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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Pre-1991 Sulfur Transfer Between Mafic Injections And Dacite Magma In The Mt. Pinatubo Reservoir
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Pre-1991 Sulfur Transfer Between Mafic Injections And Dacite Magma In The Mt. Pinatubo Reservoir

机译：1991年以前Mt.皮纳图博水库

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摘要

Before the 1991-1992 activity, a large andesite lava dome belonging to the penultimate Pinatubo eruptive period (Buag ～ 500 BP) formed the volcano summit. Buag porphyritic andesite contains abundant amphibole-bearing microgranular enclaves of basaltic-andesite composition. Buag enclaves have lower K_2O and incompatible trace element (LREE, U, Th) contents than mafic pulses injected in the Pinatubo reservoir during the 1991-1992 eruptive cycle. This study shows that Buag andesite formed by mingling of a hot, water-poor and reduced mafic magma with cold, hydrous and oxidized dacite. Depending on their size, enclaves experienced variable re-equilibration during mixing/mingling. Re-equilibration resulted in hydration, oxidation and transfer of mobile elements (LILE, Cu) from the dacite to the mafic melts and prompted massive amphibole crystallization. In Buag enclaves, S-bearing phases (sulfides, apatite) and melt inclusions in amphibole and plagioclase record the evolution of sulfur partition among melt, crystal and fluid phases during magma cooling and oxidation. At high temperature, sulfur is partitioned between andesitic melt and sulfides (Ni-pyrrhotite). Magma cooling, oxidation and hydration resulted in exsolution of a S-Cl-H_2O vapor phase at the S-solubility minimum near the sulfide-sulfate redox boundary. Primary magmatic sulfide (pyrrhotite) and xenocrystic sulfide grains (pyrite), recycled together with olivines and pyroxenes from old mafic intrusives, were replaced by Cu-rich phases (chalcopyrite, cubanite) and, partially, by Ba-Sr sulfate. Sulfides degassed and transformed into residual spongy magnetite in response to fS_2 drop during final magma ascent and decompression. Our research suggests that a complete evaluation of the sulfur budget at Pinatubo must take into account the en route S assimilation from the country rocks. Moreover, this study shows that the efficiency of sulfur transfer between mafic recharges and injected magmas is controlled by the extent and rate of mingling, hydrous flushing and melt oxidation. Vigorous mixing/mingling and transformation of the magmatic recharge into a spray of small enclaves is required in order to efficiently strip their primary S-content that otherwise remains locked in the sulfides. Hydrous flushing increases the magma oxidation state of the recharges and modifies their primary volatile concentrations that cannot be recovered by the study of late-formed mineral phases and melt inclusions. Conversely, S stored in both late-formed Cu-rich sulfides and interstitial rhyolitic melt represents the pre-emptive sulfur budget immediately available for release from mafic enclaves during their decompression.
机译：在1991-1992年活动之前，属于倒数第二个Pinatubo喷发期（Buag〜500 BP）的大型安山岩熔岩穹顶形成了火山顶峰。 Buag斑状安山岩含有丰富的玄武质安山岩组成的闪石质微带。与1991-1992年喷发周期注入Pinatubo油藏的镁铁质脉冲相比，Buag飞地具有较低的K_2O和不相容的痕量元素（LREE，U，Th）。这项研究表明，块状安山岩是由热的，贫水的和还原的铁镁质岩浆与冷的，含水的和氧化的榴辉岩混合而成的。取决于它们的大小，飞地在混合/混合期间经历了可变的重新平衡。重新平衡导致水合，氧化和将活动元素（LILE，Cu）从钠铁矿转移至铁镁铁质熔体，并促使大量的角闪石结晶。在Buag飞地，闪石和斜长石中的含S相（硫化物，磷灰石）和熔体包裹体记录了岩浆冷却和氧化过程中硫在熔体，晶体和流体相之间的分配演变。在高温下，硫在安山药熔体和硫化物（镍硫铁矿）之间分配。岩浆的冷却，氧化和水合作用导致了S-Cl-H_2O气相在硫化物-硫酸盐氧化还原边界附近的S溶解度最小值处析出。初级岩浆硫化物（硫铁矿）和异种硫化物晶粒（黄铁矿）与橄榄石和辉石从旧的镁铁质侵入物中一起再循环，被富含铜的相（黄铜矿，绿铅矿）取代，部分被硫酸钡钡取代。在最终岩浆上升和减压过程中，由于fS_2下降，硫化物脱气并转变为残留的海绵状磁铁矿。我们的研究表明，对Pinatubo硫预算的完整评估必须考虑到乡村岩石中S的同化作用。此外，这项研究表明，铁质充填物和注入岩浆之间硫的转移效率受混合，含水冲洗和熔融氧化的程度和速度控制。为了有效地汽提其主要的S含量，否则强烈地混合/混合以及将岩浆充填物转变成小飞地喷雾，否则这些S含量会保留在硫化物中。含水冲刷会增加补给的岩浆氧化状态，并改变补给的主要挥发物浓度，而后期形成的矿物相和熔体包裹体的研究无法回收这些浓度。相反，储存在后期形成的富含铜的硫化物和间隙型流纹岩熔体中的S代表着先发制人的硫预算，可在减压过程中立即从镁铁质飞地释放。

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