Due to routine maintenance, access to the Library Open Repository will be interrupted on the morning of Friday 12th February.
We apologise for any inconvenience.

Library Open Repository

An experimental study of carbonated eclogite at 3.5-5.5 GPa – Implications for silicate and carbonate metasomatism in the cratonic mantle

Downloads

Downloads per month over past year

Kiseeva, ES and Yaxley, GM and Hermann, J and Litasov, KD and Rosenthal, A and Kamenetsky, VS (2012) An experimental study of carbonated eclogite at 3.5-5.5 GPa – Implications for silicate and carbonate metasomatism in the cratonic mantle. Journal of Petrology, 53 (4). pp. 727-759.

[img]
Preview
PDF
JPet-2012-Eclog...pdf | Download (1MB)
Available under University of Tasmania Standard License.

Abstract

We have experimentally investigated a K-bearing altered mid-ocean ridge basalt (MORB) composition to which 10% CaCO3 was added (GA1+10%cc), at temperatures of 1050-1400oC and pressures of 3•5-5•5 GPa. Experiments were conducted in piston-cylinder apparatus in Pt-Gr (Pt with inner graphite) and Au-Pd capsules. Sub-solidus assemblages for both sets of experiments contain clinopyroxene, garnet, carbonate, rutile, coesite and K-feldspar. Apatite was observed only in the Pt-Gr experiments. Melting behaviour in experiments using different capsule materials contrasted markedly. Experiments in Pt-Gr capsules showed the silicate solidus to be at temperatures less than 1100oC at 3•5GPa and less than 1050oC at 4•5-5•0 GPa.These are similar (3•5GPa) or lower (4•5-5•0 GPa) temperatures compared with the carbonate solidus (1075-1125oC at 3•5-5•0 GPa). Melts in the Pt-Gr runs evolve with increasing degree of melting from K-rich silicate melts at the lowest degree of melting to carbonate-silicate immiscible liquids and silicate-carbonate melts at intermediate degrees of melting, and finally to silicate melts at the highest degrees of melting. Experiments in Au-Pd capsules were performed only at 5•0GPa. The carbonate solidus is between 1200 and 1225oC (at least 100oC higher than in the experiments in Pt-Gr capsules at the same pressure-temperature conditions).The first melts to be produced are carbonatitic and exhibit increasing SiO2 content with increasing temperature.This contrast in melting behaviour is explained by the relatively rapid diffusion of H through the Pt-Gr capsules, resulting in formation of H2O, and thus dramatically depressing both the silicate and the carbonate solidi in the Pt-Gr experiments compared with those in the Au-Pd experiments. This presumably reflects the lower permeability of Au-Pd to H, resulting in a much lower H2O/CO2 ratio in the Au-Pd encapsulated experiments. The presence of water in the melt was demonstrated by Fourier transform infrared (FTIR) spectroscopic analysis of one Pt-Gr experiment, indicating ~0•5wt % H2O in the bulk composition. Further confirmation that H2O plays such a role in the Pt-Gr experiments was provided by an additional experiment performed in a Au-Pd capsule with ~10 wt % H2Ospecifically added. In this experiment immiscible carbonate and silicate melts were observed. Carbonate- silicate liquid immiscibility is considered to occur as a result of the H2O present in the system. These results can be applied to natural systems in several ways. First, the presence of a small amount of either silicate melt or H2O-fluid in the system will act as a ‘flux’, depressing the carbonate solidus to much lower temperatures than inanhydrous systems. Second, the full trend in melt evolution from silicate-rich to carbonate-rich melts, which is also observed in inclusions in diamonds, can be explained by melting of K- and CO2-bearing, water-undersaturated MORB compositions. In cratonic environments low-degree silicate and immiscible silicate and carbonate melts will metasomatize the overlying mantle in different ways, producing, in the first instance, Si enrichment and crystallization of additional orthopyroxene, phlogopite, pyrope-rich garnet and consuming olivine, and, in the second case, carbonate metasomatism, with additional magnesite-dolomite, clinopyroxene and apatite. Both metasomatic styles have been described in natural peridotite xenoliths from the cratonic lithosphere.

Item Type: Article
Journal or Publication Title: Journal of Petrology
Page Range: pp. 727-759
Identification Number - DOI: 10.1093/petrology/egr078
Additional Information: The definitive publisher-authenticated version is available online at: http://www.oxfordjournals.org/
Date Deposited: 02 Apr 2012 04:59
Last Modified: 18 Nov 2014 04:29
Item Statistics: View statistics for this item

Repository Staff Only (login required)

Item Control Page Item Control Page