Éditeur(s) : HAL CCSD Mineralogical Society of America
Résumé : International audience
Accessory phases are important hosts of trace elements; allanite may contain >90% of the REE in a bulk rock. The mobility and redistribution of several trace elements, notably HREE, Th, U, and Y is thus controlled by reactions involving allanite and other REE phases, as well as several rock-forming minerals. As these elements are commonly concentrated in mature elastic sediments, a suite of impure quartzite was studied. Two eclogite facies samples from the Monometamorphic Cover Complex of the Sesia Zone (Western Italian Alps) are presented in some detail, as they reveal a remarkably rich spectrum of reaction relationships that involve REE phases.;Two allanite-forming reactions were inferred from textures and phase compositions;(1) monazite + Ca-silicate(?) + fluid -> allanite + apatite + thorite;;(2) monazite + thorite + Ca-silicate(?) + fluid -> Th-rich allanite + auerlite +/- apatite.;Petrographic observations and thermodynamic models suggest that allanite entered the HP assemblage at similar to 530 degrees C and 17-18 kbar during prograde metamorphism.;In one sample, allanite is rimmed by epidote rich in Y and HREE that grew at the expense of xenotime. Two net transfer reactions were derived;(3) xenotime + allanite + fluid -> Y-rich epidote + apatite + thorite;;(4) xenotime + allanite + fluid -> Y-rich epidote + aeschynite + thorite + (phosphate?).;Textural relationships and trace element analyses of coexisting allanite/monazite and xenotime/Y-rich epidote reveal systematic partitioning of the REE. Partition coefficients for the HREE are compatible with equilibrium fractionation, whereas those for the LREE show patterns that seem to be inherited from the precursor phases, in this case zircon with variable LREE composition.
ISSN: 0003-004X

hal-00745674
https://hal.archives-ouvertes.fr/hal-00745674
DOI : 10.2138/am.2012.3832

Éditeur(s) : HAL CCSD Landes Bioscience
Résumé : International audience
In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.
Autophagy

hal-00735751
https://hal.archives-ouvertes.fr/hal-00735751
PUBMED : 22966490

Éditeur(s) : HAL CCSD
CorsAlp meeting
Saint Florent, France

halsde-00952560
https://hal.archives-ouvertes.fr/halsde-00952560

Éditeur(s) : HAL CCSD Springer
Résumé : International audience
In the Dent Blanche Tectonic System, the Mont Morion biotite-bearing granite is a km-scale intrusion preserved in a low-strain volume. Zircon saturation thermometry suggests that it crystallised from a melt that reached about 800 °C. U–Pb zircon and allanite geochronology indicates crystallization of the magma in the Permian (290 ± 3 Ma; 280 ± 8 Ma, respectively). Migmatitic biotite-gneiss and amphibolite are found as xenoliths within the Mont Morion granite and constitute its country-rocks. In two samples of migmatitic biotite-gneiss zircon has metamorphic overgrowths that yield U–Pb ages of 285 ± 3 Ma and 281 ± 4 Ma, and are thus contemporaneous with the intrusion of the granite. The Mont Morion granite with its country-rocks of migmatitic biotite-bearing gneiss and amphibolite was thus emplaced at middle crustal levels while amphibolite facies metamorphism affected its country rocks. The magmatic and metamorphic record in the Mont Morion area reflects the high-temperature regime and lithospheric thinning of the Adriatic continental margin during Permian.
ISSN: 1661-8726

insu-01622179
https://hal-insu.archives-ouvertes.fr/insu-01622179
DOI : 10.1007/s00015-017-0284-1

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Slices of polycyclic metasediments (marbles and meta-cherts) are tectonically amalgamated with the polydeformed basement of the Dent Blanche tectonic system along a major Alpine shear zone in the Western Alps (Becca di Salé area, Valtournenche Valley). A combination of techniques (structural analysis at various scales, metamorphic petrology, geochronology and trace element geochemistry) was applied to determine the age and composition of accessory phases (titanite, allanite and zircon) and their relation to major minerals. The results are used to reconstruct the polyphase structural and metamorphic histories, comprising both pre-Alpine and Alpine cycles. The pre-Alpine evolution is associated with low-pressure high-temperature metamorphism related to Permo-Triassic lithospheric thinning. In meta-cherts, microtextural relations indicate coeval growth of allanite and garnet during this stage, at ~ 300 Ma. Textures of zircon also indicate crystallisation at HT conditions; ages scatter from 263 to 294 Ma, with a major cluster of data at ~ 276 Ma. In impure marble, U-Pb analyses of titanite domains (with variable Al and F contents) yield apparent 206Pb/238U dates range from Permian to Jurassic. Chemical and isotopic data suggest that titanite formed at Permian times and was then affected by (extension-related?) fluid circulation during the Triassic and Jurassic, which redistributed major elements (Al and F) and partially opened the U-Pb system. The Alpine cycle lead to early blueschist facies assemblages, which were partly overprinted under greenschist facies conditions. The strong Alpine compressional overprint disrupted the pre-Alpine structural imprint and/or reactivated earlier structures. The pre-Alpine metamorphic record, preserved in these slices of metasediments, reflects the onset of the Permo-Triassic lithospheric extension to Jurassic rifting.
ISSN: 0024-4937

hal-00758123
https://hal.archives-ouvertes.fr/hal-00758123
DOI : 10.1016/j.lithos.2012.05.007