Stratovolcano Research Articles

Volcanogenic processes and petrogenesis of the early Pleistocene andesitic-dacitic Maungatautari composite cone, Central Waikato, New Zealand

ABSTRACTMaungatautari is an extinct, andesitic-dacitic composite cone situated 35 km southwest of Hamilton, New Zealand. This study examines the volcanic history and petrologic evolution of Maungatautari using field mapping, petrography of pyroclastic successions and lavas, and whole rock and isotope analyses of selected lavas. Lavas consist of non-vesicular labradorite, pyroxene and hornblende andesites and dacites. A small cone of olivine basalt is located at Kairangi, 7 km to the northwest of the Maungatautari trig. Whole rock geochemical and strontium and neodymium analyses demonstrate that these lavas were derived from at least three distinct mantle-melt sources. Mass-wasting processes continue to shape the mountain post volcanic activity and include catastrophic failure of the north-eastern flank which produced a 0.28 km3 rock avalanche deposit. This study considers Maungatautari to reflect andesitic-dacitic arc volcanism occurring within the upper North Island c. 2 Ma.

Volcanism of the South Aegean Volcanic Arc

Volcanism along the South Aegean volcanic arc began about 4.7 Ma and has lasted until the present day, with eruptions at Methana, Milos, Santorini, Kolumbo and Nisyros volcanoes in historical times. These volcanoes can be grouped into five volcanic fields: three western fields of small, mostly monogenetic edifices, and two central/eastern fields with composite cones and calderas that have produced large explosive eruptions. Crustal tectonics exerts a strong control over the locations of edifices and vents at all five volcanic fields. Tephra and cryptotephra layers in deep-marine sediments preserve a continuous record of arc volcanism in the Aegean as far back as 200,000 years. Hazards from the volcanoes include high ash plumes, pyroclastic flows and tsunamis. Monitoring networks should be improved and expanded.

Construction of Analytical Eigensolutions for Isotropic Conical Bodies and Their Application for Estimation of Stresses Singularity

A complete set of eigensolutions is constructed for different variants of circular conical bodies: homogeneous cone with one lateral surface (solid cone), homogeneous cone with two lateral surfaces (hollow cone) and composite cone for different variants of boundary conditions on the lateral surface. It has been shown that the constructed eigensolutions can be readily applied for estimation of the character of stress singularity at the vertices of conical bodies. The character of stress singularity at the vertex of the solid and hollow cones for different variants of boundary conditions on the lateral surfaces has been defined by direct numerical simulations. Numerical results obtained for solid, hollow and compose cones under different boundary conditions on the lateral surfaces are discussed.

The Goshogake mud volcano field, Tohoku, northern Japan: An acidic, high-temperature system related to magmatic volcanism

The high-temperature (33–98 °C), highly acidic (pH 2.44–2.94) Goshogake mud volcano field in Akita Prefecture, northern Japan, is a mud volcano system associated with the Quaternary andesitic composite volcano Akita Yakeyama. The mud volcano features observed in Goshogake include salsa ponds, gryphons, and mud pots. This is a rare example of mud volcano systems linked with magmatic volcanism with the full range of landforms observed primarily in low-temperature mud volcanism in sedimentary settings. The Goshogake mud volcano field is probably not a simple hydrothermal system related to a magmatic volcano. Instead, it appears to be a hybrid system: sedimentary volcanism linked with deep mud sources and strongly influenced by its surrounding magmatic volcanism. The identified mineral species in the sampled mud include quartz group, hydrous silica, muscovite, kaolinite, pyrite, and sulfur. The presence of high-temperature silica polymorphs (tridymite and cristobalite) and/or microcrystalline opals (opal-C, opal-CT), and an amorphous form of silica (opal-A) in the mineralogy indicates that the mud volcano system likely involves conditions and processes such as high temperature, hydrothermal circulation, dehydration reaction at certain depths underneath the Goshogake mud volcano field. Although the source of the mud is not clearly determined, possible options include 1) hydrothermal alteration products of host rocks and sediments, 2) fine-grained sedimentary layer(s) at depth, or 3) a combination of 1) and 2). In-situ measurement of emitted gases from vents detected methane, which is possibly linked with the organic-rich sedimentary layer(s) aside from being a product of thermodynamic equilibrium with CO2 under the subsurface pressure-temperature conditions. The increases in δD and δ18O of water in Goshogake mud volcanoes with respect to the values of current meteoric water indicates that the water was derived not only from meteoric water, and deviation of the values may be explained by processes such as evaporation and mixing of other waters from deeper sources. Regarding the driving mechanisms at the Goshogake mud volcanoes, buoyancy of muddy sediment, high fluid pressure under overpressured or under-compacted conditions due to rapid sedimentation, together with the presence of a gas phase in the sediment, could be key factors. Although the Goshogake mud volcano field currently maintains a low-level activity resulting in only minor morphological changes of the mud volcano landforms, enhanced activities have been documented in the last half century. The historical records are inconclusive about the relationship between earthquakes and activity in the Goshogake mud volcano field.

Magma origins and geodynamic implications for the Makran-Chagai arc from geochronology and geochemistry of Bazman volcano, southeastern Iran

Bazman is an isolated voluminous (3497 m elevation; >300 km2) composite volcano that is located within the western segment of the Makran-Chagai arc. This arc obliquely tracks the modern EW-trending trench offshore the Oman sea coast of Iran and Pakistan, with several Quaternary stratovolcanoes (Bazman and Taftan in SE Iran, and Kuh-i-Sultan in western Pakistan) superimposed on a preexisting Neogene arc. High spatial resolution and high sensitivity U-Pb geochronology using Secondary Ionization Mass Spectrometry (SIMS) yielded four clusters of zircon ages for Bazman volcanic rocks which range from ca. 8.6 Ma to 41 ka. Lava and pyroclastic materials erupted between 8.6 and 5.9 Ma forming a thick Neogene volcanic succession (Ngv). These deposits were intruded by hypabyssal andesite-dacite domes at ca. 4.1 Ma. The next younger group of the Quaternary Bazman center comprises several eruptive pulses at 1.37 Ma, 1.13 Ma, 0.943 Ma, 0.853 Ma and 0.635 Ma, which constructed the main edifice around a central vent through alternating eruptions of lava and pyroclastic rocks (Qtv and Qa2). Subsequently, ignimbrite flows also sourced from the main vent erupted at 0.59 and 0.47 Ma, and covered the earlier erupted deposits. The youngest dated eruptive phase (Qa3) comprises the emplacement of dacitic to andesitic lava around the top of volcano. Based on Uranium-series (238U-230Th) disequilibrium in Qa3 zircons, model ages of ca. 41 ka define a maximum eruption age of these lavas, which tapped a long-lived magma reservoir with zircon crystallization ages predating eruption by 10’s to 100’s of ka. Low- medium-K calc-alkaline basaltic-andesitic eruptions formed parasitic cones located on northeastern flanks of the edifice as the youngest unit (Qa4) of Bazman. Both Neogene and Quaternary rocks from Bazman volcano exhibit homogeneous trace element characteristics, including enrichments in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to the high field strength elements (HFSE) and heavy rare earth elements (HREE), respectively. High Th/Yb and negative anomalies of Ta, Nb and Ti are consistent with an enriched mantle source in a continental subduction zone. Trace element modeling for the most primitive basalts erupted at Bazman suggests an origin of parental magmas through ∼15% partial melting of an enriched spinell-lherzolite mantle, whereas the genesis of Bazman acidic volcanic rocks with SiO2 > 62% involves partial melting in the middle/lower continental crust which became subsequently overprinted through assimilation – fractional crystallization (AFC) processes. Compositional continuity of Quaternary Bazman volcanic rocks with their Neogene precursors implies a steady magma source above the subducted Oman slab. Consequently, subduction geometry in the Makran-Chagai arc has experienced little modification over the past few million years.

Overview of the petrophysical and geochemical properties of the Ungaran Quarternary Volcano in relation to geothermal potential

Ungaran geothermal field is estimated to have a potential of 15 MWe. The volcano is located in the middle of Java Island which is a range of Quaternary volcanoes. As in other islands in Indonesia that indicate that this volcano has a potential energy of geothermal. This volcano is a strato volcano with andesitic composition. The Ungaran volcano geothermal system is located within a young cone depression, overgrown by Mount Gugon and Mount Megi that form the depressive ring. Geothermal manifestations contained in Gedongsongo include: fumarola, hot springs, travertine, steaming ground and alteration rocks. The temperature of the hot springs is about 50°C, the pH of hot water is acidic (ranging from pH 1.5 to 5.5), bubble gas and around fumarola are found sublimation of sulfur and pyrite.This research uses analytical methods of geochemistry (water and rock), petrography and petrophysics. Based on geothermometer analysis shows that the reservoir temperature is 300°C. The composition of fumaroles is strongly influenced by magmatic elements with temperatures greater than 300°C. While petrography analysis yields that the material of Ungaran volcano rock is andesite-basaltic. Knowing the geothermal potential of this area is expected to increase the Java-Bali power supply.

Imbabura volcano (Ecuador): The influence of dipping-substrata on the structural development of composite volcanoes during strike-slip faulting

The geology and long-term structural development of Imbabura volcano (Ecuador) have been discerned from field surveys, as well as petrographical and geochemical studies. The volcano is composed of an ancient edifice (Imbabura I), which has experienced one major volcanic landslide directed N 330–340°. After the emplacement of that debris-avalanche deposit, the petrographically and geochemically different edifices Imbabura II-1 and Imbabura II-2 developed on the N and NE flank of Imbabura I, as well as in its summit zone. Finally the smaller Imbabura II-3 edifice, a dome-complex locally known as Huarmi Imbabura, was emplaced in the SSW flank of Imbabura I. The relatively complex structure of the edifice (i.e. flank collapse direction and spatial distribution of the major stratigraphical units) cannot be explained solely by volcano-tectonic interactions with the regional left-lateral Río Ambi strike-slip fault, which traverses the edifice from NNE to SSW. Instead, the fact that the whole Imbabura edifice stands on a substratum dipping to the NW (i.e. the NW flank of the neighbor Cubilche volcano) is proposed to be the main factor influencing the departure of Imbabura structure from previously known models of volcanic edifices interacting with strike-slip faults. This hypothesis was tested with scaled experiments, during which the dip-direction of the substratum was systematically changed with respect to the strike of the fault. The structures developed by the experimental prototypes are highly coherent with those observed at Imbabura volcano.

Bond to Zirconia Ceramic: Evaluation of Different Primers and a Universal Adhesive

Objective: The aim of the study was to evaluate the effect of a universal adhesive and different primers on the bond strength to zirconia ceramic. Materials and Methods: Seventy-five zirconia ceramic samples were obtained and divided into five groups (n=15): G1–Scothbond Universal (SBU); G2 – silane + SBU; G3 - Signum Zirconia Bond; G4 - Z-Prime Plus; G5 - MZ Primer. A cone of composite resin was built. The specimens were stored in 100% relative humidity with distilled water at 37°C for 48 h and then submitted to a tensile bond strength test in a universal testing machine at a crosshead speed of 0.5 mm/min. The type of failure that occurred during the de-bonding procedure was analyzed. Results: The mean results of the bond strength test (MPa) followed by the same letter represent no statistical difference by ANOVA and Tukey’s post-hoc test (p<0.05): G2=27.55a (±6.99), G4=23.71a (±5.65), G1=22.64a (±5.67), G5=13.64b (±5.49), G3=7.54c (±4.75). G2 and G4 exhibited predominantly cohesive failure in the composite resin cone. G1 and G5 had predominantly mixed failures, and G3 exhibited only adhesive failures. Conclusion: The SBU and Z-Prime Plus provided higher bond strength to zirconia ceramic.

Sub-lithospheric origin of Na-alkaline and calc-alkaline magmas in a post-collisional tectonic regime: Sr-Nd-Pb isotopes in recent monogenetic volcanism of Cappadocia, Central Turkey

Intense Cenozoic magmatism accompanied the convergence and collision of the Eurasian, African and Arabian plates. In the Cappadocia Region of Central Anatolia, widespread and abundant volcanism developed from the late Miocene to the Quaternary. Calc-alkaline pyroclastic products and lava erupted diffusely during the late Miocene and Pliocene. Both calc-alkaline and Na-alkaline volcanic rocks were emplaced in close spatial and temporal proximity during the Plio-Pleistocene. Here we focus on the Plio-Pleistocene monogenetic activity, which produced two types of rocks: calc-alkaline volcanic rocks ranging in composition from basalts to rhyolites and occurring around the Acıgöl caldera, the Göllü Dağ dome and the Hasan Dağ and Erciyes Dağ composite volcanoes; Na-alkaline volcanic rocks ranging from alkali basalts to mugearites and cropping out in monogenetic centres in Karapınar, along the WSW flank of Hasan Dağ, in Acıgöl and near the Kızılırmak River, northwest of Nevşehir.The coeval occurrence of calc-alkaline and Na-alkaline volcanism observed here is in striking contrast with activity in the surrounding Western and Eastern Anatolia regions, where the calc-alkaline volcanic rocks are distinctly older than the Na-alkaline ones. The Sr and Nd isotopic compositions of the mantle sources of both rock types show a narrow, overlapping range of values (87Sr/86Sr~0.70395–0.70474 and 143Nd/144Nd~0.51268–0.51281 for the calc-alkaline products, 0.70334–0.70524 and 0.51268–0.51293 for the Na-alkaline ones). In addition, most of the Na-alkaline products, like the calc-alkaline rocks, show an arc-type distribution of incompatible trace elements, with marked enrichments in LILE (Large-Ion Lithophile Elements) and negative HFSE (High Field Strength Elements) anomalies. True intraplate magmas are absent in Cappadocia, where the genesis of Na-alkaline basalts is ascribed to mixing between different percentages of within-plate (OIB) and calc-alkaline magmas. Modelling reveals that the addition of 13% and 30% OIB-type melt to a calc-alkaline magma is enough to change a SiO2-oversaturated magma into an ol-hy-normative and ne-normative one, respectively, whereas the addition of 15% calc-alkaline magma to an OIB-type magma results in a negative NbTa anomaly in the primitive mantle-normalized spider diagrams.The various types of products of recent volcanism in Cappadocia reflect the complex tectonic setting of the Central Anatolian Block: characterised by strike-slip tectonics and local extensional pull-apart basins, different magma types formed contemporaneously through decompression melting at different depths.In this scenario, the calc-alkaline magmas derived from partial melting of a mantle wedge modified by a subduction component, whereas the within-plate (OIB) magmas derived from a deeper, unmodified sub-slab mantle source. Mixing between calc-alkaline and within-plate magmas during their rise to the surface produced the Na-alkaline Cappadocia basalts. The very low rate of extension allowed within-plate magmas (OIB) to reach the surface after having interacted with the overlying calc-alkaline magmas in the late stages of Cappadocia volcanism.

Overview and plumbing system implications of monogenetic volcanism in the northernmost Andes' volcanic province

Monogenetic volcanic fields are commonly related to rifts and/or intraplate tectonic settings. However, they are also less commonly recognised in subduction zones, including both front and back-arc volcanoes (e.g. monogenetic volcanoes associated with the Llaima volcano in Chile or the San Agustín Volcanic Field in Colombia). Here, we describe monogenetic volcanic fields associated with subduction-related polygenetic volcanism in the northernmost part of the Andes Northern Volcanic Zone (NVZ) (2° S to 4°30′N). These fields are associated with the main axis of the Quaternary volcanoes. They are linked to the polygenetic San Diego – Cerro Machín Volcano Tectonic Province (~140 km long; SCVTP) in Colombia, the chain that hosts the iconic Nevado del Ruiz volcano. Presently, three monogenetic volcanic fields, with a typical calc-alkaline signature, have been identified on both sides of this province. From south to north, they are: 1) Pijaos Monogenetic Volcanic Field (PMVF), 2) Villamaría – Termales Monogenetic Volcanic Field (VTMVF), and 3) Samaná Monogenetic Volcanic Field (SMVF). PMVF is located ~25 km south of Cerro Machín volcano, the southernmost active volcano of the SCVTP. This field was formed by at least two eruptions with both effusive and explosive eruptive styles. Three cones and a maar are recognised. Previous work has defined the volcanoes as basaltic andesitic in composition, which we recognised as the most mafic expression (MgO 10–11 wt%) in the whole SCVTP. Its source is related to the same, but deeper magma that feeds the volcanoes in the SCVTP. Stratigraphic relationships show that the volcanoes are younger than the underlying alluvial and volcaniclastic Ibagué fan (<2.58 Ma). VTMVF is located in the northwestern region of the SCVTP (>5 km of the axis of the province). This field is made up of at least 14 volcanoes aligned with the active Villamaría – Termales fault system, as previous work has recognised. The volcanism has been mainly effusive, represented by lava domes and some lava flows. Since the 1980s, studies have framed these andesitic to dacitic volcanoes in the context of the history of the Nevado del Ruiz volcano. It is inferred that the magmatic source is a shallow magma reservoir underneath the SCVTP. Stratigraphic and field relationships have shown that the last eruption occurred <38 ka. SMVF is located ~50 km north of Romeral composite volcano, the northernmost active volcano from the SCVTP. Previous studies have revealed that this field comprises at least two volcanoes: A maar (~20 ka years old) and a pyroclastic cone (~33 ka years old). These studies defined the volcanic products as andesitic and dacitic in composition. It is inferred that this field is a result of the same magmatism as that of the SCVTP. Overall, it is clear that monogenetic volcanism is not atypical in the area. We thus propose a SCVTP magmatic plumbing system joining both the monogenetic and polygenetic volcanoes related to the subduction arc.

The structure of composite volcanoes unravelled by analogue modelling: A review

Volcanic edifices are unstable accumulations of eruptive and intrusive products with complex internal structures. A documentation of these structures facilitates the assessing of the various hazards associated with volcanoes, e.g. flanks instabilities and eruptive events. However, structures are not easily assessed in the field, as volcanoes are regularly covered by eruptive products and are rapidly eroded. In the case of recent and active volcanoes, internal structures are generally extrapolated from the external morphology of the edifice, which can be documented using Digital Elevation Models (DEM) and geodetic data. Interpretation of such data greatly benefits from analogue models, which are idealised representations of reality used to test the impact that various processes may have on the shape of a volcanic edifice. This short review focuses on the contribution of analogue models to our comprehension of the internal structure of composite volcanic cones. The other volcanic morphologies (e.g. caldera) are excluded from this review, as they have distinct structure and evolution that have already been thoroughly reviewed. The reviewed models were used to investigate the impact that regional faults, magma injections and ductile substratum, among other processes, have on the internal structure and surface morphology of many volcanic edifices. These models were also used to locate unstable flanks and eruption sites.

Vertex angles effects in the energy absorption of axially crushed kenaf fibre-epoxy reinforced elliptical composite cones

Abstract Experimental quasi-static crushing tests were conducted by using a universal testing machine format kenaf-epoxy composite elliptical cones. The work focused on the vertex angle's effects on energy absorption capability; the vertex angles vary from 0° to 24° in 6 increments. The failure modes of the kenaf fibre epoxy composite elliptical cones were observed utilising delegate photos taken during the quasi-static crushing test. Load-deformation curves and deformation histories of typical specimens are presented and discussed. Moreover, the effects of cone vertex angles on the load carrying capacity and the energy absorption capability are also discussed. The results show that the energy absorption abilities significantly influence the ellipticity vertex angle as the load carrying capacity. We concluded that the quasi-static axial crushing behaviour of elliptical mat laminated composite cones is strongly affected by their structural geometry and the specific energy absorbed by the composite elliptical cones with vertex angles of 6°, 12°, 18°, and 24°, which is more than an elliptical cone with the vertex angle of 0° (the elliptical tube) at any given deformation. However, the specific energy absorption for the elliptical composite cone showed a positive correlation, i.e., the more the angle increased, the more energy was absorbed. In this regard, an elliptical composite cone with a 24° angle exhibited the best energy absorption capability.

Geothermal Potential Analysis Using Landsat 8 and Sentinel 2 (Case Study: Mount Ijen)

Geothermal energy is also a heat energy contained in the earth’s internal. Indonesia has a total geothermal potential of around 27 GWe. The government is eager for the development of geothermal in Indonesia can run well so that geothermal can act as one of the pillars of national energy. However, the geothermal potential has not been fully utilized. One of the geothermal potention is Mount Ijen. Mount Ijen is a strato volcano that has a crater lake with a depth of about 190 m and has a very high degree of acidity and the volume of lake water is very large. With the abundance of potential geothermal potential in Indonesia, it is necessary to have an activity in the form of integrated geoscience studies to be able to maximize the potential content that exists in a geothermal area. One of the studies conducted is to do potential mapping. This research performs image data processing of Landsat 8, Sentinel 2, RBI Map, and preliminary survey data. This research carried out the Vegetation Index, surface temperature and altitude. The equipment used in this research includes image processing software, number processing software, GPS Handheld and Laptop. Surface Temperatures in the Mount Ijen have anomalies with large temperatures ranging between 18° C to 38° C. The best correlation value of altitude and ground surface temperature is -0.89 ie the correlation of January surface temperature. While the correlation value of Landsat 8 and Sentinel 2 vegetation index was 0.81. The land cover confidence matrix scored 80%. Land cover in the research area is dominated by forests by 35% of the research area. There is a potential area of geothermal potential is very high on Mount Ijen with an area of 39.43 hectares located in Wongsorejo District and adjacent to District Sempol.

SIFAT-SIFAT TANAH YANG BERKEMBANG DARI BAHAN VOLKAN DI HALMAHERA BARAT, MALUKU UTARA

[SOIL PROPERTIES DEVELOPED FROM VOLCANIC MATERIALS IN WEST HALMAHERA, NORTH MALUKU]. West Halmahera region is dominated by soils formed from young volcanic materials that have unique properties and high productivity for agricultural use. The purpose of this study is to characterize soil properties derived from volcanic materials in that area and to test the andic soil properties according to Soil Taxonomy 2006. Four pedons of strato volcanoes from the area were described their morphological properties in the field and 16 soil samples were analyzed for physical, chemical and mineralogical properties in the laboratory. The results indicated that all the pedons show black to very dark brown colored in A horizons and dark brown to brown in B horizons. The soils are deep, loam to sandy loam texture (sand content 38-71 %). The soils have weak to moderate subangular blocky structure and very friable consistency. The soils show slightly acid to neutral reaction (pHH2O 6.0-6.8), high pHNaF (10.78-10.95), high organic carbon (3.75-4.65 %) in A horizon, moderate to high cation exchange capacity and base saturation. All the pedons show high P-retentions (45-80 %), high values of ammonium oxalate extractable (Alo+0.5Feo) (2.91-6.070 %), high volcanic glass content (>5%), and index values of [(Alo+0,5Feo) x 15,625+ (%volcanic glass)] > 36.25 that meet the requirements for andic soil properties, and thus they are classified as Andisols order. The sand minerals are dominated by volcanic glasses and dark minerals that belong to intermediary properties, and high weatherable mineral reserve.

Early 2017 Activity of the Barren Island Volcano:Facts Versus Hype

Barren Island is the northernmost active stratovolcano of the Sunda Volcanic Arc system in the northeastern Indian Ocean. It is the only active volcano in the Indian territory. The arc is a result of subduction of the Indian plate beneath the Burma plate, a sliver of the Eurasian plate. This subduction zone is a southward extension of the Himalayan convergent boundary that takes a turn at the Eastern Syntaxial Bend. Located ~135 km northeast of Port Blair (12°70'N/93°51'E), the Barren Island volcano covers a subaerial area of ~8 km.

U-Th age evidence from carbonate veins for episodic crustal deformation of Central Anatolian Volcanic Province

Central Anatolia represents one of the most outstanding examples of intraplate deformation related to both continental collision and back-arc extension generating non-uniformly distributed stress fields. In this study, we provide direct field evidence of various stress directions and investigate carbonate-filled fracture systems in the Central Anatolian Volcanic Province using U/Th geochronology and isotope geochemistry for evaluating the episodes of latest volcanic activity under regional stress. Field data reveal two independent fracture systems in the region. Successive fracture development has been controlled by two different volcanic eruption centers (Hasandağ Composite Volcano and Acıgöl Caldera). Trace element, and stable (C and O) and radiogenic (Sr) isotope compositions of carbonate veins indicate different fluid migration pathways for two different fracture systems. The U/Th age data for carbonate veins of two independent fracture systems indicate that the crustal deformation intensified during 7 episodic periods in the last 150 ka. The NNE-trending first fracture system was formed as a result of strain cycles in a period from 149 ± 2.5, through 91 ± 1.5 to 83 ± 2.5 ka BP. Subsequent deformation events represented by the ENE-trending second fracture zone have been triggered during the period of 53 ± 3.5, 44 ± 0.6 and 34 ± 1 ka BP before the first fracture zone resumed the activity at about 4.7 ± 0.15 ka BP. Although further studies are needed to evaluate statistical significance of age correlations, the periods of carbonate precipitation inferred from U-Th age distributions in this study are comparable with the previous dating results of surrounding volcanic eruption events.

Miocene volcanism in the Oaş–Gutâi Volcanic Zone, Eastern Carpathians, Romania: Relationship to geodynamic processes in the Transcarpathian Basin

We present the first comprehensive study of Miocene volcanic rocks of the Oaş–Gutâi Volcanic Zone (OGVZ), Romania, which are exposed in the eastern Transcarpathian Basin (TB), within the Eastern Alpine–Western Carpathian–Northern Pannonian (ALCAPA) block. Collision between the ALCAPA block and Europe at ~18–16Ma produced the Carpathian fold-and-thrust belt. This was followed by clockwise rotation and an extensional regime forming core complexes of the separated TB fragment. Based on petrographic and geochemical data, including SrNd isotopic compositions and KAr ages, we distinguish three types of volcanic activity in the OGVZ: (1) early Miocene felsic volcanism that produced caldera-related ignimbrites in the Gutâi Mountains (15.4–14.8Ma); (2) widespread middle–late Miocene intermediate/andesitic volcanism (13.4–7.0Ma); and (3) minor late Miocene andesitic/rhyolitic volcanism comprising the Oraşu Nou rhyolitic volcano and several andesitic–dacitic domes in the Oaş Mountains (11.3–9.5Ma). We show that magma evolution in the OGVZ was controlled by assimilation–fractional crystallization and magma-mixing processes within an interconnected multi-level crustal magmatic reservoir. The evolution of volcanic activity within the OGVZ was controlled by the geodynamics of the Transcarpathian Basin. The early felsic and late intermediate Miocene magmas were emplaced in a post-collisional setting and were derived from a mantle source region that was modified by subduction components (dominantly sediment melts) and lower crust. The style of volcanism within the eastern TB system exhibits spatial variations, with andesitic composite volcanoes (Gutâi Mountains) observed at the margins, and isolated andesitic–rhyolitic monogenetic volcanoes (Oaş Mountains) in the center of the basin.

Magnetic structure of Basse-Terre volcanic island (Guadeloupe, Lesser Antilles) inferred from 3D inversion of aeromagnetic data

We interpret aeromagnetic data to constrain the magnetic structure of the island of Basse-Terre, Guadeloupe, Lesser Antilles. Aeromagnetic data are inverted in the spatial domain with a Bayesian formulation to retrieve the 3D distribution of rock magnetization intensity and polarity. The inversion is regularized using a correlation length and standard deviation for magnetization chosen to be consistent with results from paleomagnetic measurements on lava flow samples from Basse-Terre. The resulting 3D model of magnetization is consistent at the surface with observed polarities and at depth with a 2D model obtained from a Parker and Huestis (1974) inversion in the Fourier domain. The inferred magnetic structure is compared with the available geological information deduced from published geological, geomorphological and geochronological studies. In the southern part of the island, very low magnetization is observed around the Soufrière lava dome, last activity of the Grande-Découverte-Carmichaël-Soufrière composite volcano, in relation with a high level of hydrothermal alteration. High-magnetizations in the South-East might reflect the presence of massive lava flows and lava domes from the Madeleine vents and Monts Caraïbes. Medium magnetizations in the South-West coincide with the location of debris avalanche deposits associated with the collapse of the former Carmichaël volcano and might reflect less massive lava structure at depth. Using the volume of normal polarity in the South part of Basse-Terre recovered in our 3D model of rock magnetization, we estimate an average construction rate of ∼ 9.4×10−4km3/yr during the Brunhes chron which provides new insights on the volcanic activity of La Soufrière volcano.

Grand Sarcoui volcano (Chaîne des Puys, Massif Central, France), a case study for monogenetic trachytic lava domes

The Grand Sarcoui is a prominent trachytic volcano of the intraplate Quaternary volcanic field of Chaîne des Puys (Massif Central, France), which fulfills basic requirements for being qualified as monogenetic. Grand Sarcoui looks like a simple axisymmetric lava dome, but close observation reveals a complex and dissymmetric structure and composition. The construction of the dome, about 12.5ka ago, combined both endogenous and exogenous growth which resulted in variable modes of emplacement and textures of the lava. One of its most interesting features is a large (~0.29 106m2) fan of deposits bearing hummocks and secondary hydro-eruption craters. Cross sections of these deposits demonstrate that they originated from a sector collapse accompanied by a blast-like event. The dome is covered by a thin layer of lapilli and ash, attributed to a delayed summit eruption which occurred about 10.6ka ago, surprisingly late after its construction. So, this volcano has, at a reduced scale, features that are more usually observed in large composite volcanoes. However, some of these features differ slightly from those that have been documented to date, and they remain partly unexplained. This shows that monogenetic, well preserved, trachytic lava domes, are uncommon and poorly known, unlike rhyolitic, andesitic and dacitic domes.

The Quaternary history of effusive volcanism of the Nevado de Toluca area, Central Mexico

Andesite and dacite lava flows and domes, and intermediate-mafic cones from the Nevado de Toluca area were classified into five groups using field data and 40Ar/39Ar geochronology constraints. Thirty-four lava units of diverse mineralogy and whole-rock major-element geochemistry, distributed between the groups, were identified. These effusive products were produced between ∼1.5 and ∼0.05 Ma, indicating a mid-Pleistocene older-age for Nevado de Toluca volcano, coexisting with explosive products that suggest a complex history for this volcano. A ∼0.96 Ma pyroclastic deposit attests for the co-existence of effusive and explosive episodes in the mid-Pleistocene history. Nevado de Toluca initiated as a composite volcano with multiple vents until ∼1.0 Ma, when the activity began to centralize in an area close to the present-day crater. The modern main edifice reached its maximum height at ca. 50 ka after bulky, spiny domes erupted in the current summit of the crater. Distribution and geochemical behavior in major elements of lavas indicate a co-magmatic relationship between different andesite and dacite domes and flows, although unrelated to the magmatism of the monogenetic volcanism. Mafic-intermediate magma likely replenished the system at Nevado de Toluca since ca. ∼1.0 Ma and contributed to the eruption of new domes, cones, as well as effusive-explosive activity. Altogether, field and laboratory data suggest that a large volume of magma was ejected around 1 Ma in and around the Nevado de Toluca.