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This work presents the volcanic geology of the easternmost sector of the Trans-Mexican Volcanic Belt, including the Serdán-Oriental basin and Cofre de Perote-Citlaltépetl volcanic range, two contrasting Quaternary volcanic fields. The first comprises dominant monogenetic volcanism of bimodal composition including isolated rhyolitic domes and tuff rings, basaltic andesite maar volcanoes, cinder and lava cones, and an active caldera complex (Los Humeros). The second is dominated by large composite polygenetic volcanoes of andesitic-dacitic composition, including the shield-like compound Cofre de Perote volcano, La Gloria and Las Cumbres complexes, and the active Citlaltépetl stratovolcano. Mapping units include a pre-volcanic basement made of metamorphic (Paleozoic), and sedimentary (Jurassic-Cretaceous); intrusive (Miocene) rocks; multiple basaltic-andesitic lava flows and rhyolitic domes; volcaniclastic sequences (debris avalanches and lahars; and pyroclastic deposits (block-and-ash flows, ignimbrites, fallouts, and surges) (Miocene-Holocene). This map provides a comprehensive view of the highly diverse volcanism, which may reference for future research work.

In Central Asia, the Carboniferous is a crucial period in the formation of the Tianshan Belt and associated bending of the Kazakhstan tectonic collage. In order to reveal Carboniferous magmatic events of the region and their tectonic implications, we conducted field investigations, zircon U–Pb dating, whole-rock geochemical and Sr–Nd isotopic studies on the Early Carboniferous Dahalajunshan Formation and Late Carboniferous Yishijilike Formation volcanic rocks of the Wusun Mountain Range (southern Yili-Central Tianshan Block). Volcanic rocks of the Dahalajunshan Formation consist of calc-alkaline basalt, andesite and dacite, yielding new zircon U–Pb ages of ~ 350 Ma. They have positive whole-rock eNd(t) values (+ 0.5 to + 1.6). In contrast, the Yishijilike Formation volcanic rocks dominantly comprise alkaline and calc-alkaline bimodal suites that erupted at ~ 337 Ma to 313 Ma and have higher whole-rock eNd(t) values (+ 2.3 to + 4.3). These two episodes of Carboniferous magmatism were correlated with partial melting of depleted mantle that metasomatized by slab-derived fluids. The late Carboniferous Wusun Mountain magmatic belt shows characteristics of a back-arc system that evolved due to trench retreat relative to the southern margin of the Yili-Central Tianshan Block. This mechanism induced an extensional regime with gradually depleting magma sources. The asymmetric retreat of the paleo-subduction zones of the South Tianshan Ocean and Junggar Ocean relative to the Yili-Central Tianshan Block was hence a vital driving force for the bending of the Kazakhstan Orocline.

The study of Carboniferous magmatism in northern West Junggar plays an important role in understanding the tectonic evolution of that part of the Central Asian Orogenic Belt. In this study, we present petrology, zircon U–Pb geochronology, mineral and whole-rock geochemistry, and the Sr–Nd–Hf–Pb isotope compositions of volcanic rocks from the Hamutusi area of northern West Junggar. LA–ICP–MS zircon U–Pb analysis of a representative andesite yielded an early to late Carboniferous age of 324.4 ± 6.9 Ma. The volcanic rocks are calc-alkaline, with high SiO2 (54.2–57.8 wt%), MgO (5.97–8.33 wt%), Mg# (60–69), Cr (147–448 ppm), and Ni (29.1–120 ppm) contents, and are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE), but depleted in high field strength elements (HFSE), these characteristics are similar to those of typical sanukitoids within the Setouchi volcanic belt in Japan. All samples have radiogenic initial Sr and Pb isotopic compositions, and low eNd(t) and eHf(t) values, indicating the sanukitoids were generated by partial melting of subducting sediments in which the melts interacted with the mantle. Geochemical modeling calculations indicate a proportion of 3–10% sediment melt and slab-derived fluids were mixed with the depleted mantle to produce the bulk of the Hamutusi rocks. We conclude that the studied rocks from north West Junggar record the initiation of ridge subduction related to a transition from normal subduction to subduction of young and hot oceanic lithosphere between the early and late Carboniferous.

This article documents earthquake intensity observations during early novohispanic times (A.D. 1542–1740) in the Puebla-Tlaxcala region (central Mexico), mostly based on Nahuatl-language historical annals and chronicles, and includes (as a supplement) a descriptive earthquake catalog for this period. Although it is difficult to assign intensities from fragmentary accounts, the largest shocks (A.D. 1582 and 1711) caused damage through the entire region. Earthquake ground shaking in the study area, located within the active volcanic arc crossing central Mexico, can result from intraslab normal faulting in the subducted Cocos plate, subduction interface thrust earthquakes, motion on the faults of the intra-arc Tlaxcala-Huamantla half-graben, as well as extension accommodated through magmatic injection. Most of the historical sources describe earthquakes felt only locally and sometimes report prolonged sequences of shocks, which is indicative of magmatic dike-induced earthquakes or else resulted from motion on the faults of the Tlaxcala-Huamantla half-graben. This structure, ∼70 km long and 15–20 km wide, is the only major tectonic depression in the eastern part of the trans-Mexican volcanic belt. It is filled by a volcano-sedimentary sequence, up to 400 m thick, of unknown but likely Pliocene age. The half-graben is bound in the north by an east–west-striking and south-dipping normal fault system, which is morphologically most pronounced near the town of Tlaxcala where the footwall uplift reaches a maximum of 350 m. The fault array is likely to be active; it vertically displaces Quaternary Totolqueme volcano.

The Zhaiping Ag–Pb–Zn vein deposit in the Coastal Volcanic Belt of southeastern China, which resulted from subduction of the paleo-Pacific oceanic lithosphere beneath the South China Block, is hosted by Early Cretaceous sub-volcanic rocks (rhyolite porphyry) and younger granite porphyry and quartz porphyry. Three generations of veins have been recognized: (i) pre-ore quartz + pyrite, (ii) syn-ore silver + pyrite + pyrrhotite + base metal sulfides + quartz + sericite, and (iii) post-ore quartz + calcite + fluorite veins. Rubidium–Sr dating of syn-ore pyrite yielded an isochron age of 132.2 ± 2.1 Ma (2σ, MSWD = 2.0, n = 4), which is roughly coincidental with the age of the granite porphyry and quartz porphyry (zircon U–Pb age: ca. 133 Ma). The age data, together with Pb, S, H, and O isotopic compositions, indicate a close temporal and possibly genetic relationship between mineralization and porphyry magmatism at Zhaiping. Geochemical and isotope data demonstrate that the Zhaiping sub-volcanic rocks were derived from partial melting of Proterozoic crustal sources and underwent fractionation of feldspars, monazite, and/or allanite. The 87Sr/86Sr ratios of pre-ore (Aph1) and syn-ore (Aph2) stage apatite are in the ranges of 0.71350 to 0.71441 and 0.71260 to 0.71328, respectively, which are distinct from those of the sub-volcanic intrusive rocks (0.7119–0.7125). The Sr isotope signature, together with lower fluid temperatures (

The results of seismic hazard zoning of the submerged crossing of the pipeline in the Nevelskoy Strait, between the village of Lazarev of the Nikolaevsky district, Khabarovsky krai, and Cape Pogibi near the village of Pogibi, Sakhalin oblast are presented. Along the water area, this section of the crossing is limited by a zone that is 500 m wide and 11 km long. It follows from the stock of geological documents of the Geophysical Service of the Russian Academy of Sciences and the general seismic zoning map (GSZ-2015) that the highest seismic activity in the Okhotsk region is observed in the area of the Kuril Islands, while the closest activity to the construction site manifests itself in the central zone of northern Sakhalin. Large earthquakes are recorded by a number of seismological stations in the immediate vicinity of the construction site. The foci of nearby earthquakes are displaced eastward of the construction site and are mostly confined to the systems of deep faults that result from the juncture between the West Sakhalin synclinorium and the Sikhote Alin volcanic belt. The main purpose of this research is related to the development of a procedure for forecasting seismic impacts for the areas that are prone to predicted strong earthquakes. In this context, an approach is proposed for the specific structure, which is based on the construction of a set of the most probable seismic models to reach the reference bedrock, setting of the pickup signal corresponding to initial seismicity of the area, calculating the main parameters of seismic impacts for them, and then, in the first approximation, the implementation of the technology for constructing an engineering–seismological cross-section along the pipeline construction site. The proposed approaches to forecasting seismic events for the section of the pipeline crossing in the Nevelskoy Strait are based on certain restrictions that made it possible to obtain a set of parameters of seismic impacts for predicted strong earthquakes that are necessary for design and construction of an earthquake-resistant linear structure. In improving the calculation methods and monitoring critically important objects, the advantage of this approach is the ability to recalculate seismic impacts on a structure using the constructed seismic ground-motion models.

High-grade epithermal Au–Ag veins of the Vodorazdelnaya district in far eastern Russia are hosted by Early Cretaceous volcanic rocks of the Tytylveem belt. The largest deposit is Zone 37, a 1-km long, northeast-striking vein that is up to 35-m wide, containing at least 32 t Au. The main shoot consists of crustiform—colloform banded quartz-chalcedony-adularia-sulfide veins, of low-sulfidation style. The vein is cut by late-mineral rhyolite sills and dikes. Zone 37 vein is dated at 117 ± 2 Ma, overlapping within error with the cross-cutting rhyolites (121–119 Ma) and with intrusions of the nearby Ilirney granitic pluton (119–117 Ma). The volcanic host rocks are dated at 121–115 Ma. At September Northeast, 15 km west-northwest of Zone 37, mineralisation consists of veins up to 4 m wide, with crustiform banded quartz ± chalcedony ± adularia ± chlorite, and Zn-Pb-Cu sulfides, of intermediate sulfidation style, in a 1-km-long, north-northeast striking trend. High grades are associated with gold dendrites in fine-grained quartz bands and with minor late-stage tellurides. The veins were disrupted by intrusion of rhyolite dikes and associated phreatic breccias. Some breccias host mineralisation as vein clasts and minor matrix sulfides. The Tytylveem belt is preserved below a regional unconformity that forms the base to the overlying Late Cretaceous (106–77 Ma) Okhotsk-Chukotka Volcanic Belt (OCVB). Intrusive rocks attributed to OCVB magmatism were emplaced at about 96 Ma and are associated with overprinting hydrothermal alteration, sub-economic veins and thermal resetting of some vein adularia ages at Zone 37, to 91–97 Ma.

Thermal manifestations are commonly found in central Mexico as result of the volcanic activity originating from the formation of the Trans-Mexican Volcanic Belt during the Quaternary. The Rancho Nuevo hot spring is one of them that has not been described before with a discharge temperature near 92 °C. The goal of the present study is to provide geothermal characteristics of thermal manifestations at Rancho Nuevo location based on geochemical and mineralogical results to explain deep-subsurface processes that occurred in the geothermal system. The presence of kaolinite, montmorillonite, opal, zeolite, barite, pyrite, and stibnite in altered soil sediments or around the hot springs identified by the techniques used in the present study, confirms the presence of hydrothermal activity. In addition, based on the X-ray diffraction, calcite precipitates at the surface of the thermal springs. This mineral association reflects deep geothermal processes and is eventually deposited in shallow zones. Fluid mixing processes and variations in redox conditions are suggested by mineral association and isotopic sulfur data. Finally, based on the physicochemical data provided by the water samples and the discharge conditions of the springs, stability diagrams were constructed for pyrite, barite, and zeolites using the Geochemist’s Work Bench program to corroborate these data with the mineralogical results. The mineralogical results and distribution, as well as the N-S trend of mineral associations suggest interaction processes between geothermal fluid and rocks of the stratigraphic sequence, and active major faults, enabling the upward flow of deep geothermal fluids. The approach to the conceptual model of the Rancho Nuevo geothermal prospect reveals an attractive potential for the exploration of a viable geothermal resource in central Mexico.

Multiple geological and climatic events have created geographical or ecological barriers associated with speciation events, playing a role in biological diversification in North and Central America. Here, we evaluate the influence of the Neogene and Quaternary geological events, as well as the climatic changes in the diversification of the colubrid snake genus Rhadinaea using molecular dating and ancestral area reconstruction. A multilocus sequence dataset was generated for 37 individuals of Rhadinaea from most of the biogeographical provinces where the genus is distributed, representing 19 of the 21 currently recognized species, and two undescribed species. Our analyses show that the majority of the Rhadinaea species nest in two main clades, herein identified as “Eastern” and “Southern”. These clades probably diverged from each other in the early Miocene, and their divergence was followed by 11 divergences during the middle to late Miocene, three divergences during the Pliocene, and six divergences in the Pleistocene. The ancestral distribution of Rhadinaea was reconstructed across the Sierra Madre del Sur. Our phylogenetic analyses do not support the monophyly of Rhadinaea. The Miocene and Pliocene geomorphology, perhaps in conjunction with climate change, appears to have triggered the diversification of the genus, while the climatic changes during the Miocene probably induced the diversification of Rhadinaea in the Sierra Madre del Sur. Our analysis suggests that the uplifting of the Trans‐Mexican Volcanic Belt and Chiapan–Guatemalan highlands in this same period resulted in northward and southward colonization events. This was followed by more recent, independent colonization events in the Pliocene and Pleistocene involving the Balsas Basin, Chihuahuan Desert, Pacific Coast, Sierra Madre Occidental, Sierra Madre Oriental, Sierra Madre del Sur, Trans‐Mexican Volcanic Belt, and Veracruz provinces, probably driven by the climatic fluctuations of the time.

Lahars on volcanic terrain are recurrent phenomena with a high capacity to transform landscape and cause significant economic and life losses. Lahars have been studied in most volcanic regions, mostly based on the recognition of cotemporaneous events. Yet, there is a lack of long-term record about their frequency and magnitude. Such long-term records could help to improve lahar risk assessment and understand climate triggering factors. Here, we aim at providing the longest annual resolved frequency-magnitude lahar records of the Trans-Mexican Volcanic Belt. We focus on the Jamapa Gorge of the Pico de Orizaba volcano and apply geomorphological and dendrogeomorphological methodological approaches. Besides, we used a 2D numerical model to estimate the discharge of the reconstructed lahars based on the paleostage indicators (PSIs) defined by scars on trees. A total of 78 Pinus hartwegii trees were sampled for the reconstruction of lahars. We identified 157 growth disturbances related to past lahar activity, namely scars (51%), growth suppression (35%), and compression wood (32%). A total of 8 lahars were reconstructed between 1930 and 2017 (1931, 1960, 1968, 1975, 1999, 2012, 2014, and 2016) with a reconstructed peak discharge ranging between 80 and 350 m3/s. Largest events occurred in 1975 and 2012 with lahar discharges of 160 m3/s and 91 m3/s, respectively. Lahar events were linked to intense rainfall events and the passage of hurricanes and tropical storms coming from the Atlantic Ocean. These results highlight the benefit of the combined use of dendrogeomorphology and numerical modeling to gather longer series of lahar activity in volcanoes, where such information is largely lacking. The methodological approach deployed here can be applied consistently and uniformly in other volcanic regions to characterize lahar hazard, regardless of physiographic and climatic contexts.

Los estudios sobre las áreas de distribución geográfica (ADG) proporcionan información sobre cómo se establecen las especies en el espacio y tiempo, y los efectos del cambio de uso de suelo sobre los patrones geográficos de la biodiversidad. En la provincia biogeográfica de la Faja Volcánica Transmexicana (FVT) habita un alto número de especies endémicas; sin embargo, presenta altas tasas de deforestación. En el presente trabajo: (a) se describen cuantitativa y cualitativamente las ADG histórica de 167 especies de anfibios, aves, insectos, mamíferos y plantas endémicas de la FVT, y (b) se analiza el efecto del cambio de uso de suelo actual en esas distribuciones geográficas. En general, la clase Mammalia tuvo las mayores superficies ocupadas, el promedio más alto de las tres magnitudes y fue principalmente de distribución continental. Por otro lado, la mayoría de las especies fueron transicionales y discontinuas. Considerando el cambio en el uso del suelo, el 85% de las especies tuvo cambios en sus ADG históricas, de las que dos tercios tuvieron una pérdida mayor al 50%. Los grupos taxonómicos más afectados por pérdida total de su ADG histórica, fueron Insecta y Amphibia. La mayoría de las especies ocuparon altitudes elevadas y por lo tanto, los rangos altitudinales con mayor de superficie perdida fueron entre los 1,500 y 3,000 msnm. La variabilidad en el comportamiento distribucional de las especies sugiere patrones internos y diferenciados en la FVT, y mayor complejidad biológica, geológica y evolutiva de la esperada, con múltiples relaciones de la FVT con las provincias adyacentes. Los estudios areográficos pueden constituir un punto de partida para la preservación de áreas no transformadas, que cumpla el objetivo de prevenir la posible extirpación de las especies.

First data on oxygen isotopic composition in phenocrysts in volcanic rocks from Okhotsk–Chukotka volcanic belt (106–78 Ma, North-Eastern Russia) together with Sr and Nd isotopic data gives additional geochemical evidence on belt segmentation. Calculated δ18Omelt in calc-alkaline magmas of belt vary from normal-δ18O (from +5.2 to +6.9‰) consistent with mantle-like signatures of radiogenic isotopes. Low-δ18O (from +4.7 to +4.8‰) silicic magmas were found in Western–Okhotsk segment of the belt interpreted as assimilation of hydrothermally altered rocks from pre-caldera rifted basement. The highest δ18O values were obtained for Chukotka segment of the belt reaching +10.8‰ and these are correlated with elevated 87Sr/86Sr due to assimilation of relatively mature high-δ18O continental crust. Comparison with Kamchatka volcanic belt is performed.

The Compostela area is located in the western Trans-Mexican Volcanic Belt, which consists of volcanic rocks that produced during the Pliocene to Recent volcanism. In this paper, we present petrography, whole-rock major- and trace-element concentrations, Ar–Ar ages, and Sr–Nd isotopic data of volcanic rocks from the Compostela area in the south of the city of Tepic, Nayarit, Mexico. These volcanic rocks are of intermediate composition and belong to the transitional series: basaltic trachyandesites [52.72–53.94 wt% SiO2; 0.69–2.53 wt% MgO] and subalkaline series: low-Si [55.11–60.94 wt% SiO2; 0.79–2.74 wt% MgO] and high-Si [61.60–62.71 wt% SiO2; 0.36–0.80 wt% MgO] andesites. The 40Ar/39Ar dating of two basaltic trachyandesites yields plateau ages of 1.05 ± 0.15 Ma and 1.07 ± 0.17 Ma and the andesites yielded a plateau age of 2.42 ± 0.36 Ma. These results indicate that the studied rocks were formed during the Pleistocene in two discrete episodes. The basaltic trachyandesites show enriched light rare earth elements patterns relative to high rare earth elements [(La/Yb)N = 5.81–8.07] with negligible Eu anomalies. The andesites display enriched large-ion lithophile elements (Ba, K) with anomalies of Nb (Th/Ce) and Ti in the three groups identified in the subalkaline series. The basaltic trachyandesites appear in a tight cluster of initial 87Sr/86Sr ratios (0.703519–0.703882) as compared to the basaltic andesite 87Sr/86Sr (0.704073) and positive ɛNd(t) values of +5.6 to +3.4, respectively, indicating that the basaltic trachyandesites were derived from intermediate magmas from a shallow mantle source. Geochemical modelling reveals that both basaltic trachyandesite and andesite rocks were derived by a process of crystal fractionation accompanied by assimilation of crustal rocks at the lower or middle level. Geochemical ratios and multidimensional discrimination diagrams, combined with the cross-section of the subduction zone indicates that basaltic trachyandesites were generated from a rift and/or Ocean Island Basalt-type source, whereas andesites were generated from a slab-derived source in a subduction environment.

Introduction: Extrusive volcanic rocks, such as dacite, andesite, basalto-andesite, basalt… of Chau Thoi and Nui Gio hills in Bien Hoa and Binh Phuoc provinces, southern Viet Nam, characterize volcanic island arc rocks. These rock suites formed as the convergent tectonic between the Indochina and Sibumasu geological blocks. Methods: Geochemical data of rock samples collected on the field were examined and analyzed by the Academia Sinica I E S (Institute of Earth Science, Taiwan and processed with a GCD kit (Geochemical Data Toolkit) to ascertain their characteristics and geotectonic setting. Result: Geochemical data both in major elements and trace elements of the Chau Thoi – Nui Gioshow a specific characteristic of a volcanic island arc environment. Discussion: Chau Thoi and Nui Gio rocks are suitable to correlate to the Permian Thailand Loei Phetchabun volcanic belt. However, at the current time, Chau Thoi and Nui Gio rocks have been classified as Deo Bao Loc formation - late Jurassic to early Cretaceous in ages - belong Truong Son magmatic belt. This magmatic belt resulted from the Yanshanian orogeny by the subduction of the Paleo-Pacific oceanic plate beneath the Eurasia (Indochina) continental plate. More studies needed to be performed, specially geochronological data to support the study. Conclusion: Chau Thoi and Nui Gio rock suites characterize volcanic island arc rocks, products of a convergence tectonic between Indochina and Sibumasu blocks. They are remnants of the Thailand Loei Phetchabun volcanic belt, the first time reported in Vietnam.

The Cretaceous fossil flora in deposits of the Okhotsk–Chukotka volcanic belt is drastically different in systematic composition from the paleoflora of similar ages in deposits of the Northeast Asian coastal lowlands and inland depressions. In the volcanic burials, paleoflora features are the most evident in the Chaun flora found in the Pegtymel trough in the Central Chukotka region and described in the monograph by L.B. Golovneva “The Chaun Flora of the Okhotsk–Chukotka Volcanic Belt.” Based on these data and our own experience in studying the Okhotsk–Chukotka belt stratigraphy and the vegetation cover dynamics in the Kamchatka recent volcanism area, we have proven that the Chaun flora was formed not on the volcanic highlands, as Golovneva stated, but on the lowlands, on a periodically renewed juvenile surface of the central part of the vast volcanic field separately from the background diaspora sources. This flora is not characterized by a clear lateral and stratigraphic confinement, because the characteristic plant fossils can be found in deposits of different ages throughout the volcanic belt. They are indicative of particular vegetation and burying conditions in the surface volcanism from the Turonian to the Campanian inclusive.

—Paleomagnetic studies of several Late Cretaceous volcanic sections of the Okhotsk–Chukotka volcanic belt have been carried out in the Bilibino region of the Chukotka Autonomous Okrug and along the Pevek–Egvekenot road. Extensive collections have been acquired and analyzed. The laboratory experiments isolated the ancient characteristic magnetization component reflecting the direction of the geomagnetic field at the time of formation of the studied rocks (~85 Ma ago). The primary character of the revealed characteristic magnetization component is supported by the positive regional fold test and by the coincidence of the paleomagnetic pole calculated from this component with that previously obtained for Chukotka from the rocks of similar age (Stone et al., 2009). The paleomagnetic pole calculated from the combination of the previous and our newly obtained data (Plat = 69.3°, Plong = 180.7°, N = 99, A95 = 5.1°) indicates that the sampled rocks were formed in the immediate vicinity of the geographic pole. The reliability of the existing Late Cretaceous paleomagnetic poles for Eurasia and North America is analyzed, and the refined poles are calculated for these plates for the time of ~85 Ma. The reconstruction of the Chukotka–Kolyma–Omolon block’s position relative to Eurasia and North America allowing for the paleomagnetic poles calculated for that time is proposed. The reconstruction implies that from the formation time of the studied rocks up to the present, the Chukotka–Kolyma–Omolon block has undergone relatively small (tens to first hundreds of km) southward movements relative to the North American plate and has been noticeably shifted (by a few hundred km) relative to the Eurasian plate. Our reconstruction is close to that proposed in (Otofuji et al., 2015) but, in contrast to the latter, it does not require a collision between the Chukotka–Kolyma–Omolon block and Eurasia after 80 Ma ago.

To date, there have been reported several quality factors Q(f) = Q0fα in the literature for the Trans-Mexican Volcanic Belt (TMVB), with significant variations between them. Most of these studies do not fully specify the parameters used in their analyses or they rely on seismograms of earthquakes whose epicenter lies outside the study zone. In this paper, quality factors were determined for the TMVB from the analysis of coda waves. For this purpose, there were used local records related to earthquakes with the epicenter lying inside the TMVB. A division of the study area is considered according to the geological characteristics, and a correlation with the coda Q(f) values was obtained. Results show a clear dependenceof Q(f) on the characteristics and location of the source. Important variations were identified in comparison with studies that report Q(f) values for the TMVB using different methodologies and source characteristics.

A novel dothideomycete species, Rhytidhysteron mexicanum, is described and illustrated supported by morphological and cultural characters and a phylogenetic analysis (rDNA nucleotide data set). The new species is characterized when immature by boat-shaped hysterothecia (2–4 mm long × 1.5–2.5 mm wide). In mature stage, 2.5–4 mm apothecia with fluted margins remain the same when dry. The epithecium is yellowish green to pistachio green, becoming ocher in the presence of 10% KOH. Ascospores are 34–40(–44) × 10–12(–15) µm, and reddish brown. The morphology of R. mexicanum is compared with other Rhytidhysteron species. A dichotomous key is provided to the five species of Rhytidhysteron known from Mexico.

The Uyandina–Yasachnaya volcanoplutonic belt (UYVB) is located in Northeast Asia. As one of the largest volcanic belts in the region, it extends for 900 km from the headwaters of the Kolyma River in the northwesterly direction. The Late Jurassic UYVB overlaps the folds of the Cherskii collision belt. The UYVB rocks are characterized by highly variable facies indicating the heterogeneous nature of the belt. The UYVB has been studied at the cross section of the Indigirka River. This paper reports the first data on U–Pb dating of zircons and the geochemical features of rocks. The concordant U–Pb age of volcanic rocks is 150 ± 2–152 ± 2 Ma (Kimmeridgian–Volgian of the Late Jurassic). It is concluded that the formation conditions of the volcanic rocks change upward through the section, from those typical of mature island arcs to those more typical of active continental margins.

The Burgali deposit is located in the Paleozoic Kedon volcanic belt (KVB) within the Omolon cratonic terrane. The orebodies of the Burgali deposit are veined and stockwork-type. The studies of the wallrock metasomatites demonstrate that the erosional truncation of the deposit is close to minimal. The ores of the deposit are enriched in the chalcophile elements (Au, Ag, As, Sb, Te, W, Mo, and Bi) and poor in the rare earths. The rare-earth element (REE) spectra are dominated by light lanthanides. The ores are characterized as very low-sulfidation with finely disseminated mineralization, widespread occurrence of chalcedony, and widespread colloform-banded, often combined with brecciated, structures. The late quartz veins contain Lower Carboniferous coaly siltstone fragments, filled with petrified timber remains, which indicate the Carboniferous age of the ore mineralization. The ores contain widespread Au- and Te-bearing pearceite and rare minerals such as argyrodite and the selenous petrovskaite and uytenbogaardtite. The data obtained enable the Burgali deposit to be classified as low-sulfidation epithermal. The outlook for Ag and Au reserve additions is based on the further studies and exploration of the ore-bearing stockwork.

The early Paleozoic tectonic evolution of the Xing’an–Mongolian Orogenic Belt is dominated by two oceanic basins on the northwestern and southeastern sides of the Xing’an Block, i.e., the Xinlin–Xiguitu Ocean and the Nenjiang Ocean. However, the early development of the Nenjiang Ocean remains unclear. Here, we present zircon U–Pb geochronology and whole-rock elemental and Sr–Nd isotopic data on the gabbros in the Xinglong area together with andesitic tuffs and basalts in the Duobaoshan area. LA-ICP-MS zircon U–Pb dating of gabbros and andesitic tuffs yielded crystallization ages of 443–436 ​Ma and 452–451 ​Ma, respectively. The Early Silurian Xinglong gabbros show calc-alkaline and E-MORB affinities but they are enriched in LILEs, and depleted in HFSEs, with relatively low U/Th ratios of 0.18–0.36 and eNd(t) values of −1.6 to +0.5. These geochemical features suggest that the gabbros might originate from a mantle wedge modified by pelagic sediment-derived melts, consistent with a back-arc basin setting. By contrast, the andesitic tuffs are characterized by high MgO (>5 ​wt.%), Cr (138–200 ​ppm), and Ni (65–110 ​ppm) contents, and can be termed as high-Mg andesites. Their low Sr/Y ratios of 15.98–17.15 and U/Th values of 0.24–0.25 and moderate (La/Sm)n values of 3.07–3.26 are similar to those from the Setouchi Volcanic Belt (SW Japan), and are thought to be derived from partial melting of subducted sediments, and subsequent melt-mantle interaction. The Duobaoshan basalts have high Nb (8.44–10.30 ​ppm) and TiO2 contents (1.17–1.60 ​wt.%), typical of Nb-enriched basalts. They are slightly younger than regional adakitic rocks and have positive eNd(t) values of +5.2 to +5.7 and are interpreted to be generated by partial melting of a depleted mantle source metasomatized by earlier adakitic melts. Synthesized with coeval arc-related igneous rocks from the southeastern Xing’an Block, we propose that the Duobaoshan high-Mg andesitic tuffs and Nb-enriched basalts are parts of the Late Ordovician and Silurian Sonid Zuoqi–Duobaoshan arc belt, and they were formed by the northwestern subduction of the Nenjiang Ocean. Such a subduction beneath the integrated Xing’an–Erguna Block also gave rise to the East Ujimqin–Xinglong igneous belt in a continental back-arc basin setting. Our new data support an early Paleozoic arc–back-arc model in the northern Great Xing’an Range.

Research subject. Rocks of the Paleozoic Eastern Ural microcontinent and Magnitogorsk island arc occupy a significant part of the Southern Urals and some part of the Middle Urals. The Western Urals are composed of rocks of the ancient Baltic continent and overthrust oceanic rocks. In the Eastern Urals and Trans-Urals rocks of the accretion complexes, oceanic crust, island arcs, the Eastern Ural microcontinent and the Kazakhstan Paleozoic continent are widespread. Rocks are exposed in the Denisov tectonic zone. The Magnitogorsk simatic Island Arc originated in the Ural Ocean, near the Baltic continent, in the early Devonian, developing from the Emsian to the Famennian. A collision between the Magnitogorsk arc and the Baltic continent occurred in the Famennian century. In the pre-Carboniferous age, the Eastern Ural microcontinent was located in the Ural Ocean. In the Tournaisian period, the Eastern Ural microcontinent accreted with the Baltic continent. The Kazakhstan continental massif was located on the other side of the Ural Ocean. The volcanic belt above the subduction zone was active on the edge of the Kazakhstan continent in the Early–Middle Devonian and in the Early Carboniferous. A subduction under the Baltic and Kazakhstan continents consumed most of the crust of the Ural Ocean by the middle of the Bashkir century. As a result, the Baltic continent (together with the Eastern Ural microcontinent) came into contact with the Kazakhstan continent. The formation of folded orogen began in the Moscow century following the collision of sialic terrains.Materials and methods. The research was based on the relevant data obtained by several researchers in 2000–2018 on rock paleomagnetism. Results. The paleolatitudinal positions of the Eastern Ural microcontinent were determined, comprising 5.3 ± 7.4°) in the Middle Ordovician and 8.2 ± 7.2° in the Early–Middle Silurian. The respective paleolatitudinal positions for the Early–Middle Devonian comprised: the Ural margin of the Baltic paleocontinent (7.7 ± 3.7°), the Magnitogorsk island arc (3.2 ± 3.1°) and the Ural margin of the Kazakhstan paleocontinent (20.6 ± 3.8°).Conclusion. According to the analysed paleomagnetic data, in the Early–Middle Devonian, the distance between the latitudes of the margins of the Baltic and Kazakhstan continents was not less than 600 km provided they were in the same hemisphere, and more than 2,300 km provided they were in different hemispheres. The convergence of the terrains was associated with the subduction of the Ural Ocean crust before its closure, which occurred in the Tournaisian century.

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 temp...

Microbialites are organosedimentary rocks that have occurred throughout the Earth's history. The relationships between diverse microbial metabolic activities and isotopic signatures in biominerals forming within these microbialites are key to understanding modern biogeochemical cycles, but also for accurate interpretation of the geologic record. Here, we performed detailed mineralogical investigations coupled with NanoSIMS (Nanoscale Secondary Ion Mass Spectrometry) analyses of pyrite S isotopes in mineralising microbial mats from two different environments, a hypersaline lagoon (Cayo Coco, Cuba) and a volcanic alkaline crater lake (Atexcac, Mexico). Both microbialite samples contain two distinct pyrite morphologies: framboids and euhedral micropyrites, which display distinct ranges of delta S-34 values(1). Considering the sulfate-sulfur isotopic compositions associated with both environments, micropyrites display a remarkably narrow range of Delta(pyr) (i.e. Delta(pyr) equivalent to delta S-34(SO4) - delta S-34(pyr)) between 56 and 62 parts per thousand. These measured Delta(pyr) values agree with sulfate-sulfide equilibrium fractionation, as observed in natural settings characterised by low microbial sulfate reduction respiration rates. Moreover, the distribution of S isotope compositions recorded in the studied micropyrites suggests that sulfide oxidation also occurred at the microbialite scale. These results highlight the potential of micropyrites to capture signatures of microbial sulfur cycling and show that S isotope composition in pyrites record primarily the local micro-environments induced by the microbialite.

The Las Minas area corresponds to an exhumed geothermal system considered a proxy for the deep part of the nearby Los Humeros active geothermal system. The stratigraphic succession is made up of: Palaeozoic-Miocene granitoids, a thick Jurassic- Cretaceous carbonate succession, Neogene lava flows and volcano-sedimentary deposits. Linked to a Miocene magma intrusion, marble and skarn rock-volumes developed by contact metamorphism and geothermal fluid flow. Faults are arranged in SW- and NNW-striking systems. These controlled the morphological evolution and favored Neogene-Quaternary dyke emplacement. Faulting gave rise to a tectonic depression where lacustrine sediments and pyroclastics deposited. Skarn rocks are mainly located at fault intersections and along pre-existing discontinuities, suggesting the role of bedding and/or fractures in channeling deep fluids. Results give inputs for exploration at depth of Los Humeros geothermal system.

Identification of magma sources and their role in the origination of basaltic magmas still remains one of the fundamental petrological problems. Based on new comprehensive isotope–geochemical and mineralogical data, the contribution of a pyroxenite mantle source was recognized for the first time for Oligocene basalts in the northern part of the East Sikhote Alin volcanic belt. The most important indicators of this source are significant variations in the first-row transition elements ratios (Zn/Fe = 11–17 and Zn/Mn = 6–10), Cr/Ni (1.8–6) and the Ni concentration (2000–3600 ppm) in olivine. The behavior of LIL elements suggests the presence of amphibole in a pyroxenite protolith. The obtained data can be used for the correct reconstruction of the magma generation and geodynamic environment in this territory in the Late Cenozoic.

The tectonic transition from subduction to collision is a fundamental process during orogenesis, yet the magmatic expression of this transition and related deep geodynamic processes remain unclear. This study focuses on a newly identified volcanic belt within the Moyun–Zaduo–Sulu area of the North Qiangtang Block and presents new zircon U-Pb data that indicate that this belt formed during the Middle Triassic (247–241 Ma), a time characterized by a regional transition from subduction to collisional tectonism. The volcanic belt is located to the south of a Permian to Early Triassic arc and is dominated by high-K calc-alkaline and peraluminous rhyolites. These rhyolites have low Mg#, Nb/Ta, and δEu values, contain low contents of Sr, have high Rb/Sr and whole-rock eNd(t) values, and show positive zircon eHf(t) values, all of which suggest that they formed from magmas generated by the dehydration melting of juvenile crustal material. The migration of Middle Triassic volcanism in this region was most likely caused by rollback of the subducting Longmucuo–Shuanghu Tethyan oceanic slab. Combining our new data with previously published results of numerical modeling of subduction–collisional processes and regional data from north-central Tibet yields insights into the magmatic expressions and related deep geodynamics of the transition from oceanic subduction to continental collision. This combination of data also suggests that variations in oxygen fugacity can be used as a proxy for the discrimination of magmatism related to subduction, the transition from subduction to collision, and collisional tectonism.

A morphological study based on light microscopy and scanning electron microscopy describing three new Pseudostaurosira species from mountain streams in Central Mexico is presented herein. Epilithon and water samples for physico-chemical analyses were collected from eleven mountain streams in the Basin of Mexico, located within the Trans-Mexican Volcanic Belt. The bipolar Pseudostaurosira carmonae and P. caballeroae, and the tripolar P. iztaccihuatlii are described from Coaxcacoaco, San Rafael and Ameca streams, located at elevations above 2600 m. These streams were characterized by cold, well oxygenated, and neutral to slightly alkaline water with low conductivity and low nutrient concentration, descending from Mount Tlaloc and Iztaccihuatl volcano in the south eastern part of the basin. No teratological features were observed in either of these taxa, nor an intermediate state between the co-occurring bipolar and tripolar forms. The ultrastructure features (pore structure and spines position) were consistent with the defining characteristics of the genus Pseudostaurosira. This study contributes to further unravelling the freshwater diatom flora of Mexico, while denoting the importance of protecting and studying aquatic ecosystems in this overpopulated region of the Mexico.

This study was conducted to identify the origin, hydrogeochemical processes and evolution of groundwater in a tectonic valley. This study was carried out with the aim of quantifying the proportions of groundwater flows contributing to the water chemistry abstracted in a zone of convergence favored by the presence of active faults. The study area is located in the Trans-Mexican Volcanic Belt. End members methodology was applied to identify the mixing of hydrothermal with fresh groundwater, where changes in the aquifer geology result in distinct groundwater chemical signatures. Ternary mixing was quantified using conservative elements. Moreover, other evolutionary processes, such as ion exchange and silicate weathering occur due to changes in the geology of the area. In ternary mixing, each of the end members is associated with the lithology through which it circulates. The local flow contributes 70% of the water to the system, the intermediate flow contributes 14%, and the regional flow contributes 16%. Three types of water are produced: Na-HCO3, due to the interaction of water with volcanic rocks of rhyolitic composition, Na-Mg-HCO3, due to the interaction of water with volcanic rocks of basaltic-andesite composition, and Ca-HCO3, due to the interaction of water with sedimentary calcareous rocks.

Symptoms of forest decline, apparently due to climate change, have become evident in the last 10 years on the Trans-Mexican Volcanic Belt and northwestern temperate forest of Mexico, particularly at the xeric (low elevational) limit of several forest tree species. We review and provide recent evidence of massive infestation of timberline Pinus hartwegii Lindl. by the mistletoes Arceuthobium globosum Hawksw. & Wiens and Arceuthobium vaginatum (Humb. & Bonpl. ex Willd.) J.Presl; insufficient Abies religiosa (Kunth) Schltdl. & Cham. seedling recruitment at the Monarch Butterfly Biosphere Reserve; indications of inbreeding and defoliation in endangered Picea chihuahuana Martínez, Picea martinezii T.F. Patt., Picea mexicana Martínez, and extreme southern populations of Pseudotsuga menziesii (Mirb.) Franco; and the incidence of unusual pest and disease outbreaks (e.g., Dendroctonus Erichson, 1836 spp., Neodiprion autumnalis Smith, and Phytophthora cinnamomi Rands) in several conifer and oak species. We also discuss a difficult question: Is natural genetic variation sufficient to provide populations with the adaptive variation necessary to survive the natural selection imposed by projected climate change scenarios, or will phenotypic plasticity be exhausted and populations decline? Controversial ex situ conservation within natural protected areas, assisted migration, and translocation of species ensembles are discussed as options by which to accommodate projected climatic change impacts on the management and conservation practices of the megadiverse Mexican temperate forest.

The article is devoted to the results of mineralogical and geochemical studies of argillizites at Compleksnoe Au–Ag ore occurrence, localized on the southern flank of the Kajenmyvaam volcanic uplift in the inner zone of the Late Cretaceous marginal–continental Okhotsk-Chukchi volcanic belt (OChVB). At the ore occurrence, a series of isometric (oval) in plan view argillizite “hats” with diameters of 200 to 900 m are described. They are composed of red and light gray clay formations and accompanied by complex (Au–Ag–Mo–Cu–Pb–Zn–Bi–Sn) anomalies. In the recent relief, argillizite “hats” are characterized by gently sloping domes and crown subvolcanic bodies of granitoids and explosive breccias. A series of argillizite “hats” is surrounded by elongated lenticular bodies of secondary quartzites, which form the outer boundary of a large annular volcanostructure. The argillizites are composed of the following minerals: illite-smectite (mixed-layered formation), kaolinite, muscovite, jarosite, quartz, and rutile. The average content of Au and Ag in bulk samples are 0.06 and 0.075 g/t, respectively. Au is found in invisible form. According to the geological and geochemical data, argillizite “hats” record a near-surface (up to 300 m), slightly eroded, level of a large porphyry-epithermal mineral-forming system.

Study object. The role of strike-slip fault tectogenesis in magmatism of the large (North Eastern Primorye) fragment of the Eastern Sikhote-Alin volcano-plutonic belt (ESAVPB) is studied. Materials and methods. The materials of geological mapping and field geostructural thematic-line research are used. Study methods are based on the concept of the geostructural patterns being formed by lateral, namely, strike-slip movements of crustal blocks. Results. There is recognized the system of the NE-trending sinistral faults, whose activation taken place during two stages. The pre-Late-Cretaceous fold-and-strike-slip-fault (orogenic) stage is characterized by the widely developed fold system within the stratified formations covering active strike-slip faults of the pre-Mesozoic consolidated basement. By the Late Cretaceous, the strike-slip faults cut the fold system into narrow blocks, creating the preconditions for the strike-slip faults’ activation during the next destructionand-strike-slip-fault (riftogenic) stage (Late Cretaceous – Cenozoic). During the latter, the strike-slip faults were activated under transtension (strike slip with extension) with formation of volcano-tectonic extension structures (VTES) nearcrosswise the strike-slip faults. The VTES played, on the one hand, the role of magma-feeding channels. On the other hand, the extension caused preconditions for formation of the depression subsidences that accumulated large volumes of the volcanics covering and «crosslinking» the VTES, resulting in wide development of volcanic covers within the ESAVPB. Conclusion. The VTES’ opening is thereby the effect of lateral (strike-slip) displacements of continental geoblocks that is not consistent with a priori ideas of the development of the East Sikhote-Alin volcano-plutonic belt under the oceanic plates’ subduction. The resulting materials complement the formulations according to which the East Asian volcanic belt formed under the structural-and-dynamic conditions being caused by the evolution of the East Asian global strike-slip fault zone resulting from displacement of the Asian continent to the south-west under the Earth’s rotational geodynamics.

Recent botanical explorations in Durango, Mexico, led to the discovery of a new species endemic to this state: Cunila socorroae (Lamiaceae), which is consequently here described and illustrated. The new species is morphologically most similar to C. jaliscana and C. lythrifolia. It can be distinguished from both in having less flowers per cyme, lanceolate floral bracts, longer calyx tube, and lanceolate calyx teeth and longer. It also deviates from C. jaliscana by the fewer floral internodes, longer floral bract, and generally longer corolla tube. Also, the exfoliating bark, white corollas and internally pubescent, make a clear distinction against C. lythrifolia. The distinctive geographic distribution of these species is an additional support to their separation; the new species is exclusive of the middle portion of Sierra Madre Occidental, whereas C. jaliscana is restricted to the northernmost portion of Sierra Madre del Sur, and C. lythrifolia, though mostly occurs in eastern Tans-Mexican Volcanic Belt, has also some localities in southern Chihuahuan Desert, Sierra Madre Oriental and Sierra Madre del Sur.

This article considers the conditions for the Au–Ag epithermal mineralization of the Arykevaam volcanic field (AVF) located in the middle of the Chukotka segment of the inner zone of the Okhotsk–Chukotka volcanic belt (OChVB). The results of thermo- and cryometric studies of fluid inclusions in quartz showed that epithermal mineralization was deposited by homogeneous hydrothermal fluids with low salt concentrations (0.3–1.5 wt % NaCl eq.), fluid densities of 0.77–0.83 g/cm3, at moderate temperatures, 267–229°C. In the fluid, among the cations, the main role is played by (g/kg H2O): K (1.8–10.2), Ca (4.7–12.9), and Na (3.7–5.8), and among the anions by SO42– (16.1–20.3), Cl (6.0–20.0), and $${\text{HCO}}_{{\text{3}}}^{ - }$$ (2.4–14.7). The main indicators of the fluid composition are CO2/ CH4 = 315–2818, Na/K = 0.37–3.18, and K/Rb = 324–743. According to water extracts, the real fluid salinity of the Arykevaam deposit (4.5–6.1 wt %) is significantly higher than that found by microthermometry, since the fluid is dominated by sulfates, not sodium chloride. The results allow us to attribute the mineralization studied here to the high sulfidation epithermal class.

The volcano rabbit, Romerolagus diazi, is endemic to a small region along the Trans-Mexican Volcanic Belt in central Mexico. Although its distribution in the volcanic fields of the Sierras Nevada and Chichinautzin is not debated, its occurrence in the Nevado de Toluca volcano has been controversial. In this study, we used a species identification tool using DNA isolated from fecal pellets in order to corroborate the occurrence of volcano rabbit in the Nevado de Toluca. Both PCR assays and phylogenetic analysis of fragments of cytochrome b and D-Loop mitochondrial genes provide evidence that although the morphology of collected pellets resemble those of R. diazi, they instead correspond to a Sylvilagus species. These results support the hypothesis that R. diazi is not currently distributed in the Nevado de Toluca.

—Mesozoic‒Cenozoic tectonic zoning and its evolution are characterized by analysis of geological data on the Black Sea–Caucasus–Caspian region. The following tectonic zones were located in succession to the north of the Mesotethys Ocean in the Early Jurassic: the mobile zone on the Hercynian basement; the Moesian–Black Sea–Trans-Caucasus minor plate with the Precambrian–Baikalian basement, which experienced the Hercynian tectonic and magmatic reworking in the Lesser Caucasus; the relatively deep-water Crimean–Caucasus–South Caspian Trough on the continental crust that thinned in the process of its extension; and the southern margin of the Scythian Plate with a thin sedimentary cover. In the Caucasus, the southern and northern slopes of the deep-water axial trough have been identified, where thick shelf deposits accumulated. Subduction began in the northern margin of the Mesotethys in the Bajocian and island-arc volcanism occurred in the Somkheti–Karabakh zone and Eastern Pontides, the Trans-Caucasus part of the Moesian–Black Sea–Trans-Caucasus Plate, and the southern slope of the Crimean–Caucasus–South Caspian Trough. The volcanism in the Somkheti‒Karabakh zone and the Eastern Pontides lasted into the Cretaceous. The area of island-arc volcanism was inherited by the Eocene collisional volcanic belt. The Crimean part of the Crimean–Caucasus–South Caspian Trough and its northern slope in the Caucasus underwent Cimmerian deformation and shelf facies accumulated there after deformation up to the Miocene, while relatively deep-water sedimentation occurred in the Caucasus–South Caspian part of the Crimean–Caucasus–South Caspian Trough. The Western and Eastern Black Sea basins of extension originated in the Cretaceous on the continental crust of the Moesian–Black Sea–Trans-Caucasus Plate, which thinned in the basins as they were filled by Late Cretaceous, Paleogene, and Miocene marine deposits. In the Pliocene–Quaternary, total undifferentiated subsidence and sedimentation occurred in the Black Sea, and subsidence of the South Caspian, Azov‒Kuban, and Terek‒Derbent basins accelerated. Several phases of Middle and Late Miocene fault–fold deformation formed local uplifts in the mountainous parts of the region. The total uplift of mountain systems occurred in the Pliocene–Quaternary. The formed crustal structures and the velocity inhomogeneities in the upper mantle were compared, which showed that many inhomogeneities were obliterated by sublithosphere flows that spread out of the Ethiopian–Afar superplume. In mantle volumes, where the flow intensity weakened, relics of subducted slabs remained. They are slabs of the Neotethys in the Zagros and the Mesothethys in the Lower Kura Basin, and slabs of the Scythian Plate lithosphere underthrust under the Central Caucasus and more weakly under Steppe Crimea during the Hercynian subduction.

Haemaphysalis leporispalustris is a hard tick species that have been recorded mainly parasitizing rabbits and birds across the Nearctic and Neotropical regions. Particularly in Mexico, most of the records come from historical collection journeys from before the 1960s. In this paper, we bring new geographical records for this species in Mexico to provide the first genetic data in the country through the amplification of the 16S, COI, and 18S genes, and the detection of a rickettsial agent as well.

espanolPara el desarrollo de un campo geotermico, el conocimiento de la distribucion de fracturas, la hidrologia y la evolucion tectonica del sitio a traves de la caracterizacion estructural del sistema natural es un requisito previo a la perforacion de pozos exploratorios. Fallas y fracturas representan vias preferenciales por el flujo de fluidos en el subsuelo y pueden ser detectadas mediante investigaciones geologicas en la superficie y geofisicas en el subsuelo. Una anomalia magnetica positiva y de forma sub-circular en planta se encuentra en el medio del lago Cuitzeo, Mexico. A traves de un levantamiento geomagnetico dentro y alrededor del area que comprende la anomalia tratamos caracterizar el reservorio geotermico que, al sur del lago, esta notificado por manifestaciones hidrotermales. Utilizando filtros computacionales basados sobre el uso de operaciones con las derivadas de valores de campo a los datos magneticos grabados, hemos puesto en luz algunas de las estructuras que influencian la circulacion de los fluidos en el sistema geotermal. Nuestra atencion se focalizo sobre fallas ~N-S and E-W, pertenecientes respectivamente a la tectonica Basin & Range (B&R) y a la del Cinturon Volcanico Mexicano (CVM). Segun nuestra interpretacion, la interaccion de dos o mas estructuras de diferentes origenes (B&R y CVM), ademas del entorno geodinamico especifico (subduccion de zona de fracturas), facilito el surgimiento de cuerpos magmaticos basicos del profundo que, bloqueados por la capa argilosa de sedimentacion lacustre del Cuitzeo, dieron lugar, enfriandose lentamente, al sistema geotermal y contribuyeron a la formacion de la anomalia magnetica. EnglishFor the development of a geothermal field, the understanding of fracture distribution, hydrology and tectonic evolution of the site through structural characterization of the natural system is a prerequisite to the drilling of exploratory wells. In order to image the underground shape of approximately planar, relatively permeable, geologic features (fractured rock-volumes around fault planes) and to detect hot rock volumes, geologic and geophysical surveying is carried out. A strong positive magnetic anomaly, nearly circular in 2D, characterizes the middle of Cuitzeo lake, Michoacan, Mexico, apparently not related with a volcanic structure on the surface. It may instead be associated to the geothermal system in the area which yields at present hot springs at the southern shore of the lake, at boiling temperatures. In this study, we conducted a ground magnetic survey within and around Lake Cuitzeo with the aim of characterizing this anomaly, following one-kilometer-spaced survey-lines and covering an area of approximately 100 km2. To enhance interpretability, we applied computational filters based on directional derivatives (vertical and horizontal) to our reduced-to-pole magnetic-field raw data – illuminating underground faults and other permeable pathways for fluids and delineating contacts between differently magnetized rocks, through maxima and minima on maps. While most filters used were able to define the basic configuration of the system, we found that computational filters working with ratios of derivatives (vertical and horizontal) were able to better account for the depth of a magnetic source. Also, faults were more clearly imaged on maps. We could mainly highlight ~E-W and ~N-S striking fault-systems, respectively belonging to the ~N-S TransMexican Volcanic Belt extensional tectonics and to the ~E-W Basin & Range, both with lateral movements and still active today. We interpret the magnetic source as a magma body (related to the volcanism of Michoacan-Guanajuato Volcanic Field) that remained trapped during its ascent under Cuitzeo lacustrine sedimentation, during the last 500 ka, forming the once stronger geothermal system.

Understanding the anatomy of magma plumbing systems of active volcanoes is essential not only for unraveling magma dynamics and eruptive behaviors but also to define the geometry, depth, and temperature of the heat sources for geothermal exploration. The Pleistocene–Holocene Los Humeros volcanic complex is part of the eastern Trans-Mexican Volcanic Belt (central Mexico), and it constitutes one of the most important exploited geothermal fields in Mexico with ca. 90 MW of produced electricity. With the aim to decipher the anatomy (geometry and structure) of the magmatic plumbing system feeding the geothermal field at Los Humeros, we carried out a field-based petrological and thermobarometric study of the exposed Holocene lavas. Textural analysis, whole-rock major-element data, and mineral chemistry are integrated with a suite of mineral-liquid thermobarometric models. Our results support a scenario characterized by a heterogeneous multilayered system, comprising a deep (depth of ca. 30 km) basaltic reservoir feeding progressively shallower and smaller discrete magma stagnation layers and batches, up to shallow-crust conditions (depth of ca. 3 km). The evolution of melts in the feeding system is mainly controlled by differentiation processes through fractional crystallization (plagioclase + clinopyroxene + olivine + spinel). We demonstrate the inadequacy of the existing conceptual models, where a single voluminous melt-controlled magma chamber (or “Standard Model”) at shallow depths was proposed for the magmatic plumbing system at Los Humeros. We instead propose a magmatic plumbing system made of multiple, more or less interconnected, magma transport and storage layers within the crust, feeding small (ephemeral) magma chambers at shallow-crustal conditions. This revised scenario provides a new configuration of the heat source feeding the geothermal reservoir at Los Humeros, and it should be taken into account to drive future exploration and exploitation strategies.