response of tide dominated mangrove shorelines in northern australia to anticipated sea level rise the exact response of mangrove shorelines to anticipated sea level rise will depend upon the balance between sedimentation and sea level change within the top end of the northern territory of australia there are extensive relatively unmodified tide dominated mangrove forests where tidal processes redistribute sediment harbours such as darwin harbour and tidal rivers such as the south alligator river with its associated coastal and estuarine plains represent opposite extremes in terms of holocene sedimentary infill and will respond differently to sea level rise in darwin harbour mangrove assemblages can be recognized in geomorphologically defined habitats similar topography within and between creeks implies morphodynamic equilibrium with tidal processes tidal reworking of sediment may maintain an equilibrial profile under gradually rising sea level with resuspension of lower intertidal and subtidal muds and their redeposition within upper intertidal mangrove habitats in contrast the plains along the coast and tidal rivers draining into van diemen gulf developed during the post glacial marine transgression and since sea level stabilized around 6000 years ago coastal plains have prograded these broad plains are presently not extensively influenced by salt water but are often at elevations close to or even below modern high tide levels they may therefore revert to saline conditions particularly rapidly if the sea rises the pattern of change may not be directly analogous to marine incursion experienced in the early holocene because broad plains have been able to prograde during the last 6000 years of relatively stable sea level

early human occupation of a maritime desert barrow island north west australia abstract archaeological deposits from boodie cave on barrow island northwest australia reveal some of the oldest evidence for aboriginal occupation of australia as well as illustrating the early use of marine resources by modern peoples outside of africa barrow island is a large 202 km 2 limestone continental island located on the north west shelf of australia optimally located to sample past use of both the pleistocene coastline and extensive arid coastal plains an interdisciplinary team forming the barrow island archaeology project biap has addressed questions focusing on the antiquity of occupation of coastal deserts by hunter gatherers the use and distribution of marine resources from the coast to the interior and the productivity of the marine zone with changing sea levels boodie cave is the largest of 20 stratified deposits identified on barrow island with 20 m 3 of cultural deposits excavated between 2013 and 2015 in this first major synthesis we focus on the dating and sedimentology of boodie cave to establish the framework for ongoing analysis of cultural materials we present new data on these cultural assemblages including charcoal faunal remains and lithics integrated with micromorphology sedimentary history and dating by four independent laboratories first occupation occurs between 51 1 and 46 2 ka overlapping with the earliest dates for occupation of australia marine resources are incorporated into dietary assemblages by 42 5 ka and continue to be transported to the cave through all periods of occupation despite fluctuating sea levels and dramatic extensions of the coastal plain the changing quantities of marine fauna through time reflect the varying distance of the cave from the contemporaneous shoreline the dietary breadth of both arid zone terrestrial fauna and marine species increases after the last glacial maximum and significantly so by the mid holocene the cave is abandoned by 6 8 ka when the island becomes increasingly distant from the mainland coast

connemara its position and role in the grampian orogeny in the irish and british caledonides the early ordovician grampian orogeny was the result of collision between the laurentian rifted margin and an oceanic island arc the connemara terrain in western ireland differs in position and character from all other parts of the exposed dalradian rocks of the grampian orogen in lying south of the collided arc and fore arc and in having north verging fold nappes that developed synchronously with the intrusion of huge volumes of calc alkaline magmas that provided the heat for regional barrovian metamorphism we have tested this hypothesis with a numerical model which demonstrates its admissablity connemara is not a terrane displaced with respect to the remainder of the grampian orogen but was overridden northwards by the arc and its fore arc basin south mayo trough frontal ophiolite complex deer park and accretionary complex killadangan deposition in the south mayo trough occurred below sea level and above the evolving grampian orogen which developed

archaean oil migration in the witwatersrand basin of south africa abstract the late archaean witwatersrand supergroup of south africa hosts the largest known gold uranium pyrite ore deposits oil preserved in fluid inclusions in quartz grains in siliciclastic sedimentary rocks of that supergroup implies that hydrocarbon generation and migration occurred during the archaean and may have been involved in mineralization processes through reference to phanerozoic analogues oil bearing fluid inclusions entrapped in healed microfractures in detrital quartz grains and in early syntaxial quartz overgrowths imply that the onset of oil migration coincided with early to intermediate stages of burial while intra granular porosity was still preserved multiple generations of oil migration are indicated by i oil inclusions within early diagenetic cements at different levels in the stratigraphic succession ii more than one type of oil in entrapment sites iii oil entrapment in multiple stages of the quartz paragenetic sequence oil generation and migration are considered to have occurred throughout and for some considerable time after development of the witwatersrand basin consistent with progressive burial and kerogen maturation in more than one tectonic regime oil bearing fluid inclusions within detrital sandstone fragments suggest that oil migration also occurred in a sedimentary succession on the kaapvaal craton prior to 2 9 ga oil in the witwatersrand supergroup was most likely derived from multiple source areas with the principal source probably being shales within the lower witwatersrand supergroup the hydrocarbon migration history of the basin has important implications for understanding the textural relationship between gold bituminized oil and uraninite in the giant gold uranium pyrite ore deposits

palaeomagnetism and rb sr ages of the ratagan and comrie intrusions the newer igneous rocks in the scottish highland region which post date the main grampian metamorphism and tectonism range in composition from basic to granitic two members of this suite were chosen for palaeomagnetic study in an attempt to refine the apparent polar wander path for scotland in the palaeozoic this paper describes the results of the detailed palaeomagnetic analysis which has been carried out thermal and alternating field af demagnetization was supplemented by rock magnetic experiments on a limited selection of specimens from each sampling site to help characterize the remanence carriers these consisted of thin section observations and the measurement of thermomagnetic and hysteresis properties each complex provides an example of the widespread variability in remanence behaviour which may be encountered in a single intrusion for an accurate interpretation of palaeomagnetic data from any formation an estimate of the age of the rock is required brown miller grasty 1968 give a poorly defined k ar now at bp research centre str epd chertsey road sunbury on thames middlesex tw16 7ln

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

decompressed eclogites in the sveconorwegian grenvillian orogen of sw sweden petrology and tectonic implications relict eclogites and associated high pressure rocks are present in the eastern segment of the sw swedish gneiss region the tectonic counterpart of the parautochthonous belt of the canadian grenville these rocks give evidence of sveconorwegian eclogite facies metamorphism and subsequent pervasive reworking and deformation at granulite and amphibolite facies conditions the best preserved eclogite relics suggest a clockwise p t t history beginning in the amphibolite facies progressing through the eclogite facies decompressing and partially reequilibrating through the high and medium pressure granulite facies before cooling through the amphibolite facies textures demonstrate the former coexistence of the plagioclase free assemblages garnet clinopyroxene quartz rutile ilmenite garnet clinopyroxene kyanite rutile and garnet kyanite quartz rutile the former existence of omphacite is evidenced by up to 45 vol plagioclase expelled as small grains within large clinopyroxene matrix plagioclase is secondary and occurs expelled from clinopyroxene or in fine grained granulite facies reaction domains formed during resorption of garnet and kyanite garnet shows preserved prograde growth zoning with rimward increasing pyrope content decreasing spessartine content and decreasing fe fe mg ratio but is partly resorbed and reequilibrated at the rims p t estimates from microdomains with clinopyroxene plagioclase quartz garnet indicate pressures of 9 5 12 kbar and temperatures of 705 795 c for a stage of the granulite facies decompression the preservation of the prograde zoning suggests that the rocks did not reside at these high temperatures for more than a few million years and chemical disequilibrium and frozen reaction textures indicate heterogeneous reaction progress and overstepping of reactions during the decompression through the granulite facies together these features suggest a rapid tectonic exhumation the eclogite relics occur within a high grade deformation zone with wnw ese stretching and associated oblique normal sense top to the east sensu lato displacement suggesting that extension was a main cause for the decompression and exhumation probable tectonic scenarios for this deformation are sveconorwegian late orogenic gravitational collapse or overall wnw ese extension

hydrothermal alteration in the witwatersrand goldfields abstract alteration is recorded throughout much of the 3 km thick upper witwatersrand succession in south africa and extends for 300 km around the basin and 50 km into the basin the evidence for this alteration comes from petrography mineralogy geochemistry rock fabrics and stratigraphy the alteration conceived as a giant halo enveloping each major goldfield requires a major hydrothermal event focused on the auriferous upper wits central rand group the scale and nature of the alteration and its relationship to gold distribution on various scales strongly support a hydrothermal model for gold deposition such a model can account for the 50 000 t of gold mined from the witwatersrand goldfields the model works within the context of the major advances in understanding of the geological framework of the witwatersrand basin including the recognition of the importance of post burial processes it is highly significant that the age of witwatersrand sedimentation is much older than 2700 my and thus the host rocks for gold were deposited at least 100 my before the major global archean greenstone gold event the shale units from 40 major mines covering the seven goldfields are examined to establish the nature and distribution of the alteration and to make the connection between the fluid infiltration that caused the alteration and the introduction of gold into the witwatersrand basin in the hydrothermal model described here an auriferous low salinity fluid is produced at about 500 c during the metamorphism of mafic material that was below and adjacent to the witwatersrand basin large shear zones in the footwall of goldfields are the inferred fluid pathways into the upper wits succession and then unconformities smaller shear zones veins and the reef packages guide local fluid flow in this model gold precipitation occurs in response to the reaction of the fluid with carbon and iron bearing rocks that are abundant in the reef packages immediately overlying unconformity surfaces gold precipitation occurred at about 350 c and 10 km depth with the implication of a high geothermal gradient approaching 35 c per km the alteration of the shales but lack of abundant gold in them is predicted from the paucity of appropriate rocks or minerals in the shale units to precipitate gold but fluid infiltration still changed their composition fundamentally the source of the witwatersrand gold its present distribution and the alteration are explained within this hydrothermal model with similarities to the models invoked for other major gold provinces it is worth noting that quartz pebble conglomerate is a poor term for this gold type and has almost certainly limited exploration opportunities globally

is the ventersdorp rift system of southern africa related to a continental collision between the kaapvaal and zimbabwe cratons at 2 64 ga ago abstract rocks of the ventersdorp supergroup were deposited in a system of northeast trending grabens on the kaapvaal craton approximately 2 64 ga ago contemporary with a continental collision between the kaapvaal and zimbabwe cratons we suggest that it was this collision that initiated the ventersdorp rifting individual grabens strike at high angles toward the continental collision zone now exposed in the limpopo province where late orogenic left lateral strike slip faulting and anatectic granites are recognized we relate the ventersdorp rift province to extension in the kaapvaal craton associated with the collision and see some analogy with such rifts as the shansi and baikal systems associated with the current india asia continental collision

to the islands born the research potential of submerged landscapes and human habitation sites from the islands of nw australia this paper focuses on the continental shelf of nw australia and on models for change in littoral and offshore environments of relevance to human occupation over the last 50 kyr major island groups occur on the shelf including the montebello and barrow islands and those of the dampier archipelago at lowest sea level around 22 ka these would have been uplands that then became progressively isolated by subsequent sea level rise by integrating archaeological and zooarchaeological records from excavations on these islands with the geology and geomorphology we interpret palaeoeconomic resource potential in relation to changing sea level and coastline morphology the preservation potential for submerged archaeological sites and features is also assessed current archaeological evidence from these offshore islands indicates that the submerged coastal landscape is likely to have been a potentially rich environment for resources and human occupation even at times of lowest sea level and regional aridity should any exploration of submerged archaeology be carried out in this region it is likely to be rewarding offering unique insights into late pleistocene coastal occupation

a continental narrative human settlement patterns and australian climate change over the last 35 000 years drawing on the recent synthesis of australian palaeoclimate by the oz intimate group reeves et al 2013a we consider the effects of climate systems on past human settlement patterns and inferred demography we use 5044 radiocarbon dates from 1750 archaeological sites to develop regional time series curves for different regions defined in the oz intimate compilation as the temperate tropics interior and southern ocean sectors to explore human climate relationships in australia over the last 35 000 years correlations undertaken with improved palaeoclimatic data and archaeological records indicate that the regional time series curves are robust and can be used as a proxy for human behaviour however interrogation of the datasets is essential with artificial peaks and taphonomic over correction being critical considerations the time series curves are interpreted as reflecting population growth stasis and even decline in phase with terminal pleistocene early holocene climatic fluctuations this coupling however decreases during the last 5000 years most likely due to increased population levels greater territoriality technological solutions to stress and social and ideational innovation curves from all sectors show exponential population growth over the last 5000 years we identify future research priorities highlighting the paucity of archaeological records across several parts of australia 1 dated site 4 000 km2 especially around the fringes of the arid zone and the need for improved taphonomic correction techniques finally we discuss how these time series curves represent a first order framework not dissimilar to global climate models which researchers can continue to test and refine with local regional and continental records

a detrital model for the origin of gold and sulfides in the witwatersrand basin based on re os isotopes abstract the re os systematics of gold and sulfides from the witwatersrand basin were utilized to determine whether the gold is detrital or was introduced by hydrothermal solutions from outside the basin gold from a gravity concentrate from the western areas gold plant and gold from the vaal reef have very high os concentrations of approximately 73 to 10000 ppb and 3 to 32 ppb re resulting in 187re 188os ratios of 0 010 to 0 185 the gold has subchondritic 187os 188os ratios between 0 1056 to 0 1099 and an average value of 0 1067 rhenium depletion ages trd range from 3 5 ga to 2 9 ga with a median age of 3 3 ga pyrite from the vaal reef have os concentrations ranging from 0 26 to 0 68 ppb re concentrations of 1 7 to 2 8 ppb and187re 188os ratios of approximately 14 to 87 the pyrite samples have measured 187os 188os ratios of 0 84 to 4 7 and define an isochron with an age of 2 99 0 11 ga mswd 0 77 the os isotopic data from the direct measurement of gold preclude introduction of gold to the witwatersrand basin from crustally derived metamorphic or hydrothermal fluids between 2 7 to 2 0 ga the unradiogenic 187os 188os ratios old trd ages of the western areas and vaal reef gold samples as well as the contemporaneously old age of the vaal reef pyrite are consistent with detrital deposition of gold during the formation of the witswatersrand basin the os data will allow for minor hydrothermal remobilization and or overprinting of hydrothermal gold on preexisting detrital gold grains but does not support the introduction of gold solely by hydrothermal fluids

surge zones in the moine thrust zone of nw scotland abstract the caledonian thrust zones of assynt show several examples of large fault bounded structures surge zones up to 8 km 2 in extent which have moved further than adjacent rocks extensional faults can be traced into strike slip faults and then to contractional imbricate faults there are also zones of extensional and contractional flow as shown by strained bioturbation marks in the cambrian pipe rock several other low angle extensional fault zones have been recognized along the length of the moine thrust zone notably in the kinlochewe district recognition of these extensional faults and local surge zones has solved several local problems such as the lack of continuity of the glencoul thrust and the out of sequence character of some of the large low angle faults though the thrust propagation direction was generally from east to west in the transport direction several of the eastern faults have been reactivated later and locally cut down as extensional faults the so called moine thrust shows extensional fault movement at several localities along its length the extensional structures and the surge zones suggest that body forces have been important in driving the faults rather than just a push from the rear the moines and moine thrust zone were presumably driven to the wnw by gravity spreading and thinning of the main scottish caledonides

a 30 000 yr record of land ocean interaction in the eastern gulf of guinea abstract a 30 000 yr dinocyst and pollen record from the eastern equatorial atlantic off cameroon has been investigated in order to identify land ocean linkages during the last deglacial transition a strong correlation between the abundance of brigantedinium spp and the ca fe ratio during the last glacial period suggests enhanced marine productivity in association with cool seawater temperatures and nutrient input linked to coastal upwelling and or a proximal river mouth dry conditions are recorded on the adjacent continent with a significant representation of open vegetation indicators and the afromontane taxon podocarpus after 17 cal ka bp these indicators register a sharp decline as a result of a climatic transition from the dry cooler conditions of the last glacial period to the wetter warmer conditions of the deglaciation simultaneously dinocysts show a significant shift from dominant heterotrophs to an increasing abundance of autotrophs reflecting warmer conditions significant changes are observed during the younger dryas with a return to drier conditions and higher salinities the start of the holocene is marked by very low salinity conditions reflecting optimal monsoonal conditions over west equatorial africa the end of the african humid period is observed between 6 and 5 cal ka bp followed by significant fluctuations in both terrestrial and oceanic proxies

a sm nd isotopic study of the south harris igneous complex the outer hebrides sm nd geochronology may be used to bracket the age of metamorphism in rocks which are difficult to date by other methods by coupling whole rock sm nd analyses of the principal members of the south harris igneous complex with sm nd mineral isochrons on two anothositic gabbros the age of granulite facios metamorphism has been defined whole rock analyses of three pairs of closely spaced samples of the anorthosite give consistent ages averaging 2 18 0 06 gyr but in general the data from the anorthosite do not define an isochron as a result of variable contamination of the evolving magma chamber whole rock data on the tonalite indicate that it is younger than 2 06 gyr its mean tchur age is 1 86 0 05 gyr garnet pyroxene amphibole plagioclase mineral isochrons on two anorthosite samples give identical 1 87 0 04 gyr ages which date cooling after the high pressure granulite facies metamorphism together with the tonalite whole rock data this defines the age of that metamorphism and confirms dearnley s original assignment of an early laxfordian age

high resolution last deglaciation record from the congo fan reveals significance of mangrove pollen and biomarkers as indicators of shelf transgression abstract high abundances of mangrove pollen have been associated with transgressive cycles on tropical margins but the detailed relations between systems tracts and the taphonomy of the pollen are unclear we report here the occurrence and high abundance of rhizophora pollen in association with taraxerol a rhizophora sourced biomarker from a high resolution congo fan core covering the last deglaciation an age model based on 14c dates enables the temporal changes in taraxerol content and the percentage frequencies and flux pollen grains pg cm 2 103 yr 1 of mangrove pollen to be compared quantitatively with the lateral rate of transgression across the flooding surface derived from glacio hydro isostatic model output and the bathymetry of the margin rhizophora pollen concentrations and taraxerol content of the sediment are very strongly positively correlated with the lateral rate of transgression and indicate independently of any sequence stratigraphic context that mangrove pollen spikes are associated with the transgressive systems tract rather than the highstand systems tract or maximum flooding surface lower resolution longer term records from this margin indicate an association between taraxerol concentrations and transgressive rather than regressive phases the flux of these materials to the congo fan is interpreted as a function of the erosion of flooded mangrove swamp on the shelf and less importantly changing extent of mangrove habitat during sea level rise congo river palaeoflood events also result in reworking of mangrove pollen and supply to the fan but this mechanism is subdominant rhizophora pollen has been underestimated in many palynological studies undertaken on cores from the african margin because of inappropriate sieve mesh size used during laboratory preparation

sandbox experiments of inverted listric and planar fault systems abstract the kinematic and geometric evolution of basement controlled inversion structures has been analyzed using a plane strain sandbox apparatus the results of two representative scaled analogue models comprising rigid listric and planar detachment faults that both have cut off angles of 60 to the horizontal are described in detail the hangingwall above these detachment geometries was constructed from alternate layers of sand and mica in order to simulate an anisotropic sedimentary sequence in both experiments initial shortening at the onset of inversion was accommodated by bulk strain this was followed by reactivation of the basal detachment together with the main basin controlling planar and listric faults which propagate upwards through the post rift sequence at approximately the same angle as the upper part of the detachment fault i e 60 reactivation of relatively steep intra basinal extensional faults within the cover was restricted to nucleation of reserve faults and thrusts in the region of the tips during approximately the first 10 to 15 contraction this resulted in gently dipping thrusts that propagated upwards through the post rift sequence to produce harpoon shaped structures later in the inversion phase after approximately 15 contraction backthrusts cut through and displaced the original antithetic extensional graben faults producing downward tapering wedge shaped structures at the margins of the basin although deformation in these experiments was limited to purely dip slip displacement the nature of the original extensional faults and their reactivated tip regions resulted in cross sectional geometries that have a marked resemblance to strike slip induced flower structures uplift was asymmetric and centred above the upper part of the main detachment above the listric fault but was more symmetrical and centred above the soling out point of the detachment in the case of the planar fault geometry the results of these experiments show distinct similarities to structures seen on seismic sections form the southern north sea and other inverted sedimentary basins

plastic deformation and recrystallization of garnet a mechanism to facilitate diffusion creep elongate and deformed garnets from glenelg nw scotland occur within a thin shear zone transecting an eclogite body that has undergone partial retrogression to amphibolite facies at circa 700 c optical microscopy back scattered electron imaging electron probe microanalysis and electron back scatter diffraction reveal garnet sub structures that are developed as a function of strain subgrains with low angle misorientation boundaries occur at low strain and garnet orientations are dispersed around rational crystallographic axes across these boundaries towards high strain areas boundary misorientations increase and there is a loss of crystallographic control on misorientations which tend towards random in high strain areas a polygonal garnet microstructure is developed the garnet orientations are randomly dispersed around the original single crystal orientation some garnet grains are elongate and ca rich garnet occurs on the faces of elongate grains oriented normal to the foliation commonly the garnet grains are admixed with matrix minerals and where in contact with other phases garnet is well faceted we suggest that individual garnet porphyroclasts record an evolution from low strain conditions where dislocation creep and recovery accommodated deformation through increasing strain where dynamic recrystallization occurred by subgrain rotation to highest strains where recrystallized grains were able to deform by diffusion creep assisted grain boundary sliding with associated rotations

exploring sea country through high resolution 3d seismic imaging of australia s nw shelf resolving early coastal landscapes and preservation of underwater cultural heritage abstract almost 2 million square km of australia s continental shelf was flooded following the termination of the last glacial maximum and with it the cultural heritage of the first arrival and coastal occupation of australia beginning some 65 000 years ago in order to prospect for this missing cultural record we must first identify submerged coastal landscapes and landforms that likely provided favourable environments for occupation and resource use however this task is challenged by the sheer size of the australian continental margin to help address this we use industry 3d seismic datasets that cover vast areas of australia s continental shelf to map seafloor bathymetry at high resolution 10 25 m our study focuses an area of 6500 square km on the mid outer shelf regions proximal to barrow island the 3d seismic bathymetry revealed a highly complex and geomorphically mature coastal landscape preserved at depths of 70 75 m below sea level including coastal barrier dunes lagoonal systems tidal flats and estuarine channels based on the depth of the submerged shorelines and reconstructed sea level curves the age range of these coastal landforms is constrained to marine isotope stage 3 57 29 ka which overlaps with the known onset of occupation at barrow island and the wider carnarvon bioregion and the adjacent pilbara such feature preservation has significant geoheritage value but also allows for human behavioural ecology modelling and provides targets for future dating and site survey

impacts of rapid sea level rise on mangrove deposit erosion application of taraxerol and rhizophora records we investigated a well dated marine sediment core from the tropical se atlantic covering the last 25 kyr applying taraxerol and rhizophora pollen as organic geochemical and palynological proxies for mangrove respectively taraxerol records are positively correlated with rhizophora pollen records showing an enhanced supply of mangrove materials into deep sea environments during the last deglaciation termination i sedimentation rates peaked during meltwater pulses 1a and 1b which were associated with the maxima of taraxerol and rhizophora pollen this study supports the view that mangrove input was dominantly controlled by erosion of mangrove rich shelf sediments during the transgressions whether reworked materials were penecontemporaneous or from much older deposits formed during previous sea level cycles is discussed copyright 2005 john wiley sons ltd

geochronological studies of proterozoic crustal evolution in the northern outer hebrides abstract new data on the proterozoic thermal and tectonic crustal history of the lewisian complex have been determined using sm nd and 40 ar 39 ar isotopic analyses igneous assemblages from two mafic ultramafic masses indicate crystallization at 2 54 and 2 14 ga from magmas with initial nd isotopic composition lower than predicted depleted mantle at those times sm nd isotope systematics t dm 2 45 ga in two samples of metasediment from the leverburgh belt imply that they contain a significant post archaean component and cannot therefore be part of an archaean stratigraphic sequence sm nd mineral isotope data on three samples confirm the proterozoic age of high pressure granulite facies metamorphism in the south harris igneous complex the most precise estimate is 1 827 0 016 ga on a metagabbro which was intruded after deformation of the host anorthosite under granulite facies conditions localized granulite facies assemblages in younger basic bodies further north are significantly younger at 1 63 ga whole rock sm nd data on two samples from the 1 7 ga granite injection complex of south harris indicate nd between 11 5 and 13 7 at the time of intrusion providing a strong indication that they were produced by remelting of pre existing crust similar to the exposed grey gneisses which had values close to 12 at that time 40 ar 39 ar data from 13 hornblendes generally show complex argon release patterns with indications of excess argon in most samples flat sections of the spectra range in age between 1 63 and 1 78 ga previous rb sr data on biotite showed a distinct break in age pattern across the langavat belt there is no indication of such a break in the hornblende data and it is inferred that despite variations in the timing of peak metamorphism the whole of the northern outer hebrides cooled through hornblende closure temperatures in the interval 1 7 1 6 ga

multidisciplinary approaches to australian island pasts late pleistocene to historical perspectives on australian island use in this review volume we bring together researchers and institutions involved in australian island research to provide a contemporary synthesis and benchmark on archaeological and palaeoenvironmental research of australian island environments the last major overview of australian islands archaeological research appeared 16 years ago in the volume australian coastal archaeology hall and mcniven 1999 at that time the main geographical areas of dynamic islands research in australia were northwest western australia and central and southeast queensland since 1999 torres strait has developed as the most dynamic region of islands research in australia and this new volume showcases the range of recent research from torres strait and the adjacent region of southern papua new guinea all five inqua commissions coastal and marine processes humans and the biosphere palaeoclimates stratigraphy and chronology terrestrial processes deposits and history are represented in the papers in the volume key environmental themes explored through the volume are geoarchaeology taphonomy impacts of sea level rise and climate change chronology of island formation and colonisation anthropogenic environmental modifications island terrestrial and marine resource management and intra and inter island occupation mobility and exchange relationships key socio cultural themes explored include ritual and ceremonial sites mortuary practices canoe voyaging and responses to colonial impact site types discussed include shell deposits cultural and natural villages long houses gardens rock art ritual shrines artificial reefs and ceremonial stone arrangements the contributions represent diverse multidisciplinary approaches adopting coordinated methodologies to the task of understanding the diversity of human use and modification of islands in the australian context culturally and chronologically the volume surveys the depth and breadth of australian island societies including studies of late pleistocene island use in northwest australia late holocene deltaic island societies of papuan lowland rainforests early to mid holocene tropical island use of torres strait and the great barrier reef and holocene selective occupation and abandonment of bass strait and other southern ocean islands the volume s geographic coverage is thus broadscale spread from the hot and humid tropical north to the cold temperate waters of the southern ocean uniquely the papers in this volume reveal the diversity and complexity of cultural practices e g subsistence mobility technology socio religious institutions cosmology resource manipulation and management and historical contingencies that structure and mediate long term human use engagement and modification of islands

kaapvaal craton changing first and second order controls on sea level from c 3 0 ga to 2 0 ga abstract well preserved supracrustal basin fills including the oldest large depository witwatersrand known makes the kaapvaal craton an ideal example for studying controls on first and second order stratigraphic cyclicity the duration of the three basins studied witwatersrand ventersdorp and transvaal from c 3 0 to c 2 0 ga is almost twice that of the entire phanerozoic period from which the paradigms of classical sequence stratigraphy have been derived amongst these is an assumption that cyclicity at specific hierarchical levels is predictable and repetitive through earth history this does not appear to be borne out by the precambrian record studied here instead a hierarchical order of cycles based on relative importance of sequences allied to a more flexible approach to controls on stratigraphic cyclicity at first and second orders is preferred first order cycles within the c 3 0 2 0 ga period on kaapvaal are synonymous with the entire evolution of a supracrustal basin fill defined by a specific basin type second order cycles define basin fill packages of unique character which reflect large scale shifts in the accommodation sedimentation balance early to middle archaean evolution of the kaapvaal craton encompassed amalgamation of a mosaic of subdomains to produce an early south southeastern nucleus by c 3 1 ga accretion of composite terranes from both north and west followed from c 3 0 2 7 ga this was contemporaneous with evolution of the c 3 0 2 8 ga witwatersrand basin the high grade limpopo terrane was amalgamated with the kaapvaal craton between 2 95 and 2 69 ga although a younger age for this orogensis is also possible the witwatersrand first order depositional cycle was controlled largely by subduction related tectonic loading and had a duration of c 190 my the c 5 my first order cycle of the c 2 7 ga ventersdorp basin was essentially controlled by thermal uplift induced extensional subsidence and that of the c 650 my transvaal basin by extensional and subsequent thermal subsidence it is noteworthy in the three basins examined that first order cycles controlled by plate tectonics witwatersrand and transvaal basins were about two orders of magnitude longer relative to the ventersdorp plume tectonic cycle second order cycles also varied greatly from c 100 my to c 1 my within the witwatersrand and transvaal basins subsidence allowed extensive seaways to develop within which classical sequence stratigraphic systems tracts can be recognized reflecting different stages of shoreline shifts within the short lived ventersdorp continental basin system sedimentological criteria can be used to discriminate high and low accommodation systems tracts the transvaal first order cycle was terminated at c 2 0 ga by the bushveld complex plume event

eclogitized gabbros from the eastern grenville province textures metamorphic context and implications undeformed lenses of olivine orthopyroxene gabbro belonging to the 1429 ma shabogamo intrusive suite parautochthonous belt of the eastern grenville province host the first occurrence of eclogite mineral assemblages reported from the grenville province these rocks preserve igneous textures overprinted by eclogite mineralogy and by textures related to subsequent unloading high pressure signatures include omphacite pseudomorphs after augite plagioclase replacement by garnet kyanite corundum and orthopyroxene omphacite garnet coronas between olivine and plagioclase transformations related to decompression include replacement of garnet kyanite corundum by spinel plagioclase growth of plagioclase collars between clinopyroxene and garnet and de jadeitization of omphacite clinopyroxenes with numerous plagioclase inclusions and garnets surrounded by clinopyroxene plagioclase symplectites in granoblastic mafic rocks from the same area are also evidence of decompression from high pressures these

mesoarchaean palaeoproterozoic crustal scale tectonics of the central witwatersrand basin interpretation from 2d seismic data and 3d geological modelling abstract the witwatersrand basin represents one of the largest exposures of meso neoarchaean rock on earth and hosts the vredefort dome at its geographic centre the southern half of the basin is covered by thin palaeozoic to early mesozoic marginal sequences of the karoo supergroup however visualisation and analysis of this unexposed portion of the basin can be achieved in a 3d geomodelling environment through the integration of geophysical 2d reflection seismics and traditional geological data in this study the 3d structural architecture around the vredefort dome in the witwatersrand basin is evaluated to establish strato tectonic relationships first order scale structures and a new model for the architecture of basement rocks from the geological modelling several strato structural features have been identified in the seismic sections including a well developed listric fault system in the southwest a prominent fold system observed in the transvaal supergroup and a large listric fault in the east that offsets the aforementioned fold system integration of these geophysical and geological data in 3d space has provided 3d constraints on the volumes for the witwatersrand supergroup ventersdorp supergroup and transvaal supergroup to the south southeast and east of the vredefort dome

metamorphism of the witwatersrand gold fields a review abstract there is widespread evidence for greenschist facies metamorphism in different rock types within all the witwatersrand gold mines the silicate mineral assemblages suggest near uniform peak metamorphic conditions equivalent to the chlorite zone in all the major witwatersrand gold fields assemblages of coexisting pyrophyllite chloritoid have been recorded in most of the gold mines and the critical assemblage of pyrophyllite chloritoid muscovite chlorite quartz tourmaline rutile pyrite is found in most gold fields kaolinite paragonite biotite pyrrhotite and arsenopyrite have more local distribution pelites shales quartzites meta conglomerates metabasalts and some dykes record these metamorphic assemblages albeit in different mineral proportions and pyrophyllite and chloritoid are recorded from many gold producing reefs andalusite kyanite garnet and or cordierite bearing assemblages indicate higher metamorphic grades in three discrete areas along the nw margin of the witwatersrand basin to the ne of the evander gold field and around the collar of the vredefort dome concentric metamorphic facies around the vredefort dome culminate in granulite facies assemblages near the centre it is important to note that there are no definitive published data constraining the temporal relationships between the granulites and amphibolites of the vredefort dome greenschist facies assemblages in the vredefort collar rocks thermal metamorphism related to intrusion of the bushveld complex and the regional greenschist facies metamorphism documented in the gold fields metamorphic conditions of 350 50 c and up to 3 kbars are inferred for the gold fields with temperatures increasing to around 700 c in granulites of the vredefort dome other geothermometric methods including illite crystallinity fluid inclusions carbon elemental ratios and vitrinite reflectance are compatible with the above estimates but are each associated with considerable temperature uncertainties fluids in equilibrium with pyrophyllite muscovite quartz pyrite paragonite are inferred during metamorphism suggesting slightly acid conditions and elevated sulphur activities regional greenschist facies metamorphism documented in the witwatersrand gold mines was accompanied by widespread deformation large fluxes of aqueous fluid and considerable element mobility the low intermediate pressure of this metamorphic terrain and the lack of large scale tectonic thickening favours underplating by mafic magmas as the likely cause of the metamorphic pattern no model for gold genesis in the witwatersrand basin is complete without accommodating post burial processes including metamorphism deformation and alteration any placer gold would be overprinted by these processes and any epigenetic gold could potentially be introduced during these periods of thermal and fluid activity it is also important to note at least two quite unusual features of the witwatersrand metamorphic assemblages the virtual absence of feldspar from the 3 km thick central rand group over 300 km and the narrow range of metamorphic grade inferred for the gold mines over this same distance

p t conditions of grenville age eclogite facies metamorphism and amphibolite facies retrogression of the glenelg attadale inlier nw scotland peak and retrograde p t conditions of grenville age eclogites from the glenelg attadale inlier of the northwest highlands of scotland are presented peak conditions are estimated as c 20 kbar and 750 780 c in broad agreement with previous work the eclogites subsequently followed a steep decompression path to c 13 kbar and 650 700 c during amphibolite facies retrogression peak eclogite facies metamorphism occurred 1080 ma and retrogression atc 995 ma suggesting fairly sluggish uplift rates of 0 3 km ma and cooling rates of 1 25 c ma when compared with other parts of the grenville orogeny and or modern orogens however current poor constraints on the timing of peak metamorphism mean that these rates cannot be used to interpret the geodynamic evolution of this part of the orogen the p t t data together with petrology and the field relationships between the basement rocks of the glenelg attadale inlier and the overlying moine supergroup mean that it is difficult to support the currently held view that an unconformable relationship exists between the two it is suggested that more data are required in order to re interpret the neoproterozic tectonic evolution of the northwest highlands of scotland

discussion a unifying model for the torridon group early neoproterozoic nw scotland product of post grenvillian extensional collapse by ge williams and j foden the torridonian succession in nw scotland is a well exposed sequence of sedimentary rocks that record the early neoproterozoic geological evolution of laurentia an excellent review by stewart 2002 summarised the observations on the three main torridonian units the stoer sleat and torridon groups the torridon group deposited between 1000 950 ma was initially interpreted as a rift basin stewart 1982 and williams 2001 but a number of studies rainbird et al 2001 kinnaird et al 2007 and krabbendam et al 2008 have now concluded that it represents a foreland basin positioned in front of the grenville orogen 1200 960 ma in a recent paper in earth science reviews williams and foden 2011 propose instead that the torridon group was deposited in an extensional collapse basin we question this conclusion and take this opportunity to highlight aspects of their new interpretation that we find equivocal

the morphology of the reaction front of the dissolution precipitation reaction rutile wollastonite titanite in time series experiments at 600 c 400 mpa fluid assisted mass transport reactions by dissolution precipitation where a precursor mineral reacts with a fluid play an important role in metamorphism and metasomatism we investigated titanite growth on rutile in time series experiments between one and 107 days at constant p t conditions of 600 c and 400 mpa in the system tio 2 cao sio 2 na 2 o hcl h 2 o a two capsule assemblage allows for transport of ca and si from dissolving wollastonite to dissolving rutile the ti source in a nacl bearing aqueous fluid according to the general reaction casio 3 tio 2 catisio 5 complete overgrowth of rutile by titanite occurred after just one day of experiment fine grained lozenge shaped titanite crystals of short time runs up to 14 days reorganize to larger predominantly prismatic crystals after 14 days after investigation by scanning electron microscopy the titanite overgrowth was removed from the rutile by hydrofluoric acid to provide a three dimensional view of the dissolution reaction front on the rutile surface the morphology of the rutile surface is dominated by humps or ridges beneath the central region of a titanite crystal and valleys at the grain boundaries between adjacent titanite crystals the dissolution pattern on the rutile surface mimics the titanite overgrowth and changes with changing grain size and shape of the titanite with longer run times the preferred dissolution of rutile in the valleys is clearly linked to the position of the titanite grain boundaries which served as pathways for fluid assisted element transport rutile titanite and titanite titanite boundaries show a significant porosity in transmission electron microscopy images of foils prepared by focused ion beam milling the large scale dissolution pattern on the rutile surface is independent of the crystallographic orientation of the rutile and entirely dominated by the arrangement of titanite crystals in the overgrowth dissolution features on a scale smaller than 1 m are dominated by stepwise dissolution and etch pits following the crystallographic orientation of the rutile similar observations were made in experiments with an additional al source although these experiments result in a different overgrowth pattern i e an exposed rutile surface is always present and solitary titanite crystals are accompanied by partial overgrowths quantitative characterization of the surface morphology by white light interference microscopy demonstrates that with increasing grain size of titanite dissolution of rutile is strongly enhanced at the titanite grain boundaries natural examples of titanite overgrowths on rutile show the same relations between element pathways arrangement of titanite crystals and 3d dissolution pattern on rutile as in the experimental systems we conclude that the transport of ti away from the rutile and of ca si into the reaction rim occurred in a grain boundary fluid the composition of which must have been strongly different from the composition of the bulk fluid in the experiment as well as in the natural system the reaction progress depends on the availability of a fluid and relicts of rutile in titanite indicate restricted availability of fluid in the natural system e g a fluid pulse that was consumed by the reactions the reaction examined here can serve as a proxy for other reactions of the conversion of oxide minerals e g spinel or corundum into silicates

pb u and th diffusion in natural zircon zircon zrsio4 is one of the most widely used minerals for determining the age origin and thermal history of rocks by u th pb geochronology but the parameters describing the solid state volume diffusion rates of these elements in natural zircon which are themselves important for establishing the limits on the applicability of zircon for geochronological studies have remained poorly quantified1 this is because of the measurement difficulties associated with the low p p m concentrations and low diffusion rates of these elements in natural zircon and the chemical and physical heterogeneity present in most crystals here we present direct measurements of the uranium thorium and lead loss from a thermally treated gem quality natural zircon and show that lead diffuses much faster than uranium or thorium we find that the u th pb isotopic system in natural zircon will typically have a closure temperature greater than 900 c which explains why zircon is apparently such a robust geochrometer and is capable of remaining isotopically closed through extended periods of high grade metamorphism and partial melting of the host rock

neoarchaean tectonic history of the witwatersrand basin and ventersdorp supergroup new constraints from high resolution 3d seismic reflection data abstract first order scale structures in the west wits line and west rand goldfields of the witwatersrand basin south africa were mapped using the high resolution 3d reflection seismic method structural models constrain the magnitude of displacement of thrusts and faults the gross structural architecture and neoarchaean tectonic evolution of the west rand and bank fault zones which offset the gold bearing reefs of the basin the merging of several 3d seismic surveys made clear the gross strato structural architecture of the goldfields a macroscopic fold thrust belt is crosscut by a macroscopic extensional fault array these are dissected eroded and overlain by the transvaal supergroup above an angular unconformity the seismic sections confirm that the west rand group ca 2985 2902 ma is unconformably overlain by the central rand group ca 2902 2849 ma with tilting of the west rand group syn to post erosion at ca 2 9 ga the seismic sections also confirm that an unconformable relationship exists between the central rand group and the auriferous ventersdorp contact reef vcr with an easterly verging fold thrust belt being initiated concomitant to deposition of the vcr at approximately 2 72 ga fold thrust formation included development of the 1 newly identified first order scale libanon anticline 2 tandeka and jabulani thrusts which displace the west rand group and 3 parasite folds the fold thrust belt is crosscut by a macroscopic extensional fault array or rift like system of faults which incepted towards the end of extrusion of the ventersdorp lavas and certainly during deposition of the platberg group 2709 2643 ma when a mantle plume may have heated the lithosphere the west rand and bank fault zones formed at this time and include 1 the west rand and bank faults which are scissors faults 2 second and third order scale normal faults in the immediate footwall and hanging wall of the faults 3 drag synclines and 4 rollover anticlines

nature and origin of carbon in the archaean witwatersrand basin south africa the nature and origin of the carbonaceous matter carbon in the gold bearing reefs of the archaean witwatersrand basin of south africa has long been a subject of controversy and debate the importance of the carbon results from its direct association with the gold grade the studies reported here were directed at resolving the nature and origin of carbon techniques used include stope scale macroscopic mapping mesoscopic hand specimen examination and microscopic studies incorporating the use of optical reflectance measurement macroscopic mapping has demonstrated the braided habit of carbon bodies over tens of square metres with a close parallel to sedimentology mesoscopic observations however show the vein like carbon seams are often cross cutting sedimentary features with the carbon occupying an anastomosing set of bed parallel fractures microscopic observations show a globular form for the carbon and inclusions of uraninite particles in seam carbon the globules are generally modified into elongated spindles oriented perpendicular to bedding optical properties are dominated by generally high reflectance and anisotropy with a swirling liquid crystal structure classifying seam carbon as carbonaceous mesophase it is this fine mesophase texture that has previously been wrongly attributed to plant algal morphology highly significantly the optical anisotropy is bed perpendicular rather than bed parallel as in normal sedimentary burial indicating mesophase formation during fracture opening both reflectance and bireflectance of the seam mesophase show a range of values at all scales no stratigraphic or depth trends were apparent though geographic variation points to localization of the maximum temperature event s given high anisotropies maximum reflectance values in the 4 8 r o range and minima in the 1 2 r o range give arithmetic mean reflectance values of about 4 0 r o kinetic modelling equates these values with short term 50 000 years temperature events of c 400 c or burial temperatures of c 280 c lower reflectance values of c 2 0 r o obtained from the shales suggests thermal detachment of permeable and impermeable beds a characteristic of pulsed hydrothermal flux the included uraninite grains influence the orientation of the surrounding anisotropic mesophase demonstrating that uraninite predated the mesophase formation event regional palaeo stress frozen into the mesophase anisotropy indicates a nw se deviatoric stress the combination of hydrocarbon radiation and hydrothermal fluid flow marks witwatersrand basin pyrobitumens out as being different from conventional oil putative source rocks for the oil are identified in the intra basinal witwatersrand shale units lithological control in carbon seams is explained by the poro perm and mechanical properties of the unconformity sequence of footwall reef conglomerates and hanging wall quartzites favouring fracture along the unconformity surfaces an overpressured oxidizing fluid created the fracture network that hosted the oil and also introduced uranium as uranyl ion on meeting a reducing agent oil uraninite precipitated stabilizing the oil by polymerization further hotter hydrothermal flux then coked the bitumen to often fibrous spindle shaped mesophase continued flow deposited gold in the available pore spaces most notably those formed by lateral contraction between mesophase spindles the speculative role of methane in the reductive precipitation of gold is indicated by the presence of gold in any co eval porosity largely independent of the mineral matrix

late quaternary cycles of mangrove development and decline on the north australian continental shelf mangrove communities in the australian tropics presently occur as narrow belts of vegetation in estuaries and on sheltered muddy coasts palynological data from continental shelf and deep sea cores indicate a long term cyclical component of mangrove development and decline at a regional scale which can be linked to specific phases of late quaternary sealevel change extensive mangrove development relative to today occurs during periods of marine transgression whereas very diminished mangrove occurs during marine regressions and during rarer periods of relative sea level stability episodes of flourishing mangrove cannot be linked to phases of humid climate as has been suggested in studies elsewhere rather the cycle of expansion and decline of mangrove communities on a grand scale is explained in terms of contrasting physiographic settings characteristic of continental shelf coasts during transgressive and regressive phases in particular by the existence or lack of well developed tidal estuaries copyright c 1999 john wiley sons ltd

reaction textures and fluid behaviour in very high pressure calc silicate rocks of the munchberg gneiss complex bavaria germany calc silicate rocks occur as elliptical bands and boudins intimately interlayered with eclogites and high pressure gneisses in the munchberg gneiss complex of ne bavaria core assemblages of the boudins consist of grossular ric h garnet diopside quartz zoisite clinozoisite calcite rutile and titanite the polygonal granoblastic texture commonly displays mineral relics and reaction textures such as post kinematic grossular rich garnet coronas reactions between these mineral phases have been modelled in the cao al 2 0 3 si02 c 02 h 20 system with an internally consistent thermodynamic data base high pressure metamorphism in the calc silicate rocks has been estimated at a minimum pressure of 31 kbar at a temperature of 630 c with x osq gi small volumes of a c02 n2 rich fluid whose composition was buffered on a local scale were present at peak metamorp hic conditions the p t conditions for the onset of the amphibolite facies overprint are about 10 kbar at the same temperature a co of the h20 rich fluid phase is regarded to have been 0 03 during amphibolite facies conditions these p t estimates are interpreted as representing different stages of recrystalliza tion during isothermal decompression the presence of multiple generations of mineral phases and the preservation of very high pressure relics in single thin sections preclude pervasive post peak metamorphic fluid flow as a cause of a re equilibration within the calc silicates the preservation of eclogite facies very high pressure relics as well as amphibolite facies reactions textures in the presence of a fluid phase is in agreement with fast tectonically driven unroofing of these rocks

u pb baddeleyite ages for the scourie dyke swarm scotland evidence for two distinct intrusion events precise and accurate radiometric ages for continental mafic dyke swarms are a prerequisite for global correlation of mafic magmatic events calibration of apparent polar wander paths and deciphering mechanisms of dyke emplacement precambrian dyke swarms such as the scourie dyke swarm in north west scotland are invaluable time markers so that a precise and accurate knowledge of their emplacement age is critical when unravelling the complex geological evolution of many terrains precise dating is often difficult however because magma interaction with country rock and subsequent metamorphic events can severely perturb some isotopic systems recent advances in u pb geochronology1 3 combined with the discovery that some mafic dykes contain trace amounts of uranium bearing minerals such as baddeleyite zro2 and or zircon have made it possible to obtain u pb ages for these rocks with a precision typically on the order of 1 2 myr4 5 some of the first detailed u pb studies of precambrian mafic dyke swarms5 6 have shown that large volumes of mafic magma 100 000 km3 were emplaced into the continental crust in surprisingly short periods of time 2 myr here we report the results from a u pb study of three members of the scourie dyke swarm and find at least two periods of dyke emplacement at 2 418 and 1 992 myr bp we speculate on a potential global correlation of early proterozoic mafic magmatism and hence on the origin of dyke swarms

an early holocene sea level jump and delta initiation 1 early holocene sea level change controlled the evolution of clastic coastal depositional systems radiocarbon dated borehole cores obtained from three incised valley fill systems in asia changjiang song hong and kiso river record very similar depositional histories especially between about 9000 and 8500 cal bp sedimentary facies changes from estuarine sand and mud to shelf or prodelta mud suggest that the marine influence in the incised valleys increased during this period in addition large decreases in sediment accumulation rates occurred a sea level jump causes an estuarine system and its depocenter to move rapidly landward it is possible that the final collapse of the laurentide ice sheet accompanied by catastrophic drainage of glacial lakes at approximately 8500 cal bp caused such a jump the jump was followed immediately by a period of decelerated sea level rise that promoted delta initiation

archean foreland basin tectonics in the witwatersrand south africa the witwatersrand basin of south africa is the best known of archean sedimentary basins and contains some of the largest gold reserves in the world sediments in the basin include a lower flysch type sequence and an upper molassic facies both of which contain abundant silicic volcanic detritus the strata are thicker and more proximal on the northwestern side of the basin which is at least locally bound by thrust faults these features indicate that the witwatersrand strata may have been deposited in a foreland basin and a regional geologic synthesis suggests that this basin developed initially on the cratonward side of an andean type arc remarkably similar phanerozoic basins may be found in the southern andes we suggest that the continental collision between the kaapvaal and zimbabwe cratons at about 2 7 ga caused further subsidence and deposition in the witwatersrand basin regional uplift during this later phase of development placed the basin on the cratonward edge of a collision related plateau now represented by the limpopo province similarities are seen between this phase of witwatersrand basin evolution and that of active basins north of the tibetan plateau e g the tarim and tsaidam basins the geologic evidence does not appear so compatible with earlier suggestions that the witwatersrand strata were deposited in a rift or half graben

on the role of isostasy in the evolution of normal fault systems the footwalls of west dipping normal faults that separate the west central colorado plateau from the basin and range province record at least 5 7 km and perhaps as much as 15 20 km of west side up neogene uplift with an axis just 10 20 km west of undeformed plateau strata the uplift is expressed as folding and steep faulting in pre tertiary cratonic and disconformably overlying neogene strata forming a basement cored anticline and coincident topographic high on the western margin of the plateau the authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin profound isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains calling into question several assumptions fundamental to existing models of the evolution of normal fault systems

himalayan tibetan analogies for the evolution of the zimbabwe craton and limpopo belt abstract the limpopo orogeny which lasted from 2700 to 2600 ma was characterised by nnw sse directed shortening this resulted in both crustal thickening accommodated by folding and nnw directed thrusting and associated crustal extrusion whereby a number of crustal blocks including the central zone of the limpopo belt was displaced to the west southwest along wsw ene trending shear zones this was part of a regionally distributed phase of orogenic deformation which affected the adjoining kaapvaal and zimbabwe cratons from the witwatersrand basin in the south to the harare greenstone belt in the north this deformation which migrated northwards with time postdated an earlier phase of crustal accretion during which the archaean crustal unit now marked by the kaapvaal and zimbabwe cratons and the limpopo belt grew towards the north northwest shortening of this unit during the limpopo orogeny may be regarded as the last stage of the crustal accretion process this tectonic process of continental growth by accretion followed by crustal shortening with associated crustal extrusion has many features in common with tibetan tectonics from the mesozoic to the present

geochronology of late caledonian magmatism in northern britain rb sr k ar ar ar and sm nd isotopic data are presented for mineral separates and whole rock samples from old red sandstone ors lavas associated minor intrusions and 9newer granite9 intrusive complexes from the cheviot hills north to shetland these data yield 16 internally consistent rb sr mineral ages and one each of ar ar sm nd and k ar ages when considered with precise and reliable published data it is clear that there are systematic differences in the age of late caledonian magmatism through the geological regions of scotland in the grampian highlands and the scottish midland valley magmatism was concentrated during the period 423 to 410 ma ors volcanism in the highlands occurred around 420 ma with plutonism continuing to about 408 ma volcanism and plutonism in the midland valley took place between 415 and 410 ma in the southern uplands magmatism occurred earlier in the north with all magmatism close to the southern uplands fault dated around 408 ma and that close to the iapetus suture dated at around 394 ma as no evidence exists for ocean closure prior to c 400 ma the age of igneous activity north of the southern uplands fault is consistent with chemical evidence for a relationship to active nw directed subduction the younger magmatism of the s part of the southern uplands cannot be subduction related and the c 408 ma plutons nearer the southern uplands fault can only be subduction related if tectonic construction of the southern uplands was a two stage process

integration of underground mapping petrology and high resolution microseismicity analysis to characterise weak geotechnical zones in deep south african gold mines abstract a highly stressed shaft pillar is prone to large seismic events falls of ground and rockbursts which may cause injuries and loss of production especially in weak geotechnical zones it is thus important to identify weak geotechnical zones in order to mitigate risks in this study we present integrated studies underground mapping petrology rock mechanics and high resolution microseismicity analysis to understand the different geotechnical zones in the shaft pillar of cooke 4 mine in south africa the footwall of the remnant shaft pillar comprises the upper elsburg reef of the mondeor formation while the ventersdorp contact reef vcr of the venterspost formation and soft weak lavas of the westonaria formation form the hangingwall results from underground mapping and microscopic analysis show that the shaft pillar is composed of quartzites pebbly quartzites argillaceous quartzites and conglomerates underground mapping further shows that the shaft pillar is characterized by several discontinuities which vary from minor to macro scale fractures laboratory uniaxial compressive strength ucs tests indicate that quartzite has the strongest strength followed by pebbly quartzite argillaceous quartzite and lastly conglomerate analysis of high resolution acoustic emissions aes clusters indicates that the majority of aes are associated with the mining stope faces the clusters show the formation of ortlepp shears ahead of the stope which is caused by the excavation induced stress field microseismic data further reveal that the fracture turning point occurs in the soft strata weak hangingwall lavas the integration of these datasets has allowed us to develop the fracture model for different geotechnical zones which concurs with previous models developed for the similar underground environment i e weak soft lava hangingwall and quartzite conglomerate footwall this has major implications for future mining support production and safety

evaluating the structural character and tectonic history of the witwatersrand basin abstract the witwatersrand basin in south africa has been the focus of gold exploitation for more than 100 years and the subject of hundreds of research investigations principally sedimentological and metallogenic and recently geophysical and geochronological surprisingly the basin wide structural character has not been fully investigated despite the fact that gold metallogenic models have been proposed that want structural architectures as conduits for gold mobilisation and or sites of deposition i e the modified placer and hydrothermal models these models which have polarised viewpoints on the source for gold placer versus metamorphic or hydrothermal source assume an underlying structural character to the basin and structural relationships between goldfields but these assumptions have never been tested through evaluation of the existing structural dataset as corollary the published data for the structural character of the free state welkom klerksdorp west wits line west rand central rand east rand and south rand goldfields are summarised and evaluated to search for basin wide similarities and or correlations that would support tectonic models for the witwatersrand basin and explain its metallogenic character unfortunately the large published historical database 90 years proved to be quite limited with respect to geometric kinematic and or relative chronological detail but must be evaluated against an advanced understanding of earth processes tectonics and the structural geology approach the dataset is largely qualitative rather than quantitative but is useful in establishing broad tectonic trends of the formation and tectonic evolution for the witwatersrand basin it suggests that two deformation events umzawami and ukubambana events mark the end of deposition in the witwatersrand and transvaal basins respectively with development of fold thrust belts at ca 2 7 and 2 2 2 0 ga and these can be correlated with supercontinental cycles the intervening period i e 2 7 2 2 ga was characterised by at least 4 basin forming events that culminated in the deposition of the volcanic sedimentary sequences of the klipriviersberg group and the sedimentary sequences of the platberg chuniespoort and pretoria groups basin formation was facilitated by the reactivation of structures formed during the umzawami event or older as feeder dykes normal listric faults or growth faults the limited structural data for the witwatersrand basin unsurprisingly also leads to the conclusion that gold was macroscopically to mesoscopically remobilised from a primary placer source but remobilisation was localised goldfields scale and not is a basin wide phenomena

small scale transport of trace elements nb and cr during growth of titanite an experimental study at 600 c 0 4 gpa trace element distribution in titanite overgrowths on rutile has been investigated experimentally at 600 c 400 mpa and fo2 near ninio buffer compositionally homogenous cr or nb doped synthetic rutile single crystals or nb containing natural rutile crystals were the source of cr nb and ti to synthesize titanite using the double capsule technique all element exchange with the source of si ca and al occurred via a nacl h2o fluid titanite forms quickly and exclusively around the rutile crystals the titanite overgrowth separates rutile from the bulk fluid and all elements from rutile dissolution have to pass through the titanite rim trace element concentrations in titanite show a considerable scatter in experiments with and without al although the average concentrations of cr or nb of titanite around compositionally homogeneous synthetic rutile approach the expected values for closed system conditions variability of al with cr or nb in the titanite is not correlated the al zoning is irregular and patchy and also the distribution of trace elements does not show systematic trends in the spatial distribution in experiments using zoned natural rutile the concentrations of nb in titanite are related to the nb zoning in rutile but the contents also vary unsystematically under the controlled conditions of the experiment the explanation for the strongly irregular spatial distribution is most likely due to variations in elemental concentrations during transport from the rutile along the titanite grain boundaries the transport pathway is complex because grain boundary migration is important during titanite growth such irregular element distribution is also found in a natural sample of titanite overgrowth on rutile from an eclogite with retrograde overprint in the amphibolite facies transport of ti and trace elements was focused on grain boundaries and shielded from the rutile as a source of these elements we conclude that this type of zoning is not related to changes in p t or composition in an open system but solely controlled by transport in and through the titanite rim

zircon ion microprobe studies bearing on the age and evolution of the witwatersrand triad abstract the ventersdorp and witwatersrand supergroups and the dominion group collectively referred to as the witwatersrand triad represent some of the oldest and economically most important volcano sedimentary basins within the kaapvaal craton of southern africa precise age constraints which are vital to models aimed at understanding the formation mineralisation and evolution of these basins have been hampered by analytical and geological problems these problems have been overcome by this ion microprobe study on zircons from volcanic rocks within the three basins felsic and mafic volcanics from the ventersdorp supergroup yield ages of 2709 4 ma and 2714 8 ma respectively constraining the timing of the closure of the witwatersrand basin a maximum age for the witwatersrand basin is indicated by the age of 3074 6 ma for volcanics from the underlying dominion group thus a period of c 350 ma was available for the accumulation of the full witwatersrand basin succession unfortunately dating within the witwatersrand basin itself is not complete and future work could show that extended time breaks may exist within the basin these new data show that previous age determinations on the ventersdorp witwatersrand and dominion basins were inaccurate and that the economically important witwatersrand basin must now be recognised as archaean

grenvillian age decompression of eclogites in the glenelg attadale inlier nw scotland the glenelg attadale inlier is the largest basement inlier within the caledonian moine nappe of nw scotland in the eastern part of the inlier amphibolite facies retrogression of the eclogites is associated with tectonic fabrics and p t estimates indicate significant decompression c 20 km previous sm nd mineral whole rock dates indicated that peak eclogite facies metamorphism occurred around c 1 08 ga which was correlated with the grenvillian orogeny however the middle ree enrichment of the analysed garnets suggests the influence of apatite inclusions it is therefore likely that the interpretation of the c 1 08 ga age is complex possibly reflecting re equilibration at lower temperatures sampled eclogites contain zircon in a number of distinct textural forms that are mainly associated with pargasite and plagioclase and are part of the retrograde amphibolite facies assemblages titanite extensively replaces rutile and is clearly associated with the retrograde amphibolite facies event a second textural type of titanite forms anhedral grains with plagioclase and pargasite which is developed where the retrograde amphibolite facies assemblage overprints the eclogite mineralogy u pb dating has yielded the following ages zircon age of 995 8 ma and variably discordant rutile ages between 416 and 480 ma u pb and pb pb isochrons on titanite and plagioclase quartz separates yielded ages of 971 65 ma and 945 57 ma respectively in agreement with the zircon age analysed zircons and titanites are texturally part of the amphibolite facies assemblage the new zircon age demonstrates that amphibolite facies metamorphism during exhumation occurred at 995 8 ma the titanites could have closed with respect to pb at this time or alternatively at some time between c 1000 and 900 ma these data clearly demonstrate that parts of the scottish basement underwent major thick skinned tectonics during the grenvillian orogeny rutile is part of the eclogite facies paragenesis and yet has young ages these data are best explained by reheating producing near total pb loss related to emplacement of the late to post tectonic ratagain granite complex at c 425 ma at the end of the caledonian orogeny

direct dating of stromatolitic carbonates from the schmidtsdrif formation transvaal dolomite south africa with implications on the age of the ventersdorp supergroup pb isotopic analyses of stromatolitic limestones from the schmidtsdrif formation transvaal dolomite of south africa give a late archean isochron age of 2 557 plus minus 49 2 sigma ma the new date significantly changes the position of the archean proterozoic boundary in the kaapvaal province and suggests that a possible division of the transvaal supergroup is necessary it also resolves the long standing controversy about the age of the ventersdorp supergroup whose zircon u pb data of ca 2 7 ga must be more acceptable than the rb sr dates of about 2 3 ga the study provides a new example that demonstrates the great potential of employing the u pb systems of carbonate rocks for direct dating of sedimentary sequences

post glacial sea level changes around the australian margin a review abstract it has been known since rhodes fairbridge s first attempt to establish a global pattern of holocene sea level change by combining evidence from western australia and from sites in the northern hemisphere that the details of sea level history since the last glacial maximum vary considerably across the globe the australian region is relatively stable tectonically and is situated in the far field of former ice sheets it therefore preserves important records of post glacial sea levels that are less complicated by neotectonics or glacio isostatic adjustments accordingly the relative sea level record of this region is dominantly one of glacio eustatic ice equivalent sea level changes the broader australasian region has provided critical information on the nature of post glacial sea level including the termination of the last glacial maximum when sea level was approximately 125 m lower than present around 21 000 19 000 years bp and insights into meltwater pulse 1a between 14 600 and 14 300 cal yr bp although most parts of the australian continent reveals a high degree of tectonic stability research conducted since the 1970s has shown that the timing and elevation of a holocene highstand varies systematically around its margin this is attributed primarily to variations in the timing of the response of the ocean basins and shallow continental shelves to the increased ocean volumes following ice melt including a process known as ocean siphoning i e glacio hydro isostatic adjustment processes several seminal studies in the early 1980s produced important data sets from the australasian region that have provided a solid foundation for more recent palaeo sea level research this review revisits these key studies emphasising their continuing influence on quaternary research and incorporates relatively recent investigations to interpret the nature of post glacial sea level change around australia these include a synthesis of research from the northern territory queensland new south wales south australia and western australia a focus of these more recent studies has been the re examination of 1 the accuracy and reliability of different proxy sea level indicators 2 the rate and nature of post glacial sea level rise 3 the evidence for timing elevation and duration of mid holocene highstands and 4 the notion of mid to late holocene sea level oscillations and their basis based on this synthesis of previous research it is clear that estimates of past sea surface elevation are a function of eustatic factors as well as morphodynamics of individual sites the wide variety of proxy sea level indicators used their wide geographical range and their indicative meaning some progress has been made in understanding the variability of the accuracy of proxy indicators in relation to their contemporary sea level the inter comparison of the variety of dating techniques used and the nuances of calibration of radiocarbon ages to sidereal years these issues need to be thoroughly understood before proxy sea level indicators can be incorporated into credible reconstructions of relative sea level change at individual locations many of the issues which challenged sea level researchers in the latter part of the twentieth century remain contentious today divergent opinions remain about 1 exactly when sea level attained present levels following the most recent post glacial marine transgression pmt 2 the elevation that sea level reached during the holocene sea level highstand 3 whether sea level fell smoothly from a metre or more above its present level following the pmt 4 whether sea level remained at these highstand levels for a considerable period before falling to its present position or 5 whether it underwent a series of moderate oscillations during the holocene highstand

3d edge detection seismic attributes used to map potential conduits for water and methane in deep gold mines in the witwatersrand basin south africa abstractinrushes of ground water and the ignition of flammable gases pose risks to workers in deep south african gold mines large volumes of water may be stored in solution cavities in dolomitic rocks that overlie the black reef blr formation while there are several possible sources for methane namely coal seams kerogen found in some gold ore bodies or methane introduced by igneous intrusions potential conduits that may transport water and methane to underground workings were mapped using 3d reflection seismic data edge detection attributes successfully identified many faults some with displacements as small as 10 m faults that displace the ventersdorp contact reef vcr and the blr horizons were of special interest as known occurrences of fissure water and methane in underground workings show a good correlation with faults that were imaged on the vcr and blr horizons because there are uncertainties in determining the linkage of faults with aquifers and methane sources it is considered prud

comparison of laser ablation icp ms and isotope dilution ree analyses implications for sm nd garnet geochronology abstract high precision garnet chronometry using the sm nd u pb rb sr or lu hf isotope systems is gaining widespread application for constraining the prograde and high temperature history of metamorphic belts however due to the low concentrations of the chronometrically important elements garnet analyses are often susceptible to incorporation of small quantities of accessory phases such as zircon monazite and allanite here we assess the extent to which such inclusions affect garnet analyses by comparing in situ analyses of sm and nd concentrations in the crystal lattice obtained by laser ablation inductively coupled mass spectrometry la icp ms with those obtained by isotope dilution id on separates of the same garnets the results show that the garnets studied here are largely free from inclusions in general however the low concentrations of sm and nd in the garnet lattice mean that the incorporation of even very small quantities of accessory phases will result in a significant change in the measured garnet sm and nd concentration simple modelling of the effect of such inclusions on age information shows that garnet inclusion disequilibrium and the extent to which inclusions decrease the apparent parent daughter ratio are critical such modelling demonstrates that the incorporation of old lree enriched minerals such as monazite will yield an apparently lower age than the true garnet age however this study indicates that erroneous age information can be identified if duplicate garnet analyses are performed in addition la icp ms is shown to be a useful technique in verifying the purity of samples for isotope analysis

geochemical and u pb age constraints on the occurrence of polygenetic titanites in uhp metagranite in the dabie orogen abstract relict magmatic titanite was identified in the core of a few titanite grains with the overgrown rim of metamorphic titanite in uhp metagranite in the dabie orogen la icpms u pb dating gave neoproterozoic ages for the magmatic titanite but triassic ages for the metamorphic titanite the magmatic and metamorphic titanites are clearly distinct by differences in petrological and geochemical compositions the magmatic titanite occurs as residual cores that show bright bse the presence of allanite and quartz inclusions low contents of cao al2o3 and tio2 but high contents of fe2o3 and mgo in trace elements the magmatic titanite exhibits high ree and hfse contents distinctly negative eu anomalies with flat mree hree patterns and high th u ratios in contrast the metamorphic titanite occurs as rims and grains of homogeneously dark bse that contain inclusions of epidote quartz k feldspar rutile biotite and phengite and have relatively high contents of cao al2o3 and tio2 but low contents of fe2o3 and mgo and relatively low ree and hfse contents slightly negative eu anomalies with hree depletion relative to mree and low th u ratios the zr in titanite thermometry yields 727 to 877 c at 0 5 to 1 0 gpa for the magmatic titanite and 729 to 870 c at 1 5 to 2 0 gpa for the metamorphic titanite the neoproterozoic u pb chronometric system of magmatic titanite survived the triassic continental subduction zone hp uhp metamorphism this suggests a relatively high closure temperature of 800 c for the titanite u pb system the metamorphic titanite is principally a product of retrograde metamorphism during decompression exhumation at the transition from hp eclogite facies to amphibolite facies therefore titanite holds a great potential to geochronological and petrogenetic studies of continental subduction zone metamorphic rocks

grenvillian extensional tectonics in northwest scotland new structural data indicate that eclogite bearing gneisses in the glenelg attadale inlier of the caledonian moine thrust nappe northwest scotland were involved in a major pre caledonian system of extensional top to the east ductile shear zones these shear zones coalesce upward to constitute a major extensional detachment below metasedimentary rocks of the moine supergroup both the eclogite bearing gneisses and the moinian metasedimentary rocks display evidence of extensional deformation but the latter contain structures indicative of a lower intensity of bulk finite shear strain and may have experienced only the later of two discrete phases of extension that we recognize in the inlier coplanar caledonian brittle ductile top to the west thrusting has resulted in only localized and limited reactivation timing of the extensional deformation is bracketed by a published sm nd age of 1 08 ga for eclogite equilibration and by a minimum age of deposition for the moine supergroup of 840 ma we propose that the eclogite bearing lower crust was exhumed as a result of collapse of the grenville orogen and that the evolution of the moinian basin was controlled by this extensional event

zirconium abundance in granulite facies minerals with implications for zircon geochronology in high grade rocks zircon growth in high grade metamorphic rocks may be triggered by net transfer reactions involving the breakdown of a phase bearing zirconium zr we have measured the concentration of zr in the major minerals in granulite facies rocks of differing bulk composition both garnet and hornblende contain tens of parts per million zr and no other major phase contains significant zr simple calculations show that reaction of either garnet or hornblende to form non zr bearing phases will release sufficient zr to account for at least some new zircon growth u pb ages from new zircon grown as a result of either hornblende or garnet breakdown are not expected to record the time of peak metamorphism but rather will record the time of particular metamorphic reactions allowing direct correlation of zircon ages with petrologically derived pressure temperature time paths this approach offers the potential for more rigorous interpretation of the metamorphic significance of zircon ages than has previously been possible

formation of an archaean continent about 30 of the earth is covered by continents but only about 10 small kernels of these continentsae known as archaean cratonsae are continental fragments formed before 2 5 gyr ago the kaapvaal craton of south africa which formed and stabilized between 3 7 and 2 7 gyr ago is one of the oldest reasonably sized examples of these continental fragments it consists of a mosaic of subdomains that have been welded together by processes similar to those of modern day plate tectonics the earliest subdomains may have owed their origin to the onset of efficient recycling from the earth s hydrosphere into the mantle

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

the ventersdorp contact reef model in the kloof gold mine as derived from 3d seismics geological mapping and exploration borehole datasets abstract a model of the ventersdorp contact reef vcr orebody at kloof gold mine was derived by integrating 3d reflection seismic data with information derived from underground mine mapping and exploration drilling the study incorporated the depth converted prestack time migrated pstm seismic cube the mine geomodel faults and dikes mapped in excavations mine development infrastructure and intersections of the vcr by surface and underground exploration drilling the 3d seismic data provide an accurate geometric model of the vcr orebody and its offsets the underground mapping datasets help to define minor faults and dikes that are below seismic resolution limits the integration of the these datasets allowed 1 for better mapping of fault architectures and distributions within the lease area 2 definition of the likely zones of difficult ground conditions around seismically imaged dikes and faults and 3 better predictions of the number and spacing of faults that offset the vcr within minable blocks the model is useful in mitigating both economic and safety risks of deep mining

structural controls on witwatersrand gold mineralisation abstract structural controls on the distribution of gold in the witwatersrand basin can be seen at scales ranging from that of thin sections up to regional seismic data sets at the thin section scale gold occurs largely in fractures with hydrocarbons these fractures are associated with pulses of thrusting deformation that occurred in the latter stages of the basin s development the distribution of thrust fracture networks and therefore gold is controlled by the mechanical attributes of the host stratigraphy thrust displacements are generally very low with structures exploiting depositional contacts and mesoscale sedimentary bedforms many of the small faults are isolated from each other with bimodal vergence between larger scale thrusts of the same age early formed faults and fractures become folded and faulted by subsequent propagation of larger scale thrusts these characteristics are consistent with formation of the mineralised thrust fracture networks in the frontal low displacement parts of a thrust system in the carletonville goldfield the prospectivity of the ventersdorp contact reef vcr has been evaluated by using underground observations to pinpoint the structural habitat of gold and therefore characterise the size of prospective zones around structures intersecting the vcr mapped within 3d seismic data in the welkom goldfield the controls on gold distribution at the tshepong mine have been characterised from 3d seismic data drilling and underground observations and used to develop an ore body model that aids reserve estimation and production planning

constraints on pb closure temperature in titanite based on rocks from the ungava orogen canada implications for u pb geochronology and p t t path determinations on the basis of multiequilibrium metamorphic pressure temperature p t estimates we have determined that 660 700 c is a reasonable minimum estimate of the closure t of pb diffusion in titanite a temperature significantly higher than previously suggested activity corrected reactions that produce titanite define narrow t stability fields 40 c that correspond closely to metamorphic p t determinations derived for coronitic garnet clinopyroxene hornblende samples growth of titanite occurring between 1789 and 1814 ma in the underthrust archean basement of the paleoproterozoic ungava orogen northern quebec is associated with retrograde metamorphism during underthrusting of the archean basement approx 1 b y after formation of the original granulitic assemblages

irrefutable detrital origin of witwatersrand gold and evidence of eolian signatures toroidal shaped gold particles extracted from a sample of the basal reef orebody in the welkom gold field that contained crossbedded gold have been recognized in thin section demonstrating that the form in question is not an artifact of extraction but is a genuine detrital form similar forms have been recovered in great abundance from an eolian paleosurface in yakutia and from a recent storm beach placer in new zealand indicating the likelihood that eolian processes produced these forms this has been confirmed by means of wind tunnel experiments toroids in various states of preservation have been extracted from a number of other witwatersrand paleoplacers where there is an association with ventifacts indicating that wind deflation might have played a role in concentrating gold from placer sand deposits

pb diffusion in rutile diffusion of pb was measured in natural and synthetic rutile under dry 1 atmosphere conditions using mixtures of pb titanate or pb sulfide and tio2 as the sources of diffusant pb depth profiles were then measured with rutherford backscattering spectrometry rbs over the temperature range 700 1100 c the following arrhenius relation was obtained for the synthetic rutile d 3 9 10 10exp 250 12 kj mol 1 rt m2s 1 results for diffusion in natural and synthetic rutile were quite similar despite significant differences in trace element compositions mean closure temperatures calculated from the diffusion parameters are around 600 c for rutile grains of 100 m size this is about 100 c higher than rutile closure temperature determinations from past field based studies suggesting that rutile is more resistant to pb loss through volume diffusion than previously thought

eclogite facies rocks a window into geodynamics and lithospheric evolution a celebration of the career of tony carswell this set of six papers arises from the international eclogite field symposium held in scotland during july 2007 iefs2007 a second set of papers from iefs2007 has been published elsewhere see dobrzhinetskaya et al 2008 the meeting was one of a biennial series organized under the auspices of the international eclogite conference co ordinating committee and marked the 25th anniversary of the first meeting in 1982 seventy five delegates from 20 countries gathered in portree on the isle of skye the field element of the meeting focused upon the nearby glenelg attadale inlier a basement unit of the moine nappe and part of the classic moine thrust system in the western highlands see symposium field guide storey 2008 a b this was the first place in the uk where eclogites high pressure metabasaltic garnet clinopyroxene rocks were recognized teall 1891 and has attracted several prominent researchers in metamorphic and structural geology e g tilley 1936 ramsay 1958 sutton watson 1959 o hara 1960 although one of the smaller eclogite facies terrains in global terms the glenelg attadale inlier is significant in that it is one of the very few examples of precambrian high pressure metamorphism sanders et al 1984 brewer et al 2003 storey et al 2004 iefs2007 celebrated the life and work of dennis anthony tony carswell who sadly died on 8 june 2006 while still very much at the height of his intellectual powers tony was active in research in eclogite facies rocks from the early 1960s and was consistently at the forefront of developments in the field publishing over 120 papers on the subject with an astonishing total of 85 different co authors see dobrzhinetskaya et al 2008 for a more extensive appreciation of his career he edited the book eclogite facies rocks carswell 1990 which

hydrothermal gold mineralization in the witwatersrand basin the origin of the gold mineralization in the witwaterstrand basin of south africa the largest known gold province has been controversial for decades with arguments favouring detrital1 2 placer modified placer3 4 and hydrothermal5 6 origins here we present the results of an extensive geological study of witwatersrand rocks which show that the gold and associated uranium mineralization is hydrothermal in origin and postdates a regional high temperature alteration event alteration processes identified on a small scale can be mapped out regionally as roughly strata bound zones of acid metasomatism extending far into the basin the fluid flow responsible for this alteration was concentrated in small scale structures localized along lithological boundaries we find that the gold precipitated as a consequence of interactions of the fluid with shale derived hydrocarbons present within the basin

late carboniferous high pressure metamorphism of the kassan metamorphic complex kyrgyz tianshan and assembly of the sw central asian orogenic belt abstract high pressure hp metamorphism of the kassan metamorphic complex kmc in the western kyrgyz tianshan has been related to either late ordovician or late carboniferous permian subduction processes we report sm nd ages for retrogressed eclogite samples and 40ar 39ar cooling ages for enclosing garnet muscovite samples from the kmc as new age constraints on hp metamorphism and rock exhumation these data will be used for an upgraded paleogeographic model for late paleozoic crustal consolidation in the southwestern central asian orogenic belt the retrogressed eclogite samples have transitional alkaline to tholeiitic affinity and trace element patterns consistent with protoliths derived from garnet bearing mantle sources at rifting plate margins geothermobarometric data for a retrogressed eclogite sample indicate peak metamorphic conditions of 540 30 c at 1 6 0 1 gpa samples from different lithotectonic units of the kmc provide coherent sm nd garnet whole rock ages of 317 4 ma and 316 3 ma 2 the prograde major element zoning in the mm sized garnets in combination with the moderate peak metamorphic temperature support our interpretation of the sm nd garnet ages as unambiguous evidence for late carboniferous hp metamorphism the sm nd garnet growth ages overlap within error with the 40ar 39ar mica cooling ages of 314 2 ma and 313 2 ma 2 indicating rapid uplift of the subduction complex after peak metamorphism the ca 317 313 ma hp exhumation event of the kmc is contemporaneous with those of the atbashi and akeyazi ca 500 km east in nw china hp complexes and implies similar collision histories at the south tianshan suture to the east and west of the talas fergana fault tff the exhumation of the kmc and atbashi hp complexes overlaps with the initiation of the tff rolland et al 2013 suggesting incipient separation of the chatkal and atbashi complexes during rock exhumation and early plate collision

grenville age pseudotachylite in the lewisian laserprobe 40ar 39ar ages from the gairloch region of scotland uk infrared laserprobe 40 ar 39 ar dating has been used to date pseudotachylite and host rock minerals from a crush belt in the lewisian basement of scotland it has revealed complexity in the pseudotachylite data that is attributable to the presence of refractory host rock clasts and mineral fragments in the pseudotachylite in conjunction with the host rock mineral laserprobe 40 ar 39 ar data it has been possible to simplify the pseudotachylite data for the samples and the preferred ages for these are 980 39 ma 999 31 ma and 1024 30 ma 2 these ages are the first record of grenville aged brittle deformation in the lewisian further this study serves to illustrate the complexity of dating pseudotachylites and the advantages and limitations of the ir laserprobe applied to such materials

geochemical and geochronological constraints on the nature of the immediate basement next to the mesoarchaean auriferous witwatersrand basin south africa acombined petrological geochemical and geochronological rb srand sm nd whole rock u pb and lu hf zircon and ar arhornblende study on a section of pre witwatersrand basementdrilled at the northwestern margin of thewitwatersrand basin hasrevealed new insights into the nature and tectonic setting of thelikely source area for some of the mesoarchaean auriferouswitwatersrand sediments the protolithsof intersected alteredgran ite and hornblende metagabbro are of indistinguishable age 3062 5 ma and have very similar geochemical signatures trace element characteristics typical of calc alkaline magmatismand evidence of variable contamination with older crust subchon dritic e

an inflection in the rate of early mid holocene eustatic sea level rise a new sea level curve from singapore this study presents a sea level curve from 9500 to 6500 cal bp for the farfield location of singapore on the sunda shelf in southeast asia the curve is based on more than 50 radiocarbon dates from elevations of 1 43 m to 15 09 m representing sea level index points in intertidal mangrove and shallow marine sediments deposited by sea level rise accompanying deglaciation the results indicate that mean sea level rose rapidly from around 17 m at 9500 cal bp to around 3 m by 8000 cal bp after this time the data suggest but do not unequivocally prove that the rate of sea rise slowed for a period of 300 500 years centred on 7700 cal bp shortly after the cessation of meltwater input to the oceans from the northern hemisphere renewed sea level rise amounting to 3 5 m began around 7400 cal bp and was complete by 7000 cal bp the existence of an inflection in the rate of sea level rise with a slow down centred on 7700 cal bp is broadly consistent with other available sea level curves over this interval and is supported by evidence of stable shorelines and delta initiation elsewhere at this time as well as evidence of comparatively rapid retreat of the west antarctic ice sheet beginning around 7500 cal bp stepped sea level rise occurring shortly after 7500 cal bp and also earlier during deglaciation may have served to focus significant post glacial episodes of human maritime coastal dispersal into comparatively narrow time intervals

i must go down to the seas again or what happens when the sea comes to you murujuga rock art as an environmental indicator for australia s north west the dampier archipelago properly known as murujuga is a rich rock art province in north western australia which documents an arid maritime cultural landscape but this archipelago of 42 islands has only existed since the mid holocene when people started to engrave art here the granophyre bedrock was part of an inland range more than 160 km from the coast the pilbara archaeological record demonstrates human responses through over forty thousand years of environmental change this paper discusses how rock art across murujuga can give insights to changing dynamics of people in place as well as depicting major environmental change a predictive model is developed to assist in understanding the social changes which have been wrought by sea level rise and consequential environmental changes 2014 elsevier ltd and inqua all rights reserved

coronitic metagabbro and eclogite from the grenville province of western quebec interpretation of u pb geochronology and metamorphism we present new u pb and metamorphic data on high pressure coronitic metagabbros from three distinct structural settings in the parautochthonous belt of the grenville province in western quebec intrusive ages are i for metagabbro close to the grenville front correlative with the sudbury dykes defined in ontario ii for an eclogitized lens at the base of the highest structural level sl4 a new age for mafic magmatism in the western grenville and iii for metagabbro from sl4 interpreted as correlative with metagabbros from the algonquin and shawanaga domains in ontario metamorphism in all cases is grenvillian with the best constrained age of 1069 3 ma for the metagabbro of sl4 metamorphic grade increases from the grenville front to the south the mafic rocks preserve relict igneous textures overprinted by garnet clinopyroxene that developed as coronas and or pseudomorphs after igneous phases the highest grade metagabbros contain omphacite and some lack primary plagioclase therefore b

late pleistocene and early holocene exploitation of estuarine communities in northwestern australia this contribution synthesizes archaeological studies of human economies from the barrow montebello islands and uses the area s archaeological record to determine the effects of late pleistocene and early holocene sea level rise on regional coastlines at the height of the last glacial maximum lgm australia s north western coast extended much further west than the present day shoreline during subsequent sea level rise the gently prograding continental shelf was inundated and with it nearly all archaeological evidence for coastal occupation the barrow and montebello islands are one of the few exceptions as they corresponded to inland hinterland ranges during the lgm with the coastline lying some 50 km to their west evidence from all late pleistocene and holocene occupation phases of the barrow montebello islands demonstrate that foragers continued to visit the coast and engage in the exploitation of both terrestrial and marine environments during the late pleistocene when the shoreline was 10 15 km away coastal exploitation is seen through the presence of transportable estuarine and rocky shore gastropods by the early holocene when sea levels were within close proximity of the sites there is a marked increase in marine fauna including reef fish estuarine and reef shellfish crustaceans and estuarine crocodile together this suggests that the nearby muddy procumbent coastlines were productive as well as an important component of coastal and hinterland economies

element and sr isotope signatures of titanite as indicator of variable fluid composition in hydrated eclogite abstract the trace element signature sr common pb u th ree and hfse of titanite gives important information about the formation process of metamorphic titanite we investigated titanite from different textural positions of a strongly retrogressed eclogite from the tromso norway high p area it shows characteristic titanite rims around partially absorbed rutile interpreted as grown during retrogression and hydration of the high p assemblage the titanite rims around rutile are polycrystalline and in contact with the plagioclase amphibole matrix large idioblastic single crystal titanite grew in veins without relics of precursor rutile compositional zoning of al ti f in titanite of both textural positions is irregular and not related to core or rim position in the crystals there is no evidence for systematic growth sequences or diffusion reflecting changing p t conditions or systematic changes of fluid composition trace element patterns of titanite la icp ms data however show systematic variations in the coupling and decoupling behaviour of strongly fluid mobile sr u moderately fluid mobile ree and little fluid mobile nb ta zr hf elements the trace element signatures of titanite from the two different fabric positions reflect contrasting characteristic fluid compositions single crystal titanite equilibrated with fluid that was channelled in the vein polycrystalline titanite on rutile records the composition of a fluid that had migrated along grain boundaries in the amphibole plagioclase matrix fluid from the matrix also contributed to the geochemical signature of vein titanite whereas influence of fluid from the vein on the composition of polycrystalline titanite in the matrix is not evident 87sr 86sr isotope ratios of the different titanite types support the inference from trace elements of spatially and temporally variable fluid sources