Summary Major, trace element and Sr-Nd-isotopic data on mafic volcanic rocks with shoshonitic affinity from the islands of Procida and Ventotene (Campanian Region, South Italy) are reported. Within-suite chemical and isotopic variations are interpreted in terms of open system differentiation processes held responsible for enrichment in a number of trace elements and for radiogenic Sr observed in both Procida and Ventotene volcanic sequences. Conversely, trace element contents and Sr-Nd-isotopic compositions of the least-evolved among the investigated samples are thought to reflect source region characteristics with only negligible crustal contamination of the primary magmas.The data support an origin from distinct source regions for the primary magmas. In the case of Ventotene, the source would have been asthenospheric and/or lithospheric mantle with features similar to transitional mid-ocean ridge basalts (T-MORB), modified by enriching agents made up mainly of subducted slab-released components coming from marly sediments (about 7%) similar to cherts from Tuscan Apennines plus a limestone contribution. In the case of Procida, the source would have been asthenospheric and/or lithospheric mantle with a slightly more enriched T-MORB-like feature with respect to Ventotene, modified by slab-derived enriching agents, likely represented by a small amount of sediments (about 2.5%) of oceanic nature (mostly terrigenous/pelagic). These differences are constrained by lower Zr/Nb, Y/Nb, Sc/Nb, V/Nb, LILE/HFSE, LREE/HFSE and87Sr/86Sr, higher Ba/La and143Nd/144Nd ratios, as well as by the lack of a detectable negative Eu anomaly, in the least-evolved volcanic rocks of Procida, with respect to those of Ventotene, which show conversely a significant negative Eu anomaly. Thus, a sharp heterogeneity exists in the mantle beneath the Campanian Region. It is thought to be the consequence of two different slabs which are in contact along the Volturno River Plain tectonic line: a continental slab, seismically inactive, descending beneath the Latium Region, and an oceanic slab, seismically active, descending beneath the Calabria, up to the Campanian Region.
Résumé De nouvelles analyses géochimiques d'éléments majeurs et en traces ainsi que des rapports isotopiques du Sr et du Nd sont été obtenues sur des roches volcaniques mafiques à affinité shoshonitiques provenant des îles de Procida et Ventotene (Région Campanienne, Italie du Sud). Les variations géochimiques et isotopiques observées au sein des séries volcaniques de ces deux îles sont interprétées en terme de processus de différenciation en système ouvert, tenu pour responsable d'un enrichissement d'un certain nombre d'éléments en traces et de leur composition en Sr radiogénique. Cependant, les teneurs en éléments traces et les compositions isotopiques en Sr et Nd des échantillons les moins évolués parmi ceux étudiés reflètent les caractéristiques de leur source, avec une contamination crustale très négligeable des magmas primitifs.Ces données démontrent que des sources distinctes sont à l'origine des magmas primitifs. Pour Ventotene, cette source doit être un manteau asthénosphérique et/ou lithosphérique dont la signature est similaire à celle de basaltes transitionnels de dorsale océanique (T MORB), légèrement enrichie en éléments dérivants d'une croûte plongeant dans une subduction comme des sédiments mameux (pour environ 7%) analogues aux cherts des Appenins de Toscane et comportant un apport en calcaire. Dans le cas de Procida, cette source doit être un manteau asthénosphérique et/ou lithosphérique montrant une signature de type T-MORB légèrement plus enrichie qu' à Ventotene, également modifiée par un apport venant d'une croûte en subduction, probablement une faible quantité (environ 2.5%) de sédiments de nature océanique (principalement terrigène/pélagique). Ces différences sont attestées par des rapports Zr/Nb, Y/Nb, Sc/Nb, V/Nb, LILE/HFSE, LREE/HSFE and87Sr/86Sr plus bas et des rapports Ba/La et143Nd/144Nd plus harts, ainsi que par l'absence d'une anomalie en Eu dans les compositions des roches volcaniques les moins évoluées de Procida par rapport à celles de Ventotene, qui elles, au contraire, montrent une anomalie en Eu significative.Ainsi, une importante hétérogénéité du manteau existe sous la Campanie. Cette hétérogénéité doit être la conséquence de la nature différente des croûtes en subduction et qui sont en contact le long de la ligne tectonique de la plaine de la rivière Volturno: an Nord-Ouest, une croûte continentale, sismiquement inactive, plonge sous le Latium alors qu'au Sud-Est, une croûte océanique, sismiquement active, plonge sous la Calabre et jusque sous la Campanie.
It is generally accepted that the compositions and properties of soil organic matter (SOM) are influenced by many factors. In order to reveal the effects of soil texture on characteristics and dynamics of SOM and its sub-fraction, humic acid (HA), along two soil profiles, a yellow soil profile and a purplish soil profile, under the same climate and vegetation conditions were determined. Results indicate that the decomposition and humification degrees of SOM and HA of the purplish soils are higher than those of the corresponding yellow soils indicated by A/O–A ratios of HAs, TOCs and HA yields of bulk soil samples, nevertheless, the development degree of the purplish soil is lower than that of the yellow soil. The variations of E4/E6 ratios of HAs along the soil profiles indicate the overall molecular sizes of HAs decreased downward along the soil profiles. A/O–A ratios of HAs decreased downward along both the soil profiles indicate that humification processes decrease downward along both the soil profiles. Leaching of SOM shows significant effects on the distribution and characteristics of HAs in the yellow soil profile but the purplish soil profile, which is consistent with the higher hydrophobicity of HAs in purplish soils, shows that the distribution characteristics of SOM along the soil profiles are a complex result of the combination of soil texture and characteristics of SOM itself. The remarkably different sand contents are concluded tentatively as one of reasons to the different distributions and dynamics of HAs along the soil profiles, however, to profoundly understand the evolution and transport of SOM along soil profiles needs more researches. 相似文献
Micro-Raman spectroscopy, even though a very promising technique, is not still routinely applied to analyse H2O in silicate glasses. The accuracy of Raman water determinations critically depends on the capability to predict and take into account both the matrix effects (bulk glass composition) and the analytical conditions on band intensities. On the other hand, micro-Fourier transform infrared spectroscopy is commonly used to measure the hydrous absorbing species (e.g., hydroxyl OH− and molecular H2O) in natural glasses, but requires critical assumptions for the study of crystal-hosted glasses. Here, we quantify for the first time the matrix effect of Raman external calibration procedures for the quantification of the total H2O content (H2OT = OH− + H2Om) in natural silicate glasses. The procedures are based on the calibration of either the absolute (external calibration) or scaled (parameterisation) intensity of the 3550 cm−1 band. A total of 67 mafic (basanite, basalt) and intermediate (andesite) glasses hosted in olivines, having between 0.2 and 4.8 wt% of H2O, was analysed. Our new dataset demonstrates, for given water content, the height (intensity) of Raman H2OT band depends on glass density, reflectance and water environment. Hence this matrix effect must be considered in the quantification of H2O by Raman spectroscopy irrespective of the procedure, whereas the parameterisation mainly helps to predict and verify the self-consistency of the Raman results. In addition, to validate the capability of the micro-Raman to accurately determine the H2O content of multicomponent aluminosilicate glasses, a subset of 23 glasses was analysed by both micro-Raman and micro-FTIR spectroscopy using the band at 3550 cm−1. We provide new FTIR absorptivity coefficients (ε3550) for basalt (62.80 ± 0.8 L mol−1 cm−1) and basanite (43.96 ± 0.6 L mol−1 cm−1). These values, together with an exhaustive review of literature data, confirm the non-linear decline of the FTIR absorptivity coefficient (ε3550) as the glass depolymerisation increases. We demonstrate the good agreement between micro-FTIR and micro-Raman determination of H2O in silicate glasses when the matrix effects are properly considered. 相似文献
The present study gathers a large amount of both existing and unpublished biostratigraphic data, which allows a detailed and complete definition of the stratigraphic features of the late Oligocene–late Miocene Maltese Archipelago sedimentary succession, recording in turn the tectonic and eustatic history of the Central Mediterranean region. We selected five sections in the Malta Island and three in Gozo, representative of the entire sedimentary succession, affected by well-known erosional surfaces, correlated to low-stands of the sea level, often associated with phoshatic layers, linked to the subsequent high-stands. The sedimentary interval, and thus the associated hiatuses, was constrained both by the bio-chronostratigraphic attribution and by the comparison with the third-order succession of the New Jersey passive margin, which shows strict analogy with the geodynamic context in which the Maltese succession deposited. The diachroneity at the base of the formations in the different sections, and the presence of intraformational unconformity/hiatuses, highlighted the role of the tectonic, which depicted a complex sedimentary basin, characterized by more distal versus more marginal sectors. Furthermore, the possibility to compare the sedimentary succession with the oxygen isotope curve connects the sedimentation interruptions, recorded within the Maltese Archipelago deposits, to global cooling events.