The Nevados de Payachata volcanic region (18�S/69�W, N. Chile) II. Evidence for widespread crustal involvement in Andean magmatism

Davidson, Jon P.; McMillan, Nancy J.; Moorbath, S.; Wörner, Gerhard; Harmon, Russell S.; López-Escobar, Leopoldo

doi:10.1007/bf00286829

Cited by 137 publications

(56 citation statements)

References 55 publications

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“…Trace-element abundances are enriched with light rare-earth elements (LREEs) and depleted in heavy rare-earth elements (HREEs) relative to chondrites, and they are enriched in large ion lithophile (LIL) elements and slightly depleted in high field-strength (HFS) elements relative to mid-ocean ridge basalt (MORB). Their trace and rare-earth element signatures are quite similar to modern continental-margin magmatic arc systems (e.g., Cascades, Andes) or evolved volcanic arcs, and they show very similar patterns and abundances as magmas interacting with thick crust (e.g., Davidson et al, 1990Davidson et al, , 1991Wörner et al, 1994). Some of the samples resemble Si-rich, peraluminous leucogranites found in regions of overthickened continental crust (Frost et al, 2001).…”

Section: Sample Geochemical Characteristicsmentioning

confidence: 88%

Crustal heat production and estimate of terrestrial heat flow in central East Antarctica, with implications for thermal input to the East Antarctic ice sheet

Goodge¹

2018

The Cryosphere

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Section: Sample Geochemical Characteristicsmentioning

confidence: 88%

Crustal heat production and estimate of terrestrial heat flow in central East Antarctica, with implications for thermal input to the East Antarctic ice sheet

Goodge¹

2018

The Cryosphere

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“…The partial melting is often followed by crustal contamination during the differentiation (James 1982). Recent studies carried out on volcanoes of the CVZ, such as Ollagüe, Parinacota and Tata Sabaya (Davidson et al 1990;Feeley and Hacker 1995;de Silva et al 1993), have found magmas poor in HREE and Y but having high Sr/Y ratios, similar to those of the Ubinas rocks (see also Mahlburg-Kay et al 1999). In all geochemical aspects, including radiogenic isotope ratios (Table 3), the spectra of trace elements of Ubinas fall into the same field as other typical CVZ rocks.…”

Section: Evolution and Magma Sourcesmentioning

confidence: 92%

Ubinas: the evolution of the historically most active volcano in southern Peru

et al. 2005

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Ubinas volcano has had 23 degassing and ashfall episodes since A.D. 1550, making it the historically most active volcano in southern Peru. Based on fieldwork, on interpretation of aerial photographs and satellite images, and on radiometric ages, the eruptive history of Ubinas is divided into two major periods. Ubinas I (Middle Pleistocene >376 ka) is characterized by lava flow activity that formed the lower part of the edifice. This edifice collapsed and resulted in a debris-avalanche deposit distributed as far as 12 km downstream the Rio Ubinas. Non-welded ignimbrites were erupted subsequently and ponded to a thickness of 150 m as far as 7 km south of the summit. These eruptions probably left a small collapse caldera on the summit of Ubinas I. A 100-m-thick sequence of ash-and-pumice flow deposits followed, filling paleo-valleys 6 km from the summit. Ubinas II, 376 ky to present comprises several stages. The summit cone was built by andesite and dacite flows between 376 and 142 ky. A series of domes grew on the southern flank and the largest one was dated at 250 ky; block-and-ash flow deposits from these domes filled the upper Rio Ubinas valley 10 km to the south. The summit caldera was formed between 25 and 9.7 ky. Ash-flow deposits and two Plinian deposits reflect explosive eruptions of more differentiated magmas. A debris-avalanche deposit (about 1.2 km 3 ) formed hummocks at the base of the 1,000-m-high, fractured and unstable south flank before 3.6 ka. Countless explosive events took place inside the summit caldera during the last 9.7 ky. The last Plinian eruption, dated A.D.1000-1160, produced an andesitic pumice-fall deposit, which achieved a thickness of 25 cm 40 km SE of the summit. Minor eruptions since then show phreatomagmatic characteristics and a wide range in composition (mafic to rhyolitic): the events reported since A.D. 1550 include many degassing episodes, four moderate (VEI 2-3) eruptions, and one VEI 3 eruption in A.D. 1667. Ubinas erupted high-K, calc-alkaline magmas (SiO 2 =56 to 71%). Magmatic processes include fractional crystallization and mixing of deeply derived mafic andesites in a shallow magma chamber. Parent magmas have been relatively homogeneous through time but reflect variable conditions of deep-crustal assimilation, as shown in the large variations in Sr/Y and LREE/HREE. Depleted HREE and Y values in some lavas, mostly late mafic rocks, suggest contamination of magmas near the base of the >60-km-thick continental crust. The most recently erupted products (mostly scoria) show a wide range in composition and a trend towards more mafic magmas. Editorial responsibility: D Dingwell J.-C. Thouret ( ) ) Laboratoire Magmas et Volcans,Recent eruptions indicate that Ubinas poses a severe threat to at least 5,000 people living in the valley of the Rio Ubinas, and within a 15-km radius of the summit. The threat includes thick tephra falls, phreatomagmatic ejecta, failure of the unstable south flank with subsequent debris avalanches, rain-triggered lahars, and pyroclastic flows. Should Pl...

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“…A calculation shows that, in order to obtain the high LILE concentrations of Pichincha lavas, considering their global partition coefficients close to zero (= 0.01) and a mean degree of partial melting of 10 %, concentrations of Rb, Ba and K in the oceanic crust should be as high as 6 ppm, 80 ppm and 0.2 %, respectively. These are typical values for altered MORB [Tatsumi and Kogiso, 1997] Stern and Killian, 1996] and the Central Volcanic Zone [James, 1982;Hawkesworth et al, 1982;Harmon et al, 1984;Davidson et al, 1990] hand, the hypothesis of derivation of Pichincha adakites from the subducted altered oceanic crust is reinforced by their Sr isotopic signature close to 0.7040 and also typical of altered MORB [Spooner, 1976;Tatsumi and Kogiso, 1997]. A contribution of the subducted sediments to the source of Pichincha lavas could alternatively explain the enrichments in the more incompatible elements and particularly in Ba.…”

Section: Slab Meltingmentioning

confidence: 95%

Slab melting and slab melt metasomatism in the Northern Andean Volcanic Zone : adakites and high-Mg andesites from Pichincha volcano (Ecuador)

Bourdon

Eissen²,

Gutscher

et al. 2002

Bulletin De La Société Géologique De France

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Abstract. -Situated in the fore-arc of the Northern Volcanic Zone (NVZ) of the Andes in Ecuador, Pichincha volcano is an active edifice where have been erupted unusual magmas as adakites and high-Mg andesites. The particular geodynamic setting of the ecuadorian margin (i.e. the flat subduction of the Carnegie Ridge) suggests that thermo-barometric conditions for the partial melting of the oceanic crust are accomplished beneath this volcano. Pichincha adakites possess all the geochemical and isotopic characteristics of slab melts described in various other arc settings. High-Mg andesites with geochemical characteristics close to those of adakites present strong enrichments in MgO that suggest that, once they were produced by ca. 10 % partial melting of the downgoing subducted slab, some adakites en route to the surface strongly interacted with the peridotitic mantle wedge. Adakitic magmas could then represent, as in many other arcs where slab melting occurs, the principal metasomatic agent of the mantle in the NVZ in Ecuador. Résumé. -Situé dans la zone volcanique nord des Andes en Equateur, le volcan Pichincha est un édifice actif entré ré-cemment dans un nouveau cycle éruptif. La position exacte de la plaque plongeante sous l'Equateur est difficile à dé-terminer en raison de l'absence de sismicité intermédiaire dans la zone de subduction. Gutscher et al. Les adakites et les andésites riches en[1999] ont cependant récemment proposé qu'il puisse exister sous la marge une portion de plaque horizontale portée par la ride de Carnegie de faible densité qui est actuellement en subduction. D'autre part, Gutscher et al.[2000] ont observé à l'échelle du globe une relation étroite entre les portions de plaque subductée horizontale et la production de magmas adakitiques. Cette association suggère que l'horizontalisation de la plaque subductante permet une modification importante de la structure thermique du coin de manteau et le maintien de la lithosphère subductante dans les conditions de pression et de température compatibles avec la fusion de la croûte océanique. Un échantillonnage du volcan Pichincha a permis de mettre en évidence que les produits émis sont constitués d'andésites et de dacites moyennement potassiques possédant toutes les caractéristiques des adakites (c'est-à-dire des produits de fusion directe de la croûte océanique) telles que des enrichissements en Na 2 O, de fortes teneurs en Sr, mais de faibles concentrations en yttrium et en terres rares lourdes. Par ailleurs, on trouve parmi ces laves des andésites magnésiennes possédant à la fois les caractéristiques des adakites mais également des concentrations en magnésium éle-vées. Minéralogiquement, les laves du Pichincha contiennent essentiellement des cristaux de plagioclase, d'amphibole, d'orthopyroxène, de clinopyroxène et de magnétite. L'amphibole est généralement absente dans les andésites magné-siennes où le pyroxène devient le minéral dominant.Une modélisation géochimique montre qu'il est parfaitement possible d'expliquer la formation des adakites ...

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The Nevados de Payachata volcanic region (18�S/69�W, N. Chile) II. Evidence for widespread crustal involvement in Andean magmatism

Cited by 137 publications

References 55 publications

Crustal heat production and estimate of terrestrial heat flow in central East Antarctica, with implications for thermal input to the East Antarctic ice sheet

Crustal heat production and estimate of terrestrial heat flow in central East Antarctica, with implications for thermal input to the East Antarctic ice sheet

Ubinas: the evolution of the historically most active volcano in southern Peru

Slab melting and slab melt metasomatism in the Northern Andean Volcanic Zone : adakites and high-Mg andesites from Pichincha volcano (Ecuador)

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