Diverse sources of volatile release across volcanic arcs: Insights from Kozelsky and Khangar volcanoes, Kamchatka

火山弧挥发物释放的多种来源：来自堪察加半岛科泽尔斯基火山和康加尔火山的见解

• 批准号: 2607639
• 金额: --
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2607639
• 关键词: Diverse; sources; volatile; release; across

The Kamchatka peninsula is one of the most volcanically active regions on Earth and is among the best places in the world to study the fate of subducted old (cold) oceanic crust. Uniquely the volcanoes of this arc erupt in several, rather than one, broad volcanic lineaments, possibly sampling magmatic fluid and melt sources in the forearc, beneath the main volcanic front and also from the behind-the-arc region. Recent geophysical and geochemical results show that the Kamchatka volcanoes indeed sample fluids derived from slab depths from as little as 50km to as deep as 350 km. While the majority of arc volcanoes (here and elsewhere in other arcs) result from flux melting of depleted subarc mantle wedge source, the geochemistry of the arc volcanic rocks (incl. 10Be, U- series, B & Li isotopes, B/Be, B/Nb and Sr/Y ratios, among others) also shows, sometimes significant elemental and isotopic inputs from subducted slabs. These may include subducted sediments, altered basaltic crust and/or fluids/melts resulting from the dehydration of serpentinized sections of the slabs or forearc-serpentinized (subarc) mantle wedge. Although the depleted mantle sources dominate the major and minor element budgets of the erupted products, the components released from the slab are geochemically traceable and have been shown to deliver the most important H2O, CO2, halogen and fluid mobile element (B, Cs, Li, As, Sb) contributions to arc magmas (Portnyagin et al. , 2007). However, the individual slab lithologies involved and their relative influence with depth, especially the one originating from dehydration reactions in the deeply subducted serpentinites, has not been quantified yet. This project aims to address this issue by examining the geochemistry and petrology of volcanic products erupted along a SE-NW oriented depth transect across the Eastern Volcanic Arc Front and deep into the rear arc (Sredinny Ridge) region. In previous fieldwork campaigns we have extensively sampled Avachinsky and Bakening volcanoes that are ideally situated in the middle of a cross-arc transect that represents depth to the top of the slab between 120 and 200 km, respectively. Here we will aim to conduct fieldwork in Kamchatka (2020 and/or 2021) and sample and study the volatile and fluid mobile element systematics in one additional shallow-sourced (<100 km, Kozelsky) and one very deeply sourced (>300 km Khangar) volcano from the same (arc front orthogonal) transect. Olivine- and pyroxene- bearing mafic scoria will be used to extract melt inclusions (MI). The MI will be complementary to the already available (in Durham and Leeds) Kamchatka arc MI collection. The new MI will be adding, for the first time, an exceptional high resolution look at the petrochemical variations across active volcanic arc. Moreover, we will uniquely have a chance to examine compositional changes of slab derived fluxes with increasing depth-to-slab. The proposed transect will be complementary to a cross arc transect to the north (Churikova et al., 2007), although the slab depths/geometry and the overlaying terrain boundaries there are less clear when compared with the newly proposed transect, where the Benioff zone is clearly delineated by deep regional seismicity and tomography. The project will involve training and use of various in-situ measurement techniques such as SEM, EPMA, LA-ICP-MS and SIMS (for the MI). We will provide training (mostly in-house) in textural/petrological observations, sample selection+ preparation and geochemical modelling based on bulk rock and MI datasets.References used:Churikova et al. (2007, Contrib Mineral Petrol 154, 217-239.Portnyagin et al. (2007). Earth Planet. Sci. Lett. 255, 53-69.

堪察加半岛是地球上火山活动最活跃的地区之一，也是世界上研究俯冲的旧（冷）洋壳命运的最佳地点之一。独特的是，这个弧的火山爆发在几个，而不是一个，广泛的火山线性，可能采样岩浆流体和熔体源在弧前，主火山前下方，也从弧后地区。最近的地球物理和地球化学结果表明，堪察加火山确实从50公里到350公里深的板状深度提取了流体。虽然大多数弧火山（这里和其他弧的其他地方）是亏损的弧下地幔楔源的通量熔融的结果，弧火山岩（包括火山岩）的地球化学特征。10 Be、U-系列、B & Li同位素、B/Be、B/Nb和Sr/Y比率等）有时也显示来自俯冲板片的显著元素和同位素输入。这些可能包括俯冲沉积物、蚀变玄武质地壳和/或板块或弧前-弧下地幔楔的蛇纹化部分脱水产生的流体/熔体。尽管贫化地幔源在喷发产物的主要和次要元素收支中占主导地位，但从板片释放的成分在地球化学上是可追踪的，并已被证明为弧岩浆提供了最重要的H2O、CO2、卤素和流体移动的元素（B、Cs、Li、As、Sb）（Portnyagin等人，2007年）。然而，所涉及的个别板岩性及其与深度的相对影响，特别是在深俯冲蛇纹岩的脱水反应，还没有被量化。该项目旨在解决这个问题，通过检查火山产物的地球化学和岩石学喷发沿着东南-西北方向的深度横断面横跨东部火山弧前和深入到弧后（Sredinny岭）地区。在以前的实地考察活动中，我们对Avachinsky和Bakening火山进行了广泛的采样，这些火山理想地位于一个跨弧断面的中间，该断面代表了120至200公里之间的板顶部深度。在这里，我们的目标是在堪察加半岛（2020年和/或2021年）进行实地考察，并在一个额外的浅源（<100公里，Kozelsky）和一个非常深源（>300公里Khangar）火山从同一（弧前正交）横断面的挥发性和流体移动的元素系统学进行采样和研究。含橄榄石和辉石的镁铁质火山渣将用于提取熔融包裹体（MI）。MI将补充已经可用的（在达勒姆和利兹）堪察加弧MI集合。新的MI将首次增加一个特殊的高分辨率来观察活跃火山弧的石化变化。此外，我们将唯一有机会检查成分的变化板派生通量增加深度板。拟议的样带将与北部的交叉弧样带互补（Churikova等人，2007年），虽然板深度/几何形状和覆盖的地形边界，有不太清楚时，与新提出的样带，贝尼奥夫区是明确划定的深区域地震活动和层析成像。该项目将涉及各种现场测量技术的培训和使用，如SEM、EPMA、LA-ICP-MS和西姆斯（用于MI）。我们将提供结构/岩石学观察、样品选择+制备和基于大块岩石和MI数据集的地球化学建模方面的培训（主要是内部培训）。参考文献：Churikova et al.（2007，Contrib Mineral Petrol 154，217- 239）。Portnyagin et al.（2007）。地球行星。Sci. Lett. 255，53-69.