Search results for "Geophysic"

Crystallographic preferred orientation development by dissolution–precipitation creep

2000

Abstract Crystallographic preferred orientations (CPOs) in deformed rocks are commonly interpreted as resulting from crystal plastic deformation mechanisms, where deformation is achieved by the movement of dislocations. In this paper we investigate the possibility of CPO-development by dissolution–precipitation creep or pressure solution. A numerical model is presented, which simulates the development of a grain aggregate that deforms by reaction-controlled dissolution–precipitation creep. Grains are simulated as rectangular boxes that change their shape by growth, or dissolution of their surfaces, depending on the normal stresses acting on the individual surfaces. Grains can also rotate du…

Seismic moment tensors and regional stress in the area of the December 2013–January 2014, Matese earthquake sequence (Italy)

2014

Abstract The main goal of this study is to provide moment tensor solutions for small and moderate earthquakes of the Matese seismic sequence in southern Italy for the period of December 2013–January 2014. We estimate the focal mechanisms of 31 earthquakes with local magnitudes related to the Matese earthquake seismic sequence (December 2013–January 2014) in Southern-Central Italy which are recorded by the broadband stations of the Italian National Seismic Network and the Mediterranean Very Broadband Seismographic Network (MedNet) run by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The solutions show that normal faulting is the prevailing style of seismic deformation in agreeme…

Shear strength of a compacted scaly clay in variable saturation conditions

2015

Scaly clays are stiff and highly fissured clays often used as construction materials. This paper presents the results of triaxial compression tests carried out on saturated and unsaturated samples of a compacted scaly clay. Complementary investigation on the microstructural features and their evolution with the amount of water stored into the material are also presented in order to shed light on the evolution of the micro- and macroporosity with suction. The water retention behaviour of the compacted scaly clay is also addressed. The results from the controlled suction triaxial tests are used to discuss the applicability of a single-shear strength criterion to compacted double-structured cl…

Internal dynamics and eruptive behaviour of Stromboli volcano

2015

Mollusc and brachiopod skeletal hard parts: Intricate archives of their marine environment

2015

The biogenic carbonate hard parts of fossil bivalves, cephalopods and brachiopods are among the most widely exploited marine archives of Phanerozoic environmental and climate dynamics research. The advent of novel analytical tools has led many workers to explore non-traditional geochemical and petrographic proxies, and work performed in neighbouring disciplines sheds light on the complex biomineralization strategies applied by these organisms. These considerations form a strong motivation to review the potential and problems related to the compilation and interpretation of proxy data from bivalve, cephalopod and brachiopod hard parts from the viewpoint of the sedimentologist and palaeoceano…

Minute co-variations of Sr/Ca ratios and microstructures in the aragonitic shell of Cerastoderma edule (Bivalvia) – Are geochemical variations at the…

2017

Abstract It remains a challenging task to reconstruct water temperatures from Sr/Ca ratios of bivalve shells. Although in many aragonitic species, Sr/Ca is negatively correlated to temperature – which is expected based on abiogenic precipitation experiments, the incorporation of Sr into the shell of bivalves is strongly controlled by physiological processes and occurs away from the predicted thermodynamic equilibrium. Strontium-to-calcium ratios of aragonitic shells remain far below that of the ambient water. Moreover, Sr concentrations vary considerably among shell portions consisting of different microstructures and/or organic content. Values observed at annual growth lines and within the…

Helium–strontium isotope constraints on mantle evolution beneath the Roman Comagmatic Province, Italy

2004

- European Social Fund - Scottish Universities - Carnegie Trust for the Universities of Scotland.

Fast offline data reduction of laser ablation MC-ICP-MS Sr isotope measurements: Via an interactive Excel-based spreadsheet 'SrDR'

2020

Strontium isotopes are applied to a wide range of scientific fields and to different types of sample materials, providing valuable information foremost about provenance and age, but also on diagenetic processes and mixing relationships between different Sr reservoirs. The development of in-situ analytical techniques, such as laser ablation ICP-MS, has improved our understanding of Sr isotope variability in several field of application, because of the possibility to discriminate small-scale changes and their spatial distribution. However, large outputs of Sr isotope data are produced by laser ablation MC-ICP-MS systems, which necessitate of multiple offline steps to correct and assess the da…

Strontium and argon isotopic homogenization of pelitic sediments during low-grade regional metamorphism: The pan-African upper Damara sequence of Nor…

1979

Abstract The fine mineral fractions extracted from pelitic sediments of the Eocambrian upper Damaran Mulden Group were subjected to a detailed isotopic study by the Rb-Sr and K-Ar methods in combination with a mineralogical analysis by X-ray diffractometry. The sediments contain two major parageneses of metamorphic origin which can be related to two separate low-grade regional metamorphic events of anchizonal intensity with temperatures between 250 and 300°C and pressures up to 2 kbar. These events are dated at about 535 m.y. and 455 m.y. respectively (with λ( 87 Rb) = 1.42 × 10 −11 yr −1 ). Anomalously high K-Ar ages on samples from specific stratigraphic horizons can be related to open sy…

Reproducibility of trace element time-series (Na/Ca, Mg/Ca, Mn/Ca, Sr/Ca, and Ba/Ca) within and between specimens of the bivalve Arctica islandica – …

2017

Abstract Trace element time-series in bivalve mollusk shells and other (biogenic) materials can potentially serve as environmental proxies. Yet, the applicability of element-to-calcium ratios is often challenging, because non-environmental factors such as vital effects distort or mask environmental signals. If a trace element time-series is driven by an environmental factor, it should be reproducible within and between coeval specimens of the same species. In the present study, we tested whether time-series of trace element-to-calcium ratios can be reproduced within and between coeval specimens of the bivalve Arctica islandica and thus whether an external signal is encoded in the temporal v…