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The Chapultenango trachybasalt, located in the modern Chiapanecan Volcanic Arc (CVA) in southern Mexico, is constituted by two mafic dykes. Dyke 1 shows relatively low Th/Nb and Pb/Nb ratios compared to other CVA rocks, and exhibits primitive chemical characteristics (e.g. #Mg >65, Ni > 200, Cr > 600) typical of Ocean Island Basalts (OIB). On the other hand, Dyke 2 is almost in touch with Dyke 1, is calc-alkaline, and more evolved than Dyke 1, similar to other rocks found in El Chichón volcano. Hence this work is mainly focused on Dyke 1 that represents the least differentiated melt observed so far in the Chiapanecan Volcanic Arc, and its composition helps in characterizing the mantle source in this region. Dyke 1 OIB-like magma was likely generated by a slab window resulting from the tearing of the Cocos slab along the Tehuantepec Ridge. This tearing was likely caused by differences in physical properties between the northern and southern segments of the Cocos plate, which can be attributed to their age difference (10 Ma) and velocity convergence. This configuration permits the ascent of OIB-like melts from an enriched and relatively deep mantle, which was metasomatized by subduction components (2–6%) and then underwent partial melting (∼5%), although contamination by crustal rocks (e.g., Chiapas Massif) could not be ruled out. The resulting primitive melt therefore would have ascended rapidly, carrying some phaneritic and gabbroic fragments that exhibit similar chemical characteristics to the Chiapanecan Volcanic Arc rocks. • OIB-like magmas were generated in the Chiapanecan Volcanic Arc in southern Mexico. • Tehuantepec ridge produced a slab window in the Cocos slab allowing the ascent of enriched melts. • 2% mantle melting plus 0.8% subduction agents reproduce the Chapultenango magmas. [ABSTRACT FROM AUTHOR]

La Primavera is a Quaternary rhyolitic volcanic complex located in the northwestern part of the Trans-Mexican Volcanic Belt. It consists of lavas, domes, and composite volcanoes emplaced between 143.5 and 25.5 ka, both inside and outside the caldera rim. Post-caldera volcanism occurred between ∼95 and 25.5 ka, erupting 2 lavas, 22 domes, and 5 composite volcanoes. Here, we present new petrographic descriptions, mineral chemistry, and whole-rock chemical compositions of juvenile fragments from the post-caldera pyroclastic units originated from the Nejahuete, San Miguel, Planillas, and Tajo composite volcanoes. Based on their major, trace, LREE (light rare earth elements), and isotopic compositions, we identify four compositional groups: 1) Colli dome (low-LREE and low-Zr), 2) E to N pyroclastic units (low-LREE and intermediate-Zr), 3) B to D pyroclastic units, and 4) GP to A pyroclastic units (high-LREE and high-Zr). Based on their composition, we propose a three-step model to explain the genesis of the post-caldera magmas: 1) injection of a calc-alkaline subduction-related melt modified by an OIB mantle-derived component (e.g., the Gachupín basaltic-andesite) into the magmatic chambers and generation of at least two crystal mushes, one formed from crystallization of a mantle-derived magma (i.e, Gachupín), and the other from a differentiated residual liquid derived from the same mantle-derived magma, 2) formation of the REE-poor and REE-rich compositions of the La Primavera magmas by different degrees of partial melting of the crystal mushes, and 3) generation of the REE-intermediate compositions of the La Primavera magmas by mixing of the REE-poor and REE-rich melts produced from partial melting of the crystal mushes to generate the LREE and Zr variations of the La Primavera magmas. • Post-caldera activity of La Primavera erupted four chemically different rhyolitic magmas. • Chevkinite and Fe-hedenbergite crystals occur in the post-caldera rhyolitic rocks. • Mixing of interstitial liquids obtained from variable partial melting of different crystal mushes took place. • Three different magma chambers fed the post-caldera rhyolitic magmas of La Primavera. [ABSTRACT FROM AUTHOR]

Abstract Previous studies on Jumento volcano, based on radiocarbon dating and comparative morphometric analysis, suggest that it could be the youngest volcano of the Sierra Chichinautzin. Here we establish a new chronology of the emplacement of the Late Holocene lava flows of Jumento volcano using in situ -produced 10Be cosmic ray exposure (CRE) dating of quartz xenocrysts to test this hypothesis. Depending on the choice of the cosmogenic nuclide production parameters in the exposure age calculators used, the mean 10Be CRE ages ranges between 1.86 ± 0.68 ka and 2.41 ± 0.97 ka for the inner lava flow and between 1.90 ± 0.29 ka and 2.49 ± 0.41 ka for the breakout lava flow. These preliminary mean 10Be CRE ages confirm that the Jumento volcano is one of the youngest volcanoes of the Sierra Chichinautzin although slightly older than the Xitle volcano. This first 10Be eruption chronology of the Sierra Chichinautzin shows that 10Be CRE dating represents an alternative approach to date volcanic rocks, not only for the Sierra Chichinautzin but also for other volcanic fields, especially when no charcoal or paleosoils are available for radiocarbon dating. Furthermore, it suggests that in situ -produced cosmogenic nuclide dating has considerable potential to throw light on the volcanic history and eruption recurrence of this volcanic field, in order to provide enough data for the mitigation of the hazards and related risks in Mexico City, the city of Cuernavaca and the small towns around the volcanic field. Highlights • We provide a new chronology of Jumento volcano (Sierra de Chichinautzin, Mexico). • We used in situ -produced 10Be cosmic ray exposure (CRE) dating. • Jumento volcano is one of the youngest volcanoes of the Sierra de Chichinautzin. • 10Be cosmic ray exposure (CRE) dating has considerable potential to date volcanic products worldwide. [ABSTRACT FROM AUTHOR]

Rhyolitic magmas in occasions can be related to explosive eruptions in active volcanoes that may not exhibit precursory signals, making them very dangerous for the surrounding communities. To understand the pre-eruptive conditions of such magmas it is important to decipher the mechanisms capable to produce these explosive events. In this study we analyzed the pre-eruptive conditions of Guangoche stratovolcano, located to the southwest of the Los Azufres Volcanic Field, in the central part of the Trans-Mexican Volcanic Belt. During the late Pleistocene Guangoche generated three Plinian-subPlinian eruptions and some effusive eruptions, all of them involving high-silica rhyolitic magmas. One of these Plinian events (VEI 5) occurred ~29 ka and deposited the White Pyroclastic Sequence (WPS). This eruption ejected ~0.7 km 3 (DRE volume) of rhyolitic magma and deposited a pumice fallout followed by three pumice-rich pyroclastic density currents. Petrography, combined with mineral composition, melt inclusions, and water-saturated phase equilibria experiments were used to determine the evolution of the magma storage of the WPS event. Prior to the eruption, the magma was a crystal-poor (~14 vol%) rhyolite, containing the following mineral assemblage: biotite, Fe-Ti oxides, amphibole, sanidine and quartz, set in a rhyolitic matrix (77.3 wt% SiO 2 ), with low-Ba (121 ± 16.7 ppm), Eu (0.15 ± 0.02 ppm) and Sr (37 ± 7 ppm). Based on Fe-Ti oxythermometers and phase equilibria experiments, we determine that the magma was stored between ~75 and 100 MPa (3–4 km depth), at a temperature of 769 ± 8 °C. Moreover, H 2 O-CO 2 dissolved in quartz melt inclusions and the textural features of the mineral assemblage of the WPS products, provided insights of the presence of a quartzo-feldspathic crystal-mush, located at minimum depths between 4.3 and 9.5 km (98–218 MPa). Large sanidine, quartz, plagioclase, and amphibole phenocrysts and mineral clots in the WPS rocks represent assimilated parts from this mush by a melt extraction process probably triggered by the arrival of a relatively hotter magma at the base of the crystal-mush, which in turn caused reheating and partial melting of the quartzo-feldspathic crystal-mush, generating the 29 ka rhyolitic WPS magma. [ABSTRACT FROM AUTHOR]

The Chichinautzin Volcanic Field is situated at the southern limit of the Basin of Mexico and the Metropolitan area of Mexico City, the third most populated city around the world. The Chichinautzin Volcanic field holds more than 220 monogenetic volcanoes. Xitle is the youngest of these with an estimated age of 1.6 ky BP. Xitle's eruptive activity took place during the Mesoamerican Mexican Pre-classic period and is related to the destruction of Cuicuilco Archaeological Site, the oldest civilization known in Central Mexico. However, there are still several regional cones that have not been dated. Based on 14 C ages, stratigraphic and geomorphologic criteria, we conclude that the Jumento volcano, located to the west of Xitle, is one of the youngest cones of the Chichinautzin Volcanic Field. The Jumento volcano has a basaltic andesite composition, and its eruptive activity was initially hydromagmatic, followed by Strombolian and finally effusive events occurred recorded through: (1) a sequence of hydromagmatic pyroclastic surges and ashfall layers emplaced at a radius of > 5 km from the crater with charcoal fragments at its base; this activity built the Jumento's cone with slopes of 32°; and (2) lava flows that breached the southern part of the cone and flowed for up to 2.5 km from the vent. The resulting 14 C ages for this volcano yielded a maximum age of ~ 2 ky BP. Morphometric analysis indicates that the state of degradation of Jumento cone is similar to the Xitle, suggesting that the Jumento could be in the state of degradation of a volcanic structure of similar age or younger adding credence to the probable radiocarbon age of ~ 2 ky BP for the Jumento edifice. [ABSTRACT FROM AUTHOR]

The San Lorenzo Tezonco deep well, drilled in 2012 by “Sistema de Aguas de la Ciudad de México” (Water Supply System of Mexico City) in the Mexico Basin to a depth of 2008m, offers an excellent opportunity to explore the subsurface stratigraphy and general geology of the region. Unfortunately, only chipped samples from this well were recovered, which were examined and analyzed for whole-rock chemistry, 40Ar/39Ar, and U–Pb zircon geochronology, in order to reconstruct the lithology of the well. Contrary to previous deep wells of the Mexico Basin, no basement sedimentary rocks were found in this one. While the upper 70m are composed of lacustrine sediments associated with Lake Texcoco, volcanic rocks make up the majority of the well and range in age from more than 18Ma to 0.25Ma. Andesitic lavas are the most abundant products of the stratigraphic column, followed by acidic products represented by dacitic and rhyolitic lavas and ignimbrite deposits. Less abundant are basaltic andesite lavas appearing in the upper and lower parts of the column. The thickest sequence of the well is represented not only by Miocene volcanic rocks ranging from 5 to 17Ma, suggesting a period of intense volcanic activity in this area producing mainly andesitic lavas, but also by thick rhyolitic ignimbrite deposits dated at 5Ma. These deposits suggest the presence of a caldera structure, probably buried by subsequent volcanic products and lacustrine sediments. Trace element concentrations suggest that volcanism is likely produced in a subduction environment with typical negative anomalies of Nb, Ta, Ti, and P and positive anomalies in Pb and Cs. We correlated the well units with units outcropping in mountain ranges in the surrounding area, with the recognition of the following units or formations: Eocene Andesite, San Nicolás Basaltic Andesite, Tepoztlán Formation, Miocene Volcanism, Sierra de las Cruces, and Chichinautzin Volcanic Field products. By correlating the two closest deep wells (Mixhuca and Tulyehualco) we conclude that the San Lorenzo Tezonco well is located in a graben-like structure hosting the Santa Catarina volcanic range. [ABSTRACT FROM AUTHOR]

The Malinche Pumice II is a fallout deposit produced by a Plinian-type eruption during the Pleistocene-Holocene at La Malinche volcano. La Malinche (4461 masl) is an active stratocone located in central Mexico, in the Trans-Mexican Volcanic Belt province. It is 26 km to the NE of the City of Puebla and 22 km to the SE of the City of Tlaxcala. The Malinche Pumice II was produced by one of the largest explosive eruptions of this volcano, involving a dacitic magma (63.6–65.3 wt% SiO 2 , anhydrous basis) with a mineral assemblage of plagioclase + amphibole + Fe Ti oxides and ± biotite phenocrysts. Larger plagioclase crystals are up to 1.2 mm in diameter, with resorbed margins and complex zoning (An 26 to An 43), whereas microcrysts are euhedral with homogeneous composition (An 42 to An 55). Amphibole is mainly magnesio-ferri-hornblende (Mg# = 0.65–0.82) and lesser amounts of pargasite. Geothermometry performed using Fe Ti oxides yields an average temperature of 873 ± 2 °C and oxygen fugacity of 1.8 units above the NNO buffer. Amphibole geothermobarometry yields a lower temperature (809 ± 19 °C) and a pressure of 230 ± 100 MPa, assuming 4.4 wt% of H 2 O. Considering an average density of 2650 kg/m3 for the upper crust in central Mexico, the storage region of the Malinche Pumice II dacitic magma was located at 8 ± 2 km depth. Biotite could be antecrystic or xenocrystic in origin, based on its reacted texture, large sizes (0.85–2 mm), and reaction rims. Similarly, pargasite that provides higher temperature estimates (900 ± 18 °C) and low anorthite plagioclase (An 26) could also be antecrysts or xenocrysts. The Plinian eruption was likely triggered by an input of a hotter and deeper magma batch that overpressurized the dacitic magma system that eventually provoked vesiculation and fragmentation. The eruption shifted to a hydromagmatic style because of external water's entrainment that decreased the vesicularity of pumice. Our results are in good agreement with recent seismicity recorded at depths of ~7 km probably associated with activity of the Malinche's magmatic system. • Malinche volcano located in the TMVB, central Mexico. • Pumice Malinche II is one of the largest eruptions from Malinche volcano. • Plagioclase, amphibole and Fe Ti oxides is the mineral assemblage of the MPII samples. • Dacitic magma of the MPII eruption was stored at 2 kb, 873 °C, and NNO + 1.77. [ABSTRACT FROM AUTHOR]

Abstract: The Nevado de Toluca volcano in Central Mexico has been active over the last ca. 42ka, during which tens of km3 of pyroclastic material were erupted and two important Plinian-type eruptions occurred at ca. 21.7ka (Lower Toluca Pumice: LTP) and ca. 10.5ka (Upper Toluca Pumice: UTP). Samples from both the LTP and UTP contain plagioclase, amphibole, iron-titanium oxides, and minor anhedral biotite, set in a vesicular, rhyolitic, glassy matrix. In addition, UTP dacites contain orthopyroxene. Analysis of melt inclusions in plagioclase phenocrysts yields H2O contents of 2–3.5wt.% for LTP and 1.3–3.6wt.% for UTP samples. Ilmenite–ulvospinel geothermometry yields an average temperature of ~868°C for the LTP magma (hotter than the UTP magma, ~842°C; Arce et al., 2006), whereas amphibole–plagioclase geothermometry yields a temperature of 825–859°C for the LTP magma. Water-saturated experiments using LTP dacite suggest that: (i) amphibole is stable above 100MPa and below 900°C; (ii) plagioclase crystallizes below 250–100MPa at temperatures of 850–900°C; and (iii) pyroxene is stable only below pressures of 200–100MPa and temperatures of 825–900°C. Comparison of natural and experimental data suggests that the LTP dacitic magma was stored at 150–200MPa (5.8–7.7km below the volcano summit). No differences in pressure found between 21.7ka and 10.5ka suggest that these two magmas were stored at similar depths. Orthopyroxene produced in lower temperature LTP experiments is compositionally different to those found in UTP natural samples, suggesting that they originated in two different magma batches. Whole-rock chemistry, petrographic features, and mineral compositions suggest that magma mixing was responsible for the generation of the dacitic Plinian LTP eruption. [Copyright &y& Elsevier]

Abstract: The Tacaná Volcanic Complex, located on the Mexico–Guatemala border, has had numerous small historical explosions, the latest being a phreatic explosion in 1986. The stratigraphic record, however, suggests that much more voluminous eruptions have occurred in the past. Here, we document one such eruption, the Sibinal Pumice deposit, which occurred ca. 23,540years B.P. The deposit consists of two pumice-rich units: 1) a lower stratified member (SM) that consists of at least seven, normally graded fall layers, interbedded with pyroclastic wet surge layers; and 2) an upper massive member (MM), made up of a single fall deposit. Both members can reach up to 2.5m in thickness and are separated by a single massive, indurated, yellowish, pumice-rich reworked layer. SM was dispersed to the northeast (N70°E), with its 6-cm isopach covering an area of 275km2, whereas MM was dispersed to the north (N22°E), with its 70-cm isopach covering an area of ca. 330km2. Yellow, vesicular pumice fragments, light-gray lithics, and hydrothermally altered (red and black) dense lithics are abundant in both members, although altered lithics are more abundant at the base of each, reaching 15vol.%. Pumice compositions range from basaltic to andesitic (48–61wt.% SiO2, anhydrous basis), but are highly altered. They contain plagioclase (andesine–labradorite), augite, hypersthene, Fe–Ti oxides, and rare amphibole. No compositional or mineralogical differences occur between the units indicating a common magma source during the same eruption. The Sibinal Pumice eruption started with a weak, pulsating column that reached at most 19km in height, ejecting 2.9km3 of tephra (1.1km3 DRE) at an average mass discharge rate of 4.7×107 kg/s, with repeated hydromagmatic explosions that generated wet surges down the slopes of the volcano. The eruption ceased for a while during which rainfall generated a widespread lahar that eroded the top of SM. The eruption began anew with a sustained and stable Plinian column that ejected 4.6km3 (1.9km3 DRE) of tephra at a mass discharge rate of 8.1×107 kg/s. The lack of any compositional differences in the magma suggests that the change in eruptive style was driven by influxes of external water provoking hydromagmatic explosions that cleared the conduit, then, the system changed to dry system and the eruption style changed from pulsating to stable Plinian. As the conduit became wider, the mass discharge rate also increased. [Copyright &y& Elsevier]

Abstract: Zempoala is an extinct Pleistocene (∼0.7–0.8 Ma) stratovolcano that together with La Corona volcano (∼0.9 Ma) forms the southern end of the Sierra de las Cruces volcanic range, Central Mexico. The volcano consists of andesitic and dacitic lava flows and domes, as well as pyroclastic and epiclastic sequences, and has had a complex history with several flank collapses. One of these collapses occurred during the late Pleistocene on the S–SE flank of the volcano and produced the Zempoala debris avalanche deposit. This collapse could have been triggered by the reactivation of two normal fault systems (E–W and NE–SW), although magmatic activity cannot be absolutely excluded. The debris avalanche traveled 60 km to the south, covers an area of 600 km2 and has a total volume of 6 km3, with a calculated Heim coefficient (H/L) of 0.03. Based on the textural characteristics of the deposit we recognized three zones: proximal, axial, and lateral distal zone. The proximal zone consists of debris avalanche blocks that develop a hummocky topography; the axial zone corresponds with the main debris avalanche deposit made of large clasts set in a sandy matrix, which transformed to a debris flow in the lateral distal portion. The deposit is heterolithologic in composition, with dacitic and andesitic fragments from the old edifice that decrease in volume as bulking of exotic clasts from the substratum increase. Several cities (Cuernavaca, Jojutla de Juárez, Alpuyeca) with associated industrial, agricultural, and tourism activities have been built on the deposit, which pose in evidence the possible impact in case of a new event with such characteristics, since the area is still tectonically active. [Copyright &y& Elsevier]

Abstract: The Nevado de Toluca volcano erupted explosively approximately 12.1 ka ago, producing a Plinian–subplinian eruption that deposited the Middle Toluca Pumice (MTP). The MTP consists of white and gray juvenile pumice, gray dense juvenile lapilli, and red altered lithic lapilli. The pumice is dacitic (63.54–65.06 wt.% SiO2) with phenocrysts of plagioclase>orthopyroxene>hornblende±ilmenite and titanomagnetite, and biotite xenocrysts set in a groundmass of rhyolitic glass (70–71 wt.% SiO2). The MTP has a dispersal axis to the ESE covering an area of 92 km2, with a minimum volume of 1.8 km3 (DRE). Stratigraphic relations, grain size, componentry, and vesicularity analyses suggest that the eruption occurred in five major phases: (1) an opening magmatic phase that generated a 20-km-high Plinian column dispersed to the SE; (2) a hydromagmatic explosion followed with the establishment of a subplinian eruptive column (18–19 km high) dispersed tephra to the SE and gradually waned; (3) hydromagmatic explosions emplaced dilute pyroclastic density currents followed by the formation of an eruptive column of unknown height; (4) immediately after, a new magmatic explosion established another eruptive column; and (5) the collapse of the latter column generated two pumiceous pyroclastic density currents that were fully dilute proximally, but transformed into two granular-fluid pyroclastic currents that traveled 19 km from the source. [Copyright &y& Elsevier]

In central Mexico, remnants of the early volcanic activity in the Trans-Mexican Volcanic Belt (TMVB) are exposed at Sierra de Guadalupe in the northern part of the Mexico City Basin and to the south in the Tepoztlán, Malinalco, Tenancingo, and Chiltepec areas. A few published studies indicate a general early to middle Miocene age for some of these volcanic centers. We present new geologic, geochronologic and geochemical data that refine the timing of this early volcanic activity and its geochemical character, shedding light on the geodynamic evolution during this period. The Sierra de Guadalupe is a volcanic complex with effusive and explosive activity that generated andesitic lavas with plagioclase, ortho- and clinopyroxene plus amphibole phenocrysts, as well as dacitic lava flows and domes with plagioclase, orthopyroxene, amphibole and/or biotite phenocrysts. Pyroclastic and epiclastic (lahars) deposits are also observed in the northern slopes of this volcanic complex. The chemical composition of the Sierra de Guadalupe rocks is calc-alkaline andesitic to dacitic. New 40Ar/39Ar and U-Pb zircon ages demonstrate that volcanic activity at Sierra de Guadalupe lasted ca. 5.0 Ma from ca. 20.1 Ma to 14.8 Ma. Remnants of volcanic centers found in the Tepoztlán, Malinalco, Tenancingo, and Chiltepec areas ~80 km to the south show similar compositions and eruptive styles, with 40Ar/39Ar ages ranging between 21 and 16 Ma. Rocks with similar ages and lithologies were also described in deep wells drilled in the Mexico City Basin. As a whole, the age distribution shows that early to middle Miocene volcanism, making up the initial activity of the TMVB, migrated toward the north from Tepoztlán (310 km from the trench) up to Pachuca (445 km from the trench), and is likely associated with a shallowing the subducting Cocos slab underneath this region. Our results confirm that magmatism in the TMVB began in the early Miocene by dehydration of the Cocos slab as attested by high Ba/La and Th/Yb ratios. • TMVB volcanism started in the early Miocene in central Mexico. • Remnants of the early TMVB found in an 80 km wide belt south and north of Mexico City. • Northward migration of volcanism point to flattening since the early Miocene • Slab dehydration was the main factor in magma genesis for the Miocene TMVB. [ABSTRACT FROM AUTHOR]

Since 1994 Popocatépetl volcano has extruded 85 lava domes, each of which has been destroyed by Vulcanian-style explosions. The paroxysmal Vulcanian explosion of 22 January 2001 has been unique by generating multiple pyroclastic density currents (PDCs). Scientists and Civil Protection authorities have used those PDCs to remap the high-risk hazard zone of the volcano, although little study has been carried out to understand the generation and evolution of those PDCs. Here, we examine 38 stratigraphic sections and analyze the granulometry, componentry, vesicularity, and petrology (glass, melt inclusions in plagioclase) of collected samples to interpret the origins of the Vulcanian explosions and the PDC behavior. The 22 January event generated two series of dense PDCs that detached from the base of the eruption column. The first set of PDCs traveled northwest across a glacier on the volcano, partially scouring and melting the ice that hours later generated a lahar. Two pulses of these PDCs were confined within a large ravine, surpassed the slope break, and traveled up to 3 km away from the vent. The deposits are matrix-supported throughout their extent. The second set of PDCs traveled to the northeast, mainly as unconfined currents that split into two lobes prior to the slope break. The farthest traveled current followed a western ravine and reached the forest 3.5 km from the summit. The eastern lobe buried a local hiking hut and reached 2.1 km. The deposits from these northeastern currents are massive and block-supported. All deposits (volume of 5.71 × 105 m3) have finger-like morphology with levees and frontal snouts. All PDCs flowed as a dense basal granular current with turbulent upper clouds at minimum speeds of 7–10 m/s. The components of the deposits are, in order of abundance, black scoria (53–62 wt% SiO 2), banded scoria, pumice (63 wt% SiO 2), dome lithics (60–61 wt% SiO 2), accidental lithics, and free crystals. Juvenile pumice and scoria contain phenocrysts of plagioclase (An 47±10), clinopyroxene (En 48±3), orthopyroxene (En 64±1), ilmenite, and titanomagnetite set in a rhyolitic glass (pumice clast; 74.39 wt% SiO 2) or microlite-rich matrix (scoria clast). The dome lithics also contain these phenocrysts as well as rare olivine phenocrysts (Fe2+/(Fe2 + Mg) = 0.1). Dissolved H 2 O-CO 2 contents in melt inclusions hosted by pumice-plagioclase phenocrysts suggest the felsic magma was stored at depths of 2–4 km. Thus, the 2001 event was triggered by the injection of mafic magmas into a small volume of felsic magma, probably forming dikes left from the previous eruptive episode. We propose that the Vulcanian-explosions tap a column of magma (~2 km depth) equivalent to the volume that contained the felsic dikes. This mechanism has been acting during the destruction of all summit domes of the ongoing eruption of the volcano. • The 22 January 2001 vulcanian explosions of Popocatépetl have been unique by generating pyroclastic density currents (PDCs). • PDCs melted part of a glacier on the volcano that hours later generated a lahar. • Mixing between basaltic andesite and felsic andesite magmas triggered the 2001 eruption. • H 2 O-CO 2 contents in melt inclusions suggest the felsic magma was stored at 1.4–3 km. [ABSTRACT FROM AUTHOR]

Abstract The Tacaná Volcanic Complex (TVC), shared by México and Guatemala, is considered an active volcano that resumed phreatic explosions in 1949 and 1986. The TVC has recorded at least eight eruptions emplacing block-and-ash flows (BAFs) around the volcanic edifice during the past 42,000 years. The largest event generated the Mixcun deposit some 1950 yr B.P. from San Antonio Volcano, the youngest structure of the complex. Based on the eight mapped BAF deposits of the complex, we perform numerical simulations with the TITAN2d code to recreate the distribution and extent of these deposits. The results were used to prepare the zonation of the TVC based on the surface bed friction angles, which are related to the different morphologies of the volcano. From this zonation and the features of the past BAF deposits, we define three new eruptive impact scenarios (low, medium and high), to perform a hazard assessment of this phenomenon but considering the present morphology of the complex of the four eruptive centers. Next, we ranged the input parameters for each case scenario to analyze the dispersal, thickness and maximum runout of simulated flows. From the numerical simulations, we found that the most influential parameter in the model outputs is the basal friction angle, which varied from 23° to 12°. Then, we merged the eruptive scenarios simulated to construct new hazard maps for the different mass volumes simulated for each scenario. These maps clearly evidenced that the Mexican territory would be seriously affected in case of a renewed explosive activity of the TVC. In fact, even the partial collapse of any of the TVC domes would produce BAFs capable to flow over ~70 communities affecting ca. 20,000 inhabitants, as well as promote the generation of syn -and-post eruptive lahars if they flow into the main rivers that drain the volcano. Therefore, these maps are a great advance to evaluate the destructive potential of the TVC and must serve as the basis for the construction of a new risk map by the local authorities to update the operative and evacuation plans of the region. These actions would help to the >350,000 inhabitants living in a 35 km radius from the volcano's summit to be aware of the perils posed by the volcano, and how to act and evacuate in case of a volcanic crisis. Highlights • We define eruptive scenarios based on current mapped block-and-ash flow deposits. • We performed numerical simulations using TITAN2d and varying the input parameters. • The basal friction angle is the parameter that most influences the model outcomes. • Most of the simulated flows distribute over Mexican territory. • We propose new hazard zonation maps for block-and-ash flows. [ABSTRACT FROM AUTHOR]

Based on a detailed geological map and stratigraphy aided by new 230 Th/ 238 U and 206 P/ 238 U age determinations we established the eruptive chronology of the Tres Vírgenes Volcanic Complex (TVVC). The complex consists of three northeast-southwest aligned stratovolcanoes, which from older to younger are El Viejo, El Azufre, and La Virgen and associated cinder cones and domes. The alignment was fed from fissures that mark the southern trace of the left-lateral Cimarron Fault. The TVVC was built upon the basement rocks of the Peninsular Ranges Batholith (~99 Ma), the Santa Lucia Formation (21.6 Ma), the Esperanza basalt (7.6 Ma), and the 1.1 Ma ignimbrite of El Aguajito caldera. The TVVC began its formation at ca. 300 ka mainly with dacitic lava flows and domes that formed El Viejo volcano (4.2 km 3 ). At around 173 ka, activity migrated to the southwest to build El Azufre volcano (3.8 km 3 ) with the emission of dacitic lavas and several phases of dome construction and destruction with the generation of pyroclastic density currents. El Azufre's activity ended ~128 ka with the extrusion of the summit dome. At about 112 ka, volcanism migrated 4.2 km to the southwest to begin the construction of La Virgen Volcano through the emission of andesitic and dacitic lavas that built the largest cone of the complex until ~22 ka (31.2 km 3 ). This volcano was built upon several stages of cone construction with the emission of lava flows and peripheral dacitic domes and cinder cones. Between 128 and 112 ka six cinder cones vented along the Cimarron Fault between the La Virgen and El Azufre volcanoes. By assuming a constant emission of magma the total volume of the TVVC (39 km 3 ) was erupted at an average rate of 0.13 km 3 /kyr. Of this volume, effusive eruptions dominated the evolution of the complex (89%) of which 62% are dacites and 38% andesites. The TVVC rocks have compositions of 50–67 wt% in silica, and low-medium K (0.5–2.5 wt% K 2 O). Trace element signatures of the TVVC rocks (Sr/Y <40, La/Yb <10, Nb-Ti negative anomalies and relative enrichments of LILE and LREE) suggest a post-subduction mixture between adakitic and calc-alkaline magmas. Xenoliths of granodiorites hosted in lavas and La Virgen tephra suggest that magma chambers feeding the complex have stagnated at depths >2 km within the Peninsular Ranges Batholith as confirmed by geobarometry, aeromagnetic data, and the drill-holes of the geothermal field. Today, the Tres Vírgenes geothermal field generates 10 MW of electricity although future exploration of several nearby areas may increase such capacity. [ABSTRACT FROM AUTHOR]

Volcán de Colima has an eruptive history punctuated with explosive Plinian eruptions followed by long periods of effusive events. Both of the best documented Plinian eruptions, which occurred in 1818 CE and 1913 CE, emitted andesitic magma (~ 58 wt% SiO 2 ) that contains Pl > Opx > Cpx ≫ Amph + Fe-Ti oxides + Ap ± resorbed Ol, whereas effusive magmas from the 1819–1868 and 1962–2015 periods are particularly scarce in amphibole, and are slightly more silicic (59–61 wt% SiO 2 ). Pumice from the 1818 and 1913 deposits contain three groups of amphibole with different abundance, texture and composition. Composition is the most distinctive between them; the first group consists of crystals with high Al IV (1.84–2.32), the second group of amphiboles is less abundant in Al IV (1.45–1.76) and the third has low Al IV (1.29–1.39). In contrast, amphibole from two Colima prehistoric lavas can only be grouped as medium Al IV (1.45–1.76). A set of hydrothermal experiments were carried out using a 1818 natural sample to investigate amphibole compositional variability with changes in pressure and temperature. Two groups of amphibole found in the Plinian deposits can be reproduced experimentally between 875 and 900 °C and 150–200 MPa. Another type of amphibole could not be equilibrated in the 1818 explosive Colima magma and their origin can be attributed to mixing with more mafic magmas. We found that amphibole abundance is greater in explosive events and that mafic inherited amphiboles can only be found in Colima Plinian deposits. When the influx of mafic magma is large or frequent enough, and they mix with more silicic Colima magma, then explosive events are more likely. If mafic melts cannot mix with the resident magmas or just pond and heat the reservoir, regardless of location in the plumbing system, then magmas can decompress more slowly and amphibole will have time to completely react out. [ABSTRACT FROM AUTHOR]

We present the first geochemical data (major and trace elements, as well as Sr, Nd, and Pb isotopes) on volcanic rocks from the Tepoztlán Formation in the central Transmexican Volcanic Belt. The Tepoztlán Formation is up to 800 m thick and comprises a wide range of primary volcanic rocks (lavas, pyroclastic density current deposits, pyroclastic fall deposits), and their secondary reworked products due to mass flow (lahars) and fluvial processes. Magnetostratigraphy combined with K/Ar and Ar/Ar geochronology suggests an age of Early Miocene (23–19 Ma) for this Formation. Lava flows, pyroclastic rocks, dykes and volcanic clasts range from basaltic andesite to rhyolite, with a clear dominance of andesites and dacites. All samples are subalkaline and hy-normative. These rocks show homogeneous REE patterns with LREE enrichment and higher LILE concentrations with respect to HFSE, notably the typical negative anomaly of Nb, Ta, and Ti, suggesting a subduction-related magma genesis. Major and trace element concentrations show that either assimilation of heterogeneous continental crust or crustal recycling by subduction erosion and fractional crystallization are important processes in the evolution of the Tepoztlán Formation magmas. Isotopic compositions of the Tepoztlán Formation samples range from (87Sr/86Sr) t = 0.703693 to 0.704355 and (143Nd/144Nd) t = 0.512751 to 0.512882, falling within the mantle array. All geochemical characteristics indicate that these rocks originated from a heterogeneous mantle, modified and evolved through assimilation of country rock and fractional crystallization in the upper crust. [ABSTRACT FROM AUTHOR]

Abstract: Tlaloc is a late Pleistocene stratovolcano located NE of México City. It is the northernmost volcano of the N–S Sierra Nevada Volcanic Range, which consists from north to south of Tlaloc, Telapón, Iztaccíhuatl, and Popocatépetl volcanoes. Tlaloc has always been considered the oldest (and extinct) volcano of the Sierra Nevada Volcanic Range. Recent field data revealed that Tlaloc was very active during late Pleistocene through a series of explosive eruptions. One of these eruptions produced the Multilayered White Pumice (MWP) a rhyolitic pyroclastic sequence. The eruption began with a 24-km high Plinian column MWP-F1 that was dispersed to the NE by prevailing winds. It was interrupted by fountaining of the column with the generation of a pyroclastic density current that emplaced MWP-S1 layer. Then, followed five unstable sub-Plinian columns (MWP-F2 to F6) that reached altitudes between 16 and 19km. Fall deposits as a whole are 1m thick at 12km from the vent, cover a minimum area of 577km2 for a total volume of 4.68km3 (DRE 1.58km3). The eruption ejected a total mass of 3.45×1012 kg at different mass discharges. The last sub-Plinian column (MWP-F6) collapsed and produced dense pyroclastic density currents that deposited pumiceous pyroclastic flows (MWP-PF) following main ravines to the north and east of the vent. These density currents filled gullies with 23m-thick deposits at a distance of 12km from the vent totaling a minimum DRE volume of 0.2km3. Pyroclastic flow deposits charred tree trunks that yielded an age of 31,490+1995/−1595yrB.P. that closely date the age of the eruption. Rain during this phase of the eruption generated syn-eruptive lahars (MWP-DF). Post-eruptive lahars (MWP-ED) finally swept the volcano flanks. The MWP deposits consist of abundant white pumice (up to 96vol.%), rare gray pumice, cognate lithics, accidental altered lithics, xenocrysts. White and gray pumice clasts contain phenocrysts of quartz, plagioclase, sanidine, biotite, rare Fe–Ti oxides, monazite, zircon and apatite. Xenocrysts are represented by plagioclase, microcline, orthoclase and quartz likely coming from a deeper plutonic body. Both pumices have a rhyolitic composition (74.98±1wt.% SiO2 in water free basis) representing one of the most acidic products of Tlaloc and the entire Sierra Nevada Volcanic Range. The rhyolitic liquid was likely extracted from a mush-like plutonic body reaching the minimum predicted vesicularity values for Plinian fragmentation for which the triggering mechanism of the MWP eruption is attributed to the high viscosity of the magma that provoked overpressure of the magmatic system. The parameters studied suggest that eruption behavior evolved from Plinian to sub-Plinian eruptive columns over time due to conduit dynamics rather than variations in magma properties of the MWP products. [Copyright &y& Elsevier]

Abstract: El Chichón volcano consists of a 2-km wide Somma crater compound cone 0.2 Ma old with peripheral domes with a central crater reactivated several times during the Holocene. The most recent eruption at El Chichón occurred from March 28 to April 4, 1982, resulting in the worst volcanic disaster during historical times in Mexico, killing more than 2000 people and destroying nine towns and small communities. The volcanic hazard map of El Chichón is based on detailed field work that documented twelve eruptions during the last 8000 years, and computer simulations. To validate the results, computer simulations were first performed over pre-1982 topography mimicking the extent of the actual deposits produced and afterwards run over post-1982 topography. These eruptions have produced pyroclastic fall, surge, flow and lahar deposits. Pyroclastic flows have different volumes and Heim coefficients varying from 0.2 (pumice flows), to 0.15 (block-and-ash flows) and 0.10 (ash flows). Simulations using FLOW3D and TITAN2D indicate that pumice flows and block-and-ash flows can fill the moat area and follow main ravines up to distances of ca. 3 km from the crater, with no effect on populations around the volcano. On the other hand, more mobile ash flows related to column-collapse events can reach up to 4 km from the vent, but will always follow the same paths and still not affect surrounding populations. The energy-cone model was used to simulate the outflow of pyroclastic surges based on the 1982 event (H/L =0.1 and 0.2), and shows that surges may reach some towns around the volcano. Explosive activity also produced Plinian columns higher than 27 km that were dispersed towards the NE by prevailing winds. Future fallout will seriously disturb the lives of more than 70,000 inhabitants of cities and towns located in a radius of 35 km from the volcano. Lahar events in the past originated from unconsolidated pyroclastic deposits with volumes varying from 1 to 4×106 m3 for single pulses, to a large one from dam-breakout with a volume of 40×106 m3. We used the LAHARZ code to model future events with volumes of 1, 2, and 3×106 m3 that will reach as far as 10, 14, and 16 km from the crater, posing some danger to the communities of Nicapa, Volcán, and Ostuacán, even some time after the climax of the eruption. [Copyright &y& Elsevier]

The Apan-Acoculco area is located in the eastern portion of the Mexico basin and the Trans-Mexican Volcanic Belt. The area is transected by right-stepping variably dipping NE-SW normal faults. The Apan-Tlaloc Fault System is a major discontinuity that divides the region into two contrasting areas with different structural and volcanic styles. a) The western area is characterized by a horst-graben geometry with widespread Quaternary monogenetic volcanism and scattered outcrops of Miocene and Pliocene rocks. b) The eastern area is dominated by tilted horsts with a domino-like geometry with widespread Miocene and Pliocene rocks, scattered Quaternary monogenetic volcanoes and the Acoculco Caldera. Gravity data suggest that this structural geometry continues into the Mesozoic limestones. Normal faulting was active since the Pliocene with three stages of extension. One of them, an intense dilatational event began during late Pliocene and continues nowadays, contemporaneously with the emplacement of the Apan-Tezontepec Volcanic Field and the Acoculco caldera. Statistical analysis of cone elongation, cone instability, and the kinematic analysis of faults attest for a NW50°SE ± 7° extensional regime in the Apan-Acoculco area. The activity in some portions of the Apan-Tlaloc Fault System continues today as indicated by earthquake swarms recorded in 1992 and 1996, that disrupted late Holocene paleosols, and Holocene volcanism. [ABSTRACT FROM AUTHOR]

On July 10–11, 2015 an eruption occurred at Colima volcano produced 10.5 km long pyroclastic density currents (PDCs) along the Montegrande, and 6.5 km long along the San Antonio ravines. The summit dome was destroyed and a new crater excavated and breached to the south. This new breach connects to a narrow channel that descends along Colima's southern flank and was used by a subsequent lava flow. The Montegrande PDCs represent the longest and hottest flow of this type recorded during the past 30 years but are still smaller in comparison to the 15-km long PDCs produced during the 1913 Plinian eruption. Data obtained from field reconnaissance, lahar monitoring stations, and satellite imagery suggest that at least six PDCs occurred. The two largest PDCs (H/L 0.2) were able to surmount topographic barriers or bends. Based on field reconnaissance and digital elevation models extracted from SPOT satellite imageries we estimate a minimum volume for the valley-pond and distal fan deposits of 4.5 × 10 6 m 3 . After one week, the deposits were still hot with burning trees on the surface and millimeter-sized holes from which fumes were emanating. The juvenile components of the deposits consist of gray dense blocks and vesicular dark-gray blocks and bombs with bread-crust textures and cooling joints. The mineral association of these rocks consists of plagioclase + clinopyroxene + orthopyroxene + FeTi-oxides ± olivine and resorbed hornblende in a dark glassy matrix that corresponds to an andesitic composition. [ABSTRACT FROM AUTHOR]

The Sierra Nevada Volcanic Range (SNVR), which includes Popocatépetl, Iztaccíhuatl and Tláloc-Telapón volcanoes, has been the source of multiple large explosive eruptions that have dispersed tephra across central México. Several eruptions since 40 ka have previously been described, particularly from Popocatépetl, the southernmost volcano of the range. However, the longer-term eruption history of the SNVR is poorly understood, due to challenges with correlating limited exposures of older pyroclastic sequences, and in discriminating between tephras derived from different sources. Here we describe two extensive exposures located between Popocatépetl and Iztaccíhuatl volcanoes, which provide a more complete and longer-term explosive eruption record of the SNVR: the Nepopualco and Xalitzintla tephra sequences. A detailed tephrostratigraphic survey, together with new 40Ar/39Ar geochronological analyses and glass geochemistry, has permitted the characterization of identified eruption units further leading to the determination of geochemical fields for each volcano and the subsequent discernment of volcanic sources. Our results show that, since the collapse of the Los Pies Cone, which destroyed the Paleo-Iztaccíhuatl edifice at 631 ± 44 ka (2σ), Iztaccíhuatl has produced at least 6 explosive rhyolitic eruptions. After coeval activity with Popocatépetl, between ~600 and ~500 ka, Iztaccíhuatl's explosive activity ceased while Popocatépetl's continued until present day. Popocatépetl has produced at least 27 medium to large explosive eruptions (inferred VEI 4–6), commonly of andesitic to dacitic compositions. Some of these eruptions deposited pumice fallout of >1 m thick in both the Nepopualco and Xalitzintla sequences (e.g. the 339 ± 16 ka [2σ] NT-23/WRT-7 eruption), suggesting that Popocatépetl has produced several eruptions similar in magnitude to the well-known ~14 ka Tutti Frutti Pumice (a VEI 6 eruption with a ~5 km3 tephra volume). The Popocatépetl and Iztaccíhuatl tephras are interbedded with deposits from more distal volcanoes, including some mafic to intermediate products of unknown sources (possibly from nearby monogenetic cones) and tephras related to the late Pleistocene eruptions of Tláloc-Telapón (including the tephra layer produced by the San Valentin Ignimbrite, recently 40Ar/39Ar dated in this study at ~102 ka; 2σ). Our new chemical, stratigraphic and geochronologic investigations of these pyroclastic deposits, predominantly from Popocatépetl and Iztaccíhuatl, provide information on the scale and frequency of medium to large magnitude explosive eruptions over a longer-time period than currently known and that have had potential to disperse tephra across central México since the middle to late Pleistocene. This new data can be used to determine the source of further unknown tephras in the region as well as to better assess the volcanic hazard to the densely populated megalopolis of México City. • Detailed explosive eruptive history of Popocatépetl, Iztaccíhuatl & Tláloc-Telapón. • New 40Ar/39Ar eruption ages provide constraints on the Late Pleistocene volcanism. • Glass shard major element analyses distinguish different eruption deposits. • Glass compositions can also be used to identify the source volcano. [ABSTRACT FROM AUTHOR]

Abstract: Based on the stratigraphic record of the deposits, analysis of previous works, historic archives, and eyewitness accounts the 1913 eruption of Volcán de Colima was reconstructed. The eruption started in 17 January and peaked in 20 January, 1913. It occurred in three main phases: 1) An opening phase with the generation of Merapi-type pyroclastic flows (units F1, F2, F3) and a pyroclastic surge (S1), 2) A vent-clearing phase with strong explosions that produced Vulcanian-Soufriere-type pyroclastic flows (F4) and a pyroclastic surge (S2) which destroyed the summit dome decompressing the magma system, and 3) a Plinian phase with the establishment of a ∼23km high column dispersing a fallout (C1) to the NE followed by the collapse of the column that generated a pyroclastic surge (S3) and 15-km long pumice-rich pyroclastic flows (F5). After the eruption, remobilization of the pyroclastic material generated lahars in main gullies around the crater. Fallout C1 blanketed an area of ∼191,318km2 covering the cities of Guzman, Guadalajara, and Saltillo (Coahuila) located at 725km from the source. It had a volume of 1.4km3 (0.57km3 DRE= Dense Rock Equivalent). The total volume of pyroclastic flow and surge deposits was 0.26km3 (0.07km3 DRE) giving a total volume of the eruption of 1.66km3 (0.64km3 DRE). The Plinian column lasted 4.6h with a total mass of 1.5×1012 kg and a mass eruption rate of 9.02×107 kg/s. The column height and the ejected magma volume indicate that the 1913 eruption had a VEI=5 being the largest event in the historical record of Colima Volcano. Juvenile scoria and pumice consisted of Pl>Opx>Cpx>Hbl+accessory titanomagnetite+Ap and Ol with reaction rims. Chemistry of juvenile scoria and pumice samples is andesitic very homogeneous (58.3±0.5wt.% SiO2) and similar to the 1818 juvenile products (58.9±0.2wt.% SiO2). The presence of banded scoria, olivine phenocrysts with reaction rims, and trace element variations strongly suggest that the 1913 eruption was caused by a magma mixing event. [Copyright &y& Elsevier]

Abstract: The Nevado de Toluca is a quiescent volcano located 20 km southwest of the City of Toluca and 70 km west of Mexico City. It has been quiescent since its last eruptive activity, dated at ∼3.3 ka BP. During the Pleistocene and Holocene, it experienced several eruptive phases, including five dome collapses with the emplacement of block-and-ash flows and four Plinian eruptions, including the 10.5 ka BP Plinian eruption that deposited more than 10 cm of sand-sized pumice in the area occupied today by Mexico City. A detailed geological map coupled with computer simulations (FLOW3D, TITAN2D, LAHARZ and HAZMAP softwares) were used to produce the volcanic hazard assessment. Based on the final hazard zonation the northern and eastern sectors of Nevado de Toluca would be affected by a greater number of phenomena in case of reappraisal activity. Block-and-ash flows will affect deep ravines up to a distance of 15 km and associated ash clouds could blanket the Toluca basin, whereas ash falls from Plinian events will have catastrophic effects for populated areas within a radius of 70 km, including the Mexico City Metropolitan area, inhabited by more than 20 million people. Independently of the activity of the volcano, lahars occur every year, affecting small villages settled down flow from main ravines. [Copyright &y& Elsevier]

Abstract: Magmas erupted from Quaternary volcanoes of Southern Andes between 37° and 46° S latitude are mainly basaltic to andesitic. However, PCCVC (40° S) shows a singular magmatic evolution due to the abnormal evacuation of rhyolites, especially in the last 100 ka. In addition, PCCVC is the result of juxtaposing products from the NW-trending alignment of Cordillera Nevada caldera, Cordón Caulle fissure volcano and the Puyehue stratocone. Using 40Ar/39Ar and 14C geochronology it can be established that they evolved since ca. 500 ka as coeval but separated vents with a first stage of shield volcanism, followed by repeated collapses that formed an internal NW-elongated graben. From ca. 100 ka, volcanic activity occurred in both a fissure system (Cordón Caulle) and a central volcano (Puyehue). Holocene explosive eruptions, mainly in the Puyehue crater, accompanied the dome growing along a NW-trending fissure system. Last historical eruptions were in 1921 and 1960 when NW fissures of Cordón Caulle fed rhyodacitic lava flows. In 1960, the fissure eruption was triggered by a remote Mw: 9.5 thrust earthquake. Cordillera Nevada caldera presents a reduced compositional range (52–63% SiO2) and geochemical features of low-pressure magma mixing and assimilation. Instead, Cordón Caulle and Puyehue volcanoes have a wide silica range (48–71% SiO2) and an outstanding affinity, which can be modelled with initial high-pressure fractional crystallization, moderate magma mixing and subsequent low-pressure fractional crystallization from a common parental source. The exceptional magmatic evolution and eruptive style of PCCVC in Southern Andes could be related with the physics of the plumbing system, which in turn can be controlled by external factors as the structure of the continental crust and the ongoing stress regime. [Copyright &y& Elsevier]