eoarchean paleoproterozoic zircon inheritance in japanese permo triassic granites unazuki area hida metamorphic complex unearthing more old crust and identifying source terrranes abstract u pb zircon geochronology of two permo triassic granites samples ot 52 and ot 272 with ages of 229 8 ma and 256 2 ma respectively in the unazuki area hida metamorphic belt southwest japan revealed the presence of eoarchean to paleoproterozoic inheritance inheritance is consistent with both samples showing low zircon saturation temperatures for their bulk compositions in ot 52 dark in cl low th u zircon domains have a mean 207pb 206pb age of 1940 17 ma which is consistent with an age of 1937 6 ma for anatexis in the precambrian busan gneiss complex in korea eoarchaean inherited zircons with 207pb 206pb ages from ca 3750 to 3550 ma are common in ot 272 but are few in ot 52 suggesting a source from rocks with affinities to those in the anshan area in the northeast china part of the north china craton on the other hand a hida metamorphic belt metasedimentary gneiss into which the granites were intruded contains ca 1840 1130 580 360 285 and 250 ma zircons sano et al 2000 these ages suggest that the unazuki mesozoic granites did not originate from proximal hida metamorphic complex rocks but instead from unrelated rocks obscured at depth the predominance of eoarchean to paleoproterozoic age components and the marked lack of 900 700 ma components suggest that the source was the extended fringe of the north china craton rather than from yangtze craton crust the mesozoic evolution of japan and its linkages to northeast asia are discussed in the context of these results

hydrothermal 3he and manganese plumes at 19 29 s on the central indian ridge we report the discovery of a hydrothermal helium 3 plume north of the indian triple junction on the central indian ridge at 19 29 s water column 3he anomalies show a spike of 33 8 at 2460 meter depth i e the highest 3he anomaly recorded so far in the indian ocean the helium 3 data are correlated with manganese giving a mn 3he ratio of 700 mol cm3 3 8 104 g cm3stp the ch4 3he ratio deduced from available ch4 mn data in the same area is around 7 106 these values are close to what is observed on water column plumes on the east pacific rise on a regional scale the 3he distribution over the indian triple junction exhibits a strong 3he increase at the ridge crest which appears to spread eastwards through the deep indian ocean

assimilation of radiocarbon and chlorofluorocarbon data to constrain deep and bottom water transports in the world ocean a coarse resolution global model with time invariant circulation is fitted to hydrographic and tracer data by means of the adjoint method radiocarbon and chlorofluorocarbon cfc 11 and cfc 12 data are included to constrain deep and bottom water transport rates and spreading pathways as well as the strength of the global overturning circulation it is shown that realistic global ocean distributions of hydrographic parameters and tracers can be obtained simultaneously the model correctly reproduces the deep ocean radiocarbon field and the concentrations gradients between different basins the spreading of cfc plumes in the deep and bottom waters is simulated in a realistic way and the spatial extent as well as the temporal evolution of these plumes agrees well with observations radiocarbon and cfc observations place upper bounds on the northward transports of antarctic bottom water aabw into the pacific atlantic and indian oceans long term mean aabw transports larger than 5 sv sv 10 6 m 3 s 1 through the vema and hunter channels in the south atlantic and net aabw transports across 30 s into the indian ocean larger than 10 sv are found to be incompatible with cfc data the rates of equatorward deep and bottom water transports from the north atlantic and southern ocean are of similar magnitude 15 7 sv at 50 n and 17 9 sv at 50 s deep and bottom water formation in the southern ocean occurs at multiple sites around the antarctic continent and is not confined to the weddell sea a cfc forecast based on the assumption of unchanged abyssal transports shows that by 2030 the entire deep west atlantic exhibits cfc 11 concentrations larger than 0 1 pmol kg 1 while most of the deep indian and pacific oceans remain cfc free by 2020 the predicted cfc concentrations in the deep western boundary current dwbc in the north atlantic exceed surface water concentrations and the vertical cfc gradients start to reverse

dissolved iron in the southern ocean atlantic sector abstract we report a comprehensive dataset of dissolved iron fe comprising 482 values at 22 complete vertical profiles along a 1 latitudinal section at the zero meridian in addition a shorter high resolution 00 09 surface section of the southernmost part of the transect 66 00 69 35 s is presented within the upper surface mixed layer the concentrations of dissolved fe vary between 0 1 and 0 3 nm an inverse trend versus fluorescence suggests significant fe removal by plankton blooms vertical mixing and upwelling are the most important supply mechanisms of iron from deep waters to the upper surface mixed layer at lower latitude 42 s there is a distinct maximum of 0 6 0 7 nm in the 2000 3000 m depth range due to inflow of north atlantic deep water in one region 55 s elevated dissolved fe found in the surface mixed layer is ascribed to the recent deposition of aeolian dust originating from south america close to the antarctic continent there is an indication of fe supply in surface waters from icebergs in the deep waters there is a strong indication of a hydrothermal plume of dissolved fe and mn over the ridge in the bouvet region 52 56 s in the weddell gyre basin the dissolved fe in the deep water is 0 47 0 16 nm in the eastward flow at 56 62 s and is lower with a value of 0 34 0 14 nm in the westward flow at high 62 69 s latitude at the edge of the continental ice sheet on the prime meridian the continental margin of the antarctic continent appears to be lesser source of dissolved fe than in any other place in the world this is likely because it is unique in being overlain by the extending continental ice sheet that largely prevents biogeochemical cycling

quantifying he fluxes from the mantle using multi tracer data assimilation a global coarse resolution ocean model previously fitted to geostrophic shear estimates and to data of 10 hydrographic parameters and tracers has been used to simulate the 3he and 4he distribution

tectonostratigraphic and petrogenetic setting of late mississippian volcanism in eastern canada in the aftermath of the middle devonian acadian orogeny a thick mafic body is inferred to have been emplaced at the base of the crust during development of the maritimes basin complex in eastern canada and is believed to have sourced regional late devonian to mississippian volcanism by late mississippian times volcanism was limited to central new brunswick and the magdalen islands of eastern quebec whereas late devonian to early mississippian mafic volcanism was mainly characterized by subalkaline lavas produced by the high degree partial melting of a subduction enriched lithospheric mantle source late mississippian volcanism was dominated by alkali mafic lavas produced by the low degree partial melting of a sublithospheric mantle source that shows no evidence of subduction imprint two distinct upper mississippian volcanic successions were identified in central new brunswick and are estimated to be separated by 7 million years based on u pb dates on felsic intervals they respectively belong to the

u pb ages of detrital zircons in pacheco pass metagraywackes sierran klamath source of mid cretaceous and late cretaceous franciscan deposition and underplating 1 using laser ablation icp ms techniques u pb ages are reported for 338 detrital zircons separated from four franciscan metagraywacke samples from imbricate thrust sheets cropping out in the pacheco pass area east central california coast ranges structurally higher slabs are clastic quartz albite bearing rocks typified by neoblastic lawsonite jadeitic pyroxene the lowest exposed slab lacks jadeitic pyroxene but contains traces of newly grown pumpellyite and lawsonite in addition to abundant quartz albite studied specimens contain moderate amounts of phengite titanite chlorite stilpnomelane carbonate iron oxides rock fragments and carbonaceous matter these diablo range clastic sediments were deposited in mid cretaceous and late cretaceous time the highest allochthon unit i was deposited after 102 ma unit iv was deposited after 90 102 ma and unit v was deposited after 86 ma metagraywacke depositional accretionary ages within slab iv young upward but ages of the slabs decrease progressively downward in the four sample aggregate most zircons have igneous ages falling in the 135 170 ma range with a smaller population at 85 120 ma the rocks contain rare zircons of middle proterozoic late archean ages a minor source in northern california and nw nevada seems likely for the pacheco pass metagraywackes but the sierran klamath calcalkaline arc provided most of the clastic debris judging by the volcanic nature of lithic clasts in these eastern belt metagraywackes and because massive sierran plutonism occurred at 85 120 ma the abundant 135 170 ma zircons probably were derived chiefly from the eroding comagmatic volcanic arc rather than from the less voluminous jurassic arc plutons

hydrothermal contribution to the oceanic dissolved iron inventory mineral dust and marine sediment resuspension are generally considered the primary sources of the nutrient iron to the oceans numerical model results suggest that iron released by hydrothermal activity is also an important source of dissolved iron particularly in the southern ocean iron limits phytoplankton growth and hence the biological carbon pump in the southern ocean1 models assessing the impacts of iron on the global carbon cycle generally rely on dust input and sediment resuspension as the predominant sources2 3 although it was previously thought that most iron from deep ocean hydrothermal activity was inaccessible to phytoplankton because of the formation of particulates4 it has been suggested that iron from hydrothermal activity5 6 7 may be an important source of oceanic dissolved iron8 9 10 11 12 13 here we use a global ocean model to assess the impacts of an annual dissolved iron flux of approximately 9 108 mol as estimated from regional observations of hydrothermal activity11 12 on the dissolved iron inventory of the world s oceans we find the response to the input of hydrothermal dissolved iron is greatest in the southern hemisphere oceans in particular observations of the distribution of dissolved iron in the southern ocean3 chever et al manuscript in preparation bowie et al manuscript in preparation can be replicated in our simulations only when our estimated iron flux from hydrothermal sources is included as the hydrothermal flux of iron is relatively constant over millennial timescales14 we propose that hydrothermal activity can buffer the oceanic dissolved iron inventory against shorter term fluctuations in dust deposition

an overview of dissolved fe and mn distributions during the 2010 2011 u s geotraces north atlantic cruises geotraces ga03 abstract high resolution dissolved fe dfe and dissolved mn dmn distributions were obtained using a trace metal clean rosette during the geotraces ga03 zonal transect cruises usgt10 and usgt11 across the north atlantic ocean this manuscript provides a general overview of the dfe as well as dmn and dissolved al dal distributions that reveal several fe inputs at varying depths across the study region elevated dfe concentrations correlate with elevated dal concentrations in the surface waters of the subtropical gyre indicating a significant atmospheric source of fe in contrast there is no apparent significant dust source for mn in the subsurface waters dfe maxima are a result of the remineralization process as revealed by their correspondence with dissolved oxygen minima within the oxygen minimum the ratio of dfe to apparent oxygen utilization aou is lower than would be expected from the measured fe content of surface water phytoplankton suggesting that a significant amount of dfe that is remineralized at depth 63 90 is subsequently scavenged from the water column the rate of remineralization which is based on the slope of dfe aou plot is similar across a wide area of the north atlantic in addition to the remineralization process sedimentary inputs are apparent from elevated dmn signals in the eastern basin particularly near the african coast in the western basin sedimentary input is also occurring along the advective flow path of the upper labrador sea water ulsw as ulsw transits along the north american continental shelf region the largest dfe anomaly 68 nm which also corresponds to a dmn anomaly up to 33 nm is seen in the neutrally buoyant hydrothermal plume sampled over the mid atlantic ridge and that signal is visible for 500 km to the west of the ridge

where are the undiscovered hydrothermal vents on oceanic spreading ridges abstract in nearly four decades since the discovery of deep sea vents one third of the length of global oceanic spreading ridges has been surveyed for hydrothermal activity active submarine vent fields are now known along the boundaries of 46 out of 52 recognized tectonic plates hydrothermal survey efforts over the most recent decade were sparked by national and commercial interests in the mineral resource potential of seafloor hydrothermal deposits as well as by academic research here we incorporate recent data for back arc spreading centers and ultraslow and slow spreading mid ocean ridges mors to revise a linear equation relating the frequency of vent fields along oceanic spreading ridges to spreading rate we apply this equation globally to predict a total number of vent fields on spreading ridges which suggests that 900 vent fields remain to be discovered almost half of these undiscovered vent fields comparable to the total of all vent fields discovered during 35 years of research are likely to occur at mors with full spreading rates less than 60 mm yr we then apply the equation regionally to predict where these hydrothermal vents may be discovered with respect to plate boundaries and national jurisdiction with the majority expected to occur outside of states exclusive economic zones we hope that these predictions will prove useful to the community in the future in helping to shape continuing ridge crest exploration

carboniferous volcanic rocks of the magdalen islands gulf of st lawrence volcanic rocks of mississippian age occur on the magdalen islands as cap rocks and within collapse breccias above salt diapirs that have formed the islands they consist of coarse volcaniclastic deposits and basaltic flows intruded by minor mafic dykes and plugs petrologic studies of the basaltic rocks show that they are extensively altered original plagioclase clinopyroxene olivine and interstitial glass are partially to entirely replaced by mixtures of chlorite sericite smectite sphene carbonate epidote albite potassium feldspar and iron oxides and the samples display a relatively wide range in chemical compositions especially mobile were k na and ca and most samples are classified as potash spilites poenites using standard discriminant diagrams for mafic igneous rocks it can be seen that the basalts appear to range from continental tholeiitic to continental alkalic however relict clinopyroxene compositions and the presence of kaersutitic amphibole and titaniferous biotite in so

record of late mississippian tectonics in the new perce group visean of eastern gaspesie quebec visean clastic units and structures at the northwest margin of the upper paleozoic maritimes basin provide information on tectonic events that are only poorly recorded in more central parts of the basin these continental units are time equivalent to marine sediments of the windsor group of nova scotia they are herein assigned to the new perce group which includes the la coulee and bonaventure formations as well as a new unit the cap d espoir for mation the latter unit unconformably underlies the bonaventure formation in a small but thick sub basin of the ristigouche basin in eastern quebec it is characterized by a succession of sandstone and mudstone rhythmites that contrast with the coarse alluvial fan deposits of the overlying bonaventure formation the cap d espoir formation was sourced from a broad area of subdued topography occupied by the visean la coulee formation and underlying units erosional remnants of the la coulee formation are unconformably overlain by the bonaventure formation in marginal parts of the ristigouche basin whereas these units are separated by the cap d espoir formation in more central areas of the basin the la coulee and cap d espoir formations underwent tilting and erosion during a normal faulting event that preceded deposition of the fault controlled bonaventure formation this series of events is interpreted to represent different steps in the reactivation of a pre carboniferous dextral strike slip system in response to northwest southeast compression during the visean in gaspesie resume des unites clastiques viseennes et leurs structures intrinseques dans la marge nord ouest du bassin des mari times paleozoique superieur illustrent des evenements tectoniques qui ne sont que pauvrement enregistres dans les parties plus centrales du bassin ces unites continentales sont chronologiquement equivalentes aux sediments marins du groupe de windsor en nouvelle ecosse elles sont ici assignees au nouveau groupe de perce lequel inclut les forma tions de la coulee et de bonaventure ainsi qu une nouvelle unite la formation de cap d espoir cette derniere est re couverte en discordance par la formation de bonaventure a l interieur d un petit mais relativement epais sous bassin du bassin de ristigouche dans l est du quebec elle est caracterisee par une succession de depots rythmiques de gres et de mudstone qui contraste avec les depots grossiers de cones alluviaux de la formation de bonaventure sus jacente la formation de cap d espoir est le produit de l erosion d une region source de grande etendue et a faible gradient topo graphique laquelle etait occupee par la formation de la coulee et les unites qui lui sont sous jacentes les reliques d erosion de la formation de la coulee sont recouvertes de facon discordante par la formation de bonaventure dans les parties marginales du bassin de ristigouche alors que ces unites sont separees par la formation de cap d espoir dans les parties plus centrales du bassin les formations de la coulee et de cap d espoir ont ete basculees et partiel lement erodees a l interieur d un evenement de fracturation ayant precede le depot de la formation de bonaventure dont les facies ont ete controles par des escarpements de failles cette serie d evenements est consideree comme etant le resultat de differentes etapes dans la reactivation d un systeme de coulissage dextre pre carbonifere en reponse a des contraintes orientees nw se durant le viseen en gaspesie

hydrothermal activity in the northwest lau backarc basin evidence from water column measurements 1 the northwest lau backarc basin consisting of the northwest lau spreading center nwlsc and the rochambeau rifts rr is unique in having elevated 3he 4he ratios up to 28 ra in the erupted lavas clearly indicating a hot spot or ocean island basalt oib type signature this oib type helium signature does not appear in any other part of the lau basin water column plume surveys conducted in 2008 and 2010 identified several sites of active hydrothermal discharge along the nwlsc rr and showed that the incidence of hydrothermal activity is high consistent with the high spreading rate of 100 mm year hydrocasts into the central caldera and southern caldera of the nwlsc detected elevated3he 4he 3he 55 and 100 respectively trace metals tmn tfe and suspended particles indicating localized hydrothermal venting at these two sites hydrocasts along the northern rift zone of the nwlsc also had excess 3he tmn and suspended particles suggesting additional sites of hydrothermal activity the rr are dominated by lobster caldera a large volcano with four radiating rift zones hydrocasts into lobster caldera in 2008 detected high 3he up to 239 and suspended particle and tmn signals indicating active venting within the caldera a repeat survey of lobster in 2010 confirmed the site was still active two years later plumes at lobster caldera and central caldera have end member3he 4he ratios of 19 ra and 11 ra respectively confirming that hot spot type helium is also present in the hydrothermal fluids

upper paleozoic mafic and intermediate volcanic rocks of the mount pleasant caldera associated with the sn w deposit in southwestern new brunswick canada petrogenesis and metallogenic implications abstract upper paleozoic 365 ma mafic and intermediate volcanic rocks of the piskahegan group constitute a subordinate part of the mount pleasant caldera which is associated with a significant polymetallic deposit tungsten molybdenum bismuth zones 33 mt ore with 0 21 w 0 1 mo and 0 08 bi and tin indium zones 4 8 mt with 0 82 sn and 129 g t in in southwestern new brunswick canada the epicontinental caldera complex formed during the opening of the late paleozoic maritimes basin in the northern appalachians the mafic and intermediate rocks make up two compositionally distinct associations the first association includes evolved rift related continental tholeiitic basalts and the second association comprises calc alkaline andesites although both associations were emplaced penecontemporaneously the basalts have low mg 0 34 0 40 smooth chondrite normalized ree patterns with la yb n 5 6 primitive mantle normalized trace element patterns without noticeable negative nb ta anomalies and their nd t ranges from 2 5 to 2 2 the basalts were generated by partial melting of a transition zone between spinel and garnet mantle peridotite at a depth of 70 90 km the calc alkaline andesites of the second association have chondrite normalized ree patterns that are more fractionated with la yb n 7 8 5 but without significant negative eu anomalies compared to the basaltic rocks they have lower nd t values ranging from 0 5 to 1 9 and their mantle normalized trace element plots show negative nb ta anomalies the nd t values display negative correlations with indicators of crustal contamination such as th la th nb and sio2 the andesitic rocks are interpreted to have formed by assimilation fractional crystallization processes which resulted in the contamination of a precursor basaltic magma with crustal material the parent basaltic magma for both suites underwent a different evolution the tholeiitic basalts experienced shallow seated fractional crystallization and evolved along a tholeiitic trend of early iron enrichment non oxic conditions the contaminated magma of the second association followed a calc alkaline fractionation trend of no iron enrichment oxidizing conditions characterized by a high ph2o and po2 environment at the mid crust levels the piskahegan group which is associated with an important polymetallic mineral deposit differs from the numerous non mineralized rift related volcanic suites of the regional upper devonian to lower carboniferous successions in the maritimes basin by the presence of a significant amount of coeval calc alkaline andesite which may be an indicator of potential mineralization

petrochemistry and tectonic significance of carboniferous volcanic rocks in new brunswick carboniferous volcanic rocks from the new brunswick platform in the maritimes basin are divided into three age groups late tournaisian to early visean volcanic rocks are tholeiitic basalts and andesites that in southern new brunswick are inter bedded with abundant calc alkalic rhyolite late visean to namurian volcanic rocks consist of an interbedded sequence of alkalic basalts and trachyandesites late westphalian volcanic rocks change in composition up section from trachyte to peralkalic rhyolite all three age groups display petrochemical features indicative of an intraplate tectonic setting the volcanic geochemistry is consistent with the development of the maritimes basin either as a failed rift formed along the margin of a late paleozoic ocean or as a rhomb graben formed within a transcurrent zone the former model is preferred the change in basaltic composition from tholeiitic to alkalic apparently coincided with a decrease in rate of extension between the tournaisian and namurian local peral

dissolved iron in the arctic ocean important role of hydrothermal sources shelf input and scavenging removal arctic ocean waters exchange with the north atlantic and thus dissolved iron dfe in the arctic has implications for the global fe cycle we present deep water 250 m dfe concentrations of the central arctic ocean nansen amundsen and makarov basins the dfe concentration in the deep waters varies considerably between these basins with the lowest dfe concentrations 0 2 0 4 nm in the makarov basin higher concentrations similar to 0 45 nm in the amundsen basin and highest concentrations similar to 0 6 0 7 nm in the nansen basin atlantic input from the shelf seas and slopes enhances the dfe concentration in the nansen basin moreover hydrothermal activity at the gakkel ridge causes a significant and widespread enrichment of dfe in the eurasian basins at a depth of 2000 3000 m below this maximum the important role of scavenging and absence of input sources are reflected in a strong relation with dissolved mn dmn and in very low 3000 m amundsen and makarov basins the depth profiles of dfe in the arctic ocean notably in the makarov basin deviate from the dfe distribution pattern observed in other parts of the world ocean

the distribution of helium 3 in the deep western and southern indian ocean almost a decade after the geochemical ocean sections study indian expedition the new deep 3he data from the indigo program give a further insight into the distribution of this tracer in the indian ocean this distribution exhibits some major features related on one hand to a hydrothermal 3he input in the gulf of aden and on the mid indian ocean ridge and on the other to the origin of the water masses and to the characteristics of the deep circulation the main pattern is a significant north south 3he gradient with deep waters of the southern ocean showing 3he values around 8 9 due to the influence of the atlantic deep waters poor in 3he and relatively high values in the northern and central regions 15 to 18 between 2000 m and 3000 m depth originating from the hydrothermal activity in the easternmost part of the basin the 3he values exhibit a significant increase at shallower depths around 1000 m probably due to the pacific water flow through the indonesian sills whereas the data in the indian sector of the antarctic ocean show a maximum of the order of 10 south of the polar front interpreted as showing the presence of the pacific deep waters in the antarctic circumpolar current these different aspects are summarized by mapping the horizontal distribution of the 3he maxima all over the indian basin this map points out some characteristics of the deep circulation but also stresses the need for further measurements in order to clarify the description of this tracer in several key areas

crustal thickness under the gulf of st lawrence northern appalachians from gravity and deep seismic data we have determined crustal thickness in the gulf of st lawrence an area that corresponds to an offset of the main northern appalachians units a complete bouguer anomaly was calculated from recent depth to basement compilations and sediment densities from well data the moho surface was obtained by inverting the bouguer anomaly assuming a single density contrast at depth and using an average depth provided by deep reflection seismic data the resulting crustal model shows a moho depth of 42 44 km beneath the grenville craton north of the appalachian deformation front south of this front the depth to moho displays a pronounced thinning of the crust beneath the carboniferous magdalen basin this is in striking contrast to the deep seismic data which give a moho depth of about 43 km the modelling of the bouguer anomaly in the magdalen basin taking into account the seismic reflection and refraction data reconciles these different results and suggests that a 43 km deep moho beneath the basin is as

sedimentology of the lower serpukhovian upper mississippian mabou group in the cumberland basin of eastern canada tectonic halokinetic and climatic implications the visean serpukhovian transition in atlantic canada was marked by a general humidification of the climate as the region drifted towards equatorial latitudes it also corresponds to a time when ice volume was increasing on gondwana which marked the end of mississippian marine incursions in the region glacioeustatic fluctuations of greater magnitude are thought to have increased the response of the regional climate to third order cyclicity from orbital forcing in the cumberland basin fluvial grey beds of the lower serpukhovian shepody formation were deposited in sub humid conditions during highstands whereas red playa deposits of the same unit were deposited under semi arid conditions during lowstands basin reconstruction suggests that this unit was sourced from the fault bounded cobequid and caledonia highlands and deposited in two separate salt withdrawal minibasins this fluvial system was seemingly discharging to the north into the broad lake that deposited the contemporaneous hastings formation a disconformity separates the shepody formation from mid serpukhovian red beds of the claremont formation and is tentatively associated with another increase in ice volume on gondwana followed by a recrudescence of fault activity and basin subsidence a prolonged time of aridity floral crisis non deposition deep weathering and karstification in late serpukhovian to early bashkirian times is contemporaneous with abundant glacial deposits in higher latitudes suggesting that globally low sea levels may have been at play in creating a situation of greater continentality in the study area

geochronological and geochemical implications of early to middle jurassic continental adakitic arc magmatism in the korean peninsula abstract sensitive high resolution ion microprobe shrimp zircon u pb ages and whole rock chemical compositions of early to middle jurassic plutons from the central to southern korean peninsula are reported to investigate the effect of paleo pacific plate subduction preserved along the continental margin twenty one plutonic rocks from the yeongnam massif i e sunchang and namwon plutons the okcheon belt jeongup boeun and mungyeong plutons the northeast gangreung pluton and the gyeonggi massif gonam anheung and ganghwa plutons have age ranges from ca 189 186 ma to 177 ma 177 166 ma and 177 173 ma respectively most plutonic rocks have chemical compositions similar to adakites showing high sio 2 45 62 74 96 wt low mgo 0 01 2 84 wt high na 2 o 2 65 4 83 wt high sr y and la yb low y and yb as well as low hfses nb and ta but initial sr ratios 0 7048 0 7262 k 2 o 0 50 5 88 wt and k 2 o na 2 o 0 34 2 1 were unlikely to have been formed by melting of either a thickened and or delaminated lower continental crust or an altered oceanic crust these suggest that the adakitic plutonic rocks in this region resulted from partial melting of an enriched mantle source metasomatized by dewatering from a delaminated flat slab the spatial distributions of this continental adakitic plutonic belt based on the present study together with previously reported geochronological results indicate that magmatic pulses gradually migrated toward the continent across the korean peninsula as a result of slab shallowing caused by periodic slab buckling the similar geochronological and geochemical characteristics petrogenesis and tectonic setting of the plutonic belt spanning the korean peninsula japan eastern china and eastern russia indicate a possible link to an active subduction system that existed during the early to middle jurassic although the products of the plate subduction might differ in different locations along the east asian continental margin

new insight into a subduction related orogen a reappraisal of the geotectonic framework and evolution of the japanese islands abstract the geotectonic framework and the evolutionary history of the japanese islands need revision in accordance with the various geophysical geological evidence gathered by new methodologies in the recent years including seismic tomography vibroseis ground breaking seismic experiments and detrital zircon chronology these investigations have addressed various themes such as 1 seismic profile of the crust and mantle beneath the japanese islands 2 high precision ages of the protoliths of high p t metamorphic rocks and 3 provenance of terrigenous clastics the results have led to a number of important findings including 1 detection of a large mass of slab around the mantle boundary layer suggesting the long term oceanic subduction beneath japan 2 confirmation of the subhorizontal piled nappe structure for the entire crust of japan 3 finding a new high p t metamorphosed accretionary complex unit that represents the youngest blueschist in japan 4 finding of the oldest early cambrian arc batholith and cover sediments and 5 the identification of plural arc batholiths which have already been erased from the surface based on a synthesis of these new data this article presents a re evaluation of the conventional geotectonic subdivision of the subduction related orogen in japan re definition of the elements and their mutual boundaries and re consideration of the geotectonic evolution of the japanese islands in particular the historical change in provenance suggests that proto japan has experienced large scale tectonic erosion in multiple stages and the corresponding large amounts of continental crust materials were subducted for understanding the orogenic growth of japan during the last ca 500 million years the significance of tectonic erosion coupled with continental contraction as well as the oceanward accretionary growth requires further attention

helium 3 plume over the east pacific rise at 25 s 1 we have measured helium isotopic ratios of sixty eight water samples collected in the southeastern pacific at 25 s the maximum excess 3he of 47 5 is observed just above the east pacific rise which is comparable to that of 50 5 at 15 s in literature a negative correlation between helium isotopes and neon to helium ratios of seawater samples suggests that the source of excess helium 3 in the mid depth water is considered to be a morb type mantle contour of excess 3he shows symmetrical pattern that is plume of 30 excess can be traced up to 1000 km on both east and west of the east pacific rise this pattern is consistent with a northward flow along the rise at 25 s estimated by a physical model our observation also supports a flow pattern of deep ocean currents which has been suggested by contour of excess 3he obtained from previous studies

hydrothermal helium plumes in the pacific ocean hydrothermal activity along the global mid ocean ridge system and at active seamounts introduces a 3 he rich signal into the deep ocean basins which can be used to trace patterns of ocean circulation and mixing this hydrothermal helium signal is especially strong in the pacific ocean where the spreading rate of the ridges is the greatest in several areas of the pacific the hydrothermal activity is of sufficient strength to produce intense helium plumes which clearly define the regional circulation among these are 1 a pair of helium plumes at 2500 m depth which extend westward from the east pacific rise at 10 n and 15 s into the interior of the pacific basin 2 a helium plume at 2000 m depth extending southwest from sources on the juan de fuca ridge in the northeast pacific and 3 a plume at 1100 m depth emanating from loihi seamount at 20 n which extends eastward from hawaii to the coast of mexico the flow field implied by the helium distribution appears to be in reasonable agreement with reid s 1997 steric height analysis for the pacific

slow spreading submarine ridges in the south atlantic as a significant oceanic iron source low levels of the micronutrient iron limit primary production and nitrogen fixation in large areas of the global ocean measurements in the south atlantic suggest that slow spreading submarine ridges serve as a significant oceanic iron source in these waters

provenance of trench fill deposits of the jurassic chichibu accretionary complex southwest japan abstract this study constrains the provenance of the trench fill turbidite sandstones of the jurassic accretionary complex chichibu accretionary complex in southwest japan using detrital zircon u pb ages data zircons from all sites six sites yielded mainly precambrian and permian jurassic ages the precambrian zircons were derived from the north china block whereas the permian jurassic zircons were derived from igneous rocks in and around the korean peninsula the percentage of precambrian zircons ranged from 39 9 to 52 9 average 45 5 of the total and that of the permian jurassic zircons ranged from 46 5 to 57 6 average 52 6 thus during the jurassic an equal number of zircons was continuously supplied from in and around the korean peninsula and the north china block into a trench on the eastern margin of the asian continent the percentage of permian and triassic zircons gradually decreased over time whereas the percentage of jurassic zircons gradually increased these changes likely reflected the igneous activity in and around the korean peninsula during the jurassic these results indicate that the turbidite sandstones of the jurassic accretionary complex in southwest japan comprise detritus from not only the north china block but also the igneous activity in and around the korean peninsula therefore the jurassic accretionary complex in southwest japan was likely formed near the north china block

a spectrum of alluvial deposits in the lower carboniferous bonaventure formation of western chaleur bay area gaspe and new brunswick canada the lower carboniferous bonaventure formation of western chaleur bay gaspe and new brunswick is a terrestrial redbed succession with abundant calcretes deposited in a semi arid paleoclimate facies can be grouped into three associations conglomeratic sandstone and mud dominated within two 100 150 m upward fining megasequences the megasequences are attributed to alluvial fan progradation due to tectonic rejuvenation vertical facies relationships and internal structures indicate that varied alluvial environments are represented alluvial fans formed on steep slopes adjacent to fault scarps and are dominated by deposits of the conglomeratic association lateral and downslope coalescence of fans into a braid plain is represented by transition from the conglomeratic to the sandstone facies association distally the braid plain is transitional into deposits of the mud dominated association paleocurrents and clast compositions show that sediment in the gaspe outcrops was derived from the northwest and

the late paleoproterozoic orogeny in the north china craton abstract granulite ttg and khondalite formations are the two typical types of precambrian metamorphic basement in the north china craton the former belongs to the basement of the archean craton while the latter is a paleoproterozoic metasedimentary rock series the formation of the ttg rock series took place during the period of 2500 to 2450 ma near the end of the archean and it has undergone multiple times of metamorphism the cooling rate of the ttg lower crust is quite low less than 0 3 ma developed during slow crustal cooling in a rather stable tectonic environment the khondalite rock series underwent amphibolite to granulite facies metamorphism that is isotopically constrained to 2000 to 1800 ma followed by fast crustal cooling from 2 4 to 3 4 ma based on the thermal and dynamic features of different types of metamorphic rocks the tectonic state of the crust and the obvious change of crustal cooling rate from neo archean to paleoproterozoic it is clear that continental orogeny existed in the north china craton between 2000 ma and 1800 ma

evidence of an extensive spread of hydrothermal dissolved iron in the indian ocean abstract ocean scale transect observations covering the entire water depth enable a comprehensive picture of the chemistry including the circulation and biogeochemical cycling of elements in seawater the large scale investigation of dissolved iron fe took place through the japanese geotraces study and here we report a basin scale full depth section profile of dissolved fe in the indian ocean from the arabian sea to the southern ocean the data clearly shows the hydrothermal fe distributed over 3000 km distance in the deep layer centered at a depth of approximately 3000 m around the central indian ridge segment and a large part of the dissolved fe from the hydrothermal sources was in the real soluble fraction rather than the colloidal fraction in the intermediate water in the north arabian sea another dissolved fe rich water mass existed where fe was enriched by remineralization processes from settling particles and or adjacent reducing sediments and preserved in the suboxic water the basin scale section profile indicates that there are several sources supplying dissolved fe to deep waters such as the hydrothermal sources and terrestrial fe input with a persistent condition in the oxygen minimum zone omz between the northern subtropical section though few fe sources were apparent in the southern ocean combining our size fractionated fe data with numerical modeling study suggests that the fe physical chemical form in seawater differs between the sources and is a key factor for controlling residence time and explaining the large scale distributed hydrothermal fe

truncation and translation of appalachian promontories mid paleozoic strike slip tectonics and basin initiation accreted terranes of the appalachian iapetan and peri gondwanan realms display structural trends that are mainly concordant with promontories and embayments in the laurentian margin indicating that during accretion the shape of the continental margin acted as a template around which accreted terranes were molded in north carolina and new foundland post accretion transcurrent motion appears to be recorded by displaced outboard portions of promontories no longer concordant with those in laurentia a bend in structural trends confined to the peri gondwanan realm at the north carolina south carolina state line is interpreted to represent the dextrally displaced outboard portion of the virginia promontory in newfoundland the hermitage flexure is interpreted as a dextrally displaced laurentian promontory that originated along strike to the northeast in both places promontories were truncated and dextrally translated for 220 250 km by a devonian mississippian orogen parallel transcurrent system which may well have extended for the length of the eastern laurentian margin south of the nearby st lawrence promontory extreme thinning of appalachian crust beneath the maritimes basin is consistent with extension at a releasing stepover estimates of extension are consistent with those obtained from promontory offsets

link between long lasting evaporitic basins and the development of thick and massive phreatic calcrete hardpans in the mississippian windsor and perce groups of eastern canada part of the visean upper mississippian succession in the upper paleozoic maritimes basin of eastern canada is overprinted by massive phreatic calcrete hardpans that can exceed 10 m in thickness and that are characterized by the thorough mineral replacement of most of their host sediment by calcite similar to those that are currently forming around salt lakes in quaternary sediments of central australia the precise timing and paleogeography of this carboniferous event was until now poorly known but lateral correlations over a large study area indicate that phreatic calcretization occurred in the vicinity of large evaporitic basins following a marine transgression and regression cycle in chadian to holkerian times this relation confirms that the previously proposed model for modern analogs in central australia which states a genetic link between the salt lakes and the thick and massive phreatic calcrete hardpans can be applied to ancient environments and that such occurrences may be used to infer the former presence of an evaporitic basin in their vicinity finally our relatively large dataset indicates that the stable isotopes of carbon and oxygen are successful in differentiating ancient marine carbonates from ancient phreatic calcretes 2007 elsevier b v all rights reserved

the geotraces intermediate data product 2017 the geotraces intermediate data product 2017 idp2017 is the second publicly available data product of the international geotraces programme and contains data measured and quality controlled before the end of 2016 the idp2017 includes data from the atlantic pacific arctic southern and indian oceans with about twice the data volume of the previous idp2014 for the first time the idp2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope tei sources the tei data in the idp2017 are quality controlled by careful assessment of intercalibration results and multi laboratory data comparisons at crossover stations the idp2017 consists of two parts 1 a compilation of digital data for more than 450 teis as well as standard hydrographic parameters and 2 the egeotraces electronic atlas providing an on line atlas that includes more than 590 section plots and 130 animated 3d scenes the digital data are provided in several formats including ascii excel spreadsheet netcdf and ocean data view collection users can download the full data packages or make their own custom selections with a new on line data extraction service in addition to the actual data values the idp2017 also contains data quality flags and 1 data error values where available quality flags and error values are useful for data filtering and for statistical analysis metadata about data originators analytical methods and original publications related to the data are linked in an easily accessible way the egeotraces electronic atlas is the visual representation of the idp2017 as section plots and rotating 3d scenes the basin wide 3d scenes combine data from many cruises and provide quick overviews of large scale tracer distributions these 3d scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of tracer plumes near ocean margins or along ridges the idp2017 is the result of a truly international effort involving 326 researchers from 25 countries this publication provides the critical reference for unpublished data as well as for studies that make use of a large cross section of data from the idp2017 this article is part of a special issue entitled conway geotraces edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

stratigraphy depositional setting and diagenetic history of the saint jules formation upper devonian or mississippian a newly identified post acadian red clastic unit in the southern gaspe peninsula quebec the saint jules formation a post acadian continental clastic unit previously mapped as part of the bonaventure formation pre namurian unit was recently identified in the southern gaspe peninsula of quebec the saint jules formation in the study area is confined to a small post sedimentary graben the unit is characterized by fault controlled oxidized and poorly sorted detritus that underwent short transportation by fluvial processes the saint jules formation is locally overlain by a massive groundwater calcrete several metres in thickness which is tenta tively correlated with the calcretization event that has affected the base of the la coulee formation grey clastics pre namurian unit the calcrete has developed within the karstified upper beds of the saint jules formation which brings new insights into the potential hosts of such calcretes and on the potential stratigraphic confusion that such diagenetic overprints can create partial erosion of both the la coulee and saint jules clastic rocks as well as the mas sive groundwater calcretes occurred prior to deposition of the bonaventure formation like the la coulee and bonaventure formations the saint jules is undated but unconformably overlies acadian structures middle devonian and predates mabou group units namurian

mesozoic terrane accretion in northeast china sikhote alin and japan regions abstract the nadanhada range in northeast china is composed of upper paleozoic limestone greenstone middle to late triassic bedded chert and middle jurassic siliceous shale these rocks are enclosed in post middle jurassic clastic rocks the lithologic association ages radiolarian assemblages and geologic structure of the nadanhada range are very similar to those of the tamba mino ashio terrane in southwest japan this indicates that the nadanhada range is the northern extension of the tamba mino ashio terrane mesozoic tectonostratigraphic terranes identified in northeast china sikhote alin and southwest japan are the khanka terrane a micro continent composed of precambrian metamorhic rocks and paleozoic to mesozoic sedimentary and volcanic covers the nadanhada western sikhote alin terrane a disrupted terrane composed of upper paleozoic to jurassic sedimentary rocks the eastern sikhote alin terrane a terrane composed mainly of early cretaceous clastics the tetyukhe terrane a disrupted terrane composed of upper paleozoic to early cretaceous sedimentary rocks the hida terrane a continent type stratigraphic terrane composed of precambrian and upper paleozoic basement covered with jurassic to cretaceous coarse clastics and the tamba mino ashio terrane a disrupted terrane composed of upper paleozoic to earliest cretaceous sedimentary rocks accretionary history of these terranes is discussed on the basis of paleomagnetic and paleobiogeographic data

helium isotope variations in juan de fuca ridge basalts we have measured he 4he ratios and he and ne concentrations on a suite of 24 basalt glasses from the neovolcanic zone of the juan de fuca ridge jdfr from 44 6 n near the blanco transform up to 48 0 n on the endeavour segment the helium isotope ratios exhibit a clear geographic variation with relatively constant values of 7 8 ra along the southern jdfr increasing to a maximum of 8 8 ra at 46 9 n on the cobb segment and then dropping to values of 8 0 ra at the cobb offset ratios along the endeavour segment further north are somewhat higher averaging 8 2 ra basalts dredged from axial seamount have he 4he 7 9 8 4 ra indicating that the seamount does not have a geochemical or isotopic signature distinct from other portions of the jdfr this confirms that while axial seamount is the locus of excess magma generation it is devoid of any hotspot or ocean island basalt geochemical signature for the whole sample set he 4he ratios show a negative correlation with 87sr 86sr we attribute the geographical variations in he 4he to broad scale heterogeneity in the mantle source region beneath the jdfr beginning at axial seamount and further north he 4he shows a positive correlation with fe8 0 suggesting that melting dynamics in the underlying mantle may exert some control on the helium isotope ratios along part of our survey area

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

newly identified carboniferous units the pointe sawyer and chemin des pecheurs formations in the gaspe peninsula quebec implications regarding the evolution of the northwestern sector of the maritimes basin the upper member of the cannes de roches formation was recently recognized overlying the bonaventure formation in the new carlisle area over 100 km southwest of the previously documented exposures of this unit moreover remnants of the la coulee formation which are unconformably overlain by the bonaventure formation have also been recognized underlying with a similar type of contact the lower member of the cannes de roches for mation from this and from facies similarities the lower and middle members of the cannes de roches formation are now considered to be equivalent to the bonaventure formation it is proposed to abandon these two member designa tions and to only keep the bonaventure formation the remaining upper member of the cannes de roches formation is renamed the pointe sawyer formation a late visean to early namurian age is attributed to this grey clastic forma tion from spore analysis dark reddish brown sandstone conformably overlie the pointe sawyer formation in the mal bay area they correspond to the beginning of sedimentation from more distant sources within the regional carbonifer ous stratigraphic succession which was until then characterized by sedimentation from proximal sources this previ ously unidentified unit is here referred to as the chemin des pecheurs formation

global time scale and regional stratigraphic reference scales of central and west europe east europe tethys south china and north america as used in the devonian carboniferous permian correlation chart 2003 dcp 2003 the boundaries of the devonian carboniferous and permian stages of the global stratigraphic reference scale abbreviated to global stratigraphic scale gss are described in relation to the biostratigraphic and or lithostratigraphic units of the regional stratigraphic reference scales abbreviated to regional stratigraphic scales rss of central and west europe east europe tethys south china eastern tethys and north america in their type regions the boundaries of gss units rarely coincide with those of homonymous rss units moreover the definitions of some rss units have changed several times over the last decades and subsequent misunderstanding of the stratigraphical significance of these changes has often introduced errors into proposed global correlation charts the stratigraphic framework proposed in our global devonian carboniferous permian correlation chart 2003 dcp 2003 devonian carboniferous permian correlation chart 2003 menning m schneider j w alekseev a s amon e o becker g von bitter p h boardman d r bogoslovskaya m braun a brocke r chernykh v chuvashov b i clayton g dusar m davydov v i dybova jachowicz s forke h c gibling m gilmour e h goretzki j grunt t a hance l heckel p h izokh n g jansen u jin y g jones p kading k ch kerp h kiersnowski h klets a klug ch korn d kossovaya o kotlyar g v kozur h w laveine j p martens th nemyrovska t l nigmadganov a l paech h j peryt t m rohn r roscher m rubidge b schiappa t a schindler e skompski s ueno k utting j vdovenko m v villa e voigt s wahlman g p wardlaw b r warrington g weddige k werneburg r weyer d wilde v winkler prins c f work d m 2004 abschlusskolloquium dfg schwerpunktprogramm 1054 evolution des systems erde wahrend des jungeren palaozoikums im spiegel der sedimentgeochemie abstracts univ erlangen germany 2004 p 43 herein abbreviated to dcp 2003 and cited as dcp 2003 in references is an attempt to reduce these errors the dcp 2003 is the stratigraphic base for project 1054 of the deutsche forschungsgemeinschaft dfg the evolution of the late palaeozoic in the light of sedimentary geochemistry this composite time scale has been carefully balanced as far as data allows to remove unnecessary artificial compression and expansion of time intervals biozonations and depositional events the ages selected in dcp 2003 are markedly different to those in the geologic time scale 1989 gts 1989 harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge pp 1 263 and in gradstein and ogg gradstein f m ogg j 1996 a phanerozoic time scale episodes 19 1 2 3 4 insert whereas they are closer to those of the geologic time scale 2004 gts 2004 gradstein f m ogg j g smith a g 2004 a geologic time scale 2004 cambridge univ press cambridge pp 1 589 mostly the ages are rounded to the nearest 0 5 ma in order to avoid estimates of questionable accuracy whereas ages of 0 1 ma in the gts 2004 and their error bars of 0 4 ma to 2 8 ma for the devonian to permian stage boundaries suggest an improved accuracy in contrast in the dcp 2003 questionable ages and positions of stratigraphic boundaries are marked by arrows c 2006 elsevier b v all rights reserved

an intermediate depth source of hydrothermal 3he and dissolved iron in the north pacific abstract we observed large water column anomalies in helium isotopes and trace metal concentrations above the loihi seamount the 3he 4he of the added helium was 27 3 times the atmospheric ratio clearly marking its origin to a primitive mantle plume the dissolved iron to 3he ratio dfe 3he exported to surrounding waters was 9 3 0 3 10 6 we observed the loihi 3he and dfe signal at a depth of 1100 m at several stations within 100 1000 km of loihi which exhibited a distal dfe 3he ratio of 4 10 6 about half the proximal ratio these ratios were remarkably similar to those observed over and near the southern east pacific rise sepr despite greatly contrasting geochemical and volcanic tectonic origins in contrast the proximal and distal dmn 3he ratios were both 1 10 6 less than half of that observed at the sepr dissolved methane was minimally enriched in waters above loihi seamount and was distally absent using an idealized regional scale model we replicated the historically observed regional 3he distribution requiring a hydrothermal 3he source from loihi of 10 4 4 2 mol a 1 2 of the global abyssal hydrothermal 3he flux from this we compute a corresponding dfe flux of 40 mmol a 1 global circulation model simulations suggest that the loihi influenced waters eventually upwell along the west coast of north america also extending into the shallow northwest pacific making it a possibly important determinant of marine primary production in the subpolar north pacific

paleozoic accretionary orogenesis in the paleo asian ocean insights from detrital zircons from silurian to carboniferous strata at the northwestern margin of the tarim craton a detrital zircon u pb and lu hf isotopic study was carried out in the middle silurian to late carboniferous sedimentary strata of the northwestern tarim craton in order to understand accretionary processes in the southern part of the central asian orogenic belt detrital zircons from these strata yielded u pb ages clustering around 2 8 2 3 ga 2 0 1 7 ga 1 3 0 9 ga 880 600 ma and 500 400 ma with age populations and hf isotopic signatures matching those of magmatic rocks in the tarim craton and the central tianshan block abundant 500 400 ma detrital zircons most likely reflect deposition in a retroarc foreland basin inboard of an andean type magmatic arc to the north supporting the northern tarim central tianshan connection during early paleozoic time the absence of 380 310 ma zircon population in the carboniferous siliciclastic rocks suggests that the central tianshan block may have been separated from the tarim craton in the early devonian caused by the interarc back arc opening of the south tianshan ocean we propose an accretionary orogenic model switching from advancing to retreating mode during paleozoic time in the southwestern part of the paleo asian ocean this transition most likely occurred coevally with the rifting of southeast asian blocks from the northeastern margin of gondwana

a geomagnetic polarity timescale for the carboniferous the geomagnetic polarity pattern for the carboniferous is incompletely known but with the best resolved parts in the serpukhovian and bashkirian hence data from both igneous and sedimentary units are also used in an additional polarity bias evaluation in the tournaisian to mid visean interval polarity is mainly derived from palaeopole type palaeomagnetic studies allowing identification of polarity bias chrons seven polarity bias chrons exist in the mississippian mi1nb to mi4nb with an additional 33 conventional magnetochrons and submagnetochrons mi4r to mi9r the moscovian and gzhelian polarity is best resolved in magnetostratigraphic studies from the donets basin and the southern urals dispute about the reliability of these data is ill founded since an assessment of supporting data from palaeopole type studies suggests that these datasets currently provide the best magnetic polarity data through the pennsylvanian polarity bias assessment indicates a normal polarity bias zone in the kasimovian in the pennsylvanian there are 27 conventional magnetochrons and submagnetochrons pe1n to ci1r and one normal polarity bias chron pe8nb the kiaman superchron begins in the mid bashkirian with clear data indicating brief normal polarity submagnetochrons within the superchron the magnetochron timescale is calibrated using 31 u pb zircon dates and a quantitative bayesian based age scaling procedure

743 17 ma granite clast from jurassic conglomerate kamiaso mino terrane japan the case for south china craton provenance korean gyeonggi block abstract the polymict kamiaso conglomerate mino terrane japan contains jurassic to palaeoproterozoic clasts probably derived from korean basement that lay nearby to the northwest at time of deposition clast k2 broke cleanly into two halves during sampling but the halves were recombined for zircon separation a third of the k2 zircons are colourless euhedral prisms with oscillatory zoning with no inheritance and yielded a shrimp u pb date of 743 17 ma two thirds of k2 zircons are brown oscillatory zoned corroded prisms with a date of 1860 8 ma with inherited cores up to 2460 ma a likely explanation for this could be that clast k2 might have been composite and contained undistinguished 743 ma and 1860 ma granites kamiaso granitic clast k3 igneous zircons gave a date of 179 3 2 1 ma toarcian early jurassic with 2100 2300 ma and 1860 ma inherited cores 740 ma a type magmatism related to the extension and break up of rodinia occurs in both korea gyeonggi block and the main part of the south china craton but is unknown in the sino korean craton thus from recognition of a 743 ma clast the kamiaso detritus was probably derived from the northernmost part of the south china craton in korea

mantle helium reveals southern ocean hydrothermal venting 1 hydrothermal venting along the global mid ocean ridge system plays a major role in cycling elements and energy between the earth s interior and surface we use the distribution of helium isotopes along an oceanic transect at 67 s to identify previously unobserved hydrothermal activity in the pacific sector of the southern ocean combining the geochemical information provided by the helium isotope anomaly with independent hydrographic information from the southern ocean we trace the source of the hydrothermal input to the pacific antarctic ridge south of 55 s one of the major global mid ocean ridge systems which has until now been a blank spot on the global map of hydrothermal venting we identify three complete ridge segments a portion of a fourth segment and two isolated locations on the pacific antarctic ridge between 145 w and 175 w representing 540 km of ridge in total as the potential source of the newly observed plume

a major helium 3 source at 15 s on the east pacific rise an extensive plume of water enriched with helium 3 has been discovered in the deep pacific ocean at latitude 15 s on the east pacific rise in the core of the plume at a depth of 2500 meters over the ridge crest the helium 3 helium 4 ratio is 50 percent higher than the ratio in atmospheric helium indicating a strong injection of mantle or primordial helium at the spreading center axis through local hydrothermal systems the helium 3 plume is completely absent east of the rise but it can be traced over 2000 kilometers to the west above a newly observed physical feature a density discontinuity here caled the ridge crest front the injected plume provides a unique deep sea tracer with an asymmetric distribution which shows that the deep circulation across the rise is from east to west the striking intensity and lateral extent of this helium 3 anomaly compared to observations at known oceanic hydrohrmal sites suggest that the largest hydrothermal fields in the ocean are yet to be discovered and that they will be found near 15 s on the east pacific rise