Occurrence of noble metals in aluminum- and chromium- rich objects in ordinary chondrites and of baddeleyite (ZrO2) in a chromite inclusion

Abstract— Platinum group elements (PGE) enrichments are found in Fe-Ni blebs (<1 μm) in Al- and Cr-rich objects in the ordinary chondrites Ste. Marguerite, Forest Vale, Montferré. In Ste. Marguerite, high ZrO₂ concentrations (baddeleyite) are also present in a chromite inclusion. Iridium enrichment in this material compared to its metal content is confirmed by INAA. The widespread occurrence of PGE in Al- and Cr-rich objects, mostly present in H-group chondrites of nearly equilibrated types, must be taken into account to understand their conditions of formation.     

Trace-element contents and cathodoluminescence of “trapiche” rubies from Mong Hsu, Myanmar (Burma): geological significance

Summary ?Mong Hsu rubies of the “trapiche” type are sporadically seen in the gem market. However, they have never been described in the field. The study of the nature of solid inclusions, the variation of trace-element contents, as well as the cathodoluminescence behaviour of six “trapiche” rubies permit the conclusion that these rubies crystallised in the same geological environment (marble-type deposit) as the normal rubies from Mong Hsu: (1) Cr and V are the main chromophorous elements in both ruby types; they act, together with Ti, as activators or quenchers for cathodoluminescence; (2) calcite, dolomite, rutile, mica, diaspore, apatite, chlorite, and feldspar are solid inclusions found in both ruby types; (3) the presence of bastn?site in trapiche ruby and fluorite in non-trapiche ruby indicates the circulation of F-bearing fluids during ruby deposition; (4) the distribution of trace-element contents in the crystal is similar for both ruby types. In the Cr₂O₃ vs. Fe₂O₃ and Cr₂O₃ vs. Fe₂O₃/TiO₂ diagrams, the population fields of Mong Hsu “trapiche” and non-“trapiche” rubies overlap. They are distinct from those of rubies and sapphires hosted in basalts from South-east Asia. Received October 30, 2001; revised version accepted March 25, 2002     

A short range interaction model applied to illite/smectite mixed-layer minerals

We present a solid solution model, able to take into account short-range interactions up to the third nearest neighbor. This model has been applied to illite/smectite mixed-layer clay minerals and tests the relative thermodynamic stability of each illite/smectite stacking sequence. The non-ideal energy terms have been calculated, showing a strong decrease of the interaction energy as the distance between elements grows. From ΔG _m calculations the model predicts the following succession in I/S stacking sequences as X _i tends to 1:R1, R2 and then R3. This succession agrees well with some mineralogical observations in natural series. Received: July 12, 1996 / Revised, accepted: March 21, 1997     

Elastoplastic model with loading memory surfaces (LMS) for monotonic and cyclic behaviour of geomaterials

A new elastoplastic model called loading memory surface based on the critical state concept and the multi‐surface framework is proposed for geomaterials. The model uses a hypoelastic formulation and two plastic mechanisms. The formulations of the model are made in three‐dimensional stress–strain space and work under both monotonic and cyclic loadings. A newly introduced formalism makes it possible to obtain the cyclic response directly from the monotonic loading one. This formalism gives a three‐dimensional generalization of the well‐known Masing rule. The model has been validated against test results of Hostun sand under several conditions: monotonic and cyclic, drained and undrained, tests in compression and in extension, and at different confining pressures and different densities. Copyright © 2014 John Wiley & Sons, Ltd.     

Petrochemistry of quaternary pumiceous pyroclastic products in southern Guadeloupe (F.W.I.)

Pumiceous pyroclastic products are present as flows and falls at several stages of the evolution of the southern Guadeloupe volcanic island. An understanding of this volcanism had to rely on detailed petrochemical data of these products to complement similar data for effusive rocks so as to yield complete stratigraphical coverage. On the other hand most pumiceous rocks are more or less conspicuousily banded suggesting that mixing phenomena occurred to different degrees in their genesis. Three major classes of pumiceous products are found: (1) the Axial Chain deposits (2.0–0.5 My) are characterized by An90, 75-55 + En55 + Wo42En37 + Usp35-37 ± Fo68 ± Hble, SiO₂ 60%, SiO₂/Th 35.6, and La/Th 3.9. Banded samples have components that differ in evolution indices by about 50%; (2) the Bouillante Chaine pyroclastics (0.3–0.1 My) consist of scattered deposits with variable mineralogical and geochemical compositions that seem to have erupted from a number of small eruptive centers. Qz-dacitic pumice is common with An90, 70-45 + En66-56 + Usp32-38 + Ilm94 + Hble ± Wo40-42En40-42, SiO₂ 62%, SiO₂/Th 22.9, and La/Th >4. Mixed pumice samples have highly contrasted evolution indices differing by up to 120%; (3) the Pintade pumice flows and falls correspond to the major pyroclastic event (approx. 10 km³) in the southern Basse Terre area. They are characterized by An85-70 + En66-56 + Usp32-37 ± Wo42En42, SiO₂/Th 18.7-22?6, and La/Th 3.0-4.0. Banded pumice lumps are scarce and show slight compositional contrasts; differences in evolution indices do not exceed 38%. Axial and Bouillante chain pyroclastics and Grande Découverte volcano pumice respectively, form two different families in trace element plots. Minor elements in pyroxenes also are distinctive. These trends are similar to those obtained for effusive rocks and define comagmatic series. Major and trace element data for the separated components of inhomogeneous pumice in each formation always plot in the corresponding series. These chemical discriminants can be used to attribute samples of unknown provenance to a given volcanic ensemble. An inverse relationship between differences in evolution indices in inhomegeneous pumice and the volume of any single eruptive sequence is noted. This is an indication that pumiceous pyroclastic rocks were erupted from a zoned magma chamber. We favor an interpretation where zonation is produced by influx of less envolved magma in superficial differentiated chambers which is a direct cause for eruption.     

Typical disturbances of the daytime equatorial F region observed with a high-resolution HF radar

HF radar measurements were performed near the magnetic equator in Africa (Korhogo 9°2463N–5°3738W) during the International Equatorial Electrojet Year (1993–1994). The HF radar is a high–resolution zenithal radar. It gives ionograms, Doppler spectra and echo parameters at several frequencies simultaneously. This paper presents a comparative study of the daytime ionospheric structures observed during 3 days selected as representative of different magnetic conditions, given by magnetometer measurements. Broad Doppler spectra, large echo width, and amplitude fluctuations revealed small-scale instability processes up to the F-region peak. The height variations measured at different altitudes showed gravity waves and larger-scale disturbances related to solar daytime influence and equatorial electric fields. The possibility of retrieving the ionospheric electric fields from these Doppler or height variation measurements in the presence of the other possible equatorial ionospheric disturbances is discussed.     

Vanadiferous minerals from the Nereus Deep, Red Sea

The chemical analysis by EMPEDS of 140 samples in cores from six Red Sea troughs and basins has led to the discovery in the Nereus Deep of high vanadium concentrations (up to 1.3% V₂O₃) in several bulk samples, and to the isolation of a major magnetite phase. This vanado-magnetite, remarkable for its high content of vanadium (mean = 1.45% V₂O₃) and its lack of titanium, is frequently zoned, the V-content decreasing toward the outer zones. Oxides with up to 42% V₂O₃, have also been found. Since the origin of the magnetite is clearly authigenic, its high vanadium and low titanium concentrations are traced back to the differential hydrothermal leaching of Fe—Ti-oxides which occur profusely in basic eruptive rock clasts, actually present in some of the overlying seams.     

Exact reconstruction with directional wavelets on the sphere

A new formalism is derived for the analysis and exact reconstruction of band-limited signals on the sphere with directional wavelets. It represents an evolution of a previously developed wavelet formalism developed by Antoine & Vandergheynst and Wiaux et al. The translations of the wavelets at any point on the sphere and their proper rotations are still defined through the continuous three-dimensional rotations. The dilations of the wavelets are directly defined in harmonic space through a new kernel dilation, which is a modification of an existing harmonic dilation. A family of factorized steerable functions with compact harmonic support which are suitable for this kernel dilation are first identified. A scale-discretized wavelet formalism is then derived, relying on this dilation. The discrete nature of the analysis scales allows the exact reconstruction of band-limited signals. A corresponding exact multi-resolution algorithm is finally described and an implementation is tested. The formalism is of interest notably for the denoising or the deconvolution of signals on the sphere with a sparse expansion in wavelets. In astrophysics, it finds a particular application for the identification of localized directional features in the cosmic microwave background data, such as the imprint of topological defects, in particular, cosmic strings, and for their reconstruction after separation from the other signal components.     

Behavior of arsenic and antimony in the surface freshwater reaches of a highly turbid estuary, the Gironde Estuary, France

This study reports on the behavior of two redox-sensitive elements, As and Sb, along the turbidity gradient in the freshwater reaches of the turbid Gironde Estuary. During a 17-month survey, surface water and suspended particulate matter (SPM) were sampled monthly at six sites representing both fluvial branches of the Gironde Estuary. Additionally, two longitudinal high resolution profiles were sampled along the fluvial estuary of the Garonne Branch during two contrasted seasons, i.e. with and without the presence of the maximum turbidity zone (MTZ). Seasonal variability and spatial distribution of dissolved (<0.2 μm; <0.02 μm) and particulate As, Sb and Fe were measured and combined with SPM data to understand metalloid behavior in the estuarine freshwater turbidity gradient.At the two main fluvial entries of the Gironde Estuary, dissolved As and Sb concentrations showed strong (by a factor of 2–4) seasonal variations, that were only partly controlled by discharge-related dilution. Seasonal addition of dissolved As and Sb was attributed to the degradation of particulate As and Sb carrier phases in bottom sediment and/or in the adjacent aquifers, rather than release from SPM. In the surface freshwater reaches of the Gironde Estuary, Sb behaved conservatively under all hydrological conditions. In contrast, As was strongly reactive in the presence of the MTZ, with opposite behaviors in the two fluvial branches of the estuary: in the Garonne Branch As was removed from the dissolved phase, whereas in the Dordogne Branch As was added. Redistribution of As between the dissolved and the particulate phases along the turbidity gradient in estuarine freshwater only affected the <0.02 μm fraction, as the 0.02–0.2 μm fraction remained constant (300 ng L⁻¹ in September 2005). Accordingly, As removal seemed to be decoupled from concomitant “colloidal” (0.02–0.2 μm) Fe flocculation in the turbidity gradient. The contrasting behavior of dissolved As in the fluvial estuaries of the Garonne and Dordogne Branches was attributed to sorption processes during equilibration of river-borne dissolved As with estuarine SPM forming the MTZ. This equilibrium, described by a distinct distribution coefficient K_d(As)  11,000 L kg⁻¹ in the MTZ, resulted in either As release (desorption; Dordogne Branch) or removal (adsorption; Garonne Branch) in the respective fluvial estuaries. A mixing experiment under controlled laboratory conditions tended to support that equilibration between the dissolved phase and MTZ particles may induce both As release and removal in the estuarine freshwater reaches, with As distribution evolving towards a distinct K_d value for increasing SPM concentrations. The long-term survey allowed estimating annual (2004) dissolved fluxes of As and, for the first time Sb, at the main fluvial entries of the Gironde Estuary at 30.7 t a⁻¹ and 3.2 t a⁻¹ (Garonne River) and at 8.0 t a⁻¹ and 2.3 t a⁻¹ (Dordogne River), respectively.