sedimentological characteristics and depositional processes of sediment gravity flows in rift basins the palaeogene dongying and shahejie formations bohai bay basin china abstract sediment gravity flow deposits are common particularly in sandy formations but their origin has been a matter of debate and there is no consensus about the classification of such deposits however sediment gravity flow sandstones are economically important and have the potential to meet a growing demand in oil and gas exploration so there is a drive to better understand them this study focuses on sediment gravity flow deposits identified from well cores in palaeogene deposits from the liaodong bay depression in bohai bay basin china we classify the sediment gravity flow deposits into eight lithofacies using lithological characteristics grain size and sedimentary structures and interpret the associated depositional processes based on the scale spatial distribution and contact relationships of sediment gravity flow deposits we defined six types of lithofacies associations las that reflect transformation processes and depositional morphology la1 unconfined proximal breccia deposits la2 confined channel deposits la3 braided channel lobe deposits la4 unconfined lobe deposits la5 distal sheet deposits and la6 non channelized sheet deposits finally we established three depositional models that reflect the sedimentological characteristics and depositional processes of sediment gravity flow deposits 1 slope apron gravel rich depositional model which involves cohesive debris flows deposited as la1 and dilute turbidity currents deposited as la5 2 non channelized surge like turbidity current depositional model which mainly comprises sandy slumping suspended load dominated turbidity currents and dilute turbidity currents deposited as la5 and la6 and 3 channelized subaqueous fan depositional model which consists of non cohesive bedload dominated turbidity currents suspended load dominated turbidity currents and dilute turbidity currents deposited as la2 la5 originating from sustained extrabasinal turbidity currents hyperpycnal flow the depositional models may be applicable to oil and gas exploration and production from sediment gravity flow systems in similar lacustrine depositional environments elsewhere

late archaean deep marine volcaniclastic sedimentation in an arc related basin the kalgoorlie sequence of the eastern goldfields superterrane yilgarn craton western australia abstract the kalgoorlie sequence 2658 ma is a 3000 m thick succession of volcaniclastic sedimentary rocks and subordinate rhyolite dacite andesite and basalt spatially and temporally associated with subvolcanic sills and dykes of rhyolite and dacite gabbro sills and i type granitoids although basalts are tholeiitic the felsic rocks have ttd affinity the sequence comprises mostly deep marine channel levee turbidite complexes and hemipelagites resedimented syneruptive volcaniclastic deposits are associated with coherent lavas but almost all of the sedimentary fill was recycled from prior cycle volcanic and volcaniclastic sources provenance was mainly dacitic rhyolitic with minor andesitic basaltic and polymictic compositions volcano bound and fault bound architectures and two styles of basin filling are identified progradational or aggradational transverse fans and slope aprons and retrogradational longitudinal fans of a linear trough retrogradation in longitudinal systems is consistent with basin lengthening and deepening six depositional sequences are grouped in four unconformity bounded tectonic stages that record uplift subsidence cycles coeval mafic and felsic magmatism indicate that the tectonic stages represent extensional tectonic settings whereas volcanogenic provenance spatially linked volcanism and plutonic magmatism and deep marine environments support an intra arc site cyclic uplift subsidence and basin lengthening are more consistent with strike slip controls on basin formation than with orthogonal extension the tectonic setting is interpreted to have been a pull apart basin associated with strike slip faulting and amalgamating arc related terranes similar to the modern philippines archipelago the strong similarity between archaean volcaniclastic and modern arc related volcaniclastic environments implies comparable tectonic settings and therefore comparable controlling tectonic factors

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

the late archaean melita complex eastern goldfields western australia shallow submarine bimodal volcanism in a rifted arc environment abstract the melita volcanic complex is a late archaean bimodal rhyolite basalt volcanic succession within the gindalbie terrane in the eastern goldfields province of the yilgarn craton the melita complex has been dated by ion probe at 2683 3 ma 95 and forms part of a distinctive 2681 2692 ma volcanic association that records bimodal basalt rhyolite and calc alkaline intermediate silicic volcanism at several discrete volcanic centres and which locally hosts volcanic massive sulphide mineralisation teutonic bore approximately 3 km of stratigraphic thickness is exposed in the melita area the upper 1 1 5 km of the exposed succession is dominated by subaqueously resedimented volcaniclastic sandstones and breccias rhyolite flows and sills primary subaerial pyroclastic deposits including ignimbrites have not been identified in this study although subaerial explosive activity is indicated by the occurrence of accretionary lapilli and the abundance of vitric material shards and pumice fragments in resedimented deposits the lower part of the succession is dominated by pillowed to massive basalt lavas and in situ and resedimented mafic hyaloclastites mafic extrusive and intrusive rocks are tholeiitic with trace element concentrations similar to modern arc tholeiites felsic volcanic rocks at melita are dacite to high silica rhyolite they are highly enriched in incompatible elements particularly high field strength element enriched compared to other felsic associations in the eastern goldfields province representing evolved partial melts of heterogeneous intermediate arc type crust the volcanic facies and geochemistry of volcanic rocks at melita are consistent with those observed in modern intra arc or arc rift settings and the succession is interpreted to represent the initial stages of back arc rifting within a complex convergent margin

the marinduque intra arc basin philippines basin genesis and in situ ophiolite development in a strike slip setting the marinduque basin is a marine intra arc basin in the north central philippine volcanic arc system a suite of marine geophysical observations show the basin as a whole to be rhombic in shape with its long axis trending north northwest a conspicuous volcanic ridge trends east northeast across the basin dividing it into two smaller active depocenters symmetric linear magnetic anomalies striking parallel to and centered over the central volcanic ridge indicate that it formed by extension in a north south direction by a process analogous to sea floor spreading geometric and temporal relations between the central volcanic ridge and several en echelon sets of north trending left stepping faults indicate that sea floor spreading occurred in the extensional stepover zone of a left lateral strike slip fault system and that the marinduque basin as a whole is a composite pull apart basin whose floor is in part composed of oceanic type crust the evolution of the central volcanic ridge presents an actualistic model for in situ development and emplacement of ophiolites in an island arc setting the presently active left lateral philippine fault zone truncated the eastern flank of the basin as well as the central volcanic ridge following their initial formation shortening associated with a probable restraining bend in the philippine fault has resulted in uplift of basin flank sediments which have been thrust back toward the basin interior the philippine fault has also displaced fragments of the ridge and basin floor toward the north the overall history of the marinduque basin further suggests that strike slip processes may play an important role in the origin and growth of intra arc basins such basins may ultimately become isolated in a forearc or backarc setting

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

initiation of subduction and the generation of slab melts in western and eastern mindanao philippines adakite found in both the eastern and western parts of mindanao island philippines is a rare rock type characterized by low heavy rare earth elements and y contents together with high sr y ratios and is considered to be the result of the melting of young subducted oceanic crust which leaves an eclogite residue pliocene quaternary adakites from western mindanao zamboanga peninsula are probably derived from the melting of the young miocene sulu sea crust which is currently subducting beneath zamboanga associated nb enriched basalts are thought to come from mantle metasomatized through interaction with adakitic melts in eastern mindanao pliocene quaternary cones and plugs of typical adakitic composition mark the trace of the philippine fault in surigao and north davao the underlying philippine sea crust is of eocene age and therefore cannot melt under normal subduction thermal conditions thermal models indicate that melting at the start of subduction can occur subduction of the philippine sea plate began 3 to 4 ma beneath eastern mindanao and probably accounts for the presence of adakites along the philippine fault

detrital zircon age spectra for late archaean synorogenic basins of the eastern goldfields superterrane western australia abstract the kalgoorlie gindalbie kurnalpi duketon and burtville terranes were amalgamated by 2658 ma into the eastern goldfields superterrane which was later accreted cordilleran style onto the foreland of a pre existing continent late stage synorogenic basins developed within the eastern goldfields superterrane during the early stage of accretion the basins are similar to all late stage basins of archaean provinces developing late in the tectonic cycle in a strike slip regime they developed in two stages during the gap in granite emplacement between 2658 ma and 2648 ma basin analysis suggests that the bulk of sediments was derived from rocks readily identifiable today within the superterrane consistent with the provenance style of all late stage basins sediment derivation from the foreland occurred only during stage ii and is recorded only from basins proximal to the suture detrital zircon geochronology has corroborated those interpretations eleven new shrimp u pb detrital zircon datasets and 14 previously published datasets indicate that the bulk of zircon bearing sediment was derived from the 2715 ma to 2658 ma high ca ttg granites and volcanic rocks that define the terranes moreover primary modes in the detrital zircon age spectra of 2680 3 ma 2673 ma 2666 3 ma and 2660 3 ma coincide with the peaks of emplacement of high ca granites provenance from across the suture has also been corroborated with detrital zircon age spectra of the kurrawang basin a stage ii basin close to the suture having no match to rocks of the eastern goldfields superterrane defining modes of 2730 ma and 3000 ma some as old as 3750 ma and 3540 ma can be matched to an 2735 ma calc alkaline volcanic province and quartzites with 4350 3130 ma detrital zircon in the foreland the study shows that detrital zircon age spectra can be powerful supporters of tectonic analysis but for the study presented here their interpretation has been greatly assisted by prior basin analysis and a considerable geochronological database of source rock equivalents

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

a volcaniclastic deep sea fan off la reunion island indian ocean gradualism versus catastrophism a new geophysical data set off la reunion island western indian ocean reveals a large volcaniclastic submarine fan developing in an open ocean setting the fan is connected to a torrential river that floods during tropical cyclones sediment storage at the coast is limited suggesting that the sediments are carried directly to the basin the fan morphology and turbidites in cores lead us to classify it as a sand rich system mainly fed by hyperpycnal flows in the ancient geological record there are many examples of thick volcaniclastic successions but studies of modern analogues have emphasized mechanisms such as debris avalanches or direct pyroclastic flow into the sea because the cilaos deep sea fan is isolated from any continental source it provides information on architecture and noncatastrophic processes in a volcaniclastic deep sea fan

modern sand rich and mud rich siliciclastic aprons alternative base of slope turbidite systems to submarine fans base of slope aprons that lack significant channel development and are fed by multiple sediment sources i e numerous slope failures or debris chutes represent an alternative facies organization to submarine fans that possess channels and are fed by canyon point sources of allochthonous sediment two styles of base of slope apron deposition are evident 1 sand rich aprons with rhythmic gradational sand and gravel sheets that evolve to basin plain turbidites as exemplified by crater lake aprons and 2 mud rich aprons composed of chaotic sediment flow lobes without gradation as exemplified by ebro margin aprons

a 3 d geological and structural synthesis of the leinster area of the agnew wiluna belt yilgarn craton western australia with special reference to the volcanological setting of komatiite associated nickel sulfide deposits the leinster area is situated toward the southern end of the agnew wiluna belt in the yilgarn craton of western australia and hosts the giant perseverance komatiite associated nickel sulfide deposit at in excess of 1 2 mt contained ni this is the biggest type 1 basal sulfide rich accumulation deposit in the world and it is associated with a number of smaller deposits that extend over a strike length of 20 km adjacent to the perseverance fault on the eastern margin of the belt in broad terms the greenstone sequence comprises an eastern rift proximal komatiite dacite sequence and a western and more marginal basalt dominated sequence with minor komatiite the komatiites display a wide range of compositions and textures from highly magnesian olivine meso to adcumulate rocks composed of olivine with forsterite contents of up to 94 5 to sequences of thin spinifex textured komatiite flow units this compositional range indicates considerable variation in volcanic facies from rift proximal to distal loci of focused flow termed pathways indicated by thickened cord like bodies of more olivine rich rock occur at all scales and are intimately associated with the ni sulfide mineralization the pathways are linked by thinner sequences of lower mgo rocks either layered olivine orthocumulate rocks or sequences of thin spinifex textured flow units some of the lower mgo komatiite sequences appear to emanate from the tops of pathways in the manner of breakout flows in tube fed basaltic terrains variably sulfidic black shales and cherts and barren exhalative iron sulfide horizons are intimately interlayered with the komatiitic rocks the overprinting effects of regional deformation and metamorphism spanning at least 80 m y are considerable at least eight local deformation events have been recognized by previous workers these have been used to constrain the 3 d model and can be linked to craton wide structural schemes some of the major faults are clearly accretionary and reflect reactivation of underlying basin forming structures early north over south thrusting was followed by e w directed basin closure and the development of nnw trending open regional folds extension accompanied batholithic granitoid intrusion and reactivated rift parallel nnw trending faults producing the major strike slip fault systems that divide the greenstone succession into a series of structural and stratigraphic domains the ensuing orogenic collapse resulted in overturning of the stratigraphy to the east subsequent brittle deformation events have produced fault sets in a variety of orientations that can be related to ongoing shortening with a variable principal stress orientation there is a complex interplay of structural and volcanological controls on the formation and subsequent deformation of the ni sulfide deposits in this ancient terrane three dimensional modeling has furthered a detailed understanding of the geologic and structural evolution of the belt allowed the identification of komatiite pathway positions and their plunges and provided quantitative data on the magnitude and direction of fault offsets of different generations the modeling exercise has shown that it is possible to strip away the effects of overprinting metamorphism and deformation to reveal some of the primary controls on komatiite volcanism and the location of ni sulfide deposits even in those portions of greenstone belts that are highly deformed and have undergone amphibolite facies metamorphism this is illustrated with case studies of the perseverance venus rocky s reward harmony and sir lancelot deposits three dimensional modeling has the capacity to integrate geologic geochemical and geophysical datasets in a way that fully utilizes the results of past exploration programs and produces a premium geologic product that can be used to guide further exploration the recent discovery of the venus deposit is in part a tribute to the power of this approach

metamorphic evolution of the coesite bearing ultrahigh pressure terrane in the north qaidam northern tibet nw china widespread evidence for ultrahigh pressure uhp metamorphism is reported in the dulan eclogite bearing terrane the north qaidam altun hp uhp belt northern tibet this includes 1 coesite and associated uhp mineral inclusions in zircon separates from paragneiss and eclogite identified by laser raman spectroscopy 2 inclusions of quartz pseudomorphs after coesite and polycrystalline k feldspar quartz in eclogitic garnet and omphacite and 3 densely oriented sio2 lamellae in omphacitic clinopyroxene these lines of evidence demonstrate that the dulan region is a uhp metamorphic terrane in the north dulan belt ndb eclogites are characterized by the peak assemblage grt omp rt phn coe pseudomorph and retrograde symplectites of cpx ab and hbl pl the peak conditions of the ndb eclogites are p 2 9 3 2 gpa and t 631 687 c the eclogite shows a near isothermal decompression p t path suggesting a fast exhumation in the south dulan belt sdb three metamorphic stages are recognized in eclogites 1 a peak eclogite facies stage with the assemblage grt omp ky rt phn at p 2 9 3 3 gpa and t 729 746 c 2 a high pressure granulite facies stage with grt cpx jd 30 pl an24 29 scp at p 1 9 2 0 gpa t 873 948 c and 3 an amphibolite facies stage with the assemblage hbl pl ep czo at p 0 7 0 9 gpa and t 660 695 c the clockwise p t path of the sdb eclogites is different from the near isothermal decompression p t path from the ndb eclogites which suggests that the sdb was exhumed to a stable crustal depth at a slower rate in essence these two sub belts formed in different tectonic settings they both subducted to mantle depths of around 100 km but were exhumed to the earth s surface separately along different paths this uhp terrane plays an important role in understanding continental collision in north western china

ten turbidite myths abstract during the past 50 years the turbidite paradigm has promoted many myths related to deep water turbidite deposition john e sanders 1926 1999 a pioneering process sedimentologist first uncovered many of these turbidite myths this paper provides a reality check by undoing 10 of these turbidite myths myth no 1 turbidity currents are non turbulent flows with multiple sediment support mechanisms reality turbidity currents are turbulent flows in which turbulence is the principal sediment support mechanism myth no 2 turbidites are deposits of debris flows grain flows fluidized flows and turbidity currents reality turbidites are the exclusive deposits of turbidity currents myth no 3 turbidity currents are high velocity flows and therefore they elude documentation reality turbidity currents operate under a wide range of velocity conditions myth no 4 high density turbidity currents are true turbidity currents reality ph h kuenen 1950 introduced the concept of turbidity currents of high density based on experimental debris flows not turbidity currents high density turbidity currents are sandy debris flows myth no 5 slurry flows are high density turbidity currents reality slurry flows are debris flows myth no 6 flute structures are indicative of turbidite deposition reality flute structures are indicative only of flow erosion not deposition myth no 7 normal grading is a product of multiple depositional events reality normal grading is the product of a single depositional event myth no 8 cross bedding is a product of turbidity currents reality cross bedding is a product of traction deposition from bottom currents myth no 9 turbidite facies models are useful tools for interpreting deposits of turbidity currents reality a reexamination of the annot sandstone in se france which served as the basis for developing the first turbidite facies model suggests a complex depositional origin by plastic flows and bottom currents myth no 10 turbidite facies can be interpreted using seismic facies and geometries reality individual turbidity current depositional events commonly centimeters to decimeters in thickness cannot be resolved in seismic data all turbidite myths promote falsehood and should be abandoned

visible and near infrared multispectral analysis of rocks at meridiani planum mars by the mars exploration rover opportunity multispectral measurements in the visible and near infrared of rocks at meridiani planum by the mars exploration rover opportunity s pancam are described the pancam multispectral data show that the outcrops of the burns formation consist of two main spectral units which in stretched 673 535 432 nm color composites appear buff and purple colored these units are referred to as the hfs and lfs spectral units based on higher and lower values of 482 to 535 nm slope spectral characteristics are consistent with the lfs outcrop consisting of less oxidized and the hfs outcrop consisting of more oxidized iron bearing minerals the lfs surfaces are not as common and appear primarily at the distal ends of outcrop layers and on steep more massive surfaces locations that are subject to greater eolian erosion consequently the hfs surfaces are interpreted as a weathering rind further inherent spectral differences between layers and between different outcrop map units both untouched and patches abraded by the rover s rock abrasion tool are also described comparisons of the spectral parameters of the meridiani outcrop with a set of laboratory reflectance measurements of fe 3 bearing minerals show that the field of outcrop measurements plots near the fields of hematite ferrihydrite poorly crystalline goethite and schwertmannite rind and fracture fill materials observed intermittently at outcrop exposures are intermediate in their spectral character between both the hfs and lfs spectral classes and other less oxidized surface materials basaltic sands spherules and cobbles

4d history of the nimbus vhms ore deposit in the yilgarn craton western australia abstract due to its unique mineralogy in the archaean yilgarn craton the origin of the high grade nimbus ag zn au deposit has been contentious for a number of years recent interpretations of the deposit as a shallow water and low temperature volcanic hosted massive sulphide vhms deposit with epithermal characteristics i e a hybrid bimodal felsic deposit were based on detailed studies of its volcanology mineralogy hydrothermal alteration assemblages geochemistry multiple s isotopes and trace element content of sulphide however this model has been questioned in favour of a late epithermal fault hosted system effective greenfields exploration for similar deposits elsewhere requires a robust deposit model and well understood timing of ore formation we present a comprehensive multi disciplinary study to further constrain the processes involved in the evolution of nimbus and generate a 4d evolutionary model of the system host rock dacite formation is well constrained by shrimp u pb zircon geochronology to c 2703 ma re os ages for the first sulphide phase gives an imprecise maximum age to the ore formation of 2682 110 ma high precision pb isotope variations in ore stage and late galenas track changes in the sulphides over time complemented by new geochronology the pb isotope data indicates that the polymetallic ore precipitation happened at the same time as the volcanism with the second generation indicating minor local remobilisation of pb in late quartz carbonate veins at c 2630 ma 40ar 39ar dating of sericite altered plagioclase from foliated dacite and u pb shrimp dating of syn to post deformation monazites have yielded ages of 2630 ma the late event at c 2630 ma is most likely related to widespread late low ca granite emplacement across the eastern goldfields this study provides arguments that suggest that nimbus is a syn volcanic deposit the ore timing is consistent with the model of replacement type vhms deposit with the age of the main mineralisation similar to the age of the dacitic host rocks at 2703 ma the late event modifies the pre existing ore and overprints the previous ore related alteration ages from the altered plagioclase high precision double spiked pb isotope constraints from late quartz carbonate veins provides an opportunity to vector to hidden deposits

evolution of the archaean granite greenstone terranes of the eastern goldfields western australia shrimp upb zircon constraints abstract thirty five high precision shrimp u pb zircon dates with an average 95 confidence error of 6 ma have been obtained from the granite greenstone terranes in the southern part of the eastern goldfields of western australia these dates establish the timing of major deformation metamorphism and granite intrusion events and test inferred stratigraphic relationships within the greenstones these new data reveal that felsic volcanic rocks were erupted throughout the southern part of the eastern goldfields between c 2713 and c 2672 ma analytically indistinguishable dates of c 2705 ma were obtained for felsic volcanic rocks interbedded with komatiitic lavas at three sites dates on felsic volcanic rocks within tectonostratigraphic packages that include komatiites are also consistent with an inferred eruption age for these komatiites of c 2705 ma komatiitic lavas in the southern part of the eastern goldfields were probably emplaced during a single voluminous eruption that resulted in the flooding of a vast area of the late archaean landscape filling the topographic lows around older felsic volcanic vents the stratigraphic complexity within tectonostratigraphic domains is attributed to the existence of an undulating topography during the eruption of the mafic and ultramafic lavas and to the rapid and localized deposition of felsic volcanic rocks close to a number of isolated volcanic centres prior to and after the komatiite lava eruption event between c 2685 and c 2675 ma early pre d2 intrusive equivalents of the felsic volcanic rocks were emplaced as thick granite sheets into the base of the greenstone sequences regional east west compression between c 2675 and c 2657 ma reactivated early extensional structures and resulted in the stacking of the greenstones this was accompanied by further intrusion of granite within developing antiforms burial of greenstone slices by stacking and the effect of hydrothermal fluids emanating from both the granites and buried greenstones resulted in regional metamorphism to greenschist facies prior to c 2640 ma monzogranite and granodiorite emplaced near the western southern and eastern margins of the greenstones were deformed and metamorphosed to upper amphibolite facies and converted into gneisses during d2 and d3 compression events movement along large scale transcurrent d3 shear zones had ceased by c 2635 ma remnants of a c 2958 to c 2930 ma greenstone sequence preserved near norseman and ravensthorpe in the southeastern yilgarn craton and xenocryst zircons ranging in age from c 2910 2730 ma in the c 2713 2672 ma felsic volcanic rocks indicate that the exposed greenstone sequences were deposited on continental basement the eastern goldfields granite greenstone terranes were formed by the closure of a series of narrow back arc rift basins that developed along a continental margin and above an active subduction zone located to the east of the rift basins

comparison of turbidite facies associations in modern passive margin mississippi fan with ancient active margin fans abstract our comparison of the modern passive margin mississippi fan dsdp leg 96 with ancient active margin fans e g eocene hecho group spain reveals major differences in turbidite facies associations mutti and ricci lucchi scheme and in seismic characteristics in the lower fan area the lower outer mississippi fan is composed of channel facies b and f and non channel facies c and d whereas ancient fans are characterized by non channelized thickening upward depositional lobe facies c and d an absence of depositional lobes in the lower mississippi fan is also suggested by a lack of convex upward mounded seismic reflections with bidirectional downlap continuous seismic reflections of the lower mississippi fan may represent sheet sands but not those of true depositional lobes with mounded character extensive channelization in modern passive margin fans appears to be a product of the lateral shifting of a major sinuous distributary system developed as a consequence of low gradients and the transport of sediment with a relatively low sand mud ratio in contrast channels in active margin fans are short and of low sinuosity as a result of high gradients and the transport of sediment with a relatively high sand mud ratio the turbidite facies association scheme which was developed exclusively from ancient active margin fans should be applied to mature passive margin fans with qualifications because of the differences in spatial distribution of turbidite facies and their associations

coarse grained submarine fan and slope apron deposits in a cretaceous back arc basin antarctica the cretaceous of west james ross island antarctica represents the proximal fill of a late mesozoic back arc basin that was probably initiated by oblique extension during the early development of the weddell sea the succession records sedimentation in two contrasting depositional systems a laterally persistent slope apron flanking the faulted basin margin interrupted both spatially and temporally by coarse grained submarine fans slope apron deposits are dominated by thinly interbedded turbiditic sandstones and mudstones mudstone association interspersed with non channelized chaotic boulder beds intraformational slump sheets and isolated exotic blocks representing a spectrum of mass flow processes from debris flow to submarine gliding localized sand rich sequences sandstone breccia association represent sandy debris lobes at the mouths of active slope chutes the submarine fan sediments conglomerate association are typified by coarse conglomerates and pebbly sandstones interpreted as the deposits of high density turbidity currents and non cohesive debris flows three assemblages are recognized and are suggested to represent components of the inner channelled zone of coarse grained submarine fans from major fan channels through ephemeral marginal channels or terraces to levee or interchannel environments the occurrence of both slope apron and submarine fan depositional systems during the early and mid cretaceous is attributed to localized input of coarse arc derived sediment along a tectonically active basin margin periods of extensive fan development were probably linked to regional tectonic uplift and rejuvenation of the arc source region cyclicity within individual fan sequences is attributed to migration or switching of fan channels or canyons slope apron sedimentation was controlled largely by intrabasinal tectonics local unconformities and packets of amalgamated slide sheets and debris flow deposits probably reflect episodic movement on basin margin faults differential subsidence across the basin margin anchored the basin slope for at least 20 myr and precluded basinward progradation of shallow marine environments

the tectonic setting and evolution of the 2 7 ga kalgoorlie kurnalpi rift a world class archean gold province the yilgarn craton results from three major mantle input events at ca 3 0 2 9 2 8 and 2 7 ga that have interacted with 3 0 ga continental crust zircon geochronology and sm nd isotopic data subdivide the craton into an older yilgarn proto craton and the younger more primitive eastern goldfields superterrane egst formation of the kalgoorlie kurnalpi rift kkr within the egst was associated with the 2 7 ga event which exploited weakened crust at the eastern margin of the yilgarn proto craton where thick sequences of komatiite and basalt were erupted between ca 2710 and 2690 ma in the kalgoorlie terrane calc alkaline volcanism in the kurnalpi terrane began at ca 2730 ma and continued to ca 2690 ma overlapping rifting and plume related volcanism in the kalgoorlie terrane deposition of siliciclastic sedimentary rocks within basins at ca 2660 resulted from an intra orogenic extensional event and coincided with the transition from high ca to low ca granite magmatism and peak emplacement of intrusions with a metasomatised mantle source component most aspects of the kkr are satisfied by broadly coincident plume related magmatism in the kalgoorlie terrane and westward subduction to the east of the burtville terrane geochemical characteristics of 2730 2700 ma calc alkaline volcanism and 2685 2630 ma low sio2 and alkali rich intrusions support models for a continental margin subduction zone setting world class gold deposits formed in reactivated margins of the kkr which became flux zones for mantle derived magmas hydrothermal fluids and heat during 2675 2620 ma orogenesis the orogenic gold mineralisation can be subdivided into proximal intrusion related and distal source deposits

element mobility and spatial zonation associated with the archean hamlet orogenic au deposit western australia implications for fluid pathways in shear zones mass balance equations can be used to understand metasomatism here we use 2726 multi element chemical analyses to quantify the effect of metasomatism associated with au mineralisation at the hamlet gold mine hamlet yilgarn craton western australia principal components analysis is first used to identify covarying elements and six groups of elements are identified 1 relatively immobile elements with zr and hf providing an appropriate reference frame for mass balance calculations 2 elements associated with mafic rocks such as ca co fe ge mg mn and zn 3 elements related to potassic alteration ba cs k rb and tl 4 elements related to sodic alteration be na and sr 5 chalcophile elements including bi weakly associated with au and 6 au te and s representing the main au mineralising event a statistically rigorous approach is then used to quantify element addition and depletion and provides 95 confidence limits for changes in mass to achieve this the basaltic host rocks are divided into four subunits based on cr content sample subsets are then created to select altered rocks and least altered protolith rocks using discrimination diagrams pairings of least altered altered samples from each basalt subunit are used to construct matrices via bootstrapping mass balance results from these matrices indicate similar element mobility associated with au mineralisation across the four basalt subunits with up to 24 mass loss key potassic and sodic group elements are enriched in the au mineralised zones at the expense of elements with a mafic association spatial patterns of mass change are linear and repetitive within the steeply dipping hamlet shear zone interpreted to represent a mesh like geometry of metasomatism within the plane of the shear zone localised enrichment of k na and bi are related to au distribution while ca depletion zones reflect the movement of reactive fluid along the shear plane

paragenesis and composition of ore minerals in the randalls bif hosted gold deposits yilgarn craton western australia implications for the timing of deposit formation and constraints on gold sources the randalls district comprises three individual gold deposits cock eyed bob maxwells and santa craze hosted in the same unit of banded iron formation bif in the southern eastern goldfields superterrane yilgarn craton western australia the iron formation is a silicate oxide facies unit with overprinting sulfides and has undergone metamorphism upper greenschist facies and deformation two generations of folds the gold deposits are hosted in two structural locations hinge zones of anticlinal folds e g santa craze and maxwells and overturned steeply dipping limbs of anticlinal folds e g cock eyed bob gold dominantly occurs as inclusions of native gold and or electrum within or around pyrrhotite magnetite and arsenopyrite the earliest mineral assemblage preserved in the banded iron formation at randalls is banded magnetite quartz magnetite in all forms has elevated mg al ti v mn cr zn and w but very low ni compared to other bifs globally pyrrhotite the most abundant sulfide is restricted to ore zones and occurs as laminae blebs and veinlets all of which have replaced magnetite some pyrrhotite in the hydrothermally altered bifs especially in near surface samples has been re sulfidized to pyrite trace elements associated with pyrrhotite include co ni ag sb and pb large coarse grained arsenopyrite overgrows the pyrrhotite defined foliation it is enriched in co ni sb and te but contains very little invisible gold 0 01 ppm au unlike arsenopyrite in many orogenic au systems globally commonly 0 1 ppm au petrographic studies of several mineralized bifs from randalls reveal that pyrrhotite and arsenopyrite are associated with fe ca amphibole which grew during contact metamorphism caused by granite plutons this spatial sulfide amphibole relationship indicates that gold mineralization likely occurred during granite intrusion consistent with prior studies on randalls the trace element characteristics of the sulfides show that they were not inherited from replaced magnetite further these characteristics suggest that the fluid from which sulfides crystallized was not indigenous to the bifs and that this s rich fluid either contained s in abundance originally or interacted with a lithology lithologies that were rich in s before reaching the bifs black shale containing diagenetic nodular pyrite occurs in the upper black flag group which unconformably underlies the belches supersequence at depth 3 km the trace element composition of nodular pyrite from this unit fits well with the trace element characteristics of the bif pyrrhotite and arsenopyrite and the nodular pyrite contains an average of 0 5 ppm au however the nodular pyrites have an average 34s value of 5 6 n 13 which contrasts markedly with the 34s average of pyrrhotite pyrite and arsenopyrite in mineralized bifs 0 8 n 17 thus a definitive source of gold arsenic silver and tellurium in the randalls system remains elusive although we would contend that the upper black flag group should be considered as a possible metal and s source in areas of the yilgarn where it forms a thick substrate to ore camps

young porphyries old zircons new constraints on the timing of deformation and gold mineralisation in the eastern goldfields from shrimp u pb zircon dating at the kanowna belle gold mine western australia abstract the kanowna belle gold mine is a late archaean orogenic lode gold deposit hosted by felsic volcaniclastic and intrusive rocks porphyries of the kalgoorlie terrane western australia rare gold occurs in fragments of veins and alteration that form clasts within the black flag group volcaniclastic rocks at the kanowna belle mine indicating that epithermal gold mineralisation accompanied black flag group volcanism the shrimp u pb zircon age of the volcaniclastic unit is 2668 9 ma and xenocrystic zircons with 2 68 2 70 and 2 71 ga age groupings are common the black flag group rocks are faulted by a d1 thrust and 2670 ma is thus an older limit for regional d1 deformation although shrimp u pb zircon ages of felsic porphyries commonly give the best constraints on the timing of deformation and structurally controlled gold mineralisation the data are complex and dates from single samples can be ambiguous four porphyry samples from the kanowna belle gold mine were analysed backscattered electron and cathodoluminescence imaging show that most magmatic zircon in the porphyries is either high u and metamict or restricted to rims on older xenocrysts that are too narrow to be dated by shrimp some porphyries appear to have been saturated with zircon at source and contain only xenocrystic zircons zircons that are interpreted to be magmatic in a sample of the mineralised kanowna belle porphyry gives a mean age of 2655 6 ma the kanowna belle porphyry is cross cut by regional d2 fabrics and 2655 ma is thus the maximum age for regional d2 deformation this is a maximum age for epigenetic lode gold mineralisation the age of resetting of high u zircon grains 2 63 ga and the age of ore related pb pb galenas 2 63 ga serves as an approximate date for lode gold mineralisation if the complex zircon history of the felsic porphyries at kanowna belle is typical of this suite throughout the eastern goldfields province it is clear that existing single zircon dates from this province require reevaluation backed up by careful backscattered and cathodoluminescence imaging and textural studies

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

2 7 ga plume associated vhms mineralization in the eastern goldfields superterrane yilgarn craton insights from the low temperature and shallow water ag zn au nimbus deposit economic volcanic hosted massive sulfide vhms deposits of the archaean yilgarn craton of western australia are restricted to zones of juvenile crust as revealed through regional nd pb and hf isotopic variations and the geochemistry of felsic volcanic rocks interpreted as archaean paleo rift zones one of these runs n s through the eastern goldfields superterrane broadly coincident with the kurnalpi terrane and is associated with the high grade ca 2690 ma teutonic bore jaguar and bentley deposits plus sub economic vhms mineralization further south to date only small historic cu occurrences e g anaconda and barren pyritic lenses have been recognized in the older 2 7 ga plume dominated lower stratigraphy of the eastern goldfields superterrane the nimbus ag zn au deposit 12 1 mt at 52 g t ag 0 9 zn and 0 2 g t au is located approximately 10 km east of kalgoorlie near the margin of the kurnalpi terrane its origin has been contentious for a number of years with previous models favouring seafloor sub seafloor vhms mineralization or a high sulfidation fault hosted system we present a detailed account of the deposit its host stratigraphy and associated hydrothermal alteration plus two new shrimp u pb zircon ages pb isotope galena and o isotope zircon constraints compared to other vhms occurrences in the yilgarn craton the nimbus deposit is unusual in terms of its tectono stratigraphic position the geochemistry of its host sequence i e fi affinity felsic volcanic rocks ocean plateau like low th basalts mineralogy e g abundance of ag sb pb as bearing sulfosalts high hg low cu and quartz carbonate sericite dominated alteration assemblages classification of nimbus as a shallow water and low temperature vhms deposit with epithermal characteristics i e a hybrid bimodal felsic deposit is consistent with its position near the margin of the kurnalpi paleo rift zone and radiogenic 238u 204pb values the recognition that the nimbus deposit is associated with c 2705 ma plume magmatism opens new areas for vhms exploration in the eastern goldfields superterrane over a strike length exceeding 500 km

the cosmos greenstone succession agnew wiluna greenstone belt yilgarn craton western australia geochemistry of an enriched neoarchaean volcanic arc succession abstract the geodynamic setting of the neoarchaean eastern goldfields superterrane egs of the yilgarn craton is the subject of debate some authors propose plume models while others advocate variants on a subduction accretion model for the origin of mineralised greenstone belt sequences felsic volcanism in the kalgoorlie terrane the westernmost terrane of the egs is considered to have a tonalite trondhjemite granodiorite dacite ttg d geochemical affinity the cosmos greenstone succession which lies in the agnew wiluna greenstone belt awb of the kalgoorlie terrane contains several komatiite hosted nickel sulphide deposits the volcanic footwall to which consists of an intercalated succession of fragmental and coherent rocks ranging in composition from basaltic andesite to rhyolite light rare earth elements lrees and large ion lithophile elements liles are strongly enriched relative to high field strength elements hfses across all volcanic units and the rocks display strong positive pb and negative nb anomalies these geochemical characteristics resemble closely those of modern high k calc alkaline to shoshonite continental arc successions contrasting ree lile and hfse concentrations coupled with assimilation fractional crystallisation afc modelling shows that the intercalated dacitic and andesitic volcanic rocks within the footwall succession are not co genetic xenocrystic zircons within the felsic volcanic lithologies indicate that some assimilation of older continental crust contributed to the generation of the footwall volcanic sequence the geochemical characteristics of the cosmos volcanic succession indicate that parental melts were derived via partial melting of enriched peridotite that had been contaminated by subducted crustal material within the mantle wedge of a subduction zone in contrast two younger felsic porphyry intrusions which cross cut the volcanic succession have a distinct ttg d affinity therefore these intrusions are considered to be generated via partial melting of a subducting slab and are related to local high ca granitoid intrusions the cosmos volcanic succession represents the first extrusive high k calc alkaline to shoshonitic volcanic arc sequence described in the kalgoorlie terrane and coupled with age dating of the stratigraphy is indicative of formation in a long lived volcanic arc setting active from 2736 ma to later than 2724 ma the composition and geochemical affinity of the volcanic footwall succession to the cosmos komatiite hosted nickel sulphide deposits contrasts with the majority of felsic volcanic rocks within the awb and also the wider kalgoorlie terrane suggesting that the overall architecture of this region is more complex than is currently thought our conclusions not only have consequences for recent models of the tectonic evolution of the egs but also contribute to the debate on the operation of plate tectonics during the late archaean in general the arc affinity of the cosmos volcanic succession containing abundant high k calc alkaline andesite lavas provides further support for the operation of plate tectonics in the neoarchaean

granite cored domes and gold mineralisation architectural and geodynamic controls around the archaean scotia kanowna dome kalgoorlie terrane western australia abstract granite cored domes are associated with many of the larger gold deposits of the archaean eastern yilgarn craton of western australia the scotia kanowna dome is eroded to sufficiently deep levels to provide insights into the role granite cored domes play in controlling fluid flow and gold deposition at the centre of the scotia kanowna dome is a granite batholith which is surrounded by outward dipping greenstone belts and associated shear zones this upper crustal dome sits above mid crustal domes providing a series of stacked geometries favourable to focussed fluid flow a number of small to medium sized gold deposits occur on the limbs and the centre of the dome and the world class kanowna belle gold mine occurs on the nose of the dome at least three separate gold mineralising events are defined each of regional significance which can be correlated with other well known gold deposits of the eastern yilgarn craton the palaeostress across this region was dominated by both maximum contractional and extensional vectors oriented perpendicular to the north northwest trending grain the resultant strain is seen in the architecture of the scotia kanowna dome with its margins and associated shear zones controlling the distribution of stratigraphy which is relatively linear and parallel to the margin throughout most of the tectonic history the flanking shear zones were high strain domains that recorded multiple stages of contraction with thrust and mostly sinistral strike slip shear kinematics in contrast the dome nose region was a relatively low strain domain as it was located in the strain shadow of the regional contractional events for example the early extensional record has been preserved at the nose with late stage basins formed in the hangingwall to the extensional faults adding to the stratigraphic complexity of the local region these late basins also may have contributed to the fluid budget in contrast along the flanks of the domes there is no record of these late basins or the extensional faults that controlled their deposition the architecture of the dome played an important role in controlling mineralisation during a significant deviation in the maximum contractional stress vector to an east southeast west southwest orientation at this time basins in the nose region underwent inversion with thrusting to the north and northwest shortening was accommodated along the dome flanks by sinistral strike slip shearing which was relatively free to move due to the mostly linear stratigraphy combined with limited anisotropy and perturbations along the flank however the stratigraphic and geometrical complexity around the dome nose resulted in localised maximum dilation and gold deposition at this time the dome nose area was also a favoured locus for gold enriched dominantly mafic type magmas which are seen as the extensive porphyry swarms in the region these felsic intermediate rocks also may have contributed to the complex fluid budget and are considered as indicators of particular fertility for gold they may have been the primary source for much of the metal endowment the architecture of granite cored domes has played a critical role in focussing magma as well as mineralising fluids into regions of maximum dilation they did this by virtue of their inherent competence and by influencing the position and geometry of shear zones fluid pathways and hence distribution of stratigraphy depositional sites across the region the scotia kanowna dome is a good example of this effect and inferences can be made in favour of similar controls by concealed domes such as beneath kalgoorlie

on traction carpet sedimentation traction carpets are highly concentrated bedload layers that are developed beneath and driven by turbulent overlying flows they have a convex up velocity profile and comprise a lower frictional and an upper collisional region the frictional region having a particle concentration more than 80 of the packed bed is characterized by nearly continuous grain contacts low strain rate and hampered grain segregation on the other hand the collisional region has a particle concentration between 15 and 80 of the packed bed and is characterized by active grain collisions and higher strain rate deposition from the traction carpets occurs via progressive aggradation of the bed rather than via en masse freezing while the downward grain flux from the overlying flow maintains them the thickness of a traction carpet stratum is therefore determined by the cumulative amount of sediment settled during the lifespan of a traction carpet and can be much larger than the thickness of a moving traction carpet inverse grading can be produced in the collisional region by the vertical gradient of dispersive pressure which is related to nonuniform distribution of particles when a thick frictional region develops however the inverse size distribution in the collisional region is poorly recorded in the deposits depositional features of traction carpet strata are therefore determined by the duration of a traction carpet and the thickness ratio of collisional to frictional regions the thickness ratio is further controlled by the applied shear stress sediment fallout rate and grain size generally a collisional region is better developed beneath a highly competent and coarse grained gravelly flow whereas a thick frictional region is developed beneath a heavily sediment laden fine grained sandy flow this explains the more common occurrence of inverse grading in coarse grained deposits

late archaean synorogenic basins of the eastern goldfields superterrane yilgarn craton western australia abstract siliciclastic supersequences of the kalgoorlie and gindalbie terranes post date 2660 ma deformation uplift and erosion associated with the amalgamation of arc related terranes but were tectonically buried to greenschist or amphibolite facies during the orogenic shortening that accreted the eastern goldfields superterrane to the yilgarn craton the supersequences are synclinal remnants of late stage basins that were linear zones of subsidence adjacent to north trending strike slip faults fluvial facies merougil navajo jones creek scotty creek and yandal basins are dominated by sheet sandstones that represent the deposits of medial braid plains but proximal channel and bar complexes of cobble and boulder conglomerates are also preserved submarine facies kurrawang basin range from boulder to pebble conglomerates but are dominantly bouma turbidites with rare black shales and record the filling of a proximal canyon that fed a distal submarine fan axial depositional systems are preferentially preserved in all basins but transverse systems are preserved at the base of some fluvial deposits the gross vertical succession in all basins is from proximal up to distal the basins developed during two tectonic stages separated by an intervening period of uplift tilting and erosion with the southern kalgoorlie terrane recording change from a stage i fluvial to a stage ii deep marine basin stage ii fluvial deposits are preserved in the northern kalgoorlie terrane and in the gindalbie terrane sparse palaeocurrents establish sediment dispersal was to the south or southeast implying uplift to the north or northwest controlled palaeoslopes stacking of lithofacies is aggradational and is consistent with limited lateral migration of facies tracts in fault confined basins similar lithofacies and aggradational styles of facies stacking characterise syncollisional sequences of the cenozoic coastal range basin of taiwan and the present day syncollisional basins of southeastern taiwan are good analogues of late stage basins of the kalgoorlie and gindalbie terranes

fan delta sedimentation on the basin margin slope of the cretaceous strike slip izumi basin southwestern japan abstract the late cretaceous campanian maastrichtian izumi basin is an e w trending strike slip basin some 300 km long and 15 km wide filled with turbidites and associated coarse clastic deposits in the northeastern margin of the basin steep face fan deltas were built on a steep slope and prograded directly into deep water forming conglomeratic slope aprons the fan delta deposits comprise debris flow dominated alluvial fan conglomerates delta slope conglomerates originated from various subaqueous sediment gravity flows and prodelta mudstones with intercalations of thin sandstone and channel fill pebbly sandstone the most significant feature of the izumi fan delta system is a contrast between the gravel dominated delta slope and the mud dominated prodelta the development of this fan delta system was due to tectonic activity along the northern margin of the basin sedimentation took place due to vigorous uplift of the adjacent source terrane which caused a high rate of supply of coarse detritus and rapid basin subsidence which resulted in deep water depth

the role of early formed structures on the development of the world class st ives goldfield yilgarn wa a revised structural interpretation for the victory to kambalda area of the world class st ives goldfield in the archean yilgarn craton has mapped out the distribution of wnw trending faults within this area of the field these previously cryptic wnw trending structures had been identified in gravity data and also by isopach thickness variations the wnw trending faults acted as transfers syn gold mineralization although only discrete segments of these faults were active during the main stage of gold mineralization where mineralized the faults transferred strain from a complex combination of block on block movement associated with thrusting and strike slip movement on nw and n trending faults along some segments n trending mineralized faults terminate against the wnw trending faults many of the wnw trending faults correlate with major strike changes on regional and camp scale faults and they are domain boundaries for the critical n trending fault segments that host high grade gold within contractional jogs the wnw trending faults also show evidence for an older deformation history prior to main stage gold which may extend back to early basin development associated with ultramafic and mafic volcanism they are inferred to have been a series of early wnw trending normal faults and breached relay ramps associated with oblique rifting along an older nnw trending basement boundary

density modified grain flow deposits from an early paleozoic passive margin abstract thick to very thick beds of sand to gravel matrix limestone clast conglomerate constitute an important lithology of the richmond slice of the allochthonous hamburg klippe of southeastern pennsylvania sedimentary structures in the conglomerates can be explained by both debris flow planar clast fabric nondeforming plugs and grain flow reverse grading mechanisms however the lack of a cohesive mud matrix and the great thickness of the beds rule out either one of these sediment gravity flow types previous studies have illustrated that thick flows of poorly sorted gravel size debris can move over relatively low slopes by density modified grain flow a cross between true unimodal grain flow and debris flow the coarse grained matrix conglomerates of the richmond slice can be exp ained as ancient density modified grain flow deposits in addition the presence of layers of normally graded level and parallel to cross laminated sand size material on top of some of the conglomerates is suggestive of increased turbulence toward the top of the flow this is probably related to either backward shearing of sediment and water in front of the moving sediment mass creating turbulence on top of the flow or expulsion of pore fluid during movement of the main sediment mass

proximal to distal sedimentological variation in a linear turbidite trough implications for the fan model determination of geographically dependent sedimentological variation proximality in ancient flysch deposits formed an important part of early turbidite studies attempts to quantify this variation highlighted anomalies which were neatly resolved by application of vertical sequence analysis and the use of fan models however there are many turbidite formations such as the lower cretaceous cumberland bay formation cbf of south georgia which cannot be described in terms of existing fan models but show strong proximal to distal sedimentological changes the cbf is a thick sequence of volcaniclastic sandstone turbidites deposited in a linear back arc basin principally by currents flowing wnw parallel to the basin margin four lithofacies associations are recognized on the basis of sandstone shale ratio the two finergrained associations are constant in character across the cbf outcrop in the coarse grained associations there is a change in character wnw down the palaeocurrent direction this is brought out by decreasing sandstone bed thickness and percentage amalgamation but these changes are not always marked or consistent in contrast the internal character of the sandstone beds changes strongly with a marked proportional increase in tb and tc divisions within the bed downcurrent the evidence suggests that the system was aggradational rather than progradational tectonic control of the basin margins prevented major migration of the depositional system and most areas remained in the same position relative to source through time comparison of the cbf with other turbidite formations suggests two end member states which will produce radically different vertical sequences progradational systems will produce strong vertical facies changes where beds deposited in distal environments are overlain by beds deposited in environments progressively nearer source however there will be no lateral change in the character of any particular facies type in contrast in aggradational systems the major sedimentological variation will be lateral rather than vertical

the role of strike slip fault systems at plate boundaries a new analysis shows that most 59 plate boundaries have a relative velocity vector that is markedly oblique greater than 22 to the boundary normal a significant proportion 14 have vectors that are nearly 22 parallel to the boundary accommodation of the oblique motion usually involves strike slip faulting but the kinematic role of these faults differs at divergent and convergent boundaries four main types of plate boundary related strike slip faults are distinguished ridge transforms boundary transforms trench linked strike slip faults and indent linked strike slip faults discrimination of the four types should be possible in ancient orogenic belts but is complicated by the common reactivation of the strike slip zones in other roles plate boundary related strike slip faults form major lineaments at the present day ridge transforms have a low preservation potential in continents boundary transforms and indent linked faults often re use old lineaments but trench linked strike slip faulting is an effective method of forming new lineaments in continental crust strike slip faulting in general is less commonly recognized in ancient orogenic belts than its abundance in present plate boundary orogens requires this under recognition results both from poor understanding of strike slip kinematics and from deeper prejudices about the way in which orogenic belts form

tectonostratigraphy of the late archean dharwar supergroup dharwar craton india defining a tectonic history from spatially linked but temporally distinct intracontinental and arc related basins abstract the dharwar supergroup comprises the unconformity bound bababudan and chitradurga groups the bababudan group which is best preserved in the western dharwar craton records a divergent margin comprising a basalt dominant intracontinental rift sequence a shale bif drift sequence and a sandstone shale thermal subsidence sequence the rift stage evolved from 2765 ma to 2720 ma whereas the succession was folded uplifted and eroded during development of a convergent continental margin from 2680 ma ocean opening was to the east or southeast the chitradurga group records a two stage back arc basin behind an east facing continental arc stage i evolved between 2609 ma and 2582 ma and stage ii between 2582 ma and 2540 ma the two stages are separated by a subaerial unconformity stage i comprises siliciclastic fluvial shallow marine and deep marine sedimentary rocks and bimodal volcanic rocks stage i is best preserved in the western dharwar craton but there are equivalents in the eastern dharwar craton stage ii in the western dharwar craton comprises deep marine turbidites of siliciclastic and volcaniclastic provenance and basaltic and felsic volcanic rocks volcanic stage ii sequences in the eastern dharwar craton define an arc adjacent position tectonically driven cyclic uplift and erosion were responsible for the mismatch between preserved stratigraphic thickness and time particularly for stage ii sequences a remnant of a

geology mineralogy and geochemistry of magnetite associated au mineralization of the ultramafic basalt greenstone hosted crusader complex agnew gold camp eastern yilgarn craton western australia a late archean intrusion related au deposit abstract the crusader complex part of the agnew gold camp of the lawlers anticline of the yilgarn craton western australia is located close to or along the contact between the lawlers basalt and agnew ultramafics units au mineralization within the four orebodies that form the crusader complex is dominated by very pure au containing less than 1 wt ag with au variably associated with scheelite bi tellurides and minor chalcopyrite within a magnetite and titanite gangue assemblage hydrothermal alteration associated with this style of mineralization is characterized by increasing concentrations of mo be li sn and fe and depletions in na cu ba pb mn zn si and k relative to protolith concentrations these enrichments are more typical in orebodies associated with felsic intrusive related mineralizing systems rather than the more well known orogenic au deposits found elsewhere within the lawlers anticline e g at waroonga and within the greater yilgarn craton we propose that flexures of the contact between the lawlers basalt and agnew ultramafic units acted as conduits for au bearing felsic intrusive derived fluids and generated structural traps that enhanced fluid flow the mineralizing fluids that formed the crusader deposits were derived from the lawlers granitoid pluton that intruded into the study area enhanced fluid flow promoted interaction between hydrothermal fluids and the reactive mafic ultramafic rock sequence augmenting the amount of au that was precipitated during formation of the orebodies at crusader the magnetite dominated quartz and sulfide poor intrusion related mineralization at crusader contrasts sharply with other late archean intrusion related deposits of the yilgarn craton that are usually sulfide and or quartz rich this may in turn suggest that the crusader deposit represents a new class of under explored intrusion derived deposits possibly opening new mineral exploration opportunities for the agnew region and potentially the wider eastern goldfields superterrane enrichments in mo and sn and significant depletions in cu suggest that other parts of the lawlers batholith may also be prospective for base metal mineralization integration of stratigraphic interpretation with the identification of key structural fluid pathways and the presence of felsic intrusive bodies as presented in this study enables the delineation of the key elements that underlie mineralization at the crusader complex we propose that these key elements provide vital information for future gold exploration models that can be used within other archean terranes and within the eastern yilgarn craton in particular