Temporal evolution of magma and crystal mush storage conditions in the Baroarbunga-Veioivotn volcanic system, Iceland
Temporal evolution of magma and crystal mush storage conditions in the Baroarbunga-Veioivotn volcanic system, Iceland
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DOI：
10.1016/j.lithos.2019.105234
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发表时间：
2020-01-01
期刊：
影响因子：
3.5
通讯作者：
Gunnarsson, Haraldur
中科院分区：
文献类型：
--
作者：
Caracciolo, Alberto;Bali, Eniko;Gunnarsson, Haraldur
活动火山区域下方岩浆储存库的深度可能会随着时间而变化。确定岩浆系统结构千年尺度变化的速率和原因对于开发现实的地壳演化时间积分模型至关重要。在这里，我们检查了冰岛中部暴露度极高的 Baroarbunga-Veioivotn 火山系统的一组样本，以解决冰岛生产力最高的火山系统之一内岩浆储存条件的时间演变问题。我们测量了跨越整个冰川周期（500μm）的五个喷发单元的玻璃、矿物和熔体包裹体、多矿物凝块和高结晶度结核的主要和次要元素组成，与水晶糊状体的衍生一致。粗晶边缘与其各自的载体熔体处于化学平衡，而粗晶核太原始而不能从这些熔体中结晶。每个样本都记录了不同范围的宏观晶体成分，表明储存的晶体糊状物的成分和/或喷发性随时间而变化。来自最古老单元的宏观晶体是最原始的，随着时间的推移，宏观晶体的成分范围变得更广泛，并且平均而言更加进化。单斜辉石熔体和熔体基 (OPAM) 地质气压计揭示了 1.9-2.2 +/- 0.7 (1 sigma) kbar 压力的时间不变结晶条件，对应于 6.8-7.8 +/- 2.5 km 左右的深度。所有样品还含有在接近 2.6 kbar（9.6 km）的中地壳压力下捕获的熔体包裹体。此外，来自冰下和早期全新世喷发的最原始橄榄石和斜长石中的熔体包裹体保留了位于 17.5 公里（4.9 kbar）的下地壳储存层中结晶的证据。这种深层结晶的岩石学记录可能与喷发速率的激增、下地壳岩浆库的开采有关，这与冰期后均衡回弹相关的地壳响应一致。相比之下，较年轻的喷发单元缺乏深层结晶特征可能反映了地壳稳态条件下较低的岩浆生产率，以及有利于中地壳熔体储存的新岩浆路径。皇冠版权所有 (C) 2019 由 Elsevier B.V. 出版。保留所有权利。
The depth(s) of magma storage reservoirs beneath active volcanic regions may change with time. Determining the rates and causes of millennial-scale changes in magmatic system architecture is critical for the development of realistic time-integrated models of crustal evolution. Here we examine a suite of samples from the exceptionally well-exposed Baroarbunga-Veioivotn volcanic system in central Iceland in order to resolve the temporal evolution of magma storage conditions within one of Iceland's most productive volcanic systems. We have measured the major and minor elemental composition of glass, mineral and melt inclusion from five erupted units that span a full glacial cycle, from a 500 mu m), polymineralic clots and high-crystallinity nodules, consistent with derivation from crystal mush bodies. Macrocryst rims are in chemical equilibrium with their respective carrier melts, while macrocrysts cores are too primitive to have crystallized from these melts. Each sample records a distinct range of macrocryst compositions, indicating that the composition and/or eruptibility of stored crystal mush has changed with time. Macrocrysts from the oldest units are the most primitive, and the macrocryst compositional range becomes wider and, on average, more evolved, with time. Clinopyroxene-melt and melt-based (OPAM) geobarometers reveal temporally invariant crystallization conditions of 1.9-2.2 +/- 0.7 (1 sigma) kbar pressure, corresponding to depths around 6.8-7.8 +/- 2.5 km. All the samples also contain melt inclusions trapped at mid-crustal pressures of similar to 2.6 kbar (9.6 km). In addition, melt inclusions hosted in most primitive olivines and plagioclases from subglacial and early Holocene eruptions preserve evidence of crystallization in a lower-crustal storage level(s) located at 17.5 km (4.9 kbar). This petrological record of deep crystallization may be linked to a surge in eruption rates, tapping of lower-crustal magma reservoirs, consistent with a crustal response associated with postglacial isostatic rebound. In contrast, the absence of a deep crystallization signature in the younger eruptive units may reflect lower magma production rates under steady-state conditions of the crust, and new magma pathways favouring melt storage in the mid-crust. Crown Copyright (C) 2019 Published by Elsevier B.V. All rights reserved.