Computer Science
Scientific paper
Jan 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007gecoa..71..434b&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 71, Issue 2, p. 434-451.
Computer Science
4
Scientific paper
An experimental procedure has been developed that permits measurement of the partitioning of Ar and He between crystal interiors and the intergranular medium (ITM) that surrounds them in synthetic melt-free polycrystalline diopside aggregates. 37Ar and 4He are introduced into the samples via neutron irradiation. As samples are crystallized under sub-solidus conditions from a pure diopside glass in a piston cylinder apparatus, noble gases diffusively equilibrate between the evolving crystal and intergranular reservoirs. After equilibration, ITM Ar and He is distinguished from that incorporated within the crystals by means of step heating analysis. An apparent equilibrium state (i.e., constant partitioning) is reached after about 20 h in the 1450 °C experiments. Data for longer durations show a systematic trend of decreasing ITM Ar (and He) with decreasing grain boundary (GB) interfacial area as would be predicted for partitioning controlled by the network of planar grain boundaries (as opposed to ITM gases distributed in discrete micro-bubbles or melt). These data yield values of GB-area-normalized partitioning, K¯ITMAr, with units of (Ar/m3 of solid)/(Ar/m2 of GB) of 6.8 × 103 2.4 × 104 m-1. Combined petrographic microscope, SEM, and limited TEM observation showed no evidence that a residual glass phase or grain boundary micro-bubbles dominated the ITM, though they may represent minor components. If a nominal GB thickness (δ) is assumed, and if the density of crystals and the grain boundaries are assumed equal, then a true grain boundary partition coefficient (KGBAr=XcrystalsAr/XGBAr), may be determined. For reasonable values of δ, KGBAr is at least an order of magnitude lower than the Ar partition coefficient between diopside and melt. Helium partitioning data provide a less robust constraint with K¯ITMHe between 4 × 103 and 4 × 104 cm-1, similar to the Ar partitioning data. These data suggest that an ITM consisting of nominally melt free, bubble free, tight grain boundaries can constitute a significant but not infinite reservoir, and therefore bulk transport pathway, for noble gases in fine grained portions of the crust and mantle where aqueous or melt fluids are non-wetting and of very low abundance (i.e., <0.1% fluid). Heterogeneities in grain size within dry equilibrated systems will correspond to significant differences in bulk rock noble gas content.
Asimow Paul D.
Baxter Ethan F.
Farley Kenneth A.
No associations
LandOfFree
Grain boundary partitioning of Ar and He does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Grain boundary partitioning of Ar and He, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Grain boundary partitioning of Ar and He will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1254595