Volcán Popocatépetl, Mexico. Petrology, magma mixing, and immediate sources of volatiles for the 1994- Present eruption

Volcán Popocatépetl 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 Popocatépetl is a mixture of dacite (65 wt % SiO₂, two-pyroxenes + plagioclase + Fe–Ti oxides + apatite, ∼3 wt % H₂O, P = 1·5 kbar, f_O2 = ΔNNO + 0·5 log units) and basaltic andesite (53 wt % SiO₂, olivine + two-pyroxenes, ∼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 km³ 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 Popocatépetl.