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 th e Ronda massif, southern Spain. Garnet and clinopyroxene are the main phase s in the aluminous mafic rocks. Garnet is partially to completely kelyphiti zed. Clinopyroxene (CPX I) has high Al2O3 content in the core (up to 16 wt. %) and is partially converted to spherical symplectitic aggregates consisti ng of lower-Al2O3 clinopyroxene (CPX LI) (< 5 wt.%) and plagioclase. Corund um is associated with spinel and plagioclase. Sapphirine occurs in two diff erent mineralogical associations, i.e., as elongated lamellae within CPX I and as very fine-grained crystals in plagioclase-rich domain. The sapphirin e + 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 recorde d in the aluminous mafic rock was garnet + clinopyroxene I kyanite + corund um, 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 wer e 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 compressi on of plagioclase-rich, low-pressure cumulate or residue. (C) 2001 Publishe d by Elsevier Science B.V.