Geochemical characteristics and mantle sources of the Oligo-Miocene primitive basalts from Sardinia: The role of subduction components.

During the Oligo-Miocene, the Island of Sardinia was covered by the products of voluminous magmatic activity, with a typical subduction-related signature. The mafic rocks of the Montresta (north) and Arcuentu (south) volcanic districts include primitive high MgO basalts whose trace element and Sr-, Nd- and Pb-isotope compositions constrain the nature and role of subduction-related components in the Tertiary Sardinian volcanism. The geochemical and isotopic data require an approximate degree of partial melting of 15% of a MORB-like depleted mantle prior to enrichment, and the input of two subduction components in the mantle wedge consisting of fluids from subducted oceanic crust (altered MORB) and fluids from subducted sediments. Ratios among trace elements which are variably compatible with fluid and melt phases (i.e. Th/Pb, Th/Nd and Sr/Nd) exclude the contribution of melts from the subducted slab. Models based on isotopic ratios indicate that the pre-subduction depleted mantle source of Sardinia magmas was enriched by 0.1-0.5% MORB fluid and less than 0.1% sediment fluid. The geochemical and isotopic compositions of the Montresta volcanic rocks are homogeneous, whereas those of the Arcuentu show quite heterogeneous characters, suggesting variations in mantle source over the long time-span (about 13 Ma) of volcanic activity in this district

Serum levels of total IgE and soluble CD23 in bronchial asthma

The aim of the present study was to compare, during the pollen season, serum levels of total IgE and soluble CD23 (sCD23) from patients with allergic bronchial asthma, with those from healthy subjects. Significantly higher levels of total IgE and sCD23 were found in patients with asthma compared to the control group. Both in normal controls and in asthmatic patients, a significant correlation was shown between the levels of these two molecules. In asthmatic patients, significant correlations were found for both total IgE and sCD23, with lung function measured as bronchial responsiveness to inhaled methacholine. These results suggest that in asthmatic patients, in addition to the study of total serum IgE levels, the assessment of sCD23 serum levels may be helpful in the evaluation of disease activity

Serum levels of soluble IL-2R, CD4 and CD8 in bronChial asthma

The aim of the present study was to compare serum levels of soluble forms of interleukin-2 receptor, CD4 and CD8, released by lymphocytes during activation of the immune system, in patients with allergic bronchial asthma, with those in healthy subjects. Significantly higher levels of soluble IL-2R and soluble CD4 were found in patients with asthma compared with the control group. In contrast, lower levels of soluble CD8 values were found in patients with asthma compared to the control group. Significant correlations were found for both sIL-2R and sCD4 and these two molecules, with lung function measured as bronchial responsiveness to inhaled methacholine. These results strengthen previous suggestions that in allergic bronchial asthma, activation of T cells plays a significant role in the disease pathogenesis

Blood eosinophils and serum eosinophil cationic protein in patients with acute and chronic urticaria

We have analysed the relationship of blood eosinophil count and serum eosinophil cationic protein (ECP) levels in patients with acute and chronic idiopathic urticaria. The ECP levels and eosinophil counts were measured in the peripheral blood of 15 patients with acute urticaria, 25 with chronic idiopathic urticaria and 10 normal healthy subjects. Blood eosinophil counts and serum ECP levels increased in all patients with acute urticaria. Concerning patients affected by chronic urticaria, taking into account the recrudescence of the disease at the moment of taking the blood sample, only symptomatic patients showed increased eosinophil blood values whereas serum ECP levels were increased both in symptomatic and asymptomatic patients. Furthermore, serum ECP levels in chronic urticaria did not correlate with the peripheral eosinophil counts, as they did in acute urticaria. The results of the present study indicate that eosinophils may play a role in the inflammatory mechanisms in patients with acute and chronic urticaria showing a positive correlation between serum ECP levels and disease activity

U-Pb ages, Pb-Os isotope ratios, and platinum-group element (PGE) composition of the west-central Madagascar flood basalt province

The Mailaka lava succession (central-western Madagascar) forms part of the Madagascar large igneous province and is characterized by basaltic to picritic basalt lava flows and minor evolved flows. In situ U-Pb dating of zircon in rhyodacites yields concordant ages of 89.7 \ub1 1.4 and 90.7 \ub1 1.1 Ma. Therefore, the capping rhyodacitic unit of the Mailaka lava succession was emplaced just after the underlying basalt sequence (dated paleontologically at Coniacian-Turonian). Two geochemically different lava series are present. A transitional series ranging from picritic basalts to basalts has incompatible element abundances and Pb, Os, and Nd isotope ratios within the range of mid-ocean ridge basalts. In addition, the concentrations of platinum-group elements (Ir<0.35 ng/g, Ru<0.17 ng/g, Pd p 1.0-1.6 ng/g) in the transitional basalts are generally lower than in basaltic lavas from oceanic plateaus (e.g., Ontong Java and Kerguelen) and other continental flood basalt provinces (e.g., Deccan and Etendeka). A tholeiitic series ranges from picritic basalts to rhyodacites and has relatively high concentrations of trace elements (e.g., Rb, Ba, Th, and light lanthanides) and the Pb-Sr-Nd and Os isotopic characteristic of magmas that have assimilated continental crust. The Pb isotope ratios of tholeiitic andesites indicate the involvement of a component highly depleted in radiogenic Pb, very likely old lower crust. Energy-constrained- assimilation-fractional-crystallization modeling indicates that the rhyodacites may be the result of 3c25% assimilation of upper continental crust, with a ratio between assimilated mass and subtracted solid of 3c0.35. An andesite with low Pb isotope ratios may be the result of 3c8% assimilation of lower continental crust with a mass assimilated/mass accumulated ratio of 3c0.1. Interaction of mantle-derived magmas with crustal lithologies of different age and evolutionary history thus occurred in this sector of the flood basalt province. Contamination of mantle-derived rocks by material of different crustal domains is a process also observed in other large igneous provinces, such as the Deccan Traps

magma mixing history and dynamics of an eruption trigger

The most violent and catastrophic volcanic eruptions on Earth have been triggered by the refilling of a felsic volcanic magma chamber by a hotter more mafic magma. Examples include Vesuvius 79 AD, Krakatau 1883, Pinatubo 1991, and Eyjafjallajokull 2010. Since the first hypothesis, plenty of evidence of magma mixing processes, in all tectonic environments, has accumulated in the literature allowing this natural process to be defined as fundamental petrological processes playing a role in triggering volcanic eruptions, and in the generation of the compositional variability of igneous rocks. Combined with petrographic, mineral chemistry and geochemical investigations, isotopic analyses on volcanic rocks have revealed compositional variations at different length scales pointing to a complex interplay of fractional crystallization, mixing/mingling and crustal contamination during the evolution of several magmatic feeding systems. But to fully understand the dynamics of mixing and mingling processes, that are impossible to observe directly, at a realistically large scale, it is necessary to resort to numerical simulations of the complex interaction dynamics between chemically different magmas