shear wave polarization anisotropy in the mantle wedge above the subducting pacific plate abstract research of azimuthal anisotropy in the mantle wedge above subduction zones opens up a new source of information about rising magma in the region because the physical property estimated from shear wave anisotropy is related to dynamic processes inside the earth regional variation in shear wave polarization is investigated from a teleseismic event and some local deep earthquakes using a spatially dense seismic array of the nied located in the central part of japan a characteristic pattern is found on the spatial distribution of shear wave polarization data obtained from scs waves large and small values of shear wave polarization anisotropy are observed at seismic stations located to the west and east of the volcanic front respectively the anisotropic zone with maximum velocity in n s direction is localized in the wedge portion between the surface and subducting slab using the data of the local deep events the location of the anisotropic zone corresponds with a low q zone obtained from seismic tomography data we conclude that the azimuthal anisotropic zone in the mantle wedge is caused by melt filled cracks which is consistent with models obtained by petrological studies

seismic anisotropy beneath the lau back arc basin inferred from sscs scs splitting data we determine upper mantle anisotropy just beneath active basins by comparing scs and sscs waveform splitting we have measured sscs scs shear wave splitting with data from the spanet and gsn seismic networks the observed sscs scs shear wave splitting suggests that there is a large lateral variation of anisotropy beneath the lau back arc basin scs and sscs waves which sample the southern part of the lau basin show small splitting in contrast the northern part of the lau basin which is characterized to be tectonically active is observed to have large seismic anisotropy with a wnw ese direction the cause of anisotropy may be related to the mantle dynamics of the active basin

carbonates within a pleistocene glaciomarine succession yakataga formation middleton island alaska uplifted during the 1964 alaskan earthquake extensive intertidal flats around middleton island expose 1300 m of late cenozoic early pleistocene yakataga formation glaciomarine sediments these outcrops provide a unique window intooutershelfandupperslopestratathatareotherwiseburiedwithinthesoutheast alaska continental shelf prism the rocks consist of five principal facies in descending order of thickness i extensive pebbly mudstone diamictite containing sparse marine fossils ii proglacial submarine channel conglomerates iii burrowedmudstoneswithdiscretedropstonelayers iv boulderpavements whose upper surfaces are truncated faceted and striated by ice and v carbonates rich in molluscs bryozoans and brachiopods the carbonates are decimetre scale in thickness typically channellized conglomeratic event beds interpreted as resedimented deposits on the palaeoshelf edge and upper slope biogenic components originated in a moderately shallow ca 80 m relatively sediment free mesotrophic sub photicsetting thesecomponentsareamixture of parautochthonous large pectenids or smaller brachiopods with locally important serpulid worm tubes and robust gastropods augmented by sand size bryozoan and echinoderm fragments ice rafted debris is present throughout these cold water carbonates that are thought to have formed during glacial periods of lowered sea level that allowed coastal ice margins to advance near to the shelf edge such carbonates were then stranded during subsequent sea level rise productivity was enabled by attenuation of terrigenous mud deposition during these cold periods via reduced sedimentation together with active wave and tidal current winnowing near the ice front redeposition was the result of intense storms and possibly tsunamis these sub arctic mixed siliciclasticcarbonate sediments are an end member of the phanerozoic global carbonate depositional realm whose skeletal attributes first appeared during late palaeozoic southern hemisphere deglaciation

the depth distribution of mantle anisotropy beneath the tonga subduction zone abstract shear wave splitting recorded by a temporary deployment of broadband seismometers located above the tonga subduction zone yields strong constraints on the depth distribution of anisotropy in the mantle beneath the tonga back arc region splitting parameters obtained for local s and teleseismic sks phases were modeled using a ray based method that predicts shear wave splitting on individual phase paths and determines the best fitting values of anisotropic strength orientation and depth extent splitting in teleseismic sks phases is identical to that in s phases from local earthquakes that occur at the base of the transition zone demonstrating that there is no significant splitting due to anisotropy in the lower mantle splitting times for local s phases do not vary significantly with depth and for models in which the strength of anisotropy is laterally uniform they rule out anisotropy in the transition zone finally the observed splitting indicates that anisotropy of more than 0 8 exists in the upper mantle with a fast symmetry axis at 60 w roughly parallel to the absolute plate motion vector of the subducting pacific lithosphere

shear wave splitting in the upper mantle wedge above the tonga subduction zone summary intermediate period seismograms of shear waves from deep earthquakes are examined for shear wave splitting diagnostic of seismic velocity anisotropy in the upper mantle wedge between the subducting tonga slab and stations in the fiji islands earthquakes with near vertical incidence angles are selected to minimize complications of converted phases and the free surface horizontal component seismograms for 25 deep earthquakes recorded at station lak on the lau ridge show splitting of up to 0 9 s with an average of 0 45 0 25 s between fast and slow s wave components anisotropy in the upper mantle is the most likely cause of the splitting the ese orientation of the fast velocity direction at station lak corresponds to an axis of symmetry of the anisotropic mantle and is approximately perpendicular to magnetic lineations in the lau basin and the northeastern portion of the south iiji basin the observations are consistent with a model of flow alignment of olivine 100 and orthopyroxene 001 axes parallel to the direction of basin extension seismograms for eight deep earthquakes at station sva on viti levu show up to 1 0 s splitting with an average of 0 65 0 29 s and a weak nne preferred orientation of fast velocity polarizations of shear wave particle motions corrected for anisotropy are within 36 5 26 of polarixations predicted for nine moment tensor solutions the magnitude of shearwave splitting and estimates of the thickness of the lithosphere in the fiji region imply that the anisotropy cannot be contained in the lithosphere alone either the anisotropy is distributed in both the lithosphere and asthenosphere or the asthenosphere alone is anisotropic

transpression and strain partitioning in the caribbean island arc fabric development kinematics and ar ar ages of syntectonic emplacement of the loma de cabrera batholith dominican republic abstract an integrative structural and geochronologic study of the loma de cabrera batholith lcb cordillera central dominican republic and its country rocks reveals the interplay of deformation metamorphism and plutonism produced in the caribbean island arc during late cretaceous oblique convergence the results emphasize the interference between three contemporaneous strain fields 1 a northern and southern domains produced by 40 ar 39 ar in hornblende during sinistral transpressional shearing comparison of the structural data with strain models of oblique plate convergence suggest that the lmsz is a preserved ductile signature of strike slip partitioning within a sinistral transpressional intra oceanic subduction zone in the lcb microstructural data indicate that the magmatic to high temperature solid state deformation initially occurred over a wider band of heterogeneously distributed shear deformation and was partitioned in narrow bands of mid to low temperature deformation connected with the lmsz during the cooling of the batholith field and geochronologic studies also suggest that shortening across the southern domain took place concurrently with sinistral strike slip movement along the crustal scale la guacara and macutico fault zones also consistent with a transpressional setting for the late cretaceous caribbean magmatic arc shear and fault zones were variably reactivated during upper eocene oligocene thrusting and miocene to recent uplift of the cordillera central

bioclastic carbonate sediments on the southwestern svalbard shelf the poleward continuation of one of the largest known arctic carbonate factories the western spitsbergenbank of the barents sea has been surveyed along the narrow sw svalbard shelf on this shelf formation of cold water carbonate sediments occurs under glaciomarine environmental conditions mya truncata and hiatella arctica colonized a soft glacio marine diamicton 3000 6000 years after the final retreat of the icedome from the sw svalbard shelf since 2600 yr b p an increase of along shelf bottom currents washed out the fine terrigenous deposits leaving behind a shelly lag deposit and winnowed boulders on a morainic shelf topography the most favourable depth interval promoting the establishment of an amalgamated bioclastic blanket is located in 50 80 m water depth in this interval strong bottom currents prevent sedimentation thus facilitating colonisation of filter feeding benthic communities dominated by balanus balanus and chlamys islandica additional skeletal components are supplied by echinoderms bryozoans serpulids brachiopods and gastropods in shallower water depths carbonate production is hampered by intense iceberg scouring and release of ice rafted debris from the still glaciated hinterland of svalbard in deeper water 80 m olive grey muds with dispersed pebbles rich in benthic foraminiferans clinocardium ciliatum and taxodont bivalves are present on all surveyed shelf banks the deepest unit is a blue mud in water depths 120 m with benthic foraminiferans taxodont bivalves and sipunculids compared to spitsbergenbank carbonate production is much more restricted and impoverished on the sw svalbard shelf but is still an instructive modern example for the formation of skeletal carbonates resting on tillites in the geological record

ichnology of a glacially influenced continental shelf and slope the late cenozoic gulf of alaska yakataga formation abstract the study of trace fossils in glaciomarine strata is important because of the low preservation potential of fauna but glaciomarine settings have received little attention from ichnologists widespread biological activity is recorded by ichnofossil assemblages in glaciomarine strata of the late cenozoic 6 ma to present yakataga formation alaska glacial sedimentation began in the gulf of alaska in the miocene along a deep water active margin basin dominated by turbidity currents and debris flows later strata record progradation of the continental slope by mass flow processes and the establishment of a broad shelf influenced by repeated glaciation ice rafting of coarse debris changes in water depth and salinity storms earthquakes and high sedimentation rates yakataga formation strata show overall a limited ichnological diversity and low degree of bioturbation in relation to comparable non glacial settings although certain beds are highly bioturbated twenty four ichnotaxa are identified and grouped into nine assemblages characteristic of different depositional settings and substrate types ichnogenera and body fossil evidence shows that polychaetes arthropods molluscs and echinoderms were the dominant infaunal benthic organisms with deposit feeding being the predominant feeding strategy poorly consolidated muddy sediments excluded suspension feeders and limited the development of the skolithos ichnofacies typical of non glacial shelves characterized by clean shifting sand substrates evidence of rapid sedimentation is given by escape structures fugichnia the presence of diplocraterion and by the mass mortality of bivalves firm ground burrows typical of the glossifungites ichnofacies are associated with erosional surfaces boulder pavements and coquinas diminutive feeding traces may reflect salinities lowered by glacial meltwater inputs the downslope transport of food by turbidity currents and mass flows may explain the development of a diverse cruziana ichnofacies in water depths where in non glacial settings the nereites ichnofacies is found an ichnological summary is presented for the late cenozoic gulf of alaska continental margin similar ecological conditions obtain in the modern setting and provide valuable supportive data ichnofacies identified from the yakataga formation are probably widespread in late paleozoic and late cenozoic glacially influenced marine strata

analysis of fault slip inversions do they constrain stress or strain rate fault slip data commonly are used to infer the orientations and relative magnitudes of either the principal stresses or the principal strain rates which are not necessarily parallel or equal at the local scale of an individual fault the shear plane and slip direction define the orientations of the local principal strain rate axes but not in general the local principal stress axes at a large scale the orientations of p and t axes maxima for sets of fault slip data do not provide accurate inversion solutions for either strain rate or stress the quantitative inversion of such fault slip data however provides direct constraints on the orientations and relative magnitudes of the global principal strain rates to interpret the inversion solution as constraining the global principal stresses requires that 1 the fault slip pattern must have a characteristic symmetry no lower than orthorhombic 2 the material must be mechanically isotropic and 3 there must be a linear constitutive relationship between the global stress and the global strain rate isotropic linear elastic constitutive equations are appropriate to describe the local deformation surrounding an individual slip discontinuity fault slip inversions however constrain the characteristics of a large scale cataclastic flow which is described by constitutive equations that are probably but to an unknown degree anisotropic and nonlinear such material behavior would not strictly satisfy the requirements for the stress interpretation thus at the present state of knowledge fault slip inversion solutions are most reliably interpreted as constraining the principal strain rates

mid eocene early oligocene sinistral transcurrent faulting in puerto rico associated with formation of the northern caribbean plate boundary zone left lateral transcurrent wrench faulting through the southern puerto rico fault zone sprfz in central southern puerto rico is indicated by fault orientations and motion direction indicators the sprfz is a west northwest trending 3 8 km wide diffuse system of faults and folds that within the study area bounds paleocene and eocene volcaniclastic rocks the eocene belt and is flanked by cretaceous volcanic and volcaniclastic rocks structural data show that much of central southern puerto rico is cut by strike and oblique slip faults whereas locally in the southeastern part of the eocene belt rocks are pervasively thrust northeastward over cretaceous rocks of central puerto rico structural data and the distribution of fault types support two local evolutionary scenarios 1 different structural horizons of the transpressional sprfz i e upper thrust dominated horizon and lower strike slip dominated horizon were juxtaposed along post transpressional normal faults that border the ponce basi

skeletal and isotopic composition and paleoclimatic significance of late pleistocene carbonates ross sea antarctica abstract carbonates cover an extensive area of the northwestern ross sea continental shelf radiocarbon dates yield late pleistocene stage 3 ages for these deposits hence the carbonates appear to be correlative with widespread tills and glacial marine deposits in the region four carbonate facies are recognized on the basis of skeletal composition a barnacle foraminifer facies a muddy bryozoan facies a bryozoan barnacle pelecypod foraminifer facies and a planktonic foraminiferal facies these deposits occur on the shelf and upper slope while carbonate turbidites derived from them occur on the adjacent continental slope and rise compositional analyses of ross sea carbonates lend support to previously recognized criteria for identifying cold water carbonates these include 1 the presence of an associated ice rafted component including dropstones 2 a dominance of calcite relative to other carbonate minerals the remaining fraction consists solely of aragonite 3 allochems that are entirely skeletal and 4 heavy oxygen isotopic compositions in the range of 3 0 to 5 1 pdb

solution to the volume problem in serpentinization kernel pattern consists of a rim of completely serpentinized peridotite surrounding a core of partly serpentinized or unserpentinized peridotite it is found adjacent to shear zones in some serpentinites kernels are commonly rectangular with length width ratios of 1 to 3 the boundary between the completely serpentinized rim and the unserpentinized core is commonly cut at a high angle by cross fractures the cross fractures which contain either picrolite or chrysotile asbestos taper out in the core and widen in the rim they are almost always perpendicular to the core rim boundary and point into the core of the kernel in this sense they are radially distributed in the rim the kernel pattern can be observed in thin section in outcrop and on the megascopic scale of tens of metres cross fractures represent expansion fractures in serpentinite in the rim of the kernel caused by an increase in volume acompanying serpentinization of the peridotite in the core of the kernel as the serpentinization front penetrates into the kernel the serpentinized peridotite expands however the serpentinite in the rim cannot expand and must fracture to accommodate the increase in volume as serpentinization proceeds more expansion occurs extending the fractures farther into the core and requiring the fractures in the existing serpentinite to widen these fractures are subsequently filled by serpentine minerals the resulting pattern consists of a rim of serpentinite cut by serpentine veins that surrounds a core of peridotite measured densities of cross fractures in the rims of kernels are consistent with those expected from the magnitude of the volume change accompanying serpentinization of peridotite

seismic attenuation tomography of the tonga fiji region using phase pair methods the anelastic structure of the region surrounding the tonga slab and lau back arc spreading center in the southwest pacific is studied using data from 12 broadband island stations and 30 ocean bottom seismographs two differential attenuation methods determine t over the frequency band 0 1 to 3 5 hz for earthquakes in the tonga slab the s p method measures the difference in spectral decay between p and s waves arriving at the same station the p p method measures the difference in spectral decay for p waves with different paths through the upper mantle eight hundred sixty phase pairs are used to invert for two dimensional 1 q structure using a nonnegative least squares algorithm a grid search method determines the q q ratio most compatible with both the s p and p p differential measurements the highest attenuation q 90 is found within the upper 100 km beneath the active portions of the lau basin extending westward to the lau ridge these regions probably delineate the source region for the back arc spreading center magmas expected to be within the upper 100 km based on petrological considerations the high attenuation regions also correlate well with zones of low p wave velocity determined by regional velocity tomography somewhat lower attenuation is found beneath the fiji plateau than beneath the lau basin the entire back arc is characterized by a gradual decrease in attenuation to a depth of 300 to 400 km the slab is imaged as a region of low attenuation q 900 material a q q ratio of 1 75 provides the best fit between the s p and p p data sets upon inversion spectral stacking shows no frequency dependence within the frequency band analyzed

glacially derived shallow marine gold placers of the cape yakataga district gulf of alaska abstract economic gold bearing coastal sediment of holocene age 10 ka occurs along the gulf of alaska coastal margin from cape yakataga in the west to icy bay in the east a distance of 50 km deposits have been worked since 1898 and total production since then is about 15 000 ounces gold is recovered from discontinuous sheets of ruby garnet rich beach sand exposed at low tide along the high energy storm dominated coastline similar auriferous sand facies are also present within raised marine terraces cut across outwash fans along the narrow mountainous coastal margin the area has been uplifted by glacio isostatic rebound following the last glacial maximum and by high magnitude earthquakes the area lies along the collision zone between the north american and pacific plates study of uplifted and well exposed late cenozoic strata the glaciomarine yakataga formation that outcrop along the coastal margin confirms this succession as the source of placer gold the yakataga formation records the rapid accumulation of over 6 km of gold bearing glaciomarine sediments in a rapidly subsiding forearc basin these strata have in turn been uplifted as coastal mountains and eroded by glaciers the white river glacier and yakataga glacier drainage basins can be identified as the principal source of detrital gold along the yakataga coastline auriferous beach sediment is the product of westward reworking of glacial outwash from the white and yakataga rivers and is accompanied by a well defined downcurrent reduction in the size and number of gold particles

seismic anisotropy and implications for mantle deformation beneath the ne margin of the tibet plateau and ordos plateau the northeastern tibet and the ordos plateau connects east china and west china which are dominated by horizontal extension and compression respectively knowledge of seismic anisotropy beneath this transitional region can provide important constraints on deformation pattern of the crust and lithosphere mantle during an orogeny process we measured sks wave splitting parameters from the new installed regional networks and obtained a detailed anisotropy map for 119 broadband stations beneath the ne margin of tibet the observed wnw fast polarization direction is parallel to the surface geological features the coherence between the observed geodetic motion of the crust and fast axis direction suggests that the vertical coherent deformation of the lithosphere is the dominate source for the observed seismic anisotropy further east to the qinling orogenic belt the fast axis direction tracks change in strike of the faults with the fast direction aligning almost ew we suggest that both the lithosphere mantle and east extrusion of mantle material contribute to the observed anisotropy small value of delay time is observed interior the thick rooted ordos plateau suggesting a rigid and stable lithosphere with little deformation the deviation of fast polarization direction beneath the adjacent rifting regions might be caused by the edge flow induced by sharp changes in the thickness of lithosphere our results propose that the upper crust and mantle lithosphere beneath the northeastern tibet are at least partly coupled or subjected to the same boundary conditions which is inconsistent with the channelized lower crustal flow model

flow and fabric deep down conditions in earth s mantle can be inferred from seismic wave velocities which reveal areas of anisotropy evidence emerges of such an area at mid mantle level associated with a subducting tectonic plate

frequency dependent anisotropy in wellington new zealand shear wave splitting measurements are made using teleseismic s scs and sks waveforms recorded at the gdsn broadband station snzo situated in south karori new zealand the average s and sks delay times are around 2 to 3 s among the highest in the world the average scs delay time is significantly smaller around 1 s this discrepancy appears to be due to differences in dominant frequency the most likely cause of frequency dependent anisotropy is oriented heterogeneities with a scale length much smaller than the wavelength the fast polarizations range between 21 and 79 with an average ne sw direction which is sub parallel to the trend of the local geologic structure and the strike of the hikurangi subduction zone azimuthal variations in delay time which cannot be explained by differences in period may be due to a dipping axis of symmetry or laterally varying anisotropy or a more complicated symmetry system

biofacies and sediments in an emergent late pleistocene glaciomarine sequence skerries east central ireland abstract late devensian sedimentation ca 18 ka b p on the coastal margins of the irish sea basin occurred in shallow water glaciomarine environments around retreating tidewater ice margins high relative sea levels were the result of glacioisostatic crustal depression around the periphery of the last british ice sheet at skerries in east central ireland ice proximal glaciomarine diamict mud sand and gravel facies are selectively preserved in a bedrock depression the coastal exposure about 500 m long can be divided into three lithofacies associations 1 a diamict gravel association resting on bedrock was emplaced by sediment gravity flows and records the downslope reworking of glacial debris released from a retreating ice margin 2 an overlying mud association was deposited from suspended sediment plumes with minor ice rafting and records ice retreat and increasing distality of the site muds contain a mixed foraminiferal microfaunal assemblage typical of open water shallow marine shelves species can be grouped into reworked temperate cosmopolitan and well preserved boreo arctic elements and indicate mixing of derived and retransported temperate species with an in situ glaciomarine fauna 3 at the top of the section a gravel association derived from a nearshore fan delta rests on planated muds and is attributed to wave reworking and slumping of the fan delta front in shallow water during rapid basin rebound this and other sequences elsewhere in the irish sea basin is a record of rapid evacuation of the basin by calving tidewater glaciers and the uplift and erosion of glaciomarine sedimentary sequences in response to rapid late glacial crustal rebound

very low shear wave velocity at the base of the mantle under the south pacific superswell abstract s wave velocity heterogeneity at the base of the mantle beneath the south pacific superswell has been examined using skks sks and s sdiff sks differential travel times the residuals of skks sks and s sdiff sks with respect to the preliminary reference earth model prem are compared to the residuals predicted using recently published three dimensional s wave velocity models we have obtained a three dimensional model that explains the s sdiff sks residuals well and applied this model to the correction of the skks sks residuals the corrected skks sks residuals beneath the south pacific superswell remain large and positive forward modeling reveals that these residuals can be accounted for by a 5 7 low velocity region with a lateral extent of about 500 km in the lowermost 200 km of the mantle although the magnitude of the velocity reduction and the thickness of the anomalous region trade off against one another and cannot be uniquely determined the existence of a very low s wave velocity region at the base of the mantle is a robust feature this feature lies close to the ultra low velocity zone ulvz identified by p velocity data beneath the southwestern pacific and is located just below a 2 3 low s velocity body in the lower mantle at depths of 2300 2700 km beneath the south pacific superswell

late quaternary carbonate deposition at the bottom of the world abstract carbonate sediments on polar shelves hold great potential for improving understanding of climate and oceanography in regions of the globe that are particularly sensitive to global change such deposits have however not received much attention from sedimentologists and thus remain poorly understood this study investigates the distribution composition diagenesis and stratigraphic context of late quaternary calcareous sediments recovered in 15 piston cores from the ross sea shelf antarctica results are used to develop a depositional model for carbonate deposition on glaciated polar shelves the utility of the deposits as analogs for the ancient record is explored in the ross sea carbonate rich lithofacies consisting of poorly sorted skeletal sand and gravel are concentrated in the west and along the outer reaches of the continental shelf and upper slope analysis of fossil assemblages shows that deposits were produced by numerous low diversity benthic communities dominated locally by stylasterine hydrocorals barnacles or bryozoans radiocarbon dating indicates that carbonate sedimentation was episodic corresponding to times of reduced siliciclastic deposition most accumulation occurred during a time of glacial expansion in the lead up to the last glacial maximum a more recent interval of carbonate accumulation postdates the early holocene sea level rise and the establishment of the modern grounding line for the ross ice shelf when carbonate factories were inactive fossil debris was subjected to infestation by bioeroders dissolution fragmentation and physical reworking this study reveals the episodic nature of carbonate deposition in polar settings and a reciprocal relationship with processes that deliver and redistribute siliciclastic debris carbonate production is most active during colder periods of the glacial interglacial cycle a potential new sedimentological paradigm for polar carbonate systems low accumulation rates and long residence times on the seafloor leave sediments vulnerable to significant post depositional modification processes that profoundly affect the appearance of deposits as they enter the rock record comparison with other examples of polar carbonates highlights the utility of these late quaternary deposits as a well constrained analog that can aid in the recognition and interpretation of similar deposits from the ancient record

foraminiferal sequence biostratigraphy and seismic stratigraphy of a tectonically active margin the yakataga formation northeastern gulf of alaska abstract upper miocene through recent glacial marine deposits of the yakataga formation which underlie the northern gulf of alaska continental shelf are the focus of an integrated study to understand the depositional and climatic history of the upper cenozoic gulf of alaska biostratigraphic lithologie and multichannel seismic data were integrated in a sequence stratigraphic analysis of the yakataga continental margin a paleontologically based approach to sequence stratigraphy known as sequence biostratigraphy was used to define eight seismic stratigraphic sequences on this tectonically active glaciated continental margin foraminifera provide information on the age paleoenvironments and paleoclimates of strata within these eight sequences lithologic evidence is used to infer the presence and influence of tidewater glaciers the three oldest sequences arbitrarily labeled brown red and orange early pliocene mid pliocene late pliocene respectively were deposited in mainly outer neritic through upper bathyal environments planktic foraminiferal assemblages show that sea surface temperatures during deposition of these sequences were mainly cool temperate in the gulf of alaska at this time yet benthic assemblages indicate cold bottom waters and dropstones indicate glacial marine sedimentation during the late pliocene the five youngest sequences labeled yellow green aqua blue violet which are pleistocene to recent in age were deposited in deeper environments on average upper bathyal to middle bathyal than the older sequences glacial marine sedimentation was common during deposition of these sequences abundant dropstones and foraminiferal assemblages indicate both cold sea surface and bottom water temperatures

sedimentology of shell rich deposits coquinas in the glaciomarine upper cenozoic yakataga formation middleton island alaska the yakataga formation in southern alaska contains the longest and most accessible record of late cenozoic glaciation in the world glacially influenced marine sedimentation began in the late miocene 6 ma and continues in the area to the present day upper yakataga formation sediments 1 25 km thick are exposed on middleton island gulf of alaska facies are dominated by massive glaciomarine diamicts that record deposition in an outer shelf setting of terrigenous mud and ice rafted debris released from expanded temperate glaciers around the gulf margin diamicts contain intraformational coquina beds as much as 1 m thick composed of cemented bioclastic debris and ice rafted boulders that can be traced several kilometers along strike analysis of foraminifera contained within diamicts and coquinas suggests that coquinas record intervals of relative sea level change bottom winnowing and nondeposition of mud allowing molluscan communities to develop coquinas show graded beds produced by storms and wave rippled commonly armored upper surfaces composed of densely packed chlamys valves these bioclastic deposits are of considerable significance with regard to the origin of mixed glacial and carbonate successions in the rock record analogous depositional settings can be identified from the permian of australia

paleomagnetic evidence for late miocene counterclockwise rotation of north coast carbonate sequence puerto rico a paleomagnetic study of the essentially undeformed middle tertiary carbonate sequence along the north coast of puerto rico reveals statistically significant pre pliocene discordance of characteristic component directions against those expected from cratonic north america for much of the section despite generally weak to moderately weak magnetic intensities confirmation of the magnetization as primary in origin comes from the presence of two distinct components of magnetization intrasite bipolarity and or the reproducibility of measurements the mean geographic direction for the upper oligocene to middle miocene strata is 335 2 degree 32 9 degree and the corrected mean paleomagnetic pole is 207 6 degree 66 5 degree n 3 alpha 95 4 3 degree this suggests a counter clockwise ccw block rotation of puerto rico and its microplate of 24 5 degrees plus minus 5 8 degrees during the late miocene using a width of 250 km for the northern caribbean plate boundary zone ncpbz between the north american plate and caribbean plate the mean left lateral displacement implied is 1 8 to 2 4 cm yr which agrees fairly well with published relative motion rates for the two plates average rotation rate for 50 ma to 20 ma was 0 7 degree my but perhaps as great as 4 degree my in the miocene resolution of mean paleolatitude indicates northward motion of a degree or lessmore during the period of rotation causes of this short lived rotation may include 1 tectonic escape from the inhibiting presence of the bahama banks and beata ridge during eastward motion of puerto rico along the sinistral transpressive puerto rico trench and muertos trough fault systems or 2 changes in relative plate motions of the caribbean and north american plate during the late miocene less

evidence from core reflected shear waves for anisotropy in the earth s mantle seismologists have begun to recognize that the upper mantle at depth is anisotropic and that seismological data are not fully explicable if anisotropy is ignored1 5 on entering an anisotropic zone a plane shear wave splits into two orthogonally polarized phases6 an effect observed by several researchers7 notably by ando et al 5 8 9 the near vertical scs wave an s wave reflected once at the core mantle boundary is one of the most suitable phases to study the phenomenon of shear wave birefringence because it is isolated from other phases and because its particle motion is nearly horizontal and thus free from s to p conversion the split scs shear waves travel with different velocities in the anisotropic zone and consequently there is a time delay between their arrival at stations my aim was to determine this time delay and the azimuth of polarization using the scs records of two horizontal components from the japanese islands for a deep shock beneath the sea of okhotsk from the total of 41 stations 34 show a polarization of the maximum velocity phase in the nnw sse direction with an average time advance of 0 8s from the minimum velocity phase the relevant anisotropic zone seems to be deep seated

kinematic analysis of serpentinite structures and the manifestation of transpression in southwestern puerto rico abstract faults and shear zones recorded in the monte del estado and rio guanajibo serpentinite masses in southwestern puerto rico show previously unrecognized southwestward tectonic transport the orientations of planar and linear structures and the sense of slip along faults and shear zones determined by offset rock layers drag folds in foliations and steps in slickensided surfaces and or s c fabrics from 1846 shear planes studied at more than 300 stations reveal two predominant groups of faults 1 northwesterly striking thrust faults and easterly striking left lateral faults and 2 northwesterly striking right lateral faults and easterly striking thrust faults shortening and extension p and t axes calculated for geographic domains within the serpentinite reveal early north trending shortening followed by southwestward directed movement during which older structures were re activated the sw directed shortening is attributed to transpression that accompanied late eocene left lateral shearing of the serpentinite a third younger group comprising fewer faults consists of northwesterly striking left lateral faults and north directed thrusts that also may be related to the latest transpressional deformation within puerto rico deformational events in puerto rico correlate to tectonic events along the caribbean north american plate boundary

facies and allostratigraphy of high latitude glacially influenced marine strata of the early permian southern sydney basin australia the sydney basin of new south wales australia is a foreland basin containing a thick up to 10 km permo triassic succession the southern margin of the basin exposes strata deposited during late palaeozoic glaciation of south eastern gondwana the early permian wasp head pebbley beach snapper point formations and wandrawandian siltstone were deposited between 277 and 258 ma on a polar glacially influenced continental margin adjacent to ice sheets located over east antarctica and eastern australia sedimentary facies together with related ichnofacies and fauna can be grouped into six facies associations that record marine sub environments ranging from high energy storm dominated inner shelf to turbidite dominated upper slope settings cold marine conditions with near freezing bottom water temperatures are recorded by glendonites ice rafted debris most likely deposited by icebergs occurs in almost all facies associations an allostratigraphic approach emphasizing the recognition of bounding discontinuities i e erosion surfaces and marine flooding surfaces is used to subdivide the early permian stratigraphy into facies successions three types of succession can be identified and record changes in the relative influence of allocyclic controls such as basin tectonics sediment supply and glacio eustatic sea level variation together sedimentological and allostratigraphic data allow reconstruction of the depositional history of the south western margin of the sydney basin initial marine sedimentation characterized by sediment gravity flows and storm deposited sandstones of the lower wasp head formation occurred adjacent to a faulted basin margin overlying successions within the upper wasp head pebbley beach and snapper point formations record aggradation in inner to outer shelf settings along a storm and glacially influenced continental margin tectonic subsidence and basin flooding is recorded by deeper water turbidites of the wandrawandian siltstone

serpentinites of the zermatt saas ophiolite complex and their texture evolution the zermatt saas serpentinite complex is an integral member of the penninic ophiolites of the central alps and represents the mantle part of the oceanic lithosphere of the tethys metamorphic textures of the serpentinite preserve the complex mineralogical evolution from primary abyssal peridotite through ocean floor hydration subduction related high pressure overprint meso alpine greenschist facies metamorphism and late stage hydrothermal alteration the early ocean floor hydration of the spinel harzburgites is still visible in relic pseudomorphic bastite and locally preserved mesh textures the primary serpentine minerals were completely replaced by antigorite the stable assemblage in subduction related mylonitic serpentinites is antigorite olivine magnetite diopside the mid tertiary greenschist facies overprint is characterized by minor antigorite recrystallization textural and mineral composition data of this study prove that the hydrated mineral assemblages remained stable during high pressure metamorphism of up to 2 5 gpa and 650 c the zermatt saas serpentinites thus provide a well documented example for the lack of dehydration of a mantle fragment during subduction to 75 km depth

depth extent of the lau back arc spreading center and its relation to subduction processes seismic tomography and wave form inversion revealed that very slow velocity anomalies 5 to 7 percent beneath the active lau spreading center extend to 100 kilometer depth and are connected to moderately slow anomalies 2 to 4 percent in the mantle wedge to 400 kilometer depth these results indicate that geodynamic systems associated with back arc spreading are related to deep processes such as the convective circulation in the mantle wedge and deep dehydration reactions in the subducting slab the slow regions associated with the tonga arc and the lau back arc are separated at shallow levels but merge at depths greater than 100 kilometers suggesting that slab components of back arc magmas occur through mixing at these depths

theory of slickenline patterns based on the velocity gradient tensor and microrotation abstract brittle fault zones commonly are characterized by a multitude of lineated shear planes having a wide distribution of orientations in our model we assume the faulted rock comprises an aggregate of rigid blocks whose surfaces are the shear planes we define two independent scales of motion to distinguish the local rigid rotation of the blocks with their shear planes the micromotion from the average deformation of the material on a macroscopic scale the macromotion the macromotion is defined by the macrovelocity gradient tensor which is separated into symmetric and antisymmetric parts the deformation rate and the macrospin tensors respectively the micromotion is defined by a microspin tensor on any shear plane slickenlines form parallel to the direction of the maximum rate of shear which we assume is determined by the direction of the maximum component of the macrovelocity gradient tensor tangent to the shear plane and by a component of the microspin in the shear plane for a restricted kinematic model patterns of slickenline orientations are defined on a uniform distribution of shear plane orientations by the values of d and w d is a ratio of differences in the principal values of the deformation rate tensor and w is a ratio of the net spin to the maximum rate of macroshear we distinguish between instantaneous slickenline patterns and finite deformation patterns the two are different if the shear planes rotate relative to the principal deformation rate axes in which case finite deformation slickenlines form curved or crossing lineations if w 0 the instantaneous slickenline patterns have orthorhombic symmetry 0 d d 1 or 0 if w 0 the instantaneous slickenline patterns have monoclinic symmetry for pure shear in an isotropic body instantaneous slickenline patterns have orthorhombic symmetry w 0 d 0 5 whereas for pure shear accommodated by shear on a planar anisotropy w 1 d 0 5 the pattern is monoclinic for simple shear with the rigid rotation of local shear planes defined by the shear induced spin w 0 d 0 5 the instantaneous slickenline pattern is orthorhombic but the finite deformation pattern is monoclinic for simple shear with no shear plane rotation w 1 d 0 5 the instantaneous pattern is monoclinic special cases of our hypothesis are equivalent to the hypothesis that slickenlines are parallel to the direction of maximum resolved shear stress e g angelier 1979 1984 the slickenline patterns predicted for this case are always of orthorhombic or higher symmetry and are equivalent to our instantaneous patterns for which w 0 and to our finite deformation patterns for which in addition there is no microspin