Noble gases in olivine phenocrysts from drill core samples of the Hawaii Scientific Drilling Project (HSDP) pilot and main holes (Mauna Loa and Mauna Kea, Hawaii)
Noble gases in olivine phenocrysts from drill core samples of the Hawaii Scientific Drilling Project (HSDP) pilot and main holes (Mauna Loa and Mauna Kea, Hawaii)
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夏威夷科学钻探项目 (HSDP) 试验孔和主孔（夏威夷莫纳罗亚和莫纳克亚）钻芯样品中橄榄石斑晶中的惰性气体
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发表时间：
2003
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通讯作者：
J. Erzinger
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作者：
T. Althaus;S. Niedermann;J. Erzinger
我们已经确定了所有稀有气体的浓度和同位素组成的橄榄石斑晶从夏威夷科学钻探项目（HSDP）钻芯，包括莫纳罗亚火山熔岩在顶部247米和莫纳克亚火山熔岩下降到初步深度3109米。我们的目标是描述惰性气体在夏威夷一座主要火山活跃期的一个重要时间段内的长期同位素演化。He同位素特征显示出明显的时间趋势：3 He/4 He比值从最年轻熔岩中的MORB样9 RA增加到莫纳罗亚部分的15 RA，并从107 RA增加到陆上莫纳克亚矿床的1012 RA。他们仍然接近12 RA在大多数的海底莫纳克亚山样品，除了少数游览与3 He/4 He比高达21 RA在钻孔深度之间2000和2600米。12 RA的平均3 He/4 He比低于最近基拉韦厄和洛伊希海山喷发中观察到的比值，并支持夏威夷羽流同心分区的观点[ Kurz等人，1996年]。氖同位素签名没有显示出时间的演变。在整个莫纳克亚山剖面上，它仍然是羽状的（在Ne三同位素图中靠近Loihi-Kilauea相关线），在那些不以空气样Ne为主的样品中。最大20 Ne/22 Ne和21 Ne/22 Ne比值分别为12.10 ± 0.36和0.0360 ± 0.0042。在≥1000°C的释放步骤中，40 Ar/36 Ar比值在360和3300之间变化很大，这是由于大气的贡献可变。在至少一个样品中，14，300 ± 910的40 Ar/36 Ar比率表明存在MORB样Ar组分。氪和氪的同位素组成是整个大气。讨论了如何解释稀有气体同位素变化趋势及其与其它地球化学参数的关系。类似MORB的惰性气体与羽流成分的简单混合不能解释观测结果。我们赞成一个模型，涉及早期熔体提取外羽部分，其次是放射性向内生长，并可能与周围地幔物质的一些相互作用。
We have determined concentrations and isotopic compositions of all noble gases in olivine phenocrysts from the Hawaii Scientific Drilling Project (HSDP) drill core, comprising Mauna Loa lavas in the top 247 m and Mauna Kea lavas down to the preliminary depth of 3109 m. Our aim was to describe the long‐term isotopic evolution of noble gases over a significant time fraction of the active life of a major Hawaiian volcano. The He isotopic signature displays a clear temporal trend: 3He/4He ratios increase from MORB‐like 9 RA in the youngest lavas to 15 RA in the Mauna Loa section and from ∼7 RA to ∼12 RA in the subaerial Mauna Kea deposits. They remain close to 12 RA in most of the submarine Mauna Kea samples, except for a few excursions with 3He/4He ratios of up to 21 RA in borehole depths between 2000 and 2600 m. The average 3He/4He ratio of 12 RA is lower than that observed in recent eruptions of Kilauea and Loihi seamount and supports the idea of a concentrically zoned Hawaiian plume [ Kurz et al., 1996 ]. The Ne isotopic signature does not show a temporal evolution. It remains plume‐like (plotting close to the Loihi–Kilauea correlation line in a Ne three‐isotope diagram) over the whole Mauna Kea section in those samples which are not dominated by air‐like Ne. Maximum 20Ne/22Ne and 21Ne/22Ne ratios reach 12.10 ± 0.36 and 0.0360 ± 0.0042, respectively. 40Ar/36Ar ratios vary widely between 360 and ∼3300 in the ≥1000°C release steps due to variable atmospheric contributions. In at least one sample, a 40Ar/36Ar ratio of 14,300 ± 910 demonstrates the presence of a MORB‐like Ar component. Kr and Xe isotopic compositions are atmospheric throughout. We discuss several possibilities on how to explain the isotopic trends of the noble gases and their correlation to other geochemical parameters. Simple admixture of MORB‐like noble gases to the plume component cannot account for the observations. We favor a model involving early melt extraction from the outer plume sections, followed by radiogenic ingrowth and, possibly, some interaction with ambient mantle material.