provenance and tectonic setting of the paleoproterozoic metasedimentary rocks from the liaohe group jiao liao ji belt north china craton insights from detrital zircon u pb geochronology whole rock sm nd isotopes and geochemistry abstract geochronological geochemical and isotopic studies were carried out on the paleoproterozoic metasedimentary rocks from the jiao liao ji belt north china craton to constrain their provenance and tectonic setting as well as to evaluate the effects of weathering and sedimentary processes on the source rock signature u pb isotopic dating using the la icp ms method on zircons from the paleoproterozoic metasedimentary rocks reveals that the depositional age can be constrained in the period between 1 98 and 1 9 ga geochemical data reveal low intermediate degrees of weathering of the source compositionally immature and poorly sorted detailed analysis of detrital zircon u pb geochronology whole rock sm nd isotope and geochemistry show that these metasedimentary rocks are derived from a mixed provenance the predominant derivation is from metavolcanic rocks of the liaohe group and paleoproterozoic gneissic granitoids there is also an input of archean continental crust the metasedimentary rocks were probably deposited in a back arc basin within an arc system thus supporting the paleoproterozoic arc continent collision model as already proposed by some authors

late precambrian glacially related grooved and striated surfaces in the tillite group of central east greenland abstract the tillite group of central east greenland comprises five formations of which two are dominantly glacigenic the ulveso formation formerly lower tillite and the storeelv formation formerly upper tillite both of which embrace a wide range of facies including glaciomarine nearshore and terrestrial glacial sediments evidence of periodic terrestrial conditions is indicated especially by a variety of grooved and striated surfaces on the island ella o in the ulveso formation grooves of complex geometry 0 4 m wide and 0 3 m deep were cut into a cemented conglomerate horizon they are interpreted as having formed as a result of subglacial meltwater cavitation at the base of the storeelv formation boulders thought to have been dropped into partially cemented sandstone by floating glacier ice were largely planed off by a subsequent advance of grounded ice in the middle of the storeelv formation a striated boulder pavement occurs within diamictite on the basis of stone fabric striation orientation and cross bedding data this pavement is inferred to have formed by the packing of stones along a shear surface within an accumulating lodgement till such features have rarely been observed in pre pleistocene glacigenic sequences they imply that each glacigenic formation accumulated during a complex series of advances and retreats rather than just one

grain size control on sr nd isotope provenance studies and impact on paleoclimate reconstructions an example from deep sea sediments offshore nw africa five sediment cores from offshore nw africa were analyzed for strontium and neodymium isotope ratios to reconstruct temporal variations in continental weathering regimes sediments were taken from three time slices with well known and distinctive environmental conditions present day dry and warm similar to 6 ka wet and warm and similar to 12 ka dry and cold terrigenous sediment samples were split into two size fractions to distinguish between the two dominant transport mechanisms offshore nw africa fluvial 0 10 mu m and aeolian 10 40 mu m sr isotope data record evidence of marked grain size control with higher isotopic ratios in the fine fraction in contrast epsilon nd values are largely unaffected by grain size minor variability in nd isotope data at each sampling site indicates near constant sources of terrigenous matter over the last similar to 12 ka variations in sr isotope ratios are interpreted to reflect major changes in the evaporation precipitation balance we suggest that the sr nd isotope data record a latitudinal shift of the northern limit of the african rainbelt and associated wind systems causing changes in the humidity and rate of chemical weathering over nw africa while hyperarid conditions prevailed similar to 12 ka more humid conditions and intensified monsoonal rainfall at similar to 6 ka resulted in greater breakdown of easily weathered k bearing phases and increased sr 87 sr 86 in the detritus in late holocene times the monsoonal circulation diminished resulting in a return to arid conditions our results clearly show that it is of vital importance in paleoenvironmental studies to carry out isotopic analyses on individual sediment fractions that were carried to the studied deposition site by distinct sediment transport mechanisms if isotopic analyses are carried out on bulk sediments the observed variability in isotopic values most likely represents changes in the particle size and mixing proportions of the sediment subpopulations

single zircon ages for granitoid gneisses in the central zone of the limpopo belt southern africa and geodynamic significance abstract ion microprobe evaporation and vapour digestion single zircon emplacement ages for granitoid rocks throughout the central zone cz of the limpopo mobile belt south africa define three broad age groups namely at 3188 3314 2637 2734 and ca 2500 ma respectively all these granitoids including the youngest group display polydeformational features suggesting that much of the tectonic history of the cz occurred in the late archaean and early proterozoic the oldest group of predominantly tonalitic trondhjemitic granodioritic gneisses was found in relatively small domains from the extreme w to the e of the cz and probably represents remnants of a once more widespread early archaean terrain the most abundant granitoid gneisses belong to the 2 6 2 7 ga age group and were emplaced into already ductilely deformed gneisses of the oldest group several of these rocks were derived from intracrustal melting rare metamorphic zircons with ages of 2560 2575 ma reflect a high grade metamorphic event in the cz that has also been postulated by other workers a strongly deformed orthogneiss with a protolith emplacement age of 2510 ma proves beyond doubt that at least part of the structural history in the cz occurred in the early proterozoic an anatectic granite in the extreme w of the cz intruded at 2022 ma and is probably related to the peak of granulite facies metamorphism previously dated at 2027 6 ma in the messina area the second period of granitoid magmatism is broadly contemporaneous with charnockite and enderbite emplacement and granulite facies metamorphism in the northern and southern marginal zones of the limpopo belt broad contemporaneity of extensive granitoid magmatism in all three zones raises doubts about the exotic nature of the cz and suggests a revised evolutionary model for the limpopo belt

geochemistry and detrital zircon u pb and hf isotopes of the paragneiss suite from the quanji massif se tarim craton implications for paleoproterozoic tectonics in nw china abstract the delingha paragneiss suite in the quanji massif southeastern tarim craton is composed of mica schist paragneiss leptynite and quartzite similar to the khondalite suites described from elsewhere in the world the mica schist is rich in al2o3 up to 26 wt and contains graphite and diagnostic minerals including sillimanite and garnet with metamorphism under amphibolite facies to locally granulite facies conditions as manifested by association with amphibolite and granulite the detrital zircon u pb ages and geochemical data indicate that the protolith materials of the delingha paragneiss suite were mainly sourced from 2 20 to 2 45 ga granites felsic volcanic rocks and ttg and were deposited at 2 17 1 92 ga the detrital zircon hf and whole rock nd isotopes document important crustal growth at 2 5 2 7 ga the detrital zircon age spectra the whole rock nd and zircon hf model ages the low maturity of the protolith and short distance transportation suggest that the detritus were derived from the underlying delingha complex and the lower dakendaban sub group the timing of magmatic activities in the source region the depositional age and metamorphic histories of the delingha paragneiss suite are all comparable to those recorded in the khondalite belt along northern margin of the ordos block in the north china craton our study shows that the 2 2 2 45 ga magmatic rocks were generated in arc or active continental margin settings suggesting a prolonged subduction and accretion history prior to final amalgamation 2 5 1 8 ga to form the unified north china craton and the assembly of the tarim craton in nw china

major and transition trace element abundances in the khondalite suite of the granulite belt of lapland fennoscandia evidence for an early proterozoic flysch belt abstract the granulite belt of lapland comprises two main units the more extensive unit the khondalite suite is formed of approximately equal proportions of sillimanite garnet gneisses and garnet gneisses which include impersistent layers of quartz rich gneisses calc silicate rocks and metavolcanics the less extensive unit the charnockite complex corresponds to several tholeiitic and calc alkaline series each of them ranging from gabbro to tonalite an attempt has been made to elucidate the primary features of the khondalite suite and its depositional environment major and transition trace element variations suggest that it has an overall sedimentary parentage and that it corresponded to a graywackeshale sequence turbidites original clastic sediments were mainly derived from an eroded continental crust and in lesser amount from contemporary volcanism the geochemical trends for alkalies seem to indicate that this crust was relatively silicic and that it had undergone previous granite forming events taking into consideration the geological setting the geometry and the facies of these sedimentary formations we propose to reinterpret the granulite belt of lapland as a flysch belt located at a plate junction and pre dating a continent continent collision with subducted oceanic crust

discovery of sapphirine bearing mg al granulites in the north china craton implications for paleoproterozoic ultrahigh temperature metamorphism abstract we report here for the first time the occurrence of mg al granulites within the khondalite belt of the north china craton and provide robust evidence for extreme crustal metamorphism at ultrahigh temperature uht conditions in this region the uht indicator assemblages in these rocks include equilibrium sapphirine quartz high alumina orthopyroxene sillimanite quartz and high temperature perthites the surrounding khondalites also carry spinel quartz equilibrium assemblage the sapphirines occurring in various microstructural associations are markedly magnesian x mg 0 69 0 77 with a composition varying from 7 9 3 to 2 2 1 end members spinel is a solid solution of mg spinel and hercynite x mg 0 41 0 54 with zno content varying from 0 48 to 1 79 wt garnet shows a compositional range between pyrope and almandine x mg 0 39 0 48 with minor grossular 2 6 3 8 mol and spessartine 0 5 1 8 mol the orthopyroxenes display marked compositional variations in terms of al 2 o 3 content with the core of the medium grained orthopyroxene adjacent to sillimanite in the matrix showing the highest al 2 o 3 content 8 4 wt the history of prograde to peak metamorphism of these rocks is indicated by inclusions of sapphirine spinel quartz and sillimanite within garnet sapphirine formed during the peak stage through the reaction spl qtz sil spr occurrence of sapphirine and quartz inclusions trapped in sillimanite suggests the reaction spr qtz grt opx sil a series of retrograde reactions are observed in these rocks as corona and symplectite textures around early coarse grained minerals such as opx sil qtz crd grt sil qtz crd grt qtz crd opx grt o 2 crd qtz fe 2 o 3 in mag or ilm and finally opx kfs h 2 o bt qtz whereas the stability of sapphirine quartz and orthopyroxene sillimanite quartz in the matrix assemblage suggests t 1000 c and p 10 kbar peak metamorphism conventional geothermobarometric estimates confirm the ultrahigh temperature nature and also trace the retrograde conditions 930 970 c at p 10 kbar al in opx 900 1000 c perthite 930 990 c grt opx and 910 940 c sapphirine spinel electron microprobe dating of monazites in textural association with the uht assemblages yield a sharply defined isochron age of 1917 48 ma which correlates with the 1927 11 ma obtained in a previous study from monazites in the surrounding khondalites carrying spinel quartz assemblage an evaluation of the assemblages and textures using appropriate petrogenetic grids indicate that following peak ultrahigh temperature conditions the rocks underwent initial isobaric cooling and subsequent isothermal decompression and we interpret these trajectories to be part of an overall anti clockwise p t evolution the study area located within the northern margin of the north china craton defines a collisional orogenic belt where continental collision and deep subduction was possibly followed by extensional collapse of the orogen evidence for the extensional phase is provided by the several mafic magmatic intrusives of paleoproterozoic age occurring in the region which suggest a possible link between the thermal anomaly associated with extreme crustal metamorphism in this region with mantle derived magmas the uht metamorphism in north china craton coincided with the assembly of the paleoproterozoic supercontinent columbia

geochronology and geochemistry of igneous rocks from the kongling terrane implications for mesoarchean to paleoproterozoic crustal evolution of the yangtze block abstract the kongling terrane is a high grade metamorphic complex exposed in the northern part of the yangtze block it mainly consists of ttg gneisses amphibolites migmatites and metasedimentary rocks the amphibolites occur as enclaves or layers in the ttg gneisses and both the amphibolites and the ttg gneisses are intruded by granitic and diabasic dykes u pb ages of zircons from the amphibolite migmatite granite and diabase are determined by la icp ms igneous zircons from an amphibolite have an upper intercept age of 2945 13 ma mswd 1 2 while metamorphic zircons yield an upper intercept age of 2870 13 ma mswd 0 9 igneous zircons from a migmatite and a granite have weighted average 207pb 206pb age and upper intercept age of 1987 5 ma mswd 1 7 and 1985 6 ma mswd 1 3 respectively igneous zircons from a diabase dyke yield an upper intercept age of 1783 23 ma mswd 0 86 the protoliths of the amphibolites are tholeiitic basalts and exhibit slightly depleted to variably enriched lree patterns with moderate enrichment of rb and ba and depletion in nb and zr similar to oceanic island arc volcanics they have high cr co ni mgo and feot content with negative nd t values indicating that the tholeiitic basalts resulted from high degree batch melting of enriched mantle wedge the granites are strongly peraluminous with a cnk 1 1 and they have relatively low hree and y and negative nd t values detailed elemental and isotopic data suggest that they formed by partial melting of recycled products of the ttg gneisses amphibolites and older crustal material in a continental collisional setting the diabases are characterized by relatively high al2o3 feot and tio2 contents and low zr ba ratios their high initial 87sr 86sr ratios and negative nd t values indicate that they were derived from enriched lithospheric mantle in extensional setting therefore the kongling terrane occurred as an oceanic island arc at ca 2 95 ga and experienced earliest metamorphism at ca 2 87 ga which probably contributed to the formation of the high grade metamorphic terrane this terrane experienced a strong collisional event at 2 0 ga which may have led to cratonization over all of the yangtze block and also experienced lithospheric extension during 1 85 1 78 ga the global 2 0 ga paleoproterozoic collisional events were related to the assembly of supercontinent columbia

trace elements as source indicators in cratonic sediments a case study from the early proterozoic libby creek group southeastern wyoming to understand how grain size and sorting effect trace element distributions in sediments we compare the compositions of closely associated quartzites pelites and glacial diamictites from the 2 ga libby creek group in se wyoming we found similar ree distributions lree enriched negative eu anomalies and that most compositional differences can be explained by variable quartz dilution trace element distributions from mineral separates in a fuchsite quartzite show that fuchsite contains most of the th u ree sc co and ni and controls the whole rock ree distributions zircon contains most of the zr and hf but 5 of the hree in the pelites and 20 in the quartzites other than zr and hf most trace elements in libby creek sediments are chiefly in micas and were probably in clays in the original sediments increased eu anomalies in upper libby creek sediments signal a sudden increase in eu depleted granitoids in sediment sources which reflects late tectonic uplift mixing models favor granite ba

shrimp u pb zircon geochronology of palaeoproterozoic metasedimentary rocks in the north china craton evidence for a major late palaeoproterozoic tectonothermal event abstract although metasedimentary successions are widely distributed across the north china craton those of palaeoproterozoic age are restricted to three orogenic belts namely the trans north china orogen the khondalite belt and the jiao liao ji belt prior to this work some of those successions were considered to be archaean in age the palaeoproterozoic metasedimentary rocks contain detrital igneous zircon grains with ages ranging from 3 0 to 2 1 ga with the majority recording an age between 2 3 and 2 0 ga this latter group define a series of magmatic events that occurred between formation of the archaean basement and deposition of the metasedimentary rock protoliths the metasedimentary rocks occur as two associations older volcano sedimentary units that formed between 2 37 and 2 0 ma and younger sedimentary units that formed mainly between 2 0 and 1 88 ga all these rock associations were then subjected to metamorphism during the late palaeoproterozoic 1 88 and 1 85 ga tectonothermal event named the luliang movement in early chinese literature which was a continent continent collision that led to the amalgamation of the north china craton

geochemistry of archean shales from the witwatersrand supergroup south africa source area weathering and provenance with a few exceptions shales from the archean witwatersrand supergroup 2800 ma in south africa are depleted in na ca lile ree and hfse compared to phanerozoic shales cr co and ni are enriched in all witwatersrand shales and fe and mg are high in shales from the west rand groups wrg and lower central rand group crg shales from the crg and uppermost wrg are enriched in na al lile ree hfse and transition metals relative to shales from the lower wrg chondrite normalized ree patterns for all witwatersrand shales are enriched in light ree and exhibit small to moderate negative eu anomalies a positive correlation of ree and al2o3 contents in the shales suggests that ree are contained principally in clay minerals relative to shales from the crg shales from the wrg exhibit depletions of na ca and sr a feature probably reflecting intense chemical weathering of their source rocks cia indices in witwatersrand shales are variable chiefly 70 98 even within the same shale unit such variations reflect chiefly variable climatic zones or rates of tectonic uplift in source areas with perhaps some contribution from provenance and element remobilization during metamorphism compared to present day upper continental crust all but the orange grove roodepoort and k8 shales appear to have been derived from continental sources depleted in lile ree and hfse and enriched in transition metals computer mixing models based on six relatively immobile elements th hf yb la sc co and four source rocks indicate that the relative proportions of granite basalt and komatiite increased with time in sediment source areas at the expense of tonalite the contributions of basalt and komatiite appear to reach a maximum during deposition of the booysens shale and granite during deposition of the k8 shales and possibly during deposition of the orange grove shales

geochemical and nd isotopic compositions of the palaeoproterozoic metasedimentary rocks in the kongling complex nucleus of yangtze craton south china block implications for provenance and tectonic evolution

reconstructing palaeoclimate and hydrological fluctuations in the fezzan basin southern libya since 130 ka a catchment based approach abstract we propose a novel method to evaluate regional palaeoclimate that can be used to alleviate the problems caused by the discontinuous nature of palaeoenvironmental data found in deserts the technique involves processing satellite imagery and dem s to map past rivers catchments and evaluate the areas and volumes of palaeolakes this information is used to determine the new lake evaluation index lei that allows a qualitative estimate of the amount of sediment received by lakes and how long lived those lakes are lakes with considerable longevity and large sediment stores are selected for study validation is performed using image interpretation of remote sensing data ultragpr surveys and fieldwork these techniques are also used to identify and study spring deposits and fluvial landforms that provide valuable palaeoclimate information the method is applied to the fezzan basin in southern libya focusing on the wadi ash shati and wadi el agial catchments results indicate that the palaeohydrology is accurately mapped except within dune fields we analysed the sedimentology of the key deposits identified by this methodology developing a chronology using optically stimulated luminescence osl and radiocarbon dating we find evidence for relatively humid conditions during mis 5c d and e as well as during the early to middle holocene larger lakes and more extensive river systems were present during mis 5 than are found during the holocene suggestive of greater humidity the holocene humid period started at 11 ka and continued until 5 ka being interrupted by abrupt periods of aridity at 8 2 ka and 6 ka that coincide with north atlantic cooling after each of these arid events the climate was less humid than previously suggesting that they were superimposed upon an overall drying trend the termination of the holocene humid period in the sahara has received much scrutiny in recent years and sediments of palaeolake shati provide a continuous record of this we do not find evidence to support the hypothesis of either sudden or gradual aridification of the sahara at 5 ka instead we find that that aridity started to develop at 6 5 ka whereupon the lake levels oscillated until finally drying up by 5 3 ka most of the other lakes in the fezzan also dried up at 5ka we suggest that thousands of years of aridification prior to 5 ka shrunk these lakes so that additional aridity at this time led to their final desiccation because lakes are prodigious dust sources this mechanism potentially explains the rapid rise in dust flux to the atlantic at 5 ka with this final drying being the culmination of longer term aridity albeit overprinted with considerable climate variability

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

the crustal accretion history and tectonic evolution of the ne china segment of the central asian orogenic belt abstract the basement rocks in parts of ne china constitute a khondalitic sequence of sillimanite and garnet bearing gneisses hornblende plagioclase gneiss and various felsic paragneisses zircon u pb dating of garnet sillimanite gneiss samples from the erguna xing an jiamusi and khanka blocks indicates that high grade metamorphism occurred at 500 ma evidence from detrital zircons in paleozoic sediments from the songliao block also indicates the former presence of a 500 ma component this uniformity of u pb ages across all crustal blocks in ne china establishes a 1300 km long late pan african khondalite belt which we have named the ne china khondalite belt this indicates the blocks of ne china were amalgamated prior to 500 ma contrary to current belief one scenario is that this amalgamated terrane had a tectonic affinity to the siberia craton once forming part of the late pan african 500 ma sayang baikal orogenic belt extensively developed around the southern margin of the siberia craton this belt was the result of collision between currently unidentified terranes with the southeastern angara anabar province at about 500 ma where the rocks were deformed and metamorphosed to granulite facies it appears likely that at sometime after 450 ma the combined ne china blocks rifted away from siberia and moved southward to form what is now ne china the combined block collided with the north china craton along the solonker xar moron changchun suture zone at 230 ma rather than in the end permian as previously thought local rifting at the eastern extremity of the developing central asian orogenic belt caob resulted in the splitting away of the jiamusi khanka bureya blocks however this was only transient and sometime between 210 and 180 ma these were re united with the caob by the onset of pacific plate subduction which has dominated the tectonic evolution of the region since that time

u pb zircon ages constrain the architecture of the ultrahigh pressure qinling dabie orogen china new shrimp and tims zircon ages 40ar 39ar ages and eclogite locations contribute significantly to our understanding of the ultrahigh pressure dabie shan 1 the geographic extent of the yangtze craton that was subducted to ultrahigh pressure extends to the northern edge of the dabie shan 2 the northern half of the dabie shan is a magmatic complex intruded over a 10 myr interval between 137 and 126 ma that accommodated 100 n s stretching of the pre existing collisional architecture 3 granitic orthogneisses and enclosing ultrahigh pressure paragneisses have indistinguishable zircon populations the population of triassic zircon ages ranges from 219 to 245 ma leading us to question the prevailing assumption that 219 ma zircons formed at ultrahigh pressure and to propose instead that they reflect late retrogression at crustal pressures following the bulk of exhumation

sources and evolution of arc magmas inferred from coupled o and hf isotope systematics of plutonic zircons from the cretaceous separation point suite new zealand abstract coupled o and hf isotopic compositions of zircons from early cretaceous 113 124 ma granitoids of the separation point suite sps new zealand obtained by cathodoluminescence imaging guided micro beam methods sims la icpms are used as a record of evolving magma compositions in a prominent mesozoic arc system eight representative sps samples from individual plutons in the nelson and fiordland regions yield magmatic zircons with initial hf isotope ratios expressed in e hf ranging from 4 to 11 nelson and 5 to 12 fiordland respectively initial hf isotope ratios of zircons are extremely heterogeneous within individual samples with the vast majority of values distinctly less radiogenic than depleted mantle at 120 ma e hf 16 o isotope ratios are likewise variable with 18 o zircon smow values of 2 8 nelson and 0 7 fiordland the within rock variability in both zircon hf and o isotope ratios is testimony to open system processes that operated during magma evolution and zircon crystallisation average 18 o zircon for cores and rims allow constraints to be placed on the o isotopic composition of magmas from which zircon precipitated 18 o magma 4 8 elevated 18 o magma 6 5 require involvement of 18 o enriched supracrustal material weathered continental crust or low t seawater hydrothermally altered oceanic crust while 18 o magma 18 o depleted crustal component whole rock sr isotope nb ta and nd pb systematics are inconsistent with 18 o depleted slab melts 18 o 0 6 as a source component for sps magmas instead low 18 o values suggest incorporation of high t meteoric hydrothermally altered country rocks similar to those of the largs terrane presently exposed in northern fiordland in diagrams of sio 2 versus inferred 18 o magma the most primitive sps samples from the nelson and fiordland regions plot close to the expected composition for primitive arc magmas more evolved granitoids however show strongly divergent trends of o isotope composition as a function of sio 2 suggestive of assimilation coupled to fractional crystallisation afc in contrasting crustal environments emplacement level contamination by local crust is supported by age distributions of inherited zircons which indicate a predominance of palaeozoic and mesozoic zircons in nelson and fiordland granitoids respectively

geochemical discrimination of clastic sedimentary rock sources abstract factors controlling the geochemistry of a clastic sedimentary rock can include 1 composition of source terrain 2 chemical weathering 3 hydraulic sorting 4 diagenesis 5 metamorphism and 6 hydrothermal alteration a linear solution inferring source terrain composition from geochemistry of the sediment is impossible in this multivariate system as several unknowns will commonly be present the use of graphical analysis of element pairs circumvents the problem chemically immobile elements will maintain invariant ratios during rock mass change caused by either addition or depletion of mobile elements this results in chemically immobile element scattergrams exhibiting linear trends along radians extending from the origin if the major mineral phases of the immobile elements have behaved in a hydrodynamically similar manner as chemically mobile element plots will produce a scatter of points this relationship can be used to test chemical immobility and similarity in hydrodynamic sorting history the constraint on analysis is that the source area must be compositionally uniform or the sediment well mixed prior to delivery to the basin a second technique using sio2 plots has also been developed to investigate element mobility and hydrodynamic behaviour of the mineral phases containing the elements sio2 immobile element plots result in a linear arrangement of points extending towards either 0 or 100 sio2 the 0 intercept position occurs for elements with major mineral phases concentrated in sand the 100 intercept for those concentrated in clays plotting chemically mobile elements produces different patterns and this can be used to gain information on alteration and sorting history elemental ratios for chemically immobile elements with similar hydrodynamic behaviour will be the same as those for the weighted average composition of the source material this provides a powerful tool for deducing source terrain from sediment geochemistry techniques outlined above were tested on archaean metasandstones from superior province canada immobile element ratio diagrams for nb al ti and zr al ti indicate that a calc alkaline extrusive intrusive suite lying to the north of the study area was the source and not five other volcanic suites in the region this conclusion agrees with previous clast lithology studies and accentuates the applicability of the geochemical techniques

geochemical signature of provenance in sand size material in soils and stream sediments near the tobacco root batholith montana u s a abstract trace element geochemistry of sandstones are being used to determine provenance we have conducted preliminary and limited experiments to determine to what extent daughter sands retain the geochemical signature of parent rocks six sets of first order stream sediments soils from adjacent slopes and a variety of parent rocks were collected from southwestern montana u s a sampling in a low relief area ensured that climate and residence time of soils on slopes could be eliminated as variables sand size fractions of stream sediments and soils and the corresponding parent rocks granodiorite quartz monzonite granite gneiss biotite tonalite gneiss and amphibolite were analyzed for most major elements and selected trace elements petrologic modal analysis of the parent rocks and the 0 25 0 50 mm fraction of each sand was done to monitor major mineralogic control if any on chemical compositions of the samples our data show that the abundances of the si and al in sediments do not discriminate provenance abundances of ca mg fe and ti may broadly distinguish between sands derived from metamorphic and igneous source rocks at least in the area studied differences in abundances of the ba and th and the ratio of la lu between granitic tonalitic and amphibolitic parent rocks are preserved in the daughter sediments that we studied however the size of the eu anomaly in the ree patterns of different daughter sediments is not diagnostic of parent rocks abundances of co and sc distinguish between sediments derived from felsic and mafic rocks a better provenance discrimination is obtained if the ratios la sc th sc la co ba sc and ba co are used petrologic modal data show that mineral contents and chemical compositions of parent rocks are compatible with each other the chemical composition of the sands may be roughly correlated to the petrological modal data but the abundances of some minor and trace elements of sediments cannot be inferred from modal mineralogy this is expected because these elements may concentrate in accessory minerals and or may weather out into aqueous or clay mineral fractions it is also compatible with conclusions of previous studies that some of these elements do not reside in sand size fractions of siliciclastic sediments

the controls on the major and trace element evolution of shales siltstones and sandstones of ordovician to tertiary age in the wet mountains region colorado u s a a vertical section of shales siltstones and sandstones from ordovician to eocene age in a limited geographic area east of the wet mountains and sangre de cristo mountains in colorado have been analyzed for major elements and a variety of trace element concentrations including the ree in addition the petrography of the sandstones has been determined the quartz rich arenites contain considerably lower concentrations of most elements relative to coexisting shales or siltstones at the same outcrop the arkosic sandstones contain similar to lower concentrations of most elements compared to coexisting shales or siltstones in the same area accordingly the average concentrations of al2o3 fe2o3 mgo tio2 loi rb th co sc cr cs nb y and ree are significantly lower in all sandstones relative to all shales and siltstones the exceptions are sio2 na2o and ba concentrations and the eu eu lasc and thsc ratios as they are higher in the sandstones than the shales and siltstones there is no significant difference in the mno cao k2o and sr concentrations or the sollaco thco lani crth and lalucn ratios of the average sandstones relative to the shales and siltstones many of these differences may be related to the higher quartz and feldspar and lower clay mineral amounts in the sandstones than in the shales and siltstones for example average lasc thsc eueu and lalucn ratios of th arkosic sandstones tend to be higher than the coexisting shales and siltstones due to enrichment of the arkoses in feldspar relative to the other minerals e g eueu 0 82 0 19 in average arkoses in the trinidad vermejo raton poison canyon and cuchara formations eueu 0 63 0 19 in average shales and siltstones in the same formations in addition the elemental concentrations and ratios are more variable for most elements in the sandstones than the shales and siltstones this suggests that the shales are rapidly homogenized near the source the elemental fractionation in the arkosic sandstones due to enrichment of feldspar relative to other minerals suggests that they are poorer indicators of provenance that the associated shales whereas the more homogeneous elemental distributions in the shales and siltstones suggest that they may be better indicators of provenance than the sandstones nevertheless the elemental ratios that are most similar in the sandstones and in the shales and siltstones are consistent with their derivation from similar average intermediate to silicic source rocks

rare earth element geochemistry of australian paleozoic graywackes and mudrocks provenance and tectonic control abstract in the paleozoic graywackes of eastern australia there is an increase in the total abundance of rare earth elements ree a light to heavy ree ratio and a decrease in the chondrite normalized eu anomaly with the increase in sio2 al2o3 and k2o na2o ratios this is due to the change in the dominant source rocks from andesite to dacite to granite gneiss and sedimentary rocks similarly an increase in total ree and a decrease in eu anomaly is also seen in the associated mudrocks with the increase in total clay content this correlation in paleozoic sedimentary rocks suggests that the ree characteristics of terrigenous sedimentary rocks reflect the depositional tectonic setting of the basin the oceanic island arc type graywackes are characterised by their lower total ree abundance only slight enrichment of lree over hree and the absence of a negative eu anomaly on chondrite normalised plots the continental island arc type graywackes are discriminated by their higher ree abundance and la yb ratio the presence of a small negative eu anomaly on the chondrite normalised plots and the significant enrichment of eu compared to paas post archean average australian shale the sedimentary rocks deposited on andean type active continental margins passive margins platform and cratonic basins are all characterised by the high enrichment of lree over hree and the presence of a pronounced negative eu anomaly on chondrite normalised plots and can not be discriminated from each other by ree patterns alone

contrasting geochemical and sm nd isotopic compositions of archean metasediments from the kongling high grade terrain of the yangtze craton evidence for cratonic evolution and redistribution of ree during crustal anatexis abstract twenty three clastic metasediments from the kongling high grade terrain of the yangtze craton south china were analyzed for major trace and rare earth elements and sm nd isotopic ratios associated dioritic tonalitic trondhjemitic dtt and granitic gneisses as well as amphibolites were also analyzed in order to constrain provenance the results show that the clastic metasediments can be classified into 3 distinct groups in terms of mineralogical geochemical and sm nd isotopic compositions group a is characterized by having no to slight negative eu anomalies eu eu 0 82 1 07 being high in cr 191 396 ppm and ni 68 137 ppm and low in th 3 3 7 8 ppm and ree ree 99 156 ppm these characteristics are similar to those of metasediments from archean greenstone belts in addition the group a metasediments have the value of the chemical index of alteration ciw close to felsic gneisses their sm nd isotopic ree and trace element compositions can be interpreted by mixtures of the dtt gneisses and amphibolites dating of detrital zircons from 2 group a samples by shrimp reveals a major concordant age group of 2 87 3 0 ga which is identical to the age of the trondhjemitic gneiss these results strongly suggest that group a was principally the first cycle erosion product of the local kongling dtt gneiss and amphibolite moreover the higher than amphibolite cr content and slight eu depletion exhibited by some samples from this group infer that ultramafic rocks like komatiite and granite of probably 3 0 3 3 ga in age also played a role group b is characterized by the presence of graphite and shows a more evolved composition similar to post archean shales with a prominent negative eu anomaly eu eu 0 48 0 77 and high ciw on paired cr th vs la co and co th plots group b samples conform to a two end member mixing line of the kongling granitic gneiss and amphibolite however data on nd model age and ciw suggest that the granite component should be younger than the sampled granitic gneiss and derived from a distal source both groups a and b exhibit a clear positive correlation between ciw and tdm and a negative one between ciw and eu eu these correlations point to the crustal evolution of the yangtze craton towards coupled increasing ciw and eu depletion with decreasing age this in turn reflects the change of granitoid magmatism from local na rich dioritic tonalitic trondhjemitic rocks to widespread k feldspar granite the change led to the intracrustal differentiation stabilization and growth of the craton group c is restite and contains abundant sillimanite and garnet and unusually high ilmenite 7 11vol which can be seen to be dehydration melting products of biotite under the microscope this group shows extremely varied ree distributions from lree enriched to depleted and from negative to strong positive eu eu 1 63 eu anomalies compared to groups a and b group c is severely depleted in na2o k2o lree rb and ba whereas tio2 co v sc and hree and y are considerably enriched this is accompanied by anomalous high sm nd 0 21 0 28 147sm 144nd 0 1361 0 1738 and 143nd 144nd 0 511589 0 511958 ratios tdm correlates clearly with sm nd ratio and 2 out of 3 samples give significantly older to unrealistic tdm 3 9 4 9 ga the results document redistribution of ree and an open behavior of the sm nd isotope system during the biotite dehydration melting of metasediments

lewisian gneiss geochemistry and archaean crustal development models abstract the geochemistry of lewisian amphibolite facies gneisses from northwest scotland is described with particular reference to the rare earth elements ree and compared with the geochemistry of lewisian granulite facies gneisses the results show that there are no significant differences between laxfordian amphibolite facies and scourian granulite facies gneisses in terms of ree and other immobile trace elements at equivalent silica levels although the mobile radioactive heat producing elements k rb th u are significantly lower in the granulites in both types the basic gneisses have moderately fractionated ree patterns while the intermediate and acid gneisses have strongly fractionated ree patterns with low heavy ree abundances and decreasing levels of total ree with increasing sio 2 the most silicic gneisses develop large positive europium anomalies these gross chemical similarities between gneisses from intermediate amphibolite facies and lower granulite facies crustal levels constrain models for the evolution of the archaean crust the depletion of k rb cs th and u in granulites but not other incompatible trace elements cannot be explained by magmatic processes the positive eu anomaly in the more siliceous gneisses of both facies is a function of the primary processes of crustal generation and not secondary processes such as intracrustal melting or fractional crystallisation fractionation of radioactive heat producing elements from other trace elements is a result of granulite facies metamorphism with these elements being removed by an active fluid phase the apparent lack of partial melting in lower crustal granulites suggests a model for archaean crustal growth largely through underplating by primary tonalitic magmas