formation of ripples in erodible channels formation of ripples and dunes in erodible channels is analyzed by using the hydrodynamic model developed by kobayashi and madsen this issue applying the continuity equation of sediment the propagation velocity of the wavy bed is expressed in terms of the net fluxes of bed load along the wavy bed and suspended sediment out of the bed load transport layer the spatial variation of the bed load transport rate is derived by analyzing the balance of forces acting on a representative bed load particle on a sloping bed the net flux of the suspended sediment out of the bed load transport layer is obtained by solving the diffusion equation for the suspended sediment near the bed the stability analysis predicts that a perturbation that is either fairly short or long relative to the depth of flow will initially grow depending on whether the flow is hydraulically smooth or fully rough thus the model explains why ripples are not observed in experiments involving fairly coarse sediments since in these cases the flow is rough turbulent

large scale crustal structure of the northwestern yilgarn craton western australia evidence from nd isotopic data and zircon geochronology u pb zircon geochronology and nd isotope geochemistry have been used in the northwestern yilgarn craton region of western australia to map gneiss units of different ages and to provide a model for late archean crustal evolution despite the inherent difficulties of minimal exposure and variations in the appearance of units brought about by heterogeneous strain the 3300 3730 ma gneisses and intercalated metasedimentary units crop out in a 100 km wide tract bounded on both sides by areas containing 2920 3000 ma gneisses between 2750 and 2620 ma several generations of granitoids were emplaced throughout the region regardless of whether the granitoids intruded the 3300 3730 ma or 2920 3000 ma gneisses modeling of their initial nd isotopic compositions shows that they were most likely formed by partial melting of predominantly 2920 3000 ma gneisses only a minor input from early archean sources is indicated for granitoids cutting the 3300 3730 ma gneisses and intercalated metasediments some of the granitoids that intrude the 3300 3730 ma gneisses contain 2920 ma inherited zircons supporting the nd evidence that their source is dominated by 2920 3000 ma gneisses the 3300 3730 ma gneisses are interpreted as belonging to an allochthonous terrain emplaced over a younger terrain comprising the 2920 3000 ma gneisses subsequently partial melting concentrated in the underlying 2920 3000 ma terrain gave rise to the late archean granitoids

isotopic and geochemical studies of nodules in kimberlite have implications for the lower continental crust lower crustal xenoliths from the calcutteroo kimberlitic pipes in south australia show a surprisingly diverse range in nd and sr isotopic compositions and rare earth element ree abundances mafic granulite and garnet clinopyroxenite xenoliths have measured end 0 values between 6 1 and 7 9 both light l ree enrichments and depletions low rb sr ratios 0 005 0 040 and relatively high 87sr 86sr ratios of from 0 70675 to 0 70919 a felsic xenolith has compositions more typical of upper crustal rocks with end 0 21 4 lree enrichments rb sr 1 47 and 87sr 86sr 0 85987 an approximate correlation also exists between sm nd versus 143nd 144nd and rb sr versus 87sr 86sr indicating major intracrustal differentiation in the lower crust at 2 400 myr this produced extremely low rb sr ratios and both relative lree enrichments low sm nd and depletions high sm nd if these results are typical then they indicate that the lower crust has higher 87sr 86sr and more positive end 0 values than previous estimates1 5 this may require revision of total crustal compositions and crust mantle evolutionary models1 5

sand suspension storage advection and settling in surf and swash zones a time dependent cross shore sediment transport model in the surf and swash zones on beaches is developed to predict both beach accretion and erosion under the assumptions of alongshore uniformity and normally incident waves the model is based on the depth integrated sediment continuity equation which includes sediment suspension by turbulence generated by wave breaking and bottom friction sediment storage in the entire water column sediment advection by waves and wave induced return current and sediment settling on the movable bottom the hydrodynamic input required for this sediment transport model is predicted using the finite amplitude shallow water equations including bottom friction the developed model is compared with three large scale laboratory tests with accretional neutral little and erosional beach profile changes under regular waves the model predicts sediment suspension under the steep front of breaking waves and due to bottom friction in the swash zone the computed depth averaged sediment concentration does not respond to local sediment suspension instantaneously because of the sediment storage and advection the mean sediment concentration becomes large in comparison to the oscillatory concentration with the decrease of the normalized sediment fall velocity the net cross shore sediment transport rate is shown to be the small difference between the onshore transport rate due to the positively correlated oscillatory components of the suspended sediment volume per unit area and the horizontal sediment velocity and the offshore transport rate due to the product of the mean suspended sediment volume and the mean horizontal sediment velocity relatedly the net accretion or erosion rate of the movable bottom is determined by the small difference between the mean sediment settling rate and the mean suspension rate caused by wave breaking and bottom friction the present computation is limited to the initial beach profile change but the numerical model is capable of predicting the accretional erosional and neutral profile changes

two phase flow modeling of sediment motion in sheet flows above plane beds most models of sediment transport are based on the hypothesis of a weak interaction between the fluid and the sediment phase where the main flow is subjected to the mass and momentum conservation of the fluid phase with small corrections due to the presence of the sediments these models usually give a correct answer for conditions where the concentration of sediment is really low in the case of high sediment transport some models analyze the two subdomains separately the high and the low concentration and employ different constitutive equations in the present model there is a two phase description of the whole domain the closure of the turbulence and the interaction between the sediments and the fluid introduce approximations but results are consistent with experiments and previous models

mineral systems approach applied to gis based 2d prospectivity modelling of geological regions insights from western australia abstract gis based 2d prospectivity modelling of three greenfield geological regions of western australia namely the west arunta orogen west musgrave orogen and gascoyne province was implemented for a range of deposit types including orogenic and intrusion related gold volcanic sediment hosted base metal sulfides magmatic nickel copper and magmatic platinum group element sulfides iron oxide copper gold tin tungsten igneous and metamorphic related rare earth elements surficial uranium and unconformity related uranium conceptual mineral systems models were generated to identify the targeting criteria the inputs to the models were the spatial proxies derived from 1 100 000 to 1 500 000 scale public domain data the results showed similar prospectivity patterns for all of the targeted deposit types except sediment hosted uranium and surficial uranium deposit types once a favourable geodynamic architecture is established it can sustain different mineral systems and produce diverse deposit types depending on the nature of ligands in the source regions and physical chemical environment in the trap regions through repeated reactivation in the subsequent geological history a model is proposed to explain the formation of different deposit types at different stages of tectonic evolution of a province the implication for gis based 2d prospectivity modelling at the scale of geological region is that the prospectivity model may not be deposit type specific further prospectivity modelling should be carried out sequentially at progressively finer scales regional to district to camp scale using only the targeting criteria that are relevant at the specific scale to delineate targets for specific deposit types

garnet orthopyroxene plagioclase quartz barometry refinement and application to the english river subprovince and the minnesota river valley recent experimental theoretical and thermodynamic studies permit better calibration of two reactions for geobarometry grossular pyrope quartz anorthite enstatite grossular almandine quartz anorthite ferrosilite if both reactions are applied using the same thermodynamic data and activity models they should yield the same pressure for a given garnet pyroxene plagioclase quartz assemblage application to a variety of high grade terrains generally yielded excellent results however poor results have been obtained for high fe rocks which can be traced to errors in activity models for garnet and or pyroxene either a two site ideal mixing model for orthopyroxene cf wood and banno 1973 underestimates enstatite activity for high fe orthopyroxenes or the ganguly and saxena 1984 model overestimates pyrope activity in low mg garnets

early archaean gneisses from the yilgarn block western australia the yilgarn block is an ancient crustal block which extends over 650 000km2 in the south west of western australia and consists of high grade gneiss and granite greenstone terrains1 being one of the largest segments of archaean crust in the world it is important to studies of early crustal evolution we report here a geochronological study of banded gneisses near mount narryer in the north west of the yilgarn block which has given a rb sr whole rock isochron age of 3 348 43 myr with an initial 87sr 86sr ratio of 0 7037 0 0005 the data indicate that the rocks had a prior crustal residence time of 200 myr the validity of this early archaean age is supported by model sm nd ages of 3 510 myr and 3 630 myr for two of the samples taken together these ages represent the oldest evolutionary sequence so far identified in the yilgarn block and are comparable with old ages from other archaean cratons elsewhere in the world

measurements and modeling of swash induced pressure gradients in the surface layers of a sand beach field measurements of swash induced hydraulic pressure gradients in the surface layers of a sand beach are presented and compared to a one dimensional diffusion model the model provides a description of flow through a porous quasi saturated sediment and is driven by the time varying swash depth on the beach surface the field measurements broadly show four different types of pressure propagation behavior which appear dependent on cross shore position in the swash zone the hydraulic gradients within the surface layers of the beach are typically found to be much greater than those likely to be generated by tidally induced groundwater flow in these instances the diffusion model generally provides a good description of the data however very large hydraulic gradients are frequently observed just below the beach surface and these cannot be adequately described by the diffusion model a mechanism is proposed through which these large hydraulic gradients could be generated

sediment laden flow in open channels from two phase flow viewpoint most existing analytical and mathematical models for sediment laden flows are based on the governing equations for single phase flows and are valid only for low sediment concentration situations this paper presents an analysis on the basis of the fundamental equations for fluid solid two phase flows of the velocity and sediment concentration profiles in open channel flows a new diffusion equation is established for suspended sediment concentration from a rigorous derivation of the water sediment mixture s normal velocity in the sense of mass flux conservation the differences between this new equation and schmidt s as well as hunt s are shown to be attributable to the different approximations of sediment velocity previous formulations for velocity and sediment concentration distributions are special cases of the present model for low sediment concentration flows the developed model is extensively tested against available measurements and satisfactory or fairly good agreement is obtained

two phase model for sand transport in sheet flow regime 1 we introduce a two phase model for sand transport in sheet flow regime this model uses a collisional theory and a k fluid turbulence closure to respectively model the sediment and fluid phase stresses the sediment stress closure adopts a balance equation of sediment particle fluctuation energy based on kinetic theory that incorporates two way interactions between fluid and sediment phases the fluid turbulence closure also considers the two way interaction between fluid turbulence and sand particles model data comparisons for the sheet layer for oscillatory flows in a u tube and for open channel flows demonstrate the model s predictive skill for steady open channel flows the fluid phase velocity follows closely the law of wall i e the log profile in which the von karman constant is reduced and the equivalent roughness is increased compared to the clear fluid flow conditions the model also provides information in the near bed region where the transition from the solid like to the fluid like behavior of sediment particles is resolved and both the bed load layer thickness and bed load transport rate can be evaluated for unsteady flows this model can predict time evolutions for sediment transport throughout the water column

single phase fluid modelling of sheet flow toward the development of numerical mobile bed as a first step to develop numerical mobile bed as a promising tool for the study of sheet flow problem a computational scheme based on a single phase fluid model has been constructed by formulating the vertical transport of mass and momentum within the sheet flow layer the numerical results have shown the satisfactory agreements with the experimental results in velocity profile sediment transport rate and others further the difference in the period of oscillation was found to have appreciable influence on the temporal evolution of the sheet flow thickness indicating the importance of unsteadiness in the sheet flow dynamics

reconnaissance dating of events recorded in the southern part of the capricorn orogen abstract zircon geochronology confirms the errabiddy shear zone as a major structural boundary separating two distinct geological terranes within the southern part of the palaeoproterozoic capricorn orogen of western australia rocks on the south side of the errabiddy shear zone represent parts of the archaean yilgarn craton that were variably reworked during the c 2 0 ga glenburgh and c 1 8 ga capricorn orogenies rocks on the north side represent an exotic terrane the glenburgh terrane comprising c 2500 ma and possibly older gneisses which evidently record tectonothermal activity c 2390 ma and which together with quartzitic metasedimentary units deposited after c 2270 ma collided with the yilgarn craton during the glenburgh orogeny regional deformation high grade metamorphism and voluminous felsic plutonism occurred throughout the complex in association with both the glenburgh and capricorn orogenies

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

the nature of proterozoic reworking of early archaean gneisses mukalo creek area southern gascoyne province western australia abstract the gascoyne province a key segment of the early proterozoic capricorn orogen which separates the archaean pilbara and yilgarn cratons of western australia may be divided into northern central and southern zones the southern zone comprises predominantly archaean granulite facies quartzo feldspathic gneisses and passes southwards into the western gneiss terrain of the yilgarn block this area was part of the lower crust of a stabilized continental landmass at the end of the archaean development of the capricorn orogen 2 ga ago resulted in discontinuous deformation of the northern part of this landmass deformation was concentrated in ductile shear zones leaving blocks of relatively undeformed gneiss between them the shear zones trend between ene wsw and ese wnw and dip to the south at 50 60 strong down dip stretching lineations and asymmetric feldspar porphyroclasts indicate that the shear zones are reverse faults however metamorphic assemblages in early proterozoic dolerite dykes which post date the shear zones show that the area was still in the lower crust following the earliest proterozoic deformation isothermal uplift of the southern gascoyne province northern yilgarn block by 10 km or more occurred 1 7 1 5 ga ago and was accompanied by granitoid intrusion deformation within e w trending shear zones continued after uplift and was accompanied by patchy greenschist facies retrogression of both static and dynamic style on the local scale the effects of early proterozoic deformation on the early archaean gneisses are generally confined to shear zones and their immediate surroundings they comprise 1 realignment of gneissic trends from n s to e w 2 development of quartz ribbon mylonites by elongation of quartz grains into lenses and ribbons and reduction of feldspar grainsize by crystal plastic processes 3 growth of porphyroblastic and corona garnet in felsic and mafic gneisses the later proterozoic deformation occurred at lower temperatures and resulted in 1 further realignment of gneissic trends from northerly to easterly 2 reduction of quartz grainsize by crystal plastic processes and reduction of feldspar grainsize largely by brittle fracture 3 greenschist facies retrogression that the earliest deformation in the southern gascoyne province resulted in crustal shortening and was followed by significant uplift and granitoid intrusion indicates that proterozoic reworking of this area resulted from regional n s compression this favours development of the capricorn orogen in a collision zone between the pilbara and yilgarn cratons rather than in an ensialic mobile zone

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

the narryer gneiss complex of the yilgarn block western australia a segment of archaean lower crust uplifted during proterozoic orogeny the narryer gneiss complex of the yilgarn block is a key segment of the western australian precambrian shield it is a regional granulite facies terrain comprised of predominantly quartzo feldspathic gneisses derived from granitic intrusions c 3 6 3 4 ga old granulite facies metamorphism occurred c 3 3 ga ago and conditions of 750 850 c and 7 10 kbar are estimated for the mukalo creek area mca near errabiddy in the north the p t path of the mca has been derived from metamorphic assemblages in younger rocks that intruded the gneisses during at least three subsequent events and this path is supported by reaction coronas in the older gneisses there is no evidence for uplift immediately following peak metamorphism of the mca and a period of isobaric cooling is inferred from the pressures recorded in younger rocks pressures and temperatures estimated from metadolerites which intruded the older gneisses during granite greenstone tectonism at about 2 6 ga and during early proterozoic thrusting show that the errabiddy area remained in the lower crust although it was probably reheated during the younger events isothermal uplift to upper crustal levels occurred at c 1 6 ga ago and was followed by further deformation and patchy retrogression of high grade assemblages the effects of younger deformation cooling and reheating can be discerned in the older gneisses but as there has been no pervasive deformation or rehydration the minerals and microstructures formed during early archaean granulite facies metamorphism for the most part are retained the mca remained in the lower crust for about 1700 ma following peak metamorphism and some event unrelated to the original metamorphism was required to exhume it uplift occurred during development of the capricorn orogen when some 30 35 km were added to the crust beneath the errabiddy area the recognition of early proterozoic thrusting plus crustal thickening suggests that the capricorn orogen is a belt of regional compression which resulted from convergence of the yilgarn and pilbara cratons

structural metamorphic evolution of the palaeoproterozoic bryah and padbury groups during the capricorn orogeny western australia abstract volcano sedimentary successions of the bryah and padbury groups were deposited and deformed along the northern margin of archaean yilgarn craton western australia during the ca 2 0 1 8 ga capricorn orogeny this orogeny is interpreted to record convergence and collision of the yilgarn craton with the pilbara craton to the north the bryah group with its extensive mafic and ultramafic volcanic rocks represents a short lived proto oceanic backarc basin whereas the sedimentary padbury group records the filling in of a retro arc foreland basin the two groups were deformed as a single package and are now everywhere in faulted contact with older palaeoproterozoic rocks or underlying archaean granite greenstone four events are recognized in a progressive compressional deformation regime during d1 subhorizontal high strain shear zones and tectonic interleaving developed between the volcanosedimentary succession and reworked archaean crustal fragments that were underthrust or underplated during initial basin closure movement directions were mainly north to south d2 n s shortening resulted in upright e w folds dominated by two regional basement cored anticlines which are interpreted as fault bend folds above a crustal scale frontal thrust ramp uplifted deeper crustal rocks are now represented by zones of higher grade metamorphic assemblages in the core of these anticlines d3 folds are upright n s striking and restricted to a zone depression between the two basement cored anticlines or domes d2 and d3 folds are largely mutually exclusive with little or no evidence for overprinting and are regarded as contemporaneous the d3 structures are interpreted to have formed above lateral ramps in the crustal scale thrust fault during continued n s shortening d4 is a minor event of nne ssw compression and did not influence the regional geometry this deformation history records the closure and deformation of marginal back arc and foreland basins

fluid and sediment interaction over a plane bed a mathematical model is developed for the fluid and sediment interaction in an erodible channel the model is based on the conservation of mass and momentum for the fluid and sediment the interaction between the fluid and sediment as well as the interaction of sediment particles moving in the vicinity of the bed is described in the model an analysis is performed to derive the vertical distributions of the fluid velocity and sediment concentration over a plane bed in a wide open channel the analysis yields the friction factor due to the combined effects of grain roughness and sediment movement as well as the rate of sediment transport the developed model agrees with existing data for plane beds the predicted rate of transport of coarse sediment agrees with the meyer peter and mullen formula however detailed measurements of the fluid velocity and sediment concentration over a plane bed are required for a rigorous verification of the developed model

late archaean crustal extension sedimentary basin formation flood basalt volcanism and continental rifting the nullagine and mount jope supersequences western australia abstract the mount bruce megasequence set formerly the mount bruce supergroup is a succession of volcanic and sedimentary rocks that was deposited on the pilbara craton of western australia in the late archaean to early proterozoic its history can be described and explained in terms of modern style sequence stratigraphy and of phanerozoic style plate tectonics the megasequence set comprises the chichester range megasequence that was deposited on a rifted to divergent continental margin and the overlying hamersley range megasequence that was deposited on a convergent continental margin the chichester range megasequence comprises in order of superposition the nullagine and mount jope supersequences and the marra mamba supersequence package the nullagine and mount jope supersequences are each the rock record of one phase of a protracted two phase late archaean 2770 2700 ma continental break up the nullagine supersequence consists of the mount roe sequence which comprises mostly subaerial basalt and the overlying hardey sequence package which comprises mostly terrigenous sedimentary rocks that were deposited in extensional sedimentary basins the mount jope supersequence consists of in order of superposition the kylena sequence which comprises mostly basalt the tumbiana sequence which comprises mostly tuff and tuffaceous rocks and the maddina sequence package which comprises mostly basalt the nullagine supersequence was deposited during an episode of wnw ese directed crustal extension that possibly led to the development of a rift to the west of the present pilbara craton the mount jope supersequence was deposited during the subsequent development of a wnw ese trending rift the position of which approximates the present southern craton margin regional scale uplift was associated with the development of both supersequences particularly with the nullagine supersequence basement strike slip faults were reactivated as dip slip structures during crustal extension and controlled the locations of some hardey sequence package extensional sedimentary basins nullagine supersequence and mount jope supersequence rifting led to a divergent continental margin bordering an ocean along the south and probably the far west of the craton post rift thermal subsidence was accompanied by the accumulation of mudrock carbonate sedimentary rock and iron formation of the marra mamba supersequence package in a shelf setting the implications of these interpretations are that at 2800 ma the pilbara craton was significantly larger than at present and that it had a sufficiently thick subcontinental lithosphere that divided it in a manner analogous to the break up of phanerozoic continents the nullagine and mount jope supersequences contain three stacked flood basalt successions which were erupted over a time period of between of 55 and 80 m y stacked flood basalt successions covering such a long time period are not known in the phanerozoic and are tangible evidence of a hotter late archaean mantle

grenvillian aged orogenesis in the palaeoproterozoic gascoyne complex western australia 1030 950 ma reworking of the proterozoic capricorn orogen in situ shrimp u pb geochronology of monazite and xenotime in pelitic schists from the central gascoyne complex western australia shows that greenschist to amphibolite facies metamorphism occurred between c 1030 and c 990 ma monazite from an undeformed rare element pegmatite from the same belt gives a 207pb 206pb age of c 950 ma suggesting that peak metamorphism and deformation was followed by pegmatite intrusion and coeval granite magmatism metamorphism in the central gascoyne complex was previously interpreted as barrovian largely based on the identification of kyanite in peak metamorphic assemblages and has been attributed to intense crustal shortening and substantial tectonic thickening during palaeoproterozoic continent continent collision however the stable al2sio5 polymorph has been identified in this study as andalusite rather than kyanite and the prograde assemblages of staurolite garnet andalusite biotite muscovite quartz indicate temperatures of 500 550 c and pressures of 3 4 kbar these data show that the palaeoproterozoic gascoyne complex underwent an episode of grenvillian aged intracontinental reworking concentrated in a nw se striking corridor during the edmundian orogeny until now the edmundian orogeny was thought to have involved only reactivation of structures in the gascoyne complex along with deformation and very low to low grade metamorphism of mesoproterozoic cover rocks some time between 1070 and 755 ma however we suggest that it involved regional amphibolite facies metamorphism and deformation granite magmatism and pegmatite intrusion between c 1030 and c 950 ma therefore the capricorn orogen experienced a major phase of tectonic reworking c 600 myr later than previously recognized our results emphasize the importance of in situ geochronology integrated with petrological studies in order to link the metamorphic history of a terrane with causally related tectonic events

a new paleoproterozoic tectonic history of the eastern capricorn orogen western australia revealed by u pb zircon dating of micro tuffs abstract the earaheedy basin is one of several paleoproterozoic siliciclastic basins in the eastern part of the capricorn orogen in western australia in the absence of an adequate chronostratigraphic framework multiple conflicting models have been proposed for the tectonic history of the basin we present in situ shrimp u pb zircon dates of 1971 11 ma 1954 5 ma and 1949 10 ma from three thin tuff horizons micro tuffs in the yelma formation at the base of the basin succession these micro tuffs are only slightly younger than the 1990 6 ma imbin porphyry which has been interpreted as a basement inlier our new dates combined with field mapping suggest that the imbin porphyry is a volcanic subvolcanic complex within the basin micro tuffs in the yelma formation are more than 50 m y older than c 1890 ma micro tuffs within the overlying frere formation deposition of the yelma formation was coeval with continent continent collision farther west in the orogen marked by the 2005 1950 ma glenburgh orogeny and the formation is possibly correlative with peripheral foreland deposits of the padbury group the frere formation was deposited in shallow marine conditions within an intracratonic basin about 60 m y after the glenburgh orogeny the frere formation is unconformably or disconformably overlain by the miningarra group the youngest unit of which is the mulgarra sandstone this sandstone was deposited after c 1865 ma and derived either from exposed frere formation or from a now buried source within the capricorn orogen that was uplifted by inception of the 1820 1770 ma capricorn orogeny therefore the earaheedy basin comprises at least three distinct unconformity bound successions deposited in contrasting tectonic settings