In-situ evidence for dextral active motion at the Arabia-India plate boundary

International audienceThe Arabia-India plate boundary--also called theOwen fracture zone--is perhaps the least-known boundary among large tectonic plates1-6. Although it was identified early on as an example of a transform fault converting the divergent motion along the Carlsberg Ridge to convergent motion in the Himalayas7, its structure and rate of motion remains poorly constrained. Here we present the first direct evidence for active dextral strike-slip motion along this fault, based on seafloor multibeam mapping of the Arabia-India-Somalia triple junction in the northwest Indian Ocean. There is evidence for 12km of apparent strike-slip motion along the mapped segment of the Owen fracture zone, which is terminated to the south by a 50-km-wide pull-apart basin bounded by active faults. By evaluating these new constraints within the context of geodetic models of global plate motions, we determine a robust angular velocity for the Arabian plate relative to the Indian plate that predicts 2-4mmyr−1 dextral motion along the Owen fracture zone. This transformfault was probably initiated around 8 million years ago in response to a regional reorganization of plate velocities and directions8-11, which induced a change in configuration of the triple junction. Infrequent earthquakes of magnitude 7 and greater may occur along the Arabia-India plate boundary, unless deformation is in the formof aseismic creep

Tectonic and climatic controls on rift escarpments: Erosion and flexural rebound of the Dhofar passive margin (Gulf of Aden, Oman)

International audienceWe investigate the respective roles of climatic parameters and the flexural rigidity of the lithosphere in the erosion history and behavior of two adjacent rift escarpments along the northern coast of the Gulf of Aden, in Oman. At this 25 Myr old passive margin, we define a type 1 scarp, which is high, sharp-crested and has retreated 25-30 km inland from its master fault, and a type 2 scarp, which exhibits a more rounded profile, lower relief, and still coincides with its mapped normal fault trace. Since about 15 Ma, the margin has been seasonally affected by monsoon precipitation but with contrasting effects at the type 1 and type 2 escarpments depending on the position of the Intertropical Convergence Zone in the geologic past: during peak monsoon conditions, both scarps experienced heavy rainfall and runoff, whereas during monsoon-starved conditions (such as today), the type 2 scarp experienced a foggy, moist climate while the type 1 scarp remained much drier. In order to assess the relative effects of climate and flexural parameters on the present-day morphology of the Dhofar margin, we present onedimensional numerical models of erosion and flexure along two profiles representative of the type 1 and type 2 scarps. Unlike most surface process models previously published, where present-day topography is the only criterion by which to evaluate the quality of model outputs, model behavior here is additionally constrained by independent estimates of denudation provided by geological cross sections, well-defined fault traces, and other stratigraphic markers. The best fitting models indicate that the type 1 escarpment formed under relatively arid climatic conditions and was affected by significant erosion, recession and flexural uplift due to a low (7 km) effective elastic thickness. In contrast, the morphology of the type 2 fault scarp was smoothed by a more humid climate, but a high effective elastic thickness ( 15 km) prevented it from uplifting or receding. In addition, we show that the sedimentary load acting at the foot of the escarpments exerts significant influence on their morphological evolution, though this parameter is often neglected in other scarp evolution models

The Triassic Indosinian orogeny in East Asia - Foreword

La tectonique récente, du Tertiaire à l'Actuel, est omniprésente dans l'Est et le Sud-Est asiatique, et s'y manifeste notamment sous la forme de décrochements crustaux de grande ampleur, comme celui du fleuve Rouge. Pour importante qu'elle soit, cette tectonique ne saurait faire oublier les événements orogéniques antérieurs auxquels elle s'est superposée et qui ont largement participé à la construction des confins orientaux de l'Asie. En tout premier lieu, il s'agit de l'événement orogénique qui s'est produit au Trias et qui a eu comme conséquence de rassembler, par collision, des blocs continentaux d'origine gondwanienne, alors séparés par des espaces océaniques dépendant de la Paléotéthys. La distribution actuelle des principaux blocs et microblocs engagés dans ce processus est illustrée sur la Fig. 1

A simplified model of stress-slip relationships : application to the Frøy field, northern North Sea

Tectonophysics, v. 357, n. 1-4, p. 103-118, 2002. http://dx.doi.org/10.1016/S0040-1951(02)00364-5International audienc

Northern continuation of Caledonian high-pressure metamorphic rocks in central-western Spitsbergen

Caledonian low-temperature, high-pressure metamorphic rocks, as first recognised at Motalafjella, central western Spitsbergen, include characteristic brown dolostone and serpentinite. Similar rocks are scattered in the strandflats, along the eastern marginal fault of the Tertiary Forlandsundet Graben, and along thrust faults to the east on both sides of St. Jonsfjorden. The mineral chemistries of the constituent carbonates and oxides are diagnostic of high-pressure metamorphic rocks, containing high contents of MgO in the carbonates and Cr2O3 in the oxides. Based on a surface magnetic-anomaly survey and fault-plane observations, some of these rocks are considered to have been pressed up along faults produced by strike-slip faulting during an early stage of the Forlandsundet Graben formation. The distribution of these rocks indicates that the high-pressure metamorphic rocks extend as much as 50 km to the NNW from Motalafjella to Sarsøyra

U-Pb dating of high temperature metamorphic episodes in the Kon Tum Massif (Vietnam)

In Vietnam, recent studies demonstrated that the Kon Tum Massif was part of the Indosinian mountain system, together with the Truong Son Belt. One sector of the Kon Tum Massif (Song Ba valley) is a granulite facies terrain for which Ar–Ar and U–Pb ages cluster around 245–250 Ma. In the area of Song Bien river, also metamorphosed under granulite facies conditions, Ar–Ar ages of 410 Ma are displayed by biotite. In this study, U–Pb dating of monazite and zircon has been used to understand the reason for these two groups of ages, taking into account the metamorphic mineral assemblages related to granulite facies metamorphism in the two districts. For granulites of Song Ba valley, ages of 245–250 Ma are confirmed from monazites. In the Song Bien district, ages of 465–470 Ma displayed by monazites are interpreted to correspond to the metamorphic climax. Zircons from one of these samples record the age of anatexis that has affected the granulitic rocks. The younger age recorded in the Song Ba valley is considered to reflect high temperature related to charnockitic intrusions emplaced near the end of the Indosinian orogeny, overprinting the earlier formed granulites and resetting the U–Pb and Ar–Ar ages. For the first time, two HT events are dated in the Kon Tum Massif, one occurring during the Ordovician and the other during the Permo-Triassic

Hsp90 directly interacts, in vitro, with amyloid structures and modulates their assembly and disassembly

International audienc

Structure of glycoproteins from Acacia gum: An assembly of ring-like glycoproteins modules

International audienceThe glycoprotein (GP) molecular fraction structure of the gum exudate of Acacia senegal (gum Arabic) isolated from hydrophobic interaction chromatography was investigated using high-performance size exclusion chromatography-multi angle laser light scattering (HPSEC-MALLS), small angle X-ray scattering (SAXS), synchrotron radiation circular dichroism (SRCD) and transmission electron microscopy (TEM) observations. In solution, GP would be a mixture of spheroidal monomers and more anisotropic oligomers as suggested by the two exponent values found in the R-g vs. M-w relationship and TEM observations. The GP conformation probed by SAXS was ascribed to a thin object with a triaxial ellipsoid morphology, certainly attributed to GP oligomers. A 9 nm diameter particle was also identified by SAXS in agreement with the dimensions identified by TEM on single isolated ring-like structures. The GP oligomerization process, as probed by TEM, would be the result of ring-like subunits self-association. This self-association would lead to more linear or, sometimes, cyclised assembly. At the molecular level, GP fraction was found to have secondary structures mainly made of beta-sheets and turns (64%) but also, to a lesser extent, made of polyproline II (PPII) and alpha-helices (19%). These features were characteristic of hydroxyprolin-rich glycoproteins with arabinosylated and arabinogalactan polysaccharide side chains grafted to the polypeptide backbone. The GP molecular fraction structure from Acacia gum would be an assembly of ring-like glycoproteins modules. These ring-like structures were certainly due to hydroxyproline (Hyp)-arabinogalactan (AG) subunits. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved