thermochronological investigation of fault zones abstract the timing of faulting episodes can be constrained by radiometric dating of fault zone rocks fault zone material suitable for dating is produced by tectonic processes such as 1 fragmentation of host rocks followed by grain size reduction and recrystallization to form mica and clay minerals 2 secondary heating melting of host rocks by frictional fault motions and 3 mineral vein formation as a result of fluid advection associated with the fault motions the thermal regime of fault zones consists primarily of the following three factors a regional geothermal structure across the fault zone and background thermal history of studied province bounded by fault systems b frictional heating of wall rocks by fault motions and c heating of host rocks by hot fluid advection in and around the fault zone thermochronological methods widely applied in fault zones are k ar 40ar 39ar fission track and u th methods for which methodological principles as well as analytical procedures are briefly described the thermal sensitivities of individual thermochronological systems are then reviewed which critically control the response of each method against the thermal processes based on the knowledge above representative examples as well as key issues are highlighted to date fault gouges pseudotachylytes mylonites and carbonate veins placing new constraints upon geological geomorphological and seismological frames finally the nojima fault is presented as an example for multiple applications of thermochronological methods in a complex fault zone

lightning in the anvils of supercell thunderstorms abstractthis study uses data from the oklahoma lightning mapping array ok lma the national lightning detection network and the norman oklahoma koun prototype weather surveillance radar 1988 doppler wsr 88d radar to examine the evolution and structure of lightning in the anvils of supercell storms as they relate to storm dynamics and microphysics several supercell storms within the domain of the ok lma were examined to determine whether they had lightning in the anvil region and if so the time and location of the initiation of the anvil flashes were determined every warm season supercell storm had some flashes that were initiated in or near the stronger reflectivities of the parent storm and propagated 40 70 km downstream to penetrate well into the anvil some supercell storms also had flashes that were initiated within the anvil itself 40 100 km beyond the closest 30 dbz contour of the storm these flashes were typically initiated in one of three locations 1 coincident with a local reflec

near field response to transpression along the southern san andreas fault based on exhumation of the northern san gabriel mountains southern california 1 near field mountain building is common along transpressive faults but how vertical deformation relates to oblique plate motion versus local structural complexity has not been universally established we have investigated the mechanisms of exhumation along the southern san andreas fault in the northern san gabriel mountains to examine the effects of pure shear dominated transpression obliquity 20 although rugged topography suggests near field uplift low temperature thermochronometry indicates minimal exhumation apatite u th he ages are 10 ma along narrow ridges within the fault zone implying near field rock uplift is not pervasive along this oblique plate boundary ages farther from the fault are younger 5 ma and suggest a deformation event occurred during the transition of activity from the san gabriel fault to the modern san andreas strand these results reveal a heterogeneous crustal response to transpression and imply that secondary structures or geometrical complexities play a primary role in near field bedrock uplift along transpressive faults

duration and extent of large electric fields in a thunderstorm anvil cloud after the last lightning 1 a series of balloon electric field e soundings and time correlated radar scans through the balloon locations are used to examine the evolution of charge and reflectivity inside a dissipating thunderstorm anvil the soundings cover a 75 min period during and after the final lightning flash in distant convection the first sounding measured large e magnitudes maximum 65 kv m 1 and significant charge densities of both polarities maximum 2 5 nc m 3 within and screening the anvil little change in the maximum e values occurred in the 30 min between the first and third soundings although altitudes and densities of some charge regions decreased with time maximum 0 6 nc m 3 screening charge regions were observed in close coincidence with 12 dbz radar reflectivity contours and interior positive charge was found in the reflectivity maxima of both anvil decks the fourth sounding ascended through visible but optically less dense cloud and no enhanced e values were detected overall the data indicate the interior positive charge region of the main anvil contained about 150 c and covered at least 250 km2 nearly 30 min after the last lightning flash potentially hazardous e values of 30 35 kv m 1 were measured at 9 9 10 2 km altitude a common jet aircraft cruising altitude more than 20 km away from and 32 min after the final lightning flash about 50 min after the last flash the main positive charge region contained an estimated 50 c and potentially hazardous e values associated with the anvil extended over at least 220 km2

patterns of late pleistocene proglacial fluvial sedimentation in the se lithuanian plain abstract we investigated proglacial fluvial sedimentation processes in the se lithuanian plain by means of lithofacies analysis the main parameters on which interpretations were based were depositional structures of sandy sediments paleohydraulic parameters and grain size distribution the development of the se lithuanian plain illustrates the phenomenal shift of proglacial fluvial sedimentation from outwash plain to ice marginal river during the ice retreat of the last glaciation three facies assemblages of braidplain deposits and two facies assemblages of palaeovalley deposits were distinguished in the sandy plain by means of qualitative and quantitative sedimentological research this raises the question how the commonly accepted development of a se orientated outwash plain could turn into an almost perpendicular sw running ice marginal river the vertical and lateral transitions of outwash plain facies present a classical example of braidplain evolution on slightly inclined lowlands with well expressed proximal middle and distal parts mid and side channel point bar deposits of the proglacial valley point however which is unusual for proglacial fluvial systems to a meandering character of the ice marginal river river types of various scale show a change from braided into meandering in the proglacial subenvironment lithofacies analysis and paleohydraulic parameters show distinct differences of the hydrodynamic regime during the first stage of the sandy plain development from sedimentation on an outwash plain in a proglacial valley to sedimentation on a braidplain in a wide ice marginal valley the outwash system is characterized by a distinct downstream decrease in energy whereas the ice marginal river maintained most of its power and velocity

synconvergent ductile flow in variable strength continental crust numerical models with application to the western grenville orogen 1 we present results from numerical models for a convergent orogen with laterally variable lower crustal strength representing a simplified orogenic system in which a strong craton flanked by progressively weaker terranes collides with another continent with progressive convergence crustal thickening and thermal relaxation lower crust becomes decoupled from upper and middle crust forming a ductile orogenic infrastructure beneath a stronger superstructure collision with strong external crust results in uplift and expulsion of ductile nappes from the orogenic core creating allochthonous terranes overlying a lower crustal indentor the extent of transport and exhumation of lower crustal nappes over the indentor reflects the amount of convergence and the erosion rate the western grenville orogen displays across strike variations in age tectonic history and protolith association suggesting a systematic variation in precollision crustal strength the laurentian craton margin and accreted terranes were variably reworked at synorogenic depths of 25 35 km during the ottawan orogeny deformation propagated from younger monocyclic rocks in the southeast into older polycyclic rocks flanking the craton on the northwest a comparison between numerical model results and crustal scale cross sections from the georgian bay and montreal val d or transects shows close correspondence between crustal structure and model geometry this indicates that the models produce geologically realistic results and provides a context for interpreting the tectonic evolution of the western grenville orogen contrasts between the results of homogeneous channel flow models and the present ductile nappe models suggest that the effects of different styles of ductile flow can be distinguished in the geologic record

exhuming norwegian ultrahigh pressure rocks overprinting extensional structures and the role of the nordfjord sogn detachment zone 1 the nordfjord sogn detachment zone nsdz is widely cited as one of the primary structures responsible for the exhumation of norwegian ultra high pressure uhp rocks here we review data from the considerable volume of research describing this shear zone and compile a strikeparallel cross section along the nsdz from the solund basin in the south to the soroyane uhp domain in the north this cross section highlights several previously unrecognized patterns revealing a shear zone with top to the west asymmetric fabrics that 1 initiated at amphibolite facies 2 overprints metamorphic breaks and tectonostratigraphic contacts and 3 has a gradational continuum of muscovite cooling ages these patterns constrain the kinematic evolution of the nsdz and suggest a new three step model for the exhumation of norwegian u hp rocks the initial stages of exhumation were characterized by the rise of crustal rocks from u hp depths to the base of the crust by buoyancydriven mechanisms not specified in this paper mantle exhumation was followed by top to thewest normal sense displacement within a broad noncoaxial ductile shear zone near the base of the crust that overprinted tectonostratigraphic contacts formed previously during mantle exhumation in the final stages of crustal exhumation top w brittleductile detachments soled into and partially excised this ductile shear zone dropping the devonian basins into contact with rocks of varying tectonostratigraphic levels this new interpretation of the nsdz is significant as it accounts for the extreme crustal excision observed in western norway using three sequentially overprinting structures active at different stages of uhp rock exhumation citation johnston s m b r hacker and t b andersen 2007 exhuming norwegian ultrahigh pressure rocks overprinting extensional structures and the role of the nordfjord sogn detachment zone tectonics 26 tc5001

dating pseudotachylyte of the nojima fault using the zircon fission track method 1 the zircon fission track analysis of pseudotachylyte answered how old the nojima fault is which was activated during the 1995 kobe earthquake in japan the time of seismic fault motions at the crustal interior can be constrained by dating pseudotachylyte formation we succeeded in separating zircons from the pseudotachylyte layer of the fault as well as in dating them by the fission track method here we show that the layer has a significantly younger age 56 4 ma than the initial cooling age of the host rock suggesting that the fault was already initiated at 56 ma much older than the previous estimate based on the spatial distribution of sediments around the fault

electric fields cloud microphysics and reflectivity in anvils of florida thunderstorms into the interior electric fields very frequently increased abruptly from 1 to 10 kv m 1 even though the particle concentrations and radar reflectivity increased smoothly the abrupt increase in field usually occurred when the aircraft entered regions with a reflectivity of 10 15 dbz we suggest that the abrupt increase in electric field was because the charge advection from the convective core did not occur across the entire breadth of the anvil and because the advection of charge was not constant in time also some long lived anvils showed enhancement of electric field and reflectivity far downwind of the convective core screening layers were not detected near the edges of the anvils comparisons of electric field magnitude with particle concentration or reflectivity for a combined data set that included all anvil measurements showed a threshold behavior when the average reflectivity such as in a 3 km cube was less than approximately 5 dbz the electric field magnitude was 3 kv m 1 based on these

global statistics of lightning in anvil and stratiform regions over the tropics and subtropics observed by the tropical rainfall measuring mission 1 the statistics of lighting in the anvil and stratiform regions of convective systems are summarized from tropical rainfall measuring mission trmm satellite observations from 1998 to 2009 the locations of lightning flashes in convective systems are determined by combining three dimensional precipitation radar pr observations with lightning flash center locations from lightning imaging sensor observations the geographical distributions of flashes in the anvil and stratiform regions of thunderstorms over the tropics and subtropics are presented flashes in stratiform regions are found to account for 5 6 of all lightning flashes observed within the trmm pr swath while flashes in nonraining anvil regions made up another 5 5 of the sample diurnally flashes in anvil regions peak earlier than flashes in stratiform regions 15 30 lt as opposed to 17 30 lt seasonal and regional variations of these flashes are discussed features in pr observations that likely contribute to charge separation are identified as contiguous areas with 6 km echoes exceeding 30 dbz lightning flashes are then assigned to one of these features by the nearest neighbor method convective properties of features linked with lightning in stratiform and nonraining anvil regions are then analyzed we find that features associated with lightning flashes in anvil regions are relatively weak and occur in small systems composed of a single convective region while flashes in the stratiform regions are also relatively weak but more likely occur in multicell systems about 15 of features with lightning are associated with at least one stratiform or anvil flash

long term continental deformation associated with transpressive plate motion the san andreas fault a synthesis of transpressive mountain building as evidenced by rock uplift and topography along the entire san andreas fault reveals a complex crustal response to oblique plate motion convergent deformation increases toward the fault but does not correlate with the angle of plate motion obliquity the shortening estimated from rock uplift is also insufficient to account for the fault normal motion based on relative plate velocity this suggests that near field convergence is influenced by local structural complexity and is not purely driven by regional transpression and that the fault normal component of plate motion is partly accommodated elsewhere heterogeneity in deformation and degree of slip partitioning highlight the importance of other factors in shaping transpressive continental deformation including surface processes material anisotropy and strain weakening

transpression and the build up of the cordillera the example of the bucaramanga fault eastern cordillera colombia widespread wrench tectonics have been described along the northern andes the bucaramanga fault described as sinistral strike slip bounds the high santander massif we combine structural and thermochronological data from the central southern portion of the fault to investigate the vertical displacement the structural survey data show old phases of activity preserved in the host rocks along the fault trace with the superimposition of different generations of slickenlines and both strike slip and dip slip kinematics indicators new and previous thermochronological data show that differential exhumation of the fault walls has been ongoing for the last 50 ma the hanging wall the santander massif records in the central portion decreasing exhumation rates from the early miocene to the mid to late miocene and in the southern portion constant rates from the late oligocene to the pliocene combining such observations the thermochronological offset resulting from the relative motion of the two fault walls is comparable with the observed drop in elevation across the fault suggesting that the present topography of the santander massif is related to vertical movement along the bucaramanga fault we infer that the fault has a significant neogene reverse component consistent with the present day horizontal global positioning system vector data long term exhumation rates and the structural assemblage supplementary material the supplementary materials contain methodological information on the thermochronological procedures a compilation of the previously published data used in this study and the structural geology dataset https doi org 10 6084 m9 figshare c 4620140

lightning initiation in the anvils of two supercell storms 1 previous studies of lightning in anvil clouds have reported that flashes began in or near the storm core and propagated downwind into the anvil it had been thought that flashes could not be initiated far downwind in the anvil because anvil charge was thought to be produced mainly in the storm s deep updraft and to decrease with distance into the anvil here we report observations of the in cloud development of lightning flashes in the anvils of two supercell storms including the first observations of flashes that began in the anvil 30 100 km from the cores of the storms and propagated upwind back toward the cores interaction between charge regions in the two converging anvils of adjoining storms appeared to cause some of the distant flash initiations but a local charging mechanism in the anvil likely also contributed to the flash initiations all flashes that struck ground beneath the distant anvil transferred negative charge to ground instead of the positive charge usually transferred to ground there an apparent consequence of the parent storm having an inverted polarity electrical structure

paleostress evolution of the northern andes eastern cordillera of colombia implications on plate kinematics of the south caribbean region 1 new tectonic field data and paleostress determinations in the eastern cordillera of colombia enable us to identify stress regimes that prevailed in the northern andes since late cretaceous times until present day these regimes were characterized by an e w to wsw ene active contraction from late cretaceous to late paleocene this direction subsequently changed to nw se and finally became wnw ese during the andean tectonic phase the characteristics and relative chronology of these regimes were deduced from field structures and stratigraphic criteria using stress inversion of fault slip data sets to evaluate our model we used the rotation poles of the south america caribbean and nazca plates relative to north america and paleogeographic reconstructions of the caribbean region to derive a kinematic model of the northern andes assuming a general correspondence between the regional convergence directions and the regional compression we built a theoretical model of the regional stress regimes based on kinematics of the northwestern south america since late cretaceous times this model reveals a major variation at the end of the paleocene when relative divergence shifted to convergence between the americas this is in agreement with our tectonic model based on independent tectonic field data inversion in the eastern cordillera this regional kinematic and tectonic change which affected the caribbean at the end of the paleocene was responsible for and consistent with the major change in stress patterns and structural style in the eastern cordillera it is also coeval with the development of a major regional unconformity in colombia

small lightning flashes from shallow electrical storms on jupiter lightning flashes have been observed by a number of missions that visited or flew by jupiter over the past several decades imagery led to a flash rate estimate of about 4 10 3 flashes per square kilometre per year refs 1 2 the spatial extent of voyager flashes was estimated to be about 30 kilometres half width at half maximum intensity hwhm but the camera was unlikely to have detected the dim outer edges of the flashes given its weak response to the brightest spectral line of jovian lightning emission the 656 3 nanometre h line of atomic hydrogen1 3 6 the spatial resolution of some cameras allowed investigators to confirm 22 flashes with hwhm greater than 42 kilometres and to estimate one with an hwhm of 37 to 45 kilometres refs 1 7 9 these flashes with optical energies comparable to terrestrial superbolts of 0 02 1 6 1010 joules have been interpreted as tracers of moist convection originating near the 5 bar level of jupiter s atmosphere assuming photon scattering from points beneath the clouds 1 3 7 8 10 12 previous observations of lightning have been limited by camera sensitivity distance from jupiter and long exposures about 680 milliseconds to 85 seconds meaning that some measurements were probably superimposed flashes reported as one1 2 7 9 10 13 here we report optical observations of lightning flashes by the juno spacecraft with energies of approximately 105 108 joules flash durations as short as 5 4 milliseconds and inter flash separations of tens of milliseconds with typical terrestrial energies the flash rate is about 6 1 10 2 flashes per square kilometre per year more than an order of magnitude greater than hitherto seen several flashes are of such small spatial extent that they must originate above the 2 bar level where there is no liquid water14 15 this implies that multiple mechanisms for generating lightning on jupiter need to be considered for a full understanding of the planet s atmospheric convection and composition small lightning flashes detected on jupiter by juno have shallow origins above the 2 bar level of jupiter s atmosphere where temperatures are too low for liquid water to exist

active faulting in the birjand region of ne iran 1 we use satellite imagery and field observations to investigate the distribution of active faults around birjand in eastern iran to determine how the transition between conjugate zones of faulting can be accommodated by diffuse active faulting in the south of the study area right lateral strike slip faults of the sistan suture zone end in thrusts which die away westward from the strike slip faults these thrust terminations appear to allow a northward change to e w thrusting in central parts of the study area the introduction of e w thrusting is in turn likely to facilitate a change to e w left lateral faulting north of the study region the relatively diffuse pattern of active faulting at birjand relates to the regional transition between n s and e w strike slip faulting in northeast iran which involves a change from nonrotational to rotational deformation the change from n s to e w faulting is likely to result from the orientation of preexisting structures in iran and western afghanistan which are roughly parallel to the active fault zones the features described at birjand also show the influence of preexisting structure on the location and style of active faulting at a local scale with the position of individual faults apparently controlled by inherited geological weaknesses very few modern earthquakes have occurred in the region of birjand and yet destructive events are known from the historical record the large number of active faults mapped in this study pose a substantial seismic hazard to birjand and surrounding regions

observations and numerical simulations of the origin and development of very large snowflakes abstract the canadian atlantic storms program casp ii field experiment was conducted near st john s newfoundland canada during january march 1992 and it focused on the nature of winter storms analyses of casp ii aircraft surface satellite and radar observations collected during an intensive study of the origin and development of 9 mm h 1 precipitation containing 4 5 cm diameter snowflakes are compared in this article with results of the mm5 mesoscale and mitchell microphysical models mm5 simulations of the thermal kinematic and bulk microphysical fields were in good agreement with the observations this comparison provided the basis for extending the spatial and temporal scales of the aircraft observations to a larger scale domain using the model results the mitchell analytical numerical model was used to improve the understanding of the microphysical processes that led to the development of the very large snowflakes a synthesis of results using the different techniques leads to the co

electric field measurements within a severe thunderstorm anvil the anvil cloud of a supercell severe storm in central oklahoma was penetrated by two free balloons carrying corona probes to measure electric fields the two balloons passed through the portion of the anvil upstream of the precipitation core and provided information on the charge concentrations and vertical thicknesses of the electric charge regions within the cloud the trajectories of the balloons relative to the storm were horizontally separated by approximately 35 km providing information on the horizontal extent of the charge regions contrary to the general assumption that anvil interiors are positively charged the results of the two flights indicate that extensive regions of both net positive and negative charge were present in the interior of the anvil net positive charge was observed in both balloon flights in the lower portion of the anvil interior the vertical thickness of the positive charge region was measured in each flight to be 1 6 and 2 3 km respectively a charge concentration of 0 2 nc m 3 was estimated from one of the flights net negative charge was observed by both balloons in the upper portion of the anvil interior the vertical thickness and charge concentration of the negative charge region were estimated from one flight to be 3 2 km and 0 1 nc m 3 respectively screening charge layers were identified at the upper and lower boundaries of the anvil with a typical thickness of a few hundred meters which is an order of magnitude greater than that calculated in a previous model we propose a conceptual model of the development of anvil charge regions based on our balloon measurements and previous observations of anvil dynamics in this model we suggest that the thicknesses of the anvil screening layers increase with distance from the precipitation core of the storm owing to turbulent mixing near the cloud boundaries and differences in the sedimentation rates of the cloud particles negative charge in the upper portion of the anvil interior results from the expansion of the upper negative screening layer into lower levels of the anvil cloud

the extension of lightning flashes from thunderstorms near cape canaveral florida the horizontal distance that intracloud ic and cloud to ground cg lightning flashes extend from thunderstorms is presented for warm season nonsevere storms near cape canaveral fl the warning decision support system integrated information wdss ii software allowed us to ingest display and make distance calculations using radar reflectivity data from nearby national weather service offices and lightning information from the national lightning detection network and the local lightning detection and ranging network the flash distances were determined manually using a measuring tool within wdss ii six categories of flashes were investigated a cg flashes measured from the edge of the convective core 30 dbz to the ground strike location that is beneath the attached anvil b cg bolt from the blue flashes measured from cloud edge 0 dbz to the ground strike point that contains only 0 dbz overhead c cg bolt from the blue flashes as in category b but measured from the edge of the precipitation 18 dbz d ic flashes that exit a portion of the cloud that is not an anvil measured from cloud edge 0 dbz e ic flashes within anvils measured from the edge of convective precipitation 30 dbz to the termination point within the anvil and f ic flashes exiting the edge 0 dbz of anvils results for each category are presented in the forms of frequency distributions of distances and their cumulative frequency distributions

some analytical methods for converting thermochronometric age to erosion rate 1 an analytical method is presented for converting thermochronometric ages to surface erosion or equivalently exhumation rate the method incorporates the two most important thermal processes during cooling by erosion the dependence of closure temperature on cooling rate and the advection of heat by rock motion toward the earth s surface two thermal models are considered 1 a steady state model valid for low erosion rates and 2 an eroding half space model which has no steady state but captures the transient increase of geothermal gradient with erosion in each case it is assumed that data consist of one or more thermochronometric ages present day surface geothermal gradient and topographic information including the elevation at which the age was obtained analytical solutions are provided to derive the erosion rate from these data either as an explicit expression for the steady case or as a root finding problem for the transient case a graphical method for plotting age against erosion rate and geothermal gradient is presented as a method for solving the root finding problem and for tracking analytical errors in observations of age and surface geothermal gradient the graphical method is also appropriate for comparing data from different elevations or from different thermochronometric systems examples are provided using synthetic data or published data from the literature

preservation of contrasting geothermal gradients across the caribbean north america plate boundary motagua fault guatemala 1 strike slip plate boundaries juxtapose crustal blocks that may have different geodynamic origins and therefore different thermal structures thermo kinematic modeling of this type of strike slip plate boundary predicts an asymmetric signature in the low temperature thermochronologic record across the fault age elevation profiles of zircon u th he ages across the motagua fault a 500 km long segment of the transform boundary between the north american and caribbean plates document a sharp cooling age discontinuity across the fault this discontinuity could be interpreted as a difference in denudation history on each side of the fault however a low relief miocene erosional surface extends across the fault this surface has been uplifted and incised and provides a geomorphic argument against differential denudation across the fault by integrating magmatic volcanic and heat flow data age elevation profiles and thermo kinematic modeling we propose that large horizontal displacement along the motagua fault has offset a persistent geothermal asymmetry across the fault and explains both the age discontinuities and the age elevation patterns this study illustrates how thermochronology can be used to detect large strike slip displacements and more generally opens new perspectives in understanding the impact of nonuniform thermal structures on thermochronologic results

paleomagnetism and magnetic fabric of the eastern cordillera of colombia evidence for oblique convergence and nonrotational reactivation of a mesozoic intracontinental rift we report the paleomagnetic and magnetic fabric results of 58 sites from cretaceous miocene marine and continental strata from the eastern cordillera ec and the cucuta zone at the junction between the santander massif and the merida andes of colombia the ec is an intracontinental doubly vergent range inverting a triassic to early cretaceous rift zone twenty three sites reveal nonsystematic tectonic rotations including unrotated areas of the ec range with respect to stable south america our data show that the ec inverted a nne oriented rift zone and that the orientation of the mesozoic rift and the mountain chain roughly correspond interestingly magnetic lineations from anisotropy of magnetic susceptibility analysis do not trend parallel to the chain but rather are oblique to the main orogenic trend by also considering gps evidence of a 1 cm yr ene displacement of central western colombia accommodated by the ec we suggest that the miocene recent deformation event of this belt arises from ene oblique convergence reactivating a nne oriented rift zone oblique shortening was likely partitioned into pure dip slip shear characterizing thick skinned frontal thrust sheets well known along both chain fronts and by range parallel right lateral strike slip faults which have not been identified yet but likely exist in the axial part of the ec finally the 35 9 clockwise rotation observed in four post miocene magnetically overprinted sites from the cucuta zone reflects late cenozoic and ongoing right lateral strike slip displacement occurring along faults parallel to the bocono fault system possibly connected with the right lateral faults inferred to exist along the axial part of the ec

metamorphism and deformation at different structural levels in a strike slip fault zone ross lake fault north cascades usa continental crust is displaced in strike slip fault zones through lateral and vertical movement that together drive burial and exhumation pressure temperature deformation p t d histories of orogenic crust exhumed in transcurrent zones record the mechanisms and conditions of these processes the skagit gneiss complex a migmatitic unit of the north cascades washington usa was metamorphosed at depths of 25 30 km in a continental arc under contraction and is bounded on its eastern side by the long lived transcurrent ross lake fault zone rlfz the p t d conditions recorded by rocks on either side of the rlfz vary along the length of the fault zone but most typically the fault separates high grade gneiss and plutons from lower grade rocks the ruby mt elijah ridge area at the eastern margin of the skagit gneiss exposes tectonic contacts between gneiss and overlying rocks the latter rocks including slivers of methow basin deposits are metamorphosed and record higher grade metamorphism than in correlative rocks along strike along the rlfz in this area the skagit gneiss and overlying units all yield maximum p t conditions of 8 10 kbar at 650 c indicating that slices of basin rocks were buried to similar mid crustal depths as the gneiss after exhumation of fault zone rocks to 15 km depth intrusion of granitoid plutons drove contact metamorphism resulting in texturally late andalusite cordierite in garnet schist in the elijah ridge area of the rlfz an overlapping step over or series of step overs that evolved through time may have facilitated burial and exhumation of a deep slice of the methow basin indicating that strike slip faults can have major vertical displacement tens of kilometres that is significant during the crustal thickening and exhumation stages of orogeny