subaru telescope observations of deep impact the impact cratering process on a comet is controversial but holds the key for interpreting observations of the deep impact collision with comet 9p tempel 1 mid infrared data from the cooled mid infrared camera and spectrometer comics of the subaru telescope indicate that the large scale dust plume ejected by the impact contained a large mass 106 kilograms of dust and formed two wings approximately 45 from the symmetric center both consistent with gravity as the primary control on the impact and its immediate aftermath the dust distribution in the inner part of the plume however is inconsistent with a pure gravity control and implies that evaporation and expansion of volatiles accelerated dust

controls on back arc basin formation the relationship between subduction and back arc spreading has been well known since the early days of plate tectonics however the reasons why back arc basins are associated with some subduction systems but not all has remained elusive we examine the kinematic controls on subduction and back arc basins for both the present day and cenozoic to differentiate between the major competing hypotheses for back arc basin formation and to explain their temporal and spatial distribution our new data set of subduction and back arc basin parameters uses a new set of paleo oceanic age grids muller et al 2005 associated with a moving atlantic indian ocean hot spot reference frame o neill et al 2005 the plate model includes detailed reconstructed spreading histories of back arc basins based on marine geophysical and satellite gravity data our combined rotation and oceanic paleo age model provides the age distribution of subducting lithosphere through space and time convergence rates and the absolute motion of the downgoing and overriding plates we find that back arc basins develop when the age of subducting normal oceanic lithosphere is greater than 55 million years additionally we establish an age dip relationship showing that the intermediate dip angle of the subducting slab is always greater than 30 with back arc spreading our results suggest that back arc basin formation is always preceded by an absolute motion of the overriding plate away from the subduction hinge thereby creating accommodation space between the overriding and subducting plates once back arc extension is established it continues regardless of overriding plate motion indicating back arc spreading is not a simple consequence of overriding plate behaviour the landward migration of the overriding plate as a precursor to back arc extension may indicate that extension on the overriding plate is influenced by the oceanward lateral flow of the mantle however once back arc extension is established rollback of the subduction hinge appears to be the primary force responsible for the continued creation of accommodation space our analysis indicates the driving mechanism for back arc extension is a combination of surface kinematics properties of the downgoing slab the effect of lateral mantle flow on the slab and mantle wedge dynamics

modeling compaction of olivine cumulates in the muskox intrusion we have developed numerical models for compaction of olivine cumulates by simultaneous grain boundary diffusion creep and power law creep the simulation is a coupled model of compaction porous medium flow and heat transport that includes latent heat of fusion and advective heat transport by flow of interstitial liquid it also includes precipitation from interstitial pore liquid and partial melting of cumulates caused by changes in temperature or passage of interstitial melt through regions of different temperature compositions and quantities of liquid and precipitated phases are aetermined from a fractional crystallization simulation using the computer program melts we use these models to simulate the accumulation and crystallization of the muskox intrusion simulations suggest that regardless of their initial state compaction will lithify cumulates into a cohesive mass within meters of the depositional interface upward velocity of interstitial liquid is also much too small to suspend or liquify the crystal column the simulations produced rapidly cooled marginal zones at both top and bottom of the intrusion high rates of compaction are found at the tops and bottoms of cyclic units as a result of both high temperature at the boundary and partial melting caused by upward flow of cooler interstitial liquid as it enters hotter compositionally more primitive cumulates above the cyclic unit contact in contrast upward movement of interstitial liquid into cooler cumulates contrib utes to precipitation both in the upper marginal zone and in the middle region of cyclic units the degree of compaction of cumulates is strongly a function of temperature but if temperature is sufficiently high adcumulates can form in the interior of cumulate bodies by compaction alone

geochronology of the narakay volcanic complex implications for the age of the coppermine homocline and mackenzie igneous events u pb isotope analysis of four zircon separates from a rhyolite porphyry that is part of the bimodal narakay volcanic complex dease arm great bear lake yields an age of 1663 8 ma east trending feldspar phyric dykes that cut the complex yield zircons that are within analytical error the same age as the porphyry the narakay volcanic complex occurs in the upper part of the hornby bay group the lowermost group of the coppermine homocline and the stratigraphic position of the dated rocks indicates that 1663 ma is the depositional age of the upper hornby bay group this is the first u pb zircon age determined from rocks of the coppermine homocline and has important implications for previous geochronology and extrabasinal correlation earlier rb sr dates from the conformably overlying coppermine river group basalts of ca 1200 ma when taken together with the new data suggest that the dismal lakes group which conformably overlies the hornby bay group was deposited during a period of more than 400 ma

the michael gabbro and other mesoproterozoic lithospheric probes in southern and central labrador the michael gabbro 1426 ma and the shabogamo gabbro 1459 ma represent two iarge diabase intrusive episodes that affected the northwestern margin of the northeastern grenville province both have sustained variable effects of subsequent grenvillian metamorphism other broadly contemporaneous magmatic activity in the region includes the formation of elssnian anorthosite granitoid complexes 1 46 1 29 ga that intruded churchill province and nain province rocks to the north the harp dykes 1 27 ga and mealy dykes 1 25 ga petrologic and geochemical data show that the michael gabbro and shabogamo gabbro are similar with the latter displaying more cumulate rock characteristics and the former having compositions closer to those of rapidly cooled magma both have compositions comparable to those of other continental diabases and to some continental flood basalts sr and nd initial isotopic compositions of michael gabbro 1426 ma 4 7 to 6 0 1 1426 ma 8 7832 0 7w and shabogamo gabbro i459 ma 4 0 to 5 5 1 1459 ma 8 7020 0 7060 are alike and overlap suggesting similar sources and processes of development comparisons with other nearly contemporary mafic suites in central and southern labrador show that only the mealy dykes have a distinctly more radiogenic isotopic signature paradoxically other rnafic suites that intrude older basement rocks north of the grenville front have less enriched nd signatures than do those that intrude younger basement rocks south of the front the argument is made that the subcontinental lithospheric mantle and not crustal contamination played the most influential role in evoiution of the magmas

chondrule fragments from comet wild2 evidence for high temperature processing in the outer solar system abstract terminal grains from c2063 1 154 1 0 track 154 and c2061 1 113 5 track 113 from the stardust collection of comet wild2 s coma have been studied by tem and nanosims terminal grain 2 of c2063 1 154 1 0 consists of an al rich diopside en 97 99 al 2 o 3 9 11 wt pigeonite en 85 wo 15 with tio 2 and al 2 o 3 contents of 0 5 and 5 2 wt and minor forsterite and enstatite the mineral assemblage and al rich ti poor composition of the grain are consistent with being a fragment of an al rich chondrule similar to those present in carbonaceous chondrites the oxygen isotopic composition of the c2063 1 154 1 0 grain was determined by nanosims analyses and found to be 17 o 10 6 5 7 18 o 7 5 2 5 and 17 o 1 4 4 3 18 o 6 5 1 6 1 errors for the two sections these figures are distinct from cais and consistent with an origin as al rich chondrule fragments terminal grain 5 of c2061 1 113 5 consists of low ca pyroxene en 86 87 fs 10 11 wo 3 4 and 2 wt al 2 o 3 and in one section 5 10 of a na rich silicate phase this assemblage may be a fragment of a low ca pyroxene bearing chondrule and mesostasis the original chondrule diameter for the c2063 1 154 1 0 and c2061 1 113 5 samples by analogy with carbonaceous chondrite chondrules might have been in the range 0 2 1 0 mm if they were of that size then the presence of large grains of high temperature material e g 1500 k for such refractory assemblages could be explained through commonly invoked models of radial drift from inner to outer solar system but only if the chondrules were first fragmented to dust within the inner solar system an alternative scenario is that some chondrule formation was associated with high temperature processing and planetesimals in the outer solar system

the central scandinavian dolerite group protracted hotspot activity or back arc magmatism constraints from u pb baddeleyite geochronology and hf isotopic data the central scandinavian dolerite group csdg occurs in five separate complexes in central sweden and sw finland u pb baddeleyite ages of dolerite dikes and sills fall into three age intervals 1

seismic evidence for reverse activation of a paleo rifting system in the east sea sea of japan abstract the japanese islands were separated from the eurasian plate due to continental rifting during the oligocene to mid miocene which caused the opening of the east sea sea of japan such tectonic evolution in the east sea is important for understanding the evolution of back arc regions with active convergent margins to understand the evolution of the paleo rifted back arc region we investigate seismicity crustal seismic anisotropy focal mechanism solutions and ambient stress field around the korean peninsula the korean peninsula displays diffused seismicity with small and moderate earthquakes shallow earthquakes rarely occur in the central east sea the crustal fast shear wave polarization directions in the korean peninsula are observed to vary in azimuth between 40 and 90 the focal mechanism solutions are calculated by long period waveform inversions the ambient stress field is calculated from the focal mechanism solutions the compressional stress field in the korean peninsula is observed to be in ene wsw which is consistent with the fast shear wave polarization directions the compressional stress directions in the east sea progressively change from ene to se with increasing longitude the rapid change of compressional directions in the central east sea prohibits accumulation of stress causing rare shallow seismicity high seismicity of reverse faulting events is observed at the fringes of the east sea in particular around the east coast of the korean peninsula and the west coast of japanese islands which correspond to paleo rifted margins where compressional stresses are accumulated the compressional stress field and active thrustal events suggest reverse activation of paleo normal faults that were developed during the opening of the east sea

seismic stratigraphy and structural analysis of the western south korea plateau wskp east sea abstract the western south korea plateau wskp situated on the southwestern part of east sea is characterized by rifted continental fragments that were formed in the early phase of back arc opening in this work we analyze multi channel seismic reflection profiles from the wskp to document the structural and stratigraphic framework of the area we also present fault derived stretching beta factors related to the continental rifting along two regional seismic profiles our data reveal several graben and half graben subbasins up to 1300 m thick bound by n s trending normal faults we show that on the basis of constructed isopach maps tectonic activity was the main controlling factor on the sedimentation through much of the plateau history the seismic data reveal that the sedimentation history of the wskp is characterized by four main phases phase 1 to phase 4 p1 p4 separated by regional unconformities rapid extension and subsidence took place at an early stage of p1 leading to the graben and half graben openings volcanic activity was widespread at early times and 700 m thick succession of lacustrine and fluvial sediments was deposited following p2 early mid miocene latest miocene dramatic extension and subsidence changed the lacustrine environment into marine enabling to the deposition of thick marine sediments 750 m over the subbasins extension ceased during p3 latest miocene early pliocene and less pronounced subsidence continued at this time the sedimentation was uniform over the area and included the cyclic succession of hemipelagic deposits and turbidites which were probably expressed by climatic forcing p3 was interrupted by regional compression when normal fault movement was reversed and gentle anticlines formed as a result of inversion the latter was accompanied by widespread uplift and erosion along the western margin of the plateau and substantial erosion took place on the crests of the folds the uplift also shifted the main depocenters of the plateau which were ultimately filled by thick mass transport deposits during the following phase of p4 early pliocene holocene subsidence has been dominant in the area since the beginning of p4 which was locally interspersed by inversion along the reactivated normal faults total upper crust f and whole crust extension c estimates in the wskp show similarities suggesting that the observed rift structure in wskp has resulted from uniform pure shear stretching

tectonic evolution of the japanese island arc system abstract growth of the japanese arc system which has mainly taken place along the continental margin of asia since the permian is the result of subduction of the ancient pacific ocean floor backarc basin formation in the tertiary shaped the present day arc configuration the neotectonic regime which is characterized by strong east west compression has been triggered by the eastward motion of the amur plate in the quaternary the tectonic evolution of the japanese arc system includes formation of rock assemblages common in most orogenic belts because the origin and present day tectonics of these assemblages are better defined in the case of the japanese arc system study of the system provides useful insight into orogenesis and continental crust evolution

proterozoic flood basalts from the coppermine river area northwest territories isotope and trace element geochemistry the voluminous proterozoic continental tholeiites of the coppermine river province northwest territories which are coeval with the mackenzie magmatic event 1 27 ga old and were emplaced over a short period of time 5 ma have trace element and sr nd pb isotopic characteristics comparable to those of phanerozoic flood basalts the variations of the compositional parameters are inferred to be due to a mixing of at least two components mantle and crust in addition the mantle component probably includes two end members the first is a mantle plume whereas the other represents the base of the continental lithosphere the crustal component reflects contamination of the magma by precambrian basement during its ascent to the surface

the spi lake formation of the central hearne domain western churchill province canada an axial intracratonic continental tholeiite trough above the cogenetic kaminak dyke swarm the spi group is a package of plagioclase porphyritic amygdaloidal basalt flows and sandstone spi lake formation conformably overlain by coarse conglomerate and sandstone old boot formation these unconformably overlie the kaminak lake segment of the central hearne supracrustal belt western churchill province the spi group developed in a small isolated basin 8 km2 and is older than the paleoproterozoic hurwitz group our data demonstrate that the basalts of the spi lake formation are genetically related to the ca 2450 ma kaminak dyke swarm a speculation previously promoted by some workers based on field characteristics alone they are continental tholeiites with large ion lithophile and light rare earth element enriched multielement profiles with prominent high field strength element troughs the 143nd 144nd compositions overlap the contemporaneous chondritic bulk earth data all of these are features we infer to have resulted from mixing of melts from dominantly depleted mid ocean ridge basal

geochemistry of the little dal basalts continental tholeiites from the mackenzie mountains northwest territories canada analyses of the little dal lavas and the 779 ma tsezotene sills both of the mackenzie mountains supergroup northwest territories canada show them to be continental tholeiites that are geochemically related the plagioclase and clinopyroxene phyric lavas are geochemically evolved and enriched in iron up to 20 2 wt as fe2o3 two magmatic lineages are identifiable and may represent different degrees of partial melting in the same source region but cannot be related by fractional crystallization within each lineage geochemical variation can be explained by fractional crystallization involving up to 60 crystallization of the original magma the most evolved lavas occur at the base of the pile less fractionated lavas occur toward the top of the sequence the nd isotopic composition of the little dal lavas averages e 1 4 at 780 ma trace element and isotopic compositions are permissive of contamination by continental crust but do not require a crustal component the preserved volume of the littl

slope stability change from late pleistocene to holocene in the ulleung basin east sea japan sea abstract a wide variety of mass movement deposits prevail along the entire margin of ulleung basin overlain by a hemipelagic mud unit 1 2 m thick the boundary between the lower turbidite sequence and the upper hemipelagic mud on the basin plain is distinct and approximately coincides with the well known basin wide ash layer ulleung ash of early holocene age in the absence of significant terrigenous sediment input the lithologic change from the turbidite to hemipelagic mud may reflect physical effects of glacio marine eustatic sea level change sea level lowering during the glacial period may have generated excess pore pressure within the sediments caused by reducing hydrostatic confining pressure and facilitated triggering of the deep water slope failure by earthquakes storm waves may also have affected the uppermost slope area to induce small scale slope instabilities during the lowered sea level stand these glacial factors destabilizing the slope appear to have enhanced large scale slope failures during the late pleistocene in contrast the topmost hemipelagic mud attests to a stable slope phase associated with raised sea level in the holocene consistent with the infinite slope stability analyses calculations of the sedimentation rates based on c 14 dates of several ash layers indicate that the pre holocene turbidites on the basin plain had accumulated at an average rate of 40 cm 1000 years with a minimum recurrence interval of 50 years during the late pleistocene mass flux estimations between the slumps and turbidites suggest a predominance of the nondisintegrative mode of slope failures in the ulleung basin in each event of slope failure most of the failed mass rested on the slope as slide slump blocks and only its meager portions were deposited on the basin plain as turbidite layers

pyroxenes microstructure in comet 81p wild 2 terminal stardust particles we report the examination by transmission electron microscopy tem of four stardust terminal particles extracted from two neighboring tracks 32 an 69 the particles are made of wellpreserved crystalline grains dominated by low ca pyroxene ranging from nearly pure enstatite to pigeonite some olivine grains are also found in chemical equilibrium with the surrounding pyroxenes various microstructures are observed as a function of the composition of the grains they include 100 twinned pigeonite clino ortho domains in enstatite and exsolution in a ca rich grain the microstructures are mostly consistent with a formation by cooling from high temperature phases which could be associated to igneous processes some dislocations in glide configuration are also present probably attesting for small intensity shocks possible effects of the rapid heating cooling stage and thermal shock associated to the collect are discussed it appears that most of the microstructural features reported here are plausibly pristine

back arc rifting in the korea plateau in the east sea japan sea and the separation of the southwestern japan arc from the korean margin abstract the south korea plateau is a remnant of continental crust in the middle of the eastern korean margin that was deformed by extension in association with back arc rifting and separation of the southwestern japan arc in the cenozoic multichannel seismic profiles show that the south korea plateau preserves structure of rift basins flanked by uplifted footwall blocks rift basins in the plateau are filled with distinct syn and post rift sequences separated by a prominent breakup unconformity resulting from uplift the crustal and upper mantle structures computed by ambient noise tomography indicate that the south korea plateau defines the seaward limit of rifted continental crust in addition rifting occurred with vigorous asthenospheric upwelling induced along the korean margin and depth dependent stretching therefore the south korea plateau underwent the entire sequence of tectonic events typical of a passive continental margin encompassing rifting with subsidence uplift erosion and breakup prior to the separation of the southwestern japan arc breakup at the korean margin may substantiate successive episodes of back arc spreading which migrated toward the arc in response to trench retreat we suggest that the southwestern japan arc moved to its present location from the southern part of the korean margin with a significant amount of clockwise rotation during back arc spreading

early solar system processes recorded in the matrices of two highly pristine cr3 carbonaceous chondrites met 00426 and que 99177 the mineralogy and bulk compositions of the matrices of the cr chondrites met 00426 and que 99177 have been studied using a combination of sem epma and tem techniques the matrices of these two chondrites are texturally chemically and mineralogically similar and are characterized by significant feo enrichments with respect to other cr chondrite matrices nearly flat refractory lithophile patterns variable volatile element patterns and a simple mineral assemblage dominated by amorphous silicate material and fe ni sulfides fine grained crystalline silicate phases such as olivine and pyroxene appear to be extremely rare in the matrices of both meteorites instead the mineralogy of matrices and fine grained rims of both meteorites consists of abundant amorphous feo rich silicate material containing nanoparticles of fe ni sulfides troilite pyrrhotite and pentlandite secondary alteration minerals that are characteristic of other cr chondrites e g renazzo and al rais such as phyllosilicates magnetite and calcite are also rare the texture and mineralogy of the matrices of met 00426 and que 99177 share many features with matrices in the primitive carbonaceous chondrites alh a77307 co3 0 and acfer 094 unique these observations show that met 00426 and que 99177 are very low petrologic type 3 chondrites that have escaped the effects of aqueous alteration unlike other cr chondrites which are typically classified as petrologic type 2 we suggest that these meteorites represent additional samples of highly primitive but extremely rare carbonaceous chondrites of petrologic type 3 00 according to the classification scheme of grossman and brearley 2005 the highly pristine nature of met 00426 and que 99177 provides important additional insights into the origins of fine grained materials in carbonaceous chondrites based on our new observations we infer that the amorphous silicate material and nanosulfide particles that dominate the matrices of these meteorites formed in the solar nebula by rapid condensation of material following high temperature events such as those that formed chondrules

microchondrule bearing clast in the piancaldoli ll3 meteorite a new kind of type 3 chondrite and its relevance to the history of chondrules in the piancaldoli ll3 chondrite we found a mm sized clast containing 100 chondrules 0 2 64 m in apparent diameter much smaller than any previously reported that are all of the same textural type radial pyroxene fs1 17 this clast like other type 3 chondrites has a fine grained ferich opaque silicate matrix sharply defined chondrules abundant low ca clinopyroxene and minor troilite and si and cr bearing metallic fe ni however the very high modal matrix abundance 63 8 vol unique characteristics of the chondrules and absence of microscopically observable olivine indicate that the clast is a new kind of type 3 chondrite most chondrules have feo rich edges and chondrule size is inversely correlated with chondrule core feo concentration the first reported correlation of chondrule size and composition chondrules acquired fe by diffusion from fe rich matrix material during mild metamorphism possibly before final consolidation of the rock microchondrules those chondrules 100 m in diameter are also abundant in another new kind of type 3 chondrite clast in the rio negro l chondrite regolith breccia in other type 3 chondrite groups microchondrule abundance appears to be anticorrelated with mean chondrule size viz 0 02 0 04 vol in h and co chondrites and 0 006 vol in l ll and cv chondrites microchondrules probably formed by the same process that formed normal sized droplet chondrules melting of pre existing dustballs because most compound chondrules in the clast and other type 3 chondrites formed by collisions between chondrules of the same textural type we suggest that dust grains were mineralogically sorted in the nebula before aggregating into dustballs the sizes of compound chondrules and chondrule craters which resulted from collisions of similarly sized chondrules while they were plastic indicate that size sorting of dustballs occurred before chondrule formation probably by aerodynamic processes in the nebula we predict that other kinds of type 3 chondrites exist which contain chondrule abundances size ranges and proportions of textural types different from known chondrite groups

1 700 myr greenstone volcanic successions in southwestern north america and isotopic evolution of proterozoic mantle 1 700 myr greenstone volcanic successions in southwestern north america and isotopic evolution of proterozoic mantle

constraints on the formation environment of two chondrule like igneous particles from comet 81p wild 2 using chemical and petrologic evidence and modeling we deduce that two chondrule like particles named iris and callie from stardust cometary track c2052 12 74 formed in an environment very similar to that seen for type ii chondrules in meteorites iris was heated near liquidus equilibrated and cooled at 100 c hr and within 2 log units of the iw buffer with a high partial pressure of na such as would be present with dust enrichments of 103 there was no detectable metamorphic nebular or aqueous alteration in previous work ogliore et al 2012 reported that iris formed late 3 myr after cais assuming 26al was homogenously distributed and was rich in heavy oxygen iris may be similar to assemblages found only in interplanetary dust particles and stardust cometary samples called kool particles callie is chemically and isotopically very similar but not identical to iris

vapor condensed phase processes in the early solar system abstract equilibrium thermodynamic calculations of the sequence of condensation of phases from a cooling gas of solar composition at total pressures thought to have prevailed in the inner part of the solar nebula successfully predict the primary mineral assemblages of refractory inclusions in cm2 and cv3 chondrites many refractory inclusions in cm2 chondrites contain a relatively sio2 poor assemblage spinel hibonite grossite perovskite corundum that represents a high temperature stage of condensation and some may be pristine condensates that escaped later melting compact type a and type b refractory inclusions consisting of spinel melilite perovskite ca rich clinopyroxene anorthite in cv3 chondrites are more sio2 rich and equilibrated with the solar nebular gas at a slightly lower temperature textures of many of these objects indicate that they underwent melting after condensation crystallizing into the same phase assemblage as their precursors the ti3 ti4 ratio of their pyroxene indicates that this process occurred in a gas whose oxygen fugacity was approximately 8 5 log units below that of the iron wustite buffer making them the only objects in chondrites known to have formed in a system whose composition was close to that of the sun relative to ci chondrites these inclusions are uniformly enriched in a group of elements e g ca ree zr ta ir that are chemically diverse except for their high condensation temperatures in a system of solar composition the enrichment factor 17 5 can be interpreted to mean that these objects represent either the first 5 7 wt of the condensable matter to condense during nebular cooling or the residue after vaporization of 94 3 of a ci chondrite precursor the mg and si isotopic compositions of types a and b inclusions are mass fractionated by up to 10 and 4 amu respectively when interpreted in terms of rayleigh fractionation during evaporation of mg and si from the inclusions while they were molten the isotopic compositions imply that up to 60 of the mg and up to 25 of the si were evaporated and that approximately 80 of the enrichment in refractory cao al2o3 relative to more volatile mgo sio2 in the average inclusion is due to initial condensation and approximately 20 due to subsequent evaporation the mineralogical composition including the ti3 ti4 ratio of the pyroxene in inti a particle sampled from comet wild 2 by the stardust spacecraft is nearly identical to that of a type b inclusion indicating that comets contain not only the lowest temperature condensates in the form of ices but the highest temperature condensates as well the feo feo mgo ratios of olivine and pyroxene in the matrix and chondrules of carbonaceous and ordinary chondrites are too high to be made in a system of solar composition requiring s only 1 or 2 log units below iron wustite more than 105 times higher than that of a solar gas various ways have been devised to generate cosmic gases sufficiently oxidizing to stabilize significant feo in olivine at temperatures above those where fe mg interdiffusion in olivine ceases one is by vertical settling of dust toward the nebular midplane enriching a region in dust relative to gas because dust is enriched in oxygen compared to carbon and hydrogen relative to solar composition a higher results from total vaporization of the region but the factor by which theoretical models have so far enriched the dust is 10 times too low another is by transporting icy bodies from the outer part of the nebula into the hot inner part where vaporization of water ice occurs not only does this method fail to make the needed by a factor of 30 1000 but it also ignores simultaneous evaporation of carbon bearing ices that would make the even lower

geological constraints on the origin of the mantle root beneath the canadian shield cratonic north america is composed of a cluster of archaean microcontinents centred on the canadian shield and juvenile proterozoic crust that lies mainly buried beneath the sedimentary cover of the western and southern interior platforms the shield is underlain by an anomalous low temperature mantle root that is absent beneath the platform as there appears to be no systematic difference in crustal thickness or density between the shield and the platform the long lived arching of the shield implies an intrinsic buoyancy imparted by the mantle root that more than offsets its colder temperature isotopic and seismic anisotropy data indicate an archaean age for the mantle root close to the time of formation of the overlying crust the preferential development of the mantle root beneath archaean crust is consistent with an origin by imbrication of partly subducted slabs of highly depleted oceanic lithosphere assuming that buoyant subduction was more common in the archaean formation of the mantle root was not dependent on collisional orogenesis as has been suggested but the archaean cratonic mantle was sufficiently buoyant and refractory to survive later tectonic thickening the mantle root persists beneath archaean crust that was transected by mafic dyke swarms and subjected to short lived episodes of post orogenic crustal melting but the root is reduced at mantle plume initiation sites the partitioning of archaean and proterozic crust between the shield and the platform respectively causes the shield to misrepresent precambrian crust as a whole studies of the shield falsely conclude that a high percentage of precambrian crust formed in the archaean and that the proterozoic was characterized by epicontinental volcanism and sedimentation and crustal reworking furthermore the isotopic ratios of detritus eroded from the craton may tend to overestimate the mean age of continental crust

asymmetric deformation in the backarc region of the kuril arc northwest pacific new insights from analogue modeling 1 the eocene to middle late miocene tectonic evolution of the kuril arc and backarc region has been simulated with analogue experiments the experiments simulate asymmetric deformation in the overriding plate due to anticlockwise rollback of the subducting pacific plate the results show the formation of a n s to ne sw oriented dextral shear zone near the far edge of the retreating boundary analogous to the sakhalin hokkaido dextral shear zone contemporaneously normal faults and grabens form striking parallel to the retreating boundary near the far edge but striking more oblique near the hinge point and away from the retreating boundary this is similar to extensional structures observed in the kuril basin and the sea of okhotsk furthermore the model shows that the amount of extension progressively decreases away from the retreating boundary this appears to have also happened in the kuril okhotsk region as evidenced by crustal thickness variation in the region finally the model results show that extension is increasingly accommodated by the region close to the retreating boundary with progressive deformation this can account for the eocene early miocene extension in the sea of okhotsk followed by miocene spreading in the kuril basin

structural evolution of the southwestern margin of the ulleung basin east sea japan sea and tectonic implications abstract structural mapping and restoration of depth converted seismic profiles from the southwestern ulleung basin in the east sea japan sea back arc basin reveal the structural evolution of the area since the middle miocene the back arc closure began in the earliest middle miocene ca 15 ma and caused compressional deformation that has propagated southwestward from the dolgorae to the gorae structures and further to the unnamed inversion structure immediately adjacent to se korea the accelerated convergence of the young

on folds and thrusts affecting the coppermine river group northwestern canadian shield examination of existing geological and aeromagnetic maps of the coppermine homocline reveals two periods of deformation which affect rocks of the coppermine river group but predate rocks of the rae group the oldest event generated easterly trending folds and southerly vergent thrust faults and is probably related to events along the northern margin of laurentia the younger event caused northerly trending folds possibly correlates with an east west compressional event seen in the subsurface of the interior plains and was likely a result of plate interactions along the western margin of laurentia both deformational events that affect the coppermine homocline are younger than 1267 ma and are not correlative with the pre 1268 ma racklan orogeny of the northern cordillera

neogene deformation of the back arc shelf of southwest japan and its impact on the palaeoenvironments of the japan sea abstract the evolutionary process of the back arc basins of southwest japan is presented on the basis of geological and geophysical data sets surface geology and borehole information demonstrate rapid subsidence throughout the back arc margin in the early miocene as a result of continental rifting uplift in the middle miocene and extensive truncation in the late miocene on the back arc margin tend to become more intense eastward and westward respectively palaeomagnetic studies show that the middle miocene uplift is linked to collision of the izu bonin arc with the eastern part of southwest japan and confined deformation of the island arc offshore seismic data illustrate that the late miocene unconformity event was caused by intra arc folding under n s compression coeval resumption of subduction of the philippine sea plate is the probable cause of this episode seismic profiles also indicate that the folds converge into the tsushima strait the crustal contraction brought about closure of the tsushima strait at the western end of southwest japan blocking the warm tsushima current and so impacting strongly on the neogene palaeoenvironments of the japan sea

abrupt ventilation changes in the japan sea over the last 30 ky evidence from deep dwelling radiolarians abstract the japan sea has its own deep circulation system with its deeper parts occupied by cold and highly oxygenated water formed by winter convection in its northwestern reaches we elucidate the modern depth distribution of radiolarian species and their relation to water masses from the study of plankton tows and surface sediments cycladophora davisiana occurs in a depth interval between 1000 m and 2000 m deep layer of jspw japan sea proper water and actinomma boreale leptoderma group in depths below 2000 m bottom layer of jspw the study of seven sediment cores located in water depths ranging from 807 to 3613 m show that the radiolarian assemblages have varied since 30 cal ka bp indicating changes in water ventilation strength in this marginal sea during the interval from 30 to 17 cal ka bp ventilation was restricted to an intermediate layer beneath the low salinity surface water while the deeper zone was filled with static anoxic water deep ventilation began abruptly at 14 cal ka bp cold and oxygen rich water began to sink into the bottom layer as a result of cold oceanic inflow from the northwestern pacific through the tsugaru strait in the north deep convection activity increased from 13 to 12 cal ka bp which coincides with the younger dryas like cooling event and then stopped at 12 11 5 cal ka bp bottom water ventilation during the holocene has been dependent on high salinity inflow through the tsushima strait in the south and winter cooling in the northwestern part of the japan sea deep water was being actively formed in the early holocene in contrast to the static bottom water this bottom water formation has resulted in relatively constant water composition since 9 cal ka bp with the overall increase in high salinity oceanic water inflow although the latter decreased transiently from 7 to 5 cal ka bp in concert with climatic warming

low frequency current observations in the korea tsushima strait abstract high resolution continuous current measurements made in the korea tsushima strait between may 1999 and march 2000 are used to examine current variations having time periods longer than 2 days twelve bottom mounted acoustic doppler current profilers provide velocity profiles along two sections one section at the strait entrance southwest of tsushima island and the second section at the strait exit northeast of tsushima island additional measurements are provided by single moorings located between korea and tsushima island and just north of cheju island in cheju strait the two sections contain markedly different mean flow regimes a high velocity current core exists at the southwestern section along the western slope of the strait for the entire recording period the flow directly downstream of tsushima island contains large variability and the flow is disrupted to such an extent by the island that a countercurrent commonly exists in the lee of the island the northeastern section is marked b

refractory materials in comet samples transmission electron microscope examination of more than 250 fragments 1 m from comet wild 2 and a giant cluster interplanetary dust particle gcp of probable cometary origin has revealed four new calcium aluminum rich inclusions cais an amoeboid olivine aggregate aoa and an additional aoa or al rich chondrule arc object all of the cais have concentric mineral structures and are composed of spinel anorthite cores surrounded by al ti clinopyroxenes and are similar to two previous cais discovered in wild 2 all of the cometary refractory objects are of moderate refractory character the mineral assemblages textures and bulk compositions of the comet cais are similar to nodules in fine grained spinel rich inclusions fgis found in primitive chondrites and like the nodules may be nebular condensates that were altered via solid gas reactions in the solar nebula oxygen isotopes collected on one wild 2 cai also match fgis the lack of the most refractory inclusions in the comet samples may reflect the higher abundances of small moderately refractory cai nodules that were produced in the nebula and the small sample sizes collected in the comet samples approximately 2 3 of all fragments larger than 1 m by number are cais and nearly 50 of all bulbous stardust tracks contain at least one cai we estimate that 0 5 volume of wild 2 material and 1 volume of gcp is in the form of cais arcs and aoas account for 1 of the wild 2 and gcp grains by number

characterization of preserved primitive fine grained material from the jupiter family comet 81p wild 2 a new link between comets and cp idps abstract we report the presence of preserved primitive fine grained material containing an enstatite whisker with the crystallographic characteristics of a primary condensate in a sample of the jupiter family comet wild 2 returned to earth by nasa s stardust mission the preserved primitive material is composed of silica rich amorphous material embedded with iron sulfides and silicates it is in close association with a type ii chondrule like object in the track c2052 2 74 ogliore et al 2012 the close association of a chondrule and a primary condensate shows they must have formed in different environments and probably met in the comet forming region the first observation of an enstatite whisker with properties indicating primary condensation in a comet is a new link between comets and chondritic porous idps cp idps

matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 origins and evidence for diverse primitive nebular dust components abstract the mineralogical and chemical characteristics of dark matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 have been investigated in detail by scanning electron microscopy electron microprobe analysis and transmission electron microscopy matrix and fine grained rims on chondrules and other objects are compositionally homogeneous on the scale of 10 m and there are no compositional differences between matrix and rims mineralogically both the matrix and rims are extremely diverse and consist of a highly unequilibrated assemblage of si and fe rich amorphous material olivine pyroxene fe ni metal magnetite pentlandite pyrrhotite anhydrite and mixed layer phyllosilicate phases several distinct components can be recognized within the matrix and rims based on their textural and compositional characteristics which appear to represent basic fine grained units of nebular dust the microstructures of these different components show that they have experienced significantly different thermal histories unlike the ordinary chondrites an origin for any significant component of the matrix or rims in alha77307 from chondrules is improbable based on compositional and microstructural evidence the matrix and rim components in alha77307 formed by disequilibrium condensation processes as fine grained amorphous dust that is represented by the abundant amorphous component in the matrix such condensation could have occurred under a variety of conditions at different times and locations within the solar nebula or possibly earlier in a circumstellar environment subsequent thermal processing of this primitive condensate material in a variety of environments in the nebula resulted in partial or complete recrystallization of the fine grained dust the intimate association of fine grained components with disparate compositions and thermal histories shows that mixing of fine grained dust within the nebula must have been extremely thorough

geochemistry and petrogenesis of basaltic rocks from coppermine river area northwest territories proterozoic basaltic flows 2000 m thick and associated dykes and sills from the coppermine river area northwest territories have chemical compositions typical of continental tholeiites the low mg fe ratio and abundances of ni and cr indicate that the lavas were extensively fractionated prior to extrusion the variations of incompatible elements such as k rb ree y zr nb and th suggest that the rocks were affected by interaction with continental crust the samples least affected by contamination have trace element compositions very similar to those of p type mid ocean ridge basalts it is suggested that continental tholeiites have been generated from the same source as p type oceanic tholeiites and geochemical features such as the enrichment of some lithophile elements in many of these rocks may be related to crustal contamination the variations within the volcanic pile of the coppermine river area are related to those of an exposed part of the muskox layered intrusion

sedimentary and structural evolution of the eastern south korea plateau eskp east sea japan sea the east sea japan sea is a semi enclosed back arc basin that is thought to preserve a significant record of tectonic evolution and paleo climatic changes of eastern asia during the neogene we use here 2 d regional multi channel seismic reflection profiles and borehole data from expedition 346 of the integrated ocean drilling program iodp to provide new constraints on the geological history of the eastern south korea plateau eskp the eskp represents a structurally complex basement high in the southwestern east sea which formed during rifting of the back arc basin our new observations show that the eskp is composed of numerous horsts and grabens controlled by ne trending normal faults the acoustic basement is blanketed by oligocene to recent sediments that have preferentially accumulated in topographic lows up to 1 5 km thick and have been cored during expedition 346 at site u1430 close to the southern margin of the eskp seismic profiles in the eskp reveal three units separated by regional unconformities these seismic units closely correspond to iodp lithostratigraphic units defined at site u1430 where biostratigraphic data can be used to constrain the timing of three main evolutionary stages of the eskp stage 1 was related to rifting in the late oligocene and middle miocene terminated by a regional uplift leading to an erosional phase in the middle miocene stage 2 was associated with subsidence in the middle and late miocene and uplift and accompanying erosion or non deposition in the latest late miocene stage 3 pliocene to present recorded overall uniform hemipelagic pelagic subsidence of the eskp with short lived tectonically induced uplifts in the late middle miocene and latest miocene early pliocene the three stages of evolution of the eskp closely correlate to sedimentary changes since the oligocene and suggest a direct control of regional local tectonics on sedimentation patterns in the southwestern east sea with secondary influence of regional climatic and paleo oceanographic processes

nd isotopic evolution of the precambrian mantle abstract the most convincing examples of proterozoic oceanic crust assemblages occur in the circum superior fold belt of quebec nd isotope analyses of the chukotat and hellancourt basalts from this belt constrain the e nd of the early proterozoic depleted mantle reservoir at 4 to 6 along with data for phanerozoic ophiolites and modern morb the proterozoic basalts infer a constant rate of evolution of the depleted mantle at a rate of 2 2 e nd units per ga recalculation of sm nd isotopic data for archaean greenstone belts to their most reasonable pb pb or u pb ages suggests significantly greater isotopic heterogeneity in the archaean presumed uncontaminated tholeiites and al undepleted komatiites fall within the extrapolated growth limits for the proterozoic phanerozoic depleted mantle while al depleted komatiites adk in early archaean greenstone belts have significantly higher e nd the latter require derivation from a source whose isotopic composition evolved at 2 4 times the rate of the al undepleted komatiite and tholeiite source the isotopic heterogeneities noted for the archaean indicate a compositionally layered mantle by the late archaean the adk source was either isolated by declining geothermal gradients or had become remixed with the overlying mantle giving rise to the present depleted mantle reservoir

comprehensive examination of large mineral and rock fragments in stardust tracks mineralogy analogous extraterrestrial materials and source regions abstract transmission electron microscopy examination of 87 large fragments from 16 carrot shaped and bulbous stardust sd tracks was performed to study the range and diversity of materials present in comet wild 2 olivines and low ca pyroxenes represent the largest proportions of fragments observed however a wide range of minerals and rocks were found including probable ferromagnesian al rich and si rich chondrule fragments a refractory inclusion possible matrix mineral lithic clasts and probable condensate minerals these materials combined with fine grained components in the tracks are analogous to components in unequilibrated chondrite meteorites and cluster interplanetary dust particles idps two unusual lithologies in the bulbous tracks are only observed in chondritic porous idps and may have direct links to idps the absence of phyllosilicates indicates that comet wild 2 may be a dry comet that did not accrete or form significant amounts of hydrated phases some large mineral fragments in the sd tracks are analogous to large mineral idps the large variations of the coarse grained components within and between all 16 tracks show that comet wild 2 is mineralogically diverse and unequilibrated on nearly all scales and must have accreted materials from diverse source regions that were widely dispersed throughout the solar nebula

a refractory inclusion returned by stardust from comet 81p wild 2 among the samples returned from comet 81p wild 2 by the stardust spacecraft is a suite of particles from one impact track track 25 that are ca al rich and feo free we studied three particles from this track that range in size from 5 3 x 3 2 m to 15 x 10 m scanning and transmission electron microscopy show that they consist of very fine grained typically from 0 5 to 2 m al rich ti bearing and ti free clinopyroxene mg al spinel and anorthite with trace amounts of fine perovskite feni metal and osbornite tin grains in addition to these phases the terminal particle named inti also contains melilite all of these phases with the exception of osbornite are common in refractory inclusions and are predicted to condense at high temperature from a gas of solar composition osbornite though very rare has also been found in meteoritic refractory inclusions and could have formed in a region of the nebula where carbon became enriched relative to oxygen compared to solar composition compositions of ti pyroxene in inti are similar but not identical to those of fassaite from allende inclusions electron energy loss spectroscopy shows that ti rich pyroxene in inti has ti3 ti4 within the range of typical meteoritic fassaite consistent with formation under reducing conditions comparable to those of a system of solar composition inti is 16o rich with 18o 17o 40 like unaltered phases in refractory inclusions and refractory idps with grain sizes mineralogy mineral chemistry and an oxygen isotopic composition like those of refractory inclusions we conclude that inti is a refractory inclusion that formed in the inner solar nebula identification of a particle that formed in the inner solar system among the comet samples demonstrates that there was transport of materials from the inner to the outer nebula probably either in a bipolar outflow or by turbulence

insights into solar nebula formation of pyrrhotite from nanoscale disequilibrium phases produced by h2s sulfidation of fe metal lauretta 2005 produced sulfide in the laboratory by exposing canonical nebular metal analogs to h 2 s gas under temperatures and pressures relevant to the formation of the solar system the resulting reactions produced a suite of sulfides and nanophase materials not visible at the microprobe scale but which we have now analyzed by tem for comparison with interplanetary dust samples and comet wild 2 samples returned by the stardust mission we find the unexpected result that disequilibrium formation favors pyrrhotite over troilite and also produces minority schreibersite daubreelite barringerite taenite oldhamite and perryite at the metal sulfide interface tem identification of nanophases and analysis of pyrrhotite superlattice reflections illuminate the formation pathway of disequilibrium sulfide we discuss the conditions under which such disequilibrium can occur and implications for formation of sulfide found in extraterrestrial materials

infill history of the ulleung basin east sea sea of japan and implications on source rocks and hydrocarbons abstract the ulleung basin in the east sea sea of japan has experienced back arc opening in the miocene and partial closure since the middle miocene uplift along the southern basin margin caused by the back arc closure resulted in a series of anticlines and thrusts providing large volumes of sediments into the basin mass transport deposits dominated in the southern basin while turbidite and hemipelagic sedimentation prevailed in the northern basin one dimensional basin modeling shows that late postrift early late miocene marginal marine and prodeltaic sediments are buried too shallow to generate hydrocarbons the main phase of oil generation in the synrift lacustrine and early postrift marginal marine facies late oligocene early miocene in age beneath the southern basin margin occurred in the late early to early middle miocene predating the tectonic uplift this significantly reduces the chances of large oil accumulations in the southern basin margin the dominance of massive non uniform sediments in the southern basin together with the lack of preferred avenues such as faults are not favorable for the lateral migration of hydrocarbons sourced possibly from basinal muds in the north to the traps in the southern basin margin source rocks for the recently discovered gas in the southwestern shelf are probably the lacustrine and marginal marine sediments that have been expelling gas at least since the late middle miocene

petrogenesis of the 723 ma coronation sills amundsen basin arctic canada implications for the break up of rodinia the coronation mafic sills and associated natkusiak flood basalts in arctic canada are part of the 723 ma franklin igneous events a flood basalt and dyke swarm province that extends across the southern arctic of north america and greenland two representative sills 70 and 25 m thick respectively outcrop near coronation gulf in nunavut they are composed of clinopyroxene plagioclase olivine and fe ti oxides and have tholeiitic composition similar to the natkusiak basalts their end values range between 4 2 and 5 9 and have la yb n ratios of 1 5 2 these rocks are mantle derived and were affected by minor crustal contamination compositional variations indicate that the coronation sills have experienced extensive fractionation including flow differentiation during emplacement and show increased differentiation from west to east across the province a feature similar to the mackenzie dyke swarm however the mackenzie dyke swarm and the franklin igneous events have distinct chemical composition the franklin rocks are related to a mantle plume located near victoria island at the center of the dyke swarm and could represent an offshoot from the superplume related to the break up of rodinia the absence of such dykes and sills in siberia argues against locating siberia against northern laurentia in a rodinia reconstruction 2003 elsevier b v all rights reserved

tectonic history of ulleung basin margin east sea sea of japan a geologic history analysis of an exploratory well drilled on the southern margin of the ulleung back arc basin east sea western part of the sea of japan reveals that tectonic force and sedimentary loading played a major role in the subsidence of the paleo ulleung basin where a thick clastic sequence was deposited during the neogene initial subsidence was most likely caused by a tectonic force related to the back arc rifting and spreading associated with convergent processes the southern margin underwent regional deformation uplift faulting and folding toward the late miocene this event was probably due to back arc deformation caused by changes both in plate motions and in subduction mode at the convergent zones

the control of depositional depth tectonic uplift and volcanism on sedimentation processes in the back arc basins of the western pacific ocean nine sediment types are recognized in cores recovered by the deep sea drilling project from back arc basins in the western pacific these include submarine fan turbidites debris flows silty basinal turbidites biogenic pelagic carbonate sediments resedimented carbonates biogenic pelagic silica sediments pyro clastics hemipelagic clays and pelagic clays most of these sediments were deposited independent of basinal rifting spreading processes the transition from biogenic pelagic carbonate sediments into overlying pelagic clays is the only sedimentary sequence dependent on basinal tectonic processes through post rifting subsidence associated with heat loss hemipelagic clays and silty turbidites are controlled by sediment yield from continental sources and by climatic change whereas deposition of biogenic pelagic sediments depend on ocean circulation and on latitudinally defined productivity zones coarse pyroclastics are the product of local volcanic periodicity whereas ash deposition is contr

mineralogy and petrology of stardust particles encased in the bulb of track 80 tem investigation of the wild 2 fine grained material abstract we have characterized by transmission electron microscopy the mineralogy of samples extracted from the walls of the stardust track 80 more than 500 fragments were studied using conventional imaging electron diffraction and edx microanalysis two categories of particles are distinguishable in equal proportions wt the first one is comprised of relatively large crystalline grains 1 m on average dominated by silicates olivine and pyroxene they display a wide range of compositions and microstructures comparable to those found in terminal particles minor phases including magnetite and apatite are also present their occurrence suggests that the wild 2 material underwent aqueous alteration to some extent the second type of particle called gems like material is made of silica rich glassy clumps embedding iron sulfide beads and vesicles their microstructure is characteristic of thermally modified particles that have suffered strong interaction with the silica aerogel during the hypervelocity impact this melted material may form by shedding of melted and vaporized material but given the shape of the impact track and high diversity of surviving mineral compositions much of it originated from fine grained aggregates that disaggregated during the collection chemical mapping at the nano scale allowed the localization of individual components within the silica rich glass they are dominated by mg rich components with a size less than 300 nm the average composition of this thermally modified material is close to the solar abundance for the major elements fe mg and s the fine grained material has probably not been chemically fractionated in the protoplanetary disk before its incorporation in comet wild 2 unlike the sulfur depleted matrix of chondrites from these two categories of particles we deduce that wild 2 is likely made of an assemblage of relatively large evolved grains first category cemented by a fine grained material with primitive chemistry second category the pre impact configuration of the incident material deduced from this study seems comparable to the matrix of the most primitive chondrites 3 0 or to chondritic porous interplanetary dust particles

an andean model of interplate coupling and strain partitioning applied to the flat subduction zone of sw japan nankai trough abstract transcurrent motion is commonly observed in cases of oblique subduction yet the causes remain controversial a model of increased interplate coupling linked to flat subduction is proposed as a mechanism for producing strain partitioning at a great distance several hundred km from the trench the model originally developed for the north andean margin is applied to the geodynamics of sw japan here along the nankai trough and below adjacent sw honshu flat subduction occurs due to the relatively young age m 7 and nine additional m 6 earthquakes in the past 300 years dextral strike slip focal mechanisms for 15 modern and historical events indicate a significant degree of subduction related strain partitioning manifested by right lateral strike slip faulting along the adakitic volcanic arc some 400 km from the nankai trough

wave planation surfaces in the mid western east sea sea of japan indicators of subsidence history and paleogeographic evolution of back arc basin abstract this study focuses on revealing the origin of deep marine wave planation surfaces and its geomorphic and tectonic implications for the back arc evolution based on multi channel seismic reflection profiles acquired from the mid western east sea sea of japan on seismic reflection profiles the wave planation surfaces are recognized as continuous and high amplitude single reflectors outlining the flattened top of submarine terraces or isolated topographic highs the wave planation surfaces are classified into four types depending on the geomorphic characteristics and origins of substratal landmasses i e continental margin terrace type 1 rifted continental fragment type 2 volcanic edifices type 3 and uplifted sedimentary successions type 4 which have common origin of wave erosion near the sea level but different subsidence history the mean subsidence rate of wave planated substratum is calculated by dividing the maximum depth of a wave planation surface below modified datum sea level d e by the time elapsed since the onset of subsidence t information of local subsidence history enables reconstruction of paleogeographic evolution of mid western east sea during the neogene quaternary time 1 incipient continental rifting and onset of marine incursion ca 23 18 ma 2 progressive continental rifting and onset of wave planation ca 18 11 ma 3 final eruption of post rift volcanoes ca 11 ma 4 uplifting of shelf margin banks and onset of the pliocene holocene volcanic activities ca 11 2 5 ma 5 change in the locus of volcanic eruption and cessation of contractile uplifting in the basin margin ca 2 5 0 ma

the bear river dykes 1265 1269 ma westward continuation of the mackenzie dyke swarm into yukon canada abstract the 1 27 ga mackenzie dyke swarm the largest on earth radiates from a point in the western canadian arctic and extends across much of the canadian shield possible western extensions of the swarm are largely obscured by younger sedimentary cover paleoproterozoic inliers in northern yukon host the bear river dykes brd herein dated by u pb baddeleyite and zircon methods at 1268 5 1 5 ma and 1264 6 1 2 ma the brd share similar geochemical and nd isotopic characteristics with the mackenzie dykes and the coeval coppermine river basalts and are regarded as products of the same plume hydrothermal activity at 1270 ma in breccia of the nor mineral occurrence northwest of the brd was probably generated by brd at depth the brd generally strike northwest approximately 90 to the orientation predicted by the radiating dyke model this difference may be explained by an anomalous local stress field at the time of brd emplacement or reorientation of brd during subsequent events of cordilleran deformation using the nor mineral occurrence as the westernmost locale of mackenzie dyking and assuming a model of uniform dyke radiation the arc of the mackenzie swarm is at least 50 greater than previously recognized bringing the total arc of dyke radiation to 150

fault slip analysis of quaternary faults in southeastern korea abstract the quaternary stress field has been reconstructed for southeast korea using sets of fault data the subhorizontal direction of the maximum principal stress 1 trended ene and the direction of the minimum principal stress 3 was nearly vertical the stress ratio 2 3 1 3 value was 0 65 two possible interpretations for the stress field can be made in the framework of eastern asian tectonics 1 the hmax trajectory for southeast korea fits well with the fan shaped radial pattern of maximum principal stress induced by the india eurasia collision thus we suggest that the main source for this recent stress field in southeast korea is related to the remote india eurasia continental collision 2 the stress field in korea shows a pattern similar to that in southwestern japan the origin for the e w trending hmax in japan is known to be related to the mantle upwelling in the east china sea thus it is possible that quaternary stress field in korea has evolved synchronously with that in japan we suggest further studies gps and in situ stress measurement to test these hypotheses

paleoceanographic evolution of the japan sea abstract multidisciplinary studies on nearly continuous hemipelagic sequences recovered from the deeper parts of the japan sea during odp leg 127 128 in 1989 yielded new information on the paleoceanographic conditions of the sea since its establishment as a deep marginal basin of significant size approximately at 20 ma by synthesizing these new information on surface and bottom water conditions ccd biogenic silica accumulation and paleogeog raphy it is possible to reconstruct changes in paleo ocean circulation within the sea it is also possible to specify the ultimate cause of such changes by comparing their timing and nature with those of global paleoceanographic as well as local tectonic events the result of our synthesis suggests that the japan sea has been responding to the high frequency changes of global surface conditions in very sensitive manner throughout its history however the mode of its response changed from time to time the changes in response mode have been strongly influenced by such factors as sill depth position of channels and the degree of closure of the sea which were controlled either by local tectonism or global eustatic sea level changes

seismic stratigraphy and structural characteristics of the northeastern continental margin of korea in the east sea sea of japan abstract the northeastern continental margin of korea in the east sea japan sea is a narrow sedimentary apron 20 30 km wide 50 1300 m below sea level with an average gradient of less than 2 the present study focuses on seismic stratigraphy of the sedimentary section and the underlying basement structure of the margin based primarily on multi channel seismic reflection profiles major accumulation of sediment is centred in a graben depocenter in the northern part of study area where more than 2 km of sediments have been deposited this graben widens towards north and is flanked by two major basement bounding faults the sedimentary succession of the margin can be divided into six seismic stratigraphic units based on reflection character onlapping and erosional truncation the lowermost seismic unit su1 is characterized by parallel to subparallel reflections with varying amplitudes and is interpreted to be representing shallow to non marine sediments that were deposited during the active extensional phase of margin development the presence of erosional channels in the uppermost section of su1 further suggests a lowstand period after the deposition of su1 unconformably overlying the su1 is a few hundred metres of su2 that is characterized by continuous high amplitude reflections continuous seismic reflections within su2 are indicative of sea level rise immediately following the lowstand period the overlying seismic unit sets include su3 su4 and su5 with well stratified seismic reflections the consistent reflection pattern and high continuity of the reflections within these units are indicative of relatively stable depositional environments within the margin hemipelagic sediments and turbidites are probably the main components of these units the youngest seismic unit su6 comprises well stratified seismic reflections in the upper slope and chaotic to transparent seismic reflections in the lower slope the sedimentary units characterized by well stratified seismic reflections are typical for hemipelagic slope sediments while chaotic seismic reflections are diagnostic features for mass transport sediments mtds i e slides slumps debris flow deposits the preferential occurrence of mtds adjacent to the major faults suggests that they may be due to earthquakes associated with tectonic activity seismic reflection data from the margin reveal the coexistence of four structural styles including the basement involved normal faults reverse faults reactivated normal faults and anticline folds the basement bounding normal faults are associated with the initial extension of the continental margin while the others are postulated as resulting from contractional tectonism of the eastward movement of the amur plate that began in the early pliocene the prominent seafloor erosion over the folded inverted blocks further suggests that inversion continues today

igneous ca rich pyroxene in comet 81p wild 2 the stardust spacecraft successfully returned dust from comet 81p wild 2 to earth in january 2006 preliminary examination of the samples showed abundant crystalline silicates comparable to those found in chondritic meteorites presumably formed in the asteroid belt here we report results of a transmission electron microscopy tem study of a pyroxene bearing terminal particle which contains lamellar intergrowths of pigeonite and diopside on the 001 plane this microstructure is typical for an igneous process and formation by exsolution during cooling width and wavelength of the lamellae indicate a cooling rate within the range 10 100 c h in close agreement with those of chondrules or lava from an asteroidal igneous rock this observation shows that some stardust material experienced periods of igneous processing similar to material found in the inner early solar system this implies that igneous materials were common materials in a large region of the protoplanetary disk and were not restricted to the asteroid belt their presence in comet wild 2 also supports the favored view of large radial mixing from the inner to the outer regions before the comet s accretion

hot orogens tectonic switching and creation of continental crust many granulite terrains were too hot to have formed during continental collision rather along with many high grade metamorphic terrains that typify continental crust most formed in accretionary orogens during tectonic switching when prolonged lithospheric extension was interrupted by intermittent transient contraction based on modern and ancient examples tectonic switching occurs when slab retreat induces upper plate extension causing arc splitting formation of microcontinent slivers and backarc basins then intermittent arrival of buoyant oceanic plateaus induces transient flat subduction or slab flip and crustal thickening during slab retreat basaltic magmas produced from decompressed asthenosphere advect into the extending orogen causing granulite facies metamorphism and granite generation but subsequent thickening during flat subduction cools the region thickening is focused in the thermally softened backarc region and if sediment filled a hot short lived 10 m y narrow 50 100 km orogenic belt forms such thickening is often misleadingly ascribed to arc or microcontinent collision once slab retreat mode is reestablished lithospheric extension recommences and a new arc backarc system forms generally outboard arrival of another plateau will reverse the procedure and another short lived hot orogen will form within the orogenic system cycles of tectonic switching efficiently produce continental crust

land ocean linkages over orbital and millennial timescales recorded in late quaternary sediments of the japan sea late quaternary sediments of the japan sea are characterized by centimeter to meter scale alternations of dark and light layers which are synchronous basinwide high resolution analyses of the sediments from ocean drilling program site 797 reveal that deposition of the meter scale alternations reflect variations in paleoceanographic conditions which were closely associated with glacio eustatic sea level changes through the modulation of the volume and character of the influx to the sea through the tsushima strait the centimeter to decimeter scale alternations reflect millennial scale variations which are possibly associated with dansgaard oeschger d o cycles with each dark layer appearing to correspond to an interstadial this variability is attributed to the development of a humid climate in central to eastern asia and the consequent increase in discharge from the huanghe and changjiang rivers during interstadials this caused expansion of the east china sea coastal water ecscw which penetrated more strongly into the japan sea the increased influence of the lower salinity nutrient enriched ecscw reduced deep water ventilation and enhanced the surface productivity leading to the development of anoxic bottom waters and deposition of the dark layers thus the centimeter to decimeter scale alternations of the dark and light layers record wet and dry cycles in central to eastern asia possibly associated with d o cycles

nd isotopic evidence from wopmay orogen for 2 0 2 4 ga crust in western north america abstract nd isotopic data from the 1 9 ga wopmay orogen n w t canada strongly suggest the involvement of crust in the range of 2 0 2 4 ga remnants of three compositionally diverse magmatic arcs 1940 1902 ma 1890 1880 ma and 1875 1840 ma are preserved in wopmay orogen each of the three arcs originated west of the limit of exposed archean crust nineteen samples of plutonic and volcanic rocks from the three arcs yield a narrow range of initial e nd from 1 8 to 0 3 there is no apparent correlation between e nd and geographic distribution nor with whole rock chemistry sio 2 54 75 two basalt samples from west of the archean have initial e nd s between 2 and 3 two 1 87 ga granites which intrude through archean crust have much lower initial e nd s of 5 9 and 8 6 the data from the three magmatic arcs are best interpreted in terms of a source region which had a very limited range of e nd at 1 9 ga which we interpret as 2 0 2 4 ga crust presumably hottah terrane basement wopmay fault zone is therefore the surface manifestation of a suture between 2 0 2 4 ga hottah terrane and the archean slave craton there is a growing body of data which suggests that much of western north america may be underlain by 2 0 2 4 ga crust geochronologic and isotopic data from other precambrian cratons also suggest that 2 0 2 4 ga crust may be much more widespread than previously thought models of crustal growth which interpret 1 9 1 7 ga crust as mixtures of archean crust and proterozoic depleted mantle may be overestimating the amount of juvenile material added to the crust in this time period

cometary dust in antarctic ice and snow past and present chondritic porous micrometeorites preserved on the earth s surface abstract chondritic porous interplanetary dust particles cp idps collected in the stratosphere are regarded as possibly being cometary dust and are therefore the most primitive solar system material that is currently available for analysis in laboratories in this paper we report the discovery of more than 40 chondritic porous micrometeorites cp mms in the surface snow and blue ice of antarctica which are indistinguishable from cp idps the cp mms are botryoidal aggregates composed mainly of sub micrometer sized constituents they contain two components that characterize them as cp idps enstatite whiskers and gems glass with embedded metal and sulfides enstatite whiskers appear as 2 o 6 rich high ca pyroxene roedderite k na 2 mg 5 si 12 o 30 and carbonaceous nanoglobules these components have previously been discovered in primitive solar system materials such as the cp idps matrices of primitive chondrites phyllosilicate rich mms ultracarbonaceous mms and cometary particles recovered from the 81p wild 2 comet the most outstanding feature of these cp mms is the presence of kosmochlor rich high ca pyroxene and roedderite which suggest that they have building blocks in common with cp idps and cometary dust particles and therefore suggest a possible cometary origin of both cp mms and cp idps it is therefore considered that cp mms are cp idps that have fallen to earth and have survived the terrestrial environment

paleo tsushima water and its effect on surface water properties in the east sea during the last glacial maximum revisited abstract the semi enclosed deep marginal east sea is known by limited sill flow and low sea surface salinity during the last glacial maximum lgm when sea level was about 130 m lower than the present level although three straits the tsugaru the soya and the tartar with shallower than 130 m sills were completely closed the korea strait with a maximum sill depth of 140 m seems to have persisted as a partial connection to the east sea allowing a sill flow the volume transport at the korea strait during the lgm is estimated at approximately 0 3 1 1 1012 m3 yr by using bathymetry seismic reflection profiles and current data the low sea surface salinity has been explained by the east china sea coast water ecscw and high precipitation however the existing geological observations indicate that precipitation was reduced in the glacial east sea the high resolution numerical simulation results predict that evaporation 2 16 mm day exceeded precipitation 1 43 mm day further suggesting net evaporation evaporation minus precipitation rates 0 2 1012 m3 yr over the lgm east sea this signifies that the precipitation was not the factor lowering surface paleosalinity and that the paleo tsushima water carried a huge amount of freshwater from the ecscw than previously expected the calculated surplus evaporation 0 2 1012 m3 yr and sill flow 0 3 1 1 1012 m3 yr are not identical but they could be oceanographically considered as similar the comparison between both values implies that most of the throughflow ultimately escaped the east sea through the evaporation process during the lgm the regional sea level in the almost isolated east sea might be largely maintained by a rough balance between incoming throughflow and outgoing evaporation during the lgm the geographic restriction due to lowered sea level and lower surface salinity by limited vertical mixing in the glacial east sea are analogous to modern oceanographic features in the black sea

geochemical signature and seismic stratigraphic setting of coppermine basalts drilled beneath the anderson plains in northwest canada basalts drilled in the petro canada canterra tweed lake m 47 well in the anderson plains of northwestern canada have geochemical characteristics including of major trace and rare earth elements that are similar to those of the most enriched coppermine lavas but significantly different from those of the younger proterozoic volcanics such as the natkusiak basalts this result provides a geological tie and timing constraint for structures observed on seismic reflection data in this area correlation of stratigraphic data from the well to seismic data shows that the lavas are within a sequence of layered reflections that onlap and are thus younger than easterly verging structures and that were themselves probably uplifted prior to deposition of the mackenzie mountains supergroup these relationships thus show that at least two stages of proterozoic compressional deformation one that predated and one that postdated the basalts produced structures beneath the anderson plains

evolution of the eastern margin of korea constraints on the opening of the east sea japan sea abstract we interpreted marine seismic profiles in conjunction with swath bathymetric and magnetic data to investigate rifting to breakup processes at the eastern korean margin that led to the separation of the southwestern japan arc the eastern korean margin is rimmed by fundamental elements of rift architecture comprising a seaward succession of a rift basin and an uplifted rift flank passing into the slope typical of a passive continental margin in the northern part rifting occurred in the korea plateau that is a continental fragment extended and partially segmented from the korean peninsula two distinguished rift basins onnuri and bandal basins in the korea plateau are bounded by major synthetic and smaller antithetic faults creating wide and considerably symmetric profiles the large offset border fault zones of these basins have convex dip slopes and demonstrate a zig zag arrangement along strike in contrast the southern margin is engraved along its length with a single narrow rift basin hupo basin that is an elongated asymmetric half graben analysis of rift fault patterns suggests that rifting at the korean margin was primarily controlled by normal faulting resulting from extension rather than strike slip deformation two extension directions for rifting are recognized the onnuri and hupo basins were rifted in the east west direction the bandal basin in the east west and northwest southeast directions suggesting two rift stages we interpret that the east west direction represents initial rifting at the inner margin while the japan basin widened rifting propagated southeastward repeatedly from the japan basin toward the korean margin but could not penetrate the strong continental lithosphere of the korean shield and changed the direction to the south resulting in east west extension to create the rift basins at the korean margin the northwest southeast direction probably represents the direction of rifting orthogonal to the inferred line of breakup along the base of the slope of the korea plateau after breakup the southwestern japan arc separated in the southeast direction indicating a response to tensional tectonics associated with the subduction of the pacific plate in the northwest direction no significant volcanism was involved in initial rifting in contrast the inception of sea floor spreading documents a pronounced volcanic phase which appears to reflect asthenospheric upwelling as well as rift induced convection particularly in the narrow southern margin we suggest that structural and igneous evolution of the korean margin although it is in a back arc setting can be explained by the processes occurring at the passive continental margin with magmatism influenced by asthenospheric upwelling

fe mn systematics of type iia chondrules in unequilibrated co cr and ordinary chondrites we have examined fe mn systematics of 34 type iia chondrules in eight highly unequilibrated co cr and ordinary chondrites using new data from this study and prior studies from our laboratory olivine grains from type iia chondrules in co chondrites and unequilibrated ordinary chondrites uoc have significantly different fe mn ratios with mean molar fe mn 99 and 44 respectively olivine analyses from both these chondrite groups show well defined trends in mn versus fe afu and molar fe mn versus fe mg diagrams in general type iia chondrules in cr chondrites have properties intermediate between those in uoc and co chondrites in most uoc and cr type iia chondrules the fe mn ratio of olivine decreases during crystallization whereas in co chondrites the fe mn ratio does not appear to change it is difficult to interpret the observed fe mn trends in terms of differing moderately volatile element depletions inherited from precursor materials instead we suggest that significant differences in the abundances of silicates and sulfides metals in the precursor material as well as open system behavior during chondrule formation were responsible for establishing the different fe mn trends using fe mn mg systematics we are able to identify relict grains in type iia chondrules which could be derived from previous generations of chondrules including chondrules from other chondrite groups and possibly chondritic reservoirs that have not been sampled previously

lead isotopic study of early proterozoic wopmay orogen nw canada role of continental crust in arc magmatism lead isotopes are sensitive indicators of crustal interaction in arc magmatism because of the large contrast in lead concentration between mantle derived magmas and continental crust and the three independent decay paths in the u th pb system preserved within wopmay orogen 1 94 to 1 84 ga are the remnants of three magmatic arcs the isotopic composition of lead in alkali feldspars separated from a diverse suite of samples from all three arcs fall in a relatively tight cluster with 206 pb 204 pb 15 59 15 88 207 pb 204 pb 15 27 15 36 and 208 pb 204 pb 35 15 35 54 except for samples from the only plutonic suite within wopmay orogen observed to intrude archean crust plutons intruding archean crust have 206 pb 204 pb 15 29 15 49 206 pb 204 pb 15 23 15 31 and 208 pb 204 pb 35 21 35 30 lead isotopic compositions do not correlate with rock composition both diorites and peraluminous granites have the same lead isotopic composition this isotopic composition