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首页> 外文期刊>Contributions to Mineralogy and Petrology >Textural and micro-analytical insights into mafic-felsic interactions during the Oruanui eruption, Taupo
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Textural and micro-analytical insights into mafic-felsic interactions during the Oruanui eruption, Taupo

机译：Taupo，Teurui-Felsic互动的构造和微观分析见解，Taupo

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摘要

Quenched juvenile mafic inclusions (enclaves) are an occasional but informative component in the deposits of large felsic eruptions. Typically, the groundmasses of these inclusions rapidly crystallize as the mafic magma is chilled against a more voluminous, cooler felsic host, providing a physical and chemical record of the nature and timing of mafic-felsic interactions. We examine mafic inclusions of two compositional lineages (tholeiitic and calc-alkaline) from deposits of the 25.4 ka Oruanui eruption (Taupo, New Zealand). 2-D quantitative textural data from analysis of back-scattered electron images reveal a marked diversity in the groundmass textures of the inclusions, including median crystal sizes (amphibole: 14-45 mu m; plagioclase: 21-75 mu m) and aspect ratios (amphibole: 1.7-4.2; plagioclase: 2.1-4.0), area number densities (amphibole: 122-2660 mm(-2); plagioclase: 117-2990 mm(-2)), area fractions (phi) of minerals (phi(plag) = 23-45%, phi(amph) = 0-28%, phi(cpx) = 0-6%, phi(oxides) = 0.6-5.5%), and the relative abundance of plagioclase and amphibole (phi(plag)/phi(amph) = 1.0-4.6). Textural parameters vary more significantly within, rather than between, the two compositional lineages, and in some cases show marked variations across individual clasts, implying that each inclusion's cooling history, rather than bulk composition, was the dominant control on textural development. Groundmass mineral compositions are also diverse both within and between inclusions (e.g. plagioclase from An(34-92), with typical intra-clast variability of similar to 20 mol%), and do not correlate with bulk chemistry. Diverse groundmass textures and mineral and glass chemistries are inferred to reflect complex interplay of a range of factors including the degree and rate of undercooling, bulk composition, water content and, possibly, intensive variables. Our data are inconsistent with breakup of a crystallizing ponded mafic layer at the base of the Oruanui melt-dominant body, instead implying that each inclusion partially crystallized as a discrete body with a unique cooling history. Extensive ingestion of mush-derived macro-crystals suggests that mechanical breakup of mafic feeder dikes occurred within a transition zone between the mush and melt-dominant magma body. In this zone, the mush lacked yield strength, as has been inferred from field studies of narrow (meters to few tens of meters) mush-melt transition zones preserved in composite intrusions. Evidence for plastic deformation of inclusions during eruption and the abundance of fresh residual glass in inclusions from all eruptive phases suggest that the inclusions formed syn-eruptively, and must have been formed recurrently at multiple stages throughout the eruption.
机译：猝灭的少年MAFIC夹杂物（飞地）是大型肠溶爆发的沉积物中的偶尔但信息化组件。通常，这些夹杂物的仿生速度快速结晶，因为MAFIC MAGMA对更大的较强的冷却肠道主体冷却，提供了MAFIC-FELSIC相互作用的性质和时机的物理和化学记录。我们研究了来自25.4 ka Oruanui Buluption（陶摩，新西兰）的沉积物的两种组成谱系（杂志和钙碱）的乳头夹杂物。 2-D分散电子图像分析的定量纹理数据显示夹杂物的碎屑纹理中标记的多样性，包括中值晶体尺寸（锥形晶片：14-45μm; plagioclase：21-75μm）和纵横比（锥体：1.7-4.2; Plagioclase：2.1-4.0），面积数密度（锥形：122-2660mm（-2）; Plagioclase：117-2990 mm（-2）），矿物区分数（PHI）（PHI） （PLAG）= 23-45％，PHI（AMPH）= 0-28％，PHI（CPX）= 0-6％，PHI（氧化物）= 0.6-5.5％），以及PLagioclase和锥形蛋白的相对丰度（PHI （PRAG）/ PHI（AMPH）= 1.0-4.6）。纹理参数在两种组成谱系中，两种组成谱系之间的变化更大，而在某些情况下，在某些情况下显示各个泥质的显着变化，这意味着每个包含的冷却历史，而不是散装组成，是对纹理发展的主导控制。在夹层内和夹杂物之间的血液矿物组合物也不同（例如，来自（34-92）的Plagioclase，典型的含有型内的含有相似的含量为20摩尔％），并且与散装化学不相关。推断各种仿古纹理和矿物和玻璃化学物质，以反映一系列因素的复杂相互作用，包括过冷，散装组合物，水含量和，可能是密集的变量的程度和速率。我们的数据与Oruanui熔体主体底部的结晶底层镁发射层的分解不一致，而是暗示每个包含部分结晶为具有独特的冷却历史的离散体。广泛摄入糊状的宏晶表明，在糊剂和熔融的岩浆体之间的过渡区内发生了MAFIC馈送器堤坝的机械分析。在该区域中，糊状的屈服强度，从窄（米至几十米）的现场研究中推断出在复合入侵中保存的糊状过渡区域。所有喷发阶段喷发过程中夹杂物夹杂物的塑性变形的证据表明，所有喷发阶段的夹杂物中的含量呈现出夹杂物，并且必须在整个喷发过程中在多个阶段进行常规形成。

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