late paleozoic closure of the ob zaisan ocean along the irtysh shear zone nw china implications for arc amalgamation and oroclinal bending in the central asian orogenic belt the largest accretionary orogen in the world the central asian orogenic belt has evolved through the assembly of various oceanic and continental blocks understanding the processes associated with the development of this orogenic belt relies on precise recognition of the boundaries between various terranes one such major suture zone which records the collisional history of the siberian marginal arc system chinese altai with intra oceanic arc systems east west junggar is the irtysh shear zone in nw china the spatial continuity and the tectonic nature of this shear zone are still poorly understood but its development has supposedly made a significant impact on the architecture of the western central asian orogenic belt and the formation of the kazakhstan orocline here we provide new insight into the evolution of this shear zone based on detrital zircon ages hf isotope composition structural data and ar ar age constraints on the timing of deformation our results show a major discrepancy in detrital zircon populations and hf model ages across the southern chinese altai and the northern east west junggar thus allowing us to map the exact location of the tectonic boundary detrital zircon data constrain the initial closure of the ob zaisan ocean to the late carboniferous 323 ma and new structural and ar ar geochronological data shed light on the subsequent collisional processes we propose that the collisional zone between the chinese altai and the east west junggar was initially subjected to crustal thickening at ca 323 295 ma followed by orogen parallel extension ca 295 ma and transpressional deformation ca 286 253 ma the closure of the ob zaisan ocean in nw china postdates the initial phase of oroclinal bending in the western central asian orogenic belt thus indicating that oroclinal bending initiated during subduction based on our new constraints and other available geological data we suggest that the early stage of oroclinal bending was likely driven by slab rollback

mapping gamma radiation and its uncertainty from weathering products in a tasmanian landscape with a proximal sensor and random forest kriging the radionuclides of potassium 40 k uranium u 238 and thorium th 232 emit from the land surface gamma radiation that is characteristic of the underlying rocks and the distribution of their weathering products in the landscape we measured the radiation along widely separated transects using a mobile proximal sensor over a 10 000 ha region of tasmania we supplemented the transect data with information from soil and geological maps and dense data from landsat and spot imagery a digital elevation model and terrain attributes on a grid at 30 m intervals so as to map the radionuclides we used a sequence of steps starting with a spatial bootstrap and random forests to predict emissions across the study area and at sampling points excluded from the bootstrap samples the predictions at the sampling points were compared with the observed values to obtain residuals which were then used to krige them at all points on the 30 m grid we combined the random forest and kriging predictions on the 30 m grid to obtain our random forest kriging predictions repeating the procedure 100 times provided confidence limits on our results and predictions the resulting maps of the radionuclides accord well with what we know of the soil lithology and topography of the region from other sources alluvial deposits with large amounts of potassium extend from the foot slopes of the great western tiers and along the flood plains of the meander river providing evidence of previous widespread weathering and deposition of the material the fertile red ferrosols roughly equivalent to ferralic nitisols in the world reference base wrb classification on the extensive tertiary basalt plateau emit little gamma radiation as a result of deep weathering and of potassium movement and accumulation down its talus slopes the maps show the complexity of the region in terms of soil lithology and terrain and they show the merits of gamma radiometry for mapping and understanding the distribution of materials in such regions copyright c 2013 john wiley sons ltd

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

the tectonic evolution of the irtysh tectonic belt new zircon u pb ages of arc related and collisional granitoids in the kalaxiangar tectonic belt nw china abstract precise geochronological constraints of the irtysh tectonic belt situated between the saur island arc and the altay terrane are crucial to a better understanding of the tectonic evolution of the central asian orogenic belt caob recently we discovered repeatedly deformed arc related and collisional granitoids in the kalaxiangar tectonic belt ktb which is located in the eastern part of the irtysh tectonic belt in this study we report new whole rock geochemical zircon u pb and hf isotopic data of the arc related and collisional granitoids our data reveal that 1 arc related granodioritic porphyries formed at ca 382 374 ma recrystallized zircon grains from a ultra mylonitic granodiorite of the laoshankou zone in the southern ktb display a u pb age of ca 360 ma 2 syn collisional granodioritic porphyries which distribute along faults and parallel to the cleavage were emplaced at ca 367 356 ma with e hf t values varying from 7 8 to 14 2 and hf model ages from 873 to 459 ma 3 a post collisional a type granodioritic porphyry which crosscuts the nw nnw trending schistosity of the metasedimentary country rocks at a low angle has an age of ca 324 320 ma while the e hf t values range from 7 6 to 14 4 with hf model ages from 850 to 416 ma 4 post collisional strike slip a type granite dykes exposed along strike slip faults gave ages between 287 and 279 ma whereas the e hf t values range from 4 9 to 12 7 and the hf model ages from 995 to 500 ma and 5 a type biotite granite dykes which intruded along conjugate tension joints have ages of 274 271 ma and e hf t values from 1 5 to 13 2 with hf model ages from 1196 to 454 ma consequently we propose that the collision between the saur island arc and the altay terrane occurred in the early carboniferous ca 367 356 ma and the subsequent post collisional tectonic process continued to the late carboniferous ca 324 320 ma it is further suggested that the irtysh tectonic belt underwent large scale strike slip deformation during the mid permian between 287 and 279 ma the termination of the irtysh tectonic belt orogeny is thought to have also occurred during the mid permian between 274 and 271 ma

understanding the utility of aerial gamma radiometrics for mapping soil properties through proximal gamma surveys abstract historical aerial gamma radiometrics have been proposed to be an important covariate for characterizing soil properties because it provides information about soil parent material pre existing aerial gamma radiometrics within the united states however can exhibit coarse spatial resolutions and therefore may be unhelpful for soil mapping studies therefore the objective of this work was to test the hypothesis that aerial gamma radiometrics can reliably map soil properties the hypothesis was tested using proximal radiometrics and soil sampling proximal or ground surveys were conducted within four different heterogeneous landscapes and 112 soil samples were collected and characterized for texture i e particle size fractions and or calcium carbonate equivalent proximal and soil relationships were assessed in terms of significance using pearson correlation coefficient testing and stepwise backwards linear regression proximal data were then weighted and averaged within the aerial sensor field of view and subsequently tested for significance with historical aerial data using pearson correlation tests proximal and aerial sensors were then compared in their ability to predict nearby measurements of clay and sand content relationships between texture and proximal gamma measurements were significant p

wind erodibility of soils at fort irwin california mojave desert usa before and after trampling disturbance implications for land management recently disturbed and control i e less recently disturbed soils in the mojave desert were compared for their vulnerability to wind erosion using a wind tunnel before and after being experimentally trampled before trampling control sites had greater cyanobacterial biomass soil surface stability threshold friction velocities tfv i e the wind speed required to move soil particles and sediment yield than sites that had been more recently disturbed by military manoeuvres after trampling all sites showed a large drop in tfvs and a concomitant increase in sediment yield simple correlation analyses showed that the decline in tfvs and the rise in sediment yield were significantly related to cyanobacterial biomass as indicated by soil chlorophyll a however chlorophyll a amounts were very low compared to chlorophyll a amounts found at cooler desert sites where chlorophyll a is often the most important factor in determining tfv and sediment yield multiple regression analyses showed that other factors at fort irwin were more important than cyanobacterial biomass in determining the overall site susceptibility to wind erosion these factors included soil texture especially the fine medium and coarse sand fractions rock cover and the inherent stability of the soil as indicated by subsurface soil stability tests thus our results indicate that there is a threshold of biomass below which cyanobacterial crusts are not the dominant factor in soil vulnerability to wind erosion most undisturbed soil surfaces in the mojave desert region produce very little sediment but even moderate disturbance increases soil loss from these sites because current weathering rates and dust inputs are very low soil formation rates are low as well therefore soil loss in this region is likely to have long term effects published in 2006 by john wiley sons ltd

tectonic framework of the northern junggar basin part i the eastern luliang uplift and its link with the east junggar terrane abstract the luliang uplift preserves relatively complete carboniferous strata and is an important region to study the spatio temporal framework and tectonic evolution of the junggar basin here we report new shrimp sims u pb ages whole rock sr nd data and in situ zircon hf isotopic compositions for carboniferous strata samples in the eastern luliang uplift the gravity and magnetic data suggest that the carboniferous volcanics are distributed as nw trending bands and also bring out n s oriented parallel amalgamation the sedimentary units and structural deformation of the eastern luliang uplift suggest that the basin evolution involved late carboniferous extensional graben stage and latest carboniferous early permian compressional stage the carboniferous batamayineishan formation is divided into the lower volcanic unit followed up sedimentary unit and an upper volcanic unit as inferred from the lithology and unconformities the lower volcanic unit from the drill cores mainly consists of andesite dacite rhyolite and tuff intercalated with minor basalt the middle sedimentary unit is made up of sandstone and mudstone with tuff and tuffaceous sandstone and the upper volcanic unit is composed of basalt rhyolite tuff and breccia with minor clastic sedimentary rocks zircon shrimp u pb age 337 2 ma for the tuff and sims u pb age 308 6 ma for basalt suggest that the lower and upper volcanic units belong to lower carboniferous and upper carboniferous respectively the basalts from upper volcanic unit in the eastern luliang uplift show typical calc alkaline affinity with low nb y ratios 0 17 0 28 and sio2 contents 47 54 and moderate th abundances 0 45 3 74 ppm enrichment in lree and liles and depletion in nb ta and ti they have low initial 87sr 86sr ratios 0 703571 0 705122 and positive end t values 5 5 8 6 and constant sm yb ratios 1 56 2 03 and variable trace element ratios e g ba th ba la and ba nb suggesting that the parental magmas were mainly derived from 2 to 8 partial melting of a spinel iherzolite mantle source metasomatized by hydrous fluids and melts of subducted sediments furthermore relatively high tio2 1 52 3 76 and zr contents 172 414 ppm indicate that they were formed in an extensional setting taking into account the occurrence of coeval island arc related volcanics we propose an intra arc rift basin model for the eastern luliang uplift the eastern luliang uplift and east junggar terrane display different tectonic features during the closure of the junggar ocean during the late carboniferous continued northward subduction prevailed and generated a fault controlled intra arc basin in the eastern luliang uplift intra arc basin contraction in permian is probably indicative of the closure of junggar ocean in the northern junggar basin our study confirms the important role of subduction accretion process associated with the carboniferous crustal growth in the junggar terrane

organofacies and paleoenvironment of lower carboniferous mudstones dishuiquan formation in eastern junggar nw china abstract the sedimentary rocks of the dishuiquan formation represent an important potential source for volcanic rock reservoirs and record the transition of the depositional environment from marine to terrestrial during paleo junggar oceanic subduction the source rock potential and paleoenvironment of mudstones from dishuiquan formation in eastern junggar were determined by organic petrography rock eval molecular and stable carbon 13 c analyses toc s 2 and hydrogen index hi values suggest a fair to good organic richness in mudstone samples from the c 2 well moreover an early mature to mature state for all the samples is inferred based on the rock eval and biomarker parameters the maceral composition molecular geochemistry and carbon isotopic results for kerogen reveal that all the mudstone samples are characterized by a mixed organic matter assemblage types ii iii with relatively high percentages of terrigenous organic matter the low to intermediate values of pr ph and the high abundances of carotene and gammacerane indicate the presence of a dysoxic reducing high salinity sedimentary environment during the deposition of the dishuiquan formation numerous parameters derived from the organic geochemical analyses indicate that the terrigenous organic matter increased with decreasing salinity and oxidation in the sedimentary environment this study concludes that a warm wet climate provided a continuous fluvial input of terrigenous plant debris and fresh water the organic geochemical data combined with the tectonic setting reveal a restricted semi closed marine depositional environment during the deposition of the dishuiquan formation in the early carboniferous

evolution of calc alkaline to alkaline magmatism through carboniferous convergence to permian transcurrent tectonics western chinese tianshan continuous magmatic activity occurred in the western chinese tianshan central asia from the carboniferous to the permian i e before and after the late carboniferous amalgamation of junggar and the yili blocks zircon u pb la icpms and ar ar data reveal a coincidence in time between regional wrench faulting and granitoid emplacement permian post collisional granitoids crop out within or at the margins of large scale dextral strike slip shear zones some of them show synkinematic fabrics the whole rock geochemical features of the early middle permian granitoids indicate an evolution from high k calc alkaline towards alkaline series in other places of the north tianshan alkaline magmatism occurred together with deep marine sedimentation within elongated troughs controlled by wrench faults therefore in contrast with previous interpretations that forwarded continental rift or mantle plume hypotheses the coexistence of diverse magmatic sources during the same tectonic episode suggests that post collisional lithosphere scale transcurrent shearing tightly controlled the magmatic activity during the transition from convergent margin to intraplate anorogenic processes

re os dating of two cu ni sulfide deposits in northern xinjiang nw china and its geological significance abstract mafic ultramafic intrusions in northern xinjiang are located along major fault zones some of these intrusions host cu ni sulfide deposits and amongst these are two economically important cu ni deposits kalatongke also called karatungk and huangshan east huangshandong sulfides from these deposits were selected for a re os geochronological study in order to understand the tectonic and metallogenic environment of the mafic ultramafic intrusions and the associated cu ni sulfide deposits in northern xinjiang re os dating of cu ni sulfide ores in the nos 1 and 2 intrusions of the kalatongke ore district and huangshan east deposit gave isochron ages of 282 5 4 8 290 2 6 9 and 284 14 ma respectively with initial 187 os 188 os ratios of 0 2563 0 0073 0 2721 0 0053 and 0 241 0 092 the os values of the kalatongke and huangshan east deposits range from 100 6 to 124 2 and from 25 6 to 235 9 these results indicate that the cu ni sulfide mineralization in both deposits formed during the early permian 280 290 ma integrating our field observations with published literature and the re os data presented in this work we suggest that the mafic ultramafic rocks investigated were emplaced in a post collisional extensional setting and the cu ni sulfide ores were segregated from crustally contaminated magmas

isotope provinces mechanisms of generation and sources of the continental crust in the central asian mobile belt geological and isotopic evidence abstract the available geological geochronological and isotopic data on the felsic magmatic and related rocks from south siberia transbaikalia and mongolia are summarized to improve our understanding of the mechanisms and processes of the phanerozoic crustal growth in the central asian mobile belt camb the following isotope provinces have been recognised precambrian t dm 3 3 2 9 and 2 5 0 9 ga at the microcontinental blocks caledonian t dm 1 1 0 55 ga hercynian t dm 0 8 0 5 ma and indosinian t dm 0 3 ga that coincide with coeval tectonic zones and formed at 570 475 420 320 and 310 220 ma continental crust of the microcontinents is underlain by or intermixed with juvenile crust as evidenced by its isotopic heterogeneity the continental crust of the caledonian hercynian and indosinian provinces is isotopically homogeneous and was produced from respective juvenile sources with addition of old crustal material in the island arcs or active continental margin environments the crustal growth in the camb had episodic character and important crust forming events took place in the phanerozoic formation of the camb was connected with break up of the rodinia supercontinent in consequence of creation of the south pacific hot superplume intraplate magmatism preceding and accompanying permanently other magmatic activity in the camb was caused by influence of the long term south pacific plume or the asian plume damping since the devonian

a review of the cu ni sulphide deposits in the chinese tianshan and altay orogens xinjiang autonomous region nw china principal characteristics and ore forming processes abstract several cu ni sulphide deposits and occurrences have recently been discovered along parallel deep faults in the chinese tianshan and altay orogenic belts xinjiang province nw china the kalatongke and several other cu ni mineralized intrusions are located along the irtysh fault which separates the altay orogenic belt from the junggar basin the huangshan huangshandong xiangshan tudun erhongwa tula ergen and hongling deposits occur along the kanggurtag suture which separates the jueluotage orogenic belt from the turpan hami tuha basin the baishiquan tianyu and tianxiang deposits are located along the arqikekuduke fault which separates the jueluotage orogenic belt from the central tianshan precambrian terrane the poyi poshi and luodong deposits are located along the baidiwa fault which separates the central tianshan precambrian terrane from the beishan paleozoic rift re os dating of cu ni sulphide ores reveals that these cu ni ore belts formed in a narrow age range of 298 282 ma this age range is about the same as those of associated intrusions and dykes dated by the shrimp zircon u pb method tectonic and geochronological constraints suggest that the amalgamation of continental blocks mainly occurred during the late carboniferous in the central asian orogenic belt large scale hydrothermal and magmatic metallogenesis in the region occurred during post collisional stages of latest carboniferous to early permian age the cu ni sulphide deposits are part of this metallogenic event the cu ni orthomagmatic sulphide deposits in northern xinjiang are represented by 1 net textured type deposits by segregation of a cu ni metal sulphide melt and 2 magma conduit type some mafic ultramafic suites exhibit lithological zoning caused by strong differentiation stratiform orebodies are hosted by ultramafic rocks at the base of the magma chamber good examples are the kalatongke huangshandong and poshi deposits others such as the xiangshan baishiquan tianyu and tula ergen deposits are hosted by magma conduits consisting of peridotite troctolite and pyroxenite these ultramafic rocks either occur within faults or are surrounded by gabbroic and dioritic intrusions these two types of orthomagmatic cu ni sulphide deposits are also distributed along the same ore belts for instance the differentiated sill related huangshandong deposit co exists with the magma conduit type tula ergen deposit in the jueluotage orogenic belt orthomagmatic cu ni sulphide deposits in northern xinjiang formed during post collisional extension and are possibly related to a late carboniferous early permian mantle plume event the mafic ultramafic suites and associated cu ni deposits are commonly accompanied by dyke swarms and are characterized by elongated outcrops occurring along parallel e w trending regional faults these mafic ultramafic suites and accompanying dyke swarms are generally fractionated implying that they were feeders of presently eroded flood basalts

geochronology of metarhyolites from the kangbutiebao formation in the kelang basin altay mountains xinjiang implications for the tectonic evolution and metallogeny abstract the altay orogenic belt aob situated in the middle part of the central asian orogenic belt caob is one of the most important metallogenic belts in china the kangbutiebao formation is a late paleozoic stratigraphic unit that hosts many important iron and pb zn deposits the kangbutiebao formation consists of intercalated volcanic and sedimentary rocks that have undergone regional greenschist to lower amphibolite facies metamorphism and mainly outcrops in three nw trending fault bounded volcano sedimentary basins including the maizi kelang and chonghuer basins shrimp analyses of zircons from three metarhyolites of the kangbutiebao fm in the kelang basin yield weighted mean 206 pb 238 u ages of 412 6 3 5 ma 408 7 5 3 ma and 406 7 4 3 ma respectively which can be interpreted as the eruption age of the kangbutiebao silicic volcanic rocks in the kelang basin these ages indicate that the kangbutiebao formation was formed during the late silurian to early devonian they also demonstrate that the deposits hosted in the kangbutiebao formation were formed after 412 407 ma they play a key role in understanding the paleozoic tectonic evolution and metallogenesis of the southern margin of the chinese aob

continental growth of northwest china the northwest corner of china is the most interior part of central asia and includes parts of the siberian tarim and kazakhstan plates where the junggar and tarim basins are separated by the east west trending tianshan range a preliminary terrane map divides the area into thirteen separate areas which are classified into four types l continental 2 oceanic crust 3 island arc 4 composite the boundaries for these terranes are faults that have been previously defined either by geologic mapping or holocene activity passive consolidation of the southern margin of paleo asia is marked by accretion and subduction of the paleo tethys oceanic basins and by development of volcanic arcs paleomagnetic data indicate that the major plates and associated smaller terranes did not reach final consolidation until the permian or later the stratigraphic record reveals development of intracontinental basins in the late carboniferous followed by the pan asian thermal event that gave rise to widespread intrusion of a type granites of late paleozoic age the frontal collision of india along the southern border of asia in the paleocene reactivated nearly all of the older major strike slip and thrust faults formed during the late paleozoic consolidation of paleo asia the complex nature of the continental growth of central asia has produced and destroyed many varieties of sutures and reconstruction of the original plate and terrane configurations therefore is enigmatic

palaeozoic accretionary and convergent tectonics of the southern altaids implications for the growth of central asia the southern altaids present a unidirectional section from mongolia to china through an accretionary orogen that youngs progressively from neoproterozoic in the north to permian in the south the orogen formed by forearc accretion of island arcs accretionary wedges ophiolites and precambrian microcontinents this regularity was upset by early growth within the ocean of arcs that later collided at the accreting continental margin by imbrication of old ophiolites with young arcs and by himalayan style thrust nappe tectonics when an arc collided into a microcontinent lateral growth of the southern altaids represents a massive addition of juvenile material to the palaeozoic crust

neoproterozoic to paleozoic geology of the altai orogen nw china new zircon age data and tectonic evolution abstract we present a synthesis and a new account of the geological and tectonic history of the terranes of the chinese paleozoic altai orogen together with new single zircon ages for granitic and rhyodacitic rocks a central terrane consists of neoproterozoic to silurian amphibolite facies metasedimentary rocks and abundant devonian carboniferous granites the presence of precambrian basement is indicated by sinian fossils our xenocryst ages and published nd mean crustal residence ages of granites felsic arc type lavas on the southern margin of the terrane have a mean 207pb 206pb zircon age of 505 ma reflecting the time of arc volcanism and the presence of xenocysts with ages between 614 and 921 ma suggests derivation by intracrustal melting accordingly we suggest that a cambro ordovician continental magmatic arc was built on the southern margin of the central terrane by northward subduction a low grade ordovician andean type arc with a continental basement is situated above a normal fault on

origin and accumulation mechanisms of petroleum in the carboniferous volcanic rocks of the kebai fault zone western junggar basin china abstract the kebai fault zone of the west junggar basin in northwestern china is a unique region to gain insights on the formation of large scale petroleum reservoirs in volcanic rocks of the western central asian orogenic belt carboniferous volcanic rocks are widespread in the kebai fault zone and consist of basalt basaltic andesite andesite tuff volcanic breccia sandy conglomerate and metamorphic rocks the volcanic oil reservoirs are characterized by multiple sources and multi stage charge and filling history characteristic of a complex petroleum system geochemical analysis of the reservoir oil hydrocarbon inclusions and source rocks associated with these volcanic rocks was conducted to better constrain the oil source the petroleum filling history and the dominant mechanisms controlling the petroleum accumulation reservoir oil geochemistry indicates that the oil contained in the carboniferous volcanic rocks of the kebai fault zone is a mixture the oil is primarily derived from the source rock of the permian fengcheng formation p 1 f and secondarily from the permian lower wuerhe formation p 2 w compared with the p 2 w source rock p 1 f exhibits lower values of c 19 tt c 23 tt c 19 20 tt tt ts ts tm and 20r sterane c 27 c 28 ratios but higher values of tt c 23 c 21 hhi gammacerane c 30 hopane hopane 20s c 34 c 33 c 29 and c 29 20s 20s 20r ratios three major stages of oil charge occurred in the carboniferous in the middle triassic late triassic to early jurassic and in the middle jurassic to late jurassic periods respectively most of the oil charged during the first stage was lost while moderately and highly mature oils were generated and accumulated during the second and third stages oil migration and accumulation in the large scale stratigraphic reservoir was primarily controlled by the top carboniferous unconformity with better porosity and high oil enrichment developed near the unconformity secondary dissolution pores and fractures are the two major reservoir storage space types in the reservoirs structural highs and reservoirs near the unconformity are two favorable oil accumulation places the recognition of the large scale carboniferous volcanic reservoirs in the kebai fault zone and understanding of the associated petroleum accumulation mechanisms provide new insights for exploring various types of volcanic reservoir plays in old volcanic provinces and will undoubtedly encourage future oil and gas exploration of deeper strata in the region and basins elsewhere with similar settings

remobilisation of the continental lithosphere by a mantle plume major trace element and sr nd and pb isotope evidence from picritic and tholeiitic lavas of the noril sk district siberian trap russia the late permian to early triassic siberian traps have been sampled by drill core core sg 9 and from surface exposure section 1f in the noril sk region of the siberian platform russia combined major trace element and nd sr and pb isotope data on selected samples through the siberia trap offer new chemostratigraphic criteria for the identification and characterisation of two fundamentally different magma types and 9 of the 11 formations of lava developed near noril sk a lower sequence of sub alkalic basalts tholeiites and picritic basalts upwards these are the ivakinsky syverminsky and gudchichinsky formations are overlain by an upper sequence of picritic basalts and tholeiites interbedded with tuffs upwards these are the khakanchansky tuklonsky nadezhdinsky morongovsky mokulaevsky and kharayelakhsky formations the gudchichinsky and tuklonsky formations contain both picritic and tholeiitic lavas the tuklonsky formation tholeiites and picrites have moderate gd yb 1 6 1 8 low tio2 0 45 0 95 wt a significant negative ta and nb anomaly nb la 0 42 0 57 and unradiogenic nd nd chur to 4 6 in contrast both the gudchichinsky formation tholeiites and picrites have high gd yb 2 3 3 1 and tio2 1 2 2 3 wt no significant nb or ta anomaly nb la 0 8 1 1 and radiogenic nd nd chur to 7 3 the low ti and nb la high la sm and unradiogenic nd isotope signatures of the picritic tuklonsky formation lavas and the tholeiitic lavas of the upper sequence are characteristic of magmas strongly influenced by material from the continental lithosphere whereas the high ti and nb la low la sm and radiogenic nd isotope signatures of the lower sequence are more comparable to deeper asthenospheric mantle plume generated lavas similar to oceanic island basalts the lavas overlying the tuklonsky formation have mg numbers of 0 63 to 0 68 and are more evolved than the tuklonsky mg number 0 62 and have more radiogenic nd chur tuklonsky 0 03 to 4 66 mokulaevsky 0 60 to 1 61 but have many of the incompatible trace element features of the tuklonsky sky type magma these lavas show a progressive upwards decline in sio2 55 49 wt la sm 4 6 2 0 and ur sr 67 to 13 which has previously been attributed to a decrease in the proportion of crustal material contributed to the magma this paper explores and alternative model where a component of the crustal contribution might be derived from within an ancient region of the mantle lithosphere as recycled sediment rather than from the overlying continental crust

new 40ar 39ar age constraints on the late palaeozoic tectonic evolution of the western tianshan xinjiang northwestern china with emphasis on permian fluid ingress laser probe dating of mylonite whole rock samples from the north tianshan main tianshan fault zone that cross cuts the north tianshan domain s southern margin yielded 40ar 39ar spectra with 255 285 ma ages biotite from an undeformed early carboniferous granite which cuts the steep mylonitic foliation in the proterozoic basement of the yili arcs s southern margin gave a 263 4 0 6 ma plateau age 1 pre carboniferous metasediments overlying this basement yielded plateau ages 1 of 253 3 0 3 muscovite and 252 3 0 3 biotite ma the permian ages of mylonites date movement on these ductile dextral strike slip shear zones whereas the mica ages are interpreted by recrystallisation as a result of fluid flow around such transcurrent faults we propose that the tianshan s permian syn tectonic bimodal magmatism was created in a non plume related yellowstone like extensional transtensional tectonic regime gold mineralisation tracing aqueous flow in the crust peaked in permian time and continued locally into the triassic the picture is emerging that a convective fluid system partly driven by magmatic heat existed in a strongly fractured and weakened crust with an elevated heat flow leading to regional scale isotope resetting we suggest that surprisingly young isotopic ages in the literature for early orogenic ultra high pressure metamorphism are similarly due to fluid mediated recrystallisation

iron oxide copper gold mineralization of the devonian laoshankou deposit xinjiang nw china in the central asian orogenic belt abstract the laoshankou iron oxide cu au iocg deposit 41 km southwest of qinghe city xinjiang nw china is the most important magnetite deposit with economic cu and au metal reserve 3 26 mt fe 33 5 36 4 9 8 kt cu 0 2 0 4 and 0 14 t au 0 5 1 3 g t in the east junggar terrane of the central asian orogenic belt caob the deposit is hosted by volcanic rocks of the middle devonian beitashan formation in this study four hypogene hydrothermal alteration stages have been identified including the ca silicate alteration stage i amphibole epidote magnetite alteration mineralization stage ii pyrite chalcopyrite mineralization stage iii and late hydrothermal veining stage iv mineralogical fluid inclusion including laser raman spectroscopy and mineral sulfur oxygen hydrogen and carbon isotope analyses were carried out to elucidate the nature and origin of the hydrothermal fluids at laoshankou stage i hydrothermal fluids were likely derived from a 590 c magmatic fluid with 18 o water 9 2 9 7 subsequently the magnetite epidote amphibole assemblage may have precipitated from the fluids 530 c formed by the mixing of high temperature magmatic fluids with the seawater that reacted with 18 o rich wall rocks the fluid rock reactions are reflected from the 18 o water 9 6 10 7 and d water 25 5 23 8 values the sub economic stage iii a pyrite epidote quartz garnet mineralization likely occurred at 415 c and was formed by fluids with 34 s fluid 3 7 0 5 d water 110 94 and 18 o water 7 92 8 9 the lower temperature and presence of organic matter of the stage iii a fluids may have reflected the involvement of meteoric water and organic matter from the wall rocks the economic cu mineralization stage iii b was probably formed by the mixing of a meteoric water dominated fluid medium temperature low salinity and na dominated and a ca rich formation water in equilibrium with the volcanic wall rocks medium temperature medium salinity and ca fe mg dominated with 34 s fluid 2 6 18 o water 5 6 5 8 13 c water 3 3 3 1 and d water 92 95 towards the end of the fluid evolution meteoric water incursion may have continued and generated the ore barren low temperature low salinity and na dominated fluids although the laoshankou deposit contains distinct skarn alteration the ore mineral assemblage and ore fluid features indicate that it is not a typical skarn deposit but share many similarities with many central andean iocg deposits we conclude that the iocg ore forming setting in the devonian east junggar was analogous to the cretaceous central andes in that they both occurred during basin inversion in a volcanic arc setting

late paleozoic underplating in north xinjiang evidence from shoshonites and adakites abstract shoshonitic series volcanic rocks ssvr and adakites are widely distributed in the permian terrestrial volcanic strata of the yishijilike awulale range of west tianshan north xinjiang china isotopic dating yields permian ages of 280 250 ma the ssvr include absarokite shoshonite and banakite which are characterized by enrichment of alkalis particularly in k combined with lower ti higher al a nkc 0 70 0 99 metaluminous and fe2o3 feo the ssvr that are rich in lile with high ree contents and eu eu range from 0 59 to 1 30 they are rich in lree la yb n 2 15 11 97 and depleted in nb ta and ti tnt negative anomalies the adakites are metaluminous to weakly peraluminous a nkc 0 85 1 16 and belong to the high sio2 type of adakite hsa sio2 62 71 they are characterized by lower ree with strong lree enrichment la yb n 13 35 pronounced positive eu anomalies eu eu 1 02 1 27 very low yb contents and distinct tnt negative anomalies are evident the ssvr have end t 1 28 to 4 92 and 87sr 86sr i 0 7041 0 7057 that are similar to adakites in the regions which are characterized by end t 0 95 to 5 69 and 87sr 86sr i 0 7050 0 7053 trace element ree and sr nd isotopic compositions suggest that both ssvr and adakites possess similar source regions associated with underplated mantle derived basaltic materials lithosphere extension driven by magmatic underplating was responsible for the generation of both the ssvr and adakites this magmatism serves as a petrological indicator of underplating during the permian obviously thickened crust 62 52 km a complex moho discontinuity high heat flow 100 mw m 2 widespread contemporary alkali rich granites basic dike swarms k ar ages of 187 271 ma ar ar ages of 174 270 ma and rb sr ages of 255 28 ma end t 1 84 to 10 1 87sr 86sr i 0 7035 and 0 7065 and basic granulites shrimp u pb age of 268 279 5 6 ma provide additional evidences for the underplating event in this area during permian

re os isotopic ages of pyrite and chemical composition of magnetite from the cihai magmatic hydrothermal fe deposit nw china the eastern tianshan orogenic belt of the central asian orogenic belt and the beishan terrane of the tarim block nw china host numerous fe deposits the cihai fe deposit 90 mt at 45 6 fe in the beishan terrane is diabase hosted and consists of the cihai cinan and cixi ore clusters ore minerals are dominantly magnetite pyrite and pyrrhotite with minor chalcopyrite galena and sphalerite gangue minerals include pyroxene garnet hornblende and minor plagioclase biotite chlorite epidotite quartz and calcite pyrite from the cihai and cixi ore clusters has similar re os isotope compositions with 14 to 62 ppb re and 10 ppt common os pyrrhotite has 5 to 39 ppb re and 0 6 ppb common os pyrite has a mean re os model age of 262 3 5 6 ma n 13 in agreement with the isochron regression of 187os vs 187re the re os age 262 ma for the cihai fe deposit is within uncertainty in agreement with a previously reported rb sr age 268 25 ma of the hosting diabase indicating a genetic relationship between magmatism and mineralization magnetite from the cihai deposit has mg al ti v cr co ni mn zn ga and sn more elevated than that of typical skarn deposits but both v and ti contents lower than that of magmatic fe ti v deposits magnetite from these two ore clusters at cihai has slightly different trace element concentrations magnetite from the cihai ore cluster has relatively constant trace element compositions some magnetite grains from the cixi ore cluster have higher v ti and cr than those from the cihai ore cluster the compositional variations of magnetite between the ore clusters are possibly due to different formation temperatures combined with regional tectonic evolution of the beishan terrane the re os age of pyrite and the composition of magnetite indicate that the cihai fe deposit may have derived from magmatic hydrothermal fluids related to mafic magmatism probably in an extensional rift environment

geochemical and isotopic studies of the sedimentary and granitic rocks of the altai orogen of northwest china and their tectonic implications the altai orogen northwest china represents the southwestern margin of the central asian orogenic belt geochemical and nd sr isotope analyses were carried out on the palaeozoic sedimentary and granitic rocks in order to trace their sources and to evaluate the pattern of continental growth of the orogen nd isotopic data for both the granites and sediments suggest a significant proportion of middle proterozoic crust beneath the altai orogen however addition of juvenile material arc back arc oceanic crust during palaeozoic times is also significant trace elements and isotopic data of sediments suggest their sources were immature they represent mixtures between a palaeozoic juvenile component and an evolved continental crust the early palaeozoic sediments show e nd t 3 4 to 5 0 t dm 1 5 1 8 ga and i sr 0 710 0 712 they represent a passive margin setting with a predominance of evolved crustal material in the source the devonian sequences however might have been deposited in a back arc basin setting produced by subduction of the junggar oceanic crust along the irtysh fault a significant addition of arc material into the sedimentary basin is responsible for the highly variable e nd values 6 to 0 and i sr 0 711 0 706 the carboniferous rocks were also deposited in a back arc basin setting but with predominantly arc material in the source as suggested by an abrupt increase in e nd t 6 to 3 and decrease in i sr 0 7045 0 7051 voluminous syn orogenic granitoids have e nd t 2 1 to 4 3 i sr 0 705 0 714 and t dm 0 7 1 6 ga they were not derived by melting of local metasedimentary rocks as suggested by previous workers but by melting of a more juvenile source at depth post orogenic granites have higher e nd t 4 4 than the syn orogenic granitoids indicating their derivation from a deeper crustal level where juvenile crust may predominate

elemental and sr nd pb isotopic geochemistry of late paleozoic volcanic rocks beneath the junggar basin nw china implications for the formation and evolution of the basin basement the basement beneath the junggar basin has been interpreted either as a micro continent of precambrian age or as a fragment of paleozoic oceanic crust elemental and sr nd pb isotopic compositions and zircon pb pb ages of volcanic rocks from drill cores through the paleo weathered crust show that the basement is composed mainly of late paleozoic volcanic rock with minor shale and tuff the volcanic rocks are mostly subalkaline with some minor low k rocks in the western kexia area some alkaline lavas occur in the central luliang uplift and northeastern wulungu depression the lavas range in composition from basalts to rhyolites and fractional crystallization played an important role in magma evolution except for a few samples from kexia the basalts have low la nb 1 4 typical for oceanic crust derived from asthenospheric melts zircon pb pb ages indicate that the kexia andesite with a volcanic arc affinity formed in the early carboniferous 345 ma whereas the luliang rhyolite and the wucaiwan dacite with syn collisional to within plate affinities formed in the early devonian 395 and 405 ma respectively positive end t values up to 7 4 and low initial 87sr 86sr isotopic ratios of the intermediate silicic rocks suggest that the entire junggar terrain may be underlain by oceanic crust an interpretation consistent with the juvenile isotopic signatures of many granitoid plutons in other parts of the central asia orogenic belt variation in zircon ages for the silicic rocks different ba p ti nb or th anomalies in the mafic rocks and variable nb y and la nb ratios across the basin suggest that the basement is compositionally heterogeneous the heterogeneity is believed to reflect amalgamation of different oceanic blocks representing either different evolution stages within a single terrane or possibly derivation from different terranes

accretionary growth and crust formation in the central asian orogenic belt and comparison with the arabian nubian shield kroner a windley b f badarch g tomurtogoo o hegner e jahn b m gruschka s khain e v demoux a and wingate m t d 2007 accretionary growth and crust formation in the central asian orogenic belt and comparison with the arabian nubian shield in hatcher r d jr carlson m p mcbride j h and martinez catalan j r eds 4 d framework of continental crust geological society of america memoir 200 p 181 209 doi 10 1130 2007 1200 11 for permission to copy contact editing geosociety org 2007 the geological society of america all rights reserved kroner kroener mail uni mainz de windley brian windley btinternet com tomurtogoo igmr magicnet mn hegner hegner lmu de jahn jahn earth sinica edu tw khain khain ginras ru demoux demoux uni mainz de wingate mwingate tsrc uwa edu au

devonian alaskan type ultramafic mafic intrusions and silicic igneous rocks along the southern altai orogen implications on the phanerozoic continental growth of the altai orogen of the central asian orogenic belt abstract in this contribution we have carried out an integrated study of the petrography geochronology geochemistry and mineral chemistry for the devonian alaskan type ultramafic mafic complexes and granitoids widely distributed along the southern altai orogen in order to provide a better understanding of the continental growth process and the regional tectonic evolution la icpms zircon u pb dating of three mafic samples one acidic volcanic rock sample and one granitic sample yielded the concordia ages of ca 400 ma olivine chemical compositions indicate these mafic intrusions crystallized from evolved mafic magmas and compositions of the clinopyroxene and hornblende show typical arc affinities whole rock compositions reveal their tholeiitic signature with enriched lrees and liles and intensive depleted hfses nb ta zr and hf leading to low hfse lree ratios nb la 0 1 0 4 isotopically these mafic intrusions have positive zircon e hf t 7 6 to 14 3 mostly 10 and positive whole rock e nd t 0 8 to 5 3 values which suggest that their parental magmas were derived from a time integrated depleted mantle source these features together with the presence of primary water bearing minerals biotite and or hornblende suggest that their primitive magmas were derived from a time integrated depleted lithosphere mantle which were metasomatized by fluids released from subduction slab these findings in combination with coeval voluminous granitoids and arc signature volcanic rocks indicate that the underplating of mafic magmas at the continental arc root leads to the partial melting of the continental crust it is inferred that mafic magmatic underplating in the altai orogenic belt significantly contributed to the phanerozoic vertical continental crust growth in the altai orogen

middle cambrian to permian subduction related accretionary orogenesis of northern xinjiang nw china implications for the tectonic evolution of central asia abstract middle cambrian to permian subduction related records are widely distributed in northern xinjiang which can be grouped into the chinese altay east junggar eastern tien shan west junggar yili and tarim domains by integrating paleogeographic and geological data we suppose that the chinese altay east junggar eastern tien shan domain was more closely located to siberia while the west junggar and yili domains occupied an intermediate position near the kazakhstan block in the early paleozoic paleoasian ocean distribution of andean type magmatic arcs island arcs accretionary wedges ophiolitic slices and or microcontinents shows an archipelago paleogeography forming a huge accretionary active margin sequences the tarim domain was on the opposite side of the early paleozoic paleoasian ocean remaining passive margin these tectonic units drifted northwards and approached the southern active margin of the siberian craton in the late paleozoic leading to termination of the paleoasian ocean and formation of a complicated orogenic collage between siberian craton and the tarim block between the end permian and triassic these multiple accretion processes significantly contributed to the lateral growth of central asia

geochemistry and geochronology of carboniferous volcanic rocks in the eastern junggar terrane nw china implication for a tectonic transition the carboniferous tectonic setting of the junggar terrane northern xinjiang nw china has long been a matter of debate voluminous carboniferous volcanic rocks are widely distributed in the karamaili area the southern part of the eastern junggar terrane early carboniferous rocks comprise basalts and basaltic andesites with enrichment of lree and lile and depletion of hfse and uniformly high end t 3 7 to 4 0 late carboniferous rocks consist of basalts basaltic andesites rhyolites and minor dacites and can be subdivided into basic and felsic groups the basic rocks are depleted in hfse and show variable high end t 4 8 to 6 9 they have higher cr and ni and lower na2o u and th contents than early carboniferous basic rocks the felsic rocks show a type affinity with typical enrichment of alkalis lree and hfse and strong depletion in ba sr eu and ti they have high values of end t and zircon ehf t 11 6 to 17 9 new la icpms zircon u pb analyses constrain their emplacement to late carboniferous time 306 5 314 3 ma the carboniferous basic rocks show negative zr hf anomalies and low th ce 0 07 and th la 0 06 0 16 excluding significant crustal contamination during magma evolution they have low la ba 0 03 0 12 ce y 3 and tb yb n 2 and variable ba th 28 318 and ba la 3 1 34 suggesting that they were derived from a main spinel with minor garnet lherzolite mantle source metasomatized by slab derived fluids the late carboniferous felsic rocks were produced when upwelling asthenosphere triggered partial melting of juvenile lower crust the early carboniferous volcanism occurred in an island arc setting related to the southward subduction of the paleo junggar ocean plate whereas the late carboniferous rocks erupted in a post collisional extensional setting thus a rapid tectonic transition from arc to post collisional extension may have occurred between early and late carboniferous and probably resulted from slab break off or lithospheric delamination

tectonic evolution of the west junggar region xinjiang china the west junggar region of northwestern china consists of a hercynian age fold belt occupying a late paleozoic zone of convergence between three major eurasian plates siberian tarim and kazakhstan the northern part of the west junggar area includes part of the irtysh zaysan fold belt that extends to the northwest into the ussr where it marks a broad boundary between the siberian and kazakhstan plates the central part of the west junggar area includes the southeastern extension of the chingiz tarbgatay early paleozoic island arc sequence the southern part of the west junggar area is truncated by the deep fundamental junggar alakol fault that has brought the yili microplate into juxtaposiition with the west junggar region in the vicinity of ebin nur lake to the east the junggar area is covered by sediments of the junggar basin paleogeographic reconstructions and geologic evidence indicates that these plates began converging in the middle carboniferous and by late carboniferous alkali granites began invading the imbricated leading edges of the coalescing plates paleomagnetic data reveals that the plates continued to move along strike slip faults bringing the tarim plate and yili microplate into their present positions sometime in the early mesozoic six separate ophiolite occurrences in the west junggar region are strongly tectonized and dismembered the tangbale ophiolite is considered to be late cambrian 508 20 ma and represents the earliest known oceanic crust in western china petrologic and chemical data indicate that the tangbale ophiolite represents a possible back arc or forearc tectonic setting situated close to a developing island arc the darbut ophiolite has been tectonized to a melange and is overlain by late devonian flysch ages of the radiolaria in the cherts associated with the pillow lavas indicate that it formed in the middle devonian other occurrences of ophiolite melange in the northern part of the west junggar region may be as young as late devonian these ophiolites record ocean crust formation in the early to middle paleozoic within the junggarian ocean and their present tectonic setting indicates continental accretion and imbrication shortly after their formation associated blueschist blocks in the ophiolite melange further supports the concept of imbrication brought about by b type subduction and associated obduction postcollisional alkali granites intrude the oceanic sequences of the west junggar region and are considered to represent melted lower crustal material lead isotopic systematics on feldspars from six separate granite plutons indicate ratios that could only be considered oceanic as far as the magmas are concerned the implications of this finding is that the junggar basin basement rocks in the north and west are probably oceanic evidence presented in this study shows a complex history for the development of the west junggar region major movements of consolidating plates in the late paleozoic followed by rejuvenation of these same zones of closure during the himalayan tectonic event of the late tertiary demonstrates that convergence zones and fold belts may respond to vertical and horizontal stress even after many million years of inactivity

disaggregating and harmonising soil map units through resampled classification trees abstract legacy soil maps typically consist of a tessellation of polygon soil map unit delineations where the map units consist of a defined assemblage of soil classes assumed to exist in more or less fixed proportions there are several limitations in this kind of mapping approach that relate to the original intent of the soil survey the effect of mapping scale and the nature of soil polygon boundaries yet perhaps a more fundamental limitation is the fact that most of the time the soil classes that comprise the soil map units are not mapped individually in effect their spatial distributions are unknown beyond the qualitative indications given in the accompanying soil map unit report spatial disaggregation of soil map units attempts to map the spatial distribution of the individual soil classes that comprise a legacy soil map we developed an approach called disaggregation and harmonisation of soil map units through resampled classification trees dsmart dsmart samples the polygons of a legacy soil map and uses classification trees to generate a number of realisations of the potential soil class distribution the realisations are then used to estimate the probability of occurrence of the individual soil classes these estimates are mapped as raster grids which can overcome some of the limitations of mapping scale and polygon boundaries inherent in the original legacy soil map we demonstrate the dsmart approach on a legacy soil map from the former dalrymple shire in central queensland australia we mapped the estimated probability of occurrence of the 71 soil classes in the legacy soil map as well as the most probable soil class second most probable soil class and the degree of confusion between them as determined by a confusion index validation on 285 observed soil profiles indicated that for 48 4 of the validation profiles the observed soil class was identified in the top three most probable soil classes

syn and post collisional granitoids in the central tianshan orogen geochemistry geochronology and implications for tectonic evolution abstract the eastern part of the central tianshan belt in china is characterized by abundant granitoids which are not only indicators of the interaction between crust and mantle but also can be used for tracking the tectonic evolutionary history of the orogen four granitic plutons muscovite granites mg biotite monzonitic granites bmg biotite granites bg and alkali granites ag have been recognized to have intruded in the mishigou area central tianshan belt the mg has pronounced a s type affinity which is strongly peraluminous with a high aluminum saturation index and displays positive rb th u and lree anomalies with a strong negative ba nb sr p ti and eu anomalies therefore the magma of the mg is considered to have been derived from melting of thickened continental crust which is composed mainly of the sediments eroded from a pre silurian continental island arc the u pb zircon age of 424 5 2 6 ma constrains the age of mg and crust thickening the bg and bmg granitoids display i type geochemical features and have affinities to subduction arcs both of them are characterized by calc alkaline peraluminous granites with a significant lree enrichment and a negative eu anomaly as well as a depletion in ba nb ta sr p and ti and an enrichment in rb th u nd zr and sm these characteristics indicate that they were derived from a mixed magma source between lower continental crust and the input of components derived from the mantle wedge above the subduction zone the la icpms zircon u pb ages of 411 4 7 ma and 402 3 4 ma represent the formation ages of the bg and bmg granitoids respectively which also constrain that the subduction of the south tianshan oceanic crust also occurred during early devonian time the ag shows a typical a type granite affinity with depletion of nb ta sr p ti and y it is interpreted that ag was formed in a within plate tectonic setting and related to continental up doming and rifting zones as a consequence of the extensional collapse after the collision of the tianshan orogen the u pb zircon age of 290 5 1 ma represents the formation age of the ag and the time of the extensional collapse and rifting

compositional variations of several early permian magmatic sulfide deposits in the kalatongke district southern altai western china with genetic and exploration implications abstract a permian magmatic ni cu sulfide deposit cluster occurs in the kalatongke district in the southern chinese altai orogenic belt western china these deposits are associated with the mafic units of the y1 y2 y3 y9 and g21 mafic intermediate complexes in this paper we report the first zircon u pb ages for the y3 and g21 intrusions which are 283 3 1 3 ma and 281 1 1 5 ma respectively our new age data confirm that the sulfide bearing mafic units of the y1 y2 connected with y1 at depth y3 y9 and g21 intrusions all formed in early permian between 281 and 287 ma new and existing petrological geochemical data show some important regular variations between these deposits the host lithologies change from olivine bearing rocks for the y1 y2 y9 deposits to olivine free rocks such as norite for the y3 deposit and leucogabbro for the g21 deposit the olivine fo contents of the y1 deposit are up to 82 mol which are slightly higher than those of the y2 deposit up to 81 mol and the y9 deposit up to 79 mol the average plagioclase an contents of the olivine bearing y1 y2 y9 deposits are higher than those of the olivine free y3 g21 deposits among the three deposits y1 y2 and y3 that occur closely along the same structural lineament the ni cu ratios of bulk sulfides decrease from the olivine bearing deposits y1 and y2 to the olivine free deposit y3 the pge tenors of these deposits y1 y2 and y3 and the nearby coeval deposits y9 and g21 are extremely low indicating that their parental magmas are severely depleted in pges the variations of pge tenors within a single deposit as well as among the different deposits are mainly due to variable r factors the host rocks of these deposits are all characterized by elevated initial 87sr 86sr ratios from 0 7045 to 0 7047 positive end values from 4 95 to 6 86 positive ehf values of zircon from 9 to 16 and elevated 18o values of zircon from 6 15 to 6 7 the isotope data indicate that the parental magmas for these deposits experienced up to 15 wt crustal contamination the 34s values of the sulfide minerals from these deposits are from 3 1 to 0 4 with a peak at 2 2 indicating the involvement of crustal sulfur the isotope data and mineral chemistry together indicate that both olivine fractional crystallization and addition of crustal sulfur played a role in triggering sulfide saturation in the parental magmas for these deposits based on higher ni cu ratios of sulfide mineralization in the olivine bearing intrusions y1 y2 y9 than in the coeval olivine free intrusions y3 g21 we recommend that ni exploration in the region focus on the olivine bearing intrusions that were emplaced in the early permian

analysing the proximal gamma radiometry in contrasting mediterranean landscapes towards a regional prediction of clay content abstract the analysis of radiometric data from proximal soil sensing measurements can be used to predict key soil properties for environmental and agricultural issues these predictions require prior calibrations that use a large sampling of field data that could be significantly reduced if regional predictions can be established however such predictions may be challenging for mediterranean regions because of the highly contrasted soils and specific geopedological characteristics sedimentary rocks low weathering etc our study focuses on the regional prediction of a key soil property clay content within highly contrasting geopedological groups gpg from the languedoc region the aims of the research were i to understand the relationship between radiometric data and the clay content within the different complex gpgs and ii to predict the clay content from radiometry with a regional calibration based on the gpg as an auxiliary variable a proximal soil survey using the radiometer called the mole was conducted in 8 areas of the languedoc region the plots were selected over different gpgs that are representative of the soil diversity and materials according to their weathering intensity and igneous components in total 242 sites were sampled based on a random grid cell for soil laboratory measurements the soil texture and stoniness were analysed and the particle size fractions were separated for mineral identification via x ray diffraction the activity of 232th 1 to 71 bq kg and 40k 40 to 771 bq kg exhibits the largest range between the different gpgs which spans the range of values measured in previous european studies the relationship between the clay content and 232th is significant at a regional level r2 0 60 rmse 42 g kg the residuals are significantly distributed according to the different gpgs a new linear model based on the 232th activity and the gpgs improves the prediction of the clay content r2 0 72 rmse 35 g kg our study showed that ground radiometry can be used to predict the clay content within a complex mediterranean sedimentary context the 232th radionuclide is the best predictor the disturbance of the relationship between the 232th and the clay content corresponds to the fine earth mineralogy type and the proportion of igneous pebbles

genesis of post collisional granitoids and basement nature of the junggar terrane nw china nd sr isotope and trace element evidence the post collisional magmatism of the junggar terrane is characterized by intrusion of large amounts of granitoids and minor basic ultrabasic rocks the granitoids comprise two magmatic suites calc alkaline and alkaline which were emplaced contemporaneously at about 294 ma the calc alkaline rocks are typically sodium rich na2o k2o 1 1 3 5 and metaluminous a nk 1 0 a cnk 0 78 1 04 they show mildly fractionated ree patterns la yb n 15 and spidergrams with strong depletion of nb ti and to a lesser extent sr the alkaline granites have high contents of sio2 75 78 alkalis nb hree y sn f and high feo mgo ratios and huge sr and eu depletion in the spidergrams moreover they display characteristic tetrad ree patterns and non charac trace element behaviour the two rock suites have similar initial nd and sr isotopic compositions with end t in the range 5 2 to 7 1 and isr mostly in the range 0 7031 0 7041 this points to a predominance of juvenile components in their sources the calc alkaline rocks are most probably derived by dehydration melting of a basic lower crust leaving behind a granulite residue the process was probably triggered by underplating of mantle derived basic magmas in an extensional regime the alkaline granites are considered to have formed by differentiation of the calc alkaline granitoids our study argues for a juvenile continental crust for the basement of the junggar terrane which is likely dominated by early paleozoic oceanic crust and arc complex that were deeply buried during the late paleozoic subduction and accretion

metallogenic province derived from mantle sources nd sr s and pb isotope evidence from the central asian orogenic belt abstract the central asian orogenic belt caob is one of the most important regions for cu au and polymetallic and rare metallic li be nb ta mineralization over the world most of the ore deposits in the caob are closely associated with granitoids available sr nd s and pb isotopic data indicate that the metallogenic epoch and sources of the mineral deposits in the caob are consistent with that of the regional granites available data suggest that mantle sources could have played an important role in the paleozoic to mesozoic mineralization in the caob

late paleozoic early mesozoic geodynamics of central asia abstract correlation and synthesis of published and new structural paleomagnetic and geochronological data from central asia show the important role of strike slip faulting in their evolution the pattern of major strike slip faults outlines a terrane collage produced by a late devonian early carboniferous collision of the gondwana derived altai mongolia tuva composite microcontinent with siberia and a late carboniferous permian collision of east europe and kazakhstan with siberia the accreted continental margins were cut by strike slip faults and conjugate thrusts into numerous terranes which mixed with one another and disturbed the previous structural and facies framework those complex and multi stage deformations resulted from the late devonian early carboniferous collision of gondwana derived terranes the deformations reached their peak in the late carboniferous permian due to the collision of the kazakhstan east european baltica and siberian continents a system of sinistral strike slip faults formed a mosaic block structure of central asia along the margin of the siberian continent as a result of the late carboniferous permian collision this resulted in the formation of the northern eurasia continent early mesozoic strike slip faulting and conjugate thrusting resulted from the rotation of the siberian and east european cratons

radiogenic isotope systematics of the herefoss granite south norway an indicator of sveconorwegian grenvillian crustal evolution in the baltic shield abstract a new pb pb mineral isochron dates the crystallization of the herefoss granite south norway to 926 8 ma confirming earlier rb sr evidence of a late sveconorwegian grenvillian age initial sr and nd isotopic compositions recalculated to esr 926 ma 40 end 926 ma 3 2 to 0 8 indicate that the magma has originated from a mixture of two distinct source components 1 a crustal component which has resided in a moderately lile enriched reservoir f rb 7 to 8 238 u 204 pb 17 22 since 1 6 1 9 ga this crustal component is clearly distinct from the extremely lile enriched metasedimentary country rocks of the granite f rb 21 238 u 204 pb 24 2 a mantle derived component e nd 4 6 to 5 9 e sr 12 to 9 238 u 204 pb 7 96 younger than 1 5 ga the ranges of initial sr nd and pb composition observed in the intrusion indicate that the magma was isotopically heterogeneous at the time of emplacement and that the crustal contribution amounted to 35 55 by the end of the sveconorwegian orogeny the southwestern part of the baltic shield had acquired a compositionally layered structure where an uppermost zone of the crust with extreme lile enrichment was underlain by a heterogeneous layer consisting of rocks with normal upper crustal degree of lile enrichment and mafic intrusions younger than 1 5 ga there is no evidence of involvement of lile depleted deep continental crust source material in the petrogenesis of the herefoss granite rejuvenation of the lower crust by injection of mantle derived magmas underplating has been an important process in the evolution of the southwestern part of the baltic shield the absence of a young mantle derived component from 1 12 ga charnockitic intrusions in the bamble sector and from the 989 ma grimstad granite suggests that this process may have been contemporaneous with late sveconorwegian mafic magmatism in the rogaland vest agder sector further to the west

late paleozoic volcanic record of the eastern junggar terrane xinjiang northwestern china major and trace element characteristics sr nd isotopic systematics and implications for tectonic evolution article i nfo the eastern junggar terrane of the central asian orogenic belt includes a late paleozoic assemblage of volcanic rocks of mixed oceanic and arc affinity located in a structurally complex belt between the siberian plate the kazakhstan block and the tianshan range the early history of these rocks is not well constrained but the junggar terrane was part of a cordilleran style accreted arc assemblage by the late carboniferous late paleozoic volcanic rocks of the northern part of the east junggar terrane are divided from base to top into the early devonian tuoranggekuduke formation fm middle devonian beitashan fm middle devonian yundukala fm late devonian jiangzierkuduke fm early carboniferous nanmingshui fm and late carboniferous batamayineishan fm we present major element trace element and sr nd isotopic analyses of 64 ultra mafic to intermediate volcanic rock samples of these formations all devonian volcanic rocks exhibit remarkably negative nb ta and ti anomalies on the primitive mantle normalized trace element diagrams and are enriched in more highly incompatible elements relative to moderately incompatible ones furthermore they have subchondritic nb ta ratios and their zr nb and sm nd ratios resemble those of morbs characteristics of arc related volcanic rocks the early devonian tuoranggekuduke fm middle devonian beitashan fm and middle devonian yundukala fm are characterized by tholeiitic and calc alkaline affinities in contrast the late devonian jiangzierkuduke fm contains a large amount of tuff and sandstone and its volcanic rocks have dominantly calc alkaline affinities we therefore propose that the jiangzierkuduke fm formed in a mature island arc setting and other devonian fms formed in an immature island arc setting the basalts from the nanmingshui fm have geochemical signatures between n morb and island arcs indicating that they formed in a back arc setting in contrast the volcanic rocks from the batamayineishan fm display geochemical characteristics of continental intraplate volcanic rocks formed in an extensional setting after collision thus we propose a model that involves a volcanic arc formed by northward subduction of the ancient junggar ocean and amalgamation of different terranes during the late paleozoic to interpret the formation of the late paleozoic volcanic rocks in the eastern junggar terrane and the altai and junggar terranes fully amalgamated into a cordilleran type orogen during the end of early carboniferous to the middle late carboniferous

late paleozoic post collisional magmatism in the eastern tianshan belt northwest china new insights from geochemistry geochronology and petrology of bimodal volcanic rocks abstract the late carboniferous to permian marks an important phase of terrane amalgamation through accretion collision in the central asian orogenic belt caob the tianshan belt forms part of this sequence where the post collisional event generated an e w trending bimodal volcanic zone that extends for ca 500 km from the southern bogda mt to the easternmost tianshan belt here we report the petrology geochemistry and geochronology of the bimodal volcanic rocks to characterize the post collisional tectonic evolution in late paleozoic the major element chemistry of the basalt and rhyolite samples indicates a bimodal high k calc alkaline affinity the basalts are characterized by high abundance in tio2 th u and pb and depletion in nb ta and p together with slight enrichment in lree contents and low hfse lree ratios the rhyolites show a close affinity to aluminous a type granites with enrichment in k na zr ce y and depletion in p nb ta and ti they also exhibit fractionated ree patterns with prominent negative eu anomalies the petrographic and geochemical data suggest that this bimodal rock series was generated in a post collisional setting the mafic rocks are likely derived from a metasomatized lithospheric mantle assimilation of different crustal components played a minor role in the genesis of these basaltic rocks the la icp ms analysis on zircons from four rhyolites and two basalts yielded similar ages ranging from 295 8 2 8 to 293 3 1 7 ma suggesting an early permian event zircons from the basalts show a wide ehf t range from 0 49 to 13 whereas those from the rhyolites show two groups of ehf t values from 5 to 3 and from 6 to 12 suggesting a mixing of crust mantle material the magmatic zircons from the bimodal volcanic rocks yielded two peaks of tdm2 between 600 820 ma and 1160 1360 ma probably representing two significant episodes of continental crust growth the bimodal volcanic rocks are correlated with the early stage of post collision our results suggest that vertical crustal growth through mantle derived magmas in post collisional setting also played a major role in the construction of the caob

an integrated approach to mapping and understanding of vegetation soil systems abstract this research employs a raft of incisive strategies and technologies to define and interpret spatial relationships between native plant ecosystems and classes of soil across a range of scales building on traditional vegetation zonings and soil mappings information on locations of key taxa chemical composition of pisoliths and radiometric based technologies are used collectively to identify and delineate contrasting zonings in which principal base units phytotaria are distributed in patchy but well demarcated mosaics across soilscapes at broadest scale biomes are recognised in terms of species endemism radiometric patternings and element balances of pisolithic ferricretes and in many cases shown to change predictably in stepwise fashion across environmental gradients at finer scale georeferenced data for key players in selected phytotaria are matched against information from airborne radiometry to identify hallmark signallings derived from workings of potassium uranium and thorium in parent profiles by draping radiometric signals over digital elevation models further insight was obtained on the complex relationships between specific phytotaria topography and mineralogical status across a selected area these southwest australian case studies demonstrate how multiple sources of evidence might be mined and parcelled up to provide a comprehensive picture of heterogeneity and connectivity within and between phytotaria

landscape scale exploratory radiometric mapping using proximal soil sensing abstract the soil s gamma radiometric signal is known to be a crucial indicator of the heterogeneity of soil properties most likely directly related to the mineralogy and geochemistry of the parent material however fine resolution radiometric data sourced from geophysical surveys are often not available in our study area in the lower hunter valley australia only coarse scale based on 2 km line spacing aerial radiometric maps are available an alternative solution could be to implement a smart ground based gamma ray survey when detailed radiometric information is required on larger extent the work presented here therefore details a vehicle borne gamma ray soil survey conducted in the lower hunter valley to investigate if a proximal soil sensing device with a footprint much smaller than airborne gamma ray spectrometers can be employed for regional extent mapping and still capture the soil s fine scale heterogeneity to do so we designed an algorithm for the delineation of irregular transects drive lines based on ancillary environmental information intended to be used specifically for wide ranging exploratory surveys wires at the regional scale the wires algorithm creates transects from randomised starting points that terminate at boundary points the path is defined with directional constraints that collectively ensure that the environmental variability within the domain of study is accessed and sampled the design was delineated for the entire 220 km2 study area in this exploratory work we surveyed a sub catchment of the area 15 km2 to trial the feasibility of wires we produced radiometric maps based on a regression kriging approach an external validation of the maps showed good results we also validated the maps produced with existing detailed radiometric maps across a landholding 140 ha that is situated within the sub area investigated in this study both surveys were comparable which gives us useful insights into understanding the scaling properties of the geophysical properties of soil across environments

the association of mafic ultramafic intrusions and a type magmatism in the tian shan and altay orogens nw china implications for geodynamic evolution and potential for the discovery of new ore deposits abstract the nw china region is characterised by tectonic and lithostratigraphic domains such as the tian shan and altay orogens the tarim junggar and turpan basins the tian shan and altay orogens are part of the central asian orogenic belt the nw china region was affected by a series of thermal events that occurred between the silurian and the triassic which resulted in the emplacement of numerous granitic plutons and mafic ultramafic intrusions a number of these granitic plutons are of a type affiliation which on the basis of the positive end values are likely to have been derived from mantle sources in addition at least two large igneous provinces lips can be recognised in nw china namely the 345 325 ma tian shan lip and the ca 270 280 ma tarim lip age and field data suggest a spatial and temporal relationship between the mafic ultramafic intrusions and a type granites within the lips in this paper we discuss mafic ultramafic intrusions that host magmatic ni cu sulphide deposits kalatongke in the altay huangshan and poyi poshi in the eastern tian shan these intrusions are typically zoned characterised by an envelope of early gabbroic rocks that enclose later ultramafic units these zoned mafic ultramafic intrusions have some features that are comparable with alaskan type complexes taking into consideration the spatial temporal relationship of the mafic mafic ultramafic rocks and a type granites we suggest that these magmatic events occurred during an extensional regime possibly related to a mantle superplume event that affected much of central asia during the permian of which the siberian traps and the emeishan continental flood basalts of sw china are part if the a type felsic magmatism took place during a superplume event we also suggest that these rocks may be conducive to host iron oxide copper gold iocg style mineralisation we conclude with a model that attempts to explain the relationship between the zoned mafic ultramafic intrusions and mantle plume activity in nw china during the permian

ordovician 40ar 39ar phengite ages from the blueschist facies ondor sum subduction accretion complex inner mongolia and implications for the early paleozoic history of continental blocks in china and adjacent areas we obtained 453 21 8 ma and 449 41 8 ma 2 laser step heating 40 ar 39 ar plateau ages for phengite from quartzite mylonites from the blueschist facies ondor sum subduction accretion complex in inner mongolia northern china these ages are within error of the inverse isochron ages calculated using the plateau steps and the weighted mean ages of total fusion of single grains the compositional change from glaucophane in the cores to crossite in the rims of blue amphiboles as revealed by electron microprobe analysis points to decompression probably caused by progressive exhumation of the subducted material the late ordovician ages were not affected by excess argon incorporation because in all likelihood the oceanic sediments were wet on arrival at the trench and free of older detrital mica the ca 450 ma ages are hence interpreted as the time of crystallization during mylonitization under high fluid activity at fairly low temperatures this means that accretion of the quartzite mylonite unit occured about 200 ma before final closure of the paleo asian ocean amalgamation of the siberian tarim and north china cratons and formation of the end permian solonker suture zone we argue that the early paleozoic evolution of the ondor sum complex occurred along the northeastern cimmerian margin of gondwana which was composed of micro continents fringed by subduction accretion complexes and island arcs the later evolution took place during the building of the eurasian continent following middle devonian and younger rifting along the east gondwanan margin and northward drift of the detached north china craton an extensive review shows that this type of two stage scenario probably also applies to the geodynamic evolution of other micro continents like south china tarim a number of kazakh terranes alashan qaidam and kunlun as well as south kitakami and correlatives in japan and probably indochina like the north china craton these were bordered by early paleozoic subduction accretion complexes island arcs or contained calc alkaline volcanic mar gins like for example the central tienshan north qinling north qaidam altun north qilian and kunlun belts in china as well as the oeyama and miyamori ophiolites and matsugadaira motai blueschist belt of japan and the dismembered sergeevka ophiolite of the southern part of the russian far east this implies that a vast orogenic system comprising an archipelago of micro continents seems to have existed along the cimmerian margin of east gondwana in early paleozoic time in which the ultrahigh pressure metamorphism that characterizes the early evolution of many of the asian micro continents occurred introduction and aim

formation of the maturin foreland basin eastern venezuela thrust sheet loading or subduction dynamic topography 1 the maturin basin in eastern venezuela is considered a good example of a peripheral foreland basin earthquake and tomographic data indicate that eastern venezuela is affected by the oblique subduction of the south american plate underneath the caribbean plate new forward flexural isostatic modeling of eastern venezuela has been carried out in order to determine whether the maturin basin was generated purely by thrust sheet loading from the serrania and monagas foreland thrust belts a sequence of forward models from middle miocene to present was generated for 3 profiles across the serrania del interior thrust belt the monagas foreland thrust belt and the maturin foreland basin the predictions of these models are constrained using seismic reflection and well data the flexural isostatic modeling shows that thrust sheet loading associated with the serrania del interior and monagas foreland thrust belts is insufficient to generate the observed subsidence within the maturin basin dynamic fluid flow modeling of subduction related dynamic topography of eastern venezuela has been used to investigate the influence of south american plate subduction on the generation of the accommodation space observed in the maturin basin fluid flow modeling of subduction related dynamic topography suggests that the subduction of the south american lithospheric mantle caused downward deflection of the south american crust affecting the maturin basin and the serrania thrust belt this modeling suggests that the maturin basin subsidence has two components 55 related to thrust sheet loading and 45 driven by continental subduction

paleozoic accretion and cenozoic redeformation of the chinese tien shan range central asia the tien shan range in central asia contains two late paleozoic sutures the older southern suture marks the collision of a passive margin at the north of the tarim block and an active continental margin subduction under the latter was to the north the younger northern suture separates a northern carboniferous island arc from an active continental margin developed over a south dipping subduction zone the subduction direction under the island arc is unknown mesozoic elastics were deposited over the doubly sutured orogen rate and energy of sedimentation waned until deposition of oligocene conglomerates above a regional unconformity interpreted as marking the onset of deformation induced by the india asia collision molasse deposition accelerated in pliocene and quaternary time and deposition continues today as active thrusts generate relief paleozoic structures control the gross divergence of cenozoic thrusts across the orogen

zircon u pb geochronology geochemistry and sr nd hf isotopes of granitoids in the yulekenhalasu copper ore district northern junggar china petrogenesis and tectonic implications abstract the yulekenhalasu porphyry copper deposit is located in the kalaxiange er metallogenic belt in northern junggar china we present the results from zircon u pb geochronology and geochemical and sr nd hf isotope analyses of the granitoids associated with the ore deposits with a view to constrain their petrogenesis and tectonic setting the granitoids consist of quartz diorite diorite porphyry porphyritic monzonite and quartz porphyry emplaced at 382 379 375 374 and 348 ma respectively which span late devonian to early carboniferous ages the ore bearing intrusion is mainly diorite porphyry with subordinate porphyritic monzonite the late devonian intrusions are characterized by sio2 contents of 54 5 64 79 wt na2o contents of 3 82 8 24 wt enrichment in na light rare earth elements lrees and large ion lithophile elements they also display relative depletion in y ba p nb ta and ti and weak negative eu anomalies eu 0 6 0 87 the early carboniferous quartz porphyry is characterized by high sio2 content 72 26 73 35 wt enrichment in lrees k and sr and relative depletion in y 10 82 12 52 ppm and yb 1 06 1 15 ppm the late devonian and early carboniferous granitoids are characterized by positive end t values 5 2 10 1 one sample at 1 9 positive ehf t values 7 46 18 45 low 87sr 86sr i values 0 70363 0 70476 and young crustal residence ages these data indicate that the sources of the granitoids were mainly mantle derived juvenile rocks geochemical and nd sr hf isotopic data demonstrate that the late devonian granitoids formed in an oceanic island arc and they were formed from different sources among which the mineralized diorite porphyry might have originated from a mixed slab derived and mantle wedge melt source the early carboniferous quartz porphyry was likely emplaced in a mature island arc environment and was probably derived from juvenile crust

elemental and nd sr isotopic geochemistry of granitoids from the west junggar foldbelt nw china with implications for phanerozoic continental growth we report elemental and nd sr isotopic data for two coeval postcollisional magmatic suites 300 ma the miaogou and karamay suites from west junggar foldbelt nw china aiming to determine their source regions and implications for continental growth the miaogou rocks monzonitic to granitic in composition show low mg 0 30 and depletion of hfse and are highly depleted in isotopic compositions with isr ranging from 0 7035 to 0 7045 end 300 ma from 8 4 to 6 6 and young nd model ages 0 37 0 70 ga that coincide with the ages of the ophiolites in the area these features suggest that the miaogou rocks were derived essentially by partial melting of a juvenile basaltic lower crust formed in the early to middle palaeozoic the karamay suite contains a variety of rock types from gabbroic diorite to granite these rocks show enrichment of lree and lile and depletion of hfse and have chemical composition e g mg 0 63 0 41 rather different from the miaogou suite though isotopically they are indistinguishable this suggests that the parental magma of the karamay suite originated from melting of a young lithospheric mantle that had previously been metasomatized during the palaeozoic subduction the west junggar magmatic rocks represent production of juvenile continental crust in the phanerozoic triggered by upwelling of asthenophere in an extensional regime the basement beneath the area is dominated by trapped palaeozoic arc series and oceanic crust

identifying large scale erosion and deposition processes from airborne gamma radiometrics and digital elevation models in a weathered landscape patterns of erosion and deposition are difficult to identify and measure at catchment and regional scale but it may be possible to infer their distribution from remote sensing using easily measured surrogate variables airborne geophysical surveys provide data on gamma ray emissions from surface and near surface material and allow estimation of k th and u content gamma ray signatures are largely determined by lithology but also change with weathering and with erosion and deposition and may be used as a partial surrogate for those processes comparison of gamma ray signatures with topographic characteristics closely related to sediment transport capacity downstream sorting of sediments and the extent of erosion and deposition shows strong linkages studies in four small catchments in southeastern australia indicate that k consistently increases as slopes become steeper while th and u may either increase or decrease this suggests the presence of fresh rock rather than weathered material and implies removal of material by erosion although some patterns may result from systematic changes in lithology across catchments analysis by lithology confirms the increase in k with slope in granites metamorphosed sediments and basalt and also shows a tendency for u to decrease with slope in the granites and basalt gamma ray emissions vary only slightly with catchment area a surrogate measure of water discharge suggesting that water erosion is limited or that discharge is not closely related to area gamma radiometric profiles down hillslopes averaged across the full range of gradients show that in most cases radioelements initially decrease probably reflecting increased weathering but then increase close to valley floors because of accumulation of fine sediments analysis by lithology confirms the increase in radioelements close to valley floors in granites and metamorphosed sediments but the trend is less clear in basalt gamma ray profiles down floodplains are variable and indicate the amount of deposition and accumulation of weathered material in valley openings and exposure of bedrock in valley constrictions simple erosion and deposition models based on the conservation of mass equation and applied to the four catchments show that all radioelements increase as the potential for deposition increases they reach a low point in zones of no net erosion or deposition and subsequently increase as erosion becomes more intense and weathered material is lost from slopes analysis by lithology largely confirms this pattern the usefulness of airborne geophysical survey data is limited by flight line spacing with most data being flown at a 200 400 m spacing in australia however general trends in erosion and deposition can still be distinguished and there is capacity for calibrating long term erosion and deposition models once better approaches to interpretation of gamma ray data have been developed copyright 2000 john wiley sons ltd