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首页> 外文期刊>Contributions to Mineralogy and Petrology >A cascade of magmatic events during the assembly and eruption of a super-sized magma body
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A cascade of magmatic events during the assembly and eruption of a super-sized magma body

机译：在装配和超大岩浆机构的组装和喷发过程中的山雀事件

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We use comprehensive geochemical and petrological records from whole-rock samples, crystals, matrix glasses and melt inclusions to derive an integrated picture of the generation, accumulation and evacuation of 530 km(3) of crystal-poor rhyolite in the 25.4 ka Oruanui supereruption (New Zealand). New data from plagioclase, orthopyroxene, amphibole, quartz, Fe-Ti oxides, matrix glasses, and plagioclase- and quartz-hosted melt inclusions, in samples spanning different phases of the eruption, are integrated with existing data to build a history of the magma system prior to and during eruption. A thermally and compositionally zoned, parental crystal-rich (mush) body was developed during two periods of intensive crystallisation, 70 and 10-15 kyr before the eruption. The mush top was quartz-bearing and as shallow as similar to 3.5 km deep, and the roots quartz-free and extending to >10 km depth. Less than 600 year prior to the eruption, extraction of large volumes of similar to 840 degrees C low-silica rhyolite melt with some crystal cargo (between 1 and 10%), began from this mush to form a melt-dominant (eruptible) body that eventually extended from 3.5 to 6 km depth. Crystals from all levels of the mush were entrained into the eruptible magma, as seen in mineral zonation and amphibole model pressures. Rapid translation of crystals from the mush to the eruptible magma is reflected in textural and compositional diversity in crystal cores and melt inclusion compositions, versus uniformity in the outermost rims. Prior to eruption the assembled eruptible magma body was not thermally or compositionally zoned and at temperatures of similar to 790 degrees C, reflecting rapid cooling from the similar to 840 degrees C low-silica rhyolite feedstock magma. A subordinate but significant volume (3-5 km(3)) of contrasting tholeiitic and calc-alkaline mafic material was co-erupted with the dominant rhyolite. These mafic clasts host crystals with compositions which demonstrate that there was some limited pre-eruptive physical interaction of mafic magmas with the mush and melt-dominant body. However, the mafic magmas do not appear to have triggered the eruption or controlled magmatic temperatures in the erupted rhyolite. Integration of textural and compositional data from all available crystal types, across all dominant and subordinate magmatic components, allow the history of the Oruanui magma body to be reconstructed over a wide range of temporal scales using multiple techniques. This history spans the tens of millennia required to grow the parental magma system (U-Th disequilibrium dating in zircon), through the centuries and decades required to assemble the eruptible magma body (textural and diffusion modelling in orthopyroxene), to the months, days, hours and minutes over which individual phases of the eruption occurred, identified through field observations tied to diffusion modelling in magnetite, olivine, quartz and feldspar. Tectonic processes, rather than any inherent characteristics of the magmatic system, were a principal factor acting to drive the rapid accumulation of magma and control its release episodically during the eruption. This work highlights the richness of information that can be gained by integrating multiple lines of petrologic evidence into a holistic timeline of field-verifiable processes.
机译：我们采用全岩样和岩浆物，晶体，基质眼镜和熔体夹杂物的综合地球化学和岩浆记录，以导出25.4 ka Oruanui超级晶体（新西兰）。来自Plagioclase，Orthopyroxene，Amphibole，石英，Fe-Ti氧化物，基质眼镜和石英序列玻璃和石英序列熔体夹杂物的新数据，在繁殖的不同阶段的样品中，与现有数据集成在现有数据中以构建岩浆的历史在喷发之前和爆发期间的系统。在爆发前两次强化结晶，70和10-15 kyr期间开发了热和合成的富含父母浓郁的（糊状物）体。糊状糊状物是石英，与3.5公里深的浅，根系无左右，延伸到> 10公里深度。在喷发前少于600年，提取大量的大量与840℃的低二氧化硅流纹熔体（在1到10％之间）开始，从这种糊状物开始形成熔融优势（可爆的）体最终从3.5到6公里深度延伸。从所有较轻的糊状物中夹带到矿物区区内和锥形模型压力中所见的岩溶岩浆中。从糊状物到岩浆中的晶体的快速翻译在晶体芯和熔体包裹组合物中反映了纹理和组成多样性，与最外边缘的均匀性。在喷发之前，组装的岩溶岩浆物体没有热或组成分布，并且在类似于790℃的温度下，反射与类似于840℃的低二氧化硅菱形原料岩浆的快速冷却。对比的烟草和钙碱mafic材料的下级但大量的体积（3-5km（3））与显性流纹岩共爆发。这些乳腺裂解物与组合物宿主晶体，表明麦克马斯岩浆与糊状物和熔体显性体的一些有限的预发布物理相互作用。然而，MAFIC岩浆似乎没有引发爆发的流纹岩中的喷发或受控的岩浆温度。从所有可用的水晶类型中集成了所有可用的水晶类型，跨越所有主要和从属岩浆组件，允许使用多种技术在各种时间秤上重建Oriumui岩浆机构的历史。该历史跨越了成长父母岩浆系统所需的数十千年（在锆石中的第U型崎岖数据），通过几个世纪和数十年来组装岩溶岩浆体（矫形和扩散模型）到数月，日期发生爆发的单个阶段的小时和分钟发生，通过与磁铁矿，橄榄石，石英和长石的扩散建模相关的现场观察确定。构造过程，而不是岩浆系统的任何固有特征，是一种主要的因素，用于驱动岩浆的快速积累并在喷发过程中释放其释放。这项工作强调了通过将多行岩画证据集成到现场可验证过程的整体时间表中可以获得的信息丰富。

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