ABSTRACT

Timing of magmatic activity of the late-Variscan Altenberg–Teplice Caldera was rather vaguely constrained. In this paper, we present five new laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb zircon ages, which along with published data indicate ~13 Myr lifetime. Formation of the Altenberg–Teplice Caldera commenced with the emplacement of the pre-caldera pluton at ~325–319 Ma, and terminated with the intrusion of the syn-collapse ring dykes and post-collapse granites at ~312 Ma. The main ignimbrite volcanism in the area of the ATC occurred at ~318–313 Ma and peaked at ~314–313 Ma. The latter corresponds to the age of the caldera-forming eruptions, which sourced the extra-caldera pyroclastic deposits. The same age yielded the rhyolite dyke swarm that fed the ignimbrite eruptions. Some pyroclastic fall deposits preserved in adjacent Carboniferous basins indicate similar ages of ~314–312 Ma including the widespread ~314 Ma Bělka tuff, which represents the main chronostratigraphic marker of this area. Its thickness and grain size progressively degrease from the ATC towards S and SW. This, together with the isopach map distribution and the available geochronological data suggest that the Bělka tuff was sourced from the Altenberg–Teplice Caldera. The Bělka tuff distribution and its association with the extra-caldera ignimbrites of the Altenberg–Teplice Caldera imply that this tuff is a co-ignimbrite fall deposit that accompanied pyroclastic density currents sourced from the caldera. The calculated minimum volume of fallout ash-tuffs and extra-caldera ignimbrite facies contribute 30 km³ to the 350 km³ (dense rock equivalent) estimates of the total Altenberg–Teplice Caldera products. Such volumes correspond well to similar modern analogues of collapse calderas of intermediate size.

摘要

晚期瓦里斯坎阿尔滕贝格-特普利采火山口的岩浆活动时间受到相当模糊的限制。在本文中，我们介绍了五个新的激光烧蚀电感耦合等离子体质谱法（LA–ICP–MS）的U–Pb锆石年龄，以及已发表的数据表明〜13 Myr寿命。Altenberg–Teplice火山口的形成始于火山口前岩体在约325–319 Ma处的侵入，并终止于同塌陷环堤和塌陷后花岗岩在312 Ma的侵入。ATC地区主要的火山岩火山活动发生在约318-313 Ma处，并在约314-313 Ma处达到峰值。后者对应于形成破火山口的火山喷发的年龄，该火山爆发源于破火山口的火山碎屑沉积物。相同的年龄产生了流纹岩大堤群，为火成岩爆发提供了动力。在相邻的石炭纪盆地中保存的一些火山碎屑沉积物表明相似的年龄为约314-312 Ma，包括分布广泛的〜314 Ma的Bělka凝灰岩，这是该地区主要的年代地层标志。其厚度和粒度从ATC逐渐向S和SW脱脂。这与等渗线图分布和可用的地质年代数据一起表明，Bělka凝灰岩来自Altenberg–Teplice火山口。Bělka凝灰岩分布及其与阿尔腾贝格-特普利采火山口的破火山口外着火物质的关系表明，该凝灰岩是一种共着火的秋天沉积物，伴随着来自破火山口的火山碎屑密度流。计算出的余尘灰凝灰岩和破火山口外着火岩相的最小体积为30 km³至350 km ³（相当于致密岩石）估计的Altenberg–Teplice破火山口产品总量。这样的体积与中等大小的塌陷破火山口的类似现代类似物很好地对应。