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了一些海洋板内火山已知的微量元素和同位素组成的最极端的变化。这种极端变化的部分原因是地幔源中存在再循环的地壳岩石。稳定同位素的发现为我们进一步了解地幔源区的形成提供了前景。虽然上地幔橄榄石的18 O/16 O显示出较小的变化（~δ 18 O为5.0-5.2 ‰），但沉积和大陆物质掺入地幔将显着增加δ 18 O。相反，洋壳的高温蚀变将导致δ 18 O降低。亚速尔群岛是一个理想的地点，以研究在小规模的高度可变的地幔源的O同位素变化，以确定其起源。我们提出了一个系统的研究橄榄石和单斜辉石斑晶从原始熔岩和斜长石斑晶从演化熔岩以及玻璃分析从所有的亚速尔群岛火山东部和西部的中大西洋海岭的熔岩，以更好地了解地幔源的变化和它们的起源。来自不同岛屿的玻璃中的氯和氟浓度将有助于确定亚速尔群岛岩浆的地壳同化作用，也可用于确定原始镁铁质岩石中的再循环地壳物质。这项研究将补充亚速尔群岛岩浆的大型地球化学数据集，并提供重要的地幔源的起源新的见解。

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.