into two types as followings:common granite pluton composed of monzogranite and biotite granite, and basic pluton with abundant mafic macrogranular enclaves. Both of them are all characterized by high composition of SiO2 (67.71%~76.62%) and alkali (7.92%~9.10%), low contents of CaO (0.37%~0.50%), MgO (0.19%~0.34%) and MgO (1.17%~1.23%), which indicate that the pluton belongs to the high potassium and calcium alkaline series. The ACNK ratio is from 0.98 to 1.06, which indicated it is the metaluminous and peraluminous granitoid. The REE content of the pluton ranges from 69.08×10-6 to 189.89×10-6 ,with δEu value of 0.01 to 0.40 and (La/Yb)N ratio of 1.97 to 8.18. The REE pattern is characterized with enrichment of LREE relatively to HREE and negative Eu anomaly in chondrite-normalized REE diagram. Their trace elements relatively enrich with large ion lithophile elements (LILE), high field strength elements (HFSE) and poor Ba, Sr, Ti and P. All of these geochemical characteristics indicate that these granitoids show features of highly differentiated I-type granitoids. The dating age of zircon Hf isotopic of these granitoids ranges from 408 Ma to 731 Ma suggesting sources for the granitoids. Furthermore,the Late Jurassic granitoids have relative high values of εHf (t) value (+9.9 ~ +15.9) than those of the underplated juvenile lower crust in study. It is suggested that the sources of grantoids originated mainly from the upper crust rocks and mixed with mantle-derived magma. It is indicated that the base mantle source magma carried a large amount of heat to the lower crust of the new Neoproterozoic in the tectonic setting of continental crust collision due to the closing of the Mongolia - Ehecike ocean, which resulted in the partial melting of lower crustal rocks (meta-greywacke). The molten crustal magma is mixed with the mantle source magma, and eventually it flew up into the stratum, eventually the Huaganzigou complex pluton was formed.
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