spatial distribution of focal mechanisms for interplate and intraplate earthquakes associated with the subducting pacific plate beneath the northeastern japan arc a triple planed deep seismic zone the northeastern japan arc is located in one of the most seismically active subduction zones in the world in this study we relocated hypocenters and determined focal mechanisms of small earthquakes m 5 beneath the arc in order to investigate in detail the stress distribution in and around the descending oceanic plate in the hypocenter relocation we adopted a source region station correction method in which station corrections vary with hypocenter locations we have developed a new focal mechanism determination technique named master solution method which is analogous to the master event method in hypocenter determination we applied the method to p and sh wave amplitude data to obtain 1106 focal mechanism solutions from the new mechanism solutions and relocated hypocenters we found that there occur both low angle thrust fault lt type and downdip compression dc type earthquakes at depths from 40 to 70 km near the aseismic front the dc type events are underlying the lt type events almost all the earthquake clusters are composed of lt type events the western limit of the region where lt type events have occurred is subparallel to the trench axis although it undulates considerably it delineates the westernend of the active region of interplate seismicity furthermore we found that normal fault nf type events also occur at depths from 70 km in the upper plane of the double planed deep seismic zone which is characterized mainly by dc type event these nf type events are distributed only in a thin uppermost portion of the slab close to the plate boundary below these in the lower plane are downdip extension de type events this result indicates that the deep seismic zone in the northeastern japan arc is not double planed but triple planed even beneath the land area which cannot be explained by any simple models

observed parameters for turbidity current flow in channels reserve fan lake superior abstract fine grained tailings discharged from a taconite ore processing operation near the shore of lake superior produced turbidity currents that transported the sediment from a small delta into deep water at silver bay minnesota deposition over nearly 20 years produced a sublacustrine fan with two prominent channels during 1972 and 1973 a current meter anchored 5 m above the lake floor adjacent to one of the channels recorded episodic turbidity current flow events lasting as long as two weeks to understand flow parameters for turbidity currents better a short term experiment within a channel on reserve fan in 1975 measured those variables not previously directly observed for channelized turbidity currents flow thickness flow density and concurrent velocity the observed flow thickn ss approximately 16 m is nearly four times the channel depth calculations using the average flow speeds 8 to 12 cm sec and the dilute concentration of the flow as measured during the experiment yield a value for the drag coefficient that is in remarkable agreement with estimated values commonly used for deriving speeds of turbidity currents using dimensions of submarine channels and properties of the sediments

prestack depth migration of dense wide angle seismic data abstract prestack depth migration of wide angle seismic data represents an extension of traditional imaging with near vertical incidence data because it includes a larger component of the recorded wave field to date however studies that have employed wide angle migration have suffered because only widely spaced data were available and because only very simple synthetic tests were performed although wide angle migration has the potential to increase our ability to image deep crustal structures particularly when closely spaced data are collected a thorough study of this technique has been lacking to address this we present a case study of prestack depth migration of relatively dense synthetic wide angle marine data the objectives are to identify potential benefits and limitations of this approach and answer such fundamental questions as how close the receiver spacing must be for a typical survey to image effectively with wide angle data this will facilitate the design of better seismic experiments our study employs kirchhoff prestack depth migration of variably spaced full wave field synthetic wide angle ocean bottom hydrophone obh data generated using a realistic velocity model based on the passive eastern margin of the united states we show how an increase in obh density improves the migration by increasing the lateral resolution and signal to noise ratio we also investigate the contribution of various offset ranges to the migrated image and show how the wider angle components contribute primarily to the deepest parts of the image with relatively low spatial frequency compared to the near vertical incidence components to investigate how errors in the velocity model affect imaging as a function of offset range we migrate the data using a velocity model derived from refraction and reflection traveltime inversion this example demonstrates the need to obtain an increasingly accurate model as increasingly wider angle data are migrated to effectively image structures in our 200 40 km synthetic velocity model an obh spacing of approximately 2 km is required

numerical modeling of hyperpycnal plume abstract when the density of sediment laden river water exceeds that of the ambient ocean water the river plunges to the ocean floor and generates a hyperpycnal plume hyperpycnal plumes can travel significant distances beyond the continental shelf and may be sustained for hours to weeks there are several apennine rivers in italy that are likely to develop hyperpycnal discharges on the western adriatic shelf among them river tronto is a moderately dirty river capable of producing 64 hyperpycnal flow events lasting 6 h during a 100 year period numerical simulations of hyperpycnal events have been conducted for the adriatic shelf near the mouth of river tronto using a two dimensional depth integrated finite volume model to study the spreading of the plume and its interaction with the alongshore current simulation results indicate that the alongshore current has great impact on the spreading and deposition pattern of the hyperpycnal flow sedimentary deposits generated from a series of simulated hyperpycnal flow events have developed undulating bed forms

reservoir turbidity current modeling with a two dimensional layer averaged model abstracta two dimensional layer averaged model is developed and verified to simulate turbidity current characteristics and its sluicing in reservoirs the governing equations consist of mass and momentum conservation laws for the turbidity current mixture equations for the sediment transport and bed dynamics and auxiliary relations for the interactions among clear water turbidity current and bed a finite volume unstructured polygonal mesh method is adopted so that reservoirs with complex terrains may be simulated special algorithms are developed to capture the turbidity current front movement through a clear water bed and to simulate turbidity current sluicing through reservoir outlets the developed model has been tested and verified with both conservative and nonconservative turbidity currents ranging from simple to complex reservoir terrains case studies presented include a lock exchange turbidity current with large eddy simulation and direct numerical simulation results a laboratory test of

high pressure amphibolite granulite facies metamorphism in the paleoproterozoic rudall complex central western australia abstract the rudall complex forms the basement of the paleoproterozoic to neoproterozoic paterson orogen which was deformed during at least three major orogenies the complex comprises a sequence of metamorphosed clastic and chemical sediments and basalts deposited in a marginal basin environment prior to extensive felsic intrusion deformation of the sequence during the first yapungku orogeny between 2000 and 1760 ma included extensive thrust stacking from ene to wsw the thermal peak of the associated high pressure metamorphism was late to post tectonic with respect to this deformation thermobarometry on amphibolites and mafic granulites that contain various combinations of the minerals hornblende plagioclase quartz garnet othopyroxene and clinopyroxene indicates that temperatures peaked at around 800 c while pressures reached 1200 mpa the late timing of peak temperatures together with the presence in some amphibolites of amphibole plagioclase symplectitic coronas around garnet indicates a steeply decompressive clockwise p t t path peak metamorphic pressures indicate that the crust was locally thickened by at least 40 km during an event that showed similarities to phanerozoic collisional tectonics it is suggested that this deformational and metamorphic event records the collision between the pilbara craton and a continent to the northeast the paleoproterozoic evolution of australia has previously been attributed to ensialic processes characterised by low pressure metamorphism and anti clockwise p t t paths the metamorphic history of the rudall complex is not consistent with this view and the documented high pressure metamorphism is broadly synchronous with a medium pressure metamorphic event in central australia the strangways orogeny and possibly also in northwestern australia the capricorn orogeny collisional plate tectonic processes played a significant role in the paleoproterozoic evolution of northern australia

whole process modeling of reservoir turbidity currents by a double layer averaged model turbidity current is formed as subaerial open channel sediment laden flow plunges into a reservoir the whole process of reservoir turbidity current i e formation propagation and recession is generally controlled by the water and sediment inputs from upstream and also the reservoir operation scheme specifying the downstream boundary condition enhanced understanding of reservoir turbidity current is critical to effective sediment management in alluvial rivers however until now there has been a lack of physically based and practically feasible models for resolving the whole process of reservoir turbidity current this is because the computing cost of three dimensional modeling is excessively high also single layer averaged models cannot resolve the formation process characterized by the transition from open channel sediment laden flow to subaqueous turbidity current or the upper clear water flow as dictated by the operation scheme of the reservoir which has significant impacts on turbidity current here a new two dimensional double layer averaged model is proposed to facilitate for the first time whole process modeling of reservoir turbidity current the two hyperbolic systems of the governing equations for the two layers are solved separately and synchronously the model is well balanced because the interlayer interactions are negligible compared with inertia and gravitation featuring a reasonable balance between the flux gradients and the bed or interface slope source terms and thus applicable to irregular topographies the model is benchmarked against a spectrum of experimental cases including turbidity currents attributable to lock exchange and sustained inflow it is revealed that an appropriate clear water outflow is favorable for turbidity current propagation and conducive to improving sediment flushing efficiency this is significant for optimizing reservoir operation schemes as applied to turbidity current in the xiaolangdi reservoir in the yellow river china the model successfully resolves the whole process from formation to recession the present work facilitates a viable and promising framework for whole process modeling of turbidity currents in support of reservoir sediment management c 2014 american society of civil engineers

crustal structure and seismicity beneath the forearc off northeastern japan marine seismological and other data in the japan trench area north of 38 5 n were used to infer the relation of subducting plate structure seismicity and focal mechanisms especially at the aseismic to seismogenic zone along the interface between the two interacting plates previous crustal models from ocean bottom seismographic refraction obs surveys were improved by taking into account the relative seismic amplitude characteristics and constraining the shallow structure using multichannel seismic data a wave speed discontinuity in these models is interpreted to be the contact zone of the crust of the overriding plate and the subducting pacific plate crust its dip angle increases to about 7 110 km landward of the trench axis a large increase beneath the deep sea terrace is required to reach the well defined angle of 25 beneath the tohoku east coast a large wave speed gradient within layer 2 commonly observed under normal oceans seems to vanish beneath the inner trench slope at about 10 km depth within the overriding plate apparently brittle material with a p wave speed of 6 km s can be found as near as 35 km from the trench axis the upper limit of the seismogenic zone of interplate low angle thrust events is about 15 km depth from obs seismicity and large event analyses both the strength of the crust of the overriding plate and the characteristics of subducting sediments must be investigated to define the seismic coupling of interacting plates

bending of the subducting oceanic plate and its implication for rupture propagation of large interplate earthquakes off miyagi japan in the japan trench subduction zone 1 we present the results of an onshore offshore wide angle refraction and reflection experiment off miyagi in the central japan trench forearc region there are two rupture zones of large interplate earthquakes here the landward rupture zone and the trenchward rupture zone to examine the influence of plate boundary geometry on the distributions of the rupture zones we determined reflector geometries from reflections the subducting oceanic plate increases its dip from about 5 to 13 around 143 2 e this bending point in the oceanic plate corresponds to the eastern edge of the trenchward rupture zone moreover another bending point may be present at approximately 142 3 e which corresponds to the eastern edge of the landward rupture zone the coincidence between bending points in the oceanic plate and the edges of rupture zones suggests that changes in the plate boundary geometry may affect rupture propagation of interplate earthquakes in the direction of plate convergence

extensional tectonics and mafic plutons in the ketilidian rapakivi granite suite of south greenland abstract the early proterozoic rapakivi suite in the ketilidian mobile belt of south greenland is bimodal with an abundance of mafic plutons which mingled and hybridised with the rapakivi granites basic rocks lacking signs of hybridisation and with mineralogy and bulk compositions apparently unaffected by proximity to the granites are enriched in large ion lithophile element lile relative to high field strength element hfse and have moderate nb depletion these are characteristics common to basic rocks found in back arc basins this tectono magmatic environment supports a model for the late ketilidian of crustal extension probably caused by slab roll back and is in keeping with the low pressure high temperature metamorphic conditions which prevailed when the rapakivi suite was emplaced nd and sr isotopes confirm the juvenile character of the ketilidian crust and rapakivi granites hybrid mafic rocks have low end compared to depleted mantle while apparently unhybridised examples have also undergone some isotopic modification

turbidity currents and submarine channel formation in rupert inlet british columbia 1 surge observations acoustic backscatter images obtained at 107 and 200 khz of surge type turbidity currents resulting from mine tailing discharge are presented excess densities in the head of the order of 100 kg m 3 are estimated from differences in acoustic backscatter intensity and in the amplitude of the bottom reflected signal these excess densities are comparable to estimates based on surge height and speed the speed being determined by assuming a universal head shape unlike gravity current surges from an impulsively started steady source the surge type turbidity flows consist of a high concentration slug of short duration followed by a longer lived wake in which sediment concentrations are lower by 2 3 orders of magnitude the profile of the high concentration slug resembles those for density slugs on small bottom slopes obtained in laboratory experiments discrete scatterers probably fish are observed to avoid the surges

a preliminary experimental study of turbidite fan deposits we present preliminary laboratory experimental results that demonstrate lobe switching in a turbidite fan after a significant number of individual event beds more than eight in both experimental fans made in this study the flow began to focus itself into a lobe at the center of which appeared a subtle channel form initial lobe switching occurred after nearly twenty event beds subsequent switching appeared to scale with lobe size and sedimentation rate the densest coarsest runs tended to initiate the switching of the depocenter instabilities within the turbidity current itself appear to be responsible for initial flow confinement to a lobe and ultimate switching events currently untreated scale effects and measurement difficulties limit quantitative extension of the results to natural settings though some general relationships are proposed

confirming sharp bending of the pacific plate in the northern japan trench subduction zone by applying a traveltime mapping method abstract many destructive earthquakes have occurred in the northern japan trench region owing to the subduction of the pacific plate two plate bending points where the dip of the subducting plate changes markedly have been found and correlations between the bending points and the updip limits of large earthquake rupture zones have been previously found in the regions off aomori 40 n and off miyagi 38 n in this study we investigate whether sharp plate bending is also present in the region off iwate 39 n located approximately halfway between the off aomori and off miyagi regions we analysed the existing off iwate wide angle seismic experimental data by applying a new method in which observed reflection phases are directly projected onto the depth distance domain from the time distance domain as a result we found a plate bending point in the region off iwate this is the first time such a point has been found there distances between the three bending points and the trench axis are almost uniform and sharp plate bending is a common feature in the northern japan trench subduction zone the bending axis which is defined by connecting bending points approximately coincides with the updip limit of the rupture zones of large interplate earthquakes seismic swarm activities have been observed inside the subducting oceanic crust along the bending axis and we infer that some of these activities are caused by bending of the subducting plate in addition p wave velocities of the upper plate vary across the bending axis implying that the position of the bending axis is closely related to physical properties of the upper plate and to seismic activities

dispersion model for tidal wetlands tidal wetlands in california are mostly estuarine salt marshes characterized by tidal channels and mudflats that are flooded and drained on a semidiurnal basis depths are rarely greater than 2 or 3 m except where dredging occurs for harbor operations and lengths from head to mouth are usually in the range of 1 10 km this paper presents a coupled set of models for prediction of flow solute transport and particle transport in these systems the flow and solute transport models are based upon depth integrated conservation equations while the particle transport model is quasi three dimensional common to these models is an assumption that a turbulent boundary layer extends vertically from the bed and can be described by the law of the wall this feature of the model accounts for 1 momentum transfer to the bed 2 longitudinal dispersion of dissolved material based on the work of elder 1959 and 3 advection and turbulent diffusion of particles in three dimensions a total variation diminishing finite volume scheme is used to solve the depth integrated equations using this model we show that dispersion can be accurately modeled using physically meaningful mixing coefficients calibration is therefore directed at modifying bed roughness which scales both the rate of advection and dispersion

a seismicity gap beneath the inner wall of the japan trench as derived by ocean bottom seismograph measurement abstract an ocean bottom seismograph obs array covered the area of the japan trench about 40 n off the tohoku district of northeastern honshu japan the obs array was operated for two weeks in june 1981 arrival time data of 8 obss were used to study a spatial distribution of microearthquakes around the trench during the observation period 400 500 events with a signal to noise ratio greater than 2 were detected by each obs the arrival times of 223 of these events could be picked 38 earthquakes were located in the area of the japan trench within the latitude range of 38 5 41 0 n and the longitude range of 142 0 146 0 e and about a hundred events were located beneath or near honshu island s p time distribution recorded by each obs showed seismic activities to exist on both sides of the trench axis while the seismic level was low beneath the inner wall of the trench epicentral distribution showed a seismicity gap beneath the inner wall of the trench the area of the landward activity continued eastward up to the position where the water depth is about 4000 m seismic activity existed beneath the trench axis and the seaward wall of the trench the seismicity gap suggested from the 1980 obs observations in the vicinity of the present study area was clearly confirmed by the present observations the obs array enabled us to determine the focal depth of microearthquake activity with better resolution than was possible from land observations the obs data showed that the landward activity beneath the continental slope was concentrated in the very shallow part of the lithosphere at a depth less than 30 km foci started to deepen westward with a very low dip angle of less than 10 which was the most shallow part of the upper plane of the double seismic zone the focal depth distribution showed that events just beneath the trench axis occurred to depths slightly greater than 50 km while the foci of the seaward activity were concentrated in the uppermost lithosphere at depths less than 30 km seismic cross sections clearly show that the activity beneath the trench axis and seaward wall of the trench is separated from the landward activity which is a shallow extension of the double seismic zone by the seismicity gap

spatial distribution of earthquakes associated with the pacific plate subduction off northeastern japan revealed by ocean bottom and land observation abstract precise earthquake locations in the vicinity of a trench axis elucidate the characteristics of the shallower part of a subducting plate we split the japan trench into two regions off sanriku in the north and off fukushima in the south on the basis of the seismic properties of the regions and the fine microearthquake structure investigated by ocean bottom seismographic surveys as well as recent observation of major seismic activity from ocean bottom seismograph data the hypocentral distributions along a profile perpendicular to the trench axis indicate that almost all earthquakes occur along the boundary separating the subducting pacific plate and the landward plate a difference of the hypocentral distribution between off fukushima and off sanriku is found at the shallow plate boundary level the seismic thrust zone begins at more than 100 km landwards from the trench axis off fukushima whereas it begins at 50 km off sanriku and is nearly flat between 50 and 100 km from the trench axis this reflects regional variations of the interplate coupling in spite of these variations a common characteristic in recent observations indicates that in both regions almost all the hypocenters are deeper than 10 km this suggests the plate boundary to be decoupled at least in the part shallower than 10 km

a recent turbidity current event hueneme fan california reconstruction of flow properties a recent 100 yr old turbidite is described from hueneme fan california continental borderland dense sampling over the fan surface has allowed excellent delineation of the characteristics of this deposit it exhibits bouna de sequences and has a distinctly bimodal sandy silt grain size distribution through the use of generalized fluid dynamics equations it is possible to reconstruct original flow properties of the current which deposited this material the calculated velocities ranged from 10 90 cm s 1 and excess density above ambient seawater from 0 001 0 005 g cm 3 in the lower midfan and upper fan channel regions respectively height of the current ranged from 5 15 m on slopes from 1 5 to 0 15 a total of 107 m3 of sediment was deposited during 10 days the turbidity current is conjectured to have originated from direct river input during the floods of 1884 an older event is also described which has distinctly different properties and origins the grain sizes of this older deposit are much coarser and sedimentary structures suggest higher flow regimes this turbidite is conjectured to have been deposited from a higher density faster current thought to have been generated by slumping the need for a better understanding of the controls on the characteristics of turbidity currents and their effect on fan morphology is emphasized

metallogeny of south greenland a review of geological evolution mineral occurrences and geochemical exploration data abstract south greenland has been the site of historic mining of cryolite copper graphite and gold hosts mineral deposits with gold uranium zinc niobium tantalum zirconium hafnium ree iron titanium vanadium fluorite and graphite and has additional potential for lithium beryllium phosphorus gallium and thorium data from stream sediment geochemical surveys document that south greenland is enriched in a range of these elements relative to the rest of greenland and to estimates of the upper crust composition distribution patterns for individual elements within south greenland exhibit enriched regions that are spatially related to lithological units crustal structure and known mineralisation the northern domain of south greenland includes the southernmost part of the orthogneiss dominated north atlantic craton orogenic gold mineralisation is hosted by quartz veins and hydrothermally altered rocks associated with shear zones intersecting the mesoarchaean tartoq group of mafic metavolcanic rocks geochemical exploration indicates that additional potential for gold mineralisation exists within palaeoproterozoic supracrustal rocks overlying the archaean basement rocks formed during the palaeoproterozoic ketilidian orogeny occupy a major part of south greenland and has been divided into two domains the central domain is underlain by the julianehab igneous complex forming a 100 km wide ene wsw zone centrally across south greenland intrusive and extrusive mostly felsic magmatic rocks were emplaced in two main stages 1850 1830 and 1800 1780 ma in a continental arc setting positive anomalies in aeromagnetic data indicate that mafic plutons are common in the late igneous complex intra arc mafic metavolcanic rocks contain syngenetic stratabound copper sulphide and epigenetic shear zone hosted copper silver gold mineralisation at kobberminebugt and kangerluluk whereas metasedimentary and metapyroclastic rocks contain stratabound uraninite mineralisation orthomagmatic iron titanium vanadium mineralisation is hosted by a gabbro a potential for porphyry type mineralisation related to the late intrusive stages of the julianehab igneous complex is suggested by showings with copper molybdenum and gold together with stream sediment anomalies for these elements vein type uranium mineralisation occurs in fault zones in the julianehab igneous complex related to mesoproterozoic rifting the southern domain contains an assemblage of palaeoproterozoic metasedimentary and metavolcanic rocks that underwent moderate to strong deformation peak ht lp metamorphism and partial melting with subsequent retrograde exhumation at 1790 1765 ma the supracrustal rocks contain syngenetic au as sb u and zn mineralisation in volcanic or graphite and sulphide rich sedimentary environments graphite was mined historically at two sites many stream sediment gold anomalies are located in a ne trending belt along the boundary between the early julianehab complex and the supracrustal rocks to the south they reflect a number of auriferous quartz vein occurrences including the nalunaq gold deposit hosted in a system of shear zones and probably generated as orogenic gold during ketilidian accretion the 1755 1730 ma a type ilua plutonic suite is the latest magmatic event in the ketilidian orogen the 1300 1140 ma gardar period involved continental rifting sedimentation and alkaline magmatism numerous dykes and 10 ring shaped intrusion complexes were formed across south greenland an orthomagmatic iron titanium vanadium deposit is hosted by troctolitic gabbro residual magmas and fluids resulting from extreme magmatic differentiation possibly combined with assimilation of older crust created mineral deposits including cryolite that was mined at ivigtut large low grade deposits of uranium rare earth elements zinc at kvanefjeld and tantalum niobium rare earth element zirconium at kringlerne in the ilimaussaq complex as well as tantalum niobium rare earth elements at motzfeldt so in the igaliko complex the south greenland crustal evolution records effects of mantle processes such as lithospheric extension subduction and underplating which resulted in recurrent magma emplacement in tectonically active environments as such the geology of south greenland reflects events and circumstances that are favourable to the generation and preservation of hydrothermal ore forming fluid systems during the ketilidian orogeny as well as to the development of extreme rock compositions within the gardar alkaline igneous province

tectonic features of the japan trench convergent margin off sanriku northeastern japan revealed by multichannel seismic reflection data near the japan trench convergent plate margin the seaward edge of the continental plate is deformed by subduction of the oceanic plate we report the results of a multichannel seismic survey in the northern japan trench in which this deformed zone is demarcated from the rigid continental framework by a pronounced landward dipping reflector the oceanic plate also undergoes deformation as the two plates interact in the subduction processes resulting in a progressive deformation or destruction of a horst structure along the top of the subducting oceanic crust this may eventually lead to the formation of a smooth plate boundary at the greater depth more than 45 km landward from the trench axis a smooth reflector suggesting a stable slip plane is visible along and above the oceanic crust our data indicate that the deformed zone pinches out landward 60 km from the axis at 13 km depth and the slip plane becomes less obvious there seismicity of interplate earthquakes rapidly increases landward from this location leading us to speculate that this is where coupling at the plate boundary becomes strong enough for earthquakes to occur we conclude that the updip limit of the seismogenic zone of interplate earthquakes in the study area is characterized by the tectonic feature of a pinchout of the deformed sediments which overlie the subducting oceanic crust

clockwise p t paths for crustal melting and h2o recycling in granite source regions and migmatite terrains abstract clockwise pressure temperature p t paths of metamorphism pass through two kinds of melting reactions with increasing temperature the first generates h 2 o saturated partial melts at the h 2 o saturated solidus only if excess h 2 o is present usually this accounts for less than 3 melt the second generates h 2 o undersaturated melts through dehydration melting reactions dmrs of micas or other hydrous minerals and occurs at temperatures higher than the h 2 o saturated solidus if h 2 o undersaturated melts remain in situ and the source regions are not exhumed then the crystallisation reactions encountered along the near reverse p t path may produce the same mineralogy as in the source rock in regions of exhumation along the decompression segments of clockwise p t paths two other types of crystallisation reactions occur the better known type occurs at the recrossing of the pelite h 2 o saturated solidus at shallower depth this can occur at mid crustal depths or much shallower at pressures lower than the appropriate invariant point which relates all of these reactions and will result in granitic pegmatites at the other type remaining mica can react with hydrous melt to generate anhydrous granulite with free h 2 o fluid such suprasolidus decompression dehydration reactions sddrs result in freezing of pelitic melts at mid crustal depth to k feldspar quartz assemblages and release of h 2 o which can induce h 2 o saturated melting in adjacent fertile lithologies lacking h 2 o e g psammite older granite distinct mineral proportions and textures will result from each reaction the actual reactions occurring are related through specific invariant points whose locations are known in the p t space the displacement of these invariant points due to additional components in the solid melt and fluid phases is reasonably well known the flat lying sddr very low d p d t will extend to much higher pressures if a low ah 2 o fluid is present sddr involving amphibole or epidote will occur in mafic to intermediate compositions over a large depth range depending on fe mg ca na etc of the rock compositions

numerical modeling of bottom trawling induced sediment transport and accumulation in la fonera submarine canyon northwestern mediterranean sea bottom trawling leads to recurrent sediment resuspension events over fishing grounds recent studies have shown how bottom trawling can drive seascape reshaping at large spatial scales and enhance sediment transport in submarine canyons which subsequently impacts deep sea ecosystems present knowledge on the transfer and accumulation of sediment flows triggered by bottom trawling is based on localized and infrequent measurements whilst a more complete picture of the process is needed the present work focuses on the modeling of sediment transport and accumulation resulting from trawling activities in la fonera submarine canyon northwestern mediterranean sea thus contributing to an improved assessment of trawling impacts based on mooring data within a canyon gully we use an inverse model to retrieve the unknown time series of resuspension due to trawling over the fishing grounds this resuspension is later used as forcing for the direct problem we simulate trawling induced flows through the canyon and provide a 3d visualization of potential trawling impacts on sediment dynamics including the identification of the propagation patterns of sediments resuspended by trawling flows coming from shallower fishing grounds are funneled through canyon flank gullies towards the canyon axis with part of the resuspended sediment reaching the continental rise out of the canyon across the open continental slope trawling induced sediment flows promote sediment accumulation beyond the canyon mouth given the wide geographical distribution of bottom trawling our results have far reaching implications that go much beyond la fonera submarine canyon our study represents a starting point for the assessment of the sedimentary impact of bottom trawling in deep continental margins

relay ramps as pathways for turbidity currents a study combining analogue sandbox experiments and numerical flow simulations unlike for subaerial settings the impact of subaqueous relay ramps on sediment dispersal is still poorly understood a combination of analogue laboratory experiments in a sandbox with numerical flow calculations is used to simulate relay ramp topographies on rifting continental margins and to analyse the resulting turbidity current pathways and their deposits various scenarios are investigated including inflow perpendicular and oblique to the relay ramp axis as well as flow constrained by an incised channel on the ramp and by a landward directed tilt of the ramp without channelling most sedimentation takes place on the basin floor because the bulk of the flow follows the steepest gradient down the fault and into the rift basin with a channel along the relay ramp significant flow occurs initially down the ramp axis but channel spillover and basinward ramp tilting combine to redirect much of the sediment down the fault slope into the basin when the relay ramp has a landward oriented tilt most of the current flows down the ramp and deposits its sediment load there and at the foot of the ramp however also here a considerable amount of the flow is shed over the hanging wall fault and into the basin forming a secondary depocentre while ponding redistributes thin deposits over a wider area of the basin the quantitative dependence of these results on the specific ramp geometries remains to be investigated further but may bear great importance for refined sedimentary models in subaqueous rifted settings as well as for hydrocarbon exploration therein 2009 the authors journal compilation 2009 international association of sedimentologists

new reflections on the structure and evolution of the makkovikian ketilidian orogen in labrador and southern greenland marine seismic reflection profiles across the early proterozoic makkovikian ketilidian orogen in the labrador sea region suggest that it is a doubly vergent asymmetric orogenic belt comparable in width to younger collisional orogens a southeast dipping reflector package is correlated with on land shear zones that mark the southeastern limit of exposed reworked archean crust and is also associated with a cryptic isotopic boundary in granites which documents a transition from ancient to juvenile basement this boundary is interpreted as a suture along which juvenile proterozoic crust has been juxtaposed over thrust over the archean craton a major synorogenic to postorogenic plutonic terrane to the southeast has a poorly reflective upper crust but shows strong subhorizontal reflectivity in the lower crust and moho regions the southeastern part of the profile correlates with metasedimentary terranes of the ketilidian belt in greenland and contains low angle northwest dipping reflector packages suggestive of large scale crustal imbrication by thrusting at least two broad zones of reflectivity at mantle depths up to 16 s are also recognized one dips northwest below the archean craton but the most widespread mantle reflectivity is southeast dipping in opposition to the dominant fabric in the overlying crust these contrasting crustal and subcrustal reflectivity patterns define a geometric focus beneath the orogenic belt and may provide information about subduction polarity during its development the doubly vergent reflectivity pattern resembles images from possibly correlative precambrian orogenic belts such as the penokean and svecofennian and also younger small collisional orogens such as the appalachian and pyrenean belts it also broadly resembles some results of geodynamic crustal deformation models based on detachment and underthrusting of mantle lithosphere following collision and the squeezing of weak zones between rigid bounding blocks a speculative multistage model for the belt incorporates initial northward subduction beneath the craton shifting to later southward subduction followed by oblique accretion of a composite arc terrane and juvenile continental block the accreted hotter juvenile proterozoic crust behaved differently than the stable cool archean crust and experienced subhorizontal shearing in lower crustal and moho regions associated with southeast directed imbrication of the middle and upper crust by thrusting however the present reflectivity pattern of the orogen may also include elements related to post collisional extensional collapse

fault plane geometry in the source region of the 1994 sanriku oki earthquake abstract we present the results of a seismic refraction experiment conducted off eastern aomori northeastern japan forearc region where the detailed crustal structure was poorly known an objective analysis using high quality survey data allowed us to obtain the seismic velocity structure to about 30 km depth and in particular to obtain a well constrained geometry of the plate boundary in the source region of the 1994 sanriku oki earthquake our results show that the subducting pacific oceanic plate increases its dip from about 5 to approximately 15 around the longitude of 143 5 e 80 km landward of the trench axis near the latitude of 40 n the location of this bend in the plate is 40 km east of the bending point previously proposed on the basis of hypocenter distribution a cluster of aftershocks of the 1994 sanriku oki earthquake occurred around the bending point this is because the bending of the subducting plate appears to affect the stress state in the vicinity of the plate boundary furthermore the plate geometry is also considered to be related to the coupling or slip features along the plate boundary as the bending point correlates with the spatial distribution of repeating earthquakes our results will lead to more reliable determinations of asperity areas because an accurate dip angle of the fault plane is necessary for slip distribution studies

interplate seismic activity near the northern japan trench deduced from ocean bottom and land based seismic observations the off sanriku area the landward slope area of the northern japan trench is characterized by its active seismicity which is directly related to the subduction process of the pacific plate in july august 1992 a seismic swarm activity was observed near the trench five earthquakes of m 6 occurred successively within 2 weeks at the beginning of the activity we deployed an ocean bottom seismograph obs array in the epicentral region to make an in situ observation of the spatial distribution of these events and to study the characteristics of the swarm activity in detail we relocated 357 events from 23 july to 26 august with focal depth errors less than 5 km by using both the obs and the land network data the swarm events are not distributed homogeneously over the plate boundary but form several clusters a remarkable concentration of the earthquakes was found in the vicinity of the hypocenter of the largest event during the obs observation m 6 2 29 july this formed the most active cluster almost all the earthquakes including the m 6 2 event occurred at depths of about 15 km and were concentrated along a thin plane dipping to the west at 5 the location of the plane coincides well with that of the plate boundary derived from previous seismic explorations we also relocated epicenters of the off sanriku events by introducing station corrections to the land network data during the period when the obs array was absent the corrections were estimated from the travel time residuals of the hypocenter relocation using the obs and the land network data the result of the epicenter relocation strongly indicates the existence of a zone of extremely low seismic activity beneath the inner trench wall where low seismic velocity mechanically weak unconsolidated sediments overly the subducting pacific plate

la zone tectonique du front de grenville a l est de louvicourt quebec exhumation de la croute archeenne pendant l orogenie grenvillienne the grenville front tectonic zone east of louvicourt in quebec defines a tectonometamorphic domain marked by the grenville front oriented north 50 that is locally crosscut by a north 30 reverse fault the matchi manitou fault these tectonic accidents separate the central parts of the superior province to the northwest from the grenville province to the southeast the archean age high grade polymetamorphic sequences of the grenville province consist of paragneisses and migmatitic quartzofeldspathic gneisses associated to coarse grained anatectic pegmatitic veins the whole containing shreds of two pyroxenes bearing mafic gneisses the metamorphic disequilibrium textures the chemical analyses of the mineral phases and the whole rock chemistry of these sequences indicate that a strong crustal thickening marked by the incorporation of shreds of volcanic rocks in the metasedimentary sequences led to the granulitization of the lithologies and the quartzofeldspathic pegmatitic vein formation by fluid

temperatures of granulite facies metamorphism constraints from experimental phase equilibria and thermobarometry corrected for retrograde exchange this study assesses temperatures of formation of common granulites by combining experimental constraints on the p t stability of granulite facies mineral associations with a garnet orthopyroxene grt opx thermobarometry scheme based on al solubility in opx corrected for late fe mg exchange we applied this scheme to 414 granulites of mafic intermediate and aluminous bulk compositions our findings suggest that granulites are much hotter than traditionally assumed and that the p t conditions of the amphibolite granulite transition portrayed in current petrology textbooks are significant underestimates by over 100 c for aluminous and intermediate granulites mean corrected temperatures based on our method are 890 17 and 841 11 c respectively uncertainties reported as 95 confidence limits on the mean consistent with minimum temperatures for orthopyroxene production by fluid absent partial melting in these bulk compositions in contrast mean temperatures based on grt opx fe mg exchange equilibria using the same thermodynamic data are 732 22 and 723 11 c respectively well below the minimum temperatures for opx stability for mafic granulites the mean corrected temperature using our method is 816 12 c similar to the mean temperature of 793 13 c from fe mg exchange reasons for the differences between the mafic granulites and aluminous intermediate granulites are unclear but may be due to the lower al concentrations in opx in the mafic rocks and possible deficiencies in the thermodynamic modelling of these low concentrations we discuss a number of well known granulite terrains in the context of our findings including the adirondacks the acadian granulites of new england the incipient charnockites of southern india and sri lanka and the kerala khondalite belt our findings carry implications for thermotectonic models of granulite formation a computer program to perform our thermobarometry calculations rclc is available from the journal of petrology website at http www petrology oupjournals org or from the authors at http www geo ucalgary ca pattison drm pattison rclc htm

coupling an underflow model to a three dimensional hydrodynamic model a separate underflow model is coupled to the three dimensional 3d estuary and lake computer model the underflow equations are solved on a two dimensional 2d grid underlying the 3d model grid the underflow model entrains ambient water whose properties are given by the fluid properties of the bottom boundary cells in the 3d model this new approach allows improved representation of underflow effects in z coordinate models by reducing numerical convective entrainment an idealized case is used to illustrate the benefits of the underflow model comparisons of model results and field data for a saline underflow event in lake ogawara and a cold water underflow in lake kinneret demonstrate improved model capability in representing underflow events that are thin compared to the vertical grid scale

seismic structure and seismogenesis off sanriku region northeastern japan summary in 1997 a seismic experiment using an airgun array and ocean bottom seismographs obss was performed in the forearc region of the northeastern japan nej arc the objectives of this experiment were to clarify seismic structures of the forearc region off sanriku japan using airgun obs data and to understand the nature of the japan trench seismogenic zone fundamental features of the structure are as follows i the subduction angle becomes steeper from east to west from 3 to 8 to 11 with the top of the plate located at depths of 11 km 40 km west from the trench 21 km 120 km west from the trench and 28 km 140 km west from the trench respectively ii the nej moho beneath the forearc is defined at a depth of approximately 20 km iii p wave velocity of the island arc upper mantle is approximately 8 km s 1 iv the p wave velocity of the cretaceous sedimentary layer exhibits significant lateral variability 4 0 5 5 km s 1 i nthe e w direction v the upper crust of nej forearc also has the significant lateral heterogeneity 5 0 6 3 km s 1 i nthe e w direction but not in the n s direction vi the middle crust defined on land extends in some locations 40 km east of the coastline vii lateral variability in the p wave velocity of the lower crust 6 7 7 0 km s 1 i ssmall compared with that of the upper crust according to these results it is suggested that the rupture areas of large earthquakes m7 in this region are limited within the contact zone between the nej arc crust and the subducting oceanic crust although a thin layer with low velocity is probably present within this contact zone the serpentinization of uppermost mantle wedge of the nej arc by reaction between the mantle materials and the water from the thin layer beneath forearc region is limited this might indicate that a significant volume of water and sediments subduct with the slab to depths of over 20 km

attachment formation during partitioning of oblique convergence in the ketilidian orogen south greenland subhorizontal attachment zones provide coupling between lithospheric layers in orogenic belts a mid crustal attachment zone is exposed in the palaeoproterozoic ketilidian orogen south greenland which formed as a result of north directed oblique convergence at a cordilleran type margin rifting c 2 1 ga and compressional deformation and magmatism 1850 ma on the continental margin was followed by an extended sinistral transpression from 1850 to 1730 ma now separated into three episodes or peaks of activity the first episode was focused on the back arc region and was followed by the main arc construction phase during which transpression was partitioned into strike slip and contraction components despite the longevity of this active margin system individual tectonic events took place rapidly e g development of fore arc d1 d3 and accompanying high temperature low pressure metamorphism took place over c 12 ma we explain the fore arc and batholith evolution by the upward migration of an underlying attachment structure through the upper crustal partitioned blocks this migration may be attributed to an increase in the geothermal gradient accompanied by or followed by exhumation of the mid crust the partially molten hence weak attachment zone solidified and strengthened during cooling before emplacement of the post orogenic rapakivi suite during the third distinct phase of mild sinistral transpression

rapakivi granites south greenland hydrothermal alteration of igneous layering igneous layering is developed in the proterozoic rapakivi granite suite of south greenland in an area on the south easternmost coast of the island of angnikitsoq the layering at this locality is unusual in that it is defined by interstitial phases we suggest that large scale hydrothermal alteration has converted a fine grained pyroxene cumulate in which original cumulate pyroxenes occurred in the interstices between larger feldspars to interstitial biotite and green amphibole

ray equation migration of wide angle reflections from southern alaska a kirchhoff style prestack depth migration algorithm is implemented for wide angle reflections in two dimensional variable velocity acoustic media extrapolation of both source and recorder wavefields is performed by ray tracing the imaging condition at each point in the image space is the total source to recorder travel time since the migration algorithm is based on ray tracing migration can be performed for any medium through which rays can be traced there is no inherent limitation on the size of the region to be imaged regions up to 3 6 103 km2 are utilized in this study the algorithm is illustrated by migration of two synthetic and three real data sets from the u s geological survey s trans alaska crustal transect program images are produced of inferred subduction assemblages in southern alaska emphasis in this paper is on obtaining reflector positions and shapes rather than detailed structural interpretations

the rapakivi granites of south greenland stable isotope characteristics of their black and white facies and the nature of their protolith abstract the rapakivi granites of south greenland were emplaced into the ketilidian orogenic belt at about 1 74 ga during an episode of extensional tectonics petrographically they can be subdivided into a roughly subequal black facies and white facies distinguished by the colour turbidity of the alkali feldspars and by the associated mineralogy which is more hydrous i e amphibole and biotite compared to olivine and pyroxene in the white facies the oxygen isotope composition of these rocks is notably homogeneous from thirteen outcrops sampled over an area extending some 200 km 100 km all alkali feldspars have an average 18 o of 10 2 0 4 this lack of variation is consistent with the consensus petrogenetic model which invokes a very well mixed two component protolith the high abundance of 18 o mean whole rock 18 o 9 4 argues that the major contribution perhaps 90 although originally mantle derived had undergone 18 o enrichment in a low temperature sedimentary cycle there is no oxygen isotopic distinction between alkali feldspars in the black and white facies which is argued to be a consequence of the relatively anhydrous nature of the melt hydrogen isotope compositions vary widely by 30 but are coherent on a hand specimen scale as demonstrated by approximately equal d of biotite and alkali feldspar it is not clear at which stage the d h heterogeneity was introduced

a new model for simulation of collection and conveyance sections of qanat abstract in this paper a new numerical model has been developed for simulation of qanat aquifer system this model employs quasi 3d mixed form of richards equation and 1d fully hydrodynamic form of saint venant equations to simulate subsurface and overland flow respectively in order to handle non orthogonal grids subsurface flow module benefits from coordinate transformation technique using the above mentioned governing equations the presented model is able to simulate water flow inside both collection and conveyance sections of the gallery as well as dynamics of groundwater and vadose zone from impermeable bed rock to the soil air interface since measured data corresponding to the hydraulics of qanats is scarce the overland and subsurface modules have been validated with analytical numerical and experimental benchmarks in the literature subsequently the model was employed to simulate ten different hypothetical aquifer qanat systems with different properties including the depth of groundwater aquifer roughness of the gallery and saturated hydraulic conductivity of the gallery aquifer boundary and the influence of each the parameters was monitored on the outflow rate at the appearance point of each qanat furthermore the advance of water inside two initially dry galleries were simulated at different time levels up to steady state eventually the streamlines have been shown at the steady state for two qanat aquifer systems although the presented study sheds light on some aspects of qanat aquifer hydraulics the validation of the presented model with in lab or on field data remains ongoing for the future researches

conditions for the ignition of catastrophically erosive turbidity currents abstract the basic impediment to a clear understanding of eroding and depositing turbidity currents has been the lack of a proper formulation of bed sediment entrainment this problem is addressed herein a detailed analysis indicates that the bagnold criterion is necessary but insufficient for self sustaining turbidity currents the analysis reveals two possible equilibrium states a relatively low velocity ignitive state and a high velocity dense catastrophic state a stability analysis indicates that the ignitive state is unstable flows below it invariably die out and flows above it ignite i e accelerate and entrain sediment to the catastrophic state which is stable the ignitive state thus defines the criterion for a self sustaining turbidity current estimates of the catastrophic state suggest that it is highly erosive and competent to scour out submarine canyons

textural evolution of the rapakivi granites south greenland sr o and h isotopic investigations the development of rapakivi texture in feldspars from the ketilidian granitoids of south greenland has been investigated using sr o and h isotopes a low temperature signature is found in the sr and o data which seemingly contradicts some textural features that point to a magmatic origin of the plagioclase mantles around the k feldspar ovoids an origin for these mantles involving exsolution from an original alkali feldspar solid solution is proposed which involves growth of mantles over a range of conditions determined by the mobility of the exsolving sodic feldspar this mobility may be enhanced at high temperatures in the presence of melts or increased fluid pressures and at lower temperatures by the processes responsible for the transformation of k feldspar to microcline rapakivi granites with both white and dark green feldspar occur in south greenland but show no major isotopic differences although the dark alkali feldspars contain significantly more fluid equivalent fluids in the white alkali feldspars may have escaped during plagioclase exsolution

modeling a plunging underflow a coupled three dimensional hydrodynamics and two dimensional underflow model is adapted to provide simulation of plunging inflows in reservoirs the new approach accounts for the effect of the barotropic term prior to the plunge point of the inflow simulations of plunging flows in constant width and constant slope channels are conducted and the resulting plunge depths are in agreement with prior empirical models simulation of a previously measured underflow in wellington reservoir australia demonstrates the model application to a plunging inflow in a natural water body and good agreement between field and model results

hydrodynamics of turbid underflows i formulation and numerical analysis a mathematical model is developed for unsteady two dimensional single layer depth averaged turbid underflows driven by nonuniform noncohesive sediment the numerical solution is obtained by a high resolution total variation diminishing finite volume numerical model which is known to capture sharp fronts accurately the monotone upstream scheme for conservation laws is used in conjunction with predictor corrector time stepping to provide a second order accurate solution flux limiting is implemented to prevent the development of spurious oscillations near discontinuities the model also possesses the capability to track the evolution and development of an erodible bed due to sediment entrainment and deposition this is accomplished by solving a bed sediment conservation equation at each time step independent of the hydrodynamic equations with a predictor corrector method the model is verified by comparison to experimental data for currents driven by uniform and nonuniform sediment

experiments on the thickness of beds deposited by turbidity currents abstract turbidites were produced experimentally by releasing suspensions of spherical beads from a lock into a 6 m long horizontal channel flow properties were varied by changing initial flow geometry and sediment size sorting and concentration in the initial suspension initial flow geometry was varied using two lengths of lock 0 29 and 0 59 m and four depths 0 15 0 2 0 3 and 0 4 m to vary the properties of the initial suspension three nearly uniform sizes 2 0 2 7 and 3 6 phi of glass beads and one 2 5 phi of plastic beads specific gravity 1 52 were used and all experiments were run at concentrations of 20 and 40 by volume the effect of poor sorting was investigated by mixing the coarse and fine glass beads to produce a poorly sorted sediment with a median grain size qual to that of the intermediate size glass beads bed thickness was almost uniform near the source except for beds deposited from poorly sorted sediment suspensions which tended to be wedge shaped high concentration produced more uniform bed thickness and for equal volume of sediment shorter thicker beds increases in lock height and length increased bed thickness almost equally if all other variables were held constant bed thickness was directly proportional to grain size the dimensionless ratio of the square of bed thickness divided by the volume of suspension per unit width was found to be directly proportional to the dimensionless ratio of settling velocity divided by the speed of the head of the current the constant in the regression equation appears to depend mainly on the sediment concentration the experimentally determined equation gives plausible values for turbidity current velocities when extrapolated to scales over a million times larger than those of the experiments

cellular automata model of density currents abstract cellular automata ca represent an interesting approach to the modelling of dynamical systems evolving on the basis of local interactions and internal transformations the ca model specially developed for simulating density currents is described the objective is to predict the formation and evolution of channels and the structure of deposits associated to the flow path for simulation purposes currents are represented as a dynamical system subdivided into elementary parts whose state evolves as a consequence of local interactions and internal transformations within a spatial discrete domain the model is developed for unsteady two dimensional depth averaged particle laden turbulent underflows driven by gravity acting on density gradients created by non uniform and non cohesive sediment ca is defined as a tessellation of finite state automata cells the attributes of each cell substates describe physical characteristics the natural phenomenon is decomposed into a number of elementary processes with a particular composition that makes up the transition function of the ca by applying this function to all the cells simultaneously the evolution of the phenomenon can be simulated in terms of modification of the substates the transition function includes the effects of water incorporation at the suspension ambient fluid interface a transport equation for the particle volume concentration and a toppling rule for the deposited sediments simple and flexible the obtained model constitutes a first step toward quantitative comprehension of the impact of external parameters on the turbidity current dynamics and on the organisation of the subsequent depositional sequences

control of turbidity currents in reservoirs by solid and permeable obstacles turbidity currents are often the main process for the transport and deposition of the sediments in narrow alpine reservoirs these underwater avalanches with high concentration of suspended sediments follow the thalweg of the lake to the deepest area near the dam where the sediments can affect the operation of the bottom outlet and the intake structures to control the sedimentation within the reservoir the effects of solid and permeable obstacles on the turbidity current were investigated with physical experiments and numerical simulations in the physical experiments the velocity distributions as well as the spatial and temporal evolution of the deposits were measured the investigated measures were also simulated by means of a two dimensional numerical model based on the flow solver cfx 4 4 the investigations showed that turbidity currents can be influenced effectively by properly designed constructive measures based on the results of the physical experiments and numerical simulations some design recommendations for solid and permeable obstacles are proposed

finite volume model for shallow water flooding of arbitrary topography a model based on the finite volume method is developed for unsteady two dimensional shallow water flow over arbitrary topography with moving lateral boundaries caused by flooding or recession the model uses roe s approximate riemann solver to compute fluxes while the monotone upstream scheme for conservation laws and predictor corrector time stepping are used to provide a second order accurate solution that is free from spurious oscillations a robust novel procedure is presented to efficiently and accurately simulate the movement of a wet dry boundary without diffusing it in addition a new technique is introduced to prevent numerical truncation errors due to the pressure and bed slope terms from artificially accelerating quiescent water over an arbitrary bed model predictions compare favorably with analytical solutions experimental data and other numerical solutions for one and two dimensional problems

the nagercoil charnockite a magnesian calcic to calc alkalic granitoid dehydrated during a granulite facies metamorphic event the paleoproterozoic nagercoil charnockite massif in southern india consists of garnet absent and garnet bearing varieties with garnet occurring only in those areas where the charnockite incorporates supracrustal lithologies there is a late neoproterozoic cambrian granulite facies metamorphic overprint on the charnockite massif this study examines whether orthopyroxene in the charnockites crystallized during the original magmatic stage or formed during the later high grade metamorphic event the textural association of orthopyroxene and relic garnet grains and reaction intergrowths of garnet and or biotite with orthopyroxene similar to those reported in dehydration zones within the gneisses surrounding the charnockite massif show that orthopyroxene in the charnockite massif formed during the late high grade metamorphic event from dehydration reactions and is not part of the original igneous assemblage metasomatic textures such as thin k feldspar rims together with the presence of co2 rich fluid inclusions in these rocks suggest that co2 metasomatism widely prevalent in the gneisses surrounding the massif probably resulted in the low water activity necessary to form orthopyroxene during the metamorphic overprint an oxygen isotope traverse along a metapelite enclave charnockite contact within the massif shows a distinct variation in d 18 o values with the charnockite away from the contact having the lowest d 18 o value 8 9o similar to that of typical metaluminous granitic rocks the charnockite at the contact shows an intermediate d 18 o value 10 3o and the surrounding metapelite has the highest d 18 o value 12o the intermediate d 18 o value indicates partial assimilation of metapelite with a high d 18 o value into the charnockite with a low d 18 o value both the garnet absent and garnet bearing charnockites have similar compositional ranges to tonalite granodiorite granite ttg suites irrespective of whether garnet is present or not the sr contents of the charnockites show a bimodal distribution a high sr group which is magnesian calcic to calc alkalic metaluminous showing ttg affinities and a low sr group which is dominantly ferroan calcic to calc alkalic metaluminous showing similarities to the orthopyroxene bearing dehydration zones petrogenetic characterization suggests that the protoliths of the nagercoil charnockites were high temperature melts of hydrous basalt

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