The Occurrence of Forsterite and Highly Oxidizing Conditions in Basaltic Lavas from Stromboli Volcano, Italy
The Occurrence of Forsterite and Highly Oxidizing Conditions in Basaltic Lavas from Stromboli Volcano, Italy
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DOI：
10.1093/petrology/egl012
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发表时间：
2006-07
影响因子：
3.9
通讯作者：
J. Cortés;M. Wilson;E. Condliffe;L. Francalanci
中科院分区：
文献类型：
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作者：
J. Cortés;M. Wilson;E. Condliffe;L. Francalanci
我们报告的发生不寻常的，高镁（Fo 96）橄榄石斑晶的玄武岩熔岩和喷出的岩屑块从上Vancori时期（13 ka）和最近的活动（2002-2003年）的斯特龙博利火山，意大利。含有这种独特矿物化学的样品是钾玄质玄武岩和玄武安山岩，具有异常的大块岩石化学特征，其中铁高度氧化（6-8重量% Fe 2 O3和<1重量% FeO）。在其他方面，这些样品是类似的斯特龙博利玄武岩的大多数，其特征是共存的橄榄石，单斜辉石，斜长石和铁钛氧化物的斑晶，和单斜辉石，斜长石和铁钛氧化物的基质。在高镁橄榄石样品中，铁钛氧化物（铁板钛矿）通常与橄榄石斑晶以合晶共生的形式出现，表明两相同时生长。我们建议，作为一个共生模型，Fo 96橄榄石斑晶结晶高度氧化的玄武岩岩浆中，大部分的铁是在铁的状态，因此，只有镁可形成橄榄石。岩浆的高度氧化状态反映了与岩浆房的瞬时、不可逆、瞬态脱气相关的挥发相的突然脱气;这被假定发生在与阵发性活动和火山建筑物坍塌相关的火山建筑物破裂引起的突然减压期间。
We report the occurrence of unusual, high-magnesium (Fo96) olivine phenocrysts in a basaltic lava and an ejected lithic block from the Upper Vancori period ( 13 ka) and the recent activity (2002–2003) of Stromboli volcano, Italy. The samples that contain this distinctive mineral chemistry are a shoshonitic basalt and a basaltic andesite with anomalous bulk-rock chemical characteristics in which the iron is highly oxidized (6–8 wt % Fe2O3 and <1 wt % FeO). In other respects these samples are similar to the majority of Stromboli basalts, characterized by the coexistence of olivine, clinopyroxene, plagioclase and Fe–Ti oxides as phenocrysts, and clinopyroxene, plagioclase and Fe–Ti oxides in the groundmass. In the high-magnesium olivine samples, Fe–Ti oxides (pseudobrookite) typically occur as symplectitic intergrowths with the olivine phenocrysts, indicating simultaneous growth of the two phases. We propose, as a paragenetic model, that the Fo96 olivine phenocrysts crystallized from a highly oxidized basaltic magma in which most of the iron was in the ferric state; hence, only magnesium was available to form olivine. The highly oxidized state of the magma reflects sudden degassing of volatile phases associated with instantaneous, irreversible, transient degassing of the magma chamber; this is postulated to occur during periods of sudden decompression induced by fracturing of the volcanic edifice associated with paroxysmic activity and edifice collapse.