Abstract
Volcan Popocatepetl has been the site of voluminous degassing accompanied by minor eruptive activity from late 1994 until the time of writing (August 2002). This contribution presents petrological investigations of magma erupted in 1997 and 1998, including major-element and volatile (S, Cl, F, and H2O) data from glass inclusions and matrix glasses. Magma erupted from Popocatepetl is a mixture of dacite (65 wt % SiO2, two-pyroxenes + plagioclase + Fe-Ti oxides + apatite, similar to 3 wt % H2O, P = 1.5 kbar, f(O2) = Delta NNO + 0.5 log units) and basaltic andesite (53 wt % SiO2, olivine + two-pyroxenes, similar to 3 wt % H2O, P = 1-4 kbar). Magma mixed at 4-6 km depth in proportions between 45:55 and 85:15 wt % silicic:mafic magma. The pre-eruptive volatile content of the basaltic andesite is 1980 ppm S, 1060 ppm Cl, 950 ppm F, and 3.3 wt % H2O. The pre-eruptive volatile content of the dacite is 130 +/- 50 ppm S, 880 +/- 70 ppm Cl, 570 +/- 100 ppm F, and 2.9 +/- 0.2 wt % H2O. Degassing from 0.031 km(3) of erupted magma accounts for only 0.7 wt % of the observed SO2 emission. Circulation of magma in the volcanic conduit in the presence of a modest bubble phase is a possible mechanism to explain the high rates of degassing and limited magma production at Popocatepetl.