Rancho Seco monogenetic volcano (Michoacán, Mexico): Petrogenesis and lava flow emplacement based on LiDAR images

Highlights

• Rancho Seco volcano lava flows derived from a single batch of magma that was gradually extruded.

• Lavas viscosities of Rancho Seco volcano ranged between 10⁵ and 10⁹ Pa·s.

• We suggest an eruption duration of 2 to 6 years with effusion rates of 4 to 15 m³/s.

• Our results are relevant for future eruptive scenarios and risk assessment.

Abstract

Given the high eruption recurrence in the Michoacán-Guanajuato volcanic field (MGVF) in central Mexico, the birth of a new monogenetic volcano can be expected in the future. It is important, therefore, to reconstruct the past eruptions of its many different volcanoes, including estimates of lava flow emplacement times and their rheological properties. These studies define the range of possible future eruptive scenarios and are necessary to evaluate potential risk. The Rancho Seco monogenetic volcano, located in the central part of the MGVF (19°37′03”N, 101°28′21”W), was radiocarbon-dated at ~27,845 years BP. Its eruption initiated with a violent-Strombolian phase that produced a scoria cone and was followed by the effusion of at least seven associated andesitic lava flows, reflecting drastic changes in the eruptive dynamics. Effusive activity probably involved decreases in the magma ascent and discharge rates linked to efficient degassing in an open system. Lava chemical composition suggest an origin of partial melting of a subduction-modified hydrated heterogenous mantle wedge and textural and mineralogical analysis indicates significant crystal fractionation and minor assimilation of granodioritic basement rocks. High-resolution LiDAR imagery was used to estimate lava flow viscosities and emplacement times by following a morphology-based methodology. Results indicate that lava flow viscosities ranged from 10⁵ to 10⁹ Pa·s and emplacement durations between 32 and 465 days for the flow units considered (F5 and F6). The entire eruption may have lasted from 2 to 6 years with a mean effusion rate of 4 to 15 m³/s. Our results are also pertinent to archaeologists studying the architectural remains of Angamuco, a large urban pre-Hispanic site built on Rancho Seco's lava flows.

Introduction

The Trans-Mexican Volcanic Belt (TMVB) is a continental volcanic arc containing ~8000 volcanic structures (Demant, 1978; Gómez-Tuena et al., 2005), and is tectonically related to the subduction of the oceanic Cocos and Rivera plates underneath the North American continental plate along the Mesoamerican trench (Nixon, 1982; Pardo and Suárez, 1995; Gómez-Tuena et al., 2005). It is important to highlight that since pre-Hispanic times this geologic province has grown in population and economic activity (Siebe and Macías, 2006; Ferrari et al., 2012). In the states of Guanajuato and Michoacán, the TMVB overlaps the older Oligocene to middle Miocene Sierra Madre Occidental (SMO) volcanic arc and a complex prevolcanic basement (Pasquaré et al., 1991).

The Michoacán-Guanajuato Volcanic Field (MGVF) is situated in the central part of the TMVB (Fig. 1) and comprises more than 1400 Quaternary monogenetic eruptive centres (including Rancho Seco volcano) distributed over an area of 40,000 km² (Hasenaka and Carmichael, 1985). It has one of the greatest concentrations of monogenetic volcanoes within a subduction zone in the world (Hasenaka and Carmichael, 1985; Hasenaka, 1994). It is bounded to the north by the valley of the Lerma river and to the south by the depression of the Balsas river (Fig. 1); to the east it is contained by the Tzitzio anticline (Blatter and Hammersley, 2010), and to the west by the so-called “Mazamitla Volcanic Gap” (Kshirsagar et al., 2015). The MGVF contains mainly scoria cones and associated lavas, but also isolated thick lava flows, domes, maars, and tuff rings. In addition, there are approximately 400 volcanic edifices described as small or medium-sized shield volcanoes (Hasenaka and Carmichael, 1985; Hasenaka, 1994; Chevrel et al., 2016a) and only two stratovolcanoes (Tancítaro and Patamban), both considered extinct (Ownby et al., 2007; Siebe et al., 2014). Two historical eruptions have been witnessed in this field, Jorullo (1759–1774) and Paricutin (1943–1952), hinting that the future birth of a new volcano is highly likely (e.g. Guilbaud et al., 2011; Luhr and Simkin, 1993). Recent studies of areas within the MGVF (e.g. Guilbaud et al., 2011, Guilbaud et al., 2012, Guilbaud et al., 2019; Siebe et al., 2014; Kshirsagar et al., 2015, Kshirsagar et al., 2016; Chevrel et al., 2016a, Chevrel et al., 2016b; Larrea et al., 2017, Larrea et al., 2019; Reyes-Guzmán et al., 2018; Osorio-Ocampo et al., 2018; Pérez-Orozco et al., 2018; Ramírez-Uribe et al., 2019) have shown that eruptions have not only been diverse in style, but also frequent during Late Pleistocene and Holocene time.

The Rancho Seco monogenetic volcano is an andesitic scoria cone associated with lava flows situated at the eastern margin of the Pátzcuaro lake basin (Fig. 1) in the state of Michoacán and dated at 27,845 +445/−425 years BP (before present) (Ramírez-Uribe et al., 2019). The availability of LiDAR imagery provides the means to precisely map the lava flows, determine their volumes, highlight their main morphological features in great detail and measure their geometric parameters. We, then, apply morphology-based methods to estimate flow emplacement duration and effusion rates. In addition, chemical and petrological analyses of distinct lava units were used to constrain the magma source, storage conditions, and lava rheology, and to propose an eruptive model. These parameters are crucial for constraining future eruptive scenarios and evaluating potential volcanic risk.