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Petrological insights on the last 1000 years of explosive activity at La Soufrière volcano, St. Vincent (Lesser Antilles)
Lithos ( IF 2.9 ) Pub Date : 2021-04-03 , DOI: 10.1016/j.lithos.2021.106150
L. Fedele , P.D. Cole , C. Scarpati , R.E.A. Robertson

The petrological features of scoria samples and enclosed holocrystalline xenoliths from the last ~1000 years of activity of the La Soufrière volcano of St. Vincent (Lesser Antilles) are described in detail here. The products of the investigated prehistoric eruptions (pre-1440, 1440, 1580 CE) are relatively homogeneous basaltic andesites (with a paragenesis consisting of plagioclase, clinopyroxene, orthopyroxene and opaques) commonly hosting gabbroic xenoliths. Scoria samples from the historical eruptions (1718–1812 and 1902–03 CE) are mostly similar to the former in terms of whole-rock composition, mineral chemistry and types of xenoliths, but include also a mafic-rich scoria type (plagioclase + clinopyroxene + olivine) in the products of the 1902–03 eruption that is less evolved in composition and encloses ol-gabbro and ultramafic xenoliths. Both scoria types were likely affected by crystal contamination and accumulation processes, as indicated by their moderately to strongly porphyritic textures and large compositional variation of the crystal populations. Recycling of xenocryst, protocryst and/or antecryst phases, however, did not significantly modify the original magma composition, as suggested by the overall consistency of whole-rock differentiation trends with petrography, mineral chemistry, xenolith types and glass compositions (within both inclusions and the groundmass) and experimental petrology observations, crystal fractionation therefore still appearing as the main evolutionary process. Most of the gabbro and ol-gabbro xenoliths have mineral compositions in line with that of the coexisting phenocrysts and textural features consistent with an intrusive origin, i.e., representing fully-crystallised melt aliquots. Conversely, ultramafic, troctolitic and noritic xenoliths (plus some ol-gabbro) are likely representing cumulitic assemblages, i.e., mineral phases removed from the magma by crystal fractionation. The typical association of An-rich plagioclase and relatively Fo-poor olivine of the troctolite (and ol-gabbro) cumulates is ascribed to crystallisation from a hydrous (H2O ~4.5–6 wt%) high-Al2O3 basalt/basaltic andesite magma crystallising at shallow depths (~0.2 GPa, i.e., at ~7 km). On the other hand, the ultramafic cumulitic xenoliths are thought to derive from a less hydrous basalt magma stalling at deeper levels (~0.4 GPa, ~13 km). The tapping of such magma could mark a major rejuvenation event, which is the process that likely triggered the 1902–03 eruption.



中文翻译:

关于圣文森特拉索夫里埃雷火山最近1000年爆炸活动的岩石学见解(安的列斯群岛)

这里详细描述了圣文森特拉索夫里埃雷火山(莱斯特安的列斯群岛)最近〜1000年的活动所产生的火山灰样品和封闭的全结晶异种岩的岩石学特征。被调查的史前喷发的产物(前1440年,1440年,1440年1580年)是相对均质的玄武质安山岩(具有斜长石,斜辉石,邻位辉石和不透明物组成的共生物)通常是辉长岩异岩的宿主。从历史喷发(1718–1812和1902–03 CE)的天蝎座样本在全岩成分,矿物化学和异岩类型方面与前者相似,但也包括富镁铁质的天秤座类型(斜长石+斜辉石) +橄榄石)形成于1902–03年喷发的产物中,其组成演化较少,并包裹了ol-gabbro和超镁铁质异种岩。这两种矿渣类型都可能受晶体污染和积累过程的影响,这表现为它们具有中等至强烈的斑状质构以及晶体种群的较大组成变化。然而,异岩相,原生晶和/或前岩相的再循环并没有显着改变原始岩浆成分,这是由岩石的整体趋势与岩相学,矿物化学,异岩体类型和玻璃成分(在夹杂物和地面质量)和实验岩石学观测结果,因此晶体分离仍然是主要的演化过程。大多数辉长岩和ol-gabbro异种岩的矿物成分与共存的隐晶石的矿物成分相符,并​​且其纹理特征与侵入性起源相符,即 代表完全结晶的熔体等分试样。相反,超镁铁质,三重橄榄岩和诺富特异岩(加上一些ol-gabbro)很可能代表了积云性组合,即通过晶体分级从岩浆中去除的矿物相。富含斜长石的斜长石和斜晶石(和ol-gabbro)相对富磷的橄榄石的典型组合归因于水合结晶(H2 O〜4.5–6 wt%)高Al 2 O 3玄武岩/玄武质安山岩岩浆在浅深度(〜0.2 GPa,即〜7 km)结晶。另一方面,超镁铁质积云异岩被认为源于含水量较低的玄武岩岩浆在更深的水平上失速(〜0.4 GPa,〜13 km)。这类岩浆的开采可能标志着一个重大的复兴事件,这一过程很可能触发了1902-3年的喷发。

更新日期:2021-04-06
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