structural outline of a tertiary basement cored uplift inversion structure in western spitsbergen svalbard kinematics and controlling factors the tertiary fold and thrust belt of spitsbergen can be divided into a western basement involved fold thrust stack and a central eastern foreland fold and thrust belt in western nordenskiold land the first order structure is an ene verging basement cored fold and fault complex involving paleozoic to tertiary strata the northern part reveals an upright monocline geometry of east tilted sedimentary cover units with associated layer parallel to low angle thrusts and folds these structures consist of two populations oriented both parallel to nnw sse and oblique to wnw ese the general structural trend of the fold complex in the central and southern parts of west nordenskiold land the fold complex involves tilted basement cut by steep transverse faults and late normal faults the east limb of the fold complex displays repeated basement and paleozoic strata orustdalen formation in its core and mesozoic triassic strata influenced by map scale chevron folds and two decollement levels all located above an eastward rotated major detachment fault the kleivdalen thrust establishing fold fault relations includes a three stage structural history in the fold complex as follows 1 a phase of early nne ssw shortening associated with wnw ese folds and thrusts and 2 a dominant ene wsw basement involved shortening leading to the first order nnw sse striking fold complex followed by 3 approximately e w extension the resulting structures and structural variability along strike as well as across strike appear to have been controlled by basement and carboniferous basin structures underlying the permian cretaceous platform strata restored stratigraphic sections based on thrust repetition of basement and cover e g within a type section of the carboniferous orustdalen formation support such an interpretation a tentative inversion tectonic model reproduces the position s of local and major thrust ramps and associated folds as a result of inheritance from carboniferous basin structures

evolution of the central tertiary basin of spitsbergen towards a synthesis of sediment and plate tectonic history abstract the central tertiary basin of spitsbergen developed east of a strike slip boundary between the eurasian and greenland plates in response to the initiation of rifting and later seafloor spreading in the norwegian greenland sea using a new plate model for the opening of the north atlantic we attempt to relate the sediment history of the central tertiary basin to its plate tectonic framework and suggest a basin development in four phases the central tertiary basin was formed in the early paleocene during a right lateral strike slip phase after the plate boundary between greenland and svalbard had jumped eastward to the hornsund fault zone phase 1 the onset of seafloor spreading between greenland and eurasia and a drastic counterclockwise change in spreading direction between greenland and north america after chron 25 late paleocene induced compression dominated transpression between greenland and svalbard until chron 24 lower eocene phase 2 the first sedimentary evidence for tectonic uplift along the strike slip zone is found in a wedge shaped delta fan in the northwestern part of the basin strike slip dominated transpression prevailed from chron 24 to chron 21 lower middle eocene contemporaneous with successive basin narrowing and an eastward migration of the depocenter phase 3 after chron 21 lower middle eocene the relative motion between greenland and svalbard first changed to strike slip terminating the transpressional phase and then to transtension after chron 13 lower oligocene phase 4

present day stress orientations adjacent to active strike slip faults california and sumatra present day stress directions interpreted from well bore breakouts adjacent to two crastal scale active strike slip faults the san andreas fault in california and the great sumatran fault in sumatra indicate that the maximum horizontal stress direction sh is oriented at a high angle 70 90 to both faults the regionally defined stress fields spanning these faults show that adjacent young or actively growing folds have formed orthogonal to sh and are therefore in the thrust fault orientation these observations indicate a decoupling of the strike slip and compressional components of the deformation within these broadly transpressive zones borehole breakouts in 118 wells in western california indicate a regionally consistent stress pattern with sh generally oriented ne sw nearly perpendicular 80 90 to the strike of the san andreas fault the orientation of sh nearly perpendicular to the san andreas fault implies low shear stress on the fault and is consistent with geological interpretations of the coast and transverse ranges indicating active compressional deformation fault plane solutions for recent dip slip style earthquakes principal stress directions determined from inversion of earthquake focal mechanisms and induced hydraulic fracture orientations a stress trajectory map for western california is computed using an iterative statistical algorithm in which observed directional data such as breakout directions are used to obtain a model regional stress field analysis of well bore breakouts in 25 wells within the central and southern oil districts of sumatra indicates that the regionally defined sh adjacent to the active great sumatran strike slip fault is oriented at a high angle 70 80 to the fault this orientation of sh is consistent regionally with geologic stress indicators and focal mechanisms of dip slip earthquakes preliminary analysis of the stress field in the vicinity of the philippine and alpine faults suggests sh is also oriented at a high angle to these active strike slip faults similarly the minimum horizontal stress sh is oriented at a high angle to the the kane and dead sea transforms the observation of sh and sh in the vicinity of active strike slip faults being oriented nearly perpendicular and parallel to the faults suggests that large crustal scale strike slip faults may in general be inherently weak surfaces

linked thrust and strike slip faulting during late cretaceous terrane accretion in the san juan thrust system northwest cascades orogen washington the san juan thrust system makes up the western elements of the late cretaceous northwest cascades orogen of washington a stack of metamorphic nappes with terranes ranging in age from early paleozoic to middle cretaceous the tectonic development of the nappes is an unresolved issue important to understanding plate convergent processes operating in the north american cordillera in the creta ceous as well as at other times two terrane bounding fault zones were studied in this project the lopez and the rosario fault zones the fault zone rocks were affected by two cataclastic plastic late cretaceous deformational events d1 and d2 that included accretion and lateral motion during blueschist facies metamorphic conditions d1 produced upright folds and a subvertical axial planar s1 foliation fabric in the lopez fault zone and southwest vergent folds and gently northeast dipping axial planar s1 foliation in the rosario fault zone in the lopez fault zone d2 produced northwest striking and subvertical strike slip shear zones s2 with dominant sinistral displacements whereas in the rosario fault zone d2 generated low angle s2 shear zones and various slip crenulation fabrics formed by northwest directed thrust motion the d1 fabrics are inferred to be related to initiation of subduction related accretion of the nappes by orogen normal southwest northeast shortening and accretionary tectonics the subsequent d2 fabrics developed as temporally overlapping subduction related low angle thrusts in the rosario fault zone and high angle sinistral strike slip faults in the lopez fault zone in an overall transpressive setting due to oblique convergence this model suggests that the high angle lopez fault zone d2 was located above a gently northeast dipping thrust detachment s2 expressed by the rosario fault zone that allowed the accreted nappes to move parallel to the orogen the kinematic model cannot validate regional scale dextral terrane translation of the san juan thrust system as inferred by paleomagnetic data elsewhere in the western united states but addresses important tectonic processes caused by oblique subduction and changing plate conditions

fluid production rate during the regional metamorphism of a pelitic schist phase equilibria modeling of the pressure temperature p t path of regional metamorphism and associated fluid expulsion combined with constraints on the timescale of garnet growth by sm nd geochronology elucidates the fluid production rate and fluid flux during barrovian metamorphism of pelitic rocks from townshend dam vt usa this modeling builds on a published companion study that utilized sm nd geochronology of concentric growth zones in multiple garnet grains to constrain the duration of garnet growth in a large sample of schist at townshend dam to 3 8 2 2 million years gatewood et al chem geol 401 151 168 2015 p t pseudosections combined with observed mineral compositions constrain garnet growth conditions and were utilized to construct p t path dependent thermodynamic forward models these models determine that garnet growth was initiated at 0 6 gpa and 525 c with a roughly linear loading and heating p t trajectory to 0 8 gpa and 610 c loading and heating rates of 2 4 km myear 1 with a range of 1 6 to 5 8 km million year 1 and 23 c million year 1 with a range of 14 to 54 c million year 1 respectively are consistent with model estimates and chronologic constraints for tectono metamorphic rates during orogenesis phase equilibria modeling also constrains the amount of water release during garnet growth to be 0 7 wt or 2 vol largely resulting from the complete consumption of chlorite coupling this estimate with calculated garnet growth durations provides a fluid production rate of 5 2 kg m 3 million year 1 with a range of 3 2 to 12 2 kg m 3 million year 1 and when integrated over the overlying crustal column a regional scale fluid flux of 0 07 0 37 kg m 2 million year 1 this range of values is consistent with those derived by numerical models and theory for regional scale pervasive fluid flow this study signifies the first derivation of a fluid production rate and fluid flux in regional metamorphism using a direct chronology of water producing garnet forming reactions and can provide a framework for future studies on elucidating the nature and timescales of fluid release

modelling an infiltration driven geochemical front modelling of geochemical alteration profiles e g in 18o or 87sr 86sr resulting from fluid infiltration has provided important constraints on the volumes of fluid that move through the crust during metamorphism these models consider that alteration results from a combination of advection with diffusion and or kinetically limited solid fluid exchange models incorporating advection and one of the two broadening mechanisms have analytical solutions whilst the three parameter solution does not given a particular alteration profile it is therefore important from a computational point of view to determine whether use of the more comples three parameter model places tighter limits on the characteristics of the fluid infiltration event in this paper we address this problem through modelling of a measured oxygen isotope alteration profile from naxos greece for each end member model we calculate a set of best fit parameters emphasising which features of the data control the fit of each of the models we then consider numerical solutions which allow all three processes to operate and conduct a grid search in parameter space to map out the structure of the variance between the model and data while it is not possible to distinguish a single combination of the three processes that produces a strong global minimum in variance we can distinguish a family of solutions which are equally valid and we use this minimum variance family to place bounds on the time scales fluid velocity and porosity characteristic of the fluid alteration event

electrical conductivity of mantle clinopyroxene as a function of water content and its implication on electrical structure of uppermost mantle abstract the electrical conductivity of san carlos clinopyroxene aggregates with various water contents were measured under ni nio buffer at 1 5 gpa and 600 1200 k in a dia type apparatus the conductivity increases with increasing water content in clinopyroxene hidden conduction mechanism was detected because of the much smaller iron content in clinopyroxene which was usually covered by small polaron conduction in other nominally anhydrous minerals the identified activation enthalpies ranged from 0 70 0 75 ev to 1 23 1 37 ev our result reveals that the dominant charge carrying species in electrical conductivity could change with temperature and water content at high temperatures relevant to asthenospheric condition activation enthalpy for the conductivity agrees well with that for the hydrogen self diffusion the dominant charge carrier therefore might be m site vacancy however contrary to previous view that all hydrogens contribute to increasing conductivity equally our result shows that only a limited amount 20 40 of hydrogen acts as effective charge carrier in clinopyroxene on the other hand the activation enthalpy for the conductivity at low temperatures is significantly lower than that for the hydrogen self diffusion similar to what has been observed in olivine and orthopyroxene this type of conduction is probably caused by fast diffusion of specific hydrogen or fast hydrogen grain boundary diffusion at low temperatures the proton conduction of clinopyroxene is nearly one order and two orders of magnitude lower than those of olivine and orthopyroxene respectively and tends to converge at high temperatures using the present data combined with conductivity of olivine and orthopyroxene a laboratory based conductivity depth profile in the uppermost mantle shows that hydrous clinopyroxene cannot account for the high conductive regions observed beneath the ocean floor near eastern pacific rise the presence of partial melt would be unavoidable

continent ocean transition at the western barents sea svalbard continental margin the change in crustal type at the western barents sea svalbard margin takes place over a narrow zone related to primary rift and shear structures reflecting the stepwise opening of the greenland sea regionally the margin is composed of two large shear zones and a central rifted margin segment local transtension and transpression at the plate boundary caused the early cenozoic tectonism in svalbard and the western barents sea and might explain the prominent marginal gravity and velocity anomalies

transport properties of olivine grain boundaries from electrical conductivity experiments grain boundary processes contribute significantly to electronic and ionic transports in materials within earth s interior we report a novel experimental study of grain boundary conductivity in highly strained olivine aggregates that demonstrates the importance of misorientation angle between adjacent grains on aggregate transport properties we performed electrical conductivity measurements of melt free polycrystalline olivine fo90 samples that had been previously deformed at 1200 c and 0 3 gpa to shear strains up to 7 3 the electrical conductivity and anisotropy were measured at 2 8 gpa over the temperature range 700 1400 c we observed that 1 the electrical conductivity of samples with a small grain size 3 6 m and strong crystallographic preferred orientation produced by dynamic recrystallization during large strain shear deformation is a factor of 10 or more larger than that measured on coarse grained samples 2 the sample deformed to the highest strain is the most conductive even though it does not have the smallest grain size and 3 conductivity is up to a factor of 4 larger in the direction of shear than normal to the shear plane based on these results combined with electrical conductivity data for coarse grained polycrystalline olivine and for single crystals we propose that the electrical conductivity of our fine grained samples is dominated by grain boundary paths in addition the electrical anisotropy results from preferential alignment of higher conductivity grain boundaries associated with the development of a strong crystallographic preferred orientation of the grains

the margin between senja and spitsbergen fracture zones implications from plate tectonics abstract analysis of multichannel seismic data from the continental margin off svalbard between the senja and spitsbergen fracture zones suggests that the transition between continental and oceanic crust is located at or close to the hornsund fault zone in the late paleocene early eoeene 57 m y the region between svalbard and northeast greenland was subjected to regional shear movements associated with a transform system between the young lofoten greenland basin and the arctic ocean approximately 50 m y ago the spreading axis migrated to the northeast creating a deep basin north of the greenland senja fracture zone forming the passive margin between bear island and 76 5 n north of 76 5 n the regional transform was maintained at the time of the main reorganization of relative plate motion 36 m y the northern margin evolved a continental fragment was possibly cut off from the svalbard margin forming a small microcontinent the microcontinent appears as the submarine ridge which has been associated with the hovgaard fracture zone it is suggested that the sediments west of the hornsund fault zone are not older than eocene in the south and mid oligocene in the north the position of the spreading axis has greatly influenced the margin sedimentation

electrical conductivity measurement of granulite under mid to lower crustal pressure temperature conditions summary we have developed a technique to measure electrical conductivity of crustal rocks with relatively low conductivity and complicated mineral components in order to compare with results given by magneto telluric mt measurements a granulite from hidaka metamorphic belt hmb in hokkaido japan at high temperature and pressure conditions was obtained the granulite sample was ground and sintered under the conditions similar to those of mid to lower crust we have observed smooth and reversible change of conductivity with temperature up to about 900 k at 1 gpa the results were consistent with the electrical conductivity structures suggested by the mt data analysis considering pore fluid conduction mechanism or the role of accessory minerals in the rock the mechanisms of electrical conductivity paths in dry or basic rocks should be reconsidered

fluid flux and reaction rate from advective diffusive carbonation of mafic sill margins in the dalradian southwest scottish highlands abstract greenschist facies mafic sills in the dalradian of the southwest highlands scotland have been carbonated by infiltration of a co 2 bearing hydrous fluid from adjacent calc phyllites the primary amphibole epidote bearing assemblage is preserved in the cores of many sills in which the margins were altered to calcite chlorite and quartz the asymmetric widths of the carbonated margins allow determination of flow direction and magnitude and indicate that sill margins were buffered to nearly constant fluid composition by copious flow in the more permeable phyllites partially carbonated amphibole epi dote assemblages within the reaction fronts preserve evidence for sluggish reaction kinetics downstream margins developed by diffusion against the flow direction and this allows calculation of reaction front broadening due to both diffusion and reaction kinetics an advective diffusive transport model with linear reaction kinetics has been fitted to the reaction progress profile for a sill at port cill maluaig knapdale this implies a cross layer time integrated fluid flux of 62 1 1 3 m 3 m 2 a damkohler number of 22 4 4 2 and a peclet number of 66 2 20 3 1 errors the peclet number and time integrated fluid flux imply that the flow event lasted between 0 02 and 20 ma for plausible porosities in the range 10 3 to 10 6 the inferred rate constant for the reaction kinetics is two or more orders of magnitude slower than that calculated by extrapolation of experimentally determined surface reaction rates either the kinetic dispersion arose from factors additional to reaction kinetics or fluid solid reaction was controlled by a slower mechamism such as diffusion away from flow channels the latter conclusion implicates deformation as an important control on the rates of fluid infiltration and fluid rock reaction

tertiary tectonism and basin inversion of the st jonsfjorden region svalbard abstract deformed basement and cover rocks of the st jonsfjorden area further define the character of spitsbergen s tertiary fold and thrust belt three major thrusts comprise a folded ca n060 e directed foreland propagating thust stack with likely additional subsurface thrust faults the folded vegardbreen robertsonfjellet thrust is the most significant fault in the complex and re emerges in the core of a disrupted synclinal structure in triassic strata shortening across the area indicated from line length restoration is of the order of 13 km differences in stratigraphy between and within thrust sheets indicate the thrust stack initiated along the edge of a westward deepening carbonbiferous basin with a fault step margin and represents basin inversion early structures related to basin formation had a major control on later thrust sheet evolution and the complexity of inversion structures reflects the initial complexity of the basin geometry such basin inversion could characterize the length of the fold and thrust belt the st jonsfjorden structures are primarily contractional and together with areas farther southeast in the fold thrust belt indicate shortening took place perpendicular to the fold belt across much of the length of the evolving margin

tertiary or cretaceous age for spitsbergen s fold thrust belt on the barents shelf several publications propose that main phase fold thrust development on spitsbergen was late cretaceous and not tertiary as previously thought the question of timing is crucial to models for crustal response to transpressive plate motions involvement of tertiary strata in fold thrust structures the sedimentology of the tertiary basin strata and studies of paleo stress field evolution all indicate paleocene to eocene fold thrust development during opening of the norwegian greenland oceanic basin a regional angular unconformity of 1 between paleocene and early cretaceous strata is consistently disconformable to the eye and precludes any significant older deformation in the immediate area pre unconformity deformation was likely strike slip in character and concentrated in the west the proposal for late cretaceous fold thrust belt formation is inconsistent with the geology

oligocene to lower pliocene deposits of the norwegian continental shelf norwegian sea svalbard denmark and their relation to the uplift of fennoscandia a synthesis abstract this study provides the results of the first integrated study of oligocene pliocene basins around norway within the study area three main depocentres have been identified where sandy sediments accumulated throughout the oligocene to early pliocene period the depocentre in the norwegian danish basin received sediments from the southern scandes mountains with a general progradation from north to south during the studied period the depocentre in the basinal areas of the uk and norwegian sectors of the north sea north of 58 n received sediments from the scotland shetland area because of the sedimentary infilling there was a gradual shallowing of the northern north sea basin in the oligocene and miocene a smaller depocentre is identified offshore northern nordland between ranafjorden approximately 66 n and vesteralen approximately 68 n where the northern scandes mountains were the source of the oligocene to early pliocene sediments in other local depocentres along the west coast of norway sandy sedimentation occurred in only parts of the period shifts in local depocentres are indicative of changes in the paleogeography in the source areas in the barents sea and south to approximately 68 n the oligocene to early pliocene section is eroded except for distal fine grained and biogenic deposits along the western margin and on the oceanic crust this margin was undergoing deformation in a strike slip regime until the eocene oligocene transition the early oligocene sediments dated in the vestbakken volcanic province and the forlandssundet basin represent the termination of this strike slip regime the change in the plate tectonic regime at the eocene oligocene transition affected mainly the northern part of the study area and was followed by a quiet tectonic period until the middle miocene when large compressional dome and basin structures were formed in the norwegian sea the middle miocene event is correlated with a relative fall in sea level in the main depocentres in the north sea formation of a large delta in the viking graben frigg area and uplift of the north and south scandes domes in the norwegian danish basin the sorgenfrei tornquist zone was reactivated in the early miocene possibly causing a shift in the deltaic progradation towards the east a late pliocene relative rise in sea level resulted in low sedimentation rates in the main depositional areas until the onset of glaciations at about 2 7 ma when the scandes mountains were strongly eroded and became a major source of sediments for the norwegian shelf whilst the frigg delta prograded farther to the northeast

early crystallization history of alkali olivine basalts diamond craters oregon abstract basaltic lavas form the isolated quaternary volcanic centers of diamond craters and occur at cow lakes in s e oregon the exposed rocks are olivine and plagioclase phyric alkali olivine basalts the holocrystalline groundmasses contain plagioclase titanaugite olivine fe ti oxides and minor apatite and occur in the high alumina greater than 17 petrographic province of the northwestern great basin the whole rock and phenocryst compositions provide enough information to define the equilibrium state of the magmas the solutions to the thermodynamic equations are valid for systems of known bulk composition and can be used to evaluate whether rock compositions are close to magma compositions two of the lavas from diamond craters have whole rock and phenocryst compositions consistent with their being natural melts rock compositions that reflect the effects of crystal separation open systems are recognized by significant differences in predicted versus observed phenocryst modes the p t conditions of phenocryst saturation and the crystallization history of the magmas can be inferred from petrologic data combined with thermodynamic modelling and mass balance constraints the initial melts are inferred to have equilibrated at 0 8 1 0 gpa and 1210 1240 c the majority of the lavas from diamond craters have compositions that reflect olivine and plagioclase crystal separation these lavas can be related to two possible parent rock compositions by small amounts 2 8 by weight of olivine and plagioclase separation

thermal expansion of forsterite at high pressures determined by in situ x ray diffraction the adiabatic geotherm in the upper mantle abstract volumes of forsterite were measured by in situ x ray diffraction at simultaneously high pressures and high temperatures up to 14 gpa and 1900 k in a kawai type multi anvil apparatus by fitting the present data to the mie gruneisen debye thermal equation of state with the results of the previous reliable studies we obtained 0 1 31 1 and q 3 2 1 the logarithmic volume dependence of the thermal expansion coefficient was found to be t 8 4 2 the average temperature derivative of the isothermal bulk modulus in the investigated pressure temperature ranges was found to be kt t p 0 028 1 gpa k the isobaric heat capacity and thermal pressure at high pressure and high temperature were estimated using the present volume data the adiabatic geotherm at the top and base of the uppermost mantle are 0 60 2 and 0 34 2 k km the temperature estimated from the 410 km discontinuity depth and the olivine wadsleyite transition pressure suggests a mantle potential temperature of 1520 40 k

faults shear zones in the earth s mantle abstract geodetic data support a short term continental deformation localized in faults bounding lithospheric blocks whether major faults observed at the surface affect the lithospheric mantle and if so how strain is distributed are major issues for understanding the mechanical behavior of lithospheric plates a variety of evidence from direct observations of deformed peridotites in orogenic massifs ophiolites and mantle xenoliths to seismic reflectors and seismic anisotropy beneath major fault zones consistently supports prolongation of major faults into the lithospheric mantle this review highlights that many aspects of the lithospheric mantle deformation remain however poorly understood coupling between deformation in frictional faults in the uppermost crust and localized shearing in the ductile crust and mantle is required to explain the post seismic deformation but mantle viscosities deduced from geodetic data and extrapolated from laboratory experiments are only reconciled if temperatures in the shallow lithospheric mantle are high 800 c at the moho seismic anisotropy especially shear wave splitting provides strong evidence for coherent deformation over domains several tens of km wide in the lithospheric mantle beneath major transcurrent faults yet it cannot detect narrow strain localization zones or shallowly dipping faults seismic profiling images shallow dipping seismic reflectors in the lithospheric mantle interpreted as the continuation of normal or less frequently inverse faults in the mantle however the nature of these reflectors is poorly understood there is a large discrepancy between the scale at which deformation processes are studied a few kilometers at most due to the limited size of continuous mantle exposures at the earth s surface and the scale inferred for strain localization in the mantle from geophysical observations tens of kilometers combining data on deformation microstructures and crystal preferred orientations in naturally deformed peridotites and seismologic observations allows nevertheless discussing strain localization processes that may play a role on the development of mantle shear zones

variations in the electrical conductivity of the upper mantle beneath north america and the pacific ocean variations in the electrical conductivity of the mantle beneath carty lake in the canadian shield tucson in the southwest united states and honolulu and midway in the north central pacific were determined through the inversion of long period magnetotelluric and geomagnetic depth sounding data inversion of computed response functions is carried out using a minimum structure regularized approach the upper mantle beneath carty lake is approximately an order of magnitude more resistive than the upper mantle beneath tucson and nearly 1 5 orders of magnitude more resistive than honolulu and midway island inversions were also carried out where the minimum structure constraint was removed at known upper mantle discontinuities these models show a jump in conductivity of 1 5 orders of magnitude across the 660 km discontinuity a result that is consistent with laboratory experiments on realistic mantle assemblages mantle conductivity profiles at carty lake are significantly more resistive than those at tucson honolulu and midway to depths of 300 400 km these observations likely reflect differing thermal states the presence or absence of partial melt and volatiles and may also be related to chemical differences between depleted and undepleted upper mantle the observed conductivity variations may be interpreted as lateral variations in temperature partial melt and or dissolved hydrogen in olivine

modeling metamorphic fluid flow with reaction compaction permeability feedbacks existing models of metasomatic flow do not allow for the effect that reaction has on the flow patterns instead it is assumed that the volatiles produced are negligible in volume compared to those infiltrated and that reaction does not modify permeability this is clearly unlikely to be true for infiltration driven decarbonation reactions the rates of porosity creation by reaction and porosity loss by creep have been calculated for a representative volume of calcite quartz wollastonite marble and it is found that even for a weak calcite matrix the rate of porosity generation by reaction is likely to outstrip the collapse of porosity as long as the system is out of equilibrium we have applied a self consistent 1d finite difference model to the reaction of calcite quartz to wollastonite in a 10m thick marble in response to influx of h2o rich fluid with fixed boundary conditions the model allows us to evaluate the effect of reaction on the porosity structure and fluid pressure variation across the layer from which local darcy fluxes can be evaluated the progress of reaction that we model is constrained by hydrological considerations with the requisite parameters recalculated as reaction progresses assuming creep compaction of rock under the stress difference between lithostatic and fluid pressures we fnd that the volume of fluid realised by decarbonation driven by influx of h20 is sufficient to create a back flow so that further advancement of the reaction front is only possible as a result of diffusion of water against the darcy flux the effect of creep driven by differences between fluid pressure and lithostatic pressure is to reduce the permeability of the layer and especially reduce the secondary porosity developed in the zone at and behind the advancing reaction front we predict that in a 3d situation the porous zone of reacted marble becomes a conduit for layer parallel flow and the secondary porosity is infilled by calc silicate minerals due to silica metasomatism

a geophysical interpretation of the secular displacement and gravity rates observed at ny alesund svalbard in the arctic effects of post glacial rebound and present day ice melting summary we have analysed the ny alesund very long baseline interferometry vlbi data over the period 1994 august to 2004 may and we obtain secular displacement rates relative to a nnr nuvel 1a reference frame of 0 2 0 5 mm yr 1 1 7 0 5 mm yr 1 and 4 8 1 1 mm yr 1 for the north east and vertical directions respectively the corresponding global positioning system gps station displacement rates relative to the same reference frame for the north east and vertical directions are 0 2 0 6 mm yr 1 2 3 0 6 mm yr 1 and 6 4 1 5 mm yr 1 at nya1 and 0 1 0 5 mm yr 1 1 6 0 5 mm yr 1 and 6 9 0 9 mm yr 1 at nall where these gps rates were derived from the itrf2000 velocity solution of heflin from the comparison at 25 globally distributed collocated sites we found that the difference in uplift rate between vlbi and gps at ny alesund is mainly due to a gps reference frame scale rate error corresponding to 1 6 mm yr 1 in the gps vertical rates the uplift rate was estimated to be 5 2 0 3 mm yr 1 from the analysis of the tide gauge data at ny alesund hence the uplift rates obtained from three different kinds of data are very consistent each other the absolute gravity ag measurements at ny alesund which were carried out four times period 1998 2002 by three different fg5 absolute gravimeters lead to a decreasing secular rate of 2 5 0 9 gal yr 1 1 gal 10 8 ms 2 in this analysis the actual data obtained from a superconducting gravimeter at ny alesund were used in the corrections for the gravity tide including the ocean tide effect and for the air pressure effect we have

analysis of fault populations in western spitsbergen implications for deformation partitioning along transform margins mesoscale faults expressed in the paleogene central basin and cretaceous basement along the west spitsbergen orogenic belt are used to define the history of continental deformation associated with the development of the transform system that accompanied the opening of the eurasian basin and the norwegian greenland sea a fundamental change in the orientation of faults from dominantly north south in the basal part of the basin to northeast striking in the upper units broadly correlates with a major shift in plate motion during late paleocene early eocene time the two main populations of faults are interpreted as extension fractures that were variably reactivated as shear fractures and formed in response to north south compression followed by northeast southwest compression paleostress stratigraphy or the analysis of striated faults measured in successive stratigraphic units of the central basin corroborates this interpretation and allows a time sequence of paleostress tensors to be defined results show that a late cretaceous early paleocene north south compression consistent with plate motion was followed by three relatively short lived and regionally limited faulting events leading up to a change in plate motion during late paleocene time post chron 25 major transpressive tectonism followed producing northeast trending fractures that were reactivated as dextral and sinistral faults defining a prolate shape paleostress ellipsoid with a horizontal 1 this regionally reproducible tensor consistent with the prediction of dextral transpression along the paleotransform was probably initiated at approximately the paleocene eocene boundary finally a post early eocene deformation pervasively recorded in the study area by an oblate shape paleostress ellipsoid with horizontal 3 is tentatively correlated with the dextral transtension that characterized the post chron 13 opening of the norwegian greenland sea and eurasian basin this study offers documentation of deformation partitioning during the evolution of a transform margin the late cretaceousearliest paleocene compression associated with the prototransform did not involve substantial partitioning and a north south maximum principal stress pervaded the continental crust away from the transform in contrast the late paleocene eocene transpression reflects total partitioning of deformation along the evolved mature transform margin oblique plate motion was presumably partitioned into a strikeslip zone s offshore whereas the onshore central basin recorded only the orthogonal component of oblique convergence and divergence a pattern similar to modern orogenic belts developed in zones of oblique plate motion

eurekan transpressive deformation in the wandel hav mobile belt northeast greenland 1 besides the w e trending kap cannon thrust zone and harder fjord fault zone the 300 km long and nw se striking wandel hav mobile belt represents the third major fault zone in north greenland structural analyses in several areas of this belt suggest that compressive deformation is characterized by transpressive dextral strike slip kinematics this is demonstrated by a combination of folding around w e axes approximately north and south directed reverse faulting and dextral strike slip displacements along nw se trending fault lines the initial formation of the long linear faults is interpreted to be related to deformational events in late paleozoic triassic jurassic and late cretaceous times due to the lack of structural evidence we assume that deformations led to the generation of extension faults which probably were reactivated during dextral strike slip tectonism it is suggested that dextral transpressive deformation was coeval with n s compression at the harder fjord fault zone and cap cannon thrust zone and took place during eocene eurekan times dextral strike slip tectonism in the wandel hav mobile belt was the result of n s compression due to a general northward movement of the greenland plate as a zone of crustal weakness the belt can be interpreted as the onshore equivalent of the main transcurrent fault zone de geer fault which caused the intracontinental dextral slip of svalbard barents shelf relative to north greenland during early tertiary eurekan times and prior to their separation in this configuration it represents one part of the belt of eurekan deformation which extends from the canadian arctic islands over north greenland to the barents shelf where compressive deformation is recorded in the west spitsbergen fold and thrust belt

lineament domain of regional strike slip corridor insight from the neogene transtensional de geer transform fault in nw spitsbergen lineaments on regional scale images represent controversial features in tectonic studies published models explain the presence of the lineament domains in most geodynamic environments as resulting from the enhanced erosion along strikes normal to the upper crustal regional extension despite their success in many tectonic frameworks these models fail to explain the existing lineament domains in the regional strike slip corridors that separate regional blocks including the transform faults the present paper investigates the lineament distribution in such environments and specifically presents the results from a study along the shear corridor of the de geer transform fault in the north atlantic responsible for the separation and drifting away between northern greenland and the svalbard archipelago since oligocene times the study spans from satellite image analysis and outcrop scale investigations to a more regional analysis on a digital bathymetric model of the north atlantic arctic ocean lineaments were automatically detected in the spectral band 8 0 52 0 9 m of a landsat 7 image 15 m pixel resolution a total of 320 image lineaments were extracted from both the regional and the local scale investigations and statistically analyzed results from the multi scalar lineament analyses revealed the existence of a main n s lineament domain regionally persistent from the de geer corridor to the western margin of northern spitsbergen where it relates to the youngest post oligocene tectonics observed onshore this is confirmed by field observations showing that the n s faults represent the youngest brittle deformation system and systematically cut the deformations associated with the building of the tertiary west spitsbergen fold and thrust belt the n s lineament domain is the result of the activity of a larger regional scale tectonic feature nw se oriented and responsible for the localized extension within its deformation corridor the de geer transform fault a model is presented that involves the presence of a thin upper crust with brittle behavior lying above a deeper crustal layer characterized by a more ductile deformation the lower layer suffers more diffuse homogeneous strain this strain is transmitted to the upper brittle layer forming clusters of enhanced fracturing zones aligned following the induced stress trajectories lineaments develop along these weaker fractured zones preferentially etched by erosional processes and align perpendicular to the least horizontal compression sigma3 which in turn forms an angle to the shear kinematics in the western part of spitsbergen this angle is smaller than 45 due to the transtensional tectonic regime the proposed model for lineament domain origin in strike slip environments well integrates the existing models in literature and could be applied to other similar geodynamic contests

3d modelling of electrical anisotropy from electromagnetic array data hypothesis testing for different upper mantle conduction mechanisms abstract upper mantle electrical conductivities provide besides seismic velocities or thermal diffusivities another source of information on upper mantle structure and composition we present the results of a long period magnetotelluric dataset consisting of 64 sites covering an area of 300 km 400 km in central germany mapping electrical conductivities at the base of the lithosphere to seperate the effect of crustal and upper mantle structures we interprete the obtained dataset by 3d conductivity modelling we observe high conductivities and anisotropies at asthenospheric upper mantle depth with main bulk conductivities of 1 2 s m in west east and 4 1 0 3 s m in north south direction differing by about two orders of magnitude in comparing with results from laboratory measurements on electrical conductivites for various conduction mechanisms we are able to confine the conduction mechanisms possibly dominating at these depths with melt volume fractions of 1 only partial melt can be excluded as origin of the high upper mantle conductivities instead conductivity enhancement due to hydrogen diffusion along the olivine 1 0 0 axis is favoured as the dominant conduction mechanism at the base of the lithosphere

water in the mantle results from electrical conductivity beneath the french alps 1 a deep magnetotelluric sounding in the french alps provided a vertical electrical conductivity profile between 200 1000 km two prominent features are observed first the conductivity in the depth range 400 800 km is smaller than the conductivity of a pyrolite mantle obtained from laboratory results for a normal geotherm second the data do not require the conductivity to change throughout the transition zone 410 660 km in this part of the mantle a temperature of 350 450 c less than normal explains the magnetotelluric conductivity profile at 200 400 km our model favors a cold mantle with 1000 1500 ppm of water dissolved in olivine if correct this model suggests that the subducted slab is dehydrated before reaching the transition zone

interdiffusion of h2o and co2 in metamorphic fluids at 490 to 690 c and 1 gpa interdiffusion coefficients have been determined for h 2o co2 mixtures by quantifying the flux of co2 between two fluid filled chambers in a specially designed piston cylinder cell the two chambers which are maintained at 1 0 gpa and at temperatures differing by 100 c each contain the xco2 buffering assemblage calcite quartz wollastonite in h2o the positive dependence of xco2 on temperature results in a down temperature steady state flux of co 2 through a capillary tube that connects the two chambers this flux drives the wollastonite calcite quartz equilibrium to the right in the cooler chamber producing a measurable amount of calcite that is directly related to co2 h2o interdiffusion rates diffusivities calculated from seven experiments range from 1 0 10 8 to 6 1 10 8 m 2 s for mean capillary temperatures between 490 and 690 c the data set can be approximated by an arrhenius type relation d 4 7 10 6 exp 4560 t m 2 s t in k which yields values within a factor of 2 of but slightly lower than diffusivities estimated by application of the stokes einstein relation because rates of h2o and co2 interdiffusion approach within 1 to 2 orders of magnitude rates of heat conduction in rocks rapid co2 h2o interdiffusion should be expected in deep seated fluids wherever gradients in xco2 are imposed by contrasting mineral assemblages considering the small scale heterogeneity of the crust strong gradients in xco2 are probably quite common particularly where different carbonate bearing assemblages are juxtaposed or where they are interlayered with carbonate absent rocks cross layer diffusive mass transfer of co2 and h2o may play an important role in driving dehydration and decarbonation reactions even in the absence of fluid flow copyright 2004 elsevier ltd

reaction induced fracturing during replacement processes replacement processes are common transformation mechanisms in minerals and rocks at a variety of conditions and scales the underlying mechanisms are in general poorly understood but both mechanical and chemical processes are thought to be important replacement of leucite kalsi2o6 by analcime naalsi2o6 h2o is common in silica poor igneous rocks a 10 increase in volume is associated with the replacement process and this generates stresses that eventually cause fracturing of the reacting leucite experimentally reacted leucite samples display characteristic fracturing patterns that include both spalling of concentric onion skin like layers near the reacting interface and the formation of cross cutting often hierarchically arranged sets of fractures that divide the remaining leucite into progressively smaller domains these structures may explain the patchy alteration patterns observed in natural leucite samples and similar so called mesh textures associated with the serpentinization of olivine grains during hydration of mafic or ultramafic rocks they are also strikingly similar to larger scale patterns formed during spheroidal weathering processes a simple discrete element model illustrates the mechanics that control the formation of such systems and shows how these replacement processes may be accelerated due to the generation of new reactive surface area by hierarchical fracturing processes

simultaneous calculation of metamorphic fluid fluxes reaction rates and fluid rock interaction timescales using a novel inverse modeling framework abstract to study metamorphic carbonation at greenschist facies conditions in the sw scottish highlands a novel inverse modeling framework which combines solutions of the transport equation with a global optimization method of differential evolution was developed using this framework we calculated simultaneously time integrated and time averaged metamorphic fluid fluxes of 83 4 35 4 m 3 m 2 and 10 10 1 0 5 m 3 m 2 s 1 respectively a time averaged reaction rate constant of 10 12 7 10 2 m s 1 and comparable timescales for fluid flow and fluid driven reaction of 10 4 3 0 5 yr and 10 2 7 5 2 yr respectively these parameters were calculated using an empirical estimate of the coefficient of molecular diffusion and a calculated value for metamorphic porosity our estimates are 1 consistent with single pass flow of fluid released by metamorphic devolatilization 2 within the range where heat is transported by conduction and matter is transported by advection 3 in agreement with an emerging consensus that metamorphic events are relatively short lived and 4 supportive of applying laboratory based estimates of kinetic parameters to metamorphic systems based on a sensitivity analysis we show that 1 selecting the diffusion coefficient rather than fluid velocity reaction rate or flow duration as an input parameter yields more robust estimates of metamorphic fluid flow parameters and 2 ignoring reaction dependent porosity and reaction rates can result in an order of magnitude uncertainty in best fit flow parameters evaluated from concentration profiles finally similarity between our calculated time averaged metamorphic fluid fluxes which were obtained numerically and those which were obtained analytically confirms the validity of using the quasi stationary state assumption to quantify metamorphic fluid flow parameters

magnetotelluric imaging of lower crustal melt and lithospheric hydration in the rocky mountain front transition zone colorado usa we present an electrical resistivity model of the crust and upper mantle from two dimensional 2d anisotropic inversion of magnetotelluric data collected along a 450 km transect of the rio grande rift southern rocky mountains and high plains in colorado usa our model provides a window into the modern day lithosphere beneath the rocky mountain front to depths in excess of 150 km two key features of the 2d resistivity model are 1 a broad zone 200 km wide of enhanced electrical conductivity 20 m in the mid to lower crust that is centered beneath the highest elevations of the southern rocky mountains and 2 hydrated lithospheric mantle beneath the great plains with water content in excess of 100 ppm we interpret the high conductivity region of the lower crust as a zone of partially molten basalt and associated deep crustal fluids that is the result of recent less than 10 ma tectonic activity in the region the recent supply of volatiles and or heat to the base of the crust in the late cenozoic implies that modern day tectonic activity in the western united states extends to at least the western margin of the great plains the transition from conductive to resistive upper mantle is caused by a gradient in lithospheric modification likely including hydration of nominally anhydrous minerals with maximum hydration occurring beneath the rocky mountain front this lithospheric hydration front has implications for the tectonic evolution of the continental interior and the mechanisms by which water infiltrates the lithosphere

fluid flow and diffusion in the waterville limestone south central maine constraints from strontium oxygen and carbon isotope profiles oxygen carbon and strontium isotopic profiles across the margin of the waterville limestone member are used to investigate advective and diffusive transport during metamorphism of the waterville formation in south central maine usa rb sr isotopic systematics were homogenized on the 10 cm hand specimen scale at ages that are within error of the 366 6 ma rb sr whole rock age of the syn metamorphic hallowell pluton this is consistent with a plutonic heat source for this low pressure andalusite and sillimanite grade acadian metamorphic terrane advective displacements of all three isotope profiles at the garnet grade blue rock quarry indicate fluid flow to the east into the limestone and the oxygen isotope profile implies a time integrated fluid flux of 3 2 1 5 m 3 m 2 2 error this cross layer flux is insufficient to cause the observed reaction progress of the muscovite ankerite quartz to biotite anorthite in plagioclase calcite reaction in the 100 m thick waterville limestone member and much of the fluid flow responsible may have been layer parallel the isotope profiles indicate advective diffusive homogenization over distances of 1 5 m 13 c to 6 m 18 o and such homogenization distances are difficult to reconcile with observations of order of magnitude variations in reaction progression the centimetre scale or less it is possible that infiltration occurred during events short lived compared with diffusion that the reactions started at different temperatures dependent on bulk composition or that diffusion of water from layers with less reactants to layers with more reactants was important in driving the biotite producing reaction however variations of fluid composition inferred from the mineral assemblages are apparently inconsistent with diffusion driving reactions progress and models of precursor assemblages do not indicate significant compositional control of the temperature of the first appearance of biotite in the rocks irrespective of the details of flow and diffusive exchange on the centimetre scale the average reaction progress in the waterville limestone member requires significant layer parallel fluid fluxes

the eurekan deformation in the arctic an outline the evolution of the eurekan deformation zones in the arctic is closely related to the development of the circum greenland plate boundaries in early cenozoic times 53 34 ma mostly the eurekan orogeny or deformation has been interpreted as a predominantly compressive tectonic event but the eurekan deformational history in the arctic was not the result of a single tectonic episode it rather represents a complex sequence of successive tectonic stages which produced a number of intra continental deformation zones with changing sometimes opposing lateral oblique and convergent kinematics in the canadian arctic archipelago north and ne greenland and svalbard the interaction between the continental plates especially in combination with the development of transform faults resulted onshore in the formation of several complex deformation zones and areas of eurekan deformation the eurekan deformation can be divided into two major tectonic stages the first phase in the early eocene was dominated by orthogonal compression in the west spitsbergen fold and thrust belt along the west margin of the barents shelf and contemporaneous sinistral strike slip tectonics along the wegener fault and on ellesmere island whereas the second phase in the late eocene was characterized by dextral strike slip and compression on ellesmere island and contemporaneous dextral transpression and transtension along the de geer fracture zone or hornsund fault complex between ne greenland and spitsbergen

transport mechanisms by fluid flow in metamorphic rocks oxygen and strontium decoupling in the trois seigneurs massif a consequence of kinetic dispersion

determination of time integrated metamorphic fluid fluxes from the reaction progress of multivariant assemblages an expression is derived for the calculation of time integrated metamorphic fluid fluxes in two or more dimensions in rocks undergoing multivariant reactions under conditions of varying pressure temperature and angle of flow this calcuation requires knowledge of mineral assemblages modes and compositions which are obtained from isobaric t xco2 pseudosections constructed using the program thermocalc and compared with those observed in east central vermont thermocalc is capable of reproducing peak mineral assemblages modes compositions and the observed reaction sequences within the system kcanafmasch for two kyanite grade pelitic carbonate rocks from a barrovian style regional metamorphic terrain in east central vermont u s a calculation of fluid fluxes for decarbonation reactions under conditions of horizontal layer parallel flow produces time integrated fluid flux figures of the order of 108 moles m 2 allowance for possible cross layer flow from adjacent dehydrating pelites reduces this figure significantly with episodic cross layer fluxes of the order of 105 moles m 2 being capable of driving the observed decarbonation chlorite bearing carbonate protoliths would have initially dehydrated with increasing temperature a process requiring down temperature fluid flow to produce the assemblages currently observed

electrical conductivity of stishovite as a function of water content abstract the electrical conductivity of stishovite with various al2o3 and h2o contents was measured at 12 gpa of pressure p and temperatures t up to 1900 k in a kawai type multi anvil apparatus starting materials were pre synthesized at 12 gpa and 1673 k from various mixtures of sio2 al2o3 and al oh 3 the synthesized stishovite aggregates contained various h2o concentrations up to 0 25 wt the conductivity of relatively dry stishovite was almost constant independently of al content whereas the conductivity significantly increased with increasing h2o content in stishovite all electrical conductivity data fit the formula for electrical conductivity 0 c w exp h 0 c w 1 3 kt where 0 is the pre exponential term cw is the h2o concentration h0 is the activation enthalpy at very low h2o concentration and k is the boltzmann constant the activation enthalpy decreased from 1 22 to 0 90 ev with increasing h2o content from 0 01 to 0 22 wt a nearly linear correlation of the conductivity values on the h2o content suggests that the dominant mechanism of charge transport in stishovite is proton conduction although electrical conductivity of hydrous stishovite is higher than that of garnet in the subducted oceanic crust small amount of hydrous stishovite is insufficient to raise conductivity on the other hand hydrous stishovite can contribute to the high conductivity occasionally observed at the mantle transition zone if the subducted archean continental crusts with tonalite trondhjemite granodiorite ttg composition were accumulated above the 660 km seismic discontinuity

natural constraints on metamorphic reaction rates abstract quantitative constraints on the rates at which metamorphic reactions proceed in nature are now available from several sources most common are predictions made on the basis of laboratory kinetic data however the applicability of such laboratory based predictions has long been questioned and many observations in the field now suggest much slower rates here published quantitative field based constraints on high temperature 400 c reaction rates are assembled from a variety of sources reaction rates attending regional metamorphism are four to seven orders of magnitude slower than most laboratory based predictions a general rate law for regional metamorphism has been derived which best describes these field based data log 10 r net 0 0029 t 9 6 1 where r net is the net reaction rate g cm 2 a and t is temperature c at the same time natural reaction rates attending contact metamorphism differ from laboratory based predictions by less than two orders of magnitude and are in close agreement at higher temperatures thus while existing laboratory based kinetic data may be judiciously applied to some contact metamorphic systems laboratory based kinetic predictions clearly misrepresent regional metamorphism to explain this kinetic discrepancy regional metamorphic reaction rates may be limited by slow intergranular transport due to comparatively limited or transient availability of aqueous fluid in the intergranular medium the general field based rate law may be applied to regional metamorphic and other environments i e ultrahigh pressure or ultrahigh temperature metamorphism if similar system characteristics mainly low aqueous fluid content can be inferred

quantification of carbon dioxide sourced by mineral reactions in ultradeep sedimentary basins abstract the accumulation of co 2 in some natural gas fields represents a risk for exploration and calls for a way of integrating its occurrence in basin modelling among several possible sources we investigate mineral reactions able to take place within bottom sediments of particularly deep and hot sedimentary basins i e at conditions of low grade metamorphism up to 500 c and 2500 bar these reactions involve lithologies where carbonate and alumino silicate minerals are combined to form a mixed composition for appraising decarbonation quantitatively we propose a method founded on thermodynamic calculations that follows a modelling approach commonly used in metamorphic petrology at given bulk composition and temperature pressure t p conditions the composition and proportions of solid and fluid phases that coexist at equilibrium are computed using a gibbs energy minimization gem algorithm on the basis of r g berman s database we incorporate thermodynamic parameters for a variety of solid solutions including clay minerals and for a ch 4 co 2 h 2 o fluid mixture represented by the cpa electrolyte equation of state a large range of decarbonation reactions is explored through a systematics involving 85 model compositions and a unique t p path typical of the targeted basins we confirm that pure carbonate lithologies do not behave as co 2 source in the conditions explored in contrast we demonstrate that mixed compositions are likely to yield co 2 from successive mineral reactions in which clay minerals play a prominent role we also show that the temperature of incipient decarbonation staggered over 325 425 c depends on the ca mg fe composition ratio of the bulk sediment co 2 prone reactions occurring from a selection of natural sediments are then presented the co 2 prolific character of particular facies associated to the rift phase of a basin evolution is illustrated notably in the case of lacustrine oil shales finally we indicate a protocol that integrates the decarbonation scheme derived from thermodynamics into a co 2 generation formalism compatible with the usual formalism of a basin model

tertiary west spitsbergen fold and thrust belt on broggerhalvoya svalbard structural evolution and kinematics the tertiary fold and thrust belt on broggerhalvoya is characterized by a ne vergent pile of nine thrust sheets the basal sole thrust of the pile is located in precambrian phyllites and climbs up section to the ne the lower thrust sheets consist predominantly of post caledonian cover sediments two thrust sheets in the central part of the pile contain a syncline and anticline on a kilometer scale the kilometer scale fold is cut by juxtaposed thrusts giving rise to the formation of four structurally higher basement dominated thrust sheets a five stage kinematic model is proposed 1 in sequence foreland propagating formation of the lower thrust sheets with ramp flat geometries in response to n s subhorizontal bedding parallel movements 2 change in tectonic transport to more east northeasterly directions and first out of sequence thrusting inversion and uplift of the basement in the hinterland formation of the kilometer scale fold structure 3 truncation of the kilometer scale fold by a thrust fault and stacking of the highest basement dominated thrust sheets by hindward propagating mode of thrust generation 4 n s extension due to extensional collaps of the stack 5 w e extension the strain of the thrust sheets is predominantly compressive with the exception of the structurally highest thrust sheet reflecting a temporal change to a more transpressive regime ramping of some thrust faults is suggested to be in part controlled by reactivated carboniferous normal faults the basal sole thrust of the thrust sheet stack also follows the trend of the kongsvegen fault which showed enhanced activity during late mesozoic early tertiary extension the curvature of the west spitsbergen fold and thrust belt on broggerhalvoya is interpreted to be controlled mainly by oblique ramping on the kongsvegen fault associated with pinning on the nordfjorden block as well as by along strike lithological and thickness variations of the post caledonian strata in addition this suggests that pre existing structures have controlled the tertiary geometry the temporal change in the kinematics during thrust tectonics can be linked with the plate tectonic framework in the arctic during tertiary times

discussion on pre ocean opening compression of the northwestern atlantic margin evidence from eastern greenland journal vol 157 2000 707 710 scientific editing by nick rogers h d maher jr s bergh alvar braathen write manby lyberis 2000 argue for a cretaceous palaeocene age and a convergent setting for both the fold structures of the wandel sea basin and for the west spitsbergen fold thrust belt as an alternative to models of decoupling during palaeocene eocene transpressive motions between greenland and the barents shelf in this context we discuss evidence on the timing and kinematics of the west spitsbergen fold thrust belt and constraints on the timing of deformation in the wandel sea basin multiple lines of evidence constraining the timing of fold thrust formation in spitsbergen are discussed in maher et al 1995 and clearly indicate major fold thrust development in the palaeocene eocene space limitations prevent their description here the nature of additional late cretaceous deformation on spitsbergen is another question it is partly constrained by the unconformity at the base of the tertiary sequence which is well exposed in many places and is consistently disconformable to the eye this unconformity involves differential uplift to the north with a regional tilt of a degree or less has a character inconsistent with previous fold thrust development along the islands western margin and can be related to a second pulse within the high arctic large igneous province maher 2001 more recent work confirms a palaeocene eocene age for the spitsbergen contractional structures manby lyberis refer to blythe kleinspehn 1998 as indicating a late cretaceous age for spitsbergen fold thrust belt uplift in their summary figure blythe kleinspehn indicate uplift and erosion of source terranes initiating at 70 ma and continuing until c 43 ma six detailed thermal histories generated from track length modelling of samples taken from the tertiary foreland basin sediments provide particular insight as the authors note three samples with depositional ages of

simple models of co2 release from metacarbonates with implications for interpretation of directions and magnitudes of fluid flow in the deep crust simple one dimensional models of coupled advection hydrodynamic surroundings can account for basic t fluid composition reaction dispersion reaction are used to investigate processes of co2 release progress relationships observed in much of the acadian orogen of from metacarbonate beds during deep crustal 8 kbar acadian new england the results provide an alternative to up t flow prograde metamorphism in new england usa two broad models scenarios that account for these relationships by large pervasive in which reaction progress is controlled by gradients in h2o co2 horizontal fluid fluxes up regional t gradients fluid composition between diverent rock types are presented in the first divusional exchange of volatiles across lithologic contacts is significant co2 generated during prograde temperature t rise is transported away from metacarbonate layers to surrounding 1 metapelitic layers which generate h2o by dehydration and or 2 key words metamorphism fluid flow flow direction carbon dioxide

electrical lithosphere beneath the kaapvaal craton southern africa 1 a regional scale magnetotelluric mt experiment across the southern african kaapvaal craton and surrounding terranes called the southern african magnetotelluric experiment samtex has revealed complex structure in the lithospheric mantle large variations in maximum resistivity at depths to 200 250 km relate directly to age and tectonic provenance of surface structures within the central portions of the kaapvaal craton are regions of resistive lithosphere about 230 km thick in agreement with estimates from xenolith thermobarometry and seismic surface wave tomography but thinner than inferred from seismic body wave tomography the mt data are unable to discriminate between a completely dry or slightly damp a few hundred parts per million of water structure within the transitional region at the base of the lithosphere however the structure of the uppermost 150 km of lithosphere is consistent with enhanced but still low conductivities reported for hydrous olivine and orthopyroxene at levels of water reported for kaapvaal xenoliths the electrical lithosphere around the kimberley and premier diamond mines is thinner than the maximum craton thickness found between kimberley and johannesburg pretoria the mantle beneath the bushveld complex is highly conducting at depths around 60 km possible explanations for these high conductivities include graphite or sulphide and or iron metals associated with the bushveld magmatic event we suggest that one of these conductive phases most likely melt related sulphides could electrically connect iron rich garnets in a garnet rich eclogitic composition associated with a relict subduction slab

tectonic inversion in the wandel sea basin a new structural model of kilen eastern north greenland the seminunatak kilen in eastern north greenland with its complexly deformed carboniferous cretaceous strata is a key area to understand the tectonic history of the transform plate boundary between eastern north greenland and svalbard detailed 3 d geological mapping from oblique photogrammetry along with limited ground fieldwork and interpretation of previously published data forms the basis for a new structural model of kilen previous structural models interpreted rhombic shaped fault patterns as the evidence for strike slip tectonics these structures are here interpreted to be the result of a post coniacian ne sw extension with nw se trending normal faults followed by later n s compression of presumable paleocene eocene age folding the faults passively and suggesting the presence of a basal detachment furthermore two thrust sheets have been distinguished on kilen a lower kilen thrust sheet and an upper hondal elv thrust sheet separated by a subhorizontal fault the central detachment the style of deformation and the structures described are interpreted as the result of paleocene eocene n s directed compression resulting in basin inversion with strike slip faults only having minor status this indicates that the greenland margin as exposed on kilen and the conjugate svalbard margin in the west spitsbergen fold and thrust belt are more similar than previously anticipated

grain scale stable isotope disequilibrium during fluid rock interaction 2 an example from the penninic austroalpine tectonic contact in eastern switzerland at the tectonic contact between the penninic platta nappe and the lower austroalpine err unit in eastern switzerland carbon and oxygen isotope fronts are preserved at the interface of serpentinites and low grade regional metamorphic metacarbonates the carbon and oxygen isotope compositions of calcite are delta 13 c 2 3 per mil pdb and delta 18 o 21 0 per mil smow in the unaltered metacarbonates at a distance of about 20 m from the lithologic contact and they are delta 13 c 0 0 per mil and delta 18 o 14 0 per mil at the metacarbonate serpentinite interface the concomitant shift in the oxygen isotope composition of quartz is from 24 0 to 17 0 per mil a peculiarity of the isotope pattern is the systematic variation of the quartz calcite oxygen isotope fractionations across the isotopic front quartz calcite fractionations are relatively small nearly equal 3 0 per mil in the unaltered metacarbonate and at the metacarbonate serpentinite interface and they increase in the transitional zone in between with a maximum of 7 1 per mil at a distance of about 2 m from the contact this pattern is interpreted as a result of advective dispersive material transport across the lithologic contact and coupled first order kinetic mineral fluid exchange the oxygen isotope systematics indicate that calcite fluid isotope exchange was fast and local calcite fluid equilibrium prevailed during fluid rock interaction in contrast quartz fluid exchange was relatively sluggish and the quartz calcite oxygen isotope fractionations deviated significantly from their equilibrium values front geometries suggest that dispersive processes contributed substantially to material transport across the metacarbonate serpentinite contact cross layer advective flow was minor with a maximum time integrated volumetric flux of 21 m 3 m 2 from the influence of quartz fluid exchange kinetics on the intermineral fractionations quantitative relations among transport velocities the rates of mineral fluid exchange and the duration of fluid rock interaction are derived these relations are then combined with geologic and experimental data to identify feasible scenarios of fluid rock interaction

olivine hydration in the deep upper mantle effects of temperature and silica activity 1 although water controls the biology and geology of the surface hydrogen is perhaps the most poorly constrained compositional variable in the bulk earth its concentration in the upper mantle appears to be controlled by its solubility as hydroxyl in the nominally anhydrous silicate phases olivine pyroxene garnet wadsleyite and ringwoodite here we describe a series of experiments showing that the solubility of h2o in olivine at 12 gpa increases with temperature to 8900 ppm by weight at 1250 c and decreases at higher temperature with the onset of melting sample characterization by infrared spectroscopy indicates that the primary hydration mechanism is the substitution of 2h for mg2 similar results obtained from samples coexisting with clinohumite low silica and with clinoenstatite high silica indicate that silica activity has minimal effect on hydration under these conditions single crystal x ray diffraction measurements constrain the volume of hydration and indicate significant m site vacancies hydrogen thus appears to become a geochemically compatible element as depths approach 400 km

transform normal extension and asymmetric basins an alternative to pull apart models continental transforms are commonly associated with relatively small scale pull apart basins however much larger scale basins which are not consistent with the pull apart model commonly exist adjacent to transforms structures associated with several basins along the dead sea rift and el pilar fault illustrate this these basins are remarkably asymmetric bounded by essentially linear transform segments on one side and subparallel normal faults on the other suggesting simultaneous strike slip motion and transform normal extension this observation which is incompatible with classical faulting theory can be explained along divergent plate boundaries if the transform fault is much weaker than the adjacent crust analysis of the orientation of the horizontal principal stress direction near a weak transform fault embedded in an otherwise strong crust shows that convergent and divergent plate motion results in a stress field characterized by nearly fault normal compression and extension respectively structural styles along the san andreas dead sea and el pilar transform systems show that predictable changes between these two states have occurred through time along strike of the transforms

seo3 a new model of olivine electrical conductivity summary standard electrical olivine 3 seo3 is a new model of electrical conductivity for olivine as a function of temperature and oxygen fugacity and is based on a previous study of point defect behaviour in a dunite that study produced quantitative estimates of mobility and concentration for small polarons and magnesium vacancies as a function of temperature and oxygen fucacity unlike earlier so1 and so2 models of olivine conductivity the dunite sample was buffered by pyroxene and avoided alteration at high temperature the low temperature extrapolation produced by seo3 is in good agreement with so2 while the high temperature extrapolation is significantly more conductive which is in general agreement with many field studies that show the earth s upper mantle to be more conductive than predicted by so2 for reasonable temperatures plausible variations in mantle oxygen fugacity correspond to about half an order of magnitude variation in electrical conductivity equivalent to about 100 degrees in temperature

pressure effect on electrical conductivity of mantle olivine abstract we report new measurements of electrical conductivity of olivine that were made in a multi anvil press using solid buffers mo moo2 to stabilize oxygen partial pressure the temperature range was 1000 c 1400 c and the pressure range was 4 10 gpa when pressure effects are interpreted as activation volumes in the arrhenius equation they yield values of order 0 6 0 6 cm3 mole values of the pre exponential factor 0 are of the order of hundreds of s m and the zero pressure activation energy is about 1 5 ev in agreement with laboratory measurements at lower pressure conditions in addition we analyzed older literature data which produced a similar result but with larger variation the common practice of assuming that the pressure effect on electrical conductivity of olivine in the earth s upper mantle depends weakly on pressure has rested on uncertain grounds these new observations suggest that for upper mantle conditions depths of 80 200 km neglecting pressure effects on olivine conductivity is justified a weak pressure effect also supports the small polaron fe3 model as the dominant conduction mechanism although the mainly positive activation volumes argue for a component of lattice deformation when applied to the depth range 200 400 km in the earth the laboratory data yield conductivities of order 10 2 s m slightly lower than the range of geophysical conductivity profiles but well within this range after allowing for probable effects of oxygen activity and temperature uncertainty

svartfjella eidembukta and daudmannsodden lineament tertiary orogen parallel motion in the crystalline hinterland of spitsbergen s fold thrust belt within metamorphic basement rocks of the hinterland of spitsbergen s tertiary fold thrust belt a 35 km long zone of notably deformed carboniferous strata and cretaceous intrusives forms a major orogen parallel lineament from svartfjella to eidembukta to daudmannsodden sedl orientations and geometries of map scale fault duplexes and associated fault plane striae populations of folds and associated cleavage and of tension gashes all indicate orogen parallel motion occurred along the sedl structural analyses indicates three phases 1 ene directed overthrusting 2 sinistral motion with a backthrust component and 3 dextral strike slip motion this history indicates a change from orogen perpendicular to orogen parallel movements orogen parallel movement was likely coeval with orogen perpendicular fold thrust transport to the ene in the foreland a model where dextral transpressive motion between greenland and svalbard was decoupled explains the hinterland foreland difference basement fabric aligned with carboniferous carbonates on the steep foreland face of an antiformal stack provided a through going weak surface a prerequisite for decoupling sinistral orogen parallel motion is explicable by short lived episode of sinistral plate motion or by local wedge extrusion during dextral transpression the evolution of decoupling patterns has significant implications for deducing plate motions from local kinematic and paleostress studies

thrust tectonics on broggerhalvoya and their relationship to the tertiary west spitsbergen fold and thrust belt the tertiary fold and thrust belt on broggerhalvoya is characterized by a ne vergent pile of nine thrust sheets the sole thrust of the pile is located in precambrian phyllites and climbs up section to the northeast four lower thrust sheets consisting predominantly of upper palaeozoic sediments are overlain by two thrust sheets in the central part of the stack which contain a kilometre scale syncline and anticline the fold is cut by juxtaposed thrusts giving rise to the formation of three structurally higher basement dominated thrust sheets a multiple stage kinematic model is proposed including 1 in sequence foreland propagating formation of the lower thrust sheets in response to n s subhorizontal bedding parallel movements 2 a change in tectonic transport to ene and out of sequence thrusting and formation of the kilometre scale fold structure followed by 3 truncation of the kilometre scale fold and stacking of the highest basement dominated thrust sheets by hind ward propagating out of sequence thrusting the strain of the thrust sheets is predominantly compressive with the exception of the structurally highest thrust sheets reflecting a temporal change to a more transpressive regime thrusting was followed by 4 n s extension and 5 w e extension comparison of the structural geometry and kinematic evolution of broggerhalvoya with the data reported for the fold belt further south allows us to assume a coeval evolution with the fold belt a latest paleocene early eocene age for the main phase of thrusting is suggested for the west spitsbergen fold and thrust belt the main phases therefore pre date the separation of svalbard and greenland due to right lateral movements along the hornsund fault zone the fold belt s temporal evolution followed by the formation of the forlandsundet graben can be linked with the plate kinematic framework in the span between latest paleocene and middle eocene times

lateral asthenospheric viscosity variations and postglacial rebound a case study for the barents sea the effect of lateral asthenospheric viscosity variations on observable signatures related to postglacial rebound in the barents sea is studied using a finite element approach to discretize the problem a comparison between a laterally homogeneous reference earth model and a laterally heterogeneous earth model is performed the results indicate that a change in asthenospheric viscosity of about three orders of magnitude influences predictions of land uplift up to 10 20 m present day velocities up to 0 5 1 5 mm a and present day gravity anomalies up to 0 4 0 8 mgal in the northwestern part of the barents sea region

fluid flow and chemical reaction kinetics in metamorphic systems the treatment and effects of chemical reaction kinetics during metamorphism are developed along with the incorporation of fluid flow diffusion and thermal evolution the interplay of fluid flow and surface reaction rates the distinction between steady state and equilibrium and the possible overstepping of metamorphic reactions are discussed using a simple analytic model this model serves as an introduction to the second part of the paper which develops a reaction model that solves the coupled temperature fluid flow chemical composition differential equations relevant to metamorphic processes consideration of stable isotopic evidence requires that such a kinetic model be considered for the chemical evolution of a metamorphic aureole a general numerical scheme is discussed to handle the solution of the model the results of this kinetic model allow us to reach several important conclusions regarding the factors controlling the chemical evolution of mineral assemblages during a metamorphic event 41 refs 19 figs 5 tabs

lime silicates in amoeboid olivine aggregates in carbonaceous chondrites indicator of nebular and asteroidal processes mno feo ratios in olivine from amoeboid olivine aggregates aoas reflect conditions of nebular condensation and can be used in concert with matrix textures to compare metamorphic conditions in carbonaceous chondrites lime low iron mn enriched olivine was identified in aoas from y 81020 co3 05 kaba cv 3 1 and in y 86009 cv3 y 86751 cv3 nwa 1152 cr cv3 but was not identified in aoas from efremovka cv3 1 3 4 or allende cv 3 6 according to thermodynamic models of nebular condensation lime olivine is stable at lower temperatures than mn poor olivine and at low oxygen fugacities dust enrichment 95 in our study whereas efremovka aoas are slightly fe rich fo 92 aoa olivines from kaba are mostly forsteritic but rare fe rich olivine precipitated from an aqueous fluid a combination of precipitation of fe rich olivine and diffusion of fe into primary olivine grains resulted in iron rich compositions fo97 59 in allende aoas variations from fine grained nonporous matrix toward higher porosity and coarser lath like matrix olivine can be divided into six stages represented by 1 y 81020 efremovka nwa 1152 2 y 86751 lithology b 3 y 86009 4 kaba 5 y 86751 lithology a 6 allende these stages are inferred to represent general degree of metamorphism although the specific roles of thermally driven grain growth and diffusion versus aqueous dissolution and precipitation remain uncertain

lithospheric anisotropy structure inferred from collocated teleseismic and magnetotelluric observations great slave lake shear zone northern canada 1 accurate interpretation of sks shear wave splitting observations requires inherently indeterminate depth information magnetotelluric electrical anisotropies are depth constrained and thereby offer possible resolution of the sks conundrum mt and teleseismic instruments deployed across the great slave lake shear zone northern canada investigated lithospheric anisotropy and tested a hypothesis that seismic and electrical anisotropy obliquity can infer mantle strain shear sense lithospheric mantle mt strike n60 e differs significantly from crustal mt strike n30 e sks splitting vectors outside the shear zone exhibit single layer anisotropy with fast axis parallel to upper mantle mt strike and oblique to present day plate motion n135 w back azimuth sensitivity at sites within the 30 km wide shear zone imply more complex layering with two layer inversion yielding an upper layer of n20 e and a lower layer of n66 e the mt data help to constrain the depth location of sks anisotropy and taken together support a model of fossil lithospheric anisotropy

formation of wollastonite by chemically reactive fluid flow during contact metamorphism mt morrison pendant sierra nevada california usa quartz calcite sandstones experienced the reaction calcite introduction quartz wollastonite co2 during prograde contact metaflow of chemically reactive fluid may control the minmorphism at p 1500 bars and t 560 c rocks were in eralogy stable isotope composition and trace element equilibrium during reaction with a co2 h2o fluid with xco2 chemistry of rocks during contact metamorphism e g 0 14 the transition from calcite bearing wollastonite free to labotka et al 1988 jamtveit et al 1992a 1992b nabelek wollastonite bearing calcite free rocks across the wollastonite isograd labotka 1993 bowman et al 1994 roselle et al is only several millimeters wide the wollastonite forming reaction 1999 a number of aspects of metamorphic fluid flow was driven by infiltration of quartz calcite sandstone by chemically however remain the subject of debate including the reactive h2o rich fluids and the distribution of wollastonite directly direction of flow labotka et al 1988 ferry dipple images the flow paths of reactive fluids during metamorphism the 1992 ferry 1995a hanson 1995a whether numerical mapped distribution of wollastonite and modeling of an o isotope models that assume uniform rock properties adequately profile across a lithologic contact indicate that the principal direction predict the geometry of fluid flow in aureoles that contain of flow was layer parallel directed upward with any cross layer a variety of anisotropic structural features hanson 1992 component of flow 0 1 of the layer parallel component fluid 1995b cook et al 1997 and the degree to which local flow was channeled at a scale of 1 100 m by pre metamorphic mineral fluid equilibrium is attained lasaga rye dikes thrust and strike slip faults fold hinges bedding and 1993 bolton et al 1999 lasaga et al 2000 these and stratigraphic contacts limits on the amount of fluid based on related questions were addressed in an investigation of minimum and maximum estimates for the displacement of the contact metamorphism in the mt morrison pendant wollastonite reaction front from the fluid source are 0 7 1 9 eastern sierra nevada california the location is an 10 cm fluid cm rock the sharpness of the wollastonite isograd exceptional site for the study of metamorphic fluid flow the consistency of mineral thermobarometry the uniform measured for several reasons first the mt morrison sandstone o o fractionations between quartz and calcite and model the focus of this study is ideal for application of concalculations all argue for a close approach to local mineral fluid tinuum models of coupled fluid flow and reaction because equilibrium during the wollastonite forming reaction it is unusually homogeneous in mineralogy and texture

reexamination of magnetotelluric responses and electrical anisotropy of the lithospheric mantle in the grenville province canada magnetotelluric mt responses at the proterozoic grenville front in canada have been interpreted as being caused by lithospheric electrical anisotropy and the area is often noted as a classic example of lithospheric anisotropy this study reevaluates evidence for the electrical anisotropy using 56 mt stations the spatially uniform mt responses noted at the grenville front extend to 200 km southeast and for at least 400 km along strike and are associated with rocks at less than 150 km depth examination of induction arrows at longer periods shows arrows at high angle to the mt conductive direction consistent with the presence of macroscopic resistivity structures new 2 d anisotropic inversions show that electrical anisotropy is not required to fit the mt data the results indicate that in the resistive mantle lithosphere beneath the grenville front and in conductive lithosphere in adjacent areas the maximum horizontal resistivity anisotropy is 10 much less than the factor of 15 determined in earlier 1 d studies the results suggest that the upper lithospheric mantle in the area is devoid of significant electrical anisotropy and that the observed mt response directionality is due to large scale resistivity structure we interpret the spatially consistent mt responses observed at the grenville front as being associated with the resistive archean lithosphere extending southeast beneath the grenville front the obliquity between seismic and mt responses arises because the superior fabric is oblique to the seismic fast direction if dextral shearing occurred it appears to have not caused any significant shape preferred electrical anisotropy

the effects of solid solution and diffusion on infiltration driven metamorphism with application to metaperidotite val d efra central swiss alps the complication introduced by solid solutions in the analysis of infiltration driven mineral reactions is that the mole fraction of tracer component i in fluid xi changes with reaction progress the effect was incorporated into transport models for coupled fluid flow and mineral reaction by parameterizing the relation between xi and with specific reference to carbonation and hydration during regional metamorphism of the peridotite body in val d efra whose constituent minerals are all solid solutions infiltration of a disequilibrium fluid produces a single sharp reaction front if rock is assumed uniform in composition the reaction front separates completely unreacted rock downstream from rock upstream with at a steady state limit ss max that depends on input fluid composition max is the maximum possible value novel phenomena develop however if the flow medium like the metaperidotite body is composed of many small domains that differ in initial mineral modes and compositions but with xi homogenized at a spatial scale larger than the size of the domains e g by diffusion in this case infiltration of a disequilibrium fluid produces up to as many different reaction fronts along the flow path as there are domains with 0 ss in all domains except upstream from the slowest moving front where ss in all domains measured values of in the metaperidotite all 0 max are best reproduced by down temperature infiltration of a disequilibrium fluid with x text co 2 0 1 9 6 into a multi domain medium with uniform x text co 2 at each spatial point along the flow path homogenized across the domains at the m scale by diffusion and time integrated fluid flux 1 836 mol fluid cm2 rock results resolve the paradox of the widespread spatial distribution of reactants and products of infiltration driven decarbonation dehydration reactions in regional metamorphic terrains which in the absence of solid solution and compositional domains indicate up temperature flow and the prediction of hydrodynamic models that regional metamorphic fluid flow normally is directed vertically upward and down temperature

short lived orogenic cycles and the eclogitization of cold crust by spasmodic hot fluids collision tectonics and the associated transformation of continental crust to high pressure rocks eclogites are generally well understood processes but important contradictions remain between tectonothermal models and petrological isotopic data obtained from such rocks here we use 40ar 39ar data coupled with a thermal model to constrain the time integrated duration of an orogenic cycle the burial and exhumation of a particular segment of the crust to be less than 13 myr we also determine the total duration of associated metamorphic events to be 20 kyr and of individual heat pulses experienced by the rocks to be as short as 10 years such short timescales are indicative of rapid tectonic processes associated with catastrophic deformation events earthquakes such events triggered transient heat advection by hot fluid along deformation shear zones which cut relatively cool and dry subducted crust in contrast to current thermal models that assume thermal equilibrium and invoke high ambient temperatures in the thickened crust our non steady state cold crust model satisfactorily explains several otherwise contradictory geological observations the duration of the geological processes that shape the earth generates vigorous debate mountain building where crust is consumed continuously by burial and recycled as buried remnants rise to the surface is one process where new dating methods can resolve the issue high precision dating of rock remnants left by continental collision in the caledonides of southern norway shows that the entire cycle can happen quickly in about 13 million years in addition the rapid transport of hot fluid zones through the cold crust may explain many puzzling geological observations

a transpressional origin for the west spitsbergen fold and thrust belt insight from analog modeling 1 the west spitsbergen fold and thrust belt formed along the transform plate boundary between greenland and the western barents sea during paleocene eocene breakup in the northern north atlantic approximately 20 40 km margin perpendicular shortening accumulated in the belt has been attributed to transpression and strain partitioning in a restraining bend but also to head on collision we have applied scaled analog tectonic modeling to test the former hypothesis a pack of brittle quartz sand with a shallow thin layer of silicon putty was deformed by transpression at a 15 convergence angle by movement of a basal plate the kinematics was quantified by means of digital particle image velocimetry the result was a doubly vergent transpressional wedge consisting of a steeply tapered retrowedge and a strongly internally deformed steeply tapered prowedge separated by a central strike slip zone and an adjacent low taper thin skinned fold and thrust belt the doubly vergent wedge evolved through several kinematic phases three main stages were identified namely 1 initial distributed deformation 2 development of an oblique doubly vergent wedge with progressive evolution of local strain partitioning along the marginal shear zones and finally 3 a stage of full strain partitioning between a central strike slip zone and reverse displacement along marginal shear zones with folding and thrusting in a thin skinned belt on the proside the analog model convincingly reproduced the geometry and the kinematic evolution of the west spitsbergen fold and thrust belt supporting the hypothesis of its formation by strain partitioning in transpression with a small angle of convergence and significant lateral displacement

graben inversion in nature and experiments the inversion of crustal scale basement grabens is studied here through laboratory experiments on small scale models and available oil industry seismic lines from the southern north sea two basic configurations are considered first both the basement and the sedimentary cover are brittle and inversion does not involve any potential decollement between them second the basement and sedimentary cover are separated by a weak ductile layer e g salt which can allow decollement of the cover during both extension and later compression and inversion the second configuration is more complicated and can lead to a large variety of geological structures laboratory experiments were carried out on brittle ductile models built with sand to represent brittle layers basement and sedimentary cover and silicone putty to simulate the decollement layer between basement and cover a mechanically based classification of inversion structures is proposed the effects of some crucial parameters are investigated including obliquity between the direction of shortening and normal faults as well as strength profiles and the presence or absence of salt diapirs the experimental investigation leads to the following conclusions 1 the inversion of the graben by reactivation of normal faults implies that the angle between the direction of compression and the graben is less than 45 2 if there is a superficial decollement e g basement cover interface inversion initiates low dipping thrust faults in the cover localized at graben borders 3 salt diapirs or salt walls localized along the graben borders in the cover are preferential sites for the development of thrust faults and 4 when the cover is decoupled from the basement by a decollement layer inversion induced deformation in the cover which is partitioned between thrust faults along the graben borders and strike slip faults within the graben trending oblique to the graben borders experimental results are compared with field examples in particular from the southern north sea

tectonic wedges geometry and kinematic interpretation abstract the geometry of several tectonic wedge combinations was studied in an outcrop in the basque basin western pyrenees three types of tectonic wedges were distinguished simple double and triple wedge on the surface the geometry of the observed tectonic wedges is always highly elemental emergent thrust horse or klippe the final stage in the evolution of a tectonic wedge is its delamination this can occur by the spreading of the thrusts which conform the wedge or by the development of back thrusts associated to them the relative age of the back thrust with respect to the thrust indicates whether the original structure was a simple thrust or a tectonic wedge if this criterion is applied to the pyrenean orogen this range corresponds to a tectonic wedge

electrical conductivity anisotropy of dry and hydrous olivine at 8 gpa the effects of dissolved h2o on the electrical conductivity and its anisotropy in olivine fo90 at 8 gpa were investigated by complex impedance spectroscopy at nominally anhydrous conditions conduction along 1 0 0 and 0 0 1 is slightly higher than along 0 1 0 in contrast to observations made at lower pressures in earlier studies increasing h2o content increases conductivities but activation energies are lower and h2o concentration dependent the use of polarized ftir spectroscopy to determine h2o concentrations reveals a weaker than expected effect that water has on olivine conductivity and distinguishes our results from earlier studies based on analyses using non polarized infrared spectroscopy we show that at h2o concentrations of a few hundred wt ppm or less that the dominant conduction mechanism at mantle temperatures continues via small polarons such as that observed for anhydrous olivine our results also suggest that at depths greater than 200 km the presence of h2o may not be necessary to explain regions in the upper mantle where both electrical and seismic anisotropy are observed this can be explained by differences in the pressure dependence of the activation energy for conduction along each of the three crystallographic axes however while electrical anisotropy of anhydrous olivine remains weak at 8 gpa it is nevertheless enhanced by elevated concentrations several hundred wt ppm of dissolved h2o at these conditions dominated by proton hopping conductivity along 0 1 0 is highest approximately an order of magnitude greater than along 1 0 0 additionally at 1000 wt ppm and 1500 c an isotropic conductivity derived from the data is about 1 order of magnitude higher than that for nominally anhydrous olivine thus in regions of the mantle characterized by anomalously high conductivities and both electrical and seismic anisotropy significant amounts of dissolved hydrogen can be expected

three dimensional geometry of metamorphic fluid flow during barrovian regional metamorphism from an inversion of combined petrologic and stable isotopic data inverse calculations reveal the three dimensional geometry of time integrated fluid flux over a 120 km2 area during peak barrovian regional metamorphism in southeastern vermont prograde changes in whole rock co2 18o and 13c and calculated fluid compositions at the peak of metamorphism were inverted assuming tracer mass balance to obtain the time integrated fluid flux in three dimensions peak metamorphic fluid flow was spatially nonuniform with flux magnitudes ranging from 0 to 3 105 mol fluid cm2 rock and flux directions ranging from vertical upward and downward to horizontal averaged over the entire study area the magnitude of the time integrated metamorphic fluid flux vector is 3 4 104 mol fluid cm2 rock the average flux vector trends 45 to the southwest and points upward at 36 from the present horizontal parallel to formation boundaries on a regional scale fluids in the terrain carried 3 103 mol co2 cm2 rock toward earth s surface during the peak of metamorphism results suggest that local cross layer transport processes are secondary to terrain scale metamorphic fluid flow in driving prograde decarbonation reactions regional structure exerts a first order control on the gross geometry of peak metamorphic fluid flow

electrical conductivity of san carlos olivine along 100 under oxygen and pyroxene buffered conditions and implications for defect equilibria the electrical conductivity along 100 of single crystal san carlos olivine was measured as a function of temperature between 1100 and 1200 c and oxygen fugacity between 10 6 and 10 0 5 pa at 1200 c and either with pyroxene buffered or without self buffered an added natural pyroxene buffer from a san carlos lherzolite under these temperature and o2 conditions electrical conduction in the self buffered sample is attributed to polarons fe and electrons e and in the pyroxene buffered sample is attributed to polarons fe and magnesium vacancies v mg over the range of temperature and o2 investigated the electrical conductivity of the self buffered sample is given by sb 100 2 27 s m e 0 55 ev kt o20 18 306 3 s m e 2 25 ev kt o2 0 18 and for the pyroxene buffered sample by pb 100 0 18 s m e 0 34 ev kt o20 17 15 2 s m e 1 3 ev kt where k is boltzmann s constant t is in kelvin and o2 is in atmospheres the conductivity of the pyroxene buffered sample is lower than that of the self buffered sample primarily as a result of a decrease in the polaron concentration the electrical conductivity of both samples was found to decrease irreversibly once the samples experienced an oxygen fugacity more reducing than approximately the wustite magnetite buffer electron microprobe analyses indicate that this effect results from loss of iron from the olivine samples to the iridium electrodes a series conduction model based on the observed compositional gradient adequately accounts for the magnitude of the irreversible conductivity decrease and limits the thickness of any surficial pyroxene phase to 0 1 m mantle temperature profiles based on laboratory measurements of self buffered samples predict temperatures of the order of between 25 and 150 c colder depending on the ambient oxygen fugacity than those based on measurements of pyroxene buffered samples

fluids in the crust during regional metamorphism forty years in the waterville limestone figure 1 research over the last four decades on carbonate rocks of the waterville limestone maine u s a has contributed to the development of both concepts and methodologies for understanding fluid rock interaction during regional metamorphism including 1 buffering of fluid composition by mineral reactions 2 infiltration of carbonate rocks by aqueous fluids 3 petrologic fluid rock ratios 4 infiltration driven metamorphism 5 one and two dimensional continuum models for coupled fluid flow and mineral reaction 6 time integrated fluid fluxes and 7 channelized horizontal fluid flow in the direction of increasing temperature within chemically isolated layers disagreement between the last concept and both hydrodynamic models for metamorphic fluid flow and empirical evidence for homogenization of fluid composition at a scale much larger than layer thickness motivated development of the latest models for coupled fluid flow and mineral reaction in the waterville limestone the new models consider a flow medium composed of layers that differ in the initial amounts and compositions of minerals both horizontal flow in the direction of increasing temperature and vertical flow in the direction of decreasing pressure and temperature significant but imperfect homogenization of fluid composition across layering by co2 h2o interdiffusion and infiltration by fluids that are spatially variable in composition on the kilometer scale with co2 content increasing with increasing grade of metamorphism the new models reproduce measured progress of the biotite forming reaction in the waterville limestone over a range of spatial scales spanning six orders of magnitude from differences in reaction progress of up to a factor of 100 between adjacent centimeter thick layers to the coexistence of mineral reactants and products over a distance of 13 km parallel to the metamorphic field gradient results imply that the present spatial distributions of reaction progress represent a steady state achieved when rocks closely approached equilibrium with the infiltrating fluid during metamorphism the new models resolve what for many years appeared to be fundamental discrepancies among petrologic data for regionally metamorphosed carbonate rocks hydrodynamic models of regional metamorphism and the length scales of mass transport of volatiles across layering by diffusion 1 pending yes