did the massive magnetite lava flows of el laco chile form by magmatic or hydrothermal processes new constraints from magnetite composition by la icp ms the el laco magnetite deposits consist of more than 98 magnetite but show field textures remarkably similar to mafic lava flows therefore it has long been suggested that they represent a rare example of an effusive fe oxide liquid field and petrographic evidence however suggest that the magnetite deposits represent replacement of andesite flows and that the textures are pseudomorphs we determined the trace element content of magnetite by laser ablation inductively coupled plasma mass spectrometry la icp ms from various settings at el laco and compared them with magnetite from both igneous and hydrothermal environments this new technique allows us to place constraints on the conditions under which magnetite in these supposed magnetite lava flows formed the trace element content of magnetite from the massive magnetite samples is different to any known magmatic magnetite including primary magnetite phenocrysts from the unaltered andesite host rocks at el laco instead the el laco magnetite is most similar in composition to hydrothermal magnetite from high temperature environments 500 c such as iron oxide copper gold iocg and porphyry cu deposits the magnetite trace elements from massive magnetite are characterised by 1 depletion in elements considered relatively immobile in hydrothermal fluids e g ti al cr zr hf and sc 2 enrichment in elements that are highly incompatible with magmatic magnetite rare earth elements ree si ca na and p and normally present in very low abundance in magmatic magnetite 3 high ni cr ratios which are typical of magnetite from hydrothermal environments and 4 oscillatory zoning of si ca mg ree and most high field strength elements and zoning truncations indicating dissolution similar to that formed in hydrothermal fe skarn deposits in addition secondary magnetite in altered brecciated host rock forming disseminations and veins has the same composition as magnetite from the massive lenses euhedral magnetite lining both open spaced veins in the brecciated host rock and along the walls of large hollow chimneys in the massive magnetite lenses also displays oscillatory zoning and most likely formed by fluctuating composition and or physio chemical conditions of the fluid thus the chemical fingerprint of magnetite from the supposed el laco magnetite lava flows supports the hydrothermal model of metasomatic replacement of andesite lava flows by dissolution and precipitation of magnetite from high temperature fluids rather than a magmatic origin from an effusive fe oxide liquid

the geochemical fingerprints of different tectonomagmatic environments using hygromagmatophile element abundances of tholeiitic basalts and basaltic andesites abstract using hygromagmatophile element abundances normalized to primordial mantle composition it is possible to discriminate between the tectonic settings of tholeiitic basalts and basaltic andesites 47 0 53 5 sio2 based on field and chemical evidence data from provinces or grouped localities have been compiled in order to establish chemical reference data sets for ocean island continental ocean ridge and floor subduction zone and back arc environments the disturbing effects of crustal contamination and hydrothermal alteration on the hygromagmatophile h element patterns are of minor significance in the recognition of plate tectonic settings on the basis of the data sets magmas from a number of ambiguous tectonic settings have been recognized using their h element patterns attention is directed to problems concerning rifting and drifting related basalts in an apparent continental setting and to the origin of ophiolite complexes using available data the pillow lavas of the troodos ophiolite complex cyprus are recognized as basalts erupted in a subduction zone environment

textures and chemical compositions of magnetite from iron oxide copper gold iocg and kiruna type iron oxide apatite ioa deposits and their implications for ore genesis and magnetite classification schemes

the karoo igneous province a problem area for inferring tectonic setting from basalt geochemistry tholeiitic basalts and associated intrusives are the major component of the karoo igneous province they are of mesozoic age and constitute one of the world s classic continental flood basalt cfb provinces it has been argued that most karoo basalts have not undergone significant contamination with continental crust and that their lithospheric mantle source areas were enriched in incompatible minor and trace elements during the proterozoic the only exceptions to this are late stage morb like dolerites near the present day continental margins which are considered to be of asthenospheric origin when data for the southern karoo basalts are plotted on many of the geochemical discriminant diagrams which have been used to infer tectonic setting essentially all of them would be classified as calc alkali basalts cab s or low k tholeiites virtually none of them plot in the compositional fields designated as characteristic of within plate basalts there is little likelihood that the compositions of the karoo basalts can be controlled by active subduction at the time of their eruption and no convincing evidence that a subduction component has been added to the subcontinental lithospheric mantle under the entire area in which the basalts crop out it must be concluded that the mantle source areas for cab s and the southern karoo basalts have marked similarities in contrast the data for northern karoo basalts largely plot in the within plate field on geochemical discriminant diagrams available data suggest that the source composition and or the restite mineralogy and degree of partial melting are different for southern and northern karoo basalts there is no evidence for any difference in tectonic setting between the southern and northern karoo basalts at the time they were erupted this appears to be clear evidence that specific mantle source characteristics and or magmatic processes can vary within a single cfb province to an extent that renders at least some geochemical discriminant diagrams most unreliable for classifying tectonic environment with respect to continental volcanic rocks

alteration mineralization and radiometric ages of the source pluton at the sangan iron skarn deposit northeastern iran abstract the world class sangan iron skarn deposit with a proven reserve of 1000 mt iron ore 53 fe is located in the khaf kashmar bardaskan volcano plutonic metallogenic belt kkb vpmb of northeastern iran along the e w trending regional doruneh fault north of the lut block skarn mineralization occurs at the contact of the 39 1 0 6 ma to 38 3 0 5 ma middle eocene syenite to syenogranite porphyry source pluton with cretaceous carbonate rocks the source pluton is part of an i type calcalkaline granitoid series with potassium to shoshonitic affinity metaluminous to slightly peraluminous character the granitoids are enriched in lile cs rb ba k th and u and lree la and ce are depleted in hfse nb y ta and ti hree yb and lu and eu which together with the low sr 96 to 362 ppm and la yb n contents suggest a metasomatized slab derived mantel source within the cenozoic volcanoplutonic continental arc of northeaster iran the location of the skarn orebodies is controlled by the regional e w doruneh fault structure and the spatial distribution and the two calcic and magnesian skarns is controlled by the composition of the carbonate protolith that consists of limestone in the west and dolomite in the east the chemistry of the skarn minerals reflects the composition of the protoliths the western skarn is dominated by ca rich calcsilicates that consist of prograde ca rich garnet adr 50 97 grs 0 45 sps alm 2 7 ca fe rich pyroxene hd 75 6 di 20 jo 4 5 k cl f bearing fe ca rich amphibole ferrohastingsite fe 4 4 ca 2 mg 0 5 k 0 4 na 0 3 si 6 5 al 1 8 o 22 cl f oh 2 in endoskarns and retrograde ferroactinolite fe 4 2 ca 2 mgmn 0 04 na 0 1 k 0 06 si 7 8 al 0 2 o 22 f cl oh 2 and fe rich chlorite ripidolite fe 4 3 mg 1 1 ca 0 06 mn 0 01 al 2 8 si 3 o 10 oh 8 in the exoskarns wollasonite plagioclase and k feldspar have been additionally formed together with ferrohastingsite in the endoskarns the eastern magnesian skarn is typically phlogopite rich k 0 9 mg 2 7 fe 0 2 na 0 02 si 2 9 al 1 2 o 10 oh f 2 and consists of prograde forsterite fo 97 0 fa 2 7 diopsidic pyroxene hd 0 2 di 0 88 and retrograde mg rich actinolite mg rich chlorite clinochlore mg 4 5 fe 0 1 k 0 05 al 1 8 si 2 7 o 10 oh 8 serpentine and talc iron mineralization overprints the calcsilicate skarns in both the western and the eastern skarns and is magnesian in the eastern orebodies 3 65 wt mgo the iron ore consists of a number of high grade replacement and magnetite orebodies with minor amounts of pyrrhotite chalcopyrite and pyrite indicating a large scale metasomatic transfer of iron bearing fluids during middle eocene magmatic activity at the kkb vpmb

chadormalu kiruna type magnetite apatite deposit bafq district iran insights into hydrothermal alteration and petrogenesis from geochemical fluid inclusion and sulfur isotope data abstract the chadormalu is one of the largest known iron deposits in the bafq metallogenic province in the kashmar kerman belt central iran the deposit is hosted in precambrian cambrian igneous rocks represented by rhyolite rhyodacite granite diorite and diabasic dikes as well as metamorphic rocks consisting of various schists the host rocks experienced na albite calcic actinolite and potassic k feldspar and biotite hydrothermal alteration associated with the formation of magnetite apatite bodies which are characteristic of iron oxide copper gold iocg and iron oxide apatite ioa systems iron ores occurring as massive type and vein type bodies consist of three main generations of magnetite including primary secondary and recrystallized which are chemically different apatite occurs as scattered irregular veinlets in various parts of the main massive ore body as well as apatite magnetite veins and disseminated apatite grains in marginal parts of the deposit and in the immediate wall rocks minor pyrite occurs as a late phase in the iron ores chemical composition of magnetite is representative of an ioa or kiruna type deposit which is consistent with other evidence whole rock geochemical data from various host rocks confirm the occurrence of na ca and k alteration consistent with the formation of albite actinolite and k feldspar respectively the geochemical investigation also includes the nature of calc alkaline igneous rocks and helps elaborating on the spatial and temporal association and possible contribution of mafic to felsic magmas to the evolution of ore bearing hydrothermal fluids fluid inclusion studies on apatites from massive and vein type ores show a range of homogenization temperatures from 266 to 580 c and 208 406 c and salinities from 0 5 to 10 7 wt and 0 3 24 4 wt nacl equiv respectively the fluid inclusion data suggest the involvement of evolving fluids from low salinity high temperature to high salinity low temperature in the formation of the massive and vein type ores respectively the 34s values obtained for pyrite from various parts of the deposit range between 8 9 and 14 4 for massive ore and 18 7 to 21 5 for vein type ore a possible source of sulfur for the 34s enriched pyrite would be originated from late precambrian early cambrian marine sulfate or fluids equilibrated with evaporitic sulfates field observations ore mineral and alteration assemblages coupled with lithogeochemical fluid inclusion and sulfur isotopic data suggest that an evolving fluid from magmatic dominated to surficial brine rich fluid has contributed to the formation of the chadormalu deposit in the first stages of mineralization magmatic derived fluids had a dominant role in the formation of the massive type ores whereas a later brine with higher 34s contributed to the formation of the vein type ores

trace elements in magnetite from massive iron oxide apatite deposits indicate a combined formation by igneous and magmatic hydrothermal processes iron oxide apatite ioa deposits are an important source of iron and other elements e g ree p u ag and co vital to modern society however their formation including the namesake kiruna type ioa deposit sweden remains controversial working hypotheses include a purely magmatic origin involving separation of an fe p rich volatile rich oxide melt from a si rich silicate melt and precipitation of magnetite from an aqueous ore fluid which is either of magmatic hydrothermal or non magmatic surface or metamorphic origin in this study we focus on the geochemistry of magnetite from the cretaceous kiruna type los colorados ioa deposit 350 mt fe located in the northern chilean iron belt los colorados has experienced minimal hydrothermal alteration that commonly obscures primary features in ioa deposits laser ablation inductively coupled plasma mass spectroscopy la icp ms transects and electron probe micro analyzer epma wavelength dispersive x ray wdx spectrometry mapping demonstrate distinct chemical zoning in magnetite grains wherein cores are enriched in ti al mn and mg the concentrations of these trace elements in magnetite cores are consistent with igneous magnetite crystallized from a silicate melt whereas magnetite rims show a pronounced depletion in these elements consistent with magnetite grown from an fe rich magmatic hydrothermal aqueous fluid further magnetite grains contain polycrystalline inclusions that re homogenize at magmatic temperatures 850 c smaller inclusions 500 ppm concentrations

trace element composition of iron oxides from iocg and ioa deposits relationship to hydrothermal alteration and deposit subtypes trace element compositions of magnetite and hematite from 16 well studied iron oxide copper gold iocg and iron oxide apatite ioa deposits combined with partial least squares discriminant analysis pls da were used to investigate the factors controlling the iron oxide chemistry and the links between the chemical composition of iron oxides and hydrothermal processes as divided by alteration types and iocg and ioa deposit subtypes chemical compositions of iron oxides are controlled by oxygen fugacity temperature co precipitating sulfides and host rocks iron oxides from hematite iocg deposits show relatively high nb cu mo w and sn contents and can be discriminated from those from magnetite hematite and magnetite ioa deposits magnetite iocg deposits show a compositional diversity and overlap with the three other types which may be due to the incremental development of high temperature ca fe and k fe alteration iron oxides from the high temperature ca fe alteration can be discriminated from those from high and low temperature k fe alteration by higher mg and v contents iron oxides from low temperature k fe alteration can be discriminated from those from high temperature k fe alteration by higher si ca zr w nb and mo contents iron oxides from ioa deposits can be discriminated from those from iocg deposits by higher mg ti v pb and sc contents the composition of iocg and ioa iron oxides can be discriminated from those from porphyry cu ni cu and volcanogenic massive sulfide deposits

magnetite compositions from the baba ali iron deposit in the sanandaj sirjan zone western iran implications for ore genesis abstract the economically significant baba ali iron ore deposit is located in the sanandaj sirjan zone western iran is associated with diorite the mineralization trends in a ene wsw direction with thickness that varies from 30 m up to 50 m and a length of about 250 m the main mineral assemblages are massive magnetite epidote actinolite tourmaline quartz calcite and pyrite using different magnetite compositional discrimination diagrams the low concentrations of ti 0 11 wt al 0 06 wt cr 19 62 ppm and co 20 26 and high ni cr ratios 6 34 are consistent with a hydrothermal origin similar to typical skarn mineralization the different elemental compositions of various magnetite generations might be due to an ore forming fluid that initially a high t magmatic hydrothermal character then evolved to a lower temperture meteoric water dominated system it seems that fe bearing saline fluids infiltrated the carbonate host rocks causing high temperature acid metalliferous fluids to become neutralized during reaction with carbonates causing a decrease in iron solubility and saturating as a magnetite with increasing ph and decreasing the temperature the close spatial and temporal association of the mineralization with the fracture systems suggests that a pressure decrease also had a significant impact on the iron solubility triggering ore precipitation and replacement at relatively low temperatures 300 c under reducing conditions

uncertainty of the 20th century sea level rise due to vertical land motion errors assessing the vertical land motion vlm at tide gauges tg is crucial to understanding global and regional mean sea level changes slc over the last century however estimating vlm with accuracy better than a few tenths of a millimeter per year is not a trivial undertaking and many factors including the reference frame uncertainty must be considered using a novel reconstruction approach and updated geodetic vlm corrections we found the terrestrial reference frame and the estimated vlm uncertainty may contribute to the global slc rate error by 0 2 mmyr 1 in addition a spurious global slc acceleration may be introduced up to 4 8 x 10 3 mmyr 2 regional slc rate and acceleration errors may be inflated by a factor 3 compared to the global the difference of vlm from two independent glacio isostatic adjustment models introduces global slc rate and acceleration biases at the level of 0 1 mmyr 1and 2 8 x 10 3 mmyr 2 increasing up to 0 5 mm yr 1 and 9 x 10 3 mmyr 2 for the regional slc errors in vlm corrections need to be budgeted when considering past and future slc scenarios

iron rich fragments in the yamansu iron deposit xinjiang nw china constraints on metallogenesis abstract volcanic rock hosted iron deposits are among the important iron ores in china however the nature of primary magma and petrogenesis associated with these iron ores remains controversial here we report iron rich fragments irf from the yamansu iron deposit in eastern tianshan mountains nw china which occurs in association with volcanic breccia submarine volcanic breccia and ignimbrite the irf is composed of five types including oligoclase iron oxide type oio oligoclase albite iron oxide type oaio albite iron oxide type aio albite k feldspar iron oxide type akio and k feldspar iron oxide type kio these fragments display typical volcanic fabric features such as porphyritic texture hyalopilitic texture of the groundmass and vesicles filled by minerals to form amygdales the feldspar phenocrysts of irf are dominantly albite the groundmass of irf consists of magnetite and feldspar the magnetite is distributed in between the feldspar laths and together display hyalopilitic texture which could be observed only in volcanic rocks the vesicles are filled with magnetite feldspar chlorite and calcite from the margin to the interior the irf has high si al fe ca ti na and k contents and low mg content the average total fe is 26 wt the magnetite is mostly titanium vanadium magnetite with the tio2 content ranging up to 4 86 wt and v2o3 content up to 3 20 wt the irf probably came from iron rich melts and represent the products of the fenner magma evolution the basaltic magma evolved into the fe na rich residual melts by crystallization under low oxygen fugacity condition in a closed magma chamber after intruding into the shallow crust the fe na rich residual melts were emplaced in hypabyssal environments or erupted generating the orebodies or providing the material source for the generation of the high grade iron ores which were subsequently enriched by the late stage hydrothermal fluids

non recognition of continental tholeiites using the ti y zr diagram continental tholeiites cannot be identified using the ti y zr diagram two hundred and thirteen analyses from 16 localities representing 7 continental tholeiitic provinces all plot outside the within plate basalt field of this diagram

basalt geochemistry and tectonic settings a new approach to relate tectonic and magmatic processes abstract in recent years the effects of mantle heterogeneity crustal contamination mantle metasomatism and other non differentiation related processes on the composition of basalts have been documented in various well defined tectonic settings the fact that none of these effects are unique to a specific tectonic setting illustrates the fundamental logical error in the formulation of discrete tectonomagmatic classifications of basalts using empirical discrimination diagrams a more meaningful approach to the problem of tectonics and basalt geochemistry is careful stratigrapghc geochemical studies which document important temporal and spatial variations in melt compositions using this approach it may be possible to identify certain sequences of compositions which are characteristic of specific tectonic cycles the first problem encountered in any such study is the identification of significant compositional variations within a single tectonic province the niobium normalized spidergram presented here is a simple yet powerful tool for rapid detection of source heterogeneity or other non differentiation related compositional variations in basalts

sea level budgets should account for ocean bottom deformation the conventional sea level budget slb equates changes in sea surface height with the sum of ocean mass and steric change where solid earth movements are included as corrections but limited to the impact of glacial isostatic adjustment however changes in ocean mass load also deform the ocean bottom elastically until the early 2000s ocean mass change was relatively small translating into negligible elastic ocean bottom deformation obd hence neglected in the slb equation however recently ocean mass has increased rapidly hence obd is no longer negligible and likely of similar magnitude to the deep steric sea level contribution here we use a mass volume framework which allows the ocean bottom to respond to mass load to derive a slb equation that includes obd we discuss the theoretical appearance of obd in the slb equation and its implications for the global slb

ocean bottom deformation due to present day mass redistribution and its impact on sea level observations present day mass redistribution increases the total ocean mass and on average causes the ocean bottom to subside elastically therefore barystatic sea level rise is larger than the resulting global mean geocentric sea level rise observed by satellite altimetry and gps corrected tide gauges we use realistic estimates of mass redistribution from ice mass loss and land water storage to quantify the resulting ocean bottom deformation and its e ect on global and regional ocean volume change estimates over 1993 2014 the resulting globally averaged geocentric sea level change is 8 percent smaller than the barystatic contribution over the altimetry domain the di erence is about 5 percent and due to this e ect barystatic sea level rise will be underestimated by more than 0 1 mm y over 1993 2014 regional di erences are of ten larger up to 1 mm y over the arctic ocean and 0 4 mm y in the south paci c ocean bottom deformation should be considered when regional sea level changes are observed in a geocentric reference frame

rare earth element mobility around the volcanogenic polymentallic massive sulfide deposit at que river tasmania australia abstract the que river volcanogenic base and precious metal deposit is located in the cambrian mt read volcanics of western tasmania the host andesites and dacites adjacent to mineralization have been hydrothermally altered during mineralization and the entire sequence has undergone devonian regional prehnite pumpellyite facies metamorphism rocks petrographically recognizable as andesites exhibit chondrite normalized ree patterns similar to modern orogenic high k andesitic rocks with ce yb n ratios ranging from 6 4 to 8 6 dacites are more fractionated with ce yb n ranging from 10 6 to 16 0 like the andesites the dacites are characterized by negative eu anomalies eu eu 0 73 0 85 except for a more extreme eu anomaly in one sample eu eu 0 57 polymict volcaniclastic rocks have patterns very similar to those of the andesites the chondrite normalized ree patterns for the hydrothermally altered volcanics fall into three groups that can also be distinguished petrographically a single chloriterich sample has a substantial eu anomaly and shows less relative depletion in the middle ree than do either the andesites or the dacites highly silicified samples are all characterized by large negative eu anomalies eu eu 0 37 0 46 and many are relatively unfractionated with ce yb n ratios ranging from 3 5 to 7 7 a third group of samples characterized by the development of phengitic mica and carbonate show ree patterns similar to the andesites although their eu anomalies are generally smaller a sample of massive zn 1bpb ore has very low ree abundances showing light ree enrichment and a small negative eu anomaly eu eu 0 82 massive pyrite has a similar pattern except for higher overall abundances and a small positive eu anomaly eu eu 1 10 except for the eu anomalies the andesites and dacites show no evidence for ree mobility eu anomalies in the andesites are probably due to alteration of phenocrystic plagioclase and subsequent removal of divalent eu substantial ree mobility has occurred in the hydrothermally altered volcanic rocks the degree of mobility correlating with alteration style and intensity eu has been leached from both former plagioclase phenocrysts and the groundmass some of the eu leached from zones of the most intense alteration may have been redeposited in lower temperature more distal alteration zones

bias in estimates of global mean sea level change inferred from satellite altimetry abstractestimates of regional and global average sea level change remain a focus of climate change research one complication in obtaining coherent estimates is that geodetic datasets measure different aspects of the sea level field satellite altimetry constrains changes in the sea surface height ssh or absolute sea level whereas tide gauge data provide a measure of changes in ssh relative to the crust i e relative sea level the latter is a direct measure of changes in ocean volume and the combined impacts of ice sheet melt and steric effects but the former is not since it does not account for crustal deformation nevertheless the literature commonly conflates the two estimates by directly comparing them we demonstrate that using satellite altimetry records to estimate global ocean volume changes can lead to biases that can exceed 15 the level of bias will depend on the relative contributions to sea level changes from the antarctic and greenland ice sheets the bias is also more sensitive

in situ la icp ms trace elemental analyses of magnetite the mesozoic tengtie skarn fe deposit in the nanling range south china abstract the nanling range in south china hosts numerous world class w sn deposits and some fe deposits the mesozoic tengtie fe skarn deposit in the southern nanling range is contemporaneous with the regional sn mineralization the deposit is composed of numerous ore bodies along the contacts between the late paleozoic or mesozoic carbonate rocks and the yanshanian lianyang granitic complex interaction of the magma with hosting dolomitic limestone and limestone formed calcic ca rich and magnesian mg rich skarns respectively the tengtie deposit has a paragenetic sequence of the prograde stage of anhydrous skarn minerals followed by the retrograde stage of hydrous skarn minerals and the final sulfide stage magnetite in the prograde and retrograde skarn stages is associated with diopside garnet chlorite epidote and phlogopite whereas magnetite of the final stage is associated with chalcopyrite and pyrite massive magnetite ores crosscut by quartz and calcite veins are present mainly in the retrograde skarn stage laser ablation icp ms was used to determine trace elements of magnetite from different stages some magnetite grains have unusually high ca na k and si possibly due to the presence of silicate mineral inclusions magnetite of the prograde stage has the highest co contents but that of the sulfide stage is extremely poor in co which partitions in sulfides magnetite of magnesian skarns contains more mg mn and al than that of calcic skarns attributed to the interaction of the magma with compositionally different host rocks magnetite from calcic and magnesian skarns contains 6 185 ppm sn and 61 1246 ppm sn respectively the high sn contents are not due to the presence of cassiterite inclusions which are not identified in magnetite instead we believe that sn resides in the magnetite structure regionally intensive mesozoic sn mineralization in south china indicates that concurrent magmatic hydrothermal fluids may be rich in sn and contribute to the formation of high sn magnetite our study demonstrates that trace elements of magnetite can be a sensitive indicator for the skarn stages and wall rock compositions and as such trace elemental chemistry of magnetite can be a potentially powerful fingerprint for sediment provenance and regional mineralization

concepts of the evolution of the austroalpine basement complex eastern alps during the caledonian variscan cycle the austroalpine basement complex has a complicated pre alpidic history which begins with the caledonian era in the late precambrian and early paleozoic a magmatic sedimentary rock sequence is formed presumably in an island arc or active continental margin environment subduction with eclogite formation is followed by collision high grade metamorphism and anatexis in the ordovician this caledonian basement is preserved in parts of the austroalpine crystalline mass the post caledonian deposits are mainly shelf type sediments with intercalated volcanics although there is evidence for an oceanic basin to the south the variscan facies zones are arranged in sw ne direction oblique to the alpidic trend in a first stage of variscan orogeny in the carboniferous south east vergent decollement nappes syntectonic flysch deposits and granitoids are formed along with regional metamorphism this is followed by a second stage in the permian with north west vergent thrusting renewed granite formation and metamorphism the variscan nappe pile is today exposed in a deeper level in the west or northwest than in the east or southeast

trace elements in magnetite from porphyry cu mo au deposits in british columbia canada abstract this study examines trace elements in hydrothermal magnetite from five porphyry cu mo au deposits and two skarns in british columbia canada trace element concentrations vary several orders of magnitude both within and between magnetite from skarn and porphyry deposit settings the heterogeneous composition of hydrothermal magnetite may in part be due to the short duration low temperature and multiple fluid events that attend the formation of porphyry ore deposits principal component analysis shows two dominant patterns of trace element abundances in hydrothermal magnetite firstly positive correlations of ti al and v which account for nearly 40 of the total variation in magnetite are inferred to depend on temperature and oxygen fugacity secondly antithetic abundances of lower valence cations co mn with higher valence cations sn and mo may reflect variations in the redox potential acidity and metal speciation of hydrothermal fluids the cu fe and mn fe ratios calculated for fluids in equilibrium with the hydrothermal magnetite using experimental partitioning data are similar to those measured directly in brines trapped in quartz hosted fluid inclusions from porphyry cu mo au deposits

improved methods for observing earth s time variable mass distribution with grace using spherical cap mascons we discuss several classes of improvements to gravity solutions from the gravity recovery and climate experiment grace mission these include both improvements in background geophysical models and orbital parameterization leading to the unconstrained spherical harmonic solution jpl rl05 and an alternate jpl rl05m mass concentration mascon solution benefitting from those same improvements but derived in surface spherical cap mascons the mascon basis functions allow for convenient application of a priori information derived from near global geophysical models to prevent striping in the solutions the resulting mass flux solutions are shown to suffer less from leakage errors than harmonic solutions and do not necessitate empirical filters to remove north south stripes lowering the dependence on using scale factors the global mean scale factor decreases by 0 17 to gain accurate mass estimates ocean bottom pressure obp time series derived from the mascon solutions are shown to have greater correlation with in situ data than do spherical harmonic solutions increase in correlation coefficient of 0 08 globally particularly in low latitude regions with small signal power increase in correlation coefficient of 0 35 regionally in addition to reducing the error rms with respect to the in situ data reduction of 0 37 cm globally and as much as 1 cm regionally greenland and antarctica mass balance estimates derived from the mascon solutions agree within formal uncertainties with previously published results computing basin averages for hydrology applications shows general agreement between harmonic and mascon solutions for large basins however mascon solutions typically have greater resolution for smaller spatial regions in particular when studying secular signals

trace elements in magnetite as petrogenetic indicators we have characterized the distribution of 25 trace elements in magnetite mg al si p ca sc ti v cr mn co ni cu zn ga ge y zr nb mo sn hf ta w and pb using laser ablation icp ms and electron microprobe from a variety of magmatic and hydrothermal ore forming environments and compared them with data from the literature we propose a new multielement diagram normalized to bulk continental crust designed to emphasize the partitioning behavior of trace elements between magnetite the melt fluid and co crystallizing phases the normalized pattern of magnetite reflects the composition of the melt fluid which in both magmatic and hydrothermal systems varies with temperature thus it is possible to distinguish magnetite formed at different degrees of crystal fractionation in both silicate and sulfide melts the crystallization of ilmenite or sulfide before magnetite is recorded as a marked depletion in ti or cu respectively the chemical signature of hydrothermal magnetite is distinct being depleted in elements that are relatively immobile during alteration and commonly enriched in elements that are highly incompatible into magnetite e g si and ca magnetite formed from low temperature fluids has the lowest overall abundance of trace elements due to their lower solubility chemical zonation of magnetite is rare but occurs in some hydrothermal deposits where laser mapping reveals oscillatory zoning which records the changing conditions and composition of the fluid during magnetite growth this new way of plotting all 25 trace elements on 1 diagram normalized to bulk continental crust and elements in order of compatibility into magnetite provides a tool to help understand the processes that control partitioning of a full suit of trace elements in magnetite and aid discrimination of magnetite formed in different environments it has applications in both petrogenetic and provenance studies such as in the exploration of ore deposits and in sedimentology

relationship between altered pyroxene diorite and the magnetite mineralization in the chilean iron belt with emphasis on the el algarrobo iron deposits atacama region chile north of el algarrobo one of the four main deposits of the chilean iron belt the iron mineralization magnetite etrmolite actinolite apatite is related to clinoand orthopyroxene diorite intrusions which have crystallized at shallow depth 4km under increasing oxygen fugacities the supercritical fluid phase exsolved during cooling after the consolidation of the plutons 800 900 c results in a h cl and sodic enrichment and in the sequential leaching of fe at less than 700 c then ca and mg between 600 and 500 c from minerals of the primary magmatic diorite assemblage titanomagnetite ilmenite plagioclase an70 40 augite hypersthene as a consequence of the cationic leaching the lower mobility of silica and aluminium and the enrichment in sodium residual altered dioritic rocks present a retromorphic mineral assemblage evolving down to boundary conditions of the greenchist amphibolite facies 450 c fe mg and ca are carried in cationic form associated with cl anions toward cooler rocks where they are precipitated the deposition between 550 and 450 c of magnetite followed iron mineralization paragenesis and occurred in fractured zones located both in altered diorites and contact andesites

an evolving magmatic hydrothermal system in the formation of the mesozoic meishan magnetite apatite deposit in the ningwu volcanic basin eastern china abstract the meishan iron deposit contains 338 mt of iron ore reserves at 39 fe and represents the largest magnetite apatite deposit in the ningwu basin of eastern china controversy has long existed about whether this deposit had a hydrothermal or iron oxide melt origin iron mineralization is genetically related to plutons that are composed of gabbro diorite which were emplaced at 130 1 ma these rocks have sio2 contents of 51 72 54 60 wt na2o contents of 3 47 4 04 wt k2o contents of 2 02 2 69 wt and k2o na2o ratios of 0 51 0 73 these rocks are enriched in liles and lrees and depleted in nb ta and ti which indicates that the magma originated through partial melting of an enriched lithospheric mantle source in a subduction environment a pattern of decreasing initial sr isotopic ratios and increasing end t values with time in early cretaceous magmatic rocks of the ningwu basin may indicate incorporation of increasing proportions of asthenospheric mantle material into the source magma which is consistent with the processes of lithospheric thinning and asthenospheric upwelling in eastern china related to mesozoic subduction of the paleo pacific plate two stages of magnetite are found in the gabbro diorite 1 early crystallized magnetite as euhedral subhedral crystals in larger clinopyroxene crystals and 2 later crystallized magnetite and accompanying ilmenite grains in the voids between plagioclase and clinopyroxene crystals the formation of magnetite before clinopyroxene combined with the results of fe ti oxide geothermometry and analysis of magnetite v content indicates that the oxygen fugacity of the source magma was greater than fmq 2 2 at an early stage 640 c but decreased to fmq 2 66 as abundant magnetite crystallized at a later stage 489 c the early crystallization of magnetite at a high oxygen fugacity does not support a fenner evolution trend for the primitive magma and diminishes the likelihood of liquid immiscibility which could have generated an iron rich melt and is thus inconsistent with an iron oxide melt origin for the meishan iron deposit the 34s values of pyrite 6 6 15 1 and anhydrite 15 6 16 9 in the deposit and the occurrence of evaporites under the volcanic rocks likely indicate that the iron ores and alteration rocks of the meishan deposit were formed by the circulation of fluids of evaporitic origin driven by heat from the hypabyssal gabbro diorite intrusives in the late magmatic stage oxygen fugacity decreased to a reducing range triggering the reduction of sulfate to reduced sulfur and leading to local gold and pyrite mineralization

on the origin of late holocene sea level highstands within equatorial ocean basins abstract late holocene sea level highstands of amplitude 3 m are endemic to equatorial ocean basins these highstands imply an ongoing and moderate sub mm yr sea level fall in the far field of the late pleistocene ice cover that has long been linked to the process of glacial isostatic adjustment gia clark et al 1978 mitrovica and peltier 1991 coined the term equatorial ocean syphoning to describe the gia induced sea level fall and they provided the first physical explanation for the process they argued that water migrated away from far field equatorial ocean basins in order to fill space vacated by collapsing forebulges at the periphery of previously glaciated regions we provide a complete physical explanation for the origin of equatorial ocean syphoning and the associated development of sea level highstands using numerical solutions of the equation that governs meltwater redistribution on spherical viscoelastic earth models in particular we separate the total predicted sea level change into contributions associated with ice and meltwater loading effects and by doing so isolate a second mechanism that contributes significantly to the ocean syphoning process ocean loading at continental margins induces a levering of continents and a subsidence of offshore regions that has also long been recognized within the gia literature walcott 1972 we show that the influx of water into the volume created by this subsidence produces a sea level fall at locations distant from these margins indeed over the major ocean basins that is comparable in amplitude to the syphoning mechanism isolated by mitrovica and peltier 1991

geochronological elemental and sr nd hf o isotopic constraints on the petrogenesis of the triassic post collisional granitic rocks in nw thailand and its paleotethyan implications abstract new u pb geochronological petrologic elemental and sr nd hf o isotopic data for the granites from the inthanon and sukhothai zones in nw thailand in conjunction with correlations with sw china are presented to constrain the age and position of the paleotethys ocean in this region and the associated assembly of southeast asia the geochronological data show that the granitic rocks in the inthanon and sukhothai zones herein named group 1 and group 2 granites respectively yield similar crystallization ages of 230 200 ma group 1 samples are characterized by monzogranite and granite with i and s type geochemical affinity and group 2 samples by i type monzogranite and granodiorite they have generally similar chondrite normalized ree and pm normalized multi element patterns but distinct sr nd hf o isotopic compositions group 1 samples have slightly higher initial 87sr 86sr ratios 0 7111 0 7293 but lower end t values 11 1 to 14 1 than those of group 2 samples 87sr 86sr i 0 7073 0 7278 and end t 8 3 to 11 0 group 1 samples show the lower ehf t values 5 4 to 18 2 older tdm 1 62 2 40 ga and higher 18o values 7 95 to 9 94 than those of group 2 samples ehf t of 11 1 to 4 80 tdm of 0 96 1 95 ga and 18o of 4 95 to 7 98 for the triassic crystallization zircons these geochemical signatures are similar to the kwangsian and indosinian granites in the south china and indochina blocks but distinct from those of the gangdese i type granite and sibumasu paleozoic granite our data suggest that group 1 samples mainly originated from the early paleozoic supracrustal rocks containing metapelite and metavolcanic components which had previously experienced the surface weathering group 2 samples were derived from a hybridized source of an old metamorphic and a newly underplated mafic component synthesis of our data with available regional observations indicates that the inthanon zone represents the main suture zone of the eastern paleotethyan ocean in nw thailand and links with the changning menglian suture zone in sw yunnan sw china in nw thailand a switch from the eastward subduction of the paleotethyan oceanic plate to the collision of the sibumasu with indochina blocks occurred at 237 ma and syn and post collisional time being at 237 230 ma and 200 230 ma respectively the late triassic granites in the inthanon and sukhothai zones are representative of the post collisional magmatic products

the sea level budget along the northwest atlantic coast gia mass changes and large scale ocean dynamics sea level rise and decadal variability along the northwestern coast of the north atlantic ocean are studied in a self consistent framework that takes into account the effects of solid earth deformation and geoid changes due to large scale mass redistribution processes observations of sea and land level changes from tide gauges and gps are compared to the cumulative effect of gia present day mass redistribution and ocean dynamics over a 50 year period 1965 2014 gia explains the majority of the observed sea level and land motion trends as well as almost all interstation variability present day mass redistribution resulting from ice melt and land hydrology causes both land uplift and sea level rise in the region we find a strong correlation between decadal steric variability in the subpolar gyre and coastal sea level which is likely caused by variability in the labrador sea that is propagated southward the steric signal explains the majority of the observed decadal sea level variability and shows an upward trend and a significant acceleration which are also found along the coast the sum of all contributors explains the observed trends in both sea level rise and vertical land motion in the region as well as the decadal variability the sum of contributors also explains the observed acceleration within confidence intervals the sea level acceleration coincides with an accelerating density decrease at high latitudes

the abagong apatite rich magnetite deposit in the chinese altay orogenic belt a kiruna type iron deposit abstract the abagong apatite rich iron deposit is located in the kelang volcano sedimentary basin in the southern margin of the chinese altay orogenic belt aob which is an important polymetallic belt in china the ore bodies are interbedded with the upper silurian to lower devonian metamorphosed calc alkaline felsic volcanic rocks that show well preserved porphyritic and volcaniclastic textures the ore mineralization is aligned along faults that controlled their emplacement and occurs as lenses veins and stratoids bodies that generally cut the host rocks at a high angle and show sharp contacts the ore bodies and host rocks have undergone greenschist facies metamorphism deformation and folding the iron ores have massive densely disseminated banded and brecciated structures magnetite from the abagong deposit is low in ti tio 2 0 002 0 129 wt and the apatites from different ore types p poor and p rich ores are typical igneous fluorapatites with minor cl contents apatites of different forms and from different ore types show similar rare earth element ree and trace element normalized patterns with weak to moderate enrichment in light ree th u and pb depletion in sr ba nb ta and ti and negative eu anomalies indicating a common source and genesis the similar ree patterns for the magnetite apatite and volcanic host rocks suggest their close genetic linkage and support a magmatic origin for the deposit the abagong deposit shows the typical characteristics of kiruna type deposits with regard to the mineral assemblages ore texture and structure and the apatite and magnetite geochemistry we propose that the kiruna type abagong apatite rich iron deposit was derived from fe p rich melt through liquid immiscibility and the activity of hydrothermal fluids

closing the sea level budget on a regional scale trends and variability on the northwestern european continental shelf long term trends and decadal variability of sea level in the north sea and along the norwegian coast have been studied over the period 1958 2014 we model the spatially nonuniform sea level and solid earth response to large scale ice melt and terrestrial water storage changes gps observations corrected for the solid earth deformation are used to estimate vertical land motion we find a clear correlation between sea level in the north sea and along the norwegian coast and open ocean steric variability in the bay of biscay and west of portugal which is consistent with the presence of wind driven coastally trapped waves the observed nodal cycle is consistent with tidal equilibrium we are able to explain the observed sea level trend over the period 1958 2014 well within the standard error of the sum of all contributing processes as well as the large majority of the observed decadal sea level variability

basic volcanic rocks and tectonic setting a discussion of the zr ti y discrimination diagram and its suitability for classification purposes the zr ti y diagram cannot discriminate between normal and anomalous oceanic ridge basalts the latter tend to plot as within plate basalts this indicates that it is the mantle anomaly rather than the tectonic setting that characterizes the zr ti y interelement ratios in such rocks it is shown that rocks with sio2 56 of a tholeiitic series indicate a differentiation trend from ocean floor via within plate to calc alkaline basalts this feature shows that great care should be taken when data for altered or metamorphic rocks are selected for classification by this method

hydrothermal reequilibration of igneous magnetite in altered granitic plutons and its implications for magnetite classification schemes insights from the handan xingtai iron district north china craton abstract magnetite is a common mineral in igneous rocks and has been used as an important petrogenetic indicator as its compositions and textures reflect changing physiochemical parameters such as temperature oxygen fugacity and melt compositions in upper crustal settings igneous rocks are often altered by hydrothermal fluids such that the original textures and compositions of igneous magnetite may be partly or completely obliterated posing interpretive problems in petrological and geochemical studies in this paper we present textural and compositional data of magnetite from variably albitized granitoid rocks in the handan xingtai district north china craton to characterize the hydrothermal reequilibration of igneous magnetite four types of magnetite have been identified in the samples studied pristine igneous magnetite type 1 reequilibrated porous magnetite type 2 reequilibrated nonporous magnetite type 3 and hydrothermal magnetite type 4 pristine igneous magnetite contains abundant well developed ilmenite exsolution lamellae that are largely replaced by titanite during subsequent hydrothermal alteration the titanite has a larger molar volume than its precursor ilmenite and thus causes micro fractures in the host magnetite grains facilitating dissolution and reprecipitation of magnetite during sodic alteration the igneous magnetite is extensively replaced by type 2 and type 3 magnetite via fluid induced dissolution and reprecipitation porous type 2 magnetite is the initial replacement product of igneous magnetite and is subsequently replaced by the nonoporous type 3 variety as its surface area is reduced and compositional equilibrium with the altering fluid is achieved hydrothermal type 4 magnetite is generally euhedral and lacks exsolution lamellae and porosity and is interpreted to precipitate directly from the ore forming fluids hydrothermal reequilibration of igneous magnetite has led to progressive chemical purification during which trace elements such as ti al mg zn and cr contents decrease dramatically up to 2 3 orders of magnitude different coupled with significant increase in iron concentrations from less than 64 wt to higher than 70 wt results presented here show that magnetite is much more susceptible to textural and compositional reequilibration than previously thought the reequilibrated magnetite has geochemical patterns that may be distinctively different from its precursor making existing discrimination plots questionable when applied to genetic interpretation based on textural characterization and high resolution in situ compositional analyses we propose that the fe versus v ti diagram can be more confidently used to discriminate between pristine igneous magnetite reequilibrated magnetite and hydrothermal magnetite

geochemistry petrogenesis and metallogenesis of the panzhihua gabbroic layered intrusion and associated fe ti v oxide deposits sichuan province sw china the panzhihua gabbroic layered intrusion is associated with the 260ma emeishan large igneous province in sw china this sill like body hosts a giant fe ti v oxide deposit with 1333 million ton ore reserves which makes china a major producer of these metals the intrusion has a marginal zone of fine grained hornblende bearing gabbro and olivine gabbro followed upward by lower middle and upper zones the lower and middle zones consist of layered melanogabbro and gabbro composed of cumulate clinopyroxene plagioclase and olivine these zones also contain magnetite layers the upper zone consists chiefly of leucogabbro composed of plagioclase and clinopyroxene with minor olivine most rocks in the body show variable scale rhythmic modal layering in which dark minerals primarily clinopyroxene dominate in the lower parts of each layer and lighter minerals primarily plagioclase dominate in the upper parts the oxide ores occur as layers and lenses within the gabbros and are concentrated in the lower parts of the intrusion ore textures and associated mineral assemblages indicate that the ore bodies formed by very late stage crystallization of v rich titanomagnetite from an immiscible oxide liquid in a fluidrich environment the rocks of the panzhihua intrusion become more evolved in chemistry upward and follow a tholeiitic differentiation trend with enrichment in fe ti and v they are enriched in light rare earth elements relative to heavy rare earth elements and exhibit positive nb ta and ti anomalies and negative zr and hf anomalies the silicate rocks and oxide ores of the panzhihua intrusion formed from highly evolved fe ti v rich ferrobasaltic or ferropicritic magmas the textures of the ores and the abundance of minor hydrous phases indicate that addition of fluids from upper crustal wall rocks induced the separation of the immiscible oxide melts from which the fe ti v oxide ore bodies in the lower part of the intrusion crystallized

ongoing glacial isostatic contributions to observations of sea level change studies determining the contribution of water fluxes to sea level rise typically remove the ongoing effects of glacial isostatic adjustment gia unfortunately use of inconsistent terminology between various disciplines has caused confusion as to how contributions from gia should be removed from altimetry and grace measurements in this paper we review the physics of the gia corrections applicable to these measurements and discuss the differing nomenclature between the gia literature and other studies of sea level change we then examine a range of estimates for the gia contribution derived by varying the earth and ice models employed in the prediction we find similar to early studies that gia produces a small compared to the observed value but systematic contribution to the altimetry estimates with a maximum range of 0 15 to 0 5 mm yr 1 moreover we also find that the gia contribution to the mass change measured by grace over the ocean is significant in this regard we demonstrate that confusion in nomenclature between the terms absolute sea level and geoid has led to an overestimation of this contribution in some previous studies a component of this overestimation is the incorrect inclusion of the direct effect of the contemporaneous perturbations of the rotation vector which leads to a factor of two larger value of the degree two order one spherical harmonic component of the model results aside from this confusion uncertainties in earth model structure and ice sheet history yield a spread of up to 1 4 mm yr 1 in the estimates of this contribution however even if the ice and earth models were perfectly known the processing techniques used in grace data analysis can introduce variations of up to 0 4 mm yr 1 thus we conclude that a single valued gia correction is not appropriate for sea level studies based on gravity data each study must estimate a bound on the gia correction consistent with the adopted data analysis scheme

application of proton microprobe data to trace element partitioning in volcanic rocks abstract in situ proton microprobe analyses are used to calculate partition coefficients d for mn fe cu zr ga rb sr y zr ba and pb and more restricted data for ni ge nb and as in pyroxenes olivines biotites hornblendes feldspars and fe ti oxides from 32 volcanic rocks all with glassy matrices these range from leucitite and picritic basalt to high silica and peralkaline rhyolites data for pigeonite aenigmatite allanite and leucite are included where these occur as additional phases coefficients have also been rayleigh fractionation corrected this correction being significant for those elements with high coefficients in specific mineral phases and where pronounced crystallisation has occurred partition coefficients are presented as plots vs nbo t ratios of coexisting glasses melts negative correlations are observed based on log transformed data for mn zn fe and y pyroxenes mn zn and fe olivines mn and zn fe ti oxides nb y sr and zr hornblendes sr plagioclase and ba cu zn and fe feldspars these element partition coefficients are not correlated with bulk mineral compositions zr and ga are not correlated with either glass or mineral compositions except zr in hornblende the correlations support the role of melt polymerisation in controlling element partitioning at least for those elements listed although possible effects of temperature cannot be uniquely isolated in the present data set the coefficients presented here are generally consistent with published values for equivalent rock compositions one difference being that some of the higher published coefficients e g sr in plagioclase are not matched in the present data set from a practical viewpoint the relative regularity of the coefficient data presented does facilitate choice of relevant coefficient values that are required for petrogenetic modelling procedures

dissolution reprecipitation process of magnetite from the chengchao iron deposit insights into ore genesis and implication for in situ chemical analysis of magnetite abstract magnetite formed in different environments commonly has distinct assemblages and concentrations of trace elements that can potentially be used as a genetic indicator of this mineral and associated ore deposits in this paper we present textural and compositional data of magnetite from the chengchao iron deposit daye district china to provide a better understanding in the formation mechanism and genesis of the deposit and shed light on analytical protocols for in situ chemical analysis of hydrothermal magnetite magnetite grains from the ore related granitoid pluton mineralized endoskarn magnetite dominated exoskarn and vein type iron ores hosted in marine carbonate intruded by the pluton were examined using scanning electron microscopy and analyzed for major and trace elements using electron microprobe back scattered electron images reveal that primary magnetite from the mineralized skarns and vein type ores were all partly reequilibrated with late stage hydrothermal fluids forming secondary magnetite domains that are featured by abundant porosity and have sharp contact with the primary magnetite these textures are interpreted as resulting from a dissolution reprecipitation process of magnetite which however are mostly obscure under optically primary magnetite grains from the mineralized endoskarn and vein type ores contain high sio 2 0 92 3 21 wt al 2 o 3 0 51 2 83 wt and low mgo 0 15 0 67 wt whereas varieties from the exoskarn ores have high mgo 2 76 3 07 wt and low sio 2 0 03 0 23 wt and al 2 o 3 0 54 1 05 wt this compositional contrast indicates that trace element geochemical composition of magnetite is largely controlled by the compositions of magmatic fluids and host rocks of the ores that have reacted with the fluids compared to its precursor mineral secondary magnetite is significantly depleted in most trace elements with sio 2 deceasing from 1 87 to 0 47 wt on average and al 2 o 3 from 0 89 to 0 08 wt in mineralized endoskarn and vein type ores and mgo from 2 87 to 0 60 wt in exoskarn ores on the contrary average content of iron is notably increased from 69 2 wt to 71 9 wt in the secondary magnetite grains the results suggest that the dissolution reprecipitation process has been important in significantly removing trace elements from early stage magnetite to form high grade high quality iron ores in hydrothermal environments the textural and compositional data confirm that the chengchao iron deposit is of hydrothermal origin rather than being crystallized from immiscible iron oxide melts as previously suggested this study also highlights the importance of textural characterization using various imaging techniques before in situ chemical analysis of magnetite as is the case for texturally complicated u th bearing accessory minerals that have been widely used for u pb geochronology study

mean sea level variability in the north sea processes and implications mean sea level msl variations across a range of time scales are examined for the north sea under the consideration of different forcing factors since the late 19th century we use multiple linear regression models which are validated for the second half of the 20th century against the output of a tide surge model to determine the barotropic response of the ocean to fluctuations in atmospheric forcing we find that local atmospheric forcing mainly initiates msl variability on time scales up to a few years with the inverted barometric effect dominating the variability along the uk and norwegian coastlines and wind controlling the msl variability in the south from belgium up to denmark on decadal time scales msl variability mainly reflects steric changes which are largely forced remotely a spatial correlation analysis of altimetry observations and gridded steric heights suggests evidence for a coherent signal extending from the norwegian shelf down to the canary islands this fits with the theory of longshore wind forcing along the eastern boundary of the north atlantic causing coastally trapped waves to propagate over thousands of kilometers along the continental slope implications of these findings are assessed with statistical monte carlo experiments it is demonstrated that the removal of known variability increases the signal to noise ratio with the result that i linear trends can be estimated more accurately ii possible accelerations as expected e g due to anthropogenic climate change can be detected much earlier such information is of crucial importance for anticipatory coastal management engineering and planning

in situ la icp ms trace elemental analyses of magnetite cu au fe deposits in the khetri copper belt in rajasthan province nw india abstract magnetite is common in many ore deposits and their host rocks and is useful for petrogenetic studies in the khetri copper belt in rajasthan province nw india there are several cu au fe deposits associated with extensive cu fe au ag co ree u mineralization hosted in phyllites schists and quartzites of the paleoproterozoic delhi supergroup ore bodies of these deposits comprise dominantly disseminated and vein type cu sulfide ores composed of chalcopyrite pyrite and pyrrhotite intergrown with minor magnetite there are also fe oxide ores with minor or no cu sulfides which are locally overprinted by the mineral assemblage of the cu sulfide ores in addition to the fe oxide and cu sulfide ores the protolith of the delhi supergroup includes banded iron formations bifs with original magnetite preserved i e magnetite quartzites and their sheared counterparts in the sheared magnetite quartzites their magnetite and quartz are mobilized and redistributed to magnetite and quartz bands trace elemental compositions of magnetite from these types of ores rocks were obtained by la icp ms the dataset indicates that different types of magnetite have distinct concentrations of ti al mg mn v cr co ni zn cu p ge and ga which are correlated to their forming environments magnetite grains in magnetite quartzites have relatively high al 800 8000 ppm ti 150 900 ppm and v 300 600 ppm contents compared to those of bifs in other regions such as the yilgarn craton western australia and labrador canada the high al ti and v contents can be explained by precipitation of the magnetite from relatively reduced al ti rich water possibly involving hotter seafloor hydrothermal fluids derived from submarine mafic volcanic rocks magnetite in sheared magnetite quartzites is generally irregular and re crystallized and has ni mn al cu and p contents lower than the magnetite from the unsheared counterparts suggesting that the shearing related mobilization is able to extract these elements from original magnetite however elevated contents of ti v co cr ge and mg of the magnetite in the sheared magnetite quartzites can be ascribed to involvement of external hydrothermal fluids during the shearing consistent with occurrence of some hydrothermal minerals in the samples compositions of magnetite from the fe oxide and cu sulfide ores are interpreted to be controlled mainly by fluid compositions and or oxygen fugacity f o 2 other potential controlling factors such as temperature fluid rock interaction and co precipitating minerals have very limited impacts magnetite in the cu sulfide ores has higher v but lower ni contents than that of the fe oxide ores likely indicating its precipitation from relatively reduced evolved fluids however it is also indicated that the two types of magnetite do not show large distinctions in terms of concentrations of most elements suggesting that they may have precipitated from a common evolving fluid we propose a combination of ge versus ti al and cr versus co ni co variation plots to discriminate different types of magnetite from the khetri copper belt our work agrees well with previous studies that compositions of magnetite can be potentially useful for provenance studies but also highlights that discrimination schemes would be more meaningful for deposits in a certain region if fluid water chemistry and specific formation conditions reflected in compositions of magnetite are clearly understood

eclogites from the silvretta nappe switzerland geochemical constraints on the nature and geotectonic setting of their protoliths abstract in the austroalpine silvretta nappe of central europe eclogitic rocks of presumed paleozoic metamorphic age have recently been found their chemical composition suggests that they were derived from evolved tholeiitic magmas which have undergone variable degrees of fractionation at shallow depths involving crystallization of plagioclase plus olivine and or pyroxene the igneous protoliths probably originated at a constructive plate margin although some chemical features closely resemble those of mid ocean ridge basalts the composition of the metasedimentary country rocks suggests a tectonic setting close to a continental block perhaps in a back arc basin situation or incipient oceanic ridge

petrochemistry u pb zircon age and palaeotectonic setting of the lampang volcanic belt northern thailand two ne trending belts of mainly subaerial dacitic to rhyolitic flows and tuffs occur in the area between the towns of lampang and denchai in northern thailand in the western belt doi ton the rocks have been pervasively altered to quartz keratophyre rocks in the eastern belt doi luang are generally less altered mobile chemical components such as na 2 o and k 2 o show wide variation particularly in samples from the doi ton belt however low zr tio 2 ratios and low nb and ta contents support an origin at a convergent plate margin a positive epsilon nd value of 4 9 for rhyolite from the doi luang belt supports derivation from a primitive crustal source a rhyolite sample from the doi luang belt yielded a u pb zircon age of 240 1 ma early mid triassic the doi ton and doi luang belts are part of the lampang volcanic belt which can be traced to the north into the lincang jinghong volcanic belt in southern china comparison with published petrological data from the lincang jinghong belt shows strong similarity including the widespread development of keratophyric mineralogy and chemistry the lampang lincang jinghong belt formed at an early mid triassic convergent plate margin and is similar in age and tectonic setting to the more mafic phetchabun volcanic belt on the east side of the nan river suture zone these data constrain the timing of final amalgamation between the indochina and shan thai terranes to mid triassic or younger

development of the khao khwang fold and thrust belt implications for the geodynamic setting of thailand and cambodia during the indosinian orogeny abstract the indosinian orogeny in thailand is often viewed as having developed between strongly linear terranes which today trend approximately n s the terranes were subsequently disrupted by later tectonics particularly nw se trending cenozoic strike slip faults the ene wsw to ne sw striking thrusts and folds in the khao khwang platform area of the saraburi group on the sw margin of the indochina terrane are not easily explained in the context of this traditional view reversal of the clockwise rotation shown to have affected the block north of the mae ping fault zone only enhances the e w orientation of structures in the fold and thrust belt and moves the belt further east towards cambodia one solution for the trend that fits better with regional understanding from hydrocarbon exploration of the khorat plateau is that the indochina terrane was actually a series of continental blocks separated by permian rifting during the early triassic the early stages of collision south china cathaysian terrane collision with vietnam indochina resulted in the amalgamation of disparate blocks that now form the indochina terrane by closure along the rifts at the same time or following on from the collision there was closure of the back arc area between indochina and the sukhothai zone the rift basins were thrusted and inverted during the early stages of the indosinian orogeny and only underwent minor reactivated when later sibumasu collided with sukhothai zone indochina terrane margin during the late triassic the scenario described above requires the presence of a minor e w trending suture in nw cambodia evidence for this suture is suggested by the presence of permo triassic calc alkaline volcanism

depth of origin of basalts inferred from ti v ratios and a comparison with the k2o depth relationship for island arc volcanics abstract the location of tectonic fields on the ti v discrimination diagram suggests that this ratio in least fractionated basalts may be a function of the depth to magma source the hypothesis is tested using chronostratigraphic data for selected intraplate volcanics and the idea is then applied to island arc settings the temporal trends suggest that the initial magma is mid ocean ridge basalt morb like and may be subducted oceanic crust alone this develops into a deeper source with the involvement of subducted oceanic crust and depleted upper mantle materials in the mature arc there is a dominance of mantle wedge derived materials such depth trends suggest that the subducted oceanic crust is not always directly involved in magma genesis implying that the inference of paleosubduction zones by the k 2 o depth relationships may be invalid for much of the life of an island arc the consideration of mixing models suggests that the early and mature arc volcanics obtain their k from the continental crust whereas the arc of intermediate maturity obtains its k at least partly from k bearing subcreted sediments included in the mixing of depleted upper mantle and subducted oceanic crust

geochemistry of the miocene mount noel volcanic complex british columbia and comparison with the columbia river basalt the 19 6 ma mount noel volcanic complex mnvc is located about 150 km east of the garibaldi volcanic belt and adjacent to the chilcotin plateau basalts in southwestern british columbia the mnvc unconformably overlies jurassic to cretaceous metasedimentary rocks and lower cretaceous coast plutonic rocks the complex consists of flat lying columnar jointed basalt flows along with volcaniclastic debris flows and minor pyroclastic rocks basaltic flows have olivine fo 60 to fo 85 and plagioclase an 60 to an 80 phenocrysts with clinopyroxene microphenocrysts major trace and rare earth element analyses of the mnvc indicate the flows can be divided into two groups the largest group comprises tholeiitic to transitional basalt whereas a smaller subset is alkaline basalt rare earth element patterns are slightly enriched in the light rare elements in the transitional group and more strongly enriched in the alkaline basalts in tectonic discriminant diagrams all basalts plot in the within plate fields or in overlap areas typical of continental flood basalts alkaline basalts found only at the base of the thick sequence of tholeiitic to transitional basalts are characterized by high p 2 o 5 sr and ba contents the mnvc tholeiitic to transitional basalts are comparable to the chilcotin group basalts and to the lowermost basalts of the columbia river group the origin of mnvc basalts is best interpreted as volcanism behind the pemberton volcanic arc

ferride geochemistry of swedish precambrian iron ores chemical analysis for major and trace elements have been performed on 30 swedish precambrian iron ores and on some from iran and chile the swedish ores consist of apatite iron ores quartz banded iron ores skarn and limestone iron ores from the two main ore districts of sweden the bergslagen and the norrbotten province some swedish titaniferous iron ores were also included in the investigation the trace element data show that the swedish ores can be subdivided into two major groups 1 orthomagmatic and exhalative 2 sedimentary within group 1 the titaniferous iron ores are distinguished by their high ti contents from the ferride contents of the kiruna apatite iron ores the ores are considered to be mobilization products of skarn iron ores from the norbotten province

geochemistry and tectonic setting of the central loei volcanic rocks pak chom area loei northeastern thailand abstract the central loei volcanic rocks as evidenced by those in the pak chom area were formed in the late devonian early carboniferous and can be separated into three magmatic groups transitional tholeiitic basalt tholeiitic microgabbro and calc alkalic basalt andesite on the basis of immobile element contents and ratios of least altered samples all the tholeiitic microgabbro possibly occurred as dikes chemically the transitional tholeittic basalt and tholeiitic microgabbro have higher abundances of tio 2 ni and cr relative to the calc alkalic basalt andesite at similar values for feo mgo they also contain higher ti zr but lower zr nb the transitional tholeiitic basalt has higher concentrations of p 2 o 5 and nb relative to the tholeiitic microgabbro at similar levels of feo mgo and also has higher ratios of nb y and ti v but lower values for ti zr and zr nb in terms of chondrite normalized ree and n morb normalized patterns the transitional tholeiitic basalt tholeiitic basalt and calc alkalic basalt andesite are analogous to those from north atlantic southwest indian ridge and new britain arc on this basis the central loei volcanic rocks are comprised of morbs and oceanic island arc lavas these arc lavas may have erupted on an oceanic basement in the same ocean basin as those in the chiang rai chiang mai volcanic belt

closure of the east paleotethyan ocean and amalgamation of the eastern cimmerian and southeast asia continental fragments abstract the phanerozoic record of southeast asia preserves the history of opening and subsequent consumption of the paleotethyan ocean and the assembly of continental fragments into asia as part of the broader scale reconstruction of pangea however uncertainty remains as to which of the many suture zones in southeast asia represents the relict of the main ocean when final ocean closure occurred and the assembly history of the eastern cimmerian and southeast asia continental fragments our overview of the geological features of the suture zones the bounding continental fragments and their magmatic metamorphic and sedimentary records resolves many of these key issues the sedimentary biogeographical structural lithological geochemical and geochronological data from the changning menglian inthanon and bentong raub suture zones argue for their linkage with the longmu co shuanghu suture zone in central tibet and together constitute the main east paleotethyan ocean relict the eastward subduction of the ocean resulted in the development of a series of magmatic arc back arc basin and continental fragments in southeast asia including from west to east the lincang sukhothai east malaya arc the jinghong nan sa kaeo back arc basin the simao west indochina fragment the luang prabang loei back arc basin the south indochina fragment the wusu and truong son back arc basins the north indochina fragment the jinshajiang ailaoshan song ma branch back arc basin and the south china block assembly of these fragments resulted in indosinian high temperature and high pressure metamorphism and related tectonothermal event available data indicate a switch from subduction of the main east paleotethyan ocean to the collision of the sibumasu with simao indochina blocks at 237 ma with subsequent syn and post collisional events at 237 230 ma and 230 200 ma respectively along the changning menglian inthanon and bentong raub suture zones the timing of initial syn and post collision events along the jinshajiang ailaoshan song ma suture zone with its record of back arc basin closure is at 247 ma 247 237 ma and 237 200 ma generally 10 ma older than that along the changning menglian inthanon and bentong raub suture zones our synthesis of all available data enables establishment of a comprehensive geodynamic model for the east paleotethyan evolution this model links the spatial temporal pattern across southeast asia into a series of tectonic events including ocean back arc basin opening subduction closure subsequent assemblage and orogenic collapse along with associated igneous metamorphic and sedimentary activities

new contributions to the understanding of kiruna type iron oxide apatite deposits revealed by magnetite ore and gangue mineral geochemistry at the el romeral deposit chile abstract iron oxide apatite ioa or kiruna type deposits are an important source of iron and other elements including ree u ag and co the genesis of these deposits remains controversial with models that range from a purely magmatic origin to others that involve variable degrees of hydrothermal fluid involvement to elucidate the formation processes of this deposit type we focused on the chilean iron belt of cretaceous age and performed geochemical analyses on samples from el romeral one of the largest ioa deposits in northern chile we present a comprehensive field emission electron microprobe analysis fe empa dataset of magnetite apatite actinolite pyroxene biotite pyrite and chalcopyrite obtained from representative drill core samples two different types of magnetite grains constitute the massive magnetite bodies an early inclusion rich magnetite type i and a pristine inclusion poor magnetite type ii that usually appears as an overgrowth around type i magnetite high v 2500 2800 ppm and ti concentrations 80 3000 ppm and the presence of high temperature silicate mineral inclusions e g pargasite 800 1020 c determined by micro raman analysis indicate a magmatic origin for type i magnetite on the other hand high v 2300 2700 ppm and lower ti 50 400 ppm concentrations of pristine inclusion poor type ii magnetite indicate a shift from magmatic to hydrothermal conditions for this mineralization event furthermore the composition of primary actinolite ca and mg rich cores within type ii magnetite and the presence at depth of fluorapatite and high co ni ratios 1 10 of pyrite mineralization are consistent with a high temperature up to 840 c genesis for the deposit at shallow depths of the deposit the presence of pyrite with low co ni ratios

titanium mobility in metamorphic systems a review abstract titanium is a dispersed lithophile element commonly regarded as chemically immobile at sub magmatic temperatures however a growing number of field studies demonstrate that ti is somewhat mobile in certain environments this review examines the current state of knowledge concerning the mobility of ti during alteration and metamorphism of crustal rocks also considered are relevant ti oxide solubility data from experiments and determinations of ti concentrations in natural waters where ti mobility is well documented its length scale is 10 m however ti may move greater distances in deep crustal shear zones the solubility of ti oxides in geologic fluids is strongly temperature dependent under low to medium grade metamorphic conditions ti mobility is limited by the low solubility of ti oxides in the associated fluids under eclogite conditions ti mobility is probably limited not by ti oxide solubility which reaches 1 ti but by restricted fluid flow in low permeability rocks

on the robustness of predictions of sea level fingerprints summary the rapid melting of the earth s ice reservoirs will produce geographically distinct patterns of sea level change that have come to be known as sea level fingerprints a basic gravitationally self consistent theory for computing these patterns appeared in the 1970s however recent highly discrepant fingerprint calculations have led to suggestions that the algorithms and or theoretical implementation adopted in many previous predictions is not robust we present a suite of numerical predictions including benchmark comparisons with analytic results that counter this argument and demonstrate the accuracy of most published predictions moreover we show that small differences apparent in calculations published by some groups can be accounted for by subtle differences in the underlying physics the paper concludes with two sensitivity analyses 1 we present the first ever calculation of sea level fingerprints on earth models with 3 d variations in elastic structure and density and conclude that this added complexity has a negligible effect on the predictions 2 we compare fingerprints of polar ice sheet mass flux computed under the very common assumption of a uniform melt distribution to fingerprints calculated using melt geometries constrained by analysing recent trends in grace gravity data predictions in the near field of the ice sheets are sensitive to the assumed melt geometry however this sensitivity also extends to the far field particularly in the case of antarctic mass changes because of the strong dependence of the rotational feedback signal on the melt geometry we conclude that inferences of ice sheet mass flux based on modern sea level constraints should consider these more realistic melt geometries

fluid inclusion and stable isotope study of the esfordi apatite magnetite deposit central iran a reply sir we are pleased that our recent paper in economic geology jami et al 2007 presenting the geologic setting a description of the mineralization fluid inclusion and o isotope analyses of the esfordi p fe oxide deposit in central iran has been of interest to aftabi and his colleagues aftabi et al 2009 the opportunity to discuss further some aspects of our paper is appreciated including support for a hydrothermal dominated depositional model for esfordi aftabi et al 2009 focus their comments on the question of the affinity of the esfordi p fe oxide deposit in particular they argue that esfordi and by inference other diverse fe oxide deposits within the bafq district of central iran should be considered rapitan type banded iron formations i e bif klein 2005 rather than kiruna type hitzman 2000 in discussing our results and conclusions in the light of previous work particularly forster and jafarzadeh 1994 aftabi et al 2009 have misconstrued our interpretation of some of the textural and isotopic data as providing support for an orthomagmatic model for the esfordi p fe oxide deposit based on the structure relationships between mineralization and host rocks fluid inclusion and isotopic data we concluded that esfordi exhibits strong evidence of hydrothermal origin though we did not preclude some component of precursor orthomagmatic processes in formation of the p fe mineralisation it is noted that some examples of the kiruna end member of the continuum of fe oxide deposits discussed by hitzman 2000 are controversial particularly in regard to their evolution sillitoe and burrows 2002 henriquez et al 2003 we have shown that esfordi has a number of features typical of the kiruna type deposits and does not exhibit features consistent with an affinity to rapitan type fe oxide deposits this evidence will be discussed briefly with further data

arc like volcanic rocks in nw laos geochronological and geochemical constraints and their tectonic implications abstract the loei fold belt located at the western margin of the indochina block is considered to be tectonically linked to the subduction of the paleotethyan ocean and subsequent collision in northwestern laos the volcanic rocks are traditionally mapped as permian early triassic sequences our la icp ms zircon u pb dating results show that andesitic rhyolitic and tuffaceous samples from the muang feuang region of the loei fold belt have zircon u pb ages of 330 4 2 2 ma 334 9 1 7 ma and 349 6 1 7 ma which are interpreted as their eruption ages respectively these ages are indicative of an early carboniferous origin the basaltic and basaltic andesitic samples from the pak lay region yield zircon u pb ages of 314 6 2 7 ma and 315 4 3 8 ma respectively and have a late carboniferous origin these samples exhibit depletion in hfses e g nb ta ti with high lile hfse ratios and exhibit a geochemical affinity to continental arc volcanic rocks these signatures suggest the presence of an early to late carboniferous active continental margin along the western margin of the indochina block the loei fold belt may extend north into nw laos

trace element geochemistry of magnetite implications for ore genesis of the talate skarn pb zn fe deposit altay nw china abstract the talate skarn pb zn fe deposit is hosted in the kangbutiebao formation of the abagong polymetallic belt altay nw china the talate magnetite comprises the magmatic hydrothermal hydrothermal disseminated and massive magnetite types and formed during the early skarn and quartz magnetite stage the magmatic hydrothermal disseminated magnetite is nb ta ti depleted whereas the hydrothermal disseminated magnetite associated with skarn alteration is geochemically similar to the ca skarn with slight ta mg ni depletions the massive magnetite ores have similar ni concentrations with the ca skarn but contain minor depletions in sn sc ta nb mg and co probably attributed to magma host rock interactions the talate hydrothermal disseminated magnetite contains lower sn than magnetite from typical skarn deposits and likely resulted from cassiterite crystallization as it is found co precipitated with disseminated magnetite both magmatic hydrothermal and hydrothermal disseminated magnetite are characterized by narrow ti concentration range and variable co ni ratios which likely reflect rapid cooling rate and significant fluid rock interaction during multiple successive stages of skarn alteration as the co has a higher solubility over the ni in the ore forming fluid whereas the talate massive magnetite contains wider ti concentration range and in some cases with 120 triple junctions the co ni ratios mostly

trace element geochemistry of magnetite and its relationship to cu bi co au ag u w mineralization in the great bear magmatic zone nwt canada the paleoproterozoic great bear magmatic zone is the focus of ongoing exploration for iron oxide copper gold iocg deposits and also hosts iron oxide apatite occurrences examples of iocg deposits in the great bear magmatic zone include sue dianne and nico and other smaller prospects including damp fab and nori ra the past producing terra mine property hosts significant iocg like alteration that contains dome shaped iron oxide apatite bodies petrographic study has identified multiple generations of magnetite at nico fab and nori ra and for the most part a single generation of magnetite at sue dianne damp and terra laser ablation inductively coupled plasma mass spectrometry la icp ms documents important geochemical differences in v ni cr and co concentrations within the magnetite variations of trace elements in magnetite from the great bear magmatic zone could be a result of 1 host rock fluid equilibration during regional metamorphism 2 postmetamorphic hydrothermal metasomatism of treasure lake group metasedimentary rocks 3 preferential solubility of co over ni within the fe rich fluids 4 changes in oxygen fugacity f o2 and 5 partitioning of elements into coprecipitating sulfides regionally the cr co ratio is higher in barren and pre ore magnetite compared to magnetite coprecipitated with ore minerals and or present in ore rich veins and breccias locally at the nori ra prospect the v ni ratio in magnetite differentiates between barren and ore related magnetite and at damp and sue dianne the co ni ratio is extremely high and clearly different from that of other great bear magmatic zone magnetite samples these results provide the first database for geochemically characterized magnetite from different stages of iocg alteration and illustrate the potential use of magnetite as an indicator mineral in the exploration for iocg deposits

postglacial sea level change on a rotating earth summary we present a complete derivation of the equation governing long term sea level variations on a spherically symmetric self gravitating maxwell viscoelastic planet this new sea level equation extends earlier work by incorporating in a gravitationally self consistent manner both a time dependent ocean continent geometry and the in uence of contemporaneous perturbations to the rotation vector of the planet we also outline an e cient pseudo spectral numerical methodology for the solution of this equation and present a variety of predictions based on a suite of earth models of relative sea level rsl variations due to glacial isostatic adjustment gia these results show that the contribution to the predicted rsl signal from gia induced perturbations to the rotation vector can reach 7 8 m over the postglacial period in geographic regions where the rotationally induced signal is a maximum this result is sensitive to variations in the adopted lower mantle viscosity and is relatively insensitive to variations in the adopted lithospheric thickness we also show that the rotationally induced component of rsl change is su cient to in uence previous estimates of late holocene melting events and ongoing sea level change due to giawhich were based on a rsl theory for a non rotating earth in particular estimates of antarctic melting over the last 5 kyr based on the amplitude of sea level highstands from the australian region may require an adjustment downwards of the order of 0 5 m of equivalent sea level rise furthermore present day rates of sea level change are perturbed by as much as 0 2 mm yr 1 by the rotational component of sea level change and this has implications for gia corrections of the global tide gauge record over the period from the last glacial maximum to the present we predict a distinctly non monotonic variation in the rotation induced component of rsl this is in agreement with our previous preliminary study milne mitrovica 1996 but contrasts signi cantly with predictions presented by han wahr 1989 and bills james 1996 we demonstrate that the disagreement arises as a consequence of approximations adopted in the latter studies we furthermore refute an assertion by bills james 1996 that previously published constraints on mantle viscosity and ice sheet histories which did not incorporate a rotation induced rsl component are largely invalidated by this omission

geochemistry of eclogites and associated rocks of the southeastern area of the french massif central origin of the protoliths abstract within the barrovian metamorphic series of the french massif central most of the eclogites are closely associated with metagabbros and meta ultrabasites the protoliths of the eclogites may represent basaltic or gabbroic dykes or sills of oceanic affinities erupted in either a continental domain or during early oceanization or opening up of an ensialic back arc basin both the nature and type of magma fractionation and of post magmatic evolution are consistent with a shallow crustal origin for the protoliths eclogitization postdates the low pressure magmatic differentiation and the volcano sedimentary supra crustal evolution

gushan magnetite apatite deposit in the ningwu basin lower yangtze river valley se china hydrothermal or kiruna type abstract the gushan deposit is one of the typical magnetite apatite deposits associated with dioritic porphyries in the lower yangtze river valley belt of the eastern yangtze craton the origin of this deposit is still uncertain and remains a controversial issue divergent opinions are centered on whether the iron deposits are magmatic or hydrothermal in origin however our field observations and mineralogical studies combined with previous published petrological and geochemical features strongly suggest that the main ore bodies in the gushan magnetite apatite deposit are magmatic specific evidence includes the existence of gas bubbles tubes and miarolitic and amygdaloidal structures melt flow banding structure and the presence of ore breccia new electron microprobe analyses of the pyroxene phenocrysts of the dioritic porphyry genetically associated with the gushan magnetite apatite deposit show that the fe contents in the evolving magma dramatically decrease and then gradually increase because there is no evidence of mafic magma recharge this scenario decreasing fe could be plausibly interpreted by fe rich melts separated from fe poor silicate melts i e liquid immiscibility was triggered by minor addition of phosphorus by crustal contamination the occurrence of massive iron ore bodies can be satisfactorily explained by the immiscible fe rich melt with enormous volatile contents was driven to the top of the magma chamber due to the low density the hot and volatile rich iron ore magma was injected along fractures and spaces between the dioritic intrusions and wall rocks and led to an explosion near the surface resulting in the immediate fragmentation of the roof of the intrusion and wall rocks forming brecciated ores moreover other types of ores can be considered as a result of post magmatic hydrothermal activities our proposed metallogenic model involving the kiruna type mineralization is consistent with the observed phenomenon in the gushan deposit

metallogeny of copper and iron deposits in the eastern yangtse craton east central china abstract the eastern yangtse craton of central to eastern china is an important fe cu metallogenic province based on studies of the regional geology and tectonic evolution this metallogenic belt is controlled by faults and aulacogens in the continental plate in the early yanshan epoch jurassic the dominant west northwest and east west lithospheric faults controlled the distribution of cu mo and au mineralization whereas in the late yanshan epoch cretaceous the north northeast and northeast lithospheric faults controlled cu fe mineralization in a mineral district the distribution of ore fields is under the dual control of basement fault s and near surface fault s based on the relation of ring and lineament faults to intrusions a three level model of vertical zonation is proposed systematic petrochemical studies of mesozoic igneous rocks and mineralization identify three subseries 1 a calc alkaline intermediate to silicic subseries rich in potassium 2 a calc alkaline intermediate to felsic subseries rich in sodium and 3 a calc alkaline intermediate to mafic subseries rich in sodium genetic types of ore deposits are diverse including fe and cu skarns cu porphyries fe ore magma injections ningwu luzong fe deposits from late orthomagmatic to pegmatitic pneumato hydrothermal and to mesothermal epithermal associated with subvolcanic rocks and remobilized sedimentary fe and or cu deposits the genetic types of ore deposits form two metallogenic series 1 a sedimentary metallogenic series active mainly in the paleozoic and 2 a magmatic hydrothermal metallogenic series consisting of three subseries active predominantly in the jurassic and cretaceous with the latter being more important in this region the superposition and compounding of these two metallogenic series contribute to many styles of mineralization in this mineral province

are long tide gauge records in the wrong place to measure global mean sea level rise ocean dynamics land motion and changes in earth s gravitational and rotational fields cause local sea level change to deviate from the rate of global mean sea level rise here we use observations and simulations of spatial structure in sea level change to estimate the likelihood that these processes cause sea level trends in the longest and highest quality tide gauge records to be systematically biased relative to the true global mean rate the analyzed records have an average twentieth century rate of approximately 1 6 mm yr but based on the locations of these gauges we show that the simple average underestimates the twentieth century global mean rate by 0 1 0 2 mm yr given the distribution of potential sampling biases we find that 1 probability that observed trends from the longest and highest quality tide gauge records are consistent with global mean rates less than 1 4 mm yr

decoding the origins of vertical land motions observed today at coasts in recent decades geodetic techniques have allowed detecting vertical land motions and sea level changes of a few millimetres per year based on measurements taken at the coast tide gauges on board of satellite platforms satellite altimetry or both global navigation satellite system here contemporary vertical land motions are analysed from january 1993 to july 2013 at 849 globally distributed coastal sites the vertical displacement of the coastal platform due to surface mass changes is modelled using elastic and viscoelastic green s functions special attention is paid to the effects of glacial isostatic adjustment induced by past and present day ice melting various rheological and loading parameters are explored to provide a set of scenarios that could explain the coastal observations of vertical land motions globally in well instrumented regions predicted vertical land motions explain more than 80 per cent of the variance observed at scales larger than a few hundred kilometres residual vertical land motions show a strong local variability especially in the vicinity of plate boundaries due to the earthquake cycle significant residual signals are also observed at scales of a few hundred kilometres over nine well instrumented regions forming observation windows on unmodelled geophysical processes this study highlights the potential of our multitechnique database to detect geodynamical processes driven by anthropogenic influence surface mass changes surface loading and glacial isostatic adjustment and tectonic activity including the earthquake cycle sediment and volcanic loading as well as regional tectonic constraints future improvements should be aimed at densifying the instrumental network and at investigating more thoroughly the uncertainties associated with glacial isostatic adjustment models

immiscible iron and silica rich melts and magnetite geochemistry at the el laco volcano northern chile evidence for a magmatic origin for the magnetite deposits abstract the pliocene el laco volcano northern chile hosts a large iron oxide deposit that occurs as stratiform bodies with underlying feeder zones dykes hosted by hydrothermally altered andesite lava flows phenocrysts in the andesite hosting the mineralization have abundant melt inclusions displaying strong evidence for melt immiscibility most of the pyroxene and the plagioclase phenocrysts contain abundant fe rich melt inclusions with low ti magnetite pyroxene apatite and minor anhydrite the glassy groundmass of these melt inclusions is chemically similar to sub alkaline rhyolitic rocks e g 70 sio 2 si al k na rich large resorbed plagioclase phenocrysts also host another group of melt inclusions with a similar silica rich groundmass but hosting evenly distributed immiscible and complex fe rich spheroidal globules that are enriched in ti p mg ca and s these immiscible globules and the ti poor magnetite daughter crystals in the melt inclusions in pyroxene phenocrysts are thought to be the parental iron oxide melt liquid after which their coalescence leads to the formation of magnetite melts from which the magnetite that formed the el laco iron oxide deposits crystallized and were emplaced the mineralogy and chemistry of these melt inclusions tracks the chemical evolution of the fe ox melts and supports a magmatic origin for the el laco magnetite this is mainly recognized by the continuum of compositions between volcanic separate immiscible fe oxide melts and magnetite ores the trace element composition of the fe rich melt inclusions and of the magnetite in the host andesite and the ore bodies reveals a systematic depletion in most of the elements that are compatible in magnetite the ti content of the magnetite also records the separation and crystallization of the iron rich melt typically the magnetite in the orebodies and the melt inclusions is ti poor compared with titanomagnetite found in the andesite groundmass and that hosted by the hydrothermally altered andesite that is interpreted as being attributed to its crystallization under oxidizing and sulfur rich conditions the cause of this unusual chemical behaviour is probably due to the mechanism s governing the crystallization of the iron rich melt including the temperature changes in chemistry prior to eruption and an increase in the redox conditions of the silicate melt magma oxidation facilitates the prevalence of ferric iron and formation of ti poor magnetite preventing the incorporation of ti in the exsolving iron rich melt the likely reason for the formation of these large ti poor magnetite deposits is likely the contamination of the parental andesitic magma by oxidized crustal rocks and concomitant crystallization of magnetite under oxidizing conditions something that had a significant impact on the elemental distribution

regional biases in absolute sea level estimates from tide gauge data due to residual unmodeled vertical land movement the only vertical land movement signal routinely corrected for when estimating absolute sea level change from tide gauge data is that due to glacial isostatic adjustment gia we compare modeled gia uplift ice 5g vm2 with vertical land movement at 300 gps stations located near to a global set of tide gauges and find regionally coherent differences of commonly 0 5 2 mm yr reference frame differences and signal due to present day mass trends cannot reconcile these differences we examine sensitivity to the gia earth model by fitting to a subset of the gps velocities and find substantial regional sensitivity but no single earth model is able to reduce the disagreement in all regions we suggest errors in ice history and neglected lateral earth structure dominate model data differences and urge caution in the use of modeled gia uplift alone when interpreting regional and global scale absolute geocentric sea level from tide gauge data

geochemistry and significance of metavolcanic rocks from the bou azzer el graara ophiolite morocco abstract the bou azzer el graara ophiolite has been interpreted as oceanic or backarc crust overlain by a calc alkalic arc sequence or as a composite forearc and accretionary melange seventy nine new major and trace element whole rock analyses of the metavolcanic rocks from throughout the complex support the latter interpretation the results of this study indicate that the bou azzer metavolcanics comprise three petrographically and geochemically distinct groups 1 a a siliceous metavolcanic series ranging from basaltic andesites to rhyolites with calc alkalic characteristics is the principal component of the northern section of the complex it includes distinct quartz bearing rhyolite flows isolated massive pyroclastic layers are typically associated with this series these rocks are interpreted as forearc basin volcanics and pyroclastics produced during late proterozoic north dipping subduction 2 b low ti metabasalts which display island arc tholeiitic affinities occur as isolated flows or blocks in most of the ophiolite these rocks may represent fragments of the forearc basement below the siliceous series 3 c high ti metabasalts which range from enriched tholeiitic zr y 4 compositions are the principal volcanic block in the southern melange like terrane of the complex these have high ba and sr contents 100 200 ppm average ba 260 ppm average sr they are identical to basaltic compositions from tachdamt and bleida on the southern margins of the ophiolite which have previously been interpreted as a rifted continental margin sequence these rocks could represent seamount volcanic products which have been thrust into an accretionary prism along the north dipping subduction zone or rift margin basalts which have been assembled in a tectonic melange as a consequence of a forearc continent collision both the low ti and high ti metabasalt groups include samples previously identified as ocean ridge or back arc volcanics however there is no compelling evidence for the occurrence of these lava compositions in this region the distribution of rock types within the ophiolite is most consistent with a previously proposed model which views the complex as three allochthonous terranes which were juxtaposed during collision to form the bou azzer el graara complex

preliminary geochemical study of volcanic rocks in the pang mayao area phrao chiang mai northern thailand tectonic setting of formation abstract the least altered permian mafic volcanic rocks from the pang mayao area phrao district chiang mai province part of chiang rai chiang mai volcanic belt have been analyzed and are found to be mid ocean ridge and ocean island basalts the mid ocean ridge basalts occur as lava flows or dike rocks they are equigranular fine to medium grained and consist largely of plagioclase clinopyroxene and olivine these basalt samples are tholeiitic and have compositions very similar to t morb from the region where the du toit fracture zone intersects the southwest indian ridge the ocean island basalt occurs as pillow breccia and lava flows or dike rocks they are slightly to moderately porphyritic with phenocrysts microphenocrysts of clinopyroxene olivine plagioclase and or fe ti oxide the groundmass is very fine grained and made up largely of felty plagioclase laths with subordinate clinopyroxene these basalt samples are alkalic and chemically analogous to those from haleakala volcano maui hawaiian chain these mafic volcanic rocks may have been formed in a major ocean basin rather than in a mature back arc basin

the geochemistry of titanomagnetite in magnetite layers and their host rocks of the eastern bushveld complex more than 430 analyses of magnetite separates revealed pronounced differences in composition between magnetite from magnetite layers and disseminated magnetite from the host rocks magnetite from the massive layers is among others enriched in elements such as ti mg al and si which suggests that this magnetite crystallized under conditions of disequilibrium with the magma i e by spontaneous nucleation and rapid crystallization lower vanadium values in the magnetites from the massive layers suggest crystallization at higher f sub o 2 than from the rocks containing the disseminated magnetite variation diagrams reveal a cyclicity in compositional trends upward in the sequence which is related to nucleation of the magma in the roof zone of the intrusion the periodic collapse of this crystal laden magma and its incorporation in the zone of crystallization at the base of the magma chamber deviations of this normal trend are considered to reflect a stratification of the roof zone and a gradual incorporation of the stratified roof zone liquid into the convecting magma a pronounced upward increase in the cr content of magnetite is tentatively ascribed to a combination of olivine crystallization at the expense of pyroxene in the upper subzones and a possible increase in the partition coefficient of chromium between spinel and liquid with a decrease in the crystallization temperature

trace element geochemistry of magnetite from the giant beiya gold polymetallic deposit in yunnan province southwest china and its implications for the ore forming processes abstract the beiya gold polymetallic deposit is one of the largest gold deposits in china and is considered to be a typical porphyry skarn system located in the middle of the jinshajiang ailaoshan alkaline porphyry metallogenic belt massive magnetite is widespread in the beiya ore district but its genesis is still the subject of debate five representative magnetite types are present in the beiya deposit namely magmatic magnetite m1 from the ore related porphyry disseminated magnetite m2 from the early retrograde alteration massive magnetite m3 from the early quartz magnetite stage massive magnetite m4 from the middle quartz magnetite stage and magnetite m5 from the late quartz magnetite stage compared with the m1 magnetite the magnetites from stages m2 to m5 are depleted in ti al and high field strength elements implying a hydrothermal origin distinct from the magmatic accessory magnetite in the ore related porphyry m1 the concentrations of cobalt in the hydrothermal magnetites decrease gradually from m2 to m5 and can be used to discriminate the magnetite types the al mn and ti v contents of the successively precipitated magnetite grains m2 m5 suggests that the ore forming temperature decreased from m2 to m4 but increased from m4 to m5 possibly as the result of a new pulse of magma entering the chamber which may have triggered the gold mineralization the v content in the hydrothermal magnetite suggests that the oxygen fugacity increased from m2 to m4 but decreased as soon as the sulfides entered the system m5

variation in trace element content of magnetite crystallized from a fractionating sulfide liquid sudbury canada implications for provenance discrimination abstract laser ablation icp ms analysis has been applied to many accessory minerals in order to understand better the process by which the rock formed and for provenance discrimination we have determined trace element concentrations of fe oxides in massive sulfides that form ni cu pge deposits at the base of the sudbury igneous complex in canada the samples represent the crystallization products of fractionating sulfide liquids and consist of early forming fe rich monosulfide solution mss cumulates and residual cu rich intermediate solid solution iss this study shows that fe oxide geochemistry is a sensitive petrogenetic indicator for the degree of fractionation of the sulfide liquid and provides an insight into the partitioning of elements between sulfide and fe oxide phases in addition it is useful in determining the provenance of detrital fe oxide in a sulfide melt all lithophile elements cr ti v al mn sc nb ga ge ta hf w and zr are compatible into fe oxide the concentrations of these elements are highest in the early forming fe oxide titanomagnetite which crystallized with fe rich mss upon the continual crystallization of fe oxide from the sulfide liquid the lithophile elements gradually decrease so that late forming fe oxide magnetite which crystallized from the residual cu rich liquid is depleted in these elements this behavior is in contrast with fe oxides that crystallized from a fractionating silicate melt whereby the concentration of incompatible elements such as ti increases rather than decreases the behavior of the chalcophile elements in magnetite is largely controlled by the crystallization of the sulfide minerals with only ni co zn mo sn and pb present above detection limit in magnetite nickel mo and co are compatible in fe rich mss and thus the co crystallizing fe oxide is depleted in these elements in contrast magnetite that crystallized later from the fractionated liquid with cu rich iss is enriched in ni mo and co because fe rich mss is absent the concentrations of sn and pb which are incompatible with fe rich mss are highest in magnetite that formed from the fractionated cu rich liquid at subsolidus temperatures ilmenite exsolved from titanomagnetite whereas al spinel exsolved from the cores of some magnetite locally redistributing the trace elements however during laser ablation icp ms analysis of these fe oxides both the magnetite and its exsolution products are ablated so that the analysis represents the original magmatic composition of the fe oxide that crystallized from the sulfide melt

a mantle heterogeneity in the southwest pacific abstract the occurrence in time and space of tertiary intraplate central volcanoes and associated lava fields in the eastern australia new zealand campbell plateau region of the southwest pacific is more consistent with derivation from a large scale mantle anomaly than from discrete plumes the basalt volcanics from the eastern part of the region show a pronounced geochemical similarity those near the indo australia pacific convergent plate boundary show some evidence of interaction with subduction derived basalts the lithospheric swells expected associated with the eruption of magma to form these volcanoes seem broadly correlative with sedimentary patterns off the east coast of australia and the west coast of new zealand at this time

extremely high solubility of rutile in chloride and fluoride bearing metamorphic fluids an experimental investigation rutile tio 2 is an important high field strength element sequestering phase and thus understanding its solubility in metamorphic fluids is important if we are to understand terrestrial trace element cycling titanium is often assumed to be fluid immobile and previous experimental data suggest that rutile has very low solubility in h 2 o however fluids in high temperature metamorphic rocks are known to be more complex in composition the solubility of rutile in chloride and fluoride rich hydrous fluids was determined experimentally at 0 5 gpa and high temperatures the experimental results indicate much higher rutile solubility in brines compared to pure h 2 o in chloride brines solubility was 2 4 times higher than in h 2 o and in fluoride brines solubility was elevated 20 100 times the results imply that titanium may be much more mobile in metamorphic fluids than previously anticipated as solubility is critically dependent on fluid chemistry we also present a possible mechanism for rutile precipitation in metamorphic veins due to a change in fluid chemistry following the precipitation of halogen rich minerals such as apatite

reequilibration processes in magnetite from iron skarn deposits textural and compositional data for magnetite from nine iron skarn deposits in canada romania and china show that most samples have reequilibrated by dissolution and reprecipitation oxy exsolution and or recrystallization the dissolution and reprecipitation processes are most extensive and are present in most magnetite samples examined whereas the oxy exsolution occurs only in high ti magnetite forming exsolution lamellae of fe ti al oxides electron microprobe analysis indicates that the reequilibration processes have significantly modified the minor and trace element compositions of magnetite notably si mg ca al mn and ti whereas oxy exsolution is effective in decreasing the ti content of high ti magnetite many analyses of magnetite grains from the skarn deposits plot variably in the banded iron formations bif iron oxide copper gold iocg or porphyry cu fields using the ti v versus ca al mn discrimination diagram this pattern suggests that trace element data for magnetite that has unusual composition and or reequilibrated cannot be reliably used as a petrogenetic indicator mixing of externally derived saline fluids with fe rich magmatic hydrothermal solutions an increase in temperature and local decreasing pressure and f o 2 are considered the most important causes for the dissolution and reprecipitation or recrystallization of the magnetite increasing f o 2 and decreasing temperature may facilitate oxy exsolution of fe ti al oxides in high ti magnetite results presented here highlight the importance of detailed textural characterization prior to in situ chemical analysis of magnetite grains so that mineral compositions can be properly evaluated in terms of the genesis and evolution of iron skarn deposits

magnetite geochemistry of the heijianshan fe cu au deposit in eastern tianshan metallogenic implications for submarine volcanic hosted fe cu deposits in nw china abstract the heijianshan fe cu au deposit is located in the aqishan yamansu belt in eastern tianshan nw china as a typical fe cu deposit in the region heijianshan is hosted in the upper carboniferous matoutan formation submarine volcanic volcaniclastic rocks alteration styles mineral assemblages and vein crosscutting relationships divide the hydrothermal alteration and mineralization processes into seven stages namely the chromite stage i epidote stage ii magnetite stage iii pyrite stage iv cu au stage v late veins stage vi and supergene stage vii alteration mineralization stages magnetite mineralization comprises the hematite stage iii a and main magnetite stage iii b mineralization sub stages the heijianshan magnetite ores consist of massive with mushketovite mom or sulfides mos disseminated do and magnetite clasts with chromite mwc or without chromite mnc ores magnetite in massive and disseminated ores is featured by 1 depletion in zr nb and ta 2 low ti f o 2 increased which may represent the major controls on the formation of the various magnetite ore types compositions of the ore fluids and host rocks formation of coexisting minerals and other physicochemical parameters such as t and f o 2 may have variably influenced the magnetite geochemistry in the different heijianshan ore types with fluid compositions probably playing the most important role discrimination diagrams for instance cr vs co ni cr vs ti v vs cr and ni vs cr may be useful for magnetite mineralization type differentiation in other submarine volcanic hosted fe fe cu deposits in the aqishan yamansu belt geochemical discrimination diagrams alteration and mineralization paragenesis indicate that the heijianshan fe cu au deposit is best classified as an iocg like deposit which offers a new insight for classifying and characterizing ore genetic types for similar fe and fe cu deposits in eastern tianshan

geochemistry of magnetite from porphyry cu and skarn deposits in the southwestern united states a combination of petrographic observations laser ablation inductively coupled plasma mass spectrometry la icp ms and statistical data exploration was used in this study to determine compositional variations in hydrothermal and igneous magnetite from five porphyry cu mo and skarn deposits in the southwestern united states and igneous magnetite from the unmineralized granodioritic inner zone batholith japan the most important overall discriminators for the minor and trace element chemistry of magnetite from the investigated porphyry and skarn deposits are mg al ti v mn co zn and ga of these the elements with the highest variance for i igneous magnetite are mg al ti v mn zn for ii hydrothermal porphyry magnetite are mg ti v mn co zn and for iii hydrothermal skarn magnetite are mg ti mn zn and ga nickel could only be detected at levels above the limit of reporting lor in two igneous magnetites equally cr could only be detected in one igneous occurrence copper as mo ag au and pb have been reported in magnetite by other authors but could not be detected at levels greater than their respective lors in our samples comparison with the chemical signature of igneous magnetite from the barren inner zone batholith japan suggests that v mn co and ga concentrations are relatively depleted in magnetite from the porphyry and skarn deposits higher formation conditions in combination with distinct differences between melt and hydrothermal fluid compositions are reflected in al ti v and ga concentrations that are on average higher in igneous magnetite than in hydrothermal magnetite including porphyry and skarn magnetite low ti and v concentrations in combination with high mn concentrations are characteristic features of magnetite from skarn deposits high mg concentrations 1 000 ppm are characteristic for magnetite from magnesian skarn and likely reflect extensive fluid rock interaction in porphyry deposits hydrothermal magnetite from different vein types can be distinguished by varying ti v mn and zn contents titanium and v concentrations are highly variable among hydrothermal and igneous magnetites but ti concentrations above 3 560 ppm could only be detected in igneous magnetite and v concentrations are on average lower in hydrothermal magnetite the highest ti concentrations are present in igneous magnetite from gabbro and monzonite the lowest ti concentrations were recorded in igneous magnetite from granodiorite and granodiorite breccia and largely overlap with ti concentrations found in hydrothermal porphyry magnetite magnesium and mn concentrations vary between magnetite from different skarn deposits but are generally greater than in hydrothermal magnetite from the porphyry deposits high mg and low ti and v concentrations characterize hydrothermal magnetite from magnesian skarn deposits and follow a trend that indicates that magnetite from skarn calcic and magnesian commonly has low ti and v concentrations

the geochemistry of late upper proterozoic volcanic groups in the red sea hills of ne sudan evolution of a late proterozoic volcanic arc system the kadawcb and homogar volcanic groups occur in the sudanese portion of the nubian shield and are late proterozoic in age 723 ma and 671 ma respectively the lavas of both groups display a calc alkaline character are broadly similar in terms of their lithology phenocryst mineralogy and major element composition and geochemically they are similar to modern arc lavas associated with converging plate margins however a clear distinction can be made between the two groups on the basis of the trace element geochemistry of the basaltic components of the suites the homogar basalts are chemically more evolved and are enriched in large ion lithophile elements lile and rare earth elements ree having high la nb ce yb n and 87 sr 86 sr ratios compared with those of the kadawcb group these chemical differences possibly follow an evolutionary trend as the less developed kadawcb lavas are some 50 ma older than those of the evolved homogar group it is suggested that the older kadawcb lavas were erupted along an intra oceanic island arc system while the younger homogar lavas were extruded along a more evolved transitional arc or possibly a continental margin the differences in light heavy ree and lil high field strength element ratios may reflect variation in the degree of alteration of an overlying mantle wedge possibly due to the introduction of lile and ree enriched fluids derived from dehydrating subducted oceanic lithosphere

contribution of antarctica to past and future sea level rise polar temperatures over the last several million years have at times been slightly warmer than today yet global mean sea level has been 6 9 metres higher as recently as the last interglacial 130 000 to 115 000 years ago and possibly higher during the pliocene epoch about three million years ago in both cases the antarctic ice sheet has been implicated as the primary contributor hinting at its future vulnerability here we use a model coupling ice sheet and climate dynamics including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine terminating ice cliffs that is calibrated against pliocene and last interglacial sea level estimates and applied to future greenhouse gas emission scenarios antarctica has the potential to contribute more than a metre of sea level rise by 2100 and more than 15 metres by 2500 if emissions continue unabated in this case atmospheric warming will soon become the dominant driver of ice loss but prolonged ocean warming will delay its recovery for thousands of years