behavior of rare earth elements in a paleoweathering profile on granodiorite in the front range colorado usa abstract a paleoweathering profile on the boulder granodiorite in northern colorado provides an opportunity to trace the behavior of rees from parent rock through a weathering profile into unconformably overlying permian sediments with progressive upward weathering of the granodiorite na2o cao sio2 ta hf co th cr sc cr th zr hf la sc zr y and la th decrease al2o3 and fe2o3t increase and tio2 mgo k2o p2o5 rb zr sc cr co hf nb ta y th u ree ti nb and zr nb increase to maximum values and then either level off or decrease lree enrichment is less in the weathering profile than in the parent granodiorite and although the parent does not have an eu anomaly or only a slight positive anomaly all samples from the weathering profile and overlying sediments have significant negative eu anomalies this observation is especially important in that it shows conclusively that a negative eu anomaly can be produced during chemical weathering of granitoids we suggest these eu anomalies are due to relative enrichment of the other rees and partial loss of eu during the breakdown of plagioclase the boulder weathering profile also has a very minor negative ce anomaly that is within error of a ce anomaly in the parent in the unweathered parent 50 of the ree are contained in sphene and in the case of la also in allanite from 10 20 of the ree are contained in apatite and biotite hornblende and from 7 10 of the hrees are in zircon with exception of eu for which feldspars contribute about 8 negligible amounts of rees occur in the feldspars in weathered samples 75 of the rees are contained in clay minerals the crossover between sphene and clay control of rees occurs over a distance of 1 m near the contact with fresh rock except for their small negative eu anomalies the clay minerals have ree patterns very similar to those of the parent rock isocon plots suggest apparent enrichments of many elements in the boulder weathering profile result from losses of na ca and si during plagioclase weathering in addition variable amounts of sr eu ta nb p and ba were lost during weathering although th u zr y th sc zr hf lu hf and ti zr may have been transferred relatively unchanged from granodiorite parent to the bulk weathering profile most other element ratios and ree distributions were significantly changed during weathering this observation implies that caution needs to be exercised when using ree patterns and element ratios to trace sediment provenance the fact that most element ratios and ree distributions also differ between fountain sediments and the bulk weathering profile may be related to one or a combination of four factors listed in order of probable decreasing importance contribution of other sources to the fountain sediments sorting of minerals during sediment deposition remobilization of elements during diagenesis and leaching of elements by water flow through the upper meter of the weathering profile

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

behavior of ree and other trace and major elements during weathering of granitic rocks evora portugal the distribution of elements within a weathering profile depends on several factors including the relative stability of the mineral phases of the parent rock redox and leaching conditions three main processes are involved in weathering 1 the breakdown of the parent minerals 2 the removal in solution of some of the released constituents and 3 the formation of secondary phases with components from the atmosphere water oxygen and carbon dioxide from the parent rock and from shallower levels and transported by the percolating solutions fritz and ragland 1980 nesbitt 1980 chesworth et al 1981 the purpose of this work is to investigate how major and trace elements behave during the weathering of granitic rocks from l vora portugal the prevailing climatic characteristics of this region are 700 mm annual rainfall dry summers and a mean annual temperature of 16 c

controls on caldera structure results from analogue sandbox modeling we conducted scaled analogue sandbox models of caldera formation in order to understand the effects of chamber depth and orientation on the spatial and temporal development of calderas dry sand contained in a 1 m diameter cylinder served as a crustal rock analogue and a water filled 0 6 m diameter rubber bladder served as an analogue magma chamber scaling parameters included a length ratio l of 2 5 10 5 and a stress ratio of 1 8 2 4 10 5 in contrast to some previous analogue models the viscosity of the fluid in the chamber and its withdrawal rate were properly scaled generally deformation began with broad sagging followed by an arcuate or linear outward dipping fault that formed on one side of the caldera this fault propagated laterally around the caldera in both directions sometimes joining other faults and typically forming an overall polygonal structure as subsidence continued the caldera grew incrementally outward and progressively formed a series of concentric outward dipping faults lastly a peripheral zone of extension and pronounced sagging and commonly an inward dipping outer fault related to extension developed at the surface as the depth of the chamber increased 1 the area of faulting decreased 2 the symmetry of the caldera was affected and 3 the coherence of the subsiding block decreased tilting the chamber caused highly asymmetric subsidence to occur in this case faults formed first where the bladder was shallowest subsidence then shifted rapidly to where the bladder was deepest producing an elongate trapdoor caldera that was deepest where the bladder was deepest our experiments highlight the roles of sagging and faulting during caldera subsidence surface fault patterns both in our experiments and at natural calderas are frequently not circular the aspect ratio of the block above the magma chamber controls the shape of the caldera which is frequently polygonal the faults at natural calderas determine locations and migration of eruptive vents the degree of subsidence the style of postcal dera resurgent magmatism and the extent of hydrothermal circulation our experiments reveal details of how calderas grow outward incrementally and demonstrate that asymmetric subsidence along linear and arcuate faults is common to many calderas

chemistry of modern soils as a guide to interpreting precambrian paleosols precambrian paleosols are potentially one of our best sources of information about the composition of the atmosphere early in earth s history to be used this way however an alteration profile must be shown to be an in situ product of vadose processes data from modern soils show that the ratios of less mobile elements such as zr ti and al can be used as a preliminary screen to test for the in situ nature of a profile if the ti zr ratio departs from that of the host rock by more than 40 or the ti al ratio departs by more than 50 for moderate degrees of weathering then a significant allochthonous contribution to the profile is indicated this technique correctly separates in place from allochthonous horizons when applied to independent data from two modern profiles a review of published precambrian profiles identifies two often cited examples denison and pronto as suspect based on these criteria in the interpretation of paleoatmospheres it is also necessary to show that fe is controlled not b

rare earth element and mineralogic changes in holocene soil and stream sediment a case study in the wet mountains colorado u s a size fractions of soil and stream sediment developed on plutonic metamorphic or mixed plutonic metamorphic sources in the wet mountains colorado have been analyzed for ree rare earth elements and mineralogy the clay sized fractions 0 5 m and 0 5 2 m or 2 m have ree contents that are similar to more enriched than the source eu sm ratios that are similar to the source and la lu ratios that are higher than their corresponding source the 0 5 m fractions have lower ree contents than the corresponding 0 5 2 m fraction in every stream sediment for example unweathered san isabel batholith near the sampled stream sediment contains ree 511 712 ppm and eusmratio 0 17 0 19 and lalu cn 9 8 10 3 the corresponding 0 5 and 0 5 2 m fractions of sediment formed from san isabel batholith are enriched in the ree ree 1135 and 2225 ppm respec are slightly lower in eu sm ratios 0 16 and 0 14 respec and are higher in la lu ratios 12 2 and 16 3 respec than the unweathered rocks the silts have lree light ree contents and eu sm ratios very similar to the source due to similar mineralogy but silts have hree heavy ree contents higher than the source due to high zircon for example silt sized fractions in stream sediment draining the san isabel batholith contain ree 808 ppm eusmratio 0 18 and lalu cn 7 4 in contrast the sands contain lower ree contents similar to higher eu sm ratios and lower la lu ratios than the corresponding source due to depletion in heavy minerals concentrated in the ree and containing lower eu sm ratios relative to quartz and feldspar depleted in the ree and containing higher eu sm ratios for example the sand fraction from stream sediment from the san isabel batholith has ree 206 ppm eusmratio 0 17 and lalu cn 5 6 small variations of accessory minerals concentrated in the ree like allanite or sphene may cause drastic variation in ree content in the sand fraction clays and silts derived only from the plutonic rocks have higher ree and similar to lower eu sm ratios than corresponding fractions derived only from migmatites e g ree of silt fractions from migmatites 224 ppm and from plutons 375 808 ppm eu sm ratios from migmatites 0 17 and from plutons 0 11 0 18 the ree content and the eu sm ratio of clays and silts derived from migmatites are much more similar to the average of mcps mid continent platform sediment than corresponding fractions derived from the plutons mcps has ree 192 ppm eusm 0 19 lalu 8 0 the eusm ratio of sands derived from plutons and migmatite are lower to mostly higher than the mcps the ree content of sands from plutons are not necessarily higher than the mcps due to variation in heavy minerals like allanite or sphene concentrated in the ree sediments derived from mixed sources have ree contents in fine fractions that may not necessarily reflect the ree content of the nearest source for example 0 5 2 m and silt fractions developed on the san isabel batholith with a migmatite upstream have the high ree content of the batholith ree in 0 5 2 m fraction 1100 ppm silt 573 ppm while the corresponding 0 5 m fraction has the very low ree content of the migmatites ree 110 ppm these results suggest fine grained material near the source may sample a much larger area than coarser material near the source thus analysis of fine grained sediment associated with coarse grained material near the source may give a much different impression of the source than would determination of the source using classic petrographic examination of the sand or gravels

active or passive continental margin geochemical and nd isotope constraints of metasediments in the backstop of a pre andean accretionary wedge in southernmost chile 46 30 48 30 s provenance analysis of siliciclastic sedimentary rocks gives indications of the tectonic evolution and setting of source regions and the rocks contained in them the composition of sedimentary rocks ideally reflects the nature of these regions and only indirectly the tectonic setting of the basin where the erosional debris is deposited this makes it possible to interpret late devonian to early carboniferous metasedimentary basement rocks of the andes in southernmost chile as having been deposited at a passive margin despite geochemical indications of an active margin setting for the source rocks and the position of the metasediments in the backstop of an accretionary wedge major and trace elements point to felsic source rocks from an active margin environment the nd model ages of 1170 1490 ma indicate that the source rocks were part of an old continental crust in the late palaeozoic the end t values range between 7 and 2 these characteristics in combination with the regional geology suggest that the geochemical signal is dominated by rocks formed at an active margin which later acted as feeders for the sediments deposited in a passive margin environment if corroborated by research in progress this emphasizes the problem of deducing the tectonic setting of a depositional basin from provenance data

weathering of charnockites and sediment production in the catchment area of the cauvery river southern india abstract in the cauvery catchment area charnockites are making high hills compared to gneisses in situ static weathering of a charnockitic boulder shows lesser extent of chemical weathering relative to that developed into a profile this difference is seen both in clay mineral composition their ree patterns and in the a cn k and a cnk fm triangular plots based on the chemical changes relative to ti three groups of elements are recognized ba si k na sr ca and mg show increasing depletion as the weathering intensity increases in listed order al remained relatively immobile whereas fe followed by mn cr ni ree and p show a variable extent of enrichment with increasing chemical weathering the sediment occurring on the foothills of the charnockite hills have a very uniform composition and texture without any depositional features reworking of these sediments in a first order stream has caused only minor compositional changes by the local segregation of heavy minerals on the channel bed and by the removal of small amount of clay materials as suspended load the ree pattern of the reworked channel bed sand is nearly identical to that of the channel wall sediments but with lower by 25 abundance although the rocks are 2500 ma and now located in tropical latitudes and probably had experienced several periods of warm and wet climate the soils and the sediments derived from them are chemically very immature suggesting their exposure to denudational processes very recently by tectonic uplift

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

tectonic affinity of nisutlin and anvil assemblage strata from the teslin tectonic zone northern canadian cordillera constraints from neodymium isotope and geochemical evidence we present geochemical and isotopic data for nisutlin assemblage metasedimentary rocks and anvil assemblage greenstones from the teslin tectonic zone of the northern canadian cordillera this study aims to establish the tectonic setting of formation for the sedimentary and basaltic protoliths of these highly deformed and metamorphosed rocks and thereby place constraints on the origin of these enigmatic rocks for which differing tectonic models have been proposed for the nisutlin assemblage metasedimentary rocks the geochemical and isotopic data show that two widely different source regions contributed detritus to the original sediments one source region was felsic upper crustal material with nd isotopic compositions compatible with ultimate derivation from the north american continent depleted mantle model age tdm 2 5 2 8 ga the second source region is deduced to be chemically primitive crust basaltic andesitic with a short crustal residence history 0 9 ga for the anvil assemblage greenstones immobile trace element abundances are dissimilar to within plate oceanic arc and normal mid ocean ridge basalts and similar to calc alkaline basalts in active continental margin settings we interpret the paleosetting for the nisutlin assemblage to be at the outermost margin of the ancestral north american continent in an area which received detrital input from the distal north american craton in the early paleozoic however this area also received detritus from a chemically and isotopically juvenile magmatic arc source a source type not known from paleozoic metasedimentary rocks from the miogeoclinal sequence on the basis of similar nd isotopic relationships recorded elsewhere in deformed paleozoic rocks of the orogen we infer that these geochemical signals reflect tectonic processes of regional extent the trace element geochemistry of the anvil assemblage greenstones does not support a correclation with known paleozoic greenstones of the slide mountain terrane which some tectonic models have advocated

chemical weathering of crystalline rocks in contrasting climatic conditions using geochemical proxies an overview abstract weathering profiles of granitoid rocks from the sila massif southern italy have been studied to characterize weathering processes that affect this area chemical weathering indices of the sila massif weathered granitoids were compared to those of different areas of the world characterized by different climates malaysia puerto rico georgia china nigeria colorado switzerland and sweden to decipher their weathering characteristics the geochemical indices show values of cia chemical index of alteration ranging from 55 to 97 ciw chemical index of weathering ranging from 60 to 100 pia plagioclase index of alteration ranging from 55 to 100 wip weathering index of parker ranging from 7 to 64 and rr ruxton ratio ranging from 2 14 to 3 96 all these geochemical proxies closely resemble each other and show variations mainly related to the different climatic and tectonic settings malaysia and puerto rico granitoids showing high cia values respectively 97 and 95 on average underwent very intensive chemical weathering alteration georgia china and nigeria showing medium high cia values respectively 86 90 and 92 on average underwent moderate intensive chemical weathering alteration southern italy and colorado granitoids showing medium low cia values 68 on average underwent moderate weak chemical weathering alteration whereas switzerland and sweden granitoids showing low cia values respectively 58 and 55 on average underwent weak chemical weathering alteration those values are mainly related to the climatic conditions in term of temperature and precipitation of each area cia vs climate histograms display a shift towards higher cia values with increasing of warm humidity tropical conditions whereas granitoids weathered under conditions inferred to be cold arid polar climate show lower cia values

geochemistry and isotope sr nd o study of al mg granulites from the in ouzzal archaean block hoggar algeria the in ouzzal al mg granulites are found within sedimentary units deposited after 2 7 ga the whole association being metamorphosed under extreme temperature conditions c 1000 c at 2 ga the al mg granulites are interlayered with other metasediments including metapelites quartzites and magnetite bearing quartzites forsterite spinel marbles and a few meta igneous rocks mainly pyroxenites they do not occur at a specific position in the sedimentary suite and they do not reflect any particular structural control the major and trace element compositions of al mg granulites especially the high cr ni co contents show that their peculiar refractory chemistry is more compatible with premetamorphic sedimentary characteristics rather than with metasomatic metamorphic or partial melting processes sedimentary admixtures of a common mature detrital component coming from the weathering of the local acidic igneous crustal protoliths normal pelitic component with an extremely immature component derived from reworking of basic ultrabasic lithologies al mg cr co ni rich chloritic component is consistent with the geochemistry of such rocks as in other instances the quartz garnet oxygen isotopic thermometer here records an apparent temperature close to the peak metamorphism c 1000 c although the persistence of pre existing 18o variations on a small scale during the metamorphism does not support a major pervasive fluid flow during metamorphism it does not rule out the presence of syn to post metamorphic co2 the low 18o c 5 to 6 of the most typical al mg granulites indicate that the chloritic component in these rocks was derived from hydrothermally altered mafic ultramafic protoliths rather than dominantly from palaeosols it is suggested that the presence of such al mg cr co ni rich sediments is indirect evidence for the presence of greenstone belts in the local crust of the in ouzzal at 2 6 2 7 ga

influence of metaluminous granite mineralogy on the rare earth element geochemistry of rocks and soils along a climosequence in brazil abstract the borborema province in northeast brazil represents the western portion of the extensive geological brasiliano pan african orogenic system it is characterized by voluminous granites which originate from the melting of igneous rocks we investigated the influence of metaluminous granite mineralogy on the geochemistry of rare earth elements rees in rocks and soils across a climosequence mineralogical petrographic geochemical and soil analyses were used to examine the geochemistry of rees in these samples results showed that the granites had a high proportion of accessory minerals such as allanite titanite apatite amphibole and opaque minerals bastnaesite is the major source of light rees in rock and soil samples the high ree fractionation present in metaluminous granites was normalized to the upper continental crust and it was indicative of magma fractionation la yb n and light ree heavy ree ratios showed that weathering processes had a significant impact on ree fractionation in soil profiles the highest lree hree fractionation was found in the humid zone almost all primary minerals were transformed into secondary minerals except for quartz typical kaolinitic soils developed in this climatic zone as well thus the highest lree hree fractionation was mainly associated with the abundance of kaolinites which preferentially adsorbed lrees soil profiles developed from metaluminous granites in different climatic conditions showed similar ree signatures and there was enrichment for lrees over hrees negative ce anomaly and positive eu anomaly were also observed the correlation between the index of alteration cia and lree hree ratios suggest that ree fractionation could be used to evaluate the degree of granite weathering linear regression analyses showed that ree fractionation was useful for predicting weathering intensity of soils that derived from metaluminous granites however further research is warranted to explore the influence of other types of granite on the ree geochemistry of soils in addition to seeking ree ratios that could be used to estimate weathering rates of granites in tropical environments

geochemistry and origin of ferruginous nodules in weathered granodioritic gneisses mysore plateau southern india fe nodules occur within saprolites formed from weathering of granodioritic gneisses in the rain shadow region of the mysore plateau adjacent to the sahyadri mountains in southern india these nodules and their host saprolites were studied for their geochemistry including chemical speciation to understand nodule formation and chemical redistribution processes during rock weathering from their mode of occurrence and mineralogical and geochemical data we infer that the nodules originated by a two stage process in which the initial extensive weathering of gneisses likely facilitated subsequent ferrolysis weathering and nodule formation nodules originated by precipitation of goethite hematite and gibbsite along with several amorphous phases within the matrix of weathered gneisses this is possible only under hydromorphic conditions suggesting that parts of the plateau must have gone through a humid phase prior to the present aridity in the saprolites al fe and ti become enriched because of the removal of si ca na and k however within the nodule fe ti cr and ni are deposited after their chemical transport from the saprolite titanium known for its immobile nature was also mobilized and concentrated under the conditions of nodule formation the most important elements in the nodule constitution are fe al ti and mn each having both crystalline and amorphous phases fe ti and mn oxyhydroxides grain coatings in the saprolites and discrete amorphous mn and ti phases in the nodules seem to have scavenged trace elements from the weathering profile ree were mobilized during weathering and nodule genesis in which ce and ti show a strong geochemical coherence the enrichment of only hree in saprolite and both hree and lree with significant ce in the nodule indicate the control of evolving secondary minerals in the ree redistribution during rock weathering strong enrichment of ce in the weathering profile and in nodules has important implications to the ree chemistry of river waters

crystal melt separation and the development of isotopic heterogeneities in hybrid magmas if a magma is a hybrid of two or more isotopically distinct endmembers at least one of which is partially crystalline separation of melt and crystals after hybridization will lead to the development of isotopic heterogeneities in the magma as long as some of the preexisting crystalline material antecrysts retains any of its original isotopic composition this holds true whether the hybridization event is magma mixing as traditionally construed bulk assimilation or melt assimilation once a magma scale isotopic heterogeneity is formed by crystal melt separation it is essentially permanent persisting regardless of subsequent crystallization mixing or equilibration events the magnitude of the isotopic variability resulting from crystal melt separation can be as large as that resulting from differential contamination multiple isotopically distinct sources or in situ isotopic evolution in one model a redistribution of onethird of the antecryst cargo yielded a crystal enriched sample with 87 sr 86 sr of 0 7058 whereas the complementary crystal poor sample has 87 sr 86 sr of 0 7068 in other models crystal rich samples are enriched in radiogenic sr isotopic heterogeneities can be either continuous controlled by the modal distribution of crystals and melt or discontinuous when there is complete separation of crystals and liquid the first case may be exemplified by some isotopically zoned large volume rhyolites formed by the eruptive inversion of a modally zoned magma chamber in the latter case the isotopic composition of any for example interstitial liquid will be distinct from the isotopic composition of the bulk crystal fraction the separation of such an interstitial liquid may explain the presence of isotopically distinct late stage aplites in plutons crystal melt separation provides an additional option for the interpretation of isotopically zoned or heterogeneous magmas this option is particularly attractive for systems whose chemical variation is otherwise explicable by fractionation dominated processes non isotopic chemical heterogeneities can also develop in this fashion

ree and other trace elements in a granitic weathering profile from serre southern italy abstract ree v cr ni rb sr y zr and nb behaviour in a granitic weathering profile in southern italy is studied in the saprolites of the considered profile depletion of v cr ni rb sr zr and nb is observed this is quite remarkable for sr and cr whereas ree and y are enriched in the more altered portion of the profile and especially in its m fraction such enrichment is associated with the lree hree fractionation and the positive ce anomaly the former results from an increased solubility of hree in a non acid environment as well as from the removal of the hree rich phases from the residual component the latter is related to the redox chemistry of ce which as ceo 2 is less soluble than the other ree no analogy is observed between the behaviour of ce and fe mn and cr saprolites also exhibit a negative eu anomaly which is mostly inherited from the parental material finally the influence of accessory minerals in the ree distribution of weathering products and in sediments calls for a careful evaluation of preferential settling phenomena of heavy minerals during transportation and deposition processes this is especially true in the parent material sediment relationships

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 elements in river waters we measured rare earth element ree concentrations in river waters to characterize the suspended and dissolved river flux of the ree to the oceans the ree pattern of river suspended materials is sensitive to drainage basin geology a positive correlation is observed between la yb ratios and nd model ages for the rivers studied major rivers have light ree enriched patterns relative to the north american shale composite nasc with la yb n 1 6 2 7 river water dissolved material 0 2 m is heavy ree enriched relative to suspended material and the most pronounced negative ce anomalies occur in rivers of high ph light ree concentrations vary by approximately 3 orders of magnitude and are inversely related to ph and major cation concentrations from these data we estimate that typical major river runoff has heavy ree depleted suspended material with la yb n 1 9 we conclude that the terrigenous input to the oceans from major rivers is heavy ree depleted relative to shales from the available data average river water dissolved material appears to be heavy ree enriched with la yb n 0 4 estuarine removal processes lower the dissolved ree river flux by approximately 60 and result in a flux that is more heavy ree enriched with la yb n 0 2 calculated oceanic residence times with respect to river input range from 2300 to 21 000 years are shortest for ce and greatest for the heavy ree and la such long residence times may suggest the presence of additional sources of ree in seawater

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

alluvial sandstone composition and paleoclimate ii authigenic mineralogy abstract various empirical and theoretical arguments suggest that early formed cement in sandstone is a product of meteoric water whose chemistry is controlled by climate the nature and distribution of early silicate cement in gondwana fountain and cutler sandstone support this supposition sandstones from all three units have experienced a broadly similar diagenetic history characterized by two stages of authigenesis stage i was typified by neomorphic development of kaolinite chlorite smectite quartz and additionally in the cutler formation laumontite stage ii was dominated by replacement reactions involving the production mostly of illite iron oxide carbonate minerals and mostly in the gondwana sandstone a second generation of quartz thermodynamic relations hydrologic constraints and radiometric dating of the late stage illite indicate that early authigenesis took place within a few million years of deposition at burial depths measured in hundreds of meters consequently the nature of the silicate cement was a function of the groundwater chemistry as controlled by climate during times of relative aridity ionic concentration of the groundwater was high and high proportions of smectite chlorite and more rarely laumontite formed such was the case in petrofacies i iv v of the gondwana supergroup for a definition of gondwana petrofacies see part i of this study in the cutler fm and in the upper 150 m of the fountain fm during times of high precipitation pore water was dilute which promoted authigen c formation of kaolinite and quartz this is represented by sandstones in petrofacies ii and vi of the gondwana and by sandstones in the lower 200 m of the fountain fm illite is especially abundant as a pseudomorphic replacement of kaolinite in the older gondwana sandstones illitization apparently began at burial depths of about 1 600 m at a temperature of about 75 c illite is not common in the cutler formation and is present only in subordinate amounts in the fountain formation from the study area the 18o values of early clay cement in the gondwana sandstones range systematically from base to top from 5 00 to 13 20 the systematic variation in 18o value of gondwana clay reflects the gradual migratory drift of the gondwana harm toward lower latitudes through time average 18o values for cutler cement 13 23 and fountain cement 19 82 are greater than the analogous values for gondwana cements this is consistent with the lower latitude setting of deposition for the cutler and fountain relative to the latitudinal location of the gondwana basins however the values are anomalously lower than what have been observed in modern day neoformed clays in weathering profiles from low latitudes

1984 sepm presidential address diagenetic albitization of potassium feldspar in arkosic sandstones abstract petrographic studies of subsurface cores of the fountain formation pennsylvanian in the denver region colorado show that detrital grains of potassium feldspar have been pervasively and complexly albitized during burial diagenesis in some strata all detrital grains of potassium feldspar have been convened to albite in some instances the conversion has taken place directly in others it has involved prior replacement of the potassium feldspar by other minerals particularly anhydrite calcite and dolomite which in turn are replaced by albite the albitized grains display fabrics such as perthitic intergrowths and chessboard twinning that are strikingly similar to replacement fabrics produced in feldspars by igneous and metamorphic processes if successive stages of the convers on to albite were not preserved the diagenetically albitized grains might easily be interpreted erroneously as detrital grains of plagioclase perthite or antiperthite derived from igneous or metamorphic source rocks the sodium required for the albitization is presumed to have been derived from intraformational sources particularly from diagenetically altered detrital grains of sodium rich plagioclase which have been extensively replaced by sodium free clay minerals ions released in the course of the albitization have provided important intrastratal sources of potassium aluminum and silicon which have been reprecipitated locally in authigenic minerals particularly albite illitic clays and adularia

chemical and mineralogical comparison of the pennsylvanian fountain formation colorado u s a an uplifted continental block to sedimentary rocks from other tectonic environments the mineralogic and chemical composition of composites of cobble and pebble sized rock clasts clay stones siltstones fine sandstones and size fractions of two sandstones of the fountain formation near beulah colorado were determined the sandstones are arkosic and most plot in the basement uplift or transitional continental fields of qfl diagrams the mineralogic composition of the sandstones is similar to that of the composite of rock clasts at a given location al mg fe ti mn sc th ree and cs are concentrated in the clay minerals or heavy minerals and are diluted by quartz or feldspar consequently they are inversely correlated with si cr hf k rb ba and sr are poorly correlated with si cr is concentrated in clay and in heavy minerals in the silts k rb ba and sr are correlated with k feldspar mica or clay mineral abundances sedimentary rocks from the fountain formed from an uplifted continental block the element concentrations plot in the fields of active or passive continental margins in many tectonic discrimination diagrams probably as a result of derivation from granitoid sources of similar composition the ree patterns eu anomaly size k and rb concentrations of the fine sandstones are mostly similar to those of the corresponding composite of rock clasts at a given location suggesting that these parameters might be the most reliable in distinguishing sources the most reliable discrimination diagram for uplifted tectonic blocks like the fountain may be a plot of k2o vs eu anomaly size since both of these parameters were very similar in concentration in both the sedimentary rocks and presumed source of the fountain most sedimentary rocks in this study have larger negative eu anomalies than those from the nasc north american shale composite or mcps midcontinent platform sediment this suggests a more evolved source for the fountain than that for average platform sediment

origin of loess deposits in the north tian shan piedmont central asia abstract loess deposits are widely distributed along the mountain piedmonts of central asia the transport processes and origins of central asian loess sediments remain poorly understood here we investigate the origin and formation of loess along the northern piedmont of the tian shan based on trace element including rare earth element ratios and multidimensional scaling analysis our results indicate that the loess has undergone weak chemical weathering using a selection of geochemical fingerprinting techniques based on pearson correlation and kruskal wallis h tests we establish a genetic link between alluvial proluvial fans plains deserts and loess along the tian shan piedmont in northern kyrgyzstan and southern kazakhstan the unsorted sediments on the piedmont slopes and alluvial proluvial plains are common sources for both deserts and loess to the north of the tian shan dune sediments are not the main source of the fine grained loess origin and formation of central asian loess is strongly dependent on local topographic context and wind dynamics only once loess provenance and formation has been understood across both space and time can reliable interpretations of palaeoclimatic proxies in these deposits be made

boulder weathering and erosion associated with a wildfire sierra ancha mountains arizona an april may 2000 coon creek fire burned 37 5 km 2 of the sierra ancha mountains 32 3 km miles north of globe az including 25 sandstone and 19 diorite boulders surveyed in 1989 and resurveyed after the burn after the summer 2000 monsoon season and after the winter 2001 season when viewed from the perspective of cumulative eroded area both sandstone and diorite displayed bimodal patterns with 79 of sandstone boulder area and 93 of diorite boulder area undergoing either no fire induced erosion or fire induced erosion 76 mm when stretched over cumulative boulder areas erosion due to the fire averaged 26 mm for sandstone and 42 mm for diorite post fire erosion from thunderstorm summer rains averaged i mm for 5 diorite and i mm for 10 sandstone boulders while only a single diorite boulder eroded an average of 1 2 mm after the winter winter erosion removed an average of 5 5 mm from 14 sandstone boulders thus fire appears to increase a rock s susceptibility to post fire weathering and erosion processes as predicted by goudie et al earth surf process landf 17 1992 605 in contrast to experimental research indicating the importance of size in fire weathering no statistically significant relationship exists between erosion and boulder height or boulder surface area a result similar to zimmerman et al quat res 42 1994 255 these data exclude 12 original sites and 85 boulders at sites impacted by the fire that could not be relocated with a reasonable cause for the lack of relocation being boulder obliteration by the fire given evidence from 1 0 be and 2 6 al cosmogenic nuclides earth planet sci lett 186 2001 269 supporting the importance of boulders in controlling evolution of nonglaciated bouldered landscapes geol soc amer bull 76 1965 1165 fire obliteration of boulders could be an important process driving drainage evolution in nonglaciated mountains

the effects of weathering on rare earth element y and ba abundances in tertiary basalts from southeastern australia tholeiitic basalts showing anomalously high ba y and rare earth element ree concentrations occur within the tertiary newer volcanic province of victoria and these geochemical characteristics are related to incipient alteration accompanying weathering ree and y released during weathering of basalts are retained either in secondary phosphate or clay minerals and in rocks showing very high ba concentrations the ba is present as baso4 leaching experiments suggest that glassy or fine grained rocks are more likely to release ree y and ba while more extensively altered rocks are likely to hold these elements probably because they substitute in or are adsorbed on clay minerals or because secondary baso4 and ree phosphates are resistant to acid leaching samples taken sequentially across a weathering profile in a tholeiitic basalt flow from fresh to intensively altered rock illustrate that in the very earliest stages of alteration extreme variations in the abundances of ba y and ree can occur this is reflected in the broad patterns of trace element behaviour manifested by an extensive analysed sample suite from the victorian newer volcanic province where there is no correlation between anomalous enrichments in ba y or ree and the level of incipient alteration ba anomalies are not necessarily accompanied by abnormal y and ree behaviour and this is probably because the mobility of each trace element is a function of a the ionic radius and charge of the ionic species it forms in solution b local groundwater parameters such as eh ph groundwater flux and concentrations in the groundwater of species such as so42 and c the secondary mineral assemblages developed in a particular situation sr isotopic compositions are not strongly affected by incipient weathering and do not show significant changes until alteration has progressed to the point where plagioclase begins to break down the study illustrates that relatively slight alteration at the earliest stages of weathering can produce drastic changes in the concentrations of ree y and ba and petrographic assessment of the freshness of samples is not precise enough to eliminate prior to analysis cases where these effects may be manifested where weathering has caused changes in abundance patterns these may be recognised by careful comparisons of appropriate elemental ratios e g ba rb throughout a particular analysed sample suite

constitutive mass balance relations between chemical composition volume density porosity and strain in metasomatic hydrochemical systems results on weathering and pedogenesis relations characterizing the chemical physical and mechanical changes resulting from metasomatic hydrochemical processes are developed using mass balance models which formally link chemical composition to bulk density mineral density volumetric properties porosity and amount of deformation strain rigorous analysis of aqueous solute transport effects is then made possible in a variety of porous media flow environments including chemical weathering pedogenesis soil formation diagenesis ore deposition and enrichment and metamorphism application of these linear constitutive relations to chemical weathering profiles shows that immobile and locally mobile chemical elements with masses conserved on the scale of soil profiles can be accurately identified from analysis of appropriate data arrays and then used as natural geochemical tracers to infer the nature and extent of hydrochemical weathering processes and volume changes during pedogenesis assumptions commonly made in the past about the supposed immobility of certain elements e g ti and zr become unnecessary quantitative differentiation between the effects of residual and supergene fractionation is then easily made these methods are applied to ni rich laterites developed by weathering of ultramafic rocks showing that during ordinary residual enrichment ni is concentrated by as much as 4 protolith peridotite concentrations this occurs simply by silicate mineral dissolution and removal of chemical elements other than ni e g mg with a corresponding reduction in saprolite density and increase in bulk porosity without significant deformation in contrast laterites with mineable concentrations of ni which are similarly undeformed such as the nickel mountain mine in riddle oregon have experienced in addition to residual enrichment strong supergene enrichment by fractionation of ore elements between a leached zone from which ni is extracted and a complementary enriched zone positioned farther along the direction of ground water flow soil forming processes in podzol chronosequences developed on sandy beach terraces of the mendocino coast of california involved soil column collapse of 60 percent by dissolution of silicate minerals in the albic horizon of al and fe leaching and 70 percent dilation expansion in the overlying organic rich layer by root growth the amount of erosion based upon paleosurface reconstructions using the excess mass of fe al pb ga and cu in the zone of supergene enrichment spodic horizon below the ground water table indicates that subsurface erosion by dissolutional collapse is three times that of surficial erosion finally using published chemical data for ti zr and cr on major bauxite deposits in australia where erosion rates are thought to be low we infer that there may have been major amounts of dissolutional collapse to explain the upwards increase of detrital zircon and rutile in weathering profiles

provenance and paleo weathering of tertiary accretionary prism forearc sedimentary deposits of the andaman archipelago india abstract in order to understand the provenance and tectono sedimentary processes occurring in the andaman subduction zone asz the late cretaceous to oligocene sedimentary records from the andaman islands have been studied these sedimentary records are considered to have preserved the history of the india asia collision evolution of the himalayas climatic development and palaeo drainage reorganizations on the indian and asian plates about 47 sandstones and mudstones shales and siltstones samples were analyzed for whole rock major trace and rare earth element compositions the geochemical results suggest mixing of sediments derived from the mafic igneous sources comprising local ophiolites and volcanic arc of the asz and an older archean to proterozoic age felsic cratonic source with compositions similar to average granodiorite or upper continental crustal sources the compositions were dominated by sources of the mafic arc during deposition of the mithakhari group whereas they were controlled by continental sources during deposition of the andaman flysch group the hope town conglomerate unit of the mithakhari group was mainly derived from weathering and erosion of the subaerially exposed local ophiolite thrust sheets whereas its namunagarh unit contains significant detritus from volcanic arcs the andaman flysch turbidites were deposited with a greater supply of sediments from first cycle active continental margin sources probably located in the tibetan and eastern myanmar region and recycled quartzose sedimentary sources within the nascent himalayas the sediments supplied to both the mithakhari and the andaman flysch groups were characterized by varying values of cia pia and w these variable values were either due to non steady state weathering conditions in the sources or the changing climatic conditions owing to the motion of indian plate with reference to the equator the uniformly high cia and w values in the andaman flysch rocks can be related to high precipitation and strong chemical weathering associated with the initiation of the indian monsoon

cerium anomalies in lateritic profiles the ree geochemistry and mineralogy have been studied in four lateritic profiles one derived from a syenite akongo sw cameroon the others being developed on a gneissic basement and located along a soil toposequence goyoum e cameroon there is a fractionation between lree and hree in the lateritic samples during weathering the weathered residual products being enriched in lree from la to eu and depleted in hree from gd to lu sampled waters are enriched in hree in relation to the syenite host rock a positive ce anomaly has been found systematically at the top of the saprolite beneath a zone of iron oxide accumulation in the laterite up to 2000 ppm ce may be present in the akongo profile cerianite ceo2 is present as very fine coatings in non ferruginous clayey domains primary ree bearing accessory minerals are weathered at the bottom of the profile specifically allanite and apatite are transformed into florencite and rhabdophane but these phases have no ce anomaly all the data are interpreted as the result of the following processes 1 1 ree leaching in a reducing environment 2 2 oxidation of ce3 to ce4 in an oxidizing environment 3 3 deposition of cerium as cerianite whereas the other ree remain in solution

paleoproterozoic sediment recycling during multiphase orogenic evolution in fennoscandia the tampere and pirkanmaa belts finland abstract geochronology of detrital zircons and their overgrowths combined with whole rock geochemical and sm nd isotopic data can be used to distinguish different stages of sediment recycling and metamorphism during multiphase orogenic evolution this approach is applied to the paleoproterozoic sedimentary rocks of the tampere and pirkanmaa belts southern finland in the center of the composite svecofennian orogen the lower part of the tampere belt succession and bulk of the pirkanmaa belt are characterized by turbidites whereas the upper part of the tampere belt succession is dominated by 1 90 1 89 ga mature arc type volcanic rocks detrital zircon geochronology indicates that the tampere and pirkanmaa belts have a coeval 1 92 1 89 ga depositional and tectonic history ages of pre depositional zircon overgrowths vary from 1 91 ga to 2 0 ga with clusters at 1 92 ga and 1 98 ga within the pirkanmaa belt post depositional zircon overgrowths indicate metamorphic culmination at c 1885 ma in the vammala ni zone and at c 1875 ma in the northern part the lower conglomerates and graywackes in the tampere belt and their equivalents in the pirkanmaa belt are rich both in neoarchean and paleoproterozoic grains the latter ranging in age from 1 9 to 2 1 ga compared to these a sample from the vammala ni zone has an exotic provenance with at least c 1 90 ga 2 04 2 15 ga 2 38 2 48 ga and 2 57 2 63 ga components a sedimentary recycling and tectonic model for the central fennoscandia is proposed in which the paleoproterozoic keitele bergslagen continent was formed during an unnamed orogeny at 1 98 1 97 ga the archean norrbotten microcontinent was attached to the continent at 1 97 1 93 ga upper kaleva turbidites derived from the lapland kola orogen in the north were deposited before 1 92 ga on a passive margin of the archean karelia craton the karelia craton collided with the keitele bergslagen norrbotten continent at c 1 92 ga forming the lapland savo orogen subsequent evolution led to rifting and break up of the latter continent into two microcontinents in the hinterland at 1 92 1 91 ga the rift was developed into a subsiding passive margin of the keitele microcontinent with voluminous turbidite deposition now seen as graywackes in the tampere pirkanmaa and pohjanmaa western finland belts the turbidite material was derived from the rising lapland savo orogen and included recycled upper kaleva recycled sandstones and first cycle 2 03 1 97 ga detritus from keitele 1 93 1 92 ga savo arc material as well as detritus from the archean craton and its cover deposits the collision between karelia and keitele caused a subduction reversal and the onset of tampere arc volcanism at 1 90 ga arc derived materials started to deposit and were mixed with older sedimentary rocks and trench parallel distal turbidites from exotic source were being deposited in the accretionary wedge

paleoenvironmental reconstruction of the lower mogi guacu river basin sao paulo state brazil morphopedosedimentary records and fluvial processes abstract the mogi guacu river rises in bom repouso minas gerais state brazil in the mantiqueira ridge and flows into the rio pardo river at an elevation of 483 m in pontal sao paulo state brazil after running a 530 km long course especially along the lower mogi guacu basin the river morphology is extremely sinuous characterized by intense processes of channel migration avulsion abandonment and reactivation of the channel producing an extensive alluvial plain composed of a series of associated relief forms and sedimentary facies among these forms point bar deposits by lateral accretion abandoned meanders paleo channels and fluvial terraces are notable features in this sense the objective of this work was to investigate whether these features could be linked to environmental changes to reach this goal soil properties of a catena of the jatai ecological station luiz antonio sao paulo state were analyzed in four sectors slope terrace i terrace ii and alluvial plain the results from grain size determination geochemical and isotopic studies dating paleopalynology coal fragments and micromorphology are presented in this paper from these analyses a paleo environmental evolution divided in three stages is proposed for the area 130 000 ybp upper pleistocene when the mogi guacu river base level was approximately 6 m above the present one a drier second phase 10 250 years bp lower holocene when an organic horizon was formed inside of an abandoned meander oxbow lake and a third phase 2096 ybp upper holocene of reactivation of a warm and humid climate that promoted the development of a two meters thick typic udifluvent in a sector where the mogi guacu river no more floods due to the incision of its thalweg reaching more than six meters depth in the last 130 000 years bp thus this paper used a fluvial geomorphologic approach and its interplay with climate to understand how the landscape was shaped from upper pleistocene to holocene however neotectonics might have played a relevant role as well not only in the mogi guacu river basin but also in the parana sedimentary basin

elemental mobility during the weathering of exposed lower crust the kinzigitic paragneisses from the serre calabria southern italy weathering and transportation studies of the chemical composition of sediments have determined how surface fractionation processes modify the elemental signature due to provenance and tectonic setting of siliciclastic rocks although the bulk of the exposed upper continental crust comprises granitoids metamorphic rocks from the intermediate to lower crust may be in some geological contexts the provenance of siliciclastic sediments a preferential enrichment of the lree relative to the hree is observed in weathered garnet rich kinzigitic paragneisses from the calabrian arc southern italy this fractionation is due mostly to the mineralogical control exerted by monazite which is concentrated in the silt size fraction of the soil however a significant part of hree released during garnet alteration is trapped by secondary minerals in the clay sized fraction of the soil in a manner similar to pb2 and cs cations of some concern in environmental geochemistry in the weathered material monazite is also important in controlling the eu anomaly the negative size of which increases with increasing th addition the eu anomaly in the clay sized fraction of the soil is very similar to that of the fresh rock suggesting that the eu eu index in pelitic sediments deriving from the intermediate to lower crust may be regarded as a reliable indicator of parental affinity other provenance indicators include la th which share the same mineralogical control indicators of contrasting mafic and felsic provenance e g sc th should be used with care

geochemistry of red residua underlying dolomites in karst terrains of yunnan guizhou plateau ii the mobility of rare earth elements during weathering the aim of this study is to characterize the evolution of the rare earth elements ree in the pingba red residua on karst terrain of yunnan guizhou plateau the in situ weathering and the two stage development of the profile had been inferred from ree criterions the ree were significantly fractionated and ce was less mobilized and separated from the other rees at the highly enriched top of the profile this is consistent with the increase of oxidation degree in the regolith and it is also suggested that the wet dry climate change during chemical weathering caused ce alternative change between enrichment and invariance in the upper regolith chondrite normalized ree distribution patterns for samples from dolomites and the lower regolith are characteristic of mree enrichment and remarkable negative ce anomalies patterns similar to the convex up ree patterns the following processes are interpreted for the patterns in this study 1 the accumulation of mrre rich minerals in dolomite dissolution 2 water rock interaction in the weathering front and 3 more leaching mree from the upper part of the profile the latter two explanations are considered as the dominant process for the formation of the ree patterns samples from the soil horizon exhibit typical ree distribution patterns of the upper crust i e la n yb n 10 and eu eu 0 65 all data indicate that the leaching process is very important for pedogenesis in this region the experiments demonstrating that abnormal enrichment of ree at the upper regolith bedrock interface is caused by a combination of volume change accumulation of ree bearing minerals leaching of ree from the upper regolith and water rock interaction during rock soil alteration processes our results support the conclusion that the weathering profile represents a large continental elemental storage reservoir whereas ree enrichment occurs under favorable conditions in terms of stable tectonics low erosion and rapid weathering over sufficiently long time c 2003 elsevier b v all rights reserved

geochemistry and mineralogy of the 2 45 ga pronto paleosols ontario canada abstract the ontario canada pronto paleosols which formed around 2 45 ga on archean granite were studied through field observation mineralogical study by microscope and microprobe and chemical analyses of major and 45 trace elements including rare earth elements rees since the first full description of its mineralogy and chemistry of major elements by gay and grandstaff gay a l grandstaff d e 1980 chemistry and mineralogy of precambrian paleosols at elliot lake ontario canada precambrian res 12 349 373 the pronto paleosols are among the most cited paleosols of the archean early proterozoic era though several questions have been raised as to whether they are true in place ancient soils results of this study show that the studied section meets the criteria for being in place paleosols furthermore the profile has no explicit traces of being strongly affected by hydrothermal alteration the ree containing accessory minerals were destroyed through weathering and secondary phosphate minerals with rees formed all of these observations support the weathering origin of the pronto paleosols however the profile should be identified as a saprolith rather than paleosol as even the uppermost samples exhibit the granitic texture of the parent rock the samples in this study were collected mainly from two sites site i and site ii saprolith samples from site i show the retention of fe and increases of the fe iii fe ii ratios and the chemical index of alteration cia values toward the unconformity as for the site ii samples the fe ti ratios show slight decreases with increasing cia values in the upper part of section whereas these samples also show the same trend of increasing fe iii fe ii ratios as the samples from site i microprobe analyses show that fe from the parent rock distributes mainly in mafic minerals as hornblende biotite or chlorite which were completely destroyed during the early stages of weathering in the saprolith section fe is present in sericite aggregates in the form of obscure patches of iron oxide tens of micrometers in size all these characteristics indicate that i the fe was not lost during soil formation at site i and slight amount of fe was lost at site ii and ii ferrous fe was quantitatively transformed to ferric fe i e oxidation during soil formation in the samples from both sites the ratios of al ti and si ti decrease toward the top of the profile together with the destruction of minerals toward the unconformity such as apatite biotite and chlorite the depletion of al and si suggests that the parental granite was weathered by an acidic weathering solution during the archean early proterozoic era the high atmospheric partial pressure of co 2 p co 2 is the most probable candidate for producing the acidic weathering solution

another look at rare earth elements in shales linear correlation and mass balance considerations indicate that clays are more important than zircon or other heavy minerals in hosting both light and heavy ree in cratonic shales considering the uniformity of the eu anomaly and ree distributions in cratonic shales it seems likely that detritus is thoroughly mixed during weathering and sediment transport and that the ree patterns in shales reflect the average ree pattern of the sources regardless of the ratio of clays to heavy minerals in the shales shales suspended river loads and near shore marine sediments all have broadly similar ree patterns and reported hree depletions in the latter two groups may reflect incomplete dissolution of heavy minerals during sample preparation ree distributions in shales and suspended river loads determined by inna are similar to those in average upper continent crust and ree distributions in shale averages nasc and paas seem to be reasonably representative of the average composition of post archean upper continental crust

oligocene miocene 28 13 ma climato tectonic evolution of the northeastern qinghai tibetan plateau evidenced by mineralogical and geochemical records of the xunhua basin abstract changes in sediment composition in the xunhua basin provide insights into the climatic and tectonic evolution of the northeastern qinghai tibetan plateau during the oligocene and miocene here we analyzed the clay mineralogy i e the proportions of smectite illite and chlorite and clay indicators bulk mineral composition i e the amounts of calcite quartz gypsum k feldspar plagioclase dolomite and halite and trace element indicators i e rb sr and ba sr ratios of sediments deposited from 28 to 13 ma in the xunhua basin to reveal the climate and or provenance changes the results suggest that significant changes in sediment provenance occurred at 25 1 ma and 21 6 ma caused respectively by initial uplift and accelerated uplift of the laji shan the xunhua basin experienced warm and humid conditions at 28 0 25 1 ma cool and dry conditions at 25 1 21 6 ma and somewhat warmer and wetter conditions at 21 6 19 2 ma followed by aridification in two steps at 19 2 ma and 13 9 ma the climate cooling event at 25 1 ma corresponds temporally to a major phase of uplift of central tibet relatively warmer and wetter conditions during the early miocene 21 6 19 2 ma are considered to record the influence of the asian summer monsoon and accelerated uplift of the laji shan the shift toward more arid conditions on the northeastern qinghai tibetan plateau at 19 2 13 9 ma was probably driven by uplift of the tibetan plateau and further aridification since 13 9 ma may reflect a weakening of the east asian summer monsoon and global climatic cooling

behavior of rare earth elements in groundwater during flow and mixing in fractured rock aquifers an example from the dandenong ranges southeast australia a previously defined flow system is used to investigate ree behavior at different stages along groundwater flow paths in fractured basalt and sedimentary aquifers results from this study indicate that ree concentrations and patterns predominantly reflect different types and rates of reactions taking place to those controlling major ion chemistry in areas where recharge is through sediments ree concentrations are high nd 8 62 31 61 ng l and localised processes such as source heterogeneity control ree patterns and concentrations increased concentrations of rees in these groundwaters where ph 6 1 is a result of early stage ree mobilisation in the flow system in contrast where groundwater recharges through basalt ree concentrations are low nd 2 40 4 75 ng l and ree concentrations are relatively constant along groundwater flow paths indicating steady state conditions groundwater from both the sediment and basalt aquifer systems flows into the local discharge area in contrast to tds contents and major ion ratios groundwater from the discharge area has ree concentrations nd 1 84 4 18 ng l and patterns that reflect a larger component of flow from the basalt aquifer lower ree concentrations of groundwater from the regional sedimentary aquifer may result from progressive ree sorption or co precipitation as indicated by an increase in y ho cl cn ratios and hree enrichment for groundwater with ph not vert similar 7 1 due to greater abundances of hree vs lree dicarbonato complexes

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

geochemical and geomorphological evidence for the provenance of aeolian deposits in the badain jaran desert northwestern china abstract identifying provenance of aeolian deposits in the mid latitude deserts of asia is essential for understanding formation and changes of earth surface processes due to palaeoclimatic fluctuations while some earlier studies focused on the interpretation of palaeoenvironments on the basis of aeolian deposits mainly in the desert margins and inter dune lacustrine sediments research on provenance of desert sands in the vast asian mid latitude deserts is still rare in this paper we present new geochemical data which provide insight to the provenance of dune sands in the badain jaran desert northwestern china an important part of this desert belt we sampled aeolian and lacustrine sediments in various parts of the badain jaran desert and examined their major trace and rare earth elements ree in bulk samples coarse and fine fractions respectively in addition we took and analyzed samples from a rarely known dune field with red sands northeast of the badain jaran our results show that the sands from the badain jaran desert are generally different from those in the red sand dune field in terms of ree pattern and geochemical characteristics suggesting different sediment origins geochemical composition of the aeolian sand samples indicates these sediments should be mainly derived from mixed source rocks of granite granitoids and granodiorite comparing the immobile trace elements and ree ratios of the samples from the badain jaran desert red sand dune field with rocks of granite granitoids in their potential source areas we conclude that 1 the aeolian deposits in the badain jaran desert are predominantly derived from the qilian mountains northeastern tibetan plateau initially via fluvial processes 2 the altay mountains and mongolian gobi are the ultimate source areas for the red sand dune field 3 the altai mountains and mongolian gobi in the northwest that could produce massive amounts of materials via intensive deflation and alluvial process are additional sand sources of the badain jaran desert although their contribution is of secondary significance as the badain jaran desert acts as sediment sinks of sediments from the qilian mountains of northeastern tibetan plateau via fluvial processes it is likely that zircon grains of loess on the chinese loess plateau with age distributions similar to those of the northern tibetan plateau could be derived from the badain jaran desert as the wind data suggest

ree fractionation during granite weathering and removal by waters and suspended loads sr and nd isotopic evidence very few studies deal with ree rare earth element mobility within the system soil soil solution streamwater in this article we try to characterize the fractionation and the migration of the ree in a granite derived soil system located in a small catchment of the vosges mountains icp ms and tims measurements were performed on both solid samples fresh granite soil and suspended load of the stream and waters soil solutions springwater and streamwater to determine their respective ree concentrations and sr and nd isotopic compositions the paas normalized ree pattern of the bedrock is characterized by a strong depletion in hree heavy ree and a negative eu anomaly 0 46 similarly the granite normalized ree distribution patterns of the soil samples show hree depletions that become more important with decreasing depth the correlative behavior between p2o5 th and ree with depth indicates that besides apatite other phosphate minerals such as monazite are the most important phases controlling the th and ree budget in the soil profile on the other hand at greater depth zircon seems to be another important mineral phase controlling especially the hree enrichment as shown by the positive relationship between zr content and the yb ho ratio different grain size fractions show similar ree distribution patterns and are only weakly fractionated compared with bulk soil sample however the finest fraction 0 20 m is more enriched in sr and ree suggesting a stronger concentration of ree carrying minerals in this fraction the suspended and dissolved load of the stream show as a whole an enrichment in hree if compared with the granite or with the different soil samples however compared with the uppermost soil samples the suspended load is significantly more enriched in hree its ree distribution pattern is more similar to that of the finest fraction of the deeper soil sample and to the fresh granite thus most probably the ree of the suspended load originated from a source with ree characteristics found in the deep soil horizons this source might have been situated in the uppermost soil profile which is actually ree depleted the weathering process can be compared with a leaching experiment where the waters correspond to the leachate and the soil to the residual phase of the granite the sr isotope data indicate that the suspended load originates from the finest soil fraction the sr and nd isotopic data of the suspended load suggest that it contains up to 3 sr and nd from apatite and up to 97 from feldspar most of the sr and nd in the waters originate from apatite leaching or dissolution

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

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

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

trace element mobility during spheroidal weathering of basalts and andesites in hawaii and guatemala abstract trace element mobility has been studied in spheroidally weathered corestone shell complexes developed on late tertiary and quaternary volcanic rocks the parent materials are basalts and andesites related to 1 a subduction zone tecuamburro and moyuta volcanoes guatemala and 2 a hot spot hawaiian islands of oahu maui and hawai i the initial major element compositions are largely preserved in the corestones each corestone sample shows major element abundances characteristic of the different magmatic processes through which the lavas were generated however the changes in trace element compositions due to weathering show similar patterns in the corestone shell complexes independent of the tectonic setting and age element mobility within the different corestone shell complex was determined using an isovolumetric reference frame in this method bulk density is chosen as an independent measure of the extent of weathering based on volumetric concentrations the notion of element immobility cannot be applied to all the corestone shell complexes elements commonly assumed to be immobile e g zr ti and al vary in volumetric concentration for some corestone shell complex despite petrographic evidence of only minor weathering two corestones oahu and tecuamburro have become enriched in ree 3 relative to other lava flows from the same volcanoes and display negative ce anomalies the exfoliated shells from these complexes tend to have lower concentrations of ree 3 and have positive ce anomalies the fractionation of ce from the other rare earth elements ree is inferred to be a manifestation of changes in the valence state of ce from trivalent to tetravalent under oxidizing conditions in settings where the development of corestone shell complex is advanced an acidic solution can mobilize trivalent ree leach them out of more extensively weathered materials and transport them to less acidic portions of the regolith undergoing incipient weathering the precipitation of the ree 3 in the rinds and centers of the corestones are likely due to increases of the ph of the weathering solution systematic weathering induced ree behavior enrichment of most ree with lesser ce enrichment resulting in a negative ce anomaly can be discerned even in corestone samples that exhibit major element abundances and petrographic features otherwise similar to unweathered basalts and andesites

eolian contribution to soils on mount cameroon isotopic and trace element records abstract we determined sr nd and pb isotopic compositions and major and trace element compositions of soil samples recovered from three soil profiles developed on relatively young pyroclastic deposits less than 10 000 years old of the mount cameroon volcano the time elapsed since then is short compared with the half lives of rb sm u and th suggesting that radioactive decay can be neglected we therefore assumed that i these polyphase soils developed on isotopically homogenous substrates and ii any isotopic variation within such profiles cannot be due to selective dissolution of primary minerals with isotopic compositions different from that of bulk bedrock any sr nd or pb isotopic variation would therefore record an allochtonous input occurring either in a solid or dissolved state sr and nd isotope compositions change systematically with depth in the soil profile in particular 87 sr 86 sr ratios are far greater in the humic horizons than in the underlying horizons except in the ca9h soil profile although smaller than for sr isotope compositions 143 nd 144 nd ratios displayed an inverse relationship with a decrease towards the uppermost organic rich horizons these isotope shifts correlate with changes in sr and nd contents suggesting an allochtonous input characterized by significantly different isotope compositions and slightly lower sr contents but higher nd contents pb isotopic compositions and pb concentrations in the uppermost horizons were distinct from those of underlying horizons in the soil sequences since an anthropogenic contamination such as from leaded petrol cannot explain the pb shifts a natural source has to be invoked for pb as well as for sr and nd considering both the wind paths in west africa and the isotopic shifts registered in the uppermost horizons saharan dust appears to be the best candidate to explain such variations these inputs probably happened in winter when dry warm harmattan wind blows from the northeast a maximum of 8 of saharan dust accretion was calculated for the mount cameroon soils this corresponds to average dust deposition rates between 1 3 and 0 8 g cm 2 ka 1 values that are much higher than those found in hawaiian soils by kurtz et al kurtz a c derry l a chadwick o a 2001 accretion of asian dust to hawaiian soils isotopic elemental and mineral mass balances geochim cosmochim acta 65 1971 1983 and are probably related to shorter distance between dust source and deposit any elemental mass balance calculated in the upper organic rich horizons should be then corrected from allochtonous wind borne saharan dust before evaluating weathering linked chemical mobilities

late cenozoic columnar jointed basaltic lavas in eastern and southeastern china morphologies structures and formation mechanisms late cenozoic basaltic lavas in eastern and southeastern china commonly display spectacular columnar joints in four volcanic fields in this region we have observed and classified five types of colonnade vertical inclined horizontal fanning upwards and fanning downwards that provide information on the cooling regime and emplacement mechanism of the lava flows in total we analyzed the geometry and morphology of joints across ten different lava flow areas in the changle volcanic field cvf luhe volcanic field lvf eastern zhejiang volcanic field ezvf and niutoushan linjin island nanding island volcanic field nlnvf field observations show that columnar jointed alkaline basalts commonly exhibit narrow and irregular shapes indicating fast cooling tholeiites with columnar joints in contrast show wide and regular polygons indicating slower cooling vertical columnar joints and other types horizontal and fanning shaped have different mature patterns with the implication that lavas flowed on relatively flat land and in paleo valleys respectively this study suggests a simple qualitative description of different types of colonnade can be made based on their alignment patterns which represents a direct and easy way to derive solidification processes after lava eruption from colonnaded lavas in outcrop

allochthonous surface alteration of ni laterites abstract lateritic weathering sections over ultramafic rocks in burma puerto rico venezuela malagasy and brazil display anomalous chemical variations in their upper parts these variations are not due to weathering of ultramafics but to the addition of varying amounts of weathered material from other rocks this contribution can cause a considerable increase in si al ti and zr and decrease in fe cr and ni in the surficial parts of the limonite zone in other occurrences the admixture of foreign material can only be recognized by strongly elevated ti and zr amounts in surface layers which is atypical for ultramafic rocks and their weathering products in most of the occurrences the foreign material was probably transported by colluvial alluvial processes but an eolian derivation is also possible sedimentary processes may cause large amounts of foreign material to be mixed with ni limonite smaller amounts of foreign clayey material can also be washed downwards into clearly autochthonous limonite the ni laterite deposit on the tagaung taung burma which has been explored in detail by drill holes provides an excellent example for the processes discussed above which can also influence the composition of the weathering mantle above other parent rocks

multiple alteration events in the history of a sub huronian regolith at lauzon bay ontario confusion exists over the usefulness of chemical data from precambrian weathering profiles in constraining models of atmospheric evolution one difficulty is in correctly identifying ancient weathering effects and isolating them from numerous other processes that are likely to have affected such ancient rocks in this study of a middle precambrian granitic weathering profile we have used several analytical techniques to separate weathering related chemical and mineralogical changes from those resulting from other processes the profile is exposed beneath the huronian at lauzon bay in the blind river area of ontario and has a complex history of alteration events addition of allochthonous material and low grade metamorphism much of this history can be deciphered and changes in mineralogy and bulk and mineral chemistry can be assigned to separate alteration events specifically the granite has undergone preweathering albitization resulting in na enrichment followed by chemical weathering that corrode

mobilization and re distribution of major and trace elements during extreme weathering of basalt in hainan island south china major trace and organic elements of a laterite profile developed on neogene basalts in northern hainan island south china were reported in this paper the aim of which was to investigate element mobilization and re distribution during extreme weathering the results indicate that most of the elements have been mobilized and transferred downwards along the profile by aqueous solution organic matter om can significantly improve the transport of insoluble elements among all the elements th is the least mobile as for the general conservative elements during incipient chemical weathering such as fe ti zr hf nb and ta the removals are up to 20 40 in the upper profile however these elements behave as conservatively as th in the lower profile in the middle profile oxic environment occurs accompanied with significant om decomposition the mn and ce transferred downward are readily oxidized into insoluble mn iv and ce iv and precipitate in the oxic front important om decomposition decreases the capacity of transfer of insoluble elements in aqueous solution consequently al significantly precipitates in the oxic front and rees with the exception of ce precipitate largely in the omdepleted layers co and u are also concentrated in the oxic front in association with mn and ce respectively however cr shows a negative correlation with mn because its response to redox condition changes is reversed from that of mn mn oxides hydroxides fe oxides hydroxides and secondary phosphate minerals other than clay minerals are potential hosts for rees except for ce in the profile rees with high concentrations in the profile seem closely associated with mn oxides hydroxides remarkable highly correlated ce and gd anomalies are observed in the profile ce anomalies are caused by ce precipitation in the oxic environment and successive decomposition of organic matter gd anomalies are likely to have resulted from lower stability constants of gd om complexes compared to those of neighboring rees the overall elemental behaviors in this profile suggest that organic matter plays a very important role in the mobilization and re distribution of the elements during extreme weathering

aeolian accumulation an alternative origin of laterite on the deccan plateau india abstract laterite is ubiquitous in india and has been extensively studied however it is still controversial with respect to its origin definition classification and implications in paleoclimate tectonic history and topography evolution of those the origin of laterite either in situ weathering of protoliths or weathering of allochthonous input is the most critical to address the ca 25 m thick laterite duricrust capping the deccan plateau is conventionally hypothesized to derive from in situ weathering of the topmost basalt however this thick laterite lacks upward progressive weathering which is characteristic of lateritic profile instead it displays 1 homogeneity in weathering intensity through the duricrust 2 a clear unconformable contact of laterite with red clay which together suggests that this thick laterite is genetically unrelated to in situ weathering of the topmost basalt lines of evidence in mineralogy granularity and geochemistry proved the disconnection between this laterite and basalt and in contrast indicated its correlation to aeolian accumulation in this study the laterite together with the red clay was proposed to derive from aeolian dust accumulation and weathering since 65 ma within context of indian plate drifting across the equator from southern to northern hemisphere

millennial scale evolution of elemental ratios in bulk sediments from the western philippine sea and implications for chemical weathering in luzon since the last glacial maximum abstract to reconstruct the chemical weathering history in luzon philippines since the last glacial maximum lgm major and trace elements ti al fe k ba rb v sc cr and th and grain size were determined for core md06 3054 as well as the bulk and detrital fractions of three core top samples from the western philippine sea wps in combination with previously published sr nd isotopes our new results indicate that ti normalized elemental ratios in the study samples were not controlled by the quantity of biogenic authigenic or diagenetic materials sediment provenance or grain size instead variations in ti normalized elemental ratios mainly reflect changes in chemical weathering intensity with lower values representing stronger chemical weathering in luzon to assess long term integrated chemical weathering patterns we defined a stacked chemical weathering index scwi based on all elemental ratios in the study core downcore scwi records indicate that sediments deposited during the lgm underwent a degree of chemical weathering equal to that during the holocene and sediments deposited during the last deglaciation exhibit rapid changes in chemical weathering with higher intensity during the heinrich event 1 h1 and younger dryas yd and lower intensity during the bolling allerod b a in the wps these observations are in excellent agreement with chemical weathering proxies such as the k al ratios and chemical index of alteration when applied to the same core we infer that persistent sea level lowstand and induced reworking of poorly consolidated sediments on the eastern luzon continental shelf during the lgm accounted for equal or slightly stronger chemical weathering for the lgm sediments relative to the holocene sediments rainfall rather than air temperature in luzon was responsible for the rapid changes in chemical weathering during the last deglaciation with higher precipitation generating stronger chemical weathering during the h1 and yd than during the b a our observations combined with existing data suggest that strong weathering of marine sediments during colder intervals of the middle late quaternary is likely to be a general feature of the tropical west pacific although the mechanism that underlies this phenomenon remains controversial

mineralogical and chemical changes of soil and stream sediment formed by intense weathering of the danburg granite georgia u s a abstract a series of soil and stream sediments developed during intense weathering on the metaluminous danburg granite northeastern georgia u s a have been analyzed mineralogically and chemically the concentrations of ba na rb and cs in the silt and coarser fractions are controlled mainly by feldspars and biotite hf is controlled by zircon and the ree rare earth elements and th are largely controlled by sphene variations in feldspar sphene and zircon may produce small variations in eu sm and la lu ratios ferromagnesian minerals control ta fe co sc and cr concentrations the mineralogical and chemical composition of the danburg granite is more closely reflected in the silt than in the sand or gravel fractions of stream sediments in the silt the contents of rb ree th ta fe co and sc and the ratios of la sc th sc la co th co eu sm and la lu are similar to those in the unweathered granite in contrast these element contents or ratios in the sands and gravels are 0 05 3 the concentration in the unweathered granite ta and ba contents are an exception to the above the ta and ba contents of the sands and gravels are similar to those of the granite in the kaolinite halloysite clays the content of na is depleted relative to the source rb cs ba hf and ta are depleted or enriched in the clays relative to the source while the ree th fe co sc and cr are enriched the eu sm eu anomaly size and la lu ratios and the ree patterns of the clays are similar to those of the source thus the mineralogy and element contents of a siltstone developed from metaluminous granitic sources during intense weathering would be expected to be more similar to the source rock than the sandstones and conglomerates claystones should contain similar ree patterns and eu sm ratios as the source rock but such fine grained sediments might represent much larger areas of source rocks than the more locally derived sandstones or conglomerates

precambrian superplumes and supercontinents a record in black shales carbon isotopes and paleoclimates prominent maxima in black shale abundance and in black shale total shale ratio occur at 2 0 1 7 ga with less prominent peaks in the late neoproterozoic 800 600 ma and in the late archean 2 7 2 5 ga peaks in chemical index of alteration cia of shales at the same times suggest corresponding warm paleoclimates the peaks in cia and black shale abundance are correlated in time at a 94 confidence level the black shale and cia peaks may reflect the combined effects of mantle superplume events and supercontinent formation at 2 7 and 1 9 ga mantle superplume events may have introduced large amounts of co2 into the atmosphere ocean system increasing depositional rates of carbon and increasing global warming increased black shale deposition may reflect some combination of 1 increased oceanic hydrothermal fluxes introducing nutrients 2 anoxia on continental shelves and 3 disrupted ocean currents the apparent absence of carbon isotope anomalies at these times reflects an increase in the deposition and burial rate of both reduced and oxidized carbon peaks in black shale abundance at 2 1 ga and 800 600 ma correlate with peaks in 13 c in marine carbonates increases in atmospheric oxygen and with high cia values in shales these are all consistent with higher rates of organic carbon burial in black shales at these times these peaks may record the breakup of supercontinents at 2 2 2 0 ga and again at 800 600 ma which resulted in increased numbers of partially closed marine basins disruption of ocean currents and increased hydrothermal vents at ocean ridges all of which led to widespread anoxia 2001 elsevier science b v all rights reserved

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

recognising different sediment provenances within a passive margin setting towards characterising a sediment source to the west of the british late carboniferous sedimentary basins to investigate whether sediments with subtly different provenances could be recognised within a passive margin setting samples were taken from westphalian sedimentary rocks of the pennine basin south wales coalfield culm basin of britain and from northern ireland although previous work has shown that 3 major source areas were responsible for the infill of the pennine basin this study is restricted to sediments believed to have been derived from the west their nominally similar western provenance was confirmed using sm nd isotope techniques and their deposition in a passive margin setting was established using elemental discrimination diagrams while the overall sediment provenance may have been from the west the trace element geochemistry indicates that at least two major sediment pathways can be distinguished plots of eu eu gdn ybn along with ternary plots of cr v ti zr gdn ybn or sc cr suggest different source areas for the culm basin and the south wales coalfield in the culm basin the cr v ratio generally exceeds 1 25 with a small eu anomaly and a low gdn ybn ratio the cr v ratio is less than 1 25 in the south wales with a larger eu ratio and a higher gdn ybn than the culm basin significant separation of the culm basin and the south wales coalfield during the early westphalian by the bristol channel bray fault may have been a factor contributing to the provenance differences late carboniferous dextral displacement along this fault brought these basins into close juxtaposition and it is unlikely that the bristol channel landmass formed a common source area for these two basins

behavior of major and trace elements during weathering of sericite quartz schist abstract two regolith profiles developed on the sericite quartz schist in subtropical humid environment were selected to investigate behaviors of major and trace elements during weathering in mengman gold deposit of yunnan province china one profile located in the mining district sheared by a fault and the other was outside the mining area which represented the normal weathering profile on the schist regolith samples were collected in both profiles sequentially thirteen major oxides and 23 trace elements including ree were analyzed and their behaviors were compared in these two profiles based on the idea that immobile element is just a relative notion we presented a method of immobile plateau to determine immobile elements during each stage in a progressive geochemical process and used mass ratio mr to calculate the percentage of gain or loss x gp of each element during the whole process in both profiles only tio 2 was immobile during the whole weathering the regolith profile formed on the mineralized schist recorded the weathering process more sensitively than the regolith profile on the normal schist ree was mobile and fractionated during the schist weathering lree was loss in mass during the soil development stage which resulted from the chemical leaching but was gain in mass during the pedogenesis stage because of the preferential absorption of soil to lree the lree depletion near the fault during weathering was the collective effects of chemical leaching and physical accumulation hfse were all mobile in the mineralized regolith profile especially near the fault but nb ta and zr hf were covariant in both profiles during the schist weathering

provenance weathering and erosion records in southern okinawa trough sediments since 28ka geochemical and sr nd pb isotopic evidences abstract geochemical and sr nd pb isotopic compositions of the detrital sediments from odp hole 1202b and taiwan rivers were measured in this study aiming to reveal changes in sediment provenance in the southern okinawa trough sot since 28 ka and to examine the weathering and sediment transport processes in response to monsoon climate variability large variations in sr nd pb isotopic ratios at 11 9 ka suggest changes in detrital sediment provenance in the sot from a dominance of the paleo changjiang yangtze river and or continental shelf sediment during the late deglaciation and to west taiwan rivers since 9 5 ka volcanic rocks and eastern taiwan sediments have not significantly contributed to the sot the large shift in sediment provenance during the early holocene marks a major change in oceanic circulation mainly caused by the intrusion of the kuroshio current into the trough clay mineral and geochemical proxies suggest that the taiwan derived sediments accumulated during the early mid holocene climate optimum ca 9 5 4 ka might be tightly related to the reworking of older altered sediments from terraces and floodplains rather than having experienced more intense silicate weathering than in the late holocene 4 0 ka overall silicate weathering in taiwan was greatly inhibited by accelerating sediment production and transfer from land to ocean caused by monsoon intensification in holocene our study illustrates that the radiogenic isotopic and geochemical compositions of fine grained detrital sediments are sensitive tools for fingerprinting sediment sources and for reconstructing changes in oceanic currents and monsoon climate in river dominated east asian continental margin

geochemical anatomy of a spheroidally weathered diabase major trace element concentrations and nd sr isotope ratios were measured in micro drilled samples of a 237 ga old hand specimen sized spheroidally weathered diabase from southern india a sample of the un weathered diabase dike was also analyzed x ray micro ct imaging of the weathered sample shows three dominant mineral phases which are plagioclase pyroxene and a fe bearing phase possibly hematite and or ilmenite this imaging documents the pervasive nature of two generations of ribbon like cross cutting fractures the older fracture is sealed while the more recent fracture is open without any in filling the values of the chemical index of alteration cia of the samples show a wide range but are less than 50 despite being a relatively less weathered rock we observe that concentrations of major minor and trace elements vary significantly with the percentage relative standard deviation rsd for the elements ranging from 10 2 41 8 the cia of the samples do not show any trend with the position of the sample in the hand specimen barring ca and li whose concentrations decrease from the core to the rim of the sample there is no significant spatial trend in the concentrations of the elements concentrations of na al and sr increase with increasing cia values while concentrations of mg fe and sc decrease with increasing cia the strong positive correlations of na and al as well as na and sr indicates preferential weathering of plagioclase in the diabase na ca increases while mg al mg na mg ca fe al and sc sr decrease with increasing cia values and the un weathered rock plots in the middle of these trends such variations are explained in terms of differential weathering of plagioclase in samples with lower cia than the un weathered rock w1 type and pyroxene in samples with higher cia than the un weathered rock w2 type which have varying resistance to weathering at the hand specimen scale the variability in the weathering indices like cia are controlled by differential weathering of minerals and might not accurately reflect the intensity of weathering chondrite normalized la sm and gd lu co vary with cia values indicating mobility of the rees during spheroidal weathering even at the hand specimen scale the eu anomaly also increases with increasing cia values which is explained by differential weathering of pyroxene and plagioclase we observe large percentage deviations of the nb normalized concentrations of elements from the un weathered rock in specific samples but no spatial trend is observed overall the variations in element concentrations can be explained by varying fluid mobility of the elements selective weathering of the minerals in the diabase and ambient environmental conditions considerable nd and sr isotopic variability is observed at the hand specimen scale and is explained in terms of weathering related fractionation of parent daughter ratios this elemental fractionation must have happened long time ago to allow for radiogenic decay of the long lived isotopes of rb 87 and sm 147 the spread rsd in the initial sr and nd isotope compositions of the weathered samples reach a minimum value around 12 13 ga which we interpret as the timing of the peak weathering event which led to fractionation of the parent daughter ratios for nd isotopes the average epsilon nd 1 2 ga of the weathered samples coincides with the epsilon nd 1 2 ga of the unweathered rock the timing of the weathering event coincides with the timing of the breakup of the columbia supercontinent and follows wide spread alkaline volcanism in the indian subcontinent this is the first such attempt to determine the timing of a weathering event in rocks using long lived radioactive isotopes c 2016 elsevier b v all rights reserved

enrichment of ion exchangeable rare earth elements by felsic volcanic rock weathering in south china genetic mechanism and formation preference abstract felsic volcanic rocks are an important source for generating ion adsorption type rare earth element ree resources to better understand the supergene enrichment of rees related to felsic volcanic rock weathering this study conducted an investigation of indosinian felsic volcanic rocks from guangxi southwest china which have been subjected to deep weathering the weathering has formed large areas of thick regolith with the potential to host ion adsorption type ree mineralization the felsic volcanic rocks belong to the dacite rhyolite series and are peraluminous high k calc alkaline and ree rich 325 376 ppm abundant ree bearing accessory minerals are present in the felsic volcanic rocks including titanite average ree 15 1 wt allanite average ree 14 9 wt and apatite average ree 1510 ppm and these three minerals contain an estimated 88 7 of the whole rock rees content significant ree enrichment is present in the felsic volcanic rock derived regolith a typical rhyolite derived regolith profile has ree contents that increase from 376 ppm in the rhyolite to 1737 ppm in the regolith representing an almost five fold enrichment due to weathering the rees in the regolith are present in an ion exchangeable form irees which accounts for 52 87 of the total rees present trees the occurrence of irees is closely linked to clay minerals showing an affinity in the order halloysite kaolinite illite continuous operations of rees by an eluviation illuviation process from the source minerals titanite allanite apatite to sink minerals kaolinite halloysite illite results in an iree enriched zone in the middle and lower parts of the rhyolitic regolith notably besides the studied indosinian felsic volcanic rocks there are multi epochs of such lithology outcropped in south china their related irees mineralizations however are preferentially developed in the weathered terrains of early yanshanian and indosinian felsic volcanic rocks and not in those of the yanshanian and late yanshanian felsic volcanic rocks a comparison of the mineralized and barren units indicates that the irees mineralization hosted in felsic volcanic rocks regolith is controlled by some key endogenic and exogenic ore forming factors high initial ree concentrations in the unaltered felsic volcanic rocks a suitable climate and a relatively quiescent tectonic setting are favorable for the formation and preservation of irees mineralization

geochemistry of mesoproterozoic sedimentary rocks of upper vindhyan group southeastern rajasthan and implications for weathering history composition and tectonic setting of continental crust in the northern part of indian shield abstract the upper vindhyan succession of southeastern rajasthan is divisible into kaimur rewa and bhander groups the major and trace element including rare earth elements data of the upper vindhyan shales and sandstones are investigated to determine the weathering history composition and tectonic setting of mesoproterozoic continental crust cia chemical index of alteration values a cn k plot a al2o3 cn cao na2o k k2o and depletion in u na2o cao sr and ba suggest that the source area experienced moderate to high degree of chemical weathering under warm and humid conditions provenance modeling indicates that the kaimur sandstones are best modeled with a mixture having 40 granitic gneiss 20 tonalite trondhjemite granodiorite ttg 20 mafic enclaves and 20 berach granite of the banded gneissic complex bgc a mixture of 60 granitic gneiss 20 mafic enclaves and 20 berach granite of the bgc can model the rewa and bhander groups it is suggested that the upper vindhyan sedimentation commenced at the time of delhi sausar orogeny at about 1100 1000 ma the orogenic movements uplifted the parts of old continental crust in the bgc terrain creating positive areas which exposed older crustal blocks containing ttg as important component the debris of kaimur sandstone probably derived from these uplifted blocks as indicated by palaeocurrent data the rewa and bhander formations were derived from bundelkhand granitic gneiss complex bggc occurring to the north of the basin and or the chotanagpur granitic gneiss complex cggc of eastern indian shield the derivation of lower and upper groups of vindhyan succession from different source terrains of identical composition suggests that at the time of vindhyan sedimentation the bgc of rajasthan the bggc of central india and the cggc of eastern india had similar lithological composition this implies that well before the origin of the vindhyan basin these discrete terrains evolved as a single unit that existed as a mesoarchaean nucleus in the northern part of the indian shield

heavy rare earth element enrichment in granites of the aar massif central alps switzerland abstract the paper presents rare earth element ree determinations of whole rocks and minerals of the central aar granite a hercynian composite granite intrusion in the aar massif central alps consisting mainly of granodiorites granites and leucogranites their geochemical differentation is characterized by a slight depletion of light ree lree and eu and a clear enrichment of heavy ree hree this evolution leads to hree enriched leucogranites with typical wing shaped distribution patterns in chondrite normalized diagrams these distribution patterns can be explained either by pure fractional crystallization of k feldspar and or by crystallization of accessory phases that did not deplete the melt in hree due to their affinity to highly polymerized high silica melts the latter stayed in the liquid phase until they were incorporated in solids during the final stage of bulk magma crystallization the ree contents of analyzed mineral phases allanite apatite biotite epidote garnet and zircon are used to calculate a ree budget of the whole rock these data suggest that existence of further hree rich accessory mineral phases in the felsic rock compositions which have not been analyzed qualitative x ray and eds analyses revealed the existence of accessory minerals like thorite chernovite an y ca mineral and polycrase these minerals may play an outstanding role in the distribution of ree u and th in high silica melts

influence of phosphate on mobility and adsorption of rees during weathering of granites in thailand abstract the permo jurassic north thai nt granites and the late cretaceous to paleogene western province wp granites in thailand are contrasting in terms of tectonic settings and chemical compositions the nt granites which are dominated by s type features are characterized by lower sio2 contents and higher p2o5 contents than the wp granites in this study in order to compare the mobility and adsorption of rare earth elements rees during weathering of the two granite suites geochemical analyses were conducted on the granite and weathered granites the weathered wp granites show wider ranges of rees y rey contents percentages of ion exchangeable rey and ce anomalies than the weathered nt granites these results indicate that rees were less mobile during weathering of the nt granites than those of the wp granites the low mobility of rees can be explained by the occurrences of residual monazite and secondary ree phosphates which immobilize rees during weathering therefore in the weathered nt granites rees are mostly contained in the phosphate minerals in contrast the weathered wp granites are dominated by ion exchangeable rees adsorbed rees which are likely to exist on the surface of clays previous studies and our study results suggest that the ion exchangeable rees in the weathered granites were probably sourced from weatherable allanite titanite apatite and or ree fluorocarbonate and rarely from monazite and zircon which are resistant to weathering the weathered granites of low phosphate contents potentially show high percentages of ion exchangeable rey although they can be influenced by the degree of hydrothermal alteration or weathering of granites