heat flow anomaly in the middle okinawa trough heat flow measurements in the okinawa trough were carried out on three cruises in 1984 and 48 new values were obtained non linear temperature depth profiles were obtained at some stations and interpreted as showing the results of hydrothermal circulation in the southwestern part of the trough heat flow appears to be lower in the central rift zone than in the surrounding area a high heat flow area around 126 e exists an extremely high and localized heat flow anomaly was observed in the central rift zone of the middle okinawa trough it is probably caused by present or recent igneous activity if the anomaly is due to an intrusion the maximum depth and age of the intrusive body can be assessed by the amplitude and horizontal extent of the heat flow anomaly assuming conductive cooling the age is younger than 3 105 yrs and the depth is shallower than 3 5 km when advective heat transfer is taken into account the age must be much younger

short paper the age and origin of boulders in the highland border complex constraints on terrane movements mid proterozoic rb sr muscovite ages on metasedimentary boulders within the highland border complex together with archean t dm ages on the same clasts provide constraints on terrane movements in the scottish caledonides an origin for these clasts from cratonic north america is ruled out combined radiometric age t dm and fauna1 province studies on basement materials provide a potentially productive method of determining the provenance of terranes

an early pliocene thermal disturbance of the main central thrust central nepal implications for himalayan tectonics since the beginning of the collision between india and asia at about 50 ma the convergence in the himalaya has largely been taken up along major thrust zones in this study samples of the lesser himalaya formations up to 10 km below the main central thrust mct and the greater himalaya sequence up to 12 km above the mct have been analyzed by the 40ar 39ar and u pb methods to investigate the thermal history of the mct the ages can be summarized as follows 1 the youngest ages from muscovites 3 1 ma biotites 3 4 ma and hornblendes 4 1 ma all come from within 1 km of the mct 2 there is a marked asymmetry of ages between the footwall and the hanging wall of the mct the maximum mica age in the hanging wall greater himalaya sequence is 13 ma whereas a muscovite 5 km below the mct in the footwall has an age spectrum with a gradient from 400 to 1400 ma 3 five k feldspars from 6 2 to 11 9 km above the mct all give minimum ages in the range 3 0 6 4 ma and 4 a 206pb 238u age on a brannerite from the greater himalayan sequence is 4 8 ma structural and petrologic observations preclude the possibility that this age distance distribution reflects faulting within the greater himalaya sequence and production of the necessary thermal energy by shear heating requires unrealistically high shear stresses infiltration of hot fluids through the mct zone appears to be the best hypothesis to explain these data simple numerical simulations which account for heat transfer by advection within the fluid flow zone and by conduction outside it indicate that the observed age distribution could have been produced by infiltration of hot fluids through the mct zone at circa 5 to 4 ma within the following range of conditions the fluids heated rocks to temperatures in the range 470 to 510 c for less than 1 million years in a region narrower than the entire mct zone the temperature of the thermal disturbance inferred from the 40ar 39ar data is consistent with petrologic data from albitic alteration assemblages in the greater himalaya sequence and the u pb age of the brannerite is similar to the youngest 40ar 39ar hornblende age this scenario hydrothermal heating culminating at about 4 ma is similar to the model of le fort 1981 for the generation of the high himalayan leucogranites in the late oligocene early miocene by dehydration of the footwall rocks of an active thrust in the younger instance we interpret that fluids derived from the footwall rocks of the main boundary thrust migrated upward through the lesser himalaya formations and were subsequently channeled along the mct producing the thermal disturbance

significance of the early fabric in the contact metamorphic aureole of the 590 ma ben vuirich granite perthshire scotland an early fabric is preserved in pseudomorphs of contact metamorphic cordierite and andalusite found in hornfelsed dalradian rocks at the nw margin of the ben vuirich granite as previous work had suggested that this fabric may be of regional tectonic d1 origin and taken as evidence that a pre 590 ma neoproterozoic orogenic event had affected the dalradian supergroup the textures found in the hornfelses and their porphryoblasts are illustrated and described in detail three types of hornfels are recorded unspotted cordierite and andalusite bearing cordierite was altered to mica garnet and kyanite and andalusite pseudomorphed by kyanite during the subsequent d2 regional metamorphism the early fabric is finely spaced and associated with a weak shape fabric except in the higher grade hornfelses where it is more intensely developed and formed during the deformation of irregularly shaped cross cutting granitic veinlets it is concluded that the hornfels fabric is probably bedding modified by intrusion related deformation rather than a d1 fabric parallel to bedding the implication of this finding is that intrusion of the ben vuirich granite occurred during the vendian c 650 ma rifting phase at about the time that the tayvallich lavas were being deposited and before any significant deformation of the dalradian rocks had taken place there is no unambiguous evidence to show that the early fabric in the hornfels at ben vuirich formed during a precambrian regional scale deformation of the dalradian block

the tectonostratigraphy and structure of the eastern nepal himalaya six years of geological research in eastern nepal has resulted in a new geological map of the eastern nepal himalaya which includes the region stretching from the sikkhim border in the east to the kathmandu valley in the west and from the summits of the higher himalaya in the north to the ganges plain in the south this research has permitted the determination of the tectonostratigraphy and structure of one section of the central himalayan arc south of the tibetan plateau the eastern nepal himalaya can be divided into three distinct thrust bound tectonic packages 1 the higher himalayan thrust sheet composed of the higher himalayan crystallines 2 the lesser himalayan thrust sheet composed of the lesser himalayan series and 3 the sub himalayan imbricate zone composed of sedimentary rocks belonging to the siwalik group the higher himalayan thrust sheet of eastern nepal has been thrust over the lesser himalayan metasediments a minimum of 140 km and possibly as much as 175 210 km along the main central thrust mct the lesser himalayan thrust sheet is overlain by the mct and is underlain by the main detachment fault mdf and the main boundary thrust mbt out of sequence thrust faults in the hanging wall of the mbt have breached and offset the presently inactive mct the sub himalayan imbricate zone is an emergent imbricate fan bounded by the mbt to the north and the main frontal thrust mft to the south and is underlain by the mdf which lies at a depth of between 5 km and 7 km a balanced cross section constructed across the higher lesser and sub himalaya of eastern nepal shows that the eastern nepal himalayan orogenic wedge has undergone a minimum of between 210 and 280 km of horizontal north south tectonic shortening since the initiation of the mct the lesser and sub himalaya have absorbed 70 km of north south shortening by thrusting along the basal mdf of which the sub himalayan imbricate zone has accommodated 25 km the sun kosi thrust has accommodated about 10 km and the mbt has accommodated the remaining 35 km of shortening since the initiation of the mct between 15 ma and 25 ma shortening across the eastern nepal himalaya has occurred at an average rate of 8 4 18 6 mm per year the structural geometry of the eastern nepal himalaya suggests an overall piggyback sequence of thrusting with motion transferred from the mct to the underlying mdf and its emergent splay thrust the mbt and with the mbt rotated to its present steep orientation by imbricate thrusting within the sub himalaya

testing for the presence of a terrane boundary within neoproterozoic dalradian to cambrian siliceous turbidites at callander perthshire scotland the southern highland group dalradian and keltie water grit formation which includes the lower cambrian leny limestone form an inverted 1 4 km thick largely arenaceous sequence at callander the grits have the same detrital mineralogy throughout mainly quartz plagioclase an 1 3 muscovite and biotite chlorite formed from detrital biotite during low grade regional metamorphism t 40 ar 39 ar laser fusion dating of detrital muscovites yields an age spectrum with a peak at 1600 1800 ma in the dalradian rocks similar old ages occur in the keltie water grits but are diluted by ages of 507 886 ma we interpret these new data as showing that the rocks were most likely deposited as a single sequence possibly with a disconformity in neoproterozoic to early cambrian times before the onset of grampian orogenesis in the early palaeozoic no major structural or stratigraphical breaks have been identified and there is no direct evidence for the presence of two separate terranes

geochemically unravelling the sedimentary components of archaean metasediments from western australia major and trace elements of metasediments of the granulite facies narryer and the amphibolite facies jack hills metasediments have been used to devise plots which enable the original sedimentary components of these rocks to be unravelled despite their metamorphic state these plots overcome the predominant effect of quartz which ranges up to 100 and can be used to study other metasediment suites six components controlled the composition of the clastic metasediments 1 kaolinite 2 illite muscovite 3 chlorite montmorillonite 4 dolomite 5 quartz 6 resistant heavy minerals such as rutile zircon chromite and monazite identifying the first four of these components enables the trace element composition associated with the components to be estimated feldspar was largely destroyed by chemical weathering but there is a suggestion that traces of it formed a minor seventh component in the narryer rocks there was little or no mixing of the original kaolinite bearing and illite muscovite bearing samples indicating two distinct sources although both sets of samples contain 4 ga zircons suggesting a third zircon source the old zircons may have been derived from re worked sediment or metasediment as they occur in the matrix and in the quartzite clasts of conglomerates using bhatia9s criteria a passive margin is the likely site of deposition calc alkaline tholeiites in the narryer succession are intrusive and did not contribute to the sediments which were derived from extremely heavily weathered granites komatiites schists and reworked sandstones or quartzites

new evidence that the lower cambrian leny limestone at callander perthshire belongs to the dalradian supergroup and a reassessment of the exotic status of the highland border complex

thermal conductivity and well logs a case study in the paris basin summary the estimation of thermal conductivity from well logs is of great importance for all studies on thermal evolution of sedimentary basins the approach proposed here is to first interpret the well logs in terms of mineralogic composition and porosity and then to estimate the in silu conductivity from a mixing formula the geometric average of individual conductivities weighted by the volumetric proportion of each component the validity of the model has been widely verified by laboratory measurements on isotropic samples however there is a need for validation of such an approach for in situ conditions temperature data recorded at equilibrium in two wells of the paris basin offer a unique possibility of testing this approach in the case of a steady state conductive thermal rcgime fourier s law the conductivity must be proportional to the inverse of the temperature gradient the well logs are quantitatively interpreted in terms of mineralogic composition porosity and then thermal conductivity using a conductivity law calibrated on cuttings and cores laboratory measurements for three examples of well sections the computed thermal conductivity compares reasonably well with the inverse of the gradient for each of the three examples it is possible to define a depth range where the apparent heat flow is almost constant with depth and where the conductive regime seems to prevail this allows a refinement of the conductivity model with emphasis on the contribution of clays assuming that the conductivities of non clay end terms are known it is possible to obtain the conductivity of clay giving the best fit to the temperature measurements in the three cases the conductivity of clay 1 21 4 w m k is found to be lower than the assumed one 1 8 w m k i which probably indicates an anisotropy effect finally an empirical model where the bulk conductivity is expressed directly as a function of well logs is tested in one case the results obtained are quite compatible with the previous one but in the other two sections the stability and the physical meaning of this model are found to be questionable this could be due to the lack of constraints in the underlying implicit mineralogy model

back arc rifting in the okinawa trough abstract geological and geophysical data reveal that the okinawa trough shows incipient continental rifting and crustal separation started from about 2 ma the early extensional movements in the trough are probably of miocene age in addition to the miocene phase two main periods of extension are recognized a pleistocene phase between 1 9 and 0 5 ma and the present day phase during the stage short central rifts central grabens were formed the opening however may have occurred only in the southern part of the trough basin having an average half spreading rate of 2 cm yr 1 since early pleistocene time producing its present width of several tens of kilometres these activities were well represented by igneous intrusions sedimentary facies and sedimentary structures in and around the okinawa trough the width of the zone affected by back arc extension defined as greater okinawa trough is larger than the present okinawa trough whose width is 200 250 km the present form of the greater okinawa trough started to form at the same time as that of the okinawa trough

magma transport through the crust via interconnected sill complexes three dimensional seismic data from the volcanic margin offshore norway have been used to map the complex three dimensional geometry of two major sill complexes these data show that the complexes consist of bowl shaped or inclined sheetlike discordant sills that intersect with one another over a vertical distance of 8 12 km and transect basement and sedimentary rocks of the middle to upper crust using a simple graphical technique we demonstrate the interconnectedness of the sill complex and hence the maximum time for sill emplacement we show that sills are interconnected by junctions occurring systematically at the lowest points of the overlying sills and hence that the sill complex could have acted as a single throughgoing magmatic plumbing system transporting mafic melts from mid lower crustal depths to near surface based on this imaging of the magmatic plumbing system we conclude that sills can form viable and efficient conduits for crustal magma transport in volcanic margins and may play a role in feeding large extrusive complexes

sedimentation in the southern okinawa trough rates turbidites and a sediment budget forty seven box cores collected from the westernmost part of the southern okinawa trough were analyzed for fallout radionuclides 210 pb and 137 cs and sedimentary properties to study sedimentation rates and dynamics the results indicate steady hemipelagic sedimentation in the lower slope and deep basin at water depths below ca 1000 m with sedimentation rates generally decreasing with increasing water depth or distance offshore barring a localized depression below the 1400 m isobath where sediment deposition is enhanced by episodic inputs of turbidites the time of deposition of various turbidite layers can be dated circa 2002 1986 1966 1959 1947 and 1922 ad which can be correlated not only spatially among sites but also temporally with the history of major submarine earthquakes in and around the region based on the distribution of sedimentation rates at 52 sites including five with sediment trap measured rates a finite element approach was used to calculate the budget of sediment although the study area in the southern okinawa trough occupies less than 10 of the okinawa trough s area it receives more sediment than the rest of the okinawa trough however sediment deposited in the study area approximately 14 mt annually accounts for only 5 of the sediment discharged from taiwanese rivers and barely matches the annual load discharged from the nearby lanyang river thus the southern okinawa trough as a sink for sediment in the continental margin accretion wedge is not as important as generally speculated

geometrical and mechanical properties of four species of northern european brown macroalgae abstract aquatic vegetation interacts with the flow by posing an obstruction and in return experiences drag and is reconfigured by acting forces it is suggested that plant buoyancy and stiffness affect these bio physical interactions and hence should be considered when including vegetation in physical and numerical hydrodynamic models however data on these parameters is either lacking for many species or existing information is insufficient to model flexible aquatic vegetation correctly previous studies have focused on plant stems but did not take plant foliage into account the present study extends the existing knowledge base by providing data for four northern european brown macroalgae and also provides a comparison between the mechanical properties of stem and blade tissue for these species specimens of alaria esculenta laminaria digitata fucus serratus and fucus vesiculosus were collected from a small tidal inlet in norway other than f serratus the macroalgae were positively buoyant and all stems showed bending moduli in agreement with previous studies with respect to their order of magnitude only l digitata exhibited a significant difference between bending moduli for stems and blades and also between the tip and the base of the blades however there were differences in flexural rigidities product of bending modulus and second moment of cross sectional area of both stems and blades and the tip and the base of blades of all but f serratus this highlights the important influence of cross sectional area and cross sectional shape on stiffness

the timing of sedimentation and buchan metamorphism in the grampian terrane in scotland from 40ar 39ar apparent age spectra new 40 ar 39 ar geochronological data from the buchan and barrovian metamorphic sequences on the ne coast of scotland have been obtained from in vacuo step heating experiments conducted on white mica extracted from seven samples the results confirm the synchronous formation of the barrovian and buchan metamorphic sequences with the 40 ar 39 ar apparent age spectra obtained for samples of andalusite grade and higher recording a range of ages between 470 4 1 8 and 464 6 1 3 ma these ages are close to the accepted age for peak metamorphism during the grampian orogeny c 470 ma whereas 40 ar 39 ar apparent age spectra of white mica from the lower grade cordierite zone near banff preserve pre grampian detrital ages in these spectra an age of c 560 ma is recorded this indicates that a tectonothermal event occurred at c 560 ma and may provide further insight into the timing of sedimentation these samples also preserve evidence of ages older than 750 ma supplementary material 40 ar 39 ar step heating data tables for all samples data from analyses of flux monitors determination of correction factors and mass discrimination used for data reduction and 40 ar 39 ar step heating spectra and inverse isochron plots from each sample are available at www geolsoc org uk sup18723

the okinawa trough genesis of a back arc basin developing along a continental margin abstract the okinawa trough is the only example of a marginal back arc basin type at a young stage of evolution that developed along a continental margin the first phase of crustal stretching and subsidence occurred during late miocene early pliocene times a second major phase occurred after the latest pliocene or early pleistocene with en echelon rift axes along the axes of the okinawa trough oblique to the general trend of the arc and trench crustal separation and active spreading has occurred in the central and southern okinawa trough but the north okinawa trough is only in a rifting stage the development of the basin has several correlations with the general tectonism of the arc system 1 1 there was a synchronism between opening and subsidence of the okinawa trough and tilting and subsidence of the fore arc terrace 2 2 back arc rifting was initiated in the volcanic arc and propagated along it during the neogene remnants of a volcanic arc are found on the continental side of the basin the beginning of the back arc spreading observed in the central and southern okinawa trough correspond to a relative minimum in the activity of the volcanic arc 3 3 the timing and kinematic evolution of the taiwan collision and the south okinawa trough opening suggest a connection between these two events such a collision lateral back arc opening model could explain the initiation of the opening of back arc basins but additional phenomena such as thermal convection retreating trench model or anchored slab model are indispensable to maintain extension in the back arc basin

rapid magma emplacement in the karoo large igneous province abstract understanding the dynamics of continental large igneous provinces lips relies on precise dating of basaltic rocks lip research has traditionally focused on dating lavas often neglecting the volumetrically important sill intrusions in underlying sedimentary basins here we present u pb zircon and baddeleyite ages for fourteen new samples of karoo lip sills and dykes spaced by as much as 1100 km across the half million square kilometer karoo basin the samples yield remarkably coherent ages ranging from 183 0 0 5 to 182 3 0 6 myr probability modeling indicates that basin scale emplacement took place within an interval of about 0 47 myrs less than 0 90 myrs with 95 confidence and could even have represented a single magma emplacement event combining the new ages with the estimated volume of sills in the karoo basin gives an emplacement rate of 0 78 km3 yr which is higher than previous estimates upper crustal magma storage may account for these high rates the results challenge the view that melt emplacement in a sedimentary basin is a prolonged process support a scenario of pulsating catastrophic events within a narrow time frame and strengthens the hypothesis linking lips and sill emplacement to global environmental crises

the crustal assembly of southern mongolia new structural lithological and geochronological data from the nemegt and altan ranges abstract the gobi altai region is an ideal setting for studying processes of continental growth and subsequent intracontinental and intraplate deformation including terrane accretion and dispersal ophiolite obduction crustal reactivation and intraplate mountain building to assess the diverse tectonic evolutionary models of the gobi altai and the wider region more field data and geochronological data are required to constrain the tectonic evolution of individual terranes and the relationship of adjacent crustal domains to each other throughout time in this paper we present new lithological structural and 40ar 39ar age data which constrain the crustal evolution across a previously unreported late paleozoic terrane boundary in the gobi altai nemegt and altan nuruu are topographically linked mountain ranges that were formed by miocene recent uplift at a right stepping restraining bend along the left lateral gobi tien shan fault system in southern mongolia ordovician carboniferous arc rocks and an ophiolite are exposed in the mountain ranges and form a small part of the east west arcuate trans altai zone field observations of rock types and structures combined with petrographic data are used to distinguish metamorphosed volcano sedimentary arc rocks in altan nuruu and western nemegt nuruu from arc rocks in central and eastern nemegt nuruu these distinct sequences are correlated with the dzolen and edrengin terranes in the trans altai zone along strike to the west integration of field data 40ar 39ar age data and published studies are used to describe a polyphase deformation history that includes late carboniferous ophiolite obduction mid permian to late triassic shortening and lateral terrane redistribution cretaceous rifting and late cenozoic intraplate mountain building

detailed structures of the subducted philippine sea plate beneath northeast taiwan a new type of double seismic zone we studied the detailed structure of the subducted philippine sea plate beneath northeast taiwan where oblique subduction regional collision and back arc opening are all actively occurring simultaneous inversion for velocity structure and earthquake hypocenters are performed using the vast high quality data recorded by the taiwan seismic network we further supplement the inversion results with earthquake source parameters determined from inversion of teleseismic p and sh waveforms a critical step to define the position of plate interface and the state of strain within the subducted slab the most interesting feature is that relocated hypocenters tend to occur along a two layered structure the upper layer is located immediately below the plate interface and extends down to 70 80 km at a dip of 40 50 below approximately 100 km the dip increases dramatically to 70 80 the lower layer commences at 45 50 km and stays approximately parallel to the upper layer with a separation of 15 5 km in between down to 70 80 km below that the separation decreases and the two layers seem to gradually merge into one wadati benioff zone we propose to term the classic double seismic zones observed beneath japan and kuril as type i and that we observed as type ii respectively a global survey indicates that type ii double seismic zones are also observed in new zealand near the southernmost north island cascadia just north of the mendocino triple junction and the cook inlet area of alaska all of them are located near the termini of subducted slabs in a tectonic setting of oblique subduction we interpret the seismogenesis of type ii double seismic zones as reflecting the lateral compressive stress between the subducted plate and the adjacent lithosphere originating from oblique subduction and the downdip extension from slab pulling force the upper seismic layer represents seismicity occurring in the upper crust of a subducted plate and or along the plate interface whereas the lower layer is associated with events in the uppermost mantle

vortex structure and sediment deposition in the wake behind a finite patch of model submerged vegetation abstracta submerged patch of finite width vegetation may produce vortex structures in its wake in both the vertical and horizontal planes this experimental study used velocity and deposition measu

geometry and controls on the development of igneous sill related forced folds a 2 d seismic reflection case study from offshore southern australia emplacement of magma in the shallow subsurface can result in the development of dome shaped folds at the earth s sur face these so called forced folds have been described in the fi eld and in subsur face data sets although the exact geometry of the folds and the nature of their relation ship to under lying sills remain unclear and in some cases controversial in this study we use high quality two dimensional 2 d seismic refl ection and borehole data from the ceduna sub basin offshore southern australia to describe the structure and infer the evolution of igneous sill related forced folds in the bight basin igneous complex thirty three igneous sills which were em placed 200 1500 m below the paleo seabed in upper cretaceous rocks are mapped in the ceduna sub basin the intrusions are expressed as packages of high amplitude refl ections which are 32 250 m thick and 7 19 km in diameter we observe fi ve main types of intrusion type 1 strata concordant sills type 2 weakly strata discordant trans gressive sills type 3 saucer shaped sills type 4 laccoliths and type 5 hybrid intru sions which have geometric characteristics of intrusion types 1 3 these intrusions are overlain by dome shaped folds which are up to 17 km wide and display up to 210 m of re lief the edges of these folds coincide with the margins of the underlying sills and the folds display the greatest relief where the underly ing sills are thickest the folds are therefore interpreted as forced folds that formed in response to emplacement of magma in the shallow subsurface the folds are onlapped by lutetian middle eocene strata indicat ing they formed and the intrusions were em placed during the latest ypresian ca 48 ma we demonstrate that fold amplitude is typi cally less than sill thickness even for sills with very large diameter to depth ratios suggest ing that pure elastic bending forced folding of the overburden is not the only process ac commodating magma emplacement and that supra sill compaction may be important even at relatively shallow depths based on the ob servation that the sills intruded a shallowly buried succession the discrepancy between fold amplitude and sill thickness may refl ect loss of host rock volume by fland pore fl uid expulsion from poorly lithifi ed water rich beds this study indicates that host rock composition emplacement depth and deformation mechanisms are important controls on the style of deformation that oc curs during intrusive igneous activity and that forced fold amplitude may not in all cases refl ect the thickness of an underlying igneous intrusion in addition the results of this study suggest that physical and numeri cal models need to model more complex host rock stratigraphies and rheologies if they are to capture the full range of deformation mechanisms that occur during magma em placement in the earth s shallow subsurface

short paper the depositional age of the dalradian supergroup u pb and sm nd isotopic studies of the tayvallich volcanics scotland zircons from a keratophyre associated with the tayvallich volcanics in the dalradian rocks of the sw scottish highlands have been dated by u pb methods yielding an age of 595 4 ma this age indicates that most or all of the dalradian is precambrian in age and that dalradian sedimentation may have lasted for about 200 million years the age also constrains the time interval between cessation of dalradian sedimentation and subsequent crustal thickening and regional metamorphism during the grampian orogeny sm nd isotopic data for the tayvallich volcanins and related metadolerite sills yield initial ond values of 2 to 4 which are thought to reffect the effects of melting of lithospheric mantle

current controversies in the caledonides this set of papers arose from a discussion meeting held in the department of geology applied geology university of glasgow on 9 10 september 1997 the aim of the meeting was to review the progress which had been made in resolving some of the more controversial aspects of the pre silurian caledonide geology of the british isles and scandinavia it was also held to mark the retirements of two well known caledonide geologists professors bernard leake and donald ramsay there were 34 talks and poster contributions and the meeting was attended by over 100 people we would like to thank our colleague tim dempster for helping to convene and organize the meeting it was fitting that the meeting should be held in the gregory building which was named after the glasgow professor who not only pioneered work on rift tectonics and regional uplift in africa but also wrote a perceptive book on dalradian geology gregory 1931 in this work gregory pointed out that his observations were made over a period of 25 years being made on recreational weekends and mainly in winter when the ground is less obscured by vegetation and the highland mountains most attractive an approach motivated by a spirit of enquiry and very productive but one which would be out of step with current research strategies we would like to dedicate this set of papers to mark piasecki who died on 13 june 1999 mark was the first person to draw attention to major problems concerning the relationship

submarine hydrothermal mineralization in the okinawa trough sw of japan an overview abstract the okinawa trough is a heavily sedimented rifted back arc basin formed in an intracontinental rift zone submarine hydrothermal activity is located within the six back arc rifts located in the middle and southern okinawa trough and its distribution is controlled principally by tectonic factors subduction of the daito and gagua ridges beneath the ryukyu arc has resulted in fracturing of the brittle lithosphere beneath the okinawa trough hydrothermal activity is strongest in the volcanic arc rift migration phenomenon vamp area plus the jade site and southernmost part of the okinawa trough spot area which form the prolongation of these two ridges these areas are characterized by extremely high heat flow locally submarine hydrothermal fluids from the okinawa trough tend to be strongly influenced by interaction of the hydrothermal fluids with organic matter in the sediment resulting in high alkalinity and nh 4 concentrations of the fluids the fluids also contain high concentrations of co 2 of magmatic origin submarine hydrothermal mineralization in the trough is diverse the clam site consists principally of carbonate chimneys interaction of the hydrothermal fluid with organic matter in the sediment is particularly strong at this site this is most probably a sediment hosted deposit in which sulphide minerals have deposited within the sediment column leaving spent ore fluids to emerge at the seafloor the jade site consists of active and inactive sulphide sulphate chimneys and mounds the zn pb rich sulphides at this site contain the highest concentrations of pb ag and au so far recorded in submarine hydrothermal sulphide deposits at minami ensei knoll and hatoma knoll active and inactive chimneys consist principally of anhydrite and barite as a result of phase separation of the hydrothermal fluids beneath the seafloor an intense black smoker has recently been discovered at yonaguni knoll in the spot area if it is confirmed that sulphide mineralization is dominant at this site this could be a highly prospective area the most prospective areas for economic grade minerals in the okinawa trough appear to be the jade site and the spot area

application of geochemistry to the stratigraphic correlation of appin and argyll group carbonate rocks from the dalradian of northeast scotland 240 samples from appin and argyll group carbonate rock units of the dalradian of northeast scotland have been analysed for 10 major oxides and 14 to 19 trace elements in order to classify and correlate them using geochemistry the carbonate rocks are chiefly limestones with some dolostones rocks with 0 38 mgo cao 0 03 are classed as dolomitic limestones those with mgo cao 0 38 are classed as dolostones the data have approximately lognormal distributions at a high level of significance except for cao mgo and sr cao and sr have negatively skewed distributions median values for groups of sample analyses plotted on normalized multi element variation diagrams and a nonlinear mapping nlm algorithm have been used to classify groups of samples in the appin group multi element diagram patterns are distinctive for each unit allowing correlations to be made though distinctive compositions do occur locally in argyll group carbonate rocks correlation on a regional scale is not possible the plot of nlm coordinates for suites of samples is consistent with the results from the spider diagrams suites of appin group samples cluster closely whereas there is wide spread in samples from the argyll group in several areas most notably at sandend bay the data have allowed reinterpretation of the stratigraphy the data are consistent with other geological data in suggesting that crustal conditions were relatively stable during the deposition of the appin group but not during the deposition of the argyll group

the importance of accurately representing submerged vegetation morphology in the numerical prediction of complex river flow this paper reports a novel method for the incorporation of complex plant morphologies into a computational fluid dynamics cfd model allowing the numerical prediction of flows around individual plants the morphological complexity which comprises the vertical and lateral distribution of individual branches and leaves is captured through terrestrial laser scanning tls and is maintained in the numerical prediction of flow fields this is achieved where the post processed voxelised plant representation is incorporated into a cfd scheme through a mass flux scaling algorithm mfsa flow around prunus laurocerasus has been modelled under foliated and defoliated states following the removal of leaves the complex plant morphologies are shown to produce spatially heterogeneous downstream velocity fields with velocity profiles that deviate significantly from the idealised inflected shape rapid transition between the high velocity free stream zone and the zone of reduced velocity in the plant wake indicate shearing of flow with the point of reattachment extending up to seven plant lengths downstream the presence of leaves significantly modifies the flow field response with development of a second more pronounced wake structure around the dense foliage this approach provides a full flow numerical description of the pressure field enabling the vegetative drag force to be quantified for the example given here drag force is an order of magnitude greater for the foliated state the methodology outlined here demonstrates the importance of accurately representing complex plant morphology in hydraulic models and allows drag forces and coefficients to be calculated for specific plant species this article is protected by copyright all rights reserved

the focus thermal study around the spreading center of southwestern okinawa trough abstract voluminous hydrothermal systems are corresponding to the heat flow anomaly discovered from previous geophysical surveys in the southern okinawa trough sot which is an area with a high sedimentation rate supplied by the east china sea shelf and the island of taiwan our latest fifteen field measurements around the geolin mound glm 24 36 6 n 122 53 e are located at a sedimentary basin west of the yonaguni rift which is nearby the southwestern tip of a ne sw trending volcano trail in the sot the heat flow results illustrate a concentric decrease from 31 477 to 180 mw m2 in a 1 km radius around the glm evidently proving the focus fluid migration along the major fluid conduit the ultrahigh temperature observations revealed the existence of magmatic components in shallow sediments combining the subsurface profiles with the temperature fields around the glm a 0 16 km2 acoustic blanking area of the g1 fluid conduit was recognized from the chirp sonar image and numerous interpreted igneous reflections with fluids related features from seismic profiles as a result we proposed a conceptual model which simultaneously illustrates the hydrothermal circulation pattern from the previous general surveys and the enormous thermal anomaly from current detailed measurements the sill to sill feeding sedimentary basin of the glm is capable of demonstrating the enormous thermal anomaly around the spreading center of the sot and appropriately represents the potential hydrothermal discharge and recharge by heat flow distribution around the glm

hydrothermal regime and constraints on reservoir depth of the jade site in the mid okinawa trough inferred from heat flow measurements detailed heat flow measurements revealed an enormous heat flow variation 102 to 105 mw m 2 in the jade hydrothermal field 27 16 n 127 05 e and water depth 1350 m located on the slope of the izena hole in the mid okinawa trough within the jade site heat flow is higher than 1000 mw m 2 and decreases to 100 mw m 2 with a 1 km horizontal scale near the jade black smoker heat flow varies from 30 000 mw m 2 at a hydrothermally altered area to 1700 mw m 2 less than 100 m from it a large scale heat flow variation suggests that the base of the escarpment near the jade site serves as a recharge area for the jade site linear geotherms indicate that the upward darcian flow within sediments is slower than 3 cm yr 1 thus the fluid circulation pathways would basically be restricted in permeable channels estimated conductive heat output rate from the jade site is 4 7 mw which is comparable to heat output by a single black smoker vent 8 mw one dimensional thermal modeling predicts the existence of a boiling zone at 200 m beneath the jade site which may be overlain by a fractured impermeable layer the normal chloride content of venting fluids from the black smoker may be explained either by upwelling of fluid which boiled at shallow depth but suffered no phase segregation or by upwelling of fluid above the boiling interface

temperature variations at diffuse and focused flow hydrothermal vent sites along the northern east pacific rise in the decade following documented volcanic activity on the east pacific rise near 9 50 n we monitored hydrothermal vent fluid temperature variations in conjunction with approximately yearly vent fluid sampling to better understand the processes and physical conditions that govern the evolution of seafloor hydrothermal systems the temperature of both diffuse flow low temperature and focused flow high temperature vent fluids decreased significantly within several years of eruptions in 1991 and 1992 after mid 1994 focused flow vents generally exhibited periods of relatively stable slowly varying temperatures with occasional high and low temperature excursions lasting days to weeks one such positive temperature excursion was associated with a crustal cracking event another with both positive and negative excursions demonstrated a subsurface connection between adjacent focused flow and diffuse flow vents diffuse flow vents exhibit much greater temperature variability than adjacent higher temperature vents on timescales of a week or less temperatures at a given position within a diffuse flow field often varied by 5 10 c synchronous with near bottom currents dominated by tidal and inertial forcing on timescales of a week and longer diffuse flow temperatures varied slowly and incoherently among different vent fields at diffuse flow vent sites the conceptual model of a thermal boundary layer immediately above the seafloor explains many of the temporal and spatial temperature variations observed within a single vent field the thermal boundary layer is a lens of warm water injected from beneath the seafloor that is mixed and distended by lateral near bottom currents the volume of the boundary layer is delineated by the position of mature communities of sessile e g tubeworms and relatively slow moving organisms e g mussels vertical flow rates of hydrothermal fluids exiting the seafloor at diffuse vents are less than lateral flow rates of near bottom currents 5 10 cm s the presence of a subsurface shallow reservoir of warm hydrothermal fluids can explain differing temperature behaviors of adjacent diffuse flow and focused flow vents at 9 50 n different average temperatures and daily temperature ranges are explained by variable amounts of mixing of hydrothermal fluids with ambient seawater through subsurface conduits that have varying lateral permeability

average lifetime and age spectra of detrital grains toward a unifying theory of sedimentary particles abstract the observed average lifetime of minerals as estimated by the average survival time of dated detrital grains correlates linearly with dc estimated from dissolution rates of minerals but does not correlate with dh estimated by mineral hardness the best predictor of the observed average lifetime is the total durability an estimator that combines dc and dh indices the age spectra of grains i e age frequency distributions of radiometrically dated detrital minerals tend to be right skewed as predicted by the exponential model used to describe the lifetime of mechanical parts weibull function or the radioactive decay of atoms consistent with the model the less durable grains produce age spectra that are more right skewed and leptokurtic and may yield more accurate estimates of depositional age whereas the more durable grains often depart from the exponential model and their age spectra primarily reflect long term geological changes in the rate of grain production the integration of geo

flow structure in canopy models dominated by progressive waves summary laboratory experiments were carried out to study the flow structure both inside and above different canopy models which were dominated by progressive waves a set of experimental conditions were considered in a laboratory flume three vegetation models submerged rigid submerged flexible and emergent rigid three plant densities 128 640 and 1280 stems m 2 and three wave frequencies f 0 8 1 and 1 4 hz the progressive waves followed the second order stokes theory in the intermediate depth range the observations revealed that submerged and emergent rigid vegetation models modified the wave induced velocities i e both mean current and wave velocity the submerged rigid vegetation model for plant densities higher than 640 plants m 2 and wave frequency higher than 1 hz acted akin to a false floor confining the mean current to above the plant bed a penetration depth around 2 cm below the top of submerged rigid vegetation was found for the other runs the vertical profile of mean current did not present changes with respect to runs without plants the emergent rigid vegetation model reversed the direction of the induced mean current with the highest velocity corresponding to the highest plant density in contrast the submerged flexible vegetation model had a weak effect on the mean current with the vertical velocity profile similar to that found in experiments without vegetation the wave velocities inside the vegetation for the densest submerged rigid vegetation were found to be reduced by 20 when compared to the wave velocities without vegetation while in emergent rigid vegetation this reduction was of 45

unroofing of the himalayas a view from apatite fission track analysis of bengal fan sediments apatite fission track analysis of early miocene to quaternary distal bengal fan sediments from odp leg 116 provides a unique perspective on denudation processes associated with the tertiary himalayan orogeny these sediments yield pooled apatite fission track ages that are 0 to 10 m y older than depositional ages mean track lengths range from 13 2 to 14 8 mu m these young ages and long track lengths indicate that rocks in the upper crust of bengal fan source areas cooled rapidly ge 15 degrees c m y implying denudation rates of several hundreds of meters per million years these observations support the hypothesis that nearly continuous unroofing of a large source area similar to the dimensions of the present himalayan and southern tibetan plateau deformation front and an efficient transport system similar to the present himalaya ganges brahmaputra system supplied sediment to the bengal fan since the early miocene

hydrothermal circulation within the endeavour segment juan de fuca ridge areas of the seafloor at mid ocean ridges where hydrothermal vents discharge are easily recognized by the dramatic biological physical and chemical processes that characterize such sites locations where seawater flows into the seafloor to recharge hydrothermal cells within the crustal reservoir are by contrast almost invisible but can be indirectly identified by a systematic grid of conductive heat flow measurements an array of conductive heat flow stations in the endeavour axial valley of the juan de fuca ridge has identified recharge zones that appear to represent a nested system of fluid circulation paths at the scale of an axial rift valley conductive heat flow data indicate a general cross valley fluid flow where seawater enters the shallow subsurface crustal reservoir at the eastern wall of the endeavour axial valley and undergoes a kilometer of horizontal transit beneath the valley floor finally exiting as warm hydrothermal fluid discharge on the western valley bounding wall recharge zones also have been identified as located within an annular ring of very cold seafloor around the large main endeavour hydrothermal field with seawater inflow occurring within faults that surround the fluid discharge sites these conductive heat flow data are consistent with previous models where high temperature fluid circulation cells beneath large hydrothermal vent fields may be composed of narrow vertical cylinders subsurface fluid circulation on the endeavour segment occurs at various crustal depths in three distinct modes 1 general east to west flow across the entire valley floor 2 in narrow cylinders that penetrate deeply to high temperature heat sources and 3 supplying low temperature diffuse vents where seawater is entrained into the shallow uppermost crust by the adjacent high temperature cylindrical systems the systematic array of conductive heat flow measurements over the axial valley floor averaged 150 mw m2 suggesting that only about 3 of the total energy flux of ocean crustal formation is removed by conductive heat transfer with the remainder being dissipated to overlying seawater by fluid advection

divining gold in seafloor polymetallic massive sulfide systems hydrothermal fluids on the modern seafloor are important carriers of base and precious metals in a wide range of volcanic and tectonic settings the concentrations and distribution especially of gold and silver in associated seafloor massive sulfide sms deposits are strongly influenced by variable source rocks fluid chemistry and precipitation mechanisms compositional data of 130 sms deposits around the world show a large range of gold and silver grades in part reflecting strong buffering of the hydrothermal fluids by their host rocks geochemical reaction path modeling shows that in most cases the investigated hydrothermal fluids are undersaturated with gold and silver and solubilities can be orders of magnitude higher than the au and ag concentrations measured in the corresponding fluids precipitation of gold during conductive cooling of mid ocean ridge black smoker mor fluids occurs at low temperatures but can be very rapid with 90 of the gold deposited in the first 25 c of cooling below 150 c the result is a zn au polymetallic assemblage with au and ag deposited at the same time together with pb and sulfosalts in ultramafic dominated um systems the strongly reduced hydrothermal fluids promote the deposition of gold at higher temperatures and explain the correlation between gold and copper in these deposits in this case the lower stability of the auhs complex at low o2 buffered by fayalite magnetite and quartz results in gold deposition at 250 c with early bornite and chalcopyrite and before sphalerite and silver producing a high temperature cu au assemblage in sediment hosted sed systems the much higher ph stabilizes au hs 2 and keeps gold in solution to very low temperatures after the precipitation of chalcopyrite sphalerite and galena resulting in au poor polymetallic sulfides and very late stage deposition of gold commonly with amorphous silica in arc related arc systems gold deposition occurs at somewhat higher temperatures than in the mor case in part because the fluids start with higher gold concentrations this can be explained by probable direct magmatic contributions and the high o2 of the fluids which promotes the solubility of gold at the source during cooling gold precipitates at about 160 c with sphalerite tennantite silver and galena resulting in an au rich polymetallic sulfide assemblage the mixing of hydrothermal fluids with seawater generally causes oxidation and eventually a decrease in the ph at a mixing ratio of 1 1 causing an initial increase in the solubility of gold and silver this can delay gold deposition from aqueous species to very low temperatures these complex systematics make prediction of au and ag grades difficult however important new data are coming to light on the actual concentrations of the precious metals in hydrothermal fluids in particular the input of magmatic volatiles and leaching of pre existing gold can lead to significant increases in the au and ag concentrations of the venting fluids and earlier deposition in several cases it appears that at least part of the gold load is present as nanoparticles in suspension allowing bulk gold concentrations that may be far in excess of liquid saturation boiling at the seafloor is now widely observed even at great water depths close to the critical point of seawater model calculations of phase separation during boiling show the competing effects on gold solubility of h2 h2s and co2 partitioning into the vapor which can result in highly variable gold to base metal ratios in the deposits flashing of the vent fluids into steam at high temperatures is also commonly observed and can lead to spectacular au grades with a strong cu au association in the deepest and hottest vents

the highland border complex scotland a paradox resolved a previously inexplicable difference between the highland border complex scotland and its correlative in ireland the clew bay complex is that rocks of caradoc ashgill age occur only in the former we reject evidence from supposed chitinozoa for this dichotomy no sedimentary rocks of proven age younger than arenig occur in the highland border complex consequentially the stratigraphy must be totally recast and the exotic terrane model replaced by one in which a largely autochthonous highland border complex in stratigraphical continuity with the dalradian grampian terrane was overridden by the highland border ophiolite midland valley terrane tectonic models for se laurentia are thereby considerably simplified

source of the lachlan fold belt flysch linked to convective removal of the lithospheric mantle and rapid exhumation of the delamerian ross fold belt during the cambrian ordovician the paleo pacific margin of gondwana underwent a rapid transition from a site of convergent deformation delamerian ross orogeny to one of sedimentation during which the thick turbiditic sequences of the adjacent basal lachlan fold belt were deposited laser probe 40 ar 39 ar data show that the synkinematic 523 486 ma mid crustal i and s type granites and metamorphic country rocks of the delamerian fold belt were rapidly cooled at 490 485 ma coincident with the intrusion of a suite of high level postkinematic a type granites and gabbros ca 497 481 ma 40 ar 39 ar data on detrital muscovites from the basal sections of the lachlan fold belt provide information on exhumation rather than cooling but yield an age pattern 507 480 ma identical to that of the delamerian fold belt demonstrating that this was the source of the sediments the combined data require that some 15 km of exhumation occurred very rapidly 5 15 mm yr 1 coincident as implied by overlapping ages with the cessation of convergent deformation and partial melting to form the postkinematic magmas this scenario implies a causative link which we infer to have been convective removal of lithospheric mantle following orogenic thickening the model is analogous to the tertiary uplift of the india asia orogen which provided the sediment source for the bengal fan our results suggest that similar processes were important in the evolution of mountain belts at least as far back as the early phanerozoic

plant patch hydrodynamics in streams mean flow turbulence and drag forces 1 this paper investigates the effects of a finite size vegetation patch on flow turbulence variations in drag forces experienced by individual plants within the patch and flow drag interrelations the experiments were conducted in a 32 m long laboratory flume with a 2 8 m long artificial patch the plants were arranged to form a staggered pattern and three flow scenarios were tested velocities were recorded with an acoustic doppler velocimeter whereas specifically designed devices were used to simultaneously measure the drag forces acting on nine plants within the patch for all studied cases the results show zones of increased turbulent energy close to the leading edge and along the patch canopy top where turbulence shear production is enhanced zones of negative reynolds stresses u w are found inside the patch and they reflect the influence of plant morphology which affects the shape of the longitudinal velocity profile and associated turbulent fluxes modifications to the power spectral densities of velocity by the plants indicate the emergence of two plant induced mechanisms of energy production which are most likely related to the wake turbulence and shear layer turbulence drag fluctuations appear to be correlated with the velocity field with this correlation being especially profound at the highest studied flow rate the data suggest that the highlighted correlation stems from flow plant interactions at the top of the vegetation canopy likely due to the presence of large three dimensional coherent structures

near axis heat flow measurements on the northern juan de fuca ridge implications for fluid circulation in oceanic crust present models of the cooling of oceanic crust suggest that convection of hydrothermal fluid is a major component of the process in axial regions abundant faults and open fissures are associated with the venting of high temperature hydrothermal fluid in older crust where the insulating sediment cover is thick previous studies have shown that basement topography is the dominant forcing factor for within crust fluid circulation in the intermediate region where young crust is lightly sedimented heat flow data are difficult to obtain with traditional techniques to determine whether topography or permeability is the dominant process controlling fluid circulation in the near axis region we conducted a profile of heat flow measurements using the submersible alvin on the endeavour segment of the juan de fuca ridge our data indicate that topographic forcing is responsible for the long wavelength variations with high heat flow at the ridge summits and low values in the inter ridge valleys the locations of the extreme values of heat flow taken within the context of subsurface faulting are consistent with a model where a ridge valley topographic pair comprises a single circulation cell this model predicts that the source area for the high temperature axial vents may be in the flanking inter ridge valleys

distorted drainage basins as markers of crustal strain east of the himalaya extensive lithospheric deformation on the eastern margin of the india eurasia collision has brought three major rivers into exceptionally close proximity for over 300 km the salween mekong and yangtze rivers are only tens of kilometers apart 10 times closer than rivers of comparable length elsewhere in the world we view deeply incised river valleys as displacement markers that move with the underlying crust over time scales of at least tens of millions of years accordingly the close spacing of these major rivers and their nearly parallel trends reflect the large crustal strains near the eastern himalayan syntaxis these river characteristics are consistent with two primary phases of deformation in this tectonic setting ne sw shortening of 0 5 oriented radially from the eastern syntaxis followed by dextral shear strain of 6 1 along a north trending zone pervasive shearing of this magnitude throughout the 150 km wide region of anomalous drainage would account for 1000 km of northward motion of india relative to southern china directly east of this region another 1000 km of northward motion is likely to have been accommodated by pervasive shearing through a zone hundreds of kilometers wide finally we draw attention to the remarkable accord between the arcuate paths of each of the three great rivers in the broader southeastern tibet region and small circles that curve around the eastern himalayan syntaxis

active hydrothermal mounds in the okinawa trough backarc basin japan abstract dive studies by the shinkai 2000 were made in september 1984 and july 1986 in the central axial rift of the middle okinawa trough a possible active backarc basin in a nascent stage hydrothermally active mounds were discovered on a small knoll 27 34 4 n 127 08 6 e directly south of the area where a high heat flow higher than 1 w m2 had been observed previously the largest mound 5 6 m high and 15 25 m wide has several peaks and ridges along which yellow materials are exposed shimmering water was noted at several places on the yellow materials the rest of the mound is thinly covered by brown materials the temperature of the ejecting water was higher than that of the ambient seawater by 2 3 c and a 40 cm long thermometer inserted into the mound recorded a temperature of 20 50 c analysis of the ejected water showed a methane content of about 200 nl kg it is possible that further dive studies will reveal larger scale hydrothermal activity in the area

laboratory measurements of flow and turbulence in discontinuous distributions of ligulate seagrass turbulent flow characteristics were investigated in laboratory flume studies of a ligulate plant canopy interrupted by a gap representing discontinuities observed in seagrass prairies the reliability of velocity measurements obtained using an acoustic doppler velocimeter within the canopy was shown using specifically designed experiments in relatively fast flow mean velocity 5 5 cm s 1 the mean flow profile was logarithmic above the canopy had an inflection point near its top and uniformly low values within it within the gap a recirculation cell formed reynolds stress maxima were approximately coincident with the mean flow inflection point quadrant analysis revealed an ejection dominated upper layer a sweep dominated region around the top of the canopy and within the gap and no dominant quadrant within the canopy in slower flow mean velocity 1 7 cm s 1 the plants were quasiemergent and the flow fields more uniform sweeps similarly dominated the region near the top of the canopy and within the gap in both flows autocorrelation of longitudinal velocity fluctuations showed a lagrangian time scale maximum at the downstream end of the gap

a high precision u pb age for the ben vuirich granite implications for the evolution of the scottish dalradian supergroup high precision high accuracy u pb analyses of zircons from the ben vuirich granite in the scottish dalradian succession were performed on carefully picked high integrity abraded fractions of specific morphologies zircon needles which grew during crystallization give an age of 590 2 ma stubby prisms show inheritance with an upper concordia intercept of 1448 7 ma the age of intrusion at 590 ma contrasts strongly with a previous u pb zircon age of 514 6 7 ma determined on bulk fraction unabraded grains which it is argued must have suffered significant pb loss as the ben vuirich granite was emplaced between the regional d2 and d3 deformation events in the dalradian block the new data imply that all dalradian sedimentation was precambrian supposed lower cambrian fauna1 links between the dalradian succession and laurentia are thus discounted and the possibility that the dalradian supergroup has non laurentian affinities must be considered the early d1 d2 nappe forming grampian structures are also precambrian and may be associated with terrane docking along a tectonically active ocean margin later d3 structures and associated peak barrovian metamorphism suggest a subsequent thickening event possibly c 520 ma ago

metamorphism and cooling of the ne dalradian the buchan area of dalradian rocks represents a distinct tectonothermal domain within the scottish highlands and the portsoy duchray hill lineament on the western margin of this block is one of the best examples of a long lived domain boundary rb sr mica cooling ages from metamorphic rocks from across the trace of this lineament document a prolonged ordovician cooling history delayed but then relatively rapid cooling to the west of the portsoy duchray hill lineament is recognized whereas to the east the age data point to a high heat flow regime lasting more than 50 ma the isotopic ages suggest that c 460 ma was a time of active tectonism resulting in final cooling of the low grade rocks and differential uplift and rapid cooling of deeper structural levels to the west the radiometric ages do not support previous tectonic models for the region that have invoked thrust thickening along the line of the portsoy duchray hill lineament and a new model for the metamorphism is proposed the overprinting of andalusite bearing assemblages by kyanite to the west of the portsoy duchray hill lineament is linked to pressure increases associated with the intrusion of the newer gabbros and represents a magmatic loading related to the same tectonothermal event that generated the low pressure metamorphism rather than a separate tectonic episode

revisiting the data reduction of seafloor heat flow measurement the example of mapping hydrothermal venting site around yonaguni knoll iv in the south okinawa trough abstract yonaguni knoll iv is an active hydrothermal venting site located on the southern tip of a cross back arc volcanic trail in the south okinawa trough we have compiled 22 heat flow measurements on the seafloor around the yonaguni knoll iv site that reveal drastic heat flow spatial variation to obtain the appropriate heat flow measurements from our recently rebuilt lister type marine heat probe we have updated the processing algorithm in this study to avoid utilizing the sometimes unstable temperature evolving data from the frictional heating stage we have carefully calibrated and processed the observed data to yield robust estimates of the seafloor heat flow emphasizing in particular that the previous implementation of the data reduction scheme by downsizing model parameters into two subsets to be pursued in two separate steps is not theoretically and practically essential we also examine the trade offs of sensitivity on model parameters constrained by the thermal decay data and reveal previously unclear knowledge concerning the intertwined mutual dependence that is critical to the performance the data reduction a contrast of more than 3000 mw m2 within short distances implies active local hydrothermal circulation the observed low heat flow area could be a cold seawater charging site whereas yonaguni knoll iv might stand for a close by discharging output although it demands for detailed mapping to establish the 3d geometry of the local hydrothermal circulation preliminary evidence suggests that the lateral dimension of the circulation cell is around a few kilometres

okinawa trough backarc basin early tectonic and magmatic evolution the okinawa trough lying between japan and taiwan is a backarc basin formed by extension within the continental lithosphere behind the ryukyu trench arc system stress directions associated with the two last extensional phases in the southwestern okinawa trough have been deduced from a comparison with analog modeling the direction of extension is n 150 o for the pleistocene phase of extension 2 0 1 ma and n 170 o for the late pleistocene holocene phase of extension 0 1 0 ma the present day ryukyu volcanic arc a narrow continuous feature extending from japan to taiwan is located on the eastern side of the okinawa trough 80 100 km above the wadati benioff zone the minimum depth for emplacement of arc magmatism scarce present day backarc volcanism appears in the middle and southern okinawa trough within linear en echelon bathymetric depressions a n045 o oriented seamount volcanic chain cuts across obliquely the southwestern okinawa trough and lies in the direct line of extension of the gagua ridge a n s linear volcanic feature of the philippine sea plate associated with this extension of the gagua ridge a large reentrant located at the base of the ryukyu prism the uplift of part of the nanao forearc basin and the deformation of the sedimentary arc suggest that the voluminous cross backarc volcanism could be tied to the subduction of the gagua ridge located there at a depth of 80 100 km beneath the backarc basin a second area of anomalous volcanism has been identified in the middle okinawa trough in the ene extension of the daito ridge a wnw ese 400 km long volcanic feature of the philippine sea plate we suggest that the gagua and daito ridges initially induced stress at the base of the arc which is still brittle and cracks propagated through the overlying brittle lithosphere allowing magmas with arc affinities to erupt at the seafloor this excessive magmatism reaches the seafloor through conduits which preferentially follow in their shallowest portion the crustal normal faults of the backarc rifts the okinawa trough is consequently still in an early stage of evolving from arc type to backarc activity

the nature and origin of the barrovian metamorphism scotland 40ar 39ar apparent age patterns and the duration of metamorphism in the biotite zone abstract a geochronological traverse across the barrovian metamorphic series scotland shows 40 ar 39 ar apparent age spectra that reflect the influence of progressive metamorphism during the grampian orogenic episode the lowest grade units of the barrovian metamorphic series retain pre grampian detrital ages as components of their white mica 40 ar 39 ar apparent age spectra these relict ages are progressively obliterated in the direction of increasing metamorphic grade with a grampian age 40 ar 39 ar step heating plateau first occurring in the biotite zone the microstructure at this point shows only limited recrystallization suggesting loss of argon mainly by diffusion forward modelling of argon diffusion from white mica grains was therefore carried out for various thermal histories and grain sizes to match 40 ar 39 ar step heating apparent age spectra patterns preserved within the biotite zone of the barrovian metamorphic series the results imply a thermal duration of between 1 and 10 ma for barrovian metamorphism in the biotite zone such short time scales for metamorphism place a limit on length scales for the heat sources responsible mid crustal extensional ductile shear zones that crop out in the ne of the grampian terrane once focused narrow grampian age heat sources e g magmas hot fluids shear heating that drove a brief thermal episode resulting in the barrovian metamorphism supplementary material 40 ar 39 ar data tables and plots including 1 data from analyses on flux monitors and plots used for j factor determination and 2 data from analyses on unknowns and 40 ar 39 ar step heating spectra and inverse isochron plots for each unknown are available at http www geolsoc org uk sup18442

the morphology of intrusion related vent structures and their implications for constraining the timing of intrusive events along the ne atlantic margin intrusion related vent structures found within palaeocene sediments and near the palaeocene eocene transition in basins along the ne atlantic margin have been studied in detail using 3d seismic data the vents formed at the palaeo seabed as a result of sill intrusion and the vent fill ranges in composition from entirely remobilized sedimentary to dominantly magmatic the vents are commonly developed above sill edges and crests in sills to which they are linked by pipe and diatreme like structures the vents also develop above the upper tips of deep seated faults and at fault intersections the vents can be used to constrain the approximate timing of igneous sill intrusion and duration of hydrothermal activity it is estimated that using the seismically constrained stratigraphic context of these vents to establish the timing of sill emplacement is associated with an uncertainty of 100 ka and up to as much as 800 ka interpretation of the vents indicates that sill intrusion took place during a number of discrete phases within the palaeocene and earliest eocene these structures and their timing of formation have important implications for climate change studies basin scale processes including fluid flow and diagenesis as well as hydrocarbon exploration

sediment deposition and production in se asia seagrass meadows abstract seagrass meadows play an important role in the trapping and binding of particles in coastal sediments yet seagrass may also contribute to sediment production directly through the deposition of detritus and also the deposition of the associated mineral particles this study aims at estimating the contribution of different seagrass species growing across an extensive range of deposition to inorganic carbonate and non carbonate and organic sediment production total daily deposition measured with sediment traps varied from 18 8 2 0 g dw m 2 d 1 in silaqui philippines to 681 1 102 g dw m 2 d 1 in bay tien vietnam these measurements correspond to a single sampling event and represent sedimentation conditions during the dry season in se asia coastal areas enhalus acoroides was the most common species in the seagrass meadows visited and together with thalassia hemprichii was present at sites from low to very high deposition halodule uninervis and cymodocea species were present in sites from low to medium deposition the mineral load in seagrass leaves increased with age and was high in e acoroides because it had the largest and long lived leaves up to 417 mg calcium carbonate per leaf and 507 mg non carbonate minerals per leaf and low in h uninervis with short lived leaves 4 mg calcium carbonate per leaf and 2 mg non carbonate minerals per leaf in se asia seagrass meadows non carbonate minerals accumulate at slower rates than the production of calcium carbonate by the epiphytic community consequently the final loads supported by fully grown leaves were as average lower than calcium carbonate loads our results show that organic and inorganic production of the seagrasses in se asia represents a small contribution maximum of 15 of the materials sedimented on a daily base by the water column during the sampling period the contribution of the carbonate fraction can be locally significant i e 34 in silaqui in areas where the depositional flux is low but is minor

structural and stratigraphic relationships across the continuation of the highland boundary fault in western ireland t he relationship between the dalradian supergroup and the highland border complex in scotland has remained contentious for over a century in western ireland the contact between the dalradian supergroup and the clew bay complex a correlative of the highland border complex is superbly exposed on the island of achill beg on the north mayo coast the unfossiliferous south achillbegsuccessionhasbeentraditionally assignedtotheclewbaycomplex andthisinterpretation is supported by a combination of sm nd model age data heavy mineral analysis and lithostratigraphic correlation tdm ages range from 1 99 2 66 ga mean 2 28 ga n 6 detailed structural mapping shows that both the dalradian and the clew bay complex share the same structural history a d1 high strain event is common to both units and is associated with the development of tectonic slides the d2 event is responsible for the formation of crustal scale nappes in both units beds are consistently downward facing on the s2 foliation later dextral shearing d3 resulted in the tilting of the originally recumbent s facing d2 nappes into this downward facing orientation rb sr and 40 ar 39 arradiometricdatingofmuscoviteconfirmsthatbothunitsweredeformedcontemporaneously as the s2 nappe fabric in each is dated at c 460 ma this middle ordovician age for deformation of the clew bay complex is highly significant not least because published microfossil data suggest a silurian age

flow dynamics in mid jurassic dikes and sills of the ferrar large igneous province and implications for long distance magma transport abstract magma flow paths in sill fed dikes of the ferrar large igneous province lip contrast with those predicted by classic models of dike transport in lips and magmatic rift settings we examine anisotropy of magnetic susceptibility ams flow paths in dike networks at terra cotta mountain and mt gran which intruded at paleodepths of 2 5 and 1 5 km these intrusions up to 30 m thick exhibit irregular interconnected dike sill geometries and adjoin larger sills 200 300 m thick at different stratigraphic levels both shallowly dipping and sub vertical magma flow components are interpreted from ams measurements across individual intrusions and often match macroscopic flow indicators and variations in dike attitudes flow paths suggest that intrusive patterns and magma flow directions depended on varying stress concentrations and rotations during dike and sill propagation whereas a regional extensional tectonic control was negligible or absent unlike giant dike swarms in lips elsewhere e g 1270 ma mackenzie lip dikes of the ferrar lip show no regionally consistent vertical or lateral flow patterns suggesting these intrusion were not responsible for long distance transport in the province in the absence of regionally significant colinear dike swarms or observed intrusions at crustal depths 4 km we suggest that long distance magma transport occurred in sills within beacon supergroup sedimentary rocks this interpretation is consistent with existing geochemical data and thermal constraints which support lateral magma flow for 3 500 km across the gondwana supercontinent before freezing

new uppermost cambrian u pb date from avalonian wales and age of the cambrian ordovician boundary a crystal rich volcaniclastic sandstone in the lower peltura scarabaeoideszone at ogof ddu near criccieth north wales yields a u pb zircon age of 491 1 ma this late late cambrian date indicates a remarkably young age for the cambrian ordovician boundary whose age must be less than 491 ma hence the revised duration of the post placentian trilobite bearing cambrian indicates that local trilobite zonations allow a biostratigraphic resolution comparable to that provided by ordovician graptolites and mesozoic ammonites

three dimensional measurement of river channel flow processes using acoustic doppler velocimetry this paper describes and assesses i the use of a new instrument for the determination of three dimensional flow velocities in natural rivers the acoustic doppler velocimeter adv and ii a method for positioning and orienting such measurements relative to a single local coordinate system to relate flow velocity vectors with the bed and water surface the adv uses the doppler shift principle to measure the velocity of small particles assuming to be moving at velocities similar to the fluid velocity is resolved into three orthogonal components and measured in a volume 5 cm below the sensor head minimizing interference of the flow field and allowing measurements to be made close to the bed a simple method for positioning and orienting the instrument using digital tacheometry is described and is used to obtain velocity measurements concurrently with measurements of both bed and water surface topography the paper includes a preliminary field assessment of the adv by comparing velocity profiles with those generated from marsh mcbirney electromagnetic current meters and a full field assessment of the position and orientation methodology these results suggest that the recommended methods in combination with an adv are able to provide reliable mean three dimensional velocity field information and accurate bed and surface topography copyright 1998 john wiley sons ltd

hydrodynamics of model posidonia oceanica patches in shallow water the hydrodynamics of simulated patches of the mediterranean seagrass posidonia oceanica were studied in laboratory flume experiments in which the height of the pronated canopy was always greater than half the total water depth the effects of variations in speed from 0 08 m s 21 to 0 24 m s 21 and patch configuration on the hydrodynamics were investigated significant speeds penetrated the patches to approximately half their height reducing speed did not change the flow patterns observed except to weaken and blur them flow encountering a single patch formed a turbulent wake at the height of the top of the canopy within this wake the vertical shear stress decreased monotonically downstream but the reynolds stress increased initially and then decayed when a second patch was positioned within the region where reynolds stress increased referred to as the 06 patch the wake center penetrated it causing average turbulent velocities with horizontal components 3 3 times higher and vertical components 4 2 times higher than in the upstream patch when this patch was positioned where the reynolds stress decayed referred to as the 14 patch the wake center rose above it nevertheless the turbulence in the 14 patch had horizontal components 12 higher and vertical components 22 higher on average than in the 06 patch because its upstream end was closer to the reynolds stress maximum thus the ratio of the patch separation to the length of wake in which the reynolds stress increased was identified as central to quantifying the turbulence within the downstream patch the increased turbulence is likely to be important in determining sedimentary and ecological patch characteristics by increasing retention of particulates in suspension and thus reducing depositional rates of for example larvae nutrients and dead organic matter

submarine hydrothermal activity and gold rich mineralization at brothers volcano kermadec arc new zealand brothers volcano of the kermadec intraoceanic arc is host to a hydrothermal system unique among seafloor hydrothermal systems known anywhere in the world it has two distinct vent fields known as the nw caldera and cone sites whose geology permeability vent fluid compositions mineralogy and ore forming conditions are in stark contrast to each other the nw caldera site strikes for 600 m in a sw ne direction with chimneys occurring over a 145 m depth interval between 1 690 and 1 545 m at least 100 dead and active sulfide chimney spires occur in this field and are typically 2 3 m in height with some reaching 6 7 m their ages at time of sampling fall broadly into three groups 4 23 and 35 years old the chimneys typically occur near the base of individual fault controlled benches on the caldera wall striking in lines orthogonal to the slopes rarer are massive sulfide crusts 2 3 m thick two main types of chimney predominate cu rich up to 28 5 wt cu and more commonly zn rich up to 43 8 wt zn geochemical results show that mo bi co se sn and au up to 91 ppm are correlated with the cu mineralization whereas cd hg sb ag and as are associated with the dominant zn rich mineralization the cone site comprises the upper cone site atop the summit of the recent main dacite cone and the lower cone site that straddles the summit of an older smaller more degraded dacite cone on the ne flank of the main cone huge volumes of diffuse venting are seen at the lower cone site in contrast to venting at both the upper cone and nw caldera sites individual vents are marked by low relief 0 5 m mounds comprising predominately native sulfur with bacterial mats vent fluids of the nw caldera field are focused hot 300 c acidic ph 2 8 metal rich and gas poor calculated end member fluids from nw caldera vents indicate that phase separation has occurred with cl values ranging from 93 to 137 of seawater values by contrast vent fluids at the cone site are diffuse noticeably cooler 122 c more acidic ph 1 9 metal poor and gas rich higher than seawater values of so4 and mg in the cone vent fluids show that these ions are being added to the hydrothermal fluid and are not being depleted via normal water rock interactions iron oxide crusts 3 years in age cover the main cone summit and appear to have formed from fe rich brines evidence for magmatic contributions to the hydrothermal system at brothers includes high concentrations of dissolved co2 e g 206 mm kg at the cone site high co2 3he negative d and 18oh2o for vent fluids negative 34s for sulfides to 4 6 sulfur to 10 2 and 15n2 to 3 5 vent fluid ph values to 1 9 and mineral assemblages common to high sulfidation systems changing physicochemical conditions at the brothers hydrothermal system and especially the cone site occur over periods of months to hundreds of years as shown by interlayered cu au and zn rich zones in chimneys variable fluid and isotopic compositions similar shifts in 3he 4he values for both cone and nw caldera sites and overprinting of magmatic mineral assemblages by water rock dominated assemblages metals especially cu and possibly au may be entering the hydrothermal system via the dissolution of metal rich glasses they are then transported rapidly up into the system via magmatic volatiles utilizing vertical 2 5 km long narrow 300 m diameter pipes consistent with evidence of vent fluids forming at relatively shallow depths the nw caldera and cone sites are considered to represent stages along a continuum between water rock and magmatic hydrothermal dominated end members

indentation of the philippine sea plate by the eurasia plate in taiwan details from recent marine seismological experiments abstract we analyze in this study a new set of marine data including 3d local tomography 1992 2008 relocated earthquakes and two recent multichannel seismic lines to characterize the deformation style in the collision area offshore east taiwan we have mapped in detail the mohos of the converging plates as well as the subduction interface with a resolution never reached before we show that the sharp continental subduction of the eurasia plate beneath the middle part of the central range indents the philippine sea plate psp as attested by intra oceanic slicing and incipient subduction of the psp beneath the east coast of taiwan the westernmost part of the psp slab is probably experiencing a beginning of break off as attested by nw trending en echelon shear zones beneath the southern slope of the southern ryukyu arc sra these en echelon shear zones have a sinistral component favored by the collision free subduction of the psp north of 24 30 n the down faulting of the subduction interface forms ramps along which earthquakes clusterize three m7 subduction earthquakes occurred offshore suao city along these ramps with a recurrence interval of about 40 years 1920 m w 7 7 1963 m w 7 2 and 2002 m w 7 1 events the 1966 m w 6 0 7 5 earthquakes sequence likely outlines a wnw ese left lateral intra slab shear zone the sra upper plate accommodates the complex geometry and deformation of the subducting psp through seismic deformation shallow high velocities fringing the luzon volcanic arc lva beneath the longitudinal valley and north of the southernmost ryukyu forearc basins are interpreted as relics of the lva forearc basement squeezed in the collision zone based on the accommodation of a large part of the convergence through shortening within the psp and the subsequent segmentation of the shallow subduction interface we consider that the nucleation of a m w 8 earthquake along the southernmost ryukyu megathrust is unlikely

a pre d2 age for the 590 ma ben vuirich granite in the dalradian of scotland regional mapping demonstrates that s2 is the main fabric in the central highland dalradian and that it is this fabric not s3 as previously thought which overprints the 590 ma ben vuirich granite the granite appears to have been emplaced following a tectonic event d1 in the dalradian rocks for a finely spaced penetrative fabric seen in newly discovered hornfelses from the granite aureole is overgrown by contact metamorphic cordierite and andalusite porphyroblasts now both altered which predate the d2 metamorphism the ben vuirich granite cuts the neoproterozoic dalradian sequence of the central highlands of scotland fig 1 inset and was first recognized as an older foliated granite by barrow et al 1905 later workers bradbury et al 1976 bradbury 1978 concluded that the granite was intruded between d2 and d3 in the dalradian rocks harris et al 1976 and for many years an u pb zircon age of 514 7 ma from the intrusion pankhurst pidgeon 1976 provided a valuable datum point in the evolution of the scottish caledonides however dalradian chronology has recently undergone a radical revision following the determination of a precise u pb age of 590 2 ma for the emplacement of the ben vuirich granite rogers et al 1989 in accepting the interpretation of bradbury et al 1976 that the regional penetrative fabric which affects the country rocks and is continuous with that in the granite is of d3 age rogers et al were also guided by the conclusions of harte et al 1984 and dempster harte

age of the grampian event a discussion of new evidence that the lower cambrian leny limestone at callander perthshire belongs to the dalradian supergroup and a reassessment of the exotic status of the highland border complex

hydrothermal recharge and discharge across 50 km guided by seamounts on a young ridge flank hydrothermal circulation within the sea floor through lithosphere older than one million years myr is responsible for 30 of the energy released from plate cooling and for 70 of the global heat flow anomaly the difference between observed thermal output and that predicted by conductive cooling models 1 2 hydrothermal fluids remove significant amounts of heat from the oceanic lithosphere for plates typically up to about 65 myr old3 4 but in view of the relatively impermeable sediments that cover most ridge flanks5 it has been difficult to explain how these fluids transport heat from the crust to the ocean here we present results of swath mapping heat flow geochemistry and seismic surveys from the young eastern flank of the juan de fuca ridge which show that isolated basement outcrops penetrating through thick sediments guide hydrothermal discharge and recharge between sites separated by more than 50 km our analyses reveal distinct thermal patterns at the sea floor adjacent to recharging and discharging outcrops we find that such a circulation through basement outcrops can be sustained in a setting of pressure differences and crustal properties as reported in independent observations and modelling studies

uplift patterns and orogenic evolution in the scottish dalradian rb sr and k ar mineral ages from the dalradian rocks of angus and perthshire indicate considerable diachronism of cooling following the caledonian regional metamorphism the oldest mineral ages 515 ma are similar to the independent estimates of peak metamorphic age and hence indicate very rapid cooling they occur in the highest grade samples of the angus region and are associated with localized uplift regional rapid uplift events at 460 440 ma and 410 390 ma may also be recognized and correlated with structural and igneous activity and metamorphic age dates within the scottish highlands thermal models show the importance of localized and discontinuous uplift in determining both the timing of metamorphism and the shape of the p t paths they suggest that the major diachronous metamorphism and granite production in the scottish highlands is depth controlled rather than representing major lateral diachronism of thickening or heat sources localized uplift may exercise considerable control on mineral facies variation within orogenic belts the local uplift in angus introduces hot high pressure tarfside nappe rocks into higher level tay nappe rocks thus the uniform block uplift models frequently used in the interpretation of metamorphic and structural phenomena in orogenic belts are an oversimplification of the real events

discussion on metamorphism and cooling of the ne dalradian and u pb and rb sr geochronology of magmatism and metamorphism in the dalradian of connemara western ireland authors reply

mixing layers and coherent structures in vegetated aquatic flows 1 to date flow through submerged aquatic vegetation has largely been viewed as perturbed boundary layer flow with vegetative drag treated as an extension of bed drag however recent studies of terrestrial canopies demonstrate that the flow structure within and just above an unconfined canopy more strongly resembles a mixing layer than a boundary layer this paper presents laboratory measurements obtained from a scaled seagrass model that demonstrate the applicability of the mixing layer analogy to aquatic systems specifically all vertical profiles of mean velocity contained an inflection point which makes the flow susceptible to kelvin helmholtz instability this instability leads to the generation of large coherent vortices within the mixing layer observed in the model at frequencies between 0 01 and 0 11 hz which dominate the vertical transport of momentum through the layer the downstream advection of these vortices is shown to cause the progressive coherent waving of aquatic vegetation known as the monami when the monami is present the turbulent vertical transport of momentum is enhanced with turbulent stresses penetrating an additional 30 of the plant height into the canopy

mean and turbulent velocity fields near rigid and flexible plants and the implications for deposition 1 the transport of fine sediment and organic matter plays an important role in the nutrient dynamics of shallow aquatic systems and the fate of these particles is closely linked to vegetation we describe the mean and turbulent flow near circular patches of synthetic vegetation and examine how the spatial distribution of flow is connected to the spatial distribution of suspended sediment deposition patches of rigid emergent and flexible submerged vegetation were considered with two different stem densities for the rigid emergent vegetation flow adjustment was primarily two dimensional with flow deflected in the horizontal plane horizontal shear layers produced a von karman vortex street flow through the patch shifted the vortex street downstream resulting in a region directly downstream of the patch in which both the mean and turbulent velocities were diminished net deposition was enhanced within this region in contrast for the flexible submerged vegetation flow adjustment was three dimensional with shear layers formed in the vertical and horizontal planes because of strong vertical circulation turbulent kinetic energy was elevated directly downstream of the patch consistent with this deposition was not enhanced at any point in the wake this comparison suggests that morphological feedbacks differ between submerged and emergent vegetation further enhanced deposition occurred only in regions where both turbulent and mean velocities were reduced relative to the open channel reduced deposition indicating enhanced resuspension occurred in regions of high turbulence kinetic energy regardless of local mean velocity these observations highlight the importance of turbulence in controlling deposition

very slow erosion rates and landscape preservation across the southwestern slope of the ladakh range india erosion rates are key to quantifying the timescales over which different topographic and geomorphic domains develop in mountain landscapes geomorphic and terrestrial cosmogenic nuclide tcn methods were used to determine erosion rates of the arid tectonically quiescent ladakh range northern india five different geomorphic domains are identified and erosion rates are determined for three of the domains using tcn 10be concentrations along the range divide between 5600 and 5700 m above sea level asl bedrock tors in the periglacial domain are eroding at 5 0 0 5 to 13 1 1 2 meters per million years m m y principally by frost shattering at lower elevation in the unglaciated domain erosion rates for tributary catchments vary between 0 8 0 1 and 2 0 0 3 m m y bedrock along interfluvial ridge crests between 3900 and 5100 m asl that separate these tributary catchments yield erosion rates 850 ky respectively these results highlight the persistence of very slow erosion in different geomorphic domains across the southwestern slope of the ladakh range which on the scale of the orogen records spatial changes in the locus of deformation and the development of an orogenic rain shadow north of the greater himalaya copyright 2014 john wiley sons ltd

thermal modeling of the sw ryukyu forearc taiwan implications for the seismogenic zone and the age of the subducting philippine sea plate huatung basin subduction mega thrust earthquakes in the sw ryukyu trench pose a seismic and tsunami hazard one of the objectives of this study is to estimate the downdip width of the seismogenic zone using numerical modeling to determine the temperature distribution along the plate interface however this approach depends strongly on the thermal parameters of the subducting slab while the philippine sea plate psp subducting beneath the central and eastern ryukyu arc is of eocene age 35 50 ma its age west of the gagua ridge is uncertain with proposed ages ranging from lower cretaceous 140 ma to upper eocene 35 ma since the sparse available heat flow data are insufficient to resolve this debate both end member hypotheses are tested as input parameters we examined two transects at 122 5 e and 123 5 e on either side of the n s trending 4 km high gagua ridge the shallow forearc geometry is obtained from wide angle seismic data the deep slab geometry was obtained from hypocenter distribution and tomography for an eocene slab age we obtain a 100 km and 110 km wide seismogenic zone between the 150 c and 350 c isotherms west and east of gagua ridge respectively this is in good agreement with the observed distribution of hypocenters using a cretaceous slab west of gagua ridge predicts a deep seismogenic zone 25 km 60 km depth inconsistent with observed thrust earthquakes tomographic images at 122 5 e and 123 5 e show a similar slab thickness of 70 80 km suggesting that the oceanic lithosphere has a young eocene thermal age the westernmost psp huatung basin may have been thermally rejuvenated by mantle convection near the slab corner the tectonic history since 6 ma transition from subduction to collision beneath taiwan may have also perturbed the thermal structure

tectonic significance of the highland boundary fault scotland none of the major roles assigned to the highland boundary fault such as a transcurrent fault with an orogen parallel sinistral displacement of several hundred kilometres or terrane boundary are confirmed the highland boundary fault can be traced ne sw across scotland for 240 km and defines the northern margin of the midland valley except for small outliers of late palaeozoic rocks on the nw side it separates the highland border ophiolite and dalradian rocks of neoproterozoic early ordovician age grampian terrane to the nw from late silurian early carboniferous rocks midland valley terrane to the se the present highland boundary fault is a steep nw dipping post early devonian reverse fault that probably terminates sw of bute stratigraphical and provenance links and palaeostress data limit post early devonian lateral displacement to

heat flow in the southwestern okinawa trough abstract lying to the southeast of the east china sea continental shelf the okinawa trough is believed to have been formed by crustal spreading behind the ryukyu island arc it has the highest mean heat flow among the pacific marginal basins the mean of 18 reliable measurements is3 34 2 75hfu the next highest mean heat flow for a marginal basin is2 53 1 60hfu for the fiji plateau the high mean value for the okinawa trough may be partially attributable to a sampling bias because most measurements were made in or near the well sedimented central rift or graben the reported values range from 0 36 to 10 49 hfu with low values probably resulting from hydrothermal circulation in an area of large relief the high heat flow suggests that the age of the okinawa trough may be as young as 2 ma such an estimate is in gross agreement with the inferred plio pleistocene age for the drifting in the okinawa trough the opening of the okinawa trough may continue onto taiwan but the relation between the opening of the trough and the occurrence of a nearby onshore geothermal resource area remains unsolved

episodic rapid uplift in the himalaya revealed by 40ar 39ar analysis of detrital k feldspar and muscovite bengal fan detrital k feldspar and muscovite samples from ocean drilling program leg 116 cores have been dated by the sup 40 ar sup 39 ar technique and have depositional ages from 0 to 18 ma from 4 to 13 individual k feldspars and 1 to 12 individual muscovites have been dated from 7 stratigraphic levels in every level at least one k feldspar and one muscovite yielded a minimum age identical within uncertainty to the age of deposition these results indicate that a significant portion of the material in the bengal fan is first cycle detritus derived from the himalaya therefore the substantial amount of sediment deposited in the distal fan in early to middle miocene time can be ascribed to a significant pulse of uplift and erosion in the collision zone at this time moreover these data indicate that throughout the neogene some part of the himalayan orogen was undergoing rapid erosion 1 to 10 mm yr this erosion must have been less than or equal to uplift relative to sea level the lack of granulite facies rocks in the eastern himalaya and tibetan plateau suggests to us that very rapid uplift must have been distributed in brief pulses over different parts of the mountain belt these datamore are incompatible with tectonic models in which the himalaya and tibetan plateau are uplifted either uniformly over the past 40 m y or mostly within the past 2 to 5 m y less

oceanic detachment faults focus very large volumes of black smoker fluids it is generally assumed that the seawater derived fluids that feed black smoker vent fields on the seafloor are discharged vertically from depths of 1 3 km we present new oxygen and strontium isotope data that show that fluids at black smoker temperatures of 300 400 c were focused along a low angle detachment fault at 15 45 n near the mid atlantic ridge isotopic alteration is the most extreme ever reported from oceanic rocks altered at similar temperatures indicating intensely focused fluid flow both in recharge and discharge parts of the hydrothermal system rare earth element mobility in the fault rocks demonstrates isotopic alteration by evolved hydrothermal fluids not conductively heated seawater the fault zone protolith was predominantly ultramafic but also included mafic rocks with metasomatic alteration to talc tremolite chlorite schists resulting mainly from chemical exchange between these lithologies during fluid flow fluids in equilibrium with this assemblage would be similar to ultramafic hosted black smoker fluids we present a new model in which hydrothermal circulation around detachment faults evolves from basalt hosted tag type to footwall ultramafic hosted rainbow type to low temperature ultramafic hosted lost city type key features of our model are the intrusion of gabbro bodies immediately below the detachment to provide a heat source for circulation and focusing of fluid flow into the detachment fault to allow venting away from the neovolcanic axis

formation of corrensite chlorite and chlorite mica stacks by replacement of detrital biotite in low grade pelitic rocks transmission and scanning electron microscopy were utilized to investigate the nature and mechanisms of alteration of abundant detrital biotite of volcanic origin and progressive modification of phyllosilicate aggregates in a prograde sequence of pelitic rocks illite crystallinity index 0 19 0 58 a28 from the gasp6 peninsula in quebec detrital biotite has been diagenetically altered to form corrensite and chlorite through two mechanisms 1 layer by layer replacement gave rise to interstratification of packets of layers and complex mixed layering via several kinds of layer transitions between biotite and chlorite corrensite or smectite 2 dissolution transport precipitation resulted in the formation of relatively coarse grained aggregates of randomly orientated corrensite rich flakes and fine grained corrensite intergrown with chlorite and illite in the matrix the data show that stacks consisting of alternating packets of trioctahedral and dioctahedral phyllosilicates originated during early diagenesis when lenticular fissures in strained altering biotite were filled by dioctahedral clays subsequent prograde evolution of dioctahedral clays occurred through deformation dissolution and crystallization and overgrowth illite evolved to muscovite with k in part provided through biotite alteration and corrensite chlorite to homogeneous chlorite the alteration of detrital biotite is closely related to the formation of titanite and magnetite in diagenetic rocks and pyrite calcite and anatase or rutile in the higher grade rocks the observations demonstrate that detrital biotite of volcanic origin may be the principal precursor of chlorite in chlorite rich metapelites originating in marginal basins the mineral parageneses suggest that the transitions from corrensite to chlorite and illite to muscovite may be a function of local chemistry and time