کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
4742676 | 1641602 | 2006 | 11 صفحه PDF | دانلود رایگان |
Phase relations in natural mid-oceanic ridge basalt (MORB) were investigated to depths of 700–1400 km in the lower mantle, using a laser-heated diamond-anvil cell and synchrotron X-ray diffraction (XRD). The crystalline phases, their unit-cell volumes and proportions were determined from Rietveld refinement of the in situ XRD spectra. At the top of the lower mantle, Mg-rich perovskite is the most abundant phase, followed by Ca-rich perovskite and stishovite. Two Al-rich phases occur in smaller amounts, the Ca-ferrite type and the new aluminum-rich phase (or NAL). This assemblage is stable down to 1150 km, approximately. At greater depths, the new aluminum-rich phase disappears, and the assemblage of Mg-rich perovskite, Ca-rich perovskite, stishovite and Ca-ferrite phase is stable up to at least 1400 km. In view of the present phase diagram, we discuss the nature and relations of the lower mantle Al-phases in MORB composition, and their bearing on the density evolution of the oceanic crust.
Journal: Physics of the Earth and Planetary Interiors - Volume 157, Issues 1–2, 14 August 2006, Pages 139–149