ree th and u behaviour during hydrothermal and supergene processes in a granitic environment the two mica granites which host the two main uranium deposits from the northwestern massif central france margnac fanay and le bernardan deposits were hydrothermally altered both before and during the deposition of the primary u mineralization both altered rocks and mineralizations were then subjected to supergene processes we have analyzed the rare earth elements ree th and u in fresh and altered mineralized and barren whole rocks and in the pitchblendes to study the behaviour of these elements during hydrothermal and supergene processes in a granitic environment when fluids are aqueous with a low salt content mainly chloride then irrespective of temperature 400 450 c for feldspar episyenitization 350 c for mica episyenitization and 100 150 c for the quartz coffinite montmorillonite adularia stage the ree patterns and parameters the hree lree fractionation the th concentration and the th ce ratio are not modified this indicates that monazite which controls these elements in the two mica granites remains stable under such conditions in contrast when ligands are present in the solutions co2 3 or hco 3 with the pitchblende stage at 350 c hpo2 4 or other phosphorous anions during supergene events at low temperatures ree are either leached or concentrated depending on the prevailing redox conditions and there is hree lree fractionation the ree content of the newly formed minerals pitchblende appears to be mainly controlled in such deposits by the fluid composition

the development of the central european continental crust since the early archaean based on conventional and ion microprobe dating of up to 3 84 b y old detrital zircons abstract archaean components up to 3 84 b y old have been detected by ion microprobe dating of zircon from various sediments and metasediments of the european hercynides moldanubian of northeastern bavaria and the massif central the early archaean age of 3 84 b y was obtained within the euhedral core of a detrital grain from a moldanubian paragneiss the same detrital zircon grain reveals at least three metamorphic overprints at 2 59 b y b p 1 94 b y b p and 460 m y b p and at least two cycles of mechanical abrasion during surface recycling in the early proterozoic and after the pan african cycle it is thus the crystal with the most complex geological history ever detected further archaean ages for the crystallization of primary magmatic zircons probably in the course of continental crust formation in the first cycle provenances of the two studied areas were found at 3 15 2 9 2 76 and 2 65 b y b p and in a few cases between 2 6 and 2 5 b y b p early proterozoic crust forming events between about 1 75 and 2 15 b y b p play an important role especially for the sediments and metasediments of the montagne noire at the southern rim of the massif central middle and late proterozoic ages cluster around 1 0 b y b p and 600 m y b p for all analysed samples therefore the deposition of the metasedimentary precursors took place after the pan african cycle which is in line with the rb sr whole rock systematics of central european metasediments the ages of metamorphism in the different source areas could be inferred in some cases by lower intercept ages obtained on single detrital grains the following sequence coinciding with times of magmatic events has been so far established 2 59 1 94 and 1 0 b y b p and 600 m y b p thus ion probe dating is also capable of defining secondary effects in the respective provenances which are typical for orogenic cycles the ubiquitous presence of pan african detrital zircons in european metasediments is a strong indication that the detrital material was derived from gondwana however from the presence of metamorphic units including eclogitefacies rocks which probably formed at different continental margins and at various times between about 500 m y and 330 m y ago it is probable that various gondwana derived microcontinental plates contributed to the different basin fillings the gondwana derived detritus is also supported by the observation of two periods of relative quiescence or non activity around 2 3 b y ago and especially around 1 5 b y ago which is a typical feature observed in gondwana cahen et al 1984 but not in laurasia the other possible source of the detritus the lack of zircons crystallized between 3 84 and 3 15 b y ago might have different causes thus the continental crust of the european hercynides probably developed since the early archaean and grew via many crustal accretion events to its present state

nd sr isotopic geochemical and petrographic stratigraphy and paleotectonic analysis mesozoic great valley forearc sedimentary rocks of california measurements of nd sr isotopes major and trace elements and model mineralogy were made on upper jurassic and cretaceous great valley forearc sedimentary rocks to test models for the temporal and spatial evolution of sierra nevada arc sources isotopes and major and trace elements are sensitive provenance indicators because of the large west east isotopic geochemical and age gradients in the plutonic rocks of the sierra nevada batholith and because petrographic models indicate that source areas moved east during the cretaceous isotopic and chemical variations are correlated in the forearc sandstone as nd decreases th u la nb zr hf pb rb sio2 and k2o concentrations increase and feo mgo tio2 ni and cr concentrations decrease this relation is the same as that observed in the plutonic rocks and indicates that the arc was the primary source of sediment and that the sandstone chemistry was not disturbed by sedimentary processes the nd sr relation of san joaquin valley sandstone is the same as the plutonic rocks but sacramento valley sandstone is elevated in sr because of seawater exchange weathering and diagenesis whole rock sandstone decreases in nd from 7 to 5 and increases in 87sr 86sr from 0 7045 to 0 7073 with decreasing stratigraphic age the nd sr isotopic composition is correlative with the plagioclase to feldspar ratio and indicates that source areas moved inland during the cretaceous upper cretaceous san joaquin valley shale is similar in nd to the sandstone indicating that sandstone and shale were derived from the same source and that the nd isotopic composition is independent of grain size the shale is higher in 87sr 86sr than the sandstone possibly due to concentration of biotite in the fine fraction during transport and subsequent rb loss during diagenesis nd sr isotopes were used to construct models to locate source areas parameters include lithology drainage basin geometry and erosion rate the age and isotopic compositions of the calculated igneous component of the sandstone correspond to the age and isotopic compositions of the plutonic rocks of the batholith this correspondence indicates that 1 the isotopic composition of the plutonic rocks and the coeval volcanic cover were similar 2 the volcanic front was denuded within a few million years and 3 the sediment was derived from the head of the drainage basin located at the migrating volcanic front

mineralogically mature sandstones in accretionary prisms abstract plate tectonic interpretations of sandstone composition are made in the hope that detrital framework modes of sandstone suites provide information about the tectonic setting of basins of deposition and associated provenances dickinson et al 1983 the underlying assumption that provenance tectonics are directly associated with tectonics of depositional and post depositional sedimentary settings is not however universally true as sandstones from two contemporary accretionary prism complexes nias island indonesia and barbados west indies illustrate mineralogically immature sandstones rich in feldspar and volcanic lithic fragments are expected in such tectonic settings but both nias island and barbadian sandstones are mineralogically very mature dominated by quartz in b th cases this discrepancy between inferred and actual tectonic setting has been explained by postulating that sands from a provenance petrogenetically unrelated to the arc trench system e g continental or recycled orogen sands have been introduced into the accretionary prism by sedimentary or tectonic processes sandstones which are transported sedimentologically or tectonically across the boundaries of sedimentary tectonic provinces and which therefore occur in tectonic settings petrogenetically unrelated to the tectonics of the sediment source area are important components of at least some active accretionary complexes the possibility of trans boundary sedimentary and or tectonic transport must be allowed for in making plate tectonic interpretations based on sandstone petrog aphy especially in reconstructions of ancient orogenic belts

provenance of upper precambrian lower cambrian shales in the central iberian zone spain evidence from a chemical and isotopic study geochemical and isotopic sr nd o data are presented for upper precambrian and lower cambrian shale sequences from the central iberian zone spain in order to define geochemical discriminants between them and to assess the nature of the source regions supplying these basins elemental data especially th sc ratios coupled with endt values of 2 5 suggest that the upper precambrian rocks contain a greater proportion of a much younger more mafic component than the lower cambrian sequence which has high th sc and endt of 7 3 coherent trends between elemental and o isotope data imply a homogeneous recycled source as the dominant provenance for the upper precambrian shales whereas a lack of such coherence for the lower cambrian sediments suggests a more heterogeneous provenance the sedimentological geochemical and isotopic data are consistent with the upper precambrian succession being derived ultimately from a polycyclic mixture of young pre cadomian mafic sources and older 2 ga crust in contrast the lower cambrian sequence was mainly derived from old more felsic crust which would have contributed increasingly greater proportions of material as the younger sources were progressively removed by erosion

depletion of light rare earth elements in felsic magmas contrary to simple generalizations about their behavior light rare earth elements lree do not act as incompatible elements in very felsic magmas in fact lree concentrations typically decrease often drastically during differentiation of such magmas the simplest explanation for this depletion involves the separation of minute easily overlooked quantities of an extremely lree rich accessory mineral either monazite or allanite our data indicate that felsic liquids with 50 ppm lree may be saturated in either of these accessories and that the concentration required for saturation decreases in increasingly felsic liquids this accounts for incompatible behavior of lree even at high concentrations in mafic magmas in contrast to compatible behavior at low concentrations in felsic magmas partitioning of lree into solid rather than liquid has important implications for trace element and nd isotope modeling of crustal anatexis as well as for magma differentiation

conventional and ion microprobe u pb dating of detrital zircons of the tentudia group serie negra sw spain implications for zircon systematics stratigraphy tectonics and the precambrian cambrian boundary conventional multi grain and ion microprobe dating of detrital zircons from a very low grade metagraywacke of the tentudia group upper part of the serie negra ossa morena zone sw spain reveals an uppermost vendian age for the deposition of the metagraywacke the youngest detrital zircon grain provides a maximum depositional age of about 565 ma thus these data contradict earlier middle to upper riphean ca 1350 850 ma estimates on the age of the tentudia group and favour a precambrian cambrian boundary falling into the range of 540 to 530 ma the presence of about 20 of pan african detrital zircons ranging from about 700 to 550 ma indicates the derivation from gondwana from the upper intercept ages of the fan shaped data field defined by conventionally determined zircon fractions it can be deduced that 2 1 ga old zircons as well as archean zircons existed in the provenance s of the serie negra sediments this mixing of crustal components of different ages is in line with the nd crustal residence age of 1 9 ga the latter value as well as other model ages of the iberian massif indicates unusually high amounts of ancient crust to be present in the strata this is different to other meta sediments of the european hercynides and suggests that the iberian strata of uppermost precambrian age may contain the detritus of more internal older parts of gondwana than other european strata of comparable ages geochemical data on the analysed sample and further metagraywackes of the tentudia group argue for a deposition in an arc environment such a scenario would conform with the syn to post orogenic shallow marine deposition of the studied sediments furthermore an upper time limit for the pre lower cambrian deformational history including two phases of regional deformation is given by the maximum age of deposition implying a very short time interval for deposition and deformation of the tentudia group concerning the u pb systematics of detrital zircon fractions it is probable that numerous previously published conventional multi grain zircon data on meta sedimentary rocks of the european hercynides readily can be explained by the presence of up to 20 of pan african detrital zircons and later phanerozoic lead loss during metamorphic transformation of the sedimentary protoliths moreover this implies that such metasediments originated from post pan african sedimentary precursors

siliciclastic carbonate slope apron in an immature tensional margin upper precambrian lower cambrian central iberian zone salamanca spain abstract the middle upper vendian and upper series lower cambrian of the central part of the central iberian zone of the iberian massif comprise for the most part siliciclastic sediments in the upper part of the middle series and at the base of the upper series a siliciclastic carbonate succession is predominant in the middle series the siliciclastic carbonate succession consists of limestone breccias sandstone limestone couplets and sandy limestone facies these were resedimented by debris flows low and high concentration turbidity currents and occasionally tractive flows the facies associations and the lack of well defined sequences in them suggest sedimentation on a mixed slope apron in the upper series the siliciclastic carbonate succession is composed in the east of chaotic facies conglomerates sandstones and shales corresponding to sedimentation by rockfalls slides debris flows and high concentration turbidity currents whereas in the west it is composed of conglomerates sandstones and shales that correspond to sedimentation by traction storms tides and deposition from suspension the facies associations and their sequential arrangement in the west suggest that sedimentation occurred on a prograding shelf with the development of bars and channels whereas in the east sedimentation occurred on a slope the relationship between the proposed depositional model and the previously established tectonic model ortega et al 1988 of a tensional margin suggests that the slopes were formed by faults that led to the development of horsts and grabens the faults were active during deposition of the middle and upper series the general tendency towards rising sea level observed in other parts of the world during late vendian early cambrian times shanmugam and moiola 1982 has been recorded in the study area

sedimentary rocks and crustal evolution tectonic setting and secular trends a significant change in the composition of turbidites deposited at active tectonic settings is seen at the archean post archean transition in comparison to post archean active margin turbidites archean greenstone turbidites exhibit more uniform th sc ratios but with a similar average greater hree depletion gd n yb n 2 less eu depletion eu eu mostly 0 85 and an absence of low th u ratios th u 3 these data indicate that differing mantle sources and or conditions of mantle melting existed during the archean and that intracrustally differentiated rocks older cratons or young differentiated arcs were relatively unimportant as provenance components for archean turbidites in contrast some sedimentary rocks preserved in archean platformal sequences of high grade terranes display significant negative eu anomalies similar to the majority of post archean shales indicating that the general process of cratonization including intracrustal differentiation has taken place since at least 3

the cadomian granites of mancellia northeast armorican massif of france relationship to the st malo migmatite belt petrogenesis and tectonic setting abstract the north armorican shear zone nasz divides the cadomian belt of the armorican massif of france into two major terranes the north armorican composite terrane nact and the central armorican terrane cat the nact is a pastiche of displaced blocks and terranes st brieuc terrane st malo terrane and mancellian terrane which results from the amalgamation of cadomian continental arc and basin complexes by sinistral transpression along a continental margin above a southerly dipping subduction zone in the nact the neoproterozoic brioverian succession was deformed and metamorphosed during the cadomian orogeny and intruded by syn to post tectonic plutonic complexes the st malo migmatite belt is a syn tectonic suite of anatectic migmatites derived through partial melting of the brioverian succession using the t test on whole rock geochemical data there is no evidence to suggest that a sample of st malo diatexites comes from a population with a different mean than some samples of the brioverian succession sandstones resulting homogeneous diatexites anatectic granites of the core were emplaced syn kinematically into cadomian strike slip shear zones thus the age of anatexis of 540 ma is also the date of strike slip shearing and provides a minimum age for the sinistral transpression which amalgamated the terranes of the nact the mancellian granites to the southeast of the st malo migmatites were emplaced at 540 ma and are overlain unconformably by cambrian sediments overall geochemistry and a variety of specific geochemical parameters show that the mancellian granites are similar to the diatexites and anatectic granites of the st malo migmatite belt using the t test on whole rock geochemical data there is no evidence to suggest that the sample of mancellian granites comes from a population with a different mean than the sample of st malo diatexites additionally both suites of rocks are peraluminous they have similar distributions of rb sr and ba they have k rb ratios around 225 and they plot largely within the vag field using trace element discrimination diagrams for the interpretation of tectonic setting samples of the brioverian succession sandstones the st malo migmatites and the mancellian granites all exhibit similar primordial mantle normalized element patterns preliminary results of nd and sr isotope studies reveal a similar restricted range of values for nd between 4 0 and 7 3 and sr between 3 and 42 and depleted model ages in the range 1 7 to 1 5 ga tdmur for both mancellian granites and st malo migmatites isotopic features which set these rock types apart from other cadomian granites within the nact the st malo migmatite belt and the mancellian granites are coeval at 540 ma and both developed by anatexis at intermediate crustal depths of the brioverian succession within an inverted but only moderately overthickened behindarc basin in comparison with the st malo migmatites the mancellian granites represent farther travelled products of intracrustal melting but their geochemistry still preserves the characteristic signature of the source

rare earth element mobility around the volcanogenic polymentallic massive sulfide deposit at que river tasmania australia abstract the que river volcanogenic base and precious metal deposit is located in the cambrian mt read volcanics of western tasmania the host andesites and dacites adjacent to mineralization have been hydrothermally altered during mineralization and the entire sequence has undergone devonian regional prehnite pumpellyite facies metamorphism rocks petrographically recognizable as andesites exhibit chondrite normalized ree patterns similar to modern orogenic high k andesitic rocks with ce yb n ratios ranging from 6 4 to 8 6 dacites are more fractionated with ce yb n ranging from 10 6 to 16 0 like the andesites the dacites are characterized by negative eu anomalies eu eu 0 73 0 85 except for a more extreme eu anomaly in one sample eu eu 0 57 polymict volcaniclastic rocks have patterns very similar to those of the andesites the chondrite normalized ree patterns for the hydrothermally altered volcanics fall into three groups that can also be distinguished petrographically a single chloriterich sample has a substantial eu anomaly and shows less relative depletion in the middle ree than do either the andesites or the dacites highly silicified samples are all characterized by large negative eu anomalies eu eu 0 37 0 46 and many are relatively unfractionated with ce yb n ratios ranging from 3 5 to 7 7 a third group of samples characterized by the development of phengitic mica and carbonate show ree patterns similar to the andesites although their eu anomalies are generally smaller a sample of massive zn 1bpb ore has very low ree abundances showing light ree enrichment and a small negative eu anomaly eu eu 0 82 massive pyrite has a similar pattern except for higher overall abundances and a small positive eu anomaly eu eu 1 10 except for the eu anomalies the andesites and dacites show no evidence for ree mobility eu anomalies in the andesites are probably due to alteration of phenocrystic plagioclase and subsequent removal of divalent eu substantial ree mobility has occurred in the hydrothermally altered volcanic rocks the degree of mobility correlating with alteration style and intensity eu has been leached from both former plagioclase phenocrysts and the groundmass some of the eu leached from zones of the most intense alteration may have been redeposited in lower temperature more distal alteration zones

sr nd isotopic constraints on the petrogenesis of the central bohemian pluton czech republic the sr nd isotopic data for selected granitoids of the central bohemian pluton show a broad negative correlation with the total range of 87sr 86sr 330 0 7051 0 7129 and nd330 0 2 to 8 9 the older intrusions have more depleted sr nd compositions and calc alkaline geochemistry sazava suite whereas the younger intrusions shift towards k rich calc alkaline blatna suite and shoshonitic rocks icany and certovo b emeno suites with more evolved isotopic signatures the distribution of the data is interpreted as reflecting a diversity of sources and processes rather than a single progressive crustal contamination trend the sazava suite could have originated by partial melting of metabasites or of a mantle source with an isotopic composition close to bulk earth or by hybridization of crustally derived tonalitic and mantle derived magmas variation within the blatna suite is modelled by mixing between a moderately enriched 87sr 86sr 330 0 708 nd330 3 mantle component with either an isotopically evolved metasedimentary component or with more evolved magmas of the suite the icany suite was most probably produced by partial melting of peraluminous lithologies possibly of the adjacent moldanubian unit the certovo b emeno suite evolved from strongly enriched mantle derived magmas 87sr 86sr 330 0 7128 end330 7 either through closed system fractional crystallization or interaction with magma corresponding to leucogranites of the central bohemian pluton

experimental geochemical mineralogical and o isotope constraints on the late magmatic history of the fichtelgebirge granites germany mineralogical experimental geochemical and stable isotope data give evidence for an aqueous late stage fluid which develops increasingly from the less to the more highly evolved granites of the fichtelgebirge g1 g4 in less evolved granites particularly g1 only minor chloritization and sericitization minor hydration and corrosion of zircons low leachable fractions of sr and zr the nearly chondritic ratios of zr hf and y ho and rare earth element ree patterns lacking the tetrad effect provide evidence of a less differentiated granitic melt system poor in complexing agents and water with insignificant late magmatic fluid rock interaction the subsequent low temperature alteration which is suggested by oxygen isotope composition of quartz and biotite did not affect the whole rock chemical composition in the highly evolved granites particularly g4 albitization sericitization and fluoritization ubiquitous hydration and corrosion of zircons high leachable fractions of sr and zr zr hf and y ho ratios very different from the chondritic ratios and ree patterns showing a marked tetrad effect point to the presence of a highly specialized fluid system rich in water and complexing agents such as fluorine leading to a marked magmatic hydrothermal alteration the oxygen isotopes also indicate alteration by high temperature fluids which were likely exsolved during the final stage of crystallization

relationship of temperature and light ring formation at subarctic treeline and implications for climate reconstruction abstract during the past 8 centuries light rings lrs have occasionally formed in black spruce picea mariana at treeline near bush lake northern quebec l filion s payette l gauthier and y boutin 1986 quaternary research 26 272 279 a delwaide l filion and s fayette 1991 canadian journal of forest research 21 1828 1832 new analyses of climate data compiled during the period of overlapping tree ring and instrumental records show that years of lr formation at bush lake have unusually cool may june august and september temperatures the analyses also show that august september temperatures strongly correlate with may july temperatures thus late spring and entire growing season temperatures influence lr formation at subarctic treeline lrs formed in at least 5 of the trees at bush lake when may september mean temperatures at inukjuak fell below 4 2 c and august september mean temperatures fell below 6 7 c these threshold temperature lr relationships can be used to infer limiting summer temperatures during the period preceding instrumental records for example the lr record suggests that may september temperatures at northern quebec treeline dropped below 4 2 c in a d 1601 after a major volcanic eruption of unknown source visual assessments of lr occurrence provide a new approach for extracting quantitative paleoclimatic information from tree rings

geochemistry and nd isotope signature of the collserola range palaeozoic succesion ne iberia gondwana heritage and pre mesozoic geodynamic evolution the collserola range includes a representative stratigraphic succession of the palaeozoic of the central part of the catalan coastal ranges ranging from cambro ordovician to carboniferous times in this paper we present an up to date review of the stratigraphy and structure of the palaeozoic of the collserola range and provide geochemical and sm nd isotope data to constrain the pre mesozoic crustal evolution of this sector of the variscan belt geochemical compositions indicate that the palaeozoic siliciclastic rocks of the collserola range were fed by a relatively mature heterogeneous source of sediment comprising quartz rich sediments to intermediate igneous rocks the siliciclastic rocks of the collserola range show great geochemical affinity with the turbidites of passive margins the sm nd signature of the siliciclastic rocks is compatible with those of the palaeozoic and late proterozoic fine grained siliciclastic rocks of the neighbouring terrains of sw europe there is a small decrease of the end t with decreasing age of sedimentation from the cambro ordovician to the carboniferous suggesting an increase of the amount of more juvenile material the presence of small volumes of alkaline basaltic rocks provides evidence for the input of juvenile material in the early palaeozoic basin and suggests that an extensional tectonic regime prevailed during the cambro ordovician sedimentation from a geodynamic point of view the overall analysis of the data implies that the palaeozoic rocks of the catalan coastal ranges were part of the northern gondwana passive margin before the closure of the rheic ocean and the subsequent variscan orogeny

thermal history of the southwestern meguma zone nova scotia from an 40ar 39ar and fission track dating study of intrusive rocks two geologically distinct regions within the meguma terrane have been studied in detail and are shown to have contrasting thermal histories this conclusion is based on 31 new 40ar 39ar age spectra on micas k feldspars and hornblendes from several of the plutons in southern nova scotia which are satellites to the much larger south mountain batholith smb in addition we report four k feldspar age spectra from a locality in the northeastern part of the smb and seven fission track ages from both the southern and northern areas the complex age spectrum of hornblende from a mafic phase associated with the bamngton passage pluton suggests a minimum intrusive age of 385 ma a result consistent with geologic evidence that this pluton represents an early less evolved magmatic pulse later intrusive activity appears to have been coeval with the intrusion of the smb at ca 370 ma ago in the southern region argon clocks in feldspars were completely reset and mica clocks variably reset by a later thermal event the cumulative geochronologic and geologic evidence constrains this event to 300 320 ma ago in the smb this alleghanianl hercynian thermal disturbance is much less pronounced and appears to be localized to small areas that are often associated with economic mineralization k feldspars from the southern plutons record an episode of argon loss 220 230 ma ago which is less evident in the smb to the north upper triassic dike injection in the southern region associated with the initial rifting phase of the canadian atlantic margin accompanied this milder thermal pulse apatites in the two regions record a mean fission track age of ca 180 ma which we attribute to the final cooling of the terrane below about 100 c the timing of this event coincides with regional uplift recorded in sedimentary sequences along much of the maritime continental shelf deux kgions gtologiques distinctes inttgkes au terrane de meguma ont ctt ctudites en dctai1 et leurs histoires thermales

evolution of the western european continental crust implications from nd and pb isotopes in iberian sediments abstract this paper presents smz sbnd nd and geochemical data on fine grained sediments of the iberian massif spain together with new and published uz sbnd pb results of selected sedimentary rocks profiles from two major zones cantabrian and central iberian zone have been investigated both profiles exhibit almost complete stratigraphic successions from uppermost precambrian to lower carboniferous paleozoic shallow depth platform sediments are essentially unmetamorphosed the precambrian syn orogenic succession underwent a metamorphic overprint up to biotite zone 147 sm 144 nd ratios range from 0 0988 to 0 1457 and nd contents from 6 to 112 ppm nd today values vary from 16 5 to 7 6 pb contents from 1 7 to 97 ppm samples with high nt t 3 are found to be low in 2 330ma t dm are 1 92 ga cantabrian zone and 1 96 ga central iberian zone as juvenile cadomian crust is present in the iberian massif the oldest components have to be significantly older than 2 ga within the european variscides comparably old t dm were so far only described from the armorican massif france an active margin of the gondwana continent is the most probable provenance of the uppermost precambrian strata as indicated by their cadomian age syn orogenic facies and juvenile components precambrian as well as samples from the precambrian cambrian boundary gave nt t values 4 8 significantly higher than average paleozoic rocks contributions of juvenile cadomian crust to the syn orogenic sediments must be in the order of 30 50 to fit the nd and pb data there is no evidence for any addition of mafic material according to major or trace elements or to sm nd ratios lower cambrian samples are already below 7 3 in nd t thus compared to the total pre existing crust contribution of juvenile crust was very small nd t values of almost all samples ranging in stratigraphic age from 515 to 410 ma are strikingly negative 12 9 to 10 1 and thus indicate the absence of newly differentiated continental crust in the provenance s only the tremadocian of the southern central iberian zone gave high nt t values 4 0 to 1 0 again there is no evidence for addition of mafic material to the strata as precambrian and tremadocian nt t peaks are separated by the lowermost cambrian of nt t 7 juvenile crust may have been added related to the pre ordovician unconformity sardic phase during the middle paleozoic 410 330 ma nt t values increase from 12 to 7 indicating a continuous contribution of juvenile continental crust of 20 as major terranes of the iberian massif were not amalgamated until late paleozoic it can be assumed that the respective juvenile crust was formed within the regime of one or several small subduction zones nd isotope data of this study compared with published results of brittany france suggest that the medio north armoricancentro iberian domain persisted from uppermost precambrian to the variscan

archean protoliths within early proterozoic granulitic crust of the west european hercynian belt possible relics of the west african craton granulites from the bay of biscay area have been studied by using u pb and sm nd methods results on four granulites suggest two major events of crustal growth and high grade metamorphism the first is archean 2 7 ga and the second is early proterozoic 1 9 ga in the hercynian belt the oldest basement remnants known so far are about 2 0 ga and are located in the northern armorican massif the 2 7 ga orthogneiss protolith age from the bay of biscay is the first direct evidence of archean crust involved in the hercynian belt major events at 2 7 1 8 and 0 6 ga in the hercynian belt suggest that european precambrian microplate s were part of the west african craton where the same sequence of events is observed

the oxygen isotopic composition of granulites and retrogressed granulites from the limpopo belt as a monitor of fluid rock interaction abstract from the southern marginal zone of the limpopo belt three rock systems cordierite bearing metapelites mafic rocks and ultramafic rocks are studied by whole rock oxygen isotope analysis in order to decide wether the observed variation in the o isotopic composition of the metapelites is due to granulite facies fluid rock interactions or due to earlier processes a discrimination index pelite index pi is proposed in combination with the whole rock oxygen isotopic composition this index enables one to put some constraints on the origin of the precursor rocks in the case of the limpopo metapelites it is concluded that the cordierite anthophyllite bearing metapelites are only in part true metasediments a metasomatic alteration of mafic precursors in an ocean crust environment could be responsible for both low pi indices and high with respect to unaltered mantle material 18 o values fluid rock interactions in this environment are also thought to be responsible for the observed chemical and o isotopic variation of mafic and ultramafic rocks the data do not support significant large scale co 2 infiltration during granulite facies metamorphism the retrograde regionally extended anthophyllite formation in the southern marginal zone of the limpopo belt is certainly triggered by some fluid infiltration model calculations show that the amount of fluids necessary for this readjustment is too small to have an imprint on the whole rock oxygen isotope composition

geochemistry of pelitic and psammopelitic precambrian metasediments from southwestern sri lanka implications for two contrasting source terrains and tectonic settings most of the pelitic and psammopelitic metasediments of southwestern sri lanka are compositionally transitional between shales and greywackes and are of two isotopically distinct types metasediments of the northern part have nd model ages of 1 5 ga and belong to the relatively younger nd model age province of wanni complex wc model ages of two southerly located samples are 2 8 ga being compatible with those of the highland complex hc in accordance with mostly mesoproterozoic to late archaean crustal residence ages cr ni la th and ree data also suggest that the sources of these metasediments are plagioclase fractionated post archaean upper crustal material crustal differentiation of source terrains corresponding to the hc and the wc probably occurred at distinctly different time intervals significant differences exist between the major and trace element chemistry of the metapelites from the wc north and the hc south suggesting derivation from two different source terrains metasediments of the south are slightlymmore siliceous low in sc and v and highly enriched in lree 220 ppm their sources have been chemically evolved felsic igneous rocks and or recycled sediments relatively high v sc feo mgo tio2 and slightly low sio2 in the rocks of the wc indicate contribution of more basic sources cia chemical index of alteration estimates and comparative alkali alkaline earth element patterns suggest relatively fresh source material the o isotope data indicate that the pre metamorphic isotope signatures are preserved and the clay component of the original sediments mainly consisted of illite typifying continental weathering conditions sediments of the south hc were probably deposited in a passive continental margin continental rift environment while those of the northern part wc were probably formed at an andean type active continental margin the two units were tectonically juxtaposed prior to pan african granulite metamorphism

iberian late variscan granitoids some considerations on crustal sources and the significance of mantle extraction ages a suite of post tectonic granitoids mostly peraluminous broadly i type granodiorites and monzogranites and mafic rocks from nwiberia with crystallization ages between ca 309 and 290 ma has been investigated for sm nd isotopes and inherited zircon content in order to constrain the nature of their source rocks end values at 300 ma vary from 0 2 to 5 9 and tdm values range from 1 01 to 1 58 ga inherited xenocrystic zircons yielded ages ranging from 458 to 676 ma with 90 of data between 490 and 646 ma corresponding to neoproterozoic mostly ediacaran cambrian andordovician ages only three highlydiscordant analyses yielded ages older than 650 ma based on the data reported herein and relevant data fromthe literaturewe contend that post tectonic granitoids of the iberian variscan belt with exception of the scarce anatectic s type granitoids were derived mostly from metaigneous lower crustal sources which in turn were ultimately derived from a subcontinental lithospheric mantle enriched between ca 0 9 and 1 1 ga i type granitoids and mantle derived mafic rocks both underwent varying degrees of contamination by ametasedimentary lower crust depleted in pre 650 ma zircon through previousmelting episodes with a time integrated sm nd evolution different to that of the metaigneous lower crust participation of this metasedimentary crust in the genesis of these granitoids may account for nd isotopic variability and nd model ages well in excess of 1 2 ga

k ar and 40ar 39ar geochronology of granitoid rocks from southern nova scotia its bearing on the geological evolution of the meguma zone of the appalachians k ar and or 40ar 39ar apparent ages are reported for 28 samples of biotite and muscovite from nova scotia s south mountain batholith and associated northern satellite stocks in addition 14 mica samples from the southern satellite stocks were dated previous workers using primarily k ar and rb sr techniques have reported a spread of apparent ages ranging from 240 420 ma for these intrusive rocks the present data set is internally consistent and has been calibrated against accepted interlaboratory standards a mean age of 367 ma was obtained for the south mountain batholith and the northern stocks a value consistent with results recently obtained in an rb sr study by clarke and halliday no differences in apparent age among the various phases or clear geographic age distribution patterns were evident satellite stocks in the southern part of the province have in general younger apparent ages clustered in the range 300 320 ma we suggest that in southern areas mica argon systems record the effect

the pb isotopic systematics during crustal contamination of subcrustal magmas the hercynian magmatism in the serie dei laghi southern alps italy abstract the pb isotopic composition and pb u and th concentrations of a series of hercynian granite plutons and mafic intermediate stocks and dykes belonging to the serie dei laghi western southern alps have been analyzed the initial pb isotope ratios of both the granites and the dykes are typical of the lower crust and are spread over a significant range 206 pb 204 pb 280 17 883 18 530 207 pb 204 pb 280 15 597 15 710 and 208 pb 204 pb 280 38 077 38 708 four dykes all at the same locality display evidence of post emplacement fluid circulation with mobilization of u and pb in spite of the pb isotopic crustal signature of the studied rock series the 87 sr 86 sr ratios reach values as low as 0 704 in the dykes and as low as 0 707 in the granites suggesting a mantle contribution in the genesis of both lithologies indeed when compared with the metasediments from the same area the magmatic rocks have somewhat lower initial 207 pb 204 pb ratios which weakly trend towards the less radiogenic pb isotopic composition of the mantle the relationships between the pb isotopic composition and the pb content along with the pb and sr isotopic covariation suggest that the suite under examination was generated from a mantle derived primary magma that underwent extensive crustal contamination a primary magma similar to the neighbouring ivrea mafic complex has been inferred further assimilation of crustal material is particularly evident in the dykes while the granites appear to have been generated mainly by crystal fractionation processes from the intermediate magma already contaminated

geochemical oxygen and neodymium isotope compositions of metasediments from the abitibi greenstone belt and pontiac subprovince canada evidence for ancient crust and archean terrane juxtaposition abstract the abitibi greenstone belt agb and pontiac subprovince ps in the southwestern superior province are adjacent greenstone plutonic and metasedimentary dominated terranes respectively separated by a major fault zone metasediments from these two contrasting terranes are compared in terms of major and trace element and o and nd isotope compositions and detrital zircon ages the following two compositional populations of metasediments are present in the low grade abitibi southern volcanic zone 1 1 a mafic element enriched population mep characterized by flat depleted ree patterns enhanced mg cr co ni and sc low incompatible element contents and minor or absent normalized negative troughs at nb ta and ti and 2 2 a low mafic element population lmep featuring lree enriched patterns enhanced rb cs ba th and u contents and pronounced normalized negative troughs at nb ta and ti these geochemical features are interpreted to indicate that the mep sediments were derived from an ultramafic and mafic dominated oceanic provenance whereas the lmep sediments represent mixtures of mafic and felsic arc source rocks the ps metasediments are essentially indistinguishable from abitibi lmep on the basis of majorelement and transition metal abundances suggesting comparable types of source rocks and degrees of maturity but are distinct in terms of some trace elements and o isotope compositions the pontiac metasediments are depleted in 18o and enriched in cs ba pb th u nb ta hf zr and total ree and also have higher ratios of rb k cs rb ba rb ta nb th la and ba la relative to the abitibi lmep two subtypes of ree patterns have been identified in ps metasediments both have moderately fractionated distributions with la yb n 3 9 17 and 7 8 13 6 respectively but the first has minor eu anomalies eu eu 0 89 1 16 whereas the second features pronounced negative anomalies eu eu 0 52 0 81 coupled with high concentrations of incompatible elements such as k rb th u nb and ta the first subtype is interpreted to be derived from provenances of mixed mafic and felsic volcanic rocks whereas the eu depleted type has geochemical features that are typical of post archean sediments or archean k rich granites and volcanic equivalents abitibi metasediments have nd 2 7 ga values of 0 71 to 1 83 corresponding to model tchur 2 82 2 55 ga with the majority around 2 65 ga close to the depositional age of 2 7 ga in contrast ps metasediments are characterized by nd 2 7 ga 0 95 to 3 51 corresponding to t dhur 2 7 to 3 1 ga consistent with a detrital zircon age spectrum of 2 69 ga to 3 1 ga pontiac subprovince and abitibi metasediments have contrasting provenances suggesting their separate initial geodynamic settings and later tectonic juxtaposition major and trace elements o and nd isotopic compositions and detrital zircon ages collectively suggest that some of the ps metasediments were derived mainly from juvenile rocks whereas others require various degrees of contribution from older 3 0 3 5 ga evolved crust mixed with juvenile 2 7 ga rocks older components were derived either directly from erosion of an ancient continental arc or from contemporaneous volcanic rocks which may contain recycled older components if the ps represents in part an accretionary prism to the abitibi southern volcanic zone then oblique subduction may have been involved which allowed the pontiac subprovince to juxtapose or sample exotic source rocks

ti nb ratios of clastic terrigenous sediments used as an indicator of provenance abstract geochemical data have been compiled for the clastic sedimentary rocks of late proterozoic to carboniferous age in the armorican massif northwest france these data show a great similarity in the distribution of ti and nb in most sediments due to an association of these elements during geochemical processes the ti nb ratios remain close to 300 a result which is interpreted as being an inheritance from the source areas however recent published works have indicated that ti and nb are not fractionated by either weathering or diagenetic phenomena in contrast to all the other formations studied the basal carboniferous clastic rocks are different in having abnormally low ti nb ratios compilation of geochemical data on recent volcanic suites shows that ti nb ratios are a possible indicator of mantle supply in clastic rocks

the role of fluids in granulite facies metamorphism as deduced from oxygen and carbon isotopic compositions abstract based on stable isotope data of whole rock samples the main fluid rock exchange reactions in the high grade rocks of the crystalline basement of sri lanka is deduced to have occurred prior to granulite facies metamorphism the influx of external fluids during and after granulite facies conditions was only channellized and did not give rise to the formation of interconnected fluid films in rock volumes larger than several cm3 fluid present conditions were thus only manifest for relatively short periods of time much less than 106 y so that the conditions of granulite facies metamorphism of the sri lankan basement rocks in general can be characterized as fluid absent

behaviour of ree during thermal metamorphism and hydrothermal infiltration associated with skarn and vein type tungsten ore bodies in central morocco abstract the analysis of ree in tungsten ore bodies and surrounding rocks from paleozoic schist sandstone and limestone series in central morocco shows two kinds of behaviour 1 no significant modification of lanthanide distribution occurs during thermal and hydrothermal metamorphic events and 2 important variations of ree patterns characterize highly infiltrated and mineralized samples corresponding to the mixing of scheelite and wall rock spectra a water rock ratio of 2 4 is estimated for the paleogeothermal continental system by comparison of ree patterns hydrothermal mineralizing fluids are assumed to be derived from blind evolved late acidic magmas rather than from outcropping aouam granitic stocks

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

outline of upper precambrian and lower paleozoic evolution of the iberian peninsula according to u pb dating of zircons in the northwestern part of the iberian peninsula recent geological studies have defined the following stratigraphic sequence from bottom to top basal orthogneiss of miranda do douro is overlain by a complex of schist and greywacke which have been assigned to the cambrian or late precambrian these are followed by the ollo de sapo gneisses of volcanic sedimentary origin which in turn are overlain by the fossiliferous layers of the lower ordovician the schist and greywacke complex and the lower part of the ollo de sapo formation are transected by granitic dikes viana del bollo orthogneiss all these rocks were folded faulted metamorphosed and intruded by granite plutons during variscan times the emplacement of the miranda do douro and viana del bollo orthogneisses have been respectively dated at 618 9 ma and 465 10 ma by the u pb method on zircons these data yield lower and upper limits for the deposition of the ollo de sapo formation and demonstrate the occurrence of a precambrian basement pan african or cadomian orogeny in the variscan belt in the northwestern part of the iberian peninsula the emplacement of viana del bollo orthogneiss could be genetically related to the main phase of crustal thinning 470 520 ma characteristic of the prevariscan evolution of western europe typology and u pb data of the ollo de sapo zircons indicate the occurrence of inherited old precambrian zircons and yield an age of 325 3 ma for the variscan main thermal event in the area considered four possible evolutionary models for the u pb system of the ollo de sapo zircons are discussed

evidence from zircon dating for existence of approximately 2 1 ga old crystalline basement in southern bohemia czech republic zircon ages are reported for three moldanubian amphibolite grade orthogneisses from the southern bohemian massif obtained by conventional u pb analyses for two of these orthogneisses conventional u pb data are supported by ion microprobe single zircon ages or single grain evaporation data the amphibolite grade orthogneisses occurring in three small tectonic lenses within the varied group close to the south bohemian main thrust are of tonalitic granodioritic or quartz dioritic composition

the lanthanide tetrad effect and its correlation with k rb eu eu sr eu y ho and zr hf of evolving peraluminous granite suites lanthanide tetrad effects are often observed in ree patterns of more highly evolved variscan peraluminous granites of mid eastern germany central erzgebirge western erzgebirge fichtelgebirge and northern oberpfalz the degree of the tetrad effect te1 3 is estimated and plotted vs k rb sr eu eu eu y ho and zr hf the diagrams reveal that the tetrad effect develops parallel to granite evolution and significant tetrad effects are strictly confined to highly differentiated samples mineral fractionation as a cause for the tetrad effect is not supported by a calculated rayleigh fractionation which also could not explain the fractionation trends of sr eu and eu eu the strong decrease of eu concentrations in highly evolved rocks suggests that eu fractionates between the residual melt and a coexisting aqueous high temperature fluid mineral fractionation as a reason for the tetrad effect is even more unlikely as ree patterns of accessory minerals display similar tetrad effects as the respective host rocks the accessory minerals inherit the ree signature of the melt and do not contribute to the bulk rock tetrad effect via mineral fractionation these results point in summary to significant changes of element fractionation behavior in highly evolved granitic melts ionic radius and charge which commonly control the element distribution between mineral and melt are no longer the exclusive control the tetrad effect and the highly fractionated trace element ratios of y ho and zr hf indicate a trace element behavior that is similar to that in aqueous systems in which chemical complexation is of significant influence this distinct trace element behavior and the common features of magmatic hydrothermal alteration suggest the increasing importance of an aqueous like fluid system during the final stages of granite crystallization the positive correlation of te1 3 with bulk rock fluorine contents hints at the importance of ree fluorine complexation in generating the tetrad effect as the evolution of a ree pattern with tetrad effect m type implies the removal of a respective mirroring ree pattern w type the tetrad effect identifies open system conditions during granite crystallization

sm nd isotopic evidence for the provenance of sediments from the adelaide fold belt and southeastern australia with implications for episodic crustal addition abstract in south australia late proterozoic and cambrian sediments were deposited in basins formed within archaean to early mid proterozoic basement these sequences were subsequently deformed and uplifted by the cambro ordovician delamerian orogeny to form the adelaide fold belt in using the adelaide fold belt to address models for lithospheric evolution it is necessary to understand the mechanisms of basin formation and whether the sequences merely reflect reworking of existing cratonic material or if there were new crustal additions this study presents geochemical and isotopic data on the sediments and basement rocks to complement existing data on the delamerian igneous rocks as a means of investigating these questions the data reveal that the archaean mid proterozoic basement rocks of the gawler craton have nd depleted mantle model ages which average about 2 6 ga and nd values at 800 ma in the range 9 to 24 or at 500 ma from 11 to 28 the late proterozoic adelaidean sediments however have an average model age of 1 9 ga and initial nd values in the range 5 to 11 the sequence can be divided into lowermost rift phase sediments derived from erosion of local gawler craton material and a subsequent widely distributed thermal sag phase sedimentation whose isotopic signature is not compatible with the basement this implies that a more primitive or juvenile source was accessed via broadening of the provenance region the cambrian sediments have slightly older model ages 2 1 ga and lower nd 9 to 13 and can be interpreted as mixtures of basement and reworked adelaidean detritus the early palaeozoic sedimentary sequences of the lachlan fold belt to the east have isotopic compositions very like the south australian late proterozoic and cambrian sequences they have an average model age of 1 85 ma but much higher k 2 o na 2 o this indicates that the widespread flysch of eastern australia is the result of recycling of the late proterozoic and cambrian sediments by erosion of the adelaide fold belt with some modification by the mixture of the cambro ordovician mafic and felsic magmatic rocks in this orogen our data suggest regional intracontinental crustal evolution combined with recycling of older crustal material with new additions from the mantle during orogenesis and to a lesser extent episodes of extension and sedimentation

geochemical and isotopic disequilibrium in crustal melting an insight from the anatectic granitoids from toledo spain in the hercynian anatectic complex of toledo act the anatectic granitoids include leucogranitic leucosomes leucogranitic massifs and restite rich granites they show a broad range of initial sr and nd isotope ratios from 0 711 to 0 720 and 0 51164 to 0 51203 respectively which clearly indicate the absence of isotopic homogenization in the melts broadly the ranges reflect the isotopic variation of the metapelitic protoliths if crustal melting occurs under water undersaturated conditions as is the case of the act the generated melts do not isotopically and chemically equilibrate with the granulitic residuum the preservation of heterogeneities could arise through a number of processes 1 duration of the process in which the presence of melts with disequilibrium features and the high solid content of several of the granites in the act point to a very short lived magmatic system 2 limited diffusion in which poorly segregated and volatile undersaturated granitoids have a very restricted opportunity for isotopic and chemical homogenization and 3 magma dynamics in which the low melting rates the high restite and low water contents and the silica rich composition of these granites together with the small volume and high viscosity values of the melts seriously restrict the physical processes leading to homogenization

distribution of major trace and rare earth elements in surface sediments of the wharton basin indian ocean bulk chemical analyses of eighteen surface sediments taken on an east west transect lat 15 40 s in the wharton basin indian ocean were analysed for major trace and rare earth elements ree by inductively coupled plasma atomic emission spectrometry icp aes the relationship between al and k suggests in situ formation of authigenic phillipsite the relationship between p and ca suggests accumulation of biogenic apatite fish bone debris from high biological productivity waters which is confirmed by the linear relationship with p and cu a strong positive correlation among redox sensitive metals mn fe cu ni and zn suggests that they are incorporated into a ferromanganese oxide phase probably micronodules calcareous oozes from the transect have low ree abundance la 8 ppm with a very strong negative cece value 0 41 siliceous oozes have high ree abundance la 28 ppm with moderate positive cece 1 24 and red clays have highest ree abundance la 66 ppm with a weak positive 1 05 to moderate negative cece 0 73 shale normalized ree patterns and layb n ratios record similar enrichment of heavy ree hree relative to light ree lree in all sediment types this might be due to retention of the bottom water ree pattern and the presence of fish bone debris correlation coefficient and r mode factor analyses suggest a very strong positive association r2 0 9 of ree with p and thus most likely with biogenic apatite fish bone debris as p is directly associated with biological activity it is thus related to surface primary productivity ree in the wharton basin sediments appear to reflect a combination of surface water effects and diagenetic processes

characteristics of ree and other trace elements in response to successive and superimposed metasomatism within a portion of the south mountain batholith nova scotia canada abstract successive and superimposed periods of late to post magmatic metasomatism have resulted in mineralogical and textural modification within leuco monzogranitic rocks of the big indian lake polyphase intrusive suite bipis the alteration and associated mineralization exhibit a transition from an early pervasive style to a later fracture controlled style and can be defined by diagnostic ree and other trace element behavior while the anomalous behavior of some elements mno ta u k rb hree is attributed to metasomatic hydrothermal activity the compatible behavior of b f li w and rb appears to have been governed by predominately magmatic processes all elements including al can be mobilized during repeated fluid rock interaction the behavior of ree during evolution of the bipis indicates that they also were affected by both magmatic lree depletion eu depletion and metasomatic hree lree enrichment eu enrichment depletion processes the remobilization and subsequent redeposition of trace elements is dependent upon the nature and stability of the metasomatic mineral assemblages in this respect a metasomatized granitic rock could reflect a ree pattern similar to that of an unaltered equivalent

rare earth element distributions among minerals in a granodiorite and their petrogenetic implications a study of the distribution of lanthanide rare earths in a granodiorite from the eastern peninsular ranges batholith southern california reveals that a large fraction of the ree in this rock resides in the accessory phases sphene and allanite the minerals plagioclase alkali feldspar biotite epidote and apatite each contribute approximately 1 or less of each ree to the whole rock with the exception of eu for which plagioclase contributes 7 sphene and allanite together contain 80 to 95 of each ree each of these phases is zoned in ree concentration with substantial decreases from core to margin textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma ree zoning trends in sphene and allanite and unexpectedly low ree concentrations in largely later crystallizing minerals such as feldspar indicate that the precipitation of sphene and allanite significantly reduced ree concentrations in residual melts these results illustrate the potential that sphene and allanite have for controlling the behavior of ree in granitic magmas available information collectively suggest that the sampled granodiorite existed as a complete melt that the ree contained in the assemblage of phases were derived by direct crystallization from the melt and that the melt behaved essentially as a closed system once crystallization of the phases now present began close correspondences between the major and trace element chemistries of the granodiorite and phenocryst poor lavas from similar tectonic settings support these conclusions the ree pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism the high liquidus temperature of a granodiorite melt 1000 c indicates the importance of mantle derived components within the sources of batholithic magmas in the peninsular ranges

sm nd and u pb zircon isotopic constraints on the provenance of sediments from the amadeus basin central australia evidence for ree fractionation abstract the amadeus basin of central australia is a late proterozoic to late palaeozoic ensialic depositional basin located between two proterozoic basement blocks of different nd crustal formation ages the older arunta block t dm nd 2 0 to 2 2 ga u pb zircon ages 1 5 1 9 ga to the north and the younger musgrave block t dm nd 1 7 to 1 9 ga u pb zircon ages 1 0 1 7 ga to the south initial nd isotopic compositions of the amadeus basin sediments generally fall into the region defined by the evolutionary trajectories of these two basement blocks indicating that the sediments are dominated by essentially two source components the older arunta block 147 sm 144 nd 0 114 and nd 0 20 4 and younger musgrave block 147 sm 144 nd 0 118 and nd 0 14 7 and or their equivalents stratigraphically higher sediments plot more closely to the evolutionary trajectory of the musgrave block this result together with the average provenance ages indicates the proportion of material from the musgrave block increases as the sediments become younger the sm nd isotopic data preclude a substantial involvement of archaean sources u pb zircon ion probe analyses of the late proterozoic heavitree quartzite and the late cambrian goyder formation are consistent with the sm nd isotopic constraints most of the zircons from the basal heavitree quartzite give concordant u pb zircon ages of 1500 to 1900 ma consistent with derivation from an arunta type source whilst zircons from the younger goyder sandstone give six discrete u pb zircon age groups of 511 20 615 15 960 109 1190 54 1633 24 and 1878 48 ma indicative of a dominantly musgrave type source with a minor contribution from the arunta block or reworked preexisting amadeus basin sediments the two youngest u pb zircon ages probably indicate some contribution from late proterozoic cambrian volcanics in central australia or a previously unrecognised younger local source in the basement blocks the 511 20 ma constrains the maximum depositional age of the sediment the amadeus basin sediments have a surprisingly wide range of 147sm 144nd ratios 0 077 0 136 irrespective of grain size and rock types in addition the calculated t dm nd values for samples from the same stratigraphic unit are well correlated with 147sm 144nd ratios with samples of different stratigraphic units forming sub parallel arrays these phenomena are interpreted in terms of ree fractionation and preferential sorting of preexisting ree rich phases during sedimentary recycling and deposition this process can lead to either an increase or a decrease in 147sm 144nd ratio of a sediment relative to its source and therefore an erroneous estimate of its t dm nd provenance age a theoretical model is developed which accounts for the observed correlation between t dm nd and 147sm 144nd ratios for suites of stratigraphically related sediments and allows a reliable estimate to be made of the provenance age of individual stratigraphic units assuming the average 147sm 144nd ratio of the source is known or can be estimated the provenance age for each stratigraphic unit of the amadeus basin has been calculated using this method the sm nd isotopic systematics in the amadeus basin sediments suggest that 1 1 ree fractionation during sedimentary recycling can in some cases be an important factor and needs to be considered 2 2 the provenance of the amadeus basin sediments was controlled by local source regions and cannot be used to infer large scale continental averages hence some caution must be evoked in using sm nd isotopic constraints from restricted sampling for more generalised models of crustal evolution

samarium neodymium elemental and isotopic systematics in sedimentary rocks abstract trace element sm nd th sc and nd isotopic data for sedimentary rocks are examined in order to evaluate 1 1 possible secular trends in the composition of the sedimentary mass and upper continental crust 2 2 the role of tectonic setting in controlling the chemical and nd isotopic composition of the sedimentary mass when plotted against either sedimentation age or average provenance age determined mainly from nd model ages sm nd in sedimentary rocks decreases abruptly from about 0 21 to 0 19 at the archean proterozoic transition consistent with a change towards a more felsic upper crustal composition the change is only somewhat less pronounced for turbidite sediments than for those of continental affinity a trend toward increasing sm nd approaching or exceeding archean values is observed for phanerozoic turbidites this latter change is interpreted as indicating undifferentiated young crust as a component in the sediment which has been lost from the older post archean record due to sedimentary and igneous intracrustal recycling processes when plotted against sedimentation age th sc ratios exhibit a trend directly comparable to that of sm nd in this case th sc increases abruptly at the archean proterozoic boundary from about 0 5 to 1 0 and then decreases to about 0 7 during the phanerozoic nd isotopic composition of modern sediments is affected by tectonic association with those deposited at active margin settings tending to have higher nd reflecting younger provenance and higher and more scattered sm nd reflecting less homogenized and differentiated provenance it is likely that these distinctions can be traced back for about 1 2 ga but with the current data base are not readily resolved in older sedimentary rocks the degree to which the preserved sedimentary mass is open to new additions from the mantle either through replacement during sedimentary recycling or sediment mass growth is highly variable but averages about 15 25 during the phanerozoic

intracrustal recycling and upper crustal evolution a case study from the pan african damara mobile belt central namibia abstract clastic sediments from the pan african damara mobile belt show a wide range in depositional nd nd 0 18 to 1 and several key trace element ratios notably th nd and la sm increase from 0 2 to 0 7 and 4 0 to 8 0 respectively with decreasing nd 0 such trace element ratio nd 0 data arrays are attributed to binary mixing within the sedimentary mass and the data array defined by the damara sediments is consistent with data from other regions the low nd 0 end member is characterised by high th nd th y la sm and hf zr ratios and reflects highly differentiated upper crust dominated by granitoids pb isotope data suggest that the low nd 0 end member also had relatively high time integrated th u 4 by contrast the high nd 0 end member reflects juvenile upper crust but this end member has la sm th nd and hf zr ratios 4 0 0 2 and 0 02 respectively slightly lower than those of taylor and mclennan s preferred model for bulk crust and significantly lower than those of the andesite model intracrustal differentiation is discussed in terms of bulk crust present day average upper crust post archaean shale and a highly differentiated low nd 0 end member trace element ratios which are not significantly fractionated during erosion and sedimentation e g th nd th y and la sm show relatively smooth increases between these reservoirs whereas other trace element ratios which are fractionated both by sedimentary and magmatic processes e g rb sr and rb zr increase dramatically in the more differentiated crustal reservoirs

u pb ages of zircons from meta igneous and meta sedimentary rocks of the sierra de guadarrama implications for the central iberian crustal evolution u pb data of zircons from various gneisses of the eastern sierra de guadarrama central spain make it possible to reconstruct the pre hercynian and hercynian history of this area 1 upper intercept ages 2400 ma for meta igneous and 2000 ma for meta sedimentary rocks of discordias defined by data of anhedral zircon fractions document the existence of early proterozoic crust 2 lower intercept minimum ages of anhedral zircon fractions show radiogenic lead loss at about 540 ma due to a thermal event leading to volcanism and emplacement of granitoid rocks into precambrian crust growth of euhedral zircons is possibly related to this event 3 lower intercept minimum ages of about 380 ma defined by anhedral zircon fractions in meta sedimentary rocks prove an early hercynian event according to present knowledge on the metamorphism in the sierra de guadarrama this event could be explained in terms of a barrow type medium pressure metamorphism the inferred cadomian igneous event relates the geological history of central spain with that of western africa to the south and brittany to the north furthermore similarities of the crustal evolution in the area studied and other internal zones of the hercynian belt moldanubian zone french central massiv are confirmed the early hercynian event for the first time affected all the rocks of the area together the pre hercynian evolution of the two complexes is different and the present association of the basement rocks may be explained by thrusting or in terms of early hercynian nappe transport

wolframite deposition in a hydrothermal vein system the grey river tungsten prospect newfoundland canada mineralization in the grey river tungsten prospect newfoundland is contained within a sheared devonian k feldspar megacrystic granite and metamorphic rocks which are typical of the gneissic terrain of the gander zone the mineralization is genetically related to a suite of post tectonic highly differentiated alkali rich leucogranite dikes the tungsten bearing hydrothermal veins range from tensional veinlets to lodes containing several injections of quartz major composite lodes have greisen alteration envelopes which are characterized by enrichment in volatiles k 2 o al 2 o 3 rb li f heavy rare earth elements and w the heavy rare earth elements enrichment appears to be related to deposition of carbonate and fluorite in the greisen the mineralization is divided into four stages stage i characterized by quartz feldspar molybdenite veins stage ii composite lode formation consisting of five vein types in paragenetic order quartz bismuthinite iia quartz fe rich wolframite iib greisen iic quartz sulfide iid and quartz fe poor wolframite veins iie stage iii characterized by silver bearing quartz galena sphalerite veins and stage iv composed of fluorite calcite barite veins a spatial mineral zonation from south to north matches the temporal sequence outlined above with the exception of the stage iv veins which crosscut stage ii veins fluid inclusion data indicate a complex evolutionary history for the hydrothermal fluid the simultaneous trapping of co 2 rich and h 2 o rich fluid inclusions as well as solid inclusions of calcite in quartz of the quartz feldspar molybdenite and quartz bismuthinite vein types is evidence for the existence of a heterogeneous fluid during stage i and early stage ii mineralization fluid phase equilibria indicate that the inclusions were trapped at temperatures of 330 degrees to 360 degrees c and fluid pressures of less than 500 bars in composite lodes quartz sulfide and quartz fe poor wolframite veins were deposited in open spaces created by normal faulting these movements prompted rapid decrease in fluid pressure and temperature and caused retrograde boiling of the hydrothermal fluid at 200 bars and 300 degrees to 330 degrees c during deposition of quartz sulfide veins deposition of wolframite in quartz fe poor wolframite veins occurred at 270 degrees to 300 degrees c from an aqueous fluid of low salinity 0 5 wt nacl and low co 2 content 1 0 wt co 2 and after separation of a co 2 vapor phase by retrograde boiling isotopic and fluid inclusion data suggest that deposition of fe rich wolframite may have occurred at a slightly higher temperature 330 degrees c and from a fluid of higher co 2 content than the bulk of the wolframite which has an fe poor composition progressive co 2 loss from the hydrothermal fluid by immiscibility and retrograde boiling had a marked effect on the solution ph which shifted from 5 weakly acid to 6 weakly alkaline at 300 degrees to 350 degrees c during tungsten deposition thermodynamic data on the solubility of wolframite suggest that a ph increase would provide an effective mechanism for tungsten deposition and explain the variation in wolframite composition from fe rich to fe poor with time the association of hematite fe rich wolframite and muscovite in the greisen suggests high f sub o 2 10 super 20 10 super 30 conditions and is supported by eu behavior during alteration sulfides formed after tungsten deposition at temperatures less than 300 degrees c and under f sub s 2 conditions of less than 10 super 11 co 2 rich fluids are commonly associated with tungsten deposits from a variety of environments and the evidence from the grey river tungsten prospect shows that co 2 plays an important role in the transport and deposition of tungsten in the hydrothermal environment

evidence for a panafrican volcanic arc and wrench fault tectonics in the jbel saghro anti atlas morocco the saghro hills constitute the northern branch of the panafrican mobile belt in the eastern part of the moroccan anti atlas the precambrian terranes are predominantly composed of volcaniclastic and volcanic series witnessing a mainly explosive volcanism intruded by diorites and granites their age attribution is problematic and has been reconsidered in the present study based on structural evidence and rb sr data of quartzdiorites penetratively deformed volcano sedimentaries intruded by these plutons aged between 754 and 722 ma are now considered as lower precambrian ii the upper pii series have been reattributed and only formations overlying a basal conglomerate and angular disconformity are considered piii

rare earth elements and hydrothermal ore formation processes abstract the geochemical behaviour of ree is influenced by nearly all important hydrothermal ore formation processes including fluid rock interactions fluid precipitations adsorption and scavenging onto particles and changes in fluid temperature pressure ph eh alkalinity and ligand concentration destabilization of ree complexes in response to these physicochemical changes and possible chemical crystallographic controls determine the concentration and distribution of ree within hydrothermal minerals mineraloids and amorphous phases alteration assemblages of intrusive related mineralisations may exhibit a wide range of ree distributions and ree fractionation trends the ree distribution within these hydrothermally altered lithologies will depend on the ree concentration in the rock and the fluid the partitioning behaviour of the ree between the rock phases and the fluid and the types of alteration reactions which take place reactive rocks such as carbonate rich lithologies of skarn deposits may gain or loose significant amounts of ree during fluid rock interactions ree geochemical investigations combined with fluid inclusion and stable isotope studies may point to the origin of alteration products and the source s of ore fluids ancient massive sulphide ores commonly exhibit anomalous eu concentrations similar to many recent submarine hydrothermal precipitates the recognition of hydrothermal fluid seawater sedimentary or volcanically derived ree distributions within ores chemical sediments and hydrothermally altered lithologies may help to constrain genetic modelling of massive sulphide deposits care should be taken with the interpretation of ree distributions from metamorphosed hydrothermal ore deposits becase metamorphic and diagenetic alteration reactions may change the ree distributions mobility of ree may occur during diagenesis of carbonate rich rocks and during the development of shear zones and migmatites in contrast very large fluid rock ratios are necessary to cause significant changes in ree patterns of silicate rich rocks during diagenesis and regional metamorphism

resetting of neodymium isotopes and redistribution of rees during sedimentary processes the early proterozoic chelmsford formation sudbury basin ontario canada abstract the rees abundances and neodymium isotope compositions of sandstones and siltstones from the early proterozoic chelmsford formation reveal that the rees in some samples were redistributed during the early proterozoic by surficial processes and that prior to redistribution the nd isotope system was partially reset the chelmsford formation is a coarse grained turbidite sequence the youngest of three clastic units that fill the sudbury basin in ontario it is constrained to have been derived from nearby late archean superior province rocks by petrography major and trace element chemistry and pb isotopic compositions of whole rocks and feldspar although ree patterns and nd model ages for samples from around the base of the formation reflect their derivation from undisturbed superior province rocks tdm 2800 ma five samples from higher in the stratigraphic section show evidence that up to 60 of their la has been removed and sm nd has increased by up to 60 these samples also have anomalously high nd model ages tdm 3400 to 4400 ma the presence of pronounced positive ce anomalies in the samples with anomalous tdm indicates the influence of surficial processes on the ree composition the data scatter about a vertical array on a plot of f sm nd vs ndt 1800 nd calculated at 1800 ma approximately the depositional age with values of f sm nd between 0 45 and 0 14 mixing of nd from other sources is difficult to reconcile with the petrography major and trace element geochemistry and nd and pb isotopes removal of an lree enriched phase from the sedimentary system provides a viable mechanism to produce the ree and nd isotopic characteristics of the chelmsford formation samples neodymium isotopes require that this phase was partially isotopically equilibrated with the matrix sediment near the time of sedimentation this study shows the dangers of indiscriminate use of nd model ages in provenance studies and demonstrates that the simultaneous examination of sm nd and nd isotopes on f sm nd vs nd or isochron plots is required for the recognition of sedimentary redistribution of the ree