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Title: Element partitioning between coexisting carbonate and silicate liquids
Author: Fielding, Kevin Donald
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1992
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A number of experimental studies have shown that the first melt of carbonated mantle peridotite is carbonatitic in character. This first melt will contain a sizeable portion of the mantle budget for incompatible trace elements and, owing to its physical properties, it is likely to be very mobile. If no further melting occurs, the carbonatitic melt will migrate through the mantle, scavenging incompatible elements, before freezing in the lithosphere. Alternatively, melting can progress, resulting in the incorporation of this precursor melt in more voluminous silicate melt. In any case, carbonate melt - silicate mantle equilibria are likely to influence the trace-element characteristics of material produced. One way of constraining the geochemical characteristics of mantle-derived carbonate melt is by investigation of the partitioning behaviour between coexisting carbonate and silicate liquids for trace elements of interest. This has been achieved by a series of experimental runs under a range of temperatures and pressures (0.2-2.0 GPa, 1100-1400oC), involving both natural rock compositions (phonolites, nephelinites and melilitites), and synthetic charges in the system SiO2-Al2O3-CaO-Na2O-CO2. Whilst showing that carbonate and silicate melts are likely to be completely miscible under mantle conditions, these experiments have also shown that a wide range of Ca-Mg-Na-Fe carbonate liquids can be experimentally produced by liquid immiscibility at crustal pressures. This range incorporates the vast majority of carbonatite compositions seen at the Earth's surface. Coexisting carbonate and silicate liquids in the experimental charges produced were characterised by electron probe microanalysis. Melt compositions were found to be accurately reproducible, and subject to small but consistent variations with pressure and temperature. The charges were studied optically to ensure that the coexisting liquids were in equilibrium, to investigate quenching processes occurring in the liquids on cooling, and to analyse the two-liquid textures obtained.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available