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

aeromagnetic identification and modeling of mafic ultramafic complexes in the huangshan turaergen ni cu metallogenic belt in nw china magmatic and metallogenic implications abstract aeromagnetic and bouguer gravity data are conducted to analyze the geological and metallogenic features of the huangshan turaergen ni cu polymetallic metallogenic belt in the gobi desert in northwest china the ni cu deposits are generally located to the south of the high amplitude gravity and magnetic gradient belt that marks the kanggurtag fault zone to analyze the prospecting potential of the complexes in the metallogenic belt the model depths and shapes of the complexes are calculated via euler deconvolution combined with three dimensional 3d inversion the buried complexes occur at relatively shallow depths and have ne orientations we use a method of lithology recognition based on 3d inversion modeling which enables the definition of two additional buried ultramafic complexes namely the west yaziquan wy and north yaziquan ny complexes our results reveal that these complexes have ring like shapes similar to most of the other known mafic ultramafic complexes in this metallogenic belt the upward continued bouguer gravity and aeromagnetic data reveal highly consistent gravity and magnetic anomalies which are explained as a regional magma chamber that is structurally controlled by the kanggurtag fault zone in order to determine the scale and shape of this regional magma chamber 3d gravity and magnetic inversion was carried out for the entire region according to models of the complexes and pluton the source driving mechanism and evolution of the regional magma are analyzed and the areas with mineralization and exploration potential are also discussed this work can aid in the exploration of additional ni cu deposits in eastern tianshan

changes in sulfides and platinum group minerals with the degree of alteration in the roby twilight and high grade zones of the lac des iles complex ontario canada the lac des iles complex hosts pd deposits with unusually high pd pt and pd ir ratios these high ratios have been attributed to the introduction of pd by late magmatic hydrothermal fluids the presence of hydrous silicates and low temperature sulfide mineral assemblages has been advanced as evidence for fluid overprint this idea has been investigated by documenting the change in silicate sulfide and platinum group mineralogy and texture in samples from the deposit ranging from fresh gabbronorite to extensively altered chlorite actinolite schist in addition whole rock analysis combined with laser ablation analysis of the sulfides was used to determine which phase controlled each of the pge in fresh gabbronorite the sulfide assemblage is igneous pyrrhotite pentlandite chalcopyrite and pd is present mainly in pentlandite and kotulskite pdte inclusions associated with the sulfide minerals all other pge except pt are present in solid solution in pyrrhotite and pentlandite platinum is present as sperrylite ptas2 and montcheite ptte2 inclusions associated with the sulfide minerals these observations suggest that the pge in the fresh gabbronorite were all collected by magmatic sulfide liquid in the chlorite actinolite schist the sulfide assemblage is a low temperature assemblage consisting of chalcopyrite pyrite millerite a minor amount of palladium is present in millerite but most is present as bismuth rich kotulskite and pd arsenides both of which are associated with hydrous silicate all other pge except pt are hosted by pyrite a minor amount of pt is present in pyrite but most is found as sperrylite and montcheite associated with hydrous silicate minerals the pyrite could have formed by fe loss from pyrrhotite resulting in the pyrite inheriting os ir ru and rh and fe loss from pentlandite to form millerite resulting in the millerite inheriting some pd the pge concentrations of the whole rock show there is no direct correlation between the sulfide assemblage the degree of alteration of the silicate minerals and ore grade thus although fluids have clearly altered the sulfide silicate and platinum group mineralogy and their textures it is not clear that these fluids have changed the pge content of the rocks

can we probe the conductivity of the lithosphere and upper mantle using satellite tidal magnetic signals thesis s m massachusetts institute of technology department of earth atmospheric and planetary sciences 2015

equatorial vertical drift modulation by the lunar and solar semidiurnal tides during the 2013 sudden stratospheric warming during the 2013 stratospheric sudden warming ssw period the jicamarca unattended long term investigations of the ionosphere and atmosphere julia radar at jicarmarca peru observed low latitude vertical drift modulation with lows of 0 12 m s daytime maximum drifts between 6 13 and 22 25 january and enhanced drifts up to 43 m s between 15 snd 19 january the ncar thermosphere ionosphere mesosphere electrodynamics general circulation model reproduces the prevailing vertical drift feature and is used to examine possible causes the simulations indicate that the modulation of the vertical drift is generated by the beating of the semidiurnal solar sw2 and lunar m2 tides during the ssw period the beating is observable since the magnitudes of lunar and solar semidiurnal tidal amplitudes are comparable the theoretical beating frequency between sw2 and m2 is 1 15 13 day which may be modified due to phase changes this study highlights the importance of the lunar tide during ssw periods and indicates that the equatorial vertical drift modulation should be observable at other longitudes as well

electrical conductivity of the earth s mantle from the first swarm magnetic field measurements we present a 1 d electrical conductivity profile of the earth s mantle down to 2000 km derived from l1b swarm satellite magnetic field measurements from november 2013 to september 2014 we first derive a model for the main magnetic field correct the data for a lithospheric field model and additionally select the data to reduce the contributions of the ionospheric field we then model the primary and induced magnetospheric fields for periods between 2 and 256 days and perform a bayesian inversion to obtain the probability density function for the electrical conductivity as function of depth the conductivity increases by 3 orders of magnitude in the 400 900 km depth range assuming a pyrolitic mantle composition this profile is interpreted in terms of temperature variations leading to a temperature gradient in the lower mantle that is close to adiabatic

geochronology petrology and geochemistry of the beiligaimiao magmatic sulfide deposit in a paleozoic active continental margin north china abstract the beiligaimiao magmatic ni cu sulfide deposit is located in the northern rim of the north china block which was an active continental margin related to the southward subduction of the paleo asian oceanic plate to the north in the paleozoic this deposit has never been studied before but is an excellent example of sulfide mineralization in arc settings that have been commonly overlooked by exploration geologists worldwide sulfide mineralization in the deposit is hosted in a mafic ultramafic complex that consists of a small ultramafic body surrounded by an older and much larger gabbroic intrusion disseminated sulfide zones are present in both intrusive bodies but only those close to the surface within the ultramafic body have been mined in the past the sulfide mineralized ultramafic body is composed of olivine websterite and orthopyroxenite with a gradational contact between them sims u pb dating of zircon crystals from a large olivine websterite sample yields a crystallization age of 269 4 2 1 ma which is 25 ma younger than the erbutu subduction related magmatic ni cu sulfide deposit that occurs 50 km to the north orthopyroxene crystals in the beiligaimiao ultramafic rocks have mg 100 mg mg fe molar of 77 78 significantly lower than those in the ultramafic rocks of the erbutu deposit olivine crystals in the beiligaimiao ultramafic rocks have forsterite fo contents from 72 to 75 mol which are also significantly lower than those in the ultramafic rocks of the erbutu deposit fo 86 88 mol the mineral chemical data indicate a more fractionated parental magma for the former ca depletion in olivine i e 34 s values of sulfide separates from the beiligaimiao deposit are 1 7 to 2 5 significantly lower than those for the erbutu deposit but still slightly higher than the morb value 1 5 to 0 5 olivine websterites in the beiligaimiao deposit have e nd from 8 9 to 9 5 and 87 sr 86 sr i close to 0 7075 which are similar to those of an enriched lithospheric mantle an orthopyroxenite sample from the deposit has much lower e nd 12 6 coupled with much higher 87 sr 86 sr i ratio 0 7132 indicating 25 crustal contamination the sr nd s isotope data support the premise that both crustal contamination and addition of crustal sulfur played a role in triggering sulfur saturation in the parental magma of the beiligaimiao deposit since the immediate country rocks are exclusively gabbros these processes likely took place at depth the close temporal and spatial association of the beiligaimiao and erbutu deposits points to the possibility that more permian arc type magmatic sulfide deposits are yet to be discovered in the region

a regional perspective of the quetico metasedimentary belt superior province canada alternating greenstone granite and metasedimentary gneiss belts are a first order tectonic feature of the southern superior province the tectonic development of the quetico metasedimentary belt is reviewed with regard to depositional structural and metamorphic plutonic history over its 1200 km length the belt consists of marginal metasedimentary schists of turbiditic origin and interior metasedimentary migmatite and peraluminous leucogranite polyphase deformation has resulted in a steep easterly striking foliation and regional gently east plunging stretching lineation metamorphic grade varies in a low p facies series from greenschist at the belt margins to upper amphibolite and local granulite in the central migmatite intrusive granite zone mineral assemblages in the central zone yield estimates of metamorphic pressure that increase systematically eastward over 800 km from about 250 mpa 2 5 kbar near the canada united states border to 600 mpa 6 kbar in granulites adjacent to the kapuskasi

stratigraphy and petrology of the mulcahy lake layered gabbro an archean intrusion in the wabigoon subprovince ontario

tidal signals in ocean bottom magnetic measurements of the northwestern pacific observation versus prediction summary motional induction in the ocean by tides has long been observed by both land and satellite measurements of magnetic fields while these signals are weak 10 nt when compared to the main magnetic field their persistent nature makes them important for consideration during geomagnetic field modelling previous studies have reported several discrepancies between observations and numerical predictions of the tidal magnetic signals and those studies were inconclusive of the source of the error we address this issue by 1 analysing magnetometer data from ocean bottom stations where the low noise and high signal environment is most suitable for detecting the weak tidal magnetic signals 2 by numerically predicting the magnetic field with a spatial resolution that is 16 times higher than the previous studies and 3 by using four different models of upper mantle conductivity we use vector magnetic data from six ocean bottom electromagnetic obem stations located in the northwestern pacific ocean the obem tidal amplitudes were derived using an iteratively re weighted leastsquares irls method and by limiting the analysis of lunar semidiurnal m2 lunar elliptic semidinurnal n2 anddiurnal o1 tidalmodestothenight time usinga3 delectromagnetic induction solver and the tpx07 2 tidal model we predict the tidal magnetic signal we use earth models with non uniform oceans and four 1 d mantle sections underneath taken from kuvshinov and olsen shimizu et al and baba et al to compare the effect of upper mantle conductivity we find that in general the predictions and observations match within 10 70percent across all the stations for each of the tidal modes the median normalized percent difference npd between observed and predicted amplitudes for the tidal modes m2 n2 and o1were15percent 47percentand98percent respectively forallthestationsandmodels at the majority of stations and for each of the tidal modes the higher resolution 0 25 0 25 modelling gave amplitudes consistently closer to the observations than the lower resolution 1 1 modelling the difference in lithospheric resistance east and west of the izu bonin trench system seems to be affecting the model response and observations in the o1 tidal mode this response is not seen in the m2 and n2 modes thereby indicating that the o1 mode is more sensitive to lithospheric resistance

the gravina sequence remnants of a mid mesozoic oceanic arc in southern southeast alaska fragments of upper jurassic to lower cretaceous volcanic and basinal strata constitute the gravina belt in southeast alaska in the ketchikan area the gravina belt is made up of two lithotectonic units the lower unit consists of coarse marine pyroclastic and volcaniclastic strata mafic flows breccia and fine grained tuff which are locally intruded by hypabyssal bodies of diorite and quartz diorite the volcanic rocks are characterized by tholeiitic arc basalts lack felsic volcanic strata and overlie upper triassic and older strata of the alexander terrane augite and or hornblende bearing porphyritic rocks are common and locally intrude the alexander terrane basement where they are thought to represent the intrusive equivalents of lavas within the section age constraints for the volcanic unit based on structural and stratigraphic relations with adjacent units are late middle to late jurassic the gravina belt upper unit consists of fine to coarse grained turbidites and related conglomeratic channel fill deposits the basinal rocks unconformably overlie permian and triassic rocks of the taku terrane and remnants of the lower volcanic part of the gravina sequence which overlie the alexander terrane the conglomerate units contain mostly volcanic and plutonic lithic clasts some of which yield pb u zircon ages of 154 158 ma the predominance of pyroclastic deposits interbedded with massive flows tuff breccia and argillaceous turbidites and the lithologic and chemical composition of the volcanic rocks indicate a submarine volcanic arc setting for the gravina sequence the basinal pyroclastic rocks are inferred to have been shed from submarine stratovolcanos during the late jurassic epiclastic rocks were deposited as submarine fans derived in part from erosion of a magmatic arc the presence of fine grained tuffaceous turbidites implies ongoing but distant volcanism the pyroclastic and volcaniclastic rocks represent remnants of a late jurassic oceanic arc constructed on a composite basement consisting of the alexander and taku terranes the strata accumulated in an intra arc basin on the eastern edge of the alexander terrane the volcanic and basinal rocks were deformed during a major mid cretaceous intra arc contractional event in conjunction with the emplacement of a distinctly younger arc related plutonic suite

end permian to mid triassic termination of the accretionary processes of the southern altaids implications for the geodynamic evolution phanerozoic continental growth and metallogeny of central asia the altaids is one of the largest accretionary orogenic collages in the world with the highest rate of phanerozoic continental growth and significant metallogenic importance it is widely accepted that subduction related orogenesis of the altaids started in the late precambrian and gradually migrated southward present coordinates however it is uncertain when and how the building of the altaids was finally completed based on structural geology geochemical geochronological and paleomagnetic data this paper presents late paleozoic to early mesozoic accretionary tectonics of two key areas north xinjiang in the west and inner mongolia in the east together with neighboring mongolia the late paleozoic tectonics of north xinjiang and adjacent areas were characterized by continuous southward accretion along the wide southern active margin of siberia and its final amalgamation with the passive margin of tarim which may have lasted to the end permian to early mid triassic in contrast in inner mongolia and adjacent areas two wide accretionary wedges developed along the southern active margin of siberia and the northern active margin of the north china craton which may have lasted to the mid triassic the final products of the long lived accretionary processes in the southern altaids include late paleozoic to permian arcs late paleozoic to mid triassic accretionary wedges composed of radiolarian cherts pillow lavas and ophiolitic fragments and high pressure ultrahigh pressure metamorphic rocks permian alaskan type zoned mafic ultramafic complexes intruded along some major faults of the tien shan we define a new tarim suture zone immediately north of the tarim craton that is probably now buried below the tien shan as a result of northward subduction of the tarim block in the cenozoic the docking of the tarim and north china cratons against the southern active margin of siberia in the end permian to mid triassic resulted in the final closure of the paleoasian ocean and terminated the accretionary orogenesis of the southern altaids in this part of central asia this complex geodynamic evolution led to formation of giant metal deposits in central asia and to substantial continental growth

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

petrological geochemical and geochronological constraints on the origin of the xiadong ural alaskan type complex in nw china and tectonic implication for the evolution of southern central asian orogenic belt abstract the xiadong mafic ultramafic complex is located in the central tianshan terrane the southern part of the central asian orogenic belt it is composed of dunite hornblende clinopyroxenite hornblendite and hornblende gabbro several dykes of hornblendite hornblende gabbro and gabbroic diorite cut the main body these rocks are characterized by adcumulate textures the dunites contain high fo 92 3 96 6 olivines with rare orthopyroxene and plagioclase hornblende chromite and magnetite are common phases in all of the rock types geochemically the rocks of the xiadong complex display high mgo contents and extremely low trace element abundances although the rocks of the main body show higher mgo contents and lower trace element abundance compared to the dykes both are characterized by flat ree patterns and enrichment of lile relative to hsfe these petrological mineralogical and geochemical features indicate that the xiadong complex is a typical ural alaskan type complex the cross cutting and intrusive relationships of the rock units and their distinct geochemical features suggest that the main body represents a different pulse from the intrusive dyke the positive whole rock e nd t values together with variable 87 sr 86 sr i ratios show a depleted mantle source metasomatized by subduction related material zircon u pb dating on one hornblende gabbro from the main body of the complex yields a u pb 206 pb 238 u age of 479 ma and zircons from three samples of the dykes yield ages of 477 379 and 313 ma all the zircons have positive e hf t and slightly higher 18 o than normal mantle and their hf o isotopic values are correlated to their ages the older samples are comparable to those from the permian mafic ultramafic complexes in the beishan terrane which were derived from a mantle source metasomatized by subduction of the south tianshan ocean while the younger samples are similar to those from the paleozoic complexes in the eastern tianshan which record the subduction features of the junggar ocean these results suggest that the central tianshan was a continental arc from at least the ordovician to the carboniferous the lithospheric mantle beneath the central tianshan was depleted in sr nd hf isotopic compositions and was metasomatized by melts and or fluids from the subduction of the south tianshan and junggar oceans in paleozoic the formation of the xiadong ural alaskan type complex was the product of arc magmatism via high degree melting of the lithospheric mantle beneath the southern central asian orogenic belt

petrogenesis of the magmatic complex at mount ascutney vermont usa the ascutney mountain complex of eastern vermont usa is a composite epizonal pluton of genetically related gabbro to granite intrusives nd isotopic data are reported for mafic rocks granites and nearby country rock the parental mafic magma producing the complex 122 m y ago had 87sr 86sr 0 7039 143nd 144nd 0 512678 nd 3 8 and 18o 6 1 indicating a mantle source with time integrated lithophile element depletion uniform initial radiogenic isotope ratios for granites which are undistinguishable from those for the most primitive gabbro suggest that the granite magma evolved from the mafic magma without crustal contamination and that the increase in 18o to about 7 8 is the result of fractional crystallization mafic rocks show a large range in initial 143nd 144nd ratio from about 0 51267 to 0 51236 nd 3 7 to 2 5 which is correlated with elevated 87sr 86sr ratios and 18o these data substantiate the production of mafic lithologies by fractional crystallization of the parental magma accompanied by assimilation of up to about 50 crust the local country rocks include gneiss and schist and assimilation involved representatives of both rock types the isotopic and chemical relationships preclude derivation from a single batch of magma undergoing contamination and indicate that a large magma body at depth evolved largely by fractionation with batches of melt issued from this chamber being variably contaminated at higher levels or at the level of emplacement

sm nd and rb sr isotope systematics of an archean anorthosite and related rocks from the superior province of the canadian shield sm nd and rb sr isotopic data for the bad vermilion lake anorthosite complex bvl in the rainy lake area of the superior province of northwestern ontario show that direct ages of archean anorthosites can be obtained with these isotopic systems despite the effects of low grade metamorphism there is sufficient spread in sm nd between plagioclase megacrysts and coexisting mafic groundmass to allow the determination of reasonably precise internal sm nd isochrons anorthosite samples from bvl show an unusually large range in lil concentrations such that there is sufficient spread in rb sr for a whole rock isochron 2 69 0 10 ga isr 0 70079 8 this variability may have been caused by rb introduction during hydrothermal alteration and or low grade metamorphism the sm nd isochron for bvl 2747 58 ma end 2 0 1 4 includes data for anorthosite gabbro and metabasalt and is consistent with the consanguineity of these units in the rainy lake area the age is interpreted as the time of crystallization of the anorthosite complex and related mafic plutonics and volcanics visibly altered samples show evidence for disturbance of the sm nd and rb sr isotopic systems in one altered porphyritic dike plagioclase appears to have exchanged light ree with the relatively ree rich basaltic matrix this sample yields an internal sm nd age of 2 16 0 05 ga which may correspond to the time of local heating or represent a partial resetting from a still younger event initial isotopic ratios of nd and sr determined here add to the growing body of data indicating that the superior province is underlain by depleted mantle

spherical harmonic analysis of geomagnetic tides 1964 1965 the mathematical forms chosen for analyses of s q and l by seventeen different authors are reviewed on the basis of the review and on consideration of the ionospheric dynamo theory and the hough function structure of wind velocities in the upper atmosphere a mathematical model is chosen that includes two more terms than the recent analysis by malin 1973 hourly mean values from 130 magnetic observatories for the i q s ys international quiet solar years 1964 and 1965 were prepared in machine readable form and analysed the solar and lunar transient magnetic variations were evaluated together with the lunar elliptic magnetic tide and the seasonal change at one and two cycles per year for all magnetic tides spherical harmonic analyses were made of the phase law tides and the smaller partial tides altogether 94 different spherical harmonic analyses were completed for a total of ten different magnetic tides two of the ten tides are the solar and lunar magnetic tides usually denoted s and l respectively the results are tabulated in a form that distinguishes between eastward and westward moving terms which is suitable for the evaluation of phase angle differences and amplitude ratios between internal and external parts malin s ocean dynamo calculation has been applied to the lunar and lunar elliptic magnetic tides the spherical harmonic coefficients are compared in some detail with those of malin 1973 for years of high sunspot activity the magnetic tidal potential associated with a given atmospheric tidal mode is derived theoretically and used to obtain an estimate of the hough function components of the solar and lunar semi diurnal atmospheric tides at ionospheric levels from the corresponding magnetic tidal potential

lunar tidal winds between 80 and 110 km from uars hrdi wind measurements 1 recent observations and models show the considerable effects of upward propagating lunar atmospheric tides on many aspects of the ionosphere thermosphere system a key aspect of atmosphere ionosphere coupling is the wind field in the ionospheric e region circa 100 150 km where the dynamo generation of electric fields occurs yet global specifications of lunar tidal winds exist only in theoretical predictions although years of satellite observations on atmospheric winds exist with almost global coverage in the present paper we report on quasi global semidiurnal lunar tidal winds up to 115 km from data gathered by the high resolution doppler imager hrdi on board the upper atmosphere research satellite during the early years from 1991 to 1999 the observed lunar semidiurnal tidal winds are consistent with global scale wave model gswm simulations in both amplitude and phase with maximum amplitudes located between about 40 n 60 n around the solstices the peak amplitudes of the lunar tidal winds lie in the 10 15 ms 1range whereas those simulated by gswm lie between 15 and 25 ms 1 the smaller hrdi amplitudes are likely due in part to amplitude suppression in construction of the climatological mean resulting from year to year phase variability in the lunar tide it is also possible that wave dissipation is underestimated to some degree in the gswm

roots of an archean volcanic arc complex the lac des iles area in ontario canada abstract the lac des iles area is located in the wabigoon subprovince an archean granite greenstone terrain in the superior province in ontario canada the area consists of several unmetamorphosed plutons of biotite and hornblende tonalite and mafic and ultramafic intrusions which are emplaced into an older tonalitic gneiss the mafic ultramafic bodies are concentric in shape and consist of periodotite pyroxenite gabbro and hornblende gabbro cumulates and diorite the largest intrusion the lac des iles complex consists of several mafic and ultramafic centers an internal sm nd isochron from the southern ultramafic complex gives an intrusion age of 2736 28 ma mswd 1 5 nd t 1 2 this age is also assumed to be representative of the time of emplacement of the other mafic and ultramafic bodies as well as the unmetamorphosed tonalite plutons the tonalitic gneiss represents older continental crust and had an nd value of 1 at this time the nd t values of the felsic and mafic ultramafic suites are positive ranging from 0 to 2 this range can be explained if primary magmas derived from a depleted mantle reservoir assimilated continental crust such as the tonalite gneiss during their ascent this implies that the tonalite magmas in the lac des iles area represent mixtures of the tonalite country rock and mantle magmas which formed by partial melting of depleted mantle or of mafic rocks underplated beneath the continental lithosphere the morphology and the rock assemblages of the mafic and ultramafic intrusions in the lac des iles area resemble alaskan type intrusions which are common components of phanerozoic magmatic arcs associated with subduction zones in addition the crystallization sequence in the mafic ultramafic intrusions suggests that they are derived from a parental magma with high al basalt affinities the mafic ultramafic rocks are depleted in high field strength elements but enriched in large ion lithophile elements and the tonalites belong to calc alkaline rock series displaying fractionation trends towards trondhjemitic compositions thus the archean lac des iles area and the root zones of phanerozoic active continental margins share many geological geochemical and petrological features which would suggest that the lac des iles area formed in an andean type continental margin

chromite silicate chemistry of the neoarchean sittampundi complex southern india implications for subduction related arc magmatism the neoarchean layered anorthositic complex at sittampundi in southern india is known for its chromitite layers that are mostly associated with anorthosite an 90 100 the chromitites contain feal rich chromites concentrated in layers between amphibole rich layers with a dominant mineralogy of amphibole spinel plagiocase sapphirine the chromite rich layers contain only amphibole and plagioclase mineral compositions illustrated by x ray composition maps and profiles show subtle chemical differences the chrome spinels are of refractory grade with cr2o3 and al2o3 contents varying between 34 40 wt and 23 28 wt the chromite compositions are noticeably different from those in layered igneous intrusions of the bushveld stillwater type the existence of original highly calcic plagioclase feal rich chromite and magmatic amphibole is consistent with derivation from a parental magma of hydrous tholeiitic composition that was most likely generated in a supra subduction zone arc setting in terms of mineralogy and field relations the sittampundi chromitites are remarkably similar to anorthosite hosted chromitites in the neoarchean fiskensset anorthositic complex greenland we propose that the sittampundi chromitites formed by partial melting of unusually aluminous harzburgite in a hydrated mantle wedge above a subduction zone this melting process produced hydrous aluminous basalt which fractionated at depth to give rise to a variety of high alumina basalt compositions from which the anorthositic complex with its cumulate chromite rich and amphibole rich layers formed within the magma chamber of a supra subduction zone arc c 2011 elsevier b v all rights reserved

lead isotope study of the late archean lac des iles palladium deposit canada enrichment of platinum group elements by ponded sulfide melt lead isotopic compositions of mineral separates are presented from the mineralized zones roby twilight and high grade zones of the lac des iles palladium deposit approximately 2 69 ga and tonalitic country rocks approximately 2 727 to 2 775 ga in the wabigoon subprovince of the western superior province of canada plagioclase separates show pb isotope ratios similar to those of the late archean depleted mantle sulfide minerals coexisting with plagioclase have a more radiogenic pb isotope composition but very low concentrations of u 0 2 ppb u and th 0 01 ppb compared to pb 50 ppb the isotope data are consistent with a model involving the incorporation of radiogenic pb from country rocks to sulfide melt near the base of the magma chamber or along the conduit of the parental magmas the proposed interpretation is also supported by decreasing cu pd ratios from earlier barren to late fertile gabbro intrusions in the complex the ponding sulfide melt became enriched in platinum group elements as it was interacting with a large magma volume during the evolution of the lac des iles igneous complex

lunar daily geomagnetic variations in new zealand summary lunar daily geomagnetic variations l exhibit distinctive behaviour at many sites near coasts in this study data from an array of three component magnetometers that operated for a four month summer period at 22 sites throughout new zealand are used to examine l the chapman miller method is used to determine the four main luni solar harmonics of l at each site analysis of 3 5 years of data from the geomagnetic observatory at eyrewell indicates that the array data produce representative values of l separation of the dominant lunar semidiurnal harmonic l2 into parts of oceanic and ionospheric origin indicates near uniform ionospheric contributions to the x and y field components at all sites with peak values occurring within 3 hours of lunar transit the ionospheric contribution to the 2 field component is smaller and suggests secondary electric currents flowing in the deep water to the north east and south west of new zealand the oceanic contribution to l tends not to be significant for x and y its amplitude for 2 is greatest in the eastern north island and in the south western south island and its phase angle for z is locally consistent throughout the north island and in the south western south island the difference between the phase angles that characterize these northern and southern regions is about 180 this pattern suggests near parallel in phase electric currents flowing in the deep water to the north east and south west of new zealand in response to tidal flows this is in agreement with both the general pattern seen in the united kingdom and lunar daily geomagnetic variations observed under the tasman sea and in eastern australia where the magnetic effects of tidal flows in shallow coastal waters are secondary to those from more distant deep waters the oceanic contribution to l2 might be used to estimate the poorly known tidal flows in the deep water off new zealand

magma mixing and constitution zone refining in the lac des iles complex ontario genesis of platinum group element mineralization the lac des iles complex is a 2 74 ga old composite intrusion emplaced into a granite and or granite gneiss terrane of the wabigoon subprovince northwestern ontario the complex consists of a gabbroic and ultramafic part the latter has been subdivided into northern and southern intrusive phases both the gabbroic and ultramafic parts contain platinum group element bearing ni cu sulfide mineralization although only the roby zone in the gabbro is of economic importance the southern ultramafic complex consists of a wehrlite to olivine clinopyroxenite core which is surrounded by websterite and gabbronorite cumulates petrographic and geochemical studies suggest that the northern ultramafic complex consists of at least eight cyclic units which ideally are composed of dunite and wehrlite to olivine clinopyroxenite cumulates at the base followed by clinopyroxenite and websterite locally grading into gabbronorite this indicates similar crystallization sequences in both ultramafic centers olivine olivine clinopyroxene clinopyroxene clinopyroxene orthopyroxene or plagioclase in the ultramafic complex platinum group element bearing sulfide mineralization occurs at the top of cyclic units in websterite and orthopyroxenite cumulates sulfide bearing samples up to 1 wt sulfide are enriched in au pd pt and cu relative to ni ir os and ru with pd ir ratios on the order of 250 sulfide immiscibility probably was caused by mixing of fractionated residual melt with more primitive liquid which periodically intruded the magma chamber evidence of mixing is seen in gradational chemical variations across the interface of cyclic units and in the occurrence of inclusions of olivine crystals and crystal aggregates in websterite and gabbronorite cumulates these inclusions are not in equilibrium with their present host rock and presumably formed before mixing in the more primitive magma a mineralized orthopyroxenite cumulate at the top of cyclic unit 2 could not have been produced by the normal crystallization sequence consideration of the phase relationships in the ternary system olivine clinopyroxene plagioclase quartz suggests that these cumulates are the crystallization product of a hybrid magma formed during magma mixing at the interface of cyclic units the gabbroic complex consists mainly of largely altered gabbro and gabbronorite cumulates and is intruded by mafic ultramafic dikes the center of the gabbroic complex contains the economically important roby zone with its platinum group element bearing cu ni sulfide mineralization this is a lithologically and texturally very complex zone in which high grade platinum group element mineralization is associated with pegmatite and mafic ultramaflc dikes the roby zone is characterized by strong enrichments of au pd and pt relative to ir and os and by variable but extremely high pd ir ratios of greater than 10 000 high au pt and pd pt ratios indicate a fractionation of pt from au and pd it is suggested that the high volatile content of the residual magma of the gabbroic complex triggered partial remelting of surrounding gabbro cumulates a process called constitutional zone refining by mcbirney 1987 during the partial melting event compatible elements such as ir and os are buffered by the residual silicate and oxide mineralogy whereas incompatible elements such as au pd and pt as well as volatile components such as h 2 o and h 2 s become highly concentrated in the partial melt phase eventually this newly formed magma may become sulfide saturated either by cooling and fractional crystallization or due to the continuous dissolution of sulfides when the zone of melting proceeds through the gabbro cumulates ratios such as pd ir and pd pt would strongly depend on the degree of remelting and fractional crystallization until the time of sulfide saturation the matrix of the varitextured zone is interpreted as the residuum of this melting process whereas pegmatoids and pegmatites segregationlike gabbro phases and quartz bearing plagioclase and incompatible element rich dikes are regarded as the final crystallization products of the partial melting

experimental data for a proposed empirical igneous geobarometer aluminum in hornblende at 10 kbar pressure knowledge of the depth of solidification of talc alkalic plutons is critical to understanding and unraveling the complex spatial temporal and chemical evolution of orogenic belts an empirical geobarometer has recently been proposed based on the total al content alt of near solidus calcic hornblendes in tonalite and granodiorite intrusive rocks in the pressure range 1 to 8 kbar pressures were estimated from mineral assemblages in associated metamorphic country rocks we report experimental data on newly crystallized near solidus amphiboles in partly melted vapor absent garnet tonalite at 10 kbar that provide some experimental support for the proposed geobarometer consistent with the extrapolated empirical result and confirm its limited applicability to specific multimineral assemblages

magma mixing in late archean tonalitic and mafic rocks of the lac des iles area western superior province abstract plutonic rocks in the lac des iles area of the western superior province provide a record of contemporaneous late archean mafic and tonalitic magmatism this suite of rocks consists of mafic to ultramafic intrusions mafic to intermediate dikes hornblendite and hornblende tonalite the tonalite contains net veined and disaggregated mafic to intermediate dikes mafic schlieren and zones of hornblendite to mela tonalite with skeletal hornblende these textures are interpreted to be the result of magma mixing the hornblende tonalite is geochemically characterized by high al 2 o 3 high na 2 o k 2 o low rb moderate sr and fractionated ree the hornblendite mafic to intermediate dikes and tonalite show whole rock trends of decreasing total ree increasing depletion of hree and increasing eu eu with increasing sio 2 amphiboles range in composition from edenitic and pargasitic hornblende to hornblende in dike rocks mela tonalite and hornblendite and from hornblende to actinolite in tonalite the development of skeletal amphiboles with strong normal zoning and resorbed hornblende with weak reverse zoning are attributed to conditions of supercooling and superheating respectively in zones of magma mixing the least fractionated dike rocks geochemically resemble lamprophyres derived from alkali basaltic magma variation of ree among the mafic to intermediate dikes suggests that they fractionated hornblende hornblendites and mela tonalites can be modeled as hornblende cumulates from the dike rocks the amphiboles probably crystallized rapidly during mixing leaving a feldspathic residue variation in hornblende tonalites is consistent with mixing of sio 2 rich tonalite melt with mafic to intermediate dike phases and associated hornblende cumulates and feldspathic residue open system magmatic processes at lac des iles result in a continuum of disequilibrium textures reflecting emplacement of mafic magma into a crystallizing felsic host the plutonic rocks probably formed from a zoned magma chamber with a mafic base and tonalitic top breccia zones in the tonalite suggest that explosive degassing of the chamber occurred structures similar to those reported here are common in other granitoids in the superior province and suggest that mafic magmatism and magma mixing played an important role in the development of late archean granitoid plutons

devonian alaskan type ultramafic mafic intrusions and silicic igneous rocks along the southern altai orogen implications on the phanerozoic continental growth of the altai orogen of the central asian orogenic belt abstract in this contribution we have carried out an integrated study of the petrography geochronology geochemistry and mineral chemistry for the devonian alaskan type ultramafic mafic complexes and granitoids widely distributed along the southern altai orogen in order to provide a better understanding of the continental growth process and the regional tectonic evolution la icpms zircon u pb dating of three mafic samples one acidic volcanic rock sample and one granitic sample yielded the concordia ages of ca 400 ma olivine chemical compositions indicate these mafic intrusions crystallized from evolved mafic magmas and compositions of the clinopyroxene and hornblende show typical arc affinities whole rock compositions reveal their tholeiitic signature with enriched lrees and liles and intensive depleted hfses nb ta zr and hf leading to low hfse lree ratios nb la 0 1 0 4 isotopically these mafic intrusions have positive zircon e hf t 7 6 to 14 3 mostly 10 and positive whole rock e nd t 0 8 to 5 3 values which suggest that their parental magmas were derived from a time integrated depleted mantle source these features together with the presence of primary water bearing minerals biotite and or hornblende suggest that their primitive magmas were derived from a time integrated depleted lithosphere mantle which were metasomatized by fluids released from subduction slab these findings in combination with coeval voluminous granitoids and arc signature volcanic rocks indicate that the underplating of mafic magmas at the continental arc root leads to the partial melting of the continental crust it is inferred that mafic magmatic underplating in the altai orogenic belt significantly contributed to the phanerozoic vertical continental crust growth in the altai orogen

the lac des iles palladium deposit ontario canada part ii halogen variations in apatite analysis of apatite from the mine block intrusion mbi of the lac des iles igneous complex shows two pronounced trends in the halogens apatite from relatively fresh norite and melanorites from the pd sulfide zone contain up to 57 mol chlorapatite endmember with significant hydroxyapatite component in contrast in altered rock amphibolite and greenschist assemblages the chlorapatite component is typically less than 10 mol with wide variation in the f and oh endmember components the latter trend is attributed to cl loss to degassing and alteration whereas the former is attributed to cl enrichment in the ore bearing rocks it is suggested that the relatively h2o rich and intermediate cl content of the early igneous fluids degassed from the deeper levels of the mbi can explain the high pd pt and pd ir ratios of the deposit a model is presented in which disseminated pd rich sulfides are initially introduced by a high temperature magmatic fluid that also influenced crystallization to produce the gross modal variations of the igneous host rock this high temperature mineralization event was subsequently modified by the influx of late igneous and country fluids at amphibolite to greenschist conditions

lunar tide in the equatorial electrojet in relation to stratospheric warmings 1 the relationship between sudden stratospheric warmings ssws and large amplitude lunar tides in the equatorial electrojet eej is studied analysis of ground magnetometer data shows that the lunar tide in the eej is maximum during the northern winter season except in the pacific ocean region since ssws are also a northern winter phenomenon it is suggested that the relation between the large lunar tide in the eej and the ssw may possibly be coincidental the lunar tide in the geomagnetic variations at huancayo is anomalously large compared with other eej stations an examination of geomagnetic variations at eej stations during ssw events shows that afternoon counter electrojets are frequently present at new moon and full moon though the relationship is sometimes broken the observation of large lunar eejs when no ssw is present and of various different delay times suggests that other atmospheric processes are likely to be in play

3 d modelling the electric field due to ocean tidal flow and comparison with observations 1 the tidal motion of the ocean water through the ambient magnetic field generates secondary electric field this motionally induced electric field can be detected in the sea or inland and has a potential for electrical soundings of the earth a first goal of the paper is to gain an understanding of the global distribution of the electric signal due to tidal ocean flow we simulate the electric signals for two tidal constituents lunar semidiurnal m2 and diurnal o1 tides we assume a realistic earth s conductivity model with a surface thin shell and 1 d mantle underneath simulations demonstrate that in some coastal regions the amplitudes of the electric field can reach 100 mv km and 10 mv km for m2 and o1 tides respectively the changes of lithosphere resistance produce detectable changes in the tidal electric signals we show that our predictions are in a good agreement with observations

ionosphere variability during the 2009 ssw influence of the lunar semidiurnal tide and mechanisms producing electron density variability to investigate ionosphere variability during the 2009 sudden stratosphere warming ssw we present simulation results that combine the whole atmosphere community climate model extended version and the thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm the simulations reveal notable enhancements in both the migrating semidiurnal solar sw2 and lunar m2 tides during the ssw the sw2 and m2 amplitudes reach 50 m s 1 and 40 m s 1 respectively in zonal wind at e region altitudes the dramatic increase in the m2 at these altitudes influences the dynamo generation of electric fields and the importance of the m2 on the ionosphere variability during the 2009 ssw is demonstrated by comparing simulations with and without the m2 time gcm simulations that incorporate the m2 are found to be in good agreement with jicamarca incoherent scatter radar vertical plasma drifts and constellation observing system for meteorology ionosphere and climate cosmic observations of the maximum f region electron density the agreement with observations is worse if the m2 is not included in the simulation demonstrating that the lunar tide is an important contributor to the ionosphere variability during the 2009 ssw we additionally investigate sources of the f region electron density variability during the ssw the primary driver of the electron density variability is changes in electric fields changes in meridional neutral winds and thermosphere composition are found to also contribute to the electron density variability during the 2009 ssw the electron density variability for the 2009 ssw is therefore not solely due to variability in electric fields as previously thought

the lac des iles complex ontario petrology and platinum group elements mineralization in an archean mafic intrusion the lac des iles complex is a late archean mafic to ultramafic complex that is host to 20 4 106 t pt pd and au mineralization with an average grade of 6 34 g t platinum group elements pge the 30 km2 complex located in the wabigoon subprovince consists of several coalescing mafic to ultramafic intrusive centers the complex is emplaced into early gneissic tonalite and is contemporaneous with late granitoids the magmatic evolution of the complex reflects the emplacement of multiple pulses of previously fractionated magma some of which underwent subsequent in situ fractionation distinct magma sequences are recognized on the basis of intrusive relationships differences in the cumulus minerals crystallization order and trace element chemistry these sequences are 1 hornblende gabbro 2 gabbro and gabbronorite and 3 ultramafic where there is evidence of intrusive relations the most primitive sequences are emplaced late and occur toward the north end of the complex microprobe analyses in

upper mesospheric lunar tides over middle and high latitudes during sudden stratospheric warming events in recent years there have been a series of reported ground and satellite based observations of lunar tide signatures in the equatorial and low latitude ionosphere thermosphere around sudden stratospheric warming ssw events this lower atmosphere ionosphere coupling has been suggested to be via the e region dynamo in this work we present the results of analyzing 6 years of hourly upper mesospheric winds from specular meteor radars over a midlatitude 54 n station and a high latitude 69 n station instead of correlating our results with typical definitions of ssws we use the definition of polar vortex weaking pvw used by zhang and forbes 2014 this definition provides a better representation of the strength in middle atmospheric dynamics that should be responsible for the waves propagating to the e region we have performed a wave decomposition on hourly wind data in 21 day segments shifted by 1 day in addition to the radar wind data the analysis has been applied to simulations from whole atmosphere community climate model extended version and the thermosphere ionosphere mesosphere electrodynamics general circulation model our results indicate that the semidiurnal lunar tide m2 enhances in northern hemispheric winter months over both middle and high latitudes the time and magnitude of m2 are highly correlated with the time and associated zonal wind of pvw at middle high latitudes m2 in the upper mesosphere occurs after before the pvw at both latitudes the maximum amplitude of m2 is directly proportional to the strength of pvw westward wind we have found that m2 amplitudes could be comparable to semidiurnal solar tide amplitudes particularly around pvw and equinoxes besides these general results we have also found peculiarities in some events particularly at high latitudes these peculiarities point to the need of considering the longitudinal features of the polar stratosphere and the upper mesosphere and lower thermosphere regions for example during ssw 2009 we found that m2 enhances many days before pvw which is not in agreement with most of our results

recycling processes in granite granodiorite complex genesis the querigut case studied by ndsr isotope systematics abstract using the isotopic rb sr and sm nd petrogenetic tracers we have studied the calc alkaline plutonic complex of querigut pyrenees france which is famous for its acid to mafic rock association and is a typical post tectonic hercynian granitoid its age of 280 m y is already known 2 23 24 and our purpose is to examine the relationship between its different petrographic units and the problem of their source composition the sm nd isotopic results rule out any genetic process involving a unique homogeneous source and imply the presence of old recycled continental materials in contrast the rb sr isotope system seems to have been homogenized by hot fluids maybe post magmatic this is also true for pb isotopes as shown previously by michard vitrac et al 18 on the basis of the isotopic results and the major element data a model of combined fractional crystallization assimilation of country rocks is proposed for the basic part of the complex in contrast acid parts are mainly the result of the continental anatexis this study also constrains the basement s age 1200 1900 m y of the area and suggests a scheme for the gological history of the eastern pyrenees

late archean structural and metamorphic history of the wind river range evidence for a long lived active margin on the archean wyoming craton the archean rocks of the wind river range in western wyoming record a late archean history of plutonism that extends for more than 250 m y the range is dominated by granitic plutons including the 2 8 ga native lake gneiss the 2 67 ga bridger batholith the 2 63 ga louis lake batholith and late 2 54 ga granites these plutons provide a means of distinguishing the complex metamorphism and deformation that affected the range in the late archean five deformation events are recorded d1 is a penetrative deformation that occurred during the earliest granulite facies metamorphism d2 is a folding event probably in amphibolite facies that deforms porphyritic dikes that cut the d1 fabrics both d1 and d2 predate the intrusion of the ca 2 8 ga native lake gneiss d3 is a folding event accompanied by upper amphibolite to granulite metamorphism that deformed the medina mountain sequence a sequence of rocks that was either deposited or thrust upon the native lake gneiss d4 is a fabric forming event associated with the mount helen structural belt mhsb it is represented by mylonites in the mhsb a penetrative fabric in the bridger batholith and folding of the d3 structures in the medina mountain sequence we consider d3 and d4 to be coeval with the emplacement of the bridger batholith and hence to date at ca 2 67 ga the latest structures d5 are fabrics associated with the folding and thrusting of the 2 65 ga south pass sequence we recognize at least four metamorphic events m1 is associated with the d1 fabrics and occurred at high t 750 c and high p 7 8 kilobars m2 650 750 c and 4 5 5 kilobars is associated with the intrusion of the bridger batholith and formation of the d3 and d4 structures the d5 structures of the south pass sequence record m3 which is low p 2 3 kilobars and low t 500 c the final metamorphism m4 is a contact metamorphism around the louis lake batholith in the south against the south pass sequence the metamorphism occurred at 3 kilobars and at temperatures 700 c in contrast in the north where the louis lake batholith is charnockitic the metamorphism occurred at 6 kilobars and 800 c this pressure gradient is probably a reflection of tilting of the wind river block during the laramide orogeny the composition of the plutons and the structural and metamorphic history of the wind river range indicate that during the late archean this area occupied the active margin of the wyoming province this tectonic environment is similar to the long lived phanerozoic margins of north america the wind river range represents the best documented active margin of archean age

the difference between oceanic and continental tholeiites a fluid dynamic explanation continental tholeiites have higher sio2 k2o and light rare earth element contents and more evolved isotopic characteristics than their oceanic counterparts these differences can be explained if the compositions of the parent magmas to both types of tholeiites are similar but if continental magmas assimilate significant amounts of continental crust en route to the surface although there is little doubt that most continental tholeiites have assimilated crustal material the lcoation and mechanism of assimilation remain uncertain longhi 1981 has argued that magmas derived directly from the mantle should crystallize little orthopyroxene the abundance of orthopyroxene in most continental layered intrusions suggests that they have crystallized from magmas which have assimilated continental crust since orthopyroxene is an early crystallizing phase in layered intrusions this assimilation must occur early before the magma enters the chamber assimilation can occur at the margins of the dykes which feed magma chambers depending on the nature of the flow if the flow is turbulent the high temperatures at the centre of the dyke will extend to the margins and the magma will erode the dyke walls if the flow is laminar a conductive profile develops at the margin and the flowing magma chills against the walls protecting them from thermal erosion the nature of flow in a dyke can be predicted from the reynolds number the criteria for turbulence reynolds number calculations suggest that the flow of primitive magmas in continental dykes will be fully turbulent and if this is the case assimilation of low melting point components in the walls of the dyke is inevitable it is therefore suggested that many of the geochemical characteristics of continental tholeiites result from melting at the walls of dykes as primitive magmas ascend through the crust

geochronology of the lumby lake greenstone belt a 3 ga complex within the wabigoon subprovince northwest ontario the lumby lake greenstone belt lies within the central predominantly metaplutonic terrane of the western wabigoon subprovince it is conformable with gneiss of the marmion lake tonalite batholith u pb analyses of zircons from two felsic tuffs and a quartz porphyry within the greenstone belt give a scattered lead loss pattern indicative of early disturbance the ages of the oldest concordant fractions agree however and define an age of 2999 1 m y for emplacement of these felsic units zircons from a tonalite gneiss within the marmion lake batholith are also somewhat disturbed the oldest abraded fraction is concordant and has an age of 3003 5 m y indicating that the gneiss is probably close in age to the supracrustal rocks u pb analyses of rutile from one of the felsic units give an age of 2690 5 m y and record the effect of late archean metamorphism three titanite fractions from the tonalite gneiss agree within error and have an age of 2809 1 m y the age and consistency of the titanite fractions indicate that titanite in this rock was formed as a result of a metamorphic event and was never subsequently disturbed this age is therefore a minimum estimate for high grade metamorphism of the gneiss the presence of a pre 2809 ma fabric in a gneiss of regional extent suggests that an early metamorphic deformational event affected this area these data constitute the first firm evidence for extensive 3 0 ga crust in the southern superior province and give the first evidence of a regional deformational event which predates cratonization of the superior province

daily geomagnetic variations on the iberian peninsula summary mean hourly values of the horizontal and vertical components of the geomagnetic field at six observatories on the iberian peninsula were analysed to study seasonal and spatial behaviour of the solar and lunar ionospheric and oceanic daily geomagnetic variations the results are tabulated and their characteristics are discussed the influence of local oceanic effects on the lunar oceanic contribution at the peninsular observatories is noted in particular the spatial behaviour of the lunar oceanic contribution is considered whereas the mean value for the peninsula is consistent with that expected according to an existing model for electric currents in the eastern atlantic ocean individual values are not the influence of tide in the mediterranean sea of water currents in the strait of gibraltar and of local effects in the atlantic ocean is proposed as the reason for this behaviour

the lac des iles palladium deposit ontario canada part i the effect of variable alteration on the offset zone the recently discovered offset zone of the mine block intrusion of the lac des iles complex hosts palladium mineralization with unusually high pd pt and pd ir ratios in rocks that range from relatively unaltered norite to amphibolites and chlorite actinolite talc schist quantitative assessment of the effect of progressive alteration using mineral modes was done using total silicate h2o as a monitor of reaction progress moles h2o added to form alteration minerals per 100 g of rock major mineral modal variations define three reaction regions 1 0 00 0 03 characterized by epidote clinozoisite formation and some amphibole 2 0 03 0 23 characterized by formation of chlorite amphibole quartz muscovite sericite and calcite after plagioclase pyroxene and 3 0 23 0 28 characterized by the formation of talc after earlier formed amphibole epidote occurs as an incongruent product from the destruction of plagioclase that is itself lost as the reaction proceeds pyroxene is altered at about twice the rate of plagioclase resulting in pyroxene rich protoliths to be more altered than those relatively enriched in plagioclase major elements variations largely reflect variations in the plagioclase pyroxene ratio of the protolith but compositional trends suggest a loss of na with reaction progress the base metal sulfides chalcopyrite pyrrhotite and pentlandite show decreasing abundance with reaction progress forming pyrite magnetite as an intermediate reaction product that also is lost as the reaction proceeds millerite is overall low but increases slightly a more limited data set on the platinum group minerals suggests that platinum group element pge arsenides increase whereas pge sulfides and pge bi tellurides decrease with reaction progress assuming ore element concentrations in the protolith were constant and similar to relatively fresh norites pd increases modestly by 5 whereas pt decreases by about 65 in the most altered rocks similarly cu au and s decrease by 60 82 and 94 respectively in the most altered rocks the antithetical behavior of pd and the fact that pd enrichment is not seen in altered dikes suggest that the pd originally was enriched in the more melanocratic protoliths that are most extensively altered and that pd also was lost in part these results are consistent with the mineralization having been a high temperature event that predated the amphibolite greenschist alteration

inversion for the physical parameters that control the source dynamics of the 2004 parkfield earthquake a fully dynamic inversion for the earthquake source process in which the geometry of the rupture area the stress conditions and frictional properties on the fault are obtained is carried out by inverting displacement records for the 2004 mw 6 0 parkfield california earthquake the rupture area of the earthquake is modeled using elliptical patches and seismograms from 10 near field digital stations are used synthetic tests to investigate the performance of the inversion in retrieving the rupture process demonstrate that we can reliably recover the large scale features of the spatiotemporal distribution of slip to investigate the stress conditions and frictional properties of the fault under which we produce a rupture model that fits the observed data we explore the parameter space using a monte carlo method and find an optimal region where the source models fit the data well the best fitting rupture process is shown to occur mainly within one horizontal elliptical region 22 km long along strike and 4 km wide along depth the seismic moment is 1 2 1018 n m and the stress drop over the ellipse is 4 mpa the rupture speed nearly constant during the entire rupture process is 2 9 km s the dimensionless quantity roughly the strain energy change per unit fault surface divided by the energy release rate which includes information on the stress and frictional properties on the fault is found to be 1 4 for the ellipse and strongly controls the rupture process along with the size of the initial circular patch that initiates the earthquake

satellite observations of magnetic fields due to ocean tidal flow the ocean is an electrically conducting fluid that generates secondary magnetic fields as it flows through earth s main magnetic field extracting ocean flow signals from remote observations has become possible with the current generation of satellites measuring earth s magnetic field here we consider the magnetic fields generated by the ocean lunar semidiurnal m2 tide and demonstrate that magnetic fields of oceanic origin can be clearly identified in satellite observations

geochronology and geochemistry of early permian mafic ultramafic complexes in the beishan area xinjiang nw china implications for late paleozoic tectonic evolution of the southern altaids abstract the hongshishan and pobei mafic ultramafic complexes outcrop in the beishan area in the southernmost altaids they consist of olivine gabbros dunites and pyroxenites zircons from olivine gabbros from the hongshishan complex yield a u pb age for emplacement of 281 8 2 6 ma the olivine gabbros have low sio 2 47 08 48 66 tio 2 0 14 0 29 mno 0 07 0 09 and k 2 o 0 06 0 09 but high mg values 81 t fe 2 o 3 4 93 6 29 the hongshishan and pobei mafic ultramafic complexes are characterized by negative anomalies in high field strength elements zr hf nb ta which we interpret as arc related signatures they also have spikes in large ion lithophile fluid mobile elements ba u pb sr and high mobile immobile element ratios i e primitive mantle normalized sr nd ba la 1 which are attributed to an aqueous fluid component in the source zircon hf isotopes indicate that the source magma was derived either from a depleted mantle with some crustal contamination or from an enriched mantle these data are interpreted to indicate that the hongshishan and pobei mafic ultramafic complexes were emplaced in the early permian subduction related environment which suggests that the paleo asian ocean in the southernmost part of altaids did not close until after early permian

ocean tidal signals in observatory and satellite magnetic measurements 1 ocean flow moves sea water through the earth s magnetic field inducing electric fields currents and secondary magnetic fields these motionally induced magnetic fields have a potential for the remote sensing of ocean flow variability a first goal must be to gain a better understanding of magnetic field generation by tidal ocean flow we predict the motionally induced magnetic fields for the six major tidal constituents and compare their amplitudes with the spectra of night time observatory and satellite magnetic measurements for the indian ocean the magnetic variations at the solar s2 kl and p1 periods turn out to be dominated by unrelated external fields in contrast observed lunar m2 and n2 tidal signals are in fair agreement with predictions from motional induction the lunar diurnal o1 signal visible at some observatories could be caused by ocean flow but disagrees in amplitude with our predictions

phase relations of a high mg basalt from the aleutian island arc implications for primary island arc basalts and high al basalts many volcanic centers in the aleutian islands have erupted lavas that range in composition from high mg basalt mgo 9 wt to more fractionated and voluminous high al basalts and basaltic andesites the petrogenetic relationships between these rock types and the composition of primary magmas has been vigorously debated the phase relations of a typical high mg basalt from the makushin volcanic field on unalaska island provide important constraints on petrogenetic models results of one atmosphere and moderate to high pressure 5 20 kb anhydrous experiments are similar to results obtained from primitive morb at low pressures olivine is the liquidus phase joined by plagioclase and clinopyroxene at progressively lower temperatures clinopyroxene is the second phase to crystallize at pressures greater than 5 kb and replaces olivine on the liquidus at approximately 10 kb above 10 kb the liquidus pyroxene is aluminous augite and orthopyroxene is the second phase to crystallize glasses in equilibrium with olivine and clinopyroxene at intermediate pressure 5 to 10 kb are similar in composition to high al basalt plagioclase is not involved and most likely does not become a liquidus phase until the liquid has evolved significantly although our studies do not confirm the primary nature of high mg basalts they do support a model in which high al basalts are generated by moderate amounts of crystal fractionation from more primitive high mg mg fe lower al2o3 basaltic magmas near the arc crust mantle boundary

age of the mulcahy lake intrusion northwest ontario and implications for the evolution of greenstone granite terrains abstract zircon data from a 63 km 2 layered mafic intrusion in the wabigoon subprovince the mulcahy lake gabbro show that the gabbro crystallized at 2733 2 0 9 1 0 ma the largely unaltered and unmetamorphosed gabbro intrudes tholeiites of the crow lake savant lake greenstone belt which were generated over at least a 10 ma time span rb sr and sm nd data were obtained for pristine whole rock and mineral separates from the intrusion the rb sr data show disturbances in the system particularly in the case of pyroxenes samples with low rb sr ratios indicate an initial sr ratio of 0 7007 for an age of 2733 ma the sm nd age is 2744 55ma and an epsilon nd value of 2 6 1 2 indicates a light rare earth element depleted source the sm nd data show less disturbance than the rb sr data granitic and mafic intrusives with similar initial ratios occur 80 km to the south in the quetico subprovince primary hornblende was analyzed for 40 ar 39 ar the age obtained is 2703 20ma clearly younger than the zircon age indicating some argon loss the mulcahy lake gabbro is one of four layered mafic plutons of similar petrographic character and stratigraphic age which are arrayed in an arc in the crow lake savant lake greenstone belt the plutons appear to represent subvolcanic chambers which developed simultaneously and which crystallized at the end of the volcanic cycle all intrude basalts and are intruded in turn by the atikwa batholith a massive granitic intrusion of over 1000 km 2 in area previously published zircon ages for several sample sites within the batholith indicate crystallization at 2731 8 1 3 1 6 ma to 2732 2 2 9ma these data show that the batholith overlaps the age of the gabbros or is at most 5 ma younger this virtual contemporaneity is hidden in the rb sr and sm nd data the cessation of mafic magma production and the immediate if not parallel voluminous production of calc alkaline liquid may represent a process important in the development of greenstone granite belts a process not apparent when ages are not so precisely determined

geology petrography geochemistry and genesis of sulfide rich pods in the lac des iles palladium deposits western ontario canada the lac des iles pd deposits are known for their pd rich sulfide poor mineralization however previously undocumented sulfide rich pods also occur within the intrusion that hosts the deposits given the complex magmatic and hydrothermal history of the mineralization at lac des iles the sulfide rich pods could have crystallized from magmatic sulfide liquids or precipitated from hydrothermal fluids sulfide rich pods occur throughout the stratigraphy in all rock types and along comagmatic shear zones and contain net textured to massive sulfides they can be divided into four main groups based on the variation in mineral assemblages 1 pyrrhotite pentlandite pyrite chalcopyrite magnetite ilmenite 2 chalcopyrite pyrrhotite pentlandite pyrite magnetite ilmenite 3 pyrite pentlandite chalcopyrite pyrrhotite magnetite ilmenite and 4 magnetite ilmenite pyrrhotite pentlandite pyrite chalcopyrite whole rock metal contents and s isotopic compositions do not change with the amount of pyrite present except for slight enrichments in as and bi the presence of an essentially magmatic sulfide mineral assemblage pyrrhotite pentlandite chalcopyrite with pentlandite exsolution flames in pyrrhotite in some pods suggests that the pods crystallized from magmatic sulfide liquids the very low cu contents of the pods suggests that they are mainly cumulates of monosulfide solid solution mss we propose a model whereby sulfide liquids were concentrated into dilation zones prior to crystallizing cumulus mss intermediate solid solution crystallized from the fractionated liquids at the edges of some pods leaving residual liquids enriched in pt pd au as bi sb and te these residual liquids are no longer associated with the pods during subsequent alteration pyrite replaced mss pyrrhotite but this did not affect the platinum group element contents of the pods