Volcano-sedimentary processes at Las Derrumbadas rhyolitic twin domes, Serdán-Oriental basin, Eastern Trans-Mexican Volcanic Belt

The eruption of the ∼10 km3 rhyolitic Las Derrumbadas twin domes about 2000 yrs ago has generated a wide range of volcano-sedimentary deposits in the Serdán-Oriental lacustrine basin, Trans-Mexican Volcanic Belt. Some of these deposits have been quarried, creating excellent exposures. In this paper we describe the domes and related products and interpret their mode of formation, reconstructing the main phases of the eruption as well as syn-and-post eruptive erosional processes. After an initial phreatomagmatic phase that built a tuff ring, the domes grew as an upheaved plug lifting a thick sedimentary pile from the basin floor. During uplift, the domes collapsed repeatedly to form a first-generation of hetero-lithologic hummocky debris avalanche deposits. Subsequent dome growth produced a thick talus and pyroclastic density currents. Later, the hydrothermally-altered over-steepened dome peaks fell to generate 2nd generation, mono-lithologic avalanches. Subsequently, small domes grew in the collapse scars. From the end of the main eruptive episode onwards, heavy rains remobilized parts of the dome carapaces and talus, depositing lahar aprons. Las Derrumbadas domes are still an important source of sediments in the basin, and ongoing mass-wasting processes are associated with hazards that should be assessed, given their potential impact on nearby populations.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5752296

The genetic diversity of wild grapes in Mexico

This is the first report evaluating the genetic diversity of Mexican grape species utilizing DNA-based markers to understand the distribution of grape species, and patterns of hybridization. The study utilized accessions maintained in three collections in Mexico, one in the USA and recently collected germplasm. Fifteen SSR markers were used to develop a fingerprint database to identify unique germplasm. Two different clustering analyses without prior population assignment, were used to identify groups that were verified by a Discriminant Analysis of Principal Components and a Principal Coordinate Analysis. Genetic diversity estimates were made across and within groups to validate the results obtained from the clustering analyses. Multiple clustering analyses and diversity parameters supported six genetic groups representing different geographic regions. The Northeastern group was the most diverse with a geographic range extending to Eastern and Central Mexico, while the Coahuila group was the least diverse. Vitis arizonica Engelm. and Vitis cinerea Engelm. ex Millardet were the most abundant species with many hybrid forms. We provide evidence that wild grape species in Mexico follow the physical barriers of mountain ranges like the Sierra Madre Oriental with an east–west divide and the Trans-Mexican Volcanic Belt as a corridor for gene flow among different grape species. Additional collections are required to fully understand the extent of hybridization and to clarify hybrid zones.

Risk of infestations by Dendroctonus mexicanus Hopkins and Dendroctonus frontalis Zimmermann bark beetles in forests of Michoacán

Introduction: Severe Dendroctonus spp. infestations are reported in North and Central America. Dendroctonus mexicanus Hopkins and Dendroctonus frontalis Zimmermann are recognized as forest pests and are common in the state of Michoacán, Mexico.Objective: To model current and future (2015-2039) spatial distribution of risk D. mexicanus and D. frontalis infestation in forests of Michoacán, Mexico.Materials and methods: Multicriteria evaluation techniques, including the analytic hierarchy process and fuzzy membership functions, were combined with climate and biophysical variables to obtain forest infestation risk maps for D. mexicanus and D. frontalis under current and future climate scenarios.Results and discussion: Climate, fire, tree density and topography were identified as relevant criteria influencing bark beetle outbreaks. The maximum risk value estimated for D. mexicanus was 0.78 and 0.83 for the current and future scenarios, respectively; for D. frontalis these values correspond to 0.84 and 0.85, respectively. In terms of area, high risk of infestation by D. mexicanus increased from 3.9 % (current scenario) to 5.0 % (future scenario); for D. frontalis it decreased from 10.8 % to 9.6 %. The very high-risk value remained constant (0.35 %) for both species and scenarios.Conclusions: Forests of the Transversal Volcanic Belt (in the northeastern part of Michoacán) have the highest risk of bark beetle infestation in the two modeled scenarios.

Anion Composition of Apatite in the Au-Cu Epithermal Deposit of Palai-Islica (Almería, SE Spain) as an Indicator of Hydrothermal Alteration

The Palai-Islica deposit (Almería, SE Spain) is an Au-Cu epithermal deposit hosted in Neogene calc-alkaline andesites and dacites from the Cabo de Gata-Cartagena volcanic belt in the Betic Cordillera. Major element compositions of apatite from Palai-Islica orebody and related hydrothermally altered and unaltered volcanic rock from the region hosting the deposit were obtained to clarify the processes involved in their formation. Apatite in the host volcanic rocks is rich in chlorapatite and hydroxylapatite components (50–57% and 24–36%) and poor in fluorapatite components (12–21%), indicating assimilation processes of cortical Cl-rich material in the magmatic evolution. Apatite in the orebody sometimes has corrosion textures and is mostly fluorapatite (94–100%). Apatite from the hydrothermally altered host rock of the orebody systematically bears signs of corrosion and has variable and intermediate fluorapatite (19–100%), chlorapatite (1–50%), and hydroxylapatite (0–47%) components. The style of zonation and the composition are related to the proximity to the orebody. These features can be interpreted as the result of hydrothermal modification of high Cl, OH-rich volcanic apatites into F-rich apatites. The enrichment of F is related to the intensity of hydrothermal alteration and could therefore constitute a geochemical index of alteration and of mineralization processes.

Environmental impact assessment of vernacular thatch building tradition in Mexico: Case studies of three palm species and related technology along the Trans-Mexican Volcanic Belt

<p>This project involves research into vernacular buildings, in particular traditional and contemporary coastal palm thatch buildings in the middle-west coast deciduous forest environments in Mexico. The fieldwork-based grounded theory research investigates the natural materials and techniques involved in constructing thatched vernacular buildings using three different palm species (Attalea guacuyule, Brahea dulcis and Sabal rosei) in different climatic contexts along the Trans Mexican Volcanic Belt (TMVB). The aim is to achieve a holistic approach to the environmental assessment of these building types through a life-cycle assessment. The present research emerges from the premise that vernacular buildings are generally taken for granted as sustainable, and yet they are under-investigated meaning this assumption may not be correct. In general the performance of vernacular buildings in terms of sustainability and in relation to their embodied energy is under reported, particularly in terms of vernacular case studies in Mexico. However the deterioration of the environments where such buildings are located through anthropogenic causes is of world-wide importance, therefore it is a priority for this research to study the relationship of the vernacular traditions with their immediate environment. The first section of the thesis analyses theoretical frameworks for sustainability and vernacular architecture. Both terms are widely used and carry many different meanings, so it is important to establish the definitions used in this research to better set the boundaries of the study as a basis for seeking the best methods for assessing the environmental impact of the selected vernacular thatch building technologies. The second section undertakes qualitative and quantitative fieldwork on traditional practices of palm thatch buildings in selected regions of Mexico and related case studies, six in total. The fieldwork was combined with investigation into ethnographical, ethnobotanical and historical records and data for the three palms used for thatching and their related materials and technologies in order to derive data concerning yield factors, lifespan of the building materials, carrying capacities, embodied energy of transport and embodied energy of materials. The third section applies the collected information for a life-cycle environmental assessment (LCA) of two typical buildings for each of the three different palm species and the diverse techniques involved. The assessment is carried out based on various assumptions that are commonly used in LCA to give a carbon account and an ecological footprint for each building component both after construction and for a 50 year building life. However, during the research particular variables in the analysis were revealed, such as operating energy, recycling of building elements, durability of materials and transport practices, which can vary widely from case to case, therefore the limits and scope of the assessment excluded such data for a better comparative scenario of the building process itself. This suggests that a different way of life-cycle accounting may be needed when assessing vernacular structures. The results show the environmental impact of these techniques in terms of carbon and ecological footprints, and reveal that the rural vernacular case studies had lower environmental impacts than the suburban and urban vernacular case studies as measured by their carbon content, energy expressed in Giga Joules (GJ) and their ecological footprints.</p>