biotic and geochemical response to anoxic events the aptian pelagic succession of the gargano promontory southern italy microfossil distribution patterns and high resolution 13 c and 18 o curves calibrated against planktonic foraminiferal and calcareous nannofossil data are provided for the aptian pelagic coppitella section of the gargano promontory southern italy the succession consists of cyclically arranged couplets of bioturbated grey marlstones and off white marly limestones referable to the marne a fucoidi in the lower portion of the section two thin black shales were recognized the high resolution 13 c curve presented here correlates with those of other alpine tethyan sections albeit with lower absolute values the onset of deposition of organic rich sediments falls at the top of the interval of unchanging carbon isotope values whereas the upper black shale is documented from the interval of the main aptian positive 13 c excursion according to our biostratigraphic data the deposition of organic matter in the gargano promontory persisted through early late aptian boundary time using a chemostratigraphic definition only the lower black shale is referred to the selli level as far as the biotic response is concerned the onset of the nannoconid crisis is recorded considerably below the lower black shale whereas the globigerinelloides eclipse is recorded below and within the upper black shale the distribution of meso eutrophic indices zygodiscus spp radiolaria vs moderate fertility indices rhagodiscus asper and lithraphidites carniolensis testifies to a modest increase of surface water fertility only throughout the stratigraphically higher black shale the occurrence of a benthic foraminiferal fauna albeit impoverished in both the basal and upper black horizons clearly documents dysaerobic rather than completely anoxic conditions on the sea floor relative sea level rise at the time of the selli event in the gargano promontory is documented by drowning and foundering of the apulia platform margin situated adjacent to the basin in which the marne a fucoidi accumulated

a 70 ma record of suprasolidus conditions in the large hot long duration grenville orogen petrochronology of magmatic monazite and apatite from a single paragneiss leucosome derived by insitu partial melting documents the thermal evolution of the allochthonous belt of the central grenville province monazite records suprasolidus metamorphism from ca 1080 to 1020 ma under high temperature up to 850 degrees c apatite from the same leucosome yields an age of 960 ma consistent with cooling of this crustal segment down to subsolidus conditions of ca 450 degrees c a pegmatitic granite dyke with lobate contacts previously dated at ca 1005 ma turlin et al 2017 is interpreted to intrude the paragneisses at a temperature of ca 650 degrees c close to the wet solidus these data document slow cooling at a rate of 2 6 degrees c ma for the middle crust of this part of the grenville hinterland marked by protracted suprasolidus conditions for at least 70 ma it supports the definition of the grenville orogen as a large hot long duration orogen

high precision u pb ages for granulite metamorphism and deformation in the archean kapuskasing structural zone ontario implications for structure and development of the lower crust abstract precise u pb isotopic ages for two subhorizontal granulite gneisses in the kapuskasing structural zone indicate that formation and emplacement occurred more than 50 m y after cessation of volcanism in the steeply folded nearby greenstone belts by successive stages of ductile underplating across a zone of crust mantle delamination volcanism and batholith formation had ceased by 2700 and 2680 ma respectively while granulite formation occurred between 2660 and 2640 ma and ductile deformation continued until 2585 ma emplacement of the oldest granulite caused the development of shear planes and melting in the older overlying tonalite while emplacement of the younger granulite caused rupturing and rehydration of the overlying older granulite widespread tectonic underplating is implied since all superior province granulites have similar young ages anomalous ar ages that post date accretion by about 150 m y and scrambled pb pb and rb sr whole rock systems also suggest that late low temperature alteration accompanied this event temporal relationships and the presence of post volcanic 2670 ma conglomerate cobbles at granulite grade support a model of ductile underplating of a post accretion thermally softened back arc fore arc complex with components welded onto an overlying volcanic plutonic complex at successively deeper levels multistage deformation in active fault zones and hydrothermal emplacement of major gold deposits in greenstone belts are coeval with ductile underplating with ages between 2670 and 2585 ma anomalously abundant gold production from archean rocks may indicate that shallow underplating granulitization and devolatization was a widespread phenomenon at this time post accretion ductile underplating must be considered as a primary cause of seismic reflectors in archean terrains

tentative engineering approach to scour around breakwaters in random waves an approach by which the scour depth and protection layer width around the head of vertical wall breakwaters the scour and deposition depths as well as the protection layer widths at the round head of rubble mound breakwaters in random waves can be derived is presented here the formulas for scour depth by sumer and fredsoe 1997 for vertical wall breakwaters for regular waves and fredsoe and sumer 1997 for rubble mound breakwaters for irregular waves are used they are combined with describing the waves as a stationary gaussian narrow band random process to derive the scour and deposition depths as well as protection layer widths in random waves comparisons are made between the present approach and the fredsoe and sumer 1997 random wave scour data for rubble mound breakwaters

lithoprobe line 55 integration of out of plane seismic results with surface structure metamorphism and geochronology and the tectonic evolution of the eastern grenville province lithoprobe line 55 in the grenville province of eastern quebec provides unusually good control on the three dimensional 3 d geometry and structural relationships among the major lithological units there archean basement underlies the exposed proterozoic rocks along the entire seismic line and there is a lateral ramp in this basement immediately behind a lobate stack of thrust slices of high pressure metamorphic rocks comprising the manicouagan imbricate zone miz integration of the 3 d geometry with p t and geochronological data allows derivation of a tectonic model for the region the miz was buried to depths 60 km at 1050 ma preservation of its high pressure assemblages and the absence of metamorphism at 990 ma which is characteristic of lower pressure metamorphic rocks that tectonically overlie them indicates the miz rocks were rapidly unroofed early in the tectonic history there were two discrete pulses of crustal thickening during the grenvillian orogeny in this region the first inv

petrogenetic significance of orthopyroxene free garnet clinopyroxene plagioclase quartz bearing metabasites with respect to the amphibolite and granulite facies orthopyroxene free garnet clinopyroxene plagioclase quartz bearing mineral assemblages represent the paragenetic link between plagioclase free eclogite facies metabasites and orthopyroxene bearing granulite facies metabasites although these assemblages are most commonly developed under p t conditions consistent with high pressure granulite facies they sometimes occur at lower grade in the amphibolite facies thus these assemblages are characteristic but not definitive of high pressure granulite facies compositional factors favouring their development at amphibolite grade include fe rich mineral compositions ca rich garnet and plagioclase and ti poor hornblende the generalized reaction that accounts for the prograde development of garnet clinopyroxene plagio clase quartz from a hornblende plagioclase quartz bearing amphibolite precursor is hbl pl qtz grt cpx liquid or vapour depending on whether the reaction occurs above or below the solidus there are significant discrepancies between experimental and natural constraints on the p t conditions of orthopyroxene free garnet clinopyroxene plagioclase quartz bearing mineral assemblages and therefore on the p t position of this reaction semi quantitative thermo dynamic modelling of this reaction is hampered by the lack of a melt model and gives results that are only moderately successful in rationalizing the natural and experimental data

crustal architecture above the high pressure belt of the grenville province in the manicouagan area new structural petrologic and u pb age constraints abstract recent u pb age determinations and p t estimates allow us to characterize the different levels of a formerly thickened crust and provide further constraints on the make up and tectono thermal evolution of the grenville province in the manicouagan area an important tectonic element the manicouagan imbricate zone miz consists of mainly 1 65 1 48 and 1 17 ga igneous rocks metamorphosed under 1400 1800 mpa and 800 900 c at 1 05 1 03 ga during the ottawan episode of the grenvillian orogenic cycle coevally with intrusion of gabbro dykes in shear zones the miz has been interpreted as representing thermally weakened deep levels of thickened crust extruded towards the nw over a parautochthonous crustal scale ramp mantle derived melts are considered as in part responsible for the high metamorphic temperatures that were registered new data show that mid crustal levels structurally above the miz are represented by the gabriel complex of the berthe terrane that consists of migmatite with boudins of 1136 15 ma gabbro and rafts of anatectic metapelite with an inherited monazite age at 1478 30 ma these rocks were metamorphosed at about the same time as the miz metamorphic zircon in gabbro 1046 2 ma single grains of monazite in anatectic metapelite 1053 2 ma and under the same t range 800 900 c but at lower p conditions 1000 1100 mpa they are mainly exposed in an antiformal culmination above a high strain zone which has tectonic lenses of high p t rocks from the miz and is intruded by synmetamorphic gabbroic rocks this zone is interpreted as part of the hangingwall of the miz during extrusion a gap of 400 mpa in metamorphic pressures between the tectonic lenses and the country rocks together with the broad similarity in metamorphic ages are consistent with rapid tectonic transport of the high p t rocks over a ramp prior to the incorporation of the mafic lenses in the hangingwall between the antiformal culmination of the gabriel complex and the miz 1 48 ga old granulites of the hart jaune terrane are exposed they are intruded by unmetamorphosed 1228 3 ma gabbro sills and 1166 1 ma anorthosite hart jaune terrane represents relatively high crustal levels that truncate the miz gabriel complex contact and are preserved in a synformal structure farther south the gabriel complex is overlain by the banded complex a composite unit including 1403 32 25 ma granodiorite and 1238 16 13 1202 40 25 ma granite this unit has been metamorphosed under relatively low p 800 mpa granulite facies conditions metamorphic u pb data limited to zircon lower intercept ages 971 38 ma and 996 27 ma and a titanite 990 5 ma age are interpreted to postdate the metamorphic peak the general configuration of units along the section is consistent with extrusion of the miz during shortening and finally normal displacement along discrete shear zones

petrology and u pb geochronology of mafic high pressure metamorphic coronites from the tshenukutish domain eastern grenville province abstract a suite of mafic and ultramafic rocks from the tshenukutish domain eastern grenville province have been the subject of a detailed petrographic and geochemical study combined with u pb geochronology the tshenukutish domain is the highest tectonic level in the recently discovered eclogite bearing manicouagan imbricate zone the mafic and ultramafic rocks are characteristic of two of the lithotectonic segments in the domain the lac espadon segment and the baie du nord segment in the lac espadon segment cumulate textures and geochemical characteristics suggest that the units represent a layered mafic and ultramafic complex and an unrelated apatite rich fe ti mafic pegmatite nelsonite body in contrast the samples from the baie du nord segment represent fairly homogeneous fe ti gabbros and anorthosites the samples studied show abundant petrographic evidence for high pressure metamorphism for instance the widespread development of garnet clinopyroxene and kyanite bearing metamorphic assemblages estimates of the conditions of high pressure metamorphism in previous studies and melting textures in deformed and hydrated gabbro margins are in the range 750 900 c and 1600 1800 mpa the gabbroic end members from both segments suggest within plate tholeiite petrotectonic signatures ree patterns of gabbros and cumulates in both segments suggest fractionation from a tholeiitic source cumulate textures fractionation and inherited zircons suggest high crustal level emplacement of the magmatic protoliths in the tshenukutish domain in the lac espadon segment u pb ages of igneous zircon and baddeleyite give an age range of 1643 1629 ma for the emplacement of the layered complex the nelsonite in the les gives a poorly constrained igneous zircon age of 1596 126 99 ma in the baie du nord segment baddeleyite gives an age of 1170 5 ma for emplacement of the fe ti gabbros this is the youngest intrusion in the td and thus gives a maximum limit for the onset of grenvillian metamorphism ages of high p metamorphism are further constrained by zircon formed during partial melting of deformed and hydrated fe ti gabbro margins 1046 3 ma overgrowth of igneous zircon 1042 22 28 ma in the nelsonite saccharoidal zircon replacing baddeleyite 1030 10 7 ma and 1030 12 ma and new growth of equant zircon 1012 12 ma from the undeformed interior of the gabbros these ages indicate that the high p metamorphism of the tshenukutish domain was late grenvillian ottawan retrogression to amphibolite facies is constrained by the ages of titanite 1006 997 ma in deformed gabbro margins rutile ages range between 960 and 929 ma and are interpreted as cooling ages the difference between the ages of titanite and rutile suggest slow cooling of the tshenukutish domain after initial high pressure and temperature metamorphism and exhumation

transformation of fe ti gabbro to coronite eclogite and amphibolite in the baie du nord segment manicouagan imbricate zone eastern grenville province fe ti gabbros from the baie du nord segment of the manicouagan imbricate zone metamorphosed under high p t conditions during the grenvillian orogeny have been the focus of a detailed micropetrological study textures and mineral chemistry suggest that the mineral assemblages represent progressive stages of metamorphic transformation resulting in the formation of coronas pseudomorphs after igneous phases transitional and true granoblastic eclogites the transitional and eclogitic samples also have coronas which are developed locally around igneous xenocrysts of plagioclase and olivine the deformed margins of coronitic fe ti gabbros are transformed to amphibolite and contain clinopyroxene bearing leucosomes with garnet poikiloblasts that are indicative of high p t dehydration melting interpretation of garnet zoning and thermobarometry suggest that the highest p t conditions are recorded by coronas around xenocrysts c 720 800 c at 14 17 kbar and garnet clinopyroxene cores in granoblastic assemblages c 740 820 c at 13 17 kbar in the eclogitic samples re equilibration during the early stages of exhumation at high t conditions 700 c affected all samples and is evidenced by the widespread development of pargasite bearing plagioclase collars in the coronitic and transitional metagabbros and by widespread re equilibration of the eclogites giving lower p t estimates at grain boundaries however the difference in calculated pressure conditions between coronite and eclogite samples is consistent with increasing pressure depth from the coronites 11 13 kbar to the eclogites 13 17 kbar the p t conditions recorded by these rocks define a metamorphic field gradient which suggests high heat flow through the lower crust during the grenvillian orogeny

seismic images of eclogites crustal scale extension and moho relief in the eastern grenville province quebec seismic images from a 250 km lithoprobe reflection profile in the interior of the eastern grenville province provide important new constraints on the crustal architecture of this part of the orogen prominent upper crustal reflections can be correlated with exposures of high pressure metamorphic rocks in the manicouagan shear belt providing the first direct evidence for eclogite reflectivity in the grenville province the eclogites are cut by major late grenvillian normal faults that penetrate the deep crust and preserve evidence of extensional collapse of the overthickened orogen north to south crustal thinning indicated by a change in moho reflection time from 16 to 13 s correlates well with regional bouguer gravity trends and is accompanied by a dramatic increase in the reflectivity of the lower crust these features underscore the significance of recently recognized along strike variations in tectonic style within the grenville province and point to the internal complexity that characterizes the root zones of collisional orogens

scour at the head of a vertical wall breakwater abstract this paper presents the results of an experimental investigation on the near bed flow patterns the bed shear stress amplification and scour around the head of a vertical wall breakwater using regular waves the keulegan carpenter number kc based on the diameter of the breakwater head is found to be the major parameter that governs the flow and the equilibrium scour depth basic flow structures are identified as function of kc the scour depth is found to increase with increasing the keulegan carpenter number the necessary extent of the conventional stone protection is studied an empirical formula is worked out for the width of the protection layer as function of kc also the effects of head shape the angle of attack and the presence of a co directional current are investigated the results indicate that the scour depth is increased considerably in the presence of a current likewise the scour depth is increased when the head shape is changed from a round shape to a sharp edged one it is found that the angle of attack is also an influencing factor as regards the scour depth

mechanics of the scouring and sinking of submerged structures in a mobile bed a physical model study abstract wave induced flow velocity and turbulence may cause scouring in the seabed around coastal structures depending on the wave climate and tidal water depth a 3 d physical modelling study was conducted to investigate the possible causes of the sinking of two submerged coastal structures on the santa maria del mar smm beach spain the experimental investigation was conducted by employing a froude similarity law with a geometric scale of 1 20 and the submerged modular structure was subjected to different wave climates and tidal water levels the combinations of the significant wave height and peak period were chosen from in situ real wave conditions that were monitored during the sinking of the prototype structures linking and unlinking conditions for the modules in the structure were investigated in this study the results show that the modules sank to approximately 48 of their height at the end of the tests with storm waves and semi linking conditions of low water depth most of the experimental results were compatible with the prototype monitoring results tests with proper linking among the modules and tests with an appropriate gravel foundation resulted in a sustainable solution because they presented much less or almost no scouring and sinking

contrasting tectonic styles in the northern grenville province implications for the dynamics of orogenic fronts in western labrador tectonic elements of the parautochthonous belt of the northern grenville orogen include a regional mid crustal thin skinned metamorphic fold thrust belt structurally overlain by a thick skinned thrust sheet with a high pressure metamorphic signature in central ontario the parautochthonous belt is composed of a major reverse sense shear zone along which deep crustal rocks have been uplifted and exhumed tectonic models for both areas involve crustal shortening by delamination in the lower crust and tectonically driven exhumation up a crustal scale ramp the fold thrust belt northwest of the ramp in labrador is a result of the development of critical topography in the thrust wedge at the top of the ramp and the accretion of thrust slices to the base of the wedge during its propagation onto the foreland the fold thrust belt is absent in ontario because syntectonic erosion of the thrust wedge prevented the development of critical topography

experimental study of 2d scour and its protection at a rubble mound breakwater abstract this study deals with the 2d scour at the trunk section of a rubble mound breakwater two breakwater models with slopes of 1 1 2 and 1 1 75 are employed for the experimental study of the scour in a wave flume 2d scour at a vertical wall breakwater was also included as a reference case tests were conducted with both regular waves and irregular waves it was found that the scour deposition pattern in front of the rubble mound breakwater emerges in the form of alternating scour and deposition areas lying parallel to the breakwater similar to the case of the vertical wall breakwater the maximum scour depth however was found to be smaller in the present case than that of the vertical wall breakwater case in the case of the irregular waves the scour depth at the breakwater decreases with respect to that experienced in the case of the regular waves countermeasures for toe protection were also investigated for the following cases 1 the protection apron with one layer of stones and 2 that with several layers of stones the mechanism of slumping down of stones of the protection apron was also considered the results of the toe protection study are given in the form of diagrams

chronology of devonian to early carboniferous rifting and igneous activity in southern magdalen basin based on u pb zircon dating fifteen u pb zircon radiometric age determinations have been made on igneous rocks of middle devonian to early carboniferous age from the southern margin of the magdalen basin in cape breton island and northern mainland nova scotia volcanic rocks interbed with early rift basin sedimentary rocks with some palynological biostratigraphy dated intrusive rocks cut these sedimentary units our biostratigraphically constrained ages are in close agreement with the current devonian time scale combined with previously published data the age determinations show that igneous activity occurred in four pulses middle devonian 390 385 ma early late devonian 375 370 ma latest devonian to early tournaisian 365 354 ma and late tournaisian to early visean ca 339 ma middle devonian 385 389 ma volcanic rocks are confined to the guysborough group the fisset brook formation basalt and minor rhyolite in the type area and elsewhere in cape breton island and northern mainland nova scotia is late devonian c

lateral ramps as an aid to the unroofing of deep crustal rocks seismic evidence from the grenville province we suggest that lateral ramps in the basement to orogenic wedges may be important agents in the rapid unroofing of deeply buried continental crust our suggestion is based on a study of the distribution of high pressure metamorphosed continental rocks in the mesoproterozoic grenvillian orogen in eastern quebec these rocks were buried to depths of more than 50 km through crustal thickening during a continental collision and were then rapidly unroofed they are currently exposed in a 100 km 60 km lobate embayment north of the manicouagan reservoir using a combination of surface structural data and seismic reflection data from lithoprobe line 55 we reconstruct the three dimensional form of the high pressure rocks our reconstruct ion methods are based on demonstrable correlations between the attitudes of gneissic layering at the surface and the attitudes of reflectors on the seismic profile they make extensive use of the fact that much of the seismic reflectivity on line 55 comes from outside the vertical plane of the seismic line because of the sinuous nature of the line and its obliquity to tectonic strike the validity of the reconstructions is demonstrated by the generation of a synthetic seismogram from the interpreted geometry that is very similar to the observed seismogram our reconstruction shows that a steep lateral ramp extends to the base of the crust immediately behind the broad lobe of high pressure rocks at the surface the lateral ramp probably provided a favorable pathway for the extrusion of deep seated rocks from the deep crust and their transport onto the foreland

partial melting of high p t metapelites from the tshenukutish terrane grenville province petrography and u pb geochronology

crustal architecture and tectonic assembly of the central gneiss belt southwestern grenville province canada a new interpretation the central gneiss belt southwestern grenville province is characterized by parautochthonous crust in the north and allochthonous lithotectonic domains in the south despite nearly two decades of study the basal decollement to allochthonous domains transported from the southeast known as the allochthon boundary thrust has not been precisely located throughout much of the belt between lake nipissing and georgian bay where its surface trace is known it separates 1 24 ga sudbury metadiabase in the footwall from eclogite remnants and 1 17 1 15 ga coronitic olivine metagabbro confined to its hanging wall on the premise that this relationship can be used to trace the allochthon boundary thrust elsewhere in the central gneiss belt we have sought to extend the known distribution of these mafic rock types making use of field petrographic and geochemical criteria to identify them new occurrences of all three mafic types are identified in a region extending from south of lake nipissing to western quebec

experimental investigation into 3d scour processes around a gravity based oscillating water column wave energy converter abstract experimental investigations measuring both bed elevation changes and near structure flow velocities were undertaken to investigate wave scour processes around a model oscillating water column owc wave energy converter wec for a range of incident wave conditions at approximately 1 20 scale the experiment design was informed by a proposed 200 kw owc wec deployment site at king island australia the measurements provide the first experimental data on scour around an owc wec structure and one of the most comprehensive experimental studies of wave scour around a large rectangular cross section structure high resolution scour erosion and deposition patterns were measured using an above water laser based system for normally incident waves scour holes were observed to develop on all four corners and the size of the scour holes at the four corners increased with the keulegan carpenter kc number an additional scour hole trench also formed along the upstream face of the owc wec due to the flow in out of the owc wec internal chamber changing the incident wave propagation angle by 20 has a significant effect on the observed scour patterns with reduced scour on the front and back corners but significant scour holes remaining on the other two corners it is found that if the model is not sufficiently embedded into the sediment bed scour can undermine a significant area under the structure with quadrant shaped scour holes underneath the back corners extending to approximately 25 of the total base area suggesting a risk of differential settlement in field conditions

scour at the round head of a rubble mound breakwater abstract this study complements the investigation on scour around the head of a breakwater reported in the companion paper where the case of vertical wall breakwater was considered the present study deals with the case of rubble mound breakwater two key mechanisms with regard to the scour processes around the round head of the breakwater are identified one is the steady streaming occurring around the head in plan view this generates a scour hole in front of the breakwater the second one is the plunging breaker which occurs locally at the breakwater head this generates a scour hole at the lee side of the breakwater the keulegan carpenter number based on the base diameter of the breakwater head appears to be the main governing parameter regarding the streaming induced scour while a parameter namely t p gh s h involving the peak wave period tp the significant wave height hs the water depth h and the acceleration due to gravity g appears to be the main governing parameter regarding the breaker induced scour the scour depth increases with increasing values of these parameters the conventional stone protection is investigated in the study an empirical formula is developed for the extent of the protection layer

new tectonic divisions of the grenville province southeast canadian shield on the basis of geological geophysical and geochronological data the grenville province has been divided into three first order longitudinal belts the parautochthonous belt pb allochthonous polycyclic belt apb and allochthonous monocyclic belt amb these are set apart by three first order tectonic boundaries the grenville front gf allochthon boundary thrust abt and monocyclic belt boundary zone mbbz the belts are subdivided into terranes based on internal lithological character the gf separates the archean to proterozoic foreland northwest of the orogen from reworked equivalents to the southeast continuous at the scale of the orogen its main characteristic is that of a crustal scale contraction fault the pb although less clearly identified along the length of the orogen in most places represents upgraded and tectonically reworked rocks of the adjacent foreland the boundary between the pb and the apb to the southeast the abt is most clearly delineated in the eastern half of the province it is the locus of major crustal delamination along which high grade mostly middle proterozoic polycyclic terranes were tectonically transported northwest toward and onto the pb the amb comprises two separate areas underlain by the wakeham supergroup and what is currently known as the grenville supergroup respectively its basal contact the mbbz is a decollement zone of variable kinematic significance between older polycyclic rocks and tectonically overlying monocyclic rocks this first order zonation implies a tectonic polarity to the grenville province superimposed on which are second order features evident from contrasting tectonic styles and radiometric ages these characteristics are consistent with a diachronous or oblique collisional model for the grenville orogen

high pressure high temperature rocks from the base of thick continental crust geology and age constraints from the manicouagan imbricate zone eastern grenville province the grenville province of the canadian shield is composed of crustal material with laurentian affinities involved in continental collision during the grenvillian orogeny between 1 19 and 0 98 ga in the eastern grenville province the manicouagan imbricate zone miz is composed of paleoproterozoic labradorian 1 6 ga and mesoproterozoic pinwarian 1 4 ga crustal segments that were metamorphosed under high pressure high temperature high p t conditions p 1800 mpa and 800 t 900 c and intruded by synmetamorphic gabbroic stocks and dykes and postmetamorphic granite during a 1 0 ga crustal shortening event in the grenvillian orogeny the gabbroic dykes display high p mineral assemblages and a withinplate tholeiite signature attesting to the intrusion of asthenospheric melts during the high p metamorphism the structural configuration of miz is that of a thrust stack lelukuau terrane overlain by an extensional assembly of slices tshenukutish terrane to the north lelukuau terrane overlies archean basement and paleoproterozoic supracrustal rocks of the gagnon terrane along a thrust contact tshenukutish terrane is tectonically overlain to the south by crustal slices composed of pre grenvillian and early grenvillian lithologic units that are correlative with those in miz but which were at midcrustal levels during the grenvillian orogeny low p segment of the eastern grenville province and were intruded by anorthosite and granitoids farther south a likely tectonothermal evolution of miz at 1 0 ga involves crustal shortening by imbrication in a postsubduction phase of continental collision followed by convective removal of the underlying thickened lithospheric mantle and the rise of hot asthenospheric material close to the base of the crust exhumation of miz likely occurred from the basal levels of the crust and was achieved by 1 nw directed thrusting over a crustal scale ramp archean basement of the gagnon terrane with coeval extension at the higher levels of the pile stage 1 extension and 2 a second extension event stage 2 extension coeval with emplacement of postmetamorphic granite at the boundary between miz and the low p segment

geologic transect across the grenville orogen of ontario and new york revised cross sections of the western grenville province incorporate new geologic results and reprocessed seismic reflection data the geology is presented in terms of three tectonic elements 1 pre grenvillian laurentia and its margin with ca 1740 and 1450 ma continental arc plutons and associated supracrustal rocks 2 composite arc belt of allochthonous 1300 1250 ma volcanic arcs and sedimentary rocks and 3 frontenac adirondack belt characterized by supracrustal and granitoid rocks and anorthosites of uncertain affinity that may represent a distinctive part of the composite arc belt or an offshore micro continent rocks of the composite arc and frontenac adirondack belts were amalgamated with each other by ca 1160 ma were then thrust over laurentia during ca 1080 1035 ma and ca 1010 980 ma phases of convergence and were dissected and exhumed by 1040 ma normal faults penetrative deformation was restricted to that part of the pre grenvillian laurentian margin that lies to the southeast of the grenville front and parts of the accreted composite arc and frontenac adirondack belts the laurentian rocks in the grenville province are bounded to the northwest and southeast by southeast dipping ductile thrust and or normal shear zones the composite arc and frontenac adirondack belts to the southeast are bounded by ductile and brittle ductile thrust and or normal faults that separate domains with contrasting cooling histories despite a long pre grenvillian tectonic and plutonic history the present crustal architecture and much of the seismic reflectivity were acquired during 1080 980 ma phases of compression and extension

geochronology of high pressure mafic granulite dykes in sw sweden tracking the p t t path of metamorphism using hf isotopes in zircon and baddeleyite although the u pb zircon chronometer has been widely used for dating metamorphism in moderate to high grade rocks it is generally difficult to link the u pb age of zircon to specific metamorphic reactions in this study the initial hf isotopic composition of secondary zircon is compared with the evolution of hf isotopic composition of the bulk sample back projected from the measured value through time this approach may enhance the interpretation of radiometric ages performed on metamorphic mineral assemblages here u pb sm nd and lu hf geochronology and thermobarometry have been integrated and applied to two metamorphosed diabase dykes in the sveconorwegian orogen sw sweden the dykes are located 5 km east of the nne trending gota alv deformation zone in the idefjorden terrane and trend parallel to this zone the lunden dyke is recrystallized into a coronitic granulite facies assemblage u pb isotopic analyses of baddeleyite in this dyke indicate an emplacement age of 1300 ma thermobarometric techniques applied to garnet and omphacitic clinopyroxene coronas indicate high pressure metamorphism at c 15 kbar and c 740 c growth of polycrystalline zircon at the expense of baddeleyite occurred at 1046 6 ma identical hf isotopic composition of polycrystalline zircon and baddeleyite shows that the baddeleyite to zircon transition took place before hf equilibration among the other metamorphic minerals and hence the c 1046 ma age of polycrystalline zircon sets an upper age limit of metamorphism of this sample the haregarden dyke is recrystallized into a granoblastic transitional upper amphibolite to granulite facies assemblage the estimated p t conditions are c 10 kbar and c 700 c analyses of small 30 m clear and round zircon in this sample yield a concordia u pb age of 1026 4 ma which is indistinguishable from the lu hf and sm nd mineral isochron ages of 1027 9 ma and 1022 34 ma this type of secondary zircon plots at the lower end of the lu hf isochron and indicates simultaneous growth with garnet at c 1026 ma a time when hf isotopic equilibrium among minerals must have been reached

a simplified method to downscale wave dynamics on vertical breakwaters abstract a coastal structure is usually designed with the final objective to guarantee its functionality and stability throughout its life cycle regarding stability the three main failure modes are sliding overturning and failure of the foundations to accomplish the design objectives a design sea state is usually used when calculating the loads and scour around the structure this design sea state corresponds to a certain sea state with specific return period values of a significant wave height however the combination of different simultaneous sea state parameters can produce other critical situations compromising the stability of the structure which then require the calculation of long time series of wave forces corresponding to long term historical wave situations moreover a design force associated to a certain return period can be defined from the time series of the stability parameters the most accurate techniques which can be used to estimate structure stability are based on numerical and physical models but these are very time consuming and the calculation of long time series is therefore unfeasible here we propose a hybrid methodology to transform wave conditions into wave forces acting upon vertical structures and scour around it the methodology consists of a selection of a subset of sea states representative of wave climate at the structure location using a maximum dissimilarity algorithm the wave forces acting upon the structure and scour around it for the wave situations selected are then estimated as is the reconstruction of the calculated parameters corresponding to historical sea states using an interpolation technique based on radial basis function the validation of the results through a direct comparison between reconstructed series and analytically semi empirical formulations calculated ones confirms the ability of the developed methodology to reconstruct time series of stability parameters on vertical breakwaters this methodology allows its application to numerical and physical models

sediment transport patterns in front of reflective structures under wind wave dominated conditions abstract this article presents a field study of the bed response near linear reflective structures under wind wave dominated conditions at the motril harbor spain on the mediterranean coast in 1999 the harbor breakwater was enlarged 600 m by adding vertical caissons before this enlargement took place no significant bed features had been observed in the area however at the end of 2004 high resolution bathymetry showed the existence of 3 4 bars parallel to the structure with lengths between crests of 0 70 m in the cross shore direction and heights of 0 25 cm toe erosion with an amplitude up to 25 cm was also observed along the structure the necessary conditions for the appearance of the bar system are 1 a standing wave pattern in front of the structure 2 local satisfaction of the wave height and wave period threshold limits for sediment mobility using an energy based approach we analyze the time series of sea states with sediment transport capacity after breakwater construction the cumulative distributions of the shear velocities related to wsw sw sea states show that all the bars have a greater probability of being n type features predominant bed load under generalized sediment transport conditions these conclusions were verified by matching nodal lines of standing wsw sw wave patterns with the bar locations the results suggest that the motril bar system of motril is possibly generated by the standing wave patterns induced by several sea states with peak periods of o 10 s and significant sediment transport capacity resulting from wsw sw severe storm events that occurred in motril after breakwater construction this article highlights the need to verify in field conditions the present threshold limits for sediment transport mobility

north west propagation of the grenville orogen grenvillian structure and metamorphism near key harbour georgian bay ontario canada abstract we report structural and metamorphic data from a c 25 km transect across the eastern grenville front tectonic zone gftz to the britt domain at the northern end of georgian bay near key harbour ontario constrasting grenvillian structural and fabric elements characterize the eastern gftz northern britt domain and a narrow transition zone between them moderately to steeply dipping foliations with strong down dip lineations in all three divisions appear to be associated with nw directed thrusting in the transition zone and northern britt domain early s l fabrics with steep lineations are overprinted by younger structures s l with shallow se sse plunging lineations in which sparse dominantly but not exclusively normal sense kinematic indicators are recognized pressure and temperature estimates from grenvillian metamorphic assemblages in metadi abase indicate that conditions of p 12 kbar and t c 800 c were achieved before or during the thrust related deformation with p t t paths that indicate near isothermal decompression to p c 4 kbar and t c 700 c correlation of fabric elements with points on the p t t paths suggests that exhumation occurred during two stages the first associated with thrusting 1035 ma and the second with extension and thrusting pre 1003 ma the gftz contains steeply to moderately dipping thrust related fabrics and lacks shallow extensional structures the latest episode of thrusting in the gftz is inferred to have taken place at 990 980 ma the data are interpreted in terms of a tectonic model involving two stages of propagation of the grenville orogen towards its foreland 1035 ma and 980 ma with an intervening period of extension although the tectonic regime probably remained compressional on the scale of the orogen

modelling seasonal ratcheting and progressive failure in clay slopes a validation seasonal wetting and drying stress cycles can lead to long term deterioration of high plasticity clay slopes through the accumulation of outward and downward deformations leading to plastic strain

new insights into the appalachian orogen from geology and geochronology along the cape ray fault zone southwest newfoundland reverse oblique overthrusting of high grade port aux basques gneiss over the lower grade supracrustal windsor point group along the cape ray fault zone occurred during late silurian to early devonian time and is attributed to major oblique collision between gondwanan and laurentian continental blocks new u pb zircon 40 ar 39 ar and k ar data limit the timing of this orogenic event the megacrystic granitic phase of the cape ray igneous complex and the cape ray tonalite have been dated at 488 3 ma and 469 2 ma respectively a black rhyolite from the windsor point group yielded an ordovician age 453 5 4 ma a pretectonic gabbro sill within the windsor point group dated at 424 4 3 ma is cut by the windowglass hill granite dated at 424 2 ma synkinematic hornblende and biotite from the grand bay complex mylonites of the port aux basques gneiss have 40 ar 39 ar ages of 407 4 ma and 403 4 ma respectively which is indicative of a late silurian early devonian age for the amphibolite grade deformation these ages are compatible with a previously determined 415 ma monazite age interpreted as the time of peak metamorphism in the port aux basques gneiss and suggests rapid exhumation the east west flexure of the cape ray fault zone represents a tear fault accommodating differential shortening between the cape ray fault zone and the correlative fault system in central newfoundland mid devonian granites 386 3 384 2 ma intervene between the thrusting events and a younger sinistral transcurrent movement this deformation and magmatic history can be correlated throughout the northern appalachians along other major fault boundaries

tectono thermal evolution of deep crust in a mesoproterozoic continental collision setting the manicouagan example high pressure metamorphic rocks in continental collision belts provide important information on the orogenic evolution of deep crust in the grenville province a prime example is the manicouagan imbricate zone miz a mesoproterozoic crustal section that was metamorphosed up to 1800 mpa and 850 950 c at 1050 ma high tempera tures and the presence of synmetamorphic within plate tholeiitic gabbro intrusion in the miz attest to thermal perturba tion during burial and emplacement of mantle derived melts consistent with thinning of lithospheric mantle subsequently the miz was extruded by a combination of northwest directed thrusting over a crustal scale ramp and ex tension at higher crustal levels in the middle miz extension was coeval with thrusting but perpendicular to the thrust direction and was apparently controlled by ductility contrasts between slices in contrast the highest levels show evi dence of southeast directed extension i e of opposite sense to the thrust direction that postdated thrusting within the miz this episode was followed by renewed northwest directed thrusting of medium pressure mesoproterozoic units over the miz and then by final southeast directed extension overall configuration of the miz was achieved between 1040 990 ma and is consistent with outward propagation of the orogen alternating periods of thrusting and exten sion displacement are a likely result of adjustments permitting maintenance of dynamic equilibrium within the advanc ing stack the tectonothermal characteristics of the miz allow comparison between the grenville province and younger thermally perturbed orogens i e variscan belt and may be the final product of a tibetan plateau style evo lution

himalayan metamorphic sequence as an orogenic channel insight from bhutan the bhutan himalayas differ from the rest of the himalayas in two major ways i low grade sedimentary rocks lie above the greater himalayan sequence as klippen i e erosional remains of the south tibetan detachment and ii an out of sequence thrust the kakhtang thrust lies structurally above the klippen and it doubles the exposed thickness of the greater himalayan sequence our field observations and geochronological data constrain the main kinematic events in the bhutan himalayas crystallisation ages of leucogranite dykes deformed by the main central thrust and the south tibetan detachment indicate that these two structures operated together between 16 and 22 ma the out of sequence kakhtang thrust was active at 10 14 ma and was concurrent with reactivation of the south tibetan detachment restoration of the bhutan himalayas prior to the out of sequence thrusting shows that the greater himalayan sequence was the core of a long low viscosity crustal channel extending under the tibetan plateau we propose that the gravity driven southward extrusion of the channel material from underneath the tibetan plateau caused the inverted metamorphic sequence in the lesser himalayan sequence and in the greater himalayan sequence this process also led to occurrences of present day surface rocks that were derived from variable distances down dip but from similar crustal depths such an exhumation pattern can explain the similar peak pressures for the greater himalayan sequence along the length of the himalayas

erratum the high pressure belt in the grenville province architecture timing and exhumation we propose that the grenvillian allochthonous terranes may be grouped into high pressure hp and low pressure lp belts and examine the hp belt in detail in the western and central grenville province the hp belt is developed in paleo and mesoproterozoic rocks of the pre grenvillian laurentian margin and characterized by grenvillian eclogite and co facial hp granulite in mafic rocks pressure temperature p t estimates for eclogite facies conditions in well preserved assemblages are about 1800 mpa and 850 c in the central grenville province hp rocks formed at 1060 1040 ma and underwent a single stage of unroofing with transport into the upper crust by 1020 ma whereas farther west they underwent two stages of unroofing separated by penetrative mid crustal recrystallization before transport to the upper crust at 1020 ma unroofing processes were comparable in the two areas involving both thrusting and extensional faulting in an orogen propagating into its foreland by understacking in detail thrusting episodes preceded extension in the western grenville province whereas in the central grenville province they were coeval resulting in unroofing by tectonic extrusion in the central grenville province the footwall ramp is well preserved but any former ramp in the western grenville province was obliterated by later lower crustal extensional flow continuation of the hp belt into the eastern grenville province is not established but likely on geological grounds however the pattern of deep crustal seismic reflection in the lithoprobe eastern canadian shield onshore offshore transect ecsoot line contrasts with that father west suggesting that if present the hp rocks were exhumed by a different mechanism

himalayan tectonics explained by extrusion of a low viscosity crustal channel coupled to focused surface denudation recent interpretations of himalayan tibetan tectonics have proposed that channel flow in the middle to lower crust can explain outward growth of the tibetan plateau1 2 3 and that ductile extrusion of high grade metamorphic rocks between coeval normal and thrust sense shear zones can explain exhumation of the greater himalayan sequence4 5 6 7 here we use coupled thermal mechanical numerical models to show that these two processes channel flow and ductile extrusion may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low viscosity material our models provide an internally self consistent explanation for many observed features of the himalayan tibetan system8 9 10

local scour at roundhead and along the trunk of low crested structures abstract this paper summarizes the results of an experimental study on scour around submerged breakwaters the objective of the study is to make a systematic study of scour around low crested structures submerged breakwaters both the trunk scour and the roundhead scour have been investigated the breakwater models have a side slope of 1 1 5 to substantiate scour measurements velocity measurements also were made the latter data were used to obtain steady streaming in front of the breakwater regarding the trunk scour study the experiments indicated that substantial scour may occur at the toe of the structure this is irrespective of whether the breakwater is impermeable or porous the scour data although very limited indicated that the scour depth is in the same order of magnitude as in the case of emerged breakwaters the trunk experiment further showed that scour deposition bathymetry does not exhibit the pattern experienced in the case of emerged breakwaters where the scour and deposition areas are correlated with the nodal and antinodal points of the standing wave in front of the structure furthermore it was found that scour occurs not only at the offshore side of the breakwater but also at the onshore side as for the roundhead scour study it was found that severe scour can be experienced at the roundhead the scour can occur both at the offshore side of the roundhead and at the back the one at the offshore side is caused by the combined effect of severe waves and the steady streaming and that at the back is caused by wave breaking wave overtopping it was found that the streaming induced scour is governed by the free board to wave height ratio f h and the keulegan carpenter number kc while the plunging breaker induced scour is governed by the free board to water depth ratio f h and the plunger parameter t w g h h tw being the wave period the maximum scour depth at the toe of the structure and the plan view extent of the scour hole are given in terms of the governing parameters the results from the present laboratory tests for the roundhead scour are compared with prototype observations undertaken in the present study recommendations are made for toe protection for both the trunk scour and the roundhead scour

interaction of metamorphism deformation and exhumation in large convergent orogens coupled thermal mechanical models are used to investigate interactions between metamorphism deformation and exhumation in large convergent orogens and the implications of coupling and feedback between these processes for observed structural and metamorphic styles the models involve subduction of suborogenic mantle lithosphere large amounts of convergence 450 km at 1 cm yr 1 and a slope dependent erosion rate the model crust is layered with respect to thermal and rheological properties the upper crust 0 20 km follows a wet quartzite flow law with heat production of 2 0 w m 3 and the lower crust 20 35 km follows a modified dry diabase flow law with heat production of 0 75 w m 3 after 45 myr the model orogens develop crustal thicknesses of the order of 60 km with lower crustal temperatures in excess of 700 c in some models an additional increment of weakening is introduced so that the effective viscosity decreases to 1019 pa s at 700 c in the upper crust and 900 c in the lower crust in these models a narrow zone of outward channel flow develops at the base of the weak upper crustal layer where t 600 c the channel flow zone is characterised by a reversal in velocity direction on the pro side of the system and is driven by a depth dependent pressure gradient that is facilitated by the development of a temperature dependent low viscosity horizon in the mid crust different exhumation styles produce contrasting effects on models with channel flow zones post convergent crustal extension leads to thinning in the orogenic core and a corresponding zone of shortening and thrust related exhumation on the flanks velocities in the pro side channel flow zone are enhanced but the channel itself is not exhumed in contrast exhumation resulting from erosion that is focused on the pro side flank of the plateau leads to ductile extrusion of the channel flow zone the exhumed channel displays apparent normal sense offset at its upper boundary reverse sense offset at its lower boundary and an inverted metamorphic sequence across the zone the different styles of exhumation produce contrasting peak grade profiles across the model surfaces however p t t paths in both cases are loops where pmax precedes tmax typical of regional metamorphism individual paths are not diagnostic of either the thickening or the exhumation mechanism possible natural examples of the channel flow zones produced in these models include the main central thrust zone of the himalayas and the muskoka domain of the western grenville orogen

metamorphic textures and p t evolution of high p granulites from the lelukuau terrane ne grenville province high pressure hp granulites and eclogitized metagabbro are exposed along an orogen parallel high p belt that was developed at c 1050 1020 ma in the ne grenville province among these rocks mafic granulites derived from a labradorian anorthosite suite of the lelukuau terrane contain garnet al na diopside and depending on bulk composition plagioclase and kyanite moreover the distribution of phases is influenced by the original igneous texture for instance in high xmgo leucocratic varieties garnet porphyroblasts nucleated together with kyanite in an rich cores of plagioclase domains whereas in low xmgo rocks garnet occurs together with clinopyroxene within formerly igneous ferromagnesian domains and kyanite is missing in contrast garnet pseudomorphs after igneous plagioclase in melanocratic varieties display evidence of earlier corona development metamorphic textures are consistent with a two stage evolution a development of garnet and al na diopside cpx1 under high p metamorphic conditions concomitant with elimination of plagioclase in the mesocratic to melanocratic varieties and b partial loss of al na from cpx1 resulting in production of new andesitic plagioclase and growth of new clinopyroxene cpx2 after garnet and quartz in leucocratic to mesocratic rocks consistent with decompression widespread equilibrium textures between garnet pl2 cpx2 and or reset cpx1 are consistent with development at the thermal peak estimated p t conditions for the presumed thermal peak fall in the range 1500 1800 mpa and 800 900 c and are comparable to those recorded by eclogitized gabbros from other parts of the high p belt of the ne grenville province low jadeite content of clinopyroxene from the hp granulites is attributed to the low bulk na2o na2o cao of these rocks relative to common basaltic compositions scarcity of apparent retrograde textural overprint in both the hp granulites and the eclogites suggests fast subsequent cooling consistent with extrusion of the high p belt towards the foreland shortly after the metamorphic peak

precise u pb ages for grenvillian and pre grenvillian thrusting of proterozoic and archean metamorphic assemblages in the grenville front tectonic zone canada while the position of the grenville front is placed at a structural feature associated with the onset of high grade rocks when approached from the north the time of first metamorphism in these rocks is in general pre grenvillian and highly variable at killarney amphibolite to granulite grade rocks were metamorphosed lineated and foliated to their present front parallel configuration mainly by 1453 6 ma north of north bay amphibolite grade migmatites have been subjected to a pre 2650 ma metamorphism granulite grade gneisses south of the grenville front near val d or record a 2640 ma metamorphic event south of chibougamau mafic enclaves in tonalite south of the front were converted to migmatitic amphibolite at about 2680 to 2690 ma in central labrador a 1650 ma foliated granite is present south of the grenville front and at least some of the banding is this old at the atlantic coast granulite facies metamorphism in front parallel gneisses predates a 1790 1662 ma deformation in contrast each of these areas shares a near common age of second metamorphism that is variable in degree and accompanies nw directed thrusting or crustal loading near killarney on georgian bay titanite records an episode of 977 2 ma partial resetting the degree of which increases with distance into the grenville province here grenvillian deformation where present is manifest as feldspar porphyroclastic fabric with strong se plunging lineations near north bay archean pegmatites in the grenville front zone were similarly deformed at 988 10 ma and strongly rodded ductile amphibolite underwent late melting to produce postlineation tonalite in which new zircon tips grew at 987 2 ma a 991 4 ma cooling age for titanite in this melt is analytically identical to the zircon growth age hence rapid cooling occurred south of chibougamau new zircons grew in high pressure coronite in response to tectonic loading at 995 6 ma and in central labrador melt pods that developed in 1650 granites in response to thrusting record a zircon new growth age of 995 2 ma titanite in the granitic host rock has an analytically identical age of 992 4 ma again indicating rapid cooling this second event is recorded by 28 titanite and zircon analyses for samples up to 225 km apart that record a 1651 5 ma to 988 5 ma two age mixing line grenville resetting at about 1037 19 ma in the grenville front zone on the labrador coast is indicated but major thrusting is pre 1662 ma u pb isotopic results indicate that the grenville front zone is characterized along its length by partially reset u pb systems high pressure assemblages local melting and rapid cooling crustal loading and shearing with lead loss related to mechanically induced recrystallization and local heat that was rapidly terminated by rebound and cooling are required