glaciers and rock glaciers distribution at 28 sl dry andes of argentina and some considerations about their hydrological significance the area studied includes a little known portion on the dry andes of the san juan frontal cordillera argentina where the hydrological significance of glaciers and rock glaciers was earlier never studied the surveyed sector includes cerro el potro 5 870 m asl and nearby mountain chains 28 s the predominant landforms in these areas were shaped in a periglacial environment superimposed on an earlier glacial landscape these regions comprise abundant rock glaciers a noteworthy rock glacier zone in the world of which little is known in south america this work employs geomorphological mapping to analyze the distribution of active rock glaciers in relation to altitude aspect and slope using optical remote sensing techniques with gis statistical estimation techniques were used based on a digital elevation model dem and aerial photos and spot images interpretation the specific density of rock glaciers estimation in the surveyed area argentine border is 1 56 with corresponds to 38 rock glaciers with an area of 5 86 km2 and 0 12 km3 of water equivalent furthermore the analytical results show that elevations 4 270 m asl a southeast facing aspect and slope between 2 and 40 favor the existence of rock glaciers finally a comparison with glacier water equivalent which covers an area of 16 km2 and 0 9 km3 of water equivalent shows that glaciers are the main stores of water at 28 s cerro el potro glacier however the importance of rock glaciers as water reserves in this portion of argentina should not be underestimated

origin of peraluminous a type granites from appropriate sources at moderate to low pressures and high temperatures abstract four triassic plutons from south china exhibit compositional features of s type granites high a cnk values enriched sr nd isotopic compositions and high zircon 18o values but also of a type granites alkali rich and ferroan compositions high zr nb ce y contents and high ga al ratios the s type like features suggest a metasedimentary source however the exact anatectic processes are poorly known here phase equilibrium modelling on the melting of five representative metasedimentary rocks with contrasting compositions at 0 4 1 2 gpa and fmq 1 to fmq 1 indicate that the most likely source should have a composition of mg 1 14 k2o na2o 5 two neoproterozoic volcanic sedimentary rocks adjacent to the pags have compositions that match these requirements and modelled melts at p 0 8 gpa and t 850 c match the main compositional variables of the plutons this study highlights that source composition and anatectic p t conditions are the main factors controlling the generation of peraluminous a type granites

constrained 3d modeling of the mesoproterozoic benagerie volcanics australia abstract the benagerie volcanics form part of a hotspot track that affected large sections of eastern australia during the mesoproterozoic understanding the location and controls on eruption centres of the benagerie volcanics and coeval plutons is difficult because they do not outcrop and are known only from limited drillhole data we have applied various combinations of forward and inversion modeling of magnetic and gravity to well constrained petrophysics and drillholes areas to characterize the 3d geometry and extent of the volcanic province and its crustal architecture thereby adding to a better understanding of the emplacement mechanisms involved we interpret the sw limit of the benagerie shear zone corridor to be a major terrane boundary separating relatively magnetic crust to the sw from crust with low magnetic susceptibility to the ne 2d and 3d models show a pronounced thickening of felsic material coincident with the shear zone that may be interpreted as a plutonic root thereby corroborating interpretations that this shear zone acted as a structural conduit for the ascent and emplacement of magma

geochemistry geochronology and tectonic setting of early cretaceous volcanic rocks in the northern segment of the tan lu fault region northeast china abstract we present new geochemical and geochronological data for volcanic and related rocks in the regions of the jia yi and dun mi faults in order to constrain the late mesozoic tectonic evolution of the northern segment of the tan lu fault zircon u pb dating shows that rhyolite and intermediate mafic rocks along the southern part of the jia yi fault formed at 124 and 113 ma respectively whereas the volcanic rocks along the northern parts of the jia yi and dun mi faults formed at 100 ma the rhyolite has an a type granitoid affinity with high alkalis low mgo ti and p contents high rare earth element ree contents and ga al ratios enrichments in large ion lithophile liles e g rb th and u and high field strength element hfses e g nb ta zr and y and marked negative eu anomalies these features indicate that the rhyolites were derived from partial melting of crustal material in an extensional environment the basaltic rocks are enriched in light rees and liles e g rb k th and u and depleted in heavy rees hfses e g nb ta ti and p and sr these geochemical characteristics indicate that these rocks are calc alkaline basalts that formed in an intraplate extensional tectonic setting the dacite is a medium to high k calc alkaline i type granite that was derived from a mixed source involving both crustal and mantle components in a magmatic arc therefore the volcanic rocks along the jia yi and dun mi faults were formed in an extensional regime at 124 100 ma early cretaceous and these faults were extensional strike slip faults at this time

permian rifting related fayalite syenite in the panxi region sw china abstract within the panxi rift of the permian emeishan large igneous province elip sw china a 20 km 2 quartz bearing fayalite syenitic pluton intrudes the 260 ma baima igneous complex bic the fayalite syenite is dated using shrimp zircon u pb techniques at 252 2 5 ma the panxi fayalite syenite is mainly composed of alkali feldspar ferroan augite fayalite quartz and fe ti oxides and contains 61 8 63 7 wt sio 2 5 0 7 3 wt fe 2 o 3 t and 9 9 12 1 wt total alkalis belonging to an a type variety of ferroan alkalic metaluminous granitoids the fayalite syenite displays positive eu anomalies eu eu 0 9 8 9 and is enriched in lree la yb n 6 6 11 5 the nd values and 87 sr 86 sr initial ratios of the fayalite syenite range from 1 3 to 1 9 and from 0 7035 to 0 7068 respectively the fayalite syenite and the bic had the same mantle source however the 8 myr age gap between them suggests the fayalite syenite formed by remelting of underplated mafic magmas injected into the crust during elip magmatism the ages of the fayalite syenite and bic are coincident with two permian mass extinction events and suggest that elip may have influenced both

elemental and sr nd isotope geochemistry of two neoproterozoic mangerite suites in se brazil implications for the origin of the mangerite charnockite granite series abstract neoproterozoic 625 ma mangerites are the dominant rock type in a 100 km long belt of deformed tabular bodies in the socorro guaxupe nappe sgn a high grade terrane southwest of the sao francisco craton southeastern brazil the mangerites form two suites sao pedro de caldas shows a wide compositional variation and abundant felsic rocks mangerite hornblende granite leucogranite initial 87 sr 86 sr of 0 707 and initial e nd of 4 to 5 divinol ndia is dominated by more mafic mangerites with minor charnockite granite and diorite and has initial 87 sr 86 sr of 0 710 and initial e nd of 10 to 12 the probable sources of the sao pedro de caldas mangerites were granulites depleted by previous melting events in radiogenic elements and the light rare earth element primary melts of sao pedro de caldas were generated at 950 c p 10 kbar from a biotite free and k feldspar bearing source with plagioclase as an important residual phase the amount of melting was low as required by low mg enrichment in nb and ta relative to potential sources and high nb ta and was probably controlled by exhaustion of k feldspar in the source contribution from infracrustal mafic melts cannot be ruled out and would help explain the weakly negative e nd and high nb but is not essential the divinol ndia rocks depart from typical within plate mangerites towards more mafic rocks with orogenic signatures e g higher mg sr ca lower zr radiogenic isotope data require sources with greater crustal residence time than those envisioned for sao pedro de caldas elemental data require that these sources were more depleted e g higher k rb granulites with these characteristics are exposed in the northern portion of the sgn these were probably melted at slightly higher temperatures than the sao pedro de caldas suite 970 c before a sufficient amount of melt was generated and the magmas could leave their sources in this case k feldspar was exhausted and plagioclase in amounts exceeding those of the granite minimum was dissolved

carboniferous fault reactivation at the northern margin of the metal rich gawler craton south australia implications for ore deposit exhumation and preservation abstract the formation of major palaeoproterozoic and mesoproterozoic cu au deposits at the metal rich margins of the gawler craton south australia has received a lot of attention however the relationship between metal occurrences the exhumation level of the crust and the structural architecture of the craton margins is less clear here we present results from apatite fission track thermochronology applied to basement rocks at the northern margin of the gawler craton revealing a differential cooling history with respect to the karari shear zone ksz the ksz is a major shear zone that extends to the moho in reflection seismic images and has a prolonged history of high temperature activity during the paleoproterozoic and mesoproterozoic new apatite fission track data show that samples taken to the north of the ksz record a significant pulse of carboniferous cooling in contrast to the phanerozoic monotonic slow cooling history documented for the area just south of the ksz this carboniferous cooling signal coincides with a sedimentary hiatus between the neoproterozoic devonian officer basin and the late carboniferous to early permian arckaringa basin to the north of the ksz therefore carboniferous cooling can be linked with exhumation and fault reactivation of the ksz at that time which is interpreted to be associated with far field compression caused by the alice springs orogeny 450 300 ma of central australia following carboniferous exhumation a localized thermal overprint was observed in locations associated with palaeogene palaeochannels the extent of phanerozoic exhumation shows a spatial relation with the location of au and or cu fe mineralization in the northern gawler craton areas that were significantly modified by mesoproterozoic mineralizing events such as the olympic iocg province and the central gawler gold province record post silurian exhumation histories related to the alice springs orogeny to the west of these two major mineral provinces archaean early palaeoproterozoic terranes in the northwestern gawler craton with abundant au and cu fe mineral occurrences were not affected by phanerozoic exhumation and denudation these relations suggest that the mesoproterozoic mineralized terranes were more susceptible to phanerozoic deformation compared to the archaean palaeoproterozoic terranes within the stronger parts of the gawler craton hence understanding the timing of fault reactivation and the associated relative exhumation level may provide valuable constraints for ore deposit preservation and mineral exploration within the gawler craton

1600 1500 ma hotspot track in eastern australia implications for mesoproterozoic continental reconstructions mesoproterozoic a type magmatic rocks in the gawler craton curnamona province and eastern mount isa inlier form a palaeo curvilinear belt for reconstructed plate orientations the oldest igneous rocks in the gawler craton are the hiltaba granite suite c 1600 1575 ma the youngest in the mount isa inlier are the williams naraku batholiths c 1545 1500 ma the belt is interpreted as a segment of a hotspot track that evolved between c 1600 and 1500 ma this hotspot track may define a quasilinear part of australia s motion between 1636 and 1500 ma and suggests that australia drifted to high latitudes an implication of this interpretation is that australia and laurentia may not have been fellow travellers leading to the formation of rodinia a hotspot model for a type magmatism in australia differs from geodynamic models for this style of magmatism on other continents this suggests that multiple geologic processes may be responsible for the genesis of proterozoic a type magmas

extreme effusive eruptions palaeoflow data on an extensive felsic lava in the mesoproterozoic gawler range volcanics the gawler range volcanics are the eroded remnants of a mesoproterozoic dominantly felsic large igneous province the eucarro rhyolite is one of three voluminous 675 km3 units in the upper part of the succession eight stratigraphic sections through the eucarro rhyolite were sampled for anisotropy of magnetic susceptibility ams and petrofabric analysis in order to determine the source location the ams foliations kmax kint plane consistently strike northwest and most dip steeply at sites in the western and central parts of the unit there is a change from steep southwesterly dips near the base to vertical or northeasterly dips in the middle and near the top in the same area kmax axes plunge to the south or southwest in the lower parts and to the north in upper parts of the unit at sites in the eastern part of the unit the pattern is reversed ams foliations dip northerly near the base and southerly near the top and kmax axes plunge northerly near the base and southerly near the top such up section reversals in dip or plunge directions of ams parameters resemble the patterns shown by other lavas a dominance of very steep dips and an up section reversal in dip direction are also expected for flow bands in felsic lavas furthermore the ams pattern implies a northeasterly flow direction for the western and central parts of the unit and a southerly flow direction for the eastern part the opposing flow directions may indicate that the western and central parts of the unit versus the eastern part belong to different flow lobes or that they came from separate sources lineations defined by preferred alignment of elongate phenocryst intersections on gently dipping surfaces show a less consistent pattern and alone could not be used to define palaeoflow directions this study confirms the existence of felsic lavas that have dimensions comparable with the largest known mafic lavas

1 8 1 5 ga links between the north and south australian cratons and the early middle proterozoic configuration of australia abstract the archaean and early middle proterozoic 1 8 1 5 ga terranes of the north australian craton and the south australian craton are separated by 400 km of ca 1 33 1 10 ga orogenic belts and phanerozoic sediments however there is a diverse range of geological phenomena that correlate between the component terranes of the two cratons and provide evidence for a shared tectonic evolution between approximately 1 8 and 1 5 ga in order to honour these correlations we propose a reconstruction in which the south australian craton is rotated 52 counterclockwise about a pole located at 136 e and 25 s present day coordinates relative to its current position this reconstruction aligns the ca 1 8 1 6 ga orogenic belts preserved in the arunta inlier and the gawler craton and the ca 1 6 1 5 ga orogenic belts preserved in the mount isa block and the curnamona province before 1 5 ga the south australian craton was not a separate entity but part of a greater proto australian continent which was characterised by accretion along a southward migrating convergent margin ca 1 8 1 6 ga followed by convergence along the eastern margin ca 1 6 1 5 ga after 1 5 ga the south australian craton broke away from the north australian craton only to be reattached in its current position during the ca 1 33 1 10 ga albany fraser and musgrave orogenies

40ar 39ar thermochronology of the southern gawler craton australia implications for mesoproterozoic and neoproterozoic tectonics of east gondwana and rodinia 40ar 39ar thermochronology of the southern gawler craton australia reveals a protracted history of slow cooling with local crustal heating rapid cooling and fault reactivation between 1700 and 700 ma hornblendes from most of the southern part of the craton including the kalinjala mylonite zone yield ages 1580 1610 ma with younger more discordant samples showing evidence of retrogression these results indicate that the region cooled below 500 c 100 m y after the kimban orogeny and coincident with the gawler range hiltaba suite magmatism to the north perhaps associated with postorogenic extension biotite and k feldspar data indicate that regional cooling after this time was more gradual with a few exceptions locally in the southeastern eyre peninsula rapid cooling at 1425 ma is indicated by nearly concordant hornblende and biotite ages and may record a phase of regional extension other exceptions include areas of lower grade archean rocks that cooled to 350 c by 1700 1640 ma greenschist facies reactivation of shear zones occurred at 1100 ma during the musgravian orogeny on the basis of biotite single grain data and retrogressed amphiboles k feldspar age spectra record cooling at 700 800 ma following regional intrusion of the gairdner dike swarm and or denudation during rifting along the pacific margin of east gondwana and breakup of rodinia tectonothermal events revealed by these results previous geochronological and geological studies and available paleomagnetic data are comparable to other cratons and mobile belts in australia east gondwana and laurentia providing evidence that southeastern australia and north america were adjacent during much of proterozoic time

an analysis of the ground penetrating radar direct ground wave method for soil water content measurement the spatial variability of soil water content can be measured with the ground wave velocity of ground penetrating radar gpr using short antenna offsets but picking the correct ground wave arrival time is rather difficult in applying the gpr ground wave method to soil water content estimation it is also important to know the effective sampling depth of the method uniform drainage experiments were conducted with 100 and 450 mhz gpr antennas using 1 0a nd 2 0 m fixed antenna separations on a sandy loam soil to investigate time zero picking methodologies and to estimate the sampling depth of the gpr method the gpr water content data were compared with time domain reflectometry tdr measured data using six vertical tdr probes of different lengths time zero was calculated from an air calibration at a 2 0 m antenna separation and from wide angle reflection and refraction data and a difference was found between the two time zero calibration methods a method was analysed to determine the arrival time of the leading edge of the direct ground wavelet using the arrival time of the peak amplitude since the arrival time of the leading edge of the ground wave can be difficult to pick regression analysis showed that the gpr 100 mhz measured water content was not different from the water content measured with tdr at 0 0 1 m depth implying that this may be a reasonable estimate of the gpr ground wave method s sampling depth a similar analysis based on the differences between the 0 0 2 m tdr and the gpr shows that the effective sampling depth of the direct ground wave of the 450 mhz data is less than the sampling depth of the 100 mhz data copyright 2003 john wiley sons ltd

petrology and microstructure of distal impact ejecta from the flinders ranges australia abstract the acraman impact ejecta from bunyeroo gorge in the central flinders ranges consist of clast bearing and sandy sublayers set in a shale host rock a calculated transient crater diameter for the acraman impact of at least 34 km was obtained fiom average thicknesses and estimated distances of the ejecta fiom the impact in the gawler ranges the ejecta contain numerous grains of quartz and zircon that display impact produced features including one or more sets of decorated planar deformation features there is also much unshocked material incorporated in the ejecta layer the coarse grained ejecta layer embedded within fine grained sediments allowed easy passage for diagenetic fluids that produced a porous honeycomb structure in the clays and enhanced the content of elements such as cu pb zn and u the clay fraction of the ejecta layers consists of vermiculite and kaolinite probably formed ffom alteration and weathering of glassy components it appears that quartz and zircon grains are the only remnants unaltered by diagenetic processes

exploring the interplay between infiltration dynamics and critical zone structures with multiscale geophysical imaging a review abstract infiltration is the process of water entering into and routings through the subsurface it has a profound impact on water flux in the earth s critical zone cz influencing phenomena such as overland flow stream generation plant available water and groundwater recharge as well as the associated cz processes and functions of weathering erosion slope stability and food production however reliable measurement of infiltration in structured geomedia soils and regolith with hidden subsurface features remain challenging the increasing availability of geophysical techniques has helped them emerge as viable options for minimally invasive determination of infiltration at the pedon to hillslope or catchment scales geophysical methods replace the educated guesswork of interpreting field data from traditional infiltrometers with direct visualization and quantification this paper provides a comprehensive literature review of various applications of geophysical techniques used to 1 visualize infiltration relevant structures 2 monitor non uniform or preferential infiltration patterns and 3 map soil moisture distribution after infiltration it then proposes a new conceptualization form and function dualism for subsurface hydrology to link preferential infiltration to cz structures with the goal of formulating more realistic infiltration theories related to subsurface structural heterogeneity the characterization of both subsurface structures form and infiltration dynamics function via geophysical imaging should help infiltration models currently emphasizing macroscale behaviors rooted in the continuum concept expand to accommodate the microscale nature of preferential flow integrating multiple geophysical approaches and developments into the new generation of geophysical techniques will further enhance our ability to see into the fabric of the subsurface and capture the dynamics of non uniform infiltration through the hidden half of the cz this approach offers exciting opportunities for understanding the complex interactions between cz structures and cz processes

soil moisture content estimation using ground penetrating radar reflection data abstract ground penetrating radar gpr reflection travel time data were used to estimate changes in soil water content under a range of soil saturation conditions throughout the growing season at a california winery data were collected during three data acquisition campaigns over an 80 by 180 m area using 100 mhz surface gpr antennas gpr reflections were associated with a thin low permeability clay layer located 0 8 1 3 m below the ground surface that was identified from borehole information and mapped across the study area field infiltration tests and neutron probe logs suggest that the thin clay layer inhibited vertical water flow and was coincident with high volumetric water content vwc values the gpr reflection two way travel time and the depth of the reflector at the borehole locations were used to calculate an average dielectric constant for soils above the reflector a site specific relationship between the dielectric constant and vwc was then used to estimate the depth averaged vwc of the soils above the reflector compared to average vwc measurements from calibrated neutron probe logs over the same depth interval the average vwc estimates obtained from gpr reflections had an rms error of 0 018 m3 m 3 these results suggested that the two way travel time to a gpr reflection associated with a geological surface could be used under natural conditions to obtain estimates of average water content when borehole control is available and the reflection strength is sufficient the gpr reflection method therefore has potential for monitoring soil water content over large areas and under variable hydrological conditions

neodymium isotopic constraints for the origin of mesoproterozoic felsic magmatism gawler craton south australia mesoproterozoic felsic magmatism of the gawler range volcanics and hiltaba suite granites occurred at 1585 1595 ma across much of the gawler craton south australia nd isotopic analysis of this felsic magmatism combined with petrological and geochemical arguments suggest derivation by partial melting of both paleoproterozoic and archean crust the majority of samples analyzed have nd isotopic and geochemical characteristics compatible with the involvement of paleoproterozoic crust stabilized during the 1 85 1 71 ga kimban orogeny as sources for the mesoproterozoic magmatism others require derivation from sources dominated by archean rocks this cycle of paleoproterozoic crustal stabilization followed by involvement of this crust mesoproterozoic felsic magmatism is one previously documented from many parts of mesoproterozoic laurentia on the basis of models proposing east australia antarctica to be the conjugate landmass at the rifted margin of western north america it appears that the voluminous mag

geochemistry and paleotectonic setting of felsic volcanic rocks in the finlayson lake volcanic hosted massive sulfide district yukon canada the finlayson lake volcanic hosted massive sulfide vhms district represents one of canada s most recent vhms discovery regions with 34 million metric tons mt of massive sulfide mineralization found since the mid 1990s felsic volcanic rocks are associated with three units the fire lake unit the kudz ze kayah unit and the wolverine succession significant accumulations of polymetallic felsic vhms deposits kudz ze kayah gp4f and wolverine have only been discovered in the kudz ze kayah unit and wolverine succession to date in the hanging wall of the money creek thrust felsic volcanic and high level intrusive rocks in the fire lake unit have calc alkalic and tholeiitic affinities with low high field strength element hfse contents and intermediate zr sc 9 4 43 4 and zr tio2 254 864 ratios these rocks are interlayered with mafic rocks with arc geochemical signatures to date devoid of significant vhms mineralization and represent bimodal magmatism within an evolving devonian mississippian continental arc system the kudz ze kayah unit in the footwall of the money creek thrust stratigraphically overlies the fire lake unit and consists of felsic volcanic rocks with high hfse contents within plate a type signatures and high zr sc 15 3 190 3 and zr tio2 630 2 185 ratios the kudz ze kayah unit felsic rocks are crosscut and overlain by alkalic mafic rocks are associated with abundant carbonaceous sedimentary rocks and represent magmatism within a devonian mississippian ensialic back arc rift basin environment the wolverine succession unconformably overlies the kudz ze kayah unit felsic rocks below the wolverine deposit have geochemical attributes similar to the kudz ze kayah unit with high hfse contents within plate a type signatures and high zr sc 29 9 84 2 and zr tio2 391 1 220 ratios in contrast aphyric rhyolite flows in the hanging wall of the deposit have much lower hfse contents and the lowest zr sc 3 5 27 7 and zr tio2 181 591 ratios in the district all the felsic rocks of the wolverine succession are interlayered with abundant carbonaceous sedimentary rocks and are overlain by midocean ridge basalt morb like basaltic rocks the wolverine succession is interpreted to have formed within an early mississippian ensialic back arc basin environment that eventually evolved to sea floor spreading the variation in the hfse budgets of the felsic rocks of the finlayson lake district likely reflects variations in the source and or temperature of crustal melting in particular felsic rocks of the fire lake unit have higher nb ta and lower ti sc ratios than other volcanic rocks in the district suggesting possible derivation from mafic crustal sources and or lower crustal fusion temperatures the kudz ze kayah unit and footwall rocks to the wolverine deposit are inferred to have formed from high temperature partial melting of continental crust the hanging wall aphyric rhyolites from the wolverine deposit may have formed from either lower temperature continental crustal melting or may have been derived from the mixing of hfse depleted n morb mafic magmas and evolved continental crust polymetallic felsic volcanic associated vhms deposits within the finlayson lake district are preferentially associated with hfse enriched felsic rocks with high zr sc 15 3 190 3 and zr tio2 391 2 105 ratios the hfse and rare earth element ree systematics of vhms associated felsic rocks of the finlayson lake district are different from prospective felsic rocks from archean vhms environments in the superior province and are displaced toward higher zr y and la ybn ratios their hfse and ree systematics are similar to many phanerozoic vhms environments in particular those at least partially to fully underlain by evolved continental crust the geochemical differences between the felsic rocks of the finlayson lake district and those from archean vhms environments most likely reflect differences in the substrates from which the felsic rocks were derived e g evolved versus juvenile

geochemistry and geodynamic implications of the mesoproterozoic english bay granite rhyolite complex northwestern ontario the mesoproterozoic english bay complex consists of a granite rhyolite assemblage outcropping on the shores of lake nipigon in western superior province canada it intrudes neoarchean rocks and is disconformably overlain by a rift infracratonic basin sedimentary succession recording subsidence following a heating event the granites and rhyolites are characterized by light rare earth element lree enrichment la smn 2 8 5 1 and only weakly fractionated heavy ree hree gd ybn 1 1 1 6 the felsic igneous rocks are high k enriched in zr nb y and ree satisfying all the criteria for an a type suite trace element geochemistry particularly the absence of any negative nb anomalies indicates this melt did not originate in a suprasubduction zone setting unlike the st francois mountain complex to the south the english bay complex may record the northern portion of a mesoproterozoic plume track a plume that possibly led to earlier igneous activity and infracratonic basin formation to the north and would later interact with a suprasubduction zone margin to the south

evolution and architecture of a large felsic igneous province in western laurentia the 1 6 ga gawler range volcanics south australia the gawler range volcanics grv of south australia are an intracontinental subaerial large igneous province lip formed during supercontinent assembly in the mesoproterozoic like many lips the grv are intraplate were erupted over a geologically short time 2 million years and are dominated by voluminous lavas however the grv are overwhelmingly dominated by felsic units the grv are essentially undeformed and have not been deeply buried so that their original textures are exceptionally well preserved furthermore they are well exposed in very gently northward and eastward dipping sections up to 4 km thick allowing assessment of the facies architecture and evolution of this felsic volcanic lip the evolution of the grv can be clearly separated into two main stages initial eruptions at numerous volcanic centres produced small to moderate volume geochemically distinct felsic lavas and lava domes together with ignimbrites and minor mafic and intermediate lavas forming a sequence 0 5 to 3 km thick volcanic activity in this lower sequence varied from effusive to explosive and was not much different in style or products from phanerozoic felsic volcanic provinces however the second stage produced at least three voluminous felsic units each of which represents about 1000 3000 km3 of magma moreover the dominance of evenly porphyritic textures and lack of pyroclastic textures pumice shards broken crystal lithic clasts in these units suggests that they were erupted effusively and flowed as lavas each of these felsic lavas are generally dominated by a single uniform composition and commonly mingled with a subordinate and compositionally distinct lava

yardea dacite large volume high temperature felsic volcanism from the middle proterozoic of south australia the yardea dacite is a large volume felsic volcanic unit from the middle proterozoic gawler range volcanics of south australia it has been previously described as an ignimbrite however some samples contain no petrographic evidence for a pyroclastic origin but have characteristics compatible with final crystallization from a nonfragmented magma these samples may have erupted as lavas but others are likely to be extremely densely welded ignimbrites suggesting a compound nature for the unit geothermometry and phase equilibria indicate that the yardea dacite originated from a high temperature 1000 c felsic magma with a low water content 2 the yardea dacite is not associated with a known caldera of the valles type and shares many characteristics of recently described cenozoic felsic volcanic rocks from the western united states interpreted as rheoignimbrites or as unusually extensive lavas

sources of mineralising fluids for the olympic dam deposit south australia smnd isotopic constraints abstract the olympic dam cu u au ag deposit south australia is hosted by the olympic dam breccia complex a high level hematite rich hydrothermal breccia system the deposit is characterised by extreme enrichments of ree which are a product of the ore forming process therefore making the sm nd isotopic system an ideal tool for clarifying the complex relationships between the different ore and breccia types pyrite chalcopyrite and bornite chalcocite rich hematitic ores share an initial end signature of 2 5 which suggests that these ore types are cogenetic these ores together with sulphide poor hematitic breccias yield a 14 point sm nd isochron age of 1572 99 ma the host roxby downs granite has an initial nd of 5 and therefore cannot alone have been the source of the mineralising fluids for the hematitic ores in contrast to hematitic rocks volumetrically minor magnetite rich assemblages have the same initial nd signature as the host granite suggesting that they are cogenetic assuming that both hematite and magnetite were precipitated from solution their contrasting isotopic signatures require that ore deposition involved two distinct fluids the isotopic data do not allow the distinction between a model involving concurrent activity of such fluids in a mixing regime and a model involving temporally separate overprinting of magnetite by hematite cu sulphides the ore signature of nd 2 5 cannot have been derived solely from pre existing crustal rocks of the gawler craton it must have involved a contribution from a mantle derived source rock or magma the most likely source of this nd component are the mantle derived rocks produced during the gawler range volcanics event e g altered alkaline mafic ultramafic dykes within the deposit which have initial isotopic signatures as high as nd 4 assuming end member compositions equivalent to these dykes and the roxby downs granite the ore signature implies that 30 of the nd in the ores was derived from the mafic ultramafic source if nd was leached from source rocks rather than derived from magmatic volatiles the inferred rock fractions contributing ree to the deposit are 13 mafic ultramafic rocks and 87 roxby downs granite or its volcanic equivalent massbalance calculations indicate that 13 rock fraction of mafic ultramafics can account for 50 of the cu contained in the deposit the involvement of mafic ultramafic rocks is therefore inferred to have been crucial to the genesis of the cu enriched ores at olympic dam

petrology and u pb geochronology of footwall porphyritic rhyolites from the wolverine volcanogenic massive sulfide deposit yukon canada implications for the genesis of massive sulfide deposits in continental margin environments porphyritic rhyolite sills form an important component of the footwall of the wolverine volcanogenic massive sulfide vms deposit yukon canada and occur proximal to mineralization in the immediate deposit area wolverine lynx zone and at similar stratigraphic levels along strike fisher puck and sable zones porphyritic rhyolites are of two types an older quartz feldspar porphyritic qfp rhyolite suite and a younger feldspar porphyritic fp suite both the qfp and fp suites of intrusions are semiconcordant suggesting a silllike morphology and are altered and crosscut by veinlet mineralization suggesting that they are pre to synmineralization the margins of qfp suite of intrusions contain minor xenoliths of surrounding shales and poorly developed chilled margins suggesting emplacement into partially consolidated sedimentary rocks whereas the fp suite of intrusions shows well developed chilled margins indicative of emplacement into fully solidified sedimentary rock these features suggest that the qfp suite of intrusions represents an older phase of rhyolitic magmatism whereas the fp suite represents a younger event this is supported by u pb zircon ages which indicate a 352 4 1 5 ma emplacement age for the fp suite and a 347 to 346 ma emplacement for the fp suite two ages at 347 8 1 3 and 346 0 2 2 ma both suites of porphyries have inherited proterozoic zircon and have ratios of la smucn 1 and nb thucn 1 ucn upper continental crust normalized indicating derivation from and or extensive interaction with ancient upper continental crustal materials the fp suite however has elevated high field strength element hfse and rare earth element ree contents high zircon saturation temperatures and higher nb ta ratios and lower ti sc ratios than the qfp suite these features are interpreted to reflect that the fp suite of magmas was hotter 900 c melts with a greater mantle component in their genesis both suites however are interpreted to have formed due to basaltic upwelling crustal melting and crust mantle mixing during ensialic back arc basin activity the presence of mantle heat within the wolverine basin from 352 to 347 to 346 ma a minimum of 5 m y suggests that sustained mantle heat flow was critical to the genesis of the wolverine porphyries it is also suggested that this sustained mantle heat was responsible for the wolverine hydrothermal system and that upwelling mantle may be essential in providing the heat to drive hydrothermal systems even in continental margin type vms environments e g bathurst iberian pyrite belt the wolverine porphyries are among the most hfse and ree enriched felsic rocks associated with vms mineralization globally the high hfse and ree concentrations in these rocks are interpreted to be due to

zircons from the acraman impact melt rock south australia shock metamorphism u pb and 40ar 39ar systematics and implications for the isotopic dating of impact events abstract this study presents the first optical and scanning electron microscopic characterization and u pb shrimp dating results for zircon grains separated from the most likely autochthonous impact melt rock in the central domain of the large 40 90 km eroded ediacaran acraman impact structure in south australia microtextural characteristics define five zircon subtypes corresponding to different levels of progressive shock metamorphism from virtually unshocked monocrystalline zircon grains that exhibit original magmatic zoning in cathodoluminescence images to fully granular zircons that have completely lost their primary zoning pattern and locally contain neocrystallized submicrometer sized spots of zro 2 probably baddeleyite that pseudomorph pre impact zircon the granular zircons correspond to the highest observed level of shock metamorphism and impact induced recrystallization zro 2 bearing granular zircons indicate shock pressures in excess of 65 70 gpa which are considerably higher than previous shock pressure estimates for the acraman impactites u pb systematics of untreated and chemically abraded melt rock zircons indicate that u pb ratios of the acraman zircons were variably reset during impact weakly shocked crystalline grains yield ages on concordia at 1 59 1 60 ga reflecting the magmatic age of the gawler range volcanics only the entirely granular zircon population was apparently impact reset but based on an ediacaran age from stratigraphic constraints on the ejecta layer experienced significant post impact pb loss the microcrystalline nature of granular zircons could have promoted pb diffusion and recoil in post impact time as suggested by grain size dependent diffusion and recoil modeling a positive correlation of u concentration and shock level suggests that granularization might have preferentially occurred in initially u rich probably metamict zircons 40 ar 39 ar dating of a melted yardea dacite clast from the acraman melt rock as well as k feldspar separated from shocked yardea dacite resulted in post impact alteration plateau ages suggestive of hydrothermal events at 500 ma and 450 ma that selectively affected the impactites exposed in the central domain of the acraman impact structure our study demonstrates that the acraman impact is particularly difficult to date in the absence of accurate and precise isotopic ages for acraman the ediacaran ejecta stratigraphic age of 635 541 ma is considered the most reliable age constraint currently available for the timing of the large acraman impact

partially melted lithic megablocks in the yardea dacite gawler range volcanics australia implications for eruption and emplacement mechanisms lithic megablocks ranging from 200 m felsic volcanic unit in the mesoproterozoic gawler range volcanic province grv of south australia throughout its vast extent the yardea dacite shows typical lava like features in that it is massive columnar jointed and evenly porphyritic with 30 40 crystals in a spherulitic and granophyric groundmass in addition flow banding is present at many locations the megablocks are abundant at two sites 50 km apart but isolated megablocks and smaller 6 cm lithic clasts are also scattered throughout the unit at both sites the megablocks are matrix supported non graded randomly oriented and show no evidence of being confined to a particular stratigraphic level in the dacite the most abundant and largest megablocks are granitoids derived from older basement and from early crystallised plutons of the hiltaba suite which is broadly coeval and comagmatic with the grv the granitoid megablocks have been partially melted most likely prior to eruption when resident in the thermal aureole of the yardea dacite magma chamber the lithic megablock occurrences are unlike coarse pyroclastic breccias but are similar in distribution and abundance to xenoliths in lavas consistent with the lava like character of the host dacite using reasonable estimates of megablock density magma density and magma viscosity we show that the rise rate of the dacitic magma exceeded the settling velocity of the megablocks implying that they could have been entrained and erupted effusively all but the largest and least melted megablocks would have remained suspended or else settled very slowly in the dacitic lava during outflow the rapid rate of magma withdrawal required to produce such an extensive felsic sheet could have also triggered disintegration of the thermally stressed wallrock surrounding the magma chamber dislodging megablocks that were later entrained and effusively erupted

distinguishing strongly rheomorphic tuffs from extensive silicic lavas high temperature silicic volcanic rocks including strongly rheomorphic tuffs and extensive silicic lavas have recently been recognized to be abundant in the geologic record however their mechanisms of eruption and emplacement are still controversial and traditional criteria used to distinguish conventional ash flow tuffs from silicic lavas largely fail to distinguish the high temperature versions we suggest the following criteria ordered in decreasing ease of identification to distinguish strongly rheomorphic tuffs from extensive silicic lavas 1 the character of basal deposits 2 the nature of distal parts of flows 3 the relationship of units to pre existing topography and 4 the type of source as a result of quenching against the ground basal deposits best preserve primary features can be observed in single outcrops and do not require knowing the full extent of a unit lavas commonly develop basal breccias composed of a variety of textural types of the flow in a finer clastic matrix such deposits are unique to lavas because the chilled base of an ashflow tuff generally does not participate in secondary flow primary pyroclastic features are best preserved there massive flow banded bases are more consistent with a lava than a pyroclastic origin lavas are thick to their margins and have steep abrupt flow fronts ashflow tuffs thin to no more than a few meters at their distal ends where they generally do not show any secondary flow features lavas are stopped by topographic barriers unless the flow is much thicker than the barrier ash flow tuffs moving at even relatively slow velocities can climb over barriers much higher than the resulting deposit lavas dominantly erupt from fissures and maintain fairly uniform thicknesses throughout their extents tuffs commonly erupt from calderas where they can pond to thicknesses many times those of their outflow deposits these criteria may also prove effective in distinguishing extensive silicic lavas from a postulated rock type termed lava like ignimbrite the latter have characteristics of lavas except for great areal extents up to many tens of kilometers these rocks have been interpreted as ash flow tuffs that formed from low boiling over eruption columns based almost entirely on their great extents and the belief that silicic lavas could not flow such distances however we interpret the best known examples of lava like ignimbrites to be lavas this interpretation should be tested through additional documentation of their characteristics and research on the boiling over eruption mechanism and the kinds of deposits it can produce flow bands flow folds ramps elongate vesicles and probably upper breccias occur in both lavas and strongly rheomorphic tuffs and are therefore not diagnostic pumice and shards also occur in both tuffs and lavas although they occur throughout ash flow tuffs and generally only in marginal breccias of lavas dense welding secondary flow and intense alteration accompanying crystallization at high temperature commonly obliterate primary textures in both thick rheomorphic tuffs and thick lavas high temperature silicic volcanic rocks are dominantly associated with tholeiitic flood basalts extensive silicic lavas could be appropriately termed flood rhyolites

volcanism of the palaeoproterozoic bushveld large igneous province the rooiberg group kaapvaal craton south africa abstract the volcanic rocks of the rooiberg group represent the uppermost unit in the palaeoproterozoic transvaal supergroup and form one of the largest provinces of silicic volcanic rocks in the world although stratigraphically associated with the transvaal basin fill the rooiberg group is petrogenetically linked with the larger bushveld magmatic event for which emplacement was preceded by the extrusion of the vast rooiberg lava flows in the northern part of the kaapvaal craton like many silicic dominated large igneous provinces lips which are increasingly recognised in the rock record the rooiberg group volcanics are intracontinental subaerial and are dominated by voluminous lava flows originally the rooiberg group is inferred to have covered an area of more than 200 000 km2 of which after erosion an area of 50 000 67 000 km2 remains the lava flows form a stratigraphic succession up to 6 km thick and are divided into four formations in ascending order dullstroom damwal kwaggasnek and schrikkloof due to a scarcity of reliable geochronological data the temporal span of the rooiberg group is poorly understood the rooiberg group consists of basaltic to rhyolitic lava erupted from fissural volcanism with estimated eruption temperatures of the rhyolitic lavas exceeding 1000 c minor explosive eruptions are represented by pyroclastic rocks and subordinate sedimentary interbeds originated from sandy fluvial and lacustrine processes the rocks are essentially undeformed and have not been buried so that their original textures are well preserved the bushveld complex and the associated rooiberg group lava flows are proposed to have formed as a result of partial melting of subcontinental lithosphere and lower crust by a mantle plume this thorough review of the geochronology physical volcanology and geochemistry of the rooiberg group enables construction of a geodynamic model

nd isotope and petrogenetic constraints for the origin of the mount angelay igneous complex implications for the origin of intrusions in the cloncurry district ne australia abstract the mesoproterozoic mount angelay igneous complex contained intrusions that were emplaced into amphibolite facies metasedimentary rocks during two periods of 1550 and post 1540 ma magmatism sm nd isotopic analysis together with mineralogical and chemical considerations suggest that the intrusions were produced from a paleoproterozoic crustal source with a t 2 model age 2200 ma on geochemical and petrological grounds the 1550 ma trondhjemitic intrusions are interpreted to have been produced by melting of amphibolite under garnet stable conditions 8 10 kbar the late syn to post peak metamorphic timing of these intrusions suggested that they were associated with the tectono thermal event that produced regional peak metamorphic mineral assemblages the post 1540 ma intrusions are k rich and consist of two groups of synchronously emplaced intrusions 1 a high k monzodiorite and monzogranite suite that range between 51 and 77 wt sio 2 and 2 a high k na enriched hornblende monzonite the chemistry and mineralogy of these intrusions suggested that they were derived via plagioclase stable and garnet unstable melting 2 o p 2 o 5 cr v and zn compared with slightly younger high k monzonite which is interpreted to have formed via one of two mechanisms 1 melting of a low k amphibole and plagioclase rich source or 2 melting of residual material that produces a potassic and incompatible element rich melt these magmas likely contained mantle derived material particularly the k rich intrusions of mafic composition the heat required for the production of post 1540 ma intrusions appears to have been generated by the intrusion of high t mantle derived mafic material into the crust 25 30 km 8 10 kbar this model is consistent with the synchronous emplacement of mafic and felsic magma and the lack of a consanguineous regional metamorphic association and suggests high t high degree partial melting in localised pockets within fertile source regions in the crust an increase in sm nd model source age and decrease in end with increasing sio 2 in the k rich intrusions suggests the incorporation of juvenile material in the more mafic rocks the origin of this component is unknown but it may represent either the incorporation of mantle derived material during melting or the partial melting of crust with a younger mafic component on a district scale the 30 million year period over which the k rich post 1540 ma intrusions were emplaced suggested that mantle derived material continued to be injected into the crust a mantle component to these rocks and the global distribution of proterozoic intrusions with similar geochemical affinities strongly suggests a world wide period of mantle induced crustal melting at that time the dominant paleoproterozoic isotopic composition of most of these intrusions suggests melting of similarly composed and matured source rocks

evolution and emplacement of high fluorine rhyolites in the mesoproterozoic gawler silicic large igneous province south australia the gawler range volcanics grv and the hiltaba suite hs of south australia form a silicic dominated large igneous province the gawler slip emplaced in an intracontinental setting during the mesoproterozoic emplacement of the grv lasted for a short period of time 2 ma and can be separated into two main phases the first phase lower grv is composed of thick 3 km sequences erupted from distinct centres and includes small to moderate volume up to 150 km3 felsic lavas ignimbrites and minor mafic and intermediate lavas the upper grv include extensive felsic lavas that are up to 1000 of km3 in volume and 200 km across using well preserved quartz hosted melt inclusions we investigated the composition of the lower grv including major trace and volatile elements the results indicate high concentrations of k2o 7 8 wt rare earth and high field strength elements and low concentrations of ca mg ni cr sr and ba in comparison with felsic continental crust overall melt inclusion compositions match whole rock geochemical characteristics we demonstrate that the grv magma was f rich 1 3 wt and had high temperature for a silicic magma high f concentrations and high temperature would have resulted in lower than usual polymerisation of the melt and relatively low viscosity these characteristics help explain how very voluminous felsic magma was erupted effusively and emplaced as lavas other intracontinental slip contain extensive felsic lavas and ignimbrites which appear to share similar geochemical characteristics we also show that selective alteration caused depletion of whole rock compositions in some trace elements namely pb u and sn

mesoproterozoic trans laurentian magmatism a synthesis of continent wide age distributions new sims u pb ages zircon saturation temperatures and hf and nd isotopic compositions abstract the origin and tectonic setting of the mesoproterozoic 1 50 1 34 ga granite rhyolite provinces of the midcontinent region of the united states and the coeval a type granite plutons of the southwestern united states have been an enigma for decades in this paper we review the history of this problem examine the significance of a wealth of previously published u pb zircon and whole rock sm nd data and present new u pb zircon age and lu hf isotopic data from selected zircon samples our data show that the initiation of this magmatism spans the interval 1 50 1 40 ga across the continent but there is a general younging westward younger 1 39 1 34 ga magmatism also occurred across the continent but forms a major magmatic event only in the south central mid continent there is generally a good correlation between sm nd and lu hf isotopic compositions and inferred mantle derivation model ages except possibly in southeastern oklahoma the absence of older cores in zircons is compatible with calculated zircon saturation temperatures of ca 850 c and supports mantle driven basaltic underplating and resulting crustal partial melting as a petrogenetic model for the a type magmatism our new data compilation refines the existence of the nd line that extends from southwestern texas into southeastern michigan and the western grenville province in canada it marks an isotopic boundary between granites and rhyolites of cratonal origin to the northwest 1 8 1 6 ga model ages and those of more juvenile origin to the southeast 1 5 1 4 ga model ages our suggested tectonic model for the mesoproterozoic a type magmatism across eastern and southern laurentia involves the development of an active laurentian margin extending from eastern canada across what is now the midcontinent region of the united states and at least into the current southwestern united states magmatism along this margin was likely related to asthenosphere lithosphere interactions associated with the accretion of outboard arcs and possible exotic terranes that caused complex deformational and magmatic responses in the continental interior this activity evidently spread from northeast to southwest over a period of ca 70 million years the occurrence of the younger ca 1 39 1 34 ga event indicates that similar processes occurred some 130 million years later suggesting a long lived convergent plate margin and recurring basaltic underplating in some locations perhaps due to inboard lithospheric delamination and or mantle upwelling

fluorine and chlorine behaviour during progressive dehydration melting consequences for granite geochemistry and metallogeny dehydration melting of biotite is the main control on crustal differentiation in the mid to lower continental crust because this reaction produces the most voluminous and most mobile granitic melts biotite breaks down over a broad temperature interval so the partitioning behaviour of elements between biotite and melt is likely to vary it has been hypothesized that fluorine may stabilize biotite to higher melting temperatures because biotite is typically f rich in ultra high temperature uht metamorphic rocks if true f would be an important influence on crustal differentiation because not only would it broaden the temperature range of melting but also elevated f concentration decreases melt viscosity furthermore ligand partitioning between biotite and melt may be an important influence on the metallogeny of magmas this study used electron microprobe analysis of biotite in rocks from the ballachulish and rogaland metamorphic aureoles to investigate the concentration of f and cl in biotite heated to 600 1 000 c results show a broad increase in biotite f content up to 5 04 f with temperature until 850 920 c beyond which f content decreases 2 5 f chlorine concentrations in biotite are consistently lower 1 cl and show a progressive decrease after the onset of partial melting it was found that mg content and the processes that control mg distribution are most strongly correlated with f and cl concentration in biotite calculations based on these results indicate that f enriched biotite could be a significant source of f for continental crust derived melts generation of a hot f rich melt at uht conditions could be important for transporting lower crustal metals to the upper crust

petrogenesis of the dengzhazi a type pluton from the taihang yanshan mesozoic orogenic belts north china craton abstract the voluminous mesozoic monzonitic to monzogranitic rocks in the north china craton ncc mostly show high k calc alkaline and i type granitoids features the dengzhazi granitic pluton however shows features typical of a type granites the a type pluton was emplaced in the taihang yanshan orogenic belts of the northern margin of the ncc with zircon u pb ages of around 140 ma the dengzhazi a type granites are characterized by high sio 2 70 2 77 7 wt k 2 o na 2 o zr nb ga zn and y contents as well as high ga al ratios and extremely low cao ba sr in addition they show high zircon saturation temperatures 870 950 c low water and low oxygen fugacity all these features are consistent with the a type affinity of the pluton in situ hf isotopic analyses for the dated zircons show relatively small range of e hf t 13 to 17 they also have homogeneous initial nd isotopic compositions with e nd t ranging from 15 1 to 16 3 the hf and nd isotopic data suggest that the dengzhazi a type granites originated from a homogeneous crustal source probably the archean mafic intermediate granulites taking into account the high temperatures the low h 2 o and f o 2 of the magma system we believe that partial melting of the granulites should have been triggered by underplating of mantle derived magmas at the base of the mafic lower crust in an extensional regime the dengzhazi a type granite is the oldest pluton of the taihang yanshan mesozoic magma belts signifying the commencement of extensive underplating of mafic magmas and thus of lithospheric thinning in the northern ncc

late and mid cretaceous mineralization in the northern canadian cordillera constraints from re os molybdenite dates new re os molybdenite dates are presented from three deposits casino cash and mt nansen in the dawson range yukon northern canadian cordillera the re os molybdenite dates provide constraints on the timing of sulfide mineralzation and together with 40 ar 39 ar and k ar mineral dates yield estimates for the longevity of the porphyry hydrothermal system at the casino deposit re os molybdenite dates associated with the potassic 75 05 0 28 74 69 0 28 ma alteration are nominally older to overlapping with re os molybdenite dates 74 4 0 28 ma n 2 with phyllic alteration and suggest that it is likely that potassic and phyllic mineralization alteration was contemporaneous the re os molybdenite dates are significantly older than hydrothermal k feldspar 40 ar 39 ar and k ar biotite dates 72 ma which most likely reflect the cessation of the porphyry hydrothermal system the molybdenite age data combined with silicate hydrothermal mineral dates suggest a porphyry hydrothermal system longevity of 4 16 to 1 94 casino 8 66 to 6 44 cash and 2 47 to 1 48 ma mt nansen these longevity estimates for porphyry hydrothermal systems are greater than previously proposed 50 c km may control the disparate re os molybdenite and 40 ar 39 ar k feldspar dates of the porphyry systems of this study the contrasting re os and 40 ar 39 ar dates clearly show the re os isotope system in molybdenite is resistant to prolonged 1 ma interaction with a high temperature 400 500 c hydrothermal fluid and that the re os isotope systematics in molybdenite unambiguously record directly the timing of sulfide mineralization this ability to directly date sulfide mineralization has identified mid pattison idaho creek 102 104 ma and late cretaceous zappa koffee 74 5 ma mineralization which is hosted by the mid cretaceous 104 102 ma casino plutonic suite the late cretaceous date is very similar to that for molybdenite mineralization at casino and we suggest that the zappa koffee mineralization is an area of late cretaceous porphyry mineralization for which the host pluton has not yet been discovered

a preliminary inventory of periglacial landforms in the andes of la rioja and san juan argentina at about 28 s the cerro el potro and nearby mountain chains belong to the andean frontal cordillera 28 s cerro el potro is a glaciated mountain that is surrounded by huge valleys both on its chilean and argentinean flanks its southern limit is a steep rock wall towards the trough shaped rio blanco valley in argentina with a wide valley floor the other sides of the mountain are characterized by well developed pleistocene cirques the predominant landforms in this area have been shaped in a periglacial environment superimposed on an earlier glacial landscape it is a region with abundant rock glaciers a noteworthy rock glacier zone but nevertheless it is a relatively little known area in south america in this preliminary inventory the landforms surveyed were mainly gravitational in origin including valley rock glaciers talus rock glaciers debris cones landforms originated by solifluction processes and talus detrital sheets on mountain sides ancient moraine deposits have been found on the sides of the main rivers that cross the area form west to east including the blanco and bermejo rivers present day fluvial activity is limited and restricted to these main rivers in this area of glacial valleys and small cirques there are small lakes and other water bodies grass covered patches and zones with high mountain vegetation present day glacial activity is restricted to the highest part of the area above 5500 m a s l mainly in the cerro el potro 5879 m where a permanent ice field exists as well as small mountain glaciers

thermal history of the northern olympic domain gawler craton correlations between thermochronometric data and mineralising systems abstract multi method thermochronology applied to the northern olympic domain of south australia reveals a complex thermal evolution with multiple thermal events apatite u pb closure temperature 550 350 c and muscovite 40ar 39ar ages 400 350 c record post magmatic cooling from 1850 to 750 ma for the 1850 ma donington suite and from 1560 1500 ma for the 1590 ma hiltaba suite and the gawler range volcanics potassium feldspar 40ar 39ar ages 350 150 c record disturbed spectra that are likely related to hydrothermal alteration at 1000 650 ma in the neoproterozoic adelaide rift complex apatite fission track 60 120 c zircon u th sm he 180 200 c and apatite u th sm he 45 75 c ages reveal regional low temperature thermal events at 1000 ma 430 400 ma 350 330 ma and 200 ma in addition to localised thermal events during the cretaceous the 1000 ma apatite fission track ages are amongst the oldest recorded for south australia and are only preserved near the margins of the olympic domain the 430 400 ma and 350 330 ma cooling events are interpreted to be driven by the alice springs orogeny the mesozoic thermochronometric ages are interpreted to record localised thermal perturbations possibly related with hydrothermal activity within the northern olympic domain the presence of abundant iocg deposits near these young thermal anomalies may indicate that these zones record more favourable thermal conditions and or exposure levels for iocg discoveries in the study area

validation of near field ground penetrating radar modeling using full wave inversion for soil moisture estimation we present validation results of a new ground penetrating radar gpr near field model for determining the electrical properties and correlated water content of a sand using both frequency and time domain radars the radar antennas are intrinsically characterized using an equivalent set of infinitesimal source field points and characteristic functions of antennas which were determined using measurements with the antenna at different distances from a copper plane the antenna radiation was modeled using six source and field points which was found to be a good compromise between high modeling accuracy and computing efficiency we validated our model by inverting gpr data to predict the water content of a sand layer subject to seven levels of saturation a soil dielectric mixing model was integrated into the full wave gpr inverse modeling to directly estimate the water content and to account for the frequency dependence of the electrical properties although the quality of the fit slightly decreased as the antenna approached the sand surface the results showed a close agreement between measured and modeled data resulting in accurate estimation of the water content the average errors of all water content estimates were 0 012 cm3 cm3 for the frequency domain and 0 016 cm3 cm3 for the time domain gpr however the accuracy reduced when the sand became wet by performing numerical simulations we found that it is due to the vertical heterogeneity of soil moisture under the effect of the hydrostatic pressure we also showed that the gpr inversion with the multilayered soil model could account for this heterogeneity and improved the agreement between the modeled and measured gpr data as well as the accuracy of soil moisture estimation as for the frequency dependence of the electrical properties in the frequency ranges of both gpr systems while the dielectric permittivity was approximately constant the apparent conductivity exponentially increased with increasing frequency the success of the calibration and validation in laboratory conditions demonstrates a great potential for practical applications of the radar model notably for the digital soil mapping and nondestructive testing of materials

petrogenesis of the proterozoic gawler range volcanics south australia the post orogenic bimodal gawler range volcano plutonic province developed in south australia between 1600 and 1500 ma ago vast felsic ash flow tuff units and intercalated volumetrically minor basalt flows comprise a thick comparatively undeformed volcanic pile that is intruded in many places by the extensive comagmatic hiltaba granite the geochemical and petrographic features of the felsic volcanic rocks point to an origin in high temperature dry partial melting of a comparatively refractory mafic intermediate granulitic sialic crustal source heat was probably supplied during a period of crustal rifting and underplating associated with an episode of mantle diapirism which also generated the primary basic magmas for the basaltic rock suite the primary felsic magmas differentiated along broadly calc alkaline trends to yield a variety of products many of which do not conform to a single line of liquid descent owing to appreciable incorporation of an accumulative crystal component in differentiated high k2o residual liquids the gawler range volcanics have comparable geochemical petrographic characteristics and field settings to several other proterozoic volcanic suites in australia thus implying a similar origin this analogy extends to the familiar proterozoic rapakivi granite suite of the northern hemisphere suggesting development in response to a unique globe encircling tectonic regime that was fundamentally different to that which has spawned modern calc alkaline volcanic arcs

snake river sr type volcanism at the yellowstone hotspot track distinctive products from unusual high temperature silicic super eruptions a new category of large scale volcanism here termed snake river sr type volcanism is defined with reference to a distinctive volcanic facies association displayed by miocene rocks in the central snake river plain area of southern idaho and northern nevada usa the facies association contrasts with those typical of silicic volcanism elsewhere and records unusual voluminous and particularly environmentally devastating styles of eruption that remain poorly understood it includes 1 large volume lithic poor rhyolitic ignimbrites with scarce pumice lapilli 2 extensive parallel laminated medium to coarse grained ashfall deposits with large cuspate shards crystals and a paucity of pumice lapilli many are fused to black vitrophyre 3 unusually extensive large volume rhyolite lavas 4 unusually intense welding rheomorphism and widespread development of lava like facies in the ignimbrites 5 extensive fines rich ash deposits with abundant ash aggregates pellets and accretionary lapilli 6 the ashfall layers and ignimbrites contain abundant clasts of dense obsidian and vitrophyre 7 a bimodal association between the rhyolitic rocks and numerous coalescing low profile basalt lava shields and 8 widespread evidence of emplacement in lacustrine alluvial environments as revealed by intercalated lake sediments ignimbrite peperites rhyolitic and basaltic hyaloclastites basalt pillow lava deltas rhyolitic and basaltic phreatomagmatic tuffs alluvial sands and palaeosols many rhyolitic eruptions were high mass flux large volume and explosive vei 6 8 and involved h2o poor low 18o metaluminous rhyolite magmas with unusually low viscosities partly due to high magmatic temperatures 900 1 050 c sr type volcanism contrasts with silicic volcanism at many other volcanic fields where the fall deposits are typically plinian with pumice lapilli the ignimbrites are low to medium grade non welded to eutaxitic with abundant pumice lapilli or fiamme and the rhyolite extrusions are small volume silicic domes and coulees sr type volcanism seems to have occurred at numerous times in earth history because elements of the facies association occur within some other volcanic fields including trans pecos texas etendeka parana lebombo the english lake district the proterozoic keewanawan volcanics of minnesota and the yardea dacite of australia

inherited pb components in magmatic titanite and their consequence for the interpretation of upb ages abstract the occurrence of inherited radiogenic pb components in 35 ma old magmatic titanite is reported here for the first time the about 810 ma age of the inherited components is identical to that contained in zircon from the same amphibole bearing syenite sample in both minerals the precambrian components were not totally reset during magmatic new growth at 35 ma this age pattern substantiates that the u pb chronometer in titanite is resistant to temperatures in excess of 712 c as is already known for zircon and monazite in consequence u pb ages from crystalline titanites have to be interpreted as the age of mineral formation or re crystallization rather than the time of u pb system closure during cooling of the rock

evolution of the mount woods inlier northern gawler craton southern australia an integrated structural and aeromagnetic analysis structural mapping integrated with interpretation and forward modelling of aeromagnetic data form complimentary and powerful tools for regional structural analysis because both techniques focus on architecture and overprinting relationships this approach is used to constrain the geometry and evolution of the sparsely exposed mount woods inlier in the northern gawler craton the mount woods inlier records a history of poly phase deformation high temperature metamorphism and syn and post orogenic magmatism between ca 1736 and 1584 ma the earliest deformation involved isoclinal folding and the development of bedding parallel and axial planar gneissic foliation s1 this was accompanied by high temperature upper amphibolite to granulite facies metamorphism at ca 1736 ma during subsequent north south shortening d2 open to isoclinal south southeast oriented f2 folds developed as the palaeoproterozoic successions of the inlier were thrust over the archaean nuclei of the gawler craton the syn d2 engenina adamellite was emplaced at ca 1692 ma the post d2 history involved shear zone development and localised folding exhumation of metamorphic rocks and deposition of clastic sediments prior to the emplacement of the ca 1584 ma granite balta suite the mount woods inlier is interpreted as the northern continuation of the kimban orogen

the early jurassic fe sn metallogenic event and its geodynamic setting in south china evidence from re os u pb geochronology and geochemistry of the dading magnesian skarn fe sn deposit abstract the south china block scb is one of the largest w sn polymetallic metallogenic district over the world with most of the deposits formed during the mesozoic the early jurassic of scb was considered as a magmatic and metallogenic quiescence stage as response to the tectonic transition from the paleo tethyan to the paleo pacific geodynamic domains the dading fe sn deposit is a quite rare early jurassic deposit recognized in scb sims zircon u pb and molybdenite re os dating indicate that the dading fe sn deposit 185 9 4 9 ma and related shibei granite 189 0 1 5 ma formed at the early jurassic which provides convincing evidence for a previously unrecognized early jurassic fe sn metallogenic event in scb geochemical data show that the shibei granite has high sio2 nb zr nb ce y concentrations and high ga al ratio but low y nb ratio which are similar to those of a1 type granite the large range of zircon ehf t values 2 4 to 3 4 negative correlation between zircon ehf t and 18o values and unique whole rock sr nd isotopic compositions end t 3 3 to 3 7 isr 0 7063 0 7085 suggest that the shibei granite is likely to originate from a mixed source of pre existing crust and juvenile material with oib like isotopic composition combining with the spatial distribution of the volcanic intrusive rocks sedimentary basins and tectonic deformation styles we suggest that the early jurassic fe sn mineralization occurred in an extensional environment which was probably linked to the post orogenic collapse of the indosinian orogeny between the scb and indochina block

timing of iron oxide cu au u hydrothermal activity and nd isotope constraints on metal sources in the gawler craton south australia the eastern gawler craton hosts australia s premier uranium bearing iron oxide copper gold iocg belt the 500 km long olympic cu au u province in addition to the olympic dam cu u au and prominent hill cu au deposits numerous barren and weakly mineralized iocg prospects are present in the province new geochronological data for hydrothermal minerals combined with constraints from host rock ages demonstrate that alteration and associated iocg mineralization formed between 1570 and 1600 ma in three districts of the province this iocg hydrothermal activity temporally overlaps with magmatism of the hiltaba suite and gawler range volcanics titanites in paragenetically early magnetite bearing alteration in the olympic dam and prominent hill districts yield u pb ion probe ages of 1576 5 and 1567 10 ma respectively molybdenite in veins crosscutting magnetite biotite and albitic alteration in the moonta wallaroo district have re os ages of 1574 6 and 1599 6 ma respectively these represent minimum ages of the iocg alteration assemblages in this district a muscovite 40ar 39ar age of 1575 11 ma provides a minimum age of paragenetically later hematitic alteration in the olympic dam district neodymium isotope compositions were determined for 44 whole rock samples from barren and weakly mineralized cu au prospects and host rocks in the olympic dam and prominent hill districts the new geochronological framework enables comparison of the nd isotope data across two iocg districts at the time of formation of the olympic dam deposit ca 1590 ma magnetite rich weakly cu mineralized alteration from five prospects yields a relatively narrow range end 1590 values of 5 8 to 4 1 both hematite and magnetite rich alteration yield generally similar end 1590 values that match values from fresh and weakly altered paleoproterozoic metasedimentary and metagranitic rocks 6 6 to 3 5 as well as from most felsic hiltaba suite intrusions and gawler range volcanics in the eastern gawler craton ca 6 to 4 these data are consistent with crustal sources for ree and by implication for associated copper in the barren and weakly mineralized prospects mineralization and alteration in these minor iocg systems can be geochemically discriminated from the giant olympic dam deposit where greater inputs of mantle derived ree and other ore components are evident 2007 society of economic geologists inc

petrogenetic evolution of felsic volcanic sequences associated with phanerozoic volcanic hosted massive sulphide systems the role of extensional geodynamics abstract felsic volcanic hosted massive sulphide deposits form in many different geotectonic environments usually associated with episodes of extension however empirical geochemical links between felsic volcanism geotectonic environment and extensional geodynamics have not been adequately documented so as to distill the fundamental relationships between these features and formation of volcanic hosted massive sulphide vhms mineralization which is important considering most vhms deposits are hosted in felsic volcanic bearing sequences using felsic geochemical data from six different vhms mineralized phanerozoic geotectonic settings it seems that the felsic geochemical data are consistent with the overall geotectonic interpretations for these areas which in turn helps in stratigraphic and geotectonic interpretations for detailed vhms exploration in extensional geodynamic settings bimodal volcanism is common compared to the continuum of compositions observed under compressional to neutral high stress regimes in calc alkaline arc building environments the empirical geochemical metallogenic vhms relationships evident in the archean felsic volcanic rocks in particular the low zr y n yb n 2 o conditions in different source areas and geotectonic environments they seem to be the predominant controls on the compositional evolution of felsic magmas in extensional settings because of the limited degree of assimilation and fractional crystallization afc affecting their compositions with rapid intrusion into the uppermost crust to positions were they achieve neutral buoyancy in the volcanic to subvolcanic environment within plate felsic or a type anorogenic type and anomalous ocean ridge or type felsic magmas that have tholeiitic affinities relatively low alkali elements are common within parts of the volcanic sequences hosting massive sulphide deposits reflecting in part a relationship to extension the high contents of high field strength elements zr ga lree hree y nb etc and other lines of evidence indicate they are relatively high temperature relatively reduced magmas probably derived from previously dehydrated granulitic or melted oceanic simatic or continental sialic crust low p granulites or amphibolites but also in some cases possibly mantle rocks such that they are significantly water undersaturated during melting i e a h 2 o 1 reduced viscosities typical of high temperature melts enable rapid intrusion to higher levels diking vs diapirism higher rates of heat advection from mantle mafic magmas into the thickened oceanic and or continental crust during lithospheric extension are needed to facilitate melting of these rock to form a type and or or type partial melts tholeiitic felsic this usually results in bimodal magmatism as magma mixing is not favored in extensional settings especially at high magma production intrusion and extrusion rates i e high heat flow this would inhibit ferromagnesian phase in particular hornblende and magnetite fractionation especially at low f o 2 in the felsic magmas that would deplete the melt in y hree as well as ore related elements particularly zn which is 2 to 3 times higher in a type and or type rocks compared to other magma types therefore the empirical felsic igneous geochemical metallogenic relationships observed by others low zr y n yb n

origin of hydrothermal fluids at olympic dam preliminary results from fluid inclusions and stable isotopes fluid inclusions and stable isotope data provide evidence of the temperature composition and sources of hydrothermal fluids associated with formation of the fe rich breccias that host cu u au ag ore at olympic dam early magnetite associated with pyrite and siderite precipitated from fluids of high delta 18 o content approx 10ppm at temperatures near 400 degrees c and magnetite in k feldspar apatite veins at the nearby acropolis deposit probably formed from similar fluids in contrast hematite associated with ore bearing breccias formed at lower temperatures 200 degrees 400 degrees c from fluids of lower delta 18 o content 9ppm fluid inclusion homogenization temperatures in quartz fragments within hematite breccias overlap with and are lower than those indicated by isotope geothermometry two phase liquid plus vapor inclusions mainly homogenize at temperatures between 130 degrees and 280 degrees c with a mode at 170 degrees to 190 degrees c quartz fragments within rare laminated barite clasts display a larger range of homogenization temperatures from 110 degrees to 420 degrees c and may have preserved evidence of early high temperature hydrothermal events measurement of freezing point depressions in fluid inclusions provides evidence of widely varying salinities and complex solute chemistry indicated salinities vary from a minimum of 7 3 wt percent nacl equiv 1 3 m to a maximum of 23 7 wt percent nacl equiv 4 2 m in two phase fluid inclusions and up to 42 wt percent nacl equiv in halite saturated three phase inclusions all the fluid inclusions studied displayed evidence of additional solutes in addition to nacl all required a high degree of supercooling to induce freezing and displayed initial ice melting at temperatures below 23 degrees c and many formed distinctive brown granular ice in addition several inclusions also formed co 2 clathrates and other metastable solids qualitative assessment of these characteristics indicates fluids carrying multiple solutes probably including nacl kcl cacl 2 fecl 2 caf and co 2 these preliminary results suggest that at least two sources of fluids of contrasting temperature composition and oxygen isotope characteristics were involved in the formation of olympic dam early magnetite was deposited from hydrothermal fluids of deep seated possibly magmatic origin but magnetite bearing rocks are not significant hosts for copper uranium mineralization later hematite associated with ore bearing breccias was deposited by fluids of significantly lower temperature and lower delta 18 o values the geologic setting of the deposit a fault bounded depression at or near the palcosurface implies that waters of surficial origin seawater closed basin water or ground water may have been involved in the later stages of hydrothermal activity that formed the hematite breccias although our preliminary isotopic data do not require such waters they are consistent with this conclusion

regional crustal setting of iron oxide cu au mineral systems of the olympic dam region south australia insights from potential field modeling detailed analysis and modeling of regional gravity and magnetic data from the stuart shelf around the olympic dam iron oxide copper gold iocg deposit constrained by geologic observations obtained from deep drill cores show that the eastern gawler craton basement at 1 61 to 1 59 ga consisted of an archean core with two sequences of successively younger supracrustal rocks stepping out eastward from it these were overprinted by the tectonothermal hiltaba event forward models of potential field data show no convincing evidence for the presence of widespread mafic rocks or extensional basin systems developed immediately prior to or during iocg mineralization the high intrusive level and sill like geometry of hiltaba suite plutons emplaced immediately prior to iocg mineralization is difficult to explain in terms of a genetic association with a dominantly extensional tectonic setting instead the tectonic setting inferred from the basement architecture during mineralization is one of low strain shortening consistent with regional field observations a case can be made for intrusion of the hiltaba suite in localized accommodation zones in an overall orogenic setting this style of low strain shortening 10 is consistent with maximum rates and volumes of fluid flow in the upper crust and access of these fluids to a variety of basement rock types to buffer metal scavenging fluids this fluid driving mechanism does not necessitate a role for regional mafic magmatism and volcanism in the formation of iocg deposits modeling of regional gravity and magnetic data is generally applicable to exploration for iocg systems and other mineral systems in covered terranes that have distinctive geophysical signatures resulting from fluid wall rock redox geochemical reactions

a preliminary inventory of rock glaciers at 30 s latitude cordillera frontal of san juan argentina abstract the dry andes of the cordillera frontal of san juan 30 s latitude is characterized by high relief with peaks up to 5000 m a s l this geological province is mainly made up of a suite of triassic to miocene volcanic rocks modern ice glaciers are small and few in number and persistent snow fields are similarly small and scattered the predominant landforms in these areas have been shaped in a periglacial environment superimposed on an earlier glacial landscape a preliminary inventory map of rock glaciers was constructed using optical remote sensing techniques digital topographic analysis and aerial photograph data organized in a geographic information system gis over 140 rock glaciers have been identified 90 are active or inactive and the rest are fossil a total of 88 rock glaciers are considered active the most common periglacial features recognized in the area are talus glaciers and only 23 are tongue shaped glaciers

the age of the ormiston pound granite implications for mesoproterozoic evolution of the arunta inlier central australia the ormiston pound granite southern arunta inlier intruded during the terminal stages late to post d2 of a major n directed overthrust event called the chewings orogeny which deformed supracrustal rocks of the simpsons and chewings assemblages ion probe zircon u pb analysis of the granite indicates an emplacement age of 1603 10 ma more than 500 ma older than the rb sr isochron age timing of emplacement is confirmed by an age of 1575 20 ma for zircon mantles from a gneissic xenolith in the granite zircon cores from the xenolith yield an age of 1678 14 ma which is taken to represent the protolith age of the surrounding gneisses the shrimp age is similar to but more precise than the 1586 69 ma rb sr isochron age for the chewings orogeny determined by marjoribanks and black 1975 penecontemporaneous 1600 ma magmatism is evident as pegmatites and associated fluid flow zones in the anmatjira and reynolds ranges northern arunta inlier 1100 1030 ma rb sr mica ages from the 1600 ma ormiston pound granite coeval pegmatites and 1680 ma host rock gneisses are similar to a sm nd isochron age for the mafic stuart dyke swarm of the southern arunta inlier and the contemporaneous alcarra dyke swarm in the musgrave inlier some 500 km farther south the rb sr mica ages reflect isotopic resetting by a thermal perturbation either associated with regional crustal extension during 1080 ma dyke intrusion or with the 1150 ma magmatic event in the southern arunta cf black and shaw 1992 irrespective the 1050 900 ma ormiston event described by shaw et al 1984 as granite intrusion associated with high grade metamorphism migmatization and folding needs to be re defined or abandoned

refined proterozoic evolution of the gawler craton south australia through u pb zircon geochronology abstract through the application of both conventional u pb zircon analyses and small sample u pb isotopic analyses the nature and timing of tectonic events leading to the formation of the gawler craton have been defined more precisely constraints on deposition of early proterozoic iron formation bearing sediments have been narrowed down to the period 1960 1847 ma deformed acid volcanics including the economically important moonta porphyry have zircon ages of 1790 and 1740 ma the voluminous acid gawler range volcanics and correlatives to the east were erupted over a short interval at 1592 2 ma and were intruded by anorogenic granites at 1575 ma small sample zircon analyses proved to be an extremely valuable adjunct to conventional analyses generally yielding more concordant data which forced a curved discordia through an upper intercept slightly younger than from a conventional straight line discordia

u pb geochronology of middle proterozoic felsic magmatism surrounding the olympic dam cu u au ag and moonta cu au ag deposits south australia

surface and subsurface facies architecture of a small hydroexplosive rhyolitic centre in the mesoproterozoic gawler range volcanics south australia abstract at menninnie dam south australia a drilling program has revealed a complete section through the subsurface feeder system and erupted products of a small hydroexplosive rhyolitic centre within the mesoproterozoic gawler range volcanics porphyritic rhyolite intruded near vertical faults in the palaeoproterozoic basement and at less than a few hundred metres depth interacted with fault hosted hot groundwater hydrofracturing of the wall rock occurred in advance of and at the margins of the rhyolitic intrusions the rhyolitic intrusions have peperitic margins and grade into discordant lithic rich pb facies the advancing fragmentation front intersected the palaeosurface triggering phreatic eruptions that deposited a poorly sorted lithic rich explosion breccia rhyolite then rose to the surface through the intrusive breccias and shallow seated magma water interaction occurred in the conduit within 800 m from the inferred source the products include muddy sandstone and pumice breccia at the end of the eruption rhyolitic lava was extruded in the form of a small dome the presence of contemporaneous pb zn ag mineralisation in the wall rocks suggests that an active hydrothermal system may have been involved in the formation of the menninnie dam hydroexplosive volcanic centre

lithology and hydrothermal alteration control the distribution of copper grade in the prominent hill iron oxide copper gold deposit gawler craton south australia the prominent hill iron oxide copper gold iocg deposit located in the gawler craton of south australia contains ca 278 million metric tons mt of ore at 0 98 cu 0 75 g t au and 2 5 g t ag in contrast to the predominantly granite hosted olympic dam iocg deposit prominent hill is mainly within unmetamorphosed sedimentary rocks comprising coarse clastic to laminated argillaceous lithologies with some volcaniclastic components and variable carbonate including local massive dolomite essentially unmetamorphosed sedimentary rocks and structurally underlying mafic to intermediate composition lavas inferred to be members of the lower gawler range volcanics host the economically mineralized hematite breccias the volcanic sedimentary package was downfaulted and tilted along a major east west fault north of which similar but regionally low grade metamorphosed rocks were affected by subeconomic skarn mineralization and on a more regional scale of the mount woods domain intruded by granitic and gabbroic bodies hydrothermal alteration and mineralization at prominent hill involved pervasive and texturally destructive replacement of formerly calcareous dolomitic and siliciclastic breccia components hydrothermal alteration minerals comprise hematite magnetite siderite ankerite quartz sericite chlorite kaolinite fluorapatite fluorite barite ree u minerals including monazite uraninite and coffinite together with cu sulfides including chalcopyrite bornite and chalcocite in the highest grade ore brecciation and replacement caused mechanical mixing as well as chemical alteration of primary lithologies such that sedimentary contacts became obscured mass balance calculations identify al ti si and zr as least mobile components during hematite chlorite sericite to weak hematite quartz alteration because zr was not regularly assayed in drill cores we use concentration ratios of ti al and si from the deposit scale assay database to delineate the distribution of lithochemical units prior to hydrothermal alteration and cu mineralization the resulting lithochemical model based on one horizontal and five vertical cross sections is used as a basis for mapping alteration patterns calculated from molar fe si fe si al k na and k al ratios these chemical patterns in conjunction with mineral stoichiometry indicate that the spatial distribution of hematite chlorite variably phengitic sericite and or illite kaolinite quartz bearing alteration is superimposed on the pattern of interpreted lithologic contacts the alteration patterns confirm visual logging results showing that hematite enrichment correlates only partially with the distribution of cu grades of 0 25 wt a subvertical body of complete replacement by hematite and quartz with consistent but subeconomic gold enrichment forms a cu barren core in the central and eastern parts of the deposit zones of increasing k al and k na ratios extend upward and westward from this cu barren core transgressively overprinting lithologic contacts the degree of hematite quartz replacement can be measured by a hematite quartz alteration index here termed the hmsi value fe si fe si al which inversely correlates with the normal probability for cu grade areas of highest cu grade 1 wt spatially correlate with irregular zones having intermediate molar alteration indices 0 34 k al 0 40 20 k na 36 and hmsi 0 98 hematite breccias and cu ore deposition developed after tilting of the host sequence into its present steep orientation as indicated by geopetal structures within the breccia matrix thus the economic mineralization occurred late in the deformational history of the region and after extrusion of the lower gawler range volcanics the formation of the prominent hill orebodies occurred during or after upthrusting of deeper seated rocks containing subeconomic cu in skarns north of the fault faulting as well as ore formation may be related to orogenic processes in the central and northern part of the mount woods domain iron oxide introduction was decoupled from and at least partly preceded hydrothermal deposition of high grade cu geochemical and petrographic data indicate that economic cu mineralization occurred together with mildly acidic hematite chlorite sericite siderite alteration of originally carbonate illite and feldspar bearing sedimentary rocks the presence of copper enrichment with an intermediate degree of cation leaching from the host rocks indicates that ph neutralization of initially highly acidic metal transporting fluids was an essential factor causing cu sulfide deposition distinct ranges in na k al ratios and low hmsi values offer potential as exploration indicators pointing toward higher ore grades these results from prominent hill are consistent with recently published mineralogical studies at the giant olympic dam deposit indicating similar ore depositional controls despite lithologically different host rocks

rock glacier nomenclature a re assessment several contentious issues have arisen from rock glacier nomenclature for example whether the term rock glacier implies genesis from glacial ice or genesis from permafrost the situation is compounded since rock glacier classification may be based on several different parameters some of which are measured and quantified others inferred these include gross morphology dynamics processes of formation location internal characteristics thermal regime and age uncertainties in specifying the genesis in the light of the potential complexity means that definitions should be related to recognisable topographic forms which allow mapping of such features the distinction is made between rock glaciers sensu stricto which follows the original descriptions and typology of the early years of the 20th century and protalus lobes the forms can usually be differentiated in terms of length breadth ratios as well as by their relative locations some of the most common issues of contention within rock glacier research can be solved by this approach

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

insights into magma histories through silicate oxide crystal clusters linking the hiltaba suite intrusive rocks to the gawler range volcanics gawler craton south australia the roxby downs granite rdg host to the supergiant olympic dam deposit and the gawler range volcanics grv in south australia both contain clusters of touching silicate and oxide minerals here we report on the geochemistry and petrography of these rocks and their contained mineral clusters before comparing them to similar occurrences elsewhere in the world to gain a better understand of their genesis and the links between the rdg and other members of the hiltaba suite and the grv crystal clusters in the rdg comprise magnetite apatite titanite biotite zircon which are typically enveloped in a plagioclase crystal matrix in the grv crystal clusters comprise pyroxene titanomagnetite plagioclase apatite zircon display variably glomeroporphyritic equigranular poikilitic and loosely packed habits and are enclosed by texturally varied groundmass of the grv lavas studied pyroxenes and titanomagnetite show systematic trends in major and trace element compositions conformable with the stratigraphic position of their hosts this suggests the lavas are related through differentiation in the upper crust and represent the inversion of a normally zoned reservoir there are no compositional contrasts between phenocrysts and crystals in grv clusters and mg of pyroxenes are consistent with those predicted from whole rock compositions implying that all analysed crystals including those in clusters were formed within or were at least equilibrated to the host lavas precursors rather than entire histories as isolated crystal clusters entrained by melt flow intergrowth textures and mafic magmatic enclaves suggest that the majority of grv crystal clusters were liberated from closely packed crystal masses through magma rejuvenation and associated crystal resorption consistent fe ti oxide apatite zircon plagioclase assemblages and textures in both the grv and rdg suggest a shared genetic scenario although an extended model is needed to account for the transformation of grv type to hs type crystal clusters for hot and dry magmas such as those that formed the grv and rdg cooling causes pyroxene fe ti oxide plagioclase in grv type crystal clusters to react with each other and the melt forming hs type magnetite titanite biotite feldspar crystal clusters rejuvenation events implicated in the liberation of grv type crystal clusters may be important drivers of magmatic hydrothermal iron oxide deposit formation

lithogeochemical isotopic and u pb zircon age constraints on arc to rift magmatism northwestern and central avalon terrane newfoundland canada implications for local lithostratigraphy the northwestern avalon terrane newfoundland is underlain by neoproterozoic rocks traditionally divided into older love cove group medial connecting point group and the unconformably overlying

cooling and exhumation history of the northeastern gawler craton south australia abstract we present biotite 40ar 39ar ages and from the palaeo to mesoproterozoic mount woods inlier in the northeastern gawler craton south australia in combination with garnet biotite fe mg exchange modelling using the thermal history program these data are used to constrain a post peak metamorphic p t path cooling rates and a temperature time path for the inlier consistently well defined plateaus at 1 53 ga of biotite 40ar 39ar age spectra indicate that the rocks cooled through 300 c at this time cooling rates within the inlier are 3 9 c ma from peak high temperature low pressure metamorphism at 1 59 ga to 1 53 ga cooling rates subsequently decreased to 4 c ma cooling is suggested to be a function of cessation of voluminous magmatism and mantle heat input in conjunction with exhumation initiated along the southwestern margin of the inlier ca 1 592 1 582 ga the temperature time path of the inlier has a concave shape the peak metamorphic and ensuing cooling history of the mount woods inlier are akin to the nearby curnamona province coober pedy ridge and mabel creek ridge within the south australian craton deformation during high grade metamorphism within these terranes was accommodated at mid crustal levels and large scale exhumation did not occur until the terranes cooled and were able to be exhumed as coherent rigid blocks along discrete shear zones and faults

petrogenesis of a mesoproterozoic quartz latite granitoid suite from the roxby downs area south australia abstract mesoproterozoic granitoids from the roxby downs area south australia show a range in composition from mafic quartz monzodiorites 56 sio 2 to felsic granites 71 sio 2 and are interpreted as consanguineous on the basis of similar age isotopic composition and mineralogical and geochemical characteristics these granitoids have geochemical similarities with other mesoproterozoic granitoids the world over including enrichments in k 2 o rb ba th u rare earth elements ree nb y zr and depletions in mgo cao sr cr ni v sc relative to typical phanerozoic calc alkaline granitoids the mafic granitoids have mineralogical textural and geochemical features consistent with an origin as cumulates from a more felsic primary magma and the felsic granites likely represent the fractionated residual melt to this accumulation process none of the granitoids from the batholith preserve the primary magma composition which is deduced to be similar to abundant quartz latite volcanic rocks of the region it is estimated by geochemical modeling that about 27 fractionation of observed phenocrysts from a primary quartz latite is required to produce a typical felsic granite 71 sio 2 production of the primary quartz latite magma was likely the result of partial melting of existing paleoproterozoic crust in response to intrusion into the crust of mantle derived magmas the combination of widespread crustal melting contemporaneous granulite facies metamorphism and mantle derived magmatism suggests involvement of large scale tectonothermal processes in the origin of these granitoids the petrogenesis of these rocks and similar occurrences in laurentia and baltica indicates that processes involving reworking of existing paleoproterozoic crust were similar throughout many continental areas during the mesoproterozoic

constraining models of the tectonic setting of the giant olympic dam iron oxide copper gold deposit south australia using deep seismic reflection data abstract in the gawler craton the completeness of cover concealing the crystalline basement in the region of the giant olympic dam cu au deposit has impeded any sufficient understanding of the crustal architecture and tectonic setting of its iocg mineral system to circumvent this problem deep seismic reflection data were recently acquired from 250 line km of two intersecting traverses centered on the olympic dam deposit the data were recorded to 18 s twt 55 km the crust consists of neoproterozoic cover in places more than 5 km thick over crystalline basement with the moho at depths of 13 14 s twt 40 42 km the olympic dam deposit lies on the boundary between two distinct pieces of crust one interpreted as the archean paleoproterozoic core to the craton the other as a meso neoproterozoic mobile belt the host to the deposit a member of the 1590 ma hiltaba suite of granites is situated above a zone of reduced impedance contrast in the lower crust which we interpret to be source region for its 1000 c magma the crystalline basement is dominated by thrusts this contrasts with widely held models for the tectonic setting of olympic dam which predict extension associated with heat from the mantle producing the high temperatures required to generate the hiltaba suite granites implicated in mineralization we use the seismic data to test four hypotheses for this heat source mantle underplating a mantle plume lithospheric extension and radioactive heating in the lower crust we reject the first three hypotheses the data cannot be used to reject or confirm the fourth hypothesis

mingled silicic lavas in the mesoproterozoic gawler range volcanics south australia abstract interlayered and mingled plagioclase rhyolite vesicular rhyolite and quartz rhyolite lithofacies occur in a unit of the mesoproterozoic gawler range volcanics in the southern gawler ranges south australia the three rhyolite lithofacies have distinctive phenocryst assemblages groundmass textures and compositions mingling styles include isolated lenses or blobs of one lithofacies surrounded by another lithofacies mm to m scale compositional flow banding and swirled and contorted combinations of lithofacies areas where the plagioclase rhyolite vesicular rhyolite or quartz rhyolite lithofacies are volumetrically dominant have been mapped in all sections plagioclase rhyolite occurs at the base and is succeeded by variably mingled plagioclase rhyolite vesicular rhyolite and quartz rhyolite relatively homogeneous quartz rhyolite dominates the upper parts the compositionally heterogeneous interval is 100 200 m thick and extends 25 km along strike it is the topmost part of a far more extensive 180 km strike length and thicker 350 m plagioclase rhyolite unit eucarro dacite that is relatively homogeneous all three rhyolite types are evenly porphyritic and either massive or flow banded the compositional flow banding and mingling textures imply that the entire unit was emplaced as lava and also that the eruption style was fundamentally effusive or very weakly explosive fountaining geochemical data suggest that three rhyolitic magmas existed in a magma chamber that was compositionally heterogeneous after a large volume of plagioclase rhyolite magma had been withdrawn quartz rhyolite and or vesicular rhyolite were entrained into the flow mingling occurred during laminar flow in the conduit and continued during extrusion resulting in compositional flow banding and more irregular combinations

repeated s i a type granite trilogy in the lachlan orogen and geochemical contrasts with a type granites in nigeria implications for petrogenesis and tectonic discrimination

tectonic framework and evolution of the gawler craton southern australia the gawler craton is the major crustal province in the southern australian proterozoic and is pivotal in models seeking to describe the evolution of proterozoic australia the craton is host to the olympic dam iron oxide cu au u ree deposit as well as a number of other iron oxide copper gold iocg au and iron ore deposits the evolution of the gawler craton is dominated by two major phases of tectonic activity late archean and late paleoproterozoic early mesoproterozoic in total spanning ca 1 billion years the late archean 2560 2500 ma basin development was coeval with arclike felsic magmatism and mafic ultramafic magmas including komatiites collisional deformation between 2480 and 2420 ma led to ca 400 m y of tectonic quiescence conceivably within an early paleoproterozoic continental interior the second major phase of tectonic activity was in the middle to late paleoproterozoic and early mesoproterozoic 2000 1450 ma paleoproterozoic tectonism was initially dominated by rift related events which produced a series of basins over the interval ca 1900 to 1730 ma some of which contain significant iron ore reserves transient contractional deformation at ca 1850 ma led to batholith scale granitic magmatism in part derived from melting of the late archean basement major basin development was finally terminated by the 1730 to 1690 ma kimban orogeny the effects of which are widespread and include the formation of crustal scale shear systems granitic magmatism and low to high grade metamorphism the kimban orogeny was followed by a renewed period of extension between ca 1680 and 1640 ma leading to local magmatism and sedimentation which appears in part to have been coeval with the high grade ca 1650 ma ooldean event in the western gawler craton at ca 1620 to 1615 ma the generation of the arc related st peter suite in the southern gawler craton implies that craton components were located at an active plate margin the arc environment was superseded by a transition to a continental interior regime which coincided with the voluminous gawler range volcanics 1595 1590 ma and hiltaba suite granitoids 1595 1575 ma the hiltaba suite is dominated by high t fractionated felsic rocks with coeval mafic magmatism confirming a mantle involvement emplacement of the hiltaba suite coincided with the major mineralizing interval in the gawler craton regionally two distinct mineral systems have been recognized the olympic iocg province in the eastern part of the craton and the gold dominated systems within the central gawler gold province the spatial distribution of iocg versus au dominated mineral systems appears to reflect regional variations in crustal composition and hiltaba suite petrogeneses hiltaba aged granites in the olympic iocg province are isotopically more evolved richer in u and th and oxidized compared to similar aged granites in the au dominated province modern day heat flow in the iocg province is significantly higher 90 10 mwm 2 compared to the au dominated province 54 5 mwm 2 suggesting there are important lithospheric compositional differences between the two metallogenic provinces which may reflect an older phase of craton assembly widespread northwest southeast contractional deformation coeval with the emplacement of the hiltaba suite is expressed by the formation and or reactivation of shear zones ranging up to crustal scale within this regime northwest trending structures such as those in the vicinity of the olympic dam deposit are likely to have accommodated dilation associated with strike slip movements intersection between these structures and northeast trending contractional faults may have formed suitable structural traps for 1590 to 1580 ma mineralization the timing of syn hiltaba deformation overlaps with transpression and medium to high grade metamorphism associated with the ca 1570 to 1540 ma kararan orogeny which dominates the geophysical architecture of the central northern part of the craton the youngest phase of deformation in the craton is expressed by reactivation of shear zones between ca 1470 and 1450 ma and regional cooling

staircase 40 ar39ar spectra of fine grained white mica timing and duration of deformation and empirical constraints on argon diffusion staircase 40 ar 39 ar spectra of 2 to 6 m white micas in ductile carbonate mylonites morcles doldenhorn nappe switzerland record ages between 32 and 13 ma these ages are within independent geochronologic and biostratigraphic time limits for the beginning and ending of deformation of this fold thrust nappe we interpret these data to record protracted white mica neocrystallization and growth during low temperature ductile deformation such that the differences between the maximum and minimum ages in the 40 ar 39 ar spectra record the time span over which mica formed and grew we have modeled the argon concentrations in these micas taking into account the thermal history of the nappe mica growth and diffusional loss of argon our results indicate that available experimental data underestimate the activation energy for argon diffusion in muscovite and that the retentivity of argon in white mica is greater than generally thought

u pb geochronological constraints on the genesis of the olympic dam cu u au ag deposit south australia the olympic dam cu u au ag deposit is hosted by the olympic dam breccia complex a high level hematite rich hydrothermal breccia system which occurs entirely within and clearly postdates the roxby downs granite the u pb zircon age of the roxby downs granite is well constrained at 1588 or 4 ma field evidence indicates that brecciation hydrothermal alteration and cu u au ag ree mineralization in the olympic dam breccia complex were penecontemporaneous but this is inconsistent with differing ages from previous u pb and rb sr isotopic data on pitchblende and sericite new shrimp u pb zircon data for three olympic dam breccia complex igneous rock units confirm that cu u au ag ree mineralization was contemporaneous with brecciation and alteration and directly followed cooling of the roxby downs granite by as little as several 8 million years two of the dated olympic dam breccia complex rock units are interpreted as autobrecciated felsic dikes one crosscuts laminated hematite quartz sandstones and the other crosscuts cu u mineralized hematite rich breccias zircons from these dikes yielded ages of 1592 or 8 and 1584 or 20 ma respectively the third unit dated is a disrupted ash fall tuff horizon from within a diatreme which crosscuts hematite quartz breccias near the center of the deposit the northern extremities of this diatreme also crosscut hematitic breccias containing a substantial cu u ore zone zircons from this tuff horizon have an age of 1597 or 8 ma the tuff and associated subaerial or subaqueous volcaniclastics were unconsolidated or only weakly lithified at the time of their incorporation into the diatreme so the age of the tuff also reflects the age of diatreme activity these new isotopic data indicate that the olympic dam breccia complex has an age of approximately 1590 ma and therefore imply that brecciation closely followed emplacement and cooling of the roxby downs granite because these breccias contain sulfide fragments and polyminerallic ore fragments exhibit penecontemporaneous sulfide oxide textural relationships and show a close association between cu or u or ag or ree mineralization and fe rich breccias we argue that the metals of economic interest were introduced

a 100 ma bimodal composite dyke complex in the jiamusi block ne china an indication for lithospheric extension driven by paleo pacific roll back abstract a 125 m wide bimodal composite dyke complex consisting of rhyolite and dolerite dykes was emplaced into cretaceous volcanic strata of the songmuhe formation in the jiamusi block of ne china the dolerite dykes are sub vertical strike north south and intruded into both the country rocks and rhyolite dykes soon after the latter solidified shrimp zircon u pb dating shows that the rhyolite dykes were emplaced at 100 2 ma and the dolerite dykes were also most likely emplaced at 100 2 ma the rhyolite is characterized by enrichment in large ion lithophile elements lile and light rare earth elements lree and depletion in high field strength elements hfse it shows a significant negative eu anomaly and has e nd t values ranging from 0 49 to 1 66 and two groups of initial 87 sr 86 sr ratios at 0 7045 and 0 7061 the rhyolite displays the compositional signature of peraluminous ferroan granitoid indicating it was derived by either differentiation of basalt and or low pressure partial melting of crust the dolerite is also characterized by enrichment in lile and lree and depletion in hfse it has a weak negative eu anomaly and has e nd t 1 22 to 3 26 and 87 sr 86 sr i 0 7057 0 7074 the dolerite originated from partial melting of lithospheric mantle which was affected by subducted oceanic crust and experienced different amounts of crustal contamination such bimodal dyke complexes are an important indicator of crustal extension under the influence of mantle processes thus the dyke complex in the jiamusi block indicates mid cretaceous intra plate extension in ne china related to the subduction of the paleo pacific plate along the eastern eurasian continental margin when compared with mesozoic bimodal magmatism further to the west our new data support a temporal eastward migration of magmatism over a distance 1000 km from 160 ma to 100 ma this was most likely associated with roll back of the paleo pacific plate and consequent upwelling of asthenospheric mantle

geodynamic reconstruction of the winston lake greenstone belt and vms deposits new trace element geochemistry and u pb geochronology the ca 2720 ma winston lake greenstone belt of the wawa abitibi terrane superior province is located on the northern margin of the wawa subprovince and has important regional tectonostratigraphic implications for the development of the neoarchean superior province the metallogenic importance of the belt is evident from the presence of the winston lake pick lake and zenith volcanogenic massive sulfide vms deposits however the chemostratigraphic evolution has not been fully examined at the greenstone belt scale nor have the vms deposits been examined from the perspective of the belt scale petrogenesis and volcanic reconstruction this study 1 reviews the geology and vms mineralization in the winston lake greenstone belt and 2 reconstructs its geodynamic setting and its magmatic and metallogenetic history using new geological trace element and nd isotope data constrained by new u pb geochronology the belt is subdivided into two main lithotectonic assemblages the winston lake assemblage composed of tholeiitic to calc alkalic bimodal volcanic lithofacies and the big duck lake assemblage composed of alkalic to tholeiitic mafic flows and sills the contact between the winston lake and big duck lake assemblages is intruded by the differentiated zenith gabbro which hosts the 0 16 mt zenith vms orebody as a series of xenoliths the variably altered felsic lithofacies of the winston lake assemblage host the 3 1 mt winston lake main and 1 3 mt pick lake zn rich vms deposits the felsic volcanic lithofacies of the winston lake assemblage are fiii type rhyolites and have a bimodal distribution of zr ti indicating two distinct magmas formed by different temperatures of partial melting mafic lithofacies of the winston lake assemblage are typically calc alkalic to transitional between calc alkalic and tholeiitic in composition they have arc to back arc trace element contents with distinctive negative nb and ti anomalies enrichment in the light rare earth elements lree and higher th nb ratios than the mafic rocks from the big duck lake assemblage mafic strata from the big duck lake assemblage have trace element characteristics similar to mature back arc tholeiitic basalts and oib like or oceanic plateau alkalic basalts with high nb th and ti v ratios the chemostratigraphy of the winston lake greenstone belt is consistent with a geodynamic model where arc rifting is followed by back arc development nd isotope data indicate that strata from the winston lake and big duck lake assemblages are juvenile and show no evidence of contamination by significantly older crust therefore crustal contamination signatures in the mafic flows from the winston lake assemblage must have formed by contamination from crust that is of similar age and supports a comagmatic relationship between the mafic and felsic strata the mafic flows of the big duck lake assemblage represent a mature back arc setting with evidence for enriched plume generated basalts in the upper mafic unit the winston vms deposit formed during the early rifting of the arc and the timing is tightly constrained by the hydrothermally altered 2721 2 0 9 ma vms hosting felsic strata and younger postmineralization 2719 4 ma zenith gabbro the zn dominated vms mineralization suggests that temperature of the hydrothermal fluid during discharge was relatively cool 300 c and did not maintain sufficiently high temperatures to precipitate significant amounts of copper relative to zinc this is likely due to adiabatic cooling of the fluid because of a low pressure 0 5 kb sea floor environment and or permeable volcaniclastic strata a u pb age of emplacement of 2692 1 0 7 ma from the syndeformation quartz feldspar porphyry in the big duck lake assemblage indicate it is comagmatic with syndeformation magmatic events typical of other greenstone belts along the northern margin of the wawa abitibi terrane this event is interpreted to represent the timing of terrane accretion of the wawa abitibi terrane to the superior province

neodymium isotopic study of rare earth element sources and mobility in hydrothermal fe oxide fe p ree systems rare earth element ree enriched igneous related hydrothermal fe oxide hosted fe p ree systems from four areas in north america have been analyzed for their neodymium iosotopic composition to constrain ree sources and mobility in these systems the nd isotopic results evidence a common pattern of ree concentration from igneous sources despite large differences in age proterozoic to tertiary tectonic setting subduction vs intraplate and magmatic style mafic vs felsic in the middle proterozoic st francois mountains terrane of southeastern missouri epsilon sub nd for fe p ree apatite monazite xenotime deposits ranges from 3 5 to 5 1 similar to associated felsic to intermediate igneous rocks of the same age epsilon sub nd 2 6 to 6 2 at the mid jurassic humboldt mafic complex in western nevada epsilon sub nd for fe p ree apatite mineralization varies between 1 1 and 2 4 similar to associated mafic igneous rocks minus 1 0 to 3 5 in the nearby cortez mountains in central nevada mid jurassic felsic volcanic and plutonic rocks epsilon sub nd minus 2 0 to minus 4 4 are associated with fe p ree apatite monazite mineralization having similar epsilon sub nd minus 1 7 to minus 2 4 at cerro de mercado durango mexico all assemblages analyzed in this tertiary rhyolite hosted fe oxide deposit have identical isotopic compositions with epsilon sub nd minus 2 5 these data are consistent with coevalmore igneous host rocks being the primary source of ree in all four regions and are inconsistent with a significant contribution of ree from other sources interpretations of the origin of these hydrothermal systems and their concomitant ree mobility must account for nonspecialized igneous sources and varied tectonic settings less

proterozoic iron oxide cu u au ree deposits further evidence of hydrothermal origins the emmie bluff fe oxide deposit south australia is unequivocally of hydrothermal origin and exhibits overprinting relations visible at both the meso and microscopic scale that strongly support a model involving two temporally distinct fluids as previously proposed for the enormous olympic dam deposit the evidence indicates that the first stage of magnetite rich ore formation was associated with high temperature fluids from a major mid proterozoic felsic intrusive event this was followed by infiltration of lower temperature fluids that produced the hematite rich mineralization from authors

palaeomagnetism of the ejecta bearing bunyeroo formation late neoproterozoic adelaide fold belt and the age of the acraman impact abstract a new palaeomagnetic study has been conducted on haematitic shales and siltstones of the late neoproterozoic bunyeroo formation in the adelaide fold belt geosyncline south australia which host an extensive horizon of shock deformed rock fragments and microtektite like material of probable impact origin thermal step demagnetisation of 116 samples of red shale and siltstone from six sections sites revealed a high temperature component with a bedding corrected site mean direction of remanence of d 56 6 i 29 3 95 10 7 that gives a pole at 18 1 s 16 3 e dp 6 5 dm 11 8 the high temperature component provides a positive tectonic fold test 99 level of confidence the bunyeroo high temperature remanence direction is near the remanence direction d 50 i 40 indicated by modelling the subsurface magnetic source of the central high amplitude anomaly at acraman australia s largest confirmed meteorite impact structure 220 350 km west of the adelaide fold belt and also is close to the mean direction d 48 3 i 54 7 95 5 2 determined for surface melt rock from acraman statistical tests show that the virtual geomagnetic poles indicated by the directions for the subsurface central magnetic source and surface melt rock at acraman may be regarded as subsets of the bunyeroo palaeomagnetic pole position indicating that the three pole positions are statistically indistinguishable the results imply that the subsurface magnetic source and surface melt rock acquired their remanence in the ambient geomagnetic field during cooling after the impact when structural disturbance had ceased while the bunyeroo formation was accumulating the agreement among the various remanence directions argues strongly that the ejecta horizon in the bunyeroo formation was derived from acraman the present findings confirm that the acraman impact occurred in the late neoproterozoic about 590 ma which is the age of the bunyeroo formation provided by rb sr whole rock shale dating of equivalent and contiguous strata in the adelaide fold belt region the bunyeroo palaeomagnetic data give a palaeolatitude of 15 indicating a low palaeolatitude for the acraman impact and supporting other findings that the adelaide fold belt occupied low to equatorial palaeolatitudes during the late neoproterozoic

velocity variations and water content estimated from multi offset ground penetrating radar the common midpoint cmp processing technique has been shown to be effective in improving the results of ground penetrating radar gpr profiling when radar data are collected with the cmp multioffset geometry stacking increases the signal to noise ratio of subsurface radar reflections and results in an improved subsurface image an important aspect of cmp processing is normal moveout velocity analysis our objectives are to show the effect of multiple velocity analyses on the stacked radar image and particularly to demonstrate that this velocity information can also be used to determine subsurface water content most gpr surveys are very limited in spatial extent and assume that within the survey range radar velocity structure in the shallow subsurface can be adequately approximated by a single velocity function in data processing in this study we show that variation in radar velocity can be quite significant and that the stacked profile improves as the number of velocity analysis locations is increased interval velocities can be calculated from the normal moveout velocities derived in the cmp velocity analysis with some reasonable assumptions about subsurface conditions necessary for radar propagation interval velocity can be converted to an estimate of volumetric water content therefore by collecting gpr data in the multioffset cmp geometry not only is the radar profile improved but it also allows for an interpretation of subsurface variation in water content we show the application of these techniques to multioffset gpr data from the chalk river test area operated by atomic energy of canada limited

petrogenesis of the 1 43 ga sherman batholith se wyoming usa a reduced rapakivi type anorogenic granite the 1 43 ga sherman batholith southeastern wyoming usa origin that are found throughout the proterozoic anorogenic granite provinces of the southwestern usa adirshows extreme a type petrochemical characteristics compared with other mid proterozoic granite batholiths of north america it ondacks eastern canada southern greenland and the fennoscandian shield anderson 1983 phanerozoic consists of 1 the sherman granite a coarse grained biotite hornblende granite that locally contains fayalite and pyroxenes 2 examples include paleozoic granites of southeastern australia collins et al 1982 and of corsica poitrasson et the lincoln granite a medium grained biotite granite 3 a porphyritic biotite hornblende granite that probably formed by interaction al 1995 and the mesozoic nigerian younger granites jacobsen et al 1958 and the white mountain magma of granitic and mafic magmas and 4 iron enriched mafic dikes and pods the ilmenite series metaluminous sherman granite series foland allen 1991 anorogenic granite refers to plutons that are not associated with compressional exhibits extreme values of feo feo mgo and is rich in structures and that were emplaced long after any known k ree nb and y it crystallized at temperatures exceeding orogenic event anorogenic or a type granites loiselle 900 c and a pressure of 2 5 kbar with water activity of 0 7 wones 1979 are characterized by low h2o and o2 and dlog fo2 of 0 1 to 0 5 the lincoln granite which is fugacities along with high feo feo mgo k2o peraluminous and has less extreme a type geochemical characteristics na2o and k2o contents a type granites typically are rich crystallized at temperatures as low as 750 c and dlog fo2 of in incompatible elements including rare earth elements around 0 5 units above fmq fayalite magnetite quartz the ree zr nb and ta but poor in co sc cr ni ba rocks of the sherman batholith are chemically equivalent to lavas sr and eu minimum magma liquidus temperatures are from the yellowstone hotspot like the yellowstone magmas the 900 1000 c clemens et al 1986 creaser white sherman batholith probably originated by partial melting of under1991 some workers suggest these rocks are derived plated mantle derived mafic rocks from melting of tonalitic or more felsic crust anderson cullers 1978 collins et al 1982 clemens et al 1986 creaser et al 1991 whereas others relate the granites

evaluating soil moisture estimation from ground penetrating radar hyperbola fitting with respect to a systematic time domain reflectometry data collection in a boreal podzolic agricultural field the upper 30 cm of the soil profile which hosts the majority of the root biomass can be considered as the shallow agricultural root zone of most temperate crops the electromagnetic wave velocity in the soil obtained from reflection hyperbolas in ground penetrating radar gpr data can be used to estimate soil moisture sm finding shallow hyperbolas in a radargram and minimizing the subjective error associated with the hyperbola fitting are the main challenges in this approach nevertheless we were motivated by the recent improvements of hyperbola fitting algorithms which can reduce the subjective error and processing time to overcome the difficulty of finding very shallow hyperbolas we applied the hyperbola fitting method to reflections ranging from 27 to 50 cm depth using a 500 mhz centre frequency gpr and compared the estimated moisture with vertically installed 30 cm long time domain reflectometry tdr sensors we also compared tdr and gpr sample areas in a 2 d plane using different gpr survey types and different hyperbola depths sm measured with tdr and gpr were not significantly different according to mann whitney s test our analyses showed that a root mean square error of 0 03 m m was found between the two methods in conclusion the proposed method might be suitable to estimate sm with an acceptable accuracy within the root zone if the soil profile is fairly uniform within the application depth range