赣中相山铀矿田基底变质岩原岩恢复及其形成环境  

Protoliths reconstruction and formation conditions of basement metamorphic rocks in the Xiangshan uranium orefield, Central Jiangxi

作　　者：时国[1,2,3] 郭福生[1,3] 谢财富[3] 余关美 

机构地区：[1]江西省核资源与环境重点实验室,江西南昌330013 [2]中国地质科学院地质研究所,北京100037 [3]东华理工大学地球科学学院,江西南昌330013

出　　处：《中国地质》2015年第2期457-468,共12页Geology in China

基　　金：中国地质调查局工作项目(1212011120836);江西省博士后科研择优资助项目(2014KY31);国家自然科学青年基金项目(41002007)联合资助

摘　　要：微古化石资料和前人研究表明,相山铀矿田基底变质岩原岩时代为新元古代青白口纪。文章通过野外地质调查和系统采样对这套变质岩的原岩组成和形成环境进行了分析。大部分变质碎屑岩样品以中等Si O2含量、高的K2O/Na2O值和较高的Fe2O3T＋Mg O及低的Ca O含量为特征。所有样品的稀土元素具有∑REE总量较大、轻稀土富集和Eu亏损的特征。稀土元素分布模式图解中各样品的总体组成模式相当接近,稀土配分型式为右倾式,与后太古宙页岩和上地壳相似。西蒙南图解和涅洛夫图解表明,神山组原岩主要为复矿物砂岩和长石砂岩,库里组原岩主要为石英岩质砂岩及长石砂岩;上施组原岩主要为长石砂岩及少量硅质泥灰岩、泥质砂岩。结合变余构造特征分析认为,这套变质碎屑岩形成于滨浅海—陆棚沉积环境。所有样品中Th/Sc比值变化范围较小（0.5～1.1）,而Zr/Sc比值变化范围较大（8～24）,揭示了变质岩源区成分复杂,可能经过多次沉积循环。在Th-Sc-Zr/10和La-Th-Sc图解中,大部分数据落入大陆岛弧区,说明该套岩石可能沉积于靠近大陆岛弧的相关盆地。Hf-La/Th图解表明,原岩的物源大部分来源于古老地层的抬升剥蚀,酸性岛弧源区仅占少数,说明其沉积时期岩浆活动并不明显,而物源区伴有构造隆升,结合地化特征分析推测赣中相山基底变质岩原岩形成于华夏地块与扬子板块后碰撞伸展环境下的残留海盆。Located in the suture zone of the Cathaysia and Yangtze tectonic belt and lies on the southern side of Jiangshao fault, theXiangshan uranium orefield is the largest volcanic uranium orefield and is also the earliest discovered volcanic uranium orefield in China. Its basement is a set of ancient metamorphic rock series. Micro palaeophyte fossils and previous studies indicate that the basement metamorphic rocks formed in the Qingbaikou period of Neoproterozoic. This paper mainly discusses the composition of metamorphic rock and analyzes its formation environment. Most metamorphic samples are characterized by intermediate Si O2 content, high K2O/Na2 O and Fe2O3T＋Mg O, and obviously low Ca O content. Analytical results of all samples show larger total ΣREE values and abundant LREE, as well as depletion of Eu, implying that the rock samples originated from the continental crust. The overall compositions of various sample patterns are very close to each other in the REE distribution diagram, and REE patterns of all samples are of right-oblique type, similar to patterns of the post-Archean shale and the upper crust. From the Simonen and Nielv diagram, the authors infer that the original rocks of Shenshan Formation were mainly composed of complex mineral sandstones and feldspathic sandstone, the original rocks of Kuli Formation consisted mainly of quartzite sandstone and feldspathic sandstone, and the original rocks of Shangshi Formation comprised mainly feldspathic sandstone, with a little siliceous marl and shale sandstone.Combined with residual structural features analysis, it is inferred that these metamorphic clastic sedimentary rocks formed in a shallow shore- shelf sedimentary environment. Th/Sc ratios of all samples vary in a small range（0.5-1.1）, while Zr/Sc ratios vary quite considerably（8- 24）, revealing the complex composition of the source region of the metamorphic rocks and the probable existence of several sedimentary cycles. In Th-Sc-Zr/10 and La-Th-Sc diagram, most of the data fall into the co

关 键 词：变质岩 原岩恢复 地球化学 构造环境 相山铀矿田 

分 类 号：P619.14[天文地球—矿床学] P588.37[天文地球—地质学]