Compositional variations and magma mixing in the 1991 eruptions of Hudson volcano, Chile
Compositional variations and magma mixing in the 1991 eruptions of Hudson volcano, Chile
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1991 年智利哈德逊火山喷发时的成分变化和岩浆混合
DOI：
10.1007/s00445-008-0234-x
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发表时间：
2009
影响因子：
3.5
通讯作者：
J. Naranjo
中科院分区：
文献类型：
--
作者：
D. Kratzmann;S. Carey;R. Scasso;J. Naranjo
1991 年 8 月，哈德逊火山喷发产生了约 2.7 平方公里（致密岩当量，DRE）的玄武岩至粗岩火山碎屑沉积物，使其成为南美洲历史上最大的火山喷发之一。喷发的第一阶段（P1，4 月 8 日）涉及熔岩流和火山口西北角裂缝中的岩浆喷发。几天后（4 月 12 日），阵发性阶段 (P2) 开始，从东南偏南 4 公里处的另一个喷口发生普林尼式喷发。 1991 年喷发的火山灰成分范围从玄武岩（第 1 阶段）到粗安岩（第 2 阶段），两个喷发阶段之间存在明显的差距，SiO2 含量为 54-60 wt%。从第 2 阶段喷发的最早部分（A 单元，63–65 wt% SiO2）到结束（D 单元，60–63 wt% SiO2），SiO2 减少的趋势很明显。熔体包裹体数据和结构表明，两个喷发阶段的岩浆都发生了混合。玄武岩和粗岩岩浆可以通过岩浆混合和分级结晶过程在成因上相关。观察到的相组合、推断的含水量、结晶度和地温测量的估计相结合表明，第 2 相粗安岩在水饱和条件下（log fO2 –10.33 (±0.2)）在 972±26°C、约 50–100 兆帕 (MPa) 的压力下进行了喷发前储存。据推测，上升的 P1 玄武岩浆与 P2 岩浆储存区下部 2 至 3 公里深度相交。随后两种岩浆之间的混合优先混合了腔室的下部。玄武岩岩浆作为堤坝继续向地表推进，最终在哈德逊火山口的西北部喷发。 P1 产物中存在的速石表明，一些岩浆在喷发前在靠近地表（<0.5 公里）处停滞。与岩浆运动和 P1 喷发相关的地震活动，加上与玄武岩注入相关的腔室超压，可能为粗面安岩岩浆和随后在东南偏南 4 公里处的另一个喷口的 P2 喷发创造了一条通向地表的通道。
The August 1991 eruptions of Hudson volcano produced ~2.7 km3 (dense rock equivalent, DRE) of basaltic to trachyandesitic pyroclastic deposits, making it one of the largest historical eruptions in South America. Phase 1 of the eruption (P1, April 8) involved both lava flows and a phreatomagmatic eruption from a fissure located in the NW corner of the caldera. The paroxysmal phase (P2) began several days later (April 12) with a Plinian-style eruption from a different vent 4 km to the south-southeast. Tephra from the 1991 eruption ranges in composition from basalt (phase 1) to trachyandesite (phase 2), with a distinct gap between the two erupted phases from 54–60 wt% SiO2. A trend of decreasing SiO2 is evident from the earliest part of the phase 2 eruption (unit A, 63–65 wt% SiO2) to the end (unit D, 60–63 wt% SiO2). Melt inclusion data and textures suggest that mixing occurred in magmas from both eruptive phases. The basaltic and trachyandesitic magmas can be genetically related through both magma mixing and fractional crystallization processes. A combination of observed phase assemblages, inferred water content, crystallinity, and geothermometry estimates suggest pre-eruptive storage of the phase 2 trachyandesite at pressures between ~50–100 megapascal (MPa) at 972 ± 26°C under water-saturated conditions (log fO2 –10.33 (±0.2)). It is proposed that rising P1 basaltic magma intersected the lower part of the P2 magma storage region between 2 and 3 km depth. Subsequent mixing between the two magmas preferentially hybridized the lower part of the chamber. Basaltic magma continued advancing towards the surface as a dyke to eventually be erupted in the northwestern part of the Hudson caldera. The presence of tachylite in the P1 products suggests that some of the magma was stalled close to the surface (<0.5 km) prior to eruption. Seismicity related to magma movement and the P1 eruption, combined with chamber overpressure associated with basalt injection, may have created a pathway to the surface for the trachyandesite magma and subsequent P2 eruption at a different vent 4 km to the south-southeast.