permian paleomagnetism of the tien shan fold belt central asia post collisional rotations and deformation permian volcanic and sedimentary rocks were sampled from eight localities in the western and central parts of the tien shan fold belt high temperature sometimes intermediate temperature components isolated from these rocks at seven localities after stepwise thermal demagnetization are shown either to predate folding or be acquired during deformation the conglomerate test at some localities is positive the observed inclinations fit rather well with the eurasian reference data whereas the declinations are strongly deflected westward westerly declinations have already been observed from the other parts of the tien shan from the turan plate in the west to the northern rim of tarim and the urumque area in the east our analysis shows that a considerable counterclockwise rotation of the tien shan fold belt as a rigid body is geologically improbable we hypothesize that a sinistral shear zone existed over the fold belt thus accounting for systematically westerly declinations this zone is about 300 km wide and is traced along the tien shan fold belt for 2500 km a large area of permian alkali magmatism in the west and central tien shan is interpreted as an extensional domain conjugated with the shear zone this shear zone can be accounted for by translation of the kara kum and tarim blocks along the eurasian boundary after their oblique collision in the late carboniferous two phases of rotation are recognized in the tien shan the earlier rotation took place under shear strain during the d3 stage of deformation in the artinskian ufimian the later rotation is connected with transpression d4 stage of deformation and could occur from the late permian to early jurassic 1999 elsevier science b v all rights reserved

nature of laminations and mineralization in rhinoceros enamel using histology and x ray synchrotron microtomography potential implications for palaeoenvironmental isotopic studies abstract incremental features of rhinoceros molar enamel were studied quantitatively on histological slices the different kinds of incremental features of enamel were related to one another and counted to determine the rate and duration of crown formation and to clarify the status of the laminations the mineralization and the microstructure of the enamel were examined in a rhinoceros molar germ using x ray synchrotron microtomography respectively using absorption and phase contrast mode at different levels of resolution from 45 71 m for the largest scale up to 0 28 m for the finest one the different microtomographic data were combined to obtain a multiscale integrated overview of the microstructure and mineralization in order to understand better the relationship between these two aspects additional human and herbivorous mammal teeth were examined qualitatively using histological sectioning to obtain a better understanding of laminations in mammal tooth enamel laminations regularly spaced features parallel to the retzius lines represent regular isochrons of enamel deposition this study shows that laminations and cross striations are equivalent daily features in enamel of rhinoceros humans and probably of middle sized and large herbivorous mammals in general laminations are shown to be three dimensional alignments of cross striations in addition to the fact that cross striations are visible only in prismatic enamel observation of histological slices and high resolution phase contrast x ray synchrotron microtomography demonstrate three main parameters influencing the dominant aspect of daily features in rhinoceros and human enamel the angle between prisms and retzius lines the enamel deposition rate and the thickness of the histological slices given their daily nature laminations can be used to determine the crown formation time of middle sized and big herbivorous mammals quantitative study of the enamel mineralization in the rhinoceros germ fragment using x ray synchrotron microtomography suggests that the innermost 20 m of the enamel near the enamel dentin junction are highly mineralised 77 90 of the final enamel mineralization during or just after the deposition of the corresponding enamel matrix integrated microtomographic study shows that this area corresponds to the thin aprismatic enamel layer at the edj level plus a thin layer of radial enamel directly adjacent it appears that in some parts of the enamel there may be a considerable time lag between matrix deposition and full maturation which could have important implications for geochemical studies this study reinforces the previously suggested hypothesis that isotopic measurements derived from the innermost enamel may represent the period most closely related to matrix secretion by using information derived from incremental features laminations and retzius lines and restricting the isotopic measurements to the innermost part of the enamel precise temporal calibration of isotopic signals should be possible and the complication of time averaging due to enamel maturation could be avoided or strongly reduced

high resolution stable isotope profiles of modern elephant loxodonta africana tusk dentin and tail hair from kenya implications for identifying seasonal variability in climate ecology and diet in ancient proboscideans abstract stable isotope ratios in tissues of large mammalian herbivores record diet and climate information integrated over large spatial areas and can be used to study modern and fossil ecosystems sound interpretation of data requires that tissue growth rates be determined accurately and that ecological and behavioral variables that influence stable isotope ratios of tissues be measured and related to experienced environmental conditions assessed through field observations remote sensing data and meteorological records if well understood in modern herbivores stable isotopes from closely related extinct taxa have tremendous potential for resolving paleodiet paleoenvironment and paleoclimate of terrestrial ecosystems we present multiyear high resolution i e weekly stable isotope records from bioapatite in tusk dentin 13cdentin and 18odentin and tail hair 13chair and 15nhair of an african elephant loxodonta africana from kenya that was fitted with a gps collar intermittently over a five year period and observed for nearly a decade gps and observational data provide behavioral life history and location information normalized difference vegetation index ndvi precipitation and isotopic data from plants and water provide further constraints for interpreting isotope profiles we determine tusk and hair growth rates using a combination of histological and geochemical approaches including bomb curve radiocarbon that confirm approximately weekly resolution in the stable isotope profiles tusk dentin isotope profiles spanning the periods 1982 to 1987 and 2000 to 2006 record weekly variability in 13cdentin where increases of up to 4 5 from baseline values due to diet switches from predominantly c3 browsing to mixed c3 browsing and c4 grazing occur during the twice yearly biannual rainy seasons the 13chair values show a similar trend the 13c profiles served as a proxy for seasonal changes in rainfall vegetation and diet the 18o of tusk bioapatite varied approximately biannually up to 5 likely reflecting increases in the proportion of plant water ingested during the wet season using a least squares inverse filter we show that ndvi can be used to predict 13c of dentin and vice versa offering the possibility to reconstruct seasonal changes in vegetation and rainfall in the geologic past our results demonstrate that high resolution tusk isotope profiles serve as a proxy for seasonality of diet and precipitation and thus can be used to reconstruct aspects of elephant life history vegetation and climate at unprecedented resolution from modern and fossil proboscidean samples

geochemistry and geochronology of paleozoic intrusions in the nalati narati area in western tianshan xinjiang china implications for paleozoic tectonic evolution abstract the nalati narati area in the chinese western tianshan is characterized by abundant paleozoic intrusions including granites diorites and gabbros they are not only indicators of the interaction between crust and mantle but also useful clues for tracing the tectonic history of the tianshan orogen most early paleozoic granitoids biotite monzonitic granites and muscovite granites of this study are from the yili block the biotite monzonitic granites mixed source derived i type granites have a zircon u pb age of 497 0 5 9 ma indicating the time of the subduction of the terskey oceanic crust in the late cambrian the 427 2 5 7 ma zircon u pb age of the s type muscovite granites let us interpret that these granites may have been formed during the crust thickening process after the collision between the yili block and the nalati block in western tianshan the late paleozoic biotite granites muscovite granites quartz diorites biotite monzonitic granites granodiorites and alkali granites have respectively a la icpms zircon u pb age of 371 8 6 ma 357 2 7 5 ma 313 9 2 5 ma and 296 9 2 4 ma the biotite granites display i type geochemical features and are considered to have been derived from a lower continental crust source the muscovite granites have a pronounced s type affinity and are considered to have been formed by the partial melting of thickened continental crust after the collision between the central tianshan belt and the south tianshan belt the quartz diorites are adakite like and have an i type affinity which are considered to have been formed by partial melting of a delaminated lower crust in a post orogenic extension setting the granodiorites also show some typical geochemical features of adakite their formation is considered to be related to the lower crustal delamination and the ascending of asthenosphere after the collision event the alkali granites show an a type granite affinity they may have been formed in a within plate tectonic setting and possibly related to rifting as a consequence of extension the gabbros can be divided into two groups based on their geochemical characteristics and ages the older gabbros 415 429 ma with lower tio 2 contents are formed in an arc related setting the younger ones 340 318 ma with higher tio 2 content are formed in an intracontinental setting and influenced by crustal contamination magmatic activities recorded by paleozoic intrusions can constrain the tectonic history of the tianshan region from subduction of oceanic crust to intraplate extensional collapse and to rifting and can also corroborate that the final closure of the south tianshan ocean occurred in the late devonian early carboniferous time

nd isotope systematics of coarse and fine grained sediments examples from the middle proterozoic belt purcell supergroup sm nd isotopic compositions are reported for 20 fine and 5 coarse grained samples of the belt purcell supergroup of western north america varepsilon nd and sm nd ratios for fine grained belt purcell sediments are remarkably uniform indicating crustal residence ages ranging only from 1 6 to 2 1 ga varepsilon nd and sm nd ratios for coarse grained sediments however are much more varied and contain evidence of sm nd fractionation during sedimentary recycling assuming that this ree fractionation occurred between the time source areas were eroded and when sediment was deposited a new method of calculating crustal residence age intervals is derived for the coarse grained samples which serves to place constraints on the average time since source materials were extracted from the mantle the nd data from both sample groups provide an average age estimate of 2 0 pm 0 3 ga for the middle proterozoic crust from which most of the belt purcell supergroup was derived the isotopic data toge

crustal structure across the northern cordillera yukon territory from seismic wide angle studies omineca belt to intermontane belt a seismic refraction wide angle reflection experiment shot in 1997 in the southern yukon territory crosses the omineca belt which includes the strike slip tintina fault and terminates within the intermontane belt of the northern canadian cordillera lithospheric structure is interpreted from two dimensional forward and inverse modelling of traveltimes combined with forward amplitude modelling and from 2 5 dimensional modelling of gravity data beneath the cassiar terrane and the north america miogeocline average velocities in the upper 20 km of crust are 6 1 km s in the west beneath the accreted cache creek slide mountain and yukon tanana terranes average velocities increase to 6 3 km s in the upper crust the velocity model beneath these terranes thus correlates with more mafic accreted material and not with a subsurface extension of the cassiar terrane the tintina fault is a crustal scale structure across which significant structural differences occur a mid crustal reflector terminates

first early permian paleomagnetic pole for the yili block and its implications for late paleozoic postorogenic kinematic evolution of the sw central asian orogenic belt we conducted a paleomagnetic study on the early permian volcanic and sedimentary rocks and the neoproterozoic mafic dikes in the yili block nw china magnetite and hematite were proven to be the principal magnetic remanence carriers demagnetizations revealed stable characteristic remanence magnetizations with a sole reversed magnetic polarity the magnetic remanence of only the early permian strata turned out to be primary based on positive fold tests meanwhile the magnetic remanence age of the mafic dikes is ambiguous accordingly the first early permian paleomagnetic pole for the yili block is calculated at 81 5 n 256 5 e n 11 and a95 10 9 comparisons of this new pole with published ones from the yili tarim and south junggar blocks provide new quantitative constraints on late paleozoic kinematic evolution of the sw central asian orogenic belt 1 between the yili and tarim blocks significant relative movement took place along major strike slip faults during the late carboniferous to early permian 580 290 km and the early to late permian 585 340 km and the displacement rate increased from the late carboniferous to early permian 19 3 9 7 mm yr to the early to late permian 29 3 17 0 mm yr 2 a significant relative rotation of 28 3 18 3 in the late permian and a lateral displacement of 630 295 km after the late permian occurred between the yili and south junggar blocks the significant strike slip movements played an important role in the formation of the central asian orogenic belt and should be considered with great attention in tectonic and paleogeographic reconstructions

the middle cambrian mount roosevelt formation new of northeastern british columbia evidence for rifting and development of the kechika graben system the eastern margin of the kechika graben in the vicinity of muncho and moose lakes northeastern british columbia contains middle cambrian rift related strata herein named the mount roosevelt formation the formation conformably overlies a quartzite package equivalent to the uppermost clastic unit of the informal late early cambrian gataga group bonnia olenellus zone and is conformably overlain by a thick unnamed carbonate sequence of middle cambrian age plagiura poliella zone the mount roosevelt formation is subdivided into three members the lowermost member is characterized by ooid bearing siltstone and sandstone interbedded with dolostone limestone and hematitic conglomerate conformably above this the middle member is a thick sequence of polymict cobbly pebble conglomerate the upper member includes karstified dolostone calcareous cemented conglomerate and sandstone and limestone collectively the mount roosevelt formation reflects alluvial fan delta progradation into a transgressive mar

reassessment of continental growth during the accretionary history of the central asian orogenic belt we argue that the production of mantle derived or juvenile continental crust during the accretionary history of the central asian orogenic belt caob has been grossly overestimated this is because previous assessments only considered the palaeozoic evolution of the belt whereas its accretionary history already began in the latest mesoproterozoic furthermore much of the juvenile growth in central asia occurred in late permian and mesozoic times after completion of caob evolution and perhaps related to major plume activity we demonstrate from zircon ages and nd hf isotopic systematics from selected terranes within the caob that many neoproterozoic to palaeozoic granitoids in the accreted terranes of the belt are derived from melting of heterogeneous precambrian crust or through mixing of old continental crust with juvenile or short lived material most likely in continental arc settings at the same time juvenile growth in the caob occurred during the latest neoproterozoic to palaeozoic in oceanic island arc settings and during accretion of oceanic island arc and precambrian terranes however taking together our data do not support unusually high crust production rates during evolution of the caob significant variations in zircon ehf values at a given magmatic age suggest that granitoid magmas were assembled from small batches of melt that seem to mirror the isotopic characteristics of compositionally and chronologically heterogeneous crustal sources we reiterate that the chemical characteristics of crustally derived granitoids are inherited from their source s and cannot be used to reconstruct tectonic settings and thus many tectonic models solely based on chemical data may need re evaluation crustal evolution in the caob involved both juvenile material and abundant reworking of older crust with varying proportions throughout its accretionary history and we see many similarities with the evolution of the sw pacific and the tasmanides of eastern australia

the stratigraphic sedimentological and structural evolution of the southern margin of the kazakhstan continent in the tien shan range during the devonian to permian

cassiar platform north central british columbia a miogeoclinal fragment from idaho the allochthonous cassiar platform in north central british columbia is a cratonal fragment of ancestral north america juxtaposed against autochthonous north american crust along the tintina northern rocky mountain trench fault the cassiar platform records a neoproterozoic to early paleozoic rift to passive margin history that includes lower cambrian archeocyathan bearing limestones of the rosella formation in the cassiar mountains this study indicates that an extensive oolitic shoal developed toward the western edge of this carbonate platform during the deposition of the nevadella zone parallel to the western limit of thick continental crust initial sr 0 706 isopleth paleogeographic studies from other archeocyathan bearing units in the cordillera indicate that a semicontinuous oolitic shoal was along the western margin of the continental shelf from alaska to mexico there is a distinctive gap in the passive margin record from southeastern washington to southern idaho paleogeographic constraints from the rosella formation and published paleomagnetic data from the overlying sylvester allochthon suggest that this miogeoclinal slice was originally deposited near present day idaho and was transported northward along poorly constrained dextral strike slip faults

the thermo tectonic history of the song kul plateau kyrgyz tien shan constraints by apatite and titanite thermochronometry and zircon u pb dating abstract the song kul basin sits on a plateau at the northern and middle kyrgyz tien shan junction it is a lacustrine basin occupied by lake song kul and predominantly developed on igneous basement this basement was targeted for a multi method chronological study to identify the different magmatic episodes responsible for basement formation and to constrain the timing of the development of its present day morphology zircon u pb dating by la icp ms revealed four different magmatic episodes a late cambrian 500 ma island arc system a late ordovician 450 ma subduction related intrusion an early permian 290 ma collisional stage and a middle to late permian 260 ma post collisional magmatic pulse middle to late triassic 200 230 ma titanite fission track ages and late triassic early jurassic 180 210 ma apatite fission track ages and thermal history modeling indicate the song kul basement was already emplaced in the shallow crust at that time an exhumed fossil apatite fission track partial annealing zone is recognized in the bordering song kul mountain ranges the area experienced only minor post early mesozoic denudation the igneous basement was slowly brought to apatite u th he retention temperatures in the late cretaceous palaeogene miocene to present reactivation of the tien shan does not manifestly affect this part of the orogen

three dimensional structure across the tintina strike slip fault northern canadian cordillera from seismic refraction and reflection tomography accepted 2006 june 5 received 2006 june 3 in original form 2005 september 4 summary the development of the northern canadian cordillera involved major strike slip displacement of accreted terranes relative to north america along faults such as the tintina which has experienced 425 km of dextral motion since the palaeocene the snore seismic refraction wideangle reflection experiment was carried out in 1997 as one component of lithoprobe s slavenorthern cordillera lithospheric evolution snorcle transect in addition to four 2 d profiles two sets of broadside recordings were acquired to image the 3 d structure across the tintina fault tf in areas centred at about 59 5 n and 62 n simultaneous and independent refraction and reflection traveltime tomography were applied to the combined inline and broadside data set for each region to establish the range of lower crustal velocity moho depth and upper mantle velocity structure consistent with the data our preferred models are the average of the simultaneous and independent models since they represent the robust features required by the data the preferred 3 d models are generally consistent with the 2 d models obtained from the inline data in previous independent studies there are along strike variations across the tf perhaps due to the change in strike direction or the amount of motion along the fault in the north compared to the south in the lower crust the only correlation with the tf that is required by the data is a 0 1 km s 1 drop in velocity to the southwest of the fault in the northern study area the absence of a strong correlation with the tf in the lower crust is consistent with the interpreted continuity of lower crustal units across the fault in the snorcle reflection data the moho is relatively flat throughout the study area 34 35 km depth but there is broad crustal thickening of a few kilometres centred 50 km southwest of the tf in the northern and southern study areas this thickening may be the result of a period when there was a component of compression along the tf there is strong evidence for a 0 3 0 4 km s 1 drop in upper mantle velocity to the west of the tf in the south and weak evidence for 0 1 km s 1 drop to the southwest in the north the upper mantle variations in the south indicate that the tf is the boundary between cooler and or more refractory ancestral north american mantle to the east and warmer and or more fertile mantle beneath accreted north america to the west in the north the mantle appears to be more intermediate in its properties on both sides of the tf

age and petrogenesis of the neoproterozoic chon ashu alkaline complex and a new discovery of chalcopyrite mineralization in the eastern kyrgyz tien shan abstract neoproterozoic volcanics and granitoids formed at rodinia margins within a time span of 880 ma 700 ma are well documented in many terranes of the southern central asian orogenic belt caob ages younger than 550 ma corresponding to the opening of the terskey ocean are also common however so far there were very few published ages in the range 700 ma 550 ma from the kyrgyz tien shan in this paper we present new data for the alkaline chon ashu complex emplaced at the end of the cryogenian period of the neoproterozoic 850 635 ma gradstein et al 2012 the alkaline complex intrudes the precambrian metamorphic rocks north of the nikolaev line which separates the northern and middle tien shan terranes in the eastern kyrgyzstan the undeformed shallow level alkaline rocks range from olivine gabbro to nepheline and cancrinite syenites and leucosyenites the differentiated rock assemblage can be explained by fractional crystallization of high silica mineral phases which drives nepheline normative melts away from the silica saturation boundary the alkaline rocks of chon ashu are enriched in lile and hfse indicative of their origin from lithospheric mantle an age of 678 9 ma u pb shrimp was obtained for a protolith of country gneiss and an age of 656 4 ma was obtained for the crosscutting alkaline rocks of the chon ashu complex seven zircon grains recovered from gneiss and alkaline rocks had bright overgrown rims which yielded a cumulative age of 400 8 ma a metamorphic event followed by uplift and emplacement of shallow level alkaline complex constrains the geodynamic setting alkaline rocks usually form in an extensional setting and originate from lithospheric mantle the 690 ma xenoliths of mafic granulite from the nw tarim have been interpreted to originate by mafic underplating this mafic underplating may have been responsible for metamorphism in the middle crust prior to emplacement of the chon ashu complex the 670 ma 630 ma period of extension and emplacement of enriched alkaline rocks can be also traced on a regional scale through southern kazakhstan and the northern tarim we tentatively interpret these events as a result of mafic underplating and subsequent rifting related to the break up of rodinia during field work at chon ashu rich chalcopyrite mineralization has been discovered in carbonate veinlets in leucosyenite alkaline dikes and has also been found in the adjacent cambrian gabbro and granites shown on the map as undivided devonian silurian stockwork mineralization predominates though disseminated mineralization is also present the cu content reaches 16 184 ppm and is associated with elevated concentrations of pb zn and ag the polyphase structural evolution of the area suggests that mineralization could have formed in several genetically unrelated stages based on structural and mineralogical evidence we tentatively relate the earliest stage of chalcopyrite mineralization to the late magmatic co2 rich fluids emanating from the cryogenian alkaline complex the early devonian thermal event registered by growth of new zircon at 400 ma has important metallogenic implications on a regional scale however the origin of two zones of alteration in the undivided silurian devonian granites is ambiguous because their age was not determined geochronologically the 522 4 ma cambrian gabbro of the tashtambektor formation is strongly foliated along the splays of the nikolaev line indicating a hercynian origin of the fabric superimposed mineralized stockwork postdates the foliation and suggests a late hercynian age of mineralization in gabbro the new data enable a reassessment of the metallogenic potential of the eastern kyrgyz tien shan presence of not eroded high level mineralized neoproterozoic alkaline intrusions points to a previously underestimated metallogenic potential of pre hercynian granitoids which may host preserved porphyry systems skarns and shear related mineralization finally the devonian magmato metamorphic event which caused formation of a number of ore deposits in central kyrgyzstan and kazakhstan could also create potential exploration targets in eastern kyrgyzstan

tightening the siberian connection to western laurentia newly available geological and geophysical data tighten the proterozoic connection between the rifted margins of the northern siberian craton and western laurentia and permit a siberia laurentia australia troika with northern australia connected to the southern margin of the siberian craton the continental assembly is linked by a prominent 2 0 1 8 ga collisional belt and the ca 1 3 1 0 ga grenville orogen the reconstruction also aligns a 1 5 1 45 ga dike sill swarm that extends from the wyoming province through the belt purcell basin into the northern siberian craton separation of australia and siberia may have occurred by the early neoproterozoic but separation of siberia and laurentia may not have been completed until the early cambrian continental extension began along the zigzag siberia laurentia rift zone in the early mesoproterozoic rift related igneous and sedimentary assemblages dated at ca 1 5 1 38 and 1 2 to 1 0 ga correlate across the reconstructed siberia laurentia rift zone renewed rifting in the neoproterozoic and vendian culminated with seafloor spreading and thermal subsidence of the conjugate rift shoulders correlative archeocyathan reefs endemic olenellid trilobite fauna and exchange of detritus between the cratons imply that the rift may have remained relatively narrow until the atdabanian stage black sulfidic shales buried the archeocyathan reefs on the rapidly subsiding rift margins during the botomian sinsk event

forward and inverse methods for extracting climate and diet information from stable isotope profiles in proboscidean molars abstract intratooth stable isotope profiles in enamel provide time series of dietary and environmental information that if correctly interpreted serve as archives of seasonal variability in past environments a major challenge in interpreting these profiles arises from time averaging imparted by enamel mineralization and developmental geometry whereby the primary 13c or 18o input signal is attenuated and shifted which can potentially lead to incorrect interpretations of the magnitude or frequency of seasonal variability several forward and inverse models have been developed to reconstruct the primary input signal from intratooth profiles in continuously growing teeth here the models developed by passey and cerling 2002 and passey et al 2005 are extended to molars of elephantinae which grow over a long but finite interval of time proboscidean molars are particularly attractive for intratooth profiles because they may contain a decade or more of information and they are often well preserved in the fossil record because of their thick enamel and large size forward model parameters are established using histological analysis of molar thin sections of extant african elephants loxodonta africana and a mammoth mammuthus columbi and by micro ct analysis of l africana molar plates the density of immature enamel is about 65 of the final density of mature enamel the appositional length varies from approximately 35 to 55 mm and the maturation length is about 70 mm histological methods are used to determine crown formation time cft in elephant and mammoth molar plates cft for the elephant and mammoth molar plates studied in thin section are about 5 6 years and 11 years which translate to mean growth rates of about 21 mm year and 16 mm year respectively coeval molar and tusk profiles from a zoo elephant are compared the tusk isotope profile serves as a proxy for the primary input signal and thus provides an opportunity to evaluate the forward and inverse models the results from the zoo elephant profiles demonstrate that the inverse model accurately reconstructs the amplitude and overall structure of the primary input signal inverse model results of mammoth molar profiles show double the range of 13c in measured enamel profiles inversion model results illustrate that improved reconstruction of the primary input signal can lead to more accurate interpretations of the seasonal variability of diet and body water and by extension vegetation and precipitation in past environments

middle to late ordovician arc system in the kyrgyz middle tianshan from arc continent collision to subsequent evolution of a palaeozoic continental margin new geological geochronological and isotopic data reveal a previously unknown arc system that evolved south of the kyrgyz middle tianshan mts microcontinent during the middle and late ordovician 467 444 ma ago the two fragments of this magmatic arc are located within the bozbutau mountains and the northern atbashi range and a marginal part of the arc with mixed volcanic and sedimentary rocks extends north to the semizsai metamorphic unit of the southern chatkal range a continental basement of the arc indicated by predominantly felsic volcanic rocks in bozbutau and atbashi is supported by whole rock nd and hf in zircon isotopic data epsilon nd t of 0 9 to 2 6 and epsilon hf t of 1 8 to 6 0 imply melting of neo to mesoproterozoic continental sources with nd model ages of ca 0 9 to 1 2 ga and hf crustal model ages of ca 1 2 to 1 7 ga in the north the arc was separated from the mts microcontinent by an oceanic back arc basin represented by the karaterek ophiolite belt our inference of a long lived early palaeozoic arc in the southwestern mts suggests an oceanic domain between the mts microcontinent and the tarim craton in the middle ordovician the time of arc continent collision is constrained as late ordovician at ca 450ma based on cessation of sedimentation on the mts microcontinent the age of an angular unconformity within the karaterek suture zone and the age of syncollisional metamorphism and magmatism in the kassan metamorphic complex of the southern chatkal range high grade amphibolite facies metamorphism and associated crustal melting in the kassan metamorphic complex restricts the main tectonic activity in the collisional belt to ca 450 ma this interpretation is based on the age of a synkinematic amphibolite facies granite intruded into paragneiss during peak metamorphism a second episode of greenschist to kyanite staurolite facies metamorphism is dated between 450 and 420 ma based on the ages of granitoid rocks subsequently affected or not affected by this metamorphism the latest episode is recorded by greenschist facies metamorphism in silurian sandstones and granodiorites and by retrogression of the older higher grade rocks this may have occurred at the silurian to devonian transition and reflects reorganization of a middle palaeozoic convergent margin late ordovician collision was followed by initiation of a new continental arc in the southern mts this arc was active in the early silurian latest silurian to middle devonian and late carboniferous whereas during the givetian through mississippian ca 385 325 ma this area was a passive continental margin these arcs previously well constrained west of the talas ferghana fault continued eastwards into the naryn and atbashi areas and probably extended into the chinese central tianshan the disappearance of a major crustal block with transitional facies on the continental margin and too short a distance between the arc and accretionary complex suggest that plate convergence in the atbashi sector of the mts was accompanied by subduction erosion in the devonian or early pennsylvanian this led to a minimum of 50 70 km of crustal loss and removal of the ordovician arc as well as the silurian and devonian forearcs in the areas east of the talas ferghana fault c 2016 international association for gondwana research published by elsevier b v all rights reserved

an early paleozoic collisional event along the northern margin of the central tianshan block constraints from geochemistry and geochronology of granitic rocks abstract the tianshan orogen was formed by multiple stage accretionary events ophiolites exposed in the northern margin of the central tianshan block ctb indicate the existence of an early paleozoic ocean between the tuha terrane and the ctb i e the paleo tianshan ocean however the closing history of this ocean is still controversial granitoids exposed extensively in the ctb can place a good constraint for this collisional process in this study geochemical and geochronological analyses are carried out on four granitic plutons from the ctb one mylonitic granodiorite intruding the ctb basement has a zircon u pb age of ca 496 ma and shows geochemical affinity to adakite its formation can be attributed to the subduction of the paleo tianshan ocean the 426 ma old gneissic granite that intrudes the gangou ophiolitic zone presents geochemical features of a type granite and gives an upper limit for the closure time of the paleo tianshan ocean the metamorphic age of 430 5 4 6 ma of the zircons from the mylonitic granodiorite possibly represents the event caused by the collision two other granitic samples a granodiorite and a monzodiorite yield 330 ma and 319 ma in age and display the chemical characters of i type granites that indicates a magmatic arc setting mostly related to the subduction of another ocean called the north tianshan ocean

tectonic settings of porphyry type mineralization and hydrothermal alteration in paleozoic island arcs and active continental margins kyrghyz range tien shan kyrghyzstan ore deposits in the fold belts of the northern tien shan have been formed in two stages and occur in two types of tectonic settings the first type is represented by early ordovician island arcs hosting the karakol ore district these east west trending island arcs are interpreted to have evolved above the south dipping subduction of oceanic crust of the central asian paleo ocean the second type of tectonic setting hosting the octorkoy ore district has evolved on a devonian carboniferous active continental margin of the central asian paleo ocean above north dipping subduction of the oceanic crust the second type is superposed on the first tectonic setting the oktorkoy ore district is characterized by thrusting and similar circular structures as in the first stage and its polygenic mineralization is associated with multiphase granitoid complexes zonality of porphyry copper deposits of the kyrghyz range is associated with the following hydrothermal alteration sequence potassium alteration phyllization beresitization prophyllitization epidote chlorite albite tourmalinization argillization prophyllitization epidote actinolite albite

geology and u pb geochronology of archean basement and proterozoic cover in the priest river complex northwestern united states and their implications for cordilleran structure and precambrian continent reconstructions precambrian basement rocks exposed within tectonic windows in the north american cordillera help to define the precambrian crustal structure of western north america and possible reconstructions of the late proterozoic supercontinent rodinia new geologic mapping and u pb dating in the infrastructure of the priest river metamorphic complex northern idaho documents the first archean basement 2651 20 ma north of the snake river plain in the north american cordillera the archean rocks are exposed in the core of an antiform and mantled by a metaquartzite that may represent the nonconformity between basement and the overlying hauser lake gneiss which is correlated with the prichard formation of the belt supergroup a structurally higher sheet of augen gneiss interleaved with the hauser lake gneiss yields a u pb zircon crystallization age somewhat greater than 1577 ma the slivers of augen gneiss were tectonically interleaved with the surrounding hauser lake gneiss near the base of the spokane dome mylo

geochemical and geochronological studies of granitoid rocks from the western tianshan orogen implications for continental growth in the southwestern central asian orogenic belt abstract the western tianshan orogen in northwestern china is part of the southwestern margin of the central asian orogenic belt caob which represents the largest tectonic assembly of accretionary complexes and the most significant area of phanerozoic continental growth in the world granitoid rocks have a widespread occurrence and occupy about 30 of the whole exposure of the orogen ages obtained for the granitoids vary from 896 ma to 247 ma while initial 87 sr 86 sr ratios vary from 0 70329 to 0 72070 and e nd values from 14 1 to 7 3 the occurrence of neoproterozoic granitic gneisses implies the presence of precambrian basement in this area during oceanic subduction continental growth occurred as a result of several combined processes i e by addition of oceanic crustal melts adakites the intrusion of basaltic magmas derived by partial melting of the metasomatized depleted mantle wedge and the upwelling of granitic magma derived from a mixed source of basaltic magmas and old continental basement however during the post collisional period vertical accretion of underplated juvenile mantle material may have been accomplished during slab breakoff delamination this study suggests a two stage model of continental growth of syn subduction lateral accretion of arc complexes and post collisional vertical accretion of underplated mantle material which may also be relevant for the western segment of the caob in the phanerozoic the reworking and involvement of old crust are more obvious in the western tianshan orogen compared to other parts of the caob comprising the western junggar eastern junggar alataw and altay terranes

the isotopic ecology of late pleistocene mammals in north america part 1 florida abstract mammoths and mastodons are common in pleistocene deposits yet these proboscideans and many other animals disappeared suddenly 10 000 years ago in this study we reconstruct the diets of proboscideans and associated mammals through isotopic analysis of carbonate in tooth enamel apatite in order to test nutritional hypotheses for late pleistocene extinction we analyzed specimens from six sites in florida ranging from full glacial 21 000 bp to late glacial 14 750 to 10 000 bp age the oxygen isotope composition of mammalian apatite covaries with meteoric water composition which in turn varies with climate consequently oxygen isotope analysis can be used to assess the potential for time averaging or mixing of specimens from different geographic regions within fossil assemblages the carbon isotope composition of an herbivore is controlled by the isotopic composition of the plants that it ingests carbon isotope analysis reveals that mastodons ate chiefly c3 plants presumably trees shrubs and herbs whereas mammoths consumed chiefly c4 grass several nutritional hypotheses for late pleistocene extinction entail the assumption that extinct taxa had specialized diets the resource partitioning and focused feeding preferences of florida s proboscideans corroborate this assumption but they do not in themselves prove that nutritional stress was the cause of the late pleistocene extinction

structure and diversity of oldest sponge microbe reefs lower cambrian aldan river siberia the oldest sponge reef is a small early cambrian bioherm at the base of the tommotian stage 535 540 ma in southeast siberia the mainly archaeocyath construction may be a response to turbid conditions cambrocyathellus bowls fused to create a rigid cavernous frame colonized by cryptic archaeolynthus and calcified microbes renalcis in addition to these constructors and binders other reef guilds are present bafflers other archaeocyaths spiculate sponges and hyoliths and dwellers hyoliths mollusks and many others this is the oldest known reef possessing an open skeletal frame structure built by animals and a mixed animal autotroph composition it provides a blueprint for younger phanerozoic reefs

the retention of primary oxygen isotope compositions of fossil elephant skeletal phosphate fossil elephant remains from sediments of plio pleistocene age in the vicinity of lake turkana kenya provide insights into the ability of the phosphate oxygen system to preserve original 18o values 18op in the depositional environment individual fossil specimens exhibit systematic variations in the 18op values of their various tooth and bone components differences in 18op values between these skeletal components can be as high as 3 6 despite the fact that equivalent phases for individual modern elephants have 18op values which vary by less than 0 6 xrd traces of the different skeletal phases of modern and fossil samples also infer differential preservation of primary apatite crystallinities among the various fossil phases fossil samples of dentine cementum and bone have x ray spectra with sharper and more intense peaks compared to their modern counterparts but little change in crystallinity is observed for fossil enamel samples a model based on the premise that the enamel phase preserves primary isotope signatures and that the accompanying skeletal phases are partially re equilibrated with the fluids associated with the microbial decomposition of the elephant s carcass is consistent with the features of the 18op dataset this isotopic evidence in conjunction with the physical and chemical attributes of enamel has led us to postulate that enamel could be preserving primary isotope signatures while other skeletal components are affected to varying degrees by alteration processes in the burial environment

accretionary tectonics of back arc oceanic basins in the south tianshan insights from structural geochronological and geochemical studies of the wuwamen ophiolite melange

shrimp zircon chronology of hp uhp rocks of the makbal metamorphic complex in the northern tien shan kyrgyzstan abstract in this paper we present the first results of sensitive high resolution ion microprobe shrimp u pb zircon dating obtained for the ultra high pressure uhp metamorphic rocks of the makbal metamorphic complex in the northern tien shan kyrgyzstan zircon grains from two hp eclogite samples and one sample of uhp garnet talk chloritoid schist have similar bright rims identified on cathodoluminescence cl images the rims are interpreted as zircon overgrowth during uhp metamorphism dating of zircon rims from the three samples yielded similar ages of 509 7 ma 502 10 ma and 498 7 ma the time span of 510 500 ma is considered as the minimum age of uhp metamorphism of the makbal complex this age is in accordance with middle cambrian faunal age of the kara archa ophiolite in the makbal area it is suggested that the makbal rocks were metamorphosed in the middle cambrian subduction zone dipping north under the northern tien shan microcontinent a deformed granodiorite associated with the makbal metamorphic rocks yielded an age of 514 5 ma indicating development of a magmatic arc simultaneously with the uhp metamorphism cores of zircon grains from the garnet talk chloritoid schist yielded a wide spectrum of ages 1850 800 ma characteristic for detrital zircons of continental origin a depositional age

accretionary growth and crust formation in the central asian orogenic belt and comparison with the arabian nubian shield kroner a windley b f badarch g tomurtogoo o hegner e jahn b m gruschka s khain e v demoux a and wingate m t d 2007 accretionary growth and crust formation in the central asian orogenic belt and comparison with the arabian nubian shield in hatcher r d jr carlson m p mcbride j h and martinez catalan j r eds 4 d framework of continental crust geological society of america memoir 200 p 181 209 doi 10 1130 2007 1200 11 for permission to copy contact editing geosociety org 2007 the geological society of america all rights reserved kroner kroener mail uni mainz de windley brian windley btinternet com tomurtogoo igmr magicnet mn hegner hegner lmu de jahn jahn earth sinica edu tw khain khain ginras ru demoux demoux uni mainz de wingate mwingate tsrc uwa edu au

when did the subduction first initiate in the southern paleo asian ocean new constraints from a cambrian intra oceanic arc system in west junggar nw china abstract we report here a cambrian southward subducting intra oceanic arc system in the southern west junggar nw china where an immature arc occurred initially on ssz type ophiolites and finally evolved into a more mature one the immature arc is dominantly represented by early middle cambrian 510 ma low k tholeiitic felsic rocks whereas the mature arc is characterized by late cambrian 495 ma medium and high k calc alkaline felsic and mafic rocks the ssz type ophiolites show remarkable depletion of nb and ta and contain high cr spinel cr 0 6 resembling these formed in the forearc altogether they record the initiation of subduction and transformation of crust during early subduction of the paleo asian ocean in the southern part of the central asian orogenic belt caob the subduction initiation might occur in the early cambrian 515 ma as constrained by both the ssz type ophiolites 516 ma and the oldest arc plutons 515 509 ma that crosscut the ophiolites the immature felsic plutons have high sio 2 72 wt contents and variable mgo 0 42 1 49 wt and mg values 22 62 crustal anatexis may be responsible for the genesis of those plutons and thus the transformation from oceanic to continental crust these results combined with regional data convincingly indicate that it is one of the oldest intra oceanic arc systems in the southern caob which may mark the initial subduction of the paleo asian ocean in its southern part much later than those reported in the north an archipelago type model is proposed for the evolution of the southern west junggar and has implications for the development of the southern part of the caob

tectonic evolution of the south tianshan orogen and adjacent regions nw china geochemical and age constraints of granitoid rocks geochemical and geochronological evidence was obtained from granitoids of the south tianshan orogen and adjacent regions which consist of three individual tectonic domains the kazakhstan yili plate the central tianshan terrane and the tarim plate from north to south the central tianshan terrane is structurally bounded by the early paleozoic nikolaev line north nalati fault and late paleozoic atbashy inyl chek south nalati qawabulak fault zones against the kazakhstan yili and tarim plates respectively the meta aluminous to weakly peraluminous granitic rocks which are exposed along the kekesu river and the bikai river across the central tianshan terrane have a tholeiitic calc alkaline or high potassium calc alkaline composition i type geochemical trace element characteristics and the y versus rb nb or y versus nb discrimination diagrams favor a continental arc setting for these granitoid rocks shrimp u pb and la icp ms u pb zircon age data indicate that the magmatism started at about 480 ma continued from 460 to 330 ma and ended at about 275 ma the earlier magmatism 470 ma is considered to be the result of a simultaneous southward and northward subduction of the terskey ocean beneath the northern margin of the tarim plate and the kazakhstan yili plate respectively the later magmatism 460 330 ma is related to the northward subduction of the south tianshan ocean beneath the southern margin of the kazakhstan yili central tianshan plate the dataset presented here in conjunction with previously published data support a late paleozoic tectonic evolution of the south tianshan orogen not a triassic one as recently suggested by shrimp u pb zircon dating for eclogites

late orogenic large scale rotations in the tien shan and adjacent mobile belts in kyrgyzstan and kazakhstan abstract most of kazakhstan belongs to the central part of the eurasian paleozoic mobile belts for which previously proposed tectonic scenarios have been rather disparate of particular interest is the origin of strongly curved middle and late paleozoic volcanic belts of island arc and andean arc affinities that dominate the structure of kazakhstan we undertook a paleomagnetic study of carboniferous to upper permian volcanics and sediments from several localities in the ili river basin between the tien shan and the junggar alatau ranges in southeast kazakhstan our main goal was to investigate the permian kinematic evolution of these belts particularly in terms of rotations about vertical axes in the hope of deciphering the dynamics that played a role during the latest paleozoic deformation in this area this deformation in turn can then be related to the amalgamation of this area with baltica siberia and tarim in the expanding eurasian supercontinent thermal demagnetization revealed that most permian rocks retained a pretilting and likely primary component which is of reversed polarity at three localities and normal at the fourth in contrast most carboniferous rocks are dominated by postfolding reversed overprints of probably mid permian age whereas presumably primary components are isolated from a few sites at two localities mean inclinations of primary components generally agree with coeval reference values extrapolated from baltica whereas declinations from primary as well as secondary components are deflected counterclockwise ccw by up to 90 such ccw rotated directions have previously also been observed in other tien shan sampling areas and in the adjacent tarim block to the south however two other areas in kazakhstan show clockwise cw rotations of permian magnetization directions one area is located in the kendyktas block about 300 km to the west of the ili river valley and the other is found in the chingiz range to the north of lake balkhash and about 400 km to the north of the ili river valley the timing of the ccw as well as cw rotations is clearly later than the disappearance of any marine basins from northern tarim the tien shan and eastern kazakhstan so that the rotations cannot be attributed to island arc or andean margin plate settings instead we attribute the rotations to large scale east west present day coordinates sinistral wrenching in an intracontinental setting related to convergence between siberia and baltica as recently proposed by natal in and engor natal in b a and engor a m c 2005 late palaeozoic to triassic evolution of the turan and scythian platforms the pre history of the palaeo tethyan closure tectonophysics 404 175 202 our previous work in the chingiz and north tien shan areas on ordovician and silurian rocks suggested relative rotations of 180 whereas the permian declination differences are of the order of 90 between the two areas thus we assume that about 50 of the total post ordovician rotations are of pre late permian age with the other half of late permian earliest mesozoic age the pre late permian rotations are likely related to oroclinal bending during plate boundary evolution in a supra subduction setting given the calc alkaline character of nearly all of the pre late permian volcanics in the strongly curved belts

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

hercynian post collisional magmatism in the context of paleozoic magmatic evolution of the tien shan orogenic belt abstract the hercynian tien shan tianshan orogen formed during late palaeozoic collision between the karakum tarim and the kazakhstan paleo continents in order to constrain timing of hercynian post collisional magmatism 27 intrusions were sampled for u pb zircon dating along a ca 2000 km long profile in uzbekistan and kyrgyzstan the samples were dated utilizing sensitive high resolution ion microprobe shrimp ii the obtained ages together with previously published age data allowed the timing of hercynian post collisional magmatism to be constrained and interpreted in the context of the paleozoic magmatic evolution of the region apart from hercynian post collisional magmatism two older magmatic episodes have been recognized and the following sequence of events has been established 1 approximately 10 ma after cessation of continuous caledonian magmatism a number of late silurian early devonian intrusions were emplaced in the middle and northern tien shan terranes between 420 and 390 ma the intrusions probably formed in an extensional back arc setting during coeval subduction under the margins of caledonian paleo kazakhstan continent 2 the next relatively short late carboniferous episode of subduction under paleo kazakhstan was registered in the kurama range of the middle tien shan calc alkaline volcanics and granitoids with ages 315 300 ma have distinct metallogenic affinities typical for subduction related rocks and are not found anywhere outside the middle tien shan terrane west of the talas farghona fault 3 the early permian hercynian post collisional magmatism culminated after the closure of the paleo turkestan ocean and affected the whole region across terrane boundaries the post collisional intrusions formed within a relatively short time span between 295 and 280 ma the model for hercynian post collisional evolution suggests that after collision the tien shan was affected by trans crustal strike slip motions which provided suitable conduits for ascending asthenospheric material and heat influx in the crust this produced both granitoid magmas and hydrothermal fluid flow as a result post collisional intrusions and orogenic au deposits known in the region formed coevally and were tectonically controlled 4 between 240 and 220 ma a triassic thermal event affected the region resulting in resetting and growth of new zircon grains which is detected on a regional scale probably the influx of heat into the crust during the triassic was tectonically focused and varied significantly in different terranes in the region under investigation the triassic thermal event was not accompanied by any significant magmatic activity thus after cessation of hercynian post collisional magmatism ca 280 ma ago there was a long magmatically quiet period in the tien shan

deciphering caledonian events timing and geochemistry of the caledonian magmatic arc in the kyrgyz tien shan abstract in the kyrgyz tien shan also known as tian shan in literature the caledonian cambro silurian intrusions comprise an extensive magmatic arc stretching from east to west for more than 1000 km the characteristic feature of the arc is its relatively homogeneous composition of rock types over the whole structure the kichy naryn and djetim intrusions presented in this study are slightly elongated in an east west direction and occupy an area of ca 100 km2 the main rock types are diorite granodiorite and granite geological and geochemical features of the kichy naryn and djetim intrusions demonstrate characteristics of i type granite series rocks of the two intrusions define a continuous high k calc alkaline series diorite and granite of the kichy naryn intrusion yielded early silurian crystallisation ages of 436 2 ma u pb zircon diorite from pebbles in the conglomerate sampled close to the contact of the kichy naryn intrusion yielded a significantly older early ordovician crystallisation age of 466 10 ma the obtained ages of 466 and 436 ma match ages of two major regional magmatic pulses at ca 435 440 and 460 470 ma which took place during continuous subduction from the cambrian to the silurian the amount of granites in the northern tien shan their prolonged history of formation and pronounced i type geochemical characteristics suggest their formation in an andean type active margin environment

oxygen isotope variation in the tusks of extinct proboscideans a measure of season of death and seasonality centimetre scale laminae in tusk and molar dentine of late pleistocene mastodonts and mammoths have been interpreted as annual growth bands produced in part by seasonal variation in growth rate to test this interpretation we measured the oxygen isotope composition 18 o of the co 3 fraction of dentinal hydroxyapatite from samples covering consecutive inferred years of growth in tusks in mammals changes in the 18 o value of dental tissues within individuals predominantly reflect variation in the 18 o value of body fluids which is controlled mainly by the isotopic composition of ingested water in northern hemisphere continental regions winter precipitation has substantially lower 18 o values than does precipitation in other seasons if ingested water tracks focal precipitation then seasonal variations in dentinal isotope composition should result the lowest 18 o values representing winter growth we demonstrate that there are substantial variations in the oxygen isotope composition of proboscidean dentinal apatite and that isotopic identifications of winter i e low 18 o values coincide with those based on growth rate i e slow growth zones finally the potential of oxygen isotope analyses of terrestrial mammals for assessing the seasonality of paleoclimates is considered

environmental change and seasonal behavior of mastodons in the great lakes region inferred from stable isotope analysis abstract we investigate seasonal variations in the diet and drinking water of four great lakes mastodon mammut americanum specimens using stable isotope analysis of serially sampled inner enamel bioapatite structural carbonate 13 c sc 18 o sc and previously published bulk analyses isotopic analyses and thin section measurements showed that mastodon tooth enamel extension rates 12 4 mm yr decreasing toward the cervix were lower than those of mammoths or modern elephants mastodons had distinct and highly regular seasonal variations in 13 c sc and 18 o sc which we interpret in the context of local glacial history and vegetation changes seasonal variations in 18 o were large but variations in 13 c were small and may have been obscured if coarser sampling methods than our inner enamel sampling approach were used thus our approach may be particularly useful for understanding relatively small seasonal changes in 13 c within c 3 environments the seasonal patterns though not entirely conclusive suggest that the ontario mastodons did not migrate over very long distances rather the climate and seasonal dietary patterns of mastodons within the region changed over time from 12 400 to 10 400 14 c yr bp 15 000 12 000 cal yr bp insights gained using these methods can contribute to a better understanding of megafaunal extinctions and paleoamerican lifeways

inverse methods for estimating primary input signals from time averaged isotope profiles abstract mammalian teeth are invaluable archives of ancient seasonality because they record along their growth axes an isotopic record of temporal change in environment plant diet and animal behavior a major problem with the intra tooth method is that intra tooth isotope profiles can be extremely time averaged compared to the actual pattern of isotopic variation experienced by the animal during tooth formation this time averaging is a result of the temporal and spatial characteristics of amelogenesis tooth enamel formation and also results from laboratory sampling this paper develops and evaluates an inverse method for reconstructing original input signals from time averaged intra tooth isotope profiles the method requires that the temporal and spatial patterns of amelogenesis are known for the specific tooth and uses a minimum length solution of the linear system am d where d is the measured isotopic profile a is a matrix describing temporal and spatial averaging during amelogenesis and sampling and m is the input vector that is sought accuracy is dependent on several factors including the total measurement error and the isotopic structure of the measured profile the method is shown to accurately reconstruct known input signals for synthetic tooth enamel profiles and the known input signal for a rabbit that underwent controlled dietary changes application to carbon isotope profiles of modern hippopotamus canines reveals detailed dietary histories that are not apparent from the measured data alone inverse methods show promise as an effective means of dealing with the time averaging problem in studies of intra tooth isotopic variation

structural and u pb geochronological evidence for 1 47 ga rifting in the belt basin western montana structural mapping and u pb dates from mafic sills in the perma culmination of west central montana constrain the timing of a major rifting event in the early history of the belt basin magmatic zircon from the plains and paradise mafic sills within the prichard formation yielded u pb ages of 1469 2 5 and 1457 2 ma respectively the older sill invaded unconsolidated wet sediments at a depth of less than 1 6 km and its emplacement is coeval with widespread soft sediment folding mud diapirism and bathymetric collapse of the basin between members e and f of the prichard formation the youngest sill intruded near the base of the exposed section after significant accumulation of sediment had occurred in the basin correlation of these data with recent geochronologic results from the moyie sills in british columbia and purcell lava in montana suggests that the rifting and subsidence event was basin wide and that at least two thirds of the deposition of the belt supergroup occurred between 1470 and 14

oxygen isotope evidence for progressive uplift of the cascade range oregon oxygen isotope compositions of fossil equid teeth in the cascade rainshadow reveal a v5x decrease in mean n 18 o since 27 ma isotopic changes are inconsistent with expected effects from global climate change because a the expected isotopic shift to tooth n 18 o values due to global climate change v1x is much smaller than the observed shift b predicted and observed isotopic trends are opposite for oligocene vs miocene samples and c average compositions and ranges in compositions remained unchanged for samples from before and after major global cooling in the mid miocene accounting for a decrease in relative humidity of at least 15 we infer a topographically driven secular shift in the n 18 o value of rainwater of 6 8x since the late oligocene which is approximately equivalent to the modern day difference in n 18 o values of precipitation and surface waters across the central cascades rise of the central cascades apparently occurred monotonically over the last 27 ma with a hiatus between v15 4 and 7 2 ma possibly related to eruption of the columbia river basalts progressive volcanic accumulation over tens of millions of years best explains the data rather than a short lived uplift event paleoseasonality as inferred from isotope zoning and intertooth variability decreased dramatically from 7 9x at 15 4 7 ma to v3x at 3 ma then increased to 6 8x today the cause of the decrease in seasonality at 3 ma may reflect either brief warming during the mid pliocene within the context of global tectonic reorganization or consumption by equids of water from an isotopically buffered lake idaho 2002 elsevier science b v all rights reserved

decoupling of whole rock nd hf and zircon hf o isotopic compositions of a 284 ma mafic ultramafic intrusion in the beishan terrane nw china abundant permian mafic ultramafic intrusions in the beishan terrane nw china are parts of the tarim large igneous province among these intrusions luodong intrusion is composed of dunite wehrlite and gabbro these rocks have whole rock sr nd hf and zircon hf o isotope compositions that display significant decoupling the decoupling of these generally well correlated systems demonstrates contrasting evolving trends systematic compositional and mineralogical controls on decoupling have been investigated wehrlites and gabbros show morb like trace element patterns with negligible crustal contamination they have high initial 143nd 144nd end t 6 6 to 11 2 and 176hf 177hf ehf t 12 2 to 16 9 and low initial 87sr 86sr 87sr 86sr i 0 702949 0 704098 ratios and plot within the morb field indicating that their parental magmas were derived from a depleted mantle source the enrichment features are present in the zircon crystals separated from the gabbro these homogeneously unzoned zircon crystals have high u concentrations low th u ratios and a u pb age of 284 0 2 3 ma they are therefore interpreted as having formed rapidly in a highly fractionated evolved magma their ehf t and 18o values range from 9 3 to 6 7 and 10 25 to 11 42 respectively the decoupling is linked with crustal contamination by ancient crust probably proterozoic schist in the beishan terrane that occurred during zircon crystallization however the contamination signature in the whole rock composition was soon overprinted by magma mixing process the inference is evidenced by zoning textures preserved in plagioclase clinopyroxene spinel and particularly olivine and the presence of coeval diabase dykes cutting through the intrusion the isotope decoupling observed in this mantle plume related mafic ultramafic intrusion supports the idea that nd hf decoupling and lu hf and sm nd parent daughter variations exist only on a small hand size scale in a particular growth environment and prevailing kinetics

evolution of cambrian and early ordovician arcs in the kyrgyz north tianshan insights from u pb zircon ages and geochemical data abstract geochronological geochemical and structural studies of magmatic and metamorphic complexes within the kyrgyz north tianshan nts revealed an extensive area of early palaeozoic magmatism with an age range of 540 475 ma during the first episode at 540 510 ma magmatism likely occurred in an intraplate setting within the nts microcontinent and in an oceanic arc setting within the kyrgyz terskey zone in the south during the second episode at 500 475 ma the entire nts represented an arc system these two phases of magmatism were separated by an episode of accretionary tectonics of uncertain nature which led to obduction of ophiolites from the kyrgyz terskey zone onto the microcontinent the occurrence of zircon xenocrysts and predominantly negative whole rock nd t values and hf t values of magmatic zircons suggest a continental setting and melting of precambrian continental sources with minor contributions of palaeozoic juvenile melts in the generation of the magmatic rocks the late cambrian to early ordovician 500 475 ma arc evolved mainly on mesoproterozoic continental crust in the north and partly on oceanic crust in the south arc magmatism was accompanied by spreading in a back arc basin in the south where supra subduction ophiolitic gabbros yielded ages of 496 to 479 ma the relative position of the arc and active back arc basin implies that the subduction zone was located north of the arc dipping to the south variably intense metamorphism and deformation in the nts reflect an early ordovician orogenic event at 480 475 ma resulting from closure of the djalair naiman ophiolite trough and collision of the djel tau microcontinent with the northern margin of nts comparison of geological patterns and episodes of arc magmatism in the nts and chinese central tianshan indicate that these crustal units constituted a single early palaeozoic arc and were separated from the tarim craton by an oceanic basin since the neoproterozoic

isotopic records of climate seasonality in equid teeth abstract we investigate how oxygen isotopes in equid teeth can be used as a record of seasonality first we use in situ laser ablation and conventional microsampling techniques to understand time averaging of environmental signals in intra tooth isotope profiles in modern feral horse teeth n 5 from mongolia where there is a large seasonal gradient in the oxygen isotopic composition of precipitation we demonstrate that laser ablation can be used to sample inner middle and outer enamel layers in large mammalian herbivore teeth the inner enamel layer records less attenuated isotopic signals than other layers as predicted by the mineralization patterns but intra tooth signal amplitude is similar for laser and conventional sampling methods second we use modern zebra teeth n 21 collected in eastern africa to evaluate how intra tooth oxygen isotope variation relates to rainfall patterns in the tropics we show that the intra tooth isotopic range increases with intra annual precipitation isotopic range which in turn relates to aridity in the equatorial bimodal rainfall region but is influenced by other hydroclimate processes in the region as a whole finally we address isotopic seasonality during the early pleistocene in eastern africa using oxygen isotopes in fossil equid teeth from southwestern kenya n 11 and northern tanzania n 5 we find variable isotopic seasonality in the past similar to present day eastern africa consistent with the notion that hominins and other mammals were able to accommodate environmental variability on intra annual scales in addition to well documented orbital cycles

mammoth tooth enamel growth rates inferred from stable isotope analysis and histology abstract mammoth mammuthus sp teeth are relatively abundant in quaternary deposits from eurasia and north america and their isotopic compositions can be used to reconstruct past seasonal patterns in precipitation diet and migration strategies for collecting and interpreting such data however are strongly dependent on growth rates which can vary among species individuals and within teeth in this study we use histological and isotopic measurements to determine enamel growth rates for a columbian mammoth mammuthus columbi tooth in two directions using histology the growth rate through the enamel thickness et perpendicular to the height of the tooth is estimated at 0 8 to 1 5 mm yr isotopic sampling through the innermost 0 36 mm of the et recovered less than half a period of variation i e half an inferred year of growth which is consistent with the histological estimate for et growth rate a combination of histological and isotopic measurements suggests that the enamel extension rate growth in the height of the tooth is 13 14 mm yr knowledge of enamel growth rates should improve the design and interpretation of future isotopic studies of mammoth teeth the combination of histological and isotopic measurements may also prove useful in determining growth rates for other extinct taxa

determinants of blood water δ18o variation in a population of experimental sheep implications for paleoclimate reconstruction abstract mammalian body blood and hard tissue oxygen isotope compositions 18o values reflect environmental water and food sources climate and physiological processes for this reason fossil and archaeological hard tissues which originally formed in equilibrium with body chemistry are a valuable record of past climate landscape paleoecology and animal physiology and behavior however the environmental and physiological determinants of blood oxygen isotope composition have not been determined experimentally from large herbivores this class of fauna is abundant in cenozoic terrestrial fossil assemblages and the isotopic composition of large herbivore teeth has been central to a number of climate and ecological reconstructions furthermore existing models predict blood water or nearly equivalently body water 18o values based on environmental water sources these have been evaluated on gross timescales but have not been employed to track seasonal variation here we report how water food and physiology determine blood water 18o values in experimental sheep ovis aries subjected to controlled water switches we find that blood water 18o values rapidly reach steady state with environmental drinking water and reflect transient events including weaning seasons and snowstorms behavioral and physiological variation within a single genetically homogenous population of herbivores results in significant inter animal variation in blood water 18o values at single collection times 1 s d 0 1 1 4 range 3 5 and reveals a range of water flux rates t1 2 2 2 2 9 days within the population we find that extant models can predict average observed sheep blood 18o values with striking fidelity but predict a pattern of seasonal variation exactly opposite of that observed in our population for which water input variation was controlled and the effect of physiology was more directly observed we introduce to these models an evaporative loss term that is a function of environmental temperatures the inclusion of this function produces model predictions that mimic the observed seasonal fluctuations and match observations to within 1 0 these results increase the applicability of available physiological models for paleoseasonality reconstructions from stable isotope measurements in fossil or archaeological enamel the composition of which is determined in equilibrium with blood values however significant blood 18o variation in this experimentally controlled population should promote caution when interpreting isotopic variation in the archaeological and paleontological record

on the growth of colloform textures a case study of sphalerite from the galmoy ore body ireland abstract colloform textures have been described from many of the world9s sulphide ore deposits and involve formation of distinct microcrystalline layers these textures provide information related to sequential stages of ore formation yet their mechanism of growth is poorly understood this study has analysed a series of colloform samples from the galmoy zn pb mine ireland results indicate that the growth sequence is not always intuitive and layers that appear stratigraphic upon cursory observation may not be the crystal preferred orientation cpo of discrete colloform layers abruptly switches between different orientation axes examination of the same layers using in situ laser sulphur isotope analysis reveals equally striking changes in 34 s signature between end member bacteriogenic 25 and hydrothermal 10 sources although these results combined with petrographic observation allow the determination of a probable growth history there is no correlation between shifting cpo and 34 s signature trace element analysis reveals changes in trace element sequestration between colloform layers cadmium and chlorine rich layers correspond to a hydrothermal sulphur source whereas iron rich layers correspond to a bacteriogenic sulphur source in the absence of alternative mechanisms we suggest that the most likely factors influencing cpo changes are temperature and degree of supersaturation during two fluid mixing

environmental change in the great plains an isotopic record from fossil horses abstract carbon and oxygen isotope ratios of fossil horse tooth enamel from nebraska and texas show evidence for late neogene environmental changes in the great plains the earliest unambiguous c4 dietary signal among texas equids coincides with the age of the classic late hemphillian age coffee ranch fauna which we suggest is 6 6 ma based on volcanic ash correlations c4 vegetation was present in the diets of a small fraction of late hemphillian equids in nebraska and was thereafter ordinary in the diets of both nebraska and texas equids there is no unequivocal evidence for abundant c4 vegetation in the diets of pre late hemphillian equids and we suggest that the ensuing dietary change reflects c4 biomass expansion in the latest miocene carbon isotope ratios of post hemphillian horses in nebraska can be divided into two statistically distinct populations on the basis of whether tortoise remains co occur with horse remains indicating that the two proxies carbon isotopes and presence absence of tort

isotopic paleoecology of clovis mammoths from arizona the causes of megafaunal extinctions in north america have been widely debated but remain poorly understood mammoths mammuthus spp in the american southwest were hunted by clovis people during a period of rapid climate change just before the regional onset of younger dryas cooling and mammoth extirpation thus these mammoths may provide key insights into late pleistocene extinction processes here we reconstruct the seasonal diet and climatic conditions experienced by mammoths in the san pedro valley of arizona using the carbon 13c 12c and oxygen 18o 16o isotope compositions of tooth enamel these records suggest that clovis mammoths experienced a warm dry climate with sufficient summer rainfall to support seasonal c4 plant growth monsoon intensity may have been reduced relative to the preceding time period but there is no isotopic evidence for severe drought however it is possible that the clovis drought inferred from stratigraphic evidence occurred suddenly at the end of the animals lives and thus was not recorded in the enamel isotopic compositions unlike mammoths that lived before the last glacial maximum clovis mammoths regularly increased c4 grass consumption during summer probably seeking seasonally green grasslands farther from the river valley this predictable seasonal behavior may have made mammoths easier to locate by clovis hunters furthermore clovis mammoths probably had no previous experience of such sudden climatic change as is believed to have occurred at the time of their extinction

seasonal stable isotope evidence for a strong asian monsoon throughout the past 10 7 m y o of wet season rainfall was signi cantly morenegative 29 5 smow prior to 7 5 ma than after 26 5 smow if this change is attributable to a lessening of the amounteffect in rainfall this agrees with oral and soil geochemical datathat indicate increasing aridity beginning at 7 5 ma keywords tibetan plateau monsoon stable isotopes paleohydrology seasonality introductionthe tibetan plateau is the engine that drives the modern asianmonsoon by generating a high altitude region of low pressure in thesummer as the plateau heats and a region of high pressure in the winteras the plateau cools hastenrath 1991 during the summer warm airrises from the plateau pulling moist air off the ocean across the indiansubcontinent and into the highlands this results in heavy summer rain fall on the subcontinent the opposite occurs in the winter resultingin cold dry air spilling off the plateau and effectively excluding rainfrom the subcontinent thus the presence of a strong wet season dry season alternation implies the presence of a plateau broad and highenough to drive the monsoon the timing of the uplift of the plateau remains a matter of con siderable debate because there are few direct indicators of paleotopog raphy in the geologic record consequently past workers in tibet re lying on indirect indicators of uplift have proposed dates ranging from40 to 3 4 ma on the basis of initiation of potassic volcanism chunget al 1998 turner et al 1993 or extension on the plateau harrisonet al 1995 coleman and hodges 1995 changes in marine sedimen tation rates burbank et al 1993 sediment types rea et al 1998 or biota nigrini and caulet 1992 kroon et al 1991 and changesin stable carbon isotope and palynological patterns on the indian sub continent quade et al 1989 chen 1981 although different areasof the plateau may have risen at different times many workers haveinferred rapid simultaneous uplift of large areas of the plateau at 7 8ma by a process such as lithospheric delamination molnar et al 1993 this inference was based on the following approximately coevalphenomena a major change in plant communities of the indian sub continent quade et al 1989 and shifts in marine upwelling patternsthat are linked to an intense monsoon kroon et al 1991 althoughthere is strong evidence for signi cant climate change at 7 8 ma it isunclear whether this is the onset of the monsoon the oral transitionseems to have been a global rather than local phenomenon cerling etal 1997 and monsoonally driven upwelling may have already beenpresent by 10 12 ma nigrini and caulet 1992 kroon et al 1991 because there is an intimate association between the intense sea sonality of the modern monsoon and a high tibetan plateau and be cause evaporation can be unambiguously recognized in the d

the hypothetical mesoproterozoic supercontinent columbia implications of the siberian west laurentian connection abstract the siberian west laurentian connection is a postulated reconstruction of a proterozoic craton that formed between 1800 ma and 1500 ma correlation of geological trends and of rift facies between the siberian platform and western laurentia indicates that although the two cratons underwent significant intracontinental rifting in mesoproterozoic and neoproterozoic times they did not undergo complete separation until early cambrian ca 530 ma although this interpretation does not support the hypothetical columbia supercontinent model of rogers 2000 and rogers and santosh 2002 some elements of it are compatible with that model

trace and minor element variations and sulfur isotopes in crystalline and colloform zns incorporation mechanisms and implications for their genesis abstract various models have been proposed to explain the formation mechanism of colloform sphalerite but the origin is still under debate in order to decipher influences on trace element incorporation and sulfur isotope composition crystalline and colloform sphalerite from the carbonate hosted mississippi valley type mvt deposit near wiesloch sw germany were investigated and compared to sphalerite samples from 52 hydrothermal vein type deposits in the schwarzwald ore district sw germany to study the influence of different host rocks formation mechanisms and fluid origin on trace element incorporation trace and minor element incorporation in sphalerite shows some correlation to their host rock and or origin of fluid gangue paragenetic minerals and precipitation mechanisms e g diagenetic processes fluid cooling or fluid mixing furthermore crystalline sphalerite is generally enriched in elements like cd cu sb and ag compared to colloform sphalerite that mainly incorporates elements like as pb and tl in addition sulfur isotopes are characterized by positive values for crystalline and strongly negative values for colloform sphalerite the combination of trace element contents typical minerals associated with colloform sphalerite from wiesloch sulfur isotopes and thermodynamic considerations helped to evaluate the involvement of sulfate reducing bacteria in water filled karst cavities sulfate reducing bacteria cause a sulfide rich environment that leads in case of a metal rich fluid supply to a sudden oversaturation of the fluid with respect to galena sphalerite and pyrite this however exactly coincides with the observed crystallization sequence of samples involving colloform sphalerite from the wiesloch mvt deposit

mesoproterozoic grenville age terranes in the kyrgyz north tianshan zircon ages and nd hf isotopic constraints on the origin and evolution of basement blocks in the southern central asian orogen abstract the north tianshan orogenic belt in kyrgyzstan consists predominantly of neoproterozoic to early paleozoic assemblages and tectonically interlayered older precambrian crystalline complexes and formed during early paleozoic accretionary and collisional events one of the oldest continental fragments of late mesoproterozoic grenvillian age occurs within the southern part of the kyrgyz north tianshan using shrimp zircon ages we document two magmatic events at 1 1 and 1 3 ga the younger event is characterized by voluminous granitoid magmatism between 1150 and 1050 ma and is associated with deformation and metamorphism the older event is documented by 1 3 ga felsic volcanism of uncertain tectonic significance and may reflect a rifting episode geochemical signatures as well as nd and hf isotopes of the mesoproterozoic granitoids indicate melting of still older continental crust with model ages of ca 1 2 to 2 4 ga the mesoproterozoic assemblages are intruded by paleozoic diorites and granitoids and nd and hf isotopic systematics suggest that the diorites are derived from melts that are mixtures of the above mesoproterozoic basement and mantle derived material their source is thus distinct from that of the mesoproterozoic rocks emplacement of these plutons into the precambrian rocks occurred between 461 and 441 ma this is much younger than previously assumed and indicates that small plutons and large batholiths in north tianshan were emplaced virtually synchronously in the late ordovician to early silurian the mesoproterozoic rocks in the north tianshan may be remnants of a once larger continental domain whose fragments are preserved in adjacent blocks of the central asian orogenic belt comparison with broadly coeval terranes in the kokchetav area of northern kazakhstan the chinese central tianshan and the tarim craton point to some similarities and suggests that these may represent fragments of a single mesoproterozoic continent characterized by a major orogenic event at 1 1 ga known as the tarimian orogeny

the cambrian initiation of intra oceanic subduction in the southern paleo asian ocean further evidence from the barleik subduction related metamorphic complex in the west junggar region nw china abstract in this study we present new evidence from the barleik subduction related metamorphic complex in the southern west junggar region northwestern china for the cambrian initiation of intra oceanic subduction in the southern paleo asian ocean the barleik metamorphic complex is mainly composed of blueschist and amphibolite blocks within an ophiolitic melange and their protoliths are calc alkaline andesite and alkali and tholeiitic basalts the calc alkaline andesite has a zircon u pb age of 502 2 ma obtained from magmatic cores of zircon grains and shares geochemical features similar to the 515 485 ma intra oceanic arc magmatic rocks in the west junggar region by contrast the alkali and tholeiitic basalts have trace element features similar to ocean island and enriched mid ocean ridge basalts respectively rutile and sodic calcic amphibole from the amphibolite have a u pb age of 502 25 ma and a 40 ar 39 ar age of 504 ma respectively which are in good agreement within errors with a 40 ar 39 ar age of 492 4 ma for phengite from the blueschist these metamorphic ages of 500 ma are interpreted to represent the timing of pacific type subduction related metamorphism and are also compatible with ages of the oldest supra subduction zone ophiolites 531 512 ma and intra oceanic arc plutons 515 485 ma in the southern west junggar region being one of the oldest subduction related metamorphic complexes 509 490 ma in the southern central asian orogenic belt the barleik metamorphic complex together with the oldest arc plutons definitely indicate the initial intra oceanic subduction in the southern paleo asian ocean at least in the early cambrian

thermo tectonic history of the issyk kul basement kyrgyz northern tien shan central asia abstract lake issyk kul occupies a large late mesozoic cenozoic intramontane basin between the mountain ranges of the northern kyrgyz tien shan these ranges are often composed of granitoid basement that forms part of a complex mosaic assemblage of microcontinents and volcanic arcs several granites from the terskey kungey trans ili and zhetyzhol ranges were dated with the zircon u pb method shrimp la icp ms and yield concordant late ordovician silurian 456 420 ma emplacement ages these constrain the caledonian accretion history of the northern kyrgyz tien shan in the amalgamated palaeo kazakhstan continent the ancestral tien shan orogen assembled in the early permian when final closure of the turkestan ocean ensued collision of palaeo kazakhstan and tarim a late palaeozoic structural basement fabric formed and middle late permian post collisional magmatism added to crustal growth of the tien shan permo triassic cooling 300 220 ma of the ancestral tien shan was unraveled using 40 ar 39 ar k feldspar and titanite fission track ft thermochronology on the issyk kul granitoids apatite thermochronology ft and u th sm he applied to the broader issyk kul region elucidates the meso cenozoic thermo tectonic evolution and constrains several tectonic reactivation episodes in the jurassic cretaceous and cenozoic exhumation of the studied units occurred during a protracted period of intracontinental orogenesis linked to far field effects of late jurassic cretaceous accretion of peri gondwanan blocks from the tethyan realm to eurasian following a subsequent period of stability and peneplanation incipient building of the modern tien shan orogen in northern kyrgyzstan started in the oligocene according to our data intense basement cooling in distinct reactivated and fault controlled sections of the trans ili and terskey ranges finally pinpoint important miocene pliocene 22 5 ma exhumation of the issyk kul basement late cenozoic formation of the tien shan is associated with ongoing indentation of india into eurasia and is a quintessential driving force for the reactivation of the entire central asian orogenic belt

walker creek fault zone central rocky mountains british columbia southern continuation of the northern rocky mountain trench fault zone walker creek fault zone wcfz well exposed in the western rocky mountains of central british columbia near 54 comprises a 2 km wide zone of variably deformed neoproterozoic and cambrian strata in fault bounded slivers and lozenges extensional shear bands subhorizontal extension lineations slickensides mesoscopic shear bands and other minor structures developed within and immediately adjacent to the fault zone consistently indicate right lateral displacement offset stratigraphic changes in correlative neoproterozoic strata indicate at least 60 km of right lateral displacement across the zone wcfz is the southern continuation of the northern rocky mountain trench nrmt fault zone it shows a through going moderate displacement strike slip fault system structurally links the nrmt and the north central part of the southern rocky mountain trench strike slip motion on the wcfz occurred in the late cretaceous to early eocene at the same time as northeast directed shortening in the fold and thrust

a model of fossil tooth and bone diagenesis implications for paleodiet reconstruction from stable isotopes abstract diagenesis of structural carbonate in biogenic apatite in the postmortem environment is modeled as a process of water mineral interaction both closed and open system model calculations suggest that 13 c of structural carbonate in biogenic apatite is much more resistant to diagenetic modification than 18 o apatite structural carbonate retains an original 13 c signal in closed system diagenesis for open systems 13 c of biogenic apatite with very low porosity such as tooth enamel can survive most diagenesis and retain a primary isotopic signature on the hand 18 o of structural carbonate in biogenic apatite may not be a reliable indicator of the original isotopic ratios except in a diagenetic system with low temperature and very low water biomineral ratio application of the model to teeth and carbonate cement in sediments from the badlands south dakota illustrates that 13 c values of enamel samples preserve the original signal whereas 13 c values of dentine represent varying extents of diagenesis 18 o values of fossil teeth may record an early or late part of their water biomineral interaction history during diagenesis

evidence for late rifting of the cordilleran margin outlined by stratigraphic division of the lower cambrian gog group rocky mountain main ranges british columbia and alberta the lower cambrian mcnaughton formation of the gog group occupies a stratigraphic position transitional between the rift related rocks of the underlying upper proterozoic miette group and the overlying paleozoic passive margin succession a major regional unconformity overlain by a distinctive orthoquartzite marker has been traced within the mcnaughton formation this unconformity has been shown to truncate normal faults active during the deposition of the lower mcnaughton formation the lower mcnaughton formation consists of mature coarse grained fluvial sediments accumulated in hanging wall half grabens of active normal faults these faults represent the final stage of rifting on the continental margin the unconformity on the footwall blocks of these faults can be traced into the hanging wall and is overlain by the shoreface sediments of the transgressive upper mcnaughton formation formal subdivision of the mcnaughton formation into four lithostratigraphic members is proposed in order to describ

vertical sheep mobility along the altitudinal gradient through stable isotope analyses in tooth molar bioapatite meteoric water and pastures a reference from the ebro valley to the central pyrenees abstract although the frequency of pastoral activities involving vertical sheep mobility has decreased over the last century this is a herding strategy still used in the ebro basin where animals move from overwintering valley locations up to the pyrenees from late spring to early autumn such practice allows herders to avoid the worst climatic conditions seasonally balancing the great contrast between ecological zones in this region from dry lowland mediterranean steppe to wet mountain subalpine grasslands as recent regional archaeological works have suggested the altitudinal movement of flocks may have begun with the first early neolithic groups settled in this territory here we investigate through stable isotope analyses one of the last flocks that still performs this activity sheep specimens were analyzed by sequential analyses 13c and 18o in bioapatite of tooth enamel allowing detection of seasonal changes tooth series are interpreted according to rainfall distribution seasonal patterns in 18o of meteoric water vegetation changes and 13c values in pastures along the altitudinal gradient in the area vertical movements in sheep sequential series are recognized by an inverse relationship between 13c and 18o values monthly 18o values in meteoric water obtained in valley and mountain locations describe the same type of seasonal oscillation with high values during the warm months and low values during the cold months pastures analyzed along the altitudinal gradient showed a decrease in 13c values with altitude linked to the seasonal availability of precipitation and vegetation differences among locations these results define a new analytical and conceptual framework for the interpretation of archaeological samples in this region

tooth enamel biomineralization in extant horses implications for isotopic microsampling abstract isotopic analyses of tooth enamel from fossil equids are increasingly being used to reconstruct paleoclimatic and paleoenvironmental conditions however the accuracy of these reconstructions is currently limited partly because the precise timing and spatial patterns of enamel mineralization in equids have not been documented we used radiographic analyses of mandibles collected from modern juvenile and adult domestic horses equus caballus to document the timing of enamel mineralization in equid cheek teeth premolars and molars optical and radiographic analyses of thin sections of mature and developing teeth were used to document the spatial pattern of enamel mineralization in each tooth we found that the enamel layers in equine cheek teeth took longer to mineralize than had been previously assumed largely because the enamel continued to mineralize for approximately 6 to 12 months after each tooth had begun to erupt total enamel mineralization times for individual teeth ranged from 1 5 to 2 8 years examination of thin sections revealed that retzius striae extend outward from the enamel dentin junction at an angle of 5 to 10 and run near parallel to the nonocclusal surface of the tooth daily cross striations average 5 m in width suggesting that during the initial phase of enamel mineralization matrix formation new material is added at a rate of 5 m day radiographic analyses demonstrate that the secondary mineralization front enamel maturation front is orientated approximately parallel to the retzius striae but complete maturation i e full mineralization lags behind matrix formation by several weeks to months

intra tooth stable isotope profiles in warthog canines and third molars implications for paleoenvironmental reconstructions abstract intra tooth stable isotope variations have been used to interpret seasonality and aridity in paleoenvironmental reconstructions of paleontological and archeological sites however most intra tooth datasets only permit qualitative interpretations of seasonality because the measured signal is attenuated due to the duration of enamel mineralization process and sampling geometry the common warthog phacochoerus africanus is an ideal organism to investigate stable isotope variation in enamel their canines grow continuously through the life of the individual and are therefore excellent candidates for mathematical modeling of seasonal signals and of signal attenuation further their isotope profiles a series of isotope measurements can be compared to isotope profiles of third molars m3 to provide insights into environmental reconstructions we first obtained paired intra tooth enamel samples from ever growing canines and hypsodont m3s of two extant common warthog specimens from laikipia kenya second from a different set of specimens we collected data on enamel growth patterns and geometry using histological thin sections and transmitted light microscopy and enamel mineralization parameters using micro ct scans in each tooth type third we reconstructed the timeline of unattenuated seasonal 18o signal from canine enamel using growth rate estimates and the inverse model of passey et al 2005 our results demonstrate that canines which capture 1 5 years of time exhibit near constant growth rates and simple enamel maturation geometry whereas m3s which also represent 1 5 years of time exhibit linearly decreasing growth rates and more complex maturation patterns we compare the timelines of unattenuated seasonal 18o signal and measured m3 profiles and find an average signal reduction of 50 in the m3s providing interpretations of the duration of seasonal cycles that are consistent 75 of the time we conclude that warthog canines are well suited for the inverse model approach and we established the model parameters for the forward and inverse methods timeline reconstructions based on m3 histology are promising for investigating the pattern of rainfall seasonality in the past finally we found an unexpected carbon isotopic spacing of 2 between canine and m3 enamel which suggests caution in interpreting 13c results from suid canine or molar enamel alone

conodonts from the kechika formation and road river group lower to upper ordovician of the cassiar terrane northern british columbia this study examines the lower paleozoic stratigraphy of the cassiar terrane from three key sections comprising an east west transect across the terrane the cassiar terrane west of the northern rocky mountain trench consists of a neoproterozoic to triassic succession and is a fragment of the cordilleran miogeocline that has been displaced northward the amount of displacement from its original position remains controversial conodonts from the cassiar terrane have been previously reported from only a few reconnaissance studies more than 3000 m of strata have been measured and examined in detail and 85 conodont samples collected a total of 926 identifiable conodont elements are assigned to 31 species representing 21 genera the conodonts are mainly representative of the midcontinent faunal realm but some also represent the atlantic realm conodonts from the upper kechika formation and base of the road river group are early ordovician tremadocian in age and those from the upper road river group rang

early paleozoic tectonic evolution of the chinese south tianshan orogen constraints from shrimp zircon u pb geochronology and geochemistry of basaltic and dioritic rocks from xiate nw china traditionally the chinese south tianshan has been regarded as a late paleozoic orogenic belt however little is known about the early paleozoic tectonic architecture of the region this paper presents the first evidence of cambrian ordovician morb type basalts and adakitic diorites on the southern margin of the yili plate in china basalts from xiate in southwestern tianshan show a typical transitional t morb and ferrobasalt composition which indicate a formation at a propagating spreading ridge the basalts give a weighted mean 206pb 238u crystallization age of 516 3 7 4 ma by shrimp u pb zircon dating and have experienced contact metamorphism due to the intrusion of a dioritic pluton the dioritic pluton has a weighted mean 206pb 238u crystallization age of 470 12 ma and geochemical characteristics resembling that of adakitic rocks the pluton is considered to have been formed by partial melting of garnet amphibolites from thickened lower crust in arc or continental collision settings the basalts and diorites are considered to outline the eastern extension of the early paleozoic suture zone the nikolaev line which stretches east west for hundreds of kilometers between the northern tianshan and central tianshan terranes of kyrgyzstan our findings substantiate that the yili and central tianshan plates were separated by the early paleozoic terskey ocean the terskey ocean probably closed during the early stage of the late ordovician lomize et al in geotectonics 31 6 463 482 1997 resulting in the final amalgamation of the yili and central tianshan plates consequently an early paleozoic suture zone is documented in the chinese tianshan region which is most likely represented by the north nalati fault

the initiation of the early paleozoic cordilleran miogeocline evidence from the uppermost proterozoic lower cambrian hamill group of southeastern british columbia the uppermost proterozoic lower cambrian hamill group of southeastern british columbia contains geologic evidence for a phase of extensional tectonism that led directly to the onset of thermally controlled subsidence in the cordilleran miogeocline moreover the hamill group contains the sedimentological record of the passage of the ancient passive margin from unstable tectonic conditions associated with rifting and or the earliest phases of thermal subsidence to post rift conditions characterized by stabilization of the margin and dissipation of the thermal anomaly generated during the rift phase the rift to post rift transition widespread uplift that occurred prior to and during the deposition of the lower hamill group is indicated by an unconformable relation with the underlying windermere supergroup and by stratigraphic relations between middle and upper proterozoic strata and unconformably overlying upper lower cambrian quartz arenites upper hamill group in the southern borderlands of the hami

zircon ages geochemistry and nd isotopic systematics for the palaeoproterozoic 2 3 1 8 ga kuilyu complex east kyrgyzstan the oldest continental basement fragment in the tianshan orogenic belt abstract precambrian microcontinents represent key tectonic units in the accretionary collages of the western central asian orogenic belt caob and their geological history is reasonably well established since the mesoproterozoic but remains weakly constrained for older epochs due to a scarcity of exposed palaeoproterozoic and archaean rocks early precambrian rocks were previously reported from several metamorphic complexes in the kyrgyz tianshan orogenic belt mainly based on multigrain conventional zircon dating but the present study only confirmed such rocks at one site namely in the kuilyu complex of eastern kyrgyzstan new single grain shrimp ii zircon ages geochemical data and whole rock nd isotopic compositions for granitoid gneisses of the kuilyu complex elucidate the age origin and tectonic settings of this oldest continental fragment in the tianshan the kuilyu complex is part of the basement in the ishim middle tianshan microcontinent it consist of a strongly deformed and metamorphosed supracrustal assemblage of paragneisses and schists which are tectonically interlayered with amphibolites migmatites and granitoid gneisses our zircon dating indicates that the kuilyu complex contains two suites of palaeoproterozoic granitoid gneisses with magmatic protolith ages of ca 2 32 2 33 ga and 1 85 ga granitoid magmatism at 1 85 ga was almost immediately followed by amphibolite facies metamorphism at ca 1 83 ga evidenced by growth of metamorphic zircon rims the older ca 2 3 ga granitoid gneisses chemically correspond to calc alkaline metaluminous i type magnesian quartz diorite and granodiorite the protolith of the younger ca 1 85 ga granite gneiss is an alkalic calcic metaluminous to peraluminous ferroan medium grained porphyric granite with chemical features resembling a type granites the 2 3 ga and 1 85 ga granitoid gneisses have slightly to distinctly negative initial end values of 1 2 and 6 6 and similar depleted mantle nd model ages of 2 7 2 6 ga which imply melting of neoarchaean continental crust the zircon age patterns of the kuilyu complex resemble those of exposed rocks in the tarim craton where episodes of granitoid magmatism at ca 2 3 2 4 and 1 85 ga followed by amphibolite facies metamorphism at ca 1 85 ga are also recorded similarities in the early precambrian magmatic and metamorphic episodes as well as similar histories during the neoproterozoic and early palaeozoic suggest that the ishim middle tianshan microcontinent was rifted off the tarim craton similar age patterns also suggest possible tectonic links of the kuilyu and tarim continental blocks with the baidrag block of central mongolia in contrast substantial differences in age and precambrian evolution between the anrakhai block of southern kazakhstan and the kuilyu complex argue against a previous connection and suggest the former to represent an independent continental terrane current data show that early precambrian rocks in the western caob outside tarim only occur at two sites namely in the anrakhai complex of southern kazakhstan and in the kuilyu complex of eastern kyrgyzstan

lower paleozoic stratigraphic and biostratigraphic correlations in the canadian cordillera implications for the tectonic evolution of the laurentian margin the ancient laurentian margin rifted in the latest neoproterozoic to early cambrian but appears not to have developed as a simple passive margin through a long post rift drift phase stratigraphic and conodont biostratigraphic information from four platform to basin transects across the margin has advanced our knowledge of the early paleozoic evolution of the margin in northeastern british columbia two northern transects span the macdonald platform to kechika trough and ospika embayment and a third transect spans the parautochthonous cassiar terrane in the southern rocky mountains new conodont biostratigraphic data for the ordovician succession of the bow platform is correlated to coeval basinal facies of the white river trough in total from 26 stratigraphic sections over 25 km of strata were measured and 1200 conodont samples were collected that yielded over 100 000 conodont elements key zonal species were used for regional correlation of uppermost cambrian to middle devonian strata along the cordillera the biostratigraphy temporally constrains at least two periods of renewed extension along the margin in the latest cambrian and late early ordovician alkalic volcanics associated with abrupt facies changes across the ancient shelf break intervals of slope debris breccia deposits and distal turbidite flows suggest the margin was characterized by intervals of volcanism basin foundering and platform flooding siliciclastics in the succession were sourced by a reactivation of tectonic highs such as the peace river arch prominent hiatuses punctuate the succession including unconformities of early late ordovician sub llandovery possibly early to middle silurian and early devonian ages

a nd isotope investigation of sediments related to crustal development in the british isles the times of original fractionation of the sm and nd component of clastic sediments from a mantle source crustal residence age have been estimated from sm nd model ages calculated relative to a depleted mantle evolution in this way the provenance and evolution of selected precambrian and phanerozoic sediments and metasediments from the british isles have been examined whereas some archaean and early proterozoic sediments have sm nd model ages that are close to their stratigraphic age the phanerozoic sediments analysed have model ages as much as 2 0 ga in excess of their stratigraphic age a more detailed study of lower palaeozoic sediments deposited on the northern margin of the iapetus ocean provides evidence for a marked change of provenance in the ordovician after the deposition of the dalradian supergroup a component with comparatively high143nd 144nd and sm nd ratio presumably basaltic is present in the sediments throughout the accretionary prism crustal residence age estimates average about 1 5 ga for both these lower palaeozoic sediments and modern pelagic clays and collectively fail to provide any evidence for significant continental growth during the phanerozoic