late quaternary plume nepheloid and turbidite sedimentation and effect of the gulf stream near the tail of the grand banks newfoundland abstract cores collected from the tops of the fogo seamounts southwest of the grand banks of newfoundland contain considerable amounts of detrital clay the seamounts rise at least 1 km above the surrounding sea floor and are an unlikely place for sedimentation by turbidity currents sedimentological and micropaleontological evidence suggests that large amounts of detrital clay were injected into the system during glacial and interglacial stages by turbidity currents and surface sediment plumes the main source of sediment was the laurentian channel although some sediment was injected through the canyons around the grand banks surface sediment plumes were strongly influenced by the labrador current and by the surface circulation of the gulf stream fine grained sediments injected into the system by turbidity currents through the laurentian channel were probably trapped by the deep circulation of the gulf stream and dispersed to the northeast effects of the sediment drift induced by the deep gulf stream circulation is also reflected in an abrupt eastward bent of the depositional lobes of the laurentian fan and in the shape of the newfoundland ridge

early deformation in the eastern goldfields yilgarn craton western australia a record of early thrusting the earliest pervasive deformation events in the archaean eastern goldfields superterrane of the yilgarn craton are partly obscured by subsequent deformation and pre date rocks exposed over large areas as a result uncertainty exists about the nature timing and role that early deformation events played in controlling regional architecture and gold mineralization in this world class metallogenic province the daisy milano mining camp in the southern kurnalpi terrane has opened up new exposures in relatively old geological sequences which record structures that pre date the main ene wsw d2 shortening event these d1 structures represent the earliest pervasive deformation events in the eastern goldfields superterrane and are characterized by a pervasive bedding parallel foliation s1 s0 that accommodated nw verging thrusting the same foliation planes also accommodated normal movement verging to the se interpreted to indicate periods of stress relaxation alternatively thrusting and normal movement could have been contemporaneous defining a pure shear event d1 structures are overprinted by steeply dipping nnw striking foliation planes that are axial planar to folds and local crenulation cleavage f2 folds this second foliation is parallel to and overprints post d1 sub vertical plagioclase phyric tonalite dikes at the margins of which the daisy milano gold deposits formed deposits occur stratigraphically below moderately sw dipping ultramafic layers that are sub parallel to the early thrust foliation and acted as impermeable caps to mineralizing fluids mineralization occurs also in ne sw to ene wsw quartz veins in the hinge zones of open and gently plunging f2 folds in a competent dolerite sill mineralization was either synchronous with or post dated d2 two samples of tonalite dikes at daisy milano were analyzed using zircon la icp ms u pb geochronology and yielded ages of 2687 7 ma and 2676 9 ma placing an upper bound on the timing of d2 and gold mineralization at daisy milano and a lower bound on the timing of d1

pervasive granitoid magma transfer through the lower middle crust during non coaxial compressional deformation granitic magmas migrated through early proterozoic middle lower crust at mt hay central australia via a diverse network of narrow structurally controlled channelways during a period of progressive w sw directed thrusting d1a d1d they utilized existing folds boudins and shear zones or created new channels by magmatic fracture either parallel to layering or rarely in irregular arrays the magmas rose obliquely parallel to the plunging 50 60 regional elongation direction which was defined by coaxial folds boudin necks and a strong mineral elongation lineation megacrystic charnockitic magmas migrated through metre scale conduits during d1a d1b but leucosomes were generally restricted to smaller centimetre scale structures that existed throughout the entire deformation history thus d1a d1b leucosomes were potential feeders of in situ partial melts to the adjacent larger conduits of charnockite magma thereby providing a pervasive interconnected network that allowed efficient migration of all magma types during the early stages of thrusting the upper middle crust of the anmatjira reynolds range area contains abundant megacrystic granitoid sheets that are of similar age and geochemistry to those at mt hay they are considered to have formed as syntectonic intrusions emplaced during w sw directed thrusting as at mt hay suggesting that granitic magmas formed near the base of the continental crust passed through the mid lower crustal level 25 30 km exposed at mt hay and accumulated in batholithic proportions at shallower crustal levels 12 20 km such as the anmatjira reynolds range area the observations imply that granitoid magmas in the deep crust are capable of pervasive migration through the crust during major compressive noncoaxial shear deformation localization of magmas by sequentially developed narrow compressive structures suggests that dilatancy followed successive foliation forming events a situation that can occur during steady state deformation if the effective confining pressures are low which would be a result of high and possibly variable rates of magma influx the inferred rapid melt segregation and migration during deformation suggest that large chambers do not form until magma reaches neutral buoyancy in the middle to upper continental crust

acoustic interpretation of quaternary sedimentation and erosion on the channelled upper laurentian fan atlantic margin of canada about 1000 km of single channel seismic reflection profiles from a 50 km 100 km area on the upper laurentian fan shows no evidence of the large slumps interpreted by previous workers in this area our detailed profile grid indicates that slump like masses are commonly in depositional continuity with definite autochthonous sediments and surfaces previously interpreted as slide planes are either facies changes or the result of valley wall erosion only a few small slump blocks of relatively consolidated sediment are found on the uppermost fan acoustic facies distribution shows a single early pleistocene fan valley crossing the northeast part of the survey area with thick overbank sediments to the southwest in the middle pleistocene this valley became incised its upper reaches then ceased to receive sediment and a new valley was cut extending southward from the upper slope and intercepting the lower reaches of the old fan valley this channel diversion was probably related either to the glacia

granitoid diapirism during protracted tectonism in an archaean granitoid greenstone belt yilgarn block western australia abstract the bullfinch parker dome area is an archaean granitoid greenstone terrain in the yilgarn block of western australia affected by a complex protracted tectonic event the majority of the deformation history was progressive rather than multiple discrete events finite strain patterns and structural and metamorphic zonation suggest that deformation in the greenstones was caused by regional ene wsw shortening and broadly simultaneous upward movement of granitoids by solid state diapirism and or ballooning plutonism rather than by core complex formation or multiple folding evidence for pluton related tectonism includes the foliation trends steeply plunging radial mineral lineations indications of upward movement of plutons increase of strain towards the batholith margins concordant structures in the pluton and the surrounding rocks such as lineation and foliation patterns constrictional tectonics near east west trending granitoid greenstone contacts syn to post kinematic peak metamorphism contact metamorphic zoning and pressure differences metamorphism largely of amphibolite facies was probably related to uprise of the granitoids at moderate crustal depths 10 12 km p 3 kbar causing both regional and contact metamorphism as a single thermal event relative and absolute timing defines an overlapping sequence of metamorphism progressive deformation and plutonism in this part of the yilgarn craton during the late archaean

age constraints on recycled crustal and supracrustal sources of archaean metasedimentary sequences eastern goldfields province western australia evidence from shrimp zircon dating abstract shrimp u pb zircon dating of sedimentary volcanic and subvolcanic intrusive rocks from unconformity bounded sequences in the eastern goldfields province defines maximum depositional ages for those sequences the kambalda sequence which records a backarc basin was deposited prior to 2700 ma and from at least 2715 ma the spargoville sequence which records an arc adjacent volcano bound basin was deposited between 2700 and 2683 ma the kalgoorlie sequence which records an intra arc rift basin comprises two tectonic stages with depositional ages of 2681 2670 and 2661 2655 ma deposition of the spargoville and kalgoorlie sequences overlapped with the intrusion of granitoids and subvolcanic porphyries thereby indicating that those granitoids were emplaced during crustal extension younger submarine fan kurrawang sequence and braided fluvial merougil and jones creek sequences deposits of a remnant ocean basin were deposited at when coupled to palaeocurrent data provenance dating of detrital zircon suites fingerprints southeast oriented amalgamation of felsic detritus from multiple sources within longitudinal depositional systems and longitudinal reworking of felsic detritus from single sourced transverse systems most felsic detritus was recycled from coeval volcanoplutonic arcs and the orogen to the remnant ocean basin sequences with zircon ages ranging from 2730 to 2660 ma older felsic sources with age ranges of 3570 3130 3030 2900 2870 2770 and 2760 ma could have been structural enclaves within the volcanoplutonic arcs or orogen but were more likely within a distant cratonic basement when coupled with stratigraphic data it is concluded that detrital zircon age distributions preserve evidence for the sedimentary recycling of coeval volcanoplutonic arc or orogenic sources uplifted basin floor and dissected arc successions and cratonic basement virtually all source terrains have apparently vanished presumably through the combination of tectonic and sedimentary recycling and tectonic severance increased use of detrital zircon suites from archaean sedimentary sequences is advocated in order to quantify the balance between sedimentary recycling of felsic rocks from contemporaneous volcanoplutonic sources which themselves document crustal growth in arc environments and from relict volcanoplutonic and crustal basement sources which document the degree of crustal recycling

stretching lineations in transpressional shear zones an example from the sierra nevada batholith california abstract ductile shear zones and associated stretching lineations are generally considered to be the result of two dimensional simple shear deformations with stretching lineations interpreted to rotate into parallelism with the direction of tectonic transport with increasing deformation however stretching lineations perpendicular to the inferred tectonic transport direction are displayed by some shear zones field studies in the sierra nevada batholith have revealed a single shear zone the rosy finch gem lake shear zone that contains both steeply plunging stretching lineations in older metamorphosed sedimentary and granitic rocks and shallowly plunging stretching lineations in syntectonic granitoids dextral sense of shear indicators are found in all these units and deformation occurred simultaneously along the length of the shear zone theoretical strain modeling indicates that stretching lineations can be either horizontal or vertical within transpressional shear zones to investigate the kinematics of three dimensional deformation we examine the role of stretching lineations which form as a result of finite strain including the possibility of partitioning a component of the strike slip movement onto shear bands comparing the field data with the strain modeling we interpret the along strike variation in lineation behavior within the rosy finch gem lake shear zone to be a result of the differences in finite strain recorded by different units the older units showing steeply plunging lineation have recorded more finite strain across a narrower shear zone than the syntectonic granites which record shallowly plunging lineations we conclude that the orientation of the lineation within transpressional shear zones does not necessarily correlate with the transport direction but may reflect along strike variations in finite strain and or strain partitioning

fabric attractors in general triclinic flow systems and their application to high strain shear zones a dynamical system approach high strain zones may deform by flow with a triclinic symmetry this paper describes triclinic flow in a reference frame where instantaneous stretching axes isa are fixed the operation of triclinic flow is described in two ways first in terms of flow and the nature of flow eigenvectors and in the second part of the paper in terms of finite strain in monoclinic flow at least one of the eigenvectors of the flow coincides with one of the isa and one or two of the eigenvectors act as attractors of foliation or lineation elements in triclinic flow some flow eigenvectors are undefined since the two largest eigenvalues controlling the flow are imaginary imaginary eigenvalues are particularly common at high kinematic vorticity and within flow with deviation of the vorticity vector of more than 20 from one of the isa strong deviation from monoclinic flow is therefore possible but this will not produce permanent foliations or lineations for triclinic flow that does produce permanent fabrics the angle between isa and the fabric is so small that it is unlikely that it can be recognised in nature a discussion of the potential application of such results within real shear zones is presented

deformation and recrystallization of plagioclase along a temperature gradient an example from the bergell tonalite abstract syn to post mylonitic tilting of the bergell tonalite allows investigation of the deformation and recrystallization of plagioclase grains along a temperature gradient from the lower to the upper amphibolite facies at the lowest temperatures recrystallization occurs by nucleation and growth of new grains having a different composition from the old grains in contrast at the highest temperatures recrystallization occurs by subgrain rotation associated with grain boundary migration the temperature increase is inferred to induce this transition in two ways first at higher temperatures the anorthite content of the new grains is higher and thus the comositional difference between old and new grains is lower hence the chemical driving potential is small compared with recrystallization at lower temperatures second higher temperatures facilitate climb of dislocations and thus subgrain formation as well as grain boundary mobility the temperature increase is also associated with a transition in the dominant deformation mechanism intracrystalline plasticity dominates deformation at lower temperatures whereas at higher temperatures deformation occurs primarily by diffusion accommodated grain boundary sliding as indicated by the weakening of the indicatrix preferred orientation and the formation of a mixed plagioclase biotite matrix with increasing deformation therefore the strength of the mid to lower crust may be overestimated by dislocation creep flow laws for plagioclase lower crust rheology for polyphase rocks is better approximated by constitutive relationships involving diffusion accommodated grain boundary sliding

kinematic nature and origin of regional scale ductile shear zones in the central yilgarn craton western australia abstract regional scale northwest and northeast trending ductile shear zones 1 to 6 km wide and over 100 km long are the most conspicuous structures in the central yilgarn craton western australia they are commonly developed along granite greenstone contacts but are centred in strongly foliated granite and granitic gneiss a wide range of kinematic indicators including well developed s c fabrics c type shear band cleavage and abundant asymmetric porphyroclasts consistently indicate sinistral movement on northwest trending shear zones and dextral movement on northeast trending shear zones major planar fabrics within the ductile shear zones include 1 a northwest or northeast trending foliation parallel to the shear zones 2 a northerly trending gneissic banding and 3 a northerly trending foliation the northwest and northeast trending foliations with associated asymmetric structural elements and a shallowly plunging mineral lineation were developed during a progressive inhomogeneous east west shortening event d3 characterized by low temperature noncoaxial deformation formation of the northerly trending gneissic banding and associated symmetric structural elements is attributed mainly to east west coaxial shortening d2 in a high temperature state during or shortly after granite intrusion the northerly trending foliation within the ductile shear zones commonly forms the s fabric of s c fabrics that was either developed during d3 same time as the c fabric or was reactivated from s2 foliations therefore major planar fabrics in the regional scale ductile shear zones of the central yilgarn craton can be ascribed to two tectonic events d2 and d3 and deformation within the shear zones includes both coaxial and noncoaxial components

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

laurentian fan morphology sediments processes and growth pattern thick sediment accumulations in deep water provide a new target in the search for oil and require an innovative approach to hydrocarbon exploration the laurentian fan is a large deep sea 2 000 to 5 000 m fan in the western north atlantic and has been the major depocenter off nova scotia since at least the early tertiary the main development of the present depositional and erosional fan morphology in the past 2 to 3 m y was closely related to onshore glacial history the slope above the fan has been the site of rapid sedimentation and consequent slumping a network of tributaries on the upper fan appears to feed three main channel systems incised up to 800 m between broad asymmetric levees these channels meander widely across the lower fan then die out abruptly and pass into a lobate suprafan differences between the laurentian fan and typical fan models result in part from the muddy nature of the sediment and the supply system the channels contain thick coarse gravels which probably grade distally into sandy lobes both should produce good reservoir bodies with suitable source and trapping mechanisms fine grained sediments were more important in fan construction interbedded turbidites contourites and hemipelagites are present in the late quaternary holocene sequence the distribution of these sediments and in particular the recognition of structural sequences textural trends and fabric types in the fine grained turbidites can be used to characterize particular parts of the fan environment the development of this approach should prove useful in future hydrocarbon exploration

quaternary development of channels levees and lobes on middle laurentian fan seismic reflection profiles from the middle laurentian fan show that the western fan valley has an abrupt eastward leftward hook at its terminus the right hand levee of this valley has been built across an older depositional surface in which numerous south trending channels developed before the abrupt bend formed this older channeled surface probably represents a complex depositional lobe deposit eastward deflection of turbidity current flow occurred after debris flow or slide deposits partly obstructed the valley near its termination or after aggradation of the lobe deposits this deflection produced an abrupt change in the valley trend through time the eastward growing part of the levee has migrated northward toward the axis of the channel this northward migrati n confines turbidity current flow against the levee of another valley immediately upfan this study documents progradation of muddy facies over sandy lobes thus providing conditions for an effective seal for any hydrocarbons accumulated in the lobe sands updip migration of hydrocarbons through valley fill sands that are contiguous with the lobes could be blocked locally by thick debris flow units or by fine grained turbidite fill in abandoned channels

phase boundary mobility in naturally deformed high grade quartzofeldspathic rocks evidence for diffusional creep abstract grain shape fabrics and optical microstructures of some quartzofeldspathic rocks deformed under upper amphibolite facies conditions in the southwestern grenville province ontario canada suggest that quartz and feldspar have accommodated intracrystalline plastic strains by both diffusional and dislocation creep in these rocks quartz and feldspar form polycrystalline domains separated by gently curved and locally cuspate phase boundaries whose morphology is similar in certain respects to the phase boundary morphology of rocks annealed experimentally under hydrostatic stress conditions in the naturally deformed rocks however phase boundary cusps consistently point along the foliation and parallel to the mineral fibre lineation i e in directions of inferred finite extension which implies that phase boundary motion and cusp formation occurred during deformation optical microstructures in feldspar and crystallographic preferred orientations in quartz are consistent with the accommodation of some intracrystalline plastic strains by dislocation creep however the morphology of quartz feldspar phase boundaries cannot be explained by either dislocation creep or static annealing alone we propose that phase boundary motion resulted from a diffusion assisted process involving dissolution at foliation parallel quartz feldspar phase boundaries mass transfer over length scales of the order of feldspar domain size 200 m or greater and precipitation at quartz feldspar phase boundary cusps this study extends the range of natural deformation conditions under which diffusional creep has been identified in quartzofeldspathic rocks it also has important implications for the natural rheological behavior of the mid and lower continental crust

terrane accretion in the southwestern yilgarn craton evidence from a deep seismic crustal profile abstract interpretation of a seismic gravity and magnetic traverse across the western margin of the yilgarn craton undertaken approximately 110 km north of perth together with new rb sr and u pb geochronological data from the southwestern portion of the craton have led to a re evaluation of the geological relationships and to the development of a terrane accretion model for the region the geophysical data established the three layered nature of the crust with e dipping reflectors present throughout its thickness of 32 40 km reflectors in the upper crust correlate with shear zones mapped at the surface and are interpreted as major thrusts that have transported crustal slices from the east these sole out at a depth of about 10 km along a well defined decollement and indicate thin skinned tectonism the shear zones define the boundaries of three terranes which from west to east are herein defined as the balingup boddington and lake grace terranes the balingup terrane is composed of trough facies metasediments believed to have been deposited at 2 8 ga and subsequently metamorphosed under medium pressure amphibolite facies conditions this terrane contains some of the youngest granitoids in the yilgarn craton 2612 and 2527 ma and these have been extensively sheared by late archaean movement along the darling fault zone the boundary with the boddington terrane to the east is not precisely defined partly due to lack of exposure it is marked in the south by a narrow 100 km long strip of tectonised quartz monzonite and further north by a change in the rb sr biotite ages of granitoids from 400 500 ma in the west to 2300 2600 ma in the east the boddington terrane contains a sequence of archaean shelf facies metasediments part of the jimperding metamorphic belt believed to have been deposited at 3 1 ga and metamorphosed up to amphibolite granulite transition facies under low pressure conditions these sequences occur mainly in flat lying nappes which may have been tectonically transported from the east during assembly with the lake grace terrane the boddington terrane also contains two low grade greenstone belts formed between 2650 and 2670 ma and intruded by 2640 ma granitoids the eastern boundary of the boddington terrane is marked by a major change in gravity which also corresponds with a series of shear zones at the surface a change in structural style and a major change in the nature of the granitoids east of this boundary in the lake grace terrane granitoids of two ages have been recognised charnockites formed at 2640 ma and post tectonic granodiorites formed at 2580 ma metasedimentary rocks metamorphosed to granulite facies occur as rafts and lenses with steep upright folds and are enclosed in leucocratic garnetiferous granitic gneiss greenstones also metamorphosed to granulite facies and recording ages of around 2790 ma are also enclosed within the charnockites and are thus substantially older than the low grade greenstones in the boddington terrane to the west assembly of the balingup and boddington terranes appears to have been completed prior to the emplacement of the logue brook granite at 2612 ma the boddington and lake grace terranes came together after the 2640 ma granulite facies metamorphic event but the precise timing of assembly is not currently constrained it was certainly completed by 2411 ma the time of emplacement of a major set of e w trending mafic dykes the widgemooltha dyke suite which extend for over 500 km across the yilgarn craton although the widgemooltha dyke suite appears to be absent from the balingup terrane this is possibly related to extensive nw shearing during the proterozoic which also led to extensional re activation of the decollement that marks the base of the upper crust in the region

late glacial to holocene climatic and oceanographic record of sediment facies from the south scotia sea off the northern antarctic peninsula two gravity cores were collected from the south scotia sea located off the northern antarctic peninsula during the 2002 2003 korea antarctic research program karp expedition to determine the late quaternary climatic and oceanographic history reassessment of previous sedimentological geochemical and micropaleontological analyses combined with established age model of ams 14c dates represent the reliable record of late pleistocene climatic oceanographic change for the scotia sea region of antarctica during the last glacial maximum lgm the south scotia sea received large amounts of sorted terrigenous sediments and some of the reworked diatom fossils emplaced by bottom currents from an extensively glaciated weddell sea continental margin drifting icebergs calved from the glacial fronts have dispersed glacial dropstones throughout the study area the bottom current deposits during the glacial phase comprise two lithologic units 1 bioturbated gravelly sandy mud facies 1 formed by sluggish bottom current caused by reduced dense water production originated from the ice sheet on the weddell shelf 2 indistinctly layered diatomaceous mud as shown by total organic carbon toc highs in the facies 1 deposited by sporadic bottom currents caused by intensified sea ice formation in polynya during the glacial stage the lgm is characterized by greater and longer sea ice coverage and a restricted weddell scotia summer communication as evidenced by a relative decrease in percentage thalssiosira antarctica and chaetoceros resting spores which are more abundant close to the weddell ice shelf deglaciation about 13 000 9000 14c yr bp in the south scotia sea was characterized by increasing toc diatom abundance and decreasing magnetic susceptibility and sand contents up core at this time subglacial meltwater streams began to emanate from the weddell ice sheet with peak of ice rafting sediment laden turbid plumes from melting glacier and deglaciated weddell shelf have probably been joined into the realm of contour currents weddell gyre circulation ultimately forming indistinctly laminated gravelly mud facies 2 in the south scotia sea these currents probably resulted from water exchange between the weddell ice shelf and circumpolar warm deep water during the retreating phase of the last glaciation the deglaciation was probably followed by a period of open marine conditions with variable extent of sea ice variable toc content between about 9000 and 3000 14c yr bp bottom water production occasionally appears to have diminished or ceased due to the disintegration of some of the weddell ice shelf and biogenic input became increased forming bioturbated diatomaceous mud and ooze facies 3 the climatic amelioration could have restored the weddell scotia communication during the summer as evidenced by a relative increase of t antarctica and c resting spore in facies 3 at the onset of neoglacial about 3000 14c yr bp a decrease in toc and diatom abundance and an increase of sand content reflect the formation of more extensive and seasonally persistent multiyear sea ice the weddell ice shelf advanced with increased sea ice coverage at this time and as a result bottom water might play a role in transporting terrigenous sediments and reworked fossil diatoms into the south scotia sea forming diatomaceous sandy mud facies 4 during this time it is possible that the weddell scotia communication would have been partly restricted as evidenced by a reduction of the numbers of t antarctica and c resting spores our results indicate environmental variability throughout the late quaternary that was consistent across most portions of the maritime antarctic peninsula in addition the timing of climatic transitions correlates with the northern hemisphere indicating the possibility of coherent climatic variability during the late quaternary at least for the higher latitudes

rock magnetism of late neogene and pleistocene deep sea sediments relationship to sediment source diagenetic processes and sediment lithology we use bivariate scatter plots to illustrate variations in selected rock magnetic properties low field susceptibility anhysteretic and isothermal remanence of late neogene and pleistocene deep sea sediments from 16 sites in the arctic ocean north atlantic equatorial atlantic and north pacific ocean and the arabian sea our intention is to examine the ability of the rock magnetic properties to differentiate the sediments according to factors such as lithology geographical area and the dominant mode of terrigenous sedimentation which at these sites is via ice rafting via bottom currents or via eolian processes overall correlations between sediment magnetic properties and gross lithology is poor and factors such as the source and transport path of terrigenous sediment and detrital magnetic minerals together with the action of reductive diagenetic processes are the major controls on the magnetic properties on the bivariate scatter plots sites with major ice rafted contributions tend to have high sedimentary ferrimagnetic mineral concentrations relatively coarse ferrimagnetic grain sizes and scattered sample point distributions in contrast sites where we infer significant bottom current supply of terrigenous material have tightly grouped sample point distributions carbonate sediments in which the terrigenous component is supplied by eolian processes tend to have a broad range of magnetic mineral concentration caused by glacial interglacial fluctuations in carbonate accumulation and eolian activity sediments containing significant volcanogenic material have high concentrations of relatively coarse grained ferrimagnetic material reductive diagenesis is a significant determinant of sediment magnetic properties in high productivity areas and has the effect of preferentially removing the fine grained ferrimagnetic fraction causing a coarsening of the ferrimagnetic grain size distribution and a rise in the antiferromagnetic ferrimagnetic ratio

sedimentary characteristics of late pleistocene bottom current deposits barents sea slope off northern norway abstract the barents sea slope off northern norway received large amounts of terrigenous sediments from an extensively glaciated norwegian continental margin during the late pleistocene a sedimentological study of seven gravity cores from the barents sea slope suggests that some terrigenous sediments were transported by both downslope currents and contour following bottom currents the bottom current deposits comprise four sedimentary facies 1 indistinctly laminated mud 2 layered mud 3 indistinctly layered mud and 4 bioturbated mud the indistinctly laminated mud on the mid to lower slope is characterized by a relatively low degree of bioturbation and consists of monotonous diffuse and discontinuous silt rich and silt depleted laminae 1 mm scale and or discontinuous trains of coarse grains these characteristics are suggestive of sedimentation from contour currents driven by water exchange with the north atlantic ocean these bottom current deposits can be distinguished from fine grained turbidites silt clay couplets and intensively bioturbated hemipelagites on the barents sea slope

prism and basal plane parallel subgrain boundaries in quartz a microstructural geothermobarometer empirical data on quartz subgrain patterns from various metamorphic rocks show that at least up to 10 kbar in the stability field of low quartz prismatic subgrain boundaries are dominant whereas basal subgrain boundaries are not developed in the high quartz stability field both prismatic and basal subgrain boundaries occur and form typical rectangular chessboard patterns the likely reason behind the different occurrence of these subgrain patterns is that in high quartz prismatic glide becomes as easy as or probably even easier than basal glide the two types of subgrain patterns can be clearly distinguished by optical microscopy consequently the occurrence of chessboard subgrain patterns in quartz represents a practicable geothermobarometer the possibilities of its application are far reaching and include the specification of deformation conditions at high grade metamorphism the recognition of syntectonic intrusions and the distinction between pluton emplacement at lower and at higher crustal levels

geological effects of the gulf stream system on the northern bermuda rise abstract the gulf stream system contains a clockwise rotating set of bottom currents which influence the sea bed in the northern north american basin it is possible to interpret the present day and historical record of current activity in this basin in terms of the deep flow of the gulf stream this interpretation provides a much more satisfactory and consistent explanation of the geologic record than previous interpretations based strictly on the influence of the classic abyssal circulation the present day circulation of the gulf stream actively resuspends large quantities of sediment on and near the northern bermuda rise and it is suggested that this resuspension may be due to the eddy field which is embedded in the westward flowing return flow during the late cenozoic the gulf stream system was responsible for depositing and shaping the major acoustic sedimentological units on the relatively smooth surface of the horizon a complex fine grained mont morillionite rich sediments derived from the chemically weathered saprolites of the hudson and st lawrence drainage basins were injected into the deep ocean basins by turbidity currents during the late paleogene and the neogene fine grained turbidites from the st lawrence spread southward down the southeastern sohm abyssal plain across the eastward flowing gulf stream and its westward flowing return flows portions of these fine grained sediments were entrained by the main and return flows and deposited downstream as acoustically non laminated accumulations on the corner and bermuda rises respectively the hudson river input was injected into the deep basin through the hudson canyon system the interaction of these fine grained turbidites with the northward flowing deep flow of the gulf stream system led to the formation of the gulf stream outer ridge here defined for the first time during the late neogene or early pleistocene the gulf stream outer ridge was partially eroded by the gulf stream system and portions subsequently covered by coarse grained pleistocene turbidites the coarse grained illite rich turbidites that flowed across the southeastern sohm abyssal plain also crossed the main and return flows of the gulf stream system the finer portions of these sediments were entrained and deposited as pleistocene acoustically laminated sediments on the plateaus of the bermuda and corner rises

late pleistocene sedimentation on the norwegian continental slope between 67 and 71 n abstract the northern norwegian continental margin between 67 and 71 n comprises the gentle slope off the barents sea the relatively steep lofoten islands slope and the step like slope of the voring plateau during the late pleistocene these slopes received large amounts of terrigenous sediments from an extensively glaciated norwegian continental margin through the analyses of 17 gravity cores high resolution 3 5 khz and airgun seismic profiles and sea beam bathymetric data we have examined the late pleistocene sedimentation pattern of this region eight sedimentary facies from the gravity core analysis and seven types of 3 5 khz echo characters indicate that the slopes were moulded by hemipelagic sedimentation commonly associated with iceberg rafting slope failure slump slide and debris flow turbidity currents downslope bottom currents and contour following bottom currents ice rafted debris was dispersed over a broad area including the lower slopes off the barents sea and the lofoten islands and the voring plateau and its outer slope slope failures prevailed on the lofoten islands and voring plateau slopes where the broad glacial margin directly released unsorted glacial sediments during glacial periods on the barents sea slope glacial and reworked shelf sediments were supplied by underflows which were probably caused by cooling of surface shelf water during glacial periods on the upper slope sediments were further transported by turbidity currents and slope crossing bottom currents which excavated numerous small scale channels there are indications of deep sea contour currents at the base of slope and the upper slope off the barents sea and on the voring plateau these currents probably resulted from water exchange between the norwegian greenland sea and the north atlantic ocean during interglacial periods

shear zones and magma ascent a model based on a review of the tertiary magmatism in the alps 1 the alpine oligocene plutons are spatially and temporally associated with the activity of the periadriatic fault system pfs an orogen parallel crustal scale transpressive mylonitic belt excellent three dimensional exposure combined with a wealth of structural seismic petrological geochronological geochemical and paleomagnetic data collected over the last decades help to constrain the relationships between deformation ascent and emplacement of the plutons magmas were channeled from the base of the thickened continental crust into the narrow mylonitic belt of the periadriatic fault system which was used as ascent pathway to cover vertical lengths of 20 to 40 km therefore the linear alignment of the plutons at the surface is not the expression of a linear source region at depth ascent of the melts is controlled by the mylonitic foliation of the pfs which forms the only steep anisotropy continuously traversing the entire alpine crust in contrast the flow direction is not influenced by the specific kinematics of the faults final emplacement of the plutons occurred by extrusion from the periadriatic fault system into the adjacent country rocks the transition from ascent to final emplacement is favored by partitioning of transpressive deformation

a 1 ma record of sediment flux south of the grand banks used to infer the development of glaciation in southeastern canada abstract a 20 m long piston core from a basement ridge on the continental rise off southeastern canada provides a 0 9 ma record of distal continental margin sedimentation sediment sources are distinguished by sand and clay sized mineralogy and detrital palynomorphs they include detritus eroded from a northern canadian shield and lower paleozoic rocks transported southward through the labrador sea b the grand banks and c the gulf of st lawrence and newfoundland isotopic stratigraphy allows correlation of glacial and interglacial stages with changes in sources and flux rates via different transport processes nepheloid layer ice rafting and distal turbidity currents the glacial history of southeastern canada is interpreted from variation in the flux and type of detrital material and correlation with other data from the continental margin from stages 27 to 15 the grand banks formed a forested coastal plain limited local glaciation may have occurred in stages 18 and 16 tertiary regolith and cretaceous clays were stripped from land areas in stages 14 and 12 culminating in the excavation of the laurentian channel late in stage 12 extensive cold based ice sheets are inferred for glacial stages 10 8 and 6 with less severe glaciation in stages 4 and 2 extent of this local appalachian ice correlates poorly with global ice volumes

blunt ended dyke segments two examples of blunt ended dykes from the rooi rand dyke swarm in south africa are examined in order to determine the mechanism by which such features form although other interpretations of blunt ended dykes have been proposed evidence in the rooi rand examples suggests that dilation was transferred along a zone of shear at the dyke tip oriented at a high angle to the dyke plane microscopic analysis of samples from blunt ended tip regions reveals cataclasis and mineral straining in the dyke walls in the zone of dyke linkage the indication is that adjacent blunt ended en cchelon dyke segments dilate along a shear zone producing cataclasis of the host rock both segments dilate in this manner and are blunt ended prior to linkage horns may develop at the outer corners of the blunt tips so that subsequent to linkage the overall geometry resembles that predicted by the conventional model of bridge failure between overlapped en tchelon dykes however permanently strained bridges predicted by that model are not necessary for the model described here in addition blunt ended dykes that dilate along a cross linking shear zone do not need to overlap in order to link together in contrast to existing model predictions dilation adjacent to a blunt ended dyke may also be accommodated by intrusion of magma into shear zone fractures that vary in orientation with respect to the main dyke near the dyke the near tip stress field overrides the remote stress field and generates magma filled shear related fractures at high angles to the dyke plane with increasing distance from the dyke the remote stress field becomes dominant and resultant shear related fractures are oriented at successively lesser angles to the dyke plane