Zoning of chloritoid from kyanite facies rocks, Alpi Apuane, Italy

Chloritoid with significant Mg-Fe zoning occurs as lath-shaped porphyroblasts and as clusters of subradiating crystals in the Triassic Verrucano metapsammite (quartz + muscovite + chlorite + chloritoid ± kyanite) of the Massa Unit, Alpi Apuane. Two main types of chloritoid zoning profiles were found. The first type is characterised by gradual increase in Mg from core to rim of the porphyroblasts. In the second type the Mg content is constant from the core to the inner rim, but sharply decreases in the outer rim. Both types of zoning have been interpreted as the result of prograde growth during the Alpine metamorphism. The temperature, estimated using the chlorite-chloritoid thermometer, ranges from 467 to 560°C.