Isotope and trace element evidence for late-stage intra-crustal melting in the High Andes

Hawkesworth, Chris J.; Hammill, M.; Gledhill, A.R; Calsteren, Peter van; Rogers, G.

doi:10.1016/0012-821x(82)90197-2

Cited by 115 publications

(52 citation statements)

References 33 publications

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“…Geological analyses of the late Cenozoic volcanics of the South Central Andes, which includes the Moquegua Valley where Chen Chen is located, show that the 87 Sr/ 86 Sr ratios in exposed bedrock range from 0.7055 to 0.7068 (Hawkesworth et al 1982;James 1982;Rogers and Hawkesworth 1989). In contrast, the Tiwanaku and Katari Figure 2 A map of 87 Sr/ 86 (Hawkesworth et al 1982;James 1982;Rogers and Hawkesworth 1989;Veizer 1989). Values for Chen Chen and Tiwanaku are based on analysis of modern fauna (Knudson et al 2001).…”

Section: The Geology Of the Study Areas And Field Methodologymentioning

confidence: 99%

The Use of Strontium Isotope Analysis to Investigate Tiwanaku Migration and Mortuary Ritual in Bolivia and Peru

et al. 2004

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Strontium isotope analysis is applied in South America for the first time in order to investigate residential mobility and mortuary ritual from ad 500 to 1000. While Tiwanaku‐style artefacts are spread throughout Bolivia, southern Peru and northern Chile during this time, the nature of Tiwanaku influence in the region is much debated. Human skeletal remains from the site of Tiwanaku and the proposed Tiwanaku colony of Chen Chen have been analysed to test the hypothesis that Tiwanaku colonies, populated with inhabitants from Tiwanaku, existed in Peru. Strontium isotope analysis supports this hypothesis by demonstrating that non‐local individuals are present at both sites.

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Section: The Geology Of the Study Areas And Field Methodologymentioning

confidence: 99%

The Use of Strontium Isotope Analysis to Investigate Tiwanaku Migration and Mortuary Ritual in Bolivia and Peru

et al. 2004

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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 large phenocryst-rich (up to 40-50% crystals) ignimbrites with relatively homogeneous compositions probably erupted from homogeneous magma chambers. Smaller ignimbrites, with more variable compositions, are considered to have erupted from smaller, zoned magma chambers (de Silva 1991, Hawkesworth et al 1982. In general, the ignimbrites probably resulted from massive amounts of crustal melting induced by introduction of mantle-derived magmas into the thickened crust , de Silva 1989.…”

Section: Changing Magmatic Patterns Across the Plateaumentioning

confidence: 99%

The Evolution of the Altiplano-Puna Plateau of the Central Andes

Allmendinger

Jordan²,

Kay³

et al. 1997

Annu. Rev. Earth Planet. Sci.

809

658

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▪ Abstract The enigma of continental plateaus formed in the absence of continental collision is embodied by the Altiplano-Puna, which stretches for 1800 km along the Central Andes and attains a width of 350–400 km. The plateau correlates spatially and temporally with Andean arc magmatism, but it was uplifted primarily because of crustal thickening produced by horizontal shortening of a thermally softened lithosphere. Nonetheless, known shortening at the surface accounts for only 70–80% of the observed crustal thickening, suggesting that magmatic addition and other processes such as lithospheric thinning, upper mantle hydration, or tectonic underplating may contribute significantly to thickening. Uplift in the region of the Altiplano began around 25 Ma, coincident with increased convergence rate and inferred shallowing of subduction; uplift in the Puna commenced 5–10 million years later.

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Isotope and trace element evidence for late-stage intra-crustal melting in the High Andes

Cited by 115 publications

References 33 publications

The Use of Strontium Isotope Analysis to Investigate Tiwanaku Migration and Mortuary Ritual in Bolivia and Peru

The Use of Strontium Isotope Analysis to Investigate Tiwanaku Migration and Mortuary Ritual in Bolivia and Peru

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

The Evolution of the Altiplano-Puna Plateau of the Central Andes

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