On the growth of normal faults and the existence of flats and ramps along the El Asnam active fold and thrust system

The combination of detailed topographic leveling on the southwest segment of the El Asnam thrust fault with existing seismic and geologic data implies that the geometry of this fault involves shallow dipping flats and steep ramps. The fault appears to be growing along strike toward the southwest end, where the main shock initiated in 1980. From a depth of about 10 km, the main thrust appears to ramp to the basement-Cenozoic cover interface on a plane striking N40°E and dipping 50°–55° to the northwest. Along the southwest segment where folding has not yet developed, the thrust continues steeply through the Cenozoic cover to the near surface where it flattens, causing normal faulting. Along the central and northeast segments, which display a more evolved fold structure, the deep thrust probably flattens at a depth of 5–6 km, into a decollement along the Cenozoic-Jurassic interface before ramping to the surface. The Sara El Marouf and Kef El Mes anticlines have thus formed as fault propagation folds. Normal faults at Beni Rached probably branch with the thrust to maintain kinematic compatibility between the deep ramp and decollement. The greater separation (∼7 km) between the normal faults at Beni Rached and the thrust where it crosses Oued Cheliff than along the southwest segment (∼1 km) reflects the greater depth of the ramp to flat bend. We infer that the September 9, 1954, earthquake activated only the central deep segment of the main thrust together with the Beni Rached normal faults, while that of October 10, 1980, activated the whole system of flat decollements, ramp thrusts and compatibility normal faults. Further complexities of the faulting in map view are related to changes of strike of the thrust (in particular north of Oued Cheliff)

Active Thrusting and Folding Along the Northern Tien Shan and Late Cenozoic Rotation of the Tarim Relative to Dzungaria and Kazakhstan

We have studied geometries and rates of late Cenozoic thrust faulting and folding along the northern piedmont of the Tien Shan mountain belt, West of Urumqi, where the M= 8.3 Manas earthquake occurred on December 23, 1906. The northern range of the Tien Shan, rising above 5000 m, overthrusts a flexural foredeep, filled with up to 11,000 m of sediment, of the Dzungarian basement. Our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front, within a 200-km-long zone of Neogene-Quaternary anticlines. Fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range. In all the valleys, the scarps offset vertically the highest terrace surface by the same amount (10.2±0.7 m). Inferring an early Holocene age (10±2 kyr) for this terrace, which is continuous with the largest recent fans of the piedmont, yields a rate of vertical throw of 1.0±0.3mm/yr on the main active thrust at the surface. A quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5.5±2.5 m^2/kyr. A rather fresh surface scarp, 0.8±0.15 m high, that is unlikely to result from shallow earthquakes with 6 < M < 7 in the last 230 years, is visible at the extremities of the main fold zone. We associate this scarp with the 1906 Manas earthquake and infer that a structure comprising a deep basement ramp under the range, gently dipping flats in the foreland, and shallow ramps responsible for the formation of the active, fault propagation anticlines could have been activated by that earthquake. If so, the return period of a 1906 type event would be 850 ±380 years. The small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth (≈2/3) is taken up by incremental folding near the surface. Comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising Quaternary ranges such as the San Gabriel mountains in California or the Mont Blanc-Aar massifs in the Alps. We estimate the finite Cenozoic shortening of the folded Dzungarian sediments to be of the order of 30 km and the Cenozoic shortening rate to have been 3 ± 1.5 mm/yr. Assuming comparable shortening along the Tarim piedmont and minor additional active thrusting within the mountain belt, we infer the rate of shortening across the Tien Shan to be at least 6 ± 3 mm/yr at the longitude of Manas (≈85.5°E). A total shortening of 125±30 km is estimated from crustal thickening, assuming local Airy isostatic equilibrium. Under the same assumption, serial N-S sections imply that Cenozoic shortening across the belt increases westwards to 203±50 km at the longitude of Kashgar (≈ 76 °E), as reflected by the westward increase of the width of the belt. This strain gradient implies a clockwise rotation of Tarim relative to Dzungaria and Kazakhstan of 7±2.5° around a pole located near the eastern extremity of the Tien Shan, west of Hami (≈96°E, 43.5°N), comparable to that revealed by paleomagnetism between Tarim and Dzungaria (8.6° ± 8.7°). A 6 mm/yr rate of shortening at the longitude of Manas would imply a rate of rotation of 0.45°/m.y. and would be consistent with a shortening rate of 12 mm/yr north of Kashgar. Taking such values to be representative of Late Cenozoic rates would place the onset of reactivation of the Tien Shan by the India-Asia collision in the early to middle Miocene (16 +22/−9 m.y.), in accord with the existence of particularly thick late Neogene and Quaternary deposits. Such reactivation would thus have started much later than the collision, roughly at the time of the great mid-Miocene changes in tectonic regimes, denudation and sedimentation rates observed in southeast Asia, the Himalayas and the Bay of Bengal, and of the correlative rapid change in seawater Sr isotopic ratio (20 to 15 Ma). Like these other changes, the rise of the Tien Shan might be a distant consequence of the end of Indochina's escape

Paleomagnetic Study of Mesozoic Continental Sediments Along the Northern Tien Shan (China) and Heterogeneous Strain in Central Asia

A paleomagnetic study of rocks from the northern foot of the Tien Shan and the southern border of the Dzungar Basin, east of Urumqi (44.2°N, 86.0°E), spanning ages from middle Jurassic to early Tertiary was carried out to constrain the tectonic evolution in central Asia since Mesozoic time. Five middle Jurassic sites reveal a remagnetized direction close to the present Earth field in geographic coordinates: D = 6.6°, I = 72.6° (α_(95) = 7.4°). Thirteen out of 17 upper Jurassic and lower Cretaceous sites yield a characteristic direction (stratigraphic coordinates) of D = 12.7°, I = 48.6° (α_(95) = 5.5°). Nine of 16 upper Cretaceous and lower Tertiary sites provide a characteristic direction of D = 12.5°, I = 51.3° (α_(95) = 6.9°). The latter two directions pass fold and reversal tests. The pole positions are close to each other and to the Besse and Courtillot [1989, 1990] Eurasian apparent polar wander path, for ages ranging from 130 to 70 Ma. However, the difference in paleolatitudes amounts to about 5.9° ± 3.7°, which could indicate significant continental shortening in the Altai Mountains and perhaps further north, subsequent to India-Asia collision. The pole positions from the Dzungar Basin are close to those found for the Tarim [Li et al., 1988a], leading to an insignificant paleolatitude difference (3.0° ± 6.9°), but showing a larger difference in declination (8.6° ± 8.7°). These paleomagnetic results are compatible with a model of heterogeneous deformation in the western part of the collision zone between India and Siberia. A significant shortening in the Altai, a slight counterclockwise rotation of the Dzungar block, the westward-increasing shortening in the Tien Shan with attendant clockwise rotation of the Tarim block are all consistent with this model, in which Tibet, the Tien Shan and the Altai undergo differential strain along strike in a relay fashion, with the total India-Siberia convergence remaining approximately constant

Updated Interpretation of Magnetic Anomalies and Seafloor Spreading Stages in the South China Sea : Implications for the Tertiary Tectonics of Southeast Asia

International audienceWe present the interpretation of a new set of closely spaced marine magnetic profiles that complements previous data in the northeastern and southwestern parts of the South China Sea (Nan Hai). This interpretation shows that seafloor spreading was asymmetric and confirms that it included at least one ridge jump. Discontinuities in the seafloor fabric, characterized by large differences in basement depth and roughness, appear to be related to variations in spreading rate. Between anomalies 11 and 7 (32 to 27 Ma), spreading at an intermediate, average full rate of ~50 mm/yr created relatively smooth basement, now thickly blanketed by sediments. The ridge then jumped to the south and created rough basement, now much shallower and covered with thinner sediments than in the north. This episode lasted from anomaly 6b to anomaly 5c (27 to ~16 Ma) and the average spreading rate was slower, ~35 mm/yr. After 27 Ma, spreading appears to have developed first in the eastern part of the basin and to have propagated towards the southwest in two major steps, at the time of anomalies 6b-7, and at the time of anomaly 6. Each step correlates with a variation of the ridge orientation, from nearly E-W to NE-SW, and with a variation in the spreading rate. Spreading appears to have stopped synchronously along the ridge, at about 15.5 Ma. From computed fits of magnetic isochrons we calculate 10 poles of finite rotation between the times of magnetic anomalies 11 and 5c. The poles permit reconstruction of the Oligo-Miocene movements of Southeast Asian blocks north and south of the South China Sea. Using such reconstructions, we test quantitatively a simple scenario for the opening of the sea in which seafloor spreading results from the extrusion of Indochina relative to South China, in response to the penetration of India into Asia. This alone yields between 500 and 600 km of left-lateral motion on the Red River-Ailao Shan shear zone, with crustal shortening in the San Jiang region and crustal extension in Tonkin. The offset derived from the fit of magnetic isochrons on the South China Sea floor is compatible with the offset of geological markers north and south of the Red River Zone. The first phases of extension of the continental margins of the basin are probably related to motion on the Wang Chao and Three Pagodas Faults, in addition to the Red River Fault. That Indochina rotated at least 12° relative to South China implies that large-scale "domino" models are inadequate to describe the Cenozoic tectonics of Southeast Asia. The cessation of spreading after 16 Ma appears to be roughly synchronous with the final increments of left-lateral shear and normal uplift in the Ailao Shan (18 Ma), as well as with incipient collisions between the Australian and the Eurasian plates. Hence no other causes than the activation of new fault zones within the India-Asia collision zone, north and east of the Red River Fault, and perhaps increased resistance to extrusion a long the SE edge of Sundaland, appear to be required to terminate seafloor spreading in the largest marginal basin of the western Pacific and to change the sense of motion on the largest strike-slip fault of SE Asia

Cellules souches pluripotentes induites de lapin : caractérisation moléculaire et fonctionnelle des états naïf et amorcé

Pluripotent stem cells (PSCs) can self-renew at two distinct states, the naive and primed states. Many differences exist between these two states, the most striking is the unique ability of PSCs naïve to colonize the preimplantation embryo and form chimeras. The purpose of my doctoral project was to study pluripotency in rabbits. In this context, I initially manufactured and characterized induced pluripotent stem cells (RbiPSCs) and then evaluated their ability to colonize the embryo and form chimeras. Three RbiPSCs lines were obtained by rabbit fibroblasts reprogramming. Their molecular characterization revealed mixed characteristics, naïve and primed. However, functionally, they are unable to colonize the rabbit embryo, a feature of primed pluripotency. The second part of my doctoral project was to reprogram RbiPSCs to the naïve state. To this end, I have overexpressed Klf2 and Klf4, two genes belonging to the naïve pluripotency network and the mouse PSCs culture conditions. These new cell lines have a gene expression profile closer to that of the rabbit ICM, particularly due to the reactivation of specific markers of naïve pluripotency. Finally, the reverted cells have an increased capacity of colonization of the preimplantation embryo rabbit. My work represents the first example of pluripotent stem cells reprogramming toward the naive state in rabbits. The cells thus produced pave the way for the production of somatic and germline chimerasDeux états d'autorenouvellement des cellules souches pluripotentes (PSCs) ont été définis, à savoir les états naïf et amorcé. De nombreuses différences existent entre ces deux états dont la plus marquante est la capacité unique des PSCs à l'état naïf, de coloniser l'embryon préimplantatoire et former des chimères. L'objectif de mon projet doctoral a été d'étudier la pluripotence chez le lapin. Dans ce cadre, j'ai d'abord entrepris de fabriquer et de caractériser des cellules souches pluripotentes induites (RbiPSCs), puis d'évaluer leur capacité à coloniser l'embryon et à former des chimères. Trois lignées de RbiPSCs dépendantes du FGF2 ont été obtenues par reprogrammation de fibroblastes de lapin. Leur caractérisation moléculaire et fonctionnelle a révélé des caractéristiques mixtes, naïves et amorcées. En revanche, sur le plan fonctionnel, elles sont incapables de coloniser l'embryon de lapin, une caractéristique de la pluripotence amorcée. La seconde partie de mon projet doctoral a consisté à reprogrammer des RbiPSCs vers l'état naïf. Dans ce but, j'ai surexprimé KLF2 et KLF4, deux gènes appartenant au réseau de pluripotence naïf, et utilisé les conditions de culture des PSCs de souris. Les cellules ainsi obtenues présentent un profil d'expression génique plus proche de celui de l'ICM de lapin, dû notamment à la réactivation de marqueurs spécifiques de la pluripotence naïve. Enfin, les cellules ainsi reprogrammées présentent une capacité accrue pour la colonisation de l'embryon préimplantatoire de lapin. Mes travaux constituent le premier exemple de reprogrammation de cellules souches pluripotentes vers l'état naïf chez le lapin. Les cellules ainsi produites ouvrent la voie à la fabrication de chimères somatiques et germinale

Time course of lung injury in rat acute pancreatitis

Objective: Lung injury is asevere complication of acute pancreatitis that increases the mortality rate of the disease. The pathophysiology of acute pancreatitis has been studied in several experimental models, but the kinetics of pulmonary complications in relation to the pancreatic disease is not completely understood. We then studied the severity of acute pancreatitis-associated lung injury over 18 h in rats that had taurocholic acid injection in the pancreatic duct and determined whether blood collected from rats with pancreatitis is toxic enough to induce injury in normal lungs. Design and setting: Prospective, randomized, and controlled animal study in an animal research laboratory in auniversity hospital. Interventions: We isolated lungs from rats with acute pancreatitis 2, 6, and 18 h after taurocholic acid injection in the biliopancreatic duct and perfused them with blood collected from the same rats. Additionally, blood collected from rats with acute pancreatitis (time-points: 2 and 6 h) was perfused in normal lungs. Measurements and results: Taurocholic acid injection induced asevere pancreatic injury that started as early as 2 h after the injection and persisted without recovery over the 18-h study period. In contrast, the pulmonary injury was transient, appearing at the 6-h time point with recovery by the end of the study. Pulmonary injury was moderate and evidenced mostly during lung reperfusion. Interestingly, blood collected at the 2-h time point in pancreatic rats induced pulmonary injury in normal lungs while blood collected at the 6-h time-point was not toxic. Conclusions: While pancreatic injury persists over the full experimental period, pulmonary injury is transient in our experimental model. The recovery of lung injury by 18 h might be explained by adecrease in the overall toxicity of pancreatic blood over tim

Neogene strike-slip faulting in Sakhalin and the Japan Sea opening

Laurent Jolivet est Professeur à l'Université d'Orléans au 1er Septembre 2009International audienceWe describe structural data from a 2000 km N-S dextral strike-slip zone extending from northern Sakhalin to the southeast corner of the Japan Sea. Satellite images, field data, and focal mechanisms of earthquakes in Sakhalin are included in the interpretation. Since Miocene time the deformation in Sakhalin has been taken up by N-S dextral strike-slip faults with a reverse component and associated en e'chelon folds. Narrow en échelon Neogene basins were formed along strike-sup faults and were later folded in a second stage of deformation. We propose a model of basin formation along extension al faults delimitating dominos between two major strike-slip faults, and subsequent counterclockwise rotation of the dominos in a dextral transpressional regime, basins becoming progressively oblique to the direction of maximum horizontal compression and undergoing shortening. The association of both dextral and compressional focal mechanisms of earthquakes indicates that the same transpressional regime still prevails today in Sakhalin. We present fault set measurements undertaken in Noto Peninsula and Yatsuo Basin at the southern end of the Sakhalin-East Japan Sea strike-slip zone. Early and middle Miocene formations recorded the same transtensional regime as observed along the west coast of NE Honshu. During the early and middle Miocene the strike-slip regime was transpressional to the north in Sakhalin and Hokkaido, and transtensional to the south along the west coast of NE Honshu as far as Noto Peninsula and Yatsuo basin. Dextral motion accommodated the opening of the Japan Sea as a pull-apart basin, with the Tsushima fault to the west. The opening of the Japan Sea ceased at the end of the middle Miocene when transtension started to change to E-W compression in the Japan arc. Subduction of the Japan Sea lithosphere under the Japan arc started 1.8 Ma ago. The evolution of the stress regime from transtensional to compressional in the southern part of the strike-slip zone is related to the inception of the subduction of the young Philippine Sea Plate lithosphere under the Japan arc during the late Miocene. Subduction related extension is a necessary condition for the opening of the Japan Sea. Two possible mechanisms can account for dextral shear in this area: (1) counterclockwise rotation of crustal blocks due to the collision of India with Asia, (2) extrusion of the Okhotsk Sea block squeezed between the North America and Eurasia plates

Millennial Recurrence of Large Earthquakes on the Haiyuan Fault near Songshan, Gansu Province, China

International audienceThe Haiyuan fault is a major active left-lateral fault along the northeast edge of the Tibet-Qinghai Plateau. Studying this fault is important in understanding current deformation of the plateau and the mechanics of continental deformation in general. Previous studies have mostly focused on the slip rate of the fault. Paleo-seismic investigations on the fault are sparse, and have been targeted mostly at the stretch of the fault that ruptured in the 1920 M ϳ8.6 earthquake in Ningxia Province. To investigate the millennial seismic history of the western Haiyuan fault, we opened two trenches in a small pull-apart basin near Songshan, in Gansu Province. The excavation exposes sedimentary layers of alternating colors: dark brown silty to clayey deposit and light yellowish brown layers of coarser-grained sandy deposit. The main fault zone is readily recognizable by the disruption and tilting of the layers. Six paleoseismic events are identified and named SS1 through SS6, from youngest to oldest. Charcoal is abundant, yet generally tiny in the shallowest parts of the trench exposures. Thirteen samples were dated to constrain the ages of paleoseismic events. All six events have occurred during the past 3500–3900 years. The horizontal offsets associated with these events are poorly known. However, events SS3 to SS6 appear to be large ones, judging from comparison of vertical separations and widths of fault zones. The youngest event SS1 instead seems to be a minor one, probably the 1990 M w 5.8 earthquake. Thus, four large events in 3500–3900 years would imply a recurrence interval of about 1000 years. Three events SS2 to SS4 prior to 1990 occurred sometime during 1440–1640 A.D., shortly after 890–1000 A.D. and 0–410 A.D., respectively. We tentatively associate them with the 1514 A.D., 1092 A.D., and 143 or 374 A.D. historical earthquakes. Taking 10 ‫ע‬ 2 m of slip for large events (SS3 and SS4), comparable to the 1920 M Ͼ8 Haiyuan earthquake, their occurrence times would be consistent with the long-term 12 ‫ע‬ 4 mm/yr estimate of Lasserre et al. (1999). However, a more realistic evaluation of slip rate and its possible change with time requires a more rigorous determination of coseismic slip amounts of past earthquakes

Towards a spatially and temporally constant Karakorum fault slip rate

Abstract HKT-ISTP 2013 A