the petrogenesis of the neoarchean kukuluma intrusive complex nw tanzania abstract the kukuluma intrusive complex kic is a late archean igneous complex dominated by monzonite and diorite with subordinated granodiorite the monzonite and the diorite suites have low silica content sio2 62 wt moderate mg mg average 49 high sr y sr yaverage 79 and high la yb la ybaverage 56 ratios and strongly fractionated lan ybn 9 69 ree patterns their moderate ni niaverage 50 ppm cr craverage 85 ppm variable cr ni ratio 0 65 3 56 and low tio2 tio2average 0 5 wt indicate little to no interaction with the peridotitic mantle for most major elements al2o3 feot na2o tio2 and p2o5 the monzonite and the diorite suites display subparallel trends for the same sio2 content indicating they represent distinct melts intrusions belonging to the diorite suite have high na2o na2oaverage 4 2 wt dy ybn dy ybn average 1 6 a positive sr anomaly and uncorrelated nb la and zr sm ratios suggesting derivation from partial melting of garnet bearing amphibolite intrusions belonging to the monzonite suite have higher na2o na2oaverage 5 61 wt dy ybn dy ybn average 2 21 a negative sr anomaly and correlated nb la and zr sm ratios consistent with derivation from partial melting of eclogite with residual rutile small variations in the th u ratio and near chondritic morb average values th umonzonite 3 65 th udiorite 2 92 are inconsistent with a subducting slab signature and it is proposed that the monzonite and the diorite suites of the kic formed by partial melting of garnet bearing lower mafic crust of an oceanic plateau the granodiorite suite has lower mg mg average 41 moderately fractionated ree low sr y sr yaverage 20 la yb la ybaverage 15 dy ybn dyybn average 1 24 and small negative eu anomalies suggesting derivation from partial melting of amphibolite and plagioclase fractionation near morb th u th uaverage 2 92 and zr sm zr smaverage 30 21 ratios are consistent with intracrustal melting of amphibolite archean rocks with an adakitic geochemical signature have been used to argue in favour of a plate tectonics regime in the archean the results presented here suggest that tectonic models for the tanzania craton which invoke a subduction related setting for all greenstone belts may need revision

ore metal redistribution by hydrocarbon brine and hydrocarbon halide melt phases north range footwall of the sudbury igneous complex ontario canada we report methane dominant hydrocarbon fluid inclusions ch4 c2h6 c2h2 c3h8 coexisting with primary brine inclusions and secondary halide melt solid nacl inclusions in au pt rich quartz sulfide epidote alteration veins associated with the footwall style cu pge platinum group element au deposits at the fraser mine north range of the sudbury igneous complex evidence for coentrapment of immiscible hydrocarbon brine and hydrocarbon halide melt mixtures is demonstrated a primary ch4 brine assemblage was trapped during quartz growth at relatively low t min ttrapping 145 315 c and p max ptrapping 500 bar prior to the crystallization of sulfide minerals in the veins secondary inclusions contain solid halite and a mixture of ch4 c2h6 c2h2 and c3h8 and were trapped at a minimum t of 710 c the halite inclusions may represent halide melt that exsolved from crystallizing sulfide ores that texturally postdate by replacement early alteration quartz hosting the primary lower t brine ch4 assemblage laser ablation icp ms analyses show that the brine hydrocarbon and halide melt inclusions contain significant concentrations of cu 0 1 1 wt range au bi ag and pt all 0 1 10 ppm range cu pt and cu au ratios in the inclusions are significantly up to 4 log units lower than in the host alteration veins and adjacent massive sulfide ore veins suggesting either 1 early cu loss from the volatiles by chalcopyrite precipitation or 2 enhanced au and pt solubilities relative to cu at the temperatures of entrapment concentration ratios between coexisting brine and ch4 inclusions c rm elem rm brine c rm elem rm ch 4 are lower for cu au bi and ag than for other elements na ca fe mn zn pb indicating that during interaction with the brine the hydrocarbon phase was enriched in ore metals the high concentrations of ore metals in hydrocarbon brine and halide melt phases confirm that both aqueous and non aqueous volatiles were carriers of precious metals in the sudbury environment over a wide range of temperatures volatile evolution and magmatic sulfide differentiation were clearly part of a single continuous process in the sudbury footwall the exsolution of h2o poor volatiles from fractionated sulfide liquid may have been a principal mechanism controlling the final distribution of pge and au in the footwall ore systems the study reports the first measurements of precious metal concentrations in fluid inclusions from a magmatic ni cu pge environment the sudbury district

insar observations of 2007 tanzania rifting episode reveal mixed fault and dyke extension in an immature continental rift summary in the early stages of continental rifting extension takes place by normal faulting while in mature continental rifts dyke intrusion dominates little is known about the nature of the transition between fault controlled and dyke controlled extension or about the processes in an intermediate setting here we present observations of the temporal and spatial evolution of surface displacements during the 2007 july 14 august 4 rifting episode in northern tanzania an immature section of the east african rift the ground deformation initiated with subsidence that can be attributed to 40 cm of normal motion on a ne striking fault following july 17 deformation was dominated by the intrusion of 7 km long dyke dyke opening increased gradually to a total of 2 4 m from july 21 the collapse of a shallow graben above the fault dominated the near field displacements comparison to the 2007 dabbahu dyke afar which occurred in a more mature rift shows an order of magnitude scale difference in dyke length using numerical models of dyke propagation we attribute this to the size and depth of the magma chamber in immature rifts the thick crust and slow spreading rate favour small deep magma chambers forming short buried dykes whereas in mature rifts the thinner crust and faster spreading rate favour large shallow magma chambers and long erupting dykes observing the pattern of active processes in the east african rift is key to understanding the development of rift systems and passive margins elsewhere

rhenium osmium and samarium neodymium isotopic systematics of the stillwater complex isotopic data for the stillwater complex montana which formed about 2700 ma million years ago were obtained to evaluate the role of magma mixing in the formation of strategic platinum group element pge ore deposits neodymium and osmium isotopic data indicate that the intrusion formed from at least two geochemically distinct magmas ultramafic affinity u type magmas had initial e nd of 0 8 to 3 2 and a chondritic initial 187 os 186 os ratio of 0 88 whereas anorthositic affinity a type magmas had e nd of 0 7 to 1 7 and an initial 187 os 186 os ratio of 1 13 these data suggest that u type magmas were derived from a lithospheric mantle source containing recycled crustal materials whereas a type magmas originated either by crustal contamination of basaltic magmas or by partial melting of basalt in the lower crust the nd and os isotopic data also suggest that os and probably the other pges in ore horizons such as the j m reef was derived from a type magmas the nd and os isotopic heterogeneity observed in rocks below the j m reef also suggests that a type magmas were injected into the stillwater u type magma chamber at several stages during the development of the ultramafic series

two types of neoarchean basalts from qingyuan greenstone belt north china craton petrogenesis and tectonic implications abstract geochronological geochemical and isotopic studies were carried out on the basalts from the qingyuan greenstone belt to understand the petrogenesis of the basalts and the mantle source characteristics providing insights into neoarchean geodynamic evolution of the north china craton the qingyuan greenstone belt is analogous to the typical barberton type greenstone belt in lithological units u pb isotopic dating using the la icp ms method on zircons from the basalts and the associated andesite reveals that they erupted at 2510 2545 ma and were subjected to subsequent 2486 2491 ma metamorphism the basalts are high fe tholeiitic showing coherently positive end t and ehf t values the geochemical and isotopic studies strongly imply that they experienced significant fractional crystallization and minor no crustal contamination during magma evolution on the basis of chondrite normalized ree patterns the basalts can be further divided into two types viz the enriched and the depleted the enriched basalts are abundant in lree and rees contents depleted in hfses nb zr ti endowed with arc like geochemical peculiarities modeling reveals that the parent magma of the enriched basalts has been derived from 70 to the depleted basalts the basalts from the neoarchean qingyuan greenstone belt witness the episode of the vertical growth of continental crust at ca 2 5 ga combined with other geological considerations a large archean mantle plume model is favored to account for the generation of the late neoarchean basalts from qingyuan greenstone belt in the eastern block north china craton

decorrelation in interferometric radar echoes a radar interferometric technique for topographic mapping of surfaces implemented utilizing a single synthetic aperture radar sar system in a nearly repeating orbit is discussed the authors characterize the various sources contributing to the echo correlation statistics and isolate the term which most closely describes surficial change they then examine the application of this approach to topographic mapping of vegetated surfaces which may be expected to possess varying backscatter over time it is found that there is decorrelation increasing with time but that digital terrain model generation remains feasible the authors present such a map of a forested area in oregon which also includes some nearly unvegetated lava flows such a technique could provide a global digital terrain map

toward mapping surface deformation in three dimensions using insar 1 one of the limitations of deformation measurements made with interferometric synthetic aperture radar insar is that an interferogram only measures one component of the surface deformation in the satellite s line of sight we investigate strategies for mapping surface deformation in three dimensions by using multiple interferograms with different imaging geometries geometries for both current and future missions are evaluated and their abilities to resolve the displacement vector are compared the north component is always the most difficult to determine using data from near polar orbiting satellites however a satellite with an inclination of about 60 120 would enable all three components to be well resolved we attempt to resolve the 3d displacements for the 23 october 2002 nenana mountain alaska earthquake the north component s error is much larger than the signal but proxies for eastward and vertical motion can be determined if the north component is assumed negligible inversions of hypothetical coseismic interferograms demonstrate that earthquake model parameters can be well recovered from two interferograms acquired on ascending and descending tracks

coseismic displacements from the hector mine california earthquake results from survey mode global positioning system measurements we describe the collection and processing of global positioning system gps data from 77 locations around the hector mine earthquake which we use to estimate coseismic displacements related to this shock the existence of pre event gps data some collected to monitor postseismic displacements from the 1992 landers earthquake and some to establish survey control in the meizoseismal area provided a relatively dense coverage close to the rupture zone the data available were collected mostly within the 2 years prior to the 1999 earthquake we reobserved many points within a few days after the shock and all within 6 months after we include corrections for interseismic motion to provide the best value possible for coseismic motion caused by this earthquake the displacements in general display the pattern expected for a strike slip fault though a few show significant vertical motion the maximum horizontal displacement observed was 2 m one station between fault ruptures showed little horizontal motion but significant uplift

zircon u pb ages and lu hf isotope systematics from late tectonic granites geita greenstone belt implications for crustal growth of the tanzania craton granite plutons that intruded south of lake victoria and north of the geita greenstone belt have geochemical characteristics similar to high k granites when compared to the late high k granites from the musoma mara region they have lower sio2 content and higher tio2 al2o3 cao na2o p2o5 mgo and feot they also show higher values for v sr zr ba and hf concentrations all samples display high total ree abundances ree 139 393 and weak to moderate eu depletion eu eu 0 25 0 77 their chondrite normalized pattern indicates that the light ree are moderately fractionated 3 03 lan smn 6 24 whereas the heavy ree are weakly fractionated 1 63 gdn ybn 2 80 the granite plutons are generally undeformed with 207pb 206pb ages between 2660 and 2620 ma and intruded after the main ductile deformation that affected the geita greenstone belt the 176hf 177hf ratios for zircons from all samples are identical within error suggesting evolution from an isotopically uniform reservoir the hf values plot along the chur evolution line indicating that the granite represents juvenile crustal melts derived from greenstone material available zircon ages from the tanzania craton suggest that crustal growth occurred in three distinct periods 2850 2800 ma 2770 2730 ma and 2700 2620 ma with the dominant period of crustal growth around 2700 ma zircon ages from the sukumaland and musoma mara greenstone belts indicate that the greenstone sequences formed during the same three periods of crustal growth

multiple events in the neo tethyan oceanic upper mantle evidence from ru os ir alloys in the luobusa and dongqiao ophiolitic podiform chromitites tibet in situ analysis of major elements platinum group elements and os isotope composition data for 170 grains of ru os ir alloys from podiform chromitites in the luobusa and dongqiao ophiolites tibet provide new constraints on the sources of the alloy grains the os isotope composition of the neo tethyan oceanic upper mantle and the timing of melt rock reactions in the ultramafic peridotites of the host ophiolites most alloy grains are osmiridium and iridosmine based on elemental and isotopic compositions two populations can be identified group i found in both ophiolite bodies has fractionated pge patterns typical of alloys and homogeneous 187 os 188 os 0 12645 4 2s n 145 group ii alloys from the dongqiao ophiolites show smooth pge patterns and 187 os 188 os ranges from 0 12003 to 0 12194 yielding re depletion ages 1 1 ga both the pge patterns and the os isotopic compositions of group ii resemble those of sulfides residual after melting group i alloys represent an early cumulate phase during the crystallization of magmas and are interpreted as derived from an asthenospheric melt in contrast group ii alloys are inferred to derive from the breakdown of residual sulfides from the mantle section of the ophiolite which may represent relics of a sub continental lithospheric mantle the coexistence of the two groups of alloys in dongqiao samples reflects interaction between asthenosphere derived melts and old depleted lithospheric mantle and suggests that the chromitites originated through melt rock reactions the data on the group i alloys support the hypothesis that the re os evolution of the convective oceanic mantle resembles that of enstatite chondrites 2007 elsevier b v all rights reserved

experiments and models bearing on the role of chromite as a collector of platinum group minerals by local reduction chromite is widely recognized to act as a collector for platinum group elements pge which tend to be observed as discrete grains of platinum group minerals included within magmatic chromite grains in the course of experiments involving the re equilibration or growth of chromite and cr spinel in molten silicate we observe that platinum group minerals pgm including metal alloys and laurite form at the mineral melt interface the formation of pgm to the extent observed requires a mechanism involving sustained transport of pge from a source within the experiment to the site of deposition we propose that the driving force for this process is a redox gradient developed in response to mineral growth or re equilibration with the surrounding melt the mechanism is local reduction within the mineral melt interfacial region as a consequence of the selective uptake of trivalent cr and fe from the melt by spinel relative to the divalent species we have modeled the transient perturbation of fo2 in a compositional boundary layer melt around spinel for both crystal growth and diffusive re equilibration of mineral and melt we find that metal solubilities decrease by several per cent in the silicate melt at the melt crystal interface during crystal growth providing the driving force for pgm formation in magmas that are saturated with pgm as a result of falling temperature and oxygen fugacity during spinel crystallization nucleation of pgm will be impeded by interfacial tension everywhere except in the reduced boundary layer around spinel crystals the resulting concentration and trapping of alloy particles in the growing chromite crystals can produce apparent bulk chromite melt partition coefficients exceeding 20 even if there is no solid solution of pge in the chromite the introduction of spinel grains initially equilibrated with a mafic magma into a more primitive magma with higher cr al would lead to disequilibrium between chromite and melt the perturbation of fo2 in the compositional boundary layer surrounding a chromite xenocryst would exceed 0 1 log unit leading to local reduction of alloy solubility of the order of 13 18 a small number of spinel xenocrysts could serve as collection sites for all of the excess pge in the magma leading to the eventual observation that a few chromite crystals contain many pgm inclusions whereas the rest of the chromite population may be relatively free of pgm

simulation of the supersar multi azimuth synthetic aperture radar imaging system for precise measurement of three dimensional earth surface displacement the supersar imaging system a novel multi azimuth synthetic aperture radar sar system capable of detecting earth surface deformation in three dimensions from a single satellite platform has recently been proposed in this paper we investigate the feasibility of detecting precise 3 d surface displacement measurements with the supersar imaging system using a point target simulation from this simulation we establish both a relationship between the interferometric sar phase and the across track displacement and a relationship between the multiple aperture interferometry phase and the along track displacement based on the supersar imaging geometry the theoretical uncertainties of the supersar measurement are analyzed in the across and along track directions and the theoretical accuracy of the 3 d displacement measurement from the supersar system is also investigated according to both the decorrelation and the squint and look angles in the case that the interferometric coherence is about 0 8 and that five effective looks are employed the theoretical 2 d measurement precision values are about 3 67 and 6 35 mm in the across and along track directions respectively and the theoretical 3 d measurement precision values for 3 d displacement are about 4 05 4 56 and 3 45 mm in the east north and up directions respectively the result of this study demonstrates that the supersar imaging system is capable of measuring the 3 d surface displacement in all directions with subcentimeter precision

multi track extraction of two dimensional surface velocity by the combined use of differential and multiple aperture insar in the amery ice shelf east antarctica abstract glaciers and ice streams drain the ice from the ice sheets to the ice shelves and contribute to global sea level changes therefore ice velocity is an essential parameter for the assessment of mass balance in this paper we propose an approach for the multi track extraction of two dimensional ice surface velocity by the combined use of multiple aperture interferometry mai and differential synthetic aperture radar interferometry dinsar the azimuth and ground range ice movements of each individual track are first estimated by the use of mai and dinsar respectively a seamless two dimensional ice velocity map is then achieved by calibration and mosaicking of the estimated velocity of the multi temporal and multi track measurements over a large area finally the dynamic behavior of the amery ice shelf is analyzed by formulating a long term series of ice flow velocities consisting of historical surface velocities 1968 1990 the estimated surface velocity by the proposed method with ers 1 2 data 1996 existing surface velocity products such as the radarsat 1 antarctic mapping project ramp velocities 1997 2000 and rignot s results 2007 2010 as well as the estimated velocities obtained by the use of the offset tracking method from landsat 8 images 2013 2014 the results show that the estimated velocity obtained by the use of the proposed method is superior to the other methods and the long term series of ice velocity measurements shows that the ice velocity in the amery ice shelf has hardly changed over the past 45 years 1968 2014 we conclude that the ice flow velocity of the amery ice shelf has showed a slight deceleration over the past 45 years

evidence of nonlinear elasticity of the crust from the mw7 6 manyi tibet earthquake satellite synthetic aperture radar sar interferometry shows that the magnitude 7 6 manyi earthquake of 8 november 1997 produced a 170 kilometer long surface break with up to 7 meters of left lateral slip reactivating a n76 e quaternary fault in western tibet the radar interferometric map reveals asymmetric along strike displacement profiles between the two sides of the surface rupture a pattern that cannot be explained with linear elastic theory this observation suggests that the elastic moduli of the crust in tension and in compression are different because of the presence of cracks in the crust at shallow depth a model indicates that a ratio of 2 between compressive and tensile elastic moduli can account for the observed asymmetry a ratio that is consistent with laboratory and borehole measurements

an improvement of the performance of multiple aperture sar interferometry mai multiple aperture synthetic aperture radar sar interferometry mai enables the measurement of along track surface deformations by means of split beam sar processing this paper examines the effects of flat earth and topographic phases on the mai phase and derives formulas to correct them detailed mai processing steps are introduced and discussed with particular consideration given to coherence improvement as well as to computational efficiency forward and backward looking mai pairs have different perpendicular baselines which play a key role in phase distortion consequently an orbital deviation of only a few centimeters could result in a significant flat earth phase a second order polynomial model was used to estimate the perpendicular baseline difference european remote sensing 2 satellite sar data sets of the hector mine earthquake event in 1999 were used for performance evaluation the proposed processing with the flat earth and topographic phase corrections achieved precision of along track deformation ranging from 10 2 to 13 1 cm two coseismic pairs were compared and the standard deviation of the difference between the two independent measurements was 7 0 cm with a mean difference of 0 24 cm thus the measurement accuracy of mai was improved using flat earth correction and coherence enhancement

the serra pelada au pge deposit serra dos carajas para state brazil geological and geochemical indications for a composite mineralising process the serra pelada au pge rich deposit is located in the serra dos carajas a leading mining area in brazil this region is characterised by a complex geological and structural framework and is affected by deep lateritisation which has lasted for more than 70 ma the serra pelada deposit is emplaced in a late archean low grade metasedimentary sequence rio fresco aguas claras formation which is host to other gold deposits in the region igarape bahia aguas claras the rio fresco aguas claras sequence was deposited in tectonic basins developed on archean basement and au bearing greenstone terranes which were intruded by pge rich layered mafic complexes e g luanga the serra pelada mineralisation is located along a regional complex system of strike slip faults cinzento carajas systems which were active during the late archean to early proterozoic the mineralisation appears to be concentrated along a faulted hinge zone of a fold ore zone rock facies are dominated by low grade ferruginous to carbonaceous metasiltstones and minor sandstones locally brecciated and cemented by quartz sulphide stockwork supergene alteration led to partial to total transformation into friable aggregates of kaolinite fe oxide hydroxides silica and secondary phosphate sulphates even at depths exceeding 200 m precious metals are exceptionally enriched with up to more than 1 000 ppm au pge in some peculiar ferruginous graphitic zones locally called hidrotermalito geochemistry shows complex patterns of major and trace elements particularly rare earth elements ree in mineralised vs nonmineralised samples these patterns are interpreted in terms of variable degree of superposition of hydrothermal and supergene alteration precious metals show progressive increase from samples with hydrothermal imprint to samples with supergene imprint the geological evolution of the carajas region and the characteristics of mineralisation at serra pelada may suggest a composite mineralising process hydrothermal activity by fluids likely originated from granitoids was followed by supergene alteration during long lasting lateritisation to develop extreme precious metal enrichments in a geological context probably already anomalous for au and pge

measuring ground displacements from sar amplitude images application to the landers earthquake ers sar amplitude images are utilized to map ground displacements from a sub pixel correlation method it yields a ground two dimensional displacement field with independent measurements about every 128m in azimuth and 250m in range the accuracy depends on the characteristics of the images for the landers test case the 1 uncertainty is 0 8m in range and 0 4m in azimuth we show that this measurement provides a map of major surface fault ruptures accurate to better than 1km and information on coseismic deformation comparable to the 92 gps measurements available although less accurate this technique is more robust than sar interferometry and provides complementary information since interferograms are only sensitive to the displacement in range

surface displacements and source parameters of the 2003 bam iran earthquake from envisat advanced synthetic aperture radar imagery 1 the mw 6 6 26 december 2003 bam iran earthquake was one of the first earthquakes for which envisat advanced synthetic aperture radar asar data were available using interferograms and azimuth offsets from ascending and descending tracks we construct a three dimensional displacement field of the deformation due to the earthquake elastic dislocation modeling shows that the observed deformation pattern cannot be explained by slip on a single planar fault which significantly underestimates eastward and upward motions se of bam we find that the deformation pattern observed can be best explained by slip on two subparallel faults eighty five percent of moment release occurred on a previously unknown strike slip fault running into the center of bam with peak slip of over 2 m occurring at a depth of 5 km the remainder occurred as a combination of strike slip and thrusting motion on a southward extension of the previously mapped bam fault 5 km to the east

translithospheric mantle diapirism geological evidence and numerical modelling of the kondyor zoned ultramafic complex russian far east we report new structural microstructural petrological and major and trace element data on ultramafic rocks from the kondyor zoned ultramafic complex in far east russia the ultramafic rocks are subdivided into three subconcentric lithologies from core to rim 1 a metasomatic domain where generally phlogopite rich dykes pervasively intrude dunite 2 a main dunite core 3 a pyroxenite rim the ultramafic rocks have nearly vertical contacts with the surrounding archaean basement gneisses quartzites and marbles and hornfelsed riphean sediments the hornfelsed sediments show a relatively steep 60 outward dipping layering which rapidly flattens to horizontal away from the inner contact although the riphean sediments define a dome like structure the inward shallow dipping foliation of the dunites indicates a synformal structure detailed petro structural investigations indicate that the kondyor dunites were deformed by solid state flow under asthenospheric mantle conditions the outward textural change from coarse to fine grained equigranular dunite and the outward increasing abundance of subgrains and recrystallized olivine grains suggest dynamic recrystallization while fluid circulation was channelized within the core metasomatic zone with a decreasing melt fraction from core to rim and also suggest that solid state deformation induced grain size reduction towards the cooling border of the kondyor massif based on their geochemistry the dunites are interpreted as mantle rocks strongly affected by reaction with melts similar to the jurassiccretaceous aldan shield lamproites rim pyroxenites were formed by a melt consuming peritectic reaction implying the existence of at least a small conductive thermal gradient around the dunite body while the latter was still at near solidus temperature conditions this suggests that the zoned structure of kondyor was initiated at mantle depths most probably within the subcontinental lithosphere upon cooling the lamproitic melts were progressively focused in the central part of the massif and drained into vein conduits where they reacted with the wall rock dunite two dimensional numerical modelling based on finite differences with a marker in cell technique incorporates temperature dependent rheologies for both molten and non molten host rocks the modelling consolidates the structural petrological and geochemical interpretations which show that the dunites represent the synformal flat lying apex of an asthenospheric mantle diapir triggered by fluid pressure channelized in the core which nearly reached the earths surface we conclude that translithospheric mantle diapirism is an important mode of mass transfer in the earth

the significance of partial melting processes in hydrothermal low sulfide cu ni pge mineralization within the footwall of the sudbury igneous complex ontario canada we present new results and review existing data highlighting different aspects of the genetic relationship between partial melting and hydrothermal mineralizing processes in the contact aureole of the sudbury igneous complex at the basal contact of the igneous complex in the footwall breccia crystallized partial melt pods and veins referred to as footwall granophyres are abundant and intrude all rock types including the breccia matrix as well as massive ni cu sulfide ore the final crystallization of these melts was accompanied by the segregation of high salinity fluids dominantly in the temperature range of 450 to 550 c as revealed by ti inquartz thermometry and studies on primary fluid inclusions in mineralized parts of the footwall breccia there is clear evidence that interaction of partial melts exsolved fluids and preexisting magmatic sulfides occurred in the deeper footwall of the sudbury igneous complex similar footwall granophyres occur as networks of veins intruding impact brecciated sudbury breccia country rocks and have an intimate spatial association with hydrothermal low sulfide assemblages highly enriched in pt pd and au with a unique assemblage of pgm including malyshevite and lisiguangite it is suggested that partial melting processes were widespread in the contact and proximal footwall environment of the igneous complex and they were important in providing high salinity magmatic fluids to a hydrothermal system responsible for redistribution of base and precious metals we describe observations which may evidence the migration of partial melts from the contact into the deeper footwall furthermore we suggest a cogenetic model for the precipitation of sulfide hydrous silicate assemblages in close spatial association to footwall granophyres we emphasize that the use of footwall granophyres in mineral exploration for cu ni pge ores in the footwall of the sudbury igneous complex is clearly justified mapping of footwall granophyre vein networks highlights areas that were proximal to the contact environment and point out structural pathways that may have been used by syn or postgenetic mineralizing fluids in a given area widespread partial melting appears to have occurred in the footwall of other large mafic ultramafic complexes such as bushveld and duluth and similar genetic relationships of partial melting and ore forming hydrothermal processes may have possibly existed also in these systems

the deformation field of the august 2003 eruption at piton de la fournaise reunion island mapped by asar interferometry 1 three independent asar interferograms spanning the august 2003 piton de la fournaise eruption reveal a 3 by 3 km asymmetric pattern of range changes centred on the dolomieu crater northern flank it corresponds to 30 cm of displacement towards the satellite east of the eruptive fissures and 7 cm away from the satellite west of the fissures displacements are caused by dyke emplacement below fissures we model the deformation using a 3d mixed boundary element method for elastic media this consists of a dyke defined by six geometric parameters and an overpressure gradient a neighbourhood algorithm was applied to explore this 7 dimensional parameter space the best fit model is a 57 eastward dipping dyke with a base lying around 1520 m a s l the model provides new evidence of the dyke intrusion related seaward displacements of the volcano eastern flank

mantle and slab contributions in arc magmas destructive plate margins are major sites of terrestrial magmatism that have long had a key role in models for the generation of continental crust and the development of chemical heterogeneities in the upper mantle in these models it is important to evaluate the nature and size of contributions from preexisting crust in the generation of magmas above subduction zones and to constrain the size of the fluxes of different elements from the subducted crust and the overlying mantle wedge in arc magmas kay 1 980 hawkesworth ellam 1 989 hawkesworth et al 1 99 1 a mcculloch gamble 1 99 1 the more mobile components of the subducted oceanic crust are the products of element fractionation processes in the upper continental crust the ocean basins and hydrothermal systems on the ocean floor they therefore have distinctive isotope and even trace element ratios that in principle should be readily distinguished from those in peridotite in the mantle wedge prior to subduction in practice however element ratios are almost certainly fractionated during shallow level dehydration of sub ducted material and at greater depths where material from the slab appears to contribute in the generation of arc magmas moreover the isotope signal of slab derived material may be heavily diluted by exchange with

probing the mechanical properties of seismically active crust with space geodesy study of the coseismic deformation due to the 1992 mw7 3 landers southern california earthquake 1 the coseismic deformation due to the 1992 m w 7 3 landers earthquake southern california is investigated using synthetic aperture radar sar and global positioning system gps measurements the ers 1 satellite data from the ascending and descending orbits are used to generate contiguous maps of three orthogonal components east north up of the coseismic surface displacement field the coseismic displacement field exhibits symmetries with respect to the rupture plane that are suggestive of a linear relationship between stress and strain in the crust interferometric synthetic aperture radar insar data show small scale deformation on nearby faults of the eastern california shear zone some of these faults in particular the calico rodman and pinto mountain faults were also subsequently strained by the 1999 m w 7 1 hector mine earthquake i test the hypothesis that the anomalous fault strain represents essentially an elastic response of kilometer scale compliant fault zones to stressing by nearby earthquakes fialko et al 2002 the coseismic stress perturbations due to the landers earthquake are computed using a slip model derived from inversions of the insar and gps data calculations are performed for both homogeneous and transversely isotropic half space models the compliant zone model that best explains the deformation on the calico and pinto mountain faults due to the hector mine earthquake successfully predicts the coseismic displacements on these faults induced by the landers earthquake deformation on the calico and pinto mountain faults implies about a factor of 2 reduction in the effective shear modulus within the similar to 2 km wide fault zones the depth extent of the low rigidity zones is poorly constrained but is likely in excess of a few kilometers the same type of structure is able to explain high gradients in the radar line of sight displacements observed on other faults adjacent to the landers rupture in particular the lenwood fault north of the soggy lake has likely experienced a few centimeters of left lateral motion across 1 km wide compliant fault zone having the rigidity reduction of more than a factor of 2 the inferred compliant fault zones are interpreted to be a result of extensive damage due to past earthquakes

pge mineralization in andesite explosive breccias associated with the poperechny iron manganese deposit lesser khingan far east russia whole rock geochemical 190pt 4he isotopic and mineralogical evidence abstract we report in this paper an unusual occurrence of platinum group minerals in evolved explosive breccia associated with the poperechny iron manganese deposit lesser khingan range far east russia pgms in andesite breccia are represented by fe pt solid solutions 85 and pgm mostly os ir ru solid solutions sulfides and sulfarsenides 15 textural and compositional variations in pgm assemblages suggest that pt fe and os ir ru solid solutions as well as erlichmanite laurite series sulfides were formed during high temperature fractionation of mantle derived mafic parental melt similar to alaskan type complexes and were entrained in the evolved andesitic melt during its emplacement in the crust pd pt plumbostannide and copper gold solid solutions reflect late magmatic re crystallization and metasomatism early cretaceous 125 ma age of ferroplatinum in the explosive breccia suggests that pgm bearing ultramafic material could have been sampled during regional slab window tectonics related to the late mesozoic subduction of izanagi plate along southern margin of the north asian continent

examination of the deep levels of an island arc evidence from the tonsina ultramafic mafic assemblage tonsina alaska the tonsina ultramafic and mafic assemblage located in the northern chugach mountains along the trans alaska crustal transect tact is interpreted to be the remains of a magma chamber that crystallized at the base of a mature interoceanic island arc it is one of a number of isolated masses of peridotite and gabbro that comprise the basal part of the peninsular terrane along the northern fringe of the chugach mountains in southern alaska these masses the roots of a mid jurassic island arc have been uplifted along the north dipping border ranges fault system and crop out sporadically for 700 km from kodiak island to eastern alaska the tonsina ultramafic mafic assemblage is a layered sequence whose basal rocks are dunite and harzburgite 1 km thick overlain by a narrow zone of websterite and clinopyroxenite above these ultramafic rocks is a 5 to 6 km thick layered gabbro that is garnet bearing at its base textural relationships and chemical trends throughout the series of dunite pyroxenite garnet bearing gabbro and spinel gabbronorite point to an origin by igneous accumulation from a hydrous tholeiitic parent magma at deep levels i e at the base of a mature island arc before being emplaced along the border ranges fault the rocks were crystallized from a melt at pressures between 9 5 and 11 kbar 28 to 33 km depth and equilibrated at temperatures of 800 to 90o c based on phase relationships in the cumulus assemblages pyroxene thermobarometry and olivine spinel thermometry transitional sequences from ultramafic to mafic rocks are characterized by increasingly al rich pyroxenes and spinels or garnet and the absence of olivine plagioclase assemblages deep level fractionation of al poor phases such as olivine and pyroxene at moderately high pressures and temperatures resulted in concentration of al in the evolving magma as crystallization continued the phases recorded this alumina concentration and the resultant gabbros are al rich this observed trend supports the theory of high alumina basalt generation by fractional crystallization of olivine and pyroxene comparison of the tonsina rocks with aleutian lower crustal xenoliths as well as other exposures of arc related lower crustal magma chambers in japan pakistan and western north america indicates that this process is a common mechanism for island arc magma evolution at depth

multi element geochemical modelling of crust mantle interactions during late archaean crustal growth the closepet granite south india the closepet granite in the dharwar craton of south india is a large late archaean magmatic body its composition can be explained as a result of interactions between mantle derived melts and pre existing continental crust ttg gneisses using geochemical modelling based upon major and trace element compositions the following petrogenetic model is proposed for the formation of the batholith i an enriched mantle garnet and amphibole bearing lherzolite melts to produce a basaltic liquid ii the basaltic liquid undergoes limited fractional crystallization of biotite and amphibole f 0 9 iii the differentiated liquid rises into the old continental crust and induces water saturated anatexis of the ttg gneisses k feldspar qtz plagioclase melt iv both mantle derived and anatectic liquid mix and give rise to magma compositions ranging from quartz monzonite to granite the origin of the mantle enrichment is discussed in the context of the regional geological setting the most likely possibility seems to be metasomatism by slab melts the metasomatism of a mantle wedge by slab melts this suggests a two stage evolution for the dharwar craton during the late archaean i a subduction related event with the formation of ttgs sanukitoids and with associated mantle metasomatism and ii re melting of the metasomatized mantle this evolutionary history implies that at least some of the k rich late archaean granites are juvenile rather than products of intracrustal reworking as frequently assumed

ice velocity determined using conventional and multiple aperture insar abstract we combine conventional interferometric synthetic aperture radar insar and multiple aperture insar mai to determine the ice surface velocity on the langjokull and hofsjokull ice caps in iceland in 1994 this approach allows the velocity of the 20 principal ice cap outlet glaciers to be fully resolved we show that mai leads to displacement estimates of finer resolution 15 versus 150 m and superior precision 5 versus 15 cm to those afforded by the alternative technique of speckle tracking using sar data acquired in ascending and descending orbits we show that ice flows within 15 of the direction of maximum surface slope across 66 of the ice caps it is therefore possible to determine ice displacement over the majority of the ice caps using a single sar image pair thereby reducing errors associated with temporal fluctuations in ice flow

alteration paragenesis and the timing of mineralised quartz veins at the world class geita hill gold deposit geita greenstone belt tanzania abstract the world class geita hill deposit is one of the largest gold deposits located within the geita greenstone belt in nw tanzania the deposit is hosted within a complexly deformed sedimentary package dominated by ironstone and intruded by diorite dykes the gold mineralisation is spatially associated with the geita hill shear zone which is a ne trending moderately nw dipping deformation zone consisting of a network of discontinuous shear fractures that record early thrusting overprinted by later strike slip and normal events the regional metamorphic assemblage in the meta sediments is characterised by biotite chlorite actinolite k feldspar magnetite pyrrhotite pyrite indicating upper greenschist facies conditions the gold related alteration overprints the regional metamorphic assemblage and is characterised by silicification and sulfidation fronts that generally extend out from the mineralised zone by no more than one meter the alteration assemblage includes sub vertical mineralised quartz veins that trend approximately e w the mineralised quartz veins are accompanied by alteration halos of quartz biotite k feldspar pyrite which overprints the peak metamorphic assemblage gold is closely associated with secondary pyrite and occurs as free gold and gold tellurides sylvanite calaverite and nagyagite it occurs mainly as inclusions in pyrite and as invisible gold in pyrite but also as gold inclusions in biotite and along quartz grain boundaries two distinct textural styles of auriferous pyrite can be distinguished inclusion rich subhedral pyrite hosting invisible gold and inclusion free euhedral pyrite hosting visible gold grains it is common for the inclusions rich pyrite to have thick rims of inclusion free pyrite the mineralising alteration is overprinted by barren multiphase quartz carbonate and carbonate chlorite veins this alteration is characterised by the assemblage calcite siderite chlorite quartz pyrite barite palaeostress analysis of mineralised shear fractures along the geita hill shear zone are indicative of sigma 1 being vertical and sigma 3 trending n s indicating n s extension which is consistent with the orientation of the mineralised quartz veins

platinum group elements co ni fe sulfarsenides and mineral paragenesis in cu ni platinum group element deposits copper cliff north area sudbury canada three deposits the offset sublayer 100 and 120 orebodies and contact sublayer lady violet deposit in the copper cliff north mine area sudbury were sampled with the aim of defining the mineral assemblages the ores are composed of pyrrhotite pentlandite chalcopyrite with minor titanomagnetite ilmenite accessory sulfarsenides bi te minerals and sperrylite sulfarsenides which are prominent accessory minerals contain the platinum group elements pge rh ru ir os and pt in decreasing order of abundance in solid solution some zoned sulfarsenide crystals have pge concentrated in the centers decreasing toward the edges nickeliferous cobaltite the common sulfarsenide contains as much as 16 at percent pge hollingworthite rh ru ass which occurs as cores or distinct crystals enclosed in cobaltite is a newly recognized occurrence in the 100 120 and lady violet deposits in the sudbury south range formation of primary pge bearing sulfarsenides is related to exsolution from monosulfide solid solution at about 550 to 600 c during late crystallization aqueous fluids interacted with the rocks resulting in precipitation of hydrous silicates epidote biotite chlorite and remobilization of pge bearing sulfarsenides

evidence for a very long term trend in geomagnetic secular variation reconstructions of palaeosecular variation suggest that the earth s magnetic field reversed less frequently 2 82 to 2 45 billion years ago relative to the cenozoic era this suggests a long term trend of decreasing geodynamo stability since the archaean eon the earth s inner core is believed to inhibit rapid fluctuations in the geomagnetic field from developing into full polarity reversals1 2 consequently during the precambrian the smaller size of the inner core might suggest that polarity reversals could occur more readily it is therefore surprising that there are indications that reversals were rare during this period3 4 here we use new and existing palaeomagnetic data from three continents to examine the stability of the earth s magnetic field from 2 82 to 2 45 billion years ago we show that on average geomagnetic secular variation the field variations produced by normal geodynamo action during the late archaean and early proterozoic was different from that of the past 200 million years specifically the apparent variability of the geomagnetic pole as viewed at low and mid latitudes was reduced relative to the past 200 million years according to both dynamo simulations4 and more recent palaeomagnetic field observations5 the observed pattern of secular variation suggests a lower frequency of polarity reversals 2 5 billion years ago this may imply that the geodynamo is becoming progressively less stable over long timescales consistent with some numerical simulations6 7 possibly as a result of changing outer core geometry that has accompanied inner core growth

p wave tomography of northeast asia constraints on the western pacific plate subduction and mantle dynamics abstract a high resolution model of 3 d p wave velocity structure beneath northeast asia and adjacent regions is determined by using 244 180 arrival times of 14 163 local and regional earthquakes and 319 857 relative travel time residuals of 9988 teleseismic events recorded at 2100 seismic stations in the study region our tomographic results reveal the subducting pacific slab clearly as a prominent high velocity anomaly from the japan trench to the north south gravity lineament nsgl in east china the nsgl is roughly coincident with the western edge of the stagnant pacific slab in the mantle transition zone mtz the subducting pacific slab has partly sunk into the lower mantle beneath northeast china but under the sino korean craton the slab lies horizontally in the mtz the nsgl as an important tectonic line in mainland china is marked by sharp differences in the surface topography gravity anomaly crustal and lithospheric thickness and mantle seismic velocity from the east to the west these features of the nsgl and large scale hot and wet upwelling in the big mantle wedge bmw in the east of the nsgl are all related to the subduction processes of the western pacific plate the changbai intraplate volcanic group is underlain by a striking low velocity anomaly from the upper mtz and the bmw up to the surface and deep earthquakes 410 650 km depths occur actively in the subducting pacific slab to the east of the changbai volcano we propose that the changbai volcanic group is caused by upwelling of hot and wet asthenospheric materials and active convection in the bmw the formation of other volcanic groups in the east of the nsgl is also associated with the subduction driven corner flow in the bmw

native metals and intermetallic compounds in subduction related ultramafic rocks from the stanovoy mobile belt russian far east implications for redox heterogeneity in subduction zones abstract plutonic associations in orogenic belts are potent indicators of multi stage fractionation of primitive arc magmas and growth of island arc crust under evolving redox conditions in ancient subduction zones ildeus lucha ultramafic mafic complex ilc was emplaced at 232 233 ma within the mesozoic stanovoy convergent margin and subsequently underwent multi stage hydrothermal alteration and greenschist to amphibolite facies metamorphism 140 ma followed by adakite and k lamprophyre magmatism 114 117 ma dunite wehrlite pyroxenite and gabbro in the ilc are composed of olivine clinopyroxene orthopyroxene plagioclase and late magmatic amphibole mineral compositions in the ilc are typical of island arc plutonic complexes characterized by early crystallization of orthopyroxene plagioclase intercumulus and presence of magmatic amphibole ultramafic mafic rocks display high field strength hfs element depletions coupled with large ion lithophile lil element enrichments indicating formation via crystal fractionation of mafic primary magma derived from a subduction related mantle source some ultramafic rocks from the ilc contain native metals w pt au ag zn bi and intermetallic compounds cu au ag pt rh pd cu sn zn etc included in silicate minerals or observed as discrete phases in the finer grained silicate oxide sulfide matrix textural evidence and association with either primary magmatic or secondary metasomatic or metamorphic mineral phases suggest either magmatic high temperature or metasomatic low temperature origin of metals and metallic compounds the following models of their formation can be proposed on the basis of the presented data a crystallization w and possibly pt from metal rich arc magmas under unusually reduced conditions in subduction related lithosphere b formation from magmatic sulfides during pervasive serpentinization and release of abiogenic hydrocarbons and c precipitation from chlorine rich saline aqueous fluids associated with collision related metasomatism of the stanovoy island arc crust

genetic aspects of the geita and jubilee reef archean bif hosted gold deposits tanzania the sukumaland greenstone belt new name which is located in north western tanzania hosts a large number of gold deposits prospects and occurrences the archean stratigraphy comprises an older basement of granitic gneisses dodoman system overlain by mafic and ultramafic volcanics which are succeeded by felsic volcanic rocks and a banded iron formation bif predominantly as oxide facies the volcanics and bif together make up the nyanzian system the uppermost part of the archean stratigraphy kavirondian system consists of conglomerates and quartzites which rest unconformably on the older units the sequence has been intruded by both syn and post orogenic granitoids and by several generations of felsic and intermediate dykes and sills gold mineralisation is abundant in all stratigraphic units except for the granitic rocks six types of mineralisation can be distinguished these are bif hosted hear zone type quartz vein type clastic sedimenthosted alluvial eluvial and massive sulphide type deposits the last is represented by only one deposit in this area

platinum group element geochemistry of andesite intrusions of the kelian region east kalimantan indonesia implications of gold depletion in the intrusions associated with the kelian gold deposit nineteen andesite samples from the kelian gold mine and two adjacent prospects magerang imang and nakan in east kalimantan have been analyzed for cu re au and the platinum group elements pge the aim of the study was to use variations in pge concentrations to test whether the chalcophile elements became enriched or depleted with fractionation in the igneous suites associated with the kelian deposit when the data are plotted on mantle normalized chalcophile element diagrams the patterns for the magerang imang and nakan suites are subparallel over a range of pge concentrations of about 20 times pd ir ratios for magerang imang hornblende andesites and nakan pyroxene andesites are 15 to 54 and 60 to 129 respectively the lower pd ir ratios for the magerang imang suite are due to a reversal in the slope of the mantle normalized pattern between ir and os that is not seen in the nakan suite all pge concentrations from both the magerang imang and nakan suites decrease with increased fractionation furthermore all samples which have not been subjected to strong alteration are strongly depleted in au relative to adjacent elements on mantle normalized chalcophile element plots crosscutting relationships show that the gold mineralization at kelian is younger than the associated central and eastern andesite intrusions so they cannot be the source of the gold in the deposit the gold was probably derived from slightly younger intrusions similar in age to the adjacent magerang imang hornblende andesites which appear to be coeval with the mineralization and which are also depleted in gold the subparallel pge patterns preclude the depletion of cu au and pge by sulfide fractionation which would fractionate highly chalcophile pge from less chalcophile cu and re we suggest that the parallel cu au pge patterns are due to mixing between a relatively mafic pge rich magma and a more felsic magma with lower pge concentrations

fault slip distribution of the 1999 mw 7 1 hector mine california earthquake estimated from satellite radar and gps measurements we use a combination of satellite radar and gps data to estimate the slip distribution of the 1999 m w 7 1 hector mine earthquake a right lateral strikeslip earthquake that occurred on a northwest southeast striking fault in the southern california mojave desert the data include synthetic aperture radar interferograms insar from both ascending and descending orbits radar amplitude image offset fields sario for both ascending and descending azimuth directions and campaign gps observations from 55 stations provided by agnew et al 2002 we model the fault with nine segments derived from the field mapped fault rupture the sario data and aftershock locations we first estimate the dip of each fault segment as well as a single constant strike slip component across each segment resulting in an average dip of 83 to the northeast and slip of up to 5 6 m then we fix the optimal fault segment dip discretize the fault segments into 1 5 km 1 5 km patches and solve for the variable slip distribution using a nonnegative least squares method that includes an appropriate degree of smoothing our preferred solution has both right lateral strike slip and reverse faulting the estimated geodetic moment is 5 93 10 19 n m m w 7 1 similar to seismological estimates indicating that there are insignificant interseismic and postseismic deformation signals in the data we find strike slip displacements of up to 6 0 m and reverse faulting of up to 1 6 m with the maximum slip located just northwest of the epicenter most of the slip is concentrated northwest and south of the epicenter little slip is found on the northeastern branch of the fault the sario data and our modeling indicate that the amount and extent of surface fault rupture were underestimated in the field

pge tenor and metal ratios within and below the merensky reef bushveld complex implications for its genesis the merensky reef is the consequence of several major influxes of magma into the bushveld magma chamber that gave rise to at least two cyclic units including the pre merensky and merensky cyclic units analysis of the s ni cu platinum group element pge and au contents of 1140 samples from 24 profiles through the rocks forming these units and two profiles extending downward from the reef to close to the ug 2 horizon of the western bushveld complex provide important petrogenetic constraints on the origin of the reef particular attention is paid to variations in the calculated pge tenors and cu pd ratios of sulfides both vertically and laterally all of the profiles show a decrease in pt tenor and concomitant increase in cu pd ratio upward across the pyroxenite of the merensky unit and laterally away from certain centres that are interpreted as feeder zones the data also document that more mafic horizons within the merensky to ug 2 interval of the southwestern bushveld are characterized by much lower cu pd 100 400 than the ambient ratio 4000 this is interpreted as demonstrating that these horizons are the consequence of incursions of magma whose composition has been modified in a staging chamber by reaction with sulfide resident there the favoured interpretation for the merensky reef is that the bushveld chamber s was occupied by a resident magma crystallizing orthopyroxene and plagioclase pre merensky and subsequently merensky magmas entered the chamber s intermittently from localized feeder structures mixing or mingling with the resident magma and giving rise to the more mafic cumulates at specific horizons including the merensky reef the mixing or mingling caused sulfide immiscibility in these cases as the new magma pulses flowed laterally away from the entry zones they deposited sulfide becoming depleted in pge on coming to rest the magma continued to segregate sulfide and crystallize pyroxene so that the sulfides became progressively depleted in pge and acquired a higher cu pd upward through the pyroxenite this model requires that the merensky magmas could dissolve up to two orders of magnitude more pge than current measurements on dry diopside anorthite melts have indicated it is suggested that very pge rich magmas can develop as a result of sulfide unsaturated magma reacting with early formed sulfide in a staging chamber dissolving fes and enriching the remaining sulfide in pge later magmas equilibrating with this enriched sulfide will themselves become highly enriched in pge

measuring azimuth deformation with l band alos 2 scansar interferometry we analyze the methods for measuring azimuth deformation with the l band advanced land observing satellite 2 alos 2 scanning synthetic aperture radar scansar interferometry to implement the methods we extract focused bursts from the alos 2 full aperture product which is the only product available for scansar interferometry at present the extracted bursts are properly processed to measure azimuth deformation using interferometric phase we apply the range split spectrum method to scansar to estimate the differential ionospheric phase of the interferogram and take the azimuth derivative of the differential ionospheric phase to mitigate the relative azimuth shift caused by ionosphere for the first time azimuth deformation of a large earthquake april 25 2015 nepal earthquake is nearly completely measured by the l band scansar interferometry with moderate precision the result is validated by the azimuth deformation measured by incoherent cross correlation using a pair of high resolution radarsat 2 images in addition to the final azimuth deformation we show the possibility of processing full aperture scansar product using a burst by burst approach to form regular interferograms we also show the recent strong large scale ionospheric effects on the l band alos 2 scansar interferograms other possible applications of this paper include measuring the movement of glaciers

measuring near field coseismic displacements from sar images application to the landers earthquake we describe a procedure to compute sar interferograms based on the compensation of the images mis registrations due to the ground deformation and on a specific adaptive filtering to improve the snr in the measurement where displacement gradients are large applied to the landers earthquake case the registration reduces the phase noise by 20 rms near the fault and the interferogram reveals fringes that would not show out otherwise the interferogram is validated by comparison in the far field with a gps edm based model the inferred displacement field shows discontinuities that follow the fault within few hundred meters close to the fault the measured displacements differ significantly from that predicted by elastic modeling of the far field data interferometry and measurements derived from the images amplitude offsets appear to be complementary techniques providing original measurements that may help to reconcile seismological and geodetic models of coseismic deformation with measurements of fault slip at the surface

a platinum group element and re os isotope investigation of siderophile element recycling in subduction zones comparison of grenada lesser antilles arc and the izu bonin arc os os signatures 0 134 0 164 which are even more the picritic mgo 13 5 lavas of grenada provide a unique radiogenic than peridotite xenoliths previously measured from mantle opportunity to evaluate the platinum group elements pge and wedges modified by addition of subducted material crustal conos isotope compositions of primitive subduction generated melts tamination appears unable to explain all of the os isotope enrichment compared with other arc lavas they have undergone very limited and thus elevated os os may reflect the modification of the crustal contamination 2 of sediment and or slab derived fluids enriched in range of parental melts can explain all major element variations radiogenic os despite their primitive nature the picritic lavas contain very low concentrations of pge 0 2 ppb ir 1 4 ppb pd compared with other high mgo lavas such as kimberlites komatiites and plumerelated picrites this is probably due to a combination of lower

glacier velocity measurements in the eastern yigong zangbo basin tibet china we apply the feature tracking method to l band synthetic aperture radar sar images to derive detailed motion patterns of glaciers in the yigong zangbo basin during summer 2007 the results indicate that the flow patterns are generally constrained by the valley geometry and terrain complexity the mean velocities of the 12 glaciers were 15 206 m a 1 with a maximum of 423 m a 1 for glacier no 5a the majority of the glaciers exhibited high and low velocities in their upper and lower sections respectively the glacier area ranges from 3 to 42 km 2 it is found that velocity shows a positive correlation with the glacier area and length many small scale temporal spatial variations in the glacier flow patterns were observed along the central glacier flowline

petrogenesis and emplacement of the ttg and k rich granites at the buzwagi gold mine northern tanzania implications for the timing of gold mineralization abstract the buzwagi gold mine found in the neoarchaean nzega greenstone belt of northern tanzania is underlain by neoarchaean mafic volcanic rocks which are intruded by a massive body of ultramafic rocks that are cross cut by grey colored ttg and pink microcline k rich granites geochemical alteration studies for the sheared and hydrothermally altered k granites show that the lfse and ree were significantly mobilized during the shearing and subsequent injection of hydrothermal fluid events whereas the hfse remained virtually unchanged the buzwagi mine ttg exhibit geochemical characteristics of other worldwide known ttg al2o3 15 0 wt na2o k2o ratios of 1 19 5 16 low concentration of heavy ree with y contents of 3 7 ppm and yb 0 3 0 5 ppm leading to high sr y ratios 61 152 and la yb 32 140 which are comparable to those of phanerozoic adakites the buzwagi mine ttg are characterized by strongly fractionated ree patterns la ybcn 23 100 with slightly negative to no eu anomalies eu eu 0 77 1 05 negative anomalies of nb ta and ti and end 2713 values of 1 19 to 1 77 these geochemical and isotopic characteristics are interpreted as formation of the ttg by partial melting of the hydrous basaltic crust at pressures and depths where garnet and amphibole were stable phases in the late archaean subduction zone the buzwagi mine k rich granites differ from their ttg counterparts in having elevated concentrations of incompatible elements like k zr th hf and ree they however share similar nd isotopic compositions end 2674 ma 1 19 to 1 22 and some geochemical features including fractionated ree patterns la ybcn 13 204 with slightly negative to no eu anomalies eu eu 0 78 0 89 and negative anomalies of nb ta and ti these geochemical features and isotopic signatures have been interpreted as formation of the k granites by anhydrous partial melting of the ttg and greenstones the buzwagi mine k granites were emplaced at 2674 18 ma some 40 ma years after the emplacement of ttg at 2713 8 ma the timing of the buzwagi mine granitic magmatism falls within the peak crustal growth period in the northern part of the archaean tanzania craton gold mineralization at the buzwagi mine is hosted in quartz veins that are within strongly sheared and hydrothermally altered k granites in which silica and sericite alterations and sulphides mainly pyrite and chalcopyrite although chalcocite is also present are important the buzwagi gold deposit is thus a typical archaean orogenic deposit whose mineralization is hydrothermally and structurally controlled and the abundance of sulphides silica and sericite alteration assemblages suggests that the deposition conditions were reducing and acidic in nature owing to its epigenetic nature it can be inferred that the maximum age of deposition of gold at the buzwagi mine is 2674 ma which is more or less the same age inferred for the golden pride mine 2680 ma both of which are found in the nzega greenstone belt

crustal structure of precambrian terranes in the southern african subcontinent with implications for secular variation in crustal genesis summary new estimates of crustal thickness poisson s ratio and crustal shear wave velocity have been obtained for 39 stations in angola botswana the democratic republic of congo malawi mozambique namibia rwanda tanzania and zambia by modellingp wave receiver functions using the h stacking method and jointly inverting the receiver functions with rayleigh wave phase and group velocities these estimates combined with similar results from previous studies have been examined for secular trends in precambrian crustal structure within the southern african subcontinent in both archean and proterozoic terranes we find similar moho depths 38 39 3k msd standard deviation crustal poisson s ratio 0 26 0 01 sd mean crustal shear wave velocity 3 7 0 1 km s 1 sd and amounts of heterogeneity in the thickness of the mafic lower crust as defined by shear wave velocities 4 0 km s 1 in addition the amount of variability in these crustal parameters is similar within each individual age grouping as between age groupings thus the results provide little evidence for secular variation in precambrian crustal structure including between meso and neoarchean crust this finding suggests that 1 continental crustal has been generated by similar processes since the mesoarchean or 2 plate tectonic processes have reworked and modified the crust through time erasing variations in structure resulting from crustal genesis

the complete 3 d surface displacement field in the epicentral area of the 1999 mw7 1 hector mine earthquake california from space geodetic observations we use interferometric synthetic aperture radar insar data to derive continuous maps for three orthogonal components of the co seismic surface displacement field due to the 1999 m w7 1 hector mine earthquake in southern california vertical and horizontal displacements are both predominantly antisymmetric with respect to the fault plane consistent with predictions of linear elastic models of deformation for a strike slip fault some deviations from symmetry apparent in the surface displacement data may result from complexity in the fault geometry

the sikhote alin orogenic belt russian south east terranes and the formation of continental lithosphere based on geological and isotopic data abstract the sikhote alin orogenic belt russian south east consists of folded terranes made up of jurassic and early cretaceous accretionary prisms turbidite basins and island arc terranes that are overlapped unconformably by undeformed upper cenomanian to cenozoic volcanic deposits the jurassic and early cretaceous accretionary prisms together with the early cretaceous island arc are related to subduction of the paleo pacific plate the turbidite basin which began to form at the beginning of the early cretaceous is related to left lateral movement of the paleo pacific plate along the paleo asian continental margin the collage of terranes that make up the sikhote alin orogenic belt was amalgamated in two stages the first began after jurassic subduction beneath the asian continent was terminated and the second took place in the late albian when the early cretaceous island arc collided with the continental margin intense deformation of the terranes took place along the continental margin in the form of large scale translations from south to north together with oroclinal folding the deformation resulted in rapid thickening of sediments in the upper crust resulting in turn in the formation of granitic metamorphic material in the continental lithosphere in the southwestern part of the sikhote alin orogen granites were intruded during the hauterivian aptian while the entire orogenic belt was affected by intrusions in the late albian early cenomanian synorogenic intraplate volcanic rocks and alkaline ultramafic mafic intrusions also testify to the fact that the orogenic processes in the sikhote alin were related to a transform continental margin and not to subduction geochemical and nd isotopic data indicate the primary continental crust of the sikhote alin was of a hybrid nature consisting of juvenile basic components accreted from an oceanic plate and recycled sedimentary material derived from the erosion of ancient blocks

interferometric estimation of three dimensional ice flow using ascending and descending passes satellite radar interferometry sri provides an important new tool for determining ice flow velocity interferometric measurements made from a single track direction are sensitive only to a single component of the three component velocity vector observations from along three different track directions would allow the full velocity vector to be determined a north south looking synthetic aperture radar sar could provide these observations over large portions of the globe but not over large areas of the polar ice sheets the authors develop and demonstrate a technique that allows the three component velocity vector to be estimated from data acquired along two track directions ascending and descending under a surface parallel flow assumption this technique requires that there are accurate estimates of the surface slope which are also determined interferometrically to demonstrate the technique the authors estimate the three component velocity field for the ryder glacier greenland their results are promising although they do not have yet ground truth data with which to determine the accuracy of their estimates

petrogenesis of archaean trondhjemites tonalites and granodiorites from eastern finland major and trace element geochemistry

deformation time series generation in areas characterized by large displacement dynamics the sar amplitude pixel offset sbas technique we exploit the amplitude information of a sequence of synthetic aperture radar sar images acquired at different times in order to generate displacement time series in areas characterized by large and or rapid deformation the size of which is on the order of the image s pixel dimensions we follow the same rationale of the small baseline subset sbas differential sar interferometry dinsar approach by coupling the available sar images into pairs characterized by a small separation between the acquisition orbits we exploit the amplitudes of the selected image pairs in order to calculate the relative across track range and along track azimuth pixel offsets po finally we apply the sbas inversion strategy to retrieve the range and azimuth displacement time series this approach referred to as pixel offset po sbas technique has been applied to a set of 25 envisat sar observations of the sierra negra caldera galapagos islands spanning the 2003 2007 time interval the retrieved deformation time series show the capability of the technique to detect and measure the large displacements affecting the inner part of the caldera that in correspondence to the october 2005 eruption reached several meters moreover by comparing the po sbas results to continuous gps measurements we estimate that the accuracy of the po sbas time series is on the order of 1 30th of a pixel for both range and azimuth directions

stress field variations in the swiss alps and the northern alpine foreland derived from inversion of fault plane solutions 1 this study is devoted to a systematic analysis of the state of stress of the central european alps and northern alpine foreland in switzerland based on focal mechanisms of 138 earthquakes with magnitudes between 1 and 5 the most robust feature of the results is that the azimuth of the minimum compressive stress s3 is generally well constrained for all data subsets and always lies in the ne quadrant however within this quadrant the orientation of s3 changes systematically both along the structural strike of the alpine chain and across it the variation in stress along the mountain belt from ne to sw involves a progressive counterclockwise rotation of s3 and is most clear in the foreland where it amounts to 45 50 this pattern of rotation is compatible with the disturbance to the stress field expected from the indentation of the adriatic block into the central european plate possibly together with buoyancy forces arising from the strongly arcuate structure of the moho to the immediate west of our study area across the alps the variation in azimuth of s3 is defined by a progressive counterclockwise rotation of about 45 from the foreland in the north across the helvetic domain to the penninic nappes in the south and is accompanied by a change from a slight predominance of strike slip mechanisms in the foreland to a strong predominance of normal faulting in the high parts of the alps the observed rotation can be explained by the perturbation of the large scale regional stress by a local uniaxial deviatoric tension with a magnitude similar to that of the regional differential stress and with an orientation perpendicular to the strike of the alpine belt the tensile nature and orientation of this stress is consistent with the spreading stress expected from lateral density changes due to a crustal root beneath the alps

archaean crustal growth through successive partial melting events in an oceanic plateau like setting in the tanzania craton the detrital zircon population in quartzitic conglomerates from the northern tanzania craton yield ages between 2640 ma and 2790 ma which includes most of the igneous history from this part of the craton the igneous evolution is characterised by mafic volcanism with an oceanic plateau like geochemical signature at 2800 ma followed by diorite and tonalite trondhjemite granodiorite dominated magmatism between 2790 and 2700 ma which transitioned into more evolved high k magmatism between 2700 and 2620 ma the ehf values of the detrital zircons range from 2 4 to 1 4 and change with time from radiogenic hf pre 2700 ma 98 positive ehf to unradiogenic hf post 2700 ma 41 positive ehf the petrological progression from mafic to felsic crust is reflected in the detrital age distribution and ehf isotopes and is consistent with juvenile mafic crust slowly maturing into more evolved felsic crust through a series of successive partial melting events in an oceanic plateau like environment

precambrian crustal structure in africa and arabia evidence lacking for secular variation we review the thickness and shear wave velocity structure of precambrian crust in africa and arabia where over 90 of the landmass is comprised of archean and proterozoic terranes and examine the data for evidence of secular variation the data come from many published 1d shear wave velocity profiles obtained by jointly inverting receiver functions and surface wave dispersion measurements 35 new 1d shear wave velocity profiles for locations in eastern africa and a new map of crustal thickness for africa and arabia derived from modeling satellite gravity data we find for both archean and proterozoic terranes a similar range of crustal thicknesses 33 45 km similar mean crustal shear wave velocities 3 6 3 7 km s and similar amounts of heterogeneity in lower crustal structure as reflected in the thickness of lowermost crust with shear wave velocities 4 0 km s there is little evidence for secular variation in crustal structure indicating that there may have been few changes over much of earth s history in the processes that form the continental crust post formation tectonic events also may have modified many of the terranes to such an extent that secular trends arising from crustal genesis may be difficult to recognize

nd and sr isotopic mapping of the archaean proterozoic boundary in southeastern tanzania using granites as probes for crustal growth abstract granitoids of two different generations occur across the archaean proterozoic boundary in southeastern tanzania the first generation which is confined to the archaean tanzania craton yields rb sr whole rock isochron ages of 2600 ma and low mantle like initial 87sr 86sr ratios 0 702 0 704 these coupled with positive or near zero e nd values 0 2 to 2 0 suggest that these granitoids represent juvenile mantle material which was added to the continental crust at about 2600 ma the second generation of granitoids intrudes the palaeoproterozoic usagaran belt and is characterised by rb sr whole rock isochron ages of about 1900 ma these granitoids show sm nd crustal formation ages which are 200 to 600 ma older than their emplacement ages and negative e nd values 2 2 to 6 2 mixing calculations suggest that the proterozoic granitoids may have formed by partial melting of 2000 ma usagaran mantle derived material which had incorporated between 15 and 45 of an archaean component from the adjacent tanzania craton

stabilities of laurite rus2 and monosulfide liquid solution at magmatic temperature we have reversed the equilibria ru s2 rus2 and 2feo s2 2fes o2 under controlled temperature oxygen fugacity fo2 and sulfur fugacity fs2 at 1 atm to test if the platinum group mineral laurite rus2 has a stability field at magmatic temperature outside that of magmatic monosulfide liquid the fs2 in equilibrium with ru and rus2 is given by log fs2 6 9 12190 t 1173 to 1673 k whereas the fs2 at sulfide saturation of a basaltic melt may be approximated from log fs2 6 7 12800 t 2 log xfeo log fo2 1473 to 1673 k our experiments support the notion that the sulfide mineral laurite can crystallize directly out of a sulfur bearing sulfide undersaturated silicate melt as implied by laurite chromite intergrowth textures in natural chromite ore

3d coseismic deformations and source parameters of the 2010 yushu earthquake china inferred from dinsar and multiple aperture insar measurements abstract the coseismic deformation field related to the 2010 mw6 9 yushu earthquake qinghai china has been investigated by previous studies using the satellite differential interferometric synthetic aperture radar dinsar method however one of the limiting factors in the conventional dinsar is that it can measure only one dimensional 1d ground motion along the radar line of sight los direction thus resulting in anamorphic coseismic displacements and biased source parameters in this paper the three dimensional 3d deformation maps for this earthquake were reconstructed over an area of about 100 70 km2 for the first time by a combined use of the dinsar method for detecting los motion and the multiple aperture interferometry mai method for detecting along track at motion the fault slip map for this earthquake was generated using the 3d deformation maps based on the fault traces on the fault slip map we constructed a fault model with five segments and preformed a two step inversion using the 3d deformation data as the constraint our results show that the maximum coseismic displacements in up down north south and east west directions are 40 4 113 8 and 65 7 cm respectively and the peak to peak slip offset between the southern and northern fault wall is 1 82 m our model reveals a shallow dislocation on a nw se trending fault extending about 74 km along which the four fault segments are nearly vertical 84 88 and the one fault segment dips 66 2 to the southwest the estimated seismic moment is 2 43 1019 nm mw6 92 which is close to the solution provided by the global centroid moment tensor gcmt project the slip distribution derived for each fault patch shows that the slip occurrence extends down to 12 km beneath the ground surface and a peak slip of 2 23 m appears at the depth of about 5 km right near the epicenter comparison with the results derived from the seismic waves field investigation gps and conventional dinsar observations indicates that the source parameters of the yushu earthquake can be improved due to the combined use of dinsar and mai measurements

geochronology and geochemistry of late pan african intrusive rocks in the jiamusi khanka block ne china petrogenesis and geodynamic implications abstract to constrain the early paleozoic tectonic evolution of the jiamusi khanka block and its relationship to the late pan african event in gondwana we undertook zircon u pb dating and geochemical analyses major and trace elements and hf isotopic compositions of early paleozoic intrusive rocks in the jiamusi khanka block ne china la icp ms zircon u pb age data demonstrate that these intrusive rocks were emplaced at three stages during the late pan african event represented by 540 ma syenogranite 515 ma quartz syenite and 500 ma monzogranite and gabbro geochemically the 500 ma gabbros in the jiamusi khanka block have low sio 2 50 26 51 21 wt relatively high mgo 4 08 5 67 wt ni 13 1 14 1 ppm and cr 28 4 56 0 ppm and are slightly enriched in liles e g ba k and lrees and depleted in zr hf nb ta and p the e hf t values of zircons in the gabbro range from 2 6 to 6 4 all these geochemical features indicate that the gabbros were likely produced by the partial melting of a depleted mantle that had been metasomatized by fluids derived from a subducted slab in contrast the ca 540 500 ma granites and quartz syenites contain high sio 2 64 49 72 20 wt and low mgo 0 40 0 75 wt cr 1 69 6 88 ppm and ni 1 26 3 26 ppm they have relatively low 176 hf 177 hf ratios of 0 282247 0 282599 with hf two stage model ages of 1173 2280 ma and most of the magmatic zircons have positive e hf t values varying from 0 2 4 8 indicating that these granites and quartz syenites were probably derived from a dominantly paleo mesoproterozoic old crustal source with possible different degrees of addition of juvenile materials according to the geochemical data and global geological investigations we propose that the 541 498 ma intrusive rocks in the jiamusi khanka block formed in a post collisional or post orogenic extensional setting linked to the collapse of a late pan african orogen associated within the gondwana

fluid melt trace element partitioning behaviour between evolved melts and aqueous fluids experimental constraints on the magmatic hydrothermal transport of metals abstract the fluid melt partition coefficients of ten trace metals li mn cu zn rb sr mo w and pb along with k between hydrous evolved melts and coexisting cl bearing fluid s have been experimentally determined at 850 1050 c 0 6 2 2 kbar and o2 nno 0 5 to nno 2 log units the measured compositions of the quenched fluid phases vary from low salinity 2 wt cl to 19 wt cl with maximum starting fluid concentrations of 21 wt cl the results of 15 partitioning experiments confirm that dmetalfluid melt values depend strongly on the melt and fluid composition with the greatest metal affinities for the fluid phase shown in the experiments with high cl fluids and the most fractionated melts five experiments conducted in au96cu4 capsule alloy show dcufluid melt values ranging from 40 to 80 and a strong correlation with melt feo wt contents at equivalent fluid cl contents in contrast li shows only weak partitioning in favour of coexisting fluids across all melt compositions with dlifluid melt ranging from 0 16 in low salinity fluids to 1 17 in the highest cl fluid 19 15 wt cl a procedure was employed to redissolve and analyse the aluminosilicate precipitates that form during quenching of the experiments this procedure allows for metal contents of the final quench fluids to be constrained by both mass balance and direct measurement by solution icp ms analysis a comparison of the mass balance calculated vs directly measured fluid melt partition coefficients generally gives good agreement within an order of magnitude for most trace elements however discrepancies between these methods arise due to errors inherent in the mass balance calculations for metals with low abundances in the fluids e g sr and especially those showing affinities to alloy with the experiment capsule material e g mo these discrepancies in constraining experimental fluid trace element budgets also suggest that the precious metal capsule alloys cannot always be considered completely inert containers in experimental investigations and semi quantitative la icp ms analysis of the raw capsule alloys confirms the detectable presence of several of the trace elements investigated here integrating these new partitioning data with previous experimental and natural studies confirms that aqueous cl bearing fluids exsolved by hydrous calc alkaline melts stored at mid to upper crustal conditions are capable of efficiently sequestering and transporting some economically important trace metals e g mn cu zn however the new fluid melt li partitioning data in conjunction with evidence of very late post eruptive li modification suggests that li is moderately strongly fluid immobile at depth and suffers from significant post eruptive re equilibration this has implications for deciphering the signatures of volatile fluxing in arc magmas that are preserved in mineral and melt inclusion trace element concentrations and the development of mineralised stockwork regions in porphyry style metal deposits

biotite chemistry and the role of halogens in archaean greenstone hosted gold deposits a case study from geita gold mine tanzania abstract geita hill is one of the largest tanzanian gold deposits located southwest of lake victoria and 2 km along strike from the giant nyankanga deposit the deposit is hosted by metasedimentary rocks dominated by ironstones and intruded by numerous diorite dykes textural structural and geochronological observations indicate that the gold mineralisation overprints all the ductile fabrics and the late orogenic d6 reverse faulting event suggesting that gold was introduced during later d7 and d8 events the metamorphic background is characterized by biotite k feldspar actinolite pyrhotite which is overprinted by the gold related alteration consisting of sulfidation fronts veins and micro fractures dominated by quartz biotite k feldpar pyrite the almost identical mineralogy of the mineralised assemblage and the metamorphic background makes it difficult to identify the source the effect and the spatial extent of the mineralising fluid as part of this study detailed analyses of biotite were conducted in order to identify the nature of the mineralising fluid and its spatial effect across the geita hill deposit results show that the mineralised assemblage is slightly more oxidized pyrite magnetite compared to the metamorphic background pyrrhotite magnetite the intense sulfidation within the ore zone resulted in the formation of mg rich biotite which grades into more fe rich biotite away from the ore zone this change in biotite chemistry causes a shift in the swir fe oh 2250 nm absorption feature to lower wavelengths which is also correlated with an increase in gold grade within the mineralised zone the abundance of f in biotite significantly increases within the ore zone indicating the presence of f rich hydrothermal fluids during mineralisation late timing of mineralisation synchronous with the emplacement of voluminous high k granites and the presence of k and f bearing fluids indicate a genetic connection between the mineralising fluids and the late granites biotite grains from different deposits types porphyry iocg lode au appear to have distinct composition suggesting that the source of the fluids involved in the formation of each deposit type has a characteristic halogen chemistry

the tectonic history of a crustal scale shear zone in the tanzania craton from the geita greenstone belt nw tanzania craton abstract in this contribution we present for the first time field based evidence of a crustal scale shear zone from the southern margin of geita greenstone belt the geita shear zone is a broad 800 m wide ductile high strain deformation zone that can be traced for at least 50 km along the southern margin of the geita greenstone belt it is near vertical trends e w and separates the mafic volcanics of the kiziba formation to the north from the ttg gneisses that crop out south of the shear zone the shear zone is hosted almost entirely by the ttg gneisses and is characterised by a well developed mylonitic foliation near the greenstone margin that transitions into a gneissic foliation and eventually becomes a weakly developed foliation further south it contains approximately equal amounts of dextral sinistral and asymmetric shear sense indicators suggesting that the shear zone accommodated mainly flattening strain while the mineral stretching lineation defined by quartz and feldspar ribbons and stretched biotite selvages plunges shallowly w a series of younger sub vertical nw trending brittle ductile strike slip shear zones truncate and displace the geita shear zone with dextral displacement in the order of 2 4 km deformed tonalite interpreted to predate the shear zone yielded u pb zircon ages of 2710 ma while synshearing granodiorite samples have zircon ages between 2680 ma and 2660 ma the 2630 ma age of the undeformed nyankumbu granite is interpreted to mark the minimum age of movement on the shear zone the presence of 3000 ma and 3200 ma zircon xenocrysts in the tonalite and granodiorite opens the possibility that older basement rocks underlie the greenstone belts in the northern half of tanzania craton whether or not the greenstone belts were erupted on older basement thrusted on top of older basement rocks or incorporated older basement fragments has profound implications for the tectonic framework and evolution of the tanzania craton

provenance age and tectonic implications of neoproterozoic strata in the jiamusi massif evidence from u pb ages and hf isotope compositions of detrital and magmatic zircons abstract the jiamusi massif forms part of the eastern central asian orogenic belt caob and the pacific oceanic tectonic domain but its tectonic affinity is highly controversial here we present u pb ages and hf isotope compositions of detrital zircons from five metasedimentary rocks and one monzogranite within the jiamusi massif and our aim was to constrain the depositional ages and provenance of the strata as well as the tectonic affinity of the massif two specimens of two mica schist from the upper and lower kimkanskaya groups russian far east yielded zircon age populations at 572 826 891 958 and 1776 ma and 682 752 835 and 925 ma respectively a sericite schist and muscovite schist from the majiajie group ne china yielded zircon age populations at 951 1232 1419 1643 and 2687 ma and 1151 1276 1444 1623 1805 and 2652 ma respectively and a two mica schist from the ximashan formation of the mashan group ne china yielded zircon age populations at 994 1281 1439 1647 and 1805 ma taking into account the general geological relationships in the area zircon age populations and hf isotopic compositions combined with an age of 492 ma for a monzogranite that intrudes the ximashan formation we conclude that the lower kimkanskaya group formed in the neoproterozoic and was sourced mainly from a neoproterozoic terrane whereas the majiajie group and ximashan formation formed in the neoproterozoic but were sourced dominantly from a mesoproterozoic terrane taking into account previous paleomagnetic data our dating results and comparisons with zircon age populations in precambrian rocks from northeastern gondwana and the southern siberia north china and tarim cratons suggest that the jiamusi massif has an affinity with the tarim craton

measuring two dimensional movements using a single insar pair 1 we present a new method to extract along track displacements from insar data based on split beam insar processing to create forward and backward looking interferograms the phase difference between the two modified interferograms provides the along track displacement component thus from each conventional insar pair we extract two components of the displacement vector one along the line of sight the other in the along track direction we analyze the precision of the new method by comparing our solution to gps and offset derived along track displacements in interferograms of the 1999 hector mine earthquake the rms error between gps displacements and our results ranges from 5 to 8 8cm our method is consistent with along track displacements derived by pixel offsets which are limited to 12 15cm precision the theoretical precision of the new method depends on snr and coherence for a signal to noise ratio of 30 the expected precisions are 3 11cm for coherence of 0 8 0 4 respectively

the geology of the giant nyankanga gold deposit geita greenstone belt tanzania nyankanga is the largest gold deposit in the geita greenstone belt of the northern tanzania craton the deposit is hosted within an archean volcano sedimentary package dominated by ironstones and intruded by a large diorite complex the nyankanga intrusive complex the supracrustal package is now included within the intrusive complex as roof pendants the ironstone fragments contain evidence of multiple folding events that occurred prior to intrusion the supracrustal package and nyankanga intrusive complex are cut by a series of ne sw trending moderately nw dipping fault zones with a dominant reverse component of movement but showing multiple reactivation events with both oblique and normal movement components the deposit is cut by a series of nw trending strike slip faults and e w trending late normal faults the nyankanga fault zone is a major nw dipping deformation zone developed mainly along the ironstone diorite contacts that is mineralised over its entire length the gold mineralization is hosted within the damage zone associated with nyankanga fault zone by both diorite and ironstone with higher grades typically occurring in ironstone ore shoots dip more steeply than the nyankanga fault zone the mineralization is associated with sulfidation fronts and replacement textures in ironstones and is mostly contained as disseminated sulphides in diorite the close spatial relationship between gold mineralization and the ironstone diorite contact suggests that the reaction between the mineralising fluid and iron rich lithotypes played an important role in precipitating gold intense brecciation and veining mainly in the footwall of nyankanga fault zone indicates that the fault zone increased permeability and allowed the access of mineralising fluids the steeper dip of the ore shoots is consistent with mineralization during normal reactivation of the nyankanga fault zone

moho depths and poisson s ratios of precambrian crust in east africa evidence for similarities in archean and proterozoic crustal structure abstract we investigate the structure of precambrian crust in east africa by using estimates of moho depth and poisson s ratio for 37 new seismic stations in uganda and tanzania and for 32 previously deployed seismic stations in kenya and tanzania the dataset includes estimates of crustal structure distributed between all of the major archean and proterozoic terrains obtained from modeling p wave receiver functions the average crustal thickness for the ubendian belt is 42 km and between 37 and 39 km for all of the terrains the average poisson s ratio for all of the terrains is either 0 25 or 0 26 indicating a felsic to intermediate bulk crustal composition a similar composition and thickness of the crust in east africa for terrains spanning some 4 byr of earth history is different than in many other precambrian regions our results suggest that there may have been few changes over earth s history in the processes that formed the east african crust or else that processes have been at play to homogenize crustal structure such as the flow of lower crustal material in orogenic systems or through the foundering of eclogites into the mantle the finding that crustal structure is similar between the archean and proterozoic terrains indicates that crustal structure through its influence on lithospheric rheology and strength has not had a first order effect on the location of rifting we also find that there is little correlation between moho depth and elevation across the east african plateau indicating that variations in crustal thickness exert few if any influences on topography in east africa this conclusion lends support to many studies arguing that mantle structure and processes provide the primary buoyant support for the plateau

geochemistry and geochronology of the bimodal volcanic rocks of the suguti area in the southern part of the musoma mara greenstone belt northern tanzania abstract the suguti volcanic rocks of the southern musoma mara greenstone belt in northern tanzania comprise mainly of a bimodal suite of tholeiitic basalts basaltic andesites and calc alkaline rhyolites with a subordinate amount of intermediate rocks zircon u pb and whole rock sm nd geochronology suggests that the two suites are cogenetic and were emplaced at 2755 1 ma with a common initial nd value of 2 1 the tholeiitic basalts are characterised by relatively flat chondrite normalised ree patterns with la ybcn ratios of 0 8 1 6 mean 1 0 the basalts also exhibit negative ti and nb anomalies in primitive mantle normalised multi element diagrams the flat ree patterns the presence of prominent negative nb anomalies and the positive initial nd value of 2 1 suggest that the basalts were formed by low pressure melting of a mantle wedge in an active continental margin setting compared to the tholeiitic basalts the calc alkaline rhyolites are characterised by low abundances of the transition elements cr

coseismic deformation from the 1999 mw 7 1 hector mine california earthquake as inferred from insar and gps observations we use interferometric synthetic aperture radar insar and global positioning system gps observations to investigate static deformation due to the 1999 m w 7 1 hector mine earthquake that occurred in the eastern california shear zone interferometric decorrelation phase and azimuth offset measurements indicate regions of surface and near surface slip which we use to constrain the geometry of surface rupture the inferred geometry is spatially complex with multiple strands the southern third of the rupture zone consists of three subparallel segments extending about 20 km in length in a n45 w direction the central segment is the simplest with a single strand crossing the bullion mountains and a strike of n10 w the northern third of the rupture zone is characterized by multiple splays with directions subparallel to strikes in the southern and central the average strike for the entire rupture is about n30 w the interferograms indicate significant along strike variations in strain which are consistent with variations in the ground based slip measurements using a variable resolution data sampling routine to reduce the computational burden we invert the insar and gps data for the fault geometry and distribution of slip we compare results from assuming an elastic half space and a layered elastic space results from these two elastic models are similar although the layered space model predicts more slip at depth than does the half space model the layered model predicts a maximum coseismic slip of more than 5 m at a depth of 3 to 6 km contrary to preliminary reports the northern part of the hector mine rupture accommodates the maximum slip our model predictions for the surface fault offset and total seismic moment agree with both field mapping results and recent seismic models the inferred shallow slip deficit is enigmatic and may suggest that distributed inelastic yielding occurred in the uppermost few kilometers of the crust during or soon after the earthquake

dating basaltic volcanism in the neoarchaean sukumaland greenstone belt of the tanzania craton using the sm nd method implications for the geological evolution of the tanzania craton abstract metabasalts from the sukumaland greenstone belt of north western tanzania yield a whole rock sm nd isochron age of 2823 44 ma initial e nd 2 7 mswd 1 24 this age which is interpreted as dating the eruption of the oldest mafic volcanics in the belt is at the 95 confidence level indistinguishable from 2780 3 and 2808 3 ma single zircon u pb ages previously reported from stratigraphically higher rhyolitic pyroclastic rocks from the southern margin of the belt the age equivalency suggests that the entire 5 7 km thick greenstone sequence that has been traditionally classified into a predominantly mafic lower part overlain by an upper part in which felsic volcanics and bif predominate was emplaced within a relatively short time interval not exceeding 44 ma the sm nd age of the metabasalts is significantly older than a published zircon u pb age of 2680 3 ma obtained from a migmatitic gneiss on the southernmost fringe of the sukumaland greenstone belt this corroborates previous evidence that high grade metamorphism in the tanzania craton postdates emplacement of the greenstones and is most likely associated with the regional emplacement of the large granitic bodies that intrude and flank the greenstones