552 research outputs found
Electron Capture in Charge-Tagged Peptides. Evidence for the Role of Excited Electronic States
International audienceElectron capture dissociation (ECD) was studied with doubly charged dipeptide ions that were tagged with fixed-charge tris-(2,4,6-trimethoxyphenyl)phosphonium-methylenecarboxamido (TMPP-ac) groups. Dipeptides GK, KG, AK, KA, and GR were each selectively tagged with one TMPP-ac group at the N-terminal amino group while the other charge was introduced by protonation at the lysine or arginine side-chain groups to give (TMPP-ac-peptide + H)2+ ions by electrospray ionization. Doubly tagged peptide derivatives were also prepared from GK, KG, AK, and KA in which the fixed-charge TMPP-ac groups were attached to the N-terminal and lysine side-chain amino groups to give (TMPP-ac-peptide-ac-TMPP)2+ dications by electrospray. ECD of (TMPP-ac-peptide + H)2+ resulted in 72% to 84% conversion to singly charged dissociation products while no intact charge-reduced (TMPP-ac-dipeptide + H)+âą ions were detected. The dissociations involved loss of H, formation of (TMPP + H)+, and NâC(alpha) bond cleavages giving TMPP-CH2CONH2+ (c0) and c1 fragments. In contrast, ECD of (TMPP-ac-peptide-ac-TMPP)2+ resulted in 31% to 40% conversion to dissociation products due to loss of neutral TMPP molecules and 2,4,6-trimethoxyphenyl radicals. No peptide backbone cleavages were observed for the doubly tagged peptide ions. Ab initio and density functional theory calculations for (Ph3P-ac-GK + H)2+ and (H3P-ac-GK + H)2+ analogs indicated that the doubly charged ions contained the lysine side-chain NH3+ group internally solvated by the COOH group. The distance between the charge-carrying phosphonium and ammonium atoms was calculated to be 13.1-13.2 Ă
in the most stable dication conformers. The intrinsic recombination energies of the TMPP+-ac and (GK + H)+ moieties, 2.7 and 3.15 eV, respectively, indicated that upon electron capture the ground electronic states of the (TMPP-ac-peptide + H)+âą ions retained the charge in the TMPP group. Ground electronic state (TMPP-ac-GK + H)+âą ions were calculated to spontaneously isomerize by lysine H-atom transfer to the COOH group to form dihydroxycarbinyl radical intermediates with the retention of the charged TMPP group. These can trigger cleavages of the adjacent NâC(alpha) bonds to give rise to the c1 fragment ions. However, the calculated transition-state energies for GK and GGK models suggested that the ground-state potential energy surface was not favorable for the formation of the abundant c0 fragment ions. This pointed to the involvement of excited electronic states according to the Utah-Washington mechanism of ECD
From orogenic collapse to rifting, structures of the South China Sea
The opening of the South China Sea has been a matter of debate for many years because of its internal structure, the differences between the conjugate margins and the variations of rifting and spreading directions. Although it is considered as being a back-arc basin, it is not sitting directly above a subduction zone, and the rifting process lasted for an unusually long duration.
Among the specific characteristics is the early phase of rifting which took place early in place of the former Yanshanian andean-type mountain range. This stage is marked by narrow basins filled with deformed conglomerate, and initiated around 70My ago within a framework where the oblique subduction âŠpublished_or_final_versio
Dissociation channel dependence on peptide size observed in electron capture dissociation of tryptic peptides
International audienceElectron capture dissociation (ECD) of a series of five residue peptides led to the observation that these small peptides did not lead to the formation of the usual c/z ECD fragments, but to a, b, y and w fragments. In order to determine how general this behavior is for small sized peptides, the effect of peptide size on ECD fragments using a complete set of ECD spectra from the SwedECD spectra database was examined. Analysis of the database shows that b and w fragments are favored for small peptide sizes and that average fragment size shows a linear relationship to parent peptide size for most fragment types. From these data, it appears that most of the w fragments are not secondary fragments of the major z ions, in sharp contrast with the proposed mechanism leading to these ions. These data also show that c fragment distributions depend strongly on the nature of C-terminal residue basic site: arginine leads to loss of short neutral fragments, whereas lysine leads to loss of longer neutral fragments. It also appears that b ions might be produced by two different mechanisms depending on the parent peptide size. A model for the fragmentation pathways in competition is proposed. These relationships between average fragment size and parent peptide size could be further exploited also for CID fragment spectra and could be included in fragmentation prediction algorithms
The Owen Ridge uplift in the Arabian Sea: Implications for the sedimentary record of Indian monsoon in Late Miocene
International audienceThe pelagic cover of the Owen Ridge in the Arabian Sea recorded the evolution of the Indian monsoon since the Middle Miocene. The uplift of the Owen Ridge resulted from tectonic processes along the previously unidentified Miocene India-Arabia plate boundary. Based on seismic reflection data tied with deep-sea drilling to track the Miocene India-Arabia plate boundary, we propose a new timing for the uplift of the Owen Ridge and highlight its impact on the record of climate changes in pelagic sediments. The new dataset reveals a fracture zone east of the Owen Ridge corresponding to the fossil plate boundary, and documents that the main uplift of the Owen Ridge occurred close to âŒ8.5 Ma, and is coeval with a major uplift of the east Oman margin. Late Miocene deformation at the India-Arabia plate boundary is also coeval with the onset of intra-plate deformation in the Central Indian Ocean, suggesting a kinematic change of India and surrounding plates in the Late Miocene. The uplift of the Owen Ridge above the lysocline at âŒ8.5 Ma accounts for a better preservation of Globigerina bulloides in the pelagic cover, previously misinterpreted as the result of a monsoon intensification event
Owen Ridge deep-water submarine landslides: implications for tsunami hazard along the Oman coast
International audienceThe recent discovery of voluminous submarine landslides along the Owen Ridge may represent a source of tsunami hazard for the nearby Oman coast. We as- sess the severity of this potential hazard by performing numerical simulations of tsunami generation and propaga- tion from the biggest landslide (40km3 in volume) ob- served along the Owen Ridge. A finite-difference model, assimilating the landslide to a visco-plastic flow, simulates tsunami generation. Computation results show that Salalah city(190000inhabitants)isimpactedby2.5m-hightsunami waves one hour after sediment failure. Higher wave eleva- tion values (4 m) are reached in the low populated Sawqara Bay over 80 min after slide initiation. Although large subma- rine failures along remote oceanic ridges are infrequent, this study reveals an underestimated source of tsunami hazard in theArabianSea
Cinématique et tectonique active de l'Ouest de la GrÚce dans le cadre géodynamique de la Méditerranée Centrale et Orientale
La MĂ©diterranĂ©e se situe dans une zone de convergence lente entre les plaques Eurasienne et Africaine (~5 mm/an), oĂč des restes d'anciens bassins TĂ©thysiens sont progressivement consommĂ©s par le retrait rapide de zones de subductions (~20-30 mm/an sur la zone de subduction HellĂ©nique). En MĂ©diterranĂ©e Orientale, une transition collision-subduction se produit dans l'Ouest de la GrĂšce (collision de la Plateforme Apulienne au nord et subduction HellĂ©nique au sud), pratiquement Ă l extrĂ©mitĂ© du Golfe de Corinthe et dans une rĂ©gion de propagation potentielle de la faille Nord Anatolienne. Afin d'Ă©tudier la cinĂ©matique actuelle de l'Ouest de la GrĂšce, nous adoptons une approche multi-Ă©chelle de la dĂ©formation:(1) Une modĂ©lisation grande Ă©chelle du champ de vitesses crustale horizontales mesurĂ© par gĂ©odĂ©sie est effectuĂ©e afin de contraindre la cinĂ©matique au voisinage de l'Ouest de la GrĂšce, Ă la fois Ă terre et en mer. Un rĂ©sultat majeur est qu'une zone d'extension distribuĂ©e N-S s'Ă©tendant de la Bulgarie Ă l'Est du Golfe de Corinthe a pour consĂ©quence de dĂ©sactiver la terminaison Ouest de la faille Nord Anatolienne dans le nord de la Mer EgĂ©e. Cette extension d Ă©chelle rĂ©gionale pourrait ĂȘtre causĂ©e par le retrait du slab HellĂ©nique. (2) Une Ă©tude tectonique active permet d'Ă©tablir une cartographie prĂ©cise des failles actives de la rĂ©gion, leur chronologie relative et une estimation de leur vitesse de dĂ©placement. Le demi-graben actif du Golfe Amvrakikos et la faille active N155 de Katouna-Stamna, qui constituent les frontiĂšres Nord et Est d'un bloc Iles Ioniennes-Akarnanie (IAB), sont caractĂ©risĂ©s par des vitesses gĂ©ologiques d'au moins ~ 4 mm/an et des vitesses mesurĂ©es par GPS de l'ordre de ~10 mm/an. Ce bloc IAB est limitĂ© Ă l'Ouest par la faille transformante de CĂ©phalonie et semble se comporter de maniĂšre rigide.(3) Une fois les frontiĂšres du bloc IAB connues, nous montrons que le champ de vitesse GPS mesurĂ© dans la rĂ©gion peut ĂȘtre entiĂšrement expliquĂ© par des effets transitoires de blocage Ă©lastique associĂ©s aux failles bordiĂšres de ce bloc. Le couplage sur l'interface de subduction n'a pas d'expression en surface, ce qui suggĂšre qu'il doit ĂȘtre faible. Enfin, nous justifions l'existence d'un point triple de type Rift-Faille-Faille Ă la terminaison Ouest du Golfe du Corinthe.The Mediterranean is a diffuse plate boundary zone between the slowly converging Eurasian and African plates (~ 5mm/yr), where remnants of old Tethyan basins are progressively consumed by fast trench retreat (~20-30 mm/yr at the Hellenic subduction zone). In Eastern Mediterranean, a collision-subduction transition occurs in Western Greece (collision of the Apulian Platform to the north and Hellenic subduction zone to the south), close to the westward Corinth Rift termination and in a region that may be potentially affected by the westward propagation of the North Anatolian Fault. We used a multi-scale deformation approach to investigate Western Greece active kinematics:(1) We run a large scale model of horizontal crustal velocities measured by GPS to constrain the kinematic boundary conditions of Western Greece, both onshore and offshore. A major result is the occurrence of distributed N-S extension spreading from Bulgaria to the Eastern Corinth rift, resulting in de-activation of the western termination of the North Anatolian Fault in North Aegean Sea. This large scale extension could be associated to the retreat of the Hellenic slab.(2) An active tectonics study has been performed to provide an accurate mapping of active faults in the region, to constrain their relative chronology and to estimate their geological slip-rate. The Amvrakikos Gulf active half-graben and the N155 active Katouna-Stamna Fault, which form the northern and eastern boundaries of a Ionian Island-Akarnania block (IAB), have geological slip rates of at least ~ 4mm/yr and GPS slip-rates of ~ 10 mm/yr. The IAB is bounded to the west by the Kefalonia transform fault and appears to behave rigidly.(3) Once the IAB boundaries are defined, we show that the velocity field measured by GPS in the region can be totally accounted by transient elastic loading along the IAB bordering faults. Subduction interface coupling has no surface expression, suggesting low coupling. Finally, we justify the occurrence of a Rift-Fault-Fault triple junction at the western termination of the Corinth Rift.PARIS11-SCD-Bib. Ă©lectronique (914719901) / SudocATHENES-Ecole Fr.ArchĂ©ologie (991262301) / SudocSudocFranceF
Mass wasting processes along the Owen Ridge (Northwest Indian Ocean)
International audienceThe Owen Ridge is a prominent relief that runs parallel to the coast of Oman in the NW Indian Ocean and is closely linked to the Owen Fracture Zone, an 800-km- long active fault system that accommodates today the Arabia-India strike-slip motion. Several types of mass failures mobilizing the pelagic cover have been mapped in details along the ridge using multibeam bathymetry and sediment echosounder. Here we present a synthetic map of the different types of mass wasting features observed along the ridge and we further establish a morphometric analysis of submarine landslides. The spatial variation of failure morphology is strongly related to the topography of the basement. The highest volumes of multi-events generated slides are mobilized along the southern portion of the ridge. There, the estimated volume of evacuated material during a slide is up to 45 km3. Combining these new observations with re-interpreted ODP seismic lines (Leg 117) documents sporadic mass wasting events through time along the southern segment of the ridge since its uplift in the Early Miocene, with a typical recurrence rate of the order of 105-106 years. Although seismicity may still be the final triggering process, mass wasting frequency is mainly controlled by the slow pelagic sedimentation rates and hence, time needed to build up the 40-80 m thick pelagic cover required to return to a mechanically unstable pelagic cover
Three-dimensional surface displacement of the 2008 May 12 Sichuan earthquake (China) derived from Synthetic Aperture Radar: evidence for rupture on a blind thrust
International audienceThe Sichuan earthquake,Mw7.9, struck the Longmen Shan (LMS) range front,China, on 2008 May 12, affecting an area of moderate historical seismicity where little active shortening has been previously reported. Recent studies based on space geodesy have succeeded in retrieving the far field surface displacements caused by the earthquake, but the near field (±25 km from the faults) coseismic surface displacement is still poorly constrained. Thus, shallow fault geometry and shallow coseismic slip are still poorly resolved. Here, for the first time for this earthquake, we combine C and L-band Synthetic Aperture Radar offsets data from ascending and descending tracks to invert for the 3-D surface displacement in the near coseismic field of the Sichuan earthquake. Our data, coupled with a simple elastic dislocation model, provide new results strongly suggesting the presence of a blind thrust striking along the range front and being active at depth during the earthquake. The presence of a rupture on a blind thrust brings new evidence for an out-of-sequence thrusting event and new elements for interpreting the tectonic strain partitioning in the LMS, which has important implications both for seismic hazard assessment and long-term evolution of the mountain belt
LâĂ©dification des chaĂźnes pĂ©ricratoniques, contraintes structurales et cinĂ©matiques appliquĂ©es aux reconstructions de l'Asie du SE sur SIG
Le SE asiatique est un chantier qui permet dâĂ©tudier la formation des chaĂźnes de montagnes situĂ©es au dessus
des zones de subduction Ă diffĂ©rents stades de leur Ă©volution. Dans ces rĂ©gions, la cinĂ©matique des plaques est extrĂȘmement
rapide, souvent de lâordre de 10 cm/an, et la convergence engendre lâouverture, elle aussi rapide, de bassins marginaux
qui fragmentent sous forme de laniÚres les masses continentales. Les fragments ainsi séparés comportent donc un
substratum généralement constitué de matériel correspondant à des ophiolites de supra subduction (arc, avant-arc, arriÚre-
arc) ainsi que des reliques de croûte continentale. Ce type de mécanisme aboutit à la formation de plaques étirées
qui peuvent ĂȘtre soit de nature ocĂ©anique comme pour la plaque Philippine [Karig, 1975] formĂ©e de bassins arriĂšre-arcs
ouverts Ă lâEocĂšne (Bassin ouest-philippin), puis Ă lâOligo-MiocĂšne (bassin de Parece Vela/Shikoku), et au PliocĂšne
(bassin des Mariannes) [Le Pichon et al., 1975] ; bassin de Damar [Hinschberger, 2001]), soit de nature continentale
comme dans le cas des marges Australienne et Eurasiatique [Rangin et Pubellier, 1990 ; Rangin et al., 1990] (fig. 1).
Dans ce dernier cas, la configuration rĂ©sultante est celle dâune marge Ă©tirĂ©e Ă la façon dâun Ă©ventail depuis le PalĂ©ocĂšne
jusquâau MiocĂšne moyen. Ce mĂ©canisme gĂ©nĂšre des bassins diachrones ouverts vers lâest, avec un propagateur vers le
sud-ouest comme cela est visible dans lâouest de la mer de Chine [Huchon et al., 1998], et est dĂ©duit pour la mer des CĂ©lĂšbes
et son prolongement dans le dĂ©troit de Makassar [Moss and Chambers, 1999]. Cet Ă©tirement prenait lui-mĂȘme la
suite de lâĂ©croulement gravitaire de la chaĂźne Yenshanienne depuis le CrĂ©tacĂ© supĂ©rieur, qui marquait la fin dâun processus
similaire dâaccrĂ©tion de blocs gondwaniens au cours du MĂ©sozoĂŻque [Metcalfe, 1996 ; Sewell et al., 2000]. Lâensemble
du bloc de la Sonde, avec ses bassins marginaux est soumis à un raccourcissement depuis le début du MiocÚne
[Rangin et al., 1990], les bassins marginaux rentrant en subduction, et certains blocs basculés de la marge passive étant
en cours dâaccostage contre la marge continentale. De mĂȘme que lâouverture des bassins sâĂ©tait effectuĂ©e de maniĂšre
diachrone, le serrage des bassins sâeffectue lui aussi de façon diachrone.
Les mécanismes actifs de convergence par subduction et les blocages sont maintenant bien connus, la précision
des récepteurs GPS, et surtout la répétition des mesures depuis prÚs de dix ans permettant de bien contraindre les déplacements
instantanés. Nous avons utilisé principalement les vecteurs GPS du programme GEODYSSEA [Michel et al.,
2001]. ParallĂšlement, les Ă©tudes de tomographie sismique imagent des anomalies positives de vitesse dans le manteau
pouvant indiquer des lithosphĂšres subductĂ©es. Câest le cas de la proto mer de Chine Sud, parallĂšle Ă lâactuelle mer de
Chine du Sud et probablement de géométrie similaire, maintenant disparue par subduction [Rangin et al., 1999b ; Prouteau
et al., 2001]. Dans cet article, les mouvements dĂ©duits du GPS ont Ă©tĂ© utilisĂ©s comme base cinĂ©matique jusquâĂ
lâĂąge de la derniĂšre dĂ©formation marquante, pour chaque bloc des ceintures dĂ©formĂ©es. LâĂ©volution des marges a Ă©tĂ©
revue de maniĂšre globale sur lâensemble de lâAsie du SE, de façon Ă prĂ©senter des coupes structurales synthĂ©tiques,avant et aprĂšs raccourcissement (fig. 3 Ă 10). Ces coupes montrent que lâarrivĂ©e des blocs continentaux dans les zones
de subduction entraßne un blocage, puis le plus souvent un saut de subduction qui intÚgre le bloc à la marge en créant
une déformation de la plaque supérieure [Dominguez et al., 1998 ; Pubellier et al., 1999 ; Von Huene et al., 1995 ;
Ranero et al., 2000].
Une base de donnĂ©es sur lâAsie du Sud-est est utilisĂ©e dans les reconstructions, mais seulement une partie est reprĂ©sentĂ©e
sur les planches 1 à 6 (topographie-bathymétrie, principales failles). La base complÚte comprend aussi bien
les failles actives et anciennes, que la topographie des chaĂźnes de montagnes, la morphologie des fonds sous-marins, la
gravimĂ©trie Ă lâair libre, les vecteurs de dĂ©placement GPS en diffĂ©rents points Ă partir du calcul du meilleur pĂŽle eulerien
correspondant au mouvement de chaque bloc, les épaisseurs des sédiments dans les bassins, ou encore la localisation
des profils sismiques utilisĂ©s. Lâutilisation dâun systĂšme dâinformation gĂ©ographique permet de restituer les
dĂ©placements des plaques ou des micro-blocs crustaux, soit Ă lâaide des vitesses angulaires, soit de façon interactive.
Cette dĂ©marche permet de choisir entre plusieurs hypothĂšses gĂ©ologiques en gardant une cohĂ©rence dâensemble. Les palĂ©o-
distances gĂ©odĂ©siques entre les blocs peuvent ĂȘtre mesurĂ©es, et les chaĂźnes de montagnes comme TaĂŻwan ou la
ChaĂźne centrale de Nouvelle GuinĂ©e ont Ă©tĂ© Ă©tirĂ©es pour retrouver lâespace quâelles occupaient vraisemblablement avant
leur formation. Dans les reconstructions, la profondeur des bassins correspond aux valeurs actuelles, et nâa pas Ă©tĂ© restaurĂ©e
en fonction du temps. Enfin, nous nâavons pas Ă©tendu les reconstructions Ă lâHimalaya et au Tibet, les mouvements
verticaux étant trop importants. Les reconstructions effectuées à 2, 4, 6, 10, 15 et 20 Ma (planches 1 à 6) montrent
que les parties continentales des plaques Sunda et Australie ; (SU/AU) sâĂ©loignent lâune de lâautre, alors que la plaque
philippine continue de âbrosserâ la plaque de la Sonde [Rangin et al., 1990], en transportant vers lâouest des fragments
formĂ©s au nord de la plaque australienne. Il sâagit donc dâun article qui prĂ©sente une gĂ©nĂ©ralisation de processus gĂ©odynamiques
de fonctionnement des marges actives, et dont le but est de donner une image cohĂ©rente de lâaccrĂ©tion de
blocs aux bordures des continents, et qui a nĂ©cessitĂ© des choix dans les options souvent dĂ©battues de lâĂ©volution au
deuxiĂšme ordre de secteurs dâimportance locale
Arc Deformation and Marginal Basin Opening: Japan Sea as a Case Study
Laurent Jolivet est est Professeur à l'Université d'Orléans depuis le 1er Septembre 2009International audienceWe discuss the opening mechanism of the Japan Sea in Miocene time using (1) tectonic and published paleomagnetic data along the eastern margin from the north of Hokkaido Island to Sado Island, (2) a mechanical model which is tested by small-scale physical modeling, and (3) crustal structure and bathymetric features in the Japan Sea which constrain our kinematic model and preopening reconstructions. Our main conclusions are the following. The eastern margin of the Japan Sea was, as a whole, a dextral shear zone about 100 km wide. This conclusion is supported by the existence of a ductile dextral shear zone in Central Hokkaido (Hidaka Mountains) and associated brittle deformation in western Hokkaido and northeastern Honshu. The stress field during the opening (which ended about 12 Ma ago at the end of the middle Miocene) changes from right-lateral transpression in the north to right-lateral transtension in the south. The western margin, along the Korean peninsula, during the same period, also was an active dextral shear zone. Paleomagnetic results indicate that clockwise rotations occurred in the south during the opening and counterclockwise rotations in the north. We propose a model of right-lateral pull-apart deformation with clockwise rotations of rigid blocks in the southern transtensional domain and counterclockwise rotations in the transpressional one. Small-scale physical models show that the clockwise rotation in transtension is possible provided that the eastern boundary (Pacific side) is free of stress. The opening stopped and compression subsequently began about 12 Ma ago. Finally, we show that the dextral shear, which is distributed over the whole Japan Sea area, is accommodated by N-S trending right-lateral faults and rotation of blocks located between these right-lateral faults
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