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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Understanding the collapse-eruption link at Stromboli, Italy: A microanalytical study on the products of the recent Secche di Lazzaro phreatomagmatic activity
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Understanding the collapse-eruption link at Stromboli, Italy: A microanalytical study on the products of the recent Secche di Lazzaro phreatomagmatic activity

机译：了解意大利斯特龙博利的坍塌-喷发联系：最近的Secche di Lazzaro吞噬岩浆活动产物的微观分析研究

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摘要

The Secche di Lazzaro (SDL) phreatomagmatic activity, with the associated Neostromboli sector collapse, represents the most powerful activity of the last 6 ky at Stromboli. As revealed by its present-day activity, Stromboli is one of the most eruptive volcanoes in Italy, and flank instability, along its NW flank, is a common process. Volcano instability is often dramatised by explosive eruptions, thus it is of crucial importance to understand the linking between volcano collapse and the plumbing system itself. The possible role of preemptive magmatic processes as triggers of explosive eruptions can be mainly preserved by minerals and revealed by petrochemical studies. We studied the juvenile components (scoria and pumice) of the pyroclastic deposits from the SDL phreatomagmatic activity with the aim to understand the eruption-collapse link. The SDL pyroclastic sequence has been investigated in three different outcrops: at Secche di Lazzaro (SDL-SW sequence), at Vallone del Monaco (SDL-S) and along the old path from Stromboli village to the active craters (SDL-N). Juvenile components are KS-shoshonites similar to the most evolved lavas erupted at the end of the Neostromboli potassic period. Our study indicates that the SDL system is strongly heterogeneous and made up by at least two different sequences (SDL-N and SDL-SW/SDL-S) with different textural characteristics of the deposits and composition of the juvenile components. Mineral chemistry data show a variable presence of recycled crystals (antecrysts), possibly deriving from the previous Neostromboli activity (up to 13 ky ago). Whole rocks are characterised by small but significant differences between the SDL-N and the southern samples, pointing out the presence of compositionally different potassic magmas and the crystallization and recycling of slightly different mineral assemblages. A clear isotope heterogeneity has been also found and explained by the presence of 10% minimum of less radiogenic antecrysts, whereas crustal contamination would have only affected the higher Sr-radiogenic residual melt.rnThese data suggest that the SDL phreatomagmatic eruptions were fed by compositionally distinct potassic magmas, which rested and evolved in two shallow magma conduits when the magma-supply ceased in the waning phase of the Neostromboli activity. Our results also rule out the occurrence of new arrivals of refreshing magmas in the SDL feeding system, as well as other internal magma-related causes, as triggers for the SDL explosive eruptions. Accordingly, external collapse-related causes seem effectively more suitable for triggering the SDL phreatomagmatic eruptions by decompression of the magmatic systems. We also suggest the SDL-N and SDL-SW/SDL-S sequences are generated by two respective explosive events, separated in time and/or space. They can be respectively related to multiple failures of Sciara del Fuoco which successively depressurised the SDL-N and the SDL-SW/SDL-S magma conduits.
机译：Secche di Lazzaro（SDL）的吞噬岩浆活动以及相关的Neostromboli扇形塌陷，代表了在Stromboli的最后6个ky中最强大的活动。正如其目前的活动所揭示的那样，斯特龙博利火山是意大利火山喷发性最强的火山之一，并且其西北侧的侧翼不稳定是一个常见的过程。火山爆发常常使火山不稳定，因此了解火山坍塌与管道系统本身之间的联系至关重要。先发性岩浆过程可能是爆炸爆发的触发者，其作用可能主要由矿物保留，并由石化研究揭示。我们研究了来自SDL岩浆岩活动的火山碎屑沉积物的幼年成分（火山灰和浮石），目的是了解火山爆发-塌陷的联系。 SDL火山碎屑序列已在三个不同的露头进行了调查：在Secche di Lazzaro（SDL-SW序列），在Vallone del Monaco（SDL-S）以及沿从Stromboli村到活动火山口的旧路径（SDL-N）。幼年成分是KS-shoshonites，类似于在新斯特罗波利钾质期末爆发的最演化的熔岩。我们的研究表明，SDL系统具有很强的异质性，并且由至少两个不同的序列（SDL-N和SDL-SW / SDL-S）组成，这些序列具有不同的沉积物构造特征和幼年成分的组成。矿物化学数据显示，回收的晶体（抗结晶剂）存在多种形式，可能源自先前的Neostromboli活性（最高达13年前）。整个岩石的特征是SDL-N与南部样本之间的微小但明显的差异，指出了组成上不同的钾盐岩浆的存在以及略有不同的矿物组合的结晶和再循环。还发现了明显的同位素异质性，其原因是存在至少10％的较少放射源的前驱物，而地壳污染只会影响较高的Sr放射残留熔体。钾质岩浆，当岩浆供应在Neostromboli活动的减弱阶段停止时，在两个浅岩浆管道中休息并演化。我们的结果还排除了SDL进料系统中新出现的岩浆新到以及其他内部岩浆相关原因的发生，这些都是SDL爆炸爆发的诱因。因此，与外部坍塌有关的原因似乎更适合于通过岩浆系统减压来触发SDL岩浆喷发。我们还建议SDL-N和SDL-SW / SDL-S序列是由两个分别在时间和/或空间上分开的爆炸事件生成的。它们可能分别与Sciara del Fuoco的多次故障有关，这些故障依次使SDL-N和SDL-SW / SDL-S岩浆导管减压。

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