地质论评2025，Vol.71Issue(5)：1495-1516,22.DOI:10.16509/j.georeview.2024.10.002
桂西地区古生代地层中的火山灰特征及其意义
Characteristics and significance of volcanic ashes in palaeozoic formation in western Guangxi
摘要
Abstract
Objectives:There are hardly studies on volcanic ashs in platform facies of Paleozoic so that the type and provenance remain unknown,and hinder further study on tectonic evolution,so it is great significant to find and determine the ashes of volcano. Methods:Line investigation,zircon geochronology,microscopic research and element analysis. Results:Volcanic ashes can be found in silty mudstone of Tangjiaba Formation of Furongian of Cambrian,and in aluminum-bearing rock series at the bottom of Du'an Formation of Tournaisian of Carboniferous,and in the aluminium-bearing rock series at the bottom of Lopingian of Permian and overlying transgression series,all of volcanic ashes show resorption and devitrified structures.The volcanic ashes of Furongian display quartz porphyry,feldspar baby-crystal,white glass,melt inclusion,and the rock is crystal-rich that meaning rhyolite source.Plagioclase and pyroxene are the main phenocrysts in the aluminium-bearing rock series of Tournaisian,and show a little of glass,while the U-Pb ages of zircon give several peaks,with the main series age of 392～340 Ma,with the weighted mean age of 370±7.4 Ma,and secondary series age of 503～404 Ma;meanwhile the aluminium-bearing rock series enrich in LREE,Th,U and Pb,and depleted in Nb,Ta,Sr,P,Ti,but the varies of enrichment and depletion is small,whereas the Eu anomaly are weak,and Cr,Ni and Co are strongly enriched,suggesting that the ashes derived from tholeiitic basalts nearby.The volcanic ashes in the superimposed transgression series and in the limestone adjacent the P/T boundary are mainly rhyolitic,and both of them were proximal. Conclusions:The acid volcanic ash of Furongian came from the Proto-Tethys island arc,and the Caledonian movement was the far-field reaction to the Proto-Tethys ocean-continent subduction in South China.The volcanic ash in the aluminium-bearing rock series of Tournaisian came from regional volcano within a branch ocean which contained west Guangxi.In the Late Permian,the volcanic ash came from the Song Ma belt of Paleo-Tethys in the margin of South China.The volcanic ashes provide a strong support for the determination of the"trench-arc-basin"model.关键词
火山灰/铝土矿/地球化学/特提斯/岛弧/沟—弧—盆/桂西Key words
volcanic ash/bauxite/geochemisrty/tethys/arc/trench-arc-basin/western Guangxi引用本文复制引用
张启连,辛晓卫,王学恒,周辉,刘希军,韦访,李活松,李玉坤,利奂章,谢植贵..桂西地区古生代地层中的火山灰特征及其意义[J].地质论评,2025,71(5):1495-1516,22.基金项目
本文为中国矿产地质志项目(编号:DD20221695,DD20190379,DD20160346)、广西地质矿产勘查开发局项目(编号:KD-[2023]-XZ-050)、广西地质矿产勘查开发局项目"广西寒武系生物地层划分对比及沉积环境研究"(编号:GXDK202432)和广西自然资源厅项目"广西地质遗迹综合调查评价"的成果. This study was funded by the project of"Geology of mineral resources in China"from China Geological Survey(Nos.DD20221695,DD20190379,DD20160346),"Continuation and product service of records for mineral & geology of Guangxi(No.KD-[2023]-XZ-050)","Studies on the comparison-division and sedimentary environment of Cambrian biostratigraphy in Guangxi"and"Comprehensive investigation and evaluation of geological relics in Guangxi"from Guangxi Bureau of Geology and Mineral Prospecting and Exploitation" （编号:DD20221695,DD20190379,DD20160346）
