Kinematics of compressional fold development in convergent wrench terranes

Kinematic models are presented for compressional fold development in wrench and convergent wrench terranes that relate fold shortening, axial rotation, and axial extension. Fold shortening may be derived from final fold geometry. Existing fold geometry and axial orientation, two readily measurable quantities, provide the data needed to determine the relative components of shearing and convergence within the fold system. Analyses utilizing these kinematic models indicate that folds developed in sedimentary rocks in the wrench borderlands of both the Rineonada and San Andreas wrench faults in central California are the product of strongly convergent wrenching. The axes of these folds have been rotated no more than a few degrees during the course of their development. In contrast, folds developed in the Alpine Schists along the Alpine fault in New Zealand and in Pleistocene sediments along the southern limit of the San Andreas fault suggest an almost pure wrench setting and large (>25 °) axial rotations.

Significant axial extension is inherent in wrench-related compressional folds. This axial extension is commonly manifest in the form of normal and strike-slip faults that are internal to the folds and trend at high angles to the fold axes. The relative amount of axial extension diminishes as the degree of convergence increases. This axial extension, and the associated extensional features, can be a diagnostic indication of the influence of wrenching.     

北京房山地区太平山褶皱的变形特征和形成时代:华北克拉通早白垩世挤压构造的意义

北京西山地区广泛发育轴向近E-W向的褶皱,对理解华北克拉通东部构造演化至关重要,但目前对其形成时代和构造动力学背景却没有明确的认识.北京房山地区的太平山褶皱是轴向近E-W向褶皱的典型代表.通过精细的野外构造观察和构造年代学研究,确定太平山褶皱的空间展布特征和构造样式,厘定构造变形的时代,为该区乃至华北克拉通东部的构造演化提供重要依据.通过详细的野外构造观察和系统的β图解研究,表明太平山褶皱由直立倾伏背斜和斜歪倾伏向斜构成.通过对早期卷入褶皱变形的煌斑岩席和晚期切层侵入褶皱的闪长玢岩脉进行锆石U-Pb定年,得到煌斑岩席和闪长玢岩脉的形成时代分别为147.2±2.4Ma和129.0±3.2Ma,表明太平山褶皱的形成时代为燕山运动B幕.另外,北京西山地区还存在NW-SE向的伸展构造样式.代表本区NW-SE向伸展的房山穹窿(约136Ma)晚于N-S向挤压构造,侵入切割太平山褶皱,塑造了研究区现今主体构造格架,进一步限定太平山褶皱的形成时代为147～136 Ma.因此,研究区轴向近E-W向的褶皱为早白垩世近N-S向挤压构造的产物;N-S向挤压和NW-SE向伸展的构造样式,为华北克拉通中生代构造体制的转换和动力学背景提供关键依据.     

乍得Bongor盆地反转构造特征及形成机制：来自地震剖面及沙箱模拟实验的证据

结合区域地震剖面解析和沙箱模拟实验,探讨分析了乍得Bongor盆地反转构造特征及其形成机制。结果表明：（1） Bongor盆地中发育三种典型的反转构造类型：挤压反转单斜构造、挤压反转向斜构造和挤压反转背斜构造。该类反转构造 一部分具有反转断层相关褶皱样式,主要沿高角度边界断层和基底地垒边界断面发育,形成演化与断裂活动息息相关,另 一部分呈散花状背斜构造样式,属于地层纵弯上拱褶皱,主要发育于斜坡断阶带之间;（2） 区域剥蚀作用对盆地反转构造 演化具有重要的影响,其对盆地内深部地层反转褶皱发育具有促进作用,为深部构造圈闭形成提供条件,而对浅部地层的 反转褶皱发育则表现出阻碍或破坏作用,不利于浅层构造圈闭的形成。     

川鄂湘边区褶皱构造样式及其成因机制分析

川鄂湘边区从西向东由隔槽式褶皱向隔档式褶皱的变化反映在深部构造样式上 ,其卷入的构造层次逐渐变深 ,至湘西带已由侏罗山式薄皮构造转为基底卷入式的厚皮构造 ,构造样式也更趋复杂 ;但由地表向下构造样式却普遍表现为由复杂向简单的变化。平衡剖面分析揭示了上述规律性。区域构造分析表明 ,上述构造是燕山期由南东向北西不断推进的挤压力作用的结果。     

Evolution of Eastern Ghats granulite belt of India in a compressional tectonic regime and juxtaposition against Iron Ore Craton of Singhbhum by oblique collision — transpression

Three major episodes of folding are evident in the Eastern Ghats terrain. The first and second generation folds are the reclined type; coaxial refolding has produced hook-shaped folds, except in massif-type charnockites in which non-coaxial refolding has produced arrow head folds. The third generation folds are upright with a stretching lineation parallel to subhorizontal fold axes. The sequence of fold stylesreclinedF ₁and coaxialF ₂, clearly points to an early compressional regime and attendant progressive simple shear. Significant subhorizontal extension duringF ₃folding is indicated by stretching lineation parallel to subhorizontal fold axes. In the massif-type charnockites low plunges ofF ₂folds indicate a flattening type of deformation partitioning in the weakly foliated rocks (magmatic ?). The juxtaposition of EGMB against the Iron Ore Craton of Singhbhum by oblique collision is indicative of a transpressional regime.     

Coalescence of fault‐bend and fault‐propagation folding in curved thrust systems: an insight from the Central Apennines,Italy

The coalescence and spatial variability of different thrust‐related folding mechanisms involving the same mechanical multilayer along a curved thrust system are documented in this study. The field‐based analysis of thrust‐related folds spectacularly exposed in the Gran Sasso thrust system, Central Apennines of Italy, allowed us to reconstruct the interference fold pattern between fault‐bend and fault‐propagation folding. These two thrust‐related folding mechanisms exhibit spatial variability along the differently oriented ramps of the curved Gran Sasso thrust system, passing from one style to the other. Their selective development is controlled by contrasting styles of compressional normal‐fault reactivation related to positive tectonic inversion. Fault‐bend and fault‐propagation folding interact with a characteristic interference fold pattern in the salient apex zone of the curved thrust system due to their synchronous/in‐sequence growth. This interference fold pattern might be helpful and predictive when reconstructing lateral variations in different thrust‐related folds in similar subaerial or submarine thrust belts.     

Three-dimensional Evolutionary Models of the Qiongxi Structures, Southwestern Sichuan Basin, China: Evidence from Seismic Interpretation and Geomorphology

Fold terminations are key features in the study of compressional fault-related folds. Such terminations could be due to loss of displacement on the thrust fault or/and forming a lateral or oblique ramp. Thus, high-quality seismic data would help unambiguously define which mechanism should be responsible for the termination of a given fault-related fold. The Qiongxi and Qiongxinan structures in the Sichuan Basin, China are examples of natural fault-propagation folds that possess a northern termination and a structural saddle between them. The folds/fault geometry and along-strike displacement variations are constrained by the industry 3-D seismic volume. We interpret that the plunge of the fold near the northern termination and the structural saddle are due to the loss of displacement along strike. The fault geometry associated with the northern termination changes from a flat-ramp at the crest of the Qiongxinan structure, where displacement is the greatest, to simply a ramp near the northern tip of the Qiongxi structure, without forming a lateral or oblique ramp. In this study, we also use the drainage pattern, embryonic structure preserved in the crest of the Qiongxinan structure and the assumption that displacement along a fault is proportional to the duration of thrusting to propose a model for the lateral propagation of the Qiongxinan and Qiongxi structures. Specifically, we suggest that the structure first initiated as an isolated fault ramp within brittle units. With increased shortening, the fault grows to link with lower detachments in weaker shale units to create a hybridized fault-propagation fold. Our model suggests a possible explanation for the lateral propagation history of the Qiongxinan and Qiongxi structures, and also provides an alternative approach to confirming the activity of the previous Pingluoba structure in the southwestern Sichuan Basin in the late Cenozoic.     

塔里木盆地北部构造样式

塔里木盆地北部发育５种典型的构造样式；基底卷入型压性逆冲构造组成、盖层滑脱型逆冲－褶皱构造组合、隐刺穿刺底檗同幅度褶皱构造组合及张性正断层组合，无论是构造变形时间还是组合分布，在塔北均呈现规律变化，其变形特征及发布受如下３个地质因素控制：（１）区域挤压作用；（２）岩性条件的差异：（２）先期构造格局。     

Faulting and fracturing in the Jurassic carbonate ramp folds of southern Rif ridges (Northern Morocco)

In the South Rifian ridges (SRR), the dominated structures correspond to the faulted anticline characteristic of a foreland orogeny context, front of the Rif Alpine belt. These anticlines correspond to thrust propagation folds. Geometric model of these structures shows that the normal faults have controlled the Mesozoic sedimentation during extensive episodes and participated in determining areas of thrusting during Miocene compressional phases. However, the normal fault strike which is relative to the direction of the shortening determined the geometry of diverse folds whether into the frontal ramps, lateral, or oblique. In the meantime, the systematic fracturing study in the Jurassic limestone beds, in different parts of the folds with axes oriented E-W, NW-SE, and NE-SW, permits to propose a relative fracturing chronology and tries investigating the relationship between folding and fracturing. The three main fracture families, oblique, transversal, and axial, appear simultaneously during the amplification of the fold. The simple shear in the limb contributes the latest to the folding reactivation and the density of the intensification of these microfractures. Likewise, given the important downslope fold limb dip of the ramp propagation folds, theoretically the shear intensity is more important, and micro-fractures are more important in the downslope fold limb, thus the uphill one.     

Three‐dimensional Evolutionary Models of the Qiongxi Structures,Southwestern Sichuan Basin,China: Evidence from Seismic Interpretation and Geomorphology

Fold terminations are key features in the study of compressional fault-related folds. Such terminations could be due to loss of displacement on the thrust fault or/and forming a lateral or oblique ramp. Thus, high-quality seismic data would help unambiguously define which mechanism should be responsible for the termination of a given fault-related fold. The Qiongxi and Qiongxinan structures in the Sichuan Basin, China are examples of natural fault-propagation folds that possess a northern termination and a structural saddle between them. The folds/fault geometry and along-strike displacement variations are constrained by the industry 3-D seismic volume. We interpret that the plunge of the fold near the northern termination and the structural saddle are due to the loss of displacement along strike. The fault geometry associated with the northern termination changes from a flat-ramp at the crest of the Qiongxinan structure, where displacement is the greatest, to simply a ramp near the northern tip of the Qiongxi structure, without forming a lateral or oblique ramp. In this study, we also use the drainage pattern, embryonic structure preserved in the crest of the Qiongxinan structure and the assumption that displacement along a fault is proportional to the duration of thrusting to propose a model for the lateral propagation of the Qiongxinan and Qiongxi structures. Specifically, we suggest that the structure first initiated as an isolated fault ramp within brittle units. With increased shortening, the fault grows to link with lower detachments in weaker shale units to create a hybridized fault-propagation fold. Our model suggests a possible explanation for the lateral propagation history of the Qiongxinan and Qiongxi structures, and also provides an alternative approach to confirming the activity of the previous Pingluoba structure in the southwestern Sichuan Basin in the late Cenozoic.     

Experimental (clay) models of inversion structures

Experimental modeling is used to study the geometry and evolution of inversion structures. Two main types of inversion structures are analyzed:

1. (1) structures formed by fault-propagation folding; and

2. (2) structures formed by fault-bend folding on listric faults.

Fault-propagation inversion structures initially develop as broad drape folds with possible fault breakthrough during an early extensional phase. Syn-extensional strata deposited in the hanging wall typically thicken away from the fault. Compressional reactivation results in reversal of slip on the master and secondary faults, their rotation to shallower dips, and the development of a compressional fault-propagation fold. Key features of the fault-propagation fold are basinward thickening of syn-extensional units and resulting steep dips of the front limb of the structure. Fault-bend inversion structures initiate as rollover folds within extensional half-graben. Deformation is primarily localized along a system of antithetic faults. Syn-extensional strata typically thicken across the fault but also thin basinward away from the fault. During compression, the extensional rollover folds are folded into compressional fault-bend folds. Key features of this structure are thinning of syn-extensional units into the basin. Inversion of more symmetric graben results in a doubly-convex geometry of syn-extensional units. These observations of bed geometry and thickness provide predictive models for interpreting the geometries of inversion structures in areas of poor data quality.     

Structures in the banded iron-formation of the southeastern Bababudan Hills, Karnataka, India

The banded iron-formation in the southeastern Bababudan Hills display a macroscopic synformal bend gently plunging towards WNW. The bedding planes in smaller individual sectors show a cylindrical or conical pattern of folding. The dominant set of minor folds has WNW-ESE trending axial planes and the axes plunge towards WNW at gentle to moderate angles, though there is considerable variation in orientation of both axes and axial planes. A later set of sporadically observed folds has N-S trending axial planes. The macroscopic synformal bend within the study area forms the southeastern corner of a horseshoe shaped regional synformal fold closure which encompasses the entire Bababudan range. The minor folds are buckle folds modified to a varying extent by flattening. In some examples the quartzose layers appear to be more competent than the ferruginous layers; in others the reverse is true. The folds are frequently noncylindrical and the axes show curvature with branching and en echelon patterns. Such patterns are interpreted to be the result of complex linking of progressively growing folds whose initiation is controlled by the presence of original perturbations in the layers. Domes and basins have at places developed as a result of shortening along two perpendicular directions in a constrictional type of strain. Development of folds at different stages of progressive deformation has given rise to nonparallelism of fold axes and axial planes. The axes and axial planes of smaller folds developed on the limbs of a larger fold are often oriented oblique to those of the latter. Progressive deformation has caused rotation and bending of axial planes of earlier formed folds by those developed at later stages of the same deformational episode. Coaxial recumbent to nearly reclined fold locally encountered on the N-S limb of the macroscopic fold may belong to an earlier episode of deformation or to the early stage of the main deformation episode. The E-W to ESE-WNW strike of axial plane of the regional fold system in the Bababudan belt contrasts with the N-S to NNW-SSE strike of axial planes of the main fold system in the Chitradurga and other schist belts of Karnataka.     

Identification of Quaternary thrusts, folds and faults in a low seismicity area: examples in the Southern Alps (France)

In low seismicity areas, folds, faults and striated pebbles in recent alluvial deposits can demonstrate the Quaternary activity of tectonic structures and can reveal their kinematics. In the Digne nappe (Southern Alps), an out-of-sequence thrust occurred in the late Quaternary in response to WSW-trending compression. The presence of late Quaternary compressional deformation in the Valavoire thrust could have resulted from the activity of the underlying Durance flexure with a maximum Pliocene–Quaternary uplift rate of about 0.1 mm yr⁻¹. The Quaternary top surface of the Valensole basin, that truncates SW-vergent thrust propagation folds, is folded above the Lambruissier anticline. Exceptional conditions resulted in the local preservation of this Quaternary fold morphology created with a minimum uplift-rate of 0.05 mm yr⁻¹ under a NE-trending compression. At the front of the Digne nappe the deformation is characterized by WSW to WNW trends of compression and low strain rates during the Quaternary period.     

STRUCTURAL PECULIARITIES AND POSSIBLE MODES OF FORMATION OF GEOSYNCLINAL FOLDED STRUCTURES (BASED ON THE BOL'SHOY KARATAU)

Data on peculiarities of configuration and positional interrelations of folded structure belonging to the Middle Paleozoic structural stage of the Bolshoy Karatau Ridge are given in the paper.

On the basis of both the geological-structural map of this region compiled by the author and an abundance of other materials conclusions are made as to the most important morphological features of the geosynclinal folds; considerations regarding the modes of their formation are suggested.

Within the above-mentioned structural stage three most important genetic fold types are isolated: stamped folds, warping folds, flow folds. The former originated under the effect of vertically directed forces normally applied to the stratum. The second are the results of a tangential compression of stratified beds. And the formation of the last was caused by the flow of the most plastic constituents of the section. The author is of the opinion the above fold types are generally most widespread among the folded structures of the geosynclinal regions. The stamped folds are a direct result of local uplifts and subsidences of the Earth crust and thus their origin is quite clear from the mechanical standpoint. The warping folds might have formed in the course of uplifting of previously formed downwarpings when the filling rock beds had to pass through the chord of their original arc. Moreover they might have originated as a result of broad gravitational bed sliding. And finally, the flow folds most frequently formed evidently also under the effect of gravitational forces (when the latter are great enough to provoke plastic rock deformation) or under the effect of a difference of confining pressures.—Auth. English summ.     

广东省兴梅煤田控煤构造样式及其控煤意义研究

兴梅煤田在区域构造位置上位于华南褶皱系永梅-惠阳拗陷东北段的永梅凹褶断束,区内煤系赋存特征与控煤构造样式关系密切。运用构造控煤分析方法,根据后期控煤构造几何形态、特征及形成机制,将兴梅煤田构造样式分为伸展构造样式、压缩构造样式、滑动构造样式、滑推叠加构造样式和剪切与旋转构造样式5大类13种类型。本区以轴向北西（含北北西、北西西）的褶皱控煤构造较为多见,其煤系赋存较稳定,可形成较大面积的赋煤单元;伸展构造样式常使煤系失去连续性;压缩构造样式、滑推叠加构造样式、滑动构造样式常造成煤系地层重复,增加资源量,但煤系受破坏显著,含煤块段连续性较差、面积一般较小,煤矿规模多为小型。     

Origin and terminal architecture of a submarine slide: a case study from the Permian Vischkuil Formation,Karoo Basin,South Africa

Submarine mass movement deposits exposed in the Vischkuil Formation, Laingsburg Karoo Basin, South Africa, provide a rare opportunity to analyse and interpret their emplacement history and deformation processes at a scale comparable to seismic examples. An up to 80 m thick slide deposit, continuously exposed in two 2 km long sub‐parallel sections, passes from extensionally deformed material (clastic dykes and down‐dip facing low‐angle shear surfaces) down‐dip into a compressional toe zone with large (tens of metres amplitude) folds dissected by steep, up‐dip facing thrust planes. The compressional shear planes sole out onto a highly sheared décollement and cross‐cutting relationships indicate an up‐depositional dip younging in the timing of fold dissection. Lithofacies characteristics and detailed correlation of volcanic ash and other marker beds over more than 500 km² in the bounding undeformed stratigraphy indicate a low‐gradient (<0·1°) basin floor setting. The slide is abruptly overlain by an up to 50 m thick debrite with sandy clasts supported by an argillaceous matrix. Shear loading of the debris flow is interpreted to have driven large‐scale deformation of the substrate through the generation of high shear stresses at a rheological interface due to: (i) the abrupt contact between the slide and the debrite; (ii) the coincident thickness distributions of the debrite and slide; (iii) the distribution of the most intense folding and thrusting under the thickest parts of the debrite; (iv) the preservation of fold crests with only minor erosion along fold limbs; (v) the presence of the debrite under overturned folds; (vi) the presence of laterally extensive marker beds directly above deformation units indicating minimal depositional topography; and (vii) the demonstrably local derivation of the slide as individual folded beds are mapped into undeformed strata outside the areas of deformation. The debrite is directly overlain by fine‐grained turbidite sandstone beds that show widespread vertical foundering into the debrite. This case study demonstrates that intensely deformed strata can be generated by negligible amounts of down‐dip movement in a low‐gradient, fine‐grained basin floor setting with the driver for movement and deformation being the mass imbalance resulting from emplacement of episodic debris flows. Simple interpretation of an unstable slope setting based on the presence of such deformed strata should be treated with caution.     

Structure of the Abercrombie beds south of Reids flat,new South Wales

The Late Ordovician Abercrombie Beds, south of Reids Flat, New South Wales, and adjacent to the Wyangala Batholith, show evidence of three successive fold episodes. First generation folds are tight to isoclinal, with fold axes ranging from vertical to horizontal and north‐trending, and steep axial‐plane slaty cleavage. Second generation folds are steeply plunging, tight to open with north‐striking axial planes. In pelitic rocks the axial plane structure is a crenulation cleavage which overprints the slaty cleavage. The first two fold episodes were accompanied by greenschist‐facies metamorphism. Granite emplacement occurred prior to the second fold episode. A third deformation was of relatively mild intensity and produced open, north‐trending folds with axial planes dipping moderately to the east, and crenulation cleavage as the axial plane structure in pelitic rocks. These latest folds are correlated with the latest folds in the Abercrombie Beds north of the Abercrombie River. The mapped area has no apparent macroscopic structure and may be considered as a single domain.     

Geometric and kinematic analysis of structural elements along north front of Bagharan Kuh Mountain,NE Iran

At the end of the western part of Bagharan Kuh Mountain in the northeast of Iran, mountain growth has been stopped toward the west because of the stress having been consumed by the thrusting movements and region rising instead of shear movement. Chahkand fault zone is situated at the western part of this mountain; this fault zone includes several thrust sheets that caused upper cretaceous ophiolite rocks up to younger units, peridotite exposure and fault related fold developing in the surface. In transverse perpendicular to the mountain toward the north, reduction in the parameters like faults dip, amount of deformation, peridotite outcrops show faults growth sequence and thrust sheets growth from mountain to plain, thus structural vergence is toward the northeast in this fault zone. Deformation in the east part of the region caused fault propagation fold with axial trend of WNW-ESE that is compatible with trending of fault plane. In the middle part, two types of folds is observed; in the first type, folding occurred before faulting and folds was cut by back thrust activity; in the second type, faults activity caused fault related folds with N60-90W axial trend. In order to hanging wall strain balance, back thrusts have been developed in the middle and western part which caused popup and fault bend folds with N20-70E trend. Back thrusts activity formed footwall synclines, micro folds, foliations, and uplift in this part of the region. Kinematic analysis of faults show stress axis σ₁ = N201.6, 7, σ₂ = N292.6, 7.1, σ₃ = N64.8, 79.5; stress axis obtained by fold analysis confirm that minimum stress (σ₃) is close to vertical so it is compatible with fault analysis. Based on the results, deformation in this region is controlled by compressional stress regime. This stress state is consistent with the direction of convergence between the Arabian and Eurasian plates. Also study of transposition, folded veins, different movements on the fault planes and back thrusts confirm the progressive deformation is dominant in this region that it increases from the east to the west.     

Structural styles and tectonic evolution of the Kolia-Boboti sedimentary Basin,Kédougou-Kéniéba inlier,eastern Senegal

New structural data obtained on the Birimian terranes of the Kolia-Boboti sedimentary Basin, the eastern part of the Dialé-Daléma Supergroup in the Kédougou-Kéniéba inlier show two major phases of Eburnean compressional deformation: (1) a D1 phase of thrusting tectonics affected the Lower Birimian B1 tourmalinized sediments. This first tectonic phase is characterized by isoclinals overturned to recumbent folds P1 with N040° 20°NE trending axis, associated with axial plane schistosity S₀S₁ which is mainly transposed in the bedding; (2) a D2 phase of compressional (D2a) and transpressional (D2b) tectonics is responsible for the crossfolds P2a-P2b exhibiting curved axes. These P2 folds are associated with the major schistosity S₂, north-south to SW-NE trending, mainly dipping to the south-east. The S₂ schistosity is mostly displayed in the large shear zones corridors where it steeply dips locally toward the north-west. A north-west vergence thrusting phase (D2c) of flats and ramps, associated with reverse folds, represents the last Eburnean event. This geometrical feature is characteristic of a “positive flower structure”. These different Eburnean compressional phases are separated by extensional deformation which is characterized by sedimentary deposits and volcanic flows.     

Dépliage 3-D des anticlinaux bordant le synclinal fermé de la vallée des Ponts, Jura central, Suisse

The Ponts valley syncline is a closed basin within the Neuchâtel Jura fold and thrust belt. This syncline, apparently uplifted to an altitude of around 1000m is closed in the SW by an anticline with an oblique WNW-ESE direction. The 3-D geometry of the entire structure is examined and unfolded in detail. This syncline is filled with an unexpectedly thick series (~400m) of Tertiairy Molasse, as revealed by the CS-AMT (controlled source audio-magneto-telluric) and a reflexion seismic line. The latter also documents internal compressional structures within the well layered upper freshwater Molasse series. The 3-D configuration of the top Malm limestones has been constructed for the entire area based on new detailed geologic and structural mapping, hundreds of dip measurements, as well as geophysical data. The Malm marker bed displays three distinct types of structures: 1) Thrust faults with shallow dips, vergent to the NW and/or SE that are associated with folds interpreted as fault bend folds; 2) high angle inverse faults, mostly with a SE vergence are interpreted as inverted normal faults, inherited from a modest Oligo-Miocene extensional phase in a NW-SE direction; and 3) tear faults with a dominant N-S direction, probably inherited from an Oligocene extensional phase in association with the opening of the Rhine and Bresse grabens. Tear faults accommodate important lateral changes in fold geometry during the Late Miocene main folding-and-thrusting phase. All deformations are easily explained in an entirely thin-skinned fashion, taking place above a thick detachment horizon within Triassic evaporite series.Manuscrit reçu le 31 mars 2003 Révision acceptée le 23 juin 2004