Experimental constraints on pre-eruption conditions of pantelleritic magmas: Evidence from the Eburru complex, Kenya Rift
Experimental constraints on pre-eruption conditions of pantelleritic magmas: Evidence from the Eburru complex, Kenya Rift
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DOI：
10.1016/j.lithos.2006.03.010
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发表时间：
2006-10
期刊：
影响因子：
3.5
通讯作者：
B. Scaillet;R. Macdonald
中科院分区：
文献类型：
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作者：
B. Scaillet;R. Macdonald
在150 MPa和还原条件下，在Ni-NiO固体缓冲层以下2个对数单位，测定了肯尼亚裂谷Eburru杂岩中碱碲矿的相关系和组成。温度和熔体水含量的影响相关系进行了探讨。碱长石和石英在700 °C以上的温度下单独结晶，与熔体水含量无关。在700 °C以下，钠质角闪石和单斜辉石也结晶;角闪石在富水条件下为液相。在贫晶体的碱碲矿中，角闪石斑晶与碱性长石和石英共存，意味着温度低于700 °C，熔融水含量高于4 wt.%，可能高达5-6重量%。钾碲矿的液相线温度比伴生的辉长岩低，这支持了两种岩浆类型之间的亲子关系。实验中产生的熔体扩展了天然岩系所显示的成分趋势，并再现了碱性火山岩系中偶尔观察到的一些极端成分，其FeO_（12）wt.%以上Na 2 O含量接近10重量%。因此，碱碲矿是碱性过饱和岩浆系列中真正的近最低熔融成分。
The phase relationships and compositions of a pantellerite from the Eburru complex in the Kenya Rift Valley have been determined at 150 MPa and under reducing conditions, 2 log units below the Ni–NiO solid buffer. The effects of temperature and melt water content on phase relationships have been explored. Alkali feldspar and quartz crystallise alone at temperatures above 700 °C, irrespective of melt water content. Below 700 °C, sodic amphibole and clinopyroxene also crystallise; the amphibole being the liquidus phase under water-rich conditions. The coexistence of amphibole phenocrysts with alkali feldspar and quartz in a crystal-poor pantellerite implies temperatures below 700 °C and melt water contents higher than 4 wt.%, possibly up to 5–6 wt.%. Pantellerites have lower liquidus temperatures than associated comendites, which supports a parent–daughter relationship between the two magma types. The melts produced in the experiments extend the compositional trend displayed by the natural rock series, and reproduce some extreme compositions occasionally observed in alkaline volcanic series, with FeO⁎ contents above 12 wt.% and Na2O contents approaching 10 wt.%. Pantellerites are therefore the true near-minimum melt compositions of alkaline oversaturated magma series.