mechanical interactions between rigid particles in a deforming ductile matrix analogue experiments in simple shear flow abstract the mechanical interaction between two or more particles is investigated in newtonian simple shear flow the experimental models allow observation of both the particle rotation and the deformation pattern around the particles the finite and instantaneous strain patterns around rigid particles are strongly heterogeneous and asymmetric with high finite strain zones aligned to the direction of maximum finite stretch these correspond to local flow with low vorticity number heterogeneous strain patterns around rigid particles spread over a distance of 1 2 times the particle length and this distance increases with increasing bulk strain where rigid particles are more concentrated these patterns coalesce and the overall pattern is then strongly controlled by the particles and cannot be simply related to the external boundary conditions in rocks the characteristic asymmetric strain pattern around rigid isolated particles is a reliable shear criterion which becomes unreliable with high concentrations of rigid particles particle rotation is significantly disturbed when the distance between adjacent particles of equal size is shorter than their length that is only in very concentrated suspensions of rigid particles in a composite shape fabric the development of the sub fabric corresponding to the smaller minerals will be more disturbed

the motion of rigid ellipsoidal particles in slow flows abstract preferred orientations of fabric elements in tectonites are usually interpreted with reference to two continuum models namely those of march 1932 and jeffrey 1922 it is argued that the first of these is usually inappropriate if the fabric elements are rigid inhomogeneities embedded in a deformable matrix jeffrey s model is more applicable but until recently its use has been limited to problems involving axisymmetric particles and simple flow geometries in this paper jeffrey s equations have been solved numerically in order to investigate the behaviour of more general systems the motions of two particle shapes one a prolate spheroid the other a triaxial ellipsoid are considered in parallel for four specified flow geometries which involve pure or simple shear and combinations of both any departures from particle axisymmetry or from simple flow geometries have a significant effect on particle behaviour compared with that predicted by spheroid simple flow solutions

lessons from a joint interpretation of vibroseis wide angle and near vertical reflection data in the northeastern yilgarn western australia abstract a wide angle reflection seismic experiment was carried out in the eastern goldfields granite greenstone terrane of the archaean yilgarn craton during 2001 this was the first time in australia that wide angle data were collected using a vibrator source and with a high density of observations unlike other wide angle surveys carried out in other parts of the world our survey used both a smaller number of sweeps and shorter sweeps we recorded three sweeps each with its own frequency range at each vibration point the experiment demonstrated that the sum of three 12 s sweeps using 3 large vibrators provides enough energy to record signal at offsets up to up to 60 70 km a comparison of individual shot gathers from near vertical data and receiver gathers from wide angle data demonstrated higher reflectivity in near vertical data this may be due to differences in the frequency bands of the recording equipment the after stack section obtained from dense wide angle data is different from that obtained from conventional near vertical reflection data the conventional reflection section provides higher quality image of the crust compared to the wide angle section this could be explained by the low fold in wide angle data and differences in the acquisition and processing methodology the wide angle survey which was coincident with a regional vibroseis seismic reflection transect was focused on the leonora laverton region the survey was designed to supplement the deep seismic reflection studies with velocity information this also created an opportunity to compare velocity model derived from wide angle reflection seismic data with a structural image obtained from the deep common mid point seismic reflection data and thus refine our geological understanding of the area a high velocity body reaching a maximum thickness of 2 km was identified exclusively from the seismic velocity model derived from wide angle study this body is interpreted as mafic rocks within the archaean granite greenstone belt the joint interpretation also shows that structural boundaries do not always follow lithological boundaries in our study area the combination of wide angle reflection and near vertical reflection data has facilitated a more complete geological interpretation of the seismic data

geochemistry and nd isotope systematics of archaean granites of the eastern goldfields yilgarn craton australia implications for crustal growth processes abstract the archaean granites and granitic gneisses of the eastern goldfields in the yilgarn craton western australia can be divided into two major groups high ca and low ca and three minor groups high hfse high field strength elements mafic and syenitic the high ca group 68 77 sio 2 with high al 2 o 3 na 2 o and sr and low y shares many features with typical archaean tonalite trondhjemite suites but has higher k 2 o rb and th contents the low ca group 70 76 sio 2 differs from the high ca group in having lower al 2 o 3 cao and na 2 o but higher k 2 o rb th zr y la and ce contents granites of the high hfse mafic and syenitic groups form a minor component 10 20 of the eastern goldfields granites the siliceous 74 77 sio 2 high hfse granites are restricted to a narrow nnw trending zone and are characterised by high tio 2 total feo mgo y zr and ce but only moderate rb th and pb contents the a type syenites 50 68 sio 2 are distinguished by their high total alkalies and mainly occur along tectonic lineaments the mafic group 55 70 sio 2 is lithologically diverse and exhibits a wide range of k 2 o rb th la and ce contents granite emplacement occurred between 2 69 and 2 60 ga contemporaneous with or post dating greenstone formation nd values for the high ca mafic and syenitic groups are similar mostly 0 0 to 2 5 whereas those for the low ca group show a pronounced polarity from 4 5 in the west to 2 0 in the east nd depleted mantle model ages for the low ca granites range from 3 2 ga in the west to 2 75 ga in the east model ages for the high ca group 2 75 2 9 ga overlap with ages for inherited zircons from these granites the high ca granites appear to have been derived at high pressures by partial melting of a mafic to intermediate source subducted oceanic crust crustal underplate or thickened crust or remelting of an older tonalitic source derived by such a process if the high ca granites were largely crust derived then their extensive source rocks must have formed less than 250 ma prior to granite formation the low ca granites appear to be the products of crustal reworking probably from a tonalitic to granodioritic protolith that was progressively younger towards the east perhaps in the order of several hundred million years younger or involved an additional younger component the localisation of the crustally derived high hfse granites suggests either geochemical zonation of the crust or specific tectonic processes such as rifting the mafic granites and possibly the syenites imply a significant mantle contribution and new crustal growth although the extent is equivocal the crust of the eastern goldfields appears to have been generated by both lateral and vertical accretion over a significant period from or before 3 0 ga until the time of granite emplacement

strain rates from snowball garnet spiral inclusion trails in garnet porphyroblasts are likely to have formed due to simultaneous growth and rotation of the crystals during syn metamorphic deformation thus they contain information on the strain rate of the rock strain rates may be interpreted from such inclusion trails if two functions are known 1 the relationship between rotation rate and shear strain rate 2 the growth rate of the crystal we have investigated details of both functions using a garnetiferous mica schist from the eastern european alps as an example the rotation rate of garnet porphyroblasts was determined using finite element modelling of the geometrical arrangement of the crystals in the rock the growth rate of the porphyroblasts was determined by using the major and trace element distributions in garnet crystals thermodynamic pseudosections and information on the grain size distribution for the largest porphyroblast size fraction size l 12 mm we constrain a growth interval between 540 and 590 c during the prograde evolution of the rock assuming a reasonable heating rate and using the angular geometry of the spiral inclusion trails we are able to suggest that the mean strain rate during crystal growth was of the order of 6 6 10 14 s 1 these estimates are consistent with independent estimates for the strain rates during the evolution of this part of the alpine orogen

porphyroblast inclusion trail geometries in the grand canyon evidence for non rotation and rotation abstract porphyroblasts in paleoproterozoic supracrustal rocks of the grand canyon grew during a progressive deformation that involved shortening and heterogeneous development of ne striking subvertical foliation s2 that crenulates and transposes an earlier foliation s1 inclusion trails in syn s2 porphyroblast cores show a remarkably consistent nw strike across the regional transect suggesting a lack of appreciable porphyroblast rotation relative to the trace of the ne striking s2 foliation these apparently non rotated porphyroblast cores thus preserve a regional nw striking s1 orientation porphyroblast rims and younger porphyroblasts locally overgrow ne striking s2 indicating that porphyroblast growth and continued non rotation spanned s2 apparent non rotation of most porphyroblasts across the transect is interpreted to reflect a dominance of coaxial shortening in contrast single thin sections show domains of these non rotated garnets with sigmoidal inclusion trails adjacent to domains where the characteristic sigmoids are rotated by about 45 this documents local rotation of garnets relative to s2 during a heterogeneous late or post s2 reactivation of the foliation thus these types of studies should continue to look for both rotational and non rotational behaviors at all scales and continue to specify the frame of reference

simplified geostatistical analysis of earthquake induced ground response at the wildlife site california u s a almost all natural soils are highly variable and rarely homogeneous in this study the seismic response of the wildlife site imperial valley california u s a has been analysed to assess the e

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

constraints on archaean crustal composition and structure provided by deep seismic sounding in the yilgarn block abstract new seismic reflection data from the eastern goldfields and southern cross provinces coupled with results from earlier seismic refraction profiles recorded in the western southern cross province indicate that with the exception of the greenstone belts that occupy much of the surface of the eastern goldfields province the crust in the yilgarn block is composed predominantly of felsic material with only minor mafic material within the lowest part of the crust the greenstone belts themselves are shallow features and not deep rooted features as often proposed the transition from the crust to the mantle is sharp occurs over only a few kilometres and marks a significant change in composition and density the middle and lower crust along the section have no marked lateral change in reflection character between the greenstones terranes and the adjacent granite dominated terranes except that both the mid crustal and crust mantle boundaries have been bowed downwards by approximately 6 km under the greenstones the greenstone belts of the eastern goldfields province are 6 9 km thick they are superimposed on an otherwise uniform crust their base is planar and subhorizontal and appears to be block faulted in places the ida fault which defines the western boundary of the greenstone belts is planar dips to the east at 25 30 and can be traced to depths of approximately 25 km 8 s

the multiple sulfur isotope architecture of the golden mile and mount charlotte deposits western australia the golden mile and mount charlotte deposits in the kalgoorlie terrane western australia display three main mineralization styles fimiston comprised of interconnected shear zones associated with ankerite pyrite hematite magnetite gold telluride alteration oroya made up of breccia bodies with v muscovite ankerite pyrite pyrrhotite gold telluride alteration and mount charlotte which consists of vein arrays with symmetrical ankerite sericite albite pyrite pyrrhotite gold alteration pyrite is in equilibrium with gold in all three mineralization styles and has been selected as a proxy to record the sulfur source of the mineralizing fluids as well as the nature of the hydrothermal processes the 34s 33s and 36s analyses on pyrite grains from the different mineralization styles including oxidized and reduced sulfide oxide assemblages reveal 1 a large variation in 34s from 12 6 to 23 5 and 2 a previously unrecognized occurrence of anomalous 33s and 36s signatures from 1 0 to 1 1 and from 2 3 to 0 9 respectively it is argued that the mineralizing fluids that formed the golden mile and mount charlotte deposits record mixing among three components mantle sulfur oxidized seawater sulfur e g so4 and reduced elemental sulfur e g s8 petrographic evidence in conjunction with 33s and 36s data suggest that mif s was acquired during the deposition of shales and basalts present in the kalgoorlie terrane and later mixed with mantle derived sulfur during the mineralization events the negative 34s values that predominate in fimiston style mineralization are consistent with a prevalence of oxidized fluids during the ore forming process as reflected by the presence of hematite pyrite magnetite gold assemblages conversely the positive 34s values that dominate in the mt charlotte and oroya mineralization styles reflect a reducing environment as reflected by the presence of pyrite pyrrhotite gold assemblages

interpretation of porphyroblast inclusion trails limitations imposed by growth kinetics and strain rates porphyroblast inclusion trails provide important information about the tectonometamorphic evolution of a metamorphic rock however there remains considerable controversy over whether porphyroblasts rotate during bulk non coaxial deformation with reference to an area of the scandinavian caledonides and utilizing existing data from theoretical and experimental modelling this study demonstrates that both straight and s shaped inclusion trails are consistent with an interpretation in terms of syndeformational porphyroblast growth in a regime approximating to newtonian simple shear at crustal strain rates of 10 14 s 1 and porphyroblast growth times of 0 1 1 0 ma it is shown that a maximum of 5d 9d angular rotation would occur during growth at faster strain rates of 10 12 s 1 e g those in a shear zone porphyroblast angular rotations of 90d are shown to occur in 0 1 0 25 ma i e times comparable with or faster than porphyroblastesis in view of this s shaped inclusion trails are to be expected in porphyroblasts growing in active shear zones or other situations of high shear strain whereas straight inclusion trails can be interpreted as static overgrowth of an existing fabric or as syndeformational porphyroblastesis at low strain rates

geochemistry and tectonic setting of two contrasting archaean felsic volcanic associations in the eastern goldfields western australia abstract archaean felsic volcanic rocks from two areas in the eastern yilgarn craton of western australia comprise dacite and rhyolite with subordinate basalt and andesite one suite from one of the areas black flag group is dominated by subaqueous dacite lava lobes and their reworked products the other suite from the other area melita and jeedamya volcanics consists of abundant rhyolitic and rhyodacitic pyroclastic deposits with less abundant dacitic lava flows both suites are intercalated with volumetrically subordinate basic and intermediate volcanic rocks black flag group dacites and rhyolites have steep ree patterns la yb cn about 40 and no eu anomaly high sr and al2o3 low nb and y hence high sr y melita and jeedamya dacites and rhyolites have flatter ree patterns la yb cn between 2 and 9 negative eu anomalies eu eu 0 4 0 6 and higher zr nb y and lower sr hence lower sr y on chemical grounds mafic rocks in both areas are genetically unrelated to felsic volcanic rocks black flag group andesites dacites and rhyolites are probably unrelated by fractional crystallization but resulted from 22 28 partial melting of amphibolite leaving a residual mineralogy of amphibole plagioclase garnet ilmenite clinopyroxene alternatively andesites may have been derived by partial melting of a metasomatised mantle source jeedamya rhyodacite could have been produced by 35 vapour absent melting of tonalite leaving a residual mineralogy of plagioclase orthopyroxene amphibole ilmenite the source would have had a slightly lree enriched pattern with a positive eu anomaly residual garnet in the source of black flag group rocks requires melting at depths greater than 35 km which is below the base of the present tectonically thinned crust the most likely source is subducted oceanic crust with black flag group rocks erupted in a back arc basin melita and jeedamya felsic volcanic rocks resulted from melting of thicker continental crust adjacent to the back arc

albite porphyroblasts with sigmoidal inclusion trails and their kinematic implications an example from the taconic allochthon west central vermont microstructural analyses of albite porphyroblasts in phyllite of the taconic allochthon were conducted in order to determine the origin of the sigmoidal inclusion trails within the porphyroblasts and to evaluate if and when the porphyroblasts rotated during the deformation history three cleavages s2 s3 and s4 with similar strike are present in the phyllite the albite porphyroblasts are characterized by inclusion rich cores and inclusion free rims and the boundary between the cores and overgrowths is characterized by relatively straight and parallel zones of concentrated rutile the sigmoidal inclusion trails within the cores are inferred to be trapped microfolds the zones of concentrated rutile are interpreted to be truncation planes that formed during the development of s3 in contrast to the tight orientation distribution of s3 the truncation planes show a wide distribution pattern the mean orientations of s3 and the truncation planes also differ these orientation data indicate that the porphyroblasts have not only rotated with respect to s3 but also to the geographic reference frame in addition the growth of the porphyroblasts was influenced by differentiation associated with s3 crenulation cleavage formation the porphyroblasts grew preferentially within microlithon domains where chlorite a reactant mineral for the porphyroblasts is abundant

sigmoidal inclusion trails punctuated fabric development and interactions between metamorphism and deformation porphyroblast inclusion fabrics are consistent in style and geometry across three proterozoic metamorphic field gradients comprising two pluton related gradients in central arizona and one regional gradient in northern new mexico garnet crystals contain curved sigmoidal inclusion trails in low grade chlorite schists these trails can be correlated directly with matrix crenulations of an older schistosity s1 the garnet crystals preferentially grew in crenulation hinges but some late crenulations nucleated on existing garnet porphyroblasts at higher grade biotite staurolite and andalusite porphyroblasts occur in a homogeneous s2 foliation primarily defined by matrix biotite and ilmenite biotite porphyroblasts have straight to sigmoidal inclusion trails that also represent the weakly folded s1 schistosity staurolite and andalusite contain distinctive inclusion rich and inclusion poor domains that represent a relict s2 differentiated crenulation cleavage together the inclusion relationships document the progressive development of the s2 fabric through six stages garnet and biotite porphyroblasts contain stage 2 or 3 crenulations staurolite and andalusite generally contain stage 4 crenulations and the matrix typically contains a homogeneous stage 6 cleavage the similarity of inclusion relationships across spatially and temporally distinct metamorphic field gradients of widely differing scales suggests a fundamental link between metamorphism and deformation three end member relationships may be involved 1 tectonic linkages where similar p t time histories and similar bulk compositions combine to produce similar metamorphic and structural signatures 2 deformation controlled linkages where certain microstructures particularly crenulation hinges are favourable environments for the nucleation and or growth of porphyroblasts and 3 reaction controlled linkages where metamorphic reactions particularly dehydration reactions are associated with an increase in the rate of fabric development a general model is proposed in which 1 garnet and biotite porphyroblasts preferentially grow in stage 2 or 3 crenulation hinges and 2 chlorite consuming metamorphic reactions lead to pulses in the rate of fabric evolution the data suggest that fabric development and porphyroblast growth may have been quite rapid of the order of several hundreds of thousands of years in these rocks these microstructures and processes may be characteristic of low pressure first cycle metamorphic belts

an early thrust duplex in the kalgoorlie kambalda greenstone belt eastern goldfields province western australia abstract extensive regional mapping of the stratigraphic sequence throughout the kalgoorlie kambalda greenstone belt in western australia has outlined the geometry of early subhorizontal thrust faults these thrusts stacked and repeated the stratigraphy to form a major thrust duplex south of kambalda the roof thrust to the duplex becomes a major thrust flat to the north at kalgoorlie later transpressional deformation f2 upright folds d3 sinistral shear zones and folding has rotated and displaced the d1 thrusts both sub horizontal deformation and subsequent transpression indicate that compressional tectonics rather than vertical tectonics involving solid state granitoid diapirs were crucial in the development of this granite greenstone terrain

new insights into archean granite greenstone architecture through joint gravity and magnetic inversion archean tectonic evolution and metallogenic endowment in cratonic areas are intrinsically linked to lithological diversity and complex architectures unfortunately reliable models of the deep structure of such areas are scarce due to poor surface exposure and limited availability of drill holes and high resolution geophysical information by combining multiple geophysical data sets the strategy of cross gradient joint geophysical inversion permits improved subsurface imaging of geological heterogeneity and structure in this work we showcase the application of cross gradient joint inversion of gravity and magnetic data to characterize the heterogeneity of the leonora district in the eastern yilgarn craton western australia our results harmonize both geophysical data types into integrated images of the top 15 km of the crust and successfully predict observations made by a seismic experiment and surface geological mapping

fold mechanisms in the canton schist constraints on the contribution of flexural flow abstract fold mechanisms operating in the canton schist have been resolved using the geometric relationship between folds and spiral inclusion trail geometries of the four end member fold mechanisms tangential longitudinal strain folding and slip folding are unable to produce the observed inclusion trail and fold geometries but a combination of flexural flow and pure shear folding is consistent with the geometric constraints the maximum flexural flow component during each fold event was determined from the geometric data during f 3 and f 4 flexural flow produced 27 and 37 of measured limb rotation respectively which corresponds to a maximum of 24 limb rotation by flexural flow in each fold event to satisfy the geometric constraints the remainder of limb rotation must be a product of pure shear folding the maximum possible component of flexural flow folding during f 3 and f 4 increases with increased variation in vorticity between layers in the rock mass in the flexural flow pure shear model a maximum of 28 of inclusion trail curvature is produced by rotation of porphyroblasts relative to irrotational fold limbs with a minimum 72 curvature due to rotation of fold limbs relative to irrotational porphyroblasts all model solutions produce less than 8 syn folding porphyroblast rotation relative to geographic coordinates

tectono stratigraphy of late archaean greenstone terranes in the southern eastern goldfields western australia abstract late archaean greenstone terranes in the southern part of the eastern goldfields are regionally extensive faultbounded entities defined on the basis of small but distinct differences in stratigraphy and structure the greenstones comprise volcano sedimentary successions that were all deposited at the same time c 2720 2675 ma on sialic crust hence the terranes are interpreted to represent contemporaneous probably adjacent basins these basins were affected by the same history of granite plutonism and regional deformation c 2675 2620 ma early subhorizontal deformation is poorly understood but includes at least locally significant thrust stacking d1 with a south to north movement direction this was followed by regional east west extension affecting all supracrustal successions above a province wide detachment now lying at depths between 4 and 7 km this detachment may have evolved from the greenstone basement contact but only after extensive reworking clastic basins developed along or above major extensional faults but no volcanism is associated with this extension subsequent east west d2 shortening resulted in regional scale thrusting folding and associated late stage transcurrent fault movements the d2 event is contemporaneous with a major thermal event represented by voluminous granite emplacement c 2660 ma and associated peak regional metamorphism in the greenstone succession predominantly monzo granite derived from older sialic crust was emplaced throughout the period of basin formation and deformation early synvolcanic granite c 2719 2710 ma is a minor component late synvolcanic granite c 2685 2675 ma is widespread and syn d2 granite c 2660 ma is abundant there are a few small late tectonic intrusions c 2640 ma to 2600 ma the lateral lithostratigraphic persistence of the contemporaneous basins the syn d2 low pressure regional metamorphism and the province wide monzo granite magmatism suggest that the greenstone basins possibly developed in a tectonic setting similar to that of failed rifts above aborted spreading centres the basins closed in response to far field compressional stresses

late archaean felsic alkaline igneous rocks in the eastern goldfields yilgarn craton western australia a result of lower crustal delamination numerous felsic alkaline intrusions were emplaced in the granite greenstone terrain of the eastern goldfields yilgarn craton between c 2650 and 2630 ma intrusion coincided with the waning stages of voluminous regional granitic magmatism the alkaline rocks are localized along and adjacent to major crustal structures that separate lithostratigraphic greenstone terranes and are divided into four geographically and compositionally distinct suites viz the mount monger emu claypan and ninnis suites the rocks have features in common with a type granites including high total alkalis an anhydrous primary mineralogy an apparent anorogenic setting and enrichment in some hfse although they also have low concentrations of nb and y they show a range of features that together point to a crustal source e g the alkaline rocks are not associated with voluminous mafic magmatism they have high lile concentrations they carry zircon xenocrysts of similar age to whole rock sm nd model ages they show evidence for regional source heterogeneity suites have constant and distinct la y and nb y ratios and the rocks show many compositional similarities to the slightly older voluminous crust derived granites extreme enrichments in sr and ba in the mount monger suite however suggests that their source may have been metasomatized before or during melting intrusion of the alkaline rocks heralds a poorly recognized third tectonothermal event in the evolution of the eastern part of the yilgarn craton and was broadly synchronous with the intrusion of voluminous felsic fractionated granites crustal extension and widespread au mineralization the late archaean geology of the eastern goldfields shows many features in common with phanerozoic collisional belts thought to be profoundly influenced by processes of lithospheric delamination or convective thinning this newly recognized third tectonothermal event in the eastern goldfields may relate to the delamination or convective thinning of a dense garnet rich lower crust that resulted from extraction of earlier voluminous granite magma and it is possible that such processes have had a greater influence on late archaean crustal evolution than previously recognized

deep seismic reflection profiling in the archaean northeastern yilgarn craton western australia implications for crustal architecture and mineral potential abstract deep seismic reflection data across the archaean eastern goldfields province northeastern yilgarn craton western australia have provided information on its crustal architecture and on several of its highly mineralised belts the seismic reflection data allow interpretation of several prominent crustal scale features including an eastward thickening of the crust subdivision of the crust into three broad layers the presence of a prominent east dip to the majority of the reflections and the interpretation of three east dipping crustal penetrating shear zones these east dipping shear zones are major structures that subdivide the region into four terranes major orogenic gold deposits in the eastern goldfields province are spatially associated with these major structures the laverton tectonic zone for example is a highly mineralised corridor that contains several world class gold deposits plus many smaller deposits other non crustal penetrating structures within the area do not appear to be as well endowed metallogenically as the laverton structure the seismic reflection data have also imaged a series of low angle shear zones within and beneath the granite greenstone terranes where the low angle shear zones intersect the major crustal penetrating structures a wedge shaped geometry is formed this geometry forms a suitable fluid focusing wedge in which upward to subhorizontal moving fluids are focused and then distributed into the nearby complexly deformed greenstones

the wangkathaa orogeny an example of episodic regional d2 in the late archaean eastern goldfields province western australia abstract the eastern goldfields province egp is a late archaean orogenic belt located on the eastern margin of the yilgarn craton the egp is characterised by a prominent nnw trending tectonic grain developed largely during regional e w oriented shortening a simplistic sequence of largely progressive compressional deformation events d 1 to d 4 has been used by previous workers to explain the development of the egp regional d 2 was thought to be responsible for most of the finite strain and therefore a reliable marker event for correlating deformation histories across the region a re examination of the deformation history has shown that d 2 kalgoorlie orogen of weinberg et al precambrian res 120 2003 219 239 was not a single progressive event rather it was episodic and involved several stages of switching of the tectonic mode compression extension switching between 2665 and 2655 ma the sequence of events during d 2 was an early stage of e w shortening d 2a followed by extension with basin formation and normal fault movement d 2e and finally a second stage of e w compression d 2b we introduce this sequence of events as the wangkathaa orogeny more complex in tectonics and broader in geographical scope than the kalgoorlie orogen features of the wangkathaa orogeny are well illustrated by the geometry and geological relationships that occur in the kurnalpi terrane welcome well area and the kalgoorlie terrane ora banda kambalda and the boorara domains of the central and southern egp available geochronology indicates that this sequence of events was likely to have been diachronous across the entire egp and the eastern southern cross province of the yilgarn craton recognition of these separate episodic stages of e w oriented compression and extension is important in our understanding the tectonic evolution of the egp switching tectonic mode between compression and extension will change the state of mean stress in a rock mass e g from net dilation to net constriction and vice versa and is an effective method in transporting and trapping mineral rich fluids the paradox of the different timings established for d 2 across the province are explained by the wangkathaa orogeny especially if it were diachronous as different workers dated different phases of an episodic orogeny

spatial variability drained and undrained deviatoric load response geotechnical properties vary in space geostatistical parameters such as the mean the standard deviation and the correlation length are characteristic for each sediment and formation history the effects of spatial variability on the drained and undrained shear response of soils are investigated using numerical parametric studies where multiple realisations are tested for selected geostatistical parameters results show that the mean undrained shear strength decreases as spatial variability and correlation length increase spatial variability prompts strain localisation along neighbouring weak zones under both drained and undrained loading heterogeneous contractive media show internal homogenisation during drained deviatoric loading and the drained shear resistance evolves towards the critical state media with higher variability and longer correlation length require higher strain to attain internal homogenisation anisotropy in spatial correlation causes anisotropy in shear strength an intermediate d

three dimensional quantitative textural analysis of metamorphic rocks using high resolution computed x ray tomography part i methods and techniques macroscopic textures resulting from different atomic scale mechanisms for metamorphic crystallization display different degrees of order clustering intergrowth and relative isolation of porphyroblasts data on the sizes and locations of thousands of crystals in a three dimensional volume are required to identify reliably the mechanisms governing nucleation and growth of porphyroblasts from these textural features these data can now be acquired by means of high resolution computed x ray tomography numerical models that simulate porphyroblast formation governed by either interface controlled or diffusion controlled reaction mechanisms indicate that quantitative textural analysis can discriminate between these possibilities these numerical models also allow a comparison between textures predicted for different crystallization mechanisms and textures measured in natural samples from which inferences can be drawn concerning the relative importance of these mechanisms in nature an independent test of the validity of such inferences is possible for porphyroblasts such as garnet that may preserve prograde growth zoning and allow the examination of normalized radius rate relations

deformation partitioning and porphyroblast rotation in meta morphic rocks a radical reinterpretation abstract most porphyroblasts never rotate during ductile deformation provided they do not intern ally deform during subsequent events with the exception of relatively uncommon but spectacular examples of spiralling garnets instead the sur rounding foliation rotates and reactivates due to partitioning of the deformation around the porphyroblast consequently porphyroblasts commonly preserve the orientation of early foliations and stretching lineations within strain shadows or inclusion trails even where these structures have been rotated or obliterated in the matrix due to subsequent deformation these relationships can be readily used to help develop an understanding of the processes of foliation development and they demonstrate the prominent role of reactivation of old foliations during subse quent deformation they can also be used to determine the deformation history as porphyro blasts only rotate when the deformation cannot partition and involves progressive shearing with no combined bulk shortening component

effects of spatial variability on liquefaction induced settlement and lateral spreading abstractnonlinear dynamic numerical simulations of infinite slopes are used to examine the effects of spatial variability in penetration resistances on liquefaction induced settlement and lateral spreading for gently sloping ground and to develop guidance on selecting representative properties for uniform models simulation results for models having uniform properties uniform models are compared to results for models having spatially correlated gaussian random field property distributions stochastic models results are presented for sets of stochastic model realizations and a set of ground motions scaled to a range of peak ground accelerations computed responses and ground deformations settlements and lateral displacements for these uniform and stochastic models are used to identify representative properties as a percentile of the stochastic distributions for which the uniform models produce reasonable agreement with the median of the stochastic model responses the effects of the scales of fluct

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

crustal structure of a proterozoic craton boundary east albany fraser orogen western australia imaged with passive seismic and gravity anomaly data abstract we use passive seismic and gravity data to characterize the crustal structure and the crust mantle boundary of the east albany fraser orogen in western australia a proterozoic orogen that reworked the southern and southeastern margin of the archean yilgarn craton the crustal thickness pattern retrieved from receiver functions shows a belt of substantially thickened crust that follows the trend of the orogen but narrows to the southwest common conversion point profiles show a clear transition from a wide symmetric moho trough in the northeast to a one sided northwestern moho dip in the southwest where the moho appears to underthrust the craton towards its interior this change appears to coincide with the inferred trace of the ida fault a major terrane boundary within the yilgarn craton forward modelling of gravity anomaly data using the retrieved moho geometry as a geometric constraint shows that a conspicuous elongated gravity low on the northwestern side of the east albany fraser orogen is almost certainly caused by thickened archean crust to obtain a model that resembles the regional gravity pattern the following assumptions are necessary high density rocks occur in the upper crust of the fraser zone at depth inside the moho trough and in parts of the eastern nornalup zone east of the moho trough although our gravity models do not constrain at which crustal level these high density rocks occur active deep seismic surveys suggest that large extents of the east albany fraser orogen s lower crust include a mesoproterozoic magmatic underplate known as the gunnadorrah seismic province the simplest interpretation of the imaged crustal structure is that the gunnadorrah seismic province is underthrust beneath the yilgarn craton likely as a consequence of crustal shortening during accretion further east the imaged geometry overall appears to show a wedge of archean lower crust that was driven between the exhumed fraser zone and the gunnadorrah seismic province effectively splitting the paleo to mesoproterozoic crust of the east albany fraser orogen the vertical splitting of proterozoic crust by a cratonic crustal wedge comparable to what we image in this study may be a process that contributed to forming many craton margins around the world

spatial variation in liquefaction risk basic concepts and methods of random field theory useful for characterizing distributed disordered systems are applied to a soil deposit to evaluate the spatial extent of liquefaction under typical conditions the soil deposit modelled after a site located at the wildlife management area in california is represented by a three dimensional random properties field and is subjected to multiple realizations of a space time random field of earthquake ground motion patterned after the superstition hills event of 1987 based on monte carlo analysis using a deterministic one dimensional nonlinear finite element program spatial variability of liquefaction risk is assessed and techniques for improving estimates of liquefaction risk accounting for local spatial variation are investigated les concepts et m6thodes de base de la theorie de champ aleatoire servant caracteogonriser les systemes desordonnes repartis sont appliqueogons un d pot de sol pour evaluer 1 etendue spatiale de la liquefaction dans

porphyroblast nucleation growth and dissolution in regional metamorphic rocks as a function of deformation partitioning during foliation development in regional metamorphic rocks the partitioning of deformation into progressive shearing and progressive shortening components results in strain and strain rate gradients across the boundaries between the partitioned zones these generate dislocation density gradients and hence chemical potential gradients that drive dissolution and solution transfer phyllosilicates and graphite are well adapted to accommodating progressive shearing without necessarily building up large dislocation density gradients within a grain because of their uniquely layered crystal structure however most silicates and oxides cannot accommodate strain transitions within grains without associated dislocation density gradients and hence are susceptible to dissolution and solution transfer as a consequence zones of progressive shearing become zones of dissolution of most minerals and of concentration of phyllosilicates and graphite exceptions are mylonites where strain rates are commonly high enough for plastic deformation to dominate over diffusion rates and therefore over dissolution and solution transfer porphyroblastic minerals cannot nucleate and grow in zones of active progressive shearing as they would be dissolved by the effects of shearing strain on their boundaries however they can nucleate and grow in zones of progressive shortening and this is aided by the propensity for microfracturing in these zones which allows rapid access of fluids carrying the material presumed to be necessary for nucleation and growth zones of progessive shortening also have a number of characteristics that help to lower the activation energy barrier for nucleation this includes a build up of stored strain energy relative to zones of progressive shearing in which dissolution is occuring porphyroblast growth is generally syndeformational and previously accepted criteria for static growth are not valid when the role of deformation partitioning is taken into account porphyroblasts in a contact aureole do not grow statically either as microfracturing associated with emplacement allows access of fluids in a fashion that is similar to microfracturing in zones of progressive shortening the criteria used for porphyroblast timing can be readily accommodated in terms of deformation partitioning reactivation of deforming foliations and a general lack of rotation of porphyroblasts with the spectacular exception of genuinely spiralling garnet porphyroblasts

rotation of rigid elliptical cylinders in viscous simple shear flow analogue experiments we used experiments to investigate the behaviour of rigid elliptical cylinders embedded in a viscous fluid of finite thickness and for very small ratios s between shear zone width z and the shortest principal axis e2 of the ellipse that constitutes the base of the elliptical cylinder 3 5 s z e2 1 2 former theoretical and experimental work on the rotation of rigid inclusions immersed in a viscous matrix considered infinite shear zone thickness and or a very large ratio between shear zone thickness and inclusion size s 1 and concluded that inclusions rotate continuously and synthetically with the applied bulk simple shear flow except for inclusions with infinite axial ratio our results depart greatly from the analytical predictions experiments were carried out at constant shear zone thickness but variable s and degree of coupling at the inclusion matrix interface the results show that 1 confined inclusion rotation always deviates from theoretical predictions for infinite shear zone thickness even for synthetic rotation 2 the deviation in the angular velocity and or in the sense of rotation increases as s approaches 1 and antithetic rotation is possible from a position with ellipse longest axis parallel to the shear plane and 3 a slipping inclusion matrix interface greatly enhances deviation from theoretical predictions with antithetic rotations to as much as 20

an integrated multi scale 3d seismic model of the archaean yilgarn craton australia abstract the collection of a range of different seismic data types has greatly improved our understanding of the crustal architecture of australia s archaean yilgarn craton over the last few years these seismic data include broadband seismic studies seismic receiver functions wide angle recordings and mine scale to deep seismic reflection transects each data set provides information on the three dimensional 3d tectonic model of the yilgarn craton from the craton scale through to the mine scale this paper demonstrates that the integration and rationalisation of these different seismic data sets into a multi scale 3d geological seismic model that can be visualised at once in a single software package and incorporating all available data sets significantly enhances this understanding this enhanced understanding occurred because the integrated 3d model allowed easy and accurate comparison of one result against another and facilitated the integrated questioning and interrogation across scales and seismic method as a result there are feedback questions regarding understanding of the individual seismic data sets themselves as well as the yilgarn craton as a whole the methodology used including all the data sets in the model range had to allow for the wide range of data sets frequencies and seismic modes at the craton scale p wave s wave and surface wave variations constrained the 3d lithospheric velocity model revealing noticeable large scale velocity variations within and across the craton an interesting feature of the data easily identified in 3d is the presence of a fast s wave velocity anomaly 4 8 km s 1 within the upper mantle this velocity anomaly dips east and has a series of step down offsets that coincide approximately with province and terrane boundaries of the yilgarn craton one dimensional receiver function profiles show variations in their crustal velocity across the craton these crustal velocity variations are consistent with the larger scale geological subdivision of the craton and provide characteristic profiles for provinces and terranes the receiver function results and the deep seismic reflection data both agree on the depth to the moho and both indicate an increase in moho depth to the east the 2d seismic refraction results in the south west of the craton provide crustal thickness information an indication of middle and lower crustal compositions and information regarding the broad scale architectural framework at the province and terrane scale the deep seismic reflection data and the mine scale seismic data provide geometric constraints on crustal architecture in particular the orientation of the region s fault systems as well as variations in the thickness of the granite greenstone succession integration of the results from wide angle seismic refraction data coincident with the deep seismic reflection data provided additional constraints on likely upper crustal lithologies the integrated 3d seismic model implies the dominant geodynamic process involved the development of an orogenic belt that developed with a series of contractional folding and thrusting events separated by equally important extensional events the seismic reflection data in particular suggests that extensional movement on many shear zones was more common than previously thought the seismic reflection data suggest that the dominant mineral systems involved deeply sourced fluid flowing up crustal penetrating shear zones these deeply sourced fluids were further focussed into sites located above fault breached domal regions in the upper crust

kinematics of orogenic collapse in the variscan pyrenees deduced from microstructures in porphyroblastic rocks from the lys caillaouas massif in the pyrenees a phase of bulk vertical shortening d3 is indicated by a horizontal crenulation cleavage s3 which is developed in a pre existing schistosity s2 porphyroblasts of the lys caillaouas massif regionally preserve 1 1 the initial pre d3 orientation of s2 in the form of a vertical and e w trending preferred orientation of their inclusion trails 2 2 a vertical l2 stretching lineation defined by the elongation of the inclusions these data are consistent with n s compression and crustal thickening during d2 the angle between the inclusion trails s2 i and the external schistosity s2 e records the subsequent rotation of s2 from vertical to gently dipping orientations at higher crustal levels s2 remained steep suprastructure and little d3 deformation is evidenced with depth d3 deformation progressively intensifies and zones can be distinguished with opposite dip directions of s2 opposite apparent porphyroblast rotation senses and opposite f3 crenulation asymmetries these micro structures on a n s section through the lys caillaouas and the garonne dome massifs record a regional partitioning of bulk coaxial vertical shortening this deformation partitioning was probably controlled by a not exposed gneiss dome which behaved relatively rigid as compared to its metasedimentary cover in zones of non coaxial d3 deformation s2 was extended reactivated and forms the dominant schistosity where d3 was locally more coaxial s2 was shortened isoclinally crenulated and s3 forms the macroscopic cleavage the fact that d3 extension in the lys caillaouas massif immediately followed d2 compression and that similar extension is recorded in large parts of the variscan foldbelt suggests gravitational collapse of a thickened orogen this is consistent with the flattening type of d3 strain recognized in a number of pyrenean variscan massifs peak high t low p metamorphic conditions coincide with the onset of orogenic extension when very little crustal thinning could have been accomplished yet this suggests that heat induced strain softening within the orogen may have triggered its collapse

major crustal boundaries of australia and their significance in mineral systems targeting abstract for over 35 years deep seismic reflection profiles have been acquired routinely across australia to better understand the crustal architecture and geodynamic evolution of key geological provinces and basins major crustal scale breaks have been interpreted in some of the profiles and are often inferred to be relict sutures between different crustal blocks as well as sometimes being important conduits for mineralising fluids to reach the upper crust the widespread coverage of the seismic profiles now allows the construction of a new map of major crustal boundaries across australia which will better define the architecture of the crustal blocks in three dimensions it also enables a better understanding of how the australian continent was constructed from the mesoarchean through to the phanerozoic and how this evolution and these boundaries have controlled metallogenesis starting with the locations in 3d of the crustal breaks identified in the seismic profiles geological e g outcrop mapping drill hole geochronology isotope and geophysical e g gravity aeromagnetic magnetotelluric data are used to map the crustal boundaries in plan view away from the seismic profiles some of the boundaries mapped are subsurface boundaries and in many cases occur several kilometres below the surface hence they will not match directly with structures mapped at the surface for some of these boundaries a high level of confidence can be placed on the location whereas the location of other boundaries can only be considered to have medium or low confidence in other areas especially in regions covered by thick sedimentary successions the locations of some crustal boundaries are essentially unconstrained unless they have been imaged by a seismic profile from the mesoarchean to the phanerozoic the continent formed by the amalgamation of many smaller crustal blocks over a period of nearly 3 billion years the identification of crustal boundaries in australia and the construction of an australia wide gis dataset and map will help to constrain tectonic models and plate reconstructions for the geological evolution of australia and will provide constraints on the three dimensional architecture of australia deep crustal penetrating structures particularly major crustal boundaries are important conduits to transport mineralising fluids from the mantle and lower crust into the upper crust there are several greenfields regions across australia where deep crustal penetrating structures have been imaged in seismic sections and have potential as possible areas for future mineral systems exploration

contrasts in lithospheric structure within the australian craton insights from surface wave tomography abstract contrasts in the seismic structure of the lithosphere within and between elements of the australian craton are imaged using surface wave tomography new data from the wacraton and tigger experiments are integrated with re processed data from previous temporary deployments of broad band seismometers and permanent seismic stations the much improved path coverage in critical regions allows an interpretation of structures in the west of australia and a detailed comparison between different cratonic regions improvements to the waveform inversion procedure and a new multi scale tomographic method increase the reliability of the tomographic images in the shallowest part of the model 75 km a region of lowered velocity is imaged beneath central australia and confirmed by the delayed arrival times of body waves for short paths within the cratonic lithosphere there is clearly structure at scale lengths of a few hundred kilometres resolution tests indicate that path coverage within the continent is sufficient to reveal features of this size in the upper part of our model in western australia differences are seen beneath and within the archaean cratons at depths greater than 150 km faster velocities are imaged beneath the yilgarn craton than beneath the pilbara craton in the complex north australian craton a fast wavespeed anomaly continuing to at least 250 km is observed below parts of the craton suggesting the possibility of archaean lithosphere underlying areas of dominantly proterozoic surface geology

the rotation of garnet porphyroblasts around a single fold lukmanier pass central alps abstract the orientation of the straight internal foliation s i within large 5 mm garnet porphyroblasts has been measured relative to the orientation of the external foliation s e around a single antiform of 0 5 m wavelength which folds the dominant regional foliation the internal foliation is not constant in orientation but varies consistently both with position around the fold and with the porphyroblast ellipticity the dip of s i hinge dip taken as zero is consistently less than the dip of s e it increases with increasing dip of s e and with increasing ellipticity of the porphyroblasts s i effectively defines a fold with an opening angle greater than that in the external foliation the opening angle of this fold in s i decreases with increasing porphyroblast ellipticity the observed variation in the orientation of s i can be explained qualitatively by a flattened flexural flow model for fold development as could be expected for folding of a pre existing strongly anisotropic foliation the measurements clearly demonstrate that rotation of porphyroblasts relative to geographical co ordinates did occur during the development of this fold and that a model based on the classical theories of rotation of stiff inclusions in a weaker viscous matrix is most appropriate

geochemical systematics of basalts of the lower basalt unit 2 7 ga kambalda sequence yilgarn craton australia plume impingement at a rifted craton margin abstract the 2 7 ga kambalda sequence is a mafic and ultramafic volcanic sequence in the kalgoorlie terrane of the yilgarn craton western australia the sequence is divided into the lower basalt and upper basalt units separated by the komatiite lava flow units and was erupted onto an autochthonous volcanic sequence the 2 8 ga penneshaw formation the lower basalt unit includes six basalt suites or formations with well preserved pillows and vesicles at mid greenschist facies these are the woolyeenyer and burbanks formations and lunnon wongi scotia and missouri basalts basaltic flows of the woolyeenyer formation and lunnon and wongi basalts are compositionally restricted tholeiites with mg and ni contents of 56 52 110 ppm 57 51 190 160 ppm and 63 300 210 ppm respectively heavy ree hree are flat at 4 6 times chondrite with mild lree depletion at la sm n 0 77 0 94 and nb th ratios of 8 17 signifying that these basalts were erupted through the autochthon without crustal contamination as there is no correlation of nb th with la sm n the scotia basalt is distinctive in having a range of hree fractionation where gd yb n 1 1 1 4 indicative of melting over a range of depths from above to below the garnet stability field at 90 km basalts of the burbanks and penneshaw formations have major element compositions akin to the woolyeenyer formation but near flat ree at 9 11 times chondrite both formations have two populations the most primitive have greater th contents but nb th 8 in keeping with the hottest liquids having assimilated crust but the evolved flows being uncontaminated missouri basalts are all crustally contaminated collectively the uncontaminated woolyeenyer lunnon wongi scotia basalts and burbanks formation have end values spanning from 4 5 to 1 5 whereas end values for the contaminated missouri basalt and penneshaw formation span between 2 and 1 there is a weak trend of end with nb th collectively the results are interpreted in terms of a mantle plume impinging at the edge of rifted cratonic lithosphere mantle melting over a range of depths where hotter liquids assimilated crust but cooler liquids did not

inclusion trail patterns in porphyroblasts from the foothills terrane california a record of orogenesis or local strain heterogeneity a major problem with the current use of porphyroblast matrix microstructural relationships to infer orogenic histories such as multiple orthogonal orogenic events is that other evidence for these events is typically lacking for example a comparison of regional relationships and local structures formed in and adjacent to porphyroblasts present in contact aureoles in the foothills terrane sierra nevada california shows that 1 except in shear zones contact aureoles and local zones along lithological contacts the foothills terrane has a single regional cleavage although locally formed by multiple processes 2 the regional cleavage and locally developed porphyroblast inclusion trails have variable orientations and neither dataset supports the formation of dominantly subhorizontal and subvertical cleavages in this orogen 3 structural and metamorphic heterogeneities occur at all scales and can markedly affect inclusion trail patterns in porphyroblasts 4 complex porphyroblast growth features and internal inclusion trail patterns can form in porphyroblasts that grow during short time intervals in contact aureoles indicating that local complexity in porphyroblasts does not imply regional complexity because of these conclusions multiple datasets rather than data acquired only from porphyroblasts should be considered when attempting to understand the evolution of orogens furthermore using microstructural information preserved only in porphyroblasts to infer orogenic processes and plate motions is generally unjustified

stable positions of rigid objects in non coaxial flow a study in vorticity analysis abstract distortions of a homogeneous fabric which occur around rigid objects in rocks deformed by non coaxial ductile flow are useful to determine the sense of shear but also contain information on other aspects of the flow rigid objects in a non coaxial flow fall into two categories those which are permanently rotating and those which can reach stable positions at high finite strain the orientation of such immobilized objects with respect to eigenvectors of instantaneous flow is a function of the vorticity number of the flow the ratio of instantaneous stretches and the axial ratio of the object in naturally deformed rocks immobilized rigid objects may be recognized from the geometry of the surrounding fabric tails of recrystallized material around porphyroclasts in a mylonite rotate towards parallellism with the extensional eigenvector of the flow and the shape of tails reflects the rotational behaviour of the porphyroclast the axial ratio of immobilized porphyroclasts and their orientation with respect to the tails can theoretically be used to determine the vorticity number of the flow and deviations from isochoric plane strain in practice such an analysis is as yet difficult but a tentative example is given of the way in which the vorticity number can be calculated from a population of feldspar porphyroclasts in a quartzite mylonite from the french pyrenees

deformation around rigid particles the influence of slip at the particle matrix interface abstract theoretical and previous experimental studies of rigid particle structures have only considered the behaviour of rigid particles for which the interface between particle and matrix is coherent in natural rocks the boundary behaviour may cover the whole range from free slip to complete coherence examples where slip may be promoted include crack seal deformation during the development of pressure shadows core mantle structures where the mantle is composed of much weaker fine recrystallized material and crystallizing magmas or partially molten rocks where grain boundaries are lubricated by the melt phase analogue scale model experiments have been performed under pure shear and simple shear conditions to compare the particle rotation and the flow in the matrix for both slipping and non slipping particle matrix interfaces when slip does occur particles rotate faster in pure shear and slower in simple shear than for non slip leading to the more rapid development of a shape preferred orientation the preferred orientation tends to be bimodal in simple shear flow the flow and finite strain patterns in the matrix are also strongly influenced by slip at the interface and porphyroclast systems can develop geometries with ambiguous or contradictory shear senses dependent on the original particle orientation in multi particle experiments slip on the interfaces enhances strong strain localization in non linear viscous material to produce patterns very similar to natural s c fabrics

analogue modelling of the influence of shape and particle matrix interface lubrication on the rotational behaviour of rigid particles in simple shear abstract the rotational behaviour of a rigid particle embedded in a linear viscous matrix undergoing cylindrical simple shear couette flow was studied in 2d rock analogue experiments the influence of particle shape elliptical vs monoclinic aspect ratio and the nature of the matrix particle interface lubricated vs unlubricated was investigated both matrix pdms and lubricant liquid soap were linear viscous with a viscosity ratio of ca 10 4 without lubricant the rotational behaviour of all particles closely approximates the jeffery theory lubricated monoclinic particles with the long diagonal initially parallel to the shear direction show back rotation and approach a stable position lubricated elliptical particles initially parallel to the shear direction also show back rotation but only transiently stabilize weak planar zones in the matrix adjacent to unlubricated elliptical particles do not induce backward rotation in general for elliptical particles rotation rate as a function of orientation depends on axial ratio and thickness of the lubricant mantle for thick mantles initially 10 of the volume of the particle rotation rates are faster than jeffery theory for very thin mantles they are markedly slower compared with thick mantles particularly when the long axis is nearly parallel to the shear direction rotation rates are never strictly zero so true stabilization does not occur however for more elongate particles axial ratio 6 rotation rates are so slow that a very strong shape preferred orientation would develop in a lubricated elliptical particle population in experiments the volume of lubricant is constant and the thickness adjacent to the long side of the particle progressively decreases with increasing strain in natural examples of porphyroclast systems the weak mantle continually develops by recrystallization and or cataclasis of the rigid clast core and a steady state between production and thinning could be attained potentially leading to true stabilization for particles with a high axial ratio

a two stage model for the formation of the granite greenstone terrains of the kalgoorlie norseman area western australia abstract accurate dating of granites and greenstones from the kalgoorlie norseman area shows that there is considerable overlap in time between the formation of granites and greenstones however within any given area the oldest granites are always younger than the oldest greenstones it is suggested that the long lived 100 ma thermal anomaly in the uppermost asthenosphere that gave rise to the greenstones is also responsible for regional metamorphism and widespread crustal melting leading to the production of granites the time lag between greenstone and granite formation reflects the time taken to conduct heat from the mantle to the lower crust anatexis of the lower crust produces a layer of light granitic magma that may temporarily stop the ascent of basaltic magma where this happens the basaltic magma ponds at the base of the crust supplying additional heat and accelerating the melting process eventually the granitic melt layer becomes unstable and rises within the crust areas intruded by granite become topographic highs with topographic lows forming above areas where light melt has been withdrawn from the lower crust when the topographic highs protrude above sea level they are eroded to shed sediments into the topographic lows which contain the basaltic greenstones thus the change from a basalt dominated lower greenstone succession to a sediment and felsic volcanic dominated upper whitestone sequence seen in many granite greenstone terrains results from the intrusion of granitic magma into the upper crust the crust of the kalgoorlie norseman area formed in two distinct stages separated by a time break of up to 700 ma the first stage involved the formation of primitive crust probably above subduction zones this primitive crust was characterized by low rb sr and high sm nd ratios the second stage resulted from a major change in mantle convection that produced thermal upwellings in the mantle below the continents this led to the eruption of basaltic magmas and to metamorphism and anatexis of the lower crust to produce granitic magmas melting reset the rb sr sm nd and u pb systems giving the impression that the second event which occurred at 2 7 ga was a major crust forming event it was in fact a crustal reworking process although some basalt was added to the crust at this time although the two stage history of the kalgoorlie norseman area is clearly seen in the lead isotopes and in zircons it is not readily discernible from the rb sr and sm nd systematics due to mantle like ratios of those elements in the primitive crust

structure and emplacement history of a multiple center cone sheet bearing ring complex the zarza intrusive complex baja california mexico the cretaceous zarza intrusive complex located in the peninsular ranges of baja california norte mexico is perhaps the bestpreserved multiple center cone sheet bearing ring complex documented in north america the 7 km 2 elliptical complex hosts three nested non concentric intrusive centers that are successively younger to the south the northern and central centers show the same evolutionary sequence of 1 intrusion of concentric gabbroic cone sheets 2 intrusion of massive core gabbros and 3 development of subvertical ductile ring faults ring fault kinematics indicate that both centers moved down relative to the surrounding country rocks suggesting collapse into an underlying magma chamber the southern center is composed of approximately equal proportions of gabbro and tonalite and lacks cone sheets aluminumin hornblende barometry on the tonalite indicates a maximum emplacement depth of 2 3 0 6 kbar the zarza intrusive complex is surrounded by a ductile deformation aureole and bedding is inward dipping and inward younging around the entire complex excellent preservation of the intrusive history allowed us to evaluate the origin of the aureole and the three most applicable models are 1 collapse of the complex into its underlying magma chamber 2 sinking of the complex and its chamber after solidification and 3 formation of the aureole prior to emplacement of the complex the preserved structural and intrusive relationships provide information on the dynamic evolution of subvolcanic magma chambers and suggest that the complex may have been overlain by a caldera

a review of crust upper mantle structure in the precambrian areas of australia and implications for precambrian crustal evolution the western two thirds of the australian continent are underlain by precambrian rocks seismically this region is characterised by negative teleseismic travel time residuals indicating a thick cold tectosphere despite extensive platform cover and phanerozoic crustal reworking in a few intracratonic sedimentary basins the precambrian crust can be classified broadly into archaean and proterozoic cratons and proterozoic mobile belts the archaean cratons have a two layered crust 25 35 km thick with observed velocities in the lowermost crust in the range 6 8 7 2 km s 1 the moho is a distinct feature with a velocity contrast of 1 0 km s 1 vertical reflection probes in the southern yilgarn block yielded record sections that have numerous laterally discontinuous but distinct reflections especially in the lower crustal layer that are especially concentrated around the boundary between the two crustal layers and the moho the seismic reflections and velocities are consistent with a predominantly felsic crust with mafic lenses constituting 20 35 of the lowermost crust and with the metamorphic grade ranging from granulite in the upper to middle crust to garnet granulite and even eclogite at the base of the crust the proterozoic mobile belts and cratons a have multi layered crust 45 50 km thick velocities below 25 km depth are almost always 7 0 km s 1 and reach 7 4 7 6 km s 1 in the lowermost crust velocities such as these are characteristic of gabbroic basaltic underplate the velocity contrast is 1 0 km s 1 at the moho which is less distinct than in archaean terranes record sections from vertical reflection probes show a highly reflective crust with no correlation between seismic layers in the refraction models and the distribution of vertical reflections the contrasting character of the crust in archaean and proterozoic provinces favours a tectonic model for the evolution of precambrian crust in which predominantly felsic archaean protocrust was tectonically reworked and underplated to produce proterozoic crust the simple two layered protocrust became more complicated in the process the introduction of vast amounts of underplate especially near the crust mantle boundary thickened the crust and destroyed the character of the moho it overprinted the reflection character of the crust so that the bands of reflections now do not correlate with the boundaries between the crustal layers the velocities in the lower crust are high because of the underplate

3d effects in seismic liquefaction of stochastically variable soil deposits the natural variability of soil properties within geologically distinct and uniform layers has been proven to greatly affect soil behaviour and to induce significant variability in the predicted response previous studies concluded that small scale heterogeneity greatly affects the liquefaction potential of saturated soil deposits and provided geotechnical design guidelines to account for the effects of various characteristics of spatial variability those studies were based on two dimensional analyses of soil liquefaction in a vertical plane assuming plane strain behaviour therefore the correlation distance of soil variability in a direction normal to the plane of analysis was implicitly taken as infinite i e no variability in the third direction in this study a monte carlo simulation approach involving generation of sample functions of non gaussian multivariate multidimensional random fields and non linear finite element analyses is used to investigate the effects of soil heterogeneity on the

elastic anisotropy and pore space geometry of schlieren granite direct 3 d measurements at high confining pressure combined with microfabric analysis pore space geometry of granitic rocks and its evolution with depth are key factors in large scale seismics or in projects of enhanced geothermal systems or of deep hazardous waste repositories in this study we studied macroscopically anisotropic schlieren bearing granite by experimental p wave velocity v p measurements on spherical sample in 132 directions at seven different confining pressures in the range 0 1 400 mpa in order to discriminate the phenomena affecting the rock elastic properties we analysed the orientation of microcracks and of grain boundaries and we measured the anisotropy of magnetic susceptibility of the rock three sets of microcracks were defined with two of them linked to the massif exfoliation process and one to cooling contraction of the massif during pressurization the measured mean v p and v p anisotropy degree at ambient pressure and at highest confinement 400 mpa yielded 3 3 km s 1 and 24 per cent and 6 2 km s 1 and 3 per cent respectively the associated v p anisotropy pattern was transversely isotropic and governed by the schlieren with a minimum v p direction perpendicular to them and a girdle of high v p directions parallel to them the highest change in v p was observed between 0 1 and 10 mpa suggesting a significant closure of porosity below depths of 500 m change of the v p anisotropy pattern to orthorhombic together with increase of mean v p and v p anisotropy degree during depressurization was attributed to inelastic response of one of the sets of microcracks to the loading unloading cycle

crustal structure of granite greenstone terranes in the eastern goldfields yilgarn craton as revealed by seismic reflection profiling abstract a deep crustal seismic reflection profile across granite greenstones of the eastern goldfields in the archaean yilgarn craton has revealed new constraints on upper crustal geometries the ida fault which forms the western boundary of the eastern goldfields is a 30 east dipping normal fault that can be traced to a depth of about 25 km a mid crustal boundary is displaced with a throw of some 5 km across this fault in a broad region below the ida fault the crust mantle boundary moho is gently warped from a depth of c 33 km in the west to a depth of c 38 km to the east greenstones of the eastern goldfields are underlain by a regional detachment outlined by prominent reflectors at depths between 4 and 7 km open anticlines of the greenstone succession are truncated against this basal detachment or against gently dipping reflectors that can be correlated with terrane and domain boundary faults identified during regional mapping these truncations are not associated with changes in thickness of the successions these geometries suggest several stages of large scale movement possibly including out of section north south movements unresolved by the east west seismic reflection line reflectors representing boundary faults mostly sole out into the basal detachment however the west dipping bardoc shear zone is continuous across the basal detachment and may have been reactivated as a conjugate fault to the late stage ida fault granite plutons are imaged as steep sided and flat bottomed opaque regions locally underlain by continuous reflectors indicating greenstone stratigraphy these geometries in combinations with the map observations suggest that the plutons were emplaced as elongate ovoid sheets presumably fed through fractures

experimental observations on the effect of interface slip on rotation and stabilisation of rigid particles in simple shear and a comparison with natural mylonites for axial ratios r not vert similar3 porphyroclasts from three mylonites all show a very strong spo with the long axis of the best fit ellipse at an antithetic angle of 5 10 to the shear direction this is more consistent with a stable end orientation than with the transient fabrics predicted by theory for elliptical rigid particles in simple shear the cause of this divergence is investigated in a series of high simple shear strain 15 analogue experiments performed in a ring shear machine couette flow using a linear viscous matrix pdms the rotational behaviour of elongate r not vert similar5 rigid particles with elliptical and rhomboidal shapes comparable with the natural examples is modelled for both coherent and slipping particle matrix interfaces interface slip causes a dramatic reduction in the rotation rate of the elliptical particle compared with theory when the long axis is close to the shear direction but not stabilisation interface slip does result in stabilisation of the rhomboidal particle with the long diagonal oriented at a small antithetic angle to the shear direction for monoclinic particles mirror image shapes referred to here as types 1 and 2 show different rotational behaviour for the type 1 particle with a shape comparable to porphyroclast systems and mica fish the long side rotates asymptotically into parallelism with the shear direction natural examples of type 1 particles such as hornblende and olivine porphyroclasts measured from the finero mylonites southern alps show a very strong preferred orientation for r not vert similar3 with the long side parallel or at a small 5 antithetic angle to the mylonitic foliation for type 2 particles the short side stabilises close to the shear direction or at a small synthetic angle as also observed for sillimanite porphyroclasts from the mont mary mylonites western alps in this natural case stabilisation of the short sides is against an extensional crenulation cleavage rather than the mylonitic foliation the analogue experiments establish that interface slip is one mechanism for stabilisation of elongate rhomboidal particles in natural examples decoupling from the matrix may be affected by extensional crenulation cleavage or c planes in s c fabrics

a sensitive vorticity gauge using rotated porphyroblasts and its application to rocks adjacent to the alpine fault new zealand variable aspect ratio porphyroblasts deformed in non coaxial flow and internally containing rotated relicts of an external foliation can be used to characterise plane strain flow regimes the distribution obtained by plotting the orientation of the long axis of such grains classified by aspect ratio against the orientation of the internal foliation is potentially a sensitive gauge of both the bulk shear strain as previously suggested and kinematic vorticity number we illustrate the method using rotated biotite porphyroblasts in the alpine schist a sequence of mid crustal rocks that have been ramped to the surface along the alpine fault a major transpressional plate boundary results indicate that at distances greater than or equal to similar to1 km from the fault the rocks have undergone a combination of irrotational fattening and dextral oblique normal sense shear with a bulk shear strain of similar to0 6 and kinematic vorticity number of similar to0 2 the vorticity analysis is compatible with estimates of strongly oblate bulk strain of similar to 75 maximum shortening dextral reverse transpressional flow characterises higher strain s tectonite mylonite within similar to1 km of the alpine fault these relationships provide insight into the kinematics of flow and distribution of strain in the hangingwall of the alpine fault and place constraints on numerical mechanical models for the exhumation of these mid crustal rocks c 2001 elsevier science ltd all rights reserved

mechanism of emplacement of the cannibal creek granite with special reference to timing and deformation history of the aureole abstract the ovoid cannibal creek granite consists of a minor phase emplaced during the regional d 3 deformation and a major phase emplaced during the regional d 4 deformation it possesses an intense contact parallel foliation on its margin and in the adjacent porphyroblastic schist that formed through partitioning of the shearing component of deformation against the crystallized pluton margin during synchronous e w d 4 shortening during this process a pre existing shallow s 3 foliation was updomed around the pluton and re used reactivated by d 4 shear with associated dissolution of quartz resulting in the formation of an ovoid closed foliation around the pluton thus the granite is located within a domal shaped approximately n s trending pluton scale f 3 4 antiform that formed synchronous with emplacement three successive stages of porphyroblast growth record the history of processes operating during progressive emplacement and the structures that developed space problems were solved through upward movement of the rocks above the granite due to movement on the s 4 cleavage as well as on pre existing subvertical bedding and cleavages and by reactivation of steep d 2 faults

deep crustal structure in the southwestern yilgarn craton western australia abstract the archaean rocks of the yilgarn craton comprise the largest geological entity in western australia and one of the largest areas of archaean crust anywhere in the world however poor outcrop has prevented a thorough understanding of the structure of the crust in the region a subject of particular interest being the relationship between high grade metamorphic rocks in the west and lower grade granitoid greenstone terrains further east interpretation of previously unpublished seismic refraction data combined with the re interpretation of published data allows crustal velocity structure in the southwest of the craton to be resolved overall the structure is similar to shield areas elsewhere in the world the data defining a two layered crust with an average thickness of about 35 km however significant lateral variations in velocity structure are also observed and these coincide with a terrane boundary previously postulated on the basis of geological observations and seismic reflection data the terrane boundary dips to the east extends through the entire crust and is notable for an area of anomalously high seismic velocity in the lower crust two possible interpretations of the high velocity zone are proposed firstly it is due to the presence of mafic to ultramafic intrusions secondly and the preferred interpretation the high velocity zone is a fault bounded mega sliver which may be a suspect terrane in its own right perhaps with oceanic affinities the results of the seismic experiment strongly support tectonic models for yilgarn craton based on terrane tectonics the possibility that the terrane boundary is being reactivated by contemporary stresses also provides a plausible explanation for the local intra plate seismicity

crustal signature of late archaean tectonic episodes in the yilgarn craton western australia evidence from deep seismic sounding abstract deformation in the greenstone supracrustal rocks of the eastern goldfields province of the archaean yilgarn craton in western australia is delaminated from the underlying basement along a regional detachment surface presently at 3 7 km depth this might suggest that the history of crustal deformation cannot be inferred with any certainty from that of the greenstones however seismic images of the crust below the greenstones show structures that can be interpreted in terms of a series of tectonic events similar to those within the greenstones the upper crust below and to the west of the greenstones is largely unreflective with interpreted west dipping reverse faults the middle crust is reflective with reflector geometry implying thickening by west directed thrust stacking and the lower crust has a fabric indicative of ductile deformation these reflection fabrics imply crustal shortening probably during the late archaean regional d2 ene wsw shortening event they were subsequently overprinted and disrupted by structures consistent with regional nnw sse strike slip d3 faulting and probably younger more localised d4 faulting the seismic images of the crust therefore show that the crust suffered tectonic events in which both the order and direction of deformation are similar to those of the greenstones this is evidence that the whole crust deformed when the greenstones deformed however the scale and style of deformation vary with depth through the crust and include thrusting and probably folding in the upper crust thrust stacking in the middle crust and ductile deformation in the lower crust the length scale wavelength of structures in the middle and lower crust is greater than that in the greenstones

porphyroblast rotation eppur si muove in a number of recent papers the theory has been postulated that porphyroblasts as a rule do not rotate with respect to geographical coordinates and can be used to determine the original orientation of older foliations complex inclusion patterns in spiral garnets have even been used to advocate a new model of orogenesis involving several alternating phases of horizontal shortening and extension critical assessment of the assumptions and data used to support the theory of irrotational porphyroblasts reveals numerous flaws millipede structures used as proof for flow partitioning can also form by other flow geometries evidence quoted to support irrotational behaviour of porphyroblasts is unsound porphyrobl asts do occur in sets with a preferred orientation of the internal foliation trace but these cannot be shown to represent original orientations microstructures which resemble truncation planes in spiral garnets are used as evidence that these structures developed by several phases of deformation and as proof for periodic extension and horizontal shortening in orogenesis they can however also be explained by intermittent growth of a rotating porphyroblast during a single phase of deformation finally porphyroblast sets in which orientation is a function of aspect ratio indicate that porphyroblast rotation with respect to kinematic axes does occur in at least some situations

determining finite longitudinal strains from oppositely concave microfolds in and around porphyroblasts a new quantitative method abstract this paper describes a precise new method for determining finite longitudinal strains in porphyroblastic metamorphic rocks which makes use of oppositely concave microfolds ocms formed by heterogeneous strain of the matrix around porphyroblasts the initial spacing between two foliation surfaces is measured inside a porphyroblast and compared to the spacing between the same two surfaces in the matrix which results in a measure of extension e experienced by the rock during and or after porphyroblast nucleation a natural example is provided by the well known millipede plagioclase porphyroblasts from the robertson river metamorphics in queensland australia twenty four measurements were made from 22 serial thin sections cut parallel to both the x z and x y planes of finite strain giving an average extension of 1 72 parallel to the x direction of finite strain the least squares best fit line to a plot of initial length vs change in length gives an r 2 value of 0 998 a minimum estimate of maximum shortening negative e was also made by measuring the total lengths of s 1 folia that had been crenulated during ocm formation giving a value of 0 54 which falls short of the 0 63 expected for constant volume plane strain deformation because the ocm method is particularly suited to metapelites results may provide new insight into mechanisms of folding and crenulation cleavage development pressure temperature time deformation histories mass transport during deformation and metamorphism and kinematic studies of porphyroblast behavior rotation vs non rotation during ductile deformation

garnet porphyroblast timing and behaviour during fold evolution implications from a 3 d geometric analysis of a hand sample scale fold in a schist detailed 3 d analysis of inclusion trails in garnet porphyroblasts and matrix foliations preserved around a hand sample scale tight upright fold has revealed a complex deformation history the fold dominated by interlayered quartz mica schist and quartz rich veins preserves a crenulation cleavage that has a synthetic bulk shear sense to that of the macroscopic fold and transects the axis in mica rich layers garnet porphyroblasts with asymmetric inclusion trails occur on both limbs of the fold and display two stages of growth shown by textural discontinuities garnet porphyroblast cores and rims pre date the macroscopic fold and preserve successive foliation inflection intersection axes fias which have the same trend but opposing plunges on each limb of the fold and trend nne ssw and ne sw respectively the fias are oblique to the main fold which plunges gently to the wsw inclusion trail surfaces in the cores of idioblastic porphyroblasts within mica rich layers define an apparent fold with an axis oblique to the macroscopic fold axis by 32 whereas equivalent surfaces in tabular garnet adjacent to quartz rich layers define a tighter apparent fold with an axis oblique to the main fold axis by 17 this potentially could be explained by garnet porphyroblasts that grew over a pre existing gentle fold and did not rotate during fold formation but is more easily explained by rotation of the porphyroblasts during folding tabular porphyroblasts adjacent to quartz rich layers rotated more relative to the fold axis than those within mica rich layers due to less effective deformation partitioning around the porphyroblasts and through quartz rich layers this work highlights the importance of 3 d geometry and relative timing relationships in studies of inclusion trails in porphyroblasts and microstructures in the matrix

porphyroblast rotation during crenulation cleavage development an example from the aureole of the mooselookmeguntic pluton maine usa in the low pressure high temperature metamorphic rocks of western maine usa staurolite porphyroblasts grew at c 400 ma very late during the regional orogenesis these porphyroblasts which preserve straight inclusion trails with small thin section scale variation in pitch were subsequently involved in the strain and metamorphic aureole of the c 370 ma mooselookmeguntic pluton the aureole shows a progressive fabric intensity gradient from effectively zero emplacement related deformation at the outer edge of the aureole 2900 m map distance from the pluton margin to the development of a pervasive emplacement related foliation adjacent to the pluton the development of this pervasive foliation spanned all stages of crenulation cleavage development which are preserved at different distances from the pluton the spread of inclusion trail pitches in the staurolite porphyroblasts as measured in two dimensional 2 d thin sections increases nonlinearly from 16 to 75 with increasing strain in the aureole these data provide clear evidence for rotation of the staurolite porphyroblasts relative to one another and to the developing crenulation cleavage the data spread is qualitatively modelled for both pure and simple shear and both solutions match the data reasonably well the spread of inclusion trail orientations 40 75 in the moderately to highly strained rocks is similar to the spread reported in several previous studies we consider it likely that the sample scale spread in these previous studies is also the result of porphyroblast rotation relative to one another however the average inclusion trail orientation for a single sample may in at least some instances reflect the original orientation of the overgrown foliation

granite greenstone crust formation on the archaean earth a consequence of two superimposed processes abstract new u pb zircon age data reveal that volcanism in the greenstones of the eastern part of the yilgarn craton of western australia was coeval with that in the abitibi subprovince of the superior craton of canada and that komatiites in the eastern goldfields and abitibi terranes were erupted synchronously at 2705 ma however major granitoid intrusion and compression episodes in the eastern yilgarn craton post date those in the southern superior craton by at least 15 ma intrusion of late tectonic syenites movement on major shear zones metamorphism and deposition of post tectonic clastic sequences also occurred 25 40 ma later in the eastern yilgarn craton than in the southern superior craton indicating that these cratons occupied different tectonic settings between 2720 and 2620 ma these comparisons and the synchronous eruption of ultramafic magmas in the southern superior pilbara and kaapvaal cratons at 2715 ma provide evidence of global scale magmatic eruption events during the late archaean these considerations indicate that two superimposed processes global scale catastrophic convective overturn of the earth s mantle and plate tectonic processes were in operation during formation of granite greenstone crust in the late archaean