reconstructing the pre quaternary landscape in agnew lawlers area western australia with emphasis on the permo carboniferous glaciation and post glacial weathering the pre quaternary stratigraphic section in agnew lawlers area consists of permo carboniferous glacial sediments unconformably overlain by tertiary clastics of palaeochannel sequence and quaternary alluvial and colluvial sediments the unique permo carboniferous glacial sedimentary succession in the yilgarn craton has not been studied in detail in terms of vertical chemostratigraphic variations basin and landscape evolution diagenesis and post permian weathering overprints in agnew lawlers district continental facies of glacial diamictites glaciofluvial sandstones and glaciolacustrine rhythmites vary in thickness from 28 m to 181 m and is preserved beneath cenozoic sediments as relict landforms in highly irregular asymmetrical and poorly drained basins the permo carboniferous sediments were mechanically weathered and eroded by glaciers from the surrounding archaean basement palaeohighs under a cold arid climate textural relationships of diamictites indicate that they were derived from proximal and distal source rocks the denuded palaeotopography of the basement palaeohighs source rocks and permo carboniferous sediments were subjected simultaneously to an intensive post permian chemical weathering the exposed basement rocks were deeply weathered into residual saprolite whereas the permo carboniferous sediments were differentiated into three chemostratigraphic units the diamictite and rhythmite of the lower unit are unweathered and preserves the signature of the glacial interglacial weathering mineralogical and geochemical changes dominated in this unit are related mainly to diagenesis at shallow depth eogenesis with no significant compaction the formation of a paragenetic diagenetic sequence of chlorite ferroan dolomite and pyrite indicates diagenesis has occurred under reducing and alkaline conditions below the permafrost and modern water table mineralogical and geochemical changes dominated in the middle unit are linked mainly to eogenetic redox reactions the formation of smectite and ferruginous cements in this unit is attributed to weathering of ferromagnesian and opaque heavy minerals under oxic and slightly alkaline conditions mineralogical and geochemical changes dominated in the upper unit is related mainly to post permian chemical weathering where almost all rock forming minerals are altered to kaolinite and alkali and alkaline earth elements are leached forming bleached white saprolitic diamictites a change in clay minerals from kaolinite in the weathered permo carboniferous succession to smectite in the overlying cenozoic succession demarcates the unconformity and probably reflects a change to an arid climatic condition chemically the cenozoic succession shows a sharp increase in ti al and la ce ratios and a decrease in ce anomaly that remain constant in the permo carboniferous section these mineralogical and chemical variations through the phanerozoic stratigraphic section can be used to follow the landscape and climatic evolution since the late palaeozoic glaciation

tectonostratigraphic evolution of the northern porcupine basin irish atlantic margin during the late jurassic early cretaceous implication for a regional compressional event abstract the conventional interpretation of the jurassic lower cretaceous succession in the porcupine basin suggests an extensional setting with progressive deepening of the basin however well data show a prominent gap of several million years between the upper jurassic and lower cretaceous a data base of 15 key wells and approximately 5 000 km of seismic reflection data were examined in the northern porcupine basin in order to understand the nature controls and mechanisms of this unconformity seven seismic markers constrained by well data are mapped it is shown that during the late jurassic possibly the oxfordian kimmeridgian the basin experienced extension and synrift deposition during the latest jurassic earliest cretaceous possibly the tithonian early berriasian a series of north trending structural highs and lows developed and extensive areas in the northern porcupine basin experienced folding uplift and erosion evidence from the study suggests that compression uplift and erosion played an important role in the shaping of the depositional and structural architecture of the basin and caused formation of the regional base cretaceous unconformity in the northern basin it is suggested that the deformation in the northern porcupine basin during the latest jurassic earliest cretaceous may be related to the initial closure of the alpine tethys during the late tithonian this tectonic event may also have resulted in compressional deformation and formation of the base cretaceous unconformity elsewhere in western europe

tectonic deformation by rotating parallel faults the bookshelf mechanism abstract in various tectonic environments extension of crustal parts and shear distortion has been accommodated by the rotation of an array of parallel faults because of its kinematic resemblance to the tilting of a row of books on a shelf the tectonic process may be referred to as a bookshelf mechanism its most important manifestions are cross faulting between normal faults or parallel wrench faults the extension of deltaic slope deposits and all forms of tilted block tectonics kinematically there are two basic modes of the mechanism a the dilational mode where rotating faults tend to open up and possibly become paths for fluid migration and b the domino style where reclining faults remain closed in both cases formation and rotation of the faults may take place in one tectonic event fault displacements may therefore often remain small and difficult to detect from the mechanical point of view bookshelf operations that accommodate shearing between parallel and predominantly parallel moving rock boundaries bookshelf mechanisms proper have to be differentiated from those operations responding to an imposed crustal extension or shortening after a review of geological evidence the process is addressed from a geomechanical point of view in order to determine the geological operating conditions and controlling parameters the crucial mechanical factor in the bookshelf mechanism is the component of normal stress that acts in the direction of the imposed displacement component parallel to the driving boundary plates in contrast to the usual assumption the driving shear stress on the boundary plates not only depends on the normal stress on the plates but it also varies with the value of the normal stress that acts inside the sheared material in the direction of the plate parallel displacement component it is the relationship between the two normal stresses that also determines the type of rotating parallel faults large scale rotation of parallel normal faults in domino style tilted block tectonics is primarily associated with the extension of ductile substrata from mechanical arguments and sand box experiments it has been inferred how the process and in particular the dip direction of the parallel faults is controlled by the way substratal extension progresses by means of the direction of a substratal squeeze flow the presence of a surface slope the strength anisotropy associated with fore set beds and by the configuration of competent boundaries of the extending overburden

stratigraphic and structural consequences of fault reversal an example from the franklinian basin ellesmere island faults involving growth sedimentation displace different beds by different amounts when a reversal of movement sense occurs on such faults bedding cutoffs act as a vernier scale and an immaterial point of no net displacement null point migrates along the fault trace multiple reversals generate multiple null points but neighboring points migration in opposite directions and annihilate one another when they meet as a field example the authors present stratigraphic evidence for fault reversal from the franklinian basin ellesmere island backstripping and recognition of the migrating null point permit sequential restoration of the incremental fault displacements failure to recognize fault reversals may lead to underestimates of orogenic shortening or to misidentification of accommodation folds

sandbox experiments of inverted listric and planar fault systems abstract the kinematic and geometric evolution of basement controlled inversion structures has been analyzed using a plane strain sandbox apparatus the results of two representative scaled analogue models comprising rigid listric and planar detachment faults that both have cut off angles of 60 to the horizontal are described in detail the hangingwall above these detachment geometries was constructed from alternate layers of sand and mica in order to simulate an anisotropic sedimentary sequence in both experiments initial shortening at the onset of inversion was accommodated by bulk strain this was followed by reactivation of the basal detachment together with the main basin controlling planar and listric faults which propagate upwards through the post rift sequence at approximately the same angle as the upper part of the detachment fault i e 60 reactivation of relatively steep intra basinal extensional faults within the cover was restricted to nucleation of reserve faults and thrusts in the region of the tips during approximately the first 10 to 15 contraction this resulted in gently dipping thrusts that propagated upwards through the post rift sequence to produce harpoon shaped structures later in the inversion phase after approximately 15 contraction backthrusts cut through and displaced the original antithetic extensional graben faults producing downward tapering wedge shaped structures at the margins of the basin although deformation in these experiments was limited to purely dip slip displacement the nature of the original extensional faults and their reactivated tip regions resulted in cross sectional geometries that have a marked resemblance to strike slip induced flower structures uplift was asymmetric and centred above the upper part of the main detachment above the listric fault but was more symmetrical and centred above the soling out point of the detachment in the case of the planar fault geometry the results of these experiments show distinct similarities to structures seen on seismic sections form the southern north sea and other inverted sedimentary basins

rheological and physical characteristics of crustal scaled materials for centrifuge analogue modelling abstract we characterize a set of analogue materials used for centrifuge analogue modelling simulating deformation at different levels in the crust simultaneously specifically we improve the rheological characterization in the linear viscoelastic region of materials for the lower and middle crust and cohesive synthetic sands without petroleum binding agents for the upper crust viscoelastic materials used in centrifuge analogue modelling demonstrate complex dynamic behaviour so viscosity alone is insufficient to determine if a material will be an effective analogue two series of experiments were conducted using an oscillating bi conical plate rheometer to measure the storage and loss moduli and complex viscosities of several modelling clays and silicone putties tested materials exhibited viscoelastic and shear thinning behaviour the silicone putties and some modelling clays demonstrated viscous dominant behaviour and reached newtonian plateaus at strain rates 2 s 1 while other modelling clays demonstrated elastic dominant power law relationships based on these results the elastic dominant modelling clay is recommended as an analogue for basement cratons inherently cohesive synthetic sands produce fine detailed fault and fracture patterns and developed thrust strike slip and extensional faults in simple centrifuge test models these synthetic sands are recommended as analogues for the brittle upper crust these new results increase the accuracy of scaling analogue models to prototype additionally with the characterization of three new materials we propose a complete lithospheric profile of analogue materials for centrifuge modelling allowing future studies to replicate a broader range of crustal deformation behaviours

active normal faulting and crustal extension a world wide review of fault plane solutions and focal depths for large normal faulting earthquakes on the continents shows that the overwhelming majority of such earthquakes nucleate in the depth range 6 15 km on faults dipping between 30 and 60 in the few cases where levelling or seismic data are good enough these normal faults are shown to be approximately planar from the surface to their nucleation depth at the base of the brittle crust there is evidence that in some cases as a result of the enormous transitory increase in strain rate during large earthquakes rupture continues into the normally ductile lower crust on surfaces with substantially gentler dips these low angle surfaces may be analogous to some of the detachments seen in metamorphic core complexes of the western usa but the nature of the motion on them depends on strain rate as well as on rheological contrasts between the detachments and the blocks on either side such contrasts however are unlikely to introduce substantial curvature to an originally planar shear zone if the observed spread in active normal fault dips is caused by rotation of the faults and the blocks they bound during extension then a maximum value of 1 7 can be accommodated by seismic activity on a single generation of normal faults with continued extension either a new generation of steeper faults cutting the rotated first faults is likely to form or the deformation will continue aseismically on faults dipping at less than 30 large earthquakes have not been observed to nucleate on very low angle 20 normal faults within the continental crust anywhere in the world such faults can of course move aseismically but are unlikely to do so on a large scale within the upper crust in areas where steep normal faults are seismically active thus extensional models that require concentrated simple shear on large sub horizontal faults within the brittle upper crust will also require a spatial separation between aseismic very low angle faulting and seismic highangle faulting since seismogenic high angle faults dominate the topography of extending regions upper crustal very low angle faulting if it occurs on a large scale presumably does so in areas that are relatively fiat

tectonic implications of faulting styles along a rift margin the boundary between the rhine graben and the vosges mountains 1 seismic reflection data show the effects of the miocene strike slip environment on the boundary between the upper rhine graben urg and the vosges mountains vm the border fault zone exhibits three types of responses to the new nw se directed regional stress regime where it trends n s no new deformation is observed where it trends nne ssw transpression is evident and it develops into a few kilometers wide zone of intense deformation along the ne sw trending southern boundary of vm transpression intensifies with an increase in the perpendicular shortening component and the border fault zone turns into a reverse fault the uplift of the boundary relative to the graben is estimated to be no less than 1000 m near colmar and significantly more along the boundary with the dannemarie basin these estimates and kinematics considerations support the hypothesis that the vosges mountains are mostly a transpressional feature the rhine fault is mapped and suggested to be a lower miocene structure that was formed in response to the change in the regional stress regime

a shortened intraplate rift system in the proterozoic mount isa terrane nw queensland australia the leichhardt river fault trough of the mount isa terrane developed a complex extensional architecture between approximately 1800 and 1600 ma forming the underlying template upon which compressional structures were superimposed during the 1590 to 1500 ma isan orogeny basin fill material accumulated during at least five multiphase periods of rifting and associated postrift subsidence forming a stacked succession of unconformity bounded sequences initial e w extension was associated with a massive magmatic event half graben greater than 50 km in width and of alternating asymmetry localized the extrusion of up to 4 km of continental tholeiites thereafter a period of n s extension resulted in southward tapering north tilted half graben in which synrift basaltic and siliciclastic strata accumulated n s extension was followed by regional postrift subsidence and the deposition of a laterally continuous quartzite carbonate package a multiphase period of e w to nw se extension ensued during which time two unconformity bounded sequences accumulated the stratal architectures of these sequences are strongly asymmetric in cross section exhibiting a pronounced rotational thickening toward the east consistent with their deposition in the hanging walls of east dipping tilt blocks between 15 and 40 km in width finally a period of n s extension resulted in the development of e w trending f1 drag synclines in the highest level cover rocks the association of angular unconformities and block bounding faults e w trending synclines and e w striking faults and the unique internal fold geometries of fault blocks suggest that many fault bounded blocks originated as coherent structural entities during rifting and continued to act as such during subsequent shortening

structural controls on palaeozoic basin evolution and inversion in southwest wales the tectonic evolution of sw dyfed is presented in terms of a model of basin evolution and subsequent destruction by reactivation of the basin bounding faults in contractional mode movements along long lived palaeozoic extensional faults were reversed during variscan compression with the pre existing faults accommodating the contraction in addition to the development of a thin skinned thrust and fold system basin analysis of the pre variscan extensional system uses sedimentological and stratigraphical evidence to constrain the timing of movements of the basin bounding faults thus allowing division of the stratigraphy into depositional megasequences related to these extensional movements field examples on all scales illustrate active extension during the palaeozoic structural cross sections through sw dyfed demonstrate the interrelationship of the extensional and contractional deformations with palinspastic restorations of the cross sections illustrating the complexity of the pre variscan template

how normal faulting and sedimentation interact to produce listric fault profiles and stratigraphic wedges abstract in a series of scale experiments we generated listric normal faults by extending models composed of colored sand layers deposited at regular time intervals throughout deformation during syntectonic sedimentation progressive bulk extension along a single set of faults caused domino type tilting of fault blocks underlying tilted faults propagated upwards with constant dips into newly sedimented layers hence fault profiles become progressively more listric tilting of the free surface resulted in asymmetrical depressions and in fan shaped deposits stepwise or continuous geometric models of domino tilting and synchronous sedimentation yield the same structural and stratigraphic features as observed in the sand models the continuous geometric model shows that a critical parameter governing fault curvature is the ratio r between rates of bulk strain and sedimentation both types of models reveal that synchronous sedimentation and bulk extension are capable by themselves of generating listric normal faults

model for a passive to active continental margin transition implications for hydrocarbon exploration this paper proposes a model for the transition of a passive atlantic type continental margin to an active one with reverse polarity prior to its ultimate collision with an island arc or continent significant morphological and stratigraphic patterns which are believed to characterize this transition include 1 reactivation as reverse faults of preexisting listric normal faults not gulf coast type growth faults but those affecting basement as well that were established during the margin s most recent period of extension 2 landward migration with time of this fault rejuvenation 3 development of deeper water shallower water deeper water or deeper water unconformity deeper water stratal assemblages on the margin 4 regional flexure of the continental margin a in to that known for the outer rise area of oceanic plates landward of the subduction zone and 5 landward migration of major unconformities coeval with continental margin flexure this model creates implications for hydrocarbon exploration because 1 it predicts the presence or absence of unconformities and thus potential stratigraphic traps among units of a particular basin 2 provides spatial and temporal constraints for secondary porosity development in potential reservoirs 3 allows more accurate interpretations to be made of thermal or burial history diagrams constructed for the purpose of determining relative thermal maturities of potential source units and 4 helps distinguish between basement reactivation and decollement or gulf coast type growth faulting the orogenic phase of the margin s development however may later overprint or conceal these morphological and stratigraphic patterns to the extent that they might be unrecognizable because they have implications from both academic and economic perspectives the role of these patterns in the margin s evolution should not be overlooked

numerical modelling of the response to variable stretching rate of a domino fault block system abstract using a numerical model of domino fault block development the effects of a variable stretching rate during rifting were investigated it is shown that a varable stretching rate can have an important influence on synrift sequence geometries this can lead to complex synrift sequences composed of wedge shaped units formed during periods of high stretching rate and more symmetrical units formed during periods of relative tectonic quiescence at the fault block crest increases in stretching rate can produce offlapping synrift sequences whereas decreases in stretching rate allow onlap onto the fault block crest if the rifting period contains multiple pulses of stretching complex intra synrift unconformities can be formed the initial bathymetry is also shown to have an important influence on the modelled synrift stratigraphy the modelled stratigraphies are similar to those thought to result from variations in absolute sea level pseudo facies markers based on the combined initial depth and slope of deposition of the modelled sediments are shown to be a useful tool and graphically illustrate the response of the system to pulses of tectonic activity

along strike structural variations in the southern patagonian andes insights from physical modeling abstract the southern patagonian andes between 48 and 53 sl offers a unique opportunity to study the results of orogenic growth superimposed over a previously rifted region in this sector the northern austral or magallanes basin was affected by late to middle jurassic extension followed by late cretaceous to neogene tectonic compression the resultant fold thrust belt displays significant along strike variations in width and lateral position of the structural domains that may be reflecting a first order control of the jurassic extensional depocenters as proposed in previous works this hypothesis is tested using a series of scaled sandbox analog models involving the positive inversion of two adjacent depocenters with different extensional rates accommodated by a transfer fault the correlation between structures in the southern patagonian andes and the features in the model have important first order similarities supporting the theory of a positively inverted extensional basin with a previous history of southward increase in extension moreover structural cross sections analyzed from field and seismic data have a geometry that is consistent with serial cross sections resulting from the models

seismic characteristics and identification of negative flower structures positive flower structures and positive structural inversion negative and positive flower structures and positive inverted structures imply specific modes of formation and their distinctive characteristics make them important criteria for the identification of certain structural styles a negative flower structure from the andaman sea consists of a shallow synform bounded by upward spreading strands of a wrench fault that have mostly normal separations paralleling monoclines and oblique en echelon normal faults flank the divergent wrench fault a positive flower structure from the ardmore basin oklahoma consists of a shallow antiform displaced by the upward diverging strands of a wrench fault that have mostly reverse separations en echelon folds are present on either side of this convergent wrench fault flower structures may resemble extensional or contractional fault blocks on individual seismic profiles flower structures are identified by their unique internal fault and fold architecture by their association with a straight and throughgoing zone of deformation and by their lack of a consistent sense of separation or regional upthrown side positive structural inversion at the rambutan oil field south sumatra basin has formed a shallow anticlinorium and has partly uplifted the underlying graben deeper fault segments bounding the graben have retained their normal fault profiles but at shallow levels some of these faults have reverse separations similar changes of separation with depth may be produced by strike slip but sets of faults with listric profiles and nearby blocklike trend patterns identify the inversion as a dip slip event where correlation of reflections is uncertain or deep control is unobtainable positive inverted structures may also resemble contrational fault blocks detached normal fault assemblages and certain negative inverted structures

basin inversion and magma migration and emplacement insights from basins of northern chile abstract during the structural modelling of inverted basins influenced by magmatism is very important understand the geometric and kinematic relationships between inverted structures and intrusive bodies the northern chile is a natural laboratory to analyze this situation since its cenozoic tectonic evolution was marked by the tectonic inversion of mesozoic extensional basins which occurred simultaneously with the emplacement of km scale intrusions in order to provide insights on the interplay between basin inversion and magma emplacement we completed a comparative analysis based of field data from four inverted mesozoic basins of northern chile and a series of previous and new analogue models reproducing the tectonic inversion of half grabens and magma emplacement the experiments showed that the magma migration and emplacement is controlled by the initial distribution of normal faults and occur preferentially along the inverted normal faults high magma injection rate can cause a major reactivation of the normal faults favoring a comparatively increase in bulk shortening the most favorable condition for which the magma reaches the surface is under simultaneous high magma injection and shortening rates the latter allow the magma to be emplaced along the core of inversion related anticlines such as it is recognized in northern chile

identification of wrench faults using subsurface structural data criteria and pitfalls 1 many structures imaged with reflection seismic can resemble a wrench fault system because of the great structural diversity of strike slip faults and the wide range of contractional and extensional features associated with these faults because of these resemblances numerous faults are misidentified as wrench faults by workers using subsurface structural data credible identification requires combinations of profile and map criteria 1 narrow long straight throughgoing solitary master fault or zone of deformation 2 steep to moderate dip of the master fault at depth 3 offset of the top of basement 4 changes in relative upthrown side separation sense and or fault dip direction at depth or along the strike of the master fault 5 narrow fault slices within the master fault zone that steepen and join at depth negative and positive flower structures 6 different separation sense and orientation of relative upthrown side at these fault slices and 7 coeval en echelon flanking structures the identification should be confirmed with other criteria that refute alternative interpretations the main pitfalls to a reliable identification are not considering alternative structural styles and the misinterpretation of features or patterns that superficially resemble wrench systems the profile geometries of basement involved reverse or normal faults particularly those with structural inversion can resemble the single strand of convergent or divergent wrench faults profile geometries of flower structures can be mimicked by narrow contractional horsts or narrow extensional grabens complexly faulted anticlines or synclines splay faults fault zones intruded by salt or shale and overprinted structures pitfalls in interpreting map relationships are possible when structural patterns combine several tectonic influences are controlled by rock anisotropy or include elements hat are not coeval and if the patterns characteristic of other styles are misinterpreted many erroneous identifications of wrench faults can be eliminated by demonstrating that the investigated fault or feature lacks a straight trace lateral length or throughgoing continuity

experiments on basin inversion above reactivated domino faults abstract results are presented from scaled sand box experiments which investigate the structural inversion of half graben basins generated by the contractional reactivation of extensional domino fault systems the overburden was deformed above a series of rigid basement fault blocks that were extended in a domino manner the models were constructed from either 1 sand with mica interlayers anisotropic behaviour 2 pure sand isotropic behaviour or 3 a sand clay mixture behaviour with increased competence during the extensional phase of deformation sand or alternating sand mica layers were deposited in teh half grabens associated with individual domino faults to simulate a syn extensional stratigraphic sequence together with a component of overall subsidence after termination of the extensional phase sand layers were added to represent a post rift passive subsidence stratigraphy subsequent contraction of the experimental configuration resulted in progressive reactivation of the domino fault system which was accompanied by back rotation of both the footwall and hanging wall in each of the individual fault blocks this produced null points along the profile section of the fault planes which separated net contraction above from net extension below continued shortening of the system led to further contraction being accommodated along footwall shortcut faults it is suggested that these shortcuts developed in response to 1 the accommodation of space problems generated by increased bed length in the graben acquired during extension and 2 by more efficient low angle fault trajectories in keeping with coulomb failure during horizontal to subhorizontal compression during inversion in the anisotropic model folding in the footwall partially suppressed the initiation of footwall shortcut faults footwall shortcut faulting did not occur in experiments where the dips of the original extensional faults were decreased before the inversion in all inversion experiments the contractional deformation associated with the shortening of the half graben was concentrated in the footwall to each domino basin bounding fault a control experiment in which an undeformed sand pack was deposited above an extended series of basement fault blocks revealed that the early extensional architecture formed in the other experiments had a profound influence on the resultant inversion geometries the results show clear similarities to interpreted examples of natural basin inversion structures associated with reactivated domino fault systems as well as to inferred strike slip induced flower structures

experiments on fault reactivation in strike slip mode abstract experiments were undertaken to investigate how faults reverse or normal in a cover sequence become reactivated when an underlying basement fault is itself reactivated in strike slip mode physical models properly scaled for gravity were deformed in a large 2 1 5 m apparatus divided into two halves one half can be moved laterally or vertically past the other models were constructed with a coulomb layer sand overlying a newtonian ductile layer silicone three different configurations of the basement fault reverse normal or vertical defined three series of experiments each consisted of 1 brittle model 6 cm of sand and 2 brittle ductile models 5 cm of sand overlying 1 cm of silicone or 4 cm of sand overlying 2 cm of silicone each model was deformed in two steps 1 a pure dip slip stage and 2 a reactivation in pure strike slip mode in surface views little reactivation was observed but in all cases the deformation imposed during the strike slip episode was localized by pre existing dip slip structures in cross sections however faults were seen reactivated at depth on the basis of these experiments we suggest that 1 a previously faulted zone can control the deformation of a strike slip zone and 2 reactivation of faults in strike slip mode can occur at depth without being visible at the surface we attribute the higher probability of reactivation at depth to the mechanical properties of the sand especially cohesion

sandbox model studies of inversion tectonics abstract scaled plane strain sandbox models have been used to simulate basement controlled structural inversion in a sedimentary overburden two basement configurations were tested in the first one reversal of movement along vertical and normal faults that controlled a graben relief induced only a partial recovery of displacement along the pre existing overburden faults the inversion produced new reverse faults in the footwall of the pre existing overburden faults the reactivated normal faults and the new reverse faults defined wedge shaped fault blocks at the edges of the inverted structure in the second configuration the relationship between inversion and tilted fault blocks was tested when a tilting basement block does not move parallel to its bounding fault a compression is induced in the overburden which generates an inverted structure bounded by new reverse faults both experiments show that structural inversion not only reactivates pre existing faults but also generates new faults in the overburden faults related to inversion are the result of horizontal compression either associated with rotation of one of the fault blocks or with vertical uplift of basement blocks

sandbox experiments on basin inversion testing the influence of basin orientation and basin fill analogue modelling experiments using brittle materials are performed to study the inversion of extensional structures asymmetric grabens of two different orientations are first created during a phase of extension and progressively filled they are subsequently shortened in the same direction the aim of our experiments is to determine factors affecting the style of deformation during inversion we specifically investigate variations in thickness and distribution of strong and weak layers constituting the graben fill and in initial basin orientation the main advantage of our experimental set up is that we have a complete control on graben location width infill and orientation before inversion the experiments show that shortening results only in limited reactivation of pre existing normal faults in general forward thrusts and backthrusts cut across normal faults into the footwall of the graben the forward thrusts either propagate parallel to the enveloping surface of faulted blocks or they cut across basin limiting normal faults at various angles the graben fill is mechanically extruded by displacement along forward thrusts that accommodate most of the shortening both pre existing faults and weak graben fill act as zones of weakness during inversion and determine the orientation and location of both backthrusts and forward thrusts the results of our experiments conform well to natural examples of inverted graben structures

the influence of intrabasinal faults on the development of a linked thrust system the mesozoic and cenozoic rocks exposed in the arve valley region of the external french alps are used to assess the role of early intrabasinal faults on later thrust fault evolution the early intrabasinal faults produced at some time from latest upper cretaceous to tertiary strike parallel or subparallel to later neo alpine thrusts where early faults dip away from the thrusts they are generally cut through and occasionally are overturned during this process in one example extreme overturning has allowed partial reactivation early faults dipping in the same direction as thrusts may a be reactivated b initiate ramping of the thrust ahead of the preexisting fault c be cut through by the thrust d cause pinning of the thrust at the footwall of the fault and folding against the fault as displacement continues buttressing from this work it is evident that intrabasinal faults exerted a major influence on the distribution of mechanical heterogeneities these heterogeneities include variations of stratigraphic thickness and type across faults fault related unconformities and the presence of the fault itself during the period of contraction such features strongly controlled the development of the stress field produced ahead of an advancing thrust and hence influenced the position of thrust fault propagation within the stratigraphy

sedimentation in paleogene foreland basin spitsbergen the upper part of the sedimentary succession in the tertiary central trough on spitsbergen comprising the hollendardalen gilsonryggen battfjellet and aspelintoppen formations has been studied with respect to basin formation and basin filling thickness data from the lower marine part of this succession indicate an asymmetric thickening to the west distribution of the several theories on how space was generated to accommodate the sequence tectonic subsidence driven by lithospheric loading from the flanking fold and thrust belt appears to be the most probable the position of the basin between the front of the west spitsbergen fold belt and the adjacent craton suggests a foreland basin setting most of the basin fill constitutes a major regressive sequence gilsonry gen battfjellet and aspelintoppen formations deposited by the eastward progradation of a deltaic system evidence of eastward displacement of the depocenter through time together with the incorporation of the orogenic flank of the basin fill into the deformation suggests cratonward migration of the fold and thrust belt foreland basin couplet the present tertiary central trough represents the uplifted remnants of the latest oligocene foreland basin

the araripe basin in ne brazil an intracontinental graben inverted to a high standing horst abstract the mesozoic sediments of the araripe basin peak at ca 1000 m more than 500 m above the host precambrian basement this means that an intracontinental graben has been inverted to a topographically high standing horst which raises four fundamental questions 1 where are the inversion structures 2 what is the age of the inversion 3 how can inversion occur in a thick lithosphere 4 what forces are responsible for the inversion here we show that displacement on inverted normal faults increases towards the core of the horst and new reverse faults thrust basement over basin field observations indicate that inversion has occurred on faults striking between nne ssw and e w following the structure of the host basement inversion is reverse dextral in the nne ssw system and reverse sinistral in the ene wsw system this is consistent with the mid atlantic ridge and andean pushes from the tectonic analysis of topography and gravity anomaly the nw se faults seem critical to the inversion although not clearly recognized in the field the inversion of high angle normal faults occurred by oblique slip and injection of clay rich breccias which apparently reduced friction sufficiently to allow for major inversion fault scarps with a prominent topographic expression and faults cutting through colluvium indicate that the latest stage of inversion is quaternary although older inversion episodes are likely the new tectonic data the timing and the stress field altogether indicate that inversion was due to plate wide compression which preferentially concentrated along inherited shear zones and reactivated them to form the main inversion faults of the araripe basin the high degree of inversion in the araripe basin is most likely due to its position at a bend in the major patos shear zone which worked as a restraining bend under the maximum compressive stress acting in ne brazil

basin inversion and contractional reactivation of inherited normal faults a review based on previous and new experimental models abstract compressional inversion of former extensional sedimentary basins is a particularly common phenomenon given that passive margins share the same destiny of being subsequently incorporated into fold and thrust belts during basin inversion pre existing faults may concentrate stress and localise future thrust ramps or may be reactivated recording reversal of movement from extension to reverse this process has attracted attention largely because of its economic implications related to petroleum and ore deposit prospects and seismic hazard assessment since more than two decades analogue modelling has been used to indentify and or test a number of parameters relevant for the inversion process this paper aims therefore to offer a reasoned review of the analogue modelling work done on the subject coupling such previous results with those of a new experimental series inspired to the northern apennines stratigraphy and evolution past models have explored the role of main factors governing fault reactivation susceptibility such as fluid pressure fault weakness fault steepness angle of shortening and sediment loading the new models have addressed the role played by geometry and strength of a basal ductile layer during inversion two sets of sand silicone models were first extended orthogonally at different velocities to produce dissimilar pre inversion internal geometries and then shortened coaxially at different velocities to vary the brittle ductile coupling the experimental results confirm the selectiveness of fault inversion and reveal strong similarities with structural styles of tectonic inversion reported from the northern apennines and various areas worldwide the preferred geological model inferred from this modelling involves contribution of 1 syn inversion rotation of pre existing faults to shallower dip and 2 rotation of principal stress axes which could explain the invariable reactivation of only one of the two oppositely dipping graben bounding faults these factors would thus interact with the other well established parameters controlling the fault reactivation process

investigating new materials in the context of analog physical models abstract to broaden the availability of granular materials that are suitable for the analog modeling of upper crustal deformation we investigated the mechanical behaviors of pure quartz sand and two sand mixtures quartz sand powdered barite and quartz sand mica crystals using ring shear tests and simple convergent sandbox experiments the ring shear test results indicate that the three materials have similar peak friction angles between 39 25 and 36 02 but the magnitude of the shear strain and the shear strength required to cause their failure are different the differences between the analog models are identified by distinct fault kinematics and different grain flows which are primarily related to differences in the plastic elasto frictional rheology we conclude that the use of the quartz mica mixture which showed the strongest distributed plastic deformation can improve analog models where different materials are required to simulate crystalline basement sand and supracrustal rocks sand mica mixture this is a common situation in extension and inversion tectonics such as for example in inversion tectonics when a granitic basement block acts as a buttress

oblique half graben inversion of the mesozoic neuquen rift in the malargue fold and thrust belt mendoza argentina new insights from analogue models abstract the malargue fold and thrust belt located in the andean mountains between 34 s and 36 30 s formed in response to contraction during cenozoic times its structural style and geometry was controlled by the mesozoic rift system that formed the neuquen basin in west central argentina the rift architecture in the southern sector of this belt was previously interpreted in terms of the present n s compressive structural trends assuming the inversion of pre existing normal faults with the same orientation here we propose that the nw se trending el manzano liu cullin lineament located in the northern termination of the sierra azul reflects the presence of a half graben master fault in the subsurface this hypothesis is supported by subsurface data a balanced cross section and it is tested using a series of scaled sandbox analogue models we suggest that the lineament responds to a reactivated nw trending half graben fault hidden by the mainly n s trending andean structures the proposed orientation is in agreement with the ne sw extension developed in the neuquen basin during the triassic early jurassic the modeling of the inverted oblique half graben reveals that the strikes of the main structures of inversion related belts may often be independent of the orientation of the previously developed extensional system providing a new perspective for their interpretation

far field contractional polarity changes in models and nature abstract a change in contractional polarity occurs when the direction of tectonic transport switches along strike this switch is conditioned by lateral variations in rheology or inherited asymmetries such as contrasts in structure or changes in the polarity of subduction zones the parameters controlling contractional polarity changes are less understood in situations when the strain is transferred at large distances from indenters analysing this type of strain transfer is critical for understanding the mechanics of thrusting in fore or back arc settings of orogenic areas comparison of crustal scale analogue modelling with the inversion of the black sea back arc and the formation of the new guinea new britain fore arc suggest that far field changes in contractional polarity are related to rheological contrasts across inherited normal faults the initial extension creates rheological weak zones that localize the subsequent far field contractional deformation along groups of thrusts with opposite vergence along the strike of the system the largest amount of far field contractional deformation is recorded in the transfer zone located between the two indenters moving in opposite directions and is particularly high when inverting oblique extensional systems