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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Lithofacies architecture, composition, and age of the Carboniferous Teplice Rhyolite (German-Czech border): Insights into the evolution of the Altenberg-Teplice Caldera
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Lithofacies architecture, composition, and age of the Carboniferous Teplice Rhyolite (German-Czech border): Insights into the evolution of the Altenberg-Teplice Caldera

机译：石炭质特普利采流纹岩（德国-捷克边境）的岩相构造，组成和年龄：对阿尔滕贝格-特普利采火山口的演变的见解

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摘要

The Teplice Rhyolite (TR) intra-caldera deposits of the Altenberg-Teplice Caldera (ATC, Central Europe) were investigated by lithofacies analysis, stratigraphy, and whole-rock chemistry as well as laser ablation U-Pb zircon dating. The aim was to demonstrate that the joint application of these methods can discern complex stratigraphy of ancient volcanic successions, susceptible to erosion and alteration, taking the TR as case study. The TR was regarded as a formation and divided into nine members that represent three main eruptions, each one separated by periods of volcanic quiescence. The first two eruptions mainly portrayed opening and clearing of vents, which were dominated by lithic-rich ignimbrites with lateral lithofacies changes (fiamme-rich to crystal-rich) covered by lava flows/domes. Eruption style was low pyroclastic fountaining alternated with effusive lava outpour. A sustained buoyant eruption column was exclusively interpreted at the outset of the second eruption based on the presence of a basal fallout deposit. The third eruption recorded three different phases: further vent opening, a waxing phase, and final lava extrusion. The vent opening phase was similar to those occurred in previous eruptions. The waxing phase produced voluminous, massive, poorly-sorted, very crystal-rich (>50 vol.%) ignimbrites, exhibiting progressive increase in crystal contents with height and chemical composition variations that indicate deposition by progressive aggradation. Low pyroclastic fountaining formed these high-particle concentration currents that waxed and reached quasi-steady conditions. Eruption ended with extrusion of a lava flow. The TR ignimbrites were emplaced hot and were partially to densely welded, as evidenced by eutaxitic texture, deformed glass shards, spherulites, perlitic cracks, and microcrystalline to granophyric textures. Horizontal and vertical lithofacies variations in pyroclastic deposits, together with progressive infill and association between TR feeding systems and faulting, demonstrate that eruptions developed through several fissure vents or faults. A volcanic explosivity index of 7 was estimated according to a minimum ejecta volume of similar to 320 km(3) (DRE). Volcanic architecture of the TR can be linked to sequential caldera subsidence that occurred synchronously with progressive deposition. Regional faulting (NE-SW-trending rhyolitic dykes) related to ATC feeding conduits suggests that progressive subsidence and final trap-door caldera collapse, possibly with a piece-meal component (faulted caldera floor), originated from post-Variscan tensional stress regime (similar to NNW-SSE direction). The TR Formation has a general rhyolitic composition with A-type granite affinities and a normal chemical zoning. U-Pb zircon dating yielded ages from 323 to 312 Ma, which, compared to age data from other ATC rocks, indicate that the TR was generated within a time span of similar to 325-317 Ma. (C) 2019 Elsevier B.V. All rights reserved.
机译：通过岩相分析，地层学，全岩化学以及激光烧蚀U-Pb锆石测年法研究了Altenberg-Teplice火山口（ATC，中欧）的Teplice流纹岩（TR）火山口内沉积物。目的是为了证明这些方法的联合应用可以辨别古代火山演替的复杂地层，易受侵蚀和蚀变的影响，以TR为例。 TR被认为是一个编队，分为九个成员，代表三个主要火山喷发，每个火山喷发均处于间歇期。前两个喷发主要描述了喷口的打开和清除，这些喷口主要是富含岩性的火成岩，岩相的侧向相变（从富岩性到富含晶体）被熔岩流/穹顶覆盖。火山喷发形式为低火山碎屑喷出，喷出的熔岩倾泻而来。持续浮力喷发柱仅在第二次喷发开始时才根据基底沉积物的存在进行解释。第三次喷发记录了三个不同的阶段：进一步的排气孔打开，打蜡阶段和最终的熔岩挤出。通风口打开阶段与先前爆发中发生的相类似。上蜡相产生大量，块状，分类不良，非常富晶体（> 50％（体积））的火成岩，随着高度和化学成分的变化，晶体含量逐渐增加，这表明通过逐步沉淀而沉积。低热碎屑喷泉形成了这些高颗粒浓度的电流，这些电流形成蜡状并达到了准稳态条件。爆发以熔岩流的挤出结束。 TR着火点被热熔并部分熔接，这由共晶织构，玻璃碎片变形，球晶，珍珠岩裂纹以及微晶到粒状织构所证明。火山碎屑沉积的水平和垂直岩相变化，以及TR进给系统和断层之间的渐进填充和联系，表明喷发是通过几个裂隙喷口或断层形成的。根据与320 km（3）（DRE）相似的最小喷射量，火山爆发指数为7。 TR的火山构造可以与与渐进沉积同步发生的连续火山口下陷联系在一起。与ATC进料导管有关的区域性断层（NE-SW趋势流纹岩堤）表明，逐渐下陷和最终陷井门破火山口坍塌，可能是由零食组成（破火山口底板），源于后瓦里斯卡纳张应力状态（类似于NNW-SSE方向）。 TR地层具有一般的流纹岩成分，具有A型花岗岩亲和力和正常的化学区带。 U-Pb锆石测年产生的年龄为323至312 Ma，与其他ATC岩石的年龄数据相比，表明TR的产生时间与325-317 Ma相似。 （C）2019 Elsevier B.V.保留所有权利。

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