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Статті в журналах з теми "Trachybasalte"
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Juvigné, Étienne, and Bruno Bastin. "Téphrostratigraphie et palynologie de tourbes du Boréal et de l’Atlantique dans le massif Central (France)." Géographie physique et Quaternaire 49, no. 2 (November 30, 2007): 207–16. http://dx.doi.org/10.7202/033037ar.
Повний текст джерелаАнотація:
RÉSUMÉ La composition chimique des magmas de trois téphras que l'on trouve dans des tourbières en Auvergne a été déterminée. Elle a permis de distinguer la Téphra du Montchal (trachybasalte potassique) de celle du Montcineyre (basanite) qui sont pratiquement synchrones vers 6000 BP. La Téphra de La Taphanei (8500 BP, Boréal) est un trachyte. Deux diagrammes polliniques antérieurs font état de la présence de pollen de Tilia (Atlantique) au niveau de la Téphra de La Taphanei, voire même sous elle. Une nouvelle étude de cinq tourbières démontre : (i) que des grains de pollen isolés de Tilia ne sont pas observés dans plus de 17 % des niveaux d'âge boréal; (ii) que leur présence est plus fréquente au-dessus de la Téphra de La Taphanei; (iii) que la courbe continue de Tilia ne commence que bien au-dessus de la Téphra de La Taphanei, lorsqu'il n'y a pas de lacune dans la séquence.
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Perinelli, Cristina, Silvio Mollo, Mario Gaeta, Serena De Cristofaro, Danilo Palladino, and Piergiorgio Scarlato. "Impulsive Supply of Volatile-Rich Magmas in the Shallow Plumbing System of Mt. Etna Volcano." Minerals 8, no. 11 (October 25, 2018): 482. http://dx.doi.org/10.3390/min8110482.
Повний текст джерелаАнотація:
Magma dynamics at Mt. Etna volcano are frequently recognized as the result of complex crystallization regimes that, at shallow crustal levels, unexpectedly change from H2O-undersaturated to H2O-saturated conditions, due to the impulsive and irregular arrival of volatile-rich magmas from mantle depths. On this basis, we have performed hydrous crystallization experiments for a quantitative understanding of the role of H2O in the differentiation of deep-seated trachybasaltic magmas at the key pressure of the Moho transition zone. For H2O = 2.1–3.2 wt %, the original trachybasaltic composition shifts towards phonotephritic magmas never erupted during the entire volcanic activity of Mt. Etna. Conversely, for H2O = 3.8–8.2 wt %, the obtained trachybasalts and basaltic trachyandesites reproduce most of the pre-historic and historic eruptions. The comparison with previous low pressure experimental data and natural compositions from Mt. Etna provides explanation for (1) the abundant release of H2O throughout the plumbing system of the volcano during impulsive ascent of deep-seated magmas; (2) the upward acceleration of magmas feeding gas-dominated, sustained explosive eruptions; (3) the physicochemical changes of gas-fluxed magmas ponding at shallow crustal levels; and (4) the huge gas emissions measured at the summit craters and flank vents which result in a persistent volcanic gas plume.
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Karimov, Vagif M. "Some geological and petrological characteristics of the Eocene trachybasalt-trachyandesite- basalt-phonolite formation of the Talysh zone (Azerbaijan)." Journal of Geology, Geography and Geoecology 31, no. 3 (September 23, 2022): 484–92. http://dx.doi.org/10.15421/112244.
Повний текст джерелаАнотація:
This article discusses the stages of crystallization of the Eocene trachybasalt-tra- chyandesitebasalt-phonolith formation of the Talysh zone. Determination of the composi- tion of the primary magma, evolution and melting fraction of the initial melt of the Eocene volcanism of the Talysh zone within Azerbaijan. Eocene volcanism of the trachybasalt-tra-chyandesitebasalt-phonolith formation of the Talysh zone. Petrographic, petrochemical, geochemical studies of rocks, typomorphic features of mineral paragenesis, chemical composition of rocks were carried out by X-ray spectral and X-ray fluorescence analysis. The analyzes of the conducted studies show that the Talysh zone was formed in the Eocene time. Stages of evolution of the original magma and typomorphic features of mineral parageneses have been established. The distributions of microelements in mineral parageneses, which are direct participants in the crystallization processes that took place in intermediate chambers at different depths, have been studied. At present, the question arises of the need to clarify the typomorphic features of igneous complexes, as factors that determine the geodynamic regimes of their formation, and to determine the potential ore content. The petrographic and petrochemical characteristics of the volcanic rocks are given. It was found that if the process of differentiation in the Early-Middle Eocene was more distinct with the initial formation of more magnesian rock varieties (picrite-trachybasalts), and subsequently more ferruginous ones (trachyandesites and trachyandesitebasalts), then such accumulation of iron is not observed in porphyritic trachyandesites. This petrochemical feature is obviously associated with the duration of the break in volcanism, caused by the formation of a thick sedimentary-tuffaceous stratum, accompanied by the initiation and manifestation of an intermediate chamber of medium composition. Volcanism in the Late Eocene was undifferentiated and was not accompanied by the formation of medium differences. The appearance in the late Eocene of leucite phonolites, which represent an alkaline branch, and the absence of transitional varieties indicate the autonomous development of vit- robasalts and leucite phonolites. It is concluded that from the early phases of the manifestation of Eocene volcanism to the later phases, the change in the material composition along the lateral is expressed in the manifestation of more alkaline facies with a significant predominance of K over Na and with a greater correspondence to the differentials of the shoshonite series.
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Krasnobaev, Artur A., Victor N. Puchkov, Nina D. Sergeeva, and Sofia V. Busharina. "Polychronous zircons of volcanics of the Navysh complex of the Lower Riphean Ai Formation (Southern Urals)." Georesursy 22, no. 4 (December 2020): 101–12. http://dx.doi.org/10.18599/grs.2020.4.101-112.
Повний текст джерелаАнотація:
The volcanics of the Navysh complex of the Lower Riphean Ai Formation in the Southern Urals are well studied petrochemically and dated by several methods. In 2013 zircons from a trachybasalt porphyrite (sample 2152) gave a concordant SHRIMP date 1752±11 Ma, which was used as a fundamental for the lower boundary of the Riphean with no special arguments against it. The later attempts to repeat this date for the Navysh volcanics were not successful: the collected zircons were either more ancient (> 2500 Ma), or more young (< 500 Ma). From the beginning, the zircons with such ages were regarded as xenogenic or secondary metasomatic, or belonging to paleozoic dykes intruding the Riphean volcanics. However, the clearly expressed mineralogical properties of the Paleozoic zircons and their frequent presence in volcanics, not dykes, led to a conclusion that the zircons and Navysh volcanics, containing them, and exposed within the area of development of the Ai Formation, are polychronous. To support this conclusion, the authors studied in more detail the zircons of the Navysh trachybasalts, developed in the Ai Formation. The main conclusion, obtained from this new data, was that the volcanics attributed to the Navysh complex, form a polychronous system, including both the Lower Riphean (1750 Ma) and Paleozoic (450 Ma) rocks. The zircons of these age groups differ in their mineralogical and geochemical properties supporting the idea that they belong to different primary sources which may be due to repeating plume processes, which partly reanimated – heated and melted-rocks of the previous cycle and/or created new sources of melts.
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Babayeva, Gultekin J. "Petrological-mineralogical evolutional transformation of Cretaceous teschenite-tephrite, syenite-trachyte, and essexite-trachybasalt primary meltings (Carpathian, Caucasian and North TransBaikal regions)." Journal of Geology, Geography and Geoecology 32, no. 3 (September 25, 2023): 450–60. http://dx.doi.org/10.15421/112340.
Повний текст джерелаАнотація:
This article discusses spatial and time distribution of Cretaceous teschenite-tephrite and essexite-trachybasalt complexes of the Carpathian, Caucasian, North TransBaikal regions. The main aim of the article is a comparative analysis of petrological-mineralogical features of similar complexes located in the Carpathians, North Caucasus and Transbaikal, Georgia in the Khojavand depression in the southeast of the Lesser Caucasus. Rocks of teschenite-tephrite, essexite-trachybasalt complexes were formed in the Cretaceous, early Eocene and Miocene. The differentiates of the considered complexes are localized in graben-like structures. The initial stage of graben formation is associated with the formation of rocks of the essexite-trachybasalt complex. The next stage of this process is associated with the formation of the teschenite-tephrite complex. According to stages of bedding and develop- ment of riftogenic graben structures, the essexite-trachybasalt complex formed first, at a mature stage – teschenite-tephrite one. At the initial stage high titanian olivine subalkaline basaltic melting occurred from the garnet-phlogopite lherzolite substratum. At the second stage – subalkaline picrite melting occurred from this substratum, which is primary for teschenite-tephrite and syenite-trachyte com- plexes. The metasomatized high-titanium phlogopite lherzolite substrate was subjected to melting twice. An earlier stage of melting of the substrate did not exceed 0.1%, from which a high-titanium olivine trachybasalt melt was separated. The second stage of melting of the substrate reached 10-12%. In this case, a subalkaline olivine picrite melt was formed. Evolution of primary meltings occurred in different-depth intermediate foci and intrusive chambers. The main factor in evolution along with controlling geodynamic regime was gravitational-crystallized differentiation. The identified mineral parageneses, starting from the early stage of the evolution of the subalkaline picrite melt to the late one, actually characterize the stages of crystallization of the noted melt in the intrusive chamber and intermediate chambers. The Eocene and Miocene teschenite-tephrite and essexite-trachybasalt complexes are characterized by a smaller areal distribution and petrographic diversity. Obviously, during this period, the intense activation of transverse magma-feeding faults contributed to the rapid uplift of the subalkaline picrite melt into the upper horizons of the earth’s crust.
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MAALOE, S., I. SORENSEN, and J. HERTOGEN. "The Trachybasaltic Suite of Jan Mayen." Journal of Petrology 27, no. 2 (April 1, 1986): 439–66. http://dx.doi.org/10.1093/petrology/27.2.439.
Повний текст джерела
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Yea, Nam Hee, Sung-Hyo Yun, and Jeong Seon Koh. "Plagioclase Composition of Feldspar Trachybasalt in Jeju Island." Journal of the Petrological Society of Korea 21, no. 3 (September 30, 2012): 309–33. http://dx.doi.org/10.7854/jpsk.2012.21.3.309.
Повний текст джерела
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Lipman, Peter W., and Matthew J. Zimmerer. "Magmato-tectonic links: Ignimbrite calderas, regional dike swarms, and the transition from arc to rift in the Southern Rocky Mountains." Geosphere 15, no. 6 (September 30, 2019): 1893–926. http://dx.doi.org/10.1130/ges02068.1.
Повний текст джерелаАнотація:
Abstract Radial and linear dike swarms in the eroded roots of volcanoes and along rift zones are sensitive structural indicators of conduit and eruption geometry that can record regional paleostress orientations. Compositionally diverse dikes and larger intrusions that radiate westward from the polycyclic Platoro caldera complex in the Southern Rocky Mountain volcanic field (southwestern United States) merge in structural trend, composition, and age with the enormous but little-studied Dulce swarm of trachybasaltic dikes that continue southwest and south for ∼125 km along the eastern margin of the Colorado Plateau from southern Colorado into northern New Mexico. Some Dulce dikes, though only 1–2 m thick, are traceable for 20 km. More than 200 dikes of the Platoro-Dulce swarm are depicted on regional maps, but only a few compositions and ages have been published previously, and relations to Platoro caldera have not been evaluated. Despite complications from deuteric alteration, bulk compositions of Platoro-Dulce dikes (105 new X-ray fluorescence and inductively coupled plasma mass spectrometry analyses) become more mafic and alkalic with distance from the caldera. Fifty-eight (58) new 40Ar/39Ar ages provide insight into the timing of dike emplacement in relation to evolution of Platoro caldera (source of six regional ignimbrites between 30.3 and 28.8 Ma). The majority of Dulce dikes were emplaced during a brief period (26.5–25.0 Ma) of postcaldera magmatism. Some northeast-trending dikes yield ages as old as 27.5 Ma, and the northernmost north-trending dikes have younger ages (20.1–18.6 Ma). In contrast to high-K lamprophyres farther west on the Colorado Plateau, the Dulce dikes are trachybasalts that contain only anhydrous phenocrysts (clinopyroxene, olivine). Dikes radial to Platoro caldera range from pyroxene- and hornblende-bearing andesite to sanidine dacite, mostly more silicic than trachybasalts of the Dulce swarm. Some distal andesite dikes have ages (31.2–30.4 Ma) similar to those of late precaldera lavas; ages of other proximal dikes (29.2–27.5 Ma) are akin to those of caldera-filling lavas and the oldest Dulce dikes. The largest radial dikes are dacites that have yet younger sanidine 40Ar/39Ar ages (26.5–26.4 Ma), similar to those of the main Dulce swarm. The older andesitic dikes and precaldera lavas record the inception of a long-lived upper-crustal magmatic locus at Platoro. This system peaked in magmatic output during ignimbrite eruptions but remained intermittently active for at least an additional 9 m.y. Platoro magmatism began to decline at ca. 26 Ma, concurrent with initial basaltic volcanism and regional extension along the Rio Grande rift, but no basalt is known to have erupted proximal to Platoro caldera prior to ca. 20 Ma, just as silicic activity terminated at this magmatic locus. The large numbers and lengths of the radial andesitic-dacitic dikes, in comparison to the absence of similar features at other calderas of the San Juan volcanic locus, may reflect location of the Platoro system peripheral to the main upper-crustal San Juan batholith recorded by gravity data, as well as its proximity to the axis of early rifting. Spatial, temporal, and genetic links between Platoro radial dikes and the linear Dulce swarm suggest that they represent an interconnected regional-scale magmatic suite related to prolonged assembly and solidification of an arc-related subcaldera batholith concurrently with a transition to regional extension. Emplacement of such widespread dikes during the late evolution of a subcaldera batholith could generate earthquakes and trigger dispersed small eruptions. Such events would constitute little-appreciated magmato-tectonic hazards near dormant calderas such as Valles, Long Valley, or Yellowstone (western USA).
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Hafidhah Nurul Haq, Mega Fatimah Rosana, Cipta Endyana, Katon Sena Ajie Nugraha, and Irpan Alamsyah. "Geochemistry of Igneous Rocks of Citirem Formation and Its Implications for the Tectonic Setting in Ciletuh – Palabuhanratu UNESCO Global Geopark Area." Journal of Geoscience, Engineering, Environment, and Technology 9, no. 1 (March 28, 2024): 58–68. http://dx.doi.org/10.25299/jgeet.2024.9.1.14367.
Повний текст джерелаАнотація:
The igneous rocks of the Citirem Formation in the Ciletuh – Palabuhanratu UNESCO Global Geopark area petrographically not only consist of basalt, but also andesite, dacite, and gabbro. The characteristics of basalts Citirem Formation are composed of plagioclase 43% – 58% and olivine, mostly have amygdaloidal and aphanitic textures. Andesites are composed of 45% – 65% plagioclase, absence of olivine, mostly aphanitic and trachytic, some have intergranular textures. Dacite comprises 50% plagioclase, 20% quartz, and the absence of olivine, and aphanitic, intersertal textures. Gabbros are composed of 62% plagioclase, 6% – 12% olivine, with phaneritic texture. Based on the plot of the major elements vs SiO2 diagram, MgO, FeOt (Fe2O3+FeO), CaO, and TiO2 show a negative correlation with SiO2. In comparison, Na2O and K2O show a positive correlation with SiO2. The lithology of igneous rocks of Citirem Formation are basalt, trachybasalt, basaltic trachyandesite, trachyandesite, andesite, dacite and gabbro based on a plot of the Na2O+K2O vs SiO2 diagram for volcanic and plutonic rocks. The origin of magma type can be distinguished based on the plot of K2O vs SiO2 diagrams, the igneous rocks of Citirem Formation are divided into low-K, medium-K, high-K, and shoshonite magma series. Dacite STA 2, andesite STA 7, basaltic andesite STA 8, trachyandesite STA 10 and gabbro STA 14 are calc-alkaline based on triangular diagram Th-Hf-Ta-Zr-Nb. Gabbro STA 17 indicates IAT (island arc tholeiite), trachybasalt STA 19, basalt STA 20 and basaltic trachyandesite STA 27 are E-MORB, WPT (within plate tholeiitic), In contrast, trachybasalt STA 28 is WPA (within plate alkali). Primitive mantle long, NMORB-normalized REE patterns and chondrites-normalized show some rocks have distinctive patterns that have similarities with suprasubduction zone ophiolite rocks, MORB of Mirdita ophiolite, and some show similarities with patterns from OIB and E-MORB.
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Wen-Ge, Zhou, Xie Hong-Sen, Zhao Zhi-Dan, and Guo Jie. "Garnet Growth in the Early Stage of Trachybasalt-Eclogite Transformation." Chinese Physics Letters 18, no. 11 (October 10, 2001): 1500–1503. http://dx.doi.org/10.1088/0256-307x/18/11/324.
Повний текст джерелаДисертації з теми "Trachybasalte"
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Desgrolard, Franck. "Pétrologie des laves d'un volcan intraplaque océanique : le Karthala, île de la Grande-Comore (R.F.I. des Comores)." Phd thesis, Grenoble 1, 1996. http://www.theses.fr/1996GRE10109.
Повний текст джерелаАнотація:
La Grande-Comore est la plus grande île d'un archipel localisé dans le canal de Mozambique sur une croûte dont la littérature permet de suggérer une nature océanique. Le Karthala est le principal volcan bouclier de l'île, il est le seul dont on connaisse l'activité historique, qui se localise essentiellement le long de deux rifts zones et à leur intersection dans la caldeira sommitale. Un volcanisme ancien forme le massif du Badiner situé à son extrémité sud. Le faible degré de sous-saturation en silice et les compositions de ses laves nous indiquent qu'elles sont essentiellement le produit d'un degré de fusion partielle identique affectant une source unique ou le phlogopite et le grenat sont plus ou moins résiduels. Un modèle géophysique basé sur les taux de production magmatique des panaches mantelliques, ainsi que l'utilisation de résultats expérimentaux à hautes pressions, confirment une pression de fusion partielle élevée comprise entre 24 et 33 kbar. Les laves faiblement alcalines à transitionnelles des différents stades d'édification du Karthala ont des paragenèses variées : basaltes à olivine, océanites, ankaramites et basaltes à phénocristaux de plagioclase, qui témoignent de la diversité des processus de différenciation en jeu. L'évolution des compositions de ces laves nous a permis de mettre en évidence l'existence de deux chambres magmatiques distinctes. L'une profonde localisée à une profondeur d'environ 30 km (10 kbar), ou les liquides basaltiques subissent un fractionnement wehrlitique plus ou moins important à l'origine d'un enrichissement précoce en incompatibles. L'autre plus superficielle, localisée à la base de l'édifice volcanique, ou des fractionnements principalement océanitique et clinopyroxénitique, ainsi que gabbroïque à moindre échelle, ne leur font atteindre qu'un faible stade de différenciation (hawaiites et trachy-basaltes). (Doc Thèses)
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NAZZARI, Manuela. "Unravelling the effect of undercooling on (dis)equilibrium textures and compositions of basaltic magmas." Doctoral thesis, 2020. http://hdl.handle.net/11573/1340948.
Повний текст джерелаАнотація:
Undercooling and crystallization kinetics are recognized increasingly as important processes controlling the final textures and compositions of minerals as well as the physicochemical state of magmas during ascent and emplacement. Within a single volcanic unit, phenocrysts, microphenocrysts and microlites can span a wide range of compositions, develop complex zoning patterns, and show intricate textures testifying to crystallization far from equilibrium. These petrographic complexities are not associated necessarily with magma chamber processes such as mixing or mingling of distinctly different bulk compositions but, rather, may be caused by kinetic effects controlling the crystal growth and magma evolution. Heat-dissipation and decompression are the most effective driving forces of cooling and volatile loss that, in turn, exert a primary control on the solidification path of the bulk system (i.e., crystal and melt). Understanding these kinetic aspects over the temporal and spatial scales at which volcanic processes occur is therefore essential to interpret correctly the time-varying environmental conditions recorded in igneous minerals. This PhD thesis aims to summarize and integrate experimental and natural studies pertaining to the crystallization of magmas along kinetic or time-dependent pathways, where solidification is driven by changes in temperature, pressure and volatile concentration. Fundamental concepts examined in the last decades include the effect of undercooling on crystal nucleation and growth, as well as on the transition between interface- and diffusion-controlled crystal growth and mass transfer occurring after crystals stop growing. In this thesis, static and dynamic crystallization processes are investigated for natural trachybasaltic-trachyandesitic products typically of the magmatic activity at Mt. Etna volcano (Sicily, Italy). By decoding the textural and compositional information within crystalline phases, it is possible to place quantitative constraints on the crustal transport, ascent and emplacement histories of erupted magmas. Here, I present a collection of three papers that has been published in some of the most respected peer-reviewed journals for mineralogy, petrology, geochemistry and volcanology, i.e., Chemical Geology (first paper), Geochimica et Cosmochimica Acta (second paper) and Minerals (third paper). More specifically, magma crystallization under dynamic conditions has been assessed through isothermal time-series experiments on clinopyroxene, illustrated in the first paper reported in the following thesis. In this work a variety of departures from polyhedral growth, including morphologies indicating crystal surface instability, dendritic structures, sector zoning and growth twins are linked to the rate at which crystals grow. These have implications for the entrapment of melt inclusions and plausibility for interpreting the growth chronology of individual crystals. In the second paper, deviation from chemical equilibrium, developed in response to kinetically controlled cation redistributions and related to the partitioning of major and trace elements between clinopyroxene and melt, has been evaluated by the analysis of hourglass sector-zoned phenocrysts based on equilibrium and thermodynamic principles. In the third paper, the crystallization conditions of a sill-like intrusion at Mt. Etna volcano have been elucidated by integrating major cation exchanges in clinopyroxene, plagioclase and titanomagnetite, thereby providing decompression, degassing and geospeedometric constrains on the emplacement conditions of magma. All the aforementioned papers were carried out in team, but I have contributed either in designing and performing both the experiments and analyses, or in interpreting the acquired data and in writing the original manuscripts.
Книги з теми "Trachybasalte"
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Mathis, Allyson C. Geology and petrology of a 26-Ma trachybasalt to peralkaline rhyolite suite exposed at Hart Mountain, southern Oregon. 1993.
Знайти повний текст джерелаЧастини книг з теми "Trachybasalte"
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"trachybasalt." In Dictionary Geotechnical Engineering/Wörterbuch GeoTechnik, 1416. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-41714-6_202108.
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"Trachybasalt m." In Wörterbuch GeoTechnik/Dictionary Geotechnical Engineering, 1141. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-33335-4_201509.
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Smith, Alan L., M. John Roobol, Glen S. Mattioli, George E. Daly, and Joan E. Fryxell. "Providencia Island: A Miocene Stratovolcano on the Lower Nicaraguan Rise, Western Caribbean—A Geological Enigma Resolved." In Providencia Island: A Miocene Stratovolcano on the Lower Nicaraguan Rise, Western Caribbean—A Geological Enigma Resolved, 1–101. Geological Society of America, 2021. http://dx.doi.org/10.1130/2021.1219(01).
Повний текст джерелаАнотація:
ABSTRACT The Providencia island group comprises an extinct Miocene stratovolcano located on a shallow submarine bank astride the Lower Nicaraguan Rise in the western Caribbean. We report here on the geology, geochemistry, petrology, and isotopic ages of the rocks within the Providencia island group, using newly collected as well as previously published results to unravel the complex history of Providencia. The volcano is made up of eight stratigraphic units, including three major units: (1) the Mafic unit, (2) the Breccia unit, (3) the Felsic unit, and five minor units: (4) the Trachyandesite unit, (5) the Conglomerate unit, (6) the Pumice unit, (7) the Intrusive unit, and (8) the Limestone unit. The Mafic unit is the oldest and forms the foundation of the island, consisting of both subaerial and subaqueous lava flows and pyroclastic deposits of alkali basalt and trachybasalt. Overlying the Mafic unit, there is a thin, minor unit of trachyandesite lava flows (Trachyandesite unit). The Breccia unit unconformably overlies the older rocks and consists of crudely stratified breccias (block flows/block-and-ash flows) of vitrophyric dacite, which represent subaerial near-vent facies formed by gravitational and/or explosive dome collapse. The breccias commonly contain clasts of alkali basalt, indicating the nature of the underlying substrate. The Felsic unit comprises the central part of the island, composed of rhyolite lava flows and domes, separated from the rocks of the Breccia unit by a flat-lying unconformity. Following a quiescent period, limited felsic pyroclastic activity produced minor valley-fill ignimbrites (Pumice unit). The rocks of Providencia can be geochemically and stratigraphically subdivided into an older alkaline suite of alkali basalts, trachybasalts, and trachyandesites, and a younger subalkaline suite composed dominantly of dacites and rhyolites. Isotopically, the alkali basalts together with the proposed tholeiitic parent magmas for the dacites and rhyolites indicate an origin by varying degrees of partial melting of a metasomatized ocean-island basalt–type mantle that had been modified by interaction with the Galapagos plume. The dacites are the only phenocryst-rich rocks on the island and have a very small compositional range. We infer that they formed by the mixing of basalt and rhyolite magmas in a lower oceanic crustal “hot zone.” The rhyolites of the Felsic unit, as well as the rhyolitic magmas contributing to dacite formation, are interpreted as being the products of partial melting of the thickened lower oceanic crust beneath Providencia. U-Pb dating of zircons in the Providencia volcanic rocks has yielded Oligocene and Miocene ages, corresponding to the ages of the volcanism. In addition, some zircon crystals in the same rocks have yielded both Proterozoic and Paleozoic ages ranging between 1661 and 454 Ma. The lack of any evidence of continental crust beneath Providencia suggests that these old zircons are xenocrysts from the upper mantle beneath the Lower Nicaraguan Rise. A comparison of the volcanic rocks from Providencia with similar rocks that comprise the Western Caribbean alkaline province indicates that while the Providencia alkaline suite is similar to other alkaline suites previously defined within this province, the Providencia subalkaline suite is unique, having no equivalent rocks within the Western Caribbean alkaline province.
Тези доповідей конференцій з теми "Trachybasalte"
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Calzia, J. P., O. Tapani Rämö, and D. E. Champion. "PETROLOGY AND ORIGIN OF 2.1 KA TRACHYBASALT AT UBEHEBE CRATERS, DEATH VALLEY, CA." In 112th Annual GSA Cordilleran Section Meeting. Geological Society of America, 2016. http://dx.doi.org/10.1130/abs/2016cd-274532.
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