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引用本文:何垚砚,牛志军,张遵遵,宋芳,姚华舟,杨文强,龚银杰,王忠伟,甘金木,王志宏. 黔东北沿河县奥陶系湄潭组碎屑锆石特征、物源——构造意义及其成矿年代学启示[J]. 中国地质, 2020, 47(4): 1025-1040.
HE Yaoyan,NIU Zhijun,ZHANG Zunzun,SONG Fang,YAO Huazhou,YANG Wenqiang,GONG Yinjie,WANG Zhongwei,GAN Jinmu,WANG Zhihong. Detrital zircons of the Meitan Formation during Ordovician in Northeastern Guizhou and its significance for provenance-tectonic and implications for metallogenic chronology[J]. Geology in China, 2020, 47(4): 1025-1040(in Chinese with English abstract).
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黔东北沿河县奥陶系湄潭组碎屑锆石特征、物源——构造意义及其成矿年代学启示
何垚砚1,2, 牛志军2,3, 张遵遵3, 宋芳2,3, 姚华舟3, 杨文强2,3, 龚银杰3, 王忠伟4, 甘金木3, 王志宏2,3
1.中国地质大学(武汉)地质调查研究院 湖北 武汉 430074;2.中国地质调查局古生物与生命-环境协同演化重点实验室 湖北 武汉 430205;3.中国地质调查局武汉地质调查中心 湖北 武汉 430205;4.西南石油大学地球科学与技术学院 四川 成都 610500
摘要:
黔东北沿河县位于中扬子地区,分布有众多低温热液矿床,构造上位于加里东期前陆盆地的隆后带,是研究盆地物源-构造响应的良好场所,然而在中扬子的大部分地区,奥陶纪地层序列多以碳酸盐岩为主夹泥质岩,因而从岩性上制约了碎屑锆石年代学等定量分析手段的开展。近来,笔者注意到沿河县及周边地区下—中奥陶统湄潭组(O1-2m)为泥岩、灰岩夹(钙质)砂岩,采样分析结果表明,湄潭组碎屑锆石年龄大于1.0 Ga的锆石仅8颗(占12%)且未形成峰值,最年轻一组谐和年龄的加权平均值((457.8 ±8.1)Ma)与该组沉积上限十分接近,反映湄潭组碎屑主要来自新隆升的物源区,且具有相对较高的沉积速率。根据年龄的分布和特征峰值,可分为5组:~461 Ma(Ⅰ)、~580 Ma和~606 Ma(Ⅱ)、~722 Ma(Ⅲ)、~865 Ma(Ⅳ1)和~936 Ma(Ⅳ2),其中Eu正异常的锆石集中分布于第Ⅰ组(占62%),而在第Ⅱ组和第Ⅳ2组中缺失,结合稀土元素等的分析,认为其物源主要分为3部分,第Ⅰ组、第Ⅱ组和第Ⅳ2组、第Ⅲ和Ⅳ1组,分别主要来自3个不同的物源区,分别对应黔中隆起、扬子西缘康滇古陆(另有少量来自扬子东南缘—华夏地区)、武陵—雪峰隆起。此外,第Ⅰ组年龄450~511 Ma范围内发育了高达73%的热液锆石,与区域低温热液成矿时间对应,认为其形成是物源区流体的活跃导致的,可能与奥陶纪区域构造体制从伸展到挤压的转换有关,暗示此时加里东运动已经开始波及中扬子沿河地区,但主要表现为热液活动,并没有发生大规模岩浆作用。
关键词:  奥陶纪  湄潭组  碎屑锆石  物源  热液锆石  中扬子  低温热液矿床  矿产勘查工程
DOI:10.12029/gc20200409
分类号:P597;P534.42
基金项目:中国地质调查局地质矿产调查评价专项项目(DD20179385、DD20179232)和国家自然科学基金项目(41772019)联合资助。
Detrital zircons of the Meitan Formation during Ordovician in Northeastern Guizhou and its significance for provenance-tectonic and implications for metallogenic chronology
HE Yaoyan1,2, NIU Zhijun2,3, ZHANG Zunzun3, SONG Fang2,3, YAO Huazhou3, YANG Wenqiang2,3, GONG Yinjie3, WANG Zhongwei4, GAN Jinmu3, WANG Zhihong2,3
1.Institute of Geological Survey, China University of Geosciences, Wuhan 430074, Hubei, China;2.Key Laboratory for Paleontology and Coevolution of Life and Environment, CGS, Wuhan 430205, Hubei, China;3.Wuhan Center of Geological Survey, CGS, Wuhan 430205, Hubei, China;4.School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, Sichuan, China
Abstract:
Located in northeastern Guizhou of middle Yangtze area, Yanhe County has many low-temperature hydrothermal deposits. It is a good place for studying the provenance-tectonic response of the basin due to its back-bulge position during Ordovician. However, in most area of middle Yangtze, stratigraphic sequence is composed mainly of carbonate rocks intercalated with mudstone, which restricts the development of quantitative analytical methods such as the detrital zircon geochronology. Recently, the authors noticed that there are mudstone and carbonate intercalated with sandstone around Yanhe in the Metitan Formation (O1-2m) of lower-middle Ordovician. A detrital zircon sample from the sandstone shows that only 8 zircons (12%) are older than 1.0 Ga and they have no age peaks, and the weighted average of the youngest group of zircons ((457.8 ±8.1) Ma) is close to the upper limit of the Meitan Formation. This means that the detritus of the Meitan Formation was mainly derived from a newly formed source area and had a relatively high deposition rate. The age of zircons can be divided into five groups according to their age distribution and peaks: ~461 Ma (Ⅰ), ~580 Ma and ~606 Ma (Ⅱ), ~722 Ma (Ⅲ), ~865 Ma (Ⅳ1) and ~936 Ma (Ⅳ2). On the basis of isotope ratio and REE, the authors consider that the ages can be divided into three parts:Ⅰ, Ⅱ and Ⅳ2, Ⅲ and Ⅳ1, which are mainly derived from three different source areas. Combined with the previous study, the authors hold that the three source areas are Qianzhong uplift, Kangdian ancient land, and Wuling-Xuefeng uplift, with Qianzhong and Kangdian being newly formed source area. What's more, there are many (73%) hydrothermal zircons in age group Ⅰ (450 ~511 Ma), and this age matches well with low-temperature hydrothermal mineralization, suggesting that it was caused by the activation of the fluid, probably due to the regional tectonic regime converted from extension to compression. This implies that the Caledonian movement had begun to affect the Yanhe area, but was mainly manifested as hydrothermal activity, with no large scale of magmatism.
Key words:  Ordovician  Meitan Formation  detrital zircon  provenance  hydrothermal zircon  middle Yangtze  low-temperature hydrothermal deposit  mineral exploration engineering