Identification of Source Lithology in the Hawaiian and Canary Islands: Implications for Origins
Identification of Source Lithology in the Hawaiian and Canary Islands: Implications for Origins
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DOI：
10.1093/petrology/egq075
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发表时间：
2011-01-01
影响因子：
3.9
通讯作者：
Herzberg, Claude
中科院分区：
文献类型：
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作者：
Herzberg, Claude
本文报告了利用全岩和橄榄石斑晶成分探测板内岩浆的地幔源岩性的结果。这项分析包括现代洋中脊玄武岩和太古代科马提岩作为低温和高温参考框架。结果表明，现代洋中脊玄武岩和太古代科马提岩中橄榄石斑晶的Ni、Ca、Mn和Fe/Mn含量与正常橄榄岩源区一致。相比之下，橄榄石斑晶在夏威夷的盾牌建设熔岩是较高的Ni和Fe/Mn，和较低的Mn和Ca比预期结晶从熔体的正常橄榄岩源，并指出辉石岩的重要性提出的Sobolev和同事。夏威夷盾阶段熔岩和橄榄石斑晶是类似的，预计从部分熔体的100%阶段2辉石岩源。这样的源可能由各种熔融-岩石、熔融-熔融和岩石-岩石反应形成。原生辉石岩岩浆中SiO2含量与Os-187/Os-188呈正相关，与He-3/He-4呈负相关。这些结果是一致的夏威夷羽含有回收地壳内的橄榄岩基质。在夏威夷辉石岩的来源，这有助于生产富含SiO2的岩浆中推断游离二氧化硅的变量。与此相反，橄榄岩和橄榄石辉石岩熔融推断产生SiO2-贫前屏蔽岩浆在Loihi。在夏威夷地幔柱中，富SiO2和贫SiO2岩浆的相互作用将引发结晶，而不是混合。混合是允许在低压熔体导管和岩浆房，和橄榄石托管熔融包裹体的工作将有助于评估其重要性。与夏威夷不同的是，加那利群岛等地的许多洋岛玄武岩缺乏SiO2，可能是由下地幔中再生地壳与橄榄岩之间的固态反应形成的橄榄石辉石岩部分熔融而成。有可能是一个广泛的全岩辉石组成的地幔，以及显着的变化，锰和铁/锰橄榄岩部分熔体和橄榄石斑晶。一般而言，地幔中不可能存在界限明确的端元橄榄岩和辉石岩源。然而，分类学上遇到的困难，在源岩识别可能会产生丰富的回报，如更好地了解下地幔的岩石多样性和板内岩浆作用的岩石学表达之间的关系。
Results are reported of an exploration of mantle source lithology for intraplate magmas using whole-rock and olivine phenocryst compositions. This analysis includes modern mid-ocean ridge basalts and Archean komatiites as low- and high-temperature reference frames. It is shown that the Ni, Ca, Mn, and Fe/Mn contents of olivine phenocrysts in modern mid-ocean ridge basalts and Archean komatiites are consistent with a normal peridotite source. In contrast, olivine phenocrysts in shield-building lavas on Hawaii are higher in Ni and Fe/Mn, and lower in Mn and Ca than those expected to crystallize from melts of a normal peridotite source, and point to the importance of pyroxenite as proposed by Sobolev and co-workers. Hawaiian shield stage lavas and their olivine phenocrysts are similar to those expected from partial melts of a 100% stage 2 pyroxenite source. Such a source might form from a variety of melt-rock, melt-melt, and rock-rock reactions. Primary pyroxenite-derived magmas have a range of SiO2 contents that are positively correlated with Os-187/Os-188 and negatively correlated with He-3/He-4. These results are consistent with a Hawaiian plume containing recycled crust within a peridotite matrix. Variable amounts of free silica are inferred in Hawaiian pyroxenite sources, which contribute to the production of SiO2-rich magmas. In contrast, peridotite and olivine pyroxenite melting are inferred to produce SiO2-poor pre-shield magmas at Loihi. The interaction of SiO2-rich and -poor magmas in the Hawaiian plume will trigger crystallization, not mixing. Mixing is permitted at low pressures in melt conduits and magma chambers, and work on olivine-hosted melt inclusions will be useful to evaluate its importance. In contrast to Hawaii, many ocean island basalts in localities such as the Canary Islands are deficient in SiO2, and may have been generated by partial melting of olivine pyroxenites that formed by solid-state reaction between recycled crust + peridotite in the lower mantle. There is likely to be a wide range of whole-rock pyroxenite compositions in the mantle, as well as significant variability in Mn and Fe/Mn in both peridotite partial melts and their olivine phenocrysts. In general, there are not likely to be well-defined end-member peridotite and pyroxenite sources in the mantle. Nevertheless, taxonomical difficulties encountered in source lithology identification may yield rich rewards, such as a better understanding of the relationship between lithological diversity in the lower mantle and its petrological expression in intraplate magmatism.