Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.660924
Title: Experimental element-partitioning and phase-equilibrium studies relevant to subduction zones
Author: Randle, Harriet Alice
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1994
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Abstract:
Using solid-media apparatus, synthetic trace-element-doped peridotitic starting materials were equilibrated between 1.8 GPa and 2.8 GPa, and 970°C and 1150°C under water-saturated conditions at an fO2 equal to the Ni/NiO buffer. Melt compositions were calculated from analyses of melt inclusions trapped in an olivine crystal included in the capsule. However, analysis by secondary ion mass spectrometry (SIMS) showed that many of these experiments had been contaminated by boron from the surrounding boron-nitride sleeve, apparently via holes which formed and subsequently sealed. Water had not always been lost from contaminated capsules, and hence their failure had not previously been suspected. Comparison with uncontaminated experiments shows that boron fluxes melting and thus invalidates the results from the contaminated runs. This may be a general experimental problem, affecting past studies. Some experiments performed at 1.8 GPa were not contaminated and showed that with increased temperature, the solidus is encountered, followed by the amph-out, ilm-out, ru-out, cpx-out and opx-out curves, consistent with previous studies. Calculated melt compositions were tested by reversal, i.e. equilibration of the melt composition under similar conditions to the original experiment. A forward experiment conducted at 1.8 GPa, 1020°C produced ol, opx, cpx, amph, ru, ilm, sp, and basaltic melt (53.6% SiO2, 22.7% Al2O3). However the phases on the liquidus of the calculated melt composition were opx, cpx, gt, amph, and were more aluminous than the original phases. In reversal experiments performed without a separate olivine crystal, an extra 20 wt% forsterite component was necessary to stabilise olivine. The calculated melt is therefore deficient in olivine component and is more aluminous than the true melt.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.660924  DOI: Not available
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