Mexican Volcanic Belt Research Articles

Provenance of sediments and environmental risk assessment of heavy metals in the “Mis Amores” beach, Veracruz, Gulf of Mexico, Mexico

In this study, grain-size, mineralogy, and geochemistry of Mis Amores (MA) beach sediments, Tuxpan, Veracruz State, Gulf of Mexico are analyzed. The textural parameters reveal that the sediments are fine-grained and vary from well-sorted to very well-sorted nature. The SEM-EDS analysis reveal that the sediments are abundant in minerals such as quartz, alkali feldspars, zircon, ilmenite, and pyroxene. Geochemically, the sediments are classified as sub-arkose type. The Chondrite normalized rare earth elements (REE) pattern suggest that the source area is dominated by felsic and intermediate igneous rocks (Eu/Eu* = 0.90 - 1.19, number of samples n = 16). The provenance discrimination diagrams indicated that the MA sediments were derived by the weathering of felsic igneous rocks, probably from the Trans Mexican Volcanic Belt. The results of this study reveal that the Tuxpan River played an important role in delivering sediments to the MA beach area. The environmental indices suggest that the sediments are moderately contaminated by Zn and moderate to extremely contaminated by Cu and As. The Cu (> 84%) and Zn (> 82%) concentrations are predominantly associated with the exchangeable fraction, which are readily bioavailable. Cu, As, and Zn in the MA sediments were derived from the agricultural activities and waste water discharges from the sanitary network of the Tuxpan town and port.

Species delimitation using multiple sources of evidence from the Pinus strobiformis-Pinus ayacahuite Species Complex

Background: The Trans-Mexican Volcanic Belt (TMVB) in central Mexico is characterized by peaks of high altitude and geologic instability. In this zone, Pinus strobiformis and Pinus ayacahuite form a contact zone with Pinus veitchii. The taxonomical circumscription of white pines in Central Mexico has been unstable, especially regarding the status of P. veitchii.
 Questions: What are the species boundaries of the montane Mexican white pines species complex? Is Pinus veitchii a hybrid or an independently evolving lineage?
 Studied species: Pinus strobiformis, Pinus veitchii and Pinus ayacahuite species complex.
 Study site and dates: United States of America and Mexico from 2003 to 2022.
 Methods: We performed multivariate analyses on 10 morphological characters and characterized the climatic niche divergence and the genetic differentiation using SNPs.
 Results: Our results showed that P. veitchii is morphologically similar to P. strobiformis, but does not have intermediate morphological values with P. ayacahuite. The ecological niche differentiation was not significant. Genetic analyses showed P. veitchii as an independent lineage with evidence of admixture with P. ayacahuite, suggesting a gene flow but not a hybrid origin.
 Conclusions: Two of the three lines of evidence support three independent lineages. Environmental information showed niche conservatism, morphology and genetic structure showed differentiation of all three taxa, with a greater morphological similarity between P. strobiformis and P. veitchii, and genetic analyses recovered evidence of introgression, suggesting a complex demographic history in the Trans Mexican Volcanic Belt.

The geodynamic origin of Los Humeros volcanic field in Mexico: insights from numerical simulations

Compared to normal arc-related volcanic eruptions, the formation of a volcanic caldera is a relatively atypical event. During caldera formation a series of large volumes of magma are erupted, reducing the structural support for the rock above the magma chamber and creating a large depression at the surface called caldera. Los Humeros volcanic field (LHVF) represents one of the largest volcanic calderas in Mexico. It is located some 400 km from the trench at the eastern edge of the Trans Mexican Volcanic Belt where the depth to the Cocos slab is more than 300 km. In this study we employ high-resolution two-dimensional thermomechanical numerical simulations of magma intrusions and a horizontal tectonic strain rate to better understand the influence of crustal deformation for the formation of Los Humeros caldera. A minimum number of three thermal anomaly pulses of hydrated mantle material (with diameter of 15 km or more) and a regional strain rate of 7.927 × 10–16 s−1 are required for magma to reach the surface. Modeling results show that regional extension coupled with deep thermal anomalies (with a temperature excess of ΔT ≥ 100 °C) that come in a specific chain-type sequence produce surface deformation patterns similar to LHVF. We propose an asthenospheric sub-slab deep source (> 300 km depth) for the thermal anomalies where previous studies showed the existence of a gap or tear in the Cocos slab.

Geomicrobiology of the Rincon de Parangueo maar crater: Exploring the link between an evolving extreme environment and its potential metabolic diversity

Abstract Rincon de Parangueo (RP) is a Quaternary maar crater located in the Michoacan‐Guanajuato Volcanic Field in central Mexico. Like other volcanic craters in the region, the central part was occupied by an endorheic lacustrine system. As a consequence of extensive groundwater extraction, the perennial lake started a gradual desiccation process and now the remnant ponds host a highly saline–alkaline ecosystem. The stratigraphic record indicates an exceptional and long‐term sedimentation of carbonate microbialites. Previous studies based on the 16S rRNA gene have shown that microbial communities have a widespread presence in the crater at the microbialites, the remaining saline ponds, superficial soils and below the surface. To understand the possible role of the microbial communities that generate these biogeological structures, novel analytical methods to resolve the amplicon datasets and their microbial metabolic potential were used. We describe in detail the relationship between the microbial communities, the evolution of physicochemical parameters, and carbonate morphology, in four micro‐environments. A 16S rRNA gene sequencing dataset from previous publications was re‐analysed using an ASV‐based bioinformatic pipeline to identify new insights into the microbial assemblage. Finally, a taxon‐based metabolic profile was used to predict the potential metabolic contribution of the prokaryotic community. Results indicated a refinement in terms of community composition using the ASV‐based bioinformatic methods. Functional profiling through 16S rRNA gene‐based analysis suggested metabolisms associated with carbonate precipitation, indicating a broad potential for microbially mediated carbonate precipitation (e.g., carbon fixation and photosynthesis). The possibility of biogenic methane gas production by methanogenic microorganisms was recognised, supporting the estimated flow of methane on the surface soils. The lacustrine evolution over the last years and the extreme physicochemical characteristics of RP have an impact on the microbial community structure. Prokaryotic community and metabolic potential results from RP coincide with the diversity and abundance of microbial communities and functional metabolisms reported from other microbialite‐forming lakes along the Trans Mexican Volcanic Belt. The identification of important possible phylotypes involved in carbonate precipitation might be an important factor in considering RP microbialites as active calcifying entities. These findings provide novel insights into the potential key role of metabolic pathways driving the process of carbonate precipitation inside RP and evidence of its importance as a microbial biodiversity hotspot in Mexico.

Climatic variability and plant functional traits in tropical montane cloud forest refugia along the Trans Mexican Volcanic Belt

Functional traits represent the adaptive responses of plant species to climatic changes. They are an integrative marker of the general environmental conditions at a location. Testing their patterns may help to understand how the functional traits would track these environmental changes of tropical montane cloud forests (TMCFs). These forests are characterized by the constant presence of clouds, and these are among the most threatened ecosystems by climate change worldwide. One of the main TMCF regions in Mexico is the Trans-Mexican Volcanic Belt (TMVB). This region has provided refugia during past climate-change events. We identify three current regions of distribution of TMCF in TMVB, Pacific, Center and Gulf. We used 60 years of climatic information, functional traits and plants databases. We proposed the following aims: to determine whether changes in climatic variation have occurred in the TMVB and how these changes can be related to functional trait variations for dominant tree species across the three TMCF regions, and to know the potential changes as a refuge of the TMCF of the TMVB. We found different rainfall and maximum temperature patterns among and within regions. We identified that the Pacific region forests were characterized by the lowest specific leaf area (SLA), wider leaf thickness and high leaf density, which indicates resources-conservative leaf economics and tolerance to low humidity. Center and Gulf forests were distinguished by the highest SLA, less leaf thickness, and higher leaf density values, which suggests that the leaves of dominant tree species tend to be resources-acquisitive rather than conservative-resources. Finally functional traits were associated with prevailing climatic conditions and suggested that SLA, leaf thickness and leaf density are the main functional traits that could be used to relate them to regional climate. Also, Central and Gulf regions could serve as a refuge for those species of trees demanding humidity.

Structural Traits of Cuitzeo Lake, Central Mexico, and Areas of Geothermal Potential

Cuitzeo Lake, in the central part of the Trans Mexican Volcanic Belt, is in an extensional region associated with the Cuitzeo graben, where magmatic ascent appears to provide the heat sources for the surface, geothermal manifestations. A profuse distribution of andesitic rocks is observed throughout the study area of 50×50 km2. Gravity and magnetic field 3D inversions are calculated to obtain density and magnetic susceptibility distributions to 7000 m depth, from which we analyze N-S and E-W cross-sections and obtain density and magnetic susceptibility geosurfaces that help characterize anomaly areas of interest. We use satellite-derived gravity and magnetic data in our evaluation, owing to their high-resolution characteristics and uniform coverage of the study area. Analysis initiates with the San Agustín del Maíz region (SAM), exhibiting surface geothermal manifestations, to characterize its density and susceptibility characteristics, then the analysis is extended to the whole study area. Several outcropping, low magnetic susceptibility regions, like the one associated with SAM, are suggested as potential geothermal targets. Density geosurfaces point to two volumes where magmatic material may intrude, coinciding with active geologic faults. The analysis presented here can be extended to neighboring regions in the Cuitzeo Lake area and may constitute a fast, unexpensive exploration methodology in similar geothermal districts.

Surface textures of detrital pyroxenes in coastal dune sands (western Gulf of Mexico, Mexico): Implications for their preservation and geoenvironmental processes

AbstractThis work investigates how the surface textures and morphology of pyroxene grains evolve during their source‐to‐sink history. This study applies to detrital clinopyroxenes concentrated in coastal dune sands of the Gulf of Mexico which were sourced in the Trans Mexican Volcanic Belt then transported and deposited in environments subject to limited chemical weathering. The composition and morphology of the pyroxenes was characterised using single‐grain geochemical analysis and surface texture imagery with a novel approach based on the compactness property to assess the shape of minerals. This reveals heterogenous diopside‐augite populations, displaying mineral morphologies dominantly controlled by impact breakage along cleavages, little physical abrasion along their edges and with limited evidence for chemical weathering. Mechanical surface textures dominate over mechanical/chemical and chemical surface textures. These mechanical surface textures are preserved primarily as flat cleavage surfaces and rounded edges inherited from fluvial‐intertidal and aeolian transport, respectively. Mechanically/chemically induced surface textures are preserved as elongated depressions. Chemical surface textures are sparse and mostly represented by mammillated textures that suggest local dissolution under subaqueous conditions. The scarcity of chemical surface textures is attributed to frequent fragmentation of the clinopyroxenes along cleavages and limited chemical weathering during transport of the observed populations. Clinopyroxene grains in the coastal dune sands primarily retain surface characteristics from fluvial transport. Although the breakage of minerals along cleavages can obscure their original morphology under a weathering‐limited erosion regime, this study shows how surface textures and morphology of pyroxene grains is used to determine episodes of transport and deposition close to volcanic environments. The use of the compactness property as a shape descriptor measurement of particles provides an alternative approach to observe how clinopyroxene remains unaltered despite the high energy conditions of the coastal area.

Reprint of: The ecology of the zooplankton in Mexican inland waters: What we know so far

The varied physiography and climate of the Mexican territory have produced a large mosaic of inland aquatic ecosystems. However, zooplankton ecology has been studied mainly from the water bodies of Central (Trans Mexican Volcanic Belt), eastern (the Yucatán Peninsula), and southern Mexico. In contrast, the zooplankton from the Mesa Central water bodies has been insufficiently investigated. After a long history of zooplankton taxonomic studies, the first contributions to the zooplankton ecology dated to the 1990 s, rapidly increasing afterward. Most ecological information arises from field investigations and experiments under laboratory conditions, lacking mesocosms and whole-lake experiments. In the same way, the studies have been carried out in lentic, natural, and artificial water bodies, primarily eutrophic. Differently, the zooplankton ecology of lotic ecosystems is largely unknown. Here we summarized the progress made in the study of the zooplankton ecology of Mexican inland waters, revealing the most important research topics developed so far.

The ecology of the zooplankton in Mexican inland waters: What we know so far

The varied physiography and climate of the Mexican territory have produced a large mosaic of inland aquatic ecosystems. However, zooplankton ecology has been studied mainly from the water bodies of Central (Trans Mexican Volcanic Belt), eastern (the Yucatán Peninsula), and southern Mexico. In contrast, the zooplankton from the Mesa Central water bodies has been insufficiently investigated. After a long history of zooplankton taxonomic studies, the first contributions to the zooplankton ecology dated to the 1990 s, rapidly increasing afterward. Most ecological information arises from field investigations and experiments under laboratory conditions, lacking mesocosms and whole-lake experiments. In the same way, the studies have been carried out in lentic, natural, and artificial water bodies, primarily eutrophic. Differently, the zooplankton ecology of lotic ecosystems is largely unknown. Here we summarized the progress made in the study of the zooplankton ecology of Mexican inland waters, revealing the most important research topics developed so far.

Geochemical exploration in Mesillas geothermal area, Mexico

This work presents results of geochemical exploration in the promising geothermal area of Mesillas, Nayarit, in the western border of the Mexican Volcanic Belt. The assessment of the geothermal resource was based on a geochemical approach which consisted in: (i) mapping and geological survey, (ii) chemical characterization of geothermal manifestations, (iii) diffuse flux analysis (CO2 and H2S), (iv) temperature at depth calculations using both classical and integrated multicomponent geothermometry.. Additional to the technical work, social dissemination of geochemical issues was attempted by designing and distributing a geomap among local people. The geological survey identified five andesitic units in an area of ∼1.5 km2, where 25 thermal springs discharge Na–CO3 water with temperatures between 47 and 90 °C, and pH ∼9. Geothermometric calculations indicate a bottom temperature between 125 °C and 130 °C. Andesites show high permeability generated by intense fracturing related with normal fault systems with trend NW-SE, SW-NE, NS, and EW. Surface hydrothermal alteration is mainly argillic with silicification. CO2 and H2S hydrothermal degassing are mainly restricted to thermal springs aligned in the NW-SE direction. Thermal springs with high temperature, highest degassing and high presence of hydrothermal alteration occur in the south-southwest zone of the geothermal area (MOL10, MOL13, MOL14 and MOL15); they correspond with NW-SE structural alignment. Furthermore, the estimated range of temperature at depth using geothermometers is 125–130 °C, and the surface temperature is on average 20 °C; considering local thermal gradient, it was estimated an equilibrium depth of 2.0–2.1 km. These results indicate that the Mesillas geothermal prospect may be classified as a medium temperature system with good permeability that may be exploited for electricity production as well as direct uses.

Morphological and textural analysis of basaltic pyroclasts (Atexcac maar, central Mexico): Implications for fragmentation and conduit processes

Atexcac is a maar volcano, which forms part of the monogenetic volcanic field of the Serdán-Oriental Basin, in the eastern sector of the Mexican Volcanic Belt. This volcanic landform was originated by a combination of phreatic, magmatic and phreatomagmatic explosive eruptions. During the formation of the distinct depositional facies, fluctuations in the water availability of the local aquifer, as well as in the magma flux, were probably responsible for the different mechanisms of magmatic and phreatomagmatic fragmentation and the production of the two main populations of fragments (breccia and cross-bedded deposits particles), whose morphological features, allow us to infer the dominant regime (brittle or ductile), fragmentation mechanism (magmatic or phreatomagmatic) and conditions of bubble growth dynamics and fragmentation processes during the ascent of magma through the conduit. We conclude that the breccia particles were derived from dominant magmatic explosions while the cross-bedded deposits particles are thought to be generated from explosive phreatomagmatic events. 3D imaging based on high-precision X-ray microtomography was used to determine the vesicularity of juvenile fragments of the Atexcac maar. Calculated vesicularity index, vesicle number density (VND) and vesicle morphology indicate important processes of coalescence of gas bubbles, during the ascent of the magma. VND's Atexcac clasts suggests vesicle mechanisms similar to medium-intensity eruptions, reported in the literature. The elongated and polylobular vesicle morphology of the Atexcac clasts reveals early acceleration of magma and subsequent coalescence events at most stages of gas bubble growth.

Pathé geothermal power plant, Hidalgo, Mexico: A comprehensive retrospective assessment of the first plant of its kind in the Americas

• Background is presented on the geothermal nature of the Mexico. • The location of Pathé relative to the Trans Mexican Volcanic Belt is discussed. • Early exploration and drilling of Pathé is presented. • Design and operation of the Pathé power plant is discussed. • Performance of the plant and two alternative designs is presented. • Economics of the plant are give. • Current status of the power unit and the field site are discussed. • Possible future activity at Pathé is discussed. In November 1959 geothermal power plants were in commercial operation in Italy since 1914, in New Zealand since 1958, and in only one other country, Mexico. It was here that the first geothermal power plant in the Americas was inaugurated at Pathé on November 20, 1959. The United States joined this exclusive club the next year when it inaugurated the PG&E Geysers Unit 1 in Northern California in September 1960. This article summarizes the historic development of geothermal energy with an emphasis on Mesoamerica. This account of the Pathé plant covers its geological environment, field development, unit design, operations and economics, and preservation after reaching the end of its operational life. The account concludes with some thoughts on the future of the Pathé geothermal field.

Phylogeny, Historical Biogeography, and Divergence Time Estimates of Eucnide (Loasaceae)

Abstract— Eucnide (Loasaceae) consists of about 15 species distributed across Mexico, Guatemala, and the North American Southwest, a geographically complex landscape made up of floristically unique deserts, large mountain ranges, and a large, geographically isolated peninsula. This complex geography is credited for high levels of biodiversity and endemism in the region and we examine relationships between geography and cladogenesis in Eucnide. In the most recent treatment of the genus, Thompson and Ernst recognize three sections of Eucnide differentiated based on floral morphology. To date, no molecular phylogenetic studies have broadly sampled species in this genus. We used Bayesian and maximum-likelihood phylogenetic analyses of one plastid marker (matK) and one nuclear marker (ITS) to: 1) test the monophyly of Eucnide sections and assess whether the existing taxonomy sufficiently circumscribes diversity within the genus; 2) assess the divergence times of Eucnide lineages to determine when the major clades diversified; and 3) estimate the ancestral range of Eucnide and hypothesize patterns of geographical diversification of the genus. We found that not all infrageneric units of Eucnide are monophyletic and the taxonomy needs revision. Additionally, the major clades of Eucnide are predominantly restricted to geographic regions, suggesting that species have frequently diversified within geographic areas. The ancestral range of Eucnide was inferred to be widespread, and the divergence times of the major clades coincide with major geological events, particularly, the formation of the North American warm deserts, the isolation of the Baja Peninsula, and the uplift of the Trans Mexican Volcanic Belt. This suggests that major geological/climatic events may have contributed to the diversification of the genus.

Origin of volatile species and aqueous fluids in the Los Humeros Geothermal Field, Mexico

The Los Humeros Geothermal Field, discovered in the late 1970s, is the last geothermal field in Mexico to be significantly developed in recent years. Located in a nested caldera system of the Central Mexican Volcanic Belt, the field is within an andesitic reservoir, with low porosity and permeability, limiting the recharge of the system. Here, a new dataset of noble gas and stable isotopes (δ2H and δ 18O), tritium (3H), CO2 contents, halogens (Cl content and δ37Cl, δ81Br), and isotopes of Sr (87Sr/86Sr) were analyzed and interpreted along with previously published noble gas data. The goal was to identify the fluid sources present in the Los Humeros reservoir. This study highlights a complex hydrogeological scenario, with multiple generations of meteoric waters. Furthermore, some volatile species of mantle origin (He, Ar, C) appear to be partially decoupled from the aqueous phase, providing only partial information on the origin and evolution of the waters present in the system. The northern sector of the field contains meteoric waters having interacted with the basalt-andesitic reservoir or deeper melts (87Sr/86Sr = 0.7040) and containing mantle He and Ar. Together with this fluid, a meteoric component containing tritium confirms the presence of local and rapid meteoric recharge in this sector. The central and southern sectors of the field contain meteoric waters having interacted with carbonates from the basement. However, the relationship between 87Sr/86Sr and CO2/3He suggests a possible decoupling between mantle C and He and the aqueous phase, transporting Sr. Of particular interest, limestone C seems to be sourced from subducting slab components from the northern sector of the field, while the often-cited C contribution from local basement metacarbonates could be negligible. Finally, chlorine is sourced by magmatic HCl and partitioned in the steam phase, causing acidic waters.

An approach to reconstruct the thermal history in active magmatic systems: Implications for the Los Humeros volcanic complex, Mexico

Reconstructing the thermal history in active volcanic complexes characterized by multiple magmatic events is challenging due to the limited knowledge of the nature and extent of the transient heat sources. Although understanding of the geometry and architecture of a magmatic system is of prime importance for accurate temperature assessments, it is still one of the most uncertain parameters in numerical models. In this work, we presented a methodology for thermal assessment in active volcanic systems, whereby field-based geological, geochemical and petrological data are integrated to define the transient heat sources of a magma plumbing system. This time-varying heat source conceptual model is applied in the Los Humeros Volcanic Complex, an active Quaternary caldera complex in the Trans Mexican Volcanic Belt, for evaluating the thermal footprint related to the major volcanic events. The site is characterized by two caldera-forming eruptions, the Los Humeros (164 000 years ago) and the Los Potreros (69 000 years ago) and numerous episodes of post-caldera bi-modal volcanism during Holocene period (8 000 – 3 000 years old). The transient nature of the heat sources is implemented as time-varying temperature boundary conditions and the complete temporal evolution for a period of 182 000 years is simulated in 13 modeling stages. The thermal impact due to the voluminous caldera-forming events and the later short-lived magma pockets of Holocene ages is simulated by emplacing heat sources in the numerical model distributed heterogeneously in space and active at different instants of time. The depth, volume and age of the magma pockets are constrained from geochemical, petrological, geochronological and thermo-barometric analysis of erupted material. The present temperature state obtained from this approach agrees well with the temperature data recorded in the geothermal wells. The thermal footprint of the individual volcanic events indicates that almost 80 % of the present-day thermal contribution results from the massive caldera-forming events. The post-caldera Holocene magma pockets had additionally increased temperatures locally by 10 % - 20 % depending on the volumes and ages of the magma pockets. The present-day thermal regime of the younger Holocene magma pockets suggests existence of super-hot resources at shallow depths in the southern part of the geothermal field, making it a potential site for future exploration activities.

Geophysical imaging of multiple volcanic structures at the Huichapan Caldera Complex, Mexico

Detailed processing and analyses of aeromagnetic data supported by geological constraints shed new light on the structural framework and plumbing system of Huichapan Caldera and Nopala volcano in the northern sector of the Mexican Volcanic Belt. The interpretation of magnetic anomalies is complex due to the bipolar nature of the magnetic field so we applied reduction to the pole using a double fast Fourier transform to convert the magnetic anomalies into simplified patterns. Short optimal continuous analytical field filters enhanced subsurface and surface structures. The reduction to pole analysis filtered for the upward/downward continuation of potential field data improved both regional and detailed imaging since it was applied to different depths. Shallow subsurface structures as well as at depths of 1.25 km and 0.65 km, were correlated with the surface and regional features.The Huichapan Caldera has at least two contrasting ignimbrites. Results show that there are two large magnetic anomalies associated with different volcanic structures. The first one, a circular positive anomaly corresponds to the caldera rim and the other to the structure of the younger Nopala volcano to the west. Strong magnetic sources indicate the feeder dikes. This study provides geophysical evidence for the location of the head wall of the Huichapan caldera as well as a second rim on the south but E-W and NE-SW regional faulting has destroyed this older caldera on the north. Results show that the structures are tectonically controlled and that the caldera is open on the east and southwest. The trap door structure was associated with this regional fault.

Monogenetic volcanoes with initial phreatomagmatic phases in the Ceboruco graben, western Mexico: The cases of Potrerillo I, Potrerillo II, and San Juanito

Potrerillo I, Potrerillo II, and San Juanito volcanoes are part of the 28 Late Quaternary monogenetic eruptive vents concentrated along a ~2-km-wide and ~30-km-long stripe in the vicinity of Ceboruco stratovolcano (western Mexican Volcanic Belt). The studied volcanoes are closely spaced and located within a ~12 km2 sub-drainage basin, northwest of Ceboruco's edifice. Eruptive dynamics were inferred from sedimentary, stratigraphic, and pyroclast characteristics. Unlike Potrerillo I, which was formed by an entirely dry explosive magmatic eruption, evidence for the prevalence of initial short-lived phreatomagmatic phases was found for the Potrerillo II and the San Juanito eruptions that ended effusively.In this study we examine the nature and proportion of different types of pyroclasts within the exposed deposits of these three volcanoes, as well as their sedimentary features to better understand the initiation and progression of their eruptions. Our results indicate that both Potrerillo II and San Juanito tephra ring deposits show dominantly atypical, crudely bedded, coarse-grained deposits where the evidence for energetic, diluted pyroclastic density currents is scarce or subordinated. Instead, low energy, shallow seated, phreatomagmatic explosions generated medium-to-coarse grain-sized pyroclasts that were transported within dense tephra jets that were ballistically ejected, which on deposition formed non-turbulent currents with non-extensive lateral movement. The nature of such eruptive style was controlled by the substrate hydrogeology conditions that prevailed at the time of the eruption. So, magmas of different composition (dacitic for Potrerillo II, and basaltic andesite for San Juanito) followed similar dynamics when interacting with water. We propose that fractured aquifers with shallow water tables (or even surface water) existed at the time of both eruptions and interacted explosively with the magmas.In contrast, the construction of Potrerillo I scoria cone, which is related exclusively to explosive magmatic activity, does not show evidence of phreatomagmatic activity. This eruption may have occurred when the water table was deep, or surface water was unavailable. The variations in the depth of phreatomagmatic explosions, the availability of the water involved in the phreatomagmatic phases, and the absence or presence of these phases in the studied volcanoes were probably strongly influenced by the water-bearing conditions of the aquifers at the time of the eruption, which in turn, depended on the amount and distribution of annual rainfall.This study improves our understanding of phreatomagmatic eruptions of diverse magmatic compositions in similar settings. The recognition of associated hazards will allow to further define eruptive scenarios of monogenetic eruptions and help update the volcanic hazard map of the Ceboruco volcano area in the future.

Metagenomic Approach to Bacterial Diversity and Lipolytic Enzymes’ Genes from a Steam Soil of Los Humeros Geothermal Field (Puebla, México)

Los Humeros volcanic complex, located at the eastern end of the Trans Mexican Volcanic Belt, possess superficial thermal manifestations (fumaroles, heat steam-soils and alteration zones), with temperatures between 50 °C and 90 °C. This is the first work to explore the bacterial diversity of a steam soil of Los Humeros geothermal field using a metagenomic 16S RNA gene analysis, and the presence of lipolytic enzymes’ genes after an enrichment culture by a whole-genome shotgun approach. High diversity indexes were found in soil samples, with Firmicutes, Chloroflexi, Proteobacteria, Actinobacteria and Acidobacteria as the most prevalent phyla. Alicyclobacillus was the most prevalent genus at 15 cm and Anoxybacillus at 50 cm depth; anaerobic and obligate thermophilic and hyperthermophilic members were found at 50 cm depth. Firmicutes was favored by the oil-rich medium, and the dominant genera were Geobacillus and Caldibacillus. 165 genes related to lipolytic enzymes were found; carboxilesterases and phospholipases C were the most abundant, and 43% were assigned to uncharacterized lipolytic enzymes. The diversity as well as the high percentage of non-characterized lipolytic enzymes found after soil enrichment in an oil-rich medium suggest the presence of biotechnologically promising organisms and enzymes that deserve to be investigated.

Exploring the Interactions Between Rift Propagation and Inherited Crustal Fabrics Through Experimental Modeling

AbstractContinental rifting is a geodynamic process that involves the breakup of the crust and may eventually evolve to seafloor spreading. Although it is often assumed to be a product of orthogonal divergence, continental rifting may result from oblique extension, and in several cases, it is related to the rotation of plates or crustal blocks about a vertical axis. This implies the occurrence of rifts with straight but not parallel margins and rift axis‐parallel gradients in extension velocity and amount of strain. The effects of rift propagation through the continental crust has only recently started to be addressed, and even less investigated is the interaction between rift propagation and inherited crustal fabrics. We have studied this issue by carrying out a series of analog laboratory experiments. Modeling results suggest that inherited linear discontinuities in the model brittle upper crust that are oriented above a threshold angle (≥45°) from the orthogonal to the rift axis have the ability to interact with rift‐related structures. Depending on their orientation, such inherited discontinuities are reactivated as either transfer zones or rift‐bounding faults. We compare our models with four natural prototypes in which rift propagation is likely to have occurred (the Trans Mexican Volcanic belt, the Gofa Province, the Gulf of Suez, and the Kenya Rift). For each case study, we show how the kinematics of propagating rifts is comparable to our model results, and we provide insights into how rift‐related deformation may interact with inherited crustal fabrics.

Petrogenesis of heterogeneous mantle peridotites with Ni-rich olivine from the Pujada Ophiolite, Philippines

Nickel (Ni) enrichment (>0.40 wt%) in olivine was previously recognized in mantle xenoliths and volcanic rocks. Though this enrichment is often attributed to subarc metasomatic processes, the occurrence of Ni rich olivines in mantle peridotites remains to be established. We found peridotites that randomly contain unusually high-Ni olivines (up to Ni = 0.53 wt%) from the mantle section of the Pujada Ophiolite, Philippines. The Pujada mantle peridotites can be classified into three groups based on their occurrence and spinel Cr#: Group I - massive lherzolites and harzburgites with Cr# = 0.10–0.40, Group II - lherzolite-dunite and harzburgite-dunite interlayers with Cr# = 0.10–0.40, and Group III - interlayered harzburgites and dunites with Cr# >0.40. Rare earth element composition of clinopyroxenes shows general light rare earth element (LREE) depletion and relatively flat heavy rare earth element (HREE) with minor LREE enrichment. The high-Ni olivines are associated to the occurrence of secondary orthopyroxenes, high modal abundance of orthopyroxenes (>30%) and LREE enrichment. The Ni enrichment in olivine is the result of the diffusion of Ni from a pyroxenitic melt. The crystallization of a hybridized melt formed by the combination of pyroxenite melt, primitive MORB melt and siliceous slab-derived melt, shows the same case of formation for the high Ni-olivine phenocrysts in alkali basalts from Hawaii, Kamchatka and the Mexican Volcanic Belt.