Establishing the conditions and dynamics of pre-eruptive magma storage and transfer within transient transcrustal storage networks is a major focus of quantitative volcanic petrology. In Iceland, the behaviour, conditions and timescales of magmatic processes within on-rift plumbing systems are increasingly well constrained. However, relatively little is known about magma storage and transfer in off-rift zones, despite off-rift volcanoes being able to generate hazardous explosive eruptions after centuries or millennia of dormancy (e.g. 2010 AD Eyjafjallajökull; 1362 AD Öræfajökull; 3.0 ka, 4.2 ka and 1104 AD Hekla). We present a combined geochemical and geothermobarometric study of magma storage and transfer recorded in the products of the postglacial Búðahraun (∼5.0–8.0 ka) and Berserkjahraun (∼4.0 ka) eruptions within the Snæfellsnes volcanic zone. The eruption products contain diverse and compositionally heterogeneous macrocryst cargoes recording complex petrogenetic histories of crystal evolution and inheritance from different parts of the sub-volcanic plumbing systems. Geothermobarometry indicates two compositionally and thermally heterogeneous magma storage regions located in the lower (20 ± 4 km) and upper-mid (11 ± 3 km) crust. Crystallization pressure and depth estimates coincide with comparable data from Vatnafell, a small sub-glacial table mountain (tuya) in the centre of the Snæfellsnes volcanic zone, indicating that the nature and conditions of magma storage have remained unchanged since the Upper Pleistocene. Trace element zoning of clinopyroxene macrocrysts indicates that mafic recharge into the upper-mid-crustal storage zone triggered the eruptions of Búðahraun and Berserkjahraun. Evidence for eruption-triggering mafic recharge and basaltic cannibalism involving the transfer and amalgamation of crystals with different evolutionary histories sets the Búðahraun and Berserkjahraun eruptions apart from other studied eruptions in Iceland. We propose that the compositional and textural diversity preserved within the crystal cargoes are a direct consequence of the reduced heat flow beneath the Snæfellsnes volcanic zone, which favours the formation of isolated melt pockets in which compositionally diverse macrocryst populations formed. Periodic flushes of primitive basaltic magma from depth promote widespread mixing with evolved melts, resulting in the assembly of crystals with diverse ancestries from different parts of the sub-volcanic systems. Insights gained from the diverse macrocryst cargoes of Búðahraun and Berserkjahraun and comparisons with recent off-rift volcanism in Iceland are essential for the development of future monitoring efforts and hazard evaluation. Although volcanism within the Snæfellsnes volcanic zone differs fundamentally from that in rift zones where eruptions are controlled by extensional spreading, magma ascent from depth still appears to follow pre-existing tectonic escape routes. This could result in extremely short advance warning times on the order of a few days.

中文翻译：

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冰岛西部 Snæfellsnes 火山带的岩浆储存条件和动态：来自 Búðahraun 和 Berserkjahraun 喷发的见解

在瞬态跨地壳储存网络中建立喷发前岩浆储存和转移的条件和动力学是定量火山岩石学的主要焦点。在冰岛，裂谷管道系统内岩浆过程的行为、条件和时间尺度越来越受到严格限制。然而，尽管在几个世纪或数千年的休眠后，裂谷外火山能够产生危险的爆炸性喷发（例如，公元 2010 年埃亚法拉冰川；公元 1362 年厄勒法冰川；3.0 ka，4.2 ka和公元 1104 年赫克拉）。我们提出了在冰后 Búðahraun (~5.0–8.0 ka) 和 Berserkjahraun (~4. 0 ka) Snæfellsnes 火山带内的喷发。喷发产物包含多样且成分异质的大晶体货物，记录了来自次火山管道系统不同部分的晶体演化和继承的复杂岩石成因历史。地热气压测量表明两个成分和热非均质岩浆储存区位于下地壳（20 ± 4 公里）和中上地壳（11 ± 3 公里）。结晶压力和深度估计与来自斯奈山火山带中心的小型冰下桌山（tuya）瓦特纳费尔（Vatnafell）的可比数据一致，表明自上更新世以来岩浆储存的性质和条件保持不变。单斜辉石大晶的微量元素分区表明，镁铁质补给到地壳中上层储存区引发了 Búðahraun 和 Berserkjahraun 的喷发。火山爆发引发镁铁质补给和玄武岩同类相食的证据涉及具有不同进化历史的晶体的转移和融合，这使得 Búðahraun 和 Berserkjahraun 火山喷发与冰岛其他研究的火山喷发区分开来。我们认为，晶体货物中保存的成分和结构多样性是 Snæfellsnes 火山带下方热流减少的直接结果，这有利于形成孤立的熔体袋，其中形成了成分多样的大晶体种群。来自深处的原始玄武质岩浆的周期性冲刷促进了与演化熔体的广泛混合，导致来自次火山系统不同部分的不同祖先的晶体组装在一起。从 Búðahraun 和 Berserkjahraun 的各种宏观晶体货物中获得的见解以及与冰岛最近的裂谷火山活动的比较对于未来监测工作和危害评估的发展至关重要。尽管 Snæfellsnes 火山带内的火山活动与裂谷带的火山活动存在根本不同，裂谷带的喷发受伸展扩张控制，但岩浆从深处上升似乎仍遵循预先存在的构造逃逸路线。这可能导致几天左右的极短预警时间。从 Búðahraun 和 Berserkjahraun 的各种宏观晶体货物中获得的见解以及与冰岛最近的裂谷火山活动的比较对于未来监测工作和危害评估的发展至关重要。尽管 Snæfellsnes 火山带内的火山活动与裂谷带的火山活动存在根本不同，裂谷带的喷发受伸展扩张控制，但岩浆从深处上升似乎仍遵循预先存在的构造逃逸路线。这可能导致几天左右的极短预警时间。从 Búðahraun 和 Berserkjahraun 的各种宏观晶体货物中获得的见解以及与冰岛最近的裂谷火山活动的比较对于未来监测工作和危害评估的发展至关重要。尽管 Snæfellsnes 火山带内的火山活动与裂谷带的火山活动存在根本不同，裂谷带的喷发受伸展扩张控制，但岩浆从深处上升似乎仍遵循预先存在的构造逃逸路线。这可能导致几天左右的极短预警时间。岩浆从深处上升似乎仍然遵循预先存在的构造逃逸路线。这可能导致几天左右的极短预警时间。岩浆从深处上升似乎仍然遵循预先存在的构造逃逸路线。这可能导致几天左右的极短预警时间。