The occurrence of deerite in highly oxidizing conditions within the ‘schistes lustrés’of eastern Corsica

A deerite-bearing rock occurs at the boundary between quartzite and metabasites within the ‘schistes lustres’of eastern Corsica. It contains the typomorphic assemblage pyroxene, blue amphibole, hematite and magnetite. Pyroxene shows homogeneous composition close to the aegirine end-member and blue amphibole is zoned from crossite core to riebeckite rim. The bulk chemical analysis of the rock is remarkable by its very high iron content and the presence of an unusually large amount of Zn which is concentrated in both deerite and amphibole. Electron microprobe analyses of the Corsican deerite are compared with those published in the literature; as shown by deerite from the Fransciscan iron formation, the principal substitution for Fe2+ is Mn whereas the amount of substitution for Fe3+ is low. In the system SiO2-FeO-Fe2O3-Al2O3-Na2O-MgO-H2O the typomorphic paragenesis can be described by an univariant reaction interpreted as the result of a pressure decrease. P-T conditions of metamorphism, previously estimated to be 8 kbar and 300°C, are in good agreement with present knowledge of the deerite stability field. The occurrence of hematite and magnetite in equilibrium permits an estimation of the oxygen fugacity (log fo2= -29.41 bar). Oxidation conditions are higher than those previously mentioned in the literature for similar assemblages.

[1]  R. Powell,et al.  Calcite–dolomite geothermometry in the system CaCO3–MgCO3–FeCO3: an experimental study , 1984 .

[2]  J. Caron,et al.  High-pressure-low-temperature metamorphism and polyphase alpine deformation at Sant'Andrea di cotone (eastern corsica, france) , 1981 .

[3]  W. Schreyer,et al.  Experimental results bearing on the stability of the blueschist-facies minerals deerite, howieite and zussmanite, and their petrological significance , 1981 .

[4]  J. Malavieille,et al.  Transverse lineation and large-scale structures related to Alpine obduction in Corsica , 1981 .

[5]  R. Wood.  Compositional zoning in sodic amphiboles from the blueschist facies , 1980, Mineralogical Magazine.

[6]  A. Boettcher,et al.  THE EFFECT OF MANGANESE ON OLIVINE-QUARTZ-ORTHOPYROXENE STABILITY , 1980 .

[7]  M. Gole.  Mineralogy and petrology of very-low-metamorphic grade Archaean banded iron-formations, Weld Range, Western Australia , 1980 .

[8]  R. Wood.  The Iron-Rich Blueschist Facies Minerals: I. Deerite , 1979 .

[9]  C. Klein.  Regional metamorphism of Proterozoic iron-formation, Labrador Trough, Canada , 1978 .

[10]  R. J. Floran,et al.  Mineralogy and Petrology of the Gunflint Iron Formation, Minnesota-Ontario: Correlation of Compositional and Assemblage Variations at Low to Moderate Grade , 1978 .

[11]  A. Råheim,et al.  Temperature and pressure dependence of Fe-Mg partitioning between garnet and phengite, with particular reference to eclogites , 1978 .

[12]  M. Schliestedt.  Preliminary note on deerite from high-pressure metamorphic rocks of Sifnos, Greece , 1978 .

[13]  E. C. Beutner.  Slaty cleavage and related strain in Martinsburg Slate, Delaware Water Gap, New Jersey , 1978 .

[14]  E. J. Krogh.  Origin and metamorphism of iron formations and associated rocks, Lofoten-Vesterålen, N. Norway. I. The Vestpolltind Fe-Mn deposit , 1977 .

[15]  W. Schreyer,et al.  Synthesis and stability of deerite, Fe122+Fe63+[Si12O40](OH)10, and Fe3+⇋Al3+ substitutions at 15–28 kb , 1977 .

[16]  R. Powell,et al.  Calcite-dolomite geothermometry for iron-bearing carbonates , 1977 .

[17]  J. Kienast,et al.  Repartition de quelques mineraux du metamorphisme alpin en Corse , 1976 .

[18]  E. Brown.  Comparison of the Mineralogy and Phase Relations of Blueschists from the North Cascades, Washington, and Greenschists from Otago, New Zealand , 1974 .

[19]  B. French.  Mineral Assemblages in Diagenetic and Low-Grade Metamorphic Iron-Formation , 1973 .

[20]  P. Black.  Mineralogy of New Caledonian metamorphic rocks , 1973 .

[21]  J. Bocquet,et al.  Sur une deerite de l'ensemble des calcschistes piémontais à Troncea (Italie) , 1973 .

[22]  P. Black.  Mineralogy of New Caledonian metamorphic rocks , 1973 .

[23]  S. O. Agrell.  De la deerite dans les Alpes franco˗italiennes , 1970 .

[24]  W. Ernst,et al.  Petrologic comparison of the franciscan and sanbagawa metamorphic terranes , 1967 .

[25]  R. Coleman.  Glaucophane schists from california and new caledonia , 1967 .

[26]  W. Fyfe,et al.  Omphacite in Californian metamorphic rocks , 1967 .

[27]  C. Klein.  Mineralogy and Petrology of the Metamorphosed Wabush Iron Formation, Southwestern Labrador , 1966 .

[28]  W. Ernst.  Mineral Parageneses in Franciscan Metamorphic Rocks, Panoche Pass, California , 1965 .

[29]  R. Coleman,et al.  Glaucophane-bearing Metamorphic Rock Types of the Cazadero Area, California , 1963 .

[30]  H. Eugster,et al.  Stability Relations of the Ferruginous Biotite, Annite , 1962 .