crustal reworking at nanga parbat pakistan metamorphic consequences of thermal mechanical coupling facilitated by erosion within the syntaxial bends of the india asia collision the himalaya terminate abruptly in a pair of metamorphic massifs nanga parbat in the west and namche barwa in the east are actively deforming antiformal domes which expose quaternary metamorphic rocks and granites the massifs are transected by major himalayan rivers indus and tsangpo and are loci of deep and rapid exhumation on the basis of velocity and attenuation tomography and microseismic magnetotelluric geochronological petrological structural and geomorphic data we have collected at nanga parbat we propose a model in which this intense metamorphic and structural reworking of crustal lithosphere is a consequence of strain focusing caused by significant erosion within deep gorges cut by the indus and tsangpo as these rivers turn sharply toward the foreland and exit their host syntaxes the localization of this phenomenon at the terminations of the himalayan arc owes its origin to both regional and local feedbacks between erosion and tectonics

boiling fluids in a region of rapid uplift nanga parbat massif pakistan abstract the nanga parbat massif of northern pakistan is currently undergoing rapid uplift 5 10 mm a 1 resulting in near surface elevated temperatures numerous quartz veins cut geologically young structures 100 c km 1 and the isotherms describe a giant pillar of heat above about 4 km fluid temperature is greater than conductive rock temperature in permeable zones which carry convecting boiling meteoric fluid

constraints from 40ar 39ar geochronology on the tectonothermal history of the kapuskasing uplift in the canadian superior province the kapuskasing uplift ku in the superior province of the canadian shield has been interpreted as an oblique cross section through the archean mid crust however the time of juxtaposition of the granulites of the ku against the lower grade rocks of the abitibi greenstone belt agb along the ivanhoe lake fault zone is problematic to constrain the postmetamorphic tectonothermal history of the ku we have conducted 57 40ar 39ar step heating analyses on mineral and rock samples collected in a transect across the southern ku and adjacent agb the age spectra record a complex thermal history amphiboles from the agb in the footwall of the ivanhoe lake fault zone have ca 2 66 ga dates similar to closure ages for amphiboles from farther east in the agb amphibole dates of 2 46 2 52 ga from the deepest structural levels of the ku place an upper limit on the time of major uplift of the granulites and their juxtaposition with the agb biotite and muscovite dates from the transect cluster into three age groups

evidence from aeromagnetics on the configuration of matachewan dykes and the tectonic evolution of the kapuskasing structural zone ontario canada by digital image processing of federal provincial aeromagnetic survey data for the south central superior province we have obtained an improved picture of the distribution of dykes in the huge matachewan mafic dyke swarm 2454 ma we deduce from it a picture of post emplacement deformation in the vicinity of the uplifted granulite gneisses of the kapuskasing structural zone ksz matachewan dykes are emplaced in three subswarms the two easterly subswarms are clearly truncated by the ksz s eastern boundary faults the western subswarm shows an open z bend as it crosses the ksz but it does not reveal any major fault offset on the plausible assumption supported by paleomagnetic data that the subswarms were originally intruded radially the horizontal strain suffered by the ksz since emplacement of the dykes is mainly a northeast southwest trending band of dextral transcurrent deformation which in the northeast is discontinuous and concentrated in a fault horizontal offset 60 80 km and in the south

remagnetization in keweenawan rocks part i conglomerates conglomerate tests are used to show that late precambrian keweenawan conglomerates on the keweenaw peninsula michigan and at mamainse point ontario have suffered a partial chemical remagnetization that predated tectonic tilting at mamainse point the overprint was acquired during the final normal polarity stage of keweenawan volcanism whereas on the keweenaw peninsula it occurred after cessation of volcanism and has a maximum late freda sandstone age the extent of overprinting on the keweenaw peninsula increases westwards along a 40 km strike length in the copper harbor conglomerate and may at least in part be related to secondary mineral zonation including native copper in the underlying portage lake volcanics it is shown that neither of the two overprinting episodes can be responsible for the reversal asymmetry observed in keweenawan igneous rocks

from hot to cold the temperature dependence on rock deformation processes an introduction abstract understanding rock deformation processes in solid earth materials from the crystal to the tectonic plate scale is essential for characterising the evolution of the lithosphere and for predicting how rocks behave in the subsurface temperature is a key parameter that determines what rock deformation processes are active and therefore how tectonic structures form moreover it controls the migration of fluids and melt in the earth s crust that lead to phase transformations and changes in rock rheology this special issue gathers a collection of research papers following the 21st international conference on deformation mechanisms rheology and tectonics drt 2017 which was held in inverness scotland in april may 2017 organised by the university of aberdeen these contributions provide a significant advance in the study of rock deformation and fluid melt migration at multiple crustal levels from deformation bands near the earth s surface to shear zones in partially molten rocks in the lower crust in this introductory article we first provide an overview of how temperature controls deformation mechanisms and processes and then introduce the collection of research papers ordered from those analysing deformation processes occurring at high temperatures to contributions reporting deformation at shallow crustal conditions

clear water scour and flow field alteration around an inclined pile abstract the present experimental study investigates the scour pattern and the near wake flow field alteration around an emergent rigid cylinder which is inclined towards the downstream direction three different inclination angles were tested separately namely 14 30 and 42 with respect to the wall normal axis the induced flow and scour patterns were assessed and compared with the well known case of the emergent upright cylinder inclination angle 0 the experiments were conducted for steady flow conditions in a 26 m long recirculating flume and the flow velocity measurements were conducted with an acoustic doppler velocimeter for the clear water scour experiment a false bed with a sand pit was installed within the flume and a laser scanner was utilized to render a detailed representation of the scoured bed the results show how the scouring gets mitigated with increasing inclination angle spatial distribution of time averaged and fluctuation velocity patterns are presented which exhibit that the vertical mixing gets significantly enhanced behind the inclined cylinder with increasing inclination angle while the lateral mixing gets weakened at the upper flow region an upward flow is seen at the immediate downstream of the inclined pile close to the bed which becomes stronger with the inclination angle energy spectra as well as joint frequency distributions of velocity components were analyzed together with the time series revealing that the inclination of the pile alters the wake significantly the results further indicate that with increasing inclination angle the pile becomes more streamlined and the vortex shedding gets suppressed

role of near bed turbulence structure in bed load transport and bed form mechanics the interactions between turbulence events and sediment motions during bed load transport were studied by means of laser doppler velocimetry and high speed cinematography sweeps u 0 w 0 w 0 which contribute negatively to the bed shear stress and are relatively rare individually move as much sediment as sweeps of comparable magnitude and duration however and much more than bursts u 0 and inward interactions u 0 w 0 when the magnitude of the outward interactions increases relative to the other events therefore the sediment flux increases even though the bed shear stress decreases thus although bed shear stress can be used to estimate bed load transport by flows with well developed boundary layers in which the flow is steady and uniform and the turbulence statistics all scale with the shear velocity it is not accurate for flows with developing boundary layers such as those over sufficiently nonuniform topography or roughness in which significant spatial variations in the magnitudes and durations of the sweeps bursts outward interactions and inward interactions occur these variations produce significant peaks in bed load transport downstream of separation points thus supporting the hypothesis that flow separation plays a significant role in the development of bed forms

the tectonic relationship of two early proterozoic dyke swarms to the kapuskasing structural zone a paleomagnetic and petrographic study a tea coloured cloudiness in groundmass feldspars characterizes dykes of two early proterozoic swarms 2 45 ga matachewan 2 04 ga kapuskasing that intrude amphibolite to granulite host rocks with

structural segmentation and the influence of basement structure on the namibian passive margin passive margins are segmented into discrete elements by segment boundaries exhibiting a variety of structural styles the namibian margin is bounded by a hinge line that is offset by segment boundaries the most important is the cape cross segment boundary here pre existing basement lineaments and karoo rift elements were reactivated during late mesozoic rifting it marks the northern limit of the earliest of three rift sequences and relates to a temporal change in break up and formation of the south atlantic a similar change occurs across other important segment boundaries but smaller examples lack this major segment boundaries with a temporal change in rifting and break up exhibit a strong connection to the basement province

numerical investigation of flow and scour around a vertical circular cylinder flow and scour around a vertical cylinder exposed to current are investigated by using a three dimensional numerical model based on incompressible reynolds averaged navier stokes equations the mod

paleomagnetism of the red lake greenstone belt northwestern ontario possible evidence for the timing of gold mineralization we report paleomagnetic results from 1 largely unaltered batholiths and 2 sheared and altered units in the archean red lake greenstone belt a major gold producing region in the uchi subprovince of northwestern ontario group 1 includes the hammell lake killala baird trout lake and little vermilion lake batholiths which were intruded between 2730 and 2700 ma ago u pb zircon group 2 includes the howey diorite the dome stock and dikes and andesites from the dickenson mine these units from the mineralized deformation zones dzs between the batholiths were sheared and hydrothermally altered in the same event that caused gold mineralization in supracrustal units the batholiths carry a stable reversed remanence rlr withd 159 i 74 k 20 95 16 n 4 units 14 sites rlr has high coercivities unblocking temperatures and remanence intensities and appears to be a primary thermal remanence dating from 2700 ma the altered units from the gold bearing dzs carry a different remanence rlg withd 180 i 57 k 23 95 3 n 3 units 6 sites rlg also has relatively high coercivities and unblocking temperatures but its magnetization intensities are 1 2 orders of magnitude lower than those of rlr opaque minerals and silicates observed in thin section are highly altered rlg is therefore believed to be a chemical or thermochemical remanence acquired 2580 ma ago during the late stages of cooling and gold mineralization seeing as rlg characterizes the shear zone rocks but is absent from unaltered rocks outside the dzs it could be used as a rapid prospecting tool in delineating areas of alteration and possible mineralization the paleopoles for rlr 2700 ma and rlg 2580 ma link with those of the shelley lake granite 2580 ma 40ar 39ar hornblende and biotite and the matachewan hearst dikes 2450 ma u pb zircon and baddeleyite the sense of motion on the late archean early proterozoic apparent polar wander path for laurentia as defined by this sequence of paleopoles is opposite to that previously accepted

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

seismic characterization of an active metamorphic massif nanga parbat pakistan himalaya earthquakes recorded by a dense seismic array at nanga parbat pakistan provide new insight into synorogenic metamorphism and mass flow during mountain building micro seismicity beneath the massif drops off sharply with depth and defines a shallow transition between brittle failure and ductile flow the base of seismicity bows upward mapping a thermal boundary with 3 km of structural relief over a lateral distance of 12 km anom alously low seismic velocities are observed at the core of the massif and extend to depth through the crust the main locus of seismicity and low velocities correlates with a region of high topography rapid exhumation high geothermal gradients young metamorphic and igneous ages and crustal fluid flow we suggest a genetic link between these phenom ena in which hot rocks rapidly advected from depth are pervasively modified at relatively shallow levels in the crust

fabric anisotropy controls faulting in the continental crust the influence of pre existing structural anisotropy on faulting in the continents is best tested in recently exhumed crust e g nanga parbat massif nw himalayas where earlier brittle structures have been annealed the kinematics of young faults formed in a single continuing tectonic regime nnw compression are distinctly different depending upon the orientation of the early ductile foliations around them faulting is subparallel and statistically simple where foliation is moderately dipping but highly complex where foliation is steeply dipping thus structural anisotropy does control faulting in the continental crust a result with important implications for seismogenesis fluid flow and basin evolution

influence of inclination and permeability of solitary woody riparian plants on local hydraulic and sedimentary processes the role of solitary woody riparian plants with respect to local erosion and deposition of sediments is investigated a focus is laid on the characteristics inclination and permeability of the plant s projected frontal area therefore two experimental studies using cylindrical obstacles were carried out in a laboratory flume one aiming at inclination the other at permeability the first series revealed that the total amount of mobilized sediment around the cylinder on average decreased by 8 10 per 5 increasing inclination in streamwise direction locations of maximum scour depth simultaneously shifted downstream a horseshoe vortex system causing the frontal and lateral scouring ceased to exist below inclinations of 25 30 the second series revealed that with increasing permeability frontal scour incision is delayed and the eroded sediment volume is significantly reduced with permeable obstacles two system states were observed first frontal scouring with leeside deposition at higher flow velocities and second moderate leeside scouring at lower flow velocities for up scaling and comparison a field study focussing on fluvial obstacle marks at poplars and willows in secondary channels of the river loire was additionally conducted a modified analytical model enabled us to quantify the amount of deposited sediments leeside of the plants leeside sediment ridges are significantly stabilized and have a higher preservation potential when covered by pioneer vegetation under such conditions they may indeed induce the development of stable islands eventually sediment ridge width turned out to be a suitable indicator for leeside deposited sediment volume irrespective of spatial scale copyright 2012 john wiley sons ltd

vertical stretching and crustal thickening at nanga parbat pakistan himalaya a model for distributed continental deformation during mountain building 1 the localization of strain in the continental crust during compressional tectonics is examined using the active structures at the nanga parbat massif an exhumed tract of indian continental crust in the pakistan himalaya this large scale 40 km wavelength structure is considered to involve the whole crust thrusting at the modern surface places gneisses of the indian continental crust onto holocene deposits at the raikhot transect the thrust zone carries a relatively narrow 2 km wide shear zone within which minor structures are asymmetric and the deformation apparently noncoaxial however modeling of foliation and augen preferred orientation ellipticity suggests that the bulk deformation is a combination of relatively small simple shear strains 1 with larger stretching strains heterogeneous stretching within the shear zone was accommodated by localized shearing on metabasic layers so that strain is partitioned outside this shear zone on the transect there is penetrative deformation throughout the nanga parbat massif this broadly distributed deformation shows no asymmetry or evidence of rotation rather this deformation is better described as near pure shear subvertical stretching augen ellipticities suggest subvertical stretches of greater than 200 consideration of plausible changes in crustal thickness during the amplification of the nanga parbat structure suggests the magnitude of vertical stretch decays with depth presumably these strains in the deep crust are more distributed but weaker than in the exposed middle crustal sections assuming conservation of horizontal shortening displacement with depth these studies suggest that penetrative vertical stretching through dominantly pure shear deformation is an effective mechanism for thickening the continental crust and that models which assume that simple shear zones penetrate the whole crust need not be of ubiquitous applicability

a km scale triaxial experiment reveals the extreme mechanical weakness and anisotropy of mica schists grandes rousses massif france abstract the development of andersonian faults is predicted according to theory and experiments for brittle frictional deformation occurring in a homogeneous medium in contrast in an anisotropic medium it is possible to observe fault nucleation and propagation that is non andersonian in geometry and kinematics here we consider post metamorphic brittle frictional deformation in the mechanically anisotropic mylonitic mica schists of the grandes rousse massif france the role of the mylonitic foliation and of any other source of mechanical anisotropy in brittle frictional deformation is a function of orientation and friction angle according to the relative orientation of principal stress axes and foliation a foliation characterized by a certain coefficient of friction will be utilized or not for the nucleation and propagation of brittle frictional fractures and faults if the foliation is not utilized the rock behaves as if it was isotropic and andersonian geometry and kinematics can be observed if the foliation is utilized the deviatoric stress magnitude is buffered and andersonian faults fractures cannot develop in a narrow transition regime both andersonian and non andersonian structures can be observed we apply stress inversion and slip tendency analysis to determine the critical angle for failure of the metamorphic foliation of the grandes rousses schists defined as the limit angle between the foliation and principal stress axes for which the foliation was brittlely reactivated this approach allows defining the ratio of the coefficient of internal friction for failure along the mylonitic foliation to the isotropic coefficient of friction thus the study area can be seen as a km scale triaxial experiment that allows measuring the degree of mechanical anisotropy of the mylonitic mica schists in this way we infer a coefficient of friction w e a k 0 14 for brittle frictional failure of the foliation or 20 of the isotropic coefficient of internal friction

rb sr and u pb ages of volcanism and granite emplacement in the michipicoten belt wawa ontario the michipicoten greenstone belt at wawa ontario is typical of archean volcanic belts in the superior province the supracrustal rocks are divisible into lower middle and upper metavolcanic sequences which are separated by iron formation and clastic metasedimentary rocks these are intruded by granitic stocks and embayed by granitic batholiths this study reports whole rock rb sr and zircon u pb ages for the lower and upper metavolcanics for the granitic rocks that are physically within the greenstone belt internal granites and for the granitic rocks that embay the greenstone belt external granites the apparent rb sr ages for the lower metavolcanics are 2530 90 2285 70 and 2680 490 ma the u pb ages are 2749 2 and 2744 10 ma the internal granites give an rb sr age of 2560 270 ma and a u pb age of 2737 6 ma the external granite at hawk lake indicates an rb sr age of 2550 175 ma and a u pb age of 2747 7 ma it is possible that this unit contains elements older than 2812 ma as

geochemistry of the mamainse point volcanics ontario and implications for the keweenawan paleomagnetic record the keweenawan 1100 ma mamainse point volcanics located along the eastern shore of lake superior in ontario formed in the midcontinent rift of north america they are a 5250 m thick sequence of over 350 predominantly basaltic lava flows the mamainse point section is the most continuous keweenawan volcanic sequence and spans nearly the entire igneous history of the rift the lower part of the section consists of high mgo picrites and basalts but the upper part of the section is composed of olivine tholeiites intercalated with numerous conglomerate layers major and trace element data reveal that the section consists of numerous stratigraphically constrained geochemically distinct groups of lava flows the comprehensive geochemical data on the entire sequence indicate that the section has no repetition due to faulting as has been suggested by other workers on the basis of paleomagnetic studies evidently the three paleomagnetic reversals previously found in the mamainse point section are real and

synopsis of paleomagnetic studies in the kapuskasing structural zone this paper summarizes results from paleomagnetic studies sponsored by lithoprobe on the kapuskasing structural zone ksz data from archean rocks outside the ksz indicate that the wawa subprovince has not been significantly rotated or translated 5 relative to the abitibi subprovince results from the granulites and amphibolites indicate that the ksz underwent several kilometres of uplift at ca 2 51 ga and then 10 5 west northwest tilt with several kilometres of further uplift between 2 04 and 1 88 ga from thrust faulting on the ivanhoe lake fault zone localized chemical remagnetization occurred at 1 1 ga along the west side of the shawmere anorthosite paleomagnetic data from the 2 45 ga matachewan diabase dike swarm indicate that it was emplaced within one reversed to normal polarity interval of less than 5 ma their polarity pattern indicates major north trending faults with several kilometres of dip slip displacement their remanence confirms that the superior province was deformed around th

tectonic evolution of the himalayan syntaxes the view from nanga parbat acknowledgements i was introduced to the himalayas by mike coward in the mid 1980s and remain indebted to him for inspiring a career studying orogenic tectonics i also thank the numerous colleagues both from the uk and from peshawar university who were companions on many field campaigns especially around nanga parbat this contribution has been greatly improved by incisive reviews by tom argles and phaedra upton although of course the author takes full responsibility for the views presented here finally i thank peter treloar for inviting this review and for his patience while i put it together funding over the years this research has been variously supported by the uk s natural environment research council and the royal society published in himalayan tectonics a modern synthesis

archean crust as revealed in the kapuskasing uplift superior province canada in the central superior province of the canadian shield a 120 km wide transition from the low grade michipicoten greenstone belt to the high grade kapuskasing structural zone represents an oblique section through some 20 km of archean crust uplifted along a northwest dipping thrust fault the restored vertical section through the upper and middle crust consists of three megalayers with undulating boundaries 1 0 to 25 km a high grade heterogeneous gneissic assemblage in part older than the upper supracrustal succession

regional variation in paleomagnetic polarity of the matachewan dyke swarm related to the kapuskasing structural zone ontario the 2 45 ga matachewan dykes from the abitibi subprovince of the canadian shield yield a mean paleomagnetic pole of 42 n 58 e 95 3 n sites 36 which is a composite of new and previously published data domains of paleomagnetic polarity are defined an area of dykes predominantly of reversed magnetization in the abitibi subprovince contrasts with an area of exclusively normal dykes to the north the polarity domains are separated by faults related to the 1 95 ga uplift and exposure of the lower crust in the kapuskasing structural zone and therefore reflect hudsonian age tectonics in the archean superior province

the growth of non colinear normal fault systems what can we learn from 3d seismic reflection data abstract many rift zones exhibit a range of fault orientations rather than simple colinear faults that strike orthogonal to the inferred least principal stress the formation of non colinear fault sets has implications for assessing rift zone kinematics as well as determining palaeo stress state in extensional basins using 3d seismic reflection data we deduce the likely mechanisms responsible for the formation of a population of non colinear faults in the maloy slope area of the northern north sea three basement displacing fault populations exist on the maloy slope i large 1 km throw n s striking faults ii smaller

constraints on the nature of the kapuskasing structural zone from the study of proterozoic dyke swarms petrochemical paleomagnetic and structural studies on early proterozoic dyke swarms show that the rocks of the kapuskasing structural zone ksz central superior province were upthrust about 10 15 km along the ivanhoe lake fault after intrusion of 2 04 ga kapuskasing dykes this uplift was part of a more widespread deformation in flanking terranes that involved sinistral motion along north north northwest trending faults dextral displacement along east northeast northeast trending faults and a distortion of the 2 45 ga matachewan swarm to the west and northwest of the ivanhoe lake fault the most spectacular demonstration that the ksz is largely a product of proterozoic deformation is that matachewan dykes change their magnetic polarity on crossing the zone a consequence of remanence acquisition at deep crustal levels being delayed until after a reversal of the earth s magnetic field and prior to uplift of the dykes matachewan and kapuskasing dykes within the amphibolite to granulite grade rocks o

broad scale proterozoic deformation of the central superior province revealed by paleomagnetism of the 2 45 ga matachewan dyke swarm an extensive paleomagnetic study of the 2 45 ga matachewan dyke swarm of the north american superior province suggests that the interior of an archean shield can undergo broad scale distortion as a result of later proterozoic orogenic activity around the craton margins data collected from over 300 sites of which 137 are reported here for the first time reveal that the dykes contain a dual polarity primary remanence that varies across the swarm in both inclination and declination these regional variations are statistically significant at the 95 confidence level and cannot be attributed to remagnetization or to magnetic anisotropy inclination variation is probably due to real or apparent polar wander during the emplacement of the swarm and may in part explain the declination variation as well however for dykes within and northwest of the kapuskasing structural zone ksz a positive correlation is found between regionally averaged values of declination and dyke trend here the dykes appear to hav

late precambrian keweenawan asymmetric reversals palaeopoles from the keweenawan 1 200 1 000 myr rocks of the lake superior region form the western and eastern arms of the great logan palaeomagnetic loop 1 5 fig 1a this is defined by both normal n and reversed r poles which are the consequence of at least two geomagnetic reversals4 6 7 the younger one r n has been detected throughout the lake superior region from various rock types 1 6 the older reversal n r is only recorded in the lowermost keweenawan lavas in the southern part of the lake 8 wherever found the reversals depart from the 180 symmetry fig 1a 2 6 due to these asymmetries the logan loop has large segments that are devoid of data and thus the geophysical interpretations of the loop or hairpin critically depend on the cause of the reversal asymmetry 4 four models11 secondary component6 apparent polar wander1 5 wilson s dipole offset5 7 9 and non dipole field configuration1 3 10 have been put forward to explain the asymmetries here we demonstrate that the two dipole field configuration model can explain the reversal asymmetries and discuss the global effects of this model in the light of worldwide late precambrian palaeomagnetic data

misoriented faults in exhumed metamorphic complexes rule or exception abstract low angle normal faults and other weak faults are common in the metamorphic core of collisional orogens they frequently show a phyllosilicate rich mylonitic foliation that was reactivated under brittle conditions experimental and theoretical works indicate that mechanical anisotropies exert a substantial influence on shear failure and frictional sliding eventually inhibiting the nucleation and propagation of new andersonian shear fractures and favoring the localization of brittle failure along the pre existing foliations metamorphic phyllosilicate rich rocks may show a friction coefficient varying from 0 6 at high angles to the foliation to 0 2 0 4 for shear along the inherited foliation to test the influence of mechanical anisotropies on the development of non andersonian faults we have applied a modified slip tendency analysis to three misoriented phyllosilicate rich faults of the european alps the analysis accounts for anisotropy in friction coefficients and has been named anisotropic slip tendency analysis here we show that brittle deformation along misoriented phyllosilicate rich foliations is more probable than the development of new andersonian faults the presence of a well developed network of weak phyllosilicate rich faults may influence the overall structural style and mechanical properties of the brittle lithosphere in collisional orogens

paleomagnetism of the clay howells carbonatite complex constraints on proterozoic motion in the kapuskasing structural zone superior province canada abstract the clay howells complex is located approximately 130 km east of hearst ontario at 49 50 n 82 05 w near the north end of the kapuskasing structural zone ksz of the superior province in the canadian shield the pluton is a large oviform pluton of about 16 km2 that is composed dominantly of syenite with minor carbonatite it was emplaced into an archean gneissic terrain of amphibolite to granulite facies with middle precambrian diabase dikes the complex is unmetamorphosed and late precambrian in age rb sr 1075 15 ma multistep alternating field af and thermal demagnetization was carried out on 194 specimens from 18 sites in the intrusion and three sites in the host rock dikes and gneisses the 18 syenite sites give a unit mean direction of 294 2 27 1 n 18 k 26 95 7 0 which yields a pole position of 178 8 e 26 5 n p 4 1 m 7 6 for the clay howells complex a crude contact test using the three host rock sites proved inconclusive the pole for the intrusion is concordant falling at about 1080 10 ma on the keweenawan apparent polar wander path which agrees with the rb sr age thus the complex has an untilted primary remanence that indicates that there has been no significant uplift

rb sr biotite and whole rock data from the kapuskasing uplift and their bearing on the cooling and exhumation history rb sr isotopic ratios were measured on biotite and whole rocks from a suite of 21 granitoid rocks from the southern kapuskasing uplift results of 18 of the whole rock analyses fall on an isochron with an age of 2 677 0 057 ga and sri 0 70080 biotite model ages range from 2 50 to 1 93 ga in a general spatial relationship of decreasing age with depth in the structural section as calibrated with the igneous hornblende barometer for tonalitic rocks and garnet pyroxene barometers for granulites near the michipicoten belt in the west biotite ages of 2 ga reflect disturbances also recorded by paleomagnetic and whole rock rb sr systems to the east in a 70 km long northwest southeast transect toward the ivanhoe lake fault zone ages decrease from 2 50 to 1 95 ga in a southern transect ages are in the range 2 30 2 38 ga to within 15 km of the fault reflecting consistent erosion levels corresponding to 0 53 mpa but decrease to 1 93 ga to the east in concert with paleopressures in the 0 7 1 0 gpa ra

evolution of shear zones through the brittle ductile transition the calamita schists elba island italy abstract a network of shear zones that evolved through the brittle ductile transition is exposed in the calamita schists elba island italy the shear zones formed during late miocene contractional deformation coeval with high grade contact metamorphism 650 c related to the emplacement of plutonic rocks at shallow crustal levels 7 10 km an early stage high metamorphic grade foliation was overprinted by mylonitic deformation that progressively localized on low metamorphic grade shear bands producing s c mylonites during cooling of contact aureole localization of deformation on shear bands was driven by temperature decrease that triggered strain partitioning between hard high grade relics and soft shear bands softening of shear bands occurred likely due to fluid influx and retrograde growth of fine grained phyllosilicates the interconnection of anastomosing shear bands and passive rotation of the relic high grade foliation caused widening of the shear bands producing mylonites with a composite mylonitic foliation and c shear bands an estimate of the vorticity number wk of the flow of 0 3 0 5 was obtained from the orientation of c shear bands measured at the meso and thin section scale close to the brittle ductile transition the growth of soft phyllosilicates allowed c shear bands to act as precursory structures to brittle deformation localized into an array of low angle faults and shear fractures

the matachewan dyke swarm canada an early proterozoic magnetic field reversal abstract consistent age relationships between oppositely magnetized dykes of the 2 45 ga matachewan dyke swarm suggest that only a single magnetic field reversal occurred during the period of igneous activity the magnetic field throughout most of this time was characterized by a ssw declination and shallow negative inclination but reversed toward the waning stages of magmatism the new paleomagnetic data provide the oldest known magnetic reversal for which the relative reversal sense is known

proterozoic magnetic overprinting of archaean rocks in the canadian superior province we have measured the various components of natural remanent magnetization nrm exhibited by mafic extrusive and intrusive rocks from the abitibi subprovince of the canadian precambrian shield in addition to providing what seems to be a primary archaean pole for the region the results testify to three episodes of magnetic overprinting at approximately 2 600 2 100 and 1 800 myr respectively the two earlier episodes coincide with the intrusion of matachewan and abitibi diabase dyke swarms here and elsewhere in the superior province magnetic overprinting in these cases extends far beyond areas of surficial dyke exposure the third episode postdates magmatic activity in the abitibi region but coincides in age with the 1 900 1 700 myr hudsonian orogeny in the churchill and bear provinces and the penokean orogeny in the southern province although magnetic overprints presumed to be of this age were known previously from abitibi dykes1 and nipissing sills2 4 our data are the first evidence of a 1 800 myr magnetic overprinting on a regional scale in the superior province

paleomagnetic evidence for proterozoic tectonism in the kapuskasing structural zone ontario the kapuskasing structural zone ksz in the superior province of north central ontario is thought to be an oblique cross section through middle archean crust samples from 30 sites in granulite gneisses and anorthosites of the ksz have been analyzed using alternating field and thermal demagnetization methods three remanent magnetization components were found with mean directions of d 23 i 50 k 52 95 11 n 5 sites for the a component d 73 i 68 k 50 95 5 n 18 for the b component and d 332 i 59 k 53 95 17 n 3 for the c component v constanzo alvarez and d j dunlop found similar a and b components in less metamorphosed rocks from the same units to the immediate west they attributed the a component to uplift at 2 55 ga with subsequent 15 to 30 wnw tilt and the b component to thermochemical overprinting at 1 1 ga as the ksz was reactivated during keweenawan rifting and volcanism we also attribute the a component to uplift during the 2 55 ga kenoran orogeny with concomitant 10 5 wnw downward tilting before intrusion of the 2 45 ga matachewan dikes to give its present paleopole of 33 e 67 dp 6 dm 9 n 13 using data from both studies we attribute acquisition of the b component to uplift at about 1 88 ga as suggested by recent thermal modeling and tectonic syntheses to give a paleopole of 124 w 30 n dp 7 dm 8 n 20 the c component is found in only three sites and may be either an hybrid of a 1 1 ga keweenawan crm with the b component or a fault block tilted b component near the ivanhoe lake cataclastic zone

impact of erosion and decollements on large scale faulting and folding in orogenic wedges analogue models and case studies deformation mechanisms long term kinematics and evolution of fold and thrust belts subjected to erosion are studied through 2d analogue experiments involving large convergence first order parameters tested include 1 decollements and or plastic layers interbedded at different locations within analogue materials and 2 synconvergence surface erosion weak layers depending on their location in the model favour deformation partitioning characterized by the simultaneous development of underplating domains in the inner part of the wedge basal accretion and frontal accretion where the wedge grows forward interaction between tectonics and surface processes influences this behaviour development of antiformal thrust stacks controlled by underplating shows small and large scale cyclicity thin plastic layers induce folding processes which are studied at wedge scale recumbent and overturned folds with large inverted limbs develop in a shear induced asymmetric deformation regime via progressive unrolling of synclinal hinges surface erosion and underplating at depth induce further rotation passive tilting and horizontalization of fold limbs model results give insights to discuss the mechanisms responsible for the large scale structures i e antiformal nappe stacks klippen and kilometre scale recumbent fold nappes encountered in several mountain belts such as the montagne noire french massif central the galicia variscan belt spain and the northern apennines italy supplementary material raw data of the experiments are available at www geolsoc org uk sup18658

quantitative estimates of emplacement level of postmetamorphic mafic dykes and subsequent erosion magnitude in the southern kapuskasing uplift the early proterozoic matachewan 2 454 ga and kapuskasing 2 04 ga dyke swarms of the central superior province have similar petrographic features including zoned igneous plagioclase and clinopyroxene and interstitial amphibole and quartz dyke crystallization conditions can be estimated using equilibria involving amphibole by assuming that igneous mineral rims reached equilibrium with the interstitial phases twq software using 33 amphibole bearing equilibria yields temperatures ranging from 552 to 811 c with an average of 680 c the average of two calibrated pressure sensitive equilibria 2 diopside 2 quartz tschermakite tremolite 2 anorthite and diopside 5 quartz pargasite tremolite anorthite albite ranges from 0 32 to 0 70 gpa for matachewan dykes and from 0 30 to 0 57 gpa for kapuskasing dykes because dyke pressures are lower than metamorphic pressures in the amphibolite and granulite facies archean country rocks the values represent feasible emplacement pressures the regi

paleomagnetism of alkaline complexes and remagnetization in the kapuskasing structural zone ontario canada the shenango and nemegosenda alkaline complexes of the southern kapuskasing structural zone ksz an uplifted crustal block in northern ontario preserve primary thermoremanent magnetizations with mean directions d 112 i 46 k 13 95 13 n 9 sites and d 304 i 51 k 31 95 10 n 7 sites for shenango and d 124 i 57 k 13 9520 n 4 sites and d 312 i 54 k 17 95 13 n 7 sites for nemegosenda their average paleomagnetic pole is 45 n 189 e dp 6 dm 8 falling on the keweenawan track of the north american apparent polar wander path apwp between 1098 1107 ma reverse polarity r and 1087 1098 ma normal polarity n poles of lake superior lavas and dikes unlike the keweenawan paleopoles which have a reversal asymmetry of 30 the shenango and nemegosenda r and n poles are almost 180 reversed which was found also by lewchuk and symons 1990b this symmetry of r and n poles casts doubt on the previously accepted predominance of asymmetric reversals of the earth s field in keweenawan time the archean shawmere anorthosite is overprinted by a b magnetization with mean direction d 97 i 68 k 12 95 10 n 18 sites the shawmere b paleopole at 38 n 226 e dp 13 dm l6 falls between the carbonatite poles and 1850 ma cratonic poles and the b magnetization seems to be a composite of middle and late proterozoic overprints sites in the western part of the shawmere body close to the carbonatite line of faults linking the various alkaline complexes are severely altered with an abundance of secondary magnetite and hematite virtual geomagnetic poles for these sites fall close to the keweenawan track and have an average pole of 189 53 n dp 15 dm 20 suggesting that the b nrm at these sites is an 1100 ma thermochemical overprint caused by hydrothermal fluids at the time of carbonatite intrusion more easterly sites are less altered their vgps resemble 1850 ma cratonic poles and average to 235 e 30 n dp 15 dm 17 these b natural remanent magnetizations are probably thermochemical remanent magnetizations impressed by middle proterozoic hydrothermal activity associated with intrusion of early alkaline bodies fault movement on the ivanhoe lake fault zone or late stage uplift of the ksz

tectonic controls on the uplift of the nanga parbat massif pakistan himalayas cenozoic mountain belts like the himalayas contain regions that experienced rapid uplift in comparison with the areas around them1 whether this uplift occurred by buoyant rebound of previously thickened crust2 or during the crustal thickening process itself is uncertain3 4 here we show however that the 7 mm yr 1 recent uplift5 of the nanga parbat massif pakistan himalayas was accomplished during nw directed thrusting located along its western margin this 3 km wide liachar thrust zone operated from amphibolite facies to the present topographic surface and accommodates substantial crustal shortening the adjacent indus river valley itself cut by seismogenic faulting completely transects the massif showing that erosion keeps pace with geologically rapid thrust uplift6

numerical and experimental investigation of flow and scour around a circular pile the flow around a vertical circular pile exposed to a steady current is studied numerically and experimentally the numerical model is a three dimensional model the model validation was achieved against new experimental data which include two component laser doppler anemometry lda flow measurements and the hot film bed shear stress measurements and reported in the present paper and the data of others and a k w turbulence model was used for closure the model does not have a free surface facility and therefore is applicable only to cases where the froude number is small fr 0 0 2 the flow model was used to study the horseshoe vortex and lee wake vortex flow processes around the pile the influence on the horseshoe vortex of three parameters namely the boundary layer thickness the reynolds number and the bed roughness was investigated in the latter investigation the steady solution of the model was chosen a study of the influence of the unsteady solution on the previously mentioned flow processes was also carried out the ranges of the parameters covered in the numerical simulations are the boundary layer thickness to pile diameter ratio is varied from 2 x 10 2 to 10 2 the pile reynolds number from 10 2 to 2 10 6 and the pile diameter to roughness ratio from 2 to about 10 3 the amplification of the bed shear stress around the pile including the areas under the horseshoe vortex and the lee wake region was obtained for various values of the previously mentioned parameters the steady state flow model was coupled with a morphologic model to calculate scour around a vertical circular pile exposed to a steady current in the case of non cohesive sediment the morphologic model includes i a two dimensional bed load sediment transport description and ii a description of surface layer sand slides for bed slopes exceeding the angle of repose the results show that the present numerical simulation captures all the main features of the scour process the equilibrium scour depth obtained from the simulation agrees well with the experiments for the upstream scour hole some discrepancy up to 30 was observed however for the downstream scour hole the calculations show that the amplification of the bed shear stress around the pile in the equilibrium state of the scour process is reduced considerably with respect to that experienced at the initial stage where the bed is plane

relative age of otto stock and matachewan dykes from paleomagnetism and implications for the precambrian polar wander path north trending diabase dykes within and near the otto syenite stock of the kirkland lake area of the superior province carry a stable paleomagnetic remanence identical to that of 2454 2 ma matachewan dykes far from the stock a positive baked contact test for the remanence of a dyke within the stock demonstrates that the remanence is primary thus 1 these dykes belong to the matachewan swarm 2 the otto stock has not magnetically overprinted matachewan dykes in its contact aureole as previously reported and 3 the stock must be older than 2454 ma the magnetic remanence associated with the otto stock previously thought to be primary must now be considered of uncertain age nevertheless the positive baked contact test for the remanence of the matachewan dyke within the stock demonstrates that the remanence associated with the stock predates intrusion of the matachewan swarm the conventional polar wander path for precambrian north america decreases in age from the matachewan paleopole to the otto

edge scour at scour protections around piles in the marine environment laboratory and field investigation abstract when building offshore wind turbines with monopile foundations scour protection typically is placed to avoid scouring of the soil close to the monopile an important aspect is that the scour protection itself causes erosion inflicted by the local increase in current and or wave velocities and in turn increased bed shear stresses scour of the edge material alongside the scour protection may cause deformations and failure of the scour protection of offshore wind turbine foundations this can reduce the stability of the stone layer and cause exposure of cables running between the monopiles where they go from buried to the transition piece on the foundation although much information is available on the design of scour protection systems around monopiles little is known on the mechanisms causing edge scour and the equilibrium stages of the edge scour process in steady current waves and combined waves and current this paper presents an extensive experimental campaign to explain the edge scour process in current and combined irregular waves and current as well as tidal current the three dimensional flow field around the pile and scour protection is resolved by particle image velocimetry and bed shear stress measurements showing a local increase in the flow velocities and bed shear stresses leading to increased sediment transport and scour the governing process in steady current is a pair of symmetrical counter rotating vortices emerging in the near bed region in the wake of the pile and scour protection causing a significant downstream scour hole it is found that the equilibrium scour hole depth and length scales with the pile diameter and the ratio between the thickness and the width of the scour protection in the second part of the present paper the results from the experimental campaign are compared with the edge scour experienced in practice outlined by a survey program of the offshore wind park egmond aan zee and a published field investigation of scroby sands owf by whitehouse et al 2011

influence of turbulence on bed load sediment transport this paper summarizes the results of an experimental study on the influence of an external turbulence field on the bed load sediment transport in an open channel the external turbulence was generated by 1 a horizontal pipe placed halfway through the depth ih 2 a series of grids with a clearance of about one third of the depth from the bed and extending over a finite length of the flume and 3 a series of grids with a clearance in the range 0 1 1 0 ih from the bed but extending over the entire length of the flume two kinds of experiments were conducted plane bed experiments and ripple covered bed experiments in the former case the flow in the presence of the turbulence generator was adjusted so that the mean bed shear stress was the same as in the case without the turbulence generator in order to single out the effect of the external turbulence on the sediment transport in the ripple covered bed case the mean and turbulence quantities of the streamwise component of the velocity were measured and the shields parameter due to skin friction was determined the shields parameter together with the rms value of the streamwise velocity fluctuations was correlated with the sediment transport rate the sediment transport increases markedly with increasing turbulence level

clear water scour at cylindrical piers the results of laboratory experiments on the clear water local scour of cohesionless bed sediment at cylindrical piers are presented based on the data equilibrium depth of local scour is related to the particle size distribution of the bed sediment mean particle size of the bed sediment relative to the pier diameter flow depth relative to both the pier diameter and the mean particle size of the bed sediment a formula for estimating the maximum depth of local scour is also given

experimental investigation of incipient shear failure in foliated rock abstract it has long been known that rock fabric plays a key role in dictating rock strength and rheology throughout earth s crust however the processes and conditions under which rock fabric impacts brittle failure and frictional strength are still under investigation here we report on laboratory experiments designed to analyze the effect of foliation orientation on the mechanical behavior and associated microstructures of simulated fault rock sheared at constant normal stress of 50 mpa intact samples of pennsylvania slate were sheared with a range of initial fabric orientations from 0 to 165 with respect to the imposed shear direction foliation orientations of 0 30 produce initial failure at the lowest shear stress while samples oriented at higher angles are less favorable resulting in higher peak failure strength in all samples post peak development of through going deformation zones in the r1 riedel orientation results in a residual strength that is lower than that observed for powdered gouge from the same material as shear strain increases all samples approach a residual apparent friction defined by the ratio of shear strength to normal stress of 0 4 however the final deformation microstructure depends strongly on the orientation of the pre existing foliation when fabric is oriented at low angles to the shear direction

structural anisotropy using image analysis to quantify block in matrix fabrics abstract block in matrix rock assemblages such as melanges are structurally complex units whose fabric is primarily defined not by planar or linear features as most rock units are but by the orientation and aspect ratio of irregularly shaped blocks despite this previous attempts to quantitatively characterize melange fabrics have predominantly focused on measuring the foliation using traditional techniques here we introduce a method of characterizing block in matrix fabrics using image analysis of field photos to discern the aspect ratios and orientations of blocks and define the structural anisotropy of the rock unit we also include the software to calculate structural anisotropy and the trend of the fabric from image analysis data

onaping fault system age constraints on deformation of the kapuskasing structural zone and units underlying the sudbury structure the deformation of the matachewan dyke swarm of the superior province which includes a 60 km right lateral offset and moderate uplift localized along the kapuskasing structural zone represents an

u pb zircon ages and the evolution of the michipicoten plutonic volcanic terrane of the superior province ontario the archean michipicoten greenstone belt of the superior province in ontario is made up of supracrustal rocks divided into lower middle and upper metavolcanic rocks with associated metasedimentary rocks the belt has been intruded by granitic rocks and is also surrounded by granitic terranes based on u pb zircon geochronology it appears that volcanism in the area extended from at least 2749 to 2696 ma and plutonism and tectonic activity extended from at least 2888 to 2615 ma the various granitic and also one gabbroic plutons both internal and external to the greenstone belt were emplaced concomitantly with the three volcanic cycles as well as before and after the formation of the volcanic rocks zircon ages reported here together with previously published ages show that the area evolved in six major volcanic and plutonic events i 2888 ma plutonism ii 2743 ma volcanism and plutonism iii 2717 ma volcanism and plutonism iv 2696 ma volcanism and plutonism v 2668 ma plutonism and vi

experimental investigation of clear water local scour at pile groups experiments of local scour around pile groups are carried out under steady clear water scour conditions a variety of conditions including different pile group arrangements spacing flow rates and sediment grain sizes are considered in total 112 experiments are carried out it is observed that the scour hole depth for some cases of pile groups increases as much as two times more than its magnitude for the case of single piles the data from this study and some laboratory experiment data from previous works are used to derive a correction factor to predict the maximum local scour depth for the pile groups two well known equations i e federal highway administration hydraulic engineering circular no 18 hec 18 reported by richardson and davis in 2001 and the new zealand pier scour equation reported by melville and coleman in 2000 are considered the prediction of scour hole based on the present correction agrees well with the observations

paleomagnetism of the hearst dike swarm and implications for the tectonic history of the kapuskasing structural zone northern ontario prominent north to northwest trending dikes herein termed the hearst swarm west of the kapuskasing structural zone ksz in northern ontario yield a paleomagnetic pole position of 48 6 n 69 0 e dm 6 9 dp 3 6 60 samples from 12 dikes using paleomagnetic petrographic and structural criteria the hearst swarm is correlated with the 2 6 ga matachewan swarm east of the ksz a positive correlation is observed between the trend and paleomagnetic declination of hearst matachewan dikes and may result from an 15 post 2 6 ga rotation of terranes across the ksz paleomagnetic and structural data from the hearst dikes are consistent with the regional westward tilting of the crust near the southern ksz as first proposed in 1983 by percival and card

continental rifting parallel to ancient collisional belts an effect of the mechanical anisotropy of the lithospheric mantle analysis of major rift systems suggests that the preexisting structure of the lithosphere is a key parameter in the rifting process rift propagation is not random but tends to follow the trend of the orogenic fabric of the plates systematically reactivating ancient lithospheric structures continental rifts often display a clear component of strike slip deformation in particular in the early rifting stage moreover although the close temporal and spatial association between flood basalt eruption and continental breakup suggests that mantle plumes play an important role in the rifting process there is a paradox between the pinpoint thermal and stress perturbation generated by an upwelling mantle plume and the planar geometry of rifts these observations suggest that the deformation of the lithosphere especially during rifting is controlled by its preexisting structure on the other hand 1 the plasticity anisotropy of olivine single crystal and aggregates 2 the strong crystallographic orientation of olivine observed in mantle xenoliths and lherzolite massifs and 3 seismic anisotropy data which require a tectonic fabric in the upper mantle coherent over large areas suggest that preservation within the lithospheric mantle of a lattice preferred orientation lpo of olivine crystals may induce a large scale mechanical anisotropy of the lithospheric mantle we use a polycrystal plasticity model to investigate the effect of a preexisting mantle fabric on the continental breakup process we assess the deformation of an anisotropic continental lithosphere in response to an axi symmetric tensional stress field produced by an upwelling mantle plume by calculating the deformation of textured olivine polycrystals representative of the lithospheric mantle at different positions above a plume head model results show that a lpo induced mechanical anisotropy of the lithospheric mantle may result in directional softening leading to heterogeneous deformation during continental rifting this mechanical anisotropy may induce strain localisation in domains where extensional stress is oblique 30 55 to the preexisting mantle fabric this directional softening associated with olivine lpo frozen in the lithospheric mantle may also guide the propagation of the initial instability that will follow the preexisting structural trend the preexisting mantle fabric also controls the deformation regime imposing a strong strike slip shear component a lpoinduced mechanical anisotropy may therefore explain the systematic reactivation of ancient collisional belts during rifting structural inheritance the plume rift paradox and the onset of transtension within continental rifts fl 2001 elsevier science b v all rights reserved

age of the firesand river carbonatite complex from paleomagnetism the 2 3 km diameter firesand river complex intrudes archean volcanics and granites of the wawa subprovince in the superior province about 8 km east of wawa ontario it has given differing middle proterozoic k ar biotite ages of 1018 50 and 1097 ma alternating field and thermal step demagnetization of specimens from three calcific carbonatite sites five ferruginous dolomitic carbonatite sites and one lamprophyre dike site isolated a stable mean direction of 290 33 95 12 isothermal remanent magnetization tests indicate the remanence is held by single to pseudosingle domain magnetite and hematite in the carbonatite the dike remanence is keweenawan in age thereby confirming its genetic relationship to the complex and it gives a positive partial contact test with its host rock indicating no postintrusive remagnetization the blocking temperature spectra indicate that postintrusive uplift has not exceeded about 4 km the pole position for the complex is 183 e 27 n dp 8 dm 13 this

deep crustal structure and tectonic history of the northern kapuskasing uplift of ontario an integrated petrological geophysical study the northeast trending kapuskasing uplift transects the east west belts of the central superior province over a distance of some 500 km granulite to upper amphibolite facies rocks of the uplift form three distinct geological geophysical entities from south to north the chapleau groundhog river and fraserdale moosonee blocks uplift of the granulites along a moderately northwest dipping crustal scale thrust fault is attributed to an early proterozoic compressional event major northeast striking faults that bound the kapuskasing zone on the west were examined by modelling of geophysical anomalies to determine dip and by geobarometry of garnet orthopyroxene plagioclase quartz assemblages to determine vertical displacement granulites in the kapuskasing zone have 7 to 9 kbar signatures whereas those in the quetico belt to the west indicate metamorphic pressure of 4 6 kbar individual calibrations of the barometer yield consistent pressure differences of 2 3 kbar suggesting 7 10 km of west side down movement on the faults modelling of gravity and aeromagnetic gradients indicates westerly dips of 60 65 with west side down offset of up to 14 km these major normal faults probably formed as collapse structures in response to crustal thickening which occurred during the preceding compressional uplift stage differences in the configuration of individual blocks of the kapuskasing zone can be related to variable fault slip and intersection angles between normal and reverse faults thus the groundhog river and southern fraserdale moosonee blocks are perched thrust tips analogous to the sangre de cristo range of the laramide uplift province whereas the southern chapleau block is a tilted slab with similar configuration to the laramide wind river range pop up geometry deduced for the northern fraserdale moosonee block resembles the structure of the laramide uinta mountains a normal fault crosses the surface trace of the basal thrust fault between the groundhog river and fraserdale moosonee blocks and causes a 65 km gap without granulites this article contains supplementary material