High-pressure aluminous mafic rocks from the Ronda peridotite massif, southern Spain: significance of sapphirine- and corundum-bearing mineral assemblages

We firstly present detailed microtextural relationships in sapphirine- and corundum-bearing aluminous mafic rocks alternating with peridotites from the Ronda massif, southern Spain. Garnet and clinopyroxene are the main phases in the aluminous mafic rocks. Garnet is partially to completely kelyphitized. Clinopyroxene (CPX I) has high Al2O3 content in the core (up to 16 wt.%) and is partially converted to spherical symplectitic aggregates consisting of lower-Al2O3 clinopyroxene (CPX LI) (< 5 wt.%) and plagioclase. Corundum is associated with spinel and plagioclase. Sapphirine occurs in two different mineralogical associations, i.e., as elongated lamellae within CPX I and as very fine-grained crystals in plagioclase-rich domain. The sapphirine + plagioclase aggregate suggests the former presence of kyanite as one of reactants. Sapphirine is partially converted to symplectitic aggregate of spinel and plagioclase. The earliest metamorphic mineral assemblage recorded in the aluminous mafic rock was garnet + clinopyroxene I kyanite + corundum, i.e., eclogitic mineral assemblages, at P greater than or equal to 1.5 GPa and T greater than or equal to 900 degreesC. Many reaction textures were developed during decompression possibly coupled with cooling. The latest P-T conditions recorded in the aluminous mafic rock were at P = 1 GPa and T = 800-900 degreesC. This decompression had possibly followed the compression of plagioclase-rich, low-pressure cumulate or residue. (C) 2001 Published by Elsevier Science B.V.