precise p and s wave velocity structures in the kitakami massif northern honshu japan from a seismic refraction experiment the kitakami massif which is located in the eastern part of northern honshu japan is composed of two geological units the northern kitakami terrane is characterized as a jurassic accretionary complex while the southern kitakami terrane consists of pre silurian basement and silurian lower cretaceous marine sediments the boundary region of these two units called the hayachine tectonic belt htb is composed of mafic to ultramafic rocks the kitakami massif experienced intense granitic intrusions in the cretaceous we present a detailed crustal structure model for the eastern part of the massif derived from an extensive seismic refraction experiment conducted on a 194 km n s line the uppermost crust is covered with a very thin 0 5 1 km surface layer with a velocity of 3 1 5 4 km s the velocity structure below this layer shows remarkable lateral variation in the northern kitakami terrane the p wave velocity and vp vs at the top of the basement are 5 85 5 95 km s and 1 68 1 70 respectively the seismic attenuation in this region is high qp 150 200 and qs 70 100 in contrast the uppermost crust in the southern kitakami terrane is characterized by a high p wave velocity 6 05 6 15 km s and vp vs 1 74 1 77 the qp and qs also show high values of 300 400 and 150 200 respectively such a structural difference persists to 14 to 16 km depth at which the p wave velocity increases to 6 45 km s the low velocity and high attenuation in the northern kitakami terrane represent a highly deformed structure of the accretionary complex the high p wave velocity and vp vs in the southern kitakami terrane indicate the relatively mafic crustal composition which may result from the fragment of the oceanic crust incorporated by the accretion process or the uplifting in the latest jurassic early cretaceous a midcrustal interface determined from wide angle reflections shows an abrupt southward depth decrease from 25 to 20 km under the htb the p wave velocity and vp vs between 14 and 16 km depth and the midcrustal interface are 6 45 6 55 km s and 1 74 1 78 respectively the moho depth under the northern kitakami terrane decreases southward from 34 to 32 km in the southern kitakami terrane the moho dips slightly southward the p wave velocity and the vp vs ratio in the lower crust are 6 9 7 0 km s and 1 75 1 76 respectively the p wave velocity in the uppermost mantle is not well resolved but is probably less than 7 7 km s the s wave velocity derived from relatively clear sn is 4 35 4 40 km s our results show that the htb is a prominent structural boundary extending to the moho the crust of kitakami massif was not homogenized by the cretaceous granitic intrusions and the original structural difference remains in the upper crust

crustal structure of the western new england appalachians and the adirondack mountains we present an interpretation of the crustal velocity structure of the new england appalachians and the adirondack mountains based on a seismic refraction wide angle reflection experiment in eastern north america extending from the adirondacks in new york state through the northern appalachians in vermont and new hampshire to central maine modeling of the eastern portion of the profile within the new england appalachians shows a subhorizontal layered crust with upper crustal velocities ranging from 5 5 to 6 2 km s a midcrustal velocity of 6 4 km s and a lower crustal velocity of approximately 6 8 km s crustal thickness increases from 36 km beneath maine to 40 km in vermont little evidence is seen for structures at depth directly related to the white mountains or the green mountains a major lateral velocity change in the upper and mid crust occurs between the appalachians and the adirondacks this boundary projecting to the surface beneath the champlain valley dips to the east beneath the green mountains and extends to a depth of 25 km below the eastern edge of the connecticut valley synclinorium in vermont the tahawus complex a series of strong horizontal reflections at 18 24 km depth beneath the adirondack highlands is seen to dip eastward beneath vermont upper crustal rocks in the adirondack mountains have poisson s ratios of 0 28 0 01 that can be correlated with the marcy anorthosite pois son s ratios of 0 24 0 01 calculated for rocks of the connecticut valley synclinorium indicate a siliceous upper crust in vermont the lower crust is considered to be best represented by intermediate to mafic granulites a high poisson s ratio 0 26 0 27 tends to support a mafic lower crust in the new england appalachians this seismic refraction wide angle reflection experiment provides further evidence for the obduction of the allochthonous western appalachian units onto grenvillian crust above a zone of detachment that penetrates at least to midcrustal depths and was the locus of successive paleozoic thrusting

geophysical studies of the structure of the appalachian orogen in the atlantic borderlands of canada results of 6000 km of crustal seismic profiling are presented with gravity and aeromagnetic maps for the appalachian orogen in eastern canada wide angle seismic surveys show that the central mobile belt of the orogen has a thinner crust than its margins high velocity lower crust attributed to underplating is found below the former laurentian continental margin in newfoundland and below the magdalen basin potential field data are used to trace the surface zones of the orogen from the northeast newfoundland shelf to cape breton but extrapolation to new brunswick and quebec is unclear because of late paleozoic basin development the central mobile belt of the orogen is only a few tens of kilometres wide in southwest newfoundland and cape breton but broadens substantially to around 200 km elsewhere reflection images show a strong deep crustal fabric that runs along the orogen with a margin that crosses into the avalon zone in southern newfoundland but coincides with the avalon gander zone boundary el

wave attenuation in coastal mangroves in the red river delta vietnam abstract wave attenuation was studied in a coastal mangrove system in the red river delta vietnam on the coast north of do son from sea towards land the study area consisted of a bare mudflat covered by a sandy layer with embryonic cheniers abruptly changing into a muddy tidal flat overgrown with mangroves three instrumented tripods a c placed in a cross shore profile were used to measure current velocity and water level at the open tidal flat at the beginning of the mangrove vegetation and in the mangrove vegetation respectively measurements were conducted in the wet season in july and august 2000 the elevation of the area was surveyed using a levelling instrument over the bare sandy surface of the mudflat the incoming waves are reduced in height and energy density due to bottom friction this reduction decreases with increasing water depth in the mangrove vegetation the bottom friction exerted by the clay particles is very low however the dense network of trunks branches and above ground roots of the mangrove vegetation causes a much higher drag force for the mangrove vegetation which mainly consists of kandelia candel the drag force can be approached by the function c d 0 6e 0 15 a with a being the projected cross sectional area of the under water obstacles at a certain water depth for the same muddy surface without mangroves the function would be c d 0 6

magnetic fabric implications for the relationships between deformation mode and grain growth in slates from the borrowdale volcanic group in the english lake district abstract in the less chlorite rich slates from the borrowdale volcanic group chlorite magnetic fabric almost corresponds to fabric resulting from deformation following the march fernandez model but chlorite grain rotation could be related to the first stages of the tectonic deformation in the other slates the chlorite grains probably impinging after these stages upon one another and a simple grain rotation mechanism being therefore no longer possible

crust and upper mantle velocity structure in the appalachian orogenic belt implications for tectonic evolution the crust and upper mantle structure of the northeastern united states neus was studied by combining teleseismic and regional body wave observations with surface wave dispersion measurements the velocity models suggest that structures as much as 200 km deep and even deeper can be correlated with surficial geologic and tectonic features and that the grenville and appalachian orogenic belts show marked differences in crustal structure this has the important implication that major orogenic belts have effects that reach well into the lithosphere and are stable for extended periods of time perhaps as long as 1 b y regional travel times recorded across the neus seismic network indicate that the northern appalachians are characterized by a well defined two layer crust with a relatively high velocity lower layer the crust of the grenville province in new york state is slightly thinner than that of the new england appalachians and it is vertically homogeneous with nearly constant p and s velocities lateral variations in structure were studied using time term analysis and teleseismic p wave residuals the suture between the grenville and appalachian provinces in the northeastern united states probably occurs along a north northeast trending belt extending from northwestern vermont to southwestern connecticut high crustal velocities and or crustal thinning a linear gravity high a serpentinite belt precambrian uplifts and the taconic thrusts are found along much of this belt comparison of seismic velocities with resistivity measurements suggests that the lower crust of the grenville province may be composed of rocks with hydrous mineral phases resulting in lowered velocities and a higher poisson s ratio alternatively the rocks of the lower crust beneath the grenville province may be similar to those found on the surface while higher velocity mafic mineralogies are prevalent in the lower crust of the appalachians this is consistent with the hypothesis that the grenville crust underwent substantial reactivation thickened and became vertically uniform during the grenville orogeny in contrast the rocks of the appalachian belt probably were associated with a cycle of oceanic opening and closure which suggests an ensimatic origin of the lower crust in this region recent cocorp results indicate that the orogenic belt of the southern appalachians is allochthonous and is underlain by a basal decollement that extends eastward to the coastal plain however contrasts in structural style and tectonic evolution between the northern and southern appalachians suggest that it may not be possible to extrapolate the cocorp results to the northern appalachians north of about 41 latitude and that the suture between the grenville province and the appalachian orogenic belt in new england is located in the vicinity of or just east of the serpentinite belt

mt and reflection an essential combination summary at many localities in the world there have been coincident comprehensive electromagnetic em studies and seismic reflection profiles conducted unfortunately over many more regions the seismic reflection images are interpreted without the constraints afforded by electrical conductivity information this paper is an attempt to convince the reader that a collocated magnetotelluric mt study should in almost every case be made wherever a seismic reflection survey is undertaken examples are shown from six studies in which the em results aided the geological tectonic interpretations of the seismic sections also difficulties with the mt technique are discussed and the interpretations of conducting zones within the lower crust are examined finally a generalised model is proposed for the continental crust that may account for both the reflectivity and conductivity of the zone at the top of the lower crust

geomagnetic induction soundings over the michigan basin abstract geomagnetic variation sounding and magnetotelluric results from six sites on an east west long period profile across the michigan basin are presented a strongly conductive zone on the western flank of the presumed underlying keweenawan rift system in the precambrian basement is shown to exist near cadillac michigan this zone is perhaps similar in character to the flambeau anomaly exposed at the surface in wisconsin also on the flank of the keweenawan rift whose conductivity resides in iron formations and in massive and disseminated graphite and sulphides no clear expression of the michigan basin itself or of the presumed keweenawan rift in the basement is seen in the results the limited magnetotelluric sounding results correspond to a surface conducting layer over a resistive deeper crust over a rise in conductivity at mantle depths they show several hundred seimens of crustal conductance in excess of that provided by the phanerozoic sediments of the basin but do not determine whether the excess crustal conductivity is associated with the underlying keweenawan clastics and volcanics or whether some of that conductivity is in a deeper crustal layer like that found under the adirondack dome by connerney et al

crustal structure of the adirondacks determined from broadband teleseismic waveform modeling broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of the department of energy s regional seismic test network station rsny are analyzed to examine the crustal structure beneath the adirondack highlands of upstate new york radial receiver functions are inverted in the time domain to determine the vertical shear velocity structure at four distinct back azimuths lateral changes in structure are identified by examining azimuthal variations in the vertical structure southeast of rsny our model consists of a thick crust including a broad crust mantle transition the most prominent structure is a high velocity zone shear velocity 4 0 km s between 18 and 26 km depth which overlies a lower crust of low average shear velocity 3 7 km s the extent of the high velocity zone correlates in depth with a highly reflective zone in consortium for continental reflection profiling profiles se of rsny while the deep low velocity zone may be correlated with a broad electrical conductivity anomaly in the adirondacks this general structure is also seen sw of rsny but is more difficult to document at nw and ne azimuths

shear wave structure in the grenville province beneath the lower great lakes region from rayleigh wave tomography 1 we have constructed a high resolution 3 d shear wave velocity model of the upper mantle beneath the grenville province in the lower great lakes region a two plane wave tomography method was applied to fundamental mode rayleigh wave data recorded at 35 broadband seismic stations rayleigh wave phase velocities were obtained at 15 periods from 20 s to 143 s and then inverted for shear wave velocity variation a high velocity lid to 150 km depth is imaged beneath most of the studied grenville province one low velocity anomaly of 4 appears at a failed rift in the northeast above 100 km depth coinciding with the great meteor hot spot track and the high seismicity band which can be interpreted as high temperature and high iron and or volatile content related to the hot spot activity low velocity anomaly of 2 at the depths of 100 200 km are found beneath the east of lake ontario and lake huron where the lithosphere is relatively thin these anomalies follow the nw se trend of the slow indentation imaged on the continental scale models we conclude that the location of low velocity anomalies is not only related to the hot spot track but also controlled by the pre existing lithosphere morphology and strength a high velocity column appears between southern lake ontario and the appalachian front centered at 100 km depth it is likely caused by high mg content at the formation of the lithosphere or the presence of ecologite or garnet phases generated during the opening and closure of the iapetus ocean

a tale of two sutures cocorp s deep seismic surveys of the grenville province in the eastern u s midcontinent a pair of oppositely dipping crustal scale shear zones imaged within grenville basement beneath the paleozoic cover of ohio can be correlated via geopotential lineaments with similarly oriented geologic and seismically imaged structures hundreds of kilometres to the northeast and southwest suggesting a relatively simple structural framework for the eastern midcontinent region an east dipping zone extending from lake huron through western ohio and possibly farther southwest marks the western edge of the grenville province perhaps of greater consequence to an understanding of grenville tectonics is the discovery of a west dipping zone underlying the appalachian basin from northern alabama to new york within the grenville province correlation of this feature with the seismogenic clarendon linden fault in western new york and a boundary between terranes containing magmatic arc rocks exposed in canada suggests that it could mark the site of an intra grenville province suture zone implications of this interpretation are that the precambrian foundation of the eastern u s midcontinent comprises a relatively simple assemblage of laterally extensive terranes or belts of coeval terranes accreted by familiar plate tectonic processes and that deep seismic profiling is an effective tool for mapping the three dimensional distribution of these terranes

regional wave propagation in new england and new york we validate and improve 1d velocity models of the two main crustal provinces in the northeastern united states neus using seismograms from the 20 april 2002 m 5 au sable forks earthquake which is the largest earthquake in the region to be recorded by multiple recently deployed good quality regional broad band stations to predict and mitigate the effects of future earthquakes in the north eastern united states more information is needed regarding both the local earthquake sources and how seismic waves travel through the region we investigate the source and regional wave propagation for the au sable forks earthquake the earthquake epicenter is located near the boundary of two distinct geological provinces the appalachian new england and grenville new york we use a forward modeling approach to study the waveforms recorded at 16 stations located within 400 km of the epicenter we generate synthetic seismograms using the frequency wavenumber method testing several published models for the two provinces several models per form well at low frequencies 0 1 hz we refine these models and generate two alternative 1d crustal models for intermediate frequencies 1 hz of engineering interest our new grenville model performs better than previously published models for all six source station paths modeled in that province according to goodness of fit statistics variance reduction and correlation coefficient our alternative appalachian model improves the fit of synthetics to data for five of the ten paths modeled in that province from the results we identify two specific sources of wave field complex ities that should be investigated in future studies of earthquake ground motions in neus 3 azimuthal anisotropy in the appalachian province and complex wave paths along the boundary between the two provinces

deep seismic reflection profiling and the growth of the continental crust abstract deep seismic reflection profiling provides evidence for the style and magnitude of phanerozoic crustal growth by both lateral and vertical accretion profiles across convergent zones have been interpreted as showing tectonic underplating of the continental crust by fragmented oceanic lithosphere profiling across extensional zones provides evidence for magmatic underplating of the crust in addition to studies over active areas deep reflection profiling over large areas of western europe north america and australia shows that the lower crust is strongly reflective and seismically distinct from the upper crust and upper mantle the layering is detected beneath many different terranes of varying crustal type and basement age from archaean to cenozoic and is often apparently younger than the tectonic or metamorphic age of the exposed upper crust thus continental growth curves estimated from upper crustal measurements alone may underestimate phanerozoic crustal additions and mean crustal ages similarly estimated may be too high

origin of deep crystal reflections seismic profiling across high grade metamorphic terranes in canada abstract in an attempt to better understand the origin of deep crustal reflections lithoprobe has sponsored or co sponsored seismic reflection surveys across tracts of high grade metamorphic rock in the archean superior craton the proterozoic grenville orogen and the phanerozoic cordilleran orogen common to these three diverse terranes are near surface zones of prominent seismic reflectivity that are typically associated with velocity discontinuities at highly strained contacts between gneissic rocks of varying lithology at some locations the reflective layering resulted from transposition and rearrangement of previously layered rocks stratified assemblages sills etc whereas in other regions it was generated by extreme attenuation stretching and ductile flow of weakly layered or irregularly organized rocks it seems likely that compositionally layered gneissic rock is a common source of reflections in the deep crust with reflections originating at lithological boundaries and zones of mylonite

eclogite facies shear zones deep crustal reflectors strongly foliated eclogite facies rocks in 30 150 m thick shear zones of caledonian age occur within a grenvillian garnet granulite facies gabbro anorthosite terrain in the bergen arcs of norway the predominant eclogite facies mineral assemblages in the shear zones are omphacite garnet zoisite kyanite in gabbroic anorthosite and omphacite garnet in gabbro eclogite facies rocks in shear zones are generally fine grained alternating omphacite garnet and kyanite clinozoisite rich layers define gneissic layering a strong shape preferred orientation of omphacite kyanite and white mica phengitic muscovite and or paragonite define the foliation the anorthositic eclogites show omphacite b axis maxima approximately normal to the foliation and c axis girdles within the foliation plane p wave velocities v determined at confining pressures to 600 mpa for samples from eciogite facies shear zones range from 8 3 to 8 5 km s l and anisotropy ranges from 1 to 7 the few samples with more pronounced anisotropy tend to be approximately transversely isotropic with minimum velocities for propagation directions normal to foliation and maximum velocities for propagation directions parallel to foliation the fast propagation direction lies within the c axis girdles parallel to foliation and the slow propagation direction is parallel to the b axis concentration normal to foliation in samples for which omphacite crystallographic preferred orientation was determined v for the granulite facies protoliths average about 7 5 km s high calculated reflection coefficients for these shear zones 0 04 0 14 indicate that they are excellent candidates for deep crustal reflectors in portions of crust that experienced high pressure conditions but escaped thermal reactivation

precise zircon geochronology in the adirondack lowlands and implications for revising plate tectonic models of the central metasedimentary belt and adirondack mountains grenville province ontario and new york new high precision single grain dating of leucogranites from the adirondack lowlands dated previously by multigrain zircon methods at ca 1416 ma wellesley island and ca 1285 1230 ma hyde sch

applications of seismic pattern recognition and gravity inversion techniques to obtain enhanced subsurface images of the earth s crust under the central metasedimentary belt grenville province ontario summary project lithoprobe s abitibi grenville transect seismic reflection lines 32 and 33 traverse the exposed central metasedimentary belt cmb located in the grenville province of the precambrian shield of canada in southern ontario these seismic lines image a zone with a protracted deformational history spanning more than 300 myr detailed examination of the commercially processed stacked sections reveals a number of significant deficiencies in some important areas the image quality in these zones of reduced coherency needs to be enhanced to examine specific features and their relation to the surface geology examination of near vertical seismic data from lines 32 and 33 revealed that the signal to noise ratio was not improved by stacking due to misalignment of signals even after static normal moveout corrections and residual static corrections the presumed reason is that reflected seismic energy following long ray paths in heterogeneous media suffers from relative advances and delays in its propagation and hence arrives at slightly different times at the receivers tending to be poorly aligned relative to its theoretical traveltime curves a pattern recognition pr method for signal enhancement followed by energy stacking in moving time windows was used in this study to improve the images in spite of misalignments reprocessing has refined the geometry of the reflection profiles the objective of this paper is to use enhanced images of the seismic reflection data obtained by using a pr approach together with gravity data using 2 5 d forward and 3 d inversion routines to give an improved model of subsurface structure in the vicinity of lines 32 and 33 line 32 is dominated by southeast dipping reflectors soling into the lower crust the listric geometry of the strong reflection packages of the cmb boundary thrust zone is interpreted to represent a crustal scale ramp flat geometry that accommodated northwest directed tectonic transport of the cmb this interpretation is also supported by the gravity data

geochemical evidence for a revised precambrian sequence in the northwest adirondacks new york middle proterozoic metasedimentary and metavolcanic rocks in the northwest adirondacks are assigned into four lithostratigraphic units basal hyde school gneiss that herein is given formational status lower marble popple hill gneiss formation and upper marble a variety of stratigraphic columns have been proposed for this complexly deformed terrane the most recent being a column by wiener and others 1984 their basal formation the alexandria bay gneiss is defined from rocks that include the rockport granite gneiss near rockport ontario and alexandria bay new york as well as leucogneisses in 14 structural domes throughout the northwest adirondacks we believe that these rocks have a diverse origin one being intrusive the other volcanic ash their uppermost formation the pleasant lake gneiss includes granitoid gneisses near rossie village and pleasant lake that they suggest are illitic arkoses but we give field geochemical and geochronological evidence for an intrusive origin the gneisses near rossie village have a whole rock rb sr age of 1 160 42 m y ir 0 7036 0 0004 and similar gneisses near antwerp village are 1 197 53 m y ir 0 7034 0 0005 these ages are younger than the zircon u pb ages of 1 280 1 250 m y generally obtained for metasedimentary and metavolcanic rocks in the central metasedimentary belt of ontario we urge abandonment of the five formations and two groups proposed by wiener and others 1984 on the basis of an intrusive origin for the gneisses near rockport and rossie villages and on stratigraphic correlations of recent studies the stratigraphy of four formations proposed herein with a generalized geologic map of the northwest adirondacks may lead to correlation with carbonate sequences in the central metasedimentary belt and with rocks of the adirondack highlands to the east

crustal evolution along a seismic section across the grenville province western quebec results of deep seismic reflection survey along a 375 km long transect of the grenville province in western quebec are combined with a review of geological observations and published isotopic ages the seismic profile offers a remarkably clear image of the crust mantle boundary and a good definition of the various crustal blocks crust about 44 km thick beneath the grenville front zone thins abruptly to ca 36 km southeastward perhaps the result of extension on southeast dipping surfaces extending to the moho other zones of relatively thin crust although less pronounced occur where proterozoic crust overlies archean crust and beneath the morin anorthosite complex the thickest crust is found at the extreme southeast of the transect east of the morin anorthosite from northwest to southeast three main crustal subdivisions are 1 deformed archean rocks with southeast dipping reflectors in the grenville front zone 2 an archean parautochthon with northwest dipping reflectors extending to the lower

origin of granulite terranes and the formation of the lowermost continental crust differences in composition and pressures of equilibration between exposed regional granulite terranes and suites of granulite xenoliths of crustal origin indicate that granulite terranes do not represent exhumed lowermost crust as had been thought but rather middle and lower middle crustal levels application of well calibrated barometers indicate that exposed granulites record equilibration pressures of 0 6 to 0 8 gigapascal 20 to 30 kilometers depth of burial whereas granulite xenoliths which also tend to be more mafic record pressures of at least 1 0 to 1 5 gigapascals 35 to 50 kilometers depth of burial thickening of the crust by the crystallization of mafic magmas at the crust mantle boundary may account for both the formation of regional granulite terranes at shallower depths and the formation of deep seated mafic crust represented by many xenolith suites

reconciling physical properties with surface seismic data from a layered mafic intrusion abstract compositional layering of intrusive rocks is often cited as a source of seismic reflectivity in the crystalline crust direct evidence for this is based primarily on synthetic seismograms calculated from laboratory measurements of rock velocity and density or estimates of aggregate rock properties from measurements of mineral velocities and densities little is known about how in situ effects such as fracturing chemical alteration or anisotropy may change the reflectivity character of the surface seismic data an ideal dataset for examining the hazards of using physical properties data for estimating crustal reflectivity occurs at the nellie intrusion a middle proterozoic age layered mafic intrusion that lies beneath the permian basin of west texas due to a well that penetrated 4 5 km of the intrusion we have a dataset that spans the scale from compositional data on the intrusion derived from well cuttings to log data to surface reflection data sonic and density log data from the well measure velocities and densities 10 to 15 below the values calculated from modal mineralogy we attribute this difference primarily to pervasive post emplacement alteration and fracturing of the rock mass in situ thus this unique dataset provides a quantitative estimate of the magnitude of difference between observed and theoretical velocities that can be expected for crystalline rocks in the upper crust and its cause despite the difference analysis of synthetic seismograms shows that primary compositional variation of the intrusion is still responsible for sub horizontal layered reflectivity in both the log based and petrology based synthetic seismograms boundaries of intrusive cycles are characterized by large negative reflection coefficients due to the juxtaposition of mafic rich basal layers against plagioclase rich layer tops in detail only the log based synthetic provides a good match to the surface seismic reflection data this suggests that physical properties from modal mineralogy are useful in obtaining a generalized model for reflectivity but that differences in bulk physical properties of the rock mass preclude the possiblity of obtaining a one to one match with surface seismic data

high electrical conductivity in a model lower crust with unconnected conductive seismically reflective layers summary in this paper we derive the electrical conductivity for a model lower crust containing unconnected highly conductive lamellae within a highly resistive matrix lateral overlap with small vertical separation of lamellae of the dimensions imaged by seismic reflection profiling a few hundred metres thick and a few kilometres across could increase lower crustal conductivity from the low values predicted by laboratory measurements on dry rocks to the high values observed in field experiments the model does not depend on the cause of high conductivity within the lamellae however lamellation of the lower crust may provide a way of lithologically trapping saline water in permeable conductive lamellae within an impermeable non conductive matrix and so resolve the apparent contradiction between the low crustal permeabilities required for maintenance of high pore pressure over geological time periods and the high degree of pore interconnection required for the high observed conductivity the permeable lamellae and impermeable matrix would be of very different lithologies as implied by the high amplitudes of the lower crustal reflections for a typical example the model gives resistivities that compare favourably with the modified archie s law the model can also give anisotropic resistivity effects which are quantitatively compatible with results from field experiments

hydrodynamic and geomorphological controls on suspended sediment transport in mangrove creek systems a case study cocoa creek townsville australia in tide dominated sedimentary systems close relationships exist between tidal hydrodynamics sediment transport and geomorphology tropical coastlines contain many tide dominated mangrove creeks yet few studies to date have examined the detail of such relationships for these environments time series observations of tidal height currents and suspended sediment concentrations were taken between 1992 and 1996 in cocoa creek a mangrove creek system near townsville ne australia the creek and surrounding mangrove swamps and salt flats were surveyed with an echo sounder and total survey station respectively for within channel tides the flood tide is always the fastest at up to 0 5 m s 1 in contrast for overbank tides i e tidal height 1 5 m australian height datum ahd ebb currents are fastest in july december and january but flood currents are fastest in august and september at up to 1 m s 1 in both cases the tidal asymmetry of overbank tides in cocoa creek is controlled by the interaction between offshore tidal forcing and the intertidal storage effect of the mangrove swamps and salt flats with the result being that during certain periods of the year there tends to be a predominance of either faster flood or ebb velocities on overbank tides significant tidal suspended sediment transport in the channel is only initiated at overbank height on overbank tides measured net suspended sediment fluxes in the channel are mostly seaward directed up to 180 t per tidal cycle however the net flux measured over a neap spring period may be either landwards or seawards up to 465 and 60 t respectively furthermore on the larger overbank tides where the maximum tidal height 1 85 m ahd net sediment fluxes may be reduced because of a limited supply of available material thus hydrodynamic and sediment sampling durations of up to a month may not be representative of long term trends given that our large dataset has not identified a clear long term net transport direction within the creek system we conclude tentatively that the geomorphology of cocoa creek may be near a long term equilibrium

low temperature thermal history and landscape development of the eastern adirondack mountains new york constraints from apatite fission track thermochronology and apatite u th he dating the adirondack mountains in northern new york state form an elongate domal exposure of mainly high grade metamor phic tectonites in a mountainous setting with topographic relief of 1 km the origin of the adirondack mountains and this relief has long been enigmatic since the adirondacks presently lie within an intracratonic setting inboard of the north american passive mar gin and far from any active plate boundaries through the application of apatite fi ssion track aft thermochronology and apatite u th he ahe dating within the eastern adirondack mountains this study provides constraints on both the thermal and ero sional effects of mesozoic passage near a hot spot and the timing of relief development aft thermochronology and ahe dating record relatively stable thermal conditions within the eastern adirondacks from the middle jurassic into the early cretaceous during the early cretaceous ca 130 120 ma the region underwent heating as sociated with progressive movement near the great meteor hotspot resulting in the temporary establishment of an elevated geo thermal gradient following regional heat ing cooling rates increased considerably ca 105 95 ma likely due to both thermal doming producing an increase in erosion rate and the relaxation of isotherms after passage near the hotspot the regional distribution of aft ages across the eastern adirondacks reveals no systematic age gradient from core to periph ery which would be expected under con ditions of persistent high relief during the decay of a crustal root over many tens to hun dreds of millions of years instead thermo chronological data suggest that the present relief developed during the late cretaceous cenozoic through plateau dissection during periodic base level changes

archean and proterozoic crustal evolution evidence from crustal seismology seismic velocity models for archean and proterozoic provinces throughout the world are analyzed the thickness of the crust in archean provinces is generally found to be about 35 km except at collisional boundaries whereas proterozoic crust has a significantly greater thickness of about 45 km and has a substantially thicker high velocity 7 0 km s layer at the base we consider two models that may explain these differences the first model attributes the difference to a change in the composition of the upper mantle the higher temperatures in the archean mantle led to the eruption of komatiitic lavas resulting in an ultradepleted lithosphere unable to produce significant volumes of basaltic melt proterozoic crust developed above fertile mantle and subsequent partial melting resulted in basaltic underplating and crustal inflation in the second model convection in the hot archean mantle is considered to have been too turbulent to sustain stable long lived subduction zones by the proterozoic the mantle had cooled sufficiently for substantial island and continental arcs to be constructed and the high velocity basal layer was formed by basaltic underplating

sm nd and u pb isotopic evidence of juvenile crust in the adirondack lowlands and implications for the evolution of the adirondack mts sm nd investigations of hyde school gneiss yield t dm ages only slightly older than u pb zircon emplacement ages thus indicating substantial addition of juvenile calcalkaline crust to the adirondack lowlands at ca 1300 ma juvenile crust of similar age has been recognized within the adirondack highlands the elzevir terrane further to the northwest in canada and in the green mts of vermont suggesting the presence of an extensive magmatic arc at that time while the precise nature of the arc remains uncertain an indonesian analogue is favored u pb zircon ages of ca 1150 1160 ma are reported for lowlands samples of syenitic and granitic rocks belonging to the anorthosite mangerite charnockite granite amcg suite that also occurs in the highlands as well as in the canadian sector of the frontenac terrane the regional occurrence of these anorogenic intrusions indicates that the adirondack highlands and frontenac terrane including the adirondack lowlands constituted a single contiguous entity

on the use of seismic reflection surveys from oil exploration in deep crustal studies abstract a very large number of seismic reflection surveys is carried out by the oil industry throughout the world some of these surveys are designed to study deep oil traps and may use field parameters which for the most part are not significantly different from those used in deep crustal reflection studies the one parameter which always varies is the record length listening time in the case of a vibratory source the record length can be increased at the processing stage by the equivalent reduction of vibration time through partial correlation we have used an oil exploration survey from a deep sedimentary basin in the coastal plain of israel and extended its record length using this technique we show that if a survey with appropriated field parameters i e a survey for a deep target is chosen deep crustal reflectors can be traced since a cocorp type deep crustal reflection study was also carried out in the same region we can compare the two sets of results we note that in this case the extended oil exploration record is at least equivalent to and probably of better quality than the cocorp type survey this result is due mostly to a better s n ratio in the oil exploration survey where input power was significantly larger than in special purpose study this result indicates the as yet untapped potential of oil exploration data in deep continental crustal studies

shear velocity structure and azimuthal anisotropy beneath eastern north america from rayleigh wave inversion 1 we have obtained shear velocity structure beneath the northeastern united states and southeastern canada using rayleigh wave phases and amplitudes thin crust 36 42 km is observed along the atlantic coast and in the eastern appalachian orogen and thick crust 42 46 km is imaged in the western appalachians and in the western new york portion of the grenville province the variation of crustal thickness correlates well with the observed bouguer gravity anomalies in the upper mantle the high velocity continental keel of cratonic north america is present in the western part of the study area while a broad low velocity region is imaged in new england from the hudson river valley to the white mountains this low velocity anomaly is probably the consequence of past heating of the lithospheric mantle associated with the monteregian hotspot and may represent intrusion of asthenosphere into the edge of the keel in addition to lateral variations in velocity we estimate the azimuthal dependence of phase velocity strong and relatively uniform shear wave splitting is observed in the study region but at periods of 100 s or less the average azimuthal anisotropy of rayleigh waves is less than 1 and is not significantly different from zero at any individual period this small degree of azimuthal anisotropy is not consistent with a substantial contribution to shear wave splitting from fossil anisotropy in the lithosphere much of the source of the shear wave splitting must lie deeper than 200 km

crustal velocity structure of the superior and grenville provinces of the southeastern canadian shield the 1992 lithoprobe abitibi grenville seismic refraction experiment was conducted using four profiles across the grenville and superior provinces of the southeastern canadian shield delay time analysis and tomographic inversion of the data set demonstrate significant lateral and vertical variations in crustal velocities from one terrane to another with the largest velocity values occurring underneath the central gneiss and the central metasedimentary belts south of the grenville front the grenville front tectonic zone is imaged as a southeast dipping region of anomalous velocity gradients extending to the moho the velocity anomaly maps suggest an archean crust may extend horizontally 140 km beneath the northern grenville province near surface velocity anomalies correlate well with the known geology the most prominent of these is the sudbury structure which is well mapped as a low velocity basinal structure the tomography images also suggest underthrusting of the pontiac and quetico subprovinces

adirondack highlands northwest lowlands boundary a multiply folded intrusive contact with fold associated mylonitization the boundary between the adirondack highlands and the northwest lowlands near harrisville new york is a multiply folded intrusive contact between metamorphosed sedimentary rocks of the lowlands and metamorphosed intrusive rocks of the diana complex in the highlands this is shown by detailed geologic mapping and analysis of stratigraphy and minor structural features regionally developed protomylonitic foliation in the diana complex is an axial plane foliation formed during isoclinal folding of dry quartz syenite at granulite facies metamorphic grade lack of major post intrusive fault displacement along the diana complex northwest lowlands boundary is demonstrated by correlation of xenoliths in the diana complex with immediately adjacent metamorphosed sedimentary rock units of the northwest lowlands and by continuity of major folds across the boundary a stratigraphic succession consisting of seven rock units has been recognized in northwest lowlands rocks of the harrisville area rocks in these units include from oldest to youngest 1 garnet sillimanite cordierite gneiss 2 rusty pelitic gneiss with biotite gneiss pyroxene amphibolite and quartzite 3 graphitic calcite marble 4 siliceous marble 5 rusty calc silicate rocks 6 diopside gneiss and 7 calc silicate granulite four phases of folding are evident in these stratigraphic units but only the last three phases affect intrusive quartz syenite gneisses of the diana complex first phase isoclinal folds in bedding have a pervasive axial plane foliation which is the regional foliation associated regional lineations are parallel to first phase fold axes foliation and lineation formed during the first phase of folding were deformed by second phase isoclinal folds which have a weak to strong axial plane foliation or slip cleavage quartz syenite of the diana complex intruded folded metamorphosed sedimentary rocks early during second phase folding and was itself isoclinally folded somewhat later during the second phase isoclinal folding of quartz syenite gneiss is associated with development of protomylonitic to mylonitic axial plane foliation which is most intense in the northwest border zone of the diana complex due to lithic contrast with rocks northwest of the border third phase folds are isoclinal to open and are locally characterized by axial plane slip cleavage or fracture cleavage the axial surfaces of folds associated with the first three phases of deformation have a general northeasterly trend and northwesterly dip but their axes have varied plunges two dimensional heart and anchor and hook patterns are a product of interference of second and third phase folds fourth phase deformation resulted in northwest trending open folds with locally developed axial plane slip or fracture cleavage interference of third and fourth phase folds is manifest in dome and basin patterns that are elongate to the northeast and overturned to the southeast similar to dome and basin patterns throughout the northwest lowlands late stage ductile shearing produced very fine grained thin mylonite and ultramylonite in shear zones that transect the preexisting protomylonite foliation in quartz syenite gneiss later brittle deformation resulted in closely spaced fractures quartz and epidote veins and local minor faults however no evidence for major faulting has been observed along this part of the adirondack highlands northwest lowlands boundary

adirondack appalachian crustal structure the cocorp northeast traverse reflection surveys from northeastern new york and central vermont the first elements of a cocorp seismic traverse of grenville and appalachian terranes in the northeastern united states indicate that an unusual zone of layered reflections characterizes the lower crust beneath the eastern adirondacks and that grenville age basement of the green mountains may actually be allochthonous perhaps thrust over paleozoic shelf rocks the top of the adirondack deep layered sequence is found at about 20 km beneath the marcy meta anorthosite massif it appears to dip about 10 northwestward and wedge out against more horizontal reflections at about 28 km this intracrustal sequence may correspond with a previously inferred increase in electrical conductivity possible interpretations range from its being a layered igneous complex to its representing a tectonically buried metasedimentary assemblage although graphitic schists and iron or sulfide segregations in such an assemblage might contribute to its electrical characteristics the problematical issue of water in the lower crust if and how it got there and remained is again raised if not resolved other intrabasement features include major east and west dipping reflections possibly corresponding to faults arched reflections that may represent folds a well defined lens shaped zone virtually devoid of reflections and possible moho reflections unequivocal sub moho reflections are absent superimposed at shallower levels on the eastern part of the traverse are appalachian structures reflections down to about 4 5 km beneath the taconic mountains are interpreted to represent paleozoic shelf sediments of the middlebury synclinorium underlying the taconic allochthons possibly correlative although less well defined reflections appear to extend in disrupted fashion beneath the precambrian rocks of the green mountains suggesting a major basement overthrust the inferred decollement for this overthrust steepens rapidly beneath the east flank of the green mountains east dipping reflections at the east side of the green mountains may represent another major thrust zone involving basement and overlying metasedimentary slices the basement overthrusting suggested by this study is similar in certain respects to the style if not the extent of that demonstrated by previous cocorp surveys in the southern appalachians

biophysical controls on accretion and elevation change in caribbean mangrove ecosystems abstract habitat stability of coastal ecosystems such as marshes and mangroves depends on maintenance of soil elevations relative to sea level many such systems are characterized by limited mineral sedimentation and or rapid subsidence and are consequently dependent upon accumulation of organic matter to maintain elevations however little field information exists regarding the contribution of specific biological processes to vertical accretion and elevation change this study used biogenic mangrove systems in carbonate settings in belize bz and southwest florida fl to examine biophysical controls on elevation change rates of elevation change vertical accretion benthic mat formation and belowground root accumulation were measured in fringe basin scrub and dwarf forest types plus a restored forest elevation change rates mm yr 1 measured with surface elevation tables varied widely bz dwarf 3 7 bz scrub 1 1 fl fringe 0 6 fl basin 2 1 bz fringe 4 1 and fl restored 9 9 root mass accumulation varied across sites 82 739 g m 2 yr 1 and was positively correlated with elevation change root volumetric contribution to vertical change mm yr 1 was lowest in bz dwarf 1 2 and fl fringe 2 4 intermediate in fl basin 4 1 and bz scrub 4 3 and highest in bz fringe 8 8 and fl restored 11 8 sites surface growth of turf forming algae microbial mats or accumulation of leaf litter and detritus also made significant contributions to vertical accretion turf algal mats in fringe and scrub forests accreted faster 2 7 mm yr 1 than leaf litter mats in basin forests 1 9 mm yr 1 but similarly to microbial mats in dwarf forests 2 1 mm yr 1 surface accretion of mineral material accounted for only 0 2 3 3 of total vertical change those sites with high root contributions and or rapid growth of living mats exhibited an elevation surplus 2 to 8 mm yr 1 whereas those with low root inputs and low or non living mat accumulation showed an elevation deficit 1 to 5 7 mm yr 1 this study indicates that biotic processes of root production and benthic mat formation are important controls on accretion and elevation change in mangrove ecosystems common to the caribbean region quantification of specific biological controls on elevation provides better insight into how sustainability of such systems might be influenced by global e g climate atmospheric co2 and local e g nutrients disturbance factors affecting organic matter accumulation in addition to relative sea level rise

compaction sensitive accretionary lapilli a means for recognizing soft sedimentary deformation in a region of negligible tectonic overprint soft sedimentary folding has affected beds of accretionary lapilli the folds which range from upright convolute to intraformational recumbent are truncated by the overlying beds and their pre lithification origin is further confirmed by their association with forcefully injected clastic dykes of accretionary lapilli and fluidized channel ways shape factor analysis using elliott polar graphs shows that the accretionary lapilli define weak to moderate planar fabrics that are coincident with the regional bedding attitude and which have a compactional strain symmetry x y z the lapilli fabrics were superimposed on the folds and clastic dykes and hence are axial planar to the recumbent folds and transect the convolute lamination the geometrical relations and strain pattern establish a pre tectonic timing for the folds and for their formation in unconsolidated sediment the fabrics were not generated during folding by processes akin to tectonic dewatering but were later superimposed on the folds compaction sensitive strain markers give an additional criterion for distinguishing between soft sedimentary and tectonic structures post lithification deformation would be recognized by the dispersal of the planar compaction fabrics defined by the accretionary lapilli

new constraints on the geometry of the lac bouchette gabbro anorthosite from magnetotellurics and magnetics a cross section of the resistivity structure through the lac bouchette gabbro anorthosite provides a new image of the thin skinned geometry of an allochthonous terrane in the western grenville prov

seismic velocities in the shallow crust of western new england and northern new york the ontario new york new england refraction study o nynex provides a set of high quality data for a tomographic study of an intraplate continental region with low seismic activity this study focuses on the region crossed by the united states part of the o nynex profile tomographic inversion of the travel time data is used to construct a three dimensional model of the p and s wave seismic velocity distribution within the shallow crust of this region velocity structure is resolved in the top 15 km of the crust with the most detailed picture obtained for the depth range between 1 and 5 km the upper crust of the proterozoic grenville province is found to have a p wave velocity 0 2 to 0 3 km sec higher than the paleozoic appalachians the area of anorthositic intrusions within the adirondack mountains is characterized by p wave velocities 0 3 km sec higher and s wave velocities 0 1 km sec higher than the average values for the grenville province this high velocity anomaly extends to the depth over 5 km possibly as deep as 16 km the velocity structure of central vermont is found to be closer to that of the grenville province than to the rest of the appalachians central new hampshire shows relatively small lateral variation of seismic velocity no strong correlation is seen between velocity anomalies and intrusive bodies of the white mountains magma series

reconciling deep seismic refraction and reflection data from the grenvillian appalachian boundary in western new england abstract the grenvillian appalachian boundary is characterized by pervasive mylonitic deformation and retrograde alteration of a suite of imbricated allochthonous and parautochthonous gneisses that were thrust upon the grenvillian continental margin during the lower paleozoic seismic reflection profiling across this structural boundary zone reveals prominent dipping reflectors interpreted as overthrust basement slices parautochthons of the green mountain anticlinorium in contrast a seismic refraction study of the grenvillian appalachian boundary reveals a sub horizontally layered seismic velocity model that is difficult to reconcile with the pronounced sub vertical structures observed in the green mountains a suite of rock samples was collected from the green mountain anticlinorium and measured at high pressures in the laboratory to determine the seismic properties of these allochthonous and parautochthonous gneisses the laboratory measured seismic velocities agree favorably with the modelled velocity structure across the grenvillian appalachian boundary suggesting that the rock samples are reliable indicators of the rock mass as whole samples of the parautochthonous grenvillian basement exposed in the green mountains have lower velocities by about 0 5 km s than lithologically equivalent units exposed in the eastern adirondack highlands velocity reduction in the green mountain parautochthons can be accounted for by retrograde metamorphic alteration hydration of the paragneisses seismic anisotropies ranging from 2 to 12 in the mylonitized green mountain paragneisses may also contribute to the observation of lower seismic velocities where the direction of ray propagation is normal to the foliation the velocity properties of the green mountain paragneisses are thus insufficiently different from the mantling appalachian allochthons to permit their resolution by the ontario new york new england seismic refraction profile

seismic reflectivity of a finely layered granulite facies ductile shear zone in the southern grenville province quebec abstract lithoprobe reflection profile 54 across the granulite facies morin shear zone msz in the grenville tectonic province quebec canada reveals a west dipping zone of strong reflections the origin of these reflections has been investigated by detailed field mapping laboratory measurements of p wave velocities and densities of representative rock samples from the main lithological units and forward synthetic modeling petrofabric and microstructural analyses were performed in order to interpret the measured seismic properties synthetic seismograms generated from the velocity and density data demonstrate that reflections originate from lithologic thin layers and thin layer clusters likely resulted from intensive tectonic transposition and metamorphic differentiation lattice preferred orientation lpo induced anisotropy of granulite facies mylonites except for those containing abundant sillimanite biotite or amphibole is very low and hence unlikely to be the primary cause for reflections confining pressure does not significantly affect the reflectivity of the shear zone because the reflection coefficients are not sensitive to pressure up to at least 600 mpa since composite reflections of thin layer clusters can cause high reflectivity the strong reflectivity from some deep crustal sections with low refraction velocities may be interpreted to be due to the presence of thin layer mafic clusters within dominantly felsic rocks

a new map of crustal terranes in the united states from cocorp deep seismic reflection profiling a new map has been constructed to summarize major systematic variations in seismic reflection character observed by over 10000 km of cocorp profiling in the us among the seismic characteristics represented on this map are crustal scale detachments which can be traced as relatively low angle reflectors over large areas deeply penetrating dipping reflection zones some of which mark major shear zones perhaps even crustal sutures moho reflectivity which appears to vary from craton to phanerozoic periphery seismic transparency which can sometimes be interpreted as geologic homogeneity seismic layering prominent in the lower crust in many areas and now known to dominate the upper basement in other regions and unusually strong reflections or bright spots at mid crustal levels that may mark deep crustal fluids

wave attenuation in mangroves a quantitative approach to field observations coastal mangroves dwelling at the interface between land and sea provide an important contribution to reducing risk from coastal hazards by attenuating incident waves and by trapping and stabilizing sediments this paper focusses on relations between vegetation densities wave attenuation rates sediment characteristics and sedimentation rates in mangroves these processes were studied along two cross shore transects through mangroves fringing estuaries in the southern andaman region of thailand volumetric vegetation densities in these mangroves were ranging up to 32 depending on the water depth generalized total wave attenuation rates increased from 0 002 m 1 in the sparsely vegetated forest fringes with avicennia and sonneratia species up to 0 012 m 1 in the dense rhizophora vegetation in the back of the forests the total wave attenuation rates integrate effects of shoaling and energy losses due to various bio physical interactions within the mangrove ecosystem wave attenuation in the mangroves is presumably dominated by energy losses due to vegetation drag since wave attenuation due to bottom friction and viscous dissipation on the bare mudflats is significantly lower than those inside the mangrove vegetation additionally wave attenuation in the mangroves was found to facilitate enhanced net sediment deposition and a gradual fining of the bed material these findings corroborate the coastal defence function of mangroves by quantifying their contribution to wave attenuation and sediment trapping the explicit linking of these properties to vegetation composition and structure facilitates modelling studies investigating the mechanisms determining the coastal defence capacities of mangroves

reflectivity of the crystalline crust hypotheses and tests summary the nature of reflectors within the crystalline basement remains the subject of inference except where reflections have been traced directly to outcrop geological models of basement reflectors need to be developed which incorporate geophysical constraints obtained from measurements on seismograms but most geological information still comes from speculative interpretations of seismic experiments run in different regimes pronounced lower crustal reflectivity detected worldwide is ascribed in various geological hypotheses to primary lithologic layering to ductile strain banding or to trapped fluids a birps deep crustal profile across the atlantic continental margin suggests that the observed reflectivity is not related in any simple way to the amount of extensional strain undergone study of worldwide crustal profiles shows that exposed high pressure terranes are not as reflective as in situ lower crust at high pressure suggesting either that these granulite terranes are not representative of the lower crust or that physical properties possibly the presence of fluids or thermally controlled ductile strain banding are more likely responsible for observed reflectivity than are simple lithologic boundaries the argument for the importance of physical properties in causing observed lower crustal reflectivity is strengthened by an observed negative correlation between depth to the reflective lower crust and regional surface heat flow 1 geophysical constraints the notion that geometric effects thin layer interference and focussing in the absence of otherwise significant impedance contrasts are responsible for much observed reflectivity is common in the literature because many reflections are observed on deep crustal profiles velocity and density cannot increase monotonically with depth while remaining within bounds set by refraction experiments implying the existence of a funtion of velocity with depth that is oscillatory while the concept thus developed of the existence of many thin layers in the lower crust is justly important in geologic models of the lower crust seismic interference from such laminae cannot be the only explanation of observed crustal reflectivity for normal incidence no structure embedded in a constant impedance medium gives a stronger reflection than a quarter wavelength layer which produces an amplitude twice that due to a simple interface complex structures can increase the total energy reflected but the energy is spread over longer times and the peak reflected amplitude is not increased observed reflection amplitudes from the lower crust vary by factors u2 so that the presence or absence of thin layer interference cannot be the only effect causing lower crustal

proterozoic subduction and terrane amalgamation in the southwestern grenville province canada evidence from ultrapotassic to shoshonitic plutonism a late grenvillian 1089 1076 ma subduction regime followed by terrane amalgamation is postulated as the paleoenvironment of a 400 km long belt of potassium rich alkaline and shoshonitic plutons in the central metasedimentary belt of the southwestern grenville province canada emplacement of the plutons postdates the regional metamorphism in the country rock but predates major shear zones that form a structural boundary for the plutonic belt the extent timing and magmatic affinities of the suite delineate the gatineau domain within the current mont laurier terrane of quebec and are compelling evidence for the allochthonous nature of the elzevir terrane and its extension eastward to rideau lake in ontario and northward into the gatineau domain the belt trends northeast the emplacement ages are younger to the southeast and the magmatic affinities are those of island arc ultrapotassic to shoshonitic rocks this is interpreted to reflect the existence of a southeast dipping northeast trending subduction zone beneath the combined elzevir gatineau terrane between 1089 and 1076 ma subsequent to subduction amalgamation of the elzevir terrane to the other terranes formed the central metasedimentary belt which then accreted and collided with the allochthonous polycyclic belt these events provide evidence that the ottawan orogeny commenced at ca 1090 ma in the central metasedimentary belt a modern analogue of this plutonism and its tectonic setting may have been the magmatism and arc continent collision and subduction setting of the sunda are indonesia

a comparison of reflection and refraction processing and interpretation methods applied to conventional refraction data from coastal maine abstract in 1984 the u s geological society collected 850 km of refraction data in lines parallel and perpendicular to regional strike of the appalachian orogen in maine and southeastern quebec a 100 km long strike line in coastal maine west of penobscot bay is here interpreted on the basis of both refracted and reflected phases techniques used in seismic reflection processing including normal movement velocity corrections and common mid point stacking were applied to the refraction data in order to enhance the visibility of reflected phases the geometries of the most laterally continuous reflections as defined by these techniques can be correlated with reflections seen on a crossing near vertical reflection profile conventional ray tracing analysis of refracted and wide angle reflected phases in the refraction data constrains the velocity structure to about 14 km depth and provides evidence for high veiocity material 6 5 km sec between 4 and 7 km depth and for lower velocities

heterogeneous structure around the jemez volcanic field new mexico usa as inferred from the envelope inversion of active experiment seismic data summary we analyse active experiment seismic data obtained by the 1993 jemez tomography experiment jtex programme to elucidate the heterogeneous structure of the jemez volcanic field which is located at the boundary between the colorado plateau and the rio grande rift using a single isotropic scattering assumption we first calculate the envelope green s functions for the upper and lower crust and the uppermost mantle by fitting the theoretical envelopes with the observed three component data we estimate depth dependent features of the scattering coefficients around valles caldera we estimate the ratios of scattering coefficients rather than scattering coefficients themselves because of the uncertainty of the seismic efficiency of the explosive sources and knowledge of absolute site amplification factors the strongest scattering coefficients are observed at a shallow depth beneath the valles caldera this is considered to be related to the complex structure caused by two episodes of caldera formation and the ensuing resurgent uplift in the caldera etc the depth dependent characters of the scattering coefficients for the colorado plateau and the rio grande rift are similar to each other a transparent upper crust and a heterogeneous lower crust small and large scattering coefficients respectively however the scattering coefficients beneath the rio grande rift are several times larger than those beneath the colorado plateau depths of the lower crust and the moho boundary beneath the rio grande rift are shallower than those of the colorado plateau from their geological settings and other geophysical results around the region we infer that the larger scattering coefficients of the rift are associated with rift formation and volcanic activity such as magma ascent from the upper mantle to the crust

composition of the crust in the grenville and appalachian provinces of north america inferred from v p v s ratios we use the ratios between p and s wave velocities vp vs derived from seismic refraction data to infer the composition of the crust in the grenville and the appalachian provinces of north america the crust exhibits vp vs increasing with depth from 1 64 to 1 84 there is a clear distinction between the grenville province average vp vs 1 81 and the appalachian province average vp vs 1 73 which persists at all depths the boundary between these provinces is east dipping extending for 100 km east of the champlain thrust in the appalachian province the increase in vp vs ratios with depth from 1 67 to 1 74 0 02 may reflect a normal decrease of silica content in the continental crust in the grenville province beneath the central granulite terrane an anomalous vp vs ratio of 1 82 0 02 is observed extending to a depth of 10 km this correlates with the abundance of ca plagioclase in the marcy anorthosite at greater depth 15 20 km where seismic lamination and high electrical conductivity is observed vp vs is 1 84 0 02 and correlates with the tahawus complex a layered mafic intrusion within the 25 km thick lower crust of the grenville province the vp vs is 1 84 0 02 and p velocity is 7 0 0 1 km s which are typical for plagioclase bearing rocks gabbro norite the high vp vs ratio in the grenville province has not been reported in crust of any other age since the grenville province contains 75 of the world s known anorthosites high vp vs ratio is related to high plagioclase we suggest that the composition of the grenville lower crust was significantly modified by the emplacement of the anorthosites in the mid proterozoic

cooling and inferred uplift erosion history of the grenville orogen ontario constraints from 40ar 39ar thermochronology stepwise 40ar 39ar degassing experiments of 57 mineral separates of hornblende muscovite biotite and perthitic microcline have been used in conjunction with petrologic observations to place regional constraints on the postmetamorphic cooling and the inferred uplift and erosion history of the grenville orogen in ontario the 40ar 39ar data support an interpretation of slow nearly uniform cooling 1 4 c m y from temperatures of 500 c to below 150 c in the central gneiss belt cgb hornblendes cooled through ar closure between 930 and 1025 ma whereas in the central metasedimentary belt cmb hornblendes record the following range in 40ar 39ar cooling ages 1104 ma in the frontenac terrane 1007 1067 ma in the sharbot lake terrane 919 1026 ma in the elzevir terrane and 972 ma in the central metasedimentary belt boundary zone regional uplift erosion rates of 0 03 0 14 km m y have been estimated for the grenville orogen in ontario based on the 40ar 39ar data a model retrograde p t path for rocks of the cgb and an upper time constraint provided by flat overlying cambrian and ordovician sediments these erosion rates are consistent with rates estimated for other proterozoic or archean granulite terranes but are an order of magnitude slower than active orogens such as the alps and himalayas a regular variation in hornblende 40ar 39ar cooling ages is observed in rocks that traverse highly strained often mylonitic shear zones that separate the four major terranes of the cmb the pattern of 40ar 39ar ages is interpreted to reflect late tectonic extension consistent with field observations in the central metasedimentary belt boundary zone and elsewhere in the cmb up to 13 km of vertical displacement is inferred for some rocks in the cmb between the time they cooled below closure to argon diffusion in hornblende 500 c and their exposure at the surface 25 c

crustal structure of the southeastern grenville province northern new york state and eastern ontario the grenville province exposes an oblique cross section through mid lower crustal lithologies that were pervasively deformed and subjected to regional thermal overprinting during the grenvillian orogeny 1 1 ga the southeastern grenville province is divided into two subterranes by the carthage colton mylonite zone a 110 km long lineament characterized by intense ductile shear and igneous intrusion which separates the amphibolite facies metasediments of the central metasedimentary belt to the west from the granulite facies metaplutonics of the central granulite terrane to the east the recognition of distinct lithotectonic domains separated by zones of intense ductile shear in the grenville province raises questions concerning the deep structure of these subterranes and in particular the means by which the mid lower crustal rocks exposed in the grenville province were emplaced seismic refraction wide angle reflection data were acquired to investigate the deep structural interrelationships within the southeastern grenville province a travel time inversion for velocity and interface depth was applied to the seismic data together with constraints from amplitude modeling to produce a seismic velocity model of the crust in the southeastern grenville province in the central metasedimentary belt the upper crust is characterized by velocities in the range 6 3 6 4 km s and a poisson s ratio of 0 26 0 01 which are attributed to quartzofeldspathic rocks farther east in the central granulite terrane upper crustal velocities of 6 55 km s and a poisson s ratio of 0 28 0 01 are associated with the marcy anorthosite the seismic homogeneity of the upper crust in the region of the carthage colton mylonite zone suggests that this boundary is a shallow feature limited to the upper 2 3 km of the crust the deep crustal structure of the southeastern grenville province is characterized by two discrete and laterally discontinuous seismic interfaces in the central metasedimentary belt the top of the lower crust is delineated by an eastward dipping interface at 24 28 km depth in the central granulite terrane prominent en echelon reflections referred to as the tahawus complex form a gently arched dome at 17 22 km depth interpretation of the tahawus complex as a zone of layered mafic cumulates is supported by its high velocity 7 1 km s and poisson s ratio 0 27 0 02 the lower crust is characterized by a velocity of 7 0 7 2 km s and an anomalously high poisson s ratio of 0 30 0 02 which are representative of pyroxene garnet granulites in contrast velocities of 6 8 7 0 km s are modeled beneath the central granulite terrane and appear to signify a lateral change in composition the moho lies at 44 45 km depth and is characterized by pronounced en echelon reflection segments suggesting compositional interlayering around the crust mantle boundary the velocity of the upper mantle is 8 0 8 2 km s an anomalous upper mantle layer with a reversed velocity of 8 6 km s dips eastward from 50 to 60 km depth beneath the southeastern grenville province our results indicate that remnants of magmatic intrusions that mobilized and thickened the crust during the grenvillian orogeny are preserved in the mid lower crust as a layered cumulate body tahawus complex and in the upper mantle as an eclogitic lens possibly delaminated from the overthickened crust during uplift of the southeastern grenville province

the seismic velocity structure of the newfoundland appalachian orogen the deep structure of the newfoundland appalachian orogen is investigated by analyses of three intersecting seismic refraction wide angle reflection profiles which traverse the gander and dunnage zones or central mobile belt of newfoundland a simultaneous travel time inversion for velocity and interface was applied to the in line seismic refraction wide angle reflection data and constrained by synthetic amplitude models the results of the modeling procedure show a subhorizontally layered crust with upper crustal velocities ranging from 5 4 to 6 2 km s a midcrustal velocity of 6 25 6 35 km s and a lower crustal velocity of 6 7 0 2 km s the top of the lower crust is marked by a series of prominent reflections between 18 and 23 km depth which suggest a complex layered velocity interface strong laterally coherent moho reflections indicate a sharp crust mantle transition at 35 3 km the uppermost mantle has a velocity of 8 0 0 2 km s and a reflecting horizon at 55 km depth suggests an increase to velocities approaching 8 5 km s normal moveout corrections applied to fan profiles provide constraining evidence for the reflecting horizon at the top of the lower crust and laterally continuous moho reflections at 11 12 s two way travel time comparisons with a coincident deep seismic reflection profile show that the refraction and reflection mohos match to better than 2 3 km bulk poisson s ratios of 0 23 0 24 for the whole crust calculated from pmp sms travel times suggest a crust dominated by quartzofeldspathic lithologies and a notable absence of voluminous mafic additions to the lower crust the absence of a deep crustal root coupled with the bulk intermediate composition inferred for the lower crust from the seismic refraction wide angle data implies that the crust beneath central newfoundland has undergone multiple periods of reactivation and equilibration following successive orogenic episodes

regional structural and strain analyses of terranes in the western metamorphic belt central sierra nevada california abstract a comparison of total strains in 225 samples from the western metamorphic belt sierra nevada shows that strain types and intensities strongly depend on rock type greywackes and clast supported conglomerates are least strained whereas more intense strains occur in lapilli tuffs pebbly mudstones and slates large belts of volcanic rock record plane strain whereas nearby slate and greywacke sequences record flattening type strain suggesting that volume losses of 45 65 occurred in slates and 0 26 in greywackes lapilli tuffs record less than 11 volume loss the differences in volume loss and strain from one rock type to another require that discontinuities in total strain occur at most lithologic contacts independently of the lithologic control regional structural patterns and strain fields support the delineation of three terranes foothills merced river and northern sierra and two distinct domains western and eastern foothills terranes at these latitudes within the western metamorphic belt these terranes each bordered by large ductile shear zones differ in average strain intensity and orientation but not in strain type in the foothills terrane strain intensities decrease from moderate values in the western foothills terrane to low values in the eastern foothills terrane strain intensities in the study area are highest in the melones and bear mountains fault zones and in terranes east of the melones fault structures associated with regional deformation in each terrane do not extend far across terrane boundaries multiple generations of regionally developed structures are therefore rare in this part of the western metamorphic belt outside of fault zones we see one regionally developed cleavage in the foothills terrane a single but older cleavage in the merced river terrane and two still older cleavages in the northern sierra terrane however younger deformations may have reactivated and rotated older structures in adjacent terranes the timing and kinematics of the deformation in the foothills terrane suggest that faulting and rigid body rotations preceded pervasive shortening continued fault movement and rotation of faults to steep dips if orientations of ductile structures reflect plate motions structures in the merced river terrane suggest jurassic triassic orthogonal nne convergence whereas structures in the foothills terrane support late jurassic orthogonal ne convergence changing to oblique ene convergence about 150 ma ago

crustal scale shortening and extension across the grenville province of western quebec a deep seismic reflection survey shot in 1993 crosses almost the full width of the grenville province in western quebec the seismic transect provides a very clear image of the crust mantle boundary and the most precise definition to date of the various grenvillian terranes the crust is around 44 km thick beneath the grenville front but thins rapidly to 36 km some 60 km to the southeast it is also notable that the greatest crustal thickness of 50 km occurs at the southeast end of the transect far from the inferred location of the main grenvillian collision the grenville front zone in which nw directed thrusting at about 1 ga was followed by se directed extension is defined by discontinuous se dipping reflections which extend down to the moho to the southeast the overlying migmatitic archean parautochthon almost half of the transect is characterised instead by nw dipping reflectors extending into the lower crust these reflectors are in turn truncated to the southeast by a 12 km thick zone of intense se dipping reflections the baskatong crustal ramp the base of the allochthonous terranes allochthon boundary thrust is likely located at this ramp which flattens out at around 30 km depth into the base of the relatively transparent intermediate crust a highly reflective upper crustal deck corresponding to rocks of the mont laurier terrane was thrust over the baskatong crustal ramp and is represented further to the northwest by the klippelike cabonga allochthon the synformal transparent morin anorthosite charnockite complex belongs to the same upper crustal level ramp anticlines and the overriding basal thrust of the upper allochthons demonstrate the nw directed propagation of tectonic transport during the grenvillian orogeny involving deformation and displacement along the baskatong ramp with a relay into the grenville front zone postaccretional extension appears to have been primarily accommodated along the latter two crustal discontinuities thinning the crust immediately south of the grenville front and affecting the crust up to 350 km away from the front

anomalous seaward dip of the lithosphere asthenosphere boundary beneath northeastern usa detected using differential array measurements of rayleigh waves summary rayleigh wave phase velocities and azimuth anomalies in the period range of 30 100 s are measured for a set of four triangular arrays of broad band seismometers in coastal northeastern usa this is a region in which a strong upper mantle slow shear velocity anomaly a new england anomaly crosses the continental margin earthquakes from a wide range of directions are used to detect the variation of parameters with azimuth of propagation no lateral heterogeneity in phase velocity is detected at these periods between stations at the centre and the edge of the anomaly however large 10 20 per cent azimuthal variations occur and have a cos 1 dependence which is indicative of a dipping structure in the upper mantle corresponding azimuth variations with a magnitude of 5 are also detected this behaviour is consistent with a southeasterly n150 e dip of the lithosphere asthenosphere boundary beneath new england this dip is associated with the shoaling of the new england anomaly beneath the adirondack mountains west of the array it is opposite to the dip associated with lithospheric thickening toward the interior of the craton

swan predictions of waves observed in shallow water onshore of complex bathymetry abstract swan model predictions initialized with directional wave buoy observations in 550 m water depth offshore of a steep submarine canyon are compared with wave observations in 5 0 2 5 and 1 0 m water depths although the model assumptions include small bottom slopes the alongshore variations of the nearshore wave field caused by refraction over the steep canyon are predicted well over the 50 days of observations for example in 2 5 m water depth the observed and predicted wave heights vary by up to a factor of 4 over about 1000 m alongshore and wave directions vary by up to about 10 sometimes changing from south to north of shore normal root mean square errors of the predicted wave heights mean directions periods and radiation stresses less than 0 13 m 5 1 s and 0 05 m 3 s 2 respectively are similar near and far from the canyon squared correlations between the observed and predicted wave heights usually are greater than 0 8 in all water depths however the correlations for mean directions and radiation stresses decrease with decreasing water depth as waves refract and become normally incident although mean wave properties observed in shallow water are predicted accurately nonlinear energy transfers from near resonant triads are not modeled well and the observed and predicted wave energy spectra can differ significantly at frequencies greater than the spectral peak especially for narrow band swell

precambrian basement structure and laramide deformation revealed by seismic reflection profiling in the laramie mountains wyoming the university of wyoming conducted seismic reflection profiling in the laramie mountains of wyoming to investigate the nature of precambrian crustal structure and laramide deformation in the region here the imaging of layering in the laramie anorthosite complex confirms that layered intrusions can be reflective and establishes an analog for interpreting events in other seismic reflection data sets where layered intrusions could be the cause of multicyclic events moreover the presence of prominent primary layering in the complex supports a conclusion that it formed in situ and not as the result of the emplacement of a diapiric crystal mush imaging of laramide thrusts in the laramie mountains adds credence to the idea that brittle faults can be reflective in some situations migrated apparent dips on these faults are 30 westward basement involved compressive structures consisting of monoclinal folding and a fault triple junction demonstrate that compression controlled the style of deformation during the laramide orogen in wyoming west dipping precambrian structures imaged in these data have a similar attitude to the laramide structures suggesting that laramide deformation was influenced by precambrian features these precambrian structures may be subthrust slices of exotic proterozoic terranes

exploration in the shetland faeroe basin using densely spaced arrays of ocean bottom seismometers recent exploration activity in the peripheral regions of the shetland faeroe basin offshore northwest scotland has led to the discovery of some of the largest oil reserves on the united kingdom uk continental shelf we present results from two ocean bottom seismometer profiles acquired by mobil north sea ltd across the center of the shetland faeroe basin these data provide a powerful tool for delineating long wavelength velocity variations and thus have potential for reducing the nonuniqueness associated with conventional seismic exploration methods analysis of the first arrival traveltime data using both forward and inverse ray based techniques produces a well constrained velocity depth model of the basin fill we estimate that the uncertainty in the velocity structure is 5 from a series of trial and error perturbations applied to the final models the velocity structure of the faeroe basin has three principal layers 1 a near surface layer with velocities in the range 1 6 to 2 2 km s 2 a 3

strain factorizations from lapilli tuff english lake district abstract summary two existing and two new methods of strain analysis have been used on samples of accretionary lapilli tuff from the english lake district results from each method are presented for comparison factors responsible for lapilli shape are itemized and discussed regional studies indicate that lapilli ellipsoids contain initial compaction and tectonic components the most reliable results indicate that compaction of 66 of original thickness normal to bedding during diagenesis was followed by tectonic strains due to folding and cleavage formation the effects of folding on lapilli shape are thought to be small slaty cleavage was produced by strains close to plane strain indicating a shortening of so 70 normal to the cleavage plane it is concluded that slaty cleavage does not form perpendicular to the maximum total shortening of the rock but perpendicular to the short axis of a strain ellipsoid associated solely with cleavage formation and computation of three dimensional progressive deformations

dissipation of wave energy and turbulence in a shallow coral reef lagoon received 6 april 2011 revised 14 november 2011 accepted 3 january 2012 published 10 march 2012 1 simultaneous in situ measurements of waves currents and turbulence are presented to describe dissipation rates of wave energy and turbulent kinetic energy in the windward coral reef lagoon system at lady elliot island lei australia the dissipation of wave energy in the lagoon is tidally modulated and strongly correlates with frictional dissipation due to the presence of the extremely rough bottom boundary the observed turbulent kinetic energy tke dissipation rate in this wave dominated lagoon is much larger than recently reported values for unidirectional flows over natural fringing coral reefs the correlation between the wave dissipation and is examined the average rate of dissipation induced by the rough turbulent flow was estimated directly from the observed coupled with both a depth integrated approach and with a bottom boundary layer scaling rates of tke dissipation estimated using the two approaches approximate well within a factor of 1 5 to 2 4 to the surface wave energy dissipation rate the wave dissipation and friction factor in the lagoon can be described by a spectral wave frictional model with a bottom roughness length scale that is approximately constant across the lagoon we also present estimates of dissipation induced by the canopy drag force of the coral heads the dissipation in this case is enhanced and becomes more significant for the total energy dissipation when the water depth in the lagoon is comparable to the height of the coral heads

modeling wide angle seismic data for crustal structure southeastern grenville province a modeling methodology for obtaining two dimensional 2 d crustal structure from wide angle seismic data is applied to data from the southeastern grenville province pre modeling steps include 1 assignment of arrival pick uncertainties for appropriate data fitting and weighting using an empirical relationship based on signal to noise ratio 2 using a modified form of travel time reciprocity to avoid unreasonable levels of model heterogeneity and 3 identifying data unsuitable for 2 d modeling the goal of the travel time inversion amplitude modeling approach is to obtain a minimum structure and minimum parameter model that takes into account both horizontal and vertical variations in the resolution of typical wide angle data each step of a layer stripping procedure involves a series of inversions in which a one dimensional or simple starting model is improved with additional velocity and or interface nodes until a satisfactory trade off between travel time fit parameter resolution and complete ray coverage of all source receiver pairs is achieved using zero vertical velocity gradient layers and head waves during preliminary first arrival inversion can 1 decrease the number of intermediate models 2 allow greater lateral heterogeneity to be imaged and 3 simplify incorporation of amplitude modeling constraints into the final model using amplitude distance curves allows quantitative modeling of the relative amplitude and offset variations of phases discrepancies between observed and calculated reflection amplitudes are used to infer fundamental non step like velocity changes at layer boundaries later arrivals due to unresolved velocity anomalies are modeled using reflecting segments that float within the model without an associated velocity structure these reflectors provide a spatial image like that obtained from vertical incidence reflection data as opposed to a velocity image the model of grenville crustal structure is more detailed than a model obtained from a previous interpretation of the data and includes elements analogous to those imaged in nearby deep reflection data a crustal scale zone of wide angle reflectors with an average easterly apparent dip of 13 defines a major grenvillian terrane boundary

some results of cocorp seismic reflection profiling in the grenville age adirondack mountains new york state cocorp deep seismic reflection profiling in the adirondack mountains of northern new york state has revealed a prominent zone of layered reflectors in the lower crust of the east central adirondacks the strong layered reflectors here termed the tahawus complex occur between 18 and 26 km depth beneath the sparsely reflective granulite grade surface terrane which has been uplifted from depths greater than 20 km the tahawus complex apparently represents layered rocks of some type in the lower crust of the adirondacks possibilities include gneissic layering cumulate igneous layering a layered sill complex and underthrust sedimentary strata the tahawus complex may be spatially coincident with a previously detected high conductivity zone in the lower crust suggesting that either unusual mineralogies or interstitial electrolytes are present in the tahawus complex in contrast to layered reflections discovered in the lower crust of the east central adirondacks and southeast of the adirondacks cro

sw grenville province canada the case against post 1 4 ga accretionary tectonics abstract seven accretionary sutures formed between 1 16 and 1 03 ga have been identified by different authors in the ontario quebec adirondack oqa segment of the mesoproterozoic grenville orogen in canada with one exception the inferred accretionary terrane boundaries lie within or at the margins of the central metasedimentary belt cmb located between the central gneiss belt and the adirondack highlands central granulite terrane however geological geochronological and petrological data suggest that the grenville orogen on both sides of the proposed terrane boundaries sutures preserves a common 1 4 1 03 ga tectonomagmatic history inconsistent with its origin as a post 1 4 ga collage of exotic tectonic blocks features which straddle the proposed 1 16 1 03 ga sutures from the central gneiss belt via the adirondack highlands to the mauricie area include 1 mesoproterozoic continental crust 1 5 1 4 ga forming the host and or basement to younger magmatic and supracrustal suites 2 a 1 35 1 3 ga continental arc remnants of which occur from the cmb boundary zone cmbbz in ontario to the appalachians in the united states built on the 1 5 1 4 ga continental crust 3 intrusions of 1 17 1 13 ga age in the central gneiss belt mafic suite and the adirondack highlands and their quebec extension amcg suite i e anorthosite massifs and related granitoids 4 relics of 1 18 1 14 ga sedimentary basins in the northwestern cmb and the mauricie area we propose that an alternative model can adequately account for the observed geology of this part of the grenville orogen wherein the rocks of the oqa segment were part of an andean type margin between 1 4 and 1 2 ga at 1 35 1 3 ga a continental magmatic arc was built upon the southeastern margin of laurentia represented by the 1 5 1 4 ga mesoproterozoic continental crust the arc split at 1 3 ga forming an ensialic back arc basin relics of which now occur in the northwestern part of the cmb and the back arc basin was flanked to the southeast by an active 1 28 1 25 ga arc collision between the laurentian margin and another continent amazonia occurred at 1 2 ga resulting in closure of the back arc basin and initiation of thrusting along the cmbbz post collisional lithospheric shortening led to convective removal of thickened subcontinental lithosphere upper mantle melting and extension of the overlying crust resulting in widespread magmatic activity at 1 17 1 13 ga including emplacement of the amcg massifs crustal extension generated sedimentary basins now represented by the st boniface sediments in the mauricie area 1 18 to between 1 15 and 1 09 ga and the penecontemporaneous flinton group in the northwestern cmb renewed post collisional granulite facies shortening commenced at 1 12 ga manifested as nappes in the central gneiss belt and thrusting in the mauricie area continued post collisional shortening at 1 08 1 05 ga was more localised resulting in reactivation of thrusting in the cmbbz and initiation of the kinematically compatible tawachiche shear zone along the eastern border of the quebec extension of the adirondack highlands the characteristics of the oqa segment of the grenville orogen can all be accounted for in the context of 1 a 1 4 1 2 ga southeast facing andean type margin to a laurentian upper plate associated with northwest dipping subduction 2 continental collision at 1 2 ga and 3 subsequent continued post collisional shortening without invoking accretion of exotic terranes between 1 4 and 1 0 ga

strain paths during slaty cleavage formation the role of volume loss abstract strain analyses of slates commonly investigate the sequence of shapes that must have been superimposed to produce the observed strained state methods such as rf try to quantify the cleavage forming deformation and see through that component to examine any initial shape an alternative approach is to reverse this process by considering the variation in final shapes derived when plausible cleavage forming strain ellipsoids are superimposed on realistic initial shapes specifically a deformation involving both plane strain and volume loss may be superimposed on an initial shape formed by diagenetic flattening in this case the angle between bedding and the incipient cleavage plane is an important variable in controlling final ellipsoid shapes this approach has been adopted for a data set measured from the ordovician borrowdale volcanics in the english lake district results show that neither successive increments of plane strain without volume loss nor incremental plane strain plus volume loss adequately explain the observed pattern of final shapes one permissible solution is generated if increments of pure volume loss perpendicular to the incipient cleavage plane precedes plane strain distortion initial layer parallel shortening may therefore play an important part during cleavage development in these slates

from local to global scale control factors of wave attenuation in mangrove environments and the role of indirect mangrove wave attenuation abstract wave dissipation by drag forces is considered the dominant wave transformation process in fringe mangroves even though other process may be present furthermore mangrove loss generates vertical erosion and changes in the nearshore profile that can affect wave breaking whereas changes in vegetation density owing to species composition or disturbances may affect drag dissipation the aim of this study is to identify local and global geographical control factors of wave attenuation in mangrove environments and to assess the effect of nearshore profile modifications by mangrove loss on wave breaking dissipation bottom wave attenuation from breaking and shoaling the total wave energy attenuation rate and wave reflection were estimated using modeling pressure sensors and reflection coefficients respectively at sites with contrasting wave power bathymetric slope changes vegetation density and logging disturbance wave breaking changes by mangrove loss were estimated using wave evolution modeling under three successive slope increments by 0 7 in two background mangrove nearshore profiles the wave energy attenuation rate at the study sites was affected by incident wave height 28 76 epiphytic oyster presence vegetation density tidal inundation 41 55 and wave reflection from cliffs the last two variables explained the wave attenuation rate variability at a cliffed study site 61 70 whereas the last three variables explained the wave attenuation rate variability on a global scale 92 wave attenuation rates by vegetation and bottom friction were underestimated 2 59 from global scale data when wave shoaling was not considered the wave energy increased or moved further inland in unvegetated scenarios in comparison with vegetated shores in addition to drag forces mangroves can promote wave attenuation by inducing friction wave breaking and wave reflection from prop roots epiphytic organisms shallow nearshore profiles and cliffed edges respectively

isotopic constraints on emplacement age of anorthositic rocks of the marcy masiff adirondack mts new york the igneous emplacement age of anorthositic rocks comprising the marcy massif have been constrained by fixing minimum and maximum ages for their intrusion minimum ages have been fixed by a u pb dating of cores of air abraded zircons from the anorthosite 1113 ma b u pb dating of baddeleyite within the anorthosite 1087 ma c u pb dating of baddeleyite from an olivine metagabbro crosscutting marcy massif anorthosite 1109 ma d u pb zircon dating of jotunitic rocks crosscutting the marcy anorthosite massif 1143 pm 31 ma maximum emplacement ages are based upon a sheets of anorthositic rock crosscutting mangeritic charnockitic gneiss dated by u pb zircon at 1125 pm 10 ma 1134 pm 4 ma and 1135 pm 43 ma and b anorthosite related pyroxenite dikes crosscutting mangerite that contains xenoliths of identical pyroxenite these results constrain emplacement of the marcy anorthosite to 1113 1138 ma with the most probable age in the interval 1125 1135 ma this time of in