کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
6429966 | 1634774 | 2013 | 8 صفحه PDF | دانلود رایگان |
- Melt-enriched pressure shadows were produced in torsion experiments.
- Location, shape and melt fraction of pressure shadows were consistent among samples.
- Heterogeneous melt distribution confirmed theoretical predictions.
As a two-phase, solid-melt material flows around rigid particles, melt-depleted and melt-enriched regions (i.e., pressure shadows) develop due to the coupled fluxes of melt and solid driven by pressure gradients around the particles. To study this compaction-decompaction process, samples composed of fine-grained San Carlos olivine plus mid-ocean ridge basalt containing dispersed sub-millimeter-sized, single crystal beads of olivine were deformed in torsion at a temperature of 1473 K and a confining pressure of 300 MPa. Indicated by melt distribution maps obtained from reflected-light optical and backscattered electron microscopy, melt-enriched and melt-depleted regions around the beads became observable at a local shear strain of γâ1 in samples with an initially homogeneously distributed melt fraction of Ïâ0.05. The melt-enriched regions (ϯhighâ0.06 to 0.10) and the melt-depleted regions (ϯlowâ0.02 to 0.04), extending as far as one radius of the bead, were symmetrically distributed around the bead. The flow field of the olivine matrix determined from crystallographic preferred orientations agrees with theoretical predictions based on two-phase flow analysis. These experiments are the first to produce pressure shadows in partially molten rocks. One implication of this study is that it will be possible to constrain the ratio of bulk to shear viscosity, which is inferred from the distribution of melt using a combination of experimental observations and numerical simulations.
Journal: Earth and Planetary Science Letters - Volume 382, 15 November 2013, Pages 77-84