synchronous development of type 2 and type 3 fold interference patterns evidence for recumbent sheath folds in the allendale area broken hill nsw australia abstract synchronous development of type 2 and type 3 fold interference patterns occur in the poly deformed broken hill inlier the interference patterns have resulted from the superposition of recumbent f2 folds and n s oriented upright f3 folds the synchronous development of type 2 and type 3 fold interference patterns is attributed to variation in the hinge of f2 folds by as much as 90 suggesting the development of a regional scale sheath like fold geometry during d2 overprinting relationships along the eastern limb of the pap synform suggests that it formed part of a recumbent fold hinge that was flattened during horizontal crustal shortening this has resulted in the development of a modified type 3 fold interference pattern the results of this study show that the type 2 and type 3 fold interference patterns can develop during the same deformation event in an evolving orogen

a geophysically constrained litho structural analysis of the eburnean greenstone belts and associated granitoid domains burkina faso west africa abstract interpretation of airborne geophysical data integrated with field structural and lithological observation was successfully employed in the creation of the litho structural framework in a poorly exposed paleoproterozoic granite greenstone terrain of the west african craton the geophysical data portray with sufficient detail all of the lithological units and structural features present the results suggest that the granitoid domains are formed by numerous small to medium sized plutons the existence of several generations of magmatic episodes has a significant impact on the development of a regional tectonic model the magnetic data provided a better definition of the actual pluton shapes and several highly magnetic late orogenic plutons were reliably identified relic f1 fold hinges were recognized in the hounde and boromo greenstone belts the d1 penetrative structures are generally affected by the d2 transcurrent shear zones which often form as well the granite greenstone belt boundaries previously unreported s2 shear zones including the bossie shear zone transecting the sideradougou granitoid domain and abundant small scale shear zones affecting all of the lithologies represent prospective areas for gold exploration airborne gamma ray spectrometry data aided in the mapping process in areas with less regolith cover including erosional ridges and parts of the banfora greenstone belt the magnetic data revealed at least three generations of doleritic dykes crosscutting the western burkina faso

the mount hay block central australia another puzzle piece for paleo mesoproterozoic tectonic history abstract the 100 km 2 mount hay block arunta region central australia is a 15 km thick crustal cross section comprised of granulite facies tectonites containing a tectonothermal record from ca 1803 to ca 1552 ma as demonstrated by the combination of prior work and new monazite geochronology and thermobarometry igneous and sedimentary protoliths formed ca 1803 1798 ma during 1810 1790 ma stafford tanami time between ca 1790 and 1740 ma nearly continuous magmatism in the aileron province and possibly ages of recrystallized zircon and monazite in the mount hay block record subduction along the southern margin of the proterozoic australia mawson continent geologic mapping and zircon and monazite geochronology demonstrate that the mount hay block was penetratively deformed between ca 1720 ma and 1700 ma during 1735 1690 ma strangways time this includes the 8 km thick mount hay sheath fold which records ne sw subhorizontal shear once paleozoic tilting of the mount hay block is removed while still in the deeper crust 798 33 c 7 6 0 7 kbar fabrics along the northern edge of the mount hay block were transposed by the cross cutting 7 km thick capricorn ridge shear zone at ca 1551 7 5 5 ma during chewings time once restored the capricorn ridge shear zone records ne sw extension a jump in strain rate while at high temperatures 725 c initiated severe localization accommodated initially by pseudotachylite formation and cataclasis then mylonitization during fe rich fluid flux shearing may have continued to pressure temperature conditions as low as

isobaric cooling of two regional metamorphic complexes related to igneous intrusions in southeastern australia evidence of retrograde reactions in two southeastern australian low pressure regional metamorphic complexes supports the suggestion of england and richardson that metamorphic complexes controlled largely by magmatic intrusions should cool isobarically in the early stages this behavior contrasts with the cooling of metamorphic complexes formed during major collision type processes which show evidence of marked decrease in pressure

fault reactivation and pseudotachylite generation in the semi brittle and brittle regimes examples from the gavilgarh tan shear zone central india in the sheared and foliated granitoids of the proterozoic gavilgarh tan shear zone gtsz in central india two types of pseudotachylite pt m and pt c are recognized pt m layers are interbanded with mylonite and ultramylonite show strong internal plastic deformation and buckle folding concurrent with the host rocks and appear to have formed within the greenschist facies 300 400 c in the brittle plastic transitional semi brittle regime pt c layers show sharp contacts with the host rock exhibit abundant coeval cataclasis preserve no evidence of subsequent plastic deformation and formed at shallower depths at temperature

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

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

plume modified orogeny an example from the western united states plate tectonic theory implies that orogeny at convergent margins results from several processes including subduction of oceanic crust subduction of aseismic ridges accretion of terranes and continental collision each of these processes involves the consumption of an oceanic tract and each has its own characteristic style of tectonothermal activity an additional potentially important orogenic process has been largely overlooked oceanic regions contain chains of volcanic islands formed at hotspots which are generally considered to reflect the sites of rising plumes in a hotspot reference frame where active continental margins advance and override a plume the plume9s buoyant swell may profoundly change the tectonothermal expression of subduction and hence orogenic processes at the continental margin the late cretaceous tertiary evolution of the western united states may be an example of this process which has been overlooked in the development of orogenic paradigms

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

the ca 1740 1710 ma leichhardt event inversion of a continental rift and revision of the tectonic evolution of the north australian craton abstract interpretation and modelling of high resolution regional geophysical data of the central leichhardt river fault trough in the mount isa inlier are used to determine the timing of a major basin inversion event following the development of the ca 1780 1740 ma leichhardt superbasin inversion of the leichhardt superbasin formed the regional north south trending leichhardt anticline during east west shortening the limbs of the anticline are overprinted by several east west trending wedge shaped non magnetic sub basins filled with ca 1710 ma calvert and isa superbasin successions these relationships suggest inversion of the leichhardt superbasin occurred between ca 1740 and 1710 ma the event is also known to have affected the northern and eastern north australian craton the scale of the inversion suggests it was a significant event that we have defined as the leichhardt event this event requires a major tectonic driver to the east of the north australian craton possibly the accretion of a micro continental ribbon to the east of the mount isa inlier the results of this study have implication for paleogeographic reconstruction of the australian continent during the formation of nuna because eastern north australian craton faced an ocean at ca 1740 1720 ma the results also challenge the significance and intensity of crustal shortening associated with the ca 1600 1500 ma isan orogeny throughout the western mount isa inlier

reinterpretation of the tectonic context of high temperature metamorphism in the broken hill block nsw and implications on the palaeo to meso proterozoic evolution abstract the origin of high temperatures during regional low pressure granulite facies metamorphism within the proterozoic broken hill block australia has been reinterpreted to be the result of burial of anomalously hot rock packages for which the lithospheric geothermal gradient was initially elevated during early rifting ca 1 71 1 67 ga and then maintained during a ca 1 62 ga short lived mid crustal extensional event mid crustal extension at ca 1 62 ga was associated with amphibolite facies metamorphism and elevated lithospheric geothermal gradients and occurred prior to activity along d2 high temperature shear zones peak low pressure granulite facies metamorphism ca 1 60 ga and crustal shortening during the olarian orogeny ca 1 60 1 59 ga this reinterpretation places the broken hill block within an environment in which multiple episodes of transient extension ca 1 71 1 62 ga were followed by a switch to shortening at ca 1 60 ga the interpreted tectonic environment is a continental back arc setting located in the over riding plate of a subduction zone along the southern margin of palaeoproterozoic australia

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

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

a model for low pressure facies metamorphism during crustal thickening low pressure metamorphic facies i e high t p ratios are widespread in a wide range of tectonic settings explanations offered for the occurrence of these facies include extensional and or magmatic models however these fail to explain that the low p facies metamorphism is commonly coeval with a phase of pervasive crustal thickening with t p ratios increasing during or slightly lagging behind the thickening we propose an alternative explanation based on the approximate synchroneity of crustal thickening and erosion thinning of the mantle lithosphere

internal structure of the precordilleran fault system chile insights from structural and geophysical observations abstract geological field work and audiomagnetotelluric data from two profiles crossing the west fissure zone in northern chile were used to describe the geometry and structure of the fracture damaged zone surrounding this strike slip fault system the w e profiles show that the width of the west fissure zone based on the fracture density distribution derived from aerial photographs is 4000 m on profile a and 7000 m on profile b the estimated widths correspond roughly to the region where the fault is kinematically uniform the ratio of the fault width to the fault length ranges from 0 024 to 0 041 this ratio compares favourably with the measured ratio of small metre scale natural faults audio frequency magnetotelluric imaging shows low electrical resistivity zones resistivity of 5 30 m coincident with the mapped surface traces of the fault however these zones are very narrow width about 100 m and only 50 m profile a and 200 m profile b deep respectively on profile b the shallow high conductive zone is underlain by a resistive zone 1000 m the conductivity enhancement in these shallow and narrow zones contrasts with the broad process zone revealed by structural analysis we assume that the conductivity enhancement is due to meteoric water entering a zone of ruptured rocks along the fault trace fault core at present we have no indication for seismic slip along the investigated segments of the west fissure zone fault models have shown that during aseismic periods of fault evolution fault healing i e strength recovery due to compaction and cementation is active fluids and fluid transport which are probably responsible for enhanced conductivity are confined to the remaining fractures of the fault core at shallow depth

the willyama supergroup in the broken hill and euriowie blocks new south wales abstract the willyama supergroup consists of highly deformed metasedimentary schists and gneisses with abundant quartzofeldspathic gneisses lesser basic gneisses and minor lode rocks prograde metamorphism ranged from andalusite through sillimanite to granulite grade radiometric dating in the broken hill block indicates separation of the source of the quartzo feldspathic gneisses from the mantle at 2300 2100 ma a rb sr model source age of 1820 60 ma has been interpreted as the maximum age of deposition deformation d 1 and or d 2 was coincident with high grade metamorphism at 1660 10 ma minor mundi mundi type granitoids and some pegmatites were intruded at 1490 20 ma minor pyroxenites at 561 7 ma dolerite dykes soon after and zoned pegmatites at 500 ma in association with the delamerian orogeny which reactivated retrograde schist zones at 520 40 ma subsequent history mostly comprises faulting weathering uplift and erosion the willyama supergroup has an estimated total thickness of 7 9 km with neither top nor basement exposed no unconformities have been recognized in the sequence the supergroup was deposited in a deepening environment passing upward from sandy facies to more shaly and fine sandy facies and from interpreted bimodal acid basic volcanics to non volcanic facies the metasediments have been interpreted as shelf sediments overlain by deeper water turbidites and minor contourites recently they have been reinterpreted as shallow marine with the quartzo feldspathic gneisses interpreted as fluvio deltaic arkoses in this paper the sequence to the top of thackaringa group is interpreted as mainly fluvio deltaic and lacustrine the broken hill group and sundown group are interpreted as shallow marine the paragon group may have comprised shelf muds overlain by delta front and lacustrine sediments in turn overlain by deeper water fine grained turbidites the broken hill orebody near the top of broken hill group consists of a series of stacked lenses much recent work has concluded that the deposit is volcanic exhalative in origin probably formed from seawater convected through the sequence and driven by heat from high level magma chambers however some features of the deposit are more appropriate to a sedimentary exhalative origin and models have been proposed involving seismic pumping of connate water with ore deposition on or below the seafloor devolatilization of the mantle has been proposed as a source of ore constituents deposition may have occurred in a narrow ne sw trending seafloor depression the willyama supergroup was probably deposited in a rift zone with thin crust the basic gneisses are interpreted as fe rich tholeiites similar to basalts from some oceanic spreading ridges the intense folding post folding leucogranitic intrusions and extensive granulite amphibolite facies metamorphism could have resulted from a collision following subduction however there is no direct evidence of oceanic crust or subduction and the low pressure metamorphic path does not suit a collision model the rocks were probably deposited in a continental rift with some similarities to those interpreted for proterozoic fold belts in northern australia

blind orogen integrated appraisal of multiple episodes of mesoproterozoic deformation and reworking in the fowler domain western gawler craton australia abstract the fowler domain in the western gawler craton in southern australia is a poorly exposed region that can only presented be explored using a combination of information from drilling and potential field geophysics regional maps of the total magnetic intensity tmi field of the fowler domain highlight an anastomosing system of terrain scale shear zones that bound four crustal scale tectonic blocks from west to east the colona barton central and nundroo blocks integrated thermobarometry and electron microprobe chemical dating of metamorphic monazites from drillholes in the fowler domain suggest that the colona block in the west underwent two mid crustal amphibolite grade metamorphic events at ca 1643 and 1600 ma the younger age corresponds to the timing of regional high grade metamorphism in the barton block together the age data suggest that the western fowler domain underwent a major tectonothermal event at ca 1600 ma in contrast regional lower crustal metamorphism in the nundroo block which forms the eastern fowler domain occurred at ca 1545 ma in both the barton and nundroo blocks petrological relationships mineral zoning and pressure temperature p t modelling suggest the terrains cooled in the mid to lower crust rather than undergoing exhumation immediately following peak metamorphism age data from the geophysically defined shear zone systems that bound the blocks suggest that exhumation of these lower crustal domains occurred between ca 1470 and 1450 ma and was associated with transpressional reactivation of the terrain during the coorabie orogeny a key finding of this study is that the tectonic evolution of the crustal blocks in the fowler domain was not in concert until at least 1500 ma thus the evolution of the individual blocks is unlikely to be related to the macroscopic character of the terrain defined by the regional scale shear zone systems which are one of the youngest tectonic imprints on the fowler domain coincident gravity and magnetic forward modelling of significant bounding faults suggests the shear zones form a steeply dipping transpressional array consistent with the observed metamorphic field character of the different blocks this study provides a demonstration of the integration of geophysical and petrological approaches to investigate the time integrated tectonic evolution of poorly exposed basement terrains

late quaternary sea level change in south africa abstract a late quaternary sea level curve for south africa is presented on the basis of new and published data from a range of sea level indicators and a variety of locations available evidence suggests that sea level in south africa broadly follows that described from the caribbean but that deviations occur during sea level highstands during the last interglaciation oxygen isotope stage 5 and the late holocene coastal emergence produced higher sea levels in south africa than those identified in the caribbean during the same time intervals this is tentatively ascribed to predicted lithospheric deformation in continental margin settings

9000 years of sea level change along the southern african coastline abstract beachrocks are good indicators of sea level stillstands on microtidal coastlines and data for this sea level curve is mainly based on dating a series of holocene beachrocks and planation episodes on the southeast african coastline sea level reached its present level along the southern african coastline at ca 6500 bp sea level then rose depositing a series of beachrocks at an elevation of 2 75 m this mid holocene sea level highstand persisted for a period of 2500 years with a 3 5 m stillstand dated at 4480 bp being the highest sea level reached during the holocene in post holocene sea level optimum times a regression occurred lowering sea level to its present level at 3880 bp and down to 2 m at approximately 3000 bp subsequently sea level rose to 1 5 m at 1610 bp and attained its present level at about 900 bp the mid holocene sea level highstand appears to have resulted from a combination of isostatic emergence and the steric expansion of seawater relating to warmer ocean temperatures associated with the holocene hypsithermal event on the eastern agulhas bank

the source of a type magmas in two contrasting settings u pb lu hf and re os isotopic constraints the sources of post orogenic a type magmas from two distinct geodynamic settings are compared the end of the ca 514 480 ma delamerian orogeny southeastern south australia was marked by 10 myr of bimodal a type magmatism driven by convective removal of thickened lithosphere initial os and hf isotope ratios record a heterogeneous lithospheric mantle source with some input from aesthenospheric mantle mafic parental melts fractionated to produce the granites in contrast initial os isotope ratios of the a type magmas that comprise the ca 1598 1583 ma mesoproterozoic gawler felsic large igneous province central south australia record a dominant evolved lower crust component however initial hf isotope ratios from these samples are depleted indicating a mantle source for lithophile elements this voluminous bimodal magmatism lasted for 15 myr and ended the wartakan orogeny in both cases the homogenisation of chemical rheological heterogeneities inherited from terrain amalgamation and orogenic thickening strengthened the lithosphere the contemporaneous fusion of heterogeneous mantle crust may represent a common stabilising influence on the lithospheric column regardless of tectono magmatic setting

the role of transcurrent intra arc tectonics in the configuration of a volcanic arc summary field investigations show that plio quaternary mexican and quaternary ecuadorian volcanic arcs are coeval with intra arc transcurrent or transtensional tectonics with motions along faults parallel or subparallel to the arc this relationship can also be observed in the quaternary kamchatka arc these arcs have an anomalously wide distribution of volcanic centres which cannot be explained simply by a low dip in the subducting lithosphere comparison with the intra arc tectonics and geometry of other quaternary arcs reveals that strike slip fault zones parallel to the arc favour magma rising in a broad surficial zone and may channel magma feeding mainly huge stratovolcanoes

the eucarro rhyolite gawler range volcanics south australia a 675 km3 compositionally zoned lava of mesoproterozoic age the eucarro rhyolite is remarkable in being far more voluminous 675 km3 and extensive than most felsic lavas 1 km3 its dimensions are comparable to the largest known volcanic units felsic ignimbrites and flood basalts it is one of several voluminous felsic units within the mesoprot erozoic ca 1592 ma gawler range volcanics an intracontinental intraplate volcanic province in south australia and is typical of the voluminous felsic magmatism associated with laurentia cf belt supergroup midcontinent united states the lava is 300 m thick with groundmass textures and lithofacies characteristics consistent with cooling and degassing as a single unit there are gradational compositional and textural variations throughout its highly elongate distribution 225 km east west 74 wt sio2 pyroxene is the dominant ferromagnesian phase but at the base in the west primary amphibole and olivine are present granitic and mafic clasts are ubiquitous but most abundant 5 vol in western and eastern parts of the unit the main eucarro magma was compositionally zoned and several smaller batches of compositionally distinct magma were tapped during the eruption concentrations of granitic clasts coincide with changes in bulk composition and may record the rupture of wall rock between nearby but separate magmas the distribution subtle lateral variations in composition and texture and local presence of compositional flow banding along the northern margins suggest that the eucarro rhyolite was derived from several source vents located along an east trending fissure system although very widespread outflow of the eucarro lava was probably no more than a few tens of kilometers from source vents

multi scale analysis of proterozoic shear zones an integrated structural and geophysical study abstract structural mapping of poorly exposed shear zone outcrops is integrated with the analysis of aeromagnetic and bouguer gravity data to develop a multi scale kinematic and relative overprinting chronology for the palaeoproterozoic tallacootra shear zone australia d 2 mylonitic fabrics at outcrop record kimban aged ca 1730 1690 ma n s shortening and correlate with sz 1 movements overprinting d 3 sinistral shear zones record the partitioning of near ideal simple shear and initiated riedel to regional scale sz 2 strike slip on the tallacootra shear zone sz 2 previously undocumented ne sw extension led to the emplacement of aplite dykes into the shear zone and can be correlated to the ca 1595 1575 ma hiltaba magmatic event d 4 dextral transpression during the ca 1470 1450 ma coorabie orogeny reactivated the tallacootra shear zone sz 2 r4 exhuming lower crust of the northwestern fowler domain within a positive flower structure this latest shear zone movement is related to a system of west dipping shear zones that penetrate the crust and sole into a lithospheric detachment indicating wholesale crustal shortening these methods demonstrate the value of integrating multi scale structural analyses for the study of shear zones with limited exposure

a reassessment of the archean mesoproterozoic tectonic development of the southeastern chhattisgarh basin central india through detailed aeromagnetic analysis abstract we constrained the geological framework over polydeformed paleoproterozoic sonakhan greenstone belt and addressed the tectonic evolution of singhora basin in the fringes of bastar craton central india by utilizing aeromagnetic data interpretation 2 5d forward modelling and 3d magnetic susceptibility inversions the sonakhan greenstone belt exposes volcano sedimentary sequences of the sonakhan group within nnw sse to nw se trending linear belts surrounded by granite gneisses which are unconformably overlain by sedimentary rocks of chhattisgarh basin the orientations of aeromagnetic anomalies are coincident with geological trends and appear to correlate with lithology and geologic structure regional magnetic anomalies and lineaments reveal both nnw sse and ne sw trends prominent e w trending linear high amplitude magnetic anomalies are interpreted as the trans chhattisgarh aeromagnetic lineament tcal nw se trending aeromagnetic signatures related to sonakhan greenstone belt extends below the singhora sedimentary rocks and forms the basement in the west the analysis suggests that tcal is a block fault with northern block down thrown and affected the basement rocks comprising the sonakhan greenstone belt and samblapur granitoids the episode of faulting represented by the tcal is pre singhora sedimentation and played a vital role in basin evolution the basement configuration image generated by estimates of depth to magnetic basement suggests a complex pattern of nne ssw to ne sw trending depressions separated by a linear n s trending basement ridge it is inferred from the 3d magnetic susceptibility inversion that the thickness of sediments is more towards the eastern basin margin and the n s ridge is a manifestation of post sedimentary faulting results of 2 5d modelling of a wnw ese profile across the singhora basin combined with results from 3d inversion suggest suggests the basin subsidence was controlled by ne sw trending regional faults in an active system the basin geometry evolved by e w block faulting overprinted by ne sw trending pre to syn depositional normal faults generating ne sw depression which are affected by n s trend post sedimentary faulting though the present work relates the basin evolution with the initiation of rift basin it warrants further work to establish the deformation within the basin pertaining to the proximal thrust and uplift along the craton fringe

architecture of proterozoic shear zones in the christie domain western gawler craton australia geophysical appraisal of a poorly exposed orogenic terrane abstract large scale mesoproterozoic crustal shear zones are partially exposed from beneath cover sequences in the christie domain of the northwestern gawler craton southern australia these structures are associated with gravity and magnetic anomalies that allow them to be mapped under cover and their three dimensional geometry and kinematics to be evaluated gravity and magnetic forward modelling indicate that these shear zones form an imbricate oblique thrust stack with combined top to the southeast left lateral transport the longest shear zones in the stack penetrate the crust to at least 15 km depth and dip to the northwest at 70 their inferred sense of motion are consistent with kinematic indicators from sparse outcrops from northwest to southeast the stack includes crustal slices bound by the karari fault zone tallacootra and blowout shear zones colona and coorabie fault zones and the muckanippie shear zone these structures separate discrete tectonometamorphic packages within the previously undifferentiated christie gneiss of the archean mulgathing complex and imply several generations of transport of material from the lower and middle crust three dimensional inversion of gravity data indicates that the muckanippie shear zone a shallowly rooted second order splay of the coorabie fault zone has an antithetic dip to the southeast and is part of a positive flower structure cross cutting relationships coupled with recent reconnaissance geochronology suggest that the western gawler craton part of the mawson continent was under a long lasting oblique slip deformational regime after ca 1590 ma this tectonic reworking is correlated with episodic pervasive metamorphism and deformation recorded elsewhere in the gawler craton between ca 1550 and 1450 coorabie orogeny pointing to a complex history of stabilization in proterozoic rodinia the tallacootra colona and coorabie structures are all cut at a high angle to their strikes by mesozoic rift faults of the southern rift system and may form piercing points in reconstructions of gondwana and earlier rodinia configurations

subduction evolution and mantle dynamics at a continental margin central north island new zealand 1 central north island new zealand provides an unusually complete geological and geophysical record of the onset and evolution of subduction at a continental margin whereas most subduction zones are innately two dimensional north island of new zealand displays a distinct three dimensional character in the back arc regions specifically we observe mariana type subduction in the back arc areas of central north island in the sense of back arc extension high heat flow prolific volcanism geothermal activity and active doming and exhumation of the solid surface evidence for emplacement of a significant percent of new lithosphere beneath the central north island comes from heat flux of 25 mw km of strike of volcanic zone and thinned crust underlain by rocks with a seismic wave speed consistent with underplated new crust seismic attenuation qp 1 is high 240 and rhyolitic and andesitic volcanism are widespread almost complete removal of mantle lithosphere is inferred here in pliocene times on the basis of the rock uplift history and upper mantle seismic velocities as low as 7 4 0 1 km s in contrast southwestern north island exhibits chilean type back arc activity in the sense of compressive tectonics reverse faulting low heat flow thickened lithosphere and strong coupling between the subducted and overriding plates this rapid switch from mariana type to chilean type subduction occurs despite the age of the subducted plate being constant under north island moreover stratigraphic evidence shows that processes that define the extensional back arc area the central volcanic region are advancing southward into the compressional system wanganui basin at about 10 mm yr we link the progression from one system to another to a gradual and viscous removal of thickened mantle lithosphere in the back arc regions thickening occurred during the miocene within the taranaki fault zone the process of thickening and convective removal is time and temperature dependent and has left an imprint in both the geological record and geophysical properties of central north island which we document and describe

the recognition of reactivation during continental deformation reactivation involves the accommodation of geologically separable displacement events intervals 1 ma along pre existing structures the definition of a significant period of quiescence is central to this phenomenological definition and the duration of the interval chosen represents the resolution limit of reactivation criteria found in most ancient settings in neotectonic environments reactivation can be further defined as the accommodation of displacements along structures that formed prior to the onset of the current tectonic regime this mechanistic definition cannot always be applied to ancient settings due to the uncertainties in constraining relative plate motion vectors four sets of criteria may be used to recognize reactivation in the geological record stratigraphic structural geochronological and neotectonic some structural criteria may not be reliable if used in isolation to identify reactivated structures much of the previously published evidence cited to invoke structural inheritance is equivocal as it uses similarities in trend dip or three dimensional shape of structures numerous fault and shear zone processes can cause significant weakening both synchronously with deformation and in the long term and may be invoked to explain reactivation the collage of fault bounded blocks forming most continents therefore carries a long term architecture of inheritance which can explain much of the observed complexity of continental deformation zones

provenance of the early mesoproterozoic radium creek group in the northern mount painter inlier correlating isotopic signatures to inform tectonic reconstructions abstract new in situ zircon la icpms geochronologic and hf isotope data from the radium creek group within the mount painter inlier provide important temporal constraints on the early mesoproterozoic palaeogeography of eastern proterozoic australia the entire radium creek group was deposited in a single basin forming phase and has a maximum depositional age of 1595 3 7 ma detrital zircon from these metasedimentary rocks have u pb age populations at ca 1595 ma 1660 1680 ma 1710 1780 ma ca 1850 ma and ca 2500 ma these grains are characterised by isotopically diverse and evolved sources and have crystallised within predominantly felsic igneous host rocks the relative age spectra and isotopic character has more similarity with the gawler craton than the arunta block curnamona province or the mount isa inlier these observations suggest that the mount painter province was adjacent to the gawler craton in the early mesoproterozoic our data supports a coherent south australian craton at ca 1595 ma and a contiguous continental mass that included the north and south australian cratons the mount painter inlier occupied a complex plate tectonic setting in the overriding plate of two convergent margins

constraints on long lived mesoproterozoic and palaeozoic deformational events and crustal architecture in the northern mount painter province australia abstract meta sedimentary and igneous rocks preserved in the hanging wall of the paralana fault northern mount painter province record a protracted ca 1600 myr multi staged metamorphic and poly deformational evolution related to mesoproterozoic and palaeozoic orogenic events the mount painter province was located near the margin of both the south australian craton and the north australian craton which allows comparisons of the tectonic evolution of these margins and provides context for the evolution of the eastern proterozoic australia for both the columbia and gondwana supercontinents within the mount painter province meta sedimentary rocks form part of a basin system developed adjacent to the margins of the gawler craton and curnamona province following the olarian wartakan orogenic system sedimentation was followed by ca 1590 1552 ma ductile deformation d 1 d 3 at mid to upper crustal levels preserving a rapid ca 6 myr burial and exhumation cycle initial deformation is characterised by the development of a layer parallel fabric s 1 s 1 is overprinted by recumbent north verging folds f 2 formed during mid to upper amphibolite facies peak metamorphism m 2 which are overprinted by tight upright shallow ne sw plunging folds f 3 d 3 folds developed contemporaneous with sinistral oblique shearing and the development of proto mylonitic to ultra mylonitic fabrics along the paralana fault zone the timing of d 3 deformation is constrained by the development of a penetrative steeply dipping foliation s 3 in the ca 1585 1569 ma shallowly emplaced mount neill granite and relatively undeformed granites dated at ca 1552 ma further constraint on the absolute timing of mesoproterozoic tectonism is provided through the dating of zircon growth from samples of the meta sedimentary radium creek metamorphics this dating reveals a 1555 16 ma metamorphic event interpreted to be the consequence of m 3 amphibolite facies regional metamorphism and accompanying metasomatism the transition between d 2 and d 3 is interpreted to reflect a shift from ca 1591 1585 ma n s shortening to ca 1585 1552 ma nw se shortening this episode of orogenesis is correlated with the ca 1585 1540 ma kararan orogeny in the northern gawler craton which distinctly postdates the ca 1600 1590 ma olarian orogeny as previously interpreted the mesoproterozoic structural architecture was reactivated during neoproterozoic extension d 4 and the ca 500 ma delamerian orogeny delamerian structures are formed in a predominantly brittle regime early thin skinned thrusting was followed by thick skinned deformation d 5 d 6 during which open f 5 folds developed above oblique lateral ramps and produced type 0 overprinting patterns with f 3 mesoproterozoic folds steeply plunging f 6 buckle folds with se trending axial traces are the last phase of deformation recorded both mesoproterozoic ductile deformation phases and the palaeozoic ductile brittle to brittle overprints were focussed along the paralana fault emphasising the repeated long lived evolution of this crustal scale fault system

timing of mesoproterozoic tectonic activity in the northwestern gawler craton constrained by 40ar 39ar geochronology abstract an array of northeast trending shear zones in the north west gawler craton of south australia has been implicated in widely disparate proterozoic continental reconstructions these shear zones are interpreted to have formed in response to sinistral transpression and dissect the north west gawler craton into several geological domains each with contrasting metamorphic histories new 40ar 39ar data provide age constraints for movement along these shear zones and are interpreted to indicate that the karari tallacootra and coorabie shear zones were last active at 1450 ma despite distinct differences in metamorphic grade the various geological domains bounded by shear zones exhibit evidence for commonality in event histories prior to deformation at 1450 ma albeit at different crustal levels this is interpreted to indicate that deformation at 1450 ma was responsible for reshuffling of crustal blocks that were already adjacent rather than amalgamation of exotic terranes the new data also provide additional evidence for a widespread metamorphic and deformational event at 1530 1550 ma across the north western gawler craton the timing of deformation at 1450 is 100 ma younger than suggested in several published tectonic reconstructions and importantly is also significantly older than grenvillian age tectonism in adjacent provinces to the west and north

layers and internal waves in uniformly stratified fluids stirred by vertical grids laboratory experiments in which uniformly stratified fluids are stirred by horizontally moving vertical grids or arrays of vertical rods are reviewed to examine their consistency and to compare their findings particularly those relating to the generation of layers selected experiments are of three types those in which a turbulence spreads from a horizontally confined region where it is continuously generated by an oscillating grid b grid stirring is maintained throughout a rectangular tank or c a cloud of turbulence decays after a short period of horizontally localized grid mixing in all the experiments turbulence is generated over the full vertical extent of the tank in the experiments of types a and c layers of comparable scale are observed to intrude into the ambient fluid from the turbulent region in the type b experiments layers form only when the time interval between the passage of the grid through the stratified fluid is sufficiently long allowing turbulence to decay substantially between grid strokes two mechanisms are found to be dominant in the production of layers in experiments of type a and c overturning eddies in the turbulent region of scale significantly larger than the ozmidov length scale collapse and spread intruding and forming layers in the adjoining laminar region internal shear waves propagating ahead of the intrusions have a vertical wavelength that is approximately twice the layer height in type b experiments layers are formed through a process described by holford linden dyn atmos oceans vol 30 1999 a pp 173 198 the bending of vortices shed by the grid bars the height of the layers is approximately half the vertical wavelength of internal shear waves that travel at the speed of the grid it is proposed that the flow field of the shear waves bends the vortices resulting in diapycnal mixing that forms the layers the relationship of layers and internal shear waves in the experiments is therefore as follows in type a and c experiments internal waves are generated by layers intruding from the turbulent region into the quiescent stratified region but in experiments of type b internal waves drive and dictate the height of the layers layers are generated as a consequence of vortex bending by internal waves there is insufficient evidence to establish whether zigzag instability either of vortex pairs or of vortex streets shed by a moving grid accounts for the layers in any of the three types of grid experiments the phillips and posmentier instability may reinforce layers formed by other processes the generation of pancake vortices or vortical mode motion is left for later review

late paleo mesoproterozoic plate margin deformation in the southern gawler craton insights from structural and aeromagnetic analysis abstract the integration of structural analysis of outcrop and aeromagnetic interpretation has revealed a complex tectonic evolution for the southern gawler craton that reflects the regional tectonic signal during the late paleo to early mesoproterozoic results suggest that exposures at yarlbrinda hill comprise the margin of a highly deformed st peter suite pluton emplaced within the southwestern gawler craton at ca 1611 ma d 1 at outcrop records east to northeast directed ductile thrusting regionally this deformation overprints north south trending dextral yarlbrinda shear zone fabrics within ca 1622 ma st peter suite granite and ca 1690 1670 ma tunkillia suite granite progressive east to northeast directed thrust movements led to exhumation of the deformed ca 1611 ma granite d 2 deformation is recorded by the brittle reactivation of first generation mylonitic fabrics accompanied by cataclasis alteration and pseudotachylite development d 3 records a switch to northwest southeast shortening which led to the folding and tear faulting of the d 1 2 shear zone a switch to extension and subsequent rotations of the principle stress axes led to hiltaba suite granite emplacement and contemporaneous faulting under east west extension during d 4 and west northwest east southeast extension during d 5 deformation of ca 1622 ma st peter suite granite is consistent with movement on the yarlbrinda shear zone and requires the st peter suite to have been emplaced into or adjacent to the ca 1690 1670 ma tunkillia suite prior to shear zone activity and on the overriding plate during subduction d 1 d 3 deformation is constrained by the emplacement of ca 1580 ma hiltaba suite granite and correlates with the wartakan orogeny in the southeastern gawler craton and the olarian orogeny in the curnamona province a 52 disparity between the shortening directions in these respective areas suggests different degrees of mesoproterozoic rotation which likely aided the formation of an intervening basin province the remnants of which are presently preserved in the mount painter inlier the record of convergent deformation is geochronologically constrained to a 30 myr period and places this region of the central gawler craton near a late paleoproterozoic convergent plate margin prior to a period of transient extension beginning at ca 1580 ma the continental scale signal of tectonic events can be recognized at the outcrop scale highlighting the importance of detailed outcrop studies in sparsely exposed areas

composition age and tectonic setting of amphibolites in the central bushmanland group western namaqua province southern africa abstract the western namaqua province wnp of southern africa is composed of several supracrustal assemblages and intrusive granitoid suites that were formed during the mid proterozoic 2 0 1 0 ga ago the bushmanland group bg has been the subject of intense study recently because of its considerable strategic metal potential hosting several giant stratiform base metal deposits e g gamsberg and aggeneys the bg contains amphibolites which represent metamorphosed tholeiitic basalts with mgo 9 4 and enriched in ni relative to modern basalts a feature reminiscent of archaean tholeiites post depositional mobility of elements is probably widespread and hampers recognition of parental magma composition and source region characteristics however the amphibolites have yielded a sm nd isochron age of 1649 90 ma nd t 0 48 0 89 which is interpreted as the time of extrusion of the basalt precursors and by inference a minimum sedimentation age for the underlying metalliferous bg sequence it follows that the bg sequence evolved during an intermediate period in the history of the namaqua province after major crustal stabilisation around 2 0 1 9 ga and before the last major tectonothermal event around 1 2 1 1 ga results of a parallel rb sr and u th pb study of the bg amphibolites indicate strong metamorphic resetting 1 2 1 1 ga ago thereby confirming earlier work on the wnp characteristics of the source region to the bg basalts have been inspected with morb normalised trace element abundances with the salient result being the bg basalts require derivation from a source that experienced variable geochemical modification similar to that proposed for the mantle wedge overlying modern subduction zones such a process is currently preferred over crustal contamination since the sm nd isochron for the bg amphibolites is remarkably linear but independent confirmation of the sm nd age is still required before this alternative model can be discounted to reconcile the requirement of subduction related metasomatism in the source to tholeiitic basalts erupted within what appears to be a cratonic sedimentary basin we suggest that back are continental extension could provide a satisfactory tectonic setting as such an environment is intrinsically linked to subduction

early tectonic evolution of the thomson orogen in queensland inferred from constrained magnetic and gravity data abstract the crustal architecture as well as the kinematic evolution of the thomson orogen in queensland is poorly resolved because the region is concealed under thick phanerozoic sedimentary basins and the basement geology is known from limited drill holes combined potential field and seismic interpretation indicates that the thomson orogen is characterized by prominent regional ne and nw trending structural grain defined by long wavelength and low amplitude geophysical anomalies the smooth magnetic signature is interpreted to reflect deeply buried source bodies in the mid to lower crust short wavelength positive magnetic features that correlate with negative gravity anomalies are interpreted to represent shallower granitic intrusions they appear to be focused along major fault zones that might have controlled the locus for magmatism the eastern thomson orogen is characterized by a prominent ne structural grain and orthogonal faults and fold interference patterns resulting in a series of troughs and highs the western thomson orogen consists of a series of nw trending structures interpreted to reflect reverse faults sedimentation and basin development are interpreted to have initiated in the neoproterozoic to early cambrian during e w to ene wsw extension possibly related to the rodinia break up this extensional event was followed by late cambrian shortening recorded in the maneroo platform and the diamantina river domain which possibly correlates with the delamerian orogeny renewed deposition and volcanism occurred during the ordovician and may have continued until late silurian resulting in thinned proterozoic basement crust and extensive basin systems that formed in a distal continental back arc environment our interpretation places the thomson orogen to the west of the neoproterozoic passive margin preserved in the anakie inlier the region is likely to represent the internal extensional architecture during the rodinia break up that has been subsequently extensively modified by multiple extensional basin forming events and transient episodes of crustal shortening and basin inversion

hydrogeological characterization of the kosi bay lakes system north eastern south africa this paper reports a hydrogeological characterization of a groundwater dependent lakes system the lakes kosi bay catchment located in the north eastern coast of south africa conventional hydrogeological techniques including water balance analysis hydrogeochemical and environmental isotope methodologies were applied in the study three distinct aquifer systems are recognized in the area namely the unconfined holocene cover sands the kosi bay and port durnford formations and the umkhwelane and uloa formations groundwater recharge to the topmost aquifer which is connected to the lakes is estimated using the chloride mass balance method to be 12 of the mean annual precipitation map 939 mm a evaporation rate from the lakes and evapotranspiration from the catchment are 1310 and 1135 mm a respectively the mean annual water balance components indicate a positive balance between inputs and outputs groundwater flows from the west through the lakes flow through lakes to the indian ocean groundwater in the shallow holocene aquifer and streams has similar hydrochemical and isotopic signature indicating strong interconnection these groundwater and streams have a hydrochemistry dominated mainly by a na cl hco3 water type a very low salinity ranging from 88 to 400 s cm and a negative isotopic signature negative d and 18o values the lakes are characterized by na cl hydrochemical water type have salinity that ranges from 1014 to 25 300 s cm and positive stable isotopic signature positive d and 18o signature indicating strong evaporation effects the study further reveals a salinity and isotopic series among the lakes from south to north towards the estuary

tectonic mode switches and the nature of orogenesis abstract the birth and death of many mountain belts occurs in lithosphere that over rides major subduction zones here the tectonic mode shortening versus extension can abruptly switch even during continuous and otherwise smooth convergence if the hinge line of the foundering slab rapidly retreats i e rolls back the foundering slab creates a gravitational potential well into which the orogen collapses this motion coupled with stress guides can pull the orogen apart a slowing of roll back or of hinge retreat means that the subduction flexure may subsequently begin to be pushed back or be pushed over by the advancing orogen the consequence of such changes in relative motion is that orogenic belts are affected by abrupt tectonic mode switches the change from push to pull leads to a sudden change from horizontal extension to horizontal shortening potentially throughout the entire mass of the orogenic lithosphere that over rides the subducting slab the sequencing of these tectonic mode switches affects the thermal evolution of the orogen and thus fundamentally determines the nature of orogenesis this insight led to us to our quite different views as to how orogens work it is evident that orogens affected by abrupt push pull mode switches are characterized by high pressure metamorphism whereas orogens affected by abrupt pull push mode switches are characterized by high temperature metamorphism magmatism and anatexis

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

interpretation of a ca 1600 1580 ma metamorphic core complex in the northern gawler craton australia abstract the mount woods domain in the gawler craton south australia records a complex tectonic evolution spanning the palaeoproterozoic and mesoproterozoic the regional structural architecture is interpreted to represent a partially preserved metamorphic core complex that developed during the 1600 1580 ma hiltaba event making this one of the oldest known core complexes on earth the lower plate is preserved in the central mount woods domain which comprises the mount woods metamorphics these rocks yield a detrital zircon maximum depositional age of 1860 ma and were polydeformed and metamorphosed to upper amphibolite to granulite facies during the 1740 1690 ma kimban orogeny the upper plate comprises a younger succession the skylark metasediments deposited at 1750 ma within the upper plate sedimentary and volcanic successions of the gawler range volcanics were deposited into half graben that evolved during brittle normal faulting the skylark shear zone represents the basal detachment fault separating the upper and lower plate of the core complex the geometry of normal faults in the upper plate is consistent with ne sw extension both the upper and lower plates are intruded by 1795 1575 ma hiltaba suite granitic and mafic plutons the core complex was extensively modified during the 1570 1540 ma kararan orogeny exhumation of the western and eastern mount woods domain is indicated by new 40ar 39ar biotite cooling ages that show that rock packages in the central mount woods domain cooled past 300 c 50 c at 1560 ma which was 20 million years before equivalent cooling in the western and eastern mount woods domain exhumation was associated with activity along major syn kararan orogeny faults

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

cu au mineralisation in the curnamona province south australia a hybrid stratiform genetic model for mesoproterozoic iocg systems in australia abstract the proterozoic curnamona province lies between two of the most endowed cu bearing mineral belts on the australian continent the gawler craton which hosts the giant olympic dam iron oxide copper gold iocg system and the mount isa inlier which hosts the giant mount isa cu system and iocg belt of the eastern succession this study focuses on cu au deposits within the proterozoic rocks of the benagerie ridge magnetic complex in the central curnamona province the benagerie ridge is buried beneath neoproterozoic and phanerozoic cover sequences we use drillcore and geophysical data to determine the structural architecture and structural controls of cu au mineralisation in the benagerie ridge the portia and north portia deposits are the most significant cu au mineral deposits in the benagerie ridge and lie adjacent to an extensive regional redox boundary that separates lower magnetic units from upper non magnetic units the redox boundary is extensive throughout the curnamona province and is linked with mineralisation in the region significant chalcopyrite bornite and molybdenite occur along bedding parallel layers and shear structures these factors support a strong lithological control on cu au mineralisation at all scales deformation in the benagerie ridge involved the development of a d1 layer parallel foliation s1 which is overprinted by d2 recumbent folds and d3 upright folds the deformation history is associated with the c 1610 1580 ma olarian orogeny overprinting of d2 structures during d3 has resulted in a type 2 interference pattern which we have successfully mapped using aeromagnetic data several later phases of post olarian faults overprint f2 and f3 fold interference patterns and have resulted in the remobilisation of some of the cu au mineralisation we propose that the stratiform cu au mineralisation occurred prior to the onset of the olarian orogeny mineralisation is preserved within the thickened hinge zone of a similar type f2 fold proximal to the hinge of an overprinting f3 fold which we propose has enhanced mineralisation within the north portia deposit consequently the identification of the redox boundary within f2 folds elsewhere in the curnamona province particularly when located proximal to f3 fold hinges which place the mineralised zones into structurally favourable locations provide good targets for future mineral exploration

water activity changes across an amphibolite granulite facies transition broken hill australia phase compositions in pelitic and mafic gneisses place tight constraints on pressure ranging from 3 up to 6 kb and to a lesser extent on temperature 500 up to 800 c during prograde regional metamorphism of the willyama complex broken hill se australia these limits allow an evaluation of water activity across the terrain using various equilibria in pelitic and mafic gneisses the stability of cummingtonite and biotite over much of the terrain places upper limits on temperature and the presence of syn metamorphic partial melts in the metasediments places lower limits on a h2o garnet biotitesillimanite k feldspar quartz relations combined with the partial melting data suggest a decrease in water activity from near 1 0 in the lower grade zones to 0 5 0 2 in the broken hill little broken hill part of the two pyroxene zone this result is compatible with less precise hornblende orthopyroxene clinopyroxene quartz relations

the benagerie shear zone 1100 myr of reactivation history and control over continental lithospheric deformation abstract a newly identified northwest southeast oriented deeply rooted steep to vertical large scale structural system within the proterozoic curnamona province australia which we term the benagerie shear zone is imaged in regional magnetic and gravity datasets in this study we use a combination of field analysis and quantitative geophysical methods to establish a 1100 myr history of activity along the benagerie shear zone during which the location of younger geological structures are influenced by the pre existing shear zone this deformational system is interpreted to have 1 aided ascent and emplacement of the ca 1600 ma ninnerie magmatic supersuite 2 controlled the loci of nucleation of normal faults during rifting and continental breakup at ca 800 ma and 3 influenced the development of fold structures as well as acting as a plane co linear to the rotation axis of pre existing normal faults such that they were steepened and reactivated as strike slip structures during the ca 500 ma delamerian orogeny we interpret that the benagerie shear zone has not undergone uni directional propagation during its evolution but rather through reactivation was a primary influence on controlling the nucleation of neoproterozoic rift faults thereby playing a major role in accommodating strain over a significant period of the evolution of the curnamona province this study demonstrates that crustal scale shear zones can evolve over hundreds of millions of years have strike lengths of hundreds to thousands of kilometers and have vastly different surface expressions along strike

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

kinematic variations across eastern cordillera at 24 s central andes tectonic and magmatic implications abstract the eastern cordillera central andes 24 s consists of a basement involved thrust system resulting from miocene quaternary eastward migrating compression separating the puna plateau from the santa barbara system foreland the inferred tertiary strains arising from shortening in the eastern cordillera and santa barbara system are similar higher than in the puna slip data collected on the major n s trending faults of eastern cordillera show a westward progression from dip slip contraction to dextral and sinistral motions this consistently with established tectonic models may result from partitioning due to the oblique mio quaternary underthrusting of the brazilian shield north of 24 s this strain partitioning has three main implications 1 as the dextral and sinistral shear in the eastern cordillera are 62 and 29 of the compressive strain respectively the eastern cordillera results more strained than santa barbara system foreland contrary to previous estimates 2 the partitioning in the eastern cordillera may find its counterpart in that to the west of the central andes giving a possible structural symmetry to the central andes 3 the easternmost n s strike slip structures in the eastern cordillera coincide with the easternmost mio pliocene magmatic centres in the central andes at 24 s provided that further to the east the crust is partially molten the absence of magmatic centres may be explained by the presence of pure compressive structures in this portion of the eastern cordillera

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

dating prograde amphibolite and granulite facies metamorphism using in situ monazite u pb shrimp analysis abstract in situ shrimp u pb analysis of monazite grains from pelites within an early formed high temperature shear zone in the southern broken hill block australia has been used to constrain the timing of prograde amphibolite facies and peak granulite facies metamorphism within the terrain geochronological analyses from grains inhabiting texturally distinct localities revealed two distinct age populations ca 1619 and 1600 ma the older age was obtained from grains that occur as inclusions completely enclosed within coarse grained k feldspar and garnet grains which evidently armored the monazite inclusions against resetting during younger deformation and metamorphic events the ca 1619 ma monazite population occurs as part of an amphibolite facies inclusion assemblage hosted within the peak granulite facies mineral assemblage and constrains the timing of prograde amphibolite facies metamorphism within the broken hill block the younger 1600 ma monazite age population was from grains within the pe

the behavior of a turbulent front in a stratified fluid experiments with an oscillating grid a simple laboratory model utilizes an oscillating grid to produce a turbulent front in a linearly stratified fluid the motion of the front is studied visually using laser fluorescence and neutrally buoyant tracer particles when the turbulence is vigorous near the grid stratification has no effect as the front propagates away vertical scales become limited by stratification as postulated by ozmidov the break up of the front can be identified at the nondimensional time nt 10 here a series of layers are formed which intrude into the surrounding nonturbulent fluid the vertical scale of these layers is also predicted using ozmidov s postulate it is approximately 7 times the estimated ozmidov scale at nt 10 the advance of individual intrusions comprising the front is characterized by a local froude number which decreases as the intrusions lengthen the mechanism of advance is intimately connected with wave motions produced at the turbulent end of the intrusions

electrical conductors in archean mantle result of plume interaction 1 from long period magnetotelluric data across the gawler craton we obtain a three dimensional resistivity image of the lithosphere and provide constraints on tectonothermal events dating back to the proterozoic contrary to common observations of archean cratons displaying high electrical resistivity in the mantle lithosphere the magnetotelluric data show low resistivity of around 10 m at 80km depth underneath the 1595ma gawler range volcanics a silicic large igneous province the resistivity distribution appears to be a signature of plume modified orogenesis with low degree partial melting at the base of the lithosphere in a back arc setting the enhanced conductivity is explained through higher hydrogen and iron content in the crystal lattice and also along the grain boundaries of the mantle constituting minerals older arc related magmatism to the southwest across 1620 1610ma st peter suite does not display enhanced conductivity and suggests a depleted mantle lithosphere the data show that yellowstone type mantle plume analogues are preserved through time and still display an elevated electrical signature in the lithosphere today

the late cenozoic evolution of coastal water bodies in northern kwazulu natal south africa abstract three large coastal water bodies st lucia sibaya and kosi of markedly different contemporary morphology occur on the eastern margin of the northern kwazulu natal coastal plain south africa this paper examines their late cenozoic evolution and investigates the controls on their evolution that have produced the observed differences in morphology all three systems origins were due to mio pliocene low sea level still stands allowing rivers to scour channels into cretaceous and palaeocene sedimentary sequences during the last interglacial oxygen isotope stage 5e sea level was approximately 5 m above present level and the morphology of the three systems was similar an offshore barrier archipelago partially isolated a back barrier environment that comprised intertidal sand flats localised reefs and tidal channels the area around bazaruto island mozambique provides a modern analogy river rejuvenation and associated incision up to and during the last glacial maximum 16 000 18 000 bp caused a minimum of 40 m scour which is still reflected in the bathymetry of lake sibaya and kosi accumulation of barrier sands partly against pre existing interglacial barrier remnants during the holocene marine transgression 16 000 4500 bp ramsay p j 1995 9000 years of sea level change along the south african coastline quaternary int 27 1 5 was responsible for lagoon isolation although the extent and nature of separation from the sea varies markedly between the systems the northern part of lake st lucia was closed from the sea during the late holocene probably during a sea level fall from a holocene high stand of ca 3 m at 3000 bp the kosi system had a late pleistocene to early holocene outlet situated at bhanga nek lake nhlange but this inlet mouth closed approximately at 3000 bp the present mouth was established by 1600 bp lagoonal conditions within lake sibaya terminated ca 5000 bp when coastal barrier dune formation caused complete impoundment and enabled the lake water level to rise to 20 m above mean sea level lake st lucia s large catchment has meant that fluvial sediment input has kept pace with the holocene transgression whereas the localised drainage associated with sibaya and kosi has resulted in a negligible fluvial sediment input allowing for deep lacustrine conditions to develop lagoonal segmentation is present to some extent in each system as a result of mobile coastal sediments and their reworking by short period wind waves the differential stages of lagoonal segmentation in the three systems can be explained by a the presence of cohesive sediment and bedrock around st lucia which reduce shoreline mobility and b the great water depths in sibaya compared to kosi which require longer periods of infilling before segmentation is complete

lower crustal rejuvenation and growth during post thickening collapse insights from a crustal cross section through a variscan metamorphic core complex the variscan lower crust of europe acquired its main features seismic layering intrusion of mantle derived magmas granulite grade metamorphism when the upper crust underwent post thickening extension through gravitational collapse we suggest that post thickening collapse is a geodynamic process that contributes to the growth and differentiation of continental lithosphere in collapsed mountain belts

comparing 1800 1600 ma accretionary and basin processes in australia and laurentia possible geographic connections in columbia abstract we focus on potential pinning points on the southern and eastern margins of australia and the southern and western margins of laurentia and interpret a convergent plate boundary along the southern margin of the proto australian continent during the palaeo to mesoproterozoic 1800 1600 ma specific geological events within the southern australian margin can be correlated with events preserved along the medicine bow yavapai mazatzal belt in southwestern laurentia these belts were characterised by southward continental growth with varying degrees of crustal reworking and accretion of juvenile material in australia crustal reworking appears to have been the dominant process from 1800 to 1670 ma with more juvenile material accreted at 1620 ma in contrast the southern laurentian terranes were dominated by accretion of juvenile material from 1800 to 1620 ma although reworked continental crust was also accreted to the margin in the interior of both continents basins developed with comparable histories from 1800 to 1670 ma thereafter the evolution of the interior basins diverged with sag phase processes dominant in northern australia and a protracted depositional hiatus in laurentia the geologic evolution is consistent with palaeomagnetic data and provides further evidence for geographic links between eastern australia and western laurentia from 1800 to 1600 ma

structural architecture of the southern mount isa terrane in queensland inferred from magnetic and gravity data abstract the basement rocks of the southern mount isa terrane are concealed under younger sedimentary units and its crustal architecture is understood using constrained regional potential field analysis prominent n s to nnw trending geophysical anomalies extend for 250 km south of the exposed mount isa inlier and are abruptly terminated by the ne trending cork fault palaeoproterozoic basinal successions and major palaeo to mesoproterozoic structures recorded in the mount isa inlier are interpreted to continue southward under the palaeozoic cover the intensely positive geophysical signature of the region is mostly attributed to shallowing of the barramundi aged basement and distribution of metamorphosed sedimentary and volcanic rocks deposited during the formation of the ca 1790 1730 ma leichhardt superbasin regional low magnetic and low gravity responses may reflect basinal sequences deposited during the formation of the ca 1725 1690 ma calvert superbasin and the ca 1675 1595 ma isa superbasin short wavelength magnetic anomalies and co located low intensity bouguer gravity anomalies are interpreted to represent shallow and variously magnetized granitic intrusions the geophysical signature of the southern mount isa terrane reflects the bipartite fault architecture of the region in the western fold belt palaeoproterozoic multiple basin formation was controlled by west dipping faults in half graben setting within the nnw trending leichhardt river fault trough to the east of the pilgrim fault thick palaeoproterozoic sedimentary and volcanic successions were controlled by major nnw trending east dipping normal faults the mesoproterozoic isan orogeny reactivated the existing extensional fault network deformation during the ca 1595 1580 ma early isan orogeny is not apparent in the southern mount isa terrane and may have been confined to the northern part of the terrane the ca 1570 1550 ma middle isan orogeny produced inversion of major nnw trending rift faults and resulted in regional scale culminations the ca 1550 1540 ma wrench tectonics is represented by the activation of nw and ne oriented strike slip faults overprinting the prominent n s to nnw oriented structures the emplacement of elongated batholitic bodies may be coeval to the emplacement of the ca 1540 1520 ma williams supersuite recorded in the mount isa inlier and thus may represent its southern extension the southern mount isa terrane also appears to have been affected by post isan tectonics that resulted in deposition and magmatic intrusions focused along the northern side of the ne trending cork fault

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

excess40ar in metamorphic rocks from broken hill new south wales implications for40ar 39ar age spectra and the thermal history of the region 40ar 39ar age spectrum analyses of samples from broken hill new south wales indicate that the region has experienced a complex thermal history following high grade metamorphism 1660 ma ago the terrain cooled slowly 3 c ma 1 until about 1570 ma ago when the temperature fell below about 500 c following granitoid emplacement 1500 ma ago the region remained relatively cold until affected by a thermal pulse 520 40ma ago causing temperatures to rise to 350 c in some places during this event accumulated40ar was released from minerals causing a significant ar partial pressure to develop laboratory ar solubility data combined with the40ar 39ar age spectra gives a local estimate of this partial pressure of 10 4atm the region finally cooled below 100 c about 280 ma ago 40ar 39ar age spectrum analyses of hornblende plagioclase and clinopyroxene containing excess40ar are characterized by saddle shaped age spectra detailed analysis of plagioclase samples reveals a complex diffusion behaviour which is controlled by exsolution structures this effect in conjunction with the presumed different lattice occupancy of excess40ar with respect to radiogenic40ar appears to be responsible for the saddle shaped age spectra

the influence of a mantle plume head on the dynamics of a retreating subduction zone the geological record and seismic tomography together contain multiple examples of mantle plumes and subducting oceanic slabs interacting however consequences of these interactions and a mechanism for plumes to pass from the subducting to the overriding plate are uncertain we present three dimensional numerical simulations of a retreating subduction zone encountering a mantle plume head we assess the impact a plume head has on the geometry of the trench and whether it can create a window within the subducted slab in our models we consider slab plume head interactions to be a natural consequence of plume head entrainment by plate motion combined with slab retreat strong slabs prevent plume heads from reaching the surface for weak slabs strongly buoyant plume heads cause local trench advance slab windowing and accelerated slab retreat at the margins of the plume head for large plume heads this trench advance may contribute to crustal shortening in the overriding plate opening a slab window creates a potential conduit for transfer of plume material from the subducting plate to the overriding plate without terminating an active magmatic arc away from the point where the plume head tears the slab

the luminescence chronology of dune development on the maputaland coastal plain southeast africa abstract geomorphological and lithostratigraphic mapping of dune systems on the maputaland coastal plain of northeastern kwazulu natal province south africa has defined the relative age relationships between the complex pattern of quaternary parabolic and hummocky dunes sand megaridges and the composite coastal barrier dune cordon here infra red stimulated luminescence irsl ages are presented in the context of regional stratigraphic relationships and serve to bracket the period of accumulation of the main dune systems the luminescence ages challenge the widely held belief that the north south aligned dune pattern reflects a coastward younging sequence the framework of ages highlights the spatial variations in dune mobilization and long accretion history on some dune forms weathered dune and interdune wetland sediments spanning from prior to marine isotope stages mis 11 and up to mis 7 underlie the coastal plain at least two generations of decalcified aeolianite of mis 5 and 4 form the core of the complex coastal barrier dune on the coastal plain frequent sand mobilization events during mis 3 2 resulted in the development of discrete complexes of highly extended northward directed parabolic dune systems and reworking of the crest of the central sand megaridge the luminescence dated dune mobilization history brackets the period of formation of interdune and lacustrine peat and diatomite deposits during the holocene marine transgression at least four laterally extensive complex transverse ridges of coalesced ascending parabolic dunes accreted against the aeolianite core of the coastal barrier polyphase dune formation and remobilization is discussed in the context of the regional groundwater and vegetation responses to global climatic changes wind regimes and glacio eustatic sea level fluctuations

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

the turbulent wake of a towed grid in a stratified fluid in a stable background density gradient initially turbulent flows eventually evolve into a state dominated by low froude number dynamics and frequently also contain persistent pattern information much empirical evidence has been gathered on these latter stages but less on how they first got that way and how information on the turbulence generator may potentially be encoded into the flow in a robust and long lasting fashion here an experiment is described that examines the initial stages of evolution in the vertical plane of a turbulent grid generated wake in a stratified ambient refractive index matched fluids allow optically based measurement of early nt 2 stages of the flow even when there are strong variations in the local density gradient field suitably averaged flow measures show the interplay between internal wave motions and kelvin helmholtz generated vortical modes the vertical shear is dominant at the wake edge and the decay of horizontal vorticity is observed to be independent of mathit fr stratified turbulence originating from kelvin helmholtz instabilities develops up to non dimensional time nt approx 10 and the scale separation between ozmidov and kolmogorov scales is independent of mathit fr at higher nt the detailed measurements in the near wake with independent variation of both reynolds and froude numbers while limited to one particular case are sufficient to show that the initial turbulence in a stratified fluid is neither three dimensional nor universal the search for appropriately generalizable initial conditions may be more involved than hoped for

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

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

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

age constraints on terrane scale shear zones in the gawler craton southern australia abstract electron probe micro analysis epma chemical dating of monazite from crustal scale shear zones in the late archaean to mesoproterozoic gawler craton southern australia highlights a long history of shear zone development associated with assembly and reworking of the craton in the southeast gawler craton dextral transpression was focussed into the 250 km long kalinjala shear zone which dominates the structural character of that part of the craton monazite in upper amphibolite facies shear fabrics within the kalinjala shear zone give a mean age of 1682 10 ma this is indistinguishable from an age of 1693 16 ma obtained from monazite inclusions within garnet porphyroclasts within the shear fabric in the western gawler craton monazite populations from two separate locations along the 400 km long tallacootra shear zone give ages of 1680 37 and 1679 39 ma respectively suggesting that both the kalinjala and tallacootra shear zone systems record regional scale strain partitioning toward the end of the ca 1730 1700 ma kimban orogeny in the northwest gawler craton the karari fault zone can be traced for 700 km and separates late archaean rocks from an assembly of tectonic terranes that comprise the northern and northwest gawler craton monazites from amphibolite grade mylonites associated with the karari fault zone have a mean age of 1631 12 ma this age is identical to the timing of regional arc like magmatism represented by the st peter suite in the central gawler craton and suggests that exhumation of the ca 1650 1640 ma ultra high grade granulites of the nawa domain in the northwest gawler craton was linked to the development of the st peter suite magmatic margin in the central gawler craton monazite in the 200 km long yerda shear zone which sheared granites belonging to the ca 1580 ma hiltaba suite have a mean age of 1503 16 ma similar ages of 1516 18 and 1508 14 ma are obtained from monazite inclusions in garnet porphyroclasts within mylonites along the 300 km long coorabie fault zone in the western gawler craton younger ages of 1468 12 and 1457 22 ma from the amphibolite grade mylonitic fabrics in the coorabie fault zone are similar to 40ar 39ar ages from the western gawler craton and suggest that reactivation of the coorabie shear zone in part was associated with regional cooling and stabilisation of the gawler craton at ca 1450 ma the history of deformation on the terrane scale shear zones in the gawler craton therefore does not reflect a single period of terrane assembly or reworking rather it points to a complex pattern of strain partitioning during tectonic events in the late palaeoproterozoic to early mesoproterozoic

the last 25 ma of rotational deformation in part of the new zealand plate boundary zone abstract the marlborough fault system is a zone of dextral transpression in continental crust and marks the southern end of the hikurangi subduction system between the obliquely convergent australian and pacific plates detailed mapping over an area of 100 km2 has revealed a complex history of deformation during the last 25 ma the development of a thrust belt in the miocene referred to as d1 deformation was synchronous with the deposition of a thick submarine fan complex the beginning of d1 deformation may mark the initiation of the subduction zone in this part of the plate boundary zone subsequently in the plio pleistocene the region formed a zone of dextral shear marked by major strike slip faults and zones of distributed deformation referred to as d2 deformation crustal blocks less than 5 km across may have rotated ca 60 clockwise about vertical axes relative to the pacific plate in the last 4 ma the pattern of deformation during the last 10 ka to 100 years is consistent with the long term d2 deformation and suggests that large crustal blocks resting on the subducted pacific plate have rotated clockwise about vertical axes relative to the pacific plate accommodated by dextral shear further to the sw in the marlborough fault system the overall effect of the deformation has been the rotation of the edge of the southern part of the hikurangi margin from a w to nw trend in the early miocene to a ne trend today

evidence and timing of crustal extension versus shortening in the early tectonothermal evolution of a proterozoic continental rift sequence at broken hill australia 1 low pressure p high temperature t metamorphism previously attributed to crustal thickening accompanying nappe emplacement in the paleoproterozoic willyama supergroup at broken hill is reinterpreted as a response to crustal extension d1 and bimodal magmatism commencing circa 1700 ma d1 deformation occurred under amphibolite granulite facies conditions producing layer parallel fabrics s1 and metapelitic mineral assemblages in which andalusite dominated over sillimanite crustal extension ceased soon after 1640 ma to be followed by crustal thickening higher pressure metamorphism and northeast vergent recumbent folding d2 attendant on inversion of the original d1 extensional structures d2 recumbent folding has previously gone unrecognized but probably peaked around 1600 ma before further amphibolite facies metamorphism between 1600 and 1590 ma accompanying upright folding and northwest directed thrust faulting d3 in the light of this revised tectonothermal history geodynamic models erected to explain elevated thermal gradients and low p high t granulite facies metamorphism in tectonically thickened crust may not be as relevant to broken hill as once thought above average crustal temperatures and low p high t metamorphism in the willyama supergroup more likely occurred in response to voluminous magmatic intrusion accompanying crustal thinning mantle upwelling and emplacement and unroofing of midcrustal rocks along a major detachment surface a second major structural and or stratigraphic break in the willyama supergroup is indicated by the absence of d1 fabrics from the uppermost part of the sequence

thrusting and duplex formation at mount isa queensland australia large scale repetition of mount isa and haslingden group rocks in the anticline north of mount isa is interpreted as the core of a thrust duplex which has been subsequently folded parallel to the direction of thrusting displacement of mount isa group rocks above the duplex is extremely significant to the regional geology and exploration for more mount isa style pb zn and cu orebodies interpretation of the geometry of the thrust belt indicates thrusting on different stratigraphical levels below and above the duplex during its formation horses formed from a heelwards protruding footwall ridge instead of a trough and the complex effects on stratigraphical cross sections through duplexes of sloping lateral footwall ramps on horses

strain localisation and high grade metamorphism at broken hill australia a view from the southern cross area abstract progressive localisation of strain within proterozoic high grade rocks in the southern cross area of the willyama supergroup broken hill has resulted in the formation of shear zones of highly strained d2 fabrics separated by less strained d2 zones that preserve pre tectonic relationships complex fold interference patterns and abundant pegmatites related to a d1 m1 deformation metamorphic event the metamorphic peak m1 is characterised by biotite sillimanite quartz alkali feldspar plagioclase with garnet or cordierite in metapelites formed at about 750 c and 400 500 mpa presumably relatively late in m1 as garnet has overgrown the s1 biotite sillimanite fabric the d2 strain is concentrated in high strain zones that form sub planar and anastomosing networks of apparently simple s l tectonite fabrics associated with subhorizontal shearing and are locally overprinted by d2 leucosomes in the more aluminous metasediments m2 involved identical metamorphic conditions as m1 late d2 muscovite bearing pegmatites intruded the area a further proterozoic d3 m3 event localised in the sites of d2 high strain is characterised by the growth of staurolite and garnet across a muscovite fabric at about 600 c at 400 600 mpa resulting from the addition of h2o to the original upper amphibolite facies assemblages younger phases of retrogression generally involving thrusting are usually localised in sites of pre existing high strain they are characterised by chlorite muscovite bearing assemblages it is proposed that the events d1 m1 d2 m2 and d3 m3 occur within separate heating events separated by periods of repose at the ambient geotherm