Tracing Volatiles, Halogens, and Chalcophile Metals During Melt Evolution at the Tolbachik Monogenetic Field, Kamchatka
Tracing Volatiles, Halogens, and Chalcophile Metals During Melt Evolution at the Tolbachik Monogenetic Field, Kamchatka
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DOI：
10.1093/petrology/egac087
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发表时间：
2022-08
影响因子：
3.9
通讯作者：
Alexander A. Iveson;M. Humphreys;F. Jenner;B. Kunz;I. Savov;J. D. De Hoog;T. Churikova;B. Gordeychik-B
中科院分区：
文献类型：
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作者：
Alexander A. Iveson;M. Humphreys;F. Jenner;B. Kunz;I. Savov;J. D. De Hoog;T. Churikova;B. Gordeychik-B
弧火山下的熔体储存和供应可能分布在中央成层火山和更广泛的单成因锥场之间，表明复杂的浅层管道系统。然而，这种空间变化的岩浆储存条件对挥发性脱气和微量元素地球化学的影响尚不清楚。本研究探讨了俄罗斯堪察加半岛Tolbachik火山场下的岩浆生成和储存过程，以研究岩浆挥发相的演化，特别是该系统中亲铜金属（特别是Cu）的强烈富集。我们提出了新的地球化学数据的橄榄石和单斜辉石托管熔融包裹体（和主机斑晶）从五个独立的单成锥内的Tolbachik火山场。这些高铝组成的岩浆可能反映了原始的中间镁熔体组合物的均质分馏产品，存储在浅深度后显着的分馏结晶。熔融包裹体的硼同位素组成和不相容的微量元素比率表明，一个更深的管道系统，主要是由广泛的分离结晶，并来自同位素均匀的母岩浆组合物的熔体美联储。挥发分（H2O，CO2，S，Cl，F）表明，岩浆喂养不同的单成锥有不同的初始挥发分含量，并随后经历了不同的流体饱和的存储条件和脱气历史。我们还表明，熔体供应托尔巴奇克火山场强烈富集铜相比，几乎所有其他堪察加岩石，包括样品从托尔巴奇克中央平流层锥，和其他火山位于靠近堪察加中部凹陷。熔体包裹体中Cu含量≥ 450 μg/g。4-5重量百分比MgO，这只能通过Cu的体积不相容分配行为来解释，即在硫化物欠饱和条件下的演化。我们认为，在这个地区的初始地幔熔融耗尽地幔硫化物，导致硫化物不饱和的原始熔体。这种无硫化物模型的高铝锥熔体进一步支持S/Se和Cu/Ag值，重叠的原始地幔和MORB阵列，与散装岩石Cu/Ag比也重叠其他与其他全球弧数据集岩浆演化之前的单硫化物固溶体的分馏。因此，新的亲铜金属分析与微量元素，同位素和挥发性数据相结合，是一个强大的工具，破译复杂的岩浆演化条件在整个火山领域。
Melt storage and supply beneath arc volcanoes may be distributed between a central stratovolcano and wider fields of monogenetic cones, indicating complex shallow plumbing systems. However, the impact of such spatially variable magma storage conditions on volatile degassing and trace element geochemistry is unclear. This study explores magma generation and storage processes beneath the Tolbachik volcanic field, Kamchatka, Russia, in order to investigate the evolution of the magmatic volatile phase and, specifically, the strong enrichment of chalcophile metals (specifically, Cu) in this system. We present new geochemical data for a large suite of olivine- and clinopyroxene-hosted melt inclusions (and host phenocrysts) from five separate monogenetic cones within the Tolbachik volcanic field. These high-Al composition magmas likely reflect the homogenised fractionation products of primitive intermediate-Mg melt compositions, stored at shallow depths after significant fractional crystallisation. Boron isotope compositions and incompatible trace element ratios of the melt inclusions suggest a deeper plumbing system that is dominated by extensive fractional crystallisation, and fed by melts derived from an isotopically homogeneous parental magma composition. Volatile components (H2O, CO2, S, Cl, F) show that magmas feeding different monogenetic cones had variable initial volatile contents, and subsequently experienced different fluid-saturated storage conditions and degassing histories. We also show that melts supplying the Tolbachik volcanic field are strongly enriched in Cu compared to almost all other Kamchatka rocks, including samples from the Tolbachik central stratocones, and other volcanoes situated in close proximity in the Central Kamchatka Depression. The melt inclusions record Cu concentrations ≥ 450 μg/g at ca. 4–5 wt.% MgO, which can only be explained by bulk incompatible partitioning behaviour of Cu i.e. evolution under sulfide-undersaturated conditions. We suggest that initial mantle melting in this region exhausted mantle sulfides, leading to sulfide undersaturated primitive melts. This sulfide-free model for the high-Al cone melts is further supported by S/Se and Cu/Ag values that overlap those of the primitive mantle and MORB array, with bulk rock Cu/Ag ratios also overlapping other with other global arc datasets for magma evolution prior to fractionation of a monosulfide solid solution. Therefore, the combination of novel chalcophile metal analyses with trace element, isotopic, and volatile data is a powerful tool for deciphering complex magmatic evolution conditions across the entire volcanic field.