Monogenetic Volcanoes Research Articles

Paleomagnetically defined brief lifespans for two large shield volcanoes in the Cascades Arc

Mafic to intermediate shield volcanoes with multi-cubic-kilometer eruptive volumes are common in the Cascades Volcanic Arc, but little is known about their eruptive histories as either singular or sustained episodes, or the total time required for their construction. Paleomagnetic data were collected from the lava flows of Ash Creek Butte (17 sites) and Crater Mountain (14 sites) in northern California; both volcanoes are large shields with total volumes of ∼11 km3 each. Tightly clustered paleomagnetic results at both volcanoes, when coupled with analysis of geomagnetic secular variation, suggest that each edifice was built in only a few centuries, possibly in as little time as 50–90 years, indicating sub-century to century scale eruptive durations for two sizeable regional shield volcanoes within the Cascades Arc. These rapidly built shield volcanoes are substantially larger than typically defined monogenetic volcanoes, yet both are wholly formed within a single ‘episode’ at the limits of temporal resolution. Paleomagnetic methods provide a high-resolution tool that can be applied to understanding the tempo of regional volcanism in arcs.

Risk scenarios for a future eruption in the Chichinautzin monogenetic volcanic field, South México City

The Chichinautzin Monogenetic Volcanic Field creates volcanic risks for México City. To evaluate the possible effects and economic impacts of a future eruption, three scenarios based-on the spatial distribution of the most recent eruptions and the study of their characteristic are proposed. Scenario A, a Violent Strombolian eruption at the northwestern edge of the volcanic field, with eruptive columns 6–8 km high and emission of low-viscosity lava flows. Scenario B, Santiaguito-type eruption, a thick, high-viscosity lava flow that generates rock falls and short Merapi-type pyroclastic flows in the central northern area. Scenario C, a Hawaiian to Strombolian eruption with eruptive columns <6 km high and the emission of low viscosity lavas in the central part of the field. From these scenarios, numerical simulations of lava and tephra were carried out to obtain conditional hazard maps. The risk evaluation integrates the analysis of hazard, exposure, vulnerabilities, resilience, and the estimation of the costs of possible damages with physical and sociodemographic indicators available at the city block level, including rural areas. Two vulnerability curves were integrated for housing, the first for lava flows, which considers that a thickness ≥ 2 m of lava causes total loss (considering the loss of the function and accessibility); and a second curve for tephra that considers that an accumulated thickness in dry conditions of 20 cm of tephra produces generalized damage to all type of houses. By combining the vulnerability and hazard maps, two risk maps were constructed, one for lava flows and the other for tephra. The total direct cost of the expected damages was calculated for each scenario considering the cadastral value of the land and buildings for each property at risk. The costs for the most probable and the most catastrophic scenario amount to >14 billion US dollars, equivalent to 1.2% of the national GDP. Mitigation measures, mainly of the non-structural type are proposed.

Two distinct age groups of melilitites, foidites, and basanites from the southern Central European Volcanic Province reflect lithospheric heterogeneity

Petrographic observations and in situ U–Pb ages of melilitites, foidites, basanites, phonolites, and trachytes from the southern part of the Central European Volcanic Province (CEVP) and related plutonic inclusions therein reveal two distinct age groups separated by a gap of ~ 20 Myr. A late Cretaceous to early Eocene group (~ 73–47 Ma; Taunus, Lower Main plain, Odenwald and Kraichgau area, Bonndorfer Graben and Freiburger Bucht area, Vosges and Pfälzerwald) is characterized by nephelinites and basanites mostly devoid of melilite and perovskite, and by rare haüynites, and trachytes. In contrast, a late Oligocene to late Miocene group (~ 27–9 Ma; Lorraine, southern Upper Rhine Graben, Urach, Hegau area) is dominated by melilitites, melilite-bearing nephelinites (both carrying perovskite), and phonolites. Both magmatic episodes are related to domal topographic uplift, erosion, and formation of major angular unconformities in the Upper Rhine Graben, suggesting an association with dynamic topography interrupted by phases of subsidence (or abatements of uplift). The investigated rocks in the southern CEVP (south of a line Eifel–Vogelsberg–Rhön–Heldburg), except for the Kaiserstuhl volcanic complex, mostly comprise small and isolated occurrences or monogenetic volcanic fields, whereas the northern CEVP is dominated by large volcanic complexes and dyke swarms, which are mostly SiO2-saturated to weakly SiO2-undersaturated. In the northern CEVP, evidence of spatially varying but recurrent volcanic activity exists since the Eocene, lacking the distinct 20 Myr gap as documented from the southern CEVP. While the temporal and spatial distribution of volcanism are a result of the Cretaceous to Miocene tectonic evolution in Central Europe, further studies are needed to explain the petrographic differences between the two age groups in the south.

Lateral Extent of Pyroclastic Surge Deposits at Ubehebe Crater (Death Valley, California) and Implications for Hazards in Monogenetic Volcanic Fields

AbstractHazard assessments in monogenetic volcanic fields require estimates of the runout of pyroclastic surges that result from phreatomagmatic explosive activity. Previous assessments used runout distances of 1–4 km, with large cases up to 6 km. Surge deposits at Ubehebe Crater (∼2100 y.b.p., Death Valley, California) have been traced ∼9 km from the crater center, and likely originally extended 1–3 km farther. There is no evidence that the Ubehebe Crater activity was unusually energetic; rather, its distal deposits are better preserved than those at most maar volcanoes because of its young age and the arid environment. Numerical simulations illustrate how low temperatures facilitate long runout of phreatomagmatic surges due to reduced expansion of entrained air compared to hot surges, allowing cool surges to retain higher densities than ambient air. We suggest that hazard assessments for volcanic fields with phreatomagmatic, maar‐forming eruptions should consider runout distances in the range of 10–15 km.

Shear-wave tomography of the Changbai volcanic area in NE China derived from ambient noise and seismic surface waves

A detailed 3-D shear-wave velocity (Vs) model of the crust and upper mantle beneath the Changbai volcano and adjacent areas in NE China is obtained by conducting a joint inversion of group-velocity dispersion curves at periods of 5–30 s and phase-velocity dispersion curves at periods of 5–100 s from ambient noise and earthquake surface waves. We use 1602 group-velocity dispersion curves and 3125 phase-velocity dispersion curves, which were recorded at 57 permanent stations of the China Earthquake Administration and 27 portable stations of Jilin University during 2010 to 2014. Our results reveal strong heterogeneities in the crust and upper mantle beneath the study area. A remarkable low-Vs zone is revealed in the crust beneath the Changbai volcano, indicating a hot magma chamber. The Longgang volcano is also characterized by a low-Vs anomaly reflecting partial melt in the crust. In contrast, there is no notable low-Vs anomaly in the crust beneath the Jingpohu volcano. Previous geological results and our tomographic images suggest that Changbai is a composite volcano, whereas Jingpohu and Longgang are monogenetic volcanoes. Low-Vs zones are revealed in the upper mantle beneath the three active volcanoes, which are interconnected at different depths. Combining the present results with previous findings, we deem that the three active intraplate volcanoes are caused by hot and wet upwelling flows in the big mantle wedge associated with deep subduction of the western Pacific plate beneath NE Asia.

Imaging the Volcanic Structures Beneath Gran Canaria Island Using New Gravity Data

AbstractFrom a new gravity data set that covers homogeneously the whole surface of Gran Canaria (Canary Islands, Spain) and marine gravity data in the nearest offshore, we have obtained a Bouguer anomaly gravity map of the island which improves the previous ones. Using these gravity anomalies, we have applied a gravity inversion approach to investigate the structures beneath the surface of Gran Canaria Island and derive a 3D gravity sources model. The geometry of structures with anomalous density values is constrained up to a depth of approximately 20,000 m below the sea level. The interpretation of the density model identified structures related to the different volcanic stages of Gran Canaria. Several deep‐rooted high‐density structures represent the intrusive bodies emplaced in the early formation of Gran Canaria and the magma plumbing system of the Miocene volcanic edifices. A low‐density body in the center of the island may be associated with the syenitic core of the felsic central volcanic edifice (Tejeda Caldera). Shallow low‐density structures identified fractures which acted as feeder dikes of monogenetic volcanoes during the rejuvenated stage. Finally, the NW‐SE rift, which is the most important volcano‐tectonic structure of Gran Canaria, has a characteristic gravimetric signature and represents a long‐lived extensional fracture zone that has controlled the volcanic activity at least since the Miocene.

The recent volcanism of Flores Island (Azores): Stratigraphy and eruptive history of Funda Volcanic System

Monogenetic volcanoes occur in many different geotectonic settings and are usually small and short-lived. They can experience a variety of eruptive styles, even during the same eruption. In monogenetic volcanic fields, volcanism usually migrates to different locations over time, making volcanic hazard assessment very challenging. The eruptive history of a volcanic region, including the size, style, and location of previous eruptions, provides valuable information to help predict the behaviour of future volcanic events and their associated hazards. Here, we reconstruct for the first time the eruptive history of the Funda Volcanic System (FVS), one of the most recent (∼3 ka) monogenetic eruptive centres of Flores Island (Azores), based on a detailed tephrostratigraphic work coupled with geochemical analysis of glass shards and radiocarbon dating. We identified at least three volcanic events at FVS spaced by time intervals of ∼100 yr. The first event (3430 cal yr BP) was a small Strombolian eruption, the second event (3330 cal yr BP) started as a violent Strombolian eruption and may have ended as phreatomagmatic, and the third event (3250 cal yr BP) was exclusively phreatomagmatic. Our results demonstrate that volcanism at the FVS was more prolonged and recurrent than previously reported. Moreover, we show that the FVS experienced different eruptive styles in a short timeframe, ranging from small basaltic eruptions to violent explosive phreatomagmatic events. Such diversity of eruptive styles results in different volcanic products, which have different hazard implications. Our new results contribute to the knowledge of the recent volcanic activity of Flores Island, and we anticipate them to be of paramount importance for future volcanic hazard assessment studies.

The magmatic plumbing system of the Acoculco volcanic complex (Mexico) revealed by ambient noise tomography

The GEMex project is a Mexican-European cooperation in geothermal energy focusing on enhancing the Acoculco geothermal system. The volcanic system belongs to the northeastern part of the Trans-Mexican Volcanic Belt. In this study, we present ambient noise seismic tomographies of the anisotropic shear wave velocities and reveal the magmatic plumbing system. The tomographies result from the joint inversion of the multi-mode Rayleigh and Love surface wave velocities and Horizontal to Vertical Spectral Ratios (HVSR or H/V). We also discuss the advantage of this technique compared to traditional ambient noise tomography methods and underline the importance of considering multiple surface wave modes to correctly reveal velocity anomalies buried a few kilometers in depth. A reservoir is identified at about 5 km depth at the northeast outside of the caldera. This reservoir is linked to the south caldera surface via a conduit that follows the caldera's eastern border, mainly the Chignahuapan graben. An intermediate reservoir is also observed at about 2.5 km depth, just below the three most recent monogenetic volcanoes. Results agree well with geological studies, the caldera collapse, its temporal evolution, and other geophysical studies recently reported.

Geomorphological Classification of Monogenetic Volcanoes and Its Implication to Tectonic Stress Orientation in the Middle Atlas Volcanic Field (Morocco)

The Middle Atlas Volcanic Field (MAVF) covers an area of 1500 km2, with a total erupted volume of solid products (e.g., Dense Rock Equivalent or DRE) estimated to be more than 80 km3. The MAVF comprises 87 monogenetic basaltic volcanoes of Tertiary-Quaternary age as scoria cones (71%) and maars (29%). These monogenetic basaltic volcanoes have various morphologies (e.g., circular, semi-elliptic, elliptic in map views). They can be isolated or form clustered monogenetic complexes. They are largely grouped in the Middle Atlas, in an intraplate geotectonic context forming two distinct major alignments (N160–170° and N40–50°), each closely associated with regional structural elements. By the best estimates, the preserved bulk pyroclastic products do not exceed 0.7 km3, and they show large textural and componentry diversity (e.g., bedded/unbedded, coarse/fine, dense/scoriaceous fallout and pyroclastic density current deposit, etc.). Lava flows also demonstrate great variety of preserved surface textures, including pāhoehoe, ‘a’ā, and clastogenic types. Morphostructural features of lava flows linked to lava flow dynamics have also been recognized, and the presence of hornitos, columnar jointed basaltic flow units, lava tubes, tumuli, and clastogenic lava flows have been recognized and mapped. Some half-sectioned dykes expose interior parts of magmatic shallow feeding pipes. The current morphology of the volcanoes of the MAVF reflects various syn- and post-eruptive processes, including (1) erosional features due to weathering, (2) gravitational instability during and after volcanic activity, (3) vegetation impact, and (4) successive burial of lava flows. The documented volcanic features of this typical monogenetic volcanic field form the core of the region’s geoheritage elements and are considered to be unique in the new African geoheritage context. Hence, they will likely form the basis of future geotourism, geoeducation, and geoconservation ventures.

A snapshot of the transition from monogenetic volcanoes to composite volcanoes: case study on the Wulanhada Volcanic Field (northern China)

Abstract. The transition processes from monogenetic volcanoes to composite volcanoes are poorly understood. The Late Pleistocene to Holocene intraplate monogenetic Wulanhada Volcanic Field (WVF) in northern China provides a snapshot of such a transition. Here we present petrographic observations, mineral chemistry, bulk rock major and trace element data, thermobarometry, and a partial melting model for the WVF to evaluate the lithology and partial melting degree of the mantle source, the crystallization conditions, and pre-eruptive magmatic processes occurring within the magma plumbing system. The far-field effect of India–Eurasia collision resulted in a relatively high degree (10 %–20 %) of partial melting of a carbonate-bearing eclogite (∼ 3 wt % carbonate; Gt/Cpx ≈ 2 : 8, where Gt denotes garnet and Cpx denotes clinopyroxene) followed by interaction with ambient peridotite. The primary melts ascended to the depth of the Moho (∼ 33–36 km depth), crystallized olivine, clinopyroxene and plagioclase at the temperature of 1100–1160 ∘C with the melt water contents of 1.1 wt %–2.3 wt %. Part of the primary melt interacted with the lithospheric mantle during ascent, resulting in an increase in the MgO contents and a decrease in the alkaline contents. The modified magma was subsequently directly emplaced into the middle crust (∼ 23–26 km depth) and crystallized olivine, clinopyroxene and plagioclase at the temperature of 1100–1160 ∘C. The primary melts from the same mantle sources migrated upward to the two-level magma reservoirs to form minerals with complex textures (including reverse and oscillatory zoning and sieve texture). Magma erupted along the NE–SW-striking basement fault and the NW–SE-striking Wulanhada–Gaowusu fault in response to the combined effects of regional tectonic stress and magma replenishment. The crustal magma reservoir in the WVF may represent a snapshot of the transition from monogenetic volcanoes to composite volcanoes. It is possible to form a composite volcano with large magma volumes and complex compositions if the magma is continuously supplied from the source and experiences assimilation and fractional crystallization processes in the magma plumbing system at crustal depth.

Review of geology and geomorphology of the Xalapa Monogenetic Volcanic Field, eastern Trans-Mexican Volcanic Belt

Monogenetic volcanic fields have associated volcanic hazards that are not always well constrained due to the lack of complete and well established geological and geomorphological studies, field boundaries, volcano inventories, and of detailed reconstruction of individual volcano eruptive histories. This work presents a detailed review and further insights into geology and geomorphology of the Xalapa Monogenetic Volcanic Field (XMVF), achieved by completing a comprehensive revision of all previous works on the XMVF, along with new data produced from extensive fieldwork, field and digital mapping, radiocarbon dating, and morphometric and density analyses. The main results are: (i) a renewed inventory of 72 XMVF monogenetic volcanoes - a total number larger than previously recorded (59); (ii) identification of six new and not previously identified monogenetic volcanoes: La Natividad, La Pedrera, El Puente, Rancho Sicomoro, and Puentecillas scoria cones, and the Tenampa maar; (iii) recognition of four possible new volcanoes integrating the Macuiltépetl cluster, recorded in historical documents; (iv) corrections and new volcanoes identified in the volcano clusters of Pextlan, La Joya, Ocotepec, and Cruz Negra; (v) geological mapping of all lava flows associated with the 72 monogenetic volcanoes; (vi) comprehensive morphometric analyses of all 72 reported volcanoes; (vii) three new radiocarbon ages corresponding to 780 ± 60 BP and 1340 ± 60 BP lava flows of El Volcancillo scoria cone, and to 1300 ± 60 BP and 1115 ± 80 BP lavas of La Pedrera volcano; (viii) new evidence of the late Pleistocene to Holocene age of the Acatlán scoria cone; (ix) new outline of the boundaries of the XMVF based on fieldwork and remote sensing; and (x) volcanoes and lava flows density and distribution maps. From these results, we conclude that, in case of renewed monogenetic activity in the XMVF, the most likely deterministic hazard model would comprise effusion of lavas of variable length (3–40 km), of up to extremely long tube-fed pahoehoe lava flows; explosive activity ranging from typical to violent Strombolian style eruptions producing scoria cones, extensive fallouts, and associated pyroclastic density currents; and phreatomagmatic style activity producing maars, tuff rings and/or tuff cones, and sequences of wet pyroclastic density currents. Hazard distributions in these scenarios would be mainly controlled by topography, local tectonics, groundwater level and basement rocks lithology, and would mostly affect the north and south flanks of Cofre de Perote volcano, as well as central XMVF sectors where the metropolitan area of the city of Xalapa and towns of Naolinco and Acatlán locate. From this review, we conclude that without any further studies of geology and chemistry of every single volcano, the western boundaries of the XMVF will remain unclear, and the associated volcanic risk will remain underestimated. This work provides a fundamental basis from which further and more detailed work could be attained.

Alkaline rocks of the Bobaomby volcanic field point to a petrogenetic link between Comoros and northern Madagascar lithosphere

The Bobaomby volcanic field (10–11 Ma) is the northernmost volcanic area of Madagascar, and is a monogenetic volcanic field comprising outcrops of lava flows, dykes, scoria cones, tuff rings and plugs, widely scattered over an area of roughly 500 km2. The volcanic rocks range in composition from nephelinite, basanite and tephrite, through tephritic phonolite, to F- and Cl-rich peralkaline phonolite (MgO from 13 to 0.01 wt%), and the serial affinity varies from sodic to potassic. A few mica-amphibole-rich lamprophyric dykes have tephritic composition and ultrapotassic affinity. The mafic lavas host intrusive xenoliths with evident cumulate features (wehrlites, composite olivine gabbros s.l., amphibole clinopyroxenites and “kaersutitites”), as well as various types of mantle-derived xenoliths and xenocrysts in the most primitive rocks. The very wide compositional variations of the observed phases (olivine, clinopyroxene, amphibole, oxides, feldspars, feldspathoids, apatite, titanite, aenigmatite and other accessories) in lavas, dykes and cognate xenoliths are fully consistent with the variable degree of differentiation of the host lavas/dykes, and pointing out to limited open-system or polybaric crystallization. The mafic lavas have marked enrichment in incompatible elements and light rare-earth element (LREE) (e.g., Lan/Ybn = 19–27), whereas concave REE patterns are found in the peralkaline phonolites, as a result of removal of accessory titanite starting from tephritic phonolite magmas. The gabbroic/ultramafic xenoliths are interpreted as crustal cumulates of basanitic and tephritic magmas. Several liquid lines of descent in the basanites and tephrites are evident from the trace-element distribution, and from the differing geochemistry of the evolved rocks. The isotopic compositions reach extreme values (e.g., 206Pb/204Pb = 20.065 in the ultrapotassic lamprophyre) when compared to the rest of the Cenozoic/Recent Madagascan volcanic rocks, but similar to those of the Comoros archipelago, suggesting analogies of mantle sources and enrichment processes in the lithosphere of this volcanic archipelago. The origin of the Bobaomby mafic rocks is compatible from a derivation from low degree partial melting of an incompatible element-enriched peridotite source (possibly located in the lowermost lithospheric mantle) rich in volatile-rich phases (pargasite, locally also phlogopite and possibly carbonates), matching the sources of other Cenozoic volcanic areas throughout Madagascar, and perhaps Comoros.

Constraints on the nature and evolution of the volcanic fields of the Andahua Group, Central Volcanic Zone, southern Peru

The Andahua Group is a distinct cluster of typically monogenetic volcanoes located in the northernmost part of the Central Volcanic Zone in the Andes, characterized by small-volume lava domes and scoria cones. Seven volcanic clusters have been distinguished. Using satellite imagery, geological mapping, and fieldwork, we found a total of 103 lava domes, 43 scoria cones, and 3 small composite volcanoes. Most of the lava domes are monogenetic but 9 were formed by multiple eruptions. Petrogenetic models have been developed for the magma evolution of the Andahua Group. They show local crustal influence on the magmas generated, and possible controls on the magma pathway to the surface, and potential segregation. Local compositional variation of the crustal rocks is inferred to have a strong influence on the magma that ascends through the thick continental crust. Assimilation and contamination by deeply seated granitoids of the Arequipa and Paracas massifs are also inferred to play a role in the final magmatic products. Future activity with gas emissions from the Andahua Group volcanoes may cause hazardous conditions for tourists.

Three-dimensional density tomography determined from multi-directional muography of the Omuroyama scoria cone, Higashi–Izu monogenetic volcano field, Japan

Scoria cone is one of the basic forms of volcanoes, and clarifying its detailed internal structure and magma movement during its formation is important for understanding the nature of eruptions and also for volcanic disaster mitigation. We conducted a multi-directional muographic survey of the Omuroyama scoria cone, Japan, in order to determine the three-dimensional density structure of the scoria cone. We used a nuclear emulsion detector optimized for multi-directional muography that was installed at 11 sites around the volcano. Muon tracks recorded on emulsion films were read with a high-speed automated readout system. We obtained the three-dimensional density structure by applying a linear inversion to the muographic images, and evaluated the uncertainties. High-density zones were detected in scoria cone. Based on these observations and detailed topographic and geological constraints, we infer that high-density zones are the central, highly welded vent of the scoria cone, three-directional radial dikes extending from the central vent, respectively. We also infer that an E-W-trending dike fed a small lava flow, and that a SSE-NNW-trending dike caused a small flank eruption and produced a crater on the flank of the cone. Our results visualize the three-dimensional internal structure of volcanoes with novel resolution, and thereby demonstrate that the formation process of volcanoes can be discussed in detail. Since it has been difficult to directly detect such clear visualization of the internal structures and eruptive processes in the past, multi-directional muography has resulted in providing one hope for understanding volcanic activity.

The heterogeneity of the Mexican lithospheric mantle: Clues from noble gas and CO2 isotopes in fluid inclusions

The abundance of mantle-derived rocks and lavas, in combination with its tectonic evolution, render Mexico a perfect laboratory to investigate the chemical and the isotopic heterogeneity of the lithospheric mantle. New data on the composition of noble gases and CO2in Mexican mantle xenoliths and lavas is reported. Our samples consist of six ultramafic nodules from the Durango Volcanic Field (DVF) and the San Quintin Volcanic Field (SQVF), monogenetic complexes belonging to the Mexican Basin and Range province; and four lavas from the Sierra Chichinautzin (SCN), a Quaternary monogenetic volcanic field located in the Mexican volcanic arc. Ne and Ar isotopes in fluid inclusions reveal mixing between atmospheric and MORB-like fluids (e.g.,40Ar/36Ar &amp;lt; 1,200). DVF and SQVF nodules record low40Ar/36Ar and4He/20Ne that confirm the existence of recycled atmospheric-derived noble gases in the local mantle. The averages of the Rc/Ra ratios (3He/4He corrected for atmospheric contamination) measured in Mexican localities are within the MORB-like range: DVF= 8.39 ± 0.24 Ra, SQVF = 7.43 ± 0.19 Ra and SCN lavas = 7.15 ± 0.33 Ra (1σ). With the aim of assessing the isotopic variability of the Mexican lithospheric mantle, the above results were compared with similar data previously obtained from ultramafic nodules found in the Ventura Espiritu Santo Volcanic Field (VESVF), another Quaternary monogenetic volcanic complex belonging the Basin and Range. The higher3He/4He ratios in DVF relative to those reported for the VESVF and the SQVF are explained as reflecting different ages of mantle refertilization, triggered by the retreating of the Farallon slab (∼40 Ma ago) and associated delamination slab processes. We propose that the DVF mantle was refertilized more recently (&amp;lt;10 Ma ago) than the mantle beneath the SQVF and VESVF (∼40–20 Ma ago). On the other hand, He-Ne-Ar compositions of SCN olivines share similarities with VESVF xenoliths, suggesting a relatively homogeneous lithospheric mantle in central Mexico. Finally, DVF and the SCN samples exhibit δ13C values within the MORB range (comparable to other values previously reported in fluid inclusions and fumaroles from Popocatépetl, Colima—Ceboruco volcanoes). While we explain the MORB-like carbon signatures of the DVF samples as the result of the above-mentioned refertilization process, the SCN signatures likely reflect either (i) trapping of isotopically fractionated CO2derived from magmatic degassing or (ii) a mantle source unaffected by subduction-related crustal carbon recycling.

Petrogenesis of mafic-intermediate magmatism of the Michoacán–Guanajuato volcanic field in Western Mexico. A geochemical review

The Michoacán–Guanajuato volcanic field (MGVF) in the western Trans-Mexican Volcanic Belt is one of the largest and most diverse monogenetic volcanic fields in the world holding more than 1200 volcanic vents. Its eruptive activity goes back to 7 Ma, it is considered an active volcanic field, and the composition of its rocks varies from mafic to silicic. It is essential to understand the geochemical evolution of its products, the complex petrogenetic processes, and the origin of magmas in central Mexico. Although these processes are linked to the subduction of the Cocos plate beneath the North American plate, the magmatic plumbing system of the MGVF remains not completely understood. The MGVF has been studied for decades, focusing in its dominant intermediate magmas. Nevertheless, the origin and evolution of the mafic components and their relation with the intermediate rocks have been poorly discussed. Here, we compile geological and geochemical data of the MGVF to discuss the petrogenesis of mafic magmas along the volcanic field and the role they play in the generation of intermediate melts. We used data published for 429 samples of mafic and intermediate volcanic rocks. Conventional procedures and statistical techniques were used to process the dataset. We propose that MGVF mafic magmas are derived from low degrees (∼1–15%) of partial melting of a spinel-bearing lherzolite source/mantle related to the rapid ascent of the asthenosphere caused by an extensional regime that is present in the area. In contrast, intermediate magmas where divided into two main groups based on the Mg content: high-Mg intermediate rocks, which seems to be derived from different rates of assimilation and fractional crystallization process, and low-Mg intermediate rocks, which can be related to fractional crystallization of mafic magmas. In addition, mafic and intermediate magmas display a chemical diversity which is related to mantle heterogeneity domains in the mantle wedge.

The interplay between environmental and magmatic conditions in eruption style transitions within a fissure-aligned monogenetic volcanic system of Auckland, New Zealand

Recent conceptual geological frameworks of continental monogenetic volcanism highlight that the small magma volume eruptions, resulting volcanic geology and edifice architecture in such settings are sensitive to variations in external or environmental conditions. These conditions, along with fluctuations in magma flux, can change rapidly over short time frames and cause dramatic changes in eruption style. Understanding the drivers of transitions in explosive to effusive behaviour within the short timescales of eruptions at individual volcanic centres is essential to accurately assess volcanic hazards in continental monogenetic settings. Wiri Mountain Volcanic Complex is one of the largest and most complex volcanic centres in the active Auckland Volcanic Field. Despite the significant removal of much of the original volcanic deposits, present-day exposures and historical images provide a unique opportunity to examine the growth and evolution of the volcanic complex. Wiri Mountain deposited an initial basal tuff ring (covering an area of approximately 0.67 km2) by predominantly pyroclastic density currents, followed by at least two smaller tuff rings erupted through the outer flanks of the first, in a transition from phreatomagmatic to Strombolian eruptive style. A 90 m high central scoria cone was then produced within the initial tuff ring, partially capped by lava spatter, clastogenic lava flows and lava flows that mostly covered all tuff rings, the scoria cone, and the surrounding area. A high-resolution stratigraphic study of the well-exposed tuff ring to capping magmatic succession was conducted to determine the changes in eruptive style and their driving forces. The deposit architecture of Wiri Mountain can be described using three volcanic stratigraphic units: a basal unit comprised of tuff, lapilli tuff and tuff breccia deposits, a middle unit comprised of juvenile-rich transitional tuff deposits of black scoria ash and lapilli, red scoria and spatter, and a capping unit comprised of agglutinate and lava flow successions. Most volcanic materials were either fragmented and ejected at near-optimal scaled depth, or the transition between near-optimal and shallower/deeper depths. Wiri Mountain provides a striking example of a fissure eruption likely controlled by a pre-existing tectonic fault that was fed by relatively stable melt sources over a sustained period. We infer that despite eruption within a water-saturated coastal plain, the initial phreatomagmatic phase was overridden by subsequent explosive and effusive magmatic phases through the formation of an increasingly established conduit, thus allowing sustained magma flux and melt supply. The transitions, both gradual and rapid, from an initial phreatomagmatic to subsequent magmatic explosive and effusive phases fit well to the general understanding of eruption style changes over time from other larger and more complex volcanoes of Auckland, and elsewhere worldwide. Wiri Mountain showcases the fine balance between the external and internal conditions that control eruption style variations and govern the formation of complex monogenetic volcanoes.

Pitted-Ground Volcanoes on Mercury

On the planet Mercury, pyroclastic deposits formed by explosive volcanism are developed around rimless volcanic pits that are up to dozens of kilometers in diameters. Some pyroclastic deposits on Mercury, however, host no discernable main eruption centers but feature pitted-ground terrains that each consists of many similar sized and irregularly shaped pits. Individual pits are usually much smaller and shallower than typical volcanoes on Mercury. The origin of these landforms is unknown, but it is indicative of styles of volcanism on Mercury and/or post-volcanic modifications. Here, we investigate the possible origin of these peculiar landforms based on their geological context, morphology, geometry, reflectance spectra, and geophysical background. Reflectance spectra of pyroclastic deposits around such volcanoes are comparable with those erupted from typical volcanic pits on Mercury, suggesting a genetic relation between these pitted-ground terrains with explosive volcanism, and the source magma might have similar compositions. Pitted-ground volcanoes are mainly observed in impact structures, and two cases were formed in high-reflectance smooth plains and channeled lava flows. Most pitted-ground volcanoes are relatively degraded compared with typical volcanoes on Mercury, and some might have been formed in geological recent times judged by both their pristine preservation and crosscutting relationship with impact rays. All pitted-ground volcanoes have unconfined morphology boundaries, and each case is composed by dozens of rimless pits that have similar preservation states and interconnected edges. Such morphological characteristics are unique among volcanic landforms on terrestrial bodies, and they cannot be explained by multiple post-eruption collapses of a main explosive volcano. Pitted-ground volcanoes that are developed in lava flows with the same age have different preservation states, suggesting that the pits were not formed by escape of thermally destabilized volatiles from substrate and subsequent roof collapses. The largest pitted-ground volcano (~3700 km2) is located on the Borealis Planitia, and Bouguer gravity data reveal no larger mass concentration in the subsurface than surrounding terrains, consistent with a paucity of shallow intrusions in the crust of Mercury. Short-term and spatially-clustered explosive eruptions could explain the peculiar morphology and geometry of the pits, suggesting that pits in a given pitted-ground volcano are akin to swarms of monogenetic volcanoes. However, possible magma dynamics for the formation of pitted-ground volcanoes cannot be confirmed until future high-resolution gravity mapping could reveal detailed interior structures beneath these volcanoes. Based on comparative studies with spatially-clustered and similarly aged volcanoes on Earth, we interpret that a combination of pervasive crustal fractures and regional thermal anomaly in the thin mantle of Mercury might have caused such short-term and spatially-clustered explosive eruptions. If this interpretation was true, the heavy degradation state of most pitted-ground volcanoes and the few well-preserved cases are consistent with an overall cooling trend of the mantle, indicating the existence of longstanding heterogeneous thermal structures in the mantle.

Sensitivity assessment of morphometric parameters of monogenetic volcanic landforms with global free DEMs

Improvements in the resolution of Digital Elevation Model (DEM) have greatly facilitated the research of small to moderate landforms such as dunes, landslides/rockfalls, moraines/drumlins and monogenetic volcanoes. Global free 30 m DEMs including data derived from Shuttle Radar Topography Mission (SRTM), Advanced Land Observing Satellite (ALOS) World 3D 30 m (AW3D30), and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER GDEM) are widely used. However, little is known of whether they can be used effectively in monogenetic volcanology. The focus of this study is to explore the accuracy and potential application of global free SRTM 30 m and AW3D30, as well as ASTER GDEM (previously studied) in monogenetic volcanic fields. We compared SRTM and AW3D30 with four reference higher-resolution DEM dataset, including National Elevation Dataset (NED) 10 m in Uinkaret Volcanic Field (UVF) (United States), WorldDEM 12 m in Longgang Volcanic Field (LVF) (China), Contour Line Based DEM (CLBD) 1 m in Jeju Island Volcanic Field (JIVF) (South Korea), and Light Detection And Ranging (LiDAR) 1 m in Lunar Crater Volcanic Field (LCVF) (United States). The results indicate that AW3D30 has higher accuracy than SRTM in all comparisons including elevation, slope angle and morphological parameters of scoria cones and associated lava flows. However, the accuracy of AW3D30 is almost the same as that of SRTM in that it is affected by slope angle, volume of volcanic edifices, and morphological features of scoria cones. In general, slope angle has a significant effect on the elevation and slope angle errors, which is consistent with previous studies. When the volume of the scoria cones is >5 × 106 m3 and the volume of the lava flows is above 10 × 106 m3, the average errors of their morphological parameters generated by SRTM and AW3D30 do not exceed 16.3 %. The morphological features are classified as crater (the central depression within a scoria cone), crater rim (the top 15 % of the highest elevations), lower flank (the lowest 15 % of the elevations), and middle flank (the remainder of a scoria cone). The area near the crater rim is often the area where larger errors occur, especially on the crater side. The middle and lower flank areas have milder errors. Additionally, the simulation of pre-eruptive surfaces should take into account the effects of certain factors such as roughness and flatness when calculating the volume. Overall, AW3D30 has the best potential in monogenetic volcano studies, followed by SRTM and ASTER GDEM.

New Insights into Feeder Dike Swarms in Scoria Cones and Their Structural Control: A Case Study in the Michoacán-Guanajuato Volcanic Field

HomeJoinGSA StoreDonateContact Sign in Toggle search Keyword search Toggle navigation Keyword search Abstract View Volume 33 Issue 2 (February 2023) GSA Today Article, p. 4-10 | Full Text | PDF New Insights into Feeder Dike Swarms in Scoria Cones and Their Structural Control: A Case Study in the Michoacán-Guanajuato Volcanic Field Martha Gabriela Gómez-Vasconcelos* CONACYT–Instituto de Investigaciones en Ciencias de la Tierra, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Michoacán, México, gabriela.gomez@umich.mx Denis-Ramón Avellán CONACYT–Instituto de Geofísica, Universidad Nacional Autónoma de México, Morelia, Michoacán, México, denisavellan@gmail.com José Luis Macías Instituto de Geofísica, Universidad Nacional Autónoma de México, Morelia, Michoacán, México, jlmv63@gmail.com Guillermo Cisneros-Máximo Instituto de Geofísica, Universidad Nacional Autónoma de México, Morelia, Michoacán, México, gcisneros@igeofisica.unam.mx Juan Manuel Sánchez-Núñez Instituto Politécnico Nacional–CIIEMAD, Gustavo A. Madero, Ciudad de México, México, jsancheznu@ipn.mx Daniel P. Miggins 40Ar/39Ar Geochronology Laboratory, College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA, daniel.miggins@oregonstate.edu Abstract Understanding the feeder systems in scoria cones is essential because they serve as the conduits that feed the most common eruptions worldwide. Feeder dikes and their emplacement are presumably controlled by the tectonic stress field. However, the mechanism of dike propagation and structural control in monogenetic scoria cones remains poorly understood, as well as the conditions that allow dike swarms in scoria cones and in low magma-flux monogenetic volcanic fields. This is the first direct study of a magma feeder system in the Michoacán-Guanajuato Volcanic Field in central México. Quarrying in the Cerrito Colorado scoria cone displays six orthogonal feeder dikes—four of them are N-S oriented, parallel to the least compressive stress, intruding preexisting faults, and two are E-W oriented, perpendicular to the least compressive stress, forming their own fracture at the time of the eruption. Single feeder dikes are common in monogenetic volcanoes, but dike networks (swarms) can develop locally in the vicinity of scoria cones and other vent structures. We suggest that bifurcation of feeder dikes can result from temporary blockages of the conduit and during changes in the magma ascent rate and magma pressure. Feeder dikes at the surface can appear as tabular dikes, cylindrical conduits, or as a combination of both geometries. We suggest that tabular dikes splay-off tangentially, and cylindrical conduits bifurcate radially and axially to the main vent. Our study attests to the complexity and structural control that even small scoria cones can present. *Corresponding author Manuscript received 17 Mar. 2022. Revised manuscript received 30 June 2022. Manuscript accepted 18 July 2022. Posted 10 Aug. 2022. © The Geological Society of America, 2022. CC-BY-NC. https://doi.org/10.1130/GSATG539A.1 Cover Image Search Google Scholar for Martha Gabriela Gómez-Vasconcelos Denis-Ramón Avellán José Luis Macías Juan Manuel Sánchez-Núñez Daniel P. Miggins Search GSA Today About Membership Publications Events Education & Careers Science Policy News Advertising Place a Job Ad FAQs Jobs at GSA Center for Professional Excellence Code of Ethics Events Code of Conduct Privacy Policy Join GSA Contact Us www.geosociety.org © 2023 The Geological Society of America, Inc.