| 超基性岩中锆石年龄的特征和意义——以西南天山UHP蛇纹岩中锆石U-Pb年龄为例 |
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| 引用本文： | 申婷婷,张立飞,杨经绥,张聪,邱添,BADERThomas.超基性岩中锆石年龄的特征和意义——以西南天山UHP蛇纹岩中锆石U-Pb年龄为例[J].岩石学报,2017,33(12):3783-3800. |
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| 作者姓名： | 申婷婷 张立飞 杨经绥 张聪 邱添 BADERThomas |
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| 作者单位： | 中国地质科学院地质研究所, 北京 100037,北京大学造山带与地壳演化教育部重点实验室, 北京 100871,中国地质科学院地质研究所, 北京 100037,中国地质科学院地质研究所, 北京 100037;山东科技大学地球科学与工程学院, 青岛 266510,中国地质科学院地质研究所, 北京 100037,北京大学造山带与地壳演化教育部重点实验室, 北京 100871 |
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| 基金项目： | 本文受国家自然科学基金项目（41502039、41541017、41641015、41572051）、中国博士后基金项目（2016T90011）、地调项目（DD20160023-01）和中国地质科学院基本科研业务费（J1701、YYWF201702）联合资助. |
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| 摘 要： | 超基性岩本身难以生长锆石的特性,使得研究其中的锆石需要特别谨慎。超基性岩中的锆石虽然具有多解性,但是锆石也携带了很多演化信息。产出不同地质背景的超基性岩,其中的锆石特征不同。本文总结现有的研究实例表明:(1)经历高温高压变质作用的石榴橄榄岩通常通过交代作用获得锆石,且锆石能够记录峰期变质时代,其中的继承锆石较少,可能在高温高压条件下,继承锆石发生分解重结晶;(2)大洋蛇绿岩型超基性岩和地幔岩捕掳体中通常具有年龄分布很广的锆石年龄特征,锆石年龄峰值通常与区域上构造事件相吻合,为捕掳晶锆石。接下来本文以西南天山超高压(UHP)蛇纹岩为例,对其锆石年龄进行解释。西南天山蛇纹岩为经历过超高压变质作用的大洋蛇绿岩型超基性岩,2个蛇纹岩样品中锆石的阴极发光图像分析和SIMS U-Pb定年分析结果显示,西南天山UHP蛇纹岩中的锆石包含捕掳晶锆石和变质锆石,捕掳晶锆石的年龄为2.1~1.0Ga,对应该区变泥质岩中碎屑锆石记录的年龄峰值。409~537Ma可能代表了蛇纹岩原岩结晶时代。区域上的变质压力峰期年龄(~320Ma)在蛇纹岩中没有记录,仅有1颗锆石记录了309±5Ma的近峰期时代。270~155Ma的退变质时代在西南天山蛇纹岩中出现较广,这与榴辉岩中出现的退变年龄相吻合,代表了折返过程中较为普遍的后期热液事件。基于对超基性岩中锆石特征的初步了解,结合西南天山蛇纹岩的研究实例,认为通过研究锆石的年代学,结合锆石矿物化学、包体矿物学、同位素地球化学等特征,不仅可以提供年代学信息,还可以对超基性岩的来源和演化过程进行解析。
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| 关 键 词： | 锆石U-Pb定年 年龄 超基性岩 超高压蛇纹岩 西南天山 |
| 收稿时间： | 2017/9/4 0:00:00 |
| 修稿时间： | 2017/11/20 0:00:00 |
The characteristics and significance of age of zircon from ultramafic rocks: A case study from UHP serpentinites in Chinese southwestern Tianshan |
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| SHEN TingTing,ZHANG LiFei,YANG JingSui,ZHANG Cong,QIU Tian and BADERR Thomas.The characteristics and significance of age of zircon from ultramafic rocks: A case study from UHP serpentinites in Chinese southwestern Tianshan[J].Acta Petrologica Sinica,2017,33(12):3783-3800. |
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| Authors: | SHEN TingTing ZHANG LiFei YANG JingSui ZHANG Cong QIU Tian and BADERR Thomas |
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| Institution: | Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China,MOE Laboratory of Orogenic Belt and Crustal Evolution, Peking University, Beijing 100871, China,Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China,Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;Institute of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266510, China,Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China and MOE Laboratory of Orogenic Belt and Crustal Evolution, Peking University, Beijing 100871, China |
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| Abstract: | Zircon is rare in ultramafic rocks because of their bulk compositions, wherefore studying of zircons found in them should be especially cautious. The explanation of this kind of zircon might be confounded, but these zircons also carry a wealth of evolutionary information. The characteristics of the zircons from ultramafic rocks of different geological backgrounds differ. This paper summarizes research examples from the literature and shows that (1) garnet peridotites commonly gain zircon through metasomatic processes. Zircon could record the peak metamorphic age and less inherited zircon, which may be decomposed and recrystallize because of the high pressure and temperature, is found. (2) Zircons from ophiolitic ultramafic rocks and mantle-derived xenoliths usually show a wide age range, which is associated with the tectonic events in the region. In this paper, we take Chinese southwestern Tianshan serpentinite as an example, to explain the age of zircons. Serpentinites from Chinese southwestern Tianshan are meta-ophiolitic ultramafic rocks, which have experienced ultrahigh-pressure metamorphism. Cathodoluminescence images and SIMS U-Pb dating reveal that two serpentinite samples host both inherited and metamorphic zircons. The age of the inherited zircons is 2.1~1.0Ga, consistent with the age peaks of the detrital zircons from metapelites of this area. 537~409Ma may be the crystallization age of the protoliths of the serpentinites. The peak UHP metamorphism (~320Ma) was not recorded by the serpentinite zircons, and only one zircon shows an age of the near-peak period (309±5Ma). The retrograde ages of 270~150Ma appear widely in the southwestern Tianshan serpentinites. They correspond to the retrograde ages found in eclogites of this area, representing rather common hydrothermal events from the late exhumation process. The study of the zircon chronology for ultramafic rocks, combined with analysis of zircon mineralogy, inclusions, and isotope geochemistry, can not only provide information about ages, but also about evolutionary processes and the sources of an ultramafic zircon-hosting rock. |
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| Keywords: | Zircon U-Pb dating Age Ultramafic rocks UHP serpentinite Southwestern Tianshan |
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