论文部分内容阅读
奥地利东阿尔卑斯山地区Austroalpine杂砂岩带中的石炭纪Veitsch逆冲推覆体是“Veitsch型”晶质菱镁矿化的典型地区。几十年来,对其成因的解释一直是人们争论的焦点。为了解决这一长久以来的问题,本文对Veitsch推覆体的地质学、矿物学和地球化学制约条件进行了论述。菱镁矿仅仅存在于Veitsch推覆体之中,而其它推覆体中的碳酸盐岩岩层中则无菱镁矿。赋存于Veitsch推覆体中的碳酸盐岩石中的菱镁矿以不规则的岩株状、透镜状和层状产出。块状和厚层状的菱镁矿总是被白云岩包裹。在Veitsch推覆体中,沉积作用开始于晚维宪期的后造山的类磨拉石海相建造,并晚于内部基底带的变形和变质作用(“Bretonic期”)形成,该基底带位于现代的东阿尔卑斯山地区。沉积序列研究表明,演化从浅海大陆架开始,有时还穿插有高盐度的泻湖和透镜状生物礁,发展到海退的海岸线伴随有发育强烈的三角洲沉积的分支海湾和河流。由于成矿作用有好几个期次,所以对地球化学数据的解释相当复杂。 在Hohentauern／Sunk矿床中,石膏和硬石膏层在菱镁矿质沉积主岩中互层,其δ34S值分别为+17.6±0.2‰和+17.2±0.2‰,表现出石炭纪海水的特征。白云岩和菱镁矿的REE浓度要高于石灰质主岩。在Hohentauern／Sunk矿床中,球形白云岩中的白云岩球体和白云质基质
The Carboniferous Veitsch thrust nappe in the Austroalpine grit belt in the eastern Alps of Austria is a typical “Veitsch type” crystalline magnesite mineralization. For decades, the explanation of its causes has been the focus of debate. In order to solve this long-standing problem, this paper discusses the constraints on the geology, mineralogy and geochemistry of the Veitsch nappe. Magnesite is only present in the Veitsch nappe, while other carbonate rocks in the nappe have no magnesite. Magnesite deposits in carbonate rocks in the Veitsch nappe have been produced in irregular rocky, lenticular and lamellar configurations. Massive and thickly layered magnesite is always surrounded by dolomites. In the Veitsch nappe, sedimentation began with late-stage post-orogenic mylonitic marine facies and later than the deformation and metamorphism (“Bretonic period”) of the internal basement belt, Belt located in the modern Eastern Alps region. Sedimentary sequence studies show that evolution begins with the shallow continental shelf, sometimes with high-salinity lagoons and lenticular reefs, and develops into a receding coastline accompanied by highly developed deltaic distributary bays and rivers. Due to several stages of mineralization, the interpretation of geochemical data is quite complex. In the Hohentauern / Sunk deposit, gypsum and anhydrite layers interbedded in the magnesite sedimentary host rocks show δ34S values of +17.6 ± 0.2 ‰ and +17.2 ± 0.2 ‰, respectively, indicating the characteristics of Carboniferous seawater. The REE concentration of dolomite and magnesite is higher than that of calcareous host rock. In the Hohentauern / Sunk deposit, dolomite spheres and dolomitic spheres in the spherical dolomites