the chemical composition of ree y th u rich accessory minerals in peraluminous granites of the erzgebirge fichtelgebirge region germany part ii xenotime xenotime from a geochemically heterogeneous series of mildly to strongly peraluminous granites of the erzgebirge germany displays extended compositional variability with respect to abundances of hree y u and th with few exceptions the maximum and minimum concentrations for the lanthanides and actinides exceed those noted for this mineral from other geologic environments xenotime chemistry is dominated by the theoretical end members hree po 4 and ypo 4 90 mol in total typical xenotime grains from the erzgebirge granites and from other granites worldwide contain 70 80 mol ypo 4 and 16 25 mol hree po 4 this study documents the occurrence of xenotime abnormally rich in hree in place of y with up to 45 mol hree po 4 substitutions of thorite coffinite th u pb sio 4 brabantite ca th u po 4 2 and monazite la sm po 4 are of minor importance reaching maximum levels of 5 6 mol each with a total contribution typically th u super 4 ca super 2 the total lanthanide and actinide contents in xenotime and host granite are not strongly correlated however formation of xenotime unusually rich in hree occurs only in the a type limica granites that are strongly enriched in these elements the shapes of hree patterns of xenotime and host rock are similar which combined with mass balance calculations indicate the importance of this mineral in affecting the hree as well as y evolution of late stage granitic melts late xenotime may show strong y ho fractionation thus recording the decoupling of y and the hree which can occur in the latest stages of crystallization of evolved granites and which may be associated with deuteric alteration

provenance of jurassic accretionary complex mino terrane inner zone of south west japan implications for palaeogeography of eastern asia provenance and tectonic history of the jurassic accretionary complex mino terrane located in the inner zone of south west japan were studied using sandstone framework composition and mudrock geochemistry modal analysis of sandstones shows that the tectonic setting of the source area for the studied mino terrane clastic rocks was uplifted basement largely dominated by high grade metamorphic terrain composed of quartz and feldspar especially plagioclase the textural and mineralogical immaturity extent of alkali and alkaline earth element leaching low chemical index of alteration values and depleted rare earth element ree contents suggest rapid uplift and erosion within the source terrain and a relatively weak weathering intensity factor analysis revealed that grain size effects governed compositional heterogeneity in the studied sediments provenance of the sediments is interpreted as being plagioclase enriched felsic basement rock such as granodiorite within a continental margin and evolved arc tectonic setting rather than active volcanic arc lack of a contribution from active volcanic arcs may have resulted from the cessation of volcanism during the reorganization of the subducting plate system and or erosion of arc volcanics and exposure of basement considering the previous studies on palaeogeography and palaeocurrent reconstruction the north eastern part of the yeongnam massif in the korean peninsula is interpreted as the most probable source area for the studied turbidites the results of mixing calculation for mino terrane sediments suggest that precambrian leucocratic granite and the basement rock of the cretaceous gyeongsang basin shed large amounts of sediments to the mino trench whilst precambrian granitic gneiss and the triassic pluton supplied lesser amounts the results of this study reveal that although active subduction accretion processes were occurring the mino trench was bordered by continental basement rocks this knowledge contributes to enhanced understanding of the jurassic palaeogeography of the east asia continental margin

residence of ree y th and u in granites and crustal protoliths implications for the chemistry of crustal melts a systematic study with laser ablation icp ms scanning electron microscopy and electron microprobe revealed that 70 95 wt of ree except eu y th and u in granite rocks and crustal protoliths reside within reeythu rich accessories whose nature composition and associations change with the rock aluminosity the accessory assemblage of peraluminous granites migmatites and high grade rocks is composed of monazite xenotime in low ca varieties apatite zircon thorthosilicate uraninite and betafite pyrochlore metaluminous granites have allanite sphene apatite zircon monazite and thorthosilicaie peralkaline granites have aeschinite fergusonite samarskite bastnaesite fluocerite allanite sphene zircon monazite xenotime and th orthosilicate granulite grade garnets are enriched in nd and sm by no less than one order of magnitude with respect to amphibolite grade garnets granulitegrade feldspars are also enriched in lree with respect to amphibolite grade feldspars accessories cause non henrian behaviour of ree y th and u during melt solid partitioning because elevated fractions of monazite xenotime and zircon in common migmatites are included within major minerals their behaviour during anatexis is controlled by that of their host settling curves calculated for a convecting magma show that accessories are too small to settle appreciably being separated from the melt as inclusions within larger minerals biotite has the greatest tendency to include accessories thereby indirectly controlling the geochemistry of ree y th and u we conclude that ree y th and u are unsuitable for petrogenetical modelling of granitoids through equilibrium based trace element fractionation equations

first cycle quartz arenites in the orinoco river basin venezuela and colombia modern first cycle quartz arenites are forming in the orinoco drainage basin by at least two distinct mechanisms common to both mechanisms is an environment of intense chemical weathering and extended time over which weathering can occur in the llanos andean foreland basin extended time is provided by temporary storage of orogenically derived sediments on extensive alluvial plains in lowland portions of the guayana shield long soil mineral residence times are produced by very low erosion and transport rates resulting from low relief and tectonic quiescence both weathering intensity and the duration of weathering are important in the modification of sand composition first cycle quartz arenites are produced in diverse tectonic settings and cannot be used by themselves to infer paleotectonic settings of ancient sequences furthermore although tectonic setting is of great importance in determining sand composition modifications during transport and deposition can overprint the effects of the tecto

erosional and climatic effects on long term chemical weathering rates in granitic landscapes spanning diverse climate regimes abstract we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes our 42 study sites encompass widely varying climatic and erosional regimes with mean annual temperatures ranging from 2 to 25 c average precipitation ranging from 22 to 420 cm year 1 and denudation rates ranging from 23 to 755 t km 2 year 1 long term chemical weathering rates range from 0 to 173 t km 2 year 1 in several cases exceeding the highest granitic weathering rates on record from previous work chemical weathering rates are highest at the sites with rapid denudation rates consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock a simple empirical relationship based on temperature precipitation and long term denudation rates explains 89 95 of the variation in long term weathering rates across our network of sites our analysis shows that for a given precipitation and temperature chemical weathering rates increase proportionally with fresh material supply rates we refer to this as supply limited weathering in which fresh material is chemically depleted to roughly the same degree regardless of its rate of supply from breakdown of rock the temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter comparisons of catchment mass balance data from the field our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought at least in actively eroding unglaciated terrain similar to our study sites to the extent that chemical weathering rates are supply limited in mountainous landscapes factors that regulate rates of mineral supply from erosion such as tectonic uplift may lead to significant fluctuations in global climate over the long term

petrology geochemistry and na metasomatism of triassic jurassic non marine clastic sediments in the newark hartford and deerfield rift basins northeastern usa many sandstones and associated siltstones and shales of the triassic jurassic newark supergroup in the newark hartford and deerfield rift basins are immature feldspathic alluvial and lacustrine closed basin deposits they were derived from felsic igneous and metamorphic continental blocks on the flanks of their depositional basins the provenance was dominantly calc alkaline basement rocks similar to the sierra nevada of california the physical and chemical environments of erosion and deposition were probably similar to those in moist pleistocene holocene alluvial basins and playas in the great basin of california and nevada new petrographic and geochemical data for 113 samples indicate that albite rich sandstones and shales of the stockton lockatong and passaic formations in the newark basin and in the portland and east berlin formations of the hartford basin and analcime rich shales up to 52 normative analcime of the lockatong formation have unusually high na2o contents 4 7 textural evidence indicates both sodium replacement in feldspars and formation of authigenic albite and analcime in these rocks by comparison with modem sediments derived from similar provenance using mixing models it is estimated that up to 4 na2o was diagenetically added to the detrital clastics trace metals co cr cu ni zn abundances were apparently enhanced by deposition from brines in the lockatong formation analcime deposition occurred in shales with al2o3 na2o sio2 0 46 this ratio is found only in sediments to which na has been added from salts brines source rocks and the weathering products derived from them may be considered as a closed system in which sodium was retained partly in solids as feldspar and part went into solution during weathering the dilute solution migrated into the depositional basin where evaporation yielded concentrated brine during semi arid to arid climate in the drier parts of 21 000 yr milankovitch cycles reaction of brine during diagenesis at near surface and or shallow depths 2 km with ca plagioclase k feldspar and layer silicates at estimated temperatures 50 c to 100 c and ph 7 9 yielded thermodynamically stable authigenic albite and analcime in the sodium metasomatised clastic sediments low activity of k precluded development of authigenic k feldspar however k from solution incorporated into muds and silts as smectites were transformed to illite some lockatong beds contain anomalously high p2o5 ce la y th and u in authigenic apatite or monazite suggestive of mobilization of these elements in diagenesis

long term change in regime of the new river indicated by vertical variation in extent and weathering intensity of alluvium investigations of stream history in appalachian valleys have for the most part been confined to deposits within a few meters of the valley floor where radiocarbon dating is possible detailed study of new river alluvium in the radford north and eggleston 7 5 minute quadrangles of southwest virginia shows that meaningful information can be extracted from high level unpaired terrace deposits even where solution of carbonate bedrock has obscured terrace form a statistical analysis of terrace elevations performed by superimposing a 100 m grid over terrace maps and then determining the elevation of each grid point above modern river level amrl shows that alluvial deposits are more abundant at 0 12 m 0 40 ft and 30 49 m 100 160 ft while the 12 30 m 40 100 ft interval has relatively few deposits munsell color percent sand silt and clay and point counts of the heavy mineral and light mineral sand fractions were made in the b horizon at 35 sites ranging in elevation from 1 1 to 85 4 m amrl th

monazite xenotime garnet equilibrium in metapelites and a new monazite garnet thermometer prograde suites of pelitic rocks were examined with electron microprobe introduction and laser ablation inductively coupled plasma mass spectrometry to monazite ce la th po4 plays an important role in determine the systematics of element partitioning between coexisting studies of igneous and metamorphic petrogenesis foremonazite xenotime and garnet monazite grains that grew in most monazite is used to date specific events in a equilibrium with xenotime are enriched in y and dy compared with petrogenetic sequence e g parrish 1990 harrison et al monazite that grew in xenotime absent assemblages y and heavy 1997 hawkins bowring 1999 foster et al 2000 rare earth element contents of monazite coexisting with xenotime monazite may contain a large percentage of the sample increase with rising temperature monazite xenotime y gd and rare earth element ree budget and thus exert an y dy partitioning is systematic within a metamorphic grade and important influence on the evolution of melt composition increases slightly with increasing metamorphic grade suggesting wark miller 1993 bea 1996 the thermobarometric that monazite xenotime pairs approached partitioning equilibrium potential of monazite coexisting with xenotime has been garnet and monazite in both xenotime bearing and xenotime absent recognized leading to calibration of monazite geoassemblages show a strong r 0 94 systematic relationship thermometers gratz heinrich 1997 1998 heinrich between inverse temperature and ln keq for the net transfer equiet al 1997 andrehs heinrich 1998 in addition the librium yag oh ap 25 4 qtz 5 4 grs 5 4 an recognition that nearly all lead in monazite is radiogenic 3ypo4 mnz 1 2h2o suggesting that garnet and monazite parrish 1990 montel et al 1994 has led to development crystallized in compositional equilibrium the following temand application of electron microprobe monazite dating perature keq relationship for the equilibrium above has been derived techniques suzuki adachi 1991 montel et al 1996 williams et al 1999 t c 1 45p bars 447772 32052 567 40 rln keq 273 15 full realization of monazite as a thermochronometer requires detailed understanding of the specific reactions responsible for its formation previous studies of monazite with a precision of some 30 c for temperature estimates our petrogenesis have focused on monazite compositional observations suggest that major and accessory phases interact in a zonation zhu o nions 1999a 1999b monazite coupled fashion during metamorphism and also approach a state growth kinetics ayers et al 1999 behavior of monazite of compositional equilibrium as reactions proceed during hydrothermal alteration poitrasson et al 1996 crowley ghent 1999 and melting events watt 1995 or to a limited extent the influence of major phase mineral assemblage in monazite reactivity zhu

relationship between diagenesis and reservoir quality in sandstones of the garn formation haltenbanken mid norwegian continental shelf a quantitative model is proposed for the dependence of porosity and permeability on diagenesis in subarkosic arenites of the middle jurassic garn formation porosity variation is controlled by the combined effects of compaction and quartz cementation in general more porosity has been lost by compaction than by quartz cementation but compactional porosity loss appears to have occurred relatively early in the burial history before burial below 2 km below the sea floor thus progressive reduction of the total porosity with increasing burial below 2 km results mainly from quartz cementation permeability is a function of the abundance of intergranular macroporosity which is interpreted to be a measure of effective porosity at depths less than 3 5 km below the sea fl or intergranular macroporosity generally comprises more than 50 percent of the total porosity but at greater depth as total porosity decreases below about 16 percent the ratio of effective to ineffective porosity drops below one this depth corresponds to the onset of extensive illitization and grain dissolution which results in major reorganization of the pore system generation of secondary porosity by feldspar dissolution appears not to have been beneficial to reservoir quality in the garn formation but it is regarded as an intrinsic part of the overall process of porosity destruction with increasing diagenesis

chemical processes affecting the mobility of major minor and trace elements during weathering of granitic rocks abstract the behaviour of 38 major and trace elements as well as changes in the mineralogy have been examined in 10 weathering profiles developing on some portuguese granitic rocks element mobilities are calculated from geochemical data normalized with respect to ti in the fresh parent rock chemical elements are divided into two groups immobile and mobile on the basis of their geochemical distribution during weathering elements that are immobile during weathering are zr hf fe al th nb sc and the ree very mobile are ca na p k sr ba rb mg and si mobile elements are derived mainly from leachable minerals such as feldspars micas and apatites whereas immobile elements are either concentrated in resistate phases or strongly adsorbed by secondary minerals the geochemical behaviour of mn cr v fe and ce is very dependent on redox conditions redox transformations of these elements can be used to set limits on the oxidation state of a weathering suite the ree are mobilized or fractionated during late stages of weathering but not during moderate stages of weathering this fractionation is caused by selective leaching of rocks composed of both stable and unstable minerals containing ree

petrology chemistry and texture of modern river sands amazon river system key idea following the spirit of p d krynine the sands of the world s largest tropical river system are studied to reveal much about the general origin of sand and sandstone thin section and chemical study of 95 sand samples from the amazon river system in brazil peru ecuador and colombia a river system with great contrasts in climate and rock types reveals that sands derived from the andes are lithic arenites whereas sands derived from precambrian terrains are much richer in quartz as are sands in rivers draining tertiary molasse sand becomes more mature downstream along the main stem of the amazon solimoes maranon so that a sample analyzed at the mouth does not accurately reflect headwater composition dilution by quartz rich tributaries and quartz rich tertiary outcrops possible differential elimination of rock fragments and even possible weathering on the modern flood plain of the amazon contribute to enhanced maturity downstream we speculate that although data on modern large subarti

weathering processes and the composition of inorganic material transported through the orinoco river system venezuela and colombia abstract the composition of river borne material in the orinoco river system is related primarily to erosion regime which in turn is related to tectonic setting especially notable is the contrast between material derived from tectonically active mountain belts and that from stable cratonic regions for a particular morpho tectonic region the compositional suites of suspended sediment bed material overback deposits and dissolved phases are fairly uniform are are typically distinct from whose of other regions for each region a consistent set of chemical weathering reactions can be formulated to explain the composition of dissolved and solid loads in developing these formulations erosion on slopes and storage of solids in soils and alluvial sediments are important considerations compositionally verymature sediment is derived from areas of thick soils where erosion is transport limited and from areas where sediments are stored for extended periods of time in alluvial deposits compositionally immature sediments are derived from tectonically active mountain belts where erosion is weathering limited weathering limited erosion also is important in the elevated parts of the guayana shield within areas of sleep topography compared to the mountain belts sediments derived from elevated parts of the shield are more mature a greater degree of chemical weathering seems to be needed to erode the rock types typical of the shield the major element chemistry and mineral composition of sediment delivered by the orinoco river to the ocean are controlled by rivers that have their headwaters in mountain belts and cross the llanos a region of alluvial plains within the foreland basin the composition of sediments in rivers that drain the shield seems to be established primarily at the site of soil formation whereas for rivers that drain the mountain belts additional weathering occurs during s episodes of storage on alluvial plains as sediments are transported across the llanos to the main stem of the orinoco after mixing into the main stem there seems to be little subsequent alteration of sediment

a comparative study of gabbro and granite weathering in the piedmont of the southeastern u s a gabbros and granites weather in quite different fashions granites develop extensive weathering rind systems 2 m thick in which plagioclase is altered to a gibbsite kaolinite assemblage in rindlets adjacent to the fresh rock contact in the outer rindlets the clay fraction is dominated by kaolinite and dioctahedral vermiculite not surprisingly granitic weathering rind systems display relative depletions of si na ca rb and sr and relative enrichments of sesquioxides in contrast gabbro weathering rind systems are characterized by many thin 1 cm rindlets whose alteration products are dominated by limonitization of ferromagnesian minerals apart from a decrease in feofe2o3 ratios in the outer rindlets there is little relative depletion or enrichment of major elements in gabbro weathering rinds as compared to their fresh rock cores this contradiction in goldich s stability series is explained if weathering rinds are produced faster on gabbros than in granite outcrops thus the low degree of mineral alteration in gabbro rindlets reflects a shorter time of residence for minerals in this system compared to rindlets on granitic outcrops biotite and perthitic microcline were separated from a fresh granite and its attendant weathering rind system during alteration the albitic blebs of the perthite are dissolved leaving no trace of residual clay the result is a porous microcline whose composition is equivalent to the microcline matrix in the unweathered perthite progressive alteration of biotite results in oxidation of octahedrally coordinated fe2 with concomitant loss of k this results in the formation of dioctahedral vermiculites in outer rindlet samples of granite

late collisional granites in the variscan erzgebirge germany the late collisional erzgebirge granites 325 318 ma were introduction emplaced at shallow crustal levels in the variscan metamorphic the erzgebirge is a ne sw trending antiformal structure basement shortly after large scale extension caused by orogenic exposing variscan crystalline basement rocks at the northcollapse these granites comprise mildly peraluminous transitional ern margin of the bohemian massif the region is famous i s types and strongly peraluminous s type rocks which can be among economic geologists for its extensive and highly subdivided into three major groups low f biotite granites low f variable metallic ore deposits which have been mined two mica granites and high f high p2o5 li mica granites the since the middle ages e g stemprok seltmann 1994 highest degree of differentiation is reached in the li mica granites tischendorf forster 1994 and for the classic studies which exhibit strongly elevated concentrations of p f li rb cs in the fields of economic geology mining and metallurgy ta sn w and u but very low ti mg co ni sr ba y zr chemistry and mineralogy e g werner 1791 breithaupt hf th and rare earth elements crystal melt fractionation is the 1849 agricola 1974 dominant process controlling the bulk composition of all groups of as in many of the other variscan provinces in central granites however metasomatic processes involving late stage residual europe granitic rocks make up a large proportion of the melts and high t orthomagmatic fluids became increasingly more exposed rocks in the erzgebirge and a great variety of important in highly evolved units and have modified the abundances compositional and textural types occur fig 1 knowof mobile elements p f li rb cs ba sr in the li mica ledge of the processes involved in the generation and granites particularly isotopic and geochemical characteristics suggest evolution of these silicic magmas is essential for underthat the three granite groups cannot be derived from a common standing heat and mass transport during the variscan precursor magma their discrete compositions are source related orogeny and also for the formation of metallic ore and are attributed to melting of quartzo feldspathic and pelitic deposits several lines of evidence indicate that early crustal lithologies in different proportions granites are common in high temperature sn w deposits are associated with the the central european variscides but the erzgebirge is unusual for emplacement of highly evolved volatile rich granitic the predominance of evolved li mica granites associated with melts tischendorf 1986 forster tischendorf 1992 economically important sn w and u deposits the abundance of stemprok 1993 the role of the granites in formation of li mica granites is attributed to a combination of favourable factors later permian u pb zn and younger ore mineralization 1 low degrees of anatectic melting of crustal protoliths 2 wide f ba is controversial but good evidence exists that the distribution of fertile lithologies rich in large ion lithophile elements vein type u deposits owe their uranium to leaching from and ore elements 3 extended magmatic differentiation by crystal the uraninite rich granites e g tischendorf forster melt fractionation and subsequent autometasomatism 1994

structure related geochemical ree and isotopic k ar rb sr δ18o characteristics of clay minerals from rotliegend sandstone reservoirs permian northern germany abstract euhedral illite cementing the gas bearing sandstone reservoirs of the rotliegend in the niedersachsische rift system northern germany was studied along a horst to graben cross section to examine its chemical and isotopic characteristics the data show that differentiated illite particles grew during a tectono thermal event marked by distinct episodic hydrothermal activities along fault drains and in the poral space of sandstones at 210 ma and at 195 to 190 ma in horst positions at 185 to 175 ma in the nearby graben and at 170 to 165 ma in both the horst and graben varied ree distribution patterns and initial 87sr 86sr ratios from 0 7124 to 0 7142 relative to illite particle size outline a high chemical variability of the fluids during illite growth the 18o values of illite range from 20 0 to 12 4 and those of chlorite from 12 0 to 6 9 the changing 18o values of the minerals most likely relate to varied 18o values of the fluids or to different water rock ratios during crystallization differences among the ree and 87sr 86sr tracers and the 18o values of different generations of illite also suggest a changing fluid chemistry relative to time significant positive eu anomalies and negative ce anomalies in the ree distributions of illite suggest feldspar alteration by the migrating fluids in oxidizing environments

ree distribution in the clay fraction of pelites from the southern apennines italy abstract in order to evaluate whether clay minerals or accessory phases control the ree pattern of the only illite is correlated with ree while a smectite rich sample is characterized by the lowest content in ree strong correlations exist between ree and tio2 nb zr and a less significant one with sr no correlations exist between these elements and y r mode factor analysis indicated that three factors account for 87 of the total variance the first factor var 43 2 seems to express mainly the tendency of some resistate minerals to concentrate ree in the fine fraction the second factor var 30 0 may be related to the effect of circulating fluids responsible for dickite genesis the third factor may be linked to the weathering of micaceous phases the ree do not have a significant weight in the second and third factors resistate minerals appear dominant in controlling at least the lree and nb it is proposed that in the studied samples illite likely conveyed ree via the included minerals

arkose subarkose quartz sand and associated muds derived from felsic plutonic rocks in glacial to tropical humid climates abstract in the range of climates from high latitude glacial to equatorial tropical the mineral and chemical compositions of over 600 modern nonmarine first cycle sands and muds produced from felsic crystalline basement provenance in various tectonic settings were studied under glacial conditions sediments are developed by mostly mechanical weathering and thus are mineralogically and chemically similar to their source rocks humid tropical climates yield quartz rich sands kaolinite rich muds along with si mg ca na and k in solution between these extremes a wide range of detrital sediment compositions are developed in arid to wet climates in arid climate and semi arid climate sands feldspar is commonly more abundant than quartz and plagioclase k feldspar except in the cases of granite source rocks the muds are feldspathic with smectite dominant in the clays with increasing temperature and moisture in temperate to subtropical climates mafic silicates and feldspars are destroyed so that the sands range from arkoses with plagioclase as the major feldspar to subarkoses with dominant k feldspar through this range of climate muds become more kaolinitic and thus more aluminous with increasingly severe weathering typically feldspathic sands are associated with feldspathic muds with decreasing feldspar in sands there is less feldspar in muds with increasingly intense chemical weathering rare earth elements ree are more fractionated into muds typically sands contain 150 ppm ree with much of the ree in heavy minerals abundance differences are greatest between humid tropical sands and muds in many samples the ree are mostly in monazite allanite sphene and apatite more intensely weathered samples contain more xenotime and zircon evidenced by yb enrichment

mobilization and redistribution of rees and thorium in a syenitic lateritic profile a mass balance study abstract ree th geochemistry and mineralogy have been studied in a lateritic profile derived from a syenite at akongo in sw cameroon ree and th mass balance calculations for the host rock minerals show that at least 70 of the lree s and 50 of the hrees are contained in allanite apatite titanite and epidote and at least 50 of the th is controlled by the same accessory minerals which represent about 2 wt of the unaltered syenite these accessory phases are destroyed during the first stages of weathering causing most of the rees and th to be rapidly released into the soil comparison of the variation in the zr ti and th content as a function of the apparent density of the different zones of the saprolite shows that th is the least mobile element the presence of secondary thorianite tho2 the etched surface on zircon grains and the presence of ti in secondary cerianite support this geochemical interpretation the concentration of thorium was therefore chosen as invariant relative to the concentration of the other elements especially the rees in mass balance calculations most of the rees are leached in the iron rich upper horizons loose nodular horizon iron crust and top of mottled clay horizon where the groundwater table moves saprolite and bottom of the mottled clay horizon the rees are fractionated and redistributed there is a juxtaposition of leached and accumulation zones with precipitation of lree aluminous hydrated phosphates this study supports the existence of two different cycles for the redistribution of elements in the soil 1 1 as dissolved ions in the saprolite horizon and 2 2 as individual particles in the upper part of the profile

rare earth element behavior in soils and salt pan sediments of a semi arid granitic terrain in the western cape south africa the rare earth element ree contents of soils and pan sediments of the darling hills granitic terrain of southwestern south africa were determined to study the behavior of ree during weathering in a semi arid mediterranean climate the p rich stype bedrock granite has a middle ree mree enrichment relative to post archean australian sedimentary rocks paas that primarily reflects the ree content of feldspar and accessory apatite initial chemical weathering of the granite results in the loss of ree particularly ce eu and the heavy ree hree the enrichment of ree in soils relative to bedrock granite corresponds to clay mineral and amorphous fe oxide content in the case of the light ree lree and precipitation of pedogenic calcite in the case of the hree quartz sand dilutes the ree content and concentration of k feldspar produces positive eu anomalies cerium is rapidly precipitated during weathering and retained in clayey upper soil horizons as insoluble ceo2 most pan sediments have a bowl shaped ree pattern that is derived from the accumulation of eroded catchment soils modified by precipitation of evaporative carbonates ree enrichment particularly lree and the large negative ce anomaly of oxidized basal pan sediment relative to the bedrock granite suggest that ree entering the pan by groundwater flow are sorbed onto amorphous fe oxides in contrast goethite rich nodules from the pan have a low ree content and show hree enrichment relative to the granite precipitation of pedogenic calcite and evaporative pan carbonates greatly increases the retention of the hree in these semi arid soils diagenetic pan dolomite has a ree pattern similar to pedogenic and evaporative calcite but with a significantly lower ree content the ree patterns indicate that although most abundant in the bedrock granite the mree are least retained by soils during weathering the lree are generally retained by clayey and amorphous fe oxide rich soils and sediments whereas hree are retained by precipitation of soil and pan carbonates d 2003 elsevier b v all rights reserved

new constraints on the late cenozoic incision history of the new river virginia abstract the new river crosses three physiogeologic provinces of the ancient tectonically quiescent appalachian orogen and is ideally situated to record variability in fluvial erosion rates over the late cenozoic active erosion features on resistant bedrock that floors the river at prominent knickpoints demonstrate that the river is currently incising toward base level however thick sequences of alluvial fill and fluvial terraces cut into this fill record an incision history for the river that includes several periods of stalled downcutting and aggradation we used cosmogenic 10be exposure dating aided by mapping and sedimentological examination of terrace deposits to constrain the timing of events in this history 10be concentration depth profiles were used to help account for variables such as cosmogenic inheritance and terrace bioturbation fill cut and strath terraces at elevations 10 20 and 50 m above the modern river yield model cosmogenic exposure ages of 130 600 and 600 950 ka respectively but uncertainties on these ages are not well constrained these results provide the first direct constraint on the history of alluvial aggradation and incision events recorded by new river terrace deposits the exposure ages yield a long term average incision rate of 43 m my which is comparable to rates measured elsewhere in the appalachians during specific intervals over the last 1 ma however the new river s incision rate reached 100 m my modern erosion rates on bedrock at a prominent knickpoint are between 28 and 87 m my in good agreement with rates calculated between terrace abandonment events and significantly faster than 2 m my rates of surface erosion from ancient terrace remnants fluctuations between aggradation and rapid incision operate on timescales of 104 105 year similar to those of late cenozoic climate variations though uncertainties in model ages preclude direct correlation of these fluctuations to specific climate change events these second order fluctuations appear within a longer term signal of dominant aggradation until 2 ma followed by dominant incision a similar signal is observed on other appalachian rivers and may be the result of sediment supply fluctuations driven by the increased frequency of climate changes in the late cenozoic

aspects of climatic influence on the clay mineralogy and geochemistry of soils palaeosols and clastic sedimentary rocks climate strongly influences soil clay mineralogy and bulk chemical composition in humid climates chemical weathering is at its most intense and virtually all primary bedrock minerals suffer complete breakdown they are replaced by authigenic hydrated oxides of fe and al together with halloysite and kaolinite in deep profiles these minerals develop where the residence time of water in the soil is slight longer residence times lead to higher solute concentrations and the stabilization of smectite authigenic palygorskite and sepiolite may form in highly saline alkaline soils the stability of these precipitated minerals is problematic they may be metastable or even unstable all other clays found in soils are unstable being incomplete solid state hydrolysis products of substrate minerals the balance between stable metastable and unstable minerals and the rate of profile development are both much influenced by temperature rainfall and activities of soil biota themselves reflecting climate bedrock influence is greatest under conditions of low to moderate precipitation where unstable minerals persist local topography however also strongly influences both the rate and products of chemical weathering quite independently of climate on the grand scale tectonic factors may constrain the time available for profiles to develop hence the extent to which bedrock minerals survive or are altered mountain soils reflect local climate and bedrock composition much more than latitude the sediments delivered to major basins today do not reflect global soil distribution patterns the bulk composition of suspended sediment entering the indian ocean for example is rather similar to that entering the arctic ocean sediment dispersal patterns can also confuse climatic signals a problem not encountered with palaeosols authigenic clays formed within sedimentary basins and post depositional burial alteration of both sediments and buried soil profiles must lead to interpretational ambiguities climatic signals are likely to survive best in bulk compositional data although diagenetic reactions at depths in excess of about 2 km do not appear to be isochemical and in the distribution of more stable yet climatically sensitive minerals kaolinite as opposed to illite chlorite

the effects of source rocks and chemical weathering on the petrogenesis of siliciclastic sand from the neto river calabria italy implications for provenance studies plutonic and gneissic rocks of the sila massif in the uppermost portion of the neto drainage basin calabria southern italy weather and erode under a humid mediterranean climate during the development of weathering profiles a combination of chemical weathering and granular disintegration processes occurred chemical weathering involves a loss of both plagioclase mainly during grus generation and k feldspar mainly during soil formation this loss is attributed to transformation of plagioclase to clay minerals and to leaching and dissolution of k feldspar sand composition is quartzofeldspathic and nearly homogeneous along the main channel of the neto river even where the river cuts across a blanket of sedimentary cover thus fluvial transport does not alter sand composition within the neto drainage basin petrographic indices are effective in 1 discriminating between contributions from similar granite and gneiss source rocks qm f 2 relating the provenance of plutoniclastic and gneissiclastic sand found in the headwaters to grus horizons qm f q rg and 3 distinguishing between upstream first cycle and downstream multicycle sand q rg this last distinction is further emphasized by considering both aphanitic and phaneritic varieties of rock fragments rgrmrs diagram chemical weathering is the main sand producer within the regolithic environment in northern calabria in addition rapid erosion resulting from steep slopes removes weathered products and rapid and short transport leads to minimal sediment maturation in general the f q index is climate and relief dependent thus it should be used in conjunction with palaeoclimatic and palaeophysiographic evidence for provenance interpretations of ancient quartzofeldspathic sandstones

petrology and geochemistry of siliciclastic rocks of mixed feldspathic and ophiolitic provenance in the northern apennines italy provenance in clastic sedimentary rocks in the northern apennines is determined by integrated petrographic and geochemical criteria thus mafic poor arkoses in the gottero formation senonian paleocene deposited prior to the alpine orogeny were derived from granitic provenance in the sardinian corsican massif in the gottero formation chemical criteria distinguish between very low input of detrital mafic material and co c and ni added entirely by adsorption on clay minerals post alpine orogeny feldspathic sandstones in the macigno formation mid oligocene lower miocene and cervarola formation lower miocene reflect a more diverse provenance of granitic metamorphic ophiolitic and sedimentary rocks in the apennines and alps the macigno and cervarola rocks are distinguished by serpentine gabbro and diabase fragments and higher chlorite contents than in the gottero rocks chemically the macigno and cervarola rocks contain distinctive signatures expressed in higher mgo co cr and ni contents of the mafic ultramafic detritus a wider range and more scattered cr and ni variation and higher niggli ti for a given niggli al alk content the mgo co cr and ni abundances indicate up to 10 ultramafic ophiolitic detritus in the macigno and cervarola sandstones and up to 17 ophiolitic detritus in associated shales estimated by comparison of mixtures of feldspathic sands with ligurian peridotites up to 10 basaltic ophiolitic detritus in these sediments is suggested by cao and fe2o3 total abundances petrographic data indicate that a major part of the detritus in the macigno and cervarola formations is from alpine granitic basement of calc alkaline granite to tonalite plutons and gneisses but apart from higher ba in macigno and cervarola sandstones than in the gottero sandstones this is difficult to identify chemically the trace elements cr ni ba rb ce la y co cu ga pb and zn generally have positive correlations with niggli al alk a chemical surrogate measure of sheet mineral clays micas and chlorites content whereas sr which is associated with carbonate and feldspar shows negative correlation with al alk an olistostrome unit contains the most weathered detritus but otherwise shows similar chemical variation to the other formations methods to 1 identify separately mafic and ultramafic inputs 2 recognize in shales co cr and ni derived from ophiolitic sources and non ophiolitic sources 3 estimate the minimum mafic ultramafic proportion in a sediment may have general application elsewhere in sedimentary and metasedimentary rocks

equatorial weathering landform development and the formation of white sands in north western kalimantan indonesia abstract the morphology and geochemistry of weathering profiles in miocene granodiorites from the coastal lowlands of nw kalimantan indonesia 1 n lat indicate long term weathering rates landform development and mechanisms for the formation of white sands found widely in valleys and depressions samples are analysed from convex hill piedmont glacis and valley slope profiles all profiles above the saturated zone are strongly gibbsitic but kaolinite minerals are dominant below the water table the profiles are interpreted as expressions of the perhumid equatorial climate rainfall 3000 mm y 1 acting within a dynamic regime of landscape lowering during the neogene the current profiles being largely quaternary 0 4 0 6 ka possible effects of quaternary tectonic and environmental changes are considered including those caused by a late pleistocene drier climate when there was greater water table fluctuation and surface erosion landform evolution is a form of dynamic etchplanation with a long term rate of landscape and weathering profile lowering of ca 50 mm ka 1 within this regime some of the white sands may be residual weathering products locally redistributed by colluvial or alluvial processes they originated in the podzolising environment of the weathering profile and later experienced post depositional diagenetic changes within the hydromorphic regime of the valley floor

self sedimented diatom mats as agents of exceptional fossil preservation in the oligocene florissant lake beds colorado united states microbial mats play a major role in the formation of exceptionally preserved fossil deposits by overgrowing and binding organic remains and sedimentary particles this minimizes hydrodynamic and biological disruption of dead organisms and sedimentary laminae but published works all implicate prokaryotic cyanobacteria as the microbial agent however exceptionally well preserved macrofossils of the oligocene florissant lake beds colorado united states are enveloped in matted aggregations of mucous secreting pennate diatom frustules it is suggested that the macrobiota became entrapped in mucous secreting mats of surface water blooms of planktonic diatoms in lake florissant as the mats and the incorporated macrobiota were sedimented out of the water column the mucosic mats and their associated bacterial communities arrested decay and promoted preservation of refractory tissues thus by a completely different mechanism the diatom mats fulfilled the same preservational role previously suggested for cyanobacterial mats this hitherto unrecognized mode of preservation may be an important causative factor in the formation of exceptionally preserved lacustrine fossil biotas

trace element geochemistry of a thick till and clay rich aquitard sequence saskatchewan canada abstract samples collected from a 170 m borehole penetrating till bentonitic clay and sand at the birsay site saskatchewan canada has been studied as a first step for understanding the controls on dissolution and transport of trace elements including rees in porewaters of a clay rich aquitard the ree budgets of the till clay and sand are dominated by apatite and monazite with sporadic zircon and y phosphate apatites contain 0 3 to 1 7 wt ree and monazites 12 to 55 wt all three units are characterized by unusual bulk sample ree patterns with maxima at eu gd convex down patterns from la sm with minima at ce and variably fractionated hree apatites feature maxima at eu gd consequently the complex patterns arise from variable modal proportions of apatite monazite and plagioclase feldspar relative to post archean average shale paas the till is sio2 and cao rich with about half the contents of al2o3 tio2 and fe2o3 these compositional relationship stem from relatively high proportions of quartz and carbonate but low modal abundances of ferromagnesian and ti oxide minerals similarly the till has cs co ni sc v cu pb and zn contents at about half paas the bentonite clay has slightly higher sio2 and cao contents than paas with lower abundances of most other trace elements including ree which plot at 0 7 to 0 9 paas the major and trace element composition is similar to continental arc andesites and the clay is interpreted to have a mixed provenance of arc andesite and eroded underlying sands the composition of the till appears to reflect mixed provenance erosion of the underlying cretaceous clay and sand paleozoic carbonate rocks and the precambrian shield the silicious ardkenneth sand has lower concentrations of ree and most trace elements compared to the clay but the most fractionated ree patterns the clay and till have inherited more subdued ree patterns in part from the underlying sand unit compositional variations between the units are marked by an upturn of nb th u and ree concentrations at the till clay interface 80 2 m and decrease of these elements at the clay sand boundary 156 2 m ce and eu anomalies vary erratically with depth the anomalies appear to reflect the degree of sedimentary sorting which in turn controls the modal abundances of detrital monazite apatite zircon and plagioclase feldspar zr zr hf hf and zr hf ratios are higher in the till than the clay and sand indicating an additional zr hf bearing phase with a distinctively high zr hf ratio the observed small compositional variations in the till and clay are not reflected in variations of geotechnical properties given that the ree budget of the till and clay are dominated by highly insoluble trace minerals it is unlikely that the ree patterns of porewaters will be controlled by bulk sample ree concentrations weathering of the upper 3 m of the till has oxidized fe2 bearing silicates oxides and sulphides and dissolved carbonates relative to the underlying unoxidized till weathering has not disturbed major ree or other trace element compositions

effects of chemical weathering and sorting on the petrogenesis of siliciclastic sediments with implications for provenance studies the bulk chemical compositions mineralogy and mineral proportions of sands and muds of the mallacoota basin in southeastern australia reflect the composition of weathering profiles mantling source rocks rather than bedrock muds contain abundant clay minerals that are virtually absent from the source rocks but abundant in the weathering profiles sands are strongly enriched in quartz relative to source rocks even in the headwaters of the fluvial system demonstrating that feldspar destruction occurs by in situ chemical weathering within profiles and before detritus enters the fluvial system k feldspar is proportionally more abundant in fluvial sands than in source rocks because plagioclase is more rapidly destroyed than either quartz or k feldspar in weathering profiles subsequent erosion and sorting produce sands enriched in quartz with high k feldspar plagioclase ratios relative to source rocks the composition of plagioclase incorporated into the fluvial sands is also controlled by chemical weat

geochemistry and provenance of the altendorf feldspathic sandstone in the middle bunter of the thuringian basin germany an integrated mineralogical and geochemical study of the altendorf feldspathic sandstone in the middle bunter of the thuringian basin germany was carried out to obtain more information on its provenance sedimentological history and geochemistry the fine to coarse grained sandstone has an average composition of 66 63 71 quartz 30 27 35 feldspar and a fine grained illitic matrix the heavy mineral assemblage consists mainly of tourmaline zircon rutile apatite and opaque fe ti minerals it is inferred that this terrigenous material was laid down at the margin of the bunter basin high abundances of igneous quartz grains determined by cathodoluminescence cl the lack of metamorphic heavy minerals as well as alkali feldspar with an average k2o na2o ratio of 14 9 point to material of mostly granitic origin regional geologic and paleogeographic observations suggest that granites of the older and younger intrusive complex of the western erzgebirge are possible source rocks of the feldspathic sandstone the geochemical signature of the alkali feldspar k2o na2o ratio bao content points to the bergen and kirchberg granites as possible parent rocks comparing the mineralogical and geochemical data of the presumed source granites with those of the altendorf sandstone provides information on the sedimentation processes weathering fluvial transport and sedimentation under arid climatic conditions have caused complete decomposition and removal of plagioclase and biotite lowered the bulk ree content and led to the development of a positive eu anomaly the immobile trace elements e g ta th zr sc co ti are best suited for provenance determination because of their relatively low mobility during sedimentary processes elemental ratios such as la sc th sc co th and th ta have inherited the signature of the parent rocks and thus may be particularly useful for provenance studies to evaluate the control of specific minerals and grain size fractions on the distribution of trace elements in the sandstone separated fractions of quartz feldspar the 20 m fraction and heavy minerals were additionally analyzed the concentration densities elemental concentration in the fraction fraction weight reveal that with exception of hf the influence of the heavy mineral fraction on the whole rock geochemistry is insignificant although this fraction generally plays the most important role as carrier of trace elements quartz feldspar and the 20 m fraction have similar concentration densities between 20 and 40 for the ree with exception of eu which is mainly hosted in feldspar strong positive eu anomaly the influence of the 20 m fraction on the distribution of the ree and the elements u th sc ta strongly depends on the abundance of this fraction in the sediment alkali feldspar contains most of the ba sr rb and cs in the samples concentration densities of up to 97 thus differences in the abundances of these elements in whole rock samples can be related to changes in the mineralogical composition quartz feldspar ratio of the sediment

ree geochemistry of recent clastic sediments from the kaveri floodplains southern india implication to source area weathering and sedimentary processes abstract the kaveri river drains through archean gneissic and charnockitic terranes in south india the rare earth element ree chemistry of the floodplain sediments along with their major and trace element composition in different size fractions are discussed we observe a strong coherence between ree and tio2 contents in the sediments which is suggestive of strong control by titanite or its weathered products on the ree chemistry ree concentrations also show a general increase with decreasing size of bulk sediments different size fractions and of light and heavy mineral fractions this suggests the presence of ree in the fe oxy hydroxide surface coatings on clastic grains formed by the weathering of hornblende and titanite in the granodioritic to dioritic protoliths we also interpret the data as showing that ree patterns of clastic sediments notably eu anomaly are affected by the degree of source rock weathering as well as by the fluvial processes of sorting and mineral differentiation therefore for provenance study sediments having all granulometric grades such as the floodplain sediments are preferable because they most closely represent the source particularly when the source region suffered little chemical weathering in the present case the sediments were derived from the high standing hills of archean charnockites because of their recent uplift and physical denudation

chemical weathering in granitic environments abstract factors controlling chemical weathering in granitic environments are deduced using an extensive database from the literature based on a transition state theory model we evaluated the effects on chemical weathering of runoff temperature and ph the dependence between temperature and runoff and chemical weathering is complicated by other factors such as the presence depth of soil cover soil cover favors chemical weathering when it is thin and rich in weatherable minerals in contrast it reduces chemical weathering when is thick and poor in primary minerals processes that increase the contact time and the surface of the water rock interactions such as physical denudation increase chemical weathering rates in granitic environments the effect of temperature can be quantified assuming an apparent activation energy value of 48 7 kj mol to describe chemical weathering of silica in granitic crystalline environment under high runoff conditions

micromorphology and dissolution of quartz sand in some exceptionally ancient soils abstract scanning electron microscopy sem was used to study the effect of prolonged weathering on the micromorphology of quartz sand three soil chronosequences in the southeastern united states virginia with weathering profiles ranging in age from 90 ka to 10 ma were studied detrital sand grains from soil b horizons show that dissolution features are crystallographically controlled and develop progressively over time from smaller to larger etch pits then to an interconnected network of grooves and crevasses and finally to bulk grain decomposition sem also shows that disintegrating quartzite clasts in the oldest gravelly soils have been preferentially leached of silica cement possibly due to selective weathering along dust lines and spalling off of quartz overgrowths severely etched quartz usually attributed to tropical weathering is an unreliable paleoclimate indicator because similar features can form as a result of prolonged weathering under a temperate climate however the well defined relationship between quartz micromorphology and duration of weathering suggests that sem is a useful tool for soil correlation and geomorphic analysis

mineralogy geochemistry and genesis of kaolins from the amazon region the kaolin deposits of the amazon region of brazil are of lateritic origin modified by subsequent reduced lacustrine and or swamp environment they are contemporaneous with lateritic bauxites found in the same region all formed from aluminium silicate rocks these are principally sedimentary rocks from the cretaceous period itapecuru and alter do chao but also include metamorphic and felsic volcanic rocks after erosion of the upper part of these profiles they became locally a substratum for swampy and or lacustrine environments mostly developed over the clayey saprolitic horizon where kaolin occurs the saprolitic horizon is made up mainly of iron mottled kaolinite which has been subject to an intense deferrification which has increased the kaolin brightness and thickness the kaolins are basically made up of well crystallized kaolinite quartz sometimes illite muscovite anatase and hematite in certain locations crandallite goyazite is also present the deposits studied differ from each other in the mineral content levels concentration of principal elements and in trace element distribution the greatest quantity of quartz and consequently sio2 is intrinsically related to the type of parent rock small sedimentary deposits occur in alluvial flood plains located not very far from the lateritic source

beyond whole rock geochemistry of shales the importance of assessing mineralogic controls for revealing tectonic discriminants of multiple sediment sources for the ouachita mountain flysch deposits the origin of the ouachita mountains has been the focus of significant debate for decades considerable confusion also exists concerning the provenance of the carboniferous flysch of the ouachitas trace element geochemistry of shales from the stanley group delineates the provenance of the sediments and provides clues to the plate tectonic evolution of the southern continental margin during mississippian time th sc and cr th ratios indicate a cratonic source for the majority of the stanley group sedimentary rocks however in several samples low th sc ratios and high cr th ratios suggest a contribution from a mafic source using element ratio diagrams all of the samples plot along a curve consistent with a two component mixing model consisting of a dominant felsic and a subordinate mafic source the heavy mineral fraction of these shales sequester many of the trace elements used in whole rock studies monazite is ubiquitous in trace amounts and is the probable site for much of the rare earth elements in the whole rock the occurrence of monazite almost exclusively in sialic igneous rocks implies that sm nd isotopic signatures are not sensitive to sediment input from more mafic sources in some stanley shale samples chromite and mn oxides were identified and positively identify an oceanic crustal component as a source of stanley group sediment the results of this study emphasize the importance of determining the mineralogic sites of trace elements and realization of specific mineralogic contributions from mafic or sialic tectonic provenances

single cycle cratonic quartzarenites produced by tropical weathering the nimar sandstone lower cretaceous narmada basin india abstract the world wide turonian marine transgression is represented by a thin a few tens to a few hundreds of metres thick mixed siliciclastic carbonate sequence deposited in the narmada basin presently located across the precambrian shield in central india the area was part of the interior of gondwana in the cretaceous when major changes were initiated leading to the break up of the supercontinent in the absence of any sedimentary record it is difficult to say what happened in the area between the precambrian and the early cretaceous the sandstone petrofacies of the cretaceous sequence of the narmada basin were studied with a view to understanding the nature of the basin and its tectonic setting during an important event which took place on a global scale the studied sandstones are generally quartzarenites composed mainly of several varieties of quartz and some mica rock fragments feldspar and heavy minerals derived from the underlying precambrian basement for the study of provenance of the sandstones in the light of plate tectonics the present study employed the qt f l and qm f lt triangular diagrams of dickinson on the qt f l plots 78 of the studied samples lie in the craton interior field and 22 of the samples lie in the recycled orogen field on the qm f lt plots most samples fall in the craton interior field 75 another 25 fall in the quartzose recycled field the texturally sub mature to immature locally derived quartz rich sandstones do no represent a typical stable platform succession they were derived from uplifted basement and deposited in the nearby narmada rift the ancient humid tropical climate and long residence time in the soil horizon produced quartz rich sands

accessory mineral behavior during differentiation of a granite suite monazite xenotime and zircon in the sweetwater wash pluton southeastern california u s a abstract compositional and textural characteristics of the accessory minerals monazite xenotime and zircon in the sweetwater wash granites and related aplites indicate that these phases not only controlled much of the trace element geochemistry of the suite but that they also record the melt compositional changes that occurred during magmatic differentiation fractionation of monazite due to decreasing saturation levels of its essential structural constituents with falling temperature was likely responsible for an ongoing trend of light rare earth element ree depletion this was accompanied by increasing heavy ree concentrations until xenotime joined the crystallizing assemblage subsequently combined monazite xenotime fractionation resulted in lowering of the entire ree budget zircon which contains inherited cores that were apparently resorbed and rounded during initial anatexis was saturated throughout the differentiation history of the sweetwater wash suite accessory phases in granite and aplite exhibit strong compositional differences at a variety of scales the differences are best displayed by monazite on average crystals in more differentiated rocks aplites are relatively depleted in light ree s and contain higher concentrations of the substituting elements u and th zircon displays complimentary increases in hf and y while xenotime shows a slight increase in th and in gd ho ratios both phases also exhibit higher u concentrations in aplites than in granites these differences in accessory mineral compositions are observed not only between granites and the more differentiated aplites but also within individual thin sections due to in situ fractionation on an even smaller scale strong compositional variations are present within single crystals possibly due to diffusion controlled melt compositional gradients in the regions a adjacent to growing major phases and b adjacent to the growing accessory crystal itself our observations indicate that compositional variations among accessory minerals are potentially useful for tracking of magmatic processes but that the scale of observed variations must be carefully considered

the granites of the southeast asian tin belt four granite provinces have been delineated each with its own distinctive pattern of mineralization 1 the main range province endogenous greisen bordered vein swarms of cassiterite and wolframite 2 the eastern province magnetite cassiterite skarns base metal sulphides with antimony in thailand 3 the western peninsular thailand burma province endogenous greisen bordered vein swarms and pegmatites of cassiterite and wolframite 4 the north thailand migmatitic province endogenous vein and skarn replacement scheelite and fluorite deposits with some tin and local antimony in all provinces but particularly in the main range granitoids designated as two phase variants have been recognized where xenocrysts and xenoliths of coarse primary texture granite are enclosed in and corroded by an invasive equigranular quartzo feldspathic matrix these rocks form an essential part of the granite sequence in all provinces and have probably resulted from the infiltration and disruption of the host granite by late stage magmatic fluids whole rock geochemistry from peninsular malaysia shows that the granites from the main range and eastern provinces comprise two contrasted suites which correspond approximately to the i and s type categories advocated by chappell white 1974 in addition it is shown that individual plutons within batholiths in the two provinces have distinctive geochemical parameters variation diagrams of plutons having the intrusive sequence primary texture granite two phase granite microgranite show linear trends with increasing sio 2 na 2 o rb w sn and u and decreasing sr ba th and all other major elements

chemical weathering of fluvial sediments during alluvial storage the macuapanim island point bar solimoes river brazil abstract modification of sediment composition by chemical weathering depends both on the overall intensity of weathering and on its duration at macuapanim island solimboes river amazon main channel brazil a number of alluvial deposits have been exposed to intense tropical weathering for differing lengths of time in the very fine sand fraction the detrital component shows a steady and marked increase in compositional maturity with increasing sediment age immature sands of arkosic to litharenitic composition show a progressive loss of lithic fragments feldspars and accessory minerals with a concomitant enrichment in quartz this process produces first cycle sands whose detrital component is of quartz arenite composition among the salts quartz is enriched over time relative to more nstable phases particularly plagioclase this enrichment is probably largely caused by the destruction of plagioclase through chemical weathering but silt size quartz may also be produced through the breakdown of sedimentary and metasedimentary lithic fragments in the sand fraction in the clay fraction an increase in the relative abundance of smectite accompanies the breakdown of volcanic lithic fragments in the sand fraction and probably reflects the degradation of volcanic glass the clay fractions of the oldest samples examined contain less smectite somewhat more kaolinite and markedly more vermiculite as compared to younger samples but an extensively leached cation poor clay fraction analogous to the quartz dominated silts and sands is never attained the compositional mat rity of the clay fraction is everywhere lower than that of associated silts and sands perhaps because of a continual influx into the clay fraction of immature cation rich clays derived from the physical breakdown of lithic fragments in coarser size fractions this effect is enhanced by the translocation of fines whereby younger less weathered fine material is juxtaposed with older more mature coarse material in the lower levels of the alluvial stratigraphy reworking of floodplains during channel migration results in the reincorporation of older material stored on the floodplains into the sediment load if sediments have been intensely weathered during storage on the floodplain then the result will be a net dilution and replacement of younger relatively immature sands transported by the river by older more mature material from the floodplain the relative proportion of the older sands in the bedload will increase downstream resulting in a progressive downstream increase in the compositional maturity of the bedload of the river

compaction and porosity evolution of pliocene sandstones ventura basin california sandstones of the pico and repetto formations were studied to quantify the processes involved in compaction and to determine the porosity evolution of the beds during burial the sandstones are mineralogically immature and except for local carbonate cemented beds have insufficient cement to have prevented compaction stratigraphic studies and graphic porosity depth plots suggest that the samples maximum burial depths were approximately 10 000 ft 3 048 m deeper than the present day depths of 850 13 000 ft 259 3 962 m compaction produced closer grain packing as measured by the contact index ci average number of contacts per grain and tight packing index tpi average number of long sutured and embayed contacts per grain for samples with less than 10 cement the ci depth gradient is 0 21 1 000 ft 0 69 1 000 m and tpi depth gradient is 0 27 1 000 ft 0 89 1 000 m assuming sands had 40 initial porosity the sandstones that are at present most deeply buried lost a total absolute porosity of 26 by all compactional processes which includes 14 by grain rearrangement and 6 each by pressure solution and ductile grain deformation porosity loss by nondeformational grain rearrangement was complete by a present day depth of 5 000 ft 1 524 m but in uncemented sandstones pressure solution plus associated grain rearrangement and ductile grain deformation continued to the maximum depths sampled compaction is most abrupt in sands with abundant micas and ductile rock fragments the ci gradient is 0 14 1 000 ft 0 46 1 000 m for samples with ess than 10 ductile grains but 0 22 1 000 ft 0 72 1 000 m for samples with more than 10 ductile grains compaction was almost entirely the result of overburden pressure and was not noticeably retarded in overpressured zones suggesting that overpressures developed after maximum burial was achieved for samples with less than 10 cement the ci is a better depth predictor than the tpi r2 0 58 vs 0 45 but the tpi is a better predictor of pre cement porosity than the ci r2 0 54 vs 0 31 secondary porosity averages 20 40 of the total thin section porosity secondary porosity is present at all depths but makes up the greatest percentage of total porosity between present depths of 6 000 and 9 500 ft 1 829 and 2 896 m except for grain fracturing secondary porosity formed only by dissolution of framework grains fractured grain porosity contributes up to 29 of total porosity 5 absolute porosity in some samples fractures formed during pleistocene tectonic episodes

solid liquid ree fractionation in the lateritic system of goyoum east cameroon the implication for the present dynamics of the soil covers of the humid tropical regions the ree th weathering geochemistry and mineralogy has been investigated in a lateritic soil cover in relation to the close hydrographical system at goyoum east cameroon the stutied area composed of gneissic hills covered by humid tropical forest belongs to the sanaga river basin and corresponds to a transition vegetation zone between rainforest and savannah a representative soil catena was taken as a reference zone close to the sanaga river the gneissic parent rock soil and groundwater samples have been cut off in pits in the lower part of the catena waters were also sampled both in brooks rich in organic matter and in the sanaga river all the waters were sampled seasonally during the rainy and dry periods the water rock interactions and the exportation of ree and th have been discussed as a function of the evolution of specific ratios considering th as the less mobile element during laterization variation of parent rock pr normalized ratios ln th pr vs depth show that the upper ferruginous horizons are depleted in ree while the basal saprolite presents accumulation zones which are differently located for ce and the other lrees the hrees are also depleted the la accumulations are located near the saprolite gneiss weathering front associated with negative ce anomalies ce ce 0 4 the ce accumulations inducing strong positive ce anomalies ce ce 4 are located in the upper saprolite beneath the ferruginous horizons all along the soil catena the secondary lree bearing minerals which reflect lree fractionation during incipient weathering of the gneiss are hydrous phosphates rhabdophane lreepo4 nh2o and cerianite ceo2 whose precipitation depends on the eh ph changes in the soil profiles on the other hand hree depletion is controlled by the dissolution of xenotime the major hree bearer in the parent gneiss in the 0 45 m filtered acidic groundwater ph 5 5 which have flooded the saprolite for a long residence time th contents are extremely low 0 th 10 ppt while lree contents are high 90 la 450 ppt in these filtered waters th seems to be strongly controlled by minerals i e thorianite which lead to its immobilization in the soil while lree remain in the soluble and or colloidal pools moreover the groundwaters show significant negative ce anomalies throughout the year 0 1 ce ce 0 4 the mobilization of lree except redox active ce results from the dissolution and or the mobilization in colloidal form of the secondary phosphates which may present major negative ce anomalies as indicated by the bulk soil analyses at the saprolite gneiss weathering front therefore the groundwaters have the signature of saprolitic materials we propose that the strong positive ce anomalies of the upper saprolite result from ancient weathering processes these processes would have led to much stronger ce iii ce iv dissolution reprecipitation conditions than those occurring at the present time in the saprolite in the 0 45 m filtered brook acidic blackwaters lree and th contents are high 100 th 400 ppt 400 la 1700 ppt in this organic matter rich environment lree and th are highly mobilized the colloial pool controls half of the whole lree th load the geochemical signature of these waters is independent of the gneissic parent rock and soil lree contents there is no ce anomaly this signature is similar to those of other organic rich rivers draining humid tropical ecosystems in the world in the 0 45 m filtered sanaga waters lree and th contents are lower than in the brooks 15 th 40 ppt 40 la 300 ppt these concentrations are dependent on the time and on the colloidal composition however 90 of these elements are mainly controlled by the suspended pool

a mainly crustal origin for tonalitic granitoid rocks superior province canada implications for late archean tectonomagmatic processes the central wabigoon subprovince of the superior province like introduction most plutonic domains within archean cratons is dominated by over the last decade information fundamental to undergranitoid rocks of the tonalite trondhjemite granodiorite ttg standing and resolving many questions regarding arseries heterogeneous 2 74 throughout archean time documentation of alterative ga tonalite gneiss crust by younger tonalite magmas was probably petrogenetic models for archean ttg or ttd suites is an important process unlike the model of ttgs representing direct of particular relevance to archean tectonic processes see partial melts of subducting slabs in an arc setting this model de wit 1998 hamilton 1998 smithies 2000 as well requires no direct tie to subduction careful re evaluation of the as processes of archean continental crustal growth and ttg classification is required for it can mistakingly pigeon hole recycling e g ireland et al 1994 de wit 1998 hamilton temporally and genetically unrelated rocks and perhaps assume an 1998 henry et al 1998 2000 nutman et al 1999 incorrect petrogenetic or tectonic model an important role of crustal as in most archean shield terrains plutonic domains recycling processes in central wabigoon tonalite petrogenesis is in of the western superior province typically consist mainly keeping with evidence that supports substantial rates of continental of ttg or ttd compositions but also include more recycling as far back as the earliest archean mafic and more evolved granitoid compositions thurs

using in situ trace element determinations to monitor partial melting processes in metabasites peak metamorphism 800 850 c 8 10 kbar in the harts range meta igneous complex harts range central australia was associated with localized partial melting by the reaction hornblende plagioclase quartz h2o1 4 garnet clinopyroxene titanite melt in situ trace element determinations of prograde peak and retrograde minerals in migmatitic metabasites and associated tonalitic melts using laser ablation icp ms has allowed monitoring of a range of partial melting processes melting melt segregation and back reaction between crystallizing melt and restitic minerals mass balance calculations indicate that titanite is a major carrier of trace elements such as ti nb ta sm u and th and therefore may be an important accessory phase to control the redistribution of these elements during the partial melting of amphibolites titanite preferentially incorporates ta over nb and hence residual titanite might assist in the formation of melts with high nb ta the fact that single minerals record different rare earth element ree patterns from prograde to peak to retrograde conditions demonstrates that ree diffusion is not significant up to 800 c therefore trace element analysis in minerals can be a powerful tool to investigate high grade metamorphic processes beyond the limits given by major elements

genesis and transformations of monazite florencite and rhabdophane during medium grade metamorphism examples from the sopron hills eastern alps electron microprobe studies on the age mineral chemistry and alteration on accessory lree phosphate minerals have been carried out in medium grade metamorphic rocks of the sopron hills belonging to the lower austroalpine tectonic unit monazite and xenotime is relatively common whereas rhabdophane and florencite are restricted to certain rock types a first generation of monazite was formed in mica schists during the pre alpine hercynian metamorphism at 575 700 jc and 1 8 3 8 kbar as evidenced by p t data from the literature their mineral paragenetic and textural characteristics and supported by th u total pb ages of ca 300 ma in orthogneisses monazite is rare and of igneous origin kyanite quartzites and leucophyllites that were formed by mg metasomatism contain inherited monazite from the precursor rocks a new generation of monazite was also formed during the alpine metamorphism at v550 jc 13 kbar according to the literature data giving ages around 75 ma pronounced negative eu anomalies were found in the igneous monazites eu eu 0 4 small differences have been observed in yand hree contents whereas the lree sections of the rare earth element ree patterns nearly coincide th and ca enter the monazite structure at the expense of ree nearly according to the brabantitic replacement 2ree 3 xth 4 ca 2 in some mica schists monazite is altered to rhabdophane rhabdophane distinguished from monazite by quantitative electron microprobe analysis by low oxide total is found in many mica schists and orthogneisses it forms fine grained aggregates often attached to apatite or monazite it usually has higher yand ca contents and a less pronounced negative eu anomaly than that of coexisting monazite it may have been formed either by crystallization from ree containing hydrous solutions or from monazite reacting with y ca containing solutions florencite appears only in some leuchtenbergite bearing leucophyllites kyanite quartzites and ree rich clasts it is often idioblastic and may be grown on apatite or monazite it is chemically close to its ideal composition but ca sr and th may replace ree in minor amounts in some grains tho2 may reach 10 wt the data indicate that the charge balance is maintained by different mechanisms in low and high thorian florencite no yor hree above gd could be measured in florencite no fractionation was observed between coexisting monazite and florencite however monazite inclusions in florencite are depleted in la ce and enriched in hree d 2002 elsevier science b v all rights reserved

holocene and paleogene arkoses of the massif central france mineralogy chemistry provenance and hydrothermal alteration of the type arkose abstract paleogene arkoses of the auvergne region of france represent the type arkose originally described by brongniart 1826 they are alluvial fan and fluvial deposits including traction current sandstones arenites and matrix rich debris flow deposits wackes locally they have been extensively altered by geothermal waters related to nearby tertiary holocene volcanic activity the alteration is typified by leaching of detrital grains and precipitation of ubiquitous chert cement the average gazzi dickinson composition of unaltered arenites is q40f60l0 with k f potash feldspar total feldspar 0 63 altered arenites have an average composition of q55f43l2 with k f 0 73 reflecting loss of plagioclase due to intense a teration when secondary chert is included with detrital quartz and chert the altered rocks have an average composition of q66f32l1 emphasizing silica enrichment associated with alteration holocene sands derived from crystalline basement of the massif central have the same provenance as the paleogene sandstones they have an average gazzi dickinson composition of q46f49l5 with k f 0 52 and compare favorably with their unaltered ancient counterparts arkosic alluvium at roosevelt hot springs utah is believed to represent a modern analog for alteration of the auvergne sandstones the alluvium has been altered and cemented with silica by geothermal waters at near surface conditions in the epithermal zone chemical analyses of 130 sand and rock samples demonstrate original sediment compositions and changes due to hydrothermal alteration holocene sands and unaltered paleogene clastics are compositionally similar and show variation trends similar to feldspathic clastics derived from granitic basement in other basins silica enrichment in the altered sandstones causes dilution of all other elements as an effect of constant summation consequently most element abundances decline proportionately with silica dilution na and rb however are reduced below the levels predicted by dilution due to plagioclase and biotite destruction as a result k rb ratios are higher in the altered sandstones ba s so4 as and sb are enriched in the altered rocks by precipitation from hydrother al solutions barium is in barite as fracture filling veins and scattered patches in sandstone matrix destruction of mafic minerals during alteration released fe co cr ni zn pb and th that later precipitated as oxides and sulfides in fractures and locally in chert matrix in the sandstones

factors controlling the trace element distribution in fine grained rocks the albian kaolinite rich deposits of the oliete basin ne spain abstract this paper combines mineralogical data x ray diffraction petrographic and scanning electron microscopy techniques and geochemical analyses in order to investigate the composition of a set of samples claystones siltstones and sandstones which belong to the albian deposits of the oliete basin in spain the aims of the study are to characterize the distribution of major and trace elements in kaolinite rich rocks to infer the role played by accessory phases and clay minerals on the trace element distribution and to assess the source area composition of these materials mineralogical analyses show that these rocks are mainly composed of different proportions of quartz and clay minerals kaolinite and illite with minor feldspar micron accessory minerals such as monazite zircon pyrite marcasite fe oxides and ti oxides have also been detected the sandstone framework implies that the source area of these sediments was probably a granitoid source which underwent low rank metamorphism the major element distribution reflects the mineralogy of the rocks plots in the a cn k diagram as well as their cia values indicate that these sediments were generated from an intensely weathered source area this produced the development of relatively cation poor clays such as kaolinite and claystones with large rare earth elements ree contents the fact that transition element contents in claystones are greater than in siltstones and sandstones suggests that they are preferentially linked to clay minerals probably by surficial sorption in comparison with other lithologies the high abundances of high field strength elements in siltstones imply that accessory minerals such as zircon and nb bearing phases are mainly concentrated in siltstones it should be noted that siltstones are also the lithology which displays the highest ree abundances the statistical analysis of the geochemical data suggests that ree are mainly controlled by ti and nb bearing phases such as titanite and nb and ti oxides although clay minerals are not the main phases in the ree control they probably also have some influence as the analyses show in addition other accessory phases such as monazite secondary phosphates and zircon also contribute to the ree contents although much less than amorphous fe oxides in some samples according to the ree patterns and elemental ratios such as la sc th sc th co etc the source area of the studied outcrops was probably felsic and with intermediate composition between granite and granodiorite

rare earth elemental systematics of mixed layered illite smectite from sedimentary and hydrothermal environments of the western carpathians slovakia abstract mixed layered illite smectite separates of various sizes from bentonites and shales collected in sedimentary and hydrothermal units of the western carpathians were analyzed for their major trace and rare earth elements rees the major elements fairly reflect the changes in the clay mineralogy related to illitization but a lack of correlation between this chemical composition and the ree contents suggests that their incorporation and fractionation by nucleating and growing illite type particles is complex during both burial induced diagenesis and hydrothermal activity during crystal growth of illite type fundamental particles illitization driven by burial related temperature increase does not fractionate the rees incorporated in the mineral structures but it increases their contents suggesting that the bentonite and shale units of the sedimentary sequence act as closed systems the amount of smectite layers in the i s does not relate to the sum of ree or to the la lu ratio in the bentonites and shales of the east slovak basin sedimentary sequence outlining that ree incorporation and fractionation concern s the illite layers not the smectite layers alternatively the hydrothermal system of dolna ves acts as an open system with supply of the rees by external hot fluids so that the ree contents are not determined by the precipitation of illite the mixed layers illite smectite of the shales yield a narrow span of total ree abundances from 17 3 to 36 5 g g compared to those of the associated bentonites from 1 20 to 93 7 g g of the same basin these differences result from varied origins of the original ree carriers the eu anomaly relates to alteration of the authigenic minerals in the sedimentary bentonites acting as a closed system or to the chemistry of the percolating hot fluids in the dolna ves hydrothermal deposit the data also indicate that no detectable zircon apatite monazite or any other ree carrier occurred in the size fractions at least in the finest and if any these minerals had no significant impact on the ree contents and distribution patterns of the varied analyzed size fractions consisting mainly if not exclusively of mixed layered illite smectite

ree u th and hf distribution in zircon from western carpathian variscan granitoids a combined cathodoluminescence and ion microprobe study a cathodoluminescence cl investigation on individual zircon crystals from variscan s type granites from the western carpathians has been combined with ion microprobe rare earth element ree and trace element analyses to explore possible connections between the cl emission of natural zircon crystals and their chemical composition the work was supported by single zircon u pb dating both by thermal ionization mass spectrometry tims and ion microprobe which helped to identify inherited zircon cores derived from related protoliths and to constrain the ages of inheritance and anatexis neither the ree nor trace elements such as y or th were found to have any direct correlation with the cl brightness the intensity of the cl signals was not directly reflected in the ree concentrations or the shape of the ree patterns uranium is probably the element responsible for quenching or suppressing the cl signals zircon cores inherited from different protoliths were distinguished by their ree patterns this enabled within a particular geological area the identification of inherited cores which possibly originate from the same protolith and therefore might lie on the same discordance line thereby improving the accuracy of inheritance ages inferred from tims single zircon analyses

sr and nd isotopic compositions age and petrogenesis of a type granitoids of the vernon supersuite new jersey highlands usa abstract voluminous late mesoproterozoic monzonite through granite of the vernon supersuite underlies an area of approximately 1300 km2 in the highlands of northern new jersey the vernon supersuite consists of hastingsite biotite bearing granitoids of the byram intrusive suite bis and hedenbergite bearing granitoids of the lake hopatcong intrusive suite lhis these rocks have similar major and trace element abundances over a range of sio2 from 58 to 75 wt are metaluminous to weakly peraluminous and have a distinctive a type chemistry characterized by high contents of y nb zr lree and ga al ratios and low mgo cao sr and hree whole rock rb sr isochrons of bis granite yield an age of 1116 41 ma and initial 87 sr 86 sr ratio of 0 70389 and of lhis granite an age of 1095 9 ma and initial 87 sr 86 sr ratio of 0 70520 both suites have similar initial 143 nd 144 nd ratios of 0 511267 to 0 511345 bis and 0 511359 to 0 511395 lhis values of end are moderately high and range from 1 21 to 2 74 in the bis and 2 24 to 2 95 in the lhis petrographic evidence field relationships geochemistry and isotopic data support an interpretation of comagmatism and the derivation of both suites from a mantle derived or a juvenile lower crustal parent with little crustal assimilation both suites crystallized under overlapping conditions controlled by p t fh2o lake hopatcong magma crystallized at a liquidus temperature that approached 900 c and a pressure of about 6 kbar and remained relatively anhydrous throughout its evolution initial p t conditions of the byram magma were 850 c and about 5 5 kbar bis magma was emplaced contemporaneous with or slightly preceding lhis magma and both magmas were emplaced during a compressional tectonic event prior to granulite facies metamorphism that occurred in the highlands between 1080 and 1030 ma

provenance changes for arenaceous formations of the northern apennines italy a complex pattern of provenances is displayed by 15 formations in the northern apennines composed chiefly of turbidites that were deposited during the alpine orogenesis q f l and qp lv ls values can be used to characterize specific source areas that existed in the apennine region from cretaceous through miocene time whereas sandstone mineralogy can be used to infer plate tectonic setting such an approach must make allowances for both the size of the area studied and the tectonic framework that existed prior to sandstone deposition in an early stage of the compressive phase of the tethys late cretaceous both arkose and litharenite were derived from cratonic blocks whereas volcanic sandstone was derived from uplifted oceanic sediments and lavas sediments recording the main oligo miocene collisional tectonic phases accumulated in two principal tectonic settings 1 intermontane successor basins and 2 foreland basins in the first case individual formations exhibit a wide provenance variability arkosic lithic sandstone recycled orogen volcanic sandstone magmatic arc and arkose were deposited simultaneously in the second case basins filled with thick turbidite sequences composed of arkose and lithic arkose which were supplied by basement rocks uplifted along the edge of the european craton and or by the nascent orogenic belt

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

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

distribution of ree and trace elements in size and mineral fractions of high purity quartz sands eight sample sets raw quartz sand quartz fraction 2 m clay fraction 2 20 m fraction and heavy minerals of the cretaceous quartz sand deposits of haltern and weferlingen central germany and the tertiary quartz sand of frechen western germany were studied to characterize the distribution of ree and trace elements and to get genetic information about provenance and sedimentologic history of the sediments the quartz sand samples from different localities have rather similar trace element distribution and ree patterns with enriched lree and negative eu anomalies however these relations can be modified by local changes in syn or postsedimentary geochemical conditions adsorption of ree and trace elements on humic substances under reducing conditions and postsedimentary weathering in the quartz sand of weferlingen resulted in significantly modified element abundances the concentration of trace elements is most important in the 2 m fraction and in the heavy mineral fraction where they may be enriched by a factor of up to 100 the chondrite normalized ree distribution of the 2 m fraction is quite similar to those in the north american shale nas with average eu sm ratios of 0 21 and layb cn of 6 1 low trace element abundances in the 2 and 2 20 m fractions were attributed to quartz dilution and quantified among the common minerals in the heavy mineral fractions especially zircon and the fe 1bti oxides rutile ilmenite magnetite influence the trace element distribution investigations concerning the provenance of the quartz sands illustrate that the host sediments have a rather homogeneous geochemical signature due to their sedimentological history taking into account th ta variations the quartz sands of weferlingen and haltern can be distinguished from the frechen quartz sand additionally discriminations based on element ratios within the quartz fraction th sc ba sc ba co cs sc or li sc seem to be promising

submicroscopic accessory minerals overprinting clay mineral ree patterns celadonite glauconite group examples abstract samples of glauconite representing different stages of glauconitisation as well as different formation environments were analysed for rare earth elements ree and other trace elements using a combination of bulk sample and spatially resolved in situ techniques the results indicate that the high sensitivity spatially resolved technique of laser ablation inductively coupled plasma mass spectrometry la icp ms produces values up to two orders of magnitude lower than the bulk sample analyses this suggests that submicroscopic rare earth element bearing phases are distributed within the glauconite aggregates comprising the bulk samples analytical scanning electron microscopy asem revealed the presence of micrometre sized grains of apatite and pore filling precipitates of an unidentified ree ca phosphate approximate composition ca 0 3 0 4 ce 0 4 la 0 1 0 2 nd 0 1 po 4 in some glauconite grains the inherent ree concentrations of the glauconite aggregates i e glauconite crystallites without accidental mechanical inclusions or authigenic not layer silicate mineral precipitates was found to be relatively low e g typically less than 100 ppm and this value decreased with increasing glauconitisation smectite mica transformation through a series of recrystallisation processes these results suggest that the rees substitute for ca in the interlayer space of the layer silicate structure and therefore the ree content decreases as ca is progressively removed from the interlayer smectite mica transition la icp ms when combined with electron probe microanalysis epma or asem offers an opportunity to exclude submicroscopic accessory minerals from glauconite trace element analyses and so produces reliable trace element data for the respective minerals which host those elements these results illustrate that accessory minerals are difficult to eliminate from clay samples and that care needs to be taken in the interpretation of clay mineral ree distributions irrespective of the aggregation state of the studied clay i e whether finely dispersed within the sedimentary rock or forming millimetre sized aggregates model calculations showed that authigenic apatite associated with the studied green marine clays tends to have higher ree content than bioapatites the total ree content being above 10 000 ppm

chemical weathering of metamorphic rocks from low elevations in the southern himalaya abstract early chemical weathering involving the acid hydrolysis of banded gneisses under warm temperate and subtropical conditions in the likhu catchment of the middle hills of nepal has resulted in the formation in situ of residual soils 2 3 m thickness grading downwards into saprolites that extend to thicknesses exceeding 6 m chemical analyses of bulk samples from three detailed profiles at elevations between 800 and 1000 m above sea level reveals a uniformity of chemical change throughout the weathering sequence within each profile in terms of loss of ca and na however there is also a progressive change between profiles with the more strongly weathered profiles showing almost total loss of ca and na the uniformity of change to depth within profiles is facilitated by the free draining sandy and silty textures of the weathering residues together with the frequent flushing by monsoon rains substantially greater retention of k and mg has occurred in all profiles only subtle decreases in both mgo and k2o are found to occur from the base of the residual soils upwards to the top of the soil these changes in bulk chemistry are consistent with the clay mineralogy and the stream water chemistry analyses it is suggested that the k and mg are preferentially retained in some of the clay minerals illite chlorite palygorskite and hydrobiotite whereas the na and ca are readily leached to the stream waters the general pattern of chemical erosion is consistent with that observed in other warm and humid tectonically active mountain terrains although the widespread formation of kaolinite is less commonly reported in such environments

sources of dissolved ree in mountainous streams draining granitic rocks sierras pampeanas cordoba argentina abstract stream waters draining granitic terrains from the highest part 850 to 2200 m a s l of sierras pampeanas cordoba argentina 32 s 65 w were sampled in order to define sources and distribution of dissolved rare earth elements ree and to describe the geochemical processes that govern their mobility the contribution of the regional granite to the dissolved ree pool in stream water is limited due to the physical conditions predominating in the area i e steep slopes and semiarid climate therefore precipitation is considered a seasonally significant source controlling ree concentration in stream water dissolved ree concentrations are inversely correlated with monthly precipitation and rainfall frequency during the rainy season i e the austral summer ree concentrations in stream water are lower than during the dry season i e austral winter such low concentrations reflect the balance between the ree input from precipitation and their removal by adsorption in contrast during the dry season the longer residence time of water within fractures and colluvium determines an increased ree concentration in the base flow lower ph values also contribute to raise ree concentration through desorption from mineral surfaces

early diagenetic ree phosphate minerals florencite gorceixite crandallite and xenotime in marine sandstones a major sink for oceanic phosphorus

a review on the potentiality of rare earth elements to trace pedogenetic processes abstract this review aims at considering the use of rees to trace pedogenetic processes in order to quantify the respective contribution of the successive processes on pedogenesis we first consider the origins and contents of rees in soils to assess their natural occurrence and tackle the common data treatment used to interpret their concentrations we review subsequently the impact of the different pedogenetic processes on the fate of rees in soils from their release into a soil solution by primary mineral heavy minerals phosphates silicates and carbonates dissolution during weathering to their fixation on or into main ree bearing secondary minerals clay minerals fe mn oxides and carbonates then their mobilization by plant recycling and organic matter and finally the impact of argilluviation and redox processes on their fractionation we conclude that rees much more than other trace elements can interestingly trace the considered processes that are encountered in a large diversity of non polluted soils arising from diverse parent materials weathering generally fractionates rees and accounts for a significant part of the variation in the initial ree stock of the soils plant recycling induces a weak mobilization of rees and their accumulation in topsoil argilluviation can be traced using the mree enrichment and the eu anomaly of the clay minerals redox processes can be traced by the ce anomaly caused by the precipitation of cerium on mn oxides to use rees as tracers of pedogenetic processes we recommend to i precisely characterize the ree bearing minerals ii adapt the choice of reference s for normalization and iii perform mass balance calculations

rare earth element fractionation in authigenic illite smectite from late permian clastic rocks bowen basin australia implications for physico chemical environments of fluids during illitization ree analyses were performed on authigenic illitic clay minerals from late permian mudrocks sandstones and bentonites from the bowen basin australia the mixed layer illite smectite exhibit ree patterns with an obvious fractionation of the hree from the lree and mree which is an apparent function of degree of illitization reaction the highly illitic r greater than or equal to 3 illite smectite from the northern bowen basin show a depletion of lree relative to the less illitic r 0 and 1 clays in contrast an enrichment of hree for the illite rich clays relative to less illitic clays is evident for the southern bowen basin samples the north american shale composite normalized la lu sn ratios show negative correlations with the illite content in illite smectite and positive correlations with the delta 18 o values of the clays for both the northern and southern bowen basin samples these correlations indicate that the increasing depletion of lree in hydrothermal fluids is a function of increasing water rock ratios in the northern bowen basin good negative correlations between la lu sn ratios and illite content in illite smectite from the southern bowen basin suggest the involvement of fluids with higher alkalinity and higher ph in low water rock ratio conditions increasing hree enrichment with delta 18 o decrease indicates the effect of increasing temperature at low water rock ratios in the southern bowen basin results of the present study confirm the conclusions of some earlier studies suggesting that ree in illitic clay minerals are mobile and fractionated during illitization and that this fact should be considered in studies of sedimentary processes and in identifying provenance moreover our results show that ree systematic of illitic clay minerals can be applied as an useful technique to gain information about physico chemical conditions during thermal and fluid flow events in certain sedimentary basins c 2003 elsevier science b v all rights reserved

petrology geochemistry provenance and alteration of pennsylvanian permian arkose colorado and utah late paleozoic and modern feldspathic clastic sediments of the colorado rockies were derived from dominantly igneous and meta igneous precambrian basement rocks average composition expressed as gazzi dickinson qfl quartz feldspar lithicfragments is 36 64 0 in modern stream sands for the cutler formation is 54 46 0 for the minturn formation is 57 43 0 and for the fountain formation is 51 49 0 no major mafic components are present in the provenance as indicated by low co cr and ni abundances although higher fe and mg abundances in cutler formation rocks indicate derivation from somewhat more mafic provenance than the fountain and minturn formation rocks fountain formation rocks are more altered by predepositional weathering diagenesis and holocene weathering than their equivalents in the minturn and cutler formations thus plagioclase is albitized and clay altered or absent in the fountain formation whereas it is abundant and much less altered in the minturn and cutler rocks fountain formation sandstone in the steamboat mountain section lacks remaining detrital plagioclase but contains authigenic albite as overgrowths on and replacement of detrital k feldspar and as pore filling crystals in the eldorado springs section there is extensive epithermal potassic alteration in the fountain formation from the detrital assemblage quartz plagioclase k feldspar biotite muscovite to the assemblage quartz k feldspar authigenic adularia illite muscovite kaolinite k and rb have been metasomatically added to these rocks with concomitant removal of ca na co cr cu ni ga th u zn ba ce la and y during passage of hydrothermal fluids apparently in the tertiary these fluids were probably heated by deep seated magma adjacent to the colorado lineament and or range front faults that served as geothermal water conduits toward the surface

chemical weathering in glacial environments do glaciers enhance or inhibit chemical weathering rates relative to other environments the importance of glaciers in the global carbon cycle and climate change hinges on the answer we show that catchments occupied by active alpine glaciers yield cation denudation rates greater than the global mean rate but do not exceed rates in nonglacial catchments with similar water discharge silica denudation rates are distinctly lower in glacier covered catchments than in their nonglacial counterparts because sediment yields are high from glaciers this suggests that water flux rather than physical erosion exerts the primary control on chemical erosion by glaciers potassium and calcium concentrations are high relative to other cations in glacial water probably due to dissolution of soluble trace phases such as carbonates exposed by comminution and cation leaching from biotite preferential weathering of biotite may result in higher 87 sr 86 sr in glacial runoff than expected from whole rock compositions thus although glaciers do not influence total chemical denudation rates at a given runoff they may yield compositionally distinctive chemical fluxes to the oceans disruption of mineral lattices by grinding increases dissolution rates this and high surface area should make glacial sediments exceptionally weatherable weathering of glacial erosion products in environments beyond the glacier margin deserves attention because it may figure prominently in global chemical cycles

geochronology and mass transfer in gulf coast mudrocks south central texas u s a rbsr smnd and ree systematics whole rock shale and 0 5 m sized clay separates from a well spanning 3500 m of burial in south central texas have been analyzed for there ree sm nd and rb sr contents clay rb sr and sm nd hcl leachate residue pairs yield ages which decrease with depth implying that these samples have not experienced a punctuated diagenetic event rb sr ages from the most deeply buried clay samples are younger than their depositional ages but sm nd leachate residue ages are always equal to or greater than depositional age leachate sr appears to be in isotopic equilibrium with present day sandstone formation waters implying that pore fluids readily pass between the two lithologies during and after diagenesis the ree are redistributed and fractionated on a local mineral grain scale during burial diagenesis the hcl soluble ree reservoirs decrease from 20 to 8 in whole rock and from 35 to 7 in 0 5 m clay and become progressively enriched in the middle ree relative to the light and heavy ree conversely the hcl insoluble silicate reservoirs become progressively enriched in the light and heavy ree relative to the middle ree this fractionation which is more pronounced in the clay than in the whole rock appears to be a result of authigenic illite and phosphate formation during burial diagenesis although the ree are redistributed on a local scale there is little evidence that the ree are gained or lost by the mudrocks during diagenetic redistribution combined nd and sr isotopic data show that the whole rock shale system may be modelled as a three component system composed of young volcanic derived and old craton derived detritus and a seawater derived component these three components are partially homogenized during diagenesis and as a result the sr nd provenance information originally held in the silicate fraction of whole rock shale becomes obscured

igneous petrogenesis and tectonic setting of the elkahatchee quartz diorite alabama appalachians implications for penobscotian magmatism in the eastern blue ridge

composition and trace element geochemistry of detrital clay and heavy mineral suites of the lowermost amazon river a provenance study abstract compositions of clays and heavy minerals as well as trace element geochemistry of the lowermost amazon sediments reflect source regions and the intense chemical weathering conditions illite and montmorillonite indicate mountainous sources under physical weathering conditions whereas kaolinite is related to the soil composition under humid tropical conditions where chemical weathering predominates the suite of unstable heavy minerals on the other hand reflects some sediment transport from the andes more supply from tributaries draining the basic and metamorphic rocks from the southeastern guiana shield and strongest influence of the upstream amazon and solimoes areas these source signals are damped by transitional storage and intense lateral sediment exchange between channel and floodplain the brazilian shield contribution via the xingu river seems to be of minor importance although the alter do chao and the barreiras formations which are products of erosion of the shields supply suites of stable heavy minerals that reflect recycling rare earth and trace element data from the clay and heavy mineral fractions provide additional clues to the source areas in the downstream direction superimposed upon provenance of sediments from an undifferentiated arc the andes is provenance from strongly weathered continental crust the precambrian shields as well as sedimentary recycling small scale provenance can be delineated by the most immobile elements heavy rare earth elements in the heavy mineral fraction increase downstream toward estreitos to the para river

reduced chromium in olivine grains from lunar basalt 15555 x ray absorption near edge structure xanes the oxidation state of cr in 200 mu m regions within individual lunar olivine and pyroxene grains from lunar basalt 15555 was inferred using x ray absorption near edge structure xanes reference materials had previously been studied by optical absorption spectroscopy and included cr bearing borosilicate glasses synthesized under controlled oxygen fugacity and cr doped olivines the energy dependence of xanes spectral features defined by these reference materials indicated that cr is predominantly divalent in the lunar olivine and trivalent in the pyroxene these results coupled with the apparent f sub o sub 2 independence of partitioning coefficients for cr into olivine imply that the source magma was dominated by divalent cr at the time of olivine crystallization 29 refs 8 figs 1 tab