palaeohydrogeological insights from natural tracer profiles in aquitard porewater great artesian basin australia 1 the value of using environmental tracer profiles in aquitards to quantify fluid flux and to reveal information about palaeohydrology is largely unknown for parts of the world that were not glaciated during the cenozoic we present deep continuous vertical profiles of aquitard pore water chloride concentration and 2h 18o composition from the western margin of the great artesian basin australia where upward leakage is the dominant groundwater discharge mechanism at the deeper of the two sites studied the cl and 2h profiles exhibit a distinctive s shape which we interpret as a shift in the upper concentration boundary condition over time numerical simulations are used to support an hypothesis that the shallow phreatic aquifer was more saline and more enriched in 2h compared to current conditions prior to 120 ka followed by an extended freshening phase from 120 to 20 ka then a saline phase similar to current conditions for the last 20 ka these timeframes correspond favorably with results of previous studies into the palaeohydrology of nearby playa lake eyre at the shallower site the tracer profiles decrease exponentially with depth we explore several models for the evolution of these profiles and adopt one of long term salt input at ground surface at both sites tracer concentrations for groundwater sampled from the underlying artesian aquifer provide conclusive evidence that recharge occurred within the last 10 20 ka chloride was a more useful tracer than 2h in this study primarily due to lack of recent glaciation in central australia to provide a dynamic 2h tracer signal

timing trace and origin of basaltic migration in eastern australia eastern australian cenozoic volcanism includes a prominent southward migration of activity varied explanations have invoked hotspot or linear magma sources in the asthenosphere the movement of australia over old seafloor spreading zones with direct or delayed response in volcanism or changes in stress fields the present appraisal using new data contradicts some ideas and favours volcanism triggered directly by passage of lithosphere over initial sites of coral sea spreading the conclusions suggest that eastern australia has a major complex hotspot trail established for the past 65 myr it forms an independent and key continental reference to the hawaiian emperor oceanic trail it raises the notion that both continental and oceanic trails can mark the ghosts of former spreading sites

a weathering intensity index for the australian continent using airborne gamma ray spectrometry and digital terrain analysis abstract weathering intensity largely controls the degree to which primary minerals are altered to secondary components including clay minerals and oxides as weathering intensity increases there are changes in the hydrological geochemical and geophysical characteristics of the regolith thus once calibrated weathering intensity can be used to predict a range of regolith properties a weathering intensity index wii over the australian continent has been developed at a 100 m resolution using regression models based on airborne gamma ray spectrometry imagery and the shuttle radar topography mission srtm elevation data airborne gamma ray spectrometry measures the concentration of three radioelements potassium k thorium th and uranium u at the earth s surface the total gamma ray flux dose is also calculated based on the weighted additions of the three radioelements regolith accounts for over 85 of the australian land area and has a major influence in determining the composition of surface materials and in controlling hydrological and geomorphological processes the weathering intensity prediction is based on the integration of two regression models the first uses relief over landscapes with low gamma ray emissions and the second incorporates radioelement distributions and relief the application of a stepwise forward multiple regression for the second model generated a weathering intensity index equation of wii 6 751 0 851 k 1 319 relief 2 682 th k 2 590 dose the wii has been developed for erosional landscapes but also has the potential to inform on deposition processes and materials the wii correlates well with site based geochemical indices and existing regolith mapping interpretation of the wii from regional to local scales and its application in providing more reliable and spatially explicit information on regolith properties are described

surface topography as key constraint on thermo rheological structure of stable cratons why some archean cratons survived for billions of years while the rest of the lithosphere has been reworked probably for several times is both enigmatic and fundamental for plate tectonics craton longetivity is mainly explained by their buoyancy and analyzed by testing gravitational stability of hardly detectable cratonic mantle keels as a function of a hypothesized thermo rheological structure destruction of some cratons suggests that buoyancy is not the only factor of their stability and many previous studies show that their mechanical strength is equally important the upper bounds on the integrated strength of cratons are provided by flexural studies demonstrating that te values equivalent elastic thickness in cratons are highest in the world 110 150 km yet the lower bounds on the integrated strength of stable cratons are still a matter of debate as well as the question on how this strength is partitioned between crust and mantle and which set of rheological parameters is most pertinent we show that primary observed cratonic features flat topography and frozen heterogeneous crustal structure represent the missing constraints for understanding of craton longevity the cratonic crust is characterized by isostatically misbalanced density heterogeneities suggesting that the lithosphere has to be strong enough to keep them frozen through time without developing major gravitational instabilities and topographic undulations hence to constrain thermo rheological properties of cratons one should investigate the stability of their topography and internal structure our free surface thermo mechanical numerical models demonstrate that craton stability cannot be warranted even by very high crustal strength so that dry olivine mantle and cold thick lithosphere are indispensable conditions we establish lower bound limits on the thermo rheological structure of cratons in particular we find that minimal te needed for long term stability of continents is approximately 90 110 km of which at least 70 km should be contributed by the lithosphere mantle

denudational isostatic rebound of intraplate highlands the lachlan river valley australia a range of evidence from the lachlan valley in the southeast australian highlands is consistent with neogene isostatic rebound in response to denudational unloading this evidence is found along the inland edge of the highlands in the transition zone between the highlands proper and the lachlan s inland alluviated valley and the intracratonic murray basin the amounts and rates of uplift indicated by offsets of suballuvium bedrock profiles and the long profiles of tertiary valley filling basalts are consistent with modelling of denudational rebound using known rates of highland denudation and basinal sedimentation and reasonable crustal properties the modelling shows that weak to moderately strong strong lithosphere effective elastic thickness te 1 25 km and strong lithosphere te 100 km are all consistent with the observed amounts of rebound strong lithosphere must be broken however to be consistent with the field data even in the australian setting which is characterized by very low rates of denudation isostatic rebound in response to denudational unloading must be a significant factor in maintaining highland elevation and must be incorporated in models of long term landscape evolution it would be expected that denudational isostatic rebound would be an even more significant component of long term landscape evolution in areas of higher denudation rates

rheological differences between archaean and younger crust can determine rates of quaternary vertical motions revealed by fluvial geomorphology surface uplift is widely observed in subaerial regions of continental crust that are distant from plate boundaries often revealed by river terrace staircases with altitude ranges of several hundred metres which typically span the quaternary this characteristic geomorphology has been explained by forcing of flow in the weak lower crustal layer by surface processes non steady state erosion and cyclical loading by ice sheets and sea level fluctuations this study tests this interpretation by showing that analogous river terrace staircases are absent in archaean crust which lacks the weak lower crustal layer found elsewhere

transformation of an archean craton margin during proterozoic basin formation and magmatism the albany fraser orogen western australia abstract the albany fraser orogen is a well preserved example of proterozoic modification of an archean craton margin the formation of two successive basin systems accompanied by magmatism along the southern and southeastern yilgarn craton margin in western australia reflect distinct changes in tectonic regimes resulting in significant transformations of the archean craton crust provenance analysis from detrital zircons indicates that the first basin system the c 1815 1600 ma barren basin was dominantly filled with neoarchean detritus derived from the yilgarn craton and paleoproterozoic detritus derived from coeval voluminous mostly felsic magmatism the abundance of locally derived sediment deposited onto a reworked archean yilgarn craton substrate coupled with the progressively more juvenile isotopic signature of magmas indicates a largely extensional tectonic setting consistent with either a continental rift basin or a long lived backarc basin system this extensional regime led to the formation of a passive margin and oceanic basin along the craton edge the c 1600 1305 ma arid basin and formation of an ocean continent transition in the most heavily modified outboard region of the craton margin the eastern nornalup zone a change in tectonic regime is denoted by the formation of an oceanic arc the c 1410 ma loongana arc preserved in the adjoining madura province oceanic subduction led to accretion of the loongana arc onto the craton edge recorded by the presence of exotic detritus derived from this arc deposited into a foreland basin uppermost arid basin this accretion event triggered crustal thickening and the earliest phase of magmatism of stage i of the albany fraser orogeny at c 1330 ma a change to west dipping subduction beneath the accreted portion of the loongana arc placed the orogen into a backarc setting into which the remainder of the recherche supersuite mafic and felsic magmas were intruded thus the albany fraser orogen is regarded as an archean craton margin that preserves a long history of proterozoic transformation dominated by extensional processes that resulted in the formation of orogen wide basin systems accompanied by magmatism the recognition that the albany fraser orogen has always been part of the west australia craton and the tectonic regimes that have affected it provide important constraints on reconstructions of the nuna and rodinia supercontinents

structure of a paleoproterozoic continent continent collision zone a lithoprobe seismic reflection profile across the trans hudson orogen canada abstract an 800 km reflection seismic profile across the trans hudson orogen northern saskatchewan and manitoba images crustal scale tectonic imbrication in an unprecedented picture of paleoproterozoic crustal accretion and continent continent collisional tectonism the profile is crudely symmetric about a crustal scale culmination in the western part of an accreted juvenile collage reindeer zone geologic and isotopic data suggest that this culmination is cored by microcontinental archean basement west of the culmination highly reflective juvenile crustal elements dip westward into the lower crust beneath the wathaman batholith and archean continental crust of hearne craton to the east strong reflections in the juvenile reindeer zone crust and reworked archean foreland of the thompson belt have eastward dips persisting into the middle crust and extending beneath the superior craton a continuous reflection moho well defined for 500 km in the western part of the profile shows marked relief 12 15 s including a prominent root below the crustal culmination these imaged structures give evidence of substantial crustal shortening and thickening via large scale imbrication consistent with collisional orogeny w dipping structures below the wathaman batholith and reworked hearne craton may reflect subduction polarity in this part of the orogen however geological evidence suggests that e dipping structures below superior craton are largely related to late post collisional deformation rather than to prior oceanic subduction polarity

geophysics of proposed proterozoic sutures in canada abstract sutures have been identified or proposed at several sites in the canadian shield although many authors have suggested that some form of primitive plate tectonic processes have played a major role in the formation of the archean crust of the superior structural province proterozoic sutures resembling phanerozoic examples have been proposed only within the younger churchill and grenville provinces and at or near the boundaries between the older superior and slave provinces and the younger provinces gravity magnetic seismic and paleomagnetic data related to three proposed sutures in the latter category have been interpreted and generally support the view that the shield comprises a mosaic of once separated but now joined cratonic blocks the sutures vary in complexity from wide zones containing distinctive rocks formed at ancient accreting and consuming plate margins to cryptic sutures marked only by abrupt changes in metamorphism and zones of cataclasis paired negative and positive gravity anomalies associated with these sutures have been interpreted in terms of juxtaposed crustal blocks of different density and thickness magnetic anomaly patterns change abruptly at structural province boundaries available seismic results support the concept of thickened crust in the younger province as derived from gravity modelling most authors prefer interpretation of proterozoic pole positions in terms of one plate models but in some cases the interpretation of paleomagnetic data is equivocal and two plate models have been proposed

holocene sea level change on the southeast coast of australia a review a revised holocene sea level curve for the southeast coast of new south wales australia is presented based on a review of previously published geochronological results for fossil molluscs organi

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

crustal structures revealed from a deep seismic reflection profile across the solonker suture zone of the central asian orogenic belt northern china an integrated interpretation abstract the solonker suture zone is one of the most important tectonic boundaries in the southeastern part of the central asian orogenic belt caob an 630 km long reflection seismic profile across this suture was recently completed by the chinese sinoprobe project the processed seismic data show clear crustal structures and provide new constraints on the tectonic and crustal evolution models the moho is delineated as a relatively flat boundary between a strongly reflective lower crust and a transparent mantle at a depth of 40 45 km 14 5 s two way travel time which is in agreement with the refraction data recorded along the same profile in a broad view the profile images an orogen that appears bivergent with and approximately centered on the solonker suture zone the southern portion of this profile is dominated by a crustal scale cratonward propagating fold and thrust system that formed during the late permian and triassic through collision and subsequent convergence in a post collisional stage the major thrust faults are truncated by mesozoic granitoid plutons in the upper crust and by the moho at the base of the crust this geometry suggests that the moho was formed after the thrusting event the northern portion of the profile although partially obliterated by post collisional magmatic bodies shows major south dipping folding and thrusting bands of layered reflectors immediately overlying the moho are interpreted as basaltic sills derived from the mantle episodic mafic underplating may have occurred in this region giving rise to post collisional magmatic events and renewal of the moho a few mantle reflectors are also visible the overall geometry of these mantle reflectors supports the tectonic models that the southern orogen manchurides experienced south directed subduction and the northern orogen altaids underwent north directed subduction prior to collision along the solonker suture zone

introduction and background interpretations of landscape change research into the origins of landscape has a long and distinguished tradition in america landscape studies form the core of physical geology while elsewhere the study of landscape development has spread beyond the confines of geology to develop a firmer foothold in the geographical tradition particularly in geomorphology the development of ideas in landscape study has however been neither steady nor sequential it has been characterized instead by several major conceptual shifts interspersed with periods of reinforcement or neglect within geomorphology and certainly within the english speaking world the most important of these shifts occurred in the early 1960s with the move from denudation chronology of landscapes as a core activity to an emphasis on process based investigation of individual landforms in geology the 1960s also marked an important change in perspective publication of plate tectonic theories sea floor spreading continental drift subduction and mountain building had far reaching consequences for all earth science in particular plate tectonics made the study of apparently ancient processes billions of years old applicable to the present day with for example application to earthquake studies whilst the initial shift towards process studies was a response to the desire for a better understanding of the mechanisms driving landscape change it was not long before this goal became relegated in the eyes of many of its practitioners as a consequence process study became an end in itself rather than a means to an end this movement has been reinforced in recent years by a demand for greater relevance from for example research funding bodies resulting in an emphasis on problem solving and wealth generation that has moved away from studies at the landscape scale consequently within geomorphology process studies and applied geomorphology have come to dominate the literature a dominance reinforced by the increasing division and separation of the discipline into process domains such as fluvial and glacial studies this has reached the point where many researchers would now naturally identify themselves as specialists in a particular process rather than as geomorphologists a similar trend can be identified within geology whereby studies of uplift erosion and stability clearly fall into pre plate tectonics and post plate tectonics generations in the 1920s studies of denudation were popular as evidenced by the volume of work conducted in southern england and based largely on observations of palaeovaueys tilted strata and unconformities sediment provenance became important in the 1920s and 1930s and early works on the use of heavy minerals in studies of past erosion were developed by the 1960s geologists were standing back and viewing many processes in terms of their global plate tectonic significance however this emphasis on processes inevitably led to the development of more labour intensive analytical methods as a consequence of which the wider perspective began to be neglected through the 1970s and 1980s therefore studies of uplift developed using methods that determine heating or pressurization of the uplifted rocks thermal estimates of uplift including spore or conodont alteration indexes fluid inclusion studies and diagenetic models were developed together with estimates of pressurization including studies of mineralogy and sonic borehole logs however perhaps the most significant advance in the determination of uplift rates and amounts has been in the field of apatite fission track analysis afta carter 1999 the widespread use of afta in the oil industry has provided large datasets that encompass the offshore basins formerly ignored by those concerned with land erosion buchanan buchanan 1995 studies of erosion and palaeoerosion have also developed from the study of derived clasts to clay minerals and heavy minerals requiring increasingly labourintensive and hence specialist methods to derive local or even regional perspectives specialization clearly has many advantages if however it is allowed to proceed unchecked these advantages eventually come to be outweighed by the effects of an increasingly reductionist approach whereby concentration on small scale studies and the pursuit of ever greater detail detracts from appreciation of the largescale picture and ultimately fragmentation and loss of the subject core clearly the longer this reductionist segregationist approach persists the more difficult it is to define and to justify the existence of the original parent discipline

comparing results from two continental geochemical surveys to world soil composition and deriving predicted empirical global soil pegs2 reference values analytical data for 10 major oxides al2o3 cao fe2o3 k2o mgo mno na2o p2o5 sio2 and tio2 16 total trace elements as ba ce co cr ga nb ni pb rb sr th v y zn and zr 14 aqua regia extracted elements ag as bi cd ce co cs cu fe la li mn mo and pb loss on ignition loi and ph from 3526 soil samples from two continets australia and europe are presented and compared to 1 the composition of the upper continetal crust 2 published word soil awerage values and 3 data from other continetal scale soil surveys it cab be demonstrated that average upper continetal crust values do not provide reliable estimates for natural concentrations of elements in soil for many elements there exist substantial differences between published world aoil averages and the median concentrations observed on two continets direct comparison with other continetal datasets is hampered by the fact that often mean instead of the statistically more robust median is reported using a database of the worldwide disstribution of lithological units it can be demonstrated that lithology is a poor predictor of soil chemistry climate related processes such as glaciation and weathering are strong modifiers of the geochemical signature inherited from bedrock during pedogenesis to overcome existing shortcomings of predicted global or world soil geochemical reference values we propose preliminary empirical global soil reference values based on analytical results of a representative number of soil samples from two continets pegs2

crustal architecture and geodynamics of north queensland australia insights from deep seismic reflection profiling abstract a deep crustal seismic reflection and magnetotelluric survey conducted in 2007 established the architecture and geodynamic framework of north queensland australia results based on the interpretation of the deep seismic data include the discovery of a major west dipping paleoproterozoic or older crustal boundary considered to be an ancient suture zone separating relatively nonreflective thick crust of the mount isa province from thinner two layered crust to the east farther to the east a second major crustal boundary also dips west or southwest offsetting the moho and extending below it and is interpreted as a fossil subduction zone across the region the lower crust is mostly highly reflective and is subdivided into three mappable seismic provinces but they have not been tracked to the surface in the east the greenvale and charters towers provinces part of the thomson orogen have been mapped on the surface as two discrete provinces but the seismic interpretation raises the possibility that these two provinces are continuous in the subsurface and also extend northwards to beneath the hodgkinson province originally forming part of an extensive neoproterozoic cambrian passive margin continuation of the thomson orogen at depth beneath the hodgkinson and broken river provinces suggests that these provinces which formed in an oceanic environment possibly as an accretionary wedge at a convergent margin have been thrust westwards onto the older continental passive margin the tasman line originally defined to represent the eastern limit of precambrian rocks in australia has a complicated geometry in three dimensions which is related to regional deformational events during the paleozoic overall the seismic data show evidence for a continental margin with a long history paleoproterozoic to early mesozoic but showing only limited outward growth by crustal accretion because of a repeated history of overthrust shortening during repeated phases of orogenesis

crustal structure of a proterozoic craton boundary east albany fraser orogen western australia imaged with passive seismic and gravity anomaly data abstract we use passive seismic and gravity data to characterize the crustal structure and the crust mantle boundary of the east albany fraser orogen in western australia a proterozoic orogen that reworked the southern and southeastern margin of the archean yilgarn craton the crustal thickness pattern retrieved from receiver functions shows a belt of substantially thickened crust that follows the trend of the orogen but narrows to the southwest common conversion point profiles show a clear transition from a wide symmetric moho trough in the northeast to a one sided northwestern moho dip in the southwest where the moho appears to underthrust the craton towards its interior this change appears to coincide with the inferred trace of the ida fault a major terrane boundary within the yilgarn craton forward modelling of gravity anomaly data using the retrieved moho geometry as a geometric constraint shows that a conspicuous elongated gravity low on the northwestern side of the east albany fraser orogen is almost certainly caused by thickened archean crust to obtain a model that resembles the regional gravity pattern the following assumptions are necessary high density rocks occur in the upper crust of the fraser zone at depth inside the moho trough and in parts of the eastern nornalup zone east of the moho trough although our gravity models do not constrain at which crustal level these high density rocks occur active deep seismic surveys suggest that large extents of the east albany fraser orogen s lower crust include a mesoproterozoic magmatic underplate known as the gunnadorrah seismic province the simplest interpretation of the imaged crustal structure is that the gunnadorrah seismic province is underthrust beneath the yilgarn craton likely as a consequence of crustal shortening during accretion further east the imaged geometry overall appears to show a wedge of archean lower crust that was driven between the exhumed fraser zone and the gunnadorrah seismic province effectively splitting the paleo to mesoproterozoic crust of the east albany fraser orogen the vertical splitting of proterozoic crust by a cratonic crustal wedge comparable to what we image in this study may be a process that contributed to forming many craton margins around the world

predicted and observed holocene sea levels on the australian coast what do they indicate about hydro isostatic models in far field sites data relating to holocene sea level elevations and ages obtained by radiocarbon dating of relict calcareous skeletons of intertidal organisms from widely spaced parts of the australian coast a far field region of comparative tectonic stability are divisible into two sets namely pre and post ca 3600 yr bp the older ages are from material consistently between 1 5 m and 2 2 m higher than present sea level whereas the younger ages ca 3600 1500 yr bp generally cluster around 1 m above present sea level the elevations do not display any decline in amplitude from north to south over an extensive transect contrary to predictions by hydro isostatic models also there appears to be little difference between time elevation results for the coasts of north queensland new south wales and the bass strait region adjacent to tasmania despite differences in the width of the continental shelf in these three locations and the expectation of some hydro isostatic warping of the continental shelf subsequent to the onset of the holocene transgression results from the south and southwest coasts of western australia also display similar elevations to the east coast for the same time periods there is sufficient evidence extending over 20 of latitude to suggest that north south differences related to hydro isostatic influence is limited or non existent there is insufficient data to test hydro isostatic models across continental shelves hydro isostasy and the lithological elasticity it reflects may not be as pronounced in far field sites with narrow continental shelves as models predict stable far field passive continental margins may be the best place to measure the ratio of inputs of eustatic and hydro isostatic influences on holocene relative sea levels copyright 2002 john wiley sons ltd journal of quaternary science

moho depth and crustal composition in southern africa abstract we present new results on structure thickness and composition of the crust in southern africa based on 6300 seismic receiver functions at 85 stations application of hk stacking to the entire sase dataset and use of multi frequency bands improve resolution substantially we observe a highly heterogeneous crustal structure with short wavelength variations in thickness h vp vs ratio composition and moho sharpness which defines 20 blocks that do not everywhere coincide with surface tectonic features in the zimbabwe craton the tokwe block has h 35 38 km and vp vs 1 74 1 79 whereas the thicker crust in the tati block h 47 51 km may be related to deformation of the archean crust along the cratonic margin two distinct crustal blocks with similar crustal thickness 42 46 km but significantly different vp vs ratios are recognized in the limpopo belt extreme values of 1 90 1 94 at the dyke swarms in eastern limpopo and 1 84 at the olifants river dyke swarm and easternmost bushveld intrusion complex bic indicate voluminous magmatic intrusions in the whole crust we find no evidence for magmatic intrusions in the central inferred part of bic where the crust is thick 45 50 km and vp vs is low 1 68 1 70 this thick crustal root may have deflected rising magmas to form the two bic lobes most of central kaapvaal has thin 35 40 km crust and vp vs 1 74 these characteristics are similar to the tokwe block in zimbabwe craton and may indicate delamination of pre existing lower crust which is further supported by a very sharp moho transition the exposed cross section in the vredefort impact crater is non representative of cratonic crust due to shallow moho 34 km and high vp vs 1 80 attributed to shock metamorphism high vp vs 1 76 is typical of the witwatersrand basin and anomalously low vp vs 1 66 1 67 marks the kaapvaal kheis namaqua transition highly heterogeneous crust both in thickness and vp vs ratio is typical of the namaqua natal and cape fold belts

southeast australian late mesozoic and cenozoic denudation rates a test for late tertiary increases in continental denudation throughout the tertiary average rates of erosion of southeast australia have been uniformly low about 10 3 mm yr of surface lowering indicating that this part of the australian continent did not contribute to a rapid increase in ocean basin sedimentation over the past 15 or 20 m y somewhat higher mesozoic rates may be the result of minor tectonism but explanation for the generally low cenozoic and mesozoic erosion rates may be sought in the forest cover and general tectonic stability of southeast australia over this time period australia9s gradually increasing aridity climatic seasonally over the past 20 m y has apparently not resulted in higher average rates of erosion of the continent except perhaps in the very latest tertiary and quaternary

long term landscape evolution in australia the main features of the australian physical landscape are of the order of 107 108 years old this contradicts the widely held view that little of the earth s topography predates the quaternary and that erosion cycles are carried to planation within tens of millions of years much of the australian landscape must have developed over similar timescales to that of the tectonic evolution of the continent itself the study of the geomorphology of such ancient terrains may therefore be seriously deficient unless it is considered within the context of continental scale tectonic development application of this approach shows that there are strong links between the geomorphology of australia and plate movements ocean spreading plate convergence tectonostratigraphic terranes orogenesis and epeirogenesis the most important factor contributing to the survival of ancient landscapes in australia is the low rate of denudation which the continent has experienced during the mesozoic and cenozoic this is largely a consequence of orogenic stability although the absence of significant quaternary glaciation may also be of importance however in order for landforms to have survived over such timespans denudation must not only have been low but must also have been highly localized over space and time this has been the case both on a regional scale with long term denudation rates of 0 2 m ma 1 in central australia contrasting with higher rates along the continental margins and on a local scale with denudation confined to valleys leaving divides and interfluves almost unscathed

contemporary versus long term denudation along a passive plate margin the role of extreme events short term contemporary and long term denudation rates were determined for the blue mountains plateau in the western sydney basin australia to explore the role of extreme events wildfires and catastrophic floods in landscape denudation along a passive plate margin contemporary denudation rates were reconstructed using 40 years of river sediment load data from the nattai catchment in the south west of the basin combined with an analysis of hillslope erosion following recent wildfires long term denudation rates 10 kyr 10 myr were determined from terrestrial cosmogenic nuclides apatite fission track thermochronology and post basalt flow valley incision contemporary denudation rates average several times lower than the long term average 5 5 4 mm kyr 1 versus 21 5 7 mm kyr 1 erosion of sediment following wildfires accounts for only a small proportion 5 of the contemporary rate most post fire sediment is stored on the lower slopes and valley floor with the amount transported to the river network dependent on rainfall run off conditions within the first few years following the fire historical catastrophic floods account for a much larger proportion 35 of the contemporary erosion rate and highlight the importance of these events in reworking stored material evidence for palaeofloods much larger than those experienced over the past 200 years suggests even greater sediment export potential mass movement on hillslopes along valleys incised into softer lithology appears to be a dominant erosion process that supplies substantial volumes of material to the valley floor it is possible that a combination of infrequent mass movement events and high fluvial discharge could account for a significant proportion of the discrepancy between the contemporary and long term denudation rates copyright 2006 john wiley sons ltd

the shaping of sydney by its urban geology abstract sydney s surface geology of hawkesbury sandstone capped with wianamatta shale has produced poor soils but good building material the topography derived from the subaerial erosion and extensive dissection of the permian triassic sedimentary strata of the sydney basin has been the strongest constraint on the city s growth steep sided valleys carved out of sandstone plateaux forced the direction of settlement along the flatter interfluves and in recent decades out onto the tectonic depression of the cumberland plain to the west holocene marine transgression flooded the eastern incisions of the eroded mass producing some of the few safe anchorages on the southeast australian coast as well as bedrock controlled zeta curved coastal beaches some of the geological disadvantages have turned into advantages over time the sterility of the skeletal sandstone soils made farming difficult but has allowed much of the native vegetation to be retained for conservation and recreation coastal quartz sand deposits produced equally infertile soils but provided pure sand fill for sydney s many attractive beaches along with industrial uses the depth of underlying coal deposits discouraged early mining within the city boundaries to the ultimate benefit of residential development while tectonic stability reduced complications for infrastructure engineering works

modes tempo and spatial variability of cenozoic cratonic denudation the west african example 1 quantifying long term erosion of tropical shields is crucial to constraining the role of lateritic regolith covers as prominent sinks and sources of co 2 and sediments in the context of long term cenozoic climate change it is also a key to understanding long term landform evolution processes operating over most of the continental surface and their control onto the sediment routing system we study the surface evolution of west africa over three erosion periods 45 24 24 11 and 11 0 ma recorded by relicts of three subcontinental scale lateritic paleolandsurfaces whose age is bracketed by 39 ar 40 ar dating of lateritic k mn oxides denudation depths and rates compiled from 380 field stations show that despite heterogeneities confined to early inherited reliefs the subregion underwent low and homogeneous denudation 2 20 m ma 1 over most of its surface whatever the considered time interval this homogeneity is further documented by a worldwide compilation of cratonic denudation rates over long term intermediate and modern cenozoic time scales 10 0 10 7 yr these results allow defining a steady state cratonic denudation regime that is weathering limited i e controlled by the thickness of the lateritic regolith available for stripping steady state cratonic denudation regimes are enabled by maintained compartmentalization of the base levels between river knick points controlled by relief inheritance under such regimes lowering of base levels and their fossilization are primarily imposed by long term eustatic sea level fall and climate rather than by epeirogeny the expression of steady state cratonic denudation regimes in clastic sedimentary fluxes remains to be investigated components 9 200 words 13 figures 2 tables

archean and proterozoic crustal evolution evidence from crustal seismology seismic velocity models for archean and proterozoic provinces throughout the world are analyzed the thickness of the crust in archean provinces is generally found to be about 35 km except at collisional boundaries whereas proterozoic crust has a significantly greater thickness of about 45 km and has a substantially thicker high velocity 7 0 km s layer at the base we consider two models that may explain these differences the first model attributes the difference to a change in the composition of the upper mantle the higher temperatures in the archean mantle led to the eruption of komatiitic lavas resulting in an ultradepleted lithosphere unable to produce significant volumes of basaltic melt proterozoic crust developed above fertile mantle and subsequent partial melting resulted in basaltic underplating and crustal inflation in the second model convection in the hot archean mantle is considered to have been too turbulent to sustain stable long lived subduction zones by the proterozoic the mantle had cooled sufficiently for substantial island and continental arcs to be constructed and the high velocity basal layer was formed by basaltic underplating

the teleseismic signature of fossil subduction northwestern canada 1 between june 2003 and september 2005 20 broadband three component seismometers were deployed along the mackenzie liard highway in canada s northwest territories as part of the joint lithoprobe iris canada northwest experiment canoe these stations traverse a paleo proterozoic suture and subduction zone that has been previously documented to mantle depths using seismic reflection profiling teleseismic receiver functions computed from 250 earthquakes clearly reveal the response of the ancient subduction zone on the radial component the suture is evident as a direct conversion from the moho the depth of which increases from 30 km to 50 km over a horizontal distance of 70 km before its signature disappears the structure is still better defined on the transverse component where the moho appears as the upper boundary of a 10 km thick layer of anisotropy that can be traced from 30 km to at least 90 km depth the seismic response of this layer is characterized by a frequency dependence that can be modeled by upper and lower boundaries that are discontinuous in material properties and their gradients respectively anisotropy can be characterized by a 5 variation in shear velocity and hexagonal symmetry with a fast axis that plunges at an oblique angle to the subduction plane the identification of this structure provides an unambiguous connection between fossil subduction and fine scale anisotropic mantle layering previous documentation of similar layering below the adjacent slave province and from a range of precambrian terranes across the globe provides strong support for the thesis that early cratonic blocks were stabilized through processes of shallow subduction

the geomorphological and geological importance of palaeosurfaces this special publication is a collection of papers which identifies describes and interprets the occurrence of palaeosurfaces in the geological record the concept of a palaeo surface is one which is generally understood across the geomorphological and geological sciences but according to discipline and application often differs in the emphasis and detail of its interpretation in order to encompass the widest range of contributions and views upon the subject of palaeosurfaces a broad remit was deliberately adopted during the preparation of this volume cations of ancient palaeosurfaces the research areas represented are geographically widespread and include examples from australia africa south america india and europe

the southern margin of the east european craton new results from seismic sounding and potential fields between the north sea and poland abstract the extension of eastern avalonia from britain through the ne german basin into poland is in some sense a virtual structure it is covered almost everywhere by late paleozoic and younger sediments evidence for this terrane is only gathered from geophysical data and age information derived from magmatic rocks during the last two decades much geophysical and geological information has been gathered since the european geotraverse egt which was followed by the babel lt 7 mona lisa dekorp basin 96 and polonaise 97 deep seismic experiments based on seismic lines a remarkable feature has been observed between the north sea and poland north of the elbe line el the lower crust is characterised by high velocities 6 8 7 0 km s a feature which seems to be characteristic for at least a major part of eastern avalonia far eastern avalonia in addition the seismic lines indicate that a wedge of the east european craton eec or baltica continues to the south below the southern permian basin spb a structure which resembles a passive continental margin the observed pattern may either indicate an extension of the baltic crust much farther south than earlier expected or oceanic crust of the tornquist sea trapped during the caledonian collision in either case the data require a reinterpretation of the docking mechanism of eastern avalonia and the elbe odra line eol as well as the elbe fault system together with the intra sudedic faults appear to be related to major changes in the deeper crustal structures separating the east european crust from the paleozoic agglomeration of middle european terranes

seismic velocities in southern tibet lower crust a receiver function approach for eclogite detection summary beneath the tibet plateau the deficit of crustal thickening with respect to what is expected from the plate tectonic constraints is thought to be absorbed either by lateral extrusion or by vertical rock mass transfer to nourish the unsettled debate of the relative importance of these two processes we propose a new approach based on the s to p and the p to s wave conversions enabling the precise determination of the seismic velocities the weighted amplitudes of the direct conversion and of reverberations are stacked at their predicted arrival times for various values of layer thickness and vp vs ratio separately for two sets of p and s receiver functions for each set of receiver functions coherent stack gives the vp vs ratio and thickness for the considered layer the grid search stacking method the values of vp vs ratio and layer thickness are functions of the velocity used for stacking the set of receiver functions but using the p and s receiver functions allows us to solve this indetermination and to find the effective parameters of the layer velocity vs vp vs ratio and thickness we use a bootstrap resampling of the receiver function data sets to estimate the parameters uncertainties for the southern lhasa block the migrated sections of both p and s receiver functions hi climb experiment data show a layer in the lower crust that may be related to the lower indian crust underplated beneath tibet with the grid search stacking method high shear wave velocities vs 4 73 km s 1 and low vp vs ratios 1 69 are detected in this layer such values are typical for high grade eclogites and the low vp vs ratio precludes the confusion with mafic granulites there is no evidence for partial eclogitization near and south of the yarlung tsangpo suture and the about 19 km thick eclogitic layer extends northwards only to about the middle of the lhasa terrane

the role of mobile belts for the longevity of deep cratonic lithosphere the crumple zone model many archean cratons are surrounded by proterozoic mobile belts that have experienced episodes of tectonic re activation over their lifetimes this suggests that mobile belt lithosphere may be associated with long lived inherited weakness it is proposed that the proximity of this weakness can increase the longevity of deep archean lithosphere by buffering archean cratons from mantle derived stresses the physical plausibility of this idea is explored through numerical simulations of mantle convection that include continents and allow for material rheologies that model the combined brittle and ductile behavior of the lithosphere within the simulations the longevity of deep cratonic lithosphere does increase if it is buffered by mobile belts that can fail at relatively low stress levels

foreign contemporaries unravelling disparate isotopic signatures from mesoproterozoic central and western australia abstract extensive time constrained isotopic sm nd lu hf datasets on samples with well studied geological context demonstrates that the musgrave province of central australia and the albany fraser orogen of south western australia evolved through temporally similar mesoproterozoic orogenies at 1345 1260 and 1215 1140 ma but on completely different basement the west and north australian cratons amalgamated before the 1345 1260 ma event which saw the convergence and final amalgamation of those combined cratons with the south australian craton well defined nd and hf isotopic evolution arrays for the musgrave province reflect a juvenile basement with distinct 1950 1900 1600 1550 ma crust formation events rare non radiogenic material is seen only in detritus and in magmas that assimilated this material this evolved detritus was derived from non yilgarn archean sources and reworked archean sources which were added to sedimentary basins developed over the musgrave province basement during and after c 1400 ma to the south of the musgrave province the madura province has a similarly radiogenic signature to the musgrave province and is likely contiguous with it beneath younger cover sequences it shows 2 0 1 4 ma mantle extraction ages and is dominated by juvenile rocks reflecting oceanic crust consumed to the north of the south australian craton and east of the west australian craton available data support the suggestion that the musgrave province is simply modified madura province crust situated along the edge of the north australian craton together the musgrave province and the madura province represent proterozoic australia s most juvenile crustal remnant in stark contrast to this juvenile remnant the isotopic evolution array for the albany fraser orogen reveals a much more evolved signature charting progressive juvenile input into an archean source with strong isotopic and age similarity to the yilgarn craton of the west australian craton

an integrated multi scale 3d seismic model of the archaean yilgarn craton australia abstract the collection of a range of different seismic data types has greatly improved our understanding of the crustal architecture of australia s archaean yilgarn craton over the last few years these seismic data include broadband seismic studies seismic receiver functions wide angle recordings and mine scale to deep seismic reflection transects each data set provides information on the three dimensional 3d tectonic model of the yilgarn craton from the craton scale through to the mine scale this paper demonstrates that the integration and rationalisation of these different seismic data sets into a multi scale 3d geological seismic model that can be visualised at once in a single software package and incorporating all available data sets significantly enhances this understanding this enhanced understanding occurred because the integrated 3d model allowed easy and accurate comparison of one result against another and facilitated the integrated questioning and interrogation across scales and seismic method as a result there are feedback questions regarding understanding of the individual seismic data sets themselves as well as the yilgarn craton as a whole the methodology used including all the data sets in the model range had to allow for the wide range of data sets frequencies and seismic modes at the craton scale p wave s wave and surface wave variations constrained the 3d lithospheric velocity model revealing noticeable large scale velocity variations within and across the craton an interesting feature of the data easily identified in 3d is the presence of a fast s wave velocity anomaly 4 8 km s 1 within the upper mantle this velocity anomaly dips east and has a series of step down offsets that coincide approximately with province and terrane boundaries of the yilgarn craton one dimensional receiver function profiles show variations in their crustal velocity across the craton these crustal velocity variations are consistent with the larger scale geological subdivision of the craton and provide characteristic profiles for provinces and terranes the receiver function results and the deep seismic reflection data both agree on the depth to the moho and both indicate an increase in moho depth to the east the 2d seismic refraction results in the south west of the craton provide crustal thickness information an indication of middle and lower crustal compositions and information regarding the broad scale architectural framework at the province and terrane scale the deep seismic reflection data and the mine scale seismic data provide geometric constraints on crustal architecture in particular the orientation of the region s fault systems as well as variations in the thickness of the granite greenstone succession integration of the results from wide angle seismic refraction data coincident with the deep seismic reflection data provided additional constraints on likely upper crustal lithologies the integrated 3d seismic model implies the dominant geodynamic process involved the development of an orogenic belt that developed with a series of contractional folding and thrusting events separated by equally important extensional events the seismic reflection data in particular suggests that extensional movement on many shear zones was more common than previously thought the seismic reflection data suggest that the dominant mineral systems involved deeply sourced fluid flowing up crustal penetrating shear zones these deeply sourced fluids were further focussed into sites located above fault breached domal regions in the upper crust

the moho boundary above upper mantle peridotites or lower crustal eclogites a global review and new interpretations for passive margins abstract we have performed a global study of 2d crustal scale wide angle profiles across passive margins with regard to local elevations in the moho which could possibly be interpreted as indicative of lower crustal eclogites a total of 16 candidates have been found mainly in the north atlantic and around australia these cases make up c 6 only of the total profile length studied confirming the interpretation of the moho generally representing the top of the mantle the interpreted candidates for lower crustal eclogites indicate that there may be a link between eclogite bodies and continental suture zones in the barents sea off mid norway in the newfoundland appalachians and in the yilgarn craton western australia it is also possible that there is a genetic link between the formation of caledonian eclogites and the jan mayen fracture zone which is the only major fracture zone in the north atlantic several of the inferred lower crustal eclogite bodies are located close to lines of major changes in strain such as coastlines and shelf edges indicating that lower crustal eclogite bodies may be important in guiding the evolution of basin architecture interpreting the moho beneath the bedout high on the northwest shelf of australia as the top of a body of lower crustal eclogites may imply that the northern termination of the lambert shelf represents a paleo suture zone and that the western termination of the broome platform acted as a major transfer zone the significant increase in crustal thickness implied by the eclogite model has important implications for estimates of stretching history subsidence and hydrocarbon maturation modelling

fluvial response to tectonic activity in an intra continental dryland setting the neales river lake eyre central australia abstract geomorphological studies in the centre of the australian continent have emphasised the antiquity of the australian landscape typically considered tectonically stable evidence from the neales river on the western shore of lake eyre indicates that mild epeirogenic forces have deformed sediments of miocene age deformed bedding planes small scale folds and fracture systems reflect consistent miocene and younger tectonic activity in central and southern australia this compression was mild resulting in broad gently plunging folds these folds are evident in the miocene strata but not in the overlying quaternary strata elsewhere in the study area the landscape has been rearranged to preserve features in the geomorphic record that indicate a second phase of tectonic activity in the early to mid pleistocene these include stream diversions preserved on alluvial fans and floodplains formed downstream of faults

cambrian river terraces and ridgetops in central australia oldest persisting landforms fluvial sediments in paleovaileys cut in the ashburton surface of the davenport province of central australia form terrace remnants that appear to retain their original depositional tops and have probably existed as subaerial landforms since their inception marine fossils in sediments conformable with the fluvial sediments near the southeast margin of the province give a cambrian age for the terraces the ashburton surface forming the ridgetops between the paleovalleys is cambrian or older

late cenozoic tectonics and denudation in the central kenya rift quantification of long term denudation rates abstract long term average denudation rates were calculated for the last 3 4 million years ma using digital topographic data related to the present surface of the intrarift bahati kinangop plateau in the central kenya rift well established relations between stratigraphy and faulting chronology and a detailed digital topographic database allow reconstruction of the idealized uneroded plateau surface for an area of 710 km2 the reconstruction refers to the time when the plateau came into existence 3 4 2 6 ma due to widespread deposition of ashflow tuffs and subsequent faulting the reconstruction of this palaeosurface is based on erosional surface remnants occurring within the present plateau surface relict surfaces elements were determined by analyzing the present digital surface representation and geological information within a geographical information system gis after generating digital elevation models of the present and palaeosurfaces long term denudation rates were calculated using the elevation difference method about 80 of the study area are characterized by denudation rates between 0 relict parts and 20 m per one million years m ma for deeply eroded plateau regions denudation reaches 80 100 m ma these rates are comparable to denudation rates which are known from other studies in similar settings the gis based approach provides spatially high resolution denudation rates allowing for further regional analysis of factors controlling spatial variations in sediment supply to the rift basin

geomorphological development of the eastern margin of the australian craton the denudation chronologies of five uplands of contrasting geological structure located at the eastern margin of the australian craton are examined they are the isa highlands macdonnell ranges and flinders ranges fold mountains orogenic setting the arcoona plateau dissected plateau platform setting and the gawler ranges massif of old silicic volcanics cratonic setting in each surfaces of mesozoic age many of them exhumed and of pre cretaceous age are preserved each also appears to have been uplifted recurrently each was either overwhelmed or bordered by the early cretaceous neocomian aptian sea tectonism associated with the break up of gondwana probably allowed this important marine transgression thereafter thalassostatic and erosional depositional isostatic responses have maintained the uplands as uplands and the intervening basins as negative topographic and structural units the pattern of topography has been constant for the last 60 100 ma

pre quaternary landscape inheritance in australia palaeogeographic reconstructions indicate that parts of the australian continent have been subaerially exposed for hundreds of millions of years some landforms and regolith are demonstrated to be at least 300 million years old but their persistence at or near the surface is inconsistent with long term denudation rate estimates based on cosmogenic nuclides and apatite fission track thermochronology burial and exhumation are suggested as significant preservation factors in conjunction with prolonged tectonic stability and a shift to more arid climatic regimes in the cenozoic copyright 2007 john wiley sons ltd

role of lithosphere in intra continental deformation central australia abstract since the proterozoic there has been a set of deformation cycles in central australia culminating in the alice springs orogeny around 400 ma these events occurred away from plate boundaries and involved extension as well as compression although their precise history remains difficult to unravel from the geologic record much evidence of deformation is left in the central australian crust which features significant moho topography and an associated gravity signal in the past several mechanical models invoked crustal thickening and considerable compression to explain these geophysical characteristics however it is hard to envisage extensive deformation affecting the crust alone but leaving no deformation record in the sub crustal lithosphere in recent seismic tomography studies there is continuous seismically fast lithosphere in central australia below depths of about 100 km in this region the uppermost lithospheric mantle is seismically slow but exhibits no significant attenuation of seismic waves these new constraints make simple crustal thickening unlikely to be the main mechanism to generate variations of the moho depth in central australia here we propose a mechanical model of deformation that involves the entire lithosphere we make no strong assumptions about the history of deformation cycles our model does not require lithospheric thickening at any stage of the deformation cycle and results in a present day scenario compatible with shallow as well as deep constraints on the lithosphere structure

continental rifting and drainage reversal the clarence river of eastern australia the clarence river on australia s east coast has an anomalous drainage pattern its right bank tributaries are markedly barbed suggesting reversal whereas tertiary volcanism has disrupted its left bank drainage the southeast flowing clarence is closely aligned with the northwest flowing condamine river just across the continental divide the condamine clarence alignment is continued by a large southern tributary the orara river which flows northwest away from the sea to meet the southeast flowing clarence a broad river with a quite different character flows east from near the orara clarence junction to the sea this is essentially an overflow channel this series of aligned streams the condamine clarence orara represents the remains of an earlier northwest flowing stream that extended the full length of the clarence moreton basin an eastern extension of the great artesian basin during the jurassic the clarence moreton basin was filled with sediments from the surrounding highlands including those to the east of the present coastline continental rifting from late cretaceous times onwards led to the opening of the tasman sea causing the reversal and beheading of the original northwest flowing streams and the formation of the great escarpment the evolution of the clarence river does not fit into most conventional geomorphic paradigms such as cycles climatic geomorphology or steady state landforms it is the result of a succession of unique events on a very long timescale and as such is a classic example of evolutionary geomorphology

flood magnitude frequency and lithologic control on bedrock river incision in post orogenic terrain abstract mixed bedrock alluvial rivers bedrock channels lined with a discontinuous alluvial cover are key agents in the shaping of mountain belt topography by bedrock fluvial incision whereas much research focuses upon the erosional dynamics of such rivers in the context of rapidly uplifting orogenic landscapes the present study investigates river incision processes in a post orogenic cratonic landscape undergoing extremely low rates of incision the mobility of coarse bed materials up to 2 m diameter during late holocene palaeofloods of known magnitude and age is evaluated using step backwater flow modelling in conjunction with two selective entrainment equations a new approach for quantifying the formative flood magnitude in mixed bedrock alluvial rivers is described here based on the mobility of a key coarse fraction of the bed materials in this case the d84 size fraction a 350 m3 s formative flood fully mobilises the coarse alluvial cover with b 200 300 n m2 across the upper and lower gorge riffles peaking over 500 n m2 in the knickzone such floods have an annual exceedance probability much less than 10 2 and possibly as low as 10 3 the role of coarse alluvial cover in the gorge is discussed at two scales 1 modulation of bedrock exposure at the reach scale coupled with adjustment to channel width and gradient accommodates uniform incision across rocks of different erodibility in steady state fashion and 2 at the sub reach scale where coarse boulder deposits corresponding to b minima cap topographic convexities in the rock floor thereby restricting bedrock incision to rare large floods while recent studies postulate that decreasing uplift rates during post orogenic topographic decay might drive a shift to transport limited conditions in river networks observations here and elsewhere in post orogenic settings suggest to the contrary that extremely low erosion rates are maintained with substantial bedrock channel exposure although bed material mobility is known to be rate limiting for bedrock river incision under low sediment flux conditions exactly how a partial alluvial cover might be spatially distributed to either optimise or impede the rate of bedrock incision is open to speculation observations here suggest that the small volume of very stable bed materials lining sandy creek gorge is distributed so as to minimise the rate of bedrock fluvial incision over time

radially anisotropic 3 d shear wave structure of the australian lithosphere and asthenosphere from multi mode surface waves abstract a new radially anisotropic shear wave speed model for the australasian region is constructed from multi mode phase dispersion of love and rayleigh waves an automated waveform fitting technique based on a global optimization with the neighbourhood algorithm allows the exploitation of large numbers of three component broad band seismograms to extract path specific dispersion curves covering the entire continent a 3 d shear wave model is constructed including radial anisotropy from a set of multi mode phase speed maps for both love and rayleigh waves these maps are derived from an iterative inversion scheme incorporating the effects of ray path bending due to lateral heterogeneity as well as the finite frequency of the surface waves for each mode the new s wave speed model exhibits major tectonic features of this region that are in good agreement with earlier shear wave models derived primarily from rayleigh waves the lateral variations of depth and thickness of the lithosphere asthenosphere transition lat are estimated from the isotropic voigt average s wave speed model and its vertical gradient which reveals correlations between the lateral variations of the lat and radial anisotropy the thickness of the lat is very large beneath the archean cratons in western australia whereas that in south australia is thinner the radial anisotropy model shows faster sh wave speed than sv beneath eastern australia and the coral sea at the lithospheric depth the faster sh anomaly in the lithosphere is also seen in the suture zone between the three cratonic blocks of australia one of the most conspicuous features of fast sh anisotropy is found in the asthenosphere beneath the central australia suggesting anisotropy induced by shear flow in the asthenosphere beneath the fast drifting australian continent

the tempo of geomorphological change evidence from southeastern australia a revised denudational chronology based on k ar dating of basalts for much of southeastern australia shows that many major topographic features are far older than was previously realized some upland surfaces originated in the mesozoic and others in the early tertiary in some areas the last major uplift and onset of canyon cutting occurred prior to the mid oligocene apart from the slow headward extension of canyons and localized high level stripping much of the region had taken on approximately its present day form by the mid miocene paradoxically however none of the mechanisms that have been proposed to explain the survival of paleoforms hold here these instances may well be typical of large parts of the interior of tectonic plates and a revision of widely held estimates of modal rates of denudation seems required

crustal structure beneath china from receiver function analysis 1 we collected and processed a large amount of high quality broadband teleseismic waveform data recorded by the 48 chinese national digital seismic network stations to estimate large scale lateral variations of crustal thickness and vp vs ratio hence poisson s ratio beneath china a statistical method was used to select mutually coherent receiver functions at each station which yielded over 200 traces for most of the stations with the conventional h the crustal thickness and vp vs ratio approach there is a large trade off between h and consequently multiple maxima are frequently observed in the h domain we introduced a weight function that measures the coherence between the p to s conversion and the reverberation phases at each h grid to reduce the trade off a 4th root stacking method was further applied to reduce uncorrelated noise relative to the linear stack these modifications turned out to be very effective in reducing the h trade off and yielded reliable estimates of crustal thickness and vp vs ratio the crust beneath eastern china is as thin as 31 33 km and the underlying moho is relatively flat and sharp in the western part of china the crust is considerably thicker and shows large variations the moho is observed at about 51 km depth along the tian shan fold system and about 84 km deep beneath the central part of the tibetan plateau the transition occurs at the so called n s belt between about 100 and 110 e which is featured by unusually high seismicity and large gravity anomalies the average vp vs ratio over the mainland china crust is about 1 730 0 249 significantly lower than the global average 1 78 0 27 of the continental crust this lower vp vs ratio may suggest a general absence of mafic lowermost crustal layer beneath china

tectonic evolution of proterozoic australia proterozoic australia has long been interpreted as a single intact continent in which all tectonic and magmatic activity was intracratonic this paper proposes an alternative hypothesis in which numerous fragments of continental crust were assembled by plate tectonic processes the assembly was completed between 1300 and 1100 ma when the crustal fragments were combined as an early component of the rodinian supercontinent rifting and fragmentation of archaean continents began in the late archaean and continued into the proterozoic passive margin deposits such as those of the hamersley basin accumulated on isolated fragments of archaean crust these numerous fragments were subsequently assembled into three cratons by 1830 ma a west australian craton was established by collision of the archaean pilbara and yilgarn cratons which were joined along the capricorn orogen similarly a south australian craton developed by amalgamation of the proto gawler and proto curnamona cratons along the kimban orogen a north australian craton appears to have formed by accretion of numerous crustal fragments including the kimberley pine creek lucas and altjawarra cratons with sutures marked by the king leopold halls creek tennant creek and proto isan orogens the southern margin of the north australian craton was the site of repeated terrane accretion and orogenic activity between 1880 ma and 1400 ma this included an orogenic event at 1880 1850 ma the strangways 1780 1730 ma argilke 1680 1650 ma and chewings 1620 1580 ma orogenies and the intracratonic anmatjira uplift 1500 1400 ma intracratonic rifting at 1750 to 1710 ma and 1640 to 1600 ma produced the mcarthur basin and related minor basins parts of which were deformed by the isan orogeny at 1600 and 1530 ma rifting along the line of the capricorn orogen led to deposition in the overlying intracratonic bangemall basin between 1630 and 1300 ma along the eastern margin of the south australian craton the 1670 to 1600 ma olarian orogeny marks interaction with now obscured continental crust to the east tectonic activity between 1300 and 1100 ma led to the assembly of proterozoic australia as an early component of the supercontinent of rodinia this first involved the amalgamation of the west australian and north australian cratons followed by collision with the south australian craton the centralian superbasin developed over the junction of the north south and west australian cratons between 830 and 750 ma rifting to the east formed the adelaide geosyncline at 830 ma this was followed by the breakup of rodinia with the rifting apart of laurentia and gondwanaland along the eastern margin of proterozoic australia at 750 ma and the subsequent formation of the palaeo pacific ocean after the breakup of rodinia a series of northeast southwest compressional events followed by periods of relaxation reflect the assembly of a new supercontinent old lines of weakness were reactivated culminating in the intracratonic king leopold paterson petermann ranges and pinjarra orogenies between 620 and 540 ma subsequent reactivation continued into the phanerozoic with the widespread eruption of continental flood basalts and the formation of intracratonic basins 540 530 ma

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

thermal evolution of rifted continental margins new evidence from fission tracks in basement apatites from southeastern australia the palaeozoic granitic basement of southeastern australia shows a regular pattern of apatite fission track ages which is dominated by a rapid decrease in apparent age towards the rifted continental margin apparent ages away from the margin vary between about 230 and 360 myr but drop sharply to minimum values of around 80 myr near the coast just south of the sydney basin and 150 175 myr elsewhere along the coast fission track length information allows the age pattern to be interpreted as the result of partial to complete resetting of the older ages by a widespread thermal event at about 80 100 myr this event accompanied the rift phase of passive margin development and peaked just before the onset of sea floor spreading in the adjacent tasman sea the zone of reduced apatite ages is deeply embayed around the gippsland basin supporting the suggestion that it originated as a cretaceous failed arm of the tasman rift system the thermal event has affected apatites up to about 130 km from the margin and has produced a characteristic set of bimodal track length distributions in apatites with partially reset ages the bimodality gradually disappears towards the oldest apatite ages which have negatively skewed unimodal distributions the youngest apatites also tend towards unimodal length distributions indicating that thermal annealing of pre existing tracks in these samples went almost to completion maximum temperatures reached in samples presently exposed in the coastal area were thus probably about 110 120 c thermal activity was accompanied by considerable uplift across the region followed by gradual erosion to expose the present land surface post breakup erosion was generally greater towards the new coastline with near coastal samples being previously buried a probable 1 5 2 5 km

thermotectonic evolution of the western margin of the yilgarn craton western australia new insights from 40 ar 39 ar analysis of muscovite and biotite abstract the post cratonisation history of the yilgarn craton is somewhat fragmentary due to incomplete or absent stratigraphic records for overlying sediments however the exposed archean crystalline rocks can provide important constraints on the missing thermotectonic history if appropriate thermochronological methods are used previous thermochronology studies from the southwestern yilgarn craton suggest that it was subjected to late pan african tectonism and east west compression resulting in tectonic loading thrusting of sediments onto basement rocks along its western margin however this proposed tectonic model is based largely on bulk rb sr biotite analyses with minimal petrological and geochemical control this study across a 80 km e w transect along the western yilgarn craton employed laser 40 ar 39 ar incremental heating experiments on muscovite and single biotite grains from well documented sample sites broadly comparable to those sampled previously for rb sr biotite analysis muscovites record relatively consistent 40 ar 39 ar ages ranging from 2220 to 2450 ma coexisting biotite 40 ar 39 ar results however reveal significant age variations at both intra and inter grain scales single grain biotite 40 ar 39 ar dating results show consistent ages of 2480 2580 ma across much of the yilgarn craton with ages decreasing abruptly to 1000 1100 ma over a narrow transitional zone 30 40 km wide before decreasing further to 620 630 ma along the western margin of the craton petrographic observations indicate that most biotite grains especially in the transitional zone and western margin are severely chloritized and contain abundant titanite inclusions that may have resulted from fluid induced recrystallisation under greenschist facies metamorphism the transitional zone 40 ar 39 ar biotite ages are temporally compatible with metamorphism of the adjacent northampton and mullingarra complexes suggesting either their juxtaposition along the western margin of the yilgarn craton during the mesoproterozoic pinjarra orogeny or coincidental partial re equilibration at this time during younger thermal events the westernmost biotite recrystallisation ages of 620 630 ma support palaeomagnetic indications of oblique collision between great india and the australian continent during gondwana amalgamation

precambrian tectonic history of the west australian craton and adjacent orogens this review is a synthesis of the precambrian geology of the west aus tralian craton and its fringing orogens it describes the evidence that has recently been reinvestigated and reinterpreted to reveal a long dynamic history of repeated aggregation and dispersal of crustal fragments cratons are large composite geological units of continental crust that have survived intact for significant periods of geological time they are generally tabular bodies with great areal extent millions of square kilo meters and lithospheric thickness 200 400 km orogens are narrow steep zones of tectonic and metamorphic activity associated with the deposition of sediments and the intrusion of plutonic rocks they occur within or along the margins of continents and are generally a few hundred kilometers wide thousands of kilometers long and extend to the base of the litho sphere most orogens are initially associated with compressive tectonics crustal thickening and the transient formation of mountain belts cratons and orogens may survive for very long periods of time but as part of a thin crust on a dynamic mantle they are inherently mobile and travel as rafts for great distances around the surface of the earth they may be torn apart dispersed and reassembled with other continental fragments the boundaries of these crustal fragments once established remain zones of crustal weakness that may be reactivated as intra continental mobile belts or lines along which cratons are assembled and dismembered cf hoffman 1 988

tertiary coastal dunes of the eucla basin australia abstract on the northeast margin of the nullarbor plain in western south australia there is preserved an assemblage of coastal aeolian landforms that includes coastal dune dune ridge and possible beach ridge one of these landforms is the ooldea range a 650 km long coastal dune that lies 25 300 km from the present coast these landforms are believed to have formed at the end of the eocene after maximum marine transgression in the eucla basin the ooldea barton and paling ranges formed in a tectonically stable region of topographically subdued terrain their orientation and position may be related in part to crustal fractures that were active during initial break up of australia and antarctica the large quantities of sand required for their construction were supplied to the coast by rivers which drained a hinterland of various suitable source rocks growth may have begun as chains of barrier islands which amalgamated to form large coast parallel dunes during progradation these coastal dunes provide evidence about climate at and after the time of their formation their formation indicates an atmospheric circulation of at least moderate intensity and prevailing winds with a major westerly component this occurred at a time when the climate is likely to have been temperate if the interpretation of the dunes age is correct they may be viewed as landforms bearing testimony to the global change in climate which occurred at the end of the eocene their excellent preservation in the landscape today some 34 37 million years after formation is remarkable implied is a degree of aridity for much of the remainder of the cainozoic this appears to have been more significant in the nullarbor plain region than in the southeastern part of australia other factors responsible for their preservation are likely to include vegetation cover the permeability of their quartz sands subsequent history of sea level and hydrodynamics of the basin

magnetostratigraphy of the lower cretaceous vectis formation wealden group on the isle of wight southern england magnetostratigraphic results are described from two sections within the lower cretaceous vectis formation formerly wealden shales of the isle of wight southern england the sections are located at shepherd9s chine and yaverland respectively in both of these sections a reliably established reverse polarity magnetozone herein defined as the vectis magnetozone occurs within the shepherd9s chine member this magnetozone has a thickness of some 15 m and its upper boundary is well defined in the yaverland section but is obscured in the shepherd9s chine section due to cliff slumping the lower boundary is well established in both sections and lies some 15 m above the barnes high sandstone member in the shepherd9s chine section and 12 m above this unit at yaverland this boundary provides a useful chron stratigraphic datum a comparison with established geomagnetic polarity timescales for the cretaceous indicates that the vectis magnetozone may be correlated either with lower aptian reverse polarity chron cm 0 or with lower barremian chron cm 1 with the former being the more likely an important implication of this interpretation is that the base of the aptian stage as defined from tethyan foraminiferal zones must lie within the vectis formation at least 25 30 m beneath the top of the shepherd9s chine member rather than at the top of this member as hitherto commonly accepted beds characterized by anomalously high intensities of magnetization which occur at the base of the vectis formation and a few metres above the barnes high sandstone in the two sections are tentatively interpreted as having a volcanogenic origin

new constraints on the seismic structure of west australia evidence for terrane stabilization prior to the assembly of an ancient continent we present a new near comprehensive survey of the variations in seismic structure across the west australian craton at the scale of the main terrane groups analyzing data from distant earthquakes recorded at temporary and permanent stations located across the region we found the best fi tting structure by modeling the conversions from p to s wave motion the receiver function that take place as the seismic energy travels upward through the lithosphere such methods can be used to delineate the extent of cratonic and orogenic terranes in regions where geological exposure of the surface is limited and they provide an effective alternative to active source seismic techniques for deep crustal targets the seismic structure is consistent within several of the individual archean terranes most notably the pilbara murchison and southern cross these terranes are underlain by lower crust of low seismic velocity and show a sharp seismic moho the structure shows signifi cant contrasts between neighboring terranes thus major tectonic units have a velocity profi le that is a signature of that terrane or terrane group we infer that the seismic structure of the archean crust and upper mantle was fixed before craton assembly and preserved through the subsequent collision and accretion of the tectonic units that formed the west australian craton

low temperature phanerozoic history of the northern yilgarn craton western australia abstract the phanerozoic cooling history of the western australian shield has been investigated using apatite fission track aft thermochronology aft ages from the northern part of the archaean yilgarn craton western australia primarily range between 200 and 280 ma with mean confined horizontal track lengths varying between 11 5 and 14 3 m time temperature modelling of the aft data together with geological information suggest the onset of a regional cooling episode in the late carboniferous early permian which continued into late jurassic early cretaceous time present day heat flow measurements on the western australian shield fall in the range of 40 50 mw m 2 if the present day geothermal gradient of 18 2 c km 1 is representative of average phanerozoic gradients then this implies a minimum of 50 c of late palaeozoic to mesozoic cooling assuming that cooling resulted from denudation the data suggest the removal of at least 3 km of rock section from the northern yilgarn craton over this interval the perth basin located west of the yilgarn craton contains up to 15 km of mostly permian to lower cretaceous clastic sediment however published u pb data of detrital zircons from permian and lower triassic basin strata show relatively few or no grains of archaean age this suggests that the recorded cooling can probably be attributed to the removal of a sedimentary cover rather than by denudation of material from the underlying craton itself the onset of cooling is linked to tectonism related to either the waning stages of the alice springs orogeny or to the early stages of gondwana breakup

rupture creep lamellae and crocodiles happenings in the continental crust from the observation of certain seismic reflectivity patterns in phanerozoic continental crusts a relationship is suggested between 1 rupture and seismicity generally restricted to the upper crust 2 crocodile tectonics a kind of vertical indentation observed by diverging plane reflectors preferably in the middle crust 3 creep and the formation of reflecting lamellae in the lower crust based on these observations and on viscosity depth estimates a conceptual model for the above mentioned structures is presented which is also compatible with observations in older crusts boundary conditions are given for rupture as well as for lamellae forming creep

seismic imaging of subducting continental lower crust beneath the pamir abstract exhumation of ultra high pressure metamorphic rocks testifies that the continental crust can subduct to significant depth into the mantle despite its buoyancy however direct observation of ongoing subduction of continental crust is rare the pamir is regarded as a possible place of active continental subduction because of the intermediate depth seismicity crustal xenoliths and estimates of crustal shortening versus convergence rates here we present for the first time receiver function images from a passive source seismic array traversing the tien shan and the pamir plateau showing southward subduction of eurasian continental crust in the eastern pamir we observe a southerly dipping 10 15 km thick low velocity zone lvz that extends from 50 km depth near the base of the crust to more than 150 km depth with a dip angle increasing to subvertical while the upper and mid crustal material seems to be shortened and incorporated into the pamir the lower eurasian crust detaches and subducts in its deeper part 80 km the lvz envelopes the intermediate depth earthquakes our observations imply that the complete arcuate intermediate depth seismic zone beneath the pamir traces a slab of subducting eurasian continental lower crust

volcanology of the aries micaceous kimberlite central kimberley basin western australia abstract the neoproterozoic 815 4 4 3 ma aries kimberlite intrudes the king leopold sandstone and the carson volcanics in the central kimberley basin northern western australia aries is comprised of a n nne trending series of three diatremes and associated hypabyssal kimberlite dykes and plugs the diatremes are volumetrically dominated by massive clast supported accidental lithic rich kimberlite breccias that were intruded by hypabyssal macrocrystic phlogopite kimberlite dykes and plugs with variably uniform to globular segregationary textured groundmasses lower diatreme facies accidental lithic rich breccias probably formed through fall back of debris into the vent with a major contribution from the collapse of the vent walls these massive breccias are overlain by a sequence of bedded volcaniclastic breccias in the upper part of the north lobe diatreme abundant poorly vesicular to nonvesicular juvenile kimberlite ash and lapilli with morphologies that are indicative of phreatomagmatic fragmentation processes occur in a reversely graded volcaniclastic kimberlite breccia unit at the base of this sequence this unit and overlying bedded accidental lithic rich breccias are interpreted to be sediment gravity flow deposits including possible debris flows derived from the collapse of the crater walls and or tephra ring deposits that surrounded the crater diatreme forming eruptions may have been initiated by magma water interactions along fracture and joint controlled aquifers within the king leopold sandstone the current level of exposure of the diatremes probably extends from the lower diatreme facies up into the base of a bedded upper diatreme sequence

paleothermometry of the sydney basin evidence from overprinting of magnetizations of late permian and mesozoic rocks and from the rank of permian coals and mesozoic phytoclasts coal particles suggests that surface rocks in the sydney basin eastern australia have been raised to temperatures of the order of 200 sup 0 c or higher as vitrinite reflectance an index of coal rank or coalification is postulated to vary predictably with temperature and time estimates of the paleotemperatures in the sydney basin based on observed vitrinite reflectance measurements can be made in conjunction with reasonable assumptions about the tectonic and thermal histories of the basin these estimates give maximum paleotemperatures of present day surface rocks in the range 60 249 sup 0 c depending on factors such as location in the basin the thickness of the sediment eroded and the maximum paleogeothermal gradient higher coal rank and consequently larger eroded thicknesses and paleogeothermal gradients occur along the eastern edge of the basin and may be related to seafloor spreading in the tasman sea on the basin s eastern margin a theory of thermal activation of magnetization entailing the dependence of magnetic viscosity on the size distribution of the magnetic grains is used to obtain an independent estimate of the maximum paleotemperaturesmore in the sydney basin this estimate places the maximum paleotemperature in the range 250 300 sup 0 c along the coastal region both coalification and thermal activation of magnetization models provide strong evidence of elevated paleotemperatures which in places exceed 200 sup 0 c and the loss of sediment thicknesses in excess of 1 km due to erosion less

rates of surface processes on slopes slope retreat and denudation results taken from 270 publications on rates are summarized and collated with those from 149 publications reviewed previously young 1969 1974 the data are classified by major climatic zone normal or steep relief and consolidated or unconsolidated rocks representative rates and their ranges are given for soil creep solifluction surface wash solution chemical denudation rock weathering slope retreat cliff free face retreat marine cliff retreat and denudation the last being compared with representative rates of uplift solifluction is of the order of 10 times faster than soil creep but both cause only very slow ground loss solution is an important cause of ground loss for siliceous rocks on which it may be half as rapid as on limestones total denudation brought about mainly by surface wash reaches a maximum in the semi arid and probably also the tropical savanna zones acceleration of natural erosion rates by human activities ranges from 2 3 times with moderately intense land use to about 10 times with intensive land use and considerably higher still where there is recognized accelerated soil erosion where there is active uplift typical rates are of the order of 10 times faster than denudation although in some high steep mountain ranges these may approach equality

quantitative resolution of the debate over antiquity of the central australian landscape implications for the tectonic and geomorphic stability of cratonic interiors we report the first measure of long 100 myr and short 1 myr term denudation rates from key geologically stable landforms in the davenport range central australia these landforms have previously been assigned a cambrian age which arguably places them amongst the oldest persistent landforms on the continent if not on earth our results from combined apatite fission track thermochronology and in situ cosmogenic radionuclide analyses using 10 be and 26 al show that while average exhumation rates are low the denudation history for this cratonic region is incompatible with extreme sub aerial longevity and long term tectonic and geomorphic stability our revised model for the landscape evolution of this region is consistent with one of maximum burial prior to and during the mesozoic followed by a phase of kilometre scale exhumation that was largely complete by the beginning of the cainozoic we suggest that a similar process of burial and exhumation has probably been responsible for the sub aerial preservation of seemingly ancient landforms elsewhere in australia

comment on low temperature phanerozoic history of the northern yilgarn craton western australia by u d weber et al tectonophysics 400 2005 127 151

migration in relation to possible tectonic and regional controls in eastern australian volcanism abstract the wellman mcdougall model for southward migration of central volcano activity in eastern australia is extended to the basaltic lava provinces latitude age plots of volcanic episodes are related to trails initiated from regions of active volcanism at the commencement of northward drift of australia 53 m y b p from southern ocean spreading these trails intersect at least 75 and possibly up to 95 of basaltic episodes and suggest a migratory control the migration of central volcano felsic activity however consistently exceeds sea floor spreading rates with a relative southward motion of 4 10 mm yr the trails give a mean migration direction of 24 9 w of s before 29 30 m y but 8 12 w of s after 29 m y extrapolation of the central volcano activity back in time places it across the coral sea louisiade spreading system and new guinea collision zone at the beginning of drift this suggests that these structures may provide residual thermo tectonic anomalies in the mantle with potential to initiate volcanism under the moving australian plate kinematic reconstruction of australia s drift relative to these structures shows that the western felsic and k rich ultramafic activity falls on progressive overlaps of the coral sea louisiade anomalies the basaltic volcanism generally overlies the central regions of the anomalies the young basalt fields of victoria south australia correspond with positions of the coral sea louisiade anomalies over the last 5 m y the regions of youngest volcanism conductivity anomaly and high heat flow lie near the present projected position of the anomalies some volcanic episodes are not obviously related to migration trails the young basaltic activity in northern queensland may result from movement of the australian plate towards unstable regions of volcanism and uplift in papua new guinea central volcano province spacings appear to match expected lithospheric thickness spacings of basaltic episodes suggest that other factors such as zonal rotational flow in the asthenosphere may also be involved cessation of much volcanism over the eastern australian highlands about 10 m y ago is attributed to imposition of the present regional compressive stress field probably as a result of changes in the sea floor spreading patterns an apparent change in migration direction of volcanism 29 30 m y ago may be related to changes in east west spreading and continental motions adjacent to the australian plate differences between migration directions of volcanism and absolute motions determined for the australian plate may reflect effects of the earth s rotation and migration of spreading ridges the migratory model developed here predicts future australian volcanism mostly in or south of the present regions of younger volcanics and high heat flow it would be basaltic but may be accompanied by felsic activity in tasmania

a new species of polacanthus ornithischia ankylosauria from the lower cretaceous of sussex england the first specimen of the ankylosaur genus polacanthus from the mainland barremian of southeast england is described as polacanthus rudgwickensis sp nov polacanthus rudgwickensis is larger than polacanthus foxii and there are significant differences in the dermal armour the tibia and caudal vertebrae of the two species polacanthus foxii appears to be restricted at present to the isle of wight with one specimen from southwest england whilst polacanthus rudgwickensis is only known from sussex this geographical distribution the palaeobiological implications and possible sexual dimorphism are discussed for this genus

first deep seismic reflection images of the eastern alps reveal giant crustal wedges and transcrustal ramps 1 the alps are considered as a classical example for an orogen created by continental plate collision in this study we present new images obtained from deep seismic reflection profiling in the eastern alps between munich and venice which give rise to examine and revise existing concepts the seismic sections exhibit a prominent bi verging reflection pattern at crustal scale a major ramp like structure outcropping at the inn valley fault can be traced southward over 80 km into the mountain root where relics of the subducted penninic ocean are expected new models of the evolution of the eastern alps show an upper lower crustal decoupling along transcrustal thrust faults with opposite thrust directions of both the european and the adriatic african continents

an inverted continental moho and serpentinization of the forearc mantle volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back arc region but the forearc mantle in the corner of the wedge is thought to be significantly cooler here we explore the structure of the mantle wedge in the southern cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers we find very low shear wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an inverted continental moho which reverts to normal polarity seaward of the cascade arc this observation provides compelling evidence for a highly hydrated and serpentinized forearc region consistent with thermal and petrological models of the forearc mantle wedge this serpentinized material is thought to have low strength and may therefore control the down dip rupture limit of great thrust earthquakes as well as the nature of large scale flow in the mantle wedge

cosmogenic exposure and erosion history of australian bedrock landforms exceptionally high activities of in situ produced 1 0 be and 2 6 al indicate that australian bedrock surfaces are some of the most stable in the world these cosmogenic nuclides demonstrate that australian granite exposed and sampled at 10 sites along a transect from the eyre peninsula 33 s to the kakadu area in the northern territory 14 s has in some places eroded only decimeters over the past million years however nuclide activities are not saturated in any of the 61 exposed samples we analyzed mandating that the surfaces we sampled are losing mass albeit slowly over time such mass loss indicates that inselbergs are dynamic landforms confounding the assignment of discreet ages to inselberg surfaces nevertheless the differential between slow rates of erosion measured on the very stable uppermost parts of these landforms and the more rapid rates measured below their flanks and below the adjacent grus covered planes suggests that the forms of many large inselbergs which stand meters to tens of meters high must be at least tertiary in age and possibly much older activities of 1 0 be and 2 6 al in 61 exposed australian samples range from 5 1 0 1 10 6 to 5 3 0 6 x 10 5 atoms g 1 and 2 1 0 1 x 10 7 to 3 4 0 5 x 10 6 atoms g 1 respectively normalized to sea level at latitudes of 60 using only neutron scaling activities of 1 0 be and 2 6 al in seven shielded samples 3 5 13 m below the surface are much lower ranging from 3 4 0 2 x 10 4 to 7 0 0 1 x 10 4 atoms g 1 and 1 6 0 1 x 10 5 to 2 8 0 2 x 10 5 atoms g 1 respectively 2 6 al 1 0 be ratios of exposed samples range from 3 89 0 19 to 6 29 0 82 if 2 uncertainty ranges and a nominal sea level high latitude 1 0 be production rate of 5 17 atoms g 1 yr 1 are considered ratio data for all but one surface sample are consistent with continuous surface or near surface exposure and or erosion rock surfaces farther north in australia where the climate is more humid have lower nuclide activities thus we infer that surface stability is inversely related to mean annual precipitation from 61 exposed samples we calculated maximum limiting single nuclide model erosion rates of 0 3 0 1 to 5 7 1 0 m m y and minimum limiting single nuclide model exposure ages of 105 16 to 1310 190 ka by assuming a sea level high latitude 1 0 be production rate of 5 17 atoms g 1 yr 1 seven shielded samples in which the nuclide inventory is muon generated also have nuclide activities consistent with similarly low rates of erosion but over even longer time scales it appears that the eyre peninsula inselbergs have been and are eroding so slowly that they may well be direct descendents of cenozoic and perhaps even mesozoic forms

desert aeolian origin of late cenozoic regolith in arid and semi arid southwestern australia abstract using a sedimentary geology approach the late cenozoic regolith of southwestern australia is interpreted as basement saprock and saprolite unconformably overlain by sequences of continental sedimentary deposits the sedimentary deposits which overlie saprock and saprolite are allochthonous variously altered and mainly partly to wholly desert aeolian sediments they include aeolian and fluvial sandy clayrock facies e g deposits which resemble the pallid and mottled zones of weathered precambrian bedrock of the traditional laterite profile altered aeolian sand and sandy dust facies e g hardpan lower parts of duplex soils red sandy silt claystone and calcrete valley fills altered sandy duststones e g bauxite laterite and ferricrete of the traditional laterite profile and bioturbated aeolian sand sheets e g sandplain soils lateritic sandplains of the traditional laterite profile and upper parts of duplex soils the allochthonous and desert aeolian views proposed here differ fundamentally from the traditional residual colluvial and erosional views consequently there is a need for both traditional and alternative views to be critically appraised from the perspective of sedimentary geology

crustal structure and orogenic material budget in the west central pyrenees surface and subsurface data are combined to construct a crustal scale cross section of the western central pyrenees france and spain at the boundary between the european and iberian plates the position of moho reflections in the ecors arzacq reflection profile suggests a tectonic wedge of european crust and upper mantle had indented the iberian plate at lower crustal levels the european wedge is overlain by an upper iberian wedge thus constituting a double stacked wedge geometry the upper wedge was delaminated and deformed giving rise to the pyrenean orogenic prism manifested as a bivergent fan in upper crustal levels the underthrust lower iberian plate has been imaged to depths of 55 60 km but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km total orogenic contraction calculated from surface structures is about 75 80 km which was accomplished between the latest cretaceous and the early miocene at an averaged rate of 1 2 mm yr consistent with these moderate values exhumation of the orogen is much less than in the more shortened eastern parts of the range paleozoic basement and preorogenic mesozoic rocks are little eroded and much of the exhumation involved cannibalization of early foreland basins which once covered the entire poorly emergent orogen at this transect this resulted in a continuous process of sediment recycling and coupled with a considerable lateral arrival of material a bulk negative erosion sedimentation budget

thermo mechanical controls on intra plate deformation and the role of plume folding interactions in continental topography thermo tectonic age and inherited structure exert the main controls on the bulk strength of the lithosphere in intraplate settings mechanical decoupling within the lithosphere strongly affects the interaction between deep earth and surface processes thermo mechanical models demonstrate the particular importance of the rheological stratification of the lithosphere in the preservation of ancient cratonic blocks in the surface expression of plume and mantle lithosphere interactions and their impact on the dynamic topography in general the same is true for the effect of large scale lithospheric folding on intraplate basin formation and associated differential vertical motions initiation of continental lithosphere subduction crucial for linking orogenic deformation to intraplate deformation appears to be facilitated by plume lithosphere interactions we present a discussion of these aspects focusing on better process understanding of continental deformation in the context of a number of well documented cases of intraplate deformation