Éditeur(s) : Paris : Imprimerie nationale
Siècle(s) traité(s) : 19
Droits : Domaine public
Provenance : Communauté d'agglomération de La Rochelle. Médiathèque Michel-Crépeau
Permalien : http://www.manioc.org/patrimon/MMC16007-4
MMC16007-4

Éditeur(s) : Public Library Science
Résumé : Background: Reconstructing the history of divergence and gene flow between closely-related organisms has long been a difficult task of evolutionary genetics. Recently, new approaches based on the coalescence theory have been developed to test the existence of gene flow during the process of divergence. The deep sea is a motivating place to apply these new approaches. Differentiation by adaptation can be driven by the heterogeneity of the hydrothermal environment while populations should not have been strongly perturbed by climatic oscillations, the main cause of geographic isolation at the surface. Methodology/Principal Finding: Samples of DNA sequences were obtained for seven nuclear loci and a mitochondrial locus in order to conduct a multi-locus analysis of divergence and gene flow between two closely related and hybridizing species of hydrothermal vent mussels, Bathymodiolus azoricus and B. puteoserpentis. The analysis revealed that (i) the two species have started to diverge approximately 0.760 million years ago, (ii) the B. azoricus population size was 2 to 5 time greater than the B. puteoserpentis and the ancestral population and (iii) gene flow between the two species occurred over the complete species range and was mainly asymmetric, at least for the chromosomal regions studied. Conclusions/Significance: A long history of gene flow has been detected between the two Bathymodiolus species. However, it proved very difficult to conclusively distinguish secondary introgression from ongoing parapatric differentiation. As powerful as coalescence approaches could be, we are left by the fact that natural populations often deviates from standard assumptions of the underlying model. A more direct observation of the history of recombination at one of the seven loci studied suggests an initial period of allopatric differentiation during which recombination was blocked between lineages. Even in the deep sea, geographic isolation may well be a crucial promoter of speciation.
Plos One (1932-6203) (Public Library Science), 2009-08 , Vol. 4 , N. 8 , P. 1-15

Droits : 2009 Faure 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.
http://archimer.ifremer.fr/doc/00129/24012/21972.pdf
DOI:10.1371/journal.pone.0006485
http://archimer.ifremer.fr/doc/00129/24012/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The South Liaodong Peninsula massif is the easternmost Mesozoic Metamorphic Core Complex, recognized in Eastern China. It provides a good example of the combination of ductile shearing, synkinematic plutonism and polyphase exhumation. The Jurassic granodioritic plutons, located at the footwall of the detachment normal fault, and dated here at ca 160 Ma, recorded two different phases of cooling. A slow cooling regime of about 3-10°C/my prevailing before 122 Ma, was followed by a significant increase in cooling rate of about 40-55°C/my after that time. By contrast, a single fast cooling path was recorded by the Cretaceous monzogranite situated in the footwall of the detachment normal fault. This result indicates that the Jurassic and Cretaceous plutons recorded different exhumation processes: a Jurassic slow or negligible exhumation and a Cretaceous fast one assisted by normal faulting. These two cooling stages correspond to distinct geodynamic processes during the Jurassic and Cretaceous. Extensional tectonics seems not significant before Early Cretaceous. The second stage, dominated by an extensional regime which develops after ca 120 Ma, is tentatively correlated to the lithosphere removal of the North China Craton.
ISSN: 1367-9120

Droits : http://creativecommons.org/licenses/by-nc-nd/
insu-00528171
https://hal-insu.archives-ouvertes.fr/insu-00528171
https://hal-insu.archives-ouvertes.fr/insu-00528171/document
https://hal-insu.archives-ouvertes.fr/insu-00528171/file/Lin-JAsianEarthSciences-2010.pdf
DOI : 10.1016/j.jseaes.2010.09.007

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
The ENE-WSW Autun Shear Zone in the northeastern part of the French Massif Central has been interpreted previously as a dextral wrench fault. New field observations and microstructural analyses document a NE-SW stretching lineation that indicates normal dextral motions along this shear zone. Further east, similar structures are observed along the La Serre Shear Zone. In both areas, a strain gradient from leucogranites with a weak preferred orientation to highly sheared mylonites supports a continuous Autun-La Serre fault system. Microstructural observations, and shape and lattice-preferred orientation document high-temperature deformation and magmatic fabrics in the Autun and La Serre granites, whereas low- to intermediate-temperature fabrics characterize the mylonitic granite. Electron microprobe monazite geochronology of the Autun and La Serre granites yields a ca. 320 Ma age for pluton emplacement, while mica 40Ar-39Ar datings of the Autun granite yield plateau ages from 305 to 300 Ma. The ca. 300 Ma 40Ar-39Ar ages, obtained on micas from Autun and La Serre mylonites, indicate the time of the mylonitization. The ca. 15-Ma time gap between pluton emplacement and deformation along the Autun-La Serre fault system argue against a synkinematic pluton emplacement during late orogenic to postorogenic extension of the Variscan Belt. A ductile to brittle continuum of deformation is observed along the shear zone, with Lower Permian brittle faults controlling the development of sedimentary basins. These results suggest a two-stage Late Carboniferous extension in the northeastern French Massif Central, with regional crustal melting and emplacement of the Autun and La Serre leucogranites around 320 Ma, followed, at 305-295 Ma, by ductile shearing, normal brittle faulting, and subsequent exhumation along the Autun-La Serre transtensional fault system.
ISSN: 1437-3254

insu-00596918
https://hal-insu.archives-ouvertes.fr/insu-00596918
https://hal-insu.archives-ouvertes.fr/insu-00596918/document
https://hal-insu.archives-ouvertes.fr/insu-00596918/file/Article_Morvan_v_INIST.pdf
DOI : 10.1007/s00531-011-0673-z

Éditeur(s) : HAL CCSD Springer
Résumé : International audience
NWA2268 is a polymict eucrite discovered in the Sahara, at southwest Algeria, close to the region of Tindouf. This meteorite weighs 65 g and presents a thin black fusion crust. The rock is fine- to medium-grained breccia and contains mineral fragments of plagioclases, pyroxenes, spinel, olivine and silica. The rock contains some basaltic fragments with sub-ophitic or cumulative textures, constituted by plagioclases and exsolved pigeonite. Pyroxferroite grains are present and locally destabilised in an association of hedenbergite, fayalite and silica. It also presents unequilibrated eucritic clast with heterogeneous pyroxenes and plagioclases compositions. Pyroxenes in the all of the other clasts have equilibrated composition, with exolved pigeonites with augite lamellaes. This polymict eucrite contains also partially devitrified glass that represents impact melts linked to impact event. None recrystallization of this glass confirms a lack of post-brecciation metamorphism. Diogenitic fragments are less abundant than 10 %. The oxygen isotopic composition of NWA2268 is Δ17O (−0.43). This meteorite is interpreted as belonging to the HED group attributed to the 4-Vesta asteroid.
ISSN: 1866-7411

hal-00903591
https://hal.archives-ouvertes.fr/hal-00903591
DOI : 10.1007/s12517-012-0624-4

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In this contribution we present a reconstruction of the overall lithotectonic architecture, from inner zones to external ones, of the Paleoproterozoic Trans North China Orogen, within the North China Craton. Moreover, forward thermobarometrical modeling on a kyanite-bearing gneiss yields a reliable prograde P-T-t-D path. In addition, 40Ar/39Ar dating on rocks from distinct litho-tectonic units helps us to distinguish several tectono-metamorphic events during the orogenic development. Considering these results, we propose a geodynamic model involving three cratonic blocks, namely the Western, Fuping and Eastern Blocks, separated by two oceans, the Lüliang and Taihang Oceans. The opening of oceanic basins occurred around 2.2-2.3 Ga. After the westward subductions of oceanic lithosphere, the Trans-North-China Orogen was built up through a polyphase tectonic evolution within the period 1900-1800 Ma. The first event (D1) corresponded to the emplacement of lower and upper nappes herein called the Orthogneiss-and-Volcanites Unit (OVU) and the Low-Grade-and-Mafic Unit (LGMU), respectively. The syn-metamorphic D1 deformation (1880 ± 10 Ma) is characterized by a NW-SE stretching and mineral lineation with a top-to-the SE sense of shear. During ongoing compression of the thickening orogenic crust, a second deformation event D2 (1850 ± 10 Ma) was responsible for (1) syn-anatectic lateral flow and exhumation of the orogenic root and (2) folding of the middle and upper parts of the orogenic wedge that consequently acquired a fan-type geometry. The late D3 (1830 ± 10 Ma) and D4 (1810 ± 10 Ma) events are related to late-orogenic normal and strike-slip shearing, respectively. In our present state of knowledge, the Paleoproterozoic Trans-North China Orogen might be regarded as the assemblage of two continent-continent collisional belts, both of which are characterized by nappe stacking accommodated by top-to-the E/SE ductile shearing. Continental subduction, crustal thickening, partial melting of overthickened crust, exhumation of HP rocks and deposition of syn-orogenic detrital basins are typical features of modern collisional-type orogens.
ISSN: 0301-9268

Droits : info:eu-repo/semantics/OpenAccess
insu-00628119
https://hal-insu.archives-ouvertes.fr/insu-00628119
https://hal-insu.archives-ouvertes.fr/insu-00628119/document
https://hal-insu.archives-ouvertes.fr/insu-00628119/file/Trap-PrecambrianResearch-2011.pdf
DOI : 10.1016/j.precamres.2011.09.008

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Mechanism and kinematics of the Late Mesozoic continental extension event of eastern Asia are still debated. In order to better constrain its evolution, two granodioritic plutons of the Jiaodong Peninsula have been chosen as targets for a time-constrained palaeomagnetic study. Indeed, plutons are devoid of visible deformation, did not experience rotation along horizontal axis and are precisely dated by U/Pb and 40Ar/39Ar methods. Multidomain (MD) magnetite has been identified as the principal magnetic remanent carrier. The interpolation of existing and new U/Pb and 40Ar/39Ar ages revealed that characteristic remanent magnetisation was acquired in a narrow range of 116 ± 2 Ma. Twenty out of 27 sites present stable magnetic directions calculated from high-temperature or high-coercive components. The observations of the solo normal magnetic polarity for this palaeomagnetic collection and of the magnetic remanent age consistent with the Cretaceous Normal Superchron (CNS) argue that the characteristic magnetic remanence may be considered as primary. Detailed field observations of the intrusive relationship between the plutons and country rocks and Anisotropy of Magnetic Susceptibility (AMS) study reveal the absence of the subsequent deformation of plutons, or rigid rotation of plutons along a horizontal axis. Two palaeomagnetic poles have been therefore calculated from these plutons. Among 12 out 15 Cretaceous palaeomagnetic poles, including the two new poles provided by this study, from the Jiaodong Peninsula and on both sides of Tan-Lu and Muping-Jimo faults are statistically consistent. As a result, the Jiaodong Peninsula behaved as a rigid block as internal deformation appears negligible. The remaining three derived poles are probably due to the secular variation or/and the vicinity of fault zones near of the palaeomagnetic sampling site. Thus, they can not be applied to the peninsula-scaled tectonics. Comparison of these time52 constrained Cretaceous palaeomagnetic results of the Jiaodong Peninsula with those of North China Block (NCB) indicate that the Jiaodong Peninsula was rigidly attached to NCB since, 3 at least, the Cretaceous as residual difference is clearly insignificant with respect to the error brackets. These new palaeomagnetic results confirm that the relative clockwise (CW) rotation of Eastern Liaoning-Korea Block (ELKB) with respect to NCB does not affect the Jiaodong Peninsula as a rigid block, nevertheless, some tectonic structures have been reactivated since Cenozoic and local rotations could be produced. This palaeomagnetic study reveals that the Late Mesozoic extension in Eastern Asia is heterogeneously expressed in time and space. The complete understanding of the mechanism(s) of this extensional event needs further multidisciplinary investigations.
ISSN: 0031-9201

insu-00599546
https://hal-insu.archives-ouvertes.fr/insu-00599546
https://hal-insu.archives-ouvertes.fr/insu-00599546/document
https://hal-insu.archives-ouvertes.fr/insu-00599546/file/Charles_et_al_PEPI2011.pdf
DOI : 10.1016/j.pepi.2011.05.006

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Geochronological, mineralogical, and geochemical analyses have been focussed on the Mont-Loze're- Borne plutonic complex and surrounding rocks (Ce'vennes, French Massif Central) in which B-W-Sn and As-Au-Sb mineralization is encountered. Two main results are highlighted: (1) the existence of a 301-306 Ma magmatohydrothermal event unrelated to the emplacement of the Pont-de-Montvert-Borne plutonic body at 316 Ma; (2) the magmatic and hydrothermal features are strongly associated, both in time and in space, thus demonstrating an intimate connection between mineralizing processes and magmatism in this part of the French Massif Central. We also show that mineralization and associated hydrothermal occurrences do not correspond to a simple and single geochemical signature and that a contamination model must be invoked in order to account for the complexity of isotopic results. This study demonstrates that the application of the O and H isotopic signatures as tracers of the source and nature of fluids in an orogenic context requires some specific care. Finally, a model of the tectonic-magmatic- hydrothermal evolution of the study area is suggested in which we discuss two alternative scenarios. The first one implies the existence of two different hydrothermal/ mineralizing events (Bo-W-Sn and As-Au-Sb ones). The second one suggests the same source for all hydrothermal and mineralized structures.
ISSN: 1437-3254

insu-00576546
https://hal-insu.archives-ouvertes.fr/insu-00576546
https://hal-insu.archives-ouvertes.fr/insu-00576546/document
https://hal-insu.archives-ouvertes.fr/insu-00576546/file/Chauvet-InternationalJournalEarthSciences-2012.pdf
DOI : 10.1007/s00531-011-0639-1

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This paper presents a reappraisal of the tectonic evolution of the Zanhuang Massif that lies at the eastern margin of the Trans-North China Orogen, a continent–continent collision belt that marked the amalgamation of the North China Craton in Late Paleoproterozoic. Detailed field work with focus on geometries of structures and kinematics was performed. This was completed with LA-ICP-MS U–Pb analyses on zircon, EPMA U–Th/Pb dating on monazite and 40Ar/39Ar dating on amphibole. These studies led us to propose a new three-fold litho-tectonic subdivision of the massif: The Western Zanhuang Domain (WZD) made of TTG, migmatite and pink anatectic granite is correlated to the Fuping Massif that crops out to the north-west. Both areas represent a continental block, called the Fuping Block, which acquired most of its architecture around 2100 Ma ago. The Eastern Zanhuang Domain (EZD) made of TTG and migmatite represents the western edge of an Eastern Neoarchean Block. In between, the Central Zanhuang Domain (CZD) is a NE–SW trending stack of supracrustal, gneiss and mafic magmatic rocks thrust sheets displaced toward the ESE upon the Eastern Block. The lithological features suggest that the CZD represents the remnant of an oceanic basin, called the Taihang Ocean that closed during the amalgamation of the Eastern Block and the Fuping Block around 1880–1850 Ma. In agreement with recent work done along the western margin of the belt, in the Lüliang Massif, this study documents the amalgamation of the North China Craton in response to the closure of two oceanic basins, namely the Lüliang Ocean and the Taihang Ocean. West-dipping subductions and collisions involving three distinct continental blocks, called the Western, the Fuping and the Eastern Blocks, took place around 1880–1850 Ma.
ISSN: 0301-9268

insu-00403871
https://hal-insu.archives-ouvertes.fr/insu-00403871
https://hal-insu.archives-ouvertes.fr/insu-00403871/document
https://hal-insu.archives-ouvertes.fr/insu-00403871/file/Trap-PrecambrianResearch-2009.pdf
DOI : 10.1016/j.precamres.2009.03.011

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
The current structure of the South Armorican Domain in the French Variscan Belt, provides an excellent record of the late orogenic evolution, as documented by the complex interactions between extensional structures and partial melting. In the Golfe du Morbihan, the South Brittany Migmatite Belt (SBMB), tectonically overlain by non-melted metamorphic units, was studied by combined structural and 40Ar/39Ar methods. The recognition of successive deformation stages points to a strain continuum initiated at depth at the end of a partial melting event, and continued to near-surface brittle faulting, encompassing ductile strain localization over a major top-to-the-ESE extensional shear zone (SSZ) consistent with an overall WNW-ESE orogen-parallel stretching. This multidisciplinary study making the link between structure, texture, microchemistry and 40Ar/39Ar geochronology allow distinguishing between cooling, recrystallization and syn-tectonic crystallization ages. The first extensional insights, witnessed by dyke intrusion were dated at ~319 ± 6 Ma immediately after the SBMB partial melting. Strain localization along the SSZ, occurred until ~302-298 Ma when SBMB crossed the ductile-brittle transition. Moreover, in situ 40Ar/39Ar analysis, of syn-tectonic white micas sampled in the ductile and brittle structures yield similar ~300 Ma. Formation or reactivation of the SSZ may have occurred during the rapid cooling of the SBMB settled at ~305 Ma by conventional 40Ar/39Ar analysis. Large-scale late orogenic extensional event of the previously overthickened Variscan crust thus lasted over ~20 ± 3 Myr in the same extensional tectonic regime guided by the South Armorican Shear Zone.
ISSN: 0278-7407

insu-00628699
https://hal-insu.archives-ouvertes.fr/insu-00628699
https://hal-insu.archives-ouvertes.fr/insu-00628699/document
https://hal-insu.archives-ouvertes.fr/insu-00628699/file/2010TC002788.pdf
DOI : 10.1029/2010TC002788

Éditeur(s) : HAL CCSD EDP Sciences
Résumé : No matter which production system is considered (5% milk farms, 95% meatfarms), the Salers breed of cattle carries a strong image. Our work aims at showing that the development of the main territory in which the breed is found may rely on specific and identified products afforded by the breed. Multidisciplinary research (animal science, economics, food quality) and different methods (surveys, follow-up, and experimentation) were implemented. The experiments focused on the control of various types of production (milk, carcasses) and on a detailed description of the products (meat, cheese), given the attributes and the special behaviour of the animals. A before-weaning feeding approach favouring milk and forage later proves more efficient for finishing the young Salers male (15 months). The meat from these young bulls is clear, classified as mid-range quality, and can be sold in supermarkets. Parallel observations were made on farms and specific protein markers of juiciness were identified. Milk from Salers cows differs from that of Holstein especially in the nature of the fatty acids. Calf suckling before milking reinforces the differences. Cheeses made with raw milk from the breed differ in their textures and flavours. The cow must however be milked with her calf and the level of labour required impedes economic valorisation of the breed. Consumer surveys have confirmed the strong image of the breed that has a good potential for commercial development. Willingness to pay for identified products, however, is stronger for cheese (up to 30%) than for meat (up to 10%). Recognized qualities of products identified as issued from Salers cattle and originality in production systems can bring significant gains to various local actors, which can be considered as territorial rents.
La race bovine Salers bénéficie d’une image forte et reconnue, indépendante du système de production, laitier pour 5 % des élevages, ou allaitant pour 95 %. Pour autant le développement du « berceau de la race » peut-il s’appuyer sur les combinaisons de productions spécifiques et identifiées qu’autorise cette race ? Des recherches multidisciplinaires (zootechnie, économie, qualité des aliments) et des méthodes d’investigation variées (enquêtes, suivis, expérimentation) ont été mises en œuvre pour répondre à cette question. Les expérimentations ont porté sur la maîtrise des itinéraires de production (lait, carcasses) et la connaissance fine des produits (fromages, viandes), compte tenu des aptitudes et du comportement de la race. Une conduite alimentaire privilégiant le lait et les fourrages avant sevrage est ainsi plus efficace pour la production d’un jeune bovin Salers (15 mois). La viande de ces taurillons est claire, classée en gamme intermédiaire, mais peut se valoriser en grande et moyenne distribution. Le lait des vaches Salers diffère de celui des vaches Holstein surtout par la nature de ses acides gras. La tétée d’amorçage du veau spécifique de la race et difficile à supprimer, renforce les différences de composition. Les fromages fabriqués avec ce lait traité à l’état cru diffèrent par leurs textures et arômes. Une filière laitière pérenne pourrait bien valoriser ces différences mais la pénibilité de la traite faite obligatoirement en présence du veau reste un obstacle. Des enquêtes auprès de consommateurs ont confirmé la forte image de la race vectrice de valorisation économique. Leur consentement à payer pour des produits identifiés est cependant plus fort pour le fromage (jusqu’à 30 %) que pour la viande (jusqu’à 10 %). Les qualités reconnues des produits identifiés comme issus de vaches Salers et l’originalité des systèmes de production peuvent apporter des plus-values significatives aux divers acteurs locaux, ce qui peut correspondre à une forme de rente territoriale.
ISSN: 1166-7699

hal-00992549
https://hal.archives-ouvertes.fr/hal-00992549
DOI : 10.1684/agr.2014.0687
PRODINRA : 259206