late archean quetico accretionary complex superior province canada the 1200 km long quetico subprovince consists of monotonous metagraywacke with derived migmatite and granite in thrust and or transcurrent fault contact with the adjacent wabigoon and wawa metavolcanic subprovinces imbrication of sedimentary wedges derived from volcanic arcs to the north and south produced a 10 100 km wide stratigraphically north facing pile thermal relaxation in the 20 m y following accretion of the southern arc resulted in melting of the accretionary pile to produce peraluminous granite and associated low pressure metamorphism

upper mantle processes beneath the 2 7 ga abitibi belt canada a trace element perspective abstract mantle processes associated with volcanism in the abitibi belt remain poorly understood despite numerous detailed studies of its volcano sedimentary successions this paper employs log plots of nb y and zr y to distinguish the sources of well defined abitibi volcanic suites and to clarify processes in the upper mantle during greenstone belt development mafic rocks of the southern volcanic zone in the abitibi belt define two main trends on log plots of nb y versus zr y trends for the kidd munro assemblage and malartic block correspond to mixtures of strongly deleted plume asthenosphere and adakitic melts the shared trace element systematics of these volcanic successions confirm they are parts of a single authochthonous supracrustal assemblage that extended across the southern abitibi belt the younger kamiskotia assemblage and blake river group correspond to crustal extension episodes within an abitibi island arc trace element plots establish that they were derived from mantle plume related asthenosphere and not the late archean morb source upper mantle associated with island arc assemblages elsewhere in the southern superior province the data suggests widespread lateral flow of mantle plume asthenosphere occurred in the vicinity of the abitibi arc mantle mixing with adakitic melts continued between 2716 and 2698 ma the data are not consistent with wet komatiite models that generate ultramafic volcanic rocks from typical upper mantle following hydration of a mantle wedge chemical mixing trends for mafic magma sources indicate melt hybridization of the abitibi mantle wedge the trends require a slab melt origin for adakitic magmas rather than internal differentiation of underplated mafic crust comparisons with other 2 7 ga greenstone belts suggest that mantle plume interaction with archean subduction zones as proposed for the abitibi belt can be distinguished in the nb zr y systematics of associated mafic volcanic rocks

rapid flooding of the southern vietnam shelf during the early to mid holocene a new sea level record derived from coastal deposits of the south vietnam shelf covers the deglacial sea level history between 13 0 and 9 0 ka bp this record reveals a relatively constant rate of sea level rise and matches well with model results based on the rses anu global ice sheet model however the sea level observations reveal a significant discrepancy with model results based on the ice 5g global ice sheet model which further questions the existence of meltwater pulse 1b the incised valley deposits of the south vietnam shelf also complete the deglacial coastal evolution of southern vietnam the regional sea level records of the south vietnam shelf the mekong delta and the cambodian lowlands reveal an offset of about 18 m between 9 0 and 8 2 ka bp the shoreline retreat of more than 200 km related to this offset was mainly caused by the differential hydro isostatic adjustment between the south vietnam shelf and the cambodian lowlands however the gia model results cannot fully explain this fast relative sea level rise due to the topographic changes and possibly alternative melt water sources not accounted for in the current models copyright c 2014 john wiley sons ltd

contribution of mantle plumes crustal thickening and greenstone blanketing to the 2 75 2 65ga global crisis abstract assuming that the period 2 75 2 65 ga corresponds to a single but global geodynamic event we investigate through numerical experiments the mechanisms that could have led to the profound continental reworking that occurred at that time although the extent of the crisis at the earth s surface pledges in favour of the involvement of mantle plumes our numerical experiments suggest that the thermal impact of mantle plumes is unlikely to explain both the amplitude and timing of the thermal anomaly as observed in the superior province canada and the yilgarn craton australia similarly moderate crustal thickening can not lead to significant reworking of the continental crust within the observed time constraint crustal thickening with a factor 1 5 is also unlikely because it is not consistent with the moderate metamorphic grade observed at the surface of many archaean cratons burial of a radiogenic crust under a 10 km thick greenstone cover also falls short of explaining not so much the amplitude and the extent but the timing of the thermal anomaly in contrast the combination of the thermal anomaly related to the greenstone blanketing effect with the heat transfer from a plume head spreading at the top of the thermal boundary layer can adequately explain the amplitude the timing and the extent of the 2 75 2 65 ga crisis our favoured model involves a global rearrangement of convection cells in the deep mantle and formation of multiple mantle plumes the greenstones emplaced at the surface and the plumes that spread in the thermal boundary layer contributed to heat the crust from both above and below this produced massive crustal partial melting that reached its climax ca 40 myr after the emplacement of the plumes and associated greenstone cover rocks this led to gravitational instabilities in the crust as dense greenstone cover rocks began to sink into the thermally softened crust and granite domes rose in response the extraction of heat producing elements toward the upper part of the crust has contributed to the cooling and stabilisation of the cratons this succession of events which is not incompatible with plate tectonic processes may have profoundly changed the nature of the crust exposed at the surface and could explain the contrasting geochemical signatures of archaean and post archaean shales

using hyperspectral imaging to vector towards mineralization at the canadian malartic gold deposit quebec canada abstract canadian malartic is a large tonnage low grade archean gold deposit 16 3 moz 1 08 g t au located in the abitibi region of quebec canada a large part of the mineralization is hosted in the pontiac group metasedimentary rocks which consist of mudstones to greywackes at upper greenschist to amphibolite facies in exploration and production environments these lithologies are challenging to characterize by conventional core logging methods while in a research setting thin section sized samples 2 cm 4 cm do not capture the full extent of mineralogical variability which can extend from centimeters to meters away from mineralized zones here high resolution hyperspectral imagery 0 2 1 0 mm pixel in both shortwave infrared swir 1000 2500 nm and longwave infrared lwir 8000 12000 nm is acquired for over two thousand meters of drill core and is used to visualize changes in mineralogy and mineral chemistry related to metamorphism and hydrothermal alteration unaltered metasedimentary rocks contain metamorphic white mica with alvi contents varying between 1 90 and 1 75 apfu 2195 to 2203 nm depending on metamorphic grade hydrothermal alteration is characterized by white mica which becomes progressively more phengitic with increasing alteration intensity with alvi contents ranging from 1 70 to 1 50 apfu 2204 to 2212 nm phengitic white mica extends from meters to tens of meters away from major mineralized zones and can be used as a vector towards mineralization in an exploration setting white mica composition is correlated to au content and can be used to discriminate between unmineralized 0 3 g t au 2205 2208 nm and highly mineralized 1 0 g t au 2208 nm samples which is a simple metric that can directly be applied to sort ore in a production environment the mg molar mg mg fe of biotite on the other hand is unaffected by metamorphic grade and consistently is mg 55 60 2251 2250 nm in unaltered samples in mineralized samples biotite is mg rich mg 65

u pb ages and tectonic significance of late archean alkalic magmatism and nonmarine sedimentation timiskaming group southern abitibi belt ontario the paper presents u pb ages for zircons of the calc alkalic to alkalic igneous suite and associated alluvial fluvial sedimentary rocks of the timiskaming group in the late archean abitibi greensto

geology and geochemistry of granitoid rocks in the archean northern complex michigan u s a the northern complex located in the upper peninsula of michigan is an archean greenstone granite terrane that lies at the southern margin of the superior province the origin of the plutonic suites in the northern complex can be interpreted within a plate tectonic model proposed for the superior province and related to northward directed subduction and subsequent collision along the great lakes tectonic zone the following plutonic suites are recognized based on intrusive relationships as well as textural and compositional differences i gneissic tonalite suite ii foliated tonalite suite iii trondhjemite granite suite iv hornblendite syenite suite and v late granite dike suite rocks in the gneissic and foliated tonalite suites have lithologic and geochemical characteristics typical of archean trondhjemite tonalite granodiorite assemblages exposed elsewhere in the superior province they were emplaced during a primary deformation event and are interpreted to represent partial melts that f

intracrustal extension of an archean orogen revealed using single grain u pb zircon geochronology the metaplutonic wawa gneiss domain in the southern superior province is part of an uplifted block that was exhumed during the proterozoic exposing the lower crustal 30 km levels of the late archean 2720 to 2670 ma abitibi wawa orogen previous structural and geophysical studies of the midcrustal wawa gneiss domain reveal subhorizontal shear zones that formed during orogen parallel extension and correspond to gently dipping seismic reflectors present at depth elsewhere in the orogen in order to bracket the age of this extensional deformation the ages of metre scale igneous bodies that crystallized before and after extension have been determined in four outcrops using single grain u pb zircon dating techniques the results constrain the time of extension to the interval between 2660 and 2645 ma and show that deformation was coeval with pegmatite emplacement partial melting of tonalite gneisses as old as 2925 35 ma and regional circa 2660 ma granulite facies metamorphism of adjacent more deeply eroded crust this extension and associated high grade metamorphism in the wawa gneiss domain occurred 10 to 25 m y after the cessation of regional compression major transcurrent fault movement and sediment deposition in the upper structural levels of the orogen the middle and lower crust was therefore mechanically decoupled from the upper crust during this period of orogen parallel extension this intracrustal style of deformation is interpreted to be the consequence of gravitational forces working on a thermally softened middle crust the detachment of lithosphere from the orogen base is the favored mechanism for generating these forces and for introducing the heat that caused synextension metamorphism cyclic construction and delamination of orogen lithosphere could account for even younger metamorphic strain events evident in nearby exposures of lower crust

geochemical characteristics of granitoid rocks from within the archean michipicoten greenstone belt wawa subprovince superior province canada implications for source regions and tectonic evolution three distinct tonalite trondhjemite granodiorite ttg magma series occur syngenetically with bimodal mafic felsic cyclical volcanics in the middle to late archean michipicoten greenstone belt mgb canada between 2 72 and 2 60 ga two additional series are recognised as pre tectonic late tectonic and post tectonic syenite quartz monzonite granitoid stocks smg series and an alkali feldspar syenite alkali feldspar quartz syenite stock ss series the synvolcanic ttg series such as the hawk lake granitic complex and the jubilee lake stock are characterised by moderate to low k2o 2 5 wt rb 60 ppm and sr concentrations 400 ppm moderate tio2 levels 0 1 1 0 wt lasm 2 12 and gdyb 0 8 2 9 moderate to large negative eu anomalies and small negative ta nb troughs on ocean ridge granite org normalised plots the ttg series are compositionally similar to synvolcanic mgb felsic volcanics of cycles 1 to 3 the high lasm lata and low zrth are features of sialic crust a contribution of ancient sialic crust in the genesis of the felsic volcanics and ttg series granitoids of all three felsic volcanic cycles and synvolcanic ttg stocks is required in the mgb the parental magma like that of the ttg series of the abitibi greenstone belt agb may originate in oceanic mantle the smg series have elevated k2o 2 0 6 3 wt rb 40 280 ppm ba 10 2800 ppm and sr 250 1350 ppm steep ree patterns reflected in elevated lasm 3 12 and gdyb 1 8 5 0 without eu anomalies a moderate to large negative ta nb trough on ocean ridge granite normalised plots and low tio2 0 5 wt and cao na2o k2o the smg series is compositionally different to the mgb felsic volcanic rocks and to the ttg series granitoids the source is tentatively placed in the mantle wedge overlying a southward dipping subducted plate of oceanic crust and the elevated lile signature is attributed to metasomatism of this source by fluids derived from the subducted slab of oceanic crust the smg series granitoids like those of the abitibi are different when compared to the sanukitoids in that they are compositionally more evolved however they may be related to these rocks by low pressure fractionation and may be derivatives of sanukitoid like magmas the alkali feldspar syenite alkali feldspar quartz syenite represented by the herman lake stock of the ss series has a primitive composition 60 wt sio2 with low ree abundances and relatively flat lree and hree but steep mree profiles these rocks are strongly lile enriched but do not develop pronounced ta nb troughs on org normalised profiles these rocks may be derived by low degrees of partial melting of a depleted mantle wedge previously metasomatised by alkali rich fluids released from a subducting slab the elevated tiy and zry of these rocks appear to suggest that small amounts of partial melting were responsible for the genesis of these rocks the granitoid rocks record an overall progression from contributions made from the continental crust in a continental margin environment to magmas dominated by contributions from subducted crust or the overlying variably metasomatised mantle wedge during the terminal phase of arc continent collision

u pb ages for late magmatism and regional deformation in the shebandowan belt superior province canada five precise u pb zircon and titanite ages from different lithologic units of the shebandowan greenstone belt in the western wawa subprovince of the superior province put tight constraints on the time of late archean magmatism and of two major deformation events a porphyry sill from the older supracrustal sequence has an age of 2733 3 ma another porphyritic rock a trondhjemite occurring as a clast in a conglomerate of the unconformably overlying timiskaming type supracrustal sequence formed 2704 2 ma ago and defines a maximum age for the deposition of the timiskaming type sequence an alkalic volcanic rock from this sequence has been directly dated at in accord with the above constraint and with another probable maximum age of deposition given by the date of 2696 2 ma for the shebandowan lake pluton a first deformation event d1 was related to a predominantly vertical tectonic regime and occurred during or before intrusion of the shebandowan lake pluton at 2696 2 ma the second deformatio

central superior province geology evidence for an allochthonous ensimatic southern abitibi greenstone belt published u pb geochronological geological and petrochemical data suggest that there are late archean ensialic greenstone belts gb michipicoten gb and possibly the northern abitibi gb ensima

volcanism accompanying back arc basin development in the southwest pacific abstract the age and composition of magmatism in fiji and to a lesser extent vanuatu and tonga are evaluated in the light of the fragmentation which has sundered the island arc system they once collectively constituted any of six magmatic phenomena during the past 10 m y may be consequences of adjacent plate reconfigurations trondhjemitic plutonism about 10 m y change from tholeiitic to more calc alkaline volcanism between 10 and 6 m y eruption near the rifted arc margin of voluminous crustally derived high si low k rhyolites 7 m y ago shoshonite dominated basaltic volcanism 5 5 to 3 0 m y change to ocean island like basaltic volcanism at 3 0 0 2 m y and geochemically peculiar as well as tectonically anomalous acid andesites 0 7 3 0 m y ago in kandavu southwestern fiji crustal derivation of the low k rhyolites may reflect maximal heating during initial rifting shoshonites may accompany extreme regional extension above a still arc like source eruption of ocean island like basalts begins once subducted lithosphere no longer contributes to erupted melts or separates fiji from ocean island sources coeval eruption of hybrid andesites may accompany oblique subduction of south fiji basin crust beneath kandavu along the northeast hunter fracture zone

diverse metal sources of archaean gold deposits evidence from in situ lead isotope analysis of individual grains of galena and altaite in the ross and kirkland lake deposits abitibi greenstone belt canada lead isotope compositions for individual grains of galena and altaite pbte were determined in situ using a secondary ion mass spectrometer sims galena was collected from the ross deposit and altaite from the kirkland lake kl deposits in the southern abitibi greenstone belt superior province of canada the samples from kl are more radiogenic than those from the ross deposit isotopic compositions vary significantly between different grains in each deposit and form broad linear arrays in 207pb 204pb 206pb 204pb and 208pb 204pb 206pb 204pb diagrams the linear arrays of pb isotope data are attributed to mixing of pb from different sources at least two sources are required for individual deposits one with low u pb and th pb ratios and the other with high ratios lead minerals occurring with au are less radiogenic than those that are not obviously associated with au suggesting that au was supplied from low u pb sources such as sulphides or older ultramafic mafic rocks while most data are consistent with the derivation from local rocks highly radiogenic pb with relatively low 207pb 206pb ratios recorded at kl require post archaean mineralization or derivation of the pb from an unusual crustal source with low the latter interpretation is favored because of the lack of textural evidence and because it is difficult to dissolve and precipitate altaite at low temperatures the presence of a pb reservoir with low is also inferred from the data of archaean banded iron formations and volcanogenic massive sulphide deposits different isotopic patterns of the two deposits suggest different sources of metals in the two deposits while this conclusion does not reject the derivation of fluids from the lower crust or mantle the data are not in accord with conceptual models invoking a common source reservoir for metals the study suggests that fluids which may have a common origin leached metals and other constituents from the upper crustal rocks during their ascent the proposed model different origins for different constituents explains much of the conflicting evidence presented by archaean au deposits including provinciality of mineralogy and relatively uniform fluid inclusion and c isotope data from many au deposits

geology of the orogenic cheminis gold deposit along the larder lake cadillac deformation zone ontario the larder lake cadillac deformation zone llcdz is one of two major auriferous deformation zones in the southern abitibi subprovince of the archean superior province it hosts the cheminis and the giant kerr addison chesterville deposits within a strongly deformed band of fe rich tholeiitic basalt and komatiite of the larder lake group ca 2705 ma the latter is bounded on both sides by younger less deformed timiskaming turbidites 2674 2670 ma the earliest deformation features are f1 folds affecting the timiskaming rocks which formed either during d1 extensional faulting or during early d2 north south shortening related to the opening and closure respectively of the timiskaming basin continued shortening during d2 imbricated the older volcanic rocks and turbidites and produced regional f2 folds with an axial planar s2 cleavage d2 deformation was partitioned into the weaker band of volcanic rocks producing the strong s2 foliation l2 stretching lineation and south side up shear sense indicators which characterize the llcdz gold is present in quartz carbonate veins in deformed fuchsitic komatiites carbonate ore and turbiditic sandstone sandstone hosted ore and in association with disseminated pyrite in altered fe rich tholeiitic basalts flow ore all host rocks underwent strong mass gains in co2 s k2o ba as and w during sericitization carbonatization and sulphidation of the host rocks suggesting that they interacted with the same hydrothermal fluids textural relationships between alteration minerals and s2 cleavage indicate that mineralization is syn cleavage thus gold was deposited as hydrothermal fluids migrated upward along the llcdz during contractional d2 south side up shearing the gold zones were subsequently modified during d3 reactivation of the llcdz as a dextral transcurrent fault zone

neoarchean subduction a case study of arc volcanic rocks in qinglong zhuzhangzi area of the eastern hebei province north china craton abstract we report on volcanic rocks of the qinglong zhuzhangzi area in northeastern eastern hebei province north china craton the supracrustal rock associations in the study area consist of amphibole biotite plagioclase gneiss mica plagioclase gneiss schist biotite k feldspar gneiss pyroxene plagioclase amphibolite and amphibolite twenty five new mafic intermediate to felsic samples can be geochemically classified into four groups group 1 is similar to fore arc low ti tholeiite and is characterized by low sio 2 49 7 wt and tio 2 0 43 wt slightly depleted lree and mree pattern with la yb n ratio of 0 74 gd yb n ratio of 0 82 it most likely derived from depleted mantle in a subduction initiation environment group 2 is akin to primitive arc tholeiites with low sio 2 49 7 51 8 wt slight enrichments of lree la sm n 1 06 1 53 and negative nb anomalies nb la pm 0 50 0 76 group 3 resembles evolved arc tholeiites and displays pronounced enrichments of lree la yb n of 2 38 11 3 la sm n of 1 70 2 86 and negative nb ta anomalies nb la pm 0 14 0 34 except sample 11jd28 4 with that ratio of 1 00 group 2 and 3 formed by partial melting of sub arc depleted mantle wedge modified by differing quantities of slab flux addition group 4 comprises k rich andesite dacites which are distinguished by the highest sio 2 54 0 71 8 wt k contents up to 5 03 wt strong enrichments of lree la yb n ratios of 4 83 19 and negative nb ta anomalies analogous to shoshonitic rocks marking late stage of subduction la icpms zircon u pb and lu hf analyses of evolved arc basalts and k rich andesite dacites display crystallization ages of 2511 2604 ma and single stage hf model ages of 2534 2927 ma most focus on 2650 2800 ma in contrast to 2510 2560 ma arc associations 2604 ma shoshonitic dacites most plausibly represent an older orogenic event collectively supracrustal rocks in the qinglong zhuzhangzi area constitute a series of volcanic arc associations that correspond to an entire subduction cycle ranging from orogen to primitive arc evolved arc and back to an orogenic setting which further demonstrate that by the late archean plate tectonic and subduction processes already closely resembled modern counterparts

geology and age of the late archean keivy alkaline province northeastern baltic shield abstract the keivy alkaline province kola peninsula consists of six peralkaline granite bodies alkaline syenogranite dikes and two nepheline syenite intrusions emplaced between the tonalite trondhjemite granodiorite basement and the supracrustal keivy terrane u pb zircon ages for the keivy alkaline province range from 2613 to 2682 ma and for the spatially associated gabbro anorthosite complexes from 2659 to 2668 ma the keivy alkaline granitoids are geochemically different from other late archean alkaline rocks inferred to have been emplaced in subduction zone settings the keivy alkaline province may represent the earliest example of magmatism associated with continental rifting and the involvement of a mantle plume with oceanic island basalt like characteristics

the cosmos greenstone succession agnew wiluna greenstone belt yilgarn craton western australia geochemistry of an enriched neoarchaean volcanic arc succession abstract the geodynamic setting of the neoarchaean eastern goldfields superterrane egs of the yilgarn craton is the subject of debate some authors propose plume models while others advocate variants on a subduction accretion model for the origin of mineralised greenstone belt sequences felsic volcanism in the kalgoorlie terrane the westernmost terrane of the egs is considered to have a tonalite trondhjemite granodiorite dacite ttg d geochemical affinity the cosmos greenstone succession which lies in the agnew wiluna greenstone belt awb of the kalgoorlie terrane contains several komatiite hosted nickel sulphide deposits the volcanic footwall to which consists of an intercalated succession of fragmental and coherent rocks ranging in composition from basaltic andesite to rhyolite light rare earth elements lrees and large ion lithophile elements liles are strongly enriched relative to high field strength elements hfses across all volcanic units and the rocks display strong positive pb and negative nb anomalies these geochemical characteristics resemble closely those of modern high k calc alkaline to shoshonite continental arc successions contrasting ree lile and hfse concentrations coupled with assimilation fractional crystallisation afc modelling shows that the intercalated dacitic and andesitic volcanic rocks within the footwall succession are not co genetic xenocrystic zircons within the felsic volcanic lithologies indicate that some assimilation of older continental crust contributed to the generation of the footwall volcanic sequence the geochemical characteristics of the cosmos volcanic succession indicate that parental melts were derived via partial melting of enriched peridotite that had been contaminated by subducted crustal material within the mantle wedge of a subduction zone in contrast two younger felsic porphyry intrusions which cross cut the volcanic succession have a distinct ttg d affinity therefore these intrusions are considered to be generated via partial melting of a subducting slab and are related to local high ca granitoid intrusions the cosmos volcanic succession represents the first extrusive high k calc alkaline to shoshonitic volcanic arc sequence described in the kalgoorlie terrane and coupled with age dating of the stratigraphy is indicative of formation in a long lived volcanic arc setting active from 2736 ma to later than 2724 ma the composition and geochemical affinity of the volcanic footwall succession to the cosmos komatiite hosted nickel sulphide deposits contrasts with the majority of felsic volcanic rocks within the awb and also the wider kalgoorlie terrane suggesting that the overall architecture of this region is more complex than is currently thought our conclusions not only have consequences for recent models of the tectonic evolution of the egs but also contribute to the debate on the operation of plate tectonics during the late archaean in general the arc affinity of the cosmos volcanic succession containing abundant high k calc alkaline andesite lavas provides further support for the operation of plate tectonics in the neoarchaean

geological evolution of the northwestern superior province clues from geology kinematics and geochronology in the gods lake narrows area oxford stull terrane manitoba the study of lithology geochronology and structure in the oxford stull terrane in particular in the gods lake narrows area has led to the recognition of three distinct supracrustal sequences 2 8 2 9 ga volcanic rocks a 2720 ma fault bounded package of volcanics and sandstones and 2705 ma conglomerate and alkaline volcanic rocks of the oxford lake group detrital zircon as old as 3647 ma is present in the oxford lake group an early generation of folding and shearing occurred prior to deposition of the oxford lake group and was probably synchronous with emplace ment of 2721 ma tonalite dykes the second generation of deformation caused south over north thrusting of volcanic rocks over the oxford lake group the youngest fabric resulted from east southeast trending dextral south over north shearing the youngest rock dated in the area is the 2668 1 ma magill lake pluton which records crustal melting following deformation the pattern of sedimentation and deformation in this area is similar to

ancient subcontinental mantle a source for k rich orogenic volcanics active island arc volcanoes west of the arc continent collision between the sunda arc and northwest australia are erupting mafic volcanics that range from calc alkaline basalts through shoshonitic trachybasalts to leucitites these mafic arc volcanics display a threefold enrichment in k rb sr ba la and nb contents along the arc from bali to flores increasing toward the collision zone the enrichment is very well correlated with increasing 87sr 86sr and decreasing 143nd 144nd values the geochemical and isotopic data imply that the arc volcanics are being generated from two source materials one yielding material poor in k group elements with relatively low 87sr 86sr 0 707 values and low 143nd 144nd values the k rich material appearing in the arc volcanoes is being derived from ancient subcontinental mantle involved in the collision zone eastern sunda k rich mafic volcanism first appeared after the collision began before the collision ancient northwest australian mantle erupted k rich diamond bearing ultramafics with high 87sr 86sr values and low 143nd 144nd values these form part of a typical ultrapotassic continental volcanic association yet they have ba la and ba nb values characteristic of arc volcanism showing their parent mantle to be geochemically and isotopically capable of supplying the k rich material appearing in the eastern sunda arc volcanoes terranes possibly underlain by similar gondwanaland mantles surround the collision zone which is the site of large scale mixing between oceanic and continental lithospheres other petrogenetic theories seem incapable of accounting for the regional variations in eastern sunda arc geochemistry striking geochemical and isotopic resemblances between eastern sunda leucitites and k rich orogenic volcanics elsewhere in the world such as those of the roman region imply similar origins involving k rich subcontinental mantle material where a k h correlation occurs it might only be a signal that subduction of a lithospheric slab beneath a continental margin is inducing melting in old mantle deep in the continental lithosphere

geochemical and metallogenic relations in volcanic rocks of the southern slave province implications for late neoarchean tectonics late neoarchean volcanic belts in the southern slave province include 1 in the east the cameron river beaulieu river belts which are characterized by stratigraphically thin flow rich classic calc alkaline arc type sequences with accompanying syngenetic volcanogenic massive sulphide deposits and 2 in the west the yellowknife belt which is characterized by stratigraphically thick structurally complex pyroclastic rich adakitic back arc basin type sequences with accompanying epigenetic lode gold deposits the volcanic belt association bears persuasive chemical evidence of subduction initiated magma generation however the greenstone belts together with coeval matching patterned belts in superior province of the southern canadian shield bear equally persuasive evidence of prevailing autochthonous parautochthonous relations with respect to component stratigraphic parts and to older gneissic basement the eastern and western volcanic belts in question are petrogenetically ascribed to a westerly inclined present geography subduction zone s that produced shallower east to deeper west slab initiated mantle wedge generated parent magmas this early stage microplate tectonic process involved modest mantle subduction depths small tectonic plates and small sialic cratons in the larger context of earth s progressively cooling hence subduction deepening mantle this late neoarchean greenstone belt development 2 73 2 66 ga merged with the massive end archean tonalite trondhjemite granodiorite granite ttgg bloom 2 65 2 55 ga resulting in greatly enhanced craton stability successive subduction deepening plate craton enlarging stages with appropriate metallotectonic response across succeeding proterozoic time and beyond led to modern mode plate tectonics

u pb geochronology of the central uchi subprovince superior province u pb zircon and titanite ages for rocks of the central uchi subprovince in northwestern ontario indicate a late archean magmatic and tectonic development spanning over 200 ma an early period at 2900 2800 ma formed volcano plutonic complexes presumably linked to 3 1 2 8 ga terrains of the northwestern superior province a later period of southward growth by magmatic and tectonic accretion occurred at 2750 2710 ma and was concluded by large scale compression and plutonism at 2700 ma the oldest 2890 2860 and 2840 2820 ma components occur in the pickle lake and meen dempster greenstone belts and as gneisses in the seach achapi and the lake st joseph batholiths in northern and central sectors of the region together with distinct 2750 2740 ma volcano plutonic complexes they form a collage assembled by multiple episodes of tectonic juxtaposition and magmatic accretion plutons of 2730 2710 ma age are intrusive into these older northern domains whereas their volcanic counterparts compose the lake st joseph and miminiska fort hope greenstone belts to the south late tectonic to posttectonic granitoid rocks intruded a region extending from the northern berens river subprovince to the southern english river subprovince at 2700 ma these plutons were cut by regional scale faults formed by residual north northwest directed shortening the timing of this movement seems to be recorded by titanite ages of 2690 2670 ma reactivation of the same faults may account for proterozoic pb loss observed in some of the zircon populations the age patterns are consistent with crustal growth along a continental margin in a north dipping subduction environment

u pb zircon geochronology in the southwestern abitibi greenstone belt superior province the abitibi belt is the largest continuous greenstone belt in the superior province of the canadian shield it comprises several composite komatiitic tholeiitic calc alkalic and sedimentary sequences that are folded transected by major faults and intruded by various generations of plutonic rocks precise u pb geochronology has been carried out in the belt for the past decade to solve chronostratigraphic and metallogenetic problems this paper presents new zircon ages and reassesses previously published ones now refined by the addition of abraded and concordant zircon analyses volcanic and subvolcanic units of the timmins area yield the following ages 2727 1 5 ma for a tuff of the upper deloro formation 2703 1 5 ma for a tuff of the upper tisdale formation and 2698 4 ma for the krist fragmental assigned to the top of the tisdale formation the age of a dunite intrusive into the upper deloro formation is revised at 2707 3 ma whereas the aquarius diorite east of timmins yields a poorly define

u pb garnet and titanite age for the bristol township lamprophyre suite western abitibi subprovince canada a u pb age of 2687 3 ma has been determined for a garnetite dike using melanite garnet and titanite mineral separates this is the first primary igneous u pb age reported using garnet the garne

evolution of the south central segment of the archean abitibi belt quebec part iii plutonic and metamorphic evolution and geotectonic model textural criteria permit distinction between the pre kenoran and kenoran phases of plutonism and metamorphism the pre kenoran plutons and pre kenoran metamorphic phases are directly related to the volcanic evolution synvolcanic tonalite trondhjemite plutons and swarms of mafic and felsic dykes core central volcanic complexes the volcanic rocks underwent three types of pre kenoran metamorphism namely a pervasive alteration a thermal contact metamorphism that affected narrow aureoles around synvolcanic plutons and a high intensity hydrothermal alteration that affected cross cutting pipes in central volcanic complexes synkinematic kenoran metamorphism resulted in the growth of minerals chlorite actinolite etc parallel to schistosities synkinematic metamorphic grade ranges form the pumpellyite prehnite facies to the amphibolite facies late to post kinematic metamorphic phases resulted in the growth of minerals across schistosities syn to post kinematic plutons are not voluminous in the part o

u pb evidence for abitibi gold mineralization postdating greenstone magmatism and metamorphism two widely held theories for the origin of archaean lode gold deposits the magmatic1 and metamorphic replacement2 models predict that gold emplacement should have occurred near the end of late syn kinematic greenstone magmatism here we report that at the camflo mine in the abitibi subprovince of canada u pb ages for rutile and titanite in auriferous alteration 2 625 7 myr are much younger than the age of the host quartz syenite 2 680 4 myr and ages for regional magmatism 2 670 myr 3 and metamorphism 2 680 myr 4 mineral associations and pb pb systematics indicate that the hydrothermal minerals record crystallization ages that are probably coeval with the gold mineralization these ages and others from the abitibi subprovince4 6 rule out a direct connection between gold and magmatism or metamorphism associated with regional folding of the greenstone belt they are broadly contemporaneous with metamorphism at deep crustal levels7 and may record late devolatilization of the lower crust

roman comagmatic province central italy evidence for subduction related magma genesis geochemical data on mafic volcanics show that important affinities exist between the roman and the calc alkaline rocks from the aeolian arc south tyrrhenian sea these affinities together with the close association of calc alkaline and k rich volcanics in the aeolian arc and in the naples area the continuity in the variation of abundances of incompatible elements from calc alkaline to potassic suites and the similarity in terms of major element geochemistry support a genetic relationship of the roman magmatism and the subduction processes that affected the apennines in tertiary time and are still active under the aeolian arc in the genetic model presented here both calc alkaline and k rich magmas were generated within a mantle heterogenously enriched in lil elements composition of the mantle was modified by addition of material probably sediments dragged down by the undergoing slab the geochemical and petrological differences displayed by the calc alkaline and k rich volcanics are accounted for by the different conditions of melting as well as by chemical and isotopic heterogeneities of the source 26 references 3 figures 1 table

late archean mantle composition and crustal growth in the western superior province of canada neodymium and lead isotopic evidence from the wawa quetico and wabigoon subprovinces abstract neodymium and lead isotopes are presented for late archean rocks from the wawa quetico and wabigoon subprovinces sp in the western superior province ontario canada the isotopic compositions were determined on greenstone volcanic sequences pre tectonic 2 73 2 69 ga trondhjemite tonalite granodiorite ttg suites metasedimentary rocks and post tectonic 2 69 2 67 ga dioritic to granitic plutons in order to characterize the mantle and crustal reservoirs involved in the evolution of the southern part of the western superior province although derived from a depleted mantle almost all the greenstone volcanism and pre tectonic ttg suites record contamination by crustal material as old as 3 2 ga neodymium and lead isotopic compositions of the pre tectonic ttg can be modeled as products of the melting of amphibolitic crust e g subducted basalts contaminated by 1 10 of subducted sediments moreover lead isotopes of ttg suites provide evidence that the isotopic compositions of these subducted sediments varied as a result of the addition of new ca 2 7 ga juvenile material in agreement with neodymium isotopic differences recorded by sedimentary units of the quetico sp 50 50 mix of young old crusts and wawa sp 75 25 young old neodymium and lead isotopes of the post tectonic ree enriched archean sanukitoid suites define an isotopic trend which is distinct from that of the ttg suites and which is interpreted to reflect the importance of crustal assimilation in the evolution of these suites furthemore such plutons found in the wawa sp have more juvenile neodymium and lead isotopic compositions and higher nd contents than those intruded into the quetico and wabigoon sp which have more crustal isotopic signatures and lower nd concentrations this geographical difference could be due either to differences in nd contents of initial archean sanukitoid magmas lesser assimilation in the wawa sp or more probably because the wawa crust is on average more juvenile than the quetico and wabigoon crusts in agreement with the fact that the geographical difference mirrors that recorded by metasedimentary rocks deposited in quetico and wawa sp

provenance of igneous clasts in conglomerates of the archaean timiskaming group kirkland lake area abitibi greenstone belt canada four types of igneous clasts from timiskaming conglomerates of the kirkland lake area are identified calc alkaline porphyry trachyte k2o n2o 7 25 wt trondhjemite and tholeiitic basalt clasts derived from quartz carbonate veins and carbonatized porphyries and komatiites indicate co2 rich hydrothermal activity along the larder lake cadillac fault before sedimentation calc alkaline porphyry the predominant clast is similar in appearance to feldspar porphyry intrusions widely exposed in the area but the two are not related the porphyry clasts are cogenetic with diorite granodiorite intrusions and volcanic rocks of the greenstone belt andesite clasts are only observed near the base of the assemblage and the ratio of basalt to andesite increases up stratigraphic sections the change suggests progressive erosion of arc related volcanic rocks during sedimentation composition texture and mineralogy of the trondhjemite clasts are consistent with their derivation from the marginal phases of

u pb age constraints for deposition of clastic metasedimentary rocks and late tectonic plutonism michipicoten belt superior province the study investigates the ages of clastic metasedimentary rocks and of late tectonic alkalic to calc alkalic intrusions and puts constraints on the timing of major deformation in the michipicoten greenstone belt of the wawa subprovince a trondhjemitic boulder in the dore conglomerate of the southern metasedimentary belt is dated at 2698 2 ma this is a maximum age of sedimentation that is also supported by ages of detrital zircons in the matrix and may directly reflect the time of synvolcanic deposition detrital zircons in metapsammites of the central and northern sedimentary belts yield younger ages of 2682 3 and 2680 3 ma respectively suggesting that sedimentation occurred significantly later in the northern than in the southern parts of the greenstone belt the 2682 ma sedimentary rocks were affected by multiphase deformation that is related to the development of a large scale recumbent fold and superimposed folds and faults this tectonism was followed by the emplacement of the granodiorit

archean neptunian fissures and early history of the destor porcupine fault zone timmins ontario canada neptunian dikes and fissures are intimately associated with a minor archean sedimentary basin near timmins ontario in the southwestern part of abitibi subprovince of the canadian shield these structures are associated with the late archean timiskaming unconformity and were formed by clastic sedimentation in fissures opened by the reactivation and dilation of basement faults along a major crustal shear a pull apart origin is indicated for the sedimentary basin by published township maps and the underground geology of the dome gold mine the neptunian dikes and fissures are discussed in relation to previous stratigraphic and tectonic interpretations of the timmins area

fingerprinting multiple gold mineralization events at the dome mine in timmins ontario canada trace element and gold content of pyrite abstract the dome mine is host to over 16 moz of orogenic gold deposited during a period of up to 25 ma through multi stage enrichment the earliest economic stage of veining is an extensive set of ankerite veins which were historically considered barren except where overprinted by subsequent veining events gold in these veins is intimately associated with pyrite mineralization and three stages of pyrite growth have been identified py1 2 3 the trace element content of each stage of pyrite growth determined by dynamic secondary ion mass spectrometry and synchrotron radiation x ray fluorescence reveals that there were three auriferous fluid events each with a unique gold and trace element fingerprint which can be related to deposits wide mineralization events early ankerite vein forming fluids were auriferous lower temperature 200 250 c and deposited py1 enriched in gold metals and metalloids as cu ni zn py2 growth is related to deposit wide quartz tourmaline and quartz fuchsite veining based on trace element geochemistry au ag and associated mineral assemblages this deposited ni enriched pyrite tellurides galena and gold with anomalously high au ag ratios there is also evidence for remobilization of early gold and trace elements from py1 pyrite during the py2 forming event the final stage of gold endowment in the ankerite veins is related to a deposit and camp wide quartz veining event py3 growth is trace element as ni cu and au poor with respect to py1 and py2 however this veining event contributed the bulk of the ankerite vein gold endowment the remobilization of gold and trace elements from sieve textured py1 in addition to overprinting py2 and py3 and their associated gold endowments helps explain the difficulty in applying bulk rock trace element vectors to gold at the dome mine the work also provides conclusive evidence for the auriferous nature of early ankerite veining at the dome mine and reveals that the system was fertile for a period of over 7 to 25 ma a key component for the formation of a world class deposit

the midway sequence a timiskaming type pull apart basin deposit in the western wawa subprovince minnesota the midway sequence is an assemblage of subaerially deposited clastic and volcanic rocks that forms a narrow wedge within neoarchean greenstone of the western wawa subprovince of the superior province volcanic conglomerate in the midway sequence contains clasts of stratigraphically older greenstone together with clasts of a distinctive hornblende phyric trachyandesite that is not represented among the older greenstone flows the trachyandesite forms flows and pyroclastic units that are interbedded with lenticular deposits of volcanic conglomerate in a manner interpreted to indicate approximately coeval volcanism and alluvial fan fluvial sedimentation within a linear restricted and tectonically active depocentre the midway sequence unconformably overlies greenstone on one side and is bounded by a regional scale strike slip fault on the other structural analyses show that the midway sequence was deposited after an early precleavage folding event d1 in greenstone but before the regional metamorp

new evidence for multiple periods of gold emplacement in the porcupine mining district timmins area ontario canada the porcupine mining district is the largest lode gold producing district in north america with production in excess of 62 000 000 troy oz nearly all of the au has come from quartz carbonate lode systems hosted by metamorphic rocks of greenschist facies field relationships and radioisotope ages of intrusions indicate that gold emplacement occurred over a span of at least 7 m y depositional events that predated formation of the timiskaming unconformity surface are manifested by auriferous clasts of detrital pyrite banded quartz sulfide and quartz sulfide in basal timiskaming conglomerate pyritic clasts contain on average 2 54 ppm au and are conclusive evidence for the existence of pre timiskaming aged auriferous pyritic deposits these clasts may have been derived from pyritic bodies in carbonaceous argillites of the tisdale group from sulfide facies iron formation of the deloro group or from pyritic deposits of unknown genesis auriferous banded sulfidic quartz clasts were probably derived from iron formation of the deloro group and auriferous sulfidic quartz clasts possibly from epigenetic quartz sulfide veins intrusion related and post timiskaming gold deposition is evidenced by cu au mo mineralized porphyry and younger quartz carbonate gold veins the magmatism that emplaced feldspar and quartz feldspar porphyries was accompanied by cu au mo mineralization at the dome mine where a conformable quartz feldspar porphyry intrusion and its host greenstones are pervasively and atypically copper and gold mineralized and the porphyry is anomalously molybdenum enriched a new u pb zircon date on this mineralized porphyry fixes its emplacement and the maximum age of cu au mo deposition at 2688 2 ma this mineralization was overprinted by later gold mineralization in the form of planar sheeted and en echelon auriferous quartz veins and by mineralized shear and or fault zones field relationships indicate that these veins significantly postdate emplacement of the porphyries and timiskaming sedimentation the latest vein systems form the bulk of the ore at the dome mine and are similar to the most economically significant veins of the district the largest gold deposits of the district are spatially associated with but not in porphyries similar to those exposed at the dome mine this association has led to considerable speculation regarding the genetic relationship of felsic porphyry emplacement to ore formation the results of this study show that although some au was deposited during a cu au mo event temporally linked to porphyry emplacement most of the au at the dome mine was emplaced significantly later than the porphyries the documentation of at least three broad periods of au emplacement at least two of which are premetamorphic is permissive and supportive of genetic hypotheses that invoke metamorphogenic remobilization of au from earlier formed deposits alternatively the coincidence of early gold enrichments and later economic concentrations may reflect a single unidentified gold source from which successive but unrelated hydrothermal activity mobilized transported and deposited au with no direct genetic link between early and late episodes of gold deposition

conditions and timing of metamorphism in the southern abitibi greenstone belt quebec regional metamorphism ranging in grade from the subgreenschist facies to the greenschist amphibolite facies transition affects all archean supracrustal rocks 2677 ma in the rouyn noranda area contact metamorphic minerals associated with the posttectonic preissac lacorne batholith 2643 ma show no evidence of a regional retrograde event accordingly the age of regional metamorphism can be bracketed between 2677 and 2643 ma three reaction isograds were mapped in subgreenschist facies metabasites dividing the low grade rocks into three metamorphic zones the pumpellyite actinolite zone the prehnite pumpellyite zone and the prehnite epidote zone in addition the pumpellyite actinolite epidote quartz bathograd corresponding to a pressure of approximately 200 mpa occurs on both sides of the porcupine destor fault low pressure regional metamorphism is also indicated both by the occurrence of an actinolite oligoclase zone and the persistence of pre regional metamorphic andalusite the coincidence

subduction related shoshonitic and ultrapotassic magmatism a study of siluro ordovician syenites from the scottish caledonides syenites are important or predominant components of several plutonic complexes emplaced between 456 and 415 ma along the nw margin of the caledonian orogenic belt adjacent to the lewisian foreland in w and nw scotland although there are in detail chemical differences between the syenites from each centre they form a well defined compositional group overall ratios amongst their trace elements especially very high values of la nb are quite different from those trachytes and syenites formed by fractional crystallisation of ocean island basalts and their continental equivalents emplaced in regions of anorogenic crustal tension instead the scottish caledonian syenites closely resemble chemically the fractional crystallisation residua of potassic subduction related magmas such as the shoshonitic series a comendite minor intrusion from a swarm associated with the loch borralan and loch ailsh syenitic complexes is remarkably similar in composition to recent obsidian from the shoshonitic volcano of lipari in the aeolian arc published sr and pb isotopic ratios preclude a significant component of either upper proterozoic moine schists or lower crust granulite facies archaean lewisian or proterozoic grenvillian gneisses in all these syenites except in local syenitic facies of the glenelg ratagain complex fractional crystallisation appears to be the mechanism by which the liquids which formed these syenites evolved from basic parental magmas the phases involved in this process may have included plagioclase alkali feldspar pyroxene amphibole biotite garnet fe ti oxide sphene allanite apatite zircon and zirconolite and therefore all the ratios amongst even the so called incompatible elements may have changed during the evolution of the leucocratic magmas nevertheless a detailed study of the glen dessarry complex shows that the changes are insufficient to disguise the geochemical nature of the parental magmas these appear to be picritic shoshonite mgo 15 ni 400ppm la yb 20 la nb 5 for the glen dessarry loch borralan and loch ailsh syenites and picritic ultrapotassic magmas mgo 15 ni 400 ppm la yb 60 la nb 7 such as would crystallise to minettes for the loch loyal and glenelg ratagain syenites mafic shoshonites were erupted amongst the 410 ma lome lavas of this region and also occur as widespread approximately contemporaneous volcanic feeder plugs minettes of similar age are also common as dykes in nw scotland numerous large tonalite granite complexes with minor diorites and gabbros were emplaced in w and nw scotland between 435 and 400 ma these are generally acknowledged to be mixtures of magmas from crustal and mantle sources their more mafic members show compositional features such as very high ba and sr which group them with the rare syenites and the lorne lavas of the same region into a distinctive geochemical province within which shoshonitic and allied magmas were the mantle derived component two models are presented to account for the generation of strongly potassic subduction related magmas several hundred km behind a nw directed subduction zone or during the period immediately following continental collision

evolution of gold bearing splays of crustal scale fault zones of the south central archean abitibi subprovince constraints from the kirana deformation zone kirkland lake ontario canada abstract we explored the effects of brittle ductile deformation processes on the localization of strain and hydrothermal fluid flow throughout the formation and evolution of a fault zone this was accomplished through detailed structural analysis of the kirana deformation zone kdz a splay of the archean crustal scale orogenic gold hosting larder lake cadillac deformation zone llcdz in ontario canada investigations included mapping quantification of fault related breccia by particle size distribution analysis microstructural and petrographic characterization and kinematic analysis of brittle ductile structures the kdz records three principal evolutionary stages stage 1 involved seismogenic processes that resulted in the formation of a 50 m wide fault core and damage zone stage 2 is characterized by transpressional ductile shear localized along texturally favorable mechanically weakened zones that formed during stage 1 and or along zones where coeval fluid flow facilitated reaction weakening native gold is observed within the mylonitized fault core that is interpreted to have formed syn to late ductile shear all structures are crosscut by small scale faults and shear veins with disseminated alteration halos defining stage 3 the kdz demonstrates how early fault processes may control the spatial pattern and temporal progression of strain and hydrothermal fluid localization in orogenic gold bearing fault splays

unraveling the geologic history of the hemlo archean gold deposit superior province canada a u pb geochronological study the hemlo deposit is one of canada s largest gold camps gold is both structurally and lithologically controlled but shows unusual relationships relative to many other archean lode deposits field evidence suggests that gold was emplaced within mechanical and chemical traps along a jog in a major sinistral shear zone most likely during early formation of second generation g2 structures which represent the most intense phase of regional deformation mineralization was followed by amphibolite facies regional metamorphism u pb geochronology has been carried out on zircons from rocks associated with the deposit in order to determine the precise chronology of geologic events and their relationship to mineralization zircon populations are commonly affected by both inheritance and hydrothermal metamorphic crystal growth meaningful and precise age information can only be determined by precise single zircon dating on rocks from a well constrained structural and stratigraphic context gold is mostly found near the deformed contact between the moose lake quartz porphyry volcanic complex and stratigraphically underlying metasedimentary rocks these rocks have been folded by a camp scale noncylindrical f2 fold zircon from the moose lake quartz porphyry is dominated by inheritance and gives ages that extend from 2800 to 2690 ma metasedimentary rocks that underlie and overlie the moose lake porphyry show a much narrower range of provenance ages and are dominated by 2 690 to 2 693 million year old zircon two detrital zircons from a metasedimentary rock directly beneath the porphyry define an age of 2685 4 ma this should be an older age limit on volcanism deformation and gold mineralization the four youngest near concordant zircons from the cedar lake pluton define a magmatic age of 2680 1 ma this pluton was emplaced prior to or early during g2 deformation while emplacement of gold was most likely controlled by g2 structures therefore 2680 1 ma probably also represents an older age limit on gold mineralization a feldspar porphyry dike that cuts gold ore gives a younger age bracket of 2677 1 ma the results of zircon dating suggest that a volcanosedimentary complex was constructed in the area over the period of 2693 to 2685 ma this developed on earlier crust ca 2720 ma in age but there is evidence from detritus and xenocrysts for older rocks dating back to over 2800 ma deposition of supracrustal rocks was followed by granodiorite plutonism at 2680 1 ma then major deformation g2 and gold mineralization overprinted by amphibolite facies metamorphism previously dated at 2676 ma from titanite ages late tectonic sanukitoid suite plutons were emplaced at 2677 1 ma thus the primary gold forming event occurred near the beginning of a period of plutonism and crustal reworking that lasted at most a few million years this time association supports the view that granitoid magmas were the source of auriferous fluids plutons intruded into an actively deforming crust and were probably also the heat source for regional metamorphism the most likely environment was a tectonically active timiskaming type sedimentary basin similarly aged basins are found in the timmins area to the east and the shebandowan greenstone belt to the west

geochemical oxygen and neodymium isotope compositions of metasediments from the abitibi greenstone belt and pontiac subprovince canada evidence for ancient crust and archean terrane juxtaposition abstract the abitibi greenstone belt agb and pontiac subprovince ps in the southwestern superior province are adjacent greenstone plutonic and metasedimentary dominated terranes respectively separated by a major fault zone metasediments from these two contrasting terranes are compared in terms of major and trace element and o and nd isotope compositions and detrital zircon ages the following two compositional populations of metasediments are present in the low grade abitibi southern volcanic zone 1 1 a mafic element enriched population mep characterized by flat depleted ree patterns enhanced mg cr co ni and sc low incompatible element contents and minor or absent normalized negative troughs at nb ta and ti and 2 2 a low mafic element population lmep featuring lree enriched patterns enhanced rb cs ba th and u contents and pronounced normalized negative troughs at nb ta and ti these geochemical features are interpreted to indicate that the mep sediments were derived from an ultramafic and mafic dominated oceanic provenance whereas the lmep sediments represent mixtures of mafic and felsic arc source rocks the ps metasediments are essentially indistinguishable from abitibi lmep on the basis of majorelement and transition metal abundances suggesting comparable types of source rocks and degrees of maturity but are distinct in terms of some trace elements and o isotope compositions the pontiac metasediments are depleted in 18o and enriched in cs ba pb th u nb ta hf zr and total ree and also have higher ratios of rb k cs rb ba rb ta nb th la and ba la relative to the abitibi lmep two subtypes of ree patterns have been identified in ps metasediments both have moderately fractionated distributions with la yb n 3 9 17 and 7 8 13 6 respectively but the first has minor eu anomalies eu eu 0 89 1 16 whereas the second features pronounced negative anomalies eu eu 0 52 0 81 coupled with high concentrations of incompatible elements such as k rb th u nb and ta the first subtype is interpreted to be derived from provenances of mixed mafic and felsic volcanic rocks whereas the eu depleted type has geochemical features that are typical of post archean sediments or archean k rich granites and volcanic equivalents abitibi metasediments have nd 2 7 ga values of 0 71 to 1 83 corresponding to model tchur 2 82 2 55 ga with the majority around 2 65 ga close to the depositional age of 2 7 ga in contrast ps metasediments are characterized by nd 2 7 ga 0 95 to 3 51 corresponding to t dhur 2 7 to 3 1 ga consistent with a detrital zircon age spectrum of 2 69 ga to 3 1 ga pontiac subprovince and abitibi metasediments have contrasting provenances suggesting their separate initial geodynamic settings and later tectonic juxtaposition major and trace elements o and nd isotopic compositions and detrital zircon ages collectively suggest that some of the ps metasediments were derived mainly from juvenile rocks whereas others require various degrees of contribution from older 3 0 3 5 ga evolved crust mixed with juvenile 2 7 ga rocks older components were derived either directly from erosion of an ancient continental arc or from contemporaneous volcanic rocks which may contain recycled older components if the ps represents in part an accretionary prism to the abitibi southern volcanic zone then oblique subduction may have been involved which allowed the pontiac subprovince to juxtapose or sample exotic source rocks

sedimentary basin controls on orogenic gold deposits new constraints from u pb detrital zircon and re os sulphide geochronology lynn lake greenstone belt canada abstract sedimentary basins that open and close during the last stages of mountain building represent an important exploration criterion for orogenic gold deposits however the genetic and or preservation controls of these synorogenic or timiskaming type sedimentary basins and their controlling fault systems on orogenic gold deposits remain unclear herein we address that knowledge gap and report new u pb detrital zircon and re os sulphide arsenopyrite and pyrite geochronology and sulphide pb isotope results for the paleoproterozoic lynn lake greenstone belt llgb manitoba canada the youngest detrital zircon from all six meta conglomerate and psammite samples of the synorogenic sickle group and previously reported u pb zircon ages for post sickle group intrusions are used to constrain its depositional timing from 1836 15 to 1831 4 ma replicate analyses of one highly radiogenic arsenopyrite sample from an auriferous vein at the maclellan gold deposit yield a weighted average re os model age of 1824 12 ma which is identical to previously published in situ u pb xenotime ages at the same deposit 1827 8 ma each of these hydrothermal ages demonstrate that early stage auriferous veins immediately post date deposition of the sickle group and most likely occurred prior to peak metamorphism 1814 1801 ma this sequence of events is very similar to the abitibi greenstone belt suggesting that a synorogenic phase of extension and rapid burial of auriferous veins by timiskaming type sickle group sediments may have played an important genetic and or preservation control on early stage gold mineralization in the llgb however unlike the abitibi greenstone belt none of the known gold deposits within the llgb are hosted within the sickle group younger re os model arsenopyrite ages at 1782 16 ma from the maclellan gold deposit also post date synorogenic sedimentary basins by ca 50 myr these late stage auriferous veins are unrelated to the synorogenic extensional phase and more likely reflect repeated fluid focusing along reactivated structures during a post peak metamorphic phase of hydrothermal activity the multi stage hydrothermal history of orogenic gold deposits in the llgb also provides a possible explanation for the mixture of depleted mantle like and highly radiogenic fluid components that are inferred from age corrected sulphide pb isotope compositions 1 8 ga 8 9 10 6 reworked cratonic margins and their associated greenstone belts thus represent favourable depositional settings for auriferous fluids at multiple stages throughout the lifespan of an orogen

pb isotopic geochemistry of granitoids and gneisses from the late archean pontiac and abitibi subprovinces of canada abstract initial pb isotopic compositions were determined on k feldspars for thirty granitoid plutons and gneiss complexes in the abitibi and the pontiac subprovinces of canada the gneisses cover a wide spectrum of initial pb isotopic compositions and undoubtedly demonstrate that very radiogenic reservoirs were present in the pontiac subprovince and along its southern boundary with the grenville province in the late archean the gra nitoid rocks also define a large spectrum covering 0 3 unit of the 207 pb 204 pb ratio ranging from compositions typical of mafic mantle melts to those of sedimentary banded iron formations the older intrusives emplaced between 2 72 and 2 68 ga were principally derived from juvenile mantle sources they may have been formed in a volcanic arc environment but they still frequently record the signature of crustal precursors which may have been represented by subducted sediments or by older assimilated crustal components a sharp change in the provenance of the granitoid magmas occurred close to 2 68 ga an age that also corresponds to an episode of alkaline activity and fault related sedimentation for the following 40 ma magmatism chiefly resulted from melting of crustal precursors in a thickened crustal lithosphere the pb isotopic compositions of these crustal melts demonstrate that the basement of the pontiac subprovince contains a major component of rocks older than 3 0 ga in comparison the abitibi subprovince may not contain basement components older than 2 9 ga or else they represent a negligible fraction of the crust this supports the concept that the abitibi and pontiac subprovinces formed as discrete crustal segments tectonically juxtaposed finally the grenville front tectonic zone was metamorphosed and partially melted in the late archean and is probably the deep crustal equivalent of the pontiac subprovince

mantle derivation of archean amphibole bearing granitoid and associated mafic rocks evidence from the southern superior province canada amphibole bearing late archean 2 73 2 68 ga granitoids of the southern superior province are examined to constrain processes of crustal development the investigated plutons which range from tonalite and diorite to monzodiorite monzonite and syenite share textural mineralogical and geochemical attributes suggesting a common origin as juvenile magmas despite variation in modal mineralogy the plutons are geochemically characterized by normative quartz high al2o3 15 wt na rich fractionation trends mol na2o k2o 2 low to moderate rb generally 150 ppm are comagmatic with the evolved granitoids and indicate that the suites are mantle derived isotopic studies of archean monzodioritic rocks have shown lree enrichment and initial 143nd 144nd ratios indicating derivation from mantle sources enriched in large ion lithophile elements lile shortly before melting mineral assemblages record lower ph2o with increased alkali contents of the suites this evidence in conjunction with experimental studies suggests that increased alkali contents may reflect decreased ph2o during mantle melting these features indicate that 2 73 ga tonalitic rocks are derived from more hydrous mantle sources than 2 68 ga syenitic rocks and that the spectrum of late archean juvenile granitoid rocks is broader than previously recognized comparison with phanerozoic and recent plutonic suites suggests that these archean suites are subduction related

amphibole and plagioclase chemistry in two proterozoic dyke swarms and its relation to the uplift history of the kapuskasing structural zone the gneisses of the chapleau portion of the kapuskasing structural zone ksz and of the wawa gneiss terrane wgt can be partitioned into subregions on the basis of magnetic polarity of 2 45 ga ma

petrogenesis of mantle derived lile enriched archean monzodiorites and trachyandesites sanukitoids in southwestern superior province reply in southwestern superior province diorite monzodiorite and trachyandesite sanukitoids occurring within syn to post tectonic intrusive complexes and within greenstone belts have the following chemical characteristics 55 60 wt sio2 mgo 6 wt mg 0 60 ni and cr both 100 ppm na2o k2o 6 wt sr and ba both 600 1800 ppm and rare earth element ree patterns that are strongly light rare earth element lree enriched cen 80 250 ybn 4 10 and show no eu anomalies sanukitoids and their granodioritic derivatives constitute at least 5 of the exposed crust in the study area the sanukitoids cannot be derived by melting fractionation or crustal contamination of basalts or lamprophyres that are coeval with the sanukitoids crustal contamination of komatiites fails to explain the high large ion lithophile element lile contents of the sanukitoids rather we suggest that the sanukitoids were derived by hydrous melting of lile enriched mantle peridotite at pressures between 10 and

time transgressive archean unconformities underlying molasse basin fill successions of dissected oceanic arcs superior province canada abstract late archean diachronous unconformities underlying tectonically controlled coarse clastic successions are located throughout the superior province of canada examples studied in detail include hiatuses at the base of the timmins and kirkland basins in the abitibi greenstone belt and the crowduck and stormy basins in the wabigoon subprovince the timmins molasse basin fill succession overlies a high angle subaerial unconformity separating deepwater turbiditic deposits from fluvial conglomerates a subaerial erosional unconformity defines the contact between mafic flows and overlying felsic volcaniclastic deposits and fluvial conglomerates of the kirkland basin the crowduck and stormy successions are characterized by shallow water and subaerial unconformities between quartz feldspar porphyry stocks and clastic deposits the pronounced characteristics of the molasse basins which include 1 basal unconformities with older sedimentary volcanic or plutonic rocks 2 bounding fault systems 3 ba

igneous and tectonic evolution of the batchawana greenstone belt superior province a u pb zircon and titanite study u pb isotopic dating of zircon and titanite from all the major litho tectonic units of the batchawana belt an archean greenstone belt of the abitibi subprovince of the superior province in canada shows that the belt evolved during a period of about 60 ma between about 2730 and 2670 ma ago the earliest date of 2729 3 2 ma was found in a predominantly tholeiitic metavolcanic sequence the base of which is intruded by a tonalite dated at 2716 2 ma younger ages of 2720 10 ma 2709 2ma 2711 2ma 2701 2ma and 2698 2 ma date rocks at increasingly higher stratigraphic levels of a mixed tholeiitic calc alkalic metavolcanic sequence which is itself overlain by a thick succession of clastic metasedimentary rocks subsequent deformation of the supracrustal sequences produced isoclinal folding and culminated in metamorphism ranging from lower greenschist to amphibolite facies and anatexis related to the intrusion of syn to late tectonic plutons four phases of which have ages of 2678 4 2ma 2677

thermobarometry in a subgreenschist to greenschist transition in metabasites of the abitibi greenstone belt superior province canada mineral equilibria in the system cao mgo al2o3 sio2 h2o provide a basis for mapping of four reaction isograds and one bathograd in the low pressure transition from subgreenschist to greenschist facies most of the matachewan area of the abitibi greenstone belt is in the lower pressure bathozone as indicated by the widespread occurrences of the subassemblage prh chl the higher pressure bathozone is indicated by two occurrences of pmp act ep qtz but in these samples the bathograd is displaced to anomalously low pressure by the high fe content of the coexisting minerals this illustrates the need to analyse coexisting minerals calculate activities of end member species and compute p t curves for individual samples before interpreting the isograd bathograd pattern petrographic and microprobe analysis indicates that great care must be taken in the selection of equilibrium assemblages pyroxene phenocrysts in one sample are replaced by the assemblage pmp act ep chl qtz whereas prh act ep chl qtz occurs in the groundmass compositional variation may be more cryptic as in a sample of metabasaltic hyaloclastite that contains two spatially distinct univariant assemblages prh pmp ep chl qtz and prh act ep chl qtz within the devitrified matrix whereas chlorite compositions are similar in both assemblages prehnite and epidote in the latter assemblage are significantly richer in fe and poorer in al accordingly the rock is interpreted to contain two distinct univariant assemblages rather than one invariant assemblage prh pmp act ep chl qtz the displaced univariant curves for this sample intersect at 2 2 kbar and 250 c taking account of all thermobarometric implications the low grade limit of the greenschist facies is at 250 270 c and 2 2 5 kbar corresponding to depths of 7 8 km comparison of apparent p t conditions on both sides of the larder lake cadillac break a regional co2 metasomatized fault zone that is spatially associated with many archaean gold deposits provides an upper limit of not more than c 1 km for post metamorphic south side up dip slip displacement

gold mineralization at the syenite hosted beattie gold deposit duparquet neoarchean abitibi belt canada le gisement de beattie est situe dans la ceinture de roches vertes de l abitibi a proximite de la faille porcupine destor et est associe a une syenite porphyrique les corps mineralises ont une ressource totale inferee de 2 77moz contenu dans 56 2mt de minerai a 1 53g t d or dans le gisement de beattie deux styles de mineralisation sont presents a controle lithologique et a controle structural la mineralisation a controle lithologique est limitee exclusivement a la syenite alteree en carbonates de fer cette mineralisation represente du minerai a basse teneur mais fort tonnage dans lequel l or est porte par la pyrite arsenifere et l arsenopyrite l or est invisible il se presente sous la forme de solution solide dans le c ur poreux et riche en arsenic des pyrites la mineralisation a controle structural est presente uniquement dans des zones de cisaillement adjacentes et incluses dans la syenite le minerai est a haute teneur dans des zones de breches silicifiees a caractere hydraulique et tectonique dans des veines de quartz cherteux dans des veines polymetalliques intensement silicifiees et dans des dykes de syenite trachytique tres alteree l or y est visible sous forme d electrum dans les microfractures des pyrites brechifiees les deux styles de mineralisation et les alterations font partie d une evolution paragenetique commune dans un environnement magmatique hydrothermal des phases initiales oxydantes ont evolue en conditions reduites a la faveur de fluides magmatiques et externes riches en co2 ce changement d etat d oxydation a entraine la precipitation des sulfures et la cristallisation de l or invisible dans la pyrite arsenifere et l arsenopyrite une phase d alteration ulterieure dominee par des fluides hydrothermaux riches en silice a pour resultat la brechification des sulfures et leur redistribution dans des corridors siliceux ainsi que la remobilisation de l or dans les microfractures des pyrites brechifiees les compositions calculees de 18o et d sur les veines de quartz associees a cet evenement tardif sont respectivement 7 67 o et 66 o indiquant une dominance des fluides magmatiques avec une probable composante metamorphique cet evenement syn metamorphique transition d2 d3 est associe a un fort enrichissement en hg te mo ag sb as et se le style de cristallisation de l or dans le gisement de beattie est une consequence de la dominance des regimes en systemes ouverts tant au niveau de l incorporation dans le magma de l arsenic qui controle la precipitation de l or invisible que de la circulation tardive de fluides hydrothermaux riches en silice qui sont a l origine de la remobilisation de l or le gisement de beattie partage des affinites avec des gisements associes aux intrusions intrusion related gold deposit des gisements epithermaux a tendance neutre a intermediaire et des gisements de type mesothermaux mots cles de l auteur gisement d or porphyre archeen or invisible remobilisation de l or

hydrothermal zircon and baddeleyite in val d or archean mesothermal gold deposits characteristics compositions and fluid inclusion properties with implications fortiming of primary gold mineralization zircon and baddeleyite occur within quartz tourmaline veins at four gold deposits in the val d or district of the archean abitibi southern volcanic zone host rocks have experienced intense metasomatic enrichment of zr hf y and rare earth elements the zircons contain primary inclusions of quartz tourmaline pyrite albite k mica scheelite and gold and gold occurs in primary fluid inclusions in zircons magmatic zircons in host rocks do not have this suite of inclusions consequently a wall rock inheritance model for the vein zircons is implausible compositionally the zircons feature pronounced interzone and intergrain variations of hf y yb th and u and sporadic anomalous ce contents of 1100 ppm distinct from magmatic counterparts two principal types of primary fluid inclusion occur in the vein zircons type 1 h2o co2 inclusions have low salinities variable quantities of co2 and homogenization temperatures of 260 380 c and type 2 co2 rich inclusions contain minor h2o and ch4 the vei

anthropogenic chlorofluoromethanes in the greenland and norwegian seas the concentrations of two industrially produced chlorofluoromethanes ccl3f f 11 and ccl2f2 f 12 have been measured in the water column and in the marine atmosphere of the greenland and norwegian seas measurable concentrations of these two chlorofluoromethanes have penetrated to the deep basins of both of these regions and the general characteristics of their vertical distributions are similar to those of the bomb produced radioisotopes injected into the atmosphere on a similar time scale the data have been fitted to a time dependent box model based on deep convective mixing in the greenland sea and lateral exchange between the deep basins the model calculations for the two chlorofluoromethanes in the greenland sea give similar results with a time scale for deep convection of about 40 years the time scale for lateral mixing between the deep greenland sea and the deep norwegian sea is estimated to be 20 to 30 years although the agreement between the calculations for the two chlorofluoromethanes is limited by analytical uncertainties at the low concentrations found in the deep norwegian sea and by uncertainties in the model assumptions

whole rock δ o and δ h footprint of the canadian malartic gold deposit pontiac sub province quebec canada the canadian malartic gold deposit was produced by a hydrothermal system that altered the host metasedimentary rocks of the pontiac group metavolcanic rocks of the piche group and associated porphyritic intrusions and mafic dykes the isotopic footprint in pontiac metasedimentary rocks is marked by an increase in 2h values from 91 near mineralization to background values of ca 59 whereas 18o values remain relatively constant near 10 the isotopic footprint in mafic dykes is marked by an increase in 2h values from 84 near mineralization to background values of ca 73 and a decrease in 18o values from 9 8 near mineralization to background values of ca 8 3 kriging of oxygen and hydrogen isotopic compositions around the canadian malartic deposit delineates the isotopic footprint of the deposit in greywackes the 59 2h isopleth encircles the mineralized domain and is elongated towards the northwest and southeast in mafic dykes the 73 2h isopleth encircles the mineralized domain as well as a large area to the south and southeast whereas the 8 3 18o isopleth encircles the center of the mineralized system and extends over an area towards the southeast host rock oxygen and hydrogen isotope compositions therefore define a cryptic alteration footprint up to 2 5 km outside of the canadian malartic deposit the isotopic composition of the metamorphic fluid in equilibrium with the average least altered greywacke at upper greenschist to amphibolite conditions of ca 550 c is approximately 18o 8 6 and 2h 19 this is close to the composition of the mineralizing fluid at the canadian malartic deposit reported by previous studies fluid rock oxygen and hydrogen isotope exchange modeling indicate that the isotopic footprint formed at relatively low fluid rock ratios up to 0 5 at temperatures near 350 400 c

the macassa mine archean lode gold deposit kirkland lake ontario geology patterns of alteration and hydrothermal regimes the only remaining gold producer of seven interconnected mines the district has produced over 710 000 kg au since 1913 the area is underlain by part of the timiskaming group three types of gold ore 1 native au in chloritic fault gouge or small quartz lenses within a thrust fault system called break ore 2 gold bearing quartz veins in both hanging and footwalls of this fault system termed vein ore 3 several relatively wide zones of intensely fractured bleached silicified and pyritized rock containing lenses and pods of quartz with native au and telluride minerals called breccia ore the delta 18 o and delta d of rocks and mineral separates in these three ore types suggest that the ore was precipitated from hydrothermal fluids of delta 18 o 7 to 9 6 per mil and delta d 35 to 85 per mil at 350 degrees to 460 degrees c initial hydrothermal regime was followed by downward penetration of oxidizing sulfate bearing fluids delta 18 o 0 to 2 per mil delta d 20 to 70 per mil and of probable marine and or meteoric water origin initially at temperatures of 200 degrees c waning to 50 degrees c or less a third fluid regime is indicated for quartz magnetite chlorite veins which have mineral pair fractionations corresponding to fluids of delta 18 o 4 0 to 0 5 per mil and 210 degrees to 260 degrees c these three hydrothermal fluid regimes are interpreted to reflect a sequence of crustal compression relaxation and finally uplift above sea level probably all during the archean incremental 39 ar 40 ar upper plateau age of 2 575 m y for vein actinolite the deposit is interpreted to have formed during a period of major fracturing ductile deformation and thermal perturbation accompanying the episode of batholith emplacement modified journal abstract

ach uaine hybrid appinite pipes evidence for mantle derived shoshonitic parent magmas in caledonian granite genesis the ach9uaine hybrids of northern scotland form a suite of caledonian minor intrusions with a wide range of cogenetic compositions ranging from mantle derived mafic shosonite chemically similar to the lamprophyres of the region through syenites comparable to the rare caledonian syenites to granites typical of the local newer granites they therefore provide a hitherto unsuspected direct link between these major caledonian magma types and suggest that the newer granites in the northern highlands may have mantle derived parental components of subduction related shoshonitic affinity shoshonite to granite fractionation is thought to have proceeded within a compositionally stratified caledonian magma chamber chemical data including rare earth element analyses demonstrate the control of crystal fractionation but the wide range of silica saturation may imply a significant crustal input

timing of magmatism and deformation in the kamiskotia kidd creek area western abitibi subprovince canada abstract the kamiskotia kidd creek area comprises well preserved granitoid greenstone belt lithologies of the western most abitibi subprovince similar in composition and structural style to other late archean granitoid greenstone terranes e g kalgoorlie norseman western australia belingwe zimbabwe slave province canada it contains the kidd creek volcanogenic massive sulfide deposit and lesser deposits of the kamiskotia district and lode gold deposits associated with the destor porcupine fault zone near the prolific porcupine gold district the magmatic and tectonic history for the area is provided through detailed structural mapping and high precision u pb geochronology field observations support the following sequence of magmatic and structural events in the kamiskotia area 1 formation of older mafic and intermediate volcanic rocks followed by the emplacement of the kamiskotia gabbroic complex kgc and cogenetic massive sulfide bearing bimodal volcanic rocks kv also accompanied by coeval intrusion of granitoid a into the crystallizing kgc 2 regional bulk rotation about a sub horizontal axis of this stratigraphy to form a ne facing monocline 3 emplacement of three large granitoid intrusions imparting their respective contact strain aureoles on the stratigraphy 4 regional sub horizontal bulk north south shortening that formed a non penetrative east west flattening fabric with an element of 5 late dextral transpression that formed high strain zones related to western destor porcupine fault zone dpfz within less competent volcanic units and 6 emplacement of alkalic dikes associated with the late stages of transpressive deformation u pb ages help substantiate this chronology and aid in the correlation of kamiskotia lithologies across the southern abitibi subprovince zircon ages for the kgc and a kamiskotia rhyolite are 2707 2 ma and 2705 2 ma respectively these ages are coeval with the reid rhyolite with a zircon age of 2706 2 ma but are significantly younger than the kidd creek rhyolite and the prosser rhyolite with zircon ages of 2717 2 ma data refined by the addition of an abraded concordant analysis and 2716 6 3 ma respectively two of the granitoid intrusions have zircon ages of 2696 1 5 and 2694 4 ma the older granitoid intrusion has a titanite population with a 207 pb 206 pb minimum age of 2692 5 ma which may represent a protracted cooling history or a metamorphic event after the setting of the zircon u pb system two zircon fractions from the younger granitoid intrusion exhibit inheritance with 207 pb 206 pb minimum ages up to 2926 ma indicating the presence of significantly older crust in this region timing of north south compression and late transpression may be constrained by a u pb garnet titanite age on a late to post tectonic alkalic dike at 2687 3 ma

depositional gaps in abitibi greenstone belt stratigraphy a key to exploration for syngenetic mineralization models of greenstone belt development are crucial for exploration allochthonous models predict belts to be a collage of unrelated fragments whereas autochthonous models allow for prediction of syngenetic mineral deposits within specific stratigraphic intervals superior province greenstone belts consist of mainly volcanic units unconformably overlain by largely sedimentary timiskaming style assemblages and field and geochronological data indicate that the abitibi greenstone belt developed autochthonously we describe major revisions to stratigraphy of the abitibi greenstone belt and the implications of an autochthonous development of the volcanic stratigraphy for exploration for syngenetic mineralization the abitibi greenstone belt is subdivided into seven discrete volcanic stratigraphic episodes on the basis of groupings of numerous u pb zircon ages of pre 2750 2750 to 2735 2734 to 2724 2723 to 2720 2719 to 2711 2710 to 2704 and 2704 to 2695 ma we present revised lithotectonic and or stratigraphic nomenclature using these time intervals including 1 isotopic inheritance in younger episodes which indicates that the older episodes 2750 2735 and 2734 2724 ma had greater extent than is presently seen 2 dikes feeding younger volcanic episodes 2706 ma cutting older volcanic units 2734 2724 ma and 3 2710 to 2704 ma mafic to ultramafic sills intruding the 2719 to 2711 ma episode changes to the nomenclature include the identification of pre 2750 ma volcanic episode supracrustal fragments in the northern and southern abitibi greenstone belt and subdivision of the 2719 to 2711 ma 2710 to 2704 ma and 2704 to 2695 ma episodes into lower and upper parts we present the results of this lithostratigraphic subdivision as the first geochronologically constrained stratigraphic and or lithotectonic map of the abitibi greenstone belt many of the volcanic episodes are intercalated with and capped by a relatively thin sedimentary interface zone dominated by chemical sedimentary rocks stratigraphic and geochronological analysis of these zones indicates discontinuous deposition with localized gaps of 2 to 27 m y between volcanic episodes the zones consist of up to 200 m of iron formation chert breccia heterolithic debris flows of volcanic provenance sandstone and or argillite and conglomerate modeling of the time required for deposition of the volcanic units based on rates of magma production in modern arc and plume environments is on the order of 103 to 104 years whereas the time interval between basalt rhyolite cycles is 106 years the sedimentary interface zones are therefore interpreted as condensed sections zones with very low rates of sedimentation in a basinal setting or zones with negligible rates of sedimentation marked by silicification of existing rock types the sedimentary interface zones are therefore considered submarine correlative conformities disconformities or unconformities separating the equivalent of group level stratigraphic and lithotectonic units the unconformity bounded stratigraphic model provides a new regional to deposit scale interpretive model for use in exploration for syngenetic mineralization

evolution of the south central part of the archean abitibi belt quebec part i stratigraphy and paleogeographic model the region comprises parts of the southern zone of the abitibi greenstone belt and of the bellecombe gneiss belt and the belleterre angliers greenstone belt the stratigraphic sequence of the abitibi belt consists of 1 a lower ultramafic division 2 a middle tholeiitic division and 3 an upper diverse division these divisions lap onto an older volcanic sequence to the north and west in the bellecombe belt sediments overlie the lower ultramafic division these sediments coarsen toward the abitibi belt and toward the stratigraphic top the volcanic rocks of the belleterre angliers belt overlie the sediments of the bellecombe belt five paleogeographic phases have been recognized during phase i a deep marine ultramafic lava plain covered the south part of the abitibi belt and the bellecombe belt faulting took place at the duparquet destor break during phase ii tholeiitic basalts formed a deep marine lava plain in the west of the abitibi belt whereas flows erupted mainly from central volcanic c

pontiac metavolcanic rocks within the cadillac tectonic zone mcwatters abitibi belt quebec the mcwatters metavolcanic rocks are structurally bounded lenses within the cadillac tectonic zone on the southern boundary of the abitibi greenstone belt they comprise komatiite tholeiitic basalt and gabbro and calc alkaline andesitic lavas and volcaniclastic rocks cut by calc alkaline dioritic and lamprophyric dykes the mcwatters basalts are mid ocean ridge basalt type tholeiites exhibiting low incompatible trace element contents and la yb n 1 they may have formed via relatively high degree partial melting of a rare earth element depleted mantle source the andesites exhibit chondrite normalized trace element patterns with light rare earth and large ion lithophile element enrichments and negative nb and ti anomalies comparable to those of subduction related calc alkaline andesites mcwatters units are distinct from nearby blake river group rocks despite comparable lithological assemblages and some common geochemical characteristics the mcwatters basalts exhibit lower ti y zr y and la yb tha

plutonism in the southern abitibi subprovince a tectonic and petrogenetic framework studies of plutonic rocks in archean terranes such as the southern abitibi subprovince have been an important component in the development of an accretionary tectonic model for the superior province in the southern abitibi subprovince pretectonic approximately 2 75 2 70 ga low k tholeiitic calc alkaline dioritic to tonalitic plutons e g bourlamaque batholith flavrian pluton are associated with volcanism and are interpreted to be derived from both partial melting of hydrated mantle during oceanic arc formation and fractionation of tholeiitic to calc alkaline basalt andesite pretectonic synvolcanic tholeiitic intrusions e g dundonald sill kamiskotia gabbroic complex 2 72 2 70 ga show in situ fractionation trends and locally have mixed magma textures with contemporaneous calc alkaline granitoids they are believed to be derived from a midocean ridge basalt morb like depleted mantle with little evidence for contamination by an older crustal component pre to syntectonic approximately 2 72 2 69 ga porphyry and tonalite plutons e g timmins porphyries round lake batholith have geochemical characteristics typical of archean tonalite trondhjemite suites considered to be derived from melting of basaltic rocks at high metamorphic grades late to post tectonic 2 69 ga diorite monzonite and syenite plutons e g watabeag batholith lamaque stocks otto stock have large ion lithophile element enriched calc alkaline to sho shonitic compositions these intrusions and associated timiskaming type volcanic rocks are attributed to melting of large ion lithophile element enriched mantle in the late stages of subduction late to post tectonic biotite muscovite granite intrusions contain a significant contribution of evolved crust e g s type characteristics of the preissac lacorne batholith in the southern abitibi subprovince the tectonic setting of mantle and crust derived intrusions is broadly comparable to magmatic processes in phanerozoic arcs and accreted terranes the plutonic rocks record a transition from pre to synaccretionary subduction related plutonic suites to late to postaccretionary suites derived from enriched mantle and crustal sources this framework provides a basis for understanding mineral deposits associated with intrusive rocks of the southern abitibi subprovince which range from ni cu sulfides in layered synvolcanic tholeiitic intrusions e g kamiskotia gabbroic complex ontario to volcanogenic sulfides in early tholeiitic and calc alkaline sequences e g flavrian pluton noranda district quebec to the spatial association of gold with late large ion lithophile element enriched intrusions e g lamaque plugs val d or district quebec

from intrusion related to orogenic mineralization the wasamac deposit abitibi greenstone belt canada abstract the wasamac deposit is an example of archean greenstone hosted gold deposit located in the abitibi belt 15 km southwest of rouyn noranda the deposit is hosted by a second order ductile shear zone of the cadillac larder lake fault zone cllfz known as the francoeur wasa shear zone fwsz it regionally sits at the boundary between the orogenic gold district of noranda and the kirkland lake gold district dominated by intrusion related gold systems this specific location in between two different gold mineralization environments sets the wasamac deposit apart as a prime candidate for investigating hydrothermal processes along the cllfz within the wasamac deposit gold distribution is constrained to the altered mylonitized portion of the fwsz lode systems are absent hydrothermal alteration and associated disseminated mineralization occurs as a replacement of the blake river group metavolcanic units the hydrothermal signature displays two distinct alkaline alteration assemblages potassic and albitic each associated with specific gold characteristics 1 potassic alteration is characterized by the crystallization of microcline carbonates and quartz within this assemblage gold is associated with porous pyrite enriched in te ag au mo pb bi w deposited under oxidizing conditions such characteristics are widely described in the kirkland lake area and are found in examples of syenite related mineralization such as the beattie and malartic gold deposits 2 the albitic alteration assemblage composed of albite sericite and carbonates reflects more reduced hydrothermal conditions with mineralization characterized by free native gold this hydrothermal event is coeval with the brecciation of early gold rich pyrite reflecting a structural overprint that controlled late stage gold characteristics these alteration and structural features are common in orogenic gold deposits both worldwide and regionally particularly at the neighbouring kerr addison and francoeur deposits and in lode gold systems such as in the sigma lamaque deposit the gold mineralization at wasamac has similar characteristics to both intrusion related gold systems and structurally controlled orogenic gold deposits hydrothermal and structural crosscutting relationships at wasamac indicate that a structurally controlled hydrothermal event overprinted earlier potassic magmatic hydrothermal alteration this observation supports a multistage process of gold concentration during which new gold characteristics metal anomalies fluid conditions and alteration assemblages replaced earlier stages of gold enrichment in places completely obliterating previous signatures we propose that the wasamac deposit was originally related to an alkaline intrusion buried at depth beneath the francoeur wasa shear zone

review of archean supracrustal assemblages of the southern abitibi greenstone belt in ontario canada products of microplate interaction within a large scale plate tectonic setting abstract previously formulated plate convergent models account for many aspects of the large scale regularity and parallelism between different subprovinces of the archean superior province such models do not however appear to adequately explain the within subprovince evolution of 2 75 2 68 ga supracrustal assemblages of the late archean southern abitibi greenstone belt principal supracrustal assemblage classes include l assemblages dominated by tholeiitic metabasalt and metakomatiite with varying amounts of tholeiitic intermediate to felsic metavolcanic rocks these assemblages probably formed in extensional settings the ratio of basalt to komatiite and the ratio of basalt komatiite to intermediate felsic metavolcanic rocks may be a function of mantle temperature and crustal thickness at the site of extension respectively 2 assemblages dominated by intermediate to felsic fragmental and or effusive rocks are generally of calcalkalic affinity and likely formed in island arc settings 3 assemblages containing a substantial component of iron formation may represent older supracrustal assemblages that form structural and or stratigraphic basement to some of the younger supracrustal assemblages 4 assemblages consisting almost wholly of turbidite facies metasedimentary rocks appear to postdate volcanic activity related to the previous assemblages deposition of these sediments broadly coincides with the onset of regional deformation these assemblages may represent distal deposits related to an emerging collisional orogen 5 assemblages consisting of alluvial fluvial metasedimentary rocks with or without spatially associated alkalic metavolcanic rocks are associated with crustal scale shear zones and are the youngest assemblages within the greenstone belt alluvial fluvial assemblages likely represent the final emergence of the consolidating orogen geochronological data and assemblage distribution suggest that the supracrustal assemblages of the southern abitibi greenstone belt may represent the amalgamation of products of diverse and intricate microplate tectonic settings repeated in time and space prior to the impingement of the large scale plate tectonic regime that dictated the final large scale configuration of the archean superior province

40ar 39ar geochronological evidence for multiple postmetamorphic hydrothermal events focused along faults in the southern abitibi greenstone belt thermal histories in the abitibi and pontiac subprovinces vary for three general domains 1 zones of impermeable rock with cooling rates of 8 c ma 2 zones of impermeable rock that are spatially associated with monzogranite plutons with apparent cooling rates of 1 2 cima and 3 permeable high strain zones with apparent cooling rates of 2594 ma from the volcanogenic massive sulphide related sericite alteration with the coarser mica yielding the younger date based on radiometric dating impermeable rocks were affected weakly by postmetamorphic hydrothermal events minerals in zones of higher permeability were reset during the intrusion of monzogranite plutons highly permeable zones such as the larder lake cadillac and porcupine destor faults were overprinted repeatedly this produces a drawn out series of dates from minerals with varying closure temperatures radiometric ages from fault zones or ore deposits cannot be used to interpret the cooling history and evolution of the abitibi belt as a whole

upb zircon ages for the missanabie renabie area and their relation to the rest of the michipicoten greenstone belt superior province ontario canada abstract the missanabie renabie area is the eastern portion of the michipicoten greenstone belt ten new u pb zircon ages confirm and extend the chronostratigraphy established previously for the michipicoten and the adjoining mishibishu and gamitagama greenstone belts in northern ontario the michipicoten belt evolved between 2661 and 2889 ma the igneous activity was episodic the bimodal cyclic volcanism occurred at 2700 2750 2900 ma extensive plutonic activity occurred at 2670 ma and synchronously with the three volcanic cycles the pattern of ages in the michipicoten belt is significantly different from that in the abitibi belt the felsic volcanism in this area is dated by the renabie crystal tuff at 2740 ma and by the cradle lakes porphyry at 2736 ma these ages are typical of cycle 2 volcanism in the michipicoten belt a deformed quartz feldspar porphyry at conboy lake has an age of 2675 ma which correlates with a well documented regional plutonic event it is possible that this rock unit is synvolcanic with a hitherto unrecognized volcanic episode in this belt the conboy lake tonalite a pluton in the wabatongushi lake granitoid complex which lies to the north of the supracrustal rocks has an age of 2688 ma the nudulama tonalite of the missanaibi lake batholith to the east of the supracrustal rocks has an age of 2741 ma the southern flank of the greenstone belt is bordered by the ogasiwi lake granitoid complex the hand lake tonalite in this complex has an age of 2723 ma four plutons internal to the belt are dated as follows ruby lake stock 2661 ma lochalsh bay stock 2670 ma ash lake pluton 2679 ma and rennie lake stock 2668 ma the four internal plutons dated here together with previously dated eight similar post tectonic to syntectonic plutons were emplaced between 2661 and 2679 ma along the northern margin of the greenstone belt most of the deformation in the supracrustal rocks developed between 2661 and 2741 ma but a period of late deformation related to the gold mineralization can be bracketed more precisely between 2661 and 2679 ma

geochemistry of archean alkalic volcanic rocks from the crystal lake area east of kirkland lake ontario canada abstract twelve samples of timiskaming volcanics from the crystal lake area were analyzed for major and trace elements ta th zr hf v cr sc rare earth elements ree y etc by x ray fluorescence and instrumental neutron activation analysis techniques the samples which include mafic trachytes trachytes and leucite trachytes represent several batches of archean alkalic magmas differentiated at shallow depths the cr sc cr systematics and ree zr th and zr y characteristics show however that their primary magmas generated at great depths in the enriched mantle where garnet remained in the refractory residue of partial melt the chemical similarity between the timiskaming samples and modern alkalic rocks in mature volcanic arcs strongly implies that the timiskaming volcanism represents the last stage of a late archean island arc volcanism present in the southwestern abitibi belt superior province the occurrence of timiskaming type alkalic rocks is not rare in archean greenstone belts thereby suggesting that a tectonic setting similar to modern volcanic arc system might have been common in late archean time

petrology and tectonic significance of gabbros tonalites shoshonites and anorthosites in a late paleozoic arc root complex in the wrangellia terrane southern alaska plutonic rocks intrusive into the late paleozoic tetelna formation of southern alaska are the underpinnings of the late paleozoic skolai arc of the wrangellia terrane there are four groups of intrusive rocks within the skolai arc 1 gabbro diorite plutons that contain gabbroic to anorthositic cumulates along with a differentiated series of gabbros and diorites of basaltic to andesitic composition 2 silicic intrusions including tonalite granodiorite and granite 3 monzonitic to syenitic plutonic rocks of the ahtell complex and related dikes and sills 4 fault bounded bytownite anorthosite of uncertain age and association these anorthosites may be related to post skolai nikolai greenstone magmatism the silicic rocks yield discordant u pb zircon ages of 290 320 ma early to late pennsylvanian relative age relations suggest that the oldest intrusive rocks are the gabbro diorite plutons the youngest are the monzonitic rocks and that the silicic rocks span this range the gabbro diorite pluto

sedimentology of archean greenstone belts signatures of tectonic evolution abstract stratigraphic styles in archean greenstone belts are compared to those of modern and phanerozoic depositional basins in order to test the conformity of tectonic style through time six lithological associations in greenstone belts are recognized 1 mafic ultramafic volcanic 2 calc alkaline volcanic 3 bimodal volcanic 4 quartz arenite iron formation or carbonate 5 conglomerate wacke and 6 conglomerate arenite examples of the associations are described from the kaapvaal superior and zimbabwe provinces and the pilbara block each association differs only slightly between the four regions thereby emphasizing a common tectonostratigraphic theme sedimentary rocks are a minor component of the mafic ultramafic volcanic association they were deposited in two types of volcanic basin environments one similar to barred lagoons and bays around oceanic volcanic islands and the other similar to sediment starved platforms adjacent to coalesced volcanoes in inter arc intra arc and back are basins in contrast sedimentary rocks in the calc alkaline volcanic association comprise thick wedges of epiclastic and volcaniclastic detritus deposited in elongate sedimentary basins and thick wedges of pyroclastic and volcaniclastic detritus deposited adjacent to volcanic centers sedimentary facies were identical to those of forearc trench and marine volcanoplutonic arc settings chemogenic lithofacies in both volcanic associations were deposited in shallow to deep marine waters although shallow water profiles were selectively preserved in some terrains sedimentary rocks of the bimodal volcanic association are thick wedges of siliciclastic and volcaniclastic deposits interbedded with subaerial to submarine erupted flows of komatiite basalt and rhyolite depositional environments ranged from braid plain and braid delta to coastal marine and submarine fan starved basin deposits include banded iron formation and sulfidic black shale the association is identical to that of cratonic extensional basins in arc continent and intracontinental rifts sedimentary rocks of the quartz arenite iron formation or carbonate association onlap weathered basement or bimodal volcanic association rocks depositional environments were either transitional from fluvial to siliciclastic and carbonate marginal marine to offshore pelagic hemipelagic or from inshore intrabasinal clastic and volcaniclastic to offshore pelagic hemipelagic siliciclastic deposits are supermature two tectonic sites are represented those with siliciclastic facies represent continent adjacent syn to post rift stable shelves and those dominated by banded iron formation with volcaniclastic deposits represent arc adjacent post rift stable shelves sedimentary rocks of the conglomerate wacke association are represented by thick wedges of siliciclastic or volcaniclastic sandstone with minor volcanic components these were deposited in braid plain braid delta and submarine fan environments within elongate sedimentary basins coastal plain and pelagic basin facies are also present siliciclastic detritus was derived from syndepositional magmatic and metasedimentary thrust belts two stratigraphic styles are preserved one that records a flysch like stage of deep to marginal marine environments and the other that records a molasse like stage of marginal marine to fluvial environments the association is identical to that of compressional foreland basins of arc continent collisional and compressional arc tectonic affinities the conglomerate arenite association is preserved in elongate structural basins that transgress crustal components and all other supracrustal units it is dominated by thick wedges of siliciclastic sandstone although bimodal volcanic and volcaniclastic rocks can also be present depositional environments ranged from talus and alluvial fan and braid plain to either lacustrine or coastal marine local basin margins often show lateral offsets from source terrains and vertically skewed facies patterns longitudinal facies geometries are typical the association is similar to that of strike slip collisional graben in hinterland tectonic escape and terrane accretion orogens the examples show that despite all the ramifications of secular geophysical geothermal and geochemical global change the stratigraphic style of sedimentary rocks in archean greenstone belts can be matched with modern tectonic analogues thereby emphasizing the conformity of stratigraphic style through time the inseparable link between stratigraphic and tectonic styles implies that the tectonic style of greenstone belts was not temporally unique major differences exist with regards to the chemical composition of certain magmatic and sedimentary products but these are compensated for by their constant stratigraphic function in terms of depositional processes depositional environments and tectonic sites

u pb geochronology of archean metasedimentary rocks in the pontiac and abitibi subprovinces quebec constraints on timing provenance and regional tectonics abstract u pb isotopic ages of single detrital zircons have been obtained from metasandstones in the northern part of the pontiac subprovince and from the cadillac kewagama and lac caste groups within the southern abitibi subprovince youngest detrital zircon ages from these sequences are 2685 2686 2687 and 2693 ma respectively the lac fourniere pluton which intrudes pontiac group metasedimentary rocks is dated at 2682 1 ma a similar age was previously measured from a pluton that cuts the kewagama group these data bracket deposition of greywacke in the pontiac and abitibi subprovinces to 2685 3 ma in contrast the youngest zircon found in a volcaniclastic unit interbedded with timiskaming group metawacke is 2673 2 ma while the age of a pluton that intrudes the timiskaming is 2672 1 ma thus the timiskaming group is distinctly younger than the other metasedimentary rocks the normalized probability distributions of detrital zircon ages from the pontiac and the abitibi metasedimentary rocks as well as of dated igneous rocks from the southern abitibi subprovince all show that their major zircon populations formed in the age range 2685 2710 ma the distributions for the abitibi metaturbidites and dated igneous rocks are very similar suggesting that metasedimentary rocks in the abitibi belt were mostly derived from the surrounding granite greenstone terrain the largest peak of the pontiac distribution is a few million years younger than that from the abitibi metasedimentary rocks but there is a correlation between major peaks and both groups show similar age ranges for older pre abitibi components 2750 2850 and 3020 3030 ma deposition of the ca 2685 ma sediments was virtually syn deformational based on previous field geochemical and isotopic studies as well as the detrital zircon age data the pontiac group may represent a foreland basin that may have developed from an accretionary prism the source of much of the sediment may have been an uplifted extinct continental arc to the north the arc was mostly eroded into the sediment basin and perhaps tectonically overridden by a southward advancing nappe complex comprised of its back arc basin now partly preserved in the southern volcanic zone of the abitibi subprovince metaturbidites exposed between metavolcanic assemblages within the greenstone belt may represent overturned unconformities at the structural base of the greenstones these were brought up by high angle faults which also localized deposition of non marine timiskaming type sediments it is tentatively suggested that pontiac type metasedimentary rocks extend most of the way beneath the abitibi subprovince the oldest part of the basin emerging as the quetico group in the western superior province

evolution of the archean abitibi greenstone belt and adjacent terranes new insights from geochronology geochemistry structure and facies analysis

constraints on the geodynamic evolution of the southern superior province u pb la icp ms analysis of detrital zircon in successor basins of the archean abitibi and pontiac subprovinces of ontario and quebec canada abstract to investigate the tectonic development of the southern superior province new u pb laser ablation inductively coupled mass spectrometry analysis of detrital zircon was conducted on graywacke samples from successor basins of the abitibi and pontiac subprovinces the three successor basin successions investigated are the 2690 2685 ma porcupine assemblage and the 2679 2669 ma timiskaming assemblage of the abitibi subprovince and the 2682 ma sedimentary rocks of the pontiac subprovince predominately neoarchean zircon grains 80 95 of the total zircon population reflect local sources in the abitibi and pontiac subprovinces the successor basins were deposited within 100 ma of the majority of the detrital zircon grains primary crystallization ages which is consistent with patterns observed at modern convergent margin settings porcupine assemblage samples contain 5 mesoarchean zircon while pontiac subprovince and timiskaming assemblage samples contain 18 and 13 respectively no local mesoarchean sources exist in the abitibi or pontiac subprovinces suggesting input from an adjacent hinterland the higher proportion of mesoarchean zircon in the timiskaming assemblage relative to the porcupine assemblage suggests that detritus from the hinterland was more prevalent during the later stages of collision probably as a result of progressive uplift and denudation of the hinterland the high proportion of mesoarchean zircon in the pontiac subprovince sedimentary rocks may reflect an additional mesoarchean source comparison to previously published geochronology data for the superior province indicates that the hinterland was to the northwest and is in part composed of the winnipeg river marmion and opatica subprovinces patterns of contractional deformation successor basin formation and felsic plutonism progressively young to the south in the southern superior province and are interpreted in terms of accretionary processes detrital transport across subprovince or terrane boundaries progressive hinterland emergence and foreland directed propagation of the deformational front recorded by successor basins is similar to that observed in modern style collisional or accretionary orogens

structural evolution of a gold bearing transtensional zone within the archean porcupine destor deformation zone southern abitibi greenstone belt eastern ontario canada abstract the garrison camp comprises four structurally distinct orogenic gold deposits that formed in different host lithologies during progressive deformation detailed field mapping drill core logging and geochronological constraints suggest that the 2678 2 ma garrison granitic stock played a fundamental rheological role in the location of the four deposits initial local shear movement occurred along the southwestern margin of the stock leading to the development of the nw trending sinistral ne side up buffonta shear zone which hosts the buffonta deposit subsequently a transtensional zone formed between the ne trending sinistral porcupine destor and munro deformation zones which host the 903 and jonpol deposits respectively finally a local change in shortening orientation from ne to nnw caused westerly directed extension resulting in the formation of the younger gold bearing veins composing the garrcon deposit in situ u pb laser ablation inductively coupled plasma mass spectrometry performed on monazite grains formed within the shear fabric of the munro deformation zone indicates that transtension occurred at 2657 15 ma therefore at least three of the four deposits formed subsequent to crystallization of the garrison granitic stock the reported u pb dates represent the first direct age constraints on the movement along a gold bearing deformation zone in the southern abitibi greenstone belt

late archaean geological development recorded in the timiskaming group sedimentary rocks kirkland lake area abitibi greenstone belt canada sedimentary rocks of the timiskaming group have been classified into a conglomerate sandstone unit csu and a turbidite unit tu turbidite sequences north and south of the larder lake cadillac fault llcf are significantly different the turbidite south unit tsu has elevated concentrations of ee203 tot igo tio2 cr and ni whereas the turbidite north unit tnu has compositions similar to arenites of the csu and has high sio2 u th and total ree the source of the tsu is estimated to be 120 o rhyolite 180 o komatiite and 70 andesite mostly derived from an undissected volcanic arc terrane it is proposed that the tsu formed in a fore land basin during uplift of calcalkaline volcanic rocks and obduction of oceanic crust in response to deformation related to accretion sources for the csu and the tnu were very similar comprising 60 quartz monzodiorites 20 trachytes and 20 tholeiitic basalts the tnu was either contemporaneous with or postdated the csu and their depositions probably followed juxtaposition of two tectonic blocks along the llcf the source terrane for the csu and tnu was a dissected arc which had exposed subvolcanic calc alkaline intrusions the sedimentation of csu and tnu however predated the unroofing of k rich intrusions which are presently extensively exposed abundant andesitic clasts in the tsu and the decrease in their abundances in the tnu and csu indicates that andesites were once abundantly exposed but most were removed by erosion in late archaean time

secular variation in greenstone sequence development emphasizing superior province canada abstract evidence from the superior province of the canadian shield suggests the existence of several distinct lithostratigraphic associations in greenstone belts 1 quartz arenite and carbonate bearing sequences 2 mafic ultramafic volcanic sequences 3 mafic to felsic volcanic cycles and 4 timiskaming type sequences of fluviatile sediments and calc alkaline to alkaline volcanics recently recognized quartz arenite bearing sequences in the sachigo and wabigoon subprovinces are from base to top quartz arenite stromatolite bearing carbonate oxide facies iron formation and komatiite or tholeiite primary structures in the quartz arenites indicate shallow water deposition and represent mature sedimentation granitoid provenance of these sediments is postulated based upon petrography of coarse arenites and clasts of associated conglomerates the few dated superior province quartz arenite bearing sequences are 2 85 ga the shallow water origin of the primary structures and biota and the areal extent of the quartz arenite and carbonate sequences invite comparison with platform sediments at passive margins platform sequences unconformably overlie 3 ga granitoid rocks and older mafic volcanics where original lower contacts are preserved in two localities mafic volcanic sequences contain sheet flows iron formations and deep water argillites based on physical volcanology and sedimentology these sequences are compared to modern deep water mafic plain and hawaiian volcanism they generally underlie mafic to felsic volcanic cycles and overlie platform sequences mafic sequences are 2740 2700 ma in age mafic to felsic volcanic cycles consist of deep water tholeiitic flows overlain by shallow water to subaerial intermediate to felsic pyroclastics and flows the facies style of volcanism petrography and geochemistry of the mafic to felsic cycles most closely resemble the characteristics of crust in continental magmatic arc systems this type of lithostratigraphic association varies in age from 2775 to 2700 ma in the superior province with minor exceptions timiskaming type sequences consist of fluviatile conglomerate immature arenites and wackes with subaqueous to subaerial volcanics of variable chemistry longitudinal and lateral variation within fault bounded basins is extreme and the sequences have generally been affected by only late stages of deformation the combination of rock types facies distribution the fault bounded nature of the repositories and the locus of sedimentation along zones of transcurrent displacement suggest timiskaming sequences are best compared with modern pull apart basins superior province timiskaming sequences are within the superior province platform sequences are the earliest postorogenic lithostratigraphic unit in greenstone belts followed by mafic plain sequences arc volcanics and pull apart basins we suggest that platform sequences based upon limited evidence are preceded by an orogeny and that pull apart basins represent a subsequent orogeny the lithostratigraphic units above have distinct metallogenic associations 1 platform sequences based upon compilation of several shields may contain detrital au and u and oxide facies iron formations associated felsic volcanics contain no recognized volcanogenic cu zn deposits in the superior province the following metallogenic associations are noted 2 mafic plain sequences contain komatiite flow related ni deposits cu ni and platinum group deposits are associated with flows and coeval intrusions 3 arc volcanic sequences contain volcanogenic cu zn sulphide deposits and scarce deposits of porphyry type cu mo and 4 timiskaming sequences and related plutonism are related to lode au

the age and provenance of metasedimentary rocks in the quetico subprovince ontario from single zircon analyses implications for archean sedimentation and tectonics in the superior province abstract u pb isotopic analyses have been performed on single detrital zircon grains from greywacke samples collected along the northern boundary of the quetico subprovince in northwest ontario secondary lead loss was virtually eliminated by choosing crack free grains and removing the outer surface using air abrasion thus the 207 pb 206 pb age can be considered a good approximation to the age of crystallization of each grain zircons in the quetico metasediments show a range of ages from 2698 3 ma to 3009 4 ma deposition and metamorphism of the metasediments is bracketed within a 10 5 ma time span between crystallization of the youngest detrital zircon grain and a late tectonic intrusion the blalock pluton which cuts the sediments and has a zircon age of 2688 4 ma the most easterly metasediment sample contains zircons with ages which cluster around 3007 6 ma which is within error of the age of a batholith dated in the adjacent marmion lake area of the wabigoon subprovince this along with the fact that most detrital zircons were only slightly abraded by sedimentary transport suggests that the source of many zircons may have been proximal from the north there is also a significant cluster of young zircon ages in the range 2698 2709 ma surprisingly only a few ages correspond to the time of most intense arc type felsic volcanism 2710 2745 ma in the main greenstone belt of the western wabigoon subprovince sedimentary deposition occurred at a time of extensive deformation in the adjacent wabigoon subprovince the pattern of detrital grain ages indicates that this involved uplift of a complex older sialic landmass petrographic evidence for the presence of substantial felsic volcanic detritus as well as the fact that many of the zircons only slightly pre date deposition indicates that much of the sediment was probably derived from erosion of active felsic volcanic centers these data combined with regional geochronological and field studies favour deposition in a basin formed by late orogenic collisional events

u pb zircon and monazite ages from the kapuskasing uplift age constraints on deformation within the ivanhoe lake fault zone a decade of u pb dating of zircon and monazite from high grade metamorphic rocks in the kapuskasing uplift has identified a series of magmatic and metamorphic events between 2700 and 2585 ma and indicates that the onset of regional granulite metamorphism took place at mid crustal levels of the southern superior craton ca 2660 ma new u pb ages for zircon and monazite have been used to constrain the age of ductile deformation fabrics at two sites in the ivanhoe lake fault zone the structure along which the granulite facies kapuskasing structural zone was uplifted these results suggest that the fault zone was probably active in the late archean as young as 2630 ma and again at approximately 2500 ma

fluid chemistry and evolution of hydrothermal fluids in an archaean transcrustal fault zone network the case of the cadillac tectonic zone abitibi greenstone belt canada detailed fluid geochemistry studies on hydrothermal quartz veins from the rouyn noranda and val d or areas along the transcrustal cadillac tectonic zone ctz indicate that unmineralized with respect to gold sections of the ctz contained a distinct co2 dominated h2s poor hydrothermal fluid in contrast both gold mineralized sections of the ctz e g at orenada 2 and associated higher order shear zones have a h2o co2 c h 4 nacl hydrothermal fluid their co2 h2s ratios indicate h2s rich compositions the br cl compositions in fluid inclusions trapped in these veins indicate that hydrothermal fluids have been equilibrated with the crust oxygen isotope ratios from hydrothermal quartz veins in the ctz are consistently 2 more enriched than those of associated higher order shear zones which are inter preted to be a function of greater fluid rock ratios in the ctz and lower fluid rock ratios and more efficient equilibration of the hydrothermal fluid with the wall rock in higher order shear zones an implication from this study is that the lower metal endowment of the transcrustal ctz when compared with the higher metal endowment in higher order shear zones ratio of about 1 1000 may be the result of the lack of significant amounts of h 2o h2 sr ich fluids in most of the ctz in contrast gold mineralization in the higher order shear zones appear to be controlled by the high h 2s activity of the aqueous fluids because gold was likely transported in a bisulfide complex and was deposited during sulfidation reac tions in the wall rock and phase separation in the quartz veins

mantle derived archaean monozodiorites and trachyandesites the 2 680 2 750 myr old1 5 intrusive granite greenstone terranes6 8 in the rainy lake region ontario and in and adjacent to the vermilion district minnesota of the superior province in north america include a wide variety of volcanic and intrusive rocks with initial pb sr and nd isotope ratios close to those for the mantle4 5 9 12 the isotopic constraints require the production of large volumes of silica oversaturated magmas from silica undersaturated mantle within 100 200 myr we present here geochemical data on monzodiorites and trachyandesites from the rainy lake area which are strongly enriched in large ion lithophile elements lile we conclude that they are derived by direct melting of the mantle at depths of 50km in either anhydrous or hydrous conditions their rare earth element ree abundances and initial 143nd 144nd ratios suggest that their mantle sources were enriched in lile shortly before melting the monzodiorites trachyandesites and their granodioritic derivatives may comprise up to 20 of the exposed igneous rocks in the rainy lake region and vermilion district if these rocks are as abundant in other archaean terranes a significant part of the early continental crust could have formed by direct melting of lile enriched mantle

the role of gravity and magma in the structural evolution of a deformed archean volcanic centre timmins ontario canada a deformed bimodal subaqueous volcanic centre in the western archean abitibi subprovince of the canadian shield contains structures comparable with those of relatively undisturbed igneous complexes similarities include an annular fold pattern initiated by structural doming and downsagging of basaltic flows prior to the terminal felsic volcanism during this cycle an ancestral dome was ruptured by a northeasterly regional graben defined by fossil fault scarps preserved beneath the terminal volcanic deposits fissure vents developed along the northwest boundary of the graben gradually drained the underlying magma chamber and transformed the crest of the dome into a central collapse basin surrounded by an annular anticlinal uplift marking the inner periphery of the former dome basalts on the basinward side of the fissure vents became detached along interflow argillites and glided into the central collapse forming secondary gravity folds within the uppermost basalts subaqueous deposition of felsic debris occurred in the graben and subsiding collapse basin succeeded by postvolcanic turbidites the annular folds were modified by two phases of regional deformation separated by an episode of archean molasse sedimentation along the reactivated south boundary of the paleograben

40ar 39ar age constraints on the thermal history of the archean abitibi greenstone belt and the pontiac subprovince implications for terrane collision differential uplift and overprinting of gold deposits 40ar 39ar mineral age spectra of granitic and metamorphic rocks in conjunction with existing conventional zircon geochronology indicate that at least two major late archean thermal events affected tectonic blocks of the abitibi southern volcanic zone svz and the juxtaposed pontiac subprovince the earlier thermal activity 2690 2670 ma was accompanied by the intrusion of voluminous syntectonic plutons and caused low pressure greenschist facies metamorphism in the svz and intermediate pressure metamorphism in the pontiac subprovince the second thermal event 2660 2630 ma was coeval with the emplacement of syncollisional s type garnet muscovite granites in the pontiac subprovince and the higher grade lacorne block of the abitibi svz and reset the k ar systems in preexisting rocks magmatic amphibole from the syntectonic round lake batholith 2695 ma u pb zircon age of the abitibi svz has a slightly disturbed ar release spectrum with an upper plateau age of 2669 6 ma signifying that the low gra

u pb systemstics in single zircons from the pontiac sediments abitibi greenstone belt twenty six detrital zircon grains from the late archaean pontiac sediments of the abitibi greenstone belt were dated individually by the u pb method in order to identify possible elements of an ancient pre 2 7 ga shield the results show that at least two components were present at the source areas of these sediments 1 materials of about 2700 2725 ma which were most likely derived from contemporaneous acid igneous rocks and 2 significantly older materials parts of which are at least 2940 ma old which were either part of an uplifted sedimentary basin or a sialic basement complex these results can be used to suggest a close link between igneous activity and basin subsidence and that the development of the abitibi volcanic belt was closely associated with the presence of some older sialic blocks

comment on archean hydrothermal zircon in the abitibi greenstone belt constraints on the timing of gold mineralization by j c claoue long r w king and r kerrich

geologic and structural setting of gold mineralization in the kirkland lake larder lake gold belt ontario the kirkland lake larder lake gold belt includes the giant kirkland lake and world class kerr addison chesterville gold deposits along with several smaller deposits and occurrences it corresponds to an east trending band of timiskaming clastic and volcanic rocks that unconformably overlie older volcanic assemblages in the southern abitibi greenstone belt of the archean superior province the gold belt is bounded to the south by the larder lake cadillac deformation zone which roughly follows the contact between the younger timiskaming rocks and the older volcanic units three generations of fabrics formed during post timiskaming regional deformation d2 d3 and d4 of the belt north south shortening during d2 produced a penetrative generally east striking steeply dipping s2 foliation and an east plunging l2 stretching lineation s2 is most intense within the syn d2 larder lake cadillac deformation zone and its northeast trending splay the upper canada deformation zone the d2 structures are overprinted by a north trending crenulation cleavage s3 which formed during east west d3 shortening across the belt a northeast trending regional s4 foliation associated with z shaped f4 folds and overprinting both s2 and s3 formed during northwest southeast d4 shortening gold mineralization is localized along the larder lake cadillac deformation zone anoki and mcbean deposits the upper canada deformation zone upper canada deposit and the brittle kirkland lake fault and 04 break kirkland lake deposit the upper canada mcbean and anoki deposits formed during d2 and along with kerr addison chesterville omega and cheminis deposits are probably related to a regionally extensive hydrothermal system associated with the larder lake cadillac deformation zone the sulfide poor gold and telluride bearing quartz veins of the kirkland lake deposit are interpreted to have been emplaced during d4 synchronous with reverse dextral movement along the ore controlling brittle kirkland lake fault the kirkland lake mineralization has a distinct metal signature te au mo pb ag high au ag low as and probably represents a separate hydrothermal system linked to a deep magmatic alkalic fluid source and unrelated to mineralization along the syn d2 deformation zones