Search results for " petrology"

On a new robust workflow for the statistical and spatial analysis of fracture data collected with scanlines (or the importance of stationarity)

2020

Abstract. We present an innovative workflow for the statistical analysis of fracture data collected along scanlines, composed of two major stages, each one with alternative options. A prerequisite in our analysis is the assessment of stationarity of the dataset, which is motivated by statistical and geological considerations. Calculating statistics on non-stationary data can be statistically meaningless, and moreover the normalization and/or sub-setting approach that we discuss here can greatly improve our understanding of geological deformation processes. Our methodology is based on performing non-parametric statistical tests, which allow detecting important features of the spatial distrib…

External ballistic of volcanic explosions

1983

In order to determine the kinetic energy of an explosion it is necessary to know the initial velocities of ejected fragments. Calculations of initial velocities made earlier with few exceptions did not take into account the resistance of the air and therefore, greatly underestimated the initial velocities, and consequently the energy of the explosions. A solution of the inverse problem of ballistics which takes into account air resistance makes it possible to find precise values of initial velocities of ejection, determined from the distance of ejected fragments and their ballistic coefficients. The method makes it possible to determine the kinetic energy of explosions for eruptions which w…

Kinetic and equilibrium studies for the adsorption of acid nucleic bases onto K10 montmorillonite

2011

Abstract The kinetic of the adsorption of two nucleic acid bases, namely adenine (A) and cytosine (C), on K10 montmorillonite (MMT) clay has been investigated over a wide range of nitrogenous bases concentrations, by using the spectrophotometric method. The measurements have been performed at T = 25.0 °C and pH = 4.0 where adenine and cytosine exist both in their protonated and neutral forms. Preliminary to the kinetic data treatment, the adsorption isotherms have been gathered and, then, analyzed by using the Freundlich and the Dubinin–Radushkevich model. The obtained results allow to draw the conclusion that physisorption of adenine and cytosine on MMT occurs and the process is mainly gov…

Unravelling textural heterogeneity in obsidian:shear-induced outgassing in the Rocche Rosse flow

2016

Obsidian flow emplacement is a complex and understudied aspect of silicic volcanism. Of particular importance is the question of how highly viscous magma can lose sufficient gas in order to erupt effusively as a lava flow. Using an array of methods we study the extreme textural heterogeneity of the Rocche Rosse obsidian flow in Lipari, a 2. km long, 100. m thick, ~. 800. year old lava flow, with respect to outgassing and emplacement mechanisms. 2D and 3D vesicle analyses and density measurements are used to classify the lava into four textural types: 'glassy' obsidian (<. 15% vesicles), 'pumiceous' lava (>. 40% vesicles), high aspect ratio, 'shear banded' lava (20-40% vesicles) and lo…

On the formation of laminated sediments on the continental margin off Pakistan – reply to the comment by von Rad et al.

2002

A Look Inside a Remarkably Large Beaded South Sea Cultured Pearl

2014

Comment on "Displacement along the Karakoram fault, NW Himalaya, estimated from LA-ICP-MS U Pb dating of offset geologic markers" published by Shifen…

2013

International audience; Field evidence for syn-deformation migmatization and crystallization along the Karakorum fault contradicts the study of Wang et al. (2012). The ages of such magmatic rocks provide minimum ages for the onset of deformation at similar to 23 Ma in North Ayilari and similar to 19 Ma in Tangtse. The onset of deformation at 12 Ma in the Ayilari range inferred by Wang et al. (2012) from a muscovite Ar/Ar age is a cooling age, thus only a minimum age. The similar to 60 Ma granodiorite bodies, the ophiolitic rocks and the south Kailash thrust that are correlated across the fault to provide a 52 +/- 2 km finite offset do not define reliable piercing points. Such observations a…

Dehydration of melt inclusions in olivine and implications for the origin of silica-undersaturated island-arc melts

2019

Highlights • New experiments with melt inclusions in olivine at 1200 °C and 300 MPa. • Coupled behavior H2O and SiO2 in inclusions during re-hydration and dehydration. • SiO2 mobility results from formation/destruction of metal vacant olivine. • SiO2-undersaturated arc melt inclusions may originate by dehydration. • New method to assess initial H2O in dehydrated inclusions. Abstract Primary subduction-related magmas build up modern continental crust and counterbalance massive recycling of crustal material into the deep mantle occurring at this tectonic setting. Melt inclusions in Mg-rich olivine are believed to be the best probes of primary subduction-related melts. However, unexpectedly, m…

Crystallization of late-stage MORB under varying water activities and redox conditions: Implications for the formation of highly evolved lavas and ox…

2018

Abstract In order to understand late magmatic processes that occur in the deep oceanic crust, we performed a phase-equilibria study in a representative late-stage system at a pressure of 200 MPa with a special focus on the role of water and oxygen fugacity. The starting composition for the experiments was evaluated based on a statistical approach using evolved fresh MORB glasses from the database PETDB highest in FeO and TiO2 (in average 17.92 wt% and 3.73 wt%, respectively), assumed to represent frozen liquids erupted at the seafloor generated by extensive differentiation of MORB. We conducted crystallization experiments in a range of temperatures from 850 to 1050 °C with water activities …

Melting and dynamic metasomatism of mixed harzburgite + glimmerite mantle source: Implications for the genesis of orogenic potassic magmas

2017

Abstract Tectonically young, orogenic settings are commonly the sites of post-collisional silica-rich ultrapotassic magmas with extreme K2O-contents of up to 9 wt% and K2O/Na2O > 2. Many experimental studies investigating the generation of these melts have concentrated on melting of homogenous phlogopite bearing peridotites, whereas geochemical signatures indicate the involvement of at least two types of source rocks: ultra-depleted and K and trace elements-enriched ones. We report the results of melting experiments at 1–2 GPa of mixed glimmerite and harzburgite, in which these rock types make up two halves each capsule. Melting begins in the glimmerite, and its metasomatic effects on the h…