Éditeur(s) : HAL CCSD
Résumé : International audience
Conférence MISTRALS PAELOMEX
Montpellier, France

hal-01683548
https://hal-univ-tlse2.archives-ouvertes.fr/hal-01683548

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This study investigated the clinical epidemiology and resistance mechanisms of Acinetobacter baumannii and characterised the clonal diversity of carbapenem-resistant A. baumannii (CRAB) during an ICU-associated outbreak at Cayenne Hospital, French Guiana. All non-duplicate A. baumannii isolates from 2008 to 2014 were tested for antibiotic susceptibility by disk diffusion. Multilocus sequence typing, pulsed-field gel electrophoresis (PFGE) and characterisation of carbapenemase-encoding genes were performed on CRAB. Of the 441 A. baumannii isolates, most were from males (54.0%) and were detected mainly from the ICU (30.8%) and medicine wards (21.8%). In the ICU, strains were mainly isolated from the respiratory tract (44.1%) and bloodstream (14.0%), whereas in medicine wards they mainly were from wound/drainage (36.5%) and bloodstream (25.0%). A. baumannii showed the greatest susceptibility to piperacillin/tazobactam (92.7%), imipenem (92.5%), colistin (95.6%) and amikacin (97.2%), being lower in the ICU and medicine wards compared with other wards. An outbreak of OXA-23-producing CRAB occurred in the 13-bed ICU in 2010. CRAB strains were more co-resistant to other antimicrobials compared with non-CRAB. Molecular genetics analysis revealed five sequence types [ST78, ST107 and ST642 and two new STs (ST830 and ST831)]. Analysis of PFGE profiles indicated cross-transmissions of CRAB within the ICU, between the ICU and one medicine ward during transfer of patients, and within that medicine ward. This study provides the first clinical and molecular data of A. baumannii from French Guiana and the Amazon basin. The ICU was the highest risk unit of this nosocomial outbreak of OXA-23-producing CRAB, which could subsequently disseminate within the hospital.
ISSN: 0924-8579

hal-01506828
https://hal.archives-ouvertes.fr/hal-01506828
PUBMED : 27236843

Éditeur(s) : HAL CCSD American Association of Petroleum Geologists
Résumé : International audience
We describe the structure, microstructure, and petrophysical properties of fault rocks from two normal fault zones formed in low-porosity turbiditic arkosic sandstones, in deep diagenesis conditions similar to those of deeply buried reservoirs. These fault rocks are characterized by a foliated fabric and quartz-calcite sealed veins, which formation resulted from the combination of the (1) pressure solution of quartz, (2) intense fracturing sealed by quartz and calcite cements, and (3) neoformation of synkinematic white micas derived from the alteration of feldspars and chlorite. Fluid inclusion microthermometry in quartz and calcite cements demonstrates fault activity at temperatures of 195degC to 268degC. Permeability measurements on plugs oriented parallel with the principal axes of the finite strain ellipsoid show that the Y axis (parallel with the foliation and veins) is the direction of highest permeability in the foliated sandstone (10-2 md for Y against 10-3 md for X, Z, and the protolith, measured at a confining pressure of 20 bars). Microstructural observations document the localization of the preferential fluid path between the phyllosilicate particles forming the foliation. Hence, the direction of highest permeability in these fault rocks would be parallel with the fault and subhorizontal, that is, perpendicular to the slickenlines representing the local slip direction on the fault surface. We suggest that a similar relationship between kinematic markers and fault rock permeability anisotropy may be found in other fault zone types (reverse or strike-slip) affecting feldspar-rich lithologies in deep diagenesis conditions.
ISSN: 0149-1423

hal-00903428
https://hal.archives-ouvertes.fr/hal-00903428
DOI : 10.1306/03071312127

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
11 4 : CEA/HC 12 13 Corresponding author: 14 pierre.legoff@cea.fr -+333 80 23 40 00 -+333 80 23 52 09 15 16 Abstract 17 As one of the three natural isotopes of hydrogen, tritium is ubiquitous and might potentially 18 be present in any water or organic molecule that constitutes a biological matrix. Milk is one of 19 the most frequently monitored foodstuffs in the vicinity of chronic release of radionuclides, as 20 it is a very common product and also because it integrates deposition on large areas of grass at 21 a local scale. Different parameters have been studied to assess their impact on the reliability 22 of tritium measurements. The volume of the sample, the technique used to extract the water 23 and the level of dehydration modulate the results but in different ways: dispersion of results, 24 under-or overestimation of the tritium activity. The influence of sample storage and 25 preparation has also been investigated. Methodological improvements of tritium 26 measurements in the free water of milk are proposed. 27 28
ISSN: 0265-931X

hal-01117741
https://hal.archives-ouvertes.fr/hal-01117741
https://hal.archives-ouvertes.fr/hal-01117741/document
https://hal.archives-ouvertes.fr/hal-01117741/file/Tritium%20in%20the%20free%20water%20of%20milk-FINAL.pdf
DOI : 10.1016/j.jenvrad.2013.09.006

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This study addresses the mechanical and chemical behavior of allanite during shear zone formation under high-pressure metamorphism. Understanding physico-chemical processes related to the retention or resetting of Pb isotopes in allanite during geological processes is essential for robust petrochronology. Dating of allanite in meta-granodiorite showing variable amounts of strain (from an undeformed protolith to mylonite) at Monte Mucrone (Sesia Zone, NW Italy) gave surprising results. Based on structural and petrographic observations the shear zones at Mt Mucrone are Alpine, yet allanite located within an eclogite facies mylonite yielded Permian ages (208Pb/232Th average age: 287 ± 7 Ma). These mm-sized allanite grains are rimmed by an aggregate of coarse-grained garnet + phengite, thought to derive from former epidote. These aggregates were immersed in a weak matrix that experienced granular flow, and they were thus chemically and mechanically shielded during Alpine mylonitization. In undeformed samples (8a and 8b), two populations of epidote group minerals were found. Allanite forms either coronas around Permian monazite or individual grains with patchy zoning. Both types yield Permian ages (208Pb/232Th age: 291 ± 5 Ma). On the other hand, grains of REE-rich clinozoisite of Cretaceous age are found in undeformed rocks. These grains appear as small fragments with embayed surface outlines and minute satellites or rims around Permian allanite. These (re)crystallized grains are Sr-rich and show mosaic zoning. These results indicate that allanite crystals retained their chemical and isotopic characteristics, and thus their Permian age, as a result of strong strain partitioning between the epidote group porphyroclasts and the eclogite facies matrix in HP-mylonites. The observed partial mobilization of Pb isotopes, which lead to the Cretaceous-aged rims or grains in undeformed samples was facilitated by (re)crystallization of allanite and not by mere Pb diffusion alone under the HP conditions.
ISSN: 0024-4937

insu-00679730
https://hal-insu.archives-ouvertes.fr/insu-00679730
DOI : 10.1016/j.lithos.2011.01.005

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Evidence of a changing environment in the catchment area of a small pond (Lansquenet, Lorraine, France) during the last millennium was provided by coupling palynology data and organic ratios [terrestrial to aquatic ratio: TAR(HC); the C29 vs. C27 sterols, C29/C27(ST); average chain length, ACL and aquatic/macrophytes ratio, Paq]. The depositional and alteration conditions of organic matter (OM) were provided by the 5α(H)-stanols/Δ5-sterols ratio. This study shows that quite simple organic ratios clearly allow identification of the different evolution steps of a watershed, from a swamp to the progressive settlement of a pond. During the swampy period, the C/N(at) (ca. 11.1), TAR(HC) (ca. 36.8), C29/C27(ST) (ca. 8.7) and Paq (<0.3) show a high contribution of allochthonous OM associated with the presence of particular aquatic and mesohygrophilous species. A woody level dated to the XIIIth century reflects the period of the settlement of the pond in a more oxic environment [5α(H)-stanol/Δ5sterol ratio <0.2]. Then, the progressive increase in aquatic input and the development of submerged and floating macrophytes are evidenced by low C/N(at) (<7.6), TAR(HC) (ca. 2.7), C29/C27(ST) (ca. 2) and high Paq (ca. 0.5), suggesting an increase in the water level and eutrophication of the pond. A second oxic event [5α(H)-stanols/Δ5sterols ratio averaging 0.16], associated with extensive OM degradation, corresponds to the most recent dredging in 2002 and reflects an important disturbance of sediments due to pond management.
ISSN: 0146-6380

hal-00758066
https://hal.archives-ouvertes.fr/hal-00758066
DOI : 10.1016/j.orggeochem.2012.06.004

Éditeur(s) : HAL CCSD
American Geophysical Union, Fall Meeting 2009
San Francisco, United States

hal-00483586
https://hal.archives-ouvertes.fr/hal-00483586

Éditeur(s) : HAL CCSD
Résumé : Présentation orale
Q7
besancon, France

hal-00481847
https://hal.archives-ouvertes.fr/hal-00481847

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
This paper aims to decipher the thermal evolution of the Montagne Noire Axial Zone (MNAZ,southern French Massif Central) gneiss core and its metasedimentary cover through determination ofP–T paths and temperature gradients. Migmatitic gneiss from the core of the dome record a clock-wise evolution culminating at 725 25 °C and 0.8 0.1 GPa with partial melting, followed by adecompression path with only minor cooling to 690 25° C and 0.4 0.1 GPa. Field structuralanalyses as well as detailed petrological observations interpreted in a petrogenetic grid indicate thatthe cover sequence experienced LP-HT metamorphism at <0.4 GPa. Apparent thermal gradientswithin the cover were determined with garnet–biotite thermometry and Raman Spectroscopy on Car-bonaceous Matter. High-temperature apparent gradients (e.g. 530 °C km1 along one transect) areexplained by late brittle–ductile extensional shearing evidenced by phyllonites that post-date peakmetamorphism. In areas where normal faults are less abundant and closely spaced, gradients of 20to 50 °C km1 are calculated. These gradients can be accounted for by a combination of domeemplacement and ductile shearing (collapse of isotherms), without additional heat input. Finally, thethermal evolution of the MNAZ is typical for many gneiss domes worldwide as well as with otherLP-HT terranes in the Variscides.
ISSN: 0263-4929

Droits : http://creativecommons.org/licenses/by-nc-nd/
insu-01290388
https://hal-insu.archives-ouvertes.fr/insu-01290388
https://hal-insu.archives-ouvertes.fr/insu-01290388/document
https://hal-insu.archives-ouvertes.fr/insu-01290388/file/jmg12188.pdf
DOI : 10.1111/jmg.12188

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Although magmatism may occur during the earliest stages of continental rifting, its role in strain accommodation remains weakly constrained by largely 2-D studies. We analyze seismicity data from a 13 month, 39-station broadband seismic array to determine the role of magma intrusion on state-of-stress and strain localization, and their along-strike variations. Precise earthquake locations using cluster analyses and a new 3-D velocity model reveal lower crustal earthquakes beneath the central basins and along projections of steep border faults that degas CO2. Seismicity forms several disks interpreted as sills at 6-10 km below a monogenetic cone field. The sills overlie a lower crustal magma chamber that may feed eruptions at Oldoinyo Lengai volcano. After determining a new ML scaling relation, we determine a b-value of 0.87±0.03. Focal mechanisms for 65 earthquakes, and 13 from a catalogue prior to our array reveal an along-axis stress rotation of ∼60° in the magmatically active zone. New and prior mechanisms show predominantly normal slip along steep nodal planes, with extension directions ∼N90°E north and south of an active volcanic chain consistent with geodetic data, and ∼N150°E in the volcanic chain. The stress rotation facilitates strain transfer from border fault systems, the locus of early-stage deformation, to the zone of magma intrusion in the central rift. Our seismic, structural, and geochemistry results indicate that frequent lower crustal earthquakes are promoted by elevated pore pressures from volatile degassing along border faults, and hydraulic fracture around the margins of magma bodies. Results indicate that earthquakes are largely driven by stress state around inflating magma bodies.
ISSN: 1525-2027

hal-01667198
https://hal.archives-ouvertes.fr/hal-01667198
DOI : 10.1002/2017GC007027

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Rifting in a cratonic lithosphere is strongly controlled by several interacting processes including crust/mantle rheology, magmatism, inherited structure and stress regime. In order to better understand how these physical parameters interact, a 2 yr long seismological experiment has been carried out in the North Tanzanian Divergence (NTD), at the southern tip of the eastern magmatic branch of the East African rift, where the southward-propagating continental rift is at its earliest stage. We analyse teleseismic data from 38 broad-band stations ca. 25 km spaced and present here results from their receiver function (RF) analysis. The crustal thickness and Vp/Vs ratio are retrieved over a ca. 200 × 200 km2 area encompassing the South Kenya magmatic rift, the NTD and the Ngorongoro-Kilimanjaro transverse volcanic chain. Cratonic nature of the lithosphere is clearly evinced through thick (up to ca. 40 km) homogeneous crust beneath the rift shoulders. Where rifting is present, Moho rises up to 27 km depth and the crust is strongly layered with clear velocity contrasts in the RF signal. The Vp/Vs ratio reaches its highest values (ca. 1.9) beneath volcanic edifices location and thinner crust, advocating for melting within the crust. We also clearly identify two major low-velocity zones (LVZs) within the NTD, one in the lower crust and the second in the upper part of the mantle. The first one starts at 15–18 km depth and correlates well with recent tomographic models. This LVZ does not always coexist with high Vp/Vs ratio, pleading for a supplementary source of velocity decrease, such as temperature or composition. At a greater depth of ca. 60 km, a mid-lithospheric discontinuity roughly mimics the step-like and symmetrically outward-dipping geometry of the Moho but with a more slanting direction (NE–SW) compared to the NS rift. By comparison with synthetic RF, we estimate the associated velocity reduction to be 8–9 per cent. We relate this interface to melt ponding, possibly favouring here deformation process such as grain-boundary sliding (EAGBS) due to lithospheric strain. Its geometry might have been controlled by inherited lithospheric fabrics and heterogeneous upper mantle structure. We evidence that crustal and mantle magmatic processes represent first order mechanisms to ease and locate the deformation during the first stage of a cratonic lithospheric breakup.
ISSN: 0956-540X

hal-01622078
https://hal.archives-ouvertes.fr/hal-01622078
https://hal.archives-ouvertes.fr/hal-01622078/document
https://hal.archives-ouvertes.fr/hal-01622078/file/plasmanGJI2017.pdf
DOI : 10.1093/gji/ggx177

Éditeur(s) : HAL CCSD
Résumé : Thrusting fault zone in foreland basins are characterized by highly foliated zones generally enriched in phyllosilicates which can play a major role on the mechanical behaviour of the fault. In this context, investigations of synkinematic clay minerals permit to determine the origin of the fluid from which they precipitated as well as the mechanisms of deformation. Our study is focused on clay mineral assemblages (illite and chlorite) in a major thrust fault located in the Monte Perdido massif (southern Pyrenees), a shallow thrust that affects upper cretaceous-paleocene platform carbonates and lower Eocene marls and turbidites. It implied 3 km of displacement of the Monte Perdido thrust unit with respect to the underlying Gavarnie unit. In this area the cleavage development by pressure-solution is linked to the Monte Perdido and Gavarnie thrust activity. The core zone of the fault, about 6 m thick, consists of an interval of intensely deformed clay-bearing rocks bounded by major shear surfaces. The deformed sediment is markedly darker than the protolith. Calcite-quartz shear veins along the shear planes are abundant. Detailed SEM and TEM observations of highly deformed fault zone samples indicate that clay mineral enrichment in the core zone of the fault is not only related to passive increase by pressure-solution mechanism but that dissolution-recrystallization of phyllosilicates occurs during deformation. A mineral segregation is observed in the highly deformed zone. Newly formed 2M 1 muscovite is present along the cleavage whereas IIb chlorite crystals fill SV2 shear veins suggesting syntectonic growth of phyllosilicates in the presence of fluids in low-grade metamorphic conditions. These mineralogical reactions act as weakening processes and would favour Monte Perdido fault creeping.
Swiss Journal of Geosciences

hal-00795553
https://hal.archives-ouvertes.fr/hal-00795553
DOI : 10.1007/s00015-012-0098-0

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
ISSN: 0010-7999

hal-01664653
https://hal.archives-ouvertes.fr/hal-01664653
DOI : 10.1007/s00410-017-1394-5

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
Collisional mountain belts grow as a consequence of continental plate convergence and eventuallydisappear under the combined effects of gravitational collapse and erosion. Using a decade ofGPS data, we show that the western Alps are currently characterized by zero horizontal velocityboundary conditions, offering the opportunity to investigate orogen evolution at the time ofcessation of plate convergence. We find no significant horizontal motion within the belt, but GPS andlevelling measurements independently show a regional pattern of uplift reaching ~2.5 mm/yr in thenorthwestern Alps. Unless a low viscosity crustal root under the northwestern Alps locally enhancesthe vertical response to surface unloading, the summed effects of isostatic responses to erosion andglaciation explain at most 60% of the observed uplift rates. Rock-uplift rates corrected from transientglacial isostatic adjustment contributions likely exceed erosion rates in the northwestern Alps. In theabsence of active convergence, the observed surface uplift must result from deep-seated processes.
ISSN: 2045-2322

hal-01357450
https://hal.archives-ouvertes.fr/hal-01357450
https://hal.archives-ouvertes.fr/hal-01357450/document
https://hal.archives-ouvertes.fr/hal-01357450/file/noquet2016.pdf
DOI : 10.1038/srep28404

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Isotopic fractionation of tritium is a highly relevant issue in radiation protection and requires certain radioecological considerations. Sound evaluation of this factor is indeed necessary to determine whether environmental compartments are enriched/depleted in tritium or if tritium is, on the contrary, isotopically well-distributed in a given system. The ubiquity of tritium and the standard analytical methods used to assay it may induce biases in both the measurement and the signification that is accorded to the so-called fractionation: based on an exhaustive review of the literature, we show how, sometimes large deviations may appear. It is shown that when comparing the non-exchangeable fraction of organically bound tritium (neOBT) to another fraction of tritium (e.g. tritiated water) the preparation of samples and the measurement of neOBT reported frequently led to underestimation of the ratio of tritium to hydrogen (T/H) in the non-exchangeable compartment by a factor of 5 % to 50 %. In the present study, corrections are proposed for most of the biological matrices studied so far. Nevertheless, the values of isotopic fractionation reported in the literature remain difficult to compare with each other, especially since the physical quantities and units often vary between authors. Some improvements are proposed to better define what should encompass the concepts of exchangeable and non-exchangeable fractions.
ISSN: 0160-4120

hal-01117744
https://hal.archives-ouvertes.fr/hal-01117744
https://hal.archives-ouvertes.fr/hal-01117744/document
https://hal.archives-ouvertes.fr/hal-01117744/file/Article%20review%20discrimination%20isotopique-envoy%C3%A9.pdf
DOI : 10.1016/j.envint.2013.12.020

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In fold-and-thrust belts, shortening is mainly accommodated by thrust faults which are preferential zones for recrystallisation and mass transfer. This study focuses on a detachment fault related to the emplacement of the Monte Perdido thrust unit in the southern Pyrenees. The studied fault zone consists of a 10 m thick intensively foliated phyllonite developed within the Millaris marls, of Eocene age. The lithological homogeneity of the hanging wall and footwall allows us to compare the Millaris marls outside the fault zone with the highly deformed marls located in the fault zone and to quantify the chemical, mineralogical and volumetric changes related to deformation processes along the fault. The Millaris marls are composed of detrital quartz, illite, chlorite, minor albite and pyrite, in a micritic calcite matrix. In the fault zone, the cleavage planes are marked by clay minerals and calcite ± chlorite veins attest to fluid-mineral interactions during deformation. The mineral proportions in all samples from both the fault zone and Millaris marls have been quantified by two methods: (1) X-ray diffraction and Rietveld refinement, and (2) bulk chemical analyses as well as microprobe analyses to calculate modal composition. The excellent agreement between the results of these two methods allows us to estimate mineralogical variations using a modification of the Gresens' equation. During fault activation, up to 45 wt% of calcite was lost while the amounts of quartz and chlorite remained unchanged. Illite content remained constant to slightly enriched. The mineralogical variations were coupled with a significant volume loss (up to 45%) mostly due to the dissolution of micritic calcite grains. Deformation was accompanied by pressure solution and phyllosilicates recrystallisation. These processes accommodated slip along the fault. They required fluids as catalyst, but they did not necessitate major chemical transfers.
ISSN: 0264-8172

hal-00976361
https://hal.archives-ouvertes.fr/hal-00976361
DOI : 10.1016/j.marpetgeo.2013.12.016

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : National audience
ISSN: 0761-8425

hal-01368337
https://hal.archives-ouvertes.fr/hal-01368337
PUBMED : 27209117

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
The use of recombinant antigens has been shown to improve both the sensitivity and the standardization of the serological diagnosis of Farmer's lung disease (FLD). The aim of this study was to complete the panel of recombinant antigens available for FLD serodiagnosis with antigens of Lichtheimia corymbifera, known to be involved in FLD. L. corymbifera proteins were thus separated by 2D electrophoresis and subjected to western blotting with sera from 7 patients with FLD and 9 healthy exposed controls (HEC). FLD-associated immunoreactive proteins were identified by mass spectrometry based on a protein database specifically created for this study and subsequently produced as recombinant antigens. The ability of recombinant antigens to discriminate patients with FLD from controls was assessed by ELISA performed with sera from FLD patients (n = 41) and controls (n = 43) recruited from five university hospital pneumology departments of France and Switzerland. Forty-one FLD-associated immunoreactive proteins from L. corymbifera were identified. Six of them were produced as recombinant antigens. With a sensitivity and specificity of 81.4 and 77.3% respectively, dihydrolipoyl dehydrogenase was the most effective antigen for discriminating FLD patients from HEC. ELISA performed with the putative proteasome subunit alpha type as an antigen was especially specific (88.6%) and could thus be used for FLD confirmation. The production of recombinant antigens from L. corymbifera represents an additional step towards the development of a standardized ELISA kit for FLD diagnosis. © 2016 Rognon et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
ISSN: 1932-6203

hal-01367148
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01367148
DOI : 10.1371/journal.pone.0160888

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Plio-Pleistocene diatomitic sequences in the Shamb paleo-lake (South Armenia, Lesser Caucasus) offer a rare opportunity to give new insights on the paleo-climate of Western Asia. We present an integrated palynological, 40Ar/39Ar geochronologic and magnetostratigraphic study for the most complete section in the sedimentary deposits of the Shamb paleo-lake. 40Ar/39Ar dating of two volcaniclastic layers provided ages of 1.24 ± 0.03 and 1.16 ± 0.02 Ma (2. Magnetostratigraphic data show that the entire Shamb section is of reversed polarity which, combined with 40Ar/39Ar dating, suggests that the entire section correlates with part of the Matuyama period (1.785-1.070 Ma). Pollen assemblages and macroremains diversity clearly show an alternation of glacial and interglacial phases. Age calibrations and accumulation rate extrapolation allow a direct correlation of climate changes with the global isotopic curve, and show that the Shamb section probably ranges from approximately 1.300 to 1.080 Ma (marine isotopic stages 40 to 31). The vegetation of the Lesser Caucasus developed in a mosaic pattern in a Pleistocene continental, mostly arid climate, comparable to the present-day climate. The observed vegetation changes record a dominant climate response to the obliquity orbital parameter, but the influence of precession could not be established from the Shamb data. Pollen and macroflora both indicate that glacial periods were cold and dry and that interglacials were warm with local humidity. The early Pleistocene climatic model for Western Asia is thus similar to the climatic model for the Mediterranean area.
ISSN: 0012-821X

hal-00470353
https://hal.archives-ouvertes.fr/hal-00470353
DOI : 10.1016/j.epsl.2010.01.007

Éditeur(s) : HAL CCSD E Schweizerbart Science Publishers
Résumé : International audience
Mass balance calculations have been performed through a comparison of published graphical and statistical approaches applied to two contrasted geological settings: (i) the development of a greenschist-facies ductile shear-zone that recorded a weak volume change but significant mass transfers, and (ii) the formation of exoskarns in metacarbonate xenoliths that recorded a large volume decrease related to huge mass transfers. The comparison of the four mass-balance approaches shows that, if uncertainties are ignored, (1) they yield similar results concerning the mobile vs immobile behaviour of many components; (2) they yield similar mass-change values on bulk rock and on individual chemical elements (bulk-rock mass-change values differ by a maximum of ca. 15 % between graphical and statistical treatments of the metacarbonate xenolith evolution). The main difference concerns the uncertainties on mass changes (for bulk rocks and individual elements), which are much larger with the graphical than with the statistical approaches when uncertainties on chemical elements are taken into account, as they should be.The main advantage of the graphical methods is their rapid implementation and the clarity of the diagrams. Their main disadvantages are that uncertainties on each chemical element and bulk compositions are not taken into account and the difficulty in choosing an accurate immobility field to precisely define errors. Graphical methods need to be completed by a statistical treatment that gives absolute mass transfer results. The statistical approaches have the advantage of taking into account the chemical heterogeneities of the compared populations, in conjunction to a precise data treatment. The statistical treatment is an important and necessary step to decipher and to be pertinent in interpreting mobility/immobility of chemical elements, and, thus, in the absolute quantification of mass and volume changes.
ISSN: 0935-1221

hal-01260258
https://hal.archives-ouvertes.fr/hal-01260258
DOI : 10.1127/ejm/2015/0027-2475