THE BEHAVIOR OF CR DURING METAMORPHISM OF CARBONATE ROCKS FROM THE NEVADO-FILABRIDE COMPLEX, BETIC CORDILLERAS, SPAIN

Some metacarbonate rocks from the Nevado-Filabride Complex (Betic Cord illeras, southern Spain) contain unusual quantities of Cr-rich mineral s. These occur in very thin layers concentrated in beds a few meters t hick, interbedded with other lithologies (metapelites and metacarbonat es) devoid of chromium. Cr2O3 contents reported here reach values (in wt.%) of 5.74 in epidote, 5.09 in phengitic muscovite, 1.37 in paragon ite, 2.19 in chlorite, 2.24 in amphibole, 1.15 in garnet, 0.72 in tita nite, and 1.30 in rutile. The distribution of Cr in the samples is ver y irregular, even at the scale of a single crystal. In all silicates, Cr enters octahedral sites replacing Al-VI. In epidote, Cr is mainly l ocated at the M1 site, and in most samples epidote preferentially inco rporates Cr over Al in comparison to other silicates. Rare, small incl usions of chromian spinel with anomalously high Zn contents (up to 15. 14 wt.% ZnO) are found in some of the silicate phases. We consider chr omian spinel to be the source of Cr in these metasediments, which were deposited as beach placers. The conservation of the original, sedimen tary heterogeneity in Cr distribution as well as the zoning pattern of Cr in epidote suggest very limited mobility of this element during me tamorphism. The high concentration of Zn in relict inclusions of chrom ian spinel is interpreted as a passive enrichment.