response of tide dominated mangrove shorelines in northern australia to anticipated sea level rise the exact response of mangrove shorelines to anticipated sea level rise will depend upon the balance between sedimentation and sea level change within the top end of the northern territory of australia there are extensive relatively unmodified tide dominated mangrove forests where tidal processes redistribute sediment harbours such as darwin harbour and tidal rivers such as the south alligator river with its associated coastal and estuarine plains represent opposite extremes in terms of holocene sedimentary infill and will respond differently to sea level rise in darwin harbour mangrove assemblages can be recognized in geomorphologically defined habitats similar topography within and between creeks implies morphodynamic equilibrium with tidal processes tidal reworking of sediment may maintain an equilibrial profile under gradually rising sea level with resuspension of lower intertidal and subtidal muds and their redeposition within upper intertidal mangrove habitats in contrast the plains along the coast and tidal rivers draining into van diemen gulf developed during the post glacial marine transgression and since sea level stabilized around 6000 years ago coastal plains have prograded these broad plains are presently not extensively influenced by salt water but are often at elevations close to or even below modern high tide levels they may therefore revert to saline conditions particularly rapidly if the sea rises the pattern of change may not be directly analogous to marine incursion experienced in the early holocene because broad plains have been able to prograde during the last 6000 years of relatively stable sea level

the motion of rigid ellipsoidal particles in slow flows abstract preferred orientations of fabric elements in tectonites are usually interpreted with reference to two continuum models namely those of march 1932 and jeffrey 1922 it is argued that the first of these is usually inappropriate if the fabric elements are rigid inhomogeneities embedded in a deformable matrix jeffrey s model is more applicable but until recently its use has been limited to problems involving axisymmetric particles and simple flow geometries in this paper jeffrey s equations have been solved numerically in order to investigate the behaviour of more general systems the motions of two particle shapes one a prolate spheroid the other a triaxial ellipsoid are considered in parallel for four specified flow geometries which involve pure or simple shear and combinations of both any departures from particle axisymmetry or from simple flow geometries have a significant effect on particle behaviour compared with that predicted by spheroid simple flow solutions

evolution of mica fish in mylonitic rocks abstract mineral fish are lozenge shaped porphyroclasts single crystals in a finer grained matrix which occur in ductile shear zones and which are commonly used as shear sense indicators mineral fish of biotite tourmaline k feldspar garnet hypersthene and quartz occur in mylonites but most common are white mica fish these mica fish can be subdivided into six morphological groups that develop by different mechanisms determined by different initial shapes and orientations the principal mechanisms of formation are intracrystalline deformation combined with rigid body rotation concomitant selective grain size reduction occurs by recrystallisation cataclastic separation pressure solution and diffusional mass transfer microboudinage has been proposed for the breakdown of large mica fish into smaller ones but many mica fish undergo shortening rather than extension along their long axes evidence is presented for an alternative process in which the tips of mica fish are isoclinally folded and then break off along the hinge of these microfolds all the presented fish shaped porphyroclasts or mineral fish have a specific shape preferred orientation with their long axis at a small antithetic angle with respect to the foliation they represent a special group of objects with a stable orientation due to flow partitioning into narrow shear bands

kinematics of lava flows based on fold analysis a kinematic analysis of the mingling folding structures occurring in a lava flow from porri volcano southern tyrrhenian sea has been performed in order to estimate the flow kinematic parameters folds have resulted from the deformation of enclaves and banding structures and consist of a single layer of a crystal rich andesitic magma hosted in a less competent basaltic magma results of the analysis indicate that the flow kinematic vorticity increases with the distance from the vent whereas the ratio between pure shear and simple shear strain decreases following a power law quantitative estimates of the kinematic parameters provide an opportunity to examine the deformation behaviour of the lava flow near the vent the lava is a non ideal shear flow away from the vent the lava is an ideal shear flow gravity driven mechanisms control the relative contribution of pure and simple shear to the bulk deformation

the sedimentary framework of northern spencer gulf south australia abstract northern spencer gulf is the landward extremity of a shallow marine embayment which occupies a structural depression that overlies a major precambrian lineament situated in a warm temperate climate the low rainfall and high evaporation have created high salinities resulting in an hydrological inverse estuary modern sedimentation is dominantly biogenic carbonate to mixed terrigenous carbonate it is controlled by a mesotidal regime with occasional storm surges minor wave activity and a prolific growth of seagrass in shallow water the skeletal detritus consists of bivalves gastropods forams echinoids coralline algae and bryozoa the subtidal zone between 10 25 m is divided morphologically into two provinces the wide southern part has a relatively smooth floor but the northern part is narrower and the seafloor is either scoured free of loose sediment or covered with wide belts of megaripples the subtidal zone between 0 10 m is everywhere dominated by seagrass meadows the seagrasses are largely posidonia australis and p sinuosa and occupy broad depositional platforms and discrete offshore banks the seagrass meadows produce and trap mollusc foram detritus resulting in the accumulation of very poorly sorted organically bound structureless carbonate muddy sand intertidal and supratidal zone sediments are very extensive the intertidal zone includes bare sand flats or those covered by the seagrass zostera dense mangroves avicennia marina from mean sea level to spring high tide level are followed progressively by a halophytic samphire association and an atriplex saltbush association extensive algal mats occur with the halophytes and extend into the mangrove forests the sediments are muddy and only moderately calcareous the supratidal zone consists mainly of bare carbonate flats some stranded beach ridges and coastal dunes the carbonate flats contain discoidal gypsum crystals in weakly layered fenestral calcitic mud coastal changes during historic time are limited and the dominant sedimentary regime in northern spencer gulf is the vertical growth of seagrass areas to form intertidal sand flats

the strain path and kinematics of lava domes an example from lipari aeolian islands southern tyrrhenian sea italy 1 a circular dome from lipari island consists of latitic enclaves hosted in a rhyolitic magma a strain analysis of the enclaves has been carried out and the pure shear and simple shear deformation the vorticity number wk and flow kinematics are determined the axial ratio rf of the enclaves and the angle between the long axis of the enclaves and the transport direction are measured in 131 sites concentrated in the axial zone z1 upper distal zone z2 and basal zone z3 of the flow the values depict a pattern suggesting endogenous growth in z1 1 in z2 1 0 8 lateral stretching due to the upward motion of magma from the conduit prevails in z1 here the increase of pure shear strain from the bottom to the top reflects strain accumulation due to endogenous growth z2 and z3 suffer simple shear deformation in z3 the sense of shear is consistent with the transport direction an opposite sense of shear characterizes z2 this is due to velocity gradients located in the lower and upper portions of the flow the kinematics is viscous spreading in z1 and viscous gliding hyperbolic flow in z2 z3 possible rupturing of the exterior may be important in z1 where lateral stretching occurs and in z3 where is at a maximum the effusion rate is 1 93 m3 s strain rates calculated using structural data span a range from 1 9 to 5 8 10 6 s 1

sea level control of stacked late quaternary coastal sequences central great barrier reef lithofacies analysis pollen assemblages and radiocarbon age dates of 20 stratigraphic drill holes are used to develop an evolutionary history for late quaternary sedimentation in two coastal embayments landward of the central great barrier reef different physiographic settings of the embayments result in two contrasting styles of sedimentary sequence a an exposed moderate energy beach barrier lagoon system wyvuri embayment and b a protected low energy muddy inlet fill sequence mutchero inlet despite sharp contrast in sequence style similar depositional cycles occur in both embayments in response to late quaternary sea level fluctuations including 1 a last interglacial highstand 2 m c 125 000 yr bp beach barrier wyvuri 2 an early to mid holocene 8000 6100 yr bp transgressive beach barrierlagoon wyvuri and estuarine infill mutchero and 3 mid holocene to present highstand beach barrier wyvuri and estuarine mutchero progradation preservation of such cycles in the stratigraphic record would produce a series of vertically stacked and offset linear barrier sands surrounded by lagoonal mud and fine grained shoreface sediment juxtaposed to muddy estuarine infills sea level elevations are well recorded by the upward transition from rhizaghoru dominated intertidal mangrove mud to freshwater swamp clearly identified by pollen analysis and by the basal contacts of beach barrier sediments which sharply overlie the upper shoreface transgressive sedimentation is interrupted in both embayments by a constructional beach barrier wyvuri and abbreviated progradation mutchero corresponding to a 5 m pause in relative sea level rise at c 6800 yr bp sea level control of fine scale coastal sedimentation patterns is beginning to be widely recognized and provides an accurate analogue for stacked ancient sequences

a statistic for estimating strain with confidence intervals from deformed line distributions with an application to schists and gneisses of the western gneiss region west central norway abstract it is shown how to calculate the axial ratio of the strain ellipse r s from a deformed set of lines assuming that they were initially uniformly distributed and deformed passively using an exact but simple relationship between r s and the mean resultant length r of the distribution the method applies to distributions of lines modified under a general 2d deformation w k w k is the kinematical vorticity number by using the circular variance for circular data expressions for confidence intervals and confidence levels are calculated for strain modified distributions of lines these expressions indicate that confidence interval widths decrease with increasing r s and more importantly that the method is incapable of accurately estimating low strains the method was applied to 18 gneiss and schist samples from joa west central norway and found to produce realistic strain estimates which are internally consistent and concur with field relationships

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

the middle mountain shear zone southern idaho kinematic analysis of an early tertiary high temperature detachment the middle mountain shear zone is exposed in the idaho portion of the albion raft river grouse creek metamorphic core complex the structure strikes north northeast south southwest and dips shallowly to the west it is defined on the basis of well developed mylonitic fabrics and had an initial thickness of at least 4 km at least some movement on the shear zone occurred at depths of 22 26 km during eocene amphibolite facies metamorphism but shear zone fabrics may be found in some granite bodies of late oligocene age the zone may thus have been active in the ductile regime over a period of as much as 10 15 m y mylonitic rocks within the middle mountain shear zone display both type i and type ii s c fabrics augen structures pressure shadows and quartz c axis orientations are strongly asymmetric these fabrics and textures indicate that deformation within the zone was characterized by noncoaxial laminar flow during which the hanging wall of the structure moved down and to the west northwest relative to the footwall we interpret the middle mountain shear zone as a major detachment that played an important role in middle tertiary extension of this part of the eastern great basin the top to the west displacement sense contrasts with late cenozoic predominantly top to the east extension in this area implying a major change in extension geometry in early to middle miocene time

flattening in shear zones under constant volume a theoretical evaluation abstract this paper presents a theoretical model based on strain energy and work rate calculations that evaluates the possible degrees of flattening in finite ductile shear zones with rigid and deformable walls under constant volume conditions the principal parameters governing the ratio of bulk flattening and shear rates s r b b in shear zones with rigid walls are found to be 1 the length to width ratio d f measured in the normal section parallel to the extrusion direction and 2 the inclination of shear zone normal with the bulk compression direction narrow and long shear zones d f 10 are characterized by low s r ratios implying little flattening in the shear zone even when is low in the order of a few degrees accordingly the kinematical vorticity number w k is close to one when d f is large 10 or is high 20 and is much less than one if d f or are low the stretching rate of shear zone walls relative to the shear zone r f is an additional parameter that controls the degree of flattening in shear zones with deformable walls for given d f and values the flattening rate increases with increasing relative stretching rate r f and is significant at large values of r f likewise the kinematical vorticity number w k shows an inverse relation with the relative stretching rate of shear zone walls

kinematic significance of mingling rolling structures in lava flows a case study from porri volcano salina southern tyrrhenian sea a basaltic andesite lava flow from porri volcano salina southern tyrrhenian sea is composed of two different magmas magma a 51 vol of crystals has a dacitic glass composition and magma b 18 vol of crystals a basaltic glass composition magma b is hosted in a and consists of sub spherical enclaves and boudin like banding and rolling structures rs four types of rs have been recognized type type complex types and transitional structures between sub spherical enclaves and rolling structures an analysis of the rs has been performed in order to reconstruct the flow kinematics and the mechanism of flow emplacement rolling structures have been selected in three sites located at different distances from the vent in all sites most rs show the same sense of shear kinematic analysis of rs allows the degree of flow non coaxiality to be determined the non coaxiality is expressed by the kinematic vorticity number wk a measure of the ratio sr between pure shear strain rate and simple shear strain rate the values of wk calculated from the measured shapes of microscopic rs increase with increasing distance from the vent from approximately 0 5 to 0 9 results of the structural analysis reveal that the rs formed during the early intermediate stage of flow emplacement they represent originally sub spherical enclaves deformed at low shear strain at higher strain rs deformed to give boudin like and stretched banding structures results of the kinematic analysis suggest that high viscosity lava flows are heterogeneous non ideal shear flows in which the degree of non coaxiality increases with the distance from the vent in the vent area deformation is intermediate between simple shear and pure shear farther from the vent deformation approaches ideal simple shear lateral extension processes occur only in the near vent zone where they develop in response to the lateral push of magma extruded from the vent lateral shortening processes develop in the distal zone and record the gravity driven movement of the lava the lava flow advanced by two main mechanisms lateral translation and rolling motion lateral translation equals rolling near the vent while rolling motion prevailed in the distal zones

mylonites from the towaliga fault zone central georgia products of heterogeneous non coaxial deformation abstract retrograde mylonitic rocks occur in the segment of the towaliga fault southeast of jackson georgia mylonite protoliths are heterogeneous quartz feldspathic gneisses upper amphibolite facies sillimanite zone from the pine mountain and piedmont terranes protoliths contain no distinctive lithological markers that can be used to determine fault displacement shear sense can only be determined using microstructural criteria and type porphyroclast systems shear bands asymmetric microfolded quartz ribbons subgrain fabrics in quartz ribbons the most common porphyroclast system developed in mylonites and ultramylonites is type type systems do not have readily identifiable tails but do produce distinctive asymmetrical pile ups in the matrix such that the angle of intersection between the perturbed zone and the mylonitic foliation points in the shear direction differences in morphology between and type systems can be related to differences in the recrystallization rate deformation rate ratio r reflecting changes in ductility contrast between matrix and porphyroclast that controls the amount of recrystallized material in a porphyroclast mantle that is potentially available to form tails in early stages of mylonitization with low ductility contrasts and large r ratios large mantles occur around porphyroclasts and tailed systems develop in advanced stages of mylonitization with large ductility contrasts and small r ratios either very small or partially or totally missing mantles occur and type systems develop microstructural criteria ubiquitously record a right lateral strike slip motion component to the deformation textural evidence e g unidirectional shear bands consistent vorticity recorded by porphyroclasts and asymmetrical microfolds suggest that the mylonites are the products of non coaxial deformation the local presence of fabrics with coaxial symmetry result from heterogeneity in the deformation the right lateral offset on the towaliga fault most likely occurred during the late paleozoic alleghanian orogeny

structural evolution of intermediate crustal rocks in a strike slip and extensional setting variscan odenwald sw germany differential upward transport of metamorphic complexes and changing deformation mechanisms abstract the variscan basement exposed in the odenwald mountains southwest germany is composed of several allochthonous metamorphic complexes showing low pressure metamorphism with varying pt conditions and of syntectonic plutons i and s type during the late devonian early carboniferous times rapid uplift of these rocks caused rapid cooling before and during the thermal peak of metamorphism the metamorphic rocks experienced penetrative strain d 1 d 2 which was probably generated by crustal shortening and stacking the resulting micro structures infer distributed strain activation of c slip in quartz and postkinematic annealing during and after the thermal peak of metamorphism ne sw trending zones of normal oblique sinistral strike shearing d 3 and nne ssw trending zones of normal shearing d 4 developed these episodes of deformation are characterized by strong localization of strain strain softening was caused by reorientation of the lattice of quartz toward an orientation more favorable for easy glide along a and by a change in deformation mechanisms of feldspar from dislocation creep to grain size sensitive creep normal oblique strike shearing and normal shearing caused juxtaposition of mid crustal slivers of dissimilar pt and structural histories and provided mechanisms for their denudation detachment of rocks occurred along domains in which strain softening was operative further transtension and extension facilitated uplift and emplacement of syntectonic plutons which experienced also d 3 and d 4 strain in the plutonic rocks strain was broadly distributed in the initial hot stages and became increasingly localized as the deformation continued through cooling

old radiocarbon ages in the southwest pacific ocean during the last glacial period and deglaciation marine radiocarbon 14c dates are widely used for dating oceanic events and as tracers of ocean circulation essential components for understanding ocean climate interactions past ocean ventilation rates have been determined by the difference between radiocarbon ages of deep water and surface water reservoirs but the apparent age of surface waters currently approximately 400 years in the tropics and approximately 1 200 years in antarctic waters might not be constant through time as has been assumed in radiocarbon chronologies and palaeoclimate studies here we present independent estimates of surface water and deep water reservoir ages in the new zealand region since the last glacial period using volcanic ejecta tephras deposited in both marine and terrestrial sediments as stratigraphic markers compared to present day values surface reservoir ages from 11 900 14c years ago were twice as large 800 years and during glacial times were five times as large 2 000 years contradicting the assumption of constant surface age furthermore the ages of glacial deep water reservoirs were much older 3 000 5 000 years the increase in surface to deep water age differences in the glacial southern ocean suggests that there was decreased ocean ventilation during this period

flow in natural shear zones the consequences of spinning flow regimes abstract the ancient flow regime in natural shear zones is often considered to have followed a deformation path comparable to that in theoretical shear zones i e progressive simple shear between rigid wall rocks with a persistent flow plane orientation parallel to the edges of the zone this is often based on the presence of monoclinic fabric elements in the zones which indicate a dominantly non coaxial flow regime though not necessarily persistent simple shear the deformation fabric of a shear zone from the pyrenees illustrates that even at a kinematic vorticity number of w 1 simple shear along the entire deformation path obliqueness of the flow planes with the edges of the zone is possible for some time if incremental stretching axes were rotating with respect to zone edges this implies that ductile deformation must have taken place in the wall rock of the zone such a flow regime may be difficult to recognize with the fabric criteria used at present but leads to an unusual kinematic significance of the shear zone involved in extreme cases the zone may have acted as a passive marker in a ductilely deforming medium it also means that not only w must be known to reconstruct the ancient flow regime in natural shear zones but at least also the time dependence of the orientation of the incremental stretching axes

modest movements spectacular fabrics in an intracontinental deep crustal strike slip fault striding athabasca mylonite zone nw canadian shield geometry and strain partitioning within lower crustal intraplate strike slip shear zones can be extremely complex compared with analogous structural levels of interplate strike slip shear zones sited at plate margins striding athabasca mylonite zone canadian shield is a spectacular ca 500 km long granulite facies continental intraplate shear zone the shear zone is composed of middle archean granulite facies annealed mylonites ca 3 13 ga and late archean ca 2 62 2 60 ga granulite facies ribbon mylonite belts which thread a sinuous course along a chain of crustal scale lozenges cored by relatively stiff rocks of mafic to intermediate composition to the northeast the mylonites form a n s trending 5 10 km thick dextral strike slip belt to the southwest this bifurcates into a pair of conjugate strike slip shear zones overlain by a contemporaneous dip slip shear zone striding athabasca mylonite zone was kinematically inefficient as a strike slip fault and cannot have accommodated large wallrock displacements nevertheless spectacular granulite facies ribbon mylonites were formed throughout the shear zone reflecting the very high temperatures ca 850 1000 c high recrystallization rate strain rate ratios and the transpressive nature of the deformation wk 1 possibly accommodated by significant volume loss by magma migration

relationships between deformation and mixing processes in lava flows a case study from salina aeolian islands tyrrhenian sea the massive unit of a lava flow from porri volcano salina aeolian islands displays many unusual structures related to the physical interaction between two different magmas the magma a represents approximately 80 of the exposed lava surface it has a crystal content of 51 vol and a dacitic glass composition sio2 63 64 wt the magma b has a basaltic andesite glass composition sio2 54 55 wt and a crystal content of approximately 18 vol it occurs as pillow like enclaves banding boudin like and rolling structures which are hosted in magma a structural analysis suggests that banding and boudin like structures are the result of the deformation of enclaves at different shear strain the linear correlation between strain and stratigraphic height of the measured elements indicates a single mode of deformation we deduce that the component b deformed according to a simple shear model glass analyses of the a b boundary indicate that a and b liquids mix together at high shear strain whereas only mingling occurs at low shear strain this suggests that the amount of deformation i e forced convection plays an important role in the formation of hybrid magmas high shear strain may induce stretching shearing and rolling of fluids which promote both forced convection and dynamical diffusion processes these processes allow mixing of magmas with large differences in their physical properties

porphyroclast systems as kinematic indicators porphyroclasts of relatively strong minerals in mylonites commonly have an internal monoclinic shape symmetry defined by tails of dynamically recrystallized material the geometry of a porphyroclast and its tails called a porhyroclast system can serve as a valuable indicator of the sense of vorticity porphyroclast systems have been divided into and types on the basis of the geometry of the tails types have wedge shaped recrystallized tails whose median lines lie on opposite sides of a reference plane parallel to the tails and containing the symmetry axis for the system types are further subdivided into a a types in which the porphyroclast is isolated in a relatively homogeneous matrix and b types in which the porphyroclast system is associated with a shear band foliation in the matrix types typically have narrow recrystallized tails whose median lines cross the reference plane adjacent to the porphyroclast consequently embayments of matrix material occur adjacent to the porphyroclasts and the tails display characteristic bends a porphyroclast system in a mylonite develops when the relatively weak dynamically recrystallized grain aggregate in the porphyroclast mantle changes its shape due to non coaxial flow in the adjacent matrix this behaviour has been modelled in shear box experiments passive marker lines around rigid cylinders embedded in silicone putty were subjected to simple shear the experiments were modified to simulate a change in recrystallization rate r with respect to rate of deformation by decreasing the diameter of the rigid cylinder during deformation at variable rates the ratio r appears to be one of the most important factors in determining which porphyroclast system will develop at high r values flow of recrystallized material away from the porphyroclast is continuously appended by the production of new grains and wedge shaped a type tails develop at low r values relatively few new grains are added to the tails which become thinned and deflected by drag due to the spinning motion of the porphyroclast in addition most porphyroclast systems at low shear strains are of a type or lack monoclinic symmetry whereas types are only developed at high shear strain values complex porphyroclast systems characterized by two generations of tails are observed in many of the natural and model shear zones studied and may form due to fluctuating r conditions that allow isolated a and type porphyroclast systems to be used as sense of vorticity indicators are the systems should have a monoclinic shape symmetry matrix grain size should be small with respect to porphyroclast size matrix fabric should be homogeneous deformation history should be simple and observations should be made on sections normal to the inferred bulk vorticity vector for the mylonite

evidence for smoothly falling sea level relative to north queensland australia during the past 6 000 yr post glacial sea level curves are expected to differ between different parts of the world as a result of global isostatic changes1 or perhaps other forms of geoidal changes2 i report here results from the inner part of the northern great barrier reef which seem to show a pattern of smoothly falling sea level during the past 6 000 yr the results are consistent with stratigraphical results from prograded mangrove coasts on the nearby north queensland mainland the region is remote from the tectonically active margin of the south west pacific ocean and the results contribute to the global data set relevant to isostatic changes being assembled by the international sea level project igcp project no 61 they also provide a baseline relevant to holocene coral reef growth in the inner great barrier reef

last interglacial and holocene trends in sea level maxima around australia implications for modern rates this paper defines the spatial trend in sea level around australia at 3 timescales namely at the time of the maximum of the last interglacial around 125 000 yr b p during the holocene maximum between 5000 and 6000 yr b p and over the last 20 years last interglacial elevations range from 2 m around the great barrier reef to 32 m in northeast tasmania trend surface analysis shows that over 77 of the noise in these sea level elevations can be accounted for by a pattern evidencing tectonic uplift towards the southern edge of the continent assuming a eustatic sea level at this time of 4 to 6 m most of the east coast of new south wales and the west coast of western australia can be considered tectonically stable while the southern edge of the continent has risen by at least 5 m and the north northeast corner has downwarped by at least 2 m the spatial pattern of the holocene maximum tentatively supports the continuation of this tectonic deformation sea level at this time reached 1 6 and 2 4 m above present high tide limits around the northern and southeastern coastlines of australia respectively this holocene pattern is weak because much of the data is dominated by local variations reflecting differential loading of the continental shelf by water during the holocene transgression the holocene trend surface does not support geophysical modelling implying a southern latitudinal downwarping of the crust produced by the melting of the antarctic ice sheet and the loading of the ocean crust with meltwater however the spatial pattern of modern trends appears to contain a remnant holocene signal fitting this isostatic model rather than the long term pattern of tectonic flexure since the last interglacial sea level is presently rising at a rate of 1 75 mm yr 1 in northern australia compared to only 0 75 mm yr 1 in tasmania these results imply that isostatic factors as well as previously identified climatic variables may be controlling present day variations in the rate of change of sea levels around the australian continent

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

late pleistocene and holocene sea level change along the australian coast abstract tectonically the australian continent is relatively stable and as such it provides a good platform for studying late pleistocene and holocene sea level change the observations indicate that present sea level was reached at about 6000 years ago and that since then level has remained constant to within a few metres considerable spatial variability in the amplitude of the emergence and in the time at which sea levels first reached their present values have been observed spatial variability has also been observed in the sea level during the last glacial maximum and during the late phase of the holocene transgression much of this variaiblity is the result of the earth s adjustment to the glacial melting in the late pleistocene early holocene time and the concomitant distribution of this meltwater into the oceans conclusions that are drawn from matching observations with this glacio hydro isostatic model include the following 1 the mantle viscosity increases with depth the average upper mantle viscosity is about 2 3 10 20 pa s and the average lower mantle defined as below 670 km depth viscosity is about 10 22 pa s the average lithospheric thickness for the coastal and offshore region is about 70 80 km lateral variations in these mantle parameters are indicated 2 the addition of melwater into the oceans did not cease 6000 years ago but continued at a reduced rate up to more recent times adding an amount of water equivalent to a 3 m sea level rise in this interval 3 the amplitude of the holocene emergence is a function inter alia of coastal geometry and significant variations occur over distances of a few hundred kilometres and more holocene highstands of 1 2 m are generally well developed at the continental margins but are less well developed or do not developed at all at offshore islands and reefs 4 variations in the time of maximum emergence also occur being earlier at upstream tidal river sites than at coastal sites at offshore reefs or islands the sea level curve lags the coastal curves by 1000 years or more 5 considerable spatial variability occurs in the sea levels at the time of the last glacial maximum with variations of up to 30 m occurring across the continental shelves 6 there is generally no need to invoke tectonic movements to explain the sea level data along the australian coast but possible exceptions occur for the perth region and for tasmania

rolling structures at large shear strain abstract at large shear strain shear criteria are often obliterated or become ambiguous from examination of both natural examples and experimental models we describe a new criterion called rolling structure widely represented in sheared rocks a typical rolling structure is composed of a rigid or competent object e g porphyroclast boudin fossil etc with two tails asymmetrically disposed around it in most cases tails are of the same material as that of the rotating object and result from strain softening and grain size reduction at the object periphery forming a mantle z and s asymmetries of rolling structures represent dextral and sinistral senses of shearing respectively tails must not be confused with pressure shadows which usually present an opposite asymmetry for a given shear sense besides the determination of the sense of shear the occurrence of these structures allows a minimum estimate of the strain intensity in strongly sheared rocks since rolling structure length is proportional to shear strain

superimposed fabrics due to reversal of shear sense an example from the bergen arc shear zone western norway abstract a profile through the upper margin of a large scale ductile shear zone the bergen arc shear zone western norway has been studied in detail within the shear zone asymmetric structures indicate dextral or top to nw movement which is interpreted as representing late or post caledonian extensional tectonics the hanging wall of the shear zone is characterised by kinematic indicators such as shear bands associated with curved or inclined foliation and asymmetric boudins indicating sinistral or top to se movements these are interpreted as related to thrusting during the caledonian orogeny the studied profile shows the progressive overprinting of the sinistral structures by the later dextral shear this first led to a decrease in the obtuse angle between shear bands and the curved inclined foliation subsequently backfolding of asymmetric boudins in quartz veins occurred and a composite cleavage developed from shear bands and associated curved inclined foliation dextral asymmetric extensional shear bands were developed at a later stage when the folded quartz veins had attained tight to isoclinal geometries

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

garnet rotation and the development of axial plane crenulation cleavage rotated helicitic garnets syntectonically overgrowing axial plane crenulation cleavage on the limbs of folds show the opposite sense of rotation to that undergone by the folded foliation during the development of the fold the garnet rotation is inconsistent with simple minded shear models for the development of the crenulation cleavage and it is useful to consider this problem in order to understand the development of crenulation cleavage better various models are considered in an attempt to explain both garnet rotation and cleavage morphology earlier models were based on the assumption that garnet rotation is driven by shear parallel to s2 they were mostly unsatisfactory but one involving migration of the crenulation hinges is viable when combined with other models described here the new models proposed here are based on the assumption that garnet rotation is driven by shear on the crenulated surface s1 the new foliation s2 is considered to be a passive structure at least in the early stages of its development these models satisfactorily explain garnet rotation and development of the cleavage including differentiation and they can be used to predict the morphological evolution of the cleavage microstructure as it should be preserved in garnets comparison of observed and predicted helicitic structures strongly supports the proposed models evidence is presented to show that where a garnet has an se that is a schistosity and an si that is a crenulation cleavage the schistosity can have developed by unfolding of the crenulations

great slave lake shear zone nw canada mylonitic record of early proterozoic continental convergence collision and indentation abstract great slave lake shear zone in the nw canadian shield is an excellent example of the kinematic magmatic and thermal evolution of a crustal scale shear zone associated with a collisional continental boundary it is a 25 km wide corridor of granulite to lower greenschist facies mylonites and cataclastic fault rocks developed in the deep seated parts of an early proterozoic 2 0 1 9 ga magmatic arc constructed on the upper rae plate at the contact between the archean slave and rae continents the rocks of great slave lake shear zone the thelon magmatic arc and the taltson magmatic zone are all components of the same magmatic arc but their geological histories reflect different aspects of the continental interaction

shape fabrics of particles in low concentration suspensions 2d analogue experiments and application to tiling in magma abstract jeffery s equations ascribe a theoretical cyclic nature to the shape fabric of non interacting rigid particles immersed in a viscous fluid undergoing simple shear flow this theoretical behaviour is confirmed at low shear strains 5 first experiment 134 identical particles or 1 second experiment 178 particles with two size classes then become stable at 17 first experiment and at more than 50 second experiment of the population of particles due to the contribution of the tiled particles the shape fabric becomes asymmetrical in its orientation distribution with a maximum lying above the shear plane the latter result provides a new shear sense indicator in addition to the statistical determination of the tiled features the study also suggests that crystalline fabrics in magmas could be acquired at high melt fractions i e early in the crystallization history of the magma

hydro isostasy and the sea level isobase of 5500 b p in north queensland australia abstract previous studies of holocene sea level in north queensland have been based on a variety of sea level related deposits with interpretations of mid holocene levels ranging from near zero up to 4 m above present we report data from 8 carefully controlled new sites located from the palm group northwards and extending into the gulf of carpentaria field evidence is from coral reef flats and prograded coastal deposits the highest sea level on inner shelf islands and mainland coast occurred 5500 yrs ago the results of this and of certain previous studies are reduced to a common reference surface or isobase which varies systematically in elevation across the region the isobase correlates strongly with predicted hydro isostatic deformation caused by postglacial sea level rise

the behaviour of deformable ellipsoidal particles in three dimensional slow flows implications for geological strain analysis abstract eshelby s equations governing the motion of a viscous inclusion embedded in a matrix of contrasting viscosity are solved numerically for arbitrarily shaped and arbitrarily oriented ellipsoidal particles the theory has important implications for geological strains and strain analysis specifically it predicts that particles more competent than their matrix will have deformed shapes with larger k values than equivalently shaped and oriented passive markers the effect is significant even for viscosity ratios as low as r 1 5 and increases with increase in r for general applications numerical solutions must be sought nevertheless there are useful exceptions 1 1 the two dimensional deformed shape of viscous particles can be computed graphically provided the matrix strain is irrotational pure shear and the section ellipse is a principal plane of the particle ellipsoid for sections through a three dimensional system with arbitrarily oriented particles this method and those based on sections through an elliptic cylinder is inaccurate the reliability is further diminished for simple shear 2 2 irrotational deformations in three dimensions can be computed on transformed flinn plots if the particle or average particle axial orientations are parallel with the applied flow similar diagrams may be used to make independent estimates of viscosity contrasts in polymict conglomerates

strain insensitive preferred orientation of porphyroclasts in mont mary mylonites abstract the shape preferred orientation spo of porphyroclasts was determined in high temperature mylonites the porphyroclasts approach rhomboidal sillimanite or elliptical garnet plagioclase sillimanite shapes and exhibit aspect ratios r as high as 11 particles with r 3 are dominantly rhomboidal the long axis of the best fit ellipse defines a very strong spo inclined at 5 10 to the mylonitic foliation in an antithetic sense with respect to the shear direction this angle is independent of r the inclination of the long sides of rhomboidal sillimanite increases from 10 to 20 with decreasing r in contrast the short sides have a constant orientation of 15 to 17 irrespective of r and are parallel to extensional crenulation cleavage low aspect ratio mainly elliptical objects show low intensity spo close to the shear plane the two spos appear strain insensitive in the case of r r 3 a stable position is acquired this is not explained by any of the current theoretical and experimental models of spo

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

a microstructural indicator of shear sense in volcanic rocks and its relationship to porphyroblast rotation in metamorphic rocks an asymmetrical arrangement of microfolds in flow layering adjacent to phenocrysts indicates the sense of shear and is a potential indicator of the local flow direction in flow layered volcanic rocks this microstructure is analogous to a similar arrangement of microfolds around rotated porphyroclasts in some metamorphic rocks it is also relevant to the incorporation of inclusion trails in porphyroblasts that grow while undergoing rotation relative to the matrix foliation suggesting that asymmetrical microfolds may form outside porphyroblasts during their growth and relative rotation asymmetrical microfolds adjacent to garnet porphyroblasts have been observed in some metamorphic rocks

the strain path and emplacement mechanism of lava flows an example from salina southern tyrrhenian sea italy abstract a lava flow from salina southern tyrrhenian sea consists of subcircular to ellipsoidal basaltic enclaves dispersed in a dacitic host a 2d strain and kinematic analysis of the enclaves has been performed in order to determine a the relative contribution of the coaxial and non coaxial components to the bulk flow deformation b the flow vorticity wk c the strain path and d the mechanism of flow emplacement the axial ratio r f and the angle f between the long axis of the enclaves and the transport direction have been measured in 196 sites located at different distances from the vent in the near vent zone whereas further from the vent values were always larger than 1 ranging from 1 6 in the near vent zone to 1 at the front values were between 0 2 at the back and 2 6 at the front wk was between 0 13 and 1 and increased from the back to the front the enclaves result from the injection of basalt into dacite most of the deformation was acquired during the lava flow emplacement and not during the rise in the conduit plug flow the strain path depicted by the enclaves is consistent with that resulting from experimental analogue models and reveals that the lava suffers lateral extension near the vent further from the vent the lava deforms according to an ideal non coaxial model the lava emplacement is mainly controlled by the gravity evidence of deformation induced by the magma pressure is lacking near the vent the lava behaves as a hyperbolic flow whereas at the front it behaves as a simple shear flow the mechanism of flow emplacement is consistent with a mixed viscous gliding spreading transport model at the back and with a viscous gliding model at the front

late holocene higher sea level indicators from eastern australia abstract new age data from intertidal organisms exposed on coastal cliffs in northern new south wales suggest that in that area sea level was slightly more than 1 m higher about 3420 yrs b p and may have fallen to its present level since 1780 yrs b p these findings if regionally significant are important because they indicate that the tidally constructed zonations of organisms on high energy rocky coast could provide a more precise record of sea level behaviour than the study of constructional geomorphic features often related to storm events such as beach ridges chenier plains tidal deltas etc or mangrove peats

great slave lake shear zone canadian shield reconstructed vertical profile of a crustal scale fault zone abstract the great slave lake shear zone gslsz of the northwestern canadian shield a 25 km wide early proterozoic transcurrent dextral mylonite zone is a type example of a crustal scale fault zone profile with time 1 1 the metamorphic grade decreased from granulite to greenschist facies 2 2 the locus of high strain narrowed and jumped laterally abandoning relatively older mylonites progressively younger mylonites represent both cooler temperatures and lower pressures thus the sequence of narrowing mylonite belts represents a series of progressively shallower seated sections through the gslsz 3 3 deformation evolved through the brittle ductile transition initially producing non dilational penetrative breccias followed first by discrete non dilational faulting and subsequently by dilational quartz stockworks developing crustal scale shear zones grow to an optimum width dictated by the requirement of minimum geologically reasonable strain rates for given conditions of wall rock rheology and displacement rate independent of variations in relative plate motion mature shear zones change width and migrate laterally as a function of inferred thermally activated rheological changes within the wall rocks

significance of crustal scale shear zones and synkinematic mafic dykes in the nagssugtoqidian orogen sw greenland a re examination the published accounts of the structural geology and tectonic evolution of the early proterozoic nagssugtoqidian orogen sw greenland require modification in several fundamental respects the geometry of the orogen has been attributed to important displacements on major conjugate shear zones and thrust zones from new field observations we are unable to confirm that crustal scale shear zones have played an important role in nagssugtoqidian tectonics the dextral component of conjugate shear zones is demonstrably sinistral and transpressive strike slip shear zones are incipient and a major thrust zone within the orogen cannot be confirmed at its projected inland location the sinistral strike slip nordre stromfjord shear zone is an order of magnitude smaller than previously thought it comprises an array of non linked segments of annealed mylonite and cannot have accommodated large displacements the dextral itivdleq shear zone is characterised by heterogeneous sinistral noncoaxial flow but compared with deformation elsewhere in the orogen it is not a large scale zone of strain localisation ikertoq thrust zone is not an orogen scale shear zone but appears to be part of a large scale rheological boundary application of an en relais fracture array model to what is classically identified as the kanga miut mafic dyke swarm suggests that the sinistral vorticity determined throughout much of the nagssugtoqidian orogen is detectable in the archean foreland up to 150 km south of the orogenic front

fabric development as the key for forming ductile shear zones and enabling plate tectonics abstract lithospheric deformation on earth is localized under both brittle and ductile deformation conditions as high temperature ductile rheologies are fundamentally strain rate hardening the formation of localized ductile shear zones must involve a structural or rheological change or a change in deformation conditions such as an increase in temperature in this contribution i develop a localization potential that quantifies the weakening associated with these changes the localization potential corresponds to the increase in strain rate resulting from that change under constant stress conditions i provide analytical expressions for the localization potential associated with a temperature increase grain size reduction an increase in water fugacity melt content or the abundance of a weak mineral phase i show that these processes cannot localize deformation from a mantle convection scale 103 km to a ductile shear zone scale 1 km to achieve this is it necessary to invoke a structural transition whereby the weak phase in a rock forms interconnected layers this process is efficient only if one phase is much weaker than the others or if the weakest phase has a highly non linear rheology micas melt and fine grained aggregates unless dry rheologies are used have the necessary characteristics as none of these phases is expected to be present in the dry lithosphere of venus this concept can explain why venus unlike the earth does not display a global network of plate boundaries the diffuse plate boundary in the central indian ocean may be as yet non localized because serpentinization has not reached the ductile levels of the lithosphere

depositional model for a chenier plain gulf of carpentaria australia the southern coast of the gulf of carpentaria northern australia consists of a broad chenier plain which is comparable in size and morphology to those reported on the coasts of surinam and south western louisiana the carpentaria chenier plain has at some locations prograded over 30 km since the middle holocene by deposition of low tide muds over subtidal muds during periods of increased sediment input by the rivers chenier ridges are formed during periods of reduced sediment flux by wave induced sorting and redistribution processes an alternation of increased and decreased sediment flux from fluvial sources has occurred several times during the upper holocene such variation in sediment supply is believed to be related to temporal fluctuations in rainfall over the drainage basin which surrounds the southern and eastern gulf

depositional model of a macrotidal estuary and floodplain south alligator river northern australia the south alligator river northern territory of australia has a macrotidal estuary tidal influence spring tidal range 5 6 m at the mouth extends 105 km up the channel it is dominated by freshwater in the wet season december april with a salt wedge near the mouth but is well mixed and becomes saline throughout the dry season the tidal channel can be divided into four different channel types an estuarine funnel a sinuous meandering segment a cuspate meandering segment in which the inside of bends are pointed and an upstream tidal channel the distribution of morphologically defined land classes and morphological units within each land class on the floodplain flanking the estuary differs from one channel type to another several stratigraphic and morphostratigraphic units have been recognized from drill holes on the coastal and deltaic estuarine plains and a model of development is proposed on the basis of extensive radiocarbon chronology and palynology the coastal plain has prograded with most rapid sedimentation between 5000 and 3000 yr bp a similar pattern of progradation is identified in the estuarine funnel in the sinuous segment of the estuary the channel has migrated laterally across the floodplain previous channel positions are indicated by palaeochannels and the meander tract is occupied by laminated channel sediments within the cuspate segment there are numerous sinuous palaeochannels on the plains in the upstream segment the channel and palaeochannels have long straight reaches with irregular bends and discontinuous levees and channel avulsion is indicated mangrove mud is a widespread stratigraphic unit throughout the plains the initial phase of development is a transgressive phase 8000 6800 yr bp when mangrove forests extended landwards into a pre existing valley as sea level rose as sea level stabilized the transgressive phase was followed by a widespread mangrove phase termed the big swamp 6800 5300 yr bp the mangrove forests disappeared from most of the plains as vertical accretion continued and were replaced by grass and sedge covered floodplains during the sinuous phase about 5300 2500 yr bp the channel migrated laterally and eroded the deltaicestuarine plain and deposited lateral accretion deposits laminated channel sediments part of the channel of the south alligator river has then progressed from sinuous to cuspate in form and erosion of river banks has occurred transgressive and big swamp phases occurred under rising and stabilizing sea level respectively later morphodynamic channel adjustments occurred under conditions of stable sea level the depositional model has direct application to other estuaries in northern australia and may be applied to other areas where sea level change has been similar

ductile thrusting at mid crustal level southwestern grenville province the northwestern boundary zone of the central metasedimentary belt grenville province in the haliburton area ontario is a stack of alternating tonalitic and syenitic crystalline thrust sheets transported toward the northwest on out of sequence upper amphibolite facies ductile thrust zones during the grenvillian orogeny at 1060 ma approximately 100 ma after the initiation of thrusting in the underlying central gneiss belt kinematics of the deformation are complex predominant northwestward thrusting was at least partly coeval with subordinate northeastward thrusting late synmetamorphic extensional shears cut both thrusts and thrust sheets minor late thrusting on discrete ductile shear zones postdates the extensional structures belts of mechanically weak pelite appear to have localised the thrust sheets highly mobile marble behaved as a relatively low viscosity fluid during transport able to intrude and erode more competent wall rock

deep crustal break back stacking and slow exhumation of the continental footwall beneath a thrusted marginal basin grenville orogen canada abstract granulite to upper amphibolite facies ductile thrusting in the central gneiss belt grenville orogen ontario represents the tectonic shortening of a continental scale footwall beneath the thrust emplaced central metasedimentary belt during the closure of a postulated back arc basin ca 1 19 1 18 ga break back stacking in the footwall occurred at mid to deep crustal depths ca 35 km within tectonically thickened ca 70 km continental crust and culminated with renewed thrusting at the base of the overlying central metasedimentary belt ca 1 08 1 05 ga the individual mylonite belts which constitute the ductile thrust zones and the scale of penetrative deformation of the intervening crystalline thrust sheets are comparable with the largest known examples of high grade thrust belts elsewhere they reflect the large scale thermal and theological boundary conditions of the deformation flow within individual thrust zones may reflect local boundary conditions such as the rheological behaviour of older thrust sheets and the geometry of interfaces within the thrust stack restoration of the thickness of erosionally removed crustal overburden by break back thrusting may retard the rates of exhumation and cooling of a mid to deep crustal thrust stack

natural rotated inclusions in non ideal shear abstract kinematic analysis of rotated winged inclusions is often couched in terms of ideal simple shear with reference to a specific model based upon porphyroclasts of circular section however many natural winged inclusions are not porphyroclasts commonly their geometries as well as the orientation distribution of the inclusions themselves reflect the non ideal nature of the shearing deformation during which they formed stair stepped sigma shaped geometries may reflect the immaturity of a structure developed in non ideal shear or a mature structure developed in ideal simple shear stair stepped delta shaped geometries indicate that deformation approximated to ideal simple shear in plane delta shaped geometries and skewed inclusion orientation distributions are indicators of non ideal shear

variability of holocene sealevel history along the southwestern coast of australia evidence for the effect of significant local tectonism abstract holocene sealevel records for the interval 7400 14c yrs b p to the present were determined from accretionary sequences at three separate localities within the perth basin of southwestern australia the three records all differ dramatically despite an overall separation of sites of only 170 km at the northernmost site the record shows sealevel was ca 1 0 m below present msl 7415 14c yrs b p and that it gradually rose to reach its present position ca 5100 14c yrs b p with no evidence for a raised sealevel nor for significant oscillations the record at the middle site shows a steadily declining sealevel from an initial high of ca 2 5 m at 6400 14c yrs b p and is consistent with eustatic hydroisostatic interpretations the southernmost site shows the most complex sealevel history of the three with a still stand at 2 or 3 m below present between 7000 and 5500 14c yrs b p an abrupt rise to 3 or 4 m above present msl between 4800 and 3800 14c yrs b p followed by a decline with sealevel reaching its present position ca 2800 14c yrs b p considered jointly the three differing sealevel records imply significant local tectonism during the holocene along the southwestern coast of australia the data further indicate that this coast can no longer be considered as tectonically stable as previously assumed and consequently the sealevel evidence can no longer be considered to reflect only eustatic and eustatic hydroisostatic influences

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

detailed documentation of a holocene sea level record in the perth region southern western australia abstract holocene prograded coastal sequences at becher rockingham southern western australia contain a detailed record of sea level over the last 6400 yr radiocarbon dating and use of a distinct stratigraphic indicator as a sea level marker permit reconstruction of sea level history and suggest that the sea was at least 2 5 m above present datum about 6400 yr b p before falling to its present level no evidence was found for eustatic fluctuations of the scale proposed by r w fairbridge 1961 in physics and chemistry of the earth l h ahrens f press k rankema and s k runcorn eds vol 4 pp 99 185 pergamon oxford the sea level record preserved on this coast can be explained by hydro isostasy tectonism or eustasy acting individually or in concert without a fixed reference point or analogous data from other locations a firm conclusion on which mechanism s has have operated could not be reached published sea level data from this and other coasts are often insufficiently detailed to compare with this study application of the techniques of this study to analogous sedimentary sequences elsewhere will provide data of comparable accuracy that would contribute to a more precise understanding of relative sea level movements in the late quaternary

new evidence for episodic post glacial sea level rise central great barrier reef australia abstract we present an extensive database of 364 radiocarbon dates from coastal and marine sediments of the central great barrier reef gbr shelf of which 110 are previously unpublished the elevation data have been reduced to a common datum australian height datum ahd and the various sources of error have been assessed using modern lithological and biological relationships with sea level the elements of the radiocarbon database have been converted into sea level indicators the upper bound of the assembled dataset corresponds to a best estimate sea level curve and the full dataset provides a narrow envelope for sea level rise on the gbr shelf for the last 11 12 kyr not including hydro isostatic crustal flexing the envelope is consistent with episodic rise in post glacial sea levels the rising post glacial sea level probably included stillstands or minor falls at ca 45 m ahd at ca 10 5 kyr b p 5 m 7 8 kyr b p 2 m ca 6 kyr b p and 1 7 m 5 5 kyr b p there is evidence for a significant fall in sea level between stillstands at 11 m 8 5 kyr b p and 17 m 8 2 kyr b p stillstand durations apparently ranged between the vertical spread in the derived sea level data is very wide the use of shell material for dating seems unreliable and prone to large and unpredictable errors data from bulk mangrove muds appear reliable for determination of ancient sea level but may at times result in sea level being placed up to 4 m below the true level in situ biogenic carbonates such as preserved oyster beds and coral micro atolls are the most reliable indicators of sea level position while deposits of mangrove mud give a useful first order approximation of ancient sea levels caution should be used in drawing sea level curves from few data points we conclude that the post 11 12 kyr b p relative rise in sea level was episodic on the central gbr continental margin more data are required to define clearly sea level change up to ca 20 m at 9 kyr b p

stable positions of rigid objects in non coaxial flow a study in vorticity analysis abstract distortions of a homogeneous fabric which occur around rigid objects in rocks deformed by non coaxial ductile flow are useful to determine the sense of shear but also contain information on other aspects of the flow rigid objects in a non coaxial flow fall into two categories those which are permanently rotating and those which can reach stable positions at high finite strain the orientation of such immobilized objects with respect to eigenvectors of instantaneous flow is a function of the vorticity number of the flow the ratio of instantaneous stretches and the axial ratio of the object in naturally deformed rocks immobilized rigid objects may be recognized from the geometry of the surrounding fabric tails of recrystallized material around porphyroclasts in a mylonite rotate towards parallellism with the extensional eigenvector of the flow and the shape of tails reflects the rotational behaviour of the porphyroclast the axial ratio of immobilized porphyroclasts and their orientation with respect to the tails can theoretically be used to determine the vorticity number of the flow and deviations from isochoric plane strain in practice such an analysis is as yet difficult but a tentative example is given of the way in which the vorticity number can be calculated from a population of feldspar porphyroclasts in a quartzite mylonite from the french pyrenees

sea level history 45 000 to 30 000 yr b p inferred from benthic foraminifera gulf st vincent south australia surficial sediments of gulf st vincent south australia are predominantly bioclastic cool temperate carbonates benthic foraminifera are abundant and distribution of species is closely related to water depth for example massilina milletti is most common at depths ca 40 m while discorbis dimidiatus is characteristics of shallow subtidal environments elphidium crispum a shallow water species and e macelliforme favoring deeper water provide a useful numerical ratio their logarithmic relative abundance in the sediment size fraction 0 50 0 25 mm correlates strongly with water depth vibrocores sv 4 and sv 5 recovered undisturbed sections of quaternary strata from the deepest part ca 40 m of gulf st vincent amino acid racemization and radiocarbon age determinations show that late pleistocene sections of the cores were deposited over the time ca 45 000 to 30 000 yr b p species of fossil foraminifera recovered from these sections are mostly extant in modern gulf st vincent thus allowing paleoecological inferences of late pleistocene sea levels these inferred sea level maxima can be correlated with those determined from study of huon peninsula coral reef terraces initial estimates of tectonically corrected sea levels for transgressions in gulf st vincent at 40 000 and 31 000 yr b p are 22 5 m and 22 m respectively the intervening regression lowered sea level to 28 m

winged inclusions pinch and swell objects during high strain simple shear abstract in this study we compare natural examples of isolated pinch and swell objects which have been deformed in simple shear with results of high strain numerical models such structures which have geometrical similarities with clast systems and rolling structures have been called winged inclusions we suggest a new mechanical explanation for the evolution of winged inclusions which form when pinch and swell shaped objects consisting of a core and pre existing wings rotate out of the shear plane the viscosity ratio the stress exponent and the shape of the winged inclusion have a significant influence on the rotation rate the rotational behaviour of winged inclusions differs significantly from the rotational behaviour of simple elliptical objects with comparable aspect ratios during the early stages of formation winged inclusions may resemble mirror images of sigmoids and misinterpretations may lead to a wrong determination of the shear sense during progressive shear to large strains the structures may be approximately described as consisting of a pulsating rotating core and thinning wings that rotate with different rates during rotation of the structure the core of the winged inclusions records an overall decrease of the aspect ratio influencing the rotation rate of the inclusion the wings are subject to ptygmatic folding when they rotate through the field of instantaneous shortening and may unfold again in the field of instantaneous stretching during ongoing shearing the wings on both sides of the core rotate with the core may change their positions and finally unfold after rotation about 180 resulting again in a pinch and swell shaped object therefore winged inclusions record ambiguous information about the finite strain rotating winged inclusions create a significant flow perturbation in the matrix resulting in nucleation of folds refolding and propagation of shear zones rootless intrafolial folds with opposing closures have strong geometrical similarities with winged inclusions and we therefore speculate that the formation of winged inclusions might be an efficient mechanism to produce rootless intrafolial folds

chronological studies of the quaternary marine sediments of northern spencer gulf south australia abstract four dating methods have been used to obtain chronological information about holocene and pleistocene coastal marine sediments in south australia and to check the stratigraphic reliability of each dating technique estimates of accumulation rates for holocene seagrass bank deposits vary according to the time period over which they are averaged the estimates vary from 2 0 to 2 7 mm yr 1 for measurements by the pb 210 method averaged over about 100 years to 1 4 0 2 mm yr 1 for c 14 derived measurements averaged over a period of 1000 7000 yrs radiocarbon age determinations on carbonate and organic fractions do not date the true sediment age shells shell fragments and calcareous fines predate the sediment whereas organic and seagrass detritus postdate it by dating sample pairs their age can be adequately defined thermoluminescence age estimates correlate well with available c 14 ages where the sediment grains have experienced good exposure to sunlight prior to deposition amino acid racemization and thermoluminescence measurements indicate a late pleistocene age of ca 110 000 yrs for the mambray formation of spencer gulf amino acid racemization data also support a correlation with the late pleistocene glanville formation of adelaide

diamond growth from c h n o recycled fluids in the lithosphere evidence from ch 4 micro inclusions and δ 13 c δ 15 n n content in marange mixed habit diamonds abstract mixed habit octahedral cuboid diamonds from the marange alluvial deposits in the eastern zimbabwe craton have high nitrogen and hydrogen contents that provide an opportunity to evaluate diamond growth mechanisms and c n h o bearing fluids in the lithospheric keel light grey cuboid sectors with hydrogen containing defects trap abundant dispersed ch 4 inclusions raman peaks at 2917 cm 1 associated with graphite raman peaks at 1580 cm 1 clear octahedral sectors are richer in nitrogen and free of any such inclusions core to rim co variations of 13 c 15 n and n content can be explained by a mixing trend between earlier fluids that are ch 4 rich and later fluids that are more co 3 or co 2 rich marange diamonds have limited overall 13 c variation but do show fractionation during growth towards higher 13 c values this trend can be explained by diamond precipitation from mixed ch 4 and co 2 fluids where isotopic fractionation occurs as the amount of fluid wanes calculated 15 n values for diamond source fluids evolving in this manner are between 2 3 and 6 4 these n isotopic compositions require ch 4 rich and co 3 co 2 rich end member fluids to have a recycled metasedimentary component perhaps introduced with subduction of eclogite

spatial and temporal variability in the holocene sea level record of the south australian coastline abstract studies of past sea levels based on radiocarbon dated field samples suffer variously from compilation of information from disparate locations and the imprecise nature of the dated indicators geographic segregation and systematic elimination of poor samples from time depth data sets leads to improved interpretation of holocene sea level history an example is presented from southern australia where this is achieved through selection of higher resolution palaeoenvironmental indicators separation of transgressive from regressive populations and geographic regionalisation of data in southern australia fossil sea level indicators preserved in prograding coastal plain settings include seagrass sandflat mangrove samphire and chenier ridge organo sedimentary remains these provide sea level time depth data points with a variety of elevational and dating errors preserved organic remains at the transition from posidonia seagrass to intertidal sandflat environment and from sandflat to avicennia mangrove environment provide the most precise local data for tracing sea level change time depth plots of 233 dated sea level indicators from south australia generate a broad sea level envelope tracing the southern australian transgression from 10 000 to ca 6000 radiocarbon years bp followed by a more or less consistent level to the present finer details of sea level behaviour are only apparent after systematic selection separation and regionalisation of the data the data indicate a very rapid sea level rise in the early holocene at about 16 mm year reaching present levels at 6400 years bp this was followed by regionally variable regression and emergence of the land of 1 3 m a process that continues to the present the systematic increase from 1 to 3 m in the elevation of the 6400 year bp highstand with distance away from the shelf margin is consistent with a hydro isostatic origin for the emergence as predicted by geophysical models

sense and non sense of shear reloaded abstract this paper reviews the geometrical and mechanical evolution of selected groups of kinematic indicators that are frequently used for inferring large scale geodynamics but are prone to ambiguous shear sense interpretations i flanking folds and shear bands are complex structures because under general shear conditions co rotating secondary shear zones can experience either syn or antithetic slip leading to extensional or contractional offsets on the other hand counter rotating secondary shear zones can exhibit either extensional or contractional offsets but always experience synthetic slip ii boudinaged layers may display both syn and antithetic offset across the interboudin surfaces in addition to the flow type the initial orientation of interboudin surfaces strongly influences the sense of slip under coaxial flow conditions and with high strength contrast between the boudinaged layer and the matrix domains of layer oblique parallel interboudin surfaces can form by chance and their local occurrence may hence lead to misinterpretations of shear zone kinematics in particular if the number of observable boudins is small if the viscosity contrast between the boudinaged layer and the matrix is low domino boudins may strongly deform internally during shearing so that in contrast to flanking structures antithetic slip along interboudin surface may lead to a marked normal drag resulting in shear band boudinage geometries that appear to have formed during flow with an opposite shear sense iii winged inclusions are pinch and swell shaped objects rotating into the shear direction after several revolutions these structures can resemble b type clasts or clasts with stair stepping that formed during shear flow with the opposite shear sense in this paper new and published examples of these ambiguous shear sense indicators are discussed and interpreted we give some guidelines for the correct interpretation of these structures with the caveat that if marker lines and their deflections are not well preserved these shear sense criteria are not always reliable kinematic indicators

the deformational behaviour of bimineralic limestone halite aggregates abstract a compositional foliation banding develops within synthetic limestone halite aggregates experimentally deformed in axially symmetric compression and in simple shear the strength of the bulk aggregate decreases as the foliation becomes stronger foliation weakening in calcite rich specimens the development of foliation starts with the formation of cataclastic shear systems in calcite domains between isolated halite domains with increasing deformation halite is sheared into these systems the halite domains coalesce into halite rich shear systems and accommodate an increasing amount of the bulk deformation the bulk strength of bimineralic aggregates at a given amount of strain increases with decreasing halite content the influence of halite on the bulk strength is much greater than would be expected from its volume fraction and becomes dominant with increasing deformation due to the development of the foliation it is postulated that such processes also occur during natural deformation of polyphase rocks competent clasts within a weaker ductile matrix showing no recrystallization differ in shape and rotational behaviour from recrystallizing clasts such as feldspar augen these competent clasts denoted as type clasts may cause problems in deducing the sense and direction of shear when formed as almost exact mirror images of type recrystallizing clasts

rotation rate versus growth rate of syntectonic porphyroblasts the controlling parameter of the shape of the inclusion trail abstract the development of curved inclusion trails within syntectonic porphyroblasts has long been explained in the light of the rotation of the porphyroblast with respect to the external foliation the present paper shows that both the rate of rotation and the growth rate of the porphyroblast play a role in the development of the inclusion pattern an equation is derived involving the ratio of growth rate and rotation rate that enables computation of the rotation rate from natural porphyroblasts and also offers a measure of the noncoaxiality of a deformation

efficient use of the velocity gradients tensor in flow modelling passchier c w 1987 efficient use of the velocity gradients tensor in flow modelling tectonophysm 136 159 163 for models of fabric development in rocks with vorticity as a variable parameter the choice of an unsuitable reference frame for instantaneous flow can hamper clear presentation of results the orientation of most fabric elements which develop in deforming rocks is attached to some principal direction of instantaneous flow syntaxial fibres crystallographic preferred orientation patterns steady state foliations and immobilised rigid objects seem to orient themselves in a fixed position relative to instantaneous stretching axes di while shape fabric elements and mica preferred orientation approach parallelism with the extensional apophysis i of the flow models for development of such fabric elements benefit from a choice of reference frame attached to either d or i

the holocene non tropical coastal and shelf carbonate province of southern australia abstract carbonate dominant sediments are currently forming and accumulating over the extensive marine shelf of the passive margin of southern australia a dearth of continental detritus results from both a very low relief and a predominantly arid climate the wide continental shelf is bathed by cold upwelling ocean waters that support luxuriant growths of bryozoans and coralline algae together with sponges molluscs asteroids benthic and some planktonic foraminifera the open ocean coast is battered by a persistent southwest swell resulting in erosion of calcrete encrusted pleistocene eolianites much sediment is reworked and overall shelf sedimentation rates are low high energy microtidal beach dune systems occur between headlands and along the very long ocean beach in the coorong region the northern more arid coastal areas also contain saline lakes that precipitate gypsum from infiltrated sea water and display marginal facies of aragonite boxwork to fenestral carbonate crusts with stromatolites and tepee structures in contrast the southern seasonally humid coorong region has a predominantly continental groundwater regime where sulphate is rare and the high summer evaporation precipitates dolomite magnesite and aragonite muds fenestral crusts breccias tepees and some stromatolites are also present st vincent and spencer gulfs both afford some protection from ocean swell but tidal amplitude and currents increase and a depth and inundation related zonation of plants and animals is established muddy carbonate sand accumulates on the sea floor below 30 m where filter feeding bryozoans bivalves and sponges dominate in shallower regions seagrass meadows contain a rich fauna that results in rapid accumulation of an unsorted muddy bioclastic sand mangrove woodlands backed by saline marsh with cyanobacterial mats are common and accumulate mud rich and gastropod bearing sediment as tidal amplitude and desiccation increase northward into both gulfs a supratidal zone bare of vegetation sabkha becomes the site for deposition of gypsum rich and fenestral calcitic mud

smooth or oscillating late holocene sea level curve evidence from cross regional statistical regressions of fixed biological indicators abstract what if any is the pattern of change of the late holocene sea level curve if a common pattern exists can it be better discerned in the non glaciated tectonically stable regions of the southern hemisphere and is sea level data more reliable from one type of marine sample than another to begin an investigation of these questions we present a review of regressing time elevation plots from the low to mid latitudes of the southern hemisphere based upon the differential between modern and past levels of various fixed biological indicators mainly calcareous tubeworms and corals stranded up to 2 m above present relative sea levels the sample sets come from our work in southeast australia and comparable work from north east australia the pacific islands and brazil we show that using evidence obtained from fixed intertidal tubeworm species there is no statistical exclusivity between the smooth and oscillating polynomials but corals are more problematic in situ tubeworm species with their reduced error bars in comparison to corals fulfil the condition of providing more robust results for statistical analysis regression curves based on these species point to cross regional similarities in the pattern of sea level movement of the last 6000 years across the lower latitudes of the southern hemisphere these statistical exercises while not able to yield definitive conclusions can highlight statistically equally likely alternative patterns of sea level movement which can then be tested by field evidence they can also give useful indications of the quality of sea level data obtained from different biological sources as in the difficulties in the use of corals compared to common intertidal tubeworm species

the role of intragranular fracturing on grain size reduction in feldspar during mylonitization abstract measurements of the size shape and orientation of k feldspar and plagioclase grains within a granitic mylonite in the kashio shear zone central honshu japan revealed that grain size was the most effective parameter controlling development of intragranular fracturing during mylonitization intragranular fractures are dominantly located near the centre of each grain and form preferentially along the 001 cleavage the grain size distribution of both feldspars is log normal with an average of 760 m the proportion of fractured grains expands dramatically to 100 as the grain size increases whereas few feldspar grains smaller than 300 m have been fractured during the mylonitization indicating that the fractures have preferentially developed in coarser grains furthermore the shape and shape preferred orientation of feldspar grains also affects the development of fractures the proportion of fractured grains not only increases up to 20 towards the extension direction but also rises slightly as the aspect ratio of feldspar grains increases it is therefore suggested that feldspar grains lying perpendicular to the extension direction may resist fracturing regardless of grain size unless their shape preferred orientations became sub parallel to the extension direction due to rotation or modification of their grain shapes during mylonitization the development of intragranular fractures could be statistically explained in terms of a fibre loading model although individual fractures may result from various fracture mechanisms

the age structure of a holocene barrier dune system and its implication for sealevel history reconstructions in southwestern australia abstract the leschenault peninsula in southwestern australia is a holocene retrograded barrier dune system the barrier separates an estuarine lagoon from the indian ocean and in holocene time the barrier has migrated over estuarine sediments deposited leeward of the dune system stratigraphic studies and radiocarbon dates indicate that the barrier has had a complex history resulting in composite internal structure the barrier is composed of three members each of which was emplaced during a discrete historical phase in the holocene when relative sealevel stood 1 at 2 or 3 m below present level between ca 5500 8000 14c yrs b p 2 3 or 4 m above present level about ca 3000 4800 14c yrs b p and 3 at present level ca 2800 14c yrs b p present the fact that the barrier still exists as a structure even though it has experienced such widely fluctuating sealevels indicates that rising and falling sealevels may not totally destroy barrier systems the sealevel history at leschenault peninsula also is at variance with studies of accretionary sequences elsewhere along the southwestern australian coast and suggests very localised tectonic influences a factor not fully explored in holocene sequences of the perth basin

strain analysis method using the maximum frequency of unimodal deformed orientation distributions applications to gneissic rocks abstract the effect of varying strain ratio r a on initially uniform and non uniform orientation distributions of passive marker lines is calculated the frequency graphs for uniform distributions have a unimodal form gaussian like distribution centered in the finite extension direction x of the strain ellipse the maximum frequency is related to the strain using non uniform distributions the frequency graph has a different unimodal pattern the difference between the measured strain ratio r with the maximum frequency and the true strain ratio r a to the initial distribution is quantified for different types of distribution the method is applied to samples of gneiss from southern spain using the orientation of tourmaline and feldspar lying in the schistosity plane with respect to the stretching lineation the strain of the marker distribution has been quantified and after distinguishing the initial type of distribution the true strain ratio of the whole rock in the schistosity plane can be estimated

analysis of deformation paths in shear zones the geometry of ductile shear zones can be used to solve problems of regional tectonics if the deformation path of material in the zones is sufficiently understood flow in many shear zones may have deviated from simple shear and consequently data on the final deformation state such as finite strain and volume change are insufficient for reconstruction of the deformation path even if flow parameters were constant during progressive deformation additional information on the flow vorticity number is also needed and can be obtained from fabric elements such as sets of folded boudinaged veins rotated porphyroblasts and blocked rigid objects mohr circle constructions are presented as a tool to calculate deformation parameters from fabric data to represent the deformation path graphically and to reconstruct flow parameters from the shape of this path if the vorticity number or the volume change rate changed during progressive deformation the deformation path can be partly reconstructed using sets of fabric elements which register mean and final values of these parameters

bounds on strain in large tertiary shear zones of se asia from boudinage restoration we have used surface balanced restoration of stretched boudinaged layers to estimate minimum amounts of finite strain in the mylonitic gneisses of the oligo miocene red river ailao shan shear zone yunnan china and of the wang chao shear zone thailand the layer parallel extension values thus obtained range between 250 and 870 we discuss how to use such extension values to place bounds on amounts of finite shear strain in these large crustal shear zones assuming simple shear these values imply minimum total and late shear strains of respectively 33 6 and 7 3 at several sites along the red river ailao shan shear zone for the wang chao shear zone a minimum shear strain of 7 4 is deduced assuming homogeneous shear would imply that minimum strike slip displacements along these two left lateral shear zones which have been interpreted to result from the india asia collision have been of the order of 330 60 km red river ailao shan and 35 20 km wang chao

the submarine quaternary stratigraphy of northern spencer gulf south australia abstract the seafloor morphology and lithology of northern spencer gulf south australia is related to successive transgressions and regressions accompanying glacial and non glacial periods vibrocoring has revealed a veneer of holocene bioclastics and a sequence of pleistocene marine strata which display varying degrees of pedogenesis oxidation decalcification and clay illuviation the contact between the holocene and pleistocene sediments is marked by either a thin alluvial or aeolian horizon or by a soil horizon of variable development the pleistocene marine strata have been assigned to four formations older pleistocene marine beds mambray fm false bay fm and lowly point fm based on superposition of lithofacies and intervening pedogenic horizons a sequence of slightly altered laminated lagoonal clays lowly point formation and bryozoan rich limestones false bay formation has been encountered in deeper parts of the gulf stratigraphically below these is a widespread weathered marine unit mambray formation which contains abundant remains of the bivalve anadara trapezia and the foraminifer marginopora vertebralis species absent from the present biota this unit in turn is underlain by a sedimentary sequence strongly altered by pedogenesis and clay illuviation older pleistocene marine beds its original marine character has been largely obliterated a dearth of fluvial gravels and sand from the vibrocores as well as evidence from palaeosols indicate that a predominantly semi arid to arid climate has persisted in the northern gulf region since ca 125 000 yrs ago and that there has been little subsequent terrigenous material transported to the gulf

new evidence for the holocene sea level high from the inner shelf central great barrier reef australia radiocarbon dates from fossil oyster beds of intertidal origin on magnetic island north queensland indicate that the local holocene maximum of relative sea level was attained no later than 5660 50 b p conventional uncorrected age and remained at 1 6 1 7 m above modern levels until 4040 50 b p given the tectonic stability of the area this implies that eustatic sea level remained at its holocene peak for at least ca 1600 yr the new high precision sea level data indicate sea levels 1 5 m higher than those of the same age inferred from buried mangrove deposits on the inner shelf in north queensland uncertainties in deriving relative sea level from such mangrove deposits may be a significant source of error in worldwide attempts to distinguish the eustatic and crustal warping components off relative sea level change especially in the tropics

v pull apart microstructures a new shear sense indicator abstract granitoids deformed in a low grade shear zone show conspicuous development of asymmetric pull apart microstructures in feldspars characterized by v shaped gaps between the separated fragments v pull aparts they occur beside active shear planes and result from rigid body rotation of one fragment relative to the other the shear sense in the adjacent flow surface can be easily determined through the asymmetry normally shown by v pull aparts where the fracture wall at a lower angle to the shear plane indicates which fragment has rotated synthetically to the adjacent shearing another diagnostic feature is the foliation deflection that occurs adjacent to the rotated fragment the v shaped gaps are infilled by recrystallized quartz mica aggregates showing quartz c axis patterns indicative of strong participation of crystal plastic processes in these domains evidence of crack seal by precipitation c axes parallel to the direction of separation have also been found the rigid body rotation indicated by these microstructures worked as a mechanism of removal of protruding porphyroclast edges enabling the smoothing of the shear planes rigid body rotation should operate in circumstances where other mechanisms such as dissolution or crystal plasticity did not succeed in eliminating undulations along the shear planes

the stratigraphy of coastal carbonate banks and holocene sea levels of northern spencer gulf south australia abstract stratigraphic and chronologic studies of the coastal sediments of northern spencer gulf in the vicinity of redcliff are described two pleistocene marine units are recognised beneath an extensive holocene peritidal sequence the holocene sequence is dominated by sediments of the posidonia australis seagrass facies which form a distinctive carbonate bank fringing the coastline peritidal sedimentation commenced prior to 6600 radiocarbon yrs b p and a 2 5 m higher relative sea level existed from about 6000 until around 1700 yrs b p the subsequent relative fall to present level probably resulted from local tectonic uplift after the regression mangrove and samphire colonization and beach ridge progradation occurred over the former seagrass bank