lateral variation of crustal structure and composition in the cathaysia block of south china and its geodynamic implications abstract in order to clarify lateral variations in the crustal structure and composition of the cathaysia block in south china which was affected by violent mesozoic and cenozoic tectono magmatic activities we studied the crustal thickness and the poisson s ratio in this region using the h stacking method of teleseismic receiver functions our results show that the poisson s ratio varies between 0 20 and 0 29 and the crustal thickness ranges from 26 to 34 km in the cathaysia block the crustal thickness and poisson s ratio show considerable variations across the lishui haifeng fault the southeast coast magmatic belt is characterized by poisson s ratios 0 25 and a crustal thickness of 28 33 km reflecting probably intermediate to mafic compositions of the crust the southwestern part of the cathaysia fold belt exhibits a crustal thickness of 27 30 km and poisson s ratios

the sholl shear zone west pilbara evidence for a domain boundary structure from integrated tectonostratigraphic analyses shrimp upb dating and isotopic and geochemical data of granitoids abstract the pilbara block provides a record of archaean continental growth involving the tectonic accretion of outboard island arcs and collisions with other continental scale fragments this record of continental growth is balanced by breakup and strike slip dismemberment of the continent new shrimp u pb in zircon ages and sm nd data provide evidence in the west pilbara which demonstrates that subduction related and tectonic accretion processes at the western margin of that ancestral continent between 3 15 2 78 ga were coeval with and genetically related to crustal scale tectonics and basin formation inboard of that margin the tectonic division of the west pilbara is defined by integrated tectonic analyses geochronology geochemistry and isotopic analyses geochronological studies clearly indicate that the western pilbara comparises two domains with different recorded geohistories whereas geochemistry and isotopic systematics reflect the changing tectonic regimes through time in combination these studies allow the development of a reconstruction of the relative positions of the domains through time on the western margin of the pilbara block the supracrustal rocks of the northern roebourne lithotectonic complex domain 6 in a pilbarawide scheme were formed in an island arc setting facing an ocean to the north west prior to 3260 ma the time of emplacement of voluminous granitoids into the complex in contrast the supracrustal rocks of the southern sholl belt pilbara domain 5 were formed in a back arc setting behind a north west facing arc between 3125 and 3112 ma with more or less synchronous granite emplacement at about 3115 ma the two domains were tectonically juxtaposed between 2991 and 2925 ma by the sholl shear zone a largely sinistral shear zone with subsequent volcanism in both domains to about 2925 ma the roebourne lithotectonic complex domain 6 is interpreted to be an allochthonous terrane which formed north east relative to its present position but indigenous to the pilbara block rather than an exotic terrane the east pilbara is interpreted to have acted as a cratonic hinterland during the convergent margin tectonics that affected the two west pilbara domains

syn amphibolite facies archaean lode gold mineralisation in the mt york district pilbara block western australia the archaean lode gold deposits in the mt york district pilbara block western australia are hosted in banded iron formation main hill breccia hill prospect of the ca 3 33 ga gorge creek group and in amphibolites zakanaka prospect of the ca 3 46 ga warrawoona group gold mineralisation at the main hill breccia hill prospect is associated with breccias comprising quartz clasts in a quartz pyrrhotite matrix and quartz amphibole veins with lollingite being the major host for gold minimum temperatures for gold mineralisation at the prospect are constrained as 455 c to 550 c by arsenopyrite thermometry gold mineralisation at the zakanaka prospect is spatially associated with quartzclinopyroxene calcite microcline calcic amphibole veins and biotite altered wallrock adjacent to the veins temperatures for vein emplacement are estimated as 480 c to 570 c using both plagioclase amphibole thermometry and mineral equilibria with respect to t and xco2 the timing of gold mineralisation relative to the peak of metamorphism is constrained by mineral textures and the relative temperatures of hydrothermal alteration and metamorphism gold mineralisation at both deposits was broadly synchronous with the peak of regional amphibolite facies metamorphism which reached temperatures of 520 c to 640 c based on amphibole plagioclase and garnet biotite thermometry in this respect the deposits are similar to other well documented syn amphibolite facies lode gold deposits from the archaean southern cross greenstone belt in the yilgarn block and represent the deeper section of a crustal continuum of lode gold deposits that includes mesothermal deposits such as those at kalgoorlie at higher crustal levels

receiver operating characteristics roc as validation tool for prospectivity models a magmatic ni cu case study from the central lapland greenstone belt northern finland abstract a prospectivity model for magmatic ni cu deposits was created by integrating spatially referenced geophysical and geochemical datasets based on a simple and practical exploration model the study area is the central lapland greenstone belt northern fennoscandian shield finland magmatic nickel deposits are related to rock types that are typically characterized by local magnetic and gravity anomalies these deposit types can also be a source of nickel copper and cobalt anomalies in the overlying glacial till cover this straightforward exploration criterion was translated into a fuzzy logic prospectivity model the model validation is an essential step in justifying the validity of the prospectivity model this was accomplished by using receiver operating characteristics roc technique we used the known ni cu occurrences and deposits as true positive cases and other deposit type locations or random points as true negative cases in the validation process it appears that the roc technique provides a robust model validation and optimization technique providing that suitable validation data exists

the age and origin of younger granitic plutons of the shaw batholith in the archaean pilbara block western australia the whole rock pb pb method has been used to date four of the younger mainly adamellite late tectonic plutonic phases within the ca 3 5 ga shaw batholith of the archaean east pilbara block three suites give ages within error of 2966 ma porphyritic granites at 2948 50 ma leuco adamellites at 2943 46 ma and garden creek adamellite at 3007 48 ma the post tectonic cooglegong adamellite gives an age of 2847 34 ma the sm nd model isotopic systematics of all four suites indicate derivation from crust ranging between ca 3200 and 3600 ma in age the sources for these four younger plutonic phases were heterogeneous and although exhibiting some isotopic characteristics of the older 3 5 3 3 ga calc alkali plutonic suites were more depleted in the lil elements rb u and th in addition the garden creek adamellite and the cooglegong adamellite lack the very fractionated and hree depleted ree patterns characteristic of both the older calc alkali plutonic rocks and the porphyritic granites and leuco adamellites the crust underlying the shaw batholith at ca 2950 ma must have been both markedly heterogeneous and variably depleted a conclusion consistent with the complex tectonic and plutonic evolution of this region

tensile and compressive growth structures relationships between sedimentation deformation and granite intrusion in the archaean coppin gap greenstone belt eastern pilbara western australia abstract the coppin gap greenstone belt is composed of an east west striking asymmetric synclinorium between the muccan and mount edgar batholiths along the contact with the muccan batholith the vertical to overturned northern limb is intensely sheared folded and tectonically reduced the southern limb is relatively undisturbed and irregularly intruded by the mount edgar batholith progressive unconformities and sedimentary infilling of growth structures in the gorge creek group record the deformation history the unconformities constrain which of the now steeply dipping shear zones have to be rotated with their cover sequence before they can be interpreted kinematically four mid archaean clastic systems have been recognized the first and third are transgressive littoral quartzose and feldspathic arenites the second and fourth comprise conglomeratic and ferruginous alluvial fan related deposystems east verging thrust tectonics affected the belt after unconformable deposition of the first deposystem on the early archaean warrawoona group in the western extremity of the belt primary tectonic relief was filled with the second deposystem thrust folds were overprinted at right angles by folding sub parallel to the developing belt after truncation the belt was covered by the third and fourth systems in the eastern part of the belt relief created by belt parallel folds affecting the first deposystem was filled by conglomerate overlain by basalts a sequence also assigned to the whim creek group we relate systematic depocentre shifts as observed in the bamboo creek syncline to differential doming of the adjacent batholiths buried thrusts and shear zones may have caused km scale repetition of the underlying sequences the observed relationships place uncertainty on the validity of the existing stratigraphic correlations which now need geochronologic work to resolve part of the thrusting appears to have taken place by inversion on pre existing detachment shear zones in the underlying warrawoona basalts and ultramafic rocks the shear zones descend from a high stratigraphic level in the east towards deeper levels in the west the first motion has been west block down listric normal growth faulting in places accompanied by synsedimentary explosive intrusion of black chert veins mega brecciation and back tilt of fault blocks geometrically these early structures cannot be related to the geometry of batholith doming and are interpreted as the result of either regional tensile stress local caldera collapse or both mechanisms acting synchronously the mid archaean influx of siliciclastic sediments in the coppin gap belt coincides with this change from a tensile to a complex compressive deformation the latter caused by regional thrusting and interbatholith folding late deformation of the belt includes further steepening of the strata and eastward oblique dextral and 060 sinistral strike slip

archean diapirism recorded by vertical sheath folds in the core of the yalgoo dome yilgarn craton abstract in archean granite greenstone terrains both vertical and horizontal tectonic processes can generate the typical dome and keel structural geometries one of the classic archean domes interpreted to result from a horizontal tectonic regime is the yalgoo dome in the yilgarn craton of western australia in this contribution we reassess the structural evolution of the yalgoo dome by detailing the structures exposed in the migmatitic core the core contains multi scale domes and basins these structures were previously interpreted as the result of superposed folding our structural mapping shows that the dome and basin patterns result from vertical sheath folds developed in a single progressive deformation event d1 this first event most likely resulted from diapiric ascent of a buoyant partially molten tonalitic crust and was overprinted by two contractional episodes d2 d3 both reflecting bulk ew shortening the structural evolution proposed here points towards a shift from an early history of vertical tectonics dominated by diapirism to a regional regime dominated by horizontal tectonics

geology geochronology fluid inclusion and h o isotope geochemistry of the luoboling porphyry cu mo deposit zijinshan orefield fujian province china abstract the luoboling cu mo deposit in the zijinshan orefield fujian province southeastern china is a large porphyry deposit hosted by the sifang granodiorite and the luoboling granodiorite porphyry the largest cu mo orebody is saddle shaped with various types of hydrothermal veinlets intensive hydrothermal alteration in the deposit is characterized by outward zoning from potassic overprinted by phyllic alteration to phyllic and alunite dickite alteration based on the mineral assemblages and crosscutting relationships of veins the ore forming process can be divided into three stages namely an early stage k feldspar quartz magnetite molybdenite veins associated with potassic alteration a middle stage quartz molybdenite chalcopyrite pyrite veins in phyllic zone and a late stage quartz gypsum veins in the phyllic and alunite dickite alteration zones six molybdenite separates yield a re os isochron age 104 6 1 0 ma which is identical to the age of emplacement of the sifang and luoboling granodiorite porphyries three types of fluid inclusions fis were observed at the luoboling deposit 1 nacl h 2 o aqueous 2 daughter mineral bearing and 3 co 2 h 2 o fluid inclusions fis of the early and middle stages are predominantly vapor rich aqueous and daughter mineral bearing inclusions together with minor co 2 rich and liquid rich aqueous inclusions whereas the late stage minerals only contain liquid rich aqueous inclusions homogenization temperatures and salinities of fis trapped in the early stage minerals range from 420 to 540 c and 0 4 to 62 9 wt nacl equiv respectively fis of the middle stage yield homogenization temperatures of 340 to 480 c and salinities of 0 5 to 56 0 wt nacl equiv co 2 content and the oxygen fugacity indicated by daughter minerals of fis trapped in middle stage minerals are lower than those in the early stage the liquid rich aqueous inclusions of the late stage homogenize at temperatures of 140 to 280 c yielding salinities of 0 4 to 8 4 wt nacl equiv the minimum estimated pressures of the three stages are 30 70 mpa 10 40 mpa and 1 10 mpa respectively corresponding to minimum ore forming depths of 1 2 8 km fluids trapped in early middle and late stages yield d values of 67 to 54 54 to 70 and 62 and 18 o values of 5 4 to 6 7 2 8 to 4 2 and 2 1 respectively fluid boiling which resulted in the formation of stockworks and the precipitation of sulfides occurred in the early and middle stages the fluids subsequently evolved into a low temperature low salinity system in the late stage along with an input of meteoric water the luoboling porphyry cu mo system was developed in a transition from continental arc to back arc extension region which was related to the westward subduction of the paleo pacific plate beneath the huanan orogen

gold and silver metallogeny of the south china fold belt a consequence of multiple mineralizing events abstract the south china fold belt is part of the south china block that is interpreted to be the result of multiple tectonic and magmatic events that formed a collage of accreted proterozoic and phanerozoic terranes the jurassic to early cretaceous yanshanian period 180 90 ma a time of major tectono thermal events that affected much of eastern and southeastern china is of great metallogenic importance in the fold belt this period is linked to subduction of the pacific plate beneath the eurasian continent and is manifested by voluminous volcano plutonic activity of predominantly calc alkaline affinity the distribution of gold and silver deposits in the south china fold belt indicates the presence of two distinct metallogenic provinces a region of basement uplifts which are controlled by shear zones and form neoproterozoic inliers of metamorphosed iron rich rock types defines the first province in this province orogenic lodes and volcanic related epithermal deposits represent the more significant precious metal mineralization the second province is essentially confined to a belt of yanshanian felsic intermediate volcanic and subvolcanic rocks that extends along most of the southeastern china coast in an area known as the coastal volcanic belt deposits in the coastal volcanic belt are silver and or copper rich volcanic hosted and epithermal in character the precious metal metallogeny of the south china fold belt is interpreted to have developed in at least three stages one as a result of collision events during the caledonian orogeny ca 400 ma the second during the indosinian orogeny ca 200 ma and the third during or soon after the formation of the yanshanian magmatic belt yanshanian orogeny 180 90 ma the latter was responsible for a hydrothermal event that affected large sections of the belt and its proterozoic substrate this may have resulted in the redistribution and enrichment of precious metals from preexisting orogenic gold lodes in neoproterozoic basement rocks which are now exposed as windows in zones of tectonic uplift the yanshanian hydrothermal activity was particularly widespread in the coastal volcanic belt and resulted in the formation of both low and high sulfidation epithermal gold and silver and locally copper and other base metal mineralization it is suggested that the coastal volcanic belt has greater potential for world class epithermal and porphyry deposits than previously realised

data driven predictive mapping of gold prospectivity baguio district philippines application of random forests algorithm the random forests rf algorithm has recently become a fledgling method for data driven predictive mapping of mineral prospectivity and so it is instructive to further study its efficacy in this particular field this study carried out using baguio gold district philippines examines a the sensitivity of the rf algorithm to different sets of deposit and non deposit locations as training data and b the performance of rf modeling compared to established methods for data driven predictive mapping of mineral prospectivity we found that rf modeling with different training sets of deposit non deposit locations is stable and reproducible and it accurately captures the spatial relationships between the predictor variables and the training deposit non deposit locations for data driven predictive mapping of epithermal au prospectivity in the baguio district we found that a the success rates of rf modeling are superior to those of weights of evidence evidential belief and logistic regression modeling and b the prediction rate of rf modeling is superior to that of weights of evidence modeling but approximately equal to those of evidential belief and logistic regression modeling therefore the rf algorithm is potentially much more useful than existing methods that are currently used for data driven predictive mapping of mineral prospectivity however further testing of the method in other areas is needed to fully explore its usefulness in data driven predictive mapping of mineral prospectivity

data and knowledge driven mineral prospectivity maps for canada s north abstract data and knowledge driven techniques are used to produce regional au prospectivity maps of a portion of melville peninsula northern canada using geophysical and geochemical data these basic datasets typically exist for large portions of canada s north and are suitable for a greenfields exploration programme the data driven method involves the use of the random forest rf supervised classifier a relatively new technique that has recently been applied to mineral potential modelling while the knowledge driven technique makes use of weighted index overlay commonly used in gis spatial modelling studies we use the location of known au occurrences to train the rf classifier and calculate the signature of au occurrences as a group from non occurrences using the basic geoscience dataset the rf classification outperformed the knowledge based model with respect to prediction of the known au occurrences the geochemical data in general were more predictive of the known au occurrences than the geophysical data a data driven approach such as rf for the production of regional au prospectivity maps is recommended provided that a sufficient number of training areas known au occurrences exist

the umsoli chert turbidite testament for a major phreatoplinian event at the onverwacht fig tree transition swaziland supergroup archaean south africa abstract the volcanogenic origin of accretionary grains in the oolitic umsoli chert is proved by the unequivocal identification of constituent vesicular and pumiceous ash particles by the discovery of authigenic alkali feldspars and by the k meta bentonite parentage of associated illites celadonites ash particle morphology and ash grain size distribution suggest a phreato magmatic process of eruption sedimentary structures indicate that the felsic ash precursor of this ancient chert was deposited by turbidity currents the sedimentologic model invokes the transition of parts of pyroclastic falls and base surges into turbidites accretionary lapilli forming a major constituent of this silicified tuff oolite may be indicators of subaerial eruption but they can probably not be used as evidence for subaerial deposition

extensional structures during deposition of the 3460 ma warrawoona group in the eastern pilbara craton western australia abstract structures in the granite greenstone terrain of the eastern pilbara were mapped in both the coongan belt greenstones and shaw batholith granitoids important structures that are coeval with an early magmatic event in both the granitoids and the greenstones were identified in the coongan greenstones a brittle extensional fault array is syn kinematic with felsic volcanics of the duffer formation dated at 3452 16 ma pidgeon 1978a in the underlying shaw batholith a major ductile shear zone was mapped at the contact with the coongan belt although the foliation in the shear zone forms part of a domal structure the stretching lineations constantly plunge to the ene the sense of shear as recorded in the shear zone is consistently east up with subsidiary sinistral strike slip movement on the e w trending part and dextral movement on the n s trending part a wedge shaped granitoid intruded into the shear zone during deformation this granitoid is part of the north shaw suite which has been dated at 3467 6 ma mcnaughton et al 1988 the structures in the greenstones and in the batholith have therefore formed during the same event at different crustal levels the structural kinematic magmatic metamorphic and geochronological data are consistent with a model in which these structures represent the downdip part of a dome with a core complex type of geometry in turn this implies that the domal geometry of the shaw batholith was initiated at mid crustal levels at a very early stage namely during deposition of the warrawoona group in the evolution of the pilbara craton as extension occurred during intrusion and extrusion of large volumes of magma the original distribution and thickness of granitoid bodies and greenstones were probably largely determined by the extensional geometry the initial domal shape of the shaw batholith has been enhanced during later deformation phases which caused steepening of n s trending structures

a 3500 ma plutonic and volcanic calc alkaline province in the archaean east pilbara block variably foliated predominantly granodioritic plutonic rocks from the northern part of the shaw batholith in the east pilbara archaean craton are dated at 3 499 22 ma 2 errors by a whole rock pb pb isochron these rocks intrude the surrounding greenstone sequence and their age is indistinguishable from that sequence high strain grey gneisses which occupy much of the western and southern shaw batholith are chemically and isotopically similar to the north shaw suite and are inferred to have been derived from this suite by tectonic processes felsic volcanics within the greenstones together with a major portion of the granitic batholiths apparently formed in a calc alkaline volcanic and plutonic province at 3 500 ma this volcanic and plutonic suite is similar to modern calc alkaline suites on the basis of major element rare earh element and most other trace element contents the archaean suite contrasts with modern equivalents only in having lower concentrations of hree and higher concentrations of ni and cr

timing and tectonic significance of late archaean sinistral strike slip deformation in the central pilbara structural corridor pilbara craton western australia a north south striking zone of sinistral strike slip shear 20 100 km and associated folding and thrusting within the central part of the pilbara craton is described this zone referred to herein as the central pilbara structural corridor cpsc was formed during regional d3 deformation and overprints two earlier sets of structures associated with granitoid doming it is bound to the west by a continuous north south striking curviplanar fault at greenschist facies in the east it is bound by a series of ne sw striking fault segments located along sheared fold limbs and by a kilometre wide zone of amphibolite facies mylonite within the western margin of the shaw batholith faults vary from narrow high level brittle structures and retrograde breccia zones in the north to broader more ductile structures with sc mylonitic foliations in the south suggesting a southerly increase in exhumation a set of kilometre scale en echelon folds with ne sw striking upright axial planes and ne plunging axes characterize the interior of the cpsc and are wholly contained within the bounding faults thus indicating coeval development with faulting during sinistral wrenching 1 nw se strike slip deformation in the cpsc is interpreted to have resulted from northwesterly indentation of shaw batholith and contiguous rocks to the east westerly directed tectonic escape of the strelley granite laccolith and associated supracrustal rocks from in between shaw batholith and north pole dome was followed by ramping up the concave eastern margin of the yule batholith and eastward tilting during the transition from westerly to northerly displacement continued northward translation of the strelley granite at the leading edge of the system was terminated by constriction between the carlindi batholith and the north pole dome trailing greenstone successions were crumpled into a series of ne trending en echelon folds and related faults kinematic evidence and structural geometry indicate that sediments of the lalla rookh basin de grey group were deposited in advance of the north moving strelley granite within a basin bounded by faults of opposite displacement rather than in a pull apart basin as previously suggested the age of the d3 deformation is indicated by resetting of the ar ar and rb sr isotopic systems to ca 2950 ma in the western shaw region and by u pb ages of syn kinematic granitoid rocks

gliding and overthrust nappe tectonics in the barberton greenstone belt abstract regional recumbent folds inverted stratigraphy nappes and olistostromes are described from the southern part of the 3 3 3 5 ga barberton greenstone belt overthrusting of thin rigid silicified slabs with minimum dimensions of 25 km2 and up to 500 m in thickness occurred over minimum distances of 86 km more ductile and coherent units were overfolded up to at least 2 km during their emplacement the glide planes on which these nappes travelled were zones of high fluid pressures related to hydrothermal fluid circulation patterns driven by heat sources from igneous intrusions the upwelling areas of the geothermal convection cells were sites of mud pools and hydrothermal vents which may mark the trailing edges pull aparts of the overthrust units progressive silica and carbonate precipitation due to decreasing temperatures within the zones of fluid migration distant from the areas of high heat flow probably acted as built in braking systems below the travelling slabs active sedimentation and metasomatism during this tectonism indicates a protracted history for the evolution of the greenstone belt the recognition of nappe and overthrust tectonics in the barberton belt processes which may have been commonplace in archaean terrains necessitates a re evaluation of the stratigraphy of this belt

a machine learning based approach to exploration targeting of porphyry cu au deposits in the dehsalm district eastern iran abstract the dehsalm district in the central part of the lut block is an important polymetallic belt of eastern iran this study identifies the prospective areas for cu au porphyry deposits within the dehsalm district by integrating the outputs of the restricted boltzmann machine rbm and random forest rf models based on geological metallogenic and statistical analyses seven predictor maps namely proximity to faults and intrusive rocks to aeromagnetics anomalies to hydrothermal alterations argillic and fe oxide and two multivariate geochemical signatures of the stream sediments were generated to train the models to identify anomalies indicative of cu au porphyry mineralization from the rbm results the rf model was applied as a supervised machine learning algorithm the target areas delineated in the combined model occupy 4 2 of the study region and contain 82 of the known cu au occurrences the most prospective areas identified in the combined model extend along with structures that are spatially associated with known cu au occurrences and provide clear targets for future exploration

evidence for multiphase deformation in the archean basal warrawoona group in the marble bar area east pilbara western australia abstract the results of a structural analysis of the marble bar greenstone belt in the mcphee reward area of the eastern pilbara block in western australia indicate that the area has undergone a multiphase deformation on shears which approximately parallel the trace of stratigraphy cf primary igneous layering around the talga talga anticline early extensional movements were associated with the formation of the warrawoona group chiefly the duffer formation and indicate a wnw ese extensional direction similar to the syn warrawoona extension found in the area of the north shaw batholith extension was followed by thrusting with transport to the east the talga talga anticline is a culmination which formed during this event by thrust stacking a major shear in the area the duffada shear was reactivated during granodiorite emplacement with transport to the ne in their present geometry the shears have thrust movements on the south side of the talga talga anticline but normal movements on the north side after the reactivation came a nw se shortening which was accompanied by conjugate shear activity on north trending sinistral and west trending dextral shears and constrained to 2950 ma in the north shaw area the final movements were associated with a n s shortening which resulted in an e w trending thrust which cuts the northern flank of the talga talga anticline and nw and ne trending conjugate faults there is no evidence of radially oriented stretching lineations or slickensides which would be expected if the granitoid bodies which make up the mount edgar batholith were emplaced by a solid state diapiric process the net result of deformation was tectonic disruption of the stratigraphic stacking within the type ara of the talga talga subgroup in the warrawoona group this may offer an additional explanation for anomolously young dates of the talga talga subgroup with respect to the duffer formation and also indicates that the type section for the talga talga subgroup is a lithotectonic sequence

the mulgandinnah shear zone an archean crustal scale strike slip zone eastern pilbara western australia abstract a large part of the deformation in the archean pilbara granitoid greenstone terrain is localized in relatively narrow shear zones the mulgandinnah shear zone msz is a major one of these with a width up to 8 km that can be followed for over 70 km along strike in the shaw batholith in the eastern pilbara it forms part of the mulgandinnah lineament that can be traced to the lalla rookh basin and the carlindi batholith in the north giving it a total length of over 150 km the msz contains both mylonites and ultramylonites both of which have foliations that are subvertical to steeply dipping with the ultramylonitic foliation overprinting the mylonitic foliation to form more localized zones of high strain stretching lineations are mostly subhorizontal to shallow south plunging for both the mylonites and ultramylonites but can vary between 50 n and 50 s both foliations formed under upper greenschist to amphibolite grade conditions the msz displays a consistent sinistral sense of shear as indicated by and type porphyroclasts s c fabrics and rotated pegmatite veins the mylonites and ultramylonites are interpreted to have developed as part of a progressive deformation event leading to strain localization in the ultramylonites timing constraints indicate that the msz has been active at ca 2930 ma but it is likely to have been a long lived structure that was reactivated at that stage when it acted as a conjugate shear during a nw se crustal shortening in the eastern pilbara the final juxtaposition of the various domains in the pilbara granitoid greenstone terrain occurred during this deformation phase

sedimentology of archean greenstone belts signatures of tectonic evolution abstract stratigraphic styles in archean greenstone belts are compared to those of modern and phanerozoic depositional basins in order to test the conformity of tectonic style through time six lithological associations in greenstone belts are recognized 1 mafic ultramafic volcanic 2 calc alkaline volcanic 3 bimodal volcanic 4 quartz arenite iron formation or carbonate 5 conglomerate wacke and 6 conglomerate arenite examples of the associations are described from the kaapvaal superior and zimbabwe provinces and the pilbara block each association differs only slightly between the four regions thereby emphasizing a common tectonostratigraphic theme sedimentary rocks are a minor component of the mafic ultramafic volcanic association they were deposited in two types of volcanic basin environments one similar to barred lagoons and bays around oceanic volcanic islands and the other similar to sediment starved platforms adjacent to coalesced volcanoes in inter arc intra arc and back are basins in contrast sedimentary rocks in the calc alkaline volcanic association comprise thick wedges of epiclastic and volcaniclastic detritus deposited in elongate sedimentary basins and thick wedges of pyroclastic and volcaniclastic detritus deposited adjacent to volcanic centers sedimentary facies were identical to those of forearc trench and marine volcanoplutonic arc settings chemogenic lithofacies in both volcanic associations were deposited in shallow to deep marine waters although shallow water profiles were selectively preserved in some terrains sedimentary rocks of the bimodal volcanic association are thick wedges of siliciclastic and volcaniclastic deposits interbedded with subaerial to submarine erupted flows of komatiite basalt and rhyolite depositional environments ranged from braid plain and braid delta to coastal marine and submarine fan starved basin deposits include banded iron formation and sulfidic black shale the association is identical to that of cratonic extensional basins in arc continent and intracontinental rifts sedimentary rocks of the quartz arenite iron formation or carbonate association onlap weathered basement or bimodal volcanic association rocks depositional environments were either transitional from fluvial to siliciclastic and carbonate marginal marine to offshore pelagic hemipelagic or from inshore intrabasinal clastic and volcaniclastic to offshore pelagic hemipelagic siliciclastic deposits are supermature two tectonic sites are represented those with siliciclastic facies represent continent adjacent syn to post rift stable shelves and those dominated by banded iron formation with volcaniclastic deposits represent arc adjacent post rift stable shelves sedimentary rocks of the conglomerate wacke association are represented by thick wedges of siliciclastic or volcaniclastic sandstone with minor volcanic components these were deposited in braid plain braid delta and submarine fan environments within elongate sedimentary basins coastal plain and pelagic basin facies are also present siliciclastic detritus was derived from syndepositional magmatic and metasedimentary thrust belts two stratigraphic styles are preserved one that records a flysch like stage of deep to marginal marine environments and the other that records a molasse like stage of marginal marine to fluvial environments the association is identical to that of compressional foreland basins of arc continent collisional and compressional arc tectonic affinities the conglomerate arenite association is preserved in elongate structural basins that transgress crustal components and all other supracrustal units it is dominated by thick wedges of siliciclastic sandstone although bimodal volcanic and volcaniclastic rocks can also be present depositional environments ranged from talus and alluvial fan and braid plain to either lacustrine or coastal marine local basin margins often show lateral offsets from source terrains and vertically skewed facies patterns longitudinal facies geometries are typical the association is similar to that of strike slip collisional graben in hinterland tectonic escape and terrane accretion orogens the examples show that despite all the ramifications of secular geophysical geothermal and geochemical global change the stratigraphic style of sedimentary rocks in archean greenstone belts can be matched with modern tectonic analogues thereby emphasizing the conformity of stratigraphic style through time the inseparable link between stratigraphic and tectonic styles implies that the tectonic style of greenstone belts was not temporally unique major differences exist with regards to the chemical composition of certain magmatic and sedimentary products but these are compensated for by their constant stratigraphic function in terms of depositional processes depositional environments and tectonic sites

archaean basin margin geology and crustal evolution an east pilbara traverse a palinspastic reconstruction of a 100 km long traverse through archaean rocks of the east pilbara western australia includes new observations of the deformation preceding the now visible greenstone belt pattern the restoration is time calibrated with all available u pb datings between incompletely preserved basin sequences two superposed palaeoarchaean volcano sedimentary basins the coongan and salgash basins are separated by an eastwards time transgressive interface tentatively interpreted as an onlap surface for over 140 ma the basin margin architecture was structurally controlled by superposed extensional growth fault arrays d 1 with associated dyke swarms in a curved pattern spatially not related to that of the actual distribution of granite domes and greenstone belts the basins are interpreted to have formed by collapse after arching above hotspots due to phase transitions by mini subduction of slabs of cooled water saturated basalt towards the base of an originally c 45 km mafic crust at c 3 31 ga the extension was replaced by plate driven regional nw se compression d 2 inferred from nw over se shear and ramp and flat thrusts partly reversing offsets of the d 1 extension the recognition of widespread d 2 pre doming compression is important because it triggered the c 3 18 ga start of formation of the dome and keel pattern d 3 visible today which culminated at c 2 9 ga supplementary material eight figures numbered supplementary material fig a h and a gps list of observation sites are available at https doi org 10 6084 m9 figshare c 3808243

the terminology of structures in thrust belts abstract a review of structures and geometric relationships recognized in thrust belts is presented a thrust is defined as any contractional fault a corollary being that thrusts must cut up section in their transport direction flats are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ramps are those portions of thrusts which cut across datum surfaces ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike slip movement an array of thrusts which diverge in their transport direction may form by either of two propagation models these are termed piggy back propagation which is foreland directed and overstep propagation which is opposed to the thrust transport direction an array of thrust surfaces is termed an imbricate stack and should these surfaces anastamose upwards a duplex will result the fault bounded blocks are termed horses a duplex is bounded by a higher roof thrust and a lower floor thrust the intersection of any two thrust planes is termed a branch line thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut a further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one the movement of thrust sheets over corrugated surfaces or the local development of thrust structures beneath will fold higher thrust sheets these folds are termed culminations and their limbs are termed culmination walls accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust these accommodation surfaces are termed hangingwall detachments and they need not root down into the active thrust this category of detachment includes dip slip hangingwall drop faults which are developed by differential uplift of duplex roofs and out of the syncline thrusts which develop from overtightened fold hinges back thrusts as well as forming as hangingwall detachments may also form due to layer parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp

introduction to the special issue gis based mineral potential modelling and geological data analyses for mineral exploration this introduction provides an overview of the procedures involved in mineral potential modelling the papers included in this special issue are also summarized

mapping singularities with stream sediment geochemical data for prediction of undiscovered mineral deposits in gejiu yunnan province china abstract this paper proposes the concept of singularity for characterizing hydrothermal mineralization processes a singular physical process may result in anomalous amounts of energy release or material accumulation within a narrow spatial temporal interval mineralization can be considered as a type of singular process due to large amounts of material accumulation and element enrichment a spatial singularity mapping technique is developed based on the local singularity involved in the context of multifractal theory it assembles geochemical map at different scales and calculates an index indicating the scaling characteristics of enrichment and depletion of geochemical concentration at multiple scales this index was used for quantifying spatial singularity of mineralization associated geochemical anomalies a case study for the gejiu tin polymetallic mineral district yunnan province china demonstrates that the concepts of singularity and the singularity mapping technique are applicable and useful for delineating anomalies caused by mineralization and for predicting the locations of undiscovered mineral deposits

the bulk magnetization contrast across the ocean continent boundary in the east coast of north america summary the intermediate wavelength 600 3000 km magnetic anomalies of earth derived from satellite data indicate that both continental crust and oceanic lithosphere are magnetic however no well defined and consistent magnetic anomaly is associated with the ocean continent boundary emphasizing that the bulk magnetization the vertically integrated magnetization contrast of oceanic lithosphere and continental crust is not appreciable an upper limit of 37000 a is estimated for the bulk magnetization contrast using the low altitude aeromagnetic and marine magnetic data from across the east coast of north america

machine learning predictive models for mineral prospectivity an evaluation of neural networks random forest regression trees and support vector machines abstract machine learning algorithms mlas such us artificial neural networks anns regression trees rts random forest rf and support vector machines svms are powerful data driven methods that are relatively less widely used in the mapping of mineral prospectivity and thus have not been comparatively evaluated together thoroughly in this field the performances of a series of mlas namely artificial neural networks anns regression trees rts random forest rf and support vector machines svms in mineral prospectivity modelling are compared based on the following criteria i the accuracy in the delineation of prospective areas ii the sensitivity to the estimation of hyper parameters iii the sensitivity to the size of training data and iv the interpretability of model parameters the results of applying the above algorithms to epithermal au prospectivity mapping of the rodalquilar district spain indicate that the rf outperformed the other mla algorithms anns rts and svms the rf algorithm showed higher stability and robustness with varying training parameters and better success rates and roc analysis results on the other hand all mla algorithms can be used when ore deposit evidences are scarce moreover the model parameters of rf and rt can be interpreted to gain insights into the geological controls of mineralization

tensile and compressive growth structures relationships between sedimentation deformation and granite intrusion in the archaean coppin gap greenstone belt eastern pilbara western australia1pii of original article s0301 9268 97 00065 x 1

mapping mineral prospectivity through big data analytics and a deep learning algorithm abstract identification of anomalies related to mineralization and integration of multi source geoscience data are essential for mapping mineral prospectivity in this study we applied big data analytics and a deep learning algorithm to process geoscience data to identify and integrate anomalies related to skarn type iron mineralization in the southwestern fujian metallogenic zone of china based on the geological setting and environment for the formation of skarn type iron mineralization 42 relevant variables including two geological one geophysical and 39 geochemical variables were analyzed and integrated for detecting anomalies related to mineralization using a deep autoencoder network the results indicate that the mapped prospectivity areas have a strong spatial relationship with the locations of known mineralization and demonstrate that big data analytics supported by deep learning methods is a potential technique to be considered for use in mineral prospectivity mapping

mapping mineral prospectivity for cu polymetallic mineralization in southwest fujian province china abstract in this study both the fuzzy weights of evidence fwofe and random forest rf methods were applied to map the mineral prospectivity for cu polymetallic mineralization in southwestern fujian province which is an important cu polymetallic belt in china recent studies have revealed that the zijinshan porphyry epithermal cu deposit is associated with jurassic to cretaceous yanshanian intermediate to felsic intrusions and faulting tectonics evidence layers which are key indicators of the formation of zijinshan porphyry epithermal cu mineralization include 1 jurassic to cretaceous intermediate felsic intrusions 2 mineralization related geochemical anomalies 3 faults and 4 jurassic to cretaceous volcanic rocks these layers were determined using spatial analyses in support by geodas and arcgis based on geological geochemical and geophysical data the results demonstrated that most of the known cu occurrences are in areas linked to high probability values the target areas delineated by the fwofe occupy 10 of the study region and contain 60 of the total number of known cu occurrences in comparison with fwofe the resulting rf areas occupy 15 of the study area but contain 90 of the total number of known cu occurrences the normalized density value of 1 66 for rf is higher than the 1 15 value for fwofe indicating that rf performs better than fwofe receiver operating characteristics roc were used to validate the prospectivity model and check the effects of overfitting the area under the roc curve auc was greater than 0 5 indicating that both prospectivity maps are useful in cu polymetallic prospectivity mapping in southwestern fujian province

review secular tectonic evolution of archean continental crust interplay between horizontal and vertical processes in the formation of the pilbara craton australia the archean pilbara craton contains five geologically distinct terranes the east pilbara karratha sholl regal and kurrana terranes all of which are unconformably overlain by the 3 02 to 2 93 ga de grey superbasin the 3 53 3 17 ga east pilbara terrane ep represents the ancient nucleus of the craton that formed through three distinct mantle plume events at 3 53 3 43 3 35 3 29 and 3 27 3 24 ga each plume event resulted in eruption of thick dominantly basaltic volcanic successions on older crust to 3 72 ga and melting of crust to generate first tonalite trondhjemite granodiorite ttg and then progressively more evolved granitic magmas in each case plume magmatism was accompanied by uplift and crustal extension the combination of conductive heating from below thermal blanketing from above and internal heating of buried granitoids during these events led to episodes of partial convective overturn of upper and middle crust these mantle melting events caused severe depletion of the subcontinental lithospheric mantle making the ep a stable buoyant unsubductable continent by c 3 2 ga extension accompanying the latest event led to rifting of the protocontinent margins at between 3 2 and 3 17 ga after 3 2 ga horizontal tectonic forces dominated over vertical forces as revealed by the geology of the three terranes karratha sholl and regal of the west pilbara superterrane the c 3 12 ga whundo group of the sholl terrane is a fault bounded 10 km thick volcanic succession with geochemical characteristics of modern oceanic arcs including boninites and evidence for flux melting that indicate steep archean subduction at 3 07 ga the 3 12 ga sholl terrane 3 27 ga karratha terrane and c 3 2 ga regal terrane accreted together and onto the ep during the prinsep orogeny this was followed by development of the de grey superbasin an intracontinental sag basin and widespread plutonism 2 99 2 93 ga as a result of orogenic relaxation and slab break off craton wide compressional deformation at 2 95 2 93 ga culminated with 2 91 ga accretion of the 3 18 ga kurrana terrane with the ep this compression caused amplification of the dome and keel structure in the ep final cratonization was effected by emplacement of 2 89 2 83 ga post tectonic granites

shrimp u pb zircon dating of archean core complex formation and pancratonic strike slip deformation in the east pilbara granite greenstone terrain sensitive high resolution ion microprobe shrimp u pb dating of zircons from granitic rocks in the east pilbara granite greenstone terrain has provided time constraints for main tectonic events in the shaw granitoid complex and has shown that deformation was intricately related to granitoid intrusion the earliest recognized deformation activity occurred within the split rock shear zone srsz probably between 3470 and 3420 ma the timing geometry and kinematics of this shear zone suggest that it was a midcrustal detachment in a core complex type extensional setting it was active during the intrusion of synkinematic sheeted granodiorite of the north shaw suite and brittle extensional faulting within the upper crust samples of gray migmatic gneiss and a diorite that occur structurally below the srsz were dated at 3451 1 ma and 3463 2 ma respectively indicating that melting and metamorphism took place in the lower units during extension in the middle to upper crust the 3470 3420 ma extensional event is most consistent with extensional collapse possibly as a result of delamination or convectional thinning of part of the lithosphere activity on the pancratonic strike slip mulgandinnah shear zone msz was constrained by the crystallization age of a synkinematic granitic dyke to have occurred at 2934 2 ma the msz and activity on the sholl shear zone of the western pilbara at 2960 ma smith et al 1998 are consistent with a regional nw se directed compressional stress field at this time steepening of greenstone belt stratigraphy has been attributed to diapirism but probably occurred after a 3300 3200 ma compressional event and following deposition of the youngest clastic sediments in the eastern pilbara stratigraphic sequence diapiric processes did not play a major role during the early evolution of the eastern pilbara craton from 3470 to 3300 ma

reply to comment on evidence for multiphase deformation in the archaean basal warrawoona group in the marble bar area east pilbara western australia van haaften w m white s h 1998 precambrian research 88 53 66 by m j van kranendonk a h hickman w j collins

40ar39ar laserprobe ages of metamorphic hornblendes from the coongan belt pilbara western australia abstract 40 ar 39 ar laser step heating analyses of metamorphic amphiboles and a whole rock sample from metavolcanic rocks of the archaean coongan greenstone belt in the south eastern pilbara in western australia provide evidence that these rocks with no previous age constraints belong to the ca 3460 ma old warrawoona group the western margin of the belt is formed by an east dipping ductile shear zone the eastern margin is undeformed and shows a narrow contact metamorphic zone the coongan belt shows a metamorphic gradient from amphibolite facies at the western margin to greenschist facies in the centre of the belt the rocks in the centre of the belt are transected by north south striking retrograde shear zones one of which has been constrained at ca 2940 ma and may be related to the ca 2940 ma intrusive event in the eastern pilbara foliated granodiorites from the ductile shear zone along the western margin of the belt yield dates of ca 3170 ma which are interpreted as the age of recrystallisation after deformation deformed blue green hornblendes from the adjacent foliated amphibolites however give younger and inconsistent dates of ca 3090 ma and ca 3020 ma these dates cannot be interpreted as meaningful ages and indicate an inhomogeneous distribution of argon in the shear zone age spectra from blue green hornblendes from the western part of the coongan belt constrain the age of a regional metamorphic event at 3240 ma which compares well with the metamorphic hornblende ages of ca 3200 ma obtained in the western shaw belt by wijbrans and mcdougall the same event is indicated by complex age spectra of partially metamorphosed mafic volcanic rocks which yield ca 3260 ma maximum ages in the higher temperature steps the age spectrum of contact metamorphic hornblendes from the eastern margin indicates that the cooling age of the undeformed granite in the south western corunna downs batholith is ca 3400 ma which is 70 90 ma younger than the north shaw granodiorites in the shaw batholith but considerably older than previously assumed that is ca 3300 ma all obtained ages fall within the expected range of ca 3 5 2 94 ga and generally increase from west to east through the coongan belt the effects of excess argon on the age spectra seems to be rather considerable in some of the experiments

horizontal tectonics pre dating upper gorge creek group sedimentation pilbara block western australia abstract the greenstone belt stratigraphy of the c 3500 ma old pilbara block has been subdivided into the lower dominantly volcanic warrawoona group and the upper mainly sedimentary gorge creek group regional mapping indicated that these units evolved as a near continuous succession with only minor internal unconformities and that both groups suffered their most intense tectonic imprint together as a result of granite diapirism however an upper gorge creek conglomerate a lalla rookh correlate with a basal angular unconformity contains felsic schist clasts derived from highly strained portions of the warrawoona group the folds in the conglomerate are upright as expected for diapirically generated structures and are as complex as any attributed to this process the schist clasts were therefore probably generated in a pre doming event high strain and high grade metamorphism are confined to the lower parts of the greenstone stratigraphy where a polyphase deformation history may be clearly defined the low strain low grade areas are generally regarded as having a simpler tectonic history but some examples contain very tight minor folds that pre date a widespread subhorizontal cleavage and both events pre date the doming in other low grade areas thrust structures are truncated by the angular unconformity at the base of the lalla rookh correlate and the thrust geometry suggests they formed in already folded rocks

from andesitic volcanism to the formation of a porphyry cu au mineralizing magma chamber the farallon negro volcanic complex northwestern argentina abstract the geological relations and geochemical composition of extrusive and subvolcanic intrusive rocks of the upper miocene farallon negro volcanic complex nw argentina were studied to reconstruct the evolution of a deeply eroded andesitic volcano over most its life history of some 3 5 my this paper is part of an integrated study of the processes that generate magmatic hydrothermal fluids responsible for the formation of porphyry cu au deposits here we present new data on bulk rock chemical and nd sr and pb isotopic compositions of unaltered volcanic and subvolcanic intrusive rocks for which geological relations and ages are constrained by field based stratigraphy and extensive ar ar geochronology the combined results indicate that voluminous volcanism started at ca 9 7 ma with the eruption of basaltic andesite to andesite lava flows and pyroclastic deposits this basic to intermediate volcanism persisted until 7 5 ma and was followed at 7 35 ma by the eruption of dacites as the last recorded major extrusive event the oldest andesitic intrusions emplaced at 9 0 ma were followed by hypabyssal intrusions of basaltic andesite andesite and dacite composition which intruded the volcanic sequence between 8 3 and 6 1 ma intrusions at 6 8 0 2 ma led to the formation of over 800 mt of porphyry cu au ore at bajo de la alumbrera it was formed by a large flux of magmatic hydrothermal fluids channeled through several phases of fractured dacitic porphyry which together with immediately following barren andesitic intrusions make up a composite stock after this magmatic hydrothermal event only minor rhyodacitic to rhyolitic intrusions were emplaced until magmatic activity ceased at 6 1 ma geochemical data for the magmatic rocks indicate that the evolution of the system was dominated by mixing of a mafic magma with a felsic magma that contained a component of crustal material as indicated by linear compositional correlations between compatible and incompatible elements initial strontium isotopic ratios vary between 0 7047 and 0 7118 while 143nd 144nd range from 0 5127 to 0 5124 and both isotopic variations correlate with each other and with sio2 content of the rocks after 8 5 ma a continuous increase in the silica content of intrusive rocks suggests the gradual formation of a magma chamber a substantial magma reservoir 7 km3 must have been established by the time of porphyry cu au mineralization to allow rapid release of a large volume of ore forming magmatic brine as a result of wholesale crystallization and de volatilization of the magma chamber

interplay between deformation and magmatism during doming of the archaean shaw granitoid complex pilbara craton western australia abstract the shaw granitoid complex one of the classic granitoid domes of the archaean pilbara craton western australia evolved from a plutonic complex into a 60 km diameter steep sided dome during migmatisation of the deep crust consistent stratigraphic younging of greenstones away from the dome and underlying outward dipping domical foliations indicate that the present exposure is a crustal section the section passes downward through progressively older greenstones into a near concordant high level sheeted granite complex the ca 3470 ma north shaw suite nss to a younger sill dyke complex of leucogranite the pilga leucogranite farther below the leucogranite grades via diatexite and a network of leucogranitic dykes into the lowermost unit of migmatitic orthogneisses which have protolith ages that overlap with the nss a semi continuous solid state domal foliation extends downward from the greenstones through the nss into the migmatitic orthogneiss but is less evident in the intervening pilga leucogranite a set of nnw trending upright folds with axial planar leucogranite dykes exist in both the pilga leucogranite and underlying orthogneisses but not in the nss or greenstones field relations indicate that much of the solid state dome concordant foliation developed in a sub horizontal attitude before the leucogranite sheets were emplaced above the migmatitic orthogneisses emplacement occurred along a sub horizontal high strain zone probably at a rheological boundary between the relatively rigid nss and softer underlying migmatitic orthogneisses the sheeted leucogranite complex and underlying orthogneisses were subsequently folded with later leucogranite magmas injected along the axial surfaces of the folds these leucogranite magmas locally extended into the overlying deformed nss where they also acquired a weak domical fabric suggesting syn doming emplacement although presently estimated to be 3445 3410 ma old stratigraphic constraints suggest that the leucogranite and the dome could be as young as 3300 ma the contrasting strain patterns above and below the pilga leucogranite are not expected for horizontal tectonic models invoking thrusting core complex formation or cross folding but are similar to one observed for gravity driven vertical tectonic models thermal softening initiated deformation and then deformation localised melts at a specific rheological interface once established this interface controlled the locus of pilga leucogranite intrusion during dome evolution demonstrating the interplay between deformation and magmatism

growth fault control of early archaean cherts barite mounds and chert barite veins north pole dome eastern pilbara western australia1pii of original article s0301 9268 97 00062 4 1

proterozoic crustal extension and the generation of dome and keel structure in an archaean granite greenstone terrane archaean granite greenstone terranes1 3 in which narrow belts of greenstone ultramafic and mafic volcanics and overlying sedimentary rocks occur in association with broad provinces of granite granitic igneous rocks gneiss and migmatite have long puzzled geologists because of the lack of any clear modern analogues not only is there uncertainty about how the greenstone formed in the first place4 6 but there is continuing debate about how and when the terranes developed their distinctive structural and metamorphic architecture many granite greenstone terranes display a dome and keel geometry in which belts of supracrustal volcanic and sedimentary rocks occur as structural troughs wedged between dome shaped bodies of the granite gneiss migmatite complex a metamorphic aureole typically occurs in the supracrustals adjacent to their contact with the domes and the contact itself is a shear zone here we report the results of field studies of a granite greenstone terrane in brazil showing that this architecture originated during the proterozoic more than 500 million years after extrusion of the greenstone we suggest that the thermal regime and deformation kinematics necessary to create this architecture could be generated during an episode of crustal extension when hot basement rocks were transported upwards along a transcrustal normal fault system to the base of the supracrustals

timing of gold mineralization in the mt york district pilgangoora greenstone belt and implications for the tectonic and metamorphic evolution of an area linking the western and eastern pilbara craton abstract hydrothermal gold mineralization occurs in banded iron formation and amphibolite host rocks respectively in the main hill and zakanaka deposits in the northern sector of the pilgangoora greenstone belt of the pilbara craton the supracrustal sequences of the greenstone belt have been folded into n s trending megascale isoclinal f2a folds which have been refolded into open to tight f2b folds d2 to d3 strike slip shear zones developed preferentially along the limbs of f2a isoclinal folds and along the granitoid greenstone belt contact gold mineralization is controlled by f2b folds and shear zones were interpreted to have been activated or reactivated during d2b deformation in both deposits gold associated hydrothermal alteration comprises zoned quartz calc silicate veins and pyrrhotite pyrite at the zakanaka deposit and quartz amphibole biotite diopside and pyrrhotite lollingite arsenopyrite at the main hill deposit thermobarometric and textural studies indicate that gold mineralization occurred synchronous with the peak of amphibolite facies metamorphism in both deposits lead isotope studies on gold associated hydrothermal microcline titanite and pyrrhotite in the zakanaka deposit yield a pb pb isochron with an age of 2888 2 6 1 ma for the alteration and hence gold mineralization this age is confirmed by a concordant pb pb age using shrimp on hydrothermal titanite from the zakanaka deposit of 2904 70 ma the initial isotopic ratio in the ore system estimated using the isotopic composition of hydrothermal microcline is much more primitive than 2888 ma pb from accepted growth curves lead isotope modeling using the possible ages of rock formation and metamorphic events in the eastern pilbara craton shows that the primitive pb isotope signature is consistent with the 2888 ma age of alteration if the pb was derived from old crust which underwent an early high grade depletion event the age of hydrothermal gold associated alteration at zakanaka indirectly constrains the age of the f2b folding event and the peak of amphibolite facies metamorphism in the pilgangoora greenstone belt to ca 2 89 ga the special position of the pilgangoora greenstone belt in the central pilbara permits the interpretation of the age of gold mineralization in the light of the tectonic evolution in both parts of the craton and indicates that mineralization and the associated structural and metamorphic events post dated the main magmatic evolution in both the east and the west pilbara craton but coincided with late deformational events along strike slip shear zones in the west pilbara and late syn to post tectonic granitoids and associated metamorphism in the east pilbara

origin of the 3500 3300 ma calc alkaline rocks in the pilbara archaean isotopic and geochemical constraints from the shaw batholith abstract calc alkaline plutonic rocks intruded at 3450ma comprise a major component of the shaw batholith in the archaean east pilbara block western australia new whole rock pb isotopic geochronology confirms the extent of these rocks but a minor plutonic phase is dated at 3338 52 ma and represents a second plutonic event of the same age as much of the nearby mt edgar batholith the sm nd isotopic systematics of the 3450ma rocks imply their derivation from a heterogeneous source which probably included a slightly older crustal component as well as a depleted mantle component the 3338 52 ma pluton includes components derived from crustal sources older than 3600 ma the geochemistry and sm nd isotopic systematics of these rocks are consistent with crustal growth in the early archaean from upper mantle sources as depleted as the modern upper mantle the shaw batholith calc alkaline suites exhibit very similar chemical trends on variation diagrams to modern calc alkaline plutonic rocks which can be modelled by a combination of mixing and fractionation a suite collected from outcrops displaying prominent igneous layering shows distinct geochemical trends which can be modelled by differentiation into a component enriched in ferromagnesian minerals principally hornblende and possibly sphene magnetite and epidote and into a leucocratic component containing quartz plagioclase and k feld par these archaean calc alkaline plutonic rocks in common with rocks from many other archaean calc alkaline provinces exhibit very fractionated ree patterns with depleted hree contents a feature considered to result from equilibrium with garnet at depth in lower crustal regions the geochemistry of the pilbara archaean calc alkaline rocks is identical to the subset of modern continental margin calc alkaline plutonic rocks with fractionated ree patterns such as those from the central and eastern peninsular ranges batholith western usa the tectonic setting in which the archaean calc alkaline rocks formed is still not known this reflects both uncertainty associated with the petrogenesis and environments of modern calc alkaline rocks as well as the limited knowledge of the precise timing and relationships of plutonic depositional and tectonic events in the pilbara archaean

geochronology and stratigraphic relationships of the sulphur springs group and strelley granite a temporally distinct igneous province in the archaean pilbara craton australia abstract rocks from the sulphur springs group a newly identified stratigraphic succession hosting volcanogenic massive sulphide vms base metal deposits in the soanesville belt pilbara craton northwestern australia have been analyzed by sensitive high resolution ion microprobe shrimp u pb zircon mass spectrometry to determine their age and tectonostratigraphic relationships most volcanism occurred between 3238 and 3235 ma distinctly different from the time interval spanned by the wyman formation type section is 3315 ma other dates 3325 ma with which it was previously correlated outlying volcanic rocks with similar geochemistry at the bernts and obelix prospects also produce dates from 3240 to 3235 ma and are therefore best interpreted as structurally detached fragments of the sulphur springs group the strelley granite an intrusion which shares geochemical characteristics with the overlying volcanic rocks also yields similar ages thus extending the period of temporally linked extrusive intrusive silicic magmatism in the evolution of the pilbara craton model pb pb dating of galena from the zn cu mineralization at the various vms prospects has yielded ages consistent with the zircon u pb ages of the host rocks indicating that the hydrothermal mineralizing systems were contemporaneous with and apparently initiated by igneous activity an epicontinental tectonic setting for the sulphur springs group during vms mineralization is implied by the broad range of old zircon ages obtained from a tuff at the base of the volcanic pile as the igneous episode coincides with the peak regional metamorphic event recorded in other east pilbara supracrustal rocks and with voluminous intrusive activity in nearby granitoid complexes it marks a major event in the crustal evolution of the eastern pilbara craton

palaeogeographic and tectonic evolution of the pilbara craton northwestern australia abstract two regional unconformities have been confirmed and followed throughout the greenstone belts of the pilbara craton the unconformities are usually low angle ones but each was preceded by considerable erosion in some areas granitoids are truncated at the younger unconformity a thick development of cherty banded iron formation bif and fine grained sediment has been used by most previous authors for correlations between greenstone belts when this unit and both unconformities which sandwich it are used as marker horizons considerable changes are required to the distribution of the major stratigraphic groupings as shown in most syntheses and regional maps for instance where volcanic units are in continuity of deposition with the bifs and sediments they are now grouped together the terms warrawoona gorge creek and whim creek groups are retained but they vary significantly from the accepted correlations this has engendered a new tectonic framework and history of evolution for the craton the warrawoona group is restricted to a possible protocontinent in the southeast overlapped by the gorge creek group but the whim creek group is developed essentially frontally to the protocontinent the observed distribution of tin nickel and some copper and pge mineralisation is consistent with the major tectonic provinces of the pilbara craton

critical tests of vertical vs horizontal tectonic models for the archaean east pilbara granite greenstone terrane pilbara craton western australia models for the formation of the high amplitude minimum 15 km long wavelength 120 km granitoid dome and greenstone syncline geometry of the archaean east pilbara granite greenstone terrane ep of the pilbara craton are controversial diapiric models ascribe most structural features to vertical re organisation of an inverted crustal density profile created by autochthonous magmatic processes during punctuated episodes of partial convective overturn of the upper and middle crust alternatively uniformitarian models interpret the granitoid cored domes as oversteepened metamorphic core complexes mccs that formed during periods of active extension between periods of regional alpine style thrusting a review of recent advances in lithostratigraphy and geochronology in the ep shows that the greenstone belts are composed everywhere of a coherent upward younging stratigraphy thereby precluding significant thrusting in the formation of the density inversion that drove partial convective overturn we present new geological evidence that the domes contain some or all of the predictive characteristic features of diapirs including chaotic internal geometries of domes with otherwise simple outlines ring faults along dome margins and in flanking greenstone belts mushroom shaped fold flaps around the margins of some domes and sedimentation in inter diapir synclines these data combined with a thorough review of previously proposed core complex models show that horizontal tectonic models are inadequate to explain the structural geometric geochronological and metamorphic features of the ep rather an integrated model of punctuated partial convective overturn of the upper and middle crust in response to dominantly magmatic processes is presented to explain the ca 750 myr history of the terrane

a comparison study of the c a and s a models with singularity analysis to identify geochemical anomalies in covered areas abstract fractal multifractal modeling of geochemical data is an interesting topic in the field of applied geochemistry identification of weak anomalies for mineral exploration in covered areas is one of the most challenging tasks for utilization of geochemical data in this study three fractal models consisting of the concentration area c a spectrum area s a and singularity index models were applied to identify geochemical anomalies in the covered area located in the chaobuleng fe polymetallic district inner mongolia china the results show that 1 the grassland cover weakens the concentrations of geochemical elements 2 the c a model has a limitation to identify weak anomalies in covered areas 3 the s a model is a powerful tool to decompose mixed geochemical patterns into a geochemical anomaly map and a varied geochemical background map but suffers edge effects in an irregular shaped study area and 4 the singularity index is a useful tool to identify weak geochemical anomalies

40ar 39ar age constraints on tectonothermal events in the shaw area of the eastern pilbara granite greenstone terrain w australia 700 ma of archean tectonic evolution abstract the shaw area in the eastern pilbara craton consists of granitoids with intrusion ages ranging from 3470 ma to 2850 ma and supracrustal rocks with ages ranging from 3515 ma to 3100 ma as determined by u pb and pb pb dating methods in this terrain several major deformation events have recently been recognized including late strike slip deformation compression and early extension in order to provide time constraints for these events twenty four samples from the shaw area have been used for 40ar 39ar step heating experiments twenty two hornblendes one muscovite one biotite resulting in spectra defining ages between 3520 and 2800 ma the late strike slip event occurred prior to 2944 9 ma the argon cooling ages provide time constraints for the compressional event between 3325 ma and 3200 ma cooling ages between 3300 and 3200 ma cannot be related to granitoid intrusion in this area and are interpreted as cooling after regional metamorphism related to the compressional event the best time constraint from 40ar 39ar ages for the split rock shear zone a major ductile detachment in the shaw batholith associated with early extension is that it was last active prior to 3222 13 ma a 3341 13 ma plateau age of a metabasalt sampled in contact with granites of the northwestern corunna downs batholith provides a minimum age for granitoid intrusion and a minimum age for the warrery shear zone hornblendes from the black range dolerite dyke gave a plateau age of 2796 9 ma providing a constraint on the time of cratonization of the pilbara granitoid greenstone terrain most of the cooling ages including a 3466 13 ma age for the contact zone of the north shaw granodiorite are related to intrusion of granitoids in the shaw batholith a large number but significantly not all of the sample population has been reset during the intrusion of late to post tectonic adamellites between 3050 ma and 2850 ma preservation of such a large range 700 ma in argon isotopic ages in a relatively small area is unusual the resetting of argon ages in the granitoid domain is best explained by a combination of preferential intrusion of younger granites and the difference in heat conductivity of granite versus basalt in the greenstone domain the resetting effect is more localized into a network of fluid flow channels mostly situated in shear zones

accretion of japanese island arcs and implications for the origin of archean greenstone belts the present day region of arc arc collision between the izu bonin arc and mainland japan honshu arc in the western pacific called the izu collision zone or icz provides a useful kinematic model for the development of many archean greenstone belts the compositional assemblage thermal structure and structural style of the crust in the icz are very similar to those inferred for many archean greenstone belts in both cases thick young and flaky arc crust with a high heat flux is in collision with another crustal block the icz has resulted in the imbrication of very thick slices of crust and associated sediments juxtaposed against older accretionary prisms many archean greenstone belts show similar geological features and we suggest that the incremental imbrication of the crust was a common tectonic style in some archean convergent margins

structural evolution of the warrawoona greenstone belt and adjoining granitoid complexes pilbara craton australia implications for archaean tectonic processes abstract the pilbara granite greenstone terrain 3 6 2 8 ga australia is quoted as the key area formed by passive gravity driven solid state diapirism but contrasting views have been reported recently which led us to re examine the key area the warrawoona greenstone belt and the adjoining mt edgar and corunna downs granitoid complexes we found i an asymmetric non synclinal distribution of metamorphic grade and deformation intensity across the warrawoona greenstone belt ii a major shear zone on the margin of the mt edgar granitoid complex with a unidirectional stretching lineation pattern iii a ne trending transcurrent shear zone within the central gneiss complex of the mt edgar granitoid complex iv coeval magmatic activity and doming of the granitoid complexes and v the loss of about 9 km of stratigraphic units in the warrawoona greenstone belt the area has had a prolonged history with at least four deformation phases between ca 3 47 and 2 8 ga the main domal geometry of the mt edgar granitoid complex was obtained during active ne sw extension at 3 31 ga d x 2 which appears to been in response to e w compression possibly the e w compression resulted in crustal thickening and partial melting probably of a 3 46 3 43 ga granitic basement causing crustal weakening collapse and extrusion of the 3 31 ga granitoids extension at 3 31 ga was accommodated by the mt edgar shear zone a mid crustal detachment and by the associated beaton well zone which acted as a transfer zone within the gneissic basement doming of the mt edgar granitoid complex is interpreted to have occurred in an active extensional core complex type mode an indication for deformation prior to 3 32 ga comes from syntectonically intruded gabbro diorite and dolerite sills within the mt edgar shear zone which intruded possibly as early as 3 46 3 45 ga d x 1 ultramafic schistose xenoliths within the gabbro diorite intrusions are the oldest observed deformed rocks formed during d x post doming deformation involved ne sw compression d x 3 followed by dextral transcurrent deformation d x 4 during nw se compression the latter may be related to the regional phase of deformation at 2 93 ga during which the eastern and western pilbara were amalgamated comparison of this deformation sequence to others within the marble bar domain suggests a common tectonic history from 3 46 ga onwards our structural and kinematic data especially the 3 31 ga unidirectional stretching lineation pattern lead us to reject solid state diapirism due to convectional overturn as the main cause for doming of the mt edgar granitoid complex we suggest that the cause lies in a plate tectonic process

evidence for stabilization of the pilbara block australia the stabilization of continental crust to form cratons represents one of the major features of earth history1 major structural geochemical2 3 and to a lesser extent sedimentological changes4 associated with the development of stable crustal blocks are recorded mainly around 2 500 myr ago1 this change however appears to have been globally diachronous and cratonic sequences as old as 3 100 myr are recorded5 i now present the results of a recent regional stratigraphical and sedimentological study on the 2770 myr old lower fortescue group6 7 previously classified lithologically as proterozoic8 but following the recent recommendation of a 2 500 myr archaean proterozoic chronological boundary9 is referred to as archaean in the pilhara block10 western australia a major stabilization of the underlying granitoid greenstone terrain appears to have pre dated fortescue basin formation this event which available geochronology suggests was relatively rapid marked a major changing point in the tectonic evolution of the pilhara block

structural evolution of the middle archean coastal pilbara terrane western australia 1 the middle archean coastal pilbara terrane is composed of two lithotectonic units the karratha and cleaverville roebourne supercomplexes the karratha supercomplex lies tectonically beneath the cleaverville roebourne supercomplex and consists of 3270 3250 ma granitic batholiths and metamorphosed terrigenous sediments it is identified as a juvenile continental crust with tonalite trondhjemite granodiorite type granites the cleaverville roebourne supercomplex is interpreted as a dismembered immature island arc which has a restored crustal thickness of 20 km this supercomplex consists of 3195 ma bimodal volcanic chemical sedimentary sequences metabasite low k granitic gneiss and peridotite regionally distributed granite porphyries circa 3020 3000 ma have intruded all of the coastal pilbara terrane detailed structural analyses and zircon u pb dating suggest that the coastal pilbara terrane records two phases of deformation the first phase is an immature island arc and micro continental crust collision and is represented by top to the northwest thrusting d1 circa 3100 3020 ma this phase of deformation an arc continent collision appears to represent an important transition in the formation of continental crust the 3020 ma granite porphyry event may be related to syn post collision igneous activity and may reflect a second crustal thickening associated with magmatic underplating the second phase of deformation is characterized by regional scale left lateral strike slip faulting d2 circa 3020 2925 ma and by more localized right lateral strike slip faulting d3 circa 2925 2770 ma this phase of craton scale strike slip faulting may represent stabilization of the newly formed continental crust

sequence stratigraphy of the archaean supracrustal belts of the pilbara block western australia abstract the stratigraphic succession of the 3580 2770 m y old granite greenstone terrain of the pilbara block is re assessed by the first and second order sequence stratigraphic techniques that are the standard for phanerozic terrains with the view to testing the conformity of stratigraphic cause and response a holistic tectonostratigraphic framework is presented that pairs the supracrustal and crustal rock records the resulting sequence scheme is tested against the cause of first order sequence cycles viz global sea level responses to supercontinent breakup and assembly three first order inter regional unconformities divide the stratigraphic succession of the supracrustal belts into four units of first order megasequence status in order of decreasing age these are named the warrawoona gorge creek roebourne and mount negri megasequences a total of 17 second order supersequences are also named although some may represent supersequence sets the megasequences and or their genetic crustal equivalents represent the preserved rock record of four megacycles of forearc arc and or back arc geotectonic evolution associated with the convergent margins of a pilbara continent individual supersequences are the rock record of separate second order basins or basin phases and reflect the different geotectonic components of each megasequence the four megacycles had respective longevities from oldest to youngest of 150 m y 230 m y 160 m y and 180 m y they are identical in their stratigraphic successions and predicted first order sea level cycles to phanerozoic first order tectono eustatic cycles and are interpreted as the same response to global tectonic change the warrawoona and gorge creek megacycles and the roebourne and mount negri megacycles are tectonogenetic pairs of the east pilbara and the west pilbara megacycle sets respectively the east pilbara megacycle set evolved over a period of 380 m y from 3490 ma to 3110 ma whereas the west pilbara megacycle set evolved over a period of 340 m y from 3110 ma to 2770 ma the two megacycle sets are identical in their longevity geotectonic components and predicted sea level cycles to convergent margin wilson and supercontinent cycles and are thereby interpreted individually as the oldest established records of the supercontinent cycle the implication of this interpretation is that a steady state global tectonic regime has been in operation from early in earth s history which has important consequences for theoretical modelling of the earth s early tectonic style and secular changes in its geochemical regime

vaalbara earth s oldest assembled continent a combined structural geochronological and palaeomagnetic test the only remaining areas of pristine 3 6 2 7 ga crust on earth are parts of the kaapvaal and pilbara cratons general similarities of their rock records especially of the overlying late archean sequences suggest that they were once part of a larger vaalbara supercontinent here we show that the present geochronological structural and palaeomagnetic data support such a vaalbara model at least as far back as 3 1 ga and possibly further back to 3 6 ga vaalbara fragmented prior to 2 1 ga and possibly as early as 2 7 ga suggesting supercontinent stability of at least 400 myr consistent with neoproterozoic and phanerozoic analogues

predicting landslides for risk analysis spatial models tested by a cross validation technique abstract a landslide hazard map is intended to show the location of future slope instability most spatial models of the hazard lack reliability tests of the procedures and predictions for estimating the probabilities of future landslides thus precluding use of the maps for probabilistic risk analysis to correct this deficiency we propose a systematic procedure comprising two analytical steps relative hazard mapping and empirical probability estimation a mathematical model first generates a prediction map by dividing an area into prediction classes according to the relative likelihood of occurrence of future landslides conditional by local geomorphic and topographic characteristics the second stage estimates empirically the probability of landslide occurrence in each prediction class by applying a cross validation technique cross validation a blind test here using non overlapping spatial or temporal subsets of mapped landslides evaluates accuracy of the prediction and from the resulting statistics estimates occurrence probabilities of future landslides this quantitative approach exemplified by several experiments in an area near lisbon portugal can accommodate any subsequent analysis of landslide risk