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

亚速尔群岛的熔岩在微量元素和同位素组成方面显示出一些从海洋板内火山中已知的最极端的变化。这种极端的变化部分可以用地幔源中存在的再循环地壳岩石来解释。稳定同位素为我们进一步了解地幔源的形成提供了前景。虽然上地幔橄榄石的18O/16O值变化不大（~δ18O值在5.0 ~ 5.2‰之间），但沉积和陆相物质的掺入会显著增加上地幔橄榄石的δ18O值。相反，海洋地壳的高温蚀变会导致δ18O值降低。亚速尔群岛是在小尺度上研究高变化地幔源O同位素变化以确定其起源的理想场所。我们建议对原始熔岩中的橄榄石和斜辉石斑晶和演化熔岩中的斜长石斑晶进行系统的研究，并对大西洋中脊东部和西部亚速尔群岛火山的所有熔岩进行玻璃分析，以便更好地了解地幔来源及其起源的可变性。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岩浆的地壳同化作用，也可用于确定原始基性岩石中的再循环地壳物质。这项研究将对亚速尔群岛岩浆的大量地球化学数据进行补充，并为地幔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.