Helium distributions in ocean island basalt olivines revealed by X-ray computed tomography and single-grain crushing experiments
Helium distributions in ocean island basalt olivines revealed by X-ray computed tomography and single-grain crushing experiments
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X 射线计算机断层扫描和单晶破碎实验揭示了海岛玄武岩橄榄石中的氦分布
DOI：
10.1016/j.gca.2018.10.013
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发表时间：
2019
影响因子：
5
通讯作者：
Jackson, Matthew
中科院分区：
文献类型：
--
作者：
Horton, Forrest;Farley, Kenneth;Jackson, Matthew
对美属萨摩亚奥富岛和奥罗塞加岛玄武岩中单个橄榄石晶体的x射线计算机断层扫描显示，一小部分橄榄石含有绝大多数流体包裹体。单粒破碎实验表明，He和co2主要存在于这些包裹体中。大多数颗粒中的低co2压力，对应于小于1 km的深度，提供了普遍存在的磨损和流体包裹体中相关压力降低的证据。尽管如此，包裹体体积最大的橄榄石产生了足够的He，以获得精确的He浓度和同位素组成。在分析不确定度范围内，各玄武岩橄榄石的3He/4He比值是均匀的，而玄武岩的3He/4He比值在21 ~ 35 Ra之间。所分析的橄榄石中C/3He比值的总范围为3.6 × 107 ~ 1.5 × 1010，每种玄武岩的橄榄石中C/3He比值相差近一个数量级。我们假设C/3He比值如此大的范围是由于岩浆上升和冷却过程中流体包裹体通过橄榄石晶格大量扩散导致C和3He的粒度解耦造成的。如果是这样的话，原始奥富-奥罗塞加岩浆的C/3He比值可能小于4 × 108，这比以前对热点岩浆的估计要低。
X-ray computed tomography of individual olivine crystals in basalts from Ofu and Olosega islands, American Samoa, reveals that a small fraction of the olivines contain the vast majority of the fluid inclusions. Single-grain crushing experiments demonstrate that He and CO2reside primarily in these inclusions. Low CO2pressures in most grains, corresponding to depths of less than 1 km, provide evidence of ubiquitous decrepitation and associated pressure reduction in the fluid inclusions. Even so, the olivines with the highest inclusion volumes yielded sufficient He to obtain precise He concentrations and isotopic compositions. Within analytical uncertainty,3He/4He ratios are homogeneous among the olivines from each basalt, but among basalts, the ratios range from 21 to 35 Ra. The total range in C/3He ratio within the analyzed olivines is from 3.6 × 107to 1.5 × 1010, and varies by nearly an order of magnitude within the olivines from each basalt. We postulate that this wide range of C/3He ratios is caused by grain-scale decoupling of C and3He due to extensive He diffusion out of fluid inclusions through the olivine lattice during magma ascent and cooling. If so, primary Ofu-Olosega magmas probably had C/3He ratios less than 4 × 108, which is lower than previous estimates for hotspot magmas.
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影响因子：
5.3
作者：
J. Tucker;S. Mukhopadhyay;H. Gonnermann
通讯作者：
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R. Coish;L. Taylor
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影响因子：
3.5
作者：
K. Farley;A. Basu;H. Craig
通讯作者：
H. Craig
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影响因子：
5
作者：
P. Blard;Nicolas Puchol;K. Farley
通讯作者：
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影响因子：
5
作者：
Heber, Veronika S.;Brooker, Richard A.;Wood, Bernard J.
通讯作者：
Wood, Bernard J.