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Insights Into the Eruptive Dynamics of Small Caldera-Forming Eruptions: The Case Study of the Welded Scoriae of Vulcano (Aeolian Islands, Italy)
Frontiers in Earth Science ( IF 2.9 ) Pub Date : 2020-05-27 , DOI: 10.3389/feart.2020.00223
Eugenio Nicotra , Marta Minniti , Paola Donato , Rosanna De Rosa

A multi-disciplinary study, integrating volcanological field observations, petrography, whole rock geochemistry and textural and compositional analyses on plagioclase crystals has been carried out on the products of Monte Luccia, Spiaggia Lunga, and Quadrara eruptions, occurred between 48 and 21 kyrs on the island of Vulcano. These products are all characterized by welded scoria blankets, and their eruptions have been generally related to the formation and/or re-activation of ring faults bordering the “Il Piano” caldera. The aim of the work is to reconstruct the pre- and syn-eruptive dynamics acting within their magma plumbing systems and the related link with the phases of caldera collapse. At the bottom of the stratigraphic sequences, the presence of base surge deposits suggests that all the eruptions started with a phreatomagmatic phase fed by a shallow reservoir. Textural and microanalytical study of plagioclase crystals of Spiaggia Lunga eruption revealed that the phreatomagmatic event activated the ascent of a volatile-rich, basaltic magma residing at 5–11 km of depth. This basaltic magma mixed with the resident shallow one, and was poured out during the course of the eruption producing a sustained lava-fountaining phase. The subsequent caldera collapse, identified by a layer of chaotic breccia interbedded in the scoriae deposit, has been linked to the partial emptying of the shallow magma reservoir. In contrast to what observed for recent eruptive events at Vulcano, the onset of the magmatic phase would be attributed to a self-activation due to volcano-tectonic events, and not to a pressurization of the plumbing system related to the ascent of deep magma batches. As concerns the Mt. Luccia deposits, bordering the eastern rim of the “Il Piano” caldera, the absence of plagioclase in the mineralogical assemblage suggests the eruption of a deeper magma (>11 km b.s.l.), rapidly ascending through the re-activated ring faults of “Il Piano” caldera. At Quadrara eruption, the occurrence of a layer of white biotite-bearing latitic pumices overlying the basal phreatomagmatic deposits suggests the involvement a shallow, isolated reservoir where the increase of volatile pressure allowed the crystallization of hydrous phases. A deeper shoshonitic magma was involved later in the eruption, forming the welded scoria level at the top of the sequence.



中文翻译:

小火山口形成喷发动力的洞察力:以伏尔卡诺火山接缝火山口为例(意大利风神群岛)

在蒙特卢西亚,斯皮亚齐亚隆加和夸德拉拉火山喷发的产物上进行了一项多学科研究,该研究综合了火山现场观察,岩石学,整个岩石地球化学以及斜长石晶体的质地和成分分析,发生在该地区48到21岁武尔卡诺岛。这些产品均以熔渣覆盖层为特征,其喷发通常与“ Il Piano”破火山口接壤的环形断层的形成和/或重新活化有关。这项工作的目的是重建在岩浆管道系统内作用的火山爆发前和爆发时的动力学,以及与破火山口塌陷阶段相关的联系。在地层层序的底部,基础涌涌沉积的存在表明,所有喷发均始于浅层储集层吞噬的岩浆相。斜生龙牙藻爆发的斜长石晶体的组织学和微观分析研究表明,岩浆岩事件激活了深度为5-11 km的富含挥发物的玄武岩浆的上升。该玄武岩浆与常驻浅岩浆混合,并在喷发过程中倾泻而出,形成了持续的熔岩喷泉相。随后的火山灰塌陷,由埋在火山灰沉积物中的混沌角砾岩层识别,与浅层岩浆储层的部分排空有关。与最近在Vulcano爆发的事件所观察到的相反,岩浆期的开始归因于火山构造事件的自我激活,而不是与深部岩浆批次上升有关的管道系统增压。至于山。Luccia矿床毗邻“ Il Piano”火山口的东缘,在矿物学组合中没有斜长石的出现暗示了更深的岩浆(> 11 km bsl)的喷发,并通过“ Il Piano”重新激活的环形断裂迅速上升破火山口。在Quadrara火山喷发时,在基层岩浆岩沉积层上出现了白色的黑云母浮岩粉尘层,表明该岩层浅,孤立,储层中挥发性压力的增加使含水相结晶。火山喷发后来涉及到一个更深的岩浆岩浆,在层序的顶部形成了熔渣层。

更新日期:2020-06-19
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