regional neogene exhumation of britain and the western north sea tertiary exhumation of britain and the western north sea is interpreted to have taken place in two episodes each with amplitudes of about 1 km a palaeogene phase that principally affected the present onshore britain west of the present extent of the late cretaceous danian chalk group and a neogene phase that affected both onshore areas and the western north sea consequently maximum burial of mesozoic and older rocks in the present onshore areas generally occurred in the palaeocene c 60 ma in the western north sea the preservation of the chalk group today suggests relatively stable conditions prevailed immediately after its deposition rather than substantial palaeocene exhumation in this area maximum burial is interpreted to have occurred in the neogene the proposal is consistent with published exhumation estimates based on studies of sediment compaction offshore and of fission tracks onshore it also does away with unlikely high burial rates which are implied in the latest cretaceous earliest tertiary if removal of overburden from the chalk is assumed to have occurred in the palaeocene

the history of the major rivers of southern britain during the tertiary the evolution of the drainage system of lowland britain is discussed on the basis of available geological evidence including that from terrestrial sites and that which has more recently become available from offshore exploration of the north sea the english and bristol channels and the irish sea tertiary stratigraphy throws considerable light on landform and river development paleocene destruction of a chalk cover which seems to have been incomplete in western britain was accompanied by basin sedimentation under a tropical climate the major elements the thames solent hampshire proto avon river irish sea river and possibly an early trent river existed almost throughout the cenozoic the influence of atlantic rifting and thermal doming in nw britain appears to have been stronger and more temporally focused than the persistent flexuring that determined and maintained tertiary drainage lines in the se here also the folded mesozoic terrains on the surface contrast with the more dominant block faulted relief of the palaeozoic oldlands the rivers of the se can be shown to have extended or reduced their lengths in response to relative sea level change and gentle warping drainage antecedence the destruction of the solent system and the breaching of the english channel are also evident by contrast the major river systems of the west are now entirely submerged long term stability of the drainage pattern reflects a persistent tectonic regime in the south with a subdued low relief landscape having a weathered regolith and dense vegetation cover meandering river channels and alluvial styles predominated although channel forms varied according to sediment load slope and discharge variability coarse gravel dominated accumulations are rare and localized chemically stable lithologies dominate the clastic component throughout it is apparent that the deeply incised river valleys seen today are related to high predominantly coarse sediment yields encouraged by substantial rapid climate changes in the pleistocene this emphasizes the significance of mechanical compared with chemical weathering for the rate and nature of landscape dissection and the modifications that have arisen as a result of glaciation frost climate weathering rapidly changing climates and sea levels the stratigraphical evidence here reviewed is at variance with older largely geomorphologically based landform evolution models denudational chronology but gives considerable support to the recent proposals emphasizing the significance of paleocene erosion and enduring low relief landscapes and drainage systems evolving alongside fold development during the paleogene given the depobasin evidence now available postulated fluvially active episodes can and must be linked to contemporaneous deposition some at least of the many controversies involving the identity of erosion surfaces the dating of them using only residual deposits and weathering mantles and the selection of particular tertiary episodes as ones of landscape development can now be resolved

evidence for cenozoic tectonic deformation in se ireland and near offshore 1 an integrated study of topography bathymetry high resolution aeromagnetic data and structural observations demonstrates significant cenozoic fault activity in se ireland tectonically generated knickpoints and reddened fault breccias along topographic escarpments that are underlain by greywacke bedrock and trend oblique to the regional caledonian strike provide evidence for fault displacement near offshore faults with similar geometry produce present day bathymetric scarps and localized tectonic topography in the inverted kish bank basin the integration of offshore high resolution aeromagnetic data and structural interpretation of the kish bank basin provides evidence for dextral transtension on nnw trending faults and sinistral transpression on ene trending faults bounding a lower paleozoic to carboniferous basement block these faults correlate onshore with previously recognized caledonian faults producing topographic offsets and surface uplift to the north offshore structures can be traced onshore and cut exposures of the caledonian leinster granite structural analysis of these outcrops indicates post variscan deformation a major fault on the nw margin of the batholith cuts a major erosion surface developed on carboniferous carbonate rocks and nonmarine miocene deposits are preserved above this surface fault kinematics provide evidence of two paleostress systems 1 nw se 1 subvertical 2 and ne sw 3 followed by 2 a clockwise swing of 1 to nnw sse timing of deformation in both stress systems is probably post oligocene age the mechanism driving this deformation is likely ridge push much is already known about cenozoic tectonics and exhumation from offshore basins this study shows that onshore ireland has also been affected by significant tectonic activity and exhumation during the cenozoic

the post variscan thermal and denudational history of ireland the thermal and denudational history of ireland is evaluated using an extensive new apatite fission track aft dataset derived from surface samples modelled thermal histories are used to construct maps of denudation for a number of time slices from triassic time to 10 ma using a time dependent palaeogeotherm the maps illustrate the spatial variability of denudation and subsidence within each time slice the patterns of denudation are complex showing considerable variability at the length scale of 101 102 km with especially high denudation rates found over known igneous centres such as the mournes of county down based on the onshore aft data alone there is no definitive signature of an irish sea dome extending significantly across ireland in early tertiary time the cumulative amount of denudation during tertiary time varies depending on the aft annealing model used but is generally in the region between 1 and 2 km and without clear spatial trends high amounts of denudation have been mapped over the tertiary intrusions in county down reflecting their unroofing since emplacement in paleocene time the cumulative denudation from triassic time to 10 ma shows relatively low amounts of denudation 2 km in the irish midlands and the extreme ne of the island consistent with the observation that mesozoic tertiary sediments and igneous products are preserved in the ulster basin the western flank of ireland and the region between dublin and county down show high cumulative amounts of denudation 4 km the latter being consistent with the high amounts of denudation interpreted for the irish sea region this denudation pattern explains in part the outcrop of precambrian and lower palaeozoic rocks in these areas the spatial integration of the denudation over the entire landmass gives the average denudation rate and the sediment discharge from ireland as a function of time average denudation rates are moderately high in triassic time falling to low values in cretaceous time and increasing substantially in tertiary time however the total volumetric discharge of sediment in tertiary time is an order of magnitude smaller than the preserved solid volume of tertiary sediment in the basins offshore western ireland

structure of lower carboniferous basins of nw ireland and its implications for structural inheritance and cenozoic faulting abstract the geometry of lower carboniferous basins across the northern part of ireland is characterised by a gradual change in polarity of structure from a predominantly southward dipping fault system in northern ireland through the lough allen basin and into a mainly northward dipping fault system of connemara in the southwest this polarity change is reflected in the emergence of northward facing uplifted footwall blocks such as at croagh patrick and the ox mountains in the southwest with southward facing blocks in the northeast despite these structural changes there is a great degree of along strike continuity of lower carboniferous structure strain and displacement with the system forming a link between comparable sized and coeval basins in northern england and scotland to the east and the canadian maritime provinces to the west the spatial distribution of carboniferous normal faults suggests that caledonian structure such as the fair head clew bay line plays an important role in the localisation of post caledonian strain although the reactivation of individual caledonian structures may be less common the terrain of the west of ireland is strongly influenced by major carboniferous faults offsetting the base carboniferous unconformity as opposed to previously suggested cenozoic normal faulting of a tertiary peneplain

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

new shrimp u pb zircon ages from the heilongjiang high pressure belt constraints on the mesozoic evolution of ne china the heilongjiang complex is a high pressure accretionary belt composed mainly of serpentinite glaucophane bearing metabasalt epidote glaucophane albite schist greenschist marble two mica schist muscovite albite schist quartz schist and quartzite chert located along the suture zone separating the jiamusi and songliao blocks in ne china shrimp u pb zircon analyses of two samples of granitic gneiss from yilan that are interleaved with the heilongjiang complex record diverse protolith ages that are consistent with derivation from regional permian granitoids 263 7 ma and the adjacent mashan complex 492 6 ma indicating tectonic incorporation of older granitic components into the accretionary complex the age of the basaltic protolith of two samples of glaucophane albite schist from yilan is 245 ma and is slightly younger than the protolith age of two samples of amphibole schist from mudanjiang located about 200 km south of yilan that define weighted mean 206pb 238u ages of 257 4 and 257 5 ma all four samples contain a few older inherited zircon grains and also show the effects of an isotopic disturbance at 200 to 190 ma most likely related to the subsequent high pressure metamorphism the timing of which has been determined in previous studies the basaltic rocks record rifting and ocean development from 260 to 210 ma based on previous studies in which both e morb and oib protolith signatures were identified detrital zircons in two samples of mica schist from mudanjiang show distinct populations at 700 ma 500 to 450 ma 350 to 213 ma peak at 255 ma 290 to 200 ma and 200 ma all except the youngest ages can be matched with rocks from the older components of the jiamusi block and with other areas in the central asia orogenic belt caob supporting the view that the jiamusi block was most likely the eastern segment of the caob prior to rifting the youngest concordant magmatic detrital grain with an age of 207 3 ma defines the maximum age of sedimentation this also limits the timing of high pressure metamorphism in the heilongjiang complex to post late triassic consistent with argon data obtained in previous studies final closure between the jiamusi and songliao blocks took place in the latest triassic early jurassic with the two blocks accreted as a result of pacific ocean subduction this suggests that the heilongjiang complex records the time when north south closure of the caob in china gave way to westward movement related to the pacific ocean subduction which has dominated the tectonics of ne china and far east russia since that time

the reliability of asymmetric c axis fabrics of quartz to determine sense of vorticity abstract asymmetric c axis fabrics of quartz are commonly used to determine sense of vorticity in ductile shear zones this method seems to work if the fabric pattern resembles a model fabric proposed by lister and hobbs 1980 usually however c axis fabrics are rather vague the reliability of such vague fabrics was tested in a major shear zone with known sense of vorticity only 62 of the c axis fabrics predict the correct sense great care should therefore be taken in applying this method to determine sense of vorticity

late variscan tectonic evolution by thinning of earlier thickened crust an 40ar39ar study of the montagne noire southern massif central france abstract 40ar 39ar age determinations on samples selected on deformational criteria form the basis of a proposal of a new detailed tectonometamorphic history of the montagne noire the southern part of the massif central france this range is classically divided into a cover and an axial gneissic and migmatitic core which was metamorphosed under high t medium p conditions the basement is structurally overlain by epimetamorphic paleozoic sediments in the north in the south equivalent rocks form a well known pile of recumbent nappes the variscan history of this area comprises early shortening and thickening of the continental crust the climax of this event took place around 320 ma ago as is shown by previous rb sr data and by 40ar 39ar measurements new developments in structural analyses have led to a better understanding of the late evolution of the area in terms of diapiric uplift of the core south southwestwards verging recumbent nappes have been emplaced and were weakly metamorphosed in their lower parts this movement was accompanied and followed by dextral extensional wrenching of the paleozoic cover along the northern and southern margins of the axial zone attendantly ductile shear zones were formed in order to decipher the complex history three structural levels have been dated with the 40ar 39ar method these levels are 1 the migmatitic and gneissic series in the axial core where micas yield ages of c 315 ma 2 mylonites from the northern and southern shear zones where biotites and muscovites yield ages of c 310 ma 3 muscovites and biotites from the epimetamorphic nappe structures yielding ages of c 297 ma the later ages may represent a younger thermal pulse these data are compared and discussed in the light of previous radiometric studies of the area and precise biostratigraphic constraints a detailed geodynamic evolution of the studied segment is proposed

an example of multicomponent magnetization in welded tuffs a case study of upper cretaceous welded tuffs of eastern russia abstract four distinct components of natural remanent magnetization were isolated from a single site in welded tuffs in the upper cretaceous kisin group of the sikhote alin mountain range russia in order to contribute toward a basis for an interpretation of multicomponent magnetization rock magnetic experiments were performed on the welded tuffs all four magnetization components essentially reside in magnetite the lowest temperature component up to 300 c component a d 349 3 i 60 9 95 7 3 n 7 is a present day viscous magnetization the third removed component component c d 41 4 i 51 8 95 3 5 n 8 isolated over the temperature range of 450 560 c is a primary remanence the second and fourth demagnetized components component b d 174 7 i 53 1 95 21 2 n 3 and component d d 188 1 i 64 5 95 4 0 n 8 respectively are secondary magnetizations related to a thermal event in sikhote alin between 66 and 51 ma components b and d were acquired through different remagnetization processes component b is ascribed to a thermoviscous remanent magnetization carried by single domain magnetite and component d is a chemical remanent magnetization

location and sinistral displacement of the eastern liaoyuan accretionary belt along the tan lu fault zone ne china abstract the ne to nne striking continental scale tan lu fault zone tlfz in ne china is subdivided into the 900 km long yilan yitong fault yyf in the west and the 1000 km long dunhua mishan fault dmf in the east both faults record sinistral displacement during the earliest cretaceous leading to an obvious offset of the boundary between the liaoyuan accretionary belt lab and the north china craton ncc previous studies have demonstrated that the lab in the south of the eastern central asian orogenic belt caob extends eastwards into an area between the yyf and the dmf the boundaries between the lab and ncc indicate a 35 km sinistral displacement upon the yyf however it remains unclear whether the lab extends to the east of the dmf and the amount of sinistral displacement on the dmf is poorly constrained here we present lithological observations and u pb and hf isotopic data from zircon to constrain the age and position of the lab to the east of the dmf the data indicate an eastward extension of the lab across the dmf suggesting the continuous presence of the lab east of the tlfz in ne china the u pb ages ehf t values and two stage model ages of zircons from the study area constrain the boundary between the lab and ncc to an extension of the ne dipping chifeng kaiyuan fault to the east of the dmf the geological boundaries on both sides of the dmf indicate a 170 km sinistral displacement along the fault thus the tlfz has a total sinistral displacement of 205 km in ne china the eastern branch of the tlfz records significantly more movement due to its proximity to the pacific ocean where subduction of oceanic crust might have caused sinistral faulting along the tlfz

mode of mixture of oceanic fragments and terrigenous trench fill in an accretionary complex example from southern sakhalin abstract four modes of mixture of oceanic materials such as cherts limestones and basalts and terrigenous trench fill sediments are recognized in the cretaceous accretionary complexes in southern sakhalin far eastern pacific margin of the u s s r the first mode is a thin skinned stacking of pelagic bedded cherts with black shale due to duplex formation in association with shallow underplating or off scraping the second mode is a mixture of the uppermost part of the oceanic crust with terrigenous trench fill sediments due to olistostrome formation reconstruction of the original sequence in ascending order suggests that the basement is pillow basalt with overlying pelagic sediments of chert and limestone olistostrome caused by collapse of oceanic crust due to its bending before encountering a trench and finally trenchfill sediments of turbidite this sequence is imbricated by thrusting which appears to have occurred at the time of underplating the third mode is a tectonic mixing of oceanic fragments and terrigenous sediments due to shear which is related to underthrusting of the oceanic plate a reduction in the supply of trench fill sediments causes copious accretion of the upper part of oceanic crust the fourth mode is in situ basalt volcanism at the trench where thick baked margins of terrigenous shale are formed around the injected basalts this mode appears to represent a ridge trench encounter these four different modes of mixing seem to be usual in ancient accretionary complexes in orogenic belts

further evidence of abrupt holocene drowning of the black sea shelf a 1999 survey of the black sea continental shelf off the north central turkish seaport of sinop using a side scan sonar small remotely operated vehicles and a series of dredge lowerings located inspected and sampled an exposed high energy paleoshoreline at a depth of 155 m radiocarbon dating of mollusk shells collected from this ancient beach revealed that the marine flooding of the black sea took place between 7460 and 6820 yr b p all ages are reported in radiocarbon years not calendar years without correction for reservoir age or dendro calibration changing it from a lacustrine to marine environment this relic surface remained in contact with the bottom waters of the black sea for a long period of time before being draped by a thin layer of sapropel mud wood samples recovered from this same location were very well preserved and yielded dates as old as 3580 yr b p q 2000 elsevier science b v all rights reserved

cenozoic postrift domal uplift of north atlantic margins an asthenospheric diapirism model postrift domal uplifts are a distinct feature of the northern north atlantic rifted margins uplifted regions southern norway finnmark svalbard northern united kingdom occur with a typical spacing of 900 km the amount of domal uplift is substantial 1 2 km thermochronological geomorphological and seismic stratigraphic data suggest a coincident neogene onset of uplift postdating north atlantic breakup and predating onset of glaciation the norwegian domes are characterized by strongly negative gravity anomalies and reduced mantle p wave and s wave velocities previous models for uplift around the north atlantic e g glacial erosion intraplate stresses secondary convection fail to explain the above characteristics we present an asthenospheric diapir model based on a rayleigh taylor instability wherein a hot icelandic asthenosphere layer meets cold cratonic lithosphere the generated asthenospheric diapirs and associated partial melting offer a viable explanation for updoming application of this model to the south norwegian dome succesfully explains most of the currently available data

late cretaceous paleomagnetic results from northeast asian continental margin the sikhote alin mountain range eastern russia welded tuffs in the upper cretaceous kisin group have been collected for paleomagnetic study from 24 sites in sikhote alin eastern russia normal paleomagnetic directions from 11 sites are regarded as primary directions whereas reversed paleomagnetic directions from 13 sites are ascribed to secondary origin the normal directions of the kisin group together with the characteristic directions of the sijanov group yield the late cretaceous characteristic direction of sikhote alin d 355 0 i 59 8 with 95 7 2 a significant separation 15 4 11 9 of pole positions is observed between sikhote alin 85 9 n 11 3 e with a95 10 1 and the north china block sikhote alin has been subjected to counterclockwise rotation through 20 5 17 7 with respect to north china block the rotation occurred during 66 51 ma and is ascribed to sinistral motion along the central sikhote alin fault

episodicity of mesozoic terrane accretion along the pacific margin of gondwana implications for superplume plate interactions a review of evidence for deformation and terrane accretion on the late triassic early jurassic margins of pangea and the mid cretaceous margins of the palaeo pacific ocean shows that deformation was global and synchronous with probable superplume events late triassic early jurassic deformation appears to be concentrated in the period 202 197 ma and was coeval with eruption of the central atlantic magmatic province onset of pangaea break up a period of extended normal magnetic polarity and a major mass extinction event all possible expressions of a superplume event mid cretaceous deformation occurred in two brief periods the first from approximately 116 to 110 ma in the west palaeo pacific and the second from roughly 105 to 99 ma in the east palaeo pacific with both events possibly represented in northeast siberia this deformation was coeval with eruption of major oceanic plateaus core complex formation and rifting of new zealand from gondwana the cretaceous normal polarity epoch and a major radiation of flowering plants and several animal groups all linked with the mid cretaceous superplume event a simple unifying mechanism is presented suggesting that large continental or oceanic plates when impacted by a superplume tend to break up reorganize associated with gravitational spreading away from a broad thermally generated topographic high and with a resulting short lived pulse of plate marginal deformation and terrane accretion

crustal thinning recorded by the shape of the namurian westphalian leucogranite in the variscan belt of the northwest massif central france in the western part of the variscan belt of the french massif central the gueret massif is an extensional allochthon emplaced to the southeast during namurian westphalian time the internal structure of the coeval leucogranites surrounding the western edge of the gueret massif consists of the plateau d9aigurande brame st sylvestre and st goussaud massifs these plutons are asymmetric diapirs rooted in the marche bussiere madeleine and arrenes faults respectively the plutons indicate diverging extravasation from the gueret massif whatever their shapes the plutons have a northwest trending stretching lineation that is also marked in the granite host rocks by retrograde metamorphic minerals the same extension direction is also inferred from namurian westphalian leucogranites and dikes intruding the gueret massif extension related granitoids present typical structural patterns such as asymmetric shapes extravasation from the collapsing area and persistence of a stretching lineation parallel to the regional extension direction these features may be used to diagnose crustal thinning

a latest cretaceous hotspot and the southeasterly tilt of britain the southeasterly regional dip of england and wales is usually ascribed to miocene movements loss of up to 2 km of cover from northern england shown by apatite fission track analysis has been related to uplift and erosion induced by a mantle hotspot but its effects were far more widespread than considered hitherto outcrop patterns throughout much of england wales and eastern ireland can be related to a hotspot beneath the irish sea uplift occurred within the late maastrichtian and erosion continued into the late palaeogene after post oligocene down faulting of the irish sea the modern drainage was initiated on the eroded surface unconformities provide the best means of dating orogenic movements in some localities the time interval between the youngest rocks preserved beneath the unconformity and the oldest preserved above may be small enough to enable the dating of fold movements to be determined with some precision thus in southeastern britain the major e w structures of the hampshire basin the weald and the london basin can be dated as miocene as rocks of oligocene age are involved in the folding in the hampshire basin and pliocene sands rest in erosional pockets of the chalk of se england because fold movements tend to affect large areas of the crust at discrete intervals of time the southeasterly tilt of britain evident from the fact that a nw se transect from anglesey to london crosses outcrops of rocks getting progressively younger from the precambrian of anglesey to the tertiary of the london basin has

the pre cretaceous deep seated tectonics of the abukuma massif and its place in the structural framework of japan abstract the structures and microstructures of the takanuki and hitachi areas in the abukuma massif northeast japan are described in the takanuki area the basic gosaisho series thrusts the pelitic takanuki ones in a hp metamorphic context the nappe structure is afterwards refolded by a migmatitic dome the samegawa dome in a ht metamorphic context microtectonic analysis shows that the nappe was transported from south to north along the stretching lineation geometric features suggest that the samegawa dome was emplaced by diapirism the role of the thrust surface as an instable interface promoting the doming is emphasized the hitachi metamorphic rocks composed of basic schist limestone and sandstone shist thrust the pelitic rocks of the western hitachi gneisses as for the takanuki area the thrusting occurred in ductile synmetamorphic conditions with a north or northeastward displacement owing to lithologic petrologic structural similitudes the nappe of the hitachi metamorphic rocks and that of the gosaisho series are unified into a unique nappe with a northward motion the emplacement occurred between late permian and late cretaceous likely in late jurassic the allochthonous units of the abukuma massif are correlated with the green schist nappe described in southwest japan since they are surrounded by the same zones namely the tanba zone and the kurosegawa kitakami one moreover both in southwest and northeast japan the emplacement of the green schist nappes is due to a shear deformation inducing rotational structures along the stretching lineation indicating the same sense of transport that is eastward in southwest japan and northward in northeast japan owing to the late bending of the japanese islands the late jurassic nappe structure is obliquely overprinted by a ht metamorphism ryoke in southwest japan abukuma in northeast japan and afterwards cut by late faults as the median tectonic line or the tanakura fault giving rise to the present complexity

cenozoic uplift and subsidence in the north atlantic region geological evidence revisited abstract the topographic evolution of the passive margins of the north atlantic during the last 65 myr is the subject of extensive debate due to inherent limitations of the geological geomorphological and geophysical methods used for studies of uplift and subsidence we have compiled a database of sign time and amplitude where possible of topographic changes in the north atlantic region during the cenozoic 65 0 ma our compilation is based on published results from reflection seismic studies aft apatite fission track studies vr vitrinite reflectance trends maximum burial sediment supply studies mass balance calculations and extrapolation of seismic profiles to onshore geomorphological features the integration of about 200 published results reveal a clear pattern of topographic changes in the north atlantic region during the cenozoic 1 the first major phase of cenozoic regional uplift occurred in the late palaeocene early eocene ca 60 50 ma probably related to the break up of the north atlantic between europe and greenland as indicated by the northward propagation of uplift it was preceded by middle palaeocene uplift and over deepening of some basins of the north sea and the surrounding areas 2 a regional increase in subsidence in the offshore marginal areas of norway the northern north sea the northern british isles and west greenland took place in the eocene ca 57 35 ma 3 the oligocene and miocene 35 5 ma were characterized by regional tectonic quiescence with only localised uplift probably related to changes in plate dynamics 4 the second major phase of regional uplift that affected all marginal areas of the north atlantic occurred in the plio pleistocene 5 0 ma its amplitude was enhanced by erosion driven glacio isostatic compensation despite inconclusive evidence this phase is likely to be ongoing at present

an abrupt drowning of the black sea shelf abstract during latest quaternary glaciation the black sea became a giant freshwater lake the surface of this lake drew down to levels more than 100 m below its outlet when the mediterranean rose to the bosporus sill at 7 150 yr bp 1 saltwater poured through this spillway to refill the lake and submerge catastrophically more than 100 000 km2 of its exposed continental shelf the permanent drowning of a vast terrestrial landscape may possibly have accelerated the dispersal of early neolithic foragers and farmers into the interior of europe at that time

holocene litho and biostratigraphy of the nw black sea romanian shelf abstract detailed lithological and micropaleontological studies were performed on several cores from the romanian black sea shelf located in front of the danube delta in front of the razelm sinoe lagoonal complex close to the eforie beach as well as on the romanian inner shelf all the studied cores are situated at a water depth varying between 12 m and 67 m the purpose of the investigations was to reveal upper holocene lithological changes and the associated calcareous nannoplankton fluctuations in a very shallow marine setting such as the romanian black sea inner shelf the youngest holocene unit or shallow unit is composed of alternating sequences of mud silt clay and coquina layers containing marine mollusc faunas the upper part of the shallow unit contains blooms of the nannoplankton species emiliania huxleyi while its lower part yields besides common e huxleyi rare specimens of braarudosphaera bigelowii the shallow unit overlies a shell hash layer mainly made by coquinas containing mixing marine and brackish mollusc faunas towards the upper part of this level monospecific assemblages with b bigelowii were observed in a layer rich in carbonate acicular crystals the shallow unit partly corresponds to the unit 1 finely laminated coccolith ooze and unit 2 sapropelic sediments of slope and basinal settings of the black sea the layer rich in carbonate acicular crystals could be a shallower equivalent of the oldest layer of aragonite bands placed at the lower part of the unit 2 in deep parts of the black sea in the analyzed cores the oldest lithological unit unit 3 the muddy clay sediments deposited in a brackish to freshwater environment is characterized by the deposition of green yellowish clay devoid of any holocene calcareous nannoplankton species and containing brackish mollusc faunas based on nannofloral fluctuations an increasing salinity from the base towards the upper part of the shallow unit may be supposed together with the progressive establishment of a stable marine setting similar to today

organic matter production and preservation and evolution of anoxia in the holocene black sea dating of sediments collected in gravity cores during leg 1 of the 1988 r v knorr expedition to the black sea suggests that the onset of water column anoxia at 7 5 ka was virtually synchronous across the basin over a depth range of 200 2250 m a finely laminated organic carbon oc rich sapropel unit ii was produced as a result of this anoxia the trigger for increased oc production and development of anoxia was the spillover of saline waters through the bosporus that probably began at 9 0 ka and peaked between 7 0 and 5 5 ka this spillover enhanced vertical mixing and nutrient cycling and caused a short term 2 3 kyr burst in surface water productivity during the early part of unit ii deposition continued incursion of saline waters enhanced vertical stability and inhibited mixing of nutrients into surface waters thus limiting primary production and decreasing the oc flux to sediments beginning 5 5 ka concentration accumulation rate and degree of preservation of organic matter all decreased in the upper part of unit ii as a result of decreasing productivity but anoxia persisted throughout most of the water column the end of unit ii sapropel deposition was synchronous across the black sea as the result of the first blooms of the coccolith emiliania huxleyi which presumably marked an increase in surface water salinity above 11 and the beginning of unit i deposition the high coccolith carbonate fluxes that occurred during deposition of unit i diluted the oc concentration in the sediments but oc accumulation rates are about the same as those in upper part of unit ii

apatite fission track data from southeast ireland implications for post variscan burial history the results of a reconnaissance apatite fission track study from southeast ireland are compared with modelled ages and length distributions predicted using both traditional thermal histories and the thermal history indicated by the fission track age and length data all samples have experienced total annealing during the variscan orogeny there is strong evidence for significant post variscan pre mid jurassic heating and cooling the modelling also recognizes a third thermal event subsequent to 100 ma the implications of these results are examined in terms of the timing and extent of subsidence and inversion along the northern margin of the north celtic sea basin

late cenozoic uplift and volcanism on spitsbergen caused by mantle convection regional tectonic uplift heat flow measurements and p t estimates on upper mantle xenoliths associated with neogene volcanic rocks indicate a strongly thinned 50 km thick lithosphere beneath svalbard 650 km north of scandinavia data on neogene volcanic rocks and xenoliths indicate an 50 c temperature anomaly in the underlying asthenosphere together with volatile rich conditions in the upper mantle the svalbard uplift is one of several cenozoic epeirogenic uplifts along the margins of the north atlantic boundary processes occurring where hot spot influenced asthenosphere abuts cold deep continental lithosphere seem to be likely explanations for the uplifts

a new mechanism of granite emplacement intrusion in active extensional shear zones one of the principal ways in which continental crust grows is by the incorporation from deeper within the earth of large volumes of granitic magma a space problem exists1 as to how these magmas are accommodated in the crust traditionally two main emplacement mechanisms have been emphasized forceful intrusion whereby buoyancy driven magmas physically push the crust aside creating granitic diapirs and balloons and passive emplacement characterized by replacive mechanisms such as cauldron subsidence and stoping although more recent work2 3 has demonstrated that space for granites may be created within bends and offsets of large transcurrent faults the simple view of either forceful or passive still fails to account for the intrusive mechanisms of many granites here we report the discovery of a new igneous intrusion mechanism in the superbly exposed proterozoic continental crust of south greenland we have observed that rapakivi granite was intruded as large scale sheets along ductile extensional shear zones that were active during emplacement in such a process the space problem seems to be simply resolved

tectonic evolution of the anuy metamorphic rocks sikhote alin russia and their place in the mesozoic geodynamic framework of east asia abstract in sikhote alin the anuy river provides a representative cross section of the pre eocene structure of the area east of the central sikhote alin fault the mesozoic rocks are divided into the following groups from bottom to top anuy metamorphic rocks the tithonian berriasian samarkinsk accretionary complex early cretaceous zhuravlevsk tumnin turbidite and mid cretaceous al rich khungariisk granitoids the anuy metamorphic rocks have a postfolial ne sw trending antiformal structure from bottom to top they consist of 1 low grade schist and sandstone 2 gneiss and micaschist 3 migmatite and 4 ophiolitic nappe east west trending stretching lineation isoclinal folds and top to the east shear criteria are found in the ophiolite and migmatite units these structures are related to ophiolitic thrusting that likely occurred in early cretaceous times 40 ar 39 ar dating of migmatite and metagabbro indicates mid cretaceous ages about 110 ma close to those of the khungariisk granites the main deformation coeval to a high temperature metamorphism is characterized by ne sw trending stretching lineation with divergent senses of shear 40 ar 39 ar dating of biotite and muscovite from several lithologies give late cretaceous to paleogene ages 73 58 ma this tectono thermal event is related to ne sw trending strike slip faulting along the central sikhote alin fault system the unroofing of the anuy metamorphic rocks is likely related to granite emplacement the collision of the anuy microcontinent with asia can be compared to that of the southern japan microcontinent

uplift and denudation of the central alaska range a case study in the use of apatite fission track thermochronology to determine absolute uplift parameters apatite fission track thermochronology aftt on granitic samples collected in the central alaska range in conjunction with geologic constraints from basins to the north nenana basin and south cook inlet of the range is used to constrain the timing amount rate and pattern of surface uplift rock uplift and denudation since the late miocene the conversion from a thermal frame of reference apatite fission track data to an absolute frame of reference with respect to mean sea level which requires constraining the paleoland surface elevation the paleomean annual temperature and the paleogeothermal gradient is evaluated and shown to be viable in the context of an exhumed apatite partial annealing zone paz apatite ages at denali mount mckinley range from 16 ma near the summit 6 km elevation to 4 ma at 2 km elevation a distinctive break in slope in the apatite age profile at an elevation of 4 5 km also marked by a change in confined track length distributions marks the base of an exhumed apatite paz rock uplift and denudation are greatest at denali decreasing southward away from the mckinley strand of the denali fault system as shown by progressively older apatite ages 7 35 ma from a suite of samples along the kahiltna glacier a correlative decrease in topography occurs southward from the fault the central alaska range lies within an arc defined by the denali fault with the highest peaks including denali concentrated at the arc apex patterns of rock uplift and denudation within the central alaska range mimic topography between early and late miocene and possibly earlier the central alaska range was most likely an area of relative tectonic and thermal stability rock uplift denudation and mean surface uplift of the denali region began by the late miocene 5 6 ma being 8 5 km 5 7 km and 2 8 km respectively at average rates of 1 5 km m y 1 km m y and 0 5 km m y the amount of rock uplift denudation and surface uplift decreases to 3 km 2 km and 1 km at little switzerland some 45 km south of the denali fault we conclude that the topographic and rock uplift patterns of the central alaska range the shape and proximity of the mckinley strand of the denali fault to these patterns the timing of the onset of rock uplift and denudation at 5 6 ma and a significant change in relative plate motion between north america and the pacific plates circa 5 6 ma are all inherently related

meso cenozoic morphotectonic evolution of southern norway neogene domal uplift inferred from apatite fission track thermochronology apatite fission track aft thermochronology of precambrian and paleozoic basement samples from southern norway reveals a post paleozoic exhumation history related to offshore mesozoic and cenozoic extensional basin development the data indicate two major phases of rapid exhumation a first mesozoic phase started in the triassic 220 ma in the east and south of the study area and migrated to the west where jurassic 160 ma ages of exhumation predominate a second event is indicated by thermal history modeling of aft ages and track length distributions it is inferred to be neogene in age initiated at about 30 ma and it produced a domal pattern of aft isochrons which follow present day topographic elevation youngest aft ages 100 ma are encountered at sealevel in the inner fjords near the areas of highest topography ages increase radially outward to the mountain peaks and the coastlines forward modeling of age elevation patterns suggests that mesozoic geothermal gradients were 10 15 c km higher than the present value of 20 c km during the triassic and jurassic a total of 1 3 3 5 km of overburden was removed from the study area assuming a 30 c km geothermal gradient for that period we attribute this to rift margin erosion as a result of erosional base level lowering and flank uplift as evidenced by thick continental clastic sequences deposited in triassic jurassic half grabens in the north sea basins we propose that 1 5 2 5 km of neogene exhumation were a result of late stage domal uplift this is supported by basinward dipping pre neogene strata in the basins surrounding southern norway and the infill of a 1 to 2 km thick neogene sediment wedge containing various internal unconformities domal uplift probably started in the late oligocene may have been amplified in the pliocene and was overprinted by plio pleistocene glacial erosion maximum neogene tectonic uplift is estimated at approximately 1 1 5 km radially decreasing outward to a value 500 m near the shoreline neogene domal uplift is coincident with oligocene and pliocene plate reorganizations in the north atlantic similar neogene domes are found around the norwegian greenland sea i e svalbard and the barents sea northern norway east greenland suggesting a regional tectonic cause the onset of neogene uplift postdates major volcanism and continental breakup by 25 m y and predates plio pleistocene glaciations its origin is possibly a combination of induced mantle convection resulting in thermal erosion of the lithosphere and the operation of intraplate stresses

danube river sediment input and its interaction with the north western black sea abstract the influence of the river danube is determinant to the sedimentation of the north western and western black sea area after 1970 following the building of the iron gates dam the danube river sediment discharge diminished to 30 40 of its previous value after a 12 000 year evolution marked by active progradation the danube delta has become mainly inactive over the last few decades partly due to interventions of man made origin the deficit of sediment influx has led to the intense erosional processes of the deltaic littoral on the black sea north western shelf two main areas with contrasting sedimentary processes have been identified the internal danube sediment fed shelf and the external sediment starved shelf the modern highstand sedimentary history of the north western black sea deep area is marked by the cessation of the danube deep sea fan active development the main depositional units within the north western black sea are described

discriminating geodynamical regimes of tin ore formation using trace element composition of cassiterite the sikhote alin case far eastern russia

the development of irish offshore sedimentary basins a variety of ensialic mesozoic and cenozoic sedimentary basins surround ireland three main periods of basin development occurred the first in the permo triassic produced a series of small rift basins which nucleated along reactivated generally caledonian structures the second in the mid and late jurassic represents a period of crustal extension and rifting the third phase reflects thermal subsidence of cretaceous and tertiary age and coincides with seafloor spreading in the north atlantic the basins developed in response to general east west extension simple extensional structures accompanied by crustal thinning dominated in the north south trending porcupine basin the ne sw oriented basins in the celtic sea slyne erris donegal and rockall areas developed in a transtensional setting until early cretaceous times the goban spur basins at the confluence of regional structural trends and adjacent to the continent ocean boundary are dominated by transtensional structures the effects of early tertiary alpine compression are seen especially in the celtic sea basins the basins whilst having some broad geological similarities which reflect eustatic sea level variations differ in their detailed evolution each basin experienced unique facets of local structural control tectonic history and facies distribution

holocene biostratigraphy and paleoenvironmental changes in the black sea based on calcareous nannoplankton in this study detailed micropaleontological analyses were carried out on 270 samples from eight piston cores collected in the black sea the primary goal was to elucidate the late quaternary evolution of the black sea specifically to refine its biostratigraphy and to explore the holocene paleoenvironmental changes three intervals were recognized in all the cores studied irrespective of whether they were from the basin or the shelf these intervals are characterized from old to young by the spotty occurrence the presence and the local acme of emiliania huxleyi respectively moreover the species braarudosphaera bigelowii is in contrast to the younger units absent in the oldest unit the co occurrence of the two marine species e huxleyi and b bigelowii suggests a shift from fresh brackish water to low salinity marine conditions in the black sea the spotty and very rare occurrence of e huxleyi in the lowermost unit is reported here for the first time two hypotheses are suggested the presence of reworked specimens from eemian outcrops or the presence of low salinity waters also during the lacustrine phase of the basin another feature observed in almost all the cores is the presence of a multi lamina aragonite level in the upper part of the ecozone 3 which functions as a marker for basin wide correlations the parallel study of water samples and surficial sediment assemblages demonstrates the presence of syracosphaera lamina in the surface water samples and its absence in the sediments suggesting dissolution in the water column on the other hand the occurrence of b bigelowii in all cores and its near absence in water and in recent sediment samples suggest a change in water conditions during recent times

elemental and sr nd isotopic geochemistry of cretaceous to early paleogene granites and volcanic rocks in the sikhote alin orogenic belt russian far east implications for the regional tectonic evolution abstract the sikhote alin orogenic belt in russian far east is an important late mesozoic to early cenozoic accretionary orogen related to the subduction of the paleo pacific plate this belt was generated by successive accretion of terranes made of accretionary prisms turbidite basins and island arcs to the continental margin of northeastern asia represented by the bureya jiamusi khanka block from jurassic to late cretaceous in order to study the tectonic and crustal evolution of this orogenic belt we carried out zircon u pb dating and whole rock elemental and sr nd isotopic analyses on granites and volcanic rocks from the primorye region of southern sikhote alin zircon dating revealed three episodes of granitoid emplacement permian early cretaceous and late cretaceous to early paleogene felsic volcanic rocks mainly rhyolite dacite and ignimbrite that overlay all tectonostratigraphic terranes were erupted during 80 57 ma postdating the accretionary process in the sikhote alin belt the cretaceous paleogene magmatism represents the most intense tectonothermal event in the sikhote alin belt whole rock major and trace elemental data show arc like affinity for granitoids and volcanic rocks indicating that they were likely generated in a supra subduction setting their initial 87sr 86sr ratios range from 0 7048 to 0 7114 and end t values vary from 1 7 to 3 8 mostly

structural framework and tectono stratigraphic evolution of the porcupine seabight basin offshore western ireland abstract the porcupine seabight basin is an intra cratonic rift basin which evolved through recurrent episodes of lithospheric stretching structure contour and isopach maps presented here have been constructed following the interpretation of approx 10 000 km of seismic data together with all the available well data this integrated database has allowed the tectono stratigraphic history of the basin to be traced in detail from its earliest inception the basin was initially formed during the carboniferous when up to 3 7 km of autuno carboniferous sediments were deposited on a caledonian and hercynian structured basement late permian and early mesozoic sediments at least 1 km thick are preserved in contiguous grabens and their presence is also inferred within localized sub basins late liassic crustal doming heralded the onset of the final rifting episode and in the north promoted severe erosion and a rapid discharge of clastic sediments rapid subsidence block faulting and magmatism accompanied the deposition of up to 3 5 km of middle upper jurassic sediments in asymmetrical sub basins the transition from stretching to passive subsidence across the jurassic cretaceous boundary in combination with localized inversion abrupt eustatic and environmental changes generated a basin wide unconformity the rift drift transition in the adjacent proto atlantic rift system is recorded in the porcupine seabight basin by voluminous volcanism and a late lower cretaceous unconformity cretaceous sediments are strongly transgressive and up to 6 km thick these were superseded during the early palaeogene by several regressive transgressive cycles before the arrival of an upper slope fauna in the mid middle eocene cenozoic sediments are up to 4 km thick and record the interplay between 1 the location of the basin pn the pyrenean alpine foreland superimposed on the periphery of the icelandic plume and 2 its development as a marginal atlantic shelf region the former is thought to be responsible for eo oligocene faulting subsidence and igneous activity in the north east part of the basin and the latter for unconformities and a change in the style of sedimentation principally due to oceanic circulation changes

characteristics structural styles and tectonic implications of mesozoic cenozoic faults in the eastern heilongjiang basins ne china abstract the eastern heilongjiang basins ehbs are the assemblage of a series of meso cenozoic residual basins located in the northeastern corner of china the deformation pattern of the ehbs has significant implications for the history of the pacific plate subduction beneath the eurasia since the late mesozoic in this paper research on the characteristics and structural styles of the meso cenzoic faults in the ehbs has been conducted on the basis of a comprehensive analysis of field geology drilling data and seismic reflection profiles as a result five different stages of the meso cenozoic faults in the ehbs have been recognized these are in accordance with the time and relevant characteristics of fault movements i e the early stage of the early cretaceous normal fault the early stage of the late cretaceous thrust fault the late stage of the late cretaceous thrust fault the cenozoic synsedimentary normal fault and the late stage cenozoic shear fault a regional geological section has been generated across the ehbs by linking four local seismic profiles together a step by step reconstruction has been made to help better understand the mesozoic cenozoic tectonic evolution of the ehbs two phases of extension rifting in the early cretaceous period and the paleogene respectively are demonstrated to be interfered with two phases of regional uplift compression and erosion in the late cretaceous period the complicated development of multiple fault systems within the ehbs has reflected the evolution of a complex tectonic subduction of the pacific plate beneath the eurasia since the cretaceous period

late permian tectonic evolution at the southeastern margin of the songnen zhangguangcai range massif ne china constraints from geochronology and geochemistry of granitoids abstract this paper reports the la icp ms u pb zircon dating and geochemical data for the huangqigou xiaobeihu and lalagou granitic plutons at the southeastern margin of the songnen zhangguangcai range massif which will not only place important constraints on the rock forming ages source characteristics and tectonic setting of these granitic plutons but will also provide insights into understanding the tectonic evolution of the eastern segment of the central asian orogenic belt zircons from three plutons have distinct oscillatory zoning structures in their cathodoluminescene cl images which combined with the th u ratios of 0 28 1 06 indicate their magmatic origins zircon u pb dating results for these granitic plutons indicate that the granitic magmatism occurred mainly in the late permian 256 252 ma the granites have sio2 of 58 0 74 3 na2o of 2 74 3 76 k2o of 2 75 3 95 na2o k2o of 0 77 1 13 mg 100 mg mg fe2 of 21 8 39 9 and a cnk of 0 88 1 08 with ree patterns characterized by lree hree 7 75 12 82 la yb n 7 88 14 9 and eu 0 56 0 87 the trace element spider diagrams indicate that these granites are enriched in large ion lithosphile elements rb ba th u etc and relatively depleted in high field strength elements ti nb ta with sr and pb ranging from 205 to 350 ppm and from 2 02 to 3 60 ppm respectively the in situ hf isotope analysis reveals that ehf t values range from 2 22 to 11 65 and the two stage hf model ages tdm2 range between 641 and 1274 ma these geochemical characteristics indicate that the late permian granitic plutons at the se margin of the songnen zhangguangcai range massif can be assigned to metaluminous and weakly peraluminous high potassium calc alkaline i type granites with low sr and high yb features and that the magmas to have formed these granites were originated from the partial melting of mafic igneous rocks in the lower crust the source rocks are composed mainly of the juvenile crust with small contributions of ancient continental crust considering the existence of coeval mafic intrusive rocks and sedimentary basins we propose that the late permian magmatism in the study area occurred in a post collisional extensional setting following the collision of the xingkai block and the united jiamusi and songnen zhangguangcai range massifs

terrane assemblage of the leinster massif se ireland during the lower palaeozoic compilation of irish geological survey mapping is used to construct a synthesis of the tectonic evolution of the leinster massif during the lower palaeozoic the massif is interpreted as a series of ne sw trending tectonostratigraphic terranes of diverse origin and provenance brought together along major sinistral transcurrent faults with minor discrepancies the age of these terranes decreases from se to nw the precambrian basement rosslare terrane is succeeded by the early cambrian continental margin cullenstown cahore terrane in the waterford wicklow terrane late cambrian early ordovician accreted ocean floor materials are overlain by a late ordovician volcanic arc the early to mid ordovician accreted ocean floor dublin terrane to the nw is overthrust by the early cambrian continental margin bray terrane and is followed to the nw by the mainly silurian midlands terrane these terranes were juxtaposed after substantial sinistral movement along transcurrent faults during the silurian consolidation of the massif also took place from se to nw stages in the consolidation are marked by the intrusion of the saltees 437 ma carrigmore 415 ma and leinster 404 ma stitching plutons fault movement ceased before the deposition of late devonian and carboniferous sediments on a linking unconformity across the massif

a 100 ma bimodal composite dyke complex in the jiamusi block ne china an indication for lithospheric extension driven by paleo pacific roll back abstract a 125 m wide bimodal composite dyke complex consisting of rhyolite and dolerite dykes was emplaced into cretaceous volcanic strata of the songmuhe formation in the jiamusi block of ne china the dolerite dykes are sub vertical strike north south and intruded into both the country rocks and rhyolite dykes soon after the latter solidified shrimp zircon u pb dating shows that the rhyolite dykes were emplaced at 100 2 ma and the dolerite dykes were also most likely emplaced at 100 2 ma the rhyolite is characterized by enrichment in large ion lithophile elements lile and light rare earth elements lree and depletion in high field strength elements hfse it shows a significant negative eu anomaly and has e nd t values ranging from 0 49 to 1 66 and two groups of initial 87 sr 86 sr ratios at 0 7045 and 0 7061 the rhyolite displays the compositional signature of peraluminous ferroan granitoid indicating it was derived by either differentiation of basalt and or low pressure partial melting of crust the dolerite is also characterized by enrichment in lile and lree and depletion in hfse it has a weak negative eu anomaly and has e nd t 1 22 to 3 26 and 87 sr 86 sr i 0 7057 0 7074 the dolerite originated from partial melting of lithospheric mantle which was affected by subducted oceanic crust and experienced different amounts of crustal contamination such bimodal dyke complexes are an important indicator of crustal extension under the influence of mantle processes thus the dyke complex in the jiamusi block indicates mid cretaceous intra plate extension in ne china related to the subduction of the paleo pacific plate along the eastern eurasian continental margin when compared with mesozoic bimodal magmatism further to the west our new data support a temporal eastward migration of magmatism over a distance 1000 km from 160 ma to 100 ma this was most likely associated with roll back of the paleo pacific plate and consequent upwelling of asthenospheric mantle

geochemistry and u pb zircon dating of the toudaoqiao blueschists in the great xing an range northeast china and tectonic implications abstract the toudaoqiao complex is a sequence of high pressure metamorphic rocks located along the suture zone that separates the xing an and erguna blocks in northeast china the rocks were metamorphosed up to epidote blueschist facies at p t conditions of approximately 0 9 1 1 gpa and 320 450 c lithological associations and major and trace element compositions indicate that the blueschists are metabasalts with ocean island basalt oib and normal mid ocean ridge basalt n morb affinities similar to those of the philippines intraoceanic accretionary complex formed by subduction of oceanic crust magmatic zircons extracted from two samples of the epidote blueschist facies metabasalts from the north mountain in the toudaoqiao complex exhibit 206pb 238u ages of 511 5 and 516 17 ma whereas a greenschist from the south mountain has a 206pb 238u age of 511 2 ma these data show that the protoliths of the toudaoqiao complex are of early paleozoic age in addition a granitic dike from the south mountain exhibits a weighted mean 206pb 238u age of 492 1 ma these ages constrain the timing of high pressure metamorphism in the toudaoqiao complex to 490 510 ma the new data support the view that the suture zone between the xing an and erguna blocks is the toudaoqiao xinlin fault rather than the derbugan fault as previously thought this suture which extends from xinlin through toudaoqiao and southern mongolia named the south mongolia toudaoqiao xinlin suture zone may be an important boundary between the central mongolia erguna and xing an blocks

river incision or diversion in response to bedrock uplift introductionmany researchers have examined the long term behavior of alluvialrivers i e schumm et al 1987 snow and slingerland 1990 paola et al 1992 on long time scales alluvial rivers act as sediment transport systemsthat broadly deposit sediment over low areas in their basins i e tucker andslingerland 1996 the behavior of bedrock rivers is less well understood although most workers agree that bedrock erosion is some function of streampower howard and kerby 1983 seidl and dietrich 1992 howard et al 1994 accordingly researchers addressing a river s response to bedrock up lift equate incision with relatively high stream power and diversion with rela tively low stream power e g burbank et al 1996 however these studiesassume that the erosion rate of the bedrock channel across the mountainrange controls the eventual outcome they have not examined the behavior ofthe alluvial river upstream and downstream of the uplift we propose to lookat the entire erosional and depositional river system and examine the long term response of a coupled alluvial bedrock river system to tectonic uplift our motivation is general and aims at a greater understanding offluvial and tectonic interactions but our model is necessarily both specificand simplified the tectonic uplift of a bedrock massif into the path of a later ally unconstrained alluvial river such a scenario has two possible out comes either the river maintains its original course and incises through theuplift or the river diverts and forms a new course around the uplift a sig nificant complication in the analysis of this scenario is that the evolvingriver system is partial alluvial and partial bedrock channeled because thebehaviors of these two river types are different modeling requires couplingdiverse systems we construct an analytical model to perform a first orderanalysis of this coupled system our objective is to identify the specific fac tors that determine the final outcome of river diversion or incision our model focuses on long time scales 10

carbon accumulation rates and the origin of the holocene sapropel in the black sea a detailed radiocarbon chronology obtained by accelerator mass spectrometry together with organic carbon and carbonate measurements on two black sea cores has been used to compare and contrast the burial fluxes of organic carbon in the holocene sapropel and the modern sediment at both deep water and eastern slope sites the sapropel is separated from the modern facies by a variable thickness of compositionally homogeneous sediment with low levels of organic carbon and anomalously old radiocarbon ages this homogeneous unit probably represents deposition by slumping or mudflow the age limits of the sapropel are 1600 6600 b p at the deep water site and 4000 6000 b p radiocarbon years before 1950 a d at the shallow water site the carbon accumulation rate in the deep water sapropel is higher than that in the modern deep water facies by a factor of 2 and is approximately the same as that in the modern sediment in shallow water the revised chronology of sapropel formation and the differences in the carbon accumulation rates probably indicate that the sapropel was formed by increased production during the transition from the premodern lake to the modern marine phases of the black sea this conclusion is consistent with the clear marine carbon isotope signal in the organic mattermore in the sapropel in both cores results to be reported elsewhere in contrast to the mixed source of carbon in the other facies less

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

response of alluvial rivers to slow active tectonic movement alluvial rivers respond to valley slope deformation caused by active tectonics in various ways depending on the rate and amount of surficial deformation and on the type of river on the basis of experimental results and field examples hypothetical models of river response to anticlinal uplift and synclinal subsidence were developed for different types of alluvial rivers an experimental braided channel responded to anticlinal uplift across the channel with degradation and terrace formation in the central part of the uplift with subsidence aggradation in the central reach was the main response transverse bars developed downstream of the subsidence axis an experimental meandering channel responded to slope steepening with a sinuosity increase bank erosion and point bar growth occurred downstream of the anticlinal axis and upstream of the synclinal axis upstream of the uplift axis and downstream of the subsidence axis where the slope was flattened water flooded over bars local convexity in longitudinal profiles of the middle rio grande new mexico is considered to be formed by a domal uplift local aggradation and degradation could be explained by the effect of uplift the san joaquin river california which is now highly controlled does not show clear adjustment to the rapid subsidence due to ground water withdrawal it shows however a channel pattern adjustment to active tectonic subsidence that has been occurring for a long time the san antonio and guadalupe rivers in texas both increase their sinuosity significantly where monoclinal movements steepen valley slopes

palaeogene alpine tectonics and icelandic plume related magmatism and deformation in northern ireland the cenozoic tectonic history of nw europe is generally attributed to some combination of three principal controlling factors north atlantic opening alpine collision and formation of the icelandic mantle plume using constraints from the high resolution tellus aeromagnetic survey of northern ireland we show that palaeogene tectonics can be attributed to approximately north south alpine related compression forming nnw sse trending dextral and ene wsw trending sinistral conjugate strike slip faults with the latter defined by kilometre scale displacements along reactivated caledonian or carboniferous faults this tectonism was however punctuated by pulsed magmatic intrusive and extrusive events including four distinct dyke swarms that are attributed to ne sw to east west directed plume related extension although this evidence shows for the first time that north south alpine compression was periodically overwhelmed by the dynamic stresses and uplift associated with pulsed mantle plume related deformation associated strike slip faulting may have controlled the locus of volcanic activity and central igneous complexes and the location of sedimentary depocentres

the sikhote alin orogenic belt russian south east terranes and the formation of continental lithosphere based on geological and isotopic data abstract the sikhote alin orogenic belt russian south east consists of folded terranes made up of jurassic and early cretaceous accretionary prisms turbidite basins and island arc terranes that are overlapped unconformably by undeformed upper cenomanian to cenozoic volcanic deposits the jurassic and early cretaceous accretionary prisms together with the early cretaceous island arc are related to subduction of the paleo pacific plate the turbidite basin which began to form at the beginning of the early cretaceous is related to left lateral movement of the paleo pacific plate along the paleo asian continental margin the collage of terranes that make up the sikhote alin orogenic belt was amalgamated in two stages the first began after jurassic subduction beneath the asian continent was terminated and the second took place in the late albian when the early cretaceous island arc collided with the continental margin intense deformation of the terranes took place along the continental margin in the form of large scale translations from south to north together with oroclinal folding the deformation resulted in rapid thickening of sediments in the upper crust resulting in turn in the formation of granitic metamorphic material in the continental lithosphere in the southwestern part of the sikhote alin orogen granites were intruded during the hauterivian aptian while the entire orogenic belt was affected by intrusions in the late albian early cenomanian synorogenic intraplate volcanic rocks and alkaline ultramafic mafic intrusions also testify to the fact that the orogenic processes in the sikhote alin were related to a transform continental margin and not to subduction geochemical and nd isotopic data indicate the primary continental crust of the sikhote alin was of a hybrid nature consisting of juvenile basic components accreted from an oceanic plate and recycled sedimentary material derived from the erosion of ancient blocks

inverse modelling of extension and denudation in the east irish sea and surrounding areas abstract epeirogenic uplift and denudation are difficult to quantify because unlike basin subsidence they do not leave an unambiguous record in recent years much research has been focussed on calculating regional denudation from sonic velocity measurements from vitrinite reflectance profiles and from fission track analyses here we show that inverse modelling of the remnant stratigraphy within extensional sedimentary basins yields estimates of denudation within a corridor which crosses the british isles for a variety of reasons these estimates are minima but they do broadly agree with those determined by inversion of vitrinite reflectance profiles our results also demonstrate that denudation estimates from fission track analyses are meaningful a combined stratigraphic and thermal indicator approach should now be used to map denudation across different continents

radiocarbon dating of danube delta deposits abstract the holocene history of the danube delta has been studied using 14c analyses of faunal material the principal phases of development include 1 initial letea caroarman spit 11 700 9800 yr b p in its central part 8800 5500 yr b p in its southern part 2 sf gheorghe i delta 8900 7200 yr b p 3 sulina delta 7200 2000 yr b p and 4 sf gheorghe ii delta chilia delta 2000 yr b p present other smaller scale features have also been dated including secondary deltas cosna and sinoe deltas and littoral bars age determinations carried out on whole samples were erratic and it was found that individual species had to be separated and dated in all cases the older dates were of transported material whereas the younger dates gave the true age of the formation

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

gravity gradients and upper crustal tectonic fabrics ireland gravity gradients derived from an updated bouguer anomaly map of ireland reveal large scale lineaments many of which can be related to geological structures and tectonic development first horizontal derivatives of the anomaly calculated at various azimuths accentuate linear trends in different directions while the second derivative helps resolve near surface structure the dominant ne sw caledonian trending lineaments are interpreted as due to fault boundaries and folds in pre carboniferous basement and caledonian fault reactivation during the variscan orogeny subsidiary nne ssw trending lineaments are present as well as weaker nw se trending lineaments the largest negative anomalies are produced by late caledonian granites and widespread buried granitic rock in the middle to upper crust is proposed both exposed and inferred granites appear to be spatially related to intersections of ne sw with nne ssw and nw se trending lineaments the orientation of the dominant gravity trend changes from ne sw towards ene wsw going westwards across ireland and forms part of a more regional change in the caledonian gravity fabric recognised throughout the northeast atlantic region variscan e w gravity trends in the south of ireland overlay the caledonian trends relationships between gravity lineaments and anomalies support a thin skinned model for the variscan cover

the transition between the erris and the rockall basins new evidence from wide angle seismic data abstract the rockall trough is a deep water basin west of britain and ireland the origin of the basin and the nature of the crust beneath it is controversial a series of seismic wide angle experiments carried out during 1988 and 1990 help to clarify the crustal and upper mantle structure in the region results for the crustal structure from a profile which straddles the shelf break between the basin and the irish shelf are discussed here these data together with the available geological information indicate that the basin probably formed in the late palaeozoic to early mesozoic as part of a regionally linked basin assemblage which includes the hatton basin and the shallow sea basins surrounding ireland and britain good data quality has allowed the transition between the relatively unstretched crust of the irish and british mainland defined by previous onshore seismic refraction experiments to be well resolved the erris trough one of the small late palaeozoic to early mesozoic basins which fringe the mainland shelf region north of the porcupine basin is a half graben its major bounding fault is located on its western margin and the basin is divided from the rockall trough by a narrow horst the erris ridge the shelf trajectory along the western flank of the horst deepens smoothly towards the trough centre where the crust thins to 5 km near the trough margin below a sedimentary and water column 8 km thick surprisingly the crustal thickness is slightly greater over a 150 km broad zone at the trough centre i e ca 6 km this change in crustal thickness may be due to lateral strain migration to the warmer basin margins as its centre cooled during the deformation the crustal structure beneath the sediment pile at the trough centre is two layered as opposed to the three layered seismic refraction structure found onshore however the basic character of the lower crust present in onshore ireland in particular the presence of a gradient zone defining the crust mantle transition is still preserved in the trough this similarity in structure precludes the presence of magmatic underplating the crustal structure observed in the rockall trough can be formed by differential stretching of the lithosphere in this model the lower ductile crust and mantle lithosphere are stretched over a wide region by 2 2 3 strain focusing into a much narrower region of brittle upper crust generates severe amounts of crustal thinning 1 8 10 and is responsible for the fusing of the upper and mid crustal seismic refraction layers found beneath onshore ireland and britain mediating detachment surfaces sited at the brittle ductile transition at any time served to relay the strain from the lower lithosphere into the upper crust syntectonic heat loss plays an important role in controlling the deformation pattern

upper cretaceous feldspars in the cenozoic limagne basin a key argument in reconstructing the palaeocover of the massif central france abstract the northern part of the n s trending basin of the limagne graben located in the northern part of the massif central france contains oligocene and miocene calcareous lacustrine deposits the area is known for its stromatolite reefs surrounded by marl clay and uncemented carbonate sand with oncolites because the origin of the carbonate accumulated by cyanobacteria has long been debated the clayey deposits associated with the stromatolites were analysed using xrd sem and k ar dating methods the results show a monotonous assemblage of carbonates dioctahedral smectite illite smectite reichweite r 0 glauconitic illite and abundant orthoclase detrital minerals such as quartz and detrital illite are found near the basin s borders but are very scarce in its central part indicating a lack of detrital input from the regional basement hence the abundant orthoclase found in all the clayey deposits of the limagne basin cannot be linked to erosion of the surrounding hercynian basement the sem analysis showed the orthoclase crystals to have a tabular morphology with sharp boundaries and to be embedded within a clay matrix whilst the k ar dating of the orthoclase and glauconitic illite yielded ages ranging from 90 to 66 2 ma i e turonian to maastrichtian these two results clearly indicate that the fill of the limagne basin composed mainly of carbonate clay and orthoclase must have been partly due to the erosion of an upper cretaceous sedimentary blanket once covering the massif central basement this cover was probably constituted of chalk dioctahedral smectite i s and glauconitic illite associated with authigenic orthoclase and flint flints are found reworked in the alluvial formations of the late pliocene lower bourbonnais sands and clays sables et argiles du bourbonnais and in the pleistocene terraces moreover relicts of the upper cretaceous cover were preserved during the sedimentary filling of the cenozoic limagne basin authigenic orthoclase of similar shape has been described in the chalk group of the paris basin and from localities in northern france and belgium the mineral is rare in the turonian chalk but increases rapidly at the base of the coniacian to campanian chalk it has also been noted that the number of orthoclase crystals increases as the quantity of clastic components decreases similar orthoclase crystals were found associated with dioctahedral smectite in the decarbonated residues of the coniacian to santonian chalk from fecamp and etretat northern france moreover our results are consistent with other data from within and around the paris basin such as the palaeogeography and facies distribution of the chalk formations the residual flints in the clay with flints of the southern paris basin and around the morvan and apatite fission track thermochronology data from the hercynian basement of the massif central and the morvan all these data indicate a major connection between the paris basin and the tethys and an extensive palaeocover on the massif central and morvan basement

late cretaceous palaeomagnetic results from sikhote alin far eastern russia tectonic implications for the eastern margin of the mongolia block summary wepresent palaeomagnetic results from late cretaceous welded tuffs in the kisin group monastirskaya suite primorskaya series collected at 27 sites from the sikhote alin mountain range a high unblocking temperature magnetization component 590 c was isolated after stepwise thermal demagnetization from 25 sites combined with previously reported data reliable characteristic remanence directions from 39 sites are distributed at eight areas ranging from 46 7 n 138 1 e to 43 4 n 134 8 e in the sikhote alin block the bedding tilt test is positive for two area mean directions and inconclusive for the remaining six areas the data set for all 39 sites reveals a positive bedding tilt test at the 99 per cent confidence level and their tilt corrected mean direction is d 335 6 i 54 4 95 8 5 corresponding to a palaeopole at 71 5 n 38 9 e with a95 9 9 this westerly direction is ascertained through the tilt corrected mean direction d 331 1 i 53 5 95 8 5 based on the 25 data selected from four areas kema river terney plastun and moryak rybolov where each data set passes the positive bedding tilt test or reveals an increase in the precision parameter after tilt correction palaeomagnetic declination indicates that the sikhote alin block has rotated counterclockwise by 41 16 with respect to the eurasian continent between late cretaceous times and 53 50 ma compared with palaeomagnetic data from the surrounding regions we find that the rotation recorded in sikhote alin extends westward into the interior of the mongolia block the eastern margin of the asian continent experienced both counterclockwise rotation of the eastern part of the mongolia block and clockwise rotation of the eastern part of the north china block over the cretaceous we interpret these data in terms of a strong net horizontal force towards the ocean side acting on the lithosphere at the eastern margin of the asian continent between the late cretaceous and 53 50 ma intermittently occurring upwellings of mantle and associated horizontal flows may have played an important role in producing the net horizontal force acting on the continental block during late cretaceous times

inversion and exhumation of the st george s channel basin offshore wales uk the western uk basins of the irish sea have provided one of the best natural laboratories for investigating the causes and consequences of intracratonic uplift and erosion exhumation to date the emphasis has been on igneous underplating as the chief process driving their exhumation in this paper we demonstrate that tectonic inversion the shortening of formerly extensional basins and reactivation of their constituent faults dominated the exhumation of the st george9s channel basin offshore wales based on mapping of an extensive 2d seismic grid evidence is presented for at least two major inversion episodes in the late cretaceous and the neogene plus minor shortening during the eocene inversion was distinctly noncoaxial especially during the neogene when coeval transpression and transtension was focused at discrete bends and stepovers on the basin bounding st george9s bala and northwest flank faults that the principal mechanism driving these uplift episodes was inversion as opposed to igneous underplating is corroborated by analysis of thermal history data apatite fission track and vitrinite reflectance they reveal late cretaceous and neogene geothermal gradients that were comparable with that at the present day i e no significant increase in basal heat flow sonic velocity profiles logged in hydrocarbon boreholes constrain the minimum thickness of the eroded section which varies between c 1000 m in the centre and c 2240 m at the margins of the basin given the strength of evidence for tectonic inversion in the st george9s channel basin our favoured model invokes superimposition of the effects of inversion and igneous underplating to account for the complex exhumation history of the st george9s channel basin in particular and the western uk basins in general

mesozoic strike slip movement of the dunhua mishan fault zone in ne china a response to oceanic plate subduction abstract the ne striking dunhua mishan fault zone dmfz is one of two branches of the continental scale sinistral tan lu fault zone in ne china the field data presented here indicate that the ca 1000 km long dmfz records two phases of sinistral faulting the structures produced by these two phases of faulting include ne sw striking ductile shear belts and brittle faults respectively mylonite hosted microstructures and quartz c axis fabrics suggest deformation temperatures of 450 c 500 c for the ductile shear belts combining new zircon u pb dates for 14 igneous rock samples analyzed during this study with the geology of this region indicates these shear belts formed during the earliest early cretaceous this phase of sinistral displacement represents the initial formation of the dmfz in response to the northward propagation of the tan lu fault zone into ne china a phase of early cretaceous rifting was followed by a second phase of sinistral faulting at 102 96 ma as evidenced by our new u pb ages for associated igneous rocks combining our new data with the results of previous research indicates that the dfmz records a four stage cretaceous evolutionary history where initial sinistral faulting at the beginning of the early cretaceous gave way to rifting during the rest of the early cretaceous this was followed by a second phase of sinistral faulting at the beginning of the late cretaceous and a second phase of local rifting during the rest of the late cretaceous the cretaceous evolution of the dmfz records the synchronous tectonic evolution of the ne china continent bordering the pacific ocean two phases of regional n s compression generated the two phases of sinistral faulting within the dmfz whereas two stage regional extension generated the two phases of rifting the two compressive events were the result of the rapid low angle subduction of the izanagi and pacific plates whereas the two stage extension was caused by the roll back of these respective plates the final closure of the mongol okhotsk ocean at the beginning of the early cretaceous intensified the synchronous compression in ne china causing the northward propagation of the tan lu fault zone

extensional shearing deformation and kilometer scale a type folds in a cordilleran metamorphic core complex raft river mountains northwestern utah cordilleran metamorphic core complexes are characterized by ductile mylonitic deformation and regional stretching lineations in the raft river mountains a mylonitic zone and a late superimposed detachment fault separate precambrian crystalline and metasedi mentary basement rocks from an upper plate made of allochthonous paleozoic rocks which suffered a brittle extensive deformation we suggest that the mylonitic ductile deformation is the result of tertiary extensional tectonics strain analysis shows that 1 strain results from large scale progressive shearing deformation in a non coaxial regime 2 e w regional stretching lineations represent the direction of shearing and transport 3 shear criteria indicate an east directed movement 4 strain magnitude is increasing eastward 5 kilometer scale folds parallel to the lineations are interpreted as a type folds formed by eastward shearing of a previously northward dipping layering measurement of striated faults in the upper plate gives an e w direction of extension parallel to the lineations thus ductile and brittle deformations are closely related to the same regional scale extensional tectonics a model is proposed to explain the observed geometry and kinematics of the structures the mesozoic to paleocene cordilleran compressional tectonics induced an overthickening of the crust in the hinterland belt at the future emplacement of the complexes important uplift abnormal heating and granite emplacement occurred later during the collapse of the former belt the combined effects of thermal and gravitational instabilities during tertiary extensional tectonics enabled the development of a ductile shear zone localized at the precambrian basement paleozoic cover interface the brittle extension of the upper crust is displaced laterally along this flat shear zone and transformed farther east into the extended regions of the middle and lower crust

geochemical characteristics and petrogenesis of adakites in the sikhote alin area russian far east abstract adakitic rocks of the sikhote alin area were emplaced during two main periods the cretaceous 132 98 ma and eocene 46 39 ma these rocks primarily occur in the khanka block and less commonly in the sikhote alin orogenic belt the adakitic rocks record the following chemical compositions sio2 57 74 al2o3 15 18 na2o 3 5 6 1 k2o 0 7 3 2 na2o k2o 1 1 3 9 sr y 33 145 and la yb n 11 53 the hree and hfse in these rocks are remarkably depleted the early cretaceous adakites record end t 1 0 to 3 2 and isr 0 7040 0 7090 and the eocene adakitic rocks record nd t 2 0 to 2 2 and isr 0 7042 0 7058 adakitic features suggest different modes of magma generation a comparison of the sr y and la yb ratios and geochemical data on harker diagrams between the two periods of adakitic rocks reveals differences in their petrogenesis the cretaceous adakites may have been generated by the partial melting of meta basic rocks in a subduction zone accompanied by the emplacement of volcanic arc granitoids therefore the subduction of the paleo pacific plate beneath the sikhote alin was probably initiated during this time the eocene rocks which record increasing adakitic features with increasing silica content are most likely the product of andesite that underwent fractionation of mineral assemblage including clinopyoxene orthopyroxene garnet and amphibole these rocks and associated basalts and rhyolite were formed after cretaceous arc magmatism in the sikhote alin area and were most likely generated by rollback of the subducting pacific plate after the eocene abundant adakitic granitoids of early cretaceous and eocene age occur in the kitakami and abukuma mountains of ne japan consequently it is highly probable that a geological correlation existed between sikhote alin and north japan particularly before the opening of the japan sea

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

main fault systems of the soviet far east the analysis of the distribution of thrusts normal faults and strike slip faults of various ages has allowed us to determine the character of lithospheric block displacements in the soviet far east the early mesozoic late mesozoic and cainozoic kinematics were each essentially different the early mesozoic dzhagdinsk fault system appeared as a result of the collision of the bureinsk khankaisk microcontinent with the siberian continent the largest faults of the system are neither longstanding nor deep but were formed during the latest stage of the structural evolution the multistage formation of the faults of the dzhagdinsk system is conditioned by its position at the margin of the continent the late mesozoic faults are mainly strike slip faults caused by the subduction of the oceanic crust at an acute angle with respect to the strike of the active continental margin the cainozoic faults were formed under compression on the boundary between the siberian platform and the bureinsk massif but under tension in the east of the region

seismic evidence of divergent rifting and subsequent deformation in the southern japan sea and a cenozoic tectonic synthesis of the eastern eurasian margin abstract neogene rift system configuration for the back arc of southwest japan southern rim of the japan sea is argued on the basis of reflection seismic interpretation divergent rifting and subsequent contraction provoked by an arc arc collisional event are manifested by the formation of faulted grabens and their inverted deformation respectively we identified the following four cenozoic tectonic epochs as a decomposition process of the eastern eurasian margin based on reliable paleomagnetic data 1 plate margin rearrangement on a regional left lateral fault through southwest japan and sikhote alin which constituted a continuous geologic province before the early tertiary differential motion 2 early tertiary clockwise rotation 20 of the east tan lu block relative to the north china block 3 oligocene to early miocene divergent rifting and spreading of the japan sea which divided southwest japan from the east tan lu block 4 middle miocene bending and back arc inversion of southwest japan caused by collision with the izu bonin arc according to the estimation of relative motions during these events a paleogeographic reconstruction is presented through cenozoic time

tectonic setting of western pacific marginal basins abstract global kinematics as well as magnetic anomalies of marginal basins with continental geology and paleomagnetic data as additional constraints are used to present a set of reconstructions of the western pacific marginal basins between 56 ma and the present at key periods 56 43 32 20 12 and 3 ma our model accounts for the rapid motion of exotic terranes along the whole of the western pacific convergent zone marginal basins appear to open in a great variety of tectonic settings the two extreme examples being the mariana trough where trench suction may be the predominant driving force and the south china sea where intracontinental deformation appears to be the major mechanism the study of marginal basins is a 3 d problem which must take into account the whole tectonic context subduction related tectonics in cross section and upper plate deformation in map view and not only a 2 d problem the classical trench arc back arc problem

the miocene bending of southwest japan new 39ar 40ar and microtectonic constraints from the nagasaki schists western kyushu an extension of the sanbagawa high pressure belt abstract in the westernmost part of kyushu the nagasaki metamorphics also observed in amakusa consist of oceanic sediments and fragments of ophiolite these rocks underwent a high pressure metamorphism followed by an increase in temperature up to the upper greenschist facies prior to the late cretaceous microtectonic and kinematic analyses indicate a synmetamorphic ductile shear from south to north dating of glaucophane phengite and biotite by 39ar 40ar method suggests that the peak of metamorphism and the related deformation occurred approximately 90 95 ma ago i e cenomanian but a resetting by an oligo miocene tectonic event is also evidenced due to discontinuous exposures the metamorphic rocks of kyushu cannot be continuously traced to the metamorphic belts of honshu and shikoku nonetheless the lithostratigraphy metamorphic environment radiometric data and deformation style strongly support a correlation of the nagasaki metamorphics with the green schist nappe of southwest japan which underwent the late jurassic early cretaceous high pressure sanbagawa metamorphism such a correlation implies that 1 in the amakusa area the nagasaki metamorphics form a window north of a meta olistostrome that belongs to the tanba ryoke zone 2 the trend discrepancy of the stretching lineations between west kyushu and southwest japan is in agreement with a clockwise rotation of the latter with respect to the former assumed to be fixed to eurasia such a bending occurred after paleogene times probably during the opening of the sea of japan

internal deformation of sikhote alin volcanic belt far eastern russia paleocene paleomagnetic results abstract we present paleomagnetic results of paleocene welded tuffs of the 53 50 ma bogopol group from the northern region 46 n 137 e of the sikhote alin volcanic belt characteristic paleomagnetic directions with high unblocking temperature components above 560 c were isolated from all the sites a tilt corrected mean paleomagnetic direction from the northern region is d 345 8 i 49 9 95 14 6 n 9 the reliability of the magnetization is ascertained through the presence of normal and reversed polarities the mean paleomagnetic direction from the northern region of the sikhote alin volcanic belt reflects a counterclockwise rotation of 29 from the paleocene mean paleomagnetic direction expected from its southern region the counterclockwise rotation of 25 is suggested from the paleomagnetic data of the kisin group that underlies the bogopol group these results establish that internal tectonic deformation occurred within the sikhote alin volcanic belt over the past 50 ma the northern region from 44 6 to 46 0 n in the sikhote alin volcanic belt was subjected to counterclockwise rotational motion through 29 17 with respect to the southern region the tectonic rotation of the northern region is ascribable to relative motion between the zhuravlevka terrane and the olginsk taukhinsk terranes that compose the basements of the sikhote alin volcanic belt

evidence for post early eocene tectonic activity in southeastern ireland the role played by cenozoic deformation in denudation and landscape development in ireland has historically been difficult to assess because of the lack of widespread pre glacial cenozoic deposits onshore here we combine analysis of apatite fission track data and geomorphic observations to place constraints on the timing kinematics and magnitude of onshore deformation in southeastern ireland relationships between apatite fission track central age and elevation for samples from the wicklow and blackstairs mountains and tullow lowland suggest that these rocks record an exhumed apatite partial annealing zone which after cooling was dismembered by differential vertical displacements of up to several hundred metres we use inverted models of sample thermal history to show that samples across the region experienced very similar thermal histories up to and including a cooling event in late paleocene or early eocene time this effectively rules out strongly spatially heterogeneous denudation and implies that differential rock uplift occurred in post early eocene time the central age elevation relationships define at least three spatial domains with internally consistent apatite fission track data separated by known faults or topographic escarpments geomorphic analysis of these structures shows that patterns of catchment incision and sinuosity as well as the presence of antecedent drainage are best explained by differential vertical displacements at or near the domain boundaries the kinematics and magnitudes of these displacements are consistent with those implied by the apatite fission track results and are compatible with other examples of known cenozoic deformation from ireland and the adjacent continental margin

evolution of the sakhalin fold system abstract the island of sakhalin is subdivided into two late cretaceous isopic zones the miogeosynclinal western zone and the eugeosynclinal eastern zone the boundary between these zones is marked by a band of greenschists and blueschists melange and olistostrome a thick triassic lower cretaceous formation composed of siliceous volcanogenic deposits with lenses of limestones and interlayers of tuff aleurolites clay shales and siliceous argillaceous shales occurs at the base of a miogeosynclinal upper cretaceous section the upper cretaceous deposits of this zone have a cyclic structure and are represented by terrigenous marine near shore and continental formations the paleogene neogene deposits occur on the upper cretaceous ones with a sharp erosion a lithological complex composing the eastern sakhalin eugeosynclinal zone is represented by alternations of deep water sandy aleurolite clay shale formations including olistostromal horizons with siliceous volcanogenic formations the eugeosynclinal regime remained the same up to the late cretaceous the paleogene neogene deposits occur on the cretaceous ones with a sharp structural unconformity the ophiolite blueschist belt of central sakhalin is compared with the kamuikotan belt in hokkaido the belts of granitoid magmatism and calc alkaline volcanism are nearly parallel to the cretaceous and senonian early paleogene ophiolite blueschist belts of sakhalin an eastward migration of these belts to the pacific is observed the formation stage of the mezosoic deep thrusts effecting distribution of the ophiolitic belts has been changed by the formation stage of the cenozoic wrench fault zones

pre eocene synmetamorphic structure in the mindoro romblon palawan area west philippines and implications for the history of southeast asia the structure of the pre eocene rocks considered as the basement of the philippines has been investigated in the mindoro lubang romblon tablas sibuyan and north palawan areas in the former two areas the same pre eocene succession of units is recognized from top to bottom 1 a pre eocene olistostrome 2 an ophiolitic nappe 3 a schistose sequence pelites sandstones basic schists and marbles and 4 a gneissic unit the nature of the contact between the olistostrome and the underlying units is unclear but the ophiolite and the schistose sequence form two thrust sheets of oceanic origin thrust upon the gneissic unit that is considered a part of a continental basement called the west philippines block small scale structures show that the early deformation stage is characterized by a submeridian 0 n40 e lineation formed in greenschist to amphibolite facies conditions during the thrusting kinematic analysis show that the thrusting was from north to south in north palawan metamorphic rocks with similar microtectonic and kinematic characteristics are found they are overlain by a late jurassic olistostrome which is correlated with the olistostromes found in calamian north mindoro carabao and buruanga peninsula north panay the microstructural features and the presence of the olistostrome suggest that the north palawan mindoro tablas romblon sibuyan and carabao islands belong to the same north palawan block of hamilton 1979 which is a continental fragment rifted from asia in cenozoic times it is assumed that the western panay and zamboanga areas which are characterized by mesozoic ophiolites and metamorphic rocks also belong to the north palawan block all these islands experienced to some extent the same mesozoic geohistory the south verging thrusting is interpreted as the result of an oblique collision of the west philippines block with asia the contemporaneous left lateral strike slip faulting and the calc alkaline magmatism widespread along the chinese margin are also included in the geodynamic model

late glacial to holocene benthic foraminifera in the marmara sea implications for black sea mediterranean sea connections following the last deglaciation benthic foraminifera were studied from four gravity cores that penetrated holocene marine sediments in the marmara sea morphogroup and assemblage analyses reveal that the holocene sea level rise did not result in a catastrophic flooding event as proposed by w b f ryan and others whereby well oxygenated saline mediterranean waters rapidly inundated a low lying low salinity black sea lake at v7 15 ka popularly known as the noah s flood hypothesis rather the benthic foraminiferal data confirm the hypothesis that the dardanelles sill was breached by the mediterranean at v12 ka allowing saline waters to penetrate the marmara sea these saline waters reached the level of the bosphorus sill at v9 5 ka but were unable to penetrate into the black sea until after v9 1 ka because of the persistent strong outflow of brackish to fresh water from the black sea the initial colonisation of the marmara sea by benthic foraminifera is essentially synchronous with the re establishment of marine connections through the dardanelles strait at v12 ka by v10 ka ammonia dominated faunas developed on the strait exit delta v1 at the southern end of the bosphorus and at v9 1 ka the appearance of fully marine species documents the establishment of a more stratified water column over v1 finally the increase in abundance of planktonic foraminifera at the southern exit of the bosphorus after v6 1 ka reflects a decreased volume of outflow water from the black sea quantitative analysis of benthic foraminiferal morphogroups reveals that the oxygen content of subhalocline water was low below v1 5 ml l throughout the holocene and the occurrence of sapropel sediment in the deeper part of the basin suggests bottom waters may have been anoxic at times after v4 5 ka an increase in benthic foraminiferal oxic morphotypes suggests a reduction in black sea outflow and weakening of the halocline the strong and persistent stratification of the water column in the marmara sea throughout the holocene is entirely incompatible with the noah s flood hypothesis 2002 elsevier science b v all rights reserved

mid to late cenozoic sedimentation on the continental margin off nw britain the present morphological expression of the continental margin off nw britain is a mid to late cenozoic phenomenon initiated by a major phase of rapid subsidence in the rockall trough and hatton rockall basin during the early late eocene this led to a deepening of the basins and the onset of bottom current activity in this region on seismic reflection profiles this basin subsidence event is manifest in the form of a widespread deep water unconformity caused by bottom current erosion this boundary is particularly enhanced at the basin margins and adjacent to the axial seamounts of rosemary bank and anton dohrn where the downwarped and eroded surface of lower upper eocene and older strata is onlapped by middle to upper cenozoic sediments the latter comprise two megasequences of late eocene to mid miocene and mid miocene to holocene age which consist predominantly of deep marine contourites both in the rockall trough and the hatton rockall basin although a clastic wedge has built out along the hebridean shelf margin since the mid miocene these megasequences reflect a gross two stage depositional history a response to intra plate tectonism which modified sedimentation patterns and palaeoceanographic circulation the development of the bounding unconformities early late eocene and mid miocene was coincident with major phases of regional tectonism

timing of deformation and location of the eastern liaoyuan terrane ne china constraints on the final closure time of the paleo asian ocean abstract the liaoyuan terrane lt in ne china formed as a result of accretion during the final closure of the paleo asian ocean between the north china and siberian cratons however the timing of the deformation and the location of the eastern lt remain controversial here we present structural data zircon u pb age dating and hf isotopic data to constrain the kinematics and timing of deformation and the southern boundary of the eastern lt in relation to the ne sw striking yilan yitong fault yyf one of two branches of the continental scale tan lu fault zone in ne china pre jurassic rocks in the eastern lt were widely involved in ductile deformation within wnw ese striking thrust belts the microstructures in these shear zones indicate a top to the ssw sense of shear and deformation temperatures of 450 500 c the northern margin of the north china craton ncc was also affected by the nne ssw contraction as shown by similar ductile deformation in the archean gneisses and wnw ese trending folds in the mesoproterozoic sedimentary cover the ages of crystallization in deformed and undeformed igneous rocks in the lt constrain the deformation to an interval between 241 and 193 ma u pb dating of zircons in syn kinematic migmatitic rocks indicates an age of 234 229 ma for the deformation we consider this middle triassic age to represent the final closure time of the paleo asian ocean along the eastern lt and this timing is consistent with the eastwards scissor style closure model lithological variations zircon age spectra ehf t values and model ages confirm the eastward extension of the lt across the yyf the data constrain the boundary between the lt and ncc to be roughly along the liao river to the west of the yyf and along the northern edge of the exposed archean gneisses to the east the boundary follows the bayan obo chifeng kaiyuan fault which was active as a thrust thrusting of material to the ssw during the middle triassic orogeny the newly determined boundary location indicates a 35 km sinistral displacement along the yyf

paleomagnetic evidence for post early cretaceous tectonic rotation of the sikhote alin superterrane far east russia abstract we present new early cretaceous paleomagnetic results from the zhuravlevka amur terrane of the eurasian continent far east russia out of 34 total sites 14 were collected from komsomolsk on amur area 50 6 n 137 2 e and 20 from vaninsky area 49 1 n 139 2 e thermal demagnetization reveals the presence of two interpretable magnetization components in 19 sites with laboratory unblocking temperatures of 350 c and or 500 580 c the remanent directions of the low temperature component are either parallel or anti parallel to those obtained from the high temperature component results of fold tests show that both components are secondary rock magnetic and reflected light microscopic observations indicate a chemical origin for both of these components as evident from the presence of secondary pyrrhotite and magnetite the komsomolsk on amur area provides an in situ formation mean direction of d 127 5 i 66 7 k 28 2 95 9 3 n 10 sites when combined with the reported paleomagnetic data from early to middle cretaceous accretionary wedge rocks of the kiselevka manoma terrane and the early cretaceous western sakhalin turbidite basin rocks d 94 2 and d 57 1 respectively large magnitude of clockwise rotations of 66 118 is demonstrated for the eastern part of the sikhote alin superterrane with respect to eurasia in addition these three landmasses maintained their e w elongated orientations before the start of rotation implying southward directed subduction of the oceanic plates beneath northern margins these reconstructions of the sikhote alin superterrane provide clues on the tectonic evolution of panthalassa ocean