Search results for "MINERALOGY"
showing 10 items of 1516 documents
The behaviour of zirconium, hafnium and rare earth elements during the crystallisation of halite and other salt minerals
2017
Abstract Halite crystals from Messinian and Tortonian evaporites from Sicily and Spain and current precipitated halite crystals and the relative parent brines (active evaporation systems) were investigated in order to evaluate the Zr, Hf and Rare Earth Element (REE) behaviour. Halite crystallisation from evaporating brines fractionates Zr, Hf and REE through a two-step process. During the first step, dissolved complexes of studied elements are scavenged onto the surfaces of crystallising halite. During the second step, elements are co-precipitated into the crystal lattice as it grows. The first step mechanism is determined by the dissolved REE speciation. In saltworks where carbonate-REE co…
Intra- and inter-annual uranium concentration variability in a Belizean stalagmite controlled by prior aragonite precipitation: A new tool for recons…
2016
Aragonitic speleothems are increasingly utilised as palaeoclimate archives due to their amenability to high precision U–Th dating. Proxy records from fast-growing aragonitic stalagmites, precisely dated to annual timescales, can allow investigation of climatic events occurring on annual or even sub-annual timescales with minimal chronological uncertainty. However, the behaviour of many trace elements, such as uranium, in aragonitic speleothems has not thus far been as well constrained as in calcitic speleothems. Here, we use uranium concentration shifts measured across primary calcite-to-aragonite mineralogical transitions in speleothems to calculate the distribution coefficient of uranium …
Some sedimentological and geochemical characters of the late Triassic Noto formation, source rock in the Ragusa basin (Sicily)
1990
URA 724 du CNRS a intégré UMR 6113 - ISTO CNRS Université d'Orléans; In the Ragusa basin (southeastern Sicily), the late Triassic Noto formation is considered as the main oil source rock. We provide a detailed description of the sedimentary facies determined from core samples, and discuss geochemical results, obtained for both kerogens and chloroform extractable hydrocarbons from samples where sedimentary organic matter is immature. Two main sedimentary sequences were encountered: (i) layers of limestones and of marls (or shales) alternating at a metric scale, and (ii) laminites having various types and carbonate contents. The high petroleum potentials (S2 up to 100 kg HC/t rock) are relate…
Quantitative models of hydrothermal fluid–mineral reaction: The Ischia case
2013
Abstract The intricate pathways of fluid–mineral reactions occurring underneath active hydrothermal systems are explored in this study by applying reaction path modelling to the Ischia case study. Ischia Island, in Southern Italy, hosts a well-developed and structurally complex hydrothermal system which, because of its heterogeneity in chemical and physical properties, is an ideal test sites for evaluating potentialities/limitations of quantitative geochemical models of hydrothermal reactions. We used the EQ3/6 software package, version 7.2b, to model reaction of infiltrating waters (mixtures of meteoric water and seawater in variable proportions) with Ischia’s reservoir rocks (the Mount Ep…
Petrographic and geochemical characterization of the Middle‒Upper Jurassic Fe–Mn crusts and mineralizations from Monte Inici (north-western Sicily): …
2021
AbstractFe–Mn concretions and mineralizations, associated with condensed horizons and hardground, are significant archives in ancient carbonate rocks. Their petro-chemical study allows an assessment of the palaeoenvironmental context in which they were formed also connected to their biotic or abiotic origin. At the western side of the Monte Inici (Fornazzo section, north-western Sicily) a well exposed outcrop of condensed pelagic limestones (Rosso Ammonitico facies: Middle‒Upper Jurassic) is well-known and thoroughly studied. In this section, the base of the Rosso Ammonitico facies consists of a very condensed level rich in fossils with a variable thickness deposited from the early Bathonia…
New insights on secondary minerals from Italian sulfuric acid caves
2018
Sulfuric acid minerals are important clues to identify the speleogenetic phases of hypogene caves. Italy hosts ~25% of the known worldwide sulfuric acid speleogenetic (SAS) systems, including the famous well-studied Frasassi, Monte Cucco, and Acquasanta Terme caves. Nevertheless, other underground environments have been analyzed, and interesting mineralogical assemblages were found associated with peculiar geomorphological features such as cupolas, replacement pockets, feeders, sulfuric notches, and sub-horizontal levels. In this paper, we focused on 15 cave systems located along the Apennine Chain, in Apulia, in Sicily, and in Sardinia, where copious SAS minerals were observed. Some of the…
Reaction path models of magmatic gas scrubbing
2016
Gas-water-rock reactions taking place within volcano-hosted hydrothermal systems scrub reactive, water-soluble species (sulfur, halogens) from the magmatic gas phase, and as such play a major control on the composition of surface gas manifestations. A number of quantitative models of magmatic gas scrubbing have been proposed in the past, but no systematic comparison of model results with observations from natural systems has been carried out, to date. Here, we present the results of novel numerical simulations, in which we initialized models of hydrothermal gas-water-rock at conditions relevant to Icelandic volcanism. We focus on Iceland as an example of a "wet" volcanic region where scrubb…
ASSESSING TRACE ELEMENT (DIS)EQUILIBRIUM AND THE APPLICATION OF SINGLE ELEMENT THERMOMETERS IN METAMORPHIC ROCKS
2018
Abstract Empirical and experimental calibration of single element solubility thermometers, such as Zr-in-rutile, Zr-in-titanite, Ti-in-zircon, and Ti-in-quartz, within the past 13 years has greatly expanded our ability to assess the pressure and temperature conditions of individual minerals associated with specific textures in metamorphic rocks. Combined with advances in in situ techniques for analyzing trace concentrations, this has led to an increase in the combined use of single element thermometers, geochronometers, and isotope ratios, often simultaneously, in metamorphic minerals. Here we review the calibration and application of single element thermometers at the pressure and temperat…
Element variations in rhyolitic magma resulting from gas transport
2013
Tuffisite veins are glass-filled fractures formed when magma fragments during degassing within the conduit. These veins form transient channels through which exsolved gases can escape from magma. The purpose of this study is to determine the extent to which chemical heterogeneity within the melt results from gas transport, and assess how this can be used to study magma degassing. Two tuffisite veins from contrasting rhyolitic eruptions at Torfajökull (Iceland) and Chaitén (Chile) were studied in detail. The tuffisite vein from Torfajökull is from a shallow dissected conduit (~70. ka) that fed a degassed lava flow, while the sample from Chaitén was a bomb ejected during the waning phases of …
Prodigious emission rates and magma degassing budget of major, trace and radioactive volatile species from Ambrym basaltic volcano, Vanuatu island Arc
2016
Abstract Ambrym volcano, in the Vanuatu arc, is one of the most active volcanoes of the Southwest Pacific region, where persistent lava lake and/or Strombolian activity sustains voluminous gas plume emissions. Here we report on the first comprehensive budget for the discharge of major, minor, trace and radioactive volatile species from Ambrym volcano, as well as the first data for volatiles dissolved in its basaltic magma (olivine-hosted melt inclusions). In situ MultiGAS analysis of H 2 O, CO 2 , SO 2 and H 2 S in crater rim emissions, coupled with filter-pack determination of SO 2 , halogens, stable and radioactive metals demonstrates a common magmatic source for volcanic gases emitted by…