Melt inclusions in Iceland olivines as tracers of primary mantle melt compositions

本项目的目的是通过对冰岛苦橄岩和橄榄石拉斑玄武岩早期形成的斑晶中的玻璃状包裹体所代表的原生熔体进行原位分析（主要和微量元素及同位素），调查冰岛羽流的来源化学。我们之前已经表明，在夏威夷拉斑玄武岩中，熔融包裹体中观察到的极端化学和同位素不均匀性除了显示渐进分离熔融的影响之外，还反映了真正的源不均匀性。通过研究冰岛的地幔柱，那里的熔融比夏威夷下面的熔融浅得多，我们希望获得一个地幔柱源化学变化的更清晰的图像。显然，冰岛与夏威夷的相似之处在于，两个地幔柱都含有循环的海洋地壳，而这种前地壳的特定成分，如辉长岩，可以通过它们的地球化学指纹来识别。此外，我们希望获得更好的了解机制的熔体提取和可能的化学分区的冰岛羽。地震层析成像显示，冰岛羽流的直径（100公里）比冰岛的直径（250公里）小得多。这将使我们能够绘制出源化学，并将其与羽流的断层扫描“图像”相关联。

The aim of this project is to investigate the source chemistry of the Iceland plume by insitu analysis (major and trace elements and isotopes) of primary melts represented by glassy inclusions in early-formed phenocrysts from Iceland picrites and olivine tholeiites. We have previously shown that in Hawaiian tholeiites, extreme chemical and isotopic heterogeneities seen in melt inclusions reflect true source heterogeneities, in addition to displaying the effects of progressive fractional melting. By studying the Iceland plume, where melting is at a much shallower level than beneath Hawaii, we hope obtain a clearer picture of the variations of source chemistry of a plume. Apparently, Iceland resembles Hawaii in that both plumes contain recycled ocean crust, and specific components of this former crust, such as gabbros, can be recognized by their geochemical fingerprints. In addition, we expect to gain a better understanding of mechanisms of melt extraction and of possible chemical zoning of the Iceland plume. Seismic tomography indicates that the diameter of the Iceland plume (100 km) is significantly smaller that of the island (250 km). This should enable us to map out the source chemistry and relate it to the tomographic "image" of the plume.