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Статті в журналах з теми "Bimodal volcanism"
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Ludden, John, Claude Hubert, and Clement Gariépy. "The tectonic evolution of the Abitibi greenstone belt of Canada." Geological Magazine 123, no. 2 (March 1986): 153–66. http://dx.doi.org/10.1017/s0016756800029800.
Повний текст джерелаАнотація:
AbstractBased on structural, geochemical, sedimentological and geochronological studies, we have formulated a model for the evolution of the late Archaean Abitibi greenstone belt of the Superior Province of Canada. The southern volcanic zone (SVZ) of the belt is dominated by komatiitic to tholeiitic volcanic plateaux and large, bimodal, mafic-felsic volcanic centres. These volcanic rocks were erupted between approximately 2710 Ma and 2700 Ma in a series of rift basins formed as a result of wrench-fault tectonics.The SVZ superimposes an older volcanic terrane which is characterized in the northern volcanic zone (NVZ) of the Abitibi belt and is approximately 2720 Ma or older. The NVZ comprises basaltic to andesitic and dacitic subaqueous massive volcanics which are cored by comagmatic sill complexes and layered mafic-anorthositic plutonic complexes. These volcanics are overlain by felsic pyroclastic rocks that were comagmatic with the emplacement of tonalitic plutons at 2717 ±2 Ma.The tectonic model envisages the SVZ to have formed in a series of rift basins which dissected an earlier formed volcanic arc (the NVZ). Analogous rift environments have been postulated for the Hokuroko basin of Japan, the Taupo volcanic zone of New Zealand and the Sumatra and Nicaragua arcs. The difference between rift related ‘submergent’ volcanism in the SVZ and ‘emergent’ volcanism in the NVZ resulted in the contrasting metallogenic styles, the former being characterized by syngenetic massive sulphide deposits, whilst the latter was dominated by epigenetic ‘porphyry-type’ Cu(Au) deposits.
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KEPPIE, J. D., J. DOSTAL, J. B. MURPHY, and B. L. COUSENS. "Palaeozoic within-plate volcanic rocks in Nova Scotia (Canada) reinterpreted: isotopic constraints on magmatic source and palaeocontinental reconstructions." Geological Magazine 134, no. 4 (July 1997): 425–47. http://dx.doi.org/10.1017/s001675689700719x.
Повний текст джерелаАнотація:
Palaeozoic volcanism in the Avalon Terrane of northern Nova Scotia occurred during three time intervals: Cambrian–early Ordovician, late Ordovician–early Silurian and middle–late Devonian. In the Meguma Terrane of southern Nova Scotia, Palaeozoic volcanism is limited to the middle Ordovician. Geochemical data show that most of these volcanic rocks are bimodal, within-plate suites. Initial εNd signatures range from +5.4 to −1.9 in the rhyolites and +6.8 to +2.7 in the basalts, a difference attributable to the absence or presence, respectively, of a significant crustal component. The data and regional tectonic settings of the Avalon and Meguma terranes suggest that the volcanism was generated in three different within-plate settings: (1) Cambrian–early Ordovician volcanism related to thermal decay of late Proterozoic arc magmatism during transtensional deformation; (2) middle Ordovician–early Silurian volcanism during sinistral telescoping between Laurentia and Gondwana where extensional bends in the Appalachians produced rifting; and (3) Devonian volcanism resulting from lithospheric delamination during dextral transpression and telescoping. In each setting, active faults served as conduits for the magmas. Nd isotopic data indicate that the source of the Palaeozoic felsic volcanic rocks is isotopically indistinguishable beneath southern and northern Nova Scotia and did not substantially change with time. This crustal source appears to have separated from the mantle during the Proterozoic, a conclusion consistent with the hypothesis that the Palaeozoic rocks in Nova Scotia were deposited upon a late Proterozoic oceanic–cratonic volcanic arc terrane. The Nd data, when combined with published faunal, palaeomagnetic and U–Pb isotopic data, suggest that the Avalon Terrane was peripheral to Gondwana off northwestern South America during Neoproterozoic and early Palaeozoic times.
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AWDANKIEWICZ, MAREK, RYSZARD KRYZA, and NORBERT SZCZEPARA. "Timing of post-collisional volcanism in the eastern part of the Variscan Belt: constraints from SHRIMP zircon dating of Permian rhyolites in the North-Sudetic Basin (SW Poland)." Geological Magazine 151, no. 4 (September 12, 2013): 611–28. http://dx.doi.org/10.1017/s0016756813000678.
Повний текст джерелаАнотація:
AbstractThe final stages of the Variscan orogeny in Central Europe were associated with voluminous granitic plutonism and widespread volcanism. Four samples representative of the main rhyolitic volcanic units from the Stephanian–Permian continental succession of the North-Sudetic Basin, in the eastern part of the Variscan Belt, were dated using the SIMS (SHRIMP) zircon method. Three samples show overlapping206Pb–238U mean ages of 294 ± 3, 293 ± 2 and 292 ± 2 Ma, and constrain the age of the rhyolitic volcanism in the North-Sudetic Basin at 294–292 Ma. This age corresponds to the Early Permian – Sakmarian Stage and is consistent with the stratigraphic position of the lava units. The fourth sample dated at 288 ± 4 Ma reflects a minor, younger stage of (sub)volcanic activity in the Artinskian. The silicic activity was shortly followed by mafic volcanism. The rhyolite samples contained very few inherited zircons, possibly owing to limited contribution of crustal sources to the silicic magma, or owing to processes involved in anatectic melting and magma differentiation (e.g. resorption of old zircon by Zr-undersaturated melts). The SHRIMP results and the stratigraphic evidence suggest that the bimodal volcanism terminated the early, short-lived (10–15 Ma) and vigorous stage of basin evolution. The Permian volcanism in the North-Sudetic Basin may be correlated with relatively late phases of the regional climax of Late Palaeozoic volcanism in Central Europe, constrained by 41 published SHRIMP zircon age determinations at 299–291 Ma. The Permian volcanism and coeval plutonism in the NE part of the Bohemian Massif can be linked to late Variscan, post-collisional extension.
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McDOUGALL, IAN, and FRANCIS H. BROWN. "Timing of volcanism and evolution of the northern Kenya Rift." Geological Magazine 146, no. 1 (September 19, 2008): 34–47. http://dx.doi.org/10.1017/s0016756808005347.
Повний текст джерелаАнотація:
AbstractThe northern Kenya Rift is bounded on the west by uplands of Turkana which comprise horst-like blocks that include metamorphic basement rocks, locally overlain unconformably by the Cretaceous Lubur Sandstone, in turn overlain by predominantly volcanic sequences in which relatively thin sedimentary packages occur. Amphibolite facies crystalline rocks of the basement yield Early Palaeozoic K–Ar cooling ages reflecting the Pan-African Orogeny. Volcanism in Turkana was initiated through voluminous eruptions of transitional tholeiitic basalts commencing about 36 Ma ago in the Late Eocene, with some evidence for concomitant rhyolitic volcanism. Volcanism became dominantly rhyolitic in the interval from about 27 to 23 Ma ago, but remained bimodal as basaltic lavas are also known from this period. From about 19 to 15 Ma or younger, basaltic volcanism again dominated, often alkaline in nature, with thin but significant sedimentary sequences interleaved that have yielded important vertebrate faunal assemblages. Parallels exist between the volcanic history recorded in Turkana and that found in the Nabwal Hills east of Lake Turkana. In the southern Turkana region, oil exploration by seismic methods and deep drill holes has shown the existence of northerly-trending half-graben with up to 7 km of fill, and that these developed from at least Oligocene and possibly Late Eocene times. This suggests that the widespread basaltic volcanism at about 36 Ma ago (Late Eocene) heralds an earlier initiation of the Kenya Rift in northern Kenya than most workers have previously suggested.
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Ludman, Allan, Christopher McFarlane, and Amber T. H. Whittaker. "Age, chemistry, and tectonic setting of Miramichi terrane (Early Paleozoic) volcanic rocks, eastern and east-central Maine, USA." Atlantic Geology 57 (November 11, 2021): 239–73. http://dx.doi.org/10.4138/atlgeol.2021.012.
Повний текст джерелаАнотація:
Volcanic rocks in the Miramichi inlier in Maine occur in two areas separated by the Bottle Lake plutonic complex: the Danforth segment (Stetson Mountain Formation) north of the complex and Greenfield segment to the south (Olamon Stream Formation). Both suites are dominantly pyroclastic, with abundant andesite, dacite, and rhyolite tuffs and subordinate lavas, breccias, and agglomerates. Rare basaltic tuffs and a small area of basaltic tuffs, agglomerates, and lavas are restricted to the Greenfield segment. U–Pb zircon geochronology dates Greenfield segment volcanism at ca. 469 Ma, the Floian–Dapingian boundary between the Lower and Middle Ordovician. Chemical analyses reveal a calc-alkaline suite erupted in a continental volcanic arc, either the Meductic or earliest Balmoral phase of Popelogan arc activity. The Maine Miramichi volcanic rocks are most likely correlative with the Meductic Group volcanic suite in west-central New Brunswick. Orogen-parallel lithologic and chemical variations from New Brunswick to east-central Maine may result from eruptions at different volcanic centers. The bimodal Poplar Mountain volcanic suite at the Maine–New Brunswick border is 10–20 myr younger than the Miramichi volcanic rocks and more likely an early phase of back-arc basin rifting than a late-stage Meductic phase event. Coeval calc-alkaline arc volcanism in the Miramichi, Weeksboro–Lunksoos Lake, and Munsungun Cambrian–Ordovician inliers in Maine is not consistent with tectonic models involving northwestward migration of arc volcanism. This >150 km span cannot be explained by a single east-facing subduction zone, suggesting more than one subduction zone/arc complex in the region.
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Leat, P. T., and R. S. Thorpe. "Ordovician volcanism in the Welsh Borderland." Geological Magazine 123, no. 6 (November 1986): 629–40. http://dx.doi.org/10.1017/s0016756800024146.
Повний текст джерелаАнотація:
AbstractBasaltic, andesitic and rhyodacitic/rhyolitic volcanism was widespread during Ordovician time in the Welsh Basin. New chemical data are presented for Llanvirn to Caradoc lavas and tuffs from the Welsh Borderland which, during Ordovician time, formed the southeastern margin of the Welsh Basin. In view of the observed chemical alteration, immobile elements are used in the interpretation of the original geochemical character. The data indicate that the Llanvirn Stapeley volcanic group of the Shelve inlier was a bimodal basalt/basaltic andesite – rhyodacite/rhyolite association. The basalts have trace element contents of tholeiitic associations with a subduction-related character. The Caradoc Whittery and Hagley volcanic groups of the Shelve inlier comprise lavas and tuffs of calc-alkaline andesite. Blocks sampled from the Breidden Hills show that these were also derived from a calc-alkaline volcano. Associated Caradoc pumice- and ash-flow deposits from the Breidden Hills are probably of altered calc-alkaline rhyodacite/rhyolite composition. The Sibdon Carwood basalt flow, the only known example of Ordovician volcanism east of the Pontesford–Linley and Church Stretton lineaments, has transitional tholeiitic to alkaline character, with trace element contents influenced by subduction-related processes. The overall tholeiitic to calc-alkaline nature of the magmatism is consistent with the view that, during Llanvirn to Caradoc time, the Welsh Basin was an ensialic marginal basin.
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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.
Повний текст джерелаАнотація:
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.
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Van Wagoner, Nancy A., Matthew I. Leybourne, Kelsie A. Dadd, and Miranda LA Huskins. "The Silurian(?) Passamaquoddy Bay mafic dyke swarm, New Brunswick: petrogenesis and tectonic implications." Canadian Journal of Earth Sciences 38, no. 11 (November 1, 2001): 1565–78. http://dx.doi.org/10.1139/e01-041.
Повний текст джерелаАнотація:
The volcanic and sedimentary rocks of the Passamaquoddy Bay (PB) area of southeastern New Brunswick are part of the SilurianDevonian Coastal Volcanic Belt (CVB), an extensive belt of bimodal volcanic rocks. The PB sequence is 4 km thick, has four cycles of mafic and felsic volcanism, and is intruded by mafic dykes at all levels. There are two ages of dykes, those related to the Late Silurian PB volcanism (PB dykes) and Mesozoic dykes (the Minister Island Dyke) related to the opening of the North Atlantic. The PB mafic dykes are subalkalic basalt to basaltic andesite, within-plate tholeiites. The dykes are moderately to highly evolved (Mg# = 66.6 to 26.6), with trends of major and trace elements typical of the fractionation of olivine, pyroxene, plagioclase, and ilmenite. The PB mafic dyke swarm comprises over 155 dykes which represent a greater range of compositions than the associated flows, suggesting that they give a more complete representation of the Late Silurian PB mafic magmas. They exhibit incompatible element characteristics best accounted for by crustal contamination. The dykes plot on a linear array away from mantle mixing lines between depleted and enriched mantle sources and toward the composition of the PB felsic units, suggesting that these felsic units are representative of partial melts and fractionates of the source contaminate. The variable TiO2 contents (1.24.3 wt.%) and incompatible element ratio trends plotted against a fractionation index suggest that mantle metasomatism, either fluid or melt derived, may also have influenced the mantle source of the dykes. The dykes dip steeply and have a relatively consistent strike to the north. Most dykes range in thickness from 0.5 to 2 m, but range up to 9 m. The single orientation of the dykes, along with their chemical characteristics and volume, and association with a bimodal intraplate volcanic sequence, are consistent with an extensional tectonic setting. Constraints of the regional geology suggest that this extension was associated with convergence, perhaps in a back-arc setting.
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Mazzarini, Francesco, Giacomo Corti, Piero Manetti, and Fabrizio Innocenti. "Strain rate and bimodal volcanism in the continental rift: Debre Zeyt volcanic field, northern MER, Ethiopia." Journal of African Earth Sciences 39, no. 3-5 (June 2004): 415–20. http://dx.doi.org/10.1016/j.jafrearsci.2004.07.025.
Повний текст джерела
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Murphy, J. B., K. Cameron, J. Dostal, J. Duncan Keppie, and A. J. Hynes. "Cambrian volcanism in Nova Scotia, Canada." Canadian Journal of Earth Sciences 22, no. 4 (April 1, 1985): 599–606. http://dx.doi.org/10.1139/e85-059.
Повний текст джерелаАнотація:
Cambrian volcanic rocks in Nova Scotia occur in small grabens or half grabens in the Avalon Zone (Composite Terrane) as part of a thin sequence of continental to shallow-marine Cambro-Ordovician rocks. In the northern Antigonish Highlands, the volcanic rocks occur mainly in the Lower Cambrian McDonalds Brook Group. In southern Cape Breton Island, they occur predominantly in the Middle Cambrian Bourinot Group. The chemistry of these volcanic rocks indicates that they are bimodal (basalts–rhyolites) and within plate. The basalts are alkalic in the Antigonish Highlands and tholeiitic in Cape Breton Island. The rising basaltic magma is postulated to have produced the felsic magma by anatexis of the crust. It is proposed that the Antigonish Highlands volcanic rocks erupted in a small pull-apart basin. A similar structural setting is probable in southern Cape Breton Island, but there the bounding faults are poorly exposed. These basins probably formed during a period of transpression in the last stages of the late Hadrynian Cadomian deformation.
Дисертації з теми "Bimodal volcanism"
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Lindsey, Meghan Marie. "Detailed Stratigraphy and Geochemistry of Lower Mount Rogers Formation Metavolcanic Units Exposed on Elk Garden Ridge, VA." Scholar Commons, 2009. https://scholarcommons.usf.edu/etd/1698.
Повний текст джерелаАнотація:
The lower Mount Rogers Formation (LMRF) is described by Rankin (1993) as a sequence of intercalated metabasalts and volcanogenic sediments with minor metarhyolite. We have chosen to examine the sequence of the LMRF units exposed along Elk Garden Ridge, a high shoulder between the summits of Whitetop Mountain and Mount Rogers in the Mount Rogers National Recreation Area in SW Virginia. This sequence represents an uplifted block of LMRF units enclosed by exposures of Whitetop and Wilburn metarhyolites.
In the field, progressive lithologic changes can be observed walking up-section along Elk Garden ridge that are indicative of changes in lava compositions and eruptive environments. From the bottom of the section, massive basalts with distinctive 1-2 cm long swallowtail plagioclase phenocrysts grade into vesicular basalts, then into sheet flow basalts, followed by a thick sequence of aphyric and amygdaloidal pillow basalts. Further up section, eruptive products transition into rhyolitic ignimbrites and ash and lapilli tuffs. Boulders of cobble conglomerates near the middle of the sequence and sedimentary layers in between individual sheet flows suggest short periods of relative eruptive quiescence. The only unit broken out in the LMRF by Rankin (1993), Fees Rhyolite, is not observed in the field area, suggesting local differences in topography, eruptive products and eruptive styles across the outcrop area during the deposition of these eruptive products.
Petrographically, the rocks reflect the regional greenschist facies metamorphic conditions with chlorite and epidote as primary metamorphic minerals, and unakite-like zones of mineralization. Relict plagioclase and pyroxene phenocrysts persist, as do primary igneous textures and structures. Compositionally, all of the rocks in the Elk Garden Ridge sequence are strongly enriched in alkali metals, with elevated Na2O and K2O contents, and high TiO2 in the basalts. Major and trace element systematics suggest that the chemical signatures of the metabasalts are primary controlled by shallow-level crystallization processes. The LMRF metabasalts share many compositional affinities with later (~570 Ma) rift-related basalts preserved in the Appalachians, suggesting that all of these lavas were formed by melting of a compositionally uniform mantle source, followed by shallow crystallization, despite being separated from one another by large stretches of time and space.
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Higgie, D. R. "Tectonic provenance of the Palaeoproterozoic Plum Tree Volcanics: implications for the initiation of the McArthur Basin." Thesis, 2018. http://hdl.handle.net/2440/130627.
Повний текст джерелаАнотація:
This item is only available electronically.The Palaeoproterozoic (1825 ±4Ma) Plum Tree Volcanics are a bimodal suite of basalt and rhyolite lavas forming part of the fluvial conglomerate-sandstone sequence of the upper Edith River Group. They are preserved in remnants unconformably overlying the Pine Creek Orogen north of Katherine in the Edith River, Mt Callanan and Birdie Creek Basins. These sequences directly post-date the convergent deformation of the Pine Creek Orogen and mark the beginning of the extensional regime that initiated the McArthur Basin. The tectonic setting of the Plum Tree volcanism, whether divergent intraplate rift or mantle hotspot, may suggest how the formation of the McArthur Basin began and provide insight into how the Pine Creek Orogen compression ceased. In this paper, geochemical methods were used to determine the tectonic setting of the Plum Tree Volcanics. Whole rock geochemical data were collected via XRF, ICP-MS and ICP-OES. Nd-Sm and Sr isotopic data were collected via column chromatography and TIMS. Petrographic data were collected via optical petrography. Radiogenic Sr (87Sr/86Sr= ~0.708) and non-radiogenic Nd (εNd(i)= -6 to -8) isotopes suggest a crustal component in melt evolution. Modelling of melt evolution by pure fractional crystallisation presents well-fitting liquid lines of descent, suggesting a fractional crystallisation driven melt evolution. Tholeiitic basalts and trace element geochemistry suggests a mantle derived melt driven by a mantle plume and intraplate continental rifting. Modelling of AFC processes suggest a lower crust sourced assimilant. Ambiguous basalt geochemistry supports a continental rift derived melt and an oxygen fugacity of FMQ -1 suggests a primitive, reduced melt reflecting a mantle parent. Optical petrography presents a plagioclase and clinopyroxene rich mineral assemblage reflecting a mantle parent.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2018
Книги з теми "Bimodal volcanism"
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Szary, William A. Geology of the Central and Eastern Snake River Plain Part I : : Bimodal Volcanics. Independently Published, 2021.
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Jovic, Sebastián Miguel. Geología y metalogénesis de las mineralizaciones polimetálicas del área El Tranquilo (Cerro León), sector central del Macizo del Deseado, provincia de Santa Cruz. Editorial de la Universidad Nacional de La Plata (EDULP), 2010. http://dx.doi.org/10.35537/10915/4346.
Повний текст джерелаАнотація:
La presente investigación tiene como eje principal el estudio detallado de las mineralizaciones y la geología de un área del Macizo del Deseado con características geológicas y metalogénicas únicas. La elección del área del El Tranquilo o también conocido como “anticlinal” El Tranquilo, como zona de estudio, se ha basado en el reducido conocimiento y la presencia características atípicas en las mineralizaciones y la escasa representación, en el Macizo del Deseado, de las rocas y unidades geológicas aflorantes. La investigación ha sido realizada en tres etapas: una primera con recopilación de antecedentes y trabajo de campo, una segunda analítica con trabajos de laboratorio y una tercera etapa interpretativa. Se realizó el procesado de imágenes satelitales (TM, SPOT, IKONOS) y se ejecutaron mapeos geológico-estructurales de detalle y semidetalle (con elaboración de una cartografía digital), descripción de testigos de sondeos (gran parte de los 30.000 metros de las perforaciones ejecutadas en la propiedad minera), se realizaron estudios petrográficos, calcográficos, de rayos X, determinaciones geoquímicas, estudios de inclusiones fluidas, de microscopía electrónica, microsonda electrónica, determinaciones geocronológicas y análisis de isótopos estables e inestables. Además se participó de otros trabajos complementarios realizados durante las distintas etapas de exploración minera, tales como geoquímica de suelos, muestras de trincheras y relevamientos magnetométricos y geoeléctricos terrestres y la interpretación, para la zona de trabajo, de estudios previos de magnetometría aérea y líneas sísmicas. El área del “anticlinal” El Tranquilo, está caracterizada por la presencia de rocas y unidades geológicas con escasa representación en el Macizo del Deseado, y representa una “ventana geológica” que permite el estudio del intervalo Triásico superior - Jurásico inferior, períodos que se encuentran poco expuestos en esta provincia geológica. La secuencia estratigráfica de este sector se inicia con las sedimentitas continentales, areniscas a areniscas conglomerádicas con intercalaciones de pelitas, del Grupo El Tranquilo, del Triásico medio a superior (Jalfin y Herbst 1995). Por encima, se presentan las rocas volcaniclásticas de la Formación Roca Blanca (Herbst, 1965), del Jurásico inferior. Esta es la litología más desarrollada en el área y está compuesta por tufitas, areniscas y sabulitas ricas en componentes volcánicos. Intruyendo a las sedimentitas continentales y a las tufitas, se disponen rocas básicas a intermedias del Jurásico inferior, que se presentan como filones capa de diabasa en el sector este del área y como pórfidos andesíticos de formas subcirculares en el sector noroeste, de la Formación Cerro León (Panza, 1995 y de Barrio et al., 1999). En los sectores norte y noreste del área afloran volcánitas del Jurásico medio a superior, basaltos y andesitas de la Formación Bajo Pobre, y en el sector sudoriental pequeños asomos de ignimbritas riolíticas del Grupo Bahía Laura (Panza, 1995). Estas unidades se encuentran parcialmente cubiertas por el Basalto Las Mercedes del Cretácico superior y el Basalto Cerro del Doce correspondiente al Eoceno (Panza, 1982) y finalizan esta secuencia sedimentos modernos, aluviales, coluviales y de bajos. En la presente investigación se determinó la presencia de niveles ignimbríticos ácidos y coladas basálticas intercaladas en las tufitas de la Formación Roca Blanca. A partir de las edades obtenidas, relaciones estratigráficas y composición se desvincula a los intrusivos dioríticos de la Formación Cerro León y se los asocia con el magmátismo de la Formación La Leona (Jurásico inferior). Los basaltos aflorantes en el área presentan características de basaltos continentales que se corresponden a los primeros indicios del magmatismo sinextensional jurásico y representan magmas básicos de origen mantélico que alcanzaron la superficie. Se los desvinculan de la Formación Bajo Pobre por ser ligeramente más antiguos al estar intercalados entre las tufitas de la Formación Roca Blanca (Jurásico inferior) y por presentar diferentes características isotópicas y petrogenéticas. Se define así una nueva unidad formacional para estas rocas denominándolas Formación El Piche. Los pórfidos andesíticos de la Formación Cerro León y las andesitas de la Formación Bajo Pobre presentan similitudes geoquímicas, isotópicas, petrogenéticas y edades semejantes, por lo que se interpreta un mismo origen para estas rocas, siendo los pórfidos andesíticos partes de los conductos de emisión de las coladas andesíticas. A diferencia del resto del Macizo del Deseado donde predomina casi por completo deformación con comportamiento netamente frágil, en el área de estudio se reconoció deformación tanto dúctil como frágil en las secuencias triásicas y jurásicas. Los rasgos estructurales más sobresalientes son: un domamiento regional de entre 15 a 20 km de diámetro, definido por Di Persia (1956) como “anticlinal” El Tranquilo, domamientos y plegamientos con dimensiones menores a 1 km localizados dentro de la antiforma regional, un sistema de fracturas radiales asociado al domamiento y la falla El Tranquilo con un sistema de vetas controladas por fallas. Se determinó que el “anticlinal” El Tranquilo, se formó por el emplazamiento de un cuerpo intrusivo no aflorante del orden de 8 a 10 Km de diámetro y profundidad mínima hasta su techo de 1400 m, subyaciendo al Grupo El Tranquilo y a la Formación Roca Blanca, y generando por su intrusión, el domamiento regional y los domamientos y plegamientos con dimensiones menores a 1 km localizados corresponde a una deformación producida por lacolitos o stocks no aflorantes. En el área de estudio se reconocieron gran cantidad de mineralizaciones, las que totalizan ~80 km lineales de vetas, ubicadas principalmente en el sector central del área. Las vetas se concentran hacia el este de la estructura regional, la falla El Tranquilo, son subparalelas a esta estructura y están emplazadas en las tufitas de la Formación Roca Blanca y pelitas y areniscas del Grupo El Tranquilo. Se han discriminado dos tipos distintos de vetas según su composición y expresión superficial, vetas formadas por importantes zonas de oxidación que representan la expresión superficial de vetas de sulfuros, y vetas, brechas hidrotermales, vetillas y stockworks formados principalmente por cuarzo. A partir de las distintas características observadas y datos obtenidos (composición, signatura geoquímica, mineralogía, datos de inclusiones fluidas, isótopos, controles estructurales y litológicos y edades) se ha podido diferenciar dos estilos de mineralización. La mineralización polimetálica que presenta una compleja mineralogía de sulfuros asociada a una signatura geoquímica de In, Cu, Au, As, Sn, W, Bi, Zn, Pb, Ag, Cd y Sb. Las temperaturas y salinidades de los fluidos indican un sistema epitermal para la formación de estas vetas. Su génesis esta vinculada a los cuerpos intrusivos dioríticos reducidos por sedimentos ricos en materia orgánica, concentrando en los fluidos hidrotermales In, Sn, Ag, W, Bi. Se define a esta mineralización como un depósito epitermal vetiforme polimetálico rico en In semejante a los depósitos de Japón y Bolivia. Las características de esta mineralización y la edad Jurásica inferior (193 Ma) confirman la presencia de un nuevo tipo de deposito epitermal que difiere del clásico modelo de baja sulfuración del Macizo del Deseado y que no se encuentra asociado al importante volcanismo bimodal del Jurásico medio a superior (Complejo Bahía Laura), como la mayoría de las mineralizaciones del Macizo del Deseado. Este hecho potencia el hallazgo de otros tipos de depósitos epitermales polimetálicos, asociados a otras rocas y con diferentes asociaciones metalogénicas. La mineralización argentífera está formada por cuarzo, carbonatos y en menor medida sulfuros y sulfosales con una signatura geoquímica de Ag (Au), Pb, Cu y Zn. Las temperaturas y salinidades de los fluidos indican un sistema epitermal para la formación de estas vetas. Su génesis está vinculada al magmatismo intermedio de las Formaciones Cerro León y Bajo Pobre, atribuyéndole una edad Jurásica media (168 Ma). Según sus características esta mineralización puede ser definida como un depósito epitermal de sulfuración intermedia. Esta mineralización también representa una variación en el modelo de baja sulfuración del Macizo del Deseado, pero está genéticamente asociada al volcanismo bimodal del Complejo Bahía Laura (Fm. Bajo Pobre) por lo que podría incluirse dentro de las mineralizaciones de la Provincia auroargéntifera del Deseado.
Частини книг з теми "Bimodal volcanism"
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Pahari, Arijit, and C. Manikyamba. "Arc–Back Arc Cohabitation and Associated Bimodal Volcanism: Evidence from Neoarchean Raichur Greenstone Belt, Eastern Dharwar Craton, India." In Geochemical Treasures and Petrogenetic Processes, 3–29. Singapore: Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-19-4782-7_1.
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Zhong, Fang, Xia Bang-Dong, Tao Xian-Cong, Li Hui-Min, Zhang Gen-De, and Li Hui-Min. "Twin Magma Source Model of Bimodal Volcanics in Two Continent–Margin Rifts, SE China: Constraints on Elemental and Nd–, Sr– and Pb–Isotopic Studies." In Igneous Petrology, 23–37. London: CRC Press, 2021. http://dx.doi.org/10.1201/9780429070877-3.
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Vrzhosek, Alexander A. "Late Permian bimodal volcanism in South Primorye." In Late Palaeozoic and Early Mesozoic Circum-Pacific Events and their Global Correlation, 106–8. Cambridge University Press, 1997. http://dx.doi.org/10.1017/cbo9780511564413.011.
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Michelfelder*, Gary S. "Petrology and volcanology of the Mesoproterozoic igneous rocks of the Saint Francois Mountains terrane, southeast Missouri, USA." In Field Excursions from the 2021 GSA Section Meetings, 253–89. Geological Society of America, 2021. http://dx.doi.org/10.1130/2021.0061(11).
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ABSTRACT The Saint Francois Mountains are the physiographic expression of the central part of the Ozark Dome of southeastern Missouri. The mountains are made up of a quaquaversal-dipping series of Paleozoic units cored by the Mesoproterozoic-aged rocks of the broader Saint Francois Mountains terrane. The Saint Francois Mountains terrane lies within the Eastern Granite-Rhyolite province along the eastern margin of Laurentia and contains at least four mapped caldera complexes (Eminence, Lake Killarney, Butler Hill, and Taum Sauk), associated volcanic and volcaniclastic rocks, and four distinct types of intrusive units. The Mesoproterozoic rocks represent two major pulses of magmatic activity: (1) an older 1.48–1.45 Ga episode of caldera-forming volcanism and associated subvolcanic to massif-type granitic intrusions; and (2) a younger 1.33–1.28 Ga episode of bimodal intrusions. Volcanism included primarily high-silica rhyolite and volcaniclastic sediments associated with caldera-forming volcanism with lesser amounts of basalt and basaltic andesite that formed as flows and subvolcanic intrusions. The older (ca. 1.4 Ga) intrusive rocks can be divided into three broad categories: (1) granite massifs including the Butler Hill/Breadtray massif-type granites, (2) caldera ring–type granites such as the Silvermine Granite, and (4) mafic- to intermediate-composition intrusive rocks such as the Silver Mines Mafic Series. The younger (ca. 1.3 Ga) bimodal intrusions are represented by the highly evolved felsic Graniteville-types granites and the gabbros of the Skrainka Mafic Group. This field guide provides an overview of the magmatic history of the Mesoproterozoic rocks exposed in the eastern Saint Francois Mountains. Field-trip stops are divided into two days, highlighting well-known stops and lesser-known localities that illustrate the magmatic activity of one the premier igneous locations in the midcontinent region. The field trip is focused on two main areas. Day 1 focuses on the rhyolite sequence and associated caldera-forming eruption of the Taum Sauk caldera. Day 2 focuses on the volcanic rocks and granitic intrusions related to the Butler Hill caldera and ends with a visit to one of the youngest granitoids in the terrane, the Graniteville Granite. The field guide presents a summary of the volcanic history and petrogenesis of the Saint Francois Mountains rhyolites and granites.
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Cahoon†, Emily B., Martin J. Streck†, and Mark Ferns†. "Flood basalts, rhyolites, and subsequent volcanism of the Columbia River magmatic province in eastern Oregon, USA." In From Terranes to Terrains: Geologic Field Guides on the Construction and Destruction of the Pacific Northwest, 301–52. Geological Society of America, 2021. http://dx.doi.org/10.1130/2021.0062(08).
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ABSTRACT The Miocene Columbia River Basalt Group (CRBG) is the youngest and smallest continental flood basalt province on Earth. This flood basalt province is a succession of compositionally diverse volcanic rocks that record the passage of the Yellowstone plume beneath eastern Oregon. The compositionally and texturally varied suite of volcanic rocks are considered part of the La Grande–Owyhee eruptive axis (LOEA), an ~300-km-long, north-northwest–trending, Middle Miocene to Pliocene volcanic belt that extends along the eastern margin of the Columbia River flood basalt province. Volcanic rocks erupted from and preserved within the LOEA form an important regional stratigraphic link between the flood basalt–dominated Columbia Plateau to the north, the north and bimodal basalt-rhyolite volcanic fields of the Snake River Plain to the east, the Owyhee Plateau to the south, and the High Lava Plains to the south and east; the latter two have time transgressive rhyolite centers that young to the east and west, respectively. This field-trip guide details a four-day geologic excursion that will explore the stratigraphic and geochemical relationships among mafic rocks of the CRBG and coeval and compositionally diverse silicic rocks associated with the early trace of the Yellowstone plume and High Lava Plains in eastern Oregon. The trip on Day 1 begins in Portland then traverses across the western axis of the Blue Mountains, highlighting exposures of the widespread, Middle Miocene Dinner Creek Welded Tuff and aspects of the Picture Gorge Basalt lava flows and northwest-striking feeder dikes situated in the central part of the CRBG province. Travel on Day 2 progresses eastward toward the eastern margin of the LOEA, examining a transition linking the Columbia River Basalt province with a northwestward-younging magmatic trend of silicic volcanism of the High Lava Plains in eastern Oregon. Initial field stops on Day 2 focus on the volcanic stratigraphy northeast of the town of Burns, which includes regionally extensive Middle to Late Miocene ash-flow tuffs and lava flows assigned to the Strawberry Volcanics. Subsequent stops on Day 2 examine key outcrops demonstrating the intercalated nature of Middle Miocene tholeiitic CRBG flood basalts, temporally coeval prominent ash-flow tuffs, and “Snake River–type” large-volume rhyolite lava flows cropping out along the Malheur River. The Day 3 field route navigates to southern parts of the LOEA, where CRBG rocks are associated in space and time with lesser known and more complex silicic volcanic stratigraphy forming Middle Miocene, large-volume, bimodal basalt-rhyolite vent complexes. Key stops will provide a broad overview of the structure and stratigraphy of the Middle Miocene Mahogany Mountain caldera and of the significance of intercalated sedimentary beds and Middle to Late Miocene calc-alkaline lava flows of the Owyhee basalt. Initial stops on Day 4 will highlight exposures of Middle to Late Miocene silicic ash-flow tuffs, rhyolite domes, and calc-alkaline lava flows overlying the CRBG across the northern and central parts of the LOEA. The later stops on Day 4 examine more silicic lava flows and breccias that are overlain by early CRBG-related rhyolite eruptions. The return route to Portland on Day 4 traverses the Columbia River gorge westward from Baker City. The return route between Baker and Portland on Day 4 follows the Columbia River gorge and passes prominent basalt outcrops of large volume tholeiitic flood lavas of the Grande Ronde, Wanapum, and Saddle Mountains Formations of the CRBG. These sequences of basaltic and basaltic andesite lavas are typical of the well-studied flood basalt dominated Columbia Plateau, and interbedded silicic and calc-alkaline lavas are conspicuously absent. Correlation between the far-traveled CRBG lavas and calcalkaline and silicic lavas considered during the excursion relies on geochemical fingerprinting and dating of the mafic flows and dating of sparse intercalated ashes.
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Dostal, Jaroslav, Pierre Jutras, and Reginald A. Wilson. "Geochemical and Nd isotopic constraints on the origin of uppermost Silurian rhyolitic rocks in the northern Appalachians (northern New Brunswick): Tectonic implications." In New Developments in the Appalachian-Caledonian- Variscan Orogen. Geological Society of America, 2022. http://dx.doi.org/10.1130/2021.2554(06).
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ABSTRACT Voluminous bimodal volcanic rocks of the Silurian (ca. 422–420 Ma) Dickie Cove Group in the Ganderia domain of northern New Brunswick, Canada, are subaerial units that were deposited in an extensional setting, with the mafic types corresponding to continental tholeiites. Felsic rocks are rhyolites with calc-alkaline affinities. They exhibit geochemical characteristics that are typical of A2-type felsic magmas, such as enrichments in the incompatible elements Zr, Nb, and Y, as well as high FeO*/(FeO* + MgO) and Ga/Al ratios. Their εNd(t) values are positive (+0.7 to +3.4) but lower than those of the associated basalts. Saturation thermometry has yielded average zircon crystallization temperature estimates for the rhyolites that are well above 900 °C. The geochemical data indicate that the felsic melts were likely sourced from heterogeneous Neoproterozoic lower crust and generated by dehydration melting triggered by heat derived from underplated mafic magma. Parent melts of the rhyolites underwent fractional crystallization in a complex magma chamber prior to eruption. The Nd isotopic data suggest that the lower crust of Ganderia is similar to that of Avalonia in northern mainland Nova Scotia, and that the two microcontinents shared a common Neoproterozoic history and origin as continental blocks rifted from neighboring parts of Gondwana. The tectono-magmatic setting of the Dickie Cove Group volcanic rocks is interpreted as being related to Pridolian, post-Salinic relaxation and slab breakoff, which generated volcanism initially constrained within the Chaleur zone of the Chaleur Bay synclinorium, a large domain of the northern Appalachians. This was followed later in the Pridolian by extensional collapse and widening of the area of magmatic activity, which then prograded into the Tobique zone farther to the southwest.
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Macdonald, Francis A., W. Adolph Yonkee, Rebecca M. Flowers, and Nicholas L. Swanson-Hysell. "Neoproterozoic of Laurentia." In Laurentia: Turning Points in the Evolution of a Continent. Geological Society of America, 2022. http://dx.doi.org/10.1130/2022.1220(19).
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ABSTRACT Neoproterozoic to Cambrian isolation of Laurentia during the breakup of Rodinia was associated with multiple large igneous provinces, protracted multiphase rifting, and variable subsidence histories along different margin segments. In this contribution, we develop a paleogeographic model for the Neoproterozoic tectonic evolution of Laurentia based on available stratigraphic, paleomagnetic, petrologic, geochronologic, and thermochronologic data. Early Tonian strata are confined to intracontinental basins in northern Laurentia. Breakup of Rodinia around Laurentia began in earnest with emplacement of the ca. 778 Ma Gunbarrel large igneous province, interpreted to have accompanied separation of the North China block along the Yukon promontory, and onset of localized, intracratonic extension southward along the western margin. Eruption of the ca. 760–740 Ma Mount Rogers volcanic complex along the Southern Appalachian segment of the eastern margin may record extension associated with separation of the Kalahari or South American terranes. At about the same time, the Australia-Mawson blocks began separating from the Sonoran segment of the southern margin and Mojave promontory. Emplacement of the ca. 720 Ma Franklin large igneous province along the northern margin was likely associated with separation of Siberia and was followed by widespread bimodal volcanism and extension along the western margin spanning ca. 720–670 Ma, leading to partial separation of continental fragments, possibly including Tasmania, Zealandia, and Tarim. Emplacement of the ca. 615 Ma Central Iapetus magmatic province along the eastern margin marked rifting that led to separation of Baltica and Amazonia, and partial separation of the Arequipa-Pampia-Antofalla fragments. During the late Ediacaran to Cambrian, the western, northern, eastern, and southern margins all experienced a second episode of local extension and mafic magmatism, including emplacement of the ca. 585 Ma Grenville dikes and ca. 540–532 Ma Wichita large igneous province, leading to final separation of continental fragments and Cambrian rift-drift transitions on each margin. Cryogenian rifting on the western and northern margins and segments of the eastern margin was contemporaneous with low-latitude glaciation. Sturtian and Marinoan glacial deposits and their distinctive ca. 660 Ma and 635 Ma cap carbonates provide important event horizons that are correlated around the western and northern margins. Evidence for Ediacaran glaciation is absent on Laurentia, with the exception of glacial deposits in Scotland, and putative glacial deposits in Virginia, which both formed on the poleward edge of Laurentia. Patterns of exhumation and deposition on the craton display spatial variability, likely controlled by the impingement of mantle plumes associated with mantle upwelling and extensional basin formation during the piecemeal breakup of Rodinia. Glaciation and eustasy were secondary drivers for the distribution of erosion and Neoproterozoic sedimentation on North America.
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"Bimodal (Mafic-Felsic) Volcanic-Sedimentary Association." In Phanerozoic Environments, Associations and Deposits, 307–54. Elsevier, 1985. http://dx.doi.org/10.1016/b978-0-444-42530-0.50019-6.
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"Continental Plateau Basalt and Bimodal Volcanic Association." In Empirical Metallogeny: Depositional Environments, Lithologic Associations and Metallic Ores - Phanerozoic Environments, Associations, and Deposits, 1425–56. Elsevier, 1985. http://dx.doi.org/10.1016/b978-0-444-42553-9.50008-4.
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"Continental Plateau Basalt and Bimodal Volcanic Association." In Phanerozoic Environments, Associations and Deposits, Part B, 1425–56. Elsevier, 1985. http://dx.doi.org/10.1016/b978-0-444-42554-6.50008-5.
Повний текст джерелаТези доповідей конференцій з теми "Bimodal volcanism"
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Sethuraman, Gomathi Abhirami, and M. Satyanarayanan. "Bimodal Volcanism in Betul Fold Belt, Central India: Implications on Petrogenesis." In Goldschmidt2022. France: European Association of Geochemistry, 2022. http://dx.doi.org/10.46427/gold2022.10380.
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Camp, Victor. "AN ALTERNATIVE MODEL FOR BIMODAL VOLCANISM IN THE SOUTHERN CASCADIA BACK-ARC REGION SINCE ~12 MA." In 115th Annual GSA Cordilleran Section Meeting - 2019. Geological Society of America, 2019. http://dx.doi.org/10.1130/abs/2019cd-329250.
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Mageswarii, G., Meenal Mishra, and Jaya Prakash Shrivastava. "Evidence of Rift-Related Late Paleoproterozoic Bimodal Volcanism in the Eastern Part of the Son Valley, Central India." In Goldschmidt2020. Geochemical Society, 2020. http://dx.doi.org/10.46427/gold2020.1699.
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Hampton, Brian A., Greg H. Mack, Ryan H. Creitz, and Jeffrey M. Amato. "NEW CONSTRAINTS ON THE MIDDLE–LATE EOCENE (~46–36 MA) TECTONIC TRANSITION FROM LATE-STAGE LARAMIDE DEFORMATION TO BIMODAL RIFT VOLCANISM (RIO GRANDE RIFT) IN SOUTHERN NEW MEXICO." In Joint 70th Annual Rocky Mountain GSA Section / 114th Annual Cordilleran GSA Section Meeting - 2018. Geological Society of America, 2018. http://dx.doi.org/10.1130/abs/2018rm-314411.
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Stearn, Madelaine M., and Gary S. Michelfelder. "PUMICE COMPOSITIONS AND MINERAL CHEMISTRY OF BIMODAL PUMICE ERUPTED FROM LASCAR VOLCANO, CENTRAL VOLCANIC ZONE, CHILE." In Joint 53rd Annual South-Central/53rd North-Central/71st Rocky Mtn GSA Section Meeting - 2019. Geological Society of America, 2019. http://dx.doi.org/10.1130/abs/2019sc-327403.
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Yandle, Matthew, and Mary Kate Fidler. "ERUPTIVE HISTORY OF A BIMODAL VOLCANIC TERRANE: NEW GEOLOGIC MAPPING AND WHOLE ROCK GEOCHEMISTRY OF THE BLACK HILLS, SOUTH-CENTRAL OREGON." In GSA 2020 Connects Online. Geological Society of America, 2020. http://dx.doi.org/10.1130/abs/2020am-358213.
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Yandle, Matthew, and Mary Kate Fidler. "ERUPTIVE HISTORY OF A BIMODAL VOLCANIC TERRANE: NEW GEOLOGIC MAPPING AND WHOLE ROCK GEOCHEMISTRY OF THE BLACK HILLS, SOUTH-CENTRAL OREGON." In Joint 69th Annual Southeastern / 55th Annual Northeastern GSA Section Meeting - 2020. Geological Society of America, 2020. http://dx.doi.org/10.1130/abs/2020se-345478.
Повний текст джерелаЗвіти організацій з теми "Bimodal volcanism"
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Van Wagoner, N. A., K. A. Dadd, D. K. Baldwin, and W. McNeil. Physical Volcanology, Geochemistry and Depositional Setting of a Continental Bimodal Volcanic Zone, Passamaquoddy Bay, southwestern New Brunswick. Natural Resources Canada/ESS/Scientific and Technical Publishing Services, 1990. http://dx.doi.org/10.4095/130890.
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