new insights into deformation and fluid flow processes in the nankai trough accretionary prism results of ocean drilling program leg 190 moore g f taira a klaus a becker l boeckel b cragg b a dean a fergusson c l henry p hirano s hisamitsu t et al 2001 new insights into deformation and fluid flow processes in the nankai trough accretionary prism results of ocean drilling program leg 190 geochemistry geophysics geosystems 2 article no 2001gc000166

sediment deformation and hydrogeology of the nankai trough accretionary prism synthesis of shipboard results of odp leg 131 the main objective of leg 131 was to provide data on the deformational processes and associated hydrogeology of the nankai prism toe drilling succeeded for the first time in the history of ocean drilling in penetrating the complete sedimentary sequence to basaltic basement reaching 1327 mbsf metres below seafloor with good core recovery 55 excellent correlation of the lithology and structure including the frontal thrust and the decollement with seismic reflection images was also determined bedding dips faults and shear bands analyzed in the cores confirm the pattern of deformation to be mainly due to nw se shortening as expected from the plate tectonic convergence vector below the decollement no significant deformation features were observed indicating that the decollement is a sharp discontinuity in stress transmission physical properties data show major discontinuities at the decollement notably an increase in porosity below the later this may indicate excess pore pressure in the subducted section and decollement zone a less marked increase in porosity below the frontal thrust may reflect the youthfulness of this feature attempts to make downhole measurements were severely hampered by unstable hole conditions but useful constraints have been placed on the thermal regime and some calibration of laboratory physical properties toin situ conditions has been provided andin situ stress and pore pressure were measured in the uppermost sediments evidence of channelized fluid flows is inconclusive no sharp geochemical signatures or unequivocal geochemical anomalies indicative of channelized fluid flow were found thermal measurements are not significantly different from those predicted by a purely conductive heat flow model a signature of low chloride pore water near the decollement may partly be related to smectite diagenesis but may also be due to episodic fluid flow events we conclude that dewatering probably occurred dominantly through diffuse flow throughout the accreted sediments at this site

biennial and lower frequency variability observed in the early summer climate in the western north pacific early summer climate in the western north pacific is largely represented by the baiu phenomenon the meridional fluctuations of the baiu front on interannual time scales and the associated large scale circulations are examined using the empirical orthogonal function eof analysis and composite or correlation analyses based on the eof time coefficients the first eof mode indicates a 5 or 6 yr low frequency fluctuation lf mode appearing south of 358n the development is concurrent with horseshoe sea surface temperature anomalies sstas in the entire tropical pacific that are associated with the el nino southern oscillation enso sstas in the western north pacific control the anomalous southward expansion of the baiu front through a modification of the convection at around 208 358n the lf mode is negatively correlated with the south southeast asian summer monsoon the second eof mode is characterized by a meridional seesawlike fluctuation with a node at around 28 8n and a time scale of biennial oscillation bo mode the horseshoe sstas again control the anomalous meridional circulations but with a different spatial phase through a convection off the philippines the spatial phase difference between the two horseshoe patterns is about 908 in both the zonal and meridional directions the bo mode is negatively correlated with the tropical western north pacific monsoon sstas associated with the bo mode tend to be confined to the tropical western pacific while the signals of the lf mode extend rather broadly in the tropical pacific indian ocean sector suggesting that the tropical bo is an aborted enso in the tropical central western pacific the spatial phase of horseshoe sstas adjusts the interannual variability of the meridional fluctuation of the baiu front in the western north pacific

birth death and resurrection the life cycle of suprasubduction zone ophiolites 1 suprasubduction zone ssz ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites this sequence includes the following 1 birth which entails the formation of the ophiolite above a nascent or reconfigured subduction zone this stage is typically characterized by the eruption of arc tholeiite lavas and the formation of layered gabbros and sheeted dike complex 2 youth during which is continued melting of refractory asthenosphere depleted during birth occurs in response to fluid flux from the subducting slab with extensional deformation of the older plutonic suite eruption of refractory lavas and the intrusion of wehrlite pyroxenite 3 maturity with the onset of semistable arc volcanism typically calc alkaline as the subduction zone matures and stabilizes and the intrusion of quartz diorite and eruption of silicic lavas and 4 death which is the sudden demise of active spreading and ophiolite related volcanism which in many cases is linked to collision with an active spreading center and the onset of shallow underthrusting of the buoyant spreading axis expressed as dikes and lavas with oceanic basalt compositions that crosscut or overlie rocks of the older suites 5 resurrection with emplacement by obduction onto a passive margin or accretionary uplift with continued subduction the early stages 1 3 may be diachronous and each stage may overlap in both time and space the existence of this consistent progression implies that ophiolite formation is not a stochastic event but is a natural consequence of the ssz tectonic setting

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

the triassic jurassic ecostratigraphic transition in the lombardian alps italy abstract three paleoenvironmental phases and two declines in diversity characterize the late triassic to early jurassic history of the lombardian platforms the first phase of late triassic time choristoceras zone consists of 1 5 m thick shallowing upward subtidal cycles of molluscan coralline and echinoderm wackestone and packstone of the zu limestone biotic and ecostratigraphic characteristics such as typical rhaetavicula contorta fauna and facies allow correlation to the kossen formation of the northern calcareous alps the second phase of latest triassic time upper choristoceras zone consists of shallow restricted marine or peritidal carbonates of the chonchodon formation dominated by barren lime mudstone and dolostone algal laminites and oolitic grainstone the zu conchodon transition predates the triassic jurassic boundary and represents the first and most severe diversity decline for the lombardian fauna corresponding to a fall in sea level where observed the upper and lower contacts of the conchodon formation are conformable and do not constitute sequence boundaries as suggested by some workers the lower jurassic psiloceras zone sedrina limestone marks the beginning of the third phase with the onset of transgression and return of normal marine conditions typical microfacies include molluscan echinoderm and sponge wackestone and packstone with abundant anomuran microcoprolites the second diversity decline occurred at or just above the triassic jurassic boundary at the conchodon sedrina transition where the remaining restricted marine forms disappeared with the transgression anoxia was not a factor in this decline in diversity although other mechanisms in addition to sea level change cannot be discounted

the role of strain in area constant detachment folding abstract the classical constant area relationship for balancing cross sections is reformulated to accommodate layer parallel strain leading to a general equation for the layer parallel strain in a fold formed above a stratigraphically fixed detachment horizon the strain required for area balance can be calculated from a knowledge of the fold shape and the depth to detachment the strains predicted from a simple kinematic model are realistic in the order of 10 30 layer parallel shortening the strain may be penetrative or occur as small scale disharmonic folds and faults the tip top anticline a fold at the leading edge of the wyoming thrust belt is used to illustrate the applicability of this reformulation the computed layer parallel strains in the well controlled upper portion of the structure are less than 5 because most of the shortening is accommodated by second order folds and faults

estimating the detachment depth in cross sections involving detachment folds this paper evaluates four different methods that have been proposed for the estimation of the detachment depth beneath detachment folds guidelines are presented in order to use the most suitable method in a particular region deformed by detachment folds these guidelines are constructed considering the assumptions of each method the influence of different parameters on the estimation of the detachment depth folding mechanisms cross sectional area variations position and orientation of the regional datum number of stratigraphic horizons bed length and thickness dip and position of the bounding lines initial thickness of the ductile unit single anticlines or fold trains and the available data ductile unit thickness regional datum detachment depth moreover a new simple method based on two previous methods is presented the advantages of this new method are that the calculations are extremely simple and it uses information from more than one stratigraphic horizon therefore it does not depend strongly on the accuracy of the data at one level the precision of the proposed methods is tested by their application to a number of natural and experimental single anticlines and fold trains it appears that better predictions are obtained when analysing a complete detachment fold train than when dealing with a single detachment anticline the reason might be that ductile material flow beneath the folds along the cross sectional plane is taken into account when dealing with a long enough cross section we also suggest some hypotheses concerning what the shape and dimensions of the detachment folds indicate about the detachment depth in those cases where insufficient data are available to apply the methods proposed

the stonyford volcanic complex a forearc seamount in the northern california coast ranges jurassic age volcanic rocks of the stonyford volcanic complex sfvc comprise three distinct petrological groups based on their whole rock geochemistry 1 oceanic tholeiites 2 transitional alkali basalts and glasses 3 high al low ti tholeiites major and trace element and sr nd pb isotopic data indicate that the oceanic tholeiites formed as low degree partial melts of normal mid ocean ridge basalt n morb source asthenosphere similar in isotope composition to the east pacific rise today the alkalic lavas were derived from an enriched source similar to that of e morb the high al low ti lavas resemble second stage melts of a depleted morb source asthenosphere that formed by melting spinel lherzolite at low pressures trace element systematics of the high al low ti basalts show the influence of an enriched component which overprints generally depleted trace element characteristics tectonic discrimination diagrams show that the oceanic tholeiite and alkali suites are similar to present day basalts generated at mid oceanic ridges the high al low ti suite resembles primitive arc basalts with an enriched alkali basalt like overprint isotopic data show the influence of recycled components in all three suites the sfvc was constructed on a substrate of normal coast range ophiolite in an extensional forearc setting the close juxtaposition of the morb like olivine tholeiites with alkali and high al low ti basalts suggests derivation from a hybrid mantle source region that included morb source asthenosphere enriched oceanic asthenosphere and the depleted supra subduction zone mantle wedge we propose that the sfvc formed in response to collision of a mid ocean ridge spreading center with the coast range ophiolite subduction zone formation of a slab window beneath the forearc during collision allowed the influx of ridge derived magmas or the mantle source of these magmas continued melting of the previously depleted mantle wedge above the now defunct subduction zone produced strongly depleted high al low ti basalts that were partially fertilized with enriched alkali basalt type melts and slab derived fluids

relief and shortening in detachment folds we present new thickness relief methods for determining shortening s z mean shortening s z and curvimetric shortening sc z as a function of height in well imaged structures thickness relief measurements allow us to constrain the fractions of the deformation that are layer parallel pure shear simple shear and flexural and to measure the excess area ae of fold cores caused for example by flow of evaporites the key measurements are made in the thickness domain which allows for more certain determination of regional stratigraphic gradients which is required for reliable separation of structural relief from primary stratigraphic thickness variations we apply these methods to a diverse set of active detachment folds from the fronts of the nankai trough japan cascadia accretionary wedge oregon southern tianshan china and agbami anticline deep water niger delta three of these folds can be approximated by pure shear detachment fold models because more than 95 of the shortening is by layer parallel heterogeneous pure shear plus horizontal compaction for this reason curvimetric shortening is one to two orders of magnitude less than total shortening in contrast agbami anticline shows layer parallel stretching above the excess area of the fold core in all examples the layer parallel simple shear component is negligible or absent 2006 elsevier ltd all rights reserved

sedimentation and shale tectonics of the northwestern niger delta front abstract the modern day slope and outer shelf of the niger delta are characterized by fault bounded sedimentary depocentres and intervening shale structures some of which are diapiric using two dimensional seismic reflection data and stratigraphic information from five wells the neogene history of a 70 30 km portion of the northwestern niger delta shelf and slope has been examined the shale structures were established by late miocene time probably in response to lateral shale withdrawal from beneath the advancing deltaic load combined with compressional uplift and folding of pro delta strata during pliocene and pleistocene time these structures were buried by the prograding delta and extensional growth faulting commenced stacked onlap relationships and stacked erosional channels indicate that the shale structures continued to influence sedimentation patterns throughout this period throughout the pliocene extension and subsidence were concentrated in a graben like depocentre bounded by both regional and counter regional growth faults during the early pleistocene subsidence on the regional growth fault ceased and growth was transferred to the counter regional growth fault set the geometry and history of the depocentre is analogous to salt related depocentres typical of the northern gulf of mexico and atlantic margins of brazil and angola to explain the history of the niger delta study area a model is proposed in which the miocene pleistocene sedimentary package has slid basinward breaking up during extension thereby creating seaward stepping depocentres examples from analogue modelling studies are used to suggest possible origins for the large counter regional growth faults

area balance depth to detachment and strain in extension a new lost area cross section construction and validation technique is based on the area balance of a graben system formed above a detachment area balance requires that the area displaced below the original regional level of each bed in a graben the lost area be balanced by the displaced area at the boundary of the system given by the product of the displacement times the depth to detachment this relationship is a straight line on a plot of lost area versus depth the slope of the line is the displacement and the depth intercept is the depth of the detachment in general beds within the graben system undergo both visible and homogeneous layer parallel extension the homogeneous component can be determined from the width of the graben system the lost area and the depth to detachment conversely the detachment depth may be calculated from the total layer parallel extension and the lost area the techniques are illustrated by application to models and to very well constrained natural examples an earthquake induced slope failure in alaska and kilometric sized horsts and grabens in the black warrior foreland basin of alabama a half graben without footwall uplift and a full graben are the same on a lost area diagram a half graben with footwall uplift linked to the hanging wall extension requires that both the hanging wall and footwall areas be included to determine the detachment depth and displacement all the models show layer parallel extension e in the upper levels that are less than the crustal scale strain

detachment folds with fixed hinges and variable detachment depth northeastern brooks range alaska abstract detachment anticlines in the northeastern brooks range accommodated displacement above a detachment by buckling of a competent unit over an incompetent unit meso and microstructures in hinges and a lack of relict hinge structures in limbs suggest that these folds grew with fixed hinges the structural thickness of the incompetent unit beneath the folds detachment depth varies from less than to greater than the stratigraphic thickness a model in which incompetent unit thickness varies with fold area better approximates the geometry of the folds than does a more conventional constant depth model additional discrepancies between modelled and observed incompetent unit thickness and field observations suggest non plane strain and or transport of material through the boundaries of the fold in the plane of the cross section the results of this study suggest a typical evolutionary sequence for detachment folds in the northeastern brooks range which may be applicable elsewhere anticlines initiate as fixed hinge buckle folds rapid initial increase in anticlinal cross sectional area results in a decrease in incompetent unit thickness fold area begins to decrease with tightening beyond an interlimb angle of 90 dg decreasing fold area is accommodated through some combination of structural thickening of the incompetent unit transport of solid or dissolved material out of the plane of section transport of material through the boundaries of the fold in the plane of the cross section and or truncation by thrust faults

competent unit thickness variation in detachment folds in the northeastern brooks range alaska geometric analysis and a conceptual model detailed measurements of six map scale detachment folds in the northeastern brooks range alaska document significant variations in structural thickness of the competent lisburne limestone thickness variations occur mainly by parasitic folding and penetrative strain and may be controlled by differences in mechanical stratigraphy relative thicknesses of the competent and incompetent units and structural relief of the underlying basement the geometry of these detachment folds is not consistent with key assumptions of existing geometric and kinematic models such as constant competent unit thickness or constant detachment depth we propose a new model that allows both competent and incompetent unit thicknesses to vary throughout the fold this model allows a more realistic geometric description of some natural detachment folds than previous models but the number of variables makes unique reconstruction of specific fold geometries or kinematics difficult comparison of models with natural folds demonstrates that significant error can result if shortening estimates are based on models that incorrectly assume constant competent unit thickness or constant detachment depth use of surveying techniques to quantify map scale fold geometry can provide better reconstructions of fold geometry better shortening estimates and information to constrain kinematic reconstructions

structure of the nankai trough accretionary zone from multichannel seismic reflection data new multichannel seismic reflection data collected over the nankai trough image the accretionary complex in two areas the international program of ocean drilling leg 87 transect area western area and the region of upcoming ocean drilling program leg 131 eastern area the incoming shikoku basin sedimentary section consists of hemipelagic clays and thin terrigenous turbidites the basin section is overlain by a trench wedge that is 12 16 km wide and 350 750 m thick at the thrust front accretionary deformation begins in a protothrust zone that is characterized by thickening and seaward tilting of the trench wedge the zone in the western area is 4 5 km wide and is characterized by kink folds the zone in the eastern area is only 2 5 km wide and does not exhibit such folds the frontal thrusts in each area are imaged as fault plane reflections and ramp upward from within the basin hemipelagic section the overthrusting sediments form fault bend folds over these ramps thrust spacing at the toe of the slope is 1 5 2 5 km the second thrust cuts up from an inferred decollement within the shikoku basin sedimentary section in the eastern area a reflection marking the top of the basin pelagic sediment section changes from normal to reversed polarity about 6 3 km seaward of the thrust front and underlies the entire protothrust zone this reflector continues with reversed polarity under the accretionary complex and is at the level of the basal decollement the underlying basin pelagic section is apparently thrust undisturbed beneath the accretionary prism the reversal of polarity indicates a change in reflection coefficient that is due to a combination of decreasing seismic velocity and density across the interface this decrease in velocity and density may indicate that the decollement is a zone of high porosity due to fluid expulsion from deeper within the accretionary prism the reflections from the first and second thrusts are also reversed polarity possibly indicating that they also are pathways of fluid expulsion the critical wedge taper of the western area is greater than that of the eastern area an observation that is consistent with the existence of an overpressured decollement in the eastern area

nankai trough and the fossil shikoku ridge results of box 6 kaiko survey abstract seabeam mapping and detailed geophysical surveying have been conducted over the nankai trough where the fossil shikoku ridge is subducted below southwest japan the geometry of the oceanic lithosphere bending under the margin as well as the three dimensional structure of the accretionary prism have thus been determined in detail three 350 trending probably transform faults have been identified in the area of the survey they do not extend further south and appear to be limited to the last phase of spreading within the shikoku basin probably between 15 and 12 ma this last phase of spreading would then have been accompanied by a sharp change in spreading direction from east west to n 350 the two eastern transform faults limit a zone of reduced nankai trench fill of turbidites opposite to the tosa bae embayment this observation suggests that the tosa bae embayment actually results from this reduced supply of trench fill to the imbricate thrusting process the accretionary prism can be divided into three different tectonic provinces separated by continuous mappable thrusts the lower and upper main thrusts surface shortening is limited to the lower accretionary prism south of the upper main thrust umt whereas uplift with possible extension characterizes the prism above the umt deformation due to the relative plate motion mostly affects the lower accretionary prism south of the umt

multiple geometries and modes of fault propagation folding in the canadian thrust belt abstract a multitude of fold models have been proposed to explain the variety of fold geometries which develop in front of thrust faults detailed field fabric and photogrammetric studies of 4 fault cored asymmetrical folds in the thin skinned canadian thrust belt were used to test models of fault propagation folding fold geometries include combinations of angular and rounded fold surfaces highly contorted anticlinal hinge areas and minimal penetrative deformation or changes in bedding thickness interlimb angles generally decrease with increasing shortening indicating progressive fold tightening about fixed anticlinal hinges extensive flexural slip thrusting toward the anticlinal axes of angular folds suggests that kink folding in thin skinned thrust belts is aided by material transfer from both fold limbs into hinge areas fold geometries change dramatically along the strike of individual structures demonstrating the non uniqueness of fault propagation fold geometries no single mode of fault propagation folding can explain the diverse fold geometries seen in the canadian thrust belt this geometric variability can be ascribed to the complex interplay of multiple modes of folding in strata near the causal thrusts oblique shear and flexural slip in triangular shear zones distribute thrust displacements into both rounded and angular folds simultaneous angular folding of overlying strata commonly occurs by progressive kink folding where folds tighten by flexural slip on all fold limbs until the thrust breaks through the fold regional and local differences in the amount of pervasive top to the craton shear needed for progressive kink folding may be partially responsible for the variability of fault propagation fold geometries in thin and thick skinned orogens world wide

comment and reply on geochemical evidence for the tectonic setting of the coast range ophiolite a composite island arc oceanic crust terrane in western california reply

deformation and displacement of the jura cover on its basement abstract the sedimentary cover of the internal jura displaced over its basement conforms well with the model of a thin skinned thrust sheet the wedge shaped sheet which includes a thick sequence of molasse deposited ahead of the alpine front slid over the basement cover interface the alpine crustal thrust sheets created a load at the south east end of the overthrust european plate molasse was deposited on the bent plate and the internal part of the basin was progressively affected by thrusting this process also induced deformation and displacements in the foreland gravity spreading in the internal molasse and a forward motion by rigid slipping movement led to a horizontal push causing deformation by indentation in the internal jura in the plateaux of the external jura there is very little extension in the cover and minimal shortening in the basement this shortening induced a decollement under the plateaux over the bresse graben gravity sliding occurred in the form of huge landslides these contrasts in the origin of the jura structures along a median cross section from thonon to arbois are shown by geophysical data construction of a balanced cross section and calculations of realistic mechanical models for the bending of the foreland plate and for the motion of the cover sheet

crustal velocity field of southwest japan subduction and arc arc collision we investigate crustal deformation in southwest japan over a 3 year period revealed by a permanent dense global positioning system gps array southwest japan is a part of the amurian plate a microplate moving about 10 mm yr toward the east with respect to the eurasian plate it overrides the philippine sea plate at the nankai trough and collides with the northeast japan arc in the central part of japan in this paper we first derive gps site velocities relative to the stable part of the amurian plate in order to isolate signals of crustal deformation caused by the subduction and or the collision the velocity field has a conspicuous feature indicating the interseismic elastic loading by the philippine sea plate slab at the nankai trough characterized by the northwestward movements of points throughout the studied area their amplitudes are the largest at the pacific coast and decay toward the japan sea coast with a subtle systematic shift of azimuths a model assuming an elastic half space the convergence rate at the nankai trough based on a refined euler vector and the strength of the coupling inferred from a thermal model could explain the velocity field in the western part of the studied area to a large extent those in the eastern part systematically deviate from them and the residual components there show east west shortening and north south extension this may represent crustal thickening and trenchward extrusion of crustal blocks caused by the collision between southwest and northeast japan this suggests that the collision between southwest and northeast japan gives rise to not only crustal thickening but also trenchward extrusion of crustal block a velocity contrast was found across the median tectonic line the largest inland active fault in japan but the current permanent gps network is not dense enough for us to discuss its coupling depth

three dimensional architecture of the nankai accretionary prism s imbricate thrust zone off cape muroto japan prism reconstruction via en echelon thrust propagation 1 a 9 km wide 92 km long three dimensional 3 d seismic reflection volume acquired off shikoku island japan images the seaward portion of the subduction of the philippine sea plate at the nankai trough and nankai accretionary prism detailed interpretation of the imbricate thrust and protothrust zones the portions of the prism between the deformation front and the first out of sequence thrust shows a high degree of variability in the thrust faults that all parallel the frontal thrust but are arranged in en echelon patterns along strike and frequently include complications such as piggyback faults and fault splays interestingly the sinuous seafloor morphology of the prism does not accurately reflect the en echelon 3 d architecture of the primary prism thrusts seafloor morphology appears to average across several thrusts along strike and is further modified by near surface thrust splays and backthrusts suggesting that care must be taken in interpreting seafloor relief in terms of lateral continuity or thrust fault geometry subduction of the kinan seamounts 20 km northeast of the center of the muroto 3 d volume generated a scallop shaped embayment in the prism the rebuilding process appears to influence the northeastern portion of the 3 d volume where a 625 m landward step in the position of the frontal thrust and numerous changes in prism architecture are observed these observations imply that accretionary prisms may reattain equilibrium following seamount subduction by lateral en echelon fault propagation into damaged zones that facilitate an increase accretion rate until a laterally continuous deformation front is reestablished

reverse modelling of detachment folds application to the pico del aguila anticline in the south central pyrenees spain abstract a simple method to estimate fold amplification and thrust movement rates for detachment folds is documented and illustrated by its application to a symmetrical detachment fold in the southern pyrenees spain the technique provides a complete record of the kinematic evolution of detachment folds and is based on the application of equations for detachment folds involving limb rotation the method uses the stratal pattern of the syntectonic sediments and assumes that these growth strata were deposited horizontally that the folds involve a homogeneous competent unit detached over a ductile horizon and that the folds can be represented by chevronkink bands the procedure is applicable to any detachment fold with associated growth strata that display wedge geometries progressive unconformities indicating limb rotation through time this method can be used for both detachment folds formed with constant limb length or variable limb length and it can also accommodate undecompacted or decompacted growth strata