Éditeur(s) : HAL CCSD Pacific-credo Publications
Résumé : International audience
Les sciences humaines et sociales dans le Pacifique Sud, terrain questions et méthodes

ISBN : 978-2-9537485-2-9
hal-01342961
https://hal-univ-perp.archives-ouvertes.fr/hal-01342961

Éditeur(s) : HAL CCSD De Gruyter
Résumé : International audience
Coral reefs have undergone profound ecological changes over recent decades. Areas formerly covered by scleractinian coral species are now often overgrown by macroalgae. In Martinique (West Indies), this phenomenon has lead to the colonisation of numerous coral reefs by algae, amongst which Sargassum is one of the most prominent. This study focuses on potential defence molecules produced by Sargassum polyceratium. The hexane dipping method was employed to extract surface molecules on fresh material, and their bioactivities were assessed against bacteria (marine and estuarine), and marine tropical invertebrates wan annelid (Pseudonereis sp.), a bivalve (Codakia orbicularis) and a sea urchin (Diadema antillarum)x. Extracts were active against all microorganisms tested (MICs150 or 300 mg ml-1), early stages of development in Pseudonereis sp. (MICs100 mg ml-1) and embryos of C. orbicularis and D. antillarum (MICs5 mg ml-1), suggesting the production of defence compounds by S. polyceratium.
ISSN: 0006-8055

hal-00746082
https://hal.univ-antilles.fr/hal-00746082
https://hal.univ-antilles.fr/hal-00746082/document
https://hal.univ-antilles.fr/hal-00746082/file/Publication_Sargassum_bortanica_marina.pdf
DOI : 10.1515/BOT.2011.014

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Convergent plate margins typically experience a transition from subduction to collision dynamics as massive continental blocks enter the subduction channel. Studies of high-pressure rocks indicate that tectonic fragments are rapidly exhumed from eclogite facies to mid-crustal levels, but the details of such dynamics are controversial. To understand the dynamics of a subduction channel we report the results of a petrochronological study from the central Sesia Zone, a key element of the internal Western Alps. This comprises two polymetamorphic basement complexes (Eclogitic Micaschist Complex and Gneiss Minuti Complex) and a thin, dismembered cover sequence (Scalaro Unit) associated with pre-Alpine metagabbros and metasediments (Bonze Unit). Structurally controlled samples from three of these units (Eclogitic Micaschist Complex and Scalaro-Bonze Units) yield unequivocal petrological and geochronological evidence of two distinct high-pressure stages. Ages (U-Th-Pb) of growth zones in accessory allanite and zircon, combined with inclusion and textural relationships, can be tied to the multi-stage evolution of single samples. Two independent tectono-metamorphic 'slices' showing a coherent metamorphic evolution during a given time interval have been recognized: the Fondo slice (which includes Scalaro and Bonze rocks) and the Druer slice (belonging to the Eclogitic Micaschist Complex). The new data indicate separate stages of deformation at eclogite-facies conditions for each recognized independent kilometer-sized tectono-metamorphic slice, between ∼85 and 60 Ma, with evidence of intermittent decompression (ΔP ∼ 0*5 GPa) within only the Fondo slice. The evolution path of the Druer slice indicates a different P-T-time evolution with prolonged eclogite-facies metamorphism between ∼85 and 75 Ma. Our approach, combining structural, petrological and geochronological techniques, yields field-based constraints on the duration and rates of dynamics within a subduction channel.
ISSN: 0022-3530

hal-01054335
https://hal.archives-ouvertes.fr/hal-01054335
DOI : 10.1093/petrology/egu029

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
Dating the timing of motion on crustal shear zones is of tremendous importance for understanding the assembly of orogenic terranes. This objective is achieved in this paper by combining petrological and structural observations with novel developments in in situ U-Th-Pb geochronology of allanite. A greenschist facies shear zone within the Mont Blanc Massif is documented. Allanite is synkinematic and belongs to the mylonitic assemblage. LA-ICP-MS U-Th-Pb isotope analyses of allanite reveal high contents and highly radiogenic isotopic compositions of the common-Pb component. The use of measured Pb-isotope compositions of associated minerals (feldspars and chlorite) is critical for accurate common-Pb correction, and provides a powerful mechanism for linking allanite growth to the metamorphic assemblage. A mean 208Pb/232Th age of 29.44 ± 0.95 Ma is accordingly taken for synkinematic allanite crystallisation under greenschist facies conditions. This age reflects the timing of the Mont Blanc underthrusting below the Penninic Front and highlights the potential of directly dating deformation with allanite.
ISSN: 0954-4879

hal-00963545
https://hal.archives-ouvertes.fr/hal-00963545
DOI : 10.1111/ter.12066