滇中元江地区中太古界元江群球粒状石英砂岩特征及岩石成因  

Spherical quartz sandstone of Mesoarchean Yuanjiang Group in central Yunnan and its petrogenesis

作　　者：陈光艳 刘桂春 李静 刘兵 邓仁宏 何兆荣 CHEN Guangyan;LIU Guichun;LI jing;LIU Bing;DENG Renhong;HE Zhaorong(Yunnan Institute of Geological Survey,Kunming 650216,Yunnan,China;Key Laboratory of Sanjiang Metallogeny and Resources Exploration and Utilization,MNR,Kunming 650061,Yunnan,China)

机构地区：[1]云南省地质调查院,云南昆明650216 [2]自然资源部三江成矿作用及资源勘查利用重点实验室,云南昆明650061

出　　处：《地质通报》2021年第7期1106-1116,共11页Geological Bulletin of China

基　　金：中国地质调查局项目《全国陆域及海区地质图件更新与共享》子项目《云南省系列地质图件数据处理与洋板块地质研究》(编号:DD20190370);国家自然科学基金项目《三江南段景洪大勐龙地区高压变质岩p-T-t轨迹及其对原-古特提斯构造演化的制约》(批准号:42062005);云南省科技计划重点项目《滇西格咱斑岩铜钼矿带多期复合成矿作用研究》(编号:2019FA018)。

摘　　要：元江群是中国首次确定的中太古代浅变质地层,其记录了地球发展演化早期的一系列重大地质事件。在元江群下部的曼林组、岔河组中发育一类与火山岩、火山碎屑沉积岩、化学沉积的块状石英岩共生的特殊砂岩——球粒状石英砂岩。宏观上,球粒状石英砂岩既可与凝灰质泥质板岩、泥质板岩组成递变粒序层理,也可单独呈中-厚层状与凝灰岩、火山岩、石英岩相伴产出,表明这类球粒状石英砂岩形成于活动性较强的大地构造背景。多数石英颗粒在镜下呈近等轴的球状,部分颗粒在成岩过程中显示明显的塑性变形;球粒状石英颗粒在阴极发光照片中不发光或发微弱的蓝光。对其中的热液包裹体进行测试,结果表明,这些石英颗粒形成于温度为60~100℃的热水沉积环境,是在弱水动力条件下,SiO_(2)含量过饱和的水体中沉淀形成的,属盆地内的自生矿物。对石英颗粒表面进行扫描,发现石英颗粒表面光滑,无擦痕,表明这些石英颗粒并未经历过长距离搬运,应属盆地内的原地-半原地沉积物。元江群下部曼林组中含有大量的凝灰质碎屑,与曼林组同期异相的迤纳厂组中普遍可见磁铁矿板岩、凝灰岩、块状含铜白云岩夹层等,指示了相似的沉积环境,表明当时火山活动较频繁,盆地水体温度总体较高,且变化较快。这类水体环境为最早的微生物提供了生存所需的能量,为中太古代末期蓝绿藻的大爆发奠定了基础。The Yuanjiang Group is a new lithostratigraphic unit in the central Yunnan region.It is the first time to identify the Mesoarchean shallow metamorphic strata in China,and it records a series of important geological events in the early stage of the earth's development and evolution.It was found that a typical quartz sandstone-spherical quartz sandstone was deposited in the Manlin Formation and Chahe Formation of the Lower Yuanjiang Group,associated with massive quartzite of volcanic,volcano-clastic and chemical sedimentary origin.On the macro level,the spherical quartz sandstone could be formed by graded bedding with tuff argillaceous slate and argillaceous slate,or it might be developed separately in medium-thick bedding with tuff,volcanic rock and quartzite,indicating that it was formed in an intensely active tectonic setting.The spherical quartz grains exhibit equal crystals,likely spherical crystal,showing no or slightly blue glass in the CL images,and could be formed by plastic growth.The results of hydrothermal inclusions test show that the quartz particles were formed from the SiO_(2)-saturated water in the hydrothermal sedimentary environment of 60~100℃ under weak hydrodynamic conditions.They belong to authigenic minerals in the basin.Scanning the surface of quartz particles,it is found that the surface of quartz particles is smooth and has no scratches,indicating that these quartz particles were not transported over a long distance,and should belong to the autochthonous to semi-autochthonous sediments in the basin.The Manlin Formation in the Lower Yuanjiang Group contains a large number of tuffaceous detritus,and its contemporaneous different facies Yinachang Formation commonly contains magnetite slate,tuff,and massive copper-bearing dolomite intercalation,which indicates a similar sedimentary environment.It shows that the volcanic activity was more frequent,and the water temperature in the basin was generally higher and changed rapidly.Such a water environment provided the first microorganisms with the

关 键 词：球粒状石英砂岩 自生矿物 热水沉积物 中太古代晚期 滇中元江 

分 类 号：P534.2[天文地球—古生物学与地层学] P58[天文地球—地质学]