The Contact Aureole nn Tinos (Cyclades, Greece). 1. Field Relationships, Petrography and P-T Conditions

On Tinos (Cyclades, Greece), the intrusion of Miocene granitoids caused a contact metamorphic overprint of blueschist- and greenschist-facies country rocks. The width of the contact aureole ranges from about 600-2200 m. In metabasic rocks an oligoclase-/andesine-in isograd was recognized which separates a regional metamorphic albite-actinolite zone from a contact metamorphic plagioclase-hornblende zone. In pelitic rocks, a contact metamorphic biotite zone was mapped. Application of conventional mineral geothermobarometry yielded in most cases unreasonable temperature and pressure estimates which either indicate incomplete re-equilibration at the thermal peak or which result from considerable resetting during retrograde cooling. Temperatures in the aureole are estimated at about 475-degrees-C in the peripheral zones to about 660-degrees-C close to the granite contact. Pressure during the thermal overprint is estimated at about 3 kbar.