anisotropy in the indian ocean upper mantle from rayleigh and love waveform inversion a tomographic method is applied to love and rayleigh wave seismograms in order to address the problem of upper mantle elastic anisotropy in the indian ocean the first step in our approach is a waveform inversion for each path of the study a 1 d depth dependent model compatible with the waveforms of the fundamental mode and several higher modes of love and rayleigh waves is obtained then the models related to the different paths are inverted in order to retrieve 3 d velocity heterogeneities and anisotropy in this paper both the radial anisotropy and the azimuthal anisotropy of s waves are investigated in detail we find a significant radial anisotropy in the uppermost 300 km of the mantle with an overall amplitude smaller than what is found in global studies azimuthal s wave anisotropy is also present the directions of fast s velocities show rather simple patterns from 100 to 300 km depth and strong correlations with the direction of absolute plate motion apm are found in the uppermost 100 km the pattern of fast velocity directions is complex and does not correlate simply with plate motions from 100 to 200 km depth a correlation with apm is found in most oceanic regions the main lack of correlation is located in the vicinity of la reunion and mauritius islands in this region the anisotropy exhibits a complex pattern between 100 and 150 km possibly due to a disturbing effect of the hotspot at 200 km depth and deeper azimuthal anisotropy vanishes progressively beneath most of the oceanic regions no significant azimuthal anisotropy is found beyond 300 km depth the depth extent of both azimuthal and radial anisotropy the amplitude of radial anisotropy and the pattern of azimuthal anisotropy support the idea of a preferential orientation of olivine crystals in a low viscosity zone beneath the lithosphere this region would be located between 100 and 200 km in oceanic areas and possibly deeper between 200 and 300 km in continental areas not well resolved in this study

paleogene igneous underplating and subsidence anomalies in the rockall faeroe shetland area abstract crustal thickening caused by igneous underplating related to continental break up in the northeast atlantic has been invoked as the cause of the apparent lack of thermal subsidence seen in many mesozoic basins in the northwest european area in this study we examine a set of commercial wells in the rockall faeroe shetland region and calculate tectonic subsidence histories the rate of post rift basement subsidence during the cretaceous cenozoic determined from backstripping calculations always implies a higher degree of extension than the total basement subsidence assuming uniform extension furthermore the size of this discrepancy increases northward along the rockall trough and westwards in the northern north sea towards scotland we interpret this depth anomaly to reflect the effect of igneous underplating rethickening the crust following mesozoic and cenozoic extension late paleocene extension is identified in subsidence reconstructions throughout the west of britain area and is greatest in the rockall trough assuming that the underplating is gabbroic in composition the subsidence depth anomalies indicate a regional pattern of 2 3 km underplated between the erris trough and porcupine basin increasing to 4 5 km in the west lewis basin and hebrides shelf area in the faeroe shetland basin underplating is 1 0 1 5 km in the east and increases to 4 5 km in the west the data support the hypothesis of a major asthenospheric thermal anomaly centered under the faeroes in the paleocene dynamic uplift of the region is often difficult to identify but is locally seen to develop rapidly around 63 ma implying rapid emplacement of the mantle anomaly the intrusion of gabbroic bodies to the base of the crust in the late paleocene may have had an impact on the thermal maturation of petroleum source rocks in the region however thermal maturity indicators show smaller peak heatflows than predicted from simple thermal models suggesting that underplating was a gradual process achieved through the accretion of several small rapidly cooled bodies

shear in the lower crust during extension not so pure and simple abstract as lower crustal reflectivity appears to be related to extension it is sensible to consider the role of the lower crust in the extension of the lithosphere and in particular the way the lower crust deforms the occurrence of transparent zones wrapped around by reflective bands can be interpreted as low strain regions enclosed within anastomosing shear zones suggesting that deformation in the lower crust is by the relative movements of low strain lozenges along acoustically reflective high strain zones although this deformation can easily accommodate bulk pure shear it can also develop during bulk simple shear a component of subhorizontal simple shear within the lower crust is necessary if deformation in the mantle is localised into shear zones with the geometry and distribution imaged on birps profiles the lower crust may be the critical link in the lithosphere transferring deformation between the relatively strong upper crust and upper mantle and being strongly sheared in the process the form of this shearing is a direct consequence of the way the entire lithosphere extends

scotland s denudational history an integrated view of erosion and sedimentation at an uplifted passive margin denudational history is commonly reconstructed from basin sediments derived from the denuded source area and less frequently from the source area itself northern britain is an important source area for the surrounding sedimentary basins and this paper reviews the erosional history of scotland from devonian time to the present using evidence both from onshore geology and geomorphology and from patterns of sedimentation in surrounding basins cover rocks were extensive in scotland during late palaeozoic time but the persistence of sediment source areas within the upland areas of scotland makes it unlikely that basement highs were ever completely buried and depths of post devonian erosion of basement have been correspondingly modest 1 2 km during mesozoic time scotland experienced several major erosional cycles beginning with uplift reactivation of relief and stripping of cover rocks followed by progressive reduction of relief through etchplanation and culminating in extensive marine transgressions in late triassic late jurassic and late cretaceous time mid paleocene pulses of coarse sediment to the moray firth basin coincided with major uplift this uplift was associated with major differential tectonics within the highlands with warping and faulting along the margins of the minch and the inner moray firth basins tectonic activity was renewed on a lesser scale in late oligocene time and continued into late neogene time differential weathering and erosion under the warm to temperature humid climates of neogene time created the major elements of the preglacial relief with formation of valleys basins scarps and inselbergs features often closely adjusted to lithostructural controls and in some cases with precursors that can be traced back to devonian time the history that can be read from the onshore region complements the source area history interpreted from sedimentary basins derived from these areas

basement structure and its influence on the structural configuration of the northern north sea rift the northern north sea rift basin developed on a heterogeneous crust comprising structures inherited from the caledonian orogeny and devonian post orogenic extension integrating two dimensional regional seismic reflection data and information from basement wells we investigate the pre rift structural configuration in the northern north sea rift three seismic facies have been defined below the base rift surface 1 relatively low amplitude and low frequency reflections interpreted as pre caledonian metasediments caledonian nappes and or devonian clastic sediments 2 packages of high amplitude dipping reflections 500 ms thick interpreted as basement shear zones and 3 medium amplitude and high frequency reflections interpreted as less sheared crystalline basement of proterozoic and paleozoic caledonian origin some zones of seismic facies 2 can be linked to onshore devonian shear zones whereas others are restricted to the offshore rift area interpreted offshore shear zones dip s ese and wnw in contrast to w to nw dipping shear zones onshore w norway our results indicate that devonian strain and ductile deformation was distributed throughout the caledonian orogenic belt from central south norway to the shetland platform most of the devonian basins related to this extension are however removed by erosion during subsequent exhumation basement shear zones reactivated during the rifting and locally control the location and geometry of rift depocenters e g in the stord and east shetland basins pre rift structures with present day dips 15 were reactivated although some of the basement shear zones are displaced by rift faults regardless of their orientation relative to rift extension direction

multiple post caledonian exhumation episodes across nw scotland revealed by apatite fission track analysis abstract the post caledonian exhumation history of nw scotland is a controversial issue with some studies advocating largely continual emergence whereas others suggest dominantly early palaeogene plume driven exhumation apatite fission track analysis afta data for samples of precambrian basement and permian cretaceous sediments from onshore and offshore reveal multiple phases of post caledonian cooling triassic beginning 245 225 ma cretaceous 140 130 ma 110 90 ma and cenozoic 65 60 ma 40 25 ma 15 10 ma all of which are interpreted at least in part as recording exhumation basement and sedimentary cover rocks display similar thermal histories emphasizing the regional nature of these episodes and implying that sedimentary outliers represent the remnants of previously more extensive sequences significant thicknesses of jurassic rocks may once have covered nw scotland palaeocene palaeothermal effects are most pronounced in the vicinity of igneous centres probably reflecting combined effects of heating by elevated heat flow deeper burial and hydrothermal activity most of the region underwent kilometre scale neogene exhumation contrary to the common assumption of monotonic cooling and denudation histories integration of geological evidence with afta data defines an episodic thermal history involving repeated cycles of burial and exhumation we suggest that onshore passive margins and continental interiors may also best be characterized by similar histories

basement reactivation in the development of rift basins an example of reactivated caledonide structures in the west orkney basin the west orkney basin is a poorly studied palaeozoic and mesozoic rift basin that overlies a highly seismic reflective caledonian orogenic basement terrane this study presents a novel approach of using 2d seismic data to map single intra basement reflection packages and their relationship to overlying normal faults in the west orkney basin it is demonstrated that the rift architecture of the west orkney basin is more linear with a prominence of relay zones relative to previous interpretations and that rift structures form complex discordant and concordant relationships with pre rift caledonide basement structures restoration of basement fabrics to their pre extensional geometry indicates that the reactivation of basement structures as normal faults has occurred only where the pre extensional dip of basement structures is greater than 30 the relatively high density of relay zones mapped in the west orkney basin is proposed to be the result of the rift system forming a partially exploitative relationship with basement structure where extension has been accommodated between segments that have or have not reactivated basement fabrics

origin of the oslo graben in relation to the hercynian alleghenian orogeny and lithospheric rifting in the north atlantic abstract the contemporaneous extrusion of basalts in the oslo graben and intrusion of dolentes in northern britain and southern sweden at 295 ma calls for a common explanation two hypotheses are investigated 1 1 the graben and dykes resulted from extensional stresses associated with progressive lithosphere separation to the northwest of europe in the late carboniferous 2 2 the dykes and therefore the graben were related in some way to oblique collision of plates in the hercynian orogeny which was developing to the south the first hypothesis is mechanically more satisfying and makes a number of testable predictions it states that in late carboniferous times the lithosphere separated in two places along the orogenic grain to the west of britain and norway the two embryonic oceanic rifts were divided by thick cold lithosphere with an archaean crust to the north of scotland extensional stresses were focussed in this region fanning out in an arcuate zone to the south and east causing failure where the lithosphere was relatively thin in norway the strain was restricted to a zone previously thinned and weakened in the early palaeozoic i e the oslo graben in britain the caledonoid grain is oblique to the expected direction of extensional strain and a dyke swarm trending e w and about 300 km wide was formed the first hypothesis predicts that the dykes should die out to the west but continue along an arc and widen to the east northeast under the western north sea interpretation of aeromagnetic maps shows that the dykes behave as predicted by hypothesis one but that their trends and extent are at variance with the expectations of hypothesis two the apparent contradiction of rifting to the northwest of europe occurring at the same time as compression and oblique collision in the heart of europe is resolved in principle by two plate tectonic reconstructions of pangaea drawn for late carboniferous and early permian times the oslo graben was conceived in mid carboniferous times and born towards the end of the carboniferous as the thin lithosphere failed and allowed the extrusion of basalt magma it was then abandoned as the two collinear oceanic rifts to the west and northwest joined up but the graben carried on a life of its own as the mafic magma cushion caught in the density trap beneath the crust continued to differentiate and alkali magma pods rose buoyantly to freeze in the upper crust or extrude on the graben floor

the backus gilbert approach to the three dimensional structure in the upper mantle i lateral variation of surface wave phase velocity with its error and resolution summary the backus gilbert method is applied to obtain the phase velocity variations on a sphere from the measured phase velocity narrow peak kernels with radii of about 2000 km are obtained for almost everywhere on the sphere the phase velocity results are thus interpreted as an average within such regions the most trouble comes from the antipodal peak in the resolution kernel this is evaluated as contamination and is incorporated in the error estimation the total error which is a root mean square of contamination from the antipodal peak and statistical error estimated from the data covariance matrix is about 1 per cent of the phase velocity in the average earth model which is the preliminary reference earth model prem however there is about a factor of 2 variation of errors on the sphere maximum variations of phase velocity are about 3 4 per cent of the phase velocity in the average earth model and thus there still remain anomalies which exceed estimated errors the estimated errors correspond to one standard deviation under the assumptions of uncorrelated gaussian distribution for high confidence interval they show that statistically significant anomalies are scarce for the current data set generally love wave phase velocity maps show more resolved features than rayleigh wave maps and we can see in high confidence maps fast velocities in old oceans and old continents and slow velocities in tectonically active regions like the east pacific rise and various back arc regions

upper mantle heterogeneities in the indian ocean from waveform inversion a waveform inversion method is applied to 156 love and rayleigh wave seismograms to build up a 3 d model of the shear velocity in the upper mantle beneath the indian ocean the first step of the method consists in finding for each path a radially stratified upper mantle model compatible with the love and rayleigh wave seismograms relative to that path the fundamental mode and few higher modes are modelled in the waveform inversion in a second step the models related to the different paths are used in a tomographic inversion to map the 3 d upper mantle structure the 3 d velocity model has a lateral resolution of 1000 km no significant velocity anomalies are found below 300 km although the resolution is still good continental roots are confined to the upper 300 km and low velocities below mid oceanic ridges to the upper 250 km depending on their spreading rates at shallow depths 80 km we find a positive velocity anomaly beneath the west indian ridge near the rodriguez triple junction where gravimetric and bathymetric data indicate a reduced volcanic activity at greater depth around 200 km a low velocity signature is found beneath the hot spot of reunion mauritius islands and the central indian ridge it could reflect a real connection between the two structures

development of basins in the inner moray firth and the north sea by crustal extension and dextral displacement of the great glen fault abstract reflection seismic data provide evidence that mesozoic dextral movements along the great glen fault line have had an important influence on the development of the inner moray firth basin geophysical evidence further indicates that deep structure beneath the inner basin is dissimilar to that beneath the outer part and viking and central grabens in the north sea tectonic development of the inner basin can nevertheless be fitted into a pattern of north sea extensional movements which led to the formation of the graben system with which the major north sea hydrocarbon resources are associated

a numerical study of the effect of island terrain on tropical cyclones abstract a triply nested movable mesh model was used to study the behavior of tropical cyclones encountering island mountain ranges the integration domain consisted of a 37 wide and 45 long channel with an innermost mesh resolution of 1 6 the storms used for this study were embedded in easterly flows of 5 and 10 m s 1 initially realistic distributions of island topography at 1 6 resolution were inserted into the model domain for the region of the caribbean including the islands of cuba hispaniola and puerto rico the island of taiwan and the region of luzon in the northern philippines it was found that the islands affected the basic flow as well as the wind field directly associated with the storm system the combination of these effects caused changes in the track and translational speed of the storm in particular in the case of the 5 m s 1 easterly flow the storm accelerated and veered to the north well before reaching taiwan for the other island distributions the northward deflecti

origin of anomalous tertiary subsidence adjacent to north atlantic continental margins abstract at the beginning of the tertiary the northern north atlantic continental margins were characterized by voluminous igneous activity caused by continental rifting in the presence of the iceland hot spot many of the mesozoic sedimentary basins close to these margins have been permanently uplifted by igneous underplating and remain close to or above sea level at the present day however a significant number of other basins underwent rapid subsidence at the same time sometimes by as much as 3 km of sediment loaded subsidence in 15 20 ma several hypotheses attempting to explain the cause of this tertiary subsidence have been proposed the observational data are summarized here and then each hypothesis is considered in turn it is argued that many of these are implausible one possible alternative explanation links early tertiary subsidence uplift and magmatism if basaltic melts are trapped within the lithosphere it is possible to produce either uplift or subsidence depending on the density of the trapped melt at depths greater than 50 km melts will solidify rapidly in the garnet stability field to form primary eclogite which is dense enough to cause subsidence while satisfying the constraints of long wavelength airy isostasy unfortunately such an hypothesis is difficult to test the simplest explanation for tertiary subsidence is still a minor episode of lithospheric stretching although to date there is only limited evidence for sufficient tertiary normal faulting further work must be carried out before this simple and testable hypothesis can be confidently rejected

plate tectonics and the evolution of the british isles this paper is an essay on the rationalism and difficulties of the geological corollaries of plate tectonics with illustrations particularly from the geological history of the british isles there is special emphasis on the mechanics of continental lithosphere in extension when basins are formed and in convergence whereby continental lithosphere thinned in extension is shortened and restacked to form orogenic belts an upper lithosphere stress concentrating elastic lid suffers extremely complex inhomogeneous deformations above a simpler viscoelastic lower lithosphere whose deformation drives strain and displacement in the elastic lid the very nature of plate tectonics as relative motion among a multi plate mosaic of plates provides a rational semi quantitative framework for large scale geological complexity in space and time the caledonian and hercynian history of the british isles may be explained semi quantitatively in terms of plate boundary evolution but it is not possible to define unequivocal solutions the rationalism of plate tectonics is exhibited on a smaller more direct field scale by many of the complexities of ophiolite complexes such as ballantrae scotland that can be explained as the effects of the evolution of ridge ridge transforms and by diachronous deformation and sedimentation in subduction accretion prisms such as the southern uplands deformational and sedimentary patterns in nw europe from triassic times to the present day resulted from a complex interaction of extensional events related to diachronous atlantic opening and compressional events related to sequential alpine shortening phases those widespread events are typical of intracontinental plate boundary systems and create great difficulties for the geologist wishing to decipher relative plate motion from geological sequences because huge areas much larger than the british isles must be analysed and synthesized before much sense can be extracted further difficulties arise from the palinspastic and preservation problems of convergent boundaries orogenic shortening telescopes and partially subducts facies belts most orogenic belts were assembled as a collage of displaced and rotated terrain elements that were subsequently flattened elongated and straightened to an apparent but deceiving simplicity therefore while plate tectonics provides a rational geological framework against which for example british basin evolution can be tested and explained we cannot yet use the geological effects of plate boundary evolution to reconstruct relative plate motion quantitatively

lower tertiary sand development in viking graben north sea a regional study of lower tertiary sands in the viking graben northern north sea involving heavy mineral analysis geophysical log interpretation and palynologic dating has led to the successful differentiation of sand bodies with two distinct source areas being recognized these both lie on the orkney shetland platform one being the metamorphic basement in the north the other the preexisting sediments to the south probably of late jurassic age correlation of sand bodies by these means has led to a more complete breakdown of the depositional history of the area four phases of basinal subsidence and source area uplift have been recognized in this way and these are correlated with similar events in the central north sea the changes in subsidence pattern and source area uplift are related to events in the north atlantic prior to crustal separation between greenland and rockall although provenance is the fundamental control on heavy mineral distribution intrastratal solution also plays a major role solution is largely a function of burial depth and it is estimated that up to 50 of the assemblage may have been lost by this process over a large part of the area

the british caledonides interpretations from cenozoic analogues recent interpretations of cenozoic arc systems and collision belts facilitate reinterpretation of some aspects of british caledonide evolution end cambrian grampian collision of the passive dalradian foreland following southeastwards subduction beneath an island arc was accompanied by initiation of the highland boundary fault as a high angle south directed oblique slip thrust mid ordovician to early devonian northwestward oblique subduction of the iapetus ocean beneath the grampian orogen resulted in a continental margin magmatic arc back arc thrusting and development of an accretionary prism while southeastward subduction led to arc magmatism and back arc extension followed by initiation of the rheic ocean as a back arc marginal basin this syn subduction n s asymmetry of the iapetus ocean margins was analogous to the e w asymmetry of the modern pacific closure of iapetus was diachronous earlier in the northeast during end silurian collision the southern caledonides behaved as a passive foreland post collision foreland thrusting resulted in deposition and deformation of lower old red sandstone foreland basin deposits in wales and probably in northwest directed back thrusting in the region of the longford down accretionary prism subsequent dextral movement in the suture zone juxtaposed the southern caledonides with scotland and northern ireland beneath which northwestward subduction had continued into the early devonian

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

strike slip orogens an explanation for the hercynides the nature of oblique plate interactions is not yet well understood the oblique interaction of pacific and n american plates has resulted in large scale migration rotation and accretion of microplates intervening basins are ephemeral individually filled and deformed oblique motion results in zones of both compression and extension the latter may be sufficient to generate new oceanic crust and the former to obduct it both subduction and collision are restricted in time and space the resulting orogen is extraordinarily complex in detail the far more complicated hercynides are the result of dextral interaction between continental plates europe and africa the lateral variability of the orogen the major and long lived strike slip faults the bimodal volcanism and related ore deposits of the european trough the lizard ophiolite and its melanges the nw spanish ophiolites and the iberian pyrite belt are all explained using an oblique collision model in particular the generation deformation and obduction of ophiolites in oblique slip mobile zones is discussed

asthenospheric and lower lithospheric mantle contributions to continental extensional magmatism an example from the british tertiary province abstract the compositions of palaeocene basic magmas in skye and mull british tertiary igneous province btip shed light on the general problem of the relative importance of lithospheric and asthenospheric mantle as sources of continental magmatism during extension after the effects of crustal contamination in some magmas have been detected and the samples showing it eliminated from consideration the remainder show a significant diversity of trace element compositions basic lavas from skye and mull which lack crustal contamination have contents of compatible and moderately compatible elements e g ni cr y yb and also of moderately incompatible elements e g ti p zr hf sr mree which are within the range shown by the tholeiitic and mildly alkalic ocean island basalts oib as from iceland in contrast their contents of strongly and very strongly incompatible elements e g k rb ba u th nb ta lree are within the range shown by normal mid ocean ridge basalts these btip magmas are interpreted as second stage melts from mantle which had already lost a very small melt fraction the latter is thought to be represented by the strongly alkalic permo carboniferous dyke swarms associated with rifting at that time in nw scotland residual uppermost asthenosphere from the late palaeozoic magma genesis event is postulated to have become attached to the thickening lithosphere beneath nw scotland and thus to have remained coupled to it throughout the mesozoic until reactivated by palaeocene stretching occasional hawaiites in the top third of the skye lava pile remnant and also basalt dykes of the swarm cutting the granites of the central complex the last significant magmatic event at this centre have the elemental characteristics of typical north atlantic oib notably la ta 10 12 these compositions are thought to demonstrate input from asthenospheric source basic magmas throughout the lithospheric source dominated skye and mull magmatism it is suggested that all the basic magmas in this province are ultimately derived from asthenospheric sources but that the larger magma batches became contaminated during uprise by melting and assimilating the most fusible parts of overlying lithospheric mantle followed by lower crust in many cases smaller magma batches traverse the overlying lithosphere with little or no contamination perhaps the difference between the two lies in their flow behaviour laminar or turbulent during uprise

an observational and modeling analysis of the landfall of hurricane marty 2003 in baja california mexico abstract this paper documents the life cycle of tropical cyclone marty which developed in late september 2003 over the eastern pacific ocean and made landfall on the baja california peninsula observations and best track data indicate that the center of circulation moved across the southern peninsula and proceeded northward in the gulf of california a network of surface meteorological stations in the vicinity of the storm track detected strong winds satellite and radar imagery are used to analyze the structure of convective patterns and rain gauges recorded total precipitation a comparison of marty s features at landfall with respect to juliette 2001 indicates similar wind intensity but differences in forward motion and accumulated precipitation official real time forecasts issued by the u s national hurricane center prior to landfall are compared with the best track this resulted in a westward bias of positions with decreasing errors during subsequent forecast cycles numerical simulations f

oblique rifting and sequential faulting in the jurassic development of the northern north sea abstract jurassic structural development of the northern north sea has characteristics of oblique rifting this is interpreted to result from an obliquity between jurassic nw se to wnw ese directed extension and a preexisting n s trending zone of deformation related to permo triassic rifting and thinning of the crust the zone of maximum jurassic extension i e the viking and sogn grabens defines a narrow 25 40 km depression which trends diagonally nne ssw across a broader 130 150 km permo triassic basin the jurassic rift zone consists of a system of ene chelon rift segments with changing symmetry along strike bounded by faults oblique to the overall graben envelope sequential jurassic fault development as well as the interference between n s and ne sw striking faults are explained within the context of oblique rifting the early late bajocian oxfordian rift stage was dominated by reactivation of n s striking major faults whereas a number of coeval but smaller faults have a ne sw orientation ne sw striking faults show increasing importance during the jurassic stretching phase and major faults defining this orientation accommodated most of the kimmeridgian volgian extension faults striking nesw are observed to cross cut earlier n s trending faults they interfere with n s trending faults to define faultblocks with rhombohedral shape and they are associated with partial collapse of crestal areas of n s oriented fault blocks to form structural terraces

origin of ultramafic inclusions and megacrysts in a monchiquite dyke at streap inverness shire scotland abstract spinel lherzolite nodules composed of olivine fo 88 7 89 2 clinepyroxene 6 5 al 2 o 3 and al rich spinel and websterite nodules as well as megacrysts of clinopyroxene orthopyroxene and magnetite occur in a monchiquite at streap scotland petrographic data are given and microprobe analyses of coexisting phases in six spinel lherzolite nodules and one websterite nodule are reported along with analyses of both types of pyroxene megacrysts the spinel lherzolites show internal chemical homogeneity and their mineral chemistries suggest equilibrium conditions of 1100 1200 c and 14 23 kb the websterite nodules are on the basis of mineral chemistry and petrography considered to be crustal material the megacrysts constitute a separate group differing in composition from analogous phases in associated lherzolites and websterites as well as from monchiquite phenocryst phases and show systematic chemical variations corresponding to low pressure crystal fractionation processes

structural evolution of the witch ground graben the witch ground graben is a nw se trending extensional basin in the central part of the northern north sea lying between the moray firth and the viking graben ne sw extension occurred from triassic to cretaceous times extension took place on listric normal faults along the sw margin with downthrow to the ne giving rise to the asymmetry of the basin one of the principal phases of fault controlled subsidence occurred in the lower cretaceous from the valanginian to albian compilation of biostratigraphic data from this interval shows the development of an increasing number of stratigraphic breaks across the basin from sw to ne these breaks increasing in time span also in this direction this is a result of rotation of the subsiding fault block on the listric extensional faults the rotation is recorded in dipmeter data and occurred in several distinct episodes the triassic the volgian and the valanginian to aptian in reconstructing a cross section of the basin the interpreted fault curvature is constrained by the observed rotation of bedding surfaces and the amount of extension across the listric faults is constrained by the observed basin subsidence a depth to decollement for the faults of 4 km below sea level and an extension across the basin of 40 are estimated

reply to discussion on multiple post caledonian exhumation episodes across nw scotland revealed by apatite fission track analysis journal vol 167 675 694 we thank john hudson for his welcome comments on the nature and extent of the now eroded mesozoic sedimentary cover across parts of the present day scottish landmass that is indicated by the apatite fission track analysis afta results presented by holford et al 2010 as hudson points out low temperature thermochronological techniques including afta can provide unique insights into the post palaeozoic geological evolution of basement terranes that lack significant phanerozoic cover as witnessed by studies including green et al 2000 2001 belton et al 2004 weber et al 2005 as we demonstrated holford et al 2010 these techniques become even more powerful when applied to basement terranes where some sedimentary cover is preserved whereas low temperature thermochronological methods can provide information on only the cooling histories of basement rocks often reflecting exhumation the age of a sedimentary unit however thin it may be overlying eroded basement defines a time when the basement had been exhumed to the surface and was being buried thus integration of low temperature thermochronological data from basement rocks and overlying sedimentary units can define more complex thermal histories encompassing both heating and cooling reflecting episodic burial and exhumation application of this approach to basement and cover samples from a number of regions where phanerozoic sedimentary rocks are sparsely preserved including nw scotland has revealed that some continental regions that have long been thought to

regional observations during the landfall of tropical cyclone juliette 2001 in baja california mexico abstract this paper presents an observational analysis of tropical cyclone landfall over the eastern pacific ocean the tropical cyclone that developed during the 2001 season off the mexican coast was named juliette and made landfall in the baja california peninsula juliette approached land over the southwestern peninsula and the evolution of a localized region of cyclonic circulation occurred over the gulf of california the storm passage was associated with extensive property damage to the population in the southern peninsula with most of the damage caused by heavy rainfall and strong winds the intensity of the circulation associated with juliette indicates that this was a strong system in the record of landfall during the period 1992 2002 all available sources of observations are collected to investigate characteristics of the circulation motion and structure in situ observations including surface and upper air data are applied to document the evolution of storm flow while the center was locate

cenozoic uplift and subsidence in the north atlantic region geological evidence revisited abstract the topographic evolution of the passive margins of the north atlantic during the last 65 myr is the subject of extensive debate due to inherent limitations of the geological geomorphological and geophysical methods used for studies of uplift and subsidence we have compiled a database of sign time and amplitude where possible of topographic changes in the north atlantic region during the cenozoic 65 0 ma our compilation is based on published results from reflection seismic studies aft apatite fission track studies vr vitrinite reflectance trends maximum burial sediment supply studies mass balance calculations and extrapolation of seismic profiles to onshore geomorphological features the integration of about 200 published results reveal a clear pattern of topographic changes in the north atlantic region during the cenozoic 1 the first major phase of cenozoic regional uplift occurred in the late palaeocene early eocene ca 60 50 ma probably related to the break up of the north atlantic between europe and greenland as indicated by the northward propagation of uplift it was preceded by middle palaeocene uplift and over deepening of some basins of the north sea and the surrounding areas 2 a regional increase in subsidence in the offshore marginal areas of norway the northern north sea the northern british isles and west greenland took place in the eocene ca 57 35 ma 3 the oligocene and miocene 35 5 ma were characterized by regional tectonic quiescence with only localised uplift probably related to changes in plate dynamics 4 the second major phase of regional uplift that affected all marginal areas of the north atlantic occurred in the plio pleistocene 5 0 ma its amplitude was enhanced by erosion driven glacio isostatic compensation despite inconclusive evidence this phase is likely to be ongoing at present

evidence for extensional shear zones in the mantle offshore britain and their implications for the extension of the continental lithosphere deep seismic profiles recorded in the seas around the british isles have revealed bands of seismic reflections in the uppermost mantle on the basis of their appearance geophysical characteristics and association with major crustal faults these features are best interpreted as mantle shear zones furthermore in the north sea the mantle reflectors appear to follow an extensional trend and when interpreted as extensional shear zones help explain the regional stratigraphy of the overlying basin the crosscutting relationships between mantle reflections to the west of scotland and a major strike slip fault the great glen fault ggf suggest that the mantle structure postdates the ggf and hence is probably related to subsequent extension furthermore kinematic analysis of lithospheric deformation to the north of scotland is consistent with the structure observed on the seismic data if the flannan mantle reflection is an extensional shear zone reconstruction of the lithosphere prior to permian extension restores the flannan to the edge of the rockall trough a rift probably initiated in the carboniferous thus the flannan fault may have developed during carboniferous rifting it is concluded that most of the mantle reflections are some form of extensional shear zone in the mantle and the role of such structures during lithospheric extension is considered

a dynamical model of lithosphere extension and sedimentary basin formation convection in the upper mantle can give rise to normal stresses on the base of the continental lithosphere that may cause localized elevation of its surface and extensional deviatoric stresses this possibility is investigated assuming homogeneous biaxial strain in a continental lithosphere whose strength is governed by a combination of brittle failure and power law creep in the crust and by brittle power law or dorn law behavior in the mantle for a given geotherm and for rheologies based on current laboratory data the lithosphere responds to convection induced uplift in one of three ways depending primarily on the magnitude of the driving stresses these regimes are as follows 1 when the driving stress exceeds a threshold value the resulting strain rates are high enough greater than about 3 10 16 s 1 that the lithosphere strains almost isothermally its effective rheology is strain thinning and it undergoes accelerating extension the magnitude of the dynamic uplift required to produce the threshold value of the driving stress depends on the geotherm characterized here by the moho temperature and varies from about 1 km for a moho temperature of 700 c to around 3 km for a moho temperature of 550 c an uncertainty of at least 100 c is attached to these temperatures owing to the inaccuracies in extrapolating laboratory data to geological strain rates 2 at stress levels due to less than about half of the critical uplift extensional strain is negligible 3 at intermediate stress levels moderate uplift produces extension that is bounded by strength increases due to cooling of the ductile portion of the lithosphere during extension

the geometry of listric growth faults in the devonian basins of sunnfjord w norway thick devonian clastic sequences accumulated in fault bounded basins in w norway at the close of the caledonian orogeny and mark the beginning of a phase of crustal extension traditionally the eastern boundary fault to the devonian basins has been regarded as a thrust but cross sections based on the use of a branch line reveal it to be an extension fault there is clear omission of structural section across the boundary and by matching up metamorphic rocks in the hanging and foot walls of the boundary fault over 40 km of extensional dip slip can be measured at the n end of the fault the boundary fault is a flat lying listric fault with rollover anticlines in the hanging wall the fault also cuts up and down section along strike to form lateral ramps parallel to the movement direction these ramps appear as wrench faults in outcrop the ramp flat geometry of the fault may have been inherited from a precursor caledonian thrust fault which reversed its sense of slip in early middle devonian times to form the basins over 25 km of onlapping sediment accumulated in the largest basin during faulting in 14 ma with an average slip rate on the fault of 3 mm yr 1

fracture controls on valley persistence the cairngorm granite pluton scotland valleys are remarkably persistent features in many different tectonic settings but the reasons for this persistence are rarely explored here we examine the structural controls on valleys in the cairngorms mountains scotland part of the passive margin of the eastern north atlantic we consider valleys at three scales straths glens and headwater valleys the structural controls on valleys in and around the cairngorm granite pluton were examined on satellite and aerial photographs and by field survey topographic lineaments including valleys show no consistent orientation with joint sets or with sheets of microgranite and pegmatitic granite in this granite landscape jointing is not a first order control on valley development instead glens and headwater valleys align closely to quartz veins and linear alteration zones lazs lazs are zones of weakness in the granite pluton in which late stage hydrothermal alteration and hydro fracturing have greatly reduced rock mass strength and increased permeability lazs which can be kilometres long and 700 m deep are the dominant controls on the orientation of valleys in the cairngorms lazs formed in the roof zone of the granite intrusion although the cairngorm pluton was unroofed soon after emplacement the presence of old red sandstone ors outliers in the terrain to the north and east indicates that the lower relief of the sub ors basement surface has been lowered by 1 km of vertical erosion and for 400 myr this valley persistence is a combined product of regionally low rates of basement exhumation and of the existence of lazs in the cairngorm pluton and sub parallel caledonide fractures in the surrounding terrain with depths that exceed 1 km

structural style of buried ediacaran basins in saudi arabia on seismic reflection data abstract several isolated ediacaran basins subcrop phanerozoic strata in saudi arabia the structural styles of these subcropping basins are reviewed here based on interpretation of 2d and 3d seismic reflection data and comparison with arabian shield outcrops the basins are distinguished by layered seismic reflectors that are interpreted as sedimentary and volcanic strata due to limited well penetrations these packages cannot be directly dated but a relative chronology is established anchored by constraints from the arabian shield and regional studies most of the basins are bound by extensional faults and the basin fills show growth architectures and angular unconformities the bounding faults trend broadly north south and are interpreted to be late to post orogenic reactivations of oceanic terrane margins based on their structural characteristics in comparison with sub basins exposed on the shield the basin fills are correlated with the ediacaran jibalah group an equivalent of the omani nafun group these sub basins experienced inversion and exhumation prior to ongoing volcanism and unconformable deposition of late ediacaran to earliest cambrian kurayshah group sediments the kurayshah group is disconformably overlain by the widespread tayma group siliciclastics this disconformity correlates to the angudan unconformity in oman the kurayshah group includes a late ediacaran stratovolcano over 40 km in diameter in the eastern basins evaporitic structural styles indicate the presence of hormuz ara evaporites with local igneous intrusions that correlate at least in part to the kurayshah group the tayma group infills significant accommodation space variations and was affected by ongoing but declining differential subsidence and reactivation of the underlying basin bounding faults

deep structure of the scottish caledonides revealed by the moist reflection profile the moine and outer isles seismic traverse moist is a deep crustal reflection profile shot at sea off the north coast of scotland in 1981 spectacular reflections are observed from the moho and from thrust zones within the caledonian fold belt and foreland deep reflection profiling of the continental crust of the united states under the direction of the cocorp group has amply demonstrated the value of this technique when applied to suitable geological problems see for example refs 1 2 a similar group the british institutes reflection profiling syndicate birps has now been set up in the uk to organize such projects funds are provided by the natural environment research council nerc through the core group based at cambridge university however a preliminary experiment of which moist is the result was organized through the institute of geological sciences igs

a critical analysis of the structure and tectonic significance of rift oblique lineaments transfer zones in the mesozoic cenozoic succession of the faroe shetland basin ne atlantic margin abstract nw se trending rift oblique lineaments transfer zones9 occur along the length of the ne atlantic margin previous workers have suggested that these lineaments played an important role in providing conduits and or barriers to sedimentation during the cretaceous and palaeocene it has also been suggested that they were active as discrete basin wide strike slip faults this study uses a well calibrated 3d seismic survey of regional extent to critically assess the structural and stratigraphic evidence for three rift oblique lineaments in the uk sector of the faroe shetland basin victory clair and judd lineaments structures previously attributed to basin wide strike slip deformation can be more simply explained as igneous intrusions hydrothermal vent complexes gas chimneys and or faults that transfer extensional strain between en echelon rift segments there is little evidence to suggest that activity along discrete basin wide lineaments controlled palaeocene sedimentation within the faroe shetland basin rather sediment transport and deposition at this time are likely to have been controlled by along and across strike variations in the magnitude of thermal subsidence which in turn reflect the 3d nature of the underlying mesozoic rift architecture

northern scotland as an atlantic north sea divide president9s anniversary address 1984 from the end of the caledonian orogeny until the present northern scotland has acted as a structural high separating the north sea and atlantic basins or their forerunners the geological history of this positive massif is discussed in relation to that of the adjacent cratonic basins with the objective of determining the extent to which it adapted to regional tectonic developments and the manner in which its responses were modified by the pre existing basement structure from devonian to early palaeocene times the massif was generally low lying and its behaviour with respect to vertical movements was essentially neutral the land surface carved in the crystalline basement during the devonian period was preserved with relatively small modifications and little metamorphic detritus was supplied to the adjacent basins tectonic events of major importance in the basins such as the formation of the north sea and hebridean rift systems produced little change of conditions in the intervening massif it is inferred that the underlying keel of lithospheric mantle was protected from the effects of lithospheric stretching the uneventful history of the massif was interrupted by two phases of mafic igneous activity in late carboniferous and palaeocene times which record responses to regional plate motions the formation of the palaeocene igneous province was followed by a unique phase of uplift as a result of which the ancient sub devonian land surface was elevated and dissected and abundant crystalline detritus was supplied to the north sea the style of these events and the anomalous character of the continental margin off nw britain may have been determined by the refractory nature of the precambrian basement which inhibited stretching prior to sea floor spreading

3 dimensional structure of the indian ocean inferred from long period surface waves to improve the lateral resolution of the first global 3 dimensional models of seismic wave velocities regional studies have to be undertaken the dispersion of rayleigh waves along 86 paths across the indian ocean and surrounding regions is investigated in the period range 40 300 s the regionalization of group velocity according to the age of the sea floor shows an increase of velocity with age up to 150 s only similar to the results in the pacific ocean but here this relationship vanishes more quickly at long period therefore the correlation of the deep structure with surface tectonics seems to be shallower in the indian ocean than in the pacific ocean a tomographic method is applied to compute the geographical distributions of group velocity and azimuthal anisotropy and then the 3 d structure of s wave velocity horizontal wavelengths of 2000 km for velocity and 3000 km for azimuthal anisotropy distribution can be resolved except for the central part of the south east indian ridge which displays high velocities at all depths the inversion corroborates a good correlation between lithospheric structure down to 120 km and surface tectonics low velocities along the central and southeast indian ridges velocity increasing with the age of the sea floor high velocities under african indian and australian shields at greater depths the low velocity zones under the gulf of aden and the western part of the southeast indian ridges hold but the low velocity anomaly of the central indian ridge is offset eastward the low velocity anomalies suggest uprising material and complex plate boundary

rayleigh wave group velocity studies beneath the indian ocean the fundamental mode rayleigh wave generated by 16 earthquakes which occurred in the indian ocean and were recorded at 14 seismic stations of asia africa and australia are analyzed to estimate the rayleigh wave group velocity at periods of 10 to 60 sec by using the multiple filter analysis technique in addition to this rayleigh wave group velocity data available in the literature across different propagation paths of the indian ocean forming a dense distribution of seismic wave traverses have been considered for tomographic studies the group velocity distribution maps have been obtained at periods of 10 20 30 40 50 and 60 sec for the rayleigh wave the minimum value of the group velocity of 2 0 km sec is centered near the rodriguez triple junction 25 s 70 e at 10 sec and higher value 3 4 4 0 km sec at 20 sec and greater period as we move in the north northwest direction from the rodriguez triple junction the rayleigh wave group velocity isolines at 10 and 20 sec are also increasing in the northern direction in both the east and west sides of the ridge axis another minimum value of group velocity isolines 1 9 km sec is centered near 25 s 90 e at 10 sec and there is a gradual increase in the northern direction across the ninetyeast ridge these observations are in accordance with the increase in the age of the ocean floor and there is a gradual increase in the group velocity isolines this can be interpreted as due to the hot uprising convection current the material shows low shear wave velocity along the ridge axis and farther away from the ridge axis the material has become cooler with higher shear wave velocity the inversion of rayleigh wave group velocity across the ninetyeast ridge shows 120 km thick lvz low velocity zone of shear wave velocity of 4 38 4 78 km sec at a depth of 40 km from the water surface whereas other parts of the indian ocean show 44 km thick lvz with shear wave velocity of 4 12 4 17 km sec at a depth of 40 km from the water surface the high shear wave velocity below moho 4 19 4 75 km sec beneath the ninetyeast ridge indicates the presence of a cold and dense lithosphere beneath it

low temperature effects of the skye tertiary intrusions on mesozoic sediments in the sea of hebrides basin fission track analysis of samples from the sea of hebrides basin and surrounding regions demonstrates two very distinct age groups around 50 ma and 300 ma regardless of the stratigraphic age apatite fission track results from sediments within 8 km of the tertiary igneous complex on skye were totally reset by temperatures 110 c during intrusion of the centres but now yield ages younger than the granites zircon fission track results from the granites also demonstrate ages significantly younger than their hosts mean track lengths in apatites of 13 5 m and reduced apatite and zircon ages suggest that temperatures remained elevated throughout the 6 ma during which intrusive activity occurred but were hotter within the granite bodies than the surrounding sediments prior to intrusion of the complex temperatures in the basin sediments presently at outcrop were unlikely to have been higher than 50 c and beyond the effects of the tertiary intrusions age and track length distributions from northern skye the isle of lewis and the west coast of scotland illustrate that the area is unlikely to have been buried beneath more than 2 km of sediment at any one time since the end of the devonian north of the highland boundary fault tertiary uplift and erosion in scotland is considered to have been between 1 1 5 km this is consistent with a regional pattern of tertiary erosion identified across the british isles but considerably less than that recognised in northern england the geological society 1992

the moine thrust in the birps data set a second generation of birps profiles combine with older data to form a loose 10 by 40 km spacing grid over the offshore projection of the moine thrust these profiles show clear reflections that arguably represent fault plane reflections from the moine and related caledonian thrust structures in the location suggested by some earlier workers reflectors predominate at two structural levels 8 10 km 2 5 3 5 stwt and 13 16 km 4 0 5 5 stwt depths the deeper set appears to define an antiformal stack of thrusts or duplex with possible continuation to deeper levels by analogy with onshore sections and after subsequent extension is restored this deeper set correlates with the moine thrust onshore the shallower set aligns with normal faults that bound half grabens filled with devonian and permo triassic rocks this set correlates with the naver thrust after similar restoration normal faulting appears to have reactivated some of the thrusts increasing their reflectivity detailed stacking and interval velocity studies indicate that an increase of about 1 2km s 1 occurs across the reflections here associated with the two fault zones the overall reflection pattern is consistent with a complex stack of thrust sheets but lack of resolution prevents a complete structural analysis

terrane boundary reactivation barriers to lateral fault propagation and reactivated fabrics rifting across the median batholith zone great south basin new zealand prominent pre existing structural heterogeneities within the lithosphere may localise or partition deformation during tectonic events the ne trending great south basin offshore new zealand formed perpendicular to a series of underlying crustal terranes including the dominantly granitic median batholith zone which along with the boundaries between individual terranes exert a strong control on rift physiography and kinematics we find that the crustal to lithospheric scale southern terrane boundary of the median batholith zone is associated with a crustal scale shear zone that was reactivated during late cretaceous extension between zealandia and australia this reactivated terrane boundary is oriented at a high angle to the faults defining the great south basin we identify a large granitic laccolith along the southern margin of the median batholith expressed as sub horizontal packages of reflectivity and acoustically transparent areas on seismic reflection data the presence of this strong granitic body inhibits the lateral south westward propagation of ne trending faults which segment into a series of splays that rotate to align along the margin as they approach further we also identify two e w and ne sw oriented basement fabrics likely corresponding to prominent foliations which are exploited by small scale faults across the basin we show that different mechanisms of structural inheritance are able to operate simultaneously and somewhat independently within rift systems at different scales of observation the presence of structural heterogeneities across all scales need to be incorporated into our understanding of the structural evolution of complex rift systems

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

phase velocity distribution in the indian ocean and indonesian region inferred from geoscope records to improve the lateral resolution of 3 dimensional models of seismic wave velocities in the indian ocean and surrounding regions we analyzed direct earthquake to station rayleigh waves observed on the vertical long period components of four geoscope stations tam algeria pcr la reunion paf kerguelen and agr djibouti the phase velocities along 51 well distributed paths are obtained in the period range 40 350 s after corrections for the phase pattern at the source and for the instrumental response a tomographic method is then applied montagner 1986a to compute the geographical distribution of phase velocities without any a priori regionalization the location of velocity anomalies is quite stable and well resolved the phase velocity distributions are compared with global results from nakanishi and anderson 1984b woodhouse and dziewonski 1984 tanimoto 1985 nataf et al 1986 and with regional studies using group velocities for the same region montagner 1986a b c

reactivation of intrabasement structures during rifting a case study from offshore southern norway abstract pre existing structures within crystalline basement may exert a significant influence over the evolution of rifts however the exact manner in which these structures reactivate and thus their degree of influence over the overlying rift is poorly understood using borehole constrained 2d and 3d seismic reflection data from offshore southern norway we identify and constrain the three dimensional geometry of a series of enigmatic intrabasement reflections through 1d waveform modelling and 3d mapping of these reflection packages we correlate them to the onshore caledonian thrust belt and devonian shear zones based on the seismic stratigraphic architecture of the post basement succession we identify several phases of reactivation of the intrabasement structures associated with multiple tectonic events reactivation preferentially occurs along relatively thick c 1 km relatively steeply dipping c 30 structures with three main styles of interactions observed between them and overlying faults i faults exploiting intrabasement weaknesses represented by intra shear zone mylonites ii faults that initiate within the hangingwall of the shear zones inheriting their orientation and merging with said structure at depth or iii faults that initiate independently from and cross cut intrabasement structures we demonstrate that large scale discrete shear zones act as a long lived structural template for fault initiation during multiple phases of rifting

the geometrical evolution of normal fault systems abstract the purpose of this paper is to examine the kinematic behaviour of normal fault systems and see what general conditions govern their geometrical evolution we pay particular attention to seismological and surface data from regions of present day active normal faulting as the instantaneous three dimensional geometry at the time of fault movement is better known in active regions than in areas where the faults are now static most normal faults are concave upward or listric this shape can be produced by geometric constraints either because the faults reactivate curved thrusts or because they must be curved to accommodate rotations another effect which will produce curved faults is the variation of rheology with depth brittle failure at shallow depths produces less fault rotation than does distributed creep in the lower part of the crust an important geometric feature of normal faulting is the uplift of the footwall the amount of such uplift is related not only to the elastic properties of the lithosphere but also to the throw and dip of the fault a striking feature of active normal faults is that they occur in groups in which all the faults dip in the same direction this behaviour arises because the faults cannot intersect if they do one must cease to be active the rotation which such fault systems produce reduces the dip of the faults until a new steeply dipping fault is formed once a new fault cuts pre existing faults the earlier faults become locked and a new set of faults must propagate rapidly across the whole region involved many of these geometric constraints also apply to thrust faulting

the role of structural inheritance in the development of high displacement crustal faults in the necking domain of rifted margins the klakk fault complex froya high offshore mid norway abstract the role of inherited structures during the development of normal faults in continental rifts and proximal domains of passive margins have been extensively studied few studies however have a focus on deciphering the role of inheritance in the development of high displacement 10 km low angle 25 km is present during rifting

displacement of the moho by the outer isles thrust shown by seismic modelling deep seismic data fig 1 from the caledonides off the north west coast of scotland collected 1981 82 by the british institutions reflection profiling syndicate birps show evidence that caledonian thrusts have been reactivated as mesozoic normal faults1 2 the best example is the outer isles oi thrust which is mapped on land as a compressional fault and is revealed by these data to be overlain offshore by a thick wedge shaped mesozoic rift basin1 known as the north lewis nl basin here we have used synthetic seismic sections to identify distortions of the oi thrust reflection due to the nl basin models which compensate for the effects of this distortion show that the oi thrust has a steeper angle of dip than has been predicted previously assuming no distortion causing the oi thrust to project into a 2 3 km offset of the moho and hence to penetrate the entire crust our data suggesting that shear strains affecting the lower crust may be localized in character have adverse implications for rheological models which predict to the contrary that the lower crust is a region where strain is distributed

geological constraints structural evolution and deep geology of the northwest scottish caledonides the front of the caledonian orogenic belt in nw scotland is marked by a zone of foreland thrusting which contains imbricates of lewisian basement proterozoic cover and cambrian shelf sediments faults within this moine thrust belt in most localities propagated in a foreland directed sequence therefore the earliest of these thrusts was the moine thrust which carried a basement assemblage of moine and lewisian rocks over the cambrian shelf the development of large duplex and imbricate structures in the footwall postadted movement on this thrust hence a restoration of these imbricates provides a minimum estimate of the eastern extent of the cambrian shelf no synsedimentary or prethrust extensional features are recognised within the cambrian succession which displays a remarkable stratigraphic and thickness consistency this implies a corresponding consistency in crustal structure beneath these cover rocks immediately prior to caledonian thrusting a balanced cross section constructed across the northern part of the moine thrust belt has given a restored width for the cambrian shelf of 54 km geophysical data suggest that the present foreland crustal thickness is 28 km if this is taken to be the crustal thickness beneath the cambrian shelf during caledonian thrusting a minimum cross sectional area of 1512 km of lewisian rocks must remain beneath the present outcrop of the moine thrust sheet this foreland basement wedge may have been imbricated subsequent to the development of the cambrian imbricates caledonian structures within the moine thrust sheet are interpreted as forming an imbricate stack with the moine thrust acting as a floor thrust the ductile imbricate thrusts possibly roofed into the naver slide late open folds which warp foliation slides and metamorphic isograds within the moine sheet may represent culminations in the foreland lewisian imbricates beneath the moine thrust these postulated culminations may have been sufficient to initiate gravity driven structures this may explain late movements on high level faults within the moine thrust belt

magma and sediment i emplacement mechanism of late carboniferous tholeiite sills in northern britain president s anniversary address 1981 like other great tholeiite sheets of the world the midland valley sill and whin sill were emplaced in thick accumulations of sediments which at the time of intrusion were not much older nor had been orogenically deformed however the carboniferous sediments of northern britain had been deposited under the influence of continuous differential subsidence so that they were already disposed in syn sedimentary basins and swells when intrusion began by drawing palinspastic contours of the sills relative to a late westphalian marine band approximating to the surface at the time of emplacement it is established that the dolerites mainly follow bedding planes dipping at angles of as much as 5 down to the bottoms of the basins isopachs of the sills indicate a further relationship for the intrusions are thickest at the bottoms of the basins these facts are not explained by any intrusion mechanism previously postulated though there seems to be broad agreement as to the processes which have given rise to thinning and en echelon lensing at leading edges as well as to step and stair transgression of sediment bedding it is proposed that emplacement must have been controlled in part by gravitational flow down dip from feeder dykes which extended to between 0 5 and 1 0 km below the contemporary surface thereafter hydrostatic equilibrium was attained first by accumulation at the bottom of the basins and then by further advance up dip under pressure of head the sheets are so similar in aspect to flood basalts that it must be assumed that the sediments offered only low frictional resistance to splitting and flow

crustal thinning and nature of extension in the northern north sea from deep seismic reflection profiling a regional network of deep seismic reflection profiles recorded in the northern north sea has been used to map mesozoic and cenozoic basin thickness and crustal thickness in the viking graben and adjacent platform areas depth to the reflection moho varies from about 20 km in parts of the viking graben to about 32 km beneath the shetlands and the norwegian margin the shallowing of the reflection moho beneath the viking graben implies crustal stretching factors for mesozoic extension greater than 2 in the center of the north sea basin the axis of crustal thinning is located directly beneath the viking graben the axis of the sedimentary basin steeply dipping basin bounding faults are imaged in the upper crust and several dipping reflectors are observed in the upper mantle but no continuous reflective feature extending from the sedimentary basin to beneath the moho is observed on any of the deep profiles thus these data do not support the existence of lithosphere penetrating low angle detachments zones of simple shear as the cause of extension in the northern north sea some of the mantle reflectors dip to the west and some to the east suggesting that simple shear if it occurs in the upper mantle is not of uniform sense rather these data suggest a complex depth dependent pattern of brittle extensional deformation in the upper crust pervasive ductile extension bulk pure shear in the lower crust which is decoupled from deformation in the mantle and extension accommodated by discrete dipping shear zones in the lithospheric mantle

birps deep seismic reflection studies of the british caledonides the western isles north channel winch traverse fig 1 an extension of the successful moist profile1 was recorded in 1982 at sea along the west coast of britain for birps british institutions reflection profiling syndicate by the geophysical company of norway geco the purpose of the winch traverse was to study crustal structure of the caledonian foreland to cross the caledonian orogen and to establish the three dimensional geometry of mantle reflectors originally seen on moist we describe here the data first emphasizing british caledonian structures and then discussing features of the deep crust of wider significance the data are of very good quality and contain clear moho and upper mantle reflections the lower crust is surprisingly reflective deeply penetrative thrusts are observed and there is firm evidence that several of the mesozoic basins round the shores of the united kingdom were formed by reactivation of older features

the thrust structures of southern assynt moine thrust zone the moine thrust zone of southern assynt forms part of the northwest margin of the caledonide belt and has aroused controversy concerning amounts and timing of thrust displacement and sequence of thrust development recent mapping shows it to have been a foreland propagating thrust sequence the uppermost ductile moine thrust formed first followed by sequences of imbricates a major thrust the ben more thrust and then several lower duplex zones this sequence is clear from new observations that many of the earlier thrusts were folded and or breached during the development of the underlying structures a displacement of over 54 km has been estimated for the zone as a whole an alkaline igneous complex including the large borrolan syenite was intruded during the development of the thrust zone and much of it was carried some 30 km to the west northwest onto the foreland late extensional structures in southern assynt are an integral part of the caledonide thrust sequence and probably developed from the collapse of the thrust wedge as it climbed from stronger basement rocks on to a weaker cover sequence on the foreland

upper palaeozoic basins of the british isles caledonide inheritance versus hercynian plate margin processes hypotheses to explain the origin and location of upper palaeozoic sedimentary basins are presented group a basins were those old red sandstone basins whose location and subsidence were controlled by caledonide features including active and remnant fore arc basins midland valley and major transcurrent movements orcadian basin newer granite plutonic magmas in the southern uplands subduction complex post dated subduction and resulted from post collision cratonization processes as yet little understood group b basins were those whose initial positions in space were controlled by palaeo plate factors in particular the location of granitoid plutons but whose subsidence was controlled by active hercynian neoplate processes some group a basins were regenerated by this process midland valley a new hypothesis is presented to account for the origin of a carboniferous rift to sag trend similar to that proven in modern continental margin basins such as the north sea the hypothesis is an adaptation of mckenzie9s lithospheric stretching model some of whose major features are well shown in the carboniferous history of the north and central british isles group b processes were controlled by ligurian bretonic plate consumption in the s brittany massif central vosges areas group c basins in the rheno hercynian zone also owe their location and origin to back arc rifting and continental crustal oceanization processes caused by liguro bretonic subduction

crust and upper mantle heterogeneities in the southwest pacific from surface wave phase velocity analysis abstract direct earthquake to station rayleigh and love wave data observed on high gain broadband records are analyzed in order to improve the lateral resolution of the uppermost mantle in the southwest pacific region we used data of nine permanent geoscope and iris stations located in the southern hemisphere and nine other stations as part of two temporary networks the first one installed in new caledonia and vanuatu hereafter named cavascope network by orstom and the eost from louis pasteur university in strasbourg france and the second one installed in the fiji tonga and niue islands hereafter named spase network by washington university in st louis usa in order to collect more significant details on the surficial structures we included the analysis of short period waves down to 8 s a multiple frequency filtering technique has been used to recover phase velocities of rayleigh and love waves for selected earthquakes with magnitude greater than 5 5 and with known centroid moment tensor cmt about 1100 well distributed seismograms have been processed in the period range 8 100 s and corrections for topography and water depth have been applied to the observed phase velocities the geographical distribution of phase velocity anomalies have then been computed using the tomographic method developed by montagner montagner j p 1986a regional three dimensional structures using long period surface waves ann geophys 4 b3 283 294 due to a poor knowledge of dense well distributed crustal thickness values and corresponding velocity models we did not perform or speculate on the construction of an s wave 3d velocity model therefore we limited this study to the interpretation of the phase velocity distribution the location of phase velocity anomalies are well determined and the deviations are discussed within the framework of the geological context and compared with other tomographic models at long periods from 40 s to 100 s our results agree well with most of previous studies the tomographic imaging shows a large contrast between low and high phase velocities along the solomon new hebrides and fiji tonga trenches the lowest phase velocity anomalies are distributed beneath northern and southern fiji basins and the lau basin corresponding to the volume situated just above the dipping slabs whereas the highest values are displayed beneath the pacific plate and the eastern part of indian plate downgoing under the north fiji basin at shorter periods our results show that the phase velocity distributions are well correlated with the large structural crustal domains the use of local temporary broadband stations in the central part of the studied area gives us the opportunity to observe surface waves showing well dispersed trains allowing extended velocity measurements down to 8 s although aliasing due to multipaths become important the continental regions eastern australia new guinea fiji islands and new zealand show low velocities which are likely due to thick continental crust whereas the tasmanian d entrecasteaux and the northern and southern fiji basins are characterized by higher velocities suggesting thinner oceanic crust additional analysis including the anisotropic case and s wave velocity inversion with depth is in progress

heterogeneous stretching simple shear and basin development abstract the models of basin development which involve either homogeneous stretching of the whole lithosphere or displacement on a lithospheric scale shear zone are but two end members of a range of possible extensional models the homogeneous extension model thins the lower lithosphere beneath the thinned upper crust and superimposes a thermal subsidence basin on the earlier fault bounded basin the shear zone model offsets the zone of lower lithospheric stretching and thermal subsidence it is more likely that the zones of upper and lower lithospheric stretching will be heterogeneous and patchy but will often overlap in plan view this will produce localised uplift and subsequent thermal subsidence within the faulted basin and may explain many of the anomalies between the various stretching estimates made using different structural stratigraphic and geophysical techniques the model which combines heterogeneous lithospheric stretching and associated simple shear may explain 1 variations in dip of the major detachment zones in the large basins 2 variations in types of strain on or beneath the detachment zones 3 regional uplift of part of a basin to erode the earlier fault blocks and 4 the development of volcanism in basins with only low values of upper crustal extension the zone of stretched lower crust and lithospheric mantle may lie beneath the centre of the zone of upper crustal stretching or to one side it may be linked to the upper crustal zone by faults which dip consistently in one direction or by extensional systems which change their dominant dip direction with depth pulling out the mid crust as one or more wedges possible examples are discussed from the basin and range province and northwest european continental shelf

the influence of structural inheritance and multiphase extension on rift development the northern north sea the northern north sea rift evolved through multiple rift phases within a highly heterogeneous crystalline basement the geometry and evolution of syn rift depocentres during this multiphase evolution and the mechanisms and extent to which they were influenced by pre existing structural heterogeneities remain elusive particularly at the regional scale using an extensive database of borehole constrained 2d seismic reflection data we examine how the physiography of the northern north sea rift evolved throughout late permian early triassic rp1 and late jurassic early cretaceous rp2 rift phases and assess the influence of basement structures related to the caledonian orogeny and subsequent devonian extension during rp1 the location of major depocentres the stord and east shetland basins was controlled by favorably oriented devonian shear zones rp2 shows a diminished influence from structural heterogeneities activity localises along the viking sogn graben system and the east shetland basin with negligible activity in the stord basin and horda platform the utsira high and the devonian lomre shear zone form the eastern barrier to rift activity during rp2 towards the end of rp2 rift activity migrated northwards as extension related to opening of the proto north atlantic becomes the dominant regional stress as rift activity in the northern north sea decreases through documenting the evolving syn rift depocentres of the northern north sea rift we show how structural heterogeneities and prior rift phases influence regional rift physiography and kinematics controlling the segmentation of depocentres as well as the locations styles and magnitude of fault activity and reactivation during subsequent events

three dimensional structure of the upper mantle beneath the atlantic ocean inferred from long period rayleigh waves 1 group and phase velocity distributions group and phase velocity distributions of rayleigh wave fundamental modes are determined in the atlantic ocean using a method of regionalization without a priori constraints for a period range from 50 to 200 s eighty six direct source station paths are studied and 38 out of the best data from weidner s 1974 phase velocities are added to our data set for periods lower than 100 s the importance of shallow layer corrections is described in detail the general features of the distributions agree with global models and smaller scale heterogeneities are revealed a spatial resolution of 1500 km is needed to detect fine lateral heterogeneities in the atlantic the small lateral extent of young oceanic regions and strong lateral velocity gradients do not allow to quantify velocity versus age relationships using our data set on the other hand the regionalization without a priori constraints of phase velocities confirms the presence of a high velocity anomaly beneath the central part of the atlantic for periods greater than 100 s

evidence from apatite fission track analysis for the post devonian burial and exhumation history of the northern highlands scotland abstract devonian and older rock samples from outcrops in the northern scottish highlands have undergone protracted cooling since they reached palaeotemperatures of 110 c or more in the late palaeozoic to early mesozoic the results not only suggest that the northern highlands region has experienced kilometre scale exhumation since the late palaeozoic but also that devonian and possibly permo carboniferous sedimentation was probably more extensive than current outcrop patterns would imply a permian outcrop sample from the minches basin reached a maximum palaeotemperature of 70 90 c prior to the onset of cooling in the early tertiary while data from devonian and older samples suggest an acceleration in the rate of cooling in the early tertiary the magnitude of early tertiary palaeotemperatures on the mainland adjacent to the inner moray firth imf indicate similar amounts of tertiary exhumation to those derived from compaction analyses for the imf however to the west the magnitude of tertiary cooling cannot be solely ascribed to exhumation and a contribution of heating due to hydrothermal effects and or elevated heat flow associated with the tertiary igneous complex may also need to be invoked

measurements of mantle wave velocities and inversion for lateral heterogeneities and anisotropy 3 inversion lateral heterogeneity in the earth s upper mantle is investigated by inverting dispersion curves of long period surface waves 100 330 s models for seven different tectonic regions are derived by inversion of regionalized great circle phase velocity measurements from our previous studies we also obtain a representation of upper mantle heterogeneities with no a priori regionalization from the inversion of the degree 6 spherical harmonic expansion of phase and group velocities the data are from the observation of about 200 paths for love waves and 250 paths for rayleigh waves for both the regionalized and the spherical harmonic inversions corrections are applied to take into account lateral variations in crustal thickness and other shallow parameters these corrections are found to be important especially at low spherical harmonic order the trench region and fast velocities down to 250 km under shields below 200 km under the oceans both s velocity and s anisotropy support a model of small scale convection in which cold blobs detach from the bottom of the lithosphere when its age is large enough the spherical harmonic models clearly demonstrate a posteriori the relation between surface tectonics and s velocity heterogeneities in the first 250 km all shields are fast most ridges are slow below 300 km a belt of fast mantle follows the pacific subduction zones however at greater depths large scale heterogeneities that seem to bear no relationship to surface tectonics are observed the most prominent feature at 450 km is a fast velocity region under the south atlantic ocean smaller scale heterogeneities that are not related to surface tectonics are also mapped at shallower depths an anomalously slow region centered in the south central pacific is possibly linked to intense hot spot activity a very fast region southeast of south america may be related to subduction of old pacific plate between 200 and 400 km a belt of sv sh anisotropy follows part of the ridge and subduction systems indicating vertical mantle flow in these regions the spherical harmonic results open new horizons for the understanding of convection in the mantle perspectives for the improvement of the models presented are discussed

geological inheritance and crystal dynamics of the northwest scottish continental shelf abstract deep seismic reflection profiles have been combined with conventional seismic surveys across the northwest scottish continental shelf to interpret basin development in the region post caledonian basins are built upon partially reactivated older structures which have strongly influenced their internal structure and stratigraphy we show that the minch basin along with several others developed in the hangingwall of the partially reactivated outer isles fault a planar fault dipping at about 30 ese that reaches nearly to the moho the internal structure of these hangingwall basins is compared with appropriate scaled analogue models to show that they have developed by passive hangingwall collapse above a footwall block that moved towards the wnw this geometry is incorporated into a lithospheric dynamic model with northwest extension towards the rockall trough from a fixed lithosphere beneath the scottish highlands this model requires non linear lithosphere extension which is accommodated by movements on faults and block rotation in the upper crust extension and thinning of the lower crust along a network of anastomosing ductile shears extensional movement of the flannan fault in the upper mantle and horizontal displacement along the moho beneath the outer hebrides this dynamic model has wider application for other extensional regions

a multiscale numerical study of hurricane andrew 1992 part i explicit simulation and verification abstract in this study the inner core structures of hurricane andrew 1992 are explicitly simulated using an improved version of the penn state ncar nonhydrostatic two way interactive movable triply nested grid mesoscale model mm5 a modified betts miller cumulus parameterization scheme and an explicit microphysics scheme were used simultaneously to simulate the evolution of the larger scale flows over the coarser mesh domains the intense storm itself is explicitly resolved over the finest mesh domain using a grid size of 6 km and an explicit microphysics package containing prognostic equations for cloud water ice rainwater snow and graupel the model is initialized with the national centers for environmental prediction analysis enhanced by a modified moisture field a model generated tropical storm like vortex was also incorporated a 72 h integration was made which covers the stages from the storm s initial deepening to a near category 5 hurricane intensity and the landfall over florida as

comments and reply on paleomagnetic evidence for a large 2 000 km sinistral offset along the great glen fault during carboniferous time

the thrust and shear zones of the moine thrust zone and the nw scottish caledonides the caledonian thrust belts of nw scotland exhibit many features typical of foreland fold and thrust belts the major structures propagated westwards towards the foreland the thin carapace of cambro ordovician sediments being accreted in imbricate and duplex zones beneath the major thrust sheets on a broad scale the rules of thrust geometry are obeyed but many local anomalies are found particularly in the assynt region in assynt several large fault bounded gravity spreading structures surge zones have been identified extensional faults have been traced into strike slip and then contractional faults there are zones of extensional and contractional imbricate faults and extensional and contractional ductile flow similar structures have been found along the length of the moine thrust belt suggesting that gravity spreading was an important mechanism during the later stages of movement within the main caledonian fold belt there are several major tectonic slides which are recognized by a local increase in intensity of deformation the majority are nw verging and were originally gently dipping in the highlands se of the great glen there are early major se verging recumbent folds associated with considerable crustal thickening reflected in high pressure 12kbar metamorphism many of the major slides may have formed by spreading away from this thickened crust the caledonian deformation and metamorphism occurred later in the moines and moine thrust zone than in the dalradian and grampian moines to the se of the great glen this may reflect different levels of deformation alternatively it may argue for a large strike slip displacement on the great glen fault juxtaposing crustal blocks which had experienced different ages of caledonian deformation and metamorphism the late movement on the moine thrust involved spreading from an area of thickened caledonian crust formed either by the stair step trajectory of the basal thrust to the moines and or by thickening due to intrusion of large masses of late caledonian granites

interaction of permo triassic and jurassic extensional fault blocks during the development of the northern north sea the main structural elements resulting from late permian early triassic extension have been resolved across the total width of the northern north sea the northern segment of the basin north of 61 n bounded to the west by the hutton fault and to the east by the norwegian mainland was occupied by four westerly tilted half grabens 25 35 km in width prior to jurassic extension the central segment of the basin 60 20 61 n exhibits a full graben beneath the jurassic horda platform flanked by half grabens tilted towards the basin margins the change in permo triassic fault block configuration defining structural domains is largely constrained by a basement discontinuity which runs diagonally ne sw across the basin maximum jurassic extension is represented by several centres of subsidence aligned nne ssw across a n s oriented and broader permo triassic basin jurassic extension was concentrated within the viking graben proper south of 60 n which in this area is represented by single westerly tilted en echelon half graben segments 20 25 km wide the area affected by jurassic extension becomes progressively wider to the north again governed by the basement discontinuity eventually encompassing the total width of the basin c 200 km north of 61 n the central segment of the northern north sea displays the greatest contrast in permo triassic and jurassic structural styles and basin geometry jurassic stretching and faulting was negligible to the east horda platform precisely the area which had been the site of maximum permo triassic stretching and fault activity it has generally been assumed that jurassic fault configuration along the eastern margin of the central segment of the viking graben to a large extent reflects the reactivation of major permo triassic faults this study demonstrates the interference of permo triassic and jurassic basin geometries in this area due to major faults of the two generations dipping in opposite directions as a consequence the e tilted oseberg fault block of jurassic origin and c 20km in width is underlain by a wider c 35 km and w tilted permo triassic fault block

deep structure of the foreland to the caledonian orogen nw scotland results of the birps winch profile the winch marine deep seismic reflection profile crosses the hebridean shelf the proterozoic foreland to the caledonian orogen west of scotland the data quality is very good the upper crust is largely devoid of coherent seismic reflections although this may in part be due to acquisition techniques being inappropriate for this problem in contrast the middle and lower crust 10 25 km depth exhibits good reflections the mid crust contains reflectors which may be relics of early palaeozoic caledonian or earlier grenvillian eastward dipping thrust zones which pass into an acoustically strongly layered lower crust the outer isles thrust is mapped from the surface to the mid crust and tied into its land outcrop on north lewis reactivation of this thrust offshore in a normal sense in mesozoic times caused the formation of the minch and north lewis basins the mono is defined by a strong band of reflections at about 27 km depth which correlates well with results from the hmse explosion seismic survey moho depth is apparently rather uniform in the area of the foreland crossed by winch winch and hmse results together suggest a mean crustal velocity for the hebridean shelf of 6 4 0 1 km s 1 the eastward dipping flannan thrust can be mapped into the upper mantle on three lines from about 15 to 45 km depth well into the upper mantle neither the flannan thrust nor the outer isles thrust appear to pass straight through the reflective lower crust suggesting that the lower crust is a region of high strain the outer hebrides is a positive block probably formed as an isostatic response to mesozoic normal faulting which reactivated the outer isles thrust

moist and the continuity of crustal reflector geometry along the caledonian appalachian orogen new aspects of the deep structure of the scottish caledonides are revealed by the moine and outer isles deep seismic reflection traverse moist the caledonian foreland is underlain by an easterly dipping strongly reflecting surface cutting through the moho and traceable to more than 45 km depth thrusts within the foreland basement and caledonian orogen have been reactivated as normal faults bounding half grabens filled with sediments of late palaeozoic to mesozoic age the moine thrust which carries rocks of the orogen over lewisian foreland dips at 20 25 to the e on moist and is either a the westernmost of a series of easterly dipping reflections thrusts which flatten or terminate at 17 20 km depth or b a thrust lying further e which structurally overlies these easterly dipping reflectors by comparison with easterly dipping reflections on cocorp lines in the northern and southern appalachians the latter interpretation is preferred implying that many of the easterly dipping reflections on moist correspond to off shelf metasedimentary rocks with slivers of basement stacked and imbricated against the lewisian basement edge regional seismic refraction and conductivity data from northern scotland suggest that regions of the caledonian orogen have lower mid crustal velocity gradients and higher conductivities than the foreland which might be explained by this interpretation of the easterly dipping reflections despite similarities in crustal reflector geometries there are important differences between the moist and cocorp lines including 1 a remarkably continuous relatively horizontal moho seen on moist data at about 25 km depth and 2 the sedimentary basins offshore from northern scotland which have formed by reactivation under crustal extension of the easterly dipping thrusts furthermore it is probable that the easterly dipping reflectors in these areas of the moist and cocorp lines were formed at different times in the early palaeozoic

janet watson an appreciation and bibliography with the passing of professor janet vida watson frs the earth sciences in the u k and throughout the world lost one of its most distinguished and well known personalities for while janet watson spent most of her academic career in london at imperial college after graduation with a first class general honours degree at reading university in 1943 she was known throughout the world not only for her exceptional gift of clear and persuasive exposition both at the lecture bench and the committee table but also as a major contributor to the advancement of the earth sciences her death on 29 march 1985 at the age of 61 brought to an untimely end a distinguished career which had seen many honours showered on her the geological society of london which had elevated her to the office of president in 1982 84 had previously awarded her jointly with her husband professor john sutton frs both the lyell fund 1954 and the bigsby medal 1965 they also honoured her with the lyell medal 1973 as they had her father professor d m s watson frs nearly 40 years previously the edinburgh geological society 9 awarded her the clough medal 1980 she was president of section c of the british association for the advancement of science 1972 elected a fellow of the royal society of london 1979 and a member of its council and vice president 1983 until her death to the various offices she held janet brought the directness the precision and the liveliness of mind she had shown in one of the very first offices she had held as an earth scientist that of a steward at the 18th international geological congress held in london at imperial college in 1948 tell john later to be her husband 1 2 and 3 with each part of the message clearly and precisely stated yet perhaps it was not in the professional societies congresses and committees where she received most recognition but in the student societies throughout the country they consistently put her at the top of their lists of speakers to be invited and she consistently responded by using her talent of clear precise and persuasive exposition to excite as well as instruct many a budding earth scientist it was scotland that provided janet with the outdoor laboratory that she loved the most the initial choice was that of her teacher mentor and co author of a number of books professor h h read frs who first set her to study one of his favourite topics the migmatites of sutherland an aspect of which was the subject of her first publication he then directed her and her contemporary as a research student john sutton to parts of the lewisian complex of nw scotland where there were abundant migmatitic and igneous rocks this together with the research being done by professor w s pitcher and others at imperial college on the granitic rocks of donegal was to test and apply the concepts of place and time in plutonism enunciated by professor read in his presidential addresses to the geological society of london in 1948 and 1949 the young research workers went to the rocks of nw scotland from which b n peach j horne c t clough and other members of a distinguished team from the geological survey had developed ideas that had made such a big impact on geological thinking at the turn of the century however despite such a daunting prospect both ph d theses were accepted in the summer of 1949 just in time for a wedding and a honeymoon in the channel islands a venue that accounts for a publication about the isle of sark that does not appear to be cognate to the i r main body of published work for the next three decades there flowed from their pens a succession of publications that had a profound impact on geological thinking and the direction of research particularly in basement complexes both in the uk and abroad many were under the authorship of j sutton and j watson but in 9 years as her husband progressively became more involved in administrative matters more of janet s publications were her own or with other authors including a succession of research students and officers of the british geological survey with whom she worked on a number of projects the initiation of the partnership both scientific and personal had really taken place in 1948 when after separate field studies at scourie loch laxford j w and torridon j s and joint studies in the former area with their supervisor they set off by bicycle on roads that seemed to consist largely of blocks of torridonian conglomerate to look at other parts of the lewisian complex particularly around gruinard bay they tested their conclusions that the complex contained the products of two separate orogenic episodes scourian and laxfordian and that chronological subdivision could be made using basic dykes as time markers

basin structure and tertiary magmatism on skye nw scotland the emplacement of igneous material into upper crustal rocks of sedimentary basins is likely to be strongly controlled by the geometry of the pre existing basin structures these controls are investigated using examples from the tertiary igneous complexes of skye part of the sea of hebrides basin of nw scotland the basin consists of an array of half graben related to se dipping normal faults these pre volcanic mesozoic structures are traced near the igneous complexes using geological relationships preserved unconformably beneath the widespread basaltic lava fields the unconformity represents a period of cretaceous uplift and denudation of the basin and its flanks entirely pre dating the tertiary volcanism of nw scotland this unconformity seals stratigraphically the major basin faults preserving field relationships that permit the tracing of these faults in the country rocks to the tertiary intrusions the major camasunary fault is separated from the raasay fault via a series of minor graben linked by a series of steep nw se trending faults that transfered mesozoic displacements between the principal fault strands a broad range of igneous material of various compositions was intruded into part of the mesozoic sea of hebrides basins and their flanks during palaeocene times different emplacement styles and different structural controls are found the major gabbroic centres do not appear to be controlled by upper crustal structures having been emplaced into the footwalls of major faults however minor synmagmatic displacements on the basin faults may have been sufficient to generate dilatational sites in these footwall positions thereby facilitating emplacement in contrast the granitic melts have been emplaced as sheets and domed into the sediments and overlying lava pile reactivating segments of the basin fault network doming occurred from an array of sills the stratigraphic levels of which can be reconstructed using structural relationships preserved in the roofs and walls of the intrusions the sill levels and their transgressive forms are strongly related to inferred mesozoic basin structures the major fold structures of tertiary age in southern skye are interpreted as accommodating granitic emplacement rather than crustal shortening the nw se mesozoic transfer fault trend appears to have strongly influenced the segmentation of the granite domes these interpretations are illustrated using field relationships mapped in the vicinity of the coire uaigneich granophyre it is concluded that although the higher parts of the basin faults were reactivated to facilitate the doming of granitic intrusions the deeper levels of the mesozoic faults show no evidence of substantial reactivation

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

sedimentological constraints on the late silurian history of the highland boundary fault scotland implications for midland valley basin development the relationship between movement on the highland boundary fault and deposition of the lower old red sandstone in the midland valley basin of scotland is controversial most models favour mid silurian to early devonian sinistral movement on the highland boundary fault and development of a transtensional midland valley basin to constrain highland boundary fault movement during the late silurian we examine the basal lower old red sandstone alluvial succession exposed adjacent to the highland boundary fault a lack of synsedimentary fault movement indicators coupled with an increase in stratal thickness across the fault indicates that the highland boundary fault was not active during lower old red sandstone sedimentation a transtensional basin model cannot be sustained

potassium and argon loss patterns in weathered micas implications for detrital mineral studies with particular reference to the triassic palaeogeography of the british isles abstract potassium argon ages are reported for 16 muscovite and 14 biotite samples separated from triassic sandstones of the manx furness carlisle solway firth and lough neagh arran basins disturbance of the k ar isotopic system in these minerals during weathering erosion transport and lithification is discussed and loss of potassium shown to be as important a parameter as argon loss published data from tropical weathering profiles are used to establish the pattern of loss for these two elements during the formation of clay minerals from biotite the data being displayed in a potassium argon loss diagram the loss curve so produced is then used to interpret our new biotite data and previously published age data for detrital biotite from the cheshire basin the limit of interdigitation of northerly and southerly derived materials in the irish sea basins is shown to lie north of the fylde district of lancashire age data from detrital muscovite are used to establish a potassum argon loss curve for muscovite the features of the two curves are markedly similar little effect on the apparent k ar age is observed until about 20 loss of potassium occurs at this point massive argon loss takes place with little loss of potassium due to either potassium stabilisation or structural expansion the suitability of micas as k ar chronometers may be a consequence of the correlated potassium argon loss rather than intrinsic high argon retentivity if both mica curves are applied to detrial micas of the namurian millstone grit series a source area of age of ca 900 ma is indicated for both muscovite and biotite indicating a probable pre cambrian age source area probably in scandinavia