age constraints on the paleoproterozoic tectonometamorphic history of the committee bay region western churchill province canada evidence from zircon and in situ monazite shrimp geochronology in situ u pb sensitive high resolution ion microprobe shrimp analyses of monazite from upper amphibolite facies paragneiss of the committee bay supracrustal belt central rae domain canada reveal three age populations ca 2350 1850 and 1780 ma the ca 1850 ma age also corresponds to growth of low th u zircon as indicated by u pb shrimp analyses of zircon separates from melanosome and leucosome the contextual advantage of the in situ monazite analysis allows evaluation of the geochronological data in terms of the regional structural and metamorphic evolution the region is dominated by a northeast striking s2 s1 fabric axial planar to tight northwest vergent f2 folds early garnet is enveloped by this biotite sillimanite cordierite s2 fabric garneti hosts ca 1850 ma monazite inclusions with ca 2350 ma cores placing a maximum age on garneti growth and s2 development d2 metamorphic conditions progressed through 3 5 kbar 1 kbar 100 mpa and 600 c to near peak conditions of 5 kbar and 675 c a minimum age for s2 is provided by unstrained ca 1820 ma monzogranite that locally and regionally truncates s2 dominantly ca 1780 ma matrix monazite is interpreted to date post s2 garnetii and cordierite which record 5 kbar and 675 c these data indicate that the committee bay region experienced penetrative d2 tectonometamorphism at ca 1850 1820 ma with a subsequent static overprint the absence of a ca 1 85 ga plutonic suite in the region suggests that low pressure metamorphism was a response to thick skinned crustal thickening initiated at ca 1870 ma the new data highlight the importance of paleoproterozoic reworking of the central rae domain in the hinterland of the trans hudson orogen

taltson basement gneissic rocks upb and nd isotopic constraints on the basement to the paleoproterozoic taltson magmatic zone northeastern alberta the taltson magmatic zone is a 300 km long northerly trending belt of archean to paleoproterozoic granitic basement gneiss amphibolite supracrustal gneissic rocks and voluminous paleoproterozoi

neoarchean arc magmatism and subsequent collisional orogenesis along the eastern rae domain western churchill province implications for the early growth of laurentia abstract the athabasca granulite terrane on the eastern margin of the rae domain of the western churchill province contains a well exposed record of neoarchean magmatism deformation and metamorphism circa 2 63 2 60 ga plutonic rocks range from 58 01 to 73 71 sio2 and vary from ferroan to magnesian they form shallow linear trends on modified alkali lime index diagram plotting largely in the calc alkaline field on tectonic discrimination diagrams all samples plot in the volcanic arc field samples are lree enriched and contain relatively steep negative slopes and flat depleted hree profiles when normalized to chondrites the entire neoarchean plutonic complex independent of lithology contains strong enrichments in the liles and pb and depletions in hfses monazite u th total pb results from a migmatitic paragneiss suggest that partial melting occurred at ca 2 57 ga within the chipman subdomain monazite results from the adjacent northwestern subdomain suggest that deformation occurred at ca 2 57 ga in sims and icp ms zircon u pb geochronology corroborates these conclusions although the region is dominated by paleoproterozoic localized shear zones internal to each subdomain is evidence of a widespread tectonothermal event during the neoarchean that involved arc plutonism crustal thickening lower crustal flow at pressures exceeding 1 0 gpa and extensive partial melting of the lower continental crust we interpret this sequence of magmatic deformational and anatectic processes to reflect the transition from a continental arc to a collisional tectonic setting the recognized series of events presented herein is likely correlative to the 2 60 2 50 ga macquoid orogen which has been recognized further to the northeast and likely parallels the eastern margin of the rae domain of the western churchill province these data support an important component of modern style plate tectonics during continental magmatism and accretion in the neoarchean

the amer belt remnant of an aphebian foreland fold and thrust belt aphebian supracrustal sequences occur as outliers throughout the northwestern portion of the churchill structural province of the canadian shield in the amer lake area medium to high grade poly

timing relationships between pegmatite emplacement metamorphism and deformation during the intra plate alice springs orogeny central australia in the harts range central australia the upper amphibolite facies to lower granulite facies c 480 460 ma harts range metamorphic complex hrmc and the upper amphibolite facies c 340 320 ma entia gneiss complex are cut by numerous generally peraluminous pegmatites and their deformed equivalents the pegmatites have previously been interpreted as locally derived partial melts however shrimp u pb monazite and zircon dating of 29 pegmatites or their deformed equivalents predominantly from the hrmc reveal that they were emplaced episodically throughout almost the entire duration of the polyphase c 450 300 ma intra plate alice springs orogeny episodes of pegmatite intrusion correlate with the age of major alice springs age structures and with deposition of syn orogenic sedimentary rocks in the adjacent centralian superbasin similar alice springs ages have not been obtained from anatectic country rocks in the hrmc suggesting that the pegmatites were not locally derived instead they are interpreted as highly fractionated granites and imply that much larger parental alice springs age granites exist at depth the mechanism to allow repeated felsic magmatism in an intraplate setting where all exposed rock types had a previous high temperature history is enigmatic however we suggest that episodic underthrusting and dehydration of unmetamorphosed centralian superbasin sedimentary rocks allowed crustal fertility to maintained over a c 140 ma interval during the intra plate alice springs orogeny

multistage exhumation and juxtaposition of lower continental crust in the western canadian shield linking high resolution u pb and 40ar 39ar thermochronometry with pressure temperature deformation paths 1 new u pb titanite apatite rutile and 40ar 39ar hornblende muscovite biotite data are linked with existing pressure temperature deformation paths to impose detailed temporal constraints on the juxtaposition and unroofing of domains in an extensive 20 000 km2 region of exhumed lower crust in the east lake athabasca region of the western canadian shield in the 200 m y between circa 1 9 ga high pressure granulite facies metamorphism and circa 1 7 ga unconformable deposition of athabasca basin sediments on the exhumed rocks our analysis reveals at least three distinct phases of unroofing at different rates specifically we distinguish 1 an early phase of extensional unroofing in the chipman domain at rates of 1 5 2 0 km m y from 1 0 gpa to 0 8 gpa associated with mafic magmatism and metamorphism 2 an episode of regional contractional uplift and associated unroofing along the legs lake shear zone at circa 1850 ma from 0 7 0 8 gpa to 0 4 0 5 gpa and 3 a final period of extensional unroofing at rates of 0 2 0 3 km m y from 0 4 to 0 5 gpa that culminated in transport of current exposures to near surface conditions the cooling patterns and retrograde assemblages are consistent with pauses between exhumational phases the apparent convergence of disparate higher temperature histories in several deep crustal domains at circa 1 89 1 88 ga implies their juxtaposition at 0 7 0 8 gpa conditions regional east directed thrusting of the deep crustal domains as a coherent unit at 1 85 ga juxtaposed the granulites with middle crustal hearne domain rocks at 0 4 0 5 gpa conditions the detailed exhumational history allows correlation with changing regional tectonic regimes associated with the amalgamation of laurentia the temporal and spatial heterogeneity of exhumation patterns in the east lake athabasca region may be a common feature of the unroofing histories of lower crustal rocks

trans hudsonian far field deformation effects in the rae foreland an integrated geological 3d magnetic model abstract the intracratonic rae cover sequence deposited ca 2 2 1 9 ga forms a useful marker for unravelling tectonic events that affected the archean rae province at ca 2 0 1 9 and 1 85 ga polyphase deformation is recognized within the rae cover rocks including the 70 10 km montresor belt and attributed to distal effects of the ca 1 85 ga trans hudson orogeny in this contribution we explore the 3d geometry and structural history of the montresor belt previously considered to be a simple syncline lying unconformably on archean basement new geological geophysical and geochronological results define a more complex history in which lower montresor units were thrust imbricated with basement gneisses and metamorphosed to the amphibolite facies mid to upper greenschist facies upper montresor units exposed in an open synform are superficially less deformed however using high resolution aeromagnetic data and distinct magnetic marker units considered proxies for bedding we constructed a set of forward models to explore the three dimensional geometry of the belt the re analysis outlines a set of pre synform structures defined by low angle truncations of the magnetic markers geometric relationships indicate the presence of at least three faults at low angles to bedding interpreted as d1 piggy back thrusts and bracketed by available geochronology between 1 924 and 1 87 ga d1 strain in the upper montresor strata is significantly less intense than that further south in rae cover rocks consistent with a more distal foreland setting during the trans hudson orogeny the montresor belt preserves a record of the trans hudson tectonic style at relatively shallow crustal levels as a result of its foreland setting and structural history including a syn orogenic extensional detachment event

archaean ttgs as sources of younger granitic magmas melting of sodic metatonalites at 0 6 1 2 gpa two natural low k2o na2o ttg tonalitic gneisses one hornblende bearing and the other biotite bearing were partially melted at 0 8 1 2 gpa fluid absent the chief melting reactions involve the breakdown of the biotite and hornblende the hornblende tonalite is slightly less fertile than the biotite tonalite but melt volumes reach around 30 at 1 000 c this contrasts with results of most previous work on more potassic ttgs which generally showed much lower fertility though commonly producing more potassic melts garnet is formed in biotite bearing tonalitic protoliths at p 0 8 gpa and at 1 0 gpa in hornblende bearing tonalitic protoliths all fluid absent experiments produced peraluminous granitic to granodioritic melts typically with sio2 70 wt for the biotite tonalite increasing t formed progressively more melt with progressively lower k2o na2o however the compositions of melts from the hornblende tonalite do not vary significantly with t with increasing p melts from the biotite tonalite become less potassic due to the increasing thermal stability of biotite for the hornblende tonalite again there is no consistent trend fluid absent melting of sodic ttgs produces melts with insufficient k2o to model the magmas that formed the voluminous late potassic granites that are common in archaean terranes reconnaissance fluid present experiments at 0 6 gpa imply that h2o saturated partial melting of ttgs is also not a viable process for producing magmas that formed these granites the protoliths for these must have been more potassic and less silicic nevertheless at granulite facies conditions sodic ttgs will produce significant quantities of broadly leucogranodioritic melt that will be more potassic than the protoliths upward abstraction of this melt would result in some lile depletion of the terrane younger k rich magmatism is unlikely to represent recycling of ttg crust on its own and it seems most likely that evolved crustal rocks and or highly enriched mantle must be involved

new depositional age constraints for the murmac bay group of the southern rae craton canada abstract the murmac bay group is one of several early supracrustal successions that were deposited on the southern rae craton churchill province western canadian shield and subsequently affected by paleoproterozoic tectono metamorphism where best understood the succession comprises basal quartzite and or psammite with intercalated dolostone patchy iron formation mafic volcanic flows and overlying psammopelite pelite previous attempts to date the murmac bay group have resulted in both archean and paleoproterozoic estimates re interpretation of critical field relationships together with acquisition of new geochronological data have greatly improved estimates for its age of deposition which in turn yield new constraints on the tectonic evolution of the region circa 2 33 2 32 ga detrital zircon from three of four dated samples including a rare basal conglomerate establishes a maximum age for the initiation of deposition a 2322 5 ma quartz feldspar porphyry dyke intruding mafic volcanic rocks near the base of the succession indicates that deposition of the murmac bay group was initiated ca 2 33 ga coeval with the earliest members of a 2 33 2 29 ga granitic suite these post collisional granites were emplaced following a 2 37 ga thermal culmination attributed to the arrowsmith orogeny deposition of the murmac bay group continued until at least 2 17 ga the youngest detrital zircon age analyzed from the upper part of the succession deposition was over by ca 1 93 ga when the murmac bay group underwent regional metamorphism and was intruded by the donaldson lake pluton for which a revised ca 1 93 ga crystallization age has been obtained according to our new age constraints the upper murmac bay group may be temporally correlative with the waugh lake group exposed about 100 km to the west northwest at the eastern margin of the taltson magmatic zone and with rocks of the rutledge river basin located 150 km to the northwest a stronger case can be made for lithostratigraphic correlation of the murmac bay group with the lower three of four assemblages in the amer and ketyet river groups 750 km to the northeast the abundance of ca 2 17 ga detrital zircon in the murmac bay group together with the presence of 2 2 2 07 ga detritus in the amer and ketyet river groups rutledge river basin and in younger sedimentary successions in the region are thought to record an early accretionary event on the western margin of the rae craton

construction of a composite pressure temperature path revealing the synorogenic burial and exhumation history of the sevier hinterland usa metamorphic pressure temperature p t paths derived from 16 growth zoned garnets nine from this study and seven from a previous study have been combined to construct a detailed composite path for an area in the hinterland of the cretaceous to early tertiary sevier orogenic belt in southern idaho and north west utah samples are from two proterozoic units in the footwall of the basin elba thrust the schist of mahogany peaks in the central albion mountains idaho and the schist of stevens spring in the basin creek area of the grouse creek mountains utah 40 km to the south the simulated portions of the garnets analysed in this study grew from reactions involving the breakdown of chlorite in the upper greenschist to lower amphibolite facies multiple garnets were analysed from three samples overlapping segments of p t paths from different garnets in the same sample correlate with respect to slope and garnet mn concentration the composite p t path documents three episodes of sharply increasing pressures separated by two episodes of pressure decrease all during progressively increasing temperatures the path is interpreted to represent alternating episodes of synconvergent thrusting and extensional exhumation in the hinterland of the sevier orogen burial was probably caused by the basin elba fault the only major thrust exposed in the region extensional exhumation may have occurred along the mahogany peaks or emigrant spring faults or by extensional reactivation of the basin elba fault this method of correlating partial p t paths to reveal a more complete composite path provides a powerful tool in unveiling orogenic histories in metamorphic terranes where evidence of major structures responsible for burial and exhumation is commonly obscured by later events

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

magnetotelluric investigations of the lithosphere beneath the central rae craton mainland nunavut canada new magnetotelluric soundings at 64 locations throughout the central rae craton on mainland nunavut constrain 2 d resistivity models of the crust and lithospheric mantle beneath three regional transects responses determined from colocated broadband and long period magnetotelluric recording instruments enabled resistivity imaging to depths of 300 km strike analysis and distortion decomposition on all data reveal a regional trend of 45 53 but locally the geoelectric strike angle varies laterally and with depth the 2 d models reveal a resistive upper crust to depths of 15 35 km that is underlain by a conductive layer that appears to be discontinuous at or near major mapped geological boundaries surface projections of the conductive layer coincide with areas of high grade archean metasedimentary rocks tectonic burial of these rocks and thickening of the crust occurred during the paleoproterozoic arrowsmith 2 3 ga and trans hudson orogenies 1 85 ga overall the uppermost mantle of the rae craton shows resistivity values that range from 3000 m in the northeast beneath baffin island and the melville peninsula to 10 000 m beneath the central rae craton to 50 000 m in the south near the hearne domain near vertical zones of reduced resistivity are identified within the uppermost mantle lithosphere that may be related to areas affected by mantle melt or metasomatism associated with emplacement of hudsonian granites a regional decrease in resistivities to values of 500 m at depths of 180 220 km increasing to 300 km near the southern margin of the rae craton is interpreted as the lithosphere asthenosphere boundary

geochemical and isotopic nd o evidence bearing on the origin of late to post orogenic high k granitoid rocks in the western superior province implications for late archean tectonomagmatic processes abstract the granitoid rock dominated central wabigoon subprovince of the superior province records low k trondhjemite tonalite granodiorite ttg type magmatic episodes at

late neoarchean monzogranitic syenogranitic gneisses in the eastern hebei western liaoning province north china craton petrogenesis and implications for tectonic setting abstract the medium grained monzogranitic syenogranitic gneisses expose as roughly northeast southwest trending and cover 1500 km 2 in the southern part of the eastern hebei western liaoning province north china craton these plutonic gneisses have leucocratic features and weakly gneissic to massive structures and were metamorphosed under greenschist to lower amphibolite facies la icp ms zircon u pb isotopic dating reveals that the magmatic precursors of these monzogranitic syenogranitic gneisses were emplaced during 2527 2511 ma they are characterized by high contents of sio 2 71 64 78 08 and k 2 o 3 55 6 40 and low contents of cao 0 25 1 71 mgo 0 01 0 42 and na 2 o 2 29 4 96 according to their chondrite normalized ree patterns the monzogranitic syenogranitic gneisses can be subdivided into a high ree group and a low ree group studies of petrogenesis reveal that magmatic precursors of the high ree group samples were derived from partial melting of the regionally widespread porphyritic or medium grained dioritic quartz monzonitic granodioritic monzogranitic gneisses under low pressure conditions less than ca 10 kbar the magmatic precursors of the low ree group were formed by fractionated crystallization of the high ree group magma with titanite allanite epidote apatite and zircon as the major crystallization fractionation phases combined with previous investigations on the late neoarchean metavolcanic rocks and granitoid orthogneisses in the northwestern part of the eastern hebei western liaoning province the magmatic precursors of these monzogranitic syenogranitic gneisses were most likely formed in a back arc basin along the north of the eastern block north china craton

improved hydrologic modeling for depression dominated areas abstract modeling of overland flow for a depression dominated area is a difficult task due to the spatial distribution of depressions particularly the hierarchical relationships of depressions and their variable contributing areas make the hydrologic modeling more complicated in traditional hydrologic modeling however digital elevation models dems that are used to represent surface topography are often edited by filling depressions before delineation and the impacts of depressions are considered by using certain simplified and lumped approaches due to such flaws these hydrologic models fail to account for the actual dynamic influences of surface depressions the objective of this study is to improve hydrologic modeling for depression dominated regions by developing a new modeling framework to quantify the influence of spatially distributed depressions to achieve this objective a new puddle based unit pbu probability distributed model pbu pdm is developed and coupled with the existing soil and water assessment tool swat the pbu pdm facilitates separate simulations for non depressional and depressional areas and accounts for the hierarchical relationships of depressions their filling and spilling processes and the dynamic variations in their contributing areas the pbu pdm enhanced swat was applied to the upper maple river watershed in north dakota and calibrated and validated using the observed data in particular it was also compared with the original swat model which demonstrated the abilities of pbu pdm to mimic the filling spilling overland flow dynamics and the threshold behavior the pbu pdm provides improved watershed scale hydrologic modeling especially for depression dominated areas

geology lithogeochemistry and u pb geochronology of the aberdeen lake area nunavut new insights into the neoarchean tectonic evolution of the central rae domain abstract the aberdeen lake supracrustal belt is one of several neoarchean greenstone belts preserved within the rae domain of the western churchill province we divide the belt into 1 a lower sequence of ca 2750 ma komatiite ttg tonalite trondhjemite granodiorite intrusions and ttg contaminated fe tholeiitic mafic gneiss 2 a middle sequence of ca

two neoarchean supercontinents revisited the case for a rae family of cratons abstract a variety of early paleoproterozoic supercontinents or supercratons have been proposed including kenorland superia and vaalbara improved geologic knowledge of the churchill province canadian shield suggests that the classical kenorland configuration with linked rae and hearne cratons is invalid and represents a younger ca 1 9 ga nuna configuration we review the early paleoproterozoic tectonic history of the rae craton and propose that the ca 2 55 2 50 ga macquoid and 2 50 2 28 ga arrowsmith orogens represent critical piercing points for supercontinent reconstruction utilizing the stratdb and dateview databases we have identified nearly two dozen regions worldwide that show effects of these orogenic events including the rae gawler mawson peninsular india west africa amazonia north china and sask crustal blocks we propose that these cratonic blocks form a distinct rae family lineage utilizing new time space plots for the rae family and components of the superia and vaalbara supercratons we demonstrate that the rae family lacks the distinctive early paleoproterozoic depositional and glaciogenic record characteristic of superia and vaalbara but has an important contemporaneous record of juvenile crust formation and contractional orogenesis we propose the collective history of the rae family is best reconciled if it represents the now dispersed blocks of a third earliest paleoproterozoic supercraton that we term nunavutia in this model the magmatic and tectonometamorphic record of these cratons includes an early 2 55 2 45 ga period of interior collisional orogenesis in which the supercraton amalgamated and a later phase of long lived peripheral orogenesis 2 45 2 28 ga prior to its partial break up at ca 2 05 ga forming within an otherwise globally quiescent period the history of the rae family is important for assessment of constrasting models of early paleoproterozoic geodynamic activity

characterization of the paleoproterozoic hottah terrane wopmay orogen using multi isotopic u pb hf and o detrital zircon analyses an evaluation of linkages to northwest laurentian paleoproterozoic domains abstract the paleoproterozoic wopmay orogen is modeled as a simple arc continent collision involving the archean slave craton and an enigmatic continental arc terrane termed the hottah terrane hottah is a composite terrane that includes a juvenile 2 6 2 1 ga basement and a younger 1 93 1 90 ga continental arc the extent and crustal age structure of the terrane is poorly known which limits interpretations as to its origin and eventual role in the development of the orogen multi isotopic u pb hf o analyses of detrital zircon from rocks of the hottah terrane and its cover sequence are used to indirectly evaluate its age and crustal characteristics the data confirm that ca 2 6 2 1 ga crust is an important component of the terrane but hf isotopic data indicate mostly non juvenile compositions consistent with recycled neoarchean crust sources ages of detrital zircon are distinct from those expected of the slave craton but are similar to adjacent 2 0 1 90 ga paleoproterozoic terranes of northwestern laurentia the similarity to terranes such as the ksituan buffalo head and taltson thelon magmatic zones south and east of the wopmay orogen indicate that hottah could represent a terrane that initially evolved adjacent to the earliest assembled parts of the nuna continent between 2 0 and 1 9 ga and was rifted prior to the collision with the slave margin that produced the calderian orogeny

geology geochronology and geochemistry of archean rocks in the eqe bay area north central baffin island canada constraints on the depositional and tectonic history of the mary river group of northeastern rae province results of stratigraphic u pb geochronological and geochemical study are reported for rocks in a 2800 km2 area along the southeastern margin of the archean rae province on north central baffin island archean rocks include a gneiss complex two greenstone belts of the mary river group and various younger plutonic rocks the 3000 2800 ma gneiss complex contains intrusions of orthogneiss dated at 2780 2770 ma intermediate felsic volcanism in overlying greenstone belts occurred at 2740 2725 ma and was accompanied and outlasted by calc alkaline plutonism 2730 2715 ma peraluminous plutonism at ca 2700 ma possibly associated with low to medium pressure metamorphism represents the culmination of the archean tectonic cycle dating of metamorphic zircon and titanite in archean gneissic rocks indicates that overprinting high grade metamorphism in the northwest part of the area footwall of the isortoq fault zone is paleoproterozoic ca 1820 ma a weaker somewhat older thermal disturbance ca 1850

neoarchean high potassium granites of the boothia mainland area rae domain churchill province u pb zircon and sm nd whole rock isotopic constraintsthis article is one of a series of papers published in this special issue on the theme of geochronology in honour of tom krogh the boothia mainland region of the north central rae domain is underlain by remnants of a neoarchean volcano sedimentary sequence dismembered by two regionally extensive neoarchean high potassium granitoid suites with rare occurrences of a structurally interleaved paleoproterozoic sedimentary cover sequence the granitoids and their gneissic equivalents are dominated by variably deformed and metamorphosed i type metaluminous polyphase commonly porphyritic to augen biotite hornblende monzogranite and subordinate granodiorite with rare tonalite new geochronological results the first for this area demonstrate that the widespread neoarchean granitoid plutonism is dominantly 2 61 2 59 ga with a less prominent 2 66 ga plutonic event the age of zircon recrystallization suggests that ca 2 60 ga archean metamorphism and fabric development s1 affected the 2 66 ga plutons prior to or contemporaneously with intrusion of the voluminous ca 2 6 ga suite end t for the ca 2 61 2 59 ga suite range from

timing of plutonism deformation and metamorphism in the yellowknife domain slave province canada u pb zircon titanite and monazite ages for plutonic rocks are used to constrain the timing of post 2660 ma deformational and metamorphic events in the yellowknife domain southern slave province diorite and tonalite plutons of the defeat suite yield ages of 2628 3 and 2624 3 ma older than previous less precise estimates for this suite of ca 2618 2620 ma the defeat suite plutons crosscut and postdate upright f1 folds in turbidites of the ca 2680 2660 ma burwash formation d1 deformation is therefore bracketed between 2660 and 2630 ma the d1 event significantly predates deposition of polymict conglomerates of the jackson lake formation a second folding event f2 represented by northwest to north trending steeply plunging folds of bedding and d1 structures affected the area after intrusion of the hidden lake pluton at 2606 2 ma and synchronously with intrusion of the 2596 2 ma sparrow lake pluton a member of the two mica granite prosperous suite the time of initiation and the duratio