The significance of phenocryst diversity in tephra from recent eruptions at Popocatepetl volcano (central Mexico)

Abstract

Tephra lapilli from six explosive eruptions between April 1996 and February 1998 at Popocatepetl volcano (=Popo) in central Mexico have been studied to investigate the causes of magma diversi®cation in thickcrusted volcanic arcs. The tephra particles are sparsely porphyritic (%5 vol%) magnesian andesites (SiO 2 58± 65 wt%; MgO 2.6±5.9 wt%) that contain phenocrysts of NiO-rich (up to 0.67 wt% NiO) magnesian olivine (Fo 89±91 cores) with inclusions of Cr-spinel (cr# 59±70), orthopyroxene (mg# 63±76), clinopyroxene (mg# 68±86), intermediate to sodic plagioclase (An 33±66 ), and traces of amphibole. Major and trace element systematics indicate magma mixing. The liquid mg# melt ratios inferred from the ferromagnesian phenocrysts suggest the existence of a ma®c (mg# melt % 72±76) and an evolved component magma (mg# melt % 35±40). These component magmas form a hybrid magnesian andesite with an intermediate range of mg# melt 50±72. The ma®c end member (mg# melt % 72±75) is saturated with olivine and spinel and crystallizes at temperatures %1170±1085°C with oxygen fugacities close to the fayalite±magnetite±quartz buer and elevated water contents of several wt% H 2 O. A likely location of crystallization is at lower crustal levels, possibly at the Moho. Olivine is followed by high-mg# clinopyroxene which could start to crystallize during magma ascent. At depths of %4 to 13 km, the ma®c magma mixes with an evolved composition containing low-mg# clino-and orthopyroxene and plagioclase at a temperature of %950°C. The repetitive ascent of batches of ma®c magmas spaced days to weeks apart implies multiple episodes of crystallization and magma mixing.

Mafic magma recharge supplies high CO2 and SO2 gas fluxes from Popocatépetl volcano, Mexico

“…1). Olivine host crystals for the melt inclusions are Fo 87-90 and are more Mg rich than the olivine hosts for the inclusions analyzed by Witter et al (2005), but similar to those analyzed by Straub and Martin-Del Pozzo (2005). The compositional and textural relations imply that the melt inclusions represent quenched samples of the mafi c melts that resupply and thermally sustain Popocatépetl's magmatic system (Witter et al, 2005).…”

Continental Rift Setting for the Central Part of the Mexican Volcanic Belt: A Statistical Approach

“…For the sake of quantitative interpretation, this area was divided into two regions by arbitrarily setting a geographical limit for nearer to and farther away from the MAT. The prominent volcanic areas and structures corresponding to nearer the MAT (as arranged from west to east and from nearer to and farther from the MAT) were: Zitácuaro-Valle de Bravo [37][38][39][40]; Volcán Nevado de Toluca [41][42][43]; Tenango Volcanic Field [43,44]; Sierra de Chichinautzin and nearby areas [19,26,29,43,[45][46][47][48][49][50][51][52][53][54][55][56]; Valle de México [44,45,57]; Sierra Nevada and Río Frío [45,52,57]; Volcán Popocatépetl [45,[57][58][59][60][61][62][63]; and Volcán Iztaccíhuatl [45,49,52]. Similarly, the samples from areas farther from the MAT were taken from: Caldera de Amealco [64,65]; Volcán Zamorano [66]; Qu...…”

Timing magma ascent at Popocatepetl Volcano, Mexico, 2000–2001

“…Based on olivine and pyroxene geothermometers, the temperature of the ma¢c end-member was calculated to be between 1170 and 1080 ‡C, while the evolved end-member was about 950 ‡C (Straub and Martin-Del Pozzo, 2001). The ma¢c melt ascends from lower crustal levels to mix with the evolved melt at depths between 4 and 13 km.…”