Resumen de A MnNCFMASH petrogenetic model for low-Ca amphibolites
Joan Reche Estrada, F.J. Martínez Gil
A new Petrogenetic model including various P-7 pseudosections has been developed using the software THERMOCALC and the newest Powell & Holland thermodynamic database, that accounts for variable P-T-X phase relations low-Ca amphibolites in the system MnO - Na20 - CaO - FeO - MgO - AI203 - Si0 2 - H2 0 (MnNCFMASH) including the phases: hornblende - cummingtonite - garnet - cordierite - orthoamphibole (anthophyllite and gedrite) - aluminium silicates - staurolite - chlorite - clinozoisite - plagioclase - quartz and H20. The T range is 300 - 700 °C and the P range goes up to 14 Kbar. An analysis of the literature for low-Ca amphibolites shows that the main chemical variability vector for these rocks, is defined by FeO+MgO+MnO (FMM) inversely proportional to Ca0+Na20 (CN). Values o f other parameters like AI/Tot=Al203/Al203+CaO+MgO+FeO+Na20+MnO, F/FM=FeO/FeO+MgO and C/CN=Ca0/Ca0+Na20 also influence the phase relations, but this influence will not be described here. In this paper we exclusively treat the effects of the main compositional trend of bulk composition (FMM-CN) in the phase relations of low-Ca amphibolites. The new petrogenetic MnNCFMASH model, presented here can be a tool of great usefulness in constraining the metamorphic evolution of medium and high grade areas containing low-Ca amphibolites.
