mudstone petrology of the mesoproterozoic unkar group grand canyon u s a provenance weathering and sediment transport on intracratonic rodinia abstract the synthesis of mudstone petrology and interbedded sandstone detrital zircon geochronology provides insights into the provenance weathering regime hydrodynamic effects and diagenesis of the mesoproterozoic unkar group unkar mudstones were derived largely from the grenville orogen go of southwest texas and the adjacent yavapai mazatzal ym and southern granite rhyolite sgr terranes detrital zircon data indicate distinct pulses of go derived sediment during hakatai and dox formation deposition whereas shinumo sediment contains a larger component of ym and sgr material an increase in plagioclase and biotite abundances in the dox further suggest an orogenic pulse bulk chemistry including elevated cr and ni abundances and ree systematics implicate a heterogeneous provenance for unkar sediment best approximated by a mix of granite or granodiorite with some basalt weathering of unkar sediment as determined from mudstone and crystalline source bulk chemical trends is characterized as moderate cia values between 55 and 70 indicative of a temperate climate in an orogenic setting small less than 10 wt amounts of detrital kaolinite and chlorite are consistent with a moderate temperate weathering regime illite the dominant clay mineral in the unkar group is largely the 2m1 polytype and detrital in origin however it is estimated that 7 of the k in the escalante creek member results from k metasomatism and may form up to 15 wt authigenic 1m or 1md illite the clay size fraction and zircon are the chief contributors to the ree budget in unkar mudstones lithostratigraphic variations in the hree distributions can be attributed partially to variable zircon abundance in the silt size fraction a likely function of hydrodynamic sorting age constraints on the duration of unkar group sedimentation range from 30 to 100 my for the 1100 m conformable shinumo dox succession and result in compacted sedimentation rates of between 1 0 and 3 6 cm 103 yr these rates are comparable to mesozoic foreland basin settings

geochemistry of the mesoproterozoic lakhanda shales in southeastern yakutia russia implications for mineralogical and provenance control and recycling abstract shales of the lakhanda group of late mezoproterozoic age 1050 1000 ma from the southeastern siberian craton in russia have been analyzed for major elements and a number of trace elements including the ree s shales along the maya river formed as platform sediments in a deeper shelf facies whereas shales along the belaya river formed in more active and open environments of an upper shelf carbonate ramp the log of most elemental compositions to al2o3 ratios are the same in the maya and belaya river samples suggesting a similar source rock composition for rocks in the two areas the log of sio2 mgo na2o k2o rb ba and ni to al2o3 ratios are significantly higher and the log of tio2 to al2o3 ratios are significantly lower in shales from the belaya river than the maya river sections the cia chemical index of alteration is thus significantly lower in the belaya shales than the maya shales suggesting less weathering of the in the belaya shales than the maya shales the icvs index of compositional variability fe2o3 k2o na2o cao mgo tio2 al2o3 of the lakhanda shales are less than 1 suggesting that they are compositionally mature and were likely dominated by recycling several samples have icv 1 suggesting some first cycle input the low k2o al2o3 ratios of these shales suggest that minimal first cycle alkali feldspar was present in the initial source most shales of the lakhanda plot parallel and along the a k line in a cn k plots suggestive of intense chemical weathering high cia and do not indicate any clear cut evidence of k metasomatism or direct weathering back to the original source if k metasomatism produced these rocks then they could have formed from tonalites to basalts if weathering produced these rocks then they could have been produced from varied amounts of mostly granodiorite to granite elemental ratios critical of provenance la sc la cr la co th sc th cr th co and eu eu are not significantly different between the maya river and belaya river shales and the ratios are similar to fine fractions derived from the weathering of mostly granitoids and not basic rocks the eu eu th sc and low k2o al2o3 ratios of most shales suggest weathering from mostly a granodiorite source rather than a granite source consistent with a source from old upper continental crust some samples at the bottom of the belaya river section contain very low eu eu 0 35 suggesting significant input of first cycle detritus from highly differentiated granitoids similar to those from the aldan shield

the composition and evolution of the continental crust rare earth element evidence from sedimentary rocks the composition of the present day upper crust inferred from the uniformity of sedimentary rock r e e rare earth element patterns is close to that of granodiorite a revised andesite model is used to obtain total crustal composition the lower crust is the composition remaining assuming that the upper crust one third of the total is derived from intracrustal partial melting the upper crustal r e e pattern has pronounced eu depletion eu eu 0 64 the lower crustal pattern has eu enrichment eu eu 1 17 and the total crust has no eu anomaly relative to chondritic abundances the eu depletion in the upper crust is attributed to retention of eu in plagioclase in the lower crust because plagioclase is not stable below 40 km 10 kbar the anomaly is intracrustal in origin the archaean upper crust has a different r e e pattern to that of the present day upper crust being lower in total r e e and la yb ratios and lacking an eu anomaly these data are used to infer the archaean upper crustal composition which resembles that of the present day total crust except that ni and cr contents are higher the archaean crustal composition can be modelled by a mixture of tholeiites and tonalite trondhjemites the latter have steep light r e e enriched heavy r e e depleted patterns consistent with equilibration with garnet and hence probable mantle derivation there is little reason to suppose that the archaean lower crust was different in composition from the upper crust except locally where partial melting episodes occurred the r e e evidence is consistent with isotopic and geological evidence for a low continental growth rate in the early archaean a massive increase to about 70 of the total crust between about 3000 and 2500 ma b p and a slow increase until the present day the change from archaean to post archaean r e e patterns in the upper crust is not isochronous but is reflected in the sedimentary rock r e e patterns at differing times in different continents on the basis of a model composition for the mantle 36 of the potassium 30 of uranium 15 of lanthanum and 3 of ytterbium are concentrated in the present continental crust this enrichment is related to ionic size and valency differences from common mantle cations e g mg fe pre 3 9 ga b p crusts were obliterated by meteorite bombardment no geochemical evidence exists for primordial anorthositic sialic or mafic crusts

iron solubility driven by speciation in dust sources to the ocean particulate aerosols are thought to be the primary source of iron to the oceans but the factors determining their solubility and thus bioavailability are unclear x ray absorption analysis reveals that speciation controls the solubility of iron in three large sources of aerosol iron

mineralogical and geochemical studies of glacial sediments from schirmacher oasis east antarctica schirmacher oasis east antarctica hosts loose unconsolidated sediments that consist dominantly of sand silt admixtures with minor clay these sediments were collected from different glacial environments such as polar ice sheets inland lakes exposed bedrock and coastal shelf areas two sediment fractions coarse 0 25 0 125 mm and fine 0 125 0 063 mm were separated and chemically analyzed mineralogically the mixture is composed dominantly of quartz and feldspar and a large variety of heavy minerals zircon tourmaline rutile garnet hornblende hypersthene enstatite kyanite sillimanite andalusite zoisite lawsonite chlorite spinel topaz and opaques the clay minerals i e chlorite illite smectite kaolinite and vermiculite constitute a small fraction there is a mineralogical control over the observed geochemical patterns and anomalies of these sediments the rare earth element and incompatible trace element spidergrams show relative enrichment in the coarse fraction as against fine fraction indicating enrichment of the carrier minerals of these elements mostly heavy minerals in the coarse fraction the overall geochemistry of the sediments classifies them as greywacke as per lindsey fe sand to arenite as per herron and sodic sandstones as per blatt et al these sediments show quartzose sedimentary provenance but influence of other unknown sources is also discernible transporting agencies for the sediments are commonly meltwater channels and wind however transport under influence of gravity glacier action and sea waves are also envisaged the sediments have undergone low degrees of chemical weathering ranging between incipient and moderate types

volcanic components in pelitic sediments the origin of the clay minerals present in pelitic sediments has been widely debated weaver1 suggests that illite and interstratified illite smectite i s dominate the association of illite with marine sediments2 and the proposal3 4 that illite forms from smectite an expandable clay mineral sometimes referred to as montmorillonite in the marine environment has also been discussed weaver5 argues for a continental origin of illite produced by weathering of k feldspar others6 9 have shown that smectite and i s 20 50 illite are converted to i s of higher illite content 60 80 in pelitic sediments by low grade metamorphism per cent illite will always refer to the per cent illite in i s the designation should not be confused with the content of discrete illite or mica commonly present in these sediments here we present clay mineral and k ar data for cretaceous marine shales from the western interior of north america demonstrating a volcanic origin for much of these sediments this observation is correlated with eustatic sea level rise increased volcanic activity sedimentary preservation of organic matter and incorporated into a petrogenetic tectonic model for pelitic sediments

glacial flour dust storms in the gulf of alaska hydrologic and meteorological controls and their importance as a source of bioavailable iron 1 iron is an essential micronutrient that limits primary productivity in much of the ocean including the gulf of alaska goa however the processes that transport iron to the ocean surface are poorly quantified we combine satellite and meteorological data to provide the first description of widespread dust transport from coastal alaska into the goa dust is frequently transported from glacially derived sediment at the mouths of several rivers the most prominent of which is the copper river these dust events occur most frequently in autumn when coastal river levels are low and riverbed sediments are exposed the dust plumes are transported several hundred kilometers beyond the continental shelf into iron limited waters we estimate the mass of dust transported from the copper river valley during one 2006 dust event to be between 25 80 ktons based on conservative estimates this equates to a soluble iron loading of 30 200 tons we suggest the soluble fe flux from dust originating in glaciofluvial sediment deposits from the entire goa coastline is two to three times larger and is comparable to the annual fe flux to goa surface waters from eddies of coastal origin given that glaciers are retreating in the coastal goa region and in other locations it is important to examine whether fluxes of dust are increasing from glacierized landscapes to the ocean and to assess the impact of associated fe on marine ecosystems

geochemistry of archean shales from the pilbara supergroup western australia archean clastic sedimentary rocks are well exposed in the pilbara block of western australia shales from turbidites in the gorge creek group ca 3 4 ae and shales from the whim creek group ca 2 7 ae have been examined the gorge creek group samples characterized by muscovite quartzchlorite mineralogy are enriched in incompatible elements k th u lree by factors of about two when compared to younger archean shales from the yilgarn block alkali and alkaline earth elements are depleted in a systematic fashion according to size when compared with an estimate of archean upper crust abundances this depletion is less notable in the whim creek group such a pattern indicates the source of these rocks underwent a rather severe episode of weathering the gorge creek group also has fairly high b content 85 29 ppm which may indicate normal marine conditions during deposition rare earth element ree patterns for the pilbara samples are characterized by light ree enrichment lanybn 7 5 and no or very slight eu depletion eueu 0 82 0 99 a source comprised of about 80 felsic igneous rocks without large negative eu anomalies felsic volcanics tonalites trondhjemites and 20 mafic ultramafic volcanics is indicated by the trace element data very high abundances of cr and ni cannot be explained by any reasonable provenance model and a secondary enrichment process is called for

seasonal cycles of nutrients and dissolved inorganic carbon at high and mid latitudes in the north pacific ocean during the skaugran cruises determination of new production and nutrient uptake ratios abstract the results of a 2 yr monitoring program in the north pacific march 1995 april 1997 using the commercial cargo carrier m v skaugran are presented in this paper seasonal changes in macronutrients nitrate phosphate and silicate dissolved inorganic carbon dic and total alkalinity ta were recorded in the surface waters of 12 major provinces of the north pacific ocean 35 55 n north of the subarctic boundary 40 n nitrate rarely decreased to below detection limit except in the more near shore provinces with nitrate concentrations remaining as high as 8 9 mol kg 1 in the summer in the northern provinces of the bering sea the central and western subarctic pacific there were also strong latitudinal nutrient gradients in most provinces of the subarctic pacific there was little interannual change in the nutrient cycles except in the western subarctic pacific where nitrate concentration fell to 2 6 mol kg 1 in the summer of 1996 we suggest that this large nitrate depletion was due to enhanced diatom production triggered by the supply of iron from the asian continent the relationship between salinity normalized ta and dic revealed that calcification was low or negligible in the surface waters of the bering sea and the western subarctic pacific in contrast the percent of caco 3 production to organic carbon production was found to be at times as high as 70 75 in the eastern subarctic pacific and the southern region off east japan this study also revealed east west contrasts in the seasonal nutrient depletion ratios in the east the elevated dic no 3 ratios and low si oh 4 no 3 ratios were due to high caco 3 production and low diatom production in surface waters on the contrary in the western subarctic pacific and the bering sea the low redfieldian dic no 3 ratios and the high si oh 4 no 3 ratios were due to low calcification and high diatom production the annual new production was estimated from the seasonal drawdown of nitrate at the surface it ranged from 10 1 g c m 2 yr 1 in the subtropical gyre to 76 83 g c m 2 yr 1 in the western subarctic pacific overall horizontal advection was the major source of uncertainty in the estimation of new production finally the net removal of carbon from the surface by the biological pump was then estimated to be 0 58 gt c yr 1 north of 35 n in the pacific ocean the subarctic north pacific and the bering sea accounted for 93 of the carbon removal

rapakivi granites and related rocks an introduction abstract this article is an introductory chapter for the proceedings of the last seventh meeting of the international geological correlation programme igcp project 315 correlation of rapakivi granites and related rocks on a global scale 1991 1996 based on current knowledge progress made during the six years of the project and the seven papers published in this special issue a synthesis of the age distribution geotectonic environment petrogenesis geochemistry and metallogeny of the rapakivi granites and related rocks is presented

stabilization of the aravalli craton of northwestern india at 2 5 ga an ion microprobe zircon study abstract in order to establish the stabilization age of the aravalli craton of northwestern india we have used an ion microprobe to measure 207 pb 206 pb ages of zircons from six samples collected from the southern aravalli mountains our analyses gave precise results for four granitoids whose minimum crystallization ages ranged between 2562 6 and 2440 8 ma 1 a single sample of gneiss gave an age of 2502 4 ma which is unexpectedly younger than an age of 3281 ma which we previously obtained from another gneissic sample we interpret the 2502 ma age as the time of emplacement of the sample s igneous protolith suggesting that the mewar gneiss contains multiple metamorphic components of differing ages based on our data we conclude that the southern segment of the aravalli craton had broadly stabilized by 2 5 ga this stabilized landmass formed the basement on which the younger aravalli supergroup was unconformably deposited this study represents the first application of a small geometry ion microprobe for routine geochronology

geochemistry of the 2 51 ga old rampur group pelites western himalayas implications for their provenance and weathering the late archean volcano sedimentary succession of the rampur group rg represents the oldest superacrustal rocks exposed in the himalayas the sedimentary component is pelite dominated in the lower part and siliciclastic with associated mafic volcanics dominated in the upper part indicating shallowing of the basin over time the bulk chemistry of the rg pelites shows illite chlorite control that gets diluted with increase in quartz content they have a general similarity with the post archean shales but a slightly higher average sio2 and lower al2o3 contents and severe depletion in cao na2o sr and ba relative to the north american shale composite ree patterns are highly fractionated with la yb n ratio ranging from 8 8 to 18 6 hree show slight fractionation average gd yb n b2 and all the samples have large negative eu anomalies average 0 61 la yb n decrease with increase in al2o3 na2o but lack any relationship with k2o thereby discounting clay mineral control hree have a positive correlation with tio2 th y and nb but not with p2o5 and zr the increase in hree seems likely due to the increased mobilization of hree enriched phase s during intense weathering high zr and th contents and th ni la sc and la yb n ratios as well as sc th sc relations favor a dominantly felsic source with only a minor contribution from mafic rocks the most likely source lithology compatible with the southerly paleocurrent direction and first cycle sediment textural features of the rg sediments appears to be the banded gneissic complex bgc of the northern indian shield the same conclusion is reached when rg data are plotted in al2o3 cao na2o k2o a cn k compositional space the data define a trend which indicates unweathered plagioclase k feldspar source composition similar to that of the bgc pre metasomatized high chemical index of weathering as well as the high plagioclase index of weathering for a majority of the samples conforms to the world wide warm moist climate prevalent during the time of their deposition 2001 elsevier science b v all rights reserved

the development of continental crust through geological time the south african case nd isotopic compositions and147sm144nd ratios were measured in fifty eight south african shales and greywackes with depositional ages ranging from 0 2 to 3 3 b y elements such as the rare earths which are poorly soluble in water and not fractionated during exogeneous processes preserve the signature of the original crustal source the147sm144nd ratios appear to be approximately constant throughout the time interval sampled we calculated nd model ages of crustal differentiation knowing that the shales represent a true blend of different continental areas we consider these model ages representative of the mean ages of their primitive continental sources then using the inverse technique developed by alle gre and rousseau in 1984 we computed a growth curve for the continental crust in south africa two periods of important crustal genesis archaean and around 1 5 b y can be compared with the observed geology and with other continental crust growth curves obtained in previous studies in southern africa and in australia the observation of large variations in the mgo content and ni cr u and th concentrations between archaean south african shales and post archaean samples compared to the constancy of the147sm144nd ratios leads us to propose that the archaean crust was composed of both granite 70 5 and a mafic component 29 5 which could have been komatiite the small dispersion of 147sm 144nd ratios suggests that erosion and sedimentation processes yielded homogeneous archaean shales the present day continental crust is much more heterogeneous because it has undergone several episodes of recycling thus recent shales are characterized by more variable 147sm 144nd ratios

a census of eddy activities in the south china sea during 1993 2007 1 numerous mesoscale eddies occur each year in the south china sea scs but their statistical characteristics are still not well documented a pacific basin wide three dimensional physical biogeochemical model has been developed and the result in the scs subdomain is used to quantify the eddy activities during the period of 1993 2007 the modeled results are compared with a merged and gridded satellite product of sea level anomaly by using the same eddy identification and tracking method on average there are about 32 9 2 4 eddies predicted by the model and 32 8 3 4 eddies observed by satellite each year and about 52 of them are cyclonic eddies the radius of these eddies ranges from about 46 5 to 223 5 km with a mean value of 87 4 km more than 70 of the eddies have a radius smaller than 100 km the mean area covered by these eddies each year is around 160 170 km2 equivalent to 9 8 of the scs area with water depths greater than 1000 m linear relationships are found between eddy lifetime and eddy magnitude and between eddy vertical extent and eddy magnitude showing that strong eddies usually last longer and penetrate deeper than weak ones interannual variations in eddy numbers and the total eddy occupied area indicate that eddy activities in the scs do not directly correspond to the el nino southern oscillation events the wind stress curls are thought to be an important but not the only mechanism of eddy genesis in the scs

sm nd evidence for 3 3 ga old rocks in rajasthan northwestern india abstract tonalitic to granodioritic gneisses from the basement gneiss of the aravalli region northwestern india define a sm nd isochron corresponding to an age of 3 31 0 07 ga and an initial nd isotopic ratio that is close to chondritic lenticular bodies of mafic amphibolites within the gneisses however define an isochron corresponding to a younger age of 2 83 0 05 ga and small positive initial nd this age is similar to that reported for a large intrusive granite the untala granite in this area and combined with field evidence suggests that mafic volcanism may have been associated with formation of the granite a highly hree enriched garnet separate from one of the tonalitic gneisses defines a two point garnet wholerock isochron age of 2 45 0 02 ga which also is similar to the age of a known thermal event in the region intrusion of the berach and bundelkhand granites at approximately 2 5 ga these results document in broad outline archean crustal formation events in the northwestern segment of the indian subcontinent and demonstrate the need for more detailed studies of the complex terranes mapped by heron 1953 as a single unit the banded gneiss complex

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

the himalayan leucogranites constraints on the nature of their crustal source region and geodynamic setting article i nfo late oligocene miocene leucogranites within southern tibet form part of an extensive intrusive igneous province within the himalayan orogen the main rock types are tourmaline leucogranites tg and two mica leucogranites 2 mg they have high sio2 70 56 75 32 wt al2o3 13 55 15 67 wt and 87 sr 86 sr i 0 724001 0 797297 and low mgo 0 02 0 46 wt and 143 nd 144 nd i 0 511693 0 511906 chondri te normalized rare earth element ree patterns display strong negative eu anomalies whole rock major and trace element and sr nd isotope data for the leucogranites suggest that their source region was a two component mixture between a fluid derived from the lesser himalayan lh crustal sequence and the bulk crust of the higher himalayan hh sequence trace element and sr nd isotope modeling indicate that the proportion of fluid derived from the lh sequence varied from 2 to 19 and the resulting metasomatised source experienced 7 16 melting the amount of fluid derived from the lh sequence increases from north to south northward underthrusting of the indian continent resulted in infiltration of the lh derived fluid into the overlying hh sequence subsequent decompression melting of this metasomatised crust mostly during the miocene 25 9 ma generated the leucogranites this may be linked to steepening of the subducted slab of indian lithosphere beneath the orogenic belt

iron transport by mesoscale haida eddies in the gulf of alaska abstract a two year study of the iron distributions in anticyclonic mesoscale haida eddies of the eastern north pacific ocean has shown that such eddies are a major source of iron to the high nitrate low chlorophyll hnlc waters of the central gulf of alaska basin these eddies which are typically about 100 km in diameter form off the west coast of canada in winter and then track roughly westward into the open ocean therefore they carry large quantities of iron rich coastal waters into iron limited waters of the oligotrophic gyre when the eddies had first formed their dissolved iron concentrations were nearly two orders of magnitude higher than is typically observed at station papa 50 n 145 w 3 n m versus less than 0 05 n m and the total iron in the eddies surface waters 10 40 m was more than 13 n m higher than open ocean waters of the alaska gyre 14 n m versus 0 5 n m while the overall iron content of the eddies decreased rapidly during the first year after they formed the eddy we were able to track the longest still contained 1 5 2 times more iron than the surrounding waters 16 months after its formation therefore although iron concentrations in the surface mixed layers of the eddies drop to levels observed outside very rapidly within 4 months upward transport along isopycnals and upwelling due to eddy decay as well as vertical advective and diffusive transports typical of north pacific waters probably provide steady fluxes of iron into the euphotic zone from the still iron rich eddy core waters throughout the lifetime of the eddy

geochemical evolution of archean shales from south africa i the swaziland and pongola supergroups abstract the fig tree group and moodies group part of the swaziland supergroup are exposed in the barberton mountain land and are 3 3 3 5 ga old shales from the fig tree group are characterized by variable rare earth element ree patterns with lan ybn 5 5 1 8 95 confidence and eu eu 0 97 0 18 shales from the moodies group have more fractionated ree patterns lan ybn 8 7 2 0 and less variable eu anomalies eu eu 0 92 0 02 both groups are characterized by very high abundances of cr and ni modelling of those trace elements which are relatively unfractionated during sedimentary processes ree th sc is consistent with the derivation of these sedimentary rocks from a mixture of the archean bimodal igneous suite mafic volcanics tonalites trondhjemites felsic volcanics with the moodies group requiring a larger percentage of the felsic end member the data for shales from the swaziland supergroup support models suggesting that the archean exposed crust was of more mafic composition than the post archean upper crust and that intracrustal melting was relatively unimportant in differentiating the archean crust the pongola supergroup is younger than the swaziland supergroup but older than 2 9 ga shales and mudstones from the nsuze and mozaan groups show ree characteristics intermediate between the older shales of the swaziland supergroup and typical post archean shales one quartzite sample from the witwatersrand supergroup ca 2 6 ga has a ree pattern virtually parallel to average post archean shales but with much lower abundances the change from typical archean to post archean sedimentary trace element patterns has been documented in early proterozoic successions from canada and australia this change has been related to a short interval of intense growth and chemical differentiation of the continental crust during the late archean 2 7 2 5 ga in southern africa this change appears to have taken place much earlier 3 2 2 9 ga but can be related to similar processes thus the period of crustal evolution related to the archean proterozoic boundary while virtually episodic regionally occurred over a protracted period world wide during the period ca 3 2 2 5 ga

provenance weathering conditions and tectonic evolution history of the cambrian meta sediments in the zhuguangshan area cathaysia block abstract sandstones and mudstones collected from the cambrian sedimentary sequences in the zhuguangshan area were analyzed to trace their provenance weathering conditions depositional environment and precambrian tectonic evolution in the cathaysia block south china detrital zircon geochronology defines at least five populations 2658 2370 ma 1866 1500 ma 1390 1268 ma 1250 858 ma and 830 700 ma the 2648 2370 ma population may correspond to the neoarchean global continental growth the 1816 1510 ma population may represent a subduction event caused by the assembly of the columbia supercontinent the 1390 1268 ma and 1250 858 ma population reflect the tectono thermal events associated with the assembly of the rodinia supercontinent while the 830 700 ma population may be associated with the breakup of the rodinia supercontinent detrital zircon hf isotopic compositions indicate that the mechanism involves multiple juvenile inputs and the reworking of older crustal materials the sandstones and mudstones display k2o enrichment but they are moderately to extremely depleted in na2o cao and sr the major and trace elements reveal that the sandstones and mudstones were derived from recycled felsic rocks and deposited in the passive continental margin the compositions of the protoliths are inferred equivalent to andesite to granodiorite the petrographic and geochemical features indicate that the sandstones and mudstones have undergone medium to intensive chemical weathering conversion of aluminous clay minerals to illite is inferred to be the predominant post depositional potash metasomatism

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

geochemical characteristics of mesoproterozoic clastic sedimentary rocks from the chakrata formation lesser himalaya implications for crustal evolution and weathering history in the himalaya abstract to evaluate the changes in the chemistry of upper continental crust during precambrian time in the himalaya the oldest and best preserved mesoproterozoic clastic sedimentary rocks pelites shales and quartzites from the chakrata formation nw lesser himalaya uttar pradesh have been analysed for major elements and a number of trace elements including rare earth elements rees when compared to post archean shales for e g north american shale composite the chakrata pelites have high sio 2 al 2 o 3 k 2 o rb ba contents and low cao fe 2 o 3 t tio 2 sr sc ni and cr concentrations the ree abundances are high up to 296 ppm in pelites and reveal enriched lree and depleted hree patterns la n yb n 7 9 11 1 strong negative eu anomalies are evident in the chakrata pelites eu eu 0 46 0 58 the quartzites of the chakrata formation have high silica contents and low trace element abundances when compared to phanerozoic sandstones the chemical index of alteration values of these rocks ranges from 70 to 76 indicating intense weathering conditions in the source areas most pelites of the chakrata fm plot near the a k line in the a cn k diagram which also suggests intense chemical weathering conditions major and trace element abundances and elemental ratios critical of provenance e g high sio 2 al 2 o 3 k 2 o na 2 o la sc th sc la yb and low eu eu and cr zr suggest that the source rocks of these pelites were remarkably felsic in nature the paleocurrent analyses reveal that the chakrata pelites may have been derived from the granitoid rocks from the southerly direction i e from peninsular india the geochemical similarities favour granitoid rocks from the aravalli and bundelkhand regions as the main source rocks for chakrata sedimentary rocks

using element geochemistry and detrital zircon geochronology to constrain provenance of the eocene sediments in the deep water area of the pearl river mouth basin south china sea abstract as the largest sag in the zhu ii depression within the pearl river mouth basin the baiyun sag bys lies in an area of interaction among the eurasian plate pacific plate and indian plate the bys mainly experienced the paleogene rift stage and neogene quaternary post rift stage thick syn rift sediments in the bys have recorded the nature of provenance and provide an excellent record of regional tectonic evolution prior to the opening of the south china sea in this study elemental geochemical analysis combined with published zircon detrital u pb dating results are applied to better understand the provenance change and tectonic setting of the bys during the eocene in this respect the chondrite normalized ree patterns of eocene samples from six wells are highly similar to upper continental crust ucc and post archean australian shale paas particularly with respect to lree enrichment significantly negative eu anomalies and slight ce anomalies geochemical results confirm that the bys eocene sediments were derived from a continental island arc to an active continental margin in addition the rock types of sources and the relatively narrow detrital zircon ages show that mesozoic intermediate felsic igneous and metamorphic rocks derived from local topographic highs contributed to infilling most of the bys furthermore the results show that the panyu low uplift began to accept large sediments transported by the paleo pearl river from the south china coast during the active syn rift stage prior to the opening of the south china sea

the influence of sediment recycling and basement composition on evolution of mudrock chemistry in the southwestern united states this paper reports systematic changes in mudrock composition through time on a single con tinental cmstal block the changes reflect both sediment recycling processes and changes through time in the composition of crystalline material being added to the sedimentary system and are related to tectonic evolution as the block matures from a series of accreted arc terranes to a stable craton the major and trace element distributions reflect different aspects of the provenance of the mudrocks in this study major elements record sediment recycling processes as well as changing proportions of sedi mentary and first cycle source rocks with the exceptions of kzo which tends to increase and sioz and a o3 which show no trend most major oxides tend to decline in relative abundance in younger mud rocks patterns shown by the index of compositional variability fe03 kro naao cao mgo mno tiojialro and by k20 a1203 indicate that the major oxide trends are due to decreasing proportions of nonclay silicate minerals and a concomitant increase in the proportion of clay minerals probably due to decreasing input of first cycle detritus coupled with recycling of sedimentary material excursions from progressive trends marked by increases in mgo k20 and cao reflect episodes of large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift the chemistry of low solubility trace elements in contrast is not sensitive to recycling effects and reflects the composition of first cycle input incompatible elements are progressively enriched relative to compatible elements in younger mudrocks and values for chondrite normalised rare earth elements also increase in addition the eu anomaly becomes systematically more negative in younger samples these trends cmnot be explained by diagenetic or weathering processes and therefore indicate that the proportion of fnc tionated granitic first cycle detritus being added to the sedimentary system becomes greater with time these results confirm the importance of tectonic setting in controlling mudrock chemistry and also demonstrate that there is a dynamic relationship between the tectonic evolution of a continental block and the composition of its sedimentary mantle

the application of foraminifera to reconstruct the rate of 20th century sea level rise morbihan golfe brittany france abstract foraminiferal assemblages preserved within salt marsh sediment can provide an accurate and precise means to reconstruct relative sea level due to a strong relationship with elevation which can be quantified using a transfer function we collected a set of surface samples from two salt marshes in the morbihan golfe france to determine foraminiferal distribution patterns dominant taxa included jadammina macrescens trochammina inflata haplophragmoides spp and miliammina fusca we developed a foraminifera based transfer function using a modern training set of 36 samples and 23 species the strong relationship between observed and predicted values r 2 jack 0 7 indicated that foraminiferal distribution is primarily controlled by elevation with respect to the tidal frame and precise reconstructions of former sea level are possible rmsep jack 0 07 m the application of the transfer function to a short salt marsh core 0 32 m allowed the reconstruction of former sea levels which were placed in a chronological framework using short lived radionuclides 210 pb and 137 cs the agreement between the foraminifera based sea level curve and the brest tide gauge record confirms the reliability of transfer function estimates and the validity of this methodology to extend sea level reconstructions back into the pre instrumental period both instrumental and microfossil records suggest an acceleration of sea level rise during the 20th century

nd and pb isotopic evidence for provenance and post depositional alteration of the paleoproterozoic huronian supergroup canada neodymium model ages for fine grained formations of the paleoproterozoic huronian supergroup mckim pecors gowganda gordon lake range from 3 00 to 2 55 ga and indicate a provenance dominated by the late archean superior province to the north and west the stratigraphically highest unit gordon lake formation has a distinctive nd isotopic composition with tdm being 100 400 ma younger than underlying mudstones this suggests that the provenance changed consistent with a previously documented change towards more negative eu anomalies in the gordon lake lead isotopes are consistent with a superior province provenance and in addition provide evidence for two episodes of regional post depositional disturbance of the u pb system lower huronian mckim pecors samples align along 207pb 204pb 206pb 204pb slopes equivalent to 2170 58 ma mswd 92 n 9 and 2212 92 ma mswd 9 1 n 5 respectively these ages are at the minimum age limit on sedimentation and within uncertainty of the nipissing diabase 2219 4 ma a ubiquitous regional feature parts of which may have intruded while much of the huronian was unconsolidated these pb pb ages are interpreted to represent widespread diagenetic processes possibly associated with an early phase of nipissing intrusion 206pb 204pb varies mostly from 19 to 34 up to 59 whereas implied 232th 238u are mostly between 2 and 4 only slightly below the upper crustal value of 4 changes in 206pb 204pb imply changes of 238u 204pb by factors of 2 and up to 12 5 values for are also in the range 2 4 and accordingly pb loss appears to dominate this disturbance elevated 206pb 204pb correlates with post depositional addition of potassium in the gordon lake and possibly the gowganda formations k metasomatism has been demonstrated previously in the underlying serpent formation and in paleosols developed at the unconformity beneath the huronian supergroup the latter being dated at 1690 1730 ma widespread metasomatism resulting in k addition and pb loss may have been related to northerly directed basin wide fluid movement in response to post tectonic intrusions and erosion of the ca 1 85 ga penokean orogen to the south since pb isotope systematics in the lower huronian mudstones appear unaffected apart from natural conduits provided by unconformity surfaces and possibly lower huronian sandstone aquifers that also may have been affected by k metasomatism it appears that fluid movement was more pervasive in the upper levels of this sedimentary sequence

the archean proterozoic transition evidence from the geochemistry of metasedimentary rocks of guyana and montana abstract chemical and isotopic compositions of ancient sedimentary rocks have in some cases provided evidence of first order changes yin the composition and extent of continental crust from the archean to the proterozoic we reversed the typical sampling pattern comparing metapelites and carbonates from proterozoic greenstone belts with those from an archean continental margin sequence and found the reverse of the typical age composition relations metapelites and volcaniclastic metagreywackes from the early proterozoic greenstone belts of northern guyana resemble those of many archean greenstone belts in ree trace and major element compositions mean ratios la sm 5 0 la th 5 1 eu eu 0 80 th u 3 4 median k 2 o na 2 o 0 8 schists from an archean continental marginal sequence in montana have compositions like many post archean metapelites derived from continental sources mean ratios la sm 6 8 la th 2 7 eu eu 0 67 th u 5 2 median k 2 o na 2 o 1 7 other archean continental basin sediments also resemble their post archean counterparts implying that upper continental crusts of these eras may not have differed significantly in these respects however temporal change may have occurred in upper crustal contents of ni and cr many archean clastic metasedimentary rocks of both continental and greenstone belt provenance have contents of these compatible elements higher than in their post archean equivalents dolomitic limestone from a greenstone belt of northern guyana has a very low 87 sr 86 sr ratio of 0 7007 such low values may reflect the local influence of mantle derived volcanic rocks during carbonate deposition diagenesis or metamorphism and they may not be reliable indicators of the evolution of sr in seawater archean dolomitic marbles from the continental marginal sequence of montana have 87 sr 86 sr ratios of 0 7065 and higher significantly more radiogenic than many accepted values for carbonates of archean greenstone belts

geochemistry and petrogenesis of late archaean aravalli volcanics basement enclaves and granitoids rajasthan abstract major trace and rare earth element data are presented for the basal volcanics of the aravalli supracrustal sequence for the mafic enclaves within the banded gneiss complex bgc adjacent to the supracrustals and for granitoids within the bgc and their petrogenesis discussed with regard to the problematic relationship between basement and cover in terms of major elements the aravalli lavas range from magnesian 22 mgo komatiites or picrites to fe rich tholeftes but differ from a typical archaean greenstone volcanic sequence in that their trace element patterns are relatively enriched in incompatible and light rare earth elements moreover the range of patterns observed requires a number of distinct mantle sources as well as different degrees of melting there are two distinct types of mafic enclave within the bgc the larger lenses correspond quite well with the range of variation seen in the aravalli sequence and could be feeders the other type close to the bgc aravalli junction has more alkalic characteristics high nb zr and could represent rift volcanics or tectonically accreted fragments of ocean islands the data suggest that the aravalli sequence is not an accreted oceanic terrane but are more consistent with interaction of a deep mantle plume with rather mature sub continental lithosphere the early archaean age of parts of the bgc the chemistry of the granitoids and the alkaline character of the enclaves are also broadly compatible with this model the character of the aravalli sequence is intermediate between that of an archaean greenstone belt and a phanerozoic flood basalt province

geochemical and nd isotopic compositions of the metasedimentary rocks in the la ronge domain trans hudson orogen canada implications for evolution of the domain abstract metasedimentary rocks of greenschist to amphibolite facies occur in various belts in the paleoproterozoic la ronge domain of the trans hudson orogen metasedimentary rocks in the central metavolcanic greenstone belt are low to intermediate in sio2 contents have nd values of 2 3 to 4 5 with two rare earth element ree patterns of la yb n 8 5 respectively the predominant component meta arkoses of the overlying mclennan lake belt have distinctly high k2o and sio2 contents high la yb n ratios 11 46 large negative eu anomalies eu eu 0 1 0 58 and uniformly low nd values 0 8 to 0 2 the maclean lake belt is comprised of a variety of metasedimentary gneisses the volumetrically minor amphibole and diopside rich gneisses have high ferromagnesian element sc and co concentrations high nd values of 4 1 to 5 7 and flat ree patterns with no eu anomalies the predominant lithological unit in the maclean lake belt the psammitic gneisses is geochemically more variable the mafic psammitic gneiss samples in the maclean lake belt and the metasedimentary rocks in the central metavolcanic belt are similar in trace and major element geochemistry and nd isotope composition whereas those more felsic psammitic gneisses are similar to the mclennan lake meta arkoses geochemical data combined with lithological and geochronological evidence indicate that sediments in the central metavolcanic belt were derived mainly from contiguous volcanic debris with minor addition of felsic components from exotic sources in contrast the mclennan lake meta arkoses were derived from a distinct felsic source whereas the psammitic gneisses in the maclean lake belt are mixtures of volcanic materials in the central metavolcanic belt and meta arkoses like felsic components nd isotopic data and ages of detrital zircon suggest that proterozoic juvenile materials were dominant sources for metasedimentary rocks in the la ronge domain comparison of geochemical signatures of the metasedimentary rocks with those of the felsic plutonic rocks in the central metavolcanic belt suggests that the felsic materials in the mclennan lake and maclean lake belts could not have been derived predominantly from the plutonic rocks implying more distal sources topographic changes during collision may have resulted in a shift from mixing of both local and distal sources for the rocks in the maclean lake belt to the dominance of a more distal source for the mclennan lake meta arkoses

geochemistry and mineralogy of sediments from the ventersdorp and transvaal supergroups south africa cratonic evolution during the early proterozoic approximately 100 pelite and 12 quartzite samples from the ventersdorp 2 7 ga and transvaal supergroups 2 6 2 1 ga have been analyzed to monitor the early proterozoic evolution of the kaapvaal craton southern africa from oldest to youngest pelites were sampled from the ventersdorp bothaville bot transvaal selati sel black reef br timeball hill th strubenkop str and silverton sil formations paleocurrent measurements in transvaal quartzites indicate sources lying predominantly to the north and east relative to the bot sel br pelites from the th str sil are enriched in heavy ree lile zr hf nb and ta depleted in k2o mgo ni and cr and have lower cr zr sc th k2o na2o and k rb ratios compared to sel br bot th str sil pelites have higher light ree contents and la yb ratios and lower eu eu ratios 0 61 0 66 relative to nasc north american shale composite thstr sil pelites are enriched in light ree th u ta nb sc cs have higher la yb ratios and are depleted in k2o and mgo bot sel br pelites are enriched in k2o mgo cr and ni have higher k2o na2o sc th and eu eu ratios and are depleted in th u heavy ree and high field strength elements hfse relative to nasc compositions of th str sil pelites suggest a provenance similar to average phanerozoic uppercontinental crust this source is more evolved than that of bot sel br pelites indicating a transformation from primitive mafic rich to evolved felsic rich upper crust at 2 2 ga this transition follows earlier primitive to evolved trends in moodies pongola 3 3 3 0 ga and witwatersrand 2 8 ga successions these data suggest that several cycles of changing upper continental crust occurred in the kaapvaal craton between 3 3 2 1 ga

iron flux induced by haida eddies in the gulf of alaska 1 mesoscale anticyclonic haida eddies are proposed to deliver a substantial amount of iron into the gulf of alaska goa central gyre where surface waters experience high nitrate low chlorophyll conditions in this study we calculate an averaged upwelling flux of dissolved iron into the euphotic zone 100 m of 1 17 mol m 2 d 1 based on observed iron profiles and modeled eddy dynamics and resultant vertical velocities this estimated eddy derived iron supply rate is comparable with new estimates of pulsed iron fertilization rates from rare volcanic ash deposition events despite the relatively small area affected by haida eddies they are estimated to contribute about 4 6 106 moles of dissolved iron yearly to the goa which is equivalent to the annual atmospheric dust deposition haida eddies therefore represent a major iron source that should strongly influence the regional biological productivity and carbon budget of the goa

subthermocline eddies over the washington continental slope as observed by seagliders 2003 09 abstractin the california current system subthermocline lenslike anticyclonic eddies generated within the california undercurrent cu are one mechanism for lateral transport of the warm saline waters of the cu garfield et al established the name cuddies for eddies of this type and hypothesized that they account for a significant fraction of the offshore transport of cu water this study presents observations of subthermocline eddies collected from a time series of seaglider surveys in the northern california current system gliders made 46 crossings of subthermocline anticyclones and 17 crossings of subthermocline cyclones over 5 5 yr close inspection grouped these into 20 distinct anticyclones and 10 distinct cyclones water properties at the core of anticyclonic eddies were similar to those in the core of the cu over the continental slope these anticyclones are examples of cuddies anticyclonic cyclonic eddies had average radii of 20 4 20 6 km peak azimuthal current speeds of 0 25 0 23

origin of the wunugetushan porphyry cu mo deposit inner mongolia ne china constraints from geology geochronology geochemistry and isotopic compositions abstract the wunugetushan porphyry cu mo deposit is located in the southeastern margin of the mongol okhotsk orogenic belt and in the northwestern segment of the great xing an range ne china the orebodies of this deposit are mainly hosted in the monzogranitic porphyry stock and in contact with the granitic porphyry dyke and biotite granite batholith the shrimp zircon u pb dating of the granitic porphyry dyke yielded ages of 201 4 3 1 ma 2 mswd 1 5 these results indicate that the magmatism in the wunugetushan area might have occurred at ca 201 ma in the early jurassic and that the mineralization age ca 181 ma of this deposit is later than the age of intrusive granitic porphyry in the area geochemically the wunugetushan granitoids belong to high k calc alkaline and shoshonitic series enriched in k rb nd and pb and depleted in sr nb ti and p with negative eu anomalies in situ hf isotopic analyses of zircons using la mc icp ms indicate that the ehf t values for zircons from a granitic porphyry sample vary from 2 4 to 11 8 and that the corresponding crustal model ages tdmc vary from 483 to 1088 ma the least altered monzogranitic porphyry granitic porphyry and biotite granite yielded relatively uniform end t values from 1 0 to 0 6 and low 87sr 86sr i ratios ranging from 0 704387 to 0 708385 the geochemical and sr nd hf isotopic data for the granitoids indicate that the source magma for these rocks could be derived from a juvenile lower crust the 34s values of sulfides show a narrow range 0 76 to 3 20 similar to those of magmatic sulfur further implying a lower crust origin based on the results of this study and the regional geodynamic evolution it is proposed that the formation of the wunugetushan deposit and associated granitoids should be linked to the southeastward subduction of the mongol okhotsk oceanic plate beneath the erguna massif during the early jurassic and that the monzogranitic porphyry intrusions in wunugetushan area probably provided important ore metals responsible for the large scale cu mo mineralization

the chemical signature of source rocks in size fractions of holocene stream sediment derived from metamorphic rocks in the wet mountains region colorado u s a eight stream sediments draining primarily mixed silica rich and silica poor metamorphic rocks in the wet mountains colorado were analyzed at their source for their mineralogic and selected elemental composition the low silica source rocks include amphibolite hornblende schist and muscovite biotite schist the high silica source rocks include granodioritic to leucocratic granitic gneisses the high silica source rocks tend to contain higher concentrations of ree th hf and ba lower concentrations of fe sc and cr higher la sc and thsc ratios and more negative eu anomalies than the low silica source rocks especially those low silica source rocks derived from basic sources rather than weathered silicic sources the stream sediments draining this mixed metamorphic rock terrain are dominated by sands and gravels and they are composed of feldspar quartz and 25 heavy minerals the silts contain more total biotite hornblende pyroxene and opaque minerals and less quartz and feldspar than the sands and gravels sediment especially the silts derived from mixed low and high silica sources tends to be intermediate in elemental composition between those of the end member sources so there is some hope that source rock signatures may be preserved in the sediment elemental ratios of la sc th sc la co th co and ba co and th la sc plots most clearly distinguish sediment derived from the most silicic and most basic source rocks in addition finer sediment near the source can potentially distinguish silicic sources higher ree and more negative eu anomalies from those of basic sources the clay and silt fractions contain negative eu anomalies normalized to the mcps north american mid continent platform sediment and the sands and gravels have positive eu anomalies normalized to the mcps most size fractions are similar to more enriched in la sc th sc la co and th co ratios than the mcps this suggests local sources in the wet mountains are on the average more silica rich than those that formed the mcps

the metamorphic characteristics of metapelites of the mashan group in mashan area eastern heilongjiang province china constraint on the crustal evolution of the jiamusi massif abstract mashan complex in the southeastern margin of the jiamusi massif has traditionally been interpreted to be the oldest stratigraphic sequence in eastern ne china here we investigated the mashan complex in the ximashan area and present lots of new la icp ms zircon u pb petrological and mineralogical chemical data in addition with phase equilibria modeling to constrain the timing of metamorphism p t conditions and the p t path of the mashan complex and furthermore to deduce the crustal evolution of the jiamusi massif the protoliths of the metapelites from the mashan complex in the ximashan area are clay rocks and sandstones whose provenance is dominantly felsic rocks which formed from a continental island arc three metamorphic generation assemblages m2 m4 are recognized in the studied samples a peak granulite facies stage a post peak near isothermal decompression stage and a late near isobaric cooling stage which together define a clockwise p t path it reveals important information related to the collision orogeny subsequent uplift and post collision process zircon u pb dating of two metapelitic samples yielded metamorphic ages of the older group varying from 535 6 to 480 5 ma which can be perfectly correlated with the age range 501 6 to 498 6 ma of magmatic activities recorded by the gneissic granite sample the data presented here together with those published allow us to preliminarily infer that the peak of the granulite facies metamorphism in the ximashan area of the jiamusi massif might have occurred at 530 500 ma the younger of the metamorphic ages 476 453 ma should be regarded as the age of late stage therefore a collision orogeny regime is favored to interpret the metamorphic evolution of metapelites of the mashan group in the mashan area

deep weathering of granitic rocks a case of tunnelling in nw spain abstract this paper highlights a case of extensive development of saprolith from granitic bedrock in nw spain the weathering front at the study area extends to more than 250 m in depth the drilling of a railway tunnel madrid galicia high speed line through the bedrock and saprolith resulted in significant technical issues and economic losses cross sections revealing the 3d complexity of saprolith development are mainly based on fieldwork boreholes laboratory tests and the excavation works saprock is always observed overlying unweathered igneous bedrock two saprolite facies one clay rich and the other clay poor overlie the saprock the recognition is based on several criteria these deposits gradually thicken from the boundaries between the granitoid and metasedimentary roof pendants factors controlling saprolith development are discussed and the chemical and mineralogical changes and trends that occur are described variations in some geotechnical properties and the loss of quality of the rock masses from an engineering perspective are also quantified

sr and nd isotopic evidence for punctuated clay diagenesis texas gulf coast we report rb sr sm nd and mineralogical data for leached whole rock 1200 m independent of the duration of burial the exchangeable sr in the clay has remained an open system and has undergone isotopic exchange since that time minimum fluid rock ratios of 0 2 to 2 are modeled from sr isotopic data consistent with rock dominated open system diagenesis leachates and residues of the 0 1 zm fraction below the smectite illite transition appear to have achieved nd isotopic equilibrium during clay diagenesis and show no signs of subsequent exchange the clay residues have low 147sm 144nd 0 085 indicating that authigenic illite has a lower sm nd ratio than its bulk rock protolith conversely the coexisting exchangeable ree inventory has elevated sm nd as reflected by leachate 14vsm 144nd as high as 0 188 this sm nd fractionation in conjunction with the preserved isotopic equilibrium may be useful for dating diagenesis and associated fluid rock interaction in older rocks

the lower crust of the dharwar craton southern india patchwork of archean granulitic domains u pb geochronological major and trace element and isotope geochemical data identify crustal domains of contrasted petrological origins and histories in the lower crust of the dharwar craton all affected by granulite facies metamorphism and deformation in the neoarchean four lower crustal domains have been identified and investigated across the neoarchean amphibolite to granulite facies transition zone 1 in the southern part of the western dharwar craton wdc high grade metamorphism affects rocks formed before 3 0 ga high grade metamorphism is recorded at ca 2 51 ga followed by possible complex cooling and resetting until 2 2 ga 2 the br hills mm hills domain represents the lower crust of the central dharwar province cdp which is here defined as a transitional crust between the old 3 ga wdc and the eastern dharwar province edp not older than 2 7 ga this granulitic domain contains the oldest rocks of the dharwar craton with ttg suites formed at ca 3 4 ga and ca 2 6 ga suites of probable crustal recycling origin both suites are involved in 2513 5ma granulite facies metamorphism 3 the nilgiri granulitic domain is tectonically juxtaposed with the deepest level of the wdc as a consequence of neoarchean dextral slip along the moyar shear zone the massif consists of rocks of orogenic affinities formed between 2 70 and 2 56 ga and overprinted by granulite facies metamorphism at 2518 10 ma 4 the krishnagiri domain exposes the deepest levels of the eastern dharwar craton it is composed of ttg and calc alkaline igneous protoliths formed between 2 55 and 2 53 ga migmatization in the upper part of the domain took place at 2507 6ma and granulite facies overprint in the deepest parts of the domain is constrained at 2516 5 ma the krishnagiri domain was magmatically accreted to the lower crust of both the cdp and edp by interaction with mafic magmatism inducing reworking of the 2 7 2 6 ga or older overlying crust the nilgiri granulites share several temporal and petrological properties with the madras granulites that make the easternmost outcrop of the dharwar craton we tentatively suggest that the nilgiri and madras granulites evolved as parts of a common madras domain in the lower crust of the edp before activation of the moyar shear zone in this sense the nilgiri massif may be considered as an allochtonous unit in a context of neoarchean ultra hot orogeny in south india

comment on the subsidence adjustment applied to the kemp et al proxy of north carolina relative sea level kemp et al 1 presented a new salt marsh proxy record of relative sea level rsl from north carolina ncrsl the salt marsh is slowly subsiding as a result of glacial isostatic adjustment gia and the ncrsl record needs to be adjusted to remove this vertical land movement from the sea level record kemp et al 1 corrected for a constant subsidence rate of approximately 1 mm y this is a geologic estimate based on sea level index points which are determined from linear fits to data from other north american rsl proxy records thus the geologic method implicitly assumes that the entire trend is a result of subsidence and leaves no room for any millennial scale climate driven changes in sea level it is therefore not surprising that the adjusted rsl record has a preindustrial trend near zero

geochemistry and provenance of sediments from the pongola supergroup south africa evidence for a 3 0 ga old continental craton abstract the 3 0 ga pongola supergroup of south africa is one of the oldest well preserved supracrustal successions the sequence is divided into the nsuze chiefly volcanics quartzites and pelites and the overlying mozaan groups chiefly quartzites and pelites relative to north american shale composite nasc most pongola pelites have similar la yb and eu eu ratios and large ion lithophile elements lile high field strength elements hfse ree v and sc contents ni 30 300 ppm and cr 100 800 ppm contents are greater than those of nasc while cr ni ratios are generally higher than shales and pelites of all ages these trends may reflect residual cr enrichment during intense chemical weathering of komatiitic source rocks local populations of nsuze pelites based on major and trace element data may result from source heterogeneities and or contemporaneous volcanic input into the sedimentary basin pongola quartzite compositions and detrital modes are similar to those of sandstones from phanerozoic passive margin and basement uplift tectonic settings ree lile and hfse contents in pelites suggest that pongola source rocks were remarkably similar in composition to average phanerozoic upper continental crust trace element geographic and isotopic constraints favor 3 2 to 3 0 ga hood granites as a major source for pongola detritus moderate contributions from mafic sources are also required whereas relatively minor contributions from tonalite and komatiite are allowed these results indicate the existence of a chemically evolved felsic craton in southern africa by 3 0 ga this craton appears to have been more evolved than sources for either older moodies 3 3 ga or most of the younger witwatersrand sediments 2 8 2 7 ga pelites from the kaapvaal craton record at least two mafic to felsic source area compositional cycles in pelites deposited from the mid to late archean additional cycles may be masked by a depositional or erosional hiatus between the moodies and pongola sequences these sedimentary patterns suggest that crustal development in southern africa was episodic in nature during the early precambrian

mechanisms for vertical nutrient transport within a north atlantic mesoscale eddy abstract prompted by observational evidence for an enhanced source of surface nutrients within an anticyclonic eddy in the ne atlantic we investigate vertical transport processes that may produce such a phenomenon for the eddy investigated the dominant mechanism is found to be ageostrophic circulation resulting from a perturbation of the circular flow of the eddy this can produce upwelling velocities of order 10 m d 1 ekman pumping due to wind stress on the eddy also produces upwelling within but on a smaller scale of 0 5 m d 1 there is no evidence that self propagation of the eddy leads to an enhanced nutrient flux by displacement upwards of nutrient laden deeper isopycnals over the core of the eddy deeper winter mixing within the eddy relative to the surroundings however may contribute to the elevated nutrient levels

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

atmospheric distribution and removal of volcanic ash after the eruption of kasatochi volcano a regional model study 1 in august 2008 kasatochi volcano on the aleutian islands erupted without much advance warning volcanic ash released during this eruption quickly settled out of the atmosphere mainly into the ne pacific ocean the amount of volcanic ash as well as the ash fall area and volume into the ne pacific ocean remains speculative as only a limited number of measurements is available we used a three dimensional atmosphere chemistry aerosol model to determine the atmospheric distribution of so2 and volcanic ash and its fallout after the eruption of kasatochi volcano in a first step modeled atmospheric so2 distributions are compared with satellite data thereby evaluating the model capabilities to reasonably reproduce atmospheric transport patterns for modeled volcanic ash mass a considerable reduction of the atmospheric content already occurred by 10 august the second day after the eruption in accordance with satellite observations gravitational settling is the most efficient removal process for volcanic ash mass exceeding dry and wet deposition by far assuming an ash volume of 0 3 km3 released during the eruption of kasatochi volcano and a median ash particle diameter of 4 m the mass of volcanic ash removed at ground within the 0 1 mm isopach covers an area of 7 6 105 km2 over the ne pacific ocean and makes up 49 of the removed material out of the atmosphere the amount of ash and that of iron attached to it is sufficient to explain measured seawater co2 decrease at the ocean station papa in august 2008 induced by iron fertilization and subsequent phytoplankton production

seasonal and spatial variabilities in northern gulf of alaska surface water iron concentrations driven by shelf sediment resuspension glacial meltwater a yakutat eddy and dust phytoplankton growth in the gulf of alaska goa is limited by iron fe yet fe sources are poorly constrained we examine the temporal and spatial distributions of fe and its sources in the goa based on data from three cruises carried out in 2010 from the copper river ak mouth to beyond the shelf break april data are the first to describe late winter fe behavior before surface water nitrate depletion began sediment resuspension during winter and spring storms generated high total dissolvable fe tdfe concentrations of 1000 nmol kg 1 along the entire continental shelf which decreased beyond the shelf break in july high tdfe concentrations were similar on the shelf but more spatially variable and driven by low salinity glacial meltwater conversely dissolved fe dfe concentrations in surface waters were far lower and more seasonally consistent ranging from 4 nmol kg 1 in nearshore waters to 0 6 1 5 nmol kg 1 seaward of the shelf break during april and july despite dramatic depletion of nitrate over that period the reasonably constant dfe concentrations are likely maintained during the year across the shelf by complexation by strong organic ligands coupled with ample supply of labile particulate fe the april dfe data can be simulated using a simple numerical model that assumes a dfe flux from shelf sediments horizontal transport by eddy diffusion and removal by scavenging given how global change is altering many processes impacting the fe cycle additional studies are needed to examine controls on dfe in the gulf of alaska

controls on deglacial changes in biogenic fluxes in the north pacific ocean the subarctic north pacific ocean holds a large co2 reservoir that is currently isolated from the atmosphere by a low salinity layer it has recently been hypothesized that the reorganization of these high co2 waters may have played a crucial role in the degassing of carbon dioxide to the atmosphere during the last deglaciation this reorganization would leave some imprint on paleo productivity records here we present 230th normalized biogenic fluxes from an intermediate depth sediment core in the northwest pacific rc10 196 54 7 n 177 1 e 1007 m and place them within the context of a synthesis of previously published biogenic flux data from 49 deep sea cores north of 20 n ranging from 420 to 3968 m water depth the 230th normalized opal carbonate and organic carbon fluxes from rc10 196 peak approximately 13 000 calendar years bp during the bolling allerod b a period our data synthesis suggests that biogenic fluxes were in general lowest during the last glacial period increased somewhat in the northwest pacific during heinrich event 1 and reached a maximum across the entire north pacific during the b a period we evaluate several mechanisms as possible drivers of deglacial change in biogenic fluxes in the north pacific including changes in preservation sediment focusing sea ice extent iron inputs stratification and circulation shifts initiated in the north atlantic and north pacific our analysis suggests that while micronutrient sources likely contributed to some of the observed changes the heterogeneity in timing of glaciogenic retreat and sea level make these mechanisms unlikely causes of region wide contemporaneous peaks in export production we argue that paleoobservations are most consistent with ventilation increases in both the north pacific during h1 and north atlantic during b a being the primary drivers of increases in biogenic flux during the deglaciation as respectively they were likely to bring nutrients to the surface via increased vertical mixing and shoaling of the global thermocline

geochemical constraints on the growth of the continental crust several lines of evidence indicate that the archean upper crust was considerably more mafic than the present day upper crust there has been no significant change in ree and th abundances in post archean clastic sedimentary rocks suggesting that there has been no change in the composition of the upper crust during the post archean this indicates that if there have been any additions to the post archean upper crust they must have had similar composition to the upper crust itself geochemical modelling of ree and th abundances in sedimentary rocks suggests that the minimum ratio of post archean to archean upper crustal composition required to eliminate the archean upper crustal trace element signature within analytical uncertainty is about 4 1 such a model also is supported by isotopic data using plausible assumptions regarding the volume of archean crust isostatic relations and extreme models of the earth s degassing history it is proposed that approximately 65 75 of the continental crust formed