modern sedimentary processes in the wilmington canyon area u s east coast abstract sedimentary processes active in the wilmington canyon area during the past century are documented from geochronologic sedimentologic and radiographic analysis of sediment cores collected using primarily d s r v alvin site selection for the alvin dives and for collection of box and kasten cores was achieved using sea marc and seabeam data allowing accurate sampling of numerous subenvironments from this extensively dissected area of the continental margin 210 pb sediment accumulation rates from intercanyon areas are highest on the upper slope 1 7 mm yr 140 mg cm 2 yr and decrease with water depth to about 0 4 mm yr 36 mg cm 2 yr on the upper rise within submarine canyons accumulation rates vary dramatically from a maximum of 6 mm yr 500 mg cm 2 yr to less than 0 3 mm yr 22 mg cm 2 yr higher accumulation rates in canyons occur as a result of additional supply of older sediment probably from bioerosion of the canyon walls this is supported by observations from d s r v alvin reduced 210 pb activities and indurated mud clasts observed in several canyon cores extremely low accumulation rates in wilmington and south wilmington canyons are probably the result of strong episodic boundary currents non steady state 210 pb profiles and sedimentologic data indicate small scale mass wasting in south heyes canyon and on the lower slope and rise just north of wilmington canyon

cold water coral habitats of rockall and porcupine bank ne atlantic ocean sedimentary facies and benthic foraminiferal assemblages the extent of the cold water coral mounds in the modern ocean basins has been recently revealed by new state of the art equipment however not much is known about their geological extent or development through time in the facies model presented here seven different types of seabed substrate are distinguished which may be used for reconstruction of fossil coral habitats the studied substrates include off mound settings foram sands hardgrounds dead coral debris and substrates characterized by a variable density of living coral framework whereas sediment characteristics only provide a basis for distinguishing on and off mound habitats and the loci of most prolific coral growth benthic foraminiferal assemblages are the key to identifying different mound substrates in more detail specific foraminiferal assemblages are distinguished that are characteristic of these specific environments assemblages from off mound settings are dominated by attached epifaunal species such as cibicides refulgens and cibicides variabilis the attached epibenthic species discanomalina coronata is also common in off mound sediments but it is most abundant where hardgrounds have formed in contrast the settings with coral debris or living corals attract shallow infaunal species that are associated with more fine grained soft sediments the typical living coral assemblage is composed of cassidulina obtusa bulimina marginata and cassidulina laevigata the abundance of these species shows an almost linear increase with the density of the living coral cover the benthic foraminifera encountered from off mound to top mound settings appear to represent a gradient of decreasing current intensity and availability of suspended food particles and increasing availability of organic matter associated with fine grained sediment trapped in between coral framework

210pb derived sediment accumulation and mixing rates for the washington continental slope abstract total sediment accumulation rates g yr in four canyons indenting the washington continental shelf are about twice those on the nearby open slope even though canyons comprise less than 40 of the depositional area of the entire slope this is because 210 pb derived sediment accumulation rates g cm 2 yr for astoria and quinault canyons are 3 4 times greater than those for willapa and grays canyons and intermediate open slope areas supporting the hypothesis that columbia river derived solids are preferentially transported to these two canyons quinault canyon currently appears to be accumulating solids at rates much greater than its low long term accumulation rate which is attributed to turbidity currents transporting solids down this canyon roughly every 500 years the following four different approaches all show that mixing may cause 210 pb derived sediment accumulation rates for slope and canyon sediments to be 2 3 times higher than true accumulation rates 1 comparison between accumulation rates calculated from 210 pb profiles with and without surface zones in which mixing has obviously affected 210 pb distributions 2 comparison between 210 pb derived and independently determined long term accumulation rates 3 comparison between 210 pb derived accumulation and modern columbia river discharge rates 4 comparison between two and three layer steady state one dimensional diffusion advection decay models mixing coefficients for surface sediments calculated using a one dimensional two layer vertical eddy diffusion model show large differences within the region with most in the 3 30 cm 2 yr range mixing rates are several times larger in canyon sediments from 0 2 1 1 km water depth probably due to physical reworking processes erroneously neglected mixing at depth of no more than 5 of that calculated for the surface mixed layer can cause the 2 3 fold calculated overestimation of true sediment accumulation rates and 2 4 fold calculated underestimation of true mixing coefficients

the 1971 may 12 burdur earthquake sequence sw turkey a synthesis of seismological and geological observations summary it is now widely accepted that the rapid extension observed in western turkey is mainly accommodated by large active normal faults which control the geomorphology the ne sw trending burdur acigol and baklan basins bounded by large faults form a system of half graben whose orientation is evident in both the topography and the tilting of neogene sediments adjacent to them we used long period p and sh waveforms to determine the source parameters of the two largest earthquakes of the 1971 may 12 sequence that occurred in the burdur region the main shock was followed by many aftershocks which were distributed in a broad zone elongated ne sw parallel to the long axes of the basins in the region documented surface breaks of the 1971 event suggest that the northwest dipping faults along the southern margin of the burdur basin are those which moved well exposed fault planes are found dominantly to the south of burdur lake the surface dips of these faults are greater than that of the nw dipping nodal plane obtained for the main shock combined seismological and geological observations suggest that these faults have listric geometries

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

hydrothermal alteration in the witwatersrand goldfields abstract alteration is recorded throughout much of the 3 km thick upper witwatersrand succession in south africa and extends for 300 km around the basin and 50 km into the basin the evidence for this alteration comes from petrography mineralogy geochemistry rock fabrics and stratigraphy the alteration conceived as a giant halo enveloping each major goldfield requires a major hydrothermal event focused on the auriferous upper wits central rand group the scale and nature of the alteration and its relationship to gold distribution on various scales strongly support a hydrothermal model for gold deposition such a model can account for the 50 000 t of gold mined from the witwatersrand goldfields the model works within the context of the major advances in understanding of the geological framework of the witwatersrand basin including the recognition of the importance of post burial processes it is highly significant that the age of witwatersrand sedimentation is much older than 2700 my and thus the host rocks for gold were deposited at least 100 my before the major global archean greenstone gold event the shale units from 40 major mines covering the seven goldfields are examined to establish the nature and distribution of the alteration and to make the connection between the fluid infiltration that caused the alteration and the introduction of gold into the witwatersrand basin in the hydrothermal model described here an auriferous low salinity fluid is produced at about 500 c during the metamorphism of mafic material that was below and adjacent to the witwatersrand basin large shear zones in the footwall of goldfields are the inferred fluid pathways into the upper wits succession and then unconformities smaller shear zones veins and the reef packages guide local fluid flow in this model gold precipitation occurs in response to the reaction of the fluid with carbon and iron bearing rocks that are abundant in the reef packages immediately overlying unconformity surfaces gold precipitation occurred at about 350 c and 10 km depth with the implication of a high geothermal gradient approaching 35 c per km the alteration of the shales but lack of abundant gold in them is predicted from the paucity of appropriate rocks or minerals in the shale units to precipitate gold but fluid infiltration still changed their composition fundamentally the source of the witwatersrand gold its present distribution and the alteration are explained within this hydrothermal model with similarities to the models invoked for other major gold provinces it is worth noting that quartz pebble conglomerate is a poor term for this gold type and has almost certainly limited exploration opportunities globally

budgets and behaviors of uranium and thorium series isotopes in santa monica basin sediments abstract nine natural decay series isotopes were measured in six box cores collected from a transect across the santa monica basin the 210 pb derived sedimentation rate decreases from 80 mg cm 2 yr at the slope to 20 mg cm 2 yr in the deep central basin sediment mixing prevails in sites underlying oxic waters but is subdued in the anoxic deep basin below the sill depth uranium contents in sediments are controlled by levels of authigenic u which are higher in the more reduced condition in the deep basin most of the authigenic u results from precipitation within the sediments the 232 th 228 th disequilibrium in sediments indicates that 228 ra is lost from the sediments from a depth of 10 cm upward modelling the distribution of excess 228 th and 234 th in the surficial layers of the deep basin sediments results in a mean sediment mixing coefficient of 0 2 cm 2 yr and a sedimentation rate close to that based on 210 pb there is no evidence of changing sedimentation rate in the central basin during the past century fluxes of excess 210 pb 230 th and 231 pa to the central santa monica basin sediments are much higher than what can be predicted from local supply advective input of open ocean waters coupled with enhanced scavenging of these reactive nuclides at the ocean margin is considered to be the primary cause

plutonium 241am and 137cs ratios inventories and vertical profiles in washington and oregon continental shelf sediments abstract continental shelf sediments from nine locations off washington and oregon have 239 240 pu inventories which average 8 0 2 6 mci km 2 the columbia river and seawaters advecting over the shelf supply pu which is removed to underlying sediments principally through scavenging by inorganic paniculate matter mass balance calculations argue that less than 20 percent of the advected pu need be scavenged from the water column to balance river input and total shelf sediment inventories the percentage of the pu removed through scavenging is consistent with observed participate concentrations in shelf waters and published sediment water distribution coefficients no marked separation of pu from 137 cs is observed with depth in pacific shelf sediments as has been reported in atlantic coastal sediments this interocean distinctness can be explained by differences in particle mixing and downward diffusion of cs in sediments of varying porosities the transuranic inventories and pu cs ratios in the pacific sediments do not support the hypothesis of livingston and bowen that pu is remobilized within the sediment column by complexone formation with principally organic substances excess 210 pb 239 240 pu inventory ratios in eight representative cores from the washington shelf average 100 19 even though absolute values of both inventories vary by much larger factors this reasonably constant ratio for a given water depth permits estimation of total pu inventories and prediction of sites of unusual pu accumulation from data on the more easily measured natural radionuclide

a kinematic analysis incorporating incremental strain data for the frontal pennine zones of the western french alps abstract an incremental and finite strain study of the zones adjacent to the frontal pennine thrust fpt has been undertaken using syntectonic fibres taken from veins pyrite type pressure shadows and similar fringes from around pebbles in conglomeratic rocks the resultant strain data together with detailed mapping of local deformational geometries and regional trends has shown that the pennine zones show a more complex structural history than previously envisaged the structural analysis divides the pennine zones into two regions north and south of creve tete the southern termination of the valais basin the zones to the south of creve tete mont fut valbuche nielard and aiguille d arves show an essentially piggy back thrust sequence directed towards the foreland in which the elongation of the strain ellipse initially parallels the transport direction wnw but finally rotates to become sub parallel to the tectonic strike nne ssw the structures of the valais zone to the north of creve tete are more complex with both n and wnw verging folds thrusts and strike slip faults here the long axis of the strain ellipse appears initially to parallel the tectonic strike ne sw this is followed by a rotation into the late transport direction wnw this localised alternation between strike and transport parallelism is problematic specific examples of strike parallel extension may be explained in terms of radial transport buttressing against earlier extensional structures strike slip motion and or stretching over lateral culmination walls the major division in fibre pattern north and south of creve tete however is best explained as being a function of compartmentalization of deformation styles between adjacent areas models which invoke a dominant deformation mechanism e g thrust tectonics along the entirety of the alpine chain thus need to be rethought similarly the recognition of widespread strike parallel extension suggests that two dimensional balanced section techniques are simplistic giving only minimum shortening estimates in a single direction and thus failing to reflect the true situation

the use of radon 222 as a tracer of sediment irrigation and mixing on the washington continental shelf abstract observations of the natural radioisotope rn 222 were used in conjunction with radiochemical biological and sedimentological techniques to investigate the irrigation and mixing of sediment at three sites about 90 m water depth along the washington continental shelf the rn 222 deficit difference between observed and predicted concentrations within the seabed was greatest near the columbia river during the summer molecular diffusion at most locations and times could account for only a portion of the deficit irrigation and mixing of the seabed explain the remainder biological mixing bioturbation and physical irrigation wave and tidal pumping have relatively little effect on the rn 222 deficit physical mixing erosion and deposition has a significant effect soon after a major erosion event storm however no such event occurred prior to the observations the conclusion is that biological irrigation and molecular diffusion are the primary causes of the rn 222 deficit and that biological irrigation is responsible for the observed spatial and temporal variations in the deficit therefore biological irrigation is greatest near the columbia river during the summer the spatial increase of irrigation near the columbia is probably due to a relatively large population of tube dwelling filter feeding polychaetes the temporal increases of irrigation during the summer is probably due to annual growth cycles of the benthic community and is not due to water temperature changes

structural analysis of the gachsar sub zone in central alborz range constrain for inversion tectonics followed by the range transverse faulting analysis of the gachsar structural sub zone has been carried out to constrain structural evolution of the central alborz range situated in the central alpine himalayan orogenic system the sub zone bounded by the northward dipping kandovan fault to the north and the southward dipping taleghan fault to the south is transversely cut by several sinistral faults the kandovan fault that controls development of the eocene rocks in its footwall from the paleozoic mesozoic units in the fault hanging wall is interpreted as an inverted basin bounding fault structural evidences include the presence of a thin skinned imbricate thrust system propagated from a detachment zone that acts as a footwall shortcut thrust development of large synclines in the fault footwall as well as back thrusts and pop up structures on the fault hanging wall kinematics of the inverted kandovan fault and its accompanying structures constrain the n s shortening direction proposed for the alborz range until late miocene the transverse sinistral faults that are in acute angle of 15 to a major magnetic lineament which represents a basement fault are interpreted to develop as synthetic riedel shears on the cover sequences during reactivation of the basement fault this overprinting of the transverse faults on the earlier inverted extensional fault occurs since the late miocene when the south caspian basin block attained a ssw movement relative to the central iran therefore recent deformation in the range is a result of the basement transverse fault reactivation

is burial velocity a master parameter for bioturbation abstract the intensity of biological mixing in a marine sediment is widely believed to be related to the flux of labile organic matter at the same time this flux has been shown to be strongly correlated to the burial velocity one would then expect a significant correlation between biological mixing coefficient d b and burial velocity a nonlinear regression of existing data with a power law eqns 2 and 3 of the text produces a statistically significant correlation the statistical significance of the regression in no way implies causation and in fact it accounts for only about 22 of the total variance in the dataset thus reducing its physical significance a number of additional processes contribute to the large observed variance including timing of mixing events temporal and spatial heterogeneity differences in temporal scales sampling artifacts and specific particle associations with due care the d b relationship may prove useful in defining the likely range of d b values in a particular environment a similar analysis of the tracer identified surface mixed depth shows that it is essentially independent of burial velocity with a worldwide mean of 9 8 4 5 cm depth of mixing is probably more closely related to the energetic costs of deep burrowing

bedding parallel shear thrusting and quartz vein formation in witwatersrand quartzites abstract evidence is presented which clearly demonstrates the presence of thrust faults in the gold bearing sedimentary rocks of the witwatersrand supergroup a package of these rocks subjected to shear strain allowed overlying beds on the northern margin of the witwatersrand basin to move outwards in a n nw direction movement took place on ductile shear zones which were parallel to the bedding and often reveal excellent examples of ramp and duplex structures it has also been established that syntectonic foliation planes were utilized as planes of shear in certain circumstances quantitative estimates of strain for the pile which are of necessity minimum values give 1 fluids from which vein quartz formed played a critical role in the shear plane movement and may have relieved a portion of the overburden load during deformation

sediment mixing and accumulation rate effects on radionuclide depth profiles in hudson estuary sediments measured anthropogenic radionuclide profiles in sediment cores from the hudson river estuary were compared with profiles computed by using known input histories of radionuclides to the estuary and mixing coefficients which decreased exponentially with depth in the sediment observed sup 134 cs sediment depth profiles were used in the mixing rate computation because reactor releases were the only significant source for this nuclide whereas the inputs of sup 137 cs and sup 239 240 pu to the estuary were complicated by runoff or erosion in upstream areas in addition to direct fallout from precipitation our estimates for the rates of surface sediment mixing in the low salinity reach of the estuary range from 0 25 to 1 cm sup 2 yr or less in some areas of the harbor adjacent to new york city were fine particle accumulation rates are generally 3 cm yr and often as high as 10 to 20 cm yr sediment mixing rates as high as 10 cm sup 2 yr would have little effect on radionuclide peak distributions consequently anthropogenic radionuclide maximum activities in subsurface sediments of the hudson appear to be useful as time stratigraphic reference levels which can be correlated with periods of maximum radionuclide inputs for estimating rates and patterns of sediment accumulation

the origin and preservation of a major hurricane event bed in the northern gulf of mexico hurricane camille 1969 cores collected from mississippi sound in the gulf of mexico were studied using 210 pbxs and 137 cs geochronology x radiography granulometry and a multi sensor core logger our results indicate the presence of a widespread sandy event layer that we attribute to hurricane camille 1969 an initial thickness of more than 10 cm is estimated from the cores which is large compared to the time averaged apparent accumulation rate of 0 29 0 47 cm y 31 physical and biological post depositional processes have reworked the sandy layer producing a regional discontinuity and localized truncation and resulting in an imperfect and biased record of sedimentary processes during the storm the oceanographic and sedimentological processes that would have produced an event bed during hurricane camille are simulated using a series of numerical models i e 1 a parametric cyclone wind model 2 the swan third generation wave model 3 the adcirc 2d finite element hydrodynamic model and 4 a wave current bottom boundary layer model that is coupled to transport and bed conservation equations trans98 the simulated bed ranges from 5 cm to over 100 cm within a tidal channel near the barrier islands seaward of the islands the bed is more than 10 cm in thickness with local variability the magnitude and local variability of the storm bed thickness are consistent with the observed stratigraphy and geochronology on both the landward and seaward sides of the barriers 2002 elsevier science b v all rights reserved

sediment accumulation rates and carbon fluxes to bottom sediments at the western bransfield strait antarctica abstract mean sediment and carbon accumulation rates in the western bransfield strait during the last ca 100 years were determined at three sites by using 210 pb as a radiotracer of sedimentation processes rates 210 pb profiles showed moderate mixing in the upper 8 5 12 cm which was attributed to bioturbation sediment accumulation rates calculated assuming no mixing below the surface mixed layer sml were found to be relatively high between 0 03 and 0 09 g cm 2 yr 1 in good agreement with previously reported data based on both 210 pb and 14 c dating in surrounding areas these results together with the calculated excess 210 pb fluxes to the bottom sediments and the 210 pb and 210 po distributions in the water column indicated the presence of a large net advective flux of material in the area highlighting the importance of glacial related sedimentation processes in this semi enclosed sea carbon in bottom sediments was mainly organic and its content was moderately low 0 65 1 25 being slightly higher within the sml reflecting the presence of inhabiting organisms however organic carbon oc accumulation fluxes 3 1 6 7 g c m 2 yr 1 were considerable due to the high sediment accumulation rates 210 pb dated profiles allowed us to estimate the amount of carbon exported from the water column and buried in the bottom sediment which represents about 3 7 of the mean annual primary production in the euphotic layer of the bransfield strait the burial efficiency of oc in the sediment was estimated to be approximately 60 80

evaluating the structural character and tectonic history of the witwatersrand basin abstract the witwatersrand basin in south africa has been the focus of gold exploitation for more than 100 years and the subject of hundreds of research investigations principally sedimentological and metallogenic and recently geophysical and geochronological surprisingly the basin wide structural character has not been fully investigated despite the fact that gold metallogenic models have been proposed that want structural architectures as conduits for gold mobilisation and or sites of deposition i e the modified placer and hydrothermal models these models which have polarised viewpoints on the source for gold placer versus metamorphic or hydrothermal source assume an underlying structural character to the basin and structural relationships between goldfields but these assumptions have never been tested through evaluation of the existing structural dataset as corollary the published data for the structural character of the free state welkom klerksdorp west wits line west rand central rand east rand and south rand goldfields are summarised and evaluated to search for basin wide similarities and or correlations that would support tectonic models for the witwatersrand basin and explain its metallogenic character unfortunately the large published historical database 90 years proved to be quite limited with respect to geometric kinematic and or relative chronological detail but must be evaluated against an advanced understanding of earth processes tectonics and the structural geology approach the dataset is largely qualitative rather than quantitative but is useful in establishing broad tectonic trends of the formation and tectonic evolution for the witwatersrand basin it suggests that two deformation events umzawami and ukubambana events mark the end of deposition in the witwatersrand and transvaal basins respectively with development of fold thrust belts at ca 2 7 and 2 2 2 0 ga and these can be correlated with supercontinental cycles the intervening period i e 2 7 2 2 ga was characterised by at least 4 basin forming events that culminated in the deposition of the volcanic sedimentary sequences of the klipriviersberg group and the sedimentary sequences of the platberg chuniespoort and pretoria groups basin formation was facilitated by the reactivation of structures formed during the umzawami event or older as feeder dykes normal listric faults or growth faults the limited structural data for the witwatersrand basin unsurprisingly also leads to the conclusion that gold was macroscopically to mesoscopically remobilised from a primary placer source but remobilisation was localised goldfields scale and not is a basin wide phenomena

a hectare of fresh striations on the arkitsa fault central greece abstract some large new exposures of active normal faults in central greece reveal polished surfaces that could represent as many as 50 increments of co seismic slip the slip surfaces are nearly two dimensional with the slip vector aligned down the axes of corrugations and undulations however small but regular changes in slip vector between top and bottom of the exposure and a regular asymmetry of the polishing on corrugations may be related to block rotations about a vertical axis and show how the slip vector changes with time

the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf nittrouer c a and sternberg r w 1981 the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf mar geol 42 201 232 models of fine scale 120 m shelf regions the inner shelf sand and mid shelf sandy silt are the predominant accretionary deposits on the shelf important sedimento logical observations obtained by boxcoring the upper 1 2 m of these deposits are a progressive decrease in grain size with distance from the columbia b downward coarsening within the seabed c loss of distinct sedimentary structure homogenization of sediment with distance from the columbia non dimensional parameters based on sediment transport and benthic biological studies can be used to relate rates of sediment mixing re working to rates of accumulation these parameters have the potential for quantitative prediction of strata formation from measurements of active processes physical and biological mixing can be assumed to remain relatively constant in an alongshelf direction on the washington shelf and accumulation rate is known from pb 210 geochronology to decrease away from the columbia together these factors tend to increase the ratio of mixing to accumulation with distance from the columbia and predict the sedimentological observations listed above

the vredefort structure a perspective with regard to new tectonic data from adjoining terranes abstract the deformational history of the area surrounding the vredefort structure in south africa is long and complex involving several periods of contraction and extension a general chronology of events covering a time span of 1000 ma is established the vredefort deformation is identified as a separate structural event which is distinct from the earlier deformations it is essential therefore that deformational structures related to the pre vredefort event should be identified and subtracted from the total spectrum of tectonism so that only those structures which can be related with certainty to the formation of the vredefort structure are defined this approach could influence interpretations of the origin of the vredefort structure which attribute most structural and geological associations to the deposition of sediments onto a granitoid basement followed by a vredefort deformational event

the crustal architecture of the kaapvaal crustal block south africa between 3 5 and 2 0 ga following terrane amalgamation of early oceanic lithosphere the southern and central parts of the kaapvaal craton were a coherent unit by 3 1 ga juxta position of the northern and western granitoid greenstone terranes including the murchison island arc was the result of terrane accretion that started at 3 1 ga the culmination of these events was the collision of the kaapvaal craton the pre cratonic zimbabwe block and the central zone to generate the limpopo granulite gneiss terrane coeval with these orogenic events the central kaapvaal craton underwent extension to accommodate the development of the dominion witwatersrand pongola and ventersdorp basins the craton scale thabazimbi murchison lineament development during the 3 1 ga accretion event and continued to influence the tectonic evolution of the kaapvaal block throughout the period under review as indicated by the syn sedimentary tectonics of the 2 64 ga wolkberg group overlying black reef formation and the transvaal sequence the transvaal and griqualand west basins developed in the late archaean 2 55 ga with basin dynamics influenced by far field stresses related to the limpopo orogeny during this period the thabazimbi murchison lineament lay close to the northern margin of the depository reactivation of the lineament between 2 4 and 2 2 ga resulted in inversion of the transvaal basin and formation of the northward verging mhlapitsi fold and thrust belt the half graben setting envisaged for the deposition of the pretoria group was influenced by the thabazimbi murchison lineament as was the emplacement and subsequent deformation of the bushveld complex

bedding parallel veins and their relationship to folding abstract laminated bedding parallel veins hosted in turbiditic sandstone shale sequences from central victoria australia consist of stacked millimetre thick sub parallel sheets of quartz separated by micaceous layers wall rock slivers and pressure solution seams they have very high length to thickness ratios are laterally continuous over tens to hundreds of metres and have relatively uniform thickness compared to other vein types they are intimately associated with and folded by chevron folds and the quartz grain shape elongation lineation is commonly orthogonal to mesoscopic and macroscopic fold hinge lines the bedding parallel veins have two morphological forms type i are thin commonly 5 10 cm laminated veins which have complex microstructures dominated by phyllosilicate inclusion surfaces related to oblique opening along bedding with varying rates of deposition opening relative to shear displacement slip along the bedding surfaces more common are type ii thicker generally

modern sediment dispersal and accumulation on the outer poverty continental margin abstract the poverty margin was sampled in 2005 and 2006 as part of an international initiative to examine the terrestrial and marine sedimentary response to natural and human impacts on dispersal systems at mud dominated coasts the nsf margins source to sink initiative 210pb accumulation rates generally decrease from 1 g cm2 y in the mid shelf depocenter on the outer shelf to 0 1 g cm2 y on the mid slope plateau range 0 04 2 53 g cm2 y higher accumulation rates are observed all along the outer poverty shelf extending over the shelf break onto the upper poverty slope in canyons and gullies rates are fast in gullies that incise into the shelf edge 0 75 1 g cm2 y particularly in the area between waipaoa canyon and poverty canyon and in the axis of poverty canyon 1 29 1 89 g cm2 y below 1200 m water depth rates in the axis of poverty canyon are no more rapid than those found at open slope cores in similar water depths 0 12 0 15 g cm2 y excess 210pb profiles generally exhibit steady state characteristics except in the axis of poverty canyon where non steady state 210pb profiles are observed 137cs was not found above minimum detection limits or above statistical background levels in any cores from the poverty margin 7be was found distributed widely along and across the margin during both summer and winter periods observed to depths of up to 4 cm widespread presence of 7be on the margin in both winter and summer suggests that terrestrially derived sediment is reaching the outer shelf and upper slope throughout the year a sediment budget based on 210pb accumulation rate data shows that approximately 13 18 of the waipaoa annual discharge is accumulating on the outer poverty margin as a whole and approximately 11 15 of the annual discharge is accumulating on the continental slope alone notably approximately 28 of the sediment annually accumulating in the outer margin is being sequestered in slope gullies and canyons although they represent only 6 of the area of the outer margin

accumulation rates of major constituents of hemipelagic sediments in the deep alboran sea a centennial perspective of sedimentary dynamics the accumulation rates of sediment and major constituents in three different geographic areas of the alboran sea have been assessed by means of 210pb and 137cs concentration profiles mixing is present in the top layer of the sedimentary column with mixing coefficients estimated to range from 0 2 to 15 cm2 yr 1 overall apparent sedimentation rates for the last 100 years range from 0 014 to 0 182 g cm 2 yr 1 and show a tendency to decrease with distance to the coast and water column depth however specific characteristics of the sea floor for each physiographic environment govern the actual patterns of sediment accumulation particularly noticeable are the feeding role of submarine canyons the trapping effect of slope terraces and the isolation caused by ridges sediment accumulation induced by turbiditic flows is also observed north of the almeria oran area excess 210pb inventories and surface concentrations reveal a net effect of sediment focussing and point to the role of bottom nepheloid layers in supplying a significant fraction of sediments to the deep areas this is also evidenced by comparison of bottom sediment with the sediment trap data available from the malaga area we estimate that the particle advective input below 30 m above the bottom accounts for as much as 50 70 of the material that is ultimately deposited onto the sea floor the greater abundance of lithogenic material in the malaga zone 80 reflects its larger input in the western alboran sea conversely carbonate contents increase from less than 20 in this area to about 30 in the almeria oran zone reflecting the lesser importance of the dilution by lithogenic components biogenic silica was only detected in some surface samples and no significant preservation was observed below the eh boundary abundance and accumulation rates of organic matter are in accordance with the spatial patterns of primary production in the alboran sea higher in the western part due to the presence of the western alboran gyre however near bottom redistribution leads to the homogenisation of organic matter concentrations in bottom sediments of any given area finally from comparisons with sediment trap data the degradation of organic matter has been estimated to be approximately 30 40 of what reaches the bottom

inter array and intra array kinematics of en echelon sigmoidal veins in cross bedded sandstone merimbula southeastern australia abstract the kinematics of en echelon arrays of quartz veins hosted by sandstone of the upper devonian worange point formation are strongly influenced by bedding and cross bedding bulk deformation recorded by the vein arrays inter array kinematics was influenced by the anisotropy of the host rock such that three types of arrays are observed 1 east verging arrays parallel to bedding 2 east verging arrays oblique to bedding with veins parallel to cross bedding and 3 west verging arrays parallel to cross bedding with veins parallel to bedding these three array types correspond to flats ramps and backthrusts respectively and represent the earliest stages of thrust fault formation flat and ramp arrays form a staircase geometry and conjugate ramp and backthrust arrays form pop up structures the interpretation of the morphology of veins and wall rock intra array kinematics indicates rotation of bridges was the primary kinematic process in the arrays the opening of vein space by rotation of bridges which maintain constant thickness is predicted from measurements of the orientations of vein wall rock interfaces at vein tips and at the array centre comparison of the predictions with direct measurement of the proportion of vein to wall rock along the centreline of arrays demonstrates the applicability of the bridge rotation model which has been generalised to include the thickening or thinning of bridges during rotation

formation of an archaean continent about 30 of the earth is covered by continents but only about 10 small kernels of these continentsae known as archaean cratonsae are continental fragments formed before 2 5 gyr ago the kaapvaal craton of south africa which formed and stabilized between 3 7 and 2 7 gyr ago is one of the oldest reasonably sized examples of these continental fragments it consists of a mosaic of subdomains that have been welded together by processes similar to those of modern day plate tectonics the earliest subdomains may have owed their origin to the onset of efficient recycling from the earth s hydrosphere into the mantle

particle mixing rates in deep sea sediments determined from excess 210pb and 32si profiles particle mixing rates have been determined for 5 south atlantic antarctic and 3 equatorial pacific deep sea cores using excess 210 pb and 32 si measurements radionuclide profiles from these siliceous calcareous and clay rich sediments have been evaluated using a steady state vertical advection diffusion model in antarctic siliceous sediments 210 pb mixing coefficients 0 04 0 16 cm 2 y are in reasonable agreement with the 32 si mixing coefficient 0 2 or 0 4 cm 2 y depending on 32 si half life in an equatorial pacific sediment core however the 210 pb mixing coefficient 0 22 cm 2 y is 3 7 times greater than the 32 si mixing coefficient 0 03 or 0 07 cm 2 y the difference in 210 pb and 32 si mixing rates in the pacific sediments results from 1 non steady state mixing and differences in characteristic time and depth scales of the two radionuclides 2 preferential mixing of fine grained clay particles containing most of the 210 pb activity relative to coarser particles large radiolaria containing the 32 si activity or 3 the supply of 222 rn from the bottom of manganese nodules which increases the measured excess 210 pb activity relative to 226 ra at depth and artificially increases the 210 pb mixing coefficient based on 32 si data and pore water silica profiles dissolution of biogenic silica in the sediment column appears to have a minor effect on the 32 si profile in the mixed layer deep sea particle mixing rates reported in this study and the literature do not correlate with sediment type sediment accumulation rate or surface productivity based on differences in mixing rate among three antarctic cores collected within 50 km of each other local variability in the intensity of deep sea mixing appears to be as important as regional differences in sediment properties

210pb activities in and fluxes to sediments of the washington continental slope and shelf abstract surface sediments of the washington coast have 210 pb activites which average 104 48dpm g for submarine canyon and slope regimes and 18 12dpm g for the continental shelf regime 210 pb sedimentary fluxes are also higher in canyons averaging 18 13dpm cm 2 per yr compared to 5 2 3 1 dpm cm 2 per yr for slope and 4 8 1 8dpm cm 2 per year for shelf regions these 210 pb activities and fluxes are 2 7 times greater than those reported for other coastal regions inputs from the atmosphere and the columbia river are not sufficient to supply the 210 pb but advection of seawater containing dissolved 210 pb produced in situ from 226 ra provides an input several times larger than the sedimentary fluxes the sedimentary 210 pb flux is limited by scavenging reactions rather than by supply of dissolved 210 pb calculations of maximum biological uptake and fluxes of 210 pb and selective chemical leaching experiments all show that the primary scavenging processes are due to hydrous mn and fe oxides rather than biological phases the pattern of higher 210 pb depositional fluxes in canyons than in nearby open slope areas of comparable water depth is most reasonably explained by enhanced scavenging of dissolved 210 pb near the sea floor rather than by processes operating throughout the water column relatively rapid removal of dissolved 210 pb from the near bottom nepheloid layer to slope and canyon sediments is shown by its mean residence time of less than two years in this layer

the importance of site selection sediment supply and hydrodynamics a case study of submarine paleoseismology on the northern cascadia margin washington usa abstract the washington continental margin presents both a classic test of submarine paleoseismology and an opportunity to explore advancement of the field through analysis of sediment dispersal in a heterogeneous system new and archive core bathymetric backscatter and seismic reflection data from the washington cascadia margin show that during high stand conditions the northernmost canyons barkley nitinat juan de fuca jdf and to some extent quillayute are relict systems with little holocene recharge the remaining canyons quinault grays guide and willapa are recharged to a varying degrees by northward transport of columbia river derived sediment all systems are nonetheless active conduits for turbidity currents during the holocene which are weaker and more restricted than their pleistocene counterparts sedimentologic and ct analysis supported by radiocarbon ages micropaleontology and the mazama ash datum show that the holocene sedimentary sequence consists of a series of sand to mud turbidites in the active portions of all systems interbedded with hemipelagic sediment however the pleistocene astoria and nitinat fans are largely inactive in the holocene with turbidity current activity limited to the proximal parts of the main channels within active systems the turbidite record is modulated by local landsliding and growth of active folds and faults in the relict systems the turbidite record begins in the middle canyon reaches as opposed to the actively recharged systems which have a turbidite record in the more proximal canyon reaches deposits in the relict systems increase in thickness and modal grain size downstream suggesting multiple sources and or entrainment of material along the canyon walls hydrodynamic models using monte carlo model searches for best fitting flow parameters show the most likely pathways by which holocene and pleistocene currents flowed through the complex accretionary wedge to the abyssal plain model results supported by heavy mineral distributions show that the northern canyon systems barkley nitinat jdf quillayute are independent of the southern systems quinault guide grays willapa during the holocene supporting the classic confluence test balancing of sediment volumes required suggests sediment supplied to the slope canyons and abyssal channels in turbidity current events is 2 5 times greater than that supplied by recharge to the canyon heads by external sources this implies a process that is independent of recharge that scavenges the plentiful relict and hemipelagic sediment supply on the continental slope lithostratigraphic correlation and age models suggest similar sequences were deposited in most systems independently and likely synchronously the correlated turbidite sequence suggests deposition of 23 holocene and 16 post mazama turbidites in most parts of the canyon systems with only modest variation mostly attributable to evidence of bypassing and erosion the best candidate for triggering of these sequences remains great earthquakes and the sequence correlates well to onshore and other offshore paleoseismologic evidence the new data including new cores in northern oregon suggest revisions to segmented rupture boundaries several partial ruptures segment b likely extended further north to juan de fuca canyon one event was resolved into two and one washington only event was added most segment c ruptures were found to extend further northward to the latitude of astoria canyon mean recurrence times are therefore revised to 434 years for the washington coast and 340 years for the central and northern oregon coast conditional probabilities in the next 50 years also are revised to 10 17 for the washington coast and 16 22 for the central and northern oregon coast in cascadia sumatra and other locales globally core siting spatial sample density high resolution analysis of core and regional geophysics and understanding of flow dynamics are critical to capturing a paleoseismic record sedimentary records vary across turbidity current systems of varying sediment supply physiography and sediment sources variations in the record will reflect these factors yet may still present a consistent paleoseismic history this analysis highlights the importance of a thorough understanding of flow paths hydrodynamics and the interplay of sedimentation and local tectonics when testing for evidence of earthquakes in the sedimentary record of active margins

the use of 7be to identify event and seasonal sedimentation near the po river delta adriatic sea in october 2000 a major flood event of the po river occurred the resulting seabed deposit was initially sampled in december 2000 and most sites were reoccupied on subsequent cruises over a 3 yr period using the maximum penetration depth of the short lived radioisotope 7be half life 53 3 d the flood deposit was found to be up to 15 cm thick individual depocenters of thick strata were located immediately adjacent to the distributaries at the river mouth in relatively shallow water 30 m these flood deposit thicknesses are minimum estimates because the depth of 234th half life 24 1 d exceeds that of 7be in physically stratified flood sediment indicating that the first sediment deposited during the flood event likely originated from the river channel 30 55 of the estimated sediment load delivered to the shelf during the flood event can be accounted for using 7be penetration depths seasonal deposition also can be quantified using 7be after removing the effects of biological mixing seasonal deposition rates are a maximum of 6 cm yr 1 near the pila distributary decreasing to 2 cm yr 1 in the southern portions of the dispersal system

live and dead benthic foraminiferal faunas from whittard canyon ne atlantic focus on taphonomic processes and paleo environmental applications abstract dead benthic foraminiferal assemblages were studied in the 150 m fraction of 4 5 cm deep sediment levels at 18 stations in the whittard canyon area in june 2007 this sediment layer is composed of fairly recent sediment in both canyon branches the population dynamics such as seasonal response to phytodetritus deposition certainly contribute to differences between live and dead faunas for instance bulimina marginata which is usually considered as an opportunistic species is over represented in the dead assemblage the fragility of the tests of some species can explain their total absence in the thanatocoenoses this concerns many organic cemented arenaceous tests miliolid tests sensitive to dissolution and perforate taxa with thin tests furthermore transport e g sediment gravity flows active in both canyon branches leads to an increasing relative contribution of allochthonous individuals originating from outer shelf and upper canyon sites towards the deeper canyon stations consequently the dead faunas do no reflect local environmental conditions the high abundance of transported dead foraminifera in both canyon branches leads to important biases in the foraminiferal assemblage composition but may also significantly bias the interpretation of 13 c 18 o trace elements and 14 c concentration in foraminiferal shells it may therefore strongly complicate the reconstruction of environmental parameters such as bottom water temperature or exported paleoproductivity and radiocarbon dating of the foraminiferal assemblages therefore in both canyon axes the use of dead foraminiferal faunas to reconstruct paleoenvironmental in situ conditions is precluded however the study of dead assemblages in the canyon branches in particular the quantity of allochthonous foraminifera can give important clues about the downslope sedimentary dynamics on both open slopes despite taphonomic test destruction and biological processes population dynamics the distribution and the composition of the live fauna resemble those of the dead assemblage in these areas dead foraminiferal faunas include much less material derived from downslope transport consequently on the open slope dead assemblages appear to better reflect local conditions therefore the ecological information obtained from fossil open slope samples can be more reliably used to reconstruct paleoenvironmental conditions

towards a sediment budget for the santa cruz shelf a conceptual model is presented for the northern monterey bay continental shelf in which coarse sediment moves southward along the coast in the littoral zone while fine sediment moves to the north by advection and diffusion along the midshelf data from measurements and estimates of various sediment sources and sinks show that the midshelf mudbelt is the dominant sink for fine grained sediment introduced into monterey bay the principal sources of the fine sediment are the three rivers that enter monterey bay the san lorenzo pajaro and salinas rivers accumulation rates in the midshelf mudbelt are high relative to documented yields of rivers and cliff erosion and also are high relative to other documented mud accumulations of the west coast continental shelves

models of strain variation in nappes and thrust sheets a review abstract strain within nappes and thrust sheets can be modelled using simple boundary conditions an original rectangular prism of material resting on a thrust plane is considered to be subject to various pure and simple shear components operating parallel to the thrust deformation gradient tensors are determined for the models and solutions found for the principal strains a two dimensional model considers heterogeneous simple shear combined with a stretch in the direction of shear simple shear zones arise as a special case where 1 recumbent fold nappes characteristic of gravitational collapse can be modelled with 1 and thrust sheets with layer parallel shortening and folding with differential transport of nappes gives rise to additional wrench type shears solutions for the principal strains in this type of model are found and used to interpret side wall ramps and steep zones parallel to nappe movements by including a stretch in the transport direction these differential transport models produce prolate strains 1 and oblate strains finally a brief consideration of bending strains produced in a sheet passing over a ramp indicates reversals in the shear direction during the strain history these predict possible crenulation of early thrust fabrics at ramps

fault block rotations at the edge of a zone of continental extension southwest turkey the ne sw trending burdur acigol and baklan basins of southwest turkey are bounded by normal faults which became active in quaternary times prior to this a more widely spaced system of pliocene basins had existed each of the quaternary basins has a half graben geometry with a major nw dipping fault on its southeast side previous studies of the 1971 burdur earthquake caused by movement on the fault bounding the burdur basin have shown this fault to flatten slightly at depth deformation in the hangingwall of the fault controlling the pliocene basin in the burdur region suggests a planar fault geometry it is suggested that the pliocene fault rotated to its present shallow orientation then became inactive and acted as a detachment at depth for the more recent quaternary fault quaternary faults bounding the burdur acigol and baklan basins have a sinistral strike slip component with slip vectors indicating extension in an nw se direction this is at variance with regional n s extension in western turkey a solution for this contrast is found by invoking block rotations about vertical axes in a deforming zone between the rapidly extending aegean region to the west and the stable unstretched anatolian plateau to the east

lateral and vertical distributions of living benthic foraminifera off the douro river western iberian margin impact of the organic matter quality abstract in this study we assess the impact of the quantity and quality of the organic matter on the distribution of live benthic foraminifera on a cross margin transect off the douro river western iberian margin surface sediments from five stations ranging from 50 to 2000 m water depth were collected in march 2011 at the end of the period of maximal river runoff in order to better evaluate the importance of terrestrial input living stained benthic foraminiferal assemblages 150 m and environmental parameters grain size total organic carbon toc total nitrogen tn c n ratio 13 c toc pigments and amino acids were investigated organic matter amounts follow the sediment grain size pattern with higher concentration in fine sediments and seem to control faunal density except at the shallowest station where toc is low and faunal density high at this coastal site a massive sandy deposit is identified and associated with very low faunal diversity labile organic matter is richest at the shelf stations where benthic foraminifera standing stocks are high this is particularly evident on the douro mud patch where both density and diversity are high foraminiferal faunas living at the shelf stations are dominated by species e g nonion scaphum ammonia beccari i bulimina aculeata and eggerella scabra characteristic of the rich trophic conditions with organic matter of mixed estuarine and marine origin very low total standing stocks on the upper slope are associated with coarse sediments probably resulting from intense bottom currents at this depth resulting in poor trophic conditions deeper environments are characterized by species e g hoeglundina elegans uvigerina mediterranea and reophax scorpiurus indicative of fairly abundant but low quality organic matter finally the faunal differences between the shelf stations may reflect different successional stages an early stage at 50 m water depth where unstable conditions are observed with faunas dominated by opportunistic species and a more mature fauna in the mud patch where more stable conditions prevail

differential response at the seafloor during palaeocene and eocene ocean warming events at walvis ridge atlantic ocean odp site 1262

the effect of sediment mixing on pb 210 accumulation rates for the washington continental shelf abstract nine cores from the washington continental shelf were examined by radiochemical techniques in order to evaluate the effect of mixing on the calculation of sediment accumulation rates from pb 210 profiles th 234 profiles indicate mixing coefficients of 140 cm 2 yr 1 for the seabed offshore from the columbia river and 47 cm 2 yr 1 for the seabed of the mid shelf silt deposit 75 km north of the columbia river these large mixing coefficients demonstrate that particles can penetrate to the base of the intensely mixed surface layer 10 cm within one year after emplacement at the seabed surface observed depths of cs 137 penetration within the seabed are compared with depths predicted from the surface mixed layer thickness and the pb 210 accumulation rate the observed and predicted depths agree well at all but one station at this station a combination of th 234 co 60 pb 210 and cs 137 profiles suggests that active mixing occurs below the intensely mixed surface layer the agreement of pb 210 and cs 137 data at the other stations however indicates a general absence of deep mixing on the washington shelf thus the apparent accumulation rates calculated from pb 210 profiles below the intensely mixed surface layer on the washington shelf generally reflect the true rates of sediment accumulation

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

petrographic evidence for emplacement of carbon into witwatersrand conglomerates under high fluid pressure abstract much gold in the witwatersrand conglomerates is directly associated with seams of carbon that are generally parallel with bedding some seams locally crosscut bedding and form anastomosing fracture patterns showing that emplacement of liquid hydrocarbons in those seams was postdepositional and infilled fractures that are generally parallel to bedding seams that are not observed to crosscut bedding are nonetheless petrographically identical and are believed to have a common postdepositional origin carbon also occurs along sets of bedding parallel microfractures through individual quartz pebbles in mineralized conglomerates planes of fluid inclusions parallel to the microfractures in pebbles show further evidence for the importance of bedding parallel fluid flow the occurrence of carbon seams on sedimentary discontinuity surfaces may reflect preferential emplacement of carbon along planes of weakness brittle extensional fracturing in pebbles indicates high fluid pressures which may relate to hydrocarbon generation bedding parallel minealization by quartz clays metamorphic chlorite pyrophyllite and gold which reflect a complex multistage paragenesis indicate repeated reactivation of bedding plane permeability previous arguments against a hydrocarbon origin for the carbon seams have been based upon the low intergranular permeability of the rocks however the present study shows that this condition actually caused focusing of hydrocarbon fluid flow along discontinuity surfaces and facies boundaries interaction with uranium could have caused fixation of fluid hydrocarbon by radiolytic polymerization the columnar nature of carbon in many of the seams interpreted by others as a biogenic structure could instead reflect polymer swelling normal to bedding in the direction of least confining stress

ultimate removal mechanisms of elements from the ocean abstract the surface complex formation model can adequately explain the observed partitioning of most of the elements between seawater and pelagic clays and between river water and river suspended particles the adsorption of elements on the hydrous oxide surface of iron oxide manganese oxide and clay minerals is the most important ultimate removal mechanism of most of the elements from the ocean

contrasting styles of deformation during progressive nappe stacking at the southeastern margin of the bohemian massif thaya dome abstract variscan nappe stacking at the southeastern margin of the bohemian massif is a polyphase process implying a progressive modification of the deformation regime from thrusting to wrenching associated change of finite strain axes orientations and progressive downwards migration of thrust or wrench planes a first high temperature deformation phase d 1 is related to nappe stacking of moldanubian units in a nw se direction it is recorded only in these units d 2 corresponds to the piling of the moldanubian units over the moravian ones producing internal nappe stacking of the latter and a first medium temperature mylonitization of thaya basement rocks the main feature of this stage is a switch in finite strain axes orientation and northeastward transpressional shearing strain partitioning is important within the moravian nappes and implies alternation of plane strain oblate and constrictional fabrics d 3 is also a phase connected with strong non coaxial ne directed shearing it is concentrated in zones of weakness and causes reactivation of older structures the structural pattern strongly depends on the position in the nappe pile strike slip tectonics dominate near the resistant eastern cadomian basement border foliation parallel extensional reactivation producing large scale folds is typical in moravian nappes while extensional tectonics prevail in the uppermost gfohl nappe large scale strain partitioning during d 2 stacking of moravian nappes and the extension of the upper part of the nappe pile during d 3 reactivation are mechanically controlled by a lateral ramp basement geometry along the bruno vistulian cadomian foreland

eclogites from the czech part of the erzgebirge multi stage metamorphic and structural evolution a structural and petrological study of saxothuringian eclogites in the central erzgebirge czech republic revealed their polyphase thermal and tectonic evolution the first stage of deformation is related to eclogite facies metamorphism of mafic rocks at pressures of 26 kbar and temperatures of 650 700 c the clinopyroxene crystallographic preferred orientation is consistent with high temperature flow the second stage of deformation is characterized by transport of eclogitic rocks at the base of a crustal nappe and their large scale folding during this stage hp ht metamorphic assemblages developed in the surrounding metapelites 14 5 kbar 600 c while eclogite assemblages were preserved in passively transported eclogitic boudins heat advection and similar p t conditions in the surrounding crustal material are responsible for the stability of mineral assemblages and preclude closure of isotopic systems in the eclogites therefore the published isotopic ages of the eclogites do not reflect the subduction stage but the age of cooling under crustal conditions subsequent large scale d3 folding is responsible for reorientation of previously flat lying earlier fabrics d1 d2 the final stage of deformation is marked by the development of a heterogeneous network of ductile retrograde shear zones the thermometry and geochemical study of amphibolitized eclogites in the cores of shear zones indicates thermal conditions not exceeding those in surrounding metapelites and fluid influx the fluid influx is interpreted to be the result of water producing prograde reactions in the footwall metasediments and fluid chanelling into the base of the nappe during brittle deformation of the eclogites