Subduction controls on the compositions of lavas from the Ecuadorian Andes

Barragán, Roberto; Geist, D.; Hall, Minard L.; Larson, Peter B.; Kurz, Mark D.

doi:10.1016/s0012-821x(97)00141-6

Cited by 84 publications

(69 citation statements)

References 29 publications

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“…As we have already pointed out, the Nb and Ta negative anomalies of absarokitic and shoshonitic rocks of the back-arc Sumaco volcano suggest that such metasomatism was related to a subduction zone (see also Barragan et al 1998;Bourdon et al 2003). Quaternary subduction could have been responsible for such metasomatism (e.g., Bourdon et al 2003), but it cannot be excluded that metasomatism occurred also during the Late Jurassic, when a continental arc was established on the western edge of the Amazon craton (e.g., Litherland et al 1994;Chiaradia et al, 2009) after which subduction-related magmatism ceased until the Fig.…”

Section: Back-arc (Sumaco)mentioning

confidence: 66%

“…Systematic across-arc increase in incompatible elements and relative decrease in fluid-mobile elements (Fig. 9), typical for arcs worldwide (Dickinson 1975;Stolper and Newman 1994;Davidson and De Silva 1995;Ryan et al 1995), suggest derivation of the Ecuadorian magmatic rocks from progressively smaller degrees of mantle melting towards the back-arc, induced by decreasing amounts of fluids released from the subducted slab (see also Barragan et al 1998;Bourdon et al 2002;Bryant et al 2006). The low degree of partial melting in the back-arc could explain the extreme enrichment in incompatible elements of Sumaco lavas (see also Barragan et al 1998).…”

Section: Across-arc Geochemical Variationsmentioning

confidence: 93%

“…9g-h) have primitive values in the frontal arc (Pululagua and Pichincha), then gradually shift through Ilalo to more evolved values in the main arc (Chacana) and go back to more primitive values in the back-arc (Sumaco). This trend has been considered (Barragan et al 1998;Bourdon et al 2003) as the result of a slight crustal contamination in coincidence with the main arc of an otherwise isotopically homogeneous mantle across the arc. We agree with this latter interpretation, as the least crust-contaminated rocks (base of the arrows in Fig.…”

Section: Across-arc Geochemical Variationsmentioning

confidence: 99%

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Adakite-like volcanism of Ecuador: lower crust magmatic evolution and recycling

Chiaradia

Müntener

Beate

et al. 2009

Contrib Mineral Petrol

138

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In the Northern Andes of Ecuador, a broad Quaternary volcanic arc with significant across-arc geochemical changes sits upon continental crust consisting of accreted oceanic and continental terranes. Quaternary volcanic centers occur, from west to east, along the Western Cordillera (frontal arc), in the Inter-Andean Depression and along the Eastern Cordillera (main arc), and in the Sub-Andean Zone (back-arc). The adakite-like signatures of the frontal and main arc volcanoes have been interpreted either as the result of slab melting plus subsequent slab melt-mantle interactions or of lower crustal melting, fractional crystallization, and assimilation processes. In this paper, we present petrographic, geochemical, and isotopic (Sr, Nd, Pb) data on dominantly andesitic to dacitic volcanic rocks as well as crustal xenolith and cumulate samples from five volcanic centers (Pululagua, Pichincha, Ilalo, Chacana, Sumaco) forming a NW-SE transect at about 0°latitude and encompassing the frontal (Pululagua, Pichincha), main (Ilalo, Chacana), and back-arc (Sumaco) chains. All rocks display typical subduction-related geochemical signatures, such as Nb and Ta negative anomalies and LILE enrichment. They show a relative depletion of fluid-mobile elements and a general increase in incompatible elements from the front to the back-arc suggesting derivation from progressively lower degrees of partial melting of the mantle wedge induced by decreasing amounts of fluids released from the slab. We observe widespread petrographic evidence of interaction of primary melts with mafic xenoliths as well as with clinopyroxene-and/or amphibole-bearing cumulates and of magma mixing at all frontal and main arc volcanic centers. Within each volcanic center, rocks display correlations between evolution indices and radiogenic isotopes, although absolute variations of radiogenic isotopes are small and their values are overall rather primitive (e.g., e Nd = ?1.5 to ?6, 87 Sr/ 86 Sr = 0.7040-0.70435). Rare earth element patterns are characterized by variably fractionated light to heavy REE (La/Yb N = 5.7-34) and by the absence of Eu negative anomalies suggesting evolution of these rocks with limited plagioclase fractionation. We interpret the petrographic, geochemical, and isotopic data as indicating open-system evolution at all volcanic centers characterized by fractional crystallization and magma mixing processes at different lower-to mid-crustal levels as well as by assimilation of mafic lower crust and/or its partial melts. Thus, we propose that the adakite-like signatures of Ecuadorian rocks (e.g., high Sr/Y and La/Yb values) are primarily the result of lower-to mid-crustal processing of mantle-derived melts, rather than of slab melts and slab melt-mantle interactions. The isotopic signatures of the least evolved adakite-like rocks of the active and recent volcanoes are the same as those of Tertiary ''normal'' calc-alkaline magmatic rocks of Ecuador suggesting that the source of the magma did not change 123Contrib Mineral Petrol (2009) 1...

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Section: Back-arc (Sumaco)mentioning

confidence: 66%

Section: Across-arc Geochemical Variationsmentioning

confidence: 93%

Section: Across-arc Geochemical Variationsmentioning

confidence: 99%

See 1 more Smart Citation

Adakite-like volcanism of Ecuador: lower crust magmatic evolution and recycling

Chiaradia

Müntener

Beate

et al. 2009

Contrib Mineral Petrol

138

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“…7.3 the Nd-Sr isotopic composition of the Amazonian sediments (Roddaz et al, 2005b), Andean volcanic rocks (Kay et al 1994;Rogers & Hawkesworth 1989;Barragan et al 1998) and Andean sediments (Pinto 2003) defi ne a hyperbolic relationship -one end member being the primitive Andean arc and the other the upper continental crust of the Brazilian Shield (Basu et al 1990;Roddaz et al 2005b). Sediments of cratonic origin plot closer to the Brazilian Shield end-member whereas sediments of Andean origin are related to the Andean magmatic end-member.…”

Section: Climate and Weathering In The Cratonic Source Areamentioning

confidence: 99%

“…The Nd-Sm isotopic compositions of cratonic rivers clearly differ from those of sediments of the main Amazon River. Sediments are further characterized by high europium anomalies (Eu/Eu* < 0.65), low chromium/ thorium ratios (Cr/Th < 6), high zirconium/scandium and thorium/scandium ratios (Zr/Sc > 15 and Th/Sc > 1) (Roddaz et al 2005b(Roddaz et al , 2006 (Barragan et al 1998); AM, Amazon mouth (Parra & Pujos 1998). Mesozoic and Neogene volcanic rocks from Rogers & Hawkesworth (1989) and Kay et al (1994).…”

Section: Climate and Weathering In The Cratonic Source Areamentioning

confidence: 99%

The Amazonian Craton and its Influence on Past Fluvial Systems (Mesozoic‐Cenozoic, Amazonia)

Hoorn

Roddaz

Dino

et al. 2009

Amazonia: Landscape and Species Evolution

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The Amazonian Craton is an old geological feature of Archaean/Proterozoic age that has determined the character of fl uvial systems in Amazonia throughout most of its past. This situation radically changed during the Cenozoic, when uplift of the Andes reshaped the relief and drainage patterns of northern South America. Here we review the sedimentary characteristics of Amazonian rivers and compare these with four fl uvial depositional settings from the Meso-Cenozoic sedimentary record. These sedimentary units are the Alter do Chão Formation (Brazil, Late Cretaceous-Paleogene), the Petaca Formation (Bolivia, Late Oligocene to Middle Miocene), the Mariñame and Apaporis Sand Units (Colombia, Miocene), and the Iquitos White Sand Unit (Peru, Late Miocene-Pliocene). This review illustrates that the river systems born on the craton share features such as sediment texture and composition, depositional environments and transport directions. Evidence for the diminished role of cratonic fl uvial systems and the onset of Neogene Andean uplift can be identifi ed in the sedimentary record by changes in sediment provenance and transport directions. Although the Andean uplift and related processes discontinued the major Amazonian-born fl uvial systems it also created new topographic features such as the Iquitos and Fitzcarrald Arches. These newly formed reliefs triggered a new generation of rivers, some of which are presently known as biodiversity hotspots.

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Across‐arc versus along‐arc Sr‐Nd‐Pb isotope variations in the Ecuadorian volcanic arc

Ancellin

Samaniego

Vlastelić

et al. 2017

Geochem Geophys Geosyst

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International audiencePrevious studies of the Ecuadorian arc (1°N–2°S) have revealed across-arc geochemical trends that are consistent with a decrease in mantle melting and slab dehydration away from the trench. The aim of this work is to evaluate how these processes vary along the arc in response to small-scale changes in the age of the subducted plate, subduction angle, and continental crustal basement. We use an extensive database of 1437 samples containing 71 new analyses, of major and trace elements as well as Sr-Nd-Pb isotopes from Ecuadorian and South Colombian volcanic centers. Large geochemical variations are found to occur along the Ecuadorian arc, in particular along the front arc, which encompasses 99% and 71% of the total variations in 206Pb/204Pb and 87Sr/86Sr ratios of Quaternary Ecuadorian volcanics, respectively. The front arc volcanoes also show two major latitudinal trends: (1) the southward increase of 207Pb/204Pb and decrease of 143Nd/144Nd reflect more extensive crustal contamination of magma in the southern part (up to 14%); and (2) the increase of 206Pb/204Pb and decrease of Ba/Th away from ∼0.5°S result from the changing nature of metasomatism in the subarc mantle wedge with the aqueous fluid/siliceous slab melt ratio decreasing away from 0.5°S. Subduction of a younger and warmer oceanic crust in the Northern part of the arc might promote slab melting. Conversely, the subduction of a colder oceanic crust south of the Grijalva Fracture Zone and higher crustal assimilation lead to the reduction of slab contribution in southern part of the arc

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Subduction controls on the compositions of lavas from the Ecuadorian Andes

Cited by 84 publications

References 29 publications

Adakite-like volcanism of Ecuador: lower crust magmatic evolution and recycling

Adakite-like volcanism of Ecuador: lower crust magmatic evolution and recycling

The Amazonian Craton and its Influence on Past Fluvial Systems (Mesozoic‐Cenozoic, Amazonia)

Across‐arc versus along‐arc Sr‐Nd‐Pb isotope variations in the Ecuadorian volcanic arc

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