development and demise of a fringing coral reef during holocene environmental change eastern ningaloo reef western australia abstract reefs lining the western exmouth gulf located at the northern limit of the 300 km long ningaloo reef in western australia represent modern incipient coral reefs and veneers of non reef building coral algal communities on exposed pleistocene or give up holocene reef surfaces acquisition of sixteen cores alongside u series tims dates were used to confirm the nature of the pleistocene foundation and characterise holocene reef development three calcretised pleistocene units were identified as 1 the last interglacial mis 5e reef directly underlying holocene units 2 a mid pleistocene mis 7 bioclastic conglomerate unit and 3 a pleistocene alluvial fanglomerate eight holocene reef facies total thickness of 1 8 5 3 m included coral framework facies domal arborescent mixed tabulate and encrusting and detrital facies carbonate sand skeletal rubble and alluvial fan deposits holocene ages range from 7 93 to 5 8 ka bp with vertical accretion ranging from 1 46 to 9 88 mm year avg 4 11 mm year highest rates of accretion and thickest accumulation occurred in the most seaward and deepest cores composed of massive coral framestone and coralline algal crusts a six stage holocene chronology is proposed including 1 coastal inundation from 8 to 8 5 ka bp 2 initiation start up from 8 to 7 5 ka bp 3 rapid growth catch up and back step from 7 5 to 7 ka bp 4 rapid aggradational growth catch up from 7 to 6 5 ka bp 5 reef decline give up and detrital buildup from 6 5 to 5 8 ka bp and 6 detrital buildup and progradation from 5 8 ka bp to present changes in reef facies and the ultimate demise of the holocene reef probably involved a combination of increased sea level coastal flooding and erosion during the mid holocene highstand with associated increase in sedimentation turbidity and decline in water quality burial by sediment buildup during the mid holocene highstand and detrital progradation during the mid to late holocene regression and the introduction of alluvial sediment during cyclones and other severe storms to an already stressed community modern communities have thus shifted from coral dominated to bored macroalgal pavements this study shows that integration of reef development processes with response to environmental change can be used to assess future pressures on coral reef ecosystems globally

facies outcrop gamma ray and c o isotopic signature of exposed miocene subtropical continental shelf carbonates north west cape western australia abstract exposed uplifted miocene carbonate sequences of the cape range north west cape western australia provide outcrop analogues of seismic sequences from offshore parts of the shelf facies include deep shelf marls very fine and fine packstone larger foram wackestone floatstone and muddy rudstone foram coralline algal skeletal fragment packstone wackestone shallow seagrass facies lagoonal wackestone mudstone with scattered corals and tidal flat laminites the exposed early miocene units include the mandu highstand a sequence in the tulki and one in the middle miocene trealla limestone sequences contain decameter scale 5 20 m thick 4th order parasequences evident on gamma ray logs and by facies stacking that shallow and coarsen up they appear to be due to eccentricity driven sea level changes which may have been up to 50 m higher frequency meter scale parasequences of deep water marl up into larger foram rudstone floatstone perhaps precession obliquity are evident at the base of the exposed mandu section these parasequences are not merely random storm deposits this is indicated by the covariance of c and o isotopes with the lighter values associated with deepening and deposition of deep shelf marls and the heavier values being associated with shallowing and deposition of larger foram facies the uplifted miocene continental shelf sediments of the north west cape preserve a record of eustasy paleoclimate and paleoceanography and thus provide a window into factors affecting the shelf that can be compared with coeval better studied deep sea cores

genesis of streamlined landforms and flow history of the green bay lobe wisconsin usa abstract the distribution of streamlined landforms in southeastern wisconsin suggests that drumlins and flutes formed during several phases of the green bay lobe between 18 and 14 000 bp the largest group of drumlins formed during a still stand of the ice margin during the johnstown phase presumably about 18 16 000 bp flutes and smaller drumlins are superimposed on larger forms and larger drumlins are remolded this indicates that drumlin modification continued during retreat three fields containing smaller drumlins formed after ice re advanced a short distance or stabilized during the green lake rush lake and st anna phases about 16 14 000 bp the drumlin forming process included erosion and deformation of pre existing ice marginal and proglacial sediments drumlins associated with the johnstown phase show an increase in length up glacier this is probably the result of variations in flow velocity length of time of drumlin formation and sediment availability flutes and small drumlins are associated with retreat moraines and formed near a thin retreating ice margin ice surface profile reconstructions suggest that margins were relatively steep during the johnstown milton green lake and early rush lake phases during the lake mills and late rush lake phases when flutes were forming the ice surface slopes were lower and margins were retreating during retreat minor sublobes developed some perhaps resulting from surges into small proglacial lake basins thus steep ice margins and driving stresses on the order of 15 25 kpa were typical during drumlin formation the formation of flutes and the remolding of larger drumlins into smaller forms took place beneath gently sloping ice of retreating margins associated with lower driving stresses

pre 1 87 ga development of crustal domains overprinted by 1 87 ga transpression in the palaeoproterozoic skellefte district sweden the complex structural evolution within the vms hosting skellefte district sweden has been investigated to provide a solid structural framework for the known mineral deposits in the area the are

high resolution mapping of ice marginal landforms in the barnim region northeast germany abstract despite more than a 100 year long research history timing and position of the last glacial ice margins in the northeast german lowland are still up for debate the barnim region a till plain in the northeast german young morainic landscape is traversed by the contradictorily discussed frankfurt ice marginal position it is located in a key position to reassess the current state of research with help of a geographic information system gis and field methods a qualitative geomorphological analysis of a high resolution lidar digital elevation model dem in the barnim area uncovers a variety of landforms that were previously not described the most prominent discovery is a set of about 10 lobe shaped ridges in the middle barnim area fieldwork and geophysical measurements were carried out to investigate the structure of the ridges the ridges are 1000 1500 m in length and their widths vary from 10 to 15 km they are raised some 6 10 m from their surroundings the frankfurt ice marginal position can only partially be traced in the dem sedimentological and geophysical investigations indicate that the ridges are composed of glacial till that was deposited on glaciofluvial sediments their formation most probably took place during the ice retreat of the brandenburg phase w 1b and hence represents the w 1f phase in the region

detrital zircon ages from early proterozoic quartzites wisconsin support rapid weathering and deposition of mature quartz arenites abstract the ages of more than 200 detrital zircons from two proterozoic quartzites the baraboo and hamilton mounds quartzites from central wisconsin have been measured utilizing a laser ablation icpms technique both quartzites contain penokean 1 83 1 89 ga and archean components as well as a younger post penokean component the 69 detrital zircons from hamilton mounds contain major pre penokean age populations at 3 2 2 9 and 2 55 ga penokean ages at 1895 1853 and 1811 ma and a post penokean population at 1772 ma most detrital zircon ages are similar to previously measured ages of locally underlying gneisses and intrusive rocks of the marshfield terrane the 147 detrital zircons from two samples of the baraboo quartzite show a grossly similar age distribution with populations at 1754 and 1850 ma and 2 55 ga however the zircon populations in the baraboo quartzite differ from those of hamilton mounds in having a large population at 1920 ma a broad distribution of ages from 2 0 to 2 4 ga a

the bergslagen ore province sweden review and update of an accreted orocline 1 9 1 8 ga bp abstract we have revisited and re interpreted deformation structures in the classical ore province of west bergslagen part of the 1 9 1 8 ga old svecofennian orogen in south central sweden four successive phases and styles of deformation reflect 1 continental rifting associated with bimodal magmatism in continental back arc basins d1 2 closure of the rift s by upright tight to isoclinal folds on any scale d2 3 renewed rifting d3 with deposition of argillites conglomerates and submarine basalts in restricted rift basins and 4 intense buckling and folding of west bergslagen along variably but generally steeply plunging folds d4 strain localization during d4 initiated a network of conjugate retrogressive shear zones and closely related large scale vertical drag folds with the southwest northeast striking west bergslagen boundary zone system acting as the main tectonic boundary along which west bergslagen slipped relative to the central part of the province d4 transpression and variably oblique d4 shear may have caused the preservation of a low grade domain in west bergslagen as well as the exhumation of a granulite facies domain near the hinge of the orocline d4 structures include a regional scale oroclinal bend of 135 in southwest bergslagen connecting common southwest northeast strikes in west bergslagen to east west strikes to the south and east in central bergslagen the oroclinal bend tightens to 180 to the south it lines up with another orocline the two forming an s shaped pair of large scale buckle folds the orocline finds expression in the regional patterns of form lines and magnetic anomalies and in the spatial distribution of specific intrusive rock suites the northern structural boundary of the province is known as an east west striking zone of dip slip movement and local wrenching which we also interpret as a d4 effect the d4 structures imply the evolution of a separate ribbon like bergslagen micro continent at least 700 km long rifted from the former active continental margin during the d3 event and finally accreted slightly obliquely to pre existing fennoscandia to the present north by correlating d4 deformation structures with the areal distribution and previously determined radiometric ages of late orogenic anatectic granites we derive a provisional estimate 1 83 1 82 ga as the lower age limit to the initiation of terrane accretion d4 accretion is svecofennian orogeny proper in this part of the belt younger than the currently preferred estimate of 1 86 ga west bergslagen s synsedimentary hydrothermal ore deposits originating from 1 91 to 1 89 ga old volcanism and rifting have been remobilized to various extent during the late orogenic d4 phase and show pronounced concentration along d4 shear zones

migratory tectonic switching western svecofennian orogen central sweden constraints from u pb zircon and titanite geochronology abstract the forsmark area in the western part of the svecofennian orogen central sweden is situated between two major palaeoproterozoic tectonic domains that show contrasting histories with respect to timing of igneous activity ductile deformation and metamorphism geological features common to both the adjacent domains are found at forsmark which consequently is a key area for understanding the tectonic evolution of the svecofennian orogen in this region new sims and tims geochronological data from several samples in a limited area at forsmark constrain the timing of igneous activity ductile deformation and metamorphism in this area u pb zircon dating in combination with field studies reveals the existence of two calk alkaline igneous suites at forsmark the older and most voluminous plutonic suite intruded at 1 89 1 87 ga and is affected by penetrative yet variably intense ductile deformation with the development of a ductile grain shape fabric under amphibolite facies metamorphic conditions and folding the younger and less voluminous hypabyssal suite intruded at 1 86 1 85 ga during the waning stages of this penetrative deformational phase furthermore u pb titanite dating shows that the area has been affected by one or more tectonothermal events after regional fabric development and possibly even after 1 83 ga the deformation during these events involved more restricted strain along discrete zones the forsmark data in combination with a compilation and evaluation of available geochronological data from the time interval 1 91 1 84 ga in central sweden points to the existence of at least two major tectonic cycles in this region each cycle is characterised by igneous activity associated at least partly with extension a short interval of compressional deformation and migration of the tectonic activity in this paper we discuss two highly contrasting tectonic models that may explain the cyclic tectonic evolution of the western part of the svecofennian orogen in central sweden the favoured model involves continuous subduction with a constant polarity beneath a single active continental margin combined with alternating subduction hinge retreat and advance the model involves migration of what has been described as tectonic switching in the younger accretionary orogenic systems of eastern australia palaeozoic lachlan orogen and new zealand

sediments and history of the rottnest shelf southwest australia a swell dominated non tropical carbonate margin abstract the rottnest shelf is a narrow wave dominated open shelf on the passive continental margin of southwest australia adjacent to a hinterland of low relief and sluggish drainage high physical energy low nutrients in cool subtropical waters and rapid postglacial transgression have limited carbonate productivity restricted grain types and reworked the transgressed surface to form only a thin given sufficient time the rottnest shelf could recover from drowning and form blanket like skeletal carbonates thin

biotite and muscovite 40ar 39ar geochronological constraints on the post svecofennian tectonothermal evolution forsmark site central sweden in order to characterize the post svecofennian tectonothermal evolution of the fennoscandian shield 40ar 39ar biotite and some 40ar 39ar muscovite geochronological data are reported from a total of 30 surface outcrop and 1000 m long borehole samples at forsmark central sweden the thirteen surface samples were collected across three branches of a major wnw to nw trending system of deformation zones whereas the boreholes were drilled within a tectonic lens in between two of these zones the 40ar 39ar biotite ages indicate that the present erosion surface in central sweden cooled below 300 c at 1 73 1 66 ga and that the rocks could respond to stress by brittle deformation between 1 8 and 1 7 ga the variation in surface ages is suggested to be due to faulting along the large wnw to nw trending deformation zones following the establishment of a sub cambrian peneplain the minor variation of ages within a single crustal block may be due to disturbance along ene to nne trending fracture zones possible cooling paths derived from 40ar 39ar hornblende muscovite and biotite ages were calculated for the time interval from 1 80 to 1 66 ga when the area cooled from 500 c to 300 c between 1 70 and 1 64 ga uplift rates of c 22 m m y were calculated from borehole 40ar 39ar biotite data tectonothermal histories inferred from the combined cooling and uplift rates are related to simple slow cooling after the svecofennian orogeny to crustal movement in response to far field effects of c 1 7 ga orogenic activity further to the west or to a combination of these possibilities less

the vaasa migmatitic complex svecofennian orogen finland buildup of a lp ht dome during nuna assembly tectonic evolution of the paleoproterozoic vaasa migmatitic complex vmc in the central part of the svecofennian accretionary orogen is deciphered using aeromagnetic and gravity maps deep seismic

palaeoproterozoic accretionary processes in fennoscandia abstract accretionary processes contributed to major continental growth in fennoscandia during the palaeoproterozoic mainly from 2 1 to 1 8 ga the composite svecofennian orogen covers c 1 10 6 km 2 and comprises the lapland savo fennia svecobaltic and nordic orogens it is a collage of 2 1 2 0 ga microcontinents and 2 02 1 82 ga island arcs attached to the archaean karelian craton between 1 92 and 1 79 ga andean type vertical magmatic additions especially at c 1 89 and c 1 8 ga were also important in the continental growth the palaeoproterozoic crust is the end product of accretionary growth continental collision and orogenic collapse preserved accretional sections are found in areas where docking of rigid blocks has prevented further shortening the pirkanmaa belt represents a composite accretionary prism and other preserved palaeosubduction zones are identified in the gulf of bothnia and the baltic sea areas in the southern segment of the lapland savo orogen collision between the archaean continent lower plate and the palaeoproterozoic arc microcontinent assembly upper plate produced a special type of lateral crustal growth the archaean continental edge decoupled from its mantle during initial collision and overrode the arc and its mantle during continued collision

migmatization related to mafic underplating and intra or back arc spreading above a subduction boundary in a 2 0 1 8 ga accretionary orogen sweden abstract absolute ages of migmatization and protolith formation and constraints on the timing of ductile deformation in two major lithotectonic units in the south western part of a 2 0 1 8 ga orogenic belt in the fennoscandian shield south eastern sweden have been determined using u pb ion probe analysis of different generations of zircon in veined gneisses and leucocratic granite detrital and xenocrystic zircon in paragneiss and garnet bearing leucogranite respectively in the bergslagen lithotectonic unit show ages of 2 1 2 0 ga and 1 9 ga deposition of the sedimentary material occurred during or after a subduction related magmatic event at 1 91 1 87 ga two orthogneiss protoliths formed during this magmatic event around 1 88 ga while most zircon in the leucosome in a third migmatitic orthogneiss was inherited from a 1 85 ga igneous protolith a polyphase tectonothermal evolution with anatexis under low p metamorphic conditions around 1 86 ga m1 and 1 84 1 81 ga m2 is inferred for the migmatitic gneisses in the bergslagen unit garnet bearing leucogranite crystallised around 1 84 1 83 ga close in time to major folding of the m1 gneissic fabric a previously unrecognised 1 86 1 85 ga ductile deformational event under medium grade metamorphic conditions has been identified in the adjacent lithotectonic unit to the south smaland lithotectonic unit close in time to the m1 event in the bergslagen unit to the north by constraining the timing of anatexis and comparing with information bearing on crustal thickness excess mass at depth and the character and age of magmatic activity it is inferred that anatexis in the bergslagen lithotectonic unit is related to pulses of mafic underplating during the early stages of two separate subduction related magmatic episodes after the 1 91 1 87 ga magmatic event it is suggested that each pulse was related to intra or back arc spreading above a subduction boundary which had entered a retreating mode with separate long periods 20 50 ma of extension or transtension this study challenges the need to invoke crustal thickening related to plate collision at 1 9 1 8 ga as a mechanism to explain high grade metamorphism in the southern part of the 2 0 1 8 ga orogen instead a solely accretionary tectonic model involving an overriding plate along an active continental margin with significant extensional or transtensional crustal deformation is preferred

oligocene eustasy from two dimensional sequence stratigraphic backstripping estimates of the magnitudes of changes in third order 0 522 m y eustasy were obtained for oligocene sequences defined by a suite of largely onshore boreholes of the new jersey coastal plain benthic foraminiferal biofacies and multiple age constraints in a sequence stratigraphic framework formed the database for this study the geometry of the margin through time was determined using two dimensional backstripping the depth ranges of benthic foraminiferal biofacies were determined from a combination of standard factor analysis techniques and the backstripped geometries benthic foraminiferal biofacies were then used to determine the depths of the oligocene margin profiles obtained from backstripping the water depths of 16 of these horizons were confirmed by independent benthic biofacies determinations from at least two wells this internal consistency indicates that the data and the twodimensional backstripping approach were robust where benthic biofacies require a vertical shift of the horizons generated by two dimensional backstripping eustatic changes were required and were readily calculated results indicate a major eustatic fall from the end of the eocene to the first record of oligocene deposition subsequent long term shoaling of sea level through the oligocene was 30 m in 10 m y superimposed on this long term trend were higher frequency third order variations in eustasy with amplitudes of 40 m or less

subtropical carbonates in a temperate realm modern sediments on the southwest australian shelf the southwestern continental margin of australia 19 degrees s 22 degrees s in the western indian ocean is transitional between cool water and warm water carbonate realms it comprises the incipiently rimmed flat topped steep fronted rottnest shelf in the south the uniform subtropical starved carnarvon ramp off shark bay and the ningaloo fringing reef in the north the margin is strongly influenced by the poleward flowing warm nutrient poor leeuwin current which promotes overall downwelling and strong summer equatorward blowing winds which generate local seasonal upwelling the structurally quiescent northern part of the rottnest shelf with minimum accommodation is characterized by luxuriant stands of sea grasses and macrophytes growing on coralline encrusted hardgrounds and rooted in sediments rich in coralline algae and larger symbiont bearing foraminifers together with abundant cool water elements such as bryozoans molluscs and small foraminifers halimeda is poorly calcified and does not contribute to the sediment azooxanthellate corals although present are not common such a sediment pattern has many analogs in the geologic record especially the early cenozoic the incipient rim is a morphologically complex linear ridge system interpreted to be a buried mid pleistocene barrier reef or beach dune complex the northern part of the ridge complex is capped by the houtman abrolhos reef platforms subphotic sediments on the deep outer shelf and upper slope affected by seasonal upwelling are typical cool water poorly sorted bryozoan dominated deposits rich in small foraminifers and sponge spicules the inner part of the more structurally active carnarvon ramp ranges from steep eolianite cliffs to hypersaline environments of shark bay to the ningaloo fringing reef mid ramp sediment especially off shark bay is mostly relict or stranded and foraminifer dominated sand with abundant mg calcite cemented intraclasts these sediments accumulating on a relatively barren seafloor likely represent attenuated carbonate production brought about by downwelling and episodic incursions of saline shark bay derived waters onto the ramp the outer ramp is either planktic foraminiferal sand sorted by strong bottom currents or spiculitic mud such sedimentation patterns should typify the western margins of large ocean basins during those periods in geologic history when circumglobal equatorial circulation was active and equatorial gateways narrow in contrast to eras of supercontinents when cool water carbonate sedimentation and upwelling prevailed in similar settings furthermore because low latitude trade winds relax during glacial epochs and the cool water upwelling belt moves equatorward into otherwise tropical realms temperate and subtropical sedimentation patterns in these regions should oscillate at the 100 ky scale in the stratigraphic record

two dimensional simulations of surface deformation caused by slab detachment detachment of the deeper part of subducted lithosphere causes changes in a subduction zone system which may be observed on the earth s surface constraints on the expected magnitudes of these surface effects can aid in the interpretation of geological observations near convergent plate margins where detachment is expected in this study we quantify surface deformation caused by detachment of subducted lithosphere we determine the range of displacement magnitudes which can be associated with slab detachment using numerical models the lithospheric plates in our models have an effective elastic thickness which provides an upper bound for rapid processes like slab detachment to the surface deformation of lithosphere with a more realistic rheology the surface topography which develops during subduction is compared with the topography shortly after detachment is imposed subduction with a non migrating trench system followed by detachment leads to a maximum surface uplift of 2 6 km while this may be higher for the case of roll back preceding detachment in the latter situation the back arc basin may experience a phase of compression after detachment within the context of our elastic model the surface uplift resulting from slab detachment is sensitive to the depth of detachment a change in friction on the subduction fault during detachment and viscous stresses generated by sinking of the detached part of the slab overall surface uplift of these magnitudes is not diagnostic of slab detachment since variations during ongoing subduction may result in similar vertical surface displacements d 2002 elsevier science b v all rights reserved

natural uranium in forsmark sweden the solid phase u bearing solid phases from forsmark sweden a proposed host for radioactive waste repositories havebeen identified and characterized elevated dissolved u was found in some groundwater samples d

origin of ree mineralization in the bastnas type fe ree cu mo bi au deposits bergslagen sweden the bastnas type deposits with mineral assemblages of fe oxides ca mg silicates rare earth element ree silicates ree fluorocarbonates and cu fe mo bi sulfides are associated with marble horizons in a strongly na k and or mg altered metavolcanic succession over a distance of at least 80 km in a sw ne trending zone in western bergslagen two subtypes occur 1 enriched relative to the other type in light ree lree and fe exemplified by the bastnas and rodbergsgruvan deposits and 2 enriched in heavy ree hree y mg ca and f represented by deposits in the norberg district bastnasite hosts primary fluid h2o co2 inclusions with salinities of 6 29 eq wt cacl2 and with total homogenization temperatures th tot of ca 300 400 c subtype 2 has late stage fluorite with fluid inclusions that show 1 16 eq wt nacl and th tot of ca 90 150 c molybdenite re os ages obtained from three deposits are 1 904 6 1 863 4 and 1 842 4 ma nd isotopic data from five different ree minerals yielded no defined isochron but a range in end 1 88 ga of 0 2 to 1 6 the oxygen isotope values 18osmow of dolomite and calcite from the associated ree mineralized skarn and recrystallized carbonate assemblages lie in the range 6 1 8 6 overlapping with those of the host marbles carbon isotope values 13cpdb show typical magmatic signatures of 6 7 to 4 4 while the host marbles group around ca 2 4 the sulfur isotope 34scdt values of associated sulfides range between 10 8 and 0 2 the combined evidence suggests ree mineralization beginning at 1 9 ga from mainly svecofennian juvenile magmatic 400 c fluids carrying si f cl s co2 and the ree in addition to other metals mineralization occurred through reactions with dolomitic layers in the supracrustal units coevally with regional metasomatic alteration associated with fluid circulation through an extensive active volcano plutonic complex

evidence for 1 82 ga transpressive shearing in a 1 85 ga granitoid in central sweden implications for the regional evolution abstract two crustal scale shear zone systems the storsjon edsbyn deformation zone and the hassela shear zone join in the western part of central sweden and form an anastomosing pattern of ductile shear zones several of these up to 1 km wide zones truncate an intrusion previously defined as a component of the major ca 1 80 1 77 ga magmatic suite the revsund granitoids in north central sweden however within the southern part of the intrusion titanites that are components of the fabric in a pervasively deformed shear zone forsaan have a u pb tims age of 1816 2 ma zircon porphyroclasts in the same fabric yield a u pb sims age of 1849 14 ma overlapping with the u pb tims age of 1851 2 ma for titanites from an undeformed granitoid these results are interpreted to define the ages of ductile shearing and magma emplacement respectively this interpretation is supported by microstructures as well as the regional structural pattern characterised by shear zones enveloping virtually undeformed pods of the granitoid previously reported and locally existing magmatic flow structures indicate some syn emplacement deformation the kinematic results characterised by a high proportion of pure shear within the granitoid and oblique dextral shearing along its margin reflect strain partitioning under transpressive conditions the kinematic and geochronological results fit into the regional framework of late orogenic localised deformation along crustal scale shear zones recent absolute datings of shear fabrics defines ca 1 82 1 80 ga as a period of shear zone activity in central sweden temporally this period overlaps with the emplacement of s type granites and granitoids derived from deeper crustal levels a similar situation exists in southern finland structural geochronological and geophysical data suggest that the crustal scale shear zones in central sweden and southern finland may be related temporally and spatially the age and the post tectonic nature on a regional scale of the dated 1 85 ga granitoid have important regional implications as both the age of the intrusion and the ductile shearing are older than the established age range 1 80 1 77 ga of the revsund granitoids either an extended intrusive history for the suite is indicated or the granitoids in this part of the type areas should be excluded from the revsund suite their post tectonic nature implies that the pervasive svecokarelian deformation in the area occurred earlier than generally assumed 1 85 1 80 ga on the other hand approximately coeval calc alkaline granitoids to the south east of the investigated area are folded and foliated pervasively indicating a later svecokarelian evolution in that area i e that the granitoids are located in domains with separate orogenic evolutions

brittle tectonic evolution and paleostress field reconstruction in the southwestern part of the fennoscandian shield forsmark sweden 1 six hundred fault slip data have provided robust paleostress fields within an approximately 35 km3 volume of paleoproterozoic 1 9 ga rocks in the southwestern fennoscandian shield forsmark sweden these rocks were affected by penetrative ductile strain from 1 87 to 1 86 ga folding ductile strain along discrete zones around 1 8 ga and semibrittle or brittle deformation around and after 1 8 ga compatible paleostress fields have been identified using site by site and merged data sets from outcrops and oriented drill cores transpressive deformation with a regional nnw sse 1 axis associated with clockwise stress deviation inside a tectonic lens resulted in dextral slip along regionally significant steep wnw ese and nw se deformation zones the semibrittle and most of the brittle structures including specifically the epidote bearing fractures were established during this oldest regime around 1 8 ga latest svecokarelian a younger paleostress field with a ne sw 1 axis which was also transpressive in character is inferred to have been active at 1 7 1 6 ga the best defined paleostress field is transpressive in character with a wnw ese 1 axis that resulted in sinistral reactivation along the wnw ese and nw se zones the main set of laumontite stepped faults developed at this stage at 1 1 0 9 ga sveconorwegian it is impossible to exclude fully the influence of reactivation during even younger phanerozoic tectonic events subordinate extensional paleostress fields were related either to the latest svecokarelian and sveconorwegian transpressive regimes due to 1 and 2 stress permutations or to regional extensional tectonic regimes during the meso or neoproterozoic or later during the permo carboniferous and or mesozoic

penetrative ductile deformation and amphibolite facies metamorphism prior to 1851 ma in the western part of the svecofennian orogen fennoscandian shield the svecofennian orogen in the fennosandian shield consists of several palaeoproterozoic meta igneous provinces that generally young progressively southwards and westwards the understanding of the tectonic evolution of these different provinces is linked to the ability to constrain the timing of ductile deformation and metamorphism within them in the western part of the orogen in central sweden ductile deformation and metamorphism is conventionally thought to have occurred after 1 85 ga and mainly around 1 82 1 80 ga at forsmark in central sweden we have dated two undeformed granite dykes that cross cut the tectonic fabric in their host rocks to 1851 15 and 1855 6 ma respectively since the former shows an unequivocal field relationship with respect to the tectonic fabric we establish that penetrative ductile deformation under amphibolite facies metamorphic conditions occurred prior to 1851 5 ma this u pb zircon minimum age for the timing of ductile deformation is supported by a u pb titanite age of 1844 4 ma these data as well as the field relationships at forsmark indicate that an early phase of penetrative deformation and metamorphism affected the svecofennian bedrock in the western part of the fennoscandian shield and was overprinted after 1851 5 ma by spatially more confined deformational events in conjunction with earlier results our data help to establish the presence of tectonic domains with contrasting tectonothermal histories in the western part of the svecofennian orogen c 2006 elsevier b v all rights reserved less

the accretionary svecofennian orogen insight from the babel profiles abstract the babel profiles b c 1 7 form a 1200 km long nearly continuous cross section through the svecofennides the near vertical marine reflection profiles display a wide range of crustal structures that can be associated with both the accretionary svecofennian orogeny 1 96 1 75 ga and the following subjotnian and jotnian rift stages 1 65 1 11 ga the svecofennian accretionary orogeny took place when a number of micro plates with island arc affinities and surface expression of a large archipelago accreted to the continental karelian plate some of the accreting terranes seem to have had older cores that have acted as crustal indentors during the collision babel profiles 3 and 4 image a series of collisional terrane boundaries between karelian continental margin savo arc sa and central finland arc cfa in the north the karelian margin has been both over and underthrust by the savo arc cfa comprises a folded thrust package on top of a continental nucleus and the savo arc the associated subduction zone and accretionary prism are interpreted to lie to the south underneath the bothnian basin area where prominent ne dipping lower to middle crustal reflections are found along babel profiles 1 and 4 an oblique collision of the central finland arc and the continent resulted in the development of the strike slip fault on the young hot savo arc babel profiles 1 6 7 and c image the internal architecture of the southern and central finland arcs the unusually thick crust 55 60 km hosts unreflective high density mafic intrusions acting as a crustal indentor a highly reflective antiform structure developed on the southern side of it southern finland arc complex sfa is an imbrication structure comprising stacked slices of arc related crust on an older continental nucleus bergslagen nucleus prior to the collision the sfa suffered from gravitational collapse during which the crust was thinned profile b images the architecture of the central and southern swedish svecofennides the sormland terrane sob is interpreted as the accretionary prism of the southern finland arc squeezed between the svecofennian collage in the north and the advancing continent to the south the southern continent island arc is characterised by ne dipping crustal reflections and moho offsets as well as step wise increasing thickness of the crust after the final collision large volumes of mantle derived material intruded the crust as large mushroom shaped plutons they are interpreted as the heat source for the tib magmatism in southern and western scandinavia

influence of the subducting plate velocity on the geometry of the slab and migration of the subduction hinge abstract geological observations indicate that along two active continental margins east asia and mediterranean major phases of overriding plate extension resulting from subduction hinge retreat occurred synchronously with a reduction in subducting plate velocity in this paper results of fluid dynamical experiments are presented to test the influence of the velocity of the subducting plate on the hinge migration velocity and on the geometry of the slab results show that hinge retreat decreases with increasing subducting plate velocity in addition phases of hinge retreat alternate with phases of hinge advance for relatively high subducting plate velocities due to interaction of the slab with the bottom of the box simulating the upper lower mantle discontinuity such slab kinematics could explain the episodic behaviour of back arc opening observed in convergent settings the geometry of the slab and the kinematics of subduction are significantly affected by the velocity of the subducting plate three subduction modes with accompanying slab geometry can be recognized a relatively low subducting plate velocity is accompanied by relatively fast hinge retreat with backward sinking of the slab and a backward draping slab geometry with increasing subducting plate velocity hinge migration is relatively small resulting in subvertical sinking of the slab and a folded slab piling geometry for a very high velocity the hinge migrates forward resulting in forward oriented subduction vectors and a forward draping slab geometry

glacial geomorphic study of the thajwas glacier valley kashmir himalayas india abstract glacial geomorphic studies provide vital information to make inferences about the effect of glacial advance and retreat on the geomorphology of an area in the present study glacial geomorphic landforms of the thajwas glacial valley in the upper reaches of the indus kashmir himalayas were mapped using geospatial technology validated with gps based field observations and ground photography the glacial geomorphic landforms were digitized using aster dem 30 m resolution landsat etm satellite imagery 30 m resolution and google earth 1 m resolution data results showed that google earth imagery supported by field validation is very useful for the interpretation of glacial geomorphic landscapes and relief features at micro and meso scales however morphometric characteristics of landforms are best obtained using dem overlaid onto the landsat etm satellite data glaciers in the valley are presently confined along the south and southwestern slopes however the significant role played by glaciers in shaping the geomorphic landforms and their subsequent preservation within the scenic landscape under the late quaternary climatic conditions are remarkably evident the glacial geomorphic landforms especially terminal moraine glacial trough and cirques observed in the valley aided the reconstruction of palaeo glacial setting of the area morphology shape and location of terminal and lateral moraine ridges were used to establish the palaeo glacial extents glacial volume and the number of glacial advances of the thajwas glacier the maximum elevation of the lateral moraines was used to define the former equilibrium line altitude ela the greater rock excavation to form a large valley during the last glacial maximum might have induced isostatic rock uplift exhumation in the glacier source area it is observed that the concomitant retreat of the north facing glacial cirques has played an important role in expanding the glacial valley and limiting the topographic relief

middle and upper miocene cyclostratigraphy of downhole logs and short to long term astronomical cycles in carbonate production of the great bahama bank abstract ocean drilling program site 1006 is located in the santaren channel off the western slope of the great bahama bank downhole logs of sediment physical and chemical properties from hole 1006a contain repetitive alternations cycles which using the nannofossil and planktic foraminifer biostratigraphy as a guide to the sedimentation rate we show to be paced by the earth s climatic precession the formation microscanner resistivity image log shows a high resolution record of the sedimentary cycles and we use it to measure cycle thicknesses the record of cycle thickness contains long term cycles that repeat about every 400 kyr which we correlate to the 400 kyr cycles in orbital eccentricity this broad scale tuning results in an age profile for the core that is largely consistent with previously astronomically tuned biostratigraphic dates it has previously been established that the bahama bank produces and exports carbonate preferentially during sea level highstands each highstand produces one sedimentary cycle hence we infer that sea level also fluctuates with a mainly precessional periodicity although obliquity is also found in the log records we attribute the 400 kyr period in cycle thickness to eccentricity modulation of the amplitude of sea level fluctuations a high amplitude sea level rise will cause more carbonate to be generated and deposited than a low amplitude sea level rise

widespread seagrass meadows during the early miocene burdigalian in southwestern australia paralleled modern seagrass distributions abstract the trealla limestone which forms a veneer of foraminiferal rich limestone and covers over 4000 km2 of the tectonically stable southern carnarvon platform contains the oldest evidence for seagrass meadows known in western australia it belongs to lower tf1 letter stage based on larger benthic foraminifers of the burdigalian within interval 19 16 ma and is the only miocene unit on the platform the trealla limestone here is coeval to the deeper water lower part of the much thicker trealla limestone in the exmouth sub basin to the northwest a seagrass meadow depositional environment is indicated by most of the studied microfacies based on comparisons with modern sediment composition and foraminiferal assemblages found in innermost shelf seagrass banks between 23 s and 32 s on the present western australian coast some levels in the trealla limestone on the platform e g with abundant miliolid foraminifers and absence of coral debris probably were deposited in and around dense seagrass meadows similar to those present today in the metahaline 40 55 ppt salinity reaches of shark bay whereas other levels e g coral floatstone were deposited under normal marine conditions based on comparisons with modern carbonate sediment and biota in the region the biogenic composition of the trealla limestone on the platform suggests winter minimum sea surface temperatures within the range of 17 22 c the nullabor limestone in the eucla basin at 10 further south on the southern australian margin is similar at least in part in composition and age to the trealla limestone on the southern carnarvon platform both may have been deposited during a burdigalian sea level rise and during part of the miocene climate optimum recognized elsewhere sediment composition and foraminiferal assemblages including epiphytic types found in the trealla and nullabor limestones are similar to those in the modern seagrass banks of the region this suggests that seagrasses similar to the extensive posidonia and amphibolus stands which are dominant today between 25 s and 35 s along the western australian coast were widespread during the burdigalian

the svecofennian orogen a tectonic model abstract recent geological studies have provided new concepts concerning the timing of the final break up of the archaean craton age data on detrital zircons from sedimentary rocks in sweden and finland show marked similarities and indicate pervasive homogenization of accumulated material geochemical and isotopic studies in sweden and finland suggest the existence of two volcanic belts separated by an area dominated by sedimentary rocks however the ages of metamorphism and plutonism differ in particular the late post 1 85 ga granitoid magmatism was more voluminous in sweden than in finland the svecofennian crust in finland is anomalously thick up to 65 km and is characterized by a high velocity lower crust of variable thickness the evolution of the svecofennian orogen is modelled by opening of the pre svecofennian ocean at 1 95 ga and progressive accretion of two arc complexes to the archaean craton between 1 91 1 87 ga initial accretion at 1 91 ga led to thrusting of the slices of an island arc complex and proterozoic marine strata onto the thickening craton margin subduction reversal with simultaneous anti clockwise rotation of the converging plate or convergence of another plate resulted in subduction below the newly accreted arc complex the tectonic style at the craton margin changed from thrusting to lateral displacement in the east in finland in the west in sweden the subduction zone retreated along a transform fault a large sedimentary basin closed in the east 1 89 ga ago when another arc complex collided against the accreted one collision resulted in lithospheric thickening subsequent delamination of the thickened lithosphere and compensation by a hot mantle underplate and large scale granitoid magmatism as a result of mixing between mantle magma and remelted arc complex material the thick dense layer that formed in the lower crust as the result of underplating kept the thickened crust in isostatic balance thus the exhumation rate in this area was similar to the rate in areas of thinner crust subduction and sediment accumulation continued in the west until at least 1 87 ga when large areas in the east were already stabilized an intracratonic transpressional zone developed as the result of continued convergence subsequent extensional collapse along the transpressional zone caused melting of svecofennian sedimentary rocks migmatization and generation of the 1 84 1 82 ga anatectic granites of southern finland and central sweden the voluminous post 1 85 ga granitoid magmatism in sweden is tentatively associated with an east west extension that is not related to the extensional collapse

brittle tectonothermal evolution in the forsmark area central fennoscandian shield recorded by paragenesis orientation and 40ar 39ar geochronology of fracture minerals in this paper we show how studies of fracture mineral paragenesis their orientation and ar 40 ar 39 geochronology can be applied in order to recognise the brittle tectonothermal evolution in an area samples were selected from nearly 18 km of drill cores from the upper i km of the fennoscandian shield obtained during the site investigation for a repository of spent nuclear fuel in forsmark central sweden four major events of fracturing and or reactivation of fractures associated with fracture mineralisation have been distinguished the first event was characterised by precipitation of epidote quartz and chlorite along preferably sub horizontal and gently dipping fractures or steep wnw ese to nw se fractures precipitation occurred between 1 8 and 1 1 ga possibly during the late stage of the svecokarelian orogeny close to 1 8 1 7 ga the second event is associated with precipitation of hematite stained adularia and albite prehnite laumontite calcite and chlorite preferably along steep ene wsw to nne ssw and nnw sse fractures precipitation occurred around 1107 7 to 1034 3 ma probably due to effects from the sveconorwegian orogeny this event was followed by a period with dissolution of fracture minerals and subsequent precipitation of mainly calcite quartz pyrite and asphaltite during the palaeozoic the formation fluid emanated from an overlying organic rich sedimentary cover precipitation occurred during reactivation of proterozoic fractures but formation of new fractures is also inferred possibly due to far field effects of the caledonian orogeny or elevated hydrostatic pressure due to its foreland basin the latest event is dominated by clay minerals chlorite and calcite along hydraulically conductive fractures these minerals are prominent along sub horizontal and gently dipping fractures but also occur in sets of steeply dipping fractures it is inferred that the hydraulically conductive fractures are proterozoic structures in which mineral precipitation has occurred during a long period however some of the near surface sub horizontal fractures may be quaternary in age c 2009 elsevier b v all rights reserved less

albitization and quartz dissolution in paleoproterozoic metagranite central sweden implications for the disposal of spent nuclear fuel in a deep geological repository hydrothermal alteration resulting in albitization and quartz dissolution has been identified in paleoproterozoic metagranites down to 1000 m elevation at forsmark sweden the alteration features were discovered during investigations to locate a site for the disposal of spent nuclear fuel in a deep geological repository in general albitization occurs extensively but it is also observed locally adjacent to minor intrusive bodies of amphibolite the altered rocks show a marked decrease in k feldspar and an increase in quartz relative to the unaltered equivalents resulting in an epitonalitic composition plagioclase is metamorphic in character and generally richer in albite than in the unaltered rocks it is inferred that albitization was triggered by the input of basic or intermediate melts into the crust during igneous activity close to the peak of regional metamorphism at 1 87 1 86 ga the mineralogy of the epitonalites gives rise to an increased thermal conductivity and thereby a positive influence for the design and safety of a deep geological repository for spent nuclear fuel however the increased frequency of low conductive amphibolite in the albitized volumes consistent with the proposed mechanism for alteration gives a negative influence in sharp contrast to the albitization a majority of the occurrences of quartz dissolution which resulted in the formation of episyenite are located along fracture zones quartz dissolution took place between or after 1 8 1 7 ga when the bedrock was able to respond to deformation in a brittle manner most of the vugs left after the removal of quartz are to a variable extent refilled by hydrothermal assemblages including quartz albite k feldspar hematite chlorite and calcite the geometry and spatial distribution of episyenite argue against an extreme fluid rock ratio and it is inferred that the fluids had at least a moderate salinity with a temperature in excess of 300 degrees c the dissolution process was promoted by the generation of secondary permeability localized in columnar or pipe like volumes the close spatial connection to fracture zones provides a basis to avoid bedrock affected by this type of alteration and thereby reduce the negative mechanical and hydrogeological aspects for a deep geological repository c 2012 elsevier b v all rights reserved

time constraints on magmatism mineralisation and metamorphism at the falun base metal sulphide deposit sweden using u pb geochronology on zircon and monazite abstract u th pb zircon and monazite ion probe data have provided constraints on the timing of emplacement and metamorphism of magmatic rocks close to the palaeoproterozoic falun base metal sulphide deposit in the bergslagen lithotectonic unit fennoscandian shield sweden and thereby the timing of mineralisation hydrothermal alteration and mineralisation at falun are constrained to a short interval of several million years between a 207pb 206pb weighted average age of 1894 3 ma for a rhyolitic sub volcanic rock in the felsic volcanic to sub volcanic host rock suite and a 207pb 206pb weighted average age of 1891 3 ma for a post sulphide porphyritic dacite dyke magmatism also included the emplacement of granite plutons with igneous crystallization ages of 1894 3 1894 2 ma and 1893 3 ma the felsic sub volcanic to volcanic activity and the emplacement of dacite dykes and granite plutons overlap in age within their respective analytical uncertainties indicating hydrothermal alteration and sulphide mineralisation inside a narrow time span of intense magmatic activity and burial of the supracrustal rocks two distinct patchy and homogeneous metamorphic monazite types in a felsic volcanic rock around and hydrothermally altered rocks at the falun deposit yield 207pb 206pb weighted average ages of 1831 8 ma and 1822 5 ma respectively these ages fall well within the temporal range of a younger 1 84 1 81 ga m2 metamorphic episode during the 2 0 1 8 ga svecokarelian orogeny with the older episode m1 inside the bergslagen lithotectonic unit at around 1 86 ga this shows the major influence of the m2 event in the north western part of this unit leading to a complete resetting of the u th pb isotope system in monazite

strain ellipsoids from incompetent dykes application to volume loss during mylonitization in the singo gneiss zone central sweden we describe how to constrain bulk strain ellipsoids by distinguishing the attitudes of mullioned from planar contacts in incompetent dykes our method is demonstrated by using metabasaltic dykes to

reconstruction of preglacial drainage and its diversion by earliest glacial forebulge in the upper mississippi valley region reconstructions of preglacial drainage in the upper mississippi valley region have previously been based on the pattern of bedrock valleys it has been recognized recently that many bedrock valleys have been produced during pleistocene time by glacial diversion and accompanying glacio isostasy a more speculative approach to reconstruction of preglacial drainage in the upper mississippi valley region is based on considerations of paleoslopes late pliocene landscapes and structural control in addition to bedrock topography this approach results in a pattern that is in harmony with the underlying geology but it does not lead to a single unique unambiguous reconstruction for the purposes of this study the trunk stream is assumed to lie along the axis of the wisconsin and kankakee arches like that of the wisconsin arch the drainage pattern is asymmetrical the longer tributaries entering from the west and north the present course of the mississippi river above the mouth of the rock river is postulated to be an ice marginal stream associated with an early glacial advance into iowa from the north and west a glacial forebulge may have played an important role in determining this course

late oligocene to early miocene geochronology and paleoceanography from the subantarctic south atlantic mi2 as well as several other distinctive isotope events our data suggest that the d 18 o maximum commonly associated with the oligocene miocene o m boundary falls within c6cn 2r 23 86 ma the d 13 c maximum coincides within the temporal resolution of our record with c6cn 2n r boundary and hence to the o m boundary comparison of the stable isotope record from site 1090 to the orbitally tuned stable isotope record from odp site 929 across the o m boundary shows that variability in the two records is very similar and can be correlated at and below the o m boundary site 1090 stable isotope records also provide the first deep southern ocean end member for reconstructions of circulation patterns and late oligocene to early miocene climate change comparison to previously published records suggests that basin to basin carbon isotope gradients were small or nonexistent and are inconclusive with respect to the direction of deep water flow oxygen isotope gradients between sites suggest that the deep southern ocean was cold in comparison to the north atlantic indian and the pacific oceans dominance of cold southern component deep water at site 1090 at least until 17 ma suggests that relatively cold circumpolar climatic conditions prevailed during the late oligocene and early miocene we believe that a relatively cold southern ocean reflects unrestricted circumpolar flow through the drake passage in agreement with bathymetric reconstructions index terms 4267 oceanography general paleoceanography 1035 geochemistry geochronology 4870 oceanography biological and chemical stable isotopes keywords paleoceanography 1035 geochronology stable isotopes

radium isotopes to trace uranium redox anomalies in anoxic groundwater abstract 223ra 224ra 226ra and 228ra isotopes have been measured in groundwaters from depths ranging 50 900 m in fractured crystalline bedrock forsmark sweden to understand the reason for elevated up to 150 g l aqueous uranium uaq at 400 650 m depth ra isotope data is interpreted alongside previously reported 222rn 234u and 238u data as well as phreeqc geochemical modelling and uranium mineralogy a novel 223ra 226ra gw based approach where brackets and gw subscript refer to expression of an activity ratio measured from groundwater to groundwater residence time estimation shows that elevated uaq is most common in holocene age groundwaters of marine origin although these groundwaters are geochemically reducing the 223ra 228ra corr where corr subscript refers to a correction applied to compare 223ra 228ra gw to the more commonly reported 226ra 228ra gw suggest that they interact with u rich pegmatites containing proterozoic and palaeozoic age ca u vi silicate minerals which are undersaturated in the present groundwaters local aqueous u vi can be stabilized in ca2uo2co30 complexes at pe values as low as 4 5 but is susceptible to reduction after a modest decrease in pe value alkalinity or ca concentration the 223ra 228ra corr and 224ra 228ra gw also suggest that u vi aq precipitates as uo2 x at the interface between marine and non marine groundwaters from these data local uaq is proposed to be governed by on going water rock interaction involving old u vi minerals

3d modelling and sheath folding at the falun pyritic zn pb cu au ag sulphide deposit and implications for exploration in a 1 9 ga ore district fennoscandian shield sweden the falun pyritic zn pb cu au ag deposit situated in the palaeoproterozoic 1 9 1 8 ga bergslagen lithotectonic unit in the south western part of the fennoscandian shield is one of the major b

orbitally paced climate oscillations across the oligocene miocene boundary the late oligocene and early miocene periods some 21 to 27 million years ago have generally been viewed as times of moderate global warmth and ice free conditions yet several lines of evidence suggest that this interval was punctuated by at least one and possibly several episodes of high latitude cooling and continental glaciation1 2 3 here we present stable isotope and per cent coarse fraction data from an equatorial western atlantic deep sea sediment core that provide high resolution records of the climate variability across the oligocene miocene transition 22 5 25 7 million years ago a strong 40 kyr periodicity in the oxygen isotope record is consistent with a high latitude orbital obliquity control on ice volume and temperature orbital influences are also apparent at precession and eccentricity frequencies including a series of 400 kyr oscillations that culminate in distinct maxima at the oligocene miocene boundary about 23 7 million years ago covariance between the carbon and oxygen isotope records suggests that the oceanic carbon cycle may have contributed to global cooling during the 400 kyr cycles particularly at the oligocene miocene boundary

successive 1 94ga plutonism and 1 92ga deformation and metamorphism south of the skellefte district northern sweden substantiation of the marginal basin accretion hypothesis of svecofennian evolution abstract in contrast to the prevailing arc accretion hypothesis it has recently been argued that the most extensive deformation and metamorphism d1 in the skellefte region of north central sweden took place in older metasedimentary sequences before the eruption of the 1 90 1 87 ga volcanic sequences the new data presented here provide a basis for a refined hypothesis involving accretion of a pre 1 92 ga marginal basin during an early svecofennian orogenic episode between 1 92 1 91 ga to the south of the skellefte district in a part of the metasedimentary robertsfors group dominated by ne d1 structural trends 40 sims analyses of zircon from a metasediment robertsfors 1 have been made fourteen analyses of overgrowths and structureless zircon grains provide strong evidence for a post depositional metamorphic event dated to 1916 5 ma which we correlate with the observed d1 metamorphism and migmatisation this age is indistinguishable from that of a corresponding event in the vammala migmatite belt vmb in finland this is the most important crustal thickening episode in the evolution of the svecofennian province here distinguished as the early svecofennian orogenic episode nine archaean and 15 older palaeoproterozoic op detrital zircon grains also yielded data comparable to that from the vmb the age of 1980 6 ma obtained from the total op population possibly indicates derivation from a single magmatic source area with similarly aged metamorphic overgrowths on some of the grains two sampled localities to the ne show d1 schistosity overprinted by d2 shears and granitic veining sample ronnskar 3 from a relatively homogeneous granitoid and sample ronnskar 2 from a garnetiferous felsic layer in well banded layered gneisses both contain igneous zircon populations these have been affected by d1 and d2 events but the sims data allow the age of magmatism in both rocks to be placed between 1940 and 1950 ma thus reinforcing the links to the knaften storuman areas to the wnw in the granitoid six analyses from highly luminescent rims yielding an imprecise age of 1856 25 ma are consistent with the earlier more precise 207pb 206pb dating of the d2 event at 1858 2 ma the d2 event is also recorded by id tims analyses of monazite from five widely spaced localities in the skellefte structural zone with ages ranging from 1849 3 to 1866 2 ma the d2 deformation has similar characteristics in the skellefte robertsfors and tampere vammala areas we suggest that it can be allocated to a second and middle svecofennian orogenic episode between 1 88 and 1 85 ga affecting a wide area it has been demonstrated that the protoliths of the robertsfors group were deposited before 1 95 ga the group was intruded by granitoids between 1 94 and 1 95 ga and it was strongly deformed and metamorphosed between 1 92 and 1 91 ga proximity to the post 1 90 ga skellefte group during the deposition of the latter is indicated for both robertsfors and knaften storuman areas by the presence of 1 90 ga granitoids and 1 88 ga conglomerates like those in the skellefte district the regional evidence for the continuity of metamorphic complexes over wide areas and the similarity in pre and post depositional histories of the robertsfors group and the vammala migmatite belt 300 km apart support the hypothesis that accretion of a large svionian marginal basin at 1 92 1 91 ga provided the basement for the subsequent volcanism

zircon u pb ages from the wabigoon manitou lakes region wabigoon subprovince northwest ontario three distinct stratigraphic units have been recognized in the crow lake savant lake belt these are a basal unit consisting of high magnesium tholeiitic flows a middle unit consisting mostly of tholeiitic to calc alkaline pyroclastic rocks and flows and an upper unit of high iron tholeiitic flows a zircon u pb study has been carried out on seven rocks from the wabigoon manitou lakes region of this belt in the manitou lakes area a minimum age of 2755 ma on a porphyry pluton intruded into the wapageisi volcanics gives a minimum age for the high magnesium tholeiitic sequence a trondhjemite phase of the atikwa batholith near wabigoon lake that is dated at 2732 2 2 9 ma has the same age within experimental error as a rhyolite flow from the lower wabigoon volcanics in the same area that is dated at however a trondhjemite phase of the atikwa batholith at eagle lake that is dated at is distinctly younger than a dacite flow collected nearby from the lower wabigoon volcanics that is dated at both thes

palynological and radiocarbon evidence for deglaciation events in the green bay lobe wisconsin abstract a new and significant site of organic silty sand has been found beneath the valders till at valders quarry in northeastern wisconsin this is now the earliest known late glacial site associated with red till ice advances in the western great lakes area leaves of terrestrial plants washed into a small depression provide a date of 12 965 200 yr b p wis 2293 which is significantly older than the two creeks forest bed ca 11 800 yr b p percentage and concentration pollen diagrams suggest that the site was open and distant from a closed picea forest no wood or picea needles have been found this date is statistically indistinguishable from 12 550 233 yr b p the mean of three dates for the end of inorganic varve sedimentation at devils lake 160 km southwest at the terminus of the green bay lobe assuming that the green bay lobe vacated its outermost moraine in the interval from 13 000 to 12 500 yr b p only a short time was available for retreat of the ice margin over 350 km drainage of red sediment from lake superior into the lake michigan basin readvance of over 250 km retreat of at least 80 km and advance to this site the time for these events appears to have been too short to resolve by current radiocarbon technique this extremely rapid collapse of the green bay lobe has a calibrated age of about 15 000 cal yr b p about that of the dramatic warming seen in the greenland ice cores

ecosystem development following deglaciation a new sedimentary record from devils lake wisconsin usa abstract processes and rates of ecosystem development can be reconstructed using lacustrine sedimentary sequences but this approach often requires records that contain the start of primary succession most lakes in the upper midwestern u s were formed by glaciers at the end of the last ice age approximately 11 700 cal yr bp devils lake wisconsin is a rare example of a lake from this region whose sediments extend into the pleistocene and may include the last glacial maximum sediment magnetic geochemical pollen and charcoal records were generated from a 10 m core whose basal sediments may be 28 000 years old together with a previously published pollen record these proxies combine to reveal a history of long term climatic vegetative and geologic change during the late pleistocene to holocene we identify six sedimentary units that indicate a series of consecutive events rather than a predictable trajectory of ecosystem development at the site productivity in the lake was low during the late pleistocene and increased during the holocene as reflected by the sediment lithology which shows a sudden shift from glacial vivianite rich and organic poor clastic dominated sediments to holocene diatomaceous sapropels several important processes initiated around 17 000 cal yr bp including the onset of organic matter accumulation and fire in the terrestrial ecosystem however the post glacial landscape was not devoid of vegetation because pollen assemblages indicate that terrestrial vegetation likely a spruce tundra survived near the site a switch to a hardwood forest period during the holocene also led to a change in the fire regime with increased frequency of burning aquatic ecosystem productivity lagged terrestrial ecosystem productivity throughout the record nutrient cycling as recorded by sedimentary 15n was variable but not directional and appeared to be correlated with climate conditions early in the record and terrestrial ecosystem processes later in the record throughout the holocene magnetic mineral concentration decreased as productivity increased and the source of magnetic material shifted from almost exclusively lithogenic to approximately 50 derived from soil or biogenic sources magnetic grain size ambrosia pollen percentages and charcoal concentration increased and 15n decreased in the most recent part of the record due to anthropogenic influence in the region including agricultural activities

plate motions slab dynamics and back arc deformation back arc extension or compression is often related to a particular behavior of the slab dip change and or forward backward migration with respect to the upper plate slabs act either passively when anchored in the deep mantle whereas back arc deformation accommodates the backward or forward motion of the upper plate with respect to the trench or actively when slab pull increasing with slab age forces the trench to rollback in addition to these two mechanisms i e slab anchor and slab rollback numerous observations support the existence of dynamic mantle flow that can exert an overpressure on one side of the slab causing its forward or rearward migration with respect to the arc based on a compilation of upper plate absolute motion trench absolute motion back arc deformation rate upper plate strain regime and slab age for all oceanic subduction zones excluding any kind of collision with continents arcs or plateaus we have examined how the combined effects of these parameters can account for the observed back arc deformations our main results are 1 a global correlation exists between upper plate absolute motion and back arc deformation i e back arc extension when upper plate retreats and vice versa 2 there are as many advancing trenches as retreating ones with trench motion globally limited to 50 mm y 1 furthermore there is no positive correlation between trench retreat and slab age and 3 upper plate absolute motion often fails to explain the back arc deformation rates and the trench motions observed at several subduction zones as tonga new hebrides sandwich or ryukyu we propose that the trench migration of these subduction zones are on the influence of mantle flows we conclude that spontaneous trench rollback related to slab pull is negligible with respect to upper plate motion back arc deformation regime is mostly controlled by the upper plate absolute motion relative to a partly anchored slab trench motion is limited to 50 mm y 1 even if locally mantle flows force slab to move

proterozoic extensional tectonics of the central fennoscandian shield results from the baltic and bothnian echoes from the lithosphere experiment a three dimensional crustal structure of the bothnian sea is deduced from the near vertical reflection data of the crosscutting lines 1 6 7 and c of the babel baltic and bothnian echoes from the lithosphere experiment for this study the common depth point stacked sections have been migrated with a velocity 6 5 km s and displayed as stacked envelope sections to show their enhanced large scale crustal structures the seismic sections show listric shear zones which dip toward se and flatten at major detachment zones 35 40 km and 48 km in depth the detachment zones are associated with changes in p wave velocity from 6 8 km s to 7 0 km s and from 7 4 km s to 8 2 km s and coincide with the middle and lower crustal boundary and the moho boundary respectively the geometry and crosscutting relationship of the detachment zone are well developed on the e w directed line 7 from where the moho detachment zone can be interpreted as to be younger different shear zone systems operated in the parallel n s directed lines 1 and 6 and therefore it is not easy to correlate crustal structures between lines 1 and 6 in the thinned southern part of study area the lower crust has a highly reflective lamellar structure and a strongly reflective subhorizontal moho increased reflectivity of the lower crust is attributed to stretching and mafic underplating of the crust associated with the subjotnian diabase dykes and rapakivi magmatism in the upper crust the rapakivi granite and diabase association is characterized by a rather transparent area within which strong reflections mimic graben and horst structures the distribution of the bimodal association seems to be controlled by the low angle listric shear zones the spatial distribution of outcropping lithologies combined with deeply penetrating shear zones suggests a simple shear extensional deformation the first stage of deformation which concentrated in the upper and middle crust records the collapse of the overthickened svecofennian crust the second stage involving the entire crust may record either the continuation of the postcollisional collapse or a separate anorogenic extensional period the seismic structures predict major post svecofennian deformation faulting and tilting in the central fennoscandian shield the extensional tectonics operating in the fennoscandian shield in the proterozoic is comparable to modern extensional tectonics

catastrophic flooding from glacial lake wisconsin abstract glacial lake wisconsin was a large proglacial lake that formed along the southern margin of the laurentide ice sheet during the wisconsin glaciation it was formed when ice of the green bay lobe came into contact with the baraboo hills in southwestern wisconsin and blocked the south flowing wisconsin river during early glacial recession the ice dam failed catastrophically and the lake drained in about a week despite early recognition of the former lake and the likelihood that it failed catastrophically outflow rates during the failure have not been previously evaluated estimates based on step backwater modeling indicate that peak discharge was between 3 6 and 5 3 10 4 m 3 s in the lower wisconsin river as an alternate method we used a previously derived empirical relationship between lake volume and peak discharge for dam break events from a digital elevation model altered to incorporate isostatic depression we estimated the lake volume to be 87 km 3 just prior to dam breach suggesting that the flooding magnitude was as high as 1 5 10 5 m 3 s at the outlet adjusting these results for downstream flood wave attenuation gives a discharge of around 4 4 10 4 m 3 s in the lower reach which closely matches the results of the step backwater modeling these estimates of discharge from the catastrophic failure of ice marginal lakes improve our understanding of the processes that have produced the morphology and behavior of present day upper midwest river systems

structural evolution of the accretional continental margin of the paleoproterozoic svecofennian orogen in southern sweden abstract volcanic and sedimentary rocks of the vastervik and valdemarsvik groups along the southern margin of the 1 90 1 85 ga south svecofennian crustal province in sweden have been migmatised and intruded by granitoids and gabbros during extension deformation phase d1 at a depth of at least 10 km peak metamorphic conditions were reached around 1825 ma extension switched to compression before cooling the partially molten middle crust facilitated shortening and thickening by isoclinal and sheath folds on scales from a decimetre to 10 km d2 a pervasive mylonitic s2 foliation developed these structures were refolded into eastward plunging crustal scale upright folds with e se w nw trending axial planes d3 d2 d3 deformation structures are colinear and developed during top to the wnw slip along s2 locally zones of high ductile strain in garnet bearing migmatite assemblages record considerable vertical displacement from 850 to 300 mpa possibly in nappe roots some major d2 sheath folds are embraced by d3 like but nnw trending megafolds d4 apparently resulting from shortening around the former d2 d4 deformations are interpreted to be broadly coeval and related to transpressive crustal shortening against the northern svecofennian continental back stop after cooling to high greenschist facies conditions early structures underwent renewed transpression in north south direction expressed in localized retrogressive shear zones phase d5 much d5 strain was accommodated by the 10 km wide nw se striking right lateral loftahammar linkoping deformation zone lldz operative around 1800 1780 ma regional strain partitioning caused transverse shortening in 15 20 km wide border zones of the lldz later overprints d6 involve narrow subparallel nw se striking and steeply ne dipping low greenschist facies mylonite zones some of which merge into the regional polyphase asbro norrkoping deformation zone d6 was transpressive oblique left lateral ne block up slip suggests a w sw e ne orientation of 1 peak metamorphism and partial melting in the supracrustal rocks was approximately coeval with 1800 1835 ma old subduction related magmatism in the oskarshamn jonkoping belt ojb 100 km to the south west seismic reflection profiling off the baltic coast babel line b suggests northward polarity of subduction beneath the ojb and a back arc environment of the vastervik and valdemarsvik groups between the ojb arc and the margin of the 1850 ma old svecofennian orogen we suggest that d1 d5 deformation was caused by intracontinental back arc extension and subsequent closure of the back arc basin by oblique accretion of the ojb marginal arc onto the northern continent accretion involved northward indentation by mid crustal wedges one of which coincides with and possibly caused the nucleation of the d5 stage lldz 40ar 39ar data from hornblende and white mica identify a prolonged cooling history of the area 1810 1490 ma influenced by the nearby late and postorogenic transscandinavian igneous belt and possibly by largely hidden c 1530 ma old anorogenic rapakivi type intrusions

analog modeling of one way gravitational spreading of hot orogens a case study from the svecofennian orogen fennoscandian shield abstract geodynamic models offer insight into deformation styles of syn and post collisional extensional processes such models often ignore the effect of lateral viscosity contrast between accreted terranes and inherited tectonic boundaries this paper presents a set of crustal scale analog experiments of one way post collisional gravitational spreading testing the effect of crustal heterogeneity by using two mechanically contrasting blocks pre existing cuts with varying dips and three layers with contrasting rheologies two blocks represent strong mature and weak juvenile crustal parts both blocks have three horizontal crustal layers brittle upper weak partially molten middle and dry strong lower layer cuts represent pre existing crustal scale shear zones and tectonic boundaries the experiments indicated that tectonic boundaries may facilitate exhumation and increase extensional strain when the boundaries dip opposite to the flow direction the tectonic boundaries may also split and divide the crust into separate blocks with independent deformation signatures shortening elongation or rotation the tectonic boundaries rotated along vertical axes toward the flow direction the modeling results suggest that in areas with inherited tectonic boundaries and compositional differences the amount of extension is unevenly distributed between the different parts during the widespread unilateral gravitational spreading and that the flow has different effects on the contrasting crustal units in both lateral and vertical directions to validate the modeling the results are compared to geophysical and geological data from the paleoproterozoic svecofennian orogen in the fennoscandian shield the comparison suggests that the orogen underwent 50 extension and was thinned by maximum of 20 via westward gravitational spreading this spreading rotated the crustal scale blocks shear zones and tectonic contacts it also brought exhumed high grade middle crustal blocks into contact with subsided low grade upper crustal blocks we suggest that results of the analog models can be used as proxies in both ancient and modern hot accreted orogens which have undergone post convergence continental mid crustal weakening and have comprised of juxtaposed terranes with varying rheological compositions

急速風化と成熟石英アレナイト堆積を支持する ウイスコンシン州 原生代初期珪岩の砕屑ジルコン年代

late paleoproterozoic climate tectonics and metamorphism in the southern lake superior region and proto north america evidence from baraboo interval quartzites abstract red supermature quartzites of the baraboo interval of the lake superior region contain detrital zircon that ranges in age from 1782 to 1712 ma deposition clearly occurred after the geon 18 penokean orogeny these late paleoproterozoic sedimentary rocks consist largely of quartz kaolinite or pyrophyllite and hematite detrital feldspar and muscovite are rare or absent their chemical index of alteration ranges from 96 8 to 98 6 among the most chemically mature clastic sediments in the geological record the quartzites are underlain by mature feldspar free paleosols accounting for the absence of feldspar in the overlying sediments and indicating the presence of first cycle quartzose detritus such physical and chemical characteristics imply that late paleoproterozoic deposition in the lake superior region occurred in a stable tectonic setting with subdued topographic relief in a warm humid climate folding and low grade metamorphism of the quartzites is thought to reflect 1630 ma foreland

near orthogonal deformation successions in the poly deformed paleoproterozoic martimo belt implications for the tectonic evolution of northern fennoscandia abstract structural mapping integrated with aeromagnetic and anisotropy of magnetic susceptibility ams data form complimentary and robust tools for analysis of regional structures and fabric overprinting relationships this multi scale approach is used to constrain the geometry and tectonic evolution of sparsely exposed and flat lying outcrops of the martimo belt mb of northern fennoscandia the mb records a history of near orthogonal deformations upper greenschist to lower amphibolite facies metamorphism between ca 1 92 1 79 ga the earliest deformation d1 involved east directed thin skin thrusting and the development of recumbent f1 folds and a n s trending s1 fabric d2 deformation is prominent in the central part of the mb and is characterized by n s shortening with the development of e w trending f2 folds an associated pervasive steeply dipping s2 foliation and type 2 fold interference pattern the mb and mellajoki suite exhibit regional scale d2 synformal and antiformal refolded structures respectively d3 is more heterogeneously developed and manifests bimodal orientations with nnw sse and wnw ese structural trends it is pronounced in the central and eastern parts of the mb but weakly developed in the western part the steep dip of s3 in the region suggests that it formed in response to ne sw bulk shortening d4 structures have a conspicuous nne ssw trend that is visible as lineaments on the aeromagnetic image and locally in the field the last deformation event d5 affected almost the entire mb and was characterized by broadly wsw ene oriented crustal shortening the n s oval shape geometry of the eastern part of the mb is attributed to the d5 event contrasting with well developed overprinting relationships between d1 and d3 structures the relative timing of d3 d5 could not be established in the study area but can be inferred from structures with similar trends in the central lapland granitoid complex which is located north of the mb the d1 d5 deformation scheme can be readily reconciled with the tectonic evolution of the lapland savo fennian svecobaltic and nordic orogens of the composite svecofennian orogen the age of d1 in the northern part of the lapland savo orogen is 1 91 ga based on crosscutting granitoids and maximum deposition ages of sedimentary rocks d2 1 90 1 89 ga has been linked to orogen parallel shortening during the late stage of southern part of the lapland savo orogen several orthogonal tectonic events in northern fennoscandia indicate amalgamation of crustal blocks around the core of the archean karelia continent at 1 92 1 77 ga and that fennoscandia was a key component of the columbia hudsonia nuna supercontinent

accretion tectonism in the proterozoic svecokarelides of the baltic shield the duality of early middle proterozoic terranes in the baltic shield reflects fundamental differences in history between coeval mobile belts and the manner of their interaction the karelides formed on a continent ocean transcurrent margin in which offsets developed as arcs and back arc basins on stretched continental crust at least one back arc basin was obducted onto the continental margin preserved as an allochthonous terrane in the karelian nappe pile remnant arc fragments form accreted exotic terrane in pohjanmaa the svecofennides developed as a succession of island arcs while the site of subduction moved south and successive extinct arcs were accreted onto the archean craton arc terrane impingement affected deformation style in the karelides which changed from one of major horizontal translation to one dominated by major dextral wrench faults analogies can be drawn with the phanerozoic evolution of the northeast pacific margin

seismic geomorphology and growth architecture of a miocene barrier reef browse basin nw australia abstract the cenozoic succession of browse basin is characterized by a carbonate system that developed from a non tropical ramp in eocene lower miocene times to a tropical rimmed platform in the middle miocene the evolution of the platform was unraveled through the interpretation of the seismic geomorphology and borehole data of the middle miocene tropical reef system the first reef structures developed during the early middle miocene as narrow linear reef belts with an oblique orientation with respect to shelf strike direction subsequently they prograded toward the platform margin to form a barrier reef with a minimum length of 40 km the barrier reef itself comprises three distinct ridges separated by progradational steps the second and third step are separated by a karstified horizon which is interpreted to represent the global sea level fall shortly before the serravallian tortonian boundary the following third ridge formed in a slightly downstepped position during the sea level lowstand and initial transgressive phase further sea level rise during the early tortonian first drowned the barrier reef system and subsequently also the patch reefs and relic atolls that had established in a backstepped position in the platform interior the similar evolution of the browse basin reef system and other contemporaneous carbonate systems indicates a strong impact of eustatic sea level changes relatively large subsidence rates in the study area possibly augmented the eustatic sea level rise in the tortonian and hence contributed to the drowning of the reef system however the initiation and final demise of the reef system was also governed by global and regional climate variations the first seismically defined reefs developed simultaneous to a maximum in the transport capacity of the indonesian throughflow which brings warm low salinity waters to the north west shelf reef drowning followed the restriction of this seaway close to the middle to early miocene boundary this near closure of the indonesian seaway possibly led to a regional amplification of the global middle to late miocene cooling trend and hampered the potential of the reef system to keep up with the rising sea level

supervised classification of types of glaciated landscapes using digital elevation data abstract automated approaches for identifying different types of glaciated landscapes using digitally processed elevation data were evaluated we tested the ability of geomorphic measures e g elevation relative relief roughness and slope gradient derived from digital elevation models dems to differentiate glaciated landscapes using maximum likelihood classification and artificial neural networks ann the automated methods were trained and validated using an existing quaternary geology map and a manual interpretation of the contour data portrayed on topographic quadrangles the need for such methods arises from efforts to classify types of landscapes e g ecoregions in michigan one fundamental control of the landscape structure in michigan including soil type and vegetation is the underlying sedimentary and landform assemblages produced by an array of glacial processes during the waning phase of the pleistocene traditional methods for identifying different landscapes e g ice contact landscapes stagnation landscapes have relied on printed topographic maps and have been very effective but time consuming the maps resulting from the four supervised classification trials had between 51 and 61 agreement with the original quaternary geology map the output from the maximum likelihood classification had slightly higher agreements than the output from the neural net which is attributed to the generalization inherent in the quaternary geology map compared with the nature of the classifier for the neural net the neural net however identifies significant detail and non linear relationships between classification inputs and output classes future work should incorporate a map of soils into the classification

hafnium isotope evidence for early proterozoic volcanic arc reworking in the skellefte district northern sweden and implications for the svecofennian orogen abstract the skellefte district is a seemingly juvenile and heavily mineralized crustal domain in northern sweden that formed between 1 90 and 1 87 ga it is commonly interpreted as a volcanic arc deposited on a basement known variously as the bothnian or the knaften barsele group that could be represented by older rocks 1 96 1 94 ga found in the vicinity in order to understand the potential genetic relationship between the arc and the basement hf and pb isotopes in magmatic zircons from key lithologies were measured by solution multi collector inductively coupled plasma mass spectrometry it is shown that both geological groups display similar hf isotope compositions which translate into decreasing hf with time overall the data are compatible with reworking of the knaften barsele arc to produce the skellefte rocks over a short time interval from 1 90 to 1 87 ga in a context of crustal extension with ongoing subduction when the data presented here are integrated with general models of tectonic evolution of the svecofennian orogen they fit a scenario in which the juvenile knaften barsele arc formed between 1 96 and 1 94 ga and became accreted onto the karelian continent located further north at about 1 92 1 91 ga systematic north to south variations in pb nd and hf isotope compositions throughout the svecofennides interpreted as resulting from an increase in archean crust involvement toward the south indicate a genetic link between the proterozoic crustal domains of sweden and finland

age of deformation episodes in the palaeoproterozoic domain of northern sweden and evidence for a pre 1 9 ga crustal layer it is proposed in a companion paper that the volcanic rocks of the skellefte group in northern sweden were deposited on a pre 1 9 ga basement rather than formed as a juvenile volcanic arc and subsequently accreted to the continent it is suggested that the proposed basement the robertsfors group to the south of skelleftea was already deformed during an early episode of deformation d1 prior to the deposition of the skellefte stratigraphic sequence during an extensional tectonic episode a younger episode of deformation d2 then affected both areas this hypothesis has important implications for the evolution of the svecofennian province to test it by constraining the ages of the principal deformation episodes we have undertaken both isotope dilution and ion microprobe studies of zircon and monazite from three localities in the robertsfors group a phase of migmatisation directly related to d2 shear zones allows the dating of d2 at 1860 ma other planar granitoid bodies which cut the d1 structures confirm the age of this event in the context of earlier published data we conclude that the correlation of d2 in the robertsfors group with the main folding in the skellefte group is valid another granitoid body folded by d2 but emplaced after d1 contains a suite of zircons of apparent magmatic aspect but with a spread of ages from 1870 to 1900 ma because of the high mswd the suite was divided into two groups with ages of 1896 and 1874 ma recognising the possibilities of inheritance and of updating by younger events we have preferred to interpret the younger age as a minimum age for magmatic intrusion this is consistent with the basement hypothesis but is our only definite constraint on the age of d1 however we infer using other evidence that d1 is probably older than 1900 ma xenocrysts interpreted as detrital zircons derived from the associated metasediments give ages between 2716 and 1941 20 ma the latter age provides a maximum age of deposition for part of the robertsfors group and a maximum age for d1 other sequences to the south and west considered broadly equivalent to the robertsfors group are intruded by granitoids dated between 1920 and 1960 ma providing local minimum ages of deposition for the sequences involved regional correlation with respect to age and deformation style can be made with the pre 1 9 ga kalevian rocks to the ne deposited on archaean basement on the sw margin of the karelian province we suggest that pre 1 9 ga complexes equivalent to the robertsfors group are widespread in the svecofennian province and were deposited in a marginal basin which may have been initiated as early as 2 2 ga ago this hypothesis of an extensive basement crustal layer evidently requires that a substantial volume of crustal growth occurred prior to 1 9 ga in contrast to previous hypotheses erosion of the pre 1 9 ga basin rocks after d1 is also the likely source of the 2 1 1 9 ga detrital zircons in younger sediments associated with the overlying post 1 9 ga volcanics the source of these detrital zircons has previously been problematical

integration of gamma ray spectrometry magnetic susceptibility and calcareous nannofossils for interpreting environmental perturbations an example from the jenkyns event lower toarcian from south iberian palaeomargin median subbetic se spain abstract the pliensbachian toarcian sedimentary rocks of the median subbetic betic cordillera se spain were deposited in the south iberian palaeomargin under hemipelagic conditions in the arroyo mingarron section se spain these deposits are composed by a marl and marl and limestone alternation with abundant radiolarians the application of magnetic susceptibility and gamma ray spectrometry to these deposits allows to interpret environmental changes related to the fluctuations in the continental influx of terrigenous and phytodetritus to a hemipelagic setting in the south iberian palaeomargin the increase of terrigenous input was coincident with the negative carbon isotopic excursion cie at the base of the njt6 nannofossil zone that correlates with the jenkyns event the increase of th and k content is related to enhanced detrital input especially oxides and silicates including clay minerals the gamma ray signal derived from u is comparatively low with respect to k and th nevertheless the u content shows an increase in the base of njt6 nannofossil zone that indicates a relative increase of organic matter content coincident with the jenkyns event changes in the calcareous nannofossil assemblages at the beginning of the njt6a nannofossil subzone and in particular the sharp decrease in abundance of the species mitrolitus jansae during the negative cie of the jenkyns event are interpreted as related to sea water stratification and a probable poor oxygenation making inhospitable the deep photic zone during this event

field gamma ray patterns and stratigraphic reinterpretation of offshore well log data from lower jurassic organic rich units of the lusitanian basin portugal abstract lower jurassic sinemurian pliensbachian successions cropping out in onshore areas of the lusitanian basin provide detailed information of three well characterized organic rich intervals i the unit f from the coimbra formation ii the polvoeira member of the agua de madeiros formation and the iii marly limestones with organic rich facies mlof member of the vale das fontes formation despite decades of research these source rocks have not yet been properly identified and characterized in terms of extension and thickness in the basin s offshore this paper compares detailed gamma ray gr profiles from onshore outcrops coimbra montemor o velho figueira da foz monte real sao pedro de moel and peniche regions with seven offshore wells our objective is to recognise lower jurassic organic rich intervals in offshore areas of the basin highlighting their lateral extension and improving the overall stratigraphic definition of the lower jurassic in the lusitanian basin gr field measurements indicate that the highest gr values and u contents are consistently observed in the organic rich intervals reaching up to 134 api and 9 0 ppm of u in contrast the lowest api and u contents were determined in dominantly calcareous units ranging between 5 34 api and 0 1 1 4 ppm respectively wireline gamma ray logs show a good correspondence between field patterns and offshore well logs recognizing the organic rich intervals in offshore areas the highest gr values are interpreted to be linked with the 2nd and 3rd order maximum flooding intervals previously recognised in the sinemurian pliensbachian successions in the western iberian margin detailed gr maps linked to maximum flooding intervals highlight the variation of the vertical and lateral distributions of the organic rich units in offshore areas of the lusitanian basin

brittle reactivation of ductile precursor structures the role of incomplete structural transposition at a nuclear waste disposal site olkiluoto finland abstract reactivation of discrete deformation zones that are orientated favourably with respect to the stress field is a well known phenomenon what is less clear is the role of other structural features and heterogeneities in localizing deformation in this paper we describe how brittle deformation structures are localized into zones of incomplete structural transposition inherited from earlier ductile deformation phases in our example these zones of incomplete structural transposition are characterised by localised high strain structures of the latest ductile deformation stage including short limbs of strongly asymmetric folds and anastomosing networks of minor shear fabrics when such zones are systematically organized and orientated favourable with respect to the stress field they can be very efficient in localizing deformation and forming new fault zones applied to the site of the planned geological repository of nuclear waste in olkiluoto finland the recognized structural inheritance provides tools to understand the geometries networks and kinematics of the brittle fault zones and the related secondary fracturing which together define the rock mechanical and hydrogeological framework for the repository

constraints on pb closure temperature in titanite based on rocks from the ungava orogen canada implications for u pb geochronology and p t t path determinations on the basis of multiequilibrium metamorphic pressure temperature p t estimates we have determined that 660 700 c is a reasonable minimum estimate of the closure t of pb diffusion in titanite a temperature significantly higher than previously suggested activity corrected reactions that produce titanite define narrow t stability fields 40 c that correspond closely to metamorphic p t determinations derived for coronitic garnet clinopyroxene hornblende samples growth of titanite occurring between 1789 and 1814 ma in the underthrust archean basement of the paleoproterozoic ungava orogen northern quebec is associated with retrograde metamorphism during underthrusting of the archean basement approx 1 b y after formation of the original granulitic assemblages

mega scale glacial lineations and cross cutting ice flow landforms landsat images reveal a previously unsuspected large scale pattern of streamlining within drift that is assumed to reflect former phases of ice flow such a glacial grain can be regarded as a landform assemblage comprised of a number of components drumlins and megaflutes form part of the pattern but in addition there are two previously undocumented ice moulded landform elements streamlined lineations of much greater proportions referred to as mega scale glacial lineations and a distinctive cross cutting topology within the grain the ice moulded landform assemblage is described and illustrated with reference to examples from canada possible modes of genesis of such landforms are discussed and their glaciological implications outlined the discovery of this pattern indicates the pervasive nature of subglacial deformation of sediment and demands a radical re interpretation of ice sheet dynamics

facies architecture of a late jurassic carbonate ramp the korallenoolith of the lower saxony basin the sedimentary succession of a late jurassic oxfordian to basal kimmeridgian carbonate ramp is described and interpreted the study area is located in the central part of the lower saxony basin in nw germany which forms part of the central european basin eight well exposed and undeformed sections of the study area suntel area wesergebirge and eastern part of the wiehengebirge provide detailed information about lithofacies and lateral thickness variations biostratigraphically the age of these sediments is poorly constrained twenty microfacies types are recognized that can be grouped into seven facies associations a strongly bioturbated marlstones deposited near storm wave base swb b foraminifera rich wackestones c wackestones and floatstones with biostromes and d bioclastic limestones deposited between swb and fair weather wave base fwwb e oolitic and iron oolitic limestones and f siliciclastic sediments deposited above fwwb and g lagoonal deposits these facies associations characterize a storm dominated shallow mixed carbonate siliciclastic ramp based on facies changes quartz content and gamma ray logs the korallenoolith formation can be subdivided into a lower carbonate dominated and an upper siliciclastic dominated part build up by different scales of small to large scale deepening and shallowing upward cycles a preliminary correlation of measured outcrops of this formation is presented

the depositional evolution of the svecofennian supracrustal sequence in finland and sweden abstract on the basis of six new zircon ages from metavolcanic rocks together with other isotopic geophysical and geological data the chronological and tectono stratigraphic evolution of the early proterozoic svecofennian supracrustal rocks in finland and sweden are discussed these data suggest that a nw se displacement from the bothnian bay to lake ladoga and a sinking of the southwestern block was initiated 1950 2000 ma ago accumulation of pelitic sediments and greywackes on the subsiding archaean basement continued until about 1860 ma in south central and northern sweden shallow submarine and subaerial volcanics were extruded 1880 1890 ma ago the thick sedimentary piles and volcanic rocks were subsequently intruded by plutonic rocks forming large batholiths 1860 1890 ma ago

remote sensing and gis investigation of glacial features in the region of devil s lake state park south central wisconsin usa abstract this study utilizes landsat tm aster and synthetic aperture radar sar derived dems in conjunction with geographic information systems gis in order to reevaluate previously published interpretations of glacial landforms in and around devil s lake state park south central wisconsin usa devil s lake sits in a gorge carved into the southern flank of a doubly plunging syncline known as the baraboo hills through which the wisconsin or some other river flowed prior to the last ice age during the last glacial maximum about 18 000 b p an outlet glacier of the laurentide ice sheet called the green bay lobe extended southward into south central wisconsin and left behind extensive glacial landforms such as moraines drumlins and eskers during advance of the green bay lobe into the region devil s lake gorge was plugged at both ends by glacial deposits and resulted in formation of devil s lake the wisconsin river if it originally flowed through devil s lake gorge found a new course to the east of the baraboo hills syncline this study utilizes the aforementioned remote sensing data to spatially image the following features 1 original extent of the green bay lobe 2 moraines and streamlined glacial landforms as indicators of ice flow directions and 3 former path of the old wisconsin or some other river prior to being rerouted by the green bay lobe gis analysis is also performed in order to test published interpretations of the regional glacial history this study confirms that glacial features observed today are consistent with the former advance of the green bay lobe into the area formation of glacial lake wisconsin plugging of devil s lake gorge by a moraine to form devil s lake and subsequent glacial retreat leading to the breaching of an ice dam and catastrophic flooding by 14 000 years ago the large aerial coverage of satellite imagery with resolutions up to 15 m are valuable for reevaluating regional interpretations previously based on local field mapping and aerial photography of limited extent

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

syn tectonic sulphide remobilization and trace element redistribution at the falun pyritic zn pb cu au ag sulphide deposit bergslagen sweden mineralization types at the palaeoproterozoic falun base metal sulphide deposit are predominantly pyritic zn pb cu rich massive sulphide mineralization disseminated to semi massive cu au mineraliz

facies analysis of a 1 9 ga continental margin back arc felsic caldera province with diverse zn pb ag cu au sulfide and fe oxide deposits bergslagen region sweden the bergslagen mining district in south central sweden has been a major metal producer for more than 1 000 years in geologic terms bergslagen is the intensely mineralized part of a large early proterozoic mainly 1 90 1 87 ga felsic magmatic region of mainly medium to high metamorphic grade in the baltic shield the district contains a diverse range of ore deposit types including banded iron formation magnetitecalc silicate skarn manganiferous skarn and carbonate hosted iron ore apatite bearing iron ore stratiform and strata bound zn pb ag cu au sulfide ores and w skarn most ore deposits occur in hydrothermally altered metavolcanic rocks and associated metalimestones and skarns this study is a field oriented regional facies analysis based on recognition of primary volcanic and sedimentary features through the strong overprints of hydrothermal alteration deformation and metamorphism the region is interpreted as an extensional probably back arc active continental margin magmatic region it evolved through stages of intense magmatism thermal doming and crustal extension followed by waning extension waning volcanism thermal subsidence reversal from extension to compressional deformation regional metamorphism and structural inversion the volcanic successions comprise interfingering proximal near vent medial volcano flanks and distal volcano margin facies associations of rhyolitic pyroclastic caldera volcanoes and subordinate dacite rhyolite complexes nonwelded to poorly welded pyroclastic flow and fallout units and their rapidly resedimented subaerial and subaqueous equivalents are the most abundant volcanic facies subvolcanic porphyritic intrusions and cryptodomes are also abundant the pyroclastic debris was shed from mainly shallow water and subaerial proximal areas to shallow and moderately deep water above and below storm wave base distal areas most ore deposits formed during the regional waning volcanic stage and occur in medial to distal facies associations that comprise rhyolitic ash siltstone limestone and vitric crystal sandstone and breccia these mineralized facies associations were deposited in subaqueous environments mainly below the fair weather wave base but locally above the storm wave base water depths are interpreted to have been mainly 10 to 500 m with local deeper areas although the ore deposits occur in medial to distal facies associations many occur above or laterally adjacent to subsided volcanic vent complexes this suggests a spatial temporal and possible genetic relationship between several ore deposit types and the late magmatic stage of these volcanic centers except for the apatite bearing iron deposits it is uncertain if the ores are genetically related to specific magmatic hydrothermal events from specific volcanoes this is possible especially for the base metal sulfide deposits which have intense localized footwall alteration in felsic volcanic rocks however an important role of the volcanic centers may have been to provide strong positive pertubations or magmatic hydrothermal input to the regional convective geothermal system the main zn pb ag cu au ore deposits span a range between two end member types stratiform ash siltstone hosted sea floor deposits that have similarities to some stratiform sediment hosted zn pb ag deposits especially the broken hill type deposits and strata bound volcanic associated limestone skarn subsea floor replacement deposits that more closely resemble felsic volcanic associated massive sulfide deposits facies models are presented for both the banded iron formations are interpreted as chemical suspension deposits rhythmically interbedded with rhyolitic ash siltstone the skarn iron ores are strata bound in limestones and include metamorphosed sedimentary ores and metasomatic replacements apatite bearing iron ores differ in setting from the other ores in being formed within a dacitic intrusive complex that may be the root zone of a dacite rhyolite volcanic center

age and structural constraints on the tectonic evolution of the paleoproterozoic central lapland granitoid complex in the fennoscandian shield abstract the paleoproterozoic central lapland granitoid complex clgc forms the northern core of the fennoscandian shield we present here new u pb age data and review the existing ones from plutonic and metasedimentary rocks of the clgc and integrate the results with the structural field observations to decipher the tectonic history of this region granitoids vary in age from 2 43 ga to 1 78 ga whereas metamorphic zircon overgrowths both in granites and metasedimentary rocks vary between 1 90 ga and 1 76 ga with several age peaks indicating prominent metamorphic pulses the almost continuous growth of metamorphic zircon domains favors that the central part of the clgc was near solidus for 100 120 ma a succession of five deformations and associated foliation producing events which were near orthogonal to each other have been identified east vergent thrusting and stacking d1 commenced at ca 1 92 ga and led to the onset of barrovian type metamorphism followed by a radical tectonic shift that yielded e w trending d2 structures exhumation at 1 88 1 87 ga caused decompression melting of thermally evolved thickened crust and led to the emplacement of large volumes of granites and triggering of buchan type metamorphic conditions ne sw collision d3 at the southwestern margin of fennoscandia heterogeneously overprinted the s3 fabric on d2 structures orogen parallel nnw sse buckling at 1 87 1 85 ga formed oroclines in the hot linear arc segments renewed nnw sse shortening d4 at 1 84 1 81 ga produced long wavelength folds and caused the formation of domal structure in the clgc the final 1 78 1 76 ga far field collision d5 in the west overprinted all the pre existing structures this complex multi directional tectonic scenario provoked the intermittent exhumation phases between different contraction events of the clgc

review of the deterministic modelling of deformation zones and fracture domains at the site proposed for a spent nuclear fuel repository sweden and consequences of structural anisotropy abstract this paper presents a review of the data sets and methodologies used to construct deterministic models for the spatial distribution of deformation zones and intervening fracture domains in 3 d space at forsmark fennoscandian shield sweden these models formed part of the investigations to characterize this site recently proposed as a repository for the storage of spent nuclear fuel in sweden the pronounced spatial variability in the distribution of bedrock structures formed under ductile lower amphibolite or greenschist facies and subsequently brittle conditions was controlled by two factors firstly the multiphase reactivation around and after 1 8 ga of older ductile structures with a strong anisotropy formed under higher temperature conditions at 1 87 1 86 ga and secondly by the release of rock stresses in connection with loading and unloading cycles after 1 6 ga the spatial variability in bedrock structures is accompanied by a significant heterogeneity in the hydraulic flow properties the most transmissive fractures being sub horizontal or gently dipping although the bedrock structures at forsmark are ancient features the present day aperture of fractures and their hydraulic tranmissivity are inferred to be influenced by the current stress state it is apparent that the aperture of fractures can change throughout geological time as the stress field evolves for this reason the assessment of the long term up to 100 000 years safety of a site for the storage of spent nuclear fuel in crystalline bedrock requires an evaluation of all fractures at the site not only the currently open fractures that are connected and conductive to groundwater flow this study also highlights the need for an integration of structural data from the ground surface and boreholes with magnetic field and seismic reflection data with high spatial resolution during the characterization of structures at a possible site for the storage of spent nuclear fuel in crystalline bedrock

geochemical events documented in inorganic carbon isotopes abstract screening of sampling and analytical data is crucial for the detection of real global shifts in marine 13c against the noise of diagenesis the real global shifts of 13c are of two types 1 long term secular shifts caused by changes in the fractional burial of organic carbon and 2 transient shifts caused by abrupt changes of biological productivity in the surface photic zone both are applicable to stratigraphic correlation but differ in their application to modelling of changes in oceanographic or atmospheric composition a recent compilation found 34 carbon isotope events in the phanerozoic and neoproterozoic equally distributed among positive and negative shifts this in itself attests to a variety of proximate causes of the shifts

geomorphological mapping of glacial landforms from remotely sensed data an evaluation of the principal data sources and an assessment of their quality abstract this paper presents the results of an experiment to compare glacial geomorphology mapped from remotely sensed imagery with 1 10 000 scale field mapping the field mapping was validated against high resolution lidar imagery of an area glacierized during the younger dryas and found to provide an essentially reliable if not complete representation of the glacial geomorphology the experiment consists of comparing the field mapping with digital elevation models shuttle radar topography mission c band landmap os panorama os profile nextmap and satellite imagery landsat thematic mapper of a 100 km2 region of central scotland north of glasgow that was last glaciated during the last glacial maximum and during the younger dryas respectively c 14 5 and 11 5 cal ka bp for the purposes of this exercise we concentrated on glacial lineaments flutes drumlins and crag and tail but attention was also given to moraine ridges and eskers qualitative and quantitative comparisons are performed and the results show that of the remotely sensed data sets only nextmap great britain provided results that showed any approximation to the field mapping os panorama and os profile provided very poor approximations and the other methods fail to provide any information of value attention is given to the issues of scale and the differences between a small scale detailed study such as this experiment in which a high resolution glacial geomorphological reconstruction is required and the small scale studies where the remote sensing techniques used here provide important evidence of regional significance when glaciers formed the largest elements of the landscape the paper concludes with a consideration of protocols for future geomorphological mapping exercises and outlines some of the requirements that must be adopted as these protocols are developed