SIMS analysis of volatiles in silicate glasses, 2: isotopes and abundances in Hawaiian melt inclusions
SIMS analysis of volatiles in silicate glasses, 2: isotopes and abundances in Hawaiian melt inclusions
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DOI：
10.1016/s0009-2541(01)00374-6
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发表时间：
2002-03-01
期刊：
影响因子：
3.9
通讯作者：
Hauri, E
中科院分区：
文献类型：
--
作者：
Hauri, E
对夏威夷洛伊希火山、基拉韦厄火山、莫纳罗亚火山和库劳火山的5个熔岩样品中含有橄榄石的熔融包裹体种群进行了离子探针测量，测定了H2O、CO2、F、S和Cl的浓度以及氢的同位素组成。熔体包裹体经再加热并对夹带后改性的影响进行校正后，其MgO含量在8.9% ~ 15.1%之间，平均为11%，明显高于大多数海底玻璃。熔体包裹体在H2O （0.03-0.84 ppm）、CO2 （5-862 ppm）、F （308-1000 ppm）、S （156-3330 ppm）和Cl （8 ppm - 1.11 wt.%）中的含量范围很大，同时δ d的含量范围也很大（- 165 ppm - + 40 ppm）。Loihi包裹体的实验室再加热实验表明，含橄榄石的熔体包裹体可以通过质子在橄榄石中的扩散，在一小时到一天的时间尺度上发生氢的弥漫性损失，从而使熔体包裹体中残余氢的D/H比发生正变化。与已发表的海底玻璃分析相比，基拉威厄和莫纳罗亚海底样品的大多数熔融包裹体具有低H2O （0.05 - 0.2 wt.%）和高δ d（高达+ 40%）的特征，这表明在火山喷发后不久包裹体缓慢冷却期间弥散的H损失，库劳熔融包裹体具有海洋玄武岩中测量到的最低δ d值（- 61ppm至- 165ppm）。浅层脱气在大多数Koolau熔体包裹体中产生h2o -delta关系，这可以用开系统（Rayleigh）脱气来解释，其蒸汽-熔体D/H分馏系数为1.024，与之前的估计相似。在一些包裹体中，H2O和S的平行耗尽也表明了浅脱气，但所有火山的脱气熔融包裹体都显示出广泛的CO2浓度，表明夏威夷岩浆储层中熔体的垂直三角洲（13）C对流。库劳火山3个含co2的熔体包裹体测量值均为贫化（- 12ppm ~ - 29ppm），与δ δ相关，可能与富co2岩浆的开放体系脱气以及随后与低脱气岩浆的混合相一致。少量的熔体包裹体表现出较高的Cl和Cl/K比率，其中一个极端的例子来自Loihi （I. 11 wt.% Cl, 0.48 - wt.% H2O, δ = - 118ppm）。熔体包裹体的一部分已经摆脱了H扩散、浅层脱气和地壳污染的混杂影响，并为夏威夷地幔中D/H比的非均质性提供了证据，这似乎与已公布的放射性成因（Sr, Nd, Pb, Os）和氧同位素数据相关。如果夏威夷三角洲的表观变异可以被证实是一个源信号，那么夏威夷的D/H数据表明，夏威夷羽流内部的非均质性要求规模大（数十公里）和/或年龄小（< 1 Ga），以保持氢同位素的变异，而不受地幔中氢的极快速扩散的影响。(C) 2002 Elsevier Science B.V.版权所有
Ion microprobe measurements of the concentrations of H2O, CO2, F, S and Cl and the isotopic composition of hydrogen are reported for populations of olivine-hosted melt inclusions from five lava samples from the Hawaiian volcanoes Loihi, Kilauea, Mauna Loa and Koolau. After reheating of the melt inclusions and correction for the effects of post-entrapment modification, the melt inclusions have MgO contents ranging from 8.9% to 15.1% and averaging 11%, significantly higher in MgO than most submarine glasses. The melt inclusions show large ranges in H2O (0.03-0.84), CO2 (5-862 ppm), F (308-1000 ppm), S (156-3330 ppm) and Cl (8 ppm to 1.11 wt.%), accompanied by large ranges in deltaD ( - 165parts per thousand to + 40parts per thousand). Laboratory reheating experiments on Loihi inclusions show that diffusive loss of hydrogen can occur from olivine-hosted melt inclusions on hour- to day-long time scales via proton diffusion through olivine, with consequent positive shifts in the D/H ratios of the residual hydrogen in the melt inclusion. Most melt inclusions from subaerial Kilauea and Mauna Loa samples have signatures of low H2O (0,05 - 0.2 wt.%) and high deltaD (up to + 40%) compared to published analyses of submarine glasses, suggesting diffusive H loss during slow cooling of inclusions shortly after eruption, Koolau melt inclusions have the lowest deltaD values yet measured in oceanic basalts ( - 61parts per thousand to - 165parts per thousand). Shallow-level degassing produces a H2O-deltaD relationship in most Koolau melt inclusions which can be explained by open-system (Rayleigh) degassing with a vapor-melt D/H fractionation factor of 1.024, similar to previous estimates. Shallow degassing is also indicated in some inclusions by parallel depletions in H2O and S, but degassed melt inclusions from all volcanoes display a wide range in CO2 concentrations, indicating kilometer-scale vertical delta(13)C convection of melts within Hawaiian magma reservoirs. The measured of three CO2-bearing melt inclusions from Koolau volcano are depleted ( - 12parts per thousand to - 29parts per thousand) and correlated with deltaD, possibly consistent with open-system degassing Of CO2-rich magmas and subsequent mixing with less-degassed magmas. Assimilation of seawater-derived components is indicated in a small number of melt inclusions which exhibit high Cl and Cl/K ratios, with an extreme example from Loihi (I. 11 wt.% Cl, 0.48 - wt.% H2O, deltaD = - 118parts per thousand). A subset of melt inclusions have escaped the confounding effects of H diffusion, shallow degassing and crustal contamination, and provide evidence for heterogeneity of D/H ratios in the Hawaiian mantle, which appear to correlate with published radiogenic (Sr, Nd, Pb, Os) and oxygen isotope data. If the apparent Hawaiian deltaD variability can be confirmed to be a source signature, then the Hawaiian D/H data indicate that heterogeneities within the Hawaiian plume are required to be large in scale (tens of kilometers) and/or young in age (< 1 Ga) in order to preserve hydrogen isotopic variability against the extremely rapid diffusivity of hydrogen in the mantle. (C) 2002 Elsevier Science B.V. All rights reserved.