development of p t prograde and p retrograde t prograde isogradic surfaces during blueschist to eclogite regional deformation metamorphism in new caledonia as indicated by progressively developed porphyroblast microstructures the mid tertiary blueschists eclogites and eclogitic gneisses of northern new caledonia are the products of four phases of regional meta morphism and deformation d d4 omphacite lawsonite and mn rich garnet isogradic surfaces were developed during the second deformation d2 under prograde pressure and temperature conditions subsequent deformations d3 d folded these d isogradic surfaces however within the p retrograde t prograde metamor phic environment of the d phase omphacite altered to albite and chlorite as a result a late stage sub horizontal isogradic surface developed for omphacite out where this mineral is preserved as relics within syn d albite porphyroblasts other minerals that crystallized for the first time epidote or had rim additions almandine phengite during d also form nearly horizontal isogradic surfaces porphyroblastic garnet and albite contain inclusion trails which allow their microstructural development and crystallization of the matrix to be traced from d to d late syn d the temperature increased mark edly in association with an extensive exothermic decarbonation even though the rocks were in a state of pressure retrogression this caused considerable neocrystallization recrystallization and growth of matrix and porphyroblasts such that although s foliation crenulated by d and d is readily observable almost all signs of stored strain due to d and d have been removed and the deeper schists and eclogitic gneisses superficially appear to have undergone a drastic annealing recrystallization post dating deformation

shear sense a new approach that resolves conflicts between criteria in metamorphic rocks investigation of microstructural relationships in major movement zones in metamorphic rocks where the sense of displacement is known from regional geological relationships indicates numerous problems with current concepts of shear sense criteria and their application the direction of apparent shearing commonly conflicts from one criterion to another e g from the symmetry of quartz c axis orientation diagrams to the asymmetry of extensional crenulation cleavages this implies that interpretations of shear sense along foliations from some mesoscale and microscale criteria have been erroneous a new approach to interpreting shear sense involving the use of strain fields resolves conflicts in mesoscopic and microscopic criteria and provides a method for determining coherent shear sense histories extending back before the last shearing event for any foliated metamorphic rock it also provides a powerful tool for determining the structural metamorphic path that a rock has followed within an orogen for determination of the shear sense on the last foliation developed in a rock this approach uses geometries developed around competent heterogeneities such as quartz pebbles pegmatite pods veins porphyroclasts porphyroblasts and breccia clasts a shear sense history is derived by applying this approach to earlier foliations preserved within the heterogeneities and their strain shadows

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

morphometric analysis and genetic implications of pro deltaic sea floor undulations in the northern alboran sea margin western mediterranean basin abstract several fields of seafloor undulations from pro deltaic wedges in the northern margin of alboran sea western mediterranean basin are described in this paper a series of elongated subparallel bathymetric undulations are distinguished in the foreset to bottomsets regions of the holocene pro deltaic wedges related with the guadalfeo and verde seco rivers multibeam data surficial sediment samples and high resolution seismic profiles have been used in this study and integrated in a geographical information system quantitative measurement of key morphometric parameters wave length height asymmetry length and wave form index was performed on multibeam data and seismic profiles using the arcgis software wave form index and depth data were analysed statistically and a cluster analysis was carried out in each area according to these results we infer that sea floor undulations in the study areas are best explained by the influence of strong sediment flows normal to bathymetric contours probably coupled with the effect of subsequent slow sediment deformation processes such as sediment creeps the influence of bottom current activity is considered less likely as the position of river mouths and the very high slope gradients seems to be the key factors which control the development of these sea floor undulations the alboran sea sea floor undulations are compared with those of other fields in shallow water environments and the different processes of formation evaluated

deformation partitioning and porphyroblast rotation in meta morphic rocks a radical reinterpretation abstract most porphyroblasts never rotate during ductile deformation provided they do not intern ally deform during subsequent events with the exception of relatively uncommon but spectacular examples of spiralling garnets instead the sur rounding foliation rotates and reactivates due to partitioning of the deformation around the porphyroblast consequently porphyroblasts commonly preserve the orientation of early foliations and stretching lineations within strain shadows or inclusion trails even where these structures have been rotated or obliterated in the matrix due to subsequent deformation these relationships can be readily used to help develop an understanding of the processes of foliation development and they demonstrate the prominent role of reactivation of old foliations during subse quent deformation they can also be used to determine the deformation history as porphyro blasts only rotate when the deformation cannot partition and involves progressive shearing with no combined bulk shortening component

shear band foliation as an indicator of sense of shear field observations in central spain the macizo de nevera a paleozoic basement inlier surrounded by essentially flat lying mesozoic cover rocks of central spain exhibits an extremely consistent system of steep dextral strike slip faults different faults have a variable amount of displacement but their en echelon arrangement and similar sense of displacement imply a cogenetic origin a maximum displacement of 1 0 km corresponding to an averaged angular shear strain of 1 5 and peak values of 6 6 occurs along the central part of the 6 km long truchas ductile shear zone an early axial plane cleavage is locally deflected into the truchas shear zone and superposed by coarse shear band foliation the consistent angular relationship between the new foliation and the shear zone boundary confirms the megascopic sense of shear

sedimentology and tectonic implications of cretaceous fan delta conglomerates queen charlotte islands canada the honna formation of coniacian age consists of several hundred metres of polymictic clast supported conglomerate associated with sandstone and mudstone five conglomerate facies are recognized ungraded beds inverse graded beds normal graded beds inverse to normal graded beds and parallel stratified beds these facies are interpreted as the deposits of subaqueous cohesionless debris flows and or high density turbidity currents the depositional environment was a deep water gravelly fan that draped a fault controlled basin margin slope the fan is inferred to have passed upslope directly into an alluvial fan unpreserved hence the name fan delta can be applied to the overall depositional system this type of fan delta of which the brae oilfield in the north sea is an example is defined here as a deep water fan delta the lack of a shelf is in marked contrast to other types of fan delta three facies associations are recognized in the honna formation subaqueous proximal fan conglomerates distal fan turbiditic sandstones and pro fan interfan mudstones with thin sandy turbidites the proximal fan is envisaged as an unchannelled gravel belt with a downslope length of at least 20 km such a long subaqueous gravel belt lacks a known modern analogue the distal fan was an unchannelled sandy extension of the proximal gravel belt it is postulated that the honna formation accumulated in a foreland basin which migrated westwards from the coast mountains where the wrangellia alexander terrane was colliding with north america in this model the honna fan delta was sourced by a west verging thrust sheet whose sole thrust was the sandspit fault immediately to the east deep water fan deltas appear to develop preferentially when eustatic sea level is relatively high so that the feeder alluvial fan is small and gravelly throughout in petroleum exploration and field development care should be taken to distinguish deep water fan deltas from base of slope canyon fed submarine fans because the two systems differ significantly in terms of coarse sediment distribution

foliation development and refraction in metamorphic rocks reactivation of earlier foliations and decrenulation due to shifting patterns of deformation partitioning reactivation of early foliations accounts for much of the progressive strain at more advanced stages of deformation its role has generally been insufficiently emphasized because evidence is best preserved where por phyroblasts which contain inclusion trails are present reactivation occurs when progressive shearing operating in a synthetic anastomosing fashion parallel to the axial planes of folds changes to a combination of coarse and fine scale zones of progressive shearing some of which operate antithetically relative to the bulk shear on a fold limb reactivation of earlier foliations occurs in these latter zones reactivation decrenulates pre existing or just formed crenulations generating shearing along the decrenulated or rotated pre existing foliation planes partitioning of deformation within these foliation planes such that phyl losilicates and or graphite take up progressive shearing strain and other minerals accom modate progressive shortening strain causes dissolution of these other minerals this results in concentration of the phyllosilicates in a simi lar but more penetrative manner to the for mation of a differentiated crenulation cleavage except that the foliation can form or intensify on a fold limb at a considerable angle to the axial plane of synchronous macroscopic folds reactivation can generate bedding parallel schistosity in multideformed and meta morphosed terrains without associated folds heterogeneous reactivation of bedding gen erates rootless intrafolial folds with sigmoidal axial planes from formerly through going struc tures reactivation causes rotation or refrac tion of axial plane foliations forming in the same deformation event causing reactivation in those beds or zones in which an earlier foli ation has been reactivated and results in destruction of the originally axial plane foli ation at high strains reactivation also provides a simple explanation for the apparently wrong sense but normally observed rotation of gar net porphyroblasts whereby the external foli ation has undergone rotation due to antithetic shear on the reactivated foliation alter natively the rotation of the external foliation can be due to its reactivation in a subsequent deformation event porphyroblasts with inclusion trails com monly preserve evidence of reactivation of earl ier foliations and therefore can be used to ident ify the presence of a deformation that has not been recognized by normal geometric methods because of penetrative reactivation reac tivation often reverses the asymmetry between pre existing foliations and bedding on one limb of a later fold leading to problems in the geo metric analysis of an area when the location of early fold hinges is essential the stretching lineation in a reactivated foliation can be rad ically reoriented potentially causing major errors in determining movement directions in mylonitic schistosities in folded thrusts geometric relationships which result from reactivation of foliations around porphyroblasts can be used to aid determination of the timing of the growth of porphyroblasts relative to deformation events other aspects of reac tivation however can lead to complications in timing of porphyroblast growth if the presence of this phenomenon is not recognized for example d grown porphyroblasts may be dis solved against reactivated s and hence appear to have grown syn d

ductile thrusting within subduction complex rocks on signy island south orkney islands abstract a model involving repeated nnw directed ductile thrusting in subduction complex rocks on signy island south orkney islands accounts for the consistent nnw trending alignment of fold axes stretching and shearing directions in the absence of major discrete thrust planes stratigraphic control or younging criteria the evidence for consistent ductile thrusting is more cryptic and is found in folding stretching relations porphyroblast rotations and mylonite fabrics early fold axes parallel to stretching syn tectonic garnet rotations augen lineations and sheath folds all support nnw directed thrusting as do a common late shear band foliation and minor shear zones development of late open folds with axes parallel to stretching may be due to constrictional deformation a lateral ramp or differential movement during thrusting the structures described from signy island may characterize the type of deformation in deep level ductile thrust zones at the base of an accretionary wedge or in a zone of subcretion the thrusting direction on signy island is inferred to be parallel to the direction of subduction in the south orkney islands in the early jurassic plate reconstructions suggest that this direction was at a high angle to the arcuate trend of the antarctic peninsula continental margin

bathymetry and sediment dispersal dynamics along the yallahs fan delta front jamaica abstract the shallow offshore yallahs fan delta serves as a model for the interaction of littoral processes and bathymetry and how they influence sedimentation on steep submarine slopes and in deep marine basins in tectonically active areas bottom reflection profiles show that the yallahs delta front is characterized by two bathymetric zones a narrow island shelf and a steep slope dissected by the heads of at least three submarine canyons the refraction and diffraction of waves across these canyons and shelf control sediment distribution and the alternation of erosional and depositional beaches a dominantly westward longshore drift transports coarse grained sediments until they are trapped in the heads of the submarine canyons or temporarily stored on steep unstable slopes between the canyons mass gravity processes presumably move these sediments downslope where they are deposited as turbidites in the yallahs basin and out onto the colombian abyssal plain

shear criteria in the grenville province ontario canada abstract the grenville province of canada is a major proterozoic orogenic belt mapping and structural analysis shows that the central ontario segment of this belt is composed of a stack of imbricated thrust nappes separated by mylonite zones the mylonite zones were generated at high metamorphic grades and contain a distinctive assemblage of mesoscopic and microscopic asymmetric structures these structures include rotated tectonic inclusions rotated boudins and pinch and swell structures sheath folds rotated single crystal porphyroclasts single crystal fish and shear band foliation the shear asymmetry indicated by these structures is highly consistent between members of the assemblage and over a large area of the grenville province and shows that the thrust nappes were transported to the northwest the consistency of the structures is thought to be due to cyclical dynamic recrystallization leading to steady state foliations in the mylonites

sliding thrusting tectonics caused by thermal uplift in the yunmeng mountains beijing china abstract a ductile shear zone analogous to a normal fault with a low dip angle occurs on the southeastern flank of the yunmeng anticlinorium north of beijing in huairou county the southeast dipping shuiyu ductile shear zone is composed of mylonitic granitic gneiss and has an average width of about 1 km the structures in the area show a symmetrical pattern this pattern may be generated by a process of sliding and thrusting caused by thermal uplift an alternative possible model for the area is that for the north american cordilleran regions

porphyroblast nucleation growth and dissolution in regional metamorphic rocks as a function of deformation partitioning during foliation development in regional metamorphic rocks the partitioning of deformation into progressive shearing and progressive shortening components results in strain and strain rate gradients across the boundaries between the partitioned zones these generate dislocation density gradients and hence chemical potential gradients that drive dissolution and solution transfer phyllosilicates and graphite are well adapted to accommodating progressive shearing without necessarily building up large dislocation density gradients within a grain because of their uniquely layered crystal structure however most silicates and oxides cannot accommodate strain transitions within grains without associated dislocation density gradients and hence are susceptible to dissolution and solution transfer as a consequence zones of progressive shearing become zones of dissolution of most minerals and of concentration of phyllosilicates and graphite exceptions are mylonites where strain rates are commonly high enough for plastic deformation to dominate over diffusion rates and therefore over dissolution and solution transfer porphyroblastic minerals cannot nucleate and grow in zones of active progressive shearing as they would be dissolved by the effects of shearing strain on their boundaries however they can nucleate and grow in zones of progressive shortening and this is aided by the propensity for microfracturing in these zones which allows rapid access of fluids carrying the material presumed to be necessary for nucleation and growth zones of progessive shortening also have a number of characteristics that help to lower the activation energy barrier for nucleation this includes a build up of stored strain energy relative to zones of progressive shearing in which dissolution is occuring porphyroblast growth is generally syndeformational and previously accepted criteria for static growth are not valid when the role of deformation partitioning is taken into account porphyroblasts in a contact aureole do not grow statically either as microfracturing associated with emplacement allows access of fluids in a fashion that is similar to microfracturing in zones of progressive shortening the criteria used for porphyroblast timing can be readily accommodated in terms of deformation partitioning reactivation of deforming foliations and a general lack of rotation of porphyroblasts with the spectacular exception of genuinely spiralling garnet porphyroblasts

anatomy of shelf deltas at the edge of a prograding eocene shelf margin spitsbergen although shelf edge deltas are well imaged seismic features of holocene and pleistocene shelf margins documented outcrop analogues of these important sand prone reservoirs are rare the facies and stratigraphic architecture of an outcropping shelf edge delta system in the eocene battfjellet formation spitsbergen is presented here as well as the implications of this delta system for the generation of sand prone shelf margin clinoforms the shelf edge deltas of the battfjellet formation on litledalsfjellet and hogsnyta produced a 3 5 15 km shelf edge attached slope apron 70 m of sandstones proximally tapering to zero on the lower slope the slope apron consists of distributary channel and mouth bar deposits in its shelf edge reaches passing downslope to slope channels chutes that fed turbiditic lobes and spillover sheets in the transgressive phase of the slope apron estuaries developed at the shelf edge and these also produced minor lobes on the slope the short headed mountainous rivers that drained the adjacent orogenic belt and fed the narrow shelf and the shelf edge position of the discharging deltas made an appropriate setting for the generation of hyperpycnal turbidity currents on the slope of the shelf margin the abundance of organic matter and of coal fragments in the slope turbidites is consistent with this notion evidence that many of the slope turbidites were generated by sustained turbidity currents that waxed then waned includes the presence of scour surfaces and thick intervals of plane parallel laminae within turbidite beds in the slope channels and thick spillover lobes with repetitive alternations of massive and flatlaminated intervals the examined shelf edge to slope system now preserved mainly below the shelf break and dominated by sediment gravity flow deposits has a threefold stratigraphic architecture a lower progradational part in which the clinoforms have a slight downward directed trajectory a thin aggradational zone and an upper part in which clinoforms backstep up onto the shelf edge a greatly increased density of erosional channels and chutes marks the regressive to transgressive turnaround within the slope apron and this zone becomes an angular unconformity up near the shelf edge this unconformity with both subaerial and subaqueous components is interpreted as a sequence boundary and developed by vigorous sand delivery and bypass across the shelf edge during the time interval of falling relative sea level the studied shelf margin clinoforms accreted mostly during falling stage sea level below the shelf edge but the outer shelf later became estuarine as sea level became re established above the shelf edge

eocene post rift tectonostratigraphy of the rockall plateau atlantic margin of nw britain linking early spreading tectonics and passive margin response a regional study of the eocene succession in the uk sector of the rockall plateau has yielded new insights into the early opening history of the ne atlantic continental margin data acquired from british geological survey borehole 94 3 on the rockall high provides a high resolution record of post rift early to mid eocene subaqueous fan delta development and sporadic volcanic activity represented by pillow lavas tuffs and subaerial lavas this sequence correlates with the east rockall wedge which is one of several prograding sediment wedges identified across the rockall plateau whose development was largely terminated in the mid lutetian linking the biostratigraphical data with the magnetic anomaly pattern in the adjacent ocean basin indicates that this switch off in fan delta sedimentation and volcanism was coincident with the change from a segmented transform margin to a continuously spreading margin during chron c21 however late stage easterly prograding sediment wedges developed on the hatton high during late mid to late eocene times these can only have been sourced from the hatton high which was developing as an anticline during this interval this deformation occurred in response to mid to late eocene compression along the ocean margin possibly associated with the reorganisation to oblique spreading in the iceland basin which culminated at the end of the eocene with the formation of the north hatton anticline and the deformation tilting of these wedges a series of intra eocene unconformities of which the mid lutetian unconformity is the best example has been traced from the rockall plateau to the faroe shetland region and onto the greenland conjugate margin bordering the early ocean basin whilst there appears to be some correlation with 3rd order changes in eustatic sea level it is clear from this study that tectonomagmatic processes related to changes in spreading directions between greenland and eurasia and or mantle thermal perturbations cannot be discounted

the use of asymmetric pressure shadows in mylonites to determine the sense of shear abstract asymmetric pressure shadows aps on both sides of a rigid porphyroclast are commonly observed in mylonites along the median tectonic line mtl in japan it is one of the most noticeable asymmetric microstructures showing that the porphyroclasts have rotated during non coaxial laminar flow in a ductile shear zone the shadow domains are filled with recrystallized quartz and k feldspar excepting aps various asymmetric microstructures in the mylonites indicate a sinistral sense of displacement throughout the ductile shear zone along the mtl based on the shape analysis of aps in xz section parallel to the mylonitic lineation and normal to the mylonitic foliation the following results were obtained 1 the relative position of the aps with respect to a porphyroclast is not a reliable criterion for deducing the sense of shear and 2 the drag angle of the shadow boundaries with respect to the mylonitic foliation in each quartered domain is diagnostic of the sense of shear when the shearing is sinistral in upper right and lower left hand side of a porphyroclast is larger than in upper left and lower right hand side and vice versa for dextral shearing these results demonstrate that the drag patterns of aps around porphyroclasts in mylonites are highly reliable indicators for the determination of the sense of shear

asymmetric quartz c axis fabrics and flow vorticity a study using rotated garnets abstract the development of a type i crossed girdle c axis fabric with an asymmetric density distribution and an internally asymmetrical skeletal outline is examined in a specimen of garnet bearing mylonitic quartzite from the betic movement zone in southern spain the garnets are pre mylonitic skeletal porphyroblasts that rotated during mylonitic deformation but preserved a strain free equilibrium microstructure and a random c axis fabric it follows that the asymmetry of the density distribution must result from the deformation history itself the sense of asymmetry of the c axis population and that of the skeletal outline are consistent with the sense of vorticity inferred from extensional crenulations and asymmetric microboudinage and also with the sense of rotation of the garnets analysis of the rotation angles with aspect ratio of the garnet porphyroblasts demonstrates that a pure shear component was involved in an essentially non coaxial flow this may explain the internal asymmetry of the fabric skeleton and confirms the idea that a spectrum exists of type i fabrics intermediate between the theoretically predicted fabrics for pure and simple shear a tentative reconstruction of the kinematic framework suggests that the central segment of the fabric skeleton is linked to the extensional apophysis of the flow

structural evolution of the whipple and south mountains shear zones southwestern united states the whipple and south mountains of the southwestern united states have undergone a strikingly similar sequence of deformations in both ranges gently dipping mylonitic fabrics have been overprinted by successively more brittle structures associated with a low angle detachment fault kinematic indicators reveal that the mylonitic rocks brittle structures and detachment faults are kinematically coordinated and were all formed by top to the northeast shear the structural evolution of both areas can be explained in terms of major shallow dipping shear zones that accommodated tertiary crustal extension we suggest that detachment faults and associated zones of brecciation cataclasis and seismic slip were originally continuous downdip along the low angle shear zones into mylonitic gneisses formed below or near the ductile brittle transition as the mylonites were drawn out from beneath the brittlely extending upper plate they were progressively uplifted above the ductile brittle transition and were overprinted by successively more brittle structures

deformation of leucogranites of the crystalline main central sheet in southern tibet china abstract towards the top of the main central sheet in southern tibet china leucogranites intrude metamorphic rocks related to rocks of the main central thrust in the himalayas our study shows that the leucogranites suffered a northward shear deformation the significance of this event is discussed in terms of gravity driven decollement of the 10 000 m thick tethyan sedimentary pile over its crystalline basement

geomorphology and sedimentary processes of a modern slope type fan delta fujikawa fan delta suruga trough japan abstract the fujikawa fan delta is a slope type fan delta developed on the arc arc collision boundary between the izu bonin and honshu arcs in the east asian monsoon related humid temperature climate region it comprises a stream dominated alluvial fan and a large subaqueous portion that progrades into deep water 1300 m in water depth based on a detailed subaqueous morphology obtained from remote sensing imagery including izanagi deep towing side scan sonar and deep towing video camera images the subaqueous portion is subdivided into delta front upper slope lower slope and prodelta the lower slope comprising three elongate convex upward bulges occupies the largest portion and is the main sedimentation site in the fujikawa fan delta a single feeder channel or canyon is absent instead numerous chutes are developed along the length of the bulge related to the diversion of the river course on the alluvial fan the elongate subaqueous bulge fed directly to the river is formed then switched hence the subaqueous fan shape of the fujikawa fan delta is mainly controlled by the pre existing basin topography and the diversion pattern of the river course on the alluvial fan

microstructural evidence of rotation and non rotation of mica porphyroblasts abstract mica porphyroblasts in schists from several regions show nearly planar inclusion trails that are parallel over areas much larger than the wavelengths of later folds this indicates that the porphyroblasts have not rotated with respect to geographical co ordinates during deformation instead the matrix has rotated as suggested by ramsay 1962 even in zones of marked shortening in the matrix adjacent to large rigid porphyroblasts e g of cordierite or staurolite small biotite porphyroblasts have not rotated but have become thinned by solution as indicated by parallelism of inclusion trails in separate biotite grains and by evidence of truncation of inclusion trails by the matrix foliation less common are biotite porphyroblasts that have single asymmetrical microfolds in the matrix adjacent to the porphyroblasts and so appear to have rotated these porphyroblasts are characterized by kinking

borrego springs santa rosa mylonite zone a late cretaceous west directed thrust in southern california the borrego springs shear zone section of the eastern peninsular ranges mylonite zone eprmz contains unequivocal evidence for ductile shearing with an east over west sense of movement field evidence includes the presence of s and c planes and shear bands all lines of microstructural evidence are internally consistent and support the field observations it appears that the data are compatible only with post mid cretaceous west directed thrusting on the eprmz

slope failures and stability analysis of shallow water prodeltas in the active margins of western greece northeastern mediterranean sea sediment instabilities are common on the prodeltas of the seismically active continental margins of western greece sediment failures on the low angle 0 5 2 prodelta slopes manifest themselves as successions of peripheral rotational block slumps restricted to the foresets of the late highstand systems tract hst the individual slump blocks are about 80 150 m long and are bounded by growth faults acting as curved slip planes that extend to a mean depth of 10 15 m below seafloor shear planes develop in the lower part of muddy and or gas charged hst foresets deeper basal transparent muddy layers of the early hst bottomset together with the late pleistocene transgressive systems tract sequences tst are mostly unaffected on the steeper 2 6 fan delta slopes of the western gulf of corinth debris flows and avalanches with a significant retrogressive component dominate slope destabilisation sediment cores taken from landslide scarps and slide planes penetrated gas bubble releasing sediments thereby indicating that failure planes are in the late hst foresets upper part of the early hst bottomsets gas charged zone the foresets of the hst prodelta deposits display high water content 30 80 low bulk density 1 4 1 9 g cm 3 and relatively low values of undrained shear strength 3 20 kpa the water content of the hst distal muddy bottomsets is relatively higher 50 110 and bulk density relatively lower 1 3 1 7 g cm 3 with low values of shear strength 2 10 kpa the shear strength of the gas releasing sediment layer displays lower values 2 9 kpa relative to the overlying post failure muddy sediments of the late 100 300 years slope stability was calculated using the normalised soil parameter nsp method under undrained conditions for normally consolidated prodelta sediments this analysis indicates that instabilities could be induced by critical earthquake ground accelerations of 26 6 29 6 g for the hst foresets and 12 4 14 1 g for the basal transparent layer belonging to the early hst bottomsets consequently the early hst bottomsets has to be considered a potentially unstable layer since the regional peak ground accelerations pgas for the next 50 years are expected to range from 19 to 30 g moreover our results show that new glide planes in the prodeltaic sediment bodies of the seismically active continental margins of western greece will likely develop from the gas charged sediments of the lower part of the hst foresets to the upper part of early hst bottomsets

dynamics flushing and trapping in hinchinbrook channel a giant mangrove swamp australia hinchinbrook channel is a 44 km long tidal channel connected at its northern and southern ends to the continental shelf of the great barrier reef the channel drains 164 km 2 of mangrove swamps it also drains the herbert river the dynamics within the channel and the flushing of the fringing mangrove swamps were studied both in the field and using numerical models the dominant currents are tidal semi diurnal and are due to two nearly identical tidal waves entering the channel at its norhtern and southern openings and meeting in the middle the mangrove swamps contribute significantly to the tidal dynamics when the herbert river discharge is small net residual currents are negligible even in the presence of wind and the residence time of water is about 2 months flushing of the fringing mangrove swamps is largely controlled by the trapping effect in the mangrove swamps and is slow with an e fold residence time of about 54 days on the northern end the mangrove fringed channel is wide and shallow and a barotropic coastal boundary layer is formed due to shallow water effects and trapping in mangrove swamps this results in a long term 2 weeks trapping of water along the mangrove fringed coast in calm weather thus coastal waters are continuously exchanged and mixed with mangrove swamp waters but mixing between coastal and offshore waters is much slower

stretching normal to the regional thrust displacement in a thrust wrench shear zone rehamna massif morocco the hercynian rehamna massif of morocco is located in the meseta belt on the sheared boundary between the weakly strained western meseta coastal block and an intensely deformed carboniferous basin deformation may be related to three superposed phases the most important phases d1 and d2 result in a main composite s1 2 foliation and are related to westward thrusting d4 is contemporaneous with the emplacement of syn to late tectonic granitic plutons fold asymmetry and microstructures rotated garnets s c tectonites suggest a dominant westward thrusting in eastern rehamna in central rehamna along the thrust zone front stretching lineations are almost normal to the regional coeval thrust displacement direction and microstructures rotated garnets shear bands asymmetrical pressure shadows observed along the 1 direction stretching lineation direction suggest dextral reverse southward wrenching this particular strain pattern is interpreted as a product of thrust wrench shearing combining ductile thrusting and wrenching during the progressive synmetamorphic shortening of the area along the frontal tip of the central meseta thrust units

kinematics of the northern part of the simplon line central alps abstract structural studies were carried out along the northern part of the simplon line in order to constrain the kinematic history of the line during tertiary times the ductile strain accumulated within both basement units and mesozoic cover reveals the upper units sheared towards the west southwest the simplon line can be described as a major shear zone along which the main movement occurred perpendicular to the line this shearing developed during retrograde metamorphic conditions and postdates earlier deformations associated with the high temperature lepontine episode finally it was followed by the formation of the berisal syncline back folding episode which generated some brittle movements towards the south localized at the contact between the lower and upper pennine units i e on the simplon line

on the internal geometry of mylonite zones mylonite zones are generally characterized by abrupt and very large strain transitions which commonly result in excessively anastomosing schistosities on a wide range of scales when compared with nonmylonitic foliations this geometry is very susceptible to remodification during progressive mylonitization resulting in unusual and complex fold lineation and foliation geometries and interrelationships open folds of the mylonitic foliation with axes parallel to the stretching lineation in the surrounding mylonite cannot have formed by the rotation of fold axes through a large angle within their axial planes as has been usually proposed for isoclinal and sheath folds in mylonitic zones open folds initiate with axes parallel or close to the stretching lineation due to the geometric effects of folding a mylonitic foliation which anastomoses around an ellipsoidal pod of less deformed material this initial geometry also allows the generation of fold axes curved within their axial plane through 1800 about the stretching lineation at the time of nucleation successive mylonitic foliations develop during this folding and refolding process with boundaries that truncate and isolate earlier fold hinges and portions of fold limbs as a consequence stretching and intersection lineations can vary from plane to plane through the mylonite zone although careful examination often reveals a weak overprinting stretching lineation parallel to the bulk movement direction for the whole zone fold asymmetry in mylonite zones is a potential indicator of shear sense across a zone if the fold axes lie at an angle to the bulk stretching lineation direction in such circumstances however a single asymmetry projected onto a plane perpendicular to the mylonitic foliation and containing the bulk stretching lineation can indicate either sense of shear depending on a variety of factors these include whether the foliation folded is primary or mylonitic and in the latter case whether the mylonite zone formed with a steep dip and horizontal stretching lineation or in some other orientation the most satisfactory sense of shear indicator is the asymmetry of s and c planes

lack of porphyroblast rotation in noncoaxially deformed schists from petrel cove south australia and its implications abstract inclusion trails representing an s 1 cleavage demonstrate the lack of porphyroblast rotation during subsequent highly non coaxial deformations the pelitic schists of the kanmantoo group at petrel cove south australia contain two generations of porphyroblasts the first one consists of cordierite porphyroblasts that formed early in d2 and contain straight to slightly sigmoidal inclusion trails of s 1 the second generation consists of andalusite porphyroblasts that overgrew crenulated s 2 late during d3 several hundred inclusion trail traces from cordierites measured from oriented specimens taken throughout a strongly folded area show a horizontal great circle distribution when plotted and contoured on a stereographic projection hence s 1 was planar and horizontal prior to d2 s 1 measurements on limbs and hinges of a mesoscale d2 foldpair show that folding had little effect on porphyroblast orientation as the s 1 orientation remained constant and subhorizontal around the fold hence porphyroblasts have not rotated during any of the non coaxial deformations accompanying and following their growth this is interpreted as a result of the partitioning of the deformation around them s 1 in the matrix has been totally destroyed by the formation of s 2 as a fully differentiated crenulation cleavage what has previously been regarded as inconsistent senses of shear recorded by porphyroblasts around folds is resolved by the fact that the matrix foliation rotated rather than the porphyroblasts due to the effects of deformation partitioning the presence of a subhorizontal s 1 foliation suggests horizontal movements e g thrusting or detachment faulting during the earliest phase of the adelaidian orogeny

mathematical model for folding of layering near rigid objects in shear deformation abstract the asymmetric arrangement of deformed layering around rigid objects in shear zones is among the most reliable criteria for inferring shear sense in rock a mathematical model which simulates shear deformation of a ductile medium containing a rigid inclusion gives insight into the genesis of this type of shear sense indicator the model which is based on the velocity field solution for viscous flow around a sphere demonstrates that many common strtuctures can arise in a mechanically passive matrix as the model simulates increasing shear strain structures in the matrix pass through distinct evolutionary stages similar results have been obtained in experimental models suggesting that it may be possible to read shear strain magnitude from the geometry of deformed layering near clasts and porphyroclasts in sheared rocks