Log in

Relevant bibliographies by topics / Formation de caldeira / Journal articles

To see the other types of publications on this topic, follow the link: Formation de caldeira.

Journal articles on the topic 'Formation de caldeira'

Author: Grafiati

Published: 4 June 2021

Last updated: 8 February 2022

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles

Select a source type:

Consult the top 50 journal articles for your research on the topic 'Formation de caldeira.'

Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.

You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.

Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.

1

Madeira, José, A. M. Monge Soares, António Brum Da Silveira, and António Serralheiro. "Radiocarbon Dating Recent Volcanic Activity on Faial Island (Azores)." Radiocarbon 37, no. 2 (1995): 139–47. http://dx.doi.org/10.1017/s0033822200030575.

Full text

Abstract:

Recent fieldwork on the island of Faial (Azores) led to the establishment of a detailed volcanic stratigraphic sequence, which is composed of five main geological formations. One of them, the Caldeira Formation, comprising mainly pumice fall and flow deposits, was judged to be Holocene in age. Organic materials were found preserved in or below some of the pyroclastic deposits from this formation. Wood, charcoal, peat and soil samples were radiocarbon dated, permitting correlation of deposits from different sequences and the establishment of a chronological framework for the Caldeira volcanic activity. These materials yielded ages from ca. 10–1 ka bp. The average dormant interval in the Caldeira pyroclastic activity from 4–1 ka ago is ca. 400 yr, with eruptions approximately every 200–800 yr. This frequency of activity indicates that the Caldeira volcano is an active, dangerous structure that should be closely monitored.

APA, Harvard, Vancouver, ISO, and other styles

2

Ivlev, Boris I. "On formation of long-living states." Canadian Journal of Physics 94, no. 12 (December 2016): 1253–58. http://dx.doi.org/10.1139/cjp-2016-0227.

Full text

Abstract:

The motion of a particle in a potential well is studied when the particle is attached to an infinite elastic string. This is generic with the problem of dissipative quantum mechanics investigated by Caldeira and Leggett (Ann. Phys. 149, 374 (1983). doi: 10.1016/0003-4916(83)90202-6 ). Besides the dissipative motion there is another scenario of interaction of the string with the particle attached. Stationary particle–string states exist with string deformations accompanying the particle. This is like polaronic states in solids. Our polaronic states in the well are non-decaying and have a continuous energy spectrum. These states may have a link to quantum electrodynamics.

APA, Harvard, Vancouver, ISO, and other styles

3

Legendre*, Christelle, René C. Maury, Hervé Guillou, Joseph Cotten, Martial Caroff, Sylvain Blais, and Gérard Guille. "Geological and petrologic evolution of Huahine island (Society archipelago, French Polynesia) : an unusual intraoceanic shield volcano." Bulletin de la Société Géologique de France 174, no. 2 (March 1, 2003): 115–24. http://dx.doi.org/10.2113/174.2.115.

Full text

Abstract:

Abstract Huahine (Leeward Islands, Society Archipelago) is composed of two islands, Huahine Nui and Huahine Iti, separated by the shallow Port Bourayne and Maroe bays and surrounded by a common lagoon. The two islands, however, belong to a single basaltic and trachybasaltic shield volcano, the emerged part of which was constructed during a very short period, between 2.65 and 2.52 Ma. The volcano is made of composite basaltic flows belonging to three distinct petrogenetic types, which derive from low degrees of partial melting of heterogeneous mantle sources. This building stage lead to the formation of a central caldeira. Then, a WSW-ENE trending graben formed separating Huahine Nui from Huahine Iti. As a consequence, Huahine differs from most of the other Polynesian islands which display large collapse structures opened toward the sea. After a period of inactivity of at least 0.25 m.y., magmatic activity resumed, leading to the emplacement of five trachyphonolitic intrusions along N-S trending deep regional fractures. These lavas, which do not result from the fractional crystallization of the shield basalts, are considered as derived from the melting of a deep intrusive network of dykes.

APA, Harvard, Vancouver, ISO, and other styles

4

Jeffery, A. J., R. Gertisser, R. A. Jackson, B. O'Driscoll, and A. Kronz. "On the compositional variability of dalyite, K2ZrSi6O15: a new occurrence from Terceira, Azores." Mineralogical Magazine 80, no. 4 (June 2016): 547–65. http://dx.doi.org/10.1180/minmag.2016.080.018.

Full text

Abstract:

AbstractThe rare potassium zirconium silicate dalyite has been identified for the first time on Terceira, Azores, within syenitic ejecta of the Caldeira-Castelinho Ignimbrite Formation. New quantitative analyses of this dalyite were combined with the small number of published analyses from various locations worldwide to evaluate the mineral's compositional variability. Additionally, solid-state modelling has been applied to assess the site allocations of substituting elements. The new analyses yield the average formula (K1.84Na0.15)∑=1.99(Zr0.94Ti0.012Hf0.011Fe0.004)∑=0.967Si6.03O15. Model results predict the placement of substituting Hf and Ti in the octahedral site, and highlight the overall complexity in the incorporation of Fe, Mg and Ba. The combined dataset reveals that dalyite found within peralkaline granites and syenites is generally defined by higher Na↔K substitution and lower Ti↔Zr substitution relative to dalyite from highly potassic rocks. The Terceira dalyite exhibits a bimodal variation in the degree of Na↔K substitution which is attributed to a K-enrichment trend induced by late-stage pore wall crystallization and albitization, coupled with the control of pore size upon the degree of supersaturation required to initiate nucleation of dalyite in pores of varying size.

APA, Harvard, Vancouver, ISO, and other styles

5

McCUTCHEON, S. R., H. E. ANDERSON, and P. T. ROBINSON. "Stratigraphy and eruptive history of the Late Devonian Mount Pleasant Caldera Complex, Canadian Appalachians." Geological Magazine 134, no. 1 (January 1997): 17–36. http://dx.doi.org/10.1017/s0016756897006213.

Full text

Abstract:

Stratigraphic, petrographic and geochemical evidence indicate that the volcano-sedimentary rocks of the Late Devonian Piskahegan Group, located in the northern Appalachians of southwestern New Brunswick, represent the eroded remnants of a large epicontinental caldera complex. This complex – the Mount Pleasant Caldera – is one of few recognizable pre-Cenozoic calderas and is divisible into Exocaldera, Intracaldera and Late Caldera-Fill sequences. The Intracaldera Sequence comprises four formations that crop out in a triangular-shaped area and includes: thick ash flow tuffs, thick sedimentary breccias that dip inward, and stocks of intermediate to felsic composition that intrude the volcanic pile or are localized along caldera-margin faults. The Exocaldera Sequence contains ash flow tuffs, mafic lavas, alluvial redbeds and porphyritic felsic lavas that comprise five formations. The Late Caldera-Fill Sequence contains rocks that are similar to those of the outflow facies and comprises two formations and two minor intrusive units. Geochemical and mineralogical data support the stratigraphic subdivision and indicate that the basaltic rocks are mantle-derived and have intraplate chemical affinities. The andesites were probably derived from basaltic magma by fractional crystallization and assimilation of crustal material. The various felsic units are related by episodes of fractional crystallization in a high-level, zoned magma chamber. Fractionation was repeatedly interrupted by eruption of material from the roof zone such that seven stages of caldera development have been identified. The genesis of the caldera is related to a period of lithospheric thinning that followed the Acadian Orogeny in the northern Appalachians.

APA, Harvard, Vancouver, ISO, and other styles

6

Sanchez, L., and R. Shcherbakov. "Scaling properties of planetary calderas and terrestrial volcanic eruptions." Nonlinear Processes in Geophysics 19, no. 6 (November 6, 2012): 585–93. http://dx.doi.org/10.5194/npg-19-585-2012.

Full text

Abstract:

Abstract. Volcanism plays an important role in transporting internal heat of planetary bodies to their surface. Therefore, volcanoes are a manifestation of the planet's past and present internal dynamics. Volcanic eruptions as well as caldera forming processes are the direct manifestation of complex interactions between the rising magma and the surrounding host rock in the crust of terrestrial planetary bodies. Attempts have been made to compare volcanic landforms throughout the solar system. Different stochastic models have been proposed to describe the temporal sequences of eruptions on individual or groups of volcanoes. However, comprehensive understanding of the physical mechanisms responsible for volcano formation and eruption and more specifically caldera formation remains elusive. In this work, we propose a scaling law to quantify the distribution of caldera sizes on Earth, Mars, Venus, and Io, as well as the distribution of calderas on Earth depending on their surrounding crustal properties. We also apply the same scaling analysis to the distribution of interevent times between eruptions for volcanoes that have the largest eruptive history as well as groups of volcanoes on Earth. We find that when rescaled with their respective sample averages, the distributions considered show a similar functional form. This result implies that similar processes are responsible for caldera formation throughout the solar system and for different crustal settings on Earth. This result emphasizes the importance of comparative planetology to understand planetary volcanism. Similarly, the processes responsible for volcanic eruptions are independent of the type of volcanism or geographical location.

APA, Harvard, Vancouver, ISO, and other styles

7

Martí, J., J. Mitjavila, and V. Araña. "Stratigraphy, structure and geochronology of the Las Cañadas caldera (Tenerife, Canary Islands)." Geological Magazine 131, no. 6 (November 1994): 715–27. http://dx.doi.org/10.1017/s0016756800012838.

Full text

Abstract:

AbstractAfter a long period of subaerial fissure-fed extrusions of basaltic magmas (∼ 12 to > 3 Ma) volcanic activity was then concentrated in the central part of Tenerife. Phonolitic magma chambers formed and a central volcanic complex was constructed (the Las Canadas edifice). The formation of a large depression (the Las Canadas caldera) truncated the top of the edifice. The active twin strato-cones Teide—Pico Viejo are sited in this depression. The history of the Las Canadas caldera and edifice are established from stratigraphy, geochronology (K—Ar dates) and volcanological studies. Two different groups are recognized, separated by a major unconformity. The Lower Group is dated at 2 to 3 Ma and includes the products of several volcanic centres, which together represent several cycles. The Upper Group ranges from 1.56 to 0.17 Ma and includes three different formations representing three long-term (∼ 100 to 300 Ka) volcanic cycles. The periods of dormancy between each formation were of ∼ 120 to 250 Ka duration. The Las Canadas caldera is a multicyclic caldera which formed over the period 1.18–0.17 Ma. Each cycle of activity represented by a formation culminated in caldera collapse which affected different sectors of the Las Canadas edifice. Geological observation and geochronology support an origin by collapse into a magma chamber. The minimum volume of pyroclastic ejecta is substantially greater than the present caldera depression volume (45 km3), but approaches the inferred volume of the original caldera depression (> 140 km3). After the formation of the caldera, sector collapses could also occur at the northern flank of the volcano causing the disappearance of the northern side of the caldera wall.

APA, Harvard, Vancouver, ISO, and other styles

8

Smellie, J. L. "Lithostratigraphy and volcanic evolution of Deception Island, South Shetland Islands." Antarctic Science 13, no. 2 (June 2001): 188–209. http://dx.doi.org/10.1017/s0954102001000281.

Full text

Abstract:

Deception Island is the most active volcano in the Antarctic Peninsula region. It is a large basalt–andesite shield volcano with a 10 km-wide restless caldera (Port Foster) and a complicated history of pre- and post-caldera eruptions. There has been no modern volcanological investigation of the entire island and it remains a largely unknown volcanic hazard. The pre-caldera period on the island began with the low-energy eruption of tephras from multiple centres (Fumarole Bay Formation), possibly by subaqueous fire fountaining during shoaling and likely initial emergence of the volcano. It was followed by subaerial effusive to weakly pyroclastic (Strombolian/Hawaiian) activity that constructed a small basaltic shield (Basaltic Shield Formation), and a large eruption that vented about 30 km3 of magma (Outer Coast Tuff Formation). The latter eruption may have been triggered by an influx of compositionally different magma into the main chamber feeding the volcano, and the evidence suggests that it was associated with a significant involvement with water (seawater?). The eruption was followed by caldera collapse, and there have been several small incremental caldera “collapses” subsequently. Post-caldera eruptions were all small-volume and predominantly phreatomagmatic (Baily Head and Pendulum Cove formations), but magmatic eruptions constructed several small lava deltas around the coast and also produced a local carapace of scoria and thin lavas, particularly around the caldera rim (Stonethrow Ridge Formation). Although the caldera is presently resurging, interpretation of the eruptive history of the island suggests that future eruptions are likely to be small in volume and will have only a limited regional impact.

APA, Harvard, Vancouver, ISO, and other styles

9

Sacchi, Marco, Giuseppe De Natale, Volkhard Spiess, Lena Steinmann, Valerio Acocella, Marta Corradino, Shanaka de Silva, et al. "A roadmap for amphibious drilling at the Campi Flegrei caldera: insights from a MagellanPlus workshop." Scientific Drilling 26 (December 2, 2019): 29–46. http://dx.doi.org/10.5194/sd-26-29-2019.

Full text

Abstract:

Abstract. Large calderas are among the Earth's major volcanic features. They are associated with large magma reservoirs and elevated geothermal gradients. Caldera-forming eruptions result from the withdrawal and collapse of the magma chambers and produce large-volume pyroclastic deposits and later-stage deformation related to post-caldera resurgence and volcanism. Unrest episodes are not always followed by an eruption; however, every eruption is preceded by unrest. The Campi Flegrei caldera (CFc), located along the eastern Tyrrhenian coastline in southern Italy, is close to the densely populated area of Naples. It is one of the most dangerous volcanoes on Earth and represents a key example of an active, resurgent caldera. It has been traditionally interpreted as a nested caldera formed by collapses during the 100–200 km3 Campanian Ignimbrite (CI) eruption at ∼39 ka and the 40 km3 eruption of the Neapolitan Yellow Tuff (NYT) at ∼15 ka. Recent studies have suggested that the CI may instead have been fed by a fissure eruption from the Campanian Plain, north of Campi Flegrei. A MagellanPlus workshop was held in Naples, Italy, on 25–28 February 2017 to explore the potential of the CFc as target for an amphibious drilling project within the International Ocean Discovery Program (IODP) and the International Continental Drilling Program (ICDP). It was agreed that Campi Flegrei is an ideal site to investigate the mechanisms of caldera formation and associated post-caldera dynamics and to analyze the still poorly understood interplay between hydrothermal and magmatic processes. A coordinated onshore–offshore drilling strategy has been developed to reconstruct the structure and evolution of Campi Flegrei and to investigate volcanic precursors by examining (a) the succession of volcanic and hydrothermal products and related processes, (b) the inner structure of the caldera resurgence, (c) the physical, chemical, and biological characteristics of the hydrothermal system and offshore sediments, and (d) the geological expression of the phreatic and hydromagmatic eruptions, hydrothermal degassing, sedimentary structures, and other records of these phenomena. The deployment of a multiparametric in situ monitoring system at depth will enable near-real-time tracking of changes in the magma reservoir and hydrothermal system.

APA, Harvard, Vancouver, ISO, and other styles

10

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.

Full text

Abstract:

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.

APA, Harvard, Vancouver, ISO, and other styles

11

Gathot Harbowo, Danni, and Siti Zahra. "Microscopy Observation of Samosir Formation Paleosoil, Tuktuk Sidaong, North Sumatera, Indonesia." Journal of Geoscience, Engineering, Environment, and Technology 6, no. 1 (March 24, 2021): 9–15. http://dx.doi.org/10.25299/jgeet.2021.6.1.5217.

Full text

Abstract:

Samosir is the islands that emerge and standing upon on Toba Caldera after it’s the last eruption at 74.000 years ago. Samosir Island known as the caldera floor that uplifts parallel with Toba’s caldera flooding. In this study, we have observed an outcrop in Tumutuk, Samosir Island that hypothesized as a lacustrine deposit, and we found a paleosoil layer that might give more answers about the geological process in this area at the past time. Based on this outcrop, we described it, followed to measure its stratigraphy section, and took representative samples from the paleosoil layer, then observed the samples under the stereo-microscope as polish rock section, in normal light & negative images. As the result we identify several features of paleosoil & its sedimentary grain that shown this paleosoil layer, two events of the volcanoclastic deposits flown, and exposed two-time, and forming soil, it may form in the shallow swamp in a lacustrine environment, coincide with caldera flooding and caldera floor uplift event.

APA, Harvard, Vancouver, ISO, and other styles

12

Geyer, A., and J. Martí. "Stress fields controlling the formation of nested and overlapping calderas: Implications for the understanding of caldera unrest." Journal of Volcanology and Geothermal Research 181, no. 3-4 (April 2009): 185–95. http://dx.doi.org/10.1016/j.jvolgeores.2009.01.018.

Full text

APA, Harvard, Vancouver, ISO, and other styles

13

Roche, O., T. H. Druitt, and O. Merle. "Experimental study of caldera formation." Journal of Geophysical Research: Solid Earth 105, B1 (January 10, 2000): 395–416. http://dx.doi.org/10.1029/1999jb900298.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Somr, Michael, and Petr Kabele. "Influence of the Bell-Jar Magma Chamber Geometry on a Caldera Formation." Applied Mechanics and Materials 825 (February 2016): 165–69. http://dx.doi.org/10.4028/www.scientific.net/amm.825.165.

Full text

Abstract:

The formation of a caldera poses a serious risk for the society and the environment. There are several established processes (mostly dealing with the conditions inside the reservoir), which must take place in order to reach a collapse leading to the caldera. The role of magma chamber geometry is investigated in this paper, exploiting the numerical modeling. The results indicates that the knowledge of the magmatic system dimensions can provide a helpful factor for an assessment of the caldera formation scenario.

APA, Harvard, Vancouver, ISO, and other styles

15

CITRONI, SERGIO B., MIGUEL A. S. BASEI, OSWALDO SIGA JR., and JOSÉ M. DOS REIS NETO. "Volcanism and stratigraphy of the Neoproterozoic Campo Alegre Basin, SC, Brazil." Anais da Academia Brasileira de Ciências 73, no. 4 (December 2001): 581–97. http://dx.doi.org/10.1590/s0001-37652001000400012.

Full text

Abstract:

The depositional succession of the Campo Alegre Basin (Santa Catarina - southern Brazil) was investigated having the evolution of the volcanic activity as background. The different stratigraphic units are interpreted as belonging to different volcanic stages: Bateias Formation, conglomerates and sandstones, related with a pre-volcanic stage; Campo Alegre Group, at the main volcanic stage, with each different formation corresponding to different episodes of volcanism - Rio Negrinho Formation, corresponding to the basic volcanism, Avenca Grande Formation to ignimbritic event, Serra de São Miguel Formation to the acid volcanism and Fazenda Uirapuru Formation, related to an explosive event; Rio Turvo and Arroio Água Fria formations correspond respectively to inner and extra-caldera deposits.

APA, Harvard, Vancouver, ISO, and other styles

16

Gudmundsson, Agust. "Formation of collapse calderas." Geology 16, no. 9 (1988): 808. http://dx.doi.org/10.1130/0091-7613(1988)016<0808:focc>2.3.co;2.

Full text

APA, Harvard, Vancouver, ISO, and other styles

17

Martí, J., and A. Baraldo. "Pre-caldera Pyroclastic deposits of Deception Island (South Shetland Islands)." Antarctic Science 2, no. 4 (December 1990): 345–52. http://dx.doi.org/10.1017/s0954102090000475.

Full text

Abstract:

The youngest pre-caldera volcanism of Deception Island is represented by a thick sequence of subaerial pyroclastic deposits which has been grouped as the Yellow Tuff Formation. Most of these deposits were related to the explosive activity of a central vent which was destroyed during the formation of the caldera. Two members can be distinguished in this formation. The lower member is mainly composed of 1 to 12 m thick massive pyroclastic flow deposits with interbedded air-fall and surge deposits. The upper member is in stratigraphical continuity with the lower member and consists of base surge deposits with minor air-fall and thin pyroclastic flow deposits. The pre-caldera deposits have undergone a palagonitic alteration which produced crystallization of smectites, Fe-oxides, zeolites and calcite.

APA, Harvard, Vancouver, ISO, and other styles

18

Anderson, Kyle R., Ingrid A. Johanson, Matthew R. Patrick, Mengyang Gu, Paul Segall, Michael P. Poland, Emily K. Montgomery-Brown, and Asta Miklius. "Magma reservoir failure and the onset of caldera collapse at Kīlauea Volcano in 2018." Science 366, no. 6470 (December 5, 2019): eaaz1822. http://dx.doi.org/10.1126/science.aaz1822.

Full text

Abstract:

Caldera-forming eruptions are among Earth’s most hazardous natural phenomena, yet the architecture of subcaldera magma reservoirs and the conditions that trigger collapse are poorly understood. Observations from the formation of a 0.8–cubic kilometer basaltic caldera at Kīlauea Volcano in 2018 included the draining of an active lava lake, which provided a window into pressure decrease in the reservoir. We show that failure began after <4% of magma was withdrawn from a shallow reservoir beneath the volcano’s summit, reducing its internal pressure by ~17 megapascals. Several cubic kilometers of magma were stored in the reservoir, and only a fraction was withdrawn before the end of the eruption. Thus, caldera formation may begin after withdrawal of only small amounts of magma and may end before source reservoirs are completely evacuated.

APA, Harvard, Vancouver, ISO, and other styles

19

Gephart, John W. "Deformation around the Creede Caldera: A consequence of isostatic adjustment following Caldera Formation." Journal of Geophysical Research: Solid Earth 92, B10 (September 10, 1987): 10601–16. http://dx.doi.org/10.1029/jb092ib10p10601.

Full text

APA, Harvard, Vancouver, ISO, and other styles

20

Marques, Rosa, Bruno J. C. Vieira, Maria Isabel Prudêncio, João Carlos Waerenborgh, Maria Isabel Dias, Dulce Russo, Fernando Rocha, Teresa Silva, and Francisco Ruiz. "Geochemistry and Fe speciation in active volcanic environments – the case of Fogo Island, Cape Verde." E3S Web of Conferences 98 (2019): 06009. http://dx.doi.org/10.1051/e3sconf/20199806009.

Full text

Abstract:

Topsoils developed in different geological formations/ages, and the top layer of the lava flow from the most recent eruption (2014/2015) of Fogo Island (Cape Verde archipelago), were studied. The specific objectives of this work are: i) to estimate the REE contents and patterns in the whole sample of topsoils developed on different geological formations/ages and their correlation with the iron speciation; and ii) to study the top layer of a lava flow from the most recent eruption after two years of exposure. REE contents are in general higher in the topsoils of the pre-caldera than in those developed on the post-caldera formation, particularly the light REE probably due to their incorporation into hematite. Positive Eu anomalies found in recent topsoils suggest the existence of hydrothermal processes with intrusion of hot fluids with higher concentration of Eu2+. In the top layer of the lava flow of the most recent eruption, Fe is incorporated in pyroxenes and iron oxides (magnetite and/or maghemite). This study can be a benchmark for further knowledge of the chemical evolution and weathering rate in semi-arid climate of Fogo Island.

APA, Harvard, Vancouver, ISO, and other styles

21

Renzulli, Alberto, Brian G. J. Upton, Adrian Boyce, and Rob M. Ellam. "Petrology of quartz syenite and hauyne syenite clasts from the Pitigliano Formation, Latera caldera, Vulsini District, Central Italy." European Journal of Mineralogy 10, no. 2 (March 31, 1998): 333–54. http://dx.doi.org/10.1127/ejm/10/2/0333.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

de Ronde, Cornel E. J., Susan E. Humphris, Tobias W. Höfig, and Agnes G. Reyes. "Critical role of caldera collapse in the formation of seafloor mineralization: The case of Brothers volcano." Geology 47, no. 8 (June 6, 2019): 762–66. http://dx.doi.org/10.1130/g46047.1.

Full text

Abstract:

Abstract Hydrothermal systems hosted by submarine arc volcanoes commonly include a large component of magmatic fluid. The high Cu-Au contents and strongly acidic fluids in these systems are similar to those that formed in the shallow parts of some porphyry copper and epithermal gold deposits mined today on land. Two main types of hydrothermal systems occur along the submarine portion of the Kermadec arc (offshore New Zealand): magmatically influenced and seawater-dominated systems. Brothers volcano hosts both types. Here, we report results from a series of drill holes cored by the International Ocean Discovery Program into these two types of hydrothermal systems. We show that the extent of hydrothermal alteration of the host dacitic volcaniclastics and lavas reflects primary lithological porosity and contrasting spatial and temporal contributions of magmatic fluid, hydrothermal fluid, and seawater. We present a two-step model that links the changes in hydrothermal fluid regime to the evolution of the volcano caldera. Initial hydrothermal activity, prior to caldera formation, was dominated by magmatic gases and hypersaline brines. The former mixed with seawater as they ascended toward the seafloor, and the latter remained sequestered in the subsurface. Following caldera collapse, seawater infiltrated the volcano through fault-controlled permeability, interacted with wall rock and the segregated brines, and transported associated metals toward the seafloor and formed Cu-Zn-Au–rich chimneys on the caldera walls and rim, a process continuing to the present day. This two-step process may be common in submarine arc caldera volcanoes that host volcanogenic massive sulfide deposits, and it is particularly efficient at focusing mineralization at, or near, the seafloor.

APA, Harvard, Vancouver, ISO, and other styles

23

Sevastyanov, V. S., G. A. Karpov, A. Yu Bychkov, O. V. Kuznetsova, and V. S. Fedulov. "Influence of hydrous pyrolysis on distribution of carbon and hydrogen isotopes by organic matter fractions. The nature of oil generation in the calder of Uzone Volcano in Kamchatka." Геохимия 64, no. 3 (April 3, 2019): 227–36. http://dx.doi.org/10.31857/s0016-7525643227-236.

Full text

Abstract:

The process of oil seeps transformation from the Uzon volcano caldera under the influence of hydrous pyrolysis at a temperature of 350 °C in argon and oxygen was investigated. It is shown that carbon and hydrogen isotope type curves (ITC) reflect the processes occurring in organic matter during hydrous pyrolysis in oxidizing and neutral media. The similarity in forms between carbon ITC of the Uzon oil seeps, the Bogachevka oil and biota of hydrothermal sources is revealed. Hydrogen ITCs have a more complex form, apparently associated with exchange processes occurring in hydrothermal water. Based on the conducted studies, it was assumed that on the one hand oil seeps in the Uzon caldera can serve as a source for the formation of Bogachevka oil, and on the other hand, it is possible that the circulating hydrothermal water in the caldera of the Uzon volcano brings to the surface the organic matter of the Bogachevka oil formation.

APA, Harvard, Vancouver, ISO, and other styles

24

Hughes, Gwyneth R., and Gail A. Mahood. "Location of silicic caldera formation in arc settings." IOP Conference Series: Earth and Environmental Science 3 (October 1, 2008): 012024. http://dx.doi.org/10.1088/1755-1307/3/1/012024.

Full text

APA, Harvard, Vancouver, ISO, and other styles

25

Walter, Thomas R., and Valentin R. Troll. "Formation of caldera periphery faults: an experimental study." Bulletin of Volcanology 63, no. 2-3 (June 2001): 191–203. http://dx.doi.org/10.1007/s004450100135.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

IKEDA, YASUO, TOSHIHIKO IKEDA, and HIROO KAGAMI. "Caldera-formation from geochemical aspects: A case study of the Toya caldera, southwestern Hokkaido, Japan." JOURNAL OF MINERALOGY, PETROLOGY AND ECONOMIC GEOLOGY 85, no. 12 (1990): 569–77. http://dx.doi.org/10.2465/ganko.85.569.

Full text

APA, Harvard, Vancouver, ISO, and other styles

27

Wright, I. C., and J. A. Gamble. "Southern Kermadec submarine caldera arc volcanoes (SW Pacific): caldera formation by effusive and pyroclastic eruption." Marine Geology 161, no. 2-4 (October 1999): 207–27. http://dx.doi.org/10.1016/s0025-3227(99)00040-7.

Full text

APA, Harvard, Vancouver, ISO, and other styles

28

Ort, Michael H. "Eruptive processes and caldera formation in a nested downsagcollapse caldera: Cerro Panizos, central Andes Mountains." Journal of Volcanology and Geothermal Research 56, no. 3 (June 1993): 221–52. http://dx.doi.org/10.1016/0377-0273(93)90018-m.

Full text

APA, Harvard, Vancouver, ISO, and other styles

29

Sobradelo, Rosa, A. Geyer, and J. Martí. "Statistical data analysis of the CCDB (Collapse Caldera Database): Insights on the formation of caldera systems." Journal of Volcanology and Geothermal Research 198, no. 1-2 (December 2010): 241–52. http://dx.doi.org/10.1016/j.jvolgeores.2010.09.003.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Nizametdinov, I. R., D. V. Kuzmin, S. Z. Smirnov, A. V. Rybin, and I. Yu Kulakov. "Water in parental basaltic magmasof the Menshiy Brat volcano (Iturup Island, Kurile islands)." Доклады Академии наук 486, no. 1 (May 10, 2019): 93–97. http://dx.doi.org/10.31857/s0869-5652486193-97.

Full text

Abstract:

The paper presents study of the liquidus assemblage of olivine and spinel in high-magnesian basalts (MgO up to 10 mas. %) of the Menshiy Brat volcano (Iturup Island). It was possible to reconstruct the water content and evolution of volatile components in the primary parental magmas that took part in the formation of the Medvezhya Caldera, Iturup Islands. It is shown that the initial water content in the primary melts could reach 5 mas. % with oxygen fugacity corresponding to oxygen buffer NNO + 0.4 log. units. The evolution of magmas involved continuous degassing while magma rises to the surface. The water-rich fluid, which is constantly separated by evolving magma, could play a significant role in the formation of large siliceous magma chambers, which participated in catastrophic caldera eruptions.

APA, Harvard, Vancouver, ISO, and other styles

31

Beddoe-Stephens, B., and I. Mason. "The volcanogenetic significance of garnet-bearing minor intrusions within the Borrowdale Volcanic Group Eskdale area, Cumbria." Geological Magazine 128, no. 5 (September 1991): 505–16. http://dx.doi.org/10.1017/s0016756800018641.

Full text

Abstract:

AbstractA number of garnetiferous minor intrusions have been mapped within the Borrowdale Volcanic Group. They underlie garnetiferous extrusive volcanic rocks which occur toward the top of a sequence of ignimbrite and lava – the Airy's Bridge Formation – which is the product of a major caldera-forming eruptive episode. Garnet and whole-rock geochemistry indicate that most of the intrusions are indistinguishable from garnetiferous dacite forming the final eruptive unit of the Airy's Bridge Formation: a co-magmatic link is therefore postulated. One of the intrusions, which intrudes the Airy's Bridge Formation, is distinct and may be related to the later Eskdale pluton.It is suggested that following the emplacement of ignimbrites forming the basal half of the Airy's Bridge Formation, caldera collapse partially sealed a fissure-conduit system and degassed, garnet-bearing magma was intruded as dykes and sills and locally extruded as a post-explosive lava dome. It is also postulated that garnet crystallized in a high-level magma chamber (P < 3 kb) and that reverse chemical zoning was due to growth while sinking through compositionally stratified magma.

APA, Harvard, Vancouver, ISO, and other styles

32

Troll, Valentin R., C. Henry Emeleus, and Colin H. Donaldson. "Caldera formation in the Rum Central Igneous Complex, Scotland." Bulletin of Volcanology 62, no. 4-5 (November 23, 2000): 301–17. http://dx.doi.org/10.1007/s004450000099.

Full text

APA, Harvard, Vancouver, ISO, and other styles

33

Rosera, Joshua M., Sean P. Gaynor, and Drew S. Coleman. "Spatio-Temporal Shifts in Magmatism and Mineralization in Northern Colorado Beginning in the Late Eocene." Economic Geology 116, no. 4 (June 1, 2021): 987–1010. http://dx.doi.org/10.5382/econgeo.4815.

Full text

Abstract:

Abstract Magmatism in northern Colorado beginning in the late Eocene is associated with the formation of Pb-Zn-Ag carbonate-replacement and polymetallic vein deposits, the onset of caldera-forming magmatism, and eventually, the formation of rift-related, F-rich Mo porphyries (“Climax-type” intrusions). We use high-precision U/Pb zircon geochronology to better evaluate the temporal framework of magmatism and mineralization in the region. Our results demonstrate that mineralization in the Leadville area occurred between 43.5 and 39.7 Ma and was followed by mesothermal mineralization in the Montezuma area at approximately 38.7 Ma. Mineralization is associated with a suite of approximately 43 to 39 Ma intermediate magmatic centers that extended from Twin Lakes through Montezuma. The oldest porphyries associated with F-rich Mo prospects and deposits (Middle Mountain; 36.45 Ma) intruded 900 kyr after the start of the ignimbrite flare-up in the region. Spatiotemporal analyses reveal that the pattern of magmatism shifted in orientation between 40 and 35 Ma. We propose a model wherein magmatism before 39 Ma was the result of fluids evolved from the subducted Farallon slab being focused through weak zones in the lithospheric mantle and into the lower crust. This was followed by a more diffuse and higher power melting event that corresponds to a distinct change in the spatial patterns of magmatism. Our data suggest that low-grade Mo porphyry deposits can form close in time to calderas. We hypothesize that the transition from subduction to extensional tectonics in the region was responsible for this more widespread melting and a distinct shift in the style of magmatic-hydrothermal mineralization.

APA, Harvard, Vancouver, ISO, and other styles

34

Munro, Duncan C., and Scott K. Rowland. "Caldera morphology in the western Galápagos and implications for volcano eruptive behavior and mechanisms of caldera formation." Journal of Volcanology and Geothermal Research 72, no. 1-2 (July 1996): 85–100. http://dx.doi.org/10.1016/0377-0273(95)00076-3.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Druitt, T. H., R. A. Mellors, D. M. Pyle, and R. S. J. Sparks. "Explosive volcanism on Santorini, Greece." Geological Magazine 126, no. 2 (March 1989): 95–126. http://dx.doi.org/10.1017/s0016756800006270.

Full text

Abstract:

AbstrctSantorini volcanic field has had 12 major (1–10 km3 or more of magma), and numerous minor, explosive eruptions over the last ~ 200 ka. Deposits from these eruptions (Thera Pyroclastic Formation) are well exposed in caldera-wall successions up to 200 m thick. Each of the major eruptions began with a pumice-fall phase, and most culminated with emplacement of pyroclastic flows. Pyroclastic flows of at least six eruptions deposited proximal lag deposits exposed widely in the caldera wall. The lag deposits include coarse-grained lithic breccias (andesitic to rhyodacitic eruptions) and spatter agglomerates (andesitic eruptions only). Facies associations between lithic breccia, spatter agglomerate, and ignimbrite from the same eruption can be very complex. For some eruptions, lag deposits provide the only evidence for pyroclastic flows, because most of the ignimbrite is buried on the lower flanks of Santorini or under the sea. At least eight eruptions tapped compositionally heterogeneous magma chambers, producing deposits with a range of zoning patterns and compositional gaps. Three eruptions display a silicic–silicic + mafic–silicic zoning not previously reported. Four eruptions vented large volumes of dacitic or rhyodacitic pumice, and may account for 90% or more of all silicic magma discharged from Santorini. The Thera Pyroclastic Formation and coeval lavas record two major mafic-to-silicic cycles of Santorini volcanism. Each cycle commenced with explosive eruptions of andesite or dacite, accompanied by construction of composite shields and stratocones, and culminated in a pair of major dacitic or rhyodacitic eruptions. Sequences of scoria and ash deposits occur between most of the twelve major members and record repeated stratocone or shield construction following a large explosive eruption.Volcanism at Santorini has focussed on a deep NE–SW basement fracture, which has acted as a pathway for magma ascent. At least four major explosive eruptions began at a vent complex on this fracture. Composite volcanoes constructed north of the fracture were dissected by at least three caldera-collapse events associated with the pyroclastic eruptions. Southern Santorini consists of pryoclastic ejecta draped over a pre-volcanic island and a ridge of early- to mid-Pleistocene volcanics. The southern half of the present-day caldera basin is a long-lived, essentially non-volcanic, depression, defined by topographic highs to the south and east, but deepened by subsidence associated with the main northern caldera complex, and is probably not a separate caldera.

APA, Harvard, Vancouver, ISO, and other styles

36

OHSHIMA, Osamu. "Formation of a Collapse Caldera at Miyake-jima Volcano, 2000." Journal of Geography (Chigaku Zasshi) 110, no. 2 (2001): Plate1—Plate2. http://dx.doi.org/10.5026/jgeography.110.2_plate1.

Full text

APA, Harvard, Vancouver, ISO, and other styles

37

Rolandi, G., F. Bellucci, and M. Cortini. "A new model for the formation of the Somma Caldera." Mineralogy and Petrology 80, no. 1-2 (February 1, 2004): 27–44. http://dx.doi.org/10.1007/s00710-003-0018-0.

Full text

APA, Harvard, Vancouver, ISO, and other styles

38

Pinel, V. "Influence of pre-existing volcanic edifice geometry on caldera formation." Geophysical Research Letters 38, no. 11 (June 2011): n/a. http://dx.doi.org/10.1029/2011gl047900.

Full text

APA, Harvard, Vancouver, ISO, and other styles

39

Kokelaar, Peter. "Friction melting, catastrophic dilation and breccia formation along caldera superfaults." Journal of the Geological Society 164, no. 4 (July 2007): 751–54. http://dx.doi.org/10.1144/0016-76492006-059.

Full text

APA, Harvard, Vancouver, ISO, and other styles

40

Punanova, Svetlana A., and Mikhail V. Rodkin. "Comparison of the contribution of differently depth geological processes in the formation of a trace elements characteristic of caustobiolites." Georesursy 21, no. 3 (September 1, 2019): 14–24. http://dx.doi.org/10.18599/grs.2019.3.14-24.

Full text

Abstract:

The article analyzes the correlation dependences between the logarithms of the concentrations of trace elements (TE) in various geochemical environments (oil, coal, fuel and black shales, as well as in clays, organic matter (OM) of various types and biota) in comparison with the average chemical composition of the upper, middle and lower continental crust. At the same time, along with the TE content of oils of the main oil and gas basins (OGB) – the Volga-Ural and West Siberian ones, the data on the TE content in the so-called young oils were summarized; as such, data on the oil fields of the West Kamchatka oil and gas field and oil manifestations in the area of the caldera of the Uzon volcano were used. Particular attention was also paid to the results of the analysis of the TE composition of the oils of the Romashkino group of fields, as it is possible that they are subject to the influence of deep-seated processes. The correlation coefficients between the studied parameters for the various studied oil- and gas-generating basins, including for the Romashkino group of fields, turned out to be close. For all oils, except for the young oils of Kamchatka and the caldera of the Uzon volcano, a closer connection of their TE composition with the TE composition of the lower crust was revealed. For young oils of the Uzon caldera in Kamchatka, this trend is absent, and a slightly closer relationship is revealed with the average composition of the upper but not lower crust, while for statistically more reliable data on the TE composition of the hydrothermal waters of the caldera of the Uzon volcano, a significantly closer relationship is observed with the average chemical composition of the middle and upper crust. Based on the identified correlations between the TE compositions of oil, caustobioliths and the crust of different levels, conclusions are made about the likely relationship between biogenic and deep processes in the formation of oil and gas fields. According to the authors, the obtained results support the crucially important role in the processes of naphthidogenesis of the upward flows of the low crustal fluids with the dominant source of hydrocarbons from the initial OM of sedimentary basins.

APA, Harvard, Vancouver, ISO, and other styles

41

Paris, Raphaël, and Juan Carlos Carracedo. "Formation d'une caldera d'érosion et instabilité récurrente d'une île de point chaud : la caldera de Taburiente, La Palma, îles Canaries / Formation of an erosion caldera and recurring instability on a hotspot-generated island: the caldera de Taburiente, La Palma, Canary Islands." Géomorphologie : relief, processus, environnement 7, no. 2 (2001): 93–105. http://dx.doi.org/10.3406/morfo.2001.1093.

Full text

APA, Harvard, Vancouver, ISO, and other styles

42

BRYAN, S. E., J. MARTÍ, and R. A. F. CAS. "Stratigraphy of the Bandas del Sur Formation: an extracaldera record of Quaternary phonolitic explosive eruptions from the Las Cañadas edifice, Tenerife (Canary Islands)." Geological Magazine 135, no. 5 (September 1998): 605–36. http://dx.doi.org/10.1017/s0016756897001258.

Full text

Abstract:

Explosive volcanism has dominated the large phonolitic shield volcano of Tenerife, the Las Cañadas edifice, for the last 1.5 m.y. Pyroclastic deposits of the Bandas del Sur Formation are exposed along the southern flanks, and record the last two of at least three long-term cycles of caldera-forming explosive eruptions. Each cycle began with flank fissure eruptions of alkali basalt lava, followed by minor eruptions of basanite to phonotephrite lavas. Minor phonotephritic to phonolitic lava effusions also occurred on the flanks of the edifice during the latter stages of the second explosive cycle. Non-welded plinian fall deposits and ignimbrites are the dominant explosive products preserved on the southern flanks. Of these, a significant volume has been dispersed offshore. Many pyroclastic units of the second explosive cycle exhibit compositional zonation. Banded pumice occurs in most units of the third (youngest) explosive cycle, and ignimbrites typically contain mixed phenocryst assemblages, indicating the role of magma mixing/mingling prior to eruption. At least four major eruptions of the third cycle began with phreatomagmatic activity, producing lithic-poor, accretionary lapilli-bearing fallout and/or surge deposits. The repeated, brief phase of phreatomagmatism at the onset of these eruptions is interpreted as reflecting an exhaustive water supply, probably a small caldera lake that was periodically established during the third cycle. Accidental syenite becomes an increasingly important lithic clast type in ignimbrites up-sequence, and is interpreted as recording the progressive development of a plutonic complex beneath the summit caldera.Successive eruptions during each explosive cycle increased in volume, with the largest eruption occurring at the end of the cycle. More than ten major explosive eruptions vented moderately large volumes (1−[ges ]10 km3) of phonolitic magma during the last two cycles. Culminating each explosive cycle was the emplacement of relatively large volume (>5−10 km3) ignimbrites with coarse, vent-derived lithic breccias, interpreted to record a major phase of caldera collapse. In the extracaldera record, explosive cycles are separated by ∼0.2 m.y. periods of non-explosive activity. Repose periods were characterized by erosion, remobilization of pyroclastic deposits by discharge events, and pedogenesis. The current period of non-explosive activity is characterized by the construction of the Teide-Pico Viejo stratovolcanic complex within the summit caldera. This suggests that eruptive hiatuses in the extracaldera record may reflect effusive activity and stratovolcano or shield-building phases within the summit caldera. Alternating effusive and explosive cycles have thus been important in the volcanic evolution of the Las Cañadas edifice.

APA, Harvard, Vancouver, ISO, and other styles

43

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.

Full text

Abstract:

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.

APA, Harvard, Vancouver, ISO, and other styles

44

BROWN, R. J., T. L. BARRY, M. J. BRANNEY, M. S. PRINGLE, and S. E. BRYAN. "The Quaternary pyroclastic succession of southeast Tenerife, Canary Islands: explosive eruptions, related caldera subsidence, and sector collapse." Geological Magazine 140, no. 3 (May 2003): 265–88. http://dx.doi.org/10.1017/s0016756802007252.

Full text

Abstract:

A much-revised Quaternary stratigraphy is presented for ignimbrites and pumice fall deposits of the Bandas del Sur, in southern Tenerife. New 40Ar/39Ar data obtained for the Arico, Granadilla, Fasnia, Poris, La Caleta and Abrigo formations are presented, allowing correlation with previously dated offshore marine ashfall layers and volcaniclastic sediments. We also provide a minimum age of 287±7 ka for a major sector collapse event at the Güimar valley. The Bandas del Sur succession includes more than seven widespread ignimbrite sheets that have similar characteristics, including widespread basal Plinian layers, predominantly phonolite composition, ignimbrites with similar extensive geographic distributions, thin condensed veneers with abundant diffuse bedding and complex lateral and vertical grading patterns, lateral gradations into localized massive facies within palaeo-wadis, and widespread lithic breccia layers that probably record caldera-forming eruptions. Each ignimbrite sheet records substantial bypassing of pyroclastic material into the ocean. The succession indicates that Las Cañadas volcano underwent a series of major explosive eruptions, each starting with a Plinian phase followed by emplacement of ignimbrites and thin ash layers, some of co-ignimbrite origin. Several of the ignimbrite sheets are compositionally zoned and contain subordinate mafic pumices and banded pumices indicative of magma mingling immediately prior to eruption. Because passage of each pyroclastic density current was characterized by phases of non-deposition and erosion, the entire course of each eruption is incompletely recorded at any one location, accounting for some previously perceived differences between the units. Because each current passed into the ocean, estimating eruption volumes is virtually impossible. Nevertheless, the consistent widespread distributions and the presence of lithic breccias within most of the ignimbrite sheets suggest that at least seven caldera collapse eruptions are recorded in the Bandas del Sur succession and probably formed a complex, nested collapse structure. Detailed field relationships show that extensive ignimbrite sheets (e.g. the Arico, Poris and La Caleta formations) relate to previously unrecognized caldera collapse events. We envisage that the evolution of the nested Las Cañadas caldera is more complex than previously thought and involved a protracted history of successive ignimbrite-related caldera collapse events, and large sector collapse events, interspersed with edifice-building phases.

APA, Harvard, Vancouver, ISO, and other styles

45

Hartley, M. E., and T. Thordarson. "Formation of Öskjuvatn caldera at Askja, North Iceland: Mechanism of caldera collapse and implications for the lateral flow hypothesis." Journal of Volcanology and Geothermal Research 227-228 (May 2012): 85–101. http://dx.doi.org/10.1016/j.jvolgeores.2012.02.009.

Full text

APA, Harvard, Vancouver, ISO, and other styles

46

Kusumoto, Shigekazu, Agust Gudmundsson, and Keiji Takemura. "Magma chamber volume change required for initial caldera (ring-fault) formation." Journal of the Geological Society of Japan 115, no. 12 (2009): 625–34. http://dx.doi.org/10.5575/geosoc.115.625.

Full text

APA, Harvard, Vancouver, ISO, and other styles

47

Siler, D. L., and J. A. Karson. "Subvolcanic subsidence and caldera formation during subaerial seafloor spreading in Iceland." Geological Society of America Bulletin 124, no. 7-8 (March 9, 2012): 1310–23. http://dx.doi.org/10.1130/b30562.1.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

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.

Full text

Abstract:

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.

APA, Harvard, Vancouver, ISO, and other styles

49

EVANS, ROBERT J., SIMON A. STEWART, and RICHARD J. DAVIES. "The structure and formation of mud volcano summit calderas." Journal of the Geological Society 165, no. 4 (July 2008): 769–80. http://dx.doi.org/10.1144/0016-76492007-118.

Full text

APA, Harvard, Vancouver, ISO, and other styles

50

Acocella, V., F. Cifelli, and R. Funiciello. "Formation of nonintersecting nested calderas: insights from analogue models." Terra Nova 13, no. 1 (February 18, 2001): 58–63. http://dx.doi.org/10.1046/j.1365-3121.2001.00317.x.

Full text

APA, Harvard, Vancouver, ISO, and other styles

We offer discounts on all premium plans for authors whose works are included in thematic literature selections. Contact us to get a unique promo code!