| 拉萨地块南部冈底斯~50 Ma负ε_(Nd)(t)花岗质侵入岩的发现及其地质意义 |
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| 引用本文： | 董瀚,齐玥,马涛,黄登鹏,李进喜,苟国宁,陈福坤,王强.拉萨地块南部冈底斯~50 Ma负ε_(Nd)(t)花岗质侵入岩的发现及其地质意义[J].大地构造与成矿学,2017,41(3):604-616. |
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| 作者姓名： | 董瀚 齐玥 马涛 黄登鹏 李进喜 苟国宁 陈福坤 王强 |
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| 作者单位： | 1. 甘肃省地矿局第三地质矿产勘查院,甘肃兰州,730050;2. 中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广东广州510640;中国科学院大学,北京100049;3. 中国科学技术大学地球与空间科学学院,壳幔物质与环境重点实验室,安徽合肥230026;4. 中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广东广州510640 |
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| 基金项目： | 冈底斯-喜马拉雅铜矿资源基地调查项目、中国科学院战略性先导科技专项(B类)，国家杰出青年基金，中国科学院广州地球化学研究所135项目 |
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| 摘 要： | 拉萨地块南部冈底斯岩浆带主要形成于中生代–早新生代(205~40 Ma),正的锆石ε_(Hf)(t)和全岩ε_(Nd)(t)显示了新生地壳组分的特征,其形成普遍被认为与新特提斯洋俯冲或印度–欧亚大陆碰撞后的板片断离有关。作者近期的研究工作显示,冈底斯岩浆带中部的早始新世挡顶拉和先弄错纳花岗质侵入岩具有明显的负ε_(Nd)(t)值。锆石LA-ICP-MS U-Pb年龄表明,上述侵入岩形成于~50 Ma,与冈底斯早新生代岩浆大爆发时期(~50 Ma)一致。挡顶拉和先弄错纳侵入岩具有轻稀土元素富集、重稀土元素亏损以及中等的负Eu异常特征,但先弄错纳岩体具有低的稀土元素总量和更明显的轻、重稀土元素分异。挡顶拉和先弄错纳侵入岩具有明显富集的Sr-Nd同位素组成:(~(87)Sr/~(86)Sr)i=0.7096~0.7121,εNd(t)=-7.3~-8.0。这些侵入岩主要可能来自古老地壳的重熔,且其源区组成矿物可能为黑云母+角闪石+石英+斜长石,岩浆在上升过程中经历了结晶分异。尽管目前的研究资料还无法解释这种富集的同位素特征是与拉萨古老地壳的部分熔融有关,还是与俯冲的印度古老大陆地壳物质熔融有关,但是明显负ε_(Nd)(t)值的花岗质岩石在拉萨地块南部冈底斯岩基中部的出现,有可能为新特提斯洋俯冲及印度–欧亚大陆碰撞过程提供新的启示。
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| 关 键 词： | 冈底斯 早始新世 侵入岩 负εNd(t)值 |
The Discovery of～50 Ma Granites with Negative εNd(t) in the Gangdese Area,Southern Lhasa Block and its Geological Implications |
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| DONG Han,QI Yue,MA Tao,HUANG Dengpeng,LI Jinxi,GOU Guoning,CHEN Fukun,WANG Qiang.The Discovery of～50 Ma Granites with Negative εNd(t) in the Gangdese Area,Southern Lhasa Block and its Geological Implications[J].Geotectonica et Metallogenia,2017,41(3):604-616. |
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| Authors: | DONG Han QI Yue MA Tao HUANG Dengpeng LI Jinxi GOU Guoning CHEN Fukun WANG Qiang |
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| Abstract: | The Gangdese magmatic belt,located in the southern Lhasa Block,is mainly formed in the Early Mesozoic to Eocene (205-40 Ma) and the igneous rock generally exhibit positive zircon εHf(t) and whole rock εNd(t) values.The rocks were commonly considered to be related to the Neo-Tethyan northward subduction or slab break-off following the India-Asia collision.However,our new data show that the Dangdingla and Xiannongcuona granites from the central Gangdese granitoids have negative whole rock εNd(t) values,which are strikingly different from the published data of the Gangdese magmatic rocks.The LA-ICP-MS zircon U-Pb dating suggests that they were generated in ～50 Ma,one peak time of the Gangdese magmatism.The Dangdingla and Xiannongcuona granites show light rare earth element (LREE) enriched patterns with moderate negative Eu anomalies.The Xiannongcuona granites have lower REE contents and higher (La/Yb)N than the Dangdingla rocks.Both of them have similar Sr-Nd isotopic compositions:(87Sr/86Sr)i=0.7096-0.7121,εNd(t)=-7.3--8.0,indicating ancient crustal origin.Major and trace element characteristics of these rocks indicate they were possibly derived from partial melting of biotite+amphibole+quartz+plagioclase-bearing source rock.With the data available,we could not determine whether they sourced from the ancient Lhasa basement or subducted India continental crust.However,the discovery of rocks with obviously negative εNd(t) values in central Gangdese belt may shed light on the understanding of the magma process of Neo-Tethyan lithosphere subduction and India-Asia collision. |
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| Keywords: | Gangdese belt Early Eocene intrusion negative whole rock εNd(t) values |
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