黔西北普宜地区下三叠统嘉陵江组沉凝灰岩锆石LA-ICP-MS U-Pb年龄、微量元素特征
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本文为中国地质调查局基础性公益性综合地质调查项目“乌蒙山岩溶山区昭通—毕节区域地质调查” (编号:DD20191012)的成果


Zircon LA-ICP-MS U-Pb ages,trace element characteristics of the Lower Triassic Jialingjiang Formation tuffites in the Puyi area,northwestern Guizhou,and their geological significance
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    摘要:

    早三叠世时期频繁的火山事件是导致全球性气候和海洋环境异常的主要原因,前人对早三叠世重要界线时期的火山事件地层开展了大量研究,但对典型界线时期以外的其他火山事件地层却鲜有报道。本文以上扬子西南普宜地区嘉陵江组两件沉凝灰岩为研究对象开展了岩石学、岩相学、锆石年代学及微量元素组合特征等方面的研究。沉凝灰岩样品具有典型岩浆锆石的内部结构和微量元素组合特征,两组沉凝灰岩锆石谐和年龄分别为250. 6±0. 6 Ma和249. 1±0. 8 Ma,代表了母岩岩浆中新生锆石的结晶年龄。沉凝灰岩母岩主要以酸性花岗岩类为主,次为中性正长岩类和少量基性岩类。嘉陵江组沉凝灰岩与二叠系—三叠系界线(PTB)凝灰岩及Olenekian—Anisian界线(OAB)绿豆岩具有同源性,形成于活动大陆边缘的碰撞造山环境,源区很可能位于中越边境地区长山构造岩浆带—十万大山火山带,且在陆壳碰撞过程中源区地壳处于持续的增厚阶段,下地壳增厚部位的部分熔融形成补给岩浆上涌并使早期结晶矿物发生了部分熔蚀。本文嘉陵江组沉凝灰岩样品250. 6±0. 6 Ma年龄对应着Smithian—Spathian界线时期的全球性降温及短期生物复苏事件;249. 1±0. 8 Ma年龄的样品对应Spathian亚阶中期极端高温气候和生物再次灭绝事件,再次证明了早三叠世时期频繁的火山活动是导致气候改变和生物周而复始新生和灭绝的重要因素。其原因可能是阳伞效应和温室效应等因素综合反馈的结果,但具体证据仍需要将来更多学科综合研究成果的约束。

    Abstract:

    The frequent volcanic events in the Early Triassic period were the main causes of the global climate and marine environment anomalies. A lot of research on the volcanic events during the important boundary period of the Early Triassic have conducted, but few reports have been made on the other volcanic events stratas beyond the typical boundary. Methods: In this paper, we carried out some researches of the Jialingjiang Formation tuffites in the Puyi area by petrology, petrography, zircon geochronology and trace elements assemblage characteristics in the Southwestern margin of the Upper Yangtze.Results:Most of the tuffite zircons have the internal structures of acid magma zircon, the trace elements are characterized by a strong loss of LREE and strong enrichment of HREE; obvious positive Ce anomaly and negative Eu anomaly, and Th/U ratio> 0.2, which have the characteristics of typical magmatic zircon. The two groups of the zircons concordant ages are 250.6±0.6Ma and 249.1±0.8Ma, which correspond to the Smithian—Spathian (S—S) boundary and the middle Spathian substage in the early Triassic.Conclusions: The parent rocks of the Jialingjiang Formation tuffites are mainly acid granites, followed by neutral syenites and a few basic rocks. The tuffites of Jialingjiang Formation have the homology with Permian—Triassic boundary (PTB) tuffites and Olenekian—Anisian boundary (OAB) mung bean rocks, which formed in the collision orogenic environment of active continental margin. The source area is probably located in the Changshan tectonomagmatic belt—Shiwandashan volcanic belt in the China—Vietnam border area. During the continental crust collision, the crust of the source area was in a continuous thickening stage, and the partial melting of the thickened lower crust formed the upwelling of supplementary magma caused the early crystalline minerals partially melting corrosion. Frequent volcanic events in the Early Triassic period were the main factors leading to climate change and biological rebirth and extinction, the reason may be the result of the comprehensive feedback of factors such as the parasol effect and the greenhouse effect. However, the specific evidence still needs to be constrained by the more comprehensive results of more disciplines in the future.

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缪宇,吴亮,肖长源,李锁明,李致伟,宋文婷,田瑜峰.2021.黔西北普宜地区下三叠统嘉陵江组沉凝灰岩锆石LA-ICP-MS U-Pb年龄、微量元素特征[J].地质论评,67(2):289-310,[DOI].
MIAO Yu, WU Liang, XIAO Changyuan, LI Suoming, LI Zhiwei, SONG Wenting, TIAN Yufeng.2021. Zircon LA-ICP-MS U-Pb ages, trace element characteristics of the Lower Triassic Jialingjiang Formation tuffites in the Puyi area, northwestern Guizhou, and their geological significance[J]. Geological Review,67(2):289-310.

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  • 收稿日期:2020-07-13
  • 最后修改日期:2020-12-04
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  • 在线发布日期: 2021-03-20
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