Magmatic paragonite in trondhjemites from the Sierra del Convento melange, Cuba

In the Sierra del Convento melange peraluminous trondhjemitic-tonalitic rocks, formed by partial melting of subducted oceanic crust at ca. 15 kbar, 700 degrees C, contain millimeter-sized crystals of paragonite that appear to be of magmatic origin. These crystals are replaced by plagioclase and quartz along the rims. Chemically relict paragonite cores have high K contents (up to 0.35 apfu), whereas K is low at the rims (down to ca. 0.10 apfu). Calcium is relatively high in the cores and rims (0.06-0.11 apfu). The relict core compositions contrast significantly with small matrix paragonite crystals, which formed during subsequent subsolidus retrogression of relictic magmatic plagioclase at high pressure/low temperature (ca. 400 degrees C, 8 kbar). Textural relations, mineral composition, and calculations of phase relationships in the system NCASH strongly suggest that primary paragonite formed by crystallization of a silicate melt. This appears to be the first reported occurrence of magmatic paragonite.