LETTER .fr

Melting processes in the deep mantle have important implications for the origin of the deep-derived plumes believed to feed hotspot volcanoes such as those in ...
1005KB taille 4 téléchargements 338 vues
LETTER ;

doi:10.1038/nature11294

Solid–liquid iron partitioning in Earth’s deep mantle Denis Andrault1, Sylvain Petitgirard2, Giacomo Lo Nigro1, Jean-Luc Devidal1, Giulia Veronesi2, Gaston Garbarino2 & Mohamed Mezouar2

1

trace elements, because their effect on iron partitioning can be neglected to a first approximation. We did the experiments in a diamond-anvil cell (DAC) at pressures from 40 GPa to 120 GPa, using very thin (5–10 mm) samples that were melted throughout their thickness using infrared lasers (Fig. 1). Melting criteria are based on the use of in situ X-ray diffraction, and details are reported elsewhere10. We analysed the recovered samples using simultaneous X-ray diffraction (XRD) and X-ray fluorescence (XRF) (Fig. 2), generating XRD and XRF maps with resolutions up to around 500 nm (Table 1). We successfully extracted some samples from their gaskets, and analysed them chemically using the electron microprobe (see Methods and Supplementary Information). The XRD maps (Fig. 3b, d) reveal circular zoning around the centre of the laser hotspot (CLHS). Multiphase Rietveld refinements of each XRD pattern provide maps of phase contents for each pixel in the twodimensional maps. XRF spectra recorded at the same sample positions show chemical zoning with a circular shape around the CLHS, similar a

b Mg-Pv liquidus phase

Mg-Pv liquidus phase Liquid ball

Liquid ball

20 μm

20 μm

Figure 1 | a, Optical and b, scanning-electron micrographs of samples recovered after partial melting at high pressure. Sample (a) was heated for a few seconds at 3,650 K and 78.5 GPa. Sample (b) was heated for about one minute at 3,200 K and 55 GPa. a

b 108 107 Cl K-lines

Mg-Pv Fp NaCl

Counts