middle to late holocene storminess in brittany nw france part i morphological impact and stratigraphical record our study aims to understand the recurring climatic conditions prevailing during the largest storms reaching nw france brittany these storms are responsible for the breaching of coastal barriers and major flooding of lowlands in a first part of our work we examine the morphological impact and stratigraphic record of storm events along western brittany rocky coasts with a special focus on the southern coast of the bay of audierne the most exposed coast of the region in a second paper middle to late holocene storminess in brittany nw france part ii we shall focus on the chronology of storm events and their climate forcing conditions drilling transects and stratigraphic analyses were first undertaken to constrain chronology strength and wind direction during the main holocene storm events new dates observations and a relative sea level rsl curve were then used to inform discussion of the necessary climatic and morphologic conditions leading to destructive storm events most recorded events appear to be linked with cooling episodes of the holocene and a rsl close to present some storms are clearly responsible for breaching and dune building or remobilisation we demonstrate that storm frequency and intensity appear to rise in a stepwise manner during the late holocene maximum efficiency is reached during the little ice age with clustered events probably lasting several days but major storms also occurred immediately prior to the medieval warm period we suggest that recent coastal dune building from c ad 1100 until now despite a sea level close to present and continuously rising may be a direct consequence of the restoration of beaches after periods of recurrent storminess this building activity often occurred during dry negativ

strain gradients in zones of ductile thrusting insights from the external hellenides abstract new finite strain data from a thrust sense shear zone which extends for 600 km along strike in the high pressure belt of the external hellenides greece were used to describe the variation of ductile strain with structural distance d from the basal thrust sampling was carried out along four traverses across the central and southeastern parts of the zone the strain ratio in xz sections r xz of 120 samples was obtained using the theta curve the mean object ellipse and the mean radial length methods all methods give very consistent results based on these results four strain profiles were constructed depicting a non linear increase of r xz values with proximity to the basal thrust these profiles in combination with published strain data from the northwestern parts of the zone enabled us to obtain an empirical logarithmic function describing the relationship between r xz and d this function includes only one varying parameter which represents the strain gradient in linear r xz ln d space the value of strain gradient is directly correlated with the strain level in the thrust zone and provides information for strain localization at its base the proposed function may also be used for quantifying the strain profiles of ductile to semi ductile thrust zones in other orogenic belts such as the alps the appalachians and himalaya

the limitations of three dimensional kinematic vorticity analysis abstract the kinematic vorticity number wk can be calculated for three dimensional as well as two dimensional geologic deformations for steady state deformations wk can be correlated to and analyzed in terms of finite strains the analysis shows that assumptions commonly made for two dimensional deformations are not applicable to three dimensional deformations a single wk describes an infinite number of three dimensional deformations further even knowledge of flow apophyses orientation instantaneous stretching axes orientation and or wk are not sufficient to describe deformation three dimensional deformations also require knowledge of the deformation type or boundary conditions of deformation e g transpression hence in addition to being difficult to estimate the value of knowing wk for three dimensional deformations is greatly reduced compared with plane strain the most useful methods of determining wk from naturally deformed rocks are presented

fabric transitions in the saxony granulite terrain abstract quartz fabric transitions reported from the saxony granulite terrain and from the nearby ore mountains are interesting because of the changes in the pattern types and the variation in the opening angles of the fabric skeletons a short summary is presented of salient features in research documented in the east german literature between 1961 and 1978 the changes in fabric skeleton with decreasing metamorphic grade are proposed as mainly consequent to the deactivation of prism c glide systems as temperature decreases fabrics indicative of the appearance of the c burgers vector might be diagnostic for deformation in regimes of comparatively high temperatures or low strainrates or for deformation under conditions such that there is a relatively high kinetically effective hydroxyl content in the quartz structure

strain path partitioning within thrust sheets microstructural and petrofabric evidence from the moine thrust zone at loch eriboll northwest scotland abstract quartz c axis fabrics and microstructures have been investigated within a suite of quartzites collected from the loch eriboll area of the moine thrust zone and are used to interpret the detailed processes involved in fabric evolution the intensity of quartz c axis fabrics is directly proportional to the calculated strain magnitude a correlation is also established between the pattern of c axis fabrics and the calculated strain symmetry two kinematic domains are recognized within one of the studied thrust sheets which outcrops immediately beneath the moine thrust within the upper and central levels of the thrust sheet coaxial deformation is indicated by conjugate mutually interfering shear bands globular low strain detrital quartz grains whose c axes are aligned sub parallel to the principal finite shortening direction z and quartz c axis fabrics which are symmetric both in terms of skeletal outline and intensity distribution with respect to mylonitic foliation and lineation non coaxial deformation is indicated within the more intensely deformed and recrystallized quartzites located near the base of the thrust sheet by single sets of shear bands and c axis fabrics which are asymmetric with respect to foliation and lineation tectonic models offering possible explanations for the presence of kinematic strain path domains within thrust sheets are considered

microstructural evolution of the serido belt ne brazil the effect of two tectonic events on development of c axis preferred orientation in quartz the polyphase evolution of the serido belt ne brazil includes d crust formation at 2 3 2 1 ga d 2 thrust tectonics at 1 9 ga and crustal reworking by d 3 strike slip shear zones at 600 ma microstructural investigations within mylonites associated with d 2 and d 3 events were used to constrain the tectono thermal evolution of the belt d 2 shear zones commenced at deeper crustal levels and high amphibolite facies conditions 600 650 degreesc through grain boundary migration subgrain rotation and operation of quartz q prism slip continued shearing and exhumation of the terrain forced the re equilibration of high t fabrics and the switching of slip systems from c prism to positive and negative a rhombs during d 3 enhancement of ductility by dissipation of heat that came from syn d 3 granites developed wide belts of amphibolite facies mylonites continued shearing uplift and cooling of the region induced d 3 shear zones to act in ductile brittle regimes marked by fracturing and development of thinner belts of greenschist facies mylonites during this event switching from a prism to a basal slip indicates a thermal path from 600 to 350 degreesc therefore microstructures and quartz c axis fabrics in polydeformed rocks from the serido belt preserve the record of two major events which includes contrasting deformation mechanisms and thermal paths c 2003 elsevier ltd all rights reserved

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

kinematic evolution of the ama drime detachment insights into orogen parallel extension and exhumation of the ama drime massif tibet nepal abstract the ama drime massif is a north south trending antiformal structure located on the southern margin of the tibetan plateau that is bound by the ama drime and nyonno ri detachments on the western and eastern sides respectively detailed kinematic and vorticity analyses were combined with deformation temperature estimates on rocks from the ama drime detachment to document spatial and temporal patterns of deformation deformation temperatures estimated from quartz and feldspar microstructures quartz c axis fabrics and two feldspar geothermometry of asymmetric strain induced myrmekite range between 400 and 650 c micro and macro kinematic indicators suggest west directed displacement dominated over this temperature range mean kinematic vorticity estimates record early pure shear dominated flow 49 66 pure shear overprinted by later simple shear 1 57 pure shear high strain 36 50 shortening and 57 99 down dip extension dominated flow during the later increments of ductile deformation exhumation of the massif was accommodated by at least 21 42 km of displacement on the ama drime detachment samples from the nyonno ri detachment were exhumed from similar depths we propose that exhumation on the nyonno ri detachment during initiation of orogen parallel extension 11 13 ma resulted in a west dipping structural weakness in the footwall that reactivated as the ama drime detachment

a geotechnical correction for post depositional sediment compression examples from the forth valley scotland fine grained sediments usually suffer post depositional compression compaction which reduces bed thickness and lowers the elevations of sample positions and marker horizons this reduction has been calculated for two general cases using geotechnical theory and a correction decompaction factor is presented that can be applied to many field situations its use is illustrated by two examples from the clay sediments of the claret formation of the forth valley in the first the correction is calculated for 14c samples from the bothkennar research site near grangemouth and the effect on the reconstruction of water depths is discussed in the second example corrections are obtained for published sea level index points from former shorelines in the forth valley using a method for a postiori estimation of geotechnical data general conclusions are drawn between the size of the correction and the sample position relative to the local depocentre some applications to palaeotidal modelling are also suggested 1998 john wiley sons ltd

temperature and strain rate dependent microfabric evolution in monomineralic mylonite evidence from in situ deformation of norcamphor norcamphor c7h10o was subjected to plane strain simple shear in a see through deformation rig at four different strain rate and temperature conditions two transient stages in the microfabric evolution to steady state are distinguished the grain scale mechanisms associated with the microstructural and textural evolution vary with the applied temperature strain rate and strain in high temperature low strain rate experiments computer integrated polarization microscopy reveals that the texture evolution is closely related to the crystallographic rotation paths and rotation rates of individual grains high c axis rotation rates at low to intermediate shear strains are related to the development of a symmetrical c axis cross girdle by the end of the first transient stage 1 5 to 2 during the second transient stage 1 5 to 6 the cross girdle yields to an oblique c axis single girdle as c axis rotation rates decrease and the relative activity of grain boundary migration recrystallization increases steady state 8 is characterized by a stable end orientation of the sample texture and the cyclic growth rotation and consumption of individual grains within the aggregate

deformation temperatures and flow vorticities near the base of the greater himalayan series sutlej valley and shimla klippe nw india abstract we report new deformation temperature and flow vorticity data from the base of the greater himalayan series ghs exposed in the sutlej valley and shimla klippe of nw india we focus on three groups of transects across the hanging wall of the main central thrust mct in order of relative foreland hinterland positions they are the shimla klippe western and eastern sutlej transects deformation temperatures indicated by quartz c axis fabric opening angles increase both from foreland to hinterland at a given structural distance above the mct and up structural section from the mct within individual transects deformation temperatures in the immediate hanging wall to the mct are estimated at 510 535 535 550 and 610 c on the shimla western sutlej and eastern sutlej transects respectively the steepest inferred field gradients in deformation temperatures are recorded adjacent to the mct and progressively decrease up structural section following a power law relationship comparison with temperature estimates based on multi mineral phase equilibria data suggests that penetrative shearing occurred at close to peak metamorphic conditions vorticity analyses indicate that shearing along the base of the ghs occurred under sub simple shear conditions wm values of 0 9 1 0 with a minor component of pure shear

geoarchaeological evidence of marshland destruction in the area of rungholt present day wadden sea around hallig sudfall north frisia germany by the grote mandrenke in 1362 ad abstract geophysical and geoarchaeological investigations were carried out in the wadden sea of north frisia schleswig holstein germany to elucidate major environmental changes that considerably altered the coastal landscape since medieval times between the 12 th and 14 th cent ad the present day tidal flats around the marsh island hallig sudfall belonged to the historical edomsharde district and its main settlement rungholt for north frisia it is well known that during medieval and early modern times extreme storm surges caused major land losses associated with a massive landward shift of the coastline today cultural traces like remains of dikes drainage ditches terps or even plough marks are still visible in the wadden sea and provide evidence of the once cultivated marshland based on a multi proxy analysis of sediment cores retrieved from the tidal flat zone around hallig sudfall and from the hallig itself we identified a late medieval paleosol associated with the formerly cultivated marshland most probably belonging to the edomsharde and local trade centre of rungholt around hallig sudfall remains of medieval marsh deposits were found partly eroded and covered by a coarse grained high energy deposit including abundant shell debris and artefacts based on sedimentological micropaleontological geochemical and geochronological data we conclude that these deposits are associated with the 1 st grote mandrenke or st marcellus flood an extreme storm surge event in 1362 ad our results for the first time provide geological evidence of this 1362 ad storm surge for the wadden sea of north frisia moreover marshland on hallig sudfall dating to the 17 th 18 th cent ad was found covered by a thick layer of storm surge sand and shell debris which seems to be associated with one of the major storm event that hit the german north sea coast in modern times e g the 2 nd grote mandrenke or burchardi flood in 1634 ad or the christmas flood in 1717 ad

mathematical modeling of autocompaction of a holocene transgressive valley fill deposit wolfe glade delaware six thousand years of sediment accumulation and autocompaction in a transgressive valley fill deposit are simulated numerically rates of accumulation of freshwater organic rich mud subtidal mud and organic rich mud of the modern salt marsh are specified by using existing sedimentologic paleontologic and geochronologic data processes of pore water explusion and autocompaction are determined from finite strain consolidation theory model parameters for subtidal mud facies are determined from laboratory consolidation tests model parameters for organic rich deposits are determined by sampling equivalent modern sedimentary environments and by model calibration model calibration involves 1 reproducing the present distribution of void ratios measured in a 7 6 m vibracore 2 correctly calculating the preserved thickness of lithologic units and 3 determining a history of elevation changes of the sediment surface that is consistent with the delaware sea level curve and the known sequence of paleoenvironments of wolfe glade delaware the results indicate that preserved horizons in the 10 m holocene section of wolfe glade have been lowered a maximum of 2 3 m the rate of lowering due to autocompaction alone has been one half to one third of the rate of sea level rise during most of the past 6000 yr numerical experiments suggest that organic rich freshwater wetland deposits are primarily responsible for the extensive autocompaction at wolfe glade our approach may be used to correct holocene coastal stratigraphic data for autocompaction but careful model calibration based in part on the stratigraphy will usually be required

strain and fabric analyses based on porphyroclast interaction abstract two dimensional computer models of the interaction of elliptical clasts in a variety of kinematic conditions are used to study how clast imbrication and shape fabric development relate to strain and strain history the models provide templates for a known clast density and clast ellipticity that correlate clast imbrication angle of collision and clast shape fabric to strain and kinematics of deformed rocks modeling also shows that the mode of clast interaction plays a significant role in the accumulation of imbricated clasts and the development of shape fabric upon collision between clasts the trains formed can remain fixed or rotate if they rotate imbricated clasts can become independent when they are no longer forced together by the flow based upon the mode of clast and train rotation using the march rotation of passive lines and the jeffery rotation of rigid particles as end members three models are defined in an attempt to simulate the conditions of clast interaction under varying conditions the march fixed train march rotating train and jeffery rotating train models simulate solid state intermediate and magmatic conditions respectively modeling shows that the two march models produce similar results but the jeffery model of train rotation always produces a lower proportion of imbricated clasts and a much weaker shape fabric application of the modeling to the study of a syntectonic granite in the sierra nevada suggests that deformation was dominated by simple shear some k feldspar imbrication and fabric development took place initially in the magmatic stage and culminated in the solid state to produce a large proportion of imbricated k feldspar porphyroclasts which define a strong shape fabric this type of analysis provides a rationale to determine syn vs post emplacement deformation in the granite

holocene relative mean sea level changes in the wadden sea area northern netherlands although the netherlands has a long tradition of sea level research no holocene relative sea level curve is available for the north of the netherlands previous studies hypothesised that the relative sea level reconstruction for the western netherlands is also valid for the northern part of the country however glacial isostatic adjustment gia models predict a lower and steeper relative sea level curve because of greater postglacial isostatic subsidence long term data of relative sea level change are important to inform gia models and understand postglacial vertical land motion related to the rebound of fennoscandia and neotectonic activity we compiled and evaluated a set of basal peat radiocarbon dates to reconstruct the holocene relative mean sea level rise in the dutch wadden sea area for the early holocene this reconstruction is lower than the western netherlands curve after 6400 cal a bp the curve for the wadden sea is statistically indistinguishable from that for the western netherlands a result that conflicts with gia model results it remains to be investigated whether the problem lies with the gia model predictions or with the quality of the available data additional basal peat radiocarbon dates from suitable sites should be collected to further solve this problem

strain and vorticity analysis using small scale faults and associated drag folds abstract small scale faults with associated drag folds in brittle ductile rocks can retain detailed information on the kinematics and amount of deformation the host rock experienced measured fault orientation drag angle and the ratio of the thickness of deflected layers at the fault l and further away t can be compared with and l t values that are calculated with a simple analytical model using graphs or a numerical best fit routine one can then determine the kinematic vorticity number and initial fault orientation that best fits the data the proposed method was successfully tested on both analogue experiments and numerical simulations with basil using this method a kinematic vorticity number of one dextral simple shear and a minimum finite strain of 2 5 3 8 was obtained for a population of antithetic faults with associated drag folds in a case study area at mas rabassers de dalt on cap de creus in the variscan of the easternmost pyrenees spain

calcite textures examples from nappes with strain path partitioning abstract strain path partitioning partitioning of deformation into components of pure and simple shear in two alpine nappes is qualitatively indicated by a variation in orientation of foliation microkinematic criteria quartz textures and a comparison with strain path partitioning in theoretical nappe models the degree of non coaxial deformation relative to the total deformation is quantified by using the asymmetry of textures in calcite tectonites the texture interpretation is based on both polycrystal plasticity models and experimental data calcite tectonites in the graz paleozoic thrust sheet austria and the morcles nappe switzerland were deformed in a strain path with both pure and simple shear components texture asymmetry supports the strain path derived from geological observations as an exception a high strain ultramylonite deformed nearly exclusively in pure shear it is suggested that this represents a softening instability since deformation in pure shear is energetically more favorable than in simple shear the incompatibilities caused by heterogeneous pure shear are accommodated by detachments and heterogeneous simple shear adjacent to the pure shear zone

quaternary geological mapping of the lowlands of the netherlands a 21st century perspective old borehole descriptions modern lithostratigraphical classification and geostatistics have been combined in recent geological mapping in the netherlands recent developments in geostatistics and the increased computing capacity of personal computers enable three dimensional geological mapping based on already available data the data originate from a mapping programme at the scale of 1 50 000 that was started in the 1950s by the national geological survey rijks geologische dienst although started on a lithostratigraphical basis the increased use of radiocarbon dates since the 1950s influenced the map legend the map units were largely defined by age boundaries that were supposed to coincide with transgressions and regressions more recent research revealed that not only sea level but also regional basin topography sediment supply and regional neo tectonics are important factors controlling coastal development the netherlands institute of applied geoscience tno national geological survey the successor of the rijks geologische dienst recently redefined the classification of holocene coastal and alluvial deposits in a purely lithostratigraphical way the old borehole descriptions contain purely lithological descriptions as well as interpretations that were derived from those descriptions the larger part of the originally defined map units represents boundaries that characterise a change in lithology by returning to the original lithological descriptions the borehole data and the geological maps are applicable in the new lithostratigraphical framework they are now used in modern three dimensional geological mapping modelling of the subsurface these models are very useful for applied geological research 2004 elsevier ltd and inqua all rights reserved

variations in the kinematics of deformation along the zagros inclined transpression zone iran implications for defining a curved inclined transpression zone abstract the combination of inclined collision and plate boundary shape can control the nature of deformation and the sense of shear along a transpression zone the present study investigated the effects of a boundary zone with curvilinear shape along a transpression zone on the kinematics of deformation the kinematics of the zagros transpression zone varies with the orientation of the zone boundary detailed structural and microstructural studies showed sinistral sense of shear on the southeastern part of the zagros inclined transpression zone fars arc but dextral sense of shear on the northwestern part of the zone it is inferred that the both senses of shear were developed coevally under a bulk general shear regional scale deformation along a curved inclined transpression miming the shape of the fras arc of the zagros and the reentrant of the bandar abbas syntaxis the zagros transpression zone formed by inclined continental collision between the afro arabian continent and iranian microcontinent

mid to late holocene relative sea level change in poole harbour southern england a foraminiferal transfer function for mean tide level mtl is used in combination with ams radiocarbon dated material to construct a record of relative sea level rsl change from poole harbour southern britain these new data based on multiple cores from duplicate sites indicate four phases of change during the last 5000 cal calendar yr i rising rsl between ca 4700 cal yr bp and ca 2400 cal yr bp ii stable to falling rsl from ca 2400 cal yr bp until ca 1200 cal yr bp iii a brief rise in rsl from ca 1200 cal yr bp to ca 900 cal yr bp followed by a period of stability iv a recent increase in the rate of rsl rise from ca 400 200 cal yr bp until the present day in addition they suggest that the region has experienced long term crustal subsidence at a rate of 0 5 mm c 14 yr 1 although this can account for the overall rise in mtl observed during the past 2500 yr it fails to explain the changes in the rate of rise during this period this implies that the phases of rsl change recorded in the marshes of poole harbour reflect tidal range variations or eustatic fluctuations in sea level copyright 2001 john wiley sons ltd

significance of transport parallel strain variations in part of the raft river shear zone raft river mountains utah usa this paper examines part of the raft river shear zone rrsz in northwestern utah that exhibits an extreme transport parallel increase in strain intensity coupled with a transition from flattening to constrictional strain detailed geologic mapping and finite strain quartz c axis fabric and kinematic vorticity analyses demonstrate local necking of the shear zone associated with an increase in transport parallel elongation accommodated by a stretching fault at the base of the shear zone the domain of intense deformation and necking of the shear zone is localized where the basal stretching fault cuts rheologically weak rocks this domain is characterized by strain in the constrictional field caused by transport perpendicular flow into the area of high transport parallel elongation where rocks cut by the stretching fault are rheologically strong the rrsz locally records flattening strain and lower strain intensities limiting the amount of stretching needed at the base of the shear zone in any one direction and or recording transport perpendicular flow into adjacent highly extended domains the rheology of rocks cut by the stretching fault directly controlled the amount and style of zone normal shortening and transport parallel elongation and these observations provide an example of deformation partitioning in a crustal scale structure driven by local rheological transitions

rheological control on the initial geometry of the raft river detachment fault and shear zone western united states the strain exhumation history and field orientation of a well exposed shear zone and detachment fault in the raft river mountains of northwestern utah a cordilleran metamorphic core complex have been studied to determine the kinematics of ductile shearing and initial orientations of the shear zone and detachment fault mapping and strain and kinematic analysis indicate that the top to the east raft river shear zone initially developed parallel to an unconformity separating archean rocks from overlying proterozoic quartzite and schist for at least 24 km in the shear direction experimental rock deformation data from lithologies similar to the archean and proterozoic rocks suggest the unconformity represented a significant rheological boundary at the deformation temperatures the base of the shear zone was localized along the boundary between relatively weak quartzite above and stronger monzogranite below an extensive thermochronological database is used to reconstruct the position of the basement unconformity in temperature lateral distance coordinates the initial average dip of the shear zone and basement unconformity is estimated between 7 and 30 assuming subhorizontal isotherms and geothermal gradients of 20 40 c km the east dip of the unconformity at the onset of miocene extension is interpreted to have resulted from late eocene unroofing and flexure beneath a top to the wnw extensional shear zone in the western raft river grouse creek and albion mountains the observations from the raft river shear zone suggest that the orientation of some midcrustal shear zones may not reflect the predicted orientation for ductile faults according to ductile failure criteria but rather the orientation of rheological boundaries along which deformation is localized furthermore detachment faults that are superimposed on mylonite during progressive displacement and footwall unroofing may use an inherited mechanical anisotropy from the mylonite and their orientations may not reflect the predicted orientation of shear fractures in isotropic rock the common parallelism between detachment faults and mylonitic foliation may indicate a mechanical and kinematic preference for localization of throughgoing brittle faults parallel to preexisting mylonitic foliation because of this preference studies restricted to detachment faults which lack footwall mylonite or restricted to structural levels between the breakaway and mylonitic front have more bearing on the question of the initial dip of normal sense shear fractures faults within the seismogenic crust

geometry of eclogite facies structural features implications for production and exhumation of ultrahigh pressure and high pressure rocks western gneiss region norway 1 well preserved eclogite facies structural features in metamorphosed gabbro and diorite gneiss in baltica crust formed at a minimum depth of 60 70 km during the scandian orogeny allow direct inferences to be made regarding the geometry of folds kinematics and original structural orientations related to production and exhumation of high pressure rocks folds associated with eclogite facies fabrics are isoclinal to tubular with axes parallel to the trend of a stretching lineation strain estimates and l s or l s fabrics indicate that these structures were formed in a constrictional strain field locally they are well preserved in eclogite facies mylonite zones at least 40 m thick that cut proterozoic gabbro and adjacent gneiss where steeply dipping they show a north side up shear sense across a younger northeast trending shallowly plunging amphibolite facies anticlinorium formed in a constrictional noncoaxial strain field where original structural facing direction can be inferred small circle rotation of the eclogite facies lineation about the anticline axis indicates that the relative motion vector of baltica with respect to overlying imbricated crust and laurentia was oriented 320 in a present day reference frame this result is identical to the orientation of the relative motion vector estimated from paleomagnetic plate reconstructions and consistent with late silurian to early devonian oblique sinistral convergence between baltica and laurentia results of this study indicate that coherent baltica crust at 60 70 km depth experienced subvertical and horizontal shortening while extending toward the foreland during tops southeast thrusting parallel to plate motion high pressure rocks were progressively imbricated and stacked along eclogite facies mylonite zones with the deforming zone separating coherent baltica crust from imbricated basement above the constrictional strains under eclogite facies conditions are interpreted to have resulted from stretching associated with sinking of the cool dense mantle lithosphere

driving mechanisms of coastal change peat compaction and the destruction of late holocene coastal wetlands abstract this paper examines the role of peat compaction as a driving mechanism behind the widespread inundation of a late holocene coastal wetland in southeast england uk detailed stratigraphic and dating evidence lithology grain size foraminifera pollen and radiocarbon dates from a sample site in romney marsh documents the gradual inundation of a coastal wetland after 1263 1085 cal yr bp c 700 850 ad and the establishment of a saltmarsh shortly thereafter there was a rapid increase in water depth that was associated with the deposition of nearly 4 m of laminated intertidal mudflat and tidal channel sediments prior to site reclamation from the sea by ad 1460 grain size data and statistical analysis of sand and mud laminae thicknesses suggest the laminated sediments accumulated rapidly c 0 2 m per year as heterolithic tidal rhythmites rapid compaction of the thick peat bed that underlies the study site provided the accommodation space for their deposition this process began with the gradual tidal inundation of the site but accelerated following the widening of a breach in a coastal barrier in the 13th century compaction lowered the peat surface by at least 3 m and was associated with widespread landscape change the study demonstrates the powerful influence that compaction had on the evolution of the late holocene landscape at this site and we believe at many other coastal lowlands in northwest europe this process is likely to have been a key driving mechanism behind rapid late holocene coastal change far exceeding the longer term effects of either eustatic change or crustal uplift subsidence

geoarchaeological records in temperate european river valleys quantifying the resource assessing its potential and managing its future throughout the quaternary episodes of glaciation and associated low sea level have resulted in the connection of the terrestrial landmasses of britain and mainland europe the river systems that established themselves across these newly emergent land surfaces of the coastal plain would have created important migration corridors for both animals and humans a point corroborated by the affinity of palaeolithic remains across britain and europe technological developments within the last decade have allowed these now submerged valley floors and adjacent terrestrial landscapes associated with the last cold stage and early and middle parts of the current holocene interglacial to be explored and their archaeological legacies unravelled providing geoarchaeologists with an opportunity to contribute to major cultural debates however in order to maximize knowledge it is essential that geoarchaeologists working within river valleys across both britain and the european continent are addressing similar research questions by collecting data using comparable methodologies this paper reviews the approach taken in different regions and provides a baseline assessment to allow the development of a coherent european wide framework for alluvial geoarchaeology and geoprospection particularly with respect to the holocene record

kinematic vorticity and strain rate patterns associated with ductile extrusion in the chelmos shear zone external hellenides greece abstract kinematic vorticity strain rate finite strain and structural data have been used to describe the heterogeneous nature of ductile deformation in an extruding crustal scale shear zone the chelmos shear zone csz of the external hellenides the csz has a curved shape which is marked by a frontal flat and a steep zone the spatial variation in the kinematic vorticity number is strongly correlated with the geometry and the structural depth of the shear zone the pure shear component of deformation decreases from back to front and from top to bottom the ductile thinning normal to the shear zone s boundaries is higher in the steep zone and decreases westwards quartz grain size and strain rate in the csz is distributed into two approximately homogeneous domains the higher strain rate is recorded in the steep zone and the base of the frontal flat zone with lower rates in the upper parts of the frontal flat zone based on mesoscopic structural data and the spatial distribution of the shear strain rate the existence of a west dipping back flow zone in the boarder zone between these two domains is inferred the overall pattern of deformation in the csz implies that tectonic extrusion from the steep zone occurred at the final stages of ductile deformation and was associated with the formation of the backflow zone in the front of the shear zone ductile deformation of rocks probably started close to simple shear on a planar low angle shear zone progressively became penetrative and more general shear occurred as the csz steepened up this progressive increase in pure shearing may have occurred in a heterogeneous manner and was higher close to both the eastern margin of the steep zone and the top of the frontal flat zone solid state extrusion in the csz was also associated with a heterogeneous and progressive increase in strain rate

the high resolution holocene sea level curve for northwest germany global signals local effects or data artefacts a few years ago a new relative sea level curve for northwest germany was constructed for the entire german north sea coast it is characterised by several suspected sea level fluctuations to test this curve for local effects it was broken down into five relative sea level curves representative for five coastal sections the relative sea level curves were corrected for tidal effects and also a rough first correction for compaction was applied the five curves all differ from the original curve and from each other most of the suspected sea level fluctuations in the original curve cannot be supported and are discussed as data artefacts or local effects around ad 800 1000 all curves show stagnation or drop of sea level thus this signal is discussed as of over regional stratigraphic meaning this study is a first step 1 to show that several curves are needed to demonstrate the holocene sea level history of such a big area as the entire german north sea coast and 2 to establish reliable relative sea level curves for the german north sea coast further research is necessary to apply detailed corrections especially with respect to compaction prone data and to improve the individual curves

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

ductile extrusion of the higher himalayan crystalline in bhutan evidence from quartz microfabrics quartz textures measured from deformed quartz tectonites within the lesser himalaya and higher himalaya crystalline of bhutan show similar patterns orientation and distribution of the quartz crystallographic axes were used to confirm the regional shear sense the asymmetry of c axis and a axis patterns consistently indicates top to the south shearing the obliquity of the texture and the inferred finite strain plane strain to moderately constrictional suggest the strain regime had a combination of rotational and irrotational strain path in most of the samples from the bhutan himalaya the inferred deformation mechanisms suggest moderate to high temperature conditions of deformation that produced the observed crystallographic preferred orientation much higher temperature of deformation is indicated in the quartz veins from a leucogranite the observed ductile deformation is pervasively developed in the rocks throughout the investigated area the intensity of deformation increases only slightly in the vicinity of the main central thrust simultaneous southward shearing within a large part of the higher himalaya crystalline near and above the main central thrust and normal faulting across the south tibetan detachment is explained by the tectonically induced extrusion of a ductily deforming wedge the process of extrusive flow suggested here can be approximated quantitatively by channel flow models that have been used to describe subduction zone processes channel flow accounts for some observed phenomena in the himalayan orogen such as inverted metamorphic sequences near the main central thrust not related to an inversion of isotherms and the syntectonic emplacement of leucogranites into the extruding wedge locally leading to an inversion of isotherms due to heat advection

transpressional deformations within the sanandaj sirjan metamorphic belt zagros mountains iran abstract polyphase deformation structures of the sanandaj sirjan metamorphic belt in the neyriz area zagros mountains iran are consistent with dextral transpressional deformation which is related to the oblique collision between the african arabian continent and the iranian microcontinent the collision started in the late cretaceous and is continuing to the present day quantitative kinematic analyses quartz textures suggest localized shear zones deformed with a significant pure shear component spatial orientation of lineation and semi quantitative kinematic indicators indicate shear zone parallel stretching and shear zone perpendicular shortening the occurrence of a horizontal stretching component parallel to the deformation zone boundary allows a kinematic model of combined transpression and lateral extrusion for this part of the zagros orogeny

kinematic interpretation of shearband boudins new parameters and ratios useful in ht simple shear zones partial funding to jp was provided by the centro de investigacao geolugica ordenamento e valorizacao de recursos that is supported by the pluriannual program of the fundacao para a cilncia e a tecnologia funded by the european union feder program and the national budget of the portuguese republic very insightful and helpful reviews were done by c fernandez university of huelva and two reviewers for which we are grateful we want to acknowledge to t valente university of minho for her suggestions that helped to simplify the manuscript structure and to a mccaig university of leeds for his final comments and english revision that significantly improved this manuscript

ductile shear as a cause of inverted metamorphism example from the nepal himalaya a discussion hubbard 1996 postulated the cause of well known development of kyanite as well as other index minerals representing dominant metamorphism was metamorphic inversion in a section of the eastern nepal himalaya due to the intense ductile shearing either preor synchronous with but outlasted the deformation because of paucity of growth of metawithin the main central thrust mct zone and the overlying tibetan slab on the basis of geologimorphic minerals across the main tectonic fabric hubbard 1996 p 496 cal and textural data cf hubbard 1989 the main thesis of her recent paper revolves around the fact the metamorphic belts of the nw himalaya and the eastern nepal are characterized by i ductile that the distribution of inverted metamorphic isograds is confined to intensely sheared 5 km thick shear zones of high strain revealing s c fabric and other shear structures having a top to south southzone of the mct which either post dated or outlasted predominant metamorphic assemblages p west vergence not only in the basal parts but also in the tibetan slab at higher structural levels 495 conceptually right way up metamorphic iso ii growth of metamorphic minerals is dominantly preto synchronous but occasionally outlasting grads in the young orogenic belts like the himalaya can be very efficiently inverted due to intense the main deformation iii lack of large scale overturned or recumbent folds in many sections except shearing in a broad ductile shear zone we wish to point out that the model proposed by hubbard zanskar searle et al 1992 and the beas valley himachal pradesh frank et al 1977 and iv pres 1996 for the eastern nepal is the same in principle as ours for the northwestern himalayas pubence of inverted metamorphism in the lower and middle sequences and a normal sequence in the lished in geology in 1993 earlier hubbard 1989 fixed the upper boundary upper parts near the tethyan sedimentary cover numerous structures having predominantly topof the 3 5 km thick mct zone from this area arbitrarily as she has documented that the upper and to southwest sense of ductile shearing have been frequently documented across many tectonic units lower boundaries of the mct zone are not distinct so for the sake of discussions the author defines of the lesser himalaya hhc and tethyan sedimentary zone brunel 1986 treloar and rex 1990 boundaries that include the majority of high strain zone p 20 ductile shear zones were also obpatel et al 1993 and can therefore be correlated with the intense ductile shearing irrespective of the served by her in the overlying tibetan slab where gneisses of the tibetan slab are foliated though presence of the discrete thrusts or wide thrust zones jain and anand 1988 foliation is somewhat less penetrative than probable coeval mylonitic fabric within the mct zone the ductile shear model postulated by hubbard 1996 bears strong structural similarities to the p 21 indicating synchrony of two dominant planar structures in this region within the mct zone one given earlier by jain and manickavasagam 1993 as it is evident from the simplified version she recorded that the apparent metamorphic grade across the mct zone gradually increases toof our model where effects of post metamorphic thrusting folding and other zones of high strain wards structurally higher levels p 20 where fibrolite and sillimanite are developed along the folihave not been considered figure 1 keeping in mind the regional geological and tectonic variaation as well as in the tibetan slab hubbard 1989 thus an apparent structural and metamorphic grations that may be expected over the distance of about 1000 km from the nw himalaya it is likely dation persists near the upper contact of the mct zone with the tibetan slab within the mct zone that the growth of metamorphic minerals may be diachronous within the higher himalayan shear zone one of the very basic fact of the nw hima1 manuscript received february 1 1997

deformation of granitoids at low metamorphic grade i reactions and grain size reduction abstract deformation and chemical reaction in granitoids at greenschist facies conditions were investigated in samples from three shear zones two from the alps corvatsch granodiorite and aiguilles rouges granite switzerland and one from eastern australia wyangala granite when examined by light and electron microscopy all show similar features of deformation that progressed from coarse parent rock through to fine grained mylonite quartz deformed plastically while both k feldspar and plagioclase fractured and recrystallized in conjunction with chemical change which had as its end point an assemblage albite quartz white mica caal silicates k feldspar and calcic plagioclase depending on fluid chemistry from the parent rock were unstable at low metamorphic grades in the presence of aqueous fluid since ca bearing plagioclase was not stable in these environments myrmekite did not replace k feldspar in any of the rocks examined recrystallization of feldspar which should perhaps be termed neocrystallization was initiated predominantly at clast margins or along microfractures that are marked by fluid inclusions and twin offsets in old feldspar grains particularly in plagioclases dislocations exist in wall like structures that are commonly associated with voids suggesting origins in microfractures these dislocations had severely limited mobility and subgrain rotation does not appear to have contributed to recrystallization we conclude that recrystallization mainly occurred via a classical nucleation mechanism with minor contributions from twin boundary migration we argue that the 450 550 c lower limit for recrystallization of feldspar referenced throughout the literature is not applicable to the rock systems under investigation and should be discarded as a universal limit microfracturing microboudinage and reaction are seen as the prerequisites for mylonite formation from coarse grained granitic rocks at low metamorphic grades see part ii of this paper neocrystallization fluid access and nucleation appear to have accompanied or immediately followed the first deformation increments and were primarily responsible for continued grain size reduction transgranular fracture was comparatively important only at the onset of deformation since the formation of shear zones in granitoids commonly takes place under conditions of low metamorphic grade in the presence of aqueous fluids in the earth s crust breakdown reactions and nucleation recrystallization in feldspars may be important influences upon localization of deformation in granitoids

kinematic vorticity and tectonic significance of superposed mylonites in a major lower crustal shear zone northern fiordland new zealand abstract new structural metamorphic finite strain and kinematic vorticity data from a 4 km wide subvertical shear zone in fiordland new zealand reveal a history of deformation reflecting different tectonic regimes an analysis of ductile fabrics within the shear zone and its wall rocks shows two distinctive stages of amphibolite facies mylonitic deformation dasz2 and dasz3 that are superimposed on older paleozoic or early mesozoic structures variations in strain intensity and well defined shear zone boundaries have allowed us to examine the progressive development of lasz2 sasz2 and lasz3 sasz3 fabrics and compare the types kinematics and conditions of deformation that produced them mineral assemblages defining lasz2 sasz2 provided calculated peak conditions of 11 9 1 1 kbar and 581 34 c indicative of lower crustal depths mineral assemblages defining lasz3 sasz3 provided calculated peak conditions of 8 7 1 2 kbar and 587 42 c finite strain and kinematic vorticity studies show that dasz2 involved ductile normal faulting and crustal thinning leading to decompression and exhumation of lower crustal rocks at some time during the cretaceous rifting of ancestral new zealand from gondwana dasz3 represents an episode of mid crustal dextral transpression that may have resulted from latest mesozoic or cenozoic oblique convergence reactivation of the subvertical sasz3 foliation by cataclastic shear zones and brittle faults dasz4 was accompanied by limited recrystallization at greenschist facies conditions dasz4 shear zones record upper crustal dextral strike slip faulting that resembles late tertiary deformation patterns associated with the australian pacific transform plate boundary

assessing the geochemical and tectonic impacts of fluid rock interaction in mid crustal shear zones a case study from the intracontinental alice springs orogen central australia the reynolds anmatjira ranges central australia form part of a high grade basement terrane dissected by intensely metasomatized transpressional shear zones active during the ordovician carboniferous alice springs orogeny unlike typical retrograde structures associated with discrete fluid flow the mid crustal setting and intracontinental nature of these shear systems present significant problems for the source and ingress mechanism of the fluid involved in their rehydration to address these issues we describe two detailed traverses across deformed and metasomatized basement rocks in this region and interrogate their record of fluid rock interaction from various perspectives both traverses combine structural and petrological observations with zr in rutile and ti in quartz thermobarometry oxygen and hydrogen stable isotope analysis and major trace and rare earth element mobility trends each technique is critically evaluated for its utility in this study and its more widespread applicability to alternative field areas providing a strategic framework for the general investigation of fluid affected shear zones ultimately the integrated data sets specify pressure temperature conditions of 530 c and 4 5 kbar implying average apparent thermal gradients of 29 36 c km 1 and depths of 14 18 km other characteristic features to emerge include strongly variable element mobilities and pronounced isotopic depletion fronts consistent with the alteration effects of an externally derived non equilibrium fluid this is confirmed by calculated fluid compositions indicative of contributions from a fluid of meteoric origin with estimated 18o and d values as low as 2 3 and 59 8 respectively we propose that these surficial fluid signatures are imposed on the mid crust by the prograde burial and dehydration of hydrothermally altered fault panels produced during pre orogenic basin formation progressive fluid release with continued subsidence then leads to the accumulation of increasing fluid volumes in the vicinity of the brittle ductile transition promoting extensive hydration metasomatism and reaction softening at the locus of stress transmission from plate boundary sources the sustained injection of externally derived fluids into refractory crustal material may thus stimulate a critical reduction in the long term strength of the lithosphere providing strong impetus for the initiation and advancement of intracontinental orogenesis

structural styles in the zagros simple folded zone iran arabia eurasia convergence is achieved in the nw zagros by a combination of shortening on nw se trending folds and thrusts mainly in the simple folded zone and by right lateral strike slip on the nw se trending main recent fault a balanced and restored cross section across this part of the range indicates c 49 km of shortening this probably occurred since c 5 ma providing an estimate of the long term shortening rate across the simple folded zone of c 10 mm a 1 the geometries of exposed structures suggest both basement thrusts and thin skinned decollement levels with major folds possibly nucleated above basement faults fold geometries indicate several decollement horizons shale units are candidates as well as evaporites in the neogene mesozoic lower palaeozoic and upper proterozoic successions the se part of the simple folded zone deforms by north south shortening on broadly east west trending folds and thrusts the link between these regions occurs via a set of fault blocks c 400 km wide in total each bounded by north south right lateral faults incremental changes in the strike of some of the folds occur across these right lateral faults with more east west orientations to the east

a 3 d kinematic model of fabric development in polycrystalline aggregates comparisons with experimental and natural examples abstract a 3 d generalization of the approach previously developed by etchecopar for the simulation of fabrics in polycrystalline aggregates is presented the model is based on a geometric minimization of gaps overlaps and boundary displacements between deformed neighbouring cells each cell may deform using a small number

stable positions of rigid objects in non coaxial flow a study in vorticity analysis abstract distortions of a homogeneous fabric which occur around rigid objects in rocks deformed by non coaxial ductile flow are useful to determine the sense of shear but also contain information on other aspects of the flow rigid objects in a non coaxial flow fall into two categories those which are permanently rotating and those which can reach stable positions at high finite strain the orientation of such immobilized objects with respect to eigenvectors of instantaneous flow is a function of the vorticity number of the flow the ratio of instantaneous stretches and the axial ratio of the object in naturally deformed rocks immobilized rigid objects may be recognized from the geometry of the surrounding fabric tails of recrystallized material around porphyroclasts in a mylonite rotate towards parallellism with the extensional eigenvector of the flow and the shape of tails reflects the rotational behaviour of the porphyroclast the axial ratio of immobilized porphyroclasts and their orientation with respect to the tails can theoretically be used to determine the vorticity number of the flow and deviations from isochoric plane strain in practice such an analysis is as yet difficult but a tentative example is given of the way in which the vorticity number can be calculated from a population of feldspar porphyroclasts in a quartzite mylonite from the french pyrenees

kinematic analysis of rock flow and deformation temperature of the sirjan thrust sheet zagros orogen iran microstructural finite strain and vorticity analyses of quartz rich mylonites were used in order to investigate kinematics of rock flow and deformation temperature in the sirjan thrust sheet exposed in a structural window within the sanandaj sirjan high pressure low temperature hp lt metamorphic belt that forms part of the hinterland of the zagros orogenic belt of iran a dominant top to the sw sense of shear in the study area is indicated by several shear sense indicators such as asymmetric boudins rotated porphyroclasts mica fish and s c fabrics quantitative analyses reveal approximately plane strain deformation conditions with r xz values ranging from 2 5 to 4 3 and increasing towards the sirjan thrust opening angles of quartz c axis fabrics and recrystallization regimes suggest deformation temperatures vary from 430 to 625 50 c in the hanging wall rocks oblique grain shape and quartz c axis fabrics were used to estimate the degree of non coaxiality during deformation the obtained vorticity profile indicates a down section increase in kinematic vorticity number w m from 0 6 to 0 89 this range of vorticity numbers confirms contributions of both simple 41 68 and pure shear 32 59 deformation components the structural characteristics of the study area ultimately were controlled by oblique motion of the afro arabian plate relative to the iranian plate

water level changes in the flevo area central netherlands 5300 1500 bc implications for relative mean sea level rise in the western netherlands abstract the younger post 4000 cal bc part of the water level curve for the eastern flevo area central netherlands runs below the relative mean sea level msl curve for the western and northern netherlands mededelingen rijks geologische dienst 36 1 1982 93pp we investigated if this difference can be attributed to i root rejuvenation of the bulk dated basal peat samples on which the curve for the eastern flevo area is based and or ii underestimation of the water depth in which the dated peat accumulated it appears that these potential sources of error did not influence significantly the results obtained by roeleveld and gotje de holocene laagveenontwikkeling in de randzone van de nederlandse kustvlakte noordoostpolder unpublished ph d thesis vrije universiteit amsterdam 1993 pp 76 86 on the basis of new and recently published water level data from the eastern and southwestern flevo area we confirm refine and tentatively extend the water level rise reconstruction by roeleveld and gotje and establish a relative msl trend curve for the central netherlands the systematic age differences of our radiocarbon dates on various fractions of four new basal peat samples from the eastern flevo area support the interpretation by roeleveld and gotje that the younger part of the 1982 msl curve may be based on basal peat samples all from the rotterdam area that have been dated 100 200 yr too old if this interpretation is correct the fact that the relative msl curve for the central netherlands lies below the 1982 msl curve cannot be interpreted to indicate less crustal subsidence for the rhine meuse delta as predicted by geophysical modeling j quat sci 17 2002 535

quartz shape fabric variations and c axis fabrics in a ribbon mylonite arguments for an oscillating foliation abstract this paper describes quartz ribbons parallel to foliation containing elongate recrystallized quartz grains aligned oblique to the foliation within a mylonite of the southern tasman belt southeastern australia the shape fabric of quartz grains varies in obliquity with respect to the foliation and intensity grain aspect ratio from one ribbon to another whereas the c axis fabric pattern is stable with respect to the mylonitic foliation and lineation it is argued that the grain shape fabric is an oscillating foliation due to competition between deformation and syntectonic recrystallization

middle and late holocene sea level changes in eastern maine reconstructed from foraminiferal saltmarsh stratigraphy and ams 14c dates on basal peat abstract a relative sea level history is reconstructed for machiasport maine spanning the past 6000 calendar years and combining two different methods the first method establishes the long term 10 3 yr trend of sea level rise by dating the base of the holocene saltmarsh peat overlying a pleistocene substrate the second method uses detailed analyses of the foraminiferal stratigraphy of two saltmarsh peat cores to quantify fluctuations superimposed on the long term trend the indicative meaning of the peat the height at which the peat was deposited relative to mean tide level is calculated by a transfer function based on vertical distributions of modern foraminiferal assemblages the chronology is determined from ams 14 c dates on saltmarsh plant fragments embedded in the peat the combination of the two different approaches produces a high resolution replicable sea level record which takes into account the autocompaction of the peat sequence long term mean rates of sea level rise corrected for changes in tidal range are 0 75 mm yr between 6000 and 1500 cal yr b p and 0 43 mm yr during the past 1500 years the foraminiferal stratigraphy reveals several low amplitude fluctuations during a relatively stable period between 1100 and 400 cal yr b p and a sea level rise of 0 5 m during the past 300 years

conditions of contact metamorphism papoose flat pluton eastern california usa implications for cooling and strain histories petrological study of highly strained carbonate and pelitic rocks within the contact aureole surrounding the western part of the papoose flat pluton yields thermal profiles plots of metamorphic temperature versus distance across the aureole that show temperature gradients which are relatively flat and narrow 100m the gradients occur close to the contact and indicate a slight decrease in temperature from 500 550 c at the pluton wall rock contact to 450 500 c at the outer margin of the aureole one thermal profile across low strain metasedimentary rocks located in the southern part of the aureole shows that thermal effects from emplacement extend no further than 600 m from the contact coexistence of andalusite and cordierite in pelitic rocks of the aureole constrain pressures to 4 kbar thermal modelling using an analytical solution of the conductive heat flow equation for a rectangular shaped pluton reproduces the observed thermal maxima and profile shape conductive rather than convective cooling also is supported by isotopic and field evidence for limited fluid flow along the strongly deformed margin of the pluton simple thermal models coupled with observed high temperature deformation features and a measured 90 attenuation of stratigraphic units in the plastically deformed western part of the pluton s aureole indicate that strain rates may have been of the order of 10 12s 1 evidence for episodic heating such as two distinct generations of andalusite growth in pelites from the aureole alternatively may indicate a longer heating event and therefore slower strain rates thermal models also indicate that parts of the pluton still may have been above the solidus during deformation of the pluton margin and aureole

the quaternary geology of the north sea basin the north sea is a shallow 50 400 m deep 500 km wide marine embayment that separates the uk from scandinavia and northern europe fig 1 this epicontinental shelf area has had a long and complex geological history with its present day structural configuration largely being the result of rifting during the jurassic early cretaceous followed by thermal subsidence glennie and underhill 1998 zanella and coward 2003 since the middle cenozoic the central graben region of the north sea basin has accumulated up to 3000 m of oligocene to holocene sediments which locally includes more than 800 m of quaternary sediments caston 1977 1979 gatliff et al 1994 although a detailed understanding of the depositional history recorded by this sedimentary succession is yet to be fully established these sediments preserve evidence for the advance and retreat of several ice sheets into the north sea from the adjacent landmasses at different times during the quaternary these ice masses not only resulted in periodic erosion but also made a significant depositional contribution to the infill of the basin

kinematics and vorticity of flow associated with post collisional oblique transpression in the variscan inner zone of northern sardinia italy abstract quartz c axis fabrics vorticity of flow and deformation temperatures were analyzed in samples collected in the central sector of the variscan inner zone in sardinia italy in order to constrain the kinematics of exhumation of medium and high grade metamorphic rocks during d2 post collisional deformation we investigated two shear belts with opposing shear senses these shear belts are developed parallel to the trend of the inner zone which marks the boundary between two metamorphic complexes our data suggest that the sinistral shear belt initiated during the early stage of d2 deformation in a simple shear dominated regime whereas the dextral shear belt initiated later in a pure shear dominated regime we document a general non coaxial flow regime with contemporaneous pure and simple shear components geometrical relationships reveal the operation of oblique extrusion during a compressive regime where the coaxial component acted sub horizontal and orthogonal to the trend of the axial zone changes in the kinematics vorticity of flow and strain geometry that occurred during d2 deformation may be related to post collisional orogen parallel displacement caught up in the variscan orogeny

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

holocene relative sea level change isostatic subsidence and the radial viscosity structure of the mantle of northwest europe belgium the netherlands germany southern north sea abstract a comprehensive observational database of holocene relative sea level rsl index points from northwest europe belgium the netherlands northwest germany southern north sea has been compiled in order to compare and reassess the data collected from the different countries regions and by different workers on a common time depth scale rsl rise varies in magnitude and form between these regions revealing a complex pattern of differential crustal movement which cannot be solely attributed to tectonic activity it clearly contains a non linear glacio and or hydro isostatic subsidence component which is only small on the belgian coastal plain but increases significantly to a value of ca 7 5 m relative to belgium since 8 cal ka bp along the northwest german coast the subsidence is at least in part related to the post glacial collapse of the so called peripheral forebulge which developed around the fennoscandian centre of ice loading during the last glacial maximum the rsl data have been compared to geodynamic earth models in order to infer the radial viscosity structure of the earth s mantle underneath nw europe lithosphere thickness upper and lower mantle viscosity and conversely to predict rsl in regions where we have only few observational data e g in the southern north sea a very broad range of earth parameters fit the belgian rsl data suggesting that glacial isostatic adjustment gia only had a minor effect on belgian crustal dynamics during and after the last ice age in contrast a narrow range of earth parameters define the southern north sea region reflecting the greater influence of gia on these deeper older samples modelled rsl data suggest that the zone of maximum forebulge subsidence runs in a relatively narrow wnw ese trending band connecting the german federal state of lower saxony with the dogger bank area in the southern north sea identification of the effects of local scale factors such as past changes in tidal range or tectonic activity on the spatial and temporal variations of sea level index points based on model data comparisons is possible but is still complicated by the relatively large range of earth model parameters fitting each rsl curve emphasising the need for more high quality observational data

vorticity analysis in a metachert from the sanbagawa belt sw japan abstract common tectonic features of deformed metachert include both sets of extended and shortened veins and quartz c axis preferred orientation patterns in such rocks information is also commonly available on the orientation and magnitude of the finite strain these features can be used to derive two independent estimates of the degree of non coaxiality during deformation in an example from the sanbagawa belt sw japan the two methods give consistent results and show that deformation was intermediate between simple and pure shear such types of progressive deformation distributed over a broad region could cause substantial subvertical thinning and be a significant factor in the exhumation of high p t rocks in the region

geological causes of recent 100 yr vertical land movement in the netherlands abstract geodetic levelling data record differential vertical movements of the top of the pleistocene sands of up to 1 5 mm year in the netherlands over the last century we compare these movements to a mean tectonic isostatic and compaction movements at time scales of millions of years obtained by backstripping of cenozoic stratigraphy and b estimates of recent 100 yr movements from process modelling of isostasy glacio and hydro isostasy and compaction the process rates at time scales of millions of years are insufficient to account for the geodetic observations by an order of magnitude the isostasy and compaction rates inferred for the last century are also insufficient they explain less than half of the observed movements this suggests that the residual observed rates less isostasy and compaction estimates which is interpreted to represent tectonic crustal deformation constitutes an important contribution to present day movements the surprisingly high rates of short term tectonic vertical movements in a region which is relatively inactive seismically indicate that correction of tide gauge records for the glacio isostatic signal alone does not yield an appropriate measure of eustatic sea level rise along the dutch coast

kinematics and vorticity in kangmar dome southern tibet testing midcrustal channel flow models for the himalaya 1 kinematic kinematic vorticity wm and deformation temperature analyses were completed to test the hypothesis that midcrustal rocks exposed in the core of the kangmar gneiss dome southern tibet record ductile deformation patterns of a frozen segment of a southward flowing midcrustal channel microscopic and mesoscopic kinematic indicators exhibit a downward transition from a subequal mix of top north and top south shear in garnet zone rocks to dominantly top north shear in staurolite kyanite zone and deeper rocks kinematic vorticity values indicate an increase in pure shear component with depth from 48 pure shear in chloritoid zone rocks through 62 in garnet zone to staurolite kyanite zone rocks to 68 pure shear in an orthogneiss the deepest exposed rocks deformation temperatures inferred from grain scale microstructures and quartz lattice preferred orientations increase from 300 c 400 c in chloritoid zone rocks to 600 c in the deepest exposed rocks these temperatures are equivalent to temperatures derived from garnet biotite thermobarometry indicating that wm was recorded during peak metamorphism this ductile deformation zone was cut by the brittle southern tibetan detachment system stds that juxtaposed metasedimentary rocks upon the orthogneiss on the basis of these relations midcrustal rocks in the core of kangmar dome record 1 general shear vertical thinning and n s horizontal extension with a component of top north shear during peak metamorphism within a ductile shear zone corresponding to the northern and deeper portion of the stds 2 an increase in pure shear with structural depth a consequence of an increase in lithostatic load and 3 displacement of the high temperature shear zone by the brittle stds our data are compatible with the deformation patterns predicted for the top part of a southward flowing midcrustal channel

a sensitive vorticity gauge using rotated porphyroblasts and its application to rocks adjacent to the alpine fault new zealand variable aspect ratio porphyroblasts deformed in non coaxial flow and internally containing rotated relicts of an external foliation can be used to characterise plane strain flow regimes the distribution obtained by plotting the orientation of the long axis of such grains classified by aspect ratio against the orientation of the internal foliation is potentially a sensitive gauge of both the bulk shear strain as previously suggested and kinematic vorticity number we illustrate the method using rotated biotite porphyroblasts in the alpine schist a sequence of mid crustal rocks that have been ramped to the surface along the alpine fault a major transpressional plate boundary results indicate that at distances greater than or equal to similar to1 km from the fault the rocks have undergone a combination of irrotational fattening and dextral oblique normal sense shear with a bulk shear strain of similar to0 6 and kinematic vorticity number of similar to0 2 the vorticity analysis is compatible with estimates of strongly oblate bulk strain of similar to 75 maximum shortening dextral reverse transpressional flow characterises higher strain s tectonite mylonite within similar to1 km of the alpine fault these relationships provide insight into the kinematics of flow and distribution of strain in the hangingwall of the alpine fault and place constraints on numerical mechanical models for the exhumation of these mid crustal rocks c 2001 elsevier science ltd all rights reserved

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

sea level changes in the southern north sea region a response to bungenstock and weerts 2010 the article highlights the difficulties connected with getting secure fixed points for sea level curve con struction and emphasises the care that should be taken with data interpretation as such it is a welcome contribution to this important topic on the other hand the paper has in my opinion several weaknesses it not only disregards a large body of reliable and highly relevant information on sea level changes available from investigations carried out using a variety of methodologies but also makes assumptions that seem to be based to varying degrees on misconceptions and misunderstandings many of these misunderstandings might have been avoided had the discussions that are referred to in the acknowledgements actually taken place i wish to take this opportunity to set the record straight by stating that no such discussions took place

structural signatures and 40ar 39ar geochronology of the indosinian xuefengshan tectonic belt south china block abstract to advance our understanding of the kinematics of the xuefengshan tectonic belt xfstb and the mesozoic tectonics of the south china block scb this paper presents new data and interpretations from our structural studies and thermochronological dating the xfstb is characterized by greenschist facies metamorphism and development of s and s l tectonic fabrics an asymmetric positive flower structural pattern is composed of nw wnw and se ese dipping cleavages faults and shear zones kinematic indicators indicate a dominant top to wnw thrusting with a sinistral strike slip component on the ese dipping shear zones and top to ese back thrusting on the wnw dipping shear zones the quartz c axis orientations of mylonitic rocks exhibit monoclinic point maximum asymmetry indicative of a sinistral shear sense under the a basal gliding condition the timing of the major deformation event has been constrained to the middle triassic to early jurassic 244 195 ma on the basis of 40ar 39ar geochronology and other geological observations the structural characteristics of the xfstb are probably related to an indosinian oblique convergent zone in combination with tectonic wedging and associated back thrusting all above a low angle se dipping basal detachment oblique northwestward and upward movement along the basal detachment was partitioned into the nw wnw directed thrusting se ese directed back thrusting and subsidiary strike slip movement along the ne and nne trending faults and shear zones the xfstb may represent part of a huge structural fan between the yangtze and cathaysian blocks and can be interpreted as a product of the indosinian intracontinental collision involving a weak zone

accommodation of arabia eurasia convergence in the zagros makran transfer zone se iran a transition between collision and subduction through a young deforming system 1 at iranian longitude the arabian plate is moving northward relative to eurasia 20 mm yr 1 according to gps to the east this relative motion is accommodated by northward subduction under the e w makran emerged accretionary prism to the west it is accommodated partly by the zagros fold and thrust belt and partly by the alborz kopet dagh deforming zones further north this work investigates the nnw striking transition zone that connects zagros and makran the minab zendan fault system satellite images and structural and geomorphic field observations show a distributed deformation pattern covering a wide domain five north to nw trending major faults were identified they exhibit evidence for late quaternary reverse right lateral slip and correspond to two distinct fault systems the western one transferring the zagros deformation to the makran prism and the eastern one northward transferring the deformation to the alborz kopet dagh tectonic study and fault slip vector analyses indicate that two distinct tectonic regimes have occurred successively since the miocene within a consistent regional ne trending compression 1 an upper miocene to pliocene tectonic regime characterized by partitioned deformation between reverse faulting and en echelon folding 2 a ne trending 1 axis transpressional regime homogeneously affecting the region since upper pliocene the change is contemporaneous with major tectonic reorganization regionally recorded therefore this study provides evidence for active deformation that is not localized but distributed across a wide zone it accommodates the convergence and transfers it from collision to subduction by transpressional tectonics without any partitioning process in the present day period

prism and basal plane parallel subgrain boundaries in quartz a microstructural geothermobarometer empirical data on quartz subgrain patterns from various metamorphic rocks show that at least up to 10 kbar in the stability field of low quartz prismatic subgrain boundaries are dominant whereas basal subgrain boundaries are not developed in the high quartz stability field both prismatic and basal subgrain boundaries occur and form typical rectangular chessboard patterns the likely reason behind the different occurrence of these subgrain patterns is that in high quartz prismatic glide becomes as easy as or probably even easier than basal glide the two types of subgrain patterns can be clearly distinguished by optical microscopy consequently the occurrence of chessboard subgrain patterns in quartz represents a practicable geothermobarometer the possibilities of its application are far reaching and include the specification of deformation conditions at high grade metamorphism the recognition of syntectonic intrusions and the distinction between pluton emplacement at lower and at higher crustal levels

holocene evolution of relative sea level and local mean high water spring tides in belgium a first assessment abstract holocene age depth data from the belgian coastal plain basal peat data particularly are assessed in terms of local water and tide levels basal peat formation was generally induced by sea level rise effects of local seepage were limited and significant river gradient effects were absent no relation was found between the timing of basal peat inception and substrate permeability in general edaphic moisture conditions were unfavourable for organic accumulation prior to sea level related rise of the groundwater table error envelopes for the minimum level of local mean high water spring tides and for upper and extreme lower relative mean sea level limits during the last 9400 solar years 8400 yrs b p are presented these indicate that the rate of relative sea level rise showed marked retardations at ca 7500 7000 yrs cal b p 6650 6100 yrs b p and ca 5500 5000 yrs cal b p 4400 yrs b p a eustatic explanation appears to be plausible particularly for the former prior to ca 4000 yrs cal b p ca 3600 yrs b p the relative sea level rise in belgium differs noticeably from that established for the western netherlands with both diverging progressively back in time this implies that considerable differential crustal movement occurred between the two areas in the early holocene

ductile shear as a cause of inverted metamorphism example from the nepal himalaya in many mountain belts metamorphic sequences occur in an inverted arrangement such that rocks of higher metamorphic grade overlie rocks of lower metamorphic grade in some locations such as the main central thrust mct zone of the himalaya the metamorphic inversion is coincident with the zone of ductile thrust deformation although many explanations have been suggested for the metamorphic inversion of the himalaya none are consistent with all of the observed features a new model based on observations from the eastern nepal himalaya consists of inversion of the metamorphic sequence due to ductile shearing of a pre existing zone of right way up metamorphism this simple structural explanation creates an inverted metamorphic sequence consistent with observations of 1 a zone of distributed deformation 2 metamorphic textures overprinted by deformation and 3 metamorphic isograds sub parallel to shear fabric these observations are not all well accounted for by previously proposed models in this st

late cenozoic reorganization of the arabia eurasia collision and the comparison of short term and long term deformation rates the arabia eurasia collision deforms an area of 3 000 000 km2 of continental crust making it one of the largest regions of convergent deformation on earth there are now estimates for the active slip rates total convergence and timing of collision related deformation of regions from western turkey to eastern iran this paper shows that extrapolating the present day slip rates of many active fault systems for 3 7 million years accounts for their total displacement this result means that the present kinematics of the arabia eurasia collision are unlikely be the same as at its start which was probably in the early miocene 16 23 ma or earlier in some but not all active fault systems short term 10 year and long term 5 million year average deformation rates are consistent there is little active thickening across the turkish iranian plateau and possibly the interior of the greater caucasus these are two areas where present shortening rates would need more than 7 million years to account for the total crustal thickening and where there are structural and or stratigraphic data for pre late miocene deformation we suggest that once thick crust up to 60 km built up in the turkish iranian plateau and the greater caucasus convergence took place more easily by crustal shortening in less elevated regions such as the zagros simple folded zone the south caspian region and foothills of the greater caucasus or in other ways such as westward transport of turkey between the north and east anatolian faults the time and duration of this changeover are not known for certain and are likely be diachronous although deformation started or intensified in many of the currently active fault systems at 5 2 ma

the himalayan main central thrust pile and its quartz rich tectonites in central nepal as a consequence of the india asia collision a deeply rooted crustal slice has been moved southwards over the northern boundary of the indian plate at the present level of observation the main central thrust pile a rock pile of several kilometers thickness is affected by shear deformation which imprinted a flat foliation and a constant n s trending lineation these tectonites were deformed under a wide range of metamorphic conditions grading from lower greenschists up to the sillimanite field the m c t shear zone is studied from the view point of the quartz rich rocks over 100 samples helped to define a microstructural zonation roughly parallel to the thermal one 35 samples particularly rich in quartz have been used for the preferred orientation study of their c axes and a few of them for their a axes strong lattice orientations when undisturbed by mainly secondary recrystallization attest to large plastic strains in quartz the c axes are mostly distributed along unequally populated crossed girdles which may evolve into an inclined single girdle the a axes concentrate perpendicular to the more populated girdle concerning quartz the following is suggested 1 1 the deformation has a dominant shear component responsible for the dominant stretching lineation it could be simple shear in case of inclined single girdles 2 2 one set of a axes line up parallel to the shear direction slip on various planes in the a direction may be an important deformation mechanism 3 3 asymmetry in the lattice preferred orientations could be used to predict the sense of shear for the himalayan thrusting in more than 80 of cases

analysis of deformation paths in shear zones the geometry of ductile shear zones can be used to solve problems of regional tectonics if the deformation path of material in the zones is sufficiently understood flow in many shear zones may have deviated from simple shear and consequently data on the final deformation state such as finite strain and volume change are insufficient for reconstruction of the deformation path even if flow parameters were constant during progressive deformation additional information on the flow vorticity number is also needed and can be obtained from fabric elements such as sets of folded boudinaged veins rotated porphyroblasts and blocked rigid objects mohr circle constructions are presented as a tool to calculate deformation parameters from fabric data to represent the deformation path graphically and to reconstruct flow parameters from the shape of this path if the vorticity number or the volume change rate changed during progressive deformation the deformation path can be partly reconstructed using sets of fabric elements which register mean and final values of these parameters

deformation path partitioning within the transpressional white mountain shear zone california and nevada most numerical simulations of transpression zones predict a change in finite stretching direction from subhorizontal to subvertical for simple shear dominated zones we provide a detailed description of a dextral transpression zone the white mountain shear zone wmsz with a range of lineation orientations and compare these natural data to numerical models the wmsz is characterized by steeply dipping foliations with dominant shallowly plunging lineations and coeval subordinate domains of steeply plunging lineations within shallowly lineated domains foliation geometry shear sense indicators and quartz c axis fabrics indicate a large component of simple shear while microstructural and quartz c axis fabric data from steeply lineated domains indicate a large component of pure shear geometric relationships between foliations and lineations and quartz c axis fabrics demonstrate that lineation orientation has remained constant during much of the deformation history comparison of numerical models with the data collected from wmsz shows that the shear zone geometry and the observed strain path partitioning do not match any of these models we propose a conceptual kinematic model for the wmsz involving stable segregated coeval kinematic domains of simple shear dominated fabrics and pure shear dominated fabrics that accommodate the transcurrent and contractional components of deformation respectively

cretaceous tertiary convergence and continental collision sanandaj sirjan zone western iran abstract the sanandaj sirjan zone contains the metamorphic core of the zagros continental collision zone in western iran the zone has been subdivided into the following from southwest to northeast an outer belt of imbricate thrust slices radiolarite bisotun ophiolite and marginal sub zones which consist of mesozoic deep marine sediments shallow marine carbonates oceanic crust and volcanic arc respectively and an inner complexly deformed sub zone late palaeozoic mesozoic passive margin succession rifting and sea floor spreading of tethys occurred in the permian to triassic but in the sanandaj sirjan zone extension related successions are mainly of late triassic age subduction of tethyan sea floor in the late jurassic to cretaceous produced deformation metamorphism and unconformities in the marginal and complexly deformed sub zones deformation climaxed in the late cretaceous when a major southwest vergent fold belt formed associated with greenschist facies metamorphism and post dated by abundant palaeogene granitic plutons in the southwest of the zone a late cretaceous island arc passive margin collision occurred with ophiolite emplacement onto the northern arabian margin similar to that in oman final closure of tethys was not completed until the miocene when central iran collided with the northeast arabian margin

slip partitioning and inclined dextral transpression along the zagros thrust system iran abstract flexural duplex structures and shear zones are well developed in the heneshk area in southwestern iran the zagros thrust system in this area consists of eight sheets of nw striking ne dipping dextral strike slip duplexes that are linked with imbricate fans and oblique slip thrusts the zagros thrust system is a portion of the internal zone of the zagros orogenic belt this internal zone is characterized by penetrative plastic deformation and metamorphism based on the kinematic vorticity number w k 0 73 0 02 calculated from quartz porphyroclasts of the goshti shear zones along the zagros thrust system the estimated angle between the maximum instantaneous strain axis isa and the transpressional zone boundary is 33 the estimated angle of the plate convergence or the flow apophysis of the displacement field is 25 the presence of dominantly dextral shear sense indicators in the area is consistent with dextral inclined transpressional convergence the mean estimated finite deformation w m value indicates relative contributions of 47 pure shear and 53 simple shear for the deformation which involved both strike slip and oblique slip displacements in this inclined transpression about 40 strike slip partitioning was required to accommodate the finite strain and re orientation of instantaneous strain

grain boundary migration microstructures in a naturally deformed quartzite abstract in this study several grain scale microstructures are presented that are thought to demonstrate the migration direction of once mobile grain boundaries in a naturally deformed quartzite an analysis is presented of the sense of migration of the boundaries and the characteristics of the patterns of relative grain growth and shrinkage grain boundary migration seems to be correlated with the relative crystallographic orientations of neighbouring grains for the quartz quartz grain boundaries and the pattern of preferred grain growth is roughly symmetrical about the mica foliation plane

dynamic recrystallization of quartz correlation between natural and experimental conditions quartz veins in the eastern tonale mylonite zone italian alps were deformed in strike slip shear due to the synkinematic emplacement of the adamello pluton a temperature gradient between 280 c and 700 c was effected across this fault zone the resulting dynamic recrystallization microstructures are characteristic of bulging recrystallization subgrain rotation recrystallization and grain boundary migration recrystallization the transitions in recrystallization mechanisms are marked by discrete changes of grain size dependence on temperature differential stresses are calculated from the recrystallized grain size data using paleopiezometric relationships deformation temperatures are obtained from metamorphic reactions in the deformed host rock flow stresses and deformation temperatures are used to determine the strain rate of the tonale mylonites through integration with several published flow laws yielding an average rate of approximately 10 14s 1 to 10 12s 1 the deformation conditions of the natural fault rocks are compared and correlated with three experimental dislocation creep regimes of quartz of hirth tullis linking the microstructures of the naturally and experimentally deformed quartz rocks a recrystallization mechanism map is presented this map permits the derivation of temperature and strain rate for mylonitic fault rocks once the recrystallization mechanism is known

dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred

structures and microstructures related to steady state mantle flow in the neyriz ophiolite iran abstract structural analysis in the well exposed and well preserved neyriz ophiolite suggests that it is a relatively undisturbed piece of oceanic lithosphere detailed structural mapping of high t deformation mantle flow revealed the presence of three elliptical shaped diapirs trending nw se these diapirs are characterized by vertical mantle foliations associated with vertical plunging stretching lineations which progressively incline toward parallelism with the gently ne dipping moho the nw se direction of asthenospheric upwelling of diapirs is parallel with the orientations of the vertical sheeted dike complex this suggests that the neyriz ophiolite was created by two nw se palaeo ridge axes these palaeo ridges are classified as fast spreading ridges these ridges are segmented by a dextral palaeo transform fracture zone this is consistent with fast spreading ridges comparison between the neyriz and oman ophiolites reveals that they show similar characteristics most of the oman palaeo ridge systems are oriented nw se and nnw se they also display similar sheeted dike complex orientations and crustal thickness variations these two ophiolites originally were part of the neo tethyan oceanic lithosphere and afterwards were separated by the oman line during continental collision of the iranian micro continent and afro arabian continent

fabric development during shear deformation in the main central thrust zone nw himalaya india abstract quartz microfabrics and associated microstructures have been studied on a crustal shear zone the main central thrust mct of the himalaya sampling has been done along six traverses across the mct zone in the kumaun and garhwal sectors of the indian himalaya the mct is a moderately north dipping shear zone formed as a result of the southward emplacement of a part of the deeply rooted crust that now constitutes the central crystalline zone of the higher himalaya over the less metamorphosed sedimentary belt of the lesser himalaya on the basis of quartz c and a axis fabric patterns supported by the relevant microstructures within the mct zone two major kinematic domains have been distinguished a noncoaxial deformation domain is indicated by the intensely deformed rocks in the vicinity of the mct plane this domain includes ductilely deformed and fine grained mylonitic rocks which contain a strong stretching lineation and are composed of low grade mineral assemblages muscovite chlorite and quartz these rocks are characterized by highly asymmetric structures microstructures and quartz c and a axis fabrics that indicate a top to the south sense that is compatible with south directed thrusting for the mct zone an apparently coaxial deformation domain on the other hand is indicated by the rocks occurring in a rather narrow belt fringing and structurally above the noncoaxial deformation domain the rocks are highly feldspathic and coarse grained gneisses and do not possess any common lineation trend and the effects of simple shear deformation are weak the quartz c axis fabrics are symmetrical with respect to foliation and lineation moreover these rocks contain conjugate and mutually interfering shear bands feldspar quartz porphyroclasts with long axes parallel to the macrosopic foliation and the related structures microstructures suggesting deformation under an approximate coaxial strain path on moving towards the mct the quartz c and a axis fabrics become progressively stronger the c axis fabric gradually changes from random to orthorhombic and then to monoclinic in addition the coaxial strain path gradually changes to the noncoaxial strain path all this progressive evolution of quartz fabrics suggests more activation of the basal rhomb and a slip systems at all structural levels across the mct

late quaternary sea level change and isostatic and tectonic land movements along the belgian dutch north sea coast geological data and model results early and middle holocene sea level data from belgium plot ca 2 m above data from the western netherlands reflecting differential tectonic and isostatic movements the total uplift rate of belgium relative to the western netherlands decays gradually from 0 66 m kyr 1 at 7500 cal yr bp to less than 0 25 m kyr 1 since 5000 cal yr bp the tectonic component of this relative movement inferred from eemian sea level data is in the order of 0 06 to 0 16 m kyr 1 the isostatic component of the uplift is related to the last phase of the collapse of a peripheral bulge under the netherlands and the dutch and german sectors of the north sea and to hydroisostatic subsidence of the north sea basin caused by water loading as sea level rose comparisons with isostatic rebound models show that they predict well the holocene isostatic movement between belgium and the western netherlands and that the predictions are improved when the tectonic component is removed from the observations preliminary evaluation of sea level data from the dutch sector of the north sea shows that glacio hydroisostatic subsidence relative to belgium was significantly greater than for the western netherlands coastal area and spatially highly variable copyright 2002 john wiley sons ltd