Geochemical variability in a single flow from northern Iceland
Geochemical variability in a single flow from northern Iceland
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DOI：
10.1029/2000jb000142
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发表时间：
2003
影响因子：
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通讯作者：
J. Maclennan;D. McKenzie;F. Hilton;K. Grönvold;N. Shimizu
中科院分区：
文献类型：
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作者：
J. Maclennan;D. McKenzie;F. Hilton;K. Grönvold;N. Shimizu
[1]成分的变化是目前几乎每一个元素分析70个全岩样品和40个橄榄石托管熔融包裹体从Borgarhraun熔岩流在冰岛东北部。不相容元素浓度的变化可以由部分熔体的不完全混合产生，而整个岩石样品中相容元素的变化可以通过在流动中发现的晶体的添加/去除来解释。熔体包裹体不相容元素组成比全岩成分变化大，如果每个手样由20-30批熔体与包裹体成分混合而成的岩浆制成，则全岩样品的变化幅度可以匹配。单斜辉石压力测定和全岩样品的主要元素组成表明，混合作用发生在莫霍面以下岩浆房中，压力为10.9GPa。在Borgarhraun，不相容元素浓度的空间分布不是随机的，间隔<4 km的样品的浓度比地球化学随机分布的预期更相似。这个分离距离对应于0.014-0.14立方千米的熔岩体积。这一体积可能是由岩浆混合和幕式喷发的熔体从一个亚莫霍面室。相容元素的浓度随流动位置的变化与随机变化的预期值相差不大。控制主要元素组成的晶体去除和添加过程可能会在短尺度上产生变异性。
[1] Compositional variability is present for almost every element analyzed in 70 whole rock samples and 40 olivine-hosted melt inclusions from the Borgarhraun lava flow in NE Iceland. The variation of incompatible element concentrations can be produced by incomplete mixing of fractional melts, while the compatible element variations in the whole rock samples can be explained by addition/removal of crystals found in the flow. The melt inclusion incompatible element compositions are more variable than the whole rock compositions, and the magnitude of variability of the whole rock samples can be matched if each hand specimen is made of magma that was formed by mixing of 20–30 batches of melt with the composition of the inclusions. Clinopyroxene barometry and the major element composition of the whole rock samples suggest that mixing took place at pressures of ∼0.9 GPa in sub-Moho magma chambers. The spatial distribution of the concentrations of incompatible elements is not random in Borgarhraun and samples with a separation of <4 km have concentrations that are more similar than expected from a random distribution of geochemistry. This separation distance corresponds to a lava volume of 0.014–0.14 km3. This volume may be controlled by magma mixing and episodic eruption of melts from a sub-Moho chamber. The concentration variations of compatible elements with position in the flow are little different to those expected for random variation. It is likely that the crystal removal and addition processes that control major element compositions generate variability on short length scales.