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

palaeomagnetism of red beds from the kimberley group western australia implications for the palaeogeography of the 1 8 ga king leopold glaciation abstract the 1 8 ga king leopold glaciation in northwestern australia is recorded in the kimberley basin by subglacial erosional forms cut in an unconformity surface at the top of the speewah group and buried by glaciofluvial deposits at the base of the king leopold sandstone the lowest formation of the kimberley group the glaciofluvial deposits are conformably overlain by texturally mature locally glauconitic quartzarenite of shallow marine origin implying that glaciation occurred near sea level palaeomagnetic data for five sites 29 specimens in the hematite bearing elgee siltstone of the upper kimberley group in the northeastern kimberley basin gave a dip corrected mean direction of declination d 95 4 inclination i 13 8 95 9 7 indicating a palaeolatitude 7 0 5 3 5 0 results for red beds from five sites 28 specimens in the conformably overlying pentecost sandstone gave a dip corrected mean direction of d 94 1 i 13 0 95 11 7 6 6 6 4 5 9 combining our data for the elgee siltstone and pentecost sandstone with results for the elgee siltstone in the southeastern kimberley basin li z x 2000 palaeomagnetic evidence for unification of the north and west australian cratons by ca 1 7 ga new results from the kimberley basin of northwestern australia geophysical journal international 142 173 180 yielded a dip corrected mean direction for 17 sites of d 93 5 i 15 1 95 4 4 palaeolatitude 7 7 2 3 and an overall pole position at latitude p 5 4 s longitude p 211 8 e with confidence semi axes dp 2 3 and dm 4 5 a positive fold test at 99 confidence was obtained for the combined data for the 17 sites the basinwide concordance of results for the elgee siltstone and the positive fold test argue for an early magnetisation acquired prior to late palaeoproterozoic initial folding of the kimberley group and close to the time of deposition our results imply a low palaeolatitude for the kimberley group and the king leopold glaciation palaeomagnetic data for the 1 822 ga plum tree creek volcanics in the pine creek orogen to the east of the kimberley basin are consistent with northwestern australia being in low palaeolatitudes during the late palaeoproterozoic hence the enigma of glaciation near sea level in low palaeolatitudes which marks the neoproterozoic and early palaeoproterozoic applies also to the late palaeoproterozoic red beds from the lansdowne arkose of the speewah group also were studied but only directions ascribable to tertiary regolith weathering processes were found similar findings for the late palaeoproterozoic mcarthur basin in northern australia suggest some units in that basin also record tertiary regolith processes

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

assembling and reactivating the proterozoic capricorn orogen lithotectonic elements orogenies and significance abstract the capricorn orogen was initiated during palaeoproterozoic suturing events that brought together the archaean yilgarn and pilbara cratons to form the west australian craton the orogen comprises palaeoproterozoic plutonic and medium to high grade metamorphic rocks of the gascoyne complex a series of palaeoproterozoic volcano sedimentary and sedimentary basins including the ashburton blair yerrida bryah padbury and earaheedy basins and the deformed margins of the pilbara and yilgarn cratons major pulses of deformation and metamorphism took place during the ca 2200 ma ophthalmian orogeny the 2000 1960 ma glenburgh orogeny the 1830 1780 ma capricorn orogeny and a more localized unnamed event at the end of the palaeoproterozoic 1670 1620 ma the orogen has been the site of repeated intracratonic reactivation with renewed basin formation magmatism and orogeny during the mesoproterozoic and the neoproterozoic the exhumed palaeoproterozoic components of the orogen are unconformably overlain by the intracratonic mesoproterozoic edmund and collier basins bangemall supergroup which have been deformed during the neoproterozoic edmundian orogeny the ophthalmian and glenburgh orogenies affected the northern and southern margins of the orogen respectively the former resulted in the development of a foreland basin along the pilbara craton margin whereas the latter is associated with accretion of an allochthonous element the glenburgh terrane of the gascoyne complex to the northwestern margin of the yilgarn craton effects of the capricorn orogeny extended across the entire orogen and provide a younger limit for amalgamation of the yilgarn and pilbara cratons a number of basins developed along both the northern and southern margin of the orogen during this event and were filled with sediment eroded from the yilgarn craton the gascoyne complex and a presently unexposed early palaeoproterozoic terrane the capricorn orogeny corresponds with a major phase of continental collision both in australia and world wide which appears to mark a major phase of supercontinent assembly mineralization within the orogen includes a wide variety of deposit types that can be related to collisional settings including the world class iron orebodies of the hamersley basin

high pressure amphibolite granulite facies metamorphism in the paleoproterozoic rudall complex central western australia abstract the rudall complex forms the basement of the paleoproterozoic to neoproterozoic paterson orogen which was deformed during at least three major orogenies the complex comprises a sequence of metamorphosed clastic and chemical sediments and basalts deposited in a marginal basin environment prior to extensive felsic intrusion deformation of the sequence during the first yapungku orogeny between 2000 and 1760 ma included extensive thrust stacking from ene to wsw the thermal peak of the associated high pressure metamorphism was late to post tectonic with respect to this deformation thermobarometry on amphibolites and mafic granulites that contain various combinations of the minerals hornblende plagioclase quartz garnet othopyroxene and clinopyroxene indicates that temperatures peaked at around 800 c while pressures reached 1200 mpa the late timing of peak temperatures together with the presence in some amphibolites of amphibole plagioclase symplectitic coronas around garnet indicates a steeply decompressive clockwise p t t path peak metamorphic pressures indicate that the crust was locally thickened by at least 40 km during an event that showed similarities to phanerozoic collisional tectonics it is suggested that this deformational and metamorphic event records the collision between the pilbara craton and a continent to the northeast the paleoproterozoic evolution of australia has previously been attributed to ensialic processes characterised by low pressure metamorphism and anti clockwise p t t paths the metamorphic history of the rudall complex is not consistent with this view and the documented high pressure metamorphism is broadly synchronous with a medium pressure metamorphic event in central australia the strangways orogeny and possibly also in northwestern australia the capricorn orogeny collisional plate tectonic processes played a significant role in the paleoproterozoic evolution of northern australia

timing the breakup of a proterozoic supercontinent evidence from australian intracratonic basins in the late proterozoic several broad shallow intracratonic depressions appeared across a vast area of central australia the basins which all contain shallow marine to fluvial successions appear to have been tenuously interconnected through much of their history analysis of their fill by means of tectonic subsidence curves suggests that they are the product of two separate and distinct periods of crustal extension one at about 900 ma and a second at about 600 ma these extensional episodes were probably the result of failed rifting events that almost fragmented the australian continent during the late proterozoic the second period of extension almost certainly relates to the breakup of a proterozoic supercontinent the results suggest that sediments preserved in the relatively protected environment of interior basins may provide a more subtle record of major tectonic events than continental margin sequences that were exposed to major continental interactions

precambrian tectonic evolution of part of gondwana southwestern australia southwestern australia has a long dynamic precambrian history of crustal fragmentation and aggregation by continental collision and accretion this interpretation contrasts with the widely held belief that most of australia was part of a proterozoic supercontinent in which all tectonic magmatic and metamorphic activity was intracontinental the pilbara and yilgarn cratons are two quite different fragments of archean continental crust that collided to form the capricorn orogen between 2000 and 1600 ma the albany fraser orogen formed along the southern margin of the yilgarn craton during another major continental collision at 1300 to 1100 ma rifting removed the northeastern part of these combined cratons and orogens between 1100 and 700 ma subsequent continental collision along this rifted margin formed the paterson orogen at 700 to 600 ma therefore the assembly of this considerable part of gondwana may not have been completed until about 600 ma

proterozoic accretionary tectonics in the east kimberley region australia abstract the east kimberley region contains well preserved tectonic structure dating back to the earth s most significant stage of continental growth the assembly of the nuna supercontinent an integrated geological geophysical investigation of this region has been conducted and reveals insight into its tectonic evolution including potential influence of significant crustal scale structures in the development of regional architecture the emplacement of magma and the relationship of these structures to large scale deformation some newly interpreted features include a north trending structure and three north west trending structures that segment the north east trending orogen the central segment of the orogen is a zone of higher metamorphic grade and is host to a distinct gravity high this gravity high can be explained by excess mass in the mid crust this anomaly is consistent with either a large mafic ultramafic intrusion or a high density crustal fragment possible tectonic models to explain the geophysical and metamorphic anomalies involve in the latter case the accretion of a crustal fragment to the kimberley craton prior to the 1865 1850 ma hooper orogeny or in the former case intrusion of voluminous mafic magmas into the middle crust whether by igneous or structural means we consider the development of this anomalous region to be a result of along strike variations in subduction dynamics these were perhaps driven by variations in slab geometry accommodated by the orogen normal structures we identify the orogen normal structures are interpreted to be crustal scale faults along which significant vertical displacement occurred when a crustal fragment collided with kimberley craton and exhumed high grade metamorphic rocks to the surface

palaeomagnetic evidence for unification of the north and west australian cratons by ca 1 7 ga new results from the kimberley basin of northwestern australia summary a palaeomagnetic study of the elgee formation red siltstones and shales in the palaeoproterozoic kimberley basin of northwestern australia has been carried out all seven sampling sites revealed an extremely stable magnetic remanence carried by haematite the age of the formation is confined by precise shrimp u pb ages of early diagenetic xenotime from rocks both above and below it to be 1704 7 14 ma but this may represent a minimum age the youngest detrital zircon grains in the underlying formation provide a maximum age of 1786 14 ma for the formation the extreme stability of the remanence the dissimilarity of the remanent direction from expected younger palaeomagnetic directions and the lack of regional overprint in the 1790 4 ma hart dolerite just north of the study region support a primary origin for the remanence a marginally positive fold test also supports a primary origin the mean direction of d 92 2 i 14 9 a 95 6 4 gives a palaeopole at 4 4 s 210 0 e with dp 3 3 dm 6 5 this pole a previously reported palaeopole from the hart dolerite and ca 1700 ma overprint poles from the pilbara craton all agree with palaeopoles of similar ages from the mcarthur basin of northern australia palaeomagnetic results thus suggest that the north and west australian cratons were possibly joined together by approximately 1 7 ga

isotopic insight into the proterozoic crustal evolution of the rudall province western australia abstract the proterozoic assembly of australia involved the convergence of three main archean cratonic entities the north west and south australian cratons and is recorded in the proterozoic orogenic belts surrounding these continental nuclei the rudall province of northern western australia is the sole exposure of a paleo to mesoproterozoic orogen lying between the north and west australian cratons and may record the effects of their amalgamation we present new zircon o u pb and lu hf isotope data from magmatic rocks across the rudall province to which we add existing isotope data to yield a crustal evolution overview hf evolution trends for the ca 1804 1762 ma kalkan supersuite the ca 1589 1549 ma krackatinny supersuite and the ca 1310 1286 ma camel suite indicate a significant input of archean east pilbara basement material albeit as a mix with more juvenile material including a possible ca 1900 ma component zircon 18o data suggest a contribution from supracrustal material into the magmatic source of the kalkan supersuite which may have been emplaced in an extensional setting in contrast the krackatinny supersuite and camel suite have mantle like 18o which may reflect partial melting of deeper archean sources geochemical data for the krackatinny supersuite shows geochemical trends implying that melting of thickened mafic crust progressed from deeper to shallower levels possibly in a rift setting camel suite k rich leucogranites may also have been emplaced in an extensional setting towards the end of high p metamorphism all terranes of the rudall province are para autochthonous with respect to the pilbara craton with no requirement for arc related magmatism we outline two potential scenarios for the paleo to mesoproterozoic geodynamic evolution of the rudall province an early cratonic amalgamation between the west and north australian cratons ca 1680 ma followed by mesoproterozoic intraplate events or a later assembly ca 1377 1275 ma we lean towards this later amalgamation scenario

neoproterozoic stratigraphy of the centralian superbasin australia abstract the basement of central australia includes the arunta block and the 1200 1100 ma musgrave block succeeded by 1075 1000 ma bimodal volcanic rifts and dolerite dykes a regional hiatus at 1000 800 ma interpreted as reflecting a central post volcanic underplated upland was followed at 800 ma by a second swarm of dykes in the musgrave block gawler craton and stuart shelf associated with the crustal sagging that initiated the centralian superbasin the centralian superbasin is defined here to encompass the neoproterozoic fill of the amadeus georgina ngalia officer and savory basins the intra cratonic superbasin was disrupted internally 540 600 ma ago petermann ranges orogeny by a central uplift and associated thrusts and by mid carboniferous 320 ma tectonism alice springs orogeny to form the structural basins listed above the stratigraphy and sedimentology of the relatively well known areas can be used as a basis for predicting those of the poorly known regions new results from acritarch biostratigraphy and isotope chemostratigraphy in conjunction with conventional lithostratigraphy and sequence analysis allow better stratigraphic resolution than previously possible field observations in the recently discovered savory basin in western australia provide a basis for correlations with the adjacent basins

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

dynamic cause of marginal lithospheric thinning and implications for craton destruction a comparison of the north china superior and yilgarn cratons we present a comparative tectonic analysis of the north china craton ncc which has lost parts of its root with the yilgarn and superior cratons which preserve their roots we compare the geophysical structure and tectonic histories of these cratons to search for reasons why some cratons lose their roots while others retain them based on the comparison and analysis of geological geophysical and geochemical data it is clear that the lithospheric thinning beneath craton margins is a common phenomenon which may be caused by convergence between plates however craton destruction is not always accompanied by lithospheric thinning except for cratons that suffered subduction and collision from multiple sides the western block also known as the ordos block of the ncc yilgarn and superior cratons have not experienced craton destruction the common ground among them is that they are surrounded by weak zones e g mobile belts or orogens that sheltered the cratons from deformation which contribute

high grade reworking of central australian granulites part 1 structural evolution abstract four distinct deformational events d2 d5 accompanying a granulite facies metamorphic cycle m2 m5 are shown to structurally overprint rework pre existing granulites m1 of the northeast strangways range in the central arunta block the first metamorphic cycle m1 at 1800 ma involved an anticlockwise p t path peaking at 850 950 c at 8 9 kbar m1 metamorphism involved widespread partial melting that produced stromitic migmatites and map scale concordant granitic gneisses isobaric cooling after the peak and accompanying hydration gave rise to a wide variety of coronitic and symplectitic reaction textures that enclose and replace m1 mineral parageneses no kinematic structuring is associated with m1 and the period encompassing the thermal peak and immediately subsequent are thought to have been absent of deviatoric stress the second metamorphic cycle m2 m5 possibly at 1400 1500 ma involved a clockwise p t path with a maximum p of 9 10 kbar and a thermal peak of approximately 800 c this metamorphic cycle accompanied the major ductile deformations recognized d2 d5 and has been labelled the proterozoic reworking the proterozoic reworking has been divided into two thermo barometric and structurally distinct periods d2 d3 involved regionally inclined ene wsw non coaxial shear of high bulk shear strains giving rise to an intense often mylonitic pervasive fabric s2 l2 and isoclinal and sheath folds on all scales f2 f3 s2 l2 is the first recognized kinematic fabric and does enclose and partially recrystallize m1 mineral parageneses including late m1 metamorphic reaction textures d2 d3 deformation was due to crustal shortening and gave rise to crustal over thickening loading accompanying prograde metamorphism m2 d4 d5 involved upright open and asymmetrical folding f4 and e w trending shear zone development s5 within a regionally extensive system of inclined oblique sinistral transpression both d2 d3 and d4 d5 episodes occurred under the same approximately e w directed compressive stress and are considered sequential episodes in the one tectonothermal cycle f4 folding accompanied significant melt formation and the peak of metamorphism of the m2 m5 metamorphic cycle s5 shear zones accompanied 3 4 kbar of decompression with cooling presumably during uplift in isostatic response to crustal over thickening in d2 d3 progression from inclined non coaxial shear to transpression occurred in response to an increase in the relative buoyancy forces limiting crustal thickening as is typical of many compressional orogens however the proterozoic reworking is atypical of simple linear or arcuate mountain belts because late stage shearing s5 is aligned sub parallel not at a high angle to the transport vector of the earlier ductile deformations d2 d3 consequently this region is modelled in terms of crustal shortening directed along the length of an e w trending orogen confined to the north and south by relatively stable crustal blocks when e w shortening could no longer be accommodated by crustal thickening strain was partitioned by sinistral transpression between the north and south bounding crustal blocks

evolution of neoarchaean and proterozoic basins of australia abstract this study correlates basin initiation sedimentation and major tectonic events on an australia wide scale over the neoarchaean and proterozoic an interpretation of a depth to basement surface and faults based on magnetic and gravity data was calibrated with limited well data magnetic depth models geological maps and depth data from cross sections and literature tectonic events are correlated to basin formation and deposition of basin units event maps show the interpreted active faults a principal stress direction has been assigned to basin forming tectonic events the results of this study can be used as a kinematic stratigraphic and temporal framework to examine the development of individual basins and the regional influence of tectonic events tectonic events are grouped into four major time intervals the neoarchaean and early palaeoproterozoic 2775 2000 ma the mid late palaeoproterozoic to early mesoproterozoic 2000 1400 ma the mid late mesoproterozoic 1400 1000 ma and the neoproterozoic 1000 570 ma during the neoarchaean and early palaeoproterozoic basins formed along the southern pilbara and the northern yilgarn margins mainly in response to differential movements between these and other archaean cratons events in the mid late palaeoproterozoic to early mesoproterozoic were related to the assembly and subsequent intracontinental extension of the australian continent mid late mesoproterozoic events were due to interactions between australia and other continents during assembly of the supercontinent rodinia preservation of sediments from this time period is limited neoproterozoic basin forming events mainly related to the break up of rodinia and led to the formation of the centralian superbasin sedimentation in this basin was terminated at the end of the neoproterozoic due to compression associated with the amalgamation of the gondwana supercontinent

tectono thermal evolution of the palaeoproterozoic granites tanami orogen north australian craton implications from hornblende and biotite 40ar 39ar geochronology abstract the palaeoproterozoic granites tanami orogen gto hosts a number of gold deposits located in the southern margin of the north australian craton the major stratigraphic succession is the palaeoproterozoic tanami group which is subdivided into the dead bullock formation and conformably overlying killi killi formation new geochemical data for the ca 1864 coora and groundrush dolerite sills in the dead bullock formation suggests that they have the same characteristics with the enriched back arc basin basaltic rocks from the former stubbins formation such as tholeiitic affinity high tio 2 contents 0 94 to 1 24 wt and low mg 41 45 slightly enriched lile rb th u and k weakly depleted hfse nb ta and relatively flat ree patterns their magma was generated by high degree decompressional melting 5 15 of the asthenosphere source with an input of 3 4 subduction related material the petrological and geochemical similarities of igneous rocks provide new evidence for the assignment of the ca 1864 ma former stubbins formation and the mount charles formations in the dead bullock formation of the tanami group these conclusions confirmed that the extensive palaeoproterozoic tanami group was deposited in a back arc basin environment hornblende and biotite 40 ar 39 ar geochronological study identified three major tectono thermal events in the gto since the deposition of the dead bullock formation the ca 1840 ma 40 ar 39 ar cooling age of metamorphic hornblende from the coora and groundrush dolerite sills in the dead bullock formation provided precise age constraint for the first palaeoproterozoic tectono thermal event during the evolution of the granites tanami back arc basin this age is highly consistent with the ca 1850 1840 ma subduction and peak metamorphism events in the north australian craton nac associated with the halls creek orogeny in the halls creek orogen and the tennant orogeny in the tennant creek inlier the 40 ar 39 ar age of 1753 8 ma for the early biotite bi b from the dead bullock formation is a cooling age record of the peak greenschist facies metamorphism during the ca 1795 ma tanami orogeny which is interpreted as the continental continental collisional event between the gto and the arunta orogen in the central australian craton to the south the approximately 40 million year slow cooling is a combined result of exhumation heat released from the upwelling asthenospheric mantle regional magmatism and long term crustal residence this tectono thermal event was associated with gold mineralisation in the gto and the proterozoic nac was finally cratonised during this period the late biotite bi g is a recrystallization product of hydrothermal alteration its 40 ar 39 ar age of 1718 8 ma revealed the last tectono thermal overprint to the gto and arunta orogen this age reflected the distal thermal influence by the ca 1723 ma strangways event in the arunta orogen

postglacial relative sea level history of the prince rupert area british columbia canada this paper presents a history of relative sea level rsl change for the last 15 000 years in the prince rupert region on the northern coast of british columbia canada one hundred twenty three radiocarbon ages of organic material from isolation basin cores sediment sequence exposures and archaeological sites having a recognized relation to past sea levels constrain postglacial rsl the large number of new measurements relating to past sea level provides a well constrained rsl curve that differs in significant ways from previously published results after deglaciation following the last glacial maximum the region experienced an isostatically induced rapid rsl drop from as much 50 m asl to as low as 6 3 m asl in as little as a few centuries between 14 500 bp and 13 500 bp after a lowstand below current sea level for about 2000 years during the terminal pleistocene rsl rose again to a highstand at least 6 m asl after the end of the younger dryas rsl slowly dropped through the holocene to close to its current position by 2000 1500 bp with some potential fluctuations between 3500 and 1500 bp this study highlights variation in rsl histories across relatively short distances which must be accounted for by local rsl reconstructions such as this one this rsl curve aided in the identification of an 8000 9000 year old archaeological site on a 10 12 m asl terrace which is currently the earliest dated archaeological site in the area and it provides guidance for searching for even older archaeological remains we highlight the utility and potential of this refined rsl history for developing surveys for other archaeological sites associated with paleoshorelines

development of the late proterozoic to mid paleozoic intracratonic amadeus basin in central australia a key to understanding tectonic forces in plate interiors the intracratonic amadeus basin in central australia is a complex composite basin covering 17 000 km with at least nine distinct episodes of evolution between 900 and 300 ma these have been identified in neighboring central australian basins and are characterized by intervals of renewed subsidence followed by intervals of erosion and changes in basin shape several unconformities separating the tectonostratigraphic sequences represent periods of mild regional uplifts and correlate with major episodes of compressive tectonism at the evolving margin of the early australian plate in the absence of direct geological evidence for thermal events in the amadeus basin after the initial period of subsidence ended possibly at about 800 ma the correlations found between events in the amadeus basin those in the neighboring interconnected basins and tectonic events at the continental or plate margins emphasize that regional horizontal stress fields contribute significantly to primary basin forming mechanisms this suggests that stresses generated at continental or plate margins may propagate to the plate interior with the lithosphere acting as a stress guide throughout the history of the amadeus basin both periods when compressional stresses were dominant and when extensional tectonics controlled subsidence can be identified there were also transitional periods when neither compression nor extension dominated so that other processes masked the effects of weak horizontal stresses the most recent compressional thrust belt concentrated at the northern margin between 300 and 400 ma and has partly obscured the record of earlier basin shape and size

shrimp ionprobe dating of short lived proterozoic tectonic cycles in the northern arunta inlier central australia structural and metamorphic evidence from low p high t metamorphic terranes within the northern arunta inlier central australia indicates that two discrete tectonic cycles affected the region each cycle was associated with compressive deformation coincident with peak granulite facies metamorphism and granite intrusion shrimp u th pb analysis of zircons from early syn and late tectonic granitoids allows the age of the two tectonic cycles to be directly measured the age of the first cycle d1 is determined by emplacement of the mount stafford granite dated at or before 1818 15 ma after the first two foliations of the cycle had formed but before the axial plane cleavage associated with later upright folding the regional extent of this tectono magmatic event is confirmed by an emplacement age of 1818 8 ma measured on the large discordant harverson granite 40 km away the second cycle d2 consisted of four distinct deformation stages d2a 2d the ages of which are constrained by 1785 1775 ma old early syn and late tectonic granitoids the warimbi granite emplaced at or before 1785 22 ma and the granitic protolith to the napperby gneiss inferred to be 1780 10 ma pre date or formed during the earliest foliation s2a zircon considered to have grown at peak granulite facies metamorphic conditions during generation of the dominant s2b foliation gives an age of 1774 6 ma in the possum creek charnockite leucogranite in the napperby gneiss which post dates s2b and large scale upright nw se trending f2d folds yields an age of 1775 12 ma and confirms that the entire tectonic cycle d2a 2d formed in a rapid 10 ma period younger zircons which formed at 1659 6 ma in the napperby gneiss cannot be related to any local structural event but are similar in age to a major magmatic metamorphic episode in the southern arunta black and shaw 1992 150 km away they may be the peripheral manifestation of that event further zircon growth at 1600 ma in the napperby gneiss and possum creek charnockite was caused by hydrothermal fluid fluxing associated with post tectonic pegmatite emplacement these dykes were deformed by amphibolite facies retrograde shear zones ion probe dating of zircon stratigraphy from the granitoids has confirmed the discrete successive tectonic cycles identified by earlier structural and metamorphic studies for the northern arunta inlier at least those cycles or orogenies are associated with short lived 10 ma thermal pulses related to granite magmatism not prolonged thermal perturbations spanning 100 ma or more cf dirks and wilson 1990 dirks and hand 1991 such short lived pulses are intimately associated with granite intrusion and may be a general feature of low p high t metamorphism

seismic structure of the crust and uppermost mantle of the capricorn and paterson orogens and adjacent cratons western australia from passive seismic transects abstract the seismic structure of the proterozoic capricorn and paterson orogens and adjacent archaean yilgarn and pilbara cratons western australia is determined using a passive seismic approach we use recordings of distant earthquakes made along two transects of 3 component broadband stations the stations were deployed for approximately 1 year mid 2006 2007 during which time 70 earthquakes were recorded at each station with a suitable signal to noise ratio for receiver function analysis and hence the s wavespeed profiles of the crust and uppermost mantle beneath each recording station are determined we investigate the deep crustal constraints on terrane boundary locations the patterns of seismic discontinuities in the crust and the variations in the depth and character of the moho this broad scale information regarding the present day crustal architecture and hence the crustal evolution of western australia complements previous surface geological and other geophysical studies western australia is an exceptionally large well preserved region of ancient crust and hence this work also adds to the body of knowledge regarding proterozoic orogenic processes in general the new passive seismic work shows a region of double crust or upper mantle discontinuities beneath the glenburgh terrane adjacent to the northwest yilgarn craton the upper crust of the orogens is always layered whereas the cratons have a simple upper crust both the capricorn and paterson orogens are characterised by deeper moho discontinuities with a lesser wavespeed contrast than the very sharp discontinuity observed beneath the adjacent pilbara and yilgarn cratons this is consistent with the weaker orogenic crust of the capricorn and paterson orogens accommodating most of the horizontal deformation during assembly and reworking of the west australian craton while the pilbara and yilgarn cratons acted as rigid crustal blocks

geochemical and nd isotopic systematics of granites from the arunta inlier central australia implications for proterozoic crustal evolution geochemical and sm nd isotopic results are reported for granites from the proterozoic arunta inlier of central australia these combined with new geochronological data for the granites zhao and bennett 1995 allow important constraints to be placed on proterozoic tectonic and crustal evolution in central australia granites from the arunta inlier can be divided into three major geochemical groups a calcalkaline trondhjemitic group cat a high heat production group hhp and a volumetrically significant main group the cat group which occurs only in the southern margin of the inlier is characterised by high na2o nak sr krb and sry and relatively low k2o rb rbsr th u ree nb and y analogous to calc alkaline suites occurring in modern convergent plate margins the hhp group which occurs mainly in the interior of the arunta inlier and is spatially associated with the main group is characterised by high k rb th u rbsr and rbzr and relatively low sr ba nak krb barb mgo cr and ni the main group which occurs throughout the arunta inlier is geochemically intermediate between the cat and hhp groups it is geochemically analogous to the 1880 1850 ma old barramundi igneous association recognised in other proterozoic terrains of central australia and can be further subdivided into four age subgroups 1820 1780 1750 1650 and 1615 1600 ma respectively all three groups show similar negative nb anomalies on the trace element normalized diagrams despite the geochemical diversity of the arunta granites no correlations between the nd isotopic and geochemical signatures are observed the ranges of initial nd values and nd depleted mantle model ages tnddm for the three groups of granites overlap with each other overall there are two groups of tnddm ages the most common ranging from 2 33 to 1 96 ga and the other from 1 83 to 1 72 ga although initial nd values of the granites show large variations there is a general trend for the nd values to increase i e become less negative with decreasing crystallization ages the large geochemical and isotopic variations of the arunta granites reflect considerable heterogeneity in the sources of the granites and do not support a uniform 2 3 2 1 ga old barramundi type underplate source for the origin of the granites the combined geochemical and nd isotopic data suggest the sources of the granites contain at least two main components an palaeoproterozoic mantle derived component and an older crustal component the older crustal component was incorporated into the source region of the granites either through magma assimilation of crustal materials at lower crustal levels or more probably via sediment subduction and mantle wedge metasomatism the increasing nd values with decreasing crystallization ages may be a result of progressively increasing proportions of newly accreted island arc materials being incorporated in the subducted sediments alternatively a juvenile mantle derived component may have been added to the source region of the younger granites it is apparent that the nd isotopic signatures in the granites has resulted from complex processes and neither simple mixing nor simple two stage protolith models can as yet satisfactorily explain the observations the petrogenesis of the three geochemical groups of granites can be interpreted in a plate tectonics scenario it is considered that the cat group was formed by fractionation of arc type magmas and or partial melting of arc related intrusions or underplates in a subduction related continental margin setting whilst the formation of the main group may involve partial melting of fractionated and or modified arc related underplates but not necessarily in a subduction environment the younger hhp group was probably generated by remelting of the coexisting main group during subsequent tectonothermal events

the atnarpa igneous complex southeast arunta inlier central australia implications for subduction at an early mid proterozoic continental margin abstract three distinctive igneous suites have been identified from the atnarpa igneous complex southeast margin of the arunta inlier central australia the 1879 11 10 ma gabbro diorite tonalite trondhjemite suite sio2 49 78 shows both calc alkaline and trondhjemitic affinities the overall depletion of nb ti y k and rb in this suite indicates that its parental magma must have been depleted in these elements it is the oldest zircon age so far obtained in the arunta inlier the 1873 11 10 ma low al tonalite trondhjemite granodiorite suite is also depleted in k and rb however unlike either the 1879 ma or the 1751 ma suites it has lower al2o3 and sr at comparable sio2 levels and display flat hrees and negative eu anomalies the 1751 12 ma younger tonalite suite is high in sr sr y and al2o3 and low in zr ti nb y th and u and displays a strongly fractionated ree pattern with hree depletion typical of archaean high al tonalite trondhjemite granodiorite suites such geochemical features contrast with the 1850 1880 ma old k rb ree th enriched na sr depleted barramundi igneous association widespread in proterozoic terrains of northern australia the parental magma of the 1879 11 ma suite is considered to be derived by subduction related partial melting of a metasomatised hybridised mantle wedge with phlogopite retained in the residue the parental magma of the 1873 11 ma low al suite by relatively low pressure partial melting of a mafic source with residual plagioclase left in the residue and the 1751 12 ma younger tonalite suite by partial melting of a subducted oceanic crust at mantle depth with residual garnet amphibole these processes contrast with models of restite unmixing of a geochemically uniform but fractionated preexisting mantle derived underplate previously proposed for the k rich barramundi igneous association combining geochemical features of the atnarpa igneous complex with reported data from the harts range and the alice springs areas we propose that the southeast margin of the arunta inlier represents a convergent continental margin during the early to middle proterozoic which has undergone at least two episodes of subduction related magmatism 1860 1880 ma and 1730 1770 ma such continental margin subduction could provide additional driving force for crust mantle delamination and ensialic a subduction within the preexisting continental crust further north both within plate vertical underplating and marginal lateral accretion could be important processes for proterozoic crustal evolution

shrimp u_pb zircon geochronology of granites in the arunta inlier central australia implications for proterozoic crustal evolution abstract new shrimp u pb zircon isotopic ages are reported for ten granitic suites in the eastern arunta inlier these data combined with previous u pb zircon studies in the region constrain the timing of major palaeoproterozoic igneous events within the arunta inlier and establish a geochronological framework for understanding lithostratigraphic relationships tectonic events and geochemical and isotopic evolution of the granites in the region most granites in the arunta inlier including both syn tectonic and post tectonic types yield zircon ages in the range of 1770 1710 ma which are significantly younger than the 1880 1850 ma orogenic barramundi igneous association recognised throughout many other proterozoic terrains in northern australia no rocks of the barramundi association have been identified in this study the previously proposed barramundi type suites including the jervois and dneiper granites yield ages of 1771 6 and 1771 15 ma respectively many of the granite suites contain inherited zircons with ages in the range of 1890 1830 ma similar to the age of the barramundi association this and the age of the atnarpa igneous complex zhao and cooper 1992 which is coeval with but geochemically distinct from the barramundi association suggest that the 1880 1850 ma orogenic event affected the arunta inlier but has been obscured by the younger tectonic events the youth of tectonic events in the arunta inlier as compared with other proterozoic terrains of northern australia may have resulted from the inlier being located on the southern margin of the northern australian orogenic province during the palaeoproterozoic with the generation of granites in the arunta inlier possibly being related to subduction the combined data indicate that major granitic activity occurred at 1880 1850 1820 1770 1750 1730 1710 1660 1650 and 1615 1590 ma this result is broadly consistent with earlier summaries of the other proterozoic terrains in northern australia although the intensity of each episode varies in different regions

global electrodynamics observed during the initial and main phases of the july 1991 magnetic storm data acquired by seven fortuitously positioned satellites in the interplanetary medium the magnetosphere and the topside ionosphere as well as from numerous ground magnetometers have allowed us to follow the evolution of global currents and electric fields during the geomagnetic storm on july 8 9 1991 an interplanetary disturbance collided with the magnetosphere at 1636 ut on july 8th compressing the magnetopause inside of geostationary orbit for about 3 hours as observed by magnetometers on two goes satellites the resulting storm developed in four segments with a 7 hour lull separating the initial and main phases the initial phase was characterized by 1 an extensive dp 2 current system that produced an ae perturbation of 3500 nt with reporting stations on the dayside 2 a twenty fold increase in auroral electron fluxes and 3 the immediate appearance of electric fields in the inner magnetosphere the main phase intensification and earthward movement of the ring current are associated with southward turnings of the interplanetary magnetic field imf and a polar cap potential increase above 200 kv a significant fraction of the ring current growth was observed prior to the first of several substorms that occurred during the main and recovery phases the beginning of recovery was characterized by a diminution of the southward imf component the cross polar cap potential and magnetospheric electric fields it was also marked by a substorm onset considering the timing of dst modulations relative to substorm occurrence we conclude that during this magnetic storm the electric fields responsible for ring current transport energization were mostly associated with the dp 2 current system finally in the evening sector penetration electric fields of the initial and main phases led to the formation of upward moving equatorial plasma bubbles that were detected by two dmsp satellites in the topside ionosphere

the deep crustal structure of the warakurna lip and insights on proterozoic lip processes and mineralisation abstract understanding how large igneous provinces lips formed in the proterozoic is subject to several challenges including incomplete geological exposure deformations from subsequent reworking and the lack of strong geophysical signals from the associated thermal perturbations here we apply a seismically constrained gravity inversion method to the warakurna lip region in central western australia focusing on imaging the deep crust of this region and defining the extent and intensity of mafic magmatism in particular a thick mafic underplate has been imaged in some continent scale studies but its regional extent is not well defined the results of 3d gravity inversions demonstrate an extensive area with very thick crust 45 km composed of high density materials 2830 kg m3 which is interpreted to represent a mafic underplate variations in mass excess i e underplate thickness and or density suggest that the intensity of mafic magmatism closely followed the likely lithospheric architecture of the australian continent at the time of emplacement with magmatic centres concentrated adjacent to craton margins and along translithospheric shear zones this suggests that melting was focused in the proterozoic regions with thinner lithosphere or that upwelling mantle has been diverted into this region by the roots of the archean cratons or both the mass excess is greatest beneath the magmatic centre of the lip in the west musgrave province wmp this arrangement is reflected in ni cu pge prospectivity with known deposits focused in the wmp which has a thick dense underplate in contrast the capricorn orogen and yilgarn craton which are not underplated do not possess known deposits despite extensive sills in the upper crust our results show that this method for mapping the extent and mass excess of lower crustal magmatic products provides an effective indicator of the extent and intensity of magmatism during lip events and that this can help understand lip processes including ore deposit formation

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

the northern margin of the capricorn orogen western australia an example of an early proterozoic collision zone abstract the early proterozoic 2200 1600 ma capricorn orogen is a major zone of deformation metamorphism and granite emplacement between the archaean yilgarn and pilbara cratons of northwest australia capricorn orogen structures are recognized along the southern margin of the pilbara craton deforming the archaean granite greenstone terrain of the sylvania inlier together with rocks of the hamersley ashburton and blair basins in the sylvania inlier deformation is characterized by large scale shear zones interpreted as nne directed thrusts in the hamersley basin orogenic deformation forms the ophthalmia fold belt and can be divided into two groups of structures in the southwest large scale dome and basin folds pre ashburton basin are present in the southeast folds and faults are part of a younger syn ashburton basin n directed foreland fold and thrust belt directly linked to deformation in the sylvania inlier the deformed ashburton basin and adjacent parts of the hamersley basin form the ashburton fold belt two periods of deformation are recognized early recumbent folding d1a post ashburton basin pre blair basin and later dextral wrench faulting and associated folding d2a syn or post blair basin capricorn orogen structures are interpreted as the result of an oblique continent continent collision between the pilbara and yilgarn cratons along the southern pilbara margin collision first occurred in the southeast and migrated northwest with the ashburton basin evolving as a foreland basin late stage dextral wrench faulting was the result of westward extrusion of material caught between the opposing craton margins

an assessment based on u_pb zircon data of rb_sr dating in the arunta inlier central australia abstract the chronology of the arunta inlier was originally based mostly on rb sr dating although some of the ages derived from that technique are now shown to be erroneous those which were constrained by structural observations and which relied only on whole rock and not mineral analyses have proven to be remarkably realistic ion microprobe data show that even conventional multigrain u pb zircon analysis is not a particularly appropriate dating technique in a region of this complexity three new u pb zircon ages and others previously derived from the same isotopic system date three of the main tectonic events that were imposed on the arunta inlier the widespread strangways orogeny of the northern and central provinces occurred at 1760 1750 ma the argilke event is not older than 1680 ma demonstrating that the southern province is the youngest in the inlier the dominantly thermal ormiston event is dated at 1140 ma

structural controls and timing of fault hosted manganese at woodie woodie east pilbara western australia abstract high grade fault hosted manganese deposits at the woodie woodie mine east pilbara are predominantly hydrothermal in origin with a late supergene overprint the dominant manganese minerals are pyrolusite braunite and cryptomelane the ore bodies are located on or near the unconformities between the neoarchean carawine dolomite and the paleoproterozoic pinjian chert breccia weathering product of carawine dolomite and sedimentary units of the overlying ca 1300 1100 ma manganese group stratabound manganese is typically located above or adjacent to steep fault hosted manganese the ore bodies range in size from 0 2 to 5 5 mt with an average of 0 5 mt historically over 35 mt of manganese has been mined at woodie woodie and current ore resources are 29 94 mt at 39 94 mn 6 96 fe resource and reserves statement june 2011 consolidated minerals pty ltd manganese mineralization at woodie woodie is related to northwest southeast directed extension and basin formation during the mesoproterozoic basin architecture is generally well preserved and major manganese occurrences are localised along growth faults which down throw the pinjian chert breccia into local extensional basins manganese ore bodies are typically located on steep 2nd and 3rd order structures that extend off the major growth faults mineralized structures display a dominant northeast trend reflecting the direction of maximum dilation during northwest southeast extension a paragenetic sequence is identified for the manganese ore at woodie woodie with early hydrothermal braunite pyrolusite cryptomelane todorokite hausmannite overprinted by late supergene oxides preliminary fluid inclusion studies in quartz crystals intergrown with pyrolusite and cryptomelane indicate that primary and pseudosecondary inclusions display a range of salinities from 1 to 18 eq wt nacl and trapping temperatures estimated to be from 220o to 290o at 1 kbar pressure a lead manganese oxide coronadite is common in manganese ores at woodie woodie and pb isotope studies of 40 lead rich ore samples from 16 pits indicate mineralization occurred within an age range of 955 1100 ma a mixed source is suggested for the lead but was predominantly basalts and or volcanogenic sedimentary units e g jeerinah formation of the ca 2700 ma fortescue group the typically high mn fe ratios and enrichment in elements such as pb as cu mo zn are consistent with a dominantly hydrothermal origin for the manganese at woodie woodie supergene manganese is distinguished from hypogene manganese by a marked enrichment in ree in the supergene manganese an early structural framework established during neoarchean rifting provides a major structural control on manganese ore distribution the woodie woodie mine corridor is located in a zone of oblique strike slip extension on major northwest trending transform faults and north trending oblique normal faults a major transform structure at the southern end of the woodie woodie mine corridor jewel southwest fault zone likely acted as a major fluid conduit for manganese bearing hydrothermal fluids and this would account for the concentration of significant manganese ore occurrences to the north and south of this structure

precambrian tectonic history of the west australian craton and adjacent orogens this review is a synthesis of the precambrian geology of the west aus tralian craton and its fringing orogens it describes the evidence that has recently been reinvestigated and reinterpreted to reveal a long dynamic history of repeated aggregation and dispersal of crustal fragments cratons are large composite geological units of continental crust that have survived intact for significant periods of geological time they are generally tabular bodies with great areal extent millions of square kilo meters and lithospheric thickness 200 400 km orogens are narrow steep zones of tectonic and metamorphic activity associated with the deposition of sediments and the intrusion of plutonic rocks they occur within or along the margins of continents and are generally a few hundred kilometers wide thousands of kilometers long and extend to the base of the litho sphere most orogens are initially associated with compressive tectonics crustal thickening and the transient formation of mountain belts cratons and orogens may survive for very long periods of time but as part of a thin crust on a dynamic mantle they are inherently mobile and travel as rafts for great distances around the surface of the earth they may be torn apart dispersed and reassembled with other continental fragments the boundaries of these crustal fragments once established remain zones of crustal weakness that may be reactivated as intra continental mobile belts or lines along which cratons are assembled and dismembered cf hoffman 1 988

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

the magellan pb deposit western australia a new category within the class of supergene non sulphide mineral systems abstract the magellan pb deposit is located in an outlier of the palaeoproterozoic earaheedy group overlying the southeast yerrida basin a feasibility study of the magellan prospect was completed in 2001 with at that time proven and probable ore reserves of 8 5 mt grading 7 12 pb the deposit is currently exploited from two open pits magellan and cano the lead orebodies are hosted in a silicified dolomitic collapse breccia and underlying altered and weathered sandstone and siltstone the host succession comprises from top to bottom a lateritic unit overlying a zone of silicified silcretized quartz clay breccia overlying saprolitic clay breccia and siltstone palaeoproterozoic earaheedy group and basin the footwall consists of black shales of the maraloou formation palaeoproterozoic yerrida basin magellan is a non sulphide mineral system with cerrusite and anglesite as the major ore minerals and plattnerite coronadite pyromorphite and plumbogummite as minor to negligible ore components the lack of sulphides and the sole presence of oxide minerals suggest that the ore was formed under physico chemical conditions conducive to the precipitation of pb carbonate and pb sulphate it is proposed that the magellan lead deposit represents the supergene modified residue from mississippi valley type mvt mineralisation hosted in the sweetwaters member of the yelma formation of the earaheedy group that underwent prolonged weathering which led to dissolution volume reduction and oxidation of the galena and sphalerite as well as leaching out of highly mobile zn leaving behind the pb carbonate and sulphate mineralisation the magellan mineral system likely represents a new category within the non sulphide class of ore deposits

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

geochronological constraints on orogenic events in the arunta inlier a review early workers subdivided the arunta inlier central australia into three major tectonic provinces classified the principal tectonostratigraphic units into three divisions and separated the tectonomagmatic history into five discrete events ranging in age from 1800 ma to 300 ma a review of the evidence for tectonic boundaries within the arunta inlier suggests that no major structural discontinuity exists between the northern and central tectonic provinces but that the redbank thrust zone is at least in part a province boundary the tectonostratigraphic division concept also requires revision as division 3 rocks of the northern and southern arunta cannot be time equivalents division 1 rocks grade into division 2 in the northern region and division 3 of the northern region may be equivalent to division 1 in the central region rocks originally assigned to divisions are better grouped into a larger number of lithological assemblages until better stratigraphic and isotopic correlations can be made compilation of rb sr and 40ar39ar age determinations obtained before 1984 indicate an almost complete age spectrum from 1800 ma to 1000 ma but age clusters exist at 1400 ma 1100 ma and 400 300 ma which have geological significance subdivision of older ages into discrete tectonic events was not justified from this data alone but more recent u pb isotopic analysis of zircons in rocks designated to particular structural metamorphic events has revealed a complex tectonic history in the 1880 1600 ma interval the northern and central provinces underwent major tectonism between 1780 1730 ma but much of the southern province was not deformed until 1600 ma the revised tectonic history nomenclature is proposed for the arunta inlier following deposition of a widespread turbiditic unit at or before 1880 ma possibly on thinned archaean crust the northern and central provinces underwent localized tectonism magmatism at 1880 ma yuendumu tectonic event and 1820 ma stafford tectonic event prior to the widespread strangways orogeny which is subdivided into an early phase at 1780 1770 ma and late phase at 1745 1730 ma it is not clear whether the strangways orogeny is a single arunta wide event or a series of separate short lived smaller scale events although the major deformation in all areas appears to have involved w to sw directed thrusting in the southern province the major events occurred at 1680 ma argilke tectonic event and 1600 ma chewings orogeny the latter involving n directed thrusting that was penecontemporaneous with post tectonic pegmatite intrusion in the northern province suggesting linkage of both regions at this stage the younger history of the inlier is characterised by several stages of uplift and isolated thermal magmatic events major mesoproterozoic crustal exhumation anmatjira uplift phase has been interpreted from widespread 1500 1400 ma ages including regional scale closure of 40ar 39ar systems in hornblende from mafic granulite outcrop scale rb sr total rock isotopic systems in mylonitized granitoids and sm nd garnet hornblende pairs in mylonitized amphibolites a 1150 ma thermal event in the southern part of the inlier teapot magmatic event is recorded by intrusion of granite pegmatites and the alkaline mordor igneous complex and by isotopic resetting of rb sr mineral systems dolerite dyke injection at 1050 ma reflects limited extensional tectonism that may have related to formation of the amadeus basin the second major uplift event was the alice springs orogeny at 400 300 ma an unusual intracratonic thick and thin skinned thrust event that involved limited retrograde amphibolite facies but extensive greenschist facies metamorphism and restricted pegmatite intrusion

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

the 1320 ma intracontinental wongawobbin basin pilbara western australia a far field response to albany fraser musgrave tectonics abstract the eel creek formation which crops out along the northeastern edge of the archean pilbara craton in western australia is a formerly undated siliciclastic succession with a preserved thickness of at least 500 m only a small portion of the basin is exposed at surface the bulk of it is buried beneath neoproterozoic and phanerozoic basins two tuff samples from near the base of the succession have shrimp u pb zircon ages of 1318 7 ma and 1310 8 ma which are interpreted to be igneous crystallization ages these depositional ages are indistinguishable from a shrimp u pb zircon date of 1317 11 ma previously obtained for a tuff about 80 km to the south southeast at ripon hills the three dates indicate that sedimentation and minor felsic volcanism at c 1320 ma extended over a minimum distance of 110 km along the eastern margin of the pilbara craton the succession at ripon hills has been interpreted as an outlier of the manganese group but current evidence is consistent with partial correlation between the c 1070 ma collier group and the manganese group therefore correlation of the succession at ripon hills with the c 1320 ma eel creek formation is more likely we propose that both sequences are components of the newly named wongawobbin basin an intracontinental basin that formed in response to far field stress associated with the albany fraser orogen of southeast western australia and the musgrave orogen of central australia the eel creek formation was sourced mainly from the pilbara craton but with a minor contribution from the archean gregory range inlier and the paleoproterozoic rudall province to the southeast