origin and tectonometamorphic history of the repulse bay block melville peninsula nunavut exotic terrane or deeper level of the rae craton the rae craton on melville peninsula nunavut comprises several lithotectonic domains including a structurally and lithologically distinct yet poorly known crustal terrane the repulse bay block rbb this study presents new lithological and petrographic observations combined with u pb zircon data to better understand the archean and paleoproterozoic crustal evolution of the rbb the new data demonstrate that the central eastern rbb consists of the following i upper amphibolite to granulite facies ca 2 73 2 71 ga intermediate granitoid gneisses and gabbroic sheets ii ca 2 69 ga two pyroxene charnockite to enderbite intrusions and iii thin slivers of both archean and paleoproterozoic supracrustal rocks inherited zircon also attests to the presence of a mesoarchean to paleoarchean substrate a semi pelitic gneiss from one of the paleoproterozoic supracrustal panels was deposited sometime after ca 1 89 ga and shows a similar detrital zircon age profile to a 1 92 ga semi pelitic gneiss fr

structure of a paleoproterozoic continent continent collision zone a lithoprobe seismic reflection profile across the trans hudson orogen canada abstract an 800 km reflection seismic profile across the trans hudson orogen northern saskatchewan and manitoba images crustal scale tectonic imbrication in an unprecedented picture of paleoproterozoic crustal accretion and continent continent collisional tectonism the profile is crudely symmetric about a crustal scale culmination in the western part of an accreted juvenile collage reindeer zone geologic and isotopic data suggest that this culmination is cored by microcontinental archean basement west of the culmination highly reflective juvenile crustal elements dip westward into the lower crust beneath the wathaman batholith and archean continental crust of hearne craton to the east strong reflections in the juvenile reindeer zone crust and reworked archean foreland of the thompson belt have eastward dips persisting into the middle crust and extending beneath the superior craton a continuous reflection moho well defined for 500 km in the western part of the profile shows marked relief 12 15 s including a prominent root below the crustal culmination these imaged structures give evidence of substantial crustal shortening and thickening via large scale imbrication consistent with collisional orogeny w dipping structures below the wathaman batholith and reworked hearne craton may reflect subduction polarity in this part of the orogen however geological evidence suggests that e dipping structures below superior craton are largely related to late post collisional deformation rather than to prior oceanic subduction polarity

kinematic stratification in the hinterland of the central scandinavian caledonides abstract a transect through west central norway illustrates the changing geometry and kinematics of collision in the hinterland of the central scandinavian caledonides a depth section through the crust is exposed on fosen peninsula comprising three tectonic units separated by two shear zones the lowest unit exposed in the roan window is a modestly deformed caledonian granulite complex framed by a subhorizontal decollement with nw se oriented lineations and kinematic indicators showing top to the northwest transport the middle unit the vestranden gneiss complex contains relict granulites but was penetratively deformed at amphibolite facies to produce an orogen parallel family of structures during translation on the decollement shallow plunging lineations on steep schistosities are subparallel to fold axes of the dominant upright non cylindrical folds a small component of sinistral strike slip is also recorded in contrast southernmost fosen peninsula contains an abundance of cover rocks infolded with proterozoic basement in a fold nappe with shallow e dipping schistosities down dip lineations and orogen oblique top to the west shear sense indicators a ne striking sinistral shear zone separates the gneisses from southern fosen deformation in the scandian hinterland was partitioned both in space and time with orogen parallel extension and shear at middle structural levels and orogen oblique transport at shallower levels

origin of deep crystal reflections seismic profiling across high grade metamorphic terranes in canada abstract in an attempt to better understand the origin of deep crustal reflections lithoprobe has sponsored or co sponsored seismic reflection surveys across tracts of high grade metamorphic rock in the archean superior craton the proterozoic grenville orogen and the phanerozoic cordilleran orogen common to these three diverse terranes are near surface zones of prominent seismic reflectivity that are typically associated with velocity discontinuities at highly strained contacts between gneissic rocks of varying lithology at some locations the reflective layering resulted from transposition and rearrangement of previously layered rocks stratified assemblages sills etc whereas in other regions it was generated by extreme attenuation stretching and ductile flow of weakly layered or irregularly organized rocks it seems likely that compositionally layered gneissic rock is a common source of reflections in the deep crust with reflections originating at lithological boundaries and zones of mylonite

plutonism deformation and metamorphism in the proterozoic flin flon greenstone belt canada limits on timing provided by the single zircon pb evaporation technique the authors have used the single zircon pb evaporation technique to determine the age of granitoids in the western flin flon domain of the trans hudson orogen in canada and to constrain the timing of molasse sedimentation deformation metamorphism and mesothermal gold mineralization the plutons were intruded between 1 860 and 1 834 ma about 30 m y after volcanism and provide further evidence of a major period of intrusive activity throughout the trans hudson orogen at that time the older plutons 1 860 to 1 848 ma are synchronous with p2 deformation and the early stages of peak metamorphism whereas the younger plutons are synchronous with or postdate the p3 deformation event molasse sedimentary units are deformed and metamorphosed thus deposition must have begun at about 1 860 ma mesothermal gold mineralization postdates all plutons and may be related to high grade peak metamorphism in adjacent terranes at about 1 815 ma this study also provides further support for the use of the pb evaporation technique as a suitable method for dating single zircons and indicates that the sup 208 pb sup 206 pb ratio of zircons may be a useful tool in detecting the presence and source of xenocrystic zircons

footwall involvement during arc continent collision ungava orogen northern canada geological evidence and theoretical models are presented to illustrate deformation paths followed by continental crust during underthrusting subduction and collision fieldwork in an early proterozoic collisional orogen indicates that a thrust belt and its autochthonous footwall basement are obliquely exposed in a crustal cross section with significant structural relief the collisional orogen records an evolution in the style and extent of involvement of the archaean footwall from 1 underthrusting without evidence of internal deformation 2 limited thrusting and ductile deformation of footwall rocks to 3 folding of the entire thrust belt and its footwall into cuspate lobate long wavelength structures the structural evolution occurred during hydration of basement rocks coeval with collision related metamorphism lithospheric strength profiles constrained by simple numerical heat conduction models suggest that the observed deformation path for the footwall crust was controlled by weakening due to heating of basement rocks and by changes in the relative strengths of different crustal layers the profiles predict a very weak lower crust and upper mantle at the time of footwall involved folding suggesting that the lower crust and upper mantle deformed by ductile flow concomitant with buckling of the stronger upper crust

lithoprobe reflection studies of archean and proterozoic crust in canada abstract lithoprobe canada s national collaborative earth science research project established to develop a comprehensive understanding of the evolution of the north american continent is a multidisciplinary program spearheaded by seismic reflection studies five recently recorded seismic lines discussed in this paper are located in precambrian regions the mesoproterozoic grenville province the paleoproterozoic trans hudson orogen tho the paleoproterozoic archean basement of alberta and the archean superior province data acquired across the grenville orogen in eastern quebec show strong reflectivity throughout the crust upper crustal reflections can be correlated with exposed structural elements including extensional shear zones and packages of deformed high pressure rocks eclogites in a marine survey across the grenville orogen off southeastern labrador seismic images show variably dipping reflections and a structural high associated with a major gravity anomaly data acquired across central alberta show crustal scale thrust stacking and imbrication of the archean hearne craton to the east across the trans hudson orogen images of similar collisional features are observed geochronologic constraints indicate contemporaneity of tectonic activity between the two regions at 1 8 ga suggesting that collisional tectonic activity was coeval over a broad crustal region ca 1000 km across strike in the superior province seismic data across a collision zone involving the northern abitibi greenstone belt and the arc related opatica plutonic belt show spectacular crustal reflectivity and dipping reflections that extend 8 s 30 km into the mantle the latter feature is interpreted as representing a relict 2 69 ga old suture associated with subduction providing the first direct evidence that plate tectonics was active in the late archean these five examples supported by other lithoprobe results refute a number of generalizations about crustal reflectivity that have been made in the past and illustrate how reflection studies combined with other geoscience studies can lead to a better understanding of precambrian tectonics reflectivity persists throughout the crust there is no general separation into a poorly reflective upper crust and a reflective lower crust crustal reflectivity in archean and proterozoic regions is as pervasive as that in areas of more recent tectonism the precambrian reflection moho is generally well defined but shows a range of characteristics relative ages of reflectors can be discerned and tectonic significance can be attached to characteristic features of the crustal reflectivity

the sask craton and hearne province margin seismic reflection studies in the western trans hudson orogen a three dimensional model of the regional crustal architecture of the western trans hudson orogen based on the interpretation of 590 km of deep sounding seismic reflection data and a comparable length of existing seismic reflection information is presented the seismic images identify the regional geometry of the basal detachment zone pelican thrust that separates juvenile allochthonous terranes from the underlying archean microcontinent sask craton the sask craton is inferred to have a minimum spatial extent of over 100 000 km2 with an associated crustal root that extends for 200 km along strike during terminal collision complete convergence of the rae hearne and superior continental blocks was precluded by the presence of the sask craton resulting in the preservation of anomalous amounts of oceanic and associated sedimentary juvenile material along regional tectonic strike consistency of crustal structure across the rae hearne margin reindeer zone boundary is established several phases of

constraints on the timing of crustal imbrication in the central trans hudson orogen from single zircon 207pb 206pb ages of granitoid rocks from the pelican thrust zone saskatchewan the pelican thrust is a major ductile high strain zone in the reindeer zone trans hudson orogen northern saskatchewan it is interpreted as the main sole thrust separating stacked juvenile paleoproterozoic allochthons and underlying archean microcontinental crust in this central part of the orogen exposed nonmylonitic rocks in the footwall of the thrust consist of the sahli monzocharnockite and the smaller more highly retrograded macmillan point granite protomylonitic to ultramylonitic gneisses in the thrust zone derive from a variety of prethrust protoliths a footwall internal suite mainly comprises quartzofeldspathic orthogneisses q gneisses and high grade migmatitic paragneisses hanging wall external suite mylonitic gneisses include feldspar porphyroclastic hornblendic grey gneisses probably derived from arc plutons and laminated amphibolites derived from volcanic rocks the overlying allochthon mainly comprises protoliths equivalent to those of the porphyroclastic orthogneisses and lam

origin of the archean sask craton and its extent within the trans hudson orogen evidence from pb and nd isotopic compositions of basement rocks and post orogenic intrusions u pb zircon ages from the exposed sask craton are 2450 3100 ma from the peter lake domain 2575 2640 ma and from rocks of the trans hudson orogen 1840 1880 ma u pb monazite and zircon ages of post orogenic pegmatites and aplites are 1770 1800 ma common pb and sm nd isotopic compositions of post orogenic intrusions as probes of crust beneath the orogen were compared to sask craton rocks and ca 1850 ma orogenic rocks to infer the origin and subsurface distribution of the sask craton within the internides of the trans hudson orogen results show that post orogenic intrusions within most of the glennie domain and hanson lake block were derived at least in part from archean source materials demonstrating that the sask craton lies beneath paleoproterozoic orogenic rocks present at the surface in contrast common pb and sm nd isotopic compositions from pegmatites and aplites of the la ronge domain are essentially identical with those of the paleoproterozoic orogenic rocks into which they are intruded indicating derivation by partial melting of similar rocks thus if the sask craton extended to the west beneath the la ronge domain it was beneath the zone of melting that produced the post orogenic intrusions making it unlikely that the sask craton is a detached part of the hearne craton many samples from the sask craton have elevated pb 208 pb 204 ratios unlike superior craton or hearne craton rocks suggesting that the sask craton was derived from an exotic source such as the wyoming craton which shares similar elevated pb 208 pb 204 ratios

the seismically reflective crust beneath highly extended terranes evidence for its origin in extension reprocessed seismic reflection data from near the picacho mountains metamorphic core complex in southeastern arizona show that the crust is seismically reflective from 1 5 s two way travel time twtt to the refletion moho at 10 s twtt these high amplitude subhorizontal and laterally discontinuous reflections may be a common seismic signature of highly extended areas this study presents the results of synthetic seismogram modeling of these reflections based on drill hole and outcrop data from the picacho mountains and adjacent core complexes modeling studies suggest that the prominent reflectivity beneath the picacho mountains results from a thinly layered crust where the layers are of alternating high and low velocity and their lateral extent is on the order of 500 m moreover the lack of distinctive diffractions in the seismic data is interpreted to mean that lateral changes in velocity orlayer thickness are smooth rather than abrupt on the scale of a seismic wavelength soure for the reflectivity include fracture zones compositional layering of micaceous gneisses and granitoid rocks and zones of velocity anisotropy particularly in micaceous rocks the association of the reflectivity in metamorphic core complexes with cenozoic deformation suggests that the reflections are a by product of extension

lithoprobe crustal reflection cross section of the southern canadian cordillera 1 foreland thrust and fold belt to fraser river fault seismic reflection data from the south central canadian cordillera covering the interval from the easternmost metamorphic core complexes near arrow lakes to the fraser river fault system along the fraser river reveal a highly reflective and complex crust the base of the crustal reflectivity interpreted as the reflection moho is clearly delineated by a continuous sharp boundary that is essentially planar and slopes uniformly over a distance of 250 km from about 12 0 s in the east to about 10 5 s in the west this virtual lack of relief at the base of the crust contrasts sharply with surface structures that involve 25 km or more of structural relief some of these surface structures can be readily correlated to structures that are outlined by the reflection data and that can be followed into the middle and lower crust even though part of this area was subjected to large amounts of eocene extension the crust is not divisible into transparent upper and reflective lower layers as it is in parts of the u s cordillera three structural culminations the monashee complex the vernon antiform and the central nicola horst are interpreted on the basis of the reflection configuration and the surface geological relationships to have formed initially during jurassic to eocene compression and then to have been modified and exposed during early and middle eocene extension an example of a compressional structure observed on the profiles is the monashee decollement which can be traced from the surface westward into the lower crust extension is manifested along a variety of normal faults including the regionally extensive low angle okanagan valley eagle river fault system moderately dipping faults such as the columbia river and slocan lake faults and high angle faults such as the quilchena creek and coldwater faults both jurassic to eocene compressional shear zones and early to middle eocene extensional shear zones are listric into the lower crust or moho under the intermontane belt

lithoprobe crustal reflection structure of the southern canadian cordillera 2 coast mountains transect the lithoprobe seismic reflection transect across the southern coast mountains of the canadian cordillera images fundamental crustal structures presumably related to collision of the intermontane and insular composite terranes and deep levels in the upper plate of the offshore cascadia subduction belt the eastern part of the coast mountains are characterized by east dipping upper crustal reflectors that project to exposed faults and east dipping lower crustal reflectors they are truncated by subhorizontal to west dipping middle and upper crustal reflectors these geometric relationships are interpreted to have formed during an early phase of primarily west directed contraction that created the east dipping structures of the upper and lower crust and a later phase of east directed shortening caused by wedging of the intermontane belt into the lower and middle crust of the tectonic stack subsequently the coast belt may have been displaced eastward on contractional faults that ascend from the lower crust beneath the intermontane belt and surface in the omineca and foreland belts extensional faults bounding the east flank of the coast mountains and west flank of the central nicola horst in the intermontane belt flatten into the middle and lower crust of the intervening region and geometrically outline crustal boudinage within the western coast mountains east dipping reflections spanning the middle crust to upper mantle are traced updip to vancouver island and the underlying cascadia subduction zone the c reflector on vancouver island is believed to separate wrangellia from underlying accreted terranes and is correlated to the mainland where it forms the upper boundary of a reflective lower crustal wedge that flattens into the moho if the moho is not a young feature then some accreted material appears to have wedged into the continental framework above the crust mantle boundary possibly causing shortening in the overlying crust and creating midcrustal ramps observed on the reflection data the structurally lower e reflections interpreted as shear zones originate at the subduction contact offshore and project landward into sub moho reflections within the upper plate on the mainland the region between the e reflector and the descending oceanic plate is interpreted to be subducted lower continental crust and mantle

the 1830 ma trans hudson hairpin from paleomagnetism of the wapisu gneiss dome kisseynew domain manitoba the wapisu gneiss dome is located in the northeastern part of the kisseynew domain of the trans hudson orogen tho in north central manitoba the dome is circular about 6 km in diameter with steeply dipping flanks it is composed of upper amphibolite facies gneisses derived from turbiditic sediments with leucogranitic sill like intrusions that were metamorphosed starting at about 1830 ma alternating field and thermal step demagnetization of 153 specimens from 17 sites around the perimeter of the dome isolated a characteristic remanent magnetization chrm direction of d 346 6 i 78 9 95 5 3 k 46 n 17 that gives a pole of 119 5 w 75 8 n dp 9 5 dm 10 0 unblocking temperatures and saturation isothermal remanence analyses show that the chrm resides mostly in single to pseudosingle domain magnetite or titanomagnetite with minor hematite commonly present and with minor pyrrhotite present in the leucogranites the chrm is found to be postfolding with 99 9 confidence indi

lithogeochemistry of volcano plutonic assemblages of the southern hanson lake block and southeastern glennie domain trans hudson orogen evidence for a single island arc complex this paper describes the geology geochemistry and age of two amphibolite facies volcano plutonic assemblages in the southern hanson lake block and southeastern glennie domain of the paleoproterozoic trans hudson orogen of east central saskatchewan the hanson lake assemblage comprises a mixed suite of subaqueous to subaerial dacitic to rhyolitic ca 1875 ma and intercalated minor mafic volcanic rocks overlain by greywackes similarly with modern oceanic island arcs the hanson lake assemblage shows evolution from primitive arc tholeiites to evolved calc alkaline arc rocks it is intruded by younger subvolcanic alkaline porphyries ca 1861 ma synvolcanic granitic plutons ca 1873 ma and the younger hanson lake pluton ca 1844 ma rocks of the northern lights assemblage are stratigraphically equivalent to the lower portion of the hanson lake assemblage and comprise tholeiitic arc pillowed mafic flows and felsic to intermediate volcaniclastic rocks and greywackes which can be traced as far west

comportement du systeme u pb dans la monazite et chronologie de la deformation et du metamorphisme des metasediments du domaine de kisseynew orogene trans hudsonien manitoba canada the kisseynew domain is the central unit of the reindeer zone of the paleoproterozoic trans hudson orogen in manitoba and saskatchewan the southern flank of the domain is a transition zone betwee

magnetic properties and modelling lithoprobe seismic reflection line 7c southern kisseynew gneiss belt trans hudson orogen the missi suite comprising metamorphosed magnetite bearing molasse deposits runs west northwest across the southern part of the kisseynew gneiss belt in the trans hudson orogen it flanks an internal structural boundary north of which lies the migmatitic core of the kisseynew gneiss belt formed largely of arc derived metasediments assigned to the burntwood suite lithoprobe reflection seismic images crossing the boundary indicate north facing homoclinal structures in which the missi and burntwood suites are structurally interlayered the strong magnetic signature associated with the missi suite allows an independent assessment of the seismic models through magnetic modelling constrained by rock magnetic properties along lithoprobe line 7c the pattern of a prominent magnetic high over the missi suite and a subdued magnetic field over the burntwood suite is reflected in values of magnetic susceptibilities demonstrating a close link between magnetic anomalies and surface geology measurements of natural remanent magnetization provide an additional critical constraint for modelling in the seismic model gently folded north dipping layers become progressively less steep at depth eventually becoming subhorizontal the magnetic model indicates that layers dip at approximately 45 to a depth of about 7 km a picture supported by steep reflectors in the seismic data themselves and in down plunge structural modelling it is proposed that the layers which probably contain layer parallel imbricate thrusts are rooted in a subhorizontal decollement interpreted from the seismic image at a depth of about 10 km the magnetic model is consistent with the presence of a ramp like structure developed along the ancient margin of the kisseynew basin

early proterozoic deformation along the southern margin of the kisseynew gneiss belt trans hudson orogen a 30 ma progressive deformation cycle fold axes and lineations across the southern margin of the kisseynew gneiss belt were progressively reoriented from northwesterly to northeasterly during an early proterozoic southwest directed compressive deformation cycle partitioning of deformation resulted in a concentration of non coaxial strain along the boundary between the kisseynew gneiss belt and flin flon snow lake belt the structural evolution was complicated by streamlining of the movement vector around the comparatively rigid flin flon snow lake belt the relationship of metamorphic assemblages to kinematic fabrics indicates that deformation was coeval with a prograde retrograde metamorphic cycle progressive deformation occurred during a period of 30 ma which is consistent with phanerozoic orogenic time scales

three dimensional collisional structure of the trans hudson orogen canada abstract the three dimensional structure of the eastern trans hudson orogen tho part of a paleoproterozoic continent continent collision zone in central north america is revealed through a network of lithoprobe seismic reflection profiles the seismic images are interpreted to delineate a series of stacked thrust sheets essentially confined to the crust e w profiles show strong e dipping reflections extending throughout the crust while n s profiles record events outlining antiformal and synformal structures this allows the identification of decollements that may have localized along pre existing structures e g possible basin bounding extensional faults and at major rheological boundaries e g basement cover contact upper middle crust transition the present topographic surface displays oblique crustal sections with 10 15 km of structural relief generated during post collisional intracontinental transpression of tho as a result of crustal scale folding and faulting

crustal structure of the grenville front and adjacent terranes under the auspices of the great lakes international multidisciplinary program on crustal evolution approximately 320 km of deep seismic reflection data were collected in lake huron along a profile that extends east from the manitoulin terrane across the grenville front to the interior of the grenville orogen the manitoulin terrane is characterized by a series of gently east dipping reflections at about 20 km depth that separate a highly reflective lower crustal layer from a markedly less reflective upper layer imaged by strong reflections at the western end of a spectacular band of moderately east dipping reflections the grenville front clearly truncates manitoulin terrane structures to the west these data are interpreted in terms of a speculative two stage model involving 1 creation of a major decollement during northward collision of an allochthonous terrane with the southern superior cratonic margin 1 83 1 89 ga penokean orogeny and 2 northwest directed stacking of microterranes at the southeastern margin of the craton followed by crust penetrating ductile imbrication under high pressure high temperature conditions leading to the ramping of deeply buried rocks to the near surface 1 0 1 3 ga grenvillian orogeny

age and source of detrital zircons from the missi formation a proterozoic molasse deposit trans hudson orogen canada the missi formation in the flin flon basin forms part of a discontinuous series of molasse type sediments found throughout the early proterozoic trans hudson orogen in northern saskatchewan and manitoba the flin flon basin contains a sequence of proximal fan to braided stream fluvial conglomerates and sandstones which unconformably overlie subaerially weathered amisk group volcanic rocks stratigraphic way up indicators have been preserved even though these rocks have undergone greenschist facies metamorphism and polyphase deformation the sedimentary rocks are crosscut by intrusive rocks which provide a minimum age of sedimentation of 1840 7 ma detrital zircons from each of the six stratigraphic subdivisions of the flin flon basin were analyzed using the single zircon pb evaporation technique euhedral to slightly rounded zircons dominate each sample and these zircons give ages of between about 1854 and 1950 ma the missi sediments were thus deposited between 1840 and 1854 ma possible sources for

3d seismic imaging of volcanogenic massive sulfide deposits in the flin flon mining camp canada part 1 seismic results abstracta 17 km2 3d 3c seismic survey was conducted within the active flin flon mining camp located in manitoba canada the results for the vertical component data as obtained by conventional dip moveout and prestack time migration processing sequences and comparison of images from the 3d seismic volume with the subsurface location of known ore zones and the mine horizon generally showed a very good correlation a well defined diffraction response from the shallowest ore zone was observed in the unmigrated data with a corresponding phase reversal in the migrated data at the transition from intact ore to backfilled ore zone the geometry of unmined and backfilled ore zones compared well with strong reflection amplitudes on corresponding cross sections to depths of 1000 m at greater depths the ore zone had a weaker seismic signature due to a combination of effects including imaging conditions ore composition and the increased presence of rhyolite within the mine horizon in the case of the deeper or

accretion history of the trans hudson orogen in manitoba and saskatchewan from paleomagnetism lithoprobe s sponsorship has led to the acquisition of paleomagnetic data from 20 units throughout the paleoproterozoic trans hudson orogen tho of saskatchewan and manitoba essentially the first such data for the region discussed summarily in this paper they provide an initial framework for the tho s tectonic evolution they show that the archean hearne and superior cratons were at subtropical and subpolar paleolatitudes respectively at 1875 ma with the lynn lake laronge arc midway between them in the manikewan ocean by 1855 ma this ocean was still 5500 700 km wide and its seafloor was subducting northwestward under the hearne craton and pericratonic peter lake domain margin with the coeval development of an andean type continental magmatic arc the wathaman chipewyan batholith between 1855 and 1810 ma coalescing apparent polar wander path apwp segments record closing of the ocean at a rate of 12 cm a trapping and accreting the several separate intervening terranes flin flon hanson lake lynn lake laronge rottenstone and presumably also other tho terranes from 1815 to 1775 ma the assembled terranes drifted as a coherent craton yielding a stillstand and hairpin in the apwp

mantle heterogeneities and their significance results from lithoprobe seismic reflection and refraction wide angle reflection studiesthis article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent lithoprobe contribution 1486 within lithoprobe s 10 transects data from more than 20 000 km of multichannel seismic mcs reflection profiling and 12 refraction wide angle reflection r war surveys were acquired while the

high temperature low pressure metamorphism in the kisseynew domain trans hudson orogen crustal anatexis due to tectonic thickening the kisseynew domain within the central trans hudson orogen constitutes a high temperature t and low to medium pressure p metasedimentary belt characterized by uniform peak metamorphic conditions of 750 50 c and 5 6 kbar 1 kbar 100 mpa to investigate the thermal evolution of the kisseynew domain 1 dimensional thermal modelling was conducted for a range of thermal parameters including the effects of exhumation and incorporating current information about the crustal architecture the results show that tectonic thickening of the sedimentary pile to 40 km consistent with present day thickness estimates and erosional levels is capable of producing enough crustal heating to melt the base of the sedimentary pile advect heat to shallower crustal levels and produce the observed p t conditions deep seated mantle heat sources though not excluded are not required

lithoprobe new perspectives on crustal evolution lithoprobe is canada s national collaborative multidisciplinary earth science research program directed toward an enhanced understanding of how the north american continent evolved research in i

the moho in the northern basin and range province nevada along the cocorp 40 n seismic reflection transect cocorp seismic reflection profiles across nevada at about 40 n image a prominent essentially continuous band of reflectors at a two way traveltime of 9 to 11 s the approximate correspondence of this reflection time with estimates of the two way traveltime to the moho in this area provided by seismic refraction data suggests that the prominent reflections are from the moho the relief on these reflectors the reflection moho beneath nevada across a latitudinal transect of

flin flon belt seismic anisotropy elastic symmetry heterogeneity and shear wave splitting laboratory measurements of compressional and shear wave velocities and shear wave splitting have been carried out on a set of upper greenschist lower amphibolite facies of metasediments and metavolcanics and plutonic rocks from two ductile shear zones in the flin flon belt ffb of the trans hudson orogen tho selected metamorphic rocks vary in composition from felsic to mafic test sites with outcrops of sheared metamorphic rocks were correlated with a series of inclined seismic reflectors possibly extending from the midcrust and intersecting a well mapped shear zone at the surface determination of the lithological and physical properties of highly deformed metamorphic rocks is essential for proper interpretation of the nature of observed seismic reflectors to investigate the anisotropic properties of the rocks compressional velocity was measured at confining pressure up to 300 mpa in three mutually orthogonal directions aligned with respect to visible textural features in addition on selected

u pb lu hf and ree in zircon from 3 2 to 2 6 ga archean gneisses of the repulse bay block melville peninsula nunavut abstract combined in situ u pb and lu hf isotope and ree analyses of zircons from the tonalite trondhjemite granodiorite ttg type gneisses and granitoids within the repulse bay block rbb of melville peninsula nunavut reveal that the block is composed of ca 2 86 ga and 2 73 2 71 ga granitoids that formed by reworking of a 3 25 3 10 ga basaltic crust the interpretation is supported by initial hf values for ca 2 86 ga and ca 2 73 2 71 ga gneisses of 2 7 to 0 7 and 4 8 to 2 3 respectively and the preservation of high uranium xenocrystic cores at 3 15 0 05 ga neoarchean plutonism also occurred at ca 2 69 2 66 ga and is characterized by two pyroxene bearing charnockite enderbite and hornblende biotite granitoid intrusions that yield initial hf values that range from 7 1 to 1 0 demonstrating that they were derived from juvenile magmas with significant assimilation of the existing crust the pyroxene and non pyroxene bearing granitoids also contain elevated lree in zircon a feature that is interpreted to reflect metasomatism of the source this study also demonstrates that in the rbb the results of lu hf isotopes in zircon combined with in situ u pb geochronology from inherited zircon cores differ from the results of whole rock sm nd isotopes

proterozoic orogens of the northeastern canadian shield new information from the lithoprobe ecsoot crustal reflection seismic survey as part of the eastern canadian shield onshore offshore transect ecsoot lithoprobe acquired 1250 km of deep seismic reflection data along the coast of labrador and across ungava bay to image evidence of proterozoic crustal accretion to the archean nuclei of the nain and superior provinces of the canadian shield the relatively pristine archean crust of the nain province has low reflectivity and generally lacks systematic reflector orientations reworking of archean crust on the margins of the makkovik province has little effect on this weak signature in contrast the archean crust in the eastern churchill rae province appears to have been overprinted by a strongly developed whole crustal easterly dipping reflection fabric interpreted to result from proterozoic collision of the nain and superior provinces in the paired new quebec and torngat orogens juvenile proterozoic crust in the makkovik and grenville provinces also shows strong whole crustal dipping reflection fabrics interpretable as outw

erosion timescales derived from u decay series measurements in rivers the relative importance of the factors influencing weathering of continental rocks has been a topic of debate for the last few decades the principal reasons are the lack of reliable proxies for chemical weathering and the difficulty in constraining actual physical denudation rates in this study 234u 238u 230th 238u and 226ra 238u were measured by tims and by mc icp ms in the dissolved and suspended loads of rivers from the mackenzie basin northwest territories canada the data show a complementary nature between 234u 238u 230th 238u in the dissolved and suspended loads while 226ra is characterized by a more complex behavior modeling of fractionation of u series nuclides in the particulate matter and the corresponding dissolved phase permits us to constrain the duration of chemical erosion for the suspended load currently sampled in the watershed 9 28 10 ka as well as the rates of release of u series nuclides the results also imply significant recent changes of chemical erosion rates and underline the impact of the last glaciation on current continental fluxes of northern latitude rivers such as the mackenzie river

the pelican thrust zone basal detachment between the archean sask craton and paleoproterozoic flin flon glennie complex western trans hudson orogen the pelican thrust zone is a 3 7 km wide recrystallized mylonite zone along which paleoproterozoic arc volcano plutonic and derived sedimentary rocks of the flin flon glennie complex were thrust over an archean package jan lake complex consisting of ca 3 1 ga calc alkaline orthogneisses pelitic migmatites and a ca 2 45 ga tholeiitic charnockite norite intrusive suite a regional northeast plunging stretching lineation and a variety of kinematic indicators imply southwesterly transport matching that of other coeval shallower crustal level structures observed throughout the northern flin flon domain and southern flank of the kisseynew domain e g sturgeon weir and annabel lake shear zones subsequent east side up displacement on the tabbernor fault together with domal fold interference has exposed the pelican window and mantling mylonite zone where it has been seismically profiled along lithoprobe transects tectonic windows also expose archean rocks in the glennie domain to the west where similar southwest verging recrystallized mylonite zones have been documented together these zones record collision and underplating of the flin flon glennie complex by the archean sask craton during prolonged protocontinent continent collision over a minimum 1826 1805 ma interval resume la zone de chevauchement pelican est une zone de mylonite recristallisee d une largeur de 3 7 km le long de laquelle des roches volcano plutoniques d un arc datant du paleoproterozoique et des roches sedimentaires derivees du complexe de flin flon glennie ont ete chevauchees par dessus un ensemble archeen le complexe de jan lake qui est compose d orthogneiss calco alcalins et de migmatites pelitiques gees d environ 3 1 ga ainsi que d une suite intrusive charnockite norite tholeiitique gee d environ 2 45 ga une lineation regionale d etirement a pendage nord est et divers indicateurs cinematiques correspondent a un transport vers le sud ouest rejoignant celui d autres structures contemporaines de niveaux crustaux moins profonds observees a travers tout le domaine de flin flon nord et le flanc sud du domaine kisseynew p ex les zones de cisaillement de sturgeon weir et d annabel lake un deplacement subsequent le cote est vers le haut le long de la faille de tabbernor avec une interference de plis de dome a fait affleurer la fenetre pelican et la zone mylonitique qui la recouvre elle a ete determinee par des profils sismiques le long des transects lithoprobe des fenetres tectoniques permettent aussi l affleurement de roches archeennes du do maine de glennie vers l ouest la ou ont ete documentees des zones semblables de mylonites recristallisees a pendage sud ouest ensemble ces zones enregistrent la collision et le sous placage du complexe de flin flon glennie par le craton archeen sask au cours d une collision prolongee entre le protocontinent et le continent au cours d un intervalle d au moins 1826 a 1805 ma

upb geochronology and tectonic development of the southern flank of the kisseynew domain trans hudson orogen canada abstract the southern flank of the kisseynew domain northern manitoba underwent polyphase deformation and metamorphism during the palaeoproterozoic trans hudson orogen and represents a lithological metamorphic and structural transition from greenschist grade volcano plutonic rocks of the flin flon domain to amphibolite grade paragneisses of the central kisseynew domain the timing of geological events has previously been constrained using widely dispersed sample sites but this study has integrated u pb geochronology with detailed lithological and structural mapping in the cleunion lake area pink gneisses interpreted as missi supracrustal rocks were deposited after 1855 ma but prior to 1835 ma and thus are similar in age to fluvial sedimentary rocks in the lower grade flin flon domain all the zircons in the pink gneisses appear to be inherited or resorbed during later amphibolite grade metamorphism and a late archaean component is also indicated corundum bearing gneisses in the missi group and leucosomes in burntwood river group rocks are deformed by f1 and are indicative of an early high t low p metamorphic event m1 that may have been synchronous with the intrusion of 1835 to 1827 ma intrusions and related to regional crustal extension the above rocks are folded during a continuous compressional deformation event d2 related to terminal collision between the palaeoproterozoic rocks of the trans hudson orogen and the superior province three main fold generations f1 f2 f3 have been identified which occurred during d2 a 1818 ma granitic vein is approximately synchronous with f2 and peak metamorphic m2 conditions in the cleunion lake area cooling uplift and intrusion of pegmatites during f3 at 1800 ma provides a time limit on the waning stages of compressional deformation the main phase of compressional deformation d2 in the southern flank of the kisseynew domain thus lasted for about 30 million years

crustal structure and evolution of the trans hudson orogen results from seismic reflection profiling a 400 km long deep seismic reflection transect across northeastern montana and northern north dakota reveals the crustal scale structural fabric of the early proterozoic trans hudson orogen beneath the williston basin comparison with deep seismic reflection data across the canadian portion of the same orogen 700 km to the north reveals first order similarities in crustal architecture but documents significant along strike variation in orogenic evolution both transects display a broad crustal scale antiform axial to the orogen in the north geologic data suggest that this antiform is cored by an archean microcontinent in the south west dipping reflections on the western flank of the antiform extend from the upper crust to the uppermost mantle and truncate prominent subhorizontal lower crustal reflections of the archean wyoming craton within the wyoming craton the eastern limit of east dipping midcrustal reflections coincides with the subsurface age boundary between the craton and the early proterozoic trans hudson orogen as interpreted from potential field and drill core data on the basis of subsurface geochronologic data from the crystalline basement and by analogy with the glennie domain within the exposed trans hudson orogen in canada we suggest that the southern antiform is cored by an archean crustal fragment that was caught up in the terminal collision of the wyoming and superior cratons during hudsonian orogeny the eastern side of the trans hudson orogen is characterized on both seismic transects by predominantly east dipping crustal penetrating reflections we interpret the easterly dip of these reflections as evidence that the superior province was thrust westward over the interludes of the orogen during terminal collision although juvenile early proterozoic terranes characterize the exposed segment of the trans hudson orogen in canada limited drill core information within the dakota segment of the orogen shows a predominance of granulitic archean age crust this difference in basement lithologies along strike within the orogen may indicate the following either juvenile crust comparable to that exposed in the northern trans hudson was never present in the south or it was removed by progressive over thickening erosion and or faulting postorogenic extensional collapse may be responsible for preservation of juvenile terranes in the north

how the crust meets the mantle lithoprobe perspectives on the mohorovicic discontinuity and crust mantle transition application of regional geophysical and geological methods throughout two decades of canada s lithoprobe project provides new opportunities to analyze the mohorovicic discontinuity moho and crust mantle transition the transect format employed during lithoprobe in which 10 specified regions of canada were targeted for approximately a decade each between 1984 and 2003 permitted teams of scientists to focus on geological geophysical and tectonic issues for each transect as a primary objective was to enhance knowledge of the structure of the crust and lithosphere an obvious target in each transect was the nature and origin of the moho and crust mantle transition accordingly the combined results provide new perspectives on the moho and the relationship of the moho to the crust mantle transition perhaps the most important result is that the continental geophysical moho is a deceptively simple feature it has a variety of signatures at different scales that preclude a single universally applicable interpretation in methods that provide large scale information such as regional seismic studies it is a relatively abrupt refraction velocity contrast that often displays a dramatic downward decrease in seismic reflectivity however its origin in a geological or tectonic sense is perhaps best determined by careful analyses of structural details near the geophysical moho which are complex and varied in some areas within canada it appears that the geophysical moho may be old and perhaps remains from the time the crust formed in other areas it appears to be a relatively young feature that was superimposed onto older crustal fabrics

deep probe imaging the roots of western north america analysis of the lithoprobe deep probe and southern alberta refraction experiment data sets focusing on the region between deep probe shots 43 and 55 has resulted in a continental scale velocity structural model of the lithosphere of platformal western laurentia reaching depths of 150 km three major lithospheric blocks were investigated i the hearne province a typical continental archean cratonic province lying beneath the western canada sedimentary basin ii the wyoming province an even older block of phanerozoic modified archean crust with an enigmatic lower lithosphere and iii the yavapai mazatzal province proterozoic terranes underlying the colorado plateau and southern rocky mountains in this study the northern two of these regions are investigated with a modified ray theoretical traveltime inversion routine that respects the spherical geometry of the earth the resulting crustal velocity structure combined with supporting geological and geophysical data reveals that the medicine hat block mhb lying between the hearne and wyoming provinces is a third independent archean crustal block the subcrustal lithosphere along the profile is homogeneous in velocity structure but two significant northward dipping reflectors are apparent and interpreted as relic subduction zones associated with sutures between the three archean blocks the hearne crust is typical of an archean shield or platform both in its thickness of 34 50 km and its seismic velocity structure the crust of the archean mhb and wyoming province which ranges in thickness from 49 to 60 km includes a 10 30 km thick high velocity layer interpreted to be proterozoic in age such a feature is unexpected beneath archean crustal provinces but if the region is considered to be the remanent marginal portion of a larger archean continent then the interpreted proterozoic underplating and lack of an archean lithospheric root can be explained the variable topography along the reflective upper and lower boundaries of this layer especially within the mhb suggests considerable variability in its emplacement and subsequent tectonic history

geology and evaluation strategy of the star and orion south kimberlites fort a la corne canada abstract diamond bearing kimberlites in the fort a la corne field east central saskatchewan consist primarily of volcaniclastic deposits which are interstratified with lower cretaceous continental marginal marine and marine sediments seventy kimberlite occurrences have been drill confirmed with the majority of those occurring in the fort a la corne main trend the star 352 ha and orion south 358 ha kimberlite complexes are located at the south eastern extremity of the main trend and contain some of the world s best examples of preserved primary volcaniclastic kimberlite deposits the advanced exploration programs on both the star and orion south complexes offer a rare opportunity to examine a wide variety of in situ volcaniclastic kimberlite deposits both kimberlite complexes are composed of multiple eruptive units that were deposited episodically over 4 to 6 million years separated by periods of volcanic quiescence marked by reworking of kimberlite and siliciclastic sedimentation detailed logging of core from 100 m spacing grid drilling has revealed well defined tuff ring tuff cone crater and extra crater deposits evaluation of these large tonnage lower grade coarse diamond size frequency kimberlite complexes requires a methodical and multi branched exploration strategy utilizing 1 grid pattern core drilling to gain an understanding of the three dimensional architecture of the kimberlite complexes 2 underground bulk sampling to provide appreciable carats for accurate estimates of diamond grade and price and 3 grid pattern mini bulk sampling via large diameter drilling to obtain an understanding of the diamond grade across the breadth of each kimberlite

tectonic implications of new shrimp and tims u pb geochronology of rocks from the sask craton peter lake domain and hearne margin trans hudson orogen saskatchewan this study reports new sensitive high resolution ion microprobe shrimp and thermal ionization mass spectrometry tims u pb geochronological data for thirteen rocks from the archean to paleoproterozic sask craton the peter lake domain and hearne margin saskatchewan seven samples from the exposed sask craton in both the glennie domain and pelican window record zircon growth between 2425 and 2525 ma and at 1800 ma older precursor material has been identified most notably a refined crystallization age of 3117 ma for a sample of quartzofeldspatic gneiss q gneiss in the pelican window which also experienced ca 2450 ma zircon growth three samples from the peter lake domain and a sample from the linn island inlier of the wollaston domain yield ages of 2575 ma one sample from the peter lake domain is distinctly older yielding an age of 2640 ma but also displays zircon growth at 2575 ma the simplest interpretation of these data is that the peter lake domain is likely a part of the hearne margin

deep seismic profile across a proterozoic collision zone surprises at depth collisions between continents generate the world s most striking mountains the deep structure of these collision zones inferred from seismic reflection profiles1 3 can be equally dramatic if less well understood improved knowledge of the structure of ancient collisional belts now known to have developed through plate tectonic processes4 5 can provide important new insights into the mechanisms of crustal growth although many such belts have been partly destroyed by severe post collisional deformation6 7 or magmatism8 some have been preserved in the stable interiors of continents9 one example is the early proterozoic trans hudson orogen9 10 in western canada here we present seismic reflection images across the entire orogen which reveal a broadly symmetric structure with reflections linked to island arc rocks dipping beneath both bounding archaean cratons the observed reflection geometries imply a doubling of crustal thickness during the collision along crust penetrating faults the presence of a significant amount of archaean crust at depth the extent of which could not have been determined from surface mapping suggests the need for caution in inferring crustal growth rate from the surface area of juvenile crust11 12

variable crustal structure of strike slip fault zones as observed on deep seismic reflection profiles seismic reflection profiling across strike slip faults has revealed a distinct variation in deep crustal structure profiles across the san andreas great glen and bray faults depict a near vertical reflection free zone that appears to truncate and in some cases offset reflections interpreted to have originated from the base of the crust a near vertical crustal penetrating fault zone is suggested for these continental transform faults in contrast reflection profiles across intra plate strike slip fault systems such as the northern walker lane and garlock faults suggest that they are decoupled in the middle crust by subhorizontal detachments these detachments are inferred from reflections that are traceable below the surface faults without disruption such detachments in the middle crust may act to ease the rotation of upper crustal blocks adjacent to strike slip fault zones as observed in paleomagnetic studies furthermore moderately dipping reflections interpreted to be from the fault zone project to the surface traces of the northern walker lane faults and the frontal faults of the wichita uplift indicating that these strike slip faults with large components of dip slip displacement are not vertical but dip moderately into the mid crust although the available data sets are still few they suggest that there is a primary variation in fault geometry that is related to the different behavior of transform versus intra plate strike slip fault systems

proterozoic collisional tectonism in the trans hudson orogen saskatchewan isotopic and structural data from the juvenile reindeer zone of the trans hudson orogen northern saskatchewan indicate a pre 1 85 ga thermotectonic event possibly reflecting arc continent collision followed by a more extensive nappe forming ca 1 83 1 80 ga thermotectonism during terminal continent continent collision preliminary data from the adjacent ensialic cree lake zone suggest high grade reworking of archean crust by the pre 1 85 ga event in the rae province to the west high grade metamorphism and reworking of archean crust occurred about 2 0 ga and may be related to the formation of the coeval taltson magmatic zone

seismic reflection images of high angle faults and linked detachments in the trans hudson orogen postcollisional 1 8 1 7 ga intracontinental deformation in the trans hudson orogen canada produced a series of orogen parallel high angle faults and folds in seismic reflection profiles the faults are imaged by subvertical zones of diffractions and truncated reflections that extend to 4 8 s 12 24 km the folded and faulted upper part of the crust is underlain by laterally coherent shallow dipping reflections that are locally bounded by discrete highly reflective zones these zones are interpreted as detachments shear zones and can be traced from the upper to lower crust where some of them appear to pass into laterally continuous reflections that define the moho two distinct regimes of postcollisional crustal deformation are inferred from the seismic images high angle faulting and lateral block extrusion in the upper crust and low angle ductile shearing in the mid lower crust the surface geology indicates that the faults resulted in southwest orogen parallel extrusion of the orogen s internal zone relative to the bounding archean hearne and superior cratons faulting was concurrent with the development of upright folds with trends that are subparallel to the extrusion direction the seismic images suggest that the high angle fold fault structures are kinematically linked to low angle detachments represented by laterally coherent highly reflective zones the detachment shear zones are inferred to have a top to the southwest sense of shear associated with a subhorizontal northeast southwest extension direction parallel to those observed for 1 83 1 80 ga collisional shear zones exposed in major postcollisional fold culminations long lived orogen parallel extension is interpreted as a consequence of the boundary conditions imposed by the northeast trend of both the superior and hearne margins

reconstructing past atmospheric co2 concentration based on ice core analyses open questions due to in situ production of co2 in the ice analysis of air extracted from bubbles of polar ice showed the anthropogenic increase of atmospheric co2 concentration during the past few hundred years preindustrial concentration 280 ppmv and unexpectedly that the concentration also increased due to natural causes from 200 to 280 ppmv during the transition from the last glacial epoch to the holocene however more detailed reconstructions based on ice core analyses suggested that some of the additional observed variations were actually due to the modification of co2 concentration in the bubbles by chemical reactions between impurities in the ice detailed analyses of acidity the carbonate concentration the concentration of oxidation agents like hydrogen peroxide h2o2 and organic compounds e g formaldehyde hcho along short intervals of ice cores representing only a few annual layers allowed us to investigate these chemical reactions the records are not conclusive but they indicate that the oxidation of organic compounds is at least as important as acid carbonate reactions ice containing a low mean carbonate and a low h2o2 concentration as well as a small scattering of co2 results obtained on several adjacent samples representing a few annual layers at most is at present the best guarantee for reliable results of the atmospheric co2 concentration

thermotectonic studies in the paleoproterozoic glennie domain trans hudson orogen canada abstract the glennie domain of the trans hudson orogen tho is characterized by paleoproterozoic island arc volcanogenic assemblages and granitoid rocks thrust as sheets over the archean saskatchewan craton prior to terminal collision between the archean rae hearne and superior cratons four discrete deformation events have been recorded in the domain the d1 and d2 events are associated with the southwestward directed imbrication of paleoproterozoic allochthons over the saskatchewan craton while the d3 and d4 events are associated with terminal collision and transpression respectively discernable metamorphic episodes are associated with the d2 and d3 events with peak thermal metamorphism during d3 using inveq thermobarometry metamorphic conditions during d3 in the santoy lake area were ca 655 705 c and 6 1 7 3 kbar and ca 530 595 c and 3 2 4 8 kbar for the brownell lake area 40ar 39ar hornblende and biotite ages suggest the santoy lake area remained above ca 490 c until ca 1720 ma when it underwent rapid cooling through the biotite ar closure temperature of ca 330 c 40ar 39ar biotite ages from the brownell lake area suggest moderate cooling from peak thermal metamorphism at ca 1810 1755 ma when it passed through the ca 310 c biotite ar closure temperature differences between cooling rates for the two areas are interpreted as differential exhumation of smaller lithotectonic blocks bound by domain wide deep crustal faults and shear zones zircon pb evaporation ages of variably deformed granitoid rocks from the santoy lake area show that the d2 event occurred after ca 1857 ma the oldest granitoid in the santoy lake area provides a minimum age of mafic volcanism in the area of ca 1886 ma as well as a significant hiatus ca 50 ma between deposition of the two supracrustal assemblages in the domain

intracrustal detachment within zones of continental deformation geologic mapping of active to recently active geologic structures in panamint valley western united states and in the haiyuan region and northern tibetan plateau china suggests detachment in the middle and lower crust on a scale of tens of kilometres to at least several hundred kilometres detachment occurs similarly in predominantly extensional panamint valley and in predominantly compressional china environments it involves structures with displacements of more than 10 km and displacement rates of more than 3 mm yr perhaps more than 10 mm yr the steeply dipping strike slip faults present in all three areas hunter mountain fault haiyuan fault and altyn tagh fault zone terminate in zones of extension or compression and geometric relations indicate that all structures including strike slip faults are thin skinned and restricted to the upper crust in panamint valley and in the haiyuan region deformation within these systems can be reconstructed in three dimensions displacement on the strike slip faults is absorbed by extension or compression occurring at the termination of the faults so strike slip displacement is roughly equal to and in the same direction as shortening or extension we propose that left slip on the altyn tagh fault zone in northern tibet is similarly absorbed by shortening southeast of the fault zone within the qaidam basin and the nan shan

geotectonics of the hanson lake block trans hudson orogen central canada a preliminary paleomagnetic report abstract we present paleomagnetic results from the sahli granite in the hanson lake block of the trans hudson orogen evidence shows that the sahli granite magnetization was acquired during a metamorphic event which probably peaked in the interval 1840 1800 ma the reset nature of the sahli granite data is partly supported by a negative contact test from a cross cutting mafic dyke the sahli granite results and those from the 1844 2 ma hanson lake pluton and jan lake granite in the hanson lake block indicate high paleolatitudes compared with the low paleolatitudes found for the wathaman batholith and other rocks of the slave rae hearne cratons of similar ages to the north west of the trans hudson orogen estimates of the north south width of about 4000 km for the paleoproterozoic manikewan ocean between the archean hearne and superior cratons using the hanson lake pluton and wathaman batholith poles for example are consistent with previous estimates the angular difference between the hanson lake pluton and sahli granite poles provides an apparent polar wander segment of the geomagnetic field for the hanson lake block to compare with the parallel segment given by the poles for the 1851 ma reynard lake pluton and the 1838 ma boot lake phantom lake pluton for the adjacent flin flon domain both segments indicate a relative north north easterly path direction at an apparent polar wander rate within the range 4 3 0 4 per ma assuming no large scale regional tilts of the plutons the offset between the two apparent polar wander path segments indicates either an east west component of closure of about 1000 km for the manikewan ocean or vertical axis counter clockwise rotation of units within the trans hudson orogen with respect to the superior craton plus a possible north south relative translation between the hanson lake block and flin flon domain