The effect of dissolved CO2 on melt density of a model kimberlite composition up to 9 GPa
Abstract
Volatiles play many important roles in magmatic processes, and they can have large effects on the physicochemical properties of silicate systems including melt density and viscosity as well as melting temperatures and liquidus mineralogy. In particular, magmatic volatiles like H2O and CO2 have been implicated as being essential constituents in the formation and eruption of kimberlite magmas, which are believed to have originated deep within the Earth's interior. Although previous studies have examined the effects of CO2 and H2O on various magma compositions at pressures ranging from 0.1 MPa to 20 GPa, there have not yet been many studies conducted on compositions analogous to kimberlite magmas. In the present study, we have conducted experiments up to 9 GPa (using a Walker-style Multi-anvil device) on a model kimberlite melt composition to assess the effects of melt CO2 concentration on melt density (using the sink/float method) and liquidus temperatures and mineralogy (through equilibrium crystallization experiments). The composition we used is based on the proposed primary kimberlite magma composition of Kopylova et al., 2007. Some minor and trace elements were removed to simplify the composition, and water was left out so that we could independently assess the effects of CO2 on the physicochemical properties of the kimberlite composition. We also plan to determine the partial molar volume of CO2 in the model kimberlite melt. To determine the partial molar volume, we first made two synthetic mixes of the model kimberlite composition. One composition was made CO2-free and the other one with 12 wt.% CO2 (with CO2 added as reagent grade carbonates). Mixtures of these two endmembers were then created (at 25%, 50% and 75% mixing proportions) and experiments (both sink/float and near-liquidus equilibrium crystallization) will be conducted on each set of compositions. All experiments will be analyzed by EPMA and FTIR. FTIR will be used to qualitatively confirm the presence of carbonate in the melt before EPMA analysis, and we will use EPMA to quantify the major and minor element chemistry of our runs, including carbon. Thus far our sink/float experiments have shown that the kimberlite melt composition with approximately 12 wt.% CO2 is less dense than the mineral forsterite (Fo100) over the entire pressure range investigated (up to 9 GPa). Sink/float experiments on the kimberlite melt with approximately 6 wt.% CO2 as well as experiments on the CO2-free composition are ongoing, and we anticipate significant progress on constraining the density curves of these compositions by the time of presentation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMDI21A2059S
- Keywords:
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- 3621 MINERALOGY AND PETROLOGY / Mantle processes;
- 3630 MINERALOGY AND PETROLOGY / Experimental mineralogy and petrology;
- 8439 VOLCANOLOGY / Physics and chemistry of magma bodies