new caledonia obducted peridotite nappe offshore extent and implications for obduction and postobduction processes one of the largest ophiolitic peridotite masses in the world covers a quarter of the island of grande terre new caledonia the peridotite nappe was obducted during the eocene is weakly deformed and corresponds to the highest of a structurally simple pile of thrust nappes we present new marine seismic data that allows us to track the offshore continuation of the peridotite nappe along strike for a distance of more than 500 km south of new caledonia and to image its pre syn and post obduction sedimentary records offshore the peridotite nappe underlies a c 150 km wide and 2 km deep basin flat topped horsts of peridotite are clearly bounded by major normal faults in contrast faults are obscure onland to the east the peridotite nappe roots along the eastern margin of the felicite ridge new name a c 300 x 25 km dome shaped ridge which we interpret as being the southern extension of the hp lt metamorphic core complex observed in new caledonia two alternative tectonic models address the relative timing and relationships between peridotite nappe emplacement uplift of a metamorphic core complex and extensional tectonics these models provide new ideas for the understanding the formation of the eastern margin of the zealandia continent our results contribute to an understanding of how oceanic mantle is emplaced onto continental margins

the metamorphic sole of new caledonia ophiolite 40ar 39ar u pb and geochemical evidence for subduction inception at a spreading ridge amphibolite lenses that locally crop out below the serpentinite sole at the base of the ophiolite of new caledonia termed peridotite nappe recrystallized in the high temperature amphibolite facies and thus sharply contrast with blueschists and eclogites of the eocene metamorphic complex amphibolites mostly display the geochemical features of morb with a slight nb depletion and thus are similar to the youngest late paleocene eocene babb components of the allochthonous poya terrane thermochronological data from hornblende 40ar 39ar zircon and sphene u pb suggest that these mafic rocks recrystallized at 56ma using various geothermobarometers provides a rough estimate of peak recrystallization conditions of 0 5gpa at 800 950c the thermal gradient inferred from the metamorphic assemblage 60 ckm 1 geometrical relationships and geochemical similarity suggest that these mafic rocks belong to the oceanic crust of the lower plate of the subduction obduction system and recrystallized when they subducted below young and hot oceanic lithosphere they were detached from the down going plate and finally thrust onto unmetamorphosed poya terrane basalts this and the occurrence of slab melts at 53ma suggest that subduction inception occurred at or near to the spreading ridge of the south loyalty basin at 56ma 2012 american geophysical union all rights reserved

eocene and oligocene basins and ridges of the coral sea new caledonia region tectonic link between melanesia fiji and zealandia this paper presents 34 geochemical analyses 24 ar ar ages and two u pb ages of igneous rocks from the back arc basins and submarine ridges in the coral sea new caledonia region the d entrecasteaux ridge is a composite structural feature primitive arc tholeiites of eocene age 34 56 ma are present along a 200 km length of the ridge and arguably were part of the initial line of subduction inception between fiji and the marianas substantial eocene arc edifices are only evident at the eastern end where bougainville guyot andesite breccias are dated at 40 2 ma the south rennell trough is confidently identified as a 28 29 ma early oligocene fossil spreading ridge and hence the flanking santa cruz and d entrecasteaux basins belong in the group of sw pacific eocene early miocene back arc basins that include the solomon sea north loyalty and south fiji basins the rate and duration of spreading in the north loyalty basin is revised to 43 mm yr between 28 and 44 ma longer and faster than previously recognized the direction of its opening was to the southeast that is parallel to the continent ocean boundary and perpendicular to the direction of coeval new caledonia ophiolite emplacement medium and high k alkaline lavas of 23 25 ma late oligocene age on the northern norfolk ridge are an additional magmatic response to pacific trench rollback

fission track dating of haughton astrobleme and included biota devon island canada haughton astrobleme is a major extraterrestrial impact structure located on devon island in the canadian arctic archipelago northwest territories apatite grains separated from shocked precambrian gneiss contained in a polymict breccia from the center of the astrobleme yielded a fission track date of 22 4 million 1 4 million years before the present or early miocene aquitanian this provides a date for the impact event and an upper limit on the age of crater filling lake sediments and a flora and vertebrate fauna occurring in them a geologically precise date for these fossils provides an important biostratigraphic reference point for interpreting the biotic evolution of the arctic

effect of volatiles and target lithology on the generation and emplacement of impact crater fill and ejecta deposits on mars impact cratering is an important geological process on mars and the nature of martian impact craters may provide important information as to the volatile content of the martian crust terrestrial impact structures currently provide the only ground truth data as to the role of volatiles and an atmosphere on the impact cratering process recent advancements based on studies of several well preserved terrestrial craters have been made regarding the role and effect of volatiles on the impact cratering process combined field and laboratory studies reveal that impact melting is much more common in volatile rich targets than previously thought so impact melt rocks melt bearing breccias and glasses should be common on mars consideration of the terrestrial impact cratering record suggests that it is the presence or absence of subsurface volatiles and not the presence of an atmosphere that largely controls ejecta emplacement on mars furthermore recent studies at the haughton and ries impact structures reveal that there are two discrete episodes of ejecta deposition during the formation of complex impact craters that provide a mechanism for generating multiple layers of ejecta it is apparent that the relative abundance of volatiles in the near surface region outside a transient cavity and in the target rocks within the transient cavity play a key role in controlling the amount of fluidization of martian ejecta deposits this study shows the value of using terrestrial analogues in addition to observational data from robotic orbiters and landers laboratory experiments and numerical modeling to explore the martian impact cratering record

seagrass related carbonate ramp development at the front of a fan delta burdigalian new caledonia insights into mixed carbonate siliciclastic environments abstract past shallow water carbonate environments of the main island of new caledonia nc have been subject to high terrigenous influx derived from the erosion of ultramafic obducted nappes and are therefore a relevant case study for characterizing neritic carbonate production in mixed carbonate siliciclastic systems under a tropical climate more particularly we focused on burdigalian carbonate sedimentary records cropping out on the western coast of nc in the nepoui area based on a comprehensive sedimentological study of cores and outcrops we established a new depositional model of an alluvial fan to carbonate ramp transition shallow water euphotic carbonate production was dominated by seagrass related biota and corals derived from small sized bioconstructions extensional tectonics and associated normal faulting driven by post obduction isostatic rebound favored carbonate ramp aggradation and preservation the carbonate ramp was incised by conglomerate filled terminal distributary channels which indicate that terrigenous inputs remained significant during marine transgression and did not inhibit the development of seagrass and scleractinian carbonate factories phytal substrates induced by seagrass and or macro algae seafloor colonization strongly controlled the nature of carbonate production and promoted the accumulation of foraminiferal coralline algal sediments seagrass development at the front of the fan delta is interpreted to have controlled the preservation of a diverse and significant carbonate production by reducing water turbidity and by limiting the risk of suffocation for filter feeding biota in such a high terrigenous influx setting

geological overview and cratering model for the haughton impact structure devon island canadian high arctic the haughton impact structure has been the focus of systematic multi disciplinary field and laboratory research activities over the past several years regional geological mapping has refined the sedimentary target stratigraphy and constrained the thickness of the sedimentary sequence at the time of impact to 1880 m new 40ar 39ar dates place the impact event at 39 ma in the late eocene haughton has an apparent crater diameter of 23 km with an estimated rim final crater diameter of 16 km the structure lacks a central topographic peak or peak ring which is unusual for craters of this size geological mapping and sampling reveals that a series of different impactites are present at haughton the volumetrically dominant crater fill impact melt breccias contain a calcite anhydrite silicate glass groundmass all of which have been shown to represent impact generated melt phases these impactites are therefore stratigraphically and genetically equivalent to coherent impact melt rocks present in craters developed in crystalline targets the crater fill impactites provided a heat source that drove a post impact hydrothermal system during this time haughton would have represented a transient warm wet microbial oasis a subsequent episode of erosion during which time substantial amounts of impactites were removed was followed by the deposition of intracrater lacustrine sediments of the haughton formation during the miocene present day intracrater lakes and ponds preserve a detailed paleoenvironmental record dating back to the last glaciation in the high arctic modern modification of the landscape is dominated by seasonal regional glacial and niveal melting and local periglacial processes the impact processing of target materials improved the opportunities for colonization and has provided several present day habitats suitable for microbial life that otherwise do not exist in the surrounding terrain

efficient calculation of complete differential seismograms for laterally homogeneous earth models summary differential seismograms the sensitivity of the seismogram to perturbations of parameters of the earth model are essential for waveform modelling with iterative non linear optimization techniques the growing number of broad band highdynamic range fixed and portable stations provide a rich data set of regional distance events with accurate locations and source mechanisms that are ideal for modelling lithospheric structure an efficient technique for calculating differential seismograms for complete synthetic seismograms in laterally homogeneous earth models will significantly decrease the computational burden of seismic waveform inverse modelling the technique we present here is equivalent to computing three synthetic seismograms in multilayered models contrasted with n 1 seismograms for a typical brute force approach which reduces the work to 3 n 1 or about a 90 per cent saving for 30 layers the lateral homogeneity requirement will yield path averaged structures which may form the basis for later tomographic studies to resolve lateral variations

upper mantle structure of the southwest pacific from regional waveform inversion we determine the upper mantle seismological structure of the southwest pacific by inverting complete regional seismograms recorded by the southwest pacific seismic experiment a deployment of 12 broadband seismographs in the fiji tonga and niue islands we first present a method to invert entire seismic waveforms for a laterally homogeneous velocity structure partial derivatives are computed using an efficient reflectivity code for differential seismograms randall 1994 and a conjugate gradient method is used to perform the nonlinear inversion band pass filtered 10 55 mhz vertical and radial component seismograms extending from the p arrival to the surface waves are used to constrain the structure waveforms are selected to provide regional distance 400 1500 km propagation paths predominantly within one of the tectonic regions of the southwest pacific source depths ranging from 10 to 240 km allow the deeper regions of the model to be resolved with relatively short path lengths results show extremely large lateral variability in the upper mantle structure of the southwest pacific the inactive south fiji basin shows upper mantle velocities much lower than those previously observed for the pacific lithosphere of a similar age the north fiji and lau basins containing active back arc spreading systems show upper mantle shear velocities as slow as 3 8 km s 1 the exceptionally low seismic velocities in the active back arc regions may represent the slowest upper mantle velocities in the world the velocity difference between the active back arc basins and the old pacific lithosphere immediately east of the tonga trench is maximum at 30 90 km depth with a variation of 18 indicating partial melting in this depth range velocity heterogeneity of 4 extends to a depth of 170 km velocity structure below 220 km depth is poorly resolved but there is some evidence of a 2 difference extending to depths of 350 km

linear volcanoes along the pacific cocos plate boundary 9 n to the galapagos triple junction abstract a seabeam based reconnaissance of the 500 km of the east pacific rise crest between 7 n and 2 40 n shows that the axial ridge is segmented by four 4 13 km non transform offsets into an en echelon string of distinctively different linear volcanoes these axial volcanoes are oriented orthogonal to relative plate motion except where their overlapping ends veer 15 toward each other and where small intra volcano offsets of their crestal rift zones create abrupt kinks longitudinal gradients of the crestlines are less than 5 m km except where they plunge at rift zones overlapped ends and where they rise locally to small axial peaks transverse profiles vary from trapezoidal to triangular with a steep shield shaped cross section being most common conventional sounding data indicate that this pattern continues to the 140 km offset siqueiros transform fault system at 8 2 n within this fault system is a short spreadingcenter volcano contained in a rift valley that links two strike slip fault zones immediately to the north is the shallow 9 0 8 3 n axial volcano with unusual relief mapped by a deeply towed instrument package at the southern end of the plate boundary as the rise crest enters the region of the pacific cocos nazca triple junction the axial ridge narrows deepens and acquires a more irregular long profile south of 2 30 n the rise crest has a 15 km wide rift valley that contains multiple volcanic ridges with north south strikes structural hypotheses suggested or supported by these morphologic observations include a point source magma supply to the spreading center from mantle diapirs the along strike continuity of axial magma chambers on fast spreading rises even across small rift zone offsets and the importance of magma intrusion as well as eruption for building the axial ridge hypotheses inconsistent with the new data include magma supply and long distance dispersal from a few widely spaced plumes primary control of the topographic volcanic and tectonic characteristics of the rise crest by distance from transform faults and localization of triple junctions over major mantle upwellings

slab derived origin of tremolite antigorite veins in a supra subduction ophiolite the peridotite nappe new caledonia as a case study hydration of mantle peridotites provides information on the exhumation history and on the fluid regime accompanying exhumation of these rocks reservoirs involved fluid rock ratios temperature of interaction highly depleted harzburgites and dunites of the peridotite nappe of new caledonia are crosscut by fractures which have been pervasively serpentinized producing lizardite brucite magnetite and minor chrysotile in a near static environment probably by sea water circulating in cooling joints this event is generally referred to as primary serpentinization in a next step already serpentinized joints were re opened to produce tension and shear cracks sealed by higher temperature synkinematic fibrous minerals locally tremolite bearing veins and pockets which do not display evidence for void infill were generated by metasomatic replacement of the wall rock peridotite most veins only contain fibrous antigorite but some display tremolite antigorite intergrowths or even pure tremolite the latter rocks yield high contents of ca and incompatible elements which contrast with the overall depletion of the peridotite host rock and suggest contribution of an external source whole rock geochemical and isotopic features 87sr 86sr 18o and h suggest that antigorite veins which bear highly radiogenic sr isotope signatures were strongly influenced by fluids emitted by the subducted slab and associated sediments in contrast the geochemical and isotopic signatures of tremolite bearing rocks suggest a genetic link with early eocene supra subduction dykes and fluids that leached them calcium strontium and ree bearing oxidized fluids reacted with already serpentinized fracture wall rock as shown by fibre nucleation chromite alteration and high cr contents in tremolite the bulk of syn tectonic fluid rock interaction associated with shear and tensile fracture development probably occurred at the onset of eocene intra oceanic subduction when the buoyant lower plate the south loyalty basin obliquely forced its way beneath the nascent loyalty fore arc mobile elements extracted from supra subduction dykes temporarily enriched the circulating fluids and generated tremolite antigorite mg chlorite and magnetite instead of antigorite and magnetite solely tremolite crystallization probably ceased due to the exhaustion of ca rich fluids in a globally cooling fore arc environment

eocene arc continent collision in new caledonia and implications for regional southwest pacific tectonic evolution new caledonia preserves evidence that constrains models for the tectonic evolution of the southwest pacific region onland geology reflects four main tectonic phases 1 early mesozoic development of subduction related terranes and their accretion to the gondwana margin 2 cretaceous passive margin development and sea floor spreading during the gondwana breakup 3 foundering of an oceanic basin and the eocene arrival of thinned gondwana margin crust at a southwest facing subduction zone resulting in collisional orogenesis and obduction of an ophiolitic nappe from the northeast and 4 detachment faulting during extensional collapse resulting in unroofing of metamorphic core complexes the last phase explains supposedly anomalous metamorphic gradients in the northeast of the island

application of organic geochemistry to detect signatures of organic matter in the haughton impact structure organic geochemistry applied to samples of bedrock and surface sediment from the haughton impact structure detects a range of signatures representing the impact event and the transfer of organic matter from the crater bedrock to its erosion products the bedrock dolomite contains hydrocarbon bearing fluid inclusions which were incorporated before the impact event comparison of biomarker data from the hydrocarbons in samples inside and outside of the crater show the thermal signature of an impact the occurrence of hydrocarbon inclusions in hydrothermal mineral samples shows that organic matter was mobilized and migrated in the immediate aftermath of the impact the hydrocarbon signature was then transferred from bedrock to the crater fill lacustrine deposits and present day sediments in the crater including wind blown detritus in snow ice separate signatures are detected from modern microbial life in crater rock and sediment samples signatures in haughton crater samples are readily detectable because they include hydrocarbons generated by the burial of organic matter this type of organic matter is not expected in crater samples on other planets but the haughton data show that using very high resolution detection of organic compounds any signature of primitive life in the crater rocks could be transferred to surface detritus and so extend the sampling medium

impact generated carbonate melts evidence from the haughton structure canada evidence is presented for the melting of dolomite rich target rocks during formation of the 24 km diameter 23 ma haughton impact structure on devon island in the canadian high arctic field studies and analytical scanning electron microscopy reveal that the s 200 m thick crater fill deposit which currently covers an v60 km 2 area in the center of the structure comprises fragmented target rocks set within a carbonate silicate matrix the silicate component of the matrix consists of si al mg rich glass the carbonate component is microcrystalline calcite containing up to a few wt si and al the calcite also forms spherules and globules within the silicate glass with which it develops microtextures indicative of liquid immiscibility dolomite clasts exhibit evidence of assimilation and may show calcite and rare dolomite overgrowths some clasts are penetrated by calcite and silicate injections along with the carbonate silicate glass textures the presence of pigeonite and spinifex textured diopside suggests that the matrix to the crater fill deposit was originally molten and was rapidly cooled this indicates that the impact event that generated haughton caused fusion of the predominantly dolomitic target rocks it appears that the ca mg component of the dolomite may have dissociated with mg entering the silicate melt phase while the ca component formed a caco3 dominant melt the silicates were derived by the fusion of lower paleozoic sandstones siltstones shales and impure dolomites evidence for melting is corroborated by a review of theoretical and experimental work which shows that caco3 melts at s 10 gpa and s 2000 k instead of dissociating to release co2 this work indicates that carbonate rich sedimentary targets may also undergo impact melting and that the volume of co2 released into the atmosphere during such events may be considerably less than previously estimated fl 2001 elsevier science b v all rights reserved

tsunami backwash deposits with chicxulub impact ejecta and dinosaur remains from the cretaceous palaeogene boundary in the la popa basin mexico the la popa basin in north eastern mexico features outstanding continuous three dimensional exposures of the cretaceous palaeogene boundary event deposit in shallow shelf environments pierced by salt stocks in the area to the south east of the el papalote diapir the cretaceous palaeogene deposit consists of two superimposed sedimentary units and erosively overlies upper maastrichtian sand siltstones with soft sediment deformation and liquefaction structures the basal unit 1 is an up to 8 m thick chaotic carbonate rich bed that discontinuously fills incised gutters and channels besides abundant silicic and carbonate ejecta spherules from the chicxulub impact unit 1 includes large sandstone boulders and abundant shallow water debris for example mud clasts algae bivalve shells gastropod shells and vertebrate remains unit 1 is conformably overlain by unit 2 distal to the diapir unit 2 consists of a centimetre to decimetre thick conglomeratic coarse bioclast and spherule bearing sandstone bed closer to the diapir unit 2 becomes a metre thick series of four to eight conglomeratic to fine grained graded sandstone beds rich in shell debris and ejecta spherules unit 2 is conformably overlain by structureless to parallel laminated sandstone beds that may mark the return to the pre event depositional regime the sedimentary characteristics of the cretaceous palaeogene deposit including its erosive base its sheet like geometry the presence of multiple graded beds evidence for upper flow regime conditions and the absence of bioturbation support an origin by a short term multiphase depositional event the occurrence of soft sediment deformation structures for example liquefaction below the cretaceous palaeogene deposit suggests that earthquakes were the first to occur at la popa then shelf collapse and strong backflow from the first tsunami waves may have triggered erosion and deposition by violent ejecta rich hyperconcentrated density flows unit 1 subsequently a series of concentrated density flows resulting from tsunami backwash surges may have deposited the multiple graded bedding structures of unit 2 the specific depositional sequence and the fe mg rich as well as si k rich composition of the ejecta spherules both provide a critical link to the well known deep marine cretaceous palaeogene boundary sites in the adjacent burgos basin in north eastern mexico moreover the pulse like input of chicxulub ejecta material at the base of the event deposit allows for correlation with other cretaceous palaeogene boundary sites in the gulf of mexico and the atlantic as well as in central and northern america the presence of diverse dinosaur and mosasur bones and teeth in the event deposit is the first observation of such remains together with chicxulub ejecta material these findings indicate that dinosaurs lived in the area during the latest maastrichtian and suggest that the tsunami waves not only eroded deltas and estuaries but the coastal plain as well

deep structure and seismic anisotropy beneath the east pacific rise seismic velocities in the upper mantle beneath mid ocean ridges are known to exhibit anisotropy especially at depths shallower than 200 km in this study we present evidence for deeper anisotropy beneath fast spreading ridges based on simultaneous inversion of body wave travel times waveforms and surface wave phase velocities the dverticalt bsv shear wave speed is systematically faster by more than 2 than the dhorizontalt bsh one at depths of 200 300 km beneath the east pacific rise a result that is consistent with vertical alignment of the fast crystallographic axis of olivine this anomaly is especially coherent beneath the northern east pacific rise where the observations also support the presence of a modest mantle reflector near 260 km depth the anisotropy may be associated with deep vertical flow or finite strain and the presence of this reflector could signal a rheological transition near the bottom of the asthenosphere reflecting changes in flow direction development of partial melt or the persistence of a deep pre existing strain regime d 2005 elsevier b v all rights reserved

endolithic cyanobacteria in soil gypsum occurrences in atacama chile mojave united states and al jafr basin jordan deserts 1 soil sulfates are present in arid and hyperarid environments on earth and have been found to be abundant in soils on mars examination of soil gypsum from the atacama desert chile the mojave desert united states and al jafr basin jordan revealed endolithic cyanobacteria communities just below the surface of soil gypsum samples optical and scanning electron microscope observations of the colonized layers indicated that the unicellular chroococcidiopsis is the dominant cyanobacterium in all studied communities 16s rrna gene analysis revealed that in addition to chroococcidiopsis a few other cyanobacteria are present heterotrophic bacteria are also abundant in the colonized zones of the fine grained gypsum from the atacama and mojave desert but insignificant in the fibrous gypsum from the jordan desert endolithic life forms similar to these described here may exist or have existed on mars and should be targeted by the mars science laboratory and future in situ missions

nickel dispersion and enrichment at the bottom of the regolith formation of pimelite target like ores in rock block joints koniambo ni deposit new caledonia in new caledonian ni deposits the richest ni silicate ores occur in fractures within the bedrock and saprolite generally several tens of meters to hundred meters below the present day surface fracture related ni silicate ore accounts for high ni grades at least a few weight percent above the average exploited grade 2 5 these ni rich veins are affected by active dissolution precipitation processes at the level of the water table ni in solution is precipitated as silicates in thin layer cementing joints this mineralization is characterized by chemical and mineralogical concentric zoning with an outer green rim around an inner white zone composed from the edge to the centre of the block i a highly oxidized and altered zone ii a green pure ni rich pimelite zone iii a zone limited to a few centimetres with a mixture of ni poor kerolite and ni rich pimelite and intermediate colours and iv a large white mg kerolite mineralization zone this study proposes that the concentric zonation results from evapo precipitation process related to alternate periods of hydration and drying induced by water table movements this extensive dispersion of ni in concentrically zoned ores can partly explain the rather monotonous ni grade of the bulk exploitation at the base of the regolith with values between 2 and 3 wt

motion of the rivera plate since 10 ma relative to the pacific and north american plates and the mantle abstract to better understand the influence of rivera plate kinematics on the geodynamic evolution of western mexico we use more than 1400 crossings of seafloor spreading magnetic lineations along the pacific rivera rise and northern mathematician ridge to solve for rotations of the rivera plate relative to the underlying mantle and the pacific and north american plates at 14 times since 9 9 ma our comparison of magnetic anomaly crossings from the undeformed pacific plate to their counterparts on the rivera plate indicates that significant areas of the rivera plate have deformed since 9 9 ma dextral shear along the southern edge of the plate from 3 3 2 2 ma during a regional plate boundary reorganization deformed the rivera plate farther into its interior than previously recognized in addition seafloor located north of two rupture zones within the rivera plate sutured to north america after 1 5 ma anomaly crossings from these two deformed regions thus cannot be used to reconstruct motion of the rivera plate finite rotations that best reconstruct pacific plate anomaly crossings onto their undeformed counterparts on the rivera plate yield stage spreading rates that decrease gradually by 10 between 10 and 3 6 ma decrease rapidly by 20 after 3 6 ma and recover after 1 ma the slowdown in pacific rivera seafloor spreading at 3 6 ma coincided with the onset of dextral shear across the then incipient southern boundary of the rivera plate with the pacific plate the available evidence indicates that the rivera plate has been an independent microplate since at least 10 ma contrary to published assertions that it fragmented from the cocos plate at 5 ma motion of the rivera plate relative to north america has changed significantly since 10 ma in concert with significant changes in pacific rivera motion a significant and robust feature of rivera north america motion not previously recognized is the cessation of margin normal convergence and thus subduction from 2 6 to 1 0 ma along the entire plate boundary followed by a resumption of trench normal subduction along the southern half of the rivera north america plate boundary after 1 0 ma motion of the rivera plate relative to the underlying mantle since 10 ma has oscillated between periods of landward motion and seaward motion the evidence suggests that the torque exerted by slab pull on this young and hot oceanic plate is either minimal or is effectively counterbalanced by forces that resist its motion

endolithic microorganisms in the antarctic cold desert in the frigid desert of the antarctic dry valleys there are no visible life forms on the surface of the soil or rocks yet in certain rock types a narrow subsurface zone has a favorable microclimate and is colonized by microorganisms dominant are lichens of unusual organization they survive not by physiological adaptation to lower temperatures but by changing their mode of growth being able to grow between the crystals of porous rocks their activity results in mobilization of iron compounds and in rock weatherning with a characteristic pattern of exfoliation this simple ecosystem lacks both higher consumers and predators

origin of the new caledonian ophiolites based on a french australian seismic transect abstract the origin age and nature of the new caledonian ophiolites are still debated recently as part of the joint french australian seismic transect faust program the australian research vessel rig seismic recorded a series of multichannel deep seismic profiles between the new hebrides arc and the australian margin these profiles which ran south of new caledonia image the southern prolongation of the overthrusted ophiolites and allow a new interpretation of the eocene compressive tectonism along the new caledonia norfolk ridge a model involving abduction of the whole oceanic lithosphere of the loyalty basin is consistent with the age and origin of the ophiolite variations in tectonic style along strike in the north south trending part of the norfolk ridge have produced ophiolite exposures related to uplifted and partially overthrust upper mantle slivers within the southern part of the loyalty basin

geochemistry and tectonic setting of matakaoa volcanics east coast allochthon new zealand suprasubduction zone affinity regional correlations and origin in north eastern new zealand the late cretaceous to eocene submarine volcanic rocks of the east coast allochthon referred to as matakaoa volcanics formed a dominantly mafic melange with minor abyssal sediments during the subduction of oceanic crust accreted and melanged pillow lavas and dolerites display the geochemical and isotopic features of tholeiites with some diversity referred to as midocean ridge basalts island arc tholeiites and back arc basin basalts the association of supra subduction tholeiitic magmas abyssal sediments and polymetallic volcanogenic sulphide deposits is typical of many back arc basins therefore a correlation with the alkaline and transitional basalts of the hikurangi manihiki ontong java plateau may be ruled out these petrological features and the fossil ages as well are closely similar to those of the tangihua complex northland allochthon and allow matakaoa and tangihua mafic volcanic rocks now separated by the modern havre trough to be correlated within one single late cretaceous to eocene 2 basin the consideration of possible younger ages oligocene is also discussed the occurrence of late cretaceous eocene oceanic crust with supra subduction zone affinities to the east of the norfolk ridge poses the problem of the intervening southwest dipping subduction the missing late cretaceous eocene arc and their relationship with southeast gondwana marginal break up

the importance of being cratered the new role of meteorite impact as a normal geological process this paper is a personal and in many ways incomplete view of the past development of impact geology and of the newly recognized importance of impact events in terrestrial geological history it also identifies some exciting scientific challenges for future investigators to determine the full range of impact effects preserved on the earth to apply the knowledge obtained from impact phenomena to more general geological problems and to continue the merger of the once exotic field of impact geology with mainstream geosciences since the recognition of an impact event at the cretaceous tertiary k t boundary much current activity in impact geology has been promoted by traditionally trained geoscientists who have unexpectedly encountered impact effects in the course of their work their studies have involved 1 the recognition of additional major impact effects in the geological record the chesapeake bay crater the alamo breccia and multiple layers of impact spherules in precambrian rocks and 2 the use of impact structures as laboratories to study general geological processes e g igneous petrogenesis at sudbury canada and archean crustal evolution at vredefort south africa other research areas in which impact studies could contribute to major geoscience problems in the future include 1 comparative studies between low level 7 gpa shock deformation of quartz and the production of quartz cleavage in both impact and tectonic environments and 2 the nature origin and significance of bulk organic carbon kerogen and other carbon species in some impact structures gardnos norway and sudbury canada

multistage crack seal vein and hydrothermal ni enrichment in serpentinized ultramafic rocks koniambo massif new caledonia sets of fractures and breccia sealed by ni rich silicates and quartz occur within saprock of the new caledonian regolith developed over ultramafic rocks the crystallization sequence in fractures is as follows 1 serpentine stage lizardite polygonal serpentine white lizardite 2 ni stage ni mg kerolite followed by red brown microcrystalline quartz and 3 supergene stages the red brown microcrystalline quartz corresponds to the very last stage of the ni sequence and is inferred to have precipitated within the 50 95 c temperature range it constitutes also the main cement of breccia that has all the typical features of hydraulic fracturing the whole sequence is therefore interpreted as the result of hydrothermal fluid circulation under medium to low temperature and fluctuating fluid pressure although frequently described as the result of a single downward redistribution of ni and mg leached in the upper part of the regolith under ambient temperature the ni silicate veins thus appear as the result of recurrent crack and seal process corresponding to upward medium temperature fluid convection hydraulic fracturing and subsequent fluid mixing and mineral deposition

haughton impact structure structural and morphological aspects haughton is a complex meteorite impact structure of tertiary age on devon island in the canadian arctic the 20 5 km diameter site was formed in essentially flat lying paleozoic carbonates roughly 1700 m in thickness overlying precambrian gneisses the structure comprises three concentric rings surrounding a central basin with interior peaks the outer ring diameter 20 5 km is an annulus of peaks separating the allen bay dolomites of the regional plateau from the same unit that has been downdropped towards the crater interior along a series of circumferential faults the middle ring of peaks diameter 14 15 km comprises both faulted allen bay dolomites and blocks of the underlying bay fiord formation uplifted 250 m hills of the inner elliptical ring 3 5 5 5 km in diameter are also formed from bay fiord formation and the underlying eleanor river formation brought up 600 m an interconnected series of normal faults occupies most of the annulus between the inner and outer rings within the central b

a drastic lower miocene regolith evolution triggered by post obduction slab break off and uplift in new caledonia a lower miocene coarse conglomerate that crops out in the nepoui peninsula does not represent the base of the marine transgression that followed obduction in new caledonia instead the conglomeratic alluvial fan that contains peridotite cobbles and reworked weathering products records a short lived episode of terrestrial erosion intercalated between two intervals of subsidence marked by marine carbonate deposition considering the miocene sea level evolution reported in the literature it is concluded that neither lower miocene transgression nor erosion were driven by sea level variation in contrast a southeastward propagating slab tear that initiated at the latitude of the high pressure low temperature metamorphic complex of northern new caledonia likely generated east to west tilting of new caledonia subsidence along the west coast and hence fringing reef development together with moderate erosion of older regolith coincidence between conglomerate deposition and hence prominent erosion that closely followed emplacement of postobduction granitoids influenced by a slab window suggests a genetic link therefore it is concluded that short lived lower miocene erosion was due to slab breakoff and subsequent uplift that occurred at 22 ma lower miocene erosion profoundly dissected the peridotite nappe and in the northern half of new caledonia only left isolated klippes along the west coast

re evaluating the age of the haughton impact event we have re evaluated the published age information for the haughton impact structure which was believed to have formed 23 ma ago during the miocene age and report new ar ar laser probe data from shocked basement clasts this reveals an eocene age which is at odds with the published miocene stratigraphic apatite fission track and ar ar data we discuss our new data within this context we have found that the age of the haughton impact structure is 39 ma which has implications for both crater recolonization models and post impact hydrothermal activity future work on the relationship between flora and fauna within the crater and others at high latitude may resolve this paradox

shock induced changes in density and porosity in shock metamorphosed crystalline rocks haughton impact structure canada abstract shock metamorphism can occur at transient pressures that reach tens of gpa and well over 1000 c altering the target material on both megascopic and microscopic scales this study explores the effects of shock metamorphism on crystalline quartzofeldspathic basement material from the haughton impact structure on devon island arctic canada shock levels were assigned to samples based on petrographic examination of main mineral phases conventional shock classification schemes proved to incompletely describe the haughton samples so a modified shock classification system is presented fifty two crystalline bedrock samples from the clast rich impact melt rocks in the crater and one reference site outside of the crater were classified using this system the shock levels range from 0 to 7 according to the new shock stage classification proposed here i e stages 0 iv after the stoffler classification indicating shock pressures ranging from 0 to approximately 80 gpa the second aspect of this study involved measuring bulk physical characteristics of the shocked samples the bulk density grain density and porosity were determined using a water displacement method a bead displacement method and a hepycnometer results suggest a nonlinear negative correlation between density and shock level such that densities of crystalline rocks with original densities of approximately 3 g cm 3 are reduced to 1 0 g cm 3 at high shock levels the results also show a positive nonlinear correlation between porosity and shock level these data illustrate the effect of shock on the bulk physical characteristics of crystalline rocks and has implications for assessing the habitability of shocked rocks

tectonic history of northern new caledonia basin from deep offshore seismic reflection relation to late eocene obduction in new caledonia southwest pacific new high quality multichannel seismic reflection data from the western new caledonia offshore domain allow for the first time the direct continuous connection of seismic reflectors between the deep sea drilling project 208 drill hole on the lord howe rise and the new caledonia basin a novel seismic interpretation is hence proposed for the northern new caledonia basin stratigraphy which places the eocene oligocene unconformity deeper than previously thought and revisits the actual thickness of the pre oligocene sequences a causal link is proposed between the obduction of the south loyalty basin over new caledonia nc and the tectonic history of the northern new caledonia basin here it is suggested that as the south loyalty basin was being obducted during early oligocene times the nc basin subsided under the effect of the overloading and underthrusted to accommodate the compressional deformation which resulted in 1 the uplift of the northern fairway ridge and 2 the sinking of the western flank of new caledonia this event also had repercussions farther west with the incipient subsidence of the lord howe rise

natural building stone composed of light transmissive minerals impacts on thermal gradients weathering and microbial colonization a preliminary study tentative interpretations and future directions a number of modern buildings employing claddings of granites or marbles have experienced bowing of the rock panels together with weathering of the material theoretical and field based data analysis and laboratory experimentation have assumed that heat exchange resulting from incoming solar radiation is at the material surface however a number of recent experiments have clearly shown that some lithologies including both marble and granite comprise a number of light transmissive minerals that significantly change the thermal responses in the outer few millimetres of the rock further this translucence will create mineral to mineral stresses where light transmissive minerals are in contact with opaque ones the whole is further exacerbated by differences in thermal coefficients of expansion and conductivity which themselves may depend on the mineral axis surface modifiers such as paints further complicate the situation the degree of light penetration based on field measurements can be significant and can facilitate rapid changes in temperature t t 2 c min 1 at depth within the rock thereby increasing the sub surface stresses the amount of light penetration for any given mineral will be dependent upon material slope the latitude season and albedo albedo is identified as a complex variable changing as a function of the angle of the sun to the particular surface polished surfaces as often with cladding will further influence this data analysis suggests that in the northern hemisphere south of the polar circle the summer may not be the time of the largest heat loading on the southern aspect and that larger loadings coupled with lower air temperatures occur early and late in the year this seasonal impact has great potential for thermal stresses on the southern aspect the presence of light transmissive minerals also allows sub surface biotic colonization and results in weathering overall where light transmissive minerals lithologies occur the thermal responses are highly complex and in need of more rigorous consideration

igneous rocks formed by hypervelocity impact abstract igneous rocks are the primary building blocks of planetary crusts most igneous rocks originate via decompression melting and or wet melting of protolith lithologies within planetary interiors and their classification and compositional petrographic and textural characteristics are well studied as our exploration of the solar system continues so too does the inventory of intrusive and extrusive igneous rocks settings and processes the results of planetary exploration have also clearly demonstrated that impact cratering is a ubiquitous geological process that has affected and will continue to affect all planetary objects with a solid surface whether that be rock or ice it is now recognized that the production of igneous rocks is a fundamental outcome of hypervelocity impact the goal of this review is to provide an up to date synthesis of our knowledge and understanding of igneous rocks formed by hypervelocity impact following a brief overview of the basics of the impact process we describe how and why melts are generated during impact events and how impact melting differs from endogenic igneous processes while the process may differ we show that the products of hypervelocity impact can share close similarities with volcanic and shallow intrusive igneous rocks of endogenic origin such impact melt rocks as they are termed can display lobate margins and cooling cracks columnar joints and at the hand specimen and microscopic scale such rocks can display mineral textures that are typical of volcanic rocks such as quench crystallites ophitic porphyritic as well as features such as vesicles flow textures and so on historically these similarities led to the misidentification of some igneous rocks now known to be impact melt rocks as being of endogenic origin this raises the question as to how to distinguish between an impact versus an endogenic origin for igneous like rocks on other planetary bodies where fieldwork and sample analysis may not be possible and all that may be available is remote sensing data while the interpretation of some impact melt rocks may be relatively straightforward e g for clast rich varieties and those with clear projectile contamination we conclude that distinguishing between impact and endogenic igneous rocks is a non trivial task that ultimately may require sample investigation and analysis to be conducted caution is therefore urged in the interpretation of igneous rocks on planetary surfaces

teleseismic imaging of subaxial flow at mid ocean ridges traveltime effects of anisotropic mineral texture in the mantle summary deformation of peridotite caused by mantle flow beneath an oceanic spreading centre can result in the development of seismic anisotropy traveltime anomalies and shearwave splitting will develop as seismic energy propagates through such an anisotropic region thus providing a signature of the deformation field at depth in this study we investigate the nature of deformation associated with mantle upwelling for two models of flow in the upper 100 km of the mantle the finite strain fields of the passive upwelling model versus the buoyancy enhanced upwelling model are quite different this suggests that mineral aggregates deform differently in the two models thus developing seismic signatures that are distinguishable numerical estimates of the corresponding mineral textures are made using polycrystal theory for olivine with four operative slip systems the activation of a slip system is determined for each grain on the basis of the local critical resolved shear stress the computed grain deformation reflects a balance between stress equilibrium for the aggregate as a whole and strain continuity between neighbouring grains within the aggregate this approach enables a direct link to be made between the model flow fields and the resulting texture development given these mineral orientation distributions elastic parameters are calculated and wavefronts are propagated through the anisotropic structure traveltimes for teleseismic body waves are computed using ray theory and amplitudes are estimated for an across axis profile extending 100 km from the ridge axis relative p wave residuals of up to 1 s are predicted for the buoyant model with on axis arrivals being earliest since near vertical velocities are fastest beneath the axis on axis p wave arrivals for the passive model are half a second earlier than arrivals 60 km off axis and relative delays continue to increase slowly as distance from the ridge increases s wave splitting of almost a second is predicted for the buoyant model whereas less than a half second of splitting is determined for the passive model

syn tectonic meteoric water derived carbonation of the new caledonia peridotite nappe exceptional outcrops recently exposed in the koniambo massif allow the study of the serpentine sole of the peridotite nappe of new caledonia southwest pacific ocean many magnesite veins are observed with characteristics indicating that they were emplaced during pervasive top to the southwest shear deformation the oxygen isotope composition of magnesite is homogeneous 27 4 18o 29 7 while its carbon isotope composition varies widely 16 7 13c 8 5 these new data document an origin of magnesite from meteoric fluids laterization on top of the peridotite nappe and carbonation along the sole appear to represent complementary records of meteoric water infiltration based on the syn kinematic character of magnesite veins we propose that syn laterization tectonic activity has enhanced water infiltration favoring the exportation of leached elements like mg which has led to widespread carbonation along the serpentine sole this calls for renewed examination of other magnesite bearing ophiolites worldwide in order to establish whether active tectonics is commonly a major agent for carbonation

origin of the central magnetic anomaly at the haughton impact structure canada the 23 km diameter well preserved haughton impact structure shows a rather unique combination of a positive magnetic anomaly with a negative gravity anomaly over the center of its central uplift using a new ground magnetic dataset and several modeling approaches we investigate the properties and geometry of its central magnetized source our results confirm that a km sized magnetic body with a narrow near surface extension is necessary to account for the anomaly additional measurements of rock magnetic properties of samples of all lithologies encountered in and outside the crater show that the target sedimentary rocks and the vast majority of the precambrian basement rocks cannot be the source of the magnetic anomaly while in larger impact structures such magnetic anomalies are often explained by magmatic mafic intrusions or highly magnetic glass lenses in the impact melt rocks we propose that impact generated hydrothermal activity enhanced the magnetization of the highly porous unmelted uplifted basement rocks such a process may be considered for the interpretation of the geophysical signature of planetary impact craters

geochemistry of drill core samples from yaxcopoil 1 chicxulub impact crater mexico the chemical composition of suevites displaced cretaceous target rocks and impactgenerated dikes within these rocks from the yaxcopoil 1 yax 1 drill core chicxulub impact crater mexico is reported and compared with the data from the yucatn 6 y6 samples within the six suevite subunits of yax 1 four units with different chemical compositions can be distinguished a upper lower sorted and upper suevite depth of 795846 m b middle suevite depth of 846861 m c brecciated impact melt rock depth of 861885 m and d lower suevite depth of 885895 m the suevite sequence a b and d display an increase of the cao content and a decrease of the silicate basement component from top to bottom in contrast the suevite of y6 shows an inverse trend the different distances of the yax 1 and y6 drilling sites from the crater center 60 and 47 km respectively lead to different suevite sequences within the cretaceous rocks of yax 1 a suevitic dike depth of 916 m does not display chemical differences when compared with the suevite while an impact melt rock dike depth of 1348 m is significantly enriched in immobile elements a clastic breccia dike depth of 1316 m is dominated by material derived locally from the host rock while the silicate rich component is similar to that found in the suevite significant enrichments of the k2o content were observed in the yax 1 suevite and the impact generated dikes all impactites of yax 1 and y6 are mixtures of a crystalline basement and a carbonate component from the sedimentary cover an anhydrite component in the impactites is missing yax 1 or negligible y6

u pb zircon dating of post obduction volcanic arc granitoids and a granulite facies xenolith from new caledonia inference on southwest pacific geodynamic models in new caledonia the occurrence of one of the world s largest and best exposed subduction obduction complex is a key point for the understanding of the geodynamic evolution of the whole southwest pacific region within the ophiolite pre and post obduction granitoids intrude the ultramafic allochthon and provide new time constraints for the understanding of obduction processes at 27 4 ma a new east dipping subduction generated the active margin magmatism along the western coast of the island saint louis massif at 24 3 ma the eastward shift of the magma activity and slightly different geochemical features koum borindi massif was either related to the older slab break off or alternatively due to the eastward migration of the mantle wedge following the collision of the eastern margin of the low howe rise finally the occurrence of a granulite facies xenolith in the koum borindi massif with comparable 24 5 ma u pb zircon age and isotopic features initial end 5 1 suggests that these evolved magmas were generated within the lithospheric mantle beneath a continental crust of normal thickness geochronological evidence for continuous convergence during the oligocene infers an east dipping eocene oligocene subduction obduction system to have existed in the southwest pacific from the d entrecasteaux zone to the north island of new zealand

impact induced impoverishment and transformation of a sandstone habitat for lithophytic microorganisms sandstones are a common habitat for lithophytic microorganisms including cryptoendoliths we describe laboratory experiments on the colonization of impact metamorphosed sandstones from the haughton impact structure canadian high arctic colonization experiments with the coccoid cyanobacterium chroococcidiopsis sp and the motile gram positive bacterium bacillus subtilis show that in contrast to initially low porosity crystalline target rocks which can become more porous as a result of impact bulking by closing pore spaces the sedimentary cryptoendolithic habitat can be impoverished by impact however the heterogeneous distribution of collapsed pores melt phases and subsequent recrystallization results in heterogeneous colonization patterns cavities and vesicles formed during melting can yield new habitats for both cryptoendoliths and chasmoendoliths manifested in the natural cryptoendolithic colonization of shocked sandstones by contrast post impact thermal annealing and recrystallization of impact melt phases destroys the cavities and vesicles in extreme cases complete recrystallization of the rock fabric makes the material suitable only for epilithic and potentially hypolithic colonists these experiments further our understanding of the influence of the target lithology on the effects of asteroid and comet impacts on habitats for lithophytic microorganisms

seismic structure of the southern apennines as revealed by waveform modelling of regional surface waves summary we investigate the crust and upper mantle structures beneath the southern apennine mountain chain using three component seismograms from the calabria apenninetyrrhenian subduction collision accretion network cat scan array surface wave waveforms from three moderate sized m w 5 0 regional earthquakes are modelled using multiple frequencies 0 03 0 06 and 0 05 0 2 hz and both forward and linearized inversion algorithms our best fitting shear velocity models clearly reflect the major tectonic units where for example the average seismic structure at depths above 50 km beneath apulia is substantially faster than beneath the apennine mountain chain we identify a prominent low velocity channel under the mountain belt at depths below 25 30 km and a secondary low velocity zone at 6 12 km depth near mt vulture a once active volcano speed variations between love and rayleigh waves provide further constraints on the fabric and dynamic processes our analysis indicates that the crustal low velocity zones are highly anisotropic maximum 14 per cent and allow transversely polarized shear waves to travel faster than vertically polarized shear waves the upper crustal anomaly reveals a layer of highly deformed rocks caused by past collisions and by the active normal faults cutting across the thrust sheets whereas hot mantle upwelling may be responsible for a high temperature partially molten lower crust beneath the southern apennines

evidence for a spatially extensive hydrothermal system at the ries impact structure germany the 15 ma 26 km diameter ries impact structure in south central germany was one of the first terrestrial impact structures where evidence of impact associated hydrothermal alteration was recognized previous studies suggested that pervasive high temperature hydrothermal activity was restricted to the area within the inner ring i e the crater fill impactite units here we present mineralogical evidence for localized hydrothermal activity in the ejecta beyond the crater rim in two previously unstudied settings a pervasively altered lens of suevite ejecta directly overlying the bunte breccia at the aumuhle quarry and suevite ejecta at depth overlain by 20 m of lacustrine sediments sampled by the wornitzostheim 1965 drill core a comprehensive set of x ray diffraction analyses indicates five distinct alteration regimes 1 surficial ambient weathering characterized by smectite and a minor illitic component 2 locally restricted hydrothermal activity characterized by an illitic component and minor smectite 3 hydrothermal activity at depth characterized by smectite a minor illitic component and calcite 4 hydrothermal activity at depth characterized by smectite a minor illitic component calcite zeolites and clinochlore and 5 pervasive hydrothermal activity at depth characterized by smectite a minor illitic component and minor clinochlore these data spatially extend the ries postimpact hydrothermal system suggesting a much more extensive complex and dynamic system than previously thought constraining the mineralogical alteration regimes at the ries impact structure may also further our understanding of impact associated phyllosilicate formation on mars with implications for climate models and habitability

upper mantle structure beneath the eastern pacific ocean ridges 1 we analyze vertical component body and surface waves for 10 mw 5 earthquakes recorded by ocean bottom seismometers at regional and teleseismic distances through waveform modeling we place new constraints on along axis variation in temperature and partial melt beneath the eastern pacific ridges the resulting best fit models show over 9 variation in average lithosphere shear velocities between different ridge segments we demonstrate that lid velocity correlates with the square root of plate age consistent with a conductive cooling process but we find a more rapid dependence on age close to the rise axis we map the average plate age into a mean lithospheric temperature for each of our profiles using a half space cooling model and the temperature derivatives dvs dt determined from least squares linear fits are 1 1 and 0 26 m s 1 deg 1 respectively for temperatures above and below 1000 c the former estimate is more negative than values determined by earlier reports 0 4 to 0 7 m s 1 deg 1 using global or regional data from a much wider range of seafloor age but with less resolution at young ages the high dvs dt value may suggest the presence of limited partial melt at shallow mantle depths even after accounting for the strong effect of anelasticity and anharmonicity resulting from temperature and grain size variations our data also show a strong north south difference in mantle structure the surface waves that traverse the southern east pacific rise epr experience shear velocities as low as 3 75 km s 1 more than 0 2 km s 1 slower than the average mantle structure at comparable depths beneath the northern epr and the galapagos spreading center this difference cannot be explained by the simple conductive cooling process or spreading rate variations between ridge segments the slow seismic speeds in the low velocity zone lvz appear to require partial melt the velocity difference might be solely caused by higher temperatures under the southern epr but it may also suggest more melt in the lvz beneath the southern ridge axis due to potential differences in melt production or extraction compared to the north in addition differences in width or symmetry of the partial melt zones can affect the observed path averaged velocities beneath these two segments finally we determine more accurate depths for ocean transform earthquakes by analyzing the amplitude ratios between body and surface waves the depths of these transform earthquakes are consistent with brittle deformation within the oceanic crust

catastrophic emplacement of the heart mountain block slide wyoming and montana usa the mechanism that allowed many tens of km of movement of the enormous block slide floored by the rootless heart mountain detachment fault in nw wyoming has long been a puzzle carbonat rich microbreccia that is widespread along the fault and in dikes in the upper plate contains accreted grains indistinguishable from those observed as fallout from volcanic eruption clouds accretionary lapilli and impact ejecta clouds and in intrusive diatremes in these settings and also in industrial processing accreted grains form when particles in a turbulent gaseous suspension containing limited water adhere to a nucleating grain or to each other elongate grains in thick microbreccia have strong but diverse shap preferred orientations unlike those reported from other fault rocks but instead suggestive of turbulent flow and the microbreccia contains layering and other features of sedimentary character that appear to record deposition from suspension rather than frictional processes along a fault we suggest that frictional heating led to dissociation of carbonate rock along the fault producing supercritical co 2 as the suspending medium high co 2 pressure drastically reduced friction along the fault and allowed continuation of catastrophic movement probably initiated by a volcanic or phreatomagmatic explosion resulting in very large displacement on a low dipping surface earlier slower sliding may have occurred but final emplacement was rapid minutes and spectacular

co2 release due to impact devolatilization of carbonate results of shock experiments a study of pure single crystal calcite shocked to pressures from 9 0 to 60 8 gpa was conducted to address contradictory data for carbonate shock behavior the recovered materials were analyzed optically and by transmission electron microscopy tem as well as by thermogravimetry tga x ray diffraction xrd and raman spectroscopy in thin section progressive comminution of calcite is observed although grains remain birefringent to at least 60 8 gpa tga analysis reveals a positive correlation between percent of mass loss due to shock and increasing shock pressure r 0 77 and suggests that shock loading leads to the modest removal of structural volatiles in this pressure range xrd patterns of shocked iceland spar samples produce peaks that are qualitatively and quantitatively less intense more diffuse and shift to lower o2 however the regularity observed in these shocked powder patterns suggests that structures with very uniform unit cell separations persist to shock pressures as high as 60 8 gpa raman spectral analyses indicate no band asymmetry and no systematic peak shifting or broadening tem micrographs display progressively diminishing crystallite domain sizes selected area electron diffraction saed patterns reveal no signatures of amorphous material these data show that essentially intact calcite is recovered at shock pressures up to 60 8 gpa with only slight mass loss 7 this work suggests that the amount of co2 gas derived from shock devolatilization of carbonate by large meteorite impacts into carbonate targets has been substantially overestimated

paired stable isotopes o c and clumped isotope thermometry of magnesite and silica veins in the new caledonia peridotite nappe abstract the stable isotope compositions of veins provide information on the conditions of fluid rock interaction and on the origin of fluids and temperatures in new caledonia magnesite and silica veins occur throughout the peridotite nappe in this work we present stable isotope and clumped isotope data in order to constrain the conditions of fluid circulation and the relationship between fluid circulation and nickel ore forming laterization focusing on the koniambo massif for magnesite veins occurring at the base of the nappe the high 18 o values between 27 8 and 29 5 attest to a low temperature formation clumped isotope analyses on magnesite give temperatures between 26 c and 42 c that are consistent with amorphous silica magnesite oxygen isotope equilibrium the meteoric origin of the fluid is indicated by calculated 18 o water values between 3 4 to 1 5 amorphous silica associated with magnesite or occurring in the coarse saprolite level displays a narrow range of 18 o values between 29 7 and 35 3 for quartz veins occurring at the top of the bedrock and at the saprolite level commonly in association with ni talc like minerals the 18 o values are lower between 21 8 and 29 0 and suggest low temperature hydrothermal conditions 40 95 c thermal equilibration of the fluid along the geothermic gradient before upward flow through the nappe and or influence of exothermic reactions of serpentinization could be the source s of heat needed to form quartz veins under such conditions

regional implications of u pb shrimp age constraints on the tectonic evolution of new caledonia abstract u pb shrimp ages for zircons from plagiogranites indicate a late carboniferous age of formation for ophiolitic basement of the koh terrane in the central chain mountains of new caledonia samples from ophiolites at koh and koua yielded ages of 302 7 ma and 290 5 ma respectively the similarity of these ages to those of plagiogranites in the dun mountain ophiolite belt maitai terrane of new zealand and the comparable structural positions of the two terranes potentially constrain reconstructions of the cretaceous sw pacific margin detrital zircons from late mesozoic sediments that overlap the koh terrane also provide potential constraints on the location of new caledonia prior to its break up and dispersal from eastern australia

complex polarization analysis of particle motion knowledge of particle motion polarization aids in identifying phases on three component seismograms the scheme of montalbetti and kanasewich 1970 is extended to analytic three component seismograms where the imaginary part of the signal is the hilbert transform of the real part this scheme has only one free parameter the length of the time window over which the polarization parameters are estimated so it can be applied in a routine way to three component data the azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained polarization analysis of strong motion data from the 1971 san fernando earthquake aids in the discrimination between wave types which is important for the understanding of the complicated earthquake induced shaking observed in basins most arrivals are incident on the receivers in the direction of the back azimuth to the epicenter which suggests that despite the complicated motions two dimensional finite difference methods are sufficient to understand the effect on seismic waves of the los angeles and san fernando basins vidale and helmberger 1986b

first palaeomagnetic dating of ferricrete in new caledonia new insight on the morphogenesis and palaeoweathering of grande terre terra nova 24 77 85 2012 abstract comparing palaeolatitudes estimated from remanent magnetization data of ferricrete developed over laterite at two sites goro and tiebaghi against the apparent polar wandering path of australia provides new time constraints for the peridotite weathering in new caledonia the tiebaghi massif of the west coast klippes displays a single episode of ferricrete development during latest oligocene times by contrast the goro site in the southern part of the massif du sud reveals a more complex history with several episodes of ferricrete development from latest oligocene to pliocene quaternary times these data have made it possible to constrain the post obduction geodynamics and associated morphogenesis of new caledonia since related uplift probably prevented regolith development until latest oligocene times moreover the later uplift and deep erosion of the west coast klippes during the early miocene probably prevented further regolith preservation

mid sized complex crater formation in mixed crystalline sedimentary targets insight from modeling and observation large impact crater formation is an important geologic process that is not fully understood the current paradigm for impact crater formation is based on models and observations of impacts in homogeneous targets real targets are rarely uniform for example the majority of earth s surface is covered by sedimentary rocks and or a water layer the ubiquity of layering across solar system bodies makes it important to understand the effect target properties have on the cratering process to advance understanding of the mechanics of crater collapse and the effect of variations in target properties on crater formation the first bridging the gap workshop recommended that geological observation and numerical modeling focussed on mid sized 15 30 km diameter craters on earth these are large enough to be complex small enough to be mapped surveyed and modelled at high resolution and numerous enough for the effects of target properties to be potentially disentangled from the effects of other variables in this paper we compare observations and numerical models of three 18 26 km diameter craters formed in different target lithology ries germany haughton canada and el gygytgyn russia based on the first order assumption that the impact energy was the same in all three impacts we performed numerical simulations of each crater to construct a simple quantitative model for mid sized complex crater formation in a subaerial mixed crystalline sedimentary target we compared our results with interpreted geological profiles of ries and haughton based on detailed new and published geological mapping and published geophysical surveys our combined observational and numerical modeling work suggests that the major structural differences between each crater can be explained by the difference in thickness of the pre impact sedimentary cover in each case we conclude that the presence of an inner ring at ries and not at haughton is because basement rocks that are stronger than the overlying sediments are sufficiently close to the surface that they are uplifted and overturned during excavation and remain as an uplifted ring after modification and post impact erosion for constant impact energy transient and final crater diameters increase with increasing sediment thickness

northern east pacific rise magnetic anomaly and bathymetric framework the oceanic crust in the eastern pacific between 7on and 30on and east of 127ow contains a fairly complete history of the spreading centers associated with the east pacific rise since 25 m y b p late oligocene in this paper we have summarized the seafloor spreading magnetic anomaly data and the bathymetric data that reflect the record of this tectonic history the well defined magnetic lineations north of the clarion fracture zone in the mouth of the gulf of california and on the east flank of the east pacific rise epr are carefully examined and used to provide a guide for interpreting the spreading pattern between the clarion and clipperton fracture zones southward of the rivera fracture zone over the mathematician ridge and over the entire epr east of the mathematician ridge between the rivera and siqueiros fracture zones the bathymetric data provide a trace of the fracture zone pattern in each of the above mentioned areas the fracture zone bathymetry and the seafloor spreading magnetic lineations on the epr south of the rivera fracture zone have a distinctive fanning pattern caused by close poles of rotation and plate boundary reorganizations all these data provide a good record of the plate reorganizations in the middle miocene at magnetic anomaly 5a time 12 5 to 11 m y b p in the late miocene at magnetic anomaly 3 4 time 6 5 m y b p and in the pliocene at magnetic anomaly 2 3 time 3 5 m y b p several abandoned spreading centers including the mathematician ridge were left behind as a result of these reorganizations the mathematician ridge is shown to be a set of ridges and trough whose origin is related to the tectonic activity associated with each of the above mentioned reorganizations since anomaly 5a

on modeling the thermal evolution of the oceanic upper mantle an assessment of the cooling plate model the plate cooling model for the thermal evolution of the oceanic upper mantle has been widely accepted to explain observed variations of depth to oceanic basement and conductive heat flow with the age of the seafloor several estimates of best fitting plate model parameters derived from depth heat flow and age data have been proposed but the viability of the plate model itself has not been rigorously evaluated we have used published mean depths and depths to basement at deep sea drilling project ocean drilling program dsdp odp drilling sites to test the plate cooling model based on two criteria first viable plate models must have coefficients that are consistent with the slope of the corresponding root t line because the half space or root t subsidence of young seafloor is implicit in the plate model i e the slope of the root t line can be calculated directly from the coefficients of the plate subsidence model second any viable physical model must fit the data with an acceptable degree of systematic misfit large systematic misfits indicate that the model cannot explain the observations fits of half space root t models to depth versus age data for young 80 ma seafloor indicate basal temperatures in the range 1300 to 1370 c based on the age at which the depths deviate from the root t line the minimum plate thickness that is compatible with the best fitting half space models for young seafloor is 120 km in contrast all best fitting plate models yield systematically higher temperatures 1450 to 1470 c and thinner plates 102 118 km the plate model can explain the depth to basement at dsdp odp drill sites with a satisfactory degree of systematic misfit but we find that there is no plate cooling model that can explain the variation of the mean depths derived from the dbdb5 database with age over the entire range of ages 0 to 165 ma models that best fit the entire data set have unacceptably large systematic misfits over the entire range of seafloor age whereas models that minimize the systematic misfit for young seafloor 0 to 81 ma fail for older seafloor the plate model clearly fails to explain the observations the cooling history of old seafloor is not simply an extension of the cooling history of young seafloor according to a simple plate cooling model previous studies have suggested as an alternative to the plate model that observed variations of basement depth with age are best explained by the combined effects of a normal half space cooling process and the dynamic and or thermal effects of hot spots or mantle plumes our results are entirely consistent with the half space cooling model and we find that the best reference model for normal subsidence is d t 2600 20 m 345 3 m m y t we also find that the heat flow predicted by this half space model is consistent with the most reliable average heat flow values from the pacific

the effects of meteorite impacts on the availability of bioessential elements for endolithic organisms meteorite impacts one of the most ubiquitous processes in the solar system have the ability to destroy as well as create habitats for life the impact process can increase the translucency and porosity of the target substrate as well as mobilize biologically relevant elements within the substrate for endolithic organisms this process has important implications especially in extreme environments where they are forced to seek refuge in the interior of rocks here we show that unshocked target rocks and rocks that have experienced pressures up to about 80 gpa from the haughton impact structure devon island canada possess a small but discernible change in bulk chemistry within the major oxide analysis however changes in the distribution of elements did occur with increasing shock level for both the sedimentary and crystalline target both the crystalline and sedimentary target rocks contain significant amounts of glasses at higher shock levels up to about 95 by volume which would improve the availability of these elements to potential microbial endoliths as glasses are more easily dissolved by organic acids the implication that impact events do not impoverish their capacity to serve as a substrate through volatilization is important with respect to analogous impact structures on mars after the deleterious effects of the direct meteorite impact any microorganisms on mars would have benefited from the input of heat the mobilization of a possible frozen groundwater system as well as increased translucency porosity and trace nutrient availability of the target substrate

probing the history of the mathematician paleoplate using surface waves abstract this paper investigates the shear velocity structure under the northern east pacific rise at the latitude range of 9 18 n using intermediate period rayleigh and love waves the selected ocean bottom seismic records provide source receiver paths that ideally constrain the lithospheric mantle structure beneath the southern rivera plate and the mathematician paleoplate the rayleigh wave data infer a relatively thin 30 km lithosphere under the eastern side of the present day east pacific rise the associated shear velocities are consistent with existing models of oceanic mantle beneath this region and the estimated plate age of 2 3 million years agrees with results from magnetic dating the west of the rise axis is characterized by a thicker and faster lithosphere than the eastern flank and such structural differences suggest the presence of a relatively old mathematician paleoplate the discontinuous change in mantle structure across the east pacific rise spreading center are observed in both isotropic and anisotropic velocities the young oceanic lithosphere east of the rise axis shows strong polarization anisotropy where the dominant orientation of crystallographic axes roughly parallels the spreading direction however the western flank of the rise axis is approximately isotropic and the lack of anisotropy suggests complex deformation mechanisms associated with earlier episodes of ridge segmentation propagation and dual spreading on and around the mathematician paleoplate

hyperspectral mapping of alteration assemblages within a hydrothermal vug at the haughton impact structure canada meteorite impacts on earth and mars can generate hydrothermal systems that alter the primary mineralogies of rocks and provide suitable environments for microbial colonization we investigate a calcite marcasite bearing vug at the 23 km diameter haughton impact structure devon island nunavut canada using imaging spectroscopy of the outcrop in the field 0 65 1 1 m and samples in the laboratory 0 4 2 5 m point spectroscopy 0 35 2 5 m major element chemistry and x ray diffraction analyses the mineral assemblages mapped at the outcrop include marcasite marcasite with minor gypsum and jarosite fibroferrite and copiapite with minor gypsum and melanterite gypsum fe3 oxides and jarosite and calcite gypsum clay microcline and quartz hyperspectral mapping of alteration phases shows spatial patterns that illuminate changes in alteration conditions and formation of specific mineral phases marcasite formed from the postimpact hydrothermal system under reducing conditions while subsequent weathering oxidized the marcasite at low temperatures and water rock ratios the acidic fluids resulting from the oxidation collected on flat lying portions of the outcrop precipitating fibroferrite copiapite that assemblage then likely dissolved and the changing chemistry and ph resulting from interaction with the calcite rich host rock formed gypsum bearing red coatings these results have implications for understanding water rock interactions and habitabilities at this site and on mars

organic geochemistry of impactites from the haughton impact structure devon island nunavut canada organic matter in impactites from the 24 km wide and 39 ma old haughton impact structure canadian high arctic is a mixture of fossil and modern biological components the fossil component represents a conventional oil that was generated from lower palaeozoic marine source material before impact and permeates bedrock dolomites biomarker maturity parameters record the thermal effect of the mid tertiary impact maturity influenced sterane rearranged hopanoid and triaromatic steroid ratios all increase towards the centre of the impact structure where thermal alteration was greatest the heating was probably dominated by an impact related hydrothermal system as such systems last long enough for kinetically based thermal alteration to occur kinetically related biomarker data suggest that the hydrothermal heating lasted for c 5000 years biomarkers are also preserved in dolomite clasts within impact melt breccia and indicate strong thermal alteration modern biological contamination of the rocks is responsible for the superposition of two geochemical signatures which could be cyanobacteria non marine algae or higher plant matter onto the fossil component but they can be recognized and distinguished the data show that the impact structure system holds a record of both the pre impact organic signature and the thermal signature of the impact and thereby indicates that organic geochemistry is a valuable tool in documenting the response of rocks to impacts

the transfer of organic signatures from bedrock to sediment abstract a case study in the canadian arctic demonstrates how an organic geochemical signature in the regional bedrock can be transferred by erosion and redeposition to younger geological formations and surface sediments the hydrocarbon composition recorded in laurentian lower palaeozoic carbonate bedrock was incorporated into overlying miocene and quaternary formations and modern mass waste alluvium snow ice and proglacial deposits and further distant in ice rafted detritus the retention of the original geological organic signature is reflected in consistent thermal maturities hopane ratios and environmental indicators sterane distributions in the modern sediments the geological signature is variably mixed with a modern microbial organic signature reflected in high values of carbon preference index and diploptene these data show that hydrocarbon occurrences in bedrock may be detected by the analysis of surface detritus especially in carbonate terrains however they also indicate that environmental signatures may be misleading if they are inherited from older geological units

late ordovician brachiopod distribution and ecospace partitioning in the tvaren crater system sweden abstract patterns of distribution and ecospace utilization of late ordovician brachiopods in a recently formed contemporary meteorite crater are described and analyzed rhynchonelliformean brachiopod communities dominated by a wide range of orthides and strophomenides colonized the newly formed crater at the crater rim communities were established early on although the crater depression was not inhabited until deposition of the upper third of the remaining crater fill the crater formed a protected but restricted microenvironment where sediments four times the thickness of the nearby basinal succession accumulated within this narrow space environments varied from shallow water to deeper waters about 200 m in depth and from well oxygenated to hypoxic such varied environments generated a rough ecological landscape facilitating niche partitioning across a relatively small geographic area analysis of the guild structure of the fauna permits explanation of a local biodiversity hotspot in otherwise low diversity strata elsewhere in the scandinavian region the tvaren impact event had an important palaeobiologic effect upon the fossil record as it served as a local pump and reservoir for biodiversity moreover the development of new community types and narrowly defined niches helped further drive both and biodiversity during a critical phase of the great ordovician biodiversification event

tectonic accretion and underplating of mafic terranes in the late eocene intraoceanic fore arc of new caledonia southwest pacific geodynamic implications this paper deals with the tectonic events that result in the accretion of mafic terranes in the fore arc region and a close juxtaposition of ultramafic rocks low grade and high grade mafic terranes in many collisional orogens the example is taken from new caledonia where tectonic accretion subduction underplating and obduction of mafic terranes took place during the late eocene in an intra oceanic forearc setting the late eocene tectonic complex comprised three major terranes an overlying ultramafic mainly harzburgitic allochthon named the ophiolitic nappe an intermediate mafic mainly basaltic off scraped melange composed of kilometre scale slices of oceanic upper crust called the poya terrane parts of which have been metamorphosed into an eclogite blueschist facies complex the pouebo terrane and a lower continental basement formed by the norkolk ridge terranes based upon exhaustive sampling of the mafic terranes and field surveys our tectonic micropaleontologic and geochemical data reveal that poya and pouebo terranes rocks originally formed within one single campanian to late paleocene oceanic basin floored by tholeiitic basalt associated with some minor seamount related intraplate alkali basalt the tholeiitic basalt displays a continuous range of compositions spanning between undepleted and depleted end members the former being volumetrically predominant the overall geochemical and isotopic features indicate an origin from a prominently heterogeneous mantle source during the opening of a marginal basin the south loyalty basin which almost completely disappeared during eocene convergence the opening of this basin originally located to the east of the norfolk ridge was synchronous with that of tasman sea basin as a consequence of oceanward migration of the west dipping pacific subduction zone establishing the origin of the ultramafic ophiolitic nappe is beyond the scope of this paper however it appears to be genetically unrelated to the mafic poya and pouebo terranes although it was located in the late eocene fore arc the ophiolitic nappe and the corresponding oceanic lithosphere originated before the late cretaceous to the east of the south loyalty basin in a back arc setting or alternatively in a much older trapped basin for reasons that remain unclear a new east dipping subduction started in the eocene and consumed most of the south loyalty basin forming the intra oceanic loyalty arc due to a changing subduction regime underplating of the diahot terrane the mafic slices that now form the poya terrane were tectonically accreted in the loyalty fore arc region and remained under low pressure low temperature conditions possibly at the subsurface until the norfolk ridge reached the subduction zone diachronously this resulted in the final obduction of the fore arc area the two step obduction involved first the mafic complex forming the poya terrane and thereafter the lithospheric mantle that now forms the ophiolitic nappe in contrast pieces of the accretionnary complex were dragged down into the subduction zone underplated at depth ca 70 km and metamorphosed into high temperature eclogite to form the pouebo terrane metamorphics that display the same geochemical features as the poya terrane basalt a mid to late eocene syntectonic piggy back sedimentary basin the nepoui flysch basin mainly filled with mafic clastic material and shallow water carbonates that record the progressive uplift of the fore arc region due to the accretion and underplating of mafic ocean related and other material in contrast a slightly younger foreland basin located upon the norfolk ridge the priabonian bourail flysch basin received a massive input of detrital material derived from the norfolk ridge itself and a time increasing amount of mafic poya derived material that recorded the first step of obduction thereafter the bourail flysch was overthrust by the poya terrane and finally by the ophiolitic nappe at the same time buoyancy driven uplift and exhumation of the high pressure metamorphic complex occurred as a consequence of the diachronous blocking of the subduction zone finally for a short time a new subduction started along the west coast of new caledonia and generated small amounts of active margin related magmas these events have resulted in the close juxtaposition of unmetamorphosed and highly metamorphosed mafic and ultramafic terranes that may represent a good pre collision analogue of mafic ultramafic belts found in many collisional mountain ranges

a dual layer chicxulub ejecta sequence with shocked carbonates from the cretaceous paleogene k pg boundary demerara rise western atlantic abstract an up to 2 cm thick chicxulub ejecta deposit marking the cretaceous paleogene k pg boundary the k t boundary was recovered in six holes drilled during odp leg 207 demerara rise tropical western atlantic stunning features of this deposit are its uniformity over an area of 30 km2 and the total absence of bioturbation allowing documentation of the original sedimentary sequence high resolution mineralogical petrological elemental isotopic sr nd and rock magnetic data reveal a distinct microstratigraphy and a range of ejecta components the deposit is normally graded and composed predominantly of rounded 0 1 to max 1 mm sized spherules spherules are altered to dioctahedral aluminous smectite though occasionally relict si al rich hydrated glass is also present suggesting acidic precursor lithologies spherule textures vary from hollow to vesicle rich to massive some show in situ collapse others include distinct fe mg ca ti rich melt globules and lath shaped al rich quench crystals both altered glass spherules and the clay matrix site 1259b display strongly negative e nd t 65 ma values 17 indicating uptake of nd from contemporaneous ocean water during alteration finally fe mg rich spherules shocked quartz and feldspar grains few lithic clasts as well as abundant accretionary and porous carbonate clasts are concentrated in the uppermost 0 5 0 7 mm of the deposit the carbonate clasts display in part very unusual textures which are interpreted to be of shock metamorphic origin the preservation of delicate spherule textures normal grading with lack of evidence for traction transport and sub millimeter scale compositional trends provide evidence for this spherule deposit representing a primary air fall deposit not affected by significant reworking the odp leg 207 spherule deposit is the first known dual layer k pg boundary in marine settings it incorporates compositional and stratigraphic aspects of both proximal and distal marine sites its stratigraphy strongly resembles the dual layer k pg boundary deposits in the terrestrial western interior of north america although there carbonate phases are not preserved the occurrence of a dual ejecta layer in these quite different sedimentary environments separated by several thousands of kilometers provides additional evidence for an original sedimentary sequence therefore the layered nature of the deposit may document compositional differences between ballistic chicxulub ejecta forming the majority of the spherule deposit and material falling out from the vapor ejecta plume which is concentrated in the uppermost part

seismic anisotropy beneath the continents probing the depths of geology seismic anisotropy beneath continents is analyzed from shear wave splitting recorded at more than 300 continental seismic stations anisotropy is found to be a ubiquitous property that is due to mantle deformation from past and present orogenic activity the observed coherence with crustal deformation implies that the mantle plays a major if not dominant role in orogenies no evidence is found for a continental asthenospheric decoupling zone suggesting that continents are coupled to general mantle circulation

carbonate silicate liquid immiscibility upon impact melting ries crater germany the 24 km diameter ries impact crater in southern germany is one of the most studied impact structures on earth the ries impactor struck a triassic to upper jurassic sedimentary sequence overlying hercynian crystalline basement at the time of impact 14 87 0 36 ma storzer et al 1995 the 350 m thick malm limestone was present only to the south and east of the impact site to the north and west the malm had been eroded away exposing the underlying dogger and lias the largest proportion of shocked target material is in the impact melt bearing breccia suevite the suevite had been believed to be derived entirely from the crystalline basement calcite in the suevite has been interpreted as a postimpact hydrothermal deposit from optical inspection of 540 thin sections of suevite from 32 sites i find that calcite in the suevite shows textural evidence of liquid immiscibility with the silicate impact melt textural evidence of liquid immiscibility between silicate and carbonate melt in the ries suevite includes carbonate globules within silicate glass silicate globules embedded in carbonate deformable and coalescing carbonate spheres within silicate glass sharp menisci or cusps and budding between silicate and carbonate melt fluidal textures and gas vesicles in carbonate schlieren a quench crystallization sequence of the carbonate spinifex textured quenched carbonate separate carbonate spherules in the suevite mineral fragment matrix and inclusions of mineral fragments suspended in carbonate blebs given this evidence of liquid immiscibility the carbonate in the suevite therefore has like the silicate melt a primary origin by impact shock melting evidence of carbonate silicate liquid immiscibility is abundant in the suevites from the southwest to east of the ries crater the rarer suevites to the west to northeast of the crater are nearly devoid of carbonate melts this correspondence between the occurrence of outcropping limestones at the target surface and the formation of carbonate melt indicates that the malm limestones are the source rocks of the carbonate impact melt this correspondence shows that the suevites preserve a compositional memory of their source rocks from the regional distribution of suevites with or without immiscible carbonate melts it is inferred that the ries impactor hit the steep albtrauf escarpment at its toe in an oblique impact from the north

the mathematician paleoplate the pacific seafloor is littered with small fragments of lithosphere captured from adjacent plates by past plate boundary reorganizations one of the clearest examples of such a reorganization is documented in the mathematician seamounts region where a distinctive geomorphology and well developed magnetic anomalies are present this reorganization involved a short lived microplate between the failing mathematician ridge and a new propagating spreading center the east pacific rise it produced a transfer of a fragment of lithosphere from the farallon to the pacific plate and also created a number of landforms and magnetic patterns within and on the margins of the captured fragment these make up the mathematician paleoplate in many cases two sides of a microplate are active spreading ridges a microplate evolves into a paleoplate when dual spreading ceases and full spreading resumes at the prevailing spreading ridge we define a paleoplate as the area of the seafloor from the axis of a failed rift to the boundary of resumed full spreading it includes a fragment of captured lithosphere and the lithosphere slowly accreted to it during the period of dual spreading prior to complete abandonment of the failed rift the mathematician paleoplate has the following boundaries and components from west to east the axis of the mathematician failed rift the fragment of captured farallon plate a complex rift initiation site at the moctezuma trough a zone of slow spreading and an as yet ill defined eastern boundary where dual spreading stopped and full spreading resumed the northern boundary of the paleoplate is the rivera fracture zone its southeastern boundary a now inactive transform fault the west o gorman fracture zone in this case as well as in other more poorly documented ones relict landforms and magnetic patterns are carried on the aging lithosphere away from the spreading ridge recording a former geometry

a new miniaturized extraction chromatography method for precise u pb zircon geochronology abstract in this paper we describe a new method for the concomitant separation of u and pb in zircons for radiometric dating purposes the proposed separation scheme is based on a blend of two extraction chromatographic materials referred to as tru spec and sr spec respectively these afford a straightforward separation of u and pb with high yield good purity and satisfactory blank levels on micro columns using very small volume 5 l of mixed resins owing to the selectivity and high capacity of the specific extraction chromatographic materials for u and pb this new technique could be further scaled down the validity of the method is illustrated by measurements of u pb isotopic ratios and determination of corresponding ages in 0 2 0 8 mg fragments of the zr91500 zircon standard

segment scale variations in the crustal structure of 150 300 kyr old fast spreading oceanic crust east pacific rise 8 15 n 10 5 n from wide angle seismic refraction profiles summary we have simultaneously inverted seismic refraction and wide angle moho reflection traveltimes for the 2 d crustal thickness and velocity structure of 150 300 kyr old crust along the east pacific rise epr between the siqueiros and clipperton fracture zones fzs our results show a strong correlation between ridge segmentation and upper and mid crustal seismic velocities with higher velocities near segment centres and lower velocities near segment ends low crustal velocities at the clipperton and siqueiros fzs are interpreted as fracturing resulting from brittle deformation of the crust in the transform domain a relict overlap basin left on the pacific plate by the 9 03 n overlapping spreading centre osc as it propagated southward is associated with a large 1 km s 1 negative upper and mid crustal velocity anomaly this anomaly is consistent with the presence of an unusually thick extrusive section within the basin and with tectonic alteration fracturing and shearing arising from rotation of the basin as it was formed the discordant zone left by this osc on the cocos plate is characterized by moderately low crustal velocities probably because of crustal fracturing as the osc propagated into older crust higher crustal velocities near segment centres may reflect a higher ratio of dikes to extrusives in the upper crust and lower intensity tectonic alteration of the crust than near segment ends the mean crustal thickness along the epr between the siqueiros and clipperton fzs is 6 7 6 8 km the thickest crust is found beneath the lamont seamounts 9 km and in a southward pointing v shaped band located just north of the off axis trace of the 9 03 n osc 7 3 7 8 km the thinnest crust 6 km is found proximal to the clipperton and siqueiros fzs the crust associated with the off axis trace of the 9 03 n osc is not anomalously thin suggesting that magma supply beneath the osc is similar to that of the northern and southern segments we see a similar pattern of crustal thickness variation to that determined using multichannel reflection data including a gradual thickening of the crust from north to south along the northern ridge segment and the location of the thickest crust just north of the 9 03 n osc however the magnitude of the along axis crustal thickness variation we observe along the northern ridge segment between 9 50 n and 9 15 n 1 3 1 8 km excluding the lamont seamounts is significantly less than the 2 3 km of variation previously reported weakening the case for the existence of a low density mantle diapir at 9 50 n inferred from gravity data the band of thick crust located just north of the off axis trace of the 9 03 n osc suggests a close genetic link between this feature and the osc thus we attribute the pattern of crustal thickness variations along the northern segment to the kinematics of the southward propagating 9 03 n osc over the past 0 5 myr and not to along axis melt migration away from a mantle diapir as previously proposed

effects of asteroid and comet impacts on habitats for lithophytic organisms a synthesis asteroid and comet impacts can have a profound influence on the habitats available for lithophytic microorganisms using evidence from the haughton impact structure nunavut canadian high arctic we describe the role of impacts in influencing the nature of the lithophytic ecological niche impact induced increases in rock porosity and fracturing can result in the formation of cryptoendolithic habitats in some cases and depending upon the target material an increase in rock translucence can yield new habitats for photosynthetic cryptoendoliths chasmoendolithic habitats are associated with cracks and cavities connected to the surface of the rock and are commonly increased in abundance as a result of impact bulking chasmoendolithic habitats require less specific geological conditions than are required for cryptoendolithic habitats and their formation is likely to be common to most impact events impact events are unlikely to have an influence on epilithic and hypolithic habitats except in rare cases where for example the formation of impact glasses might yield new hypolithic habitats we present a synthetic understanding of the influence of asteroid and comet impacts on the availability and characteristics of rocky habitats for microorganisms

hydrocode simulation of the chicxulub impact event and the production of climatically active gases we constructed a numerical model of the chicxulub impact event using the chart d squared csq code coupled with the analytic equation of state aneos package in the simulations we utilized a target stratigraphy based on borehole data and employed newly developed equations of state for the materials that are believed to play a crucial role in the impact related extinction hypothesis carbonates calcite and evaporites anhydrite simulations explored the effects of different projectile sizes 10 to 30 km in diameter and porosity 0 to 50 the effect of impact speed is addressed by doing simulations of asteroid impacts vi 20 km s and comet impacts vi 50 km s the masses of climatically important species injected into the upper atmosphere by the impact increase with the energy of the impact event ranging from 350 to 3500 gt for co2 from 40 to 560 gt for s and from 200 to 1400 gt for water vapor while our results are in good agreement with those of ivanov et al 1996 our estimated co2 production is 1 to 2 orders of magnitude lower than the results of takata and ahrens 1994 indicating that the impact event enhanced the end cretaceous atmospheric co2 inventory by at most 40 consequently sulfur may have been the most important climatically active gas injected into the stratosphere the amount of s released by the impact is several orders of magnitude higher than any known volcanic eruption and with h2o is high enough to produce a sudden and significant perturbation of earth s climate

present day kinematics of the rivera plate and implications for tectonics in southwestern mexico we model the present day motion of the rivera plate relative to the pacific north america and cocos plates and combine the results with the nuvel i model for cocos north america motion to examine present day deformation in southwestern mexico the pacific rivera data which include 25 three m y average spreading rates determined from original surface ship magnetic data and 22 azimuthal data along the rivera transform are systematically misfit by the nuvel i pacific north america and pacifie cocos euler vectors indicating that the rivera plate is kinematically distinct from north america and cocos an f test shows that the improvement in fit to the pacific rivera data from a model with a distinct rivera plate exceeds that expected solely from adding three model parameters the rivera north america euler vector derived from closure of the rivera pacific north america plate circuit predicts slower and more trenchnormal convergence along the acapulco trench than prior models in addition the model predicts convergence normal to the eastern tamayo fracture zone at a rate 60 slower than the right lateral strike slip predicted by prior models an observed systematic misfit of the pacific rivera euler vector to azimuths from the western rivera transform fault may have several causes there may be a time averaging problem between the 3 0 m y average rates and the shorter time average transform fault azimuths and earthquake slip vectors alternatively rivera transform trends may be biased by deformation within lithosphere adjacent to the transform valley or future detailed mapping of the transform may reveal the misfit to be an artifact of the presently available bathymetry along the entire pacific rivera rise spreading rates averaged over the past 0 7 m y are systematically faster than 3 0 m y average rates with the difference increasing southward along the rise the post 3 ma change in the rate gradient has caused a southward migration of the pacific rivera euler pole since 3 ma possibly in response to the 3 ma completion of a spreading reorganization that doubled the length of the rivera transform fault and halved the area of the rivera plate we hypothesize that deformation in southwestern mexico including opening along the colima rift is related to oblique subduction of the cocos plate along the northern middle america trench three unes of evidence support this hypothesis first the sense of oblique subduction predicted by nuvel i along the middle america trench is consistent with a model in which part of western mexico located southeast of the colima rift moves to the southeast relative to north america second field geologic data and landsat imagery suggest that in the past few million years the chapala oaxaco fault zone has accommodated several kilometers of sinistral motion and sinistral transtension has occurred along the trans mexican volcanic belt either or both of these fault zones could accommodate any southeastward coastal block motion that might result from oblique subduction third the observation that earthquake slip vectors from the northern middle america trench trend systematically counterclockwise from the predicted cocos north america convergence direction is also consistent with southeastward motion the discrepancy between the observed and predicted slip directions along the middle america trench suggests sinistral slip is 0 10 mm yr 1 if oblique subduction is driving southeastward transport of a coastal sliver the colima rift is a passive pull apart zone at the northwestern end of this sliver rather than an incipient spreading ridge that will replace the pacific rivera rise

shock induced devolatilization of calcite the amounts of co 2 and co evolved upon shock compression and decompression of calcite to 18 gpa 180 kbar have been determined using a new gas phase shock recovery technique and gas source mass spectrometry the data demonstrate that from 0 03 to 0 3 mole percent of calcite is devolatilized at shock pressures significantly lower than those predicted 30 gpa for the onset of volatilization by continuum thermodynamic theory and are in qualitative agreement with release adiabat data for calcite and aragonite carbon and oxygen isotope ratios in the shock released co 2 are the same as those in the unshocked hydrothermal calcite demonstrating that the co 2 comes from the calcite rather than other potential sources

carbonate accretionary lapilli in distal deposits of the chicxulub impact event the petrography and chemical composition of carbonate accretionary particles of chicxulub impact origin are described from cretaceous paleogene boundary deposits at brazos river texas and bass river borehole new jersey the particles consist of lapilli and lapilli fragments ranging in size from 0 05 to 0 3 cm they are white in color have an accretionary fabric at several scales and are composed of micrometer sized microspar of low mg calcite with an elevated sulfur content the internal aggregate microfabric indicates that they formed by accretion of small solid particles suggesting an origin from carbonate crystals generated within the vapor plume of the chicxulub impact carbonate accretionary lapilli occur with altered glass spherules in cretaceous paleogene boundary deposits at sites in texas and northern mexico and in the spherule layer in new jersey indicating that a large amount of particulate carbonate was present within the impact plume

cryptoendolithic alteration of antarctic sandstones pioneers or opportunists 1 the cryptoendolithic habitat of the antarctic dry valleys has been considered a good analogy for past martian ecosystems if life arose on the planet yet cryptoendoliths are thought to favor the colonization of rocks that have a preexisting porous structure e g sandstones this may weaken their significance as exact analogues of potential rock colonizing organisms on mars given our current understanding of the dominant volcanic nature of martian geology however the production of oxalic acid by these lichen dominated communities and its weathering potential indicate that it could be an aid in rock colonization enabling endoliths to inhabit a wider variety of rock types utilizing icp aes and scanning electron microscope techniques this study investigates elemental and mineralogical compositions within colonized and uncolonized layers in individual sandstone samples this is in order to determine if the weathering of mineral phases within the colonized layers causes an increase in the amount of pore space available for colonization the results show that colonized layers are more weathered than uncolonized deeper portions of the rock substrate layers within uncolonized samples have uniform compositions differences between the colonized and uncolonized layers also occur to varying extents within colonized rocks of different mineralogical maturities the results confirm that cryptoendoliths modify their habitat through the production of oxalic acid and suggest that over time this directly increases the porosity of their inhabited layer potentially increasing the biomass it can support

impact induced microbial endolithic habitats asteroid and comet impacts on earth are commonly viewed as agents of ecosystem destruction be it on local or global scales however for some microbial communities impacts may represent an opportunity for habitat formation as some substrates are rendered more suitable for colonization when processed by impacts we describe how heavily shocked gneissic crystalline basement rocks exposed at the haughton impact structure devon island nunavut arctic canada are hosts to endolithic photosynthetic microorganisms in significantly greater abundance than lesser shocked or unshocked gneisses two factors contribute to this enhancement a increased porosity due to impact fracturing and differential mineral vaporization and b increased translucence due to the selective vaporization of opaque mineral phases using biological ultraviolet radiation dosimetry and by measuring the concentrations of photoprotective compounds we demonstrate that a covering of 0 8 mm of shocked gneiss can provide substantial protection from ultraviolet radiation reducing the inactivation of bacillus subtilis spores by 2 orders of magnitude the colonisation of the shocked habitat represents a potential mechanism for pioneer microorganisms to invade an impact structure in the earliest stages of post impact primary succession the communities are analogous to the endolithic communities associated with sedimentary rocks in antarctica but because they occur in shocked crystalline rocks they illustrate a mechanism for the creation of microbial habitats on planetary surfaces that do not have exposed sedimentary units this might have been the case on early earth the data have implications for the microhabitats in which biological signatures might be sought on mars

the emplacement of the peridotite nappe of new caledonia and its bearing on the tectonics of obduction the peridotite nappe of new caledonia is one of the few ophiolites worldwide that escaped collisional orogeny after obduction here we describe the deformation associated with serpentinization in two klippes of the nappe in northwestern new caledonia the klippes are flat lying and involve s sw vergent reverse slip shear zones which are true compressional structures in origin further northeast the nappe is folded in association with the development of a steep schistosity in low grade metasediments this difference in structural style indicates that the peridotite nappe experienced compression at greater depths toward its root zone suggesting a push from the rear mechanism of emplacement this supports the view that the nappe has been emplaced through horizontal contraction sustained by plate convergence we establish a crustal scale cross section at the end of the obduction event before neogene extension this involves a large fold nappe of high pressure rocks bounded from below by a major thrust furthermore we show that obduction in new caledonia occurred through dextral oblique convergence oblique convergence probably resulted from the initial obliquity between the subduction trench and the continental ribbon that became incorporated in it this obliquity can solve the paradox of the peridotite nappe seemingly being emplaced at the same time the high pressure rocks were exhumed oblique convergence together with focused erosional denudation on the northeastern flank of the island led to exhumation of the metamorphic rocks in a steep fold nappe rising through the rear part of the orogen

evidence for the shock melting of sulfates from the haughton impact structure arctic canada abstract sulfate minerals can form an important component of the matrix to carbonate rich impact melt breccias at the 24 km diameter 23 ma haughton impact structure arctic canada the textural and chemical features of the matrix forming sulfates indicate that these phases in addition to co existing carbonates and silicates crystallized directly from an impact generated melt evidence for this includes 1 the matrix supported nature of the crater fill lithologies 2 sulfate carbonate silicate liquid immiscible textures 3 possible quench textures in anhydrite and 4 flow textures developed between anhydrite and silicate rich glasses further supporting evidence includes the presence of si al and mg in the anhydrite structure which were probably trapped by quenching from a melt irregular blebs and globules of shock melted carbonates within anhydrite also suggest a common origin for the two phases field studies reveal that clasts of anhydrite bearing target material are also present in the crater fill deposits several clasts of anhydrite quartz lithologies exhibit evidence for incipient shock melting in both phases previous assumptions about the response of sulfates and carbonates to hypervelocity impact i e lack of melting may therefore be incorrect

compositional heterogeneity of impact melt rocks at the haughton impact structure canada implications for planetary processes and remote sensing connecting the surface expression of impact crater related lithologies to planetary or regional subsurface compositions requires an understanding of material transport during crater formation here we use imaging spectroscopy of 6 clast rich impact melt rock outcrops within the well preserved 23 5 ma 23 km diameter haughton impact structure canada to determine melt rock composition and spatial heterogeneity we compare results from outcrop to outcrop using clasts groundmass and integrated clast groundmass compositions as tracers of transport during crater fill melt rock formation and cooling supporting laboratory imaging spectroscopy analyses of 91 melt bearing breccia and clast samples and microscopic x ray fluorescence elemental mapping of cut samples paired with spectroscopy of identical surfaces validate outcrop scale lithological determinations results show different clast rich impact melt rock compositions at three sites kilometers apart and an inverse correlation between silica rich sandstone gneiss and phyllosilicate rich shales and gypsum rich rocks that suggests differences in source depth with location in the target stratigraphy gypsum is primarily sourced from 1 km depth while gneiss is from 1 8 km depth sandstone from 1 3 km and shales from 1 6 1 7 km observed heterogeneities likely result from different excavation depths coupled with rapid quenching of the melt due to high content of cool clasts results provide quantitative constraints for numerical models of impact structure formation and give new details on melt rock heterogeneity important in interpreting mission data and planning sample return of impactites particularly for bodies with impacts into sedimentary and volatile bearing targets e g mars and ceres

chemical and physical studies of type 3 chondrites vii annealing studies of the dhajala h3 8 chondrite and the thermal history of chondrules and chondrites abstract samples of the dhajala h3 8 chondrite have been annealed for 10 hours at 600 700 800 900 and 1000 c and at 1000 c for 1 2 20 and 100 h and their thermoluminescence tl properties measured the tl sensitivity decreased by a factor of 2 after annealing at but at higher temperatures fell by an order of magnitude an abrupt increase in the temperature of the tl peak from 172 9 cto231 8 c and a steady increase in the width of the peak from 169 7 cto212 5 c were caused by the annealing treatment the tl phosphor in dhajala is thought to be feldspar predominantly in the high temperature disordered form but the present data indicate that a contribution from the low temperature form is also present and that this low temperature component is converted to the high form by the annealing treatment the low temperature feldspar is located in a few of the chondrules 20 of those separated from the meteorite which are also noteworthy for having high tl sensitivities these chondrules must have suffered greater crystallization of their mesostasis than the other chondrules and equilibrated to lower temperatures it is argued that for compositional reasons their mesostasis constituted less of a barrier to diffusion and therefore equilibration presumably the post metamorphic cooling rate of the meteorite through the stability field of the low form was slow enough to permit some crystallization and the width and temperature of the tl peaks for petrologic types 3 5 3 9 are somehow related to cooling rate based on tl there is no indication of a correlation between petrologic type and cooling rate for types 3 5 3 9 this is not consistent with a simple single internally heated meteorite parent body

southwest pacific absolute plate kinematic reconstruction reveals major cenozoic tonga kermadec slab dragging tectonic plates subducting at trenches having strikes oblique to the absolute subducting plate motion undergo trench parallel slab motion through the mantle recently defined as a form of slab dragging we investigate here long term slab dragging components of the tonga kermadec subduction system driven by absolute pacific plate motion to this end we develop a kinematic restoration of tonga kermadec trench motion placed in a mantle reference frame and compare it to tomographically imaged slabs in the mantle estimating tonga kermadec subduction initiation is challenging because another new caledonia subduction zone existed during the paleogene between the australia and pacific plates we test partitioning of plate convergence across the paleogene new caledonia and tonga kermadec subduction zones against resulting mantle structure and show that most if not all tonga kermadec subduction occurred after ca 30 ma since then tonga kermadec subduction has accommodated 1 700 to 3 500 km of subduction along the southern and northern ends of the trench respectively when placed in a mantle reference frame the predominantly westward directed subduction evolved while the tonga kermadec trench underwent 1 200 km of northward absolute motion we infer that the entire tonga kermadec slab was laterally transported through the mantle over 1 200 km such slab dragging by the pacific plate may explain observed deep slab deformation and may also have significant effects on surface tectonics both resulting from the resistance to slab dragging by the viscous mantle

upper mantle low anisotropy channels below the pacific plate a new 3d anisotropic model has been obtained at a global scale by using a massive dataset of seismic surface waves though seismic heterogeneities are usually interpreted in terms of heterogeneous temperature field a large part of lateral variations are also induced by seismic anisotropy of upper mantle minerals new insight into convection processes can be gained by taking seismic anisotropy into account in the inversion procedure the model is best resolved in the pacific plate the largest and the most active tectonic plate superimposed on the large scale radial parameter and azimuthal anisotropy of vsv velocity within and below the lithosphere correlated with present or past pacific plate motions are smaller scale 1000 km lateral variations of anisotropy not predicted by plate tectonics channels of low anisotropy down to a depth of 200 km hereafter referred to as lac are observed and are the best resolved anomalies one east west channel between easter island and the tonga kermadec subduction zones observed on both radial and azimuthal anisotropies and a second one only observed on azimuthal anisotropy extending from the south west pacific up to south east hawaii and passing through the polynesia hotspot group for plate older than about 40 ma these features provide strong constraints on the decoupling between the plate and asthenosphere they are presumably related to cracking within the pacific plate and or to secondary convection below the rigid lithosphere predicted by numerical and analog experiments the existence and location of these lacs might be related to the current active volcanoes and hotspots possibly plumes in the central pacific lacs which are dividing the pacific plate into smaller units might indicate a future reorganization of plates with ridge migrations in the pacific ocean

dynamic compression and volatile release of carbonates particle velocity profiles upon shock compression and adiabatic release were measured for polycrystalline calcite solenhofen limestone to 12 24 gpa and for porous calcite dover chalk o 1 40 g cm 3 49 porosity to between 5 and 11 gpa the electromagnetic particle velocity gauge method was used upon shock compression of solenhofen limestone the hugoniot elastic limit was determined to vary from 0 36 to 0 45 gpa transition shocks at between 2 5 and 3 7 gpa possibly arising from the calcite ii iii transition were observed for the solenhofen limestone the release paths lie relatively close to the hugoniot evidence for the occurrence of the calcite iii ii transition upon release was observed but no rarefaction shocks were detected initial release wave speeds suggest retention of shear strength up to at least 20 gpa with a possible loss of shear strength at higher pressures the measured equation of state is used to predict the fraction of material devolatilized upon adiabatic release as a function of shock pressure the effect of ambient partial pressure of co 2 on the calculations is demonstrated p co 2 should be taken into account in models of atmospheric evolution by means of impact induced mineral devolatilization mass fractions of co 2 released expected on the basis of a continuum model are much lower than determined experimentally this discrepancy and radiative characteristics of shocked calcite indicate that localization of thermal energy shear banding occurs under shock compression even though no solid solid transitions occur in this pressure range release adiabatic data indicate that dover chalk loses its shear strength when shocked to 10 gpa pressure at 5 gpa the present data are ambiguous regarding shear strength for dover chalk continuum shock entropy calculations result in a minimum estimate of 90 devolatilization upon complete release from 10 gpa for calcite isentropic release paths from calculated continuum hugoniot temperatures cross into the cao solid co 2 vapor field at improbably low pressures for example 10 gpa for a shock pressure of 25 gpa however calculated isentropic release paths originating from pt points corresponding to previous color temperature under shock measurements cross into the melt plus vapor field at pressures greater than 0 5 gpa suggesting that devolatilization is initiated at the shear banding sites

new images of the earth s upper mantle from measurements of surface wave phase velocity anomalies 1 the sensitivity of a surface wave to the lateral structure of the earth s mantle depends on the local structure and thickness of the crust particularly at short periods the strong lateral heterogeneity of the crust has a significant nonlinear effect on the surface wave sensitivity functions thus far this effect has not been quantified and tomographic studies of the upper mantle based on surface wave observations have not taken it into account on the basis of a jeffreys wentzel kramers brillouin jwkb description of surface wave propagation we find and discuss the lateral variations of the sensitivity of love and rayleigh waves to mantle seismic anomalies associated with a realistic model of the crust mooney et al 1998 we then use the resulting laterally varying sensitivity kernels to determine a new tomographic image of horizontally and vertically polarized shear velocity in the upper mantle from love and rayleigh wave phase velocity measurements periods from 35 to 300 s in terms of large scale patterns of high and low velocity our model is similar to previously published ones confirming among other features the anomalous anisotropy underlying the central pacific ekstrom and dziewonski 1998 we find however that the lateral dependence of the surface wave sensitivity kernels has a significant effect on the absolute amplitude of the anomalies which should not be neglected as we attempt to obtain higher resolution images of the upper mantle