structural history and granite emplacement in the rottenstone domain during closure of the trans hudson orogen davin lake northern saskatchewan the rottenstone domain at davin lake northern saskatchewan exhibits structural and granite emplacement evidence for crustal thickening and possible himalayan style extrusion overprinted by transpressional strain increasing toward the contact with the wathaman batholith three discrete rottenstone subdomains parallel the regional strike of the trans hudson orogen i the southeast rottenstone subdomain sersd with gently northwest dipping migmatitic straight gneiss s1 and white granitoid rocks with pinch and swell structures parallel to the straight gneissosity ii the central rottenstone subdomain crsd which partly preserves the same nw dipping fabric s1 but is overprinted at its margins by tight upright f2 folds and includes a stockwork of pink monzogranitic aplites and pegmatites and iii the northwest rottenstone subdomain nwrsd in which the f2 folds are generally tighter and penetrative and its network of narrow white granitoid rocks is deformed and transposed by the f2 folds but in

paleoproterozoic arc and ophiolitic rocks on the northwest margin of the trans hudson orogen saskatchewan canada their contribution to a revised tectonic framework for the orogen abstract a new lithotectonic framework for the northwestern reindeer zone of the trans hudson orogen divides rocks into five northwest to north dipping volcano sedimentary assemblages 1 at the structural base the 1 92 1 87 ga largely sedimentary levesque bay assemblage partly equivalent to former maclean lake gneisses which lies within the confines of the kisseynew domain and is tectonically imbricated with metasedimentary rocks of the the lawrence point assemblage is interpreted as a dismembered supra subduction zone ophiolite high mgo refractory harzburgite group 1 ultramafic rocks at the structural base of the assemblage is geochemically identical to the upper mantle section of selected supra subduction zone ophiolites and mantle tectonites chromite and olivine compositions of the group 1 ultramafic rocks are also comparable to those of ophiolitic harzburgite and mantle tectonite mafic metavolcanic rocks of the assemblage are classified as subalkaline tholeiitic basalts their trace element patterns and hf ta th y nb and la element ratios resemble those of modern back arc basin basalts the reed lake assemblage represents a subduction generated arc complex that was built on top of the lawrence point assemblage its mafic metavolcanic rocks are subalkaline basalts with calc alkaline trends and elevated th and ce concentrations and negative nb anomalies feldspar porphyry dykes intruding the lawrence point and duck lake assemblages constrain timing of lawrence point ophiolite emplacement onto the duck lake assemblage to 1 86 1 84 ga the trace element geochemistry of the dykes suggests continued arc volcanism after ophiolite emplacement mafic metavolcanic rocks of the levesque bay assemblage are geochemically similar to those of the lawrence point assemblage other ultramafic rocks peridotite to pyroxenite are abundant in the lawrence point assemblage but have similar geochemistry to small ultramafic bodies intruding the reed lake duck lake and levesque bay assemblages they represent a separate later phase 1 86 ga of ultramafic plutonism which post dates ophiolite emplacement timing of lawrence point ophiolite emplacement between 1 86 and 1 84 ga and geochemistry of later felsic and mafic ultramafic volcanism suggest that the lawrence point ophiolite and overlying reed lake arc assemblage were not accreted to the hearne craton prior to 1 86 ga but were first accreted to the flin flon glennie complex after 1 86 ga

alteration mineralogy and stable isotope geochemistry of paleoproterozoic basement hosted unconformity type uranium deposits in the athabasca basin canada unconformity type uranium deposits are characterized by mineralization developed along the contact between younger sandstone cover and underlying crystalline basement rocks mineralization may extend up to 400 m into the underlying basement rocks whereas sandstone hosted unconformity type deposits have been well studied deposits hosted primarily in the basement have not this study examines the deposits at rabbit lake dawn lake and mcarthur river in the athabasca basin of canada which are hosted by the metamorphic archean and early paleoproterozoic rocks forming the basement to younger late paleoproterozoic sandstones alteration is similar in the three deposits and is characterized by three distinct paragenetic stages 1 preore alteration involving illitization of plagioclase and amphibole followed by chloritization of biotite and illite which formed at ca 230 c 2 ore stage alteration characterized by uraninite and coarse grained illite which formed at ca 240 c 3 postore alteration comprising spherulitic dravite vein chlorite quartz calcite and fe cu co and pb sulfides which formed at ca 135 c fluid circulation associated with emplacement of later mackenzie dikes initiated partial recrystallization of uraninite a later stage of alteration includes kaolinite and iron hydroxide precipitation formed at much lower temperatures of ca 50 c stable isotope compositions of the alteration minerals in conjunction with their paragenesis indicate that oxidized basinal fluids d 43 to 21 18o 3 8 were derived primarily from evolved seawater and leached uranium from the overlying sandstones of the athabasca formation and transported it into the basement via infiltration along fracture zones associated with reverse faults graphitic units in the basement and preore alteration served as both physical fractured zones and chemical reductants traps for the uranium mineralization the basinal fluids were responsible for the preore illite chlorite synore uraninite illite and the early postore alteration events this differs from many other sandstone hosted deposits where both oxidized basinal and reduced basement derived fluids were responsible for uranium precipitation

sulphur isotope characteristics of recrystallisation remobilisation and reaction processes a case study from the ramsbeck pb zn deposit germany syntectonic hydrothermal pb zn vein systems of the ramsbeck deposit germany have been extensively overprinted by late stage fluids responsible for fissure vein mineralisation this has caused remobilisation of vein components notably of sphalerite and galena as well as the formation of various sb sulphosalt minerals including boulangerite semseyite tetrahedrite and bournonite a detailed sulphur isotope study of sphalerite galena and sulphosalts related to different stages of recrystallisation remobilisation and reaction has been carried out using an insitu laser combustion technique primary sphalerite galena ores from flat lying thrust zones are characterised by homogeneous positive 34s values in the range 6 5 to 7 7 in contrast recrystallised and remobilised sphalerite and galena from both overprinted thrust zones and extensional fissure veins show 34s values in the range 1 1 to 2 9 and 0 7 to 8 7 respectively sulphosalt minerals show a similar variation in their sulphur isotope compositions which range between 1 7 and 7 7 fissure vein hosted sphalerite and sulphosalts display significantly more negative 34s values than the primary pb zn ores sphalerite which recrystallised in situ and boulangerite which formed by reactive replacement of primary galena show slightly more positive 34s values than fissure vein hosted minerals the compositional range of remobilised mineral phases can be best explained by varying contributions variable mixing of sulphur derived from 1 the primary sphalerite galena ores of the flat thrust systems and 2 the hydrothermal fluid responsible for the fissure vein mineralisation equilibrium fractionation temperatures calculated for sphalerite galena pairs contrast strongly with fluid inclusion data isotopic fractionation related to the remobilisation has to be interpreted in terms of kinetic processes

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

nd sr and o isotopic constraints on the petrogenesis of mafic intrusions in the proterozoic trans hudson orogen of central canada sm nd isotopic data from five mafic intrusions in the la ronge lynn lake domain indicate crystallization between 1 88 and 1 79 ga the data from a single intrusion in the glennie lake domain suggest a slightly younger age of about 1 71 ga these results indicate a cogenetic origin of the mafic intrusions with the associated volcanic and plutonic rocks initial end values vary from 4 5 to 0 6 and can be modeled by mixing proterozoic mantle derived magmas with 17 archaean crust or subduction of 3 sediment similar to pelites from the wollaston domain the initial end value of 0 for a late proterozoic mackenzie dike is compatible with an origin from mantle sources affected by hudsonian subduction processes rb sr data indicate variable and generally high initial 87sr 86sr isotopic ratios which reflect in part isotopic redistribution during metamorphism 18o values of coexisting clinopyroxene orthopyroxene and plagioclase indicate isotopic disequilibrium plagioclase samples show variable degrees o

fabric analysis using the intercept method abstract the intercept method is a convenient yet powerful method for the numerical analysis of fabrics for geological applications it can be used when a set of objects e g pores grains or aggregates of a specific mineral lineaments etc with unique characteristics can be identified in an image the intercept method analyses boundaries of objects as a population of lines how intercepts are definined is therefore important in order to establish the significance of the intercept counts when the method is applied to digital images the subdivision of the information into square pixels must also be considered we apply a linear filter which minimizes the effects of grid anisotropy on the counting of intercepts analysis of the resulting rose of intercept counts by a fourier series considerably facilitates the interpretation of the data a rose of directions can readily be derived for the phase boundaries if a population of objects can be assumed to have started with an originally isotropic orientation and to have been deformed passively the fourier components of the rose of intercepts also give the sectional strain the fourier components also permit an objective test of the validity of describing a fabric as resulting from a homogeneous strain on an initially isotropic section two computer programs for the counting and analysis of intercepts on digital images are presented and applied in four examples which illustrate the usefulness of the intercept method for magmatic fabric measurement strain analysis and lineament analysis we also illustrate the importance of fourier series decomposition of rose of intercept counts for fabric interpretations intercept results are also shown to be compatible with those derived by other methods eigenvector surfor inertia tensor autocorrelation methods

quantification of the spatial distribution of mineral phases and grains in rock using a 2 d multiple area density map technique abstract the most widely used method for quantitative analyses of the spatial distribution of grains in a rock body is the nearest neighbor method a position based method which recognizes the grain center as the position of the grain without consideration of grain size or shape however the spatial distribution of grains is influenced by their size and shape as well as their position here we propose a multiple area density map madm method to quantify the spatial distribution of phases or grains the method is based on image analysis and simultaneously considers the position size shape and proportion of grains the madm constructed by overlaying density maps of grain areas with a set of template size produces a normalized standard deviation nsd value of phase area density which represents the degree to which it is spatially clustered the nsd value is used to quantify the distribution of the phase without considering individual grains to identify the spatial distribution of individual grains the method employs the clustering index ci which is calculated from the ratio of nsd to the reciprocal of the number of grains in a log log plot

crustal history of the rae and hearne provinces southwestern canadian shield saskatchewan constraints from geochronologic and isotopic data abstract the cree lake zone hearne province and western granulite domain rae province in northern saskatchewan are contrasting parts of the variably reworked upper plate western hinterland of the paleoproterozoic trans hudson orogen their junction is defined by the virgin river shear zone a part of the more extensive snowbird tectonic zone subsurface extension of the 2 0 ga thelon orogen lies west of the western granulite domain we present u pb zircon ages sm nd and rb sr isotopic data from the cree lake zone and western granulite domain and from the junction granite which intrudes the virgin river shear zone data from the western granulite domain indicate that prevalent granulite facies metamorphism occurred between 2 3 and 2 0 ga but is imposed on archean protoliths 2 8 3 0 ga old low amphibolite facies retrogression which increases toward the virgin river shear zone probably postdates 2 1 ga data from the cree lake zone also yield archean protolith ages as old as 3 0 ga and some rocks yield interpreted high grade metamorphic overprint ages of 2 3 2 0 ga however two samples yield data indicating hudsonian high grade metamorphic overprint 1 87 to 1 81 ga the junction granite has a u pb zircon age of 1 82 0 30 ga but relict zircons and sm nd data show that it was derived by melting of archean crust high grade mid crustal thermal resetting in the western granulite domain may be coeval with the 1 9 2 0 ga thelon orogen although the data do not preclude an earlier event or events similar 2 3 2 1 ga reworking extends into the cree lake zone but high grade hudsonian 1 87 1 84 ga reworking is also evident in parts of this zone well to the west of the wollaston domain and may extend entirely across the zone to the virgin river shear zone relative importance of the thelon and hudsonian overprints in cree lake zone is unknown data from the junction granite and western granulite domain suggest that all recorded high strain events in the virgin river shear zone postdate 2 3 ga and are thus unrelated to deep crustal archean granulite facies mylonites in the tantato black lake segment of the snowbird tectonic zone north of the athabasca basin

combined quantification of anisotropy and inhomogeneity of magmatic rock fabrics an outcrop scale analysis recorded in high resolution abstract magmatic mineral distribution patterns in a syntectonic syenite pluton have been recorded at high resolution over several square metres on quarried faces the anisotropy and inhomogeneity of k feldspar and mafic mineral distribution patterns have been quantified using two methods originally based on fractal geometry 1 map counting based on box counting illustrates an inhomogeneity on the decimetre to metre scale and highlights diffuse structures that can be related to mafic schlieren or felsic dykes that are not visible on the rock surface 2 we have developed a mapping of rock fabric anisotropy morfa method that leads to the detection of further magmatic structures that are not visible in the field with morfa a magmatic lineation and its variation over large areas is determined as well as fabrics on the decimetre to 1 m scales which possibly represent flow or fracture structures in the crystallising magma

shape preferred orientation of object populations automatic analysis of digitized images abstract an automatic technique is presented for systematic shape preferred orientation spo analysis of crystal fabrics in rocks this technique is based on digitization of an image with a ccd camera and separation of an object population from its matrix the image is analysed globally using a rotating grid that is superimposed on the square pixel grid of the computer screen the parametric method is based on counting intercepts in all directions the interceps rose provides information on both the orientation and strength of the spo problems of hardware related counting noise anisotropy are avoided using an original method of filtering the intercept function with a linear sliding mask on the counting grid the technique was tested both on single objects of different shapes and on different populations of identical objects a very high degree of accuracy was obtained for orientation measurements fabric shape parameters are introduced which are specific to this intercept technique they compare favourably with shape parameters used in axial fabric analysis

geochemistry and tectonic setting of lewisian clastic metasediments from the early proterozoic loch maree group of gairloch nw scotland abstract the early proterozoic 2 0 ga loch maree group lmg of the lewisian complex consists of a supracrustal sequence of metasedimentary schists and associated tholeiitic metavolcanic amphibolites within the archaean basement the metasediments comprise three main mapped units the flowerdale schists kerrysdale schists and charlestown schists together with numerous narrower bands the dominant clastic metasediments within the schist units semipelites and psammites are chemically distinguished as a series of greywackes and lithic sandstones with variable lil and transition element abundances fractionated ree patterns and overall compositions similar to paas three chemical groups are recognized whose range of composition largely reflects the mixing between two main source components lewisian gneissose basement with an intermediate acid continental crust composition and local rift related amphibolites with a primitive tholeiitic composition which also incorporates components not preserved within the lmg the geochemistry of the clastic metasediments confirms a previous tectonic model for the lmg as an intracontinental extensional rift receiving clastic detritus from the adjacent uplifted basement as well as from internal volcanogenic sources

automatic reconstruction of fault networks from seismicity catalogs three dimensional optimal anisotropic dynamic clustering 1 we propose a new pattern recognition method that is able to reconstruct the three dimensional structure of the active part of a fault network using the spatial location of earthquakes the method is a generalization of the so called dynamic clustering or k means method that partitions a set of data points into clusters using a global minimization criterion of the variance of the hypocenters locations about their center of mass the new method improves on the original k means method by taking into account the full spatial covariance tensor of each cluster in order to partition the data set into fault like anisotropic clusters given a catalog of seismic events the output is the optimal set of plane segments that fits the spatial structure of the data each plane segment is fully characterized by its location size and orientation the main tunable parameter is the accuracy of the earthquake locations which fixes the resolution i e the residual variance of the fit the resolution determines the number of fault segments needed to describe the earthquake catalog the better the resolution the finer the structure of the reconstructed fault segments the algorithm successfully reconstructs the fault segments of synthetic earthquake catalogs applied to the real catalog constituted of a subset of the aftershock sequence of the 28 june 1992 landers earthquake in southern california the reconstructed plane segments fully agree with faults already known on geological maps or with blind faults that appear quite obvious in longer term catalogs future improvements of the method are discussed as well as its potential use in the multiscale study of the inner structure of fault zones

timing constraints of orogeny to cratonization thermochronology of the paleoproterozoic trans hudson orogen manitoba and saskatchewan canada abstract a comprehensive thermochronometric investigation across a 600 km transect of the paleoproterozoic trans hudson orogen tho in canada has resolved two first order thermal events 1 widespread peak metamorphism at 1 82 1 79 ga associated with terrane amalgamation and 2 a late collisional metamorphic episode at ca 1 77 ga that is characterized by significant strike slip deformation and rapid cooling geophysical observations of the lithosphere beneath the tho reveal crust that is markedly different on either side of the crustal scale tabbernor sturgeon weir tsw strike slip fault system which offsets lower crustal reflectors the tho east of the fault system records u pb titanite and total pb monazite domain ages that are relatively indistinguishable from 40ar 39ar hornblende and mica cooling ages indicating rapid cooling and perhaps exhumation following 1 77 ga metamorphism seismic imaging indicates the eastern orogen is an irregular package of stacked crustal blocks and our thermochronometric data demonstrate it behaved as a single coherent element shortly 20 30 m y following cessation of convergence in contrast rocks located west of the tsw fault system cooled distinctly later preserving 40ar 39ar muscovite and biotite ages between 1 74 and 1 72 ga this crustal architecture delineated from seismic surveys illustrates a more homogeneous slightly 5 km thinner crust in the case of this orogen apparent stabilization and cratonization occurred ca 100 m y after peak terrane amalgamation and notably the orogen was likely cratonized as two blocks east and west of the tsw fault system

lead isotopic evidence for the origin of paleo and mesoproterozoic rocks of the colorado province u s a abstract lead isotopic ratios of k feldspars and whole rocks from 1 7 and 1 4 ga plutonic rocks of the colorado province are relatively non radiogenic for 207 pb 204 pb plotting below the average crust model curve of stacey and kramers 1975 indicating that the terrane was derived primarily from juvenile mantle material slightly more radiogenic ratios in the northern part of the terrane near the archean wyoming province suggest minor inclusion of an older component the data from 1 7 ga plutons plot in a broad field suggesting two episodes of re equilibration with whole rock pb probably related to heating events in the mesoproterozoic 1 4 ga and cretaceous 70 ma possible differences in calculated whole rock th u coupled with slight pb isotopic variations along the north south transect suggest either a terrane boundary through central colorado near salida and gunnison or fundamental differences in source rocks metasedimentary vs metavolcanic u pb analyses of multigrain splits of detrital zircons from quartzites throughout the colorado province have failed to identify archean detritus the oldest 207 pb 206 pb ages found in two samples of quartzite from northern colorado are about 2 0 ga perhaps derived from rocks of the trans hudson orogen in contrast to 2 75 ga detrital zircon in a paleoproterozoic quartzite from the southern part of the wyoming province while we are not yet able to discern if these ages are true provenance ages or mixtures of archean and paleoproterozoic components the absence of easily recognizable archean zircons supports other isotopic data and a conclusion that most of the paleoproterozoic crust of the colorado province was ultimately derived from a juvenile at 1 8 ga mantle reservoir

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

paleoproterozoic 1 90 1 86 ga arc volcanism in the flin flon belt trans hudson orogen canada geochemical and isotopic nd sr data are reported on paleoproterozoic 1904 1864 ma maficintermediate 1870 ma collision and subsequent intra arc deformation

u pb zircon ages and rb sr whole rock isotope studies of early proterozoic volcanic and plutonic rocks near tampere southern finland abstract the tampere schist belt southern finland is a well preserved volcanic sedimentary belt in the early proterozoic svecofennian terrain the metasedimentary rocks of the belt are dominated by turbiditic greywackes siltstones and mudstones the metavolcanics range from basalt to rhyolite in composition intermediate rocks being the most common near tampere the belt comprises an east west trending major syncline the u pb zircon ages of the 1 9 ga old metavolcanics cover an age interval of 15 ma the oldest age 1904 4 ma is from the intermediate unit at orivesi which is dominated by calc alkaline high k dacites and andesites this unit is the lowest in the northern limb of the syncline at orivesi at ylojarvi a sample from the lower volcanic unit has an age of 1898 4 ma while a sample from the upper volcanic unit has the youngest crystallisation age of 1889 5 ma these ages agree with the structure and stratigraphy of the belt the implications of the 1891 16 and 1889 19 ma ages of two feldspar porphyries remain obscure here the error limits are wide and it is not known with certainty whether the rocks are dykes sills or volcanics an age of 1901 28 ma was obtained for the varmala granitoid which intrudes the schists although the error is large it is possible that some of the zircon has been inherited from older rocks the rb sr whole rock ages of the volcanics agree within error limits with the u pb zircon ages the rb sr age of the hameenkyro batholith is however about 100 ma lower than the equivalent u pb age the i sr values of the metavolcanics and the 1 882 ga old hameenkyro batholith range between 0 7020 and 0 7033 these low figures suggest that their protoliths separated from upper mantle sources within a short time interval the sm nd and lu hf isotopic data available in the literature support the conclusion that the period around 1 9 ga represents an important episode of continental growth which is particularly evident in the svecofennian ketilidian trans hudsonian terrains

metamorphism of the maclean lake and central metavolcanic belts la ronge domain trans hudson orogen pressure temperature variations and tectonic implications metamorphic assemblages differ between the metasedimentary maclean lake belt and the adjacent central metavolcanic belt in the la ronge domain trans hudson orogen the former consists of meta arkoses psammitic gneisses metaconglomerates and calc silicate gneisses of upper amphibolite facies 600 740 c 440 660 mpa with local migmatization whereas the latter is comprised mainly of metavolcanic and plutonic rocks with minor metasedimentary schists of greenschist to lower amphibolite facies 480 630 c 520 560 mpa petrographic evidence indicates that peak metamorphic conditions were reached towards the end of d1 deformation during which the central metavolcanic belt was thrust onto the maclean lake belt along the mclennan lake tectonic zone which separates the two belts peak metamorphic assemblages did not undergo retrograde alteration during d2 deformation indicating that high temperature was maintained during d2 deformation differences in pressure p and temperature t between the northeastern and southwestern parts of the central metavolcanic belt may have resulted from tilting along strike after peak metamorphism peak temperatures increase gradually from the central metavolcanic belt to maclean lake belt across the mclennan lake tectonic zone peak pressures in the two belts are similar implying that the central metavolcanic belt thrust sheet was probably thin the p t data for the maclean lake belt indicate a relatively high thermal gradient 40 50 c km similar to that in the metasedimentary kisseynew domain in the orogen

le batholite de de pas nouveau quebec infrastructure composite d arc magmatique proterozoique the de pas batholith in new quebec is a mass of granitoids elongated in a n s direction covering 7000 km2 in the southeastern part of the archean rae province it is located between the paleopro

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

the wathaman batholith largest known precambrian pluton the early proterozoic wathaman batholith in northern saskatchewan and manitoba is a 900 km long megacrystic granite granodiorite intrusion that straddles the junction between ensialic miogeoclinal and probably ensimatic eugeoclinal island arc terranes of the trans hudson orogen of the western churchill province although the largest precambrian batholith known it is apart from marginal complexities remarkably homogeneous throughout and unlike comparably sized and situated phanerozoic batholiths shows no evidence of multiple intrusion nor does it have comagmatic early mafic phases however it may be considered as just one phase of a larger batholithic belt that also includes numerous smaller plutons taken as a whole the composite batholithic belt is similar in many aspects to mesozoic pacific rim batholithic belts and like them probably was emplaced during plate collision the batholith is affected by pervasive internal deformation is bounded on the northwest by major blastomylonite zones a

magnetite grain shape fabric and distribution anisotropy vs rock magnetic fabric a three dimensional case study abstract shape fabric and distribution anisotropy of magnetite grains in a highly ferromagnetic s l syenite are determined for three mutually perpendicular planes on about 600 magnetite grains the grains are lenticular with an average aspect ratio of about 2 0 their preferred orientation determined by the inertia tensor method is consistent with the principal directions of the magnetic susceptibility ellipsoid and the axial ratios of the magnetic fabric ellipses are very close to those of the shape fabric ellipses e g 1 41 and 1 39 in the section plane perpendicular to the magnetic foliation and parallel to the magnetic lineation the anisotropic wavelet transform can detect and quantify the anisotropic distribution of the magnetite grains which are located interstitially along the feldspar grain boundaries this anisotropic distribution has no noticeable effect on the rock s anisotropy of magnetic susceptibility ams since only a few percent of grains are close enough to interact magnetically therefore it is realistic to consider that the ams of ferromagnetic granitic rocks originates mainly from the shape fabric of anisotropic magnetite grains and a close correlation between the magnetic fabric and the magnetite grain shape fabric is expected

detrital zircon evidence for non laurentian provenance mesoproterozoic ca 1490 1450 ma deposition and orogenesis in a reconstructed orogenic belt northern new mexico usa defining the picuris orogeny detrital zircon and igneous zircon u pb ages are reported from proterozoic metamorphic rocks in northern new mexico these data give new insight into the provenance and depositional age of a 3 km thick metasedimentary succession and help resolve the timing of orogenesis within an area of overlapping accretionary orogens and thermal events related to the proterozoic tectonic evolution of southwest laurentia three samples from the paleoproterozoic vadito group yield narrow unimodal detrital zircon age spectra with peak ages near 1710 ma igneous rocks that intrude the vadito group include the cerro alto metadacite the picuris pueblo granite and the penasco quartz monzonite and yield crystallization ages of 1710 10 ma 1699 3 ma and 1450 10 ma respectively within the overlying hondo group a metamorphosed tuff layer from the pilar formation yields an age of 1488 6 ma and represents the first direct depositional age constraint on any part of the proterozoic metasedimentary succession in northern new mexico detrital zircon from the overlying piedra lumbre formation yield a minimum age peak of 1475 ma and 60 grains 25 yield ages between 1500 ma and 1600 ma possibly representing non laurentian detritus originating from australia and or antarctica detrital zircons from the basal metaconglomerate and the middle quartzite member of the marquenas formation yield minimum age peaks of 1472 ma and 1471 ma consistent with earlier results we interpret the onset of ca 1490 1450 ma deposition followed by tectonic burial regional al 2 sio 5 triple point metamorphism and ductile deformation at depths of 12 18 km to reflect a mesoproterozoic contractional orogenic event possibly related to the final suturing of the mazatzal crustal province to the southern margin of laurentia we propose to call this event the picuris orogeny

the north american central plains conductivity anomaly and its correlation with gravity magnetic seismic and heat flow data in saskatchewan canada abstract the north american central plains conductivity anomaly nacp lies virtually in its entirety within the trans hudson orogen accordingly should these two features prove to be contemporaneous then the geometrical relationship between these two is of foremost importance to any evolutionary tectonic model proposed to explain the collision of the superior and churchill provinces in the hudsonian and a model that does not include a mechanism for the generation of this anomaly is obviously untenable in order to map better the trend of the nacp in the province of saskatchewan canada two magnetotelluric mt profiles were conducted over the nacp previously defined by magnetometer arrays and profiles data from these two profiles along with an earlier mt profile just north of the u s canadian border suggest that the nacp is not a continuous feature but rather that it exhibits a definite break at latitude 51 n other geophysical evidence examined herein is concordant with this characteristic if a second mt anomaly mapped to the northwest of this break is in fact a manifestation of the same geological structure then one possible interpretation is of a major nw se trending sinistral fault in the deep crust previously undetected with a movement of some 100 150 km along strike the mt data from the southernmost profile after correction for static shift are modelled in a 2d manner and it is shown that the nacp is consistent with an arcuate structure in vertical section of high conductivity 2 s m 1 beginning at a depth of 10 km centred on 103 w dipping down to the west reaching possibly the base of the crust it is also shown that such an arcuate shape in section can explain an observed gravity high of 40 mgal such high conductivities cannot be explained in terms of connected fluids as it would require implausibly high porosities 12 20 a comprehensive interpretation of all the geophysical data would have to account for the observed characteristics of the anomalous region which are high electrical conductivity positive density contrast no magnetization and high heat flow in the basement in terms of a single causative body one possible explanation is presented in terms of a zone of lithospheric weakness along which was emplaced low density differentia from a mantle derived body an alternative explanation could be the phase transformation of obducted material into eclogite or serpentinite however difficulties exist with both of these explanations and further data are required

quantitative textural analysis of packings of elongate crystals the spatial distribution of grains in a solidifying igneous rock controls the physical properties of the crystal mush and in turn is controlled by the rate of crystal growth and accumulation a predominant non spherical habit for igneous minerals brings into question the use of spherical particles in reference packings used for quantification of spatial distribution furthermore variations of crystal clustering ordering with length scale require spatial statistics which take into account the distribution of particles beyond nearest neighbours using random close packings of spherocylinders we demonstrate the importance of aspect ratio for the aggregation index usually known as r and show that packings of spherical particles have more structure than packings of rods the spatial distribution functions demonstrate that the plagioclase grains in the colonnade from the holyoke basalt are clustered on a length scale of 0 5 mm understanding the controls on grain spatial distribution in igneous rocks will depend on the application of these techniques to well understood environments

age of the richmond gulf group and implications for rifting in the trans hudson orogen canada abstract the aphebian richmond gulf group of the east coast of hudson bay is a fluvial sandstone sequence containing basalt flows it was shed eastward from a rifting related thermal dome situated in the present central part of hudson bay sandstone from the base of the group contains a uraniferous diagenetic apatite cement u pb and pb pb isochron analysis from this material show the age of the apatite haematite cement to be 2025 25 ma old these data provide an older age bracket for the deposition of the richmond gulf nastapoka and belcher groups they also date the formation of the richmond gulf graben an aulacogen related to the initial rifting of the trans hudson orogen

short lived 1 9 ga continental margin and its destruction wopmay orogen northwest canada a 1 9 ga continental margin in the northwest of the canadian shield evolved in less than 15 m y from a zone of crustal stretching through a phase of passive margin subsidence to attempted subduction beneath an exotic microcontinent reversal of subduction polarity and generation of a major episutural magmatic arc occurred within 15 m y following microcontinental accretion terminal collision occurred 90 m y at most after initial rifting certain differences in detail between this collided margin and those of phanerozoic age may be related to subduction of newly rifted lithosphere rapid evolution of the orogen the contracted passive margin phase in particular is consistent with but does not prove more rapid recycling of oceanic plates at that time

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

effects of magnetic interactions in anisotropy of magnetic susceptibility models experiments and implications for igneous rock fabrics quantification besides granites of the ilmenite series in which the anisotropy of magnetic susceptibility ams is mainly controlled by paramagnetic minerals the ams of igneous rocks is commonly interpreted as the result of the shape preferred orientation of unequant ferromagnetic grains in a few instances the anisotropy due to the distribution of ferromagnetic grains irrespective of their shape has also been proposed as an important ams source former analytical models that consider infinite geometry of identical and uniformly magnetized and coaxial particles confirm that shape fabric may be overcome by dipolar contributions if neighboring grains are close enough to each other to magnetically interact on these bases we present and experimentally validate a two grain macroscopic numerical model in which each grain carries its own magnetic anisotropy volume orientation and location in space compared with analytical predictions and available experiments our results allow to list and quantify the factors that affect the effects of magnetic interactions in particular we discuss the effects of i the infinite geometry used in the analytical models ii the intrinsic shape anisotropy of the grains iii the relative orientation in space of the grains and iv the spatial distribution of grains with a particular focus on the inter grain distance distribution using documented case studies these findings are summarized and discussed in the framework of the generalized total ams tensor recently introduced by canon tapia canon tapia e 2001 factors affecting the relative importance of shape and distribution anisotropy in rocks theory and experiments tectonophysics 340 117 131 the most important result of our work is that analytical models far overestimate the role of magnetic interaction in rock fabric quantification considering natural rocks as an assemblage of interacting and non interacting grains and that the effects of interaction are reduced by i the finite geometry of the interacting clusters ii the relative orientation between interacting grains iii their heterogeneity in orientation shape and bulk susceptibility and iv their inter distance distribution we reconcile analytical models and experiments with real case studies that minimize the role of magnetic interaction onto the measured ams limitations of our results are discussed and guidelines are provided for the use of ams in geological interpretation of igneous rock fabrics where magnetic interactions are likely to occur

shrimp u_pb zircon geochronology of granites in the arunta inlier central australia implications for proterozoic crustal evolution abstract new shrimp u pb zircon isotopic ages are reported for ten granitic suites in the eastern arunta inlier these data combined with previous u pb zircon studies in the region constrain the timing of major palaeoproterozoic igneous events within the arunta inlier and establish a geochronological framework for understanding lithostratigraphic relationships tectonic events and geochemical and isotopic evolution of the granites in the region most granites in the arunta inlier including both syn tectonic and post tectonic types yield zircon ages in the range of 1770 1710 ma which are significantly younger than the 1880 1850 ma orogenic barramundi igneous association recognised throughout many other proterozoic terrains in northern australia no rocks of the barramundi association have been identified in this study the previously proposed barramundi type suites including the jervois and dneiper granites yield ages of 1771 6 and 1771 15 ma respectively many of the granite suites contain inherited zircons with ages in the range of 1890 1830 ma similar to the age of the barramundi association this and the age of the atnarpa igneous complex zhao and cooper 1992 which is coeval with but geochemically distinct from the barramundi association suggest that the 1880 1850 ma orogenic event affected the arunta inlier but has been obscured by the younger tectonic events the youth of tectonic events in the arunta inlier as compared with other proterozoic terrains of northern australia may have resulted from the inlier being located on the southern margin of the northern australian orogenic province during the palaeoproterozoic with the generation of granites in the arunta inlier possibly being related to subduction the combined data indicate that major granitic activity occurred at 1880 1850 1820 1770 1750 1730 1710 1660 1650 and 1615 1590 ma this result is broadly consistent with earlier summaries of the other proterozoic terrains in northern australia although the intensity of each episode varies in different regions

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

u pb geochronology of late neoarchean tonalites in the flin flon belt trans hudson orogen surprise at surface the flin flon volcanic belt of the trans hudson orogen in northern manitoba comprises magmatic rocks 1 88 1 90 ga generated in an intra oceanic arc and identified as one of the best examples of juvenile paleoproterozoic crust in the flin flon athapapuskow lake area the belt consists of a series of fault bounded blocks each having distinct stratigraphic and magmatic affinities juxtaposed to form an accretionary collage two tonalitic bodies within the northeast arm shear zone a major deformation corridor separating two of the most important blocks in the area have been dated by the u pb zircon method at and these results indicate the presence of fragments of late neoarchean crust within the flin flon belt possibly related to ca 2 5 ga granitic bodies found in terranes beyond the western limit of the belt the presence of ca 2 5 ga tonalites within the flin flon belt herein reported for the first time has major implications for basement involvement in the early tectonic evolution of the f

a cordilleran type batholitic belt in the churchill province in northern saskatchewan abstract the rottenstone and western la ronge domains of the south central churchill province in saskatchewan consist mostly of hudsonian batholithic complexes spatially and structurally related to an aphebian hudsonian volcanic arc the batholithic belt is of comparable dimensions and compositional variation to cordilleran type phanerozoic batholiths and appears to be emplaced in close proximity to a prior late archean early aphebian continental crustal margin a quartz diorite line separating dominant quartz diorite tonalite granodiorite plutonic rocks from dominant granodiorite quartz monzonite granite intrusives can be defined these general characteristics as well as more detailed features of aphebian deposition and hudsonian thermotectonism within and on either side of the rottenstone domain suggest a continental margin rather than an intracontinental location for evolution of the hudsonian orogenic belt of the south central churchill province and provide some insights into the possible development of this part of the canadian shield as part of a hudsonian wilson cycle

geochemical and nd isotopic compositions of the metasedimentary rocks in the la ronge domain trans hudson orogen canada implications for evolution of the domain abstract metasedimentary rocks of greenschist to amphibolite facies occur in various belts in the paleoproterozoic la ronge domain of the trans hudson orogen metasedimentary rocks in the central metavolcanic greenstone belt are low to intermediate in sio2 contents have nd values of 2 3 to 4 5 with two rare earth element ree patterns of la yb n 8 5 respectively the predominant component meta arkoses of the overlying mclennan lake belt have distinctly high k2o and sio2 contents high la yb n ratios 11 46 large negative eu anomalies eu eu 0 1 0 58 and uniformly low nd values 0 8 to 0 2 the maclean lake belt is comprised of a variety of metasedimentary gneisses the volumetrically minor amphibole and diopside rich gneisses have high ferromagnesian element sc and co concentrations high nd values of 4 1 to 5 7 and flat ree patterns with no eu anomalies the predominant lithological unit in the maclean lake belt the psammitic gneisses is geochemically more variable the mafic psammitic gneiss samples in the maclean lake belt and the metasedimentary rocks in the central metavolcanic belt are similar in trace and major element geochemistry and nd isotope composition whereas those more felsic psammitic gneisses are similar to the mclennan lake meta arkoses geochemical data combined with lithological and geochronological evidence indicate that sediments in the central metavolcanic belt were derived mainly from contiguous volcanic debris with minor addition of felsic components from exotic sources in contrast the mclennan lake meta arkoses were derived from a distinct felsic source whereas the psammitic gneisses in the maclean lake belt are mixtures of volcanic materials in the central metavolcanic belt and meta arkoses like felsic components nd isotopic data and ages of detrital zircon suggest that proterozoic juvenile materials were dominant sources for metasedimentary rocks in the la ronge domain comparison of geochemical signatures of the metasedimentary rocks with those of the felsic plutonic rocks in the central metavolcanic belt suggests that the felsic materials in the mclennan lake and maclean lake belts could not have been derived predominantly from the plutonic rocks implying more distal sources topographic changes during collision may have resulted in a shift from mixing of both local and distal sources for the rocks in the maclean lake belt to the dominance of a more distal source for the mclennan lake meta arkoses

composition age and origin of granitoid rocks in the davin lake area rottenstone domain trans hudson orogen northern saskatchewan the rottenstone domain of the trans hudson orogen is a 25 km wide granitic migmatitic belt lying between the la ronge volcanic plutonic island arc 1890 1830 ma to the southeast and the ensialic wathaman batholith 1855 ma to the northwest the rottenstone domain consists of three lithotectonic belts parallel to the orogen i southeast gently folded migmatized quartzo feldspathic metasedimentary and mafic metavolcanic rocks intruded by small concordant and discordant white tonalite monzogranite bodies ii central intensely folded and migmatized metasedimentary rocks and minor metavolcanic rocks intruded by largely discordant xenolith rich pink aplite pegmatite monzogranite bodies and iii northwest steeply folded migmatized metasedimentary rocks cut by subvertical white tonalite monzogranite sheets emplacement of granitoid rocks consists predominantly of contiguous orogen parallel steeply dipping syntectonic and post tectonic sheets with prominent magmatic schlieren bands overprinted by parallel solid state deformation features the white granitoid rocks have a cnk mol al2o3 mol cao na2 o k 2o 1 14 1 22 k rb 500 ree sum of rare earth elements 1 87 sr 86 sri 0 7032 and endi 2 the pink monzogranites have a cnk 1 11 1 16 k rb 500 ree 90 ppm eu eu 1 87 sr 86 sri 0 7031 and endi 2 the white granitoid rocks show a wider compositional range and more compositional scatter than the pink monzogranites reflecting some combination of smaller volume melts less homogenization and less control by crystal melt equilibria all metavolcanic metasedimentary and granitic rocks in the rottenstone domain have the distinctive geochemical signatures of an arc environment new sensitive high resolution ion microprobe shrimp u pb geochronology on the rottenstone granitoid rocks reveals complex growth histories for monazite and zircon variably controlled by inheritance magmatism and high grade meta morphism monazite ages for the granitoid bodies and migmatites cluster at 1834 and 1814 ma whereas zircon ages range from 2480 ma rare cores to 1900 1830 ma cores and mantles but also 1818 1814 ma for low th u recrystallized rims overgrowths and rare discrete euhedral prisms these results demonstrate that at least some source material for the granitic magmas included earliest paleoproterozoic crust sask craton or its derived sediments and that rottenstone granitic magmatism postdated plutonism in the bounding la ronge arc and wathaman batholith we estimate the age of terminal metamorphism in the davin lake area to be 1815 ma petrogenetically the rottenstone migmatites and granitoid rocks appear for the most part locally derived from their metasedimentary and metavolcanic host rocks shed from the la ronge arc sask craton and possibly the hearne craton the rottenstone domain was the least competent member in the overthrust stack and probably underwent a combination of fluid present melting and fluid absent decompression melting resulting in largely syntectonic granitoid magmatism 1835 1815 ma analogous to granite production in the high himalayan gneiss belt

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

an early proterozoic vgp from an oriented drillcore into the precambrian basement of southern alberta summary we report paleomagnetic results for 25 samples from a fully oriented pancanadian petroleum drillcore which penetrated the precambrian basement of southern alberta at a depth of 2550 m samples were taken at approximately 1 m intervals over a 7 m section of core intensities of natural remanent magnetization nrm were 0 5 14 a m over the section which consists mainly of granodiorite with one short granite interval x ray and curie temperature data indicated magnetite as the only important nrm carrier most of the nrm was an intense steeply inclined drilling remanence with coercivities 20 mt and distributed low to intermediate unblocking temperatures after magnetic cleaning a weak but stable primary nrm with high coercivities and high unblocking temperatures was isolated with d 157 i 52 k 118 mg5 3 n 20 the corresponding virtual geomagnetic pole vgp is 4 s 93 w dp 3 dm 4 which falls on the north american apparent polar wander path around 1850 ma the basement of this part of alberta is probably an extension of the churchill structural province of the laurentian shield

plate tectonics model for proterozoic continental accretion in the southwestern united states proterozoic crustal provinces in the southwestern united states decrease in age south from the archean wyoming province supracrustal rocks define three major age provinces from north to south 1 72 to 1 80 1 65 to 1 72 and 1 1 to 1 2 b y successions within each province are similar and define two assemblages a bimodal volcanic assemblage commonly overlain by a quartzite shale assemblage precambrian granitic plutons intrude all three provinces geochemical and sr isotope data indicate a variably depleted upper mantle source for basalts and a short lived these observations can be explained by a plate tectonics model involving successive marginal basin closures and andean type orogenies associated with southward migrating arcs the net result is to accrete 1 300 km of continental crust to the southwestern margin of north america between 1 8 and 1 1 b y ago

proterozoic transcurrent movements along the kapuskasing lineament superior province canada and their relationship to surrounding structures abstract analysis of large scale geological and geophysical lineaments provide evidence for a new model to explain the kapuskasing structural zone ksz and james bay james bay is interpreted to have formed due to rifting related to lateral strike slip along the ksz the sutton arc is interpreted to be an extension from hudson bay arc which has been displaced by rifting of james bay magnetic anomalies which terminate at the ksz on the west have correlated magnetic anomalies on the east which are displaced left laterally it is proposed that these displacements and the rifting of james bay and the strike slip along the ksz were caused as a result of 160 km of left lateral motion between east and west superior terranes with an accompanying 5 of anticlockwise rotation of the west superior terrane additional support for this model comes from structural evidence drawn from previous reports from the last twenty six years

the autocorrelation function an image processing tool for fabric analysis abstract the use of the autocorrelation function acf is proposed as a method for fabric and or strain analysis its chief purpose is to extend fabric analysis to fine grained materials such as clays micrites etc or to materials where the determination of individual grain shapes is tedious or impossible the main advantage of the method is that no segmentation of the image prior to analysis is necessary in other words any bias associated with identifying grain boundaries and the like is avoided in as much as the recognition of grains or grain boundaries is a matter of scale the acf can be used without loss of generality whenever the grain size is small in comparison with the size of the analysed area the method is computer based it requires a scanner for the digitization of the images and sufficient storage space and computing power for digital image processing the method uses half tone images as input these can be obtained from thin sections acetate peels polished surfaces photographic negatives or positives etc the acf is a two dimensional function that is related to the average shape that occurs in the fabric it is scaled with respect to the original image and allows simultaneous analysis of small and large features the acf enables a a quantitative description of the fabric in general terms b an efficient grain size determination and c if strain is a valid interpretation of the fabric the derivation of the finite strains in the plane of observation in the first part of the paper the acf method is introduced by way of a few numerically generated fabrics and compared to other methods of fabric and strain analysis in the second part an application to three samples of experimentally deformed solnhofen limestone is demonstrated

u pb zircon ages from the lynn lake and rusty lake metavolcanic belts manitoba two ages of proterozoic magmatism two ages of magmatism have been determined from zircon in felsic flows and plutons in the churchill province of manitoba a rhyolite flow from the lynn lake metavolcanic belt has a u pb age of and a rhyolite flow from the adjacent rusty lake metavolcanic belt has an age of tonalite and quartz diorite from two composite plutons emplaced into the volcanic rocks at lynn lake have ages of and indistinguishable from the age of the rusty lake belt rhyolite the arcuate domain of metavolcanic rocks that includes the rusty lake belt in the southeast the lynn lake belt in the north and the la ronge belt saskatchewan in the southwest has previously been considered a single structural sub province with similar ages throughout our results and published u pb ages from saskatchewan indicate that an older magmatism is represented by volcanic rocks in the lynn lake belt a younger magmatism by volcanic rocks in the rusty lake and la ronge belts and plutons in the lynn lake belt at lynn lake the older magmati

riding the right wavelet quantifying scale transitions in fractured rocks the mechanics of brittle failure is a well described multi scale process that involves a rapid transition from distributed microcracks to localisation along a single macroscopic rupture plane however considerable uncertainty exists regarding both the length scale at which this transition occurs and the underlying causes that prompt this shift from a distributed to a localised assemblage of cracks or fractures for the first time we used an image analysis tool developed to investigate orientation changes at different scales in images of fracture patterns in faulted materials based on a two dimensional continuous wavelet analysis we detected the abrupt change in the fracture pattern from distributed tensile microcracks to localised shear failure in a fracture network produced by triaxial deformation of a sandstone core plug the presented method will contribute to our ability of unravelling the physical processes at the base of catastrophic rock failure including the nucleation of earthquakes landslides and volcanic eruptions

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

upb geochronology of the western cape smith belt canada new insights on the age of initial rifting and arc magmatism abstract the cape smith belt of northern quebec is the foreland to hinterland transition of the ungava orogen a component of the paleoproterozoic trans hudson orogen of north america u pb ages for rift and volcanic arc related units from the cape smith belt are presented and used to evaluate models of its tectonic evolution a gabbroic sill intrusive into the rift related sediments near the base of the povungnituk group is 2038 2 4 ma old indicating that rifting of the superior province was initiated prior to that time 80 m y earlier than previously reported a granodiorite intrusive into the volcanic rocks of the povungnituk group is dated at 1991 2 ma indicating that magmatism associated with the rifting event was active at that time 30 m y earlier than formerly thought the age of parent group arc related magmatism ranges from 1874 3 4 ma the age of a diorite intrusion to 1860 2 ma the age of another diorite intrusion and of a rhyolite a granodiorite intrusive in the parent group yields an age of 1845 6 ma magmatism of the parent group is thought to be related to northward dipping subduction of the superior province margin below the watts group a gabbroic intrusion in the 2000 ma old watts group is dated at 1858 2 ma these ages are consistent with a tectonic model in which the rocks of the cape smith belt formed in a single continental rift to oceanic progression followed by subduction which led to an arc continent collision a comparison of u pb ages for similar events in different sectors of the trans hudson orogen in canada reveals that early events are diachronous and range from 2169 ma to 2038 ma the main collisional events are coeval in the ungava and new quebec orogens and in some of the western sectors at 1830 1860 ma younger ages of 1800 1820 ma are obtained for the late collisional stages throughout the trans hudson orogen

the normalised optimised anisotropic wavelet coefficient noawc method an image processing tool for multi scale analysis of rock fabric the 2d anisotropic wavelet transform 2dawt is an image analysis tool which is able to decipher signals where information obtained from different scales are intermixed extended from the optimised anisotropic wavelet coefficient method oawc of ouillon et al 1995 we present a method which discriminates the objects and groups of objects depending on their area shape ratio orientation and position illustrated in a synthetic example we show that this method allows one to distinguish between different sub populations of objects within a single phase and quantify the anisotropies of shape orientation and spatial distribution at different scales objects clusters of objects alignments of objects or clusters applied to a natural rock sample sidobre granite montagne noire france the 2dawt has permitted us to detect and accurately characterise the different levels of mineral organisation and thus to contribute to the understanding of the physical processes such as crystallisation fluid migration deformation etc responsible for such organisations

electromagnetic image of the trans hudson orogen tho94 transect the north american central plains nacp anomaly in enhanced electric conductivity and its relationship with the paleoproterozoic trans hudson orogen tho has been studied under the auspices of lithoprobe for over a decade the nacp anomaly was the first geophysical evidence of the existence of the tho beneath the phanerozoic sediments of the central plains this anomaly detected geomagnetically in the late 1960s has been the subject of a number magnetotelluric studies from the early 1980s the pancanadian and geological survey of canada experiments in the 1980s and the lithoprobe experiments in the 1990s together comprise four east west and one north south re gional scale profiles in saskatchewan perpendicular to the strike of the orogen in this paper data from the northern most line coincident with seismic line s2b are analysed and interpreted and are shown to be key in determining the northern extension of the nacp anomaly dimensionality analysis confirms the rotation of deep crustal structures east ward to hudson bay as earlier proposed on the basis of broad scale geomagnetic studies on this profile as with the profile at the edge of the paleozoic sediments the nacp anomaly is imaged as lying within the la ronge domain in contact with the rottenstone domain and structurally above the guncoat thrust a late compressional feature the location of the anomaly together with the surface geology suggests that the anomaly is caused either by sulphide mineralization concentrated in the hinges of folds by graphite or by a combination of both our interpretation of the data is consistent with that from other profiles and suggests that the nacp anomaly was formed as a consequence of subduction and collisional processes involving northward subduction of the internides of the tho beneath the hearne craton on the southern part of this profile a resistive structure is identified as the sask craton suggesting that proterozoic rocks are above archean rocks in the tho 493

structural evolution of basement gneisses and hadrynian cover bulldog creek area rocky mountains british columbia two gneiss bodies are contained in thrust sheets on the west edge of the rocky mountain main ranges near valemount british columbia the bulldog gneiss comprises aphebian or older paragneiss and amphibolitic gneiss intruded by aphebian orthogneiss sheets the yellowjacket gneiss is granodioritic orthogneiss of unknown age both gneiss bodies are basement highs with thin hadrynian metasediment cover sequences the cover sequences are assigned to the lower miette group and are correlated with horsethief creek group internal shortening of gneiss thrust sheets is expressed by recumbent folding and stacking of thin thrust sheets of gneiss and cover the bulldog gneiss and its cover were carried on the postmetamorphic purcell thrust the yellowjacket gneiss and its cover were carried on the pre to synmetamorphic bear foot thrust northeast and northwest displacement is documented on the moderately southwest dipping bear foot thrust and a dextral oblique slip thrust model is proposed to explain the duality

submagmatic microfractures in granites microstructures in hercynian granite plutons of the pyrenees indicate fracturing of plagioclase crystals in the presence of melt this is represented mainly by quartz and or feldspar that fills fractures electron microprobe analyses demonstrate that in compositional agreement with the rims of the zoned plagioclase the feldspar infillings are more sodic with decreasing melt fraction fracturing resulted from concentration of stress at contacts between grains while the granite was submagmatic i e when the melt was below the critical fraction for magmatic flow material compositionally far from eutectic is petrologically the best candictate to develop submagmatic fractures because during cooling the volume fraction of melt remains low for a large temperature range a strong tendency for microfractures to be oblique to flow foliation may constitute a new criterion for shear sense in magmas

the geology and geochemistry of an early proterozoic volcanic arc association at cartwright lake lynn lake greenstone belt northwestern manitoba the geology of the cartwright lake area consists of a 2 km thick conformable sequence of early proterozoic supracrustal rocks intruded by calc alkaline granitoid plutons the supracrustal successi

on the cluster analysis of grains and crystals in rocks cluster analysis has the potential to quantify the size and characteristics of groups or clusters of grains and crystals within a rock texture we present two techniques 1 the complete linkage hierarchical cluster analysis clhca technique that we use to analyze grain center distributions and 2 the density linkage cluster analysis dlca technique that we use to analyze grain boundary distributions clhca applies a cluster algorithm to the distance matrix calculated from grain center coordinates this produces a hierarchical cluster distribution that is characteristic of the spatial pattern of the texture this cluster distribution is normalized to that of a random distribution of points to identify clustered and ordered patterns in the data the technique successfully identified 3 d cluster sizes from 2 d sections of a modal data set in the application to real rock textures the clhca of a komatiite cumulate identified a glomerocryst population with cluster sizes in the range of 0 3 2 5 mm and also a variation of cluster patterns up through the cumulate pile the clhca of a polymodal texture from a pyroxene scapolite sphene granulite indicated a clustered distribution for the sphene which was restricted in growth pattern by the pyroxene and scapolite in the texture dlca computes a single solution of clusters that conforms to the search criteria input into the algorithm dlca performed poorly when used to identify distributions of large randomly packed clusters of small spheres mainly identifying smaller cluster patterns within each large cluster application of dlca to the komatiite cumulate example indicated cluster lengths of 0 72 0 80 mm similar to the clhca results and an average aspect ratio of 1 52

the depositional evolution of the svecofennian supracrustal sequence in finland and sweden abstract on the basis of six new zircon ages from metavolcanic rocks together with other isotopic geophysical and geological data the chronological and tectono stratigraphic evolution of the early proterozoic svecofennian supracrustal rocks in finland and sweden are discussed these data suggest that a nw se displacement from the bothnian bay to lake ladoga and a sinking of the southwestern block was initiated 1950 2000 ma ago accumulation of pelitic sediments and greywackes on the subsiding archaean basement continued until about 1860 ma in south central and northern sweden shallow submarine and subaerial volcanics were extruded 1880 1890 ma ago the thick sedimentary piles and volcanic rocks were subsequently intruded by plutonic rocks forming large batholiths 1860 1890 ma ago

tectonothermics of the north american great plains basement abstract heat flow and heat generation data from the superior churchill and wyoming provinces of western north america contribute to our understanding of the nature of the crust beneath the sedimentary cover of the great plains a major structural boundary defined by gravity gradient data thomas et al 1987 splits the terrains between the cratons into two distinct geothermal provinces the wyoming and churchill provinces are characterised by higher heat flow than the superior province and the eastern part of the intervening hudsonian terrain the proterozoic mobile belt pmb heat flow in the pmb is typical of that of the superior craton this suggests on the basis of a model by ballard and pollack 1987 that the pmb is underlain by archaean cratonic lithosphere the similarity in heat flow between the pmb and the superior craton suggests that the crust of the pmb is akin to that of the superior craton rather than to that of the more radiogenic wyoming and churchill cratons geochronologic gravity aeromagnetic and geothermal data suggest that the structural boundary defining the western boundary of the pmb is also the eastern boundary of the wyoming craton geothermal data alone suggest that the wyoming craton might extend as far north as the cratonic segment of the churchill province or that the wyoming and churchill provinces may gradually merge together

metamorphism of high grade pelites in the brabant lake area eastern la ronge domain northern saskatchewan the brabant lake area mostly comprises early proterozoic clastic metasediments of the maclean lake belt eastern la ronge domain reindeer zone the belt underwent upper amphibolite facies metamorp

geochronology at the namew lake ni cu orebody flin flon area manitoba canada thermal history of a metamorphic terrane intermediate composition orthogneisses of the southward extension of the flin flon greenstone belt surround the ultramafic host rock of the namew lake ni cu deposit in northern manitoba the gneiss

u pb geochronology in the trans hudson orogen northern saskatchewan canada we have obtained u pb ages on zircons from volcanic and plutonic units in several lithotectonic domains of the southern trans hudson orogen in northern saskatchewan these data constrain the timing of early proterozoic orogenic events in the region and enhance our understanding of both the relationships among local domains and the relationship of the trans hudson orogen to other early proterozoic orogens in north america with one exception all units studied so far yield zircon ages of 1890 1835 ma most of which are systematically earlier than previously reported rb sr isochron ages on the same or similar units suggesting open system behavior in the rb sr systems five metarhyolites from volcanic sequences in the la ronge domain glennie domain and hanson lake block give ages ranging from 1888 to 1876 ma most of the plutons we dated ranging from gneissic syntectonic tonalites and granodiorites to less deformed late intrusions such as the wathaman batholith and other smaller bodies yield ages of 18

wavelet transform a future of rock fabric analysis abstract although twenty years ago fabric was defined as the complete spatial and geometrical configuration of all those components that make up a deformed rock fabric was mainly synonymous with lattice preferred orientation very little attention has been paid to the multi scale geometrical and spatial relationships of the rock components fabric quantification in terms of size shape orientation and location at all scales is now performed in two dimensions using anisotropic wavelets as a first example the wavelets are applied to the famous colour plate of sander and the results compared to his axial distribution analysis applied to the k feldspars of a rock section from the sidobre granite pluton montagne noire france the wavelet analysis shows i alignment of grains resulting from mechanical interactions between grains and shows that shearing occurred within the crystalline frame ii preferred grain orientation the classical grain shape fabric parallel to the overall mineral lineation and iii small tensional domains elongate perpendicular to the lineation infilled by the residual melt just before total crystallisation attesting to the stretching nature of the mineral lineation the future of rock fabric analysis will come from new steps in understanding the processes acting during fabric development along with a further development of wavelet analysis using high resolution three dimensional fabric data

rb sr study of metavolcanic rocks from the la ronge and flin flon domains northern saskatchewan two whole rock suites of metavolcanic rocks from separate volcanic belts of the churchill province in northern saskatchewan have been dated by rb sr samples from the amisk group of the flin flon snow lake domain provide an isochron date of 1784 44 ma suites from the waddy lake and devil lake areas of the la ronge lynn lake domain yield isochron dates of 1814 26 and 1854 100 ma respectively all are regarded as minima for but close approximations to emplacement ages the maximum crustal age of any suite cannot greatly exceed 1850 ma previous rb sr and u pb isotopic dates together with these new determinations confirm the contemporaneous existence of two volcanic arcs active during the late aphebian 1875 1784 ma in the churchill province low initial 87 sr 86 sr ratios 0 7017 0 7022 are consistent with a petrochemically inferred subduction related origin for the volcanic rocks with no closed system reworking of archean crust and a linear evolution of 87 sr 86 sr ratio in the magmatic arc mantle source region from 4 55 ga to the present

structural analysis of hypocentral distribution of an earthquake sequence using anisotropic wavelets method and application 1 spatial organization of earthquake sequences is investigated to localize active rupture planes and to reconstruct the geometry of the inferred rupture zone we have developed a new approach the normalized optimized anisotropic wavelet coefficient noawc method to extract from a set of hypocenters the active ruptures planes our approach permits the detection of organized structures within a plane regardless of its size location shape anisotropy and orientation it includes the determination of a system of three perpendicular sections minimizing the effects of projections of the hypocenters and intrinsically accounts for uncertainty in the location of the seismic events the accuracy and the effectiveness of the noawc procedure are illustrated on both synthetic and real data an application to the m 5 1 arudy french pyrenees aftershock sequence shows how a combination of the possible mathematically reconstructed geometries can be combined with the available fault plane solutions and geomorphological markers to determine the active rupture planes and to propose and validate a local tectonic model this new multitool approach lends itself to quantitative and computer assisted analyses of large data sets

geochemistry of the metavolcanic rocks in the vicinity of the maclellan au ag deposit and an evaluation of the tectonic setting of the lynn lake greenstone belt canada evidence for a paleoproterozoic aged rifted continental margin abstract the paleoproterozoic ca 1900 ma lynn lake greenstone belt of northern manitoba canada has been previously characterized as comprising a series of tectonically juxtaposed intra oceanic derived metavolcanic rocks the results of more recent local and regional studies however support a significant contribution of continental crust during formation of the metasedimentary metavolcanic and intrusive igneous rocks that comprise the majority of the lynn lake greenstone belt the tectonic model previously proposed for the lynn lake greenstone belt however did not consider the geodynamics of the lynn lake greenstone belt in the context of all available data in this study we report the results of outcrop mapping and petrographic analysis as well as major minor and trace element geochemical analyses for 54 samples from the northern terrane and integrate and compare the results with data from previously published studies these data are used to recharacterize the metavolcanic rocks and to develop a new geodynamic model for the formation of the lynn lake greenstone belt ultramafic to intermediate rocks in the vicinity of the maclellan au ag deposit are characterized primarily by e morb like trace element characteristics and th nb la systematics which are interpreted to be the result of a primary plume derived melt interacting with continental lithosphere at a thinned i e rifted continental margin similarly the majority of the mafic to intermediate rocks that comprise the lynn lake greenstone belt are characterized by flat to e morb like trace element patterns and th nb la systematics which are consistent with mantle plume derived contaminated oceanic continental rift or rifted margin setting rocks this study suggests that the metavolcanic rocks of the lynn lake greenstone belt were derived via rifting between the superior and hearne cratons which resulted in the formation and growth of the manikewan ocean alternatively the metavolcanic rocks could have been derived from an upwelling plume generated from a back arc style subduction zone that formed between the rae and hearne cratons during the closure of the snowbird ocean which resulted in rifting of the passive hearne margin