新疆东天山旱草湖环状岩体锆石U-Pb年龄、地球化学特征及成因
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摘要
以新疆东天山旱草湖地区中酸性环状岩体为研究对象,进行LA-ICP-MS锆石U-Pb年龄和全岩地球化学研究,探讨其成因和地质意义。结果表明,侵入英云闪长岩的最老年龄为275.0±2.9Ma(MSWD=4.8),侵位时代为二叠纪。岩体Al_2O_3含量为14.46%～17.05%,A/CNK为0.93～1.09,属准铝质和弱过铝质系列,较富集K_2O,MgO含量较低,为0.71%～2.84%,Mg~#值为33.3～48.6。微量元素高Sr、低Y,Sr含量为217×10~(-6)～740×10~(-6),Y含量为4.26×10~(-6)～21.4×10~(-6),Sr/Y值为16.87～145.07,富集大离子亲石元素Rb、Sr、Ba,亏损高场强元素Nb、Ta、Ti。稀土元素配分模式图呈现平坦右倾的轻稀土元素富集、重稀土元素亏损,表明岩体来源于石榴子石和金红石较稳定而斜长石不稳定的区域,属于角闪岩相向榴辉岩相过渡阶段,可能是同时期底侵的产物。地球化学特征表明岩体不是一期岩浆事件结晶分离演化的结果,不同岩性的岩体之间没有发生结晶分离。部分熔融程度和新生幔源组分的不同导致了旱草湖环状花岗质岩体的形成,二叠纪旱草湖地区存在较强烈的中酸性岩浆活动,是东天山二叠纪构造-岩浆演化的响应。
Choosing the Hancaohu intermediate-acid annular pluton distributed in East Tianshan Mountains of Xinjiang as the study object, the authors used LA-ICP-MS zircon U-Pb isotope chronology and geochemical characteristics to study the petrogenesis and geological significance of the pluton. The results indicate that the age of the earliest intrusive tonalite pluton is 275.0 ± 2.9 Ma(MSWD=4.8),suggesting that its emplacement epoch is Permian. The Al_2O_3 of the ringed pluton is 14.46%～17.05%, and A/CNK is0.93～1.09, suggesting metaluminous and weak peraluminous series. The rocks are enriched in K_2O, and their MgO content is 0.71%～2.84% and Mg#value is 33.3～48.6. Their trace elements are high in Sr and low in Y, the content of Sr is 217×10~(-6)～740×10~(-6),that of Y is 4.26×10~(-6)～21.4×10~(-6),and Sr/Y ratio is 16.87～145.07. They are enriched in LILEs(Rb, Sr, Ba)and depleted in HFSEs(Nb, Ta,Ti). They are characterized by LREE enrichment and HREE depletion, implying that they were formed in an area with stable garnet, rutile and unstable plagioclase, belonging to the transitional stage from amphibolite facies to eclogite facies; they were probably formed by underplating in the same period. The variation of main elements and race elements content and discontinuous LREE/HREE show that the pluton was not formed by crystallization evolution of one magmatic event, and the plutons of different lithologies are not separately crystallized from each other. Comprehensive analyses show that the lithospheric extension after Permian collision in Huangshan-Jingerquan area caused asthenosphere mantle upwelling and lithosphere delamination. The lithosphere vertical accretion at the boundary of the underplating crust and mantle induced the partial melting and produced high K calc-alkaline magma. With the instant intrusion of the magma, the difference of partial melting and newly formed mantle source components led to the formation of Hancaohu granitic pluton. It is shown that there was violent intermediate-acid magmatism in the Hancaohu area in Permian, and it was the response to tectonic-magmatism evolution in Permian in East Tianshan Mountains.
Choosing the Hancaohu intermediate-acid annular pluton distributed in East Tianshan Mountains of Xinjiang as the study object, the authors used LA-ICP-MS zircon U-Pb isotope chronology and geochemical characteristics to study the petrogenesis and geological significance of the pluton. The results indicate that the age of the earliest intrusive tonalite pluton is 275.0 ± 2.9 Ma(MSWD=4.8),suggesting that its emplacement epoch is Permian. The Al_2O_3 of the ringed pluton is 14.46%～17.05%, and A/CNK is0.93～1.09, suggesting metaluminous and weak peraluminous series. The rocks are enriched in K_2O, and their MgO content is 0.71%～2.84% and Mg#value is 33.3～48.6. Their trace elements are high in Sr and low in Y, the content of Sr is 217×10~(-6)～740×10~(-6),that of Y is 4.26×10~(-6)～21.4×10~(-6),and Sr/Y ratio is 16.87～145.07. They are enriched in LILEs(Rb, Sr, Ba)and depleted in HFSEs(Nb, Ta,Ti). They are characterized by LREE enrichment and HREE depletion, implying that they were formed in an area with stable garnet, rutile and unstable plagioclase, belonging to the transitional stage from amphibolite facies to eclogite facies; they were probably formed by underplating in the same period. The variation of main elements and race elements content and discontinuous LREE/HREE show that the pluton was not formed by crystallization evolution of one magmatic event, and the plutons of different lithologies are not separately crystallized from each other. Comprehensive analyses show that the lithospheric extension after Permian collision in Huangshan-Jingerquan area caused asthenosphere mantle upwelling and lithosphere delamination. The lithosphere vertical accretion at the boundary of the underplating crust and mantle induced the partial melting and produced high K calc-alkaline magma. With the instant intrusion of the magma, the difference of partial melting and newly formed mantle source components led to the formation of Hancaohu granitic pluton. It is shown that there was violent intermediate-acid magmatism in the Hancaohu area in Permian, and it was the response to tectonic-magmatism evolution in Permian in East Tianshan Mountains.
引文
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[8]周涛发,袁峰,张达玉,等.新疆东天山觉罗塔格地区花岗岩类年代学、构造背景及其成矿作用研究[J].岩石学报,2010,26(2):478-502.
[9]王银宏,薛春纪,刘家军,等.新疆东天山土屋斑岩铜矿床地球化学、年代学、Lu-Hf同位素及其地质意义[J].岩石学报,2014,30(11):3383-3399.
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[12]张连昌,秦克章,英基丰,等.东天山土屋-延东斑岩铜矿带埃达克岩及其与成矿作用的关系[J].岩石学报,2004,20(2):259-268.
[13]Wang Y H,Xue C J,Wang J P,et al.Early Carboniferous adakiticrocks in the area of the Tuwu deposit,eastern Tianshan,NW China:Slab melting and implications for porphyry copper mineralization[J].Journal of Asian Earth Sciences,2015,103:332-349.
[14]Wang Y H,Xue C J,Wang J P,et al.Petrogenesis of magmatism in the Yandongregion of Eastern Tianshan,Xinjiang:Geochemical,geochronological and Hf isotope Constraints[J].International Geology Review,2015,57(9/10):1130-1151.
[15]黄汲清,任纪舜,姜春发,等.中国大地构造及其演化[M].北京:科学出版社,1980:1-124.
[16]王洪亮,徐学义,何世平,等.中国天山及邻区地质图及说明书(1∶100万)[M].北京:地质出版社,2008:22-23.
[17]Anderson T.Correction of common lead in U-Pb analyses that do not report204Pb[J].Chemical Geology,2002,192(1/2):59-79.
[18]Rubatto D.Zircon trace element geochemistry:Partitioning with garnet and link between U-Pb ages and metamorphism[J].Chemical Geology,2002,184:123-138.
[19]Kosler J,Fonneland H,Sylvester P.U-Pb dating of detrital zircons for sediment provenance studies)A comparison of laser ablation LA-ICPMS and SIMS techniques[J].Chemical Geology,2002,182:605-618.
[20]吴元保,郑永飞.锆石成因矿物学研究及其对U-Pb年龄解释的制约[J].科学通报,2004,16:1589-1604.
[21]王海然,赵红格,乔建新,等.锆石U-Pb同位素测年原理及应用[J].地质与资源,2013,3:229-242.
[22]Le Maitre.Igneous Rocks:A classification and Glossary of Terms(2nd edition)[M].Cambridge University Press,2002:23-86.
[23]Maniar P D,Piccoli P M.Tectonic discrimination of granitiods[J].Geological Society of American Bulletin,1989,101:635-643.
[24]邱家骧.岩浆岩岩石学[M].北京:地质出版社,1985:282-287.
[25]Collins W J.Nature and origin of A type granites with particular referen-ce to Southeast Austrilia[J].Contributions to Mineralogy and Petrology,1982,80:189-200.
[26]Sun S S,McDonough W F.Chemical and isotopic systematics of oceanic basalts:Implications for mantle composition and processes[C]//Saunders A D,Norry M J.Magmatism in the Ocean Basins.Geological Society,London,Special Publications,1989,42(1):313-345.
[27]熊小林,蔡志勇,牛贺才,等.东天山晚古生代埃达克岩成因及铜金成矿意义[J].岩石学报,2005,3:967-976.
[28]赵振华,王强,熊小林,等.新疆北部的两类埃达克岩[J].岩石学报,2006,5:1249-1265.
[29]张旗,王焰,李承东,等.花岗岩的Sr-Yb分类及其地质意义[J].岩石学报,2006,9:2249-2269.
[30]罗照华,黄忠敏,柯珊.中酸性岩石的基本问题[J].地质评论,2007,53(增刊):180-226.
[31]张旗,潘国强,李承东,等.花岗岩混合问题:与玄武岩对比的启示--关于花岗岩研究的思考之一[J].岩石学报,2007,23(5):1141-1152.
[32]Boztu D,Arehart G B,Platevoet B,et al.High-K,calc-alkaline I-type granitoids from the composite Yozgat batholith generated in a post-collisional setting following continent-oceanic island arc collision in central Anatolia,Turkey[J].Mineralogy and Petrology,2007,91(3):191-223.
[33]Pitcher W S.Granite type and tectonic environment[C]//Hsu K J.Mountain Building Process,London,1983:19-40.
[34]张旗,王焰,李承东,等.花岗岩按照压力的分类[J].地质通报,2006,25(11):1274-1278.
[35]Petford N,Atherton M.Na-rich partial melts from newly underplated basaltic crust:the Cordillera Blanca bathloith,Peru[J].Journal of Petrology,1996,37:1491-1521.
[36]金振民,高山.底侵作用(underplating)及其壳-幔演化动力学意义[J].地质科技情报,1996,(2):1-7.
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