copper mobility in the eastern creek volcanics mount isa australia evidence from laser ablation icp ms of iron titanium oxides the palaeoproterozoic eastern creek volcanics are a series of copper rich tholeiitic basalts which occur adjacent to the giant sediment hosted mount isa copper deposit in queensland australia the volcanic rocks are often cited as the source of metals for the deposit new laser ablation icp ms analyses of iron titanium oxides from the basalts provide evidence for the local mobilisation of copper during regional greenschist facies metamorphism this interpretation is based on the observation that copper bearing magmatic titanomagnetite was destabilised during greenschist facies metamorphism and the new magnetite which crystallised was copper poor petrological observations regional geochemical signatures and geochemical modelling suggest that the mobilised copper was concentrated in syn metamorphic epidote rich alteration zones creating a pre concentration of copper before the main mineralisation event at mount isa geochemical modelling demonstrates this process is enhanced by the addition of co2 from adjacent carbonate rich sediments during metamorphic devolatilisation regional geochemical data illustrate elevated copper concentrations in epidote rich zones high cao but where these zones are overprinted by potassic alteration high k2o copper is depleted a two stage model is proposed whereby after metamorphic copper enrichment in epidote titanite alteration zones an oxidised potassium rich fluid leached copper from the epidote altered metabasalts and deposited it in the overlying sedimentary rocks to form the mount isa copper deposit this ore forming fluid is expressed regionally as potassium feldspar rich veins and locally as biotite rich alteration which formed around major fluid conduits between the metabasalt metal source rocks and the overlying deposit host sequence this model is consistent with the remobilisation of copper from mafic source rocks as has been found at other world class copper deposits

dem control in arctic alaska with icesat laser altimetry use of ice cloud and land elevation satellite icesat laser altimetry is demonstrated for control of a digital elevation model dem that is synthesized from repeat pass ers 1 and 2 synthetic aperture radar sar imagery using interferomet ric sar insar our study area is 15 650 km2 of the barrow ak coastal plain adjacent to the arctic ocean a vast expanse of tundra lakes and arctic wetlands of such low relief as to be nearly devoid of terrain features the accuracy of the icesat derived elevation measurements is assessed by comparison with differential global positioning system dgps data acquired along icesat ground tracks the icesat derived elevations have a mean accuracy relative to the dgps elevations of 0 01 plusmn 0 18 m icesat derived elevations on the arctic coastal plain provide an excellent source for dem control we employ the icesat derived ground control points gcps in two distinct insar processing steps 1 selected points are used to perform baseline refinements which improves the ers 1 and 2 interfero grams and 2 the icesat derived gcp position data latitude longitude elevation are then used as control in mosaicking multiple insar derived dems the resulting icesat controlled dem has a mean accuracy of 1 11plusmn 6 3 m relative to an independent standard which is a commercial airborne insar derived dem having 0 5 m rms accuracy this easily meets dted 2 standards and suggests that dems derived using only icesat altimetry for ground control would meet similar standards in other regions of low relief

fracture propagation to the base of the greenland ice sheet during supraglacial lake drainage surface meltwater that reaches the base of an ice sheet creates a mechanism for the rapid response of ice flow to climate change the process whereby such a pathway is created through thick cold ice has not however been previously observed we describe the rapid 2 hours drainage of a large supraglacial lake down 980 meters through to the bed of the greenland ice sheet initiated by water driven fracture propagation evolving into moulin flow drainage coincided with increased seismicity transient acceleration ice sheet uplift and horizontal displacement subsidence and deceleration occurred over the subsequent 24 hours the short lived dynamic response suggests that an efficient drainage system dispersed the meltwater subglacially the integrated effect of multiple lake drainages could explain the observed net regional summer ice speedup

shallow water and hypersaline features from the middle proterozoic mt isa sequence fundamental differences of opinion exist about the depositional environment of sediments which host the middle proterozoic1 mt isa cu and pb zn deposits2 3 of northwestern queensland australia the copper host has been repeatedly interpreted as an algal reef2 4 and recently as a sabkha5 whilst models as diverse as saline lakes6 and deep oceanic basins3 7 9 have been proposed for the deposition of both the cu and pb zn ore bodies we now report the discovery of stromatolites halite casts large cross bedded channel deposits and flat pebble conglomerates in sediments closely associated with the ore deposit these sedimentary structures provide evidence of shallow water deposition with intermittent hypersaline and emergent conditions during deposition of the upper mt isa group3 6 sequence the assemblage of sedimentary structures strongly supports a shallow marine or shallow lacustrine depositional model either model is inconsistent with the previously postulated red sea type submarine exhalative mineralization model3 7 9 for mt isa instead we argue that mt isa ore formation took place in a shallow water system possibly aided by the action of evaporite derived brines

the microfossils from the proterozoic urquhart shale mount isa queensland and their significance in relation to the depositional environment diagenesis and mineralisation the urquhart shale from mount isa queensland hosts major lead zinc and copper orebodies re examination of organic matter from the lead zinc ore bodies has shown that abundant microfossils characteristic of lacustrine environments are present and substantiates earlier results of love and zimmerman 1961 the framboid residues described by these authors are not microfossils but nevertheless the occurrence of framboidal pyrite has important implications for the timing of lead zinc mineralisation a diagenetic model is proposed for the lead zinc ore bodies and a later transgressive event accounts for the mode of occurrence of the copper ore bodies

greenland ice sheet motion coupled with daily melting in late summer 1 we use ground based and satellite observations to detect large diurnal and longer period variations in the flow of the greenland ice sheet gris during late summer that are strongly coupled with changes in its surface hydrology the diurnal signals are associated with periodic changes in surface melting and the longer period signals are associated with the episodic drainage of supra glacial lakes ice velocity doubles around 2 hours after peak daily melting and returns approximately to wintertime levels around 12 hours afterwards demonstrating an intimate link between the surface and basal hydrology during late summer the ice sheet accelerates by 35 per positive degree day of melting the observed link between surface melting and enhanced flow is typical of alpine glaciers which may provide an appropriate analogue for the evolution of the gris in a warming climate

fast recession of a west antarctic glacier satellite radar interferometry observations of pine island glacier west antarctica reveal that the glacier hinge line position retreated 1 2 0 3 kilometers per year between 1992 and 1996 which in turn implies that the ice thinned by 3 5 0 9 meters per year the fast recession of pine island glacier predicted to be a possible trigger for the disintegration of the west antarctic ice sheet is attributed to enhanced basal melting of the glacier floating tongue by warm ocean waters

volume and velocity changes at mittivakkat gletscher southeast greenland we document changes for mittivakkat gletscher the peripheral glacier in greenland with the longest field based observed mass balance and surface velocity time series between 1986 and 2011 this glacier changed by 15 in mean ice thickness and 30 in volume we attribute these changes to summer warming and lower winter snow accumulation vertical strain compensated for 60 of the elevation change due to surface mass balance smb in the lower part and 25 in the upper part the annual mean ice surface velocity changed by 30 which can be fully explained by the dynamic effect of ice thinning within uncertainty mittivakkat gletscher summer surface velocities were on average 50 60 above winter background values and up to 160 higher during peak velocity events peak velocity events were accompanied by uplift of a few centimeters

hf isotope geochemistry of the galapagos islands 1 we report 176hf 177hf ratios determined by multicollector inductively coupled plasma mass spectrometry on 49 basalts from the galapagos islands the hf values range from about 8 a value typical of many oceanic island basalts to about 15 a value typical of mid ocean ridge basalt the hf shows the expected correlation with nd and inverse correlations with sr and pb isotope ratios the range of values and correlations observed is consistent with galapagos mantle plume asthenosphere mixing inferred from previous geochemical studies while oceanic island basalt isotopic arrays suggest that multicomponent mixing is common in the sources of such basalts the galapagos is unusual in that depleted upper mantle appears to be a principal component thermal and dynamic interaction between the galapagos mantle plume and the lithosphere and shallow asthenosphere is the most likely cause of mixing and of the geographic pattern of geochemical variation the galapagos hf nd sr pb isotopic array diverges toward the plume end indicating the plume is heterogeneous this heterogeneity is geographic with distinct northern central and southern components the central component and to a lesser degree the northern component are compositionally similar to the common component of plumes variously called phem fozo and c while the southern component is unique with relatively high hf and 206pb 204pb compared to 87sr 86sr and nd

observations of ice sheet motion in greenland using satellite radar interferometry we present interferometric observations of ice sheet motion in western greenland based on pairs of ers 1 synthetic aperture radar sar images these observations provide the first detailed regional view of ice motion associated with dynamically supported topography near the margin of an ice sheet the interferograms of this area are much more complicated than other interferograms of ice sheets presented to date we devote the largest part of this paper to explaining the source of the complexity in these interferograms a synthetic interferogram based on a simple model helps to illustrate the effects of different components of the ice velocity field in interferometric data and suggests a method for estimating the large scale ice velocity field from such data

satellite radar interferometry for monitoring ice sheet motion application to an antarctic ice stream satellite radar interferometry sri provides a sensitive means of monitoring the flow velocities and grounding line positions of ice streams which are indicators of response of the ice sheets to climatic change or internal instability the detection limit is about 1 5 millimeters for vertical motions and about 4 millimeters for horizontal motions in the radar beam direction the grounding line detected by tidal motions where the ice goes afloat can be mapped at a resolution of 0 5 kilometer the sri velocities and grounding line of the rutford ice stream antarctica agree fairly well with earlier ground based data the combined use of sri and other satellite methods is expected to provide data that will enhance the understanding of ice stream mechanics and help make possible the prediction of ice sheet behavior

a fluid inclusion and stable isotope study of synmetamorphic copper ore formation at mount isa australia earlier structural studies indicate that the dolomitic and siliceous breccias and contained copper mineralization at mount isa queensland australia formed during regional deformation and greenschist facies metamorphism of their host mid proterozoic metasediments the metasomatic breccia body locally called silica dolomite is zoned with an outer halo of sparry dolomitic alteration replacing finely laminated dolomitic pyritic metasediments the core of the dolomitic breccia next to the underlying altered greenstones is overprinted by siliceous breccia containing the bulk of the chalcopyrite ore fluid inclusions in quartz and dolomite were studied by microthermometry micro raman spectrometry and semiquantitative electron microprobe analysis of inclusion salts two types of aqueous inclusions are restricted to dolomitic breccia cacl 2 rich group 1 with a cation ratio na ca k mg nearly equal 30 10 3 1 and salinity approximately 25 wt similar to recent salton sea geothermal brines and low salinity with 10 to 20 mole percent co 2 co 2 rich group 2 these two aqueous inclusion types are intimately associated in the same crystals and have probably both been trapped during dolomitic alteration siliceous alteration superimposed on dolomitic breccia contains nacl rich fluid inclusions group 3 na ca k mg nearly equal 300 10 30 1 minor ch 4 microstructures suggest that earlier higher salinity 10 20 wt and later lower salinity 4 9 wt variants of this nacl rich fluid bracket the main stage of chalcopyrite introduction there are no low density vapor inclusions indicative of any stage of fluid boiling rare high density ch 4 or co 2 rich carbonic inclusions are associated with nacl rich aqueous inclusions in a few samples secondary inclusions of a highly calcic low temperature brine group 4 occur along late healed cracks and postdate all major stages of mineral precipitation the c o and h isotope compositions of dolomites quartz and hydrous silicates and of fluid inclusion extracts from samples of the siliceous alteration zone were imposed by the externally derived weakly ch 4 co 2 bearing nacl rich fluid at high fluid rock ratios and over a small range of temperatures this fluid may have originated as a highly evolved basin brine or an evaporite derived metamorphic fluid the early cacl 2 rich fluid may have had an origin similar to the nacl rich ore fluid but its different delta d and the mass balance constraints arising from its chemical composition suggest that it has not been derived from the nacl rich fluid by progressive rock interaction within the zoned alteration system similarly an independent source is likely for the co 2 rich fluid the absolute pressure temperature ranges for the two alteration processes seem to be slightly different but it is uncertain whether the quartz chalcopyrite mineralization occurred at slightly lower temperature or higher pressure compared with the dolomitic alteration the latter is confined to 270 degrees to 350 degrees c and 700 to 1 500 bars by isochore and mineral stability data the following working hypothesis for the syntectonic and synmetamorphic fluid rock interaction and copper ore formation at mount isa is proposed in an initial stage dolomitic alteration occurred by chemical interaction between the urquhart shale and moderate amounts of two fluids of different chemical and hydrological origin represented by the cacl 2 rich and the co 2 rich fluid inclusions fluid mixing may have been aided by extension on the limb of a regional fold which temporarily lowered fluid pressures thus leading to hydraulic brecciation and fluid influx from two fluid regimes above and below the co 2 rich fluid probably represents the local metamorphic fluid of the urquhart shale whereas the cacl 2 rich brine was introduced from the underlying altered greenstones the initial stage of brecciation and dolomitic alteration was followed by the main stage of silicification and copper introduction by the much more copious nacl rich fluid probably at near lithostatic fluid pressure quartz and chalcopyrite precipitation occurred by a combination of slight cooling a ph increase and possibly an increase in sulfur activity as the initially reduced acid and possibly s deficient nacl rich fluids reacted with the previously dolomitized pyritic and dolomitic urquhart shale

local and regional controls on the lateral emplacement of the ben hiant dolerite intrusion ardnamurchan nw scotland abstract sub volcanic and related satellite intrusions record the delivery storage and accommodation of magma before eruption however when several volcanic centres are in close proximity the relationship between centre and satellites may be ambiguous here we examine the structure of the ben hiant dolerite satellite intrusion discuss its relationship with the ardnamurchan central complex located 2 km to the northwest and explore the possibility of a genetic connection with the next nearest centre the mull central complex 35 km to the southeast structural field observations and anisotropy of magnetic susceptibility ams fabric analyses reveal that the ben hiant dolerite was emplaced as a series of lobes in a sequence of stacked sheets the ams fabric data further indicate that the ben hiant dolerite intruded laterally and may have been sourced from either the ardnamurchan central complex or the mull central complex testing either model and discriminating between these two possible source reservoirs remains an outstanding challenge however the potential implications of the lateral movement of magma over many 10 s of kilometres between upper crustal magmatic centres suggests hidden complexities associated with volcanic plumbing systems that must be tested structurally as well as geochemically

re os geochronology and systematics in molybdenite from the endako porphyry molybdenum deposit british columbia canada precise re os molybdenite ages for the endako porphyry molybdenum deposit and the nithi mountain occurrence british columbia canada yield new information on the timing of molybdenite deposition three episodes of mineralization are indicated 1 154 ma 2 148 to 146 ma and 3 145 ma re os dates agree well with new u pb and 40 ar 39 ar data from granitoids of the nithi phase 155 2 1 5 ma the endako phase 148 4 1 5 ma and a preore dike 147 4 0 6 ma and the casey phase 145 1 0 2 ma plus hydrothermal biotite 144 5 0 75 ma villeneuve et al 2001 the excellent correlation between the re os dates from molybdenite and the ages of granitoids from the area indicates a direct genetic relationship between these plutons and molybdenite mineralization these re os data also provide further insight into the systematics and robustness of re os in molybdenite the endako molybdenum deposit is the product of two episodes of mineralization both associated with moderate salinity 5 15 wt nacl equiv and high temperature 440 c fluids a third low temperature 190 300 c hydrothermal event is associated with eocene faulting selby et al 2000 the clear distinction between two of the re os molybdenite dates in the deposit and the close agreement of these dates to the ages of granitoid intrusions suggest that the re os system in molybdenite is not reset by high temperature 440 c moderate salinity hydrothermal fluids in contrast magmatic biotite in a 147 ma preore dike has a 40 ar 39 ar age of 145 ma identical to the age of the hydrothermal biotite indicating that 440 c fluids reset the ar ar system in biotite hence we interpret that the re os isotope system in molybdenite is resistant to resetting by high temperature fluids 440 c in contrast to the 40 ar 39 ar system in biotite the re os system in molybdenite is also unaffected by postore hydrothermal fluids these data show that molybdenite can provide critical information in understanding sulfide mineral deposition in ore systems which is not recorded by other isotopic systems in alteration minerals

depositional ages of the stratiform base metal deposits at mount isa and mcarthur river australia based on u pb zircon dating of concordant tuff horizons potassium rich tuff beds occur interbedded with major stratiform pb zn mineralization in shales and dolomitic shales of the mount isa group northwest queensland and the mcarthur group northern territory these deposits are some 600 km apart yet they exhibit many similarities which together with regional correlations suggest that the deposits formed by similar processes and that the successions developed more or less contemporaneously zircon is sparsely distributed as tiny crystal fragments or phenocrysts in the tuffs and its morphology and u pb systematics affirm that it is primarily of igneous origin u pb zircon data from a tuff in the mineralized h y c pyritic shale member of the mcarthur group give an age of the tuff of 1 690 super 29 sub 25 m y and from a tuff in the mineralized urquhart shale of the mount isa group an age of 1 670 super 20 sub 17 m y these results are consistent with all other geologic controls and are regarded as the best estimates of the depositional ages of the groups the ages of the mount isa and mcarthur groups are thus the same to within the present experimental uncertainties essentially confirming geologic synchrony of these important sedimentary successions pooled whole rock data from several of the mount isa tuff marker beds give an updated rb sr age of about 1 480 m y interpreted as indicating that isotopic exchange and regional metamorphism had essentially ceased by this time

re os study of fe ti v oxide and fe cu ni sulfide deposits suwalki anorthosite massif northeast poland the suwalki anorthosite massif located in extreme northeast poland beneath more than a kilometer of phanerozoic cover hosts major fe ti v deposits these deposits discovered in 1962 are contained in fe and ti oxide minerals that coexist with subordinate quantities of fe cu ni and co sulfides in massif style anorthosites norites and gabbronorites accessibility and other considerations preclude development of this natural resource in the present economic climate detailed work by polish geologists during the last 35 years provides a sound geologic framework for this re os study of the age and origin of oxide and sulfide deposits associated with a major but lesser known anorthosite massif rhenium and osmium abundances and os isotopic compositions were measured for nine sulfides and four titanomagnetites from the suwalki anorthosite massif the titanomagnetites are over an order of magnitude lower in re 0 4 1 5 ppb and os 0 036 0 144 ppb concentrations than co precipitated pyrrhotite pyrite and chalcopyrite that yield consistent concentrations for re 30 55 ppb and os 1 6 ppb parallel lines connecting co existing titanomagnetite and sulfides have slopes of 1 on re versus common os concentration plots indicating that both re and os behave similarly during crystallization in their high preference for any sulfide phase over magnetite samples from three deposits within the anorthosite massif were analyzed an age of 1559 37 ma n 10 with an initial 187os 188os of 1 16 0 06 for the jezioro okr gle and krzemianka deposits is essentially identical to an age of 1556 94 ma n 3 for the udryn deposit udryn however yielded a marginally lower initial 187os 188os of 0 87 0 20 the high initial 187os 188os combined with the proterozoic re os age indicates that the source for suwalki oxides sulfides is older crust and hypothetically could involve archean rocks an average crustal value of 50 for 187re 188os yields a 2777 ma age for suwalki source rocks widespread phanerozoic cover severely limits knowledge of basement rocks in poland however and no archean rocks are known in the immediate region more likely 187re 188os ratios may be higher than average continental crust reflecting mafic crust in the source and may move the source age for suwalki anorthosite and mineral deposits toward younger values that easily include 2 0 ga proterozoic rocks this more favorable case also accommodates paleoproterozoic nd model ages regardless of archean or proterozoic source age the high initial 187os 188os ratios derived from the re os isochron indicate that the source for the oxide sulfide mineral deposits is more likely the crust and not the mantle given that these deposits are clearly magmatic the re os results add a new dimension to the long standing origin of anorthosite problem implying a crustal source for the anorthosite as well the 1559 ma suwalki age is compatible with a well exposed east west band of 1530 1660 ma rapakivi granite anorthosite magmatism to the immediate north transecting western russia southern finland estonia and latvia and central sweden in particular the age and isotopic character of suwalki are not unlike those of the well studied salmi rapakivi granite anorthosite batholith in western russia karelia

diffusion of osmium in pyrrhotite and pyrite implications for closure of the re os isotopic system abstract in order to better constrain the extent to which common sulfide minerals will retain their osmium isotopic composition subsequent to crystallization we have conducted experiments to quantify the diffusion behavior of osmium in pyrite and pyrrhotite experiments consisted of either 1 isothermal soaking of diffusion couples consisting of natural pyrite or pyrrhotite crystals packed against powdered os bearing fe sulfide or 2 relaxation of initially high near surface osmium concentrations produced in the latter experiments pyrite only osmium penetration into samples was characterized by depth profiling using rutherford backscattering spectroscopy rbs pyrite or electron microprobe analyses across sectioned run products pyrrhotite results of the first type of diffusion experiment involving pyrite show only limited osmium penetration into sample surfaces with the extent of penetration uncorrelated with run duration images of pyrite samples using atomic force microscopy show roughening of initially smooth surfaces as a consequence of step formation and suggest that osmium incorporation into the near surface occurred by solute uptake during step growth and not by volume diffusion prolonged 1000 h relaxation experiments revealed no additional osmium penetration into pyrite surfaces and based on the depth resolution for rbs a maximum diffusion coefficient of 2 5 10 23 m2 s at 500 c was calculated experiments involving pyrrhotite over the temperature range of 950 1100 c showed extensive osmium uptake and osmium concentration gradients that conform with fickian diffusion behavior we found that pyrrhotite fe s could be varied by changes in the composition of the starting material and osmium source and over the range of fe s produced in experiments molar fe s 0 83 0 90 we observed no systematic variation in the osmium diffusion coefficient diffusion coefficients measured parallel to the a crystallographic axis were on average 1 4 higher than values measured parallel to c and regression of the c axis data yielded the arrhenius relation d t 1 31 0 16 10 5 m 2 s exp 211 5 14 7 kj mol rt the application of these diffusion data to simple models of diffusive exchange during static or polythermal time temperature histories is used to assess the conditions under which radiogenic osmium will be retained during isothermal annealing calculations indicate that the cores of millimeter sized spherical pyrrhotite crystals undergoing diffusive exchange with an external osmium reservoir will have their initial compositions perturbed in 0 5 ma at temperatures exceeding 400 c pyrite undergoing the same process at 500 c requires in excess of 10 ma before crystal cores are affected the relatively short core retention time scales for pyrrhotite indicates that this mineral may be prone to isotopic resetting following relatively brief crustal thermal events thus possibly accounting for the scatter that commonly occurs in re os isochrons generated from massive sulfide samples calculated closure temperatures tc for osmium exchange in pyrrhotite yielded values of 300 400 c for grain sizes ranging from 10 to 1000 m these values of tc are similar to those calculated for ar retention in biotite and considerably lower than for sr in apatite and plagioclase for example such low closure temperatures for pyrrhotite suggest this mineral will date the final stage in the cooling of a magmatic system and possibly be susceptible to open system osmium exchange in the presence of late stage hydrothermal fluids this latter result infers that caution be applied when interpreting elevated initial osmium isotopic ratios as a product of crustal assimilation at the magmatic stage

the role of komatiitic and picritic magmatism and s saturation in the formation of ore deposits abstract the introduction of high temperature high magnesium komatiitic and picritic magmas into the earth s upper crust has given rise either directly or indirectly to many of the world s major ore deposits there is a direct association between komatiitic magmatism and kambalda style ni cu pge deposits the link between magma type and mineralization is not as clear cut in the case of the noril sk cu ni pge deposits but nevertheless there is an association between picritic magmatism and ore deposit development komatiitic and or picritic magmatism may also have contributed to the formation of many types of hydrothermal ore deposits recent nd isotope data generated by kent et al 1994 provide strong evidence for the hypothesis proposed by keays in 1983 that the au in archaean au deposits was derived either directly or indirectly from komatiites through the action of metamorphic fluids the importance of komatiitic and picritic magmas in ore forming processes arises from the fact that they are among the few mafic ultramafic magma types that are s undersaturated at the time of magma formation s saturation of magmas leads to marked depletion in the chalcophile metals for example czamanske and moore 1977 estimated that a third of the original cu and ni contents of morb were lost from the magmas due to extraction into magmatic sulphides the depletion in au and the pge is much greater due to their much larger partition coefficients keays and scott 1976 komatiitic and picritic magmas are s undersaturated because they are high temperature magmas produced by large degrees of partial melting of upper mantle sourc regions that were already depleted in s through earlier partial melting events most mafic magmas produced by less than 25 partial melting are s saturated and hence depleted in the ore forming chalcophile elements in contrast komatiitic and picritic magmas have their full complement of chalcophile metals when they do become s saturated they form sulphides that are strongly enriched in ni cu au pge and other strongly chalcophile metals these may accumulate to form ore deposits directly e g magmatic ni cu pge sulphides or be dispersed in komatiitic picritic rocks or their fractionation products making these source rocks for hydrothermal au or vms deposits

lead isotope studies bearing on the genesis of copper orebodies at mount isa queensland significant differences between the lead zinc silver and copper ore bodies unlike the lead zinc silver deposits the copper orebodies appear epigenetic two texturally distinct generations of iron sulfides later relative to the lead zinc mineralization origin of the main copper ore bodies from the basement metamorphic and granitic complexes direct relationship between the regional metamorphism generation of hypersaline fluids and metal extraction modified journal abstract

rhenium osmium systematics of the mount isa copper orebody and the eastern creek volcanics queensland australia implications for ore genesis the syn tectonic breccia hosted mount isa cu deposit in northwest queensland is the largest sediment hosted cu deposit in australia whole rock samples of chalcopyrite rich cu ore form an isochron with a re os age of 1 372 41 ma this age is more than 100 ma younger than the previously accepted age of cu ore formation an ar ar mineral age for biotite separated from the host rocks within the alteration envelope to the cu orebody this discrepancy cannot be unequivocally resolved due to a lack of other absolute geochronological constraints for cu mineralisation or the deformation event associated with cu emplacement the 1 372 41 ma date may reflect a the time of cu deposition b the time of a hydrothermal event that reset the re os signature of the cu ore or c mixing of the re os isotope systematics between the host rocks and cu bearing fluids however a range of published ar ar and rb sr dates for potassic alteration associated with cu mineralisation also records an event between 1 350 and 1 400 ma and these are consistent with the 1 372 ma re os age the 1 8 ga eastern creek volcanics are a series of tholeiitic basalts with a primary magmatic cu enrichment which occur adjacent to the mount isa cu deposit the whole rock os isotopic signature of the eastern creek volcanics ranges from mantle like values for the upper pickwick member to more radiogenic crustal values for the lower cromwell member the re os isotope signature of the cu ores overlaps with those calculated for the two volcanic members at 1 372 ma hence the os isotope data are supportive of the concept that the os in the cu ores was sourced from the eastern creek volcanics by inference it is therefore postulated that the eastern creek volcanics are the source of cu in the mount isa deposit as both os and cu are readily transported by oxidised hydrothermal fluids such as those that are thought to have formed the cu orebody the pickwick member yields a re os isochron age of 1 833 51 ma which is within error of previously reported age constraints the initial 187os 188os isotopic ratio of 0 114 0 067 os 0 7 is slightly subchondritic and together with other trace element geochemical constraints is consistent with a subcontinental lithospheric mantle source the pickwick member records a minimum age of ca 1 95 ga for melt depletion in the subcontinental lithospheric mantle beneath the mount isa inlier prior to the extraction of the magmas which formed the eastern creek volcanics this corresponds with the end of subduction related magmatism along the eastern margin of the northern australian craton which included the mount isa inlier

timing of superposed volcanism in the proterozoic mount isa inlier australia metamorphosed proterozoic successions in the mount isa inlier contain a variety of volcanic suites interspersed at several intervals throughout the 30 km thick stratigraphic pile the u pb isotopic systematics of zircons crystallised in superposed felsic volcanic units allow detailed definition of the chronology of this volcanism and therefore of the major depositional cycles this supracrustal development spanned a 270 ma interval in the early to mid proterozoic new u pb zircon data from the earliest recognised volcanic cycle leichhardt metamorphics yield a pooled age for this event at 1867 5 ma a far northern segment of the same basement succession contains a geochemically similar felsic sequence 1852 7 ma old these results confirm the coevality between this felsic volcanism and nearby intrusive bodies of the same age the second major cycle of volcanism is 60 80 ma younger than the first this interval representing the maximum duration of the intervening regional unconformity dacitic and mafic volcanic rocks bottletree formation which unconformably overlie the western flank of the 1870 ma basement are dated in two areas at 1790 810 and 1808 1722 rhyodacites argylla formation on the eastern side of the basement have a similar age 1783 5 ma so for purposes of correlation and crustal evolution these two sequences flanking either side of the basement can be considered to comprise a single volcanic cycle subsequent cycles of felsic volcanism are recognised in stratigraphically younger sequences which include rhyolites with well resolved u pb zircon discordance patterns indicating ages of 1720 7 ma doherty formation and 1678 3 ma carters bore rhyolite the youngest volcanic cycle 1603 6 ma is evidenced by rhyolitic lavas in a part of the sequence previously considered to be much older at least 1740 ma recognition of such a young volcanic episode has an important economic bearing for it implies that rocks equivalent in age to the prospective pb zn rich mount isa group in the west ca 1670 ma could well exist in the eastern succession of the inlier

direct radiometric dating of the devonian mississippian time scale boundary using the re os black shale geochronometer many phanerozoic time scale boundaries are characterized by oceanic anoxia and mass extinction events with the deposition of black shale the re os isotope system in black shale can be used to provide depositional ages for these rocks thus yielding direct radiometric ages for time scale boundaries we demonstrate that the re os black shale geochronometer can yield precise ages useful for time scale research through study of the devonian mississippian boundary within the exshaw formation canada the re os date determined places the devonian mississippian boundary at 361 3 2 4 ma 2 including uncertainty model 1 mean square of weighted deviates 1 2 in accord with recent calibration interpolated from u pb zircon dates 360 7 0 7 ma for the hasselbachtal section germany

re os dating of low level highly radiogenic llhr sulfides the harnas gold deposit southwest sweden records continental scale tectonic events to obtain geologically meaningful and precise results on low level sulfides that are highly radiogenic blank corrections that account for the extreme difference in the os isotope composition of sample and blank are necessary and the resulting data is best plotted in 187 re 187 os space much like the approach used for molybdenites we here introduce the acronym llhr as a means of characterizing low level and highly radiogenic sulfides use of the traditional 187 re 188 os vs 187 os 188 os plot for llhr sulfides leads to large analytical uncertainties and highly correlated errors as 188 os is poorly determined and can generally be accounted for by the blank we now recognize that llhr sulfides such as those encountered at the harnas au deposit are a common occurrence and characteristic of many crustally affiliated ore systems the harnas au deposit in southwest sweden is located in the mjosa vanern mineral belt that transects from northwest to southeast the prominent geologic fabric of the sveconorwegian province including the mylonite zone the deposit is hosted in a strongly sheared and locally brecciated sulfide bearing quartz vein that crosscuts the foliation of orthogneisses belonging to the 1600 maa mal granitoid suite a 187 re 187 os isochron of 973 34 ma 2 for samples of pyrite and chalcopyrite from outcrops of the harnas alma and silvergruvan veins was obtained the harnas and subsidiary alma veins are au bearing whereas the silvergruvan 2 5 km to the southeast is not of the au bearing type four replicate analyses of an additional pyrite sample from the harnas vein yield a model age of 616 40 ma 95 c l in all samples re and 187 os concentrations are extremely low 0 35 to 7 1 and 0 005 to 0 074 ppb respectively and total common os 0 002 0 028 ppb is less than half the calculated radiogenic 187 os two samples of galena from the harnas vein yielded blank level re and os neither the 973 nor 616 ma time of mineralization is related to development of the mylonite zone at 920 ma or intrusion of the anorogenic bohus blomskog granites at 920 to 900 ma previously proposed sources for generating mjosa vanern mineral belt ore fluids an age of 973 ma for harnas alma silvergruvan suggests that sulfide deposition was associated with the waning stages 0 97 0 90 ga of the sveconorwegian grenvillian orogeny 1 15 0 90 ga postdating metamorphism and deformation that produced a regionally overthickened crust in the northern part of the sveconorwegian province the vein systems for these and numerous other small deposits in the mjosa vanern mineral belt could have resulted from regional exhumation in the late sveconorwegian with associated extension and the development of fracture systems at cooler middle to upper crustal levels in the southern part of the sveconorwegian province dominated by granulitic facies rocks no mineralization is present perhaps due only to increased exhumation and erosion that has exposed deeper crustal levels the late sveconorwegian age 973 ma records the main period of sulfide deposition for the harnas alma silvergruvan vein systems and indicates the robustness of the chronometer within tectonically complex terranes the late neoproterozoic age 616 ma records a later time of pyrite deposition probably associated with shearing and reopening of the harnas vein system because the au mineralization at harnas has been described as associated with shearing and occurring in fracture fillings in early pyrite we suggest that part or all of the au mineralization could have been introduced at 616 ma during reactivation of the vein system the 616 ma age for pyrite suggests a previously unrecognized and much younger mineralizing episode in the harnas region most likely reflecting continental scale extension and the late neoproterozoic opening of the iapetus ocean

measurement of ice sheet topography using satellite radar interferometry detailed digital elevation models dems do not exist for much of the greenland and antarctic ice sheets radar altimetry is at present the primary in many cases the only source of topographic data over the ice sheets but the horizontal resolution of such data is coarse satellite radar interferometry uses the phase difference between pairs of synthetic aperture radar sar images to measure both ice sheet topography and surface displacement we have applied this technique using ers 1 sar data to make detailed i e 80 m horizontal resolution maps of surface topography in a 100 km by 300 km strip in west greenland extending northward from just above jakobshavns isbrae comparison with a 76 km long line of airborne laser altimeter data shows that we have achieved a relative accuracy of 2 5m along the profile these observations provide a detailed view of dynamically supported topography near the margin of an ice sheet in the final section we compare our estimate of topography with phase contours due to motion and confirm our earlier analysis concerning vertical ice sheet motion and complexity in ers 1 sar interferograms

ice sheet motion and topography from radar interferometry both topography and motion information are present in repeat pass ers 1 interferograms over ice sheets the authors demonstrate that the topography is separable from the surface displacement field when a sequence of radar images are available if the velocity field is constant over the time span of observation the topography can be derived from differential interferograms formed from sequential observations with this measurement a pure displacement field can then be obtained by removal of the topographic contribution to the interferometric phase at each pixel further they discuss how the vertical and horizontal components of displacement affect the interferometrically derived motion field they illustrate their approach with four successive 3 day repeat ers 1 images of a flow feature in northeastern greenland

anticlockwise p t path of granulites from the monte castelo gabbro ordenes complex nw spain the study of mafic and aluminous granulites from the monte castelo gabbro ordenes complex nw spain reveals an anticlockwise p t path that we interpret as related to the tectonothermal activity in a magmatic arc probably an island arc the p t path was obtained after a detailed study of the textural relationships and mineral assemblage succession in the aluminous granulites and comparing these with an appropriate petrogenetic grid additional thermobarometry was also performed the granulites are highly heterogeneous with distinct compositional domains that may alternate even at thin section scale garnets are generally idiomorphic to subidiomorphic and in certain domains of the aluminous granulites they show overgrowths forming xenomorphic coronas around a more or less idiomorphic core both types of garnets show significant ca enrichment at the crystal rims which together with the other mineralogical and textural characteristics is compatible with a pressure increase with low t variation p t estimations indicate a peak of t 800 c and p 9 5 kbar attained after a significant increase in pressure that took place at high temperatures in the sillimanite field we suggest that this kind of trajectory probably anticlockwise is compatible only with a terrane heated by an intense magmatic activity after or during tectonic crustal thickening magmatic injection at the base and or into the crust which is characteristic of magmatic arcs

radar interferometry and its application to changes in the earth s surface geophysical applications of radar interferometry to measure changes in the earth s surface have exploded in the early 1990s this new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times the resulting interferogram is a contour map of the change in distance between the ground and the radar instrument these maps provide an unsurpassed spatial sampling density 100 pixels km 2 a competitive precision 1 cm and a useful observation cadence 1 pass month 1 they record movements in the crust perturbations in the atmosphere dielectric modifications in the soil and relief in the topography they are also sensitive to technical effects such as relative variations in the radar s trajectory or variations in its frequency standard we describe how all these phenomena contribute to an interferogram then a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments including the four satellites currently in orbit ers 1 ers 2 jers 1 and radarsat the next chapter suggests some guidelines for interpreting an interferogram as a geophysical measurement respecting the limits of the technique assessing its uncertainty recognizing artifacts and discriminating different types of signal we then review the geophysical applications published to date most of which study deformation related to earthquakes volcanoes and glaciers using ers 1 data we also show examples of monitoring natural hazards and environmental alterations related to landslides subsidence and agriculture in addition we consider subtler geophysical signals such as postseismic relaxation tidal loading of coastal areas and interseismic strain accumulation we conclude with our perspectives on the future of radar interferometry the objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intuition necessary to interpret it

syndeformational carbonate replacement model for the copper mineralization at mount isa northwest queensland a microstructural study the mount isa base metal deposits show a definite spatial separation between stratiform ag pb zn lenses generally regarded as syngenetic and cu ores within a recrystallized and brecciated host lithology the silica dolomite microstructural evidence indicates that the cu orebodies and the silica dolomite formed during early syndeformational syn d 3 replacement processes in a dolomitic shale sequence three stages of alteration are distinguished 1 dolomite recrystallization silicification 2 dolomitization and 3 chalcopyrite or fe sulfide or quartz or chlorite deposition structural timing constraints suggest a post d 2 to pre s 3 interval for the first stage whereas the last two stages occurred during early d 3 the formation of the silica dolomite with the cu orebodies is separated in time from the adjacent syngenetic stratiform ag pb zn ores by a period including at least two regional deformation events

stratiform copper deposits hosted by low energy sediments iii aspects of metal transport the approximate compositions of closed basin saline waters that existed in probable source rocks of stratiform copper deposits hosted by low energy sediments were derived by the simulated evaporation of dilute inflow waters from basalt and granite provenances the saline water derived from dilute inflow water in the basalt provenance had a ph of 7 6 and was saturated with talc dolomite and gypsum the saline water derived from dilute inflow water in the granite provenance had a ph of 7 7 and was saturated with quartz calcite talc and gypsum both waters were 3 molal in chloride and were also saturated with hematite fluorite and fluorapatite the waters probably represent likely end members in the compositional spectrum of metal transporting waters which existed in the source rocks of the stratiform copper deposits copper and cobalt exhibit solubility maxima of 1 500 ppm or greater and 150 ppm respectively at oxygen fugacities in the range 10 super 35 to 10 super 55 bars lead solubility is similar in the two waters and is a maximum of 20 ppm at oxygen fugacities greater than 10 super 60 bars zinc solubility is a maximum of 80 ppm in the basalt derived saline water and 20 ppm in the granite derived saline water silver solubility is a maximum of 200 ppm at oxygen fugacities above 10 super 35 bars barium and iron solubilities are less than 5 ppm abundances of copper silver and in some instances cobalt in all common source rocks result in concentrations of these metals in the saline waters less than their saturation limits concentrations of barium iron lead manganese and zinc in the saline waters are limited by water composition rather than by abundance in source rocks the high copper cobalt lead and zinc solubilities are consistent with the hypothesis haynes 1986a that most sulfides in stratiform copper deposits hosted by low energy clastic sediments are deposited within 50 cm of the sediment water interface during bacterial sulfate reduction porosity and permeability constraints imposed by uncompacted analogs of ore hosting sediments show that the copper contents of the metal transporting waters must be greater than 100 ppm for formation of ore which grades 1 percent or more copper the modeling demonstrates that the proposed waters are potentially effective metal transporters capable of forming stratiform copper ore when the prevailing oxygen fugacity is within the range 10 super 35 to 10 super 55 bars the saline waters are capable of transporting at least 100 ppm copper and therefore are likely to produce copper ore under the porosity and permeability constraints imposed by the hypothesis

fluctuations of local glaciers in greenland during latest pleistocene and holocene time abstract this paper is the first to summarize research on fluctuations of local glaciers in greenland e g ice caps and mountain glaciers independent of the greenland ice sheet during latest pleistocene and holocene time in contrast to the extensive data available for fluctuations of the greenland ice sheet surprisingly little data exist to constrain local glacier extents much of the available research was conducted prior to wide spread use of ams radiocarbon dating and the advent of surface exposure and luminescence dating although there is a paucity of data generally similar patterns of local glacier fluctuations are observed in all regions of greenland and likely reflect changes in paleoclimate which must have influenced at least the margins of the inland ice absolute age data for late glacial and early holocene advances of local glaciers are reported from only two locations disko island and the scoresby sund region subsequent to late glacial or early holocene time most local glaciers were smaller than at present or may have disappeared completely during the holocene thermal maximum in general local glacier advances that occurred during historical time 1200 1940 ad are the most extensive since late glacial or early holocene time historical documents and more recent aerial photographs provide useful information about local glacier fluctuations during the last 100 yrs in all but one area north greenland local glaciers are currently receding from historical extents

early ordovician orogenic event in galicia nw spain evidence from u pb ages in the uppermost unit of the ordenes complex new u pb data zircon monazite and rutile obtained from rocks of the uppermost allochthon in the variscan belt of nw spain indicate that the hangingwall to the suture includes an allochthonous unit with a pre variscan tectonothermal evolution this evolution is characterised by an early ordovician 498 500 ma bimodal magmatism followed almost immediately 493 498 ma by a barrovian style metamorphism up to the granulite facies the metamorphism subsequent to the igneous intrusions requires convergence and crustal thickening in order to generate the barrovian facies pattern shown by the lithologies of the uppermost allochthon the almost coeval magmatism and metamorphism and the chemistry of the metabasites suggest an accretionary complex probably related to a volcanic arc as the most probable setting for the origin of the uppermost unit the implications of the existence of early ordovician convergent plate boundaries are discussed in the context of gondwana laurentia avalon interactions

intra annual and intra seasonal flow dynamics of a high arctic polythermal valley glacier measurements of surface dynamics onpolythermaljohn evans glacier nunavut canada over two winter periods and every 7 10 days throughout two melt seasons june july 2000 2001 provide new insight into spatio temporal patterns of high arctic glacier dynamics in the lower ablation zone mean annual surface velocities are 10 21ma 1 but peak velocities up to 50 higher are attained during latejune earlyjuly in the upper ablation zone and lower accumulation zone mean annual surface velocities are typically10 18ma 1 and peak velocities up to 40 higher occur during latejuly in the upper accumulation zone mean annual surface velocities are 2 9ma 1 and motion in mid to latejuly exceeds this by up to 10 rapid drainage of ponded supraglacial water in the upper ablation zone to an initially distributed subglacial drainage system in mid june may force excess surface motion in the warm based lower glacier the data indicate thatthe durationof the velocity response maybe relatedto the rate of channeliz ation of the basal drainage and the velocity response may be transmitted up glacier by longitudinal coupling an increase in surface velocities in the middle glacier in latejuly occurs in conjunction with the opening of two further moulins in the accumulation zone

recent discoveries of proterozoic microfossils in south central brazil abstract twenty two precambrian microfossiliferous localities seven newly reported here are known from the sao francisco block and associated brasilia fold belt of south central brazil reported from outcrop and drill core samples of mesoand neoproterozoic cherts carbonates and siliciclastics of the 1170 to 950 ma old paranoa group and the 950 to 700 ma old sao francisco supergroup composed of the jequitai formation and the overlying bambui group representatives of nearly 30 genera of proterozoic microfossils chiefly cyanobacteria and subsidiary acritarchs have been reported from these strata preserved mostly within carbonaceous black chert in flat laminated and high relief stromatolites and represent a wide spectrum of environments evidently ranging from nearshore lagoonal to supratidal intertidal subtidal and offshore marine settings contrary to previously held views the microfossils are generally more abundant and better preserved in the older unit paranoa group than in the younger one sao francisco supergroup nevertheless among the newly reported assemblages one from the lower part of the bambui group stands out as probably the best preserved and most diverse microbiota known from any precambrian unit of south america although paleobiologic studies of the brazilian proterozoic are still in a formative stage recent discoveries are highly promising such as the detection in the work presented here of possible differences 1 between the microfossil sizes in stromatolites of the paranoa and bambui groups 2 in the abundance and size of acritarchs with respect to lithology and facies and 3 in the microfossil assemblages preserved in morphologically distinct stromatolites

insar observations of ice elevation and velocity fluctuations at the flade isblink ice cap eastern north greenland 1 the 8500 km2 flade isblink ice cap fiic 81 15 n 15 0 w is the largest ice cap in greenland we use repeat pass interferometric synthetic aperture radar insar techniques to investigate the form and flow of the fiic european remote sensing satellite ers 1 and ers 2 data acquired in winter 1996 were used to form a 100 m resolution digital elevation model dem which we constrained using ice cloud and elevation satellite icesat laser altimeter elevation measurements from 2007 this insar dem was used to isolate the phase due to motion from seven ers tandem 1 day pairs of sar scenes acquired between 15 august 1995 and 7 february 1996 to produce one wintertime and two summertime velocity maps five of the eight major outlet glaciers draining the fiic are marine terminating and two terminate at a lake margin a maximum ice velocity of 581 m yr 1 was observed in mid august 1995 six of the eight major outlet glaciers exhibit seasonal velocity variations between late summer and winter and flow speeds vary by up to 20 over a 10 day period in august 1995 our findings show that while marine terminating glaciers flow faster than land terminating glaciers there is no simple relationship between glacier type and seasonality of ice motion

surface melt induced acceleration of greenland ice sheet flow ice flow at a location in the equilibrium zone of the west central greenland ice sheet accelerates above the midwinter average rate during periods of summer melting the near coincidence of the ice acceleration with the duration of surface melting followed by deceleration after the melting ceases indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice bedrock interface interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting with larger increases accompanying higher amounts of summer melting the indicated coupling between surface melting and ice sheet flow provides a mechanism for rapid large scale dynamic responses of ice sheets to climate warming

proterozoic low pressure high temperature metamorphism and an anticlockwise p t t path for the hazeldene area mount isa inlier queensland australia in the hazeldene area situated in the mount isa inlier queensland the metamorphic grade changes from chlorite zone through biotite and cordierite zones to sillimanite k feldspar zone microstructural studies of rocks near the sillimanite isograd demonstrate that cordierite grew early during the development of a steep foliation s2 was replaced by biotite andalusite and sillimanite at the metamorphic peak late in s2 and in turn by kyanite chlorite adjacent to localized small post d2 shear zones although the anticlockwise p t t path is well defined the precise p t conditions are uncertain because of problems with experimental and thermodynamic data the best estimate for the metamorphic peak for rocks close to the sillimanite isograd is around 600 c at 4 kbar the metamorphism has been dated at 1544 ma and was synchronous with a major crustal shortening event because proposed extensional events occurred more than 60 ma earlier their contribution to the peak metamorphic thermal perturbation would have been insignificant the syn metamorphic mica creek pegmatites the abundance of high heat producing elements in the nearby pre d2 sybella granite and advective heat by fluids which caused considerable metasomatism in the hazeldene area may have each contributed to the thermal budget however the metamorphic thermal gradient may be 80 c km 1 or higher strongly suggesting a local magmatic control as none are known in the area such syn metamorphic plutons would have to lie beneath the exposed high grade rocks

surface mass balance ice velocity and near surface ice temperature on qaanaaq ice cap northwestern greenland from 2012 to 2016 to better understand the processes controlling recent mass loss of peripheral glaciers and ice caps in northwestern greenland we measured surface mass balance smb ice velocity and near surface ice temperature on qaanaaq ice cap in the summers of 2012 16 the measurements were performed along a survey route spanning the terminus of an outlet glacier to the upper reaches 243 968 m a s l the ice cap wide smb ranged from 1 10 0 29 to 0 13 0 26 m w e a 1 for the years from 2012 13 to 2015 16 mass balance showed substantially large fluctuations over the study period under the influence of summer temperature and snow accumulation ice velocity showed seasonal speedup only in the summer of 2012 suggesting an extraordinary amount of meltwater penetrated to the bed and enhanced basal ice motion ice temperature at a depth of 13 m was 8 0 c at 944 m a s l which was 2 5 c warmer than that at 243 m a s l suggesting that ice temperature in the upper reaches was elevated by refreezing and percolation of meltwater our study provided in situ data from a relatively unstudied region in greenland and demonstrated the importance of continued monitoring of these processes for longer timespans in the future

an alternative emplacement model for the classic ardnamurchan cone sheet swarm nw scotland involving lateral magma supply via regional dykes abstract sub volcanic intrusive networks of which cone sheets are recognised as a major constituent partially control volcano growth and eruption style the accepted cone sheet model is that these confocally dipping intrusions originate from an unexposed central magma chamber through dip parallel magma flow however the emplacement mechanism of cone sheets remains poorly understood the 58 ma cone sheet swarm of ardnamurchan nw scotland offers an excellent opportunity to further resolve the emplacement dynamics of cone sheets through studying magma flow and their importance in volcanic edifice construction structural measurements and anisotropy of magnetic susceptibility ams analyses have constrained a lateral magma flow pattern consistently oriented nw se in the majority of the ardnamurchan cone sheets field observations also highlight the importance of host rock structure and interference between competing local and regional stress fields in controlling intrusion geometry our observations suggest cone sheet formation may be linked to laterally propagating nw se trending regional dykes sourced from laterally adjacent magmatic systems likely the palaeogene mull central complex which are deflected around the central complex by stress field interference implicitly edifice construction and potential eruption precursors observed at a volcano may instigate or result from magmatic activity in laterally adjacent volcanic systems

petrology geochronology and isotope geochemistry of the post 1820 ma granites of the mount isa inlier mechanisms for the generation of proterozoic anorogenic granites four distinct episodes of granitic intrusion occurred in the mount isa inlier at 1820 1800 ma 1760 1740 ma 1700 1670 ma and 1560 1480 ma combined these granites cover at least 4700 km2 and they contrast in composition and intrusive style with an earlier major felsic magmatic event which occurred between 1870 and 1840 ma post 1820 ma granite batholiths are of two types large major coarse grained anorogenic i type intrusives and small minor microgranites which are probably s type the i type granites are all pink to red colour and most contain fluorite rapakivi textures are common they have a high ratio of fe mg and are more enriched in tio2 zr nb y and u than the 1870 1840 ma felsic igneous rocks the post 1820 ma i types are interpreted to have formed by small degrees of partial melting of a mafic underplate the smaller microgranites are relatively k2o enriched and are sometimes muscovite bearing they are interpreted to be derived from proterozoic feldspathic metasediments the first three episodes of granite magmatism are coeval with major extensional sedimentary sequences but they are generally spatially displaced from the maximum area of surface rift development this separation is predicted by the asymmetric detachment model of continental extension the tectonic relationship of the youngest granite episode is not clearly defined the 143nd 144nd initial ratios of the post 1820 ma granites fall into two groups one having positive relatively primitive nd values of 1 8 to 3 5 the other having negative nd values ranging from 2 9 to 3 7 samples with positive nd values are interpreted as partial melts of mafic sources formed post 1870 ma whilst the group with negative nd values are derived from significantly older sources formed probably around 2300 2000 ma the sources of these granites are produced by significant underplating events that may occur during either extension or compression

age of the barramundi orogeny in northern australia by means of ion microprobe and conventional u pb zircon studies abstract u pb zircon geochronological studies are used to quantify the tectonostratigraphic history of a major crust forming event in early proterozoic terranes of northern australia magmatism and tectonic processes associated with this event the barramundi orogeny appear similar over very wide areas about one third of the australian continent the barramundi event marks the deformation metamorphism and cratonization of the earliest proterozoic 2 0 1 9 ga basinal successions and it was followed by and closely linked to extensive orogenic felsic magmatism the yaringa metamorphics are an inlier of paragneiss and schist that pre dates 1865 3 ma leichhardt felsic magmatism and younger basin formation in the mount isa inlier from an ion microprobe u pb zircon study of massive and migmatitic gneiss the time of yaringa metamorphism is established at 1890 8 ma recognized younger proterozoic deformations in the interval 1610 1550 ma are generally not evident in zircon u pb systems but have totally reset local rb sr whole rock values conventional u pb work on multi grain zircon samples of yaringa gneiss gives a geologically meaningless age 2090 40 ma that is an artifact of complex zircon growth part of which was initially inherited from a 2 55 to 2 2 ga provenance and the other major part of which was formed in situ during the 1890 ma high grade metamorphism predictably for simple zircon systems in low grade metavolcanic terranes conventional and ion microprobe zircon ages are in close agreement dating of volcaniclastic sequences above and below the barramundi tectonic break in the pine creek inlier brackets the orogeny in this terrane to a similar time frame 1885 1870 ma some zircons which crystallized at this time form selvedges around older cores whose age of 2100 2000 ma may be relics of an earlier deep crustal underplating the uniform chemistry of post barramundi felsic magmatism and the similar tectonic setting of the areally extensive barramundi event are mirrored by their temporal coherency cycles of geosynclinal deposition burial metamorphism and uplift took place during intervals of several million years or less implying comparable rates for early proterozoic orogenesis to those established for tertiary and quaternary settings

topography and penetration of the greenland ice sheet measured with airborne sar interferometry a digital elevation model dem of the geikie ice cap in east greenland has been generated from interferometric c band synthetic aperture radar sar data acquired with the airborne emisar system gps surveyed radar reflectors and an airborne laser altimeter supplemented the experiment the accuracy of the sar dem is about 1 5m the mean difference between the laser heights and the sar heights changes from 0 m in the soaked zone to a maximum of 13 m in the percolation zone this is explained by the fact that the snow in the soaked zone contains liquid water which attenuates the radar signals while the transparency of the firn in the percolation zone makes volume scattering dominate at the higher elevations for the first time the effective penetration has been measured directly as the difference between the interferometric heights and reference heights obtained with gps and laser altimetry

recharge of a subglacial lake by surface meltwater in northeast greenland observations of rapid persistent elevation gains that occur on the ice surface above a subglacial lake as the lake is refilled with surface meltwater during the summer melt period in greenland show that surface meltwater may be trapped and stored at the bed of an ice sheet affecting ice dynamics downstream the discovery of a 70 metre deep collapse basin near the summit of the largest and most northerly peripheral ice cap of greenland and the use of high resolution stereo satellite imagery to monitor its evolution suggests that surface meltwater can be trapped and stored beneath the greenland ice sheet previously meltwater from the surface of the ice sheet had been assumed to drain efficiently through the basal hydrologic system during the summer melt period rapid persistent elevation gains occur on the ice surface above a subglacial lake as the lake is refilled with surface meltwater and stored at least on annual time scales these findings have potential implications for our understanding of ice sheet temperature and velocity in a warming climate surface meltwater production on large ice sheets is expected to increase if this water is delivered to the ice sheet base it may have important consequences for ice dynamics for example basal water distributed in a diffuse network can decrease basal friction1 2 and accelerate ice flow3 4 5 6 7 8 whereas channelized basal water can move quickly to the ice margin where it can alter fjord circulation and submarine melt rates9 10 less certain is whether surface meltwater can be trapped and stored in subglacial lakes beneath large ice sheets here we show that a subglacial lake in greenland drained quickly as seen in the collapse of the ice surface and then refilled from surface meltwater input we use digital elevation models from stereo satellite imagery and airborne measurements to resolve elevation changes during the evolution of the surface and basal hydrologic systems at the flade isblink ice cap in northeast greenland during the autumn of 2011 a collapse basin about 70 metres deep and about 0 4 cubic kilometres in volume formed near the southern summit of the ice cap as a subglacial lake drained into a nearby fjord over the next two years rapid uplift of the floor of the basin which is approximately 8 4 square kilometres in area occurred as surface meltwater flowed into crevasses around the basin margin and refilled the subglacial lake our observations show that surface meltwater can be trapped and stored at the bed of an ice sheet sensible and latent heat released by this trapped meltwater could soften nearby colder basal ice11 and alter downstream ice dynamics12 13 heat transport associated with meltwater trapped in subglacial lakes should be considered when predicting how ice sheet behaviour will change in a warming climate

rb and sr diffusion in alkali feldspars with implications for cooling histories of rocks volume diffusion of sr and rb have been measured in orthoclase feldspar as well as sr diffusion in albite using isotope exchange hydrothermal solutions and analysis by ion microprobe for water pressures of 1000 bars the kinetics of diffusion parallel to the c axis are given by the arrhenius relations strontium transport in the or is isotropic to within a factor of four the measurements use a new procedure in which only the elements in question are present in the starting fluid cooling rates of igneous rocks can now be determined from closure temperatures material balance and the rb sr dating method based on the departures of the mineral data from the whole rock isochron for cooling rates less than approximately 100 c my

greenland ice sheet high elevation balance and peripheral thinning aircraft laser altimeter surveys over northern greenland in 1994 and 1999 have been coupled with previously reported data from southern greenland to analyze the recent mass balance of the greenland ice sheet above 2000 meters elevation the ice sheet is in balance on average but has some regions of local thickening or thinning thinning predominates at lower elevations with rates exceeding 1 meter per year close to the coast interpolation of our results between flight lines indicates a net loss of about 51 cubic kilometers of ice per year from the entire ice sheet sufficient to raise sea level by 0 13 millimeter per year approximately 7 of the observed rise

reos dating of molybdenites from ore deposits in japan implication for the closure temperature of the reos system for molybdenite and the cooling history of molybdenum ore deposits abstract rhenium and osmium abundances were determined on molybdenites from eighteen ore deposits in japan fifteen vein type a skarn type a greisen type and a pegmatite type deposit re os ages obtained for molybdenites from northeastern central and southwestern japan are 100 130 ma 50 75 ma and ca 10 ma respectively reflecting the ages of regional igneous activities in individual areas for vein type ore deposits re os ages for molybdenites agree with rb sr whole rock ages of host granitoids while they are 3 12 ma older than k ar mineral ages of the host rocks on the other hand re os ages of molybdenites from skarn pegmatite and greisen type ore deposits agree with k ar ages of the host rocks the comparison of re os ages for molybdenites with rb sr and k ar ages of host rocks in vein type deposits suggests that re os closure temperature for vein molybdenite is close to whole rock rb sr closure temperature for host granitic rocks i e roughly estimated to be around 500 c and higher than k ar closure temperature for host granodiorites i e 230 370 c if the thermal history of vein molybdenites is essentially equivalent to that of host rocks one possible explanation for age discrepancies of 3 12 ma between re os ages for molybdenites and k ar ages for the wall rocks observed in vein type molybdenum deposits is that later thermal events after formation of molybdenum ores may reset k ar ages hydrothermal alteration might have occurred in such a temperature condition as to disturb k ar mineral systems in wall rocks and made them younger but not the re os system in molybdenite the other explanation might be that the age discrepancies correspond to a cooling interval from ca 500 to 300 c of host granitoid on the other hand the agreement of re os ages of molybdenites and k ar ages of host rocks in skarn pegmatite and greisen type deposits in this study indicates no later disturbance for k ar system in the wall rock or the rapid cooling of the ore and wall rocks after the formation of molybdenite deposits

re os ages for archean molybdenite and pyrite kuittila kivisuo finland and proterozoic molybdenite kabeliai lithuania testing the chronometer in a metamorphic and metasomatic setting seven 187re 187os ages were determined for molybdenite and pyrite samples from two well dated precambrian intrusions in fennoscandia to examine the sustainability of the re os chronometer in a metamorphic and metasomatic setting using a new 187re decay constant 1 666 10 11y 1 with a much improved uncertainty 0 31 we determined replicate re os ages for molybdenite and pyrite from the kuittila and kivisuo prospects in easternmost finland and for molybdenite from the kabeliai prospect in southernmost lithuania these two localities contain some of the oldest and youngest plutonic activity in fennoscandia and are associated with newly discovered economic au mineralization ilomantsi finland and a cu mo prospect kabeliai lithuania two re os ages for vein hosted kabeliai molybdenite average 1486 5 ma in excellent agreement with a 1505 11 ma u pb zircon age for the hosting kabeliai granite pluton the slightly younger age suggests the introduction of cu mo mineralization by a later phase of the kabeliai magmatic system mean re os ages of 2778 8 ma and 2781 8 ma for kuittila and kivisuo molybdenites respectively are in reasonable agreement with a 2753 5 ma weighted mean u pb zircon age for hosting kuittila tonalite these re os ages agree well with less precise ages of 2789 290 ma for a rb sr whole rock isochron and 2771 75 ma for the average of six sm nd tdm model ages for kuittila tonalite three re os analyses of a single pyrite mineral separate from the same sample of kuittila pluton that yielded a molybdenite separate provide individual model ages of 2710 27 2777 28 and 2830 28 ma re 17 4 12 1 and 8 4 ppb respectively with a mean value of 2770 120 ma in agreement with the kuittila molybdenite age the re and 187os abundances in these three pyrite splits are highly correlated r 0 9994 and provide a 187re 187os isochron age of 2607 47 ma with an intercept of 21 ppt 187os mswd 1 1 it appears that the re os isotopic system in pyrite has been reset on the millimeter scale and that the 21 ppt 187os intercept reflects the in situ decay of 187re during the 160 to 170 m y interval from 2778 ma time of molybdenite pyrite deposition to 2607 ma time of pyrite resetting when the re os data for molybdenites from the nearby kivisuo prospect are plotted together with the kuittila molybdenite and pyrite data a well constrained five point isochron with an age of 2780 8 ma and a 187os intercept 2 4 3 8 ppt of essentially zero results mswd 1 5 we suggest that the pyrite isochron age records a regional metamorphic and or hydrothermal event possibly the time of au mineralization a proposed re os age of 2607 ma for au mineralization is in good agreement with radiometric ages by other methods that address the timing of archean au mineralization in deposits worldwide so called late au model molybdenite in contrast provides a robust re os chronometer retaining its original formation age of 2780 ma despite subsequent metamorphic disturbances in archean and proterozoic time

isotopic and structural responses of granite to successive deformation and metamorphism within the sybella granite west of mount isa in northern australia differential response of u pb and rb sr isotopic systems to deformation metamorphism enables ages of emplacement and three discrete deformation metamorphic events to be determined based on zircon u pb systems two of the plutons were emplaced at 1671 pm 8 ma and 1668 pm 26 21 ma and the third at 1610 pm 10 ma a separate microgranite body gives aberrantly old u pb ages of up to 1780 ma due to partial inheritance of older zircon the three discrete deformation metamorphic events d 1 d 2 and d 3 occurred at 1610 pm 13 ma 1544 pm 12 ma and 1510 pm 13 ma respectively based on whole rock rb sr isotopic systems the youngest body was emplaced syntectonically and has possible significance to the origin of the mount isa ag pb zn orebodies homogenization of rb and sr isotopes via extensive syntectonic fluid migration associated with deformation partitioning and resultant solution transfer appears to have been

inland thinning of pine island glacier west antarctica the pine island glacier pig transports 69 cubic kilometers of ice each year from 10 of the west antarctic ice sheet wais it is possible that a retreat of the pig may accelerate ice discharge from the wais interior satellite altimetry and interferometry show that the grounded pig thinned by up to 1 6 meters per year between 1992 and 1999 affecting 150 kilometers of the inland glacier the thinning cannot be explained by short term variability in accumulation and must result from glacier dynamics

the proterozoic mount isa fault zone northeastern australia is it really a ca 1 9 ga terrane bounding suture abstract in marked contrast to palaeoproterozoic laurentia the location of sutures and boundaries of discrete crustal fragments amalgamated during palaeoproterozoic formation of the north australian craton remain highly speculative interpretations of suture locations have relied heavily on the analysis of regional geophysical datasets because of sparse exposure of rocks of the appropriate age the mount isa fault zone has been interpreted as one such palaeoproterozoic terrane bounding suture furthermore the coincidence of this fault zone with major shale hosted massive sulphide pb zn ag orebodies has led to speculations that trans lithospheric faults may be an important ingredient for the development of this deposit type this study has integrated geophysical and geochemical data to test the statute of the mount isa fault as a terrane bounding suture forward modelling of gravity data shows that basement rocks on either side of the mount isa fault have similar densities these interpretations are consistent with geochemical observations and sm nd data that suggest that basement lithologies on either side of the mount isa fault are geochemically and isotopically indistinguishable from each other and that the mount isa fault is unlikely to represent a suture zone that separates different palaeoproterozoic terranes our data indicate that the crustal blocks on both sides of the mount isa fault zone must have been in within close proximity of each other since the palaeoproterozoic and that the western fold belt was part of the ancestral north australian craton well before the 1 89 1 87 ga barramundi orogeny it appears that deep crustal variations in density may be related to the boundary between a shallowly west dipping high density mafic to ultramafic plate and low density basement rocks this interpretation in turn impacts on crustal scale models for the development of shale hosted massive sulphide pb zn mineralisation which do not require trans lithospheric faults to tap deep seated metal reservoirs and or mantle plumbing systems the approach applied herein demonstrates the value of multi disciplinary investigations to the critical assessment of long lived proterozoic fault systems which in the absence of methodical analysis are commonly assumed to represent terrane bounding sutures

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

illegitimate magmas of the galapagos insights into mantle mixing and magma transport roughly 1 2 of the flows erupted from flank vents of the western galapagos shield volcanoes have anomalous compositions we call these illegitimate magmas because of their uncertain parentage because some illegitimate magmas are compositionally indistinguishable from lavas of an adjacent volcano and erupt from the flank facing the adjacent volcano such magmas apparently result from lateral intrusion of magma from the adjacent volcano other illegitimate magmas come from parts of the galapagos plume that have incompletely mixed or result from unusually advanced melting of part of the mantle

the osmium isotopic composition of the continental crust osmium isotopic compositions and concentrations have been determined for deltaic and continental shelf sediments from three major rivers the amazon changjiang and mississippi and for two loesses from the upper mississippi river valley the loesses have heavy mineral and clay compositions characteristic of mississippi river and delta sediment concentrations range from 15 to 120 pg os g and 187os 186os ratios range from 8 2 to 10 9 sediments which are polluted surface sediment from the changjiang estuary or which have scavenged metals from seawater gulf of mexico slope surface sediment and distal amazon shelf sediment have high osmium concentrations and less radiogenic isotopic compositions purely terrigenous sediments have 15 90 pg os g and 187os 186os 10 0 10 9 north american loess and mississippi delta sediment osmium isotopic compositions are indistinguishable we believe that 187os 186os 10 11 is a good average for currently eroding upper continental crust these sediments have neodymium isotopic compositions close to the global mean for river sediment terrigenous 187os 186os is significantly more radiogenic than seawater 187os 186os 8 6 requiring a nonriverine source of osmium to seawater terrigenous osmium is also significantly more radiogenic than bulk pelagic clay osmium we use the improved estimate of terrigenous 187os 186os to recalculate the flux of extraterrestrial osmium to pacific marine sediment if the residence age of osmium in an upper crustal region is similar to the neodymium model age of a sediment derived from that region a model dependent upper crustal 187re 186os ratio can be calculated for the model ages of the sediments analyzed in this study tdm 1 5 1 7 ga model 187re 186os ratios are 340 360 and can be used to correct for bias resulting from the preferential erosion of young crust the 187os 186os ratio of 2 2 ga crust with 187re 186os 400 is 14 2 we have also used the data from this study to estimate upper crustal osmium and rhenium concentrations of 50 pg g and 390 pg g respectively

the relationship between subglacial water pressure and velocity of findelengletscher switzerland during its advance and retreat findelengletscher switzerland advanced about 250 m between 1979 and 1985 and retreated thereafter subglacial water pressure surface velocity and surface strain rate were determined at several sites the measurements were made early in the melt seasons of 1980 1982 1985 and 1994 and in the autumn of 1983 and the winter of 1984 changes of surface geometry were assessed from aerial photographs the estimated basal shear stress changed little between 1982 and 1994 nevertheless large changes in the relationship of subglacial water pressure and surface velocity were observed which cannot be reconciled with the most commonly used sliding law unless it is modified substantially consideration of possible reasons indicales that a change in the subglacial drainage system occurred probably involving a change in the degree of cavity interconnection isolated cavities damp the variations in sliding velocity that normally result from changes in water pressure because the pressure in isolated cavities decreases as the sliding speed increases in contrast by transmitting water pressure fluctuations to a larger area of the bed interconnected cavities amplify the effect of water pressure fluctuations on sliding speed thus we suggest that an observed decrease in velocity for a given water pressure between 1982 and 1994 was a consequence of a decrease in the interconnectedness of the subglacial cavity system

textural and geochemical analysis of chalcopyrite galena and sphalerite across the mount isa cu to pb zn transition implications for a zoned cu pb zn system abstract the genesis of the mount isa cu pb zn system northern australia is highly debated three metallogenic models have previously been proposed to explain the close spatial relationship between a world class cu and pb zn deposit 1 ca 1650 ma syngenetic pb zn mineralisation that has been re mobilised and overprinted by ca 1520 ma epigenetic cu mineralisation 2 ca 1650 ma syn sedimentary cu pb zn mineralisation 3 ca 1520 ma epigenetic cu pb zn mineralisation to assess the viability of these models detailed petrography and core logging was completed on numerous samples across eight sections of drill core that intersect both cu and pb zn mineralisation this was accompanied by the analysis of trace elements in chalcopyrite galena and sphalerite from various samples across the lateral transition from cu to pb zn rich mineralisation across the cu to pb zn transition there is a primary change in host lithology from cu rich silica dolomite breccia to highly stratiform pb zn rich carbonaceous carbonate rich and fine grained pyrite rich shale petrography suggests that sphalerite galena and chalcopyrite co crystallised consistently enveloping and or replacing pre mineralisation silica dolomite siderite calcite arsenopyrite fine and coarse grained pyrite from cu to pb zn rich mineralisation sphalerite and galena transition from micro inclusions primarily located within coarse grained chalcopyrite to dominant fine to coarse grained components that infill around deformed carbonaceous shale and selectively replace carbonate rich and fine grained pyrite rich shale chalcopyrite transitions from a coarse grained component that replaces silica dolomite alteration to an uncommon medium to fine grained component residing within stratabound pb zn mineralisation trace element trends demonstrate that as pb zn mineralisation is approached the concentrations of bi in chalcopyrite cd se te bi in galena and bi and co in sphalerite decrease or are relatively depleted conversely the concentrations of pb in chalcopyrite sb in galena and pb sb and ag in sphalerite increase or are relatively enriched these trends are consistent with a temperature gradient between cu and pb zn mineralisation during ore emplacement the sphalerite ggimfis geothermometer yields a median homogenisation temperature of 343 44 c consistent with previous temperature estimates of cu mineralisation silica dolomite formation and chlorite alteration an epigenetic and coeval cu pb zn model is favoured where a slight temperature gradient

initial field observations on qaanaaq ice cap northwestern greenland to study the glaciological processes controlling the mass budget of greenland s peripheral glaciers and ice caps field measurements were carried out on qaanaaq ice cap a 20 km long ice cap in northwestern greenland in the summer of 2012 we measured surface melt rate ice flow velocity and ice thickness along a survey route spanning the ice margin 200 m a s l to the ice cap summit 1110 m a s l melt rates in the ablation area were clearly influenced by dark materials covering the ice surface where degree day factors varied from 5 44 mm w e k 1 d 1 on a clean surface to 8 26 mm w e k 1 d 1 in the dark regions ice velocity showed diurnal variations indicating the presence of surface meltwater induced basal sliding mean ice thickness along the survey route was 120 m with a maximum thickness of 165 m ice velocity and temperature fields were computed using a thermomechanically coupled numerical glacier model modelled ice temperature obtained by imposing estimated annual mean air temperature as the surface boundary condition was substantially lower than implied by the observed ice velocity this result suggests that the ice dynamics and thermodynamics of the ice cap are significantly influenced by heat transfer from meltwater and changing ice geometry

sedimentologic petrographic and sulfur isotope constraints on fine grained pyrite formation at mount isa mine and environs northwest queensland australia fine grained pyrite is the earliest generation of pyrite and the most abundant sulfide within the urquhart shale at mount isa northwest queensland the pyrite is intimately interbanded with ore grade pb zn miner alization at the mount isa mine but is also abundant north and south of the mine at several stratigraphic horizons within the urquhart shale detailed sedimentologic petrographic and sulfur isotope studies of the urquhart shale mostly north of the mine reveal that the fine grained pyrite delta 34 s 3 3 to 26 3 parts per thousand formed by thermochemical sulfate reduction during diagenesis the sulfate source was local sulfate evaporites pseudo morphs of which are present throughout the urquhart shale i e gypsum anhydrite and barite deep burial diagenetic replacement of these evaporites resulted in sulfate bearing ground waters which migrated parallel to bedding fine grained pyrite formed where these fluids infiltrated and then interacted with carbon rich laminated siltstones comparison of the sulfur isotope systematics of fine grained pyrite and spatially associated base metal sulfides from the mount isa pb zn and cu orebodies indicates a common sulfur source of ultimately marine origin for all sulfide types different sulfur isotope ratio distributions for the various sulfides are the result of contrasting formation mechanisms and or depositional conditions rather than differing sulfur sources the sulfur isotope systematics of the base metal and associated iron sulfide generations are consistent with mineralization by reduced hydrothermal fluids perhaps generated by bulk reduction of evaporite sourced sulfate bearing waters generated deeper in the mount isa group the sedimentary sequence which contains the urquhart shale the available sulfur isotope data from the mount isa orebodies are consistent with either a chemically and thermally zoned evolving cu pb zn system or discrete cu and pb zn mineralizing events linked by a common sulfur source

wolf volcano galapagos archipelago melting and magmatic evolution at the margins of a mantle plume wolf volcano an active shield volcano on northern isabela island in the galapagos archipelago has undergone two major stages of caldera collapse with a phase of partial caldera refilling between wolf is a typical galapagos shield volcano with circumferential vents on the steep upper carapace and radial vents distributed in diffuse rift zones on the shallower sloping lower flanks the radial fissures continue into the submarine environment where they form more tightly focused rift zones wolf s magmas are strikingly monotonous estimated eruptive temperatures of the majority of lavas span a total of only 22 c this homogeneity is attributed to buffering of magmas as they ascend through a thick column of olivine gabbroic mush that has been deposited from a thin shallow 2 km deep subcaldera sill that is in a thermochemical steady state wolf s lavas have the most depleted isotopic compositions of any historically active intraplate ocean island volcano on the planet and have isotopic compositions except for he he indistinguishable from midocean ridge basalt erupted from the galapagos spreading center gsc 250 410 km away from the peak of influence of the galapagos plume wolf s lavas are enriched in incompatible trace elements and have systematic major element differences relative to gsc lavas however wolf s magmas result from lower extents of melting deeper melt extraction and a greater influence of garnet compared with gsc magmas but wolf and the gsc share the same sources these melt generation conditions are attributed to melting in a thermal and mechanical boundary layer of depleted asthenosphere at the margins of the galapagos plume the lower degrees of melting and extraction from deeper levels result from a thicker lithospheric cap at wolf than exists at the gsc

the petrology and geochemistry of alteration assemblages in the eastern creek volcanics as a guide to copper and uranium mobility associated with regional metamorphism and deformation mount isa queensland

eruptive stratigraphy of the tatara san pedro complex 36 s southern volcanic zone chilean andes reconstruction method and implications for magma evolution at long lived arc volcanic centers

subdivision and correlation of late precambrian sequences in australia abstract the diversity of the australian precambrian record is used to empirically assess the application of all available techniques of correlation of late precambrian rocks lithofacies isotopic ages palaeontology and palaeomagnetism within the framework of latest lithostratigraphic geochronologic correlation charts lithostratigraphy is the main tool for intrabasinal correlation and mapping but isotopic ages will continue for some time yet to provide the main criteria for interregional correlation lithostratigraphic correlation is demonstrated over hundreds of kilometres but is generally constrained by tectonic controls to individual major crustal blocks climatic markers such as tillites may be correlated interregionally over thousands of kilometres the most exciting recent development in platform geochronology is the application of u pb zircon dating to fine grained tuffs illite may provide reliable minimum estimates but can be shown to be up to 150 ma too young glauconite and rb sr total rock shale ages have provided useful broad age estimates of sequences for which better methods are unavailable but only when based on cautious assessment and multiple sampling their ages may be either minimum or maximum stromatolites continue to demonstrate their potential for broad correlation when based on rigorous taxonomic study but the framework of time ranges of known taxa must be expanded for stromatolites to achieve their full potential especially for rocks older than 1000 ma acritarchs in black shales provide diverse and complex assemblages with excellent correlation potential but once again the australian taxonomic framework is still inadequate black cherts contain an evolutionarily conservative biota with only limited correlation potential recent palaeomagnetic studies based on both apwp and magnetostratigraphy demonstrate excellent potential for detailed correlations down to at least 1700 ma old however the present chronologically calibrated data base is sparse and must be supplemented by many more detailed studies through thick continuous rock sequences spanning substantial intervals of time the value of multidisciplinary correlation is elegantly demonstrated by very detailed and unambiguous correlation of combined palaeomagnetic isotopic age and stromatolite data across the 1700 ma mcarthur basin previous regional lithostratigraphic correlations have been conclusively and significantly revised with major implications to regional palaeogeography

plume ridge interaction lithospheric stresses and the origin of near ridge volcanic lineaments 1 in many hot spot ridge systems formation of off axis volcanic chains or lineaments occurs between the hot spot centers and nearby mid ocean ridges in some cases such as galapagos kerguelen and possibly the mid pac mountains and tristan these lineaments appear to meet in a focus zone near the hot spot and fan outward in the direction of the ridge axis the origins of these lineaments are not well known and do not easily fit into typical conceptual models of ridge or hot spot volcanism it has been proposed for the galapagos region that such lineaments are caused by channeling of hot asthenosphere from off axis mantle plumes toward mid ocean ridges where enhanced volcanism initiates island formation morgan 1978 alternatively other workers suggest that these lineaments are controlled by patterns of stress in the lithosphere we examine this latter hypothesis by considering the effects of buoyant uplift and asthenospheric shear on the base of the lithosphere induced by an expanding mantle plume using thin plate theory we calculate the two dimensional plan view pattern of depth integrated stresses in a plate of varying thickness both a straight continuous ridge and a ridge transform ridge system are simulated by a displacement discontinuity boundary element model ridge and transform segments have imposed normal and zero shear tractions and we test different idealized tectonic or far field stress conditions assuming that volcanism is promoted by lithospheric tension and aligns along lineaments parallel to trajectories of least tensile stress calculations reproduce the rough fan shaped pattern of lineaments between the galapagos archipelago and the galapagos spreading center the focus of the fan shape is over the plume center when it interacts with a straight ridge but the fan focus appears closer to a segmented ridge offset by a transform fault if the ridge segments are more tensile than the far field stress this condition provides a plausible explanation for the apparent focus at the galapagos north of the hot spot center the width of the fan pattern along the ridge axis is predicted to increase as the plume ridge separation increases and as the far field stress becomes more tensile parallel to the ridge the observed width along the galapagos spreading center is consistent with a nearly isotropic remote stress models predict the lithospheric tension caused by plumes to promote lineament formation on only young lithosphere in support of this prediction a compilation of data from 23 hot spots shows that lineament formation is common near hot spots with plume ridge separations of 1250 km or on lithosphere of 25 ma but not on older lithosphere

deep mantle plume osmium isotope signature from west greenland tertiary picrites picrites from nuussuaq peninsula and qeqertarssuaq disko island west greenland preserve trace element and isotopic signatures reflecting the composition of the icelandic plume head os isotope ratios are low 187os 188os i 0 1272 0 1371 in terms of global plume related magmatism and this is coupled with anomalously high os abundances and radiogenic 143nd 144nd i isotopes crustally contaminated basalts within the west greenland sequences possess os and nd isotopic signatures consistent with mixing between initial plume head compositions and two discrete types of west greenland continental crust one crustal component is of a local sedimentary origin and the other is typical of ancient felsic crust the low os isotopic signatures of the picritic units are considered to be those of the initial mantle plume the fact that such low os isotope ratios occur in sequences with high 3he 4he and the non systematic variation in os isotopes with indices of fractionation accumulation and pb isotopes argue against mixing with depleted morb mantle or ancient subcontinental lithospheric mantle the high os concentrations in the picrites are attributed to high degrees of partial melting 25 of mantle containing no residual sulphide this is consistent with models for plume heads in which anomalous mantle temperatures initiate melting at high pressures generating large degrees of partial melting unradiogenic os and radiogenic nd components in plume related cfb magmatism may preserve contributions from a reservoir which is sampled only occasionally in young oceanic basalts such a reservoir shares os isotopic features with the primitive upper mantle pum which may also be manifest in the kea component of hawaiian magmatism therefore portions of the west greenland continental flood basalt province arguably represent the first direct sampling of unmodified plume head material derived from the lower mantle or lower portions of the upper mantle

re os dating of sulfides associated with gold mineralization in central victoria australia we report re os isotope ages that are the first for sulfides closely associated with gold mineralization at the bendigo and maldon goldfields in central victoria two arsenopyrite samples from bendigo contain 11 ppb re and 0 08 ppb highly radiogenic os llhr samples stein et al 2000 and have model ages of 444 7 and 447 7 ma with a mean model age of 446 5 ma a five point isochron based on these arsenopyrite analyses plus three pyrite analyses including one replicate gives an age of 438 6 ma molybdenite associated with au te cu and sb mineralization at maldon gives an re os age of 376 2 ma similar to the age of the nearby har court granite these results support previous 40 ar 39 ar data indicating that initial emplacement of gold mineralization in central victoria occurred in the late ordovician during the earliest stages of accretionary development of the southern lachlan fold belt the molybdenite data are also consistent with the mobilization and or introduction of gold during late devonian magmatism

a geochemical process model for the mount isa copper orebodies in this paper we present new data and review existing data on the distribution lithochemistry and paragenesis of copper ore at mount isa and provide the first description of a body of anhydrite dolomite barite and hematite recently intersected at the northern end of the copper system it has been previously proposed that the extraordinary spatial coincidence of giant copper and lead zinc deposits at mount isa is due to the emplacement of copper into host rocks made chemically favorable for copper mineralization by enrichment in dolomite and or pyrite and mechanically favorable by the presence of preexisting layers of ductile lead and zinc sulfide ore several recent studies however suggest that copper and much if not all of the lead and zinc were deposited contemporaneously we provide evidence that high grade 2 5 copper is associated with fractured and silicified rocks early breccia cementing quartz is commonly euhedral and contains numerous growth zones defined by disordered carbon and brine inclusions containing ch4 this quartz is inferred to have been deposited from a cooling brine basement brine that equilibrated with rocks beneath the level of the deposit consistent with earlier studies we have noted that there is often late dolomite dolomite ii infilling of vuggy porosity defined by this euhedral quartz chalcopyrite however postdates both phases and there is textural evidence of both dolomite and quartz dissolution during chalcopyrite formation the nature of the copper bearing fluid basinal brine was deduced from the intimate association of chalcopyrite and anhydrite and from previous fluid inclusion studies this brine was oxidized and sulfur rich but undersaturated in quartz consistent with this fluid being introduced from above as proposed in several previous studies new reaction path modeling suggests that reduction of the oxidized brine by the carbonaceous and urquhart shale was the most likely depositional process many other rock types in the region also had the capacity to reduce oxidized ore forming brines thus ore can be anticipated in these other units provided that sufficient porosity and permeability existed during ore formation the modeling further suggests that the presence of dolomite is not a prerequisite to economic copper grades although carbonate dissolution possibly contributed with fracturing to enhanced porosity and permeability furthermore sulfide rich rocks were no more effective at precipitating copper than sulfide absent rocks consistent with several lines of evidence demonstrating that pyrite or other sulfide minerals were not consumed during ore formation mixing of the basinal and basement brines could also have caused precipitation of copper but the predicted gangue assemblages differ from those observed in nature various radiometric ages are consistent with formation of the mount isa copper deposits after initiation of the unconformable south nicholson basin although we recognize that more precise and accurate dating of the ore and fluid flow events are required basal red bed sediments of the south nicholson basin would have provided suitable aquifers for the oxidized copper rich basinal brines we speculate that the driving force for brine flow was the development of topography to the east of mount isa

melting and freezing beneath filchner ronne ice shelf antarctica 1 we use remote sensing data sets to evaluate the spatial distribution of melt beneath the filchner ronne ice shelf fris the net melt rate of 83 4 24 8 gtons yr is 2 5 5 times lower than previous glaciological estimates but is similar to existing oceanographic estimates the spatial distribution however differs significantly from standard conceptual and numerical models in which most melt occurs along the grounding lines our results suggest most grounding line melt is refrozen while the dominant ice shelf water isw source is melting near the ice shelf front probably associated with tidal action this suggests that changes in ice shelf extent can impact isw production rates in the weddell sea

on the recent elevation changes at the flade isblink ice cap northern greenland 1 we have used radar altimeter 2 ra 2 onboard esa s envisat and geosciences laser altimeter system glas onboard nasa s icesat to map the elevation change of the flade isblink ice cap fiic in northern greenland based on ra 2 data we show that the mean surface elevation change of the fiic has been near zero 0 03 0 03 m a between fall 2002 and fall 2009 we present the elevation change rate maps and assess the elevation change rates of areas above the late summer snow line 0 09 0 04 m a and below it 0 16 0 05 m a the glas elevation change rate maps show that some outlet glaciers previously reported to have been in a surge state are thickening rapidly using the ra 2 measured average elevation change rates for different parts of the ice cap we present a mass change rate estimate of 0 0 0 5 gt a for the fiic we compare the annual elevation changes with surface mass balance smb estimates from a regional atmospheric climate model racmo2 we find a strong correlation between the two r 0 94 and p 0 002 suggesting that the surface elevation changes of the fiic are mainly driven by net smb the correlation of modeled net smb and measured elevation change is strong in the southern areas of the fiic r 0 97 and p 0 0005 but insignificant in the northern areas r 0 38 and p 0 40 this is likely due to higher variability of glacier flow in the north relative to the south

polyphase deformation in the western mount isa inlier australia episodic or continuous deformation abstract the polyphase deformation history of the mount novit ranges western mount isa inlier australia involved the development of four generations of n s to nw plunging folds development of which alternated with movement on n s striking faults shear zones with west over east displacement the spatial relationships between successive structures and the distinct similarities in the kinematics style and asymmetry are all consistent with continuous deformation during e w to ne sw shortening additional support for this hypothesis is based on the development of the three major fold generations and the intervening faults and shear zones during low p high t metamorphism although the duration of this metamorphic event cannot be constrained recent studies have linked low p metamorphism to heat advection by migrating melts thermal modelling indicates that such metamorphic events will be short lived in comparison to those associated with thermal relaxation of over thickened crust low p metamorphism is unlikely to persist through two or more separate tectonic events therefore syn metamorphic polyphase deformation in the mount novit ranges apparently formed during a single continuous tectonic episode this structural history differs from both the regional scheme and that of previous workers in this area the main differences are i no evidence was found for early thrust faulting prior to n s folding ii there are four generations of n s to nw se folds as opposed to two and iii this study favors a single consistent tectonic regime in contrast to the interpretation of three discrete isolated tectonic events

penetration depths inferred from interferometric volume decorrelation observed over the greenland ice sheet radar interferometry provides a novel way to study the subsurface of glaciers interferometric correlation since the two complex images that comprise the interferogram have slightly different incidence angles at each point on the ground a decorrelating phase noise with statistics related to the scattering medium is present in the interferogram the amount of surface decorrelation is increased by volume scatter the larger the vertical extent of the scatterers contributing to the radar echo the greater the decorrelation will be by modeling this effect the authors can estimate radio wave penetration depths within the upper layers of the glacier or ice sheet observations of the greenland ice sheet using ers data yield penetration depths one way 1 e point for power that range from 12 to 35 m due to the contribution of volume scatter the critical interferometer baseline is decreased and the authors find for the greenland data the baseline must be restricted to be less than 300 m the authors also compare penetration depths measured within the dry snow zone with those found in the percolation zone and coastal areas they find that as expected the rocky coastal areas evidence minimal penetration interestingly the penetration depths that the authors measure in the percolation zone spl sim 23 m indicate a large degree of volume scatter which is contrary to earlier results that found the scattering in the percolation zone dominated by structures in the first few meters this discrepancy may be due to unmodeled scattering behavior or the radar return may indeed include significant contributions from scatterers far beneath the surface

precise re os ages of organic rich mudrocks and the os isotope composition of jurassic seawater rhenium and osmium isotope and abundance data have been obtained on precisely located samples from three suites of immature organic rich mudrocks from jurassic coastal outcrops in england the data provide accurate whole rock ages of 207 12 ma 181 13 ma and 155 4 3 ma for suites of hettangian toarcian exaratum subzone and kimmeridgian sensu anglico wheatleyensis subzone samples these new re os ages are indistinguishable within the assigned analytical uncertainties from interpolated depositional ages estimated from published geological timescales and establish the importance of the re os dating technique for chronostratigraphic studies early diagenetic pyrite nodules possess levels of re and os which are 1 2 orders of magnitude lower than in the enclosing organic rich mudrocks indicating that these elements had already been removed from sediment pore waters at the time of nodule formation thus the re os isotope system in these organic rich mudrocks has been closed since or from very soon after the time of sediment deposition because most of the re 98 and os 95 99 8 in the mudrocks is shown to be hydrogenous the 187os 188os i of the samples is interpreted to be that of contemporaneous seawater the data thereby provide the first estimates of the os isotope composition of jurassic seawater during the earliest jurassic hettangian the seawater 187os 188os ratio was extremely unradiogenic 0 15 it had increased to 0 8 at the end of the early jurassic toarcian 20 ma later while in the late jurassic kimmeridgian the seawater 187os 188os ratio was 0 59 the most likely explanation for the unradiogenic os isotope composition of hettangian seawater is that the contribution of unradiogenic os to the oceans from the hydrothermal alteration of oceanic crust greatly exceeded the input of radiogenic os from the continents at that time this interpretation is in line with observations suggesting that global weathering rates were low in the hettangian and that increased hydrothermal and volcanic activity preceded the break up of pangea the re os ratios of hettangian mudrocks and by inference of contemporaneous seawater are similar to those of mudrocks deposited at later times during the jurassic and argues against the unradiogenic os in hettangian seawater being derived from extraterrestrial meteoritic sources

seasonal evolution of subglacial drainage and acceleration in a greenland outlet glacier an acceleration of ice mass loss has been observed near the margin of the greenland ice sheet partly as a result of faster ice motion observations by gps receivers reveal high seasonal variability in ice motion with summer motion up to 220 higher than winter background levels the greenland ice sheet contains enough water to raise sea levels by 7 m however its present mass balance and future contribution to sea level rise is poorly understood1 accelerated mass loss has been observed near the ice sheet margin partly as a result of faster ice motion2 3 4 surface melt waters can reach the base of the ice sheet and enhance basal ice motion5 6 however the response of ice motion to seasonal variations in meltwater supply is poorly constrained both in space and time here we present ice motion data obtained with global positioning system receivers located along a 35 km transect at the western margin of the greenland ice sheet throughout a summer melt season our measurements reveal substantial increases in ice velocity during summer up to 220 above winter background values these speed up events migrate up the glacier over the course of the summer the relationship between melt and ice motion varies both at each site throughout the melt season and between sites we suggest that these patterns can be explained by the seasonal evolution of the subglacial drainage system similar to hydraulic forcing mechanisms for ice dynamics that have been observed at smaller glaciers

the role of hydrologically driven ice fracture in drainage system evolution on an arctic glacier 1 observations from ellesmere island suggest that the connection between surface and subglacial drainage on a predominantly cold glacier is made abruptly by hydrologically driven propagation of fractures from the surface to the bed where ice is 150 m thick water ponded to a depth of 6 9 m within a supraglacial stream system before establishing a permanent bed connection multiple premonitory drainage events preceded the final drainage of ponded water implying that fracturing is necessary but insufficient to establish a permanent link between surface and subglacial drainage refreezing of water that penetrates the first fractures to form may reseal the connection while flow resistance within the subglacial system may delay the onset of continuous through flow a large volume of ponded water is required to enlarge fractures sufficiently by melting to maintain continuous drainage while feedbacks between subglacial hydrology and ice dynamics may assist in maintaining the connection and initiating subglacial outflow

multiple deformations with successive subvertical and subhorizontal axial planes in the mount isa region their impact on geometric development and significance for mineralization and exploration the first orogeny to affect most rocks exposed in the mount isa province caused significant repetition of stratigraphy through north south shortening geological maps are dominated however by younger folds with subvertical north south striking axial planes these folds were produced by east west shortening during a second orogeny both orogenies produced several foliations however some foliations have negligible geometric consequences allowing the geometry of the region to be described generally in terms of just the three deformations d 1 d 2 and d 3 which produced macroscopic folds and the younger deformations which produced brittle faults one of the weak events that appears superficially to have had little or no geometric impact played a highly significant role in the generation of structurally controlled mineralization that role has been identified following advances in conceptual understanding of fold development and associated foliation the deformation which occurred between the d 2 and d 3 events produced geometric effects that were masked by overprinting of north south trending d 2 folds by similarly trending d 3 folds significantly these d 3 folds which control the localization or upgrading of much mineralization in the mount isa province did not form in rocks unaffected by this intermediate event because the near parallelism of s 2 and s 3 in such rocks resulted in intensification of s 2 rather than development of a new s 3 the intermediate deformation event called d sub 2 5 locally produced highly asymmetric deflections in bedding and s 2 with subhorizontal axial planes that were subsequently overprinted by d 3 folds and an s 3 cleavage no mesoscopic foliation was produced during d sub 2 5 and its rotational effects on bedding were commonly subsumed within younger d 3 structures thus d 3 disguises the presence of d sub 2 5 except in relatively rare locations where d 2 folds were isoclinal such as in the tommy creek block and on the northern end of the snake creek anticline southeast of cloncurry and northwest of mount isa in these three locations in the latter locations both limbs were affected resulting in large scale overturning of bedding on one limb prior to overprinting by d 3 the asymmetric folds developed during d sub 2 5 created sites where bedding could be pulled apart during d 3 resulting in implosion because of the high fluid pressure in the surrounding country rock with brecciation jostling fluid access and mineralization large scale zones of mineralization form where d sub 2 5 was localized at an earlier formed heterogeneity such as a thrust surface e g at mount isa mine or a granite country rock contact in these locations early formed angular bedding relationships were locally rotated into orientations which created sites that could implode during d 3 this role of d sub 2 5 in the generation of d 3 allows recognition of regional zones for exploration that previously have received little attention recognition of the role of d sub 2 5 reveals a cyclicity in successive subvertical and subhorizontal events not recognized by most workers in this terrain that may occur in other orogens around the world but has similarly gone unnoticed after the first orogeny finished a succession of three near vertical and two subhorizontal events occurred during the east west shortening orogeny at mount isa these were succeeded by younger kinks with east west to northeast southwest trending axial planes that appear to be the youngest ductile deformation to have affected the mount isa province