Pre-Permian uplift and diffuse extensional deformation in the High Zagros Belt (Iran): integration in the geodynamic evolution of the Arabian plate     

Saeid?Tavakoli-ShiraziEmail author  Dominique?Frizon de Lamotte  Jean-Christophe?Wrobel-Daveau  Jean-Claude?Ringenbach 《Arabian Journal of Geosciences》2013,6(7):2329-2342

The High Zagros Belt includes exposures of Lower Palaeozoic rocks in the core of several thrusted anticlines developed during the Cenozoic Zagros orogeny. The structural style and tectonic evolution of this area during the Palaeozoic remain poorly understood due to the complexity of the subsequent deformation. We present the preliminary results of a field study focusing on the structural geology of Palaeozoic rocks in this area. We confirm the existence of an angular unconformity below the Lower Permian Faraghan formation. In the geological literature, this unconformity is reported as the “Hercynian Unconformity” suggesting a relationship with the Hercynian (Variscan) orogeny, which affected Western Europe and westernmost Africa during the Carboniferous. Surprisingly the only observable structures sealed by this unconformity are N to NE trending normal faults and tilted blocks without any evidence of compressional deformation. This pre-Permian extensional deformation, which is general at the scale of the HZB, raises questions about the geodynamic significance of the “Hercynian unconformity” in the study area and, more generally, in the Arabian plate.  相似文献   

Storage conditions of Bezymianny Volcano parental magmas: results of phase equilibria experiments at 100 and 700 MPa   总被引：1，自引：1，他引：0  

Renat R. Almeev  Francois Holtz  Alexei A. Ariskin  Jun-Ichi Kimura 《Contributions to Mineralogy and Petrology》2013,166(5):1389-1414

The crystallization sequence of a basaltic andesite from Bezymianny Volcano, Kamchatka, Russia, was simulated experimentally at 100 and 700 MPa at various water activities (aH₂O) to investigate the compositional evolution of residual liquids. The temperature (T) range of the experiments was 950–1,150 °C, aH₂O varied between 0.1 and 1, and the log of oxygen fugacity (fO₂) varied between quartz–fayalite–magnetite (QFM) and QFM + 4.1. The comparison of the experimentally produced liquids and natural samples was used to constrain the pressure (P)–T–aH₂O–fO₂ conditions of the Bezymianny parental magma in the intra-crustal magma plumbing system. The phase equilibria constraints suggest that parental basaltic andesite magmas should contain ~2–2.5 wt% H₂O; they can be stored in upper crustal levels at a depth of ~15 km, and at this depth they start to crystallize at ~1,110 °C. The subsequent chemical evolution of this parental magma most probably proceeded as decompressional crystallization occurred during magma ascent. The final depths at which crystallization products accumulated prior to eruption are not well constrained experimentally but should not be shallower than 3–4 km because amphibole is present in natural magmas (>150 MPa). Thus, the major volume of Bezymianny andesites was produced in a mid-crustal magma chamber as a result of decompressional crystallization of parental basaltic andesites, accompanied by mixing with silicic products from the earlier stages of magma fractionation. In addition, these processes are complicated by the release of volatiles due to magma degassing, which occurs at various stages during magma ascent.  相似文献   

Coamps<Superscript>®</Superscript>-Les: Model Evaluation and Analysis of Second-and Third-Moment Vertical Velocity Budgets     

Jean-Christophe?GolazEmail author  Shouping?Wang  James?D.?Doyle  Jerome?M.?Schmidt 《Boundary-Layer Meteorology》2005,116(3):487-517

The Naval Research Laboratory Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS^®) has been extended to perform as a large-eddy simulation (LES) model. It has been validated with a series of boundary-layer experiments spanning a range of cloud nighttime, and includes a nighttime stratocumulus case, a trade wind cumulus layer, shallow cumulus convection over land, and a mixed regime consisting of cumulus clouds under broken stratocumulus. COAMPS-LES results are in good agreement with other models for all the cases simulated. Exact numerical budgets for the vertical velocity second\((\overline{w^{'2}})\) and third moment\((\overline{w^{'3}})\) have been derived for the stratocumulus and trade wind cumulus cases. For the\(\overline{w^{'3}}\) budget in the stratocumulus, the buoyancy contribution from the updraughts and downdraughts largely cancel each other due to their similar magnitudes but opposite signs. In contrast, for the cumulus layer, the negative buoyancy contribution from the environmental downdraughts is negligible and the positive contribution from the updraughts completely dominates due to the conditional instability in the environment. As a result,\(\overline{w^{'3}}\) is significantly larger in the cumulus than in the stratocumulus layer.  相似文献   

Anisotropie verticale de la perméabilité de l'horizon fissuré des aquifères de socle : concordance avec la structure géologique des profils d'altération     

Jean-Christophe Maréchal  Robert Wyns  Patrick Lachassagne  Kambhampati Subrahmanyam  Frédéric Touchard 《Comptes Rendus Geoscience》2003,335(5):451-460

Pumping tests carried out in the fissured layer of a granitic hard-rock aquifer, interpreted at the observation wells by means of the analytical solution of Neuman and at the pumping wells with that of Gringarten show the existence of a strong vertical anisotropy of this layer of the aquifer; the horizontal permeability is clearly and systematically higher than the vertical one. These results agree perfectly with the geological observations, the fissured layer of the weathered granite profile showing the existence of many sub-horizontal fissures. It confirms that, within the fissured layer, the permeability of sub-horizontal fissures due to the weathering process dominates over that of sub-vertical fissures of tectonic origin. To cite this article: J.-C. Maréchal et al., C. R. Geoscience 335 (2003).To cite this article: J.-C. Maréchal et al., C. R. Geoscience 335 (2003).  相似文献   

Mixed-magma pyroclastic surge deposits associated with debris avalanche deposits at Colima volcanoes,Mexico     

Claude Robin  Jean-Christophe Komorowski  Christian Boudal  Philippe Mossand 《Bulletin of Volcanology》1990,52(5):391-403

The transition between the terminal cones and the ancestral edifices of Nevado de Colima and Fuego de Colima volcanoes is marked by the deposits of gigantic volcanic debris avalanches of the Mount St. Helens (MSH) or Bezymianny type. Unusual mafic juvenile fragments and cauliflower bombs as well as juvenile fragments of mixed and more evolved composition are abundant in dune-bedded pyroclastic-surge deposits directly associated with these catastrophic events at both volcanoes. At Nevado, these mafic juvenile fragments represent the most primitive magma ever erupted by the volcano (SiO₂52.50%). The lavas directly preceding and following the debris-avalanche event are silicic andesites (SiO₂59%). At Fuego these juvenile fregments have 56% SiO₂. The lavas from the upper parts of the caldera wall are dacites (65% SiO₂), whereas the terminal cone is composed of andesites (57% to 62% SiO₂). At Nevado, petrologic evidence for interaction of mafic magma with andesitic or dacitic magma in a high-level magma chamber, just before the eruption of pyroclastic surge deposits, consists of: (1) banded juvenile bombs of intermediate composition; (2) the range of composition of these bombs from SiO₂52% to 58%; (3) the presence of highly magnesian olivine with reaction rims; (4) inverse zoning in clinopyroxene with strong Mg enrichment towards the rim; (5) resorption of plagioclase; and (6) significant compositional heterogeneity in the vitric phase. Volcanic debris-avalanche events at Nevado and Fuego de Colima may thus correspond with major breaks in the petrological evolution of the volcanoes and the start of a new magmatic cycle. Injection of mafic magma into the presently perched viscous surface dome of the active Fuego cone, as occurred in 1818 and 1913, could enhance the likelihood of southward collapse of the flank of an already unstable edifice, and it must be considered in future hazard assessment of this active volcano. Risk to life and property for the entire Colima region associated with such catastrophic phenomena would be immeasurably greater in comparison with hazards related to the last explosive outburst in 1913, which resulted in emplacement of pyroclastic flows over uninhabited areas of the upper flanks of the volcano.  相似文献   

Morphology and tectonics of the Australian-Antarctic Discordance between 123° E and 128° E     

Jeb Palmer  Jean-Christophe Sempéré  David M. Christie  Jason Phipps Morgan 《Marine Geophysical Researches》1993,15(2):121-152

The Australian-Antarctic Discordance (AAD) is an anomalously deep and rugged zone of the Southeast Indian Ridge (SEIR) between 120° E and 128° E. The AAD contains the boundary between the Indian Ocean and Pacific Ocean isotopic provinces. We have analyzed SeaMarc II bathymetric and sidescan sonar data along the SEIR between 123° E and 128° E. The spreading center in the AAD, previously known to be divided into several transform-bounded sections, is further segmented by nontransform discontinuities which separate distinct spreading cells. Near the transform which bounds the AAD to the east, there is a marked change in the morphology of the spreading center, as well as in virtually every measured geochemical parameter. The spreading axis within the Discordance lies in a prominent rift valley similar to that observed along the Mid-Atlantic Ridge, although the full spreading rate within the AAD is somewhat faster than that of slow-spreading centers (~ 74 mm a^–1 vs. 0–40 mm a^–1). The AAD rift valleys show a marked contrast with the axial high that characterizes the SEIR east of the AAD. This change in axial morphology is coincident with a large (~ 1 km) deepening of the spreading axis. The segmentation characteristics of the AAD are analogous to those of the slow-spreading Mid-Atlantic Ridge, as opposed to the SEIR east of the AAD, which exhibits segmentation characteristics typical of fast-spreading centers. Thus, the spreading center within and east of the AAD contains much of the range of global variability in accretionary processes, yet it is a region free from spreading rate variations and the volumetric and chemical influences of hotspots. We suggest that the axial morphology and segmentation characteristics of the AAD spreading centers are the result of the presence of cooler than normal mantle. The presence of a cool mantle and the subsequent diminution of magma supply at a constant spreading rate may engender the creation of anomalously thick brittle lithosphere within the AAD, a condition which favor, the creation of an axial rift valley and of thin oceanic crust, in agreement with petrologic studies. The morphologies of transform and non-transform discontinuities within the Discordance also possess characteristics consistent with the creation of anomalously thick lithosphere in the region. The upper mantle viscosity structure which results from lower mantle temperatures and melt production rates may account for the similarity in segmentation characteristics between the AAD and slow-spreading centers. The section of the AAD which overlies the isotopic boundary is associated with chaotic seafloor which may be caused by an erratic pattern of magmatism and/or complex deformation associated with mantle convergence. Finally, the pattern of abyssal hill terrain within a portion of the AAD supports previous models for the formation of abyssal hills at intermediate- and slow-spreading ridges, and provides insights into how asymmetric spreading is achieved in this region.  相似文献   

Fine scale study of a small overlapping spreading center system at 12°54′ N on the East Pacific Rise     

Lisa Antrim  Jean-Christophe Sempere  Ken C. Macdonald  E. N. Spiess 《Marine Geophysical Researches》1988,9(2):115-130

Overlapping spreading centers (OSCs) are a type of ridge axis discontinuity found along intermediate and fast spreading centers. The ridges at these locations overlap and curve towards each other. and are separated by an elongate overlap basin. A high resolution Deep-Tow survey was conducted over the 12°54 N OSC (offset 1.6 km) on the East Pacific Rise in order to study the structure of a small OSC on a fine scale. A detailed tectonic study and Deep-Tow 3-D magnetic inversion were performed on the data. Towards the tips of both limbs, the apparent age of lava flows increases, the density of exposed faults and fissures increases, and the axial graben loses definition and disappears. No active hydrothermal vents were detected in the area. These observations suggest that the magmatic budget steadily decreases along axis approaching and OSC, even where the offset is small. In contrast with OSCs which have a large offset (>5 km), the 3-D magnetic inversion solution for this OSC produced no evidence for highly magnetized areas near the tip of either spreading center.  相似文献   

Detailed study of the Brunhes/Matuyama reversal boundary on the east Pacific rise at 19°30′ S: Implications for crustal emplacement processes at an ultra fast spreading center     

Jean-Christophe Sempere  Ken C. Macdonald  Stephen P. Miller  Loren Shure 《Marine Geophysical Researches》1987,9(1):1-23

We have conducted the first detailed survey of the recording of a geomagnetic reversal at an ultra-fast spreading center. The survey straddles the Brunhes/Matuyama reversal boundary at 19°30 S on the east flank of the East Pacific Rise (EPR), which spreads at the half rate of 82 mm yr^-1. In the vicinity of the reversal boundary, we performed a three-dimensional inversion of the surface magnetic field and two-dimensional inversions of several near-bottom profiles including the effects of bathymetry. The surface inversion solution shows that the polarity transition is sharp and linear, and less than 3–4 km wide. These values constitute an upper bound because the interpretation of marine magnetic anomalies observed at the sea surface is limited to wavelengths greater than 3–4 km. The polarity transition width, which represents the distance over which 90% of the change in polarity occurs, is narrow (1.5–2.1 km) as measured on individual 2-D inversion profiles of near-bottom data. This suggests a crustal zone of accretion only 3.0–4.2 km wide. Our method offers little control on accretionary processes below layer 2B because the pillow and the dike layers in young oceanic crust are by far the most significant contributors to the generation of marine magnetic anomalies. The Deep-Tow instrument package was used to determine in situ the polarity of individual volcanoes and fault scarps in the same area. We were able to make 96 in situ polarity determinations which allowed us to locate the scafloor transition boundary which separates positively and negatively magnetized lava flows. The shift between the inversion transition boundary and the seafloor transition boundary can be used to obtain an estimate of the width of the neovolcanic zone of 4–10 km. This width is significantly larger than the present width of the neovolcanic zone at 19°30 S as documented from near-bottom bathymetric and photographic data (Bicknell et al., 1987), and also larger than the width of the neovolcanic zone at 21° N on the EPR as inferred by the three-dimensional inversion of near-bottom magnetic data (Macdonald et al., 1983). The eruption of positively magnetized lava flows over negatively magnetized crust from the numerous volcanoes present in the survey area and episodic flooding of the flanks of the ridge axis by extensive outpourings of lava erupting from a particularly robust magma chamber may result in a widened neovolcanic zone. We studied the relationship between spreading rate and polarity transition widths obtained from 2-D inversions of the near-bottom magnetic field over various spreading centers. The mean transition width corrected for the time necessary for the reversal to occur decreases with increasing spreading rate but our data set is still too sparse to draw firm conclusions from these observations. Perhaps more interesting is the fact that the range of the measured transition widths also decreases with spreading rate. In the light of these results, we propose a new model for the spreading rate dependency of polarity transition widths. At slow spreading centers, the zone of dike injection is narrow but the locus of crustal accretion is prone to small lateral shifts depending on the availability of magmatic sources, and the resulting polarity transition widths can be narrow or wide. At intermediate spreading centers, the zone of crustal accretion is narrow and does not shift laterally, which leads to narrower transition widths on the average than at slow spreading centers. An intermediate, or even a slow spreading center, may behave like a fast or hot-spot dominated ridge for short periods of time when its magmatic budget is increased due to melting events in the upper mantle. At fast spreading centers, the zone of dike injection is narrow, but the large magmatic budget of fast spreading centers may result in occasional extensive flows less than a few tens of meters thick from the axis and off-axis volcanic cones. These thin flows will not significantly contribute to the polarity transition widths, which remain narrow, but they may greatly increase the width of the neovolcanic zone. Finally the gabbro layer in the lower section of oceanic crust may also contribute to the observed polarity transition widths but this contribution will only become significant in older oceanic crust (50–100 m.y.).  相似文献   

Modeling environmental effects on the size-structured energy flow through marine ecosystems. Part 1: The model   总被引：2，自引：3，他引：2  

Olivier Maury  Blaise Faugeras  Yunne-Jai Shin  Jean-Christophe Poggiale  Tamara Ben Ari  Francis Marsac 《Progress in Oceanography》2007,74(4):479-499

This paper presents an original size-structured mathematical model of the energy flow through marine ecosystems, based on established ecological and physiological processes and mass conservation principles. The model is based on a nonlocal partial differential equation which represents the transfer of energy in both time and body weight (size) in marine ecosystems. The processes taken into account include size-based opportunistic trophic interactions, competition for food, allocation of energy between growth and reproduction, somatic and maturity maintenance, predatory and starvation mortality. All the physiological rates are temperature-dependent. The physiological bases of the model are derived from the dynamic energy budget theory. The model outputs the dynamic size-spectrum of marine ecosystems in term of energy content per weight class as well as many other size-dependent diagnostic variables such as growth rate, egg production or predation mortality.In stable environmental conditions and using a reference set of parameters derived from empirical studies, the model converges toward a stationary linear log–log size-spectrum with a slope equal to −1.06, which is consistent with the values reported in empirical studies. In some cases, the distribution of the largest sizes departs from the stationary linear solution and is slightly curved downward. A sensitivity analysis to the parameters is conducted systematically. It shows that the stationary size-spectrum is not very sensitive to the parameters of the model. Numerical simulations of the effects of temperature and primary production variability on marine ecosystems size-spectra are provided in a companion paper [Maury, O., Shin, Y.-J., Faugeras, B., Ben Ari, T., Marsac, F., 2007. Modeling environmental effects on the size-structured energy flow through marine ecosystems. Part 2: simulations. Progress in Oceanography, doi:10.1016/j.pocean.2007.05.001].  相似文献   

Optimizing a piezometric network in the estimation of the groundwater budget: a case study from a crystalline-rock watershed in southern India   总被引：1，自引：0，他引：1  

Faisal K. Zaidi  Shakeel Ahmed  Benoit Dewandel  Jean-Christophe Maréchal 《Hydrogeology Journal》2007,15(6):1131-1145

An estimate of the groundwater budget at the catchment scale is extremely important for the sustainable management of available water resources. Water resources are generally subjected to over-exploitation for agricultural and domestic purposes in agrarian economies like India. The double water-table fluctuation method is a reliable method for calculating the water budget in semi-arid crystalline rock areas. Extensive measurements of water levels from a dense network before and after the monsoon rainfall were made in a 53 km² watershed in southern India and various components of the water balance were then calculated. Later, water level data underwent geostatistical analyses to determine the priority and/or redundancy of each measurement point using a cross-validation method. An optimal network evolved from these analyses. The network was then used in re-calculation of the water-balance components. It was established that such an optimized network provides far fewer measurement points without considerably changing the conclusions regarding groundwater budget. This exercise is helpful in reducing the time and expenditure involved in exhaustive piezometric surveys and also in determining the water budget for large watersheds (watersheds greater than 50 km²).  相似文献