implications of estimated magmatic additions and recycling losses at the subduction zones of accretionary non collisional and collisional suturing orogens

the age of yellow river water in the bohai sea 1 to quantitatively understand the transport timescales of dissolved material discharged from large rivers into a semienclosed sea the age of yellow river water in the bohai sea was calculated with the constituent oriented age and residence time theory cart and particle tracking method yellow river water has a mean age of 3 0 years for the entire bohai sea the spatial variation of the water age is significant 1 2 years near the yellow river estuary but 3 9 years in the liaodong bay however the temporal variation in water age is insignificant the water particles released at the river mouth need only several days to reach the estuary area the great water age 1 2 years near the yellow river estuary is caused by the presence of old water particles that initially left this area but returned to this area again without the reentry of yellow river water from the yellow sea to the bohai sea the mean age of yellow river water in the entire bohai sea decreases to 1 2 years calculations without tidal forcing give a reduction in water age by more than 50 suggesting that tidal forcing plays the most dominant role in controlling the age of yellow river water in the bohai sea calculations without winds give an increase in water age by 20 30 suggesting that wind forcing is secondary factor to the age of yellow river water changes in discharge of the yellow river and in thermal stratification have limited influence on the age of yellow river water

bio physical changes in the coastal ocean triggered by typhoon a case of typhoon meari in summer 2011 abstract based on the combination of synchronous satellite and in situ observations we here for the first time provide the compelling evidence of bio physical response of coastal environment in the bohai sea china to the passage of typhoon meari over the northern yellow sea on june 26 2011 strong sustained winds induced a tongue like intrusion of cool water from the northern yellow sea into the bohai sea resulting in significant surface cooling and an anomalous increase in sea surface height along the coast of the western bohai sea this in return produced downwelling and transport of the warm and nutrient rich coastal water from the western coast to the central bohai sea as driven by the barotropic pressure gradient force in situ observational data confirmed the cooling of both surface and bottom layers with salinity increase however the measured temperature increase by 2 3 c concomitant salinity decrease by 0 3 psu and two fold increase in chlorophyll a in the middle layers suggested an influence from coastal downwelling ekman transport and typhoon enhanced mixing redistributed the nutrients and thus resulted in higher chlorophyll a concentrations in the upper layers

sedimentary recycling in arc magmas geochemical and u pb hf o constraints on the mesoproterozoic suldal arc sw norway the hardangervidda rogaland block within southwest norway is host to 1 52 to 1 48 ga continental building and variable reworking during the 1 1 to 0 9 ga sveconorwegian orogeny due to the lack of geochronological and geochemical data the timing and tectonic setting of early mesoproterozoic magmatism has long been ambiguous this paper presents zircon u pb hf o isotope data combined with whole rock geochemistry to address the age and petrogenesis of basement units within the suldal region located in the centre of the hardangervidda rogaland block the basement comprises variably deformed grey gneisses and granitoids that petrologically and geochemically resemble mature volcanic arc lithologies u pb ages confirm that magmatism occurred from 1 521 to 1 485 ma and conspicuously lack any xenocrystic inheritance of distinctly older crust hafnium isotope data range from ehf initial 1 to 11 suggesting a rather juvenile magmatic source but with possible involvement of late palaeoproterozoic crust oxygen isotope data range from mantle like 18o 5 to elevated 10 suggesting involvement of low temperature altered material e g supracrustal rocks in the magma source the hf o isotope array is compatible with mixing between mantle derived material with young low temperature altered material oceanic crust sediments and older low temperature altered material continent derived sediments this combined with a lack of xenoliths and xenocrysts exposed older crust afc trends and s type geochemistry all point to mixing within a deep crustal magma generation zone a proposed model comprises accretion of altered oceanic crust and the overlying sediments to a pre existing continental margin underthrusting to the magma generation zone and remobilisation during arc magmatism the geodynamic setting for this arc magmatism is comparable with that seen in the phanerozoic e g the sierra nevada and coast range batholiths with compositions in the suldal sector reaching those of average upper continental crust as within these younger examples factors that drive magmatism towards the composition of the average continental crust include the addition of sedimentary material to magma source regions and delamination of cumulate material underthrusting of sedimentary materials and their subsequent involvement in arc magmatism is perhaps a more widespread mechanism involved in continental growth than is currently recognised finally the suldal arc magmatism represents a significant juvenile crustal addition to sw fennoscandia

the proterozoic of nw mexico revisited u pb geochronology and hf isotopes of sonoran rocks and their tectonic implications several proterozoic basement units crop out in the sonora state of nw mexico and the same can be correlated with crustal provinces of southern laurentia in the neighboring southwestern usa zircon u pb and hf isotopic determinations in more than 300 grains separated from igneous and metaigneous rocks from these units indicate that the crystalline basement in sonora is made up of different components which are from west to east 1 the caborca mojave province to the west characterized by the so called bamori complex have u pb ages between 1696 and 1772 ma with moderately juvenile to slightly evolved ehf values yielding t dm ages of ca 2 1 2 4 ga 2 in the intermediate area east of hermosillo the palofierral and la ramada orthogneiss units yield an age of 1640 and 1703 ma respectively both having juvenile ehf with the palofierral overlapping the depleted mantle curve at ca 1 65 ga and 3 in the northeastern sonora samples from the southern extension of the mazatzal province represented by the pinal schist yielded ages between 1674 and 1694 ma with moderately juvenile to juvenile ehf values and a t dm age of ca 1 9 ga in addition a suite of post tectonic granites was also studied in caborca san luis granite as well as in northeastern sonora cananea granite both yielding ages of ca 1 44 ga with moderately juvenile ehf values ranging from 1 to 8 and t dm dates of ca 1 8 1 9 ga and 1 6 1 7 ga respectively these two isotopically contrasting provinces may imply the existence of a proterozoic paleo suture however if the palofierral gneiss of which the hf signature straddles the depleted mantle array is taken as the source for the 1 44 ga cananea granite then the location of such a suture zone should lay farther south than the proposed trace of the mojave sonora megashear

tectonic framework of a paleoproterozoic arc continent to continent continent collisional zone trans hudson orogen from geological and seismic reflection studies vertical incidence seismic data were collected along a 300 km long profile across the northwestern flank of the trans hudson orogen in saskatchewan line s2b the present study integrates the seismic data with previously published geological maps and recent results from the la ronge lynn lake bridge project that provide new constraints on the lithological structural and tectonic framework of this collisional zone an interpretative section based on the seismic reflectivity and surface geological constraints is presented the integrated data suggest the following key elements 1 although an early foreland vergent accretion history is suggested by surficial geological constraints the predominant fabric is reflected by penetrative hinterlandward vergence 2 a zone of more reflective lower crust with hinterland verging fabric may represent fossil reflectors from a pre collisional accretionary phase 3 the archean to paleoproterozoic sask craton may extend in the lower middle crust to at least

african easterly wave variability and its relationship to atlantic tropical cyclone activity abstract automatic tracking of vorticity centers in european centre for medium range weather forecasts analyses has been used to develop a 20 yr climatology of african easterly wave activity the tracking statistics at 600 and 850 mb confirm the complicated easterly wave structures present over the african continent the rainy zone equatorward of 15 n is dominated by 600 mb activity and the much drier saharan region poleward of 15 n is more dominated by 850 mb activity over the atlantic ocean there is just one storm track with the 600 and 850 mb wave activity collocated based on growth decay and genesis statistics it appears that the 850 mb waves poleward of 15 n over land generally do not get involved with the equatorward storm track over the ocean instead there appears to be significant development of 850 mb activity at the west african coast in the rainy zone around 10 n 10 w which it is proposed is associated with latent heat release based on the tracking statistics it has been shown th

relationship between tropical easterly waves and precipitation during the north american monsoon abstract relationships between tropical easterly waves tews and precipitation over mexico and the united states are examined during the north american monsoon nam the national centers for environmental prediction national center for atmospheric research reanalysis data are used to identify 137 tews that cross mexico north of 20 n after monsoon onset over a 31 yr period from 1975 to 2005 mean precipitation anomalies over two day periods both before and after tew passage are determined using climate prediction center daily precipitation analyses results indicate that positive precipitation anomalies occur along the west coast of mexico and extending into the west central united states in association with tew passage negative precipitation anomalies are found in the south central united states these precipitation anomaly patterns share many similarities to precipitation anomaly patterns previously defined in association with gulf surge events on longer time scales correlations between the total nu

three proterozoic orogenic episodes and an intervening exhumation event in the black canyon of the gunnison region colorado abstract u pb zircon titanite geochronology in situ monazite geochronology and 40ar 39ar thermochronology provide an unusually complete data set for reconstructing the tectonic history of proterozoic rocks exposed in the black canyon gunnison colorado these new geochronologic data record three protracted orogenic episodes and an exhumation event between orogenic pulses 1 yavapai orogeny 1741 1689 ma 2 exhumation marked by an angular unconformity beneath post yavapai pre mazatzal quartzites 3 mazatzal orogeny postquartzite deposition and 4 1434 1403 ma intracratonic tectonism supracrustal rocks of the black canyon succession were deposited or crystallized at or prior to documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wn

net sediment transport patterns over the bohai strait based on grain size trend analysis grain size trend analysis indicates two distinct characteristics of sediment transport in bohai strait eastward transport dominates the western area and along the coast of the shangdong peninsula this result supports the previous work which indicated that the yellow river sediments are transported from the bohai sea to the yellow sea through the south channel of bohai strait and dispersed into the southern yellow sea along the coast of shangdong peninsula in the central eastern bohai strait net deposition is taking place as indicated by the convergence of the grain size trends this result is consistent with current circulation pattern on bohai strait and the interpretation of strata disclosed by seismic reflection profile this study supports the use of grain size trend analysis for large scale areas on the continental shelf

an analysis of the landfall of hurricane nora 1997 abstract the changes to the motion and structure of the eastern pacific tropical cyclone nora 1997 during landfall are investigated nora developed south of the mexican coast intensified into a hurricane and made landfall over northwestern mexico and the southwestern united states in this study the authors document the evolution of the structure of nora from a variety of sources observations derived from satellite imagery show the approach of the hurricane to the baja california peninsula and the development of a localized area of mesoscale convection that intensified while moving over the gulf of california the propagation of this convective system became the dominant feature of the landfall and provided heavy precipitation over a region confined to western arizona numerical simulations with the pennsylvania state university national center for atmospheric research mesoscale model version 5 are used to examine the details of the evolution of the observed area of convection over the gulf simulat

electron microprobe monazite dating of ca 1 71 1 63 ga and ca 1 45 1 38 ga deformation in the homestake shear zone colorado origin and early evolution of a persistent intracontinental tectonic zone the homestake shear zone one of the principal precambrian structures within the colorado mineral belt has a history of tectonism that extends from the proterozoic to the tertiary new field mapping microstructural analysis and electron microprobe u th pb monazite dates define the style kinematics and timing of multistage proterozoic ductile deformation early subhorizontal shearing d1 progressed to northwest southeast crustal shortening d2 during a protracted ca 1710 1630 ma orogeny involving high temperature metamorphism partial melting and emplacement of the ca 1 7 ga cross creek batholith the subvertical northeast trend of the shear zone was established by d2 shortening a major episode of simple shear displacement occurred ca 1 4 ga during emplacement of the st kevin batholith complex kinematics are recorded by 1380 ma southeast side down dextral mylonite zones d3 and post 1380 ma southeast side up dextral ultramylonite pseudotachylyte zones d4 that were both localized in d2 foliation domains the succession of ductile tectonites in the homestake records 300 m y of episodic deformation at progressively shallower crustal levels as colorado evolved from an active accretionary margin 1 8 1 7 ga through crustal assembly 1 7 1 6 ga to a tectonically active continental interior post 1 45 ga the homestake shear zone constitutes a classic example of ductile shear zone reactivation and the development of persistent tectonic zones in the continental lithosphere

residual currents in a semi enclosed bay of the seto inland sea japan 1 on the basis of the princeton ocean model a robust diagnostic model is developed to calculate the residual currents in the hiuchi nada a semi enclosed bay of the seto inland sea the input water temperature and salinity data are from six hydrographic surveys in 2002 and the model results in the summer show a clockwise eddy in the western part of the bay and an anticlockwise eddy in the eastern part the magnitude of two eddies is 10 cm s the modeled flow pattern is consistent with early observations derived from moored arrays the two eddies are persistent throughout the summer because winds are usually weak and cannot influence their existence the tide induced residual currents are appreciable only in the close vicinity of the kurushima strait and bisan strait the two straits connecting the bay to the other bays and have little affect on the two eddies that are inside the bay thus the two density driven eddies in the hiuchi nada are the basic pattern of circulation in the summer using the calculated residual currents we examined the intrusion route of waters from the kurushima strait and bisan strait with passive tracer experiments the results show that the water in the kurushima strait intrudes into the bay mainly through the middle and bottom layers while the water in the bisan strait intrudes mainly through the surface layer furthermore the tracer cannot reach the center of the anticlockwise eddy in the eastern part of the bay this indicates that the eddy prevents water exchange between its center and outer edges and provides favorable conditions for the formation of oxygen deficient waters in the central part of the eddy

principal component analysis of the summertime winds over the gulf of california a gulf surge index a principal component analysis of the summertime near surface quick scatterometer quikscat winds is used to identify the leading mode of synoptic scale variability of the low level flow along the gulf of california during the north american monsoon season a gulf surge mode emerges from this analysis as the leading eof with the corresponding principal component time series interpretable as an objective index for gulf surge occurrence this index is used as a reference time series for regression analysis and compositing meteorological fields of interest to explore the relationship between gulf surges and precipitation over the core and marginal regions of the monsoon as well as the manifestation of these transient events in the large scale circulation it is found that although seemingly mesoscale features confined over the gulf of california gulf surges are intimately linked to patterns of large scale variability of the eastern pacific itcz and greatly contribute to the definition of the northward extent of the monsoonal rains

upscale effects of deep convection during the north american monsoon abstractthe ability of deep monsoon convection to influence the larger scale circulation over north america is investigated for a 6 day long case study during the 2006 north american monsoon results from rossby wave ray tracing and numerical simulations using the advanced research weather research and forecasting model indicate that north american monsoon convection provides a source region for stationary rossby waves two wave trains are seen in the numerical model simulations with behaviors that agree well with expectations from theory and ray tracing the shorter and faster moving wave train moves eastward from the source region in mexico and reaches the western atlantic within 4 days the longer and slower moving wave train travels northeastward and reaches the coastal new england region within 6 days an upstream tail of anticyclonic vorticity extends westward from the source region into the central pacific ocean the monsoon convection appears to help cut off the low level anticyclonic flow by deve

proterozoic farwell mountain lester mountain suture zone northern colorado subduction flip and progressive assembly of arcs this paper considers the amalgamation of arc and oceanic terranes to be the main mechanism of ca 1 8 1 6 ga continental crustal growth in southwestern laurentia on the basis of geologic and seismic reflection data and teleseismic images we propose the farwell mountain lester mountain suture zone as the northern most paleoproterozoic arc arc suture north dipping farwell mountain seismic reflections project from 18 km depths to the surface and are interpreted to represent conjugate thrusting as the 1 79 1 77 ga green mountain arc was partially underthrust beneath the archean craton we speculate that a north dipping high velocity mantle slab in the teleseismic image is a continuation of this thrust zone south dipping lester mountain reflections project from 22 km depths to the surface and are interpreted to be a thrust zone between the green mountain arc and the 1 76 1 72 ga rawah block surface features of the farwell mountain lester mountain suture zone are 1 marble chert rock with sillimanite pods ultramafic rocks sulfide deposits and pillow basalts which we interpret to be a dismembered accretionary complex 2 an axial planar fabric to north verging isoclinal folds f 2 which we interpret to be part of a north vergent fold and thrust system and 3 a metamorphic break between 500 c rocks to the north and 610 c rocks to the south which we attribute to reactivation of the zone movement on the farwell mountain backthrust is inferred to relate to cheyenne belt suturing at 1 78 1 75 ga we correlate suturing in the farwell mountain lester mountain suture zone to s 1 d 1 1 746 1 74 ga in the soda creek fish creek shear zone we attribute the complexity of this broad suture zone to initial conjugate thrusting plus overprinting and steepening of accretionary structures by subsequent tectonism

oceanic inflow from the coral sea into the great barrier reef long term current meter data from the continental shelf region of the great barrier reef show that there exists a zone of oceanic inflow onto the shelf this oceanic inflow splits into two branches on meeting the continental shelf slope resulting in two net longshore currents on the slope one to the north and the other to the south of the separation point in 1981 this separation point was located between 17 s and 18 s this circulation was successfully predicted using a depth averaged two dimensional model in which the regional sea level gradient is explicitly added in the momentum equations the resulting circulation on the continental shelf is controlled by an oceanic inflow of 0 58 sv spread over 500 km of the shelf edge both north and south of the separation point the inflow appears measurably impeded by the presence of coral reefs with 50 of the inflow occurring in a 150 km long area where reef density is small satellite images confirm this spatial variability longshore currents on the shelf generated by the inflow are modulated by the wind and tides which can deflect the mean current away from areas of high reef density and generate localized outflows to the coral sea oceanic inflow is believed to be important because it flushes the shelf even in the absence of wind it controls the dominant direction of across shelf and along shelf spread of spawn material from reefs it makes it possible for upwelled water to spread quickly over the gbr shelf it may also protect coral reefs by preventing river plumes from spreading onto the outer shelf

lead isotopic evidence for the origin of paleo and mesoproterozoic rocks of the colorado province u s a abstract lead isotopic ratios of k feldspars and whole rocks from 1 7 and 1 4 ga plutonic rocks of the colorado province are relatively non radiogenic for 207 pb 204 pb plotting below the average crust model curve of stacey and kramers 1975 indicating that the terrane was derived primarily from juvenile mantle material slightly more radiogenic ratios in the northern part of the terrane near the archean wyoming province suggest minor inclusion of an older component the data from 1 7 ga plutons plot in a broad field suggesting two episodes of re equilibration with whole rock pb probably related to heating events in the mesoproterozoic 1 4 ga and cretaceous 70 ma possible differences in calculated whole rock th u coupled with slight pb isotopic variations along the north south transect suggest either a terrane boundary through central colorado near salida and gunnison or fundamental differences in source rocks metasedimentary vs metavolcanic u pb analyses of multigrain splits of detrital zircons from quartzites throughout the colorado province have failed to identify archean detritus the oldest 207 pb 206 pb ages found in two samples of quartzite from northern colorado are about 2 0 ga perhaps derived from rocks of the trans hudson orogen in contrast to 2 75 ga detrital zircon in a paleoproterozoic quartzite from the southern part of the wyoming province while we are not yet able to discern if these ages are true provenance ages or mixtures of archean and paleoproterozoic components the absence of easily recognizable archean zircons supports other isotopic data and a conclusion that most of the paleoproterozoic crust of the colorado province was ultimately derived from a juvenile at 1 8 ga mantle reservoir

the relationship between tropical easterly waves and surges over the gulf of california during the north american monsoon abstract coastally trapped disturbances which occur over the gulf of california and are commonly referred to as gulf surges are an important mechanism in the transport of low level moisture into the southwestern united states to determine whether or not gulf surges develop in association with the passage of tropical easterly waves as hypothesized in previous studies standard surface observations and european centre for medium range weather forecasts reanalysis data during the months of july and august over a 14 yr period are examined results indicate that tropical easterly wave troughs often cross western mexico 1 3 days prior to surge onset at yuma arizona indicating a strong correlation between these two events this analysis documents yet another mechanism by which the tropics influences convection in the midlatitudes

case study of an intense african easterly wave abstract the life cycle of an intense african easterly wave aew over the african continent is examined using european centre for medium range weather forecasts ecmwf operational analyses meteosat satellite images and synoptic observations this system the strongest aew of 2000 can be tracked from central north africa into the eastern atlantic ocean where it is associated with the genesis of hurricane alberto synoptic analysis of the kinematic and thermodynamic fields is supplemented by analysis of potential vorticity pv allowing exploration at the role of multiple scales in the evolution of this aew the authors analysis promotes the division of the aew life cycle into three distinctive phases i initiation the aew development is preceded by a large convective event composed of several mesoscale convective systems over elevated terrain in sudan this convection provides a forcing on the baroclinically and barotropically unstable state that exists over tropical north africa ii baroclini

diurnal variation and horizontal extent of the low level jet over the northern gulf of california abstract this note describes aspects of the diurnal variation and geographical location of the summertime low level jet over the gulf of california based on wind soundings made at two sites near the northern end of the gulf during a two week summer field program in 1995 the low level wind observations from puerto penasco a site along the northern shore of the gulf showed a strong diurnal cycle decreasing in amplitude to near 0 by the 1800 m altitude a weaker but deeper diurnal cycle was observed at mexicali an inland site some 200 km west northwest of puerto penasco the strongest winds were observed at the coastal site the observations suggest that the strongest southerly winds in the northern gulf lie closer to the eastern shore of the gulf

early proterozoic oceanic crust in the northern colorado front range implications for crustal growth and initiation of basement faults 1 early proterozoic oceanic crust exposed in a shear zone in the northern colorado front range provides insight into the tectonic evolution of the colorado province tectonically intermingled mylonitic amphibolite locally pillowed metagabbro clinopyroxenite metachert and melange are preserved within the buckhorn creek shear zone west of fort collins whole rock geochemical data support formation of the igneous protoliths in an oceanic environment major and trace element data overlap samples from modern oceanic ridges and are distinct from modern arc trends metagabbros and clinopyroxenites preserve a subhorizontal lineation defined by igneous pyroxenes core and mantle microstructures indicate initial deformation at temperatures 900 c secondary amphiboles define both subhorizontal and subvertical lineations kinematic analysis indicates that the rocks experienced e w strike slip deformation prior to and during amphibolite facies metamorphism followed by n s shortening 40ar 39ar data from secondary hornblende yield age steps as old as 1 9 ga based on the chemical data and kinematic evidence for strike slip deformation we propose that the buckhorn creek rocks originated at an oceanic ridge transform intersection the high t pyroxene fabrics formed during ocean floor deformation prior to 1 7 ga regional deformation of the colorado province the buckhorn creek fragment likely represents original oceanic basement for 1 8 1 7 ga arc magmatism and sedimentation that ultimately formed the colorado province continental crust reactivation of original oceanic fracture zones may be responsible for the network of regularly spaced northeast trending shear zones in colorado once formed subvertical transform faults are likely to survive the transition from oceanic to continental crust and persist as long lived crustal discontinuities

a proterozoic volcano plutonic terrane gunnison and salida areas colorado early proterozoic supracrustal rocks near gunnison and salida colorado include tholeiitic basalt dacite to rhyolite and intercalated sedimentary rocks these were intruded by essentially synchronous gabbroic sheets folded and intruded by major plutons ranging from quartz diorite to granite preservation of primary volcanic and sedimentary features is good to excellent sedimentary rocks in the gunnison area are mostly turbidite wackes whereas near salida they are mostly near source volcaniclastic rocks u pb age measurements on zircons indicate that the earliest bimodal volcanic rocks erupted between 1770 and 1760 m y ago and were intruded by granitic plutons between 1760 and 1750 m y ago renewed bimodal volcanism occurred between 1740 and 1730 m y ago and was followed by a period of deformation producing two fold sets before 1725 m y ago when the first of a series of younger plutons was emplaced the compositions and features of the sedimentary rocks and their association with volcanics are con

characteristics of african easterly waves depicted by ecmwf reanalyses for 1991 2000 abstract several interesting characteristics of african easterly waves aews were observed and investigated by previous studies two separate propagation paths genesis mechanisms restriction of vertical development and the interaction with the african easterly jet aej however some aspects of these characteristics have been neglected the contrast of the aew population along the two propagation paths the aew genesis mechanism over the saharan thermal low and the role played by the low level north african circulation in this mechanism the dynamical mechanism restricting the vertical development of aews and the synoptic relationship and interaction between the aej and the aews along the two propagation paths the ecmwf reanalyses for the 1991 2000 period supplemented with those of 1979 were analyzed to explore these aew features major findings of this effort are the following the population of aews along the propagation path north of the aej aewn is approximately 2 5 times of that along the pr

early proterozoic bimodal volcanic rocks in central colorado u s a part i petrography stratigraphy and depositional history abstract early proterozoic metamorphic rocks of the salida area include two exceptionally well preserved sections of undeformed volcanogenic rocks a northern section nearly 4000 m thick and a southern section 1700 m thick the stratigraphic and lithologic character of the sections are the same indicating that they were formed contemporaneously in the same subaqueous environment the suite is strongly bimodal consisting of felsic volcaniclastic rocks 50 mafic volcanic and volcaniclastic rocks 22 and gabbro diabase sheets 23 the remaining rocks are mostly pelitic metasediments the felsic rocks which dominate the upper portions of both sections comprise four distinct facies crystal lithic tuff breccia crystal lithic lapilli breccia tuff bedded tuff and massive tuff lithic fragments are typically foreign dominated by pelitic material crystal clasts are feldspar mainly plagioclase and quartz sequences of these facies representing cycles of eruptive activity are uniform in thickness and extend along strike for the entire width of precambrian exposure up to 4 km but individual facies units especially the coarser ones are limited in their lateral extent individual sequences average about 100 m thick but continuous exposures of felsic rocks locally exceed 600 m primary sedimentary structures and vertical and lateral variations indicate deposition typically following remobilization as debris flows and turbidites in a shallow marine environment of low relief mafic volcanic and volcaniclastic rocks form accumulations up to 600 m thick and extend uniformly for several kilometers along strike although individual units are more restricted laterally the principal rock types are basalt flows basaltic lithic breccia pillow lava pillow breccia bedded basaltic lapillistone and laminated basaltic tuff all deposited in a submarine setting accumulations typically including several types are interbedded with felsic rocks but mechanical mixing of mafic and felsic volcaniclastics is rare suggesting separate eruptive centers for the mafic and felsic volcanics the northern section may be more proximal than the southern section as indicated by the greater abundance of flows the thicker sheets of gabbro and the greater abundance of mafic rocks relative to felsic rocks gabbro diabase sheets up to 350 m thick and dominantly concordant intrude throughout both sections they are characterized by lack of internal differentiation simple mineralogy consisting of plagioclase and hornblende pseudomorphous after pyroxene and sub ophitic texture the minor pelitic material indicates that the area was accessible to continental sediment sources although their location is not known the salida bimodal volcanic suite is part of a more extensive accumulation of similar 1700 1800 ma supracrustal rocks that extends west to the gunnison area and perhaps south into northern new mexico

does the arc accretion model adequately explain the paleoproterozoic evolution of southern laurentia an expanded interpretation comment and reply comment assembly of lithosphere in southern laurentia is best interpreted to have taken place along a long lived 1 8 1 0 ga active margin via subduction accretion processes broadly analogous to present day convergence between australia and indonesia karlstrom and bowring 1988 1 karlstrom et al

isotopic geochemical and temporal characterization of proterozoic basement rocks in the quitovac region northwestern sonora mexico implications for the reconstruction of the southwestern margin of laurentia a detailed geochemical characterization of 19 representative proterozoic basement rocks in the quitovac region in northwestern sonora mexico has identified two distinct paleoproterozoic basement blocks that coincide spatially with the previously proposed caborca and north america blocks new u pb zircon geochronology revises their age ranges the caborca 1 78 1 69 ga and north america 1 71 1 66 ga blocks at quitovac and precludes a simple age differentiation between them in addition grenvillian age granitoids ca 1 1 ga spatially associated with the caborca block have been identified at quitovac nd isotopes and major and trace element geochemistry support the distinction of these paleoproterozoic blocks granitoids of the north america block are characterized by depleted end values 3 4 3 9 and younger nd model ages 1800 1740 ma and have lower k 2 o y rb ba th ree and fe mg values than coeval rocks of the caborca block the caborca block granitoids are likewise characterized by slightly less depleted end 0 6 2 6 and older nd model ages 2070 1880 ma despite the subtle differences granitoids from both the caborca and north america blocks exhibit island arc like affinities we propose that the proterozoic basement rocks from the quitovac region are an extension of the proterozoic crustal provinces in the southwestern united states specifically rocks of the caborca block exhibit an affinity to rocks of either the yavapai province or the mojave yavapai transition zone whereas rocks of the north america block have signatures similar to those of the mazatzal province or possibly the yavapai province of arizona the new isotopic ages and geochemical data do not support the existence of the late jurassic mojave sonora megashear at quitovac as originally proposed however the quitovac region accounts only for a small fraction of the proterozoic basement in sonora so these findings do not eliminate the possibility of a megashear elsewhere in northern sonora our new data create the possibility of alternative hypotheses for the distribution of paleoproterozoic crustal provinces in southwestern north america that affect reconstructions of the original southwestern margin of laurentia and reduce uncertainties in the configuration timing and existence of the proterozoic supercontinent rodinia

the low level circulation of the north american monsoon as revealed by quikscat five years 1999 2003 of near surface quikscat ocean winds over the gulf of california and northeast pacific ocean are used to characterize the changes in the low level circulation associated with the north american monsoon our analysis shows that the onset of the summer season is accompanied by a seasonal reversal of the flow along the gulf of california with the establishment of a time mean southerly wind throughout the gulf this reversal not evident in the global reanalysis products occurs in late spring and precedes the onset of the monsoonal rains in the core of the monsoon the time mean flow is found to be modulated by transient events namely gulf surges detected in the near surface wind field as periods of enhanced southerly flow which typically originate at the southern end of the gulf and propagate northward the histogram of the summertime along shore winds identifies these surges as a distinct population of events readily distinguishable from the background flow

an index of interannual precipitation variability in the core of the north american monsoon region abstract seasonal precipitation anomalies associated with the continental north american monsoon system are characterized using a land based dataset derived from in situ observations across the southwestern united states and northwestern mexico coherent regions of interannual continental precipitation variability are derived from principal component analysis after defining separate early and late summer monsoon seasons the gravest mode of late season interannual variability captures precipitation anomalies in the core of the continental monsoon domain a simple spatial average is developed as an index of this core variability the seasonal separation allows examination of persistence of precipitation anomalies as an indicator of practical late season predictability possible influences of large scale oceanic interannual fluctuations enso and pacific decadal oscillation pdo on core index precipitation anomalies are also considered the core precipitation index exhibits considerably more early to

surges over the gulf of california during the mexican monsoon abstract northward surges of relatively cool moist maritime air from the tropical pacific into the southwestern united states occur via the gulf of california every summer during the mexican monsoon season these surges advect large amounts of moisture northward and promote increased convective activity in arizona mesoscale model output from 32 successive 24 h simulations are used to examine both the large scale and mesoscale features associated with surge events model data are compared to high resolution aircraft measurements on two days showing clearly that the model is capable of reproducing many of the detailed structures found in the observations results from a large scale analysis indicate that strong surges are produced in the model when a midlatitude trough is in the proper phase relationship with a tropical easterly wave weak surges occur when this relationship is missing

hydrology and circulation in the strait of hormuz and the gulf of oman results from the gogp99 experiment 1 strait of hormuz in october and early november 1999 the gogp99 experiment collected hydrological currentmeter tide recorder thermistor and drifting buoy data near the strait of hormuz data analysis provides the water mass structure in the strait persian gulf water pgw core is banked against the omani coast while indian ocean surface water iosw lies near the iranian coast these water masses are most often covered by a homogeneous surface layer thermohaline characteristics of the pgw core decrease substantially downstream from the persian arabian gulf to the gulf of oman pgw and iosw thermohaline characteristics and distribution also exhibit notable changes at periods shorter than a month as shown by repeated hydrological sections the tidal signal measured south of the strait by moored adcp and thermistor chains has predominant semi diurnal m2 and s2 and diurnal k1 components and possesses a complex vertical structure tidal intensification near the surface pycnocline is associated with noticeable internal waves at subtidal timescale mooring recordings confirm the water mass variability observed in the repeated hydrological sections the mixed layer also deepens substantially during the 1 month period finally trajectories of surface buoys drogued at 15 m exhibit reversals over periods characteristic of changes in wind direction

what processes control the net currents through shallow straits a review with application to the bohai strait china we review the key processes controlling the net water circulation in shallow straits the circulation is mainly barotropic driven by the difference in mean sea level and tides on either side of the strait the wind the meandering of the currents in the adjoining seas the bathymetry including the shape and width of the mouths and the presence of narrows shoals sills islands and lateral embayments as the oceanography forcing can be non synchronised on either side of the strait the resulting net currents through the strait may appear chaotic we apply these findings to the net circulation through the bohai strait in china using local wind remote sensing data of currents and sea level and a hydrodynamic model the net currents through the bohai strait were episodic they were largest during winter storms when the wind generated a cyclonic coastal current in the northern yellow sea that flowed across the width of the bohai strait like the luzon strait this current meandered and a branch of the current intruded into the northern bohai strait along the deeper channel the wind set up in the bohai sea and the wind driven longshore current in the southern bohai sea generated a seaward flow through the southern bohai strait somewhat like in irbe strait as with the straits of the seto inland sea stagnation occurred in some embayments as in the torres strait the islands in the southern bohai strait retarded the net flow and increased the width of the outflow zone these flows were also modulated at very long periods 60 days by long waves in the yellow sea possibly generated by meandering of the kuroshio current that created an additional sea level slope through the strait the transit time in the bohai strait was 60 and 10 days respectively during calm weather and winter storms the residence time in the bohai sea was estimated to be about 1 68 years by the loicz model and 1 56 years by the hydrodynamic model and the influence of the river runoff including the yellow river was negligible

modelling of seasonal exchange flows through the dardanelles strait abstract the dardanelles strait is a remarkable example of a long narrow shallow and strongly stratified strait with bidirectional exchange that is governed by both baroclinic and barotropic forcing with a wide spectrum of variability a three dimensional free surface primitive equation model is applied to study seasonal hydrodynamics variability in this strait the calculated vertical structure of temperature salinity and velocity fields agrees well with available survey data seasonal monthly values of the volume exchange at the aegean and marmara exits are estimated it is found that the seasonal exchange dynamics is governed by the turbulent friction and entrainment at the nara passage area the mean annual water transport in the upper layer is increased by 80 after the nara passage about 25 of water entering in the dardanelles bottom layer reaches the marmara sea in winter and 50 reaches it in summer the estimate of the dardanelles hydrodynamics according to hydraulic and viscous advective diffusive regime classification shows significant deviation from the two layer hydraulic asymptotic however according to three layer hydraulic theory the flow is found to be critical in the nara passage area

paleoproterozoic rocks of central colorado accreted arcs or extended older crust paleoproterozoic 1770 1735 ma bimodal volcanic rocks in central colorado have been considered to represent southward growth of laurentia by arc accretion although the bimodality of these rocks suggests an extensional continental setting rather than continental or oceanic arcs there has been little evidence for pre 1800 ma crust south of the wyoming craton other than the 1840 1 ma elves chasm pluton in the upper granite gorge of the grand canyon arizona we report shrimp u pb ages of inherited zircons from metarhyolites and plutons in central colorado that are latest archean earliest proterozoic 2520 2000 ma and trans hudson penokean 1878 1814 ma associated quartzites contain detrital zircons with mean ages of 1735 ma indicating only local derivation a meta arkose however contains detrital zircons of trans hudson penokean and archean ages we believe it likely that the 1900 1800 ma trans hudson penokean orogens including archean enclaves extended farther south and west than is currently thought and were the source of the bimodal volcanic rocks and associated plutons during the period 1770 1700 ma

refining the early history of the mojave yavapai boundary zone rifting versus arc accretion as mechanisms for paleoproterozoic crustal growth in southwestern laurentia abstractthree outstanding questions regarding paleoproterozoic crustal growth and assembly in southwestern laurentia are 1 the mechanisms of crustal growth back arc rifting and associated juvenile magmatism vs accretion of juvenile arcs 2 the nature and significance of pre yavapai orogeny 1 70 ga deformation and 3 how the isotopically mixed boundary zone between the mojave and yavapai paleoproterozoic crustal provinces formed supracrustal successions associated with the mojave yavapai boundary zone in northwestern arizona are dominated by 1730 ma bimodal metavolcanic sequences and compositionally siliciclastic metasedimentary rocks with minor ultramafic rocks chert and carbonate this lithologic assemblage requires juvenile mafic volcanism in a basin that also received abundant quartz rich i e continental detritus a pre d1 first deformational event back arc rift setting for northwestern arizona best explains the observed supracrustal assemblage plutonic rocks that intrude the s

a climatological perspective of transient synoptic features during name 2004 abstract this note provides a first look at a recently developed long term climatology of transient synoptic features in northern mexico key features investigated include inverted troughs cutoff lows cold fronts and open troughs westerly short waves this 35 yr analysis of transient systems crossing northern mexico 1967 2001 was developed to help place the summer climatology of the 2004 north american monsoon experiment name into a broader perspective inverted troughs are found to be the most commonly occurring transient synoptic feature during the monsoon with a mean frequency of occurrence of 55 days per summer season june september inverted troughs are found to contribute from 20 to 25 of the average summer rainfall observed in northern mexico rainfall doubles during inverted trough days compared to days without transient systems being present in 2004 the monsoon season was greatly shortened due to a poorly developed subtropical high compared to long term means inverted troughs cont

early proterozoic assembly of tectonostratigraphic terranes in southwestern north america a 500 km wide early proterozoic orogenic belt in arizona and adjacent areas is divided into lithotectonic blocks by northeast and north trending shear zones structural and u pb zircon studies suggest that these blocks may have experienced different tectonic histories prior to their juxtaposition by thrust and strike slip movements on shear zones a northwestern province here called the yavapai province is composed of at least five tectonic blocks and was assembled at about 1700 ma a southeastern province here called the mazatzal province is composed of at least three blocks and was assembled and juxtaposed with the northwestern province during the mazatzal orogeny between 1695 and 1630 ma the diversity of seemingly incompatible 1700 ma tectonic regimes now in close proximity to each other and the absence of systematic cross strike changes in age and character of deformation plutonism and metamorphism suggest a model whereby the orogenic belt developed and north america grew by assembly of d

early proterozoic bimodal volcanic rocks in central colorado u s a part ii geochemistry petrogenesis and tectonic setting abstract the early proterozoic supracrustal rocks of the salida area of central colorado consist of strongly bimodal sequences of volcanogenic rocks the mafic rocks basalts basaltic volcaniclastics and related gabbro sheets are distinctly tholeiitic display a strong iron enrichment trend and typically contain less than 50 sio 2 the felsites are rhyolites to dacites and contain more than 70 sio 2 major and trace element modeling show that the mafic rocks underwent two stages of crystal fractionation the first involving olivine and plagioclase the second involving plagioclase and clinopyroxene fractionation occurred within individual injections as they rose toward the surface rather than in a single magma chamber at depth field relations and major element data support the derivation of the felsic rocks from a magma generated by anatexis of sialic crust however the low sr and high heavy ree concentrations in these rocks are not compatible with a partial melting model and suggest that the felsic volcanic rocks could have been derived by extensive fractional crystallization of the mafic magma normalized trace element abundances and trace element ratios of the mafic rocks are most like continental flood basalts such as the columbia river basalts they also display some similarity to immature back arc basin tholeiites developed on continental crust such as those of the sarmiento complex the felsic rocks have strong chemical affinities to within plate rhyolites rather than calc alkaline rhyolites from orogenic areas the chemical data as well as the petrographic stratigraphic and regional field data all indicate that the early proterozoic supracrustal rocks of the salida area developed along a continental margin probably within an immature back arc basin underlain by sialic crust remnants of the arc system of similar age may lie to the south in northern new mexico and southwestern colorado

analysis of the 13 14 july gulf surge event during the 2004 north american monsoon experiment abstract gulf surges are disturbances that move northward along the gulf of california goc frequently advecting cool moist air from the goc or eastern tropical pacific ocean into the deserts of the southwest united states and northwest mexico during the north american monsoon nam little attention has been given to the dynamics of these disturbances because of the lack of reliable high resolution data across the nam region high temporal and spatial observations collected during the 2004 north american monsoon experiment are used to investigate the structure and dynamical mechanisms of a significant gulf surge on 13 14 july 2004 integrated sounding systems deployed along the east coast of the goc and an enhanced network of rawinsonde sites across the nam region are used in this study observations show that the 13 14 july gulf surge occurred in two primary stages the first stage was preceded by anomalous low level warming along the northern goc on 13 july sharp cooling moistening and increased

u pb geochronologic constraints on the paleoproterozoic crustal evolution of the upper granite gorge grand canyon arizona new field observations and u pb zircon and monazite ages are used to outline a geologic history of paleoproterozoic rocks beneath the colorado plateau in the grand canyon of northern arizona the upper granite gorge of the grand canyon exposes three lithotectonic units including supracrustal rocks mafic to intermediate composition plutons and peraluminous granite dikes that are variably deformed and metamorphosed new u pb ages indicate that layered supracrustal rocks were deposited or erupted over at least 8 m y between 1750 2 and 1741 1 ma mafic to intermediate composition plutons intruded the supracrustal rocks at 1741 1 ma zoroaster granite 1737 1 ma grapevine camp granite 1730 3 ma trinity granodiorite 1717 1 ma ruby granodiorite and 1713 2 ma horn diorite both supracrustal and plutonic rocks are intruded by 1698 1662 ma peraluminous granite and pegmatite dikes that locally form 50 of the rock volume u pb ages of foliated plutonic rocks and crosscutting granite dikes bracket the timing of fabric development for three groups of fabrics group 1 fabrics formed between 1730 3 and 1698 1 ma group 2 fabrics formed between 1713 2 and 1685 1 ma the timing of group 3 fabric formation is poorly constrained although the 1662 ma phantom pluton contains shear bands that offset pegmatitic dikes that crosscut the pluton metamorphic grade varies across the transect from lower amphibolite facies to lower granulite facies we suggest that single crystal u pb ages 1706 1697 of metamorphic monazite from a 1741 ma supracrustal rock directly date the timing of lower granulite facies metamorphism in the eastern upper gorge u pb ages 1685 1680 ma of granite dikes that postdate the development of leucosomal pegmatite pods in migmatitic supracrustal rocks in the eastern upper gorge are consistent with this suggestion the paleoproterozoic geologic history of the upper granite gorge is similar to that of the yavapai province in central arizona however unlike the juvenile crust that characterizes the yavapai province rocks in the western upper gorge preserve evidence for pre 1 8 ga crust first the 1840 1 ma elves chasm pluton the oldest known rock from the southwestern united states has a pb isotopic signature similar to that of rocks in the mojave province second the tuna creek granodiorite a member of the 1710 1750 ma arc related plutonic suite contains inherited zircons with minimum ages of 1998 and 2178 ma and exhibits whole rock pb isotopic signatures similar to rocks of the mojave province these data indicate that pre 1 8 ga crustal components participated at least locally in the development of the 1740 1710 ma arc related magmatic suite and suggest that a boundary between reworked crust and juvenile crust may be present in the western upper gorge

the low level structure of african easterly waves in 1995 abstract the existence of african easterly waves aews north of the african easterly jet aej core with maximum amplitude at low levels has been confirmed and clarified using radiosonde data and the u k meteorological office global model analysis from the hurricane season of 1995 at bamako 12 5 n 8 0 w the aews were characterized mainly by maximum amplitudes at the level of the aej around 700 mb whereas at dakar 14 7 n 17 5 w the waves were characterized by maxima between 850 and 950 mb the low level waves to the north of the aej arise in association with baroclinic interactions between the negative meridional potential vorticity pv gradients in the jet core and the positive low level gradient of potential temperature enhanced by the presence of low static stability air north of the aej these waves follow the positive meridional gradients over northern africa in contrast to the jet level aews that follow the meridional pv gradients at the level of the aej cross correlation analysis

fluctuations in northern hemisphere 700 mb height field associated with the southern oscillation abstract variations in the mid troposphere circulation associated with the southern oscillation so are investigated and documented using mean monthly 700 mb height data for the period 1951 79 the so was defined by a southern oscillation index soi consisting of the difference in normalized mean monthly sea level pressures at tahiti and darwin results for all four seasons are presented in the form of lagged as well as contemporaneous correlations and composites of height anomalies obtained separately for high and low soi values different so teleconnection patterns are observed for each season strongest so signals appear in the winter with soi leading the height field by one to two seasons the time lead may he useful in prognostic applications the correlation in the summer is negligible the winter teleconnection pattern over the north pacific north america north atlantic sector is similar to that shown by bjerknes and others patterns for other seasons are also presented the statistical signifi

atlantic tropical systems of 1994 and 1995 a comparison of a quiet season to a near record breaking one abstract totals of 70 and 63 tropical waves also known as african or easterly waves were counted in the atlantic basin during the 1994 and 1995 hurricane seasons these waves led to the formation of 9 of the 12 total number of tropical cyclones in 1994 and 19 of the 21 total number of tropical cyclones in 1995 tropical waves contributed to the formation of 75 of the eastern pacific tropical cyclones in 1994 and 73 in 1995 upper and lower level prevailing wind patterns observed during the below normal season of 1994 and the very active one of 1995 are discussed tropical wave characteristics between the two years are compared

crustal evolution of southern laurentia during the paleoproterozoic insights from zircon hf isotopic studies of ca 1 75 ga rocks in central colorado lu hf depleted mantle model tdm ages obtained by analysis of zircons previously dated by u pb methods demonstrate that ca 1 75 ga bimodal paleoproterozoic rocks in the gunnison salida region of central colorado and by extension in much of the southwestern u s were formed by partial melting of preexisting crustal rocks the ages of which mostly ages greater than 2 0 ga indicate that range from 1 83 to 1 87 ga some calculated lu hf tdm even older crust was probably involved consistent with the limited presence of ca 2 5 ga xenocrystic zircons in some rocks these results suggest that rocks related to the trans hudson and penokean orogens are cryptically present much farther to the south than previously believed coupled with the bimodality of the volcanic suite in central colorado and indeed in much of the southwestern u s these results indicate that in contrast to current juvenile arc accretion models melting of older crust related to extensional tectonics played an important role in the genesis of many magmatic rocks between 1 6 and 1 8 ga

sensitivity analysis of the physical dynamics of the fly river plume in torres strait abstract the intrusion in the torres strait of the fly river plume polluted by mine tailings is an international water issue to investigate the physical mechanisms involved in the intrusion process numerical simulations were conducted to assess the relative influence of the bathymetry and the external forcing namely the tides the mean sea level slope across the strait river runoff and wind forcing the wind data from horn island the only long term wind station in the torres strait is shown to be unreliable due to orographic effects mean sea level data from altimetry compare well with those from tide gauges in these shallow reef studded waters the wind has a dominant effect on the mean sea level at seasonal and inter annual periods the resulting mean sea level difference across the strait fluctuated seasonally and strongly influenced the intrusion of the fly river plume in the torres strait the 3d finite volume mohid model reproduced the observation that the river plume starts by being stratified in the gulf of papua where it originates and it mixes vertically when it enters the torres strait the mohid and the slim models were applied with different resolution to the torres strait and responded similarly to the external forcings the predicted and observed fly river plume intrusion in the eastern torres strait agreed well with each other including the formation of patches due to flow reversals however the two models predicted a widely different fly river plume in its far field in the western torres strait the differences were attributed to the different bathymetry in the australian and british us bathymetry data for these poorly charted waters which demonstrated the importance of the details of the bathymetry in controlling the extent of plume intrusion

new models for paleoproterozoic orogenesis in the cheyenne belt region evidence from the geology and u pb geochronology of the big creek gneiss southeastern wyoming the disputed age of the deep crust of the colorado province is central to hypotheses for paleoproterozoic crustal growth in the region we studied the high grade big creek gneiss southeastern wyoming as a potential exposure of pre 1780 ma basement rocks new geologic mapping and u pb geochronological data indicate that the big creek gneiss exposes a deeper but coeval level of the green mountain arc relative to the predominantly supracrustal section to the west the big creek gneiss is composed of supracrustal rocks a ca 1780 ma green mountain arc correlative bimodal intrusive suite a ca 1763 ma extensional bimodal intrusive suite and widespread ca 1630 ma pegmatitic leucogranite the mafic member of the younger bimodal suite is documented here for the first time u pb zircon ages from migmatite leucosomes indicate penetrative deformation of the big creek gneiss at ca 1750 ma we find that the postarc intrusive suite is mantle involved implying a second period of crustal growth shortening postdates arc magmatism by 20 m y implying that termination of arc magmatism and accretion were separate events finally criteria previously used to constrain the polarity of subduction for the green mountain arc are not reliable we propose two competing models 1 southward dipping green mountain arc subduction present coordinates with slab breakoff related magmatism following arc accretion or 2 northward dipping subduction with extensional postarc magmatism in both models high temperature deformation coincides with accretion along the cheyenne belt and extensional magmatism is an important component of crustal growth we prefer the northward dipping subduction model because it can be better integrated with regional tectonic events and published isotopic compositions of the igneous rocks

composite basement along the southern margin of the north australian craton evidence from in situ zircon u pb o hf and whole rock nd isotopic compositions abstract hafnium isotope compositions of emplacement age zircon grains are integrated with zircon 18o and whole rock nd isotope data in order to characterise the age and composition of the sources of paleoproterozoic granites along the southern margin of the north australian craton the petrogenesis of the granitic rocks is interpreted in terms of partial melting of distinct crustal components with variable crustal residence ages at different crustal levels reflecting the local paleoproterozoic crustal architecture this finding implies a composite nature of the unexposed deep crust which comprises paleoproterozoic supracrustals and subordinate discontinuous and local neoarchean meta igneous components the limited lateral extension of neoarchean deep crust does not support tectonic models for the paleoproterozoic amalgamation of the craton that consider intracratonic and or continent continent collision settings the composite nature of the basement and the presence of cryptic boundaries are consistent with the accretion of paleoproterozoic supracrustal elements as back arc and island arc to a neoarchean proto craton the dominant paleoproterozoic reworking of archean derived supracrustal materials indicates that accretionary orogenesis was an important setting for crustal reworking and craton stabilisation in the paleoproterozoic

does the arc accretion model adequately explain the paleoproterozoic evolution of southern laurentia an expanded interpretation a common model for the paleoproterozoic crustal evolution of southern laurentia involves southerly accretion of successively younger island arcs from 1780 to 1650 ma this model may be oversimplified however for although andesite and basaltic andesite major components of modern island arcs occur they are relatively rare and large volumes of rocks are dominantly bimodal metavolcanic assemblages and related granitoids ophiolites occur but they are also rare and only one accretionary melange has been described inherited zircons and common pb and nd isotopic data indicate involvement of older crust in ca 1750 ma rocks of the mojave province of southeastern california and western arizona and the bimodal assemblages of central colorado these data suggest that the bimodal volcanic rocks were derived from pre existing continental crust likely of ca 1850 ma trans hudson penokean age during extension and partial melting associated with the development of transpressional crustal scale shear zones the occurrence of the 1840 1 ma elves chasm pluton in the grand canyon demonstrates that rocks of trans hudson penokean age are present in southwestern laurentia

mean state and wave disturbances during phases i ii and iii of gate based on era 40 abstract using ecmwf s second generation reanalysis era 40 the large scale mean state and synoptic scale features associated with african easterly wave disturbances aews are examined over west africa and the adjacent eastern atlantic ocean during the three 21 day observing periods of the global atmospheric research program garp atlantic tropical experiment gate in 1974 phase i 26 june 16 july phase ii 28 july 17 august phase iii 30 august 19 september results are partitioned into four geographical boxes in order to highlight differences among the aew vortices as they propagate westward along two tracks northern and southern over west africa land and the adjacent eastern atlantic ocean water this marks the first time that a detailed diagnosis of the northerly track aews has been conducted results are also compared to previous gate studies and a 30 yr climatology is extracted from era 40 in general the subjectively analyzed wind fields presented in earlier studies compare favorabl

on kuroshio front fluctuations in the east china sea using satellite and in situ observational data fluctuations of the kuroshio front in the east china sea and their relation to variations of the kuroshio stream around the tokara strait are investigated using consecutive satellite images sea level data as well as water temperature records from a japan meteorological agency buoy station and a ferryboat which crosses the tokara strait meanders of the kuroshio front with typical horizontal scales of 100 to 150 km and wave periods of 14 to 20 days are found to appear ubiquitously in the east china sea the front meanders originate upstream over the continental slope and evolve rapidly while propagating downstream at speeds of 20 to 26 cm s 1 downstream southwest of kyushu the fully developed meanders sometimes take the form of warm filaments and when the volume transport of the kuroshio is large they may develop into shed off warm eddies previous observations based on ferryboat temperature records have revealed the repeated northward migration of a clear sea surface temperature sst front across the tokara strait it is shown that this northward migration of the sst front corresponds to the passage of the kuroshio front meanders across the tokara strait and that the unclear southward migration of the sst front is due to the presence of mixed water behind each meander the kuroshio front meanders in the east china sea are further found to be closely related to the north southward movement of the entire kuroshio stream in the tokara strait a lag of about 10 days exists between the time the front meanders reach the tokara strait and the kuroshio stream there shifts to its northernmost position

strain accumulation and fluid rock interaction in a naturally deformed diamictite willard thrust system utah usa implications for crustal rheology and strain softening abstract structural and geochemical patterns of heterogeneously deformed diamictite in northern utah usa record interrelations between strain accumulation fluid rock interaction and softening processes across a major fault willard thrust different clast types in the diamictite have varying shape fabrics related to competence contrasts with estimated effective viscosity ratios relative to micaceous matrix of 6 and 8 for large quartzite clasts respectively in the willard hanging wall and footwall 5 and 2 for less altered and more altered granitic clasts respectively in the hanging wall and footwall and 1 for micaceous clasts that approximate matrix strain within the footwall matrix x z strain ratios increase from 2 to 8 westward along a distinct deformation gradient microstructures record widespread mass transfer alteration of feldspar to mica and dislocation creep of quartz within matrix and clasts fluid influx along microcracks and mesoscopic vein networks increased westward and led to reaction softening and hydrolytic weakening in conjunction with textural softening from alignment of muscovite aggregates consistent si al and ti concentrations between matrix granitic clasts and protoliths indicate limited volume change mg gain and na loss reflect alteration of feldspar to phengitic muscovite within the hanging wall strain is overall lower with matrix x z strain ratios of 2 to 4 microstructures record mass transfer and dislocation creep concentrated in the matrix greater al and ti concentrations and lower si concentrations in matrix indicate volume loss by quartz dissolution na gain in granitic clasts reflects albitization large granitic clasts have less mica alteration and greater competence compared to smaller clasts differences in strain and alteration patterns across the willard thrust fault suggest overall downward up temperature fluid flow in the hanging wall and upward down temperature fluid flow in the footwall

hydrology and circulation in the strait of hormuz and the gulf of oman results from the gogp99 experiment 2 gulf of oman art no c12038 hydrological adcp and drifting buoy data obtained during the gogp99 experiment in october and early november 1999 are analyzed to describe the persian gulf water pgw core and the regional circulation in the gulf of oman the warm and salty pgw core flows out of the strait of hormuz heading southeastward unto 25degrees20 n 57degreese approximately from there it cascades down the continental slope veers southwestward and joins the omani coast near 24degrees50 n 56degrees50 e to form a slope current this pgw current has then thermohaline maxima on isopycnal sigma 0 26 5 near 220 m depth its thermohaline characteristics decrease along its progression to ra s al hadd and then offshore into the arabian sea but maintain a sharp contrast with surrounding waters outflow variability at the strait of hormuz can be related to downstream fluctuations of the thermohaline maxima in the pgw core at gulf scale and over a 2 to 3 week period moreover several mechanisms baroclinic instability flow intermittency cape effects are examined to explain the widening of this pgw core upstream and downstream of ra s al hamra in the eastern part of the gulf of oman the regional circulation is a cyclonic gyre the circulation in the western part of the gulf is more complex with the outflow of pgw and southeastward currents in the upper 250 m near the omani coast and a recirculation of upwelled waters near ra s jagin on the iranian coast the large cyclonic gyre occupies at least the upper 300 m of the water column and undergoes little variation over a month the pgw outflow in the northern arabian sea is southward and located 50 100 km from the coast it borders a shallower northward current located offshore

geochemistry of the dubois greenstone succession an early proterozoic bimodal volcanic association in west central colorado abstract the dubois greenstone succession an early proterozoic supracrustal succession in west central colorado is composed of fine grained felsic volcaniclastic sediments ash flow tuffs and tholeiitic flows sills and dikes the volcanic rocks comprise a bimodal suite of tholeiite and rhyolite the tholeiites are divided into two groups group i exhibiting nearly flat ree patterns 20 30 chondrites and group ii with light ree enriched patterns 40 70 chondrites these groups can be produced by two stage melting of an undepleted or enriched garnet lherzolite source in which garnet remains in the residue of only the first melting stage which produces group ii magmas the felsic magmas can be produced by partial melting of a high grade gneiss in the lower crust in which zircon is entrained in the magma the dubois greenstone succession appears to have formed by felsic and mafic subaqueous eruptions in which some ash flows upon entering water underwent phreatomagmatic explosions giving rise to detritus which formed the volcaniclastic sediments although tectonic setting cannot be assigned to the succession with a high degree of confidence an immature back arc basin developed on sialic crust in consistent with most data

the formation of continental crust part 1 a review of some principles part 2 an application to the proterozoic evolution of southern north america understanding of the evolution of continental crust has been dominated by work in tectonics experimental petrology and geochemistry and geochronology and isotope geochemistry in part 1 these approaches are discussed in the light of keynote articles most published by the geological society of america in an attempt to show how new data and new thinking have influenced understanding of the formation and modification of continental crust in part 2 the evolution of continental crust in southern north america from 1 8 ga until 1 3 ga is discussed as an application of ideas generated during the past 30 years

flow resistance in the great belt the biggest strait between the north sea and the baltic sea abstract the danish straits are part of the transition area between the north sea and the central baltic sea more precisely the danish straits connect kattegat to the arkona basin and includes the relatively narrow and shallow sub areas great belt little belt fehmarn belt and sound the flow resistances in the straits are hydraulically determined by among other factors the contractions sills and stratification found in the straits close to the entrance to the arkona basin the darss and drogden sills are located that trap inflowing dense water partially before it enters the central baltic sea hence the resistances in the danish straits are of crucial importance for the stratification and ecosystems in the central baltic sea the present work comprises calculations of flow resistance in the great belt based on measurements collected as part of the great belt fixed link investigations the specific resistance in the great belt is determined to be an average of 41 2 10 12 s 2 m 5 but it depends heavily on the interface position when calculating long term discharge time series on the basis of the momentum equation it is advised to apply a seasonal varying resistance

precambrian basement geology of north and south dakota combined analysis of drill hole gravity and magnetic data indicates that the buried precambrian basement rocks of the dakotas can be divided into several lithotectonic terranes eastern north dakota and northeastern south dakota are underlain by archean gneiss except for the black hills region of south dakota where archean rocks are also exposed the western third of both dakotas is underlain mainly by early proterozoic gneiss and metasedimentary rocks part of this region is underlain by archean crust with an early proterozoic tectonic overprint a broad transition zone of strongly overprinted archean crust occurs between the proterozoic rocks to the west and the archean rocks to the east south central south dakota is underlain by an early proterozoic batholith early proterozoic felsic volcanic rocks occur in southeast south dakota the bootheel portion of south dakota contains a diverse assemblage of basement rocks that are partly archean in age churchill province rocks of the trans hudson foldbel

climate simulations of african easterly waves the three dimensional structure and propagation characteristics of african easterly waves for the 1986 94 period are studied with june august european centre for medium range weather forecasts ecmwf operational analyses national centers for environmental prediction ncep reanalyses and canadian centre for climate modelling and analysis gcm output specific consideration is given to the differences in the timemean circulation synoptic scale variance covariance and principal oscillation patterns the african easterly waves derived from the ecmwf and ncep analyses are very similar with both providing a reasonably realistic depiction of african easterly waves given the agreement with one another earlier station data studies and theory where significant differences exist between the results from the two data assimilation systems they expectably do so over the tropical atlantic and in fields that are not directly observed such as vertical velocity the situation with the gcm is not as favorable but there are some encouraging areas of agreement despite the gcm s relatively coarse resolution and absence of observed data to constrain it selected points of agreement and disagreement between the gcm and the analyses include the following i the gcm african easterly wave energetics are comparable with the analyses in terms of the sign and magnitude of the energy transfers from the time mean state to the waves ii the northern track of easterly waves seen in the analyses terminates prematurely in the gcm at the african coast iii the southerly track of moist easterly waves seen in the analyses near the seasonal rainband is absent in the gcm possible reasons for the deficiencies are discussed the sensitivity of the gcm simulated african easterly waves to co2 doubling is investigated together with significant mean warming and moistening over the northern sahara the level of simulated african easterly wave activity increases with co 2 doubling

the sulu sea internal soliton experiment abstract we present the results of a comprehensive study of large amplitude internal solitons generated in the sulu sea in the philippines by intense tidal flow over a sharp bathymetric feature surface signatures of these waves have been observed in images from the dmsp landsat and nimbus 7 satellites and the space shuttle sir a synthetic aperture radar a two week experiment was conducted in the sulu sea in may 1980 from r v oceanograher during which a three mooring phased array of current meters and thermistors was implanted near the wave source and at 82 km and 200 km from the source seventeen soliton packets were observed whose properties underwent significant change as they propagated across the sea vertical profiles of density temperature and acoustic backscatter as well as radar and photographic surface signatures were obtained from the ship data from satellites moorings and the ship give unprecedented information on the spatial and temporal characteristics of solitary waves which ha

a numerical study of transport dynamics and seasonal variability of the yellow river sediment in the bohai and yellow seas abstract a sediment numerical model was embedded into a wave tide circulation coupled model to simulate the transport processes of the yellow river derived sediment considering the wave induced vertical mixing bv and the wave current coupled bottom shear stress bss numerical results show that the main stream of the yellow river derived sediment moves first eastward off the northern shandong peninsula and then southward into the south yellow sea all year round in spring the sediment moves northeastward in the bohai sea in summer there is a northeastward branch of sediment in the bohai sea off the west coast of the liaodong peninsula while the main part goes eastward to the yellow sea the yellow river derived sediment transport from the bohai sea to the north yellow sea across the bohai strait is mainly limited to the top 10 m and with a maximum centered at 37 9 n in summer the transport from the north yellow sea to the south yellow sea across the transect of 37 n is mainly in the 0 30 m layer with a maximum around 123 7 e in autumn the simulated yellow river discharged sediment deposits along the shandong peninsula and between 20 and 30 m isobaths in the yellow sea which is consistent with observation if surface waves are not considered in the model the sediment deposits westward to the nearshore area in the south yellow sea the sediment would deposit further southward in the numerical experiment results without wind influence in the numerical experiment of no tide there is hardly any sediment deposited on the yellow sea floor while in the bohai sea most of the sediment is transported southward and northwestward around the river mouth instead of eastward as in the control run indicating the tides play a key role in forming the deposition pattern