부산대학교 도서관

Since late 1994, open-vent eruptive activity and degassing at Popocatepetl volcano, Mexico, have released large masses of C[O.sub.2] and S[O.sub.2]. Tephra and lava produced by these eruptions show evidence for mixing of mafic and silicic magmas shortly before eruption. We present the first measurements of dissolved C[O.sub.2] in the mafic magma end member based on analyses of olivine-hosted melt inclusions that were trapped at pressures as high as ~400 MPa (~15 km depth) beneath the volcano. We combine our data with thermodynamic models to show that degassing of mafic magma at ~150-350 MPa pressure can explain the C[O.sub.2]/S[O.sub.2] mass ratios (1-8) of volcanic gases released from the volcano during 1995-1997. Our results demonstrate that mafic magma recharge was responsible for the high measured fluxes of C[O.sub.2] and S[O.sub.2] from 1995 to 1997. The total S[O.sub.2] emission of 9 Mt during this period requires intrusion and degassing of a minimum of 0.8 [km.sup.3] of mafic magma. Only ~0.3% of this new mafic magma has been erupted in the form of mixed (hybrid) lava and tephra. Our results suggest that the ongoing eruption of Popocatepetl is essentially an intrusive event. More generally, we suggest that intrusion and deep degassing may explain the high gas fluxes at some other open-vent volcanoes rather than convection of magma in the uppermost parts of subvolcanic conduits.