浙江大桥坞铀矿床火山岩锆石形态学与年代学研究

发布时间：2018-05-25 05:34

本文选题：锆石形态学 + U-Pb年代学　；参考：《地质学报》2017年03期

【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 Daowu uranium deposit is located in the eastern section of Ganhang structural belt, and its host rock is a set of fluid-magmatic volcanic-intrusive complex. At present, the understanding of the diagenetic timing of the complex is still controversial and lack of accurate chronological data. Therefore, the zircon morphology and geochronology of volcanic rocks and granitic breccia of the Xiaowu uranium deposit are studied in this paper in order to determine the volcanic eruption cycle in this area. The results of scanning electron microscope (SEM) show that there are five types of zircon crystals in the volcanic rocks of Huangjian formation: S24 S25 P3P4 and P5. The frequency statistics of crystal patterns show that the magma of the upper and lower reaches of Huangjian formation are different in nature, which are alkaline and subalkaline to alkaline, respectively. The results of zircon U-Pb dating show that the diagenetic ages are 128Ma and 133135Ma, respectively. The above characteristics indicate that the lower volcanic clastic rocks in the upper Huangjian formation are the product of different magmatic eruptions. The diagenetic age of granitic breccia in pyroclastic rocks is 138 MaA, which represents the earliest magmatism in the area, suggesting that the granitic intrusive basement may exist in this area. According to the geochronology, lithologic characteristics and borehole data, magmatism in this area can be divided into the following stages: 1) granitic intrusive basement formation and early volcanism (136Ma-1), forming Laocun formation red conglomerate and volcanic sedimentary rock Yao3) strong volcanic eruption period. In the first stage, 135U 133 Ma) formed giant thick fluvial tuff in the lower member of Huangjian formation. In the second stage, the upper member of Huangjian formation is gray, greyish green tuff and grayish green tuff and gravelly grained tuff are formed in the second stage, and the granite porphyry vein and diabase vein are formed in the intrusive stage, and the granitic porphyry vein and diabase vein are formed at the late stage of volcanism, and the Shouchang formation shale and fine sandstone are formed. Sedimentary tuff and crystalline tuff. The felsic volcanic rocks in the Ganhang tectonic belt were mainly formed in the early Cretaceous, and the volcanism in the eastern part is stronger than that in the western part. The volcanic rock type uranium deposits in the eastern section of the Ganghang structural belt are younger than those in the western section, and the ages are mainly concentrated at 135U 127 Ma.
【作者单位】：内生金属矿床成矿机制研究国家重点实验室南京大学地球科学与工程学院;
【基金】：国家重点基础研究发展计划“973”项目(编号2012CB416703) 中国核工业地矿事业部十二五高校基础科研项目联合资助的成果
【分类号】：P619.14

【相似文献】