fossil leaves and fruits as indicators of paleotransport in a miocene lake from northern idaho abstract fossil leaves in clayey lake sediments of the miocene oviatt creek flora idaho were mapped in order to determine their usefulness for indicating paleocurrent flow leaves from the oviatt creek florule p 42 were measured with respect to their size orientation and position within a 0 5 m thick section over an area of about 20 m2 to determine patterns in leaf sorting orientation and species distribution leaf taphonomy indicates that the p 42 lake deposits represent infilling from a southwestern site by a slow moving source preliminary geological mapping in the area supports this interpretation none of these leaf parameters could be used alone to make this interpretation leaf orientation appears to be reliable only for determining flow lineation this is because leaf etioles may point either up or down flow leaves with heavy petioles i e platanus were aligned almost exclusively parallel to flow fruits of acer longer than 4 cm were consistently orientated in the same direction both types of plant parts provide useful data to assist in the determination of paleocurrents in fine grained sediments where primary sedimentary structures are lacking also leaf orientation perpendicular to flow appears to be a possibility in weak currents

rethinking conditions necessary for pseudotachylyte formation observations from the otago schists south island new zealand abstract pseudotachylytes and two distinct types of cataclasite in the otago schist at tucker hill south island new zealand provide evidence for both seismic slip and aseismic creep on a normal fault zone during regional crustal extension in late cretaceous time regional geologic evidence suggests that the fault had its present low angle dip ca 10 at the time it was active type a cataclasites presumably aseismic can be recognized by bi fractal grain size distributions monomict composition angular clasts of uniform textural maturity and a crude fabric defined by oriented grains and transgranular fractures type b cataclasites possibly cosesimic have characteristics consistent with fluidized grain flow including heterogeneous clast shapes and types a bimodal grain size distribution intrusive relationships with other rocks and the absence of any fabric or transecting fractures pseudotachylyte which occurs as fault veins injection veins and more complex types of intrusive structures consistently cuts across and invades type a cataclasites but is both intrusive into and included as clasts in type b cataclasites these relationships are consistent with a fault evolution model in which the development of a damage zone through aseismic cataclasis type a facilitates the formation of pseudotachylyte in a subsequent seismic event by providing a permeable matrix through which fluids can drain in the early stages of slip thereby maintaining frictional contact between rock surfaces the formation of pseudotachylyte in turn may seal the fault zone and lead to thermal pressurization in a later seismic cycle forming fluidized type b cataclasites seismic slip on the low angle normal fault zone at tucker hill may have occurred by two distinct modes of dynamic weakening melt lubrication and thermal pressurization in successive seismic events although there is a perception among geologists that pseudotachylyte is most likely to form in intact crystalline rocks geophysical models of fault zones clearly demonstrate that pseudotachylyte formation is actually suppressed in low permeability rock because any fluids present would be unable to escape the fault zone and thermal pressurization would rapidly reduce frictional resistance the paradigmatic occurrences of pseudotachylyte in otherwise pristine crystalline rocks probably represent somewhat exceptional circumstances single rupture events at very high effective stress in dry rock coseismic frictional melts may actually be more common in hydrated rocks like the schist at tucker hill but harder to recognize and also vulnerable to overprinting as a fault zone matures in such rocks pseudotachylyte may represent an intermediate stage in the evolution of a fault zone the period between the formation of a high permeability damage zone and the development of a low permeability fault core

numerical simulations of tidal and wind driven circulation in the cretaceous interior seaway of north america twenty two numerical experiments using a multi layer numerical model of turbulent flow in shallow seas better define fluid circulation and sediment transport paths in the cretaceous interior seaway of north america each experiment consists of a different combination of paleogeography paleobathymetry coriolis acceleration boundary tidal amplitudes wind stresses and bed friction the paleogeographies and paleobathymetries represent three seaway configurations a seaway of intermediate size and depth 200 m during a transgressive peak t5 in late albian time a seaway of maximum size and depth 400 m during peak transgression t6 in early turonian time and a seaway of minimum size and depth 100 m during a peak regression r8 in the campanian values for the other key model parameters are m 2 co oscillating boundary tides of 0 1 to 0 2 m range at the arctic ocean boundary and 0 5 to 1 m range at the proto gulf of mexico boundary coriolis accelerations corresponding to 30 n 45 n and 60 n latitude chezy friction factors ranging from 31 to 70 m s 1 and average winter winds and two winter storms computed by the community climate model at the national center for atmospheric research for paleogeographic conditions during the late albian results of the numerical experiments and comparison of these results with geologic observations allow the following conclusions 1 circulation in the seaway was generally storm dominated 2 typical winter storms crossing the seaway from west to east generated 0 3 m s 1 shore parallel geostrophic currents on the shelves north of arizona at first flowing weakly to the north but later during the storm flowing strongly to the south 3 extreme storms could have produced 0 8 m s 1 currents over the shelves and 0 3 m s 1 currents in 200 m of water 4 co oscillating tides propagated into the seaway as progressive kelvin waves and therefore tidal ranges in the seaway were mesotidal to macrofdal along the southeastern margin but microtidal everywhere else 5 significant deep water wave heights and periods of the fully developed wave field are predicted to have been 5 to 6 m high and 10 s respectively the northwestern shore of the seaway would have experienced these storm waves approaching from the north and thus net sediment drift should have been to the south limited available field data support these conclusions

rotation of ductile fabrics across the alpine fault and cenozoic bending of the new zealand orocline this study examines the role and kinematic mechanism of vertical axis rotations and folding during early development phases of a transform plate boundary in continental crust near the alpine fault in new zealand this involved an initial period of widely distributed shear including wrench folding together with vertical axis rotations and orocline development followed by a focusing of slip onto a single fault in the south island the haast schist has been displaced horizontally in the neogene by c 480 km of dextral slip on the alpine fault ls tectonites on either side of the fault lie on different limbs of a profound z shaped orocline rotation of these limbs took place about a vertical axis resulting in 25 30 of clockwise rotation of fabrics to the nw of the alpine fault relative to those to the south foliation anisotropy caused bending to take place locally by folding about an inclined hinge in the limbs of a pre existing synform which tightened during the deformation on both sides of the fault involvement of post oligocene age structures in wrench folding and bending suggests that the bending took place entirely in the cenozoic before or during miocene development of the alpine fault as a through going structure during this early phase of plate boundary deformation shear was distributed across a zone 100 km wide vertical axis rotation affected fault bounded basement slivers that shortened perpendicular to their strike a style of deformation like that in the transverse ranges in california today

synmetamorphic vein spacing distributions characterisation and origin of a distribution of veins from nw sardinia italy abstract the spatial distribution of a single generation of axial planar synmetamorphic veins exposed in greenschist facies rocks on nw sardinia was investigated with the aim of gaining insight into the processes controlling the fracture spacing the vein spacing distribution measured along linear profiles is non uniform and approximately log normal although the vein abundance and absolute vein spacing is strongly influenced by rock type the vein spacing distribution is independent of rock type comparison of the observed data with synthetically generated fracture distributions indicates that the observed distribution can be reproduced by kolmogorov fragmentation but cannot be reproduced by a random even bisection or a fractal cantor dust process these results are interpreted to indicate that the positions of fractures that become veins are interdependent in an attempt to explain the interdependency of fracture positions the perturbations of stress and fluid pressure associated with an isolated underpressured axial planar fracture were investigated simple calculations show that the fluid pressure drop inside a fracture coinciding with failure locally perturbs the stress and fluid pressure fields such that the surrounding rock extending over a lateral extent equivalent to approximately two fracture lengths is instantaneously driven into a critical stress state that satisfies the failure condition numerical simulations demonstrate that this process tends to localise the nucleation of subsequent fractures close to existing fractures this mechanism can explain the existence of non random or clustered fracture or vein spacing distributions forming by hydrofracture

three dimensional structure of vp vs and vp vs beneath northeastern japan implications for arc magmatism and fluids we estimated both p v p and s wave velocity v s structures beneath northeastern japan by applying a tomographic method to 169 712 p and 103 993 s wave arrival time data from 4338 local events the average value of v p v s ratio is 1 69 in the upper crust 1 75 in the lower crust and 1 77 in the uppermost mantle these differences in v p v s ratio may mainly reflect the lithological variations with depth low v p low v s and high v p v s zones are extensively distributed along the volcanic front in the uppermost mantle and are downward to the back arc side in the mantle wedge here the low v p low v s and high v p v s values are interpreted because of partial melting materials which imply the presence of a vast amount of melt in the uppermost mantle in the lower crust low v p low v s and high v p v s zones are not continuously visible along the volcanic front but are confined to individual volcanic areas which suggests that melting of lower crustal materials occurs just beneath each active volcano in contrast the upper crust beneath active volcanoes exhibits low v p low v s and low v p v s these results suggest that the partial melting zones under northeastern japan spread out from the uppermost mantle along the volcanic front up to the midcrust right beneath active volcanoes the low v p low v s and low v p v s features in the upper crust suggest the existence of h 2 o rather than melt right beneath active volcanoes

newly imaged shape of the deep seismic zone within the subducting pacific plate beneath the hokkaido corner japan kurile arc arc junction 1 the geometry of the deep seismic zone associated with the subducting pacific plate beneath the north american plate in the hokkaido corner japan kurile arc arc junction has been investigated based on the hypocenters accurately relocated by a dense local seismographic network with three dimensional p and s wave velocity structures the model suggests that the lateral changes in the dip of the subduction zone are more rapid than previously believed we found that the deep seismic zone in the pacific plate dips at 20 to 30 on the side of the japan arc the dip angle increased in a narrow region around 143 144 e by 10 to 20 and the dip was 40 to 50 on the side of the kurile arc in the transitional zone around 143 144 e an unusual distribution of microearthquakes has been discovered within the pacific plate which was located on a near vertical plane with an area of 50 100 km2 with strike that was perpendicular to the kurile trench axis this feature was named the tokachi oki slab cracking zone we suggest that this is a slab cracking zone torn by the extensional stress due to the rapid lateral changes in the dip of the subduction zone the slab cracking zone may possibly grow into the large disruption or tear of the slab in the future

global seismicity of 2002 centroid moment tensor solutions for 1034 earthquakes abstract centroid moment tensor solutions are presented for 1034 earthquakes that occurred during 2002 the solutions are obtained using the method of dziewonski et al dziewonski a m chou t a woodhouse j h 1981 determination of earthquake source parameters from waveform data for studies of global and regional seismicity j geophys res 86 2825 2852 and applying corrections for aspherical earth structure represented by the whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l acoustic imaging at the planetary scale in emert h harjes h p eds acoustical imaging vol 19 plenum press new york 1992 pp 785 797 the model of anelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 a radial model of anelasticity consistent with long period surface wave attenuation bull seism soc am 86 144 158 is used to predict the decay of the waveforms the focal mechanisms of the largest or otherwise significant earthquakes of 2002 are reviewed

configuration of subducting philippine sea plate beneath southwest japan revealed from receiver function analysis based on the multivariate autoregressive model 1 we construct a detailed image of velocity discontinuity beneath southwest japan by using receiver functions we first propose an improved receiver function estimation method based on the statistical multivariate autoregressive model then we apply the new method to the teleseismic waveform data recorded by the high density seismograph network in southwest japan the results show a clear velocity discontinuity at 30 km depth beneath the southern shikoku region this discontinuity corresponding to the boundary between the oceanic crust and the high velocity layer the oceanic moho of the philippine sea plate phs continues down to the north indicating that the aseismic phs extends to the central chugoku region the continental moho is also clearly imaged beneath the chugoku region the depth contour of the phs shows a rather complicated feature with ridges and valleys the most significant ridge is located around longitude 133 e west of which the contours are basically directed north south changing to west east to the east beneath the western part of this ridge hypocenters of microearthquakes are located above this velocity discontinuity while earthquakes mainly occur below the discontinuity within the oceanic mantle beneath the eastern part of the ridge

relation of paleovegetation to geometry and cyclicity of some fluvial carbonaceous deposits abstract the fluvial lower eocene willwood formation bighorn basin wyoming is composed largely of red oxidized overbank sediment that has been extensively altered by soil formation within this matrix are two different types of dominantly fine grained drab to dark colored deposits that contain abundant plant remains the first are areally restricted lenticular bodies that truncate underlying mudstone layers these are interpreted as having formed in abandoned sections of channels deposits of the second type are tabular as much as 10 km in lateral extent and rest conformably on other floodplain sediment these units show a cyclic arrangement of sedimentary subunits sedimentologic and paleobotanic evidence suggests that these tabular deposits accumulated under a sequence of vegetatio al types including in succession a floodplain marsh a swamp forest and a drier ground floodplain forest these interpretations stress the interaction of vegetational succession soil characteristics and fluvial morphology in creating the chemical conditions that led to the preservation of organic matter the stratigraphic distribution of the two types of deposits within the willwood formation suggests that in the bighorn basin tectonism exerted a greater influence on the geometry of carbonaceous deposits than did climate

depositional facies of high energy beach to offshore sequence comparison with low energy sequence a study of the nearshore zone and continental shelf of a high energy coast was made in the ventura port hueneme area of california during the summer of 1974 to investigate depositional facies characteristics and compare them with similar facies from a low energy coastal setting analysis of box cores can cores and vibracores permits recognition of three principal zones 1 nearshore facies backshore to 9 m water depth made up primarily of parallel ripple and cross bedded clean sand bioturbation is only locally significant 2 transition facies 9 to 18 m water depth a zone of fine sand and silty sand characterized by an increase in biogenic over physical sedimentary structures that are commonly preserved as laminated to burrowed beds wave ripple bedding and parallel lamination are important structures in this facies 3 offshore facies 18 m water depth sandy silt is the primary texture and bioturbation is the dominant sedimentary structure remnant parallel lamination is the only physical sedimentary structure present comparison of the results of this study with a previous description of a low energy beach to offshore sequence at sapelo island georgia indicates that the two areas do not differ greatly in their facies or overall vertical sequence of sedimentary structures the principal difference is in the thickness of the three facies the california facies are significantly thicker than their georgia counterparts this difference is in direct response to the role of higher wave energy on the california coast

macroflora paleogeography and paleoecology of the upper cretaceous turonian santonian saanich member of the comox formation saanich peninsula british columbia canada morphotypes of plant macrofossil assemblages of the basal unit of the upper cretaceous turonian santonian comox formation nanaimo group vancouver island were investigated to provide insight into the character of the macroflora environment of deposition and paleogeography of vancouver island three floristic assemblages were documented one dominated by angiosperm morphotypes such as platanus menispermites and zizyphus like leaves another dominated by gymnosperm morphotypes such as those synonymous with glyptostrobus comoxensis bell and pseudoctenis latipennis heer seward and a third assemblage transitional between the previous two these assemblages suggest the saanich member was likely deposited in a barrier island estuarine floodplain complex with fluvial sedimentary input the macrofloral assemblage also includes many endemic taxa suggesting a barrier to floral migration between the paleocontinent and the vancouver island precursor during the upper cretaceous which supports the existe

palaeo digital elevation models for use as boundary conditions in coupled ocean atmosphere gcm experiments a maastrichtian late cretaceous example abstract palaeogeography specifically palaeotopography and palaeobathymetry provides an essential boundary condition for computer based atmosphere and ocean modelling it also provides the geographic context for understanding surface processes palaeodrainage palaeoweathering and biotic interactions palaeoecology palaeobiogeography with increased model resolution coupled ocean atmosphere general circulation models gcms and the addition of vegetation soil weathering ice and chemical modules there is now a need for more robust detailed palaeotopographies and palaeobathymetries that are fully integrated with the processes being modelled especially the hydrological system here we present a new geographic information system gis based hydrologically correct palaeo digital elevation model dem for the maastrichtian late cretaceous we describe the methods and concepts used to construct the map and draw attention to the limits imposed by scale and uncertainty and how these factors must be considered as part of the error analysis of derived model results the underlying palaeogeography is one of a series of 27 global maps that represent the stages of the cretaceous and sub epochs of the cenozoic each map is generated at a scale of 1 30 million in arcview gis and arcinfo using data from the lead author s own databases of lithologic tectonic and fossil information the lithologic databases of the paleogeographic atlas project the university of chicago a survey of published literature and dsdp odp data interpretations of elevation are derived following the methods outlined in ziegler et al ziegler a m rowley d b lottes a l sahagian d l hulver m l gierlowski t c 1985 paleogeographic interpretation with an example from the mid cretaceous annual review of earth and planetary sciences 13 385 425 an understanding of the tectonic regime and evolution of each feature and the age depth relationship for the ocean the global palaeo dem was derived using the elevation contours from the paleogeography and the suite of hydrological tools available in arcinfo grid the palaeo dem has been constrained by defining areas of internal palaeodrainage palaeoriver mouths and known palaeoriver courses the maastrichtian has been completed first to provide the boundary conditions for a series of coupled atmosphere ocean experiments when integrated with the results of the coupled ocean atmosphere model the result is a powerful tool for understanding surface processes and an important step towards the development of a continuous series representing a fully evolving palaeolandscape

fractal vein distributions within a fault fracture mesh in an exhumed accretionary melange chrystalls beach complex new zealand a well developed fault fracture mesh is observed in the chrystalls beach complex an accretionary melange within the otago schist on the south island of new zealand in this study an analysis of vein thicknesses and clustering of veins is presented both shear and extension veins have a power law thickness distribution measures of vein spacing best fit a power law distribution but a small data set limits this interpretation to a small fractal range vein clustering varies from random to moderately clustered between outcrops and is the greatest where a large proportion of relatively competent blocks occurs within the melange fractures are distributed within the melange matrix and this localized deformation requires heterogeneity in rheology and or fluid pressure distribution whereas pervasive distributed deformation occurs in relatively homogeneous rock the overall trend of this deformation being mainly accommodated by thin veins required that new fractures formed preferentially over refracturing existing veins which highlights the distributed nature of deformation within a fault fracture mesh the predominance of new fractures may result from vein material being stronger than the cleaved wall rock such that wall rock failure occurred instead of reopening of pre existing shear and extension veins

sediment composition and hydrography in six high gradient estuaries of the northwestern united states abstract small estuaries of the northwestern united states are fed by high gradient streams which range widely in mean fluvial discharge rates sediment composition in these estuaries differs with grain size and with the relative abundances of river and beach derived sand in order to determine to what degree sediment composition is related to the relative influence of tidal and river flow in these active margin estuaries the modern sediment compositions in six pacific northwest estuaries were analyzed by standard grain size and heavy mineral techniques the average textural and sand source compositions for each bay were calculated on a percent surface area basis estuarine sediment compositions are compared and found to be correlated with a hydrographic parameter hr mean tidal p ism volume mean fluvial discharge rate 6 hours computed for each bay both mud and beach sand increase as the dimensionless hydrographic ratio hr increases unusual results in two of the estuaries are attributed to man made alterations in one estuary and to eolian transport of beach sand into the other estuary

melange rheology and seismic style shear displacements in crustal fault zones are accommodated by a range of seismic styles including standard earthquakes non volcanic tremor and continuous and transitory aseismic slip subduction channel shear zones containing highly sheared fluid saturated trench fill sediments intermingled with fragments of oceanic crust are commonly inferred to occur along active subduction megathrusts if this interpretation is correct these plate boundary faults are not discrete planes but may resemble the melange shear zones commonly found in exhumed subduction related rock assemblages melange deformation appears to depend critically on the ratio of competent to incompetent material with shear surfaces localized along lithological contacts or within competent domains while matrix flow accommodates shearing by distributed strain if the style of strain and or displacement accommodation in a melange reflects the partitioning between aseismic and seismic slip the proportion of competent material seems likely to be a significant factor affecting seismic style within subduction channel shear zones and along comparable mixed lithology fault zones

upper boundary of the pacific plate subducting beneath hokkaido japan estimated from scsp phase abstract three dimensional geometry of the upper boundary of the pacific plate subducting beneath hokkaido japan was obtained using the scsp phase the phase converted from scs s wave reflected at the core mantle boundary to p wave at the plate boundary taking the advantage of a dense seismic network hi net recently deployed across the japanese islands we applied several seismic array analyses to the recorded waveform data for a large nearby deep earthquake in order to enhance very weak scsp signals in the original records at first we set up five blocks for the region in plate dip directions after aligning the travel times of scs and stacking seismograms among stations in a given sub block perpendicular to each dip direction we searched for the optimal plate model i e two dimensional geometry of the upper boundary for each block the model was parameterized by seven depth grids and seismograms were stacked based on the travel time of scsp as a time lag of each sub block so that the optimal model would yield the maximum spectral energy of scsp after stacking this model parameter search was conducted using ray tracings of scsp with a reference velocity model and a non linear inversion scheme neighbourhood algorithm the optimal model of each block was combined each other by cubic spline interpolation in order to construct an overall three dimensional geometry of the upper boundary of the plate next we performed the frequency wavenumber f k spectral analysis to refine the above result assuming each station as a reference point we made beam output from records of its adjacent stations as a function of wavenumber vector k x k y and frequency the peak of its power spectrum was considered to represent the wavenumber vector of scsp that is azimuth of arrival and slowness so that we can estimate the position and depth of the corresponding scs scsp conversion in the frequency range from 0 5 to 1 5 hz we could estimate the conversion points for 21 stations or hypothetical arrays and revised the geometry of the upper boundary obtained by the non linear stacking approach in the previous step the final plate model was compared with the distribution of intraplate earthquakes in the pacific plate this comparison clearly reveals that the upper seismic zone merges with the lower from 150 to 200 km in depth deviating systematically away from the upper boundary where the boundary is slightly bumped in a convex manner

fault growth and landscape development rates in otago new zealand using in situ cosmogenic 10be abstract we use in situ cosmogenic 10 be measurements in quartzites to examine the growth and propagation rates of a late quaternary anticline forming above a blind reverse fault in central otago new zealand we obtain average uplift and propagation rates of 0 10 0 15 mm yr 1 and 1 0 2 0 mm yr 1 respectively over the last 450 000 yr though it is probable that growth occurred episodically with more rapid development in the periods 600 400 kyr and 200 100 kyr and relative quiescence between about 400 and 200 kyr ago these results quantify and confirm a qualitative analysis of the fault evolution based on geomorphology and drainage patterns we obtain minimum 10 be exposure ages of up to 750 000 yr for the quartzites some of the oldest ages obtained by this method outside antarctica which are made possible by the extremely low erosion rates of less than 0 6 mm kyr 1 in the resistant quartzites these rocks consequently provide an opportunity to study geomorphic and tectonic processes in this region over unusually long time periods

north american nonmarine climates and vegetation during the late cretaceous abstract analyses of physiognomy of late cretaceous leaf assemblages and of structural adaptations of late cretaceous dicotyledonous woods indicate that megathermal vegetation was an open canopy broad leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year with a moderate increase at about 40 45 n many dicotyledons were probably large massive trees but the tallest trees were evergreen conifers megathermal climate extended up to paleolatitude 45 50 n mesothermal vegetation was at least partially an open broad leaved evergreen woodland perhaps a mosaic of woodland and forest but the evapotranspirational stress was less than in megathermal climate some dicotyledons were large trees but most were shrubs or small trees evergreen conifers were the major tree element some mild seasonality is evidenced in mesothermal woods precipitational levels probably varied markedly from year to year northward of approximately paleolatitude 65 n evergreen vegetation was replaced by predominantly deciduous vegetation this replacement is presumably related primarily to seasonality of light the southern part of the deciduous vegetation probably existed under mesothermal climate comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational climatic patterns suggested from north american data limited data from equatorial regions suggest low rainfall late cretaceous climates except probably those of the cenomanian had only moderate change through time temperatures generally appear to have warmed into the santonian cooled slightly into the campanian and more markedly into the maastrichtian and then returned to santonian values by the late maastrichtian the early eocene was probably warmer than any period of the late cretaceous latitudinal temperature gradients were lower than at present for the campanian and maastrichtian a gradient of about 0 3 c 1 latitude is inferred equability was high a mean annual range of temperature of about 8 c is inferred for paleolatitude 51 56 n during the campanian most late cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation a brief low temperature excursion and a major long lasting increase in precipitation occurred at the cretaceous tertiary boundary in megathermal climates these events selected for plants that could exist in rainforest environments in mesothermal climates deciduousness and contamitant structural adaptations were selected the events at the cretaceous tertiary boundary had a major and long lasting impact on the evolution of land plants and their ecosystems low precipitation at low to middle late cretaceous latitudes is suggested to be the result of high levels of atmospheric co2 which in turn are probably related to inability of warm saline oceans to store large amounts of carbon conditions appear to have rapidly changed at the cretaceous tertiary boundary when oceanic circulation and stratification may have been fundamentally altered after the boundary the oceans were apparently able to store much greater amounts of carbon and the oceans withdrew large amounts of co2 from the atmosphere in turn more precipitation fell at low to middle latitudes the resulting high biomass vegetation formed a second major carbon reservoir to keep atmospheric co2 low relative to the late cretaceous changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean atmosphere system

seismic evidence for deep water transportation in the mantle we report seismic evidence for the transportation of water into the deep mantle in the subduction zone beneath northeastern japan our data indicate that water is released from the hydrated oceanic crust at shallow depths approximately 100 kilometers and then forms a channel of hydrated mantle material on top of the subducting plate that is the pathway for water into the deep mantle our result provides direct evidence that shows how water is transported from the ocean to the deep mantle in a cold subduction zone environment

the hawkesbury sandstone south of sydney australia triassic analogue for the deposit of a large braided river abstract the hawkesbury sandstone is a triassic sheet sandstone extensively exposed in the sydney basin new south wales particularly along the coast near sydney unidirectional paleoflow in the sandstone its freshwater biota and abundant mudrock intraclasts indicate fluvial deposition sheet morphology low paleocurrent variance abundant erosion surfaces and the paucity of in situ mudrocks point to a braided fluvial system three facies assemblages have been recognized stratified sandstone massive sandstone and a minor mudrock assemblage the stratified sandstone assemblage is dominated by stacked sets of planar cross strata and minor trough cosets in sequences 6 23 m thick bounded by erosion surfaces significant paleocurrent changes between channel sequences indicate that they were initiated by the avulsion of major channel systems in some cases the channel sequences fine upward with planar cross stratal sets overlain by trough sets that decrease in magnitude upwards fining up into mudrocks the massive sandstone assemblage occurs principally as massive sandstone in elongate erosional features oriented transverse to paleoflow the massive sandstone commonly contains large mudrock intraclasts and is attributed to failure of high channel banks and or large bedforms during falling water stages the mudrock assemblage comprises rippled and horizontally laminated fine sandstone siltstone and shale with minor mudstone it is attributed primarily to floodplain deposition but abandoned channel fills are also present the hawkesbury sandstone does not conform to existing models for braided fluvial deposition in that planar cross strata accumulated in deeper parts of channels whereas trough cross strata formed in shallower water the large scale of planar cross strata sets up to 7 5 m thick mudrock intraclasts up to 38 m long bank collapse scars up to 11 m deep and abandoned channel fills up to 18 m deep show that the hawkesbury river was very large with deep main channels and high but variable discharge

diminutive trace fossils in the chengjiang lagerstatte diminutive trace fossils described here have been well preserved in connection with certain pliable carapaces or skeletons of the chengjiang animals taphonomic evidence suggests that these traces were formed in situ the peculiar preservation indicates that some bilaterians of uncertain affinities seem to have been active at the burial site constituting an important group of the hidden majority of cambrian marine community this may be an essential feature closely associated with the palaeoecology and exceptional preservation of the cambrian fossil lagerstatten the rare preservation of such millimetre sized trace fossils raises further doubts about the timing of the initial benthic bilaterians by applying trace fossil evidence

geological evidence against major displacement in the nares strait early continental drift1 3 and later plate tectonic reconstructions4 14 indicate left lateral sinistrai movement along nares strait of between 150 and 400 km during the cretaceous tertiary a basic concept in such reconstructions is the substantial part played by seafloor spreading in the origin of labrador sea baffin bay until recently geological knowledge of the area adjacent to nares strait was insufficient to put tight constraints on displacement along nares strait fig 1 of seven independent lines of evidence from bedrock geology termed markers all are consistent with sinistrai net displacement of greenland along nares strait of 0 25 km the three most imprecise markers can be reconciled with maximum movement of 100 km this refutes conventional plate tectonic reconstructions which suggest movement of 150 km or more new mechanisms should now be considered to explain the broad area of oceanic crust in baffin bay

simple relationship between seismic activity along philippine sea slab and geometry of oceanic moho beneath southwest japan summary many earthquakes with various types of focal mechanisms occur along the subducting philippine sea slab phs beneath southwest japan and the hypocentre distribution is quite inhomogeneous in this region distinct non volcanic deep low frequency tremors are often observed to clarify the cause of these apparently complicated and peculiar seismic activities we first construct a detailed configuration of the oceanic moho slab moho within the phs based on a receiver function rf analysis to convert the time domain rfs into their depth domain equivalents we adopt a fine scaled velocity model based on the traveltime tomography the depth contours of the oceanic moho exhibit complexities but the active region of the intraslab earthquakes corresponds well to the oceanic moho geometry in the western part of shikoku the intraslab seismicity is very high and the focal mechanisms mainly exhibit normal faults with east west extension axes since the phs is subducting to the west and the dip angle of the slab becomes steep in the western part of this region the stress field in this region can be attributed to the slab pull induced by the westwards slab subduction similar types of focal mechanisms are observed in the tokai district with a focal depth greater than 35 km since the oceanic moho exhibits a ridge shape in this region its stress field can be attributed to the slab pull and the effect of slab bending shallow earthquakes in the tokai and eastern shikoku regions have strike slip focal mechanisms and their extension axes are parallel to the strike of the oceanic moho these focal mechanisms may be influenced by both the oblique subduction of the slab and low slab dip angle earthquakes beneath the kii peninsula exhibit strike slip or downdip compression focal mechanisms with east west compression axes since the moho beneath this peninsula shows a valley shape compressional stress occurs around the moho moreover the slab convergence compresses this valley this also induces the east west compression field in this region we have newly confirmed the existence of an aseismic slab beneath the northern part of the kinki district central part of japan in this aseismic region the dip direction of the slab is parallel to that of the slab convergence direction this tendency is observed in the central part of shikoku where the slab seismicity is relatively low these features imply that the intraslab seismicity is constrained by the interaction between the slab geometry and slab motion we also revealed the possibility that the oceanic moho beneath not only ise bay but also the kii channel has a ridge shape in both these regions the non volcanic low frequency tremor activity becomes low more than 80 per cent of the tremor epicentres are distributed within contour depths of 38 3 km of the oceanic moho we find that the interaction between the moho geometry and the plate motion of the subducting phs plays an important role in determining the local stress field and the location of both seismicity and low frequency tremors

nd and sr isotopic signatures of metasedimentary rocks around the south pacific margin and implications for their provenance an nd sr isotope database including c 200 new analyses is presented for palaeozoic and mesozoic metasedimentary successions extending through southeastern australia new zealand west antarctica and the antarctic peninsula to southern south america combining with u pb detrital zircon age data this enables characterization of new zealand terranes especially within the eastern province where there is a progression from westernmost terranes of both volcanic volcaniclastic and accretionary origin with primitive sediment sources to easternmost terranes with mature continental sediment inputs in southern south america west antarctica and the antarctica peninsula similar accretionary complexes have nd model ages principally reflecting mixing of sedimentary material from multiple sources both mature and juvenile a mature gondwana continental provenance dominates in sedimentary basins inboard of the active margin especially in the palaeozoic western province new zealand interior west antarctica and nw argentina and contributes significantly to pre mesozoic sedimentary rocks of patagonia east of the andes along the gondwanaland margin nd systematics for younger late palaeozoic to early mesozoic accretionary complex metasediments reflect younger source inputs notably in the scotia metamorphic complex many of the accretionary complex deposits must involve significant crustal reworking there is no apparent south american equivalent of the primitive provenance of the westernmost accretionary terranes of new zealand

seismic evidence for a 920 km discontinuity in the mantle analysis of hundreds of seismograms from a seismic array in the japanese islands reveals a seismic discontinuity at a depth of about 920 km in the mantle beneath the tonga subduction zone this discontinuity is also evident beneath subduction zones in the japan and flores seas the discontinuity probably represents either a change in mantle chemical composition or the signature of the subducted slab s garnet layer

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

evolution of cretaceous cenozoic quartz pebble conglomerate gold placers during basin formation and inversion southern new zealand abstract numerous auriferous fluvial quartz pebble conglomerates qpcs are present within the late cretaceous recent sedimentary sequence in southern new zealand the qpcs formed in low relief settings before during and after regional marine transgression in alluvial fan and a variety of fluvial and near shore depositional settings in particular during slow thermal subsidence associated with late cretaceous early cenozoic rifting and during the early stages of orogenic uplift following mid cenozoic marine regression qpc maturity characteristics are complex and vary with sediment transport and recycling history stratigraphic proximity to the transgressive waipounamu erosion surface and the amount of first cycle detritus incorporated during recycling for pre marine qpcs the amount of first cycle detritus varies with tectonic intensity and proximity of the depositional setting to remnant cretaceous topography for post marine qpcs it varies with tectonic intensity and proximity to late cenozoic uplift of basement ranges qpcs do not form during a single bedrock erosion sediment deposition cycle non oxidised and or oxidized groundwater alteration kaolinisation of labile minerals in immature sediment and the upper part of underlying basement and repeated sedimentary recycling are fundamental processes of qpc formation regardless of the tectonic or sedimentary settings altered immature rock disaggregates easily upon erosion and alteration clays are winnowed to leave quartz rich residues containing resistant heavy minerals such as zircon and gold detrital sulfide survives recycling if deposition and burial in saturated sediments are rapid qpcs result only if sediment recycling is not accompanied by excessive erosion of fresh basement rock uplift of many parts of the otago schist belt since late miocene has raised rocks above the water table increased erosion rates and inhibited groundwater alteration and qpc formation qpc formation is still occurring in southland where the water table is high sediments are saturated and undergoing alteration and uplift and erosion rates topography and fluvial gradients are all low the qpcs accumulate as residual gravel on the valley floors of low competence streams that are slowly incising pervasively altered dominantly late miocene pliocene immature conglomerates qpcs formation essentially represents physical and chemical lagging of precursor strata accumulation of detrital gold and other heavy minerals is an inevitable consequence and most qpcs contain some gold three types of significant gold placer have developed in the qpcs type 1 placers are essentially eluvial and or colluvial in origin and form without significant fluvial transport by residual accumulation in low competence valleys during low rate uplift fluvial incision and qpc formation type 2 placers have formed during significant fluvial transport and subsequent fluvial incision mainly in higher energy proximal and medial reaches of larger pre marine eocene and post marine fluvial systems type 3 placers formed by wave base and marine current winnowing in the shallow shelf setting during low rate regional marine transgression especially in the eocene

reactions leading to the formation and breakdown of stilpnomelane in the otago schist new zealand semi pelitic rocks ranging in grade from the prehnite pumpellyite to the greenschist facies from south eastern otago new zealand have been investigated in order to evaluate the reactions leading to formation and breakdown of stilpnomelane detrital grains of mica and chlorite along with fine grained authigenic illite and chlorite occur in lower grade rocks with compactional fabric parallel to bedding at higher grades detrital grains have undergone dissolution and metamorphic phyllosilicates have crys tallized with preferred orientation sub parallel to bedding leading to slaty cleavage stilpnomelane is found in metapelites of the pumpellyite actinolite facies and the chlorite zone of the greenschist facies but only rarely in the biotite zone of the greenschist facies illite or phengite is ubiquitous whereas chlorite occurs only rarely with stilpnomelane upgrade of the pumpellyite out isograd chemical and textural relationships suggest that stilpnomelane formed from chlorite phengite quartz k feldspar and iron oxides stilpnomelane was produced by grain boundary replacement of chlorite and by precipitation from solution overprinting earlier textures some relict 14 achlorite layers are observed by tem to be in the process of transforming to 12 astilpnomelane layers the aem analyses show that fe is strongly partitioned over mg into stilpnomelane relative to chlorite k d 2 5 and into chlorite relative to phengite k d 1 9 modified aaefm diagrams projected from the measured phengite composition rather than from ideal kal 3 si 3 o 10 oh 2 are used to elucidate reactions among chlorite stilpnomelane phengite and biotite in addition to pressure temperature and bulk rock composition the stilpnomelane in isograd is controlled by variations in k fe3 fe2 o oh and h 2 o contents and the locus of the isograd is expected to vary in rocks of diverent oxidation states and permeabilities biotite quartz and less phengitic muscovite form from stilpnomelane chlorite and phengite in the biotite zone projection of bulk rock compositions from phengite naalo 2 sio 2 and h 2 o reveals that they lie close to the polyhedra defined by the aaefm minerals and albite other extended aaefm diagrams such as one projected from phengite naalo 2 caal 2 o 4 sio 2 and h 2 o may prove useful in the evaluation of other low grade assemblages

paleodepositional setting of the late cretaceous pautut flora from west greenland as determined by sedimentological and plant taphonomical data abstract preservation of the santonian campanian pautut flora in west greenland is mainly the result of a high energy river system that flowed across a well vegetated delta plain to carry and deposit plant parts and terrestrial clastic sediments into a low energy marine setting a diverse flora is represented mainly in three depositional settings 1 a dominant angiosperm vegetation preserved with fern and a few conifer species is found within backswamp lakes possibly near rivers 2 conifer organs and a sparse angiosperm leaf association occur in nearshore marine deltaic deposits dominated by fluvial sedimentation and 3 a unique pautut angiosperm vegetational assemblage with a few conifer and cycad species preserved in a brackish to fully marine bay setting fossil plant material preserved in the backswamp lakes and fluvial settings probably were deribed mostly from local sources indicating that angiosperms were able to a degree to invade into the backswamp arctic habitats considered to have been dominated by conifers however these backswamp habitats probably were short lived oxbow lakes with a successional angiosperm vegetation plant material in the fully marine setting is allochthonous very diverse and probably derived mostly from the upper delta palin the observed differences within the fossil plant assemblages deposited in the marine setting those containing mostly conifer parts occur in nearshore marine environments as compared to assemblages with mostly angiosperm leaves in more distal marine environments are used to interpret sorting of different plant parts due to individual taphonomical characters this means that the heavier conifer cones in the nearshore marine setting sank sooner than the lighter leaves which were dispersed further out to sea strengthening the argument for sorting is that both types of plant parts had a final resting position due to subaqueous transport the unique angiosperm leaf assemblage found in the fully marine setting is used to support the interpretation that the upper delta plain levees or extrabasinal sites were inhabited by a vegetational community distinct from that near the backswamp areas of the lower delta plain there are a few angiosperm species in common between the distal and nearshore marine and the backswamp lake settings these species are found througout the pautut area and exemplify a riparian element which was more prone to enter a depositional regime nearshore habitats were inhabited by non woody plants

shear veins observed within anisotropic fabric at high angles to the maximum compressive stress some faults seem to slip at unusually high angles 45 relative to the orientation of the greatest principal compressive stress1 2 3 4 5 this implies that these faults are extremely weak compared with the surrounding rock6 laboratory friction experiments and theoretical models suggest that the weakness may result from slip on a pre existing frictionally weak surface7 8 9 weakening from chemical reactions10 elevated fluid pressure11 12 13 or dissolution precipitation creep14 15 here we describe shear veins within the chrystalls beach accretionary melange new zealand the melange is a highly sheared assemblage of relatively competent rock within a cleaved anisotropic mudstone matrix the orientation of the shear veins compared with the direction of hydrothermal extension veins that formed contemporaneously indicates that they were active at an angle of 80 5 to the greatest principal compressive stress we show that the shear veins developed incrementally along the cleavage planes of the matrix thus we suggest that episodic slip was facilitated by the anisotropic internal fabric in a fluid overpressured heterogeneous shear zone a similar mechanism may accommodate shear at high angles to the greatest principal compressive stress in a range of tectonic settings we therefore conclude that incremental slip along a pre existing planar fabric coupled to high fluid pressure and dissolution precipitation creep may explain active slip on severely misoriented faults

deep structure of japan subduction zone as derived from local regional and teleseismic events we have determined a detailed three dimensional p wave velocity structure of the japan subduction zone to 500 km depth by inverting local regional and teleseismic data simultaneously we used 45 318 p wave arrivals from 1241 shallow and deep earthquakes which occurred in and around the japan islands the arrival times are recorded by the japan university seismic network which covers the entire japan islands densely and uniformly we also used 4211 travel time residuals from 100 teleseismic events which are read from seismograms recorded by seismic stations in northeastern japan in comparison with the previous results obtained from only local and regional events the present result for the area around the lower plate boundary and the mantle below the plate is determined more reliably because of the addition of 7035 data from 100 teleseismic events and 41 very deep earthquakes in the crust and uppermost mantle low velocity zones are clearly visible beneath active volcanoes in the mantle wedge the low velocity zones generally parallel with the slab and exist continuously to a depth of about 200 km which is consistent with the petrological geochemical and geodynamic studies we consider that the existence of volcanism related low velocity anomalies in the mantle wedge is a general seismological characteristic of subduction zones in light of all the available tomographic results for many subduction zones in the world the pacific slab beneath japan is imaged more clearly than in previous studies as a high velocity zone with a thickness of 80 90 km and a p wave velocity 4 6 higher than the normal mantle lower velocity anomalies are found in the mantle below the slab

study of the structure of the slab mantle interface using reflected and converted seismic waves summary seismic waves reflected and converted at the interface between a downgoing slab and the mantle above it can provide important constraints on the velocity contrast at the interface and hence on the properties of the downgoing lithosphere modelling studies suggest that different physical mechanisms may contribute to the velocity contrast at different depths along the interface to explore the possible mechanisms we examine the amplitudes of seismic waves reflected and converted at the slab mantle interface in japanese subduction zones slab face p reflection amplitudes suggest a velocity contrast ranging upwards to 10 per cent at depths of between 300 and 400 km pis amplitude ratios from scs to p conversions at the slab mantle interface depend on the depth of conversion and are large 0 14 and 0 12 at stations shk and mat the size of the velocity contrasts and amplitude ratios suggests that a model of the interface more complicated than one involving merely temperature and or compositional effects is required we use these observations to constrain layered models of the slab mantle interface using thomson haskell matrix modelling comparing observations with calculated amplitude ratios the results suggest that the crustal layer of basaltic composition persisting to depth during subduction plays a role in the generation of the shallow converted waves the deeper conversions appear to require layering as well perhaps involving eclogite at the slab surface in addition to oriented olivine in the overlying mantle and the a p and a y phase transformations in olivine within the slab

scsp observed on north island new zealand implications for subducting plate structure seismic phase conversions provide important constraints on the layered nature of subduction zone structures recordings from digital stations in north island new zealand have been examined for converted scs to p scsp arrivals from deep 150 km tonga kermadec earthquakes to image layering in the underlying hikurangi subduction zone consistent p wave energy prior to scs has been identified from stations in eastern and southern north island where the subducted plate interface is at a depth of between 15 and 30 km two scs precursors are observed ray tracing indicates that the initial precursor scsp1 corresponds to conversion from the base of an 11 14 km thick subducting pacific crust the second precursor is interpreted as a conversion from the top of the subducting plate the amplitude ratio scsp1 scs increases from 0 10 to 0 19 from northern to southern north island this is within the range expected from a simple first order velocity discontinuity at an oceanic moho a 1 2 km thick layer of low velocity sediment at the top of the subducting plate is required to explain the remaining scsp waveform our results imply that the abnormally thick hikurangi chatham plateau has been subducting beneath new zealand for at least 2 9 myr thus explaining the high uplift rates observed across eastern north island

some limitations in using leaf physiognomic data as a precise method for determining paleoclimates with an example from the late cretaceous pautut flora of west greenland abstract plant parts of the late cretaceous west greenland pautut flora are derived from vegetation growing in lower delta plain delta upland and levee habitats a large river system drained the uplands and deposited leaves from species there and levee areas into a shallow bay setting the large drainage area of the rivers caused a great diversity of species to be preserved in the bay when these upland and levee species are combined with those that grew and were deposited in the lower delta plain areas 12 fern six cycad cycadeoid 1 ginkgoalean 35 conifer and over 85 angiosperm species represent the pautut flora when the paleotemperature derived from the angiosperm leaf margin ratio of the complete pautut flora 8 c is compared to other paleobotanical data and oxygen isotope values warm temperate to subtropical there is a serious discrepancy that puts the leaf physiognomic approach for precisely determining paleoclimate in the cretaceous in serious doubt also paleoclimatic interpretations based on the angiosperm leaf margin data of leaves from the lower delta plain species would indicate slightly cooler conditions than that suggested by the upper delta plain species leaf size would indicate wetter conditions in the lower delta plain even though other leaf features e g drip tips suggest moist conditions did occur in the upper delta plain these preservation enough that regional paleoclimate scenarios drawn from only one depositional setting or loclity can be erroneous a sampling size of less than 30 angiosperm species for a fossil flora also is suspect for reliably indicating climatic conditions unless the flora was originally impoverished of angiosperm species taphonomic factors play a significant role in fossil leaf preservation so collected fossil assemblages must closely represent the original vegetation before paleoclimatic interpretations based on leaf physiognomy can have a degree of credibility a limit to plausibility is especially significant in cretaceous floras because they have a limited diversity due to evolutionary constraints and appear to have consisted of more successional species than younger floras thus displaying intermediate climatic conditions moisture and arctic light levels further restrict determination of paleoclimatic conditions derived from leaf margin ratios and leaf size

subduction zone thermal structure and mineralogy and their relationship to seismic wave reflections and conversions at the slab mantle interface seismological studies of the interface between downgoing slabs of subducted lithosphere and the overriding mantle provide constraints against which models of mantle and slab temperature and bulk composition can be tested these studies employing waves reflected and converted at the slab mantle interface suggest that a velocity contrast of 5 10 occurs over a distance of 10 20 km to depths of at least 350 km the authors have investigated whether such sharp contrasts can result form thermal structure compositional differences phase changes or other effects such as preferred mineral orientation using a mantle and slab temperature model a petrologic model of mantle and slab mineralogy and a data base of elastic properties of mantle and slab phrases theoretical seismic velocities were calculated and compared with the observed velocity contrast and boundary thickness constraints at 9 6 gpa and 1000c conditions modeled at the slab mantle interface at approximately 280 km depth cooler temperatures in the slab interior produce at constant composition only approximately a 1 75 v sub p increase into the slab in any of the peridotitic and eclogitic mineralogies investigated variation in v sub p among the different bulk compositions is only approximately 0 5 these contrasts are substantially lower than those obtained from the seismological studies andmore indicate that temperature and bulk compositional differences between mantle and slab are inadequate to cause the observed velocity contrasts they propose that phase transformations in mantle and slab mineralogies notably elevation of the olivine spinel phase change normally occurring at 400 km depth are important factors in these sharp contrasts other contributing effects may include preferential mineral orientation near the slab surface and at shallower depths the presence of partial melt or hydrous fluid evolved from dehydration reactions along the interface less

seismic interferometry of teleseicmic s wave coda for retrieval of body waves an application to the philippine sea slab underneath the japanese islands summary the reconstruction of surface waves from the cross correlation of random wavefields has recently been extensively inspected by theoretical and experimental approaches however the reconstruction of body waves has not been extensively studied in this study we present a method for extracting body waves that is direct p and s waves and reflected waves from the philippine sea slab we use the cross correlation of the wavefield generated by the teleseismic s waves observed by hi net tiltmeters with a passband of 0 07 0 5 hz to enhance the contribution of the s coda we reduced the source time function and the deterministic phases ss scs and ss and the surface wave in s coda the records of the processed s coda observed at every station pair are cross correlated for each teleseismic event the cross correlation functions ccfs of different earthquakes are stacked to retrieve wavefields propagating between the station pairs as a result direct p s and the reflected waves could be extracted when the stacked ccfs are aligned as a function of distance of separation between two stations the gradients of the traveltime curves for the direct p and s waves are approximately 5 7 and 3k m s 1 respectively these velocities correspond to the seismic velocities of the crust or the p wave velocity of the uppermost mantle in order to enhance the reflected waves we searched for the reflection points by assuming that the later phases in the ccfs are ss reflections and map the amplitudes onto the depth sections as a result the negative phases dipping to the north can be traced right below the region of hypocentre distribution these negative phases probably correspond to the oceanic moho within the philippine sea slab we also show that the oceanic moho can also be traced by assuming pp reflections these results indicate that the ccfs plausibly contain information regarding both p and s waves propagating between the two receivers and are capable of detecting reflected phases in addition to the direct waves

crack seal fibre growth mechanisms and their significance in the development of oriented layer silicate microstructures abstract an analysis of crack seal fibre growth mechanisms has shown two important implications of the crack seal process for the interpretation of microstructures in low grade metamorphic rocks 1 1 the ability of fibre growth to track the incremental separation history of crack walls depends on details of the nucleation and growth mechanisms 2 2 fibrous crystals may develop cristallographic preferred orientations in certain crack seal situations the microstructures of layer silicates and associated phases developed in several examples of syntectonic intragranular microfracture sites and veins indicates that layer silicate 001 and grain shape preferred orientation can develop during crack seal deformation by oriented growth mechanisms during successive crack seal increments preferred orientation may develop in response to an interaction between anisotropic growth kinetics and the displacement history resulting in preferential rejoining by syntaxial overgrowth of pulled apart grains having fast growth directions parallel to the incremental displacement direction across a microcrack preferred orientation may also be developed and enhanced in crack seal growth sites by overgrowth of previously oriented layer silicates in the microcrack walls in this case the crystallographic preferred orientation need not be simply related to the displacement history during crack seal fibre growth since crack seal processes may operate on all scales down to the minimum size of a microfracture in a deforming rock such mechanisms of layer silicate preferred orientation development are expected to be very significant in developing and enhancing foliation during deformation involving microfracture and solution transfer processes

numerical modelling of mechanical controls on coeval steep and shallow dipping auriferous quartz vein formation in a thrust zone macraes mine new zealand the hyde macraes shear zone hmsz is a regionally continuous low angle ne dipping 15 late metamorphic thrust zone in the mesozoic otago schist the shear zone which is host to large volumes of mineralised schist consists of foliated fissile schist with some massive schist pods two sets of quartz veins are found within the hmsz thrust related shallowly dipping veins that were emplaced parallel or sub parallel to the shears and swarms of steeply dipping extensional veins which cut across the metamorphic foliation the latter are restricted to the massive schist pods mutual cross cutting relationships occur between steep extensional veins and shallow dipping veins suggesting that they formed contemporaneously the co existence of these two vein types locally implies local rotation of the principal stress axes to produce extensional veins within a regional thrust setting the steep extensional veins are spatially related to lateral and oblique ramps within the hmsz three dimensional mechanical models show that these lateral or oblique ramps can produce favourable conditions for extensional vein formation when combined with a high fluid pressure and oblique convergence mechanical requirements include a reduced differential stress a positive volumetric strain and an increase in the horizontal shear stress our models show that under certain conditions it is possible for extension related structures to form during shortening because of local changes in the stress state without the need for a regional scale switch in the imposed stress field the convergence direction across the hmsz during formation of the steep extensional veins was wnw

fractal clustering of metamorphic veins metamorphic veins record the fracture controlled flow of fluids throughout the oceanic and continental crust i show that the spatial distributions of veins from three diverse metamorphic settings are fractal and self similar vein densities were measured by counting the number of macroscopic veins intersected along linear transects the localities included wol lastonite quartz veins in marbles for which the fractal dimension d is 0 46 actinolite chlorite veins in hydrothermally altered oceanic diabases d 0 81 and epidote quartz veins in contact metamorphosed basalts d 0 25 0 63 the fractal clustering of veins provides a geometric framework for understanding spatial and temporal patterns of fluid flow and mineral reaction during metamorphism