uncertainties in the relative positions of the australia antarctica lord howe and pacific plates since the late cretaceous we determined parameters that describe finite rotations and their uncertainty regions for relative plate motion at the spreading centers between the pacific and antarctica plates between australia and antarctica and between the lord howe rise and australia we combined these to yield a range of possible finite rotations describing the relative positions of the pacific australia antarctica and lord howe plates since the late cretaceous if the pacific australia plate boundary has had its present trend since anomaly 18 time reconstructions show 330 110 km of motion of the pacific plate relative to the lord howe rise since anomaly 5 time 9 8 m y 420 110 km since anomaly 6 time 19 5 m y 770 330 km since anomaly 13 time 35 6 m y and 820 260 km since anomaly 18 time 43 0 m y we examined two cases for times prior to anomaly 18 assuming a late cretaceous age of australia antarctica separation if a plate boundary existed between the lord howe rise and pacific plates since the late cretaceous with no plate boundary in antarctica reconstructions with the lord howe rise fixed predict 610 200 km of westward motion of the pacific plate between the times of anomalies 31 and 22 followed by 260 100 km of northward motion between the times of anomalies 22 and 18 if the lord howe rise was fixed to the pacific plate until the eocene but a plate boundary existed between east and west antarctica reconstructions show very little motion across this boundary between the times of anomalies 31 and 22 followed by convergence between the times of anomalies 22 and 18 this second case also brings 70 80 m y paleomagnetic poles from the pacific and east antarctica plates into better agreement than the first case but large uncertainties in the reconstructions do not allow the first case to be conclusively eliminated

ice mass loss in greenland the gulf of alaska and the canadian archipelago seasonal cycles and decadal trends over the past several decades mountain glaciers and ice caps have been significant contributors to sea level rise here we estimate the ice mass changes in the canadian archipelago the gulf of alaska and greenland since 2003 by analyzing time varying gravimetry data from the gravity recovery and climate experiment prior to 2013 interannual ice mass variability in the gulf of alaska and in regions around greenland remains within the average estimated over the whole data span beginning in summer 2013 ice mass in regions around greenland departs positively from its long term trend over greenland this anomaly reached almost 500 gt through the end of 2014 overall long term ice mass loss from greenland and the canadian archipelago continues to accelerate while losses around the gulf of alaska region continue but remain steady with no significant acceleration

thermochronology of the south cyclades shear zone ios greece effects of ductile shear in the argon partial retention zone micas and potassium feldspars from the south cyclades shear zone ios cyclades greece yield varied and complex 40ar 39ar apparent age spectra a correlation exists between 40ar 39ar apparent ages and the relative timing of different episodes of recrystallization and grain growth as indicated by fabric and microstructural analysis the 40ar 39ar apparent age spectra record the effects of variation in the degree of recrystallization and grain growth and partial to complete resetting of argon systematics in potassium bearing minerals during hercynian m0 alpine m1 and late oligocene early miocene m2 metamorphism deformation was strongly partitioned within the shear zone and this led to localized recrystallization and heterogeneous resetting of argon systematics within preexisting minerals modeling suggests the oligo miocene thermal events were of insufficient magnitude and or duration to completely reset the isotopic systematics in these samples our data lead to the concept of the argon partial retention and resetting zone prz defined as that portion of the crust where temperatures are insufficient to completely reset argon systematics within preexisting potassium bearing minerals within the prz some radiogenic argon in preexisting potassium bearing minerals will be outgassed and only partially retained tectonic exhumation of the prz involves movement on crustal scale ductile shear zones accompanied by strongly partitioned deformation and localized recrystallization recrystallization leads to resetting of argon systematics and thus will result in heterogeneous 40ar 39ar age distributions within these ductile shear zones e g in the south cyclades shear zone

strain partitioning in the transition area between oblique subduction and continental collision hikurangi margin new zealand spatial differences in late quaternary structural style and deformation rates indicate a complex pattern of strain partitioning within the transition area from oblique subduction beneath southern north island to oblique continental collision in northern south island new zealand the late quaternary structure of the offshore southern hikurangi margin is determined here using seismic reflection profiles mr1 side scan sonar swath images em12dual multibeam swath bathymetry and backscatter images and sediment core and dredge samples where oblique 50 subduction of the oceanic hikurangi plateau is occurring beneath southern wairarapa region the steep dissected upper margin consists of a wedge of rocks that are being deformed by strike slip and reverse faults beneath the lower margin an accretionary wedge of quaternary age has developed rapidly by frontal accretion of a thick succession of turbidites on the pacific plate estimates of late quaternary geological strain rates have been made on two margin perpendicular transects across southern north island and the offshore margin to budget the predicted nuvel 1a plate motion more than 33 55 of the total plate motion is expressed in the offshore part of the upper plate above the subduction detachment in the central hikurangi margin between 40 s and 41 s this offshore deformation could potentially include margin parallel fault slip of up to 14 15 mm yr across the upper plate strain is partitioned into zones of folding and thrust faulting and possibly more than one zone of strike slip faulting but the partitioning may be incomplete with oblique slip thrusting an important component of the deformation the wide distribution of deformation within the upper plate partially reflects strong coupling between the subducting oceanic plateau and the leading edge of the overriding plate this coupling increases toward the southwest where the continental part of the subduction zone beneath marlborough may now be inactive or very strongly coupled toward the southwest the transpressive deformation style of the upper wairarapa margin continues into the upper marlborough margin and onshore into the strike slip marlborough fault system of northern south island in contrast the accretionary wedge narrows to the southwest and terminates in southeastern cook strait approximately above the transition from subducted oceanic crust to subducted continental crust of the pacific plate farther southwest beneath the lower marlborough margin low strain folding and thrust faulting is occurring but the style of deformation is not typical of the accretionary wedge this shortening results either from a small amount of subduction slip beneath marlborough and or from contractional strain partitioned to the southeast of the continental transpression zone whereas the initial onset of continental collision occurs in marlborough the surface expression of deformation of the pacific plate occurs south of 42 30 s normal faulting of the northwestern margin of the continental chatham rise possibly reflects flexural extension of the pacific plate crust at the southern end of the subduction zone whereas folding and thrust faulting of the north canterbury coastal region results from nw se contraction of the delaminated upper crust entering the southern alps collision zone

spurious velocity changes caused by temporal variations in ambient noise frequency content ambient seismic noise cross correlations are now being used to detect temporal variations of seismic velocity which are typically on the order of 0 1 per cent at this small level temporal variations in the properties of noise sources can cause apparent velocity changes for example the spatial distribution and frequency content of ambient noise have seasonal variations due to the seasonal hemispherical shift of storms here we show that if the stretching method is used to measure time shifts then the temporal variability of noise frequency content causes apparent velocity changes due to the changes in both amplitude and phase spectra caused by waveform stretching with realistic seasonal variations of frequency content in the los angeles basin our numerical tests produce about 0 05 per cent apparent velocity change comparable to what meier et al observed in the los angeles basin we find that the apparent velocity change from waveform stretching depends on time windows and station pair distances and hence it is important to test a range of these parameters to diagnose the stretching bias better understanding of spatiotemporal noise source properties is critical for more accurate and reliable passive monitoring

holocene deceleration of the greenland ice sheet recent peripheral thinning of the greenland ice sheet is partly offset by interior thickening and is overprinted on its poorly constrained holocene evolution on the basis of the ice sheet s radiostratigraphy ice flow in its interior is slower now than the average speed over the past nine millennia generally higher holocene accumulation rates relative to modern estimates can only partially explain this millennial scale deceleration the ice sheet s dynamic response to the decreasing proportion of softer ice from the last glacial period and the deglacial collapse of the ice bridge across nares strait also contributed to this pattern thus recent interior thickening of the greenland ice sheet is partly an ongoing dynamic response to the last deglaciation that is large enough to affect interpretation of its mass balance from altimetry

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

detecting seasonal variations in seismic velocities within los angeles basin from correlations of ambient seismic noise summary we analyse 3 yr of continuous seismic records from broad band stations of the caltech regional seismic network ci in vicinity of the los angeles basin using correlations of ambient seismic noise relative velocity variations in the order of 0 1 per cent can be measured between all interstation pairs it is the first time that such an extensive study between 861 interstation pairs over such a large area has been carried out we perform these measurements using the stretching technique assuming that one of the two waveforms is merely a stretched version of the other obviously this assumption is always violated and the two waveforms are generally decorrelated due to temporal changes in the earth crust due to different sources or simply because the cross correlations are not fully converged we investigate the stability of these measurements by repeating each measurement over various time windows of equal length on average between all interstation pairs in the los angeles basin a seasonal signal in the relative velocity variation is observed with peaks and troughs during winter and summer time respectively generally the observed signal decreases with increasing interstation distance and relative traveltime perturbations can only be measured up to an interstation distance of 60 km furthermore the traveltime perturbations do not depend on azimuth of station pairs suggesting that they are not related to seasonal variations of the noise sources performing a simple regionalization by laterally averaging measurements over a subset of stations we found the sedimentary basin showing the most consistent signal and conclude that the observed seasonality might be induced either by changes in the ground water aquifer or thermo elastic strain variations that persist down to a depth of 15 22 km

balance mass flux and ice velocity across the equilibrium line in drainage systems of greenland estimates of balance mass flux and depth averaged ice velocity through the cross section aligned with the equilibrium line are produced for each of six drainage systems in greenland the estimates are based on a model equilibrium line fitted to field data and on a revised distribution of surface mass balance for the conterminous ice sheet ice drainage divides and six major drainage systems are delineated using surface topography from ers radar altimeter data ice thicknesses at the equilibrium line and throughout each drainage system are based on the latest compilation of airborne radar sounding data described elsewhere the net accumulation rate in the area bounded by the equilibrium line is 399 gt a 1 and net ablation rate in the remaining area is 231 gt a 1 excluding an east central coastal ridge reduces the net accumulation rate to 397 gt a 1 with a range from 42 to 121 gt a 1 for the individual drainage systems the mean balance mass flux and depth averaged ice velocity at the cross section aligned with the modeled equilibrium line are 0 1011 gt km 2 a 1 and 0 111 km a 1 respectively with little variation in these values from system to system in contrast the mean mass discharge per unit length along the equilibrium line ranges from one half to double the overall mean rate of 0 0468 gt km 1 a 1 the ratio of the ice mass in the area bounded by the equilibrium line to the rate of mass output implies an effective exchange time of approximately 6 ka for total mass exchange the range of exchange times from a low of 3 ka in the se drainage system to 14 ka in the ne suggests a rank as to which regions of the ice sheet may respond more rapidly to climate fluctuations

a new ice thickness and bed data set for the greenland ice sheet 1 measurement data reduction and errors ice thickness data collected between 1993 and 1999 using a coherent ice penetrating radar system developed at the university of kansas have been combined with data collected by the technical university of denmark in the 1970s to produce a new ice thickness grid for greenland crossover analysis was used to assess the relative accuracy of the two data sets and they were weighted accordingly and interpolated onto a regular 5 km spacing grid using a kriging interpolation procedure a high resolution land ice mask was used to help constrain the interpolation of the ice thickness data near the ice sheet margins where in the past the relative errors have been largest the ice thickness grid was combined with a new digital elevation model of the ice sheet and surrounding rock outcrops to produce a new bed elevation data set for the whole of greenland the ice thickness grid was compared with the currently available data set differences in the center of the ice sheet where the ice is thickest were of the order of a few percent near the margins however large differences of as much as a factor of 10 were found the total volume of ice contained in the ice sheet was reestimated and found to have a value of 2 93 x 10 6 km 3 the ice thickness grid was used to calculate the spatial pattern of gravitational driving stress over the ice sheet anomalous patterns of stress were found in areas that appeared to be associated with areas of rapid flow

deformation processes in an accretionary prism a study from the torlesse terrane of new zealand abstract the style of deformation observed in rocks of the torlesse pahau terrane exposed in the aorangi range of the north island records accretion of thick trench fill by offscraping at the toe of a growing accretionary prism during the early cretaceous the relatively coherent nature of the aorangi range rocks enables detailed study of the deformation processes produced by offscraping and subsequently within the prism and many of the structures observed in these rocks are consistent with those described from both modern accreting margins and other ancient accretionary terranes overprinting relationships indicate three phases of folding and multiple faulting events early deformation involved large scale sheath like folding oblique to the overall trend of the margin and development of an anastomosing axial planar cleavage folding of the sediments promoted dewatering the subsequent disruption of strata by shearing parallel to bedding and low angle to bedding faulting records the transition to more brittle responses to the deformation the most widespread folding phase d 2 produced numerous upright typically isoclinal folds with local development of an axial planar s 2 cleavage in macroscopic and some mesascopic fold hinges the variable plunge of the fold axes to the nne and ssw within the axial surface indicates progressive rotation of the fold axes after formation mesozoic strike slip faulting most likely produced the open e w trending folds and warps of the third folding phase d 3 in bedding already rotated to moderate dips faults which overprint the mesozoic deformation were formed in response to renewed subduction along the eastern coast of the north island during the cenozoic

accumulation over the greenland ice sheet from historical and recent records water accumulation defined as precipitation minus evaporation was estimated over all of greenland as part of a program to understand changes in ice sheet mass and elevation over 360 historical and recent point accumulation estimates on the greenland ice sheet were evaluated and 276 estimates that were judged to be high quality were used to develop the accumulation map the data set includes 99 points developed as part of four investigations of the past 5 15 years these are judged to have the greatest accuracy using kriging the average accumulation over greenland is estimated to be 30 g cm 2 yr 1 for the interior part of the ice sheet above 1800 m elevation where most of the data were acquired the average accumulation is also estimated to be 30 g cm 2 yr 1 there are still many areas on the ice sheet including northwest southeast and southern greenland where accumulation is highly uncertain exceeding the mean ice sheet uncertainty at a point of 20 25 in these regions further sampling will be required to reduce uncertainty in both regional and ice sheet wide accumulation

fission track lengths in the apatite annealing zone and the interpretation of mixed ages abstract measurements of confined fission tracks in apatites from deep boreholes show that their mean length is reduced and the length distribution becomes progressively broader through the fission track annealing zone at subsurface temperatures of around 100 c and above the length distribution characteristically becomes very broad without a pronounced peak the lengths of the longest tracks remain essentially constant at all stages of natural annealing observed in the boreholes this pattern is similar to that found in laboratory annealing of spontaneous fission tracks in apatite from an outcrop sample of the same formation these observations show that confined track lengths can be used as important indicators of the type of thermal history that a sample has experienced in the temperature zone of increasing track stability the length distributions reported here provide a basis for interpretation of fission track ages that might otherwise be ambiguous an apatite age which results from a uniform slow cooling history will have a broad negatively skewed length distribution while a bimodal distribution provides clear evidence of a two stage history involving partial annealing by a discrete thermal event the apparent fission track age associated with a bimodal length distribution will be a mixed age intermediate between the original age and that of the later event

short paper a note on rb sr whole rock ages from cleaved mudrocks in the welsh basin two cleaved epizone grade palaeozoic mudrock suites from snowdonia yield a mean rb sr whole rock age of 409 11 ma this is consistent with resetting of the rb sr whole rock isotope systems of the mudrocks during cleavage development in end silurian early devonian acadian deformation in contrast cleaved palaeozoic anchizone mudrocks from north and central wales give a silurian mean age of 430 9 ma this dates either a pre tectonic isotopic event preserved through acadian anchizone metamorphism or mid silurian deformation and metamorphism at anchizone grade unaffected by the acadian event the precise timing of the main caledonian deformation in wales has never been established firmly powell phillips 1985 suggest that it occurred in north and south wales in latest silurian time whereas ashgill and end llandovery tectonic events were dominant in central wales see also george 1963 however woodcock 1984 1987 and soper et al 1987 have argued in favour of a single tectonic event of early to middle devonian age this chronological study was undertaken to address this controversy the only previous attempt to define precisely the timing of cleavage development in wales was the k ar dating of cleavage parallel chlorite from a volcanic greywacke from north wales fitch et al 1969 when recalculated using modern decay constants these data give an age of 399 10 ma bath 1974 demonstrated the feasibility of obtaining rb sr ages from cleaved mudrocks of the welsh caledonides and this work produced caledonian ages of 409 20ma and 393 22ma from north wales and late

mass changes of the greenland and antarctic ice sheets and shelves and contributions to sea level rise 1992 2002 changes in ice mass are estimated from elevation changes derived from 10 5 years greenland and 9 years antarctica of satellite radar altimetry data from the european remote sensing satellites ers 1 and 2 for the first time the dh dt values are adjusted for changes in surface elevation resulting from temperature driven variations in the rate of firn compaction the greenland ice sheet is thinning at the margins 42 2g t a 1 below the equilibrium line altitude ela and growing inland 53 2g t a 1 above the ela with a small overall mass gain 11 3g t a 1 0 03 mm a 1 sle sea level equivalent the ice sheet in west antarctica wa is losing mass 47 4g t a 1 and the ice sheet in east antarctica ea shows a small mass gain 16 11 gt a 1 for a combined net change of 31 12 gt a 1 0 08 mm a 1 sle the contribution of the three ice sheets to sea level is 0 05 0 03 mm a 1 t he antarctic ice shelves show corresponding mass changes of 95 11 gt a 1 in wa and 142 10 gt a 1 in ea thinning at the margins of the greenland ice sheet and growth at higher elevations is an expected response to increasing temperatures and precipitation in a warming climate the marked thinnings in the pine island and thwaites glacier basins of wa and the totten glacier basin in ea are probably ice dynamic responses to long term climate change and perhaps past removal of their adjacent ice shelves the ice growth in the southern antarctic peninsula and parts of ea may be due to increasing precipitation during the last century

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

basal melt at northgrip modeled from borehole ice core and radio echo sounder observations from temperature measurements down through the 3001 m deep borehole at the north greenland icecore project northgrip drill site it is now clear that the ice at the base 3080 m below the surface is at the pressure melting point this is supported by the measurements on the ice core where the annual layer thicknesses show there is bottom melting at the site and upstream from the borehole surface velocity measurements internal radio echo layers borehole and ice core data are used to constrain a time dependent flow model simulating flow along the north northwest trending ice ridge flow line leading to the northgrip site also time dependent melt rates along the flowline are calculated with a heat flow model the results show the geothermal heat flow varies from 50 to 200 mw m 2 along the 100km section of the modeled flowline the melt rate at the northgrip site is 0 75 cm a 1 but the deep ice in the northgrip core originated 50 km upstream and has experienced melt rates as high as 1 1 cm a 1

melting at the base of the greenland ice sheet explained by iceland hotspot history basal melting is widespread in the north central greenland ice sheet geophysical data and numerical modelling suggest a geothermal anomaly in this region resulting from the earlier passage of greenland over the iceland mantle plume

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

natural long term annealing of the zircon fission track system in vienna basin deep borehole samples constraints upon the partial annealing zone and closure temperature abstract fission track ft analysis of zircon from cretaceous and tertiary sandstone samples in vienna basin boreholes has provided constraints for the thermal stability of the zircon ft system over a geological timescale confined track lengths and ages were measured for samples from depths of 1 5 7 5 km the deepest with a present environmental temperature of 200 c mean track lengths range from 10 3 to 10 8 m indistinguishable within error from the unannealed reference length of 10 7 0 1 m 1 standard error thus showing no sign of systematic downhole reduction central zircon ages are consistently older than stratigraphic ages of parent rocks with no single grain ages significantly younger than their respective stratigraphic ages such ft age and length evidence strongly suggests that the tracks have not been significantly annealed since sediment deposition because the present geothermal regime as well as sample burial depths have been near constant for at least the past 5 m y the lower temperature limit of the zircon ft partial annealing zone is 200 c for a heating duration of the order of 5 10 m y such evidence from long term natural annealing is compatible with a zircon ft partial annealing zone cf 200 350 c derived by the extrapolation of laboratory annealing results based on onfined track length measurements but cannot alone discriminate between different annealing models for the zircon ft closure temperature a perhaps over simplified concept these results are consistent with the oft quoted temperature of 250 c for cooling rates of 10 100 c m y

a mesozoic time scale we present an integrated geomagnetic polarity and stratigraphic time scale for the triassic jurassic and cretaceous periods of the mesozoic era with age estimates and uncertainty limits for stage boundaries the time scale uses a suite of 324 radiomenc dates including high resolution 40 ar 39 ar age estimates this framework involves the observed ties between 1 radiometric dates biozones and stage boundaries and 2 between biozones and magnetic reversals on the seafloor and in sediments interpolation techniques include maximum likelihood estimation smoothing cubic spline fitting and magnetochronology

bedrock displacements in greenland manifest ice mass variations climate cycles and climate change the greenland gps network gnet uses the global positioning system gps to measure the displacement of bedrock exposed near the margins of the greenland ice sheet the entire network is uplifting in response to past and present day changes in ice mass crustal displacement is largely accounted for by an annual oscillation superimposed on a sustained trend the oscillation is driven by earth s elastic response to seasonal variations in ice mass and air mass i e atmospheric pressure observed vertical velocities are higher and often much higher than predicted rates of postglacial rebound pgr implying that uplift is usually dominated by the solid earth s instantaneous elastic response to contemporary losses in ice mass rather than pgr superimposed on longer term trends an anomalous pulse of uplift accumulated at many gnet stations during an approximate six month period in 2010 this anomalous uplift is spatially correlated with the 2010 melting day anomaly

uplift across long valley caldera california the results of levelings along u s highway 395 between lee vining and toms place california in 1957 1975 1980 1982 and 1983 define the development of a dome shaped uplift across the long valley caldera these levelings indicate that toms place remained virtually invariant with respect to lee vining during the full interval 1957 1983 implying that the end points of the survey route lie beyond the range of the developing dome no significant uplift occurred before 1975 but by october 1980 the uplift near casa diablo hot springs reached 0 25 m and the half width of the dome was of the order of 25 km the uplift of casa diablo hot springs increased to 0 35 m by august 1982 and to about 0 40 m by august 1983 without any appreciable increase in the lateral extent of the dome the august 1982 to august 1983 uplift apparently occurred before february 1983 with little or no uplift during the period february august 1983 the 1975 1983 uplift is attributed to the injection of 0 19 km3 of magma into a spherical chamber at a depth of 10 km beneath the southern quadrant of the ancient resurgent dome within the caldera examination of the full vertical control record through the long valley area indicates that the 1975 1983 uplift is unique within the period 1905 1983 although comparisons of the results of a 1932 leveling against a 1914 datum disclose a 1914 1932 down to the northwest tilt of about 10 rad over the reach between toms place and lee vining this tilt if real is more reasonably attributed to regional tectonic deformation than it is to the movement of magma at depth

deformation warming and softening of greenland s ice by refreezing meltwater when basal meltwater refreezes the resulting warm ice can influence the flow dynamics of the ice sheet above an analysis of airborne gravity and radar data identifies extensive basal ice units across the northern greenland ice sheet that coincide with areas of deformed ice and fast ice flow

tracking crustal processes by ft thermochronology in a forearc high hikurangi margin new zealand involving cretaceous subduction termination and mid cenozoic subduction initiation abstract raukumara peninsula is a forearc high on the pacific margin of new zealand its basement comprises two sedimentary terranes that formed in subduction prisms during the late jurassic mid cretaceous marking the end of subduction along the pacific margin of eastern gondwanaland the cover includes allochthonous late cretaceous oligocene passive margin slope to basin facies emplaced into the forearc during the early miocene initiation of the current subduction regime as well as autochthonous neogene sediments apatite and zircon fission track ft data are reported and interpreted for the basement and cover sediments the detrital zircon ft ages constrain the maximum depositional ages of the low grade zeolite and pumpellyite facies basement pahau terrane is no older than 152 13 ma this zircon ft mode and older ones 198 8 ma 232 58 ma recording cooling denudation in the source areas probably including rakaia terrane waioeka terrane located oceanward of pahau terrane is no older than 125 2 ma being the age of volcanic derived zircons and supports early cretaceous dinoflagellate ages reported previously omaio petrofacies comprises the youngest part of the waioeka terrane and has a zircon ft age of 108 6 3 ma this indicates that basement sequences accumulated in the northeast contemporaneously with cover sequences koranga fm in the southwestern part of the peninsula these zircon ft ages together with the results of thermal history modelling of certain waioeka terrane samples are consistent with migration of a thrust system in a subduction prism environment during the late jurassic cretaceous until about 85 ma as proposed earlier when mesozoic subduction terminated apatite ft data indicate for all basement samples a phase of neogene heating and cooling associated with basin formation sediment accumulation and subsequent uplift and erosion resulting in almost complete removal of the neogene stratigraphic record over western parts of the peninsula forward modelling of the data imply rapid earliest miocene downwarping of the crust in bay of plenty coinciding with initiation of subduction of pacific plate followed by emplacement of a 1 5 2 0 km thick wedge of east coast allochthon from the northeast early miocene sediments accumulated in a foredeep along the front sw margin of the allochthon probably sourced from a block of pahau basement west of whakatane fault which was exhumed and denuded by 4 km contemporaneously during the late early to middle miocene the basin depocentre migrated further to the southwest while areas previously downwarped northeast were uplifted and eroded the depocentre migration and subsequent inversion is a pattern that affected most of north island and is related to mechanical or dynamical interaction of the two plates as the slab of pacific oceanic lithosphere was emplaced beneath north island this may be a general feature of young subduction zones

thermochronology of the torlesse accretionary complex wellington region new zealand the torlesse complex comprises several mesozoic accretionary prism complexes together forming continental basement over large parts of new zealand this study focuses on the thermal history of relatively low grade graywacke rocks exposed in a transect in southern north island that crosses the structural grain of the torlesse complex including its older and younger parts zircon fission track ft ages for the late triassic rakaia terrane which is the most inboard of the accretionary complexes are partially annealed some possibly reset and may indicate early cretaceous 134 10 ma cooling from maximum temperatures tmax probably related to imbrication of younger complexes of the pahau terrane numerical modeling of the zircon ft ages and published 40ara 39ar muscovite and biotite ages for the rakaia terrane suggest tmax values of 265 310 c and exhumation from depths of 10 12 km the rocks underlying the aorangi range and involving the youngest accretionary complex have experienced much lower tmax values of 210 and 110 c bracketed by reset apatite ft ages and detrital zircon ft ages the occurrence of a circa 100 ma component of zircon ft ages in both the weakly and highly indurated rocks beneath the aorangi range as well as in remnants of an overlying albian accretionary slope basin whatarangi formation imply multistorey accretion and incorporation of sediment into the youngest prism this circa 100 ma zircon ft age component also places a maximum age on the termination of mesozoic subduction beneath the new zealand region the occurrence of reset apatite ft ages across the whole of the wellington transect indicates that at least 4 km of exhumation occurred during the late miocene

high geothermal heat flow basal melt and the origin of rapid ice flow in central greenland age depth relations from internal layering reveal a large region of rapid basal melting in greenland melt is localized at the onset of rapid ice flow in the large ice stream that drains north off the summit dome and other areas in the northeast quadrant of the ice sheet locally high melt rates indicate geothermal fluxes 15 to 30 times continental background the southern limit of melt coincides with magnetic anomalies and topography that suggest a volcanic origin

seismic noise interferometry reveals transverse drainage configuration beneath the surging bering glacier subglacial drainage systems are known to critically control ice flows but their spatial configuration and temporal evolution are poorly constrained due to inaccessibility here we report a 12 year long monitoring of the drainage underneath bering glacier alaska by correlating ambient noise recorded at two seismic stations on the sides of the glacier we find that the seismic surface waves traveling across bering glacier slowed down by 1 2 during its latest 2008 2011 surge likely due to the switch of the subglacial drainage from a channelized system to a distributed system in contrast to current models the relative amplitude of velocity reductions for rayleigh and love waves requires the distributed drainage to be highly anisotropic and aligned perpendicular to the ice flow direction we infer that the subglacial water flow is mainly through a network of transverse basal crevasses during surges and thus can sustain the high water pressure and ice flow speed

rb sr resetting ages and chemical characterization of turbidites in an accretionary wedge torlesse complex otaki gorge new zealand whole rock geochemical and rb sr isotopic analyses have been undertaken on turbidites from three discrete localities each about 2 km apart across strike within the torlesse complex a permian cretaceous accretionary wedge in new zealand overall the three suites show similar petrographic and geochemical compositions to turbidites from elsewhere in the torlesse complex but between the suites there are detectable differences for most major and trace elements particularly sr mgo and na 2 o the individual suites define three parallel rb sr whole rock isochrons with identical dates of about 205 ma the presence of monotis bivalves provides a depositional age of norian 219 225 ma hence the isochrons suggest that the rb sr clock was reset some 15 20 m y after deposition during low grade metamorphism associated with accretion and deformation of the sediment pile there is a wide variation in the initial 87 sr 86 sr ratios from 0 70683 to 0 70955 which is best explained by changes in the composition of the detritus being provided from the source area as detected by the chemical differences sea water is not considered to have played a significant role in contributing to the initial ratios the failure of some samples collected away from the main sample localities to plot on their respective isochrons suggests that domains of sr isotopic equilibration are small in the order of a few cubic meters as a result of this study we have extended the rb sr whole rock dating method of sediments now widely applied to shales and cherts to the more complex turbidite sequences from accretionary wedges and have shown that meaningful dates can be obtained this should provide an invaluable method of dating these sparsely fossiliferous terranes

a new high resolution digital elevation model of greenland fully validated with airborne laser altimeter data a new digital elevation model of the greenland ice sheet and surrounding rock outcrops has been produced at 1 km postings from a comprehensive suite of satellite remote sensing and cartographic data sets height data over the ice sheet were mainly from ers 1 and geosat radar altimetry these data were corrected for a slope dependent bias that had been identified in a previous study the radar altimetry was supplemented with stereophotogrammetric data sets synthetic aperture radar interferometry and digitized cartographic maps over regions of bare rock and where gaps in the satellite altimeter coverage existed the data were interpolated onto a regular grid with a spacing of 1 km the accuracy of the resultant digital elevation model over the ice sheet was assessed using independent and spatially extensive measurements from an airborne laser altimeter that had an accuracy of between 10 and 12 cm in a comparison with the laser altimetry the digital elevation model was found to have a slope dependent accuracy ranging from 1 04 1 98 m to 0 06 14 33 m over the ice sheet for a slope range of 0 0 1 0 the mean accuracy over the whole ice sheet was 0 33 6 97 m over the bare rock areas the accuracy ranged from 20 to 200 m dependent on the data source available the new digital elevation model was used as an input data set for a positive degree day model of ablation the new elevation model was found to reduce ablation by only 2 compared with using an older 2 5 km resolution model which suggests that resolution induced errors in estimating ablation are no longer important

provenance of the detrital component of deep sea sediments from the sw pacific ocean based on mineralogy geochemistry and sr isotopic composition abstract clay mineralogy and chemical and strontium isotope compositions have been used to determine the detrital components of deep sea sediments from the sw pacific ocean continental detritus derived mainly from the new zealand landmass is characterised by high illite and chlorite contents and 87 sr 86 sr ratios close to 0 7110 this material eroded from the eastern margin of both islands is transported into deeper water by turbidity currents and hemipelagic processes and is carried northwards by the strong western boundary current as far north as the samoan basin due to the great distance from source and unfavourable prevailing winds the contribution of aeolian dust from the australian deserts to the sediment appears to be relatively small particularly in the northernmost part of the region in the vicinity of the oceanic volcanic islands of tonga samoa and the cook islands volcaniclastic material including heavy minerals pyroxene and magnetite pumice glass shards proximally and smectite clays distally is dispersed into the sediments by turbidity currents and airfall in areas of very low sedimentation distant from landmasses the sediments contain significant amounts of authigenic material rsos characterised by high concentrations of transition metals and rare earth elements strontium isotopes together with trace element compositions have proved particularly useful in determining the relative proportions of the detrital types the contrasting 87 sr 86 sr ratios and sr contents of the various source rocks permit the use of binary mixing relationships whch indicate that sediments less than 35 km from the cook islands contain 80 volcanic detritus and those more than 1200 km away contain up to 20 volcanic detritus

a synthesis of the basal thermal state of the greenland ice sheet the basal thermal state of an ice sheet frozen or thawed is an important control upon its evolution dynamics and response to external forcings however this state can only be observed directly within sparse boreholes or inferred conclusively from the presence of subglacial lakes here we synthesize spatially extensive inferences of the basal thermal state of the greenland ice sheet to better constrain this state existing inferences include outputs from the eight thermomechanical ice flow models included in the searise effort new remote sensing inferences of the basal thermal state are derived from holocene radiostratigraphy modern surface velocity and modis imagery both thermomechanical modeling and remote inferences generally agree that the northeast greenland ice stream and large portions of the southwestern ice drainage systems are thawed at the bed whereas the bed beneath the central ice divides particularly their west facing slopes is frozen elsewhere there is poor agreement regarding the basal thermal state both models and remote inferences rarely represent the borehole observed basal thermal state accurately near northgrip and dye 3 this synthesis identifies a large portion of the greenland ice sheet about one third by area where additional observations would most improve knowledge of its overall basal thermal state

kar and rbsr age studies of the metamorphism and quartz vein au mineralisation on terawhiti hill near wellington new zealand abstract k ar and rb sr ages have been determined for low grade torlesse terrane metagreywacke sequences wellington greywackes at terawhiti hill near wellington and the more schistose rocks in a narrow sheared zone containing aubearing quartz reefs a rb sr whole rock isochron age of 200 7 ma provides the best age estimate late triassic or earliest jurassic for regional metamorphism of the wellington greywackes and their initial 87 sr 86 sr ratio at this time 0 70690 0 00009 is characteristic of the extensive torlesse terrane elsewhere that is derived from a silicic continental source both k ar and rb sr ages indicate a local but intense shearing event at terawhiti hill at 125 130 ma early cretaceous after earlier metamorphism and uplift of the greywackes and possibly during imbrication of torlesse rocks on a regional scale formation of quartz veins and some deposition of au in schists and cataclastic rocks is possibly synchronous with this event but au is more importantly associated with isolated and rare later quartz reefs formed at 100 110 ma from sr isotope evidence the earlier quartz veins have a local in situ origin but the younger veins have an extraneous possibly deeper source

duplex arrays and thickening of accretionary prisms an example from boso peninsula japan part of the emi group a miocene accretionary prism in the boso peninsula japan displays an extensive west trending duplex array the intense faulting there is divided into five stages the first stage involving layer parallel to subparallel faulting is primarily responsible for thickening and horizontal shortening of the strata this stage thickened the sequence by a factor of 3 5 duplex formation is here interpreted to be essential to thicken trench turbidites at a relatively early stage of deformation just after sedimentation even in shallow levels of accretionary prisms the east to west vergence of duplex formation might be attributed to the unique tectonics around the boso trench trench trench type triple junction

paleofluvial landscape inheritance for jakobshavn isbrae catchment greenland subglacial topography exerts strong controls on glacier dynamics influencing the orientation and velocity of ice flow as well as modulating the distribution of basal waters and sediment bed geometry can also provide a long term record of geomorphic processes allowing insight into landscape evolution the origin of which may predate ice sheet inception here we present evidence from ice penetrating radar data for a large dendritic drainage network radiating inland from jakobshavn isbrae greenland s largest outlet glacier the size of the drainage basin is 450 000 km2 and accounts for about 20 of the total land area of greenland topographic and basin morphometric analyses of an isostatically uplifted ice free bedrock topography suggests that this catchment predates ice sheet initiation and has likely been instrumental in controlling the location and form of the jakobshavn ice stream and ice flow from the deep interior to the margin now and over several glacial cycles

limestone and chert in tectonic blocks from the esk head subterrane south island new zealand the esk head subterrane is a continuous belt generally 10 20 km wide of tectonic melange and broken formation on the south island of new zealand this subterrane separates older and younger parts of the torlesse terrane which is an extensive accretionary prism composed mostly of quartzo feldspathic submarine fan deposits ranging from permian to early cretaceous in age the torlesse is the most pacific ward of several permian and mesozoic accreted terranes in new zealand that record tectonic amalgamation and ultimate accretion against the pacific facing gondwana margin the esk head subterrane of the torlesse is especially informative because it includes within it conspicuous tectonic blocks of submarine basalt and a variety of basalt associated seamount and sea floor limestones and cherty rocks thought to be representative of the subducted plate limestones in tectonic blocks are of late triassic and probably jurassic ages and include 1 submarine cemented pelagic bivalve geopetal packstone grainstone 2 brachiopod bryozoan encrinite and 3 radiolarian pelagic lime mudstone most of the triassic blocks have been dated using conodonts which have remarkably low color alteration index cai values paleogeographic inferences drawn from megafossils bioclasts and radiolarians as well as from carbonate cements indicate deposition of the oceanic sedimentary rocks at paleolatitudes somewhat lower than that of the new zealand part of the gondwana margin but higher than paleoequatorial latitudes these oceanic sediments and their basaltic substrates were evidently emplaced in the torlesse accretionary prism following off scraping from an extensive subducting oceanic plate probably the phoenix plate which was obliquely convergent with the northwest trending gondwana margin during late jurassic and or early cretaceous time

resolution of the age structure of the detrital zircon populations of two lower cretaceous sandstones from the weald of england by fission track dating modes in the frequency of distribution of fission track ages obtained from detrital zircon grains may prove characteristic of individual sandstone bodies supporting the identification of the sources from which a particular flow of sedimentary detritus was derived and thus allowing new inferences to be made concerning palaeogeography a computer program has been written and used to identify modes in the zircon fission track age distribution within two lower cretaceous sandstone samples from the weald of southern england pronounced modes appear in one rock around 119 ma 160 ma 243 ma and 309 ma and in the other around 141 ma 175 ma 257 to 277 ma and 394 to 453 ma the geological implications of these quite dissimilar zircon age spectra are discussed it is concluded that they support the palaeogeographical models of allen 1981 and indicate that the provenance of the first sample from the top ashdown sandstone member at dallington in east sussex was almost entirely southerly while that of the second from the netherside sand member at northchapel in west sussex was more varied but predominantly westerly and northerly

assessment of resolution and accuracy of the moving window cross spectral technique for monitoring crustal temporal variations using ambient seismic noise summary temporal variations in the elastic behaviour of the earth s crust can be monitored through the analysis of the earth s seismic response and its evolution with time this kind of analysis is particularly interesting when combined with the reconstruction of seismic green s functions from the cross correlation of ambient seismic noise which circumvents the limitations imposed by a dependence on the occurrence of seismic events in fact because seismic noise is recorded continuously and does not depend on earthquake sources these cross correlation functions can be considered analogously to records from continuously repeating doublet sources placed at each station and can be used to extract observations of variations in seismic velocities these variations however are typically very small of the order of 0 1 per cent such accuracy can be only achieved through the analysis of the full reconstructed waveforms including later scattered arrivals we focus on the method known as moving window cross spectral analysis that has the advantage of operating in the frequency domain where the bandwidth of coherent signal in the correlation function can be clearly defined we investigate the sensitivity of this method by applying it to microseismic noise cross correlations which have been perturbed by small synthetic velocity variations and which have been randomly contaminated we propose threshold signal to noise ratios above which these perturbations can be reliably observed such values are a proxy for cross correlation convergence and so can be used as a guideline when determining the length of microseismic noise records that are required before they can be used for monitoring with the moving window cross spectral technique

modelling the effect of arbitrary p t t histories on argon diffusion in minerals using the macargon program for the apple macintosh argon diffusion in mineral grains has been numerically modelled using p t t histories that may be relevant to multiply metamorphosed orogenic terranes and for rocks that have resided at high ambient temperatures in the earth s crust for long durations the macargon program1 generates argon concentration profiles in minerals assuming argon loss occurs via volume diffusion it can be run on an apple macintosh computer with arbitrary p t t histories used as input finite difference equations are used in the calculation of 40ar concentration profiles across individual diffusion domains the associated macspectrometer generates model spectra after a p t t history has been specified the form of model 40ar39ar apparent age spectra suggests that considerable caution needs to be exercised in the use of the closure temperature concept and in the interpretation of the significance of plateaux observed in many 40ar39ar apparent age spectra particularly in cases involving metamorphic rocks where complex p t t histories might apply although modelled spectra cannot be directly compared to experimentally determined 40ar39ar age spectra especially when hydrous phases are involved or in cases where loss of argon has not occurred via volume diffusion they do provide insight into theoretically expected age spectra for samples that have experienced complex p t t histories

seasonality and increasing frequency of greenland glacial earthquakes some glaciers and ice streams periodically lurch forward with sufficient force to generate emissions of elastic waves that are recorded on seismometers worldwide such glacial earthquakes on greenland show a strong seasonality as well as a doubling of their rate of occurrence over the past 5 years these temporal patterns suggest a link to the hydrological cycle and are indicative of a dynamic glacial response to changing climate conditions

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data

mapping basal melt under the northern greenland ice sheet ice sheets in greenland and antarctica are based on continental rock and are coupled strongly to changes in global sea level their beds may be frozen or thawed but it has not been known how much or where basal melt occurs except in special cases where a borehole has reached the bed or where airborne radar has revealed subglacial lakes and reflective ice stream beds in antarctica we have used a previously published technique to detect subglacial melt water in the general case and have here applied it to radar sounder data collected over northern and central greenland we have found extensive subglacial water along between 13 and 20 of the flight paths this paper provides maps of the measured locations and probable extent of subglacial water

changes in greenland ice bed conditions inferred from seismology abstract basal conditions of the greenland ice sheet gris are a key research topic in climate change studies the recent construction of a seismic network has provided a new opportunity for direct real time and continuous monitoring of the gris here we use ambient noise surface wave data from seismic stations all over greenland for a 4 5 year period to detect changes in rayleigh wave phase velocity between seismic station pairs we observe clear seasonal and long term velocity changes for many pairs and propose a plausible mechanism for these changes dominant factors driving the velocity changes might be seasonal and long term pressurization depressurization of the gris and shallow bedrock by air and ice mass loading unloading however heterogeneity of the gris basal conditions might impose strong regionalities on the results an interesting feature is that even at adjacent two station pairs in the inland gris one pair shows velocity decrease while another shows velocity increase as a response to the high air and snow pressure the former pair might be located on a thawed bed that decreases velocity by increased meltwater due to pressure melting whereas the latter pair might be located on a frozen bed that increases velocity by compaction of ice and shallow bedrock the results suggest that surface waves are very sensitive to the gris basal conditions and further observations will contribute to a more direct and quantitative estimation of water balance in the arctic region