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  • 551  (6)
  • Cerro Galán; Puna ignimbrite chemistry; 40Ar/39Ar ages; Delamination; Plateau evolution  (1)
  • 1
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    Petrology, Geochemistry, and Geodynamic Implications of Basaltic Dyke Swarms from the Southern Continental Part of the Cameroon Volcanic Line, Central Africa (2018)
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    Publication Date: 2021-03-29
    Description: Basaltic dyke swarms in the southern continental part of the Cameroon Volcanic Line (Bangangte, Dschang, Manjo areas) are tholeiitic in composition with 46 to 50 wt.% SiO 2 and have moderate Mg-numbers (53–59), medium TiO 2 contents (1.48–2,05 wt.%), and flat to mildly enriched incompatible trace element patterns. Comparison with trace element patterns of representative Cenozoic basaltic rocks of the Cameroon Volcanic Line (Bana anorogenic complex, Mt. Bambouto, Adamawa Plateau basalts) indicates that these dykes are less enriched in light REE and show different incompatible trace element ratios (La/Yb: 5.7 to 8.6; Zr/Nb: 7.6 to 12.0; Ba/Th: 87.7 to 93.3). The trace element patterns of the dykes and their Sr- and Nd- isotope compositions, however, are similar to those of the pre-Cenozoic volcanic rocks of the Benue Trough in Nigeria. Our data therefore suggest that these dykes represent the magmatic history related to the break-up of Africa and South America and are unrelated to the Tertiary volcanism of the Cameroon Line.
    Keywords: Basalt dykes; Tholeiites; Phanerozoic; Cameroon volcanic line; West Gondwana ; 551
    Language: English
    Type: article , publishedVersion
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  • 2
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    Magma chamber evolution prior to the Campanian Ignimbrite and Neapolitan Yellow Tuff eruptions (Campi Flegrei, Italy) (2018)
    Springer-Verlag | Berlin/Heidelberg
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    Publication Date: 2021-03-29
    Keywords: Campi Flegrei; Phlegraean fields; Campanian Ignimbrite; Neapolitan Yellow Tuff; Geochemistry; Sr and Nd isotopes; Magma batches; Precursor activity ; 551 ; Geosciences; Sedimentology ; Mineralogy ; Geophysics/Geodesy ; Geology
    Language: English
    Type: article , publishedVersion
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  • 3
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    Mafic Late Miocene–Quaternary volcanic rocks in the Kamchatka back arc region: implications for subduction geometry and slab history at the Pacific–Aleutian junction (2018)
    Springer-Verlag | Springer-Verlag
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    Publication Date: 2021-03-29
    Description: New 40Ar/39Ar and published 14C ages constrain voluminous mafic volcanism of the Kamchatka back-arc to Miocene (3–6 Ma) and Late Pleistocene to Holocene (〈1 Ma) times. Trace elements and isotopic compositions show that older rocks derived from a depleted mantle through subduction fluid-flux melting (〉20%). Younger rocks form in a back arc by lower melting degrees involving enriched mantle components. The arc front and Central Kamchatka Depression are also underlain by plateau lavas and shield volcanoes of Late Pleistocene age. The focus of these voluminous eruptions thus migrated in time and may be the result of a high fluid flux in a setting where the Emperor seamount subducts and the slab steepens during rollback during terrain accretions. The northern termination of Holocene volcanism locates the edge of the subducting Pacific plate below Kamchatka, a “slab-edge-effect” is not observed in the back arc region.
    Keywords: Kamchatka; Back-arc; Plateau-basalts; Subduction; Trace elements; Isotopes ; 551 ; Earth Sciences; Mineralogy ; Mineral Resources ; Geology
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  • 4
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    Geochemical, isotopic and single crystal 40Ar/39Ar age constraints on the evolution of the Cerro Galán ignimbrites (2018)
    Springer-Verlag | Berlin/Heidelberg
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    Publication Date: 2021-03-29
    Description: The giant ignimbrites that erupted from the Cerro Galán caldera complex in the southern Puna of the high Andean plateau are considered to be linked to crustal and mantle melting as a consequence of delamination of gravitationally unstable thickened crust and mantle lithosphere over a steepening subduction zone. Major and trace element analyses of Cerro Galán ignimbrites (68–71% SiO2) that include 75 new analyses can be interpreted as reflecting evolution at three crustal levels. AFC modeling and new fractionation corrected δ18O values from quartz (+7.63–8.85‰) are consistent with the ignimbrite magmas being near 50:50 mixtures of enriched mantle (87Sr/86Sr ~ 0.7055) and crustal melts (87Sr/86Sr near 0.715–0.735). Processes at lower crustal levels are predicated on steep heavy REE patterns (Sm/Yb = 4–7), high Sr contents (〉250 ppm) and very low Nb/Ta (9-5) ratios, which are attributed to amphibolite partial melts mixing with fractionating mantle basalts to produce hybrid melts that rise leaving a gravitationally unstable garnet-bearing residue. Processes at mid crustal levels create large negative Eu anomalies (Eu/Eu* = 0.45–0.70) and variable trace element enrichment in a crystallizing mush zone with a temperature near 800–850°C. The mush zone is repeatedly recharged from depth and partially evacuated into upper crustal magma chambers at times of regional contraction. Crystallinity differences in the ignimbrites are attributed to biotite, zoned plagioclase and other antecrysts entering higher level chambers where variable amounts of near-eutectic crystallization occurs at temperatures as low as 680°C just preceding eruption. 40Ar/39Ar single crystal sanidine weighted mean plateau and isochron ages combined with trace element patterns show that the Galán ignimbrite erupted in more than one batch including a ~ 2.13 Ma intracaldera flow and outflows to the west and north at near 2.09 and 2.06 Ma. Episodic delamination of gravitationally unstable lower crust and mantle lithosphere and injection of basaltic magmas, whose changing chemistry reflects their evolution over a steepening subduction zone, could trigger the eruptions of the Cerro Galán ignimbrites.
    Keywords: Cerro Galán; Puna ignimbrite chemistry; 40Ar/39Ar ages; Delamination; Plateau evolution ; 551 ; Earth Sciences; Sedimentology; Geophysics/Geodesy; Mineralogy; Geology
    Language: English
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  • 5
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    Evolution of the West Andean Escarpment at 18°S (N. Chile) during the last 25 Ma: uplift, erosion and collapse through time (2018)
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    Publication Date: 2021-03-29
    Description: The geological record of the Western Andean Escarpment (WARP) reveals episodes of uplift, erosion, volcanism and sedimentation. The lithological sequence at 18°S comprises a thick pile of Azapa Conglomerates (25–19 Ma), an overlying series of widespread rhyodacitic Oxaya Ignimbrites (up to 900 m thick, ca. 19 Ma), which are in turn covered by a series of mafic andesite shield volcanoes. Between 19 and 12 Ma, the surface of the Oxaya Ignimbrites evolved into a large monocline on the western slope of the Andes. A giant antithetically rotated block (Oxaya Block, 80 km×20 km) formed on this slope at about 10–12 Ma and resulted in an easterly dip and a reversed drainage on the block's surface. Morphology, topography and stratigraphic observations argue for a gravitational cause of this rotation. A “secondary” gravitational collapse (50 km3), extending 25 km to the west occurred on the steep western front of the Oxaya Block. Alluvial and fluvial sediments (11–2.7 Ma) accumulated in a half graben to the east of the tilted block and were later thrust over by the rocks of the escarpment wall, indicating further shortening between 8 and 6 Ma. Flatlying Upper Miocene sediments (〈5.5 Ma) and the 2.7 Ma Lauca–Peréz Ignimbrite have not been significantly shortened since 6 Ma, suggesting that recent uplift is at least partly caused by regional tilting of the Western Andean slope.
    Keywords: Central Andes; Western slope; uplift; erosion; sedimentation; volcanism; gravitational collapse ; 551
    Language: English
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  • 6
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    Hydrated sub-arc mantle: a source for the Kluchevskoy volcano, Kamchatka/Russia (2018)
    Details
    Publication Date: 2021-03-29
    Description: Oxygen isotope ratios of olivine and clinopyroxene phenocrysts from the Kluchevskoy volcano in Kamchatka have been studied by CO2 and ArF laser techniques. Measured δ18O values of 5.8–7.1‰ for olivine and 6.2–7.5‰ for clinopyroxene are significantly heavier than typical mantle values and cannot be explained by crustal assimilation or a contribution of oceanic sediments. Positive correlations between δ18O and fluid-mobile elements (Cs, Li, Sr, Rb, Ba, Th, U, LREE, K) and a lack of correlation with fluid-immobile elements (HFSE, HREE) suggest that 18O was introduced into the mantle source by a fluid from subducted altered oceanic basalt. This conclusion is supported by radiogenic isotopes (Sr, Nd, Pb). Mass balance excludes simple fluid-induced mantle melting. Instead, our observations are consistent with melting a mantle wedge which has been hydrated by 18O-rich fluids percolating through the mantle wedge. 18O-enriched fluids are derived from the subducted oceanic crust and the Emperor seamount chain, which is responsible for a particularly high fluid flux. This hydrated mantle wedge was subsequently involved in arc magmatism beneath Kluchevskoy by active intra-arc rifting.
    Keywords: subduction zones; Kamchatka Peninsula; isotopes; slabs; Emperor Seamounts; fluid phase; hydration; trace elements ; 551
    Language: English
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