high precision isotopic characterization of usgs reference materials by tims and mc icp ms the pacific centre for isotopic and geochemical research pcigr at the university of british columbia has undertaken a systematic analysis of the isotopic sr nd and pb compositions and concentrations of a broad compositional range of u s geological survey usgs reference materials including basalt bcr 1 2 bhvo 1 2 andesite agv 1 2 rhyolite rgm 1 2 syenite stm 1 2 granodiorite gsp 2 and granite g 2 3 usgs rock reference materials are geochemically well characterized but there is neither a systematic methodology nor a database for radiogenic isotopic compositions even for the widely used bcr 1 this investigation represents the first comprehensive systematic analysis of the isotopic composition and concentration of usgs reference materials and provides an important database for the isotopic community in addition the range of equipment at the pcigr including a nu instruments plasma mc icp ms a thermo finnigan triton tims and a thermo finnigan element2 hr icp ms permits an assessment and comparison of the precision and accuracy of isotopic analyses determined by both the tims and mc icp ms methods e g nd isotopic compositions for each of the reference materials 5 to 10 complete replicate analyses provide coherent isotopic results all with external precision below 30 ppm 2 sd for sr and nd isotopic compositions 27 and 24 ppm for tims and mc icp ms respectively our results also show that the first and second generation usgs reference materials have homogeneous sr and nd isotopic compositions nd isotopic compositions by mc icp ms and tims agree to within 15 ppm for all reference materials interlaboratory mc icp ms comparisons show excellent agreement for pb isotopic compositions however the reproducibility is not as good as for sr and nd a careful sequential leaching experiment of three first and second generation reference materials bcr bhvo agv indicates that the heterogeneity in pb isotopic compositions and concentrations could be directly related to contamination by the steel mortar pestle used to process the materials contamination also accounts for the high concentrations of certain other trace elements e g li mo cd sn sb w in various usgs reference materials

40ar 39ar whole rock phyllite ages from late precambrian rocks of the avalon composite terrane new brunswick evidence of silurian devonian thermal rejuvenation several variably deformed and metamorphosed late precambrian volcanic sedimentary successions have been recognized within the avalon composite terrane exposed in the caledonian highlands of southern new brunswick whole rock samples of metasedimentary phyllite and phyllitic metatuff from the oldest ca 600 635 ma avalonian succession display similar internally discordant 40ar 39ar age and apparent k ca spectra intermediate temperature gas fractions were experimentally evolved solely from very fine grained cleavage aligned white micas these yield apparent ages between ca 430 and 410 ma and are interpreted to closely date a static late silurian early devonian thermal rejuvenation evidence for a silurian devonian thermal event has not been previously documented in avalonian rocks of the caledonian highlands caledonia assemblage however a thermal overprint of similar age ca 400 ma is recorded by metamorphic muscovite in high grade gneisses and platformal metasedimentary rocks brookville a

numerical reconstructions of lgm climate across the eurasian arctic abstract although limits of the eurasian ice sheet at the last glacial maximum lgm are known relatively well from geological evidence the palaeoclimate coexistent with this ice sheet has yet to be identified confidently a simple ice sheet model has been used to determine lgm climate conditions by finding the ice sheet mass balance configuration that permits model results to match with geological data relating to the extent of lgm ice cover these conditions are compared with atmospheric general circulation model agcm calculations of the climate at the lgm which reveal the meteorological conditions associated with the ice sheet mass balance the western margin of scandinavia is characterised by a maritime climate influenced by the nearby warm seasonally sea ice free ocean conditions however further east the warming effect of the north atlantic diminishes and an extreme polar desert climate dominates across the kara sea similar to east antarctica today the lgm climate that we establish is in contrast to many previous reconstructions involving snow laden warm westerly winds originating from the north atlantic affecting the entire eurasian arctic severely cold conditions across the eurasian arctic are compatible with a stable circulation cell over the kara sea that isolates the region climatically and or cold dry westerly winds from the fennoscandian ice sheet that flow across the rest of the eurasian arctic

triassic paragonite and garnet bearing epidote amphibolite from the hida mountains japan paragonite and garnet bearing high grade epidote amphibolite pgea in the ise area of the hida mountains japan is characterized by the high pressure hp epidote amphibolite facies parageneses m1 garnet hornblende clinozoisite paragonite quartz rutile paragonite and garnet of the peak m1 stage are locally replaced by retrograde albite oligoclase and chlorite m2 respectively phase equilibria constrain peak metamorphic conditions of p 1 1 1 4 gpa and t 530 570 c and a decompressional p t path for this rock mineral parageneses of prograde epidote amphibolite facies are comparable to some hp rocks from the hongan region of western dabie but differ from other hp mafic schists with cooling ages of c 330 ma in the hida mountains new paragonite k ar dating for the pgeayields a triassic cooling event at 210 ma that is coeval with regional cooling and exhumation of the sulu dabie qinling sdq belt both petrological and geochronological data of the triassic hp epidote amphibolite in hida mountains support our earlier hypothesis that the sdq belt extends across the korean peninsula to sw japan

laurentide ice sheet instability during the last deglaciation the factors leading to the full retreat of ice sheets during deglaciation are debated numerical modelling suggests that the laurentide ice sheet retreated only after a threshold for warming and radiative forcing was passed in the holocene

unpairing metamorphic belts p t paths and a tectonic model for the ryoke belt southwest japan southwest japan is divided into outer and inner zones by the median tectonic line mtl a major transcurrent fault the outer zone is composed of the sambagawa high pressure intermediate or high p t type metamorphism chichibu and shimanto belts in the inner zone the ryoke belt andalusite sillimanite or low p t type metamorphism was developed mainly within a jurassic accretionary complex this spatial relationship between high p t type and low p t type metamorphic belts led miyashiro to the idea that metamorphic belts were developed as paired systems textural relationships and petrogenetically significant mineral assemblages in pelites from the ryoke belt imply peak p t conditions of 5 kbar and up to 850 c in migmatitic garnet cordierite rocks from the highest grade metamorphic zone it is likely that the thermal anomaly responsible for metamorphism of the ryoke belt was related to a segment of the farallon izanagi ridge as it subducted under the eastern margin of the asian continent during the cretaceous the sequence of mineral assemblages developed in pelites implies a metamorphic field gradient with shallow dp dt slope inferred to have been generated by a nested set of hairpin like clockwise p t paths these p t paths are characterized by limited prograde thickening minor decompression at peak t and near isobaric cooling features that may be typical of p t paths in low p t type metamorphic belts caused by ridge subduction a ridge subduction model for the ryoke belt implies that juxtaposition of the high p t metamorphic rocks of the sambagawa belt against it was a result of terrane amalgamation belt parallel ductile stretching recorded as syn metamorphic predominantly constrictional strain in both ryoke and sambagawa belt rocks and substantial sinistral displacement on the mtl are consistent with left lateral oblique convergence diachroneity in fast cooling of the ryoke belt is implied by extant thermochronological data and is inferred to relate to progressive sw to ne docking of the sambagawa belt thus an alternative interpretation of paired metamorphic belts in japan is that they represent laterally contemporaneous terranes rather than outboard and inboard components of a trench arc paired system amalgamation of laterally contemporaneous terranes during large translations of forearcs along continental margins may explain other examples of paired metamorphic belts in the geological record

greenland glacial history and local geodynamic consequences summary space time reconstructions of the continental ice sheets that existed at last glacial maximum lgm have previously been produced using two entirely independent methodologies one based upon the use of theoretical models of ice sheet accumulation and flow and one based upon the geophysical inversion of relative sea level rsl histories from previously ice covered regions the analyses described in this paper demonstrate the significant advantages that derive from the simultaneous application of both methods to the particular case of greenland we thereby show that the ice 4g reconstruction of the glaciation history of this region from lgm to present which was based upon the geophysical inversion of rsl data alone was reasonably accurate in the peripheral regions where rsl data were available but inaccurate in the interior of the ice sheet which was unconstrained by such information we test the new model of greenland glacial history determined by the simultaneous application of the constraints that derive from ice sheet modelling and the geophysical inversion of rsl data by employing recently published geodetic inferences of mass balance over the entire interior region of the ice sheet and of gps measurements of vertical crustal motion these observations which were not employed to constrain the ice sheet reconstruction provide significant support for the new glacial history for greenland that our analyses have led us to infer

remote sensing of the albedo and detection of the slush line on the greenland ice sheet advanced very high resolution radiometer images of a section of the greenland ice sheet western part between 64 5 and 70 5 n with a size of 667 n s by 700 w e km were processed in order to retrieve the surface albedo the images were for the summer seasons of 1990 1997 inclusive and results were compared to simultaneous mass balance measurements carried out along the transect 67 n the main findings are as follows first many images show a distinct transition from low spatial variability of the albedo at higher elevations to higher spatial variability of the albedo at lower elevations it is argued that these transitions most likely correspond to transitions at the surface slush line in short from the area that is uniformly covered by snow to a mosaic of snow patches slush and ice second 70 of the interannual variations in the mean specific mass balance can be explained by interannual variations in the maximum elevation of the slush line i e the slush limit however a higher percentage 82 can be explained by interannual variations in the sum of positive degree days third in 3 years with a relatively large amount of melt the inland migration of the slush line stopped or slowed considerably down at a fixed distance from the ice sheet margin we believe that this so called maximum slush line coincides with an abrupt change in the density profile the maximum slush line forms an important limitation for the use of satellite data to monitor interannual variations in the mass balance its position is a climate indicator and was determined for the entire section of the greenland ice sheet investigated

balance mass flux and ice velocity across the equilibrium line in drainage systems of greenland estimates of balance mass flux and depth averaged ice velocity through the cross section aligned with the equilibrium line are produced for each of six drainage systems in greenland the estimates are based on a model equilibrium line fitted to field data and on a revised distribution of surface mass balance for the conterminous ice sheet ice drainage divides and six major drainage systems are delineated using surface topography from ers radar altimeter data ice thicknesses at the equilibrium line and throughout each drainage system are based on the latest compilation of airborne radar sounding data described elsewhere the net accumulation rate in the area bounded by the equilibrium line is 399 gt a 1 and net ablation rate in the remaining area is 231 gt a 1 excluding an east central coastal ridge reduces the net accumulation rate to 397 gt a 1 with a range from 42 to 121 gt a 1 for the individual drainage systems the mean balance mass flux and depth averaged ice velocity at the cross section aligned with the modeled equilibrium line are 0 1011 gt km 2 a 1 and 0 111 km a 1 respectively with little variation in these values from system to system in contrast the mean mass discharge per unit length along the equilibrium line ranges from one half to double the overall mean rate of 0 0468 gt km 1 a 1 the ratio of the ice mass in the area bounded by the equilibrium line to the rate of mass output implies an effective exchange time of approximately 6 ka for total mass exchange the range of exchange times from a low of 3 ka in the se drainage system to 14 ka in the ne suggests a rank as to which regions of the ice sheet may respond more rapidly to climate fluctuations

atmosphere driven ice sheet mass loss paced by topography insights from modelling the south western scandinavian ice sheet abstract marine terminating glaciers and ice streams are important controls of ice sheet mass balance however understanding of their long term response to external forcing is limited by relatively short observational records of present day glaciers and sparse geologic evidence for paleo glaciers here we use a high resolution ice sheet model with an accurate representation of grounding line dynamics to study the deglaciation of the marine based south western norwegian sector of the scandinavian ice sheet and its sensitivity to ocean and atmosphere forcing we find that the regional response to a uniform climate change is highly dependent on the local bedrock topography consistent with ice sheet reconstructions our simulations suggest that ocean warming is able to trigger initial retreat in several fjords but is not sufficient to explain retreat everywhere widespread retreat requires additional ice thinning driven by surface melt once retreat is triggered the underlying bedrock topography and fjord width control the rate and extent of retreat while multi millennial changes over the course of deglaciation are modulated by surface melt we suggest that fjord geometry ice ocean interactions and grounding line dynamics are vital controls of decadal to centennial scale ice sheet mass loss however we postulate that atmospheric changes are the most important drivers of widespread ice sheet demise and will likely trump oceanic influence on future ice sheet mass loss and resulting sea level rise over centennial and longer time scales

processes of buildup and retreat of the greenland ice sheet sensitivity experiments were conducted to study the influence of several physical processes on the evolution of the greenland ice sheet over the last 250 000 years the experiments were carried out by means of a three dimensional thermodynamical model the mass balance is modeled by a surface energy balance model this means that variations in orbital parameters following from the astronomical milankovitch theory can be incorporated in the ablation calculations it is shown that with regard to the greenland ice sheet variations in shortwave radiation are only of minor importance for the changes in volume over time calculations of the various components of the energy balance under glacial and interglacial conditions show that the changes in absorbed shortwave radiation resulting from changes in orbital parameters are considerably smaller than the variations in the sensible heat flux caused by temperature variations thermodynamics are only of importance for the volume changes of the ice sheet if the climate is on average stable over a long period in between 110 kyr b p and 20 kyr b p the ice volume increased slowly due to the cooling of the ice which resulted in a higher effective viscosity and thus a thicker ice sheet the long response time of the thermodynamics means that the thermodynamics cannot play a crucial role during transition from a glacial to a deglacial period which occur typically within several thousands of years the mass balance height feedback has an important function in the buildup of the ice sheet after a warm period like the eemian without isostatic bedrock compensation the ablation will remain very high in some marginal parts yielding a considerably smaller ice sheet volume for the last glacial period

triassic 40ar 39ar ages from the sakaigawa unit kii peninsula japan implications for possible merger of the central asian orogenic belt with large scale tectonic systems of the east asian margin the 218 4 0 4 228 8 0 9 and 231 9 0 7 ma 40ar 39ar laser probe pseudo plateau ages 2 49 63 39ar release of very low grade meta pelitic whole rocks from the sakaigawa unit date high p t metamorphism we argue that this event occurred in a subduction accretion complex not along the east asian continental margin but on the pacific side of the proto japan superterrane proto japan was a permian magmatic arc presently dispersed in the japanese islands which also contained older subduction accretion complexes the arc system was fringing but not yet part of the eurasian continent the middle to late triassic high p t tectono metamorphic event was partly coeval with proto japan s collision with proto eurasia along the southward extension of the central asian orogenic belt causing the main metamorphism in the hida oki terrane it is possible that this system continued via the cathaysia block china to indochina the late permian to middle triassic indosinian event might stem from docking of pacific derived terranes with southeast asia s continental margin the concept of the proto japan superterrane implies that the qinling dabie sulu suture zone joined the central asian orogenic belt to the east of the north china craton and did not continue to japan as commonly assumed

glacial flow of floating marine ice in snowball earth 1 simulations of frigid neoproterozoic climates have not considered the tendency of thick layers of floating marine ice to deform and spread laterally we have constructed a simple model of the production and flow of marine ice on a planetary scale and determined ice thickness and flow in two situations when the ocean is globally ice covered hard snowball and when the tropical waters remain open soft snowball in both cases ice flow strongly affects the distribution of marine ice flowing ice probably carries enough latent heat and freshwater to significantly affect the transition into a snowball earth climate we speculate that flowing marine ice rather than continental ice sheets may be the erosive agent that created some neoproterozoic glacial deposits

surface mass balance observations and automatic weather station data along a transect near kangerlussuaq west greenland surface mass balance data from the kangerlussuaq transect k transect located on the western part of the greenland ice sheet near 678n are presented the series covers the period 1990 2003 and is the longest series of surface mass balance measurements in greenland the surface mass balance measurements cover an altitude range of 390 1850m and show a linear increase of the specific mass balance with a mass balance gradient of 3 7 10 3 mm 1 and a mean equilibrium line altitude of 1535ma s l interannual variability shows a weak 4yearly periodicity in addition to the surface mass balance data automatic weather station data at an elevation of approximately 1010m are available for the period 1997 2002 these data are used to explain observed surface mass balance anomalies over the same 5years it is shown that variations in shortwave radiation dominate interannual variability the mean annual cycle of temperature is characterized by a maximum in summer around the melting point leading to a mean summer outgoing longwave radiation of approximately 314wm 2 the mean annual cycle in wind speed shows a maximum in winter on average around 8ms 1 and a minimum in summer on average around 5ms 1 which is characteristic for a katabatic forcing during summer the net radiation is on average about 61wm 2 which is used for ice melting at a rate of typically 2cmw e d 1 net radiation contributes 84 of the total energy used for summer melting averaged over the 5years

links between acceleration melting and supraglacial lake drainage of the western greenland ice sheet 1 the impact of increasing summer melt on the dynamics and stability of the greenland ice sheet is not fully understood mounting evidence suggests seasonal evolution of subglacial drainage mitigates or counteracts the ability of surface runoff to increase basal sliding here we compare subdaily ice velocity and uplift derived from nine global positioning system stations in the upper ablation zone in west greenland to surface melt and supraglacial lake drainage during summer 2007 starting around day 173 we observe speedups of 6 41 above spring velocity lasting 40 days accompanied by sustained surface uplift at most stations followed by a late summer slowdown after initial speedup we see a spatially uniform velocity response across the ablation zone and strong diurnal velocity variations during periods of melting most lake drainages were undetectable in the velocity record and those that were detected only perturbed velocities for 1 day suggesting preexisting drainage systems could efficiently drain large volumes of water the dynamic response to melt forcing appears to 1 be driven by changes in subglacial storage of water that is delivered in diurnal and episodic pulses and 2 decrease over the course of the summer presumably as the subglacial drainage system evolves to greater efficiency the relationship between hydrology and ice dynamics observed is similar to that observed on mountain glaciers suggesting that seasonally large water pressures under the ice sheet largely compensate for the greater ice thickness considered here thus increases in summer melting may not guarantee faster seasonal ice flow

the geological composition of the hidden wilhelm ii land in east antarctica shrimp zircon nd isotopic and geochemical studies with implications for proterozoic supercontinent reconstructions abstract in this paper we present new u pb zircon age sm nd isotopic and chemical composition data for rocks cropping out in a few isolated nunataks in wilhelm ii land in east antarctica namely mirny oasis mt brown and gaussberg volcano which contains xenogenic crustal material these outcrops were subjects of geological investigations during the soviet antarctic expedition of 1956 1957 our data show that this region is underlain by a uniform crust which experienced a high grade metamorphic event at ca 980 920 ma co eval with the rayner orogeny in kemp land and the northern prince charles mountains extensive indications of a ca 500 ma event in coastal areas granitoid intrusions in mirny oasis and inherited zircons found in gaussberg volcano together with the lack of indications of this age in mt brown point to a concentration of ca 500 ma processes roughly co eval with the prydz orogeny in the coastal part of wilhelm ii land and their attenuation inland we also determined a ca 1480 ma age for a mafic magmatic protolith in mt brown which may be correlated with roughly co eval orthogneiss in the bunger hills area these observations suggest the conjugate positions of these crustal blocks in the early mesoproterozoic and argue against a cambrian suture running between them in gaussberg volcano a range of zircon 206 pb 238 u ages of ca 320 ma ca 500 ma ca 980 ma and ca 2000 1800 ma has been determined the presence of ca 2000 1800 ma zircons indicates involvement of mid palaeoproterozoic rocks in the structure of wilhelm ii land this argues for possible conjugation of this region with other east antarctic blocks experienced the palaeoproterozoic tectonic evolution and which have been considered to comprise the mawson palaeocontinent

contribution to the glaciology of northern greenland from satellite radar interferometry interferometric synthetic aperture radar insar data from the ers 1 and ers 2 satellites are used to measure the surface velocity topography and grounding line position of the major outlet glaciers in the northern sector of the greenland ice sheet the mass output of the glaciers at and above the grounding line is determined and compared with the mass input we find that the grounding line output is approximately in balance with the input except for the three largest glaciers for which the mass loss is 4 3 km3 ice year 1 or 11 8 of the mass input along the coast we detect a systematic retreat of the grounding lines between 1992 and 1996 with insar which implies that the outlet glaciers are thinning the inferred coastal thinning is too large to be explained by a few warm summers glacier thinning must be of dynamic origin that is caused by spatial and temporal changes in ice velocity iceberg production from the glaciers is uncharacteristically low it accounts for only 8 of the ice discharge to the ocean about 55 of the ice is lost through basal melting 5 8 m ice year 1 on average from the underside of the floating glacier tongues that are in contact with warm ocean waters mass losses are highest in the first 10 km of floating ice where ice reaches the greatest depths and basal melting is 3 times larger than on average only a small increase in basal melting would suffice to disintegrate the floating glacier tongues copyright 2001 by the american geophysical union

in situ u pb geochronology and hf isotope analyses of the rayner complex east antarctica in situ zircon u pb and hf isotopic analysis via laser ablation microprobe inductively coupled plasma mass spectrometer lam icpms of samples from kemp and macrobertson lands east antarctica suggests that the kemp land terrane evolved separately from the rest of the rayner complex prior to the ca 940 ma rayner structural episode several archaean metamorphic events in rocks from western kemp land can be correlated with events previously reported for the adjacent napier complex recently reported ca 1 600 ma isotopic disturbance in rocks from the oygarden group may be correlated with a charnockitic intrusion in the stillwell hills before ca 1 550 ma despite being separated by some 200 km t hf dm ages indicate felsic orthogneiss from rippon point the oygarden group havstein island and the stillwell hills share a ca 3 660 3 560 ma source that is indistinguishable from that previously reported for parts of the napier complex more recent additions to this crust include proterozoic charnockite in the stillwell hills and the vicinity of mawson station these plutons have distinct 176hf 177hf ratios and formed via the melting of crust generated at ca 2 150 2 550 ma and ca 1 790 1 870 ma respectively

the geochemistry and sm nd isotopic systematics of precambrian mafic dykes and sills in the southern prince charles mountains east antarctica

paleoceanographic affinities of radiolarian faunas in late aalenian time middle jurassic recorded in the jurassic accretionary complex of japan abstract a total of 140 polycystine radiolarians 84 nassellarians and 56 spumellarians called mn 03 assemblage herein were identified from a manganese nodule in mudstone of the chert clastic sequence distributed in the jurassic accretionary complex of the kuzumaki kamaishi belt northern kitakami mountains northeast japan the horizon yielding this well preserved assemblage was correlated to the uppermost part of the radiolarian jr4 zone the upper aalenian middle jurassic on the basis of the presence of tricolocapsa tegiminis the probable decendant of laxtorum jurassicum and the absence of l jurassicum and tricolocapsa plicarum the mn 03a assemblage is of high diversity but shows nearly half of the diversity of the contemporaneous assemblage which was reported from manganese nodules in another jurassic accretionary complex of the mino belt in japan both assemblages are considered to have been derived from the same province due to faunal similarity the difference between both assemblages is explained by lower productivity in the depositional region of the mn 03a assemblage comparison of the mn 03a assemblage to the contemporaneous assemblage indicates that the fauna lived in the equatorial to lower latitudinal zone of the pacific superocean in late aalenian time

ocean plate stratigraphy in east and southeast asia abstract ancient accretionary wedges have been recognised by the presence of glaucophane schist radiolarian chert and melange recent techniques for the reconstruction of disrupted fragments of such wedges by means of radiolarian biostratigraphy provide a more comprehensive history of ocean plate subduction and successive accretion of ocean floor materials from the oceanic plate through offscraping and underplating reconstructed ocean floor sequences found in ancient accretionary complexes in japan comprise from oldest to youngest pillow basalt limestone radiolarian chert siliceous shale and shale and sandstone similar lithologies also occur in the melange complexes of the philippines indonesia thailand and other regions this succession is called ocean plate stratigraphy ops and it represents the following sequence of processes birth of the oceanic plate at the oceanic ridge formation of volcanic islands near the ridge covered by calcareous reefs sedimentation of calcilutite on the flanks of the volcanic islands where radiolarian chert is also deposited deposition of radiolarian skeletons on the oceanic plate in a pelagic setting and sedimentary mixing of radiolarian remains and detrital grains to form siliceous shale in a hemipelagic setting and sedimentation of coarse grained sandstone and shale at or near the trench of the convergent margin radiolarian biostratigraphy of detrital sedimentary rocks provides information on the time and duration of ocean plate subduction the ages of detrital sediments becomes younger oceanward as younger packages of ops are scraped off the downgoing plate ops reconstructed from ancient accretionary complexes give us the age of subduction and accretion direction of subduction and ancient tectonic environments and is an important key to understanding the paleoenvironment and history of the paleo oceans now represented only in suture zones and orogenic belts

pumpellyite actinolite facies of the sanbagawa metamorphism the pumpellyite actinolite facies proposed by hashimoto is defined by the common occurrence of the pumpellyite actinolite assemblage in basic schists it can help characterize the paragenesis of basic and intermediate bulk compositions which are common constituents of various low grade metamorphic areas the dataset of mutually consistent thermodynamic properties of minerals gives a positive slope for the boundary between the pumpellyite actinolite and prehnite pumpellyite facies in p t space in the sanbagawa belt in japan the mineral parageneses of hematite bearing and free basic schists as well as pelitic schists have been well documented the higher temperature limit of this facies is defined by the disappearance of the pumpellyite epidote actinolite chlorite assemblage in hematite free basic schists with xfe3 of epidote around 0 20 0 25 and the appearance of epidote actinolite chlorite assemblage with xepfe3 0 20 in hematite bearing basic schists there is a continuous change of paragenesis to higher grade epidote glaucophane or epidote blueschist facies in pelitic schists the albite lawsonite chlorite assemblage does occur but only rarely and its assemblage cannot be used to determine the regional thermal structure the lower temperature equivalence of the pumpellyite actinolite assemblage is not observed in the field the mikabu greenstone complex and the northern margin of the chichibu complex which are located to the south of the sanbagawa belt are characterized by clinopyroxene chlorite or lawsonite actinolite assemblages which are lower temperature assemblages than the pumpellyite actinolite assemblage these three metamorphic complexes belong to the same subduction metamorphic complex the pumpellyite actinolite facies or subfacies can be useful to help reveal the field thermal structure of metamorphic complexes

continental mafic dyke swarms as tectonic indicators an example from the vestfold hills east antarctica abstract the two main types of magma that were emplaced as mafic dyke swarms in the vestfold hills are high mg tholeiite hmt and fe rich tholeiite frt the former magma type is less dense than the vestfold hills felsic crust whereas the latter is more dense at deep to intermediate crustal levels therefore frt dyke emplacement requires a higher deviatoric extensional stress as is reflected in a more constant orientation palaeoproterozoic hmt frt bimodal dyke swarms were emplaced around 2 4 ga and 2240 ma the geometry and orientation of 2240 ma hmt dykes imply a low deviatoric extensional stress field inconsistent with a mantle plume origin for magmatism current petrogenetic models for hmt magmatism suggest generation at active convergent plate boundaries although this is broadly consistent with emplacement of the bimodal dyke swarms subsequent to a crustal thickening event at 2 5 ga the exact mechanisms for melting and the generation of crustal extensional stress are unknown a possible scenario involves the sinking of gravitationally unstable oceanic crust a major mesoproterozoic magmatic extensional event in the vestfold hills started with normal faulting followed by lamprophyric dyke emplacement and by two distinct episodes of frt dyke emplacement at 1380 and 1245 ma a consistent direction of the stress field during this event suggests control of a linear belt of crustal uplift by comparison with other mafic dyke swarms this is interpreted to be due to a sheet of upwelling asthenosphere elongated plume around 1 4 ga rather than a low angle detachment this upwelling led to thermal erosion of the base of the lithosphere that channelled a subsequent magma pulse at 1245 ma erosion during a long period of uplift prior to 1380 ma was followed by sedimentation during thermal subsidence as suggested by segmentation of 1245 ma dykes the lithospheric structure inherited from the mesoproterozoic magmatic extensional event was probably reactivated during two high grade tectono metamorphic events around 1 0 and 0 5 ga the vestfold hills formed part of a relatively stable craton peripheral to the mobile belt that was formed during these events

crustal development of the hida belt japan evidence from nd sr isotopic and chemical characteristics of igneous and metamorphic rocks abstract chemical and sr nd isotopic investigations were performed on the igneous and metamorphic rocks in the hida belt central japan to clarify their ages and possible sources and to provide constraints on the crustal evolution of the eastern margin of the asian continent igneous rocks of three main stages in the hida belt represented by the late silurian amphibolites first stage the middle carboniferous mafic dikes second stage and the late triassic to early jurassic granite gabbro plutons third stage show alkaline to calc alkaline chemical affinity major and trace element characteristics show that the three stages of igneous rocks were emplaced in a continental margin or continental arc environment the mafic igneous rock suites have relatively high e nd 0 5 to 5 5 and low 87 sr 86 sr 0 7049 to 0 7061 values indicating their origin from upper mantle sources though the third stage granitoids contain recycled crustal components the hida gneisses of clastic origin show two groups of model ages t dm middle proterozoic 1 4 2 2 ga and late proterozoic to early paleozoic 0 55 0 74 ga consistent with geological geochemical and radiometric age data are that the sedimentation and basaltic volcanism occurred in early to middle paleozoic and the protoliths with middle proterozoic model ages are detritals from the proterozoic continental provenances a synthesis of available geological and geochemical data for the basement metamorphic and igneous rocks in eastern asia suggests two possibilities for the paleozoic to early mesozoic history of the hida belt 1 the hida belt was formed at the eastern margin of the north china block with later evolution as a suture zone between the north and south china blocks or 2 it evolved as a part of the east central asian orogenic belt ecaob to the north

low p high t metamorphism and the role of heat transport by melt migration in the higo metamorphic complex kyushu japan this paper characterizes the metamorphic thermal structure of the higo metamorphic complex hmc and presents the results of a numerical simulation of a geotherm with melt migration and solidification reconstruction of the geological and metamorphic structure shows that the hmc initially had a simple thermal structure where metamorphic temperatures and pressures increased towards apparent lower structural levels subsequently this initial thermal structure has been collapsed by e w and nne ssw trending high angle faults pressure and temperature conditions using the analysis of mineral assemblages and thermobarometry define a metamorphic field p t array that may be divided into two segments the array at apparent higher structural levels has a low dp dt slope whereas that at apparent lower structural levels has a high dp dt slope this composite array cannot be explained by heat conduction in subsolidus rocks alone migmatite is exposed pervasively at apparent lower structural levels but large syn metamorphic plutons are absent at the levels exposed in the hmc transport and solidification of melt within migmatite is a potential mechanism to generate the composite array thermal modelling of a geotherm with melt migration and solidification shows that the composite thermal structure may be formed by a change of the dominant heat transfer from an advective regime to a conduction regime with decreasing depth the model also predicts that strata beneath the crossing point will consist of high grade solid metamorphic rocks and solidified melt products such as migmatite this prediction is consistent with the observation that migmatite was associated with the very high dp dt slope the melt migration model is able to generate the very high dp dt segment due to the high rate of heat transfer by advection

early to middle proterozoic dykes in the mt riiser larsen area of the napier complex east antarctica tectonic implications as deduced from geochemical studies

juxtaposition of india and antarctica during the precambrian inferences from geochemistry of mafic dykes abstract there are several geological geochemical and geophysical evidences which corroborate reconstruction of gondwanaland and juxtaposition of india and antarctica petrology of the precambrian mafic dykes of east antarctica and central east india also support juxtaposition of india and antarctica mafic dykes of different generations are emplaced in the archaean granite gneisses of these regions these dykes appear to be an important tool to support juxtaposition of india and antarctica geological and petrological data of the central east india precambrian mafic dykes suggest four episodes of mafic magmatism in the region three tholeiitic and one noritic similarly east antarctica also comprises four dyke suites emplaced during three distinct periods these suites are 2 4 ga meta tholeiites 2 4 ga high mg tholeiites 1 8 ga dolerites and 1 2 1 4 ga dolerites geochemical compositions of these mafic dykes are compared and they show good relationships with each other similarities in petrological and geochemical characteristics of precambrian mafic dykes of east antarctica and central east india strongly support juxtaposition of these two continents

modelling of large scale melt parameters with a regional climate model in south greenland during the 1991 melt season large scale positive degree day based melt parameterizations for the greenland ice sheet are highly sensitive to their parameters standard temperature deviation snow and ice degree day factors in this paper these parameters are simulated with a coupled atmosphere snow regional climate model for southern greenland during summer 1991 forced at the lateral boundaries with european centre for medium range weather forecasts re analyses at a high horizontal resolution of 20 kin the calculated from net ablation i e melt minus refreezing snow and ice positive degree day factors vary considerably over the ice sheet at low elevations the modelled snow degree day factor closely approaches the generally accepted value of 3 mm w e d 1 degreesc 1 higher up the ice sheet large values up to 15 mm w e d 1 degreesc 1 are simulated for ice melt maximum values of 40 mm w e d 1 degreesc 1 are found the snow and ice positive degree day factor distributions peak respectively at 3 and 8 mm w e d 1 degreesc 1 refreezing is of small importance close to the ice sheet margin higher up the ice sheet refreezing considerably lowers the amount of net ablation the monthly simulated 2 in air temperature standard deviation exhibits a strong seasonal cycle with the highest 3 0 5 0degreesc values in may and june july shows the lowest temperature fluctuations due to the melting of the surface

gently north dipping median tectonic line mtl revealed by recent seismic reflection studies southwest japan abstract the median tectonic line mtl with a length of more 1000 km is the most significant fault in japan it juxtaposes the high p t sambagawa metamorphic rocks against the low p t metamorphic rocks of the ryoke belt the mtl was probably formed in the cretaceous with many subsequent reactivations the western segment of the mtl is still active with an almost pure right lateral sense of motion although a great amount of geological information on the mtl has been accumulated information about the subsurface especially the deep seated structure of the mtl is still insufficient it has been generally assumed that the mtl is vertical or steeply dipping at depth because of its straight surface trace and its recent lateral motion recently new geophysical data have suggested that the mtl dips gently northward at depth we have acquired a complementary set of geophysical profiles seismic reflection and refraction gravity and mt across the mtl in east shikoku our results confirm that the mtl dips northward at about 30 to 40 degrees from the surface to about 5 km depth where it becomes listric this fault geometry more reasonably explains the reactivation history of the mtl the motion has occurred on a listric type fault in so called oblique or lateral ramp manner

ice flux evolution in fast flowing areas of the greenland ice sheet over the 20th and 21st centuries this study investigates the evolution of greenland ice sheet flux focusing on five of the main fast flowing regions petermann glacier north east greenland ice stream kangerdlugssuaq glacier helheim glacier and jakobshavn glacier in response to 20th and 21st century climate change a hybrid shallow ice and shallow shelf ice sheet model ism is forced with the combined outputs of a set of seven cmip5 models and the regional climate model mar the ism simulates the present day ice velocity pattern topography and surface mass balance smb in good agreement with observations except for the kangerdlugssuaq glacier over the 21st century all the fast flowing areas have exhibited a decrease in ice flux as a result of a negative smb rather than dynamical changes only the fronts of kangerdlugssuaq and helheim glaciers have shown an interannual variability driven by dynamical rather than climate changes finally the results predict a substantial inland ice margin retreat by the end of the 21st century especially along the northern coasts

the higo metamorphic complex in kyushu japan as the fragment of permo triassic metamorphic complexes in east asia abstract the higo terrane in west central kyushu island southwest japan consists from north to south of the manotani higo and ryuhozan metamorphic complexes which are intruded by the higo plutonic complex miyanohara tonalite and shiraishino granodiorite the higo and manotani metamorphic complexes indicate an imbricate crustal section in which a sequence of metamorphic rocks with increasing metamorphic grade from high northern part to low southern part structural levels is exposed the metamorphic rocks in these complexes can be divided into five metamorphic zones zone a to zone e from top to base i e from north to south on the basis of mineral parageneses of pelitic rocks greenschist facies mineral assemblages in zone a the manotani metamorphic complex give way to amphibolite facies assemblages in zones b c and d which in turn are replaced by granulite facies assemblages in zone e of the higo metamorphic complex the highest grade part of the complex zone e indicates peak p t conditions of ca 720 mpa and ca 870 c in addition highly aluminous spr bearing granulites and related high temperature metamorphic rocks occur as blocks in peridotite intrusions and show uht metamorphic conditions of ca 900 mpa and ca 950 c the prograde and retrograde p t evolution paths of the higo and manotani metamorphic complexes are estimated using reaction textures mineral inclusion analyses and mineral chemistries especially in zones a and d which show a clockwise p t path from lws including pmp act field to act chl epi field in zone a and st ky field to and field through sil field in zone d the higo metamorphic complex has been traditionally considered to be the western end of the ryoke metamorphic belt in the japanese islands or part of the kurosegawa paleo ryoke terrane in south west japan however recent detailed studies including permo triassic age ca 250 ma determinations from this complex indicate a close relationship with the high grade metamorphic terranes in eastern most asia e g north dabie terrane with similar metamorphic and igneous characteristics protolith assembly and metamorphic and igneous ages the north dabie high grade terrane as a collisional metamorphic zone between the north china and the south china cratons could be extended to the n ne along the transcurrent fault tan lu fault as the sulu belt in shandong peninsula and the imjingang belt in korean peninsula the higo and manotani metamorphic complexes as well as the hida oki terrane in japan would also have belonged to this type of collisional terrane and then experienced a top to the south displacement with forming a regional nappe structure before the intrusion of younger shiraishino granodiorite ca 120 ma

the treatment of meltwater retention in mass balance parameterisations of the greenland ice sheet retention of melt water runoff by percolation and or refreezing in the snowpack cannot be neglected when studying the surface mass balance of the greenlandice sheet in this paper we make a detailed comparison of several treatments proposed in the literature to account for this process in large scale mass balanceparameterizations the melt on the greenland ice sheet is calculated with a revised degree day model using updated datasets of surface elevation and precipitationrate on a 5 km grid crucial model parameters are recalibrated by comparing mass balance characteristics with available observations on a regional basis wediscuss the role of meltwater retention in the light of the overall mass balance of the greenland ice sheet and its sensitivity to climatic change and displaypatterns of effective retention fractions for the various methods as a main conclusion it appears that overall results are quite similar for the various models butthat meltwater retention has a large spatial variation not described by the simple treatments using the most comprehensive retention model the sensitivity of therunoff is found to be 0 35 mm deg c of sea level change per year we also present a new map of the different zones facies that characterize the accumulationarea of the greenland ice sheet that is useful for interpreting field data and calibrating satellite observations

constriction structures related to viscous collision southern prince charles mountains antarctica macroscopic structures are investigated in a zone of highly contorted migmatites from the southern prince charles mountains antarctica here l tectonite fabrics rods mullions boudin pods elongate enclaves and fold hinges are persistent linear features all plunging gently to the northeast in contrast amoeboid folds ptygmatic folds and folded boudins with different orientations are the characteristic structures in transverse sections perpendicular to the lineation no consistent shear sense is recognised in any dimension together with strain and shape analysis these observations strongly suggest that the deformation pattern is one of folding and stretching by constriction previous timing constraints indicate that this deformation overlapped with the waning stages of anatexis during decompression at approximately 510 ma up to 30 million years after initial orogeny at 540 ma the zone affected by constriction is several kilometres wide and has a contorted flower like shape confined between two broad domal antiforms in this context the constricted zone is interpreted as a relatively late tectonic feature that could have formed via deep seated viscous collision in response to orogenic collapse and doming

10 years of mass balance measurements along a transect near kangerlussuaq central west greenland in this letter we present surface mass balance measurements carried out by members of the institute for marine and atmospheric research of utrecht university imau along the kangerlussuaq sondre stromfjord in danish transect k transect located on the western part of the greenland ice sheet along 67 n at present these measurements comprise 10 years 1990 2000 which makes them longer than any other published time series of mass balance measurements in greenland

u pb zircon dating of mafic dykes and its application to the proterozoic geological history of the vestfold hills east antarctica the vestfold hills one of several archaean cratonic blocks within the east antarctic shield comprises a high grade metamorphic basement complex intruded by at least nine generations of early to middle proterozoic mafic dykes extensive u pb ion microprobe shrimp analyses of zircons derived predominantly from late stage felsic differentiates of the mafic dykes provide precise crystallisation ages for several dyke generations these new ages enable constraints to be placed on both the history of mafic magmatism in the vestfold hills and the timing of the various interspersed proterozoic deformation events in addition to demonstrating the utility of zircons derived from felsic late stage differentiates for the dating of co genetic mafic dykes this study also places doubt on previous wholerock rb sr dating of mafic dyke suites in this and other areas of east antarctica the 207pb 206pb zircon ages of 2241 4 ma and 2238 7 ma for the homogeneous and mottled norites respectively provide a younger emplacement age for associated group 2 high mg tholeiite dykes than the whole rock rb sr date 2424 72 ma originally interpreted as the age of all high mg intrusives in the vestfold hills zircon ages of 1754 16 ma and 1832 72 ma confirm the previously defined rb sr age of the group 2 fe rich tholeiites two later dyke generations the group 3 and 4 fe rich tholeiites are distinguished on the basis of field orientations and cross cutting relationships and yield zircon emplacement ages of 1380 7 ma and 1241 5 ma which also define minimum ages for two suites of lamprophyre dykes xenocrystic zircons within both felsic segregations and mafic dykes yield zircon ages of 2478 5 ma to 2740 ma indicating the presence of archaean crustal source rocks of this antiquity beneath the vestfold hills

orogeny and relative plate motions example of the japanese islands abstract the paleogeography of the eastern margin of asia near japan for the past 250 ma has been reconstructed on the basis of the relative motions between the oceanic plates and the eurasian plate engebretson et al 1982 and on land geology the relationships between the plate kinematics and orogeny are as follows calc alkaline magmatism is related to the presence of subduction when a plate boundary is a transform fault there is no volcanism very slow convergence rates do not give rise to magmatism migration of rft type triple junctions or ridge subduction produces forearc volcanism near the trench and also a wider volcanic zone uplift of low p t type regional metamorphic belts is related to collision episodes the uplift of the high p t blueschist belts on the contrary is not contemporaneous with them they appear to be related to the start of the subduction of a young plate after the migration of an rft type triple junction because the formation of a voluminous accretionary complex is contemporaneous with this and thrusting of this young accretionary complex beneath the uplifted metamorphic belt is often observed the underplating of the young accretionary complex beneath the older accretionary complex would be the cause of the uplift of the high p t type metamorphic belt the subduction of a young plate would thus be an important factor causing these orogenic events highly oblique convergence also results in formation of a serpentinite melange zone with fragments of blueschists presumably along a mechanical plate boundary in the forearc

superimposed tectonic events at 2450 ma 2100 ma 900 ma and 500 ma in the north mawson escarpment antarctic prince charles mountains abstract the north mawson escarpment in antarctica s prince charles mountains forms part of a palaeoproterozoic crustal complex which separates archaean cratonic material to the south from early neoproterozoic and early palaeozoic metamorphic belts to the north it consists of nappe like masses of grey gneiss and metasupracrustal rocks that were subjected to repeated ductile deformation under upper amphibolite to lower granulite facies metamorphic conditions in this paper we report zircon u pb dating results that constrain the principal tectonothermal events to the periods 2490 2420 ma 2180 2080 ma 940 880 ma and 530 490 ma the magmatic precursors of volumetrically important grey gneiss were produced and reworked at least partly during the 2490 2420 ma and 2180 2080 ma events the superimposition of these events is clearly documented by u pb ages from several composite zircons the formation of associated metasupracrustals possibly in a passive margin setting occurred between the 2490 2420 ma and 940 880 ma events both grey gneiss and metasupracrustals were subsequently reworked during the 940 880 ma and 530 490 ma events corresponding to the superposition of both the rayner and prydz belts onto palaeoproterozoic lithosphere of the lambert complex transposition and peak metamorphism preceded the intrusion of leucogranite dykes at 905 ma and based on metamorphic zircon growth at around 930 ma in metapelitic schist are related to the rayner orogeny it is suggested that the north mawson escarpment was assembled to most coastal regions of the antarctic sector between 45 and 80 e by at least 900 m y ago

mass balance of the northeast sector of the greenland ice sheet a remote sensing perspective synthetic aperture radar interferometry data and airborne ice sounding radar isr data are employed to obtain modern estimates of the inland ice production from nioghalvfjerdsbrae nb and zachariae isstrom zi the two largest glaciers draining the northeast sector of the greenland ice sheet ice fluxes are measured at the grounding line 14 2 1 km3 ice a 1 for nb and 10 8 1 km3 ice a 1 for zi with an ice thickness deduced from ice shelf hydrostatic equilibrium and along an isr profile collected upstream of the grounding line 14 3 0 7 km3 ice a 1 for nb and 11 6 0 6 km3 ice a 1 for zi balance fluxes calculated from a map of snow accumulation and model predictions of surface melt are 11 9 2 km3 ice a 1 for nb and 10 0 2 km3 ice a 1 for zi at the grounding line and 12 2 and 10 3 km3 ice a 1 respectively at the isr line the two glaciers therefore exhibit a negative mass balance equivalent to 14 of their balance flux with a 12 uncertainty independently we detect a retreat of the grounding line of nb between 1992 and 1996 which is larger at the glacier center 920 250 m than on the sides 240 50 m the corresponding ice thinning rates 2 1 m a 1 at the glacier center and 0 6 0 3 m a 1 on the sides are too large to be accommodated by temporal changes in ablation or accumulation and must be due to dynamic thinning

thermal modelling in shallow subduction an application to low p t metamorphism of the cretaceous shimanto accretionary complex japan this paper presents the results of numerical modelling to investigate the regional occurrence of prehnite bearing metamorphic rocks at shallow levels in subduction zones the modelling assumes a simple geometrical configuration in which the thermal structure in a prism is controlled by boundary conditions at the top and base of the prism it is expected that the predominant metamorphic facies in a prism will change with decreasing age of the descending slab the results of thermal modelling show that the facies boundary between pumpellyite actinolite and prehnite actinolite facies including prehnite pumpellyite facies overlaps with an array of p t conditions in the prism when the age of a descending slab is younger than 10 myr this implies that the change of the predominant metamorphic facies from pumpellyite actinolite to prehnite actinolite facies will switch drastically the critical age of the switch depends on subduction parameters in particular the critical age of the descending slab is 5 myr in the case of no shear heating with a subduction rate of v 75 200 mm y 1 and subduction angle of 5 15 for shear heating constant shear stress 30 mpa with a subduction rate of v 75 mm y 1 and subduction angle of 10 the critical age is 7 myr to test this switching behaviour in the development of prehnite actinolite facies in the prism petrologic data from the cretaceous shimanto accretionary complex csac in kyushu japan were compiled the regional occurrence and mineral assemblages of prehnite bearing metamorphic rocks suggest that the most of csac was metamorphosed under prehnite actinolite facies this conclusion is consistent with subduction of a young hot slab as has been proposed based on other geological observations this suggests that the regional extent of the prehnite actinolite facies metamorphic rocks may be a unique evidence for the subduction of a young hot slab

shrimp u pb zircon dating of quartz bearing eclogite from the sanbagawa belt south west japan implications for metamorphic evolution of subducted protolith in order to decipher the origin of eclogite in the high p t sanbagawa metamorphic belt shrimp u pb ages of zircons from quartz bearing eclogite and associated quartz rich rock metasandstone were determined one zircon core of the quartz rich rock yields an extremely old provenance age of 1899 79 ma suggesting that the core is of detrital origin eight other core ages are in the 148 134 ma range and are older than the estimated age for trench sedimentation as indicated by the youngest radiolarian fossil age of 139 135 ma from the sanbagawa schists ages of metamorphic zircon rims 132 112 ma from the quartz rich rock are consistent with metamorphic zircon ages from the quartz bearing eclogite indicating that eclogite facies metamorphism peaked at 120 110 ma these new data are consistent with both the iratsu eclogite body and surrounding highest grade sanbagawa schists undergoing coeval subduction zone metamorphism and subsequent re equilibration under epidote amphibolite facies conditions during exhumation

the dynamic response of the greenland and antarctic ice sheets to multiple century climatic warming new calculations were performed to investigate the combined response of the greenland and antarctic ice sheets to a range of climatic warming scenarios over the next millennium use was made of fully dynamic 3d thermomechanic ice sheet models which were coupled to a two dimensional climate model the experiments were initialized with simulations over the last two glacial cycles to estimate the present evolution and were subsequently forced with temperature scenarios resulting from greenhouse emission scenarios which assume equivalent co2 increases of two four and eight times the present 1990 a d value by the year 2130 a d and a stabilization after that the calculations brought to light that during the next century short term effect the background evolution trend would dominate the response of the antarctic ice sheet but would be negligible for the greenland ice sheet on that timescale the greenland and antarctic ice sheets would roughly balance one another for the middle scenario similar to the ipcc96 is92a scenario with respective contributions to the worldwide sea level stand on the order of about 610 cm on the longer term however both ice sheets would contribute positively to the worldwide sea level stand and the most important effect would come from melting on the greenland ice sheet sensitivity experiments highlighted the role of ice dynamics and the height massbalance feedback on the results it was found that ice dynamics cannot be neglected for the greenland ice sheet not even on a century timescale but becomes only important for antarctica on the longer term the latter is related to an increased outflow of ice into the ice shelves and to the grounding line retreat of the west antarctic ice sheet which are both found to be sensitive to basal melting below ice shelves and the effective viscosity of the ice shelves stretching parameters to their limits yielded a combined maximum rate of sea level rise of 85 cm century21 of which 60 cm would originate from the greenland ice sheet alone

the late jurassic oblique collisional orogen of sw japan new structural data and synthesis the structural configuration of sw japan mainly reflects a late jurassic early cretaceous orogeny the region is divided into an inner belt and an outer belt on the japan sea and pacific ocean sides respectively by a strike slip fault the median tectonic line mtl both consist of a series of stacked nappes the inner belt is divided into a jurassic olistostrome known as the tanba zone and a hinterland area comprising continental triassic jurassic sediments the tanba zone is sliced into two units a lower one with late jurassic matrix and triassic early jurassic radiolarite olistoliths tectonically overthrust by an upper unit comprising an olistostrome with middle jurassic matrix and blocks which include late paleozoic limestone basic lava and radiolarite the tanba zone is overthrust by a paleozoic nappe complex derived from the hinterland the basal sole of the nappe corresponds to a peculiar unit called the ultra tanba zone in the chugoku area the hinterland is divided into an upper nappe the oga nappe formed by permo carboniferous limestone and permian clastic rocks and a lower one the sangun maizuru nappe formed by paleozoic high pressure hp metamorphics the sangun schists the permian maizuru olistostrome and the dismembered paleozoic yakuno ophiolites in the northern part of sw japan the tanba zone is in faulted contact with the circum hida and the hida zones the former is interpreted as the equivalent of the oga and sangun maizuru nappes of the chugoku domain crushed by post cretaceous tectonics the latter consists of paleozoic high temperature ht metamorphic rocks and late triassic early jurassic granite locally mylonitized and covered by early jurassic sandstone the outer belt is formed by a superficial nappe similar to the tanba zone thrust upon a deep domain characterized by a synmetamorphic ductile deformation the deep domain is divided into a lower unit the oboke unit formed by continental derived arenites and a green schist nappe consisting of oceanic sediments and resedimented ophiolites the green schist nappe overthrusts the oboke unit under synmetamorphic conditions with an eastward displacement the two belts are separated by the ryoke zone which corresponds to the southern part of the tanba zone affected by a cretaceous ht metamorphism and sharply cut by the mtl a geodynamic model is proposed for the jurassic orogeny of sw japan assuming that the evolution of the inner and outer belts are linked in the late triassic early jurassic sw japan is an active plate margin the upper plate or south china block consisted of the hinterland and the tanba belt a forearc basin the lower plate consisted of an oceanic area and the south japan continent the basic mechanism of the orogeny is ascribed to the oblique subduction and collision of the south japan continent

modelling the short term response of the greenland ice sheet to global warming a two dimensional vertically integrated ice flow model has been developed to test the importance of various processes and concepts used for the prediction of the contribution of the greenland ice sheet to sea level rise over the next 350 y short term response the mass balance is modelled by the degree day method and the energy balance method the lithosphere is considered to respond isostatically to a point load and the time evolution of the bedrock follows from a viscous asthenosphere according to the ipcc is92a scenario with constant aerosols after 1990 the greenland ice sheet is likely to cause a global sea level rise of 10 4 cm by 2100 ad it is shown however that the result is sensitive to precise model formulations and that simplifications as used in the sea level projection in the ipcc 96 report yield less accurate results our model results indicate that on a time scale of a hundred years including the dynamic response of the ice sheet yields more mass loss than the fixed response in which changes in geometry are not incorporated it appears to be important to consider sliding as well as the fact that climate sensitivity increases for larger perturbations variations in predicted sea level change on a time scale of hundred years depend mostly on the initial state of the ice sheet on a time scale of a few hundred years however the variability in the predicted melt is dominated by the variability in the climate scenarios

a nonsteady state firn densification model for the percolation zone of a glacier 1 a simple steady status firm densification model is modified to account for short term time variations of accumulation rate and surface temperature the temporal surface elevation and mass changes at two sites in the percolation zone of an ice sheet in response to various climate histories are determined it is shown that a straight forward translation of observed short term ice sheet surface elevation variations into mass changes may be completely misleading particularly for the percolation zone of the ice sheet where temperature driven variations of melting refreezing rates have a strong impact on near surface density in the lower percolation zone the mass change associated with a temperature anomaly in respect to the mean climate may for example amount to as little as 10 percent of the observed simultaneous surface elevation change moreover significant surface elevation change may occur even in periods of constant surface climate and consequently unchanged mass balance as a delayed response to previous changes of the local surface climate forcing the model with cyclic temperature variations mimicking fluctuations of west greenland instrumental temperature records during the past hundred years shows that surface elevation may increase by as much as 1 m in 5 years in periods with no mass change at all in the lower percolation zone temperature induced density changes rather than fluctuations of accumulation rate are the dominant cause of short term surface elevation changes in contrast to the situation in the higher percolation zone where short term surface elevation change is dominated by fluctuations of accumulation rate

whole rock geochemistry and sr isotopic compositions of phanerozoic sedimentary rocks in the inner zone of the southwest japan arc abstract pre cretaceous metasedimentary rocks occurring in the inner zone of the southwest japan arc can be divided into three major groups namely high p t metamorphic renge and suo belts low p t metamorphic hida oki ryoke and higo belts and accretionary terranes akiyoshi maizuru mino tamba and ashio belts major and trace element compositions of most of the sedimentary rocks are typical of relatively mature sedimentary rocks although abundances of ferromagnesian elements also suggest the presence of a significant mafic to intermediate igneous component the sedimentary rocks with older nd model ages 2 0 ga have high esr values and major and trace element geochemical signatures typical of mature sediments whereas those with younger model ages

middle precambrian detrital monazite and zircon from the hida gneiss on oki dogo island japan their origin and implications for the correlation of basement gneiss of southwest japan and korea abstract monazite and zircon from seven paragneiss samples of the upper amphibolite facies grade from oki dogo island in the hida terrane western japan were analyzed for th u and pb on an electron microprobe most monazite grains are chronologically unzoned and give unequivocal chime chemical th u total pb isochron ages of 250 ma but some grains show a distinct core overgrowth relationship the cores retain evidence of pre 250 ma ages and are interpreted to be of detrital origin suggesting that monazite can be more immune to diagenetic and low grade metamorphic decompositions than had been thought previously zircon grains rounded to nearly euhedral give chime ages ranging from 3000 to 350 ma of particular interest are several rounded 3000 ma recycled zircons which perhaps originated from an archean terrain in the sino korean craton the youngest age of detrital zircons constrains that the gneiss protolith deposited after the 350 ma event the chime monazite and zircon ages for the paragneisses from oki dogo island and from the main part of the hida terrane reveal that the gneisses formed from permo carboniferous clastic sediments during a single metamorphism at ca 250 ma the results are in marked contrast to the current view that 1 the hida gneiss is a polymetamorphosed precambrian complex 2 the central part hida gneiss region and the eastern marginal part unazuki schist region of the hida terrane are correlative with the precambrian kyonggi massif and the paleozoic okchon zone in the korean peninsula respectively instead we consider that the okchon zone alone can be correlatable with the paleozoic hida terrane

present and past ice sheet mass balance simulations for greenland and the tibetan plateau net annual mass balance was evaluated for greenland and the tibetan plateau using the meteorological forcings from the ncep reanalysis and two gcms foam1 0 and csm1 4 for modern climate and for different time periods extending back to the beginning of the holocene 11 000 years ago for the climate models the ice sheet budget calculations using the degree day methodology were performed on a finer grid than the model output by interpolating monthly precipitation and surface temperature and correcting the latter to account for the gcm s smoothed topography the computed net mass balance for greenland in the present day is positive and it ranges between 290 300 mm water equivalent w e year for the two models values close to the ncep estimate of 250 mm year the past climate simulations show that the greenland mass balance has become slightly more positive since the beginning of the holocene the tibetan plateau s present day area average net mass balance is negative and ranges between 1200 and 2000 mm w e year for the two models values bracketing the ncep estimate of 1700 mm year although the balance is positive over small regions of the plateau consistent with the existence of small ice caps and glaciers the calculated past mass balance shows an increasingly less negative value for foam from 11 000 years ago towards the present and expansion of the positive mass balance areas mainly due to decreased snow ablation as the summertime insolation decreases with the changes in orbital forcing in csm the opposite trend occurs but changes are smaller and less systematic the result from foam shows that the likelihood of ice sheets developing on the tibetan plateau may have increased since 11000 years ago which is consistent with some glacial records

permian rugose coral faunas of inner mongolia northeast china and japan paleobiogeographical implications the faunal characteristics successions and geographical distribution of the permian rugose corals in inner mongolia northeast china and japan are reviewed using current coral taxonomy and the recently revised permian global time scale the co occurrences of cathaysian compound corals abundant non dissepimented solitary corals and endemic corals indicate that inner mongolia and northeast china represent an independent biogeographical entity quite separate from south china and the japanese terranes however the common occurrence in south china of permian taxa such as wentzellophyllum lonsdaleiastraea yatsengia ipciphyllum and waagenophyllum indicates in a broad sense a tethyan affinity for the akiyoshi and mino terranes in japan rocks from the asselian to the artinskian in the south kitakami terrane of japan contain eleven large dissepimented solitary and compound genera including huangia iranophyllum laophyllum polythecalis sestrophyllum wentzelella wentzellophyllum and yatsengia these genera are all typical of and common in south china but are absent from coeval strata in northeast china middle permian rocks in the south kitakami terrane also contain rugose corals that are abundant in south china in some cases the same species such as parawentzelella regularis waagenophyllum indicum waagenophyllum virgalense and yatsengia kiangsuensis thus the coral faunas from the south kitakami terrane indicate a close paleobiogeographical affinity with those from south china which is consistent with the paleobiogeography based on ammonoids and bivalves

geochemistry and geochronology of proterozoic tholeiite dykes of east antarctica evidence for mantle metasomatism two episodes of tholeiite dyke emplacement have been identified in archaean high grade metamorphics of the napier complex in enderby land middle proterozoic amundsen dykes are typical continental tholeiites and most of the chemical variation in individual suites can be explained in terms of different degrees of partial melting and low pressure crystal fractionation group i amundsen tholeiites were derived from a relatively homogeneous source region 1 190 200 m y ago whereas that of the group ii amundsen tholeiites was chemically and isotopically heterogeneous group ii dykes have various degrees of enrichment in incompatible elements and commonly show normalised trace element abundance patterns with negative nb anomalies these features imply variable metasomatism of the source region by a volatile rich fluid phase rather than a melt of any observed igneous composition enriched in k rb ba th and possibly la and ce early proterozoic 2 350 48 m y tholeiites were emplaced at considerable depths in the crust during the waning stages of granulite facies metamorphism and include a high mg suite of possible komatiitic affinity ranging in composition from hypersthene rich tholeiite norite to quartz rich tholeiite they tend to have higher ratios of highly to moderately incompatible elements e g k zr k ce and larger nb anomalies i e higher k nb compared with middle proterozoic tholeiites suggesting derivation from more enriched source regions isotopic data are not compatible with significant crustal contamination but constrain source metasomatism to a time immediately before emplacement metasomatism of the source region of the much younger group i tholeiites may have been contemporaneous with that of the high mg suite

the difficulties of dating mafic dykes an antarctic example archaen gneisses of the vestfold hills of east antarctica are transected by several compositionally discrete suites of tholeiitic dykes a representative of one of those suites which has been dated in the present study shows that not only rb sr whole rock isochrons but also u pb zircon techniques if not properly applied can produce erroneous crystallisation ages two zircon populations were recovered from the mafic dyke itself one of which is 2 483 9 ma in age and clearly of xenocrystic origin the other yields an age of 1 025 56 ma which is not ascribed to the magmatic crystallisation of the dyke but rather to the time that it underwent metamorphic metasomatic alteration as a response to high grade tectonism in the adjacent mobile belt it is presumed that the zircon in question formed by the breakdown of another mineral or minerals possibly magmatic baddeleyite due either to ingress of a siliceous fluid or more probably by the release of silica from the breakdown of pyroxene to amphibole a cogenetic 1 2 cm wide felsic vein of late magmatic early hydrothermal origin also contains two zircon populations again most of the grains therein which are interpreted as of xenocrystic origin grew at 2 483 9 ma however a few euhedral zircons with very high u and th contents grew at 1 248 4 ma which is taken to be the formation age of both the felsic vein and the enclosing mafic dyke

restoration of exotic terranes along the median tectonic line japanese islands overview abstract this paper reviews recent progress on the geotectonic evolution of exotic paleozoic terranes in southwest japan namely the paleo ryoke and kurosegawa terranes the paleo ryoke terrane is composed mainly of permian granitic rocks with hornfels mid cretaceous high grade metamorphic rocks associated with granitic rocks and upper cretaceous sedimentary cover they form nappe structures on the sambagawa metamorphic rocks the permian granitic rocks are correlative with granitic clasts in permian conglomerates in the south kitakami terrane whereas the mid cretaceous rocks are correlative with those in the abukuma terrane this correlation suggests that the elements of northeast japan to the northeast of the tanakura tectonic line were connected in between the paired metamorphic belt along the median tectonic line southwest japan the kurosegawa terrane is composed of various paleozoic rocks with serpentinite and occurs as disrupted bodies bounded by faults in the middle part of the jurassic chichibu terrane accretionary complex it is correlated with the south kitakami terrane in northeast japan the constituents of both terranes are considered to have been originally distributed more closely and overlay the jurassic accretionary terrane as nappes the current sporadic occurrence of these terranes can possibly be attributed to the difference in erosion level and later stage depression or transtension along strike slip faults the constituents of both exotic terranes especially the ordovician granite in the kurosegawa south kitakami terrane and the permian granite in the paleo ryoke terrane provide a significant key to reconstructing these exotic terranes by correlating them with paleozoic granitoids in the eastern asia continent

backarc deformation along the eastern japan sea margin offshore northern honshu abstract the structural evolution of the eastern japan sea margin offshore northern honshu is discussed on the basis of single channel seismic profiles backarc structures evolved in response to late oligocene middle miocene extension which was generated at high angles to the arc trench system the evolution of a late miocene recent compressional plate tectonic regime resulted in widespread basement inversion the eastern japan sea margin is characterized by variable inverted half graben systems which are obliquely oriented to the island arc the area is underlain by three major structural blocks which are separated by a nw and a wnw trending structural discontinuity these blocks experienced a northward increase in extension the two southern blocks contain nne ne oriented reverse faults while the northern block is underlain by n nnw trending reverse faults the orientation and geometry of basement faults compares well with faults mapped onshore honshu the evaluation of the eastern japan sea margin can be explained by early miocene ese directed extension followed by a middle miocene sse directed extension pliocene recent east dipping reverse faults extend along the base of the continental slope and form a discontinuous thrust front which is characterized by minor fault offsets these reverse faults are locally associated with small active arc volcanoes

40ar 39ar mineral age constraints for the tectonothermal evolution of the sambagawa metamorphic belt central shikoku japan a cretaceous accretionary prism abstract the sambagawa metamorphic belt exposed in central shikoku japan is tectonostratigraphically represented by the oboke and structurally overlying besshi nappe complexes oboke units consist of metamorphic rocks largely derived from clastic protoliths sandstone and conglomerate whereas besshi units are dominated by rocks with oceanic protolith affinities shale chert and greenstone whole rock schist samples from low grade oboke units record intermediate temperature 40 ar 39 ar plateau ages of 70 77 ma which are interpreted to closely date attainment of maximum metamorphic conditions whole rock schist samples from besshi units chlorite zone record plateau ages of 85 94 ma suggesting an earlier metamorphic climax within this structural level amphibole within the albite biotite zone in besshi records 36 ar 40 ar vs 39 ar 40 ar plateau isotope correlation ages of 84 87 ma which are interpreted as dating the post metamorphic cooling through temperatures required for intracrystalline retention of argon a slightly older isotope correlation age 94 ma is recorded by amphibole from the higher grade oligioclase biotite zone contrasts in amphibole cooling ages are interpreted as reflecting thrust related metamorphic inversion and resultant earlier cooling of higher grade structural units muscovite from all structural levels of the besshi nappe complex records 40 ar 39 ar plateau ages of 76 89 ma these are interpreted to date post metamorphic cooling through appropriate closure temperatures following structural assembly of the besshi nappe complex protoliths of the besshi units originated at approx 130 ma and attained maximum metamorphic conditions during entrainment in an accretionary complex at approx 90 100 ma higher grade sequences developed at deeper levels along the hanging wall of the accretionary complex during subsequent structural uplift to shallower crustal levels the besshi nappe complex was tectonically emplaced over oboke units

the geodynamic evolution of the eastern eurasian margin in mesozoic times abstract the cenozoic features of eurasia such as marginal seas and intracontinental deformation are unraveled using available paleomagnetic and field data the late cretaceous shape of eurasia is then reconstructed from the examples of sw japan and south russian far east the major features of the mesozoic eurasian margin suture zones marked by ophiolites or high pressure metamorphic rocks olistostromes characterized by the lithology of the olistoliths calc alkaline magmatism and strike slip faults are outlined correlations of the ophiolitic belts and the olistostromes along the eastern eurasian margin from borneo to siberia allow the definition of four microcontinents the west philippines south japan and the anuy and okhotsk sea microblocks from south to north the mesozoic structure of the eurasian margin is due to three processes 1 1 oceanic subduction and the accretion of subduction complexes 2 2 the collision of these microcontinents with eurasia between the late jurassic and the late cretaceous and 3 3 the reactivation of the ophiolitic sutures by left lateral wrench faulting

impact of solar forcing on the surface mass balance of northern ice sheets for glacial conditions abstract the climate of the last glacial period has been punctuated by abrupt changes termed the dansgaard oeschger do events occurring every 1500 4500 yr so far the cause of these events which involve changes in the thermohaline circulation remains an open issue it has been proposed that small changes in the freshwater flux in the north atlantic possibly coming from cyclic variations in solar activity could act as a pacemaker and synchronize the events here we use the general circulation model ipsl cm4 to investigate the impact of changes in the total solar irradiance tsi on the freshwater flux coming from ablation of the northern hemisphere ice sheets we test four different tsi values between 1360 and 1375 w m 2 and in this range establish a linear relationship between tsi and ablation rates over different sectors of the ice sheets our results show that a change in tsi smaller than 1 that would be undetectable in paleo records can trigger changes in the freshwater flux in the north atlantic at an amplitude similar to the one required to synchronize abrupt events in the climate model of intermediate complexity climber given the uncertainties on the past solar activity we conclude that the hypothesis of a solar origin of the periodicity of d o events cannot be ruled out and that the relationship between ice ablation and tsi variations is worth being further investigated

jurassic dextral and cretaceous sinistral movements along the hida marginal belt abstract the hida marginal belt hmb which consists of various kinds of fault bound blocks is located between the continental massif of the hida belt and the mesozoic accretionary complex of the mino belt in central japan detailed field investigation reveals that the hmb had grown through the two different movements i e jurassic dextral and cretaceous sinistral movements the jurassic dextral ductile shear zones run in the southern marginal part of the hida belt and the northern part of the hmb whereas the cretaceous sinistral cataclastic shear zones occur in the southern part of the hmb and the northern marginal part of the mino belt geologic map and field evidence seem to suggest that the jurassic dextral movement form the fault bound blocks of the hmb to form the basic structure of the hida marginal belt i e formation of the proto hmb following the dextral movement the sinistral one restructured the proto hmb to complete the present feature of the hida marginal belt the cretaceous sinistral movement might result in the sinistral collision between the proto hmb and the mino belt

mesozoic tectonothermal development of the sambagawa mikabu and chichibu belts south west japan evidence from 40ar 39ar whole rock phyllite ages five whole rock 40ar 39ar plateau ages from low grade sectors of the sambagawa belt besshi nappe complex range between 87 and 97 ma two whole rock phyllite samples from the mikabu greenstone belt record well defined 40ar 39ar plateau ages of 96 and 98 ma together these ages suggest that a high pressure metamorphism occurred in both the sambagawa and mikabu belts at c 90 100 ma the northern chichibu sub belt may consist of several distinct geochronological units because metamorphic ages increase systematically from north c 110 ma to south c 215 ma the northern chichibu sub belt is correlated with the kuma nappe complex sambagawa belt two whole rock phyllite samples from the kurosegawa terrane display markedly older metamorphic ages than either the sambagawa or the chichibu belts accretion of sambagawa chichibu protoliths began prior to the middle jurrasic depositional ages decrease from middle jurassic kuma chichibu nappe complex to c 100 ma oboke nappe complex toward lower tectonostratigraphic units the ages of metamorphic culmination also decrease from upper to lower tectonostratigraphic units the kurosegawa belt and the geological units to the south belong to distinctly different terrances than the sambagawa chichibu belts these have been juxtaposed as a result of transcurrent faulting during the cretaceous

permian geodynamic setting of northeast china and adjacent regions closure of the paleo asian ocean and subduction of the paleo pacific plate abstract northeast china and adjacent regions are located in the central east asian continent and consist tectonically of both the paleo asian and paleo pacific orogens between the siberian platform and sino korean north china block this paper discusses some hotly debated issues concerning the permian geodynamic setting of these regions based on a comprehensive analysis of available geological geochemical paleobiogeographical and paleomagnetic data spatial and temporal distribution of ophiolites and associated continental marginal sequences permian sedimentary sequences spatial distribution and geochemistry of permian magmatic rocks and the evolution of paleobiogeographical realms imply 1 that the permian marine basins in northeast china and adjacent regions include remnants of the paleo asian ocean in southeastern inner mongolia and central jilin province and active continental margins of the paleo pacific ocean 2 that the suture between the siberian and sino korean paleoplates was finally emplaced in the permian and is located in areas from suolunshan solonker eastwards through regions north to the xar moron river in southeastern inner mongolia and then central jilin province to the yanji area and 3 that the permian crustal evolution of northeast china and adjacent regions as well as parts of the siberian paleoplate was influenced by subduction of the paleo pacific oceanic plate finally the permian tectonic framework and paleogeography of northeast china and adjacent regions in central east asia are discussed briefly and early and late permian palinspastic reconstruction maps are provided

a new present day temperature parameterization for greenland near surface air temperature 2 m over the greenland ice sheet gris is parameterized using data from automatic weather stations located on land and on the ice sheet the parameterization is expressed in terms of mean annual temperatures and mean july temperatures both depending linearly on altitude latitude and longitude the temperature parameterization is compared to a previous study and is shown to be in better agreement with observations the temperature parameterization is tested in a positive degree day model to simulate the present 1996 2006 mean melt area extent of the gris the model accounts for firn warming rainfall and refreezing of meltwater with different degree day factors for ice and snow under warm and cold climate conditions the simulated melt area extent is found to have reasonable agreement with satellite derived observations

comparison of 40ar 39ar conventional and laser dating of biotites from the north tregor batholith bulk samples and single grains of biotites from the north tregor batholite armorican massif france were analysed by the 40ar39ar method apparently pure single biotite grains analysed by the step heating procedure with the laser probe displayed plateau ages or slightly disturbed age spectra one strongly chloritized single biotite grain gave a very disturbed age spectrum with younger ages the bulk samples of biotites of the same rocks displayed disturbed age spectra characterized by younger low temperature ages and a hump at intermediate temperature steps these disturbances are explained by 39ar recoil from the biotite into the chlorite which is clearly evidenced by hrtem observations and not by excess 40ar the more concordant results obtained on single biotites are probably due to a more careful selection of the minerals in most cases we obtain good concordance of the ages 600 610 ma measured on the apparently pure single biotite grains and the high temperature ages of both the bulk samples of amphiboles and biotites from the same rocks

the importance of thermodynamics for modeling the volume of the greenland ice sheet two different kinds of ice flow models one two dimensional 2 d and the other three dimensional 3 d have been used to test the importance of the thermodynamic response of the greenland ice sheet the basic difference between the two models is that the thermodynamics are neglected in the two dimensional model whereas these are incorporated in the three dimensional model the 2 d and 3 d models are compared in terms of volume response time and total volume of the ice sheet results indicate that the sawtooth character of the ice volume on glacial interglacial timescales is among other possible reasons a result of the thermodynamic coupling the changes in elevation over the last 130 000 years calculated with the three dimensional version are 230 m for the summit drill site and 190 m for the n grip site the standard deviation of the changes in elevation is 55 m for the summit site and 43 m for the n grip site the present day imbalance is merely a result of the rather constant climate over the last 10 kyr and is not determined by the thermodynamics consequently pleistocene temperatures do still exist in the ice sheet but are not important for volume calculations of the present day ice sheet for short term perturbation experiments in the future the pronounced sensitivity of the mass balance will determine the response of the greenland ice sheet whereas thermodynamics will play only a minor role

ordovician 40ar 39ar phengite ages from the blueschist facies ondor sum subduction accretion complex inner mongolia and implications for the early paleozoic history of continental blocks in china and adjacent areas we obtained 453 21 8 ma and 449 41 8 ma 2 laser step heating 40 ar 39 ar plateau ages for phengite from quartzite mylonites from the blueschist facies ondor sum subduction accretion complex in inner mongolia northern china these ages are within error of the inverse isochron ages calculated using the plateau steps and the weighted mean ages of total fusion of single grains the compositional change from glaucophane in the cores to crossite in the rims of blue amphiboles as revealed by electron microprobe analysis points to decompression probably caused by progressive exhumation of the subducted material the late ordovician ages were not affected by excess argon incorporation because in all likelihood the oceanic sediments were wet on arrival at the trench and free of older detrital mica the ca 450 ma ages are hence interpreted as the time of crystallization during mylonitization under high fluid activity at fairly low temperatures this means that accretion of the quartzite mylonite unit occured about 200 ma before final closure of the paleo asian ocean amalgamation of the siberian tarim and north china cratons and formation of the end permian solonker suture zone we argue that the early paleozoic evolution of the ondor sum complex occurred along the northeastern cimmerian margin of gondwana which was composed of micro continents fringed by subduction accretion complexes and island arcs the later evolution took place during the building of the eurasian continent following middle devonian and younger rifting along the east gondwanan margin and northward drift of the detached north china craton an extensive review shows that this type of two stage scenario probably also applies to the geodynamic evolution of other micro continents like south china tarim a number of kazakh terranes alashan qaidam and kunlun as well as south kitakami and correlatives in japan and probably indochina like the north china craton these were bordered by early paleozoic subduction accretion complexes island arcs or contained calc alkaline volcanic mar gins like for example the central tienshan north qinling north qaidam altun north qilian and kunlun belts in china as well as the oeyama and miyamori ophiolites and matsugadaira motai blueschist belt of japan and the dismembered sergeevka ophiolite of the southern part of the russian far east this implies that a vast orogenic system comprising an archipelago of micro continents seems to have existed along the cimmerian margin of east gondwana in early paleozoic time in which the ultrahigh pressure metamorphism that characterizes the early evolution of many of the asian micro continents occurred introduction and aim

a new concept on tectonic correlation between korea china and japan histories from the late proterozoic to cretaceous abstract the dabie sulu collision belt in china extends to the hongseong odesan belt in korea while the okcheon metamorphic belt in korea is considered as an extension of the nanhua rift within the south china block the hongseong odesan belt divides korea s gyeonggi massif into northern and southern portions the southern gyeonggi massif and the yeongnam massif are correlated with china s yangtze and cathaysia blocks respectively while the northern gyeonggi massif is part of the southern margin of the north china block the southern and northern gyeonggi massifs rifted from the rodinia supercontinent during the neoproterozoic to form the borders of the south china and north china blocks respectively subduction commenced along the southern and eastern borders of the north china block in the ordovician and continued until a triassic collision between the north china and south china blocks while subduction was occurring on the margin of the north china block high p t metamorphic belts and accretionary complexes developed along the inner zone of southwest japan from the ordovician to the permian during the subduction the hida belt in japan grew as a continental margin or continental arc collision between the north and south china blocks began in korea during the permian 290 260 ma and propagated westwards until the late triassic 230 210 ma creating the sinistral tanlu fault in china and the dextral fault in the hida and hida marginal belt in japan phanerozoic subduction and collision along the southern and western borders of the north china block led to formation of the qinling dabie sulu hongseong hida yanji belt

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

short paper accretion and uplift in the shimanto belt sw japan k ar cleavage dating and fission track cooling ages have been combined with existing stratigraphic data to constrain the evolution of the shimanto belt a cretaceous neogene accretionary complex cleavage ages record two major phases of accretion during the late cretaceous and late eocene early oligocene the minimum time periods between sedimentation and deformation are constrained to 9 5 9 and 0ma intervals within four tectonic units containing youngest sediments of maastrichtian late eocene late eocene and early oligocene ages respectively one phase of middle to late miocene uplift is indicated for the whole study area by the fission track cooling ages frontal underplating combined with out of sequence thrusting are suggested as mechanisms for this regional uplift the cretaceous neogene shimanto belt fig la forms the outermost onshore exposure of accreted material in sw japan the boundaries of constituent accreted units of the shimanto belt are defined by a detailed stratigraphy taira et al 1980taira et al 1988 providing an opportunity to test the application of cleavage dating and fission track studies to accretionary complex evolution the butsuzo tectonic line fig la juxtaposes the shimanto belt to the jurassic sanbosan belt in the north younger accreted material extends offshore to the south as far as the present day boundary of the eurasian plate the nankai trough fig la continued accretion seaward of the shimanto belt has back rotated older accreted units to their present day steeply dipping orientations the type section of the shimanto belt taira et al 1980 lies in the eastern hata peninsula fig 1b which contains the study

greenland s contribution to global sea level rise by the end of the 21st century the greenland ice sheet holds enough water to raise the global sea level with 7 m over the last few decades observations manifest a substantial increase of the mass loss of this ice sheet both enhanced melting and increase of the dynamical discharge associated with calving at the outlet glacier fronts are contributing to the mass imbalance using a dynamical and thermodynamical ice sheet model and taking into account speed up of outlet glaciers we estimate greenland s contribution to the 21st century global sea level rise and the uncertainty of this estimate boundary fields of temperature and precipitation extracted from coupled climate model projections used for the ipcc fourth assessment report are applied to the ice sheet model we implement a simple parameterization for increased flow of outlet glaciers which decreases the bias of the modeled present day surface height it also allows for taking into account the observed recent increase in dynamical discharge and it can be used for future projections associated with outlet glacier speed up greenland contributes 0 17 cm to global sea level rise by the end of the 21st century this range includes the uncertainties in climate model projections the uncertainty associated with scenarios of greenhouse gas emissions as well as the uncertainties in future outlet glacier discharge in addition the range takes into account the uncertainty of the ice sheet model and its boundary fields

estimating the contribution of arctic glaciers to sea level change in the next 100 years in this paper we report on an approach to estimate the contribution of arctic glaciers to sea level change in our calculation we assume that a static approach is feasible we only calculate changes in the surface balance from modelled sensitivities these sensitivities summarized in the seasonal sensitivity characteristic can be used to calculate the change in the surface mass budget for given anomalies of monthly temperature and precipitation we have based our calculations on a subdivision of all arctic ice into 13 regions four sectors of the greenland ice sheet the canadian arctic 74 n the canadian arctic 60 n as forcing for the calculations we have used the output from five climate models for the period 2000 2100 these models were forced by the same greenhouse gas scenario ipcc b2 the calculated contributions to sea level rise in the year 2100 vary from almost zero to about 6 cm the differences among the models stem first of all from differences in the precipitation the largest contribution to sea level change comes from the greenland ice sheet the glaciers in alaska also make a large contribution not because of the area they cover but because they are more sensitive than other glaciers in the arctic the climate models do not agree on regional patterns the runoff from svalbard glaciers for instance increases for two models and decreases for the three other models we conclude that the uncertainty due to a simple representation of the glaciological processes is probably smaller than the uncertainty induced by the differences in the climate change scenarios produced by the models

three dimensional inversion modelling of a neoproterozoic basin in the southern prince charles mountains east antarctica abstract three dimensional inversion modelling of airborne magnetic data acquired in the prince charles mountains east antarctica provides an insight into the sub ice distribution and three dimensional geometry of a neoproterozoic sedimentary basin a three dimensional starting model was created from two two dimensional gm sys modelling and our current geological understanding of the study area three dimensional vpmg inversion modelling was performed on the aeromagnetic data to obtain an acceptable fit between the observed response collected in the field and the calculated response of the three dimensional model modelling suggests that the base of the basin undulates and is relatively unstructured however the margins of the basin thicken from north 4 km to south 11 km the volume of the sodruzhestvo group that in fills the sedimentary basin has been calculated at approximately 35 000 km3 modelling of banded iron formations at the southern margin of the basin and a sharp magnetic contrast in the north reveal that both contacts dip toward the south we interpret this asymmetric geometry of the sedimentary basin as having began as a set of half grabens bounded by an underlying listric fault that flattened at depth below the sedimentary basin subsequent early palaeozoic inversion of this structure resulted in reactivation along the low angle basal detachment but rather than taking its original course underneath the sedimentary basin the fault ramped up along the southern margin this process caused exhumation of the underlying banded iron formations which are now juxtaposed at similar crustal levels to the neoproterozoic cover rocks