new constraints on the evolution of the mallina basin and their bearing on relationships between the contrasting eastern and western granite greenstone terranes of the archaean pilbara craton western australia abstract the northeast trending mallina basin in the central part of the archaean pilbara craton separates western and eastern granite greenstone terranes with significantly different structural histories and age distribution patterns the basin which is up to 70 km wide and has a strike length of more than 150 km is mainly composed of metamorphosed turbidites assigned to the de grey group in the north these rocks are in faulted contact with metamorphosed volcanosedimentary rocks of the whim creek group new shrimp u pb zircon dates show that the turbidite sequence and the whim creek group were deposited within the same period between ca 3010 and 2940 ma and that the basement to the mallina basin is as young as ca 3015 ma geochronological structural and stratigraphic data now mitigate against previous models which suggested that the whim creek group was significantly younger than the turbidite sequence and that the whim creek group evolved in a late ensialic pull apart basin the mallina basin reinterpreted to include at least part of the whim creek group is now believed to be an extensional basin containing an overlap sequence an ensialic setting is preferred in which the basement to the basin consisted of ca 3170 3020 ma granites and greenstones rifted by major northeast trending faults a continental block to the south and east of which the presently exposed east pilbara granite greenstone terrane is a remnant influenced sedimentation in most of the basin previous tectonostratigraphic models that correlated across and beneath the mallina basin and interpreted the entire granite greenstone terrane of the pilbara craton in terms of evolution during two cycles of arc accretion are not compatible with the new geochronological data and stratigraphic interpretations

bioerosion structures in crepidula mollusca gastropoda as indicators of latitudinal palaeoenvironmental changes example from the marine quaternary of argentina abstract late quaternary marine skeletal concentrations from argentina are rich in molluscs exhibiting a great variety of bioerosion structures the shells of crepidula a characteristic gastropod occurring along more than 2000 km of coastline between the rio de la plata margin and southern patagonia show traces of dwelling predation and anchoring activities made by porifers bryozoans annelids other gastropods and brachiopods caulostrepsis entobia maeandropolydora iramena oichnus finichnus pennatichnus pinaceocladichnus podichnus and renichnus occur on the outer shell surface finichnus and oichnus are the only traces present along the entire area and the full time span considered the most characteristic structures are produced by bryozoans polychaetes and predatory gastropods traces produced by annelids and predatory gastropods occur preferentially in the central shell sector where predators gained access to the soft parts of the prey by contrast encrusting or branching bryozoan colonies are widely distributed as they can attach to any sector regardless of shell features available no strict correlation is evident between ichnodiversity and either time or latitude but ichnodiversity is linked to local oceanographical biotic controls for patagonia with a great majority of ichnotaxa made by bryozoans the general trend of higher bioerosion degree and ichnodiversity at higher latitudes is controlled by sea surface temperature productivity for the modern and the holocene several ichnodiversity peaks match with well constrained conditions substrate salinity thermal fronts by contrast this does not hold for the pleistocene dissimilar conditions probably prevailed especially during the last interglacial colder waters richer in nutrients

polydiapirism of the archean mount edgar batholith pilbara block western australia structural analysis of the mount edgar batholith and the enveloping greenstone belt indicates that the batholith and rocks around its margin were subjected to similar deformation events that involved progressive and stepwise diapiric uplift of the batholith these events may be correlated on the basis of fold style orientation and fabric development early recumbent to reclined structures d1 including thrusts were buckled d2 by rounded upright folds prior to shearing d4 along normal faults parallel with the batholith margin d4 deformation was responsible for uplifting the batholith to its present structural position a deep seated linear deformation zone d3 within the batholith did not affect the supracrustal belt syntectonic granite intrusion amphibolite facies metamorphism and migmatisation were associated with d1 in the batholith whereas greenschist facies metamorphism was associated with d1 in the lowermost unit of the greenstone belt the talga talga subgroup amphibolite facies conditions were maintained within the batholith throughout the structural history but this grade was reached in the supracrustal belt only near the batholith margin progressive deformation d1 d2 and metamorphism occurred in response to early massive granite generation and emplacement producing a first order plutonic dome that reached full maturity during d2 solid state diapirism d4 followed producing a gneiss dome of similar dimension restriction of early recumbent folds and thrusts in the supracrustal belt to areas within or adjacent to the batholith is consistent with the model elsewhere deformation is minor the late stage diapirism brought a gneiss complex within the batholith into juxtaposition with lowermost greenschist facies rocks of the pilbara supergroup this complex represents in part sialic material that existed below the pilbara supergroup before diapirism began the complex closely resembles other archean high grade gneiss terranes which suggests that some of these terranes are deeper crustal exposures of granite greenstone terranes

archaean tectonic processes a case for horizontal shortening in the north pilbara granite greenstone terrane western australia abstract the archaean pilbara granitoid greenstone terrane ggt has been the focus of numerous studies on archaean geology especially the classic dome and basin area around marble bar in the east pilbara this area has been used as evidence for different tectonic processes i e that vertical tectonics or diapirism was a cause for archaean deformation this paper provides evidence to support regional horizontal plate interaction stresses as being largely responsible for the compressive deformation of the pilbara ggt at least from ca 3 2 ga the relative chronology of meso to macro scale structural elements are presented for a number of selected areas across the pilbara ggt these locally identified events are correlated with a regional pilbara wide structural framework of deformation events that are constrained by geochronological and stratigraphic controls the dome and basin geometry characteristic of the east pilbara was established after 3 2 ga and was successively modified by repeated orthogonal extensional and compressive subhorizontal events the result has been a locally complex development of polyphase structural elements with consistent overprinting relationships that can be correlated across much of the pilbara from 3 2 ga diapirism did not cause these deformation elements although it may have modified them

tegula atra lesson 1830 mollusca gastropoda in the marine quaternary of patagonia argentina sw atlantic biostratigraphical tool and palaeoclimate palaeoceanographical signal results of the systematic review and regional palaeobiogeographical context of tegula atra including morphometric multivariate and cladistic analyses show that it is a keystone species in the marine quaternary of argentina that can be used as pleistocene biostratigraphical tool and paleoclimate palaeoceanographical signal while it was absent in warmer than present high sea level episodes during the miocene entrerriense transgression ca 10 ma and pleistocene mis11 it exhibits an excellent and abundant fossil record within dominantly cool coastal settings exclusively during the late pleistocene mis9 7 and 5 between rio negro and southern santa cruz provinces patagonia it first appeared in the sep during the late pliocene cooling trend dispersed during the late pleistocene into the swa presumably by rafting on macroalgae along the cabo de hornos and malvinas falkland currents but became extinct in the mar argentino magellan malacological province during the holocene amelioration trend its absence at present represents a climate change driven range shift and independent evidence of palaeoceanographical changes after the lgm and at the pleistocene holocene transition changes in sst ca 2 c higher wind velocities less light less nutrient availability less extension and intensity of cold less and warm increased shallow water currents altering water masses and biogeographical boundaries altogether these changes and the holocene scenario were disadvantageous causing direct effects on its physiology and survival in turn preventing the occurrence of the associated macroalgae durvillaea antarctica and its successful dispersal in the swa or retraction to the cold humboldt system waters this study reinforces the importance of dispersalist models to explain the origin of key taxa adding for a better understanding of molluscan taxonomic differences along the swa and sep margins of south america with implications for future coastal scenarios the distribution of t atra across time is a new example of the strong linkage between earth history climatic cycles atmospheric and oceanic circulation and the late quaternary biotic responses showing a possible consequence of future climate change on nearshore communities

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

late quaternary marginal marine deposits and palaeoenvironments from northeastern buenos aires province argentina a review the late quaternary marginal marine deposits along eastern argentina southwestern atlantic are reviewed according to our present knowledge in the northeastern coastal area of buenos aires province they have been assigned to a series of transgressions and regressions ranging from the late pliocene to the late quaternary the most widely accepted model is frenguelli s 1957 classical chronostratigraphical scheme of belgranense late pleistocene marine sediments at 3 6 m above m s l and ca 26 000 35 000 14c years bp the querandinense pleistocene holocene estuarine sediments below or at present m s l and the most extensive platense mid holocene marine deposits at 4 5 2 m above m s l dated at ca 8000 1340 14c years bp the restricted belgranense deposits recorded in samborombon bay in magdalena at ca 32 000 bp near mar chiquita at ca 24 900 and 30 500 bp and southwards in bahia blanca at ca 26 000 35 500 bp may belong to an interstadial gonzalez et al 1986 the molluscan composition suggests a marine invasion of the area but not a typical interglacial cycle characterized by euhaline and warm water elements however the oxygen isotope record argues against an interstadial during the interval 34 27 ka and the chronological control for these deposits is very poor suggesting that they most probably have been elevated neotectonically the pleistocene holocene querandinense deposits extensively distributed along the bonaerensian coastal plain and continental shelf ca 11 000 14c years bp with very low faunal diversity abundance of freshwater ostracods and absence of the warm water molluscs characteristic of the holocene ridges indicate low salinity and cool water conditions further dating and isotope analysis of these deposits are required for a better understanding of the chronology of climatic events by the end of the pleistocene in this area and to establish whether or not they could correspond to the younger dryas event of the northern hemisphere platense littoral ridges formed between ca 7600 and 2500 bp extend in several subparallel rows from ca 34 s to ca 39 s they formed either as beaches or possibly as sublittoral bars in samborombon bay where they reach 120 km long 10 30 m wide and up to 5 m thick at 4 5 5 m above m s l or in the supratidal and intertidal zones in mar chiquita at 2 4 m above m s l molluscs and ostracods suggest a brackish marine to marine brackish environment of lower salinity than the modern atlantic littoral during the mid holocene the oceanic waters were mixing with large amounts of antarctic ice melting in the south atlantic isla 1990 probably reducing salinity along the bonaerensian littoral the oldest littoral ridges accumulated during the hypsithermal and in the punta indio area their different geometry and alignment greatest age highest diversity and warmer affinity of the molluscan fauna suggest a short interval of reversal of the atmospheric circulation pattern further research is necessary for a better understanding of the chronology of the marine late quaternary deposits coastal evolution and climatic changes in this area

a multi proxy lacustrine record of holocene climate change on northeastern baffin island arctic canada reconstructions of past environmental changes are critical for understanding the natural variability of earth s climate system and for providing a context for present and future global change radiocarbon dated lake sediments from lake cf3 northeastern baffin island arctic canada are used to reconstruct past environmental conditions over the last 11 200 years numerous proxies including chironomid inferred july air temperatures diatom inferred lakewater ph and sediment organic matter reveal a pronounced holocene thermal maximum as much as 5 c warmer than historic summer temperatures from 10 000 to 8500 cal yr b p following rapid cooling 8500 cal yr b p lake cf3 proxies indicate cooling through the late holocene at many sites in northeastern canada the holocene thermal maximum occurred later than at lake cf3 this late onset of holocene warmth is generally attributed to the impacts of the decaying laurentide ice sheet on early holocene temperatures in northeastern canada however the lacustrine proxies in lake cf3 apparently responded to insolation driven warmth despite the proximity of lake cf3 to the laurentide ice sheet and its meltwater the magnitude and timing of the holocene thermal maximum at lake cf3 indicate that temperatures and environmental conditions at this site are highly sensitive to changes in radiative forcing

ice sheet collapse following a prolonged period of stable sea level during the last interglacial sea level during the last interglacial period reached a peak of between 5 and 9 m above the present day level a detailed reconstruction of sea level and isostatic rebound from western australia indicates a prolonged period of sea level stability at 3 4 m above present followed by an abrupt sea level rise of 5 6 m

correlation and dating of quaternary littoral zones along the patagonian coast argentina six areas of the patagonian coast argentina were investigated in order to determine the number characteristics geomorphology and development of quaternary littoral zones it became apparent that utilizing dl ratios of aspartic acid and leucine of various molluscan species would be the most useful in correlation relative age dating and estimating the ages of these zones the oldest littoral zone is found at elevations between 24 and 41 m above mean sea level and is judged to be older than oxygen isotope substage 5e in age based on relatively high amino acid ratios and extrapolated from non linear kinetic models an intermediate aged littoral zone may be present at some locations based upon beach ridges or platforms varying in elevation between 16 and 28 m above mean sea level dl ratios are generally lower than those for the oldest zone but show a greater variation this zone may represent the substage 5e sea level stand well defined young beach ridges 8 12 m above mean sea level are found in most locations and have been 14c dated and verified by amino acid ratios as being holocene the presence of quaternary aged emerged littoral zones at roughly the same elevation suggest that the glacio eustatic contribution is the primary cause of the high sea level stands whereas secondary variations are attributed to other factors

bathymetric zonation of modern microborers in dead coral substrates from new caledonia implications for paleodepth reconstructions in holocene corals abstract microboring endoliths were studied in dead modern corals collected at various depths and in growth position on la surprise atoll in new caledonia eight taxa of microborers were regularly observed three cyanobacteria hyella caespitosa mastigocoleus testarum and plectonema terebrans two chlorophytes ostreobium quekettii and phaeophila dendroides and three fungal forms dodgella priscus and two unidentified fungi the relative abundance of each taxon was determined in the modern corals throughout the studied sampling interval from 0 down to 40 m water depth this allowed us to propose for the first time a bathymetric model based on microendolith assemblages colonizing in situ hard substrates of corals in this model the occurrence of the cyanobacteria hyella and mastigocoleus indicates a bathymetric range from 0 down to a water depth of 3 and 6 m respectively the chlorophyta o quekettii associated with the cyanobacterium p terebrans and fungi is dominant from 10 to 40 m depth which is the lower limit of our sampling the distribution ranges of individual taxa observed in the dead coral substrates from new caledonia are much narrower than those reported in the literature for other substrates the bathymetric model based on distribution of microborers in modern corals was then applied to interpret the trace assemblages of microborers observed in holocene corals collected by drilling on two reef sites of new caledonia la surprise islet in the vicinity of the sampling sites of the modern corals and the barrier reef of bayes on the ne coast of grande terre the paleodepth interpretations performed at various levels along the cores allow identification of several shallowing upward sequences during the last 7000 years of reef growth in new caledonia differences in the thickness of these sequences between la surprise and bayes sites were interpreted as differences in the space available for accommodation between the two sites in turn related to the differential subsidence that affected new caledonia during holocene times the use of the microendolith trace assemblages in paleodepth reconstructions of holocene reefs from new caledonia allowed detection of relative sea level variations finer than those deduced from changes in coralgal assemblages

bioerosion structures in high salinity marine environments evidence from the al khafji coastline saudi arabia abstract salinity is one the major stress factors that controls the biotic activities in marine environments in general the mixture with fresh water has been mention as a great stress factor but the opposite i e high salinity conditions is less developed in the ichnological literature along the al khafji coastline saudi arabia hard substrates constituted by gastropods bivalves and coral skeletons contain diverse and abundant bioerosion traces and associated encrusters field and laboratory observations allowed the recognition of eight ichnospecies belong to the ichnogenera gastrochaenolites entobia oichnus caulostrepsis and trypanites which can be attributed to various activities produced by bivalves sponges gastropods and annelids the borings demonstrate two notable ichnological boring assemblages namely entobia dominated and gastrochaenolites dominated assemblages the highly diversified bioerosion and encrustation in the studied hard organic substrate indicate a long exposition period of organic substrate with slow to moderate rate of deposition in a restricted high salinity marine environment this bioerosion study shows that high salinity at least for the study area is not an important controlling factor for ichnology

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

joint pp ps angle stack analysis and ava inversion in grane field offshore norway eleven years ago publication of the uk north sea alba field obc converted wave ps image examples by macleod et al caused quite a stir the authors provided convincing evidence that the alba survey is the first 3d obc survey in which successful converted wave imaging of the reservoir has created significant economic benefit most of us with an interest in multicomponent seismology know it well as alba has become one of the classic examples of a stealth reservoir rape et al 2005 having low p but high s impedance contrast the alba reservoir and others like it are difficult to recognize on conventional p wave images but they stand out quite nicely when viewed on their ps equivalents

partial convective overturn of archaean crust in the east pilbara craton western australia driving mechanisms and tectonic implications strain varies systematically from weakly developed outward dipping s tectonites in the 3320 3310 10 ma mount edgar batholith to intensely deformed subvertical l tectonites in greenstones of the warrawoona syncline a consistent greenstone down batholith up sense of shear is recorded in batholithic domal margins and adjacent high grade supracrustal rims lineations converge to a central zone of subvertical extension zone of sinking along the synclinal axis at domal margins early kinematic granitoid sheets and intrusive diatexites are subconcordant to a well developed dome parallel schistosity but late to post kinematic intrusives are discordant high level plutons all granitoids are the same age within analytical error these syn doming features conform with structural tests for diapirs and differ from those expected during metamorphic core complex formation and cross folding diapirism is part of a larger process involving partial convective overturn of the crust based on strain patterns and kinematic criteria we argue that deformation was initiated by sinking of greenstones which rapidly subsided the domes then rose passively as accommodation structures ongoing doming d4 partitioned strain to the southern rim of the batholith and uplifted a wedge of the warrawoona syncline keel we consider that crustal overturn occurred in response to mantle plume activity eruption of a 5 10 km thick 3325 ma mafic ultramafic greenstone pile onto an older granite greenstone terrain created a negatively buoyant crust but convective overturn occurred some 5 20 ma later triggered by widespread anatexis thermal softening convective overturn may have been a common archaean process occurring in response to a hotter mantle and represents an end member deformation mechanism that includes thrust accretion of lithotectonic assemblages in other archaean terranes such as the superior province of canada

the geometrical relationship between the stretching lineation and the movement direction of shear zones abstract the geometrical relationship between foliations and lineations in shear zones is considered quantitatively assuming that the internal structures of shear zones have monoclinic symmetry the common practice of directly correlating the pitch or plunge of the stretching lineation with the obliquity of the shear direction is challenged it is the orthogonal projection of the stretching lineation on the shear zone boundary that is parallel to the shear direction a shear zone is parallel to a plane containing both the pole to the symmetry plane and the strike of the shear zone and the shear direction is parallel to the intersection of the symmetry plane and the shear zone boundary the symmetry plane is determined by the stretching lineation and the poles to the s foliation the implications of this study for the interpretation of shear zones are discussed with reference to an actual example

pleistocene and holocene interglacial molluscan assemblages from patagonian and bonaerensian littoral argentina sw atlantic palaeobiodiversity and palaeobiogeography abstract our analysis of palaeobiodiversity and palaeobiogeography of quaternary molluscan assemblages provide information on the last coastal scenarios in the sw atlantic we present patterns of species richness areas of endemism and between areas relationships based on records 721 taxa from argentina and northwards in south america surinam brazil uruguay including pleistocene holocene and modern sites 48 localities in argentina our data since the mid late pleistocene mis11 1 ca 400 ka b p to present suggest environmental changes linked to sea level and climatic fluctuations large enough to alter benthic associations compositional geographical variations including a few extinctions the southwards decreasing diversity trend for modern bivalves mostly infaunal taxa and gastropods mostly epifaunal taxa from surinam to tierra del fuego responds mainly to latitudinal sst salinity barriers hydrodynamic forces rivers and shallow currents minima peaks fit with local estuarine and marginal marine sites influenced by the rio de la plata plume highest peaks with fully marine warmer waters influenced by the brazilian current bonaerensian sector a similar trend applies for the holocene pleistocene maxima peaks in patagonia belong to mis11 and mis5 highstands warmer than today multivariate cluster analysis ca minimum spanning trees superimposed to principal coordinates analysis pco and cladistic parsimony analysis of endemicity pae methods showed congruent relationships between localities discriminating marginal from open marine environments but pco combined with pae was most advantageous for our area and dataset 382 gastropods 339 bivalves 29 pleistocene 28 holocene and 35 modern sites allowing objective quick comparisons shifts of areas of endemism during the holocene and pleistocene relate with sst and salinity changes a more homogeneous mid holocene ca 7 5 ka b p scenario of regionally increased salinity and higher ca 2 c sst defined the bonaerensian and northern patagonian sectors facilitating southwards shifts of bivalve and gastropod taxa for patagonia a colder pleistocene scenario south of sao is documented by tegula atra exclusive pleistocene cold water species extinct in the swa probably a signal of post lgm palaeoceanographical changes in the mar argentino

archean magmatism and deformation were not products of plate tectonics abstract the granite and greenstone terrains that dominate upper crust formed from about 3 6 to about 2 6 ga and record magmatic and tectonic processes very different from those of a younger time they indicate heat loss by the archean earth primarily by voluminous magmatism from a mantle much hotter than that of the present plate tectonic processes were not then operating the distinctive array of petrologic structural and stratigraphic features that characterize phanerozoic convergent plate systems ophiolites magmatic arcs accretionary wedges fore arc basins etc have no viable analogues in archean terrains purported archean plate tectonic indicators consist merely of rock types that even superficially resemble actual phanerozoic indicators only when considered in isolation from their association and structure archean ultramafic and mafic volcanic rocks neither resemble ophiolitic rocks in petrology nor occur in ophiolite type successions they often depositionally overlie felsic basement rocks and often overlie and are intercalated with sedimentary and felsic volcanic rocks and they require a mantle about 200 c hotter than now archean graywackes are coherent strata derived from nearby volcanic rocks late in the histories of their regions and they lack the setting and disruption that characterize modern accretionary wedges the lithologic structural and stratigraphic assemblages that typify proterozoic and phanerozoic rifted and reassembled margins also lack archean analogues and no evidence has been found for archean rifting rotation and reassembly of continental plates conversely characteristic archean assemblages lack modern equivalents in any tectonic setting ultramafic lavas erupted at liquidus temperatures are voluminous granite and greenstone terrains have no modern analogues greenstone belts are typically anastomosing networks of upright synforms formed by crowding aside by and sinking between large rising diapiric elliptical composite batholiths the batholiths include both the products of new crustal melts and variably remobilized mid crustal gneisses the greenstone belts are defined by late deformation of regionally semiconcordant volcanic and sedimentary successions and are not relics of successively formed volcanic chains little deformation generally preceded the diapirism and metamorphism was primarily of contact type the regionally uniform areal density and accordant crustal level of the diapiric batholiths their contacts primarily against the oldest strata of the synforms their general age 10 20 million years younger than most of the flanking stratiform rocks and considerations of high archean radiogenic heat productivity all fit the explanation that the batholiths were mobilized by partial melting of hydrous lower crust by radiogenic heating diapirism was accompanied by modest regional orthogonal shortening and extension of the hot upper crust producing the orientations of the batholiths rise of the batholiths greatly increased the petrologic fractionation of the crust and the concentration of radionuclides high in it resulting in cooling of the deeper crust and subjacent mantle and thus cratonization the upper crust containing the granite and greenstone aggregates was decoupled from the gneissic middle crust which underwent flattening and extension subparallel to the elongation of the shallow batholiths this deep deformation may have been driven by flow of dense restites toward delamination loci from which they sank into the mantle the early earth was probably wholly molten the surface of the earth like that of the moon must have been wholly recycled by impacts before 3 9 ga and heavily modified by them until 3 8 ga zircons as old as 4 2 ga have been found as clastic grains in much younger archean quartzites and polycyclic migmatites last partly melted and reconstituted under hydrous conditions only after 3 6 ga contain relict zircons as old as 4 0 ga the lithologies of the early earth protoliths in which these zircons formed have not been established but impact melts and breccias must be represented and magma ocean fractionates may be the nature of the transition in tectonic style into the granite and greenstone mode is unknown plate tectonic rifting and convergence were operating by about 2 0 ga and were in an essentially modern mode by about 0 8 ga the nature of the transition from the granite and greenstone mode at about 2 6 ga to plate mode by about 2 0 ga has yet to be defined the change may have been facilitated by the increasing content of water and carbon dioxide in the mantle as dense but hydrated delaminated archean crust sank into it

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

first record of podichnus in orthide brachiopods from the lower ordovician tremadocian of nw argentina and its relation to the early use of an ethological strategy abstract well preserved etchings from the pedicle attachment of brachiopods occur on orthide brachiopod shells from lower ordovician tremadocian of nw argentina under the name podichnus conicus isp n this trace fossil is interpreted as a fixichnia produced by the attachment of brachiopod pedicles upon hard substrates the trace is characterized by an irregular and asymmetrical cluster of circular pits each individual pit has a typical conical shape and presents the external mean diameter length ratio close to 1 the occurrence of p conicus isp n in the tremadocian is the oldest record of this ichnogenus and points to orthide brachiopods as podichnus producers for the first time the presence of this structure provides new information regarding colonization of biogenic hard substrates during the early ordovician and an adaptive strategy of its use by orthide brachiopods

deformation style way back when thoughts on the contrasts between archean paleoproterozoic and contemporary orogens abstract in many important ways archean and paleoproterozoic older orogens differ structurally from contemporary examples this essay examines the premise that contrasts between older orogens and contemporary orogens reflect long term changes in the temperature of the continental crust in the density of supracrustal sections and in exhumation rates for example if continental crust were warmer and exhumation rates faster earlier in earth history then higher grade rocks would occur closer to the surface of older orogens and the orogens would be lower and wider this situation might contribute to the formation of wide belts of high grade gneiss found in ancient crust if the high strength layer of the crust were thinner and supracrustal sequences denser earlier in earth history then regional extensional tectonism might lead to crustal scale boudinage and diapirism this situation might explain formation of the extensive dome and keel provinces found in ancient crust testing such speculations through the application of structural analysis coupled with petrologic studies dating and rheological modelling will constrain models of earth s long term physical evolution

duration and structure of the past four interglaciations reanalysis and additional dating of the devils hole 18o paleotemperature record confirm that the last interglaciation in the great basin the continental analog of marine isotopic substage 5e lasted 22 000 yr consistent with the vostok paleotemperature record which suggests a duration of 19 000 yr for this event in antarctica the three preceding interglaciations in the devils hole record analogs of marine isotopic substages 7e 9c and 11c range from 20 000 to 26 000 yr in duration a 20 000 yr duration for the last interglaciation is consistent with tims uranium series dated sea level high stands thus the widely held view that interglaciations were of 11 000 to 13 000 yr duration and constituted only about 10 of mid to late pleistocene climatic cycles needs reexamination the warmest portion of each interglaciation in the devils hole time series is marked by a 18o plateau signifying apparent climatic stability for periods of 10 000 to 15 000 yr duration

contributions of ichnology to palaeoecology palaeogeography and sedimentology a special issue related to the second latin american symposium on ichnology slic 2013 fil melchor ricardo nestor consejo nacional de investigaciones cientificas y tecnicas instituto de ciencias de la tierra y ambientales de la pampa universidad nacional de la pampa facultad de ciencias exactas y naturales instituto de ciencias de la tierra y ambientales de la pampa argentina

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

volcanic sedimentary and tectonostratigraphic environments of the 3 46 ga warrawoona megasequence a review abstract the warrawoona megasequence comprises a 3 46 ga assemblage of tholeiitic and calc alkaline volcanic rocks interlayered with cherty sedimentary rocks deposition occurred in a range of shallow to deeper water environments ranging from the shoreline to distal deposits in sediment starved basins volcanism provided the dominant or only source of clastic sediment sedimentary rocks also contain evaporites probable stromatolites other evidence for the existence of microbial life and possible evidence of meteorite impact the tectonostratigraphic assemblage and its contained facies associations are most similar to those developed in younger volcanic arc or near arc settings the compositions of volcanic rocks are also comparable with those of younger tholeiitic and calc alkaline suites developed above subduction zones the calc alkaline suite has a complex petrogenesis which probably involves mantle derived basaltic melts intermediate to silicic melts derived from subducted mafic crust magma mixing and fractional crystallization intense hydrothermal alteration and a distinctive association of metal deposits are also compatible with the interpretation that the warrawoona megasequence contains examples of early archaean volcanic arc and near arc assemblages

correction for nmo stretch and differential attenuation in converted wave data a key enabling technology for prestack joint inversion of pp and ps data in many parts of the world p or s wave impedance i p or i s or seismic velocities v p or v s are not good indicators of lithology in these cases estimation of density or v p v s is essential for reservoir characterization conventional inversion of pp mode data is known to yield i p and i s but a reliable estimate of density requires prestack inversion of very large angle pp data roy et al 2008 such large angle pp data sets necessitate acquisition and true amplitude processing of unusually large offsets

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

chlorophyll a variability off patagonia based on seawifs data 1 seasonal to interannual variability of satellite derived chlorophyll a over the patagonia shelf and shelf break in the western south atlantic are studied based on 7 years of ocean color data 1998 2004 from the sea viewing wide field of view sensor seawifs strong chlorophyll a seasonal variability 4 mg m 3 is observed compared to the open ocean 3 5 mg m 3 extends from the midshelf to the shelf break between 37 s and 44 s and southward to 51 s along a narrow shelf break band in summer the shelf break maximum persists from 37 s to 51 s and two inner shelf blooms develop off valdes peninsula and along a near coastal band between 46 s and 52 s 3 mg m 3 chlorophyll a concentrations in the northern midshelf sharply decay in late spring reaching lowest concentrations in summer february and march and a secondary maximum in early winter june though all regions present substantial interannual variations the bloom locations are stable the shelf break maximum is located inshore of the front between the low salinity shelf waters and the cold salty and nutrient rich malvinas current waters the inner shelf maxima are offshore of fronts separating well mixed coastal waters from the stratified midshelf north of 41 s the midshelf bloom is also associated to a bottom trapped thermal front thus all the high chlorophyll a regions are associated to well defined fronts

the alba field ocean bottom cable seismic survey impact on development alba field in the central north sea uk block 16 26 consists of eocene age high porosity unconsolidated turbidite channel sands sealed by low permeability shales at an average subsea depth of 1900 m the main channel is approximately 9 km long and 1 5 km wide and can be up to 100 m thick figure 1 the channel contains discrete bodies of intrareservoir shales that can cause significant drilling completion and production problems immediately overlying the main alba sand channel several wells have encountered thin discontinuous oil saturated brioc sands

quaternary marine terraces sea level changes and uplift history of patagonia argentina comparisons with predictions of the ice 4g vm2 model of the global process of glacial isostatic adjustment abstract quaternary marine terraces have been investigated along a 1000 km stretch of the coast of argentinian patagonia fossil mollusc shells most in living position and collected from raised beaches were dated using the u series esr and 14 c methods our analyses show that holocene sea level in this region culminated 7000 to 8000 bp at 6 7 m amsl this beach slightly increases in altitude southward the last interglacial stage 5e was identified at 16 17 m amsl whereas the highest and morphologically most distinctive radiometrically dated terrace at 250 000 to 330 000 bp exists at an elevation of 33 35 m amsl we estimate a constant rate of tectonic uplift of 0 09 m 1000 yr since the middle pleistocene using this estimate of the local rate of tectonic uplift we correct relative sea level r s l observations for the holocene epoch in turn the inferred holocene sea level histories are compared with those predicted using the ice 4g vm2 model of the global process of glacial isostatic adjustment this model accurately predicts r s l history from all sites along the northern part of the east coast of the south american continent venezuela brazil however along the southern part of the coast of argentinian patagonia there is evidence of an influence that is not accurately represented in this version of the model of the global process of glacial isostatic adjustment we suggest that this influence could be connected to the presence of the broad continental shelf that is located offshore of this region but the influence of significant neotectonic uplift cannot be dismissed

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

taphonomic comparison between two bivalves mactra and brachidontes from late quaternary deposits in northern argentina which intrinsic and extrinsic factors prevail under different palaeoenvironmental conditions quaternary records of unique skeletal deposits studied at two coastal areas of the bonaerensean littoral bahia samborombon in the north at puente de pascua and canal 15 area and bahia blanca southwards are thick 4 5 m and exceptionally rich in molluscan assemblages ca 75 90 bivalve shells indicating different high sea level episodes through taphonomical aspects of target bivalves mactra brachidontes which differ in shell structure life habit and habitat abundantly present in the marine late quaternary from both areas the aims were 1 to establish quantitative grades of taphonomic alteration of mactra from four lithostratigraphical units at bahia samborombon and identify which signature s better discriminates palaeoenvironments 2 test whether mactra shows different alteration than does brachidontes in response to differences in intrinsic features and ecological requirements 3 compare isotaphonomic assemblages complementing independent geological and palaeoenvironmental interpretations attributes articulation fragmentation abrasion colour encrustation bioerosion were classified for about 5400 shells from 11 samples bar plots ternary taphograms and q mode cluster analysis discriminate beach beach ridges and tidal flat environments and two taphofacies late pleistocene and holocene high energy units and low energy holocene units only abrasion and colour allow discrimination between high and low energy conditions rules cannot be applied to the processes of deposition of shells at least for the late quaternary marine deposits along the buenos aires province coastal area despite the harder mactra or more fragile brachidontes shell architecture in softer mactra muddy substrates infaunal or harder brachidontes varied sandy rocky bottoms epibyssate and deeper mactra infralittoral or shallower waters brachidontes intertidal to supratidal the taphonomic grades of alteration are similar a product mainly of long after death exposure along the taphonomically active zone in high to moderate wave energy conditions

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

3430 to 3417 ma calc alkaline volcanism in the mcphee dome and kelly belt and growth of the eastern pilbara craton abstract the mcphee dome and kelly belt in the eastern pilbara craton contain well preserved proximal shallow marine dominantly intermediate volcanic successions these have shrimp u pb zircon ages of 3430 3 and 3417 9 ma respectively which are younger than geochemically similar 3 52 and 3 47 to 3 45 ga suites in other eastern pilbara greenstone belts basalts andesites and dacites from the mcphee dome are similar in composition to modern arc rocks whereas dacites and rhyodacites from the kelly belt have geochemical characteristics of archaean tonalite trondhjemite granodiorite ttg magmas the geochemistry of the mcphee dome basalts basaltic andesites and dacites most likely reflects infracrustal fractional crystallization of a mantle derived magma combined with assimilation of older crust or a silicic melt in contrast the kelly belt dacites and rhyodacites were most likely derived by melting of subducted mafic crust the extensional submarine environment of pre 3 4 ga dominantly mafic and intermediate volcanism in the eastern pilbara differs from that of approximately coeval granitoid magmatism the pre 3 4 ga granitoids have the major and trace element features of ttg suites and appear to have been emplaced into already thick crust culminating in core complex formation available data are most consistent with growth of the eastern pilbara craton in convergent tectonic settings involving pulses of extensional shallow marine arc like volcanism between 3 52 and 3 42 ga overlapping with and or punctuated by periods of crustal thickening and the intrusion of complex ttg granitoid batholiths

timing and magnitude of holocene sea level changes along the middle and south patagonian atlantic coast derived from beach ridge systems littoral terraces and valley mouth terraces abstract geomorphologic and chronostratigraphic investigations in various coastal localities along the middle and south patagonian atlantic coast from bahia vera 44 s in the north to san julian 49 s in the south confirm a rich sequence of holocene beach ridge systems and littoral and valley mouth terraces beach ridges are present up to 10 m above current highest tide level htw and date to the early mid holocene transgression maximum beach ridge deposits represent high energy wave dominated coastal environments whereas valley mouth terraces and littoral terraces elevations of 5 5 6 5 m above htw developed in wave protected coastal environments the surface elevation of these littoral forms suggest that the middle and south patagonian atlantic coast is likely undergoing a slow glacio isostatic uplift on the order of 0 3 0 4 mm a since the mid holocene the early holocene sea level rise reached the modern coastline by 8100 14 c years ago c 8600 cal bp at the latest sea level at that time was most likely near its present position the holocene transgression maximum lasted from 6900 to at least 6200 14 c bp c 7400 to 6600 cal bp raising relative sea level to about 2 m to a maximum of 3 m above the present level after which sea level declined to the present level two significant sea level falls of at most 1 m occurred a between 6200 and 6000 14 c bp c 6600 to 6400 cal bp and b between 2600 and 2400 14 c bp c 2300 to 2050 cal bp we assume that both significant sea level falls were predominantly driven by eustatic changes of ocean volume whereas both thermo steric changes and changes of tides may also have contributed to these relatively strong sea level drops gravitational changes driven by greenland ice growth sensu mitrovica et al 2001 may also have amplified any eustatic portion of sea level fall the trend of a general sea level decline since the mid holocene transgression maximum seems to be predominantly glacio isostatically driven

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