Andesitic Lava Flows Research Articles

Early Jurassic petrogenesis of the retro-arc volcanism of northwestern Patagonia, Argentina: Evidence from Lu-Hf isotopes and whole-rock geochemistry

Located in the north-western Patagonian Massif, the Loncón Complex offers insight into the Upper Sinemurian syn-rift phase of this Patagonian sector. New whole-rock geochemistry and zircon Lu–Hf isotopic data, combined with adjacent volcanic depocentres such as the Lonco Trapial Formation, the Cañadón Chileno Complex, the Cerro Piche Graben Formation, the Comallo Volcanic Sedimentary Complex as well as the Colomichicó Formation from the Neuquén syn-rift phase, allow us to constrain the tectonic characteristics and evolution of the Jurassic retro-arc system of Patagonia. The effusive and explosive volcanism registered by andesitic lava flows and dykes and rhyolitic pyroclastic deposits defines subalkaline and calc-alkaline series. Additionally, the eruptive rocks show significant enrichment in light rare-earth elements and large-ion lithophile elements, and lower La/Ta, Ba/Ta and higher Th/Ta than the effusive rocks. Both units show depletion in high field strength elements (e.g., Nb, Ta, Zr, and Hf), and relatively high Nb/U, Ta/U, moderate La/Yb and low Th/Ta and Sr/Y ratios. Negative and positive εHf zircon values (−4.8 to +4.1) reveal the rocks were derived from the partial melting of a metasomatised mantle, which underwent moderate crustal contamination during its emplacement. These I-type hybrid magmas are generated on an extensional tectonic setting, probably caused by the retreating of the orogen, during Sinemurian times. This intraplate extension is considered slightly before the Early Jurassic Chon Aike (V1) episode.

New evidence of Holocene pyroclastic density currents at Galeras volcano, Colombia

The Galeras Volcanic Complex (GVC) is a composite volcano located between the Central and Western cordilleras in southern Colombia. It is considered one of the most active volcanoes in Colombia, with typically Vulcanian eruptions. The complex has been divided into different stages based on stratigraphic and geochronological differences. The most recent one is called the Galeras stage and is considered to have started ca. 4500 years. This study presents the results of new stratigraphic and geochronological analysis of the deposits that outcrop along the El Barranco river valley, NW of the GVC, which allowed us to identify newer and older deposits within the most recent stage (i.e., the Galeras stage). The deposits were analyzed via distribution, stratigraphy, geochronology, componentry and granulometry, as well as vesicularity and microtexture of the pumice fragments. We identified three previously unreported deposits, which results in a total of eight pyroclastic density current (PDC) deposits in the valley, which discordantly overlie andesitic lava flows of the previous stage (i.e., Genoy stage; 150–40 ka) of the GVC. They were named from Unit U1 to Unit U8, with units U1, U2 and U8 representing events not previously recorded in the eruptive history of Galeras volcano. Units U1 (8303 ± 97 and 8284.5 ± 90.5 cal BP), U2 (7667 ± 78 cal BP), U3 (5082 ± 198, 5096.5 ± 226.5, 5801.5 ± 481.5 and 5966 ± 235 cal BP) and U6 (2215.5 ± 101.5 and 2033 ± 91 cal BP) are interpreted as formed by PDCs generated by pumice-rich flows linked to the collapse of Subplinian eruptive columns, while units U5 (3201.5 ± 129 cal BP), U7 (1066.5 ± 109.5 and 944.5 ± 115.4 cal BP) and U8 (390.5 ± 80.5 cal BP) are interpreted as formed by PDCs generated by block and ash flows linked to the destruction of intracrater domes and the collapse of Vulcanian eruptive columns. U4 (4625 ± 181 cal BP) is associated with a “blast” type event, caused by the overpressure exerted by the gases of a viscous magma. The above mentioned record allows us to propose that the eruptive history of Galeras volcano began at the beginning of the Holocene (∼8300 years BP), and not 4500 BP, as previously established, which has hazard implications. Unit U8 in the town of La Florida as well as the nearby recorded deposits, indicates a probable PDC hazard for this population.

Pre-Choiyoi volcanism at Cordillera del Viento, southwestern margin of Gondwana (∼37° S): Geological characterisation, geochronology and regional implications

This contribution provides a comprehensive description and classification of fifteen lithofacies within the Carboniferous rocks attributed to the Arroyo del Torreón Formation and Sofía Dacite in order to understand the eruptive dynamics and the evolution of volcanism associated with the onset of the Gondwanan Orogenic Cycle at the Cordillera del Viento (Argentina). The outcrops of Carboniferous volcanic and volcaniclastic rocks linked to this cycle are restricted to the Cordilllera del Viento range. In consequence, they offer a valuable opportunity to research the volcanic arc products of the pre-Choiyoi magmatism.The Arroyo del Torreón Formation lithofacies interpretation and its distribution indicate that the volcanism commenced with local andesitic lava flows followed by a volcano-sedimentary sequence formed by multiple pumice-rich quasi-steady concentrated pyroclastic density currents alternating with episodes of epiclastic sedimentation. The latter are covered ignimbrites developed by boiling over eruptions. Crystal-rich tuffs overlie the ignimbrites and represent a transition to a plinian eruption. This eruption style continued, developing concentrated pyroclastic density currents with highly unsteadiness conditions and scarce fall-out deposits. Conversely, the Sofía Dacite, represent a notable shift in the volcanism style, characterized by dacitic to rhyolitic lava flows with minor pyroclastic beds. Zircon dating of a pumice-rich lapilli-tuff from the Arroyo del Torreón Formation yielded a minimum age of 327.77 ± 1.79 Ma that was interpreted as the maximum depositional age for this unit. Similarly, zircons from a porphyritic dacite representing the Sofía Dacite provided a Concordia age of 329.11 ± 1.31 Ma that was interpreted as the crystallisation age of this rock.Consequently, we propose a new stratigraphic division of the Arroyo del Torreón Formation into two members. The Cerro San Pedro Member will comprise the pyroclastic rocks at the base of the sequence, while the Sofía Member will include the upper lava-dominated portion of the unit. In this sense, the whole lithostratigraphic unit represents a distinctive Carboniferous basin associated with arc-related volcanism representative from the pre-Choiyoi magmatism.

Rock Mass Quality Type Analysis On The New Kretek Girijati Road Construction Site Based On Reconnaissance Survey

Abstract The research activity was carried out at the location of the national road construction plan for The Kretek-Girijati Road Section. The National Kretek-Girijati Section is in the Nglanggran Formation, which consists of volcanic breccias, agglomerates, tuffs, andesitic-basalt and andesitic lava flows, and the Wonosari Formation, which is dominated by carbonate rocks consisting of layered limestone and massive limestone. This investigation aims to obtain a typical analogy of excavation slopes at road construction sites, making recommendations for additional drilling locations and geophysical surveys for appropriate data by making an engineering geological map. Based on the geological engineering description, the location plan for the construction of The Kretek-Girijati Road Section is dominated by limestone and andesite. The types of limestone rock mass quality consist of Massive limestone (very hard) with good to very good rock mass quality with a GSI value of >80 and Clastic limestone with poor to medium rock quality with a GSI value of 30 – 60. The types of andesite rock mass quality consist of massive andesite (weakly jointed) with good – excellent rock mass quality with an RMR value of 70-80 and moderately fractured andesite with moderate rock mass quality (good 50 – 70).

A mantle origin for Pliocene SiO2-rich ignimbrites in the modern Colombian magmatic arc

The generation of voluminous SiO2-rich magmas has been extensively investigated due to their petrologic implications and because they pose a significant natural hazard. Two main petrogenetic models have been proposed to explain these volcanic products: partial melting of the continental crust and fractional crystallization and assimilation of mantle-derived magmas. In the central segment of the modern Colombian magmatic arc, the northernmost Andean magmatic arc, the eruption of voluminous rhyolitic pyroclastic rocks occurred at 2.6 Ma, covering an area of ∼3000 km2. This contribution presents Hf-Nd-Sr-Pb whole-rock isotopes, zircon UPb geochronology, and major/trace-element data from Pliocene rhyolitic ignimbrites and Quaternary andesitic lava flows from the modern Colombian magmatic arc to understand the mechanisms responsible for the formation of high-silica magmas.The whole-rock and zircon geochemistry and Nd-Sr-Pb-Hf isotopic signatures indicate that this high-silica magmatism is mantle-derived and underwent extensive crystal fractionation and limited assimilation of the continental crust. Extreme magma fractionation at low temperatures and crustal thicknesses above 45 km could have favored the production of cumulates and fast (< 5 Ma) crustal thickening. These results highlight the major role of the mantle in generating high-silica magmatism and the associated crustal thickening, a process that has been poorly understood in the Northern Andes.

Brecciation and fracturing by water ingress into the Genbudo basaltic andesitic lava flow, Iwate volcano, northeastern Japan

The Genbudo lava, the late Pleistocene basaltic-andesitic lava flow in the southwestern part of Iwate Volcano, Japan, is a 70 m thick columnar jointed flow that can be divided into three parts from bottom to top: the colonnade, the entablature, and the partly-brecciated uppermost part. Two main types of fractures developed in the entablature: pseudopillow fractures that formed in a branching network-like pattern throughout the entablature, and sheet fractures with curved surfaces that are nearly parallel to each other. At the uppermost part of the flow, finger-like structures of lava extend upward from the coherent lava, and cogenetic autoclastic rocks form between the fingers. This occurrence suggests that hyaloclastites were generated during emplacement in the uppermost part of the flow, apparently when water from a dammed river valley covered the flow. The texture of the lava near the pseudopillow fractures in the entablature is commonly hypocrystalline, while the texture in other parts is holocrystalline. There are two types of pyroxene microlites, large prismatic (average size ~ 30 µm) and dendritic (< 10 µm in length) crystals in the lava near the pseudopillow fractures. These suggest that the cooling rate of the lava was greatest in the vicinity of the pseudopillow fractures. Networks of palagonite-filled micro-fractures (less than 10 µm in width) are found in this part of the flow, and many bubbles are observed along the fractures. This is clear evidence that the rapid cooling of the lava was caused by water infiltration through the pseudopillow fractures. From the measurement of Fe-rich droplet sizes that formed due to liquid immiscibility within the lava, we estimate the cooling rate within the colonnade as about 49 °C/h and within the entablature as 642 °C/h, consistent with much more rapid cooling by water infiltration from above.

Protracted metallogenic and magmatic evolution of the Kirazlı epithermal Au-Ag and porphyry Cu deposits, Biga Peninsula, NW Turkey: evidence from zircon U-Pb, muscovite 40Ar/39Ar, and molybdenite Re-Os geochronology

The Kirazlı deposit is located at the center of the Biga Peninsula metallogenic province, in a geological setting characterized by an extensional tectonic environment. A NNW-SSE trending high-sulfidation (HS) orebody with a total reserve of 33.86 Mt @ 0.69 g/t Au and 9.42 g/t Ag lies beneath the Kirazlı Main zone. A porphyry Cu orebody hosted by Eocene intrusive and volcanic rocks has been intersected by drilling within its vicinity. The HS epithermal deposit is hosted by a partly silicified and brecciated Oligocene volcanic and volcaniclastic sequence consisting mainly of basaltic andesite lava flow and lithic/crystal tuff. Lithogeochemistry and zircon U-Pb radiometric ages allow us to distinguish three distinct high-K calc-alkaline magmatic events at ca. 41, 38, and 32 Ma, sourced by metasomatized mantle melts, which have interacted with the crust during their ascent. Porphyry Cu mineralization took place at 36.7 ± 0.4 Ma (muscovite 40Ar/39Ar age) with subsequent re-opening and base metal deposition. Crosscutting quartz-pyrite-molybdenite veins were emplaced at 33.6 ± 0.2 Ma (molybdenite Re-Os age), and followed by the HS epithermal Au-Ag event at ca. 31 Ma, based on a previous study. Our radiometric data indicate that the Kirazlı deposit has recorded a long-lasting Cenozoic magmatic and metallogenic evolution during about 10 Myr. Our study demonstrates that successive, independent, and overprinting, but genetically unrelated, HS epithermal precious metal, hydrothermal Mo, base metal, and porphyry Cu systems have been active at the same location during protracted extensional tectonics of the Biga Peninsula.

The effect of fault systems on volcanic activity: Insights from the subduction-related, Quaternary Villamaría-Termales monogenetic volcanic field in Colombia

Structural control of volcanic activity is a topic of great significance around volcanic fields, mostly associated with risk management near cities. Structural geology provides valuable information for understanding the magmatic processes associated with the rise of magma and the presence of volcanoes. The Villamaría-Termales Monogenetic Volcanic Field (VTMVF) is a group of Quaternary monogenetic volcanoes settled in an active fault system, which allows us to propose the role that these faults play in the volcanic activity. The field is located near the city of Manizales (∼475.000 inhabitants), Colombia, on an active fault system at the western flank of the Cordillera Central in the northern Andes. The VTMVF is characterized by andesitic lava domes and flows, which individually reach volumes of up to 2.5 km3. This work uses 1) geometry and kinematics of the faults that affect the VTMVF to define the structural features associated with the emplacement of the volcanoes, and 2) new and published ages to evaluate periods of volcanic activity. Three trends of fault systems associated with the location of the volcanoes were identified: 1) NW-SE (Villamaría-Termales), 2) NE-SW (Sancancio, El Perrillo, Santa Rosa and Palestina), and 3) N-S to NNE-SSW (San Jerónimo and Samaná-sur). The fault kinematics are dominantly normal, with dextral (NE) and sinistral (NW) movements. Analysis of ages shows that the field has temporally evolved since 2 Ma in different time intervals (2.0–1.2 Ma, 0.18–0.045 Ma, and 0.045 Ma – Present). This supports the presence of different emplacement mechanisms related to both the movement in the strike of some faults and the intersection between faults. The pauses of volcanic activity could coincide with the absence of structural conditions (interseismic cycles for faults, where the sealing of the faults is generated) to facilitate the rise of magma; this is related to temporary compressive conditions. Despite the apparent structural controls, there is no clear spatial or temporal pattern of volcano distribution within the field. There is evidence of seismic activity in the area. Thus, the future formation of dilatating zones that allow the magma to rise and the emplacement of new monogenetic volcanoes is feasible not only in the area defined for the volcanic field but also in the continuation of the fault lines around it.

Mineralogy, fluid inclusion and stable isotope characteristics of the Inlice (Konya, Turkey) high sulfidation epithermal gold deposit: Implications for hydrothermal evolution and ore genesis

The Inlice high sulfidation epithermal gold deposit with 262,300 oz of gold ore is located in the Erenlerdağ-Alacadağ Volcanic Complex (EAVC) at the northern part of central Taurides. The volcanic succession of the study area is stratigraphically represented by andesite, block and ash flow, basaltic andesite lava flow and andesite lava flow. The deposit consists of seven neighboring mineralized veins termed Ana East, Ana West, West, Discovery, Güllü, Merkez and North Zone and is associated with an andesite (ca 8–9 Ma). Hydrothermal alteration from the innermost to the outermost parts of the deposit includes silicification, advanced argillic, intermediate argillic and propylitic. At the surface, quartz veins related to silicification are exposed as linear topographic relief trending mainly northwest-southeast and secondarily northeast-southwest and east-west. Deep drill core samples, including magnetite, quartz, biotite and anhydrite, imply the presence of potassic alteration in depth (50 to 970 m) possibly related to a porphyry Cu system. Ore assemblages are described as hypogene and supergene. The hypogene ore mainly includes pyrite (Py-I and Py-II) and enargite, and to a lesser extent chalcopyrite, sphalerite and marcasite. The supergene ore incorporates hematite and goethite, and minor covellite, chalcocite, malachite and native copper. Hypogene gold precipitation is associated with the mineral association of Py-II, chalcopyrite and enargite, while enargite mineral is a major host for gold (up to 600 ppm). Supergene oxidation resulted in the development of a secondary enrichment zone for gold (up to 14 g/t) extending to a depth of about 45 m.Microthermometric measurements show that the silicification associated with the mineralization was formed at homogenization temperatures ranging between 147 and 360 °C and salinities up to 6.5 wt% NaCl. This suggests that the fluid mixing and/or fluid dilution processes were important factors controlling the precipitation of gold. δ34S isotope compositions are between −0.9 and − 9 ‰, and further indicate a significant involvement of magmatic components into the hydrothermal fluids. Thus, it is concluded that at Inlice the hydrothermal fluids responsible for the alteration and mineralization processes were derived by relatively dilute fluids formed by the mixing of magmatic fluids with meteoric waters.

Neoproterozoic potassic andesitic and lamprophyric rocks in the tupanci area, southernomost Brazil: Petrology and associated mineralization

Au and sulfide mineralizations occur in the Sul-Rio-Grandense Shield, and important occurrences of these metals are reported and attributed to the Lavras do Sul Shoshonitic Association (LSSA). Several authors point to a significant participation of andesitic and lamprophyric rocks in the formation of these deposits. The Tupanci area has the presence of andesites and lamprophyres, stratigraphically correlated to LSSA volcanic rocks (Hilário Formation), representing the northernmost exposures of this magmatism. The LSSA is one of the most complete Neoproterozoic Shoshonitic associations (ca. 592-590 Ma) in southern Brazil, containing plutonic, volcanic and hypabyssal rocks, related to the post-collisional stage of the Brasiliano/Pan-African orogeny. The andesitic rocks of the Tupanci area occur in the form of the lava flows, overlayed by volcanoclastic deposits, product of the reworking of the volcanic unit. Lamprophyres occur in the form of dykes, with N-NW direction, which are intruded in rocks of the metamorphic basement and in andesitic lava flows, being texturally separated and classified as spessartite and lamprophyric lapilli-tuff. The singular occurrence of the lamprophyric lapilli-tuff stands out, is analogous to Kimberley-type pyroclastic kimberlitic intrusions, depicting explosive manifestations linked to LSSA lamprophyres. The andesites and lamprophyres that ocour in Tupanci area show characteristics of high-K calc-alkaline or shoshonitic rocks, evidenced by LILE and LREE enrichment, negative Ti and Nb anomalies, plus positive Pb anomalies and the absence of Eu anomalies. These attributes reinforce the relationship of andesitic and lamprophyric rocks with related LSSA rocks. The presence of Au and Pt grains in the matrix of lamprophyric lapilli-tuff, highlights the economic importance of these rocks for the mineral occurrences in the region, where future studies can better define the metallogenetic potential for the rocks of the Tupanci area.

New geological and geochronological constraints on the evolution of the Cotacachi - Cuicocha volcanic complex (Ecuador)

Extensive fieldwork at the Cotacachi-Cuicocha Volcanic Complex (CCVC, North of Ecuador) resulted in a new collection of geological data including cartography, chronology, petrography, geochemistry, and morphology. This volcanic complex is formed by a central volcano (Cotacachi: 4939 m asl, current bulk volume of 56 ± 4 km3), several peripheral domes, and a 3 km wide volcanic caldera (Cuicocha: 4.2 ± 0.1 km3). CCVC comprises three stratigraphic members: The first, Cotacachi Basal, represents the initial phase of construction, which started at 173 ± 4 ka with a basal andesitic lava flow succession (∼500 m-thick) including isolated basaltic-andesitic lavas (Verde Tola unit; NE: 113 ± 6 ka, SE: 133 ± 9 ka), the construction of some peripheral amphibole-bearing andesitic domes, such as Muyurcu and Loma Negra (138 ± 4 ka and <108 ka, respectively), and a debris-avalanche deposit to the north-west (0.5–1.8 km3, older than 108 ka). The second member, Upper Cotacachi, consists of an andesitic lava flow succession (∼300 m-thick), younger than 108 ± 6 ka. A gap of activity occurred afterwards from 100 to 70 ka, during which a second debris-avalanche (0.2–1.1 km3, 108 to 65 ka) occurred to the NE, followed by the effusion of the dacitic Piribuela dome (65 ± 2 ka). Afterwards, several superimposed andesitic lava flows were emplaced at the summit, possibly around 15–10 ka since they lack glacial erosion. The third member includes the extrusion of the andesitic Cuicocha pre-caldera domes, which marks the beginning of a new eruptive stage of activity of CCVC during the Holocene, resulting in a violent eruption (3525 ± 35 to 2980 ± 30 a BP; VEI = 5) that partially destroyed the young dome and formed a funnel-shaped caldera (Cuicocha Caldera-Lake), ending with the emplacement of the Wolf and Yerovi post-caldera domes.

Early Jurassic tectonomagmatic stages in the western North Patagonian Region, Argentina: insights from the Comallo volcanic sedimentary complex

ABSTRACT The Comallo volcanic sedimentary Complex in the western North Patagonian Region begins with the development and collapse of Plinian-type eruptive columns of rhyolitic and dacitic composition associated to vent at approximately 192 Ma. Synchronous deposits are originating in alluvial and lagoon environments. The ƐHf(t) values obtained in zircon grains indicate possible derivation by melting Paleoproterozoic and Mesoproterozoic crust. Upwards in the sequence appears basaltic and andesitic lava flows, as well as pyroclastic deposits produced during the eruptions. This volcanism is related to sustained pyroclastic fountains with a U-Pb zircon age of 185 Ma. The volcanic rocks were possibly derived from Paleoproterozoic, Mesoproterozoic, and Neoproterozoic crust affected by juvenile magmas in volcanic-arc environments. Chemical and isotopic variations are mainly due to changes in the local and regional tectonic conditions, the thickness of the continental crust, as well as the dip and age of the subducted oceanic crust.

Monitoring ground movement at Volcán de Colima, Mexico, using Sentinel-1 data and SqueeSAR ®

Volcán de Colima is a highly active stratovolcano in western Mexico, which presents a significant hazard to over 300 000 people who live within c. 40 km of the volcano. Because of its persistent activity, the volcano is actively monitored and researched, and understanding the patterns of behaviour is vital to accurate hazard assessment. Sentinel-1 synthetic aperture radar (SAR) images from ascending and descending orbits allow 1D and 2D ground motions to be retrieved using multi-interferogram techniques. SqueeSAR ® 's unique processing allows a better characterization of subtle ground movements in remote, rural mountainous areas compared with many other multi-interferogram techniques. A dataset of 147 SAR scenes (2017–19) has been processed to show patterns of lava subsidence (&lt;150 mm of downward vertical deformation over 2 years), as well as volcano deflation and apparent westward lateral movement. These data indicate that viscous andesitic lava flows may remain mobile for years following eruption and emplacement, and that the entire volcanic edifice is subsiding. Despite the apparent quiescence, volcanic edifices can remain highly dynamic after the termination of explosive or effusive activity. We interpret that the western flank of Volcán de Colima may become steeper with time and may be of long-term concern for hazard assessment activities. Thematic collection: This article is part of the Remote sensing for site investigations on Earth and other planets collection available at: https://www.lyellcollection.org/topic/collections/remote-sensing-for-site-investigations-on-earth-and-other-planets

Environmental risk assessment associated with acidic volcanics in Egypt

The present work aims to study gamma rays emitted by radionuclides such as 238U, 232Th and 40K from acidic Monqul volcanics. The studied volcanics are represented by a thick stratified lava flows interbanded with their pyroclastics. They are composed of thick lava flows of andesite and, to a lesser extent of basalt, and acidic volcanics including rhyolite and dacite. The average values of 238U, 232Th and 40K are (46 ± 24 Bq kg-1), (62 ± 11 Bq kg-1) and (1227 ± 318 Bq kg-1) in the rhyolite-dacite samples are greater than the worldwide average. The variation of radioactive bearing minerals observed inside granite faults produced the great amounts of radioactivity perceived in the samples. Calculating radiological risks is used to assess the public's radioactive risk from radionuclides revealed in the studied Rhyolite-dacite samples. The acceptable limit for excess lifetime cancer (ELCR) evaluations has been exceeded. As a result, Rhyolite-dacite are inappropriate for apply in building materials.

Advanced characterization of hydrothermal flows within recharge and discharge areas using rare earth elements, proved through a case study of two-phase reservoir geothermal field, in Southern Bandung, West Java, Indonesia

Rare earth element (REE) analysis is effective for tracing water–rock interactions and solute transport in geothermal and groundwater systems. This study aimed to clarify hydrothermal flows within recharge and discharge areas of a geothermal system. We selected a well-known high-temperature geothermal field with two-phase reservoir in Southern Bandung, West Java (Indonesia) as a case study target, and collected 31 river/spring samples and 8 well rock samples. The measured total REE series concentrations ranged widely in the water samples, i.e., rivers: 3.4–35 ppt, cold springs: 0.3–284 ppt, and hot springs: 1.4 ppt to 102 ppm. Enrichment of light REEs (LREEs) in the water samples was characterized more clearly by Post Archean Australian Shale normalization than by chondrite normalization. Speciation analysis derived the following interpretations: dissolved REEs in the river water originated from free ions or Ln3+ that are typically contained in near-surface groundwater, and the dominant components were carbonate (LnCO3+) and Ln3+ complexes in the cold springs and LnCO3+ complexation in the hot springs. Steam and gas condensation into less-oxygenated groundwater can be indicated by rich LnCO3+. Only one hot spring was interpreted as being directly connected with the reservoir by strong H2S condensation and LREE enrichment. The water of the other cold and hot springs probably underwent dilution, evaporation, and magmatic gas condensation through shallow, deep, and deep-perched aquifers, permeable zones, and a major fault within the recharge and discharge areas. REE results also suggest that the main constituents of the aquifers are carbonates and silicate minerals and hydrothermally altered lahars, andesitic lava, and pyroclastic flow deposits. REEs facilitate detailed interpretation of geochemistry facies in shallow–deep waters of a hydrothermal system. Finally, integration of the analysis results of REEs, major anions and cations, water isotopes, and strontium isotopes improved a conceptual model of groundwater flows and recharge–discharge interactions in aquifers feeding a geothermal reservoir.

Digital geologic map, petrography and U-Pb geochronology of the Río Santiago Shear Zone, southernmost Sierra Madre Occidental, western Mexico

The boundary between the Sierra Madre Occidental (SMO) and the Trans-Mexican Volcanic Belt (TMVB) is well exposed along the Santiago River, on the border of the states of Nayarit and Jalisco. This region includes a polydeformed belt produced by the relative motion between the Jalisco Block and the SMO, here defined as the “Rio Santiago Shear Zone” (RSSZ). In this work, we present detailed geological cartography, petrographic descriptions, and new zircon U-Pb ages that allow us to establish the stratigraphy of the region surrounding the RSSZ, providing temporal constraints to its tectonic evolution. In the mapped area, the base of the SMO stratigraphic column consists of a succession of massive andesitic lava flows intruded by felsic dikes and a felsic subvolcanic body of 27.5 and 27.2 Ma, and it is covered by a series of ignimbrites of 26.8 and 25.3 Ma. A red beds succession separates a second package of ignimbrites of ∼20-19 Ma, in turn capped by rhyolitic lava domes of 19.7 and 18.6 Ma and a rhyodacitic lava flows of 15.6 Ma, this Miocene succession is also intruded by a felsic body of 18.3 Ma west of the La Yesca dam. The SMO succession is covered by rocks belonging to the bimodal volcanism of the TMVB, emplaced between the end of the Miocene and the Pleistocene. The RSSZ developed through several deformation phases that occurred since the end of the Oligocene. The Oligocene succession of the SMO is affected by NE-SW and WNW-ESE trending lateral faults, NW-SE open folds and WNW-ESE and E-W trending reverse oblique faults. Some of the reverse oblique faults were later reactivated as normal faults. WNW-ESE trending normal faults associated with the Tepic-Zacoalco Rift affected the area south of the Santiago River during the Pliocene and Pleistocene. Normal faulting produced an accumulated vertical offset up to 700 m between the northern and southern regions of the Santiago River.

The eruptive chronology of the Carihuairazo volcano (Ecuador): Recurrent sector collapses of a Middle Pleistocene stratovolcano of the northern andes

The eruptive chronology of arc volcanoes consists of construction stages usually punctuated by large collapse events affecting the edifice. In this paper, we reconstruct the eruptive chronology of Carihuairazo volcano, a Middle Pleistocene edifice from the Ecuadorian segment of the Andean Northern Volcanic Zone. This study is based on extensive fieldwork on both the proximal flanks of the volcano and the medial-to-distal deposits of the nearby Ambato basin, as well as a large dataset of geochronological (40K-40Ar, 14C) and geochemical (major and trace element) data. The Basal Carihuairazo edifice is mainly composed of an andesitic lava flow succession dated at 230–200 ka. The resulting edifice suffered a first sector collapse that was responsible for a relatively large (4 ± 1 km3) debris avalanche deposit (DAD-1) that covers the entire Ambato basin. This event occurred between 206 ± 4 and 216 ± 5 ka. Then, Carihuairazo started a succession of construction (Intermediate and Terminal lava flow successions) and destruction stages lasting about 50 ky (i.e., from 200 to 150 ka), which are composed by thick block-and-ash flow deposits (L- and U-BAFD) and debris avalanche deposits (DAD-2). This volcanic succession is recorded in the Ambato basin, interlayered with several tephra fallout deposits (TFD-1 to −4) whose source is the neighbouring Huisla-Mulmul volcanic complex. The current morphology of Carihuairazo results from two additional sector collapses (DAD-3 and -4) that occurred during the past 40–50 ka, i.e., following a long period (at least 100 ka) without volcanic activity. We stress these debris avalanches were not related with magmatic activity. Samples from the Carihuairazo volcano defines a medium-K magmatic trend composed of andesites and dacites with a mineral assemblage of plagioclase, amphibole, ortho- and clino-pyroxene, and Fe–Ti oxides. The evolution of the Carihuairazo edifice, recorded in the medial-distal deposits of the Ambato basin, represents a unique example in the Ecuadorian arc of an edifice that experienced successive destruction and construction stages during a major part of its volcanic history.

Reconstruction of ancient volcanic complexes using magnetic signature: A case study from Cambrian andesite lava flow, Bohemian Massif

Reconstruction of the Upper Cambrian Křivoklát-Rokycany Volcanic Complex was made using anisotropy of magnetic susceptibility (AMS). The correlation of AMS with visible structures at a few sites showed that the most important and reliable information was the direction of magnetic lineation K1 that determines the direction of a lava flow. The analysis of K1 directions together with radially propagating dikes helped to determine the feeding area along the NW rim of the volcanic complex. One andesite feeder and one rhyodacite feeder were recognized with certainty. In addition, K1 directions pointed to a suspicious area with the presence of another andesite feeder in a caldera-like structure. The evaluation of data strongly suggests that magnetic susceptibility in andesite lavas increases with the distance from the feeder and also with the distance towards the upper part of the andesitic lava flow. We suggest that this might be related to the degree of oxidation of the lava flow before solidification as a reaction with oxygen in the atmosphere. Oxygen can react with FeO in the andesite melt, which consequently results in the formation of magnetite.

Central vs. lateral growth and evolution of the < 100 ka Peinado composite volcano, southern Central Volcanic Zone of the Andes

Composite volcanoes often display shifts in activity between central and lateral vents that are related to the local stress field and the underlying magmatic plumbing system. The Quaternary Peinado composite volcano in the southern Central Volcanic Zone (CVZ) of the Andes exhibits a striking symmetrical configuration of lateral vents around a main central cone and vent. In this contribution, we carry out detailed mapping, morphometric analysis and unspiked K-Ar dating, together with petrographic and whole-rock major oxides, trace element and Sr-Nd-Pb isotopic analyses, to constrain the growth history of the volcano and the interplay between central and lateral activity. Ten new unspiked K-Ar ages ranging between 36.8 ± 3.8 and 72.6 ± 8.0 ka highlight that Peinado is a young potentially active volcano. A main central cone-building stage ≥70–60 ka of mostly andesitic composition formed the bulk of the edifice. During this stage, vents around the cone base erupted basaltic andesite lava flows that are among the most mafic compositions of CVZ composite volcanoes, possibly related to the location of Peinado on an alignment of mafic monogenetic centers. At ~50–40 ka, the locus of activity shifted to mid-flank vents emplaced around the central vent, with eruption of andesite > basaltic andesite lava flows of similar composition to the central cone. Minor coeval-to-younger activity from the central vent was progressively more felsic, with eruption of dacitic lavas and block and ash flows, and possibly minor fallout. The shift of the bulk of activity from the central to the lateral mid-flank vents was likely related to the effects of the edifice load and magma compositions, with more mafic and dense magmas erupting preferentially through the flank vents and more differentiated magmas from the central vent. Although activity has been dominantly mafic and effusive, an evolution towards more felsic products from the central vent suggests that future activity may be somewhat explosive. The particular configuration of the lateral vents and structures around the central cone, together with other features, point towards a possible future collapse of the edifice, either a sector collapse or a caldera collapse.

The importance of overbank deposits and paleosol analyses for comprehensive volcanic hazard evaluation: the case of Holocene volcanism at Miravalles Volcano, Costa Rica

On the flanks of the dormant Miravalles volcano, systematic fieldwork and radiocarbon dating of buried humus-rich soils (paleosols) and wood fragments, augmented by mineralogical and geochemical analysis, reveal extensive and previously undocumented Holocene activity. Phase 1 consisted of a ~ 6300 BCE (8.3 ka) volcanic debris avalanche and thick lapilli blast and fallout deposit that appear coeval. Hiatus 1 marks 2600 years of inactivity followed by Phase 2 lapilli interbedded with two lahars below a basaltic lava flow that dates to 3400 BCE (5.3 ka). Hiatus 2 lasted 1800 years from 3300 to 1500 BCE (5.3 ka to 3.5 ka), after which a very active Phase 3 ensued from 1600 BCE to 1500 CE (3.5 to 0.5 ka) with ≥ four lapilli eruptions, ≥ 4 lahars, ≥ 6 layers of ash and pumice, and small andesitic lava flows. The most recent evidence for eruption is a 1070 CE lapilli overlain by poorly-sorted gravels that may represent distal lahar sediments. Evidence indicates the occurrence of at least two, if not three, destructive lahars on the west flank of Miravalles in the past 500 years. The floodplain sedimentary record indicates much more activity of Miravalles volcano over the past 3500 years (since ~ 1500 BCE) than previously known, with a minimum of 24 events in that span. Overbank floodplain deposits are likely to contain the most compete record of recent activity in active and dormant volcanoes, and in the absence of dateable vegetation fragments, radiocarbon dating of paleosol A-horizons is very useful, with a precision of ~ 5 to 10% for a given age, e.g., 1200 ybp ± 60 to 120 y.