Publication Date:
2017-04-04
Description:
A series of experiments created melt inclusions
in plagioclase and pyroxene crystals grown from a basaltic
melt at 1,150 C, 1.0 GPa to investigate diffusive fractionation
during melt inclusion formation; additionally, P
diffusion in a basaltic melt was measured at 1.0 GPa. Melt
inclusions and melts within a few 100 microns of plagioclase–
melt interfaces were analyzed for comparison with
melt compositions far from the crystals. Melt inclusions
and melt compositions in the boundary layer close to the
crystal–melt interface were similar, but both differ significantly
in incompatible element concentrations from melt
found greater than approximately 200 microns away from
the crystals. The compositional profiles of S, Cl, P, Fe, and
Al in the boundary layers were successfully reproduced by
a two-step model of rapid crystal growth followed by diffusive
relaxation toward equilibrium after termination of
crystal growth. Applying this model to investigate possible
incompatible element enrichment in natural melt inclusions
demonstrated that at growth rates high enough
to create the conditions for melt inclusion formation,
*10-9–10-8 m s-1, the concentration of water in the
boundary layer near the crystal was similar to that of the
bulk melt because of its high diffusion coefficient, but
sulfur, with a diffusivity similar to major elements and
CO2, was somewhat enriched in the boundary layer melt,
and phosphorus, with its low diffusion coefficient similar to
other high-field strength elements and rare earth elements,
was significantly enriched. Thus, the concentrations of
sulfur and phosphorus in melt inclusions may over-estimate
their values in the bulk melt, and other elements with
similar diffusion coefficients may also be enriched in melt
inclusions relative to the bulk melt.
Description:
Natural Sciences and Engineering Research Council of
Canada Discovery grant;
Istituto Nazionale di Geofisica
and Vulcanologia, Italy
Description:
Published
Description:
377-395
Description:
2.3. TTC - Laboratori di chimica e fisica delle rocce
Description:
JCR Journal
Description:
reserved
Keywords:
Melt inclusions
;
Phosphorus diffusion
;
Crystal growth
;
Diffusive Fractionation
;
04. Solid Earth::04.08. Volcanology::04.08.03. Magmas
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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