Petrological Insights into Shifts in Eruptive Styles at Volcán Llaima (Chile)
Petrological Insights into Shifts in Eruptive Styles at Volcán Llaima (Chile)
复制标题
对莱马火山（智利）喷发类型变化的岩石学见解
DOI：
10.1093/petrology/egs073
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发表时间：
2013
影响因子：
3.9
通讯作者：
A. Burgisser
中科院分区：
文献类型：
--
作者：
C. Maisonneuve;M. Dungan;O. Bachmann;A. Burgisser
火山灰和熔岩对从两个峰会爆发（公元2008年和1957年）和侧面裂缝喷发（公元1850年）进行了比较，在纹理，斑晶含量，矿物分区模式，以阐明负责的过程中，在典型的喷发事件在火山Llaima喷发风格的转变火山灰和熔岩的矿物学和全岩成分在喷发期内相似，表明Strombolian爆发和熔岩溢出的共同岩浆库。斜长石的分区剖面和纹理记录了富含挥发分的镁铁质岩浆的连续和离散侵入，伴随着这些补给岩浆与通常存在于Llaima系统浅层的玄武安山质晶体浆的混合。每次补给事件使斜长石与常驻晶体泥熔体处于平衡状态，并使相对富An斜长石稳定，如许多再吸收带所记录。熔岩通常比火山灰多15^20体积%的斑晶。斜长石和橄榄石结构和分带的差异，结合不同的斑晶含量，表明更大的体积分数的补给岩浆存在于爆发喷发的岩浆比在随后的喷出岩浆。我们认为，Volcan Llaima的Strombolian爆发是由与大体积的补给岩浆相互作用触发的，这降低了整体粘度，增加了喷发岩浆的挥发分含量，导致了玄武安山岩破碎所需的条件。熔岩喷出物是由于在部分脱气和结晶后，与补给岩浆的相互作用减少，从而阻碍了快速上升。这一过程可能在其他稳定状态的玄武岩火山中发生，在这些火山中，浅层储层定期被新鲜的、富含挥发性的岩浆重新填充。
Tephra and lava pairs from two summit eruptions (AD 2008 and 1957) and a flank fissure eruption (� AD 1850) are compared in terms of textures, phenocryst contents, and mineral zoning patterns to shed light on processes responsible for the shifts in eruption style during typical eruptive episodes at Volcan Llaima (Andean SouthernVolcanic Zone, Chile).The mineralogy and whole-rock com- positions of tephra and lavas are similar within eruptive episodes, suggesting a common magma reservoir for Strombolian paroxysms and lava effusion. The zoning profiles and textures of plagioclase record successive and discrete intrusions of volatile-rich mafic magma accompanied by mixing of these recharge magmas with the resident basaltic-andesitic crystal mushes that are commonly present at shallow levels in the Llaima system. Each recharge event destabil- izes the plagioclase in equilibrium with the resident crystal mush melt and stabilizes relatively An-rich plagioclase, as is recorded by the numerous resorption zones. Lavas typically have � 15^20 vol. % more phenocrysts than the tephra. Differences in plagioclase and olivine textures and zoning, combined with different phenocryst contents, indicate that a greater volume fraction of recharge magma is present in the explosively erupted magma than in subsequent effu- sively erupted magma. We propose that Strombolian paroxysms at Volcan Llaima are triggered by interactions with large volume frac- tions of recharge magma, which decrease the bulk viscosity and in- crease the volatile contents of the erupted magmas, leading to the conditions required for the fragmentation of basaltic-andesite. Lava effusion ensues from reduced interactions with the recharge magma, after it has partially degassed and crystallized, thereby impeding rapid ascent. This process could be operating at other steady-state basaltic volcanoes, wherein shallow reservoirs are periodically re- filled by fresh, volatile-rich magmas.