| 喜马拉雅造山带中新世岩浆型石榴子石的矿物化学特征:从高Sr/Y花岗岩到淡色花岗岩 |
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| 引用本文： | 曾令森,赵令浩,高利娥,侯可军,王倩.喜马拉雅造山带中新世岩浆型石榴子石的矿物化学特征:从高Sr/Y花岗岩到淡色花岗岩[J].岩石学报,2019,35(6):1599-1626. |
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| 作者姓名： | 曾令森 赵令浩 高利娥 侯可军 王倩 |
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| 作者单位： | 自然资源部深部动力学重点实验室, 中国地质科学院地质研究所, 北京 100037,自然资源部深部动力学重点实验室, 中国地质科学院地质研究所, 北京 100037;中国地质科学院国家地质实验测试中心, 北京 100037,自然资源部深部动力学重点实验室, 中国地质科学院地质研究所, 北京 100037,中国地质科学院矿产资源研究所, 北京 100037,中国地质科学院国家地质实验测试中心, 北京 100037 |
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| 基金项目： | 本文受第二次青藏高原科学考察项目（2019QZKK0702）、国家重点研发计划（2016YFC0600304）、国家自然科学基金项目（41425010、41873023）和中国地质调查局地质调查项目（DD20190057）联合资助. |
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| 摘 要： | 石榴子石是演化花岗岩常见的重要副矿物之一,但石榴子石地球化学特征如何随岩浆演化而变化是有待探讨的问题之一。雅拉香波片麻岩穹隆发育年龄分别为20. 3±0. 5Ma和20. 1±0. 3Ma(锆石U-Pb年龄)的高Sr/Y比二云母花岗岩(TMG)和淡色花岗岩(Grt-LG)。虽然两类花岗岩都含石榴子石,且在形成时代和Sr-Nd同位素组成上相似,但在元素地球化学特征上具有明显的差异,淡色花岗岩和二云母花岗岩分别代表演化程度较高和较原始的岩浆。在同一件样品中,在石榴子石颗粒之间,存在一定程度的微量元素地球化学特征的不均一性,反映了局部熔体地球化学特征。在两类花岗岩中,岩浆型石榴子石具有以下相似的地球化学特征:(1)从核部到边部,Mn和HREE含量降低,表现出典型的生长环带特征;(2)富集HREE,亏损LREE;和(3)显著的Eu负异常。但在关键微量元素Zn、Sc和Y上,具有明显的差异性。在花岗质岩浆演化过程中,贫Fe、Mg和Mn矿物相的分离结晶作用,导致残留熔体的Ca和Sr含量降低,Eu负异常幅度增大,Sc、Zn、Y和HREE增高,是导致淡色花岗岩石榴子石相应元素含量增高的主要原因。上述观测表明:高Sr/Y花岗岩也可以结晶石榴子石,与通常的淡色花岗岩石榴子石相比,这些石榴子石的Sc、Zn和Y含量和Eu异常幅度明显较低。但随分异程度的升高,石榴子石的元素地球化学特征与源自变沉积岩的淡色花岗岩的类似。因此,花岗岩中的石榴子石矿物化学特征变化记录了花岗岩岩浆演化的重要信息。
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| 关 键 词： | 喜马拉雅造山带 高Sr/Y花岗岩 石榴子石 淡色花岗岩 微量元素地球化学 |
| 收稿时间： | 2019/2/9 0:00:00 |
| 修稿时间： | 2019/4/27 0:00:00 |
Magmatic garnet from Mid-Miocene co-genetic high Sr/Y granite and leucogranite from the Himalayan orogenic belt, southern Tibet |
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| ZENG LingSen,ZHAO LingHao,GAO LiE,HOU KeJun and WANG Qian.Magmatic garnet from Mid-Miocene co-genetic high Sr/Y granite and leucogranite from the Himalayan orogenic belt, southern Tibet[J].Acta Petrologica Sinica,2019,35(6):1599-1626. |
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| Authors: | ZENG LingSen ZHAO LingHao GAO LiE HOU KeJun and WANG Qian |
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| Institution: | MNR Key Laboratory of Deep-Earth Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China,MNR Key Laboratory of Deep-Earth Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;National Research Center for Geoanalysis, Chinese Academy of Geological Sciences, Beijing 100037, China,MNR Key Laboratory of Deep-Earth Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China,Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China and National Research Center for Geoanalysis, Chinese Academy of Geological Sciences, Beijing 100037, China |
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| Abstract: | Garnet is one of the common accessory phases in evolved A-type, I-type, and particularly S-type granitic rocks; however how the garnet mineral chemistry changes as granitic magma evolves is still an outstanding question that deserves careful investigation. High Sr/Y two-mica granite (TMG) and leucogranite (Grt-LG) crystallized at 20.3±0.5Ma and 20.1±0.3Ma (zircon U-Pb ages), respectively, within the Yardoi Gneiss Dome (YGD) of the Tethyan Himalaya. Though both of them are formed at similar ages, contain magmatic garnet grains, and show similarity in radiogenic (Sr and Nd) isotope compositions, they display pronounced differences in major as well as trace element geochemistry. Such differences indicate that Grt-LG represent the more evolved one, whereas TMG the more primitive one. Garnet grains in both suites of granites are characterized by similar features including:(1) typical growth zoning of rim-ward decreases in Mn and HREE; (2) enrichment of HREE and depletion of LREE; and (3) substantial negative Eu anomalies. However, they show significant differences in key trace elements such as Zn, Sc, and Y. As a granitic magma evolves, early crystallization of phases poor in Fe, Mg, and Mn would drive the residue melts toward progressive enrichment of Fe, Mg, and Mn as well as trace element of Zn, Sc, and Y. Garnet grains crystallized from such residual melts would incorporated much of those enrichment signatures as seen in the garnet-bearing leucogranites. Data presented in this contribution suggest that magmatic garnet could both crystallize in both high Sr/Y granites and common leucogranites. Variations in mineral chemistry of garnet grains from granitic rocks provide important records on the differentiation processes of an evolved granitic magmatic system. |
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| Keywords: | Himalayan orogenic belt High Sr/Y granite Garnet Leucogranite Trace element geochemistry |
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