Noble gas and carbon isotopic compositions of petit-spot lavas from southeast of Marcus Island
Noble gas and carbon isotopic compositions of petit-spot lavas from southeast of Marcus Island
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马库斯岛东南部小点熔岩的稀有气体和碳同位素组成
DOI：
10.1016/j.epsl.2018.06.020
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发表时间：
2018
影响因子：
5.3
通讯作者：
Sano Y.
中科院分区：
文献类型：
--
作者：
Yamamoto J.;Kawano T.;Takahata N.;Sano Y.
我们测量了从海山（所谓的小点火山）中取样的淬火熔岩的稀有气体同位素组成，这些火山位于有1.6亿年历史的西北太平洋板块上。样品的~ 3 He/~ 4 He和~（40）Ar/~（36）Ar比值分别为2.5-8.3 Ra和1735（Ra为大气~ 3 He/~ 4 He），与MORB的比值相近或低于MORB的比值。考虑到取样区域狭窄，造成数据变化的一个次级效应可能是岩浆在大洋岩石圈中上升和随后冷却的过程中，岩浆中的化学成分将与岩石圈中的化学成分同化。CO2/3 He比值与碳同位素比值之间的相关性表明，碳的掺入海底碳酸盐的影响。惰性气体也是如此。稀有气体在地幔源、溶解在海水中的大气组分和放射成因组分之间的混合可以解释数据分布。No3 He/4 He比值超过类MORB值。小斑岩浆的地幔源区可能具有类似于MORB的3 He/4 He比值。小点岩浆的喷发与俯冲洋板块的弯曲有密切的关系。类似于MORB的3 He/4 He比值支持小斑岩浆起源于岩石圈-软流圈边界的假说。
We measured noble gas isotopic compositions of quenched lavas sampled from seamounts, so-called petit-spot volcanoes, on the 160-million-year-old northwestern Pacific Plate. The samples3He/4He and40Ar/36Ar ratios were, respectively, 2.5–8.3 Ra and up to 1735, where Ra stands for atmospheric3He/4He, which are analogous to or lower than those of MORB. Considering narrow sampling regions, a secondary effect might be responsible for variation of the data.During ascent and subsequent cooling of magma in the oceanic lithosphere, chemical components in the magma will be assimilated with those in the lithosphere. Correlation between CO2/3He ratios and carbon isotopic ratios suggests that carbon was affected by the incorporation of seafloor carbonate. The same would be true of noble gases. The mixing of noble gases among a mantle source, an atmospheric component dissolved in seawater and a radiogenic component can explain the data distribution. No3He/4He ratio exceeds the MORB-like value. The mantle source of the petit-spot magma was likely to have had a MORB-like3He/4He ratio originally. The eruption of petit-spot magma shows a close relation with the bending of subducting oceanic plates. The MORB-like3He/4He ratio supports the hypothesis that the petit-spot magma is derived from the lithosphere–asthenosphere boundary.