Origin and length scale of compositional anomalies in the convecting Earth: constraints from the Azores

来自亚速尔群岛的熔岩显示出一些从大洋板内火山中已知的最极端的微量元素和同位素组成变化。这种极端的变化部分是由于地幔来源中存在再循环的地壳岩石。稳定同位素为我们提供了增加我们对这种地幔来源生成的理解的前景。而上地幔橄榄石的18O/16O变化较小(~δ18O为5.0~5.2‰)，沉积物质和陆源物质进入地幔将显著增加δ18O。相反，洋壳的高温变化将导致较低的δ18O。亚速尔群岛显示了一个理想的场所，可以在小范围内研究高度可变的地幔源区的氧同位素变化，以确定其起源。我们建议对原始熔岩中的橄榄石和单斜辉石斑晶以及演化熔岩中的斜长石斑晶进行系统的研究，并对大西洋中脊以东和以西所有亚速尔火山的熔岩进行玻璃分析，以更好地了解地幔来源的变异性及其来源。来自不同岛屿的玻璃中氯和氟的浓度将有助于确定亚速尔群岛岩浆的地壳同化作用，也可以用来确定原始镁铁质岩石中的再循环地壳物质。这项研究将补充关于亚速尔群岛岩浆的大量地球化学数据，并为地幔来源的起源提供重要的新见解。

Lavas from the Azores islands show some of the most extreme variation in trace element and isotope compositions known from oceanic intraplate volcanoes. This extreme variation has partly been explained by the presence of recycled crustal rocks in the mantle sources. Stable isotopes provide the prospect to increase our understanding of the generation of such mantle sources. While the 18O/16O of upper mantle olivines shows a small variability (~δ18O of 5.0-5.2 ‰) the incorporation of sedimentary and continental material into the mantle will significantly increase the δ18O. Contrastingly, the high temperature alteration of the oceanic crust will result in lower δ18O. The Azores archipelago displays an ideal site to study the O isotope variation of highly variable mantle sources on a small scale in order to determine their origin. We propose a systematic study of olivine and clinopyroxene phenocrysts from primitive lavas and plagioclase phenocrysts from evolved lavas as well as glass analyses from all lavas of the Azores volcanoes both east and west of the Mid-Atlantic Ridge in order to better understand the variability of mantle sources and their origin. Chlorine and F concentrations in glasses from different islands will help to define crustal assimilation of the Azores magmas and can also be used to define recycled crustal material in pristine mafic rocks. This study will complement the large geochemical data set on the Azores magmas and provide important new insight into the origin of mantle sources.