geological and isotopic geochemical constraints on the evolution of the fuping complex north china craton abstract the neoarchean to paleoproterozoic fuping complex together with the adjacent hengshan and wutaishan complexes form the middle part of the central zone that separates the north china craton into the eastern and western archean continental blocks the fuping complex comprises three major lithological assemblages the 2 50 ga fuping trondhjemite tonalite granodiorite ttg gneisses the wanzi paragneisses and the 2 08 and 2 02 ga nanying granitic gneisses the ttg gneisses contain abundant enclaves of highly metamorphosed supracrustal rocks including 2 70 ga mafic granulites and amphibolites with endt of 3 29 to 3 96 and tdm of 2 72 2 82 ga and are characterized by tdm of 2 76 3 04 ga and a linear correlation between endt 1 64 to 0 96 and 1 nd indicative of mixing of melts derived from the 2 70 ga metabasic rocks and 3 0 ga crustal materials mafic dikes along the chengnanzhuang shear zone were most likely emplaced at 2 31 ga and have endt of 2 24 to 4 78 and tdm of 2 34 2 59 ga the nanying granitic gneisses with endt of 4 04 to 5 24 were most likely related to partial melting of the 2 70 ga supracrustal rocks and or the 2 50 ga ttg gneisses these geological relationships and isotopic data suggest that the fuping complex probably formed from the following five major tectonomagmatic events 1 mafic magmatism and early crustal growth at 2 7 ga with the possible existence of older 3 0 ga crust s 2 collision related crustal thickening underplating of basaltic magma high grade metamorphism crustal anatexis and ttg magmatism at 2 5 ga 3 extensional deformation and emplacement of the mafic dikes and the nanying granitic plutons along the chengnanzhuang shear zone 2 5 to 2 0 ga 4 s type granitic magmatism and associated amphibolite facies metamorphism 2 0 to 1 80 ga and 5 emplacement of granitic pegmatite dikes at 1 80 ga

geochemistry of shales from the archean 3 0 ga buhwa greenstone belt zimbabwe implications for provenance and source area weathering abstract phyllites from the archean 3 0 ga buhwa greenstone belt zimbabwe were deposited on a stable cratonic platform analyses of the phyllites generally define a single geochemical group based on major and trace element abundances the phyllites are strongly depleted in cao na2o and sr with respect to average archean upper crust by contrast k2o ba and rb are enriched several times relative to average archean upper crust reflecting basin scale k metasomatism transition metals are somewhat depleted whereas high field strength elements are typically enriched relative to average archean upper crust samples generally have fractionated lree patterns average cen smn 2 4 with small negative eu anomalies average eu eu 0 78 and generally flat hrees average gdn ybn 1 3 such geochemical characteristics suggest that the source dominantly consisted of tonalite with less common occurrences mafic volcanic rocks and granite mixing calculations which massbalance the rees and th sc suggest 70 tonalite 15 mafic volcanic rocks and 15 granite as possible proportions for the source of the phyllites a nearby early archean 3 5 ga continental nucleus preserves similar lithologies and is the probable source intense chemical weathering of the source terrane is indicated by premetasomatized chemical index of alteration values of 95 100 nearly complete depletion of cao and na2o and high al2o3 na2o ratios fine grained sediments of comparable age and presumed tectonic setting elsewhere in southern africa show similar geochemical characteristics implying that source area compositions and weathering intensities were similar these mature platformal deposits suggest a tectonically stable environment where intense chemical weathering took place at 3 0 ga across southern africa

composition of modern deep sea sands from arc related basins summary petrographic and chemical examination of modern deep sea sands shows a clear distinction between active and passive plate tectonic settings among active settings sands from forearc basins of island arcs and basins from strike slip continental margins can be distinguished but those from other arc related settings overlap considerably in composition in particular sands from continental margin subduction zones and those from the backarc of island arcs appear to be indistinguishable chemically arc related sands are very close in composition to ancient greywacke sandstones for instance sodium almost always exceeds potassium thus it is not necessary for sodium to be added to sands diagenetically to make greywackes as has been suggested the influence of tectonics on the composition of sandstones has long been a central feature of sandstone petrology the geosynclinal model of global tectonics stimulated much thought on this subject probably the best known ideas are those of krynine e g 1942 subsequently such research declined but the plate model for global tectonics has produced a new wave of interest e g crook 1974 schwab 1975 potter 1978 dickinson suczek 1979 much of this work has relied on data from ancient sediments where diagenetic changes and difficulty in de ciphering the tectonic setting limit the useful ness of the conclusions much more work is needed on recent sediments to establish a base line against which ancient sediments can be compared we have previously reported valloni maynard 1981 the results of our work on the petrography of a set of recent deep sea sands from piston cores in this paper we shall com pare this petrographic information with bulk chemistry and attempt to relate these to tecto nics in arc related settings

geochemistry of metasedimentary rocks of the proterozoic xingxingxia complex implications for provenance and tectonic setting of the eastern segment of the central tianshan tectonic zone northwestern china the eastern segment of the central tianshan tectonic zone in northwestern china includes the proterozoic metasedimentary xingxingxia complex because these rocks have been extensively deformed and metamorphosed to greenschist or amphibolite facies a geochemical and nd isotopic study was undertaken to constrain their provenance and tectonic setting as well as to evaluate the effects of weathering and sedimentary processes on the source rock signature major and trace element data indicate that these samples are characterized by negative eu anomalies low chemical index of alteration values and high index of compositional variability values chemical index of alteration values and the plot of molecular proportions al2o3 cao na2o k2o suggest low degrees of weathering of the source they are compositionally immature and poorly sorted geochemical data and immobile elemental ratios for example al2o3 tio2 cr th eu eu and la yb n indicate that the clastic materials were derived predominantly from

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

palaeozoic collisional tectonics and magmatism of the chinese tien shan central asia abstract the chinese tien shan range is a palaeozoic orogenic belt which contains two collision zones the older southern collision accreted a north facing passive continental margin on the north side of the tarim block to an active continental margin on the south side of an elongate continental tract the central tien shan collision occurred along the qinbulak qawabulak fault southern tien shan suture the time of the collision is poorly constrained but was probably in in the late devonian early carboniferous we propose this age because of a major disconformity at this time along the north side of the tarim block and because the youshugou ophiolite is imbricated with middle devonian sediments a younger probably late carboniferous early permian collision along the north tien shan fault northern tien shan suture accreted the northern side of the central tien shan to an island arc which lay to its north the north tien shan arc this collision is bracketed by the middle carboniferous termination of arc magmatism and the appearance of late carboniferous or early permian elastics in a foreland basin developed over the extinct arc thrust sheets generated by the collision are proposed as the tectonic load responsible for the subsidence of this basin post collisional but palaeozoic dextral shear occurred along the northern suture zone this was accompanied by the intrusion of basic and acidic magmas in the central tien shan late palaeozoic basic igneous rocks from all three lithospheric blocks represented in the tien shan possess chemical characteristics associated with generation in supra subduction zone environments even though many post date one or both collisions rocks from each block also possess distinctive trace element chemistries which supports the three fold structural division of the orogenic belt it is unclear whether the chemical differences represent different source characteristics or are due to different episodes of magmatism being juxtaposed by later dextral strike slip fault motions because the southern collision zone in the tien shan is the older of the two the tarim block sensu stricto collided not with the eurasian landmass but with a continental block which was itself separated from eurasia by at least one ocean the destruction of this ocean in late carboniferous early permian times represented the final elimination of all oceanic basins from this part of central asia

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

diagenetic modification of sm nd model ages in tertiary sandstones and shales texas gulf coast sm nd model ages of sandstones and shales from the oligocene frio formation of south texas and the paleocene eocene wilcox group of south central texas increase with increasing depth of burial depleted mantle model ages tdm of frio shales increase from ca 800 ma at 1 km of burial to ca 1000 ma at 4km in frio sandstones tdm increases from ca 750 ma at 1 km to over 1200 ma at 4 km of burial in wilcox shales tdm increases from ca 1300 ma to ca 1500 ma over a burial depth of 1 5 to 4 5 km tdm of wilcox sandstones increases from ca 1450 ma at 2 5 km of burial to as much as ca 2000 ma at 4 0 km the sampling scheme employed minimizes but does not eliminate the possibility that these trends in tdm are due to detrital variability close correlation of these trends with diagenetic changes in the rock and evidence of rare earth element mobility preserved in the diagenetic products suggests that diagenesis has modified tdm diagenetic modification of tdm in frio sandstone and wilcox shale is due primarily to loss of radiogenic nd whereas increased 147sm 144nd produces elevated tdm in deeper wilcox sandstones the tdm of frio shales does not change appreciably with depth owing to the opposite effects on tdm of decreased 147sm 144nd and decreased nd 0 loss of radiogenic nd is due primarily to reactions involving unstable volcanic detritus which is more abundant in the frio than in the wilcox decreased 147sm 144nd in authigenic illite and consequent increased 147sm 144nd in pore fluids results in elevated tdm in wilcox and frio sandstones containing late diagenetic cement and in decreased 147sm 144nd in deeper frio shale the similar tdm trends observed in both units which have different detrital characteristics suggest that modification of sm nd model ages in siliciclastic rocks may be commonplace during burial diagenesis

the mineralogy petrology metamorphic ptdt trajectory and exhumation mechanism of blueschists south tianshan northwestern china abstract the south tianshan blueschist belt extends for about 200 km along the south tianshan suture from changawuzhi to the upper kekesu river the high pressure low temperature high p low t metamorphic rocks contain sodic amphibole garnet phengite albite quartz epidote chlorite and stilpnomelane these blueschists occur as small blocks lenses laminae and bedded slabs or sheets in greenschist facies country rocks a few dismembered ophiolitic nappe slices and marble lenses are interlayered in the high p t metamorphic belt metabasite blueschists are mainly e type morb less commonly n type the protoliths of the meta sedimentary rocks are graywackes which contain volcaniclastic material of e type morbs and probably some continental basement materials derived from the tarim plate these protoliths may represent subduction complexes or meta melanges which formed within an accretionary wedge on the southern side of the yili central tianshan plate yctp at the end of the early paleozoic the mineral assemblages include sodic amphibole mainly crossite garnet phengite epidote chlorite albite estimated to have crystallized at 450 c and 9 10 kbar these conditions correspond to the epidote blueschist facies and are the peak metamorphic conditions the prograde metamorphism is represented by lawsonite blueschist facies and the retrograde is greenschist facies the metamorphic ptdt trajectory of the blueschists runs clockwise and reveals that the metamorphism revolved from laumontite facies lawsonite blueschist facies epidote blueschist facies 408 ma to greenschist facies 345 ma during the creation and exhumation of the blueschists in the south tianshan suture we have recognized six stages of deformation in the blueschists the earlier three stages were concomitant with metamorphism the later three postdated the metamorphism on the basis of the deformation characteristics of the blueschists and coherent rocks the regional geology and the metamorphic ptdt path we discuss the exhumation mechanism of the blueschists the post collisional ductile thrust within the suture probably exhumed the blueschists and coherent rocks allowing them to escape retrograde overprinting in the greenschist facies the influence of erosion on the exhumation of blueschists could not be considered directly and quantitatively because of the absence of devonian strata and the few exposures of early carboniferous clastic rocks all without detritus of blueschists

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

geochemical and nd pb isotopic evidence for the provenance of the early proterozoic virginia formation minnesota implications for the tectonic setting of the animikie basin the early proterozoic animikie basin is located at a major crustal boundary between archean crust of the superior craton and penecontemporaneous early proterozoic crust of the wisconsin magmatic terranes the provenance of sedimentary rocks within the animikie basin constrains the tectonic evolution of the early proterozoic margin of the superior craton published geological petrographic and nd pb isotopic data indicate that the pokegama quartzite lower passive margin unit of the animikie group has a late archean provenance in contrast the virginia formation upper deep water turbidite shale unit of the animikie group was derived from dominantly early proterozoic sources with isotopic compositions similar to igneous rocks of the wisconsin magmatic terranes shales of the virginia formation have nd depleted mantle model ages 2 14 to 2 35 ga and mu 1 of 7 81 to 8 09 ashes within the virginia are more evolved geochemically than shales and have younger model ages of 1 86 and 1 99 ga and simila

geochemistry of fine grained clastic sediments in the archean abitibi greenstone belt canada implications for provenance and tectonic setting abstract archean sandstone and shale samples from turbiditic tf and alluvial facies af in the southern volcanic zone of the abitibi greenstone belt canada have been analyzed for major and trace elements the sandstones from tf are mainly greywackes whereas those from af are lithic arenite sio 2 ranges from 51 to 68 geochemically the clastic sediments cluster into mafic element mep and low mafic element lmep populations the mep sediments which include turbiditic facies sediment samples from the larder lake group in the kirkland lake area are characterized by elevated abundances of mgo 5 ni 200 ppm cr 400 ppm sc 22 ppm and feo 7 5 abundances lower contents of incompatible elements such as th u ta hf zr and total rees n ratios are 4 5 with eu eu 1 the lmep sediments which include samples from the beatty dome and three nations lake formations in timmins the kewagama group noranda area and timiskaming group in the kirkland lake area however show reverse abundance distributions the geochemical gaps shown by the major and trace elements define two populations of sediments suggesting contrasting provenances for them the mep sediments require a dominantly mafic and ultramafic 90 source with 10 felsic contribution whereas the lmep sediments require a mixture of felsic 75 and mafic 25 rocks this compositional distribution of the sediments is closely related to their tectonic environments the mep was formed in basins proximal to or within an active oceanic rift consequently having ultramafic and mafic rocks as the major source for the lmep calc alkaline volcanic sequences formed in an island arc like setting were the major source these two contrasting volcanic plutonic terranes were tectonically juxtaposed during late archean collisional tectonics

closing history of the southern tianshan oceanic basin western china an oblique collisional orogeny abstract the tianshan tien shan range is an important paleozoic collisional orogenic belt and the key to understand the central asia tectonic evolution this paper integrates our research results with the existing chinese and international literature on sedimentology geochemistry isotopic geochronology paleontonology and paleomagnetism of the tianshan and tarim regions to propose that the oblique collision may have played an important role in the late paleozoic closing of the southern tianshan oceanic basin as a result of the sinian latest proterozoic younger than 800 ma continental extension and rifting process the tarim and yili blocks separated from their parent continent in the late cambrian ordovician the southern tianshan oceanic crusts between the two blocks subducted northward beneath the southern margin of the yili block in the silurian during the devonian early carboniferous the tarim block rapidly drifted to the north and rotated about 46 clockwise this process induced the collision of the yili micro continent with the eastern segment present geographical position of the tarim continent in the late devonian and the southern tianshan oceanic crust evolved to be a west facing remnant oceanic basin during the late carboniferous early permian the tarim block located within an almost constant latitude range rotated about 26 clockwise with respect to the yili micro continent which ultimately closed the remnant oceanic basin in a scissors like manner from east to west and completed the tarim yili collision subsequent a type subduction of the tarim continental crust and lithosphere scale sinistral shearing generated a magmatic arc on the southern margin of the tarim yili suture zone the late permian early triassic clastics deposited in a peripheral foreland basin developed above the arc

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

evidence for major mass transfer and volume strain during regional metamorphism of pelites systematic examination of published sedimentary and metamorphosed pelite analyses has revealed evidence of significant mass transfer and volume strain during regional metamorphism statistical analysis of the data shows that barrovian zone metamorphism of pelitic schist generally causes increases in the whole rock concentrations of the low solubility elements ti and all the observed increases in ti and al contents as functions of metamorphic grade are almost certainly due to residual enrichment caused by the removal of other more soluble species application of mass balance principles to the petite compositional trends indicates that the average pelite may lose as much as 30 of its mass and volume during progressive metamorphism from subgreenschist to amphibolite facies conditions the bulk of the lost mass is silica not volatiles in addition other elements particularly ca na and k appear to be highly mobile in deep crustal metamorphism contrary to conventional interpretations it is concluded that the regional metamorphism of pelites is not an isochemical process

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

characteristics and genesis of kanggur gold deposit in the eastern tianshan mountains nw china evidence from geology isotope distribution and chronology abstract the kanggur gold deposit lies in east tianshan mountains eastern section of central asia orogenic belt the gold mineralization occurs on the northern margin of the aqishan yamansu island arc in the tarim plate it is mainly hosted in lower carboniferous volcanic rocks and controlled by syn tectonic intrusions and the ductile shear zone the host rock is a calc alkaline volcanic rock series consisting of andesite dacite tuff and subvolcanic rocks the gold ore bodies were distributed in transition zone from strong ductile deformation to weak deformation ore controlling structure is ew trending normal brittle ductile shear zone the gold ore bodies are composed of au bearing altered rocks and a few au bearing sulfide quartz veins the mineralization shows vertical zonation in which au was enriched in the upper orebodies au pb zn were enriched in the middle and au cu were enriched in the lower orebodies according to mineral assemblages and alteration intensity hydrothermal alteration could be divided into three zones silicification chloritization pyritization and magnetization zone major ore body pyrite phyllic rock and or sericite alteration zone and sericite chlorite alteration zone five mineralization stages are identified on the basis of mineral assemblage and crosscutting relationship of veins the 34 s values of sulfide in the ores range from 0 9 to 3 3 similar to those of the volcanic and subvolcanic rocks 3 21 1 3 indicating that the sulfur isotope composition is characterized by unfractionated mantle sulfur the lead isotope compositions of ores are between those of the volcanic rocks and subvolcanic rocks the initial 87 sr 86 sr ratios of the ores vary between 0 7077 and 0 7106 similar to those of the host rocks 0 7079 0 7125 according to the sr s and pb isotopic data it is indicated that the ore forming materials were derived from the surrounding volcanic rocks and feature deep source the 18 o values of the ore fluids vary from 3 83 to 1 77 and the d values from 46 to 66 the 18 o vs d and 18 o vs 87 sr 86 sr diagrams indicate that ore fluids were derived from dynamic metamorphic water magmatic water and meteoric water the ore forming ages of kanggur gold deposit are determined by rb sr and sm nd isochron methods the results show that the main ore forming stages of kanggur gold deposit are 290 282 ma secondary mineralization stages are 275 254 ma studies on regional geology ore geology isotope geochemistry and ore forming ages have proved that the kanggur gold deposit was formed in the compression extension transition stage during the latest paleozoic continental collision and is characterized by orogenic gold deposits

the negative eu anomaly in archean sedimentary rocks implications for decomposition age and importance of their granitic sources abstract a negative correlation between eu anomaly eu eu and chemical index of weathering ciw is found for archean pelites in both greenstone belts and high grade terrains from southern africa western greenland north america western australia and china a similar negative correlation betweeneu eu and chemical index of alteration cia is also found for worldwide young deep sea sediments from various tectonic settings the increase in the indices of weathering and alteration coincide with both shifts in mineral composition and mineral decomposition from plagioclase k feldspar to mica kaolinite and from amphibole to chlorite smectite juvenile crustal materials from local sources are only slightly decomposed due to little or no transport they are characterized by low ciw cia and negligible eu anomalies in contrast crustal materials from large provenance areas have usually suffered long transport and recycling which results in decomposition of high temperature minerals and large ciw cia values that are negatively correlated with significant negative eu anomalies thus the observed trends are interpreted as mainly reflecting increasing contributions of recycled and decomposed materials from large provenances relative to juvenile crustal additions through arc magmatism at local sources in this context there is no obvious distinction between archean greenstone and high grade metasediments and young deep sea sediments the large provenance areas have contained a significant proportion of granitic and rhyolitic materials which in part have not resisted decomposition and erosion due to their occurrence in shallow crustal layers granites received their distinctive negative eu anomaly from equilibration with a feldspar rich residuum the negative eu anomaly of archean metaclastic sediments apparently increased with decreasing age trends of minimum and averageeu eu values of metaclastic sediments evolving with time are calculated for the archean and lead us to infer that the negative eu anormaly eu eu

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

the controls on the major and trace element variation of shales siltstones and sandstones of pennsylvanian permian age from uplifted continental blocks in colorado to platform sediment in kansas usa shales siltstones and sandstones of pennsylvanian permian age from near the source in colorado to those in the platform in eastern colorado and kansas have been analyzed for major elements and a number of trace elements including the rees the near source sandstones are significantly more enriched student t test at better than the 99 confidence level in sio2 and na2o concentrations and more depleted in al2o3 fe2o3 total tio2 th hf sc cr cs rees y and ni concentrations and laco and lani ratios than the near source shales and siltstones most likely due to more plagioclase and quartz and less clay minerals in the sandstones than in the shales and siltstones there are no significant differences in k2o and sr concentrations and eueu lalu lase thsc thco and crth ratios between the near source sandstones and the near source shales and siltstones samples of the molas hermosa and cutler formations near the source that were formed in different environments in the same area contain no significant difference in eueu lalu lasc thsc thco and crth ratios so a generally silicic source and not the environment of deposition was most important in producing these elemental ratios for example crth ratios of near source shales siltstones and sandstones range from 2 5 to 17 5 and eueu range from 0 48 to 0 78 which are in the range of sources of sediments derived from mainly silicic and not basic sources near source shales and siltstones contain significantly higher student t test and more varied concentrations of most elements al2o3 fe2o3 mno tio2 ba th hf ta co sc rees nb y but significantly lower concentrations of na2o and eueu than platform shales and siltstones in kansas e g la 65 7 40 and eueu 0 55 0 07 in near source shales and siltstones and la 23 7 8 7 and eueu 0 64 0 08 in platform shales and siltstones the sio2 and cao concentrations are not significantly different in platform shales and siltstones compared to the near source shales and siltstones so dilution of other minerals by quartz and calcite is not the main reason for the lower concentration of most elements in the platform relative to the near source shales and siltstones rather the lesser concentrations of most elements in clay minerals of the platform shales and siltstones can account for the lower concentration of most elements compared to corresponding near source shales and siltstones the lower concentrations of many elements in clay minerals in the platform shales and siltstones may be a result of having been derived from recycling of clay minerals from older rocks the greater homogeneity of elemental concentrations of the platform shales and siltstones compared to those in the source is also consistent with homogeneous mixing of such recycled material also there is no significant difference in thsc laco thco lani and crth ratios of the near source sedimentary rocks in colorado to the platform shales and siltstones in kansas and the latter are also consistent with derivation from mostly silicic source rocks

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

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

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

paleozoic accretion and cenozoic redeformation of the chinese tien shan range central asia the tien shan range in central asia contains two late paleozoic sutures the older southern suture marks the collision of a passive margin at the north of the tarim block and an active continental margin subduction under the latter was to the north the younger northern suture separates a northern carboniferous island arc from an active continental margin developed over a south dipping subduction zone the subduction direction under the island arc is unknown mesozoic elastics were deposited over the doubly sutured orogen rate and energy of sedimentation waned until deposition of oligocene conglomerates above a regional unconformity interpreted as marking the onset of deformation induced by the india asia collision molasse deposition accelerated in pliocene and quaternary time and deposition continues today as active thrusts generate relief paleozoic structures control the gross divergence of cenozoic thrusts across the orogen

late paleozoic tectonic amalgamation of northwestern china sedimentary record of the northern tarim northwestern turpan and southern junggar basins sedimentary rocks contained in basins adjacent to the tian shan provide a long and complex record of the late paleozoic continental amalgamation of northwestern china complementing that provided by rocks preserved within the range this record which comprises dramatic changes in sedimentary facies sediment dispersal patterns sandstone provenance and basin subsidence rates broadly supports previous interpretations of a two part evolution of the tian shan late devonian to early carboniferous collision of the tarim continental block with the central tian shan followed by collision of this combined block with island arcs in the north tian shan and bogda shan in late carboniferous early permian times the first collision resulted in widespread angular unconformities within the tarim basin continued convergence following the collision created a long lived flexural foredeep along the northern margin of the tarim block which received at least 2000 m of lower carboniferous through lower permian fluvial and marine sediment derived from the interior of tarim subsequent early permian continental extension of the northern tarim basin resulted in the deposition of interbedded nonmarine siliciclastic sedimentary rocks and mafic to felsicvolcanic rocks sandstone within this interval was derived from the paleo tian shan and is composed predominantly of lithic volcanic grains similar to the rhyolite in contrast to the tarim basin calc alkaline volcanic rocks and volcanogenic sedimentary rocks dominated carboniferous and permian sedimentation in the northern turpan and northwestern junggar basins volcanic arcs remained active in the north tian shan and bogda shan through the early late carboniferous depositing a kilometers thick interval of deep marine sediment gravity flows in the northwestern junggar basin major arc magmatism ceased in the late carboniferous in response to closure of the oceanic basin between the combined tarim central tian shan block and the north tian shan bogda shan arcs upper carboniferous through lower permian rocks in the northwestern junggar basin compose the sedimentary fill of a bathymetric basin of oceanic depth on the northern side of the volcanic arcs culminating in a 1000 m thick marine regressive sequence middle to upper permian sandstones were derived from the uplifted paleo tian shan and bear the distinctive provenance imprint of granitic rocks presently exposed within the range late permian subsidence of the junggar basin accommodated 5 km of nonmarine sediments however the cause of this subsidence and its relationship to regional tectonic events remain controversial

identification of sedimentary diagenetic facies and reservoir porosity and permeability prediction an example from the eocene beach bar sandstone in the dongying depression china abstract accurate prediction of reservoir porosity and permeability is essential for prospecting hydrocarbon reserves and petroleum production capacity we propose an innovative reservoir porosity and permeability prediction method through identifying sedimentary diagenetic facies determining the porosity permeability trends using core measurement data extrapolating the spatial distribution of the sedimentary diagenetic facies using log data through the bayes discriminant analysis and predicting the reservoir porosity and permeability the essence of the method was illustrated and its effectiveness was demonstrated using the eocene beach bar sandstones in the dongying depression bohai bay basin eastern china the eocene beach bar sandstones are classified into fine sandstone siltstone and argillaceous siltstone based on grain sizes sorting and matrix contents the major diagenetic processes that influence the porosity and permeability of the beach bar sandstones are compaction carbonate cementation and feldspar dissolution seven sedimentary diagenetic facies were identified in the beach bar sandstones based on the lithological types and their corresponding diagenesis and influence extent on reservoir properties the variation ranges of porosity and permeability log k of these sedimentary diagenetic facies are typically less than 6 and 1 2 respectively both the porosity and permeability have well defined functional relationships with depth the sedimentary diagenetic facies can be identified effectively from logging data through the use of the bayes discriminant analysis and corresponding cross plots the porosity and permeability log k of the well evaluated in the study were predicted with errors in the range of 3 and 0 6 respectively based on the distribution and the fitting equation of the trend lines for the seven sedimentary diagenetic facies the predicted porosities and permeability of sedimentary diagenetic facies match the measured porosities and permeability well

archaean metasedimentary rocks from the northwestern pontiac subprovince of the canadian shield chemical characterization weathering and modelling of the source areas abstract the northwestern pontiac subprovince is dominated by a monotonous greywacke sequence metamorphosed and deformed during the late archaean kenoran orogeny limited chemical weathering of the source rocks is suggested by 1 low values of the chemical index of alteration 2 no preferential leaching of ca sr and ba 3 well defined correlations among mgo k2o and al2o3 and 4 small variations of cr ni the source was dominantly felsic as indicated by high th sc average 0 39 la co 1 06 zr cr 0 7 zr y 11 2 and sio2 mgo 19 4 the composition of these metasedimentary rocks can be modelled by mixing of three end member components 1 tonalites trondhjemites 65 in order to explain the sio2 al2o3 th u zr sr and ba abundances na k ratios strong depletion in hree and hfse relative to lree and lile low th y and k2o and fractionated la yb 19 4 2 komatiites 5 in order to explain the high cr 220 ppm and ni 66 ppm contents and 3 tholeiitic basalts 30 accounting for the observed tio2 0 62 wt v 144 ppm and sc 17 ppm concentrations the source region may be considered as a deeply eroded greenstone belt intruded by abundant tonalite trondhjemite plutons possibly now located to the south and east in the grenville province or possibly to the north underlying the dominantly volcanic abitibi subprovince