identification of the fortnightly wave observed along the northern coast of the gulf of guinea abstract numerical calculations of coastally trapped wave modes along the northern coast of the gulf of guinea using representative bottom topography and continuous stratification on a plane were carried out to identify the observed fortnightly propagating coastal wave results showed that the propagation speed of the observed wave approximately 53 cm s 1 for sea level and 54 cm s 1 for sea surface temperature is close to that of the second mode 64 cm s 1 and no other off the shelf this mode has a baroclinic structure having considerable amplitude at 2 km depth ray theory calculations indicate that if as is likely the observed wave were generated on the shelf a vertically standing modal structure with large amplitude at 2 km depth is not possible therefore no coastally trapped vertically standing wave modes are consistent with the observed wave consequently it is most likely that the wave is a vertically propagating coastally trapped wave as has been observed recently in other contexts th

evolution of the early proterozoic colorado province constraints from u pb geochronology the colorado province represents an addition of a belt of rocks more than 500 km wide to the southern margin of the archean wyoming craton during the early proterozoic between about 1790 and 1660 ma correspondence in ages between metamorphism deformation and plutonism association of volcanic rocks with comagmatic calc alkalic plutons and lack of older basement are all consistent with the interpretation that the rocks of the province are products of arc magmatism and cannibalistic sedimentation along a convergent margin at the southern edge of the craton

the pinal schist an early proterozoic quartz wacke association in southeastern arizona abstract at the type locality near globe arizona the pinal schist of early proterozoic age is comprised largely of quartz wacke turbidites which appear to have been deposited as a submarine fan sand grains are principally monocrystalline and polycrystalline quartz derived chiefly from plutonic sources with a minor contribution from low grade metamorphic sources the subrounded to rounded shapes of quartz sand and the sparsity of detrital feldspar indicate a significant pre turbidite erosional history felsic volcanic fragments also comprise variable proportions of the clasts qfl modal parameters indicate a source for pinal sediments comprised chiefly of granites and felsic volcanics representing a recycled terrane major and trace element contents of pinal sediments also suggest that they are largely quartz wackes and that none are graywackes ree elements exhibit typical phanerozoic shale patterns and reflect the importance of granite or rhyolite with negative eu anomalies in the source area high u th rb and hf contents and high rb sr la th and k na ratios also favor a source of dominantly granite and rhyolite an arc setting is clearly unacceptable for the pinal sediments geochemical and petrographic results favor either a continental ridt or collisional orogen a model is proposed in which pinal turbidites accumulate in an inundated continental rift granite and felsic volcanic sources lay to the east and represent older uplifted segments of the rift intense erosion in an intertidal zone may have rounded quartz grains and selectively removed feldspars prior to turbidity current transport

the pinal schist southeast arizona usa contraction of a palaeoproterozoic rift basin the palaeoproterozoic pinal schist of southeast arizona comprises mainly greenschist facies turbiditic metasedimentary rocks with associated volcanic rocks the deformation history of the pinal schist includes foliation and elongation lineation development within sedimentary protoliths during early basin contraction followed by gentle warping of the metamorphosed sediments into upright regional scale horizontal folds with 10 km wavelengths continued contraction caused development of shear zones approximately parallel to anticlinal axial surfaces and syn kinematic granitic rocks intruded into anticlinal cores such shear zones occur throughout southeast arizona in the turbiditic rocks of the pinal schist as well as in rocks of more continental character associated with the tonto basin supergroup in the mazatzal mountains it is proposed that shear zone distribution in both the pinal schist and the adjacent tonto basin supergroup reflects control by a pre existing rift margin the pinal schist and tonto basin supergroup therefore represent distal and proximal rift margin facies respectively reactivation of early extensional faults as reverse shear zones during margin contraction controls shear zone distribution in southeast arizona with deformation character changing from ductile to brittle with shallowing crustal level this model explains shear zone and lithological distribution and deformational style in southeast arizona and it also implies a continuum of sediment deposition and deformation throughout this part of the mazatzal orogeny

circulation and low frequency variability near the chilean coast remotely forced fluctuations during the 1991 92 el nino results are reported from the first long recording current meter observations over the slope off chile these observations at 308s during the 1991 92 el nino event are analyzed together with observations of currents at a local deep sea site local wind and sea level sea level from the peru and chile coasts and wind temperature and currents from the equatorial pacific mean poleward flow of 12 cm s21 was observed within the peru chile undercurrent over the slope mean flow in the depth range of antarctic intermediate water was not distinguishable from zero in the presence of strong low frequency lf variability which dominated slope currents at all depths the strongest lf fluctuations had periods of about 50 days but periods of 10 and about 5 days were also observed significant local wind forcing of slope currents was only found in the period band 6 10 days and may be related to coastal trapped waves in the atmosphere our analysis shows that free coastal trapped waves in the ocean arriving from the north dominated the lf variability over the shelf and slope off northern and central chile during the 1991 92 el nino event strong 50 day period fluctuations there started their journey about two months earlier and 15 000 km farther up the coastal equatorial waveguide near the date line in the equatorial pacific as equatorial kelvin waves forced by westerly wind events of similar period upon reaching the south american coast these waves forced coastal trapped waves which propagated along the peru coast into the study region likewise a scenario of equatorial trapped waves forcing coastal trapped waves may explain 10 day as well as 6 day and 4 5 day period coastal trapped waves off chile stemming from mixed rossby gravity and inertia gravity waves trapped at the equator since the large 50 day period coastal trapped waves may strongly modify coastal upwelling source water such remotely forced waves may have a significant influence on the pelagic ecosystem off chile at least during el nino events

coastal trapped wave propagation along the southwest african shelf as revealed by moored observations abstractcoastal trapped waves ctws that propagate poleward along the southwest african shelf potentially leak energy from lower latitudes into the benguela upwelling system bus thus in additi

forced oscillations on the equatorial atlantic basin during the seasonal response of the equatorial atlantic program 1983 1984 a subset of data from an array of eight inverted echo sounders and a meteorological station deployed and maintained for 15 months in the equatorial atlantic as part of the seasonal response of the equatorial atlantic program are analyzed to determine the variability of forced oscillations of the basin the analysis is done to study both low and high frequency variability at low frequencies the equatorial basin responds as a whole to the seasonally varying winds the dominant signal is the annual cycle of the equatorial system as a composite of the response to the strong seasonal wind curl that is maximum in the western basin and the part of the zonal transfer to mass associated with the seasonal equatorial upwelling and downwelling system three bands of energy appear as dominant in the combined spectrum of the ocean and the atmosphere at higher frequencies 20 30 days 13 16 days and the inertial gravity wave band each one of the bands is analyzed and discussed instability waves are detected on the echo sounder records the waves have periods centered at 30 2 days and propagate westward with a wavelength of 1000 km and a phase speed of 0 35 m s the most energetic oscillation in the analyzed wind records is at periods centered around 14 days the response of the ocean to this oscillation has a meridional distribution with maximum amplitude at 3 n the most significant oceanic oscillations in the inertial gravity band are centered at 5 2 and 3 5 days from the study of their meridional structure it is concluded that those oscillations correspond to forced inertial gravity waves with meridional structures corresponding to the meridional numbers n 1 and n 3 respectively

oceanic kelvin waves and tropical atlantic intraseasonal variability 1 kelvin wave characterization 1 oceanic kelvin waves from the equator to the west african coast are investigated in the framework of tropical atlantic intraseasonal variability in order to better highlight the wave propagations a 25 95 day band pass filter was applied to the sea surface height ssh product derived from the topex poseidon altimeter and an ocean general circulation model simulation for the 1993 2000 period in addition to equatorial eastward propagations our analysis reveals recurrent and continuous propagations distinguishable over thousands of kilometers poleward along the coasts as far as about 10 15 latitude a novel result with altimeter data the variance of the filtered ssh signal goes from 1 cm at the equator to 2 cm at the african coast estimates of the phase speed range from 1 5 to 2 1 m s along the equator and the west african coastline such values are very close to those of equatorial kelvin wave propagations likely dominated by the first two baroclinic modes supporting the fact that the coastal propagations are coastally trapped kelvin waves in order to simplify the description of these kelvin waves we present an intraseasonal climatology which reveals regular boreal autumn winter equator to coast propagations an improved description is achieved thanks to the computation of an extended empirical orthogonal function for the boreal autumn winter propagations lag correlation of ssh signals allows for a twofold quantification the phase speed and the importance of remote forcing along the coast the remote forcing effect of intraseasonal kelvin waves is clearly evidenced over coastal upwelling regions as far as 10 15 latitude the physical mechanism associated with the forcing of the kelvin waves and its impacts will be investigated in a future paper

the pinal schist of southern arizona a paleoproterozoic forearc complex with evidence of spreading ridge trench interaction at ca 1 65 ga and a proterozoic arc obduction event the pinal terrane of southern arizona is composed mostly of quartz sericite schists meta wackes metavolcanic rocks and granitoid and gneissic rocks with minor meta chert meta conglomerate and carbonate rocks various tectonic settings have been suggested for the origin of this terrane the existence of tectonic melanges within the terrane the presence of granitic rocks in close proximity to the melanges the presence of both oceanic and arc like metavolcanic rocks within the terrane the age distributions of igneous and meta igneous rocks within the terrane the deformational patterns within the terrane and the width of the terrane all support a model in which the terrane was formed as a forearc subduction complex that experienced a ridge subduction event at ca 1 65 ga the pinal terrane was likely the forearc subduction complex to the mazatzal arc terrane which lies immediately to the north regional variations in the mineralogy of metavolcanic and metasedimentary rocks exposed within the terrane together with structural data suggest the terrane may have experienced an arc obduction event in the proterozoic after the ridge subduction event if it did most of this arc terrane was eroded off the pinal terrane in the 300 m y following the obduction event and prior to deposition of the apache group at ca 1 32 ga there is a paleoproterozoic arc terrane exposed in northern mexico that may represent remnants of an obducted arc terrane high pressure high temperature metamorphic rocks e g blueschists have not been identified within the pinal terrane

equatorial atlantic variability and its relation to mean state biases in cmip5 coupled general circulation model gcm simulations participating in the coupled model intercomparison project phase 5 cmip5 are analyzed with respect to their performance in the equatorial atlantic in terms of the mean state 29 out of 33 models examined continue to suffer from serious biases including an annual mean zonal equatorial sst gradient whose sign is opposite to observations westerly surface wind biases in boreal spring play an important role in the reversed sst gradient by deepening the thermocline in the eastern equatorial atlantic and thus reducing upwelling efficiency and sst cooling in the following months both magnitude and seasonal evolution of the biases are very similar to what was found previously for cmip3 models indicating that improvements have only been modest the weaker than observed equatorial easterlies are also simulated by atmospheric gcms forced with observed sst they are related to both continental convection and the latitudinal position of the intertropical convergence zone itcz particularly the latter has a strong influence on equatorial zonal winds in both the seasonal cycle and interannual variability the dependence of equatorial easterlies on itcz latitude shows a marked asymmetry from the equator to 15 n the equatorial easterlies intensify approximately linearly with itcz latitude when the itcz is south of the equator on the other hand the equatorial easterlies are uniformly weak despite serious mean state biases several models are able to capture some aspects of the equatorial mode of interannual sst variability including amplitude pattern phase locking to boreal summer and duration of events the latitudinal position of the boreal spring itcz through its influence on equatorial surface winds appears to play an important role in initiating warm events

book reviewthe techniques of modern structural geology vol 1 strain analysis j g ramsay and m i huber academic press london 1983 xiii 307 pp us 55 00 28 00 hardcover

geochemistry and tectonic setting of lower proterozoic supracrustal rocks of the pinal schist southeastern arizona two lithologic assemblages are identified in the early proterozoic 1700 ma supracrustal rocks of the pinal schist in southeastern arizona a western assemblage is composed largely of quartz wacke turbidites and an eastern assemblage includes bimodal volcanics and variable amounts of sediment chiefly feldspathic quartzite and conglomerate basalts from the eastern assemblage have incompatible element distributions similar to those found in basalts from continental margin arcs or evolved oceanic arcs whereas those from the western assemblage have distributions similar to within plate or back arc basin basalts felsic volcanics range in composition from rhyodacite to rhyolite and exhibit incompatible element distributions similar to those found in felsic volcanics from continental rifts and back arc basins near continents provenance studies of sediments from both assemblages indicate sources rich in granite and felsic volcanics the quartz wackes are similar in composition to sediments from continental margin arcs and associated back arc basins an increase in mafic components in these rocks from north to south in the pinal basin may reflect compositional polarity in an arc system the eastern assemblage may represent remnants of a major northeast trending continental margin arc system and the western assemblage may have been deposited in an intra arc basin or a northwest trending aulacogen which opened on the southwest

diagnosing the annual cycle of the equatorial undercurrent in the atlantic ocean from a general circulation model abstract ten year long output series from a general circulation model forced by daily realistic winds are used to analyze the annual cycle of the equatorial undercurrent euc in the atlantic ocean two well defined transport maxima are found one present during boreal summer and autumn in the central part of the basin is generally recognized and regarded as a near equilibrium response to the equatorial easterly trades that culminate in this period another one most pronounced near the western boundary occurs in april may when the trades relax this second maximum is less patent in the observations but concomitant signals in previously published analyses of the north brazil current and surface velocity seasonal variations might be indirect manifestations of its reality because this intensification appears at periods when the boundary between the tropical and equatorial gyres nears the equator the authors relate its existence to wind stress curl variations at subequatorial latitudes a link between

the mean flow field of the tropical atlantic ocean the mean horizontal sow eld of the tropical atlantic ocean is described between 20in and 20is from observations and literature results for three layers of the upper ocean tropical surface water central water and antarctic intermediate water compared to the subtropical gyres the tropical circulation shows several zonal current and countercurrent bands of smaller meridional and vertical extent the wind driven ekman layer in the upper tens of meters of the ocean masks at some places the sow structure of the tropical surface water layer as is the case for the angola gyre in the eastern tropical south atlantic although there are regions with a strong seasonal cycle of the tropical surface water circulation such as the north equatorial countercurrent large regions of the tropics do not show a signi cant seasonal cycle in the central water layer below the eastward north and south equatorial undercurrents appear imbedded in the westward sowing south equatorial current the antarcic intermediate water layer contains several zonal current bands south of 3in but only weak sow exists north of 3in the sparse available data suggest that the equatorial intermediate current as well as the southern and northern intermediate countercurrents extend zonally across the entire equatorial basin due to the convergence of northern and southern water masses the western tropical atlantic north of the equator is an important site for the mixture of water masses but more work is needed to better understand the role of the various zonal under and countercurrents in cross equatorial water mass transfer 1999 elsevier science ltd all rights reserved

growth stabilization and reactivation of proterozoic lithosphere in the southwestern united states growth of proterozoic continental lithosphere in the southwestern united states involved assembly of tectonostratigraphic terranes during several pulses of convergent tectonism ca 1 74 1 70 and 1 65 1 60 ga prograde metamorphism accompanied orogenic assembly and peak metamorphic conditions outlasted deformation regions now characterized by the highest metamorphic grades underwent slow isobaric cooling and were not uplifted until more than 200 m y after assembly regions of low metamorphic grade were not uplifted substantially after assembly we suggest that 1 relatively thin lithospheric fragments were assembled into isostatically stable normal thickness continental lithosphere 2 assembly did not erase lithospheric scale heterogeneities 3 the present juxtaposition of different crustal levels reflects differential uplift related to 1 4 1 1 ga tectonomagmatic activity and 4 the boundaries between different lithospheric blocks were repeatedly reactivated from precambrian through tertiary time

evidence of two independent modes of convection at intraseasonal timescale in the west african summer monsoon 1 two main independent modes of convection at intraseasonal timescale in the west african summer monsoon are highlighted one depicts a meridional dipole of convection over west africa linked to a modulation of the latitude of the inter tropical convergence zone itcz it is associated with a westward propagative signal of the convection over the sahel and to a modulation of cyclonic vorticity at these latitudes the other one is characterized by a stationary uniform modulation of convection in the itcz without any significant modulation of its latitudinal location it is associated with a modulation of the zonal wind component over the eastern equatorial atlantic the dominant periodicity of these two modes is around 15 days it is necessary to take into account the relative parts of these two modes in order to accurately analyze the mechanisms involved in intraseasonal variability of the african monsoon

the equatorial source of propagating variability along the peru coast during the 1982 1983 el nino using data obtained from tide gages in south america current meters along the equator and the peru coast and an array of pressure gages and inverted echo sounders within and around the galapagos archipelago we have analyzed the equatorial origin of coastal trapped waves observed by cornejo rodriquez and enfield this issue along the peru coast during the intense 1982 1983 el nino the propagating fluctuations along the coast were much stronger at that time than either before or after the el nino and the variability was not locally forced by coastal winds we find that the coastal variability was also more energetic during previous el nino occurrences at periods of 1 2 weeks the meridional component of currents on the equator is up to an order of magnitude more energetic than the zonal fluctuations and is consistently associated with sea level that fluctuates antisymmetrically between hemispheres at periods longer than 2 weeks the zonal velocity component is more energetic and the cross equatorial sea level variability is symmetric the meridional and zonal phase structures of cross spectra involving the currents and sea level establish the 1 to 2 week equatorial fluctuations as mixed rossby gravity yanai waves of low wave number with infinite phase speed standing oscillations in the middle of the band 10 days the corresponding structures for longer periods are consistent with nondispersive kelvin waves frequency domain eof modes of the sea level and current data establish the mixed rossby gravity waves as the principal source of the strong trapped wave variability in the 1 to 2 week band along the ecuador peru coast during the 1982 1983 el nino episode

temporal and spatial aspects of the cusp inferred from local and global ground and space based observations in a case study 1 global and local observations from both ground and space facilities are brought to bear to understand the origin of a stepped cusp ion dispersion observed 3 hours prenoon under an interplanetary magnetic field characterized by strongly positive by conditions under which the cusp is believed to be shifted postnoon our main aim is to distinguish the temporal from the spatial cusp features the local observations from svalbard are from approximately the 0900 1200 mlt sector while the in situ observations are from polar at 0900 mlt the global auroral observations were acquired by the earth camera on polar the aurora from the ground perspective appeared as a periodic sequence of brightening events located on either side of a midday gap aurora centered at about 1030 mlt at noon the aurora appeared as a semiperiodic sequence of brightening events these were concurrent with enhancements of the overhead ionospheric hall current polar observed two steps of a staircase ion energy latitude dispersion these two steps were in turn concurrent with two consecutive auroral brightening events we argue from this complement of observations that the stepped cusp was temporal in nature and resulted from a time varying reconnection process global uv imagery was employed to complement the ground observations for the purpose of separating the temporal from the spatial aspects the imager captured namely two bands of strong uv emission in the prenoon and postnoon sectors between which there appeared a persistent weak uv aurora we interpret this to be an underlying spatial substratum patchy and bursty uv enhancements coincided with the transients seen in the local ground and space measurements corroborating further our distinction between space and time in the cusp comparing these inferences with recent work on the response of the dayside aurora to reconnection at the magnetopause we find a close correspondence in addition we document the field aligned currents associated with the stepped cusp which in turn compare favorably with recent theoretical ideas this work is a contribution to the current debate on the nature of the stepped cusp and suggests that multiple data sets are essential to study this problem

remotely forced biweekly deep oscillations on the continental slope of the gulf of guinea current meter measurements on the continental slope of the gulf of guinea at 7 20 s and 1300 m depth have revealed biweekly oscillations of the currents bottom intensified and oriented along the bathymetry we develop a three dimensional primitive equation model of the gulf of guinea to study the oscillations and their forcing mechanism the high resolution 1 12 regional model reproduces remarkably well the main characteristics of the deep currents on the continental slope experiments with different forcings demonstrate that the biweekly variability at 1300 m depth is remotely forced by equatorial winds deep yanai waves generated by the wind propagate eastward along the equator upon reaching the african coast the energy propagates poleward in both directions as coastal trapped waves the selection of the dominant biweekly period is explained by the absence of equatorial waves with westward group velocities in that frequency band contrary to a previous hypothesis involving tidal forcing our interpretation is coherent with the significant interannual variability of the biweekly energy

tectonic evolution of the fundy rift basin canada evidence of extension and shortening during passive margin development seismic and field data show that the fundy rift basin of southeastern canada experienced two distinct episodes of deformation during mesozoic time the first episode during middle triassic to early jurassic time was extensional rifting associated with nw se extension reactivated ne trending paleozoic compressional structures as normal faults forming the northwestern boundary faults of the fundy basin displacements on the low angle boundary faults locally exceeded 10 km rifting also reactivated east trending paleozoic compressional structures as oblique slip faults with normal and sinistral strike slip components forming the northern boundary faults of the fundy basin several kilometers of sediments and lava flows filled the basin during rifting the second deformational episode occurred during or after early jurassic time and probably before or during early cretaceous time inversion associated with nw se shortening occurred along all faulted margins of the fundy basin the northwestern boundary faults experienced several kilometers of reverse displacement broad anticlines developed within their hanging walls and the fundy basin acquired its synclinal form the northern boundary faults of the fundy basin became oblique slip faults with reverse and dextral strike slip components gentle synclines tight anticlines and faults with reverse separation deformed the synrift strata near the northern margin of the fundy basin neither collision nor subduction zones existed near the fundy basin during mesozoic time hence we believe that tectonic processes associated with seafloor spreading e g incipient ridge push forces continental resistance to plate motion produced the shortening in the fundy basin shortening occurred during the transition from rifting to drifting as north america separated from northern africa and or during the early stages of drifting as the seafloor spreading centers of the north atlantic propagated northward

does the aurora provide evidence for the occurrence of antiparallel magnetopause reconnection 1 antiparallel merging at the magnetopause predicts a longitudinal bifurcation of the cusp during intervals of southeast or southwest interplanetary magnetic field imf orientation in the aurora this should manifest itself as a longitudinal gap in the midday sector bracketed by bright auroral forms on either side with the purpose of testing this prediction we searched for an auroral signature in our database from the arctic islands of svalbard focusing on strong isolated auroral brightenings belonging to the category of events which has been previously established as a signature of transient magnetopause reconnection flux transfer events ftes we found some very interesting events showing clear brightenings in the eastern and western parts of the field of view fov with a gap in between in this paper we present a 1 hour long interval of auroral observations in the 1100 1400 mlt sector showing two strong isolated auroral events which were separated by 20 min the imf was steady and directed southeast by 3 nt bz 3 nt clock angle 135 in a solar wind of low speed 370 km s 1 and low dynamic pressure 0 2 npa each auroral event is characterized by an initial strong brightening of the cusp equatorward boundary previously referred to as equatorward boundary intensification ebi which is followed by a westward and poleward moving auroral form pmaf the main point here is that the initial brightening is longitudinally bifurcated with near simultaneous auroral brightenings in the eastern 1300 1400 mlt and western 1100 1130 mlt parts of the all sky camera fov being separated by a 500 km wide gap the brightening event is discussed as a possible signature of transient antiparallel reconnection taking place at high magnetopause latitudes while the gap aurora is attributed to quasi steady component reconnection in the subsolar region

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

a comparison of foreland and rift margin sedimentary basins foreland and rift margin basins are compared on the basis of 1 their tectonic setting 2 reasons for subsidence and 3 their large scale geophysical and geological characteristics the thermal and mechanical properties of the underlying lithosphere are shown to be fundamental to the form of tectonic subsidence the lithosphere beneath foreland basins is flexurally downwarped by the loading of the adjacent fold thrust belt whereas tectonic subsidence at rifted margins is caused by mass replacement at depth during lithospheric extension on rifting and subsequent thermal contraction as the lithosphere cools the effects of rheology thermal maturity and lateral changes in properties of the lithosphere are outlined for foreland basins as is the topographic effect of possible phase changes beneath the fold thrust belt the thermal and rheological consequences of lithospheric extension at rift margins makes flexural subsidence relatively less important than in foreland basins flexure may however be partly responsible for uplift landward of the hinge line that is associated with rifting other mechanisms that could cause such uplift include depth dependent extension and thermal expansion due to the lateral diffusion of heat the models describing the evolution of these basins are shown to predict characteristics that are in accord with observations the superposition of foreland and rift margin basins as a result of ocean closure can lead to an overall basin stratigraphy that is complex such phases of basin subsidence must be separated according to the tectonic environment in which they formed in any analysis of the cause and consequences of basin evolution

tropical instability waves at 0 n 23 w in the atlantic a case study using pilot research moored array in the tropical atlantic pirata mooring data temperature salinity velocity and wind from a mooring at 0 n 23 w are used along with satellite data for sea surface temperature and sea level to examine the contribution of tropical instability waves tiws to the energy and heat balance of the equatorial atlantic mixed layer the tiws appear as periodic 20 30 day fluctuations of currents temperature and salinity which intensify beginning in june and peak in late boreal summer the intensification occurs in phase with strengthening of the southeasterly trade winds and the seasonal appearance of the equatorial tongue of cold mixed layer temperatures in 2002 these waves which warm the mixed layer by 0 35 c during summer months are maintained by both barotropic and baroclinic conversions that are of comparable size salinity fluctuations previously neglected increase the magnitude of baroclinic energy conversion

an eddy permitting model of the atlantic circulation evaluating open boundary conditions as part of the french clipper project an eddy permitting model of the atlantic circulation has been run for 22 years the domain has open boundaries at drake passage and at 30 e from africa to antarctica the simulated mean circulation as well as the eddy activity is satisfactory for a 1 3 model resolution and the meridional heat transport at 30 s is within the range estimated from observations we use the mixed open boundary algorithm of barnier et al 1998 which has both a radiation condition and a relaxation to climatology the climatological boundary forcing strongly constrains the solution in the whole domain the model heat balance adjusts through the surface heat flux retroaction term more than the open boundaries the radiation phase velocities calculated within the algorithm are analyzed this shows quite surprisingly that both the eastern and western boundaries have a similar behavior regardless of the preferred directions for advection mainly eastward and wave propagation mainly westward our results confirm that open boundary algorithms behave differently according to the dynamics of the region considered the passive boundary condition that penduff et al 2000 applied successfully in the north eastern atlantic does not work in the present south atlantic model we emphasize the need for a careful prescription of the climatology at the open boundary for which a new approach based on synoptic sections is implemented

lead isotopic compositions of diverse igneous rocks and ore deposits from southwestern new mexico and their implications for early proterozoic crustal evolution in the western united states u pb zircon measurements from some of the basement rocks in southwestern new mexico have ages that range from 1 650 to 1 450 m y the largest ore deposits occur near silver city in the southwest part of the region studied they are associated with laramide alkali to calc alkaline plutons and their lead isotopic compositions are the least radiogenic in the region this lead exhibits lower crustal upper mantle characteristics and for the major producing porphyry copper deposits the 206 pb 204 pb ratios are less than 18 0 lead from more silicic mid tertiary volcanic rocks and associated ore deposits has somewhat higher 208 pb 204 pb ratios that reflect a greater crustal involvement in their origin in a regional trend to the northeast ore lead becomes more radiogenic and at hansonburg 200 km from silver city lead in the mississippi type deposits is clearly derived from upper crustal sources on the 207 pb 204 pb 206 pb 204 pb plot data from all of the rocks and ores that we have analyzed form an array that lies below the average orogene curve of doe and zartman 1979 a common source is implied for the lead the isotopic composition of which was similar to that found in 1 750 m y old stratiform deposits as far apart as pecos new mexico and jerome arizona such a composition indicates that over a large region of the southwestern united states continental crust developed between 1 750 and 1 450 m y ago possibly in an island arc environment basement rocks that are 1 750 m y old extend northward through colorado to utah galena data obtained in previous studies show that the fraction of older sialic lead in those rocks increases toward the archean craton in wyoming the crust apparently developed southward from wyoming in stages at 2 400 m y ago or before 2 100 m y ago and 1 750 m y ago with incorporation of older sialic material in each stage as far south as milford utah

wind driven coastal trapped waves off the island of gotland baltic sea an analysis is presented of repeated density and current profiles and recording current meter rcm data collected off the northwest coast of gotland island baltic sea during the late summer and fall of 1977 large low frequency fluctuations were found in alongshore flow and isopycnal displacements and were significantly correlated with winds observed at gotland s west coast the best correlations were found with winds from the island s southern tip rather than with local winds coherence was high between rcm current fluctuations at 70 and at 90 m 100 m water depth 4 km from the coast whereby flow at 90 m led flow at 70 m an eof analysis of profile observations showed a 7 day baroclinic wave with a two and a three layer current structure trapped in the coastal zone the time series of the weaker three layer mode was found to lag that of the stronger two layer mode by about one day wind forced coastal trapped wave ctw theory with bottom friction and scattering was applied to the gotland west coast and model output was compared with data this application assumed zero ctw amplitude at the island s southern tip the starting point for the forced wave integration and used two coastal segments a late summer and a winter stratification and winds from three coastal sites a very simple model version first two ctw modes only no bottom friction or scattering winds from the island s southern tip only was able to reproduce reasonably well structure amplitudes and phases of observed alongshore current fluctuations in the lower part of the water column observed upward phase propagation was explained by lagged superposition of the two ctw modes in the strongly stratified baltic sea buoyancy forces may act to reduce the effects of bottom friction on low frequency flow a combination of island length scale and synoptic wind scales act to filter out higher ctw modes the effects of scattering were greatest for weaker winter stratification

deformational styles in the proterozoic pinal schist pinal peak arizona microstructural and quartz caxis analyses a 5 km thick north dipping shear zone in the pinal peak map area near globe arizona reveals contact metamorphism of the pinal schist through intrusion of the proterozoic madera diorite in pinal schist sillimanite and rare andalusite occur in the metamorphic aureole around the diorite but not elsewhere in this or adjoining map areas where metamorphic grade is interpreted to be low greenschist facies deformation was synchronous in the schist and the diorite and is recorded by a well developed generally n and nw trending elongation lineation field interpretations of ductile deformation fabrics generally indicate top to the south or reverse present day coordinates displacement microstructures in the pinal schist the madera diorite and the pinal madera contact zone include s c fabrics mica fish asymmetric type tails on porphyroclasts and grain shape and lattice preferred mineral orientation most of which indicate top to the south locally se to sw displacement consistent with field

variability of the horizontal velocity structure in the upper 1600 m of the water column on the equator at 10 w this paper presents initial results from new velocity observations in the eastern part of the equatorial atlantic ocean from a moored current meter array during the equalant program 1999 2000 a mooring array was deployed around the equator near 10 w that recorded one year of measurements at various depths horizontal velocities were obtained in the upper 60 m from an upward looking acoustic doppler current profiler adcp and at 13 deeper levels from current meters between 745 and 1525 m to analyze the quasiperiodic variability observed in these records a wavelet based technique was used quasiperiodic oscillations having periods between 5 and 100 days were separated into four bands 5 10 10 20 20 40 and 40 100 days the variability shows i a strong seasonality the first half of the series is dominated by larger periods than the second one and ii a strong dependence with depth some oscillations are present in the entire water column while others are only present at certain depths for the oscillations that are present in the entire water column the origin of the forcing can be traced to the surface while for the others the question of their origin remains open phase shifts at different depths generate vertical shears in the horizontal velocity component with relatively short vertical scales this is especially visible in long duration events 100 days of the zonal velocity component comparison with a simultaneous lowered acoustic doppler current profiler ladcp section suggests that some of these flows may be identified with equatorial deep jets a striking feature is a strong vertical shear lasting about 7 months between 745 and 1000 m these deep current meter observations would then imply a few months of duration for the jets in this region

plate tectonics model for proterozoic continental accretion in the southwestern united states proterozoic crustal provinces in the southwestern united states decrease in age south from the archean wyoming province supracrustal rocks define three major age provinces from north to south 1 72 to 1 80 1 65 to 1 72 and 1 1 to 1 2 b y successions within each province are similar and define two assemblages a bimodal volcanic assemblage commonly overlain by a quartzite shale assemblage precambrian granitic plutons intrude all three provinces geochemical and sr isotope data indicate a variably depleted upper mantle source for basalts and a short lived these observations can be explained by a plate tectonics model involving successive marginal basin closures and andean type orogenies associated with southward migrating arcs the net result is to accrete 1 300 km of continental crust to the southwestern margin of north america between 1 8 and 1 1 b y ago

role of poleward moving auroral forms in the dawn dusk auroral precipitation asymmetries induced by imf by 1 in a case study we document the detailed spatial temporal structure of the aurora in the 0900 1500 magnetic local time mlt sector during an interval of steady southeast imf orientation emphasis is placed on ground based observations of structure that is often averaged out in large statistical studies a central feature is the phenomenon of poleward moving auroral forms pmafs an ionospheric manifestation of pulsed magnetopause reconnection in the form of flux transfer events ftes whose evolution in both prenoon and postnoon mlts can be monitored under similar interplanetary conditions differences in auroral precipitation associated with pmafs about the noon meridian related to imf by are documented while the prenoon pmafs develop in three stages spanning a latitude range of 500 km the highest latitude stage is absent in postnoon pmafs for by 0 which after the initial intensification progressively fade we suggest that this auroral precipitation asymmetry is closely related to the different field aligned current configuration in pmafs prenoon and pmafs postnoon and the underlying plasma convection pattern we detail the association between the high latitude component of pmafs in the prenoon sector by 0 and a channel of plasma convection located in the dawnside convection cell the latter convection channel located in the regime of old open flux represents an aspect of the svalgaard mansurov effect which is not included in the traditional description the auroral and plasma convection data are placed in the context of recent work on solar wind magnetosphere interconnection topology for a southward pointing imf with a strong by component

long shelf waves generated by a coastal flux solutions are presented for the shelf response of barotropic and stratified oceans to an oscillatory coastal flux through a strait the flux is modeled as the return interior flow due to an ekman transport that arises from a fictitious square wave longshore wind stress the width 2 d of the square wave stress is taken to be that of the strait and the response due to the coastal flux determined from longwave wind forced solutions that exist in the literature the net longshore energy flux for the nth strait forced shelf wave mode wave number kn is shown to be proportional to u2 bnsin knd knd 2 where u2 is the coastal flux spectrum and bn the modal wind coupling coefficients results compare favorably with existing barotropic theories and estimates of net longshore energy flux obtained for the australian coastal experiment region are shown to be in reasonable agreement with observations at periods of 9 days when forcing by bass strait is assumed greatest

turbidity events observed in situ along the congo submarine channel abstract as part of the multidisciplinary programme biozaire devoted to studying deep sea benthic ecosystems in the gulf of guinea particulate input and its relationship with near bottom hydrodynamics were monitored using long term moorings from 2000 to early 2005 particular attention was given to material input through the congo ex zaire submarine channel that extends 760 km from the congo river mouth to the abyssal plain 5100 m near 6 s due to its direct connection to the congo river the congo canyon and channel system are characterised by particularly active recent sediment transport during this first in situ long term monitoring along the channel an energetic turbidity event was observed in january 2004 at three locations along the channel from 3420 to 4790 m in depth this event tilted and displaced the moorings installed at 3420 m site zr and 4070 m site zd and resulted in high sediment deposition at all three mooring sites the event moved at an average velocity of 3 5 m s 1 along the numerous channel meanders between 3420 and 4070 m then at 0 7 m s 1 between 4070 m and the end of the channel at 4790 m the particle cloud rose above the top of the valley at 4070 m site zd but not at 3420 m site zr where the channel was too deep lastly the mooring line broke at site zd in october 2004 probably due to a strong event like that of 2001 previously described by khripounoff et al khripounoff a vangriesheim a babonneau n crassous p denniellou b savoye b 2003 direct observation of intense turbidity activity in the zaire submarine valley at 4000 m water depth marine geology 194 151 158 between these strong events several peaks of high turbidity and particle flux occurred but without noticeable current increases these events were probably due to local sliding of sediment accumulated on the walls or terraces on the side of the channel the area near 4000 m depth and the lobe appear to be the main depocentres of particulate input rich in organic matter derived from the congo river

on the internal geometry of mylonite zones mylonite zones are generally characterized by abrupt and very large strain transitions which commonly result in excessively anastomosing schistosities on a wide range of scales when compared with nonmylonitic foliations this geometry is very susceptible to remodification during progressive mylonitization resulting in unusual and complex fold lineation and foliation geometries and interrelationships open folds of the mylonitic foliation with axes parallel to the stretching lineation in the surrounding mylonite cannot have formed by the rotation of fold axes through a large angle within their axial planes as has been usually proposed for isoclinal and sheath folds in mylonitic zones open folds initiate with axes parallel or close to the stretching lineation due to the geometric effects of folding a mylonitic foliation which anastomoses around an ellipsoidal pod of less deformed material this initial geometry also allows the generation of fold axes curved within their axial plane through 1800 about the stretching lineation at the time of nucleation successive mylonitic foliations develop during this folding and refolding process with boundaries that truncate and isolate earlier fold hinges and portions of fold limbs as a consequence stretching and intersection lineations can vary from plane to plane through the mylonite zone although careful examination often reveals a weak overprinting stretching lineation parallel to the bulk movement direction for the whole zone fold asymmetry in mylonite zones is a potential indicator of shear sense across a zone if the fold axes lie at an angle to the bulk stretching lineation direction in such circumstances however a single asymmetry projected onto a plane perpendicular to the mylonitic foliation and containing the bulk stretching lineation can indicate either sense of shear depending on a variety of factors these include whether the foliation folded is primary or mylonitic and in the latter case whether the mylonite zone formed with a steep dip and horizontal stretching lineation or in some other orientation the most satisfactory sense of shear indicator is the asymmetry of s and c planes

structural and kinematic evolution of the teslin suture zone yukon record of an ancient transpressional margin abstract the teslin suture zone tsz yukon which forms the fundamental boundary between rocks deposited along the ancient margin of north america and allochthonous terranes to the west preserves a complex history of pre mid jurassic convergence and dextral strike slip translation which is overprinted locally by late cretaceous dextral strike slip shear the tsz comprised of a 15 20 km thick structural sequence of ductilely deformed sedimentary and volcanic strata basalt peridotite and granitoids is divisible into distinct elongate structural domains based on the distribution of two well defined but differently oriented stretching lineations lds and lss lds and lss both formed during non coaxial ductile deformation lds trends e w and plunges down dip whereas lss trends nnw sse and plunges shallowly two 1 2 km wide nnw trending anastomosing shear zones of lss cross cut lds structures indicating lss is younger other field relations indicate further that lds began forming earlier than lss followed by a period of coeval lds and lss formation latest motion was dominantly parallel to lss synkinematic mineral assemblages associated with both lds and lss related structures record greenschist to albite epidote amphibolite facies conditions lds tectonites record a complex movement history to the west textural asymmetries indicate west side down or normal shear whereas in eastern domains top to the east thrust style asymmetries dominate lss tectonites consistently record dextral or top to the north shear parallel to lss tectonic motion began as chiefly penetrative dip slip shear lds at a high angle to the present trend of the tsz and evolved to dominantly dextral strike slip shear lss parallel to the trend of the zone the geometry kinematics and sequence of deformation in tsz tectonites evoke a general model of terrane accretion during oblique plate convergence involving initial shortening at a high angle to the convergent margin and progression to margin parallel translation

crustal growth in southern arizona u pb geochronologic and sm nd isotopic evidence for addition of the paleoproterozoic cochise block to the mazatzal province terranes composed of arc related igneous and sedimentary rocks were accreted onto the continental margin of southwestern north america from 1 9 to 1 6 ga they formed the yavapai mazatzal province in arizona of which the so called pinal schist and associated rocks in southeastern arizona form an integral part 148 u pb analyses on magmatic and detrital zircons were performed on 21 samples to constrain timing of geologic events in paleoproterozoic time in the area of southeastern arizona 25 sm nd whole rock analyses were made to infer sources of sedimentary and igneous rocks our results allow us to delineate a suture zone between the pinal tectonostratigraphic unit pinal block which consists primarily of basinal metaturbiditic rocks and a southeastern allochthonous juvenile volcano sedimentary domain the location of the suture is constrained by lithologic contrast across the boundary an increase in age of detrital zircons a marked decrease of end t and an intervening subduction complex swift and force this issue we propose the name cochise block for the southeastern part because it represents a faultbound allochthonous tectonic unit in the cochise block we document volcanic activity from about 1630 to 1647 ma quartzitic sedimentary rocks were largely derived from almost contemporaneous volcanic rocks and show detrital zircon ages from 1630 to 1729 ma with the majority 85 percent between 1630 to 1674 ma quartzites and intermediate to felsic metavolcanic rocks show a tight cluster of end t values 2 9 3 8 close to the depleted mantle model and therefore represent juvenile additions to the crust post tectonic metabasalts with end 1500 4 5 are interpreted as being derived from a depleted upper mantle source around 1 5 ga in the pinal block detrital zircons yield values from 1678 to 1731 ma end t values of metapelites and wackes range from 0 2 to 2 3 values decrease from southeast to northwest indicating progressive input of more evolved material toward the craton our data suggest that sedimentation within the pinal block was proximal to the continental margin and occurred later than 1 68 ga and ended before the intrusion of granitoids at 1 65 ga we show that the north american crust grew rapidly and progressively by addition of juvenile but evolved metavolcanic arc rocks and derived quartz rich metasedimentary rocks as documented in the cochise block timespans between depleted mantle model age and zircon crystallization on the order of 50 my attest to rapid crustal processing during this significant time of crustal growth