Magnetic fabrics of rhyolite ignimbrites reveal complex emplacement dynamics of pyroclastic density currents, an example from the Altenberg–Teplice Caldera, Bohemian Massif
Magnetic fabrics of rhyolite ignimbrites reveal complex emplacement dynamics of pyroclastic density currents, an example from the Altenberg–Teplice Caldera, Bohemian Massif
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DOI：
10.1007/s00445-022-01577-1
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发表时间：
2022-07
影响因子：
3.5
通讯作者：
Petr Vitouš;F. Tomek;M. Petronis
中科院分区：
文献类型：
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作者：
Petr Vitouš;F. Tomek;M. Petronis
磁化率各向异性（AMS）通常用于推断年轻破火山口（即，新生代）。在较老的破火山口，主要记录往往被定位后的变形和/或长期侵蚀所掩盖。在这里，我们专注于~314 - 313 Ma的Altenberg-Teplice破火山口（ATC;波希米亚地块）内的熔结凝灰岩。小体积，适度焊接熔结凝灰岩侵位之前，破火山口形成喷发产生一个总体上向西流动的方向确定的岩浆和磁性叶理平面的叠瓦。它们的喷发口位于未来破火山口的东部边缘沿着。最大的高品位熔结凝灰岩，火山口形成事件的产品，表明了高度的焊接和流变韧性褶皱，掩盖了主要的流动织物。根据织物图案，从ATC公布的放射性和现场地质数据，我们解释说，这些熔结凝灰岩来源于一个岩墙群沿着西北破火山口边缘。PDC随后穿过正在下沉的破火山口向南部和东南偏南方向流动，在那里有额外的破火山口熔结凝灰岩暴露出来。最后的活板门破火山口坍塌触发了微花岗岩环岩脉的就位。这些岩脉，沿着后破火山口花岗岩，可能推动了当地复苏沿着东部破火山口边缘。作为例证的ATC，AMS织物可以成功地应用到更老的火山口熔结凝灰岩，包括那些具有高度的焊接和rheomorphism解释流动方向，沉积，定位，和后定位动态。
The Anisotropy of Magnetic Susceptibility (AMS) is commonly used to infer the flow dynamics, source areas, and post-emplacement processes of pyroclastic density currents (PDC) of young calderas (i.e., Cenozoic). In older calderas, the primary record is often obscured by post-emplacement deformation and/or long-term erosion. Here, we focus on the ~314–313 Ma welded ignimbrites inside the Altenberg–Teplice Caldera (ATC; Bohemian Massif). The small-volume, moderately welded ignimbrites emplaced prior to caldera-forming eruption yield a generally westward flow direction as determined from the imbrication of the magmatic and magnetic foliation plane. Their eruptive vents were located along the eastern margin of the future caldera. The most voluminous high-grade ignimbrites, products of the caldera-forming event, indicate a high degree of welding and rheomorphic ductile folding that obscured the primary flow fabrics. Based on the fabric pattern, published radiometric and field geology data from the ATC, we interpret that these ignimbrites were sourced from a dike swarm along the northwestern caldera rim. The PDCs then flowed across the subsiding caldera toward the south and south-southeast, where extra-caldera ignimbrites are exposed. The final trap-door caldera collapse triggered the emplacement of the microgranite ring dikes. These dikes, along with the post-caldera granites, may have driven a local resurgence along the eastern caldera rim. As exemplified by the ATC, the AMS fabric can be applied successfully to much older caldera ignimbrites including those with a high degree of welding and rheomorphism to interpret flow direction, deposition, emplacement, and post-emplacement dynamics.