archean gold mineralization in the wabigoon subprovince a product of crustal accretion evidence from u pb geochronology in the lake of the woods area superior province canada within the lake of the woods greenstone terrain in the wabigoon subprovince of northwest ontario gold is in faults shears and tension veins that developed in response to a late archean northwest directed contraction and emplacement of contemporaneous plutons nine rocks in this area have been dated using u pb analyses of zircon in order to obtain precise time constraints on gold mineralization and to compare its timing with the age of major crustal events in the region a mineralized dike at the duport mine shoal lake is 2716 pm 2 ma old whereas a later dike that cuts mineralized rocks has an age of 2709 pm 2 ma gold mineralization is therefore distinctly younger than calc alkaline and tholeiitic rocks dated at 2724 pm 2 ma in the shoal lake area and 2727 pm 2 ma in the high lake area to the north hydrothermal activity associated with mineralization at the duport mine overprints the amphibolite facies contact metamorphic aureole of the snowshoe bay batholith 2708 pm 7 ma

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

multistage zircon and titanite growth and inheritance in an archean gneiss complex winnipeg river subprovince ontario abstract the paper presents results from a u pb isotopic investigation of zircon and titanite from three phases of the archean sioux lookout gneiss complex at the margin of the gneissic plutonic winnipeg river subprovince wrs of the superior province the data reveal an intricate data pattern caused by inheritance and multistage crystallization and record the timing of two major orogenic events followed by a protracted post metamorphic evolution a zircon age of 2889 3 ma for a foliated pink granite correlates with that of similar units elsewhere in the superior province and reflects one of the first major episodes of crustal assembly in the pre kenoran evolution of the region tonalite and diorite from the same site yield zircon and titanite ages of 2704 2 and 2705 5 ma which correspond to the timing of major magmatism related to kenoran collision of the wrs with the adjacent wabigoon volcanic domains tonalite and diorite both contain abundant xenocrystic zircon moreover the late kinematic diorite also includes xenocrystic titanite which has a minimum age of 2730 ma and coexists with younger ca 2705 ma titanite and zircon two generations of titanite are also present in both the tonalite and the granite the earliest one reflects the 2704 ma plutonic metamorphic event whereas the second one indicates post metamorphic crystallization at 2650 and 2627 ma caused by superimposed hydrothermal activity and retrogression the data support the concept that the titanite can remain a closed system to pb diffusion at elevated temperatures as long as the crystals escape magmatic or metamorphic recrystallization conversely they also show that titanite can easily be produced by low temperature processes hence generalized interpretation of titanite ages in terms of regional cooling can be inappropriate

basement terrane correlations and crustal recycling in the western superior province nd isotopic character of granitoid and felsic volcanic rocks in the wabigoon subprovince n ontario canada abstract the western superior province represents a collage of mesoarchean continental 3 2 2 8 ga and neoarchean continental arc and oceanic 2 8 2 66 ga crustal fragments nd isotope data presented here for 89 felsic volcanic and plutonic rocks have been combined with compiled data to generate a data set of over 240 analyses from the wabigoon and winnipeg river subprovinces these samples from both oceanic and continental environments have been used as crustal probes their nd isotopic character used to investigate the extent of basement terranes the ancestry of crustal fragments their interaction with each other and the degree of sialic crustal reworking the wabigoon and winnipeg river subprovinces include three isotopically distinct terranes 1 the winnipeg river terrane comprises the winnipeg river subprovince the north central wabigoon and the north eastern wabigoon subprovince this region is dominated by neoarchean granitoid rocks with mesoarchean vestiges of previous workers have suggested that the boundary between the western wabigoon and winnipeg river terranes represents a cryptic suture resulting from a collision at circa 2 71 ga the boundary between the western wabigoon and marmion terranes although obscured by late intrusions may be a continuation of this suture zone the boundary between the winnipeg river and marmion terranes in the central wabigoon is also cryptic isotopic data suggest that the marmion terrane is allochthonous with respect to the winnipeg river terrane common magmatism in these two terranes at 2 93 2 87 ga suggests that they may have collided during this time in the eastern wabigoon subprovince this collision zone is speculated to occur at the humboldt bay high strain zone a complex history of crustal recycling throughout the mesoarchean and neoarchean is revealed which demonstrates the importance of autochthonous development of granite greenstone terranes in a continental environment the data also support models of tectonic accretion during the archean indicated by the presence of granite greenstone terranes of allochthonous origin

shallow velocity structure of stromboli volcano italy derived from small aperture array measurements of strombolian tremor abstract the properties of the tremor wave field at stromboli are analyzed using data from small aperture arrays of short period seismometers deployed on the north flank of the volcano the seismometers are configured in two semi circular arrays with radii of 60 and 150 m and a linear array with length of 600 m the data are analyzed using a spatiotemporal correlation technique specifically designed for the study of the stationary stochastic wave field of rayleigh and love waves generated by volcanic activity and by scattering sources distributed within the island the correlation coefficients derived as a function of frequency for the three components of motion clearly define the dispersion characteristics for both rayleigh and love waves love and rayleigh waves contribute 70 and 30 respectively of the surface wave power the phase velocities of rayleigh waves range from 1000 m sec at 2 hz to 350 m sec at 9 hz and those for love waves range from 800 to 400 m sec over the same frequency band these velocities are similar to those measured near puu oo on the east rift of kilauea volcano hawaii although the dispersion characteristics of rayleigh waves at stromboli show a stronger dependence on frequency such low velocities are consistent with values expected for densely cracked solidified basalt the dispersion curves are inverted for a velocity model beneath the arrays assuming those dispersions represent the fundamental modes of rayleigh and love waves

crustal evolution of archean rocks in the kakagi lake area wabigoon subprovince ontario as interpreted from high precision u pb geochronology the evolution of the archean volcanic plutonic complex in the kakagi lake area occurred during a time interval of ca 32 ma the earliest age is from analysis of zircon and baddeleyite in a gabbro intruding the lowermost katimiagamak volcanic group an age of 2723 2 1 8 ma on a tonalite gneiss from the interior of the underlying sabaskong batholith is indistinguishable from a previously dated massive border phase of the batholith and shows no evidence for inheritance from an older sialic component an early tonalite phase from the adjacent aulneau batholith is dated at and the latest granodiorite phase is dated at this defines a time span of about 7 ma for intrusion of the bulk of the batholith and indicates that previously dated felsic volcanism from the uppermost sequence above the kakagi lake volcanic group is coeval with late plutonic activity in the aulneau batholith the end of regional deformation in the area is given by the ages of two late tectonic intrusions the heronry lake pluton and

sedimentary and structural evidence for 2 7 ga continental arc oceanic arc collision in the savant sturgeon greenstone belt western superior province canada the western superior province sustained rapid crustal growth in the interval 2 72 2 68 ga through amalgamation of microcontinental crustal blocks and juvenile oceanic terranes recent field isotopic and geophysical surveys provide insight on the nature timing and scale of this accretionary growth however few places offer the rich tectono stratigraphic and structural detail with which to establish accretion of oceanic and continental blocks as does the savant sturgeon area here 3 4 2 8 ga continental crust of the winnipeg river terrane is juxtaposed with 2 775 2 718 ga juvenile oceanic rocks of the western wabigoon terrane across a 2 85 2 75 ga southwest facing continental margin sequence the continental margin was reactivated at 2 715 ga with the establishment of an arc recorded by 2 715 2 70 ga tonalite and associated intermediate volcanic rocks this magmatic activity is interpreted to reflect north and east dipping subduction that led to consumption of a small tract of oceanic crust betwe

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

zircon u pb and lu hf systematics of the major terranes of the western superior craton canada mantle crust interaction and mechanism s of craton formation abstract paleo to neoarchean granitoid gneisses ca 3 30 to 2 49 ga are well preserved in the western superior craton protoliths of these gneisses are mainly i type granitoids characterized by high sr y and la yb ratios and low mg consistent with archean tonalite trondhjemite granodiorites zircons from granitoid gneisses commonly contain three growth phases inherited cores zircon i magmatic rims zircon ii and outer rims that have undergone pb loss zircon iii the 3 12 ga to 2 86 ga zircon i represent early crustal material that was captured in younger zircons zircon ii preserve crustal re working and younger crustal additions that are constrained between 2 85 to 2 72 and 2 69 to 2 65 ga zircon ii contains both positive and negative ehf t values 6 3 to 8 1 with both depleted mantle and older crustal signatures half of the magmatic rims ii are characterized by depleted mantle signatures with positive ehf t values representing juvenile crust forming events whereas the other half are characterized by recycled crustal signatures with negative ehf t values ehf t results show that the north caribou and the island lake terranes and the northern uchi domain are isotopically more enriched than the southern uchi english river wabigoon and winnipeg river terranes suggesting the northern uchi margin represents a major terrane boundary based on mass balance calculations large volumes of juvenile material at circa 3 0 ga mixed with smaller amounts of older crust the vast majority of the granites were derived from a source with about 50 mantle material during the peak crust formation events after 2 8 ga the decline in the volume of felsic magmatism in the later archean is coeval with a reduced supply of both heat and material from depleted mantle sources combined with previously published geochemical geochronological and isotopic data this suggests an evolution in felsic magma sources consistent with crustal thickening

neoarchean evolution of differing convergent margin assemblages in the wabigoon subprovince geochemical and geochronological evidence from the lake of the woods greenstone belt superior province northwestern ontario abstract the neoarchean lake of the woods greenstone belt is subdivided into three lithostratigraphic assemblages a lowermost mafic volcanic assemblage a compositionally diverse predominantly volcanic middle assemblage and a predominantly sedimentary uppermost assemblage the secular evolution and geodynamic settings of these assemblages are constrained with detailed geochronological and geochemical data the lower keewatin is the oldest assemblage with a zircon u pb age of 2738 2 0 ma it consists of mg and fe tholeiitic basalts mg number 30 65 with flat to slightly enriched rare earth elements ree la yb cn 0 9 1 6 elevated large ion lithophile elements lile and undepleted high field strength elements hfse the tholeiites do not appear to have exact modern analogs but do have some similarities to primitive arc tholeiites and back arc basin basalts suggesting an archean destructive margin setting the upper keewatin assemblage disconformably overlies the lower keewatin assemblage it consists of volcanic and sedimentary groups two geochemically distinct volcanic suites are recognized the dominant suite consists of compositionally diverse calc alkalins basalt to rhyolite felsic end members have yielded zircon u pb ages ranging from 2712 to 2723 ma the suite exhibits highly fractionated ree la yb cn 4 35 elevated lile and nb and ta depletion anomalies which are very similar to modern island arc volcanic rocks developed in proximity to continental margins a coeval suite of mafic to ultramafic volcanic rocks consists of mg tholeiite komatiitic basalt and ultramafic komatiite mg numbers 45 80 the suite exhibits depleted lree la yb cn 0 6 1 0 slightly elevated lile and undepleted to slightly enriched hfse suggesting that this geochemically primitive suite was produced by partial melting of a refractory mantle source perhaps as second stage melts of the same mantle source from which the lower keewatin assemblage basalts were previously derived the electrum assemblage unconformably overlies the upper keewatin assemblage in the northern part of the belt it consists of conglomerates sandstones and minor volcanic rocks having detrital ages indicating deposition after 2699 ma the volcanic rocks consists of andesite to rhyolite with shoshonitic to calc alkaline geochemical affinity as indicated by highly fractionated ree la yb cn 12 112 highly enriched lile and pronounced nb ta and ti depletion anomalies samples from the syenitic falcon island pluton appear to be coeval with electrum assemblage volcanics having an u pb isotopic age of 2694 ma and similar but even more alkaline chemistry consisting of highly fractionated lree and lile trace elements with very pronounced nb ta and ti depletion anomalies these late tectonic suites are geochemically similar to modern shoshonites with a continental influence formed in the late stages of a mature island arc or a continental arc setting

nd isotopic evidence for early to late archean 3 4 2 7 ga crustal growth in the western superior province ontario canada abstract new sm nd analyses of archean metavolcanic plutonic gneissic and metasedimentary rocks from sachigo and berens river subprovinces north caribou terrane and winnipeg river and wabigoon subprovinces in conjunction with previously published data are used to trace the crustal evolution of the western superior province wsp from ca 3 4 to 2 7 ga the extensive wsp geochronological database which contains 3 17 2 55 ga plutonic rocks allows the calculation of precise e t nd values and the identification of the main periods of new crustal addition at 3 4 0 1 3 02 2 92 and 2 76 2 69 ga mass balance calculations indicate that the western superior province represents a collage of archean crusts comprising 7 44 and 48 wt of crust created at 3 4 3 0 and 2 7 ga respectively although these calculations depend on the isotopic signatures of the mantle and those of the average crust at different times several important observations can be made 1 the importance of pre 2 7 ga terranes recycled in the 2 7 ga orogen 2 the existence of time intervals of 150 300 ma dominated by intra crustal processes resulting in a large range of crystallization ages u pb zircon ages that do not reflect new additions from the mantle 3 much of the new crustal additions at 2 7 ga were contaminated by crustal material subducted into the source region ttg suites or were contaminated during intrusion into the crust sanukitoids

near surface velocity structure of pacaya volcano guatemala derived from small aperture array analysis of seismic tremor knowledge of the typically complicated near surface structure on volcanoes is critical for determining accurate seismic event locations and seismic source mechanisms associated with precursory and eruptive activity to generate a near surface velocity model for the active cone of pacaya volcano guatemala we recorded seismic tremor and ambient noise with a small aperture array of 11 short period seismometers in january 2011 the diffuse wavefield was investigated using the spatial autocorrelation spac method and we computed rayleigh and love dispersion curves at the array location the phase velocities for rayleigh waves range from 1000 m s at 2 hz to 230 m s at 10 hz those for love waves range from 600 to 250 m s over the same frequency band such low velocities are consistent with the presence of unconsolidated tephra on the surface of the volcano interspersed with lava flows assuming they represent the fundamental modes of rayleigh and love waves we inverted the dispersion curves to produce a shear wave velocity model of the upper 500 m beneath the array online material s wave velocity models obtained from inversion and love and rayleigh wave dispersion curves

can lamprophyres resolve the genetic controversy over mesothermal gold deposits associations between calc alkaline lamprophyres and mesothermal gold deposits archean to tertiary in which the lamprophyres are coeval as well as cospatial with mineralization are increasingly recognized worldwide our suggested hypothesis regards lamprophyres as transporting agents for au from au rich sources in the deep mantle which then undergo extensive crustal interactions generating felsic magmas or releasing their au into metamorphic hydrothermal systems such a model not only may reconcile the conflict between the extant magmatic and metamorphic models for mesothermal deposits but also may resolve the inconclusive relations between gold deposits and felsic porphyry granitoid intrusions because lamprophyres may act as parents to both the gold lamprophyre association implies that exceptionally deep seated magmatism repeatedly accompanied gold mineralization in postcollisional orogenic island arc oblique subduction or graben environments this has important implications for the late stage evolution of mineralized archean greenstone belts in particular and for gold deposit genesis in general

u pb ages constraining structural development of an archean terrane boundary in the lake of the woods area western superior province canada layered gneisses in the winnipeg river subprovince contain magmatic zircon with u pb ages of 3317 9 and 3055 4 ma at tannis lake and 3170 and 3255 5 ma at cedar lake indicating widespread occurrence of mesoarchean crust this is in contrast to the well documented neoarchean age of the western wabigoon subprovince further geochronology using both shrimp sensitive high resolution ion microprobe and id tims isotope dilution thermal ionization mass spectrometry combined with structural observations in the kenora area and lake of the woods greenstone belt show the effects of juxtaposition of these two terranes isoclinally folded gneiss north of the subprovince boundary zone near kenora gives a magmatic age of 2882 2 ma with 3051 6 ma inheritance ages of syntectonic dykes show that asymmetric refolding of these gneisses occurred between 2717 2 and about 2713 1 ma subsequent regional vertical flattening and horizontal extension are dated at 2708 2 ma by syntectonic tonalite sheets t

archean gold relation to granulite formation or felsic intrusions two current models for archean au deposits appeal to granulitization or magmatic processes but new data reveal that neither of these schemes is viable most tonalitic archean granulites are characterized by primary large ion lithophile element lile depletion and so there is no complementary relation to lile enrichment in au deposits nor are k rb k ba k li k cs and th u systematics of granulites and gold deposits complementary published c isotope systematics and c he flux calculations do not support the model of granulitization by influx of mantle c0 2 nor is the total population of 13 c values of au deposits comparable to mantle co 2 or the granulite c reservoir archean tonalite trondhjemite granodiorite ttg magmas are characterized by uniform 87 sr 86 sr whereas the deposits range between 0 701 and 0 720 and average 13 c ranges between 9 and 0 4 with provinciality of sr o and c isotopic signatures moreover fractionated granites trend to normal k rb but higher rb sr and k ba ratios whereas the gold deposits are characterized by main trend or higher k rb and k ba ratios coupled with little cs li or tl enrichment and scattered rb sr ratios many of the deposits postdate the stocks with which they are associated by 20 to 30 m y the variable sr pb c and o isotope systematics but uniform lile trends reflect equilibration of internally or externally derived fluids with compositionally variable crust at low water rock ratios in transpressive accretionary regimes

convergent margin tectonics central wabigoon subprovince superior province canada abstract best known for its neoarchean greenstone granite terranes in the east and west the wabigoon subprovince of the superior province features a central transverse corridor of meso and neoarchean gneissic granitoid and minor supracrustal rocks resembling an eroded intermontane plateau structural analysis and u pb geochronology in the north central wabigoon subprovince reveal a complex history of plutonism supracrustal rock deposition polyphase deformation and amphibolite facies metamorphism between 3075 and 2670 ma the geometric and kinematic character of d 1 and d 2 deformational events recorded in 2890 2718 ma tonalitic gneisses remain cryptic as a result of magmatic and structural d 3 5 overprinting but the early structures are bracketed in age between 2725 and 2713 ma by a polydeformed gneiss and tonalite dyke these events occurred deep within an active continental magmatic arc and correspond in age to a collision between the juvenile wabigoon and continental winnipeg river subprovinces recognized to the west clastic sediments deposited after 2701 ma are the youngest rocks involved in subsequent regional deformation a d 3 event is responsible for rapid burial of supracrustal units to 15 km within warm arc crust and imposition of a regional penetrative s 3 foliation that accommodated some relative uplift prior to 2697 ma the age of a discordant granodiorite dyke this event corresponds to variably preserved steep north trending d 1 structures recognized in adjacent greenstone belts subsequent d 4 ductile deformation defines the map pattern in the deep crustal rocks of the central wabigoon subprovince upright east trending f 4 folds developed synchronously with d 2 dextral transpressive structures that formed throughout the wabigoon subprovince prior to 2698 ma the final d 5 sinistral shearing event occurred during emplacement of mantle derived granodiorites of sanukitoid affinity 2688 ma and crust derived granites 2685 ma this event appears to have triggered rapid cooling reflected in 2680 2670 ma titanite dates and late brittle increments of displacement

differential response of u pb systems in coexisting accessory minerals winnipeg river subprovince canadian shield implications for archean crustal growth and stabilization the u pb isotopic systems of zircon monazite titanite and some apatite and the pb isotopic composition of k feldspar have been investigated in three areas of the winnipeg river subprovince wrs of the superior province canada in order to define the timing of magmatic and metamorphic processes in this archean gneissic granitoid terrain

a large magmatic sill complex beneath the toba caldera an understanding of the formation of large magmatic reservoirs is a key issue for the evaluation of possible strong volcanic eruptions in the future we estimated the size and level of maturity of one of the largest volcanic reservoirs based on radial seismic anisotropy we used ambient noise seismic tomography below the toba caldera in northern sumatra to observe the anisotropy that we interpret as the expression of a fine scale layering caused by the presence of many partially molten sills in the crust below 7 kilometers this result demonstrates that the magmatic reservoirs of present non eroded supervolcanoes can be formed as large sill complexes and supports the concept of the long term incremental evolution of magma bodies that lead to the largest volcanic eruptions

oxygen isotope ratios of archean plutonic zircons from granite greenstone belts of the superior province indicator of magmatic source zircons commonly preserve primary magmatic oxygen isotope ratios even through high grade metamorphic events unlike quartz which more readily loses its primary 18o value by subsolidus exchange intrusive bodies from the superior province canada have an average 18o zircon of 5 8 0 6 n 59 rocks those from granite greenstone belts have an average 18o zrc 5 8 0 6 n 55 in contrast to those from metasedimentary belts that average 18o zrc 6 7 0 2 n 4 the 18o zircon values from granite greenstone belts indicate a maximum allowable input of 14 supracrustal high 18o material into archean magmas of the superior province relative to mantle 18o values igneous bodies of the superior province have been separated into two groups based on geochemistry unenriched plutons and sanukitoids magmatic oxygen isotope ratios inferred from these zircons indicate up to a subtle but significant division of 1 between the two geochemical sets of rocks this distinction is apparent only in the 18o zrc and not in more commonly analyzed less refractory minerals such as quartz and feldspar oxygen isotope data correlate with geochemical modeling of sanukitoids the average 18o zrc for sanukitoids is 6 4 0 2 in comparison to 5 5 0 4 for unenriched plutons there is almost no overlap in values the elevation of sanukitoid 18o zrc indicates input from a high 18o source such as fluids from the subducting oceanic crust melts of subducted sediments or continental crust all of the plutons analyzed in this study have been dated by u pb zircon techniques and the combination of u pb ages and 18o zrc indicates little variability of 18o versus age during archean plutonism in the superior province therefore recycling of sediments and other high 18o sources was not a dominant process during crustal growth from 3003 to 2670 ma in the superior province

geochronological constraints on the timing of magmatism deformation and gold mineralization in the red lake greenstone belt northwestern ontario the paper presents u pb ages on zircon baddeleyite titanite rutile and monazite from volcanic and plutonic rocks of the red lake greenstone belt in the northern superior province the purpose of the study was to refine a previously outlined time frame for the volcanic evolution of the belt define the time of major plutonism and deformation and constrain the age of formation of gold deposits volcanism spanned at least 270 ma between 3000 and 2730 ma new ages of 2989 3 and 2894 2 ma for units of a lower volcanic sequence and and 2744 1 ma for units of an upper volcanic sequence corroborate and refine the previously established relationships local gabbroic and felsic intrusions cutting through the lower sequence yield ages of 2870 15 and respectively volcanism was succeeded by major plutonism deformation alteration and metamorphism between about 2730 and 2700 ma these processes were interrelated and progressed as a relatively continuous sequence of events accentuated by major activity d

seabed property estimation from ambient noise recordings part i compliance and scholte wave phase velocity measurements the ability to derive a near surface shear velocity profile from ambient noise records is useful for seismic applications such as shear wave statics estimation and geohazard prediction measurements of seafloor compliance and scholte wave velocity and amplitude are all related to the near surface shear velocity profile i analyzed a data set of 33 minutes of continuous noise records recorded by an ocean bottom cable deployed in 273 m deep water for seafloor compliance and scholte waves i failed to observe seafloor compliance because of limitations in the record length i have detected scholte waves on the inline and vertical component geophones and love waves on the crossline component using f k spectra both the scholte and love wave phase velocities can be explained by a simple 1d isotropic near surface model the scholte waves may have been excited by acoustic energy from the recording vessel while no satisfactory excitation mechanism has been found for the love waves

a special issue devoted to abitibi ore deposits in a modern context preface the abitibi greenstone belt which is part of the larger abitibi subprovince in the superior province of the canadian shield e g card and ciesielski 1986 is the largest known archcan greenstonegranite terrane 300 km n s x 400 450 km mineral production and reserves are significant particularly in relation to volcanogenic massive sulfide deposits and structurally controlled archcan goldbearing quartz vein systems the term au quartz vein being used in the sense of lindgren 1933 e g the gold quartz veins of ontario p 662669 volcanogenie massive sulfide production and reserves to 1989 1990 total 424 million metric tons

zircon u pb ages from the kakagi lake area wabigoon subprovince northwest ontario five rocks have been dated from the kakagi lake area of the wabigoon subprovince by means of u pb analysis of zircons using the techniques of air abrasion and high gradient magnetic separation zi

u pb age and nd isotopic evidence for archean terrane development and crustal recycling in the south central wabigoon subprovince canada u pb geochronology is presented for 19 volcanic and associated plutonic rocks from nine greenstone belts within the southern part of the central wabigoon subprovince cws western superior province data indicate that early felsic volcanism 3 014 2 999 ma was coeval with emplacement of the marmion batholith at 3 002 ma this was followed by periods of mafic volcanism with minor felsic and komatiitic compositions between 2 963 and 2 898 ma across the south cws plume driven mafic and komatiitic volcanism occurred in the lumby lake and lac des mille lacs belts at ca 2 828 ma eruption of komatiitic tuffs in the steep rock belt at 2 780 ma was proceeded by more widespread mafic and minor intermediate to felsic volcanism at 2 729 2 726 ma zircon inheritance and nd isotope data indicate that the cws south of the garden lake belt comprises a juvenile 3 0 ga terrane the marmion terrane subsequent magmatism was ensialic occurring in a continental although submerged setting recycling of the 3 0 ga marmion basement during successive volcanic events although somewhat cryptic was widespread and represents a significant archean process 2 726 ma rhyolite in the garden lake belt has a 3 22 ga nd model age and lies at the southern boundary of the distinct north cws which has a 3 3 3 2 ga crustal prehistory the north cws may represent a heavily reworked extension of the adjacent 3 3 ga winnipeg river subprovince and was probably separate from the marmion terrane at 3 0 ga these two recycled terranes differ significantly from the juvenile neoarchean volcanic dominated western wabigoon although the boundaries between these terranes are in most places cryptic they may indeed represent suture zones which were fundamental to the development of the wabigoon subprovince

shallow seismicity triggered seismicity and ambient noise tomography at the long dormant uturuncu volcano bolivia using a network of 15 seismometers around the inflating uturuncu volcano from april 2009 to 2010 we find an average rate of about three local volcano tectonic earthquakes per day and swarms of 5 60 events a few times per month with local magnitudes ranging from 1 2 to 3 7 the earthquake depths are near sea level more than 10 km above the geodetically inferred inflation source and the altiplano puna magma body the mw 8 8 maule earthquake on 27 february 2010 triggered hundreds of earthquakes at uturuncu with the onset of the love and rayleigh waves and again with the passage of the x2 x3 overtone phases of rayleigh waves this is one of the first incidences in which triggering has been observed from multiple surface wave trains the earthquakes are oriented nw se similar to the regional faults and lineaments the b value of the catalog is 0 49 consistent with a tectonic origin of the earthquakes we perform ambient noise tomography using love wave cross correlations to image a low velocity zone at 1 9 to 3 9 km depth below the surface centered slightly north of the summit the low velocities are perhaps related to the hydrothermal system and the low velocity zone is spatially correlated with earthquake locations the earthquake rate appears to vary with time a seismic deployment from 1996 to 1997 reveals 1 5 earthquakes per day whereas 60 events day were seen during 5 days using one seismometer in 2003 however differences in analysis methods and magnitudes of completeness do not allow direct comparison of these seismicity rates the rate of seismic activity at uturuncu is higher than at other well monitored inflating volcanoes during periods of repose the frequent swarms and triggered earthquakes suggest the hydrothermal system is metastable

space age geodesy the nasa crustal dynamics project the nasa crustal dynamics project has deployed satellite laser ranging slr systems and very long baseline interferometer vlbi systems for measurements of global and regional crustal motions and earth rotation parameters in 1984 the several year buildup of the network approached full capability during 1984 the slr systems measured 142 unique baselines between stations for the purpose of determining plate motion between the north american pacific south american nazca australian and eurasian plates 31 baselines for internal deformation of the same plates and 9 baselines for regional deformation in the area of the western north american plate boundary during 1984 the vlbi systems measured 24 baselines for plate motion between the north american pacific and eurasian plates 37 baselines for internal deformation of the same plates and 101 baselines for regional deformation in the area of the western north american plate boundary both the slr and vlbi stations operated throughout the september 1983 to october 1984 international merit campaign of measurements of the earth s polar motion and changes in rotation rate nasa s future plans are to continue these measurements through at least 1990 and to initiate a joint nasa european slr measurement campaign for determining regional crustal deformation in the mediterranean area

the genesis and tectonic control on archaean gold deposits of the western australian shield a metamorphic replacement model abstract gold deposits occur in greenstone belts world wide and contribute to anomalously high gold production from archaean terranes as in other cratons archaean gold mineralization of western australia represents a complex array of deposit styles despite this most deposits are clearly epigenetic and large deposits have a number of features in common including their strong structural controls distinctive wallrock alteration fe sulphide k mica albite ca mg fe carbonates consistent metal associations au ag as sb w b low base metals commonly fe rich host rocks great depth extension and lack of appreciable vertical zonation these shared characteristics combined with their ubiquitous occurrence indicate that archaean gold deposits had a common origin related to the tectonic evolution of greenstone belts auriferous hydrothermal systems were broadly synchronous with regional metamorphism and emplacement of synkinematic granitoids and felsic porphyry intrusions although these gold systems involved low salinity lowdensity reduced near neutral h 2 o co 2 fluids carrying gold as reduced sulphur complexes the origin of the fluids is equivocal most timing evidence and stable isotope data cannot distinguish metamorphic from magmatic granitoid or felsic porphyry orggins but the lack of consistent spatial relationships between specific volumetrically significant intrusive phases and large gold deposits in a number of cratons strongly favours metamorphic derivation of fluids the metamorphic replacement model for gold mineralization involves devolatilization of the lower portions of the greenstone pile with high geothermal gradients inhibiting significant melting co 2 possibly formed by the decarbonation of early alteration related to mantle degassing along crustal scale synbasinal fault zones auriferous fluids were channelled along greenstone scale faults in part developed during reactivation of crustal scale faults in a strike slip regime gold deposition occurred largely under greenschist facies conditions about 300 400 c 1 2 kb in response to decreasing gold solubility with declining temperature however a major control on gold deposition was fluid wallrock interaction many large deposits formed by sulphidation of fe rich host rocks with synchronous deposition of fe sulphides and gold however the variable nature of gold depositing reactions including lowering of fo 2 and ph allowed a multitude of small and some large deposits to form wherever that fluid circulation occurred in consequence several of the relatively small deposits currently worked from open pit are hosted by ultramafic and felsic rocks there are few constraints on the source of components au s k co 2 added to gold deposits but even giant deposits such as the golden mile kalgoorlie could have formed from a realistic greenstone source volume ca 8 8 5 km convective circulation of fluids could have contributed to the generation of high fluid rock ratios on the regional scale the markedly heterogeneous distribution of large gold deposits gold productivity and host rocks to deposits can be accommodated by the metamorphic replacement model the most favourable conditions for development of auriferous hydrothermal systems operated in younger ca 2 7 0 1 ga rift phase greenstones where greatest extension and crustal thinning produced high geothermal gradients crustal scale synbasinal faults and rapid extrusion and burial of volcanics including abundant komatiites iron rich tholeiitic basalts and dolerites were preferred host rocks for large gold deposits the least favourable conditions existed in older ca 3 5 3 4 ga platformphase greenstones where gentle sagging on submerged continental crust produced eruption of mainly mafic volcanics with few komatiites commonly in very shallow water environments this allowed intense synvolcanic alteration of both gold source rocks and potential host rocks the generally smaller gold deposits formed mainly in ultramafic or greywacke hosts younger ca 3 0 ga platform phase greenstones appear intermediate in nature but unlike other greenstones have significant epigenetic gold deposits in originally oxide facies bif which were deposited on relatively deep water platforms similar controls appear to exist on a world scale with gold mineralization peaking at ca 2 7 0 1 ga in response to development of major rift zones in thickened relatively mature continental crust interestingly the giant witwatersrand goldfield formed at about the same time

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

retrieval of local surface wave velocities from traffic noise an example from the la barge basin wyoming abstract in regions where active source seismic exploration is constrained by limitations of energy penetration and recovery cost and logistical concerns or regulatory restrictions analysis of natural source seismic data may provide an alternative in this study we investigate the feasibility of using locally generated seismic noise in the 2 6 hz band to obtain a subsurface model via interferometric analysis we apply this technique to three component data recorded during the la barge passive seismic experiment a local deployment in south western wyoming that recorded continuous seismic data between november 2008 and june 2009 we find traffic noise from a nearby state road to be the dominant source of surface waves recorded on the array and observe surface wave arrivals associated with this source up to distances of 5 kms the orientation of the road with respect to the deployment ensures a large number of stationary points leading to clear observations on both in line and cross line virtual source receiver pairs this results in a large number of usable interferograms which in turn enables the application of standard active source processing methods like signal processing common offset stacking and traveltime inversion we investigate the dependency of the interferograms on the amount of data on a range of processing parameters and on the choice of the interferometry algorithm the obtained interferograms exhibit a high signal to noise ratio on all three components rotation of the horizontal components to the radial transverse direction facilitates the separation of rayleigh and love waves though the narrow frequency spectrum of the surface waves prevents the inversion for depth dependent shear wave velocities we are able to map the arrival times of the surface waves to laterally varying group and phase velocities for both rayleigh and love waves our results correlate well with the known geological structure we outline a scheme for obtaining localized surface wave velocities from local noise sources and show how the processing of passive data benefits from a combination with well established exploration seismology methods we highlight the differences with interferometry applied to crustal scale data and conclude with recommendations for similar deployments

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

timing between granitoid emplacement and associated gold mineralization examples from the ca 2 7 ga harare shamva greenstone belt northern zimbabwe structurally controlled late archaean gold mineralizations associated with felsic plutons in the harare shamva greenstone belt zimbabwe are synchronous with the emplacement of their hosts the ages of these mineralizations are identical to those reported from other mesothermal gold deposits elsewhere in the zimbabwe craton the pb and nd isotopic signatures of the host plutons are compatible with a direct mantle or a short crustal residence period for the protoliths to the host intrusions the coincidence of the pb isotope data from ore minerals with the whole rock trends errorchrons of their host intrusives strongly suggests that the gold could have a magmatic rather than a metamorphic source there is no evidence from the pb isotopes of significant involvement of older basement in the genesis of gold deposits associated with felsic intrusions in the harare shamva greenstone belt on a craton wide scale the time frame around 2 65 ga represents a period of significant crustal growth through additi

archean gold relation to granulite formation and redox zoning in the crust the archean was the principal period for gold mineralization these rocks compose 12 of the exposed crust but have produced more than half of the world9s gold most major lode deposits formed at 2 7 0 2 ga this corresponds to the principal time of crustal thickening and stabilization an essential part of which was formation of granulite the anhydrous refractory base for the crust upward streaming of mantle co 2 along shear zones in the lower crust is one means for dehydrating amphibolite to form granulite and is accompanied by removal of large ion lithophile lil elements to higher crustal levels archean lode gold deposits were formed along major shear zones at intermediate crustal depths they are enclosed by zones of co 2 metasomatism many of them kilometres in extent 13 c data indicate that the co 2 is juvenile some major archean deposits have been shown to have formed from relatively oxidized hydrothermal fluids co 2 streaming with lil element depletion could only have occurred under relatively oxidized conditions that permitted a free co 2 vapor to exist in the lower crust such conditions would also have favored dissolution of gold and associated sulfide and their transfer to the mid crust in a co 2 h 2 o fluid the h 2 o coming from dehydration of amphibolite

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

structure of the los angeles basin from ambient noise and receiver functions a velocity v s and structure model is derived for the los angeles basin california based on ambient noise surface wave and receiver function analysis using data from a low cost short duration dense broad band survey lassie deployed across the basin the shear wave velocities show lateral variations at the compton los alamitos and the whittier faults the basement beneath the puente hills san gabriel valley shows an unusually high velocity 4 0 km s 1 and indicates the presence of schist the structure of the model shows that the basin is a maximum of 8 km deep along the profile and that the moho rises to a depth of 17 km under the basin the basin has a stretch factor of 2 6 in the centre grading to 1 3 at the edges and is in approximate isostatic equilibrium

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

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

green s functions extraction and surface wave tomography from microseisms in southern california we use crosscorrelations of seismic noise data from 151 stations in southern california to extract the group velocities of surface waves between the station pairs for the purpose of determining the surface wave velocity structure we developed an automated procedure for estimating the green s functions and subsequent tomographic inversion from the 11 325 station pairs based on the characteristics of the noise field we eliminate specific events by a procedure that does not introduce any spurious spectral distortion in the band of interest 0 05 0 2 hz further we only used the emerging arrival structure above a threshold signal to noise ratio the result is that mostly station pairs with their axes oriented toward the sea are used consistent with the noise having a microseism origin finally it is the time derivative of the correlation function that is actually related to the green s function the emergence of the time domain green s function is proportional to the square root of the recording time and inversely proportional to the square root of the distance between stations the tomographic inversion yields a surface wave velocity map that compares favorably with more conventional and elaborate experimental procedures

evolution of an archean subprovince boundary a sedimentological and structural study of part of the wabigoon quetico boundary in northern ontario a prograded clastic wedge represented by formation to group scale units of metasedimentary strata in the beardmore geraldton terrane developed in a transitional zone at the southern margin of a