An Experimental Study of Fe-Al Solubility in the System Corundum-Hematite up to 40 kbar and 1300{degrees}C |
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Authors: | FEENSTRA, A. SAMANN, S. WUNDER, B. |
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Affiliation: | 1 GEOFORSCHUNGSZENTRUM POTSDAM, DEPARTMENT 4, TELEGRAFENBERG, D-14473 POTSDAM, GERMANY 2 FREIE UNIVERSITÄT BERLIN, DEPARTMENT OF EARTH SCIENCES, MALTESERSTRASSE 74100, D-12249 BERLIN, GERMANY |
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Abstract: | The mutual solubility in the system corundumhematite[-(Al, Fe3+)2O3] was investigated experimentally using bothsynthetic and natural materials. Mixtures of -Al2O3 and -Fe2O3(weight ratios of 8:2 and 10:1) were used as starting materialsfor synthesis experiments in air at 8001300°C withrun times of 734 days. Experiments at 840 kbarand 4901100°C were performed in a piston-cylinderapparatus (run times of 0·87·4 days) usinga natural diasporite consisting of 6070 vol. % diasporeand 2030 vol. % Ti-hematite. During the diasporitecorunditetransformation, the FeTiO3 component (1218 mol %) ofTi-hematite only slightly increased, implying that oxygen fugacitywas maintained at high values. Run products were studied byelectron microprobe and X-ray diffraction (Rietveld) techniques.An essentially linear volume of mixing exists in the solid solutionwith a slight positive deviation at the hematite side. Up to1000°C, corundum contains <4 mol % Fe2O3 and hematite<10 mol % Al2O3; at 1200°C these amounts increase to9·3 and 17·0 mol %, respectively. At 1300°Chematite was no longer stable and coexists with the orthorhombic phase . The present results agree with corundum (solvus) compositions obtained inprevious studies but indicate a larger solubility of Al in hematite.The miscibility gap in the solution can be modelled with anasymmetric Margules equation with interaction parameters (2uncertainties): ; ; ; . Application of the corundumhematite solution as a solvus geothermometer is limited because of thescarcity of suitable rock compositions. KEY WORDS: corundum; hematite; corundumhematite miscibility gap; experimental study; Margules model; metabauxite |
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Keywords: | : corundum hematite corundum hematite miscibility gap experimental study Margules model metabauxite |
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