Journal articles on the topic 'Rhyolite calderas'
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1
Coyle, Marylou, and D. F. Strong. "Geology of the Springdale Group: a newly recognized Silurian epicontinental-type caldera in Newfoundland." Canadian Journal of Earth Sciences 24, no. 6 (June 1, 1987): 1135–48. http://dx.doi.org/10.1139/e87-110.
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Volcanic–sedimentary facies and structural relationships of the Silurian Springdale Group in west-central Newfoundland are indicative of a large collapse caldera with an area of more than 2000 km2. Basaltic flows, andesite flows and pyroclastic rocks, silicic ash-flow tuffs, high-silica rhyolite domes, and volcanically derived debris flows and breccias, fluviatile red sandstones, and conglomerates make up the group. It is bounded on the east and west by up-faulted basement rocks, which include gneisses, amphibolites, and pillow lavas, and in the northwest it unconformably overlies Lower Orodovician submarine volcanics. These margins are intruded by cogenetic and younger granitoid rocks. The volcanic rocks form a calc-alkaline series, although gaps in silica content at 52–56, 67–68, and 73–74% separate them into four groups: basalts, andesites–dacites, rhyolites, and high-silica rhyolites.The high-silica rhyolites are chemically comparable to melts thought to form the upper parts of large, layered silicic magma chambers of epicontinental regions. Such an environment is also suggested by the large area of the Springdale caldera and the fact that it is one of a number of calderas that make up a large Silurian volcanic field in western Newfoundland. An epicontinental tectonothermal environment for central Newfoundland in Silurian–Devonian times is readily explained by the fact that this magmatic activity followed a period of destruction and closure of the early Paleozoic Iapetus Ocean, with trapped heat and basaltic magma causing large-scale melting of thickened and subducted continental crust in an overall transpressional tectonic regime.
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Amanda, Fajar F., Ryoichi Yamada, Masaoki Uno, Satoshi Okumura, and Noriyoshi Tsuchiya. "Evaluation of Caldera Hosted Geothermal Potential during Volcanism and Magmatism in Subduction System, NE Japan." Geofluids 2019 (January 21, 2019): 1–14. http://dx.doi.org/10.1155/2019/3031586.
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Deep-seated geothermal reservoirs beneath calderas have high potential as sources of renewable energy. In this study, we used an analysis of melt inclusions to estimate the amount of water input to the upper crust and quantify the properties of a deep-seated geothermal reservoir within a fossil caldera, the late Miocene Fukano Caldera (formation age 8–6 Ma), Sendai, NE Japan. Our research shows that Fukano Caldera consists of the southern part and northern part deposits which differ in the age and composition. The northern deposits are older and have higher potassium and silica contents than the southern deposits. Both the northern and southern deposits record plagioclase and plagioclase–quartz differentiation and are classified as dacite–rhyolite. The fossil magma chamber underlying the caldera is estimated to have a depth of ~2–10 km and a water content of 3.3–7.0 wt.%, and when the chamber was active it had an estimated temperature of 750°C–795°C. The water input into the fossil magma chamber is estimated at 2.3–7.6 t/yr/m arc length based on the magma chamber size the water content in the magma chamber and the length of volcanism periods of Fukano Caldera, NE Japan arc. The total amount of water that is stored in the chamber is ~1014 kg. The chamber is saturated in water and has potential as a deep-seated geothermal reservoir. Based on the shape of the chamber, the reservoir measures ~10 km × 5 km in the horizontal dimension and is 7–9 km in vertical extent. The 0th estimate shows that the reservoir can hold the electric energy equivalent of 33–45 GW over 30 years of power generation. Although the Fukano reservoir has great potential, commercial exploitation remains challenging owing to the corrosive nature of the magmatic fluids and the uncertain permeability network of the reservoir.
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Berg, Sylvia E., Valentin R. Troll, Chris Harris, Frances M. Deegan, Morten S. Riishuus, Steffi Burchardt, and Michael Krumbholz. "Exceptionally high whole-rock δ18O values in intra-caldera rhyolites from Northeast Iceland." Mineralogical Magazine 82, no. 5 (May 29, 2018): 1147–68. http://dx.doi.org/10.1180/mgm.2018.114.
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ABSTRACTThe Icelandic crust is characterized by low δ18O values that originate from pervasive high-temperature hydrothermal alteration by18O-depleted meteoric waters. Igneous rocks in Iceland with δ18O values significantly higher than unaltered oceanic crust (~5.7‰) are therefore rare. Here we report on rhyolitic intra-caldera samples from a cluster of Neogene central volcanoes in Borgarfjörður Eystri, Northeast Iceland, that show whole-rock δ18O values between +2.9 and +17.6‰ (n= 6), placing them among the highest δ18O values thus far recorded for Iceland. Extra-caldera rhyolite samples from the region, in turn, show δ18O whole-rock values between +3.7 and +7.8‰ (n= 6), consistent with the range of previously reported Icelandic rhyolites. Feldspar in the intra-caldera samples (n= 4) show δ18O values between +4.9 and +18.7‰, whereas pyroxene (n= 4) shows overall low δ18O values of +4.0 to +4.2‰, consistent with regional rhyolite values. In combination with the evidence from mineralogy and rock H2O contents, the high whole-rock δ18O values of the intra-caldera rhyolites appear to be the result of pervasive isotopic exchange during subsolidus hydrothermal alteration with18O-enriched water. This alteration conceivably occurred in a near-surface hot spring environment at the distal end of an intra-caldera hydrothermal system, and was probably fed by waters that had already undergone significant isotope exchange with the country rock. Alternatively,18O-enriched alteration fluids may have been produced during evaporation and boiling of standing water in former caldera lakes, which then interacted with the intra-caldera rock suites. Irrespective of the exact exchange processes involved, a previously unrecognized and highly localized δ18O-enriched rock composition exists on Iceland and thus probably within the Icelandic crust too.
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Campbell, S. D. G., A. J. Reedman, M. F. Howells, and A. C. Mann. "The emplacement of geochemically distinct groups of rhyolites during the evolution of the Lower Rhyolitic Tuff Formation caldera (Ordovician), North Wales, U.K." Geological Magazine 124, no. 6 (November 1987): 501–11. http://dx.doi.org/10.1017/s0016756800017349.
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AbstractRhyolites in the vicinity of Snowdon (North Wales) are intimately associated with the evolution of the Lower Rhyolitic Tuff Formation (LRTF) caldera of Ordovician (Caradoc) age. They occur as deep-seated dykes, sills and small stocks, shallow-level intrusive domes, and domes extruded within a predominantly shallow-marine environment. Extrusion occurred during three main phases, indicating the episodic availability of rhyolite magma. The rhyolites can be divided on their trace element ratios (e.g. Nb/Zr) into five main groups. Extrusive representatives indicate that each group correlates strongly with a single phase of rhyolite extrusion. Within each group, the distribution and variation of intrusive form with stratigraphic level suggests that geochemically similar rocks were emplaced at approximately the same time. Consequently, the groups represent discrete magma compositions tapped from the evolving Snowdon subvolcanic magma system. Differences in distribution of the groups reflect changes in structural controls of emplacement before and after development of the LRTF caldera.
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Saubin, E., B. Kennedy, H. Tuffen, A. R. L. Nichols, M. Villeneuve, I. Bindeman, A. Mortensen, et al. "Textural and geochemical window into the IDDP-1 rhyolitic melt, Krafla, Iceland, and its reaction to drilling." GSA Bulletin 133, no. 9-10 (January 6, 2021): 1815–30. http://dx.doi.org/10.1130/b35598.1.
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Abstract The unexpected intersection of rhyolitic magma and retrieval of quenched glass particles at the Iceland Deep Drilling Project-1 geothermal well in 2009 at Krafla, Iceland, provide unprecedented opportunities to characterize the genesis, storage, and behavior of subsurface silicic magma. In this study, we analyzed the complete time series of glass particles retrieved after magma was intersected, in terms of distribution, chemistry, and vesicle textures. Detailed analysis of the particles revealed them to represent bimodal rhyolitic magma compositions and textures. Early-retrieved clear vesicular glass has higher SiO2, crystal, and vesicle contents than later-retrieved dense brown glass. The vesicle size and distribution of the brown glass also reveal several vesicle populations. The glass particles vary in δD from −120‰ to −80‰ and have dissolved water contents spanning 1.3−2 wt%, although the majority of glass particles exhibit a narrower range. Vesicular textures indicate that volatile overpressure release predominantly occurred prior to late-stage magma ascent, and we infer that vesiculation occurred in response to drilling-induced decompression. The textures and chemistry of the rhyolitic glasses are consistent with variable partial melting of host felsite. The drilling recovery sequence indicates that the clear magma (lower degree partial melt) overlays the brown magma (higher degree partial melt). The isotopes and water species support high temperature hydration of these partial melts by a mixed meteoric and magmatic composition fluid. The textural evidence for partial melting and lack of crystallization imply that magma production is ongoing, and the growing magma body thus has a high potential for geothermal energy extraction. In summary, transfer of heat and fluids into felsite triggered variable degrees of felsite partial melting and produced a hydrated rhyolite magma with chemical and textural heterogeneities that were then enhanced by drilling perturbations. Such partial melting could occur extensively in the crust above magma chambers, where complex intrusive systems can form and supply the heat and fluids required to re-melt the host rock. Our findings emphasize the need for higher resolution geophysical monitoring of restless calderas both for hazard assessment and geothermal prospecting. We also provide insight into how shallow silicic magma reacts to drilling, which could be key to future exploration of the use of magma bodies in geothermal energy.
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de Silva, S. L., J. Roberge, L. Bardelli, W. Báez, A. Ortiz, J. G. Viramonte, J. M. Arnosio, and R. Becchio. "Magmatic evolution and architecture of an arc-related, rhyolitic caldera complex: The late Pleistocene to Holocene Cerro Blanco volcanic complex, southern Puna, Argentina." Geosphere 18, no. 2 (January 25, 2022): 394–423. http://dx.doi.org/10.1130/ges02294.1.
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Abstract Through the lens of bulk-rock and matrix glass geochemistry, we investigated the magmatic evolution and pre-eruptive architecture of the siliceous magma complex beneath the Cerro Blanco volcanic complex, a Crater Lake–type caldera complex in the southern Puna Plateau of the Central Andes of Argentina. The Cerro Blanco volcanic complex has been the site of two caldera-forming eruptions with volcanic explosivity index (VEI) 6+ that emplaced the ca. 54 ka Campo Piedra Pomez ignimbrite and the ca. 4.2 ka Cerro Blanco ignimbrite. As such, it is the most productive recent explosive volcano in the Central Andes. The most recent eruptions (younger than 4.2 ka) are dominantly postcaldera effusions of crystal-rich domes and associated small explosive pulses. Previous work has demonstrated that andesitic recharge of and mixing with rhyolitic magma occurred at the base of the magma complex, at ~10 km depth. New isotopic data (Sr, Nd, Pb, and O) confirm that the Cerro Blanco volcanic complex rhyolite suite is part of a regional southern Puna, arc-related ignimbrite group. The suite defines a tight group of consanguineous siliceous magmas that serves as a model for the evolution of arc-related, caldera-forming silicic magma systems in the region and elsewhere. These data indicate that the rhyolites originated through limited assimilation of and mixing with upper-crustal lithologies by regional basaltic andesite parent materials, followed by extensive fractional crystallization. Least squares models of major elements in tandem with Rayleigh fractionation models for trace elements reveal that the internal variations among the rhyolites through time can be derived by extensive fractionation of a quartz–two feldspar (granitic minimum) assemblage with limited assimilation. The rare earth element character of local volumes of melt in some samples of the Campo Piedra Pomez ignimbrite basal fallout requires significant fractionation of amphibole. The distinctive major- and trace-element characteristics of bulk rock and matrix of the Campo Piedra Pomez and Cerro Blanco tephras provide useful geochemical fingerprints to facilitate regional tephrochronology. Available data indicate that rhyolites from other neighborhood centers, such as Cueros de Purulla, share bulk chemical characteristics with the Campo Piedra Pomez ignimbrite rhyolites, but they appear to be isotopically distinct. Pre-eruptive storage and final equilibration of the rhyolitic melts were estimated from matrix glass compositions projected onto the haplogranitic system (quartz-albite-orthoclase-H2O) and using rhyolite-MELTS models. These revealed equilibration pressures between 360 and 60 MPa (~10–2 km depth) with lowest pressures in the Holocene eruptions. Model temperatures for the suite ranged from 695 to 790 °C. Integrated together, our results reveal that the Cerro Blanco volcanic complex is a steady-state (low-magmatic-flux), arc-related complex, standing in contrast to the flare-up (high-magmatic-flux) supervolcanoes that dominate the Neogene volcanic stratigraphy. The silicic magmas of the Cerro Blanco volcanic complex were derived more directly from mafic and intermediate precursors through extensive fractional crystallization, albeit with some mixing and assimilation of local basement. Geochemical models and pressure-temperature estimates indicate that significant volumes of remnant cumulates of felsic and intermediate composition should dominate the polybaric magma complex beneath the Cerro Blanco volcanic complex, which gradually shallowed through time. Evolution to the most silicic compositions and final equilibration of some of the postcaldera domes occurred during ascent and decompression at depths less than 2 km. Our work connotes an incrementally accumulated (over at least 54 k.y.), upper-crustal pluton beneath the Cerro Blanco volcanic complex between 2 and 10 km depth. The composition of this pluton is predicted to be dominantly granitic, with deeper parts being granodioritic to tonalitic. The progressive solidification and eventual contraction of the magma complex may account for the decades of deflation that has characterized Cerro Blanco. The presently active geothermal anomaly and hydrothermal springs indicate the Cerro Blanco volcanic complex remains potentially active.
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Barker, Simon J., Michael C. Rowe, Colin J. N. Wilson, John A. Gamble, Shane M. Rooyakkers, Richard J. Wysoczanski, Finnigan Illsley-Kemp, and Charles C. Kenworthy. "What lies beneath? Reconstructing the primitive magmas fueling voluminous silicic volcanism using olivine-hosted melt inclusions." Geology 48, no. 5 (February 27, 2020): 504–8. http://dx.doi.org/10.1130/g47422.1.
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Abstract Understanding the origins of the mantle melts that drive voluminous silicic volcanism is challenging because primitive magmas are generally trapped at depth. The central Taupō Volcanic Zone (TVZ; New Zealand) hosts an extraordinarily productive region of rhyolitic caldera volcanism. Accompanying and interspersed with the rhyolitic products, there are traces of basalt to andesite preserved as enclaves or pyroclasts in caldera eruption products and occurring as small monogenetic eruptive centers between calderas. These mafic materials contain MgO-rich olivines (Fo79–86) that host melt inclusions capturing the most primitive basaltic melts fueling the central TVZ. Olivine-hosted melt inclusion compositions associated with the caldera volcanoes (intracaldera samples) contrast with those from the nearby, mafic intercaldera monogenetic centers. Intracaldera melt inclusions from the modern caldera volcanoes of Taupō and Okataina have lower abundances of incompatible elements, reflecting distinct mantle melts. There is a direct link showing that caldera-related silicic volcanism is fueled by basaltic magmas that have resulted from higher degrees of partial melting of a more depleted mantle source, along with distinct subduction signatures. The locations and vigor of Taupō and Okataina are fundamentally related to the degree of melting and flux of basalt from the mantle, and intercaldera mafic eruptive products are thus not representative of the feeder magmas for the caldera volcanoes. Inherited olivines and their melt inclusions provide a unique “window” into the mantle dynamics that drive the active TVZ silicic magmatic systems and may present a useful approach at other volcanoes that show evidence for mafic recharge.
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Ewart, A., R. W. Schon, and B. W. Chappell. "The Cretaceous volcanic-plutonic province of the central Queensland (Australia) coast—a rift related ‘calc-alkaline’ province." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 83, no. 1-2 (1992): 327–45. http://dx.doi.org/10.1017/s0263593300008002.
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ABSTRACTSilicic and minor intermediate and mafic pyroclastics, lavas, and dykes occupy a NW-trending zone through the Whitsunday, Cumberland and Northumberland Island groups, and locally areas on the adjacent mainland, over a distance of more than 300 km along the central Queensland coast. K-Ar and Rb-Sr data indicate an age range of 95–132 Ma, with the main activity approximately between 105–120 Ma; there is, however, evidence for easterly increasing ages. Comagmatic granites, some clearly intrusive into the volcanics, occur together with two localised areas of Triassic potassic granites (229 Ma), that form the immediate basement.The volcanics are dominantly rhyolitic to dacitic lithic ignimbrites, with intercalated surge and bedded tuffs, accretionary lapilli tuffs, and lag deposits. Associated rock types include isolated rhyolitic and dacitic domes, and volumetrically minor andesite and rare basalt flows. The sequence is cut by abundant dykes, especially in the northern region and adjacent mainland, ranging from dolerite through andesite, dacite and rhyolite. Dyke orientations show maxima between NW-NNE. Isotope data, similarities in petrography and mineralogy, and alteration patterns all suggest dyke intrusion to be broadly contemporaneous with volcanism. The thickness of the volcanics is unconstrained, although in the Whitsunday area, minimum thicknesses of >1 km are inferred. Eruptive centres are believed to occur throughout the region, and include at least two areas of caldera-style collapse. The sequences are thus considered as predominantly intracaldera.The phenocryst mineralogy is similar to modern “orogenic” volcanics. Phases include plagioclase, augite, hypersthene (uralitised), magnetite, ilmenite, with less common hornblende, and even rarer quartz, sanidine, and biotite. Fe-enriched compositions only develop in some high-silica rhyolites. The granites range from quartz diorite to granite s.s., and some contain spectacular concentrations of partially disaggregated dioritic inclusions.Chemically, the suite ranges continuously from basalt to high-silica rhyolite, with calc-alkali to high-K affinities, and geochemical signatures similar to modern subduction-related magmas. Only the high-silica rhyolites and granites exhibit evidence of extensive fractional crystallisation (e.g. pronounced Eu anomalies). Variation within the suite can only satisfactorily be modelled in terms of two component mixing, with superimposed crystal fractionation. Nd and Sr isotope compositions are relatively coherent, with εNd + 2·2 to +7·3, and ISr (calculated at 110 and 115 Ma) 0·7031-0·7044. These are relatively primitive, and imply mantle and/or newly accreted crustal magma sources.The two end-members proposed are within-plate tholeiitic melt, and ?low-silica rhyolitic melts generated by partial fusion of Permian (to ?Carboniferous) arc and arc basement. The arc-like geochemistry is thus considered to be source inherited. The tectonic setting for Cretaceous volcanism is correlated with updoming and basin rifting during the early stages of continental breakup, culminating in the opening of the Tasman Basin. Cretaceous volcanism is also recognised in the Maryborough Basin (S Queensland), the Lord Howe Rise, and New Caledonia, indicating the regional extent of volcanism associated with the complex breakup of the eastern Australasian continent margin.
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Swanson, Eric. "History of Field Observations on Volcanic Rocks of Western Mexico, Pre-Columbian to Recent." Earth Sciences History 30, no. 1 (December 1, 2011): 106–34. http://dx.doi.org/10.17704/eshi.30.1.p68hl442l6w11036.
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By the time the first detailed reports on western Mexico's volcanic rocks had begun to appear in the 1970s, most of the earlier observations on these rocks and most knowledge of those who made these observations were all but forgotten. A review of previous field observations in this region shows, however, a long history of geologic discovery reflecting or even preceding developments elsewhere.Ethnological studies suggest that the Pre-Columbian inhabitants of the Sierra Madre Occidental (SMO) observed the characteristics of rock formations in their sierra homeland and understood something of the regional stratigraphic relationships. Late sixteenth and early seventeenth century explorers of the Spanish Colonial Period singled out volcanic rock known to them as piedra de malpaís for special recognition, and Padre Kino and his fellow explorers clearly recognized the volcanic origin of piedra de malpaís decades prior to similar observations in Europe. As the Spanish Colonial Period came to a close, Andrés Manuel del Río help organize a state-of-theart mining college in Mexico City where students were instructed in Werner's geognosy prior to their taking positions in Mexico's mining industry, most of it located in western Mexico's volcanic rocks.Although the first part of the tumultuous period between Mexico's revolutions of 1810 and 1910 saw few advances in geological knowledge, the reign of President Porfirio Díaz produced a geologic map of Mexico, the founding of the Instituto de Geología, and an ‘American invasion’ of geologists and mining engineers who locally gathered information on the nature of volcanic rocks of western Mexico. During the same period, Instituto geologist Ezequiel Ordóñez established the general stratigraphic sequence in the SMO, recognized the widespread occurrence of rhyolite there, and applied the petrographic microscope to the study of SMO volcanic rocks. The first identification of ignimbrites in the SMO came as a result of the World War II-era search for strategic minerals, and NASA's push to put a man on the Moon supported a series of student mapping projects producing the SMO's first geologic maps showing individual ignimbrite units and calderas.
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Juliani, Caetano, Rafael Rodrigues de Assis, Lena Virgínia Soares Monteiro, Carlos Marcello Dias Fernandes, José Eduardo Zimmermann da Silva Martins, and Jhoseph Ricardo Costa e Costa. "Gold in Paleoproterozoic (2.1 to 1.77 Ga) Continental Magmatic Arcs at the Tapajós and Juruena Mineral Provinces (Amazonian Craton, Brazil): A New Frontier for the Exploration of Epithermal–Porphyry and Related Deposits." Minerals 11, no. 7 (July 1, 2021): 714. http://dx.doi.org/10.3390/min11070714.
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This review paper aims to integrate geological, tectonic and metallogenetic data, including new data, and propose a regional model for the gold (and base metal) mineralization in the south Amazonian Craton to support the mineral exploration concerning magmatic–hydrothermal deposits. The Proterozoic evolution of the Amazonian Craton comprises the accretion of terrains to the Archean Carajás Mineral Province. In the Tapajós and Juruena mineral provinces, located at the south part of the Amazonian craton, a long-lived ocean–continent subduction event produced ca. 2.0 to 1.77 Ga continental magmatic arcs. Extensive lava flows, volcaniclastic, sedimentary, and plutonic rocks were originated during at least four major orogenic magmatic events (ca. 2.1, 1.9, 1.88, and 1.80 Ga) and two post- to anorogenic events (ca. 1.87 and 1.77 Ga). Gold mineralization occurs in: (i) alluvial/colluvial occurrences, (ii) orogenic carbonate–sulfide-rich quartz veins in shear zones, (iii) stockworks, veins, and dissemination in granites, (iv) contact of basic dikes, (v) well-preserved high-, intermediate- and low-sulfidation epithermal mineralization, and (vi) porphyry-like and intrusion-related gold systems associated with late- to post-orogenic epizonal granites. The estimated historical gold production, mainly in secondary deposits, is over 27 Moz at the Tapajós and 6 Moz at the Juruena provinces. A total resource of over 5 Moz Au is currently defined in several small to large primary gold deposits. Andesite to rhyolite, volcaniclastic, and clastic sedimentary rocks (1.96–1.88 Ga) host epithermal (high-, intermediate-, and low-sulfidation) Au–(Ag–Pb–Zn) mineralization, whereas Au–Cu and Cu–M–Au mineralization is hosted in sub-volcanic tonalitic to granitic plutons. Advanced argillic alteration (alunite, pyrophyllite, enargite) associated with high-sulfidation mineralization occurs in ring volcanoes around nested volcanic calderas. This zone grades outward to propylitic or chlorite alteration, often covered by silica caps with vuggy silica. Lava flows and volcaniclastic rocks within faults or associated with volcanic edifices and rhyolitic domes host low- and intermediate-sulfidation mineralization. Low-sulfidation alteration zones typically have adularia and illite or sericite. Chalcopyrite, sphalerite, galena, pyrite, digenite, and manganiferous calcite are related to intermediate-sulfidation gold mineralization. Late- to post-orogenic evolved oxidized I-type granitoids host alkalic-type epithermal and porphyry-like gold mineralization. Porphyry-style hydrothermal alteration is analogous to those of modern systems, with inner sodic and potassic (potassic feldspar ± biotite or biotite) alterations grading to propylitic, muscovite-sericite, chlorite–sericite, and chlorite alterations. Potassic alteration zones are the locus of Cu–Mo mineralization, and gold-rich zones occur in muscovite/sericite–quartz–pyrite alteration. The Paleoproterozoic epithermal and porphyry-like mineralization in these large provinces defines a new frontier for the exploration of world-class gold deposits in the worldwide Proterozoic arc-related magmatic terrains.
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Hübner, Marcel, Christoph Breitkreuz, Alexander Repstock, Bernhard Schulz, Anna Pietranik, Manuel Lapp, and Franziska Heuer. "Evolution of the Lower Permian Rochlitz volcanic system, Eastern Germany: reconstruction of an intra-continental supereruption." International Journal of Earth Sciences 110, no. 6 (July 14, 2021): 1995–2020. http://dx.doi.org/10.1007/s00531-021-02053-5.
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AbstractExtensional tectonics in the Late Paleozoic Central Europe was accompanied by rift magmatism that triggered voluminous intracontinental caldera-forming eruptions. Among these, the Lower Permian Rochlitz Volcanic System (RVS) in the North Saxon Volcanic Complex (Eastern Germany, Saxony) represents a supereruption (VEI 8, estimated volume of 1056 km3) of monotonous rhyolites followed by monotonous intermediates. Mapping, petrography, whole-rock geochemistry along with mineral chemistry and oxygen isotopes in zircon display its complex eruption history and magma evolution. Crystal-rich (> 35 vol%), rhyolitic Rochlitz-α Ignimbrite with strong to moderate welding compaction erupted in the climactic stage after reheating of the magma by basaltic injections. Due to magma mixing, low-volume trachydacitic-to-rhyolitic Rochlitz-β Ignimbrite succeeded, characterized by high Ti and Zr-values and zircon with mantle δ18O. Randomly oriented, sub-horizontally bedded fiamme, and NW–SE striking subvolcanic bodies and faults suggest pyroclastic fountaining along NW–SE-oriented fissures as the dominant eruption style. Intrusion of the Leisnig and the Grimma Laccoliths caused resurgence of the Rochlitz caldera forming several peripheral subbasins. In the post-climactic stage, these were filled with lava complexes, ignimbrites and alluvial to lacustrine sediments. Significant Nb and Ta anomalies and high Nb/Ta ratios (11.8–17.9) display a high degree of crustal contamination for the melts of the RVS. Based on homogenous petrographic and geochemical composition along with a narrow range of δ18O in zircon Rochlitz-α Ignimbrite were classified as monotonous rhyolites. For the Rochlitz-β Ignimbrites, underplating and mixing with basic melts are indicated by Mg-rich annite–siderophyllite and δ18O < 6.0 in zircon. The wide spectrum of δ18O on zircon suggests an incomplete mixing process during the formation of monotonous intermediates in the RVS.
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Shcherbakov, Vasily, Ilya Bindeman, and Viktor Gazeev. "Geochemical, Isotopic and Petrological Constraints on the Origin and Evolution of the Recent Silicic Magmatism of the Greater Caucasus." Minerals 12, no. 1 (January 16, 2022): 105. http://dx.doi.org/10.3390/min12010105.
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Significant volumes of rhyolites and granites of the Pliocene-Pleistocene age are exposed in the collision zone of the Greater Caucasus, Russia. The volcanic history of the region includes ignimbrites and lavas associated with the Chegem caldera (2.9 Ma) and Elbrus volcano (1.98 and 0.7 Ma) and rhyolitic necks and granites in Tyrnyauz (1.98 Ma). They are characterized by a similar bulk and mineral composition and close ratios of incompatible elements, which indicates their related origin. The 1.98 Ma Elbrus ignimbrites, compared to the 2.9 Ma Chegem ignimbrites, have elevated concentrations of both compatible (Cr, Sr, Ca, Ni) and incompatible elements (Cs, Rb, U). We argue that the Elbrus ignimbrites were produced from magma geochemically similar to Chegem rhyolites through fractionation crystallization coupled with the assimilation of crustal material. The 1.98 Ma Eldjuta granites of Tyrnyauz and early ignimbrites of the Elbrus region (1.98 Ma) are temporally coeval, similar mineralogically, and have comparable major and trace element composition, which indicates that the Elbrus ignimbrites probably erupted from the area of modern Tyrnyauz; the Eldjurta granite could represent a plutonic reservoir that fed this eruption. Late ignimbrites of Elbrus (0.7 Ma) and subsequent lavas demonstrate progressively more mafic mineral assemblage and bulk rock composition in comparison with rhyolites. This indicates their origin in response to the mixing of rhyolites with magmas of a more basic composition at the late stage of magma system development. The composition of these basic magmas may be close to the basaltic trachyandesite, the flows exposed along the periphery of the Elbrus volcano. All studied young volcanic rocks of the Greater Caucasus are characterized by depletion in HSFE and enrichment in LILE, Li, and Pb, which emphasizes the close relationship of young silicic magmatism with magmas of suprasubduction geochemical affinity. An important geochemical feature is the enrichment of U up to 8 ppm and Th up to 35 ppm. The trace element composition of the rocks indicates that the original rhyolitic magma of Chegem ignimbrites caldera was formed at >80%–90% fractionation of calc-alkaline arc basalts with increased alkalinity. This observation, in addition to published data for isotopic composition (O-Hf-Sr) of the same units, shows that the crustal isotopic signatures of silicic volcanics may arise due to the subduction-induced fertilization of peridotites producing parental basaltic magmas before a delamination episode reactivated the melting of the former mantle and the lower crust.
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Alatorre‐Zamora, M. A., and J. O. Campos‐Enríquez. "La Primavera caldera (Mexico): Structure inferred from gravity and hydrogeological considerations." GEOPHYSICS 56, no. 7 (July 1991): 992–1002. http://dx.doi.org/10.1190/1.1443132.
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La Primavera geothermal field (Mexico) is associated with a Pleistocene rhyolitic caldera. This gravity study was conducted to assist its development and explotation. Digital processing of the gravity data (upward and downward continuations, vertical derivatives) enabled delineation of the main features of the caldera’s subsurficial structure. A 3-D structural model was established, which could be supported by gravity modeling (2-D and 3-D forward modeling). Accordingly, the caldera is featured by an asymmetric subsurface structure: a major depression in its northern half, and a boomerang‐shaped structural high to the south. Lineaments reflecting the regional northwest‐southeast and northeast‐southwest structural fabric were observed. The basal volcanics units are affected by lineaments of the northwest‐southeast system, whereas the northeast‐southwest system affects only the shallower units. The structural high has a northwest‐southeast trend at the western and southwestern portion of the caldera. From its middle part eastward, it has a northeast‐southwest direction. The actual geothermal production zone is located above this structural high, on the portion where it changes orientation. Correlation with hydrogeological and geochemical data enabled interpreting the different geologic structures in the context of the hydrothermal system: at depth the northwest‐southeast structures seem to control lateral fluid migration, and connect areas of enhanced permeability (i.e., the central production zone and the hydrothermal manifestations located at the caldera’s western rim). Enhanced zones of fracturing favorable for entrapping hydrothermal fluids and structural accidents that may act as conduits (respectively as barriers) for fluids are delineated. In particular, a new target zone, where the production of geothermal fluids may extend, has been identified to the south of the production zone. The structural image elaborated here constitutes a geologic frame for the prevailing hydrogeological conceptual model. This structural information is also useful for the tasks of selecting sites for the reinjection of geothermal brines.
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Chernyshev, Igor V., Vlastimil Konečný, Jaroslav Lexa, Vladimir A. Kovalenker, Stanislav Jeleň, Vladimir A. Lebedev, and Yurij V. Goltsman. "K-Ar and Rb-Sr geochronology and evolution of the Štiavnica Stratovolcano (Central Slovakia)." Geologica Carpathica 64, no. 4 (August 1, 2013): 327–60. http://dx.doi.org/10.2478/geoca-2013-0023.
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Abstract The Štiavnica Stratovolcano in Central Slovakia is the largest volcano in the Neogene to Quaternary Carpathian volcanic arc. A large caldera, an extensive subvolcanic intrusive complex and a resurgent horst with late stage rhyolite volcanites are the most characteristic features. The results of new K-Ar and Rb-Sr isotope dating using more sophisticated methodical approaches have changed our view on the timing of volcanic and intrusive activity. K-Ar dating of groundmass fractions combined with Rb-Sr isochron dating in the cases of possible rejuvenation has provided highly reliable results. The lifespan of the stratovolcano is apparently shorter than assumed earlier. Evolution of the stratovolcano took place in five stages during the Early Badenian to beginning of Early Pannonian time: (1) construction of the extensive andesite stratovolcano during the interval 15.0-13.5 Ma; (2) denudation of the volcano concluded with the initial subsidence of a caldera and the contemporaneous emplacement of a subvolcanic intrusive complex of diorite, granodiorite, granodiorite porphyries and quartz-diorite porphyries during the interval 13.5-12.9 Ma; (3) subsidence of the caldera and its filling by differentiated andesites during the interval 13.1-12.7 Ma - volcanic activity overlapping with the emplacement of the youngest intrusions; (4) renewed explosive and effusive activity of less differentiated andesites during the interval 12.7-12.2 Ma; (5) uplift of the resurgent horst in the central part of the caldera accompanied by rhyolite volcanic/intrusive activity during the interval 12.2-11.4 Ma. Extensive epithermal mineralization was contemporaneous with the uplift of the resurgent horst and rhyolite volcanic activity and continued till 10.7 Ma
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Thorne, Kathleen G., Leslie R. Fyffe, and Robert A. Creaser. "Re-Os geochronological constraints on the mineralizing events within the Mount Pleasant Caldera: implications for the timing of sub-volcanic magmatism." Atlantic Geology 49 (August 14, 2013): 131. http://dx.doi.org/10.4138/atlgeol.2013.007.
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The Mount Pleasant granite-related polymetallic deposit, located on the southwestern margin of the Late Devonian to Early Carboniferous Mount Pleasant Caldera Complex in southwestern New Brunswick, contains a significant resource of tin, tungsten, molybdenum, zinc, indium, and bismuth. The Caldera Complex comprises Intracaldera, Exocaldera, and Late Caldera-Fill sequences and associated subvolcanic granitic rocks. Three granitic phases of the Mount Pleasant Granitic Suite (Granite I, II, and III) are recognized in the vicinity of the Mount Pleasant deposit and are interpreted to be fractionates of the more regionally exposed McDougall Brook Granitic Suite. Granite I and Granite II are associated with tungsten-molybdenum-bismuth, and tin-zinc-indium mineralization, respectively. Despite extensive research within the Caldera Complex, the exact age of mineralization at Mount Pleasant has never been firmly established. An inferred age of 363 ± 2 Ma was based on the proposed synchronicity of the U-Pb dated Bailey Rock Rhyolite of the Exocaldera Sequence with that of the undated McDougall Brook Granitic Suite, which intrudes the Intracaldera Sequence. Here, we present Re-Os dating of two molybdenite samples associated with the tungsten mineralization related to Granite I at the Fire Tower Zone, that constrain the initial onset of mineralization at Mount Pleasant to be between 369.7±1.6 Ma and 370.1±1.7 Ma. The new Re-Os ages clearly indicate that the McDougall Brook Granitic Suite, which pre-dates mineralization, must be at least seven million years older than the Bailey Rock Rhyolite, whose type-section is located within the Exocaldera Sequence. A re-examination of the gradational relationship between the McDougall Brook Granitic Suite and purported rocks of Bailey Rock Rhyolite within the Intracaldera Sequence revealed that the latter should instead be assigned to the Seelys Formation. Thus, deposition of the polymetallic mineralization likely took place contemporaneously with caldera collapse and an early phase of resurgent doming in response to degassing of the magma chamber rather than being coincident with erosion of the volcanic edifice as inferred from previous modeling of the eruptive history at Mount Pleasant.
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Troch, Juliana, Ben S. Ellis, Chris Harris, Peter Ulmer, Anne-Sophie Bouvier, and Olivier Bachmann. "Experimental Melting of Hydrothermally Altered Rocks: Constraints for the Generation of Low-δ18O Rhyolites in the Central Snake River Plain." Journal of Petrology 60, no. 10 (October 1, 2019): 1881–902. http://dx.doi.org/10.1093/petrology/egz056.
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Abstract Quantifying the relative contributions of crustal versus mantle-derived melt is important for understanding how silicic magmas are generated, stored, and interact with country rock in trans-crustal magmatic systems. Low-δ18O rhyolitic ignimbrites and lavas erupted during Miocene volcanic activity in the central Snake River Plain (14–6 Ma) have been inferred to be the result of large-scale partial or bulk melting of pre-existing hydrothermally altered lithologies of the Idaho batholith and Challis volcanic field. In this study, we assess the melting behaviour of heterogeneously altered source materials via partial melting experiments over a range of run times at conditions of 750–1000°C and 1–2 kbar, and apply our observations to current models for the petrogenesis of low-δ18O rhyolites along the Yellowstone hotspot track. Partial melt produced in the experiments inherits the bulk oxygen isotope composition from hydrothermally altered peraluminous source materials independent of the melt fraction, excluding the possibility for preferential, disequilibrium melting of 18O-depleted mineral phases during incipient melting. We propose a new model to explain the generation of low-δ18O rhyolites in the central Snake River Plain, whereby mantle-derived magmas assimilate ∼30–40% of crustal material that was hydrothermally altered at high temperatures in two stages: (1) a preceding episode of hydrothermal alteration during intrusion of Eocene plutons (‘pre-existing source’); (2) syn-magmatic hydrothermal alteration within a nested caldera complex. During assimilation, dilution of peraluminous crustal lithologies with mantle-derived magma maintains the metaluminous character of rhyolites erupted along the Yellowstone hotspot track. These results link previous models favouring melting of either pre-existing or syn-magmatically altered lithologies for the generation of low-δ18O rhyolites along the Yellowstone hotspot track and provide direct experimental observation of the chemical processes occurring during assimilation processes in magmatic environments.
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Brugman, Karalee K., and Christy B. Till. "A low-aluminum clinopyroxene-liquid geothermometer for high-silica magmatic systems." American Mineralogist 104, no. 7 (July 1, 2019): 996–1004. http://dx.doi.org/10.2138/am-2019-6842.
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Abstract Several geothermobarometric tools have focused on clinopyroxene due to its prevalence in igneous rocks, however clinopyroxene produced in high-silica igneous systems is high in iron and low in aluminum, causing existing geothermometers that depend on aluminum exchange to fail or yield overestimated temperatures. Here we present a new clinopyroxene-liquid geothermometer recommended for use in natural igneous systems with bulk SiO2 ≥ 70 wt%, which contain clinopyroxene with Mg# ≤ 65 and Al2O3 ≤ 7 wt%. (1) T ( ∘ C ) = 300 [ − 1.89 − 0.601 ( X CaTs Cpx ) − 0.186 ( X DiHd 2003 Cpx ) + 4.71 ( X SiO 2 liq ) + 77.6 ( X TiO 2 liq ) + 10.9 ( X FeO liq ) + 33.6 ( X MgO liq ) + 15.5 ( X CaO liq ) + 15.6 ( X KO 0.5 liq ) ] The new geothermometer lowers calculated temperatures by ~85 °C on average relative to Putirka (2008, Eq. 33) and reduces the uncertainty by a factor of two (standard error of estimate ±20 °C). When applied to natural systems, we find this new clinopyroxene-liquid geothermometer reconciles many inconsistencies between experimental phase equilibria and preexisting geothermometry results for silicic volcanism, including those from the Bishop Tuff and Yellowstone caldera-forming and post-caldera rhyolites. We also demonstrate that clinopyroxene is not restricted to near-liquidus temperatures in rhyolitic systems; clinopyroxene can be stable over a broad temperature range, often down to the solidus. An Excel spreadsheet and Python notebook for calculating temperature with this new geothermometer may be downloaded from GitHub at http://bit.ly/cpxrhyotherm.
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Pierosan, Ronaldo, Evandro F. Lima, Lauro V. S. Nardi, Cristina P. de Campos, Artur C. Bastos Neto, José M. T. M. Ferron, and Maurício Prado. "Paleoproterozoic (~1.88Ga) felsic volcanism of the Iricoumé Group in the Pitinga Mining District area, Amazonian Craton, Brazil: insights in ancient volcanic processes from field and petrologic data." Anais da Academia Brasileira de Ciências 83, no. 3 (September 2011): 921–37. http://dx.doi.org/10.1590/s0001-37652011000300012.
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The Iricoumé Group correspond to the most expressive Paleoproterozoic volcanism in the Guyana Shield, Amazonian craton. The volcanics are coeval with Mapuera granitoids, and belong to the Uatumã magmatism. They have U-Pb ages around 1880 Ma, and geochemical signatures of α-type magmas. Iricoumé volcanics consist of porphyritic trachyte to rhyolite, associated to crystal-rich ignimbrites and co-ignimbritic fall tuffs and surges. The amount and morphology of phenocrysts can be useful to distinguish lava (flow and dome) from hypabyssal units. The morphology of ignimbrite crystals allows the distinction between effusive units and ignimbrite, when pyroclasts are obliterated. Co-ignimbritic tuffs are massive, and some show stratifications that suggest deposition by current traction flow. Zircon and apatite saturation temperatures vary from 799°C to 980°C, are in agreement with most temperatures of α-type melts and can be interpreted as minimum liquidus temperature. The viscosities estimation for rhyolitic and trachytic compositions yield values close to experimentally determined melts, and show a typical exponential decay with water addition. The emplacement of Iricoumé volcanics and part of Mapuera granitoids was controlled by ring-faults in an intracratonic environment. A genesis related to the caldera complex setting can be assumed for the Iricoumé-Mapuera volcano-plutonic association in the Pitinga Mining District.
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Pulvirenti, Fabio, Francesca Silverii, and Maurizio Battaglia. "A New Analysis of Caldera Unrest through the Integration of Geophysical Data and FEM Modeling: The Long Valley Caldera Case Study." Remote Sensing 13, no. 20 (October 11, 2021): 4054. http://dx.doi.org/10.3390/rs13204054.
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The Long Valley Caldera, located at the eastern edge of the Sierra Nevada range in California, has been in a state of unrest since the late 1970s. Seismic, gravity and geodetic data strongly suggest that the source of unrest is an intrusion beneath the caldera resurgent dome. However, it is not clear yet if the main contribution to the deformation comes from pulses of ascending high-pressure hydrothermal fluids or low viscosity magmatic melts. To characterize the nature of the intrusion, we developed a 3D finite element model which includes topography and crust heterogeneities. We first performed joint numerical inversions of uplift and Electronic Distance Measurement baseline length change data, collected during the period 1985–1999, to infer the deformation-source size, position, and overpressure. Successively, we used this information to refine the source overpressure estimation, compute the gravity potential and infer the intrusion density from the inversion of deformation and gravity data collected in 1982–1998. The deformation source is located beneath the resurgent dome, at a depth of 7.5 ± 0.5 km and a volume change of 0.21 ± 0.04 km3. We assumed a rhyolite compressibility of 0.026 ± 0.0011 GPa−1 (volume fraction of water between 0% and 30%) and estimated a reservoir compressibility of 0.147 ± 0.037 GPa−1. We obtained a density of 1856 ± 72 kg/m3. This density is consistent with a rhyolite melt, with 20% to 30% of dissolved hydrothermal fluids.
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Macdonald, R., B. Bagiński, B. G. J. Upton, P. Dzierżanowski, W. Marshall-Roberts, and M. Prieto. "The Palaeogene Eskdalemuir dyke, Scotland: long-distance lateral transport of rhyolitic magma in a mixed-magma intrusion." Mineralogical Magazine 73, no. 2 (April 2009): 285–300. http://dx.doi.org/10.1180/minmag.2009.073.2.285.
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AbstractThe Palaeogene Eskdalemuir dyke, part of the Mull dyke swarm in the Southern Uplands of Scotland, is ~60 km long and up to 40 m thick. Its southern tip is 230 km from the inferred source on Mull. The dyke is composite, with tholeiitic basaltic margins and a vitreous central facies ranging from basaltic andesite to andesite in composition. Plagioclase and pyroxene phenocrysts and matrix crystals in the central facies show unusually large compositional ranges and complex textural relationships. Wholerock major and trace-element abundances show linear variations against MgO content, consistent with the rocks in the central facies having formed by mixing of basalt and rhyolite magmas. The rhyolite can be closely matched by rocks from the Mull centre. The mafic and silicic magmas were intruded from a compositionally zoned chamber beneath Mull, perhaps during collapse of the Centre 1 caldera. The lower-viscosity basaltic magma was emplaced before, but lubricated the lateral propagation of, the silicic magma, which mixed with the partially solidified basalt, the proportion of rhyolite increasing towards the dyke centre. The Eskdalemuir dyke represents an unusual, perhaps unique, example of a rhyolite magma being emplaced >200 km from its inferred source. The supposed correlative of the Eskdalemuir dyke north of the Southern Uplands Fault, the Dalraith-Linburn dyke, is not comagmatic with it.
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Hildreth, Wes, Judy Fierstein, and Andrew Calvert. "Early postcaldera rhyolite and structural resurgence at Long Valley Caldera, California." Journal of Volcanology and Geothermal Research 335 (April 2017): 1–34. http://dx.doi.org/10.1016/j.jvolgeores.2017.01.005.
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McConnell, V. S., C. K. Shearer, J. C. Eichelberger, M. J. Keskinen, P. W. Layer, and J. J. Papike. "Rhyolite intrusions in the intracaldera Bishop Tuff, Long Valley Caldera, California." Journal of Volcanology and Geothermal Research 67, no. 1-3 (August 1995): 41–60. http://dx.doi.org/10.1016/0377-0273(94)00099-3.
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Maguire, Ross, Brandon Schmandt, Jiaqi Li, Chengxin Jiang, Guoliang Li, Justin Wilgus, and Min Chen. "Magma accumulation at depths of prior rhyolite storage beneath Yellowstone Caldera." Science 378, no. 6623 (December 2, 2022): 1001–4. http://dx.doi.org/10.1126/science.ade0347.
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Seismic tomography has provided key insight into Yellowstone’s crustal magmatic system that includes attempts to understand the melt distribution in the subsurface and the current stage of the volcano’s life cycle. We present new tomographic images of the shear wave speed of the Yellowstone magmatic system based on full waveform inversion of ambient noise correlations, which illuminates shear wave speed reductions of greater than 30% associated with Yellowstone’s silicic magma reservoir. The slowest seismic wave speeds (shear wave speed less than 2.3 kilometers per second) are present at depths between 3 and 8 kilometers, overlapping with petrological estimates of the assembly depth of erupted rhyolite bodies. Assuming that Yellowstone’s magmatic system is a crystal mush with broadly distributed melt, we estimate a partial melt fraction of 16 to 20%.
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Lipman, Peter W. "Evolution of silicic magma in the upper crust: the mid-Tertiary Latir volcanic field and its cogenetic granitic batholith, northern New Mexico, U.S.A." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 79, no. 2-3 (1988): 265–88. http://dx.doi.org/10.1017/s0263593300014279.
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ABSTRACTStructural and topographic relief along the eastern margin of the Rio Grande rift, northern New Mexico, provides a remarkable cross-section through the 26-Ma Questa caldera and cogenetic volcanic and plutonic rocks of the Latir field. Exposed levels increase in depth from mid-Tertiary depositional surfaces in northern parts of the igneous complex to plutonic rocks originally at 3–5 km depths in the S. Erosional remnants of an ash-flow sheet of weakly peralkaline rhyolite (Amalia Tuff) and andesitic to dacitic precursor lavas, disrupted by rift-related faults, are preserved as far as 45 km beyond their sources at the Questa caldera. Broadly comagmatic 26 Ma batholithic granitic rocks, exposed over an area of 20 by 35 km, range from mesozonal granodiorite to epizonal porphyritic granite and aplite; shallower and more silicic phases are mostly within the caldera. Compositionally and texturally distinct granites define resurgent intrusions within the caldera and discontinuous ring dikes along its margins; a batholithic mass of granodiorite extends 20 km S of the caldera and locally grades vertically to granite below its flat-lying roof. A negative Bouguer gravity anomaly (15–20 mgal), which encloses exposed granitic rocks and coincides with boundaries of the Questa caldera, defines boundaries of the shallow batholith, emplaced low in the volcanic sequence and in underlying Precambrian rocks. Palaeomagnetic pole positions indicate that successively crystallised granitic plutons cooled through Curie temperatures during the time of caldera formation, initial regional extension, and rotational tilting of the volcanic rocks. Isotopic ages for most intrusions are indistinguishable from the volcanic rocks. These relations indicate that the batholithic complex broadly represents the source magma for the volcanic rocks, into which the Questa caldera collapsed, and that the magma was largely liquid during regional tectonic disruption.Volcanic and plutonic magmas (1) changed from early high-K calc-alkaline to alkalic prior to caldera eruptions; (2) differentiated to a weakly peralkaline rhyolite and equivalent acmiteartvedsonite granite cap (underlain by calc-alkaline granite) when the caldera formed at 26·5 Ma; then (3) reverted to calc-alkaline compositions. Concentrations of alkalis and minor elements such as Rb, Th, U, Nb, Zr, and Y reached maxima at the caldera stage. The volcanic rocks constitute intermittently quenched samples of upper parts of Questa magma bodies at early stages of crystallisation; in contrast, the comagmatic granitic rocks preserve an integrated record of protracted crystallisation of the magmatic residue as eruptions diminished. Multiple differentiation processes were active during evolution of the Questa magmatic system: crystal fractionation, replenishment by mantle and lower crustal melts of varying chemical and isotopic character, mixing of evolved with more primitive magmas, upper crustal assimilation, and perhaps volatile-transfer processes. As a result, an evolving batholithic cluster of coalesced magma chambers generated diverse assemblages of broadly cogenetic rocks within a few million years. Evolution of the Questa magmatic system and similar high-level Tertiary granitic batholiths nearby in the southern Rocky Mountains provides broad insights into magmatic processes in continental regions such as the overall shapes of batholiths, time and compositional relations between cogenetic volcanic and plutonic rocks, density equilibration of magmas with country rocks, and thermal evolution of continental crust.
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Colman, T. B., and A. K. Appleby. "Volcanogenic quartz-magnetite-hematite veins, Snowdon, North Wales." Mineralogical Magazine 55, no. 379 (June 1991): 257–62. http://dx.doi.org/10.1180/minmag.1991.055.379.14.
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AbstractIn the Ordovician Snowdon Volcanic Group caldera quartz-magnetite-hematite-pyrite assemblages occur in a breccia vein in rhyolitic tuff and vein swarms in basalt. The veins developed pre-cleavage. Elevated levels of tin and tungsten in the veins, and of fluorine in the wall rocks, suggest a magmatic contribution to the mineralising fluids. The chemistry of the veins differs from that of the base-metal sulphide veins found elsewhere in the caldera.
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King, Georgina E., Nicholas J. G. Pearce, Helen M. Roberts, Victoria C. Smith, John A. Westgate, David R. Gaylord, and Mark R. Sweeney. "Identification of a Kulshan caldera correlative tephra in the Palouse loess of Washington State, northwest USA." Quaternary Research 86, no. 2 (September 2016): 232–41. http://dx.doi.org/10.1016/j.yqres.2016.06.004.
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AbstractThe Kulshan caldera formed at ∼1.15 Ma on the present-day site of Mt. Baker, Washington State, northwest USA and erupted a compositionally zoned (dacite-rhyolite) magma and a correlative eruptive, the Lake Tapps tephra. This tephra has previously been described, but only from the Puget Lowland of NW Washington. Here an occurrence of a Kulshan caldera correlative tephra is described from the Quaternary Palouse loess at the Washtucna site (WA-3). Site WA-3 is located in east-central Washington, ∼340 km southeast of the Kulshan caldera and ∼300 km east-southeast of the Lake Tapps occurrence in the Puget Lowland. Major- and trace element chemistry and location of the deposit at Washtucna within reversed polarity sediments indicates that it is not correlative with the Mesa Falls, Rockland, Bishop Ash, Lava Creek B or Huckleberry Ridge tephras. Instead the Washtucna deposit is related to the Lake Tapps tephra by fractional crystallisation, but is chemically distinct, a consequence of its eruption from a compositionally zoned magma chamber. The correlation of the Washtucna occurrence to the Kulshan caldera-forming eruption indicates that it had an eruptive volume exceeding 100 km3, and that its tephra could provide a valuable early-Pleistocene chronostratigraphic marker in the Pacific Northwest.
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Lowell, G. R., and P. D. Noll. "Fe-Cu-Au-bearing scapolite skarn in moat sediments of the Taum Sauk Caldera, southeastern Missouri, USA." Mineralogical Magazine 65, no. 3 (June 2001): 373–96. http://dx.doi.org/10.1180/002646101300119466.
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AbstractStromatolitic carbonate in moat-fill of a 1.48 Ga caldera was converted to mineralized calc-silicate skarn by interaction with magma-derived brine at Ketcherside Gap in southeastern Missouri. The skarnrecords early low fO2 conditions similar to those of reduced W and Au skarns. Initial skarn-forming conditions were: PL ≤ 221 bar (22.1 MPa), XCO2 ≤ 0.10, T = 450–;400°C, log fO2 ≈ –30, and log fS2 ≤ –13. Late skarn records combined effects of T↓, fO2↑,fS2↑, XCO2↓, and appearance of an immiscible CO2-rich vapour. The absence of a contact aureole indicates that skarn reactions were driven by advective heat transfer from an infiltrating fluid. Elsewhere in the region, hypersaline, synvolcanic fluids produced oxidized endoskarn in rhyolite. Development of carbonate-hosted, reduced skarn in caldera moat sediments is attributed to: (1) the nature of the host rock and reaction along a lengthy flow path; (2) early, but temporary, dilution of brine influx by CO2-producing reactions; and (3) cooling, possibly accompanied by increased brine influx with time.
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Wannamaker, P. E., P. M. Wright, Zhou Zi‐xing, Li Xing‐bin, and Zhao Jing‐xiang. "Magnetotelluric transect of Long Valley caldera: Resistivity cross‐section, structural implications, and the limits of a 2-D analysis." GEOPHYSICS 56, no. 7 (July 1991): 926–40. http://dx.doi.org/10.1190/1.1443126.
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Twenty‐four magnetotelluric (MT) soundings have been collected in an east‐west profile across the center of Long Valley caldera. The average station spacing is approximately 1 km and appears adequate to sample the important features of the upper crustal and deeper resistivity structures. Additional control on the shallowest resistivity is provided by a continuous profile of time domain electromagnetic soundings coincident with the western portion of the MT line. Our MT data set reveals numerous resistivity structures which illuminate the evolution and present state of the Long Valley system. Many of these have been quantified through two‐dimensional (2-D) finite element modeling emphasizing the transverse magnetic (TM) mode. Important structural components include low‐resistivity layers 0.5–1.5 km deep under the eastern half of the caldera, beneath the axial graben of the resurgent dome, and under the west caldera moat. Most of this layering appears to lie in post‐caldera Early Rhyolite tuffs, and the uppermost unwelded Bishop Tuff. These rhyolite units have been observed to be porous and highly altered and to commonly contain Pleistocene intercalated lacustrine clays. The remainder and majority of the Bishop Tuff appears highly resistive. A low resistivity layer also occurs below the axial graben near the base of the Bishop Tuff (1.5 km). Hydrothermal fluids or alteration in precaldera volcanic strata or, less likely, carbonaceous metasediments may be the cause of this. Resistive, probably crystalline basement at high levels is apparent beneath the center of resurgence. Low resistivities are modeled at a depth around 5 km below the entire west moat and central graben and may represent a zone of hydrothermal fluids released from magma crystallization, with potential magmatic contributions at greater depths. The correspondence between this low resistivity and teleseismic delay and low density zones found in other studies is quite striking. A subtle anomaly in the transverse electric (TE) mode impedance is weakly suggestive of a midcrustal conductive axis centered beneath the central graben and resurgent dome. However, it cannot be simulated by two‐dimensional transverse electric calculations and requires a full three‐dimensional evaluation to ensure that the anomaly does not represent resistivity complexity in just the upper few kilometers. A fundamental, caldera‐wide 3-D effect is documented by comparison of observed and computed TE impedance and vertical magnetic field data. The abrupt termination of conductive caldera sediments less than 10 km north and south of our profile greatly depresses the observed TE apparent resistivity and vertical magnetic field relative to the model calculations for periods greater than 0.3 s for the central and eastern caldera. Analysis of the TE mode data also suggests that a similar finite‐strike effect lies in the response at periods greater than 3 s due to the mid‐crustal west moat conductor. The TM mode measurements are judged to also contain some large‐scale departure from the 2-D assumption related to horizontal current gathering from the north and south. This inflates the apparent resistivity and decreases the phase somewhat around 10 s over the central portion of the caldera relative to the 2-D model response. The regional profile of resistivity for the data at hand can be modeled with a 40 ohm‐m basal half‐space beneath 30 km of crust of 1000 ohm‐m or more. Although stations outside the caldera are very desirable to constrain this deep profile better, there is no evidence for a discrete low‐resistivity layer deep below Long Valley in contrast to our interpretation in the northeastern Basin and Range.
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Mangan, Margaret T., Christopher F. Waythomas, Thomas P. Miller, and Frank A. Trusdell. "Emmons Lake Volcanic Center, Alaska Peninsula: source of the Late Wisconsin Dawson tephra, Yukon Territory, Canada." Canadian Journal of Earth Sciences 40, no. 7 (July 1, 2003): 925–36. http://dx.doi.org/10.1139/e03-026.
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The Emmons Lake Volcanic Center on the Alaska Peninsula of southwestern Alaska is the site of at least two rhyolitic caldera-forming eruptions (C1 and C2) of late Quaternary age that are possibly the largest of the numerous caldera-forming eruptions known in the Aleutian arc. The deposits produced by these eruptions are widespread (eruptive volumes of >50 km3 each), and their association with Quaternary glacial and eolian deposits on the Alaska Peninsula and elsewhere in Alaska and northwestern Canada enhances the likelihood of establishing geochronological control on Quaternary stratigraphic records in this region. The pyroclastic deposits associated with the second caldera-forming eruption (C2) consist of loose, granular, airfall and pumice-flow deposits that extend for tens of kilometres beyond Emmons Lake caldera, reaching both the Bering Sea and Pacific Ocean coastlines north and south of the caldera. Geochronological and compositional data on C2 deposits indicate a correlation with the Dawson tephra, a 24 000 14C BP (27 000 calibrated years BP), widespread bed of silicic ash found in loess deposits in west-central Yukon Territory, Canada. The correlation clearly establishes the Dawson tephra as the time-stratigraphic marker of the last glacial maximum.
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Bindeman, Ilya N., and John W. Valley. "Formation of low-δ18O rhyolites after caldera collapse at Yellowstone, Wyoming, USA." Geology 28, no. 8 (August 2000): 719–22. http://dx.doi.org/10.1130/0091-7613(2000)028<0719:folora>2.3.co;2.
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Bindeman, Ilya N., and John W. Valley. "Formation of low-δ18O rhyolites after caldera collapse at Yellowstone, Wyoming, USA." Geology 28, no. 8 (2000): 719. http://dx.doi.org/10.1130/0091-7613(2000)28<719:folrac>2.0.co;2.
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NICOLL, GRAEME R., MARIAN B. HOLNESS, VALENTIN R. TROLL, COLIN H. DONALDSON, EOGHAN P. HOLOHAN, C. HENRY EMELEUS, and DAVID CHEW. "Early mafic magmatism and crustal anatexis on the Isle of Rum: evidence from the Am Màm intrusion breccia." Geological Magazine 146, no. 3 (March 25, 2009): 368–81. http://dx.doi.org/10.1017/s0016756808005864.
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AbstractThe Rum Igneous Centre comprises two early marginal felsic complexes (the Northern Marginal Zone and the Southern Mountains Zone), along with the later central ultrabasic–basic layered intrusions. These marginal complexes represent the remnants of near-surface to eruptive felsic magmatism associated with caldera collapse, examples of which are rare in the North Atlantic Igneous Province. Rock units include intra-caldera collapse breccias, rhyolitic ignimbrite deposits and shallow-level felsic intrusions, as well the enigmatic ‘Am Màm intrusion breccia’. The latter comprises a dacitic matrix enclosing lobate basaltic inclusions (~1–15 cm) and a variety of clasts, ranging from millimetres to tens of metres in diameter. These clasts comprise Lewisian gneiss, Torridonian sandstone and coarse gabbro. Detailed re-mapping of the Am Màm intrusion breccia has shown its timing of emplacement as syn-caldera, rather than pre-caldera as previously thought. Textural analysis of entrained clasts and adjacent, uplifted country rocks has revealed their thermal metamorphism by early mafic intrusions at greater depth than their present structural position. These findings provide a window into the evolution of the early mafic magmas responsible for driving felsic magmatism on Rum. Our data help constrain some of the physical parameters of this early magma–crust interaction and place it within the geochemical evolution of the Rum Centre.
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Furukawa, Kuniyuki, and Hiroki Kamata. "Internal structures of the Takanoobane Rhyolite Lava in the western part of Aso caldera, Japan." Journal of the Geological Society of Japan 111, no. 10 (2005): 590–98. http://dx.doi.org/10.5575/geosoc.111.590.
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Watts, Kathryn E., Ilya N. Bindeman, and Axel K. Schmitt. "Large-volume Rhyolite Genesis in Caldera Complexes of the Snake River Plain: Insights from the Kilgore Tuff of the Heise Volcanic Field, Idaho, with Comparison to Yellowstone and Bruneau–Jarbidge Rhyolites." Journal of Petrology 52, no. 5 (April 8, 2011): 857–90. http://dx.doi.org/10.1093/petrology/egr005.
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Spell, Terry L., and T. Mark Harrison. "40Ar/39Ar Geochronology of Post-Valles Caldera Rhyolites, Jemez Volcanic Field, New Mexico." Journal of Geophysical Research: Solid Earth 98, B5 (May 10, 1993): 8031–51. http://dx.doi.org/10.1029/92jb01786.
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Simakin, A. G., and I. N. Bindeman. "Remelting in caldera and rift environments and the genesis of hot, “recycled” rhyolites." Earth and Planetary Science Letters 337-338 (July 2012): 224–35. http://dx.doi.org/10.1016/j.epsl.2012.04.011.
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Swallow, Elliot J., Colin J. N. Wilson, Bruce L. A. Charlier, and John A. Gamble. "The Huckleberry Ridge Tuff, Yellowstone: evacuation of multiple magmatic systems in a complex episodic eruption." Journal of Petrology 60, no. 7 (June 28, 2019): 1371–426. http://dx.doi.org/10.1093/petrology/egz034.
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Abstract The 2·08 Ma, ∼2500 km3 Huckleberry Ridge Tuff (HRT) eruption, Yellowstone, generated two fall deposits and three ignimbrite members (A, B, C), accompanying a ∼95 x 65 km caldera collapse. Field data imply that the pre-A fall deposits took weeks to be erupted, then breaks of weeks to months occurred between members A and B, and years to decades between B and C. We present compositional and isotopic data from single silicic clasts (pumice or fiamme) in the three ignimbrite members, plus new data from co-eruptive mafic components to reconstruct the nature and evacuation history of the HRT crustal magmatic complex. Geochemical data, building on field characteristics, are used to group nine silicic clast types into seven compositional suites (A1-A3; B1; C1-C3) within their respective members A, B and C. Isotopic data are then added to define four magmatic systems that were tapped simultaneously and/or sequentially during the eruption. Systems 1 and 2 fed the initial fall deposits and then vented throughout member A, accompanied by trace amounts of mafic magma. In member A, volumetrically dominant system 1 is represented by a rhyolite suite (A1: 73·0–77·7 wt % SiO2, 450–1680 ppm Ba) plus a distinct low-silica rhyolite suite (A2: 69·2–71·6 wt % SiO2, >2500 ppm Ba). System 2 yielded only a low-Ba, high-silica rhyolite suite (A3: 76·7–77·4 wt % SiO2, ≤250 ppm Ba). Glass compositions in pumices from systems 1 and 2 show clustering, indicative of the same multiple melt-dominant bodies identified in the initial fall deposits and earliest ignimbrite. Member B samples define suite B1 (70·7–77·4 wt % SiO2, 540–3040 ppm Ba) derived from magmatic system 1 (but not 2) that had undergone mixing and reorganisation during the A: B time break, accompanying mafic magma inputs. Mafic scoriae erupted in upper member B cover similar compositions to the member A clasts, but extend over a much broader compositional range. Member C clast compositions reflect major changes during the B: C time break, including rejuvenation of magmatic system 2 (last seen in member A) as suite C3 (75·3–77·2 wt % SiO2, 100–410 ppm Ba), plus the appearance of two new suites with strong crustal signatures. Suite C2 is another rhyolite (74·7–77·6 wt % SiO2, with Ba decreasing with silica from 2840 to 470 ppm) that defines magmatic system 3. Suite C2 also shows clustered glass compositions, suggesting that multiple melt-dominant bodies were a repetitive feature of the HRT magmatic complex. Suite C1, in contrast, is dacite to rhyolite (65·6–75·0 wt % SiO2, with Ba increasing with silica from 750 to 1710 ppm) that defines magmatic system 4. Compositions from magmatic systems 1 and 2 dominantly reflect fractional crystallization, but include partial melting of cumulates related to earlier intrusions of the same mafic magmas as those syn-eruptively vented. Country rock assimilation was limited to minor amounts of a more radiogenic (with respect to Sr) evolved contaminant. In contrast, systems 3 and 4 show similar strongly crustal isotopic compositions (despite their differences in elemental composition) consistent with assimilation of Archean rocks via partial melts derived from cumulates associated with contrasting mafic lineages. System 3 links to the same HRT mafic compositions co-erupted in members A and B. In contrast, system 4 links to olivine tholeiite compositions erupted in the Yellowstone area before, sparsely during, and following the HRT itself. All four magmatic systems were housed beneath the HRT caldera area. Systems 1 and 2 were hosted in Archean crust that had been modified by Cretaceous/Eocene magmatism, whereas systems 3 and 4 were hosted within crust that retained Archean isotopic characteristics. The extreme compositional diversity in the HRT highlights the spatial and temporal complexities that can be associated with large-volume silicic magmatism.
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Breitkreuz, Christoph, Alexandra Käßner, Marion Tichomirowa, Manuel Lapp, Shan Huang, and Klaus Stanek. "The Late Carboniferous deeply eroded Tharandt Forest caldera–Niederbobritzsch granite complex: a post-Variscan long-lived magmatic system in central Europe." International Journal of Earth Sciences 110, no. 4 (April 8, 2021): 1265–92. http://dx.doi.org/10.1007/s00531-021-02015-x.
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AbstractSamples and documentation of outcrops and drillings, facies analysis, whole rock geochemistry and radiometric ages have been employed to re-evaluate the Late Carboniferous Tharandt Forest caldera (TFC) and the co-genetic Niederbobritzsch granite (NBG) in the eastern Erzgebirge near Dresden, Germany. The c. 52 km2 TFC harbours strongly welded ignimbrites with a preserved minimum thickness of 550 m. Composition of initial fallout tephra at the base of the TFC fill, comprising lithics of rhyolitic and basic lava, and of silica-rich pyroclastic rocks, suggests a bimodal volcanic activity in the area prior to the climactic TFC eruption. The lower part of the TFC fill comprises quartz-poor ignimbrites, overlain by quartz-rich ignimbrites, apparently without a depositional break. Landslides originating from the collapse collar of the caldera plunged into the still hot TFC fill producing monolithic gneiss mesobreccia with clasts ≤ 1 m in a pyroclastic matrix. Aphanitic and porphyritic rhyolitic magma formed ring- and radial dykes, and subvolcanic bodies in the centre of TFC. Whole rock geochemical data indicate a high silica (most samples have > 73 wt% SiO2) rhyolitic composition of the TFC magma, and a similar granodiorite–granitic composition for the NBG. Based on drillings and caldera extent, a minimum volume of 22 km3 of TFC fill is preserved, the original fill is assumed at about 33 km3. This estimate translates into a denudation of at least c. 210 m during Late Paleozoic to pre-Cenomanian. Telescopic subsidence of the TFC took place in two, perhaps three stages. A possible TFC outflow facies has been completely eroded and distal TFC tuff has not been recognized in neighboring basins. New CA-ID-TIMS measurements on two TFC samples gave mean zircon ages of 313.4 ± 0.4 Ma and 311.9 ± 0.4 Ma; two samples from NBG resulted in 318.2 ± 0.5 Ma and 319.5 ± 0.4 Ma. In addition, for one sample of the ring dyke an age of ca. 314.5 ± 0.5 Ma has been obtained. These ages, together with field relations, allow for a model of a long-standing evolution of an upper crustal magmatic system (~ 5 Ma?), where pulses of magmatic injection and crustal doming alternate with magmatic quietness and erosion. Together with the Altenberg–Teplice Volcanic Complex, located some 10 km to the southeast, the TFC–NBG Complex represents an early post-Variscan magmatic activity in central Europe.
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Till, Christy B., Jorge A. Vazquez, Mark E. Stelten, Hannah I. Shamloo, and Jamie S. Shaffer. "Coexisting Discrete Bodies of Rhyolite and Punctuated Volcanism Characterize Yellowstone's Post‐Lava Creek Tuff Caldera Evolution." Geochemistry, Geophysics, Geosystems 20, no. 8 (August 2019): 3861–81. http://dx.doi.org/10.1029/2019gc008321.
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Mothes, Patricia A., and Minard L. Hall. "Rhyolitic calderas and centers clustered within the active andesitic belt of Ecuador's Eastern Cordillera." IOP Conference Series: Earth and Environmental Science 3 (October 1, 2008): 012007. http://dx.doi.org/10.1088/1755-1307/3/1/012007.
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Vazquez, Jorge A., Noel O. Velasco, Axel K. Schmitt, Heather A. Bleick, and Mark E. Stelten. "238 U– 230 Th dating of chevkinite in high-silica rhyolites from La Primavera and Yellowstone calderas." Chemical Geology 390 (December 2014): 109–18. http://dx.doi.org/10.1016/j.chemgeo.2014.10.020.
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Novak, Steven W., and Gail A. Mahood. "Rise and fall of a basalt-trachyte-rhyolite magma system at the Kane Springs Wash Caldera, Nevada." Contributions to Mineralogy and Petrology 94, no. 3 (November 1986): 352–73. http://dx.doi.org/10.1007/bf00371444.
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Rooyakkers, Shane M., John Stix, Kim Berlo, and Simon J. Barker. "Emplacement of unusual rhyolitic to basaltic ignimbrites during collapse of a basalt-dominated caldera: The Halarauður eruption, Krafla (Iceland)." GSA Bulletin 132, no. 9-10 (January 13, 2020): 1881–902. http://dx.doi.org/10.1130/b35450.1.
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Abstract Deposits of the ca. 110 ka Halarauður eruption of Krafla caldera (reconstructed volume = 7 ± 6 km3 dense rock equivalent) include the only spatter-rich ignimbrite known in Iceland, and an exceptionally rare lava-like basaltic ignimbrite. We present a revised stratigraphy and new whole-rock major-element data set for products of this unusual event, one of only three Quaternary ignimbrite eruptions identified in Iceland. Compositions of Halarauður products span a broad range (50.0–74.6 wt% SiO2), reflecting mixing of rhyolite with underplating basalt. Small-volume, valley-ponded, basal pumice- and spatter-bearing lithic breccias and ignimbrite (rhyolite to andesite) reflect rapid column collapse during early opening of ring-fault vents. A transition to voluminous, regionally dispersed spatter agglomerates (dacite to basaltic andesite) marks an abrupt eruptive intensification, as gas-poor magma was squeezed into a developing ring-fault system by the subsiding chamber roof. Spatial heterogeneities in ascent rates and outgassing through this variably dilated fault system caused coeval formation of collapsing plumes and spatter fountains at separate vents. Spatter was entrained into flows from the more explosive vents, which deposited proximal spatter agglomerates and more distal spatter-bearing ignimbrite. Overlying lava-like ignimbrite deposits (basaltic andesite to basalt) reflect a final opening of vents, as mafic magma from deep levels of the chamber was squeezed through a dilated ring-fault system by the subsiding roof block and erupted at uncharacteristically high mass flux. Development of a mature ring-fault conduit system during early tapping of silicic magma appears to be a prerequisite for the emplacement of welded basaltic ignimbrites, and it should be considered as a possible eruption scenario in basalt-dominated systems where silicic magma has been known to also accumulate. Poor preservation of the Halarauður deposits exemplifies the challenges of studying ignimbrite eruptions in frequently glaciated regions like Iceland, where they may be more common than the geological record suggests.
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Suhendro, Indranova, Bachtiar W. Mutaqin, Dyan Primana Sobaruddin, Lestari Agustiningtyas, Hanik Humaida, Muh Aris Marfai, and Danang Sri Hadmoko. "Dynamics of Two Caldera-Forming Eruptions (Banda Besar and Naira) in the Marine Conservation Zone of Banda, Maluku, Indonesia." Geosciences 12, no. 11 (November 21, 2022): 428. http://dx.doi.org/10.3390/geosciences12110428.
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This is the first study discussing the dynamics of two caldera-forming eruptions in the Banda volcanic complex (BVC) in the marine conservation zone of Banda, Maluku, Indonesia. The first and second caldera episodes are, hereafter, termed as Banda Besar and Naira, respectively. The formation of Banda Besar caldera (ca. 8 × 7 km) ejected homogeneous rhyolitic magmas (bulk-rock, 73.1–73.8 wt.% SiO2) in the following three stages: (1) sub-Plinian (BB-5a), (2) intra-sub-Plinian flow (BB-5b), and (3) caldera collapse (BB-5c and BB-5d). The BB-5a stage produced a reversely graded white pumice fall layer with moderate lithics (2–11%), which originated from a sub-Plinian eruption with an estimated plume height of 22–23 km. Subsequently, intensive erosion of wall rock (13–25%) causes conduit enlargement, leading to the partial collapse of the eruption columns, forming intra-sub-Plinian flow deposits (BB-5b). It is likely that conduit size surpassed the minimum threshold value for a buoyant plume during the final phase of the second stage, causing the complete formation of a pumice-rich pyroclastic density current (PDC) during the early-third stage (BB-5c). Finally, the evacuation of voluminous magma from the reservoir yields the first caldera collapse during the late-third stage, producing a lithic-dominated PDC with minor pumices (BB-5d). The formation of the Naira caldera (ca. 3 × 3 km) ejected homogeneous dacitic magmas (bulk-rock, 66.2–67.2 wt.% SiO2) in the following three stages: (1) early sub-Plinian (N-2a and 2b), (2) late sub-Plinian (N-2c, 2d, 2e), and (3) caldera collapse (N-2f). This research distinguishes the sub-Plinian into two stages on the basis of different vent locations (assumed from the isopach map). In particular, this research suggests that the early sub-Plinian stage (N-2a and 2b) erupted from the northern vent, producing 14 and 8 km eruption plume heights, respectively. Additionally, the late sub-Plinian stage (N-2c, 2d, 2e) was generated from a newly-formed conduit located in the relatively southern position, producing 12–17, 9, and 6 km eruption plume heights, respectively. Conduit enlargement is expected to occur during at both sub-Plinian stages, as lithic portions are considerably high (10–72%) and ultimately generate PDCs during the third stage (caldera collapse; N-2f). Because most of the erupted materials (for both caldera-forming eruptions) are emplaced in the ocean, estimating the erupted volume becomes difficult. However, with the assumption that the caldera dimension represents the erupted volume of magma (Vmagma), and that the total erupted volume (Vtotal) is a summation of Vmagma and the now-vanished pre-caldera island (Vvanished, represented by average lithic fractions), the first and second caldera might produce (at least) 35.2 and 2.4 km3 of erupted materials, scaling them as VEI (volcano explosivity index) 6 and 5, respectively. That VEI is more than enough to initiate a secondary hazard in the form of tsunamis triggered by volcanic activities.
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Myers, Madison L., Paul J. Wallace, Colin J. N. Wilson, James M. Watkins, and Yang Liu. "Ascent rates of rhyolitic magma at the onset of three caldera-forming eruptions." American Mineralogist 103, no. 6 (June 1, 2018): 952–65. http://dx.doi.org/10.2138/am-2018-6225.
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Shane, Phil. "Contrasting plagioclase textures and geochemistry in response to magma dynamics in an intra-caldera rhyolite system, Okataina volcano." Journal of Volcanology and Geothermal Research 297 (May 2015): 1–10. http://dx.doi.org/10.1016/j.jvolgeores.2015.03.013.
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Spell, Terry L., Ian McDougall, and Anthony P. Doulgeris. "Cerro Toledo Rhyolite, Jemez Volcanic Field, New Mexico: 40Ar/39Ar geochronology of eruptions between two caldera-forming events." Geological Society of America Bulletin 108, no. 12 (December 1996): 1549–66. http://dx.doi.org/10.1130/0016-7606(1996)108<1549:ctrjvf>2.3.co;2.
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Fiske, Richard S., Jiro Naka, Kokichi Iizasa, Makoto Yuasa, and Adam Klaus. "Submarine silicic caldera at the front of the Izu-Bonin arc, Japan: Voluminous seafloor eruptions of rhyolite pumice." Geological Society of America Bulletin 113, no. 7 (July 2001): 813–24. http://dx.doi.org/10.1130/0016-7606(2001)113<0813:sscatf>2.0.co;2.
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Eichelberger, John, Alexey Kiryukhin, Silvio Mollo, Noriyoshi Tsuchiya, and Marlène Villeneuve. "Exploring and Modeling the Magma–Hydrothermal Regime." Geosciences 10, no. 6 (June 18, 2020): 234. http://dx.doi.org/10.3390/geosciences10060234.
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This special issue comprises 12 papers from authors in 10 countries with new insights on the close coupling between magma as an energy and fluid source with hydrothermal systems as a primary control of magmatic behavior. Data and interpretation are provided on the rise of magma through a hydrothermal system, the relative timing of magmatic and hydrothermal events, the temporal evolution of supercritical aqueous fluids associated with ore formation, the magmatic and meteoric contributions of water to the systems, the big picture for the highly active Krafla Caldera, Iceland, as well as the implications of results from drilling at Krafla concerning the magma–hydrothermal boundary. Some of the more provocative concepts are that magma can intrude a hydrothermal system silently, that coplanar and coeval seismic events signal “magma fracking” beneath active volcanoes, that intrusive accumulations may far outlast volcanism, that arid climate favors formation of large magma chambers, and that even relatively dry rhyolite magma can convect rapidly and so lack a crystallizing mush roof. A shared theme is that hydrothermal and magmatic reservoirs need to be treated as a single system.
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Fuentes-Guzmán, Edith, Antoni Camprubí, Janet Gabites, Eduardo González-Partida, and Vanessa Colás. "The Pliocene Xoconostle high sulfidation epithermal deposit in the Trans-Mexican Volcanic Belt: Preliminary study." Boletín de la Sociedad Geológica Mexicana 72, no. 3 (November 28, 2020): A260520. http://dx.doi.org/10.18268/bsgm2020v72n3a260520.
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The Xoconostle prospect in northeastern Michoacán state, south-central Mexico, is constituted by high sulfidation epithermal breccias and stockworks with Au and Hg prospective anomalies. The mineralization is hosted by latest Miocene to Pliocene rocks grouped into the El Terrero ignimbrite and the Siete Cruces dome complex and a stock of intermediate composition and undetermined (Pliocene?) age. Two alunite samples from deep hypogene advanced argillic alteration assemblages within the deposit yielded 40Ar/39Ar ages at 5.57 ± 0.44 (Messinian) and 3.67 ± 0.20 Ma (Zanclean). Such ages are in good agreement with those of volcanic rocks at a semi-regional scale, especially those associated with the nearby Amealco caldera. Assuming that the formation of Xoconostle deposit could be genetically related to any of the eruptive units in this caldera, it would be associated with dacitic-andesitic rocks at ~4.7 Ma or with bimodal andesite-basalt volcanism at ~3.7 Ma, with which rhyolites at the southwest rim of the caldera (nearer to the epithermal deposit) are contemporaneous. The obtained ages are also in good agreement with those determined for the youngest stages in the evolution of the Trans-Mexican Volcanic Belt (TMVB). In addition, such ages compare well with those established for the E-W striking Morelia-Acambay normal fault zone (or Acambay graben). The occurrence of E-W structural features in the study area support their correlation with those in the Acambay graben. Although the metallogenesis of the TMVB needs further endeavours that contribute to its understanding, the Xoconostle prospect adds up to other dated magmatic-hydrothermal deposits that may collectively constitute a Pliocene metallogenic province whose inception was geologically circumscribed to this volcanic arc. However, this and its companion papers in this issue confirm the metallogenic potential of the TMVB in most of its stages of evolution, particularly in the late Miocene-Pliocene stage of acid and bimodal volcanism.