Monogenetic Volcanism Research Articles

Subplinian monogenetic basaltic eruption of Sunset Crater, Arizona, USA

Sunset Crater volcano, located ~25 km northeast of downtown Flagstaff (Arizona, USA) in the San Francisco volcanic field, represents an interesting case of highly explosive monogenetic volcanism. Sunset Crater is a young (ca. 1085 CE) scoria cone, ~290 m high, that produced 0.52 km3 dense rock equivalent (DRE) of basaltic magma (0.16, 0.12, and 0.24 km3 DRE for the scoria cone, lava flows, and tephra deposit, respectively). The activity developed in three distinct phases: an initial fissure phase, followed by a highly explosive phase, and a final low-explosivity waning phase. The first phase was characterized by the opening of a 10-kmlong fissure, which produced the Gyp Crater spatter mounds and the Vent 512 lava flow ~10 km SE of the main scoria cone, followed by lava fountaining activity that produced the first tephra layer (unit 1, 0.01 km3 DRE). During the second highly explosive phase, the activity migrated to the northwest to evolve into a single-vent eruption, which formed the main scoria cone. The central vent activity was initially characterized by variable eruptive styles, which started the process of cone building, including deposition of a second tephra layer (unit 2, 0.01 km3 DRE), and the effusion of the two main lava flows (Bonito and Kana’a). Following the initiation of effusive activity, the eruption increased in explosivity to produce three subplinian tephra layers from the central vent (units 3, 4, and 5), which emitted more than 0.22 km3 DRE of basalt, with associated eruption columns >20 km high. By the end of this phase, the Kana’a lava flow was almost completely emplaced, but the Bonito flow continued to grow, forming a 3-km-diameter flow field. A final waning phase produced several tephra units, commonly discontinuous and reworked, with <0.01 km3 DRE cumulative volume. The comparatively large volume of tephra, the high eruptive columns, and high mass eruption rates make Sunset Crater the most explosive monogenetic eruption studied to date (volcano explosivity index [VEI] 3–4). Sunset Crater volcano represents an interesting case of monogenetic volcanism in that its activity was characterized by highly explosive eruptive phases up to subplinian in scale and intermittent episodes of lava effusion that heavily affected prehistoric communities in the area. Explosive basaltic volcanism should be considered when assessing volcanic hazards in continental settings, such as in the western United States.

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 eruptive history of the Pátzcuaro Lake area in the Michoacán Guanajuato Volcanic Field, central México: Field mapping, C-14 and 40Ar/39Ar geochronology

Monogenetic volcanic fields occur in many tectonic settings representing an unpredictable and uncertain volcanic hazard. The Pátzcuaro Lake is located in the central part of the Michoacán-Guanajuato Volcanic Field (MGVF). Field mapping of an area of 560 km2, stratigraphy and new radiometric ages (40Ar/39Ar and 14C) aided in the identification of 45 individual volcanic landforms formed during the past 3.9 Ma. These landforms comprise five medium-size shield volcanoes, 25 scoria cones, 10 lava domes, two lavas associated to scoria cones, one fissural lava flow, and two volcanic complexes. These volcanic edifices erupted a minimum volume of 20 km3 since Pliocene with an output rate of 0.02 km3/ka. Chemical composition of magmas ranges from 47.6 to 65.3 wt% silica, being dominantly andesites (~76 vol%), followed by basaltic-andesites (~12 vol%), dacites (~9 vol%) and basalts (~3 vol%). Volcanic products vary from mainly andesitic during the Pliocene, basaltic to dacitic during the Pleistocene and basaltic-andesitic to andesitic during the Holocene. All these rocks are the result of low-dipping slab subduction-related magmatism. Alignment of cones and structures follow NE-SW, N-S and E-W directions. The youngest faults are associated with the E-W Morelia-Acambay Fault System, with historic earthquake activity. The volcanic complexes, El Estribo and La Muela, have cone collapses to the north that correspond with the direction of maximum regional extension associated with the E-W fault system. The 3.9 Ma history of monogenetic volcanism around the Pátzcuaro Lake demonstrates that monogenic fields can be long-lived volcanic features.

Felsic-intermediate magmatism and brittle deformation in Sierra del Tzirate (Michoacán-Guanajuato Volcanic Field)

The Tzirate volcanic complex (TVC) is located in the central part of the Michoacán-Guanajuato volcanic field (MGVF), central Mexico. It is characterized by a series of andesitic-dacitic domes and by active faulting of the Morelia-Acambay fault system. Its age and the relationship between the magmatic processes that generated the TVC rocks and the evolution of the local stress field were determined with field work, structural analysis, 40Ar-39Ar dating, geochemistry and petrography of the lavas. The dacitic volcanism of the TVC occurred during the Pleistocene (1 Ma) with the eruption of lavas that formed a series of domes (SiO2 = 63–69 wt.%) aligned in NNE-SSW and NW-SE directions. The area is covered by andesitic-basaltic cinder-lava cones and andesitic lava cones of Pleistocene-Holocene age (2.5 Ma – 0.011 Ma) produced by monogenetic volcanism of the MGVF that surrounds the TVC.The TVC magmas produced rocks that can be classified in four mineral groups. One group contains olivine and pyroxene phenocrysts. The second biotite and amphibole euhedral phenocryst, and the other two contain biotite euhedral phenocryst, amphibole microphenocrysts and biotite subhedral crystals surrounded by a rim of plagioclase microcrysts. The diversity of textures in biotite crystals and the linear trends of major and trace elements between La Huacana granite and the less evolved lavas of the TVC suggest that assimilation of a granitic body in the crust might have influenced the evolution of the TVC rocks.The results of the structural analysis show that when the minimum principal stress was vertically oriented the rise of magma to the surface is hindered, favoring the entrapment of magma in shallow magma chambers. The magmatic assimilation process possibly occurred during the same phase, forming the felsic magmas. Subsequently, the local stress field became extensional, and the vertical principal maximum stress developed normal or extensional faults that affected the magma chamber and served as plumbing system for the rise of felsic lava.

Timing the evolution of a monogenetic volcanic field: Sierra Chichinautzin, Central Mexico

The unique nature of monogenetic volcanism has always raised questions about its origin, longevity and spatial distribution. Detailed temporal and spatial boundaries resulted from a morphometric study, mapping, relative dating, twenty-four new 40Ar/39Ar dates, and chemical analyses for the Sierra Chichinautzin, Central Mexico. Based on these results the monogenetic cones were divided into four groups: (1) Peñón Monogenetic Volcanic Group (PMVG); (2) Older Chichinautzin Monogenetic Volcanic Group (Older CMVG); (3) Younger Chichinautzin Monogenetic Volcanic Group (Younger CMVG) and (4) Sierra Santa Catarina Monogenetic Volcanic Group (SSC).The PMVG cover the largest area and marks the northern and southern boundaries of this field. The oldest monogenetic volcanism (PMVG; 1294±36 to 765±30ka) started in the northern part of the area and the last eruption of this group occurred in the south. These basaltic-andesite cones are widely spaced and are aligned NE-SW (N60°E). After this activity, monogenetic volcanism stopped for ~527ka.Monogenetic volcanism was reactivated with the birth of the Tezoyuca 1 Volcano, marking the beginning of the second volcanic group (Older CMVG; 238±51 to 95±12ka) in the southern part of the area. These andesitic to basaltic andesite cones plot into two groups, one with high MgO and Nb, and the other with low MgO and Nb, suggesting diverse magma sources. The eruption of the Older CMVG ended with the eruption of Malacatepec volcano and then monogenetic volcanism stopped again for ~60ka.At ~35ka, monogenetic volcanism started again, this time in the eastern part of the area, close to Popocatépetl volcano, forming the Younger CMVG (<35±4ka). These cones are aligned in an E-W direction. Geochemical composition of eruptive products of measured samples varies from basalts to dacites with low and high MgO. The Younger CMVG is considered still active since the last eruptions took place <2ka.The SSC (132±70 to 2±56ka) is located in the northern part of the area, in the old Chalco Lake and is separated by faults from the rest of the volcanic groups as a different range. The SSC formed closely spaced basaltic andesites to andesitic cones oriented NE-SW (N70°E). The SSC samples have high Zr, P2O5, and Nb, indicating a different magma source.The northern and southern spatial boundaries of the field (the surface area with monogenetic volcanoes) became smaller with time: 78km for PMVG, ~40km for the Older CMVG and ~25km for the Younger CMVG, concentrating the volcanoes in the central part of the area. The alignment of the cones changed progressively from NNE-SSW to NE-SW to E-W through the time, associated with the changes in the stress field which appears also to have caused the gaps.Results suggest that the Sierra Chichinautzin is actually four different volcanic fields, some partially overlapping, instead of one as previously considered. The differences in age, emplacement orientation and geochemistry support this conclusion.

Magmatic plumbing systems of the monogenetic volcanic fields: A case study of Tolbachinsky Dol, Kamchatka

Clusters of small-volume volcanoes that individually may be defined as monogenetic, but have interlinked and interconnected plumbing systems, are used to be categorized as monogenetic volcanic fields (MVF). We argue that such volcanic clusters should be distinguished as separate type of volcanism, intermediate between monogenetic and polygenetic. The magma plumbing system structure of the MVF (its complexity and polymagmatic character) is the key argument for the potential separation of them in a classification. To avoid confusion caused by genetic meaning of the used words we suggest using a term “areal volcanism” or “areal volcanic fields” (AVF instead of MVF) as defining this special type of volcanic activity. Here we provide a review of the main characteristic features of one of the largest Holocene AVF, which is active now – the Tolbachik field of cinder cones in the southern part of Klyuchevskaya volcano group (Kamchatka), known in the literature as Tolbachinsky Dol. This paper is focused on the research of magma plumbing system. We consider structural, morphological, geological, geochemical and petrological data on the erupted basalts and their genesis. Specially planned seismic experiments made in 2010–2015 (seismic tomography and microseismic sounding) allowed modeling of the principal elements of the magma plumbing system of Tolbachik AVF. Analysis of the investigations made in this area shows that Tolbachik AVF has a complex, dynamic, variable magmatic feeding system, which can be visualized as a superposition of subvertical and sublateral magma conduits. The contrast composition of the erupted rocks is caused by their different, although genetically connected, magma sources and mixing processes. One of the long-lived eruptive centers of Tolbachik AVF is Plosky Tolbachik stratovolcano, which lost its independent activity and was captured by Tolbachik AVF in Holocene. The AVF formed rejuvenated volcanism using the feeding system of the stratovolcano like an “old anthill”. The magma plumbing system characteristics of Tolbachinsky Dol strongly support the idea of separation of AVF from monogenetic volcanism type in the classification.

Geology and radiometric dating of Quaternary monogenetic volcanism in the western Zacapu lacustrine basin (Michoacán, México): implications for archeology and future hazard evaluations

The Zacapu lacustrine basin is located in the north-central part of the Michoacan-Guanajuato volcanic field (MGVF), which constitutes the west-central segment of the Trans-Mexican Volcanic Belt. Geological mapping of a 395 km2 quadrangle encompassing the western margin of the basin, 40Ar/39Ar and 14C radiometric dating, whole-rock chemical and petrographic analyses of volcanic products provide information on the stratigraphy, erupted volumes, age, and composition of the volcanoes. Although volcanism in the MGVF initiated since at least 5 Ma ago, rocks in the western Zacapu lacustrine basin are all younger than ~ 2.1 Ma. A total of 47 volcanoes were identified and include 19 viscous lava flows (~ 40 vol.%), 17 scoria cones with associated lava flows (~ 36 vol.%), seven lava shields (~ 15 vol.%), three domes (~ 6 vol.%), and one maar (~ 2 vol.%). Erupted products are dominantly andesites with 42 km3 (~ 86 vol.%) followed by 4 km3 of dacite (~ 8 vol.%), 1.4 km3 of basaltic trachy-andesite (~ 3 vol.%), 1 km3 of basaltic andesite (~ 2 vol.%), and 0.14 km3 of rhyolite (~ 0.3 vol.%). Eruptive centers are commonly aligned ENE-WSW following the direction of the regional Cuitzeo Fault System. Over time, the high frequency of eruptions and consequent accumulation of lavas and pyroclastic materials pushed the lake’s shore stepwise toward the southeast. Eruptions appear to have clustered through time. One cluster occurred during the Late Pleistocene between ~ 27,000 and ~ 21,300 BC when four volcanoes erupted. A second cluster formed during the Late Holocene, between ~ 1500 BC and ~ AD 900, when four closely spaced monogenetic vents erupted forming thick viscous ‘a’a to blocky flows on the margin of the lacustrine flats. For still poorly understood reasons, these apparently inhospitable lava flows were attractive to human settlement and eventually became one of the most densely populated heartlands of the pre-Hispanic Tarascan civilization. With an average eruption recurrence interval of ~ 900 years during the Late Holocene the western Zacapu lacustrine basin is one of the most active areas in the MGVF and should hence be of focal interest for regional volcanic risk evaluations.

NW-SE Pliocene-Quaternary extension in the Apan-Acoculco region, eastern Trans-Mexican Volcanic Belt

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.

Petrogenesis of the alkaline and calcalkaline monogenetic volcanism in the northern sector of the Michoacán-Guanajuato Volcanic Field (Central Mexico)

In the Michoacán-Guanajuato Volcanic Field, Quaternary monogenetic alkaline volcanism is mostly present in its northern sector in association with coeval calcalkaline volcanism. Their respective geochemical signatures reveal the existence of two suites of differentiated alkaline lavas, one with a typical OIB-like signature and another that displays intermediate characteristics with the coeval calcalkaline lavas. Petrogenetic modelling supports that each suite followed independent fractionation paths from distinct initial magmas with no interaction between them. In all cases similar AFC processes prevailed with ~30% crystallization and contamination (r~0.3) with heterogeneous granitic and rarely granulitic components, involving different paragenetic assemblages mainly controlled by olivine, plagioclase, pyroxenes as well as some minor phases such as apatite and oxides. The geochemical characteristics of the initial magmas suggest that they derived from distinct mantle sources.The approximate N-S distribution of alkaline volcanism in the area, which coincides with a major geodynamic boundary at about the 101° W longitude, both at crustal levels and also concerning the configuration of the Cocos plate in the area, supports the existence of some disruption of the subducting plate that would favour the ascent of enriched sublithospheric melts. These would either ascend to the surface to produce OIB-like magmas or act as metasomatic agents in the mantle wedge, also influenced by components derived from the subducting slab. Such a hybrid mantle would represent the source of both the calcalkaline and the intermediate mildly alkaline melts, resulting from selective sampling (by different degrees of melting) from compositionally distinct domains within the mantle wedge.

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.

Basaltic ignimbrites in monogenetic volcanism: the example of La Garrotxa volcanic field

Ignimbrites are pyroclastic density current deposits common in explosive volcanism involving intermediate and silicic magmas and in less abundance in eruptions of basaltic central and shield volcanoes. However, they are not widely described in association with monogenetic volcanism, where typical products include lava flows, scoria and lapilli fall deposits, as well as various kinds of pyroclastic density current deposits and explosion breccias. In La Garrotxa basaltic monogenetic volcanic field, part of the Neogene-Quaternary European rift system located in the northeast of the Iberian Peninsula, we have identified a particular group of pyroclastic density current deposits that show similar textural characteristics to silicic ignimbrites, indicating an overlap in transport and depositional processes. These deposits can be clearly distinguished from other pyroclastic density current deposits generated during phreatomagmatic phases that typically correspond to thinly laminated units with planar-to-cross-bedded stratification. The monogenetic ignimbrite deposits correspond to a few meters to several tens of meters thick units rich in lithic- and lapilli scoria fragments, with an abundant ash matrix, and internally massive structure, emplaced along valleys and gullies, with run-out distances up to 6 km and individual volumes ranging from 106 to 1.5 × 107 m3. The presence of flattened scoria and columnar jointing in some of these deposits suggests relatively high emplacement temperatures, coinciding with available paleomagnetic data that suggests an emplacement temperature around 450–500 °C. In this work, we describe the main characteristics of these pyroclastic deposits that were generated by a number of phreatomagmatic episodes. Comparison with similar deposits from silicic eruptions and previous examples of ignimbrites associated with basaltic volcanism allows us to classify them as ‘basaltic ignimbrites’. The recognition in monogenetic volcanism of such pyroclastic products, which may extend several kilometres from source, has an important consequence for hazard assessment in these volcanic fields, which previously have been considered to present only minor hazards and risks.

B40 島原半島地域の第四紀火山活動発達史 : 玄武岩・輝石安山岩質単成火山群から雲仙火山へ

B40 島原半島地域の第四紀火山活動発達史 : 玄武岩・輝石安山岩質単成火山群から雲仙火山へ

3D seismic imaging of the shallow plumbing system beneath the Ben Nevis Monogenetic Volcanic Field: Faroe–Shetland Basin

Seismic reflection data allow for the 3D imaging of monogenetic edifices and their corresponding plumbing systems. This is a powerful tool in understanding how monogenetic volcanoes are fed and how pre-existing crustal structures can act as the primary influence on their spatial and temporal distribution. This study examines the structure and lithology of host-rock as an influence on edifice alignment and provides insight into the structure of shallow, sub-volcanic monogenetic plumbing systems. The anticlinal Ben Nevis Structure, located in the northerly extent of the Faroe–Shetland Basin, NE Atlantic Margin, was uplifted during the Late Cretaceous and Early Paleocene by the emplacement of a laccolith and a series of branching sills fed by a central conduit. Seismic data reveal that multiple intrusions migrated up the flanks of the Ben Nevis Structure after its formation, c. 58.4 Ma (Kettla-equivalent), and fed a series of scoria cones and submarine volcanic cones. These monogenetic edifices are distributed around the crest of the Ben Nevis Structure. The edifices are fed from a complex network of sills and transgressive sheets, involving lateral magma migration of tens of kilometres before extrusion at the surface. This work highlights the importance of underlying basin structures in influencing the sites and development of subaerial monogenetic fields, and the importance of lateral magma flow within volcanic systems. Supplementary materials: The results of the statistical alignment analysis of the monogenetic edifices are available at https://doi.org/10.6084/m9.figshare.c.3662809 .

About this title ‐ Monogenetic Volcanism

The nature and origin of the small-scale volcanic systems, generally referred to as ‘monogenetic’, have enjoyed an elevated level of interest during the past decade. There has been recognition that their ostensibly simple volcano types are a window into the nature of explosive volcanism, landscape evolution and the processes of magma generation in the Earth's upper mantle. In the past few years, major conferences have offered specialized technical sessions dealing with monogenetic volcanism and there have been thematic conferences, such as the IAVCEI International Maar Conference series, which have provided a focus for discussion of volcanological and geochemical aspects of small-scale basaltic volcanism. Many new aspects of monogenetic volcanism have emerged and have clearly demonstrated that this volcanism can be very complex on a fine scale. This book is a collection of papers arising from two recent Maar Conferences (the fifth in Queretaro Mexico and the sixth in Changchun, China) and serves as a snapshot of current research on monogenetic volcanism.

Source to surface model of monogenetic volcanism: a critical review

Abstract Small-scale volcanic systems are the most widespread type of volcanism on Earth and occur in all of the main tectonic settings. Most commonly, these systems erupt basaltic magmas within a wide compositional range from strongly silica undersaturated to saturated and oversaturated; less commonly, the spectrum includes more siliceous compositions. Small-scale volcanic systems are commonly monogenetic in the sense that they are represented at the Earth's surface by fields of small volcanoes, each the product of a temporally restricted eruption of a compositionally distinct batch of magma, and this is in contrast to polygenetic systems characterized by relatively large edifices built by multiple eruptions over longer periods of time involving magmas with diverse origins. Eruption styles of small-scale volcanoes range from pyroclastic to effusive, and are strongly controlled by the relative influence of the characteristics of the magmatic system and the surface environment.

Stress Controls of Monogenetic Volcanism: A Review

The factors controlling the preparation of volcanic eruptions in monogenetic fields are still poorly understood. The fact that in monogenetic volcanism each eruption has a different vent suggests that volcanic susceptibility has a high degree of randomness, so that accurate forecasting is subjected to a very high uncertainty. Recent studies on monogenetic volcanism reveal how sensitive magma migration is to the existence of changes in the stress field caused by regional and/or local tectonics or rheological contrasts (stratigraphic discontinuities). These stress variations may induce changes in the pattern of further movements of magma, thus conditioning the location of future eruptions. This implies that a precise knowledge of the stress configuration and distribution of rheological and structural discontinuities at crustal level of such volcanic systems would aid in forecasting monogenetic volcanism. This contribution reviews several basic concepts relative to the stress controls in monogenetic volcanic fields, and uses this information to explain how magma migrates inside such volcanic systems and how it prepares to trigger a new eruption.

The Role of Cultural and Indigenous Values in Geosite Evaluations on a Quaternary Monogenetic Volcanic Landscape at Ihumātao, Auckland Volcanic Field, New Zealand

The Ihumātao Peninsula is located within the wider Mangere region in South Auckland, New Zealand. Significant sites of geological, cultural and ecological value are a recorded feature of this area. One of the most significant sites in the region is the Otuataua Stonefields Historic Reserve (OSHR). Geologically, this area is a Quaternary lava flow field with tuff rings, scoria and spatter cones. It sits within the Auckland Volcanic Field (AVF), and the landscape of the OSHR and the wider Ihumātao Peninsula may be seen as the physical expression of a unique convergence of ecological, geological and cultural values. Geosite evaluation methods applied to the Ihumātao Peninsula, following two distinct methods, shed light on potential high geoheritage values the region holds. These values may be looked at as a good base to develop effective geoeducational, geoconservational and geotouristic programs. The study also showed that implementing management strategies to add and conserve geosite values in the region could provide positive outcomes; however, reduction of its main geosite values would be inevitable and irreversible should proposed urban development take place on a block of land immediately bordering the OSHR. The Ihumātao Peninsula is one of several areas of South Auckland where urbanization has left significant areas relatively untouched until the present, whereby they are now threatened by intense housing and industrial development. The geological features of these areas unquestionably hold geological heritage values, allowing understanding of the interplay between low coastal land and rising basaltic magma. This interplay has resulted in a landscape potentially featuring the greatest volcanic geodiversity of the entire AVF. In addition, this relatively undeveloped land provides an unbroken physical and cultural record dating to arrival of the first humans in New Zealand. Of particular note is the physical artefacts and archaeological sites telling a story of settlers attracted to, utilizing and shaping this discrete region of the AVF. Geosite evaluations demonstrate that high geoheritage values of regions like the Ihumātao Peninsula are influenced by the strong cultural link between the community (in particular the indigenous population) and the volcanic landscape. These cultural factors could be given more weight in currently used geosite evaluation methods, enabling such geoheritage values to be demonstrated in a more explicit and meaningful way and providing a basis for further community education and protection of specific sites within the geographical context of the Ihumātao Peninsula.

Neogene monogenetic volcanism from the Northern Puna region: products and eruptive styles

Abstract The Neogene mafic volcanism of the Northern Puna region in the Central Andes is represented by scoria cones and lava flows dispersed over a wide region ( c. 9150 km 2 ) as isolated or poorly clustered centres. Although all the products are basaltic andesites to andesites, the behaviour of these magmatic systems resembles that seen in basaltic monogenetic fields. These centres were studied with the aim of defining the main volcanic lithofacies and evaluating the eruptive styles. The results suggest that the eruptions developed under a dry strombolian dynamic, with brief periods of lava fountaining and hydrovolcanism, the latter usually restricted to the early stages of cone construction. Changes in eruptive style are thought to be caused by variations in both the internal (e.g. magma ascent) and external (e.g. surficial water availability) conditions. The transitions do not reflect compositional changes, as evidenced by the small chemical differences observed among the products of the studied eruptive centres. Stratigraphic analysis, in addition to a few pre-existing radiometric dates, suggests that this volcanic activity occurred during the Late Miocene to Early Pliocene. This information supports the inference that these eruptions occurred before the peak of Southern Puna mafic volcanism and that they were coeval with eruptions of some of the most important silicic calderas of the Altiplano-Puna Volcanic Complex. The good preservation of volcanic edifices reveals that erosion rates were extremely low, in agreement with the high aridity conditions that have prevailed in the Puna region since the Mid- to Late Miocene.

The Carrán–Los Venados volcanic field and its relationship with coeval and nearby polygenetic volcanism in an intra-arc setting

Understanding the relationship between monogenetic and polygenetic volcanism has been a long-standing goal in volcanology, especially in cases where these two styles of volcanism are coeval and geographically adjacent. We studied the Carrán–Los Venados (CLV) volcanic field and made comparisons with published data on CLV's polygenetic neighbor Puyehue–Cordón Caulle (PCC) in the Southern Andean arc, using quantitative tools and recent numerical simulations of magma reservoir formation. CLV is a basaltic to basaltic andesitic volcanic field composed of 65 post-glacial scoria cones and maars and a 1-km-high Pleistocene stratovolcano, whereas PCC is a basaltic to rhyolitic composite volcano. Our results point to three main differences between CLV and PCC: (1) the CLV magmas differentiate at low-crustal reservoirs, followed by rapid ascent to the surface, while the PCC magmas stagnate and differentiate in lower- and upper-crustal reservoirs; (2) CLV is elongated in the NE direction while PCC is elongated in the NW direction. Under the current stress field (N60°E σHmax), these two volcanic alignments correspond, respectively, to local extensional and compressive deformation zones within the arc; and (3), the post-glacial CLV magma flux was estimated to be 3.1±1.0km3/ky, which is similar to the average magma flux estimated for PCC; however, the PCC magma flux is estimated at approximately twice this value during peak eruptive periods (5.5±1.1km3/ky). Based on numerical simulations, CLV is in a limit situation to create and sustain a mush-type upper-crustal reservoir containing highly crystalline magma, which is however not eruptible. The PCC volcanic system would have been able to create a stable reservoir containing eruptible silicic magma during periods of peak magma flux. We postulate that monogenetic volcanism occurs at CLV due to both low magma flux and an extensional/transtensional regime that favors rapid magma rise without storage and differentiation in stable upper-crustal reservoirs. However, the CLV system seems to be at an inflection point, and could become polygenetic if magma flux increases. For PCC, high magma flux during some periods together with compressive deformation would have led to the construction of one or several stable upper-crustal magma reservoirs, with subsequent silicic volcanism and construction of central conduits for magma extrusion, resulting in polygenetic volcanism with evolved compositions. In this model, monogenetic volcanic systems can become polygenetic despite extensional regime if magma flux increases sufficiently to create and sustain a stable upper-crustal magma reservoir.