the timing of gold mineralization across the eastern yilgarn craton using u pb geochronology of hydrothermal phosphate minerals the highly mineralized eastern goldfields of the eastern yilgarn craton is an amalgamation of dominantly neoarchaean granitoid greenstone terranes and domains that record a history of early rifting followed by westward directed collision with initial arc formation collision and clastic basin formation and final accretion to the western yilgarn proto craton between 2 66 and 2 60 billion years ago the gold deposits that define this region as a world class gold province are the product of orogenic processes that operated during accretion late in the tectonic history after initial compressional deformation d1 d2 and the majority of granitoid magmatism minor gold was also deposited throughout the entire tectonic history in magmatic hydrothermal related systems however such mineralization mostly 0 3 g t gold is nowhere economic unless it overprints or is overprinted by much higher grade orogenic gold lodes robust shrimp u pb geochronology of gold related hydrothermal xenotime and monazite supports structural studies that gold mineralization occurred during late transpressional events d3 d4 shortly before cratonization however westward migration of collision and accretion produced a complementary diachroneity in the timing of gold mineralization of 5 to 20 m y between c 2 65 ma in the east including laverton district kurnalpi terrane to c 2 63 ma in the west including kalgoorlie terrane across the eastern part of the craton the robust geochronology refutes previous suggestions that significant gold mineralization events extended from de to d4 in the evolution of the orogen and that the kalgoorlie gold deposits formed over a period of 45 m y the crustal continuum model is applicable within terranes where orogenic gold depositional events were penecontemporaneous but must be modified to account for diachroneity of orogenic events and gold mineralization across the eastern goldfields

the largest au deposits in the st ives goldfield yilgarn craton western australia may be located in a major neoarchean volcano sedimentary depo centre the largest neoarchean gold deposits in the world class st ives goldfield western australia occur in an area known as the argo junction region e g junction argo and athena why this region is so well endowed with large deposits compared with other parts of the st ives goldfield is currently unclear because gold deposits at st ives are hosted by a variety of lithologic units and were formed during at least three different deformational events this paper presents an investigation into the stratigraphic architecture and evolution of the argo junction region to assess its implications for gold metallogenesis the results show that the region s stratigraphy may be subdivided into five regionally correlatable packages mafic lavas of the paringa basalt contemporaneously resedimented feldspar rich pyroclastic debris of the early black flag group coarse polymictic volcanic debris of the late black flag group thick piles of mafic lavas and sub volcanic sills of the athena basalt and condenser dolerite and the voluminous quartz rich sedimentary successions of the early merougil group in the argo junction region these units have an interpreted maximum thickness of at least 7 130 m and thus represent an unusually thick accumulation of the neoarchean volcano sedimentary successions it is postulated that major basin forming structures that were active during deposition and emplacement of the voluminous successions later acted as important conduits during mineralisation therefore a correlation exists between the location of the largest gold deposits in the st ives goldfield and the thickest parts of the stratigraphy recognition of this association has important implications for camp scale exploration

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

late little ice age palaeoenvironmental records from the anzali and amirkola lagoons south caspian sea vegetation and sea level changes abstract two internationally important ramsar lagoons on the south coast of the caspian sea cs have been studied by palynology on short sediment cores for palaeoenvironmental and palaeoclimatic investigations the sites lie within a small area of very high precipitation in a region that is otherwise dry vegetation surveys and geomorphological investigations have been used to provide a background to a multidisciplinary interpretation of the two sequences covering the last four centuries in the small lagoon of amirkola the dense alder forested wetland has been briefly disturbed by fire followed by the expansion of rice paddies from ad1720 to 1800 on the contrary the terrestrial vegetation reflecting the diversity of the hyrcanian vegetation around the lagoon of anzali remained fairly complacent over time the dinocyst and non pollen palynomorph assemblages revealing changes that have occurred in water salinity and water levels indicate a high stand during the late little ice age lia from ad

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

age constraints on recycled crustal and supracrustal sources of archaean metasedimentary sequences eastern goldfields province western australia evidence from shrimp zircon dating abstract shrimp u pb zircon dating of sedimentary volcanic and subvolcanic intrusive rocks from unconformity bounded sequences in the eastern goldfields province defines maximum depositional ages for those sequences the kambalda sequence which records a backarc basin was deposited prior to 2700 ma and from at least 2715 ma the spargoville sequence which records an arc adjacent volcano bound basin was deposited between 2700 and 2683 ma the kalgoorlie sequence which records an intra arc rift basin comprises two tectonic stages with depositional ages of 2681 2670 and 2661 2655 ma deposition of the spargoville and kalgoorlie sequences overlapped with the intrusion of granitoids and subvolcanic porphyries thereby indicating that those granitoids were emplaced during crustal extension younger submarine fan kurrawang sequence and braided fluvial merougil and jones creek sequences deposits of a remnant ocean basin were deposited at when coupled to palaeocurrent data provenance dating of detrital zircon suites fingerprints southeast oriented amalgamation of felsic detritus from multiple sources within longitudinal depositional systems and longitudinal reworking of felsic detritus from single sourced transverse systems most felsic detritus was recycled from coeval volcanoplutonic arcs and the orogen to the remnant ocean basin sequences with zircon ages ranging from 2730 to 2660 ma older felsic sources with age ranges of 3570 3130 3030 2900 2870 2770 and 2760 ma could have been structural enclaves within the volcanoplutonic arcs or orogen but were more likely within a distant cratonic basement when coupled with stratigraphic data it is concluded that detrital zircon age distributions preserve evidence for the sedimentary recycling of coeval volcanoplutonic arc or orogenic sources uplifted basin floor and dissected arc successions and cratonic basement virtually all source terrains have apparently vanished presumably through the combination of tectonic and sedimentary recycling and tectonic severance increased use of detrital zircon suites from archaean sedimentary sequences is advocated in order to quantify the balance between sedimentary recycling of felsic rocks from contemporaneous volcanoplutonic sources which themselves document crustal growth in arc environments and from relict volcanoplutonic and crustal basement sources which document the degree of crustal recycling

sefidrud delta and quaternary evolution of the southern caspian lowland iran abstract the southern caspian sea lowland in iran forms a thick sedimentary prism produced by interactions of marine deltaic and fluvial processes during the late neogene and quaternary deltaic and fluvial deposits have been developed mainly by the sefidrud which is the largest river of the country its drainage area ca 61 600 km 2 includes nearly the entire alborz mountain range and forms deep valleys gorges and a large delta at the southern coast of the caspian sea the sefidrud delta is so large that it covers one third of the large guilan mazanderan plain both from an aerial and volumetric point of view consequently the drainage network of the sefidrud represents the quaternary evolution of northern iran and can be used to test the hypothesized evolution of the region the sefidrud delta has been investigated using many short and long cores satellite images and lithofacies maps and the results show that this delta complex 1680 km 3 consists of a covered lower part and exposed upper deltaic sequences the lower and upper parts of the complex were formed during the early pleistocene and late pleistocene respectively the upper exposed alluvial and deltaic sediments represent a total progradation of approximately 50 km forming three separate delta subsequences d1 3 of which the last one d3 is the modern sefidrud delta the modern delta is a wave dominated blanket like sediment cover ca 30 m thick and 1550 km 2 produced during the last three millennia it was formed by 30 km progradation of six juxtaposed lobes each lobe corresponds to a long term sea level fluctuation of the caspian sea the active lobe ca 50 km 2 has been forming since 1550 ad late pleistocene deltaic sequences d1 3 particularly the modern one d3 were produced by relatively fast deposition due to high volume sediment load of the sefidrud it is suggested that they were produced after the opening of the rudbar gorge by river capture that in turn six times enlarged the drainage area previous deltaic progradation and marine transgressions were relatively slow and the development of the whole lowland at the southern caspian sea lasted ca 1 1 2 ma bp

the invincible deposit early gold mineralisation truncated by unaltered c 2665 ma conglomerate st ives eastern goldfields western australia abstract two distinct styles of mineralisation are recognised at the invincible deposit with bedding parallel shear related gold mineralisation type 1 and shallow dipping mineralised extension veins type 2 the different styles of mineralisation reflect formation during two discrete deformation events type 1 mineralisation is hosted in laminated mudstone of the upper black flag group and mineralised quartz veins and breccia zones are distributed throughout the mudstone rather than being associated with a single shear mineralised zones are associated with intense sodic alteration the early mineralised structures are strongly modified by east west horizontal d2 3 compression in contrast type 2 extension veins are undeformed and are best developed in the massive sandstone conglomerate footwall but also overprint type 1 veins in the mudstone unit throughout the mine the early type 1 mineralisation is truncated by unaltered conglomerate of the c 2665 ma merougil formation a 10 20 difference in strike dip is commonly present and indicates that the main mineralising event at invincible occurred prior to erosion and deposition of the merougil formation the strong modification of the mineralisation by horizontal east west d2 3 compression is also consistent with formation early in the deformation history during the c 2672 2660 ma d1 event gold deposition in the egt was episodic occurring over a prolonged period during extension and compression bedding vein relationships indicate southwest side down kinematics during the early mineralising event in weakly mineralised zones sub vertical extension veins cut across beds that dip 70 to the southwest in strongly mineralised zones bedding is sub vertical and large quartz breccia veins develop along the bedding above moderately west dipping shears that extend across the steep bedding the location of the steep strongly mineralised zones where bedding is sub vertical reflects enhanced dilation in these zones during southwest side down movement southwest side down movement could represent extensional slip on the laminated mudstone beds if the bedding was tilted into a developing basin early merougil basin the location of the invincible system at the eastern edge of the merougil basin likely reflects an association with early basin controlling faults

structural geology across a proposed archaean terrane boundary in the eastern yilgarn craton western australia abstract the eastern goldfields province of the archaean yilgarn craton western australia can be divided into several nw se trending terranes with different stratigraphic signature at least two main phases of penetrative ductile deformation affect the terranes d1 is a phase of nappe type transport mainly to the north along gently dipping ductile shear zones it is interpreted as a phase of regional extension contemporaneous with intrusion of massive granitoid plutons and possibly contemporaneous with deposition of felsic volcanics and metasediments in the greenstone belts terrane boundaries were probably formed during d1 d2 gave rise to steep nw se to n s trending foliations and upright folds d2 is strongly partitioned over the area for strain and vorticity the pattern of partitioning seems to be dependent on the position of granitoid plutons which give rise to development of d2 strain shadows d1 structures have been preserved mainly in these strain shadows terrane boundaries are transected by boundaries of d2 structural domains minor intrusion of granitoids continued during and after d2 d1 is possibly associated with arrival of a mantle plume below the yilgarn craton and d2 may be a phase of regional shortening in a thinned lithosphere weakened by the thermal event

the granny smith gold deposit the role of heterogeneous stress distribution at an irregular granitoid contact in a greenschist facies terrane the granny smith gold deposits formed late in the structural history of the yilgarn block at a high crustal level in a largely brittle structural regime gold mineralisation is located along a n s striking fault which wraps around the contact of a small granitoid intrusion in different sections of the fault mineralisation may be developed in the granitoid in the adjacent sedimentary sequence and or along the contact between them in the granitoid gold mineralisation is in conjugate networks of thin carbonate quartz veins and their alteration halos small displacements along veins are common in contrast veins and faults in the sedimentary rocks are subparallel to bedding spatial variations in the conjugate vein orientations indicate that the local stress field was heterogeneous and controlled by the shape of the granitoid contact the greatest variations in vein and implied stress orientations occur in zones where the contact is most irregular these are also the areas of richest mineralisation fluid flow was thus focused in a regional scale low mean stress region created by the geometry of the granitoid intrusion its irregular contact caused deposit scale variations in fluid flow and resulted in heterogeneous gold grades along the contact zone

evidence for late holocene highstands in central guilan east mazanderan south caspian coast iran abstract the iranian caspian coast in the central guilan and east mazanderan were investigated using the analysis of samples retrieved from outcrops cores and through geophysical campaign the analysis of particle size organic matter calcium carbonate and fossil content as well as radiometric dating extends the caspian sea level records through the latest holocene ca 2500 years ground penetrating radar provides information about the internal stratigraphy of exposures along the central guilan coast lagoonal sediments that contained caspian mollusc shells have been dated at 2500 900 and 500 bp their dated horizons are located at altitudes of 22 24 and 25 m respectively which indicate higher sea levels during the late holocene the internal architecture and morphology of the coastal areas demonstrate spit lagoon development through littoral drift on the central guilan and east mazanderan coasts these structures also indicate lagoon formation due to rapid sea level rise a wide shallow lagoon in the central guilan sefidrud area was formed due to the last sea level rise 500 bp this lagoon then dried up as the result of falling sea level and infilled due to diversion of the sefidrud course these coastal developments show three highstands during the last 2500 years

timing of deformation in the norseman wiluna belt yilgarn craton western australia establishing relative and absolute time frameworks for the sedimentary magmatic tectonic and gold mineralisation events in the norseman wiluna belt of the archean yilgarn craton of western australia has long been the main aim of research efforts recently published constraints on the timing of sedimentation and absolute granite ages have emphasized the shortcomings of the established rationale used for interpreting the timing of deformation events in this paper the assumptions underlying this rationale are scrutinized and it is shown that they are the source of significant misinterpretations a revised time chart for the deformation events of the belt is established the first shortening phase to affect the belt d1 was preceded by an extensional event d1e and accompanied by a change from volcanic dominated to plutonic dominated magmatism at approximately 2685 2675 ma later extension d2e controlled deposition of the ca 2655 ma kurrawang sequence and was followed by d2 a major shortening event which folded this sequence d2 must therefore have started after 2655 ma at least 20 ma later than previously thought and after the voluminous 2670 2655 ma high ca granite intrusion younger transcurrent deformation d3 d4 waned at around 2630 ma suggesting that the crustal shortening deformation cycle d2 d4 lasted approximately 20 30 ma contemporaneous with low volume 2650 2630 ma low ca granites and alkaline intrusions time constraints on gold deposits suggest a late mineralisation event between 2640 2630 ma thus d2 d4 deformation cycle and late felsic magmatism define a 20 30 ma long tectonothermal event which culminated with gold mineralisation the finding that d2 folding took place after voluminous high ca granite intrusion led to research into the role of competent bodies during folding by means of numerical models results suggest that buoyancy driven doming of pre tectonic competent bodies trigger growth of antiforms whereas non buoyant competent granite bodies trigger growth of synforms the conspicuous presence of pre folding granites in the cores of anticlines may be a result from active buoyancy doming during folding 2002 elsevier science b v all rights reserved

biostratigraphy of the marine holocene on the iranian coasts of the caspian sea abstract marine holocene deposits of the coast of iran are represented by the upper khvalinian and new caspian beds upper khvalinian sediments are faunistically barren whereas the new caspian beds contain abundant fossil molluscs that allow subdivision into the daghestan new caspian and modern layers the only fossil species found in the daghestan layer is didacna cristata the new caspian sediment layer is characterized by a taxonomically diverse molluscan assemblage dominated by cerastoderma glaucum it is subdivided into the upper and lower new caspian sub layers modern sediments are lithologically diverse besides the new caspian fauna they also contain the valves of the species mytilaster lineautus which is known to have immigrated from the black sea

extension and gold mineralization in the archean kalgoorlie terrane yilgarn craton abstract this paper focuses on two extensional events affecting late archean crust of the kalgoorlie terrane in the eastern goldfields and which are associated with gold mineralization these events bracket the duration of the crustal shortening event known as the kalgoorlie orogen the early extension phase is preserved around the raeside batholith and gave rise to the earliest recognized structures d 1e this event is characterized by multi directional horizontal extension in contrast to unidirectional extension associated with core complexes extension uplifted the batholith in relation to the overlying greenstone sequence and produced recumbent folds gold including the large deposits at leonora was deposited in normal shear zones around the batholith we propose that extension triggered doming of gravitationally unstable granitic rocks buried under a greenschist sequence and amplified the growth of extensional nappes the late phase of extension is evident in a number of gold deposits in the kalgoorlie terrane this phase is characterized by a overprinting crustal shortening structures that suggests it is the latest structure in all localities b gently dipping foliation associated with recumbent folds which are dragged into moderately dipping normal shear zones c maximum stretching axis nw se or n s at high angles to the maximum shortening axis inferred from regional shortening phases of the kalgoorlie orogen and d hosting gold this phase records relaxation of the kalgoorlie orogen and the findings suggest that gold mineralization was not restricted to a single deformation phase but started before the kalgoorlie orogen and waned at the end of the orogeny

geochronological constraints on pre syn and postmineralization events at the world class cleo gold deposit eastern goldfields province western australia recent geological and geochronological studies have led to a reevaluation of whether or not the majority of the lode gold deposits of the yilgarn craton formed nearly synchronously during an archean craton wide hydrothermal event as previously proposed the majority of reliable data indicate that gold mineralization took place at ca 2640 to 2625 ma however recent work in the far north of the eastern goldfields province provides structural evidence for instances of earlier gold mineralization and geochronological data for interpreted postore rocks that are considerably older than 2640 ma the documentation of xenotime and monazite in association with ore minerals at the cleo deposit provides a valuable means of determining the absolute age of gold mineralization at the cleo deposit high grade western lodes veins crosscut the sunrise shear zone at a high angle with only centimeter scale offset given that the stratigraphic sequence indicates at least several hundred meters offset across the shear zone the minimal offset of the western lodes veins indicates that gold mineralization was late in the history of movement in the shear zone the absolute ages of pre syn and postmineralization elements in the mine stratigraphic succession have been determined using a variety of geochronological techniques fuchsite micas formed in the sunrise shear zone yield an 40ar 39ar isochron age of 2667 19 ma rhyodacite porphyry dikes postdate the formation of the shear zone but predate the main phase of gold mineralization dike intrusion is constrained to 2674 3 ma by shrimp ii u pb analysis of zircons from these dikes rhenium os analysis of molybdenite from quartz chalcopyrite molybdenite veins that crosscut the porphyry dikes gives an age of formation at 2663 11 ma consistent with their relationship to the porphyry dikes both the dikes and these veins are crosscut by gold bearing western lodes veins mutually crosscutting relationships with ore minerals indicate that microscopic xenotime and monazite grains were deposited during ore formation in the western lodes ore zones shrimp ii u pb analyses of xenotime and monazite grains indicate that western lodes mineralization took place at 2654 8 ma at least 9 m y after the intrusion of the porphyry dikes 95 confidence evidence for substantial temporal separation between intrusive activity and gold mineralization is recorded by other researchers for other deposits associated with granitic intrusions in the leonora laverton area phlogopitic micas from a lamprophyre that crosscuts the whole succession including the sunrise shear zone yield an ar ar plateau age of 2080 4 ma this study constrains the timing of multiple events at cleo including the main phase of gold mineralization during a relatively short span of time however in the context of the larger debate about the existence of a dominant 2640 to 2625 ma period of gold mineralization and the extent of a proposed widespread pre 2660 ma mineralization event in the yilgarn craton the data from cleo are equivocal the 2654 8 ma age for mineralization being significantly older than 2640 ma but not significantly pre 2660 ma even if the maximum possible age is accepted

architecture and geodynamic evolution of the st ives goldfield eastern yilgarn craton western australia abstract a new structural evolution consisting of both extensional and contractional events has been defined for the st ives goldfield in the south central kalgoorlie terrane of the eastern yilgarn craton in western australia these events shaped the development of the fault architecture which controlled the location of the regional anticlines the magmatic centres and the deposition of the archaean greenstone successions the fundamental grain of the st ives goldfield is north northwest trending this trend is marked by faults which developed during d1 extension which was oriented east northeast west southwest across these faults we map major stratigraphic changes in the thickness and composition of units especially of the previously undivided black flag group volcaniclastic rocks the centre of the st ives goldfield is dominated by the kambalda anticline this north northwest trending regional fold was likely established early during the d1 extensional history and was fully established during subsequent east northeast oriented d2 contraction the regional anticline is an important architectural element because 1 magmatism and gold mineralising fluids were focussed into this domed region and 2 deformation was partitioned across the limbs and crest of this structure the d3 event involved regional uplift and extension resulting in the formation of late basins merougil conglomerate locally and the emplacement of granitoids sourced from a metasomatised mantle wedge mafic type porphyries the most significant gold event in terms of endowment occurred during d4b sinistral strike slip shearing and associated thrusting e g tramways and republican thrusts these thrusts were previously interpreted as the first contractional structures to deform the area d1 but are here reinterpreted as relatively late d4b in this d4b event the north northwest trending faults underwent sinistral strike slip shearing and were linked across the kambalda anticline by accommodation structures represented by generally east to east northeast trending thrusts reactivation of d1 transfer structures may have influenced the location of these later accommodation structures late stage mineralisation during d5 was the result of dextral strike slip brittle shearing

evolutionary trend of the gorgan bay southeastern caspian sea during and post the last caspian sea level rise abstract the gorgan bay gb is a semi confined sedimentary environment at the southeastern corner of the caspian sea cs high sensitivity to eustatic sea level variations resulted in changes in the sedimentary facies and patterns of erosion sedimentation for the gb in the last caspian sea level cycle 1977 1995 therefore the evolutionary trend in coastal sedimentary environments was studied to determine the pattern of erosion and sedimentation related to sea level fluctuation cycles the sedimentology of the bay basin was studied in 500 km2 of the study area in 2001 in addition coastal changes over the two past and post periods of sea level rise were studied using satellite images landsat 7 with a resolution of 30 m and arcgis 10 1 software waves wave induced currents and sediment transport were simulated using the mike 21 software package mixed sediments particularly at the western and southern areas of the bay basin were detected through reworking of coarser barrier island sediments into deeper areas well sorted 0 35 0 5 sediments with 98 31 2 8 sand size particles were identified as the common texture along the wave dominated coasts sea progradation destruction of the beach profile and an increase in sea coverage of approximately 15 600 ha around the gb were other impacts of the cs level rise additional impacts included severe erosion and submergence of a 9000 ha area of the flat coastal plains slope 0 035 the results demonstrate that water level rise has strengthened the sediment accumulation in the bay inlet and basin at a mean rate of 0 430 mcm and 12 7 mcm respectively both field measurements and simulation results revealed the notable shoaling of the bay entrance at a mean rate of 0 2 m simulations concluded that annual longshore transport toward the bay inlet has occurred at a net rate of 80 000 m3 during the last cs level rise natural events after the eustatic cycle in the southeastern corner of the cs resulted in severe shoaling of the gb inlet and basin and restriction in the water exchange between the bay and open sea therefore comprehensive management practices to restore the gb capacity and its natural habitats are critically needed

character and regional implications of the sheared archaean granite greenstone contact near leonora western australia abstract the boundary between greenstone belt rocks and deformed domal bodies of granite and gneissic granite in the area west and northwest of leonora is marked by a wide zone of high strain within which the dominant fabric elements are parallel to the boundary the high strain zone is arcuate the granitic body is domal in form consistent sense of shear movement indicators show that the greenstones moved down relative to the granite rocks from a continuous core of 1 6 km drilled 4 km southeast of leonora exhibit mesoscale recumbent folding and ductile faulting the upper 900 m of core is characterised by recumbent flexural slip folds with half wavelengths up to 660 m separated by discrete shear zones below about 1200 m rock type and structural character change at this depth greenschistfacies rocks are juxtaposed against amphibolite facies rocks across a major ductile shear thermodynamic data give estimates of 370 c 2 1 kbar for greenschist and 610 c 5 6 kbar for amphibolite facies with high fluid pressures dominated by water in low grade rocks and co 2 in high grade ones several kilometres of section have therefore been lost across this zone the amphibolite hosts broad and narrow shear zones within which movement sense is consistently normal the structural and metamorphic data suggest that emplacement of the domal granitic and gneissic rocks was temporally linked with normal ductile shearing the regional structural setting and juxtaposition of high and low grade rocks across the shear zone with abrupt changes in temperature and fluid composition suggests that the domes were emplaced as uprising hot deep seated rock in a regional extensional tectonic environment comparable to the tectonic setting of metamorphic core complexes

geodynamics of the eastern yilgarn craton abstract over the last decade there have been significant advances in our understanding of the stratigraphy magmatism deformation metamorphism and timing of mineralisation in the eastern yilgarn craton eyc of western australia the integration of these disciplines has enabled a holistic review of the tectonic history of the eyc which favours a paraautochthonous tectonic model a significant advance has been the recognition of a 2810 ma rifting event off the eastern margin of the youanmi terrane which set up the north northwest trending architecture of the eyc rifting was followed by a 100 myr long phase of tectonic activity initiated by the establishment of a convergent margin at 2715 ma characterised by a west dipping subduction zone to the east of the eyc subduction was associated with the deposition of 2715 2670 ma volcanic stratigraphy and the emplacement of voluminous tonalite trondhjemite granodiorite magmatism which resulted in magmatic thickening of the crust volcanism was terminated by a 5 myr pulse of east northeast contraction followed by mid orogenic extension possibly linked to lithospheric and lower crustal delamination the lack of ultra high pressure metamorphism and the presence of high geothermal gradients preclude this contractional event from recording continent continent collision mid orogenic extension at 2665 ma resulted in the introduction of metasomatised mantle melts mafic granites and syenites deposition of siliciclastic basins which record metamorphic anticlockwise ptt paths and the start of significant economic gold mineralisation in the eyc high stretching factors and or delamination associated with this extension event resulted in significant heat input into the base of the crust which eventually led to the emplacement of low ca crustal melt granites and cratonisation of the eyc major gold mineralisation postdates mid orogenic extension and was associated with renewed compression transpression 2650 ma and the development of steep predominantly north northwest striking sinistral and later north to north northeast striking dextral strike slip faults during low ca granite emplacement

lithofacies and ichnofacies distribution in offshore sediments of the langarud rudsar region of iran southern caspian sea innovative computerized co axial tomography cat scan methods have been applied to two short cores collected in the southern caspian sea offshore from the langarud rudsar region of iran to the east of the sefidrud delta magnetic susceptibility ms readings in association with other lithological criteria are used to correlate the cores and calibrate to real time the cores provide a sedimentary record from this largely unstudied region covering the last 200 years 1784 to 2008 ce three principal lithofacies types were recognized the more distal locality t2 3 water depth 117 m consists entirely of poorly fossiliferous silty muds whereas the more proximal locality t2 2 water depth 51 m contains beds with rich ostracod gastropod and bivalve assemblages peak ms readings occur between 1872 and 1918 ce and are linked to erosion of sediments deposited during the little ice age lia highstands of the caspian sea cat scan results reveal the presence of the non marine mermia ichnofacies type which is reported for the first time in the caspian sea horizontal burrows feeding structures by treptichnus ichnofauna coincide with periods of lia highstand in caspian sea level and suggest low energy conditions on the marine shelf vertical burrows feeding structures occur at times of relatively stable but variable caspian water levels interbedded dark coloured organic rich muds and lighter silt rich layers within the last 100 years show potential cyclicity which may be linked to climatic and or river discharge events

propagation mechanism of long period ground motions for offshore earthquakes along the nankai trough effects of the accretionary wedge a thick accretionary wedge with low seismic velocity overlying a subducting plate is an important factor affecting the amplitudes and durations of long period ground motions for great offshore earthquakes we performed a series of 3d long period ground motion simulations to obtain a better understanding of the effects of the accretionary wedge along the nankai trough japan the simulation results demonstrate that the accretionary wedge has the effect of decreasing the peak amplitude and velocity response but amplifying and elongating later phases of long period ground motions in the land area these effects depend significantly on the focal depth and are pronounced for shallow seismic sources the amplified and elongated later phases originate mainly from prominent basin induced surface waves excited near the trough axis we also identified hard sediments with intermediate s wave velocity in the accretionary wedge as a key layer that enhances the propagation of long period ground motions from offshore to onshore in the case of the nankai trough the hard sediments allow long period ground motions developed inside the accretionary wedge to be efficiently transmitted outward in the longer period than 10 s comparisons between the observed and simulated records suggest that for more accurate predictions of long period ground motions velocity structure models of not only the accretionary wedge but also the surrounding upper crust should be validated and revised using seafloor observations

rapid holocene sea level changes along the iranian caspian coast abstract the caspian sea is well known for its rapid sea level change during 1929 1995 a full sea level cycle was observed first the sea level dropped 3 m with a lowstand in 1977 followed by a 3 m rise to 1995 after which the sea level has been relatively stable these oscillations are a specific feature of the caspian sea and its sedimentary record the main purpose of this study is to reconstruct the sea level curve in the holocene by using sedimentological and biostratigraphic analysis and radiocarbon dating along the iranian part of the caspian shore remote sensing images and historical maps show that two lagoons totally emerged and the gorgan delta prograded rapidly at a rate of around 160 m y 1 until the 1975 lowstand gorgan bay was reduced in size considerably and the connection to the sea was blocked due to growth of a spit and change in base level when sea level started to rise again the coastal morphology rapidly changed and the gorgan delta retrograded at the rate of around 140 m y 1 these sedimentary dynamics can be recognized in the preserved deposits in addition to the recent dynamics core data from the southeastern lowlands show four earlier highstands using characteristic barrier lagoon deposits early holocene sea level rose until a highstand was reached of ca 34 m this phase was followed by fluvial deposition in the gorgan delta associated with a base level fall there is also an evidence of sea level rise between 5000 and 2300 bp at ca 27 7 m on top of these deposits there is evidence of a highstand between 2700 and 2300 bp at ca 23 5 m the fourth highstand from the core data is dated to the little ice age at ca 24 m data from these last two highstands correspond well with other observations from the caspian region

multistage gold mineralization at the lapa mine abitibi subprovince insights into auriferous hydrothermal and metasomatic processes in the cadillac larder lake fault zone the lapa gold deposit contains reserves of 2 4 mt at 6 5 g t au and is one of the few deposits located directly within the cadillac larder lake fault zone cllfz a first order crustal scale fault that separates the archean abitibi subprovince from the pontiac subprovince to the south gold mineralization is predominantly hosted in highly strained and altered upper greenschist lower amphibolite facies mafic to ultramafic rocks of the piche group auriferous ore zones consist of finely disseminated auriferous arsenopyrite pyrrhotite pyrite and native gold disseminated in biotite and carbonate altered wall rocks native gold which is also present in quartz dolomite calcite veinlets is locally associated with sb bearing minerals especially at depth 1 km from surface where the deposit is characterized by a au sb as association at vertical depth greater than 1 km gold is associated with arsenopyrite and pyrrhotite au as association the mineralogy and paragenesis of the lapa deposit metamorphosed ore and alteration assemblages record the superposition of three metamorphic episodes m1 m2 and m3 and three gold mineralizing events spatial association between biotitized wall rocks and auriferous arsenopyrite indicates that arsenopyrite precipitation is concomitant with potassic alteration the predominant au as association recognized across the deposit is related to gold in solid solution in arsenopyrite as part of a pre m2 low grade auriferous hydrothermal event however the occurrence of hornblende oligoclase porphyroblasts overprinting the biotite alteration and the presence of porous clusters and porphyroblasts of arsenopyrite with native gold and pyrrhotite indicate an auriferous metasomatic event associated with peak m2 prograde metamorphism late retrograde metamorphism m3 overprints the hornblende oligoclase m2 assemblage within the host rocks proximal to ore by an actinolite albite assemblage by precipitation of free gold and sb sulfosalts at lower p t the complex relationships between ore structural features and metamorphic assemblages at lapa are related to the tectonometamorphic evolution of the cadillac larder lake fault zone at different times and crustal levels and varying heat and fluid flow regimes the lapa deposit demonstrates that early low grade gold mineralization within the cadillac larder lake fault zone has benefited from late gold enrichment s during prograde and retrograde metamorphism suggesting that multi stage processes may be important to form gold rich orogenic deposits in first order crustal scale structures

orogenic gold common or evolving fluid and metal sources through time abstract orogenic gold deposits of all ages from paleoarchean to tertiary show consistency in chemical composition they are the products of aqueous carbonic fluids with typically 5 20 mol co 2 although unmixing during extreme pressure fluctuation can lead to entrapment of much more co 2 rich fluid inclusions in some cases ore fluids are typically characterized by significant concentrations of ch 4 and or n 2 common estimates of 0 01 0 36 mol h 2 s a near neutral ph of 5 5 and salinities of 3 7 wt nacl equiv with na k ca mg this fluid composition consistency favors an ore fluid produced from a single source area and rules out mixing of fluids from multiple sources as significant in orogenic gold formation nevertheless there are broad ranges in more robust fluid inclusion trapping temperatures and pressures between deposits that support a model where this specific fluid may deposit ore over a broad window of upper to middle crustal depths much of the reported isotopic and noble gas data is inconsistent between deposits leading to the common equivocal interpretations from studies that have attempted to define fluid and metal source areas for various orogenic gold provinces fluid stable isotope values are commonly characterized by the following ranges 1 18 o for precambrian ores of 6 to 11 and for phanerozoic ores of 7 to 13 2 d and 34 s values that are extremely variable 3 13 c values that range from 11 to 2 and 4 15 n of 10 to 24 for the neoarchean 6 5 to 12 for the paleoproterozoic and 1 5 to 10 for the phanerozoic secular variations in large scale earth processes appear to best explain some of the broad ranges in the o s and n data fluid rock interaction particularly in ore trap areas may cause important local shifts in the o s and c ratios the extreme variations in d mainly reflect measurements of hydrogen isotopes by bulk extraction of waters from numerous fluid inclusion generations many which are not related to ore formation radiogenic isotopes such as those of pb sr nd sm and os measured on hydrothermal minerals are even more difficult to interpret for defining metal source particularly as the low salinity ore fluids transport limited amounts of these elements and significant amounts of these may be locally added to the minerals during alteration reactions at the sites of gold deposition noble gas and halogen data are equally equivocal fluid exsolution from granitoids emplaced into the upper and middle crust metamorphism of the crust or fluids entering trans crustal fault zones from below the crust all remain as permissive scenarios associated with orogenic gold formation as the abundant geochemical data are equivocal however geological and geochronological data weigh heavily against a magmatic hydrothermal model in the upper to middle crust there is no universal temporal association between orogenic gold and magmatism and where there is an overlap in age there is no specific type of magmatism consistently associated with gold formation nor element zonation around any specific pluton a crustal metamorphic model for fluid and metal sources is very consistent with geological geochronological and geochemical data although metamorphism on a regional scale that releases these components into major fault zones can be associated with many processes along active continental margins these can include crustal thickening and radiogenic heating slab rollback and heating during crustal extension or subduction of a spreading ridge heating the base of an accretionary prism in rare examples where phanerozoic orogenic gold deposits are hosted in precambrian high grade metamorphic terranes fluids and metals must however enter a transcrustal fault system from a sub crustal source this could either be a devolatilized subducted relatively flat perhaps stalled slab and its overlying sediment or the corner of the fertilized mantle wedge that releases a fluid during a thermal event