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高校地质学报 ›› 2020, Vol. 26 ›› Issue (5): 481-496.DOI: 10.16108/j.issn1006-7493.2019109

• 岩石学与矿物学 •    下一篇

冈底斯中段谢通门县查布中新世埃达克质岩石成因及其地质意义

洪宇飞,邱检生*,王睿强,温定军,徐航,李艳芳   

  1. 南京大学地球科学与工程学院, 内生金属矿床成矿机制研究国家重点实验室,南京 210023
  • 出版日期:2020-10-20 发布日期:2020-10-28

Petrogenesis of the Miocene Adakitic Rocks from Chabu of Xietongmen County in the Middle Segment of the Gangdese Belt, and Its Geological Significances

HONG Yufei,QIU Jiansheng*,WANG Ruiqiang,WEN Dingjun,XU Hang,LI Yanfang   

  1. State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
  • Online:2020-10-20 Published:2020-10-28

摘要: 查布复式花岗质岩体位于冈底斯岩浆岩带中段,出露面积约400 km2。文章报道了该岩体浅成相黑云母二长花岗斑岩和次火山岩相英安斑岩的锆石U-Pb年龄、元素地球化学和Sr-Nd-Hf同位素组成,据此探讨了岩石的成因及其所蕴含的地质意义。锆石LA-ICP-MS U-Pb定年结果表明,它们的成岩年龄为13~16 Ma,属中新世时期岩浆活动的产物。地球化学组成上,这套岩石为高钾钙碱性、准铝质—弱过铝质,富集轻稀土和Rb、Th、U等大离子亲石元素,亏损Nb、Ta、Ti等高场强元素,Cr、Ni的含量低,缺乏显著铕负异常,并具有高Sr和低Y、Yb含量,以及高的Sr/Y及(La/Yb)N比值,可归之为埃达克质岩石。它们的(87Sr/86Sr)i 比值偏高(=0.706347~0.707584),εNd(t)值明显偏低(=-4.15~-7.33),并具有散布于负值到正值之间的锆石εHf(t)值(=-5.99~7.78)。综合分析表明,中新世时期印度陆壳已俯冲至拉萨地块之下,查布埃达克质岩形成于后碰撞的伸展背景,应为增厚的初生镁铁质下地壳部分熔融岩浆与深俯冲而进入拉萨地块之下的印度古老地壳组分经混合作用的产物。

关键词: 埃达克质岩, 岩石成因, 中新世, 印度陆壳, 谢通门县查布

Abstract: The Chuabu composite granitic pluton, with an outcrop area of about 400 km2, is located in the middle segment of the Gangdese belt. This paper presents comprehensive zircon U-Pb age, elemental geochemistry and Sr-Nd-Hf isotopic compositions for the hypabyssal biotite monzogranite porphyry and subvolcanic dacite porphyry within the pluton, aiming to elucidate their origin and to discuss their geological significances. Zircon LA-ICP-MS U-Pb dating yields crystallization ages of about 13-16 Ma for these rocks, indicating that they were generated during Miocene. Geochemically, these rocks are high-K calc-alkaline, metaluminous-weakly peraluminous, enriched in light rare earth elements and large ion lithophile elements (LILEs, e.g., Rb, Th and U), and depleted in high field strength elements (HFSEs, e. g., Nb, Ta and Ti). They also have low Cr, Ni contents, and show indistinct Eu negative anomalies. These rocks have high Sr, low Y and Yb concentrations, with high Sr/Y and (La/Yb)N ratios, suggesting that they can be grouped into adakitic rocks. Isotopically, these rocks have higher (87Sr/86Sr)i ratios (=0.706347-0.707584), negative εNd(t) values (=-4.15- -7.33), and with wide range of zircon εHf(t) values varying from negative to positive (=-5.99-7.78). The integrated petrology, and elemental and isotopic compositions suggest that during Miocene, the Indian ancient continental crust had been subducted underneath the Lhasa terrane. The Chabu adakitic rocks were formed under a post-collisional extensional setting, and were likely produced by mixing between magmas from partial melting of the thickened mafic juvenile crust and components from the subducted ancient Indian continental crust.

Key words: adakitic rocks, petrogenesis, Miocene, Indian continental crust, Chabu, Xietongmen County

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