the amazon river plume during amasseds spatial characteristics and salinity variability the amazon river discharge forms a plume of low salinity water that extends offshore and northwestward over the north brazilian shelf observations acquired as part of a multidisciplinary amazon shelf sediment study amasseds are used to characterize the spatial structure and temporal variability of the amazon plume four shipboard conductivity temperature depth ctd surveys spanning the shelf from 1 s to 5 n during rising march 1990 maximum may 1990 falling august 1989 and minimum november 1991 discharge show the amazon plume is typically 3 to 10 m thick and 80 to over 200 km wide northwest of the river mouth the plume is often characterized by a wedge of low salinity water adjacent to the coast and a separate tongue of low salinity water extending offshore over the middle to outer shelf a bottom front separating the low salinity plume water from oceanic water is consistently located between the 10 and 20 m isobaths a moored array deployed about 300 km northwest of the river mouth from february to june 1990 included inner and midshelf moorings in 18 and 65 m of water on which temperature conductivity measurements were made the moored observations reveal salinity variations within the amazon plume of over 10 psu on timescales of days to weeks this variability includes intermittent events in which plume water pools up in the vicinity of the river mouth and the plume width can exceed 200 km these accumulation events are apparently due to wind events with a southeastward component which impede or block the normally northwestward freshwater transport the resulting bulges in the plume are then released northwestward when the wind reverses volume budgets indicate the amazon plume entrains roughly twice the river discharge between the river mouth at the equator and 3 n estimates of gradient richardson numbers from the moorings suggest entrainment due to the strong semidiurnal tidal currents occurs where the plume intersects the bottom and over the outer portion of the plume where salinities approach oceanic values

flow and fabric development during the diapiric rise of magma scaled isothermal experiments of the internal circulation induced by viscous drag at a diapir country rock interface are compared with published theoretical studies of flow induced finite deformation inside a rising sphere and new numerical results are presented for the incremental strain pattern developed in spherical diapirs the results predict a time dependent deformation history within rising diapirs that produces finite strains characterized by strong oblate flattening strains at the margin and strong vertical prolate strains in the center with an intervening zone of low plane strain finite strains are discussed in terms of the different sub fabrics expected to form in granitoids after considering the history of rheology and temperature distribution in rising magma strong rheological and temperature gradients are predicted for the margins of internally circulating diapirs that can lead to the formation of strong penetrative foliations at the margin and magmatic or even isotropic fabrics in the i

multi year wind dynamics around lake tanganyika lake tanganyika is the second largest freshwater lake in the world by volume and is of prime importance for the regional economy in east africa although the lake is recognized as a key component of the regional climate system little is known about atmospheric dynamics in its surroundings to understand this role we analyze winds around lake tanganyika as modeled by a high resolution 7 km regional climate model consortium for small scale modeling in climate mode over the period 1999 2008 modeled surface wind speed and direction are in very good agreement with high resolution 12 5 km quick scatterometer quikscat satellite wind observations during the dry season comparison of a control run with a model simulation where all lake pixels are replaced by representative land pixels indicates that mean surface wind speed over lake tanganyika almost doubles due to lake presence furthermore a region of higher surface wind speed in the central part of the lake is identified and confirmed by quikscat observations a combination of wind channeling along valley mountains and wind confluence on the upwind side of the lake is responsible for this speed up the lower wind speeds in the rest of the lake result from blocked conditions due to more pronounced orography finally the model captures a zone of higher wind speed at around 2 km height associated with the low level somali jet these results demonstrate that high resolution climate modeling allows a detailed understanding of wind dynamics in the vicinity of lake tanganyika

shell concentration dynamics driven by wave motion in flume experiments insights for coquina facies from lake margin settings abstract coquinas are important carbonate oil reservoirs in the sin rift sequence of the brazilian marginal basins mainly in campos and santos basins they are generated from shell accumulations in lake margin environments in which waves and bottom currents at storm conditions were the main hydrodynamic agents of transport and reworking in order to investigate the role of wave transformation processes in shallow waters swash breaking and wave shoaling in shell concentrations a physical modelling of the coastal environment was performed in laboratory the experimental setup consisted of a 2d flume a wave generator and a sedimentary bottom composed by quartz sand and shells bivalves gastropods and fragments an underwater camera wave gauges and an adv were used to record the sedimentary processes and to perform a quantitative analysis of the hydrodynamics the experimental scenario reproduced a rift lake margin a coastal sector of lake tanganyika tanzania africa was used to set the model boundary conditions in a 1 20 scale as well as the coastal gradient and wave conditions from 54 h of wave experiments which alternated from fair weather to storm wave conditions three shell concentration dynamics were observed reworking winnowing and dynamic bypassing the reworking erosion was characterized by traction rolling and saltation of bioclasts together with the traction and suspension of sand the occurrence of the latter was restricted to the breaking and swash zone in both fair weather and storm conditions the winnowing erosion was featured by sand suspension and the gentle traction and rotation of the bioclasts on the bottom the winnowing occurred at the proximal area of the shoaling zone just behind the first wave breaking point in storm wave conditions the dynamic bypassing omission was identified by the ripples migration over static shells on the bottom of the distal shoaling zone which produced alternated burial and exhumation of bioclasts the quantitative analysis of the oscillatory flow indicated higher velocities at the breaking zone reworking domain than at the shoaling zone winnowing domain mainly during storm conditions this study provided new and more accurate insights to depositional models of lake margin coquinas suggesting that each wave transformation process control a specific dynamic of shell concentration also the limit between the breaking zone and the shoaling zone in storm conditions 1st wave breaking point was identified as a better criterion to bound the reworking domain where fragmented coquinas are produced from the winnowing and dynamic bypassing domains where non fragmented coquinas occur in contrast to the fair weather wave base criterion

a convection permitting model for the lake victoria basin evaluation and insight into the mesoscale versus synoptic atmospheric dynamics aiming for an improved understanding of the different factors that determine the regional climate of the lake victoria basin the cosmo clm regional climate model is set up in a tropical convection permitting configuration and is directly nested in a recent reanalysis product era5 the convection permitting simulation outperforms state of the art climate integrations that rely on convection parametrisations yet the domain averaged model precipitation is larger than in the multi observational ensemble but the latter shows large spread overestimations of outgoing toa shortwave and longwave radiation are much reduced compared to the cosmo clm cordex africa integration but still suggest a general underestimation of the cloud fraction or frequency comparing the control with a no lake simulation the presence of lake victoria implies strong intensification of over lake rainfall but it only slightly increases the total domain averaged precipitation in addition the easterly trade winds are shown to largely affect the mesoscale circulation and precipitation patterns during daytime fast trades and anabatic slope winds trigger convection at the lee wind slopes and subsidence over the basin slow trades allow the stationary air to produce spontaneous convective cells and to develop anabatic winds that result in orographic precipitation during night time trade winds curl around the eastern branch of the east african rift generating a southerly and northerly evening convergence front entering the lake victoria basin thus our results highlight the key importance of the easterly trade winds and the complex orography in determining the total accumulation and location of precipitation in the lake victoria region

finite deformation in and around a fluid sphere moving through a viscous medium implications for diapiric ascent abstract different types of geodynamically active regions like mountain belts hot spots or areas of salt tectonics are characterized by diapirism one key for the reconstruction of the dynamic history of such structures is the progressive strain which can sometimes be determined from field observations successful interpretation of such observations requires a quantitative model of the finite strain in and around a rising diapir a constant viscosity fluid sphere of radius r rising through another isoviscous fluid is assumed to approximate the buoyant motion of a diapir known analytical solutions for the velocity fields are used to numerically evaluate the finite deformation in and around the sphere regions of very high strains are found in a tube with a radius 1 2 r behind the sphere and in a shell of thickness of 0 1r around the sphere the following three dimensional strain regimes can be identified in the half space above the sphere down to its equator finite strains are oblate behind the sphere they progressively change to plane strain in the diapiric source region they are prolate viscous drag at the sphere s surface leads to an internal circulation with one overturn after 10r of rise if the sphere has a relatively low viscosity finite strains within the fluid sphere show a continuous increase with superimposed cyclic straining and unstraining after several body radii of rise the strains become highly inhomogeneous inside the sphere except along the vertical axis and just inside the sphere s surface where strong prolate and oblate strains are observed respectively finite strain determinations in a falling ball experiment cruden 1988 are compared with the theoretical results at horizontal distances of a few body radii from the fall axis the effect of confining container walls is clearly seen in the experimental strain data the results are compared briefly with available strain data from the field which seem to be significantly lower than predicted proposed explanations include a short memory of the rock fabric and a lack of recognition of the strain concentration which would be expected for a temperature dependent rheology it might also be possible that few natural diapirs rise more than a few radii in the solid state

mapping climatological seasonal variations of surface currents in the tropical atlantic using ship drifts the seasonal variability of current velocities in the tropical atlantic was studied by grouping ship drift velocity observations into 2 5 boxes and calculating monthly mean velocity values these values were used to calculate and map the annual mean velocity the seasonal variation about the mean the annual and semiannual harmonics and the first two empirical orthogonal functions eofs the seasonal variation is primarily zonal in the equatorial band and in the north equatorial countercurrent necc and primarily alongshore near the coast of south america maxima of seasonal variation of 23 cm s are centered in the necc near 6 n 42 5 w and in the gulf of guinea near 2 n 7 5 w most 80 of the variance in the necc and along the western boundary of the area studied has an annual period most of the variance along the equator in the mid atlantic has a semiannual period over the whole region 49 of the seasonal variance is explained by the annual harmonic and 69 is explained by a combination of the annual and semiannual harmonics the second eof contains 29 of the variance of the data set and shows a simultaneous speeding slowing of the major equatorial currents the south equatorial current sec the north brazil current the necc and the guinea current along their principal axes of variation with a concurrent slowing speeding of the guyana current and the brazil current the pattern of variation resembles a large equatorial gyre centered along 4 n that flows clockwise from may to september and counterclockwise most of the rest of the year the first eof accounts for 35 of the variance and shows a simultaneous speeding slowing of eastward velocity from 5 s to 10 n except in the western sec the western end of the north brazil current and the guinea current the out of phase fluctuations apparent in the western sec near the equator are explained by the slowing and reversal of the south equatorial current near 2 n 40 w between april and june this slowing of the sec is associated with the start up of the necc which accelerates eastward in may june and july and flows eastward across the atlantic from july through december the sec divides seasonally near the eastern tip of brazil where residual alongshore velocities are northward for half the year peaking during may and june and southward for the other half of the year a second division can be seen north of the amazon where the north brazil current continues up the coast into the guyana current during the first half of the year but partially retroflects into the necc during the last half of the year a fast eastward flow in the necc coincides with below average velocities in the guyana current and above average velocities in the western sections of the north brazil current and the sec north of the equator

observed and modeled meridional overturning circulation related flow into the caribbean 1 a major pathway of the atlantic meridional overturning circulation moc is the warm inflow into the caribbean sea the transport and the contribution of water from the south atlantic is calculated from observations adcp data and hydrography and compared to the results of the flame model the model and the observations show high consistency in the strength of the mean total inflow and its range of variability as well as in the general distribution of water from south atlantic origin the measurements give an annual mean south atlantic water saw transport into the caribbean of 9 3 sv with high variability this estimate has to be regarded as a lower bound since the present method using temperature and salinity data cannot identify the saw included in the north equatorial current nec which recirculated and was transformed in the interior tropical atlantic the model transport reproduces the observational values rather closely with an annual mean inflow of 8 6 sv and similar high variability closer inspection of the saw pathways in the model suggest that the additional contribution by the nec pathway is only about 2 sv the model results confirm the relative importance of the moc pathways suggested by observations the caribbean inflow seems to be the main pathway 63 for the warm and central water 27 1 kg m 3 whereas for the intermediate water a larger fraction 59 is transported northward at the eastern side of the lesser antilles

investigation of the north brazil current retroflection and north equatorial countercurrent variability 1 eight years of topex poseidon altimeter derived sea height anomaly and climatological hydrographic data are used to investigate the temporal and spatial variability of the north brazil current nbc retroflection and the north equatorial countercurrent necc the nbc retroflection exhibits a mean position of 6 6 n 2 0 with a strong annual signal and year to year variability the annual cycle of its location follows the meridional migration of the itcz and the strength of the wind stress curl over the equatorial atlantic a marked shift in the annual mean location of the nbc retroflection is observed in 1998 1999 that appears to be linked to an increase in wind stress curl during this period the mean latitude of the necc is estimated to be 6 0 n 1 3 with a semiannual cycle showing maximum northerly locations in february and august the baroclinic transport of the necc varies predominantly on an annual cycle with maximum transport of 12 sv occurring in november

thermal mechanical modeling of the role of thermal stresses and stoping in magma contamination mantle derived magmas emplaced in the upper crust depth 10 km are in thermal disequilibrium with the surrounding country rock as a consequence of the large temperature contrasts not only will the magma cool quite rapidly but the surrounding country rock will be heated and affected by large thermal stresses using coupled time dependent thermal mechanical models we find that a a single stage 3 km radius magma body has an eruptive life of on the order of 104 years b near the magma wall rock boundary large thermal stresses develop over short time spans 10 years and c material stoped into the chamber as a result of these thermal stresses will be assimilated either in the upper reaches of the chamber or at its base leaving a relatively uncontaminated central core these results indicate that contamination of a primary magma by stoped crustal blocks is an efficient mechanism for producing hybrid lava sequences

local displacement of diapir contacts and its importance to pluton emplacement study abstract the extent to which mid crustal plutons have grown by diapirism cannot be deduced from the horizontal shortening of ductilely deformed host rocks and associated displacement of lateral intrusive contacts by contrast the vertical shortening above plutons and upward displacement of their roof contacts may provide a good measure of the diapiric component of pluton emplacement this is related to the vertical bulk translation of buoyant material in immature diapirs and associated escape flow of overlying rocks the length change of a vertical material line situated above the crest of an immature upright diapir corresponds to the upward displacement of the local contact the length change of horizonal material lines situated at lateral contacts of model diapirs however differs markedly from the contact displacement this is related to the absence of horizontal symmetry planes in the finite strain field about upright diapirs of any shape and the importance of vertical shear at the lateral contacts the host rock strain held of a hypothetical pluton grown in situ by spherical expansion ballooning has an infinite number of symmetry planes the strain held is characterized by large volume losses but the length change of all radial lines corresponds to the local magnitude of contact displacement this precludes the possibility of differentiating in ductile host rocks above plutons between vertical diapirism and spherical expansion unless gauges of volume change are available

oblique diapirism the criffel granodiorite granite zoned pluton southwest scotland abstract strain trajectories strain gradients and quartz c fabrics have been used to propose an emplacement history of the criffel zoned pluton strain has been estimated from the microdioritic xenoliths included in the outer granodiorite textural criteria have been used to complete the pattern of strain variations throughout the pluton strain gradients are found to be related to the granodiorite granite boundary zone with highest strain towards the northeast side of the pluton giving an asymmetric horseshoe pattern quartz c fabrics allow two strain histories to be distinguished within the pluton an early coaxial flattening in the granodiorite followed by a non coaxial deformation in the granite and the adjacent granodiorite these features are interpreted as the result of an oblique diapiric intrusion of the inner granite into the partially emplaced and crystallized granodiorite

a view from the roof magmatic stoping in the shallow crust chita pluton argentina nearly 2 km of vertical relief and exposure of continuous pluton roof wall corners around the chita pluton northwest argentina provides constraints on the 3 d host rock displacement field attending magma emplacement in the shallow crust the pluton is rectangular in crosssectional view and consists of weakly to non deformed granite to granodiorite structures in surrounding metasedimentary host rocks are truncated at a knife sharp contact and are only weakly deflected from their regional orientations final emplacement occurred by stoping together with minor doming of the earth s surface structural restoration of a cross section indicates that host rocks above the pluton may have been domed upwards during emplacement by as much as a few hundred meters accounting for up to 20 of the exposed pluton volume the remaining 80 of the space for pluton emplacement was made by downward removal of host rock from the present level of exposure although mechanisms such as floor subsidence are permissive late stoping has destroyed evidence for the early emplacement history however geometrical constraints provided by exposure of continuous wall to roof contacts indicate that early emplacement mechanisms at this level in the crust and immediately below were also dominated by the downward displacement of host rocks through a conduit that now is represented by the solidified pluton q 2002 elsevier science ltd all rights reserved

granitic magma transport by fracture propagation granitic magmas commonly ascend tens of kilometres from their source terranes to upper crustal emplacement levels or to the earth s surface apart from its obvious bearing on the interpretation of the geology and geochemistry of felsic igneous rocks the magma ascent mechanism critically affects any modelling of the metamorphic evolution of the upper lithosphere as well as its rheology we propose that in general granitic magmas ascend via propagating fractures as dykes in extremely short time periods long distance diapiric transport of granitoid magmas through crustal sections is not viable on thermal or mechanical grounds and there is an apparent total absence of field evidence for diapiric rise of such magmas even in supposed type localities neither the shapes nor internal or external characteristics of granitic plutons necessarily reveal anything about the transport of their precursor magmas these are purely arrival phenomena dictated by local structure kinematics and stress states based on existing numerical treatments of the problem we show that granitic magmas are apparently sufficiently inviscid to travel through fractures to high crustal levels without suffering thermal death by freezing for example a 2000 km3 granitic batholith can be inflated by a 1 km 3m 20 km deep dyke system in less than 900 years the model proposed has numerous far reaching petrological and rheological consequences some of which are outlined

diurnal winds around lake tanganyika regular diurnal variations of coastal winds are observed around lake tanganyika during the dry season when insolation is intense and the prevailing trade winds are weak the long deep lake is at the bottom of the east african rift valley a two dimensional mesoscale model across the schematic rift valley topography is used to study these local tropical winds the full model gives a good simulation when compared with the observed winds on the east coast it turns out that about half of the strong diurnal wind variation there in the form of slope winds is due to the sloping mountains roughly one quarter is due to the thermal lake effect sea breeze and one quarter is due to the existence of the south easterly trade wind which enhances the sea breeze circulation component considerably during daytime and adds on to the downslope winds during night time the wind field across the lake is quite variable from hour to hour and from place to place yet predictable to a good extent during the dry season when the external conditions are rather similar from day to day

the retroflection paradox abstract the classical question of what happens when a warm western boundary current such as the north brazil current nbc retroflects is addressed analytically using a reduced gravity nonlinear model the traditional view is that the northwestward flowing current separates from the wall turns to the right looking offshore and forms a zonal boundary current that flows eastward integration of the steady inviscid momentum equation along the boundary gives the longshore momentum flux or flow force and shows that such a scenario leads to a paradox to resolve the paradox the separated current must constantly shed anticyclones which propagate to the northwest due to and an interaction with the boundary this new eddy shedding mechanism which is not related to the traditional instability of a zonal jet may explain why the nbc must produce rings a nonlinear analytical solution to the problem is constructed with the aid of a powerful theoretical approach based on the idea that nonlinear periodic

the influence of oceanographic features on the foraging behavior of the olive ridley sea turtle lepidochelys olivacea along the guiana coast abstract the circulation in the western equatorial atlantic is characterized by a highly dynamic mesoscale activity that shapes the guiana continental shelf olive ridley sea turtles lepidochelys olivacea nesting in french guiana cross this turbulent environment during their post nesting migration we studied how oceanographic and biological conditions drove the foraging behavior of 18 adult females using satellite telemetry remote sensing data sea surface temperature sea surface height current velocity and euphotic depth simulations of micronekton biomass pelagic organisms and in situ records water temperature and salinity the occurrence of foraging events throughout migration was located using residence time analysis while an innovative proxy of the hunting time within a dive was used to identify and quantify foraging events during dives olive ridleys migrated northwestwards using the guiana current and remained on the continental shelf at the edge of eddies formed by the north brazil retroflection an area characterized by low turbulence and high micronekton biomass they performed mainly pelagic dives hunting for an average 77 of their time hunting time within a dive increased with shallower euphotic depth and with lower water temperatures and mean hunting depth increased with deeper thermocline this is the first study to quantify foraging activity within dives in olive ridleys and reveals the crucial role played by the thermocline on the foraging behavior of this carnivorous species this study also provides novel and detailed data describing how turtles actively use oceanographic structures during post nesting migration

the mean flow field of the tropical atlantic ocean the mean horizontal sow eld of the tropical atlantic ocean is described between 20in and 20is from observations and literature results for three layers of the upper ocean tropical surface water central water and antarctic intermediate water compared to the subtropical gyres the tropical circulation shows several zonal current and countercurrent bands of smaller meridional and vertical extent the wind driven ekman layer in the upper tens of meters of the ocean masks at some places the sow structure of the tropical surface water layer as is the case for the angola gyre in the eastern tropical south atlantic although there are regions with a strong seasonal cycle of the tropical surface water circulation such as the north equatorial countercurrent large regions of the tropics do not show a signi cant seasonal cycle in the central water layer below the eastward north and south equatorial undercurrents appear imbedded in the westward sowing south equatorial current the antarcic intermediate water layer contains several zonal current bands south of 3in but only weak sow exists north of 3in the sparse available data suggest that the equatorial intermediate current as well as the southern and northern intermediate countercurrents extend zonally across the entire equatorial basin due to the convergence of northern and southern water masses the western tropical atlantic north of the equator is an important site for the mixture of water masses but more work is needed to better understand the role of the various zonal under and countercurrents in cross equatorial water mass transfer 1999 elsevier science ltd all rights reserved

new insights in the french guiana continental shelf circulation and its relation to the north brazil current retroflection 1 moored current measurements carried out from 6 october 2003 to 18 february 2004 over the french guiana continental shelf are presented two contrasted situations have been evidenced in which the currents were either weak and oscillating during the first period from october to early december or strong and northwestward during the rest of the survey further analysis of these measurements in light of moderate resolution imaging spectroradiometer satellite images have revealed that these situations are mainly due to the motion of an outer shelf mesoscale feature the north brazil current nbc retroflection two other main results have also been evidenced in this survey 1 when the nbc retroflection occurs northwestward of the french guiana continental shelf part of the nbc climbs over the shelf slope and propagates to the inner shelf and 2 the guyana current does not persist throughout the year at a 22 m depth and below finally the location of the nbc retroflection has also a strong impact on the spread of the amazon plume over the french guiana continental shelf and is felt to have an influence on the nutrient supply in this region

hydrographic and current observations on the continental slope and shelf of the western equatorial atlantic abstract hydrographic and current profiling data from december 1980 and current meter data obtained between september 1980 and november 1981 from the continental slope and shelf of the western equatorial atlantic between 2 and 7 n are used to describe the character of the north brazil coastal current nbcc system hydrographic data and the profiling results show that the nbcc has three distinct branches during the boreal fall in the near surface a strong current flows northwestward parallel to the coast at least as far as 6 n current speed within the near surface nbcc over a one year period were between 75 and 250 cm s 1 while the transport in december 1980 was between 15 and 20 106 m3 s 1 there was a southeastward near surface flow farther offshore which appears to be the return of the nbcc the ultimate destination of which is the north equatorial countercurrent offshore of the southeastward flow was a portion of a low salinity lens of amazon water the waters within and below the thermocline

deformation around a rising diapir modeled by creeping flow past a sphere a new experimental method for determining the pattern of flow and three dimensional progressive finite deformation of fluid elements in low reynolds number re viscous flow has been applied to creeping flow past a rigid sphere falling in a cylinder this is intended as a model analogue of natural rock deformation associated with magmatic and solid state diapirs rising through ductile crust the kinematics of finite strain in such analogue experiments may give useful information on the development of natural structures the experiment and a new method for quantifying the progressive finite deformation of fluid volumes in the transparent newtonian test fluid used sgm36 are discussed in detail the progressive finite deformation of fluid flowing along specific streamlines passing the sphere appears to be complex and largely a function of the initial distance of fluid volumes and the particular streamlines which they follow from the flow axis the progressive deformation history in the material surrounding a rising spherical diapir is characterized by progressive flattening and rotation of material above and progressive stretching below the sphere the results compare favorably with the external strain pattern associated with post tectonic mesozonal diapiric intrusions

aureole deformation by flattening around a diapir during in situ ballooning the cannibal creek granite the cannibal creek granite a foliated pluton within a strongly deformed aureole shows several diagnostic features of a diapir the intensity of the aureole deformation diminished away from the contact the aureole foliation is continuous with that of the granite and forms closed elliptical trend lines and the contact metamorphic minerals are synkinematic with regard to the aureole foliation the pluton deformed its aureole in three stages involving initially brittle then ductile and finally brittle deformation styles initial intrusion of a low strength magma stoped kinked and flexed aside its overburden crystallization of the magma prevented further rise and it ballooned and deformed its aureole evidently entirely by ductile bulk shortening perpendicular to the contact this the major stage of aureole deformation records no evidence of vertical movement of the pluton or of progressive simple shear along its margin during this stage the magma may have been theologically a high strength bing

erratum crude quantitative estimates of the original northwest southeast dimension of the sudbury structure south central canadian shield the sudbury structure central ontario is the remnant of a large cryptoexplosion structure whose oval map pattern diameter ratio 2 2 differs markedly from the circular outline of many meteorite impact craters finite element modelling shows that i the original northwest southeast dimension could have been 2 3 times larger than at present and ii the vertical dimension of the sudbury structure was 10 km before tectonic deformation although our structural analyses furnish data that govern the geometric modelling large uncertainties remain where the state of tectonic deformation is poorly constrained a series of two dimensional models was made to cope with kinematic uncertainties and to assess their effect on the estimates of the geometry of the original sudbury structure

seasonal cycle of velocity in the atlantic north equatorial countercurrent as measured by surface drifters current meters and ship drifts this report describes the general circulation and seasonal variation of currents in the equatorial atlantic concentrating on the north equatorial countercurrent necc using data collected as part of the seasonal response of the equatorial atlantic and programme francais ocean et climat dans l atlantique equatorial experiments plus historical ship drifts during 1983 1985 the lagrangian circulation was studied by launching and tracking 30 freely drifting drogued buoys in the north equatorial countercurrent and 23 in the south equatorial current sec in addition continuously recording current meters were moored for 20 months at depths from 20 to 300 m near the center of the necc at 6 n 28 w these measurements are the longest series ever obtained in this current and provide information about its seasonal and interannual variations and zonal meridional and vertical structure the seasonal cycle of the necc is very regular from year to year each year the necc starts up in may june it flows eastward across the atlantic with surface speeds of up to 143 cm s in the west extending down to 350 m at 28 w and flowing into both the guinea current and north equatorial current it disappears or reverses from about january june west of 18 w some near surface water of the necc is inferred to downwell and flow equatorward toward the equatorial undercurrent the sec flows into the north brazil current which during spring continues up the coast into the caribbean during fall however the whole north brazil current retroflects or turns back on itself between 45 and 50 w forming the western necc the retroflection establishes a meander pattern in the necc that slowly propagates westward during fall at a speed of 4 cm s the meanders have a displacement of about 300 km in latitude a wavelength of 900 km and meridional velocity fluctuations of up to 100 cm s the swift currents and time dependent meanders in the western necc cause a high eddy kinetic energy 2400 cm2 s2 equivalent to that of the energetic part of the gulf stream

differential cooling drives large scale convective circulation in lake tanganyika field data scaling analysis and three dimensional numerical experiments demonstrate that the dominant large scale circulation pattern during the southeast trade winds in lake tanganyika east africa is a downwind flow in the metalimnion with a returning southward upwind flow in the upper region of the epilimnion this is in the opposite direction to all prior literature available on the lake which has assumed that the southeast trade winds must drive a northward surface flow due to momentum induced by the wind the gradient in wind speed and humidity along the length of the lake and the resulting gradient in heat exchange with the atmosphere result in warm water accumulating at the northern end of the lake the north basin of lake tanganyika thus acts as a heat sink while the south basin is a net source of heat to the atmosphere the resulting variation in buoyancy flux is strong enough to drive a convective flow in the upper layer in the opposite direction to the wind a large scale convective circulation results in an annual exchange of 6 2 1012 m3 of water and an annual net transport of heat averaging 0 2 terawatt from the northern to the southern region of the lake currents in the upper 100 m layer with a mean flow of 0 2 sverdrup and flow speed of 0 08 m s 1 can be described by the superposition of a parallel convective flow with the internal seiche motion

the relationship between the southern hemisphere annular mode and antarctic peninsula summer temperatures analysis of a high resolution model climatology abstract the large regional summer warming on the east coast of the northern antarctic peninsula ap which has taken place since the mid 1960s has previously been proposed to be caused by a trend in the southern hemisphere annular mode sam the authors utilize a high resolution regional atmospheric model climatology 14 km grid spacing to study the mechanisms that determine the response of the near surface temperature to an increase in the sam t sam month to month variations in near surface temperature and surface pressure are well represented by the model it is found that north of 68 s t sam is much larger on the eastern lee side than on the western windward side of the barrier this is because of the enhanced westerly flow of relatively warm air over the barrier which warms and dries further as it descends down the lee slope the downward motion on the eastern side of the barrier causes a decrease in surface mass balance and cloud cover south of 68 s vertical deflection across

on the seasonal variability and eddies in the north brazil current insights from model intercomparison experiments the time dependent circulation of the north brazil current is studied with three numerical ocean circulation models which differ by the vertical coordinate used to formulate the primitive equations the models are driven with the same surface boundary conditions and their horizontal grid resolution isotropic 1 3 at the equator is in principle fine enough to permit the generation of mesoscale eddies our analysis of the mean seasonal currents concludes that the volume transport of the north brazil current nbc at the equator is principally determined by the strength of the meridional overturning and suggests that the return path of the global thermohaline circulation is concentrated in the nbc models which simulate a realistic overturning at 24 n of the order of 16 18 sv also simulate a realistic nbc transport of nearly 35 sv comparable to estimates deduced from the most recent observations in all models the major part of this inflow of warm waters from the south atlantic recirculates in the zonal equatorial current system but the models also agree on the existence of a permanent coastal mean flow to the north west from the equator into the carribean sea in the form of a continuous current or a succession of eddies important differences are found between models in their representation of the eddy field the reasons invoked are the use of different subgrid scale parameterisations and differences in stability of the nbc retroflection loop because of differences in the representation of the effect of bottom friction according to the vertical coordinate that is used finally even if differences noticed between models in the details of the seasonal mean circulation and water mass properties could be explained by differences in the eddy field nonetheless the major characteristics mean seasonal currents volume and heat transports appears to be at first order driven by the strength of the thermohaline circulation

quaternary rate of folding of the ventura avenue anticline western transverse ranges southern california upper quaternary terraces of the ventura river california are uplifted tilted and folded over the ventura avenue anticline rates of uplift and tilting have decreased since inception of the structure over the past 200 ka assuming that the chronology based on amino acid racemization 14c dates and soils correlation is approximately correct then the minimum possible average rate of uplift in the axial region of the fold has decreased from 14 mm yr to 2 mm yr during the past 200 ka interval rates of uplift for the periods 200 ka to 80 or 105 ka 80 or 105 ka to 30 ka and 30 ka to present are respectively about 20 mm yr 9 mm yr and 5 mm yr the rate of tilting shows a similar trend decreasing from 5 8 urad yr 2 5 urad yr and 1 2 urad yr for the same time intervals respectively based on the mechanics of flexural slip folds in stratified sedimentary rocks these data suggest that the rootless ventura avenue anticline is a fold that has been shortening at a relatively constant rate of about 9 mm yr since its inception

a census of north brazil current rings observed from topex poseidon altimetry 1992 1998 six years of topex poseidon altimeter data are used to investigate the formation of rings and eddies shed by the north brazil current upper layer thickness maps were used to identify 34 of these features formed in the north brazil current retroflection region an average of more than 5 rings and eddies per year the ensemble of ring trajectories closely parallels the 500 m isobath and one out of six rings penetrate into the caribbean sea through the southern lesser antilles the rest of the rings and eddies follow a northern trajectory past barbados once they reach 58w their estimated mean translation speed is 14 km day and their mean length scale is approximately 100 km our results suggest that the formation rate of nbc rings and eddies is nearly twice that previously thought and that they may account for more than 1 3 of the interhemispheric transport within the atlantic meridional overturning cell

petrochemistry of the late archaean granites of the chinamora batholith zimbabwe abstract at least the lowermost successions of the main greenstone belts which surround the chinamora batholith were intruded by several discrete granite plutons prior to the intrusion of the great dyke into the rhodesian craton ca 2500 ma ago but after ca 2800 ma ago the intruded granites constitute the chinamora igneous granite suite c i g s the c i g s was emplaced over a time period spanning two tectonic events and the granites display considerable variation in both field and petrochemical characteristics the oldest plutons contain rather higher contents of mafic minerals than the younger ones and have on the whole undergone more intense deformation hence the recognition of two groups of plutons the older gneissic granites mainly trondhjemites and the younger late granites mainly granites samples from each of 22 plutons were analysed for both major and trace elements consideration of the major element data indicates that the c i g s plutons show characteristics of a calc alkaline suite the trace element data suggest that the c i g s has evolved by fractional crystallization in order to explain the origin of the oldest of the gneissic granite plutons a model deriving these plutons from a magma formed by a major addition of basaltic magma to the lower crust and its mixing with a partial melt derived from sialic crust is postulated the ultimate source material for the late granites is not known but simple modelling does show that their origin can be explained by fractionation along a liquid line of descent

emplacement kinematics of a granite diapir the chindamora batholith zimbabwe the geometric features of a large 50 40 km granitic batholith and its surrounding greenstone belt envelope are described the batholith is made up of several intrusive components and an intrusion sequence based on contact relations and xenoliths has been established the igneous rocks show a local foliation s fabric and preferred orientation of minerals the intensity of this fabric accords with the finite strain determined from xenolith shape analysis when the strain variations are analysed in detail it appears that the batholith was built up by a succession of magmatic pulses each of which led to a stretching of the previously consolidated igneous material so called balloon tectonics evidence is presented that xenolith deformation commences only when the surrounding igneous material has crystallized and a method is suggested whereby the position of the surface separating crystal supported phase plastic behaviour from melt supported phase liquid behaviour at different stages in the plutonic history can be determined ductile shear zones are present and their geometry accords well with the shape changes necessary to allow the outer parts of the pluton to stretch

on granitoid emplacement and related structures a review granitoid magmas are emplaced at the upper crust under a complex interaction of gravitational processes and horizontal tectonics natural intrusive bodies show a wide variety of structural patterns that must be strongly related with their dynamic history of ascent and emplacement comparisons of natural structural patterns with experimental and numerical models are necessary to interpret in a coherent fashion the emplacement mechanism involved from natural experimental numerical and theoretical considerations one can reach important conclusions on the problem of ascent and final emplacement of granitoid magmas in the earth s crust the present paper reviews the principal emplacement mechanisms referred to in the literature that is doming diapirism ballooning stoping cauldron subsidence and dike propagation dike propagation is the most effektive process in magma transport from deep zones in the crust and upper mantle extensional fractures for dike propagation and magma ascent can be developed at depth in the crust according to the modern dike propagation theory in orogenic domains magmas reach the upper crust through narrow channels or dikes and are accumulated in a final reservoir in the form of a discordant supracrustal pluton or a ballooning pluton if during emplacement any regional deformation acts simultaneously

structure and emplacement history of a multiple center cone sheet bearing ring complex the zarza intrusive complex baja california mexico the cretaceous zarza intrusive complex located in the peninsular ranges of baja california norte mexico is perhaps the bestpreserved multiple center cone sheet bearing ring complex documented in north america the 7 km 2 elliptical complex hosts three nested non concentric intrusive centers that are successively younger to the south the northern and central centers show the same evolutionary sequence of 1 intrusion of concentric gabbroic cone sheets 2 intrusion of massive core gabbros and 3 development of subvertical ductile ring faults ring fault kinematics indicate that both centers moved down relative to the surrounding country rocks suggesting collapse into an underlying magma chamber the southern center is composed of approximately equal proportions of gabbro and tonalite and lacks cone sheets aluminumin hornblende barometry on the tonalite indicates a maximum emplacement depth of 2 3 0 6 kbar the zarza intrusive complex is surrounded by a ductile deformation aureole and bedding is inward dipping and inward younging around the entire complex excellent preservation of the intrusive history allowed us to evaluate the origin of the aureole and the three most applicable models are 1 collapse of the complex into its underlying magma chamber 2 sinking of the complex and its chamber after solidification and 3 formation of the aureole prior to emplacement of the complex the preserved structural and intrusive relationships provide information on the dynamic evolution of subvolcanic magma chambers and suggest that the complex may have been overlain by a caldera

eddies in the north brazil current retroflection region observed by geosat altimetry mesoscale fluctuations in the western tropical atlantic are analyzed in geosat altimetry sea surface height ssh and geostrophic velocity anomalies to investigate the role of eddies in the north brazil current nbc retroflection zone the detachment of anticyclonic eddies from the nbc retroflection is observed during november through january when the nbc retroflection into the north equatorial countercurrent necc weakens and finally breaks down these eddies are traced over more than 2 months between 50 and 60 w on their way toward the caribbean at average speeds of 15 cm s 1 in one case an apparent merger of two anticyclonic eddies occurs one detached from the retroflection zone and one detached from the necc cyclonic eddies are also observed but are generally less persistent mesoscale ssh variance just west of the retroflection increases by a factor of 2 from early summer to winter mainly because of the anticyclonic eddies interhemispheric water mass transfer associated with the eddy flux out of the nbc retroflection may amount to an average transport of 3 sv

north brazil current retroflection and transports 1 a subset of data collected as a part of a larger program the north brazil current rings nbcr experiment is analyzed to study the variability of the transport of the north brazil current nbc and its relation with the shedding of rings it is concluded that there is a direct relation between the latitude of penetration the number of rings shed and the intensity of the nbc the data set consists of dynamic height time series derived from three inverted echo sounders and a shallow pressure gauge deployed along a section perpendicular to the south american coast between the continent and 7 n and between 48 and 45 w velocity and hydrographic data collected during the nbcr cruises are also analyzed and used to validate the results the 15 month mean transport of the nbc is 16 2 sv the 18 month mean of the retroflected southeastward flow is 22 2 sv both flows display considerable variability the retroflected southeast flow reaches its maximum value during september 1999 near the time when the climatological north equatorial countercurrent necc reaches its maximum strength and it is minimum when the climatological necc reverses or is not present in the basin the mean difference between the nbc flow and the retroflected flow during august december 1999 when the necc is fully established is 7 sv the excess in the retroflected flow is due to north atlantic water joining the retroflected flow from the south atlantic the combination of both flows constitutes the necc

the solid body tilt of deformed paleohorizontal planes application to an archean transpression zone southern canadian shield abstract the solid body tilt sbt of deformed paleohorizontal planes is equal to the angle between their unstrained top direction and an upward pointing vertical axis kinematic models of important tectonic processes such as transpression and ductile thrusting have specific sbt requirements these models can be tested in ancient and modern orogens by determining the actual sbt of strata early magmatic sills and late horizontal intrusions with relict primary layering classical transpression models predict that except for sheath structures all folds in bedding be upright and horizontal i e that sbt values be close to zero within the hinge zones moreover all passive folding is accomplished by amplification of asperities and caused by the pure shear component of the transpression tensor nine sbt analyses were made in the archean crust of northwest ontario to test the transpression hypothesis north of the quetico wabigoon boundary western superior province central canada the nine sbt values do not discredit the hypothesis that the quetico fault marks an archean transpression zone which included the wabigoon rocks adjacent to the quetico metasediments

granite emplacement in orogenic compressional conditions the la alberca bejar granitic area spanish central system variscan iberian belt abstract the la alberca bejar granitic area comprises a set of intrusions of upper carboniferous to lower permian age located in the hinterland of the variscan belt of western spain gravity data anisotropy of magnetic susceptibility and microstructural studies carried out in the granitoid and its country rocks indicate that the granitoids of this region have tabular and inverted drop shapes and show sub horizontal magmatic fabrics and sw ne lineations the granitoid bodies were intruded episodically with single intrusive pulses recorded by deformation in the country rocks all intrusive events took place during d 3 compressive stage in the core of large d 1 anticlines and are not related to structures in the country rock a syn orogenic emplacement model for granite intrusion in such conditions is proposed the proposed model implies the activity of coeval emplacement mechanisms and room generation

magmatic arc asymmetry and distribution of anomalous plutonic belts in the batholiths of california effects of assimilation crustal thickness and depth of crystallization in order to better understand geologic fac tors controlling pronounced regional variations in whole rock chemistry mineralogy and mineral chemistry in the batholiths of california we calculate the magmatic intensive variables f hf f h 2 o f hf f hcl and f o 2 regional scale west to east increases in f oh in mafic silicates corresponding to the systematic i wc to i mc and i sc progression reflect orders of magnitude increase in f hf f h 2 o attending pluton crystallization low f hf f h 2 o of formation of western i wc types is consistent with their derivation from low fluorine source rocks in subducted oceanic slabs or the upper mantle in contrast higher f hf f h 2 o of crystallization of i mc and i sc types to the east implies the involvement of 1 progressively greater amounts of continental crustal source material such as biotite bearing metamorphic rocks their unweathered sedimentary derivatives retaining f rich mafic minerals or their fusion products and or 2 source materials which become more f rich toward the continental interior the regional distribution of i mc and i sc types suggests that the precambrian craton of western north america or derivative sediments may extend farther north in california and be morphologically more complex than previously thought from seemingly out of place occurrences of i wc plutons on the eastern slopes of the sierra nevada batholith we infer the existence of regions where precambrian basement was thin or absent in mesozoic time which prevented extensive cratonal contamination of subducted slab or upper mantle derived magmas new methods for estimating t f o 2 relations in the magmas demonstrate that i scr granites crystallize at oxygen fugacities as much as five orders of magnitude lower than those of i wc i mc and i sc types under conditions at or below the maximum stability limit of graphite in equilibrium with a c o h s gas phase the local scale formation of i scr granites in plutonic belts within specific wall rock terranes containing highly reducing sediments or metasediments may occur by contamination of i types with graphitic pelite or in some cases by the direct fusion of this reducing pelitic wall rock the spatial distribution of i scr granite provinces therefore is controlled simply by wall rock lithology amphibole geobarometry demonstrates a general west to east decrease in crystallization pressure across the sierra nevada batholith in contrast the peninsular ranges batholith displays a west to east crystallization pressure increase the bulk of the california batholiths crystallized at pressures less than 4 5 kb and depths less than about 15 19 km in the southern sierra nevada batholith the san gabriels and the eastern peninsular ranges however plutons crystallized at pressures exceeding 6 kb at deep crustal levels 23 km reconstruction of the pre erosion top of the batholith shows that in an east west cross section the central sierra nevada batholith was a horizontal tabular body with an aspect ratio of at least five to one

cannibal creek granite post tectonic ballooning pluton or pre tectonic piercement diapir a discussion groves d i eds recent advances in understanding precambrian gold deposits univ west australia geology dept and extension pub 11 and 1989 paleosols and their relevance to the precambrian atmospheric composition jour geology v 97 p 77 92 phillips g n 1988 widespread fluid infiltration during metamorphism of the witwatersrand goldfields generation of chloritoid and pyrophyllite jour meta geol v 6 p 311 332 meyers r e et al 1988 recent advances in the geology of the witwatersrand goldfields including the importance of postdepositional processes ext abs bicentennial gold 88 melbourne p 319 324

emplacement related fault patterns around the northern granite arran scotland conspicuous faults in the new red sandstone nrs mainly permian triassic of arran are shown to be kinematically related to the intrusion of the northern granite in paleocene time early inflation of the granite pluton in the upper crust induced radial stretching in the overlying sedimentary cover recorded in predominantly normal offsets on the faults in the nrs continued ballooning of the pluton superimposed strong concentric dip slip displacement over its flanks both stretching and uplift were heterogeneous strongly controlled by a nonuniform stratigraphy and by reactivation of older faults striking predominantly north northwest and northeast and dating back at least to permian time the paleocene displacements on these discrete weak sub nrs faults diffused upward through nrs sandstones on numerous minor faults each with only small offset this behavior resulted from slip hardening on each fault in the poorly cemented nrs rocks late in the intrusion history the major faults on the southeast side of the granite formed a conjugate strike slip system that accommodated radial expansion of the pluton mainly during intrusion of a discrete magma batch that now forms the inner fine grained granite other structures around and within the northern granite are shown to be more compatible with this two stage ballooning model than with a vertical plug emplacement model previous assessments of the ballooning process in general have been made on deep level lateral margins of plutons where radial shortening dominates in the envelope north arran is an important example of the complexities of ballooning at shallow levels in a heterogeneous crust

on the role of diapirism in the segregation ascent and final emplacement of granitoid magmas only bodies of magma with a high crystal content and partially molten crustal country rocks can ascend as diapirs once such an envelope is pierced the diapiric ascent of the pluton is arrested by the high viscosity of a solid aureole deformation by shortening of the carapace of these bodies may lead to the expulsion of a magma with a relatively low crystal content which may then continue ascent via fractures and dykes the details of the mechanisms of granitoid magma segregation are still unknown but it appears that many magmas hegin their ascent through the crust as mushes with at least 50 melt and that such magmas are rheologically able to ascend through a thickness of crust this ascent mechanism explains the dearth of structures attributable to the ascent of granitoids in contrast to the abundance of structures that developed during their final emplacement when a magma becomes too crystalline melt 25 to continue its ascent via dykes it is immobilised at approximately this stage a hydrous magma may become saturated with water and release fluids into the aureole making it particularly susceptible to deformation magma that continues to arrive at this level is also immobilised and the pluton grows as a ballooning diapir these characteristically deform themselves and their aureoles by bulk shortening magmas that are able to ascend to shallow depths largely by virtue of lower water contents and higher initial temperatures tend to become finally accommodated by such brittle processes as stoping and cauldron subsidence high level intrusions lend to be tabular are also fed by dykes or conduits and assemble in tabular batholiths

evaluation of multiple emplacement mechanisms the huichizi granite pluton qinling orogenic belt central china three end member granite emplacement mechanisms host rock ductile shortening hrds host rock rigid displacement hrrd and magmatic absorption ma are identified in this study of the huichizi pluton the internal fabrics are mainly flattening typesona 0 4 0 9u and strain is highoesa 1 0 0 6u near the boundaries and lowoesa 0 7 0 30u toward the central parts of the pluton in the 1 5 km wide contact aureole extension e is measured in syn emplacement deformed veins and the calculated average shortening normal to the sides and tips of the pluton are 1 14 km and 0 74 km respectively from this we conclude that the hrds produced only about 20 space for the present volume of the pluton the regional hrrd derived from the uplift by about 8 km of the qinling group in a flower structure contributed 19 032 space ms including stoping and material transfer processes yielded another 37 space of this stoping contributed a minimum of 1 space estimated from the surface area of 2 8 km 2 covered by xenoliths transfer processes provided about 36 of the needed space deduced from the average 64 36 ratio of hybridization of mantle derived to crustal qinling group derived magma the three mechanisms may act nearly simultaneously as a multiple emplacement mechanism this situation may apply to many other plutons as well 2000 elsevier science ltd all rights reserved

granitoid emplacement and deformation along a major crustal lineament the cordillera blanca peru abstract the cordillera blanca batholith and ignimbrites of the intermountain callejon de huaylas basin represent the last magmatic event in the andean cycle of central northern peru this most spectacular example of an extensional regime is characterised by acid magmatism spanning some 10 ma with both magma emplacement and subsequent deformation being fundamentally controlled by a ca 300 km lineament known as the cordillera blanca fault complex the western margin of the batholith has been strongly deformed by the cordillera blanca fault resulting in a series of ductile to brittle structures that increase with intensity away from the relatively undeformed core towards the margin the late stage brittle fabrics are coeval with extensional structures in the callejon de huaylas basin and relate to uplift and extension along the fault zone the more ductile fabrics as indicated by combined k ar and 40 ar 39 ar mineral dates formed earlier in the intrusion history and are consistent with emplacement into an active dextral strike slip shear zone the rapid uplift and high erosion rates seen from the late miocene onwards and the current state of stress in this region of thickened crust are due to gravitational instability body forces set up at high topographical levels and buoyancy forces resulting from the intrusion of young acid magmas at high crustal levels

re examining pluton emplacement processes discussion in a recent review paterson fowler 1993 showed decreasing away from the pluton as discussed by gughow estimated volumes of displaced wall rock are lielmo 1993b smaller than pluton volumes and how the widths of laboratory experiments indicate that rocks behave as strain aureoles around natural plutons are considerably power law fluids with exponents n between 2 5 and 5 narrower than in models of diapirs where spheres rise hansen carter 1982 kirby 1983 wilks carter through newtonian fluids cruden 1988 schmeling et 1990 the power law exponent n of a viscous fluid is a al 1988 they then argued that mechanisms other than measure of the sensitivity of its viscosity stress or ductile flow of the wall rocks were necessary to account strain role for n 1 newtonian fluid the viscosity is for these observations although i accept that several constant for any strain rate for n 1 the fluid softens mechanisms may act simultaneously and change in imwith increased strain rate the strain rate dependency of portance as plutons are emplaced i argue here that i the viscosity of power law fluids has important effects on the displaced volumes of wall rocks may be underestithe velocity and flow patterns of the ambient fluid mated because of difficulties in assessing the shape and around rising spheres or diapirs and therefore the size of the three dimensional flow cell in the wall rocks width of their strain aureoles crochet et al 1984 caused by pluton emplacement and more importantly kawase moo young 1986 weinberg podladchikov ii the narrow strain aureoles may result from diapiric in press in the following discussion the difficulties in rise of plutons through power law rocks and or result determining the volumes of rock displaced by diapir from the effects of thermal softening of the wall rocks emplacement are first considered the effect which several field studies have measured the width of the power law rocks might have on the width of the strain strain aureole caused by pluton emplacement see gugaureole is then discussed and finally the possible effects lielmo 1993a paterson fowler 1993 and references of thermal softening of the wall rocks by the diapir are therein the measured width depends on three main examined factors i the finite strain of the wall rocks which depends on the velocity field imposed by the diapir this in turn depends on the diapir s mechanism and depth of rock volumes displaced by diapirs emplacement and on the rheology and physical boundaries of its wall rocks the longer a rock volume is paterson fowler 1993 studied horizontal shortensubmitted to a particular strain rate velocity field the ing in strain aureoles around plutons and then integrated larger is its strain the velocity of flow decreases with shortening to three dimensions around plutons of differdistance from the contact of rising spheres so that ent shapes the amount of shortening they obtained for strains have to accumulate a long time to be distinguishseveral natural examples only accounted for about 30 able from any background strain ii late deformation of the volume of the plutons they argued that this will mask the strain aureoles of pre tectonic plutons volume difference implies that other mechanisms such while interference with regional tectonic strains will as doming of the roof stoping assimilation and rigid affect the width of the aureoles of syn tectonic plutons translation of wall rock must have operated at the same guglielmo 1993b iii the measurable width of the time as viscous flow of the wall rock aureole depends on distinguishing the strain due to the however this discrepancy may largely be due to pluton from regional strains of any age paterson difficulties in measuring small pluton related strains fowler 1993 this distinction becomes increasingly beyond the obvious strain aureole and difficulties in more difficult as strains are spread over larger volumes determining the shape of the flow cell around the pluton the width of the strain aureole around a rising sphere depends on the power law exponent n of the country current address research school of earth sciences anu act rocks it is widest in newtonian fluids and narrows as n 6200 canberra australia increases however even in the case of rocks with high n

late twentieth century warming in lake tanganyika unprecedented since ad 500 lake tanganyika has become warmer increasingly stratified and less productive over the past 90 years analyses of lake sediments show that this recent warming is unprecedented within the past 1 500 years

magma emplacement during arc perpendicular shortening an example from the cascades crystalline core washington it is increasingly inferred by others that active arcs at all crustal levels are undergoing arc perpendicular extension and that magma utilizes this extension or extension along arc parallel strike slip faults during emplacement however a review of stress fields in modern arcs and deformation which occurred during magmatism in ancient arcs and our own emplacement studies of individual plutons indicate that magma emplacement typically occurred during arc perpendicular shortening without the aid of strike slip faulting this conclusion raises the question of how host rock is displaced during magma emplacement in shortening and thickening orogens evaluation of host rock material transfer processes that operated during emplacement of the 93 ma 10 to 14 km deep mount stuart batholith washington provides one example and includes the following 1 ductile downward flow in a narrow 0 2 body radii structural aureole 2 stoping and of lesser importance 3 regional folding thrusting and subhorizontal arc parallel extension we see no evidence that arc perpendicular extension or local extension along strike slip faults made space for this pluton nor for most other plutons in contractional arcs instead we argue that both localized and rapid around plutons and regional and slower downward flow during growth of crustal roots is a common process in such arcs

preliminary estimates of the amount of continuous horizontal shortening across an archean greenstone belt simple two dimensional techniques are used to make an estimate of the total shortening across a narrow greenstone belt in northwestern ontario the techniques are based on the basic principle of restoring the predeformational geometry of a horizontal traverse across the belt depending on the technique used this traverse is a string of line elements or a chain of finite elements the strain ratios available for the restoration are minimal values and need to be increased significantly to obtain realistic results depending on the strain values selected for the restoration amounts of horizontal shortening range from 17 to 49 the actual amount remains unknown but is thought to be 50 in view of the apparent variation in longitudinal strain along the greenstone belt a three dimensional treatment seems to be necessary this would require that strain measurements be taken systematically throughout rather than along a single traverse across a greenstone belt segment

analysis of three dimensional strain modified uniform distributions andalusite fabrics from a granite aureole a method of analysing finite strain from an initial random distribution of lines or planes is presented the shape of the strain ellipsoid is mapped to the eigenvalue ratios of an orientation matrix the method is used to interpret the andalusite fabrics from the aureole of the ardara granite county donegal ireland the high flattening strains determined in the aureole are accompanied by oblate strains in the granite margins and support the concept of deformation produced by expansion of the pluton

re examining pluton emplacement processes abstract previous pluton emplacement studies have attempted to explain how space is made during pluton emplacement in fact the only means of making space during emplacement of mantle derived magmas in the crust are 1 lowering the moho or 2 outward displacement of the earth s surface other pluton emplacement mechanisms are material transfer processes mtps that do not increase the volume of the crust one frequently cited mtp for emplacement of concentrically zoned and ballooning plutons is ductile flow of wall rocks around the plutons the expected structures and total strains near such plutons are dependent on the three dimensional pluton shape the width of the deforming aureole whether the pluton is a piercing or non piercing diapir and in the latter case the number of body radii the pluton travels we have re examined a few such plutons and calculated the amount of material transfer caused by ductile flow in no case is more than 40 and in most cases only 15 35 of the required material transfer accommodated by wall rock flow the contact aureoles around these plutons are too narrow and or strains too low indicating that the plutons are predominantly discordant bodies with narrow 0 1 0 4 pluton radii concordant aureoles a comparison of strains in natural contact aureoles and those made in mechanical models of diapirs indicates that natural strains are at least an order of magnitude less than model strains we suggest that the similarities between models of diapiric ascent of spherical bodies and concentrically zoned plutons are superficial because the models are too simplistic instead we argue that the ascent and emplacement of magmas require multiple near field and far field mtps these mtps will show gradients with depth distance from the magma and with time rates of near field mtps must be rapid whereas far field rates are probably nearer to long term average rates of orogenic processes

igneous emplacement in a shear zone termination the biotite granite at strontian scotland deformed xenolith strain data together with other structural information indicate that the biotite granite body 90 sq km of the strontian complex scotland was emplaced in the extensional termination of a dextral transcurrent shear zone this shear zone is a splay of the major great glen fault which lies along the southern boundary of the granite siting of the shear zone splay was probably controlled by a a slight releasing bend in the great glen fault in this area and b a large pre existing asymetric synform in proterozoic metasedimentary country rocks which intersects the great glen fault trace at a high angle a model is proposed in which moine thrust caledonian compression at ca 435 ma activated the great glen fault dextrally dextral movements around the releasing bend detached a flat segment from the inside fault wall and the biotite granite was emplaced side ways at depths of about 15 km as a sheet into this extensional listric fault bounded cavity

the amazon river plume during amasseds subtidal current variability and the importance of wind forcing current variability over the north brazilian shelf particularly within the amazon plume is characterized using observations from a moored array deployed about 300 km north of the amazon river mouth from february to june 1990 as part of a multidisciplinary amazon shelf sediment study amasseds the moored array consisted of a transect perpendicular to the coast with inner shelf 18 m depth and midshelf 65 m moorings and a third mooring near the shelf break in 100 m of water to our knowledge the amasseds moored array includes the first long term 2 months moored observations made within the amazon plume the current variability is dominated by two components semidiurnal cross shelf currents with peak velocities of 50 to 200 cm s and vertically sheared subtidal timescales days to weeks along shelf currents this study focuses on the subtidal flow within the amazon plume which is strong and variable with along shelf currents ranging from 50 cm s to over 150 cm s the variability in the along shelf current within the plume is wind driven the relatively weak 0 5 dyn cm2 along shelf wind stresses in this region drive strong along shelf current variability because the amazon plume is thin and the interfacial drag is weak however in the absence of an along shelf wind stress the plume flow is northwestward at 40 to 80 cm s indicating that direct wind forcing does not account for the mean northwestward flow of the amazon plume in the cross plume direction there is a tendency for the onshore wind stress due to the persistent trade winds to balance the typically offshore buoyancy force and the coriolis force associated with the wind driven along shelf flow thus the wind stress is a key factor influencing variability in both the flow and cross shelf structure of the amazon plume in the vicinity of the moored array

cannibal creek granite post tectonic ballooning pluton or pre tectonic piercement diapir the cannibal creek granite in northern queensland australia previously has been interpreted to be a post tectonic pluton which underwent solid state deformation during in situ ballooning a reinterpretation of structures in and around the pluton indicates that this pluton is more appropriately viewed as a pierce ment diapir emplaced by magmatic flow significant deformation took place after pluton emplacement in fact the cannibal creek granite has some characteristics similar to pre tectonic granites examined elsewhere therefore it is somewhat misleading to view the granite as a post tectonic pluton

rates of processes in magmatic arcs implications for the timing and nature of pluton emplacement and wall rock deformation abstract the construction of arcs and in many cases the emplacement of plutons occur in tectonically active regions it is critical therefore to evaluate the rates of structural and magmatic processes when trying to understand the evolution of arcs and the associated pluton wall rock systems our best estimates of average rates or durations of processes in shallow to moderate level arc environments are the following 1 crystal growth rates in magma of 10 4 cm year 1 2 growth rates of metamorphic porphyroblasts between 10 5 and 10 2 cm year 1 3 long term magma supply rates of 10 1 km 3 year 1 and short term rates of up to 350 km 3 year 1 4 diapiric ascent rates for mafic plutons of 1 3 m year 1 5 cooling of plutons to ambient wall rock temperatures in 10 5 10 6 years 6 final crystallization of plutons in a small fraction of the time needed for complete cooling 7 fault displacements of 3 cm year 1 8 development of cleavages in fault zones in less than 10 6 years at strain rates of 10 13 s 1 or higher and 9 the development of regional cleavages in 10 6 years at strain rates of 10 14 s 1 these rates indicate that processes operating in magmatic arcs are relatively rapid pluton emplacement cleavage development etc occur over time spans of tens of thousands to no more than a few million years however the rate of ascent and crystallization of plutons at shallow levels is generally shorter than that needed to get large displacements on faults or widespread cleavages developed at deeper levels or in zones undergoing faster strain rates the time spans of the various processes approach one another thus plutons with otherwise similar characteristics emplaced in regions undergoing fast strain rates or at deeper crustal levels may appear quite different structurally from those emplaced at shallow levels or in regions undergoing slower strain rates comparison of these data also suggests that the rate at which wall rock deforms is the limiting factor controlling the rates of other structural processes during emplacement of plutons unless fast strain rates or multiple deformation mechanisms are considered thus emplacement mechanisms that rely on the transport of magma over 10 5 to 10 6 years are favored and need further consideration finally we argue that the structural and other characteristics of pluton wall rock systems will depend on rates of various processes involved and that these rates at the very least influence and sometimes invalidate the timing criteria previously published by us and others

seepage rate of hydrothermally generated petroleum in east african rift lakes an example from lake tanganyika acknowledgements we thank michael king and cgg npa satellite mapping for providing us with the gosd dataset of tanzania and the permission to publish the sar images of cape kalumba oil seeps funding this research did not receive any specific grant from funding agencies in the public commercial or not for profit sectors

origin of intraseasonal variability in lake tanganyika 1 intraseasonal thermocline oscillations in lake tanganyika are analysed using observations near mpulungu and simple analytical numerical models in order to understand their origin the region around the lake is characterised by strong and persistent southeast winds during the four months dry season lasting from may to august the associated wind stress causes the tilting of the thermocline which oscillates for the whole year the wavelet transform spectra of temperature at 30 m depth of the lake near mpulungu indicates the presence of various scales of motion localised in frequency and time the dominant modes of thermocline oscillations are intraseasonal variability with 3 4 weeks periods similar results are obtained from a reduced gravity model with various wind forcing including the observed forcing and a simple analytical solution in addition the model results indicates that the dominant mode of oscillation exhibits one node only from the study it is inferred that the free modes of oscillations of the lake are in resonance with wind pulses

interference between pluton expansion and non coaxial tectonic deformation three dimensional computer model and field implications abstract structures in orogenic belts are greatly controlled by interactions between pluton related and tectonic related strain fields however many aspects of the geometry and evolution of these structures are poorly known for example 1 what is the geometry of these structures if regional deformation is coaxial 2 how does this geometry change with progressive deformation this paper describes a three dimensional simulation of strain shape and magnitude as well as foliation and lineation patterns formed by interactions between pluton expansion and homogeneous coaxial deformation this simulation suggests that interactions between pluton expansion and regional uniaxial shortening generate patterns that are distinct from the patterns produced by regional uniaxial extension or regional non coaxial deformation for example shortening produces doughnut shaped constrictional rings about the pluton whereas extension produces apple shaped flattening regions around the pluton in addition shortening produces one continuous doughnut shaped low strain region around the pluton on the other hand extension creates two separate ellipsoidal low strain regions at the ends of the pluton furthermore shortening forms foliation rings that have triangular two dimensional sections and lineation is concentric around the axis of maximum shortening in contrast extension produces two separate foliation and lineation cones at the ends of the pluton all these structural and strain elements migrate away from the pluton with increasing expansion rates and towards the pluton with increasing tectonic deformation rates although structural studies around plutons should always integrate microstructural radiometric and field measurements simulation generated patterns can be used to evaluate 1 origin geometry and evolution of structures around plutons 2 mechanisms that explain inclusion trails within porphyroblasts 3 contribution of pluton related strains to strains measured in the country rock and 4 type and three dimensional orientation of regional kinematic schemes

emplacement of rapakivi granite and syenite by floor depression and roof uplift in the palaeoproterozoic ketilidian orogen south greenland in the palaeoproterozoic ketilidian orogen of south greenland tabular intrusions of the rapakivi granite suite exposed at graah fjelde lindenow fjord and qernertoq and a mesoproterozoic syenite of the gardar province exposed at paatusoq were emplaced by a combination of roof uplift and floor depression the strain associated with the emplacement of the intrusions mainly involved redistribution of mass vertically within the lithosphere space for the emplacement of the rapakivi plutons was not created during regional extension on low angle ductile shear zones as claimed by some previous workers and there is no evidence that emplacement of the intrusions coincided with extensional collapse of the orogen following crustal thickening the rapakivi granites post date peak metamorphism in the orogen by 35 46 ma and their contacts cross cut and clearly post date intense flat lying d1 d2 fabrics that formed by partitioning of deformation into arc normal and arc parallel components during oblique convergence

controls on emplacement of the caledonian ross of mull granite nw scotland anisotropy of magnetic susceptibility and magmatic and regional structures abstract anisotropy of magnetic susceptibility ams was measured from 139 sites across the exposed portion of the caledonian ross of mull granite argyllshire nw scotland to investigate the internal architecture of the pluton field and petrographic observations support the results of the ams study and a complementary suite of rock magnetic experiments was used to quantify the magnetic mineralogy of the granite ams data reveal a fabric that records a partial tectonic overprint of an emplacement related magma inflow fabric the partially preserved inflow pattern indicates a south to north emplacement of subhorizontal sheets that coalesced to form a tabular pluton the ams data are remarkably consistent across the intrusion with clear north south strikes and trends dominating the magnetic foliation and lineation patterns respectively these ams fabrics are discordant to internal zonation in the granite in the southernmost part of the granite ams data are parallel to bedding cleavage orientations preserved in many large 100 m proterozoic moine blocks the scarcity of moine blocks in the northern part of the intrusion and the prevalence of randomly oriented stoped blocks suggest that this part of the intrusion is nearer to the ceiling of the pluton the partial tectonic overprint consistent with east west compression occurred during the latter stages of emplacement and mainly affected the younger granite facies rm2 while the oldest granite facies rm1 and certain magmatic structures diorite enclaves preserve the original emplacement fabric an alternative explanation interprets the magnetic lineations as an intersection fabric between a shallowly dipping emplacement fabric and a steep tectonic fabric we argue that emplacement was not associated with eastward orogenic collapse of the scandian moine nappes as proposed by previous workers but occurred either before orogenic collapse or during a period of compressional reactivation

dike transport of granitoid magmas thermal and fluid dynamical analyses suggest that for viscosities and density contrasts spanning the range considered typical for many calc alkalic granitoids dike ascent is a viable mechanism for the transport of large volumes of granitoid melt through the continental crust we present calculations showing that a granitoid melt with calculated viscosity of the order of 10 6 pa s and a density contrast between magma and crust of 200 kg m 3 can be transported 30 km through the crust in 1 month corresponding to a mean ascent velocity of 1 cm s using analysis modified from numerical studies of the flow of basaltic magmas in dikes we also present an expression that allows the calculation of the critical minimum dike or fault width required for granitic magma to ascend without freezing for all reasonable estimates of cordilleran granitoid viscosity and density contrast the critical dike width is determined to be between 2 and 7 m calculated peak batholith filling rates are orders of magnitude greater than mean cavity opening rates based on estimated fault slippage which is consistent with chemical evidence for intermittent supply of magma pulses