Kinematics, topography, shortening, and extrusion in the India-Eurasia collision

Laurent Jolivet est Professeur à l'Université d'Orléans depuis le 1er Septembre 2009International audienceWe examine the problem of partitioning between shortening and extrusion in the India-Asia collision since 45 Ma. We compute the amount of shortening expected from the kinematics of India's motion with respect to Eurasia, using the reconstruction at collision time to put bounds on the possible amounts of surface loss within Greater India and within Eurasia. We then compute the amounts of surface loss corresponding to the thickened crust of Tibet and of the Himalayas, assuming conservation of continental crust. The spatial distribution of the topography reveals a large systematic deficit of crustal thickening distributed rather uniformly west of the eastern syntaxis but an excess of shortening east of it. This distribution indicates an important eastward crustal mass transfer. However, the excess mass east of the eastern syntaxis does not account for more than one third to one half of the deficit west of the eastern syntaxis. The deficit may be accounted either by loss of lower crust into the mantle, for example through massive eclogitization, or by lateral extrusion of nonthickened crust. A mass budget of the crust of the Himalayas indicates that lower crust has not been conserved there, but the deficit is so large that local loss in the mantle is unlikely to be the unique cause of the deficit. Alternatively, following Zhao and Morgan [1985], lower crust may have been transferred below the Tibetan crust. We conclude that a combination of possible transfer of lower crust to the mantle by eclogitization and lateral extrusion has to account for a minimum of one third and a maximum of one half of the total amount of shortening between India and Asia since 45 Ma. This conclusion leaves open the possibility that the partitioning between extrusion and loss of lower crust into the mantle on the one hand and shortening on the other hand has significantly changed during the 45 m.y. history of the collision

Thermal regime of the NW shelf of the Gulf of Mexico. 1) Thermal and pressure fields

National audienceThe thermal field of the Gulf of Mexico (GoM) is analyzed from a comprehensive temperature-depth database of about 8500 Bottom Hole Temperatures and Reservoir Temperatures. Our stochastic analysis reveals a widespread, systematic sharp thermal gradient increase between 2500 and 4000 m. The analysis of the pressure regime indicates a systematic correlation between the pressure and temperature fields

Crustal structure and the mechanism of extension in the northern Red Sea: Constraints from gravity anomalies

Gravity data from detailed marine surveys were used to investigate the density structure of the crust and upper mantle beneath the northern Red Sea, a continental rift considered by many to be in the process of establishing a mid-ocean ridge type spreading center. A gravity and bathymetry profile across the sea near 27°N was analyzed in detail. Model constraints include single-channel and multichannel seismic reflection lines coincident with the gravity profile, which provide detailed information on sedimentary layers, a series of ESP seismic experiments centered nearly on the gravity line which constrain the sediment and crustal thickness, and a series of 58 closely spaced heat flow measurements nearly coincident with the gravity line which closely constrain the mantle thermal structure and thus density variations within the mantle. The calculated gravity anomalies based on the known crustal and mantle structure fail to match the observed data. Specifically, the model anomalies become steadily more negative from the margins toward the center of the sea with the result that the calculated gravity is approximately 25 mGal more negative near the axis relative to the marginal areas than are the observed anomalies. Two possible solutions were investigated. One is to introduce a lower crustal layer resulting from crustal underplating within what was originally considered to be the upper mantle beneath the marginal areas. The other is to introduce an area of slightly denser crust resulting from intrusion of new mafic crustal material within the axial depression. Both solutions can reproduce the observed gravity anomalies within the Red Sea. However, the complete set of geophysical data, and in particular the heat flow in the Red Sea and gravity and seismic refraction data on land, suggests that the most satisfactory model is that the crust of the axial depression is denser than that of the marginal areas. This implies that crustal extension in the northern Red Sea is presently occurring in large part by intrusion of new mafic material

Preparation of mono-substituted malonic acid half oxyesters (SMAHOs).

The use of mono-substituted malonic acid half oxyesters (SMAHOs) has been hampered by the sporadic references describing their preparation. An evaluation of different approaches has been achieved, allowing to define the best strategies to introduce diversity on both the malonic position and the ester function. A classical alkylation step of a malonate by an alkyl halide followed by a monosaponification gave access to reagents bearing different substituents at the malonic position, including functionalized derivatives. On the other hand, the development of a monoesterification step of a substituted malonic acid derivative proved to be the best entry for diversity at the ester function, rather than the use of an intermediate Meldrum acid. Both these transformations are characterized by their simplicity and efficiency, allowing a straightforward access to SMAHOs from cheap starting materials

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

La catastrophe sismique de Haïti

Le 12 janvier, à 16h53, à 13 kilomètres de profondeur, la faille d’Enriquillo commença à céder à 25 kilomètres au sud-sud-ouest de Port-au-Prince. La rupture se propagea vers l’ouest pendant 35 secondes sur une cinquantaine de kilomètres, sans jamais atteindre la surface, mais l’essentiel de l’énergie mécanique fut dissipée dans les dix premières secondes avec un déplacement qui atteignit quatre mètres. Le bord nord de la faille glissait vers l’ouest par rapport au bord sud. C’est ce que l’on..

RTN3 Is a Novel Cold-Induced Protein and Mediates Neuroprotective Effects of RBM3.

Cooling and hypothermia are profoundly neuroprotective, mediated, at least in part, by the cold shock protein, RBM3. However, the neuroprotective effector proteins induced by RBM3 and the mechanisms by which mRNAs encoding cold shock proteins escape cooling-induced translational repression are unknown. Here, we show that cooling induces reprogramming of the translatome, including the upregulation of a new cold shock protein, RTN3, a reticulon protein implicated in synapse formation. We report that this has two mechanistic components. Thus, RTN3 both evades cooling-induced translational elongation repression and is also bound by RBM3, which drives the increased expression of RTN3. In mice, knockdown of RTN3 expression eliminated cooling-induced neuroprotection. However, lentivirally mediated RTN3 overexpression prevented synaptic loss and cognitive deficits in a mouse model of neurodegeneration, downstream and independently of RBM3. We conclude that RTN3 expression is a mediator of RBM3-induced neuroprotection, controlled by novel mechanisms of escape from translational inhibition on cooling