shrimp u pb zircon dating of grenville age events in the western part of the musgrave block central australia shrimp u pb zircon dating of structurally constrained felsic orthogneiss samples in the western musgrave block has been used to delineate discrete magmatic and metamorphic events at c 1300 and c 1200 ma the dating of pre d1 and post d1 felsic orthogneiss constrains d1 to have occurred at 1312 16 to 1324 4 ma this is the first geochronological study to identify such a metamorphic and deformation event in the musgrave block d1 was accompanied by a major magmatic event involving the emplacement of voluminous felsic orthogneiss between 1296 and 1324 ma zircon overgrowths on numerous igneous zircon cores give a consistent age of c 1200 ma reflecting zircon growth during a second high grade metamorphic event d2 this c 1200 ma metamorphic event was followed by the intrusion of a c 1190 ma megacrystic granite the c 1300 and c 1200 ma events in the musgrave block can be tentatively correlated with metamorphic events in the albany fraser orogen and the windmill islands and bunger hills in east antarctica a major continuous grenville age orogenic belt joining these areas may have represented a plate boundary between the pre rodinian proto australian continent and proto antarctica during the formation of rodinia in the mesoproterozoic

some isotopic constraints on the evolution of the granulite and upper amphibolite facies terranes in the eastern musgrave block central australia abstract the central to eastern musgrave block central australia consists of the meso to neoproterozoic fregon and mulga park subdomains that are separated by a zone of mylonites and pseudotachylytes known as the woodroffe thrust the subdomains were previously considered to have undergone different geological histories but the differences relate mainly to metamorphic grade the fregon subdomain attained at least transitional granulite facies metamorphic conditions and the mulga park subdomain reached upper amphibolite facies felsic gneisses from both the fregon and mulga park subdomains contain zircons that are structured with euhedral centres overgrown by round elongate rims ion microprobe u pb analyses of the cores yield ages of 1557 24 and 1554 28 ma respectively and are interpreted to represent the time of igneous crystallization these ages place a maximum age constraint on the deposition or emplacement of the gneiss precursor high grade metamorphism grading from upper amphibolite to granulite facies took place between 1200 and 1150 ma and prior to the intrusion of several granitoid suites at around 1150 ma the kulgera adamellite and ayers ranges adamellite granitoid suites of the fregon subdomain yield ion microprobe u pb crystallization ages of 1150 12 and 1152 11 ma respectively a concordant u pb isotope dilution analysis on the ayers ranges adamellite yields a more precise age of 1152 3 ma the porphyritic suite intruding the mulga park subdomain yield an ion microprobe u pb magmatic age of 1159 20 ma these emplacement ages indicate extensive grenvillian felsic magmatism not previously recognized in australia the woodroffe thrust formed during a period of substantial crustal shortening the petermann orogeny 550 ma when the fregon subdomain was thrust onto the mulga park subdomain synkinematic muscovite and biotite record k ar and rb sr ages between 560 and 520 ma this petermann event is not recorded in the fregon subdomain due to confinement of the strain and associated mineral recrystallization to the underlying mulga park subdomain we suggest that the granulites were not exposed prior to the petermann orogeny as the basal quartzites of the amadeus basin occur only on the amphibolite facies mulga park subdomain

the mechanism of ascent and emplacement of granite magma during transpression a syntectonic granite paradigm we propose a model for syntectonic ascent and emplacement of granite magma based on structural relations in part of the northern appalachians in the study area in western maine strain was distributed heterogeneously during devonian acadian transpression metasedimentary rocks migmatites at high grades record two contrasting types of finite strain in zones that alternate across strike rocks in both types of zones have a penetrative moderately to steeply ne plunging mineral elongation lineation defined by bladed muscovite fibrolite sillimanite at high grades in straight belts of enhanced deformation rocks have s l fabrics that record apparent flattening to plane strain apparent flattening zones afzs but rocks between these belts have l s fabrics that record apparent constriction apparent constriction zones aczs at metamorphic grades above the contemporary solidus rocks in afzs developed stromatic structure in migmatite which suggests that percolative flow of melt occurred along the evolving flattening fabric stromatic migmatites are intruded by concordant to weakly discordant m scale composite sheet like bodies of granite to suggest magma transport in planar conduits through the afz rocks inhomogeneous migmatite is found in the intervening aczs which suggests migration of partially molten material through these zones en masse probably by melt assisted granular flow inhomogeneous migmatites are intruded by irregular m scale bodies of granite that vary from elongate to sub circular in plan view and seem cylindrical in three dimensions these bodies apparently plunge to the northeast parallel to the regional mineral elongation lineation to suggest magma transport in pipe like conduits through the acz rocks we postulate that the form of magma ascent conduits was deformation controlled and was governed by the contemporaneous strain partitioning magma ascent in planar and pipe like conduits through migmatites is possible because oblique translation during contraction displaces isotherms upward in the orogenic crust to form a thermal antiform within this hot corridor it is the difference in temperature between melt producing reactions in the anatectic zone and the wet solidus for granite melt that enables magma to migrate pervasively up through the orogenic crust without congealing heat advected with the migrating melt promotes amplification of the thermal antiform in a feedback relation that extends the zone of plastic deformation and pervasive melt migration to shallower levels in the crust at the wet solidus we suggest melt flows obliquely toward axial culminations in the thermal antiform which are sites of melt accumulation and perturbations from which magma may escape to form plutons batches of melt that escape from these perturbations may be trapped by tectonic structures higher in the crust or ascent may become inhibited with decreasing depth by thermal arrest and solidification if the rate of arrival of subsequent melt batches exceeds the rate of crystallization at the site of pluton construction melt pressure ultimately may lead to sub horizontal magma fracture or viscous flow of wall rocks may allow lateral spreading the resultant plutons have sub horizontal tabular geometries with floors that slope down to the ascent conduit as the thermal antiform decays the height of sub solidus crust that separates the deepest part of the pluton from the anatectic zone increases consequently pluton inflation declines and solidification leads to infilling of the magma feeder channel to form a root zone that passes downward into migmatite which may explain the difficulty of determining precisely the floor to these deeper segments of large plutons using gravimetry

control of granite emplacement by regional deformation abstract a combination of structural measurements and gravity data is used to investigate the mode of granite emplacement in various tectonic settings the deepest zones revealed by gravity data provided those zones also show vertical lineations in outcrop are interpreted as magma feeder channels these structures or root zones reflect the flow pattern of the upwelling magma while being emplaced they can be interpreted within the regional stress field active during that time granites intruded during transcurrent shearing have only a few feeder channels these roots are not connected to the main shear zone all of them lie within locally extensional areas of the regional stress field this situation is also observed in granites emplaced during a compressional phase of deformation when emplaced during a regionally extensional phase the granitic plutons are very thin with many small deeper zones in which variously evolved granite types may be intrusive these regions vertically differentiated are also interpreted as feeder channels the different morphology at depth as well as the difference in the number of root zones suggest that deformation controls the emplacement of granitic plutons the root zones are oriented at a high angle to the direction of maximum compression when magma is emplaced in a plastic crust if the pluton is emplaced higher in a brittle crust then the roots are aligned with the maximum compression according to the andersonian theory of fracture the orientation of the root zone along the direction of extension in a plastic crust may be explained by shearing which acts as a valve mechanism for segregating magma in all the examples the geometry of the root zone relative to the major fault plane implies that the shear zone does not induce magma generation and that it does not serve as a guide for magma emplacement

development of the australian proterozoic crust as inferred from gravity and magnetic anomalies abstract gravity anomalies in australia have been used to map trends within basement blocks to map the margins of the blocks and to determine the relative ages of the blocks the inferred pattern of continental growth is consistent with that found by isotopic dating and from exposed geology the ages of cratonization of the total area of land basement are 18 archaean 53 proterozoic and 29 phanerozoic exposed basement generally has higher gravity variability than basement overlain by cover sediments the higher gravity variability is due to alternating bands of granite volcanics and the relative uplift and exposure is attributed to associated crustal underplating proterozoic crustal reworking takes several forms parts of archaean blocks were remobilized by extensive proterozoic metamorphism young blocks cratonized against older blocks caused reworking at least 50 km into the older blocks crustal rifts over 700 km long and 70 300 km wide were formed simple rifting resulted in crustal attenuation and sedimentation while more complex rifting resulted in the introduction of new igneous material and reworking of the older crustal material

warakurna large igneous province a new mesoproterozoic large igneous province in west central australia coeval mafic igneous rocks emplaced rapidly over 1 5 3 10 6 km 2 in western and central australia represent the erosional rem nants of a late mesoproterozoic large igneous province named here the warakurna large igneous province shrimp u pb dating of rocks separated by as much as 1500 km indicates that the main episode of magmatism occurred between 1078 and ca 1070 ma the warakurna large igneous province includes layered mafic ultramafic intrusions and mafic to felsic volcanic rocks and dikes in central australia a 1000 km long mafic sill province in western australia and several swarms of mafic dikes the large areal ex tent and short duration imply emplacement above a mantle plume head despite their wide separation the mafic rocks have similar mid oceanic ridge basalt normalized trace element patterns and rare earth element characteristics west directed paleocurrents westward radiating dike swarms and the occurrence of high mg rocks indicate that the center of the plume head was located be neath central australia other late mesoproterozoic large igneous provinces in the laurentia and kalahari cratons appear to be significantly older than the warakurna large igneous province in australia and thus are unlikely to be related to the same mantle plume head

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

geologically constrained gravity inversion for the voisey s bay ovoid deposit constructing a general three dimensional model of the subsurface density distribution by minimum structure or occam style inversion of gravity data has been practical now for several years the usual approach is to seek a model that is simple in the sense of having the least amount of spatial variation while still reproducing the observations hence the description minimum structure this has the advantage of generating models with few if any fictitious features however often the models produced bear only a gross diffuse resemblance to geology it has been recognized since the inception of the minimum structure inversion technique that geological information can be incorporated by seeking a model that is simple in the sense of being as close as possible to a reference model while still fitting the observations this is rarely done often because insufficient geological information is available or because inversion of geophysical data is no longer thought to be useful once a target has been fou

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

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

multi scale integrated structural and aeromagnetic analysis to guide tectonic models an example from the eastern musgrave province central australia abstract in many polydeformed precambrian provinces the understanding of their tectonic history is limited by insufficient exposure which leads to difficulty in developing links between local and regional architecture and results in poorly constrained models of their regional scale architecture high resolution aeromagnetic data allows interpretation and modelling at a scale comparable to structural mapping and by integrating these methods these links can be developed with high confidence as an example we integrate structural mapping aeromagnetic data interpretation and 3d magnetic inversions in a multi scale structural analysis of the polydeformed eastern musgrave province in central australia deformation during the ca 1200 ma musgravian orogeny is characterised by an originally northeast trending structural grain defined by shear zones and tight to isoclinal folds at all scales 3d magnetic inversion models of syn to post musgravian granites indicate that this structural grain is predominantly west dipping this architecture suggests that a northeast oriented fold and thrust belt developed as a result of northwest southeast compression in central australia during the musgravian orogeny the next deformation event is characterised by an array of originally east southeast trending shear zones that truncate and offset the musgravian structural grain with apparent dextral displacements of up to 1 km these shear zones are commonly co located with mafic and granitic dykes suggesting a dilational origin and they are interpreted to have initiated under northeast southwest extension during the ca 1080 ma giles event the architecture of these two mesoproterozoic events was later extensively overprinted by two deformation events during the pan african aged ca 550 ma petermann orogeny the first is characterised by the widespread reactivation of mesoproterozoic structures resulting in a network of shear zones of variable orientation and the second is characterised by the development of crustal scale transpressional shear zones motion on which has caused the rotation of lithospheric blocks and the reorientation of prior structural trends by up to 90 collectively the architecture of these two events suggests broadly north south crustal shortening in central australia as an intraplate response to gondwana assembly this example demonstrates that the integration of structural geology with aeromagnetic interpretation and modelling can be used to develop high confidence links between local and regional structures these links permit the derivation of better constrained models of major tectonic events particularly in regions where outcrop is poor and the structural architecture is complex

a new radar auroral backscatter experiment in 1982 a new radar auroral backscatter system sabre sweden and britain radar experiment commenced operation in northern europe observations with this ground based system allow estimates to be made of the electric fields in the auroral e region as an electric field probe the coherent radar technique is unique in that measurements are made over a large area 200 000 km2 with good spatial resolution 20 20 km2 and with a temporal resolution of typically 20 s the system field of view covers an l value range 4 3 5 8 this region in the magnetosphere ionosphere system is now accessible for the first time for detailed electric field studies we present here observations of two pulsation events

tectonic evolution of proterozoic australia proterozoic australia has long been interpreted as a single intact continent in which all tectonic and magmatic activity was intracratonic this paper proposes an alternative hypothesis in which numerous fragments of continental crust were assembled by plate tectonic processes the assembly was completed between 1300 and 1100 ma when the crustal fragments were combined as an early component of the rodinian supercontinent rifting and fragmentation of archaean continents began in the late archaean and continued into the proterozoic passive margin deposits such as those of the hamersley basin accumulated on isolated fragments of archaean crust these numerous fragments were subsequently assembled into three cratons by 1830 ma a west australian craton was established by collision of the archaean pilbara and yilgarn cratons which were joined along the capricorn orogen similarly a south australian craton developed by amalgamation of the proto gawler and proto curnamona cratons along the kimban orogen a north australian craton appears to have formed by accretion of numerous crustal fragments including the kimberley pine creek lucas and altjawarra cratons with sutures marked by the king leopold halls creek tennant creek and proto isan orogens the southern margin of the north australian craton was the site of repeated terrane accretion and orogenic activity between 1880 ma and 1400 ma this included an orogenic event at 1880 1850 ma the strangways 1780 1730 ma argilke 1680 1650 ma and chewings 1620 1580 ma orogenies and the intracratonic anmatjira uplift 1500 1400 ma intracratonic rifting at 1750 to 1710 ma and 1640 to 1600 ma produced the mcarthur basin and related minor basins parts of which were deformed by the isan orogeny at 1600 and 1530 ma rifting along the line of the capricorn orogen led to deposition in the overlying intracratonic bangemall basin between 1630 and 1300 ma along the eastern margin of the south australian craton the 1670 to 1600 ma olarian orogeny marks interaction with now obscured continental crust to the east tectonic activity between 1300 and 1100 ma led to the assembly of proterozoic australia as an early component of the supercontinent of rodinia this first involved the amalgamation of the west australian and north australian cratons followed by collision with the south australian craton the centralian superbasin developed over the junction of the north south and west australian cratons between 830 and 750 ma rifting to the east formed the adelaide geosyncline at 830 ma this was followed by the breakup of rodinia with the rifting apart of laurentia and gondwanaland along the eastern margin of proterozoic australia at 750 ma and the subsequent formation of the palaeo pacific ocean after the breakup of rodinia a series of northeast southwest compressional events followed by periods of relaxation reflect the assembly of a new supercontinent old lines of weakness were reactivated culminating in the intracratonic king leopold paterson petermann ranges and pinjarra orogenies between 620 and 540 ma subsequent reactivation continued into the phanerozoic with the widespread eruption of continental flood basalts and the formation of intracratonic basins 540 530 ma

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

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

high resolution aeromagnetic data over central australia assist grenville era 1300 1100 ma rodinia reconstructions 1 high resolution aeromagnetic data covering the polydeformed and poorly exposed musgrave province of australia reveals the grenville aged crustal architecture a combination of upward continuation and the potential field tilt filter out magnetic anomalies relating to a late neoproterozoic orogenic event and emphasize the more subtle magnetic structural grain formed during the ca 1320 1150 ma musgravian orogeny the resulting images indicate that crustal architecture is defined by the distribution of ca 1150 ma magnetic granitoids within less magnetic basement and is dominantly northeast trending continuous beneath the amadeus and officer basins and defines an orogenic belt that connects mesoproterozoic provinces the orogenic belt is truncated within australia and precludes a direct east trending connection between the musgrave province and contemporaneous orogens in laurentia clockwise rotation of the south australian craton and subsequent collision with the north and west australian cratons is our preferred model to explain the grenville aged architecture observed in australia

zircon u pb chronometry of the pressure and temperature history of granulites in the musgrave ranges central australia ion microprobe u pb measurements of zircon in the musgrave ranges of central australia date the emplacement of a charnockite which is cut by a shear zone containing a garnet clinopyroxene assemblage m2 pt conditions 11 kb and 720 c at 1200 ma veinlets of a post m2 adamellite cut an m4 assemblage pt conditions 6 kb and 670 c contained in a metadolerite inclusion suggesting that the adamellite was emplaced during or after m4 igneous and metamorphic zircons in the adamellite however grew at about 1200 ma indicating that m2 and m4 were synchronous at the level of precision of our data the time interval between the growth of the two assemblages can not have been more than 20 ma we interpret the pressure temperature and time ptt path obtained by combining our thermobarometric data and zircon u pb ages in terms of magmatic heat input in a thickened crustal segment followed by rapid possibly technically driven uplift of the lower part of the thickened crust to a depth of 15 20 km

a 28 ka history of sea surface temperature primary productivity and planktonic community variability in the western arabian sea 1 uranium series radionuclides and organic biomarkers which represent major groups of planktonic organisms were measured in western arabian sea sediments that span the past 28 ka variability in the past strength of the southwest and northeast monsoons and its influence on primary productivity sea surface temperature sst and planktonic community structure were investigated the average alkenone derived sst for the last glacial period was 3 c lower than that measured for the holocene prior to the deglacial the lowest ssts coincide with the highest measured fluxes of organic biomarkers which represent primarily a planktonic suite of diatoms coccolithophorids dinoflagellates and zooplankton we propose that intensification of winter northeast monsoon winds during the last glacial period resulted in deep convective mixing cold ssts and enhanced primary productivity in contrast postdeglacial 17 ka ssts are warmer during times in which biomarker fluxes are high associated with this transition is a planktonic community structure change in which the ratio of the average cumulative flux of diatom biomarkers to the cumulative flux of coccolithophorid biomarkers is twice as high during the deglacial and holocene than the average ratio during the last glacial period we suggest that this temporal transition represents a shift from a winter northeast monsoon dominated pre 17 ka to a summer southwest monsoon dominated post 17 ka wind system

multiply deformed terrains problems of correlation abstract the best tools available for carrying out a structural analysis in a complex area are overprinting style and patterns of orientation unfortunately all have limitations which are reviewed briefly and discussed in areas of continuous unfaulted outcrop the deformational history can be established purely on the basis of overprinting but even in such areas there can be problems since not all overprinting relationships are unambiguous most fold interference patterns are reliable overprinting relationships based on foliations however are commonly unreliable and various examples are cited and discussed even in areas where the sequence of deformational events can be established their temporal significance is unclear since the methods applied only determine local relative timing and absolute relationships must vary in space and time across an orogen

melting of a subduction modified continental lithospheric mantle evidence from late proterozoic mafic dike swarms in central australia geochemical and nd isotopic studies of two postorogenic late proterozoic 1083 23 ma high mg tholeiitec dike swarms in central australia indicate that the dike swarms were derived by partial melting of the continental lithospheric mantle which was modified by subduction processes during major crust formation events in the region both dike swarms stuart and kulgera which intrude the arunta and musgrave inliers respectively resemble island arc tholeiites in terms of geochemical features they yield whole rock sm nd ages of 1853 189 ma with nd 4 2 4 2 stuart and 1589 165 ma with nd 1 7 3 6 kulgera the two whole rock ages and initial nd values are remarkably similar to the oldest u pb zircon ages and initial nd values obtained from the corresponding basement blocks these isotopic data are interpreted as recording sm nd fractionation events in the continental lithospheric mantle associated with major episodes of crust formation in the early proterozoic