桂西二叠系铝土岩系中的灾变事件
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广西壮族自治区地质调查院

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The catastrophe events in bauxite-bearing rock series of the Upper Permianin western Guangxi
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Guangxi Institute of Geological Survey

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    摘要:

    灾变事件赋存着重要的地质信息,其遗迹具有很高的经济和科学价值,发现和研究灾变事件是解决地质问题的方法之一,也是提高地质科学认识水平的途径。本文通过桂西地区铝土矿床野外调查、显微特征研究和含矿岩系重金属元素分析,列举桂西地区二叠系含铝岩系主要灾变事件,阐释其形成诱因。含铝岩系灾变事件主要为火山灰季、重金属异常和地震幕;火山灰降落时长跨度可达10Myr,火山灰岩性为基性到酸性均有出现,为岛弧岩浆系列;相对于华北、黔北等铝土矿矿集区,桂西含铝岩系中Cr强烈富集,剖面平均值为400~900μg/g,Ni在部分剖面中强烈富集,平均值300~600μg/g,Cd在大多数剖面中富集,Co在少数剖面中富集,在含酸性火山灰的岩层中Sb、As强烈富集,Cr、Ni、Cd、Sb、As、Co等六种元素构成重金属异常;元素地球化学特征表明存在玻安岩;地震遗迹主要为地裂缝,其次为震浊积岩、层内断层、软变形。火山灰降落和地震幕的诱因应为印支板块与华南板块西南缘之间的俯冲,汇聚发展到高角度俯冲时形成岛弧岩浆,同时弧后盆地拉张引发了地震。火山灰不仅为含铝岩系提供了铝、铁、硅等物质,还提供了重金属,导致重金属异常,Co的富集与铁矿有关,稀贵金属亦与火山灰有一定的联系;地震事件对铝土矿的影响体现在对地形的分异,维持风化壳发展格架,扩大矿体规模。

    Abstract:

    The hosts of catastrophic events contain important geological information, and being worthy of high economy and science, so to find and study catastrophic events are one of the methods to solve geological problems, additionally a way to raise the understanding of geology. Based on the field investigation on bauxite deposits in western Guangxi, and the microscopic characteristics and the data of heavy metal elements of ore-bearing rock series, this paper lists the main catastrophic events of Permian aluminum-bearing rock series in western Guangxi, and try to explain its geneses. The catastrophic events in aluminium-bearing rock series are mainly volcanic ash season, heavy metal anomaly and earthquake episode; The duration of volcanic ash fall could live 10Myr, and the volcanic ash lithology consequence ranks from basic to acid, which is consistent to island arc magma; Compared with another bauxite deposits such as North China and North Guizhou, the Cr is strongly enriched in rock series, with an average value of 400 ~ 900μg/g in all sections, Ni is strongly enriched in some sections, with an average value of 300 ~ 600μg/g, Cd is enriched in most sections, Co is enriched in few sections, Sb and As are strongly enriched in the rock containing acid volcanic ash, thus the Cr, Ni, Cd, Sb, As and Co constitute heavy metal anomalies. The geochemical characteristics of the elements indicate that boninite had developed; The seismic relics are mainly groundfissures, followed by seismic turbidite, intraformational faults and soft deformation. The volcanic ash fall and seismic episode were caused by the subduction of the Indosinian plate with the southwestern margin of the South China plate, and soon the island arc magma were formed when the convergence developed to high-angle subduction, and soon the back~arc basin extension caused earthquake. Volcanic ash not only provided aluminum, iron, silicon for aluminiferous rock series, but also heavy metals, resulting in heavy metal anomalies. The enrichment of Co was related to iron ore, and rare and precious metals were somewhat related to volcanic ash. The influence of seismic events on bauxite was making out the differentiation of topography to maintain the elevation of weathering crust and expanding the scale of ore bodies.

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  • 收稿日期:2024-02-04
  • 最后修改日期:2024-06-15
  • 录用日期:2024-06-18
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