geochemical characteristics of the permian basins and their provenances across the solonker suture zone assessment of net crustal growth during the closure of the palaeo asian ocean abstract the solonker suture zone is commonly recognised as the location of the late permian to early triassic closure of the palaeo asian ocean in the southeastern segment of the central asian orogenic belt however the absence of typical suture related features as a consequence of uncommon collisional geometries gave it a cryptic nature thus the tectonic setting which led to suturing still remains enigmatic a geochemical characterisation of permian sedimentary and volcanic rocks across the suture was carried out supplemented with hf and nd isotopic analyses this approach enables not only a better definition of such regional suture but also estimates on the long controversial issue of net crustal growth in accretionary tectonic environments the results indicate short sedimentary transport distances between the arc basins and their provenances of which the studied volcanic rocks were a major contributor similar enrichment and depletion patterns with respect to n morb and average continental crust further corroborate a close source sediment relationship immobile element provenance analyses indicate that the active continental northern margin of the north china craton was a major source for arc basins to the south of the solonker suture zone to its north arc basins are interpreted to be sourced by a more complex mixture of provenances e g the baolidao volcanic arc suite and the heterogenous precambrian basement of southern mongolia an overall collisional tectonic setting across the suture is recognised the geochemical signature of sedimentary rocks to the south of the suture points at an active continental arc setting whereas the bimodal geochemical distribution of the samples to the north shows a contemporaneous active oceanic island arc as well as a passive margin environment these features favour a double sided subduction of the palaeo asian ocean beneath the north china craton and the mongolian arcs throughout the palaeozoic including back arc basin opening north of the suture in the permian analysis of hf and nd isotopic compositions revealed that magmas to the south were produced involving significant crustal contamination thus having less radiogenic compositions north of the suture however isotopic compositions tend to be more radiogenic implying a more juvenile contribution however the bulk isotopic compositions are close to present day chur suggesting that crustal reworking appears to be equally balanced by juvenile addition during the palaeozoic closure of the palaeo asian ocean across the solonker suture zone

u pb zircon and geochemical constraints on the age origin and evolution of paleozoic arc magmas in the oyu tolgoi porphyry cu au district southern mongolia abstract uranium pb zircon ages are linked with geochemical data for porphyry intrusions associated with giant porphyry cu au systems at oyu tolgoi to place those rocks within the petrochemical framework of devonian and carboniferous rocks of southern mongolia in this part of the gurvansayhan terrane within the central asian orogenic belt the transition from devonian tholeiitic marine rocks to unconformably overlying carboniferous calc alkaline subaerial to shallow marine volcanic rocks reflects volcanic arc thickening and maturation radiogenic nd and pb isotopic compositions e nd t range from 3 1 to 7 5 and 206 pb 204 pb values for feldspars range from 17 97 to 18 72 as well as low high field strength element hfse contents of most rocks mafic rocks typically have 2 are consistent with magma derivation from depleted mantle in an intra oceanic volcanic arc the late devonian and carboniferous felsic rocks are dominantly medium to high k calc alkaline and characterized by a decrease in sr y ratios through time with the carboniferous rocks being more felsic than those of devonian age porphyry cu au related intrusions were emplaced in the late devonian during the transition from tholeiitic to calc alkaline arc magmatism uranium pb zircon geochronology indicates that the late devonian pre to syn mineral quartz monzodiorite intrusions associated with the porphyry cu au deposits are 372 ma whereas granodiorite intrusions that post date major shortening and are associated with less well developed porphyry cu au mineralization are 366 ma trace element geochemistry of zircons in the late devonian intrusions associated with the porphyry cu au systems contain distinct th u and yb gd ratios as well as hf and y concentrations that reflect mixing of magma of distinct compositions these characteristics are missing in the unmineralized carboniferous intrusions high sr y and evidence for magma mixing in syn to late mineral intrusions distinguish the late devonian rocks associated with giant cu au deposits from younger magmatic suites in the district

determining the burial time of single grains of quartz using optically stimulated luminescence abstract in the optical dating of sediments it is usually assumed that the optically stimulated luminescence osl signal has been completely reset by light exposure prior to burial this assumption is often not valid one approach to testing and perhaps circumventing this assumption is to examine the apparent date of last exposure to daylight of individual sediment grains this paper reports on the application for the first time of 2 new measurement protocols to the estimation of the radiation dose received during burial for individual quartz grains from an aeolian deposit of known age 10 000 year old which is considered likely to have been completely reset by sunlight at deposition additive dose laboratory doses added to the burial dose before osl measurement and regenerative dose doses added after measurement of osl from burial dose single aliquot protocols are applied to 28 and 25 individual grains respectively each grain provides an independent estimate d e of the burial dose the average d e from the additive dose protocol 21 8 1 1 gy is in good agreement with the average from the regenerative dose protocol 23 8 1 0 gy both agree well with 1 13 multiple grain regenerative dose single aliquot measurements each on 1 mg sub samples of 23 9 0 3 gy 2 9 multiple grain additive dose single aliquot measurements also on 1 mg sub samples of 22 4 0 7 gy and 3 one previously published multiple aliquot additive dose estimate of 23 5 0 6 gy using 52 sub samples each of 5 mg the resulting optical ages are in good accord with 14 c and thermoluminescence age determinations the distribution of equivalent doses in the single grains is however unexpectedly large 23 of mean d e given the very likely complete resetting of the osl signal at deposition possible reasons are discussed and it is concluded that heterogeneity in beta dosimetry is the most likely explanation the single grain optical dating protocols reported here allow a detailed examination of the dose distribution in very small samples thus they should enable accurate dates to be obtained for sediments and soils that contain poorly bleached or mixed age components as well as deposits in which quartz grains are present in extremely low abundance

contrasting styles of mineralization in the chinese altai and east junggar nw china implications for the accretionary history of the southern altaids abstract the chinese altai east junggar collage in the southern altaids hosts three metallogenic belts which are from north to south 1 a volcanogenic massive sulphide vms cu pb zn belt 2 a belt of shear zone related gold deposits 3 a porphyry cu au mo belt the vms deposits formed in two pulses c 405 ma and c 375 ma in the chinese altai arc the porphyry deposits developed in three pulses in the east junggar arc the first two synchronous with the vms mineralization and the third at c 330 ma the shear zone related gold deposits developed in the late carboniferous to permian at the contact between the chinese altai and east junggar arcs time space distributions of diverse ore deposits across the altai east junggar collage indicate that the collage developed from two independent arcs the chinese altai and the east junggar the vms and porphyry deposits developed in the chinese altai and east junggar arcs respectively the chinese altai arc is interpreted to be a japanese type arc and the east junggar arc a mariana type arc during the latest palaeozoic the two arcs were juxtaposed by the erqis fault when many shear zone related lode gold deposits were emplaced these metallogenic distributions were a likely response to spatially localized mechanisms of crust growth and to the tectonic evolution of the altai east junggar collage and they are consistent with interpretation of the altaids as a multiple subduction accretion collage

major types characteristics and geodynamic mechanism of upper paleozoic copper deposits in northern xinjiang northwestern china abstract syn and post orogenic cu mineralization in the northern xinjiang paleozoic accretionary and collisional orogenic belt in northwestern china is of great economic interest about 40 cu bearing deposits have been discovered in the area making it one of the most important metallogenic belts in china according to their host rocks these deposits can be classified into four principal types 1 volcanic hosted massive sulfide cu pb zn deposits 2 porphyry cu mo au deposits 3 magmatic cu ni sulfide deposits and 4 cu mo au ag skarn deposits tectonically the development of these upper paleozoic deposits was closely associated with subduction and collision of the ancient asian ocean between the siberian block and the tarim craton an important metallogenic epoch involving formation of cu pb zn polymetallic deposits formed during southwestern rollback and associated slab detachment during devonian time 400 370 ma in southern altay southwestern direct rollback and associated slab detachment occurred during the devonian 400 370 ma in response to later collision at the accreted continetal margin xiao w j windley b f badarch g sun s li j l qin k z wang z h 2004 palaeozoic accretionary and convergent tectonics of the southern altaids implications for the lateral growth of central asia journal of the geological society of london 161 339 342 during which the ashele cu pb zn and keketale pb zn deposits formed subduction led to the accretion of the junggar ocean arc system in the middle devonian in the lower to middle carboniferous north dipping subduction beneath the dananhu arc triggered the emplacement of granitic porphyries in the tousuquan and dananhu island arc belt in the east tianshan leading to the formation of the tuwu and yandong porphyry cu mo au ag deposits in the upper carboniferous to lower permian large mafic ultramafic complexes were emplaced during closure of the ancient tianshan ocean resulting in the formation of several magmatic cu ni sulfide deposits including the kalatongke cu ni deposits in north junggar and cu ni sulfide deposits in the huangshan jing erquan area of east tianshan mountains also associated with this extensional event were emplacement of voluminous anatectic granitoids and eruption of volcanic rocks which led to formation of skarn cu mo suoerkuduk cu mo deposit and cu ag deposits weiquan cu ag deposit the tectonic settings geological features and temporal and spatial distribution of these different types of cu deposits reflect to a great extent the accretionary and collisional tectonics that occurred between the siberian block and tarim block

re os molybdenite age of the cu mo skarn ore deposit at suoerkuduke in east junggar nw china and its geological significance the suoerkuduke cu mo ore is a medium sized skarn deposit in the east junggar orogen of the southern altaids xinjiang northwest china we measured re os isotopes of a molybdenite veinlet from the

conditions of rhodochrosite nodule formation in neogene pleistocene deep sea sediments evidence from o c and sr isotopes calcic rhodochrosite occurs as nodules around burrows in late neogene early pleistocene pelagic sediments of the galapagos ridge in the guatemala basin eastern equatorial pacific dsdp leg 68 site 503 growth was accomplished in the suboxic zone delta

valley and interfluve sediments in the southern ganga plains india exploring facies and magnetic signatures the western ganga plains of india show narrow incised valleys that contain the major himalayan sourced rivers separated by broad interfluves traversed by small plains fed rivers from analysis of four cores and outcrop sections to 50 m sub surface this geomorphic setting appears to be of late quaternary antiquity a major river paleo ganga has been located near its present position since at least 26 ka bp with indications of southward migration between 11 and 6 ka valley fill cores show repeated cycles of valley aggradation in response to late quaternary climatic oscillations in accord with simulation models of drainage basin response to climate change and reflect interplay of discharge and sediment supply floodplain sediments within the valley fill show a generally weakly magnetic signature and only modest pedogenic activity the valley margin records a major discontinuity that marks reduction of discharge in the ganga river during the last glacial maximum when monsoonal precipitation was greatly reduced and lakes and eolian dunes occupied areas distant from the main channel the lacustrine facies show marked magnetic enhancement probably reflecting bacterial action and the availability of organic matter the interfluve record yields no indication of major river activity during the past 100 ka instead the near continuous activity of small plains fed rivers generated cycles of alluviation and pedogenesis the latter yielding strong magnetic signatures enhanced magnetic signatures are apparent in both valley and interfluve holocene records possibly linked to increased monsoonal strength warmer conditions and enhanced rates of pedogenesis

minor elements in quaternary sediment from the sea of japan a record of surface water productivity and intermediate water redox conditions sediment of quaternary age from oki ridge 903 m depth in the sea of japan 3500 m deep records six episodes of high accumulation rates of cd cr cu mo ni u v and zn the high rates correspond to periods of sulfate reduction in the water column at the intermediate depth of oki ridge the intervening low values correspond to periods of denitrification and oxygen respiration the maxima have a period of 41 k y the youngest having an age of 1 10 ma the 41 k y cycle is similar to the cycle of 18 o values of open ocean plankton of the same age the similarity between the cycles of minor element accumulation in sea of japan sediment and 18 o values of atlantic ocean foraminifera indicates that redox changes in the water column of the sea of japan during the quaternary forced by major shifts in water column advection and minor shifts in photic zone productivity reflect global events

composition and origin of early cambrian tiantaishan phosphorite mn carbonate ores shaanxi province china abstract the tiantaishan phosphorite mn carbonate ores occur in the early cambrian tananpo formation in complexly folded and faulted rocks located in southern shaanxi province about 65 10 6 tonnes of 17 p 2 o 5 ore reserves exist and mn ore reserves are about 8 3 10 6 tonnes of 18 mn the stratigraphic sequence in ascending order consists of black phyllite black to gray phosphorite ore black phyllite rhodochrostone ore mn mixed carbonates and dolostone data are presented from microprobe mineral chemistry whole rock chemistry stable isotopes of carbonates x ray mineralogy petrographic and sem observations and statistical analysis of chemical data the dominant ore forming minerals are hydroxy and carbonate fluorapatite and ca rhodochrosite with mg kutnahorite and dolomite comprising the mn mixed carbonate section pyrite occurs in all rock types and alabandite mns occurs throughout the rhodochrostone section the mean p 2 o 5 content of phosphorite is 31 and argillaceous phosphorite is 16 while the mean mno content of rhodochrostone ore is 37 phosphorite ores are massive spheroidal laminated and banded while rhodochrostone ores have oolitic spheroidal and granular fabrics the most distinguishing characteristics of the ores are high total organic carbon toc contents mean 8 4 in the phosphorite and high p 2 o 5 contents mean 2 7 in the rhodochrostone ore the atypically high toc contents in the tiantaishan phosphorite probably result from very strong productivity leading to high sedimentation rates accompanied by weak reworking of sediments poor utilization of the organic matter by bacteria and or partial replacement of bacterial or algal mats by the apatite the depositional setting of the ores was the margin of an epicontinental seaway created as a direct consequence of global processes that included break up of a supercontinent formation of narrow seaways creation of extensive continental shelves overturn of stagnant metal rich deep ocean waters and marine transgression water depth increased from deposition of the black phyllite sequence through deposition of the mn mixed carbonate sequence then shallowed again during deposition of the overlying dolostone sequence bottom waters were mostly dysoxic to suboxic but fluctuated from oxic to anoxic productivity was high during deposition of the black phyllite sequence increased during precipitation of phosphorite and then decreased to moderate levels during precipitation of rhodochrostone ores biosilica contributions occur in each lithology but are greatest in rhodochrostone changes in sedimentation were determined by changes in water depth productivity upwelling sea level change and ventilation of the depositional basin the source of the phosphorus was organic matter produced in great quantities during deposition of the black phyllite and phosphorite sequences in a zone of coastal upwelling organic matter accumulation was rapid globally mn was supplied by overturn of stagnant metal rich deep ocean waters which were redistributed to areas of coastal upwelling and seaways that process may have been initiated by latest proterozoic glaciations which would have promoted density stratification and accumulation and storage of metals regionally mn was supplied by terrigenous input into the shallow seaway and hydrothermal input into the deeper water parts of that seaway locally mn sources included leaching and transport of metals from the sediment column manganese was stored locally in low oxygen not anoxic seawater prior to mn ore formation the source of the carbon in the mn carbonates and dolostones was predominantly seawater bicarbonate and secondarily co 2 derived from the oxidation of organic matter in the bacterially mediated diagenetic zone of sulfate reduction

uranium disequilibrium dating of phosphate deposits from the lau group fiji uranium series methods of absolute age determinations were first applied to fossil coral reefs1 and more recently to fossil bone2 marine apatite3 6 and insular apatite7 8 past sea level stands climatic conditions primary productivity and other factors are thought to be influential in the deposition of avian guano and subsequent insular phosphorite formation9 some deposits appear to have formed during high stands of the sea while others may be related to glacial epochs8 we report here an attempt to determine the absolute age of two phosphate deposits in the lau group fiji by uranium series disequilibrium techniques in order to assist in the evaluation of their origin in terms of known palaeoclimatic information

in situ u pb hf and re os isotopic analyses of the xiangshan ni cu co deposit in eastern tianshan xinjiang central asia orogenic belt constraints on the timing and genesis of the mineralization abstract the timing and genesis of the major ni cu co sulfide deposit in the xiangshan intrusion have been studied based on newly obtained in situ u pb hf and re os isotopic analyses the sims u pb zircon ages of the gabbro hosting the ni cu co sulfide deposit indicate that the xiangshan intrusion was emplaced at 279 6 1 1 ma 95 confidence level mswd 1 30 n 15 on the basis of combined geological and geochronological evidence we suggest that the xiangshan and other adjacent ni cu deposits were formed in the same period sulphides have low common os concentrations and high re os ratios similar to sulphide ores from the duluth sally malay and voisey bay complexes the re os isotopic data from the disseminated and massive ores from the xiangshan intrusion do not form a single isochron as they have different initial os ratios the hf and os isotopic data suggest that the xiangshan intrusion and associated ni cu co mineralization were derived from crustally contaminated mantle melts the geochemical data show a tholeiitic affinity and a strong suprasubduction zone signature with negative nb sr and ti anomalies similar to n morb and e morb we suggest that the mafic ultramafic rocks and associated ni cu mineralization of the eastern tianshan orogen formed in an alaska type subduction zone arc setting some diagnostic features of ridge trench interaction are present in the chinese east tianshan orogen e g granites adakites high mg andesites near trench magmatism alaskan type mafic ultramafic complexes high temperature metamorphic belts that prograde rapidly from low grade belts and orogenic gold deposits the above distinctive rock groups are probably related to the same thermal event ridge subduction as in the cenozoic orogen of alaska we suggest that ridge subduction is the most plausible mechanism to provide the necessary heat ridge subduction provides an important promising model for understanding many aspects of the evolution of the chinese eastern tianshan orogen and by inference throughout much of central asia

uranium mineralization and its radioactive decay induced carbonization in a black shale hosted polymetallic sulfide ore layer southwest china the black shale in the lower cambrian niutitang formation southwest china which has been dated to 532 3 0 7 ma by u pb radiometric measurements hosts a sedimentary layer with abnormally high ni mo pge au contents this layer is enriched in ni up to 3 8 wt mo up to 7 7 wt and u up to 595 ppm but its genesis is still controversial here we report the first direct observation of uranium bearing minerals and their radioactive effects on the surrounding matter in the polymetallic sulfide ore x ray absorption fine structure analyses confirmed the reduced valence state of uranium in combination with high resolution electron microscopy and electron probe microanalysis the mineral was identified as coffinite usio4 a strong positive correlation between the sizes of the coffinite crystals and their surrounding carbonized rings reveals that the coffinite is authigenic and its crystallization produced radiation resulted in the radiolysis of surrounding organic matter the association of various biogenic metal sulfides phosphates and abundant organic substances within the ni mo sulfide enriched ore suggests that biological adsorption may have participated in the enrichment of soluble u vi and that microbial sulfate reduction might have facilitated the uranium mineralization

post accretionary permian granitoids in the chinese altai orogen geochronology petrogenesis and tectonic implications the altai orogen is an important constituent of the central asian orogenic belt caob the main orogenic processes occurred mainly in the early to middle paleozoic and involved a series of northward subduction and terrane accretion however termination of the accretionary and post accretionary processes remains poorly defined the chinese altai is located in the southern part of this orogeny which is widely intruded by permian granitic plutons these plutons are approximately circular in shape free of deformation and generally cutting pre permian structures suggesting a post tectonic formation we report the results of geochronological and geochemical data from five specific granitic plutons buerjin xibodu daqiaonan aweitan and adenbluk which all yielded magmatic zircon u pb ages of about 270 ma these plutons are composed of high k calc alkaline rocks including k feldspar megaphyric granite biotite granite and monzogranite that have metaluminous to weakly lree enriched coupled with negative eu anomalies significant negative anomalies of ba sr p and ti are also observed in the primitive mantle normalized diagram they have positive whole rock end t 1 3 to 7 2 and zircon ehf t values 5 6 to 12 9 yielding sm nd model ages of 0 9 ga therefore these granitoids are proposed to have been generated by differentiation of mantle derived magmas with variable crustal contamination in view of the field occurrence structural analysis regional tectonics and geochemical characteristics these permian plutons are concluded to be post accretionary or post collisional asthenospheric upwelling after the collision and amalgamation of the altai and junggar blocks could have caused the mantle derived magmas that evolved to form the granitoids we note that permian intrusions are not only widespread but also voluminous in the caob they mostly are post collisional products and some of them might have been related to the large igneous province activity in the tarim block

chemical depositional environments of calcic marine black shales the economically important black shale facies contains several discrete chemical groupings in visually similar rocks we examined the elemental compositions of more than 300 black shales and anoxic sediments in order to understand the relation of their chemical variability to the depositional environment the low calcic shales were found to contain at least four discrete groupings 1 4 whose depositional and early diagenetic redox conditions are suggested by their fe mn and v concentrations the calcic shales 72 paleozoic 50 mesozoic and 42 cenozoic 50 000 ppm al 4 000 ppm ca were examined in terms of the four thermodynamic groups previously defined for the low calcic shales the ca mn ratios of the calcic black shales fall into four i iv discrete clusters as opposed to a continuum this differentiation reflects the stability of mn minerals in overlying and interstitial waters under varying redox conditions one cluster ca mn i from a period of glaciation ordovician silurian boundary has high mn concentrations and falls on the line mn 0 065 ca 1 280 ppm r 0 95 n 7 a second group ca mn ii from many different localities and ages falls on a line with a lower slope mn 0 038 ca 187 ppm r 0 92 n 21 the third group ca mn iii falls on the line mn 0 011 ca 152 ppm r 0 95 n 19 the greatest number of samples ca mn iv fall on the line mn 0 0027 ca 144 ppm r 0 85 n 69 in order to establish the depositional environment associated with each of the groups more modern sediments whose depositional settings are better defined were explored as a result the samples from both ca mn i and ii can be associated with deposition under oxic water those from ca mn i remained oxic during early diagenesis after deposition ca mn ii samples became anoxic releasing mn to interstitial waters the ca mn iii and iv group samples were deposited under anoxic waters in order to establish the thermodynamic environment of the shale component of the calcic shales it is necessary to extrapolate to the no calcium intercept to determine the mn content then apply the rules determined for the low calcic shales this study demonstrates the wide variety of black shale depositional environments from oxic to methanogenic accordingly black shales can not all be assigned to anoxic sulfidic environments without additional chemical analysis and interpretation the proper environmental assignment should be useful in assessing the economic potential of particular black shale deposits

late permian triassic metallogeny in the chinese altay orogen constraints from mica 40ar 39ar dating on ore deposits abstract the central asian orogenic belt caob constitutes the largest phanerozoic accretionary orogen on earth it extends over 5000 km and hosting numerous metal deposits the chinese altay orogen an important element of the caob hosts abundant devonian ca 410 370 ma deposits the 40 ar 39 ar dating of seven mica separates from the representative samples syngenetic with orogenic type mineralization is summarized to record a poorly studied permian to triassic metallogenic episode in the chinese altay orogen the kelan and maizi basins in the chinese altay orogen which likely represent an arc accretionary complex contain a series of polymetallic lode deposits hosted in low grade metamorphic volcano sedimentary rocks two muscovite and five biotite separates were obtained from the ore forming veins paragenetically associated with au bearing polymetallic sulfides in the keketale pb zn wulasigou cu tiemurt pb zn dadonggou pb zn and sarekuobu au deposits these separates yielded 40 ar 39 ar plateau ages ranging from 260 ma to 205 ma integration of these results with other published geological and geochronological data indicates that the au cu pb zn mineralization post dated the final caob assembly with fluid movement and mineralization possibly driven by regional metamorphism and deformation it is herein proposed for a metallogenic model that the metamorphic fluid migration following final assembly of the caob results into the formation of the deposits

geochemical study of the cambrian ordovician meta sedimentary rocks from the northern altai mongolian terrane northwestern central asian orogenic belt implications on the provenance and tectonic setting abstract the altai mongolian terrane am is a key component of the central asian orogenic belt caob but its tectonic nature has been poorly constrained this paper reports geochemical compositions of cambrian ordovician meta sedimentary rocks from the northern am to trace their source nature and depositional setting which in turn place constraints on the geodynamic evolution of the am the cambrian ordovician meta sedimentary rocks from the northern am show variable major element compositions with negative correlation between sio2 and tio2 al2o3 fe2o3t mgo and k2o their high icv values 1 18 2 53 and relatively low cia values 37 9 76 3 indicate that the sediments were immature and probably underwent mild to moderate chemical weathering the low sio2 samples are characterized by relatively restricted sio2 al2o3 mostly 2 60 6 07 and low rb sr ratios 0 02 1 89 implying their proximal deposition without obvious sedimentary sorting and recycling in contrast the high sio2 samples show much higher sio2 al2o3 ratios 15 4 19 9 possibly due to sedimentary sorting and or silicification all these samples yield relatively high al2o3 tio2 ratios 15 6 22 8 strong lrees hrees differentiation la yb n 4 86 10 7 and obvious negative eu anomalies eu 0 61 0 83 combined with their th sc zr sc la th and co th ratios comparable with intermediate acidic magmatic rocks we infer that these kinds of magmatic rocks served as a major source for the investigated meta sedimentary rocks the tio2 al2o3 and fe2o3t mgo concentrations are mostly higher than typical sediments from passive margin and the th u la sc th sc eu eu zr hf zr th and la th ratios are quite similar to sediments from continental arcs these data suggest that the cambrian ordovician meta sedimentary rocks from the northern am were most likely deposited in an environment related to a continental arc setting rather than a passive regime these rocks show strong similarities to their counterparts in the chinese altai ca southern am and tseel terrane southeastern extension of the ca in western mongolia in terms of geochemical compositions and depositional setting with combination of recent isotopic studies for detrital zircons our data suggest that the am probably represented a coherent accretionary prism along a continental arc in the early paleozoic

compositional polarity of triassic granitoids in the qinling orogen china implication for termination of the northernmost paleo tethys abstract the qinling orogen was formed from the closure of the northernmost paleo tethys sea and the tectonic suturing of the yangtze and north china cratons the timing of this collision and the tectonic framework are debated the widely developed triassic granitoids in the western qinling orogen offer a key to understand the tectonic evolution of this region here we compile the geological geochemical and geochronological data of the triassic granitoids from the qingling orogen and conclude that the granitoids north of the mian lue suture were emplaced in an active continental margin related to the northward subduction of the mian lue oceanic plate during 248 200 ma the granitoids can be classified into i and s types with the former constituting the major variety northward from the mian lue fault an s type granite belt appears followed by and locally overlapping with an i type granite belt the i type granite belt can be subdivided into four sub belts from south to north with increasing contents of k2o k2o na2o sio2 th and u and the ratios of k2o na2o rb sr and 87sr 86sr i but decreasing contents of na2o al2o3 mg and ehf t except for the northernmost belt which occurs in the huaxiong block of the north china craton this geochemical polarity of i type granitoids and the zoned distribution of s and i types granitoids cannot be explained through continental collision orogeny including syn to post collision but can be well interpreted by considering the progressive subduction of the northernmost branch of the paleo tethys as represented by the mian lue ocean thus the termination of the northernmost paleo tethys and the onset of the continental collision between the yangtze and the north china plates are considered to have occurred at about 200 ma during the transition from triassic to jurassic our model is also supported by the available data from other studies and provides a revised framework for the timing and tectonics of assembly of the yangtze and the north china cratons

geochemical studies on permian manganese deposits in guichi eastern china implications for their origin and formative environments abstract permian manganese ore deposits are widely distributed in southwestern and eastern china guichi permian manganese district in southern anhui province central eastern china is currently the most important manganese metal producers in eastern china manganese ores mno 18 2 45 4 wt in guichi region occur in calcareous argillaceous and siliceous mn bearing sequence of the permian gufeng formation in contrast to mn bearing rocks the ores have higher mn fe p sr more than 1500 ppm and ni contents 480 ppm higher mn fe 5 and lan cen 2 values and lower co ni

equivalent dose determinations for polymineralic fine grains using the sar protocol application to a holocene sequence of the chinese loess plateau abstract a single aliquot regenerative dose sar protocol involving stimulation of the same disc with an infra red laser diode followed by blue leds was applied to polymineralic fine grains infra red stimulated luminescence irsl and post ir optically stimulated luminescence osl ages are presented for a series of 19 fine grain 4 11 m samples taken from a loess section duowa in the western chinese loess plateau there are significant differences between the equivalent doses and thus the ages for the irsl and post ir osl measurements three potential explanations are investigated incomplete bleaching prior to deposition thermal transfer of charge and initial sensitivity change the question regarding which sequence of ages ir or post ir osl is correct if either is not resolved although the 19 post ir osl ages yield more consistent results it is proposed that the double sar protocol employed may not be correctly monitoring the sensitivity changes relating to either or both natural signals

ubiquity of anomalous fading in k feldspars and the measurement and correction for it in optical dating anomalous fading rates were measured in k feldspars separated from 49 sediment samples mainly from north america the intensity of the optically stimulated luminescence was found to decrease linea

glacial and nonglacial events in the eastern james bay lowlands canada marine and continental records indicate that the laurentide ice sheet lis was highly dynamic throughout the last glacial cycle with significant reorganizations of its ice divide system the extensive depositional record of the hudson bay lowlands hbl is particularly important for the study of ice sheet dynamics because this region was once located near two important ice domes of the lis however important stratigraphic issues remain in the hbl notably regarding the chronology of nonglacial units and the direction and extent of the ice flow events recognized here we focus on the northeastern sector of the lis by documenting the provenance of tills and dating nonglacial deposits in sedimentary sequences east of james bay our investigations indicate that the regional stratigraphy comprises at least five distinct tills and an important unit of glaciolacustrine rhythmites this glacial sequence lies on massive lacustrine clay and fluvial sand containing abundant organic debris and wood fragments the

geology fluid inclusion geochemistry and 40ar 39ar geochronology of the wulasigou cu deposit and their implications for ore genesis altay xinjiang china abstract the wulasigou cu deposit occurs as veins controlled by a nw trending structure in a devonian volcano sedimentary basin of the altay orogenic belt xinjiang china igneous and sedimentary rocks exposed in the area have undergone greenschist facies metamorphism the ore forming process can be divided into early middle and late stages represented by respectively pyrite quartz polymetallic sulfide quartz and carbonate quartz veins veinlets and or replacement bodies the early veins were deformed and brecciated during a compressional or transpressional event the middle stage veinlets filled fractures in the early stage vein and alteration assemblages and are undeformed suggesting a tensional shear setting the late stage veinlets are mainly open space fissure fillings that cut veins and replacement bodies formed in the earlier stages four types of fluid inclusions fis including aqueous w type mixed carbonic aqueous m type purely carbonic c type and daughter mineral bearing s type have been identified in copper related quartz and calcite from the wulasigou deposit the early stage quartz contains m and w type primary fis that completely homogenized at temperatures of 322 412 c with low salinities of 0 9 6 5 wt nacl equiv in contrast the late stage quartz or calcite contains only the w type fis with homogenization temperatures of 101 234 c and salinities of 0 9 2 9 wt nacl equiv this indicates that the metallogenic system evolved from co 2 rich metamorphic to co 2 poor through input of meteoric fluids all four types of fis can only be observed in the middle stage minerals where they show evidence of vein formation during an episode of fluid immiscibility these fis homogenized at temperatures ranging mainly from 230 to 347 c with salinities clustering 2 7 10 2 wt nacl equiv for the w m and c types and 34 7 38 2 wt nacl equiv for the s type respectively the metal precipitation resulted from a decrease in copper solubility during the fluid immiscibility episode the estimated trapping pressures for the middle stage fluids are 1 55 3 55 kbar suggesting an alternating lithostatic hydrostatic fluid system controlled by fault valve activity at a depth of 13 15 5 km muscovite separates from the middle stage polymetallic quartz veinlets yield a well defined 40 ar 39 ar isotopic plateau age of 219 41 2 10 ma and an 39 ar 36 ar 40 ar 36 ar isochron age of 219 73 2 17 ma this age postdates the final paleo asia ocean closure at ca 250 ma by about 30 ma and indicates that the cu mineralization at wulasigou has occurred in the triassic continental collision setting hence the wulasigou cu deposit may be the first example of orogenic lode cu deposits formed in accretionary orogeny or continental collision

paleo redox depositional conditions inferred from trace metal accumulation in two cretaceous paleocene organic rich sequences from central egypt abstract cretaceous paleocene organic rich sediments in egypt occur as an east west trending belt extending from the quseir safaga district red sea to the kharga dakhla western desert region they are associated with the duwi formation phosphate bearing and the overlying dakhla formation deeper epicontinental shale marl this study aims to reconstruct the paleo redox conditions during deposition of these thermally immature organic rich sediments using carbon sulfur iron systematics and trace metal proxies in two cores one each from the quseir and abu tartur areas paleoproductivity based on p content seems to have been higher in the quseir section than in the abu tartur section the quseir section also records a relatively greater occurrence of anoxic conditions during the accumulation of these sediments than the abu tartur section this difference is indicated by its markedly higher total organic carbon toc content as well as higher contributions of redox sensitive and sulfide forming metals mo u ni v and co a weak correlation exists between s and toc and a positive s intercept 1 was observed in most of the rock units of the study sections a high consistency between the toc s fe relations and trace metals findings was found the uppermost duwi and the lowermost dakhla strata which have the highest toc and represent a maximum sea transgression during the late cretaceous have the highest contents of redox sensitive trace metals the carbonate dominated transgressive baris and beida members of the dakhla formation record relatively stronger oxygen depleted conditions during their accumulation than others which led to relatively higher toc contents and redox sensitive metal accumulations a scenario for the environmental conditions that existed during the deposition of these organic rich successions based on compiled trace metals and toc s fe implications is reconstructed here

manganese mineralogy and diagenesis in the sedimentary rock record oxidation of manganese ii to manganese iii iv demands oxidants with very high redox potentials consequently manganese oxides are both excellent proxies for molecular oxygen and highly favorable electron acceptors when oxygen is absent the first of these features results in manganese enriched sedimentary rocks manganese deposits commonly mn ore deposits which generally correspond to the availability of molecular oxygen in earth surface environments and yet because manganese reduction is promoted by a variety of chemical species these ancient manganese deposits are often significantly more reduced than modern environmental manganese rich sediments we document the impacts of manganese reduction and the mineral phases that form stable manganese deposits from seven sedimentary examples spanning from modern surface environments to rocks over 2 billion years old integrating redox and coordination information from synchrotron x ray absorption spectroscopy and x ray microprobe imaging with scanning electron microscopy and energy and wavelength dispersive spectroscopy we find that unlike the mn iv dominated modern manganese deposits three manganese minerals dominate these representative ancient deposits kutnohorite camn co 3 2 rhodochrosite mnco 3 and braunite mn iii 6mn ii o 8sio 4 pairing these mineral and textural observations with previous studies of manganese geochemistry we develop a paragenetic model of post depositional manganese mineralization with kutnohorite and calcian rhodochrosite as the earliest diagenetic mineral phases rhodochrosite and braunite forming secondarily and later alteration forming mn silicates

the variegated vt tephra a new regional marker for middle to late marine isotope stage 5 across yukon and alaska abstract the variegated vt tephra likely sourced from the eastern aleutian arc has a geographic distribution that places it amongst the most widespread tephra beds in eastern beringia first identified in the fairbanks area of interior alaska it has been identified at eight additional sites ranging from togiak bay in southwestern alaska to the klondike area of west central yukon correlation of these occurrences is established through the equivalence of glass major and trace element geochemistry fe ti oxide geochemistry stratigraphy and independent age data in yukon and alaska vt tephra has a minimum bulk tephra volume estimate of 32 km3 previous age estimates for vt tephra have varied ranging from a glass fission track age of 125 30 ka to a weighted mean thermoluminescence tl age of 77 8 4 1 ka from bracketing ages on loess a new infrared stimulated luminescence irsl age of 106 10 ka paleoenvironmental data and several tl and irsl ages from togiak bay suggest that the time of deposition is more likely between these previous age estimates post marine isotope stage mis 5e but underlying a prominent soil likely associated with mis 5c placing it within late mis 5d

architecture and mineral deposit settings of the altaid orogenic collage a revised model abstract the altaids are an orogenic collage of neoproterozoic paleozoic rocks located in the center of eurasia this collage consists of only three oroclinally bent neoproterozoic early paleozoic magmatic arcs kipchak tuva mongol and mugodzhar rudny altai separated by sutures of their former backarc basins which were stitched by new generations of overlapping magmatic arcs in addition the altaids host accreted fragments of the neoproterozoic to early paleozoic oceanic island chains and neoproterozoic to cenozoic plume related magmatic rocks superimposed on the accreted fragments all these assemblages host important many world class late proterozoic to early mesozoic gold copper molybdenum lead zinc nickel and other deposits of various types in the late proterozoic during breakup of the supercontinent rodinia the kipchak and tuva mongol magmatic arcs were rifted off eastern europe siberia and laurentia to produce oceanic backarc basins in the late ordovician the siberian craton began its clockwise rotation with respect to eastern europe and this coincides with the beginning of formation of the mugodzhar rudny altai arc behind the kipchak arc these earlier arcs produced mostly cu pb zn vms deposits although some important intrusion related orogenic au deposits formed during arc arc collision events in the middle cambrian and late ordovician the clockwise rotation of siberia continued through the paleozoic until the early permian producing several episodes of oroclinal bending strike slip duplication and reorganization of the magmatic arcs to produce the overlapping kazakh mongol and zharma saur valerianov beltau kurama arcs that welded the extinct kipchak and tuva mongol arcs this resulted in amalgamation of the western portion of the altaid orogenic collage in the late paleozoic its eastern portion amalgamated only in the early mesozoic and was overlapped by the transbaikal magmatic arc which developed in response to subduction of the oceanic crust of the paleo pacific ocean several world class cu mo porphyry cu pb zn vms and intrusion related au mineral camps which formed in the altaids at this stage coincided with the episodes of plate reorganization and oroclinal bending of magmatic arcs major pb zn and cu sedimentary rock hosted deposits of kazakhstan and central asia formed in backarc rifts which developed on the earlier amalgamated fragments major orogenic gold deposits are intrusion related deposits often occurring within black shale bearing sutured backarc basins with oceanic crust after amalgamation of the western altaids this part of the collage and adjacent cratons were affected by the siberian superplume which ascended at the permian triassic transition this plume related magmatism produced various deposits such as famous ni cu pge deposits of norilsk in the northwest of the siberian craton in the early mesozoic the eastern altaids were oroclinally bent together with the overlapping transbaikal magmatic arc in response to the northward migration and anti clockwise rotation of the north china craton the following collision of the eastern portion of the altaid collage with the siberian craton formed the mongol okhotsk suture zone which still links the accretionary wedges of central mongolia and circum pacific belts in the late mesozoic a system of continent scale conjugate northwest trending and northeast trending strike slip faults developed in response to the southward propagation of the siberian craton with subsequent post mineral offset of some metallogenic belts for as much as 70 400 km possibly in response to spreading in the canadian basin india asia collision rejuvenated some of these faults and generated a system of impact rifts

extreme enrichment of polymetallic ni mo pge au in lower cambrian black shales of south china an os isotope and pge geochemical investigation extreme metal enrichments occur in the lower cambrian niutitang formation a thick black shale sequence deposited on the yangtze platform of south china and form a regionally distributed conformable polymetallic ni mo pge au sulfide horizon the origin for the extreme enrichment of metals in these black shales is discussed based on a comprehensive geochemical investigation of re os isotopes and platinum group elements the black shales of the lower cambrian niutitang formation in guizhou province yielded an re os isochron age of 535 11 ma with an initial 187 os 188 os ratio of 0 80 0 04 which is similar to the initial 187 os 188 os ratio 0 78 0 19 of the ni mo sulfide ores but slightly lower than the initial 187 os 188 os ratio 1 18 0 02 of lower cambrian black shales from the lesser himalaya india a comparison of os isotope data among the chinese ni mo sulfide ores the seafloor massive sulfide deposits and contemporaneous seawater suggests a possible similar hydrothermal forming mechanism for these deposits the pge concentrations pt anomaly pt pt pt pd ir pd au pd ratios of the chinese ni mo sulfide ores are similar to those metal rich black shales of submarine volcanogenic hydrothermal origin from czech republic namibia and canada but are different from those data of the ocean floor fe mn crusts that have scavenged their pge and other metals directly from seawater it is therefore suggested that the ni mo sulfide ores from the niutitang black shale sequence in south china had a submarine hydrothermal origin the anoxic environments and abundant organic matter in the ocean basin also played a key role for the extreme metal enrichments the discharge of hydrothermal fluids into the cambrian ocean may have had a great effect on life during the cambrian explosion 2007 elsevier b v all rights reserved

the western central asian orogenic belt a window to accretionary orogenesis and continental growth abstract the architecture of accretionary orogens is a key to understand continental growth here we present an overview of the orogenic components and their amalgamation in the western central asian orogenic belt caob the caob records the convergence and interactions among various types of orogenic components including the japan type mariana type and alaska aleutian type arc systems as well as the active marginal sequences of the siberia craton which incorporated wide accretionary complexes and accreted arcs and terranes during construction of the caob the kazakhstan arc chain was characterized by multiple subduction whereas the northern fringe of the tarim craton remained mostly as a passive margin the multiple convergence and accretions among these various orogenic components generated huge orogenic collages in the late paleozoic and even in the early triassic involving parallel amalgamation circum microcontinent amalgamation and oroclinal bending the preservation of trapped basins played a significant role in orogenesis with some parts of the oceanic plate being subducted and others behaving as rigid units the orogenesis in the caob was long lived lasting for more than 800 m y involving multiple subduction and long continuous accretion and featuring the complexity of accretionary orogenesis and continent growth

rare earth elements in the phosphatic enriched sediment of the peru shelf abstract apatite enriched materials from the peru shelf have been analyzed for their major oxide and rare earth element ree concentrations the samples consist of 1 the fine fraction of sediment mostly clay material 2 phosphatic pellets and fish debris which are dispersed throughout the fine grained sediment 3 tabular shaped phosphatic crusts which occur within the uppermost few centimeters of sediment and 4 phosphatic nodules which occur on the seafloor the bulk ree concentrations of the concretions suggest that these elements are partitioned between the enclosed detrital material and the apatite fraction analysis of the fine grained sediment with which the samples are associated suggested that this detrital fraction in the concretions should have shale ree values the analysis of the fish debris suggested that the apatite fraction might have seawater values the seawater contribution of ree s is negligible in the nodules and crust in which the apatite occurs as a fine grained interstitial cement that is the concentration of ree s and the ree patterns are predominantly a function of the amount of enclosed fine grained sediment by contrast the ree pattern of the pelletal apatite suggests a seawater source and the absolute ree concentrations are relatively high the ree p 2 o 5 ratios of the apatite fraction of these samples thus vary from approximately zero in the case of the crust and nodules to as much as approximately 1 2 10 3 in the case of the pellets the range of this ratio suggests that rather subtle variations in the depositional environment might cause a significant variation in the ree content of this authigenic fraction of the sediment pelletal glauconite was also recovered from one sediment core its ree concentrations closely resemble those of the fish debris

sedimentary geochemistry of manganese implications for the environment of formation of manganiferous black shales the sedimentary geochemistry of manganese is dominated by the redox control of its speciation higher oxidation states mn super 3 and super 4 occurring as insoluble oxyhydroxides in well oxygenated environments and the lower oxidation state mn super 2 being much more soluble in oxygen deficient settings its geochemical behavior is therefore quite different in oxic and anoxic environments and where oxic and anoxic conditions are juxtaposed mn is recycled between the two environments in modern marine sediments mn is present above its crustal abundance as an oxyhydroxide in all slowly accumulating pelagic sediments of the deep ocean and in surficial deposits of continental margin environments diagenetic recycling of mn in the latter causes surficial deposits to have larger mn enrichments than in many pelagic sediments bottom sediments of permanently anoxic basins show no enrichments and have mn concentrations that are controlled solely by the aluminosilicate fraction manganese carbonates kutnohorite and calcic rhodochrosite are found only in anoxic sediments accumulating beneath surface oxic horizons and therefore under oxygenated bottom waters in many nearshore environments such enrichments are due to delivery of mn by burial of surface oxyhydroxides into the subsurface anoxic environment where they are dissolved pore water mn levels can reach saturation with respect to a mixed mn ca carbonate phase in such sediments the diagenetic origin for these phases is shown by their carbon isotope compositions which typically indicate a carbon source from decomposing organic matter the presence of mn carbonates therefore signifies that the host sediment must have accumulated under oxygenated bottom waters on the basis of this information it is proposed that in contrast to several current explanations for the formation of mn carbonates kutnohorite and rhodochrosite in ancient organic rich shales limestone and marl sequences and in many mn ore deposits the occurrence of these mineral phases indicates that the sediments originally accumulated beneath oxygenated bottom waters by analogy with the present mn carbonates could not have formed in the bottom waters of anoxic basins these diagenetic phases however did form where mn was supplied at a high rate namely by the burial of oxyhydroxide enriched surface sediments to a subsurface anoxic environment this situation could only have occurred under oxygenated bottom waters the presence of mn carbonates in ancient black shales and in some carbonate rich rocks lends strong support to the notion that these rocks did not necessarily form in anoxic basins but owe their carbon richness to a high supply of organic matter to sediments deposited under oxygenated bottom waters probably in continental margin settings

investigation on the role of microorganisms in manganese mineralization from abadeh tashk area fars province southwestern iran by using petrographic and geochemical data abstract hydrothermal manganese and ferromanganese deposits associated with neyriz ophiolite colored melange occurred as small ore deposits in the abadeh tashk area se of fars province sw iran the deposits are found in three types a banded syngenetic ores b massive boudin and lens shaped diagenetic ores and c vein and veinlet epigenetic ores microtextural geochemical and mineralogical data associated with petrographic raman ftir and sem studies indicated that the primary fe compounds formed series of microbially mediated biomats and mn compounds were precipitated as an amorphous oxide on an active oxide surface accompanying silica gels field relationships between ore and host rock high mn fe ratio 17 43 to 40 79 lree positive eu and negative ce anomalies in syngenetic ore types reveal that the ores were formed by hydrothermal fluid in an oceanic floor environment manganese was fractionated from iron due to physicochemical changes as well as microbial activities in the sedimentary environment microbial remains as filamentous beads with regular circular shapes vermiform structures series of fe rich biomats traces of embedded organic material besides trace metals and ree concentrations in mn ores emphasize the role of microorganisms in fe and mn precipitation syngenetic mineralization took place under suboxic neutrophilic conditions while diagenetic processes resulted in variably reduced fe and mn oxides via organic matter decomposition forming rhodochrosite as the end product braunite formation occurred most probably as a biogeochemically mediated early diagenetic product diagenetic and epigenetic mn ores were formed when primary mn deposits underwent subsequent diagenetic and remobilization redeposition events respectively

seawater as the source of minor elements in black shales phosphorites and other sedimentary rocks many of the minor elements in seawater today have a concentration depth profile similar to that of the biologically essential nutrients no 3 and po3 4 they show a relative depletion in the photic zone and enrichment in the deep ocean the difference between their surface and deep ocean values normalized to the change in po3 4 approaches the average of measured minor element p ratios in marine plankton although individual analyses of the latter show extreme scatter for a variety of reasons despite this scatter in the minor element analyses of plankton agreement between the two sets of data shows unequivocally that an important marine flux of many minor elements through the ocean is in the form of biogenic matter with a composition approaching that of plankton this interpretation is further supported by sediment studies particularly of sediments which accumulate in shelf slope environments where biological productivity in the photic zone is exceptionally high and organic carbon contents of the underlying sediment elevated the interelement relations observed for some of these sediments approach the average values of plankton these same interelement relations are observed in many marine sedimentary rocks such as metalliferous black shales and phosphorites rocks which have a high content of marine fractions e g organic matter apatite biogenic silica and carbonates many previous studies of the geochemistry of these rocks have concluded that local hydrothermal activity and or seawater with an elemental content different from that of the modern ocean was required to account for their minor element contents however the similarity in several of the minor element ratios in many of these formations to minor element ratios in modern plankton demonstrates that these sedimentary rocks accumulated in environments whose marine chemistry was virtually identical to that seen on continental shelf slopes or in marginal seas of the ocean today the accumulation of the marine fraction of minor elements on these ancient sea floors was determined largely by the accumulation of organic matter settling from the photic zone and with a composition of average plankton a second marine fraction of minor elements in these rocks accumulated through precipitation and adsorption from seawater the suite of elements in this fraction reflects redox conditions in the bottom water as determined by bacterial respiration for example high mn high cr v and high mo concentrations above those which can be attributed to the accumulation of planktonic matter characterize accumulation under bottom water oxidizing denitrifying and sulfate reducing conditions respectively

characteristics of the devonian xialei manganese deposit guangxi zhuang autonomous region china abstract the xialei mn deposit occurs in the late devonian famenian wuzhishan formation and consists of three ore horizons composed of three ore types 1 mn carbonate 2 mn silicate mn carbonate and 3 mn oxide mn silicate mn carbonate ore beds consist of mn carbonates and associated rhodonite stilpnomelane actinolite chlorite mn epidote biotite and mn fe antigorite these minerals are mixed with each other and form thin beds bands pelletal and pisolitic grains and horizontal or wavy laminae abundant oolitic and pisolitic grains in mn ore beds show distinct boundaries and nuclei of mn carbonate and mn silicate minerals rarely clastic grains the ore deposit is divided into three zones 1 an inner zone composed of mn carbonate silicate and oxide minerals 2 a transitional zone consisting of mn carbonate and stilpnomelane and 3 an outer zone characterized by mn carbonate argillaceous limestone at the base of the ore beds has a mean 13 c pdb of about 0 0 indicating that the carbon was derived from seawater bicarbonate the 13 c pdb of mn carbonate ranges from 2 8 to 14 3 mean 7 1 indicating that the carbon was derived from both degradation of organic matter and seawater bicarbonate ores formed in a trough on a carbonate platform primary sedimentary mn carbonates precipitated from alkaline and negative eh waters in the diagenetic zone of sulfate reduction which occurred either during shallow burial or at the seafloor oolites and pisolites formed by sedimentary processes on the seafloor in places deposits were reworded and transported by gravity flow processes the region where these sedimentary diagenetic mn deposits formed was intruded by magma and hydrothermal fluids with dissolved metals leached from volcanic and sedimentary rocks ascended along fractures the mn silicate mn carbonate ore may have been produced by contact metamorphism of primary carbonate ore and metal sulfides deposited by hydrothermal fluids which overprinted the primary sedimentary ore

the paleozoic metamorphic history of the central orogenic belt of china from 40ar 39ar geochronology of eclogite garnet fluid inclusions abstract the pressure temperature time evolution of the uhp eclogites of dabie sulu in the eastern sector of the central orogenic belt of china shows a complex pattern of predominantly triassic and to a lesser extent early paleozoic ages 40 ar 39 ar stepwise crushing analysis of eclogitic garnets yielded consistently paleozoic ages because our initial results from the bixiling eclogite were of limited areal extent their significance required further testing data for garnet bearing gneiss and eclogites from new locations in northern and southern dabieshan shuanghe ganghe and hongmiao confirm the paleozoic garnet results obtained from bixiling eclogite we also tested the technique on a garnet sample of known paleozoic age from altyn tagh in the western central orogenic belt these new results indicate that light colored garnets from dabieshan and altyn tagh yield concordant 40 ar 39 ar ages ranging from 445 465 ma by in vacuo crushing and confirm that a paleozoic u hp metamorphic event took place in the central orogenic belt from altyn tagh in western china to dabieshan in eastern china in contrast dark colored garnets from mafic metavolcanics do not yield 40 ar 39 ar plateaux or isochrons ages

optical dating of sediments a new method for dating sediments is proposed which determines the time since the sediment was last exposed to sunlight an argon ion laser is used to excite electrons from thermally stable light sensitive traps and the subsequent luminescence used as a measure of the past radiation dose two sample sequences spanning the periods 0 700 kyr and 0 6 kyr show steadily increasing luminescence with age an age of 62 8 kyr is obtained for a silt radiocarbon dated at 58 8 0 3 kyr problems were found with two much younger samples

nd sr isotopic mapping of the chinese altai and implications for continental growth in the central asian orogenic belt article i nfo the chinese altai orogen is a typical domain of the central asian orogenic belt and in previous syntheses was divided into six tectonic units or terranes in this paper 41 new and 36 published whole rock nd and sr isotopic data for granitoid intrusions and mafic dykes within units 2 and 3 of the central altai and units 4 to 6 of the southern altai were used for isotopic mapping the age of the samples used is known from u pb zircon dating end t values range from 4 to 2 in the central altai units 2 and 3 and from 1 4 to 6 in the southern altai units 4 and 5 and up to 8 4 in unit 6 correspondingly nd model ages tdm decrease from 1 6 1 1 ga in the central altai to 1 0 0 5 ga in the southern altai except for a continental fragment in unit 4 isr is elevated in the central units decreasing to b0 705 in the southern units 5 and 6 these results demonstrate that the central altai contains widespread old crustal components in its basement whereas the southern altai comprises a higher proportion of juvenile crust when integrated with published u pb zircon ages our data show that new crust grew southwards in the chinese altai in addition our data suggest that units 2 and 3 are a single tectonic unit whereas the southern altai unit 4 which previously was regarded as a single young accretionary terrane should be subdivided into two units a younger arc and an older continental fragment the granitoids in the chinese altai can be divided into syn and post non orogenic groups the syn orogenic granitoids have ca 50 80 mantle derived component whereas the post non orogenic granitoids contain ca 70 90 the generation of syn and post non orogenic granitoids represents horizontal lateral and vertical crustal growth which contributed ca 18 28 and 7 8 respectively to the area of the chinese altai this work shows that isotopic mapping is an effective approach to elucidate terrane composition in the central asian orogenic belt and thereby better constrain palaeozoic crustal growth

two major cenozoic episodes of phosphogenesis recorded in equatorial pacific seamount deposits seamount phosphorites have been recognized since the 1950s but this is the first study to provide an in depth exploration of the origin and history of these widespread deposits representative samples from equatorial pacific cretaceous seamounts were analyzed for chemical mineralogical and stable isotope compositions the phosphorites occur in a wide variety of forms but most commonly carbonate fluorapatite cfa replaced middle eocene and older carbonate sediment in a deep water environment 1000 m element ratios distinguish seamount phosphorites from continental margin plateau and insular phosphorites uranium and thorium contents are low and total rare earth element ree contents are generally high ree ratios and shale normalized patterns demonstrate that the rees and host cfa were derived from seawater strontium isotopic compositions compared with inferred cenozoic seawater curves define two major episodes of cenozoic phosphatization late eocene early oligocene 39 34 ma and late oligocene early miocene 27 21 ma three minor events are also indicated the major episodes occurred at times of climate transition the first from a nonglacial to glacial earth and the second from a predominantly glacial to warm earth the paleoceanographic conditions that existed at those times initiated and sustained development of phosphorite by accumulation of dissolved phosphorus in the deep sea during relatively stable climatic conditions when oceanic circulation was sluggish fluctuations in climate sealevel and upwelling that accompanied the climate transitions may have driven cycles of enrichment and depletion of the deep sea phosphorus reservoir as temperature gradients in the oceans increased antarctic glaciation expanded and oceanic circulation and upwelling intensified expansion and intensification of the oxygen minimum zone may have increased the capacity for midwater storage of phosphorus supplied by dynamic upwelling around seamounts however the bottom waters never became anoxic during the phosphogenic episodes fluctuations in the ccd and lysocline co2 fluxes and changes in bottom water circulation and temperatures may have bathed the seamount carbonates in more corrosive waters which coupled with increased supplies of dissolved phosphorus promoted replacement processes the late eocene early oligocene phosphogenic episode recorded in seamount deposits is not matched by large phosphorite deposits in the geologic record whereas the late oligocene early miocene episode and middle miocene event are matched by large deposits distributed globally the seamount phosphorites are exposed at the surface of the seamounts and have been for most of the neogene and oligocene the phosphorites do not show signs of etching that would indicate substantial undersaturation of seawater phosphate with respect to cfa mass balance calculations indicate that about 5 4 19 1012 g of p2o5 are locked up in equatorial pacific seamount phosphorites that amount is equivalent to about 2 7 years of the present annual input from rivers

keketuohai mafic ultramafic complex in the chinese altai nw china petrogenesis and geodynamic significance abstract devonian magmatism was very intensive in the tectonic evolutionary history of the chinese altai a key part of the central asian orogenic belt caob the devonian keketuohai mafic ultramafic complex in the chinese altai is a zoned intrusion consisting of dunite olivine gabbro hornblende gabbro and pyroxene diorite the pyroxene diorite gives a zircon u pb age of 409 5 ma variations in mineral assemblage and chemical composition suggest that the petrogenesis of the keketuohai complex was chiefly governed by fractional crystallization from a common magma chamber low sio 2 k 2 o and na 2 o contents negative covariations between p 2 o 5 tio 2 and mg value suggest insignificant crustal assimilation contamination thus the positive e nd t values 0 to 2 7 and slight enrichments in light rare earth elements e g la yb n 0 98 3 64 suggest that their parental magma was possibly produced by partial melting of the lithospheric mantle model calculation suggests that their parental magma was high mg mg 66 tholeiitic basaltic melt the keketuohai intrusion was coeval with diverse magmatism high temperature metamorphism and hydrothermal mineralization which support a previously proposed model that ridge subduction most likely played an important role in the tectonic evolution of the chinese altai

fe mn hydr oxide carbonate crusts from the kebrit deep red sea precipitation at the seawater brine redoxcline lithified crusts located within the sediment and recovered from the kebrit deep red sea are composed of fe and mn hydr oxides carbonates and sulfides mineralogical and geochemical features of these crusts suggest that they are metalliferous layers lithified by carbonates and formed in the narrow band where the transition zone between the anoxic brine and deep seawater crossed the seafloor carbonates cementing the fe mn hydr oxides precipitated from normal saline seawater at t 20 30 degrees c precipitation of fe mn hydr oxides was superimposed the carbonate precipitation in the transition zone a pumping mechanism involving cyclic fe and mn hydr oxide precipitation redissolution operated through the transition zone and produced an enrichment of a number of elements in the crusts the microbiota played an important role in the geochemical cycle of the elements through the redoxcline and in the mineralogy of the sediments underlying the redoxcline waters diagenetic processes led to formation of bi and ternary carbonates and disulfides c 2006 elsevier b v all rights reserved

first occurrence and stable isotope composition of authigenic γ mns in the central gotland deep baltic sea the occurrence of authigenic mns in organic matter rich sediments of the central gotland deep is reported for the first time the hexagonal manganese sulfide was found in a thin sediment layer with an approximate age of 1130 years and has an isotopic composition of 34s 13 vs v cdt this indicates that the bonded sulfur is derived from the anaerobic microbial reduction of pore water sulfate sem analysis reveals that mns occurs as idiomorphic crystals of about 200 m length and 150 m width much larger than the diameters of co existing calcian rhodochrosite globules 6 m it is suggested that formation of mns took place in a diagenetic environment which was locally free from reactive iron

optical dating in archaeology thirty years in retrospect and grand challenges for the future in 1982 when richard klein first became one of the editors of this journal the luminescence dating community was embarking on a new phase of exploratory research attention was turning from the use of thermoluminescence tl dating to estimate the time of last heating of archaeological objects such as pottery and burnt flint to the tl dating of unheated sediments that had been transported by wind and then deposited on the landscape this revolutionary development enabled the extension of tl dating to sedimentary deposits in a variety of environmental settings and to the multitude of archaeological sites that lack suitably heated artefacts in sediment dating the age of most interest is usually the time elapsed since grains of quartz or feldspar were last exposed to sunlight as the energy of the sun s rays is sufficient to evict electrons from their light sensitive traps these traps are steadily refilled after sediment deposition and the longer the grains remain buried the more tl they will emit when measured in 1985 huntley and colleagues proposed optical dating as a simpler and superior means of stimulating the light sensitive traps in quaternary sediments and this is now the principal luminescence based method of dating geological and archaeological deposits optical dating is an umbrella term for an armada of acronyms the most common in archaeological contexts being osl optically stimulated luminescence tt osl thermally transferred osl irsl infrared stimulated luminescence and pirir post infrared irsl all of these variants are founded on the same basic tenet measurement of a light sensitive signal to determine typically the last time that sediment grains were sun bleached but each approach has its virtues and vices in this paper we review this family of luminescence dating techniques and look back on 30 years of optical dating in archaeology some of the more interesting and important achievements are highlighted including the critical insights gained in the last two decades from osl measurements of individual grains of quartz we also look to the future of optical dating in archaeological contexts efforts to extend the age limits of optical dating to older hominin and archaeological sites will remain a key goal and understanding how archaeological sites of all ages form and evolve over time could be improved greatly by combining micromorphology analysis with optical dating of undisturbed intact sediments the latter poses a series of particularly formidable technical challenges but if the past is any guide to the future then we can expect optical dating to illuminate much more of human history before celebrating its golden jubilee

chronology of the marine terraces of the crotone peninsula calabria southern italy by means of infrared stimulated luminescence irsl abstract the crotone peninsula southern italy preserves a well developed flight of marine terraces generated by the interplay of uplift of the calabrian arc and late quaternary eustatic oscillations good chronologic control on the formation of these raised geomorphic features would help constrain regional tectonic and stratigraphic models however precise age assignment and correlation of the individual terraces is hampered by lack of material suitable for radiometric dating with the goal of improving the resolution of the chronology of the terraces nine samples were collected from four stratigraphically distinct terraced units and dated with the infrared stimulated luminescence irsl technique applied on feldspar grains the obtained ages are consistent with the stratigraphic arrangement of the terraces with samples from higher terraces older or overlapping in age with those from lower terraces three samples from the highest cutro terrace indicated a minimum age mis marine isotope stage 7 two samples from the second of the four examined terraces which is generally correlated with mis 5 3 gave ages that correlate instead with mis 5 5 and 5 1 revealing more internal complexity and tectonic disruption than previously inferred from this terrace luminescence dating was applied for the first time to the deposits of the capo colonna terrace with results indicating a mis 5 1 age finally one sample from the lowermost le castella terrace confirmed the preservation of raised marine deposits from mis 3 a relatively uncommon finding for the mediterranean region these results highlight how irsl dating can contribute to the development and refinement of a chronostratigraphic context for a flight of marine terraces and ultimately to a clearer understanding of the combined tectonic and eustatic controls affecting the morphodynamic evolution of a marine coastal sector more specifically they confirm the persistence of relatively high average uplift rates on the order of 1 mm yr over the last two glacial cycles in the crotone peninsula and the important role of a local component of tectonic and deformative displacement superimposed on the regional uplift

new insights into late pleistocene glacial and postglacial history of northernmost ungava canada from pingualuit crater lake sediments abstract the pingualuit crater was formed by a meteoritic impact ca 1 4 million years ago in northernmost ungava canada due to its geographical position near the center of successive north american ice sheets and its favorable morphometry the pingualuit crater lake water depth 246 m promises to yield a unique continuous sedimentary sequence covering several glacial interglacial cycles in the terrestrial canadian arctic in this paper we suggest the existence of a subglacial lake at least during the last glacial maximum lgm by hydraulic potential modeling using lgm ice surface elevation and bed topography derived from a digital elevation model these results support the hypothesis that the bottom sediments of the crater lake escaped glacial erosion and may contain a long term continental sedimentary sequence we also present the stratigraphy of a 9 m long core retrieved from the deep basin of the lake as well as a multiproxy reconstruction of its deglacial and postglacial history the base of the core is formed by very dense diamicton reflecting basal melt out environments marking the end of subglacial conditions at the coring site the overlying finely laminated silt are related to the onset of proglacial conditions characterized by extremely low lacustrine productivity infra red stimulated luminescence and ams 14 c dating as well as biostratigraphic data indicate sediment mixing between recent e g holocene and much older pre to mid wisconsinan material reworked by glacier activity this process prevents the precise dating of these sediments that we interpret as being deposited just before the final deglaciation of the lake two finer grained and organic rich intervals reflect the inception of lacustrine productivity resulting from the cessation of glacial meltwater inputs and ice free periods the lower organic interval corresponds to the early postglacial period 6850 5750 cal bp and marks the transition between proglacial and postglacial conditions during the holocene thermal maximum while the uppermost organic rich core section represents late holocene sediments 4200 600 cal bp the organic intervals are separated by a basin scale erosive slide occurring around 4200 cal bp and likely related to 1 a seismic event due to the glacio isostatic rebound following the last deglaciation or 2 slope instabilities associated with rapid discharge events of the lake

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

combined irsl osl single aliquot regeneration sar equivalent dose de estimates from source proximal chinese loess tectono sedimentary systems are readily recognized in northeastern tibet and elsewhere but they have proved difficult to date via conventional absolute dating techniques in the qilian shan the application of cosmogenic methods is complicated by the presence of terrace blanketing loess deposits we have chosen to explore the potential of applying optical dating techniques to directly date the loess cover deposits to provide minimum ages for terrace abandonment events we focussed on a suite of six loess mantled terraces cut into an abandoned alluvial fan sequence which was uplifted by thrust faulting on the zhangye thrust fault east of the hei he river at its exit from the qilian shan application of single aliquot regeneration sar optical dating techniques provides a chronology of terrace age we employ a double sar procedure in which aliquots are subjected to both infrared lin 830 nm and blue lin 470 nm stimulation and two sets of de determinations are produced and assumed to relate predominantly to feldspathic and quartz fine grain populations respectively our de and age determinations are stratigraphically sensible and we do not observe a significant difference between irsland osl de estimates which has been the case in previous studies r 2003 published by elsevier science ltd

evolution of neodymium isotopic signature of seawater during the late cretaceous implications for intermediate and deep circulation neodymium isotopic compositions end have been largely used for the last fifty years as a tracer of past ocean circulation and more intensively during the last decade to investigate ocean circulation during the cretaceous period despite a growing set of data circulation patterns still remain unclear during this period in particular the identification of the deep water masses and their spatial extension within the different oceanic basins are poorly constrained in this study we present new deep water end data inferred from the nd isotope composition of fish remains and fe mn oxyhydroxide coatings on foraminifera tests along with new end data of residual partly detrital fraction recovered from dsdp sites 152 nicaraguan rise 258 naturaliste plateau 323 bellinghausen abyssal plain and odp sites 690 maud rise and 700 east georgia basin south atlantic the presence of abundant authigenic minerals in the sediments at sites 152 and 690 detected by xrd analyses may explain both middle rare earth element enrichments in the spectra of the residual fraction and the evolution of residual fraction end that mirror that of the bottom waters at the two sites the results point towards a close correspondence between the bottom water end values of sites 258 and 700 from the late turonian to the santonian since the deep water nd isotope values at these two sites are also similar to those at other proto indian sites we propose the existence of a common intermediate to deep water mass as early as the mid cretaceous the water mass would have extended from the central part of the south atlantic to the eastern part of proto indian ocean sites beyond the kerguelen plateau furthermore data from south and north of the rio grande rise walvis ridge complex sites 700 and 530 are indistinguishable from the turonian to campanian suggesting a common water mass since the turonian at least this view is supported by a reconstruction of the rio grande rise walvis ridge complex during the turonian highlighting the likely existence of a deep breach between the rio grande rise and the proto walvis ridge at that time thus deep water circulation may have been possible between the different austral basins as early as the turonian despite the presence of potential oceanic barriers comparison of new seawater and residue end data on nicaraguan rise suggests a westward circulation of intermediate waters through the caribbean seaway during the maastrichtian and palaeocene from the north atlantic to the pacific this westward circulation reduced the pacific water influence in the atlantic and was likely responsible for more uniform less radiogenic end values in the north atlantic after 80 ma additionally our data document an increasing trend observed in several oceanic basins during the maastrichtian and the palaeocene which is more pronounced in the north pacific although the origin of this increase still remains unclear it might be explained by an increase in the contribution of radiogenic material to upper ocean waters in the northern pacific by sinking to depth these waters may have redistributed to some extent more radiogenic signatures to other ocean basins through deep water exchanges

paleozoic early mesozoic gold deposits of the xinjiang autonomous region northwestern china the late paleozoic early mesozoic tectonic evolution of xinjiang autonomous region northwestern china provided a favorable geological setting for the formation of lode gold deposits along the sutures between a number of the major eastern asia cratonic blocks these sutures are now represented by the altay shan tian shan and kunlun shan ranges with the former two separated by the junggar basin and the latter two by the immense tarim basin in northernmost xinjiang final growth of the altaid orogen southward from the angara craton is now recorded in the remote mid to late paleozoic altay shan accreted early to middle devonian oceanic rock sequences contain typically small precious metal bearing fe cu zn vms deposits e g ashele orogenic gold deposits are widespread along the major irtysh e g duyolanasayi saidi taerde kabenbulake akexike shaerbulake and tuergen hongshanzui e g hongshanzui fault systems as well as in structurally displaced terrane slivers of the western junggar e g hatu and eastern junggar areas geological and geochronological constraints indicate a generally late carboniferous to early permian episode of gold deposition which was coeval with the final stages of altaid magmatism and large scale right lateral translation along older terrane bounding faults the tian shan an exceptionally gold rich mountain range to the west in the central asian republics is only beginning to be recognized for its gold potential in xinjiang in this easternmost part to the range northerly and southerly directed subduction accretion of early to mid paleozoic and mid to late paleozoic oceanic terranes respectively to the precambrian yili block central tian shan was associated with 400 to 250 ma arc magmatism and carboniferous through early permian gold forming hydrothermal events the more significant resulting deposits in the terranes of the southern tian shan include the sawayaerdun orogenic deposit along the kyrgyzstan border and the epithermal and replacement deposits of the kanggurtag belt to the east in the chol tagh range gold deposits of approximately the same age in the yili block include the axi hot springs epithermal deposit near the kazakhstan border and a series of small orogenic gold deposits south of urumqi e g wangfeng gold rich porphyry copper deposits e g tuwu define important new exploration targets in the northern tian shan of xinjiang the northern foothills of the kunlun shan of southern xinjiang host scattered small placer gold deposits sources for the gold have not been identified but are hypothesized to be orogenic gold veins beneath the icefields to the south they are predicted to have formed in the tianshuihai terrane during its early mesozoic accretion to the amalgamated tarim qaidam kunlun cratonic block

the vendian cambrian δ13c record north iran evidence for overturning of the ocean before the cambrian explosion continuous fossilliferous successions across the precambrian cambrian pc c boundary in the elburz mountains of northern iran show a remarkable negative 13c excursion just below the pc c boundary high concentrations of manganese phosphorus barium and high abundances of fossil phytoplankton and black shale coincide with the excursion worldwide stratigraphic correlation shows that the isotopic anomaly is a global event the initial metazoan diversification coupled with13c enrichment occurs stratigraphically just above the excursion we propose the following scenario for oceanic environmental changes before the cambrian faunal explosion based on new data from iran a global warm climate following the last precambrian glaciation resulted in a generally stagnant oceanic condition so that surface water was oxic deep water was dysoxic depleted in13c and enriched in nutrients massive upwelling of deep water vertical advection of nutrients and13c depleted co2 caused enhanced phytoplankton productivity and a sharp drop in 13c in shallow water carbonate and organic carbon we conclude that latest cryptozoic overturning of ocean stratification preceded the cambrian explosion

phosphorus phosphorites and skeletal evolution at the precambrian cambrian boundary clustering of sedimentary phosphate deposits around the precambrian cambrian boundary is related to a global phosphogenic event this event probably resulted from a complex interplay of factors and had a profound effect on the biota with high concentrations of phosphorus in the photic zone producing an increase in the total shallow marine biomass faunal diversification the precipitation of skeletal structures and explosive evolution

accretionary orogenesis of the chinese altai insights from paleozoic granitoids zircon u pb dating and whole rock major oxide trace element and nd sr isotope compositions have been determined for four representative granitic intrusions in the sw chinese altai in order to understand the orogenesis and history of crustal growth in the central asian orogenic belt caob the ashile and halatas bodiesare relatively small intrusions formed in the late carboniferous 318 6ma andpermian 267 4ma respectively thelargertarlang tb andkeketuohaibatholiths kb havemagmaticagesof 359 to 412 ma the granitoids consist chiefly of tonalite granodiorite and granite and are metaluminous to weakly peraluminous in composition asi 0 8 1 1 the ashile pluton is characterized by relatively high mgo 2 73 3 54 wt and sr 395 456 ppm contents with low k2o na2o ratios 0 31 0 42 and mantle like nd sr isotopic compositions endt 2 85 to 3 26 initial 87 sr 86 sr 0 7047 0 7051 it probably formed by fractional crystallization of a mantle derived magma with limited assimilation of oldcrustalmaterial theotherintrusionshavenear zeroornegative endtvalues 0 67to 4 41 andhighersrisotopiccompositions initial 87 sr 86 sr 0 7067 0 7092 indicating a mixture of juvenile and old components in their genesis these intrusions are characterized by relatively low k rb cs contents and low rb sr ratios mostly b0 6 and generally exhibit moderate to high heavy rare earth element hree concentrations ybn 8 26 and weak hree fractionation dy ybnb1 5 with or without negative europium anomalies eu eu 0 5 1 0 these characteristics are consistent with an origin by dehydration melting of a hornblendebearing mid crustal source above the garnet stability field dominated by mafic to intermediate rocks this suggests that the deep crust of the chinese altai may contain a considerable proportion of juvenile material mantle derived magmatism probably in an active extensional continental margin setting played an important role in the formation of the chinese altai acting not only as a heat sourceforcrustalmeltingbutasasourceofjuvenilecomponents therelativelysmallvolumesanddistinctgeochemicalcompositions of the ashile and halatas plutons may imply a substantial change in the geodynamic setting in the late paleozoic 2007 elsevier b v all rights reserved

a review of apatites iron and manganese minerals and their roles as indicators of biological activity in black shales abstract biological contribution to the formation of minerals has become more than a descriptive area in geological thought and research mechanisms of specific mineral accumulation and deposition in oceancs lakes and even desert environment are studied using interdisciplinary approaches and applied in the interpretation of earth processes phosphorus iron and manganese are and probably were essential elements in life forms the common minerals of these elements apatite and magnetite for example can be found in a variety of sedimentary environments both ancient and modern where they could be useful indicator minerals to interpret geologic environments the crystal morphological structural and chemical including isotopic attributes of these usually fine grained minerals can be compared with bulk chemical and stratigraphic information to augment our understanding of the mechanisms of formation and diagenesis in sediments such as black shales

the geochemistry of manganese carbonate in panama basin sediments abstract the mn distribution in panama basin area sediments and interstitial waters is discussed striking surficial mn enrichments produced by a well known diagenetic recycling process characterize the sediments of the region thermodynamic solubility calculations indicate that in at least one core interstitial waters approach saturation with respect to mnco3 a mixed carbonate phase of composition mn48 ca47 mg5 co3 was recovered from an ash band in the same core the association of this material with the coarse volcaniclastic debris is thought to result from facile manganous carbonate precipitation in sediment horizons of coarser mean grain size since sulphate reduction in the upper two metres of panama basin sediments is fairly minor little increase in alkalinity is observed and it is postulated that significant production of carbonate alkalinity is not a prerequisite for manganous carbonate generation in hemipelagic sediments a more important factor appears to be the availability of mn oxides for solution during early diagenesis stable c isotopic analyses indicate that little c of organic origin is used in the precipitation reaction in either panama basin or loch fyne scotland sediments

origin and environment of manganese rich sediments within black shale basins abstract sediments with unusually high manganese contents occur in anoxic basins of the central baltic sea we present a new model for the enrichment of manganese which is based on sedimentological and geochemical analyses of holocene sediments from the gotland deep and on published hydrographic data due to salinity stratification and high primary production bottom waters of the central baltic sea are anoxic and rich in dissolved mn 2 episodically bottom waters become oxygenated by inflows of denser water from the north sea mixing results in oxidation of mn 2 to fine grained particulate oxides which accumulate in the deepest parts of the basins where currents are mostly absent here anoxic conditions are re established within a few months or years and manganese oxides are again dissolved causing high concentrations of mn 2 in the near bottom layer alkalinity is high as a consequence of bacterial reduction of manganese oxides and sulphate under these conditions manganese is reprecipitated and forms a layer of ca rich rhodochrosite on the top of laminated sapropels occasionally periods of such extremely and rapidly changing redox conditions are followed by long term oxygenation of bottom waters in that case a layer rich in manganese oxides forms on the top of a bioturbated layer due to dissolution of rhodochrosite and oxidation of manganese in the near surface sediment return of anoxic conditions results again in the transformation of manganese oxides into rhodochrosite varying rhodochrosite contents in the basinal sediments therefore record a detailed history of redox conditions in bottom waters the manganese rich sediments of the baltic sea share many features with some occurrences of lower jurassic and lower carboniferous manganese ores in western and central europe we therefore suggest that these manganese enrichments were formed by similar processes

sedimentary manganese metallogenesis in response to the evolution of the earth system abstract the concentration of manganese in solution and its precipitation in inorganic systems are primarily redox controlled guided by several earth processes most of which were tectonically induced the early archean atmosphere hydrosphere system was extremely o2 deficient thus the very high mantle heat flux producing superplumes severe outgassing and high temperature hydrothermal activity introduced substantial mn2 in anoxic oceans but prevented its precipitation during the late archean centered at ca 2 75 ga the introduction of photosystem ii and decrease of the oxygen sinks led to a limited buildup of surface o2 content locally initiating modest deposition of manganese in shallow basin margin oxygenated niches e g deposits in india and brazil rapid burial of organic matter decline of reduced gases from a progressively oxygenated mantle and a net increase in photosynthetic oxygen marked the archean proterozoic transition concurrently a massive drawdown of atmospheric co2 owing to increased weathering rates on the tectonically expanded freeboard of the assembled supercontinents caused paleoproterozoic glaciations 2 45 2 22 ga the spectacular sedimentary manganese deposits at ca 2 4 ga of transvaal supergroup south africa were formed by oxidation of hydrothermally derived mn2 transferred from a stratified ocean to the continental shelf by transgression episodes of increased burial rate of organic matter during ca 2 4 and 2 06 ga are correlatable to ocean stratification and further rise of oxygen in the atmosphere black shale hosted mn carbonate deposits in the birimian sequence ca 2 3 2 0 ga west africa its equivalents in south america and those in the francevillian sequence ca 2 2 2 1 ga gabon are correlatable to this period tectonically forced doming up attenuation and substantial increase in freeboard areas prompted increased silicate weathering and atmospheric co2 drawdown causing glaciation on the neoproterozoic rodinia supercontinent tectonic rifting and mantle outgassing led to deglaciation dissolved mn2 and fe2 concentrated earlier in highly saline stagnant seawater below the ice cover were exported to shallow shelves by transgression during deglaciation during the sturtian glacial interglacial event ca 750 700 ma interstratified mn oxide and bif deposits of damara sequence namibia was formed the varangian marinoan ca 600 ma cryogenic event produced mn oxide and bif deposits at urucum jacadigo group brazil the datangpo interglacial sequence south china liantuo nantuo varangian event contains black shale hosted mn carbonate deposits the early paleozoic witnessed several glacioeustatic sea level changes producing small mn carbonate deposits of tiantaishan early cambrian and taojiang mid ordovician in black shale sequences china and the major mn oxide carbonate deposits of karadzhal type central kazakhstan late devonian the mesozoic period of intense plate movements and volcanism produced greenhouse climate and stratified oceans during the early jurassic oae organic rich sediments host many mn carbonate deposits in europe e g urkut hungary in black shale sequences the late jurassic giant mn carbonate deposit at molango mexico was also genetically related to sea level change mn carbonates were always derived from mn oxyhydroxides during early diagenesis large mn oxide deposits of cretaceous age at groote eylandt australia and imini tasdremt morocco were also formed during transgression regression in greenhouse climate the early oligocene giant mn oxide carbonate deposit of chiatura georgia and nikopol ukraine were developed in a similar situation thereafter manganese sedimentation was entirely shifted to the deep seafloor and since ca 15 ma b p was climatically controlled glaciation deglaciation assisted by oxygenated polar bottom currents aabw nadw the changes in climate and the sea level were mainly tectonically forced

a solution to anomalous fading and age shortfalls in optical dating of feldspar minerals abstract recent reports of age underestimations for events of interest in both palaeoclimatology and archaeology have led to questioning the validity of using luminescence for dating sediments the commonly designated culprit is anomalous fading of feldspar luminescence we investigated the differential fading rates of single feldspar grains in sediment samples from different geological domains of north america and deduced how one could extrapolate to zero fading this is shown to resolve an extreme case of optical age underestimation documented for the late pleistocene norfolk formation a key palaeoclimate stratigraphic unit exposed along the north american atlantic coast

paleozoic accretionary orogenesis in the paleo asian ocean insights from detrital zircons from silurian to carboniferous strata at the northwestern margin of the tarim craton a detrital zircon u pb and lu hf isotopic study was carried out in the middle silurian to late carboniferous sedimentary strata of the northwestern tarim craton in order to understand accretionary processes in the southern part of the central asian orogenic belt detrital zircons from these strata yielded u pb ages clustering around 2 8 2 3 ga 2 0 1 7 ga 1 3 0 9 ga 880 600 ma and 500 400 ma with age populations and hf isotopic signatures matching those of magmatic rocks in the tarim craton and the central tianshan block abundant 500 400 ma detrital zircons most likely reflect deposition in a retroarc foreland basin inboard of an andean type magmatic arc to the north supporting the northern tarim central tianshan connection during early paleozoic time the absence of 380 310 ma zircon population in the carboniferous siliciclastic rocks suggests that the central tianshan block may have been separated from the tarim craton in the early devonian caused by the interarc back arc opening of the south tianshan ocean we propose an accretionary orogenic model switching from advancing to retreating mode during paleozoic time in the southwestern part of the paleo asian ocean this transition most likely occurred coevally with the rifting of southeast asian blocks from the northeastern margin of gondwana

chemostratigraphy of paleoproterozoic carbonate successions of the wyoming craton tectonic forcing of biogeochemical change the archean wyoming craton is flanked on the south and east by belts of paleoproterozoic supracrustal successions whose correlation is complicated by lack of geochronologic constraints and continuous outcrop however carbonate units in these successions may be correlated by integrating carbon isotope stratigraphy with lithostratigraphy the 10 km thick paleoproterozoic snowy pass supergroup in the medicine bow mountains was deposited on the present day southern flank of the wyoming craton it contains three discrete levels of glacial diamictite correlative with those in the huronian supergroup on the southern margin of the superior craton the nash fork formation of the upper snowy pass supergroup is significantly younger than the uppermost diamictite and was deposited after the end of the paleoproterozoic glacial epoch carbonates at the base of the nash fork formation record remarkable 13 cenrichment up to 28 v pdb whereas those from overlying members of the lower nash fork formation have d 13 c values between 6 and 8 carbonates from the upper nash fork formation above the carbonaceous shale have carbon isotope values ranging between 0 and 2 5 the transition from high carbon isotope values to those near 0 in the nash fork formation is similar to that at the end of the ca 2 2 2 1 ga carbon isotope excursion in fennoscandia this chemostratigraphic trend and deposition of bifs mn rich lithologies carbonaceous shales and phosphorites at the end of the global ca 2 2 2 1 ga carbon isotope excursion are likely related to ocean overturn associated with the final breakup of the kenorland supercontinent correlative carbonates from the slaughterhouse formation in the sierra madre wy and from the whalen group in the rawhide creek area in the hartville uplift wy have highly positive carbon isotope values in contrast carbonates from other exposures of the whalen group in the hartville uplift and all carbonate units in the black hills sd have carbon isotope values close to 0 combined with existing geochronologic and stratigraphic constraints these data suggest that the slaughterhouse formation and the succession exposed in the rawhide creek area of the hartville uplift are correlative with the lower and middle nash fork formation and were deposited during the ca 2 2 2 1 ga carbon isotope excursion the estes and roberts draw formations in the black hills and carbonates from other exposures in the hartville uplift postdate the ca 2 2 2 1 ga

the process of formation of manganese carbonate deposits hosted in black shale series the two most important types of manganese deposits in china are sedimentary and supergene which account for 71 and 15 percent of the total manganese reserves respectively according to the host rock associations sedimentary manganese deposits can be classified into 1 a mud rock type 2 a black shale series type 3 a carbonate rock type and 4 a chert limestone mudstone type the black shale series type manganese deposits account for 48 percent of the total manganese reserves and are large or medium sized deposits the black shale series or dark colored sedimentary association consists of dark colored mudrock chert carbonate rocks rich in sulfides and organic matter c organic or 1 the term black shale series type manganese deposits is a general name for all manganese deposits hosted in black shale black chert black siliceous shale dark gray limestone etc black shale series type manganese deposits are distributed in 13 stratigraphic horizons from middle proteozoic to early triassic they can be divided into three subtypes 1 a black shale subtype 2 a black chert siliceous shale subtype and 3 a dark gray limestone subtype subtype 1 consists mainly of primary mn carbonate ores subtypes 2 and 3 consist mainly of mn containing limestones weathering and leaching processes can change the mn limestones into mn oxide ores which form large and high quality supergene deposits for example the mugui and dongxiangqiao deposits manganese carbonate ores hosted in the black shale series consist mainly of rhodochrosite calcio rhodochrosite kutnohorite manganocalcite mn containing calcite mn containing dolomite etc the ores are black dark gray light gray yellowish and pink in color and have banded laminated massive oolitic spotted and brecciated structures commonly changes in the ore bearing sequences show from bottom to top 1 black shale series 2 mn carbonate ore bed 3 light colored rocks this indicates that ore beds formed in the transition from reduced to slightly oxidized and from weakly alkaline to alkaline conditions the evolution of the ore bearing sequence indicates that manganese mineralization occurred during the early stage of regression the important mn carbonate deposits hosted in the black shale series resulted from three main processes during formation concentration in seawater precipitation from seawater and enrichment in the sediments anoxic conditions are a basic factor for manganese concentration in seawater a weak oxic and alkaline environment is favorable for mn carbonate precipitation and microbiological activities play an important role for early diagenetic enrichment of manganese in the deposits

combined irsl and post ir osl dating of romanian loess using single aliquots of polymineral fine grains abstract the paper reports on continuing luminescence investigations of romanian loess using samples collected from the loess palaeosol sequence near mircea vod se romania previous optically stimulated luminescence osl studies using different grain sizes of quartz 4 11 m and 63 90 m yielded discrepant chronologies for the last interglacial glacial cycle in this study a double sar protocol is used to determine the age of polymineral fine 4 11 m grains through their infrared stimulated luminescence irsl and post ir optically stimulated luminescence post ir osl emissions in the uv laboratory tests confirm the suitability of the protocol for both signals fading measurements indicate a significant feldspathic contribution to the post ir osl signal in general the fading corrected irsl and post ir osl age results are mutually consistent and they agree with previously reported osl ages for fine grained 4 11 m quartz this agreement enhances the reliability of the ages obtained using luminescence signals from fine grains and allows more confident correlation of the weakly developed palaeosol in the uppermost loess unit l1 with marine isotope stage 3 mis3 the fading corrected ages underestimate the depositional age of older material units l2 l4 probably owing to limitations of the correction model

characteristics and origin of the middle proterozoic dongshuichang chambersite deposit jixian tianjin china abstract the jixian type boron manganese b mn deposits include both chambersite and rhodochrosite deposits from which dongshuichang is economically the best chambersite deposit although the ore bodies of the region are relatively small they contain a rare b mn ore that is scientifically significant chambersite mn 3 b 7 o 13 cl is a rare mineral discovered as a mineral in 1957 and as an ore in 1971 at the dongshuichang deposit near jixian tianjin city the deposit forms a monocline with a southwest dip and covers an area of 2 km 2 in the mine area the gaoyuzhuang formation the upper member of the middle proterozoic changcheng system consists mainly of stromatolitic and muddy dolostone with b mn bearing siliceous shale and dark gray dolostone individual ore lenses range in length from 1 to 4 m with a mean thickness of 0 25 m the ores can be divided into high grade and low grade the former is composed of spindle and granular chambersite aggregates and the latter of spheroidal chambersite in dark gray micritic dolostone the center of spheroids is commonly composed of micritic and columnar chambersite dolomite clay minerals and organic matter around which columnar chambersite grew forming a sunflower shape the organic carbon content in high grade ores is 0 63 in low grade ores 0 83 and in overlying black siliceous shale 3 75 total rare earth element ree contents of two chambersite ore samples are 29 and 35 ppm whereas that of rhodochrosite ore is 22 ppm the chondrite normalized ree patterns of chambersite and rhodochrosite ores are similar with small negative ce and eu anomalies and a small positive gd anomaly the 13 c pdb values of two rhodochrosite ore samples are 4 3 and 7 3 indicating that the carbon source of mn carbonate minerals was mainly seawater bicarbonate with a small contribution from the degradation of organic carbon the source of the dongshuichang ore components was mainly submarine volcanic eruptions and a small amount from the weathering of pre proterozoic boron deposits the chambersite precipitated under conditions of high salinity high b mn and mg concentrations and weak alkalinity low oxygen conditions might be favorable for precipitation of chambersite

isochron dating of sediments using luminescence of k feldspar grains sponsorship research grant council of the hong kong special administrative region china project 7106 02p 7032 05 and 7035 06

optical dating of pottery burnt stones and sediments from selected quebec archaeological sites recent developments in luminescence technologies applied to sediment dating is used to better constrain the age of archaeological events suitable geoarchaeological material includes sediments and fired objects such as pottery and burnt stones the assessment of archaeological ages illustrated here are based on single aliquot regeneration sar with both infrared and blue stimulation on the same fine grained aliquot being detected these new approaches in optical dating were tested on polymineralic extracts of an archaic burnt stone a woodland ceramic and a soil containing plano artefacts the results demonstrate that whether or not these sites had yielded datable radiocarbon material luminescence would have provided a reliable chronological framework given that the appropriate procedures to correct anomalous fading are incorporated

stable isotope chemical and mineral compositions of the middle proterozoic lijiaying mn deposit shaanxi province china abstract the lijiaying mn deposit located about 250 km southwest of xian is a high quality ore characterized by low p and fe contents and a mean mn content of about 23 the ore deposit occurs in shallow water marine sedimentary rocks of probable middle proterozoic age carbonate minerals in the ore deposit include kutnahorite calcite mn calcite and mg calcite carbon 0 4 to 4 0 and oxygen 3 7 to 12 9 isotopes show that with a few exceptions those carbonate minerals are not pristine low temperature marine precipitates all samples are depleted in rare earth elements rees relative to shale and have negative eu and positive ce anomalies on chondrite normalized plots the fe mn ratios of representative ore samples range from about 0 034 to

ore geology and fluid inclusion geochemistry of the tiemurt pb zn cu deposit altay xinjiang china a case study of orogenic type pb zn systems abstract the tiemurt pb zn cu deposit is hosted in a devonian volcanic sedimentary basin of the altay orogenic belt and is thus interpreted to have formed by sea floor hydrothermal exhalation in previous studies our investigation discovered that the deposit is not stratiform or stratabound but structure controlled instead the hydrothermal ore forming process can be divided into the early middle and late stage represented by pyrite quartz polymetallic sulfide quartz and carbonate quartz veinlets respectively the early stage veins and contained minerals are structurally deformed and brecciated suggesting a compressional or transpressional tectonic regime the middle stage veinlets intrude and infill the fissures of the early stage assemblages and show no deformation suggesting a tensional shear setting the late stage veinlets mostly infill open space fissures that crosscut veins and replacements formed in the earlier stages four types of fluid inclusions fis including aqueous type w carbonic aqueous type c pure carbonic type pc and solid bearing type s are identified at the tiemurt deposit the early stage minerals contain the c and w type primary fis that are totally homogenized at temperatures of 330 390 c with low salinities of 0 8 11 9 wt nacl eqv whilst the late stage quartz or calcite contains only the w type fis with homogenization temperatures of 118 205 c and salinities of 1 4 3 4 wt nacl eqv this indicates that the ore fluid system evolved from co2 rich probably metamorphic to co2 poor meteoric fluids and that a significant co2 escape must have occurred all the four types of fis can be only observed in the middle stage minerals and even in a microscopic domain of a crystal representing an association trapped from a boiling fluid system these fis homogenize at temperatures ranging from 270 to 330 c with two salinity clusters of 1 9 14 5 and 37 4 42 4 wt nacl eqv respectively this implies that metal precipitation resulted from fluid boiling co2 escape and transient oversaturation the estimated trapping pressures of fis range from 130 to 380 mpa suggesting an alternating lithostatic hydrostatic fluid system controlled by a fault valve at the depth of 13 km therefore the tiemurt pb zn cu deposit is likely an example of orogenic pb zn cu systems formed in collision orogeny rather than a pre collision vms or sedex system developed in devonian and a new metallogenic model is proposed to interpret the formation of the tiemurt pb zn cu deposit

bacterially mediated diagenetic origin for chert hosted manganese deposits in the franciscan complex california coast ranges numerous manganese deposits in the franciscan complex california occur as conformable lenses within bedded radiolarian chert argillite sequences that are in turn intercalated within thicker sections of sandstone and shale the field relations composition and petro graphic and isotopic characteristics indicate that the manganese was concentrated by diagenetic reconstitution of siliceous and hemipelagic sediment during burial the ore lenses are mn rich and fe poor assemblages consisting largely of rhodochrosite manganese silicates opal ct disordered cristobalite tridymite and quartz highly negative 13 c values for the carbonate carbon in rhodochrosite indicate that co 2 likely originated from oxidation of methane less negative values result from mixing of methanogenic carbon and co 2 derived from bacterial degradation of organic matter the 18 o values for the carbonate of rhodochrosite indicate temperatures of formation between 12 and 100 c the oxidation of methane prior to carbonate precipitation may have used the minor 0 4 0 5 mn and fe oxyhydroxides and oxides deposited with the sediment the mobilization of manganese from biogenic and terrigenous sources in the sediment column into discrete horizons and the fractioriation of manganese from iron reflect the presence of oxidation reduction boundaries and gradients in the sediment column fluids derived from compaction and silica dehydration reactions in the transformation of opal a x ray amorphous biogenic silica to quartz were involved in transportation of principal components sedimentary and geochemical attributes suggest that the deposits formed in a deep water environment in a zone of oceanic upwelling near a continental margin

relationship between inferred redox potential of the depositional environment and geochemistry of the upper pennsylvanian missourian stark shale member of the dennis limestone wabaunsee county kansas u s a analyses of 21 samples collected from a core of the 52 8 cm thick stark shale member of the dennis limestone in wabaunsee county kansas demonstrate four cycles with two orders of magnitude variations in contents of cd mo p v and zn and order of magnitude variations in contents of organic carbon cr ni se and u the observed variability in amounts and or ratios of many metals and amounts and compositions of the organic matter appear related to the cause and degree of water column stratification and the resulting absence presence of dissolved o2 or h2s high cd mo u v zn and s contents a high degree of pyritization dop 0 75 0 88 and high high v v ni 0 84 0 89 indicate the presence of h2s in a strongly stratified water column intermediate contents of metals and s intermediate dop 0 67 0 75 and intermediate v v ni 054 0 82 indicate a less strongly stratified anoxic water column whereas low metal contents and low v v ni 0 46 0 60 indicate a weakly stratified dysoxic water column high p contents at the top of the organic matter rich intervals within the stark shale member indicate that phosphate precipitation was enhanced near the boundary between anoxic and dysoxic water compositions relatively abundant terrestrial organic matter in intervals deposited from the more strongly stratified h2s bearing water column indicates a combined halocline thermocline with the fresher near surface water the transport mode for the terrestrial organic matter the predominance of algal organic matter in intervals deposited from a less strongly stratified water column indicates the absence of the halocline and the presence of the more generally established thermocline relatively low amounts of degraded hydrogen poor organic matter characterize intervals deposited in a weakly stratified dysoxic water column the inferred variability in chemistry of the depositional environments may be related to climate variations and or minor changes in sea level during the general phase of deeper water deposition responsible for this widespread shale member

luminescence dating of the pasado core 5022 1d from laguna potrok aike argentina using irsl signals from feldspar in this paper we develop and test a luminescence chronology for the pasado core 5022 1d taken in the laguna potrok aike maar lake because of unsuitable quartz osl characteristics sand sized k feldspar extracts were chosen as a dosimeter and the dose was measured using a recently developed post ir irsl pirir290 measurement protocol using this approach we were able to access a stable signal and thus avoid the ubiquitous problem of signal instability in feldspar dating extensive laboratory tests show that the chosen pirir290 protocol is applicable to these samples we also develop a new criterion based on the known relative bleaching rates of the conventional irsl signal ir50 and the pirir290 signals and the relationship between the resulting equivalent doses this is used to identify and reject poorly bleached samples fourteen samples out of 35 were rejected based on this criterion the resulting age depth profile is self consistent increases smoothly with depth and is in agreement with the independent age control reclus mt burney and hudson tephras at the top of the core our new luminescence chronology suggests the 5022 1d core reaches back to 65 ka at 96 m below lake floor