The 1875 eruption of Askja volcano, Iceland: combined fractional crystallization and selective contamination in the generation of rhyolitic magma
The 1875 eruption of Askja volcano, Iceland: combined fractional crystallization and selective contamination in the generation of rhyolitic magma
复制标题
1875 年冰岛阿斯贾火山喷发：流纹质岩浆生成过程中分步结晶和选择性污染的结合
作者：
R. Macdonald;R. Sparks;H. Sigurdsson;D. Mattey;D. McGarvie;R. L. Smith
本文给出了1875年阿斯卡火山喷发的铁玄武岩、冰安岩、流纹岩、混合浮岩和硅质包体的主量元素、微量元素和锶、钕、氧同位素数据。微量元素模拟和锶、钕数据在很大程度上证实了以前的主元素计算结果，即玄武岩-铁玄武岩-冰安岩-流纹岩系列的形成以分离结晶为主。这种机制不能单独解释流纹岩中Rb(以及Th和U？)的相对富集、Cs的亏损和δ18O/16O的低值。硅质岩浆受到部分熔融的花岗岩围岩扩散的选择性污染，目前在喷发产物中发现了包体，这一过程特别明显地表现为流纹岩中的δ18O和Cs/Rb比伴生玄武岩中的低。这是冰岛硅胶复合体中首次记录的联合分离结晶-选择性污染过程。
Abstract Major and trace element and Sr, Nd and O isotopic data are presented for ferrobasalts, icelandites, rhyolites, mixed pumices and silicic xenoliths of the 1875 eruption of Askja. Trace element modelling and Sr and Nd data largely confirm previous major element calculations that fractional crystallization was dominant in the generation of the basalt-ferrobasalt-icelandite-rhyolite suite. Relative enrichment in Rb (and Th and U?), depletion in Cs, and low values of δ18O/16O, in the rhyolites are not explained by this mechanism alone. The silicic magmas were selectively contaminated by diffusion from partially molten granitic wall rocks, now found as xenoliths in the eruptive products, the process being particularly marked by lower δ18O and Cs/Rb ratios in the rhyolites than in the associated basalts. This is the first record of a combined fractional crystallization-selective contamination process in an Icelandic silicic complex.