Evidence for mantle exhumation along the Arabian margin in the Zagros (Kermanshah area, Iran)     

Jean-Christophe Wrobel-Daveau  Jean-Claude Ringenbach  Saeid Tavakoli  Geoffrey M. H. Ruiz  Pierre Masse  Dominique Frizon de Lamotte 《Arabian Journal of Geosciences》2010,3(4):499-513

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Formation and preservation of pedogenic carbonates in South India, links with paleo-monsoon and pedological conditions: Clues from Sr isotopes, U-Th series and REEs     

Aurélie Violette  Jean Riotte  Jean-Jacques Braun  Priscia Oliva  Jean-Christophe Marechal  M. Sekhar  Catherine Jeandel  Jonathan Prunier  Laurent Barbiero  Bernard Dupre 《Geochimica et cosmochimica acta》2010,74(24):7059-7085

The influence of the pedogenic and climatic contexts on the formation and preservation of pedogenic carbonates in a climosequence in the Western Ghats (Karnataka Plateau, South West India) has been studied. Along the climosequence, the current mean annual rainfall (MAR) varies within a 80 km transect from 6000 mm at the edge of the Plateau to 500 mm inland. Pedogenic carbonates occur in the MAR range of 500-1200 mm. In the semi-arid zone (MAR: 500-900 mm), carbonates occur (i) as thick hardpan calcretes on pediment slopes and (ii) as nodular horizons in polygenic black soils (i.e. vertisols). In the sub-humid zone (MAR: 900-1500 mm), pedogenic carbonates are disseminated in the black soil matrices either as loose, irregular and friable nodules of millimetric size or as indurated botryoidal nodules of centimetric to pluricentimetric size. They also occur at the top layers of the saprolite either as disseminated pluricentimetric indurated nodules or carbonate-cemented lumps of centimetric to decimetric size.Chemical and isotopic (⁸⁷Sr/⁸⁶Sr) compositions of the carbonate fraction were determined after leaching with 0.25 N HCl. The corresponding residual fractions containing both primary minerals and authigenic clays were digested separately and analyzed. The trend defined by the ⁸⁷Sr/⁸⁶Sr signatures of both labile carbonate fractions and corresponding residual fractions indicates that a part of the labile carbonate fraction is genetically linked to the local soil composition. Considering the residual fraction of each sample as the most likely lithogenic source of Ca in carbonates, it is estimated that from 24% to 82% (55% on average) of Ca is derived from local bedrock weathering, leading to a consumption of an equivalent proportion of atmospheric CO₂. These values indicate that climatic conditions were humid enough to allow silicate weathering: MAR at the time of carbonate formation likely ranged from 400 to 700 mm, which is 2- to 3-fold less than the current MAR at these locations.The Sr, U and Mg contents and the (²³⁴U/²³⁸U) activity ratio in the labile carbonate fraction help to understand the conditions of carbonate formation. The relatively high concentrations of Sr, U and Mg in black soil carbonates may indicate fast growth and accumulation compared to carbonates in saprolite, possibly due to a better confinement of the pore waters which is supported by their high (²³⁴U/²³⁸U) signatures, and/or to higher content of dissolved carbonates in the pore waters. The occurrence of Ce, Mn and Fe oxides in the cracks of carbonate reflects the existence of relatively humid periods after carbonate formation. The carbonate ages determined by the U-Th method range from 1.33 ± 0.84 kyr to 7.5 ± 2.7 kyr and to a cluster of five ages around 20 kyr, i.e. the Last Glacial Maximum period. The young occurrences are only located in the black soils, which therefore constitute sensitive environments for trapping and retaining atmospheric CO₂ even on short time scales. The maximum age of carbonates depends on their location in the climatic gradient: from about 20 kyr for centimetric nodules at Mule Hole (MAR = 1100 mm/yr) to 200 kyr for the calcrete at Gundlupet (MAR = 700 mm/yr, Durand et al., 2007). The intensity of rainfall during wet periods would indeed control the lifetime of pedogenic carbonates and thus the duration of inorganic carbon storage in soils.  相似文献   

A landscape mosaics approach for characterizing swidden systems from a REDD+ perspective   总被引：1，自引：0，他引：1  

Cornelia Hett  Jean-Christophe Castella  Andreas Heinimann 《Applied geography (Sevenoaks, England)》2012,32(2):608-618

Swidden agriculture is often deemed responsible for deforestation and forest degradation in tropical regions, yet swidden landscapes are commonly not visible on land cover/use maps, making it difficult to prove this assertion. For a future REDD+ scheme, the correct identification of deforestation and forest degradation and linking these processes to land use is crucial. However, it is a key challenge to distinguish degradation and deforestation from temporal vegetation dynamics inherent to swiddening. In this article we present an approach for spatial delineation of swidden systems based on landscape mosaics. Furthermore we introduce a classification for change processes based on the change matrix of these landscape mosaics. Our approach is illustrated by a case study in Viengkham district in northern Laos. Over a 30-year time period the swidden landscapes have increased in extent and they have degraded, shifting from long crop-fallow cycles to short cycles. From 2007 to 2009 degradation within the swidden system accounted for half of all the landscape mosaics change processes. Pioneering shifting cultivation did not prevail. The landscape mosaics approach could be used in a swidden compatible monitoring, reporting and verification (MRV) system of a future REDD+ framework.  相似文献   

Heat Tracing in a Fractured Aquifer with Injection of Hot and Cold Water     

Richard Hoffmann  Jean-Christophe Maréchal  Adrien Selles  Alain Dassargues  Pascal Goderniaux 《Ground water》2022,60(2):192-209

Heat as a tracer in fractured porous aquifers is more sensitive to fracture-matrix processes than a solute tracer. Temperature evolution as a function of time can be used to differentiate fracture and matrix characteristics. Experimental hot (50 °C) and cold (10 °C) water injections were performed in a weathered and fractured granite aquifer where the natural background temperature is 30 °C. The tailing of the hot and cold breakthrough curves, observed under different hydraulic conditions, was characterized in a log–log plot of time vs. normalized temperature difference, also converted to a residence time distribution (normalized). Dimensionless tail slopes close to 1.5 were observed for hot and cold breakthrough curves, compared to solute tracer tests showing slopes between 2 and 3. This stronger thermal diffusive behavior is explained by heat conduction. Using a process-based numerical model, the impact of heat conduction toward and from the porous rock matrix on groundwater heat transport was explored. Fracture aperture was adjusted depending on the actual hydraulic conditions. Water density and viscosity were considered temperature dependent. The model simulated the increase or reduction of the energy level in the fracture-matrix system and satisfactorily reproduced breakthrough curves tail slopes. This study shows the feasibility and utility of cold water tracer tests in hot fractured aquifers to boost and characterize the thermal matrix diffusion from the matrix toward the flowing groundwater in the fractures. This can be used as complementary information to solute tracer tests that are largely influenced by strong advection in the fractures.  相似文献   

Integrating aerial geophysical data in multiple-point statistics simulations to assist groundwater flow models     

Neil E. M. Dickson  Jean-Christophe Comte  Philippe Renard  Julien A. Straubhaar  Jennifer M. McKinley  Ulrich Ofterdinger 《Hydrogeology Journal》2015,23(5):883-900

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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   

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