magmatic effects of the lunar late heavy bombardment abstract large volumes of mare basalts are present on the surface of the moon located preferentially in large impact basins mechanisms relating impact basins and mare basalt eruptions have previously been suggested lunar impacts removed low density material that may have inhibited eruption and created cracks for fluid flow icarus 139 1999 246 and lunar basins have long been described as catchments for magma e g rev geophys space phys 18 1980 107 and references therein we present a new model for melt creation under near side lunar basins that is triggered by the impacts themselves magma can be produced in two stages first crater excavation depressurizes underlying material such that it may melt in situ second the cratered lithosphere rises isostatically warping isotherms at the lithosphere asthenosphere boundary which may initiate convection in which adiabatic melting can occur the first stage produces by far the largest volume of melt but convective melting can continue for up to 350 ma we propose that giant impacts account for a large portion of the volume and longevity of mare basalt volcanism as well as for several compositional groups including high alumina high titanium kreep rich and picritic magmas

isotopic test of a thermally driven intraplate orogenic model australia a recently proposed model for intraplate orogenesis couples long term self heating of basement rocks by radioactive decay with thermal blanketing by overlying sedimentary deposits this model has been tested in one of the type areas in central australia the proterozoic musgrave complex which was reworked in an early cambrian orogeny we have determined the source of the pre orogenic and postorogenic sediments in the amadeus basin immediately to the north of the reworked basement including the fan deposits associated with uplift comprising uluru ayers rock and kata tjuta olgas detrital zircon age populations indicate that all basin sediments were derived from the musgrave complex which was therefore emergent rather than covered by sediments as required by the model in the basement the preservation of mesoproterozoic mica ages during transpressive burial to depths of 40 km ca 550 ma indicates that the associated thermal pulse was short lived not long lived as envisaged in the model we conclude therefore that the thermal blanketing model is inconsistent with the isotopic data and that the localization of deformation in intracratonic settings is associated with regions of contrasting strengths in central australia these are along the margins of the amadeus basin with the musgrave complex and arunta inlier

seismic slip in the lower crust inferred from granulite related pseudotachylyte in the woodroffe thrust central australia pseudotachylytes generated in granulite facies rocks are found in the woodroffe thrust central australia petrologic evidence and structural and textural features show that these pseudotachylytes contain typical melting origin features including injection occurrence rounded and embayed clasts and microlites within the fine grained matrix which formed contemporaneously with the wall granulite facies rocks under conditions of 8 kbar and 650 700 c these granulite related pseudotachylyte g pt veins are overprinted in subsequent deformation stages by three other types of pseudotachylytes including mylonite related m pt and ultramylonite related um pt pseudotachylytes that are then transcut by cataclasite related pseudotachylytes c pt the overprinting occurred following uplift of the lower crust where the g pt veins formed through the brittle plastic transition zone where the m pt and um pt veins occurred within the brittle dominated regime of the c pt generation zone in the upper crust the coexistence of multiple generations of large voluminous c pt m pt um pt and g pt veins indicates that numerous large earthquakes accompanying distinct seismic slip which produced the pseudotachylytes occurred over an extended period of seismicity and various depths of the crust within the woodroffe thrust zone the spatial distribution and structural features of the multiple stage pseudotachylytes suggest that coseismic slipping caused by large earthquakes which nucleated in the brittle dominated seismogenic zone propagated downward through the brittle plastic transition zone into the plastic dominated granulite facies depth from the upper to lower crust

on the petrogenesis of lunar troctolites new insights into cumulate mantle overturn mantle exposures in impact basins abstract we investigate lunar troctolite petrogenesis with a series of forward models we simulate the cumulate mantle overturn hypothesis by modeling the adiabatic ascent and decompression melting of primary mantle cumulates produced during differentiation of a lunar magma ocean lmo combined equilibrium and fractional crystallization of candidate liquids generated by the melting model can reproduce the predominant constituents of the lunar magnesian suite mg suite troctolites and norites contrary to previous hypotheses model results are consistent with previous studies challenging the proposed and long standing genetic relationship between mg suite and gabbronorites our mg suite petrogenetic model validates a direct temporal and chemical link between mg suite melt production and pressure release melting of primary lmo cumulates if so mg suite crystallization ages 4345 15 ma can be used to constrain the onset and duration of melting associated with mantle overturn based on our model results we propose an alternative mantle overturn hypothesis whereby upwelling olivine dominated cumulates experience decompression melting to produce the mg suite primary melt 1 9 melt at 2 1 gpa but that this melt was extracted from depth akin to lunar picritic glass magmas low degree partial melts at depths corresponding to 1 3 2 5 gpa thus our revised mantle overturn hypothesis reconciles mg suite petrogenesis without the expanse of an olivine dominated upper mantle as suggested by the current paradigms but contradicted by orbital data this hypothesis supports the presence of a low ca pyroxene dominated upper mantle consistent with mantle stratigraphy constrained by experimental and numerical simulations of lmo differentiation and proposed mantle exposures within impact basins

tectonic feedback intraplate orogeny and the geochemical structure of the crust a central australian perspective the geological record of intraplate deformation in central australia implies that past tectonic activity basin formation deformation and erosion has modulated the response of the lithosphere during subsequent tectonic activity in particular there is a correspondence between the localization of deformation during intraplate orogeny and the presence of thick sedimentary successions in the preserved remnants of a formerly widespread intracratonic basin this behaviour can be understood as a kind of tectonic feedback effected by the longterm thermal and mechanical consequences of changes in the distribution of heat producing elements induced by earlier tectonism from a geochemical point of view one of the most dramatic effects of intraplate orogeny in central australia has been the exposure in the cores of the orogens of deep crustal rocks largely depleted in the heat producing elements the geochemical structuring of the crust associated with the erosion of the heat producing upper crust resulted in long term cooling of the deep crust and upper mantle with associated lithospheric strengthening this is illustrated here by mapping the consequences of deformation and associated tectonic responses onto the h qc plane where h is the characteristic length scale for heat production distribution and qc is the total crustal heat production because rates of intraplate deformation in central australia appear to be much slower than that typical of plate margin orogens it is possible that the ongoing geochemical structuring of the crust has played an important role in terminating intraplate orogeny in central australia by providing a thermal lock the diagnostic geophysical signature of this lock may be the extraordinary gravity anomalies of the central australian intraplate orogens central australia provides an intriguing record of intraplate deformation resulting in the development of a number of extraordinary orogens that expose deep crustal rocks in their cores forman 1971 teyssier 1985 goleby et al 1989 the spatial distribution of intraplate deformation during the alice springs and petermann orogenies suggests that the mechanical response of this region has varied through time consequently this response is important for our understanding of the processes controlling reactivation in intraplate settings in previous contributions it has been argued that the distribution of deformation in central australia has been strongly influenced by prior tectonic processes such as basin formation and erosion sandiford hand 1998a hand sandiford 1999 this paper focusses on the way in which intraplate deformation modifies the geochemical structure of the crust in this region in particular the distribution of heat sources recognizing that the distribution of heat sources provides a first order control on the thermal structure of the crust the consequences of intraplate deformation for the longterm thermal and mechanical evolution of the crust is then explored our aim is to demonstrate the relevance of a novel style of tectonic feedback which seems to have modulated the longterm tectonic behaviour of the central australian region and which may be relevant to continental interiors in general the notion of tectonic feedback is compatible with a highly temperature dependent lithospheric rheology as suggested by many experimental studies of natural rocks such feedback has profound implications for the longterm tectonic evolution of continental interiors particularly their potential for reactivation the record of intraplate deformation in

the succoth cu ni pd deposit a new taxite hosted magmatic sulphide system in the west musgrave province western australia abstract the succoth cu ni pd deposit is large taxite hosted magmatic sulphide deposit located in the west musgrave province of western australia mineralisation consists of disseminated matrix and massive cu fe sulphides and lesser ni fe sulphides hosted within a mafic intrusive body the intrusive was emplaced within a sequence of earlier proterozoic mafic intrusives and meta volcanics during the giles event 1085 1040 ma and subsequently ductile deformed and strongly overprinted by hydrous alteration phases predominantly amphiboles an igneous architecture is presented based on contact and xenolithic relationships and internal fractionation trends in existing diamond drill holes and the silicate and sulphide mineralogy of the host and wall rock units are detailed sulphide geochemistry and stable isotope data are interpreted to reflect modifications to the magmatic signature of the mineralised intrusion as a consequence of wall rock contamination and hydrothermal overprinting genetic implications of different pge chemistry between disseminated and massive sulphides in the system are discussed

interior of the moon the presence of garnet in the primitive deep lunar mantle new trace element data have been generated by inductively coupled plasma mass spectrometry icp ms for 65 high and low ti mare basalts from the apollo 11 12 14 15 and 17 landing sites these data demonstrate that ratios of the high field strength elements and yttrium are generally chondritic in the mare source regions for the low ti basalts but nonchondritic in the high ti basalts and potassium rare earth elements and phosphorus kreep such differences can be explained by addition and subtraction respectively of ilmenite this interpretation is consistent with derivation of the basalts from lunar magma ocean lmo cumulates through which late stage ilmenite has sunk and mixed with earlier magma ocean products compositional differences between the mare basalts and volcanic glass beads suggest that at least some of the latter were derived from a garnet bearing source region siderophile and chalcophile element data suggest that the garnet bearing source escaped the lmo melting event and thus represents primitive moon material the remaining glasses are generally very low ti vlt and appear to have been derived from early lmo cumulates i e olivine and orthopyroxene similar to the vlt basalts the remaining glasses were derived from below the lmo cumulates and as the magmas rose they underwent sequential assimilation to varying degrees initially of an ilmenite rich cumulate followed by a kreep component this study presents geochemical evidence for the existence of garnet in a mare source and demonstrates the likelihood that the lmo was not whole moon thus preserving primitive lunar material which has acted as the source region for at least some of the volcanic glasses

a model for the thermal and chemical evolution of the moon s interior implications for the onset of mare volcanism crystallization of the lunar magma ocean creates a chemically stratified moon consisting of an anorthositic crust and magma ocean cumulates overlying the primitive lunar interior within the magma ocean cumulates the last liquids to crystallize form dense ilmenite rich cumulates that contain high concentrations of incompatible radioactive elements the underlying olivine orthopyroxene cumulates are also stratified with later crystallized denser more fe rich compositions at the top this paper explores the chemical and thermal consequences of an internal evolution model accounting for the possible role of these sources of chemical buoyancy rayleigh taylor instability causes the dense ilmenite rich cumulate layer and underlying fe rich cumulates to sink toward the center of the moon forming a dense lunar core after this overturn radioactive heating within the ilmenite rich cumulate core heats the overlying mantle causing it to melt in this model the source region for high tio2 mare basalts is a convectively mixed layer above the core mantle boundary which would contain small and variable amounts of admixed ilmenite and kreep this deep high pressure melting as required for the generation of mare basalts occurs after a reasonable time interval to explain the onset of mare basalt volcanism if the content of radioactive elements in the core and the chemical density gradients above the core are sufficiently high but within a range of values that might have been present in the moon regardless of details implied by particular model parameters gravitational overturn driven by the high density of magma ocean fe rich cumulates should concentrate high tio2 mare basalt sources and probably a significant fraction of radioactive heating toward the center of the moon this will have important implications for both the thermal evolution of the moon and for mare basalt genesis

transformation of fe ti gabbro to coronite eclogite and amphibolite in the baie du nord segment manicouagan imbricate zone eastern grenville province fe ti gabbros from the baie du nord segment of the manicouagan imbricate zone metamorphosed under high p t conditions during the grenvillian orogeny have been the focus of a detailed micropetrological study textures and mineral chemistry suggest that the mineral assemblages represent progressive stages of metamorphic transformation resulting in the formation of coronas pseudomorphs after igneous phases transitional and true granoblastic eclogites the transitional and eclogitic samples also have coronas which are developed locally around igneous xenocrysts of plagioclase and olivine the deformed margins of coronitic fe ti gabbros are transformed to amphibolite and contain clinopyroxene bearing leucosomes with garnet poikiloblasts that are indicative of high p t dehydration melting interpretation of garnet zoning and thermobarometry suggest that the highest p t conditions are recorded by coronas around xenocrysts c 720 800 c at 14 17 kbar and garnet clinopyroxene cores in granoblastic assemblages c 740 820 c at 13 17 kbar in the eclogitic samples re equilibration during the early stages of exhumation at high t conditions 700 c affected all samples and is evidenced by the widespread development of pargasite bearing plagioclase collars in the coronitic and transitional metagabbros and by widespread re equilibration of the eclogites giving lower p t estimates at grain boundaries however the difference in calculated pressure conditions between coronite and eclogite samples is consistent with increasing pressure depth from the coronites 11 13 kbar to the eclogites 13 17 kbar the p t conditions recorded by these rocks define a metamorphic field gradient which suggests high heat flow through the lower crust during the grenvillian orogeny

a young solidification age for the lunar magma ocean abstract the time at which the lunar magma ocean solidified can be determined from the lu hf isotope systematics of lunar rocks derived from magma sources that formed during crystallization of the lunar magma ocean the final magma ocean crystallization product termed urkreep is enriched in incompatible elements including k ree and p we have determined the initial hf isotopic compositions of four samples two kreep basalts and two mg suite norites the incompatible trace element compositions of these samples are controlled by an urkreep component and therefore the initial hf isotopic compositions of these samples represent the hf isotopic evolution of urkreep in order to correct the effects of neutron irradiation on the hf isotopic compositions of these samples we have developed a model that uses the stable hf and sm isotopic compositions measured on an irradiated sample to determine and correct for the thermal and epithermal neutron fluence that has modified the hf isotopic composition of the sample we use our corrected results to calculate a 176 lu 176 hf urkreep model age of 4353 37 ma and the 176 lu 177 hf of urkreep to be 0 0153 0 0033 the lu hf model age is concordant with the re calculated sm nd urkreep model age of 4389 45 ma and we take the average of these ages 4368 29 ma to represent the time at which urkreep formed this age is concordant with the age of the most reliably dated ferroan noritic anorthosite as well as 142 nd model ages for the formation or re equilibration of mare basalt sources taken together these ages indicate that the moon experienced a widespread large scale magmatic event around 4370 ma most plausibly attributed to solidification of the lunar magma ocean

proterozoic evolution and tectonic setting of the northwest paterson orogen western australia abstract the proterozoic igneous deformation and metamorphic histories of the palaeoproterozoic rudall complex in the northwestern paterson orogen can be linked to those of the arunta inlier in central australia and in part with the capricorn orogen in central western australia the similarities in deformation and metamorphic histories for these widely separated regions indicate a palaeoproterozoic continent continent collisional event between the palaeoproterozoic west australian and north australian cratons between c 1830 and 1765 ma in the paterson orogen this palaeoproterozoic collisional event resulted in the yapungku orogeny which included thrust stacking of clastic sedimentary and volcanic rocks deposition of the protoliths for the c 1790 ma siliciclastic paragneiss succession contemporaneous with granitic intrusion and metamorphism up to granulite facies during this 65 million year period the arunta inlier and capricorn orogen were deformed metamorphosed at medium to high grades and intruded by granitoids during the strangways orogeny in the arunta inlier and the capricorn orogeny in the capricorn orogen the neoproterozoic tarcunyah throssell and lamil groups are clastic sedimentary sequences that were deposited after 1070 ma in the northwestern paterson orogen and deformed by the miles orogeny before 678 ma the miles orogeny produced a northwesterly trending fold and fault system of tight to isoclinal upright and overturned folds and thrust faults the orogeny may have been coincident with the c 750 720 ma areyonga tectonic movement affecting the arunta inlier and the lower neoproterozoic part of the amadeus basin in central australia at c 550 ma the paterson orogeny which is most likely equivalent to the petermann orogeny in the musgrave complex of central australia deformed the northwestern paterson orogen and was preceded by local intrusion of granites the similarities of styles and timing of deformation in the northwestern paterson orogen arunta inlier and capricorn orogen indicate that these three regions were probably linked during most of the proterozoic

the musgrave province stitching north west and south australia abstract the musgrave province in central australia is an east west trending 120 000 km2 region composed of lithologic units that range in age from earliest mesoproterozoic to neoproterozoic it is one of the few terrains in australia that records significant grenvillian aged tectonism and has a distinctly younger geological history than the surrounding fragments of proterozoic australia compared to other proterozoic terranes of australia the evolution of the musgrave province is poorly understood the region contains evidence for the development of earliest mesoproterozoic arc related magmatism with major juvenile crustal additions comprising intercalated felsic and mafic gneisses with protolith ages ranging from ca 1 60 to 1 54 ga this period of arc magmatism was followed by closure of the ocean separating the north australian craton nac from the south australian craton sac at ca 1 54 ga arc magmatism and collision was followed by a period of extension during which protoliths to the metasedimentary rocks of the eastern musgrave province were deposited at ca 1 4 ga the combined juvenile nd isotopic signature and detrital zircon ages from these metasediments suggests provenance from non australian sources with possible sources originating from laurentia granitic magmatic events occurred at ca 1 3 and 1 20 1 14 ga the latter comprising the voluminous a type granites of the pitjantjatjara supersuite the intrusion of these magmatic units provide key temporal constraints on deformational events and are coeval with the voluminous a type suites of laurentia which would invite correlation of australia with laurentia at ca 1 30 1 14 ga these magmatic episodes are accompanied by deformation at granulite facies at ca 1 30 ga unnamed event and 1 23 1 15 ga musgrave orogeny these deformation metamorphic events have completely recrystallised any primary layering within the pre 1 30 ga rocks forcing interpretations on their genesis to be inferred from geochemical and isotopic data the tectonic significance of these events is not clear however they may form part of a larger grenville aged deformational belt extending into the western australian albany fraser province and antarctica emplacement of the voluminous mafic ultramafic giles complex and associated granulite facies metamorphism of the giles event occurred at ca 1 078 ga the layered intrusions of the giles complex are generally fault bound and are considered to represent discrete bodies emplaced in an extensional regime associated with generation of the warakurna large igneous province the ca 1 08 ga alcurra dolerite unnamed ca 1 0 ga olivine dolerites and ca 0 8 ga amata dolerite dissect much of the musgrave province the alcurra dolerite and unnamed olivine dolerite dykes have been proposed as originating from a modified sub continental lithospheric mantle whereas the amata dolerite is proposed to be plume related coinciding with the initiation of rifting creating the centralian superbasin an earliest cambrian intraplate transpressional event is recorded in the ca 550 ma petermann orogeny this resulted in deep crustal exhumation of much of the northern musgrave province from beneath the centralian superbasin with mylonitic deformation recorded at pressures of 12 kbar and temperatures of 700 750 c

controls on the locus of intraplate deformation in central australia abstract the locus of intraplate deformation in central australia changed from the presently preserved southern margin of the amadeus basin during the late neoproterozoic to early phanerozoic petermann orogeny to the northern margin in the late phanerozoic alice springs orogeny immediately prior to each event the thickness of the amadeus basin sediments varied from as little as 1 5 km in the central parts of the basin to as much as 7 km in the vicinity of the presently preserved margins of the basin with the locus of deformation mimicking the locus of maximum sedimentary thicknesses at the onset of each orogenic event as such these orogenies represent extreme examples of basin inversion a process observed in many intracratonic basins worldwide we show that differential burial of the central australian proterozoic basement complexes beneath the amadeus basin is capable of producing variations in moho temperature of up to 30 c prior to the petermann orogeny and up to 110 c prior to the alice springs orogeny for a brace goetze model of lithospheric rheology the variations in moho temperature equate to variations in effective lithospheric strain rate of 1 4 orders of magnitude implying that variations in thickness of the sedimentary blanket may have played a primary role in localising phanerozoic intraplate deformation in central australia an appealing aspect of this model lies in its corollary that the removal of the sedimentary blanket during denudation of the orogen will be accompanied by dramatic cooling and strengthening of the lithosphere this may provide a plausible explanation for the long term persistence of the extraordinary gravity anomalies 150 mgal developed during these central australian intraplate orogenies

monazite behaviour and age significance in poly metamorphic high grade terrains a case study from the western musgrave block central australia abstract integrated in situ textural chemical and electron microprobe age analysis of monazite grains in a migmatitic metapelitic gneiss from the western musgrave block central australia has identified evidence for multiple events of growth and recrystallisation during poly metamorphism in the mesoproterozoic garnet sillimanite bearing metapelite underwent partial melting and segregation to palaeosome and leucosome during metamorphism between 1330 and 1296 ma with monazite grains in leucosome recording crystallisation at 1300 ma monazite breakdown during melting is inferred to have occurred in the palaeosome during a subsequent granulite facies event at 1200 ma deformation and metamorphism of leucosome and palaeosome resulted in partial disturbance of ages and potential minor growth on 1300 ma monazite in leucosome growth of new high y hree monazite in palaeosome domains occurred during garnet breakdown in the presence of sillimanite to cordierite and spinel as a result of post peak isothermal decompression diffusive enrichment of resorbed garnet rims in y hree suggests garnet breakdown occurred slower than volume diffusion of ree monazite in both palaeosome and leucosome were subsequently partially to penetratively recrystallised during a retrogression event that is suggested to have occurred at 1150 1130 ma the intensity of recrystallisation and disturbance of ages appears linked to proximity to retrogressed garnet porphyroblasts and their occurrence in the relatively reactive or fertile local environments provided by the palaeosome mesosome volumes which caused localised changes in retrogressive fluids towards compositions more aggressive to monazite like reaction textures it is apparent that domainal equilibrium and reaction may control or at least strongly influence monazite ree and u th pb chemistry and hence ages

post orogenic 1500 ma thermal history of the proterozoic eastern fold belt mount isa inlier australia the paucity of sedimentary rocks younger than 1500 ma within the mt isa inlier renders it difficult to determine its post orogenic exhumation and tectonic history except by inference from the stratigraphy of the surrounding areas we present hornblende white mica biotite and alkali feldspar 40ar 39ar data from the eastern fold belt of the inlier which reveal a previously unrecognised complex post orogenic non linear cooling history plateau and total fusion 40ar 39ar ages range between 1500 and 1130 ma and record increases in regional cooling rates of up to 18 c my during 1460 1410 and 1280 1050 ma forward modelling of the alkali feldspar 40ar 39ar arrhenius parameters reveals subsequent increases in cooling rates during 740 640 and 600 500 ma the cooling episodes were driven by both erosional exhumation at maximum rates of 0 9 km my and thermal relaxation following magmatic events early mesoproterozoic cooling is synchronous with exhumation and shearing during the anmatjira event in the arunta block and late mesoproterozoic cooling occurred at the same time as magmatic events in the arunta and musgrave blocks as well as grenville aged orogenesis in the albany fraser belt more localised cooling during the middle neoproterozoic may be a far field response to the separation of australia and laurentia whereas latest neoproterozoic cambrian cooling and exhumation was probably driven by collisional tectonics associated with the petermann ranges and delamerian orogenic events major changes in the stress field of the australian plate that are synchronous with the assembly and break up of rodinia and gondwana resulted in the repeated brittle reactivation of the eastern fold belt probably via the displacement of long lived basement faults

pristine lunar glasses criteria data and implications major element analyses of several thousand glasses from all of the apollo landing sites have resulted in the identification of 25 groups of pristine i e volcanic glass the nickel in these pristine glasses is shown to be indigenous not meteoritic contamination and to be correlated with mg the chemical data indicate that these glasses are consistently better candidates for primary magmas than the majority of crystalline mare basalts the pristine glasses support the view that assimilative processes ringwood and kesson 1976 involving two cumulate systems in the differentiated mantle operated during mare petrogenesis the reality of those assimilative interactions is evident by the occurrence of two linear arrays among the chemistries of the glasses data suggest that these cumulate components in the differentiated mantle persist for lateral distances of at least 1000 km and therefore appear to be products of a vast magma ocean that existed early in lunar history alternative hypotheses claiming that the highlands crust and mare source regions were produced by serial magmatism without a magma ocean have not yet considered all of the constraints derived from the pristine glasses

chronological evidence that the moon is either young or did not have a global magma ocean a new age determination for a moon rock collected close to the site of the apollo 16 lander has yielded a surprisingly young age of around 4 360 million years this age would require either that the moon solidified some 200 million years after the formation of the solar system significantly later than is assumed by most lunar formation models or that the long held theory that the moon once had a primordial global magma ocean is flawed in the latter case much of the lunar crust could have been produced by non magma ocean processes such as serial magmatism chemical evolution of planetary bodies ranging from asteroids to the large rocky planets is thought to begin with differentiation through solidification of magma oceans many hundreds of kilometres in depth1 2 3 the earth s moon is the archetypical example of this type of differentiation evidence for a lunar magma ocean is derived largely from the widespread distribution compositional and mineralogical characteristics and ancient ages inferred for the ferroan anorthosite fan suite of lunar crustal rocks the fans are considered to be primary lunar flotation cumulate crust that crystallized in the latter stages of magma ocean solidification according to this theory fans represent the oldest lunar crustal rock type2 3 4 attempts to date this rock suite have yielded ambiguous results however because individual isochron measurements are typically incompatible with the geochemical make up of the samples and have not been confirmed by additional isotopic systems5 6 7 8 9 by making improvements to the standard isotopic techniques we report here the age of crystallization of fan 60025 using the 207pb 206pb 147sm 143nd and 146sm 142nd isotopic systems to be 4 360 3 million years this extraordinarily young age requires that either the moon solidified significantly later than most previous estimates or the long held assumption that fans are flotation cumulates of a primordial magma ocean is incorrect if the latter is correct then much of the lunar crust may have been produced by non magma ocean processes such as serial magmatism10

unique spinel rich lithology in lunar meteorite alha 81005 origin and possible connection to m3 observations of the farside highlands 1 a new lunar rock type rich in mg fe al spinel and lacking abundant olivine and pyroxene was recently detected by near infrared reflectance spectroscopy by the m3 instrument on the chandrayaan 1 spacecraft no such material has been described from lunar rocks either returned samples or meteorites here we describe a fragment of rock containing 30 mg fe al spinel from the lunar meteorite alha 81005 although the fragment is not identical to the material detected by m3 it contains 20 olivine pyroxene both share the defining feature of an unusual enrichment in spinel the fragment 350 150 m is so fine grained that it reasonably could represent a larger rock body it is not spinel rich merely by chance incorporation of a few spinel grains the fragment is so rich in spinel and consequently in al2o3 that it could not have formed by melting a peridotitic mantle or a basaltic lunar crust the clast s small grain size and its apparent disequilibrium between spinel and pyroxene suggest fairly rapid crystallization at low pressure it could have formed as a spinel cumulate from an impact melt of troctolitic composition or from a picritic magma body that assimilated crustal anorthosite on its margins the latter mechanism is preferred because it not only explains the petrographic and chemical features of our clast but is also consistent with the regional setting of the moscoviense spinel deposit in that area m3 spectra have defined areas rich in olivine and in orthopyroxene these could represent igneous cumulate rocks formed during crystallization and differentiation of a picritic magma body and thus suggests a possible link between the analyzed clast and the observed spinels at moscoviense

parent rock and climatic evolution control on the genesis of ni bearing clays in ni co laterites new inferences from the wingellina deposit western australia abstract oxide type ni laterites seldom contain significant ni phyllosilicates reserves this study is focused on the mineralogy of ni clays mainly occurring in the saprolite zone of the wingellina oxide type ni co laterite deposit despite most of the wingellina reserves occur in the oxide zone the deposit also has a well developed high ni grade saprolite horizon this study presents a mineralogical and chemical characterization of the ni phyllosilicates of the wingellina saprolite ore aimed to understand the role of diverse bedrocks gabbro and serpentinite and the influence of climate on the formation of different clay types the main phyllosilicate in the gabbro derived saprolite consists of dioctahedral al and ni montmorillonite originated from the weathering of pyroxene the genesis of al and ni rich montmorillonite from pyroxene can be explained by an open system alterative process in which al mainly derives from the dissolution of plagioclase in the serpentinite derived saprolite the alteration pathway followed a multistage evolution i lateritic alteration of serpentine i into ni serpentine ii and tri and dioctahedral smectites saponite and nontronite ii late precipitation of interstratified ni clays chlorite smectite and talc smectite as a replacement of former phyllosilicates and as neoformed minerals the latest phenomenon may be related to the late miocene shift from humid and acid tropical climate to saline and alkaline conditions arid to semi arid climate and represents an example of post lateritization processes rarely observed in laterites located on stable cratons the aridity driven precipitation of ni rich interstratified clays in the wingellina laterite can be seen as a new model for explaining the evolution of ni laterites in stable cratonic settings experiencing post lateritization aridity

origin of the apollo 14 15 and 17 yellow ultramafic glasses by mixing of deep cumulate remelts abstract we examine the fo2 dependent melting conditions of the apollo 14 yellow intermediate ti ultramafic glasses and the melting processes that formed the full suite of lunar yellow ultramafic glasses multiple saturation experiments indicate that the apollo 14 yellow glass would have been in equilibrium with residual olivine and low ca pyroxene near 1530 c and 2 4 gpa at iw 2 at iw 2 the multiple saturation point moves to greater depth and higher temperature to 1580 c and 3 0 gpa combining the results of this study with that of krawczynski and grove 2012 on more ti rich apollo orange and red glass indicates that the fo2 induced change in multiple saturation pressure correlates with the fe ti molar feo tio2 mgo feo tio2 where tio2 all ti calculated as ti4 of the liquid further a decrease in the olivine fe mg exchange coefficient at lower fo2 suggests that fe2 is complexing more efficiently with ti3 at the expense of mg in the melt than it did with ti4 at higher fo2 processes involving assimilation and or fractionation and or melt wall rock reaction all fail to produce the within suite compositional variability observed in the apollo 14 15 and 17 yellow glasses mixing of remelted source cumulates combined with small amounts of olivine fractionation are the only mechanisms that can reproduce all three trends we present a quantitative model of the mixing process with simultaneous olivine fractionation remarkably the trends can be explained by mixing melts of an ultramafic source olivine pigeonite or orthopyroxene a clinopyroxene ilmenite bearing cumulate and kreep lunar mantle overturn is the most likely process that can reconcile the observed major and trace element compositional characteristics and the experimental results these two constraints are consistent with different models of lunar magma ocean crystallization snyder et al 1992 eklins tanton et al 2011 a complex hot thermal history is necessary to generate the magmas that mixed to form the yellow ultramafic glasses

lunar magma ocean crystallization revisited bulk composition early cumulate mineralogy and the source regions of the highlands mg suite abstract crystallization of the lunar magma ocean lmo has been numerically modeled and its products inferred from sample observations but it has never been fully tested experimentally this study is a reexamination of the lmo hypothesis by means of the first experimental simulation of lunar differentiation two end member bulk moon compositions are considered one enriched in refractory lithophile elements relative to earth and one with no such enrichment a two stage model of magma ocean crystallization based on geophysical constraints is simulated and features early crystal suspension and equilibrium crystallization followed by fractional crystallization of the residual magma ocean an initially entirely molten moon is assumed part 1 of this study presented here focuses on stage 1 of this model and considers the early cumulates formed by equilibrium crystallization differences in mantle mineralogy resulting from different bulk moon compositions and implications for the source regions of the highlands mg suite refractory element enriched bulk moon compositions produce a deep mantle that contains garnet and trace cr spinel in addition to low ca pyroxene and olivine in contrast compositions without refractory element enrichment produce a deep dunitic mantle with low ca pyroxene but without an aluminous phase the differences in bulk composition are magnified in the residual melt the residual lmo from the refractory element enriched composition will likely produce plagioclase and ilmenite earlier and in greater quantities both compositions produce mg rich early cumulate piles that extend from the core mantle boundary to 355 km depth if 50 equilibrium crystallization and whole moon melting are assumed these early lmo cumulates provide good fits for the source regions for a component of the high mg ni and co poor parental magmas of the mg suite cumulates if certain conditions are called upon the olivine in early lmo cumulates produced by either bulk moon composition is far too rich in cr to be reasonable for the source regions of the mg suite meaning either core formation in the presence of s and or c must be invoked to deplete the lmo and the crystallizing olivine in cr or that current estimates of the bulk lunar cr content are too high we infer that melts meeting the criteria of the mg suite parents could be produced from early lmo cumulates by solid state kreep and plagioclase hybridization near the base of the crust and subsequent partial melting additionally we propose a revised model for mg suite petrogenesis

magnetotelluric constraints on the tectonic setting of grenville aged orogenesis in central australia abstract magnetotelluric mt data were collected over a 480 km long profile in central australia extending from the mesoarchaean palaeoproterozoic gawler craton into the mesoproterozoic neoproterozoic musgrave province the two regions have contrasting geological histories and many reconstruction models of proterozoic australia propose that they were juxtaposed during the mesoproterozoic despite the significant differences in geological background between the gawler craton and the musgrave province the mt data did not image an electrical structure or any change in electrical character between them mt models suggest that southern central australia is electrically separated into two parts the first comprising the northernmost gawler craton and the musgrave province has a 5 km thick layer of moderate resistivity overlying highly resistive crust the second comprising the central northern gawler craton displays moderate resistivity to the base of the crust the lithospheric mantle underlying both electrical regions is uniformly highly resistive our results suggest that the musgrave province and gawler craton are more closely related than is currently recognized we propose that the gawler craton forms basement to the musgrave province and that the grenvillian musgrave orogeny was an intracratonic reworking event that overprinted the older basement

subdivision of the mg suite noritic rocks into mg gabbronorites and mg norites mg suite noritic rocks can be divided into two groups the mg gabbronorites and the mg norites the rocks of these groups differ in ratios of high ca pyroxene to total pyroxene compositions of pyroxene and plagioclase assemblages of ti nb and zr bearing minerals compositions of chrome spinel bulk rock ti sm and sc sm and measured ages the two groups probably crystallized from different types of parent magmas two hypotheses are offered for the differences in composition of the parent magmas one hypothesis ascribes the differences to compositional heterogeneity of the mantle source areas the other hypothesis ascribes the differences to variations in extent of partial melting of the mantle source regions and variations in extent of assimilation of the anorthosite and the highly differentiated residual liquid that were produced during the primordial lunar differentiation

possible mantle origin of olivine around lunar impact basins detected by selene the composition structure and evolution of the moon s mantle is poorly constrained a global survey of the moon s surface using the spectral profiler onboard the lunar explorer selene kaguya identifies a number of exposures of olivine in concentric regions around lunar craters with a possible mantle origin

magnetotelluric constraints on subduction polarity reversing reconstruction models for proterozoic australia two dimensional lithospheric scale magnetotelluric imaging in the central australian proterozoic has constrained the large scale architecture of terrane assembly during paleoproterozoic accretion and collision the comparatively conductive north australian craton consisting of rocks between 2500 and 1730 ma in age has been imaged to extend for 150 km under the 1690 1620 ma warumpi province which forms part of a large comparatively juvenile terrane in central southern australia collision between the north australia craton and warumpi province occurred ca 1640 ma the boundary between these domains is modeled to be subvertical at crustal scale but dips south at 45 in the mantle to depths of 150 km we interpret this geometry to reflect lithospheric scale underthrusting of the north australian craton beneath the warumpi province and suggest that it provides a first order constraint on subduction polarity during collision ca 1640 ma in contrast most contemporary models for the evolution of paleoproterozoic australia propose that the north australian craton was located on the overriding plate of a long lived ca 1800 1550 ma north directed subduction system the polarity of these models is not consistent with the lithospheric scale geophysical architecture

detrital zircon provenance constraints on the evolution of the harts range metamorphic complex central australia links to the centralian superbasin until recently it has been widely accepted that protoliths to metasediments of the harts range metamorphic complex central australia were deposited prior to c 1 75 ga and form part of the palaeoproterozoic arunta inlier however new sensitive high resolution ion microprobe u pb analyses of detrital zircon together with recently published data suggest that they were deposited coeval with c 545 520 ma sediments from the adjacent little metamorphosed neoproterozoic to palaeozoic centralian superbasin protoliths of the harts range metamorphic complex were deposited in the irindina sub basin an early to mid cambrian rift located between the present day amadeus and georgina basin remnants of the centralian superbasin deposition occurred during a widespread and long lived interval of extension in parts of central australia associated with eruption of the voluminous kalkarinji continental flood basalts the harts range metamorphic complex was metamorphosed to upper amphibolite to granulite facies conditions within c 40 ma of deposition of its sedimentary protoliths

imaging the basement architecture across the cork fault in queensland using magnetic and gravity data abstract the basement rocks in central queensland are largely obscured by the phanerozoic sedimentary succession and direct information comes only from sparse geological data 2 5d forward modelling of regional aeromagnetic and bouguer gravity data has been undertaken to unveil the crustal architecture at the junction of the proterozoic mount isa terrane and the phanerozoic thomson orogen in queensland the most prominent geophysical character is represented by the abrupt termination of positive nnw trending geophysical anomalies of the mount isa terrane against ne trending low amplitude gravity and magnetic anomalies of the diamantina river domain of the thomson orogen potential field forward modelling indicates that the lower basement crust of the thomson orogen is petrophysically indistinguishable from the crust of the proterozoic mount isa terrane we interpret that the prominent gradients associated with the cork fault represent the displacement and burial of the mount isa terrane crust under the thomson orogen in this context the cork fault is inferred to represent a fundamental crustal discontinuity but does not represent the eastern margin of rodinia because the thomson orogen is floored by precambrian continental crust initiation of the cork fault might have occurred as early as the mesoproterozoic at that time the cork fault was a major structure that developed during the separation of the mount isa terrane and the curnamona province it is inferred that this break up occurred during initial n s to nnw sse extension the cork fault formed part of a network of major north and south dipping normal faults active at that time the cork fault was repeatedly reactivated during the neoproterozoic rodinia break up and during the phanerozoic evolution of the tasmanides we suggest that the segment of the inferred tasman line along the southern termination of the mount isa terrane should be regarded as a set of structures offsetting the proterozoic crust rather than a simple lineament dividing the proterozoic and the phanerozoic australian continent

geometry of a large scale low angle midcrustal thrust woodroffe thrust central australia the musgrave block in central australia exposes numerous large scale mylonitic shear zones developed during the intracontinental petermann orogeny around 560 520 ma the most prominent structure is the crustal scale over 600 km long e w trending woodroffe thrust which is broadly undulate but generally dips shallowly to moderately to the south and shows an approximately top to north sense of movement the estimated metamorphic conditions of mylonitization indicate a regional variation from predominantly midcrustal circa 520 620 c and 0 8 1 1 gpa to lower crustal 650 c and 1 0 1 3 gpa levels in the direction of thrusting which is also reflected in the distribution of preserved deformation microstructures this variation in metamorphic conditions is consistent with a south dipping thrust plane but is only small implying that a 60 km long n s segment of the woodroffe thrust was originally shallowly dipping at an average estimated angle of 6 the reconstructed geometry suggests that basement cored thick skinned midcrustal thrusts can be very shallowly dipping on a scale of many tens of kilometers in the direction of movement such a geometry would require the rocks along the thrust to be weak but field observations e g large volumes of syntectonic pseudotachylyte argue for a strong behavior at least transiently localization on a low angle near planar structure that crosscuts lithological layers requires a weak precursor such as a seismic rupture in the middle to lower crust if this was a single event the intracontinental earthquake must have been large with the rupture extending laterally over hundreds of kilometers

evidence for aseismic deformation rate changes prior to earthquakes abstractfor ten earthquakes in nonmagmatic settings there are credible published accounts of pre earthquake deformation rate changes lasting hundreds of seconds to more than a decade although most m 7 5 earthquakes have occurred without detectable pre earthquake deformation the detection threshold for aseismic deformation remains high in that aseismic slip with moment equivalent to an m5 earthquake would in most although not all cases have been missed interseismic deformation rates vary without being followed by earthquakes and a strain rate change prior to the 1989 mw6 9 loma prieta california earthquake is shown to be similar in size to many other rate changes that have occurred since that time most examples of pre earthquake aseismic deformation lasting hundreds of seconds or more probably originate adjacent to or downdip of the seismic rupture plane rather than within the zone that undergoes seismic failure

density and compressibility of the molten lunar picritic glasses implications for the roles of ti and fe in the structures of silicate melts abstract the density and compressibility of four synthetic molten lunar picritic glasses was investigated from 0 to 10 gpa and 1748 to 2473 k the picritic glasses were collected from the lunar surface during the apollo missions and they are hypothesized to have rapidly quenched as glass beads during pyroclastic fire fountain eruptions the specific melt compositions investigated in the present study are the apollo 15 green glass type c a15c tio 2 0 26 wt the apollo 14 yellow glass a14y tio 2 4 58 wt the apollo 17 orange glass 74220 type a17o tio 2 9 12 wt and the apollo 14 black glass a14b tio 2 16 40 wt these glasses are reported to represent primary unfractionated melts making them a prime candidate for experimental studies into lunar basalt density and compressibility during partial melting of the lunar mantle sink float experiments were conducted on the synthetic molten lunar glass compositions using a piston cylinder apparatus p p 2 5 gpa in order to bracket the density of the melts new sink float data are reported for a15c a14y and a17o which are combined with previously published density and compressibility data on a15c a17o and a14b although the ti rich liquids are highly compressible at lower pressures they become nearly incompressible at much higher pressures when compared to the molten low ti glasses consequently the melts with the most tio 2 a14b are the least dense at higher pressures a reversal of what is seen at lower pressures this change in density and compressibility is attributed to changes in coordination of ti and fe in the silicate melt structure as ti 4 abundances in the silicate melt increase predominantly iv ti 4 and iv fe 2 change to vi ti 4 and vi fe 2 in the melt structure all of the data from the present study were used to calculate a birch murnaghan equation of state bm eos for each melt composition the bm eos model for each composition was then combined with previously published estimates for the residual mantle source mineralogy and depth of origin for each of the glasses to assess the density of the partial melt with respect to its point of origin this information was used to determine whether or not the melt would rise or sink with respect to its source region we determined that all melt compositions with the exception of the a17o melt should have been able to rise to the crust mantle boundary as a result of buoyancy forces alone although different mechanisms are likely required for magma ascent through the lunar crust for the rise of a17o other modes of ascent through the lunar mantle are required to extract this melt composition from the mantle and volatiles are not a plausible solution on the grounds of melt density alone

intraplate deformation in central australia the link between subsidence and fault reactivation abstract central australia has experienced two intraplate orogenic events involving significant north south shortening the late neoproterozoic to early cambrian petermann orogeny and the devonian to carboniferous alice springs orogeny in each event pre existing structures inherited from mesoproterozoic terrain amalgamation were reactivated and basement rocks exhumed from beneath thick sedimentary successions accumulated in the centralian superbasin the pattern of fault reactivation during these events shows a striking similarity to the pattern of subsidence in the overlying basin immediately prior to the petermann orogeny the centralian superbasin was thickest in the vicinity of the musgrave block the region in which deformation was subsequently localised at the same time crustal scale faults elsewhere in central australia that were covered by a relatively thin sheet of sediment remained inactive despite being favourably oriented to accommodate the north south shortening between the petermann and alice springs orogenies subsidence patterns shifted such that fault systems in the arunta block and also those in the southern musgrave block were buried by significant thicknesses of sediment whereas the major structures that were exhumed during the petermann orogeny were not significantly buried during the alice springs orogeny reactivation once again occurred along the most deeply buried faults even in the instances where those faults had remained inactive during the earlier petermann orogeny importantly the major petermann aged structures that were not buried during renewed subsidence remained inactive during the alice springs orogeny the record of reactivation implies that the presence of pre existing crustal scale faults alone was insufficient to localise deformation rather fault reactivation appears to have required a priming process that modulated the strength of the lithosphere on a regional scale the correspondence between the distribution of basement fault reactivation and subsidence patterns during both the petermann and alice springs orogenies implies a link between relatively thick sedimentation and long term lithospheric weakening we show that this link is compatible with the thermal effects of a thick sedimentary blanket in the context of central australia the mechanical impact of basin formation is likely to be enhanced by the presence of regionally elevated heat production in the proterozoic basement

thermal rheological and kinematic conditions for channelized lower crustal flow in a threshold example abstract lower crustal flow zones occur in large and hot orogens and rifts where they occur in association with large areas possessing high gravitational potential energy gpe and low lower crust viscosity lower crustal flow zones are also known from regions where neither the rheological nor gpe conditions are sufficiently well developed for widespread flow to occur for these examples the conditions required to form crustal flow zones are less well defined one such case occurs within the ca 600 530 ma petermann orogeny in central australia this work investigates the conditions under which this flow zone developed considering differences with the adjacent regions where flow is not observed a transect of crustal structure in the central petermann orogen is developed that takes into account geological and geophysical data including time constrained pressure and temperature estimates for the petermann orogeny the deformation of this region is reconstructed showing that lower crustal flow was driven by high amplitude crustal scale folding the folding extruded the lower crust towards the foreland causing crustal thickening and buoyant uplift of the orogenic core channelized lower crustal flow is not known from either the eastern or western parts of the orogen and a comparison with these regions suggests three main conditions are required firstly the lower crust must be sufficiently hot and volatile rich to allow melt weakening secondly crustal rheology must allow ductile deformation of the mid to lower crust without high strength layers finally a high degree of lateral confinement is required to form pressure gradients capable of driving flow these three conditions were met only in the central petermann orogen and not in the east or the west this example of a lower crustal flow zone illustrates the combined influence of thermal rheological and kinematic threshold conditions on the initiation and development of channelized lower crustal flow in orogens

constraints from diffusion profiles on the duration of high strain deformation in thickened crust diffusion profiles in garnet are used to determine the duration of movement on shear zones in the musgrave block central australia grenville age granulites were overprinted at depths of 40 km by high strain zones during the intracratonic petermann orogeny ca 550 ma ago in these zones quartzofeldspathic mylonites contain garnet from the early granulite facies event that developed compositional gradients during the high pressure overprint the diffusion of ca into garnet is linked with the release of ca in plagioclase the only calcic mineral in the rock during neocrystallization of sodic feldspar during high strain deformation available diffusion data on garnet directly define the duration of high strain deformation at eclogite facies our results indicate that the integrated time scales of movement in individual high strain zones were short lived between 0 07 ma and 1 4 ma and that wide shear zones were active longer than narrow ones in addition we find that relict k feldspar in one of the narrow eclogite facies shear zones yields a 40 ar 39 ar age that is partially reset indicating that the thermal event was also short lived these short time scales support the hypothesis that shear heating was the dominant source of heat for the eclogite facies overprint

regional high pressure metamorphism during intracratonic deformation the petermann orogeny central australia the petermann orogeny is a late neoproterozoic to cambrian c 560 520 ma intracratonic event that affected the musgrave block and south western amadeus basin in central australia in the mann ranges within the central musgrave block mesoproterozoic granulite facies gneisses granites and mafic dykes have been substantially reworked by deep crustal non coaxial strain of late neoproterozoic to early cambrian age dolerite dykes have recrystallized to garnet granulite facies assemblages associated with the development of a mylonitic fabric at p 12 13 kbar and t 700 750 c migmatization is restricted to discrete shear zones which represent conduits for hydrous fluids during metamorphism peak metamorphism was followed by decompression to c 7 kbar reflecting exhumation of the terrane along the south dipping woodroffe thrust in scattered outcrops north of the mann ranges peak metamorphism occurred at p 9 10 kbar and t c 700 c the woodroffe thrust separates these deep crustal mylonites from granites that were metamorphosed during the petermann orogeny at p c 6 7 kbar and t c 650 c the similarity in peak temperatures at different crustal levels implies an unusual thermal regime during this event the existence of a relatively elevated geotherm corresponding with th and k enriched granites that were in the mid crust during the petermann orogeny suggests that radiogenic heat production may have substantially contributed to the thermal regime during metamorphism this potentially has implications for the mechanisms by which intra plate strain was localized during this event

indian derived sediments deposited in australia during gondwana assembly abstract sedimentary exchanges across continents during the collisional assembly and lifespan of supercontinents provide a powerful way of testing the assembling process and configuration of supercontinents the ord basin in north western australia contains mid cambrian shallow marine and deltaic sedimentary successions that post date the ca 650 520 ma paterson petermann orogeny ppo but are synchronous with the ca 530 470 ma kurgiakh orogeny in north india we report new u pb ages and hf isotopes of detrital zircons from the mid cambrian ord basin that suggest indian derived sedimentary input to australian cambrian basins compilations of published ediacaran ordovician samples from the centralian superbasin indicate that during the ca 650 520 ma ppo the 1200 1100 ma musgrave province in central australia was exhumed and fed sediments to the syn ppo centralian superbasin soon after the ppo termination the musgrave province likely remained a topographic high and continued to supply detritus to the amadeus and officer basins that were fragmented from the centralian superbasin supplemented by the 630 ma granites of the paterson orogen conversely we conclude that the mid cambrian ord basin did not record similar sedimentary provenance from the musgrave province rather indian derived detritus travelled along the northeastern gondwanan continental margin via longshore currents and in turn incorporated paterson granitic detritus during the assembly of gondwana including the kurgiakh orogeny in north india a broad provenance comparison between potential eastern gondwanan source regions and relevant asian neighbours suggests that south china and south qiangtang are affiliated with northern india but lhasa appears to have had a mixed affiliation between india and australia

thermal history and differential exhumation across the eastern musgrave province south australia insights from low temperature thermochronology abstract multi method geo and thermochronological data obtained for palaeo and mesoproterozoic granitoids traversing the main structural architecture of the eastern musgrave province within south australia reveal multiphase cooling histories apatite u pb dating on six samples yield consistent ages of 1075 1025 ma suggesting a thermal reset coinciding with mantle derived magmatism of the greater warakurna large igneous province 1080 1040 ma apatite fission track aft analysis indicate that four discrete thermal events affected the study area inducing cooling through the aft partial annealing zone 60 120 c supported by apatite and zircon u th sm he data late neoproterozoic cooling from deep crustal levels to temperatures the results highlight a complex phanerozoic thermal history for the eastern musgraves and help to elucidate the poorly appreciated tectonic evolution of inland australia this study further demonstrates how high density sample transects across structural architecture can assess the relative crustal level and associated preservation of the thermal history record within fault reactivated terranes

architecture and emplacement of the nebo babel gabbronorite hosted magmatic ni cu pge sulphide deposit west musgrave western australia the nebo babel ni cu platinum group element pge sulphide deposit in the west musgrave block western australia is the largest nickel sulphide discovery in the last 10 years the deposit is hosted within a concentrically zoned olivine free tube like chonolithic gabbronorite intrusion associated with the approximately 1 078 ma giles complex layered intrusions in the warakurna large igneous province emplaced into sulphide free amphibolite facies orthogneiss the fault offset nebo babel chonolith extends for 5 km and has a cross section of 1 0 5 km igneous mineralogy fabrics and textures are well preserved the lithostratigraphy includes variably textured leucogabbronorites vlgn that form an outer shell around mineralised gabbronorite mgn with barren gabbronorite bgn and oxide apatite gabbronorite oagn in the middle and lower parts of the chonolith mineral and whole rock geochemistry indicate that the units become progressively evolved in the order vlgn mgn bgn and oagn and that incompatible trace element concentrations increase downwards within the mgn and bgn the mineralisation which is confined to the early more primitive units vlgn and mgn occurs as massive sulphide breccias and stringers and as disseminated gabbronorite hosted sulphides the massive sulphides were emplaced late in the intrusive sequence have different pge chemistry and cu tenor to the disseminated sulphides and have undergone sulphide fractionation the distribution of disseminated sulphides which are primary magmatic in origin is related to chonolith geometry and magma flow regimes rather than to gravitational settling sulfur bearing country rocks are absent in the nebo babel deposit area and thus local crustal s addition was unlikely to have been the major mechanism in achieving sulphide immiscibility the nebo babel intrusion is part of an originally continuous magma chonolith with multiple and related magma pulses the parental magma was medium to low k tholeiite with 8 9 wt mgo the initial magma pulse vlgn the most primitive and sulphide saturated was probably emplaced along a linear weakness in the country rock after crystallisation of vlgn marginally more fractionated sulphide saturated magma was injected through the thermally insulated core of the conduit forming the mgn successive pulse s of more fractionated magma bgn were emplaced in the core of the intrusion after magma flow ceased closed system crystal fractionation produced consistent mineral and chemical fractionation trends within bgn and oagn after crystallisation the intrusion was overturned and then offset by the jameson fault resulting in the apparent reverse chemical and mineral trends in nebo babel

the pattern of ni and co abundances in lunar olivines abstract near liquidus experiments on peridotite and other olivine normative compositions from 1 7 to 6 gpa confirm the applicability of exchange based empirical models of ni and co partitioning between olivine and silicate liquids with compositions close to the liquidus of peridotite given that most estimates of lunar bulk composition are peridotitic the partitioning models thus lend themselves to calculation of olivine compositions produced during the early stages of magma ocean crystallization calculation of olivine compositions produced by fractional crystallization of a model lunar magma ocean initially 700 km deep reveals a prominent maximum in ni concentration versus fraction crystallized or mg molar mgo mgo feo but a pattern of monotonically increasing co concentration these patterns qualitatively match the puzzling patterns of ni and co concentrations observed in lunar rocks in which forsteritic olivines in magnesian suite cumulates have lower ni and co abundances than do less magnesian olivines from low ti mare basalts and olivines from the ferroan anorthosite suite fas have lower ni but similar co to mare basalt olivines the ni and co abundances in olivines from the magnesian suite cumulates can be reconciled in terms of fractional crystallization of a deep magma ocean which initially produces a basal dunite comprised of the hottest and most magnesian olivine overlain by an olivine orthopyroxene harzburgite layer that is in turn overlain by an upper zone of plagioclase bearing cumulates the ultramafic portion of the cumulate pile overturns sending the denser harzburgite layer which later becomes a portion of the green glass source region to the bottom of the cumulate pile with ni and co rich olivine meanwhile the less dense but hottest most magnesian olivines with much lower ni and co abundances are transported upward to the base of the plagioclase bearing cumulates where subsequent heat transfer leads to melting of mixtures of primary dunite norite and gabbronorite with kreep a k ree p enriched component widely believed to be derived from the very latest stage magma ocean liquid these hybrid melts have al 2 o 3 ni and co abundances and mg appropriate for parent magmas of the magnesian suite ni and co abundances in the fas are consistent with either direct crystallization from the magma ocean or crystallization of melts of primary dunite norite mixtures without kreep

duration of high pressure metamorphism and cooling during the intraplate petermann orogeny abstract the ediacaran cambrian petermann orogeny central australia is an exceptional example of intraplate orogenesis it involved sub eclogite facies metamorphism and extreme basin inversion during the exhumation of musgrave province basement from beneath the formerly contiguous centralian superbasin sensitive high resolution ion microprobe shrimp u pb geochronology of zircon titanite and rutile along with ti in zircon thermometry from meta igneous samples have been used to determine the timing and duration of high pressure metamorphism and subsequent cooling associated with this orogenic event peak metamorphic temperatures of 720 760 c were attained at 544 7 ma u pb zircon subsequent cooling to 600 660 c by 521 ma occurred at a rate of 2 6 7 0 c myr 1 as recorded by the closure of pb diffusion in titanite further cooling to 585 560 c by 498 472 ma occurred at a rate of 0 9 4 8 c myr 1 as recorded by pb closure in rutile the duration of tectonism was long lived 40 myr across the central and western parts of the orogenic system and deformation occurred in a comparatively warm and weak portion of crust characterised by regional thermal gradients of 17 26 c km 1 this proposed duration of tectonism is much longer than that permitted by a shear heating mechanism which requires an exceptionally short duration of tectonism and additionally an overall cold lithosphere characterised by geothermal gradients of 9 c km 1

petrogenesis of lunar troctolites models of petrogenesis for lunar troctolites are severely constrained by the high mg 88 values of the most primitive members of the mg rich suite melts derived by partial melting of olivine cumulates to the lunar magma ocean have high mg but are strongly undersaturated with respect to plagioclase assimilation of lunar crust cannot bring these melts to the plagioclase liquidus without unduly reducing the mg values of olivine partial melts derived by melting a iherzolite primitive interior have higher normative plagioclase contents but require sources with mg 90 more terrestrial like mg 88 values are permitted if rising thermal plumes are capable of entraining the most mg rich cumulates of the magma ocean the mg values of lunar troctolites may therefore reflect a hybrid source composed of primitive mantle and mg rich cumulates of the magma ocean higher mg values may also arise from the reduction of small amounts of feo to fe alternatively the parent magmas to lunar troctolites may be impact melts of the anorthositic crust and the mg rich dunite cumulates of the magma ocean the latter were brought to the upper mantle during the overturn of the unstable cumulate pile of the magma ocean

intracratonic strike slip partitioned transpression and the formation and exhumation of eclogite facies rocks an example from the musgrave block central australia mountain belts developed in an intracratonic setting during the neoproterozoic in the center of australia mesoproterozoic granulite and amphibolite facies gneisses of the musgrave block were overprinted during the petermann orogeny 550 ma with zones of high strain concentrated along broadly east west trending shear zones these zones formed under eclogite facies t 650 c and p 12 kbars to greenschist facies conditions and may form part of a strike slip related crustal scale flower type structure granulite facies gneisses preserve ages older than 700 ma suggesting that these rocks did not experience temperatures greater than 350 c at 550 ma for these rocks not to have been thermally equilibrated to temperatures of 350 c at a depth of 12 kbars requires either an extraordinarily low geothermal gradient 9 c km 1 or if the geothermal gradient was more typical 20 c km 1 then transport to that depth and subsequent exhumation occurring in a short time interval 40 myr

evidence for shear heating musgrave block central australia the phenomenon of shear heating is generally difficult to recognise from petrologic evidence alone establishing that shear zones attain higher temperatures than the surrounding country rocks requires independent evidence for temperature gradients in the musgrave block central australia there is a clear spatial association between shear zones and interpreted elevated temperatures eclogite facies shear zones that formed at 550 ma record temperatures of 650 700 c outside the high pressure shear zones minerals with low closure temperatures such as biotite 450 c in the 40ar 39ar and rb sr systems preserve ages 800 ma suggesting that these rocks did not experience temperatures greater than about 450 c at 550 ma for any extended period thus the shear zones record temperatures that are 200 c higher than the surrounding country rocks simple calculations show that the combination of relatively high shear stresses 100 mpa and high strain rates 10 11 s 1 for short durations 1 ma can account for the observed apparent temperature variations the evidence indicates that shear heating is the dominant mechanism for localised temperature increases in the shear zones while the country rock remained at relatively lower temperatures

post orogenic 1500 ma thermal history of the palaeo mesoproterozoic mt isa province ne australia abstract we present hornblende white mica biotite and alkali feldspar 40 ar 39 ar data from paleo mesoproterozoic rocks of the mt isa inlier australia which reveal a previously unrecognised post orogenic non linear cooling history of part of the northern australian craton plateau and total fusion 40 ar 39 ar ages range between 1500 and 767 ma and record increases in regional cooling rates of up to 4 c ma during 1440 1390 and 1260 1000 ma forward modelling of the alkali feldspar 40 ar 39 ar arrhenius parameters reveals subsequent increases in cooling rates during 600 400 ma the cooling episodes were driven by both erosional exhumation at average rates of 0 25 km ma and thermal relaxation following crustal heating and magmatic events early mesoproterozoic cooling is synchronous with exhumation and shearing in the arunta block and gawler craton late mesoproterozoic cooling could have either been driven by increased rates of exhumation or a result of thermal relaxation following a heat pulse that was synchronous with dyke emplacement in the arunta musgrave and mt isa province as well as grenville aged orogenesis in the albany fraser belt latest neoproterozoic cambrian cooling and exhumation was probably driven by the convergence of part of the east antarctic shield with the musgrave block and western australia petermann ranges orogeny as well as collisional tectonics that produced the delamerian ross orogen major changes in the stress field and geothermal gradients of the australian plate that are synchronous with the assembly and break up of parts of rodinia and gondwana resulted in shearing and repeated brittle reactivation of the mt isa inlier probably via the displacement of long lived basement faults within the northern australian craton

the lunar magma ocean reconciling the solidification process with lunar petrology and geochronology abstract the moon is thought to have originated with a magma ocean that produced a plagioclase flotation crust as solidification proceeded ages of anorthositic crust range over at least 200 million years the model for solidification presented here integrates chemical and physical constraints of lunar magma ocean solidification to determine 1 the final thickness of flotation crust generated by a fractionally solidifying magma ocean 2 the timescale of crystallization before plagioclase is a stable phase 3 the timescale of solidification after the formation of the plagioclase flotation crust and 4 the post overturn lunar mantle composition and structure we find that magma oceans of as much as 1000 km depth are consistent with creating an anorthositic crust 40 to 50 km in thickness solidification of the magma ocean prior to formation of the flotation crust may occur on the order of 1000 years and complete solidification would require additional ten to tens of millions of years reconciling these short model timescales with radiometric dates of crustal samples requires either a very late forming moon combined with finding older crustal ages to be incorrect or calling on tidal heating of the crust by the early earth to prolong solidification gravitationally driven overturn of cumulates during tidal heating provides a mechanism for creating the compositions and ages of the lunar mg suite of crustal rocks further we find that upon crystallization the moon likely began with an azimuthally heterogeneous gravitationally stable mantle after magma ocean cumulate overturn this result may help explain the experimentally determined origin of picritic glasses at similar depths but from different source materials

timing and exhumation of eclogite facies shear zones musgrave block central australia timing constraints on shear zones can provide an insight into the kinematic and exhumation evolution of metamorphic belts in the musgrave block central australia granulite facies gneisses have been affected to varying degrees by mylonitic deformation some of which attained eclogite facies the davenport shear zone is a dominant strike slip system that formed at eclogite facies conditions t 650 c and p 12 0 kbar sm nd mineral isochrons obtained from equilibrated high pressure assemblages as well as 40ar 39ar data show that the eclogite and greenschist facies high strain overprints were coeval at c 550 ma mylonitic processes do not appear to have reset the u pb system in zircon but may have partially disturbed it the thermal gradient in the musgrave block crust at c 550 ma was c 16 c km 1 and at c 535 ma was c 18 c km 1 based on p t estimates of eclogite and greenschist facies shear zones respectively these estimates are similar to present day geothermal gradients in many stable continental shield areas suggesting that the region did not undergo a significant transient perturbation of the geotherm therefore in the musgrave block cooling subsequent to eclogite facies metamorphism appears to have been controlled by exhumation rather than by the removal of a heat source estimated exhumation rates in the range 0 2 to 1 5 mm year 1 are comparable with other orogenic belts rather than cratonic areas elsewhere

nd isotopic and geochemical constraints on provenance of sedimentary rocks in the eastern officer basin australia implications for the duration of the intracratonic petermann orogeny sm nd isotopic and geochemical data from neoproterozoic to cambrian sedimentary rocks in the intracratonic eastern officer basin in central australia highlight the evolving provenance roles of the basement complexes that underlie and bound the basin initial e nd values of around 12 for the basal units indicate that both were largely derived from the late archaean to mesoproterozoic gawler craton which bounds the basin to the south at c 720 ma an influx of juvenile glacially derived sediment indicates partial uplift of the mesoproterozoic musgrave block along the basin9s northern margin in a regime interpreted to be broadly extensional at around 600 ma synchronous with the development of a foreland architecture there was a large influx of musgrave block derived sediments this is interpreted to mark the onset of the intracratonic petermann orogeny which was a long lived event or series of events spanning more than 70 ma subsequent to c 600 ma the nd isotopic composition of sequences within the officer basin indicates an increasing contribution from the gawler craton despite up to 45 km of denudation of part of the musgrave block this suggests that the majority of sediment derived from the petermann orogen bypassed the eastern officer basin for much of the history of the petermann orogeny

mineralogical association and ni co deportment in the wingellina oxide type laterite deposit western australia abstract the wingellina deposit currently owned by metals x limited is an oxide type ni co laterite with 168 mt of ore grading 0 98 ni and 0 08 co the laterite profile is derived from the weathering of the olivine rich mafic ultramafic layered intrusion of the giles complex mesoproterozoic and consists of a well developed limonitic ore and a thin saprolite horizon xrpd sem eds and empa analyses revealed that the ore zone is dominated by fe and mn hydr oxides which are the main carriers of both ni and co the mineralogy of the mn hydroxides is complex and high concentrations of co and ni occur mainly in a lithiophorite asbolane intermediate phase which has been subdivided into types i ii iii and iv with significant differences in their co ni ratios and al content the enrichment of metals in the lithiophorite asbolane phases is mainly controlled by the co and ni replacement of al in gibbsite like layers and rarely by ni incorporation in the vacancies of mn hydr oxides other less important metal bearing mn hydr oxides at wingellina include romanechite ernienickelite jianshuiite manganite and birnessite the texture and chemistry of the mn hydr oxides suggest that the lithiophorite asbolane phases were formed at a later stage with respect to the other manganiferous phases after repeated leaching and re precipitation of the mn hydr oxides this process could be one of the main factors controlling the enrichment of co and ni in the limonite zones during lateritization

the burning heart the proterozoic geology and geological evolution of the west musgrave region central australia the musgrave province is one of the most geodynamically significant of australia s proterozoic orogenic belts lying at the intersection of the continent s three cratonic elements the west north and south australian cratons while remoteness and cultural sensitivity have slowed geological research into this region recent collaborative programs in western australia the west musgrave province have done much to address this this focus review provides a synthesis of this and previous work investigating the mesoproterozoic to neoproterozoic geological evolution of the province the musgrave province is a mesoproterozoic to neoproterozoic belt dominated by granites formed and deformed during several major events a cryptic juvenile basement is exposed mainly in the east musgrave province as c 1600 1550 ma orthogneiss and in the west musgrave province as isolated outcrops of granulite facies metagranites of the c 1575 ma warlawurru supersuite zircon hf isotopic data suggest an earlier major juvenile crust forming event at c 1950 1900 ma there is however no evidence that the province evolved over archean crust the c 1600 1550 ma period probably involved evolution within a primitive arc setting perhaps developed on c 1950 1900 ma oceanic or oceanic arc crust voluminous calc alkaline plutonism was accompanied by clastic and volcaniclastic basin formation during the 1345 1293 ma mount west orogeny this stage traced the evolution of a continental arc reflecting the final amalgamation of the combined north and west australian craton with the south australian craton the intervening c 1400 ma primitive crust the madura province on which the proto musgrave province had evolved was consumed during amalgamation the thickened crust resulting from this accretion was drastically thinned at the beginning of the c 1220 1150 ma musgrave orogeny as this central part of the new combined craton entered an extraordinary period of high heat flow characterised by c 100 m y of ultrahigh temperature metamorphism and high temperature anhydrous alkali calcic magmatism sourced from mash chambers developed at the base of the thinned crust the ridged cratonic architecture and a massive accumulation of high radiogenic heat producing granites within the mid crust perpetuated a thin crustal regime voluminous magmatism was again triggered during the c 1090 1040 ma giles event with the evolution of the magmatism dominated ngaanyatjarra rift this event was likely initiated through renewed movement along translithospheric faults that intersected the thermally perturbed musgrave province pinned at a cratonic junction mantle derived bimodal magmatism extended more or less continuously for 50 m y producing one of the world s largest layered mafic intrusions and supervolcano sized additions of juvenile felsic crust in the form of alkali calcic to alkali a type rhyolite deposits together the albany fraser orogen which developed over the southern margin of the west australian craton and the musgrave province mark the preserved edge of the north and west australian craton these two belts show remarkable chronological links between c 1345 and 1150 ma but contrasting histories before and after that period their period of shared evolution reflects collision and accretion of the south australian craton but their tectonic setting and basement geology throughout that event were very different