182W and 187Os constraints on the origin of siderophile isotopic heterogeneity in the mantle
182W and 187Os constraints on the origin of siderophile isotopic heterogeneity in the mantle
复制标题
DOI：
10.1016/j.gca.2023.11.003
复制
发表时间：
2023-11-15
影响因子：
5
通讯作者：
Chauvel，Catherine
中科院分区：
文献类型：
--
作者：
Walker，Richard J.;Mundl-Petermeier，Andrea;Chauvel，Catherine
主量和微量元素丰度，包括高度亲铁元素，以及187 Os和182 W同位素组成测定为。89 Ma来自戈尔戈纳岛（哥伦比亚）和库拉索岛（荷属加勒比）的镁铁质和超镁铁质岩石。这两个岛屿的火山系统可能与地幔柱有关，地幔柱产生了加勒比大火成岩普罗旺斯。的主要和亲石微量元素的岩石检查的特征是一致的，与以前的研究结果，并表示衍生从化学高度亏损的地幔成分，和富集，或高度亏损的地幔成分。这些岩石的高亲铁元素丰度一般与全球具有可比性MgO的岩石相似，表明主要来源组分在这些元素中没有显著富集或贫化。两个岛屿的大部分岩石的铼-锇同位素系统学表明，从地幔源与初始187 Os/188 Os之间的同期平均亏损洋中脊地幔和散装硅酸盐地球的比例。该组成可能反映了平均下地幔签名，或全球规模的Os同位素在上地幔的不均匀性。一些玄武岩以及两个科马提岩的特征是计算出的初始187 Os/188 Os比值比南极参考值高10- 15%。这些放射性同位素组成不相关的主要或微量元素的系统学，并表示地幔源的组成部分，最有可能产生的硫化物交代作用或古老的Re/Os分馏。两个岛屿岩石的钨-182同位素组成特征是μ 182 W值变化很大，从现代块状硅酸盐类地球到强烈的负值。μ 182 W值与主、微量元素丰度及187 Os/188 Os初始组成无关。然而，与一些现代洋岛玄武岩系统一样，在戈尔戈纳橄榄辉长岩中测得的最低μ 182 W值（-53）与之前在该套岩中测得的最高3 He/4 He值（15.8 R/RA）相对应。由于缺乏与其他化学/同位素组成的相关性，以负μ 182 W和可能的高3 He/4 He为特征的地幔组分被最粗略地解释为是核幔边界处地幔与核之间同位素平衡的结果。
Major and trace element abundances, including highly siderophile elements, and187Os and182W isotopic compositions were determined forca. 89 Ma mafic and ultramafic rocks from the islands of Gorgona (Colombia) and Curaçao (Dutch Caribbean). The volcanic systems of both islands were likely associated with a mantle plume that generated the Caribbean Large Igneous Provence. The major and lithophile trace element characteristics of the rocks examined are consistent with the results of prior studies, and indicate derivation from both a chemically highly-depleted mantle component, and an enriched, or less highly-depleted mantle component. Highly siderophile element abundances for these rocks are generally similar to rocks with comparable MgO globally, indicating that the major source components were not substantially enriched or depleted in these elements. Rhenium-Os isotopic systematics of most rocks of both islands indicate derivation from a mantle source with an initial187Os/188Os ratio between that of the contemporaneous average depleted mid-ocean ridge mantle and bulk silicate Earth. The composition may reflect either an average lower mantle signature, or global-scale Os isotopic heterogeneity in the upper mantle. Some of the basalts, as well as two of the komatiites, are characterized by calculated initial187Os/188Os ratios 10–15 % higher than the chondritic reference. These more radiogenic Os isotopic compositions do not correlate with major or trace element systematics, and indicate a mantle source component that was most likely produced by either sulfide metasomatism or ancient Re/Os fractionation. Tungsten-182 isotopic compositions measured for rocks from both islands are characterized by variable μ182W values ranging from modern bulk silicate Earth-like to strongly negative values. The μ182W values do not correlate with major/trace element abundances or initial187Os/188Os compositions. As with some modern ocean island basalt systems, however, the lowest μ182W value (−53) measured, for a Gorgona olivine gabbro, corresponds with the highest3He/4He previously measured from the suite (15.8 R/RA). Given the lack of correlation with other chemical/isotopic compositions, the mantle component characterized by negative μ182W and possibly high3He/4He is most parsimoniously explained to have formed as a result of isotopic equilibration between the mantle and core at the core-mantle boundary.