metallogeny of the northern norrbotten ore province northern fennoscandian shield with emphasis on iocg and apatite iron ore deposits the northern norrbotten ore province in northernmost sweden includes the type localities for kiruna type apatite iron deposits and has been the focus for intense exploration and research related to

evidence for tilted toroidal circulations in cumulus intense vortical circulations often organized in counterrotating vortex pairs were detected in midcontinental cumulus congestus over southeast wyoming in july 2003 the sampled clouds developed in dry environments and at cold temperatures and were a few kilometers in depth and width observations were obtained with the wyoming cloud radar from aboard the wyoming king air research aircraft dualdoppler analyses of the data yielded high resolution 30 45 m depictions of the horizontal components of air motions across vigorously growing clouds the vortices found in the horizontal cross sections are interpreted as components of the toroidal circulations in thermals when those are tilted because of the effect of ambient cross flow this configuration also leads to a partial stabilization of the vertical trajectory of the updraft by opposing the drag by the ambient wind additionally dry air intrusions were seen to accompany these features when the vortices developed near the cloud outer boundaries recirculation of hydrometeors occurred when the vortices were adjacent to in cloud downdrafts these features are also evident in the radar reflectivity patterns in general gradients of velocities and vorticity values in horizontal planes are comparable to those found in vertical planes

chemistry of proterozoic orogenic processes at a continental margin in northern sweden abstract sm nd isotopic major trace and rare earth element data for two separate age groups of plutonic rocks have been used to characterize early proterozoic crust formation mechanisms in the vicinity of the exposed archaean of northern sweden the granitoid rocks of the older 1 89 1 87 ga group show calc alkaline trends diorite quartz monzonite adamellite and have negative nd values ranging from about 8 to 5 they represent variable contamination of isotopically juvenile mantle melts with archaean crustal material the younger 1 80 ga group of plutonic rocks are of true granitic composition they show a restricted range of nd values which is encompassed by those of the older group trace and major element data are consistent with the derivation of the younger group of rocks by remobilization of the earlier formed proterozoic continental crust this is in contrast to the temporally similar but isotopically more juvenile granitoids of the skellefte district to the south

in situ la icp ms u pb dating of metavolcanics of norrbotten sweden records of extended geological histories in complex titanite grains in situ u pb dating of a variety of mineral phases is an important goal in petrology this study reports data chiefly from titanite but also from rutile and apatite obtained using the laser ablation la icp ms methodology on polished thick sections in order to retain as much petrologic information as possible and allowing trace element analyses from adjacent areas to the u pb analyses the samples analysed come from svecofennian intermediate to acid volcanic rocks of the porphyry group within the major iron ore province of norrbotten northern sweden where titanite is a common phase associated with the mineralisation using a laser beam of 30 45 m in diameter accurate and relatively precise 2 3 2 on 206pb 238u ratios data can be obtained on titanite similar precision on pb u ratios can be obtained in rutile but accuracy cannot be assessed because of the lack of well characterised standards however the data are a priori accurate as they are geologically reasonable apatite shows reverse discordance which could be explained by a number of scenarios however the 207pb 206pb ages are fairly precise 1 3 2 and the calculated age is geologically reasonable suggesting that the data may be accurate the titanite grains studied show complex internal structures rare earth element ree analysis by la icp ms demonstrates that the core and rim zones are distinct and supports a model for two stage evolution in two out of three samples with the rims in these samples being enriched in total ree and particularly in lree in one sample and displaying a positive y anomaly in contrast to the cores in situ u pb analysis reveals that core zones from all samples retain distinct older ages of c 2050 ma whereas the reworked rims have either distinct younger or strongly reset ages the older cores are interpreted as representing the first alteration metamorphism of the volcanic pile titanite rims record a u pb age of 1870 24 ma 2 at luossavaara and 1826 15 ma 2 at the smaller fe oxide apatite body at gruvberget in both cases the ages are consistent with previous age determinations from the fe oxide apatite deposits a sample from malmberget records a slightly different scenario where u pb ages spread along concordia from c 1920 to 1708 ma we attribute this pattern to metamorphic reworking of primary metasomatic titanite rutile ages from inclusions within the core of gruvberget titanite essentially mimic the ages obtained from the surrounding titanite and suggest that they have undergone the same history apatite inclusions within titanite at malmberget record a younger age of 1584 12 ma 2 which we attribute to later events known to have affected the area these data indicate that the porphyry group volcanics must be at least c 2050 ma in age in contrast to previous age determinations from zircon which suggested a deposition age of c 1960 to 1880 ma the large grain size of the titanites studied coupled with the ability for the first time to obtain in situ u pb ages from small areas has allowed probing of this hitherto unrecognised event smaller zircon grain size coupled with extremely saline hot pressurised high p t metasomatic fluids relating to regional magnetite apatite mineralisation in the period 1900 to 1800 ma may have resulted in resetting of zircon u pb systematics 2007 elsevier b v all rights reserved

pressure perturbations and upslope flow over a heated isolated mountain abstract surface and upper air data collected as part of the cumulus photogrammetric in situ and doppler observations cupido experiment during the 2006 monsoon season around the santa catalina mountains in southeast arizona are used to study the diurnal variation of the mountain scale surface convergence and its thermal forcing the thermal forcing is examined in terms of a horizontal pressure gradient force which is derived assuming hydrostatic balance the mountain is 30 km in diameter 2 km high and relatively isolated the environment is characterized by weak winds a deep convective boundary layer in the afternoon and sufficient low level moisture for orographic cumulus convection on most days the katabatic divergent surface flow at night and anabatic convergent flow during the day are in phase with the diurnal variation of the horizontal pressure gradient force which points toward the mountain during the day and away from the mountain at night the daytime pressure deficit over the mo

the archaean proterozoic palaeoboundary in the lulea area northern sweden field and isotope geochemical evidence for a sharp terrane boundary abstract extensive sm nd isotope work has been carried out in northern sweden with the intention of studying crustal reactivation and assimilation processes relative to juvenile arc accretion at an archaean cratonic margin previous regional work has shown a gradual change from negative nd t values in northernmost sweden to positive values towards the skellefte sulphide ore district farther south isotopic variation and geophysical data show a break in the character of the crust along a wnw trending zone it is suggested that this zone which passes close to the towns of lulea and jokkmokk represents the transition from the archaean craton in the northeast to proterozoic juvenile crust in the southwest a profile across the eastern part of this transition zone has been studied in detail in the lulea area where archaean rocks recently have been discovered the distribution and character of the archaean rocks have been studied these occur as fragments ranging in size from several km 2 to dm in scale and consist of ca 2 7 ga orthogneisses of granodioritic to dioritic composition and porphyritic granitoids of quartz monzodioritic to granodioritic composition plutonic rocks of ca 1 9 ga age and archaean rocks were analysed for major and trace elements and for sm nd isotopes the calc alkaline ca 1 9 ga granitoids are dominated by granodiorites tonalites quartz diorites and quartz monzodiorites and there is a distinct boundary rather than a transition zone between intrusions with postive nd t values in the southwest and intrusions with negative nd t values in the northeast the locations of the outcropping archaean fragments coincides with this distinct boundary which is interpreted as a terrane boundary separating a ca 1 9 ga juvenile arc terrane in the southwest from the archaean continent in the northeast a possible explanation for this is that the proterozoic juvenile terrane was obducted onto the archaean craton during the final stages of the svecofennian orogeny

8 precambrian geodynamics and ore formation the fennoscandian shield abstract compared with present day global plate tectonics archaean and palaeoproterozoic plate tectonics may have involved faster moving hotter plates that accumulated less sediment and contained a thinner section of lithospheric mantle this scenario also fits with the complex geodynamic evolution of the fennoscandian shield from 2 06 to 1 78 ga when rapid accretion of island arcs and several microcontinent continent collisions in a complex array of orogens was manifested in short lived but intense orogenies involving voluminous magmatism with a few exceptions all major ore deposits formed in specific tectonic settings between 2 06 and 1 78 ga and thus a strong geodynamic control on ore deposit formation is suggested all orogenic gold deposits formed syn to post peak metamorphism and their timing reflects the orogenic younging of the shield towards the sw and west most orogenic gold deposits formed during periods of crustal shortening with peaks at 2 72 to 2 67 1 90 to 1 86 and 1 85 to 1 79 ga the ca 2 5 to 2 4 ga ni cu pge deposits formed both as part of layered igneous complexes and associated with mafic volcanism in basins formed during rifting of the archaean craton at ca 2 5 to 2 4 ga svecokarelian ca 1 89 to 1 88 ga ni cu deposits are related to mafic ultramafic rocks intruded along linear belts at the accretionary margins of microcratons all major vms deposits in the fennoscandian shield formed between 1 97 and 1 88 ga in extensional settings prior to basin inversion and accretion the oldest cyprus type deposits were obducted onto the archaean continent during the onset of convergence the pyhasalmi vms deposits formed at 1 93 to 1 91 ga in primitive bimodal arc complexes during extension of the arc in contrast the skellefte vms deposits are 20 to 30 million years younger and formed in a strongly extensional intra arc region that developed on continental or mature arc crust deposits in the bergslagen uusimaa belt are similar in age to the skellefte deposits and formed in a microcraton that collided with the karelian craton at ca 1 88 to 1 87 ga the bergslagen uusimaa belt is interpreted as an intra continental or continental margin back arc extensional region developed on older continental crust iron oxide copper gold iocg deposits are diverse in style at least the oldest mineralizing stages at ca 1 88 ga are coeval with calc alkaline to monzonitic magmatism and coeval and possibly cogenetic subaerial volcanism more akin to continental arcs or to magmatic arcs inboard of the active subduction zone younger mineralization of similar style took place when s type magmatism occurred at ca 1 80 to 1 77 ga during cratonization distal to the active n s trending subduction zone in the west possibly interaction of magmatic fluids with evaporitic sequences in older rift sequences was important for ore formation finally the large volumes of anorthositic magmas that characterize the sveconorwegian orogeny formed a major concentration of ti in the sw part of the sveconorwegian orogenic belt under granulite facies conditions about 40 million years after the last regional deformation of the sveconorwegian orogeny between ca 930 and 920 ma

a study of thermals in cumulus clouds air motions in the thermals contained within shallow florida cumulus clouds were observed to be similar to the circulation observed in laboratory thermals there was outward flow in the updraughts of individual thermals at most levels and there were usually downdraughts observed at the edges of the updraught or of the cloud widespread inward flow towards the centre of the cloud and a narrow but strong updraught was occasionally observed reminiscent of the tail found at the rear of the laboratory thermals a region of reduced liquid water content was frequently observed in the centre of several thermals where the updraught and horizontal 1d divergence were strongest and complete holes were observed on two occasions although horizontal wind shear was generally weak it was significant in a few cases causing the flow pattern in the cloud to be asymmetric ascending regions of cloud with high values of liquid water content cloud cores were commonly observed at all altitudes but generally the percentage of clouds measured with high liquid water content decreased with altitude the observations of airflow and liquid water content structure in warm cumulus clouds described in this paper are consistent with the schematic model of a thermal where a core of high liquid water content survives for several kilometres above cloud base but erodes as it ascends copyright 2005 royal meteorological society

crust and upper mantle of the western mediterranean constraints from full waveform inversion abstract we present a full waveform tomographic model of the western mediterranean crust and mantle constructed from complete three component recordings from permanent and temporary networks the incorporation of body and multi mode surface waves in the period range from 12 150 s allows us to jointly resolve crustal and mantle structures including the guadalquivir tajo and ebro basins at shallow depth as well as the western mediterranean subduction system in the transition zone no mantle plumes can be detected beneath the european cenozoic rift system including the massif central in addition to the well studied alboran slab a strong e w trending high velocity anomaly is present around 200 300 km depth beneath the algerian coast this previously undetected african slab is detached from the surface and broken into two segments it may be interpreted as the slab that caused the opening of the liguro provencal basin through successive roll back between 35 15 ma

chronology of proterozoic orogenic processes at the archaean continental margin in northern sweden abstract the proterozoic svecofennian orogeny was characterized by the rapid formation of great amounts of juvenile continental crust and extensive remobilization of older crust this paper considers u pb zircon ages and some geochemical and lithostratigraphic features of the svecofennian in the continental margin area between the skellefte ore district and the boundary of the archaean craton farther north in sweden new u pb zircon ages constrain the igneous activity of svecofennian crust formation in northern sweden to between 1930 and 1870 ma ago the same time constraints apply also to crust formation farther east in finland orogeny along the entire archaean proterozoic boundary zone was thus simultaneous and does not represent an east to west event succession it is argued that rocks with similar major element compositions but distinctly different trace element characteristics were formed simultaneously but in different plate tectonic environments by 1875 ma ago the svecofennian volcanic arc had matured and a variety of syn to late orogenic igneous rocks appeared in both tensional and compressional settings shortly thereafter the svecofennian magmatic activity ceased altogether probably as a result of collision between the arc and the archaean continent in the north it is also suggested that pre svecofennian rifting of the archaean craton had created a passive continental margin and that the transition to an active margin with subsequent island arc magmatism and subduction beneath the archaean craton commenced prior to 1930 ma ago it may well have been initiated by a relative drift of the archaean craton towards the present southwest as a consequence of the formation of the collisional proterozoic lapland granulite belt in the northernmost baltic shield

conflicting zircon vs titanite u pb age systematics and the deposition of the host volcanic sequence to kiruna type and iocg deposits in northern sweden fennoscandian shield abstract the northern norrbotten region and in particular the kiruna area hosts a number of large apatite iron oxide deposits e g the huge kiirunavaara ore of significant economic importance age data from rock lithologies hosting these ores represented by metamorphosed rocks of the porphyrite and kiirunavaara groups are complex to interpret this is illustrated by la icp ms data for titanite and to some extent for rutile which scatter considerably yielding ages within a span from ca 2 1 ga to 1 7 ga these analysed hydrothermal minerals characterized by complex bse images revealing darker and brighter zones are located in ore zones and associated with e g strong scapolitisation albitisation and actinolitisation previous tims zircon ages of host rocks on the other hand define a more narrower age interval between ca 1900 and 1870 ma and this is supported by new u pb zircon results presented here furthermore one coherent set of sims data for titanite from the luossavaara ore favour that crystallization took place at ca 1 88 ga although laser icp data from the same locality are much more complex an implication arising from published pre 1 9 ga laser ablation ages for titanites is that the emplacement of host rocks started already at around 2 1 ga as the depositional time of these rocks is crucial for the understanding of the overall crustal formation in northern norrbotten additional rocks were selected for age dating new zircon age data la icp ms and sims give support to a scenario where host rocks to ores started to develop at around 1900 ma and this calls for a re evaluation of published la icp ms data of hydrothermal mineral phases here we present four models that aim to explain how pre 1 9 ga titanite ages believed to have a questionable geological significance may develop the principal idea is that 2 1 ga alteration events were not responsible for the crystallization of the hydrothermal minerals instead it is believed that apparent old age domains carry excess radiogenic lead due to the effect of 1 9 ga hydrothermal processes currently the interpretation of u pb isotope data in the study area remains enigmatic and further radiometric analyses are required

diversity of 1 8 ga potassic granitoids along the edge of the archaean craton in northern scandinavia a result of melt formation at various depths and from various sources the edge of the archaean craton in northern scandinavia had been intensively reworked during the svecofennian orogeny 1 93 1 86 ga ago and was subsequently intruded by potassic granitoids of 1 79 1 80 ga age despite similar or even identical ages and overlapping areas of occurrence these rocks belong to two different groups the edefors and lina granitoids which have contrasting geochemistries and sm nd isotopic characteristics the edefors granitoids range from syenites to granites and are alkali rich and distinctly metaluminous they crystallized from dry magmas this is indicated by the scarcity of pegmatites and aplites the contacts to older rocks are often distinct but gradual transitions to lina type granitoids are common the edefors granitoids have high contents of zr but not of elements such as y ree ta and nb and have low mgmg fe ratios they also frequently have positive eu anomalies even in the quartz rich varieties initial nd values range from 2 1 to 1 4 indicating that the edefors granitoids were formed by the mixing of mantle derived magmas and continental crustal materials the amount of crustal component was probably less than 35 in most cases the lina granitoids are accompanied by abundant pegmatites and aplites ghost structures and remnants of country rock are common true granites predominate but also quartz monzonites occur the content of hfs elements is low and the mgmg fe ratios are higher than in the edefors granitoids initial nd values range from 9 3 to 3 7 reflecting a significant portion of archaean nd in the source materials the lina granitoids are largely the result of remobilisation of continental crust with a small input of juvenile material however the dominant source for these crustally derived granitoids are c 1 9 ga old granitoids these carry a large proportion of archaean nd the most probable environment of the formation of potassic migmatite granitoids such as the lina type is a collision zone between two masses of felsic crust e g arc continent or continent continent but the details of such a collision in the baltic shield remain to evaluated the formation of the edefors granitoids could have been associated with an extensional zone developed due to delamination caused by separation of the down dip oceanic lithosphere from the continental lithosphere

on the age of the kiruna greenstones northern sweden abstract three types of zircons from an albite diabase sill within the kiruna greenstone group have been investigated to determine their age and order of crystallization the youngest pink and transparent zircons probably crystallized in late fissures and in association with a thermal event the intermediate white zircon populations could not be readily dated because of significant lead loss the lead 207 206 ages of both the pink and white zircons agree roughly with that of the sm nd isochron about 1 93 ga on secondary minerals from a kiruna greenstone skiold and cliff the oldest brown zircons indicate an age of about 2 2 ga and probably reflect the initial crystallization of the rock the formation of the early proterozoic greenstones in the kiruna area thus commenced about 2 2 ga ago or earlier these results are consistent with the proposed chronostratigraphy of the jatulian formations in finland e g simonen merilainen a time interval of at least 0 3 ga is assumed for the volcano sedimentary period which pre dates the svecokarelian orogeny of the kiruna area

isotope systematics of the kiruna magnetite ores sweden part 1 age of the ore u pb isotope dating of zircons from a granophyric dike complex which crosscuts the kiirunavaara magnetite apatite body demonstrates that the ore was emplaced before 1 880 or 0 003 ga whole rock sm nd isotope compositions for five out of six samples from the footwall and hanging wall complexes lie on a 1 89 or 0 09 ga isochron the initial ratio of 0 50991 or 0 00007 corresponds to epsilon nd t 5 6 and suggests a substantial late archean component in the igneous rocks since the ore cannot have been emplaced after the granophyre nor before the host rocks ore formation is limited to the period between 1 90 and 1 88 ga however the granophyre remains at present in the form of a crosscutting dike largely unaffected by the ductile and brittle deformation that has affected both the ore and host rocks this implies that ore formation igneous activity and deformation were all confined to a short time interval during this period and suggests that the kiruna magnetite apatite ores were generated during orogenesis this association of orogenesis emplacement temperatures up to 600 degrees c abundant evidence of hydraulic processes during ore formation and extensive porphyries is reminiscent of other types of intrusion related high temperature ore forming processes

archean proterozoic collision boundary in central fennoscandia revisited abstract archean proterozoic ap collision boundary in central fennoscandia is a complex collage of archean basement rocks its paleoproterozoic supracrustal cover rocks and svecofennian 1 93 1 78 ga supracrustal and plutonic rocks the apparent steep nature and complexity of the ap boundary has led to contradictory tectonic models varying from arc continent collision via back arc closure to accretion of arc terranes along a strike slip shear zone we present new geochronology data from detrital zircons combined with whole rock geochemical and sm nd isotopic data on paleoproterozoic sedimentary and volcanic rocks across the boundary to revise its nature the 2 06 ga siilinjarvi volcanic complex and associated turbidites with an inferred deposition age at 2 1 2 06 ga are part of the cover sequence the siilinjarvi volcanic rocks derive from both plume oib and sub continental lithospheric mantle sclm magma sources and are often contaminated by the archean crust the sahara suite sedimentary cover rocks are derived from local 1 95 1 92 ga bimodal volcano plutonic source which source also explains the common age population found in younger sedimentary rocks the nalantojarvi suite psammites with maximum depositional ages of 1 97 1 93 ga are continental slope to deep water sediments deposited at the continental margin contemporaneous mafic magmatism seen as lavas and dykes show a change from sclm dominated present east to asthenospheric depleted mantle dm dominated present west melts the interpretation of the nalantojarvi suite as cover rocks of the lower plate indicates that the archean crust continues at least 50 km more to the west than thought earlier parautochthonous sedimentary rocks from salahmi eastern kansanneva and loutemaki with maximum depositional ages at 1 92 1 91 ga are inferred as collision related foredeep deposits from local sources both the lampaanjarvi suite and pyhajarvi suite sedimentary rocks have deposited at 1 89 1 88 ga or later whereas the lampaanjarvi suite rocks are dominated by a local source and the pyhajarvi suite rocks derive from a mixture of older sediments and 1 89 1 88 ga granitoids at least two tectono metamorphic stages separated with a major unconformity can be differentiated in the study area the early deformation and metamorphic stage in the nalantojarvi suite has occurred before the intrusion of the late to post collisional pyroxene granitoids at 1 88 ga the pyhajarvi suite sedimentary rocks have been deposited after the intrusion of these granitoids between 1880 and 1875 ma and then subsequently deformed and metamorphosed at 1875 ma we propose a tectonic model where the continental breakup occurred at 2 1 2 06 ga followed by a new spreading within the pre existing passive margin at 1 98 1 93 ga during initial continent arc collision the subducted slab steepened strongly at high angle subduction ceased rapidly and finally detached and shallow slab breakoff occurred at 1 92 1 91 ga followed subsequently by ophiolite obduction and a formation of a foreland fold and thrust belt mantle crust decoupling of the archean lithosphere occurred and a crocodile jaw formed where the arc rocks are partly buried beneath the bounding archean continent similar features have been recorded in other ap collision zones which could indicate that the buoyant nature of the archean lithosphere combined with denser paleoproterozoic lithosphere may be a general cause for decoupling of archean crust and mantle during arc continent collision in paleoproterozoic

modification of a palaeoproterozoic porphyry like system integration of structural geochemical petrographic and fluid inclusion data from the aitik cu au ag deposit northern sweden the aitik cu au ag deposit in the gallivare area in northern sweden is sweden s largest sulphide mine with an annual production of 35 mt of ore and the biggest open pit operation in northern europ

160 ma of magmatic hydrothermal and metamorphic activity in the gallivare area re os dating of molybdenite and u pb dating of titanite from the aitik cu au ag deposit northern sweden host rocks to the aitik cu au ag deposit in northern sweden are strongly altered and deformed early proterozoic mica amphibole schists and gneisses the deposit is characterised by numerous mineralisation styles vein and alteration types four samples were selected for re os molybdenite dating and 12 samples for u pb titanite dating in order to elucidate the magmatic hydrothermal and metamorphic history following primary ore deposition in the aitik cu au ag deposit samples represent dyke vein and alteration assemblages from the ore zone hanging wall and footwall to the deposit re os dating of molybdenite from deformed barite and quartz veins yielded ages of 1 876 10 ma and 1 848 8 ma respectively a deformed pegmatite dyke yielded a re os age of 1 848 6 ma and an undeformed pegmatite dyke an age of 1 728 7 ma u pb dating of titanite from a diversity of alteration mineral associations defines a range in ages between 1 750 and 1 805 ma with a peak at ca 1 780 ma the ages obtained together with previous data bracket a 160 ma 1 890 1 730 ma time span encompassing several generations of magmatism prograde to peak metamorphism and post peak cooling events resulting in the redistribution and addition of metals to the deposit this multi stage evolution of the aitik ore body suggests that the deposit was affected by several thermal events that ultimately produced a complex ore body the re os and u pb ages correlate well with published regional re os and u pb age clusters which have been tied to major magmatic hydrothermal and metamorphic events primary ore deposition at ca 1 890 ma in connection with intrusion of haparanda granitoids was followed by at least four subsequent episodes of metamorphism and magmatism early metamorphism at 1 888 1 872 ma overlapping with haparanda 1 890 1 880 ma and perthite monzonite 1 880 1 870 ma magmatism clearly affected the aitik area as well as late metamorphism and lina magmatism at 1 810 1 774 ma and tib1 magmatism at 1 800 ma the 1 848 ma re os ages obtained from molybdenite in a quartz vein and pegmatite dyke suggests that the 1 850 ma magmatism recorded in parts of northern norrbotten also affected the aitik area

new constraints on the timing of host rock emplacement hydrothermal alteration and iron oxide apatite mineralization in the kiruna district norrbotten sweden high spatial resolution zircon u pb geochronological data obtained directly on the kiirunavaara iron oxide apatite ioa deposit related orebodies and host rocks provide new constraints on the timing of mineralization in these deposits these data raise new arguments in the debate of a magmatic versus hydrothermal metasomatic genesis of these major 2 500 mt 30 70 wt fe paleoproterozoic deposits the main orebody at kiirunavaara contains ti poor magnetite and minor 0 05 5 wt p apatite located between a trachyandesite footwall and a rhyodacite hanging wall which also hosts smaller orebodies nukutus rektorn and tuolluvaara the pervasive na and k metasomatism in the host rock is documented by whole rock geochemical data and cathodoluminescence cl microscopy zircon u pb data for the metavolcanic rocks in the footwall and hanging wall cluster between 1884 4 and 1880 3 ma in the footwall a syenite aplite system yields ages of 1880 7 and 1881 4 ma a granite pluton exposed underground has an age of 1874 4 ma zircons in two ore samples never directly dated before this study yield ages of 1877 4 and 1874 7 ma brecciation at the contacts between the ore and host rocks the tight age at ca 1880 ma for most volcanic and plutonic rocks in the footwall and hanging wall and the marginally younger age for ore at ca 1877 to 74 ma matching the age of the spatially related granite pluton suggest a magmatic hydrothermal emplacement model for the kiruna area ioa ores

in situ u pb and trace element analysis of accessory minerals in the kiruna district norrbotten sweden new constraints on the timing and origin of mineralization northern norrbotten sweden is a key part of baltic shield and provides a record of magmatic tectonic and related superimposed fe oxide apatite and iron oxide copper gold iocg mineralization during the svecokarelian orogeny titanite and allanite from a range of mineral deposits in the area have been analysed for u pb isotope systematics and trace element chemistry using laser ablation quadrupole inductively coupled plasma mass spectrometry la icp ms analyses of a single sample from the regional scapolite albite alteration give an age of 1903 8 ma 2 and may be contemporaneous with the early stages of fe mineralization 1890 1870 ma analyses of titanite and allanite from undeformed iocg deposits indicate initial alteration at 1862 16 ma in many deposits subsequent metamorphic effects reset titanite isotope systematics from 1790 to 1800 ma resulting in a spread of u pb isotope analyses along concordia in some instances core regions may record evidence of early thermal events at around 2050 ma titanite and allanite from deformed iocg deposits on major shear zones record ages from 1785 21 ma to 1777 20 ma corresponding to deformation metamorphism and secondary hydrothermal alteration as a result of late orogenic movements the lack of intracrystalline variations in titanite and allanite trace element chemistry suggests that hydrothermal fluid chemistry and metal source were the main controls on mineral trace element chemistry titanite from undeformed fe oxide apatite and iocg deposits is typically light rare earth element lree enriched and shows low u th ratios and low ni in both intermediate to acid and basic volcanic hosted deposits this is consistent with a granitic source for metals minor variations in trace element patterns are consistent with the influence of aqueous complex formation on relative ree solubility deposits related to the nautanen deformation zone have relatively heavy ree hree enriched titanite and lree depleted allanite with high u th ratios and elevated ni contents consistent with leaching of metals from the local basic volcanic rocks all hydrothermal titanites are high field strength element enriched nb ta zr indicating their transport as a result of either high salinities or high f contents or both the data overall support models of iocg type mineralization as a result of regional circulation of saline hydrothermal fluids in association with major crustal structures with at least some metallic components derived from the granitoid rocks of the area all the deposits here show evidence of subsequent metamorphism although penetrative fabrics are restricted to regional scale deformation zones

timing of plutonism in the gallivare area implications for proterozoic crustal development in the northern norrbotten ore district sweden zircon ion probe secondary ion mass spectrometry or sims data from a set of intrusive rocks emplaced in the vicinity of major ore bodies as well as from large igneous intrusions in the gallivare

delineation and character of the archaean proterozoic boundary in northern sweden abstract before the deposition of a proterozoic cover and the repeated proterozoic reworking of the older rocks the presently exposed archaean areas in northern sweden formed part of a coherent craton in the present study we have used sm nd isotopic analyses of proterozoic granitoids and metavolcanics to delineate the archaean palaeoboundary in a regional context the transition from strongly negative nd t values in the northeast to positive values in the southwest is distinct and approximately defines the border of the old craton the archaean palaeoboundary extends in a wnw direction and is subparallel to the longitudinal axis of the skellefte sulphide ore district but it is situated 100 km farther to the north the 1 9 ga old granitoids on the two sides of the palaeoboundary were all formed in compressional environments but those situated to the north have higher contents of lile and lree at similar contents of si this indicates that they were generated in an area with thicker crust and supports the location of the archaean proterozoic palaeoboundary there is no simple correlation between the archaean palaeoboundary as defined by the isotopic results and any of the major fracture systems as interpreted from regional geophysical measurements reflection seismic work indicates that juvenile volcanic arc terrains to the south have been thrust onto the archaean craton possible thrust faults have been identified from aeromagnetic measurements rifting of the archaean craton created a passive margin 2 0 ga ago spreading shifted to convergence with subduction beneath the archaean continent 1 9 ga ago subsequently the resulting juvenile volcanic arc collided with the old continent and the archaean palaeoboundary as existing today was formed by a collision characterized by overthrusting the boundary then was disturbed by later deformation predominantly along nne trending fracture systems

subsiding shells around shallow cumulus clouds abstract in this study large eddy simulations les are used to gain more knowledge on the shell of subsiding air that is frequently observed around cumulus clouds first a detailed comparison between observational and numerical results is presented to better validate les as a tool for studies of microscale phenomena it is found that horizontal cloud profiles of vertical velocity humidity and temperature are in good agreement with observations they show features similar to the observations including the presence of the shell of descending air around the cloud second the availability of the complete 3d dataset in les has been exploited to examine the role of lateral mixing in the exchange of cloud and environmental air the origin of the subsiding shell is examined by analyzing the individual terms of the vertical momentum equation buoyancy is found to be the driving force for this shell and it is counteracted by the pressure gradient force this shows that evaporative cooling at the cloud edge

composite vertical structure of vertical velocity in nonprecipitating cumulus clouds abstractvertical transects of doppler vertical velocity data obtained from an airborne profiling millimeter wave cloud radar are composited for a large number of cumulus clouds cu at various stages of their life cycle to examine typical circulations patterns the cu clouds range in depth between 500 and 6000 m and are generally nonprecipitating they were sampled on board the university of wyoming king air over a mountain in southern arizona during the summer monsoon and over the high plains of southeastern wyoming the composite analysis shows clear evidence of an updraft downdraft dipole in the upper cloud half consistent with a horizontal vortex ring a single cloud scale toroidal circulation emerges notwithstanding the complex finescale structure with multiple vortices commonly evident in individual transects of cu clouds the stratification of all cu samples as a function of their buoyancy and mean vertical velocity shows that the vortex ring pattern tends to be more pronounced in positively

sm nd isotope evidence of a collisional event in the precambrian of northern sweden abstract the sm nd isotope characteristics of c 1 9 and c 1 8 ga granitoids occurring close to the edge of the archaean craton in northern sweden have been studied strongly negative e nd t values occur farther southwest in the potassic 1 8 ga granitoids than in the calc alkaline 1 9 ga granitoids intrusions of the younger granitoids with distinctly negative e nd t values are surrounded by granitoids of the older group with positive values northeast of the 1 8 ga granitoids discussed here the c 1 9 ga calc alkaline intrusions formed within the archaean continent have the same sm nd isotope characteristics as the 1 8 ga granitoids to the southwest our interpretation is that a juvenile volcanic arc terrane to the south collided with and was thrust onto the archaean continent after the formation of the 1 9 ga granitoids the outcome was that these juvenile rock masses were obducted onto the reworked archaean continent the 1 8 ga granitoids were formed by remobilisation of continental crust partial melting at 1 8 ga resulted in the intrusion of granitoids carrying the sm nd isotopic signature of the archaean continent into juvenile rocks it is probable that the collision discussed here was part of a major accretion and amalgamation to the archaean craton after the formation of the calc alkaline 1 9 ga granitoids but before the formation of the 1 8 ga granitoids

u pb dating of columbites a geochronologic tool to date magmatism and ore deposits we have developed techniques for the u pb analysis of the mineral columbite fe mn ta nb 2o6 and report u pb ages obtained for three early proterozoic columbites from the baltic shield of northern sweden the u pb ages of these columbites agree with other available geochronological data u pb dating of columbite is therefore a potentially powerful tool in establishing reliable ages of pegmatites alkaline and carbonatitic intrusions and ore deposits of sn w and rees all of which often contain columbite furthermore columbite can be used to date peraluminous granites as it often occurs within li p ree pegmatites associated with such granites

the structure of thermals in cumulus from airborne dual doppler radar observations abstract a newly developed technique for airborne dual doppler observations with the wyoming cloud radar is used to characterize the velocity fields in vertical planes across cumulus turrets the clouds sampled were continental in nature with high bases near 0 c and with depths of 2 3 km clear evidence was found that the clouds evolved through sequences of bubbles or thermals with well defined toroidal circulations or vortex rings the ring core and tube diameters were about 200 600 m leading to turret sizes of 1 2 km in the horizontal the largest updraft speeds were observed in the ring centers but regions of turbulent ascending air extended behind the thermals to distances comparable with the toroid sizes vertical shear of ambient winds when present led to a tilting of the updrafts and toroids patterns in the reflectivity and velocity fields indicated regions of major intrusions into the thermals accompanied by entrainment of ambient air or recycling of larger hydrometeors depending on

geochronology of the kiruna iron ores and hydrothermal alterations the magnetite apatite iron ores at kiruna are hosted in a suite of alkaline volcanic and subvolcanic rocks that was formed in a short time interval of about 20 m y between 1900 and 1880 ma u pb dating of titanite from magnetite titanite dikes in the footwall of the luossavaara orebody indicates that the age of the magnetite apatite ores is 1888 or 6 ma titanite actinolite calcite assemblages in amygdules are related to the hydrothermal and metasomatic alteration of the wall rocks and the ore the u pb titanite age of the amygdule fill is 1876 or 9 ma the geographic distribution of the alteration suggests that it is not related to the formation of the iron ores the youngest major magmatic units in the kiruna area are 1792 or 4 ma syenites that intruded the supracrustal rocks the kiruna area underwent a weak metamorphic overprint during the caledonian orogeny our data are inconsistent with a hydrothermal event at ca 1 5 ga as has been suggested earlier

dynamics of the cloud environment interface and entrainment in small cumuli two dimensional simulations in the absence of ambient shear abstract we employ a two dimensional numerical model with interacting nested domains to simulate the evolution of a small nonprecipitating cumulus cloud in the absence of shear grid nesting permits the use of a realistic boundary layer forcing to initiate cloud growth and at the same time the specification of very high spatial resolution in the vicinity of the cloud the finest mesh employed in this study 5 m gives about 160 points across the base of the cloud initially the model produces a cloud which has a smooth upper surface about eight to nine minutes after the onset of condensation nodes appear on the upper cloud boundary these nodes have a characteristic tangential length scale which is small compared to the width of the cloud base in one of our simulations a down draft forms above the center of the cloud top and penetrates into the interior of the cloud the entrainment of this unsaturated air reduces the liquid water content of the cloud below the adiabatic value and curtails growth o

upb systematics of stilbite bearing low temperature mineral assemblages from the malmberget iron ore northern sweden minerals with a low thermal stability strongly constrain the history of cooling and later tectonic reworking of an area provided these minerals can be dated the possible use of stilbite a ca al silicate of the zeolite group for geochronologic studies was investigated open fractures in the palaeoproterozoic malmberget iron ore northern sweden contain low temperature mineral assemblages with various combinations of apatite stilbite calcite biotite and less commonly titanite and monazite two generations of fractures that are characterized by calcite and stilbite with distinctly radiogenic initial 87sr 86sr at ca 0 720 and ca 0 708 are dated at ca 1740 ma monazite and 1620 1613 ma titanite respectively apatite samples even those intimately intergrown with ca 1740 ma old monazite yield u pb ages at 1620 1600 ma which indicates that apatite apparently recrystallized and reset its u pb system older stilbite yields a secondary lead isochron at 1730 6 4 ma 2 which unequivocally demonstrates that the ambient temperature in the malmberget area from then on remained below the thermal stability of stilbite ca 150 c stilbite is a natural ion exchanger and its u pb systematics indicates recent mobility of uranium and lead however the 1730 6 4 ma 2 age demonstrates that some of the older stilbite was not disturbed during younger fracturing hydrothermally altered and secondary stilbite samples yield scattered lead arrays that correspond to secondary isochrons at ca 1650 1600 d4a which agrees with the u pb titanite and apatite ages thus in combination with other geochronometers the generally imprecise stilbite ages provide information on the cooling history of an area

post svecokarelian andinotype evolution in central sweden granitoids and associated volcanics postorogenic in relation to the svecokarelian orogeny constitute a belt in central sweden evidence presented in this paper suggest that the belt originated in an andinotype orogenic environment the inferred development of the belt was characterized by fracture controlled high level emplacement of batholiths in an ensialic setting voluminous venting of ignimbrites and formation of grabens through cauldron subsidence accompanied the recurrent intrusive activity block movements and episodes of burial metamorphism appear to have been prominent features throughout the history of the post svecokarelian belt

implications of new upb zircon chronology to early proterozoic crustal accretion in northern sweden abstract u pb ages ranging from 1 89 to 1 78 ga are reported for zircon populations formed during major magmatic events in the proterozoic development of northern sweden the studied area includes parts of the continental and the marine svecokarelian domains of the baltic shield the ages record crustal accretion and reactivation off the margin of an exposed archaean craton and show that magmatism was broadly coeval throughout the entire north swedish portion of the svecokarelian province irrespective of regions involved a detailed chronostratigraphy is presented for the skellefte district of northern sweden and comparisons are made with the evolution in other parts of the svecokarelian province two main magmatic phases commencing at 1 89 and 1 79 ga ago are recognized the first represents large scale volcanism and plutonism which in the skellefte district was characterized by the introduction of mainly mantle derived magmas or by magmas formed from rocks with short crustal residence time in the vicinity of the archaean craton some distance to the north the crust generating processes included the mobilization of archaean sources and appear to have continued until c 1 85 ga ago a relatively long period of consolidation and denudation separates this magmatic phase from the one at c 1 79 ga ago the generation of these later migmatite associated granites in the svecokarelian province coincided in time and was possibly associated with those processes which gave rise to the initial plutonism in the neighbouring transscandinavian granite porphyry belt