A young source for the Hawaiian plume
A young source for the Hawaiian plume
复制标题
DOI：
10.1038/nature10321
复制
发表时间：
2011-08
期刊：
影响因子：
64.8
通讯作者：
A. Sobolev;A. Hofmann;K. Jochum;D. Kuzmin;B. Stoll
中科院分区：
文献类型：
--
作者：
A. Sobolev;A. Hofmann;K. Jochum;D. Kuzmin;B. Stoll
洋壳通过俯冲、地幔上涌和地幔柱重熔的再循环是解释洋岛火山作用的一个被广泛接受的机制。这种循环的时间尺度对我们理解地幔循环速率很重要。从大洋岛屿，如夏威夷或冰岛的熔岩中的铀成因铅同位素的相关性，当解释为模式等时线，产生源分化年龄之间的1和25亿年（Gyr），。然而，如果这种相关性是由不相关的地幔成分混合产生的，它们就没有直接的年龄意义。Re-Os衰变模型年龄考虑了具有不同历史的源的混合，但它们依赖于假定的俯冲地壳的初始Re/Os比，这是很差的约束，因为俯冲期间的高流动性的Re-Os。本文首次报道了来自夏威夷莫纳罗亚盾状火山熔岩中橄榄石斑晶138个熔融包裹体的87 Sr/86 Sr比值数据，表明地幔源区具有巨大的不均一性。我们发现，在严重贫铷熔体包裹体中的高放射性锶与200- 6.5亿年前海水的同位素组成相匹配。我们推断，这样的海水必须污染莫纳罗亚源岩，俯冲之前，赋予这个源一个独特的“时间戳”。羽流来源中的少量海水锶可能很常见，但只有在源自一般高度（不相容元素）贫化源成分的超贫化熔体中才能清楚地识别。在夏威夷熔岩源中存在200- 6.5亿年前的洋壳意味着一般地幔环流的时间尺度，平均速率约为2（±1）cm/年，比以前认为的要快得多。
Recycling of oceanic crust through subduction, mantle upwelling, and remelting in mantle plumes is a widely accepted mechanism to explain ocean island volcanism. The timescale of this recycling is important to our understanding of mantle circulation rates. Correlations of uranogenic lead isotopes in lavas from ocean islands such as Hawaii or Iceland, when interpreted as model isochrons, have yielded source differentiation ages between 1 and 2.5 billion years (Gyr),,,. However, if such correlations are produced by mixing of unrelated mantle components they will have no direct age significance. Re–Os decay model ages take into account the mixing of sources with different histories,, but they depend on the assumed initial Re/Os ratio of the subducted crust, which is poorly constrained because of the high mobility of rhenium during subduction. Here we report the first data on87Sr/86Sr ratios for 138 melt inclusions in olivine phenocrysts from lavas of Mauna Loa shield volcano, Hawaii, indicating enormous mantle source heterogeneity. We show that highly radiogenic strontium in severely rubidium-depleted melt inclusions matches the isotopic composition of 200–650-Myr-old sea water. We infer that such sea water must have contaminated the Mauna Loa source rock, before subduction, imparting a unique ‘time stamp’ on this source. Small amounts of seawater-derived strontium in plume sources may be common but can be identified clearly only in ultra-depleted melts originating from generally highly (incompatible-element) depleted source components. The presence of 200–650-Myr-old oceanic crust in the source of Hawaiian lavas implies a timescale of general mantle circulation with an average rate of about 2 (±1) cm yr−1, much faster than previously thought.