fold origin of the ne lobe of the sudbury basin canada evidence from heterogeneous fabric development in the onaping formation and the sudbury igneous complex structural analysis of the onaping formation a heterolithic impact melt breccia and the granophyre in the ne lobe of the 1 85 ga sudbury igneous complex sic assist in understanding the formation of the sudbury basin previously the lack of mesoscopic strain fabrics in the sic in contrast to pervasive fabrics in the onaping formation of the ne lobe led to interpretations of the shape of the ne lobe as primary we demonstrate that the structures of the onaping formation are consistent with deformation in a fold core controlled by the mechanically stronger granophyre of the ne lobe evidence for this interpretation includes the 1 presence of open structural domes and basins 2 geometry of planar mineral shape fabrics 3 variation in shape fabric intensity and 4 kinematics of prominent faults folding of the onaping formation affected the sic because fold geometry is based on dip data in the sic and fold related faults cut both the onaping formation and granophyre microstructural observations point to different temperatures during deformation in both units that are consistent with initiation of folding during cooling of the sic upon reaching middle greenschist facies metamorphic conditions

ground motion attenuation relationships for cascadia subduction zone megathrust earthquakes based on a stochastic finite fault model the number of strong ground motion recordings available for regression analysis in developing empirical attenuation relationships has rapidly grown in the last 10 years however the dearth of strong motion data from the cascadia subduc tion zone has limited this development of relationships for the cascadia subduction zone megathrust which can be used in the calculation of design spectra for engi neered structures a stochastic finite fault ground motion model has been used to simulate ground motions for moment magnitude m 8 0 8 5 and 9 0 megathrust earthquakes along the cascadia subduction zone for both rock and soil site condi tions the stochastic finite fault model was validated against the 1985 m 8 0 mi choacan mexico and the 1985 m 8 0 valpariso chile earthquakes these two subduction zone megathrust earthquakes were recorded at several rock sites located near the fault rupture for the cascadia megathrust earthquakes three different rup ture geometries were used to model the m 8 0 8 5 and 9 0 events the geometries only differ in their respective fault lengths a fault dip of 9 to the east with a rupture width of 90 km was selected to represent average properties of the cascadia sub duction zone geometry a regional crustal damping and velocity model was used with the stochastic finite fault model simulations ground motions were computed for 16 site locations the parametric uncertainties associated with the variation in source path and site effects were included in the development of the ground motions a functional form was fit to the ground motion model simulations to develop region specific attenuation relationships for the cascadia megathrust rupture zone for both rock and soil site conditions the total uncertainty was based on a combination of the modeling and parametric uncertainties sigmas these newly developed atten uation relationships for cascadia subduction zone megathrust earthquakes can be used in both the probabilistic and deterministic seismic hazard studies for engineer ing design for the pacific northwest

superimposition of a thrust transfer fault system on a large impact structure implications for ni cu pge exploration at sudbury a 2 0 km wide metamorphic aureole has been mapped beneath the northern margin of the 2 5 km thick sudbury igneous complex of the 1 85 ga sudbury impact structure the aureole is difficult to observe in the field because it overprints archean granitoids and high grade polydeformed gneisses which do not yield diagnostic thermal minerals at the macroscopic scale however detailed petrography and electron microscopy reveal four zones albite epidote 1 000 m wide hornblende 900 m and pyroxene 200 m hornfels facies and an innermost zone of partial melting 25 m using metamorphic isograds as markers we have revealed previously undetected thrust faults between the sudbury igneous complex and the archean footwall we demonstrate that in places all or part of the aureole has been overthrust and obscured at surface thrust units are segmented by northwest trending strike slip faults which together form thrust transfer fault systems that were active after the impact melt sheet had solidified this post impact deformation is attributed to late penokean 1 85 ga and possibly grenvillian 1 ga compression overthrusting of the footwall by the sudbury igneous complex may conceal sublayer footwall breccia and embayment units that are traditionally the hosts of massive ni cu sulfides and related platinum group element deposits an example is provided by the ministic offset dike located in the west of the sudbury basin which as an intrusion derived from the impact melt is atypical in not being associated with an exposed embayment structure

constraints on central uplift structure from the manicouagan impact crater recent drilling operations at the 90 km diameter late triassic manicouagan impact crater of quebec canada have provided new insight into the internal structure of a complex craters central region previous work had indicated that the impact event generated a 55 km diameter sheet of molten rock of relatively consistent originally 400 m thickness floran et al 1978 the drilling data reveals melt sheet thicknesses of up to 1500 m with kilometer scale lateral and substantial vertical variations in the geometry of the crater floor beneath the melt sheet the thickest melt section occurs in a 1500 m deep central trough encircled by a horseshoe shaped uplift of precambrian basement the uplift constitutes a modified central peak structure at least part of which breached the melt sheet mineralogical and compositional segregation differentiation of the thicker melt sheet section coupled with a lack of fractionation in the thinner units shows that the footwall geometry and associated trough structure were in place prior to melt sheet solidification marked lateral changes in sub melt sheet basement relief support the existence of a castellated footwall that was created by high angle impact related offsets of 100s to 1000s of meters this indicates that deformation during the modification stage of the cratering process was primarily facilitated by large displacement fault systems this work suggests that manicouagan is a central peak basin with rings which does not appear to fit with current complex crater classification schemes

new insights on the tectonics along the new hebrides subduction zone based on gps results 1 at the new hebrides nh subduction zone ridges born by the subducting australia plate enter the trench and collide with the overriding margin results from gps surveys conducted on both sides of the trench and new bathymetry maps of the nh archipelago bring new light on the complex tectonics of this area convergence vectors present large variations that are not explained by australia pacific a p poles and that define four segments vectors remain mostly perpendicular to the trench and parallel to the earthquake slip vectors slow convergence i e 30 40 mm yr is found at the central segment facing the d entrecasteaux ridge the southern segment moves faster than a p motion predicts 89 to 124 mm yr relatively to a western north fiji basin wnfb reference the northern and southern segments rotate in opposite directions consistently with the extension observed in the troughs east of both segments both rotations combine in central vanuatu into an eastward translation that bulldozes the central segment into the wnfb at 55 mm yr that model suggests that the motion of the central segment forced by the subduction collision of the d entrecasteaux ridge influences the motion of the adjoining segments the new caledonia archipelago is motionless with respect to the rest of the australia plate despite the incipient interaction between the loyalty ridge and the nh margin southeast of the interaction area convergence is partitioned into a 50 mm yr trench normal component accommodated at the trench and a 90 mm yr trench parallel component close to the a p convergence and presumably accommodated by a transform boundary at the rear of the nh arc

unusual braarudosphaera bigelowii and micrantholithus vesper enrichment in the early miocene sediments from the slovenian corridor a seaway linking the central paratethys and the mediterranean abstract during a stratigraphic survey of an early miocene sedimentary sequence outcropping in se slovenia an unusual enrichment of the calcareous nannoplankton assemblage with pentaliths pentagonal nannoliths consisting of five crystal units and showing radial symmetry was detected pentaliths were only abundant in a short interval which was sampled in detail the lithological composition of this interval was indistinguishable from that of the underlying and the overlying strata the composition of nannoplankton assemblages and distribution patterns of different taxa were studied mineral composition total calcite content and 13c values of chosen sediment samples were analysed as well the pentalith enriched strata were deposited in the lower early miocene corresponding to the egerian stage of the central paratethys and the aquitanian of the mediterranean in the slovenian corridor a seaway linking the central paratethys and the mediterranean the presence of rare specimens of discoaster druggii and helicosphaera carteri allows stratigraphic correlation with the transition of nn1 triquetrorhabdulus carinatus zone and nn2 discoaster druggii zone of martini martini e 1971 standard tertiary and quarternary calcareous nannoplankton zonation in farinacci a ed proceedings of the ii planctonic conference roma 1970 ed technoscienza pp 739 785 pentaliths belong to two species braarudosphaera bigelowii and micrantholithus vesper both species display a wide range of morphological variation and most likely represent a group of sibling species the pattern of distribution of both species displays obvious similarities throughout most of the studied interval in the upper part of the studied interval b bigelowii reaches maximum abundance while m vesper disappears since the ability of b bigelowii to thrive in hyposaline water is well known it appears that m vesper tolerates reduced water salinity as well but to a lesser extent than b bigelowii no significant paleoclimatic and paleogeographical changes are known in this particular region during the early miocene however the onset of far reaching extensional tectonic processes took place during this time the enrichment of nannoplankton assemblage with pentaliths may represent a reflection of a short lived episode of hyposaline conditions enhanced influx of freshwater and terrigenous material is indicated by a drop in 13c values a rise in nannoplankton productivity and the presence of sand in some samples from the pentalith enriched strata the most likely causes of this episode are regional tectonic changes associated with the onset of intensive tectonic activity in the western part of the central paratethys

vredefort sudbury chicxulub three of a kind vredefort sudbury and chicxulub are the largest known terrestrial impact structures all have been cited as multi ring basins the available data indicate that all have some form of multiple ring attributes most commonly structural features chicxulub however is the only example with morphological ring features there are also commonalities in the structural and lithological features of vredefort and sudbury and it is possible to construct a generalized compilation of the character of 200 300 km diameter impact basins on earth it is not clear however that any of these structures had the original morphological characteristics of large lunar multi ring basins additional data and synthesis are required to fully characterize these structures in order to realize their potential to constrain large scale cratering processes if this is not sufficient incentive for further studies the environmental effects of chicxulub aside the vredefort sudbury and chicxulub impact events are also the reason for

crater floor topography and impact melt sheet geometry of the sudbury impact structure canada terra nova 00 000 000 2010 abstract based on high resolution topography data and the geometry of geological contact traces at the surface we determined the orientation of layer interfaces of the sudbury igneous complex sic our analysis provides for the first time quantitative structural evidence for the thickness variation of its layers which supports an impact melt origin of the sic the present crater floor topography varies up to 400 m over distances of hundreds of metres to a few kilometres and up to 1500 m over a distance of about 25 km crater floor depressions are spatially associated with economically important sulphide mineral deposits which points to a viable exploration strategy finally observed variations in the width of the thermal aureole imparted by the sic on its host rocks are due to primary thickness variations of the sic rather than post impact deformation

observations and interpretations at vredefort sudbury and chicxulub towards an empirical model of terrestrial impact basin formation the structural topographic and other characteristics of the vredefort sudbury and chicxulub impact structures are described assuming that the structures originally had the same morphology the observations interpretations for each structure are compared and extended to the other structures this does not result in any major inconsistencies but requires that the observations be scaled spatially in the case of vredefort and sudbury this is accomplished by scaling the outer limit of particular shock metamorphic features in the case of chicxulub scaling requires a reasoned assumption as to the formation mechanism of an interior peak ring the observations interpretations are then used to construct an integrated empirical kinematic model for a terrestrial peak ring basin the major attributes of the model include a set of outward directed thrusts in the parautochthonous rocks of the outermost environs of the crater floor some of which are pre existing structures that have been reactivated during transient cavity formation inward directed motions along the same outermost structures and along a set of structures at intermediate radial distances during transient cavity collapse structural uplift in the center followed by a final set of radially outward directed thrusts at the outer edges of the structural uplift during uplift collapse the rock displacements on the intermediate inward and innermost outward sets of structures are consistent with the assumption that a peak ring will result from the convergence of the collapse of the transient cavity rim area and the collapse of the structural uplift

the δ15n of nitrate in the southern ocean nitrogen cycling and circulation in the ocean interior we report analyses of the nitrogen isotopic composition of nitrate in the eastern indian and pacific sectors of the southern ocean in this paper we focus on the subsurface data as well as data from the deep waters of other ocean basins nitrate 15n is relatively invariant in much of the abyssal ocean i e below 2 5 km with a value of 4 8 0 2 observed in lower circumpolar deep water north atlantic deep water and central pacific deep water the isotopic invariance of deep ocean nitrate stems fundamentally from the completeness of nitrate utilization in most of the global surface ocean the southern ocean surface being an important exception in the subantarctic zone north of the polar frontal zone the nitrate 15n of upper circumpolar deep water is 0 7 greater than that of lower circumpolar deep water this isotopic enrichment appears to result from denitrification in the low latitude water masses with which upper circumpolar deep water communicates the isotopic enrichment of upper circumpolar deep water is diminished in the antarctic probably because of the remineralization of sinking organic n which has a low 15n in the antarctic relative to the other water masses of the southern ocean the subantarctic thermocline has a very low nitrate 15n for its nitrate concentration because of exchange with the low latitude thermocline where this isotopic signature appears to originate this signature of the low latitude thermocline has two probable causes 1 mixing with low nitrate surface water and 2 the oxidation of newly fixed n

magnetic fabric and microstructural evidence for a tectono thermal overprint of the early proterozoic murray pluton central ontario canada abstract the 2 38 ga old murray granite pluton intruded the southern footwall of the sudbury igneous complex and was subjected to repeated ductile deformation its nw and se domains display differences in strain state ams signature and the nature and distribution of fe oxide minerals the magnetic foliation is parallel to the visible foliation in the nw domain but discordant to it in the se domain microstructural data show that the magnetic fabric in the nw domain coincides with a foliation formed at high temperature probably in response to thermal softening during the emplacement of the adjacent sudbury igneous complex this tectono thermal overprint affected pre existing shape fabrics and was facilitated by incipient melting of the granite near the intrusive contact with the sudbury igneous complex rocks of the se domain are only partially overprinted and two mineral subfabrics are preserved prolate susceptibility ellipsoids and clusters of maximum susceptibility directions at the intersections of the two planar fabrics suggest oblique superposition of strain increments increases in bulk magnetic susceptibility and magnetic anisotropy degree towards the intrusive contact with the sudbury igneous complex can be explained by respective increases in the proportion of magnetite over ilmenite and strain intensity in the murray pluton

the mw 7 5 1999 ambrym earthquake vanuatu a back arc intraplate thrust event 1 on 26 november 1999 a mw 7 5 thrust earthquake occurred in the vanuatu back arc seismic zone the aftershocks seismicity defines a west dipping plane down to a depth of 20 km consistent with the focal mechanism geometry the shallow focal depth of the main shock and the coincidence of the surface projection of the plane of aftershocks with a 600 m high sea bottom fault scarp indicate the fault plane ruptured up to the surface the size of the fault has been estimated to 50 25 km2 from the aftershocks distribution and modeling of coseismic vertical motion inferred from biological markers the inferred length indicates the rupture affected the whole ambrym segment but inversion of gps horizontal displacement data indicates most of the seismic moment has been released on a smaller 35 20 km2 fault surface with an average slip of 6 5 m foreshock and aftershock seismicity are organized in planar seismic zones parallel to the inferred main shock rupture plane this spatiotemporal distribution of imaged fault suggests that the thrust front propagates in times by eastward jumps to new intraplate faults occurring in the western edge of the north fiji basin the back arc present setting could eventually represent the very early stages of an incipient subduction zone with reverse polarity the intraplate fault model yields shortening by thickening of the back arc crust using crustal balanced sections to model the deformations over the last 1 8 m y period a maximum shortening of 55 km has been found

abrupt increase in seasonal extreme precipitation at the paleocene eocene boundary a prominent increase in atmospheric co at the paleocene eocene boundary ca 55 ma led to the warmest earth of the cenozoic for similar to 100 k y high resolution studies of continental flood plain sediment records across this boundary can provide crucial information on how the hydrological cycle responds to rapidly changing co2 here we show from continental records across the paleocene eocene boundary in the spanish pyrenees a subtropical paleosetting that during the early most intense phase of co2 rise normal semiarid coastal plains with few river channels of 10 200 m width were abruptly replaced by a vast conglomeratic braid plain covering at least 500 km 2 and most likely more than 2000 km 2 this braid plain is interpreted as the proximal parts of a megafan carbonate nodules in the megafan deposits attest to seasonally dry periods and together with megafan development imply a dramatic increase in seasonal rain and an increased intra annual humidity gradient the megafan formed over a few thousand years to similar to 10 k y directly after the paleocene eocene boundary only repeated severe floods and rainstorms could have contributed the water energy required to transport the enormous amounts of large boulders and gravel of the megafan during this short time span the findings represent evidence for considerable changes in regional hydrological cycles following greenhouse gas emissions less

untangling the palaeocene climatic rhythm an astronomically calibrated early palaeocene magnetostratigraphy and biostratigraphy at zumaia basque basin northern spain abstract the magnetostratigraphy of a 54 m long section above the cretaceous tertiary boundary at the sea cliff section of zumaia in the basque basin northern spain has been established the section encompasses the entire danian and the lower part of the selandian stages as indicated by calcareous plankton biostratigraphy the studied interval consists of hemi pelagic limestone marl alternations in the form of couplets and bundles which range from centimetre decimetre to metre scale respectively and a few thin bedded calcareous turbidites the magnetostratigraphy based on samples from about 200 stratigraphic levels allows the identification of six reversal boundaries from chron c29r to c26r at a bed level the spatial or temporal evolution of periodicities from a lithologically coded series is studied with the continuous wavelet transform technique a preliminary age model based on the standard ck95 gpts indicates that the basic lithologic carbonate marl couplet corresponds to the 19 23 kyr precession cycle 21 31 cm cycle in the depth domain and that a bundle cycle usually groups of four to six basic couplets with global periodicity centred at 1 22 m corresponds to the 110 kyr eccentricity cycle we have tuned the bundle cycles to the va03 r7 eccentricity orbital solution astrophys j 592 2003 620 630 following an initial match of a node of the 2 4 ma eccentricity modulatory cycle in the target time series to particularly carbonate rich bundles from the upper part of the zumaia section that displays significant power of a 4 4 m period cycle corresponding to the 404 kyr eccentricity cycle consistency between lithologic patterns and characteristics in the eccentricity target is reasonably met although the 404 kyr eccentricity cycle is not persistent throughout the tuning however appears robust as it brings the age of the k t boundary at 65 8 ma it is argued that a sea level signal tectonically driven is superimposed on the climatic forcing at the milankovitch band masking the full expression of the low frequency astronomical periods we provide a cycle tuned duration for all intervening early palaeocene polarity chrons and estimate relative ages for bioevents the cycle tuned chronology indicates that the ck95 gpts overestimates the duration of chrons c28 and c27 by 20 and 26 respectively our data may prove useful to better constrain early palaeocene biostratigraphy of calcareous plankton and in the redefinition of the boundary between the danian and selandian stages

structural characteristics of the sudbury impact structure canada impact induced versus orogenic deformation a review orogenic deformation both preceding and following the impact event at sudbury strongly hinders a straightforward assessment of impact induced geological processes that generated the sudbury impact structure central to understanding these processes is the state of strain of the sudbury igneous complex the solidified impact melt sheet its underlying target rocks overlying impact breccias and post impact sedimentary rocks this review addresses 1 major structural metamorphic and magmatic characteristics of the impact melt sheet and associated dikes 2 attempts that have been made to constrain the primary geometry of the igneous complex 3 modes of impact induced deformation as well as 4 mechanisms of pre and post impact orogenic deformation the latter have important consequences for estimating parameters such as magnitude of structural uplift tilting of pre impact huronian strata and displacement on major discontinuities which collectively have not yet been considered in impact models in this regard a mechanism for the emplacement of offset dikes is suggested that accounts for the geometry of the dikes and magmatic characteristics as well as the occurrence of sulfides in the dikes moreover re interpretation of published paleomagnetic data suggests that orogenic folding of the solidified melt sheet commenced shortly after the impact uncertainties still exist as to whether the sudbury impact structure was a peak ring or a multi ring basin and the deformation mechanisms of rock flow during transient cavity formation and crater modification

seismic recurrence intervals and timing of aseismic subduction inferred from emerged corals and reefs of the central vanuatu new hebrides frontal arc the recognition and dating of corals that have been killed by tectonic uplift allow us to date paleoseismic uplifts in the vanuatu island arc we recognize corals that record paleouplifts by their similarity to those known to have died during contemporary sudden uplifts and date them 1 by counting annual coral growth bands only if part of the coral is alive at the time of collection or 2 by newly developed techniques for obtaining 230 th ages by mass spectrometry the mass spectrometric method produces isotopic ages with precisions of 3 to 9 years 2 in the 0 1000 years b p time range the 230 th ages in this time range appear to be accurate samples whose ages are known by counting coral growth bands give 230 th ages that are indistinguishable from their growth band ages by dividing the average increment of uplift for the latest holocene uplifts by the mean holocene uplift rate we can estimate average seismic uplift recurrence intervals for the past 6000 years the results for each of four central vanuatu arc segments are 1 north santo emerged 1 2 m in 1866 a d and 0 6 m 107 years later in 1973 a d the average coseismic uplift of 0 9 m and mean holocene uplift rate of 4 3 mm yr 1 suggest a longer recurrence interval of 212 years 2 south santo emerged 0 29 m in 1946 and 0 26 m 19 years later in 1965 including the related 1971 event here the mean holocene uplift rate is 5 5 mm yr 1 the uplift data suggest a longer average recurrence interval of about 51 years 3 north malekula emerged 1 23 m near 1729 a d and 1 05 m 236 years later in 1965 the mean holocene uplift rate of 2 7 mm yr 1 and mean coseismic uplift of 1 14 m for dated events suggest a longer recurrence interval of 422 years 4 part of southernmost malekula has uplifted continuously or episodically by about 0 35 m from about 1957 until at least mid 1983 a d the maximum uplift of 2 7 mm yr 1 occurs near a nest of small earthquakes both the earthquakes and rapid uplift suggest that interplate slip beneath south malekula may be continuous rather than episodic episodes of 0 35 m uplift would have to recur every 130 years to maintain the 2 7 mm yr 1 uplift rate in contrast we find no evidence of interseismic vertical movements for the other three blocks the most reasonable interpretation of these results is that the seismic recurrence intervals and processes for accommodation of slip are quite different on adjacent arc segments we have used the most widely accepted moment magnitude relationship to evaluate the accumulated seismic slip caused by large earthquakes occurring since 1920 in all four arc segments this analysis suggests that the seismically radiated moments account for less than one third to one tenth of the slip associated with plate convergence the similarity between the paleoseismic record of uplifts and the contemporary record of coseismic uplifts suggests that this analysis can be generalized to times before 1920 for the northern three segments of central vanuatu aseismic slip probably occurs in the same years as large earthquakes because the contemporary coral record records uplifts only in years having large historic earthquakes this suggests that aseismic slip is not continuous and does not occur at rates which vary slowly over the course of the earthquake cycle the south santo segment may have the highest proportion of seismic slip because the mean recurrence interval of 51 years is shortest and the mean holocene uplift rate of at least 5 5 mm yr 1 is the fastest

upper crustal basement involved folding in the east range of the sudbury basin ontario inferred from paleomagnetic data and spatial analysis of mafic dykes tilting of crystalline basement rocks associated with folding strain at uppermost crustal levels is difficult to recognize if basement rocks are devoid of traceable marker planes here we use the spatial variation in strike of paleoproterozoic mafic dyke segments complemented by compiled paleomagnetic data to identify tilting in archean basement rocks associated with kilometre scale folds of the eastern sudbury basin ontario spatial analysis of the strike of dyke segments is consistent with generation of the ne lobe and a newly identified anticline referred to as the west bay anticline in the layered sudbury igneous complex sic this anticline accounts better for the structural characteristics of the eastern sudbury basin than a previously proposed anticline with west plunging hinge line the west bay anticline is characterized by abrupt plan view thickness variations in the lower sic and curved faults displaying significant strike separations of sic contacts these structural characteristics are co

paleocene oceanography of the eastern subtropical indian ocean an integrated magnetobiostratigraphic and stable isotope study of odp hole 761b wombat plateau surface and deep water circulation patterns in the eastern indian ocean during the paleocene epoch are inferred based on an integrated magnetobiostratigraphic and stable isotope investigation of ocean drilling program hole 761b drilled on the wombat plateau a combination of magnetostratigraphy biostratigraphy and isotope stratigraphy demonstrates that numerous deep sea sites that have been considered to show continuous or nearly continuous sedimentation through the paleocene are punctuated by a series of hiatuses some of which exceeding a duration of 1 myr therefore our study is based on a detailed temporal interpretation of the stratigraphic successions we used for paleoceanographic reconstructions we compare detailed planktonic and benthic foraminiferal carbon and oxygen isotope records from hole 761b with several temporally correlative records published from different oceanic provinces in order to distinguish between local and global patterns within the eastern indian ocean although site 761 was situated at low latitudes during the paleocene its surface waters were predominantly influenced by circulation originating from the southern ocean as indicated by inferred cool sea surface temperatures and reduced surface to deep water temperature gradients we suggest that deep waters in the eastern indian ocean were not directly fed by the southern or tethys oceans rather the more negative n 13 c composition of the bottom waters recorded by benthic foraminifera implies the presence and or active contribution of aged deep waters from the pacific during this time at least prior to v60 2 ma and subsequent to v59 0 ma the indian continent ninetyeast ridge kerguelen plateau and broken ridge may have played a significant role as submarine barriers to deep water circulation during the paleocene 2002 elsevier science b v all rights reserved

spatial and temporal seismic energy release in the efate region central new hebrides island arc evidence for buckling a study of the spatial and temporal dismbutions of the seismicity in the central new hebrides island arc shows that the efate region including the interplate boundary and the uppa plate can be considered as a single block under stress r xied activation of very specific m nes within this block as indicated by seismic clusters is temporally correlated with larger than average energy release rates these relative high rates are associated with main shocks with magnitude ms mb 5 0 in the upper pan of the interplate boundary and indicate that slip at the plate boundary is not steady no correlation is found with main shocks located in the lower pars of the interplate boundary where slip occurs more freely we propose that these observations are consistent with a buckling process with a wavelength of about 170 km within the ovemding plate buckling or bending of the upper plate may be due to the impingement of a seamount on the subduction system elevating the stress level of the efate region which behaves like a single mechanical entity

the sudbury structure controversial or misunderstood the origins of the sudbury structure and associated igneous complex have been controversial most models call for a major impact event followed by impact induced igneous activity although totally igneous models are still being proposed much of the controversy is due in our opinion to a misunderstanding of the size of the original sudbury structure by analogy with other terrestrial impact structures the spatial distribution of shock features and huronian cover rocks at the sudbury structure suggest that the transient cavity was 100 km in diameter which places the original final structural rim diameter in the range of 150 200 km theoretical calculations and empirical relationships indicate that the formation of an impact structure of this size will result in 104 km3 of impact melt more than sufficient to produce a melt body the size of the igneous complex present volume 4 8 103 km3 for the igneous complex to be an impact melt sheet it must have a composition similar to that of the target rocks evidence for this has been presented previously for sr and nd isotopic data which suggest a crustal origin here we also present new evidence from least squares mixing models that the average composition of the igneous complex corresponds to a mix of archean granite greenstone terrain with possibly a small component of huronian cover rocks this is a geologically reasonable mix based on the interpreted target rock geology and the geometry of melt formation in an impact event of this size the igneous complex is differentiated which is not a characteristic of previously studied terrestrial impact melt sheets this can be ascribed however to its great thickness and slower cooling that large impact melt sheets can differentiate has important implications for how the lunar samples and the early geologic history of the lunar highlands are interpreted if this working hypothesis is accepted namely that both the sudbury structure and the igneous complex are impact in origin then previous hybrid impact igneous hypotheses can be discarded and the sudbury structure can be studied specifically for the constraints it provides to large scale cratering and the formation of basin sized multiring impact structures

mapping of low p wave velocity structures in the subducting plate of the central new hebrides southwest pacific arrival times of compressional p and shear s waves generated by earthquakes located in the new hebrides subduction zone and recorded by local and regional arrays of seismographs are used to determine large scale one and three dimensional elastic wave velocity structures of the subduction zone between 15 and 20 s and from the surface to about 250 km depth the results obtained from inverting the locally and regionally recorded arrival times individually corroborate each other and they are inverted jointly in order to improve the resolution of shallow to intermediate depth structures the results for one dimensional structure indicate a gradual increase of velocity with depth until a 9 reversal appears between 60 and 100 km depth the three dimensional structure determined from the joint inversion shows that these low velocities lie within a sizable seismic gap in the descending benioff zone taken with other observations such as the attenuation of high frequency shear waves travelling across this gap and the locations of active volcanoes at the surface we infer that the low velocity region represents a thermal anomaly of about 750 c which alters the physical properties of the descending plate in this region at shallower depths there is evidence of low velocity structures included in the descending plate one beneath north malekula island and another between malekula and efate islands corresponding to the large embayment of the leading edge of the upper plate the locations of these structures combined with previous investigations of the area lead us to infer that these low velocities are due to the subduction of small scale features such as seamounts and accretionary wedges

recent tectonics associated with the subduction collision of the d entrecasteaux zone in the central new hebrides abstract recent data from the new hebrides vanuatu subduction zone have enabled a morphological description and tectonic interpretation to be made of the complex plate contact between the d entrecasteaux zone and the west torres massif on the one hand and the old santo malekula block on the other between latitudes 14 30 and 17 s no trench occurs owing to the presence of the old rigid santo malekula block at the edge of the overriding plate the outer limit of plate contact describes a tortuous line westward of the projected line of the adjacent trenches this may be explained by local collision of the north d entrecasteaux ridge and the south d entrecasteaux chain with the west flank of santo this collision is compensated for by lateral plastic flow of the inner wall downward into the small basins which separate the d entrecasteaux zone ridges a process which may be explained by plastic plane strain theory the westward jump of the plate contact zone here may result from pieces of the north d entrecasteaux ridge being cut off and incorporated in the frontal arc a review of the geological evidence and the shallow seismicity of the central new hebrides shows that radiant horizontal stresses resulting from this collision have generated a specific compressive stress regime which influences the whole width of the arc the resultant deformation shows a close resemblance to a theoretical strain field produced by the indentation of a long narrow plastic body cf the arc by a rigid flat die cf the d entrecasteaux zone thus the central new hebrides block is both elastically bent under vertical stresses and plastically deformed and pushed eastwards by horizontal stresses recent uplift of the eastern chain can be explained by this model in contrast at the rear of both the northern and southern sections of the arc the tectonics are mainly controlled by a tensional stress regime the strong plate interaction due to the subduction of the d entrecasteaux zone is thought to be responsible for the compressive stress regime across the central new hebrides the same cause can be invoked to account for the tensional stress regime observed in north and south new hebrides rear arc regions

two high precision u pb zircon ages for the sudbury nickel irruptive two independent u pb zircon ages were measured using norite samples from the north and south ranges of the sudbury nickel irruptive ages of and ma were obtained with a probability of fit within experimental error of 51 and 57 respectively previous determinations by the rb sr whole rock method gave ages between about 1700 and 2000 ma with errors of the order of 100 ma the difference in precision is inherent in the two methods zircons from the norite are highly radiogenic and almost concordant whereas rb sr whole rock ages are determined by very small increments in radiogenic 87sr the two zircon ages have completely different discordia so that all simple models for lead loss by continuous diffusion can be excluded

rupture across arc segment and plate boundaries in the 1 april 2007 solomons earthquake the largest earthquakes are generated in subduction zones and the earthquake rupture typically extends for hundreds of kilometres along a single subducting plate these ruptures often begin or end at structural boundaries on the overriding plate that are associated with the subduction of prominent bathymetric features of the downgoing plate here we determine uplift and subsidence along shorelines for the 1 april 2007 moment magnitude m w 8 1 earthquake in the western solomon islands using coral microatolls which provide precise measurements of vertical motions in locations where instrumental data are unavailable we demonstrate that the 2007 earthquake ruptured across the subducting simbo ridge transform and thus broke through a triple junction where the australian and woodlark plates subduct beneath the overriding pacific plate previously no known major megathrust rupture has involved two subducting plates we conclude that this event illustrates the uncertainties of predicting the segmentation of subduction zone rupture on the basis of structural discontinuities

astronomical calibration of the paleocene time the first complete cyclic sedimentary successions for the early paleogene from drilling multiple holes have been retrieved during two odp expeditions leg 198 shatsky rise nw pacific ocean and leg 208 walvis ridge se atlantic ocean these new records allow us to construct a comprehensive astronomically calibrated stratigraphic framework with an unprecedented accuracy for both the atlantic and the pacific oceans covering the entire paleocene epoch based on the identification of the stable long eccentricity cycle 405 kyr high resolution x ray fluorescence xrf core scanner and non destructive core logging data from sites 1209 through 1211 leg 198 and sites 1262 1267 leg 208 are the basis for such a robust chronostratigraphy former investigated marine odp sites 1001 and 1051 and land based e g zumaia sections have been integrated as well the high fidelity chronology is the prerequisite for deciphering mechanisms in relation to prominent transient climatic events as well as completely new insights into greenhouse climate variability in the early paleogene we demonstrate that the paleocene epoch covers 24 long eccentricity cycles we also show that no definite absolute age datums for the k pg boundary or the paleocene eocene thermal maximum petm can be provided by now because of still existing uncertainties in orbital solutions and radiometric dating however we provide two options for tuning of the paleocene which are only offset by 405 kyr our orbitally calibrated integrated leg 208 magnetostratigraphy is used to revise the geomagnetic polarity time scale gpts for chron c29 to c25 we established a high resolution calcareous nannofossil biostratigraphy for the south atlantic which allows a much more detailed relative scaling of stages with biozones the re evaluation of the south atlantic spreading rate model features higher frequent oscillations in spreading rates for magnetochron c28r c27n and c26n

large scale deformation associated with ridge subduction summary continuum models are used to investigate the large scale deformation associated with the subduction of aseismic ridges formulated in the horizontal plane using thin viscous sheet theory these models measure the horizontal transmission of stress through the arc lithosphere accompanying ridge subduction modelling was used to compare the tonga arc and louisville ridge collision with the new hebrides arc and d entrecasteaux ridge collision which have disparate arc ridge intersection speeds but otherwise similar characteristics models of both systems indicate that diffuse deformation low values of the effective stress strain exponent n are required to explain the observed deformation deformation is somewhat insensitive to the vertically integrated strength of the arc inversely proportional to the argand number ar but indicates that the arc lithosphere is not extremely weak ar 100 low values of both ar and n suggest that the thermal structure is typical of cold or normal arcs and that deformation is dominated by flow in the lower crust and mantle in addition low values of n approaching newtonian flow may indicate that specific deformation mechanisms dictate deformation of the arc lithosphere possible mechanisms include low stress grain size dependent creep pyroxenite controlled rheology and mechanisms associated with water weakening changes in the boundary conditions greatly affect deformation within island arcs high rates of arc ridge intersection speed tonga louisville system yield arc parallel tension and crustal thickening in the wake of ridge subduction in contrast low rates of arc ridge intersection speed new hebrides d entrecasteaux system yield compressional deformation directly arcward of the collision zone and transverse strike slip faulting adjacent to the region of compressional deformation localized regions of extensional deformation along the frontal part of the arc adjacent to the collision zone may contribute to the formation of re entrants

the sudbury igneous complex viscous emulsion differentiation of a superheated impact melt sheet the sudbury igneous complex of ontario canada is the remnant of a voluminous melt sheet produced in a few minutes by impact of a massive meteorite into continental crust 1 85 ga ago the transient cavity and melting zone reached the moho and instantly 2 min relaxed to form a more familiar large shallow crater holding a thick superheated 1700 c melt sheet covered by 2 km of breccia there is little about the resulting bimodal igneous complex that resembles crystallization of well known sheet like bodies of similar composition yet the norite and granophyre exhibit a remarkable similarity in isotopic and trace element compositions suggesting an intimate common parentage from the surrounding crust this petrogenetic enigma is explained here as a natural unavoidable consequence of the impact process in the rapid formation of a superheated magmatic emulsion which we take as the high temperature equivalent of breccia a wide spectrum of viscously discrete interdispersed parcels of mafic and felsic liquids reflecting the compositional heterogeneity of the target crustal materials formed the emulsion within days to months the emulsion components separated according to their relative densities into a bimodal norite granophyre assemblage that formed the basic structure of the present sudbury igneous complex there is clear evidence of this emulsion in the earliest dikes i e offsets which likely give the earliest state of the nascent melt sheet immediately following emulsion separation the strongly superheated bimodal melt sheet underwent vigorous thermal convection in each layer these convective motions homogenized and rapidly cooled the magma to the liquidus temperatures whereupon convection ceased the pattern of convection was pinned in place by the embayment topography of the crater floor which in turn played a pivotal role in directing sulfide deposition into the embayments all further cooling was by conduction of heat through the upper and lower boundaries during which time solidification fronts were established and propagated inward from the upper and lower margins there is clear evidence of solidification from the floor upward and the roof downward minimal differentiation and compositional modification took place throughout cooling and solidification nevertheless during the solidification stage granitic rock fragments on the crater floor and rafts of fallback breccia from the thick overlying onaping formation became unstable and entered the melt sheet and the partially melted remnants collected at the interface between the norite and granophyre some interstitial melt from the norite also percolated upward and altogether the blocks and melt produced the distinctive chemical and physical characteristics of the unusual transition zone the sudbury melt sheet is in essence a full scale magmatic experiment the conditions of formation relative to any other large terrestrial magma are precisely known thus the clear lack of any significant modal layering the overall homogeneous nature of each unit and the lack of any significant chemical differentiation through crystal fractionation establish sudbury as a valuable example of what does not happen under the initial conditions long assumed to prevail at the formation of most large magma chambers

a complete high resolution paleocene benthic stable isotope record for the central pacific odp site 1209 1 we have compiled the first stratigraphically continuous high resolution benthic foraminiferal stable isotope record for the paleocene from a single site utilizing cores recovered at pacific odp site 1209 the long term trend in the benthic isotope record suggests a close coupling of volcanic co2 input and deep sea warming over the short term the record is characterized by slow excursions with a pronounced periodic beat related to the short 100 kyr and long 405 kyr eccentricity cycle the phase relationship between the benthic isotope record and eccentricity is similar to patterns documented for the oligocene and miocene confirming the role of orbital forcing as the pace maker for paleoclimatic variability on milankovitch time scales in addition the record documents an unusual transient warming of 2 c coeval with a 0 6 carbon isotope excursion and a decrease in carbonate content at 61 75 ma this event which bears some resemblance to eocene hyperthermals marks the onset of a long term decline in 13c the timing indicates it might be related to the initiation of volcanism along greenland margin

danian selandian boundary criteria and north sea basin tethys correlations based on calcareous nannofossil and foraminiferal trends in sw france abstract high resolution calcareous nannofossil and foraminiferal investigations of the bidart and loubieng outcrop sections allow to define a time calibrated sequence of 47 bio events within the danian selandian d s boundary interval 61 2 59 7 ma of aquitaine sw france the d s boundary as originally defined in denmark start of clastic sedimentation at the base of the lellinge greensand formation is marked by the end of the acme of the nannofossil family braarudosphaeraceae this bio event dated at 59 9 ma has also been identified at the lithological change from limestone dominated lasseube formation to marly sedimentation latapy member of the pont labau formation in sw aquitaine and at the base of the red marls of the itzurun formation at zumaia spain recently designated as global stratotype section and point gssp for the d s boundary this implies contemporaneity of this lithological shift throughout europe and a gssp proposal which is consistent with the original boundary definition the braarudusphaeraceae event is believed to be due to the interruption of freshwater influx probably related to a sudden decrease in precipitation it is located at the top of nannofossil zone np4 and within planktonic foraminiferal zone p3b and bracketed between the lowest occurrence lo of morozovella velascoensis below and the lo of fasciculithus tympaniformis above it is coincident with the lo of bomolithus elegans the lcso cs consistent of fasciculithus janii and the lo of subbotina velascoensis the d s boundary as originally defined is 400 k y posterior to a major discontinuity recorded throughout the tethyan realm tunisia egypt and up to now erroneously considered to correspond to the d s boundary this break in sedimentation dated at 60 3 ma and coinciding with the p3a p3b boundary is due to a major sea level fall it is correlated with sedimentation changes in the aquitaine zumaia area start of development of marly interbeds and in the north sea basin transition bryozoan limestone calcisiltite in denmark transition shallow marine mons formation continental hainin formation in belgium the loubieng section supplements the zumaia section because of its rich and well preserved fossil content and continuous sedimentation it constitutes an excellent auxiliary section for the d s boundary

the d entrecasteaux zone southwest pacific a petrological and geochronological reappraisal abstract the d entrecasteaux zone southwest pacific is an arched submarine horst and graben structure which extends from the northern end of the new caledonia ridge to the western border of the new hebrides island arc a review of the bathymetry seismic reflection data paleomagnetism gravimetry seismology and dsdp data available for this area is combined with a study of basaltic samples dredged along the horsts of this regional fracture zone these basalts show strong petrographic and chemical affinities with morb their fissiontrack ages range between 56 ma paleocene eocene boundary and 36 ma eocene oligocene boundary it is suggested that the d entrecasteaux zone represents the northern arcuate extension of the northeast dipping eocene subduction obduction zone located along the new caledonia loyalty islands ridge while its present morphology appeared from post obduction extensional movements resulting in a progressive uplift of basaltic ocean floor since middle miocene times

structural analysis of the central and southwestern sudbury structure southern province canadian shield the sudbury structure ss is an unusual crater structure which acquired its present oval surface shape during northwest directed ductile thrusting lower amphibolite facies metamorphism accompanied the thrusting which generated a major reverse shear zone at least 50 km long the south range shear zone srsz transects the south range of the sudbury structure and exhumes a low level of the sudbury igneous complex sic assuming heterogeneous simple shear in the northwest southeast vertical plane on northeasterly striking glide surfaces minimal estimates of net displacement across the srsz exceed 8 km this displacement magnitude and the map pattern of the sic require the southwest closure of the ss to be steeply plunging in accord with a hypothetical funnel shape of the sic the rocks of the metasedimentary core of the ss are deformed into a family of second order buckle folds the tangent surface of which forms an upright open flexure within the first order structure of the sudbury synclinorium the

coseismic and long term vertical displacement due to back arc shortening central vanuatu offshore and onshore data following the mw 7 5 26 november 1999 ambrym earthquake 1 this paper presents a combined analysis of data collected both onshore and offshore in the epicentral region of the mw 7 5 26 november 1999 ambrym earthquake this offshore event occurred at the southern end of the back arc thrust belt of the vanuatu subduction zone east of the island of ambrym and resulted in permanent uplift of the eastern tip of the island the data presented include 1 interpretation of older seismic lines across the tectonic front 2 compilation of aftershock sequences 3 postseismic bathymetry from multibeam surveys 4 measurements of permanent coseismic ground motion using desiccated red algae uplifted beaches and uplifted coral colonies and 5 dating of raised corals exposed along the coastal cliff the active scarp of the main fault appears 13 km east of the eastern tip of ambrym 40 km long 2 km depth 950 m maximum step uplift rates of 3 5 4 mm yr for the past 8000 years are calculated by dating raised corals this leads to a longer seismic recurrence interval of 375 years for events similar to that of 1999 assuming no interseismic subsidence postseismic ground motion was monitored using stainless steel marks set at three sites along the uplifted coast in january 2000 no significant motion could be recorded during the 2 years following the event but slight subsidence cannot be ruled out finally our results confirm that the back arc belt of central vanuatu is an active tectonic crustal wedge propagating eastward that accommodates more shortening than the vanuatu subduction zone to the west

palaeoenvironmental changes across the danian selandian boundary in the north sea basin abstract the danian selandian boundary 60 ma marks the cessation of 40 million years of carbonate deposition in the north sea basin and a shift to siliciclastic deposition on the basis of variations in lithology benthic and planktonic foraminifera and calcareous nannofossils in three cores from storebaelt in the eastern part of the north sea basin we have reconstructed the palaeoenvironmental changes across the boundary the benthic foraminiferal faunas belong to the midway type fauna they are extremely rich and more than 260 taxa have been recognized q mode cluster analysis groups the benthic assemblages into four biofacies which correspond fairly closely to lithological units correlation of the storebaelt records with marine palaeorecords from the danish basin and the north sea basin indicate that the transformation of the north sea from a carbonate to a siliciclastic basin occurred in four steps separated by relatively long stable periods the most important external factors involved in the change are firstly a drop in the relative sea level during the late danian leading to the disappearance of bryozoans from the north sea basin and to non deposition and erosion in many areas secondly coinciding with the danian selandian boundary an uplift of the scotland shetland area resulting in a massive input of siliciclastic deposits to the north sea basin thirdly during the early selandian inversion of the sorgenfrei tornquist zone and mesozoic basins in the southern and eastern part of the north sea basin resulted in a huge influx of reworked cretaceous chalk and an almost complete stop of carbonate production finally later in the early selandian in connection to a general sea level rise and a reduction in the gateway between the north sea basin and the tethys sea the sea bottom conditions became colder and more acidic this resulted in partial dissolution of the carbonates and the deposition shifted from marl to clay comparison with records from the western pyrenees the nile basin and the eastern north america suggests that sea level changes across the danian selandian boundary are primarily of eustatic nature

sea level humidity and land erosion records across the initial eocene thermal maximum from a continental marine transect in northern spain in two continental sections in the tremp basin northern spain the initial eocene thermal maximum also known as the paleocene eocene thermal maximum is registered by an 6 fall in 1 3 c values in soil carbonate nodules high resolution correlations using the 1 3 c excursion can be made to nearby shelf and bathyal marine settings allowing a detailed reconstruction of soil formation on land and transport of detritus to the sea during the initial eocene thermal maximum soils that formed before and after the initial eocene thermal maximum in the tremp region reflect arid to semiarid conditions with abundant evaporative minerals whereas initial eocene thermal maximum soils reflect seasonally wetter but generally dry conditions during the initial eocene thermal maximum land erosion was intensified and accumulation rates of terrigenous detritus in the sea increased this reflects both increased topographic relief associated with a prominent sea level lowstand and enhanced seasonal precipitation over a dry landscape with sparse vegetation deeper erosion led to an increase in the flux of kaolinite from buried mesozoic soils to the oceans the association of the initial eocene thermal maximum with a sea level lowstand in northern spain as well as at other marginal north atlantic sites may reflect coeval large scale magmatic activity in the northernmost atlantic

rapid microplate rotations and backarc rifting at the transition between collision and subduction using global positioning system velocities from convergent plate boundaries in papua new guinea new zealand tonga vanuatu and the marianas we note a spatial correlation between rapid tectonic block rotations and the transition from subduction to collision we present a mechanism for the block rotations in which the change from collision of a buoyant indentor to normal subduction exerts a torque on the upper plate microplate this work improves our understanding of the causes of rapid vertical axis rotations often observed in paleomagnetic studies we also show how collision induced rotations may lead to backarc rifting

emplacement of sharp walled sulfide veins during the formation and reactivation of impact related structures at the broken hammer mine sudbury ontario broken hammer is a hybrid cu ni platinum group element pge footwall deposit located in archean basement rocks below the impact induced sudbury igneous complex sic canada the deposit consists

high resolution nannofossil biochronology of middle paleocene to early eocene at odp site 1262 implications for calcareous nannoplankton evolution abstract over the last several decades debates on the tempo and mode of evolution have centered on the question whether morphological evolution preferentially occurs gradually or punctuated i e with long periods of stasis alternating with short periods of rapid morphological change and generation of new species another major debate is focused on the question whether long term evolution is driven by or at least strongly influenced by changes in the environment or by interaction with other life forms microfossils offer a unique opportunity to obtain the large datasets as well as the precision in dating of subsequent samples to study both these questions we present high resolution analyses of selected calcareous nannofossils from the deep sea section recovered at odp site 1262 leg 208 in the south eastern atlantic the studied section encompasses nannofossil zones np4 np12 equivalent to cp3 cp10 and chrons c27r c24n we document more than 70 biohorizons occurring over an about 10 myr time interval 62 5 ma to 52 5 ma and discuss their reliability and reproducibility with respect to previous data thus providing an improved biostratigraphic framework which we relate to magnetostratigraphic information and present for two possible options of a new paleocene stratigraphic framework based on cyclostratigraphy this new framework enabled us to tentatively reconstruct steps in the evolution of early paleogene calcareous nannoplankton through documentation of transitional morphotypes between genera and or species and of the phylogenetic relations between the genera fasciculithus heliolithus discoasteroides and discoaster as well as between rhomboaster and tribrachiatus the exceptional record provided by the continuous composite sequence recovered at walvis ridge allows us to describe the mode of evolution among calcareous nannoplankton new genera and or new species usually originated through branching of lineages via gradual but relatively rapid morphological transitions as documented by the presence of intermediate forms between the end member ancestral and descendant forms significant modifications in the calcareous nannofossil assemblages are often related to significant changes in environmental conditions but the appearance of structural innovations and radiations within a single genus also occurred during stable environmental conditions these lines of evidence suggest that nannoplankton evolution is not always directly triggered by stressed environmental conditions but could be also driven by endogenous biotic control

current tectonics of the tonga new hebrides region abstract this paper proposes a present day tectonic map of the tonga new hebrides region the result of combining data from bathymetry satellite derived gravity seismicity magnetic measurements and gps observations focal mechanisms and a large amount of bathymetric data collected during the last decade in the lau and north fiji back arc basins indicate a deformation distributed over numerous spreading ridges rather than diffuse and shear dominated as was previously thought the region is also characterised by a large variation of both consumption rate along the arcs and opening rate along the back arc basins spreading centres geometry and rate of spreading in the lau and north fiji back arc basins and segmentation of the tonga and new hebrides arcs are closely related to and significantly influenced by the subduction of aseismic ridges namely the louisville d entrecasteaux and loyalty ridges where subducting aseismic ridges enter the trenches we observe slower convergence arc transverse strike slip faulting thrusting at the rear of arcs and slow or absent back arc spreading rapid subduction correlates with fast back arc opening sometimes parallel spreading ridges in the back arc domain are required to accommodate the fast motion of convergence

expansion of the aftershock zone following the vanuatu new hebrides earthquake on 15 july 1981 following a large ms 7 0 interplate earthquake on 15 july 1981 in the vanuatu new hebrides islands the area defined by the aftershocks dramatically increased over a two week period of time the aftershocks were located using the cornell orstom seismograph network that has been monitoring earthquakes with magnitudes larger than mb 2 9 in the region since mid 1978 in the first few hours following the mainshock the area defined by the aftershocks was consistent with the rupture zone of a typical interplate earthquake with the observed seismic moment of 5 8 1026 dyne cm however during the 16 days following the mainshock the area of the aftershock zone increased to approximately 10 times the area of expected coseismic rupture the final aftershock zone included earthquakes that were located within the overriding and descending plates as well as along the interplate fault zone the migration of aftershocks away from the rupture zone of the 1981 mainshock indicates that at least in some cases the aftershock zone can overestimate the extent of coseismic rupture

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

the danian selandian boundary at site 1262 south atlantic and in the tethyan region biomagnetostratigraphy evolutionary trends in fasciculiths and environmental effects of the latest danian event abstract a high resolution calcareous nannofossil analysis of the danian selandian boundary was conducted at site 1262 walvis ridge south atlantic to pinpoint the lowest occurrence of fasciculiths and to unravel the evolutionary trends throughout nannofossil zone np4 using quantitative analyses numerous primary and secondary bioevents were identified improving the biostratigraphic resolution of this interval the main events recorded at site 1262 were also identified at the zumaia section global stratotype section and point gssp of the base of the selandian and at the qreiya section egypt the lowest occurrence of fasciculiths represented by the lo of gomphiolithus magnicordis and gomphiolithus magnus was observed in the middle part of chron c27r above the lo of toweius pertusus and prior to the lo of the genus sphenolithus the synchroneity of the lo of fasciculiths was also verified at various latitudes such as dsdp site 384 nw atlantic odp site 761b indian ocean and dsdp site 577a pacific ocean the first and second diversification events steurbaut and sztrakos 2008 or radiation events bernaola et al 2009 of fasciculiths have been thoroughly discussed and well characterized by a succession of events the occurrence of the latest danian event lde and several paleoenvironmental changes recognized during this time interval coupled with an ecological competition with sphenolithus appear to be the probable causes of the first and second radiations and the fasciculith barren interval between them the occurrence of new morphostructures and taxa suggests evolutionary trends and a strict link between morphological evolution and paleoclimate

patterns of seismicity associated with asperities in the central new hebrides island arc in the central part of the new hebrides island arc efate malekula region 16 s 18 6 s a sequence of moderate sized earthquakes their aftershock sequences and other clusters of small earthquakes together form an intricate but coherent time space pattern that probably reveals a major asperity complex along the interplate boundary of the subduction zone this pattern is determined by study of data from a local network the sequences including one event with magnitude mw 7 1 eight events with magnitudes mw between 5 8 and 6 3 and nearly 13 000 smaller events occurred during the six year period 1978 1984 the seismicity is very unevenly distributed in space a sharply defined east west line near 17 2 s separates the very active efate region to the south where nearly 10 500 earthquakes occurred from the less active malekula region to the north where less than 2 500 earthquakes occurred during the six year period in the efate region several spatial patterns are highlighted first the seismic regimes of the updip and the downdip part of the interplate boundary are different the updip part is characterized by a low background activity and main shocks with large aftershock zones while the downdip part is characterized by a very high level of background activity and main shocks with much smaller aftershock zones or no aftershocks this difference in seismic regimes suggests that asperities are located in the updip part of the interplate boundary while the downdip part may slip predominantly by creep a creep episode may have been responsible for the tilt signal observed by periodic relevelings of a l km aperture network of benchmarks on efate island second specific locations along the interplate boubdary are identified either as sites of very intense and repeatedly activated concentrations of hypocenters or as sharp boundaries limiting the spatial development of aftershock zones two areas of concentrated activity particularly stand out one located in the updip part of the interplate boundary and the other in the downdip part most of the clustered activity that occurred during the six years of observation is concentrated in these two areas four boundaries limiting the spatial development of aftershock zones are located in the updip part of the interplate boundary one of these boundaries coincides with one of the areas of intense activity epiceniers of moderately large events that occurred in the region since 1960 are also concentrated along the boundaries the zones of concentrated activity and the boundaries limiting the development of aftershock zones can be interpreted either as locations of penties or as edges of asperities an alternative interpretation is that a giant asperity is located in the ylekula region with the different spatial patterns observed in the efate region being interpreted as the southern edge of that asperity a transition zone between a locked part to the north and normal i subduction to the south study of the temporal patterns of the seismicity shows that the main shocks in tbe downdip part of the interplate boundary are not preceded by obvious long term months to year nor short term days to week precursory activity in the updip part of the interplate boundary short term fipreshocks preceded each main shock but only one of these foreshock sequences is outstanding although no clear cyclic pattern related to the main shocks is evident clustered activity that occurred in the two zones of concentrated activity and two other zones located in the back arc region are correlated ih time with the occurrence of the major sequences located in the updip part of the interplate boundary activation of these four zones always follows the sequences in the updip part of the interplate boundary qith varying time intervals days to months these four zones are also sometimes activated before sequences in the updip part of the interplate boundary in particular one of the zones of concentrated a ctivity shows possibly repeated long term few months precursory activity this phenomenon could b e an indicator of increasing probability of occurrence of main events in the updip part of the interplate b oundary i tuk ukiis lmcui l ilu tl6aj2 qfiztqf

factors controlling 13c contents of sedimentary organic compounds principles and evidence the carbon isotopic composition of any naturally synthesized organic compound depends on 1 the carbon source utilized 2 isotope effects associated with assimilation of carbon by the producing organism 3 isotope effects associated with metabolism and biosynthesis and 4 cellular carbon budgets these factors are reviewed and quantitative considerations summarized particularly with regard to active and passive modes of carbon assimilation by phytoplankton and the existence of discernible regularities in isotope effects associated with lipid biosynthesis it is concluded that n alkyl lipids are in general depleted in 13c by about 1 5 relative to polyisoprenoid lipids produced by the same organism the effects of biological reworking on isotopic compositions of organic carbon are examined and it is suggested that enrichment of 13c in sedimentary organic carbon may result from loss of ch4 from zooplanktonic gut communities isotopic methods for estimation of ancient co2 levels are considered and a hyperbolic form favored for the relationship between concentrations of dissolved co2 and isotopic fractionation

a shallow double seismic zone beneath the central new hebrides vanuatu evidence for fragmentation and accretion of the descending plate a shallow double seismic zone sdsz has been found in the descending australian plate beneath the central part of the new hebrides island arc directly above a large gap in intermediate depth seismicity and between two seismic boundaries ambient seismicity occurs mostly in the upper part of the sdsz while earthquakes in the lower part occur in clusters swarms or aftershocks of large earthquakes the distance between the upper and lower levels of the sdsz is 50 70 km and they are joined at 80 km depth by a near horizontal band of seismicity thrust faulting mechanisms predominate for earthquakes in the upper level of the sdsz those in the lower level however appear to be normal faulting despite their being aftershocks of large thrust events we suggest that with the absence of a pull from the detached lithosphere the upper part of the australian plate in the region of the sdsz is resistant to subduction and thus the downward displacements caused by large earthquakes in the adjoining regions result in a localized rebound the location of the aftershocks within the plate suggests that a new plate boundary is forming which will eventually replace that outlined by the residual seismicity in the upper level thus the leading edge is decoupling and the boundary will eventually shift back to the lower level of the sdsz

revisiting thrusting reverse faulting and transpression in the southern sudbury basin ontario abstract the synformal sudbury igneous complex sic is the deformed relic of a large impact melt sheet understanding the geometry and kinematics of deformation of the sic is paramount for mineral resource deposit exploration of this complex constraining its pre impact configuration and understanding paleoproterozoic tectonism at the southern margin of the archean superior province in particular it is uncertain to what extent thrusting on the south range shear zone srsz a ductile shear zone transecting the southern portion of the sic is coeval with folding of the sic geometric properties of 1090 discontinuities mapped from air photos and geometry of metamorphic l s fabrics revealed the presence of two spatially and kinematically distinct deformation regimes in the southern sic the so called south range nw directed thrusting on the srsz dominates in the western south range whereas dextral transpression prevails in the eastern south range the two deformation regimes are geometrically and kinematically related to the srsz we propose that the srsz transects the south range south of the se lobe a tight fold of the sic this is at variance with previous hypotheses in which the srsz continues into the hinge zone of the se lobe and in which dextral transpression is spatially confined largely to this lobe the curvature of the srsz and its mechanical coupling to its footwall rocks imparted dextral transpressive deformation to the eastern south range dextral component shear of this deformation was associated with shortening of the sic oblique to its contacts collectively this led to map view corrugation of sic contacts and thickness variations of the sic that culminated in the formation of the se lobe our study suggests that thrusting on the srsz is kinematically linked and thus coeval with folding of the sic

the great sumatra andaman earthquakes imaging the boundary between the ruptures of the great 2004 and 2005 earthquakes segmentation along convergent margins controls earthquake magnitude and location but the physical causes of segment boundaries and their impact on earthquake rupture dynamics are still poorly understood one aspect of the 2004 and 2005 great sumatra andaman earthquakes is their abrupt termination along a common boundary this has led to speculation on the nature of the boundary its origin and why it was not breached for the first time the boundary has been imaged and with newly acquired marine geophysical data we demonstrate that a ridge on the subducting indo australian oceanic crust may exert a control on margin segmentation this suggests a lower plate influence on margin structure particularly its segmentation the ridge is masked by the sedimentary cover in the trench its most likely trend is nne ssw it is interpreted as a fracture zone on the subducting oceanic plate a ramp or tear along the eastern flank of the subducting fracture zone beneath simeulue island may be considered as an intensification factor in terms of rupture propagation barrier

the december 1994 seismic swarm near aoba ambae volcano vanuatu and its relationship with the volcanic processes abstract a seismic swarm which occurred in december 1994 near the aoba volcano vanuatu is investigated in detail by analyzing local and regional broad band seismic records the seismic area is situated in a poorly instrumented region although major seismic and volcanic events are possible the data collected by four permanent short period stations the nearest one being installed in the espiritu santo island located 80 km from the volcano allowed us to locate epicenters with a 2 3 km precision and to document the present local seismicity the quality of available regional broadband data allows us to determine reliable focal parameters though the magnitude of the strongest event is 4 8 data have been selected from the permanent geoscope and iris stations located in the south western pacific region and from two temporary networks one installed in new caledonia and vanuatu by i r d and the e o s t and another one installed in fiji and tonga islands by the washington university st louis usa results obtained either with local epicentral distance d km body waves or regional 500 km surface waves lead us to conclude that the swarm is associated with the volcanic edifice but is not of volcanic type according to the definitions given by minakami phys volcanol 1974 1 and schick bull volcanol 44 1981 491 the observed mechanisms evidence an important local influence of the volcano itself on the stress field and the observed near horizontal p axis argues against a strong increase of phreatic activity in addition seismic and volcanic observations are analyzed in the framework of the interpretation of earthquake swarms occurring in the vicinity of active volcanoes

interseismic and coseismic motions in gps series related to the ms 7 3 july 13 1994 malekula earthquake central new hebrides subduction zone on july 13 1994 an earthquake ms 7 3 occurred at malekula in the new hebrides archipelago the gps data collected across the new hebrides trench between 1990 and 1996 were processed in order to separate the interseismic and coseismic motions from the drifts related to the convergence with the australian plate the gps derived coseismic displacements at the gps site in malekula are 49 15 mm southward 230 30 mm westward and 170 37 mm downward when the cmt derived displacements are 50 mm southward 210 mm westward and 150 mm downward taking into account the interseismic strain accumulation 25 mm yr at the source established from historical seismicity 7 5 mm yr at the gps site the strain free convergence rate at malekula is 49 3 mm yr other gps derived convergence rates are 95 1 mm yr at efate and 37 2 mm yr at santo these rates imply a regional right lateral motion between the efate and the santo malekula segments in contrast the focal mechanism of the earthquake mostly indicates a left lateral motion therefore we hypothesize that the earthquake is related to variations in the interplate coupling along the converging boundary of the santo malekula segment

a 100 km long paleomagnetic traverse radial to the sudbury structure canada and its bearing on proterozoic deformation and metamorphism of the surrounding basement abstract the 1850 ma sudbury igneous complex sic considered to be a composite melt sheet of a major meteorite impact has been deformed into an oval shaped basin known as the sudbury structure this paper explores to what extent this deformation has been communicated to the surrounding archean basement around the northern margin of the sic paleomagnetism of 2450 ma matachewan dykes and 1850 ma impact breccia along a traverse about 100 km long and normal to strike of the contact between the sic and the basement suggests that the basement beneath the nw corner of the sudbury structure has been tilted to the se within about 10 km of the contact at this distance a possible fault separates the tilted region from one that shows no evidence of tilting petrographically the dykes out to a distance of about 50 km distant from the sic are altered to upper greenschist facies of metamorphism with a fibrous amphibole replacing pyroxene and with loss of primary texture that characterizes less altered matachewan dykes at distances greater than 50 km the direction of magnetization found in the altered matachewan dykes is an overprint which is probably associated with regional metamorphism related to orogenesis or possibly with thermo chemical alteration associated with sic emplacement the direction of the component is compatible with an age of about 1 8 to 1 9 ga suggesting that the penokean orogen is the most likely cause if not the impact event the paleomagnetism of the breccias together with shatter cone orientation data suggests that within 10 km of the sic basement contact basement tilting to the southeast increases towards the sic

probabilistic seismic hazard model for vanuatu abstract this study develops a preliminary probabilistic seismic hazard model for vanuatu the area of investigation formerly referred to as the new hebrides lies in the center of a chain of partly vulcanologically active islands that mark the present day boundary between the australia india plate and the microplate of the north fiji basin the seismicity of the vanuatu arc is dominated by an east dipping subduction zone which shows striking structural anomalies in the central part between 14 and 18 s our historical catalog contains 7519 events within the vanuatu region for the period from 1964 to 2003 drawn from the global teleseismic catalogs by the united states geological survey national earthquake information center usgs neic see data and resources section and engdahl et al 1998 as a measure of seismic hazard we use horizontal peak ground acceleration pga and horizontal spectral ground acceleration sga at a period of 1 sec the hazard estimates are based on a logic tree approach to account for the epistemic uncertainties associated with our analysis our results suggest that the entire island arc experiences a high and uniform seismic hazard typical values for pgas range from 0 65 g to 0 77 g with a 10 probability of exceedence in 50 yr for port vila the capital and largest city in vanuatu we additionally present a pga hazard curve and a uniform hazard spectrum over the period range 0 1 2 sec

the evolution of the onaping formation at the sudbury impact structure the 1 4 1 6 km thick onaping formation consists of a complex series of breccias and melt bodies lying above the sudbury igneous complex sic at the sudbury impact structure based on the presence of shocked lithic clasts and various glassy phases the onaping has been described as a suevitic breccia with an origin at least in part as fallback material recent mapping and a redefined stratigraphy have emphasized similarities and differences in its various vitric phases both as clast types and discrete intrusive bodies the nature of the onaping and that of other suevitic breccias overlying impact melt sheets is reviewed the relative thickness internal stratigraphic and lithological character and the relative chronology of depositional units indicate multiple processes were involved over some time in the formation of the onaping the sudbury structure formed in a foreland basin and water played an essential role in the evolution of the onaping as indicated by a major hydrothermal system generated during its formation taken together observations and interpretations of the onaping suggest a working hypothesis for the origin of the onaping that includes not only impact but also the interaction of sea water with the impact melt resulting in repeated explosive interactions involving proto sic materials and mixing with pre existing lithologies this is complicated by additional brecciation events due to the intrusion of proto sic materials into the evolving and thickening onaping fragmentation mechanisms changed as the system evolved and involved vesiculation in the formation of the upper two thirds of the onaping

the formation of infilled craters on mars evidence for widespread impact induced decompression of the early martian mantle flat floored craters have long been recognized on mars with early work hypothesizing a sedimentary origin more recently high resolution thermal inertia measurements show that these craters contain some of the rockiest materials on the planet inconsistent with poorly consolidated sedimentary materials in this study the distribution physical properties morphology and thermal inertia and composition of these craters are thoroughly investigated over the entire planet the majority of the 2800 rocky crater floors identified are concentrated in the low albedo 0 1 0 17 cratered southern highlands these craters were infilled at 3 5 ga and are associated with the highest thermal inertia values and some of the most mafic materials identified on the planet although several processes may have led to the formation of the crater floors the most likely scenario is volcanic infilling through fractures created by the impact event the primitive magma source directly results from decompression melting of the martian mantle by the removal of the crustal material excavated by the impactor volcanic infilling of craters by decompression melting appears to only have occurred in early martian history when the lithosphere was still relatively thin and the thermal gradient was high this process was widespread and responsible for the eruption of significant volumes of primitive material inside and likely outside of craters impact induced decompression melting of the martian mantle accounts for the unusual infilling of martian craters and is a widespread planetary process that has gone previously undocumented

unfolding the subducting plate in the central new hebrides island arc geometrical argument for detachment of part of the downgoing slab in the central part of the new hebrides island arc a sizable gap exists in the seismic activity seismic observations in the zone of the gap have been previously interpreted as either related to a detachment of part of the downgoing slab or associated with a continuous slab we give a geometrical argument which added the seismic observations from these previous studies adds one step in favor of the detachment hypothesis after unfolding the downgoing plate and restoring it to its initial state using a 3d balance technique we show that the gap can be filled with three pieces two of these pieces are seismic zones located beneath the seismic gap and the third one is a deep 550 650 km seismic zone located about 200 km north east of the arc these three pieces could be detached parts of the subducting plate

partial melt topology in statically and dynamically recrystallized granite microstructures of the murray granite pluton central ontario canada show evidence of both static and dynamic crystallization subsequent to partial melting backscattered electron analyses reveal interstitial k feldspar and plagioclase at triple junctions of strain free isometric quartz grains the geometry of the quartz feldspar boundaries mimics the original topology of the quartz melt contacts during crystallization this conclusion is suggested by the occurrence of both rounded and planar faces of quartz grains and by low 27 dihedral angles of quartz quartz feldspar boundaries similar to dihedral angles in experimentally crystallized quartz quartz silicic melt systems in contrast feldspar seams in deformed granites have high axial ratios are usually elongated perpendicular to the foliation plane and are located preferentially along individual grain boundaries quartz grains are dynamically recrystallized and occasionally transected by feldspar seams indicating that fracturing occurred in the presence of melt during crystal plastic deformation of quartz the subparallel orientation in quartz grains of intragranular feldspar bearing fractures and interstitial feldspar seams suggests that these features originated as intragranular and intergranular fractures respectively partial melt topology was therefore controlled by intergranular and occasionally by intragranular fracturing

high resolution intra and interbasinal correlation of the danian selandian transition early paleocene the bjala section bulgaria and the selandian gssp at zumaia spain abstract the danian selandian d s boundary has been identified for the first time in the black sea coast at bjala bulgaria based on a new integrated bio magneto and cyclostratigraphic study several correlation criteria as established for the basal selandian gssp from zumaia basque basin are evaluated noteworthy is the almost complete lack of calcareous nannoplankton species braarudosphaera bigelowi in the bulgarian sections a sharp decrease of which was indicated as suitable criteria for defining the d s boundary as it occurred both at zumaia and in the classical locations of the north sea basin conversely the second evolutionary radiation of the calcareous nannofossil genus fasciculithus together with the occurrence of fasciculithus tympaniformis that define the np4 np5 zonal boundary seem to be reliable criteria to approximate the d s boundary in detail however the best approach is to integrate biostratigraphic data within a magnetostratigraphic and or cyclostratigraphic framework refinements on the placement of chron c27n at zumaia and robust bed by bed correlation between several basque sections and bjala indicates that the d s boundary is located 30 precession cycles 630 ky above c27n in addition to the precession related marl limestone couplets and 100 ky eccentricity bundles recognized in the studied sections expression of the stable 405 ky long eccentricity allows direct tuning to the astronomical solutions a correlation of the land based sections with previously tuned data from odp site1262 from the southern atlantic is challenged our choice is consistent with original tuning at zumaia but shifts one 100 ky cycle older previous tuning from site 1262 along the interval above c27n under the preferred tuning scheme the d s boundary can be given an age of 61 641 0 040 ma on the la04 orbital solution

latest danian carbon isotope anomaly and associated environmental change in the southern tethys nile basin egypt abstract during the palaeocene and eocene epochs 65 5 33 9 ma the earth experienced the warmest conditions of the cenozoic this palaeogene greenhouse episode is characterized by several short lived negative carbon isotope 13 c excursions which are usually interpreted as transient warming events hyperthermals9 as indicated by rising temperatures of surface and bottom waters and accompanied carbonate dissolution in deep sea settings among these events the palaeocene eocene thermal maximum petm c 55 5 ma is globally the best documented and most prominent further negative 13 c anomalies have recently been identified in the eocene but the early to middle palaeocene has mostly been neglected here benthic foraminiferal 13 c records are presented from four upper danian lower selandian sections in the nile basin eastern egypt all records show a negative 13 c shift with an amplitude of up to 2 at the base of planktonic foraminiferal subzone p3b c 61 ma the supra regional nature of this event is emphasized by correlation with a well dated similar 13 c record from zumaia spain lithological changes the 13 c signature and biotic responses strongly resemble those of the petm in egypt which leads to the hypothesis that this latest danian event9 lde may represent another early palaeocene hyperthermal

a new seismic hazard model for new zealand we present a new probabilistic seismic hazard analysis psha for new zealand an important feature of the analysis is the application of a new method for the treatment of historical distributed seismicity data in psha the psha uses the seismicity recorded across and beneath the country to define a three dimensional grid of a values i e parameter a of a gutenberg richter distribution log n yr a bm in which n yr is the number of earthquakes per year recorded inside each grid cell equal to or greater than magnitude m parameter b and the limiting maximum cutoff magnitude of the gutenberg richter distribution are defined from the surrounding region 14 crustal and 23 subcrustal seismotectonic zones are defined for the country and then smoothed across the boundaries of the zones the methodology therefore combines the modern method of defining continuous distributions of seismicity parameters frankel 1995 frankel et al 1996 with the traditional method of defining large area sources and the associated seismicity parameters e g algermissen et al 1990 the methodology provides a means of including deep subduction zone seismicity in a psha preserves the finer scale spatial variations of seismicity rates across a region avoids the undesirable edge effects produced in the traditional method when adjacent area sources enclose areas of significantly different seismicity rates and also enables parameters most reliably defined at a regional scale parameter b and maximum cutoff magnitude of a gutenberg richter distribution and slip type to be incorporated into the psha the psha combines the modeled seismicity data with geological data describing the location and earthquake recurrence behavior of 305 active faults and new attenuation relationships for peak ground acceleration and spectral acceleration developed specifically for new zealand different attenuation expressions are used for crustal and subduction zone earthquakes the resulting psh maps for a 150 year return period show the highest hazard to occur in the center and southwest of the country in the areas of highest historical crustal and deep subduction zone seismicity in contrast the longer return period maps 475 and 1000 year return period show the highest hazard to occur from the southwest to northeast ends of the country along the faults that accommodate the majority of the motion between the pacific and australian plates the maps are currently being used to revise new zealand s building code which has previously been based on pshas that did not explicitly include individual faults as earthquake sources manuscript received 10 april 2001

3 d kinematic restoration of the eastern sudbury igneous complex canada and its importance for cu ni pge sulphide exploration abstract kinematic restorations of deformed igneous terranes have rarely been attempted due to the general absence of 1 planar primary lithological contacts 2 tightly constrained deformation kinematics and 3 geometric constraints on lithologies and structures at depth because of the vast number of exploration drill holes the deformed and layered 1 85 ga sudbury igneous complex sic in ontario canada is reasonably well understood with respect to 1 and 3 we therefore explored the kinematics of folding and faulting in the eastern sic and use the subsurface geometry of faults extracted from a model integrating surface mapping and drill core logs in an attempt to restore the geometry of part of the sic specifically we identified rotation magnitudes and the tilt axis of a kilometer scale plunging fold the west bay anticline which appears to have folded the eastern part of the sic we combined a 3 d model of the faults and lithological contacts of the sic fault kinematics calculated from the inversion of brittle shear faults at surface and limb rotations of the west bay anticline to kinematically restore the eastern part of the sic results of restorations using simple shear and flexural slip algorithms highlight the importance of slip on prominent curved faults that displaced the sic and facilitated its folding flexural slip appears to be the more plausible mechanism of the two as it removed the curvature of and displacement on prominent faults flexural slip restoration helps to estimate primary thickness variations of the sic and the results show that thickened parts of the main mass of the sic correspond spatially with known cu ni pge sulfide deposits this result demonstrates that 3 d restoration can be an important tool for mineral exploration in igneous terranes

inferred pseudo cryptic speciation in the coccolithophore species braarudosphaera bigelowii gran and braarud during the early paleocene danian abstract pseudo cryptic speciation occurs commonly in living oceanic plankton in the coccolithophores recent genetic studies have revealed that braarudosphaera bigelowii has a number of unique genotypes that correlate well with pentalith size indicating that this coccolithophore species actually contains multiple pseudo cryptic taxa in order to look for evidence of pseudo cryptic speciation in the past we measured the radii of 2800 b bigelowii pentaliths from the braarudosphaera rich limestones that contain the gssp for the lower middle paleocene danian selandian boundary at zumaia spain analysis of the radius measurements using the expectation maximization algorithm yielded two size groups herein termed form x

origin of large volume pseudotachylite in terrestrial impact structures large volume pseudotachylite bodies in impact structures are dike like and consist of angular and rounded wall rock fragments enveloped by a microcrystalline and sporadically glassy matrix that crystallized from a melt knowledge of the formation of pseudotachylite bodies is important for understanding mechanics of complex crater formation most current hypotheses of pseudotachylite formation inherently assume that fragmentation and melt generation occur during a single process based on the structure of pseudotachylite bodies at sudbury canada and vredefort south africa we show that these processes differ in time and space we demonstrate that the centimeter to kilometer scale bodies are effectively fragment and melt fi lled tension fractures that formed by differential rotation of target rock during cratering highly variable pseudotachylite characteristics can be accounted for by a single process i e drainage of initially superheated impact melt into tension fractures of the crater fl oor

detachment of part of the downgoing slab and uplift of the new hebrides vanuatu islands several seisniological observations suggest that there is a gap within the downgoing slab of australian lithosphere plunging beneath the new hebrides and ages of elevated coral tenaces on the new hebrides islands suggest that the islands arc rising rapidly we suggest that the creation of the gap in the slab within the last 1 m y occurred by part of the slab detaching from the rest and sinking rapidly into the underlying asthenosphere this lowered the downward force on the slab at shallower depths and therefore on the overriding plate and the continued decrease of this force as the deeper slab sinks freely has allowed the islands above it to rise although this suggestion cannot account for all aspects of the uplift of the islands it provides a simple mechanism for explaining the fairly young uplift and its distribution along the new hebrides arc

deep geometry of the sudbury structure from seismic reflection profiling seismic reflection data show the deep geometry of the sudbury structure to be markedly asymmetric the sudbury north range comprises shallowly south dipping sedimentary strata overlying a thick unit of heterolithic breccia and melt bodies layered rocks of the sudbury igneous complex and footwall gneiss reflections from the upper layers are interrupted by faults near the center of the sudbury basin whereas the basal mafic units and footwall gneiss continue dipping southward and appear to be tightly folded or truncated near the creighton fault in contrast the seismic image of the south range is dominated by a distinctive series of moderately south dipping reflections interpreted as thrust faults or shear zones on which severe telescoping and imbrication of lithological units and considerable northwest southeast shortening of the sudbury structure have occurred such shortening explains the noncircular shape of the structure and thus removes a critical objection to the sudbury impact crater hypothesis the new structural model is shown to be consistent with regional magnetic and gravity fields a large hidden ultramfic mafic mass is no longer required to explain the potential field data

foraminiferal and δ13c isotopic event stratigraphy across the danian selandian transition at zumaya northern spain chronostratigraphic implications unconformity characterized by a ma jor lithological shift from greyish white oxic limestone chalk of the danskekalk fm upper danian to suboxic glauconitic green sand of the lellinge greensand fm lower selan dian overlain by grey marl and clay of the kerteminde marl fm middle selandian this unconformity was correlated with the sequence bound ary between cycles ta 1 3 and ta 1 4 abstract the zumaya section northern spain is a suitable candidate to define the global stratotype section and point for the base of the selandian stage palaeocene because of its excellent accessibility exposure and stratigraphic continuity uncertain ties exist however with regard to the stratigraphic horizon where to place the danian selandian d s boundary five potential stratigraphic horizons hds1 to hds5 to define the d s boundary have been identified at zumaya based on integrated stratigraphic studies that include quantitative plank tic and benthic foraminiferal results as well as d 13 c isotopic and lithological data two of these horizons hds2 and hds4 placed in zone c26r appear to have particularly good potential for serving as the d s boundary marker because they may represent significant global palaeoceanographic palaeoclimatic and eustatic events

seismotectonics and present day relative plate motions in the new hebrides north fiji basin region abstract relative motions between the pacific plate p indo australian plate ia new hebrides nh arc microplate and the north fiji basin nfb microplate are estimated using shallow seismicity 276 focal mechanism solutions bathymetry magnetism and the rm 2 plate model of minster and jordan 1978 within the nfb we define the western nfb wnfb eastern nfb enfb and southern nfb snfb microplates a 8 cm y spreading in a n72 e direction occurs along the n s trending spreading ridge of nfb wnfb enfb boundary along the enfb ia boundary located at 176 e a 3 cm y extension in a n108 e direction is proposed the wnfb p boundary which includes the hazel holme extensional zone hhez is complex and a general n25 e extension 2 cm y is inferred the fiji fracture zone ffz is composed of two segments along the eastern zone p ia boundary trending n80 e a left lateral strike slip motion occurs 9 6 cm y accommodated by minor n109 e extension pull apart while along the western zone enfb p boundary a n84 e trending left lateral strike slip motion 7 cm y is inferred the wnfb snfb boundary corresponds to a n70 e broad fracture zone along which an e w left lateral strike slip motion is proposed the snfb microplate moves rapidly eastwards 10 5 cm y at 172 e and is almost attached to the ia plate within the nfb an improved model is discussed which includes deformations within the ia and p plates and rotations with euler poles close to the nfb along the new hebrides trench the consumption rates are respectively 16 15 9 and 12 cm y at 11 12 5 15 5 and 20 s the minimum rate occurs where the d entrecasteaux ridge collides with the new hebrides arc rates of extension at the rear of the nh arc are 7 5 5 and 2 cm y at 11 12 5 and 20 s respectively back arc compression occurs between 13 30 s and 17 s the western end of the hazel holme extension zone coincides with the 13 30 s boundary separating the nh back arc compressive belt and the northern nh back arc troughs south of 21 22 s the trend of the slip vector changes along the nh trench from n70 e to n20 w this implies a n s motion of convergence along the e w trending southern part of the nh trench motion snfb ia of 1 5 cm y at 172 e and the existence of a n70 e trending left lateral fracture zone crossing the southern part of the nfb this fracture should be considered as a major plate boundary

thermal evolution and interaction between impact melt sheet and footwall a genetic model for the contact sublayer of the sudbury igneous complex canada 1 the sudbury igneous complex sic and associated ni cu pge mineralization has been interpreted in terms of a large meteorite impact event in this study the thermal relationship between the large cooling melt sheet and the surrounding country rock is examined in terms of its role in an evolving thermal gradient rather than as a passive receptacle for the melt sheet above thermal modeling of this environment is undertaken using physical and thermal constraints appropriate to the sic and assuming heat dissipation from the 2 5 km thick superheated melt sheet 1800 c by either diffusion with zero convection or by rapid convection within the melt sheet with zero convection basal cooling produces a solid base which lowers conductivity such that the immediate footwall rocks reach 1000 c producing partial melting that extends 200 m into the footwall in a rapidly convecting melt sheet the initial footwall chill is remelted and high temperatures maintained within the sheet close to the contact this results in higher temperatures being attained in the immediate footwall 1100 1200 c inducing complete melting of proximal footwall and partial melting to depths of 500 m below the melt sheet proximal footwall consists of paleoproterozoic huronian basalts granitoids and sediments exposed in the south range overlying archaean gneisses and granitoids total and partial melting of this material early in the cooling history of the melt sheet and the subsequent gravitational accommodation of these melts according to density would produce a basalt dominated basal liquid corresponding to the so called contact sublayer the thermal aureole predicted by our models is consistent with that preserved around the north range of the sic assuming 800 m of thermally induced erosion at the contact

the paleozoic to mesozoic carbon cycle revisited the carbon isotopic composition of terrestrial organic matter 1 two thousand one hundred forty eight carbon isotope values for terrestrial organic matter plant fossils coal bulk terrestrial organic matter provide a proxy record for temporal changes in the global carbon cycle 13ctom 13ccarb and 13cco2 allow a full evaluation of carbon transfer in the atmosphere ocean system as well as between the marine and the terrestrial realm the temporal evolution of 13ctom parallels respective data sets from marine carbonate carbon thus reflecting the linkage between both reservoirs via atmospheric carbon dioxide on the basis of a comparison between measured and predicted isotope records for 13ctom changes in the carbon isotopic fractionation associated with plant metabolism are discernible this contradicts the notion of an invariable carbon isotopic fractionation associated with c3 plant metabolism in light of results from current plant growth experiments these changes are viewed as dependent on the atmospheric o2 co2 hence 13ctom might serve as a proxy signal for atmospheric composition

a trishear model for the deformation of the sudbury igneous complex canada abstract the sudbury igneous complex sic canada is an impact induced layered sheet of crystalline rocks deformed into an asymmetrical fold basin the sudbury basin the basin geometry at depth is largely unknown as few attempts were made to quantify displacement and rotation of layer contacts we propose that the dip of layer contacts and foliation surfaces in the southern sic can be approximated by trishear fault propagation folding trishear deformation accounts for 1 angular discordances between upper and basal sic contacts 2 local overturning of the sic 3 progressive steepening of foliation surfaces from nw to se 4 strain gradient in the sudbury basin sedimentary rocks and 5 thickness variations in sic layers moreover the south range shear zone a zone of moderately strong metamorphic fabrics coincides with the surface manifestation of the proposed trishear zone we demonstrate the use of structural data together with forward kinematic modelling to identify the strain distribution within the sic rotation of sic contacts and thickness changes of sic layers backward kinematic modelling provides information on the initial geometry of the sic and is used to restore the shape of the igneous sheet showing that the sic was shortened by approximately 10 km in nw se diameter most of the shortening was accommodated by 40 reduction in the thickness of the upper sic layer

geodetic measurements of convergence across the new hebrides subduction zone between 1990 and 1994 geodetic measurements gps observations have been conducted across the new hebrides subduction zone where the australia plate subducts under the new hebrides arc this paper establishes convergence rate variations along the trench in the south at tanna the relative motion is oriented n244 4 and has a uniform rate of 11 7 0 8 cm yr the rate at efate is 10 3 0 9 cm yr oriented n242 4 both azimuths very well compare with slip vectors of the last major earthquakes in the north the rate at santo is only 3 6 1 2 cm yr oriented n253 26 the difference in the convergence rates between santo on the one hand and efate and tanna in the other hand points to a right lateral shear zone between santo and efate at santo where the plate coupling is very high the very low convergence rate might be related to the absence of recent strong earthquakes no significant variations are detected for the baselines within the australia plate

evidence of an abrupt environmental disruption during the mid paleocene biotic event zumaia section western pyrenees an abrupt environmental disruption occurred in the photic zone and at the seafloor during the mid paleocene biotic event mpbe calcareous nannoplankton planktic foraminifer and benthic foraminifer assemblages at zumaia section western pyrenees underwent a rapid and remarkable transformation the major calcareous plankton assemblage changes suggest a shift from relatively cooler mesotrophic to warmer more oligotrophic conditions indicating a disturbed environment due to the warming of the ocean benthic foraminifer assemblages were also significantly affected by the mpbe diversity of the assemblages and buliminids show net decline and the low food and opportunistic taxa increase in abundance the reorganization of the planktic ecosystem possibly involved changes in the food flux type and quantity to the seafloor thus triggering changes in the benthic communities a 1 negative 13 c shift and a 30 carbonate content decrease are recorded in connection with the biotic event this suggests that during the mpbe as in the paleocene eocene thermal maximum petm an input of a large mass of isotopically depleted carbon into the ocean and atmosphere could have lowered the deep sea ph triggering a rapid shoaling of the lysocline and contributing to greenhouse warming the mpbe was short lived according to the counting of limestonemarl couplets the stratigraphic expression of precession cycles throughout the zumaia section the mpbe lasted for 52 53 k y with the core of the event representing 10 11 k y the zumaia section is the first land based locality in which the mpbe is recognized and described in detail due to its expanded character and excellent paleontological record this section may prove to be a global reference section for the study of this short lived event