| 1. |
- Godoy, Benigno, et al.
(author)
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Boron isotope variations in a single monogenetic cone : La Poruña (21°53′S, 68°30′W), Central Andes, Chile
- 2023
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In: Lithos. - : Elsevier. - 0024-4937 .- 1872-6143. ; 440
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Journal article (peer-reviewed)abstract
- La Poruña is a monogenetic volcano located within the Altiplano-Puna Volcanic Complex (21°-24°S) in the Central Andean subduction zone. Since crustal contamination of Andean magmas is ubiquitous, and because extensive geochemical data exist for La Poruña, we employ this volcano as a case study to examine the behavior of boron isotopes during crustal assimilation. We present whole-rock boron concentration and 11B/10B ratios (as δ11B values) for La Poruña lava samples that were prepared as nano-particulate pressed pellets. La Poruña B contents range from 14 to 20 μg/g and δ11B values range from −1.39 ± 0.54 ‰ (2σ) to +0.94 ± 0.30 ‰ (2σ), which overlap with the range of available whole-rock data for Central Andean lavas. Moreover, La Poruña δ11B values correlate negatively with 87Sr/86Sr ratios from the same samples. Since 87Sr/86Sr is a proxy for crustal contamination at La Poruña, the data lead us to suggest that La Poruña magmas assimilated a low-δ11B, high 87Sr/86Sr component such as Andean continental crust. Mixing models based on B and Sr isotopes support a broadly two-step magma evolution for La Poruña. In step 1, mantle-derived primary melts interacted with boron-rich slab-derived fluids with high δ11B values, which yielded subduction-modified parental magmas with ca. 3 μg/g B and relatively high δ11B values. In step 2, the high δ11B parental magmas ascended through the crust where they assimilated up to 20% crustal material, which further modified their δ11B values and 87Sr/86Sr ratios. In comparison to available regional values for B and δ11B, it appears that La Poruña and nearby volcanic centers shared a similar source and magmatic history, whereas volcanoes south of 23°S differ. We stress, however, that deconvolving the roles of various subduction and crustal inputs in the Central Andes would require further studies on individual volcanoes along the arc.
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| 2. |
- Gonzalez-Maurel, Osvaldo, et al.
(author)
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Constraining the sub-arc, parental magma composition for the giant Altiplano-Puna Volcanic Complex, northern Chile
- 2020
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In: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 10:1
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Journal article (peer-reviewed)abstract
- The Andean continental arc is built upon the thickest crust on Earth, whose eruption products reflect varying degrees of crustal assimilation. In order to robustly model magma evolution and assimilation at subduction zones such as the Andes, the compositions of parental magmas feeding crustal magma reservoirs need to be defined. Here we present new olivine and clinopyroxene oxygen isotope data from rare mafic volcanic rocks erupted at the margins of the giant Altiplano-Puna Magma Body (APMB) of the Altiplano-Puna Volcanic Complex, Central Andes. Existing olivine and pyroxene delta O-18 values for the Central Andes are highly variable and potentially not representative of sub-arc parental compositions. However, new olivine (n=6) and clinopyroxene (n=12) delta O-18 values of six Central Andean volcanoes presented here display a narrow range, with averages at 6.0 parts per thousand +/- 0.2 (2 sigma S.D.) and 6.7 parts per thousand +/- 0.3 (2 sigma S.D.), consistent with a common history for the investigated minerals. These data allow us to estimate the delta O-18 values of sub-arc, parental melts to ca. 7.0 parts per thousand +/- 0.2 (2 sigma S.D.). Parental melts feeding the APMB and associated volcanic centres are postulated to form in the felsic continental crust following assimilation of up to 28% high-delta O-18 basement rocks by mantle-derived magmas.
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| 3. |
- Gonzalez-Maurel, Osvaldo, et al.
(author)
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The great escape : Petrogenesis of low-silica volcanism of Pliocene to Quaternary age associated with the Altiplano-Puna Volcanic Complex of northern Chile (21 degrees 10 '-22 degrees 50 ' S)
- 2019
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In: Lithos. - : ELSEVIER. - 0024-4937 .- 1872-6143. ; 346/347
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Journal article (peer-reviewed)abstract
- The Pliocene to Quaternary volcanic arc of the Central Andes formed on 70-74 km thick continental crust. Physical interaction between mafic and acid magmas for this arc are therefore difficult to recognize due to the differentiation of mantle-derived magma during ascent through the thickened crust and a corresponding lack of erupted primitive lavas. However, a rare concentration of less evolved rocks is located marginal to the partially molten Altiplano-Puna Magma Body (APMB) in the Altiplano-Puna Volcanic Complex of northern Chile, between 21 degrees 10'S and 22 degrees 50'S. To unravel the relationship between this less evolved magmatism and the APMB, we present major and trace element data, and Sr and Nd isotope ratios of fourteen volcanoes. Whole-rock compositional and Sr and Nd isotope data reveal a large degree for compositional heterogeneity, e.g., SiO2 = 53.2 to 63.2 wt%, MgO = 1.74 to 6.08 wt%, Cr = 2 to 382 ppm, Sr = 304 to 885 ppm, (87)sr/(86)sr = 0.7055 to 0.7088, and Nd-143/Nd-144 = 0.5122 to 0.5125. The combined dataset points to magma spatial compositional changes resulting from magma mixing, fractional crystallization and crustal assimilation. The least evolved products erupted along the periphery of the APMB and are likely equivalent to the replenishing magmas that thermally sustain the large APMB system. We suggest that the mafic to intermediate eruptives we have investigated reflect mafic melt injections that underplate the APMB and escape along the side of the large felsic body to avoid significant compositional modifications during ascent, which helps to assess the evolution of the APMB through space and time. (C) 2019 Elsevier B.V. All rights reserved.
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