the hydrogeological and cultural background for two sacred springs bo telemark county norway of the many sacred springs in norway most dedicated to st olav several have disappeared two of the sacred springs that still exist are located in bo in telemark southern norway and have been surveyed for their sedimentology and hydrology the springs are embedded in a cultural landscape with several ancient monuments the aquifers have been mapped by drilling monitoring wells and ground penetrating radar and analyzed by gis models the area is at the marine limit and most of the sediments have been deposited in the sea the aquifer of the first spring occurs in subglacial and submarine sediments covered by a series of moraines the aquifer of the other spring is above the confining till layer bounded by moraines and located inside a 20 m thick glacial delta deposit both aquifers have documented properties that produce springs which under normal climatic conditions never dry and show stable temperatures close to the yearly mean air temperature the residence time of the water is long for both of the aquifers both springs are point features and are not parts of large seepage faces the locations of the springs may indicate a sacred position in an area of prehistoric farmland iron age burial mounds stone monuments of unknown age and cup mark carvings the springs are contaminated from old landfills but are reverting and one of them is under threat from sand pit expansion

ultrahigh temperature metamorphism under isobaric heating new evidence from the north china craton abstract the khondalite belt within inner mongolia suture zone imsz in the north china craton ncc preserves evidence for extreme crustal metamorphism under ultra high temperature uht conditions at ca 1 92 ga associated with the subduction collision tectonics between the yinshan and ordos blocks here we report a new locality in hongsigou where cordierite and spinel bearing granulites record uht metamorphism the prograde peak and retrograde mineral assemblages in these pelitic granulites have been identified based on petrography and mineral chemistry as bt1 grt1 sil1 kfs1 pl1 ilm qtz1 grt1 sil2 kfs2 pl2 spl ilm qtz2 liq and crd grt2 sil3 kfs2 pl2 ilm qtz2 respectively the peak metamorphic conditions of the pelitic granulite were estimated as 930 1050 c and 6 5 7 5 kbar based on pseudosection analysis in the system nckfmashto suggesting extreme thermal metamorphism we report la icpms zircon u pb data from the granulite which show weighted mean 207pb 206pb age of 1881 6 6 ma marking the timing of uht metamorphism lu hf analyses of the zircons show ehf t values within a restricted range of 4 2 to 0 3 and together with hf model ages a paleoproterozoic arc magmatic source is inferred for the detrital zircons the estimated p t path for the uht granulite suggests isobaric heating followed by cooling and decompression along a clockwise trajectory different from the anti clockwise p t paths defined in earlier studies for the 1 92 ga uht rocks from the imsz the younger age and the isobaric heating trajectory suggest that the hongsigou uht rocks are related to heat input from underplated mafic magmas following continental collision

flow laws for rocks containing two non linear viscous phases a phenomenological approach abstract mylonitic rocks and rock analogue materials reveal two basic types of structure 1 a load bearing framework lbf of strong phase contains isolated pockets of weak phase 2 interconnected layers of weak phase iwl separate boudins and clasts of strong phase aggregates with the lbf microstructure are characterized by nearly uniform strain rate stress is concentrated in the load bearing framework in aggregates with an iwl microstructure strain rate and sometimes also stress are higher in the interconnected weak phase than in the boudins and clasts of strong phase the degree of stress and strain partitioning depends strongly on the viscous strength contrast and on the relative amounts of the constituent mineral phases based on these observations the rheology of two phase rock is modelled with separate functions for lbf and iwl microstructures a new flow law is derived for rock with iwl structure in which two phases undergo dislocation creep the flow law expresses composite creep strength in terms of temperature bulk strain rate and the volume proportions and creep parameters of the minerals in the rock strain rate and stress are averaged in the constituent phases and slip along phase boundaries maintains strain compatibility within the aggregate composite strengths predicted with the iwl flow law fall well within the uniform stress and uniform strain rate bounds and are generally consistent with the viscous strengths of experimentally deformed bimineralic aggregates a hypothesis of viscous strain energy minimization is used to determine the relative stability of the lbf and iwl microstructures during steady state creep the iwl microstructure is predicted to be stable over a broad range of two phase compositions and mineral strength contrasts whereas the lbf microstructure is stable only in rocks with low volume proportions of weak phase and low to moderate mineral strength contrasts the iwl flow law indicates that rheological stratification in the lithosphere depends strongly on rock composition especially in rocks with low volume proportions of a weak phase and high mineral strength contrasts

rheological behavior of high temperature garnet bearing migmatites the khondalite belt example north china craton the contribution presents microstructural and petrological results obtained on garnet bearing felsic migmatites from the khondalite belt north china craton the study focused on low melt fraction felsic migmatites in which peritectic garnet are strongly elongated and show plastic deformation these peritectic garnet grains show different typology depending on their petrographic location within the layered migmatite an elongated shaped garnet with sillimanite and biotite inclusion lies within al rich layer whereas poecilithic garnets are located within s rich layers forming a garnet quartz aggregate the study presents petrological microstructural observation and ebsd analyses of the garnet grains and garnet quartz aggregates phase diagram sections modeling allows to constrain the p t conditions of the deformation at 850 1000 c and 0 6 1 1 gpa at such high to ultra high temperature conditions a low melt fraction was produced between 1 and 12 generally under 7 forescattered diffraction and misorientation maps with orientation pole figure argue for dislocation creep with development of subgrains in garnets our results suggest that at high to ultra high temperature the quartz feldspar garnet solid framework of felsic migmatites strongly accommodate the deformation and contribute to weakening of migmatite even at low melt fraction

uisge meinne mine water hydrogeology in the celtic lands from kernow cornwall uk to ceap breattain cape breton canada

garnet plasticity in the lower continental crust implications for deformation mechanisms based on microstructures and sem electron channeling pattern analysis abstract elongated garnets which preserved deformational microstructures boudinage pinch and swell structures occur in granulite facies quartzites in the highland complex of sri lanka in spite of these microstructures and in contrast with previous reports on garnet plasticity there are no or only few signs of intracrystalline deformation like subgrains or lattice distortion this can be explained by annealing and slow static cooling from high temperatures sem electron channeling pattern analysis reveals that the garnets have a significant crystallographic preferred orientation aspect ratio grain size analysis shows that the deformation mechanism is grain size sensitive these features indicate a diffusion assisted dislocation glide mechanism with dominant 1 2 110 slip system a comparison of the deformation behavior between garnet quartz and feldspar shows that differences in flow strength are low under the high grade conditions 850 50 c garnet is still the phase with the highest flow strength but dry quartz is slightly stronger than feldspar

the saline waters of llandrindod and builth central wales saline or brackish mineral waters have been recorded at several locations in mid wales and the welsh borderlands the main groups are centered on llandrindod wells and builth wells where maximum salinities of 5340 and 16 380 mg l 1 respectively are found the total discharge from these springs is very low combined 2 l s 1 yet their flow remains almost constant residence times of several thousand years are derived using 14 c analysis and 18 o and 2 h results suggest that the waters at llandrindod although not at builth contain a component of late pleistocene water evidence from the br cl ratios and trace elements indicates that the origin of the salinity lies within the lower palaeozoic formations and has not been derived from evaporites the mineral waters have undergone complete reduction of sulphate which has led to high concentrations of ba maximum 53 2 mg l 1 at llangammarch wells the most likely origin of these waters is the deep circulation of meteoric water over a residence time of several thousand years which has risen slowly along minor fracture systems to the points of outlet the interconnected fracture storage of these waters implied from the various lines of evidence must be of the order 30 mm 3

spatial distribution of 1950 1800 ma metamorphic events in the north china craton implications for tectonic subdivision of the craton abstract great progress has been made in the last twenty years in understanding the unification of the north china craton according to a prevailing model it developed by amalgamation of four sub blocks by three spatially and temporally separate orogenic belts the first at 1950 ma formed the western block the second at 1900 ma created the eastern block and the third at 1850 ma unified the eastern and western blocks however new data show that the 1950 ma orogen was affected by granulite facies reequilibration at 1800 ma and parts of the 1850 ma orogen have evidence of metamorphism at 1950 1900 ma new zircon u pb ages enable the paleoproterozoic metamorphic events to be statistically sub divided into four at 1955 ma m 1 1920 ma m 2 1885 ma m 3 and 1850 ma m 4 the m 1 2 events always appear together mainly in two belt areas including the helanshan qianlishan northern ordos yinshan liangcheng huai an lushan jiaobei and liaodong regions whereas the m 3 4 events are distributed over larger areas and were superimposed on the m 1 2 activities this age distribution is inconsistent with previous models of three separate orogens it should also be noted that the igneous rocks contemporary with the regional ultra high temperature high pressure granulite facies metamorphisms m 1 2 were previously described as arc related series i e the gabbro norites i s type granites and trimodal volcanics based on the spatial distribution of the paleoproterozoic metamorphic events m 1 4 and of the coeval igneous rocks we speculate that the assembly of the ncc was created by one orogen which formed between the eastern and western cratons in two tectonic stages two marginal arcs the korean and xuwujia developed against both eastern sides of the two sub cratons and were both accreted and deformed at 1965 1900 ma m 1 2 subsequently the amalgamation of the two sub cratons resulted in metamorphism on the western side of the eastern craton and in metamorphism that was superimposed on both accreted arcs at 1900 1790 ma m 3 4

calculation of partial melting equilibria in the system na2o cao k2o feo mgo al2o3 sio2 h2o nckfmash a thermodynamic model for haplogranitic melts in the system na2o cao k2o al2o3 sio2 h2o nckash is extended by the addition of feo and mgo with the data for the additional end members of the liquid incorporated in the holland powell 1998 internally consistent thermodynamic dataset the resulting dataset with the software thermocalc is then used to calculate melting relationships for metapelitic rock compositions the main forms for this are p t and t x pseudosections calculated for particular rock compositions and composition ranges the relationships in these full system pseudosections are controlled by the low variance equilibria in subsystems of nckfmash in particular the solidus relationships are controlled by the solidus relationships in nkash and the ferromagnesian mineral relationships are controlled by those in kfmash however calculations in nckfmash allow the relationships between the common metapelitic minerals and silicate melt to be determined in particular the production of silicate melt and melt loss from such rocks allow observations to be made about the processes involved in producing granulite facies rocks particularly relating to open system behaviour of rocks under high grade conditions

diffusion creep of fine grained garnetite implications for the flow strength of subducting slabs creep experiments were performed on synthetic fine grained garnetite to investigate the flow strength of the earth s subducting slabs experiments were conducted at temperatures t of 1373 1543 k and total pressure p of 0 1 mpa in controlled atmospheres of f 02 10 17 10 8 mpa the mechanical data indicate a grain size sensitive diffusion flow and the creep behavior can be described by an equation of the form e 5 32 3 10 10 6 td 2 5 0 3 f 0 o2 1 1 0 2 exp 347 46 kj mol rt where t in kelvin d in meter and f o2 in mpa based on the diffusivities d calculated from creep and diffusion experiments we proposed that grain boundary diffusion is the dominant mechanism for high temperature creep of the fine grained garnetite normalized creep strength of the garnetite is found to be comparable to those of feldspar and olivine in diffusion creep regime suggesting that garnetite may not form a strong layer in the subducted oceanic lithosphere if it deforms by grain boundary diffusion creep

groundwater in the celtic regions this book covers a diverse range of hydrogeological environments that occur in the celtic regions of britain and ireland these include hard rock aquifers of lower palaeozoic and precambrian age generally dominated by fracture flow within a shallow zone of weathering carboniferous limestone aquifers often characterized by conduit flows in karstic systems dual porosity permo triassic sandstone aquifers and quaternary deposits many of which form shallow granular aquifers the papers presented here address a number of current issues common to the celtic regions including groundwater protection policies groundwater management in karst aquifers groundwater development in quaternary aquifers groundwater evaluation in data scarce aquifers and groundwater supplies to small island communities

combining multi scale geophysical techniques for robust hydro structural characterisation in catchments underlain by hard rock in post glacial regions summary accurate conceptual models of groundwater systems are essential for correct interpretation of monitoring data in catchment studies in surface water dominated hard rock regions modern ground and surface water monitoring programmes often have very high resolution chemical meteorological and hydrological observations but lack an equivalent emphasis on the subsurface environment the properties of which exert a strong control on flow pathways and interactions with surface waters the reasons for this disparity are the complexity of the system and the difficulty in accurately characterising the subsurface except locally at outcrops or in boreholes this is particularly the case in maritime north western europe where a legacy of glacial activity combined with large areas underlain by heterogeneous igneous and metamorphic bedrock make the structure and weathering of bedrock difficult to map or model traditional approaches which seek to extrapolate information from borehole to field scale are of limited application in these environments due to the high degree of spatial heterogeneity here we apply an integrative and multi scale approach optimising and combining standard geophysical techniques to generate a three dimensional geological conceptual model of the subsurface in a catchment in ne ireland available airborne lidar electromagnetic and magnetic data sets were analysed for the region at field scale surface geophysical methods including electrical resistivity tomography seismic refraction ground penetrating radar and magnetic surveys were used and combined with field mapping of outcrops and borehole testing the study demonstrates how combined interpretation of multiple methods at a range of scales produces robust three dimensional conceptual models and a stronger basis for interpreting groundwater and surface water monitoring data

discovery of sapphirine bearing mg al granulites in the north china craton implications for paleoproterozoic ultrahigh temperature metamorphism abstract we report here for the first time the occurrence of mg al granulites within the khondalite belt of the north china craton and provide robust evidence for extreme crustal metamorphism at ultrahigh temperature uht conditions in this region the uht indicator assemblages in these rocks include equilibrium sapphirine quartz high alumina orthopyroxene sillimanite quartz and high temperature perthites the surrounding khondalites also carry spinel quartz equilibrium assemblage the sapphirines occurring in various microstructural associations are markedly magnesian x mg 0 69 0 77 with a composition varying from 7 9 3 to 2 2 1 end members spinel is a solid solution of mg spinel and hercynite x mg 0 41 0 54 with zno content varying from 0 48 to 1 79 wt garnet shows a compositional range between pyrope and almandine x mg 0 39 0 48 with minor grossular 2 6 3 8 mol and spessartine 0 5 1 8 mol the orthopyroxenes display marked compositional variations in terms of al 2 o 3 content with the core of the medium grained orthopyroxene adjacent to sillimanite in the matrix showing the highest al 2 o 3 content 8 4 wt the history of prograde to peak metamorphism of these rocks is indicated by inclusions of sapphirine spinel quartz and sillimanite within garnet sapphirine formed during the peak stage through the reaction spl qtz sil spr occurrence of sapphirine and quartz inclusions trapped in sillimanite suggests the reaction spr qtz grt opx sil a series of retrograde reactions are observed in these rocks as corona and symplectite textures around early coarse grained minerals such as opx sil qtz crd grt sil qtz crd grt qtz crd opx grt o 2 crd qtz fe 2 o 3 in mag or ilm and finally opx kfs h 2 o bt qtz whereas the stability of sapphirine quartz and orthopyroxene sillimanite quartz in the matrix assemblage suggests t 1000 c and p 10 kbar peak metamorphism conventional geothermobarometric estimates confirm the ultrahigh temperature nature and also trace the retrograde conditions 930 970 c at p 10 kbar al in opx 900 1000 c perthite 930 990 c grt opx and 910 940 c sapphirine spinel electron microprobe dating of monazites in textural association with the uht assemblages yield a sharply defined isochron age of 1917 48 ma which correlates with the 1927 11 ma obtained in a previous study from monazites in the surrounding khondalites carrying spinel quartz assemblage an evaluation of the assemblages and textures using appropriate petrogenetic grids indicate that following peak ultrahigh temperature conditions the rocks underwent initial isobaric cooling and subsequent isothermal decompression and we interpret these trajectories to be part of an overall anti clockwise p t evolution the study area located within the northern margin of the north china craton defines a collisional orogenic belt where continental collision and deep subduction was possibly followed by extensional collapse of the orogen evidence for the extensional phase is provided by the several mafic magmatic intrusives of paleoproterozoic age occurring in the region which suggest a possible link between the thermal anomaly associated with extreme crustal metamorphism in this region with mantle derived magmas the uht metamorphism in north china craton coincided with the assembly of the paleoproterozoic supercontinent columbia

crystal plasticity of natural garnet new microstructural evidence scanning electron microscope sem orientation contrast images of mantle nodules show that garnets contain cellular domains of different crystallographic orientation electron backscatter diffraction shows small crystallographic mismatches

cool season sea level anomalies and storm surges along the u s east coast climatology and comparison with the 2009 10 el nino abstractclimatologies of sea level anomalies 0 05 m and daily mean storm surges 0 3 m are presented for the 1960 2010 cool seasons october april along the east coast of the united states at boston massachusetts atlantic city new jersey sewells point norfolk virginia and charleston south carolina the high sea level anomaly and the number of storm surges among the highest in the last half century during the 2009 10 cool season are comparable during strong el nino cool seasons high numbers of daily storm surges occur in response to numerous east coast extratropical cool season storms and have a positive correlation with the el nino phase of the el nino southern oscillation enso patterns of anomalously high sea levels are attributed to el nino related changes to atmospheric pressure over the gulf of mexico and eastern canada and to the wind field over the northeast u s continental shelf

regional sea level variability and trends 1960 2007 a comparison of sea level reconstructions and ocean syntheses several existing statistical and dynamical reconstructions of past regional sea level variability and trends are compared with each other and with tide gauges over the 48 yr period 1960 2007 partially pre dating the satellite altimetry era evaluated statistical reconstructions were built from tide gauge data tgr and dynamical reconstructions from ocean data assimilation oda approaches although most of the tgrs yield global mean time series of sea level with trends deviating within only 0 1 mm yr 1 the spatial anomalies of the trends deviate substantially between the reconstructions over the period predating altimetry in contrast tgrs match observed regional trend patterns fairly well during the satellite altimetry era tgrs match tide gauge data better than oda results however they exhibit less variability in the open ocean compared to altimetric data over the pre altimetry period all reconstructed regional sea level trend patterns deviate substantially from each other in terms of detrended correlations in this earlier period the reconstructions match tide gauges and each other much better in the pacific than in the atlantic an ensemble of all tgr and oda estimates provides some improvements in correlations and trends to both tide gauges and altimetry nevertheless a lack of independent open ocean sea surface height data predating altimetry makes impossible the validation of the ensemble for pre altimetry open ocean sea level trends and variability estimating regional sea level changes prior to altimetry therefore remains an unsolved challenge

mean sea level variability in the north sea processes and implications mean sea level msl variations across a range of time scales are examined for the north sea under the consideration of different forcing factors since the late 19th century we use multiple linear regression models which are validated for the second half of the 20th century against the output of a tide surge model to determine the barotropic response of the ocean to fluctuations in atmospheric forcing we find that local atmospheric forcing mainly initiates msl variability on time scales up to a few years with the inverted barometric effect dominating the variability along the uk and norwegian coastlines and wind controlling the msl variability in the south from belgium up to denmark on decadal time scales msl variability mainly reflects steric changes which are largely forced remotely a spatial correlation analysis of altimetry observations and gridded steric heights suggests evidence for a coherent signal extending from the norwegian shelf down to the canary islands this fits with the theory of longshore wind forcing along the eastern boundary of the north atlantic causing coastally trapped waves to propagate over thousands of kilometers along the continental slope implications of these findings are assessed with statistical monte carlo experiments it is demonstrated that the removal of known variability increases the signal to noise ratio with the result that i linear trends can be estimated more accurately ii possible accelerations as expected e g due to anthropogenic climate change can be detected much earlier such information is of crucial importance for anticipatory coastal management engineering and planning

north sea storminess from a novel storm surge record since ad 1843 the detection of potential long term changes in historical storm statistics and storm surges plays a vitally important role for protecting coastal communities in the absence of long homogeneous wind records the authors present a novel independent and homogeneous storm surge record based on water level observations in the north sea since 1843 storm surges are characterized by considerable interannual to decadal variability linked to large scale atmospheric circulation patterns time periods of increased storm surge levels prevailed in the late nineteenth and twentieth centuries without any evidence for significant long term trends this contradicts with recent findings based on reanalysis data which suggest increasing storminess in the region since the late nineteenth century the authors compare the wind and pressure fields from the twentieth century reanalysis 20crv2 with the storm surge record by applying state of the art empirical wind surge formulas the comparison reveals that the reanalysis is a valuable tool that leads to good results over the past 100 yr previously the statistical relationship fails leaving significantly lower values in the upper percentiles of the predicted surge time series these low values lead to significant upward trends over the entire investigation period which are in turn supported by neither the storm surge record nor an independent circulation index based on homogeneous pressure readings the authors therefore suggest that these differences are related to higher uncertainties in the earlier years of the 20crv2 over the north sea region

storm surge along the pacific coast of north america storm surge is an important factor that contributes to coastal flooding and erosion storm surge magnitude along eastern north pacific coasts results primarily from low sea level pressure slp thus coastal regions where high surge occurs identify the dominant locations where intense storms make landfall controlled by storm track across the north pacific here storm surge variability along the pacific coast of north america is characterized by positive nontide residuals at a network of tide gauge stations from southern california to alaska the magnitudes of mean and extreme storm surge generally increase from south to north with typically high amplitude surge north of cape mendocino and lower surge to the south correlation of mode 1 nontide principal component pc1 during winter months december february with anomalous slp over the northeast pacific indicates that the dominant storm landfall region is along the cascadia british columbia coast although empirical orthogonal function spatial patterns show substantial interannual variability similar correlation patterns of nontide pc1 over the 1948 1975 and 1983 2014 epochs with anomalous slp suggest that when considering decadal scale time periods storm surge and associated tracks have generally not changed appreciably since 1948 nontide pc1 is well correlated with pc1 of both anomalous slp and modeled wave height near the tide gauge stations reflecting the interrelationship between storms surge and waves weaker surge south of cape mendocino during the 2015 2016 el nino compared with 1982 1983 may result from changes in hadley circulation importantly from a coastal impacts perspective extreme storm surge events are often accompanied by high waves

melt enhanced deformation a major tectonic process convergent tectonics between continental crustal blocks result in deep burial and anatexis of supracrustal rocks anatectic and or mantle derived melts combine to form a melt weakened zone in the thickened lower crust the accumulation of melt eventually leads to crustal failure along melt lubricated shear zones rapid 1 mm yr vertical component movements of large crustal blocks result we refer to these crustal displacements as tectonic surges the melt lubricated shears are characterized by the close association of sheared country rocks with foliated or massive igneous sills and plutons rocks that formed at different crustal levels are juxtaposed across these shear zones one result of surges with large lateral component of movement is metamorphic inversion with high pressure and high temperature metamorphic rocks structurally over lower pressure and temperature assemblages large and rapid vertical surges may displace crust containing abundant melt and may result in high t p including granulite facies metamorphism and preservation of metamorphic textures caused by rapid decompression

fluid flow in crystalline rocks relationships between groundwater spring alignments and other surface lineations at altnabreac united kingdom the strath halladale granite in the region around altnabreac northern scotland united kingdom has been studied with a view to establishing a relationship between the regional distribution of faults and fracture zones surface discharges of groundwater and groundwater flow systems a major component of the groundwater flow is through the rock fractures because of the extensive superficial cover the surface expression of major fractures was difficult to identify from the limited surface exposures geophysical surveys and aerial photography enabled the authors to define lineations which could be related to the presence of fractures the areal distribution of groundwater spring discharges was mapped using thermal infrared line scan techniques the distribution of these springs has been studied to assess their relationships to surface lineaments and to correlations with geophysical and fracture mapping data

variability of winter storminess in the eastern united states during the twentieth century from tide gauges interannual to multidecadal variability of winter storminess in the eastern united states was studied using water level measurements from coastal tide gauges the proximity to the coast of the primary winter storm track in the region allows the use of tide gauges to study temporal modulations in the frequency of these storms storms were identified in high passed detided sea level anomalies in 20 gauges from all coasts of north america to assess variability in winter storminess along particular storm tracks the primary result is a significant multidecadal increase in the number of storms affecting the southeastern united states from the earlytolatetwentiethcentury theauthorsproposethatthischangeisduetoanincreasedtendencyforthejet streamtomeandersouthovertheeasternunitedstatessincethe1950s thismechanismissupportedby longtermchangesin thelarge scalesealevelpressurepatternovernorthamerica thenatureofthemultidecadal change in storm frequency is unclear because limited tide gauge record lengths prevent distinguishing between a trend and an oscillation

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