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Petrography, major-trace elements and isotopic compositions of the lavas from El Tigre volcano (Fonseca Gulf, Honduras): increasing data on the Central America Volcanic Front
Full text linkEl Tigre volcano is located within the Fonseca Gulf, Honduras, where there is a break in the strike of the Central
America Volcanic Front (Walker et al., 2000; Carr et al., 2003; Bolge et al., 2009). The origin of this gulf arise from the
intersection of three first-order tectonic structures, and such a complex tectonic setting is the result of the oblique
subduction on the Central American trench (Carr et al., 2003; Burkart & Self, 1985). For these reasons, the knowledge
of El Tigre is of paramount importance for unravelling the magmatological and volcanological evolution of this area.
Lavas from El Tigre consist of basalts and basaltic andesites with calc-alkaline affinity. The fundamental
mineralogical assemblage is typical of relatively primitive subalkaline rocks, and is made of plagioclase, olivine,
clinopyroxene, orthopyroxene and opaques. Lavas show a significant LILE enrichment and Nb depletion, a strong slab
signature and incompatible element contents similar to those in the main front of the adjacent volcanoes from El
Salvador and Nicaragua (e.g. Ba/La up to 80). However, a small group of basalts from El Tigre, with higher MgO
content (> 5 wt%) and lower Ba/La, Ba/Nb and Zr/Nb ratios (34-39, 35-49 and 5-7, respectively), emphasizes that
mantle-derived magmas were not produced by the same source or process throughout the span-time activity of the
volcano. El Tigre lavas are characterized by higher 87Sr/86Sr (0.7038) and lower 143Nd/144Nd (0.51301) with respect to arc
volcanoes of El Salvador and Nicaragua, whereas 208Pb/204Pb and 206Pb/204Pb isotope ratios are very similar (38.2 and
18.5, respectively)
Magma Differentiation, Contamination/Mixing and Eruption Modulated by Glacial Load—The Volcanic Complex of The Pleiades, Antarctica
Full text linkThe Pleiades Volcanic Field is made up of some 20 monogenetic, partly overlapping scoria and spatter cones, erupted in the last 900 ka, cropping out from the ice close to the head of the Mariner Glacier in northern Victoria Land, Antarctica. Erupted products vary from hawaiite to trachyte, defining a complete mild Na-alkaline differentiation trend. Mafic samples are characterized by multi-elemental patterns typical of OIB magmas, moderately low 87Sr/86Sr (0.7037) and high 143Nd/144Nd (0.51284), with a clear within-plate affinity, indicating a subcontinental lithospheric source. With increasing SiO2, 87Sr/86Sr ratios increase up to 0.7052 and 143Nd/144Nd decrease to 0.51277, supporting the hypothesis of open-system evolution, with significant crustal assimilation during fractional crystallization. The erupted volume of most evolved products (similar to 7 km3), according to fractionation models, suggests that primitive magmas should have been more than 10 times larger, indicating the occurrence of a large magma plumbing system, unexpected for a volcanic field of monogenetic scoria cones. The occurrence of a complete fractionation trend with large magma chambers and large assimilation rate is unusual, if not unique, among the alkali basaltic volcanic fields and it is matched by a climax of activity during the last glacial maximum (30 ka), as indicated by new 40Ar-39Ar ages (30 +/- 3 ka and 25 +/- 2 ka) for samples from the two most prominent edifices. Therefore, we hypothesize a role of a thick ice cap in suppressing eruptions and ultimately leading to prolonged magma residence time in the subsurface, favoring significant fractionation coupled with unusual high rates of crustal assimilation.The Pleiades volcanic field is made up of some 20 monogenetic scoria and spatter cones, which erupted in the last 900 ka close to the head of the Mariner Glacier in northern Victoria Land, Antarctica. The erupted products are very unusual for alkali basaltic volcanism: indeed, whereas few samples show clear within-plate subcontinental lithospheric characteristics and were directly derived from the mantle source, most of the products formed after extensive fractional crystallization matched by significant crustal assimilation, implying that primitive magma volumes are 10 times larger than outcropping products in an unusually large magma plumbing system. These peculiar features coincided with a climax of activity during the last glacial maximum (30-25 ka). Therefore, we speculate that a thick ice cap favored high rates of crystal fractionation coupled with crustal assimilation and was responsible for increasing magma residence times in chambers at crustal depths and suppressing the eruptive potential of magmas.The Pleiades complex (NVL, Antarctica) is made up of some 20 monogenetic cones aged 900-0 ka, defining a complete Na-alkaline trend Fractionation models show much larger volumes of primitive magmas, indicating the occurrence of an unusually large magma plumbing system A climax of activity occurred during the last glacial maximum (30 ka). Thickness variation of the ice cap may have influenced volcanic activit
EVIDENCE FOR SERPENTINITE FLUID IN CONVERGING SYSTEMS: THE EXAMPLE OF EL SALVADOR (CENTRAL AMERICA) ARC LAVAS
No full textThe shallow water record of the “Monterey Event” within the Central Mediterranean area: a major controlling factor of the carbonate platforms evolution
No full textStrontium isotope signature of the PGI lemons Limone Costa d'Amalfi and Limone di Sorrento, and of the orchard soils from Sorrento peninsula
No full text: The Limone Costa d'Amalfi and Limone di Sorrento lemons from the Sorrento Peninsula have Protected Geographical Indication (PGI) and are subject to origin fraud. The 87Sr/86Sr ratio (SrIR) signature of lemons and soils was investigated to verify its reliability to trace the PGI lemons and to highlight environmental factors responsible of the lemon SrIRs. The SrIR ranges of each PGI lemon were not discriminating as they overlapped with each other and some non-PGI lemon SrIRs fell within these ranges. The lemon SrIRs were generally not correlated with bulk and bioavailable soil SrIRs, rather, they were the result of plant Sr uptake with different SrIRs depending on interaction between water supplied to soil and soil with different chemical and physical characteristics. The study of lemon SrIRs and the causes of their origin and variability provides a reliable forecast reference for the other PGI agri-food products in the study area
The Monterey event within the Central Mediterranean area. The shallow-water record
No full textThe middle Miocene is an important time to understand modern global climate evolution and its consequences on marine systems. The Mid-Miocene Climatic Optimum (MCO, between 17 and13.5 Ma), was the warmest time interval of the past 35 million years during which atmospheric CO2 concentrations were lower than today. In the MCO a significant carbon cycle perturbation occurred, expressed as a last long-term positive carbon isotope shift, known in literature as the Monterey Carbon Isotope Excursion and recorded in open-ocean settings. In this work, the lower to middle Miocene carbon isotope records from three different domains of the Central Mediterranean are analyzed with the aim of identifying the local carbonate platform response to the major global carbon cycle perturbation of the Monterey event. Carbon and Oxygen isotope ratios have been measured on samples belonging to three different stratigraphic sections, two of them representative of shallow water settings (Latium-Abruzzi and Apula Platforms), the latter of a hemipelagic setting (Umbria-Marche Basin). A well-defined Monterey Carbon Isotope Excursion is recorded also in these shallow-water sections. Despite their expected problematic stratigraphic constraints, a reliable age model is provided by calcareous nannofossil biostratigraphy and Strontium Isotope Stratigraphy.
In both carbonate platform successions examined, the Monterey Carbon Isotope Excursion coincides with a spread of bryozoans over other carbonate-producing biota. The high productivity of the bryozoan dominated factory in the aphotic zone had an important control on the platform depositional profile. The high rates of sediment production in the deeper aphotic and oligophotic zones produced a depositional profile of a low-angle ram
Magmas with slab fluid and decompression melting signatures coexisting in the Gulf of Fonseca: evidence from Isla El Tigre volcano (Honduras, Central America)
No full textIsla El Tigre volcano is located in the Gulf of Fonseca (Honduras) along the Central America volcanic front, where a significant change in the strike of the volcanic chain is observed. The studied samples of this poorly investigated volcano are mainly subalkaline basic to intermediate lavas (basalts and basaltic andesites) and subordinate subalkaline/alkaline transitional basalts, both having the typical mineralogical and geochemical characteristics of arc volcanic rocks. On the basis of petrographic and geochemical features, two groups of rocks have been distinguished. Lavas from the main volcanic edifice are highly porphyritic and hy-qz normative, and have lower MgO contents (5 wt%), are ol-hy normative and show lower HFSE depletions relative to LILE and LREE, with lower Ba/La, Ba/Nb and Zr/Nb ratios. This suggests that mantle-derived magmas were not produced by the same process throughout the activity of the volcano.
The bulk rock geochemistry and 87Sr/86Sr (0.70373-0.70382), 143Nd/144Nd (0.51298-0.51301), 206Pb/204Pb (18.55-18.58), 207Pb/204Pb (15.54-15.56) and 208Pb/204Pb (38.23-38.26) isotopic data of Isla El Tigre compared with the other volcanoes of the Gulf of Fonseca and all available literature data for Central America suggests that this stratovolcano was mainly built by mantle-derived melts driven by slab-derived fluid-flux melting, while magmas erupted through its parasitic cones have a clear signature of decompression melting with minor slab contribution. The coexistence of these two different mantle melting generation processes is likely related to the complex geodynamic setting of the Gulf of Fonseca, where the volcanic front changes direction by ca. 30° and two fundamental tectonic structures of the Chortis continental block, mainly the N-S Honduras Depression and the NE-SW Guayape Fault Zone, cross each other
THE TRANSITION BETWEEN OROGENIC AND INTRAPLATE MAGMATISM IN WESTERN ANATOLIA-AEGEAN REGION
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