archean gold mineralization in the wabigoon subprovince a product of crustal accretion evidence from u pb geochronology in the lake of the woods area superior province canada within the lake of the woods greenstone terrain in the wabigoon subprovince of northwest ontario gold is in faults shears and tension veins that developed in response to a late archean northwest directed contraction and emplacement of contemporaneous plutons nine rocks in this area have been dated using u pb analyses of zircon in order to obtain precise time constraints on gold mineralization and to compare its timing with the age of major crustal events in the region a mineralized dike at the duport mine shoal lake is 2716 pm 2 ma old whereas a later dike that cuts mineralized rocks has an age of 2709 pm 2 ma gold mineralization is therefore distinctly younger than calc alkaline and tholeiitic rocks dated at 2724 pm 2 ma in the shoal lake area and 2727 pm 2 ma in the high lake area to the north hydrothermal activity associated with mineralization at the duport mine overprints the amphibolite facies contact metamorphic aureole of the snowshoe bay batholith 2708 pm 7 ma

u pb zircon ages from the eastern savant lake crow lake metavolcanic metasedimentary belt northwest ontario five rocks from three areas in the eastern part of the savant lake crow lake metavolcanic metasedimentary belt have been dated by u pb analysis of zircons the sioux lookout area is composed of a sequence of generally fault bounded metavolcanic and metasedirnentary belts the age of a felsic tuff in the central volcanic belt is 2732 72 ma this is possibly the youngest sequence in the area the savant lake volcanic belt comprises the jutten volcanic unit at its base separated by an angular unconforrnity from the handy lake volcanic sequence the age of a dacitic tuff near the base of the handy lake volcanic sequence is 2745 22 i ma the south sturgeon lake volcanic belt is composed of four volcanic cycles the age of a felsic tuff from the top of the uppermost cycle is 2717 92 ma the felsic beidelman bay pluton and the mafic pike lake pluton which both intruded the lower art of the sequence give ages of 2733 82 and 2732 721 a respectively this establishes a minimum time span of 15 921 ma for deposition of the sequence this interval along with the 27 ma span between the ages of the handy lake sample and the volcanic sample from the south sturgeon lake area suggests that the sequences were laid down by a series of discrete volcanic episodes for samples subjected to multistage lead loss the reliability of ages has been greatly enhanced by air abrasion of zircons several cases of suspected biasing of analyses by the air abrasion process have been encountered it appears that this biasing problem can be overcome by selection and abrasion of low uranium grains that are free of imperfections

highly variable coastal deformation in the 2016 mw7 8 kaikōura earthquake reflects rupture complexity along a transpressional plate boundary abstract coseismic coastal deformation is often used to understand slip on offshore faults in large earthquakes but in the 2016 m w 7 8 kaik ura earthquake multiple faults ruptured across and sub parallel to the coastline along 110 km of coastline a rich dataset of coastal deformation comprising airborne lidar differencing field surveying and satellite geodesy reveals highly variable vertical displacements ranging from 2 5 to 6 5 m these inform a refined slip model for the kaik ura earthquake which incorporates changes to the slip on offshore faults and inclusion of an offshore reverse crustal fault that accounts for broad low amplitude uplift centered on kaik ura peninsula the exceptional detail afforded by differential lidar and the high variability in coastal deformation combine to form the highest resolution and most complex record of coseismic coastal deformation yet documented this should prompt reassessment of coastal paleoseismic records that may not have considered multi fault ruptures and high complexity deformation fields

basement terrane correlations and crustal recycling in the western superior province nd isotopic character of granitoid and felsic volcanic rocks in the wabigoon subprovince n ontario canada abstract the western superior province represents a collage of mesoarchean continental 3 2 2 8 ga and neoarchean continental arc and oceanic 2 8 2 66 ga crustal fragments nd isotope data presented here for 89 felsic volcanic and plutonic rocks have been combined with compiled data to generate a data set of over 240 analyses from the wabigoon and winnipeg river subprovinces these samples from both oceanic and continental environments have been used as crustal probes their nd isotopic character used to investigate the extent of basement terranes the ancestry of crustal fragments their interaction with each other and the degree of sialic crustal reworking the wabigoon and winnipeg river subprovinces include three isotopically distinct terranes 1 the winnipeg river terrane comprises the winnipeg river subprovince the north central wabigoon and the north eastern wabigoon subprovince this region is dominated by neoarchean granitoid rocks with mesoarchean vestiges of previous workers have suggested that the boundary between the western wabigoon and winnipeg river terranes represents a cryptic suture resulting from a collision at circa 2 71 ga the boundary between the western wabigoon and marmion terranes although obscured by late intrusions may be a continuation of this suture zone the boundary between the winnipeg river and marmion terranes in the central wabigoon is also cryptic isotopic data suggest that the marmion terrane is allochthonous with respect to the winnipeg river terrane common magmatism in these two terranes at 2 93 2 87 ga suggests that they may have collided during this time in the eastern wabigoon subprovince this collision zone is speculated to occur at the humboldt bay high strain zone a complex history of crustal recycling throughout the mesoarchean and neoarchean is revealed which demonstrates the importance of autochthonous development of granite greenstone terranes in a continental environment the data also support models of tectonic accretion during the archean indicated by the presence of granite greenstone terranes of allochthonous origin

quantitative analysis of abyssal hills in the atlantic ocean a correlation between inferred crustal thickness and extensional faulting a recent cruise to the office of naval research atlantic natural laboratory obtained 100 hydrosweep bathymetrie coverage 200 hawaii mrl hmrl side scan coverage gravity and magnetics over an area spanning three ridge segments along axis 25 25 n to 27 10 n and crustal ages from 0 to 26 30 ma 400 km on the west flank of the mid atlantic ridge this data set represents a first opportunity for an extensive regional analysis of abyssal hill morphology created at a slow spreading ridge the primary purpose of this work is to investigate the relationship between abyssal hill morphology and the properties of the ridge crest at which they were formed we apply the method of goff and jordan 1988 for the estimation of two dimensional statistical properties of abyssal hill morphology from the gridded hydrosweep bathymetry important abyssal hill parameters derived from this analysis include root mean square rms height characteristic width and plan view aspect ratio the analysis is partitioned into two substudies 1 analysis of near axis 7 ma abyssal hills for each of the three segments and 2 analysis of temporal variations 2 29 ma in abyssal hill morphology along the run of the south segment the results of this analysis are compared and correlated with analysis of the gravity data and preliminary determination of faulting characteristics based on hmrl side scan data principal results of this study are 1 abyssal hill morphology within the study region is strongly influenced by the inside outside corner geometry of the mid ocean ridge segments abyssal hills originating at inside corners have larger rms height and characteristic width and smaller plan view aspect ratio than those originating at outside corners 2 the residual mantle bouguer gravity anomaly is positively correlated with intersegment and along flow line variations in rms height and characteristic width and it is negatively correlated with plan view aspect ratio from this result we infer that lower relief narrower and more elongated abyssal hills are produced when the crust being generated is thicker 3 intersegment variations in near axis rms height negatively correlate with average fault density as determined from analysis of hmrl side scan imagery

magnetic felsic intrusions associated with canadian archean gold deposits felsic intrusions spatially and temporally associated with archean au deposits in the superior province of the canadian shield are magnetic due to high magnetite content in comparison to felsic igneous rocks in most of the archean terrain examples are found in au camps of hemlo red lake harker holloway mishibishu lake wawa missanabie geraldton matachewan and bouquet east cadillac these archean intrusions are comparable with phanerozoic magnetite series plutons accompanying metallic mineralization and magnetiterich intrusions hosting au rich porphyry deposits the evidence shows a distinct tectonic setting for the gold mineralization involving the generation of the particular magmas the association of the two indicates either the derivation of the ore constituents from the intrusions or the emplacement of the magmas along dilation zones which also provided fluid flow from depth the identification of magnetite rich felsic intrusions may aid in targeting favorable exploration areas for archean au deposits

late archean mantle composition and crustal growth in the western superior province of canada neodymium and lead isotopic evidence from the wawa quetico and wabigoon subprovinces abstract neodymium and lead isotopes are presented for late archean rocks from the wawa quetico and wabigoon subprovinces sp in the western superior province ontario canada the isotopic compositions were determined on greenstone volcanic sequences pre tectonic 2 73 2 69 ga trondhjemite tonalite granodiorite ttg suites metasedimentary rocks and post tectonic 2 69 2 67 ga dioritic to granitic plutons in order to characterize the mantle and crustal reservoirs involved in the evolution of the southern part of the western superior province although derived from a depleted mantle almost all the greenstone volcanism and pre tectonic ttg suites record contamination by crustal material as old as 3 2 ga neodymium and lead isotopic compositions of the pre tectonic ttg can be modeled as products of the melting of amphibolitic crust e g subducted basalts contaminated by 1 10 of subducted sediments moreover lead isotopes of ttg suites provide evidence that the isotopic compositions of these subducted sediments varied as a result of the addition of new ca 2 7 ga juvenile material in agreement with neodymium isotopic differences recorded by sedimentary units of the quetico sp 50 50 mix of young old crusts and wawa sp 75 25 young old neodymium and lead isotopes of the post tectonic ree enriched archean sanukitoid suites define an isotopic trend which is distinct from that of the ttg suites and which is interpreted to reflect the importance of crustal assimilation in the evolution of these suites furthemore such plutons found in the wawa sp have more juvenile neodymium and lead isotopic compositions and higher nd contents than those intruded into the quetico and wabigoon sp which have more crustal isotopic signatures and lower nd concentrations this geographical difference could be due either to differences in nd contents of initial archean sanukitoid magmas lesser assimilation in the wawa sp or more probably because the wawa crust is on average more juvenile than the quetico and wabigoon crusts in agreement with the fact that the geographical difference mirrors that recorded by metasedimentary rocks deposited in quetico and wawa sp

shortening of an overriding plate and its implications for slip on a subduction thrust central hikurangi margin new zealand 1 at subduction plate boundaries strains accumulate within the overriding plate in response to motion of the down going plate to a first approximation margin normal interplate slip and shortening in the overriding plate sum to the total plate convergence therefore margin normal interplate slip can be estimated by measuring shortening in the overriding plate and total plate convergence here we quantify margin normal interplate slip by measuring shortening of the upper plate along a profile which extends up to 480 km across and approximately normal to the central hikurangi margin new zealand long term deformation is estimated for periods of millions of years using data from seismic reflection lines and cross sections while contemporary strain rates are derived from global positioning system gps geodetic velocities these data permit comparison of plate convergence rates determined by seafloor spreading data with the rates of contraction over short 7 years and long 2 5 and 5 myr periods of time on this part of the plate boundary total margin normal shortening in the overriding plate over the last 5 myr was 9 28 km and accounts for 6 19 of the total convergence 145 160 km at rates of 2 6 mm yr the remaining 80 or more of plate convergence has been accommodated by slip on the subduction thrust gps contraction along approximately the same profile indicates 14 16 mm yr of contemporary shortening across the terrestrial part of the upper plate which is approximately modeled by 80 interplate coupling on the subduction interface down to depths of 30 km the contrasting proportions of inferred interplate coupling for contemporary and geological data sets are consistent with stick slip behavior on the plate interface and with slip being principally achieved during intermittent large earthquakes the general shapes of short and long term shortening profiles are similar and suggest that the highest strains occur at or immediately east of the mohaka fault these strain profiles are consistent with a model where high strains in the upper plate are concentrated near the down dip end of the contemporary locked zone on the plate interface this model requires that the down dip end of the interseismic locked zone has on average been approximately stable over a period of at least 2 5 5 myr

quantifying the distribution and transport of pelagic sediments on young abyssal hills the post depositional transport of pelagic sediments on rough seafloor is approximated as a nonlinear diffusive process the topographic slope distribution of the sediment water interface depends primarily on the apparent sediment diffusivity the average sediment load l and the root mean square height of the abyssal hill basement h these parameters have been determined for the arsrp corridor on the west flank of the mid atlantic ridge by fitting theoretical models to the slope distribution observed from center beam hydrosweep data the average value of the apparent diffusivity is h varies between 188 and 285 m with a mean of 230 7 m l is estimated to be as thin as 10 m on 5 ma crust near the ridge crest thickening to values greater than 50 m at 10 15 ma and then decreasing to less than 30 m on 25 ma crust in the western portion of the corridor the decrease in sediment load with age may be associated with a shallower carbonate compensation depth prior to the late miocene

new insights into archean crustal development from geochronology in the rainy lake area superior province canada precise isotopic analyses of zircon titanite and rutile from units in the rainy lake area of northwest ontario are combined with structural investigations to develop new stratigraphic interpretations in which lithotectonic sequences were juxtaposed by thrusting prior to steepening by wrenching ages for the oldest volcanic and plutonic rocks in the area range from 2725 pm 2 ma to 2728 4 3 ma the age of metagray wackes of the coutchiching group is bracketed between 2704 pm 3 ma and 2692 pm 2 ma by detrital zircon and a crosscutting intrusion alluvial conglomerate of the seine group is bracketed between 2696 5 3 ma the age of a clast and 2686 2 1 ma the age of the undeformed ottertail lake pluton the coutchiching group is younger than structurally overlying metavolcanic rocks and is therefore allochthon ous these data suggest that sedimentation and deformation were controlled by collisional plate interactions and subsequent transpression at the subprovince boundary combined with dat

u pb zircon geochronology of the yellowknife volcanic belt nwt canada new constraints on the timing and duration of greenstone belt magmatism volcanic and sedimentary rocks in the slave province collectively termed the yellowknife supergroup have long been considered to represent laterally continuous and correlative stratigraphically coherent homoclinal sequences correlation based on the lithologic analysis of certain distinctive units has been most intensely applied to the yellowknife volcanic belt in the southern slave province u pb zircon data for seven samples collected from within the belt are reported here the distinctiveness of the townsite formation a term applied to three lenticles of rhyodacitic to dacitic tuffs breccias and pillowed flows in comparison to the overlying and underlying tholeiitic basalts kam group has led to its use as a key marker unit for stratigraphic correlations and palinspastic restorations of offsets on proterozoic faults in the area a sample from each of the three segments was collected for u pb zircon geochronology in addition numerous thinner tuffaceous beds from the kam group were also dated

a review of the superior province of the canadian shield a product of archean accretion abstract the superior province consists of northern and southern high grade gneiss subprovinces and a central region of alternating granite greenstone and metasedimentary belts subprovinces are commonly fault bounded and display contrasting lithological assemblages metamorphic and structural styles geophysical characteristics and ages they are comparable to phanerozoic suspect terranes the middle and late archean rocks of the superior province are of mantle and juvenile crustal origin with little evidence of inheritance of components older than ca 3 1 ga high grade gneiss subprovinces are mainly deeper level equivalents of the supracrustal rich belts but one minnesota river valley is part of an older ca 3 6 ga terrane that was juxtaposed late in the tectonic history granite greenstone terranes are characterized by low grade volcano sedimentary sequences tholeiitic komatiitic submarine lava plain tholeiitic calc alkalic submarine to subaerial central complexes early platform type quartz arenite stromatolitic carbonate late timiskaming type shoshonitic alkalic volcanic fluvial sediment that range in age from ca 3 0 ga to 2 7 ga the volcanics represent oceanic island arc and continental arc volcanism the quartz arenite carbonate sequences deposition on relatively stable early formed ca 3 0 ga crust and the timiskaming type sequences deposition in pull apart basins developed along strike slip faults late archean ca 2 75 2 70 ga greenstone sequences occur throughout the superior province middle archean ca 3 0 2 8 ga sequences are common in northern and central superior province rare or absent in the south volcanism was accompanied by mafic to trondhjemitic plutonism the metasedimentary belts consist of variably metamorphosed volcanogenic turbidites with detrital zircons ranging in age from ca 3 0 ga to 2 7 ga the metasediments were deposited after major volcanism and probably represent accretionary prisms late archean orogenesis accompanied and followed by calc alkalic plutonism youngs southward from about 2 73 2 72 ga to 2 70 2 68 ga it involved large scale north south compression and dextral transpression and displays thin to thick skinned transitions the contemporaneity of events along the lengths of the belts and their southward younging coupled with the evidence of major compression are consistent with subduction driven oblique accretion of oceanic and continental volcanic arcs accretionary sedimentary wedges older microcontinental fragments etc in a convergent margin setting analogous to parts of the pacific rim differences eg abundance of komatiites and tonalitic plutonic suites are attributable to a hotter archean mantle

crustal evolution of archean rocks in the kakagi lake area wabigoon subprovince ontario as interpreted from high precision u pb geochronology the evolution of the archean volcanic plutonic complex in the kakagi lake area occurred during a time interval of ca 32 ma the earliest age is from analysis of zircon and baddeleyite in a gabbro intruding the lowermost katimiagamak volcanic group an age of 2723 2 1 8 ma on a tonalite gneiss from the interior of the underlying sabaskong batholith is indistinguishable from a previously dated massive border phase of the batholith and shows no evidence for inheritance from an older sialic component an early tonalite phase from the adjacent aulneau batholith is dated at and the latest granodiorite phase is dated at this defines a time span of about 7 ma for intrusion of the bulk of the batholith and indicates that previously dated felsic volcanism from the uppermost sequence above the kakagi lake volcanic group is coeval with late plutonic activity in the aulneau batholith the end of regional deformation in the area is given by the ages of two late tectonic intrusions the heronry lake pluton and

sedimentary and structural evidence for 2 7 ga continental arc oceanic arc collision in the savant sturgeon greenstone belt western superior province canada the western superior province sustained rapid crustal growth in the interval 2 72 2 68 ga through amalgamation of microcontinental crustal blocks and juvenile oceanic terranes recent field isotopic and geophysical surveys provide insight on the nature timing and scale of this accretionary growth however few places offer the rich tectono stratigraphic and structural detail with which to establish accretion of oceanic and continental blocks as does the savant sturgeon area here 3 4 2 8 ga continental crust of the winnipeg river terrane is juxtaposed with 2 775 2 718 ga juvenile oceanic rocks of the western wabigoon terrane across a 2 85 2 75 ga southwest facing continental margin sequence the continental margin was reactivated at 2 715 ga with the establishment of an arc recorded by 2 715 2 70 ga tonalite and associated intermediate volcanic rocks this magmatic activity is interpreted to reflect north and east dipping subduction that led to consumption of a small tract of oceanic crust betwe

fault slip distribution of the 2014 iquique chile earthquake estimated from ocean wide tsunami waveforms and gps data we applied a new method to compute tsunami green s functions for slip inversion of the 1 april 2014 iquique earthquake using both near field and far field tsunami waveforms inclusion of the effects of the elastic loading of seafloor compressibility of seawater and the geopotential variation in the computed green s functions reproduced the tsunami traveltime delay relative to long wave simulation and allowed us to use far field records in tsunami waveform inversion multiple time window inversion was applied to tsunami waveforms iteratively until the result resembles the stable moment rate function from teleseismic inversion we also used gps data for a joint inversion of tsunami waveforms and coseismic crustal deformation the major slip region with a size of 100 km 40 km is located downdip the epicenter at depth 28 km regardless of assumed rupture velocities the total seismic moment estimated from the slip distribution is 1 24 1021 n m mw 8 0

seamount statistics in the pacific ocean we apply the wide beam sampling technique of jordan et al 1983 to approximately 157 000 km of wide beam profiles to obtain seamount population statistics for eight regions in the eastern and southern pacific ocean population statistics derived from wide beam echograms are compared with seamount counts from sea beam swaths and with counts from bathymetric maps we find that the average number of seamounts with summit heights h h is well approximated by the exponential frequency size distribution h oe h the exponential model for seamount sizes characterized by the single scale parameter 1 is found to be superior to a power law self similar model which has no intrinsic scale in describing the average distribution of pacific seamounts and it appears to be valid over a size spectrum spanning 5 orders of magnitude in abundance large scale regional variations in seamount populations are documented we observe significant differences in seamount densities across the murray fracture zone in the north pacific and the eltanin fracture zone system in the south pacific the eltanin discontinuity is equally evident on both sides of the pacific antarctic ridge in the south pacific regions symmetrically disposed about the ridge axis have very similar seamount densities despite the large difference between pacific plate and antarctic plate absolute velocities evidently any differences in the shear flows at the base of the pacific and antarctic plates do not affect seamount emplacement systematic variations in o and are observed as a function of lithospheric age with the number of large seamounts increasing more rapidly than small seamounts these observations have been used to develop a simple model for seamount production under the assumptions that 1 an exponential size frequency distribution is maintained 2 production is steady state and 3 most small seamounts are formed on or near the ridge axis the limited data available from this study appear to be consistent with the model but they are insufficient to provide a rigorous test of the assumptions or determine accurately the model parameters however the data from the south pacific indicate that the off axis production of large seamounts probably accounts for the majority of seamounts with summit heights greater than 1000 m

two regions of seafloor deformation generated the tsunami for the 13 november 2016 kaikoura new zealand earthquake the 13 november 2016 kaikoura new zealand m w 7 8 earthquake ruptured multiple crustal faults in the transpressional marlborough and north canterbury tectonic domains of northeastern south island the hikurangi trench and underthrust pacific slab terminate in the region south of kaikoura as the subdution zone transitions to the alpine fault strike slip regime it is difficult to establish whether any coseismic slip occurred on the megathrust from on land observations the rupture generated a tsunami well recorded at tide gauges along the eastern coasts and in chatham islands including a 4 m crest to trough signal at kaikoura where coastal uplift was about 1 m and at multiple gauges in wellington harbor iterative modeling of teleseismic body waves and the regional water level recordings establishes that two regions of seafloor motion produced the tsunami including an m w 7 6 rupture on the megathrust below kaikoura and comparable size transpressional crustal faulting extending offshore near cook strait

geochronology of the belmont lake metavolcanic complex and implications for crustal development in the central metasedimentary belt grenville province ontario u pb analyses of zircon and titanite were carried out on eight rocks from the belmont lake metavolcanic complex a volcano sedimentary sequence in the central metasedimentary belt of the grenville province of southeastern ontario the ages of concordant supracrustal rocks within the complex do not accord with stratigraphic position the youngest volcanic age is from a rhyolite near the base of the sequence the oldest age is from a dacite in the middle this is overlain by a rhyolite in age a rhyolite at the top of the sequence appears to contain zircon inherited from a source about 1870 ma old the complex is therefore interpreted as comprising a lithotectonic sequence composed of structurally interleaved segments of contrasting age tectonic emplacement of these segments was most likely along previously unrecognized thrust faults the supracrustal rocks were subjected to at least two major deformational events as well as a late metamorphism the earliest event was probably associated with thrusting t

multiscale spectral analysis of bathymetry on the flank of the mid atlantic ridge modification of the seafloor by mass wasting and sedimentation the results of a multiscale spectral analysis of bathymetric data on the flank of the mid atlantic ridge are described data were collected during two cruises using hydrosweep multibeam tens of kilometers to 0 2 km scale range and mesotech scanning pencil beam sonar attached to remotely operated vehicle jason 1 km to 0 5 m scale range these data are augmented by visual data which enabled us to identify bathymetric profiles which are over unsedimented or thinly sedimented crust our analysis therefore is focused primarily on statistical characterization of basement morphology work is concentrated at two sites site b on 24 ma crust in an outside corner setting and site d on 3 ma crust in an inside corner setting at site b we find that an anisotropic band limited fractal model i e the von karman model proposed for abyssal hill morphology by goff and jordan 1988 is not sufficient to describe the full range of scales observed in this study our observations differ from this model in two ways 1 strike and cross strike dip spectral properties converge for wavelengths smaller than 300 m and 2 in both strike and dip directions the fractal dimension changes at 10 m wavelength from 1 27 at larger scales to 1 0 at smaller scales the convergence of strike and dip spectral properties appears to be associated with destruction of ridge parallel fault scarps by mass wasting which develops canyon like incisions that cross scarps at high angles the change in fractal dimension at 10 m scale appears to be related to a minimum spacing of significant slope breaks associated with scarps which are created by faulting and mass wasting at site d although there is no significant abyssal hill anisotropy the spectral properties at all scales are consistent with the von karman model the fractal dimension at this site 1 15 is less than at site b this difference may be reflect different morphology related to crustal formation at inside corner versus outside corner position or more likely differences in the degree of mass wasting the smoothing of seafloor morphology by sediments is evident in hydrosweep periodograms where relative to basement roughness spectral power decreases progressively with decreasing wavelength

long term denudation of ocean crust in the central north atlantic ocean near bottom sidescan bathymetric and visual observations of fault scarps in 4 24 ma sea floor show that basaltic ocean crust undergoes extensive denudation that creates wide complex scarp zones most denudation is caused by mass wasting probably accompanied by abrasion by disaggregated debris in 11 24 ma crust trellis drainage patterns are formed by deep cross scarp canyons and intersecting scarp parallel gullies that appear to follow weak zones of fracturing and intracrustal weathering until stabilized e g by sediment burial fault scarps will continue to degrade with time yielding increasingly distorted representations of apparent fault geometry in remotely sensed morphological data

neoarchean evolution of differing convergent margin assemblages in the wabigoon subprovince geochemical and geochronological evidence from the lake of the woods greenstone belt superior province northwestern ontario abstract the neoarchean lake of the woods greenstone belt is subdivided into three lithostratigraphic assemblages a lowermost mafic volcanic assemblage a compositionally diverse predominantly volcanic middle assemblage and a predominantly sedimentary uppermost assemblage the secular evolution and geodynamic settings of these assemblages are constrained with detailed geochronological and geochemical data the lower keewatin is the oldest assemblage with a zircon u pb age of 2738 2 0 ma it consists of mg and fe tholeiitic basalts mg number 30 65 with flat to slightly enriched rare earth elements ree la yb cn 0 9 1 6 elevated large ion lithophile elements lile and undepleted high field strength elements hfse the tholeiites do not appear to have exact modern analogs but do have some similarities to primitive arc tholeiites and back arc basin basalts suggesting an archean destructive margin setting the upper keewatin assemblage disconformably overlies the lower keewatin assemblage it consists of volcanic and sedimentary groups two geochemically distinct volcanic suites are recognized the dominant suite consists of compositionally diverse calc alkalins basalt to rhyolite felsic end members have yielded zircon u pb ages ranging from 2712 to 2723 ma the suite exhibits highly fractionated ree la yb cn 4 35 elevated lile and nb and ta depletion anomalies which are very similar to modern island arc volcanic rocks developed in proximity to continental margins a coeval suite of mafic to ultramafic volcanic rocks consists of mg tholeiite komatiitic basalt and ultramafic komatiite mg numbers 45 80 the suite exhibits depleted lree la yb cn 0 6 1 0 slightly elevated lile and undepleted to slightly enriched hfse suggesting that this geochemically primitive suite was produced by partial melting of a refractory mantle source perhaps as second stage melts of the same mantle source from which the lower keewatin assemblage basalts were previously derived the electrum assemblage unconformably overlies the upper keewatin assemblage in the northern part of the belt it consists of conglomerates sandstones and minor volcanic rocks having detrital ages indicating deposition after 2699 ma the volcanic rocks consists of andesite to rhyolite with shoshonitic to calc alkaline geochemical affinity as indicated by highly fractionated ree la yb cn 12 112 highly enriched lile and pronounced nb ta and ti depletion anomalies samples from the syenitic falcon island pluton appear to be coeval with electrum assemblage volcanics having an u pb isotopic age of 2694 ma and similar but even more alkaline chemistry consisting of highly fractionated lree and lile trace elements with very pronounced nb ta and ti depletion anomalies these late tectonic suites are geochemically similar to modern shoshonites with a continental influence formed in the late stages of a mature island arc or a continental arc setting

three dimensional topography of the sediment basement interface in the tokyo metropolitan area central japan abstract an extensive seismic refraction experiment was conducted in the tokyo metropolitan area central japan to reveal the three dimensional basin structure in this area sixty three explosions were fired over 14 years and more than 2000 travel times were picked for several phases for our inversion the basement is divided into two homogeneous regions where the sediment is assumed to be of uniform velocity the interface separating the sediment and basement is then parameterized by bi cubic b splines and a smoothness constraint is imposed to avoid oscillatory artifacts in the solution the relative weight of the constraint to data residuals is determined by minimizing akaike9s bayesian information criterion about 1500 travel times of refracted p waves are inverted tomographically and the interface shape determined agrees well with the results of other geophysical surveys such as borehole measurements and gravimetric observations the basement velocities in the northern and southern regions are 5 7 and 5 4 km sec respectively previous two dimensional analyses suggested there is a 4 5 km sec layer in the uppermost part of the southern basement but we ignore it for simplicity so that estimated depths are likely underestimated by 1 2 km in the southern region nevertheless this study provides the first detailed image of the basin structure in the area which will help strong motion and earthquake hazard studies as additional constraints

diffusion transport model for pelagic sediments on the mid atlantic ridge the diffusion model is potentially useful for quantifying the effect of downslope gravity transport on sedimentation rate variations which are commonly found between deep sea drilling project and ocean drilling program sites if appropriate the model and stratigraphy could be used for example to constrain the amount and timing of fault block rotation deep tow profiler records from the french american mid ocean undersea study area of the mid atlantic ridge are examined to determine whether they are consistent with a diffusion model sedimentary contacts with basement show that a variety of processes may be operating some of which are inconsistent with the diffusion model for example there are moats around some contacts which are typical of scouring or nondeposition due to high current velocities more than half of the contacts however show onlapping which is qualitatively consistent with the diffusion model sediments generally fill low areas of the topography and have smooth surfaces as expected from a diffusion model where the fluxes of sediment entering a basin are constant the diffusion model predicts that the sediment surface should evolve to a parabola the steady state solution some 20 curved surfaces in the profiler data were digitized and least squares parabolas fitted to them with rms errors of less than 1 m the slopes of the model parabolas provide values for the ratio of sediment flux to diffusivity at the edges of the basins steep surfaces are produced by low diffusivity or high fluxes this ratio is combined with estimates of the fluxes to determine the apparent sediment diffusivity kapp for eacri basin flux is estimated by assuming the abyssal hill topography acts as a simple sediment trap so that the lateral flux equals the width of a basin s pelagic catchment area times the area s mean sedimentation rate s using this method median kapp is 0 04 0 11 m2 yr 1 assuming s 10 30 m m y 1 variations in kapp and the assumptions behind the diffusion model are discussed and alternative causes of sediment surface tilts are considered in particular differential compaction which is modelled using a simple porosity depth function

the kinematics of a transition from subduction to strike slip an example from the central new zealand plate boundary 1 we develop a kinematic model for the transition from subduction beneath the north island new zealand to strike slip in the south island constrained by gps velocities and active fault slip data to interpret these data we use an approach that inverts the kinematic data for poles of rotation of tectonic blocks and the degree of interseismic coupling on faults in the region convergence related to the hikurangi subduction margin becomes very low offshore of the northern south island indicating that in this region the majority of the relative plate motion has been transferred onto faults within the upper plate as suggested by previous studies this result has implications for understanding the likely extent of subduction interface earthquake rupture in central new zealand easterly trending strike slip faults such as the boo boo fault are the key features that facilitate the transfer of strike slip motion from the northern south island faults further north into the southern north island and onto the hikurangi subduction thrust our results also indicate that the transition from rapid forearc rotation adjacent to the hikurangi subduction margin to a strike slip dominated plate boundary with negligible vertical axis rotation in the south island occurs via a crustal scale hinge or kink in the upper plate compatible with paleomagnetic and structural geological data despite the ongoing tectonic evolution of the central new zealand region our study highlights a remarkable consistency between data sets spanning decades gps thousands of years active faulting data and millions of years paleomagnetic data and bedrock structure

abyssal hill segmentation quantitative analysis of the east pacific rise flanks 7 s 9 s the recent r v maurice ewing ew9105 hydrosweep survey of the east pacific rise epr and adjacent flanks between 7 s and 9 s provides an excellent opportunity to explore the causal relationship between the ridge and the abyssal hills which form on its flanks these data cover 100 of the flanking abyssal hills to 115 km on either side of the axis we apply the methodology of goff and jordan 1988 for estimating statistical characteristics of abyssal hill morphology rms height characteristic lengths and widths plan view aspect ratio azimuthal orientation and fractal dimension principal observations include the following 1 the rms height of abyssal hill morphology is negatively correlated with the width of the 5 to 20 km wide crestal high consistent with the observations of goff 1991 for northern epr abyssal hill morphology 2 the characteristic abyssal hill width displays no systematic variation with position relative to ridge segmentation within the ew9105 survey area in contrast with observations of goff 1991 for northern epr abyssal hill morphology in which characteristic widths tend to be smallest at segment ends and largest toward the middle of segments 3 abyssal hill rms heights and characteristic widths are very large just north of a counterclockwise rotating nannoplate suggesting that the overlap region is being pushed northward in response to microplate style tectonics and 4 within the 7 12 s 8 38 s segment abyssal hill lineaments are generally parallel to the ridge axis while south of this area abyssal hill lineaments rotate with a larger radius of curvature than does the epr axis approaching the epr wilkes ridge transform intersection

the 2016 kaikōura earthquake simultaneous rupture of the subduction interface and overlying faults abstract the distribution of slip during an earthquake and how it propagates among faults in the subduction system play a major role in seismic and tsunami hazards yet they are poorly understood because offshore observations are often lacking here we derive the slip distribution and rupture evolution during the 2016 mw 7 9 kaik ura new zealand earthquake that reconcile the surface rupture space geodetic measurements seismological and tsunami waveform records we use twelve fault segments with eleven in the crust and one on the megathrust interface to model the geodetic data and match the major features of the complex surface ruptures our modeling result indicates that a large portion of the moment is distributed on the subduction interface making a significant contribution to the far field surface deformation and teleseismic body waves the inclusion of local strong motion and teleseismic waveform data in the joint inversion reveals a unilateral rupture towards northeast with a relatively low averaged rupture speed of 1 5 km s the first 30 s of the rupture took place on the crustal faults with oblique slip motion and jumped between fault segments that have large differences in strike and dip the peak moment release occurred at 65 s corresponding to simultaneous rupture of both plate interface and the overlying splay faults with rake angle changes progressively from thrust to strike slip the slip on the papatea fault produced more than 2 m of offshore uplift making a major contribution to the tsunami at the kaik ura station while the northeastern end of the rupture can explain the main features at the wellington station our inversions and simulations illuminate complex up dip rupture behavior that should be taken into consideration in both seismic and tsunami hazard assessment the extreme complex rupture behavior also brings new challenges to the earthquake dynamic simulations and understanding the physics of earthquakes

roots of an archean volcanic arc complex the lac des iles area in ontario canada abstract the lac des iles area is located in the wabigoon subprovince an archean granite greenstone terrain in the superior province in ontario canada the area consists of several unmetamorphosed plutons of biotite and hornblende tonalite and mafic and ultramafic intrusions which are emplaced into an older tonalitic gneiss the mafic ultramafic bodies are concentric in shape and consist of periodotite pyroxenite gabbro and hornblende gabbro cumulates and diorite the largest intrusion the lac des iles complex consists of several mafic and ultramafic centers an internal sm nd isochron from the southern ultramafic complex gives an intrusion age of 2736 28 ma mswd 1 5 nd t 1 2 this age is also assumed to be representative of the time of emplacement of the other mafic and ultramafic bodies as well as the unmetamorphosed tonalite plutons the tonalitic gneiss represents older continental crust and had an nd value of 1 at this time the nd t values of the felsic and mafic ultramafic suites are positive ranging from 0 to 2 this range can be explained if primary magmas derived from a depleted mantle reservoir assimilated continental crust such as the tonalite gneiss during their ascent this implies that the tonalite magmas in the lac des iles area represent mixtures of the tonalite country rock and mantle magmas which formed by partial melting of depleted mantle or of mafic rocks underplated beneath the continental lithosphere the morphology and the rock assemblages of the mafic and ultramafic intrusions in the lac des iles area resemble alaskan type intrusions which are common components of phanerozoic magmatic arcs associated with subduction zones in addition the crystallization sequence in the mafic ultramafic intrusions suggests that they are derived from a parental magma with high al basalt affinities the mafic ultramafic rocks are depleted in high field strength elements but enriched in large ion lithophile elements and the tonalites belong to calc alkaline rock series displaying fractionation trends towards trondhjemitic compositions thus the archean lac des iles area and the root zones of phanerozoic active continental margins share many geological geochemical and petrological features which would suggest that the lac des iles area formed in an andean type continental margin

robust description of statistically heterogeneous seafloor topography through its slope distribution statistical heterogeneity of abyssal hill properties is often evident in seafloor topography even under periods of relatively constant spreading direction and rate in this paper we relate the statistics of topographic slopes computed on finite spatial scales to the autocovariance function and investigate the practicality of using these functions in describing such heterogeneous abyssal hill terrains for a two dimensional homogeneous surface a direct relation exists between the sample autocovariance and the slope distributions at different spatial scales however for a heterogeneous field characterized by large transient signals the computed autocovariance estimate no longer has a clear statistical interpretation and becomes dominated by the transients in contrast the family of slope distributions can still be used to derive stable descriptors of the field slope statistics are thus useful in deriving a more robust estimate of the autocovariance than the usual sample autocovariance moreover slope statistics may also be used to derive stable estimates of quantities not measurable with the autocovariance function or power spectra such as the statistical asymmetry of features examples of the use of slope statistics and a comparison with autocovariance methods are presented we document and quantify evidence of statistical asymmetry in a region of abyssal hills in the northeast pacific and in a second example the presence of multiple lineations in a region where a fracture zone cuts through abyssal hill terrain

effects of inundation by the 14th november 2016 kaikōura tsunami on banks peninsula canterbury new zealand at 12 02 56 a m monday november 14 2016 nzdt 11 02 56 a m november 13 2016 utc a magnitude 7 8 earthquake struck near kaik ura on the north eastern coast of the south island of new zealand this earthquake caused a tsunami along new zealand s east coast that was recorded on a number of sea level gauges outside of the kaik ura region north facing bays along banks peninsula were most affected by the tsunami of these little pigeon bay experienced extensive inundation and an unoccupied cottage was destroyed by the wave run up we report on the inundation extent and inferred flow directions at little pigeon bay including a study on temporal changes in the field evidence of this inundation preliminary modelling results indicate that the waves may have excited resonance in the bay we also present results from inundation surveys of nearby north facing bays on banks peninsula the excitation of resonance in little pigeon bay provides an explanation for the more severe inundation and damage there in comparison to these nearby bays

rb sr and u pb ages of volcanism and granite emplacement in the michipicoten belt wawa ontario the michipicoten greenstone belt at wawa ontario is typical of archean volcanic belts in the superior province the supracrustal rocks are divisible into lower middle and upper metavolcanic sequences which are separated by iron formation and clastic metasedimentary rocks these are intruded by granitic stocks and embayed by granitic batholiths this study reports whole rock rb sr and zircon u pb ages for the lower and upper metavolcanics for the granitic rocks that are physically within the greenstone belt internal granites and for the granitic rocks that embay the greenstone belt external granites the apparent rb sr ages for the lower metavolcanics are 2530 90 2285 70 and 2680 490 ma the u pb ages are 2749 2 and 2744 10 ma the internal granites give an rb sr age of 2560 270 ma and a u pb age of 2737 6 ma the external granite at hawk lake indicates an rb sr age of 2550 175 ma and a u pb age of 2747 7 ma it is possible that this unit contains elements older than 2812 ma as

the temporal evolution of sanukitoids in the karelian craton baltic shield an ion microprobe u th pb isotopic study of zircons abstract the u th pb isotopic systematics of zircons from six sanukitoid intrusions in the karelian craton has been investigated using the secondary ion mass spectrometer sims our results show that karelian sanukitoids formed between 2745 and 2705 ma ago and that there is an age difference of about 30 ma between sanukitoids in the eastern and western karelia results for intrusions made up of a number of magmatic phases show no internal age variation in the east of the study region zircons from a monzodiorite and two quartz monzonites from the panozero pluton were dated at 2737 11 2739 11 and 2741 8 ma in the hautavaara pluton a monzodiorite and a subalkaline granite were dated at 2743 8 and 2742 23 ma and a quartz diorite from the elmus pluton gave an age of 2741 7 ma in addition a lamprophyre dyke within the sjargozero pluton gave an age of 2742 14 ma in the west zircons from a quartz monzonite and a granodiorite in the njuk intrusion gave ages of 2709 10 and 2716 11 ma in the kurgelampi pluton zircons from a diorite and two granodiorites were dated at 2707 9 2719 6 and 2712 9 ma respectively zircons from the granodiorites and the alkaline granites contain older cores with 207 pb 206 pb ages greater than 2800 ma the absence of inherited zircons in the more mafic sanukitoids is attributed to their higher saturation levels for zirconium sanukitoid zircons have th u ratios above 0 5 and often higher whereas nearby tonalite tondhjemite granodiorites ttgs have th u ratios below 0 5 typically tonalites are older than sanukitoids by more than 100 ma and it is possible that tectonic processes associated with the collision of the belomorian mobile belt provided the heat necessary to initiate the generation of the sanukitoid melts

the 2016 kaikōura earthquake revealed by kinematic source inversion and seismic wavefield simulations slow rupture propagation on a geometrically complex crustal fault network the 2016 kaik ura new zealand earthquake generated large ground motions and resulted in multiple onshore and offshore fault ruptures a profusion of triggered landslides and a regional tsunami here we examine the rupture evolution using two kinematic modelling techniques based on analysis of local strong motion and high rate gps data our kinematic models capture a complex pattern of slowly vr 2km s propagating rupture from the south to north with over half of the moment release occurring in the northern source region mostly on the kekerengu fault 60 seconds after the origin time both models indicate rupture re activation on the kekerengu fault with the time separation of 11 seconds between the start of the original failure and start of the subsequent one we further conclude that most near source waveforms can be explained by slip on the crustal faults with little 8 or no contribution from the subduction interface

complex multifault rupture during the 2016 mw 7 8 kaikōura earthquake new zealand the 2016 moment magnitude m w 7 8 kaik ura earthquake was one of the largest ever to hit new zealand hamling et al show with a new slip model that it was an incredibly complex event unlike most earthquakes multiple faults ruptured to generate the ground shaking a remarkable 12 faults ruptured overall with the rupture jumping between faults located up to 15 km away from each other the earthquake should motivate rethinking of certain seismic hazard models which do not presently allow for this unusual complex rupture pattern science this issue p eaam7194 1 1 lookup doi 10 1126 science aam7194

geochemistry nd pb and sr isotope systematics and u pb zircon ages of the neoarchean bad vermilion lake greenstone belt and spatially associated granitic rocks western superior province canada abstract the ca 2720 ma neoarchean bad vermilion lake bvl greenstone belt in the western superior province canada is composed of a suite of tholeiitic to calc alkaline basalts to rhyolites volcaniclastic rocks gabbros and timiskaming type siliciclastic sedimentary rocks the greenstone belt was intruded by neoarchean granitic rocks and underwent greenschist facies metamorphism and intense deformation resulting in mobilization of many elements e g rb ba sr k u pb the high field strength element and rare earth element systematics of the volcanic and volcaniclastic rocks and gabbros are consistent with subduction zone geochemical signatures suggesting that the bvl greenstone belt formed in a magmatic arc setting on the basis of lithological associations and trace element systematics the bvl greenstone belt is defined as a fragment of a neoarchean subduction related ophiolite three rhyolite samples from the belt have yielded 2722 18 ma 2706 13 ma and 2710 28 ma u pb zircon ages representing the approximate age of the arc volcanism in the study area and development of a subduction zone between the western wabigoon terrane to the north and the wawa abitibi terrane to the south the intrusion of the ca 2664 15 ma late to post tectonic potassic ottertail lake granite marks the end of tectonic accretion in the study area both the volcanic rocks and gabbros display large ranges of nd 143 nd 144 nd 0 511600 0 512849 e nd 2720 ma 0 8 to 4 0 pb 206 pb 204 pb 13 80 60 67 and sr 87 sr 86 sr 0 701481 1 01154 isotopic compositions suggesting that these isotope systems were variably affected by post magmatic element mobility neither the sm nd 2921 200 ma nor rb sr 2130 610 ma system has yielded reliable regression isochron ages reflecting the open system behavior of these systems during metamorphism despite large uncertainties pb pb regression ages yielded by all rock types 2661 60 ma and basalts and gabbros 2725 83 ma agree with the zircon u pb ages of the rhyolites suggesting that the u pb system was the most robust among all three systems

magma mixing in late archean tonalitic and mafic rocks of the lac des iles area western superior province abstract plutonic rocks in the lac des iles area of the western superior province provide a record of contemporaneous late archean mafic and tonalitic magmatism this suite of rocks consists of mafic to ultramafic intrusions mafic to intermediate dikes hornblendite and hornblende tonalite the tonalite contains net veined and disaggregated mafic to intermediate dikes mafic schlieren and zones of hornblendite to mela tonalite with skeletal hornblende these textures are interpreted to be the result of magma mixing the hornblende tonalite is geochemically characterized by high al 2 o 3 high na 2 o k 2 o low rb moderate sr and fractionated ree the hornblendite mafic to intermediate dikes and tonalite show whole rock trends of decreasing total ree increasing depletion of hree and increasing eu eu with increasing sio 2 amphiboles range in composition from edenitic and pargasitic hornblende to hornblende in dike rocks mela tonalite and hornblendite and from hornblende to actinolite in tonalite the development of skeletal amphiboles with strong normal zoning and resorbed hornblende with weak reverse zoning are attributed to conditions of supercooling and superheating respectively in zones of magma mixing the least fractionated dike rocks geochemically resemble lamprophyres derived from alkali basaltic magma variation of ree among the mafic to intermediate dikes suggests that they fractionated hornblende hornblendites and mela tonalites can be modeled as hornblende cumulates from the dike rocks the amphiboles probably crystallized rapidly during mixing leaving a feldspathic residue variation in hornblende tonalites is consistent with mixing of sio 2 rich tonalite melt with mafic to intermediate dike phases and associated hornblende cumulates and feldspathic residue open system magmatic processes at lac des iles result in a continuum of disequilibrium textures reflecting emplacement of mafic magma into a crystallizing felsic host the plutonic rocks probably formed from a zoned magma chamber with a mafic base and tonalitic top breccia zones in the tonalite suggest that explosive degassing of the chamber occurred structures similar to those reported here are common in other granitoids in the superior province and suggest that mafic magmatism and magma mixing played an important role in the development of late archean granitoid plutons

u pb ages constraining structural development of an archean terrane boundary in the lake of the woods area western superior province canada layered gneisses in the winnipeg river subprovince contain magmatic zircon with u pb ages of 3317 9 and 3055 4 ma at tannis lake and 3170 and 3255 5 ma at cedar lake indicating widespread occurrence of mesoarchean crust this is in contrast to the well documented neoarchean age of the western wabigoon subprovince further geochronology using both shrimp sensitive high resolution ion microprobe and id tims isotope dilution thermal ionization mass spectrometry combined with structural observations in the kenora area and lake of the woods greenstone belt show the effects of juxtaposition of these two terranes isoclinally folded gneiss north of the subprovince boundary zone near kenora gives a magmatic age of 2882 2 ma with 3051 6 ma inheritance ages of syntectonic dykes show that asymmetric refolding of these gneisses occurred between 2717 2 and about 2713 1 ma subsequent regional vertical flattening and horizontal extension are dated at 2708 2 ma by syntectonic tonalite sheets t

convergent margin tectonics central wabigoon subprovince superior province canada abstract best known for its neoarchean greenstone granite terranes in the east and west the wabigoon subprovince of the superior province features a central transverse corridor of meso and neoarchean gneissic granitoid and minor supracrustal rocks resembling an eroded intermontane plateau structural analysis and u pb geochronology in the north central wabigoon subprovince reveal a complex history of plutonism supracrustal rock deposition polyphase deformation and amphibolite facies metamorphism between 3075 and 2670 ma the geometric and kinematic character of d 1 and d 2 deformational events recorded in 2890 2718 ma tonalitic gneisses remain cryptic as a result of magmatic and structural d 3 5 overprinting but the early structures are bracketed in age between 2725 and 2713 ma by a polydeformed gneiss and tonalite dyke these events occurred deep within an active continental magmatic arc and correspond in age to a collision between the juvenile wabigoon and continental winnipeg river subprovinces recognized to the west clastic sediments deposited after 2701 ma are the youngest rocks involved in subsequent regional deformation a d 3 event is responsible for rapid burial of supracrustal units to 15 km within warm arc crust and imposition of a regional penetrative s 3 foliation that accommodated some relative uplift prior to 2697 ma the age of a discordant granodiorite dyke this event corresponds to variably preserved steep north trending d 1 structures recognized in adjacent greenstone belts subsequent d 4 ductile deformation defines the map pattern in the deep crustal rocks of the central wabigoon subprovince upright east trending f 4 folds developed synchronously with d 2 dextral transpressive structures that formed throughout the wabigoon subprovince prior to 2698 ma the final d 5 sinistral shearing event occurred during emplacement of mantle derived granodiorites of sanukitoid affinity 2688 ma and crust derived granites 2685 ma this event appears to have triggered rapid cooling reflected in 2680 2670 ma titanite dates and late brittle increments of displacement

a zoned low p high t complex at the level of anatexis structural and plutonic patterns in metasediments of the archean yellowknife supergroup near bathurst inlet n w t canada abstract within metagreywackes and schists of the archean yellowknife supergroup the development of an anatectic stratigraphy during the late stages of regional deformation has resulted in the formation of a complex with a metamorphicplutonic structural zoning similar to that occurring in phanerozoic low p high t terrains from bottom to top the stratigraphy consists of 1 small folded migmatite grading with decreasing partial melting to 2 sillimanite schist strongly strained by the emplacement of two mica granites 3 andalusite cordierite schist the site of large folds related to the emplacement of the complex each zone is characterized by a different structural style resulting from the interplay between metamorphic grade and deformation for instance in the sillimanite zone the structure was influenced by the extraction of syntectonic melt and its emplacement into fractures at low effective pressure this zone was also the ductile envelope into which sills and plutons of two mica granites derived from the lower migmatites migrated the time taken for evolution of the complex has been constrained by u pb zircon and monazite dating of a member of the early tonalite diorite suite and members of the two mica granite suite this shows the evolution of the complex was rapid ca 10 ma but possibly polyphase the formation of a distinctively styled complex accompanied by syn tectonic anatexis and plutonism may be typical of lower crustal levels of the yellowknife supergroup and other low p high t terrains

source of the july 2006 west java tsunami estimated from tide gauge records 1 the source of the west java tsunami of july 17 2006 which was generated during a large earthquake near the sunda trench is constrained by tsunami waveforms that were recorded on six tide gauges around the indian ocean the tsunami travel times poorly constrain the source area probably because shallow bathymetry near these gauges is not well known inversion of tsunami waveforms however reveals that the tsunami source was about 200 km long the largest slip about 2 5 m for instantaneous rupture model was located about 150 km east of the epicenter most of the slip occurred on shallow parts of the fault indicating that this earthquake shares the same characteristics with tsunami earthquakes which generate abnormally large tsunamis compared with ground shaking the slip distribution yields a total seismic moment of 7 0 1020 nm mw 7 8

a global and regional stochastic analysis of near ridge abyssal hill morphology this paper presents the results of a global and regional stochastic analysis of near ridge abyssal hill morphology the analysis includes the use of sea beam data for the estimation of stochastic parameters up to order 4 these parameters provide important quantitative physical information regarding abyssal hills including their rms height azimuthal orientation characteristic width aspect ratio hausdorff dimension skewness tilt and peakiness the global data set consists of 64 sea beam swaths near the rivera cocos and nazca spreading sections of the east pacific rise the mid atlantic ridge and the central indian ridge in one form of analysis the parameters are averaged among spreading rate bins each of the spreading rate subsets can be identified as unique from the others in at least one aspect the slowest spreading rate subset mid atlantic data exhibit the largest scales rms height and characteristic width and length of abyssal hills these parameters generally decrease as spreading rate increases up to the fast spreading rate data pacific cocos but increase going from fast to very fast pacific nazca spreading rate data this indicates some complexity in the relationship between spreading rate and abyssal hill morphology the plan view aspect ratio is nearly twice as large for the fast spreading rate data than for any of the other subsets and is smallest for the very fast spreading rate data the fractal dimension is nearly identical for all spreading rate subsets the vertical skewness is positive for the slow and medium spreading rate data indicating larger peaks than troughs and negative for the fast spreading rate data indicating larger troughs than peaks the kurtosis or peakiness is everywhere larger than the gaussian value of 3 and tends to be larger in the atlantic than the pacific the tilting parameter provides substantial evidence indicating steeper inward facing slopes in the medium and fast spreading rate data but only marginal evidence for it in the slow spreading rate data from an analysis of correlations among parameters it is found that subsets sometimes behave differently from the entire data set in particular while over the global data set the characteristic width exhibits a well resolved positive trend when plotted versus rms height these parameters exhibit a more gradual positive trend in the mid atlantic data and a negative trend in the pacific cocos data in addition the plan view aspect ratio while generally uncorrelated with rms height for the global data set is positively correlated with rms height for the pacific cocos data set these results emphasize a strong uniqueness of the pacific cocos data relative to the rest of the data global set the pacific cocos data consist of 27 swaths concentrated between the siquieros and orozco fracture zones these data provide very good abyssal hill coverage of this well mapped and well studied region and form the basis of a regional analysis of the correlation between ridge morphology and stochastic abyssal hill parameters in this analysis it is found that abyssal hill parameters are correlated with the depth of the adjacent ridge axis indicating that the relative abundance in magma supply which likely controls the ridge axis depth may also be an important influence on the formation of abyssal hills

pelagic sedimentation on rough seafloor topography 2 inversion results from the north atlantic acoustic reverberation corridor seafloor slope distributions are sensitive to basement topography the surface shape of sediment distributions and the average thickness of sediment within a region by comparing slope distributions computed from bathymetric data to distributions from realistic models of sedimented topography we determine how characteristic values of average sediment thickness l rms basement variability h and apparent diffusivity vary throughout the office of naval research acoustic reverberation corridor located on the western flank of the mid atlantic ridge north of the kane fracture zone 25 5 27 25 n 44 5 49 w values of l from basin centered subregions show thinner sediments near the axis thickening westward with maximum values found on 10 20 ma seafloor lower values of l are found for older late oligocene early miocene seafloor values of l on young seafloor suggest a sediment accumulation rate of 6 5 2 3 m m y since 10 ma values of h computed from hill centered regions range from 217 to 306 m with an average of 267 27 m hills are generally larger to the north of a low running through the study area values of range from 0 12 to 0 77 m2 yr with an average of 0 32 0 19 m2 yr lower values of kbetter describe the surface shapes of individual high standing ponds while higher values are needed to model the surface shapes of thick deposits in regional lows this difference in with geological setting is probably due to variations in sediment transport mechanisms

geochemical and u pb zircon geochronological constraints on the development of a late archean greenstone belt at birch lake superior province canada abstract this paper presents new high precision u pb zircon ages that place constraints on the timing of magmatic activity volcanic and plutonic deformation and gold mineralization within the late archean birch confederation lakes greenstone belt within the uchi subprovince of the superior province geochemical data including sm nd isotopic analyses place additional constraints on the nature of the magmatic activity three volcanic rocks from the birch lake area have similar ages 2742 2 1 8 1 7 2739 1 2 8 and 2741 7 2 3 2 2 ma and together with previously published data suggest that a major proportion of the volcanic rocks of the greenstone belt were erupted in a narrow time interval from 2742 to 2735 ma older volcanic rocks recognized to the south of the birch lake area are either absent or of limited extent plutonic rocks include the pre to syn tectonic horseshoe island stock 2725 0 2 5 ma the syn tectonic mainprize lake batholith 2724 3 1 8 1 5 ma and the late to post tectonic shabumeni lake stock 2710 8 1 9 1 3 ma and okanse lake pluton 2700 8 1 9 1 4 ma these ages and structural relationships indicate that the development of a d2 regional penetrative fabric at least in part post dates the emplacement of the horseshoe island stock this is consistent with the interpretation that d2 deformation developed synchronously with and perhaps in response to the emplacement of the mainprize lake batholith an earlier d1 penetrative deformational event as well as possible large scale subhorizontal structures d0 developed subsequent to the deposition of the youngest volcanic rocks and prior to d2 plutons are younger than and unrelated to volcanism in contrast to volcanic rocks plutons show no indication of having interacted with older felsic crustal rocks and are interpreted to be derived from partial melting of metasomatized mantle and subducted tholeiitic basalt the okanse lake pluton has affinities with the sanukitoid suite and is closely comparable in age to similar plutons over a wide area it is proposed that a 2700 ma sanukitoid magmatic event may reflect melting of previously metasomatized mantle in response to thermal re equilibration associated with the transition from an earlier subduction dominated regime to a later post collisional stage culminating in the stabilization of the northern superior province

the lac des iles complex ontario petrology and platinum group elements mineralization in an archean mafic intrusion the lac des iles complex is a late archean mafic to ultramafic complex that is host to 20 4 106 t pt pd and au mineralization with an average grade of 6 34 g t platinum group elements pge the 30 km2 complex located in the wabigoon subprovince consists of several coalescing mafic to ultramafic intrusive centers the complex is emplaced into early gneissic tonalite and is contemporaneous with late granitoids the magmatic evolution of the complex reflects the emplacement of multiple pulses of previously fractionated magma some of which underwent subsequent in situ fractionation distinct magma sequences are recognized on the basis of intrusive relationships differences in the cumulus minerals crystallization order and trace element chemistry these sequences are 1 hornblende gabbro 2 gabbro and gabbronorite and 3 ultramafic where there is evidence of intrusive relations the most primitive sequences are emplaced late and occur toward the north end of the complex microprobe analyses in

zircon u pb ages from the wabigoon manitou lakes region wabigoon subprovince northwest ontario three distinct stratigraphic units have been recognized in the crow lake savant lake belt these are a basal unit consisting of high magnesium tholeiitic flows a middle unit consisting mostly of tholeiitic to calc alkaline pyroclastic rocks and flows and an upper unit of high iron tholeiitic flows a zircon u pb study has been carried out on seven rocks from the wabigoon manitou lakes region of this belt in the manitou lakes area a minimum age of 2755 ma on a porphyry pluton intruded into the wapageisi volcanics gives a minimum age for the high magnesium tholeiitic sequence a trondhjemite phase of the atikwa batholith near wabigoon lake that is dated at 2732 2 2 9 ma has the same age within experimental error as a rhyolite flow from the lower wabigoon volcanics in the same area that is dated at however a trondhjemite phase of the atikwa batholith at eagle lake that is dated at is distinctly younger than a dacite flow collected nearby from the lower wabigoon volcanics that is dated at both thes

geochronological constraints on the timing of magmatism deformation and gold mineralization in the red lake greenstone belt northwestern ontario the paper presents u pb ages on zircon baddeleyite titanite rutile and monazite from volcanic and plutonic rocks of the red lake greenstone belt in the northern superior province the purpose of the study was to refine a previously outlined time frame for the volcanic evolution of the belt define the time of major plutonism and deformation and constrain the age of formation of gold deposits volcanism spanned at least 270 ma between 3000 and 2730 ma new ages of 2989 3 and 2894 2 ma for units of a lower volcanic sequence and and 2744 1 ma for units of an upper volcanic sequence corroborate and refine the previously established relationships local gabbroic and felsic intrusions cutting through the lower sequence yield ages of 2870 15 and respectively volcanism was succeeded by major plutonism deformation alteration and metamorphism between about 2730 and 2700 ma these processes were interrelated and progressed as a relatively continuous sequence of events accentuated by major activity d

archean tectonic and metallogenic evolution of the superior province of the canadian shield abstract the superior province of the canadian shield has mainly experienced an archean tectonic history comprising several cycles of volcanism plutonism and tectonism although the rocks of the superior province span more than 500 million years of archean time most mineral deposits formed in an interval of 100 million years or less corresponding to a period of accretion of oceanic and pre existing continental fragments in the late archean at 2 7 ga in accord with recent tectonic syntheses which argue for the accretionary origin of the superior province the metallogenic history of the superior province can also be interpreted in the same context provided secular anomalies in the early history of the earth are acknowledged for relatively unique deposit types such as komatiitic nickel deposits and voluminous iron formations volcanogenic massive sulphide iode gold and granitoid associated deposits as well as ni cu pge cr and ti deposits associated with mafic ultramafic intrusions are readily interpreted in terms of the construction and accretion of late archean island arcs

abnormal tsunamis caused by the june 13 1984 torishima japan earthquake an earthquake with an m s 5 6 m b 5 5 which occurred near torishima japan on june 13 1984 generated abnormally large tsunamis tsunami magnitude m t 7 3 for its relatively small earthquake magnitude the maximum amplitude of the tsunamis is not a simple function of distance as the magnitude formula implies in order to quantify the abnormal tsunamis we modeled the tsunami source using a finite difference computation on the actual bathymetry the source of these abnormal tsunamis is modeled as a water surface displacement with a radius of 12 km and maximum water height of 13 cm the displaced water volume is 4 10 13 cm 3 and the potential energy is calculated as 2 10 17 ergs if this water displacement is due to a fault motion at 5 km depth a moment magnitude m w is estimated to be 6 3 this value is larger than m w estimated from seismic waves by 0 7 but smaller than m t by 1 0 the former difference suggests that the earthquake source is very different from an ordinary faulting if we assume the source is a horizontally lying tensile crack at shallow depth about 2 km that explains both the water surface displacement and the seismic moment tensor the tensile crack is interpreted as an injection of material as suggested by a seismological study the discrepancy between m w and m t indicates that the propagation path is responsible for the observed large tsunamis the numerical computation shows a focusing of energy during the propagation of the tsunami along the shallow izu bonin ridge system thus the abnormally large tsunamis from the torishima earthquake are a result of both source and path effects

traveltime delay and initial phase reversal of distant tsunamis coupled with the self gravitating elastic earth systematic tsunami traveltime delays of up to 15 min relative to the numerically simulated long waves from the 2010 chilean and 2011 tohoku oki earthquakes were widely observed at deep ocean tsunamimeters enigmatic small negative phases appearing before the main peak were commonly found only at the trans oceanic locations the frequency dependence of the measured tsunami phase velocities shows reverse dispersions at long periods i e the tsunami speed becomes slower at periods beyond 1000 s this is consistent with the phase velocities of a tsunami mode coupled with a self gravitating elastic earth suggesting that the effects of compression and dilatation of seawater elastic tsunami loadings on a solid earth and the geopotential variations associated with the motion of mass during tsunami propagation are responsible for the traveltime delays and the initial negative phases simple 1 d tsunami propagation tests confirm that the reverse dispersion creates a small negative phase that precedes the main peak at large distances a new method to simulate tsunami waveforms on real ocean bathymetry that takes into account seawater compressibility the elasticity of the earth and geopotential perturbations has been developed by applying a phase correction to the simulated long waves the simulated waveforms in which phase corrections are applied for the dispersion effects accurately reproduce the observed waveforms including a small initial negative phase that appears at distant locations the traveltime difference between the observed and simulated waveforms has been decreased to less than 5 min and the waveform difference between them remarkably diminishes

stratigraphy and petrology of the lower part of the mulcahy gabbro northwestern ontario origin of reverse and normal fractionation trends and implications for tectonic setting of late archean mafic magmatism the mulcahy gabbro 2 73 ga is an exceptionally well preserved tholeiitic layered intrusion located in the wabigoon subprovince of the superior province the intrusion has a 900 m thick marginal z

comparison of a stochastic seafloor model with seamarc ii bathymetry and sea beam data near the east pacific rise 13 15 n a recent seamarc ii survey along the hanks and crest of the east pacific rise between 13 and 15 n edwards et al 1988 provides us with a unique opportunity to compare stochastic models of the seafloor against bathymetric data stochastic models can be used to quantitatively characterize intermediate to small scale 100 km seafloor features such as abyssal hills in a recent paper goff and jordan 1988 introduced a model for the two point covariance function having five free parameters which describe the amplitude orientation characteristic wavelengths and hausdorff fractal dimension of seafloor topography these parameters can be estimated from multibeam data such as sea beam by inverting auto and cross covariance functions for the beams the stochastic model can be used to generate synthetic topography to arbitrary resolution and scale by assuming appropriate sea beam noise and response characteristics we can use the synthetic topography to produce synthetic data sets comparison of real and synthetic data is an important means of assessing the performance of the stochastic model unfortunately the limited spatial extent of sea beam in the across track direction and lack of 100 coverage over large areas severely limit our ability to compare the full two dimensional stochastic model with real seafloor morphology especially with respect to abyssal hill length characteristics the recent seamarc ii survey included sufficient off axis topography over 100 km 70 000 km2 to permit a comparison of a complete two dimensional synthetic topographic field with a region of abyssal hill terrain that has close to 100 data coverage we have estimated stochastic models for various regions of the seamarc ii survey area from several sea beam tracks which cross it synthetic fields are generated from these models using a fourier method these comparisons indicate the extent to which the model succeeds in characterizing seafloor topography and the directions we will need to take to improve our modeling a change in ridge complexity at 14 n and the location of a propagator pseudofault appear to be correlated with changes in stochastic character modeled in this region such correlations may provide important new constraints on the understanding of ridge processes

slip distribution of the 2007 bengkulu earthquake inferred from tsunami waveforms and insar data 1 joint inversion study using tsunami waveforms and insar data provides a new way to understand the magnitude and spatial extent of subduction zone earthquakes a great earthquake mw 8 5 occurred on 12 september 2007 off the west coast of bengkulu indonesia the tsunami generated by the event was recorded by tide gauge stations around the indian ocean and by two bottom pressure sensors in the deep sea the ground surface displacements produced by the earthquake on pagai islands and on sumatra island were observed by interferometric synthetic aperture radar insar we estimated the slip distribution of the earthquake by joint inversion incorporating a spatial smoothness constraint using tsunami waveforms and insar data the total released seismic moment calculated from the slip distribution is 6 7 1021 n m mw 8 5 consistent with the seismic moment of the global cmt solution 6 71 1021 n m the maximum observed tsunami heights along the coast of bengkulu agree with those computed from the slip distribution the slip amount of the 2007 earthquake is smaller than the amount of potential slip that has been accumulated since after the 1797 and 1833 events the premise is that averaged over long periods of time the entire fault must slip equal amounts therefore the 2007 great earthquake could be followed by several great earthquakes that will rupture the plate interface until the potential slip that has been accumulated is completely released

geochronological constraints on the tectonic evolution of a late archaean greenstone belt wabigoon subprovince northwest ontario canada abstract u pb isotopic age analyses have been carried out on zircon and titanite from rocks near the contact between the kakagi lake savant lake volcanic belt ksvb within the wabigoon subprovince and the english river subprovince in northwest ontario canada two tonalite gneisses intruded by mafic dykes at tannis lake and caribou lake have minimum zircon ages of 3051 ma and 3075 ma respectively this contrasts with a 2775 1 ma age on zircon from a felsic tuff located within a lower predominantly mafic volcanic sequence in the interior of ksvb these data combined with previous studies indicate that ksvb is presently flanked by older sialic crust in the sioux lookout and kashaweogama lake areas lower mafic volcanic sequences are unconformably overlain by sedimentary units that are in sheared contact with overlying calc alkaline volcanic units titanite and zircon analyses from clasts within a basal conglomerate indicate a maximum age for deposition of 2698 4 ma this late age is confirmed by a 2703 2 ma zircon age for an unconformably underlying porphyry intrusion one clast gives a zircon age of 2903 16 ma suggesting that the sediments were at least partly derived from older material in the english river subprovince data from previous studies show that the structurally overlying calc alkaline volcanic sequences are at least 30 ma older than the sediments the absence of zircon inheritance in all but the youngest ksvb sequences as well as geological and geochemical arguments suggest that the greenstone belt evolved largely in an ensimatic environment in isolation from older sialic material the intervening oceanic crust must therefore have been consumed by subduction which led to arc magmatism and eventual collision between the arc ksvb and continental material english river subprovince the sediments unconformably overlying the lowermost mafic volcanic sequences were deposited in a partly subaerial continental environment since chemical and textural evidence suggests the lower mafic volcanic sequences were deposited in an oceanic environment they must have been obducted onto the edge of a continental block this was perhaps followed by nappe and thrust emplacement on top of the sediments of calc alkaline sequences derived from earlier arc magmatism continued compression resulted in isoclinal folding of the supracrustal sequences into their present vertical positions

contribution from multiple fault ruptures to tsunami generation during the 2016 kaikoura earthquake the 2016 kaikoura new zealand earthquake was one of the most complex ruptures ever recorded the epicentre was located well inland but the rupture area extended offshore and generated a modest tsunami which was recorded by tide gauges here we present a detailed estimate of seafloor vertical displacement during the earthquake sequence by a joint inversion of tsunami waveforms and vertical displacement data observed at gps stations and obtained by field surveys the combined dataset provides a solution with good resolution capable of resolving test sources of 20 km of characteristic diameter throughout the study area we found two seafloor uplift regions which are located very close to the coast one is located offshore of the kaikoura peninsula and the other larger uplift region is located near the kekerengu and needles faults to estimate crustal deformation with a complete spatial coverage of the event the estimated seafloor vertical displacement was combined with the inland vertical displacement from insar and gps datasets this vertical displacement is then inverted for the fault slip distributions of the needles jordan kekerengu papatea hundalee hump faults and a newly identified fault beneath kaikoura we also found that the needles fault is probably an offshore extension of the kekerengu fault the seismic moment calculated from the fault slip distributions by assuming a rigidity of 2 7 1010 n m2 is 5 19 1020 nm or equivalent to mw 7 8 this total seismic moment estimate is consistent with that of the global centroid moment tensor solution the tsunami potential energy calculated from the seafloor vertical displacement is 9 40 1012 j of which about 70 is attributed to movement on the faults known to have ruptured suggesting a secondary source for tsunami generation

excepftonally strong near bottom flows on the continental rise of nova scotia recent current velocity measurements across the lower continental rise of nova scotia show a deep equatorwardflow with speeds maximum 73 centimeters per second among the highest recorded for the deep sea silicate measurements indicate that this flow usually consists of southern source antarctic bottom water these measurements confirm the existence of a second and deeper western boundary flow that was earlier inferredfrom geological observations

zircon u pb ages from the kakagi lake area wabigoon subprovince northwest ontario five rocks have been dated from the kakagi lake area of the wabigoon subprovince by means of u pb analysis of zircons using the techniques of air abrasion and high gradient magnetic separation zi

shallow sampling by multi shot laser ablation and its application within u pb zircon geochronology abstract the interaction of incident laser radiation and sample substrate is complex and difficult to predict natural zircons are often both structurally and chemically heterogeneous in 3 dimensional space encountering growth related structural micro heterogeneities inclusions and chemical complexities is almost inevitable during a static ablation of several tens of seconds a multi shot approach to laser ablation described here implements a minimal sample exposure time to incident laser radiation by applying multiple 1 hz shots to a single sample location in delayed succession this process can be conceptualised as a slowing down of a high frequency 5 20 hz static laser ablation inductively coupled plasma mass spectrometry la icp ms analysis until each laser pulse is distinct albeit transient the ability to integrate and collate signal pulses for a small number of consecutive laser shots as opposed to continuously pulsing the laser produces precise age determinations 1 reproducibility 2 level on small sample volumes 704 23 m3 on 91500 zircon standard the multi shot la icp ms protocol employed here significantly reduces the effect of downhole fractionation as the resultant craters are extremely shallow as shallow as 0 56 0 02 m on 91500 zircon standard and maintain an aspect ratio of 1 further benefits include a reduced probability of thermally induced effects e g substrate melting plasma loading and the potential for signal mixing with depth in a heterogeneous sample

reassessment of archean crustal development in the barberton mountain land south africa based on u pb dating this paper presents u pb ages for 23 samples from the barberton mountain land an archean granite greenstone terrain in the kaapvaal craton of south africa a reexamination of the geology of this area in the light of previous u pb dating and the new ages indicates that much of its deformation can probably be accounted for by a single short lived compressional event within the time span 3230 3215 ma which was synchronous with deposition of the moodies group and the upper part of the fig tree group sediments this event may have been responsible for thrusting of much older sequences in the onverwacht group including slivers of 3 54 ga old gneiss circa 3 47 ga old komatiitic and tholeiitic sequences and circa 3 45 ga old felsic sequences key constraints on the timing of deformation are previously determined 3227 3225 ma ages for detrital zircons in thrusted units of the fig tree group a 3229 4 3 ma age for a deformed porphyry which is pre or synthrusting a previously determined 3227 3 ma age for an undeformed porphyry in an inferred thrust fault 3227 1 ma ages for both the kaap valley pluton and an ignimbrite in the stolzburg syncline both of which predate regional upright folding and a 3216 2 ma age for the dalmein pluton which appears to cut regional upright ne sw trending folds in the kromberg syncline part of the final phase of deformation associated with regional compression areally extensive granitoid sheets and syenogranitic plutons were subsequently emplaced into the barberton region at about 3105 ma the linear configuration of the syenogranitic plutons which are also aligned with the gabbroic usushwana complex as well as the geometry of the granitoid sheets suggests that the circa 3105 ma magmatism was caused by incipient rifting around a nw se trending crustal fracture this episode was probably coeval with a late regional transtensional phase of deformation recorded in the greenstone belt some of the above interpretations are in conflict with previous models for early development of the barberton greenstone belt a 3352 6 ma age from a metagabbro which is comagmatic with a proposed ultramafic sheeted dike complex is over 100 m y younger than the probable age of volcanic rocks which host the dikes this conflicts with the suggestion that much of the onverwacht group comprises an ophiolitic section obducted in an intraoceanic setting at circa 3 45 ga that partially melted to form trondhjemitic magmas which intruded along active thrust faults present data suggest that despite its antiquity and the diversity of ages and lithologies found within it the barberton greenstone belt can generally be understood in terms of actualistic tectonic processes at convergent margins

tsunami runup and tide gauge observations from the 14 november 2016 m7 8 kaikōura earthquake new zealand the 2016 m w 7 8 kaik ura earthquake was one of the largest earthquakes in new zealand s historical record and it generated the most significant local source tsunami to affect new zealand since 1947 there are many unusual features of this earthquake from a tsunami perspective the epicentre was well inland of the coast multiple faults were involved in the rupture and the greatest tsunami damage to residential property was far from the source in this paper we summarise the tectonic setting and the historical and geological evidence for past tsunamis on this coast then present tsunami tide gauge and runup field observations of the tsunami that followed the kaik ura earthquake for the size of the tsunami as inferred from the measured heights the impact of this event was relatively modest and we discuss the reasons for this which include the state of the tide at the time of the earthquake the degree of co seismic uplift and the nature of the coastal environment in the tsunami source region

surface rupture of multiple crustal faults in the 2016 mw 7 8 kaikōura new zealand earthquake multiple 20 20 crustal faults ruptured to the ground surface and seafloor in the 14 november 2016 m w mw 7 8 kaik ura earthquake and many have been documented in detail providing an opportunity to understand the factors controlling multifault ruptures including the role of the subduction interface we present a summary of the surface ruptures as well as previous knowledge including paleoseismic data and use these data and a 3d geological model to calculate cumulative geological moment magnitudes m g w mwg and seismic moments for comparison with those from geophysical datasets the earthquake ruptured faults with a wide range of orientations sense of movement slip rates and recurrence intervals and crossed a tectonic domain boundary the hope fault the maximum net surface displacement was 12 m 12 m on the kekerengu and the papatea faults and average displacements for the major faults were 0 7 1 5 m south of the hope fault and 5 5 6 4 m to the north m g w mwg using two different methods are m g w mwg 7 7 0 3 0 2 7 7 0 2 0 3 and the seismic moment is 33 67 of geophysical datasets however these are minimum values and a best estimate m g w mwg incorporating probable larger slip at depth a 20 km seismogenic depth and likely listric geometry is m g w mwg 7 8 0 2 7 8 0 2 suggests 32 32 of the moment may be attributed to slip on the subduction interface and or a midcrustal detachment likely factors contributing to multifault rupture in the kaik ura earthquake include 1 the presence of the subduction interface 2 physical linkages between faults 3 rupture of geologically immature faults in the south and 4 inherited geological structure the estimated recurrence interval for the kaik ura earthquake is 5 000 10 000 yrs 5 000 10 000 yrs and so it is a relatively rare event nevertheless these findings support the need for continued advances in seismic hazard modeling to ensure that they incorporate multifault ruptures that cross tectonic domain boundaries

pelagic sedimentation on rough seafloor topography 1 forward model this is the first paper in a four part sequence exploring the factors that govern the distribution of pelagic sediments in regions of the world mid ocean ridge system where basement outcrops and sediment deposits both contribute to local topography in this paper we present a simple numerical model of pelagic sedimentation in which sediments travel from topographic highs to lows with flux regulated by a diffusivity parameter by applying the forward model to realistic models of basement topography we investigate how various basement structures sediment rain rates and values of affect the morphology of the seafloor through time we quantify the effect of sedimentation as a nonlinear smoothing filter on topography which acts to reduce spectral power at high wavenumber to decrease the root mean square variability of topography to increase the spacing between hills and to lower the relative proportion of high slope seafloor we find that local accumulation rate is highly dependent on local topography and varies greatly with time we also find that sediment compaction does not contribute directly to the surface concavity exhibited by many intrahill sediment ponds

flow line variations in abyssal hill morphology for the pacific antarctic ridge at 65 s we present the results of a statistical study on the morphological characteristics of abyssal hills recently mapped along two adjacent segments of the pacific antarctic ridge at 65 s the studied area is a densely surveyed corridor 60 km wide by 600 km long which is centered on the pitman fracture zone pfz and extends to 12 ma crust on both sides of the ridge abyssal hill size parameters rms height h and characteristic width are estimated using hydrosweep multibeam data variations in abyssal hill characteristics are compared with spreading rate history and crustal structure as inferred from the mantle bouguer gravity in order to indirectly quantify the evolution of this ridge crest system the magnetic data document an abrupt acceleration in spreading rate from 36 to 63 mm yr full rate at chron 3a 5 7 6 4 ma our results indicate a statistically significant negative correlation between abyssal hill size parameters and full spreading rates abyssal hills formed during the slower spreading period ages 8 ma full rates 36 44 mm yr are 31 86 taller and 21 100 wider than hills created during the faster spreading interval ages 4 ma full rates 52 63 mm yr the well resolved positive correlation between h and is interpreted as an indication of temporal changes in the flexural rigidity of the lithosphere near the vicinity of the ridge crest and by implication axial thermal structure however we cannot rule out that such positive trend is due to constructional volcanism the lack of correlation between crustal thickness and abyssal hill size parameters is likely to be caused by the small magnitude of crustal thickness variations along flow lines 0 4 km in contrast to 2 km reported in previous studies for the mid atlantic ridge the most significant variations in crustal thickness are seen across the pfz thinning from north to south by 0 5 0 7 km which coincide with a well resolved increase in the averaged estimate the predictions of the detachment surface model in terms of morphological and structural inside outside comer asymmetries are not supported by our observations the main variations in h and that cannot be explained in terms of either the spreading rate or crustal thickness effect include the following 1 anomalously large abyssal hills north of the pfz for 4 6 ma age crust 2 abyssal hill size estimates for crustal ages greater than 8 ma show significant asymmetry for opposite ridge flanks north of the pfz and 3 toward the segment ends h estimates are 27 68 larger while estimates either do not significantly change to the north of the pfz or are up to 40 smaller to the south of the pfz we suggest that the h and changes seen toward the segment ends are related to either an increase in the amount of extension without a corresponding increase in the strength of the lithosphere or variations in the relative contribution of constructional volcanism to overall abyssal hill morphology

stochastic modeling of seafloor morphology inversion of sea beam data for second order statistics at scale lengths less than 100 km or so statistical descriptions of seafloor morphology can be usefully employed to characterize ridge crest processes off ridge tectonics and vulcanism sedimentation and postdepositional transport we seek to develop methods for the estimation of seafloor statistics that take into account the finite precision resolution and sampling obtained by actual echo sounding systems in this initial paper we restrict our attention to the problem of recovering second order statistics from data sets collected by multibeam devices such as sea beam the seafloor is modeled as a stationary zero mean gaussian random field completely specified by its two point covariance function we introduce an anisotropic two point covariance function that has five free parameters describing the amplitude orientation characteristic wave numbers and hausdorff fractal dimension of seafloor topography we formulate the general forward problem relating this model to the statistics of an ideal multibeam echo sounder in particular the along track autocovariance functions of individual beams and the cross covariance functions between beams of arbitrary separation using these second moments as data functionals we then pose the inverse problem of estimating the seafloor parameters from realistic noisy data sets with finite sampling and beamwidth and we solve this inverse problem by an iterative linearized least squares method the inversion method is applied to sea beam transit data from both the pacific and atlantic oceans sea beam system noise stands out as a sharp spike on the along track autocovariance function and can be modeled as a white noise process whose amplitude generally increases with beam angle the five parameters in our second order model can be estimated from the inversion of data sets comprising 100 200 km of track length in general the cross track wave number is the most poorly determined although uncertainties in the assumed sea beam response may bias the values of the fractal dimension using the assumed beamwidth the measured noise values and the seafloor parameters recovered from the inversion we generate sea beam synthetics whose statistical character can be directly compared with raw sea beam data for most of the track segments we have processed thus far the synthetics are similar to the data in the case of one atlantic profile however the comparison clearly indicates the necessity of incorporating higher order statistics the space domain procedures described in this paper can be extended for this purpose

late cretaceous and cenozoic seafloor and oceanic basement roughness spreading rate crustal age and sediment thickness correlations abstract single channel seismic data from the south australian basin and argentine basin and bathymetry data from the flanks of the mid atlantic ridge east pacific rise and southwest indian ridge are analysed to determine the root mean square rms roughness of the seafloor and oceanic basement created at seafloor spreading rates ranging from 3 to 80 km ma half rate for these data crustal ages range from near zero to 85 ma and sediment thicknesses range from near zero to over 2 km our results are consistent with a negative correlation of basement roughness and spreading rate where roughness decreases dramatically through the slow spreading regime

possible dual earthquake landslide source of the 13 november 2016 kaikoura new zealand tsunami a complicated earthquake m w 7 8 in terms of rupture mechanism occurred in the ne coast of south island new zealand on 13 november 2016 utc in a complex tectonic setting comprising a transition strike slip zone between two subduction zones the earthquake generated a moderate tsunami with zero to crest amplitude of 257 cm at the near field tide gauge station of kaikoura spectral analysis of the tsunami observations showed dual peaks at 3 6 5 7 and 5 7 56 min which we attribute to the potential landslide and earthquake sources of the tsunami respectively tsunami simulations showed that a source model with slip on an offshore plate interface fault reproduces the near field tsunami observation in terms of amplitude but fails in terms of tsunami period on the other hand a source model without offshore slip fails to reproduce the first peak but the later phases are reproduced well in terms of both amplitude and period it can be inferred that an offshore source is necessary to be involved but it needs to be smaller in size than the plate interface slip which most likely points to a confined submarine landslide source consistent with the dual peak tsunami spectrum we estimated the dimension of the potential submarine landslide at 8 10 km

creep in pelagic sediments and potential for morphologic dating of marine fault scarps cores from the flanks of the galapagos spreading centre show that the top 25 cm of pelagic sediments is highly bioturbated kenyan and turcotte 1985 have proposed that bioturbation may cause down slope creep of the sediment surface and bioturbation may therefore smooth sediment topography in a similar way to hillslope creep on land assuming this produces movement consistent with the diffusion transport model sediment topography across scarp crests digitised from deep tow profiler records is modelled with a simple analytic solution to the diffusion equation and with a mean diffusion constant k of 0 007 m yr this small value suggests creep rates are modest for example 2 cm yr for a 30 slope and is an upper bound since sediment avalanching and bottom currents probably also remove sediment from scarp crests although requiring further work these results suggest that morphologic dating methods may be applicable to marine fault scarps and could be useful in relatively sediment free areas such as mid ocean ridges where it is commonly not possible to use datable offset seismic horizons

a semi quantitative model for fractionation of rhyolite from rhyodacite in a compositionally altered archean volcanic complex superior province canada abstract the phinncy dash lakes complex pdlc of the western wabigoon subprovince northwestern ontario consists of subvolcanic and pyroclastic rhyodacite subordinate rhyolite pyroclastic rocks and lava flows minor intercalated basalt lava flows and related clastic and chemical sediments which have been metamorphosed to low greenschist grade the basalt lying stratigraphically below the complex is intruded by tonalite that is coeval with the felsic volcanic rocks rhyolite in pdlc differs from the associated rhyodacite by containing k feldspar and having lower la yb ratios negative eu anomalies and generally lower fe mg ca ti al p zr sc and cr but higher si k rb ba and nb major and trace element calculations using estimates of rhyodacite and rhyolite primary phenocryst compositions and estimates of partition coefficients were done to determine if the rhyolite may have been generated by fractional crystallization from the rhyodacite it was found that fractionation of plagioclase clinopyroxene quartz and small amounts of apatite zircon allanite and fe ti oxides from the rhyodacite would produce a composition similar to the rhyolite only if the abundances of the mobile elements si ca na sr ba and mg in the rhyodacite initial composition were adjusted from the measured values if the rhyolite fractionated from the rhyodacite then there must have been a net addition of si 2 net depletion of ca na sr and ba and 3 net depletion of mg but conservation of fe in the rhyodacite during synvolcanic alteration or regional metamorphism these inferences are supported by thin section evidence of 1 addition of quartz in microfractures and groundmass 2 breakdown of primary plagioclase and 3 breakdown of primary mafic silicates plots of mgo versus tio2 and feo versus tio2 also demonstrate that by comparison with the nearby and coeval kishkutena tonalite mg is depleted and fe is conserved in the pdlc rocks the secondary mineral assemblages combined with the apparent chemical reconstitution suggest that during alteration of the pdlc rocks 1 the water to rock ratio was small 2 the fluid temperature was low probably below about 300 c 3 if the temperature and water to rock ratio were large however then the fluid source was probably not seawater because of the limited precipitation of mg to the rocks

evolution and tectonic significance of intermediate to felsic plutonism associated with the hemlo greenstone belt superior province canada abstract plutonic rocks from the hemlo area in the southern superior province span a period from ca 2720 to 2677 ma early ttg plutons intruded into lower basaltic volcanic sequences and were probably derived from melting of basaltic crust at upper mantle depths they predate major regional deformation and span ages from 2719 to 2697 ma felsic to intermediate volcanism 2697 2688 ma partially overlaps ttg plutonism but is mostly slightly younger and lacking plutonic equivalents regional deformation and metamorphism of the greenstone belt and ttg plutons progressed rapidly following deposition of the youngest supracrustal rocks syn to late tectonic plutons emplaced between 2684 and 2677 ma have a distinctive dual primitive evolved character that is interpreted to reflect their derivation by direct melting of long term depleted mantle that was metasomatically enriched in a wide range of lile and hfse this secular evolutionary change in the nature of intermediate to felsic plutonism at hemlo and its relationship to regional deformation and metamorphism parallels that occurring more regionally within the superior province and is interpreted to be the consequence of a transition in the nature of large scale tectonic processes intermediate to felsic magmatism within a protracted period of volcanism and ttg plutonism originated primarily by melting of subducted basaltic crust probably in an oceanic arc related environment the termination of this style of magmatic activity and initiation of regional deformation and metamorphism at ca 2688 ma is interpreted to be a consequence of collisional orogeny the petrogenetic characteristics of the latest period of magmatism at 2684 2677 ma requires that the melting regime migrate into sub arc lithospheric mantle that was metasomatized during the earlier magmatic stage slab breakoff following terrane accretion is suggested as one possible mechanism for the abrupt termination of ttg magmatism and ensuing rapid and progressive introduction of large amounts of heat into sub arc mantle and basal portions of the crust this pattern of development is seen in many superior province greenstone belts but is older in the north therefore it is probably an inevitable consequence of the tectonic processes that led to accretion of the superior province

a stochastic model for the creation of abyssal hill topography at a slow spreading center the present study is an attempt to model abyssal hill topography i e the randomly varying topography that is superimposed on the subsidence of the ocean floor due to thermal contraction we assume that abyssal hill topography is created by faulting and that it can be represented as the convolution of a series of stochastic fault offsets with a fault impulse response as a constraint the power spectrum of the model generated topography will have to resemble the power spectrum of a profile of abyssal hill topography across a typical slow spreading ridge such as found in the south atlantic using a series of fault offsets positively correlated in space and fault impulse responses limited to a finite width w profiles that statistically resemble abyssal hill topography have been generated if the fault offsets are constrained to be positive i e to cause uplift the synthetic profiles contain a steady state depression at the axis the fit of the synthetically derived topography to the observed topography is very sensitive to the width w of the fault impulse response our results suggest that the effects of a faulting event must be limited to distances of about 3 5 km and that tectonic activity must take place in the immediate vicinity of the inner wall of the axial valley if faulting is indeed the process that creates abyssal hill topography the best fit flexural impulse response to faulting implies a flexural rigidity of 5 1017 n m if instead constructional volcanism contributes significantly to the topography our study suggests that the emplacement of volcanic constructions must also take place within a narrow width w about the axis

age and isotopic composition of late archean leucogranites implications for continental collision in the western superior province u pb and sm nd isotopic data are presented for leucogranites and pegmatites from the boundary zones of the english river winnipeg river and wabigoon subprovinces in the late archean superior prov

optimum sea surface displacement and fault slip distribution of the 2017 tehuantepec earthquake m w 8 2 in mexico estimated from tsunami waveforms

quantitative comparison of bathymetric survey systems spatially coincident deep tow sea beam and seamarc ii bathymetric data are statistically analyzed to determine the scales at which each system is reliable for mapping seafloor features the methods we employ including ruler measures of contours and profiles and the covariance function and power spectrum of profiles allow us to investigate the size of features measured as a function of scale

accretion of japanese island arcs and implications for the origin of archean greenstone belts the present day region of arc arc collision between the izu bonin arc and mainland japan honshu arc in the western pacific called the izu collision zone or icz provides a useful kinematic model for the development of many archean greenstone belts the compositional assemblage thermal structure and structural style of the crust in the icz are very similar to those inferred for many archean greenstone belts in both cases thick young and flaky arc crust with a high heat flux is in collision with another crustal block the icz has resulted in the imbrication of very thick slices of crust and associated sediments juxtaposed against older accretionary prisms many archean greenstone belts show similar geological features and we suggest that the incremental imbrication of the crust was a common tectonic style in some archean convergent margins

oxygen isotope ratios of archean plutonic zircons from granite greenstone belts of the superior province indicator of magmatic source zircons commonly preserve primary magmatic oxygen isotope ratios even through high grade metamorphic events unlike quartz which more readily loses its primary 18o value by subsolidus exchange intrusive bodies from the superior province canada have an average 18o zircon of 5 8 0 6 n 59 rocks those from granite greenstone belts have an average 18o zrc 5 8 0 6 n 55 in contrast to those from metasedimentary belts that average 18o zrc 6 7 0 2 n 4 the 18o zircon values from granite greenstone belts indicate a maximum allowable input of 14 supracrustal high 18o material into archean magmas of the superior province relative to mantle 18o values igneous bodies of the superior province have been separated into two groups based on geochemistry unenriched plutons and sanukitoids magmatic oxygen isotope ratios inferred from these zircons indicate up to a subtle but significant division of 1 between the two geochemical sets of rocks this distinction is apparent only in the 18o zrc and not in more commonly analyzed less refractory minerals such as quartz and feldspar oxygen isotope data correlate with geochemical modeling of sanukitoids the average 18o zrc for sanukitoids is 6 4 0 2 in comparison to 5 5 0 4 for unenriched plutons there is almost no overlap in values the elevation of sanukitoid 18o zrc indicates input from a high 18o source such as fluids from the subducting oceanic crust melts of subducted sediments or continental crust all of the plutons analyzed in this study have been dated by u pb zircon techniques and the combination of u pb ages and 18o zrc indicates little variability of 18o versus age during archean plutonism in the superior province therefore recycling of sediments and other high 18o sources was not a dominant process during crustal growth from 3003 to 2670 ma in the superior province

contrasting types of late archean plutonic rocks in northwestern ontario implications for crustal evolution in the superior province abstract the late archean aulneau and lount lake batholiths have contrasting geochemical characteristics that are interpreted to be a consequence of derivation from different sources the aulneau batholith which was intruded into low grade metavolcanic rocks of the wabigoon subprovince is characterized by high na2o and low k2o rb and y together with enriched light rare earth elements lree near chondritic heavy rare earth elements hree negligible eu anomalies and mantle type initial sr and nd isotopic compositions these geochemical characteristics are consistent with derivation from the partial melting of metamorphosed tholeiitic basalt in contrast the lount lake batholith which was intruded into older 2 83 3 17 ga tonalitic plutonic rocks of the winnipeg river subprovince has relatively high k2o rb y and ree low na2o and prominent eu anomalies the initial sr and nd isotopic compositions of the lount lake batholith are consistent with a crustal source at least 200 400 ma older than the crystallization age of the batholith these geochemical characteristics indicate that the lount lake batholith originated from the partial melting of deeper level equivalents of the tonalitic metaplutonic rocks 2 83 3 17 ga which they intrude these results suggest that reworked 3 0 ga crust may be extensive in the winnipeg river subprovince and that the geochemical and isotopic signature of late archean plutonic rocks may be a useful reconnaissance tool in the identification of areas of extensive older crust the results can be interpreted within a uniformitarian model diachronous ensimatic magmatic arcs represented by the winnipeg river and western wabigoon subprovinces developed independently collision of these arcs at 2707 8 ma marks the cessation of subduction and related magmatic activity and the initiation of high grade metamorphism and melting in tectonically thickened portions of the crust

polyphase deformation and crustal evolution in the pipestone lake area of the archean wabigoon subprovince superior province canada archean supracrustal rocks in the western wabigoon subprovince superior province canadian shield have undergone four phases of deformation d1 d4 d1 confined to the oldest rocks includes a large refolded reclined isoclinal anticline f1 with moderately developed axial planar cleavage s1 rocks affected by d1 are overlain by a regional unconformity d2 includes post unconformity steeply plunging north northeast south southwest striking isoclinal folds f2 that are approximately coaxial with f1 but have contorted the f1 axial trace d3 is represented by east west striking steeply plunging folds at various scales f3 which occur mainly in rocks near the regional manitou stretch pipestone lake shear zone also interpreted to be a d3 structure d4 is represented by pervasive cleavage s4 locally penetrative but mainly spaced including crenulation cleavage fractures small faults and brittle ductile shears s4 is parallel to the margin of the jackfish lake pluton d1 d3 are ascribed to convergence of the wabigoon subprovince with adjacent subprovinces ending with formation of the manitou stretch pipestone lake shear zone as a presently steep thrust and oblique ramp structure d4 is the result of either diapiric emplacement of the jackfish lake pluton or marginal strain intensification due to the rigidity of the older ash bay dome during late north south compression previously available zircon u pb geochronology provides a maximum age for d1 of 2728 ma and an approximate age for d4 of 2698 ma the unconformity developed between d1 and d2 2725 2713 ma