calcic amphibole equilibria and a new amphibole plagioclase geothermometer there is currently a dearth of reliable thermobarometers for many hornblende and plagioclase bearing rocks such as granitoids and amphibolites a semi empirical thermodynamic evaluation of the available experimental data on amphibole plagioclase assemblages leads to a new thermometer based on the aliv content of amphibole coexisting with plagioclase in silica saturated rocks the principal exchange vector in amphiboles as a function of temperature in both the natural and experimental studies is left na square 1 right a left alsi 1 right t1 we have analysed the data using 3 different amphibole activity models to calibrate the thermometer reactions 1 edenite 4 quartz tremolite albite 1 2 pargasite 4 quartz hornblende albite 2 the equilibrium relation for both 1 and 2 leads to the proposed new thermometer t frac 0 677p 48 98 y 0 0429 0 008314 ln k and k left frac si 4 8 si right x ab plag where si is the number of atoms per formula unit in amphiboles with p in kbar and t in k the term y represents plagioclase non ideality rtln ab from darken s quadratic formalism dqf with y 0 for xab 0 5 and y 8 06 25 5 1 xab 2 for xab 0 5 the best fits to the data were obtained by assuming complete coupling between al on the t1 site and na in the a site of amphibole and the standard deviation of residuals in the fit is 38 c the thermometer is robust to ferric iron recalculation procedures from electron probe data and should yield temperatures of equilibration for hornblende plagioclase assemblages with uncertainties of around 75 c for rocks equilibrated at temperatures in the range 500 1100 c the thermometer should only be used in this temperature range and for assemblages with plagioclase less calcic than an92 and with amphiboles containing less than 7 8 si atoms pfu good results have been attained on natural examples from greenschist to granulite facies metamorphic rocks as well as from a variety of mafic to acid intrusive and extrusive igneous rocks our analysis shows that the pressure dependence is poorly constrained and the equilibria are not suitable for barometry

experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

on vertical advection truncation errors in terrain following numerical models comparison to a laboratory model for upwelling over submarine canyons 1 submarine canyons which indent the continental shelf are frequently regions of steep up to 45 three dimensional topography recent observations have delineated the flow over several submarine canyons during 2 4 day long upwelling episodes thus upwelling episodes over submarine canyons provide an excellent flow regime for evaluating numerical and physical models here we compare a physical and numerical model simulation of an upwelling event over a simplified submarine canyon the numerical model being evaluated is a version of the s coordinate rutgers university model scrum careful matching between the models is necessary for a stringent comparison results show a poor comparison for the homogeneous case due to nonhydrostatic effects in the laboratory model results for the stratified case are better but show a systematic difference between the numerical results and laboratory results this difference is shown not to be due to nonhydrostatic effects rather the difference is due to truncation errors in the calculation of the vertical advection of density in the numerical model the calculation is inaccurate due to the terrain following coordinates combined with a strong vertical gradient in density vertical shear in the horizontal velocity and topography with strong curvature

postcumulus processes in layered intrusions during the postcumulus stage of solidification in layered intrusions fluid dynamic phenomena play an important role in developing the textural and chemical characteristics of the cumulate rocks one mechanism of adcumulus growth involves crystallization at the top of the cumulate pile where crystals are in direct contact with the magma reservoir convection in the chamber can enable adcumulus growth to occur to form a completely solid contact between cumulate and magma another important process may involve compositional convection in which light differentiated melt released by intercumulus crystallization is continually replaced by denser melt from the overlying magma reservoir this process favours adcumulus growth and can allow adcumulus growth within the pore space of the cumulate pile calculations indicate that this process could reduce residual porosities to a few percent in large layered intrusions but could not form pure monomineralic rocks intercumulus melt may also be replaced by more primitive melt during episodes of magma chamber replenishment dense magma emplaced over a cumulate pile containing lower density differentiated melt may sink several metres into the underlying pile in the form of fingers reactions between melt and matrix may lead to changes in mineral compositions mineral textures and whole rock isotope compositions another important mechanism for forming adcumulate rocks is compaction in which the imbalance of the hydrostatic and lithostatic pressures in the cumulate pile causes the crystalline matrix to deform and intercumulus melt to be expelled for cumulate layers from 10 to 1000 metres in thickness compaction can reduce porosities to very low values 1 and form monomineralic rocks the characteristic time scale for such compaction is theoretically short compared to the time required to solidify a large layered intrusion during compaction changes of mineral compositions and texture may occur as moving melts interact with the surrounding matrix both compaction and compositional convection can be interrupted by solidification in the pore spaces compositional convection will only occur if the rayleigh number is larger than 40 if the residual melt becomes lower in density and the convective velocity exceeds the solidification velocity measured by the rate of crystal accumulation in the chamber orthocumulates are thus more likely to form in rapidly cooled intrusions where residual melt is frozen into the pore spaces before it can be expelled by compaction or replaced by convection

aftershocks of the andreanof islands earthquake of june 10 1996 and local seismotectonics three questions have been addressed in connection with an mw 7 7 earthquake that occurred in the andreanof islands alaska on june 10 1996 first was there any variation in seismic activity rate during the previous five years that might have been diagnostic of the imminent occurrence of this event the answer based on the usgs pde catalog is no second though there were abundant pre event earthquakes and aftershocks on both sides of adak canyon why was there very little activity under the canyon itself a property that has been observed previously it is not possible to resolve the cause of the behavior with existing seismological data finally how does one explain the eastern group of aftershocks which fell within the zone of abundant aftershocks of the 1986 mw 8 andreanof islands earthquake when very little of the 1996 mainshock moment was released under or to the east of adak canyon one explanation of these aftershocks is that the recent aftershocks are late aftershocks of 1986 whose occurrence within a short time was induced by the stress pulse but not seismic slip from the 1996 earthquake though large earthquakes in the aleutians occur in distinct tectonic blocks the boundaries of these blocks may not always be defined reliably by aftershock zones

late mesozoic intrusive complexes in the coastal area of fujian se china the significance of the gabbro diorite granite association abstract the pingtan and daiqianshan igneous complexes southeastern china are typical of calc alkaline series developed at active continental margins these two complexes are dominated by granites or gabbros with minor diorites and granodiorites and these rock types closely coexisted both temporally and spatially the major and trace element signatures of gabbros indicate they were crystallised from high aluminium basaltic magmas which were generated from metasomatised upper mantle the typical metaluminous calc alkaline composition trace element patterns and sr nd isotopes indicate the granites in the complexes are i type granites which may have been generated from the deeper crust by a thermal contribution from the mantle field relationships petrography and geochemistry favour a mechanical mingling together with a limited chemical mixing between high aluminium basaltic magma and granitic magma resulting in the formation of diorites or granodiorites the essentially bimodal character of these complexes reflects the general character of back arc extensional magmatism which was induced by the subduction of the pacific plate beneath the eurasian continent in late mesozoic time

petrogenesis of the leo lake and lyndhurst plutons frontenac terrane central metasedimentary belt southeastern ontario canada the 1167 2 ma leo lake pluton located at the southern part of the frontenac terrane in central metasedimentary belt of southeastern ontario is a bimodal pluton that is dominated by olivine gabbro gabbro syenite and lesser monzonite the adjoining 1166 3 ma lyndhurst pluton is composed of syenite and granite and exhibits magma mingling even though geochemical data from both plutons suggest fractional crystallization as the main crystallization process magma mingling is evident in the lyndhurst pluton hornblende from the leo lake syenite yields a 40ar 39ar age of 1120 6 ma and titanite from the adjacent st lawrence skarn yields a u pb age of 1147 8 ma the 40ar 39ar age indicates that the pluton cooled to 550 c at a rate of ca 2 c ma following emplacement the two plutons are similar in petrology to several other granitic syenitic and monzonitic intrusions of the frontenac suite in the frontenac terrane moreover the spatial distribution textural features and geochemistry indicate

dynamics of advection driven upwelling over a shelf break submarine canyon 1 the response over a submarine canyon to a several day upwelling event can be separated into three phases an initial transient response a later much longer steady advection driven response and a final relaxation phase for the advection driven phase over realistically steep deep and narrow canyons with near uniform flow and stratification at rim depth we have derived scale estimates for four key quantities observations from 5 real world canyon studies and 3 laboratory studies are used to validate the scaling and estimate the scalar constant for each scale based on 4 geometric parameters of the canyon the background stratification the coriolis parameter and the incoming current we can estimate 1 the depth of upwelling in the canyon to within 15 m 2 the deep vorticity to within 15 and 3 the presence absence of a rim depth eddy can be determined based on laboratory data 4 the total upwelling flux can also be estimated the scaling analysis shows the importance of a rossby number based on the radius of curvature of isobaths at the upstream mouth of the canyon this rossby number determines the ability of the flow to cross the canyon isobaths and generate the pressure gradient that drives upwelling in the canyon other important scales are a rossby number based on the length of the canyon which measures the ability of the flow to lift isopycnals and a burger number based on the width of the canyon that determines the likelihood of an eddy at rim depth generally long canyons with sharply turning upstream isobaths strong incoming flow small coriolis parameter and weak stratification have the strongest upwelling response

mean circulation and high frequency flow amplification in the sable gully abstract the sable gully a broad shelf break submarine canyon approximately 40 km east of sable island on the eastern scotian shelf separates banquereau and sable island banks unique among canyons on the eastern canadian continental shelf because of its depth steep slopes and extension far onto the shelf its ecological significance and increasing human pressures led to its designation in 2004 under canada s oceans act as the first marine protected area mpa in the atlantic region to improve the state of knowledge of the gully mpa a multi disciplinary field program was carried out in 2006 07 the physical oceanographic component consisted of the deployment april 2006 and recovery august 2007 of four current meter moorings and ctd surveys analysis of this 16 month mooring deployment demonstrates that the mean circulation above the canyon rim 200 m is characterized by a southwestward flow that appears unaffected by the canyon topography there is also some indication of the existence of an eddy at rim depth below 500 m the circulation is dominated by an upcanyon flow of order 0 02 m s 1 at the mooring array halfway between the canyon head and mouth the mean 200 m bottom transport towards the head of the gully was estimated as 35 500 m3 s 1 implying an upwelling velocity of 1 7 10 4 m s 1 14 m d 1 over the area results also show bottom intensified tidal flows and non linear constituents due to the interaction of k1 o1 m2 and s2 components along the thalweg of the canyon the strong overtides and compound tides observed in the gully make it unique among canyons further analyses provide evidence of enhanced mixing in the gully kv 180 10 4 m2 s 1 which is approximately 20 times that observed on the adjoining scotian shelf total variance of the currents in the gully is about 2 5 times greater than that observed on the nearby continental slope with an equivalent water depth

thermodynamic calculation of emplacement pressures for batholithic rocks california implications for the aluminum in hornblende barometer the aluminum in hornblende ah barometer has been widely used to estimate the emplacement pressure p of granitic rocks application of the barometer has remained controversial because the controls on the aluminum content of hornblende imposed by temperature t magma composition and fluid composition remain incompletely understood in this paper the p t conditions of equilibration for 19 rocks from the mesozoic batholiths of california are estimated by simultaneous evaluation of 1 the p sensitive reaction tremolite phlogopite 2 anorthite 2 albite 2 pargasite 6 quartz k feldspar and 2 previously published amphibole plagioclase thermometer equilibria p estimates for the batholiths range from 1 2 to 7 4 kbar and are consistent with independent geologic evidence the highest p samples 5 1 7 4 kbar are located near the san andreas fault furthermore it appears that regional p gradients determined by previous ah barometry studies are valid but that the absolute values of the p estimates will need to be revised somewhat 1 5 kbar i suggest that the method of this study provides a viable thermodynamics based alternative to conventional ah barometry that requires no a priori assumptions about t or bulk composition

reexamining the source parameters of the 2010 ml 6 4 jiasian taiwan earthquake using the inversion of teleseismic p waves abstract a moderate sized earthquake ml 6 4 named the 2010 jiasian earthquake occurred in southern taiwan on march 4 2010 reports from several institutes indicated that the jiasian earthquake had focal depths of 18 28 km and ruptures with a thrust mechanism however modeling of teleseismic p waves in previously reported source parameters revealed significant differences between the observed and synthetic p waves therefore this study reexamined the source parameters of the 2010 jiasian earthquake using a teleseismic p wave inversion method the inversion showed that the earthquake had a depth of 22 km a best double couple of 304 28 48 and 170 70 110 strike dip rake and a seismic moment of 2 31 1018 n m mw 6 2 rupture directivity analysis also suggested that the earthquake was a unilateral faulting event on the fault plane of 304 28 48 the average source duration and the rupture length were 5 2 s and 19 4 km respectively the optimal rupture direction measured counterclockwise from the strike on the fault plane was 347 which was projected onto the surface to correspond to the northwestward rupture consistent with the aftershock distribution the analysis also suggested a high rupture velocity during faulting probably approximate to the crustal s wave velocity which may have resulted in a low static stress drop and caused the differences in pga distribution along the direction of earthquake rupture the dip angles of the fault plane estimated from the initial and centroid depths showed the initial rupture at a lower dip angle plane and the later rupture at a higher dip angle one

a simple three dimensional model of the circulation off newfoundland a simple numerical model is developed to study the three dimensional structure of the steady circulation off newfoundland the model uses linear dynamics a vertical eddy viscosity to parameterize the vertical mixing and a linear parameterization of bottom friction in which the bottom stress is related to the bottom velocity realistic geometry and bottom topography are included the results presented here are for an ocean of uniform density the model is driven by specifying the sea level along the northern boundary the inflow corresponding to the inshore and offshore branches of the labrador current the model can reproduce the circulation pattern found by greenberg and petrie 1988 who used a vertically integrated nonlinear primitive equation model it also enables dynamical interpretation to be given in terms of flow along f h contours and frictional diffusion across these contours in this connection we investigate the dependence on the friction parameters of the transport through several sections we also examine the onshore offshore mass exchange over the southeastern edge of the grand banks we find that the model labrador current flowing southward along the shelf break leads to an onshelf flux in the upper part of the water column and an offshelf flux in the bottom ekman layer this is caused by the frictional torque and leads to an along slope decay of the current amplitude finally the limitations of the model and plans for its further development are discussed

using the effects of depth phases on p wave spectra to determine earthquake depths for shallow earthquakes the surface reflected depth phases pp and sp arrive shortly after the primary arrival and the time separation among the three phases can be used to determine the origin depth of the earthquake to model the relative arrival times and amplitudes of these phases and the core reflections and water column reverberations for a given earthquake we construct stick seismograms using the iaspei91 velocity model and the harvard cmt focal mechanisms at the distances and azimuths of the recording seismometers while the differing arrival times and amplitudes are features observable in the time series they also affect the spectrum and we compute the spectrum for a time window that includes the p wave and subsequent arrivals we quantify the effects of variations in these properties over the focal sphere in terms of differences in the slope of the log spectrum at different stations to determine the depth of an earthquake we compare our observed spectral variations with the predicted spectral variations for earthquakes originating at depths within 30 km of the pde depth and identify the depth with the smallest l1 misfit as the true earthquake depth we demonstrate the effectiveness of this method by applying it to a group of 35 thrust earthquakes in the aleutian arc near the andreanof islands but we also describe some complications introduced by strongly directive ruptures as illustrated for the 1995 jalisco mexico event online material observed and predicted variations in pulse width for aleutian island earthquakes

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

noncharacteristic behavior and complex recurrence of large subduction zone earthquakes the last few years have been remarkable with respect to the number of large underthrusting earthquakes in subduction zones that reruptured plate boundary segments that failed in previous great events availability of modern seismic data for two consecutive large earthquakes rupturing the same portion of the plate interface provides the opportunity to compare the spatial distribution of moment release for both events such comparisons have been made for the plate boundary segments that failed in 1 the 1957 mw 8 6 1986 mw 8 0 and 1996 mw 7 9 aleutian islands earthquakes 2 the 1963 mw 8 5 and 1995 mw 7 9 kuril islands earthquakes 3 the 1971 mw 8 0 and 1995 mw 7 7 solomon islands earthquakes and 4 the 1968 mw 8 2 and 1994 mw 7 7 northern honshu earthquakes the spatial distribution of moment release for all four of the initial great earthquakes and two of the repeat events has been determined in previous studies here slip distributions for the three most recent events are determined from inversion of source time functions derived by empirical greens function analysis of long period surface waves and broadband body waves comparisons of the spatial distribution of moment release for sequential earthquake ruptures reveal considerable differences in the pattern of recurrent fault slip the 1994 northern honshu and 1995 solomon islands earthquakes primarily fill in areas of slip deficit left by their preceding events rather than rerupture identical asperities the 1995 kuril islands and the 1996 aleutian islands earthquakes both rerupture portions of an asperity distribution defined by preceding events but with variable amounts of slip this study provides the first direct evidence that recurrence of large circum pacific plate boundary events is more complex than repeat rupture of dominant asperities recurrent fault slip for the four plate boundary segments studied does not support characteristic slip models either where failure on an entire fault segment occurs repeatedly in events with nearly identical rupture lengths locations and slip magnitudes or where failure of individual asperities occurs with identical slip functions through consecutive earthquake cycles these sequential slip patterns are not consistent with physical models of earthquake rupture where slip complexity is exclusively controlled by invariant geometric and or material heterogeneity but suggest that dynamic considerations are also important

timescales of orogeny jurassic construction of the klamath mountains an electronic supplement of this material may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type exit to leave the system paper 94ycj2454 timescales of orogeny jurassic construction of the klamath mountains b r hacker m m donato c g barnes m o mcwilliams and w g ernst diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order classical interpretations of orogeny were based on relatively imprecise biostratigraphic and isotopic age determinations that necessitated grouping apparently related features that may in reality have been greatly diachronous isotopic age techniques now have the precision required to resolve the timing of orogenic events on a scale much smaller than that of entire mountain belts forty five new 40ar 39ar ages from the klamath mountains illuminate the deformation metamorphism magmatism and sedimentation involved in the jurassic construction of that orogen leading to a new level of understanding regarding how preserved orogenic features relate to ancient plate tectonic processes the new geochronologic relationships show that many jurassic units of the klamath mountains had 200 ma or older volcanoplutonic basement subsequent formation of a large 170 ma arc was followed by contractional collapse of the arc collision with a spreading ridge may have led to large scale nw se extension in the central and northern klamaths from 167 to 155 ma coincident with the crystallization of voluminous plutonic and volcanic suites marked cooling of a large region of the central klamath mountains to below 350 c at 150 ma may have occurred as the igneous belt was extinguished by subduction of colder material at deeper structural levels these data demonstrate that the klamath mountains and perhaps other similar orogens were constructed during areally and temporally variant episodes of contraction extension and magmatism that do not fit classical definitions of orogeny

differential unroofing within the central metasedimentary belt of the grenville orogen constraints from 40ar 39ar thermochronology an 40ar 39ar thermochronological investigation of upper greenschist to granulite facies gneiss amphibolite and marble was conducted in the central metasedimentary belt cmb ontario to constrain its cooling history incremental 40ar 39ar release spectra indicate that substantial differential unroofing occurred in the cmb between 1000 and 600 ma a consistent pattern of significantly older hornblende and phlogopite 40ar 3ar cooling ages on the southeast sides of major northeast striking shear zones is interpreted to reflect late displacement due to extensional deformation variations in hornblende 40ar 39ar age plateaus exceeding 200 ma occur over distances less than 50 km with major age discontinuities occurring across the robertson lake shear zone and the sharbot lake mylonite zone which separate the sharbot lake terrane from the elzevir and frontenac terranes extensional displacements of up to 14 km are inferred between the frontenac and elzevir terranes of the cmb no evidence for significant post argon closure vertical displacement is indicated in the vicinity of the perth road mylonite within the frontenac terrane variations of nearly 100 ma in phlogopite 40ar 39ar plateau ages occur in undeformed marble on either side of the bancroft shear zone phlogopites from sheared and mylonitized marble within the shear zone yield 40ar 39ar diffusional loss profiles but have older geologically meaningless ages thought to reflect incorporation of excess argon by 900 ma southeast directed extension was occurring throughout the cmb possibly initiated along previous zones of compressional shearing an easterly migration of active zones of extension is inferred possibly related to an earlier overall easterly migration of active zones of regional thrusting and easterly migration of an ancient subduction zone the duration of extensional shearing is not well constrained but must have ceased before 600 ma as required by the deposition of overlying undeformed cambrian and or ordovician sedimentary rocks

a two layer model of shelfbreak jets with application to the labrador current abstract the role played by bottom friction bottom slope effect and density mixing in exchange between the shelf and a frontal jet is examined in the light of a two layer model the model uses linear dynamics and bottom and interfacial friction to parameterize vertical momentum mixing and newtonian cooling to parameterize density mixing it is assumed that the dynamics approximately obey csanady s diffusion equations in both shelf and frontal regions assuming a velocity profile appropriate to a shelfbreak jet the authors examine how the various dynamical factors can affect cross shelf exchange in the frontal region and derive some front solutions by assuming a simple torque balance it is shown that the effect and density mixing both produce onshore geostrophic fluxes and counteract the offshore flux due to the frictional torque consideration of the conditions at the intersection point of the front with the bottom shows an important role of the jebar effect in changing the cross shelf circulati

the formation of a subsurface anticyclonic eddy in the peru chile undercurrent and its impact on the near coastal salinity oxygen and nutrient distributions the formation of a subsurface anticyclonic eddy in the peru chile undercurrent pcuc in january and february 2013 is investigated using a multi platform four dimensional observational approach research vessel multiple glider and mooring based measurements were conducted in the peruvian upwelling regime near 12 30 s the dataset consists of 10000 glider profiles and repeated vessel based hydrography and velocity transects it allows a detailed description of the eddy formation and its impact on the near coastal salinity oxygen and nutrient distributions in early january a strong pcuc with maximum poleward velocities of 0 25 m s at 100 to 200 m depth was observed starting on january 20 a subsurface anticyclonic eddy developed in the pcuc downstream of a topographic bend suggesting flow separation as the eddy formation mechanism the eddy core waters exhibited oxygen concentrations 1 mol kg an elevated nitrogen deficit of 17 mol l and potential vorticity close to zero which seemed to originate from the bottom boundary layer of the continental slope the eddy induced across shelf velocities resulted in an elevated exchange of water masses between the upper continental slope and the open ocean small scale salinity and oxygen structures were formed by along isopycnal stirring and indications of eddy driven oxygen ventilation of the upper oxygen minimum zone were observed it is concluded that mesoscale stirring of solutes and the offshore transport of eddy core properties could provide an important coastal open ocean exchange mechanism with potentially large implications for nutrient budgets and biogeochemical cycling in the oxygen minimum zone off peru

upwelling flow dynamics in long canyons at low rossby number 1 submarine canyons topographic features incising the continental slope vary in both shape and size the dynamics of short canyons have been observed and described in the field in the laboratory and with numerical simulations flow within long canyons such as juan de fuca canyon located between vancouver island and washington state in the pacific northwest is less well understood physical models of both long and short canyons have been constructed to understand the upwelling dynamics in long canyons and how upwelling changes as compared with the dynamics of short canyons at low rossby number stratification and rotation both important parameters in determining the dynamics in canyons can be controlled and scaled accordingly for replication of oceanic conditions the physical model is spun up to an initial rotation rate and the flow is forced by increasing the rotation rate over the equivalent of several days flow visualization is used to determine the strength and location of upwelling the strength and mechanisms generating vorticity as well as the differences between the flow within the long and short canyons the pattern of upwelling between the two canyons is significantly different in the horizontal with upwelling occurring through the canyon head in the short canyon and upwelling occurring close to the mouth along the downstream rim in the long canyon at high rossby number upwelling is similar in both the long and short canyon and is driven by advection however as rossby number decreases the flow in the long canyon is more strongly affected by the strong convergence of the isobaths near the canyon than by advection alone

numerical study of the circulation in a steep canyon off the catalan coast western mediterranean we use a limited area fine resolution primitive equation model to carry out a case study of the circulation in the steep and narrow blanes canyon located off the catalan coast western mediterranean this area is characterized by a permanent along slope density driven current and strong northerly and easterly wind bursts in autumn in a first step the slope current is allowed to adjust to the bottom topography leading to a stationary circulation pattern which presents large vertical variations related to the canyon geometry in the surface layer the strong stratification allows the current to flow straight over the canyon rim ignoring bottom topography in the intermediate layer the canyon is wide and waters are isolated in a geostrophic anticyclonic eddy maintained by friction at the edge of the slope current in the deep layer the canyon is narrow and a topographic upwelling lifts bottom waters toward the canyon head in a second step the circulation is forced by easterly along shore with the coast on its right and northerly seaward 1 day wind bursts which induce significant vertical and cross shore motions steered by the bottom slope this ageostrophic circulation is substantially amplified in the canyon where the flow pattern presents large amplitude oscillations characterized by a downwelling upwelling during the easterly northerly wind burst followed by a rebound upwelling downwelling as the wind relaxes the upwelling induced by the northerly wind burst is capable of renewing waters trapped in the canyon eddy our results appear to be in fairly good agreement with in situ physical and biogeochemical data collected in blanes canyon and comparable canyons of the world ocean the three dimensional features obtained in this study can explain some of the observed patterns of larvae distribution and exchanges between the coastal zone and the open sea

wind and topographic effects on the labrador current at carson canyon carson canyon is located on the eastern slope of the grand bank and is about 10 km wide 80 km long and 700 m deep where it intersects the shelf break 110 m data from june of 1980 and 1981 are interpreted in terms of steady and time dependent wind driven interactions of the labrador current with the canyon the mean velocity field is estimated from direct measurements and the dynamic topography relative to 200 dbar up and downstream of the canyon the flow was predominantly along isobath with speeds of 0 20cm s near the shelf break 10 m above bottom and 48 cm s at the velocity axis over the 500 m isobath a 20 m thick cold core of 1 c water upstream of the canyon separated into inner and outer cold cores over the canyon axis and coalesced to reform a single core downstream the degree to which the canyon perturbed the mean flow changed with position both along and perpendicular to the canyon axis with along isobath flow near the shelf break cross isobath flow on the upstream side and cross canyon flow in the center further off shelf the flow remained undisturbed by the canyon divergence of the mean flow in the vicinity of a secondary head on the upstream side is indicated by the measurements implying steady upwelling this is supported by a 0 9 cm s residual near bottom flow toward the secondary head a single upwelling event lasting 5 d was observed following 18 23 m s southwesterly winds of about 0 5 d duration current reversal at the shelf break occurred soon after the high speed winds ceased following by abrupt temperature 2 8 c and salinity 1 2 ppt increases up to 1 d later at 167 m depth in the central canyon region isohalines rose at rates of 0 2 0 5 cm the reversal was baroclinic the labrador current continued to flow southwestward but with reduced speeds and the reversal itself was confined to a layer centered at about 130 m depth the reversal and decreased upper layer speeds probably arise from the barotropic response to a wind induced decrease in sea surface slope the upwelling represents the slower baroclinic response steady upwelling in the presence of a shelf break jet in the upper layer is modeled using a two layer system and a vertical wall at the shelf break the model results differ from the usual no jet case upwelling is suppressed by 26 at the coast but extends to greater distances offshore

near inertial internal waves observed on the outer shelf in the middle atlantic bight in the wake of hurricane belle abstract on 10 august 1976 hurricane belle passed rapidly over the highly stratified shelf of the new york bight records from aanderaa current meter moorings show that the response to the hurricane depended strongly on bathymetry at deeper stations 70 m depth intense first mode internal near inertial oscillations were generated at frequencies 1 less than the local inertial frequency at shallower stations 50 m depth only weak heavily damped second mode oscillations were observed in the current records with no corresponding inertial signals in temperature in the hudson shelf valley inertial motion occurred only near the surface this was probably due to topographic effects the divergence and curl of the wind stress contributed equally to the forcing the response at the deeper stations is consistent with geisler s 1970 theory for the open ocean in which a hurricane leaves a wake of internal inertial oscillations if it travels faster than the internal phase speed and if its horizontal s

application of a cepstral f statistic for improved depth estimation the depth of a seismic event can be determined using peaks corresponding to depth phase delay times found in the cepstrum of the seismic signal until now however there has been no method available to determine the significance of various peaks in the cepstrum we have formulated a cepstral f statistic by using a classic approach to detect a signal in a number of stationarily correlated time series the method attaches a statistical significance level to peaks in the cepstrum of seismic data caused by echoes in the signal the method is particularly well suited for detecting depth phase echoes pp and sp recorded on regional seismic arrays detections determined from the peaks in the cepstral f statistic are then stacked as a function of pp p and sp p travel times predicted from the iaspei global 1 d model kennett and engdahl 1991 using a modification of the method of depth phase beamforming woodgold 1998 murphy et al 1999 tests on synthetic data show the method is most successful when the p wave arrival has a signal to noise ratio snr greater than 4 7 and the depth phase exhibits an snr greater than 2 tests on complex regional data suggest that the depth phase snr must be between 4 and 8 for consistent successful application of the method we tested the method by using events from the hindu kush region of afghanistan with well determined depths as recorded on arrays at teleseismic distances we determined the correct depths for 14 of the 19 events in this dataset 74 success rate and we determined incorrect depths for two events for a false alarm rate of 10 5 the difference between the depths calculated by the cepstral method and the prototype international data center pidc decrease with increasing magnitude for events with m b 3 8 the average difference between the cepstral and pidc depths was 7 9 km with no false alarms to test the operational capabilities of this method as a tool for data center use we first analyzed 32 events that occurred on 12 february 2000 as located by the pidc additionally we analyzed 29 events located in central and south america between 05 may and 15 june 2000 with event characteristics published by the international data center idc most of these events were also located by the national earthquake information center our method determined statistically significant depths for 40 of these 61 events with 11 having a low snr at three or more recording arrays while another 10 were either too shallow for analysis or did not exhibit depth phases only seven of the 61 events had depth phases listed in the reviewed event bulletin produced by the pidc and idc for these events the average difference between the reported and cepstral f statistic depths was 4 0 km the pidc idc fixed the depth of 26 of 61 events to 0 0 the cepstral f statistic method determined depths ranging from 16 to 92 km for 15 of the events that had been constrained as surface foci overall we believe the method would be most valuable when used by analysts to detect possible depth phases that could then verify or improve network calculated focal depths manuscript received 25 february 2001

dynamics of the 2015 m7 8 nepal earthquake the 2015 m7 8 nepal earthquake ruptured part of the main himalayan thrust beneath kathmandu to study the dynamics of this event we compute p wave spectra of the main shock and of two large aftershocks to estimate stress drop and radiated energy we find that surface reflections depth phases of these shallow earthquakes produce interference that severely biases spectral measurements unless corrections are applied measures of earthquake dynamics for the main shock are within the range of estimates from global and regional earthquakes we explore the azimuthal and temporal variations of radiated energy and highlight unique aspects of the m7 8 rupture the beginning of the earthquake likely experienced a dynamic weakening mechanism immediately followed by an abrupt change in fault geometry correlation of backprojection results with frequency dependent variations in the radiated energy rate and with the suggested geometry of the main himalayan thrust yields new constraints on dynamic ruptures through geometrical barriers

the pan african toro complex northern nigeria magmatic interactions and structures in a bimodal intrusion the toro complex is one of the pan african older granites of nigeria first described as a reversely zoned pluton made of a central dioritic mass surrounded by a broad granitic rim it has been thoroughly reinvestigated both from the petrographic and structural points of view with the help of systematic anisotropy of magnetic susceptibility ams measurements the granite main body is a hornblende biotite porphyritic monzogranite characterized by an early submagmatic fabric displaying a concentric pattern of foliations and west plunging lineations stage 1 this fabric is overprinted by a later one due to solid state strain along north south subvertical dextral shear zones stage 2 in the vicinity of the diorite an evengrained granite displays magmatic structures that are contemporaneous with this strike slip event the diorite granite contact is a complex zone where field petrographic and geochemical data enable recognition of the effects of mixing and mingling between a mafic and a felsic magma tonalites cropping out within this contact zone are interpreted as hybrid rocks the reverse zonation of the diorite itself is also the result of some hybridization process magmatic interactions mainly resulted from in situ infiltration of granitic liquid into the dioritic mass the detailed history of this bimodal intrusion began with the emplacement of the granitic magma acquiring a first stage fabric before full crystallization of the granitic core intrusion of the dioritic magma permitted reheating of the granitic magma that then crystallized with specific structural characters the second stage structures whether characterized by magmatic fabric near the diorite or by solid state strain features in north south shear zones elsewhere in the granite are related to late pan african dextral strike slip tectonics in the basement of northern nigeria the bimodal toro complex is therefore considered as a late pan african syntectonic pluton

transient wind driven upwelling in a submarine canyon a process oriented modeling study 1 a hydrodynamic model is employed to study flow near a submarine canyon during conditions of upwelling favorable coastal winds findings reveal that up canyon flow is the rapid geostrophic adjustment to barotropic pressure gradients establishing across the canyon stratification leads to the formation of a cyclonic eddy within the canyon trapping neutrally buoyant matter and limits the upwelling depth only when a strong seasonal pycnocline is located below shelf break depth typical speeds of up canyon flow are 10 30 cm s constrained by the timescale of synoptic weather patterns 5 days only stronger events high upwelling index can move slope water from a depth 300 m onto the continental shelf and close toward the coast where it can be lifted into surface layers during a subsequent upwelling event

microgranitoid enclaves in granites globules of hybrid magma quenched in a plutonic environment microgranitoid enclaves autoliths cognate xenoliths mafic inclusions are common in high level granitoid plutons they have relatively fine grained igneous microgranitoid microstructures1 and many show evidence of having flowed in a magmatic condition2 these features counter interpretations that the enclaves represent transformed solid fragments of diverse wall rocks3 5 or restite6 11 an alternative interpretation is that the enclaves represent globules of mafic magma that have mingled commingled and quenched in the granitoid host magma12 16 a detailed review of the literature occurrence morphology and composition of micro granitoid enclaves strongly supports this view hut indicates that the enclave magmas range in composition from mafic to felsic and that magma mixing may be involved in their formation17 i summarize here the main features of microgranitoid enclaves and briefly outline the possible processes leading to their incorporation as magma globules in the host granitoid

the 1995 colima jalisco mexico earthquake mw 8 a study of the rupture process in this study we map rupture characteristics of the great shallow thrust earthquake of october 9 1995 which caused extensive damage to the coastal towns of colima and jalisco to isolate the earthquake rupture details we deconvolve surface waves with two empirical green s functions the aftershock of october 12 1995 mw 5 9 and the foreshock of october 6 1995 mw 5 8 from the corresponding mainshock records specifically we use a spectral water level deconvolution to obtain 80 apparent source time functions astf at 62 stations rayleigh and love waves durations of the astf as a function of azimuth indicate that the rupture propagated toward n70 w the duration of the source time function stf is around 62 s with a large pulse at 45 s to map the main characteristics of the rupture we use an inverse radon transform of the astfs assuming a ribbon fault model aligned in the direction of the rupture propagation our analysis indicates that the rupture initiated about 20 km offshore of manzanillo and propagated almost unilaterally for 150 km towards n70 w with an average rupture velocity of approximately 2 8 km s the earthquake was a composite of three significant subevents the largest occurred 45 s after the initiation of the rupture and was located about 100 km away this result is in good agreement with the inversion of deformation data measured with gps melbourne et al 1997

predominance of unilateral rupture for a global catalog of large earthquakes the manner in which an earthquake rupture propagates across a fault reflects both the initial properties of the fault and the dynamical stresses produced by the rupture we quantify the propagation of an earthquake rupture using the second moments of the earthquake space time distribution in particular the second moments provide a simple way to differentiate between approximately bilateral and predominantly unilateral ruptures we determined the second moments for a catalog of m w 7 earthquakes that have occurred since 1994 the results show that approximately 80 of large shallow ruptures are predominantly unilateral our result agrees well with strong motion inversions from previous studies on moderate and large earthquakes the predominance of unilateral propagation in large earthquakes is explained by a simple characteristic earthquake model in which large events rupture an entire structurally defined fault segment and nucleation points are uniformly distributed along the fault the predominance of unilateral rupture may also be enhanced by the dynamic stress field produced by contrasts in the elastic properties between the two sides of plate boundary faults manuscript received 16 november 2001

current response at the shelf break to transient wind forcing an analysis of current meter and hydrographic data collected from an array of moorings situated at the shelf break off nova scotia is presented in particular the focus is on the ocean response to moderate 10 to 20m s 1 transient winds of two or more days duration blowing parallel to the local bathymetry under these conditions upwelling occurs at the shelf break from depths of 400 m and with peak vertical velocities of about 2 mm s 1 the upwelling appears to be confined to within 10 km of the slope acceleration coriolis and pressure gradient terms are important for the along and cross slope momentum balances local topographic variations contribute to the anomalously large bottom currents on the shoreward side of the shelf break both coastal sea level and the shelf break circulation respond coherently to synoptic wind forcing but quantitative agreement with two layer shelf models is poor

water saturated and undersaturated melting of metaluminous and peraluminous crustal compositions at 10 kb evidence for the origin of silicic magmas in the taupo volcanic zone new zealand and other occurrences

new perspectives on self similarity for shallow thrust earthquakes scaling of dynamic rupture processes from small to large earthquakes is critical to seismic hazard assessment large subduction earthquakes are typically remote and we mostly rely on teleseismic body waves to extract information on their slip rate functions we estimate the p wave source spectra of 942 thrust earthquakes of magnitude mw 5 5 and above by carefully removing wave propagation effects geometrical spreading attenuation and free surface effects the conventional spectral model of a single corner frequency and high frequency falloff rate does not explain our data and we instead introduce a double corner frequency model modified from the haskell propagating source model with an intermediate falloff of f 1 the first corner frequency f1 relates closely to the source duration t1 its scaling follows m0 t13 for mw 7 5 and changes to m0 t12 for larger earthquakes an elliptical rupture geometry better explains the observed scaling than circular crack models the second time scale t2 varies more weakly with moment m0 t25 varies weakly with depth and can be interpreted either as expressions of starting and stopping phases as a pulse like rupture or a dynamic weakening process estimated stress drops and scaled energy ratio of radiated energy over seismic moment are both invariant with seismic moment however the observed earthquakes are not self similar because their source geometry and spectral shapes vary with earthquake size we find and map global variations of these source parameters

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

petrogenesis of a high temperature metamorphic terrane a new tectonic interpretation for the north dabieshan central china the northern dabie terrane consists of a variety of metamorphic rocks with minor mafic ultramafic blocks and abundant jurassic cretaceous granitic plutons the metamorphic rocks include orthogneisses amphibolite migmatitic gneiss with minor granulite and metasediments no eclogite or other high pressure metamorphic rocks have been found granulites of various compositions occur either as lenses blocks or layers within clinopyroxene bearing amphibolite or gneiss the palaeosomes of most migmatitic gneisses contain clinopyroxene melanosomes and leucosomes are intimately intermingled tightly folded and may have formed in situ the granulites formed at about 800 830 c and 10 14 kbar and display near isothermal decompression p t paths that may have resulted from crust thickened by collision plagioclase amphibole coronae around garnets and matrix pi hbl assemblages from mafic and ultramafic granulites formed at about 750 800 c partial replacement of clinopyroxene by amphibole in gneiss marks amphibolite facies retrograde metamorphism amphibolite facies orthogneisses and interlayered amphibolites formed at 680 750 c and c 6 kbar formation of oligoclase orthoclase antiperthite after plagioclase took place in migmatitic gneisses at t 490 c in response to a final stage of retrograde recrystallization these p t estimates indicate that the northern dabie metamorphic granulite amphibolite facies terrane formed in a metamorphic field gradient of 20 35 c km 1 at intermediate to low pressures and may represent the sino korean hangingwall during triassic subduction for formation of the ultrahigh and high p units to the south post collisional intrusion of a mafic ultramafic cumulate complex occurred due to breakoff of the subducting slab

the role of manganese in the paragenesis of magmatic garnet an example from the old woman piute range california a reply strongly peraluminous plutons of the old woman piute range southeastern california display the differentiation sequence muscovite biotite granite rightarrow muscovite garnet biotite granite rightarrow garnet muscovite granite rightarrow garnet muscovite aplite and pegmatite the garnets show no evidence of reaction but biotites in garnet bearing rocks are rimmed by muscovite metamorphic assemblages in the country rocks suggest pressures of emplacement less than 4 5 kb the plutons become relatively enriched in manganese with differentiation whole rock ratios of molar mn fe mg increase from 0 01 in least felsic garnet free rocks to 0 3 in most felsic garnet rich rocks mno concentrations show a corresponding rise in biotites 0 4 to 1 8 wt and less clearly in garnets 9 to 25 the differentiation sequence textural relations and mineral and whole rock compositions suggest that garnet paragenesis was controlled by the reaction biotite mn rich liquid rightarrow garnet

the use of waveform shapes to automatically determine earthquake focal depth earthquake focal depth is an important parameter for rapidly determining probable damage caused by a large earthquake in addition it is significant both for discriminating between natural events and explosions and for discriminating between tsunamigenic and nontsunamigenic earthquakes for the purpose of notifying emergency management and disaster relief organizations as well as issuing tsunami warnings potential time delays in determining source parameters are particularly detrimental we present a method for determining earthquake focal depth that is well suited for implementation in an automated system that utilizes the wealth of broadband teleseismic data that is now available in real time from the global seismograph networks this method uses waveform shapes to determine focal depth and is demonstrated to be valid for events with magnitudes as low as approximately 5 5

spin up and the effects of a submarine canyon applications to upwelling in astoria canyon 1 a parameterization for the on shelf mass flux induced by upwelling through a shelf break submarine canyon is estimated by laboratory spin up experiments we determine the effects of a submarine canyon on flow evolution implicitly by measuring the topographic drag force in the context of a heuristic model trials were performed across a range of values for the shelf break velocity coriolis frequency and buoyancy frequency assuming the drag force within the canyon is balanced locally by rotation we propose a parameterization for upwelling through a canyon provided that the coriolis frequency buoyancy frequency shelf break velocity and canyon dimensions at the shelf break depth are known we use our results to compare wind forced and canyon forced upwelling over astoria canyon off the coast of washington state the analysis suggests that canyon forced upwelling through astoria canyon is of equal importance to wind forced upwelling directly above it on seasonal scales

oxygen isotope constraints on terrane boundaries and origin of 1 18 1 13 ga granitoids in the southern grenville province granitic rocks related to 1 18 to 1 13 ga anorthosite mangerite charnockitegranite plutonism stitch three terranes in the southwestern grenville province adirondack highlands morin terrane frontenac terrane elzevir terrane because of the refractory nature of zircon zrn analysis of oxygen isotope ratios of dated igneous zircon from these rocks allows calculation of 18 o values of original magmas even if the rocks were subjected to late magmatic assimilation postmagmatic alteration or metamorphism documented variability in 18 o zrn for these granitic rocks corresponds to their geographic location seven plutons from the central frontenac terrane ontario have a high average 18 o zrn 11 8 1 0 which corresponds to 18 o magma values of 12 4 14 3 in contrast twenty seven other plutons and dikes of this suite new york ontario and quebec average 18 o zrn 8 2 0 6 with a typical igneous range of 8 6 to 10 3 for 18 o magma values high 18 o values in the frontenac terrane are some of the highest magmatic oxygen isotope ratios recognized worldwide but these plutons are not unusual with respect to whole rock chemistry or radiogenic isotope compositions such high 18 o values can result from mixing between paragneiss 18 o 15 and hydrothermally altered basalts and or oceanic sediments 18 o 12 in the source region we propose that high 18 o hydrothermally altered basalts and sediments were subducted or underthrust to the base of the frontenac terrane during closure of an ocean basin between the frontenac terrane and the adirondack highlands at or prior to 1 2 ga

the origin of the cretaceous gabbros in the fujian coastal region of se china implications for deformation accompanied magmatism the cretaceous gabbros in the fujian coastal region southeastern china experienced different magmatic and tectonic processes associated with deformation of the changle nanao shear zone group 1 gabbros 115 ma show marked lile e g sr ba and k and lree enrichment and hfse e g ta nb zr and hf depletion strongly suggesting an island arc affinity the parental magma of group 1 gabbros arguably derived from an arc related source mantle modified by previous subduction rose into and interacted with the coexisting syntectonic granitic magma generated during the main stage of shear zone deformation and produced the gabbro diorite granite complexes group 2 and 3 gabbros 106 95 ma possibly formed by coupling of the subduction modified source mantle with part of undepleted mantle e g nb enrichment in an extensional environment at the end of deformation their parental magmas did not undergo significant magma mixing but produced a cumulate nature all the three groups of gabbros were contaminated by crustal material during the processes of intrusion and emplacement

u pb zircon ages of granitoid rocks in the north dabie complex eastern dabie shan china the north dabie complex ndc comprises a high temperature metamorphic suite dominated by amphibolite facies granitoid orthogneiss intruded by voluminous granites u pb zircon dating on these rocks yields the following new results 1 two of the granitoid orthogneiss samples have early cretaceous protolith emplacement ages of 133 7 2 3 ma and 134 0 2 8 ma 2 an undeformed granodiorite intrusive into granitoid gneiss yields an emplacement age at 125 6 0 3 ma these early cretaceous ages entirely post date late triassic early jurassic continental subduction and exhumation evident in the neighboring ultrahigh and high pressure metamorphic terrains to the south in the dabie shan hence they do not support previous tectonic models that infer paleozoic or triassic protolith emplacement ages for these granitoid orthogneisses 3 a mylonitic granite from the northern boundary of the ndc yields a concordant age of 756 6 0 8 ma which is interpreted as magma emplacement age the concordance of this late

sharbot lake terrane and its relationships to frontenac terrane central metasedimentary belt grenville province new insights from u pb geochronology the sharbot lake terrane of the central metasedimentary belt in ontario comprises marbles minor tholeiitic basalts and siliciclastic rocks metamorphosed at low to moderate degrees and is intruded by several suites of mafic to felsic plutons gabbroic and associated monzogranitic phases of the lavant complex in northwestern parts of the terrane yield ages of 1224 2 ma for zircon and monazite and 1221 1211 ma for titanite the wolf grove structure a gneissic domain in the northeastern part of the area was migmatized and intruded by granites at 1168 ma prior to its tectonic juxtaposition on amphibolites and marbles of the sharbot lake terrane correlative events recorded by gneiss quartzite and marble from carleton place farther east stress the strong affinity of the wolf grove structure with rocks of the frontenac terrane the 1156 2 ma posttectonic maberly stock intrudes rocks near the boundary zone between the frontenac and sharbot lake terranes suggesting that the two terranes were linked by

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

geochemical evidence for magmatic fluids in porphyry copper mineralization the koloula igneous complex comprises 26 different intrusive phases that have been divided into two major magmatic episodes cycle 1 intrusions 4 5 ma and cycle 2 intrusions 2 4 to 1 5 ma the cycle 2 intrusions are further divided into the inamumu zoned pluton izp which is composed of 6 concentrically disposed quartz diorite and tonalite units and several satellite intrusions the izp is host to porphyry copper mineralization whereas the cycle 1 and cycle 2 satellite intrusions are barren presently exposed mineralization in the izp a system represents the deeply eroded core of a porphyry copper system where widely spaced veinlet alteration envelopes 1 mm thick are separated by large volumes of unaltered rock

the effect of a submarine canyon on the river sediment dispersal and inner shelf sediment movements in southern taiwan abstract this study examines the influence of a submarine canyon on the dispersal of sediments discharged by a nearby river and on the sediment movement on the inner shelf the study area includes the head region of the kao ping submarine canyon whose landward terminus is located approximately 1 km seaward from the mouth of the kao ping river in southern taiwan within the study area 143 surficial sediment samples were taken from the seafloor six hydrographic surveys along the axis of the submarine canyon were also conducted over the span of 1 yr three different approaches were used in the analysis of grain size distribution pattern they include 1 a combination of filtering and the empirical orthogonal eigen function eof analysis technique 2 the mclaren model and 3 the transport vector technique the results of the three methods not only agree with one another they also complement one another this study reveals that the kao ping submarine canyon is relatively a stratified and statically stable environment the hydrographic characteristics of the canyon display seasonal variability controlled primarily by the temperature field and the effluent of the kao ping river the hydrographic condition and the bottom topography in the canyon suggest the propagation of internal tides during the flood season summer of the kao ping river the submarine canyon acts as a trap and conduit for mud exchange between the kao ping river and offshore near the head of the canyon there is a region of sediment transport convergence this region is also characterized by high mud abundance on the seafloor that coincides with the presence of high suspended sediment concentration ssc spots in the bottom nepheloid layer outside the submarine canyon on the shelf where the evidence of wave reworking is strong the northwestward alongshore transport dominates over the southeastward transport which is a common theme on the west coast in southern taiwan

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

high 18o granitic plutons from the frontenac axis grenville province of ontario canada abstract 18 o 16 o ratios have been determined for whole rock as well as coexisting minerals from nine syn to post tectonic monzonite and quartz monzonite plutons in the westport gananoque area covering approximately 2500 km2 the plutons fall in two distinct isotopic groups 1 i low 18o group 8 0 11 2 rideau lake westport and wolfe lake plutons and 2 ii high 18o group 12 7 16 2 lyndhurst perth road battersea gananoque south lake and crow lake plutons the 18 o 16 o ratios of granitic rocks from the latter group are among the highest ever reported in the literature the isotopic compositions of samples within each pluton bear no relationship to the sample distance from the intrusive contacts nor are they affected by the types of country rocks marbles vs pelitic gneisses into which they are emplaced oxygen isotope fractionations among coexisting quartz feldspar biotite and magnetite all show normal plutonic values thus all lines of evidence suggest that the monzonite and quartz monzonite plutons did not acquire their characteristic 18 o 16 o ratios at the present level of exposure either by isotopic exchange with the surrounding metasedimentary country rocks or by any post crystallization low temperature alteration processes the distinct 18o 16o ratios observed in the high and low 18o groups probably reflect the difference in the isotopic compositions of the source materials the most plausible source for the high 18o group plutons is the grenville supergroup metasedimentary rocks and that for the low 18o group plutons the grenville basement gneisses mixed with a small amount of grenville supergroup metasedimentary rocks

source spectra of great earthquakes teleseismic constraints on rupture process and strong motion short period body waves recorded at teleseismic distances from great earthquakes provide information about source rupture processes and strong motions first we examine mostly wwssn records of 19 earthquakes of moment magnitude m w of 6 5 to 9 5 four parameters are measured from the short period p wave train the maximum amplitude the period at maximum amplitude the time between the first arrival and when the maximum amplitude is attained and coda length an extension m b of the teleseismic magnitude m b is defined using the maximum amplitude of the entire short period p wave rather than the amplitude achieved in the first few p wave cycles a least squares fit to the data yields the following relationship between m b and m w m b 0 53 m w 2 70 for m w 6 5 to 9 5 the time from the first arrival until the maximum amplitude is achieved and the coda length are roughly proportional to m w but are further interpreted by a simple asperity model of the rupture process these data support that short period waves are on average generated preferentially in the same regions of the fault plane as long period waves with periods of 10 to 50 sec we analyze the spectra of short and intermediate period teleseismic gdsn records for seven earthquakes with m w s of 6 4 to 7 8 and hand digitized short period wwssn records of the 1971 san fernando earthquake significant differences exist between the spectra of different events due partly to variations in tectonic setting or seismic coupling using the digital data we also investigate the relationship between time domain amplitude and spectral amplitude for short period p waves from our empirical relation between spectral amplitude and time domain amplitude we estimate the spectral amplitudes implied by the m b data we compare our results to the 2 and gusev spectral models neither model can completely represent the data nevertheless we consider the 2 model a useful reference model for comparing different events the average source spectrum of six large events with m w 7 4 to 7 8 does not have the spectral structure suggested by gusev an application to strong motion modeling is presented in which a 1971 san fernando teleseismic short period record is summed up to simulate teleseismic records produced by five great earthquakes the summation procedure matches the moment of the event to be simulated and includes rupture propagation fault plane roughness and randomness the m b data provide an important constraint on the summation procedures thus constrained this summation procedure can be more confidently used with near field strong motion records as green s functions to predict strong motions from great earthquakes

internal tides in monterey submarine canyon abstract the m2 internal tide in monterey submarine canyon is simulated using a modified version of the princeton ocean model most of the internal tide energy entering the canyon is generated to the south on sur slope and at the head of carmel canyon the internal tide is topographically steered around the large canyon meanders depth integrated baroclinic energy fluxes are up canyon and largest near the canyon axis up to 1 5 kw m 1 at the mouth of the upper canyon and increasing to over 4 kw m 1 around monterey and san gregorio meanders the up canyon energy flux is bottom intensified suggesting that topographic focusing occurs net along canyon energy flux decreases almost monotonically from 9 mw at the canyon mouth to 1 mw at gooseneck meander implying that high levels of internal tide dissipation occur the depth integrated energy flux across the 200 m isobath is order 10 w m 1 along the majority of the canyon rim but increases by over an order of magnitude near the canyon head where internal ti

u pb geochronology of the grenville orogen of ontario and new york constraints on ancient crustal tectonics based on lithological structural and geophysi cal characteristics the proterozoic grenville orogen of southern ontario and new york has been divided into domains that are separated from each other by ductile shear zones in order to constrain the timing of meta morphism u pb ages were determined on metamorphic and igneous sphenes from marbles calc silicate gneisses amphibolites granitoids skarns and pegmatites in addi tion u pb ages were obtained for monazites from meta pelites and for a rutile from an amphibolite these mineral ages constrain the timing of mineral growth the duration of metamorphism and the cooling history of the different domains that make up the southern part of the exposed grenville orogen based on the ages from metamorphic minerals regional and contact metamorphism occurred in the following intervals central granulite terrane

a geochemical traverse across the north chilean andes evidence for crust generation from the mantle wedge major and trace element and sr and nd isotope analyses are presented on 186 0 ma magmatic rocks along an east west traverse across north chile at 22 s esr ranges from 25 to 100 and end from 6 to 9 but the low end and high esr values are in rocks generated in the last 15 ma it is argued that previous discussions of petrogenesis in north chile have been hampered because the changes in magma chemistry in this area of unusually thick crust reflect not one but two processes one results in a progressive shift of esr from 25 to 20 and end from 6 to 6 in jurassic to recent rocks which is accompanied by increasing ta sm and sr and decreasing th ta the second is largely confined to the younger rocks and it is characterised by esr increasing up to 100 with increasing sio2 and decreasing sr and it results in relatively shallow trends on an end esr diagram the preferred interpretation is that trend 1 is due to the mobilisation of old late proterozoic mantle lithosphere as magmatism migrated eastwards and that trend 2 is due to crustal melting and contamination with differentiation in this area of thickened continental crust it follows that the mantle wedge is the principal site of crust generation and it is argued that 20 of the sr in the recent northern chile rocks is derived from the subducted ocean crust

isotopic study of the manaslu granite himalaya nepal inferences on the age and source of himalayan leucogranites a detailed isotopic study of the manaslu leucogranite was carried out a u pb age of 25 ma and a whole rock rb sr age isochron of 18 ma were obtained suggesting that the magmatic activity lasted at least 7 ma initial sr isotopic ratios are very high 0 740 to 0 760 and initial nd isotopic ratios are low nd in 13 to 16 and they show the existence of large isotopic variations even at the metre scale these are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes e g fusion mixing by convection these results also support the crustal origin of this leucogranite the tibetan slab paragneisses whose sr and nd isotopic ratios are very similar to those of the granite at an age of 20 ma are the most probable parental material nd model ages for both the leucogranite and the gneisses are in the range 1 5 2 ga a model of formation of the manaslu granite by coalescence of different batches of magma is in agreement with the present data

field chemical and physical constraints on mafic felsic magma interaction in the lamarck granodiorite sierra nevada california evidence of magma interactions resulting in both hybridization and mingling are preserved in a diverse suite of gabbroic to intermediate rocks associated with the compositionally zoned hornblende biotite lamarck granodiorite of the eastern sierra nevada california ellipsoidal mafic enclaves were formed by quenching of small amounts of high alumina basaltic magma upon injection into and dispersal through granodiorite magma early in its crystallization synplutonic intrusions of hornblende gabbro through hybridized mafic granodiorite represent injection of mafic magma at a later stage of crystallization of the granodiorite as they crosscut regional trends in foliation and compositional zoning in the host pluton where compositional contrasts between intrusion and host granodiorite are large contacts are sharp and abundant enclaves derived from the mafic intrusion are present in the granodiorite where the host is relatively mafic or where the local scale proportion of mafic magma is large contacts are zones of extensive hybridization that contain both enclaves and hybrid schlieren uncontaminated mafic intrusions have high alumina basaltic compositions whereas hybridized intrusions have silica contents as high as 63 5 mafic intrusions locally contain coarse grained cumulus gabbro inclusions mafic schlieren in granodiorite far from mafic intrusions represent localized accumulations of hornblende fe ti oxides and biotite from the granodiorite intrusion of late mafic dikes mobilized and entrained granitic residue from the granodiorite and formed composite dikes of aplite and pillowed diorite whether interacting magmas mix or mingle is a function of the heat contents and mass fractions of the end members calculations that account for compositions heats of fusion heat capacities of liquids and crystals and a range of initial temperatures crystallinities crystal sizes and magma water contents indicate that in most circumstances the basalt end member quenches the resulting large viscosity contrast between the end members prevents hybridization homogenization is likely only if the compositional difference between host and injected mafic magma is less than 10 sio2 or if the mass fraction of mafic magma is greater than 0 5 resulting mixtures have the composition of tonalite or mafic granodiorite thus the more silicic rocks of the granodiorite pluton must represent differentiation products rather than direct hybrids of mafic or intermediate magma and felsic magma

petrogenesis of mesozoic granitoids in the dabie uhp complex central china trace element and nd sr isotope evidence post collisional magmatism in the dabie orogen is characterized by the near contemporaneous intrusion of voluminous granitoids and minor mafic magmas in the late mesozoic 135 110 ma the granitoids are represented by three major batholiths in northern dabie zhubuyuan baimajian and tiantangzhai the largest zhubuyuan batholith comprises hornblende bearing intermediate rocks penghe suite and hornblende free granitic rocks huangbai suite the huangbai granites show limited variation in chemical composition but are highly variable in textures ranging from medium to coarse grained they have rather homogeneous sr and nd isotopic compositions with 87sr 86sr i 0 708 0 709 and end t 19 to 24 the penghe intermediate suite covers a wide spectrum of rock types including diorite monzodiorite quartz monzonite to monzogranitic rocks and all of them contain hornblende and mafic enclaves the existence of compositional and textural disequilibrium e g calcic and resorbed cores of plagioclase and the nature of chemical variation in these rock types indicate that magma mixing between an evolved mafic and a granitic magma was involved in their genesis fractional crystallization fc could have coupled with the process of magma mixing but with minor contamination by the upper continental crust during magma ascent isotopically the intermediate rocks show a variation in end t values from 13 7 to 18 while their 87sr 86sr i ratios vary from 0 7074 to 0 7088 the genesis and evolution of the dabie post collisional magmatic rocks may be summarized as follows intrusion of mantle derived mafic ultramafic magmas into thickened continental crust induced dehydration melting of the lower crust rocks with intermediate compositions and subsequent production of large amounts of granitic melts huangbai suite extensive interaction between the crustal and mantle derived melts through mixing produced a hybrid parental magma which subsequently underwent a fc process en route to higher crustal levels producing a wide variety of rock types as shown by the penghe intermediate rock suite injection of successive pulses of basic magma into upward mobile magma chambers could have resulted in the formation of the mafic enclaves as well as mafic dykes

teleseismic inversion for the second degree moments of earthquake space time distributions summary determining detailed descriptions of the space time distribution of an earthquake s rupture using only teleseismic data is often a difficult and non unique process however a description of an earthquake that goes beyond a point source is often needed for many seismotectonic problems we have developed a method that inverts measurements of the shifts in traveltime and amplitude of various seismic phases at global stations for the second degree polynomial moments of an event s space time distribution our values for the second moments of the 1995 mw 8 0 jalisco mexico thrust event correspond to a characteristic rupture length of 121t10 km along strike a characteristic rupture width of 76t11 km downdip a characteristic duration of 29t2 s and a direction of rupture propagation along the strike of the subduction zone to the nw for the 1995 mw 7 2 gulf of aqaba earthquake our estimates of the second moments correspond to a characteristic rupture length of 53t2 km a characteristic duration of 12t1 s and rupture propagation to the ne along the strike of the dead sea transform our estimates of the first and second moments agree well with values from local seismic and geodetic networks for both the jalisco and aqaba events we are able to resolve the fault plane ambiguity associated with the events moment tensors using our estimates of the second spatial moment

element fluxes associated with subduction related magmatism destructive plate margin magmas may be subdivided into two groups on the basis of their rare earth element ree ratios most island arc suites have low ce yb and remarkably restricted isotope ratios of 87 sr 86 sr 0 7033 143 nd 144 nd 0 51302 206 pb 204 pb 18 76 207 pb 204 pb 15 57 and 208 pb 204 pb 38 4 however they also have rb sr 0 03 th u 2 2 and ce yb 8 5 ratios which are significantly less than accepted estimates for the bulk continental crust the high ce yb suites have higher incompatible element contents more restricted heavy ree and much more variable isotope ratios such rocks are found in the aeolian islands grenada indonesia and philippines and their isotope and trace element features have been attributed both to contributions from subducted sediment and or old trace element enriched material in the mantle wedge it is argued that for isotope and trace element models the slab component can usefully be taken to consist of subducted sediment and altered mid ocean ridge basalts since these may contain ca 80 of the water in the subducted slab and the distinctive trace element features of arc magmas are generally attributed to the movement of material in hydrous fluids the isotope data indicate that not more than 15 of the sr and th in an average arc magma were derived from subducted material and that the rest were derived from the mantle wedge the fluxes of elements which cannot be characterized isotopically are more difficult to constrain but for most minor and trace elements the slab derived contribution in arc magmas is too small to have a noticeable effect on the residual slab

circulation in the hudson shelf valley mesa physical oceanographic studies in new york bight 1 over 900 days of current velocity data were obtained at mainly two locations in the inner and outer hudson shelf valley hsv the large cross axis depth gradients in the hsv together with the strong winter cyclones and the baroclinic density distribution over the shelf are primarily responsible for the major circulation features observed in the valley cstd data from 12 cruises and meteorological data from jfk international airport and an environmental buoy were collected concurrently with the current meter data although the mean cross shelf pressure gradient is generally seaward in the middle atlantic bight it is shoreward in the hsv below the level of the adjacent continental shelf shelf horizon thus imposing a bias toward upvalley flow the average velocity below the surrounding shelf horizon in the hsv is upvalley or shoreward west northwestward 290 t in the range of 2 5 cm s the circulation in the hsv is seasonal and individual events can drastically alter the mean picture the several day average upvalley flow can sometimes approach 20 cm s when intense winter cyclones pass over the bight and can sometimes also be directed downvalley depending upon the path of the winter cyclone a topographically controlled barotropic flow commonly opposes the dominant southeast ward wind direction even near the surface in the winter in the context of circulation on the open shelf upvalley downvalley flow events generated by winter cyclones are associated with reduced enhanced southwestward flow or flow reversals that are northeastward in the lower half of the water column at ltm a typical mid shelf site mayer et al 1979 current meter data suggest that whether or not reversals occur on the open shelf depends upon the interannual variability of the winter wind regime upvalley flow events are not confined only to the winter unstratified season but are stronger in the winter and can last for several days and longer during the summer stratified season the maximum horizontal ke in the upper part of the water column shifts from the meteorological forcing band characteristic of winter to diurnal inertial and semidiurnal frequencies in the diurnal band there appears to be a strong relationship between the diurnal wind and currents near the surface in the hsv as well as on the open shelf ltm the structure of the semidiurnal motions in the inner valley where the depth gradients are larger than in the outer valley has a significant depth dependence unlike most regions on the shelf i e during all times of the year the semidiurnal tidal ellipse is anticlockwise in the lower 20 m of the water column

flow modification and shelf slope exchange induced by a submarine canyon off the northeast spanish coast we present results from a study of the modifications induced by the short timescale response of a shelf break baroclinic jet to the presence of a downstream canyon the field site was the canyon of palamos located in the northeastern edge of spain to determine the short time scale variability of the area three intensive surveys were carried out at approximately 10 day intervals data indicate that the jet s location usually over the slope is subjected to significant onshore offshore displacements analysis of the data has shown the importance of a small scale temporal variability induced by river runoff and the climatology of the area this variability generates on off shore displacements of the jet which interacts with the head mouth of the canyon the different interactions with the canyon induced by these displacements produce different regimes of shelf slope exchange in the canyon domain that strongly modify the biomass patterns in the area