潘亮,周斌,鲁麟,韩奎,高峰,乔新星.冈底斯带东段日多地区航木多岩体地球化学、锆石U-Pb年代学、Lu-Hf同位素特征及其地质意义[J].西北地质,2021,54(4):59-81 PAN Liang,ZHOU Bin,LU Lin,HAN Kui,GAO Feng,QIAO Xinxing.Geochemistry, Zircon U-Pb Chronology, Lu-Hf Isotopic Compositions and Geological Significance of the Hangmuduo Granite in Riduo Area of Eastern Gangdise Belt[J].Northwestern Geology,2021,54(4):59-81
冈底斯带东段日多地区航木多岩体地球化学、锆石U-Pb年代学、Lu-Hf同位素特征及其地质意义
Geochemistry, Zircon U-Pb Chronology, Lu-Hf Isotopic Compositions and Geological Significance of the Hangmuduo Granite in Riduo Area of Eastern Gangdise Belt
投稿时间:2020-07-15  修订日期:2021-04-18
DOI:10.19751/j.cnki.61-1149/p.2021.04.005
中文关键词:  航木多岩体;锆石U-Pb年代学;锆石Lu-Hf同位素;新生地壳;日多地区
英文关键词:Hangmuduo granite;Zircon U-Pb chronology;Lu-Hf isotopic composition;Juvenile crust;Riduo area
基金项目:中国地质调查局“冈底斯-喜马拉雅铜矿资源基地调查”(DD20160015),陕西省地质勘查基金“陕西省勉略宁地区锰矿地质调查”(61202009346)。
作者单位
潘亮 陕西省地质调查院, 陕西 西安 710054
陕西省矿产地质调查中心, 陕西 西安 710068 
周斌 陕西省地质调查院, 陕西 西安 710054 
鲁麟 陕西省地质调查院, 陕西 西安 710054 
韩奎 陕西省地质调查院, 陕西 西安 710054 
高峰 陕西省地质调查院, 陕西 西安 710054 
乔新星 陕西省地质调查院, 陕西 西安 710054 
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中文摘要:
      冈底斯带古新世岩浆岩被认为是新特提斯洋消亡到印度与欧亚大陆碰撞过程的产物。林子宗群典中组火山岩及同期酸性侵入岩是冈底斯带东段典型的古新世岩浆岩组合,其对于研究冈底斯带地球动力学背景的判别有重要的指示意义。前人对林子宗群典中组火山岩虽进行过大量的研究工作,而对同期侵入岩研究较少,尤其是其成因和演化过程仍然存在较多分歧。本次以冈底斯带东段日多地区古新世航木多岩体为研究对象,进行岩石地球化学、锆石LA-ICP-MS U-Pb年代学及锆石Lu-Hf同位素分析。结果表明,3件花岗岩锆石LA-ICP-MS U-Pb年龄加权平均值分别为(62.6±0.6) Ma、(64.9±0.7) Ma和(62.2±0.7) Ma,与林子宗群典中组火山岩(69~60 Ma)同期形成。岩石地球化学分析表明,岩石具有高SiO2(72.23%~76.02%)、高铝Al2O3(12.73%~14.72%)、高K2O (2.19%~4.84%),低MgO (0.01%~0.52%)、低TiO2(0.12%~0.24%),高分异(86.35%~95.02%),过铝质(A/CNK=1.01~1.26)的地球化学性质,为S型花岗岩特征。但是,锆石Lu-Hf同位素结果显示,εHft)值为-10.64~10.79,二阶段模式年龄(tDM2)为443~1 810 Ma,暗示航木多岩体源区主要为新生地壳部分熔融,具有I型花岗岩特征。根据岩石微量元素对物源的判别,航木多岩体具有与日多盆地内晚侏罗世—晚白垩世的碎屑岩沉积物一致的岩石学特征和地球化学特征,显示出轻稀土富集的稀土配分模式,并且富集大离子亲石元素Rb、K、Th、U和亏损高场强元素Nb、Ta、P、Ti。综合前人成果,研究认为,航木多岩体为叶巴火山弧快速风化后在日多盆地内形成的具有类似新生地壳岩石学和地球化学特征的沉积物于同碰撞背景下发生部分熔融,同时还加入少量古老结晶基底,并经历了分离结晶作用而形成的具有弧岩浆特征的S型花岗岩。
英文摘要:
      The Paleocene magmatic rocks in the Gangdese belt are considered to be the product of the demise of the New Tethys Ocean to the collision between India and Eurasia. The volcanic rocks and the contemporaneous acidic intrusive rocks of the Dianzhong Formation of the Linzizong group are typical paleocene magmatic assemblages of the eastern Gangdise belt, which is an important indictor to the geodynamic background of the Gangdisebelt. Previus researchers have done much work on the volcanic rocks of the Dianzhong Formation of the Linzizong group, but few on the contemporaneous intrusions. There are still disputes on its genesis and evolution. This paper studied the Paleocene Hangmuduo granite in Riduo area of eastern Gangdise belt with the bulk-rock geochemistry, zircon U-Pb geochronology, and Lu-Hf isotope in order to shed light on this issue. The results showed that the zircon U-Pb ages of the three granites samples are (62.6±0.6) Ma,(64.9±0.7) Ma and (62.2±0.7) Ma respectively, in accordance with the ages of the Dianzhong Formation of the Linzizong group. Geochemically, the rocks show the characteristics of high SiO2 (72.23%-76.02%), Al2O3 (12.73%-14.72%) and K2O(2.19%-4.84%); low MgO (0.01%-0.52%) and TiO2(0.12%-0.24%); high differentiation(DI 86.35%-95.02%) and pera luminous (A/CNK1.01-1.26), belonging to S-type granites. However, the zircon Lu-Hf isotope results show that the εHf (t) value is mainly between-10.64 and 10.79, and the two-stage model age(tDM2) is between 443 and 1810 Ma. It suggests that the source of the Hangmuduo granitic pluton is mainly the partial melting of the juvenile crust and has the characteristics of I-typegranite. the identification of trace elements of Hangmuduo granite shows the enrichment of LILE (Rb, K, Th and U) and the depletion of HFSE (Nb, Ta, P and Ti), with the light rare earth-enriched rare earth distribution model petrologically and geochemically, which is in consistent with clastic sedimentsin Riduo basin from late Jurassic to late Cretaceous. Combined with the previous research in Gangdese belt, it is held that the Hangmuduo granite had been derived from the partial melting of clastic sediments under the co-collision from the rapid weathering of the Yeba volcanic arc in Riduo basin, which has similar lithological and geochemical characteristics to juvenile crust. Meanwhile, a small amount of ancient crystallization basement mingled and formed S-type granite with the arc magmatic characteristics through crystallization differentiation.
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