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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Recent remobilisation of shallow-level intrusions on Montserrat revealed by hydrogen isotope composition of amphiboles
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Recent remobilisation of shallow-level intrusions on Montserrat revealed by hydrogen isotope composition of amphiboles

机译：闪石的氢同位素组成揭示了对蒙特塞拉特浅层侵入体的近期修复

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摘要

Ion probe measurements of hydrogen isotopes were made on amphiboles representing different stages of the ongoing eruption of the Soufriere Hills Volcano, Montserrat. The majority (80%) of the andesitic amphiboles show relative intra- and inter-crystal δD homogeneity, with a mean of -38 ± 12‰, consistent with known primary magmatic values. The remainder (20%) of amphiboles show marked δD heterogeneity, with a mean of -6 ± 30‰. The heterogeneous amphiboles have ～100 μm rims with δD values similar to the homogeneous crystals, but core values which are significantly heavier than primary magmatic values. Early in the eruption 50% of amphiboles are isotopically heterogeneous but post spring 1996 all amphiboles are homogeneous. We interpret these ion probe data in terms of development of a shallow andesitic magma chamber by repeated emplacement of andesitic magma in the shallow crust, over at least the last 100 yr. We suggest such shallow intrusions, emplaced during the volcano-seismic crises preceding the ongoing eruption, solidified. Some regions interacted with hydrothermal fluids and isotopic exchange took place generating the heavy hydrogen isotope signatures in the heterogeneous amphiboles. On onset of the ongoing eruption, such old igneous material was remobilised, with intimate mixing between the new magma batch and the old intrusions indicated by the close proximity of homogeneous and heterogeneous crystals. The isotopically primary magmatic rims on the heterogeneous crystals indicate hydrogen isotope exchange over a period of a few weeks, consistent with timescales of magma ascent at the Soufriere Hills Volcano. Once the old igneous material was flushed out, by spring 1996, the eruption proceeded by extruding material dominated by the new batch of magma. This resulted in a marked increase in extrusion rate.
机译：氢同位素的离子探针测量是在代表蒙特塞拉特Soufriere Hills火山正在进行喷发的不同阶段的闪石上进行的。大部分（80％）安山石闪石显示出相对的晶体内和晶体间δD均匀性，平均值为-38±12‰，与已知的初级岩浆值一致。其余的（20％）闪石显示出明显的δD异质性，平均值为-6±30‰。非均质闪石的边缘约为〜100μm，其δD值与均质晶体相似，但其核心值明显比初级岩浆值重。喷发初期，50％的闪石是同位素异质的，但1996年春季以后，所有的闪石都是同质的。我们通过至少在过去的100年中，在浅地壳中重复安山岩浆的沉积，来解释浅层安山岩浆室的发育，解释了这些离子探针数据。我们建议在火山喷发之前发生的火山喷发之前发生的这种浅层侵入物要固化。一些区域与热液相互作用，发生了同位素交换，在异质闪石中产生了重氢同位素标记。在持续的喷发开始时，这些旧的火成岩物质被移动，新的岩浆批次与旧的侵入体之间紧密混合，这表明均质晶体和异质晶体非常接近。异质晶体上的同位素一次岩浆边缘表明，氢同位素在几周的时间内发生了交换，这与苏弗雷里山火山的岩浆上升的时间尺度一致。一旦冲走了旧的火成岩物质，到1996年春季，火山喷发就开始进行，新的岩浆占主导地位。这导致挤出速率显着增加。

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