Structure and texture of organic matter in CV and CO carbonaceous chondrites. Relationship to metamorphic process

Abstract 5199International audienc

Structure and texture of organic matter in CV and CO carbonaceous chondrites. Relationship to metamorphic process

Abstract 5199International audienc

Metamorphic Control of Noble Gas Abundances in Pristine Chondrites

International audienceThe structure and texture of IOM was studied by HRTEM in Kaba, Leoville, Mokoia, Allende,Tieschitz. We revisit the question of the metamorphic control of the Q (P1), P3 and P6 components, the carrier of the Q phase

Carbon Thermometry Applied To Chondrites and Terrestrial Rocks: Effect of Organic Precursor

International audienceWe evidence that carbon thermometers are precursor dependent and need internal calibration. We also report the first 244 nm excitation Raman measurements on kerogens

Maturation grade of coals as revealed by Raman spectroscopy: Progress and problems

International audienceThe present study questions the sensitivity and the accuracy of Raman spectroscopy as a tool for determining the maturity of natural organic matter (NOM). It focuses on the definition of optimized experimental parameters in order to maximize the quality of the Raman signal and control the accuracy and reproducibility of measurements. A series of 11 coals has been investigated, sampling a wide maturity range (2–7% vitrinite reflectance VR). The role of experimental parameters is first investigated. An excitation wavelength of 514.5 nm gives better results than 457.9 and 632.8 nm, minimizing the fluorescence background observed in the spectra of low-rank coals. Both Raman and fluorescence spectra were investigated with time-resolved experiments in air and argon. These data show that fluorescence and Raman spectra are sensitive to acquisition time and laser power parameters, and reveal a physicochemical instability of the samples under laser irradiation, mostly due to photo-oxidation processes. These data clearly show that the experiments, especially in air, should be performed with strictly constant acquisition parameters. In addition, the results of a whole series of coal measurements performed in air under constant experimental conditions show that Raman spectroscopy is definitely sensitive to the maturity of coal samples with VR > not, vert, similar1%. The most sensitive spectral maturity tracers are the width of the D-band (FWHM-D), the ratio of the peak intensities of the D- and G-bands (ID/IG), the normalized ratio of the band integrated intensities AD/[AD + AG] for the maturity range VR = 3–7% and the width of the G-band (FWHM-G) for VR = 1–5%. However, the accuracy and reproducibility are definitely weaker in such measurements compared to the standard VR. Future work must solve the problem of sample stability under laser irradiation, and greatly increase the number of samples to improve the statistical significance of the results

High velocity frictional properties of clay-bearing fault gouges : experiments and modelling

see Abstract volumeIstituto Nazionale di Geofisica e Vulcanologia, Italy (INGV) Centre National de la Recherche Scientifique (CNRS) ExxonMobil Upstream Research CompanyUnpublishedErice, Italyope

High velocity frictional properties of clay-bearing fault gouges : experiments and modelling

see Abstract volum

The High Resolution Transmission Electron Microscopy: A Powerful Tool for Studying the Organization of Terrestrial and Extra-Terrestrial Carbons

International audienceHigh Resolution Transmission Electron Microscopy (HRTEM) makes possible the imaging of the profile of the polyaromatic layers, allowing a knowledge of carbons, such as disordered natural carbons from meteorites and from Precambrian metasediment

High resolution TEM of chondritic carbonaceous matter: Metamorphic evolution and heterogeneity

International audienceThe insoluble carbonaceous matter from 12 chondrites (CI, CM, CO, CV, EH, and UOC), was characterized by high resolution transmission electron microscopy (HRTEM). Besides ubiquitous nanoglobules, the insoluble organic matter from petrologic type 1 and 2 chondrites and Semarkona (LL 3.0) is composed of a highly disordered polyaromatic component. No structural differences were observed between these IOMs, in agreement with the limited thermal metamorphism they all experienced. In chondrites of petrologic type >3.0, the evolution of the IOM is controlled by the extent of thermal metamorphism. The polyaromatic layers, shorter than 1 nm in petrologic type =3.0 chondrites, grow up to sizes between 5 and 10 nm in petrologic type >3.6 chondrites, contributing to the increase of the degree of structural order. In addition, we find rare, but ubiquitous onion-like carbons, which may be the product of nanodiamond graphitization. The insoluble carbonaceous matter of the enstatite chondrite Sahara 97096 (EH 3) is different from the other meteorites studied here. It is more heterogeneous and displays a high abundance of graphitized particles. This may be the result of a mixture between (1) the disordered carbon located in the matrix, and (2) catalytic graphitized phases associated with metal, potentially originating from partial melting events. The structural and nanostructural evolution are similar in all IOMs. This suggests that the structure of the accreted precursors and the parent body conditions of their secondary thermal modifications (temperature, duration, and pressure) were similar. The limited degree of organization of the most metamorphosed IOMs compared with terrestrial rocks submitted to similar temperature suggests that the conditions are not favorable to graphitization processes, due to the chemical nature of the precursor or the lack of confinement pressure