mid ocean ridge and island arc affinities in ophiolites from iran palaeographic implications complementary reference abstract fifty six samples of ophiolitic rocks from various late cretaceous eocene suture zones in iran have been analyzed for major and trace elements in order to assess their petrogenetic affinity and to determine their original tectonic setting in both southern baluchestan i e between the makran range and the lut block the fanuj maskutan sequence and northeastern baluchestan i e in the east iranian ranges the tchehel kureh sequence the ophiolitic complexes are well developed the rocks display affinities with mid ocean ridge tholeiites the basaltic rocks are comparable to respectively transitional fanuj maskutan and normal tchehel kureh morb in contrast the sequence along the zagros the sahneh sequence appears to have formed in an island arc setting in iranshar i e in southeastern baluchestan ophiolites are dismembered into a melange which includes cumulate intrusives similar to those from fanuj maskutan and lavas with island arc tholeiitic affinity a similar island arc origin may be inferred for the sabzevar ophiolitic sequence north of the lut block studied by other authors the chemical data thus help to elucidate the development of the jigsaw puzzle of microplates of gondwanian origin that during the mesozoic were intermediate in position between afro arabia india and eurasia and that now constitute the middle east ophiolite obduction in iran occurred during arc basin continent or ocean continent collisions in the late cretaceous early paleogene largely predating the final suturing between arabia and india with eurasia to which the intermediate microplates were already attached which did not take place before the neogene

rare earth element characteristics and k ar ages of the band ziarat ophiolite complex southeastern iran the band ziarat complex of southeastern iran is located on the western boundary c f the jaz murian depression rand is bounded by two ma jar fault systems the principal rock units of this complex are a gabbro sequence that includcs low and high level cumulate gabbros a late intrusive sequence that consists of diorite and plagiogranite and a volcanic sequence that includes diabase dikes and a lesser anaount of basaltic lava mantle rocks are virtually absent because of the presence of the two bounding fault systems but we consider the complex to be an ophiolite in nature rare earth cleislcnt ree whole rock data clearly diffcremtiate the classic ophiolitic lithologies for the crustal rocks in this complex bas4 on the ree data there are two distinct types of basalt presenl at band ziarat i those that formed from an initial basaltic melt with a light rare earth element lree enriched signature similar to intraplate hasalts and ii those that have lree depleted patterns similar to normal mid ocean ridge basalts the data also suggest i that the gabbros are adcumulates and were derived from a source slightly enriched in lree with fractic natioam controlled by removal of clinopyroxene or hornblende and plagioclase and ii that the late intrusive rocks as well as a ma jority of the cliabnse dikes are cogenetic and were derived from thc same lree enriched source k ar ages ranging from 134 4 to 146 5 ma for lowlevel gabbros and from 821 4 to 930 4 ma for high level gabbros were measured on five hornblende and two whole rock samples which suggests that these rocks may have formed early in the cretaceous period

87sr86sr in late proterozoic carbonates evidence for a mantle event at 900 ma ago abstract strontium isotopic measurements were made on late proterozoic carbonates from west african craton comparison of samples with acceptable trace element patterns with coeval data from southern africa and with the published australian results suggests that the 87 sr 86 sr ratio of the late proterozoic sea water evolved in the following manner about 0 7075 at 1000 50 ma 0 7056 to 0 7074 at 900 50 ma 0 7068 to 0 7091 0 7106 at 800 50 ma 0 7074 to 0 7077 at 700 50 ma and 0 7076 to 0 7089 0 7096 at 600 50 ma ago the variations are comparable in magnitude and frequency to those described previously for the phanerozoic strontium isotopic values in the radiogenic part of this range suggest that the continental river flux of sr into late proterozoic oceans was of comparable isotopic composition to its present day counterpart 0 711 consequently the non radiogenic 87 sr 86 sr value at 900 50 ma ago signifies a large flux of mantle strontium into the ocean at this time because the present time resolution is only about 75 25ma additional sampling as well as better stratigraphie resolution and more definite selection criteria are required for construction of a more detailed late proterozoic sea water curve

field measurements of the flux and speed of wind blown sand a field experiment was conducted to measure the flux and speed of wind blown sand under known conditions in a natural setting the experiment run at pismo beach california involved a tract 100 m long parallel with the wind by 20 m wide the site was instrumented with four arrays of anemometers to obtain wind velocity profiles through the lower atmospheric boundary layer temperature probes to determine atmospheric stability and wind vanes to determine wind direction from these measurements wind friction speeds were derived for each experimental run in order to measure sand saltation flux a trench 3 m long by 10 m wide transverse to the wind direction by 0 5 m deep was placed at the downwind end of the tract and lined with 168 collector bins forming an egg box pattern the mass of particles collected in each bin was determined for four experimental runs in order to assess various sand trap systems used in previous experiments 12 leatherman traps one fryberger trap and one array of ames traps were deployed to collect particles concurrently with the trench collection particle velocities were determined from analysis of high speed 3000 and 5000 frames per second motion pictures and from a particle velocimeter sand samples were collected from the trench bins and the various sand traps and grain size distributions were determined fluxes for each run were calculated using various previously published expressions and then compared with the flux derived from the trench collection results show that bagnold s 1941 model and white s 1979 equation most closely agree with values derived from the trench comparison of the various collector systems shows that the leatherman and ames traps most closely agree with the flux derived from the trench although these systems tended to under collect particles particle speeds were measured from analysis of motion pictures for saltating particles in ascending and descending parts of their trajectories results show that particle velocities from the velocimeter are in the range 0 5 7 0 m s 1 compared to a wind friction velocity of 0 32 0 43 m s 1 and a wind velocity of 2 7 3 9 m s 1 at the height of the particle measurements descending particles tended to exceed the speeds of ascending particles by 0 5 m s 1

meso tethyan oceanic sutures and their deformation abstract on the basis of comparative stratigraphie and paleontologic analysis supported by some key paleomagnetic data and interpretations it is shown that during the mesozoic and the cenozoic the eurasian continent grew by accretion of microcontinents these microcontinents separated basins with oceanic crust from the main ocean during the late cretaceous and the early cenozoic the collision of the microcontinents with eurasia resulted in the closure of the basins and meso tethyan oceanic sutures originated in the region under consideration from the carpathians to tibet there are two main meso tethyan sutures the carpathian lesser caucasus and the afghan tibet suture the above mentioned main structures also had branches which remained as sutures of small basins the kamennopotock interpontide nain baft basins and others in the west carpathians the carpathian lesser caucasus suture is overlain by a widespread gemeric tatric allochton from the west carpathians the suture passes through the pannonian basin into the vardar ophiolite zone and farther to the ophiolites of the izmir ankara zone being displaced along the north anatolian right lateral strike slip fault the main suture passes from the eastern pontides into the lesser caucasus where it is marked by ophiolites of the amasia area the shirak bozum and zangezur ridges sunsequently it can be observed through the iranian qara dagh mountains to lake urumiyeh and the north anatolian strike slip fault being again shifted along the strike slip fault the carpathian lesser caucasus meso tethyan suture ends in the western zagros near the cenozoic neo tethyan suture the afghan tibet meso tethyan suture is situated in the pamirs in the rushan pshart zone the east prolongation of the suture has been displaced along the pamir karakorum right lateral strike slip fault in tibet west of the pamirs this suture is also displaced along strike slip faults and continues in the farahrud zone in afghanistan and than passes through the zabol baluch and daz murian ophiolite zones and approaches the neo tethyan suture the paleomagnetic data allow us to reconstruct the location of those sutures in the late cretaceous early cenozoic if one compares the present position of the carpathian lesser caucasus and afghan tibet meso tethyan sutures with the late cretaceous early cenozoic reconstructions of these sutures it is possible to trace the inner deformation of the alpine belt according to these data the carpathian lesser caucasus suture moved northwards over 1200 km ahead of the arabian turkish syntaxis with the displacement direction across the fold belt at the border of the dinarides and hellenides the displacement decreases to 400 500 km and its direction is along the fold belt the amplitude of the suture displacement increases in the pannonian region and again decreases towards the eastern alps the displacement of the afghan tibet suture was 2000 km during the alpine deformation a great ensemble of cenozoic nappes folds and structural arcs of the pamir punjab and arabian turkish syntaxes and carpathian loop is the result of lateral shortening of the alpine belt through the collision

metamorphism at the base of the samail ophiolite southeastern oman mountains metamorphic rocks showing an inverted metamorphic zonation from upper amphibolite facies to greenschist facies occur beneath the samail ophiolite the metamorphic protolith was a section of marine basalts mn rich cherts and argillites garnet clinopyroxene amphibolites occur within 2 m of the contact hornblende clinopyroxene assemblages occur within 80 m of the contact and lower amphibolite facies rocks persist to 130 m from the contact the higher grade rocks show polyphase deformation cataclastic fabrics and partial retrogression to greenschist facies assemblages however lower grade phyllites show evidence of only one episode of metamorphic crystallization unmetamorphosed sediments in contact with the basal metamorphic sheet do not show evidence of polyphase deformation the distribution coefficient kd feo mgo gar feo mgo cpx ranges from 4 4 to 5 3 suggesting a t range of 755 865 c at 200 mpa low jadeite content in clinopyroxene and low glaucophane content of ca amphiboles are consistent with moderate pressures of crystallization the metamorphic sheet is inferred to be of composite origin the highest grade rocks were tectonically transported the greatest distance and the lower grade rocks were successively incorporated into the sheet as the peridotite was thrust over progressively cooler rocks residual heat from the ophiolite is the dominant heat source for the metamorphism and this could have been augmented by a limited amount of frictional heat generated during thrusting these thermal constraints suggest that the metamorphism occurred early in the tectonic transport history of the samail ophiolite

brittle tectonic reconstruction of palaeo extension inherited from mesozoic rifting in west zagros kermanshah iran abstract the present day zagros mountain belt of sw iran corresponds to the former arabian passive continental margin of the southern neo tethyan basin which existed since a permian triassic rifting episode and underwent later collisional deformation in mid to late cenozoic time in west zagros the kermanshah radiolarian trough separated from the neo tethyan basin by the narrow continental platform of the bisotun limestone resulted from the triassic jurassic rifting of the passive margin brittle tectonic analyses of syndepositional normal fault slip data have been undertaken to study the extensional history of the passive margin in terms of palaeostress reconstruction dominant east west trends of the inherited rift related normal faults in west zagros indicate an approximately north south trend of extension that prevailed during the entire mesozoic syn to post rift evolution of the radiolarian trough this extension characterizes a stretched continental margin similar to the present day passive margin of the british isles considering the structural pattern of the inherited basement faults as revealed by the present day earthquake focal mechanisms an oblique crustal stretching model is proposed for the rifting process

mineral chemistry and geochemical behavior of hydrothermal alterations associated with mafic intrusive related au deposits at the atud area central eastern desert egypt abstract vein type gold deposits in the atud area are related to the metagabbro diorite complex that occurred in gabal atud in the central eastern desert of egypt this gold mineralization is located within quartz veins and intense hydrothermal alteration haloes along the nw se brittle ductile shear zone as well as along the contacts between them by using the mass balance calculations this work is to determine the mass volume gains and losses of the chemical components during the hydrothermal alteration processes in the studied deposits in addition we report new data on the mineral chemistry of the alteration minerals to define the condition of the gold deposition and the mineralizing fluid based on the convenient geothermometers two generations of quartz veins include the mineralized grayish to white old vein trending nw se and the younger non mineralized milky white vein trending ne sw the ore minerals associated with gold are essentially arsenopyrite and pyrite with chalcopyrite sphalerite enargite and goethite forming during three phases of mineralization first second main ore and third supergene phases three main hydrothermal alteration zones of mineral assemblages were identified zones 1 3 placed around mineralized and non mineralized quartz veins in the underground levels the concentrations of au ag and cu are different from zone to zone having 25 790 ppb 0 7 69 6 ppm and 6 93 8 ppm 48 6 176 1 ppb 0 9 12 3 ppm and 39 6 118 2 ppm and 53 9 155 4 ppb 0 7 3 4 ppm and 0 2 79 ppm for zones 1 2 and 3 respectively the mass balance calculations and isocon diagrams calculated using the geoiso windows program revealed the gold to be highly associated with the main mineralized zone as well as sericitization kaolinitization and muscovitization in zone 1 more than in zones 2 and 3 the sericite had a higher muscovite component in all analyzed flakes average x ms 0 89 with 0 10 0 55 phengite content in wall rocks and 0 13 0 29 phengite content in mineralized quartz veins wall rocks had higher calcite caco 3 contents and lower mgco 3 and feco 3 contents than the quartz veins the chlorite flakes in the altered wall rocks were composed of pycnochlorite and ripidolite with estimated formation temperatures of 289 295 c and 301 312 c respectively albite has higher albite content 95 08 99 20 which occurs with chlorite in zone 3

comparisons between tethyan anorthosite bearing ophiolites and archean anorthosite bearing layered intrusions implications for archean geodynamic processes

direct measurements of bed stress under swash in the field 1 utilizing flush mounted hot film anemometry the bed stress under swash was measured directly in a field experiment conducted on barret beach fire island new york the theory development and calibration of the instrument package are discussed and results from the field experiment are presented examples of bed stress time series throughout a swash cycle are presented and an ensemble averaged swash bed stress cycle is calculated strong asymmetry is observed between the uprush and backwash phases of the swash flow the maximum bed shear stress exerted by the uprush is approximately double that of the backwash while the duration of the backwash is 135 greater than that of the uprush friction coefficients in the swash zone are observed to be similar in magnitude to those from steady flow with the mean observed friction coefficient equal to 0 0037 swash friction coefficients derived from the current measurements exhibit a reynolds number dependence similar to that observed for other flows a systematic difference between coefficients for uprush and backwash is suggested

wave beach and dune interactions in southeastern australia abstract a morphodynamic classification of surfzones beaches and dunes of the microtidal low to high energy southeast australian coast is presented the first section a waves and beaches briefly deals with the transformation of deep water wave energy as it crosses the shelf nearshore and surfzone depending on the deep water wave characteristics and shelf and inshore morphology resultant breaker wave energy may be high moderate or low and the accompanying beach surfzone morphodynamic state in fine to medium sand beaches either dissipative intermediate or reflective dissipative beaches have wide surfzones with shore parallel bar s and channel s and predominantly shore normal circulation intermediate beaches are characterised by rip circulation crescentic transverse bars and megacusps and reflective beaches by a barless surfzone and steep cusped or bermed beach each beach form has a characteristic level of beach stability zone of sediment storage and mode of beach and dune erosion landward aeolian sediment transport of swash deposited sand section b is dependent on the subaerial beach topography and the aerodynamic flow regime across that topography characteristic profile shapes are ascribed to each beach type dissipative intermediate and reflective aeolian sand transport rates are potentially highest on dissipative beaches moderate on intermediate beaches and lowest on reflective beaches these rates determine the potential size of foredunes which are correspondingly largest on dissipative beaches and smallest on reflective beaches the combination of mode and frequency of beach dune erosion rates of aeolian sand transport and foredune volume and morphology provide an explanation of the nature and morphology of landward occurring large scale dune systems dissipative beaches are frequently characterised by large scale transgressive dune sheets intermediate by a trend from large scale parabolic dune systems high wave energy to small scale blowouts low wave energy and reflective beaches by minimal dune development

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

40ar39ar ages and tectonic setting of ophiolite from the neyriz area southeast zagros range iran abstract an ophiolite considered to be an allochthonous fragment of tethyan oceanic crust and mantle crops out near neyriz in the zagros range iran 40 ar 39 ar ages ranging from 76 8 23 8 ma to 105 23 3 ma were measured on hornblende from five samples of plagiogranite and diabase from the ophiolite the most precise ages are 85 9 3 8 ma for a diabase and 83 6 8 4 ma for a plagiogranite the weighted mean age of hornblende from the five samples is 87 5 7 2 ma which indicates that the igneous part of the neyriz ophiolite formed during the early part of the late cretaceous pargasite from amphibolite below peridotite of the neyriz ophiolite has a 40 ar 39 ar age of 94 9 7 6 ma the pargasite age agrees within analytical uncertainty with the ages measured on diabase and plagiogranite comparable ages have been measured on igneous rocks from the samail ophiolite of oman and on amphibolite below peridotite of the samail ophiolite

swash oscillations on a natural beach run up swash oscillations were measured on a gently sloping beach face for a variety of incident wave conditions run up energy spectra at wind wave frequencies show an 3 dependence and energy levels that are independent of incident wave height this suggests saturation in contrast run up energy at surf beat periods increase approximately linearly with increasing incident wave energy thus in the inner surf zone where wave breaking limits the energy at wind wave frequencies the principal manifestation of large incident wind waves is energetic surf beat

petrology geochemistry and tectonics of the sabzevar ophiolite north central iran abstract the sabzevar ophiolite is a highly dismembered ophiolite complex located along the northern boundary of the central iranian microcontinent cim and is one of the internal iranian group of ophiolites and colored melanges the igneous rocks of this complex consist of peridotites harzburgite dunite and lherzolite serpentinite minor pyroxenite gabbros and a volcanic sequence that exhibits a wide range of composition from basalts and basaltic andesites to rhyodacite dacites rhyolites and basanites sedimentary rocks include a variety of upper triassic to lower cretaceous deep and shallow marine rocks these include pelagic fossiliferous carbonates that are mixed with the pillow basalt and basaltic andesite as interlayers or exotic blocks ranging in size from 10 to 100 m also present are extensive units of radiolarian chert which are interbedded within the basalts and basaltic andesites a combination of petrographic observations and analyses of incompatible trace elements and rare earth elements indicates the presence of at least four different types of extrusive rocks in the sabzevar ophiolite the geochemical data clearly identifies some of the extrusive rocks to have formed from three distinct types of basaltic melts i the group 1 basaltic rocks which formed from an initial melt with n morb like lree depleted chemical signatures and are petrogenetically related to the gabbros ii group 2 basaltic rocks which have e morb chemical signatures and iii group 3 basaltic rocks with lree enriched signatures and incompatible trace element patterns that suggest an island arc affinity the data also suggest that the gabbros and the group 1 basaltic rocks are petrogenetically related and produced by fractionation of plagioclase and to a lesser extent clinopyroxene and hornblende similar to other studied iranian ophiolites e g khoy band e zeyarat dar anar neyriz kermanshah and baft the results from the sabzevar ophiolite demonstrate the presence of relics of mid ocean ridge basalt morb like signatures in the extrusive units of neo tethyan ophiolites and suggests that the fossil oceanic lithosphere preserved in these ophiolites developed at an oceanic spreading center in addition the sabzevar ophiolite contains other volcanic rocks that have non morb like geochemical signatures e g within plate island arc the differences between these geochemical signatures could be a result of a differing upper mantle composition or different degrees of partial melting of the same upper mantle the presence of sizable nb anomalies in the extended rare earth element ree patterns for andesites and the group 3 basalts is characteristic of volcanic arc magmas or possibly are products of the ascending magma that was modified by crustal contamination the presences of the basanites and the silica undersaturated rocks could be attributed to extrusive activity following ophiolite emplacement plate reconstructions suggest that rocks of the sabzevar ophiolite were part of the tethyan oceanic crust that was formed during rifting of a narrow but deep seaway that separated the cim from the eurasian plate the ophiolite was emplaced during northeast dipping subduction i e closure of this segment of the tethyan seaway sabzevar ocean

influence of high water levels on aeolian sand transport upper beach dune evolution on a macrotidal coast wissant bay northern france abstract aeolian sand transport measurements and detailed topographic surveys were carried out during 1 year along a macrotidal upper beach dune system experiencing rapid coastal retreat aeolian transport measurements coupled with wind records showed extreme spatial and temporal variability along a spatially limited upper beach sector analysis of wind velocity rainfall and water level showed that aeolian sand transport may occur all year long on the upper beach with the most energetic conditions occurring during winter and spring analysis of volume change revealed that aeolian sedimentation on the upper beach occurred only during the summer period while the rest of the year was characterised by upper beach and dune scarp erosion this erosion due to storm events combined with high water levels completely eliminated summer aeolian sand accumulation our results show that aeolian transport and upper beach dune evolution on this macrotidal beach is strongly controlled by the magnitude and frequency of occurrence of high water levels this study illustrates the fact that upper beach dune evolution cannot be completely understood and satisfactorily modelled if only potential aeolian sand transport is considered

seabed shear stress and bedload transport due to asymmetric and skewed waves abstract a simple conceptual formulation to compute seabed shear stress due to asymmetric and skewed waves is presented this formulation generalizes the sinusoidal wave case and uses a variable friction factor to describe the physics of the boundary layer and to parameterize the effects of wave shape predictions of bed shear stresses agree with numerical computations using a standard boundary layer model with a k e turbulence closure the bed shear stress formulation is combined with a meyer peter and muller type formula to predict sheet flow bedload transport under asymmetric and skewed waves for a horizontal or sloping bed the predictions agree with oscillatory water tunnel measurements from the literature

kinematic vorticity flow analysis and 40ar 39ar geochronology related to inclined extrusion of the hp lt metamorphic rocks along the zagros accretionary prism iran abstract the zagros accretionary prism in southwestern iran is exposed along the nw se trending of the zagros thrust system and inclined zagros transpression zone this accretionary prism consists of two units the upper sedimentary melange unit on top and the high pressure metamorphic melange unit at the bottom both units show characteristics of a tectonic wedge the upper unit consists of type i ii and iii melanges which display s c and c type shear band cleavages quartz ribbons and rectangular or fish head boudins the lower unit fabrics display and type porphyroclasts and quartz ribbon mylonites these fabrics formed from a combination of 60 5 simple shear and 39 5 pure shear both components were involved in a lateral exhumation of the high pressure low temperature metamorphic rocks in an inclined transpression wedge shaped geometry the estimated kinematic vorticity number wk was calculated from quartz c axis patterns rotation of porphyroclasts and orientation of finite strain with respect to shear zone boundaries using the mean estimated wm value of 0 84 the inclination angle for the thrust wedge on top of the ne subducting neo tethyan oceanic lithosphere is 18 the 40ar 39ar plateau ages of early generations of biotite from the lower metamorphic melange are 119 95 0 88 ma and 112 58 0 66 ma this late aptian age is related to early thrusting and formation of hp lt metamorphic rocks the dating of two amphibole samples from the amphibolite yields a weighted mean age of 91 23 0 89 ma this turonian cenomanian age suggests a later metamorphic event associated with subduction and obduction of the neyriz ophiolite and later lateral extrusion of hp lt metamorphic rocks along the inclined zagros accretionary prism

estimating swash zone friction coefficients on a sandy beach abstract video based swash motions from three studies on two separate beaches were analyzed with respect to theoretical swash trajectories assuming plane beach ballistic motions under quadratic friction friction coefficient values for both the uprush and backwash were estimated by comparing measured swash space time trajectories to these theoretical expectations given an initial velocity and beach slope observations were made spanning high tides and in one case during a light rain analysis of over 4500 individual swash events showed that the uprush friction coefficient was nearly constant during all three studies with a mean value of roughly 0 007 and showed no trends over a tidal cycle in contrast backwash friction coefficient values varied over the tidal cycles ranging between 0 01 and 0 07 with minimum values corresponding to the highest tides although these values are close to the theoretical estimates based on a law of the wall formulation and values commonly referenced in the literature these observations show a consistent tendency for backwash friction estimates to greatly exceed uprush friction estimates the disparity between uprush and backwash friction coefficients can be partially attributed to the exclusion of a pressure gradient term in the ballistic model however results indicate that backwash friction coefficients adjusted to account for this effect may be three times larger than the uprush friction values during lower tides this tidal dependence for backwash friction coefficients is attributed to a complex interaction between swash infiltration and entrained sediment loads these findings imply that friction estimates necessary for sediment transport calculations and hydrodynamic predictions based solely on grain roughness may not be correct for backwash flows

tectono magmatic evolution of the west philippine mariana region and the origin of boninites re examination of published data on the tectomagmatic evolution of the west philippine mariana region indicate that arc magmatism and back arc extensional pulses are not synchronous but are largely asynchronous arc volcanism ceases within a few million years of the development of a back arc basin and recommences oceanward on a new arc during the final stages in the development of the back arc basin following karig s model we believe that ascent beneath the arc axial chain of a line of diapirs of morb source mantle interferes with processes of arc magma generation and arc magmatism wanes partial melting of the diapirs produces voluminous morb type tholeiites which split the arc and form the crust of a widening back arc basin we show for both the west philippine mariana region and occurrences of boninite like lavas in ophiolites that boninites appear to be erupted after arc magmatism and immediately before eruption of morb type lavas passage of a diapir of hot morb source mantle through refractory sub arc peridotite which has been enriched in lile and h2o will result in limited partial melting of the hydrous peridotite and the restricted production of boninitic magmas these are more likely to erupt modified or only slightly modified by crystal fractionation through the thin forearc crust continued ascent of the morb source mantle diapir will result in it partially melting to yield morb tholeiites which erupt shortly after and in considerably more voluminous amounts than the boninites finally we suggest that forearcs regions are likely to be incorporated into foldbelts and that boninite or low ti lava bearing ophiolites may characterize such regions

geologic section through the samail ophiolite and associated rocks along a muscat ibra transect southeastern oman mountains regional mapping at a 1 60 000 scale of a 30 km strip from the gulf of oman muscat across the oman mountains 130 km to the south provides the geologic setting for the 95 m y ibra section of the samail ophiolite where best preserved the ibra ophiolite section is an 8 km thick section of oceanic consisting of 0 5 km of pillow lavas 1 2 1 6 km of sheeted diabase dike complex 0 2 1 0 km of high level noncumulate gabbro and 3 0 5 0 km of cumulate gabbro that is underlain by tectonite peridotite 9 12 km thick the ibra section is found on the southward dipping limb of the sayah hatat antiform the tectonite peridotite represents uniformly depleted harzburgite and dunite that have been deformed by high temperature low stress asthenospheric flow discordant dunites within the tectonite peridotite appear to represent either flow crystallization products from primary picritic liquids or reaction products of these liquids with the harzburgite the structural base of the tectonite peridotite is overprinted by a high stress low temperature deformation that can be related to its oceanic detachment the layered gabbros are predominantly olivine clinopyroxene plagioclase cumulates and orthopyroxene does not occur as a cumulus phase occurrence of cumulate wehrlites and picrites at high stratigraphic levels within the layered gabbros is evidence that the gabbroic section crystallized predominantly from the bottom upward in a periodically replenished magma chamber high level gabbro represents remnants of crystallization at the roof of the magma chamber and intrudes most overlying diabase dikes both the diabase dike complex and pillow lavas are hydrothermally altered and alteration and metamorphism increase downward zeolite to epidote amphibolite facies in spite of pervasive alteration relict primary mineralogy and bulk chemistry suggest that the diabase dikes and pillow lavas are cogenetic with the underlying gabbros the present day samail thrust surface truncates ophiolite stratigraphy and puts the samail ophiolite on top of unmetamorphosed hawasina melange the last motion on this surface was probably no older than maestrichtian 70 65 m y garnet amphibolites exposed as remnants of earlier thrusting 90 m y record initial ophiolite detachment at a 14 20 km depth within the tethyan oceanic lithosphere the hawasina group which underlays the samail ophiolite is a block melange where exposed near muscat in the north and it grades into an imbricated broken formation at the southern limit of the map area the hawasina group is thrust over permian to late cretaceous shelf carbonates that represent autochthonous arabian continental shelf deposits recent post miocene collapse and dome structures such as the ibra dome have complicated ophiolite stratigraphy south of jabal dimh our geologic studies strongly indicate the samail ophiolite represents a large coherent slab of transported oceanic lithosphere formed at a late cretaceous spreading center in the tethyan sea

k ar ages of metamorphic rocks at the base of the samail ophiolite oman hornblendes from amphiobolities in the sheet of metamorphic rocks beneath the peridotite member of the samail ophiolite and phyllites farther from the peridotite contact have weighted mean sup 40 ar sup 39 ar total fusion ages of 90 0 3 0 m y and 79 5 3 0 m y respectively the amphibolities represent the first tectonic slice welded to the base of the samail ophiolite after it was detached from the tethyan oceanic crust formation of the amphiobolities occurred no more than 3 to 7 m y after crystallization of plagiogranite in the ophiolite the phyllites represent another tectonic slice of ocean floor sediments welded to the ophiolite as it was transported further from the tethyan spreading axis the k ar ages suggest assuming a half spreading rate of 2 to 5 cm yr that detachment of the samail ophiolite and formation of amphibolite facies rocks occurred no more than 60 to 350 km from spreading center using the same spreading rate one can calculate a minimum half width of 300 to 750 km for the tethyan ocean during the late cretaceous

wind tunnel modelling of the influence of vegetation structure on saltation threshold the influence of vegetation structure on saltation threshold was investigated using uniformly spaced arrays of non erodible roughness elements on a bed of erodible sand in an wind tunnel structural variables tested using arrays of solid cylinders included element aspect ratio height diameter and lateral cover total frontal silhouette area per unit ground area in agreement with previous studies increase in saltation threshold above the value for bare sand was strongly related to lateral cover increasing aspect ratio from 0 25 to 4 tended to enhance the increase in saltation threshold at a given lateral cover an approximate fit to the results could be obtained using a relation proposed by raupach et al journal of geophysical research 1993 98d 3023 3029 porous elements were constructed as clusters of narrow vertically oriented cylinders model stems forming porous model plant bodies that were cylindrical in overall shape low porosity elements were found to be approximately 50 per cent more effective in increasing saltation threshold than either solid or high porosity elements the ratio of plant body frontal silhouette area based on overall dimensions to total stem frontal silhouette area was found to be a useful measure of plant body porosity for wind erosion studies some conventional measures of vegetation amount fail to account for changes in vegetation structural attributes that may strongly influence aeolian processes

observations and predictions of fluid velocities in the surf and swash zones 1 surfzone and swashzone water level fluctuations and cross shore fluid velocities observed at seven cross shore locations for 139 51 min periods on a low sloped fine grained sandy beach are shown to be modeled well by the depth averaged nonlinear shallow water equations the model initialized with observations about 150 m from the shoreline in 300 cm water depth accurately predicts the observed decrease in sea swell wave heights and orbital velocities with decreasing water depth across the surf zone and the observed maxima in infragravity orbital velocities and offshore directed mean flows near the outer edge of the swash zone in the surf zone both the observed and predicted velocity fluctuations are dominated by sawtoothed shaped pitched forward asymmetrical sea swell waves in the swash zone infragravity waves contribute substantially to the total velocity variance and asymmetry shoreward of the outer swash zone observed and predicted total and infragravity velocity asymmetry decrease onshore changing sign from positive to negative in the upper swash

age and petrogenesis of na rich felsic rocks in western iran evidence for closure of the southern branch of the neo tethys in the late cretaceous abstract intermediate to felsic volcanic and granitic rocks with high na2o concentrations 5 2 9 1 wt are widely distributed in the harsin area along the zagros thrust zone in western iran most of these rocks are classified as low potassium tholeiite display affinity with oceanic plagiogranite and contain somewhat high na content and low concentrations of k2o al2o3 rb sr and ca thus we prefer to apply the term na rich felsic rocks to this complex u pb dating yielded ages of 94 6 2 7 ma 2 from baddeleyite and 95 0 2 4 ma 2 from zircon grains indicating that the complex crystallized in the late cretaceous based on the mineral compositions the crystallization occurred at low pressures mostly

ophiolites as indicators of the geodynamic evolution of the tethyan ocean abstract reviewing the ophiolites of the alpine chain from the western mediterranean to the indian ocean we subdivide them into ten groups of outcrops the geological environment through time the internal composition and history are given for each emphasis is put on the variegated and successive geodynamic processes which can be reconstructed for the different ophiolitic belts since their birth as an ocean like crust to their incorporation through accretion to a continent one can distinguish low versus high tholeiitic partial melting fairly or poorly established ridges simple ridge type crust versus complex ridge ensimatic arc and even more complex type long lived versus short lived oceanic crust stages abrupt large scale pure obduction versus progressive collision related obduction or simple progressive juxtaposition to continent the major events through time in the tethyan ophiolitic belts can be listed as follows spreading ridge activity during the jurassic liguria dinaro hellenides lesser caucasus and the cretaceous peri arabic nain sabzewar with a jump of ridge in between repeated change from ridge to ensimatic arc dinaro hellenic lesser caucasus peri arabic west indian during the latest jurassic and cretaceous upper cretaceous tertiary collision related obductions pontic lesser caucasus liguria squeezing out the elevated portions of these basins lack of oceanic magmatism during the cenozoic but progressive accretion along accretionary wedges of the elevated portions of the remaining mesozoic crust van nain sabzewar zahedan mekran

geochemical characteristics 40ar 39ar ages and original tectonic setting of the band e zeyarat dar anar ophiolite makran accretionary prism s e iran abstract the makran accretionary prism in southeastern iran contains extensive mesozoic zones of melange and large intact ophiolites representing remnants of the tethys oceanic crust that was subducted beneath eurasia to the north of the makran accretionary prism lies the jaz murian depression which is a subduction related back arc basin the band e zeyarat dar anar ophiolite is one of the ophiolite complexes it is located on the west side of the makran accretionary prism and jaz murian depression and is bounded by two major fault systems the principal rock units of this complex are a gabbro sequence which includes low and high level gabbros an extensive sheeted diabase dike sequence late intrusive rocks which consist largely of trondhjemites and diorites and volcanic rocks which are largely pillow basalts interbedded with pelagic sedimentary rocks including radiolarian chert chondrite and primitive mantle normalized incompatible trace element data and age corrected nd pb and sr isotopic data indicate that the band e zeyarat dar anar ophiolite was derived from a midocean ridge basalt like mantle source the isotopic data also reveal that the source for basalts was indian ocean type mantle based on the rare earth element ree data and small isotopic range all the rocks from the band e zeyarat dar anar ophiolite are cogenetic and were derived by fractionation from melts with a composition similar to average e morb fractionation was controlled by the removal of clinopyroxene hornblende and plagioclase three 40ar 39ar plateau ages of 140 7 2 2 142 9 3 5 and 141 7 1 0 ma and five previously published k ar ages ranging from 121 4 to 146 5 ma for the hornblende gabbros suggest that rocks from this ophiolite were formed during the late jurassic early cretaceous plate reconstructions suggest that the rocks of this complex appear to be approximately contemporaneous with the masirah ophiolite which has crystallization age of 150 ma like masirah the rocks from the band e zeyarat dar anar ophiolite complex represent southern tethyan ocean crust that was formed distinctly earlier than crust preserved in the 90 100 ma bitlis zagros ophiolites including the samail ophiolite

the sabzevar blueschists of the north central iranian micro continent as remnants of the neotethys related oceanic crust subduction the sabzevar ophiolites mark the neotethys suture in east north central iran the sabzevar metamorphic rocks as part of the cretaceous sabzevar ophiolitic complex consist of blueschist amphibolite and greenschist the sabzevar blueschists contain sodic amphibole epidote phengite calcite omphacite quartz the epidote amphibolite is composed of sodic calcic amphibole epidote albite phengite quartz omphacite ilmenite and titanite the greenschist contains chlorite plagioclase and pyrite as main minerals thermobarometry of a blueschist yields a pressure of 13 15 5 kbar at temperatures of 420 500 c peak metamorphic temperature depth ratios were low 12 c km consistent with metamorphism in a subduction zone the presence of epidote in the blueschist shows that the rocks were metamorphosed entirely within the epidote stability field amphibole schist samples experienced pressures of 5 7 kbar and temperatures between 450 and 550 c the presence of chlorite actinolite biotite and titanite indicate greenschist facies metamorphism chlorite albite and biotite replacing garnet or glaucophane suggests temperatures of 300 c for greenschist facies the formation of high pressure metamorphic rocks is related to north east dipping subduction of the neotethys oceanic crust and subsequent closure during lower eocene between the central iranian micro continent and eurasia north iran

biostratigraphic zonation and 40ar 39ar ages for the neotethyan khoy ophiolite of nw iran abstract the khoy ophiolite in northwestern iran represents a piece of oceanic lithosphere formed in the mesozoic neotethys this ophiolite consists from bottom to top of well defined basal metamorphic rocks peridotites gabbros and a variety of upper to lower cretaceous deep marine rocks these include pelagic fossiliferous carbonates and basalts as interlayers or exotic blocks four hornblende separates from gabbros and amphibolites give values from 108 to 111 ma the results from microfossil studies show the presence of late cretaceous e g marginotruncana globotruncana and middle to late eocene e g globorotalia orbulonoides planktonic foraminifera the data suggest that although the initial rifting and crystallization of the oceanic crust of the khoy ophiolite began in the late albian the volcanic activities continued through to the late eocene time another possibility for such variation of lithofacies and biofacies and disturbances in the fossil record may be the result of bioturbation and transportation and rapid changes of depositional conditions during eruption of the basaltic lava flows pelagic sediments alone have been listed and of the foraminiferas the first three are planktonic as would be expected only orbulonoides is a benthic form and aberrant the third possibility is that the khoy ophiolite may represent a classic supra subduction type ophiolite where volcanic members of the different parts of oceanic environment e g morb volcanic arc ocean island are now juxtaposed

the petrochemistry of ophiolite gabbroic complexes a key for the classification of ophiolites into low ti and high ti types ophiolites have been divided into two groups high ti and low ti types these can be discriminated by studying the fractionation trends of both gabbroic complexes this work and lavas and dykes 16 particularly in the tio2 m i diagram the first type typically shows morb like magmas whereas in the second the magma types have a spectrum of composition from mid ocean ridge basalts to island arc tholeiites and boninite like magmas often occur high ti ophiolites are petrologically and geochemically similar to major oceanic and ensialic back arc basin crusts as well as oceanic crust generated during the intermediate and late stage opening of intraoceanic back arc basins parental magmas and fractionation processes of low ti ophiolites fit with an hypothesis of their formation in the early stage of opening of intraoceanic back arc basins

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

the effect of wind speed and bed slope on sand transport this paper reports on a wind tunnel study of the effects of bed slope and wind speed on aeolian mass transport the use of a sloping wind tunnel has enabled estimation of the friction angle to be about 40 for saltating particles in the range 170 540 m a formula relating dimensionless mass transport to friction speed and bed slope is proposed and mass transport data for five uniform sand samples and one non uniform sand sample are shown to fit the equation well in particular the relationship reveals an overshoot in mass transport slightly above threshold collisions a feature also evident when previous experimental data is re examined as the number of mid air collisions between the saltating particles increases greatly with wind speed the overshoot may occur as a result of increasing energy losses resulting from the collisions finally it is demonstrated that data for saltating snow shows a similar overshoot in the dimensionless transport rate

uranium lead isotopic ages of the samail ophiolite oman with applications to tethyan ocean ridge tectonics plagiogranites are a minor but widespread component of the samail ophiolite plutonic member they crystallized from the most fractionated melts generated by magmatic crystallization and differentiation of a steady state magma chamber beneath the tethyan spreading ocean ridge and their ages are thought to mark the time of ocean crust formation isotopic u pb ages of zircons from 13 plagiogranites collected along a 270 km segment of the samail ophiolite subparallel to the regional trend of the sheeted dike complex the former spreading ridge axis direction define a narrow time interval of 93 5 97 9 m y with a pronounced clustering about 95 m y the zircon ages of the plagiogranites agree remarkably well with the early cenomanian to early turonian biostratigraphic ages of sediments that are intercalated within the ophiolite pillow lavas and that lie just above them tippit et al 1981 the agreement of radiometric and biostratigraphic ages provides strong support for the conclusion that the plagiogranite u pb ages closely date the time span of ocean crust formation no step changes in age patterns are observed along the ridge axis sheeted dike direction suggesting that there are no major internal offsets of the ophiolite by transform or other faults along most of the traverse one possible exception occurs at the southeastern end of the sampled interval ibra area where a 3 m y discontinuity might be caused by an unmapped fault assuming that the regional trend of the sheeted dikes n10 25 w marks the direction of the former spreading ridge axis the present array of sample localities spans a distance of 130 to 195 km normal to that axis i e in the spreading direction the data as a whole do not define a clear cut age trend normal to the spreading axis but by eliminating samples that may be aberrant due to faulting the data array suggests a pattern of increasing ages from east to west this would indicate that the samail ophiolite is derived from the western southwestern side of the tethyan spreading system a conclusion reached independently from geological evidence also the gentle age gradient in the spreading direction i e between 130 and 195 km of ocean crust were formed within an age span of no more than 2 m y suggests a very fast spreading rate this conclusion also is supported by independent geologic evidence

u pb zircon ages field geology and geochemistry of the kermanshah ophiolite iran from continental rifting at 79ma to oceanic core complex at ca 36ma in the southern neo tethys abstract the geodynamic evolution of the zagros mountains of iran remains obscure in particular the time of formation of the zagros ophiolites and the closure of the neo tethys ocean are highly controversial here we present new precise zircon u pb ages that show that the younger part sahneh kamyaran of the kermanshah ophiolite formed at 35 7 0 5 ma and the older part harsin at 79 3 0 9 ma field relations and geochemical evidence show that the younger sahneh kamyaran part is probably a fossil oceanic core complex and the older sahneh part is probably a continental oceanic transition complex both the sahneh kamyaran and sahneh parts were later emplaced into an accretionary complex we conclude and infer that the final closure time of the southern neo tethys ocean was after the late eocene our data and tectonic model have crucial implications for the geodynamic evolution of the zagros region

backshore coarsening processes triggered by wave induced sand transport the critical role of storm events spatial backshore processes were investigated through field observations of topography and median sand grain size at a sandy beach facing the pacific ocean in japan a comparison of the backshore profile and cross shore distribution of the median sand grain size in 1999 and 2004 revealed an unusual sedimentary process in which sand was coarsened in a depositional area in the 5 year period although sediment is generally coarsened in erosional areas in support of these observations monthly spatial field analyses carried out in 2004 demonstrated a remarkable backshore coarsening process triggered by sedimentation in the seaward part of the backshore during a storm event in order to elucidate mechanisms involved in the backshore coarsening process thresholds of movable sand grain size under wave and wind actions a uniform parameter for both these cases in the onshore and offshore directions were estimated using wave tide and wind data the cross shore distributions of the estimated thresholds provided reasonable values and demonstrated a coarsening mechanism involving the intermediate zone around the shoreline under alternating wave and wind actions as a result of which coarse sand was transported toward the seaward part of the backshore by large waves during storms and then toward the landward part by strong onshore winds the 5 year backshore coarsening is most certainly explained by repetition of short term coarsening mechanisms caused by wave induced sand transport occurring from the nearshore to the intermediate zone copyright 2010 john wiley sons ltd

is the critical shields stress for incipient sediment motion dependent on channel bed slope data from laboratory flumes and natural streams show that the critical shields stress for initial sediment motion increases with channel slope which indicates that particles of the same size are more stable on steeper slopes this observation is contrary to standard models that predict reduced stability with increasing slope due to the added downstream gravitational force processes that might explain this discrepancy are explored using a simple force balance model including increased drag from channel walls and bed morphology variable friction angles grain emergence flow aeration and changes to the local flow velocity and turbulent fluctuations surprisingly increased drag due to changes in bed morphology does not appear to be the cause of the slope dependency because both the magnitude and trend of the critical shields stress are similar for flume experiments and natural streams and significant variations in bed morphology in flumes is unlikely instead grain emergence and changes in local flow velocity and turbulent fluctuations seem to be responsible for the slope dependency due to the coincident increase in the ratio of bed roughness scale to flow depth i e relative roughness a model for the local velocity within the grain roughness layer is proposed based on a 1 d eddy viscosity with wake mixing in addition the magnitude of near bed turbulent fluctuations is shown to depend on the depth averaged flow velocity and the relative roughness extension of the model to mixed grain sizes indicates that the coarser fraction becomes increasingly difficult to transport on steeper slopes

eulerian flow velocities in the swash zone field data and model predictions measurements of eulerian flow velocity obtained within the swash zone on a relatively steep beach face gradient 1 23 are compared with an extended ballistic swash model the model only requires a friction factor beach slope and terminal bore velocity as input the following model predictions matched well with observations 1 the maximum eulerian flow velocity is the shoreline velocity when it arrives at the fixed point of interest on the beach face 2 at any location the time of flow reversal occurs prior to the shoreline reaching its maximum landward excursion 3 the maximum flow velocity in the backwash is the velocity recorded as the shoreline recedes past the fixed point of interest and this is less than the maximum uprush velocity and 4 the duration of the uprush flow is shorter than the duration of the backwash flow previous studies have already confirmed that the ballistic swash model including friction can accurately predict shoreline motion and maximum run up on steep beaches this study shows that it is similarly successful in predicting eulerian flow velocities during individual swash events the model does not presently account for interacting swash however and so may be less appropriate on gently sloping beaches

the time bound character of uranium mineralising processes with special reference to the proterozoic of gondwana abstract it is more useful to consider the time bound character of uranium mineralising processes than the time bound character of uranium deposits this is because present uranium deposits are the result of a series of mineralising steps which occurred over hundreds of millions of years we have identified five periods which are characterised by moderately distinct mineralising processes 1 1 before 2800 ma uranium was fractionated into the upper crust during late archaean early proterozoic cratonisation by magmatic and metamorphic processes the granitic terranes were an important source of uranium for subsequent mineralising events 2 2 2800 2200 ma although the atmosphere was probably not reducing at this time the level of oxygen was sufficiently low for uraninite to be transported and concentrated in sedimentary basins cratonisation was a prerequisite for the formation and preservation of long lived basins rapid burial and reducing conditions during diagenesis were important for preserving the uranitite the uranium was mobilised during diagenesis and metamorphism 3 3 2200 1200 ma after 2000 ma when the oxygen level in the atmosphere increased markedly the movement of uranium in solution as uranyl ions became more important the first marine shelf sequences containing chemical and organic sediments to be deposited on the cratons formed excellent sites for the syn sedimentary diagenetic or metamorphic concentration of uranium in some cases this mineralisation was economic in other cases it may have been just a step in a succession of mineralising events continental clastic sediments which overlie these shelf sediments were excellent hosts for large hydrothermal circulation systems which could remobilise the uranium from either granites or sediments the lack of organic and argillaceous material in these continental sequences resulted in the precipitation of uranium near the basal unconformity where there were reducing sediments 4 4 1200 400 ma with the start of modern plate tectonics there was greater potential for the thermally activated remobilisation of uranium the period 1200 900 ma marked the final mineralisation in some important deposits the pan african and brazilian events 700 400 ma mobilised uranium of uncertain origin and concentrated it in previously deposited marginal marine sediments 5 5 400 0 ma the incorporation of organic material into continental clastic sediments allowed uranyl ions to be precipitated before they reached the sea to form the important sandstone type of deposits any time bound mineralising process may be either the final or an intermediate step in forming an economic uranium deposit which of these it is depends on the subsequent history of the area on whether the uranium is preserved dispersed or reconcentrated that many major uranium deposits occur on late archaean early proterozoic cratons emphasises the importance of the long term preservation of sedimentary sequences even though the uranium may be remobilised several times within the sediments

the sediment response of a dissipative beach to variations in wave climate abstract using wave and wind data topographic survey data and a robust video record we have quantified the large scale coastal behavior lscb of agate beach a dissipative end member beach in the pacific northwest usa nine years of study 1992 2001 contain important observations of the intra and interannual sediment response under variations in wave climate in order to describe the variability of the nearshore system wave forcing and beach response were modeled as annually periodic functions superimposed upon long term trends the amplitudes of the seasonal periodicity in significant wave heights ahs 0 94 m 0 06 dominant wave period atp 2 1 s 0 1 and mean wave direction a 12 3 2 0 exhibit larger variability than the long term trends observed within a year hs 6 7 cm year 2 6 tp 0 15 s year 0 04 3 s year 1 0 assuming alongshore transport of sediment at agate beach is mostly wave driven and that the northward flux of sediment goes to zero at the northern end of the beach the observed long term increase in significant wave heights hs and change to a more southerly approach in wave direction coincident with the 1997 1998 el nino 1998 1999 la nina sequence result in net accretion along agate beach beach survey data collected by rtk gps and lidar quantify the increase in subaerial sediment volume vb 1 84 105 m3 this change in volume corresponds to a mean bed elevation increase of 0 21 m over the 8 7 105 m2 area of study the amplitude of annual variation in sediment volume was avb 7 85 104 m3 2 13 104 m3 video image analysis 1992 2001 also quantifies a long term offshore migration of the outer sand bar obx 11 0 m year 0 8 coincident with the increase in subaerial beach sediment volume at the northern end of the newport littoral cell this result suggests accretion of sediments in a much wider cross shore region than observed within the beach survey record similar to the signature of beach volume variations the cross shore position of the outer sand bar also varies with season ao x 114 9 m 4 2 the agreement between long term trends in wave statistics and morphology suggests a directly forced beach response an empirical orthogonal function eof analysis of the topographic survey record at agate beach resolves two distinct eigen modes of variance associated with seasonal patterns of sediment flux the first mode 34 is related to the summer growth of a dune field that is limited to elevations above mhw z 1 076 m analysis of concurrent wind field measurements shows this mode of variance is well correlated with aeolian processes the second mode 21 is wave driven and corresponds to the seasonal behavior of the beach surface below mhw observations show the mhw elevation serves as a transitional zone between dune related and wave driven processes that affect the seasonal evolution of agate beach

jurassic rifting at the eurasian tethys margin geochemical and geochronological constraints from granitoids of north makran southeastern iran this study focuses on an east west trending belt of granitic to intermediate intrusions and their volcanic cover in the northern dur kan complex a continental slice outcropping to the north of the exposed makran accretionary wedge in southeastern iran field observations petrographic descriptions trace element and isotope analyses combined with u pb zircon geochronology are presented to determine the time frame of magmatism and tectonic setting during the formation of these rocks results document three magmatic episodes with different melt sources for 1 granites 2 a diorite trondhjemite plagiogranite sequence and 3 diabases and lavas granites dated at 170 175 ma represent crystallized melt with a strong continental isotopic contribution the diorite trondhjemite plagiogranite sequence is 165 153 ma old and derives from a mantle magma source with minor continental contribution east west trending diabase dikes and bodies intruded the granitoids which were eroded and then covered by valanginian 140 133 ma alkaline lavas and sediments alkaline dikes and lavas have a mantle isotopic composition temporal correlation with plutonites of the sanandaj sirjan zone to the northwest defines a narrow nw se striking and nearly 2000 km long belt of jurassic intrusions the increasing mantle influence in the magma sources is explained by thinning of continental lithosphere and related mantle upwelling decompression melting accordingly the formation of the studied igneous rocks is related to the extension of the iranian continental margin which ultimately led to the formation of the tethys related north makran ophiolites

the archean proterozoic transition evidence from the geochemistry of metasedimentary rocks of guyana and montana abstract chemical and isotopic compositions of ancient sedimentary rocks have in some cases provided evidence of first order changes yin the composition and extent of continental crust from the archean to the proterozoic we reversed the typical sampling pattern comparing metapelites and carbonates from proterozoic greenstone belts with those from an archean continental margin sequence and found the reverse of the typical age composition relations metapelites and volcaniclastic metagreywackes from the early proterozoic greenstone belts of northern guyana resemble those of many archean greenstone belts in ree trace and major element compositions mean ratios la sm 5 0 la th 5 1 eu eu 0 80 th u 3 4 median k 2 o na 2 o 0 8 schists from an archean continental marginal sequence in montana have compositions like many post archean metapelites derived from continental sources mean ratios la sm 6 8 la th 2 7 eu eu 0 67 th u 5 2 median k 2 o na 2 o 1 7 other archean continental basin sediments also resemble their post archean counterparts implying that upper continental crusts of these eras may not have differed significantly in these respects however temporal change may have occurred in upper crustal contents of ni and cr many archean clastic metasedimentary rocks of both continental and greenstone belt provenance have contents of these compatible elements higher than in their post archean equivalents dolomitic limestone from a greenstone belt of northern guyana has a very low 87 sr 86 sr ratio of 0 7007 such low values may reflect the local influence of mantle derived volcanic rocks during carbonate deposition diagenesis or metamorphism and they may not be reliable indicators of the evolution of sr in seawater archean dolomitic marbles from the continental marginal sequence of montana have 87 sr 86 sr ratios of 0 7065 and higher significantly more radiogenic than many accepted values for carbonates of archean greenstone belts

iranshahr blueschist subduction of the inner makran oceanic crust the makran accretionary prism in se iran and sw pakistan is one of the most extensive subduction accretions on earth it is characterized by intense folding thrust faulting and dislocation of the cenozoic units that consist of sedimentary igneous and metamorphic rocks rock units forming the northern makran ophiolites are amalgamated as a melange metamorphic rocks including greenschist amphibolite and blueschist resulted from metamorphism of mafic rocks and serpentinites in spite of geodynamic significance of blueschist in this area it has been rarely studied peak metamorphic phases of the northern makran mafic blueschist in the iranshahr area are glaucophane phengite quartz omphacite epidote post peak minerals are chlorite albite and calcic amphibole blueschist facies metasedimentary rocks contain garnet phengite albite and epidote in the matrix and as inclusions in glaucophane the calculated p t pseudosection for a representative metabasic glaucophane schist yields peak pressure and temperature of 11 5 15 kbar at 400 510 c these rocks experienced retrograde metamorphism from blueschist to greenschist facies 350 450 c and 7 8 kbar during exhumation a back arc basin was formed due to northward subduction of neotethys under eurasia lut block exhumation of the high pressure metamorphic rocks in northern makran occurred contemporarily with subduction several reverse faults played an important role in exhumation of the ophiolitic and hp lt rocks the presence of serpentinite shows the possible role of a serpentinite diapir for exhumation of the blueschist a tectonic model is proposed here for metamorphism and exhumation of oceanic crust and accretionary sedimentary rocks of the makran area vast accretion of subducted materials caused southward migration of the shore this article is protected by copyright all rights reserved

the effect of wind gusts moisture content and fetch length on sand transport on a beach this paper reports on an analysis of instantaneous sediment transport in relation to wind gusts moisture content and fetch length from a field study carried out at skallingen denmark wind speeds were measured with cup anemometers and instantaneous sediment transport with vertical traps coupled to electronic balances moisture content was measured gravimetrically using samples taken along a beach profile at intervals of 1 to 2 h sediment transport and wind speeds were sampled at 1 hz and a 5 s running mean was used to smooth the data from the trap because of limitations of the balance resolution three measures of the threshold of sediment motion the intermittency threshold minimum threshold and maximum threshold were explored using data from five runs carried out on october 26 2000 the intermittency threshold and maximum threshold were largely insensitive to wind speed but varied spatially along the fetch distance the minimum threshold increased significantly with increasing mean wind speed as a result of reduced time for drying of the surface layer examination of time series for instantaneous wind speed and sediment transport for a number of runs on october 26 and november 6 2000 showed close agreement between fluctuations in wind speed and fluctuations in sediment transport cross spectral analysis of instantaneous wind speed and sediment transport for one run on each day where there was continuous transport showed high coherence between the two variables over a range of frequencies from 0 2 hz to 0 01 hz plots of all non zero instantaneous sediment transport values versus wind speed show considerable scatter in general transport rates are highest for traps located further from the upwind non erodible boundary i e along the fetch best fit power relationships show r2 values generally ranging from 0 4 to 0 6 and exponents ranging from 4 5 to 6 94 i e much higher than the traditional value of 3 found in most transport equations traps located close to the upwind boundary had lower r2 values and exponents 2 5

building the zagros collisional orogen timing strain distribution and the dynamics of arabia eurasia plate convergence he zagros mountains are the result of the arabia eurasia collision initiated at 35 ma as the rifted arabian lithosphere was underthrusted beneath the iranian plate due to its negative buoyancy the onset of crustal thickening started at 25 ma as recorded by the hinterland exhumation and foreland clastic deposition deformation throughout the arabia eurasia collision zone and the uplift of the iranian plateau occurred after 15 12 ma as a result of shortening thickening of the thin iranian crust we emphasize that only 42 of the post 35 ma convergence is partitioned by shortening within central iran tomographic constraints show ongoing slab steepening or breakoff in the nw zagros whereas underthrusting of the arabian plate is observed beneath central zagros the current subduction dynamics can be explained by the original lateral difference in the buoyancy of the distal margin that promoted slab sinking in nw zagros and underthrusting in central zagros critical wedge approach applied to the zagros favors the hypothesis of strong brittle crust detached above a viscous lower crust in contrast the weak sedimentary cover deforms by buckling of a thick multilayered cover thrust faulting associated with folding occurs in the competent layers and is responsible for most of the earthquakes there is evidence that the role of the slab pull force in driving the arabian plate motion was reduced after 12 ma large scale mantle flow induced by mantle upwelling at the afar plume appears to be the main driver of the arabia plate motion we stress that the main kinematic change in the zagros region occurred at 15 12 ma as the zagros uplifted before the arabian slab detached the zagros appears key to investigate coupling between continental rheology plate driving forces and mountain building in which the role of rift inheritance appears to be central

a systematic analysis of eight decades of incipient motion studies with special reference to gravel bedded rivers data compiled from eight decades of incipient motion studies were used to calculate dimensionless critical shear stress values of the median grain size t c 50 calculated t c 50 values were stratified by initial motion definition median grain size type surface subsurface or laboratory mixture relative roughness and flow regime a traditional shields plot constructed from data that represent initial motion of the bed surface material reveals systematic methodological biases of incipient motion definition t c 50 values determined from reference bed load transport rates and from visual observation of grain motion define subparallel shields curves with the latter generally underlying the former values derived from competence functions define a separate but poorly developed field while theoretical values predict a wide range of generally higher stresses that likely represent instantaneous rather than time averaged critical shear stresses the available data indicate that for high critical boundary reynolds numbers and low relative roughnesses typical of gravel bedded rivers reference based and visually based studies have t c50 ranges of 0 052 0 086 and 0 030 0 073 respectively the apparent lack of a universal t 50 for gravel bedded rivers warrants great care in choosing defendable t c50 values for particular applications

the effect of surface moisture on the entrainment of dune sand by wind an evaluation of selected models reliable predictions of wind erosion depend on the accuracy of determining whether erosion occurs or not among the several factors that govern the initiation of soil movement by wind surface moisture is one of the most significant some widely used models that predict the threshold shear velocity for particle detachment of wet soils by wind were critically reviewed and evaluated wind tunnel experiments were conducted on pre wetted dune sand with moisture contents ranging from 0 00 to 0 04 kg kg 1 sand samples were exposed to different wind speeds for 2 min moisture content was determined gravimetrically before and after each experiment and the saltation of sand particles was recorded electronically with a saltiphone shear velocities were deduced from the wind speed profiles for each moisture content the experiments were repeated at different shear velocities with the threshold shear velocity being determined by least squares analysis of the relationships between particle number rates and shear velocity within the 2 min test runs temporal changes in particle number rates and moisture contents were detected a steep increase in the threshold shear velocity with moisture content was observed when comparing the models large differences between the predicted results became apparent at a moisture content of 0 007 kg kg 1 which is half the moisture content retained to the soil matrix at a water tension or matric potential of 1 5 mpa the increase in wet threshold shear velocity predicted with the different models relative to the dry threshold shear velocity ranged from 117 to 171 the highest care should therefore be taken when using current models to predict the threshold shear velocity of wet sediment nevertheless the models of chepil 1956 proc soil sci soc am 20 288 292 and saleh fryrear 1995 soil sci 160 304 309 are the best alternatives available

the influence of rainfall on transport of beach sand by wind this paper deals with the effect of rainfall on the process of wind erosion of beach sands and presents results from both field and wind tunnel experiments although sediment transport by splash is of secondary importance on coastal dunes splash saltation processes can move sediments in conditions where no motion is predicted by aeolian processes the effect of raindrop impact on the movement of soil particles by wind was measured on a sand beach plain using an acoustic sediment sampler in general an increase of particle movement by wind at the sensor heights was observed during rainfall rainfall also affected the wind erosion process during and after rain by changing the cohesive conditions of the surface the influence of the surface moisture content on the initiation of wind erosion and on the vertical distribution of transported sand particles was studied in a wind tunnel moisture significantly increased threshold wind velocities for the initiation of sediment transport and modified vertical sediment profiles

convergence history across zagros iran constraints from collisional and earlier deformation the zagros orogen provides a unique opportunity within the alpine system to evaluate the interplay between a young tertiary collision and earlier subduction obduction processes within the crush zone and the sanandaj sirjan internal zone separating the zagros fold belt from central iran we document several major tectonic events taking place at the end of the cretaceous of the eocene and from the mio pliocene onwards ca 20 15 ma contrary to recent interpretations our data cross sections and description of the overall deformation style strongly suggest that the main zagros thrust mzt is deeply rooted possibly to moho depths and that the suture zone effectively runs along the mzt field observations show that the final resorption of the oceanic domain took place slightly after 35 ma and that collision must have started before ca 23 25 ma in northern zagros the shortening rate across the crush zone since the mid miocene 20 15 ma is estimated at a minimum 3 4 mm year shear movements in the crush zone during the eocene oligocene period and extensional strike slip movements in the internal zones during the late cretaceous point to an oblique setting early in the convergence history a geotectonic scenario for convergence from the time of obduction to the present is finally proposed

a new tectonic scenario for the sanandaj sirjan zone iran abstract recent geochemical studies of volcanic rocks forming part of the ophiolites within the zagros and naien baft orogen indicate that most of them were developed as supra subduction ophiolites in intra oceanic island arc environments intra oceanic island arcs and ophiolites now forming the naien baft zone were emplaced southwestward onto the northeastern margin of the south sanandaj sirjan zone while those now in the high zagros were emplaced southwestward onto the northern margin of arabia thereafter subduction continued on opposite sides of the remnant oceans the floor of neo tethys ocean was subducted at a low angle beneath the entire sanandaj sirjan zone and the floor of the naien baft ocean was subducted beneath the central iranian micro continent the naien baft ocean extended into north west iran only temporarily this failed ocean arm between the urumieh dokhtar magmatic assemblage and the main zagros thrust was filled by thick upper triassic upper jurassic sediments the naien baft ocean finally closed in the paleocene and neo tethys closed in the early to middle eocene after arabia was sutured to iran the urumieh dokhtar magmatic assemblage recorded slab break off in the middle eocene

the petrogenesis and tectonic setting of lavas from the baft ophiolitic melange southwest of kerman iran a late cretaceous ophiolite complex in the baft area southwest of kerman iran is characteristic of the central iranian ophiolitic melange belt which wraps around the lut block despite the extensive tectonic disruption of the baft complex most ophiolitic lithologies are present and many original igneous contacts are preserved a lack of cumulate gabbros within the sequence suggests that a large and continuous magma chamber did not exist beneath the baft spreading axis geochemical data confirm the presence of two distinct compositional groups in the mafic lavas 1 tholeiitic basalt and 2 transitional tholeiitic basalt the tholeiitic lavas are similar to typical mid ocean ridge basalt compositions whereas the transitional tholeiites are similar to intraplate basalts the available data suggest that the baft ophiolite complex formed in a small ocean basin possibly at or near a ridge transform intersection emplacement may have occurred as a result of conversion of the transform fault to a subduc

petrology geochemistry and tectonic setting of the khoy ophiolite northwest iran implications for tethyan tectonics abstract the khoy ophiolite in northwestern iran represents a remnant of oceanic lithosphere formed in the mesozoic neo tethys this northwest southeast trending ophiolite complex consists from bottom to top east to west of a well defined basal metamorphic zone peridotites dunite harzburgite and serpentinized peridotite gabbros sheeted dikes pillow and massive lava flows and pelagic sedimentary rocks including radiolarian chert the rocks of the metamorphic zone have an inverse thermal gradient from amphibolite facies to greenschist facies the high grade metamorphic rocks are immediately adjacent to the peridotite and the gabbros and the low grade rocks are in contact with the precambrian kahar formation based on mantle normalized incompatible trace element diagrams there are two distinct types of basalt flows present at the khoy ophiolite 1 massive basalts that have patterns virtually identical to e morb and 2 pillow basalts that have more primitive chemical composition whose trace element patterns plot between e morb and n morb the chondrite normalized ree patterns for the pillow basalts are lree depleted lan smn ave 0 70 similar to patterns for the mean diabase composition for the oman ophiolite and lree depleted basalts of the band e zeyarat ophiolite of southern iran the ree patterns for the massive basalts are similar in general ree abundances to the pillow basalt patterns but they are slightly lree enriched lan smn ave 1 09 and their patterns cross those of the pillow basalts the ree patterns for the gabbros and diorites indicates that the crustal suite rocks were most likely derived by a process of fractional crystallization from a common basaltic melt this basaltic melt was most likely generated by approx 20 25 partial melting of a simple lherzolite source and had ree concentrations of roughly 10 chondrite a comparison between the results from the khoy ophiolite and the data from other iranian ophiolites reveals geochemical evidence to suggest a tectonic link between the khoy ophiolite and the rest of the iranian ophiolites our results suggest that khoy ophiolite is equivalent to the inner group of iranian ophiolites e g nain shahr babak sabzevar tchehel kureh and band e zeyarat and was formed as a result of closure of the northwestern branch of a narrow mesozoic seaway which once surrounded the central iranian microcontinent

saltation threshold on earth mars and venus new formulations valid for wide ranges of particle diameter and density and gas density are presented for prediction of saltation threshold speed for small particles a low air density wind tunnel was used to extend the range of previous investigations and to separate the effects of reynolds number and interparticle forces of cohesion the new formulations are used to predict saltation threshold for atmospheric conditions on the surface of the earth mars and venus

late cretaceous infant intra oceanic arc volcanism the central pontides turkey petrogenetic and tectonic implications abstract a tectonic slice of an arc sequence consisting of low grade metavolcanic rocks and overlying metasedimentary succession is exposed in the central pontides north of the izmir ankara erzincan suture separating laurasia from gondwana derived terranes the metavolcanic rocks mainly consist of basaltic andesite andesite and mafic cognate xenolith bearing rhyolite with their pyroclastic equivalents which are interbedded with recrystallized pelagic limestone and chert the metasedimentary succession comprises recrystallized micritic limestone with rare volcanogenic metaclastic rocks and stratigraphically overlies the metavolcanic rocks the geochemistry of the metavolcanic rocks indicates an arc setting evidenced by depletion of hfse ti p and nb and enrichment of fluid mobile lile identical trace and rare earth elements compositions of basaltic andesites andesites and rhyolites suggest that they are cogenetic and derived from a common parental magma the arc sequence crops out between an albian turonian subduction accretionary complex representing the laurasian active margin and an ophiolitic melange absence of continent derived detritus in the arc sequence and its tectonic setting in a wide cretaceous accretionary complex suggest that the kosdag arc was intra oceanic zircons from two metarhyolite samples give late cretaceous 93 8 1 9 and 94 4 1 9 ma u pb ages these ages are the same as the age of the supra subduction ophiolites in western turkey which implies that that the kosdag arc may represent part of the incipient arc formed during the generation of the supra subduction ophiolites the low grade regional metamorphism in the kosdag arc is constrained to 69 9 0 4 ma by 40 ar 39 ar muscovite dating indicating that the arc sequence became part of a wide tethyan cretaceous accretionary complex by the latest cretaceous non collisional cessation of the arc volcanism is possibly associated with southward migration of the magmatism as in the izu bonin mariana arc system

review of platinum group element distribution and mineralogy in chromitite ores from southern iran abstract the platinum group element pge potential of four chromite mining districts in southern and south eastern iran was investigated using geochemical and mineralogical methods a total of 20 mines and prospects were sampled in the neyriz ophiolite the abdasht and sikhuran complexes in the esfandagheh district and the faryab district chromitite and dunite were analysed for major trace element and pge geochemistry and the platinum group element mineralogy pgm in all mining districts chromites analysed from mantle tectonite probable transition zone and cumulate zone chromitites are refractory low in tio2 pge concentrations range from 5000 ppb with median values around 200 ppb in all complexes investigated the 187os 188os isotope ratios of chromitite indicate chondritic to slightly suprachondritic initial os mantle normalised pt ir ratios are generally low in the sikhuran complex pods of sulphide bearing chromitite 0 2 1 2 sulphides occur in a dunite zone interpreted as an ultramafic cumulate zone chromites in chromitite are characterised by high cr 75 81 and intermediate mg numbers 45 65 in associated dunite chromites cr 74 80 are more fe rich mg 29 50 chromitite and dunite carry up to 5 2 ppm total pge and are characterised by high normalised pt ir up to 5 pt pd large degrees of partial melting in a supra subduction zone geotectonic setting probably in a two stage melting process produced boninitic melts that crystallised refractory cr mg rich and ti poor chromite in some cases sulphide saturation was achieved during and after chromite formation saturation during chromite crystallisation is evidenced by ni cu rich sulphide droplets preserved in some chromitites sulphur saturation after chromite crystallisation governed the formation of ni rich sulphide liquids that exsolved monosulphide solid solution which later crystallised to form pge bearing pentlandite platinum and pd did not partition into pentlandite but crystallised as pt and pd rich pgm associated with the pentlandite

particle size and sorting characteristics of sand in transport on the stoss slope of a small reversing dune studies of the particle size and sorting characteristics of sand on the stoss slope of a 6 m high reversing dune show that the sand in transport is generally finer and better sorted than surface sand at the same position on the slope the sand in transport becomes coarser and more poorly sorted as wind speed and rates of mass transport increase toward the dune crest these patterns reflect changes in the competence of the wind which is capable of transporting larger grains and a wider range of grain sizes as its speed increases in space and time our field observations suggest that the particle size and sorting characteristics of surface sand are highly dependent on antecedent wind conditions and are not an invariant property of the dune as is widely assumed the wide range of particle sizes on the surface as well as its change through time also has important implications for modeling sediment transport on dunes transport thresholds may vary by as much as 30 on the stoss slope of the study dune

the geology of the kuh e dalneshin area of southern iran and its bearing on the evolution of southern tethys the kuh e dalneshin area lay close to the northern margin of the arabian continent during mesozoic and palaeogene times recent mapping has shown that except perhaps in the late cretaceous it was inactive until it collided with central iran in the miocene the collision represented by a neogene melange zone in the ne resulted in the zagros orogeny and is expressed in the shelf sediments by folding parallel faulting and a possible arcuate sinistral shear in the late cretaceous a localized deepening of the shelf dates from the cenomanian a narrow trough in the w subsided to abyssal depths in the turonian following a period of faulting a more wide spread subsidence affected the shelf in the coniacian and santonian autochthonous cherts and associated sediments accumulated basaltic volcanics were erupted in the ne part of this basin and permian to cenomanian neritic exotic blocks were derived presumably from an uplift at the shelf edge the rocks from the outer edge of this basin slid westwards over their autochthonous counterparts probably in the campanian accompanied by further gliding of masses of earlier mesozoic cherts which had previously been emplaced on the continental margin a sheet of mantle peridotite partly serpentinized and enclosing neritic and metamorphic exotics in turn slid into the basin shelf sedimentation was renewed in the late campanian or maestrichtian but the transgression did not reach the area until the eocene the derivation and emplacement of the allochthonous rocks in the late cretaceous are still imperfectly understood alternative models are discussed one involving gliding from an aborted spreading ridge along the continental margin the other more conventionally based on subduction processes a preference is expressed for the former

the effects of surface moisture on aeolian sediment transport threshold and mass flux on a beach this paper presents results from a study designed to explore the effects of beach surface moisture and fetch effects on the threshold of movement intensity of sand transport by wind and mass flux the experiment was carried out over a period of five weeks at greenwich dunes prince edward island canada in may and june 2002 moisture content was measured with a delta t moisture probe over a 50 m by 25 m grid established on the beach measurements of wind speed and direction were made with arrays of cup anemometers and a two dimensional sonic anemometer transport intensity was measured at a height of 2 4 cm above the bed using omnidirectional saltation probes which count the impact of saltating grains on a piezoelectric crystal anemometers and saltation probes were sampled at 1 hz sand transport was measured with vertical integrating sand traps over periods of 10 20 minutes results show that where there is a considerable supply of dry sand the saltation system responds very rapidly 1 2 s to fluctuations in wind speed i e to wind gusts where sand supply from the surface is limited by moisture mean transport rates are much lower and this reflects in both a reduction in the instantaneous transport rate and in a transport system that becomes increasingly intermittent threshold wind speed is significantly correlated with an increase in surface moisture content near the upwind end of the beach fetch but the relationship is not significant at the downwind end where sediment transport is initiated primarily by saltation impact from upwind mass flux increases with increasing fetch length and the relationship is described best by a power function further work is necessary to develop a theoretical function to predict the increase in transport with fetch distance as well as the critical fetch distance copyright 2007 john wiley sons ltd

geology of the onshore makran accretionary wedge synthesis and tectonic interpretation abstract this contribution is a synthesis of studies carried out since 2004 in the makran accretionary wedge exposed in se iran these studies were intended to improve our understanding of the behaviour of accretionary wedges and of the significance of the makran wedge in the frame of tethys tectonics reassessing the stratigraphy and structure of the iranian makran has allowed distinguishing four main litho tectonic units the lithological content of these four units is briefly described to discuss the sedimentary environments which record the general filling of an oceanic basin with clastic sediments derived from the north the petrology of ophiolites exposed in the backstop region to the north of the accretionary wedge itself demonstrates the existence of an oceanic basin formed in the jurassic late cretaceous to the north of continental slivers which had separated from central iran there is petrological evidence for a subduction related magmatic arc during the late cretaceous which sourced much of the clastic material in the cretaceous lower miocene turbidites present throughout the wedge the literature survey shows that the late cretaceous to present evolution of the pakistan part of the makran fold and trust belt is in its major attributes similar to that of the iranian makran these observations and results are discussed in a tectonic model that integrates knowledge on the oman mountains on the other side of the current oman subduction

shear stress and sediment transport calculations for swash zone modelling it is shown that the observed difference in sediment transporting efficiency by the swash uprush compared with the downrush could be mainly due to greater bed shear stress for a given velocity in the more abruptly accelerated uprush the bed shear stress generated by an arbitrary free stream velocity time series is modelled in terms of usual wave boundary layer models plus a phase lead phi tau of the bed shear stress compared with the free stream velocity at the peak frequency with this approach the total transport amounts in uprush and downrush can be modelled satisfactorily with the same sediment transport formula without the need for different uprush and downrush coefficients while the adaptation of sediment transport formulae from steady flow can thus lead to the right total amounts of sediment moved by this method the timing of the instantaneous sediment transport rates are probably not accurately modelled due to the highly unsteady nature of the swash and the presence of pre suspended sediment in the uprush nevertheless the proposed method is a useful intermediate step before we have a complete understanding of sediment transport under very rapid accelerations and of the relative contribution of pre suspended sediment to the onshore sediment transport in swash zones c 2002 published by elsevier science b v

swash infiltration exfiltration and sediment transport field measurements of vertical pore pressure gradients within the bed are used to quantify instantaneous 8 hz rates of swash infiltration exfiltration across the beach face cyclic infiltration exfiltration is associated with individual swash events with observed vertical flow rates o 10 3 m s rates of net swash groundwater exchange i e through bed flow integrated over several swash cycles are two orders of magnitude smaller at the timescale of individual swashes vertical pore pressure gradients within the beach face are much greater than horizontal pore pressure gradients this permits application of the numerical solution of darcy s law for one dimensional vertical flow to model fluctuating pore pressures and hence vertical through bed flow vertical flow through a porous bed modifies sediment mobility in at least two ways 1 seepage forces change the effective weight of surficial sediments and 2 boundary layer thickening or thinning result in altered bed shear stresses by considering these two opposing effects separately a new shields parameter is derived that incorporates terms for through bed flow simulation of time varying seepage force and bed stress effects over an uprush backwash cycle suggests that the effect of altered bed stresses dominates over the change in effective weight and that infiltration exfiltration effects are most important during uprush simulated transport rates are increased by up to 40 of the peak transport rate during uprush and reduced by 10 during backrush in summary swash infiltration exfiltration across a saturated beach face enhances the net upslope transport of sediment

wave transformation and swash oscillation on gentle and steep slopes the numerical model developed previously for coastal structures is slightly modified and applied to predict the wave transformation in the surf and swash zones on gentle slopes as well as the wave reflection and swash oscillation on relatively steep beaches the numerical model is one dimensional in the cross shore direction and is based on the finite amplitude shallow water equations including the effect of bottom friction which are solved in the time domain for the incident wave train specified as input at the seaward boundary of the computation located outside the breakpoint the slight modification is related to the effect of the time averaged current on the seaward boundary condition and improves the agreement between the computed and measured mean water levels on gentle slopes the modified numerical model is compared with available small scale test data for monochromatic waves spilling on gentle slopes as well as for monochromatic waves plunging and surging on a relatively steep slope additional comparisons are made with small scale tests conducted using transient monochromatic and grouped waves on a 1 8 smooth slope with and without an idealized nearshore bar at the toe of the 1 8 slope as a whole the numerical model is shown to be capable of predicting both time varying and time averaged hydrodynamic quantities in the surf and swash zones on gentle as well as steep slopes

swash zone sediment suspension and transport and the importance of bore generated turbulence a study of swash zone sediment transport was conducted at gleneden beach oregon during february 25 28 1994 the data collected included suspended sediment concentration ssc sea surface elevation and velocity initially 4 and 8 cm above the bed at three cross shore locations within the swash zone spanning high tides ensemble averages of 6 9 and 12 s duration swash events showed that the uprush suspension was high concentrated in the leading edge and nearly vertically uniform above the lower 1 2 cm of the water column shortly after the sensors were inundated by run up the sediment rapidly settled out of the water during flow reversal the ssc was small but increased again in the backwash backwash vertical profiles were markedly different from uprush profiles with much of the suspension being confined to very near the bed where strong vertical gradients in ssc existed these marked differences show that the backwash is not simply the reverse of the uprush implying significant differences in the underlying fluid dynamics and sediment transport mechanisms backwash sediment suspension increased with flow duration however ensemble averaged ssc profiles of varying duration showed that the backwash concentrations were not consistent at the same temporal phases which suggests that water depth in addition to flow duration may be a controlling factor strong cross shore gradients in ssc suggest that bore derived turbulence may affect local sediment transport specifically our data show this bore generated turbulence turbulent kinetic energy directly influences local sediment suspension hence standard bed shear bagnold type sediment transport models may no longer be valid in the vicinity of the bore in the vicinity of the bore a higher correlation between bore generated turbulence and suspended sediment transport was found than between a bagnold type formulation and suspended sediment transport

mixing characteristics and compositional differences in mantle derived melts beneath spreading axes evidence from cyclically layered rocks in the ophiolite of north oman within the ophiolite of north oman interlayered gabbros and peridotites form a unit up to 3 5 km thick between pervasively foliated harzburgites and dunites of mantle origin and isotropic gabbros and plagiogranites spatial and chemical relationships within this sequence require the existence of a large reservoir 20 km wide 3 5 km high of tholeiitic magma that was periodically replenished by mantle derived picritic to tholeiitic melts during the spreading process cyclicity in the appearance of minerals during cooling of the magma is marked by the repetition of stratigraphies in the layered rocks within these cyclic units basal peridotites with magnesian olivines and pyroxenes are abruptly overlain by gabbros with less magnesian mafic phases this abrupt discontinuity is explained by density stratification set up at the base of the chamber whenever a picritic melt influx occurs by virtue of its greater density than tholeiitic magma sparks et al 1979 any picritic magma emplaced into the base of the tholeiitic magma reservoir would spread out along the floor of the chamber with only limited mixing taking place across the liquid liquid interface cooling of this basal layer by contact with the cooler overlying magma would result in the precipitation of olivine chrome spinel pyroxene from the picritic liquid this process would continue until the now more evolved input liquids were incorporated into the tholeiitic magma resevoir the precipitation of a gabbroic layer would then take place until a new magma input occurred to repeat the cycle variable thicknesses of the cyclic units different liquid lines of descent and various entry points within the liquid line of descent represented by the lowermost layered rocks reveal that the input liquids varied in volume primary composition and the extent and nature of prefractionation in the mantle liquids expelled from the chamber as lavas and dykes are shown to be more fractionated than liquids precipitating the layered rocks and are considered to have undergone additional fractionation within a zone of underplated gabbro and plagiogranite beneath the dyke swarm the existence of a large magma reservoir supports earlier interpretations based on age tilton et al 1981 and geochemical data pearce 1980 that the oman ophiolite is an analogue for fast spreading ridges

prediction of swash motion and run up including the effects of swash interaction modifications to a model describing swash motion based on solutions to the non linear shallow water equations were made to account for interaction between up rush and back wash at the still water shoreline and within the swash zone inputs to the model are wave heights and arrival times at the still water shoreline the model was tested against wave groups representing idealized vessel generated wave trains run in a small wave tank experiment accounting for swash interaction markedly improved results with respect to the maximum ran up length for cases with rather gentle foreshore slopes tan beta 0 07 for the case with a steep foreshore slope tan beta 0 20 there was very little improvement compared to model results if swash interaction was not accounted for in addition an equation was developed to predict the onset and degree of swash interaction including the effects of bed friction less

geochemical constraints on the growth of the continental crust several lines of evidence indicate that the archean upper crust was considerably more mafic than the present day upper crust there has been no significant change in ree and th abundances in post archean clastic sedimentary rocks suggesting that there has been no change in the composition of the upper crust during the post archean this indicates that if there have been any additions to the post archean upper crust they must have had similar composition to the upper crust itself geochemical modelling of ree and th abundances in sedimentary rocks suggests that the minimum ratio of post archean to archean upper crustal composition required to eliminate the archean upper crustal trace element signature within analytical uncertainty is about 4 1 such a model also is supported by isotopic data using plausible assumptions regarding the volume of archean crust isostatic relations and extreme models of the earth s degassing history it is proposed that approximately 65 75 of the continental crust formed