Relations entre dynamismes éruptifs et réalimentations magmatiques d'origine profonde au Popocatépetl

Abstract

The modern volcano Popocatépetl is 30 000 – 50 000 years old. Until 5000 years BP, its volcanic activity led to the construction of a 2000 m high cone, the El Fraile volcano. This edifice was later topped by the Popocatépetl summit. The volcanic activity was characterized by long-term construction by lava flows, alternating with periods of 1000–2000 years of mixed explosive and effusive activity. The El Fraile volcano experienced three periods of this type, marked by back-falling pyroclastic flows with heterogeneous magma products and thick air-fall deposits (ash and scoria). The first one occurred more than 10 000 years BP; the second, between 10 000 and 8000 years BP; the third, from 5000 to 3800 years BP. Each of these periods showed violent explosive episodes alternating with lava flows in cycles of 100 to several hundreds of years in duration. Whenever the explosive activity occurred, it destroyed the upper part of the volcano, opening large craters. After a ~ 2500 year period of lava-flow construction (from ~ 3800 to 1200 years BP), the Popocatépetl summit began a similar activity. The last event, producing pyroclastic flows, occurred just before me Hispanic Conquest, and since that time the activity has been effusive and Plinian.Heterogeneous to subhomogeneous pyroclastic flow products exhibit a complex mineralogy: Fe clinopyroxene, Mg clinopyroxene, Fe orthopyroxene, Mg orthopyroxene, plagioclase in equilibrium or disequilibrium, and scarce olivine. All lava flows show a similar paragenesis, suggesting magma-mixing processes. A model in which a basaltic magma is periodically injected in a differentiated chamber at the beginning of each explosive period (or each cycle?) is proposed to explain the heterogeneous products. However, calculations of mixing models do not agree with the high Mg and Ni values observed in some hybrid lavas. This excess is probably due to the remobilization of cumulative olivine by basic magma supplies in the lower part of the reservoir. On the other hand, lava flows emitted during the long phases of effusive activity correspond to evolution in a closed and zoned chamber, partly affected by convective movements. The convection explains the complex mineralogy of these lavas, which result from differentiation of a previously homogenized magma rather than directly from magma mixing.

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

“…Interstitial glass in dacitic pumice from the June 30, 1997, eruption is rhyolitic (74 wt% SiO 2 ; Table 7) and very similar to groundmass glass that has been measured in tephra clasts from Holocene pyroclastic¯ows (Boudal and Robin 1987). The high K 2 O (=3.4 wt%) content, and the low CaO (%1.4 wt%) and FeO* (%2.4 wt%) abundances demonstrate that the interstitial glass results from extreme fractionation and does not represent a Popo bulk magma.…”

“…The volcanic history of Popo is characterized by alternating periods of cone formation and destruction. The ®rst andesite volcano collapsed in a cataclysmic event approximately 36 ka ago (Robin and Boudal 1987). This event was succeeded by the repetitive formation of dome complexes and summit cones, the youngest of which is the presently active summit Popo.…”

“…Throughout the most recent history of Popo, low-energy ash eruptions produced gas and small-volume ash clouds. These eruptions alternated with high-energy explosive eruptions that have distributed ash-and lapilli-sized tephra fallout and pyroclastic¯ows several tens of kilometers from the source (Robin and Boudal 1987). The last major explosive eruption was associated with widespread deposition of tephra and took place before the Spanish conquest (1521 AD), probably around 1,000 years ago (Martin-Del Pozzo et al 1997).…”

“…Previous investigations of Popo lavas and pyroclastic ows gave clear petrographic and chemical evidence for magma mixing (e.g., Boudal and Robin 1987). The ubiquitous presence of magnesian, Cr-spinel-bearing fosteritic olivine in andesites and dacites suggests that magma homogenization beneath Popo was incomplete and that the traces of the ma®c component magma that is thought to be parental to arc magma suites (e.g., Gill 1981) have not been erased.…”

Geochemistry of summit fumarole vapors and flanking thermal/mineral waters at Popocatepetl Volcano, Mexico

“…(Siebe et al, 1995a(Siebe et al, , 1995b. Explosive and effusive activity continued for 20,000 to 10,000 years with explosive activity occurring in cycles of 1000 to 3000 years, as determined by C-14 dating of pyroclastic deposits on the modern cone (Cantagrel et al, 1984;Boudal and Robin, 1988;Siebe et al, 1996). Major eruptions occurred between 3195 to 2830 BC, 800 to 215 BC, and 675 to 1095 AD (Siebe et al, 1996).…”