Pre-eruptive conditions and reheating of dacitic magma (Malinche Pumice II Plinian eruption) at La Malinche volcano, Central Mexico

https://doi.org/10.1016/j.jvolgeores.2021.107368Get rights and content

Highlights

  • Malinche volcano located in the TMVB, central Mexico.

  • Pumice Malinche II is one of the largest eruptions from Malinche volcano.

  • Plagioclase, amphibole and Fesingle bondTi oxides is the mineral assemblage of the MPII samples.

  • Dacitic magma of the MPII eruption was stored at 2 kb, 873 °C, and NNO + 1.77.

Abstract

The Malinche Pumice II is a fallout deposit produced by a Plinian-type eruption during the Pleistocene-Holocene at La Malinche volcano. La Malinche (4461 masl) is an active stratocone located in central Mexico, in the Trans-Mexican Volcanic Belt province. It is 26 km to the NE of the City of Puebla and 22 km to the SE of the City of Tlaxcala. The Malinche Pumice II was produced by one of the largest explosive eruptions of this volcano, involving a dacitic magma (63.6–65.3 wt% SiO2, anhydrous basis) with a mineral assemblage of plagioclase + amphibole + Fesingle bondTi oxides and ± biotite phenocrysts. Larger plagioclase crystals are up to 1.2 mm in diameter, with resorbed margins and complex zoning (An26 to An43), whereas microcrysts are euhedral with homogeneous composition (An42 to An55). Amphibole is mainly magnesio-ferri-hornblende (Mg# = 0.65–0.82) and lesser amounts of pargasite. Geothermometry performed using Fesingle bondTi oxides yields an average temperature of 873 ± 2 °C and oxygen fugacity of 1.8 units above the NNO buffer. Amphibole geothermobarometry yields a lower temperature (809 ± 19 °C) and a pressure of 230 ± 100 MPa, assuming 4.4 wt% of H2O. Considering an average density of 2650 kg/m3 for the upper crust in central Mexico, the storage region of the Malinche Pumice II dacitic magma was located at 8 ± 2 km depth. Biotite could be antecrystic or xenocrystic in origin, based on its reacted texture, large sizes (0.85–2 mm), and reaction rims. Similarly, pargasite that provides higher temperature estimates (900 ± 18 °C) and low anorthite plagioclase (An26) could also be antecrysts or xenocrysts. The Plinian eruption was likely triggered by an input of a hotter and deeper magma batch that overpressurized the dacitic magma system that eventually provoked vesiculation and fragmentation. The eruption shifted to a hydromagmatic style because of external water's entrainment that decreased the vesicularity of pumice. Our results are in good agreement with recent seismicity recorded at depths of ~7 km probably associated with activity of the Malinche's magmatic system.

Introduction

Plinian-type eruptions likely occur each decade in the world and are of large magnitude events (>1 km3 of magma), signifying severe volcanic hazards (Newhall and Self, 1982). These type of eruptions are more common in evolved magmas, specially in dacitic magmas, such like those produced by the Malinche volcano in central Mexico. Dacitic magmas could be generated by different processes, i.e.: magma mixing, fractional crystallization, or contamination (Eichelberger, 1978; Gill, 1981). The storage conditions of such evolved melts are key to define the thermal structure of volcanoes' plumbing systems. In active volcanoes, it is essential to know the pressure, temperature, volatile contents, and oxygen fugacity of the magma stored at depth (Gardner et al., 1995; Cottrell et al., 1999). These parameters influence the physical properties of the magma and the eruptive style (Cassidy et al., 2018), as well as the crystallization sequence in magmas (e.g.: Knafelc et al., 2020). Several large-magnitude explosive eruptions are associated with dacitic magmas, such as the Pinatubo eruption in 1991, Phillipines (Pallister et al., 2006), and the Upper Toluca Pumice at Nevado de Toluca volcano, Mexico (Arce et al., 2006). Hence, it is crucial to understand in which conditions these felsic magmas could produce such eruptions, especially in active volcanoes like La Malinche, located in the highly populated region of Mexico (Fig. 1A).

This paper investigates the pre-eruptive temperature, oxygen fugacity, and pressure conditions of a dacitic magma associated with the Plinian-type eruption that emplaced the Malinche Pumice II fallout (Castro-Govea and Siebe, 2007) sourced in La Malinche volcano. This volcano (4461 m above sea level; masl) is an active stratocone (currently in a quiescent state), located in the central part of the Trans-Mexican Volcanic Belt (Fig. 1A). Around the volcano lie the cities of Puebla (~26 km to the SW), Tlaxcala (~22 km to the NW), and only 115 km from the Mexico City located to the W-NW. This eruption occurred during the late Pleistocene-Holocene time (Heine, 1971; Castro-Govea and Siebe, 2007; Macías and Arce, 2019). We estimate the conditions at which the erupted mineral assemblage of the natural dacitic rocks was crystallizing and where the dacitic magma was stored before the eruption.

Section snippets

Geologic background

Many Mexican volcanoes are clustered in N-S ranges (Popocatépetl, Iztaccíhuatl, Telapón, and Tláloc stratovolcanoes; Volcán de Fuego, Volcán de Colima, and Cántaro stratovolcanoes) (Macías, 2007), on the contrary, Malinche volcano is an isolated structure in the valley of Puebla (Fig. 1B). La Malinche has a symmetrical shape with a 28 km basal diameter (including fan deposits; Fig. 1B). Its summit is constituted of unforested and scarped lava domes. In a wider view, there is a large,

Samples and analytical methods

Samples of the Malinche Pumice II deposit were taken from two different outcrops (see Fig. 1 for sample location). Samples from sites Ma-1801 (subunits A-E) and Ma-1802 (E-G), were used for petrographic descriptions, microprobe analyses, whole-rock chemistry, componentry, and vesicularity analyses. Additionally, we made polished sections of Fesingle bondTi oxides and amphibole concentrates from yellowish pumice fragments of the lower unit.

The Malinche Pumice II deposit

The Malinche Pumice II (MPII) is a fallout deposit that mainly crops out to the northern slopes of the Malinche volcano (Castro-Govea and Siebe, 2007) underlaid by a brown paleosoil (Fig. 3). The deposit consists of three main units: the basal part is made of centimeters-thick, lapilli to coarse ash fall layers (A-D subunits; Fig. 3), at a distance of 10 km from the vent it commonly shows normal grading; the middle part is constituted by two massive subunits (E-F, Fig. 3), with abundant gray

Biotite source

Biotite represents around 1 vol% of the crystals found in the MPII samples. It is commonly large in size (up to 2 mm), with resorbed margins and sometimes with reaction rims made of amphibole and Fesingle bondTi oxides (Fig. 6). By comparing the storage conditions of the MPII magma with other dacitic magmas (see next section), only the Lower Toluca Pumice and the magma from Pinatubo (1991 eruption) have some similar characteristics, and both contain biotite. Although the Lower Toluca is more reduced, and

Conclusions

This research is the first attempt to decipher the storage conditions of La Malinche volcano, one of the largest and active volcanoes of the Trans-Mexican Volcanic Belt province. Our results confirm that Malinche volcano has a homogeneous dacitic composition for the majority of its products. The Plinian-type Malinche Pumice II eruption varies from 63.6–65.3 wt% SiO2, constituted by two main units, the basal unit rich in yellowish pumice fragments and minor red lithic contents, whereas the upper

Credit author statement

Victor Daniel Espinosa: fieldwork, sample preparation (thin sections, geochemical analysis, microprobe analysis), conceptualization, investigation.

José Luis Arce: conceptualization, fieldwork, formal analysis, investigation, writing, field and lab funding, supervision.

Renato Castro: Writing, discussion of the results.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research was funded by PAPIIT grant IN101620 to J.L. Arce. We thank E. Rangel and A. Vasquez for fieldwork support, and M.C. Macías-Romo for the mineral separation. P. Girón performed XRF analysis at Laboratorio Nacional de Geoquímica y Mineralogía, UNAM and O. Pérez-Arvizu conducted ICP-MS analysis at Centro de Geociencias, UNAM. Microprobe analysis was performed at Laboratorio Universitario de Petrología, UNAM, by C. Linares-López. Thanks to J.L. Macías and L. Caricchi for their

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