survival of ancient landforms in a collisional setting as revealed by combined fission track and u th he thermochronometry a case study from corsica france abstractthe age of high elevation planation surfaces in corsica is constrained using new apatite u th he data field observations and published work zircon fission track apatite fission track aft data and landform stratigraphical analysis thermal modeling results based on aft and u th he data and the eocene sediments uncomformably overlapping the variscan crystalline basement indicate that present day elevated planation surfaces in corsica are the remnants of an erosion surface formed on the basement between 120 and 60 ma during the alpine collision in the paleocene eocene the variscan crystalline basement was buried beneath a westward thinning wedge of flysch and the eastern portion was overridden by the alpine nappes resetting of the apatite fission track thermochronometer suggests an overburden thickness of 4 km covering variscan corsica protected by soft sediment the planation surface was preserved in the latest oligocene to miocene times the surface was re exposed and offset by

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

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

influence of secular variation of the geomagnetic field on production rates of in situ produced cosmogenic nuclides abstract scaling factors are presented that allow a full description of the cosmic ray flux modulation during secular variation of the geomagnetic field these scaling factors are analogous to those determined in a similar work dunai t j earth planet sci lett 2000 176 157 169 that were accurate for field strengths equivalent to present day field strength but cannot accommodate field strength variations strategies to derive the relevant geomagnetic field parameters are discussed and are tested with existing production rate calibrations for 3 he a production rate of 103 4 2 atoms g olivine yr sea level and for zero cutoff rigidity was derived from calibration sites from hawaii western usa and canary islands covering the time range of 2 281 kyr

sediment residence times in catchments draining to the gulf of carpentaria northern australia inferred by uranium comminution dating abstract uranium u isotopes are useful for constraining the timescales of weathering and erosion processes the 234u 238u activity ratio parentheses denote activity ratio of fine grained detrital minerals is proposed to record the time elapsed since mineral grains were reduced to

early mesozoic triassic landscapes in australia evidence argument and implications abstract australia has strong claims to be known as the old continent in addition to landscapes of later cretaceous early tertiary derivation remnants of early mesozoic triassic jurassic surfaces which are part of the contemporary landscape are also recognized being of etch type they have two ages one referring to the period of preparation by subsurface weathering and the other to their date of exposure in many instances exposure can be dated and the period of preparatory weathering closely inferred such old paleosurfaces are demonstrated on kangaroo island and are strongly implied in for example the flinders gawler and macdonnell ranges in arnhem land and the arcoona plateaus in many parts of the eastern uplands and on several bornhardts in the yilgarn and gawler cratons they reinforce the suggestion that once in positive relief and shedding water surfaces persist with little change for long periods such ancient features are incompatible with several well known models of landscape e

erosion rates in and around shenandoah national park virginia determined using analysis of cosmogenic 10be we use cosmogenic 10be analysis of fluvial sediments and bedrock to estimate erosion rates 104 105 year timescale and to infer the distribution of post orogenic geomorphic processes in the blue ridge province in and around shenandoah national park virginia our sampling plan was designed to investigate relationships between erosion rate and lithology mean basin slope basin area and sediment grain size fifty nine samples were collected from a variety of basin sizes inferred erosion rates for the medium sand fraction of all fluvial samples from all lithologies range from 3 0 to 21 m my the area weighted mean erosion rate for single lithology basins in the park is 12 2 m my single lithology erosion rate ranges for fluvial samples are granite 7 0 to 20 m my metabasalt 3 8 to 21 m my quartzite 3 8 to 15 m my and siliciclastic rocks 5 2 to 15 m my multilithology basins erode at rates between 3 0 16 m my the shenandoah river basin 3305 km2 is eroding at 6 6 m my bedrock erosion rates range from 1 8 to 11 m my across all lithologies with a mean of 6 5 4 3 m my grain size specific 10be analysis of four samples showed no consistent trend of concentration with grain size cosmogenic analysis of bedrock and sediment from the shenandoah national park area allows us to speculate about why some parts of the appalachian mountains erode more slowly and some more rapidly overall it appears that steep drainage basins erode more rapidly than gently sloped basins climate and lithology may also influence basin scale rates of erosion as suggested by the difference in average erosion rates east and west of the divide and the difference between the erosion rates of quartzite and granite dominated basins data are conflicting in regards to the evolution of relief over time analyses made of exposed bedrock along ridgelines suggest that such rock is eroding either more slowly than adjacent drainage basins susquehanna river shenandoah national park region or at similar rates great smoky mountains providing a mechanism for growing relief at the scale of individual ridgelines however considering relief on a landscape or physiographic province scale by comparing erosion rates of the highlands versus the lowlands suggests that relief of the range as a whole is either steady or very slowly decreasing over multi millennial timescales the presence of significant erosion rate slope relationships negates a broad hackian view of the landscape because there is not uniform erosion across this landscape the aspect erosion rate and slope erosion rate relationships present in the shenandoah area suggest that the landscape is not fully adjusted to rock strength

late quaternary landscape evolution in the keep river region northwestern australia abstract this paper evaluates the late quaternary chronostratigraphic context of archaeological sites in the keep river region northern territory australia cosmogenic dating luminescence dating and sediment characterisation reveal sedimentary processes commencing from erosion of the escarpment and plateaux source through temporary storage in sand sheets to final deposition in alluvial floodplains erosion of the sandstone plateaux 5 mm ka 1 and escarpment faces probably 50 100 mm ka 1 provide the main sediment source for the adjacent sand sheets which have evolved over the past 100 000 years as the product of ongoing cycles of accumulation and denudation the rate of sediment accumulation is lowest near the escarpments on the low energy sediment limited sand sheets 1 and greatest near the main streams 400 mm ka 1 that have more numerous sediment sources collectively luminescence ages indicate an apparent increase in sediment accumulation rate in the sand sheets from 100 mm ka 1 in the late pleistocene to over 200 mm ka 1 in the holocene this most likely reflects enhanced monsoonal activity following postglacial marine transgression palaeosol horizons in the creek profile distinguished by sediment mottling mark potentially significant palaeoenvironmental and palaeoclimatic changes during the quaternary

the silver deposits at cobalt and gowganda ontario ii an experiment in age determinations employing radiometric and paleomagnetic measurements u pb analyses of primary baddeleyite and vein related secondary rutile separated from a nipissing diabase sill at the castle mine gowganda yield ages of 2217 5 1 6 and 2217 0 6 ma respectively the data allow for the possibility that i the vein formed at essentially the same time as diabase intrusion defined within the limits of the intercept age or ii the vein could have formed up to 8 1 ma later than intrusion paleomagnetic analyses of the diabase suggest that it is part of the older n2 phase of this widespread intrusive event paleomagnetic analyses of a pre vein granite dike intrusive into the diabase provide a minimum time interval of 20 000 50 000 years separating intrusion and vein formation 40ar 39ar analyses of silicates obtained from ore veins in the cobalt camp yield highly disturbed age spectra paleomagnetic analyses of altered wall rocks to ore veins in both the castle mine and the cobalt camp provide a wide range of apparent ages inconsistent with the u pb data the 4

the proterozoic davenport province central australia regional geology and geochronology abstract the davenport province forms the southern part of the tennant creek inlier and lies to the north of the arunta inlier the oldest rocks exposed are turbidites and minor 1880 1870 ma old felsic volcanics of the warramunga group these were folded probably during the barramundi orogeny and intruded by granite before being overlain by the hatches creek group a sequence up to 10 000 m or more thick of fluvial to shallow marine sedimentary and bimodal volcanic rocks a rift sag model of basin development involving crustal extension in an intracratonic setting is suggested for this group interpretation of u pb zircon data for felsic volcanics in the lower part of the hatches creek group is hampered by problems of ancient pb inheritance but a preferred crystallization age of 1820 1810 ma is indicated two episodes of upright concentric folding about nw se and ne sw trending axes preceded emplacement of granite at 1660 ma or earlier rb sr whole rock data for felsic volcanics from the hatches creek group are tentatively interpreted to indicate a region wide hydrothermal alteration event at 1645 44 ma this alteration may have been associated locally with w cu bi and mo mineralization

u th he dating of apatite a potential thermochronometer abstract we found a gem quality crystal of durango fluorapatite to have a 4he content consistent with complete retention of radiogenic helium since its formation at about 31 ma isothermal heating and step heating analysis reveal 4he loss to occur systematically by volume diffusion at low temperatures the linear low temperature portion of the diffusion data yields an activation energy of 38 5 8 1 kcal mol and a frequency factor of in d 0 a 2 16 4 2 8 sec 1 corresponding to a closure temperature of 105 c 30 c cooling rate 10 c m y it appears that u th he dating of apatite might represent a useful new thermochronometer with a range similar to that of fission track dating of apatite from these results we infer that a number of the too young u th he dates reported in the literature on minerals such as zircon and magnetite may in fact represent valuable records of the low temperature thermal history of their host rocks

global changes in intensity of the earth s magnetic field during the past 800kyr recent advances in palaeomagnetic and dating techniques have led to increasingly precise records of the relative intensity of the earth s past magnetic field at numerous field sites the compilation and analysis of these records can provide important constraints on changes in global magnetic field intensity and therefore on the earth s geodynamo itself a previous compilation for the past 200 kyr integrated 17 marine records into a composite curve1 with the geomagnetic origin of the signal supported by an independent analysis of 10be production made on different cores2 the persistence of long term features in the earth s magnetic intensity or the existence of long term periodic changes cannot however be resolved in this relatively short time span here we present the integration of 33 records of relative palaeointensity3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 into a composite curve spanning the past 800 kyr we find that the intensity of the earth s dipole field has experienced large amplitude variations over this time period with pronounced intensity minima coinciding with known excursions in field direction reflecting the emergence of non dipole components no stable periodicity was found in our composite record and therefore our data set does not support the hypothesis that the earth s orbital parameters have a direct and strong influence on the geodynamo

mongolian summits an uplifted flat old but still preserved erosion surface in gobi altay and altay mongolia several flat surfaces worn through basement rocks and uplifted during the ongoing tectonic episode to a similar altitude of 4000 m suggests disruption of a single large scale surface new thermochronology and field data show that the plateau surfaces represent uplifted parts of an ancient peneplain that formed during jurassic time the gobi altay and altay flattopped massifs are tectonically and geomorphologically unique their preservation for 150 m y implies that no further tectonic movements occurred before the onset of the last deformation episode 5 3 m y ago it also suggests that very low erosion rates were maintained by a dry climate over millions of years

constraining long term denudation and faulting history in intraplate regions by multisystem thermochronology an example of the sudetic marginal fault bohemian massif central europe 1 the rychlebske hory mountain region in the sudetes ne bohemian massif provides a natural laboratory for studies of postorogenic landscape evolution this work reveals both the exhumation history of the region and the paleoactivity along the sudetic marginal fault smf using zircon u th he zhe apatite fission track aft and apatite u th he ahe dating of crystalline basement and postorogenic sedimentary samples most significantly and in direct contradiction of traditional paleogeographic reconstructions this work has found evidence of a large cretaceous sea and regional burial to 6 5 km of the carboniferous permian basement in the late cretaceous 95 80 ma during the burial by sediments of the bohemian cretaceous basin system the smf acted as a normal fault as documented by offset zhe ages across the fault at 85 70 ma the basin was inverted cretaceous strata eroded and basement blocks were exhumed to the near surface at a rate of 300 m ma as evidenced by late cretaceous paleocene aft ages and thermal modeling results there is no appreciable difference in aft and ahe ages across the fault suggesting that the smf acted as a reverse fault during exhumation in the late eocene oligocene the basement was locally heated to 70 c by magmatic activity related to opening of the eger rift system neogene or younger thermal activity was not recorded in the thermochronological data confirming that late cenozoic uplift and erosion of the basement blocks was limited to less than 1 5 km in the study area

reply to discussion on multiple post caledonian exhumation episodes across nw scotland revealed by apatite fission track analysis journal vol 167 675 694 we thank john hudson for his welcome comments on the nature and extent of the now eroded mesozoic sedimentary cover across parts of the present day scottish landmass that is indicated by the apatite fission track analysis afta results presented by holford et al 2010 as hudson points out low temperature thermochronological techniques including afta can provide unique insights into the post palaeozoic geological evolution of basement terranes that lack significant phanerozoic cover as witnessed by studies including green et al 2000 2001 belton et al 2004 weber et al 2005 as we demonstrated holford et al 2010 these techniques become even more powerful when applied to basement terranes where some sedimentary cover is preserved whereas low temperature thermochronological methods can provide information on only the cooling histories of basement rocks often reflecting exhumation the age of a sedimentary unit however thin it may be overlying eroded basement defines a time when the basement had been exhumed to the surface and was being buried thus integration of low temperature thermochronological data from basement rocks and overlying sedimentary units can define more complex thermal histories encompassing both heating and cooling reflecting episodic burial and exhumation application of this approach to basement and cover samples from a number of regions where phanerozoic sedimentary rocks are sparsely preserved including nw scotland has revealed that some continental regions that have long been thought to

role of in situ cosmogenic nuclides 10be and 26al in the study of diverse geomorphic processes the central premises of applications of the in situ cosmogenic dating method for studying specific problems in geomorphology are outlined for simple and complex exposure settings in the light of these general models we discuss the information that can be derived about geomorphic processes utilizing concentrations of in situ produced cosmogenic radionuclides 10be half life 1 5 ma and 26a1 half life 0 7 ma in a variety of geomorphic contexts glacial polish and tills meteorite impact craters alluvial fans paleo beach ridges marine terraces sand dunes and bedrock slopes we also compare 10be 26al data with results obtained by other dating methods we conclude that the technique of measuring in situ cosmic ray produced nuclides holds promise for quantitative studies of processes and time scales in a wide range of geomorphological problems

26al 10be dating of an aeolian dust mantle soil in western new south wales australia abstract aeolian dust mantle soils are an important element of many landscapes in south eastern australia though the age of these aeolian deposits has not been radiometrically determined at fowlers gap in western new south wales surface cobbles of silcrete and quartz overlie a stone free aeolian dust mantle soil which has a thickness of about 1 6 m the clay rich aeolian dust deposit in turn lies upon a buried silcrete and quartz stone layer modelling in situ cosmogenic 26 al and 10 be concentrations measured in both the surface quartz stones and in the buried quartz layer of rocks reveals that each has experienced a complex exposure burial history due to the absence of quartz stones or sand at intermediate depths our cosmogenic 26 al and 10 be modelling was not able to determine a definitive mechanism of stone pavement formation and stone burial various scenarios of stone formation transport burial and exhumation were tested that constrain the age of the deposit to range from 0 9 0 2 ma to 1 8 0 2 ma based largely on different assumptions taken for the time dependency of the net sedimentation rate this corresponds with the initiation of the simpson desert dune fields and the deflation of lakes in central australia which probably responded to the shift to longer wavelength larger amplitude quaternary glacial cycles at around 1 ma sensitivity analyses were carried out to identify those parameters which better constrained model outputs within model errors which largely are the result of analytical errors in measured 26 al and 10 be concentrations all three competing theories of colluvial wash upward displacement of stones and cumulic pedogenesis are possible mechanisms for the formation of the surface stone pavement

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

fission track dating of phosphate minerals and the thermochronology of apatite several phosphate minerals have been investigated for their usefulness in geochronology and thermochronology by the fission track method of these apatite ca5 po4 3 f cl oh has proved pre eminently suitable for this purpose for reasons discussed below apatite was one of the first minerals amongst many others to be investigated for fission track dating by fleischer and price 1964 and has subsequently become by far the most important of all the minerals used for dating by this method the usefulness of apatites for fission track dating arises from their near universal tendency to concentrate uranium within their structure at the time of crystallization and their widespread occurrence in all of the major rock groups price and walker 1963 first recognized the possibility that the accumulation of radiation damage tracks in natural minerals from the spontaneous nuclear fission of 238u within their lattices could be used for geological dating they also demonstrated that a simple chemical etching procedure served to enlarge these fission tracks to optical dimensions so that they could be observed and measured under an ordinary optical microscope price and walker 1962b 1963 this simple procedure quickly opened the way for a wide range of nuclear particle track studies in natural minerals and glasses e g fleischer et al 1975 the most important of which was fission track dating fleischer et al 1964 also showed that spontaneous or fossil fission tracks provided an explanation for various anomalous etch pits in apatite which had puzzled crystallographers over many years the essence of a fission track age determination involves measuring the number of tracks that have accumulated over the lifetime of the mineral along with an estimate of the amount of uranium that is present knowing the rate of spontaneous fission decay a geological age can be calculated detailed

cosmic ray produced 10be and 26al in antarctic rocks exposure and erosion history we have measured cosmic ray produced t1 2 1 5 million years 10be and t1 2 0 705 million years 26al in purified quartz fractions of selected rock samples from antarctic mountains from these data we calculate 1 mean erosion rates for the limiting case of steady state surface exposure to cosmic rays and 2 minimum exposure ages for the limiting case of no erosion calculated mean erosion rates are very low on the order of a few times 10 5 cm yr we believe the sampling to be sufficient to generalize this result to exposed bedrock in antarctica in favorable cases it is possible to distinguish between the limiting cases steady state erosion seems a better description in such cases most samples including some taken a few meters above the present ice level seem to have been exposed for millions of years without major episodes of burial or abrasion by ice

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

mesozoic and cenozoic tectonic history of the central chinese tian shan reactivated tectonic structures and active deformation 1 the present day topography of the tian shan range is considered to result from crustal shortening related to the ongoing india asia collision that started in the early tertiary in this study we report evidence for several episodes of localized tectonic activity which occurred prior to that major orogenic event apatite fission track analysis and u th he dating on apatite and zircon indicate that inherited paleozoic structures were reactivated in the late paleozoic early mesozoic during a cimmerian orogenic episode and also in the late cretaceous paleogene around 65 60 ma these reactivations could have resulted from the accretion of the kohistan dras arc or lithospheric extension in the siberia mongolia zone activity resumed in the late mesozoic prior to the major tertiary orogenic phase finally the ongoing deformation which again reactivates inherited tectonic structures tends to propagate inside the endoreic basins that were preserved in the range leading to their progressive closure this study demonstrates the importance of inherited structures in localizing the first increments of the deformation before it propagates into yet undeformed areas

growth of south rough ridge central otago new zealand using in situ cosmogenic isotopes and geomorphology to study an active blind reverse fault 1 in situ cosmogenic 10be and 26al measurements on sedimentary quartzites together with analysis of abandoned river terraces can be used to show how drainage responded to the lateral propagation of a late quaternary anticline forming above a blind reverse fault in central otago new zealand a close link between the progression of cosmogenic ages and the tectonic geomorphology allows us to confirm that uplift and propagation rates on the anticline are in the ranges 0 08 0 12 mm yr 1 and 0 8 1 5 mm yr 1 respectively over the last 550 000 years the agreement between the isotopic and geomorphological evidence in turn requires that minimum 10be exposure ages as great as 660 ka are not in steady state with respect to erosion this is a geochemical result of significance as it opens the possibility of a more regional analysis of landscape evolution in this region using the same rocks on an adjacent anticline thought to be even older on geomorphological arguments 10be concentrations give minimum exposure ages in the range 750 1400 ka these extremely old minimum ages are rare worldwide as they are usually limited to smaller values by erosion they are attributable to the very resistant nature of the quartz rich boulders in which the measurements were made which in places are shown to have erosion rates lower than 0 5 mm kyr 1

cretaceous reactivation and intensified erosion in the archean proterozoic limpopo belt demonstrated by apatite fission track thermochronology abstract cratons are generally assumed to be regions of long lasting tectonic stability in particular the study of the phanerozoic exhumation history of cratons has been largely hampered by the scarcity of suitable stratigraphic controls onshore this fact is even more pronounced in terranes lacking mesozoic or younger penetrative structural fabrics and metamorphic overprinting our study in the limpopo belt shows that modern apatite fission track thermochronology provides a hitherto unavailable perspective in the study of these rocks and has profound implications for the crustal evolution of the zimbabwe craton apatite fission track data from 35 samples taken along two transects in the southern edge of the zimbabwe craton and in the central zone of the limpopo belt suggest that extensive regions experienced kilometer scale exhumation in two discrete events as recently as the cretaceous the first occurred at around 130 ma and the second at around 90 ma basin subsidence and sedimentation loads on the mozambique margin support the timing of these events and provide strong indications of the source and pathways for the eroded material further the results indicate that young and old surfaces in a geomorphological sense may be structurally juxtaposed in regions of high elevation in zimbabwe this is contrary to early ideas of surface chronologies based on summit accordances or invoking pediplanation

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

the antiquity of landscapes on the north australian craton and the implications for theories of long term landscape evolution the longevity of landscapes on cratons has set them apart from those in other tectonic settings this is exemplified over much of the north australian craton where landscapes that have for over half a century been argued to be largely the product of cycles of erosion throughout the cainozoic are in fact composed mainly of ranges valleys and plains which pre date the cretaceous valleys incised into upland plateaus and graded to lowland plains are in numerous places filled with cretaceous sediments many of the lowland plains are exhumed proterozoic and pre late jurassic features and appear to be older than neighboring areas of upland plateaus which were likely graded to the cretaceous sea the antiquity of these landscapes and the disparity in age between higher and lower elevation planation surfaces highlights the inadequacy of global applications of existing models of long term landscape evolution and theories concerned with the preservation of paleoforms in cratonic settings

erosion of a high altitude low relief area on the korean peninsula implications for its development processes and evolution the processes involved in the development of high altitude low relief areas hlas are still poorly understood although cosmogenic nuclides have provided insights into the evolution of hlas interpreted as paleo surfaces most studies focus on estimating how slowly they erode and thereby their relative stability to understand actual development processes of hlas we applied several techniques of cosmogenic nuclides in the daegwanryeong plateau a well known hla in the korean peninsula our denudation data from strath terraces riverine sediments soils and tors provide the following conclusions 1 bedrock incision rate in the plateau 127 m myr 1 is controlled by the incision rate of the western part of the korean peninsula and is similar to the catchment wide denudation rate of the plateau 93 m myr 1 2 the soil production function we observed shows weak depth dependency that may result from highly weathered bedrock coupled with frequent frost action driven by alpine climate 3 a discrepancy between the soil production and catchment wide denudation rates implies morphological disequilibrium in the plateau 4 the tors once regarded as fossil landforms of the tertiary do not reflect tertiary processes and 5 when compared with those of global paleo surfaces 20 m myr 1 our rapid denudation rates suggest that the plateau cannot have maintained its probable initial paleo landscape and thus is not a paleo surface our data contribute to understanding the surface processes of actively eroding upland landscapes as well as call into question conventional interpretations of supposed paleo surfaces around the world copyright 2015 john wiley sons ltd

u th he dating of phosphates apatite monazite and xenotime the common phosphate minerals apatite ca 5 po 4 3 f oh cl monazite ce la th po 4 and xenotime ypo 4 have found widespread use in geochronology because they incorporate u and th into their structures for example apatite usually has a few tens of ppm of both u and th while monazite and xenotime usually have hundreds of ppm to weight percent levels of these elements as a consequence these phosphates can be dated using several fundamentally different isotopic techniques elsewhere in this volume harrison et al describe phosphate dating using ingrowth of radiogenic pb the final daughter of u and th series decay and gleadow et al describe dating based on damage tracks from the spontaneous fission of 238 u the most recently developed dating technique applied to phosphates described in this chapter uses the accumulation of particles from u and th series decay u th he dating while phosphate u th pb dating is usually used to date high temperature events such as crystallization of igneous rocks and the timing of prograde metamorphism fission track and u th he dating are more commonly used to establish cooling histories through low temperatures for example in the range 110 40 c in the case of apatite dating of minerals using radiogenic he was first explored shortly after the discovery of radioactivity strutt 1908 and was investigated extensively in the 1950s and 1960s mostly on very u and th rich minerals such as zircon and titanite hurley 1952 1954 damon and kulp 1957 damon and green 1963 apatite he dating was first investigated by zeitler et al 1987 who studied the diffusion rate of he from apatite and proposed that apatite he dating might provide a useful thermochronometer recording cooling through about 100 c further studies both in the laboratory lippolt et al 1994 wolf et al 1996b warnock et al 1997 farley 2000 and in the natural setting house et al 1999 stockli et al 2000 have confirmed this idea and the technique has now been applied to a range of tectonic geologic and geomorphologic problems e g house et al 1997 1998 spotila et al 1997 farley et al 2001 stockli et al 2000 monazite and xenotime have only recently come under scrutiny for he geochronology e g pik and marty 1999 and little is yet known of their potential for routine geo or thermochronometry

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

scaling factors for production rates of in situ produced cosmogenic nuclides a critical reevaluation abstract new scaling factors are presented describing the altitude and latitudinal dependence of production rates for in situ produced cosmogenic nuclides the new factors incorporate the influence of the non dipole contributions to the geomagnetic field on the cosmic ray flux the currently used scaling factors of lal earth planet sci lett 104 1991 424 439 are based on the assumption of a dipole field the overall strategy used in deriving the new scaling factors is however very similar to that of lal and relies on the same and or similar nuclear data in this reevaluation data are only used if the effective geomagnetic parameters inclination horizontal field strength can be reconstructed for the time of measurement the absorption free pathlengths for cosmic rays selected for this study are based on observational data at altitudes relevant for exposure age dating sea level to 7000 m at sea level and latitudes between 20 and 40 the new factors are up to 18 lower and at high altitudes more than 30 higher than those of lal in addition to accounting for the influence of the effective geomagnetic field and providing more applicable estimates of the new factors also allow for correction for the significant deviations from the standard pressure altitude relationship that exist in the atmosphere 10

the origins of the intraplate stress field in continental australia the ridge push force acting on the indo australian plate exerts a significant torque 8 5 1025n m about a pole at 30 3 n 34 5 e the angular difference between this torque pole and the observed pole of rotation for the plate 19 2 n 35 6 e is less than 12 and suggests that the ridge push force plays an important role in the dynamics of the indo australian plate we have used an elastic finite element analysis to study the predicted intraplate stress field in continental australia for four models which employ different boundary conditions to balance the ridge push torque acting on the plate the modeling indicates that a number of important features of the observed stress field within the australian continent can be explained in terms of balancing the ridge push torque with resistance imposed along the himalaya papua new guinea and new zealand collisional boundaries segments these features include n s to ne sw oriented compression in the northern australia and e w oriented compression in southern australia our analysis also shows that subduction processes along the northern and eastern boundaries provide only second order controls on the intraplate stress field in continental australia

low temperature thermal evolution of the azov massif ukrainian shield ukraine implications for interpreting u th he and fission track ages from cratons abstract the low temperature thermal evolution of the azov massif eastern part of the ukrainian shield ukraine is investigated by combined zircon fission track zft apatite fission track aft and apatite u th he ahe thermochronology the data help to better understand the geodynamic evolution of the azov massif and the adjacent intra cratonic rift basin dniepr donets basin as follows zft data reveal that the precambrian crystalline basement of the azov massif was heated to temperatures close to 240 c during the late palaeozoic the heating event is interpreted in terms of burial of the basement beneath a several kilometres thick pile of devonian and carboniferous sedimentary deposits of the adjacent dniepr donets basin during permo triassic times large parts of the basement were affected by a thermal event related to mantle upwelling associated magmatic activity and increased heat flow in the adjacent rift the major part of the basement cooled to near surface conditions in the early to middle triassic and since then was thermally stable as suggested by aft and ahe data further aft data confirm late triassic magmatic activity in the azov massif which however did not influence regional thermal pattern the northern part of the basement and its sedimentary cover record a cooling event in the jurassic which was probably related to erosion however although ar ar data of jurassic magmatic activity in the donbas foldbelt are about 20 my younger than the aft data thermal relaxation after elevated heat flow associated with this magmatic event cannot be completely ruled out our results reveal apparent inconsistencies between aft and ahe data the ahe ages corrected for alpha ejection according to the standard procedure farley k a wolf r a silver l t 1996 the effect of long alpha stopping distances on u th he ages geochim cosmochim acta 60 21 4223 4229 farley k a 2002 u th he dating techniques calibrations and applications mineral soc am rev mineral geochem 47 819 844 are older than corresponding aft ages in order to test the relevance of alpha ejection correction mechanical abrasion of several apatite grains was applied we found that in case of relatively slow cooling alpha ejection correction of raw u th he ages leads to erroneously high ages this shows that alpha ejection correction should be used with caution we propose that this correction should only be applied to samples with a fast cooling history whereas it should not be applied to slowly cooled samples and to samples whose thermal history is not constrained by other means

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

erosion rates and weathering history of rock surfaces associated with aboriginal rock art engravings petroglyphs on burrup peninsula western australia from cosmogenic nuclide measurements abstract the burrup peninsula and surrounding dampier archipelago in western australia contain the world s largest known gallery of rock art engravings petroglyphs estimated to number up to 1 million images the peninsula is also the site of major industrial development and there are concerns that industrial emissions may adversely affect the stability and longevity of the rock art we have studied the natural processes and rates of weathering and erosion including the effects of fire that affect the stability of rock surfaces and hence the longevity of the rock art using cosmogenic nuclides the concentration of 10 be in quartz yields erosion rates in the range 0 15 0 48 mm 1000 years on horizontal rock surfaces and 0 34 2 30 mm 1000 years on vertical rock faces the former largely caused by mm scale surface flaking are amongst the lowest erosion rates measured by cosmogenic nuclides anywhere in the world the latter are inferred to represent a combination of mm scale flaking and very rare centimetre to metre scale block falls controlled by failure along joint planes such low erosion rates result from a combination of resistant rocks low relief and low rainfall favouring long term preservation of the petroglyphs long enough to encompass the known period of human settlement in australia

bicadinanes in oils from the surma basin bangladesh abstract bicadinanes c 30 pentacyclic triterpanes have only been reported in crude oils and sediment extracts from s e asia the present investigation indicates that they are also widely present in land plant derived tertiary oils from the surma basin of n e bangladesh oleanane is also abundant in these oils though its distribution does not correlate with those of the bicadinanes this is consistent with separate specific land plant sources for these two classes of triterpanes and with the formation of bicadinanes during maturation of polymerised angiosperm tree resin