Magma and volatile supply to post-collapse volcanism and block resurgence in Siwi caldera (Tanna island, Vanuatu arc)
Magma and volatile supply to post-collapse volcanism and block resurgence in Siwi caldera (Tanna island, Vanuatu arc)
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岩浆和不稳定的供应对塌陷后的火山活动和西维火山口的复苏（塔纳岛，瓦努阿图岛弧）
DOI：
10.1093/petrology/egr019
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
Massare D.
中科院分区：
文献类型：
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作者：
Metrich N;Allard P;Aiuppa A;Bani P;Bertagnini A.;Shinohara H;Parello F;Di Muro A;Garaebiti E.;Belhadj O;Massare D.
Siwi破火山口，在瓦努阿图弧（塔纳岛），是一个罕见的火山复杂的持续喷发活动（Yasur火山）和快速块复苏（Yenkahe地垒）可以同时在后破火山口阶段进行调查。在这里，我们提供了新的限制，这个火山复合体的进料系统的基础上，详细研究的岩石学，地球化学和挥发分含量的Yasur Siwi大块岩石和熔融包裹体，结合测量的化学成分和质量通量的Yasur火山气体。Yasur Siwi火山岩的主要和微量元素分析，与其他火山中心的文献数据一起，指向一个单一的岩浆系列，并可能长期喂养塔纳火山作用的均匀弧玄武岩。橄榄岩熔体包裹体显示，玄武岩浆的母岩浆中挥发分（H_2O_3 ~ 1wt%，S_2O_3 ~ 0.1wt%，Cl ~ 0.055wt%）中等富集，经50%~ 70%的结晶分馏作用，形成玄武粗安岩-粗安岩。玄武粗安岩岩浆侵位在距地表4-5 km的深度，保持高温（1107 ± 15°C）和恒定的H2O含量（101%），直到非常浅的深度，在那里它广泛脱气并结晶。这些条件，保持在过去1400年的Yasur活动，需要早期的水损失在玄武岩分化，普遍的开放系统脱气，和一个相对较高的热流（109 W）。亚苏尔火山平均释放出13·4 × 103吨/d的H2O和680吨/d的SO2，但也有适量的CO2（840吨/d）、HCl（165吨/d）和HF（23吨/d）。结合熔融包裹体数据，这些气体输出限制了大量岩浆的脱气速率为105 × 107 m3 a-1，其中约一半是由于玄武粗安岩的脱气造成的。我们计算出，25 km 3的这种岩浆已经脱气，而没有喷发，并积累下Siwi破火山口在过去的1000年，这是一个数量级大于累计体积隆起的Yenkahe复活块。因此，玄武岩供应和未喷发的脱气玄武粗安岩的逐渐储存可以很容易地解释（或有助于）延卡河块复苏。
Siwi caldera, in the Vanuatu arc (Tanna island), is a rare volcanic complex where both persistent eruptive activity (Yasur volcano) and rapid block resurgence (Yenkahe horst) can be investigated simultaneously during a post-caldera stage. Here we provide new constraints on the feeding system of this volcanic complex, based on a detailed study of the petrology, geochemistry and volatile content of Yasur–Siwi bulk-rocks and melt inclusions, combined with measurements of the chemical composition and mass fluxes of Yasur volcanic gases. Major and trace element analyses of Yasur–Siwi volcanic rocks, together with literature data for other volcanic centers, point to a single magmatic series and possibly long-lived feeding of Tanna volcanism by a homogeneous arc basalt. Olivine-hosted melt inclusions show that the parental basaltic magma, which produces basaltic-trachyandesites to trachyandesites by ∼50–70% crystal fractionation, is moderately enriched in volatiles (∼1 wt % H2O, 0·1 wt % S and 0·055 wt % Cl). The basaltic-trachyandesite magma, emplaced at between 4–5 km depth and the surface, preserves a high temperature (1107 ± 15°C) and constant H2O content (∼1 wt %) until very shallow depths, where it degasses extensively and crystallizes. These conditions, maintained over the past 1400 years of Yasur activity, require early water loss during basalt differentiation, prevalent open-system degassing, and a relatively high heat flow (∼109W). Yasur volcano releases on average ≥ 13·4 × 103tons d−1of H2O and 680 tons d−1of SO2, but moderate amounts of CO2(840 tons d−1), HCl (165 tons d−1), and HF (23 tons d−1). Combined with melt inclusion data, these gas outputs constrain a bulk magma degassing rate of ∼5 × 107m3a−1, about a half of which is due to degassing of the basaltic-trachyandesite. We compute that 25 km3of this magma have degassed without erupting and have accumulated beneath Siwi caldera over the past 1000 years, which is one order of magnitude larger than the accumulated volume uplift of the Yenkahe resurgent block. Hence, basalt supply and gradual storage of unerupted degassed basaltic-trachyandesite could easily account for (or contribute to) the Yenkahe block resurgence.