浙江大桥坞铀矿床火山岩锆石形态学与年代学研究
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南京大学,南京大学,南京大学,南京大学,南京大学,南京大学

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中国核工业地矿事业部十二五高校基础科研项目和国家重点基础研究发展计划(973计划)(编号:2012CB416703),


Zircon Morphology and Geochronology for Volcanic Rocks in the Daqiaowu Uranium Deposit, Zhejiang Province
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Nanjing University,Nanjing University,Nanjing University,Nanjing University,Nanjing University,Nanjing University

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    摘要:

    大桥坞铀矿床位于赣杭构造带东段,其赋矿围岩为一套流纹质火山-侵入杂岩。目前对该套杂岩成岩时序的认识仍有争议,且缺少精确的年代学数据。因此,本文对大桥坞铀矿床火山岩及花岗质角砾开展锆石形态学和年代学的研究,以厘定本区的火山喷发旋回。扫描电镜形貌研究结果表明,黄尖组火山岩中锆石晶型主要为S24、S25、P3、P4和P5五种。晶型频率统计显示黄尖组上、下段火山岩岩浆性质不同,分别为碱性和亚碱性到碱性。锆石U-Pb定年结果显示两者成岩时代也不同,分别为128 Ma和133 ~ 135 Ma。以上特征表明黄尖组上、下段火山碎屑岩是不同期次、不同来源岩浆喷发的产物。火山碎屑岩中花岗质角砾的成岩时代为138 Ma,代表了大桥坞地区最早的岩浆作用,暗示该地区可能存在花岗质侵入岩基底。综合年代学、岩性特征以及钻孔资料,本区岩浆作用可分为如下阶段:(1)花岗质侵入岩基底形成(138 Ma);(2)早期火山作用(136 Ma),形成劳村组红色砾岩和火山沉积岩;(3)强烈火山喷发期,第一阶段(135 ~ 133 Ma)形成黄尖组下段巨厚层熔结凝灰岩。第二阶段(128 Ma)形成黄尖组上段灰白、灰绿色沉凝灰岩和含砾晶屑凝灰岩;(4)脉岩侵入阶段(128 ~ 125 Ma),形成花岗斑岩脉和辉绿岩脉;(5)晚期火山作用(123 Ma),形成寿昌组页岩、细砂岩、沉凝灰岩和晶屑凝灰岩。赣杭构造带长英质火山岩主要形成于早白垩世,且东段火山作用明显强于西段。赣杭构造带东段的火山岩型铀矿床赋矿层位较西段年轻,时代主要集中在135 ~ 127 Ma。

    Abstract:

    The Daqiaowu uranium deposit hosted in volcanic-intrusive rocks is located in the eastern Gan-Hang Tectonic Belt (GHTB). Currently, episodic volcanic eruptions in this area are still controversial, and the volcanic rocks have been lack of accurate geochronological data. Thus, this study focuses on zircon morphology and geochronology of volcanic rocks and their granitic breccias to elucidate the volcanism in Daqiaowu area. Morphological results obtained by scanning electronic microscopy indicate that zircon crystal types of volcanic rocks in the Huangjian Formation are mainly S24, S25, P3, P4 and P5. Typological statistics suggest that the magma of volcanoclastic rocks from the upper Huangjian formation is alkaline, while that from the upper Huangjian formation is calc-alkaline to alkaline. Zircon U-Pb dating suggests that the upper and lower Huangjian Formations were formed at 128 Ma and 133~135 Ma, respectively. These characteristics imply that they could be ascribed to different volcanic eruptions. The crystallization age of granitic breccias is 138 Ma, which represents the earliest magmatism in the Daqiaowu area, suggesting a possible basement of granitic intrusive body under volcanoclastic rocks. Based on the geochronology, petrography and drill cores, the volcanic eruption cycles in the Daqiaowu area can be divided into following stages: (1) the formation of a basement of granitic intrusive body (138 Ma); (2) Early stage of volcanic eruption (136 Ma), the Laocun Formation was formed with red conglomerate and volcanic sedimentary rocks; (3) intense volcanic eruption stage, this stage can be divided into two subcycles. The early subcycle, named the lower Huangjian Formation, was formed at 135 ~ 133 Ma and mainly composed of massive ignimbrite. The late subcycle, named the upper Huangjian Formation, was formed at 128 Ma and composed of greyish-white to greyish-green tuff and breccia-bering crystal tuff; (4) dike intrusion stage, granite and diabase dikes were formed during 128 ~ 125 Ma; (5) late eruption stage, shale, fine-grained sandstone, tuff and crystal tuff of the Shouchang Formation were formed at 123 Ma. Volcanic rocks along the GHTB were formed during the Early Cretaceous, and volcanic activities were more intense in the eastern part of GHTB than in the western part. In addition, Uranium-bearing volcanic sequences in the eastern part are younger than those in the western part, and mainly have ages of 135 ~ 127 Ma.

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王洪作,陈培荣,吴俊奇,凌洪飞,赵友东,任海涛.2017.浙江大桥坞铀矿床火山岩锆石形态学与年代学研究[J].地质学报,91(3):571-587.
wang hong zuo, chen pei rong, wu jun qi, ling hong fei, zhao you dong, ren hai tao.2017. Zircon Morphology and Geochronology for Volcanic Rocks in the Daqiaowu Uranium Deposit, Zhejiang Province[J]. Acta Geologica Sinica,91(3):571-587.

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  • 收稿日期:2015-02-13
  • 最后修改日期:2015-08-09
  • 录用日期:2016-01-15
  • 在线发布日期: 2017-03-16
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