AUTHIGENIC MONAZITE AND XENOTIME FROM PELITIC METACHERTS IN PUMPELLYITE ACTINOLITE-FACIES CONDITIONS, SESTRI VOLTAGGIO ZONE, CENTRAL LIGURIA, ITALY

Abstract

Monazite-(Ce) and xenotime-(Y) were found in the metacherts (pumpellyite–actinolite-facies conditions: 3 ≤ P ≤ 4 kbars and 300 ≤ T ≤ 350°C) of the Monte Figogna Unit, Sestri–Voltaggio Zone, Liguria, in Italy, as scattered submillimetric grains in pelitic beds and as euhedral crystals in both millimeter-thick quartz veins and open fissures. Their composition is comparable to those of known occurrences in metapelites from greenschist-facies conditions. The textural evidence points to a synmetamorphic authigenic origin of these phases related to local mobilization and reconcentration of the REE during the metamorphic recrystallization of the clay fraction.