seismic structure of the mid atlantic ridge 8 9 s 1 the mid atlantic ridge at 8 9 s is characterized by a transition from axial valley to axial high and recent episodes of ridge jumping and ridge propagation we present constraints on the structure of 0 4 ma crust in this region on the basis of the analysis of wide angle seismic data from a grid of profiles across and parallel to the current and abandoned spreading centers a 350 800 m thick oceanic layer 2a interpreted as high porosity extrusive basalts is underlain by a 2 0 2 5 km layer 2b with velocities which increase with age and decrease in the vicinity of the pseudofaults layer 3 velocities are uniform across the area except for a possible localized anomaly at the ridge axis the crustal thickness varies from 6 7 km near the pseudofaults formed by ridge propagation to 9 10 km at the segment center of the recently 0 3 ma abandoned spreading center seismically determined crustal thickness and density variations and age related lithospheric cooling can plausibly account for all observed variations in gravity across the area and there is no requirement for the thicker crust at the segment center to be underlain by hot mantle the transition from axial valley to axial high occurs at a crustal thickness of 8 km

lithospheric structure across oblique continental collision in new zealand from wide angle p wave modeling 1 oblique convergence between the australian and pacific plates in south island new zealand has resulted in crustal thickening and distributed deformation within both plates we measure this thickening and image the deformation with seismic wide angle data along a 600 km long transect that spans the plate boundary p wave arrival times from 34 000 rays are used to construct a two dimensional model for seismic velocity with depth crustal velocities average 6 1 and 6 2 0 23 km s for the australian and pacific sides of the boundary respectively upper mantle velocities average 8 1 0 25 km s distributed deformation is indicated by the following observations a reduction in upper crustal and midcrustal velocities by 4 west of the plate boundary ascribed to flexural bending stresses a velocity reduction of 8 immediately east of the alpine fault linked to high pore fluid pressures 17 km of crustal thickening to form a 44 1 4 km deep crustal root that is offset 10 20 km se of the highest mountains a velocity reversal below the midcrust in the eastern part of the crustal root caused either by heating or an artifact from seismic anisotropy strong thickening of a 7 0 0 4 km s fast lower crust within the crustal root and a low velocity zone in the australian upper mantle due to sampling the slow orientation of upper mantle anisotropy

record of plate boundary metamorphism during gondwana breakup from lu hf garnet geochronology of the alpine schist new zealand

quartz fabrics in the alpine fault mylonites influence of pre existing preferred orientations on fabric development during progressive uplift strong quartz crystallographic preferred orientations cpos were developed during dislocation creep in the mylonite zone exposed in the hanging wall of the dextral reverse alpine fault zone new zealand the cpos have a consistent asymmetry indicating a high ratio of simple to pure shear strain with a shear sense of dextral up to the nw consistent with the mesoscopic shear sense indicators and with slip on the active fault there is a transition from y maxima and asymmetric single girdles in mylonites and ultramylonites within 300 m of the present fault trace to cross girdle fabrics in the protomylonites further from the fault the strong y maxima or single girdle cpos are ascribed to high ductile shear strains under amphibolite facies conditions while the cross girdle patterns found in the protomylonites are interpreted to represent deformation under lower temperature conditions however the observed fabric transition cannot logically be attributed to variations in temperature during the last increment of deformation the highly oriented y maximum fabrics formed at high temperature contain very few grains suitably oriented for basal slip so that the slip systems activated during subsequent shear at lower temperatures during exhumation were prism or rhomb further from the fault where shear strains under high temperature conditions were lower weaker fabrics developed under these conditions were modified at higher levels in the crust into crossed girdle patterns this interpretation implies that intense localisation of shear strain along the fault zone within the lower crust must have occurred in order for the high temperature fabrics to become sufficiently intense to be preserved this in turn implies that deep seated localised shear was taking place early during the evolution of the current oblique slip plate boundary fault the results of this study also indicate that the current model that operation of certain slip systems in quartz is mostly a function of temperature is incorrect future work should consider the effects of deformation history total strain and the presence of other mineral phases

fission track analysis reveals character of collisional tectonics in new zealand during the late cenozoic the pacific plate has been obliquely converging with the australia plate in south island new zealand this has resulted in westward obduction of continental crust of the pacific plate and consequently a major mountain range the southern alps has formed east of the alpine fault and within the leading edge of the pacific plate we have applied the apatite and zircon fission track dating technique to a suite of outcrop samples from three transects across the southern alps starting at the alpine fault to better understand the uplift age and structure of the continental collision the results show the following 1 uplift was underway at 7 ma in the south at haast pass and by 5 ma in the north at arthur s pass 2 profiles of the total amount of late cenozoic uplift show an exponential increase toward the alpine fault adjacent to the alpine fault there has been 14 5 to 21 5 km of uplift in the vicinity of haast pass 14 5 to 21 km near mt cook and 12 5 to 15 5 km in the arthur s pass transect adjacent to the alpine fault in the mount cook region the average uplift rate from 5 5 ma to 1 ma was 2 3 to 2 5 mm yr between 1 ma and the present it has averaged 6 2 mm yr the strongly asymmetric uplift pattern is responsible for the exposure of a 13 25 km wide belt of greenschist to midamphibolite facies rocks immediately east of the alpine fault known as the alpine schists 3 late cenozoic uplift of torlesse greywackes and alpine schists was preceeded during the jurassic early cretaceous by 5 8 km of uplift the otago schist belt to the south was uplifted much more during this interval and in addition western parts of the otago schists were uplifted 5 6 km during the late cretaceous 4 the fission track data do not support the notion of significant late cenozoic shear heating about the alpine fault as previously suggested from spatial variations in k ar ages of the otago and alpine schists

some thermal and mechanical consequences of rapid uplift an example from the southern alps new zealand abstract the thermal evolution of continental crust during active collision is modeled through numerical solutions of the two dimensional heat conduction equation for a rapidly moving medium the boundary conditions used in the modeling are derived from geological and geophysical observations from the active collision zone in the south island of new zealand the problem domain over which the solutions are obtained consists of a 40 km horizontal by 25 km vertical spatial plane with a vertical discontinuity at 10 km from the western boundary to the east of this discontinuity vertical uplift rates of up to 10 mm a occur over a timespan of up to 4 ma temperature distributions are calculated at 10 ka intervals over the 4 ma duration a two dimensional high temperature region is established upon initiation of uplift of the eastern block due to the advective component carrying heat upwards more rapidly than it can be dissipated laterally from the problem domain temperatures within the upper 5 km are greater than 400 c after 2 25 ma with geothermal gradients of up to 200 c km attained within the upper 3 km at times greater than 2 5 ma the vertical temperature distribution changes little while the anomalously high temperatures spread laterally into the stationary crust using rheological equations to describe the brittle behaviour of a water saturated upper crust and the ductile behaviour of a quartz dominated lower crust together with the thermal distribution of the conduction models the mechanical evolution of a collision zone is investigated in addition to high crustal temperatures and associated high heat flow rapid uplift produces a weakening of the crust by raising of the depth of transition from brittle to ductile behaviour within the zone of most rapid uplift the brittle ductile transition rises from 13 km to less than 5 km after 1 5 ma of uplift further uplift reduces the brittle layer to 3 km thickness and causes lateral spreading of the low strength zone the reductions in crustal strength caused by the thermal weakening produce a high strain zone within the region of maximum uplift which is incapable of sustaining large differential stresses this causes horizontal and vertical stress transfer and results in shallow seismicity increases in the adjacent crust as well as in intermediate depth seismicity within the high strength upper mantle because the thermal and mechanical anomalies discussed are a function of rapid uplift all regions of active continental collision may be expected to exhibit similar behaviour some mechanical and thermal characteristics of the himalayan collision zone are briefly examined in light of the numerical modeling

metamorphic response to collision in the central himalayan orogen abstract closure of the neotethys ocean and high angle continent continent collision between india and asia after about 55 ma resulted in low angle subduction of the indian plate below the tibetan plateau and by 30 ma established an arcuate 2300 km long shallow north dipping metamorphic fold thrust belt in the foreland this himalayan metamorphic front quickly established an upper plate lower plate paired metamorphic architecture centred on the median high himal thrust that largely controlled subsequent evolution the upper plate is a thick slab of high t moderate p high grade migmatized metamorphic rocks whereas the lower plate is an inverted series of moderate t high p schists in two crustal wedges the broad main central thrust zone and at lowest structural levels the footwall below the basal main central thrust spatial and temporal patterns of metamorphic response in the evolving himalayan metamorphic front has been characterized in a large scale integrated structural metamorphic study based on 8 profiles across eastern nepal metamorphic response at all structural levels is established using a large dataset n 160 of internally consistent quantitative pt determinations petrology of metapelite samples semi quantitative p t paths metamorphic mapping and metamorphic field gradients these results are integrated with previously published metamorphic studies structural profiles and metamorphic chronology from these datasets the architecture and evolution of the himalayan metamorphic front is constrained by rock kinematics metamorphic field gradients showing discontinuities and diachronous metamorphism with contrasting p t evolutions at different structural levels each of the three panels constituting the himalayan metamorphic front upper plate main central thrust zone and footwall experienced distinctly different tectono metamorphic histories crustal processes operating during metamorphism and exhumation differ between the upper and lower plates the upper plate experienced long lived metamorphism starting from at least 28 38 ma and tracking low p t clockwise p t paths that culminated at 19 27 ma in peak high grade condition with 27 31 c km thermal regimes protracted high grade conditions produced significant partial melt which facilitated gravity driven southward extrusion involving internal ductile flow processes southward extrusion of the upper plate was accommodated by coeval reverse movement on the high himal thrust and top down to the north normal reactivation of the south tibet detachment system between 22 10 ma transport of this thick slab to the south resulted in further prograde burial of the lower plate below culminating in peak metamorphism at the highest pressures attained in the lower plate rocks the lower plate consists of at least two deeply buried 7 5 9 4 kb crustal wedges both of which experienced steep p t hairpin clockwise p t paths with isothermal decompression the main central thrust zone experienced 20 26 c km metamorphism at 12 22 ma and was exhumed along the basal main central thrust after 11 ma whereas loading by the main central thrust zone gave rise to further prograde burial of the footwall which experienced 16 21 c km metamorphism at 4 10 ma and was exhumed along the main boundary thrust at 3 9 ma in contrast to the upper plate both crustal wedges were exhumed by a process of out wedging which involved upthrusting along basal and internal thrusts with coeval extensional slip in the hanging walls this three stage foreland propagating lateral exhumation history resulted in telescoping of the himalayan metamorphic front in concert with peak metamorphic events at different structural levels during main phase orogenesis and is not the result of superimposed retrograde reactivation of the belt

the early metamorphic history of the haast schists and related rocks of new zealand rare but widespread relics of sodic amphibole occur in metabasites and metacherts of the haast schists and related caples terrane rocks present main stage metamorphic assemblages are frequently chemically equivalent to earlier sodic amphibole bearing assemblages indicating that these rocks underwent an earlier higher p tmetamorphism prior to formation of the present pumpellyite actinolite and greenschist facies assemblages the earlier assemblages were stable during and after early isoclinal folding but were replaced by the present moderate p t assemblages prior to the last major fabric forming deformation the change in conditions was due to thermal relaxation probably accompanied by uplift and erosion and peak metamorphic temperatures were about 350 370 c in the pumpellyite actinolite zone of the caples terrane and near 390 c in the greenschist facies chlorite zone near queenstown according to henley 1975 these greenschist facies rocks attained a pressure of at least 6 4 0 4 kb during their history but a pressure of 4 6 0 6 kb has been estimated for a chlorite zone rock from middlemarch and so the 6 4 kb estimate probably refers to the maximum pressure attained during the earlier higher p t metamorphism similar changes in metamorphic facies series with time occur in some older and more complex metamorphic belts such as the caledonides and this study suggests that it may be possible to interpret particular elements in the metamorphic development of such belts in terms of specific circum pacific analogues

inversion of seismic refraction and wide angle reflection traveltimes for three dimensional layered crustal structure summary we present a method for the determination of crustal structure by simultaneous inversion of seismic refraction and wide angle reflection traveltimes for 3 d interface geometry and layer velocity crustal structure is represented by layers in which velocity varies linearly with depth separated by smooth interfaces with a cubic b spline parametrization lateral variations in structure are therefore represented by variations in interface depth only the model parametrization we have chosen means that ray paths consist of piecewise circular arc segments for which analytic expressions of trajectory and traveltime are calculated the two point problem of finding the first arrival ray path and traveltime of a specified phase between a given source and receiver is solved using a shooting technique a subspace inversion method is used to solve the inverse problem which is formulated as a non linear optimization problem in which we seek to minimize an objective function that consists of a data residual term and a regularization term before performing the inversion each data pick must be assigned as a refraction or reflection from a particular layer or interface since our method represents structure in terms of interfaces fewer parameters would generally be used in a reconstruction compared to an equivalent 3 d variable velocity inversion the method is well suited to wide angle surveys that consist of many sources and relatively few receivers or vice versa such as marine shot lines used in conjunction with land based receivers data coverage in this kind of survey is often sparse and especially if near offset ray paths are unavailable highly variable a 3 d synthetic test with an array consisting of eight sources lying within a three sided square of 79 receivers is described the test model consists of a three interface structure that includes a layer pinch out and the synthetic data set comprises 987 refraction and 930 reflection travel times contaminated with 75 ms of data noise six iterations of an 18 d subspace method demonstrate that the method can produce an accurate reconstruction that satisfies the data from a 1 d starting model we also find that estimates of a posteriori model covariance and resolution obtained from linear theory are useful in analysing solution reliability despite the non linear nature of the problem application of the method to data collected as part of the 1995 tasgo project in tasmania shows that the method can satisfy 1345 refraction and reflection traveltime picks with a geologically reasonable and robust 254 parameter three interface model the inversion results indicate that the moho beneath nw tasmania varies in depth from 27 km near the coast to 37 km near central tasmania with the major increase in depth occurring across the arthur lineament

grain boundary migration of water and carbon dioxide during uplift of garnet zone alpine schist new zealand deformed quartz veins in garnet zone schist adjacent to the active alpine fault new zealand have fluid inclusions trapped along quartz grain boundaries textures suggest that the inclusions formed in their present shapes during annealing of the deformed veins many of the inclusions are empty but some contain carbon dioxide with densities that range from 0 16 to 0 80 g cm 3 no water nitrogen or methane was detected the inclusions are considerably more co2 rich than either the primary metamorphic fluid 5 co2 or fluids trapped in fracture related situations in the same or related rocks 50 co2 enrichment of co2 is inferred to have resulted from selective migration wicking of saline water from the inclusions along water wet grain boundaries after cooling induced immiscibility of a water co2 mixture inclusion volumes changed after loss of water non wetting co2 remained trapped in the inclusions until further percolation progressively removed co2 in solution this mechanism of fluid migration dominated in ductile quartz rich rocks near but below the brittle ductile transition at deeper levels hydraulic fracturing is also an important mechanism for fluid migration whereas at shallower levels advection through open fractures dominates the fluid flow regime

3d simultaneous seismic refraction and reflection tomography of wide angle data from the central chilean margin we present an application of three dimensional 3d simultaneous seismic refraction and reflection tomography for velocity and interface structure the inversion technique and method for developing the starting model are specifically designed for relatively sparse wide angle data acquired across strongly varying structure the data were recorded in a region of seamount subduction on the chilean margin and consist of seven receivers and ten intersecting airgun profiles over a 90 90 km area providing constraint to 25 km depth the tomographic method and the final model are assessed through a comparison with the large scale geologic features of the margin and a resolution test the 3d model shows the valparaiso forearc basin the accretionary wedge the subducting plate and possibly a subducted seamount our results show the potential of relatively sparse 3d wide angle data

textural changes of graphitic carbon by tectonic and hydrothermal processes in an active plate boundary fault zone alpine fault new zealand graphitization in fault zones is associated both with fault weakening and orogenic gold mineralization we examine processes of graphitic carbon emplacement and deformation in the active alpine fault zone new zealand by analysing samples obtained from deep fault drilling project dfdp boreholes optical and scanning electron microscopy reveal a microtextural record of graphite mobilization as a function of temperature and ductile then brittle shear strain raman spectroscopy allowed interpretation of the degree of graphite crystallinity which reflects both thermal and mechanical processes in the amphibolite facies alpine schist highly crystalline graphite indicating peak metamorphic temperatures up to 640 c occurs mainly on grain boundaries within quartzo feldspathic domains the subsequent mylonitization process resulted in the reworking of graphite under lower temperature conditions 500 600 c resulting in clustered in protomylonites and foliation aligned graphite in mylonites in cataclasites derived from the mylonitized schists graphite is most abundant 50 as opposed to 10 elsewhere and has two different habits inherited mylonitic graphite and less mature patches of potentially hydrothermal graphitic carbon tectonic hydrothermal fluid flow was probably important in graphite deposition throughout the examined rock sequences the increasing abundance of graphite towards the fault zone core may be a significant source of strain localization allowing fault weakening

origin of the torlesse terrane and coeval rocks south island new zealand the carboniferous to lower cretaceous torlesse terrane and haast schist derivatives constitute the major part of the complexly deformed facies of the eastern province of new zealand strata consist mainly of quartzofeldspathic graywacke and mudstone intercalated with minor but widely distributed conglomerate and volcanics with associated chert and limestone clastic rocks were deposited largely by sediment gravity flow mechanisms in a deep marine environment also present are a few highly fossiliferous shallow marine and terrestrial deposits of limited areal extent which rest unconformably on or in fault contact with torlesse flysch several periods of deformation are recognized and melange is present on both local and regional scales metamorphism ranges from zeolite to greenschist facies the bulk of the rocks fall into five areally extensive and mutually exclusive fossil zones of the following ages permian atomodesma middle triassic early late triassic torlessia late triassic monotis and late jurassic early cretaceous contacts between major fossil zones are mainly tectonic petrographic analysis permits subdivision of torlesse sandstones into five major petrofacies that correspond in age to the five major fossil zones the sandstone petrofacies mainly arkosic together with the composition of conglomerate clasts mainly indurated torlesse rocks indicate that the source terrane was a continental volcano plutonic arc probably part of gondwanaland coupled with autocannibalistic reworking of older uplifted torlesse rocks in contrast to the quartzofeldspathic nature of the torlesse coeval sedimentary rocks of the eastern province are volcanogenic they are thought to represent related forearc basin maitai murihiku terranes and trench complex caples terrane deposits derived from a volcanic island arc brook street terrane three petrofacies are established for maitai murihiku and caples sandstones the petrofacies indicate a common evolving immature to submature volcanic island arc source for these terranes a reconstruction of new zealand s eastern and western provinces is proposed in permian and triassic times the torlesse was deposited in trench slope or borderland basins along a trench transform margin fronting a continental volcano plutonic arc source western province gondwanaland deposition was spasmodic but voluminous and was accompanied by concurrent deformation and accretion resulting in parallel belts of torlesse rock younging outward from the gondwanaland margin at the same time the brook street terrane volcanic arc and associated terranes were forming to the west of the torlesse site separated from gondwanaland by a marginal sea in latest triassic or early jurassic times the torlesse was rafted into the volcanic arc system via transform faulting approximately parallel to the gondwana margin the collision event resulted in tectonic thickening of torlesse and caples rocks at the plate interface and metamorphism to haast schist the source was then dominated by older partly metamorphosed torlesse terrane newly uplifted along the collision front closing of the marginal sea behind the brook street terrane in late jurassic early cretaceous times resulted in juxtapositioning with the western province gondwanaland along the median tectonic line

effect of grossular content in garnet on the partitioning of fe and mg between garnet and biotite in contrast to ferry 1980 x ca values in garnet even lower than 0 1 have a significant effect on the calculated equilibrium temperature using the experimental calibration of the fe and mg paritioning between garnet and biotite garnet compositions and mg fe distribution coefficients from samples of the eoalpine staurolite in zone in the southern otztal are related by the quadratic regression equation ink d 1 7500 0 0226 2 978 0 5317 x ca gt 5 906 2 359 x ca gt 2 temperatures derived by the ferry and spear 1978 calibration using chemistry corrected k d values are petrologically realistic analysis of our data supports non ideal mixing of grossular with almandine pyrope solid solution the derived excess mixing energies are quite small for the almandine pyrope solution w femg 133 cal mole and about 2775 cal mole for the difference between pyrope grossular and almandine grossular solutions w mgca w feca at metamorphic conditions of 570 c and 5 000 bar the mixing parameters proposed by ganguly and saxena 1984 are not confirmed by our data as they would result in significantly lower temperatures

crustal and upper mantle seismic structure of the australian plate south island new zealand abstract seismic reflection and refraction data were collected west of new zealand s south island parallel to the pacific australian plate boundary the obliquely convergent plate boundary is marked at the surface by the alpine fault which juxtaposes continental crust of each plate the data are used to study the crustal and uppermost mantle structure and provide a link between other seismic transects which cross the plate boundary arrival times of wide angle reflected and refracted events from 13 recording stations are used to construct a 380 km long crustal velocity model the model shows that beneath a 2 4 km thick sedimentary veneer the crust consists of two layers the upper layer velocities increase from 5 4 5 9 km s at the top of the layer to 6 3 km s at the base of the layer the base of the layer is mainly about 20 km deep but deepens to 25 km at its southern end the lower layer velocities range from 6 3 to 7 1 km s and are commonly around 6 5 km s at the top of the layer and 6 7 km s at the base beneath the lower layer the model has velocities of 8 2 8 5 km s typical of mantle material the mohorovicic discontinuity moho therefore lies at the base of the second layer it is at a depth of around 30 km but shallows over the south central third of the profile to about 26 km possibly associated with a southwest dipping detachment fault the high variable sub moho velocities of 8 2 km s to 8 5 km s are inferred to result from strong upper mantle anisotropy multichannel seismic reflection data cover about 220 km of the southern part of the modelled section beneath the well layered oligocene to recent sedimentary section the crustal section is broadly divided into two zones which correspond to the two layers of the velocity model the upper layer down to about 7 9 s two way travel time has few reflections the lower layer down to about 11 s two way time contains many strong subparallel reflections the base of this reflective zone is the moho bi vergent dipping reflective zones within this lower crustal layer are interpreted as interwedging structures common in areas of crustal shortening these structures and the strong northeast dipping reflections beneath the moho towards the north end of the mcs line are interpreted to be caused by paleozoic north dipping subduction and terrane collision at the margin of gondwana deeper mantle reflections with variable dip are observed on the wide angle gathers travel time modelling of these events by ray tracing through the established velocity model indicates depths of 50 110 km for these events they show little coherence in dip and may be caused side swipe from the adjacent crustal root under the southern alps or from the upper mantle density anomalies inferred from teleseismic data under the crustal root

thermochronological analysis of the dynamics of the southern alps new zealand the isotopic ages of material exposed close to the alpine fault in the southern alps new zealand vary in a consistent fashion along the orogen for the k ar system muscovite and biotite ages display two distinct spatial trends that meet in the area of fox glacier where a strong relationship is observed between k ar age and altitude excess argon is present in samples between mount kinnaird and haast pass in the southwest of the southern alps giving unrealistically old inconsistent k ar ages across this region incorporation of excess argon appears to be highly variable however and minimization of its influence on dynamical interpretations of thermochronology is possible through considering only the youngest age from a given area such treatment indicates that excess argon contamination does not play an important role in the systematic k ar age variation identified along the southern alps the observed age distribution is consistent with estimates of the modern rapid uplift and exhumation of the southern alps beginning ca 5 ma k ar mica ages older than this south of the copland valley indicate that substantial late cenozoic exhumation occurred along the southern alps prior to the development of the modern tectonic regime but at rates lower than at present total exhumation during the current phase of tectonism in the southern alps decreases from the whataroa river southward north of fox glacier the southern alps have attained a dynamical steady state such that the observed distribution of exhumation will not change significantly with further deformation and denudation under current conditions

a seismic investigation of the crust and moho underlying the peace river arch canada abstract the peace river arch is a structural uplift in northwestern alberta which has experienced an anomalous history of movement with respect to the surrounding western canada sedimentary basin the supracrustal geology of the region provides a detailed record of the vertical motion of the arch in the phanerozoic era in an attempt to gain information on the underlying crystalline crust and upper mantle in the region the peace river arch seismic experiment prase was carried out by the geological survey of canada and several canadian universities in the summer of 1985 four reversed seismic refraction lines each 300 350 km in length were shot the two dimensional laterally homogeneous models developed from the in line data suggest that there is little lateral variation in velocity in the region the upper 2 4 km of each section was modelled by sedimentary layers the upper 20 km of the models are composed of horizontal laterally homogeneous layers with velocities increasing from 6 0 to 6 5 km s the data from three of the lines indicate an intracrustal discontinuity at a depth of 16 24 km the data from a line running along the axis of the arch suggests a second discontinuity at 30 km the lower half of the crust increases in velocity to 6 6 7 2 km s the upper mantle has an average velocity of 8 13 0 08 km s and has a much lower velocity gradient than the overlying crust there is some variation in the nature of the moho which is generally well defined nearly horizontal and occurs at a depth between 36 and 43 km there is little correlation of the arch uplift structure with the structure in the underlying crust there appears to be some local thickening of the crust immediately below the axis of the arch upward warping of the velocity contours below the axis of the arch in the lower half of the crust may also be an indication of the uplift at depth no definite driving mechanism can be established for the origin of the peace river arch

seismic structure of the crust and upper mantle in the peace river arch region canada four intersecting 300 km long reversed refraction lines within northwestern alberta and northeastern british columbia have been interpreted for crustal and upper mantle seismic velocity structure in the peace river arch pra region of the western canada sedimentary basin the data have been modeled using a two dimensional ray trace forward modeling approach based on asymptotic ray theory to match travel times and amplitudes of first and coherent later arrivals in addition an inversion of first arrival travel times along a fan shot profile has been performed to constrain crustal thickness northwest of the arch in a region not sampled by the reversed profiles the major features of the structural models are 1 weak to moderate lateral variations in crustal structure with no evidence of significant layering or thick low velocity zones within the crust 2 an average sub basement rms crustal velocity of 6 6 km s average upper mantle velocity of 8 25 km s and average crustal thickness of 40 km 3 regional variations in structure which appear related to the dominant n s trending cratonic structure including crustal thickness upper crustal and upper mantle velocities and pmp character and 4 subtle variations in structure that may be associated with the e w trending devonian axis of the pra including a shallowing of high lower crustal velocities thickening of the crust and an anisotropic pmp character beneath the arch and a weak trend in the dip of intracrustal reflectors away from the center of the pra region evidence from the refraction and other geophysical data for the presence of a local crustal expression of the pra is weak but suggests a thermal as opposed to flexural origin for its anomalous vertical movements

lithospheric pressure depth relationship in compressive regions of thickened crust we investigate the pressure distribution with depth in regions undergoing horizontal shortening and experiencing crustal thickening both analytically and numerically our results show that in a convergent tectonic setting pressure can be considerably higher than lithostatic the pressure resulting from the weight of the overburden increases in pressure with respect to lithostatic conditions result from both the contribution of horizontal stresses and the flexural vertical loads the latter generated by the deflection of the upper crust and of the mantle because of the presence of topographic relief and a root respectively the contribution of horizontal stresses is particularly relevant to the upper crust and uppermost mantle where rocks are thought to deform brittlely in these domains pressure gradients twice lithostatic can be achieved the contribution of horizontal stresses is less important in the ductile domains as diverential stresses are progressively relaxed nevertheless the evects are still noteworthy especially close to the brittle ductile transition flexural vertical loads generated by the deflection of the upper crust and lithospheric mantle are relevant for rocks of the weaker lower crust as a result of the combination of the two mechanisms the pressure gradient varies vertically through the lithosphere ranging from negative inverted gradients to gradients up to several times the lithostatic gradient the pressure values range from one to two times the lithostatic values 1rgz to 2rgz

potassium argon age studies of a low grade progressively metamorphosed greywacke sequence dansey pass south island new zealand 39 potassium argon age determinations from a progressively metamorphosed greywacke schist sequence in southern new zealand prehnite pumpellyite to greenschist facies range from 199 to 154 ma early to late jurassic they show an inverse correlation of age with metamorphic grade concordant ages from varied lithologies at all metamorphic grades show that degassing of detrital potassium bearing minerals was completed during metamorphism the lowest grade metamorphic rocks which yield the oldest ages about 200 ma have only just exceeded the argon closure temperature and hence their ages date closely their time of metamorphism in the earliest jurassic thus it is shown that the jurassic cretaceous rangitata orogeny in new zealand commenced earlier is more complex and of longer duration than previously supposed the remaining ages from pumpellyite actinolite and lower greenschist rocks range uniformly through the jurassic and are interpreted as cooling ages from these data a long term uplift rate of 0 23 mm yr is calculated for the jurassic cretaceous

peristerite compositions in quartzofeldspathic schists franz josef fox glacier area new zealand plagioclase compositions vary from an0 1 2 5 to an32 with increasing grade in chlorite zone to oligoclase zone quartzofeldspathic schists franz josef fox glacier area southern alps new zealand this change is interrupted by the peristerite composition gap in rocks transitional between greenschist and amphibolite facies grade oligoclase an20 24 and albite an0 1 0 5 are found in biotite zone schists below the garnet isograd with increasing grade the plagioclase compositions outline the peristerite gap which is asymmetric and narrows to compositions of an12 and an6 near the top of the garnet zone in any one sample oligoclase is the stable mineral in mica rich layers above the garnet isograd whereas albite and oligoclase exist in apparent textural equilibrium in adjacent quartz plagioclase layers the initial appearance of oligoclase in both layers results from the breakdown of epidote and possibly sphene carbonate is restricted to the quartz plagioclase rich layers and probably accounts for the more sodic composition of oligoclase in these layers the formation of more ca rich albite and more na rich oligoclase near the upper limit of the garnet zone coincides with the disappearance of carbonate and closure of the peristerite gap garnet appears to have only a localized effect on ca enrichment of plagioclase in mica rich layers within the garnet zone the na content of white mica increases sympathetically with increasing ca content of oligoclase and metamorphic grade comparison of the peristerite gap in the franz josef fox glacier schists and schists of the same bulk composition in the haast river area 80 km to the s indicates that oligoclase appears and epidote disappears at lower temperatures and that the composition gap between coexisting albite and oligoclase is narrower in the franz josef fox glacier area it is suggested that a higher thermal gradient 38 40 c km and variations in si al ordering during growth of the plagioclases between the two areas may account for these differences in the alpine schists the peristerite gap exists over a temperature and pressure interval of about 370 515 c and 5 5 7 kbar 550 700 mpa ph2o

reprint of extensional shear band development on the outer margin of the alpine mylonite zone tatare stream southern alps new zealand abstract schistose mylonitic rocks in the central part of the alpine fault af at tatare stream new zealand are cut by pervasive extensional c shear bands in a well understood and young natural ductile shear zone the c shears cross cut the pre existing mesozoic aged foliation displacing it ductilely synthetic to late cenozoic motion on the af using a transect approach we evaluated changes in geometrical properties of the mm cm spaced c shear bands across a conspicuous finite strain gradient that intensifies towards the af precise c attitudes c foliation dihedral angles and c s intersections were calculated from multiple sectional observations at both outcrop and thin section scales based on these data the direction of ductile shearing in the alpine mylonite zone during shear band activity is inferred to have trended 20 clockwise down dip of the coeval pacific australia plate motion indicating some partitioning of oblique slip motion to yield an excess of dip slip relative to plate motion azimuth or some up dip ductile extrusion of the shear zone as a result of transpression or both constant attitude of the mylonitic foliation across the finite strain gradient indicates this planar fabric element was parallel to the shear zone boundary szb across all examined parts of the shear zone the mean dihedral angle between the c shears and the mylonitic foliation s remains a constant 30 1 1 the aggregated slip accommodated on the c shear bands contributed only a small bulk shear strain across the shear zone 0 6 0 8 uniformity of per shear slip on c shears with progression into the mylonite zone across the strain gradient leads us to infer that these shears exhibited a strain hardening rheology such that they locked up at a finite shear strain inside c bands of 12 15 shear band boudins and foliation boudins both record extension parallel to the szb as do the occurrence of extensional shear band sets that have conjugate senses of slip we infer that shear bands nucleated on planes of maximum instantaneous shear strain rate in a shear zone with w k

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

structural boundaries and biotite and garnet isograds in the otago and alpine schists new zealand the otago and alpine schist belts of southern new zealand have traditionally been treated as structurally continuous metamorphic belts with minor modification by brittle faulting mapping of biotite and garnet isograds has been hindered by rock types unfavourable for index mineral growth closer examination of well exposed boundaries between metamorphic zones shows that they juxtapose rocks of different type and structural history apparent structural continuity across these zones is due to development of a locally pervasive boundary parallel foliation on both sides of the boundary in a broad boundary zone up to 2 km wide this feature has implications for mapping and metamorphic petrology in other metamorphic belts where structural continuity has traditionally been assumed true metamorphic isograds may be rare and metamorphic zones may more commonly represent structural slices of complex tectonically disrupted metamorphic piles

assessment of crustal velocity models using seismic refraction and reflection tomography two tomographic methods for assessing velocity models obtained from wide angle seismic traveltime data are presented through four case studies the modelling inversion of wide angle traveltimes usually involves some aspects that are quite subjective for example 1 identifying and including later phases that are often difficult to pick within the seismic coda 2 assigning specific layers to arrivals 3 incorporating pre conceived structure not specifically required by the data and 4 selecting a model parametrization these steps are applied to maximize model constraint and minimize model non uniqueness however these steps may cause the overall approach to appear ad hoc and thereby diminish the credibility of the final model the effect of these subjective choices can largely be addressed by estimating the minimum model structure required by the least subjective portion of the wide angle data set the first arrival times for data sets with moho reflections the tomographic velocity model can be used to invert the pmp times for a minimum structure moho in this way crustal velocity and moho models can be obtained that require the least amount of subjective input and the model structure that is required by the wide angle data with a high degree of certainty can be differentiated from structure that is merely consistent with the data the tomographic models are not intended to supersede the preferred models since the latter model is typically better resolved and more interpretable this form of tomographic assessment is intended to lend credibility to model features common to the tomographic and preferred models four case studies are presented in which a preferred model was derived using one or more of the subjective steps described above this was followed by conventional first arrival and reflection traveltime tomography using a finely gridded model parametrization to derive smooth minimum structure models the case studies are from the se canadian cordillera across the rocky mountain trench central india across the narmada son lineament the iberia margin across the galicia bank and the central chilean margin across the valparaiso basin and a subducting seamount these case studies span the range of modern wide angle experiments and data sets in terms of shot receiver spacing marine and land acquisition lateral heterogeneity of the study area and availability of wide angle reflections and coincident near vertical reflection data the results are surprising given the amount of structure in the smooth tomographically derived models that is consistent with the more subjectively derived models the results show that exploiting the complementary nature of the subjective and tomographic approaches is an effective strategy for the analysis of wide angle traveltime data

the approach to steady state thermochronological distribution following orogenic development in the southern alps of new zealand a diachronous sequence of isotopic ages along the southern alps of new zealand illustrates details of the development of the modern tectonic regime of this orogen at about 5 ma coupled with the rapid cooling rates experienced in the southern alps which ensure negligible residence time at temperatures allowing partial radiogenic product retention during exhumation and thus effectively instantaneous thermochronological closure this record presents important general insight into the transient physical and thermal effects of changes in tectonic conditions the tectono thermal response of the southern alps to the change in dynamical conditions at 5 ma is resolved into two evolutionary stages that are observed with progressive exhumation the removal by erosion of material that had cooled below the relevant closure temperature prior to the change in dynamics at 5 ma results in an initial decrease in age this is followed by a sharp drop to younger ages as material subjected to thermal re equilibration associated with the modern orogenic regime is exposed culminating in the eventual exposure of time invariant ages reflecting the new steady state dynamics of the region this two step response is a direct result of the relationship between cooling and exhumation and illustrates the care needed in reconstructing physical histories from isotopic ages and cooling rates in tectonically active regions

paleogeothermal gradient and deformation style pacific front of the southern alps orogen constraints from fission track thermochronology abstract the application of apatite fission track ft thermochronology to a suite of samples from different elevations within the exhumed apatite partial annealing zone in rakaia valley region of the southern alps new zealand establishes a pre cooling denudation latest miocene early pliocene upper crustal geothermal gradient value of 20 3 c km within indurated triassic sandstone this is comparable to the equivalent modern value of 23 6 c km in basement outside the oblique continent continent collision zone that is where isotherms have not been perturbed by late cenozoic advection resulting from crustal thickening rock uplift and denudation the normalisation of the maximum paleotemperature estimates for sample sites at various elevations to those expected at a standard elevation 1000 m shows that the exhumed late cenozoic partial annealing zone is disrupted by reverse faults striking parallel throws of 1000 2400 m and orthogonal throw of 500 1000 m to the orogen and by an open symmetrical dome dimensions 20 km long and 13 km wide that conforms to the shape of the mt hutt range an effect of this deformation is repetition of the exhumed partial annealing zone across the eastern margin of the southern alps interpretation of existing geological maps suggests that the basement folding quantified for the mt hutt range from ft data is widespread in mid and south canterbury a triangular zone along the eastern range front which increases in width along the orogen to the southwest comprises numerous antiformal reverse faulted basement ranges flanked by outliers of mid cenozoic marine cover rocks that were formerly continuous across the region this basement folding and reverse faulting represents propagation of the orogen back across the incoming pacific plate as predicted by recent numerical and geodynamical models

the obliquely convergent plate boundary in the south island of new zealand implications for ancient collision zones abstract the alpine fault of new zealand forms the western boundary of a zone of distributed deformation formed by the oblique convergence of continental crust belonging to the pacific and australian plates structural and geodetic data from the alpine fault show that a large proportion of the total plate displacement is accommodated by rapid oblique slip on the fault the remaining displacement is distributed over a 200 km wide zone to the east the collision may be modelled as a two sided deforming orogen with the partitioning of deformation being controlled by erosional differences between the narrow high strain inboard and broad low strain outboard sides in ancient collision zones little evidence may remain of the nature and amount of displacement on the inboard side partitioning of deformation among pre existing structures complicates interpretation of the outboard zone radiometric ages may post date collision by several tens of millions of years and indicate slow isostatic uplift and unroofing collision ages if preserved may be recognized by high uplift rates calculated from muscovite biotite pairs

al fe super 3 and ca sr super 2 epidotes in metagreywacke quartzofeldspathic schist southern alps new zealand al fe super 3 or and sr super 2 or bearing epidotes are a common constituent in chlorite and biotite albite zone metagreywacke quartzofeldspathic schist in the southern alps of new zealand on the basis of electron microprobe backscattered electron scanning of complexly zoned grains five generations of epidote growth are recognized first generation epidotes ps sub 29 25 are typically fractured as a result of cataclasis during d1 deformation and presumably represent relics of prehnite pumpellyite and or pumpellyiteactinolite facies conditions of metamorphism second generation epidote ps sub 25 20 rims first generation epidote and replaces fragmented grains third generation epidote involved sr replacement up to 8 5 wt sro of earlier grains along fracture planes and grain margins single grains exhibit a range of sr ca replacement that can vary by up to 4 wt sro fourth generation post d 1 epidote ps sub 20 9 occurs as overgrowths on earlier generation epidotes and as continuously zoned grains within the lowest grade part of the biotite albite oligoclase zone fourth generation epidote cores ps sub 10 13 are overgrown by slightly more fe rich fifth generation rims ps sub 16 14 suggesting involvement of the epidote ca 2 al 3 si 3 o 12 oh component in an oligoclase producing reaction in quartzofeldspathic lithologies epidote disappears at higher grades than the appearance of oligoclase epidote compositions plot within the miscibility gap defined and a discontinuity between compositions of ps 20 and ps 16 in chlorite zone rocks is attributed to the persistence of relic cores due to incomplete fe super 3 al diffusional exchange at low temperature and textural grade with increasing grade there is a decrease in the range of zoning in individual epidote grains resulting in a more homogeneous population of epidote compositions with the most al rich epidotes becoming fe super 3 or rich and the most fe super 3 or rich epidotes becoming more al rich the formation of sr epidote appears to be related to the release of sr into the fluid phase from the breakdown of detrital plagioclase over the pumpellyite clinozoisite isograd during d1 deformation early formed oligoclase in the biotite albite oligoclase zone resulting from the disappearance of epidote contains up to 0 4 sro mobility of sr and ca is indicated by veins containing sr bearing epidote and calcite the complex zoning of epidotes is a function of bulk composition time variation in fluid composition temperature pressure and deformation of the rocks

3 d velocity structure from simultaneous traveltime inversion of in line seismic data along intersecting profiles summary a method for simultaneously inverting in line seismic traveltime data recorded along a network of intersecting linear profiles is presented consistency of the models at the intersection points is assured and permits 3 d structural and velocity variations to be inferred by interpolation between the profiles common model parameters are used at the intersection points thereby minimizing the number of independent model parameters and maximizing the degree of constraint of each 2 d model the method has two main applications 1 to obtain the most constrained set of 2 d models for each profile if subsequent 3 d modelling is not possible and 2 to provide a 3 d starting model for subsequent 3 d modelling if there is sufficient azimuthal data coverage some ideal line geometries are suggested but the method is applicable to any set of two or more lines with one or more intersection point a new interpretation of crustal seismic data from the peace river arch region of the western canada sedimentary basin consisting of four profiles is presented using the simultaneous inversion method for both refracted and reflected arrivals the results are generally consistent with a previous interpretation of the data in which each profile was modelled independently of the others using 2 d forward modelling however the models obtained by inversion contain less lateral heterogeneity that more accurately reflects the resolution limits of the data this illustrates the need to reconsider data that have only been analysed by forward modelling

shallow level metamorphic fluids in a high uplift rat metamorphic belt alpine schist new zealand fluids some of which are co2 rich up to 40 mol co2 and some of which are highly saline up to 18 wt nacl equivalent are trapped as fluid inclusions in quartz calcite metallic minerals veins which cross cut the pumpellyite actinolite to amphibolite facies rocks of the alpine schist fluids were commonly trapped as immiscible liquid vapour mixes in quartz and calcite showing open space growth textures fluid entrapment occurred at fluid pressures near 500 bars possibly as low as 150 bars at temperatures ranging from 260 to 330 c saline fluids may have formed by partitioning of dissolved salts into an aqueous phase on segregation of immiscible fluids from a low density co2 rich fluid calcite deposited by these fluids has 13c ranging from 8 4 to 11 5 and 18o from 4 to 13 isotopic data fluid compositions and mode of occurrence suggest that the fluids are derived from high grade metamorphic rocks fluid interaction with wall rock has caused biotite crystallization and or recrystallization in some rocks and retrogression of biotite to chlorite in other rocks fluid penetration through the rock is almost pervasive in many areas where permeability probably related to alpine fault activity has focussed fluids on a regional scale into fractured rocks the fluid flow process is made possible by high uplift rates in excess of 10 mm year bringing hot rocks near to the surface

dislocation generation slip systems and dynamic recrystallization in experimentally deformed plagioclase single crystals abstract three samples of gem quality plagioclase crystals of an60 were experimentally deformed at 900 c 1 gpa confining pressure and strain rates of 7 5 8 7 10 7 s 1 the starting material is effectively dislocation free so that all observed defects were introduced during the experiments two samples were shortened normal to one of the principal slip planes 010 corresponding to a hard orientation and one sample was deformed with a schmid factor of 0 45 for the principal slip system 001 010 corresponding to a soft orientation several slip systems were activated in the soft sample dislocations of the 001 010 and 110 001 system are about equally abundant whereas 110 111 and 101 in 131 to 242 are less common in the soft sample plastic deformation is pervasive and deformation bands are abundant in the hard samples the plastic deformation is concentrated in rims along the sample boundaries deformation bands and shear fractures are common twinning occurs in close association with fracturing and the processes are clearly interrelated glissile dislocations of all observed slip systems are associated with fractures and deformation bands indicating that deformation bands and fractures are important sites of dislocation generation grain boundaries of tiny defect free grains in healed fracture zones have migrated subsequent to fracturing these grains represent former fragments of the fracture process and may act as nuclei for new grains during dynamic recrystallization nucleation via small fragments can explain a non host controlled orientation of recrystallized grains in plagioclase and possibly in other silicate materials which have been plastically deformed near the semi brittle to plastic transition

mode of crustal shortening adjacent to the alpine fault new zealand the late cenozoic episode of crustal shortening in the south island new zealand which has caused present day uplift rates of greater than 10 mm yr and has formed the southern alps may have also caused clockwise rotation of the alpine fault by up to 20 in contrast to the northern end of the alpine fault which appears to have remained fixed relative to the australian plate increasing westward movement of the fault trace has occurred southward along the fault this westward movement may exceed 100 km where the fault crosses the coastline in northern fiordland most shortening adjacent to the southern end of the alpine fault has occurred within australian plate continental crust which has been thrust beneath pacific plate continental crust this zone of continental underthrusting merges with the fiordland subduction zone further south where australian plate oceanic crust is being subducted gravity modelling of the continental collision zone beneath the southern alps indicates that the leading edge of underthrust australian plate crust may be close to a relatively sharp 10 km change in moho depth inward dipping thrust faults on both plates mark the outer limits of the collision zone which is over 300 km wide near the southern end of the alpine fault the probable increase in crustal thickness due to the late cenozoic shortening suggests that the amount of crustal thickening is similar in size to the amount of eroded crust

potentially active faults in the rapidly eroding landscape adjacent to the alpine fault central southern alps new zealand 1 potentially active faults are exposed in the steep glaciated topography of the central southern alps new zealand immediately adjacent to the alpine fault plate boundary four major faults exposed along the flanks of three of the highest mountain ranges strike 10 23 km potentially 40 km nne oblique to the alpine fault dipping 57 12 nw in the opposite direction youngest discernable motions were reverse dip slip accommodating both margin perpendicular shortening and dextral margin parallel components of plate motion kinematic analysis yields a compression axis 295 10 9 trend or plunge equivalent to the contemporary shortening determined from seismological and geodetic studies suggesting the faults may be active although definitive evidence for recent movement or single event displacements is lacking there are 106 other potentially active faults mapped in central southern alps with strike lengths 4 73 km earthquake parameters were assigned from fault trace lengths and historical earthquake statistics indicating potential for mw 5 5 7 4 earthquakes at recurrence intervals of 1000 10 000 years such long recurrence intervals are consistent with the faults having little surface expression with rapid erosion of these seismically agitated mountains erasing any evidence of surface rupture during periods between earthquakes the central southern alps faults exemplify the difficulty in fully deciphering long term e g holocene or quaternary records of seismicity in tectonically active regions with rapidly evolving landscapes although there may be little evidence of surface ruptures remaining in the landscape the faults are still an important potential source of earthquakes and seismic hazard

small scale fractures glaciated surfaces and recent strain adjacent to the alpine fault new zealand small displacements of recently deglaciated surfaces across mesoscopic fractures at several localities adjacent to the alpine fault allow the determination of the direction unknown principal horizontal shortening as 126 10 this is consistent with estimates from geodetic studies microearthquake fault plane solutions and macroscopic faulting and suggests that the displacements represent the release of accumulated regional tectonic strain the rapid development of the features following ice removal over the past few centuries suggests a mechanism whereby ice loading allowed the accumulation of tectonic elastic strain in the near surface rocks which was subsequently released on unloading

the tectonic evolution of the southern alps new zealand insights from fully thermally coupled dynamical modelling summary we present here the results of numerical models of the southern alps in which the thermal and dynamical developments of the orogen are fully coupled to one another this interlinkage allows the use of a wide range of thermal and physical features of the orogen as constraints on the applicability of our models in particular the thermal aspect of this method enables the prediction of the distribution of thermochronological ages at the surface of the model perturbation of the geothermal structure due to rapid uplift and exhumation causes an intrinsic weakening and concentration of strain along the equivalent of the alpine fault zone in these models this thermal weakening of the crust also produces a zone of high strain antithetic to the alpine fault in the upper crust that is comparable to the main divide fault zone within the southern alps the introduction of orographic rainfall and erosional processes into the model leads to the development of high asymmetric topography comparable to that of the southern alps this topographic profile results from the capture of available precipitation by the windward side of the orogen and the resultant rain shadow on the leeward side due to the time required to accumulate suycient topography for this rain capture evect to become significant the establishment of this high asymmetric topography lags the initiation of surface uplift by several million years comparison of the observed thermal history of the southern alps with that seen in models based on divering hypotheses of the tectonic evolution of the south island shows that the present tectonic regime of the orogen most probably developed in a single rapid reorganization of plate motions at approximately 5 ma with relative stability of the tectonic regime since that time the variation in isotopic ages along the southern alps is consistent with that expected from variation in accumulated uplift and exhumation along the orogen arising from the obliquity of convergence of the australian and pacific plates

evidence for a landslide origin of new zealand s waiho loop moraine the waiho loop moraine has been interpreted as evidence for younger dryas cooling in southern new zealand but recent dating and climatological studies have questioned this idea a detailed analysis of the sedimentology of the moraine suggests it was formed after a large landslide onto the franz josef glacier triggered a glacial surge independent of climate forcing

continental crust under compression a seismic refraction study of south island geophysical transect i south island new zealand 1 the 1996 south island geophysical transect sight active source seismic survey was designed to show the style of lithospheric thickening due to late cenozoic oblique convergence across the australian pacific plate boundary in new zealand as part of this study two seismic refraction lines were shot across central south island and offshore extensions of the continental crust in the tasman sea and pacific ocean we present the data and a 603 km long seismic velocity profile of the crust and uppermost mantle along one of these seismic transects a tomographic inversion of 62 563 travel times from crustal and upper mantle refractions and wide angle reflections resulted in a model with a two layer crust upper crustal velocities were between 5 9 and 6 3 km s and lower crustal velocities were between 6 5 and 7 0 km s continental compression has locally reduced the seismic velocities in the pacific plate crust by 0 2 0 3 km s a possible effect of high strain and fluids in the crust the thickening of the crust from 28 km at the east coast of south island to 37 km beneath the southern alps can account for about 25 of the 80 110 km shortening of pacific plate crust while the rest must be accounted for by rapid erosion of mesozoic sedimentary rocks on the west side of the orogen in our model the lower crust forms a continuous 2 6 km thick layer beneath central south island the asymmetric topography of the southern alps is reflected in the crustal root which has a steeper flank at the west coast this observation is consistent with westward underthrusting of pacific lower lithosphere beneath south island that has been suggested in earlier studies

a comparison of forward modeling and inversion of seismic first arrivals over the kapuskasing uplift abstract a comparison has been made between the results of trial and error forward modeling and a tomographic inversion of first arrival travel times from a reversed seismic refraction profile across the kapuskasing uplift northern ontario the data were collected as part of a crustal scale experiment and were originally interpreted using forward modeling with synthetic seismograms the original analysis utilizing refracted arrivals imaged a high velocity anomaly 6 5 to 6 6 km sec beneath the chapleau block of the kapuskasing uplift that extended to 17 to 20 km depth with a dip of 15 2 based on the surface geological exposures this dipping anomaly was interpreted as a zone of granulites up thrust from the mid crust in early proterozoic times to test the significance of this anomaly a tomographic inversion was performed on the first arrivals from the profile the inversion results corroborate the main features of the original velocity model a high velocity anomaly 6 5 to 6 6 km sec at the surface in the granulite zone flanked by lower velocities 6 0 to 6 1 km sec in the wawa terrane to the west and 6 2 to 6 3 km sec in the abitibi belt to the east however resolution analysis and test inversions indicate that the first arrival travel times alone can only image the western edge of the dipping high velocity anomaly to less than 10 km depth at depths greater than 7 5 to 10 km in the west and 2 5 km in the east model resolution significantly deteriorates and the sensitivity of the final velocities to the starting model used for inversion increases resolution analysis also demonstrates how additional intermediate shot points or increased aperture would have improved resolution of the anomaly at greater depth emphasizing the importance of performing resolution analysis during the planning stages of refraction experiments

brittle and ductile deformation in a zone of rapid uplift central southern alps new zealand schists exposed in the central southern alps new zealand 1 5 km east of the alpine fault zone have been rapidly uplifted during the late cenozoic a regionally consistent sequence of mesoscopic structures discordant to the schistosity is recognized extending backward in time from recent brittle displacements of deglaciated surfaces through structures exhibiting brittle ductile transitional behaviour to ductile deformational features kinematic analysis of these structures gives consistent principal subhorizontal shortening directions similar to the present day principal horizontal shortening direction indicating their relation to late cenozoic uplift of the southern alps analysis of deformed veins suggests a minimum shortening strain of about 50 perpendicular to the foliation the veins crosscut upright mesoscopic to macroscopic folds which commonly develop high strain zones on their limbs within such zones a strong stretching lineation plunges gently sw approximately perpendicular to the stretching lineation in the mylonites along the alpine fault the folds and high strain zones do not appear to be related to late cenozoic uplift but may have originated during an earlier phase of dominantly strike slip motion fluid inclusion studies give depth temperature estimates of around 3 km and 285 c for the development of the brittle structures and 6 8 km at 310 350 c for the brittle ductile transition the deformed veins show evidence of extensive fluid infiltration during the later phases data from fluid inclusions and metamorphic assemblages give an estimate of 15 20 km and 400 450 c for their deformation these data combined with uplift rates determined by other studies allow the construction of a depth temperature time path which indicates nearly isothermal decompression associated with rapid uplift a shallow brittle ductile transition 6 8 km is consistent with numerical modeling of thermal and mechanical behavior of the crust during rapid uplift associated with continental collision and with the presence of high heat flow in the area because of the small temperature change over a large amount of decompression pressure may be an important factor in controlling the depth of the brittle ductile transition the marked temperature drop above the brittle ductile transition is thought to be enhanced by the influence of convection as an effective cooling mechanism

40ar 39ar thermochronologic constraints on deformation metamorphism and cooling exhumation of a mesozoic accretionary wedge otago schist new zealand abstract structural thickening of the torlesse accretionary wedge via juxtaposition of arc derived greywackes caples terrane and quartzo feldspathic greywackes torlesse terrane at 120 ma formed a belt of schist otago schist with distinct mica fabrics defining i schistosity ii transposition layering and iii crenulation cleavage thirty five 40ar 39ar step heating experiments on these micas and whole rock micaceous fabrics from the otago schist have shown that the main metamorphism and deformation occurred between 160 and 140 ma recorded in the low grade flanks through 120 ma shear zone deformation this was followed either by very gradual cooling or no cooling until about 110 ma with some form of extensional tectonic exhumation and cooling of the high grade metamorphic core between 109 and 100 ma major shear zones separating the low grade and high grade parts of the schist define regions of separate and distinct apparent age groupings that underwent different thermo tectonic histories apparent ages on the low grade north flank hanging wall to the hyde macraes and rise and shine shear zones range from 145 to 159 ma n 8 whereas on the low grade south flank hanging wall to the remarkables shear zone or caples terrane range from 144 to 156 ma n 5 most of these samples show complex age spectra caused by mixing between radiogenic argon released from neocrystalline metamorphic mica and lesser detrital mica several of the hanging wall samples with ages of 144 147 ma show no evidence for detrital contamination in thin section or in the form of the age spectra apparent ages from the high grade metamorphic core garnet biotite albite zone range from 131 to 106 ma n 13 with a strong grouping 113 109 ma n 7 in the immediate footwall to the major remarkables shear zone most of the age spectra from within the core of the schist belt yield complex age spectra that we interpret to be the result of prolonged residence within the argon partial retention interval for white mica 430 330 c samples with apparent ages of about 110 109 ma tend to give concordant plateaux suggesting more rapid cooling the youngest and most disturbed age spectra come from within the alpine chlorite overprint zone where samples with strong development of crenulation cleavage gave ages 85 107 and 101 ma due to partial resetting during retrogression the bounding remarkables shear zone shows resetting effects due to dynamic recrystallization with apparent ages of 127 122 ma whereas overprinting shear zones within the core of the schist show apparent ages of 112 109 and 106 ma these data when linked with extensional exhumation of high grade rocks in other parts of new zealand indicate that the east gondwana margin underwent significant extension in the 110 90 ma period

lithospheric structure in the southern canadian cordillera from a network of seismic refraction lines lithospheric velocity structure and its relationship to regional tectonics and development of the southern canadian cordillera are derived from a synthesis of interpretations from nine in line seismic refraction wide angle reflection profiles and broadside data recorded during the lithoprobe southern cordillera refraction experiment score and other refraction experiments across southern british columbia and one profile in northwestern washington consistency of the score two dimensional models at their intersection positions is achieved through application of a simultaneous inversion of all relevant traveltime data the cross sectional and map presentations demonstrate the strong degree of three dimensional heterogeneity within the crust and upper mantle a first order characteristic is the continuous increase in crustal velocities westward from the foreland belt to the insular belt the variations do not correlate with the morphogeological belts they do correspond with large scale geological and or

metamorphic response and crustal architecture in a classic collisional orogen the damara belt namibia abstract the damara belt is a well exposed mid crustal section through a collisional orogen of cambrian age that closed the khomas ocean basin between passive margins on the congo and kalahari cratons collision resulted in a bi vergent orogen with a distinct paired metamorphic pattern of foreland vergent high p low t orogenic margins and a broad high grade low p high t orogen core spatial and temporal patterns of the metamorphic response to collision have been characterized for all parts of the belt using a large dataset n 240 of internally consistent quantitative pt determinations evolution of mineral parageneses and semi quantitative p t paths metamorphic mapping and quantitative metamorphic field gradients integration with deformation history structural profiles metamorphic chronology magmatic history and stratigraphy constrains a dynamic model of crustal architecture during peak metamorphic events the pattern of zonal metamorphic response is demarcated by three major metamorphic discontinuities md with steep pressure gradients inferring crustal scale structures that accommodated lateral exhumation of crustal wedges discontinuities are confirmed by deformation features in the field and metamorphic mineral growth indicates that vertical flattening at the peak of metamorphism progressing through ductile to brittle extensional structures crustal wedges along the orogenic margins experienced steep clockwise p t paths with peak pt conditions terminated by isothermal decompression during rapid exhumation in isostatic response to deep burial metamorphic chronology and over printing metamorphic fabrics constrain a sequence of foreland propagating out wedging of crustal thrust wedges that resulted in telescoping of the orogenic margins peak metamorphism at a geothermal gradient of 20 25 c km and 8 9 kb in the southern zone wedge i was attained between 517 530 ma followed by south directed out wedging at the uis pass suture accommodated by relative extension md1 at high structural levels near the boundary with the high grade orogen core out wedging of the southern zone further buried the southern margin zone wedge ii in the footwall below the uis pass suture peak metamorphism at 17 c km and 9 5 11 5 kb in the southern margin zone was attained at 517 4 ma and followed by out wedging on basal thrusts accommodated by vertical flattening and extensional reactivation of the uis pass suture md2 peak metamorphism at 17 c km and 10 5 kb in a high p low t crustal wedge in the northern margin wedge iii occurred at 510 4 ma peak metamorphism in this wedge was terminated by isothermal decompression during north directed thrusting accommodated by extension at higher structural levels near the high grade orogen core md3 granulite facies metamorphism in the high grade orogen core which formed the upper plate to the deeper thrust wedges occurred at significantly lower pressures 4 3 6 0 kb higher t depth ratios 38 47 c km and low p t clockwise p t paths indicating only moderate burial and protracted high grade conditions metamorphic chronology confirms high grade conditions 540 505 ma persisted beyond isostatic adjustment of the high p low t orogenic margins high heat flow conditions and long thermal lag are best explained by lithospheric breakoff during collision in contrast to the high p low t margins that experienced lateral exhumation in a convergent system the high grade orogen core was exhumed vertically as a broad core complex during extensional collapse of the orogen peak metamorphic conditions in the central part of the orogen core record higher pressures than marginal lower grade zones to both the north and south indicating vertical exhumation as a broad massif this post peak vertical exhumation of the central core occurred after 505 ma was accommodated by brittle extensional detachments at high stratigraphic levels with km scale omission of crustal section

uplifted marine terraces along the alpine fault new zealand three types of evidence indicate that marine terraces are widespread in the southern alps of new zealand i remnants of shore platforms occur as distinct levels of notched ridge crests and flat summits degraded sea cliffs are common ii scattered quartz beach pebbles occur on 16 of 18 levels of exhumed shore platforms in the fox franz josef type area to altitudes as high as 1700 meters iii altitudinal spacings of new zealand terrace flights allow correlation with 18 dated global marine terraces at new guinea which were formed during glacio eustatic highstands of sea level within the last 336 x 10 3 years inferred uplift rates at fox franz josef increased from 3 2 to 7 8 meters per 10 3 years since about 135 x 10 3 to 140 x 10 3 years ago presumably because of increased convergence between the pacific and australian plates

catastrophic landslides glacier behaviour and moraine formation a view from an active plate margin the influence of large bedrock landslides rock avalanches on the behaviour of glaciers is incompletely recognised here we present an example from an active tectonic margin in south island new zealand where large earthquakes leave a significant imprint on glacial records we demonstrate that terminal moraines on the western side of the southern alps record both ordinary i e climate driven and landslide initiated glacial advances following consideration of the processes involved in rock avalanche initiated moraine construction we suggest ways of determining the nature of the advance that built the terminal moraine the implications of these observations are important in breaking the conventional linkage of individual terminal moraines with climate forcing

middle to late miocene age for the end of amphibolite facies mylonitization of the alpine schist new zealand implications for onset of transpression across the alpine fault

metamorphism and uplift of alpine schist in the franz josef fox glacier area of the southern alps new zealand geothermometry and geobarometry of 10 garnet oligoclase zone schists in the franz josef fox glacier area southern alps new zealand give temperatures ranging from 415 to 625 c and pressures from 5 2 to 9 2 kbar indicating a t p array of about 50 c kbar and inferred peak temperature conditions over a c 15 km thick section at depths between c 20 and 34 km the present day distribution of the schist samples implies that only about one third of the original crustal section is now exposed the garnet oligoclase zone schists represent the deeper part of a metamorphosed and deformed accretionary complex that was associated with late palaeozoic early mesozoic subduction along the gondwana continental margin partial uplift c 0 2 m ma and erosion of the complex during jurassic cretaceous times rangitata uplift was synchronous with d2 deformation and recrystallization as recorded by the p t array cenozoic kaikoura uplift and exhumation of the schist since c 30 ma to form the southern alps was associated with oblique slip movement on the alpine fault the present day position and steep eastward dip of isograds and d2 structures suggest considerable clockwise rotation during uplift associated with ductile attenuation and tectonic thinning by over two thirds of the original schist sequence largely due to simple shear along schistosity planes as the schist generally shows only incipient greenschist facies retrograde recrystallization an apparently complete although contracted prograde mineral sequence has been preserved by rapid uplift 5 km ma of hot rock and the effects of limited shear heating near the alpine fault

two sided orogen collision and erosion from the sandbox to the southern alps new zealand in continental collision zones the indentor is of approximately the same vertical dimension as the material being deformed thereby allowing material to move over the indentor and out of the deforming orogen this simple constraint on the height of the indentor differs from that imposed by the bulldozer model of wedge deformation and results in the formation of an orogen with two opposite dipping topographic slopes these two wedges are mechanically coupled and the mechanics are strongly influenced by the erosion conditions imposed on the wedge where the growing mountains perturb prevailing moisture laden winds the erosion pattern is highly asymmetric erosional work being concentrated at the toe of the steep wedge facing the indentor the inboard wedge concentration of erosional energy results in concentration of mechanical energy in the same region and produces the distinctive geological and geophysical patterns associated with continental collision these include rapid uplift and exposure of deep crustal assemblages adjacent to the indentor accompanied by high crustal heat flow and anomalously low seismicity the outcrop pattern along the inboard wedge evolves from that of a crustal cross section currently exposed in the southern alps to one dominated by repetitive nappe structures consisting predominantly of lower crustal units as in the western alps of europe the other wedge the outboard wedge undergoes relatively little erosion is broad with a more gentle surface slope and maintains an outcrop pattern consisting of upper crustal material

study of out of plane effects in the inversion of refraction wide angle reflection traveltimes abstract in the presence of three dimensional 3d inhomogeneous structure the results of 2d traveltime inversion will be in error since the effects of out of plane or 3d ray sampling are ignored we have inverted synthetic data using 2d and 3d algorithms to examine the errors caused by 3d inhomogeneities which produce significant out of plane ray bending the results of inverting data from 2d experiments are compared with vertical slices through 3d models obtained by inverting data using a number of recently employed 3d recording geometries our results show that even for strong 3d inhomogeneities out of plane effects are relatively small with crustal velocity errors of less than 0 15 km s and intra crustal boundary depth errors generally less than 2 km these errors are approximately equal to the uncertainties commonly assigned to crustal models derived from traveltime inversion the artifacts are also similar in magnitude to the lateral smearing that occurs in 3d models when using relatively coarse 3d geometries only for a dense network of profiles will a 3d inversion using off and in line data provide greater lateral resolution than a 2d independent or simultaneous inversion of in line data along each profile 2d and 2 5d inversion of crooked line data in the presence of strong velocity variations produces erroneous small scale velocity structure we conclude that most 3d crustal experiments cannot be justified on the basis that the results from a 2d experiment or a network of 2d profiles will be significantly in error due to out of plane effects 3d experiments can be justified when a dense grid of shots and receivers is used or if a volume image as opposed to a cross sectional image is required

metamorphic response in orogens of different obliquity scale and geometry abstract investigation of material flow within transpressional orogens must involve integration of structural and metamorphic datasets to illustrate the problems in documenting flow vectors we present integrated structural metamorphic datasets from two transpressional systems the kaoko belt in namibia and the kalinjala shear zone in south australia these orogens experienced widely differing metamorphic responses to transpressional deformation integration of kinematic and metamorphic datasets from the kaoko belt indicate shallow up plunging extrusion trajectories in the orogen core and show that the maximum stretching direction pattern matches the inferred flow vectors high grade domains 800 840 c and 7 0 8 0 kb in the orogen core developed low angle upward verging maximum stretching direction trajectories whereas a low grade domain 575 600 c and 5 0 5 5 kb in the orogen core has downward verging lineation trajectories the barometric differential between these high grade and low grade domains is entirely consistent with the angle of plunge of maximum stretching directions within the high grade domains that were extruded obliquely for the amount of lateral shear estimated for the orogen core the kalinjala shear zone in south australia contrasts strongly with the kaoko belt in this example the high grade and high strain shear zone core of the orogen experienced high t high p metamorphism with low thermal gradients of 21 26 c km and steep decompressive p t paths the lower grade external domains experienced lower t lower p metamorphism with high thermal gradients of 35 37 c km sub horizontal maximum stretching directions do not match the vertical extrusional flow in the high grade core that is indicated by the metamorphic data this comparison shows that in general and on a gross scale maximum stretching directions do not necessarily correlate with the real flow vectors experienced during orogenesis in some cases maximum stretching direction recorded by deformation structures is to some degree decoupled from the vertical component of material flow consequently information pertaining to flow is often partitioned into information derived from deformation structures and information derived from the metamorphic record these two datasets must be used in concert to obtain realistic constraints on first order material flow trajectories at orogenic scales the horizontal component of flow is typically best recorded by structural fabrics maximum stretching direction and sense of shear whereas the vertical component is typically best recorded by metamorphic information such as p t paths temperature over depth ratio g and metamorphic field gradients i e t p and g across the orogen

modeling wide angle seismic data for crustal structure southeastern grenville province a modeling methodology for obtaining two dimensional 2 d crustal structure from wide angle seismic data is applied to data from the southeastern grenville province pre modeling steps include 1 assignment of arrival pick uncertainties for appropriate data fitting and weighting using an empirical relationship based on signal to noise ratio 2 using a modified form of travel time reciprocity to avoid unreasonable levels of model heterogeneity and 3 identifying data unsuitable for 2 d modeling the goal of the travel time inversion amplitude modeling approach is to obtain a minimum structure and minimum parameter model that takes into account both horizontal and vertical variations in the resolution of typical wide angle data each step of a layer stripping procedure involves a series of inversions in which a one dimensional or simple starting model is improved with additional velocity and or interface nodes until a satisfactory trade off between travel time fit parameter resolution and complete ray coverage of all source receiver pairs is achieved using zero vertical velocity gradient layers and head waves during preliminary first arrival inversion can 1 decrease the number of intermediate models 2 allow greater lateral heterogeneity to be imaged and 3 simplify incorporation of amplitude modeling constraints into the final model using amplitude distance curves allows quantitative modeling of the relative amplitude and offset variations of phases discrepancies between observed and calculated reflection amplitudes are used to infer fundamental non step like velocity changes at layer boundaries later arrivals due to unresolved velocity anomalies are modeled using reflecting segments that float within the model without an associated velocity structure these reflectors provide a spatial image like that obtained from vertical incidence reflection data as opposed to a velocity image the model of grenville crustal structure is more detailed than a model obtained from a previous interpretation of the data and includes elements analogous to those imaged in nearby deep reflection data a crustal scale zone of wide angle reflectors with an average easterly apparent dip of 13 defines a major grenvillian terrane boundary

thermal regime in the central alpine fault zone new zealand constraints from microstructures biotite chemistry and fluid inclusion data abstract the thermal state within plate boundary fault zones is likely to influence the dimensions of large co seismic fault ruptures and strain localisation in underlying mylonitic shear zones vein microstructures biotite chemistry and fluid inclusion data offer new insights into the thermal structure of the mylonitic shear zone down dip of the alpine fault the main pacific australian plate boundary structure through southern new zealand quartz veins within the fault rocks were formed and deformed at temperatures ranging from 500 c to immediately above that of the brittle viscous transition 325 c illustrating that fluids are present throughout the fault zone microthermometric data from primary mixed co 2 h 2 o fluid inclusions in boudin neck quartz carbonate veins indicate that these inclusions were trapped at temperatures of 325 15 c and pressures of c 40 mpa vein microstructures indicate that fluid temperatures were equal to rock temperatures assuming hydrostatic fluid pressure the veins were trapped at depths of 2 o co 2 fluids in the shallower crust of 500 kg m 3 biotite grains in the mylonites are a mixture of porphyroclastic grains with high r ti mg inherited from the parent alpine schist and smaller low r grains that recrystallised during mylonitisation particularly those that are found within syn mylonitic shear bands assuming a simple step function model approximating diffusive equilibration the changes in biotite chemistry indicate t during mylonitic deformation of 340 c according to the ti in biotite thermometer of henry et al 2005 a best fit uplift p t path to existing data and these new results indicate that the uplift path p t gradient of fault zone rocks above the brittle viscous transition is of the order of 40 c km 1 below the brittle viscous transition the uplift path p t gradient is 10 c km 1 the p t profile within the fault rocks is comparable to that in the immediate hanging wall alpine schist indicating there is no peak in the crustal isotherms in the fault hanging wall as was indicated by previous numerical models and analyses that did not consider data from the fault rocks themselves

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

least squares inversion of spatial seismic refraction data a method is demonstrated for recording and inverting in line and broadside seismic refraction and reflection data to obtain three dimensional structure and velocity information this technique of spatial seismic refraction recording produces a superabundance of common ray intersections at the target horizon the full power of the linear least squares inversion method may be used in the overconstrained case a large number of recording instruments are required to perform the experiment efficiently but this has the advantage of reducing the number of sources and difficult source corrections a damped least squares inversion method has been found to give rapid convergence even in the case of complex faulted models using noisy data the spatial seismic refraction recording method has been applied in a suboptimal experiment over the williston basin in southern saskatchewan the crustal structure consists of several normally faulted blocks defined by aeromagnetic anomalies over an area notable for its thick crust local seismicity and a linear conductive anomaly

extrusional tectonics in the core of a transpressional orogen the kaoko belt namibia the pan african kaoko belt of nw namibia provides a wellexposed example of material flow in the evolving middle and lower crust during sinistral transpressional orogenesis the kaoko belt is a composite metamorphic belt with shear zone bounded zones of contrasting metamorphic style that were metamorphosed at approximately the same time 575 550ma it is divided into a barrovian style escape zone with inclined nappes and thrusts that verge outward towards the foreland a steep high grade orogen core that experienced intense wrench style deformation and in the hinterland an older 650ma exotic coastal terrane that was reworked at moderate t low p conditions during transpressional orogenesis the kinematic lineation array defined by stretching lineations and shear sense indicators shows variation in degree and polarity of lineation obliquity to the grain of the belt lineation plunge and different polarity of vergence along the plunge with respect to the overall sinistral shear sense the gross regional lineation pattern defines an arcuate array from near orogen parallel in the orogen core to higher angle obliquity across the escape zone reflecting lateral escape towards the orogen margin two highgrade lobes within the orogen core are coincident with obliqueinclined upward flow trajectories based on the kinematic lineation array and represent oblique extrusion of lower crustal material into middle crustal levels an intervening low grade metamorphic trough within the orogen core and the coastal terrane coincides with acute oblique downward and outboard directed apparent flow trajectories these kinematic patterns are consistent with barometric constraints for peak metamorphism of 5 2kbar and 4 5kbar in the low grade trough and coastal terrane and 8 0kbar in the two high grade lobes integration of the kinematic and metamorphic datasets shows that oblique shallowly inclined extrusion trajectories occurred within the orogen core of this classic transpressional orogen and that stretching lineations approximately reflect the particle paths experienced across orogen metamorphic gradients indicate a marked contrast between the escape zone and orogen core the escape zone experienced an inverted barrovian style high p moderate t metamorphism and low thermal gradients of 20 c km the orogen core experienced moderate p high t metamorphism and high thermal gradients of 30 40 c km clockwise p t paths were experienced in all parts of the kaoko belt tight and shallow conduction dominated p t paths were experienced in all orogen core domains involving heating dominated prograde paths followed by decompression consistent with extrusional tectonics steeper and more open advection dominated p t paths were experienced in the crustal over thrust escape zone which experienced low thermal gradients