processes of forearc and accretionary complex formation during arc continent collision in the southern ural mountains the southern ural mountains of russia contain a well preserved well exposed paleozoic accretionary wedge and forearc that can be readily compared to those in active arc continent collision zones the early convergent history in the southern ural mountains is marked by the generation of boninite bearing arc tholeiites in the magnitogorsk forearc followed by arc tholeiite to calc alkaline volcanism with the entry of the east european craton continental crust in the subduction zone volcanism waned and stopped and high pressure metamorphism of its leading edge took place the arrival of the full thickness of the continental crust at the subduction zone is marked by increased sedimentation in the forearc basin and deposition of arc derived volcaniclastic turbidites across the subducting slab these together with offscraped continental material the exhumed high pressure rocks and a lherzolite massif formed an accretionary wedge a broad melange zone containing ultramafic fragments separates the forearc basement from the accretionary wedge and marks the damage zone that developed along the backstop region shallow water carbonates deposited unconformably on top of the mildly deformed arc record the end of the collision and the collapse of the arc

structural architecture of the southern and middle urals foreland from reflection seismic profiles structural architecture of the southern and middle urals foreland from reflection seismic profiles

formation of patterned ground and fine scale soil development within two late holocene glacial chronosequences jotunheimen norway abstract chronosequences of 250 to 130 years were established on two late holocene glacier forelands in the jotunheimen region of southern norway patterned features occurring within chronologically established time units were studied young patterned features forming 10 20 years after deglaciation are frost active vegetation cover is minimal within the young patterned features consisting of bryophytes organic crusts soil development within patterned ground is also minimal absent because frost action retards horizonization with time and distance from the glaciated ice margin frost activity declines within the patterned features suggesting that a thin active periglacial zone exists near the ice margin initially frost activity decreases at the borders of the features with the centers stabilizing later in time this results in fine scale soil heterogeneity and variations of soil development fine scale pedogenic development is first encountered at the borders of patterned ground that has developed on terrain exposed since the 1930s yet soil development is predominantly absent at the centers of patterned ground with time and distance from the ice margin frost activity declines and allows patterned features to homogenize from border to center positions in regard to soil characteristics across the chronosequences soils within patterned features pedogenically follow previous soil chronosequence studies evolving from usda classifications of entisols into inceptisols frost disturbance within patterned ground however produces a lag effect that results in longer periods of time for pedogenesis to occur and thinner soils than that of the surrounding terrain

tracking arc continent collision subduction zone processes from high pressure rocks in the southern urals subduction related high pressure metamorphic rocks in the southern urals confirm material flux was active within the subduction zone suprasubduction zone ophiolitic material was tectonically eroded in an intraoceanic setting metamorphosed under mantle conditions and exhumed with the entrance of the east european craton into the subduction zone the upper continental crust was removed at a shallow level whereas middle crustal material was subducted to mantle depths metamorphosed under eclogite facies conditions and interacted with the mantle wedge eclogite bearing rocks were exhumed to an upper mantle level and juxtaposed against material that was tectonically eroded from the fore arc region of the upper plate

sample preparation effects on illite crystallinity measurement grain size gradation and particle orientation abstract specimen thickness is the main experimental factor controlling the results of illite crystallinity ic or crystallite size measurements on sedimentation slides different values obtained from thick and thin preparations are due to grain size gradation effects which may exclude larger and higher ordered grains from contributing to the diffraction orientation effects control the measured peak intensity the change from poor particle orientation in thick slides to high orientation in very thin slides is marked by an increase in specimen density diminishing non basal reflections and by a strong increase in peak intensity a plateau with constant peak breadths is observed if thin slides of well ordered platy illites are used a similar plateau can be recognized for thick preparations of specimens from less ordered materials but not from well ordered ones therefore it is suggested that ic is determined on very thin sedimentation slides with a thickness of 0 25 mg cm2 or less ultrasonic and h2o2 treatments enhance the degree of particle orientation by destruction of grain aggregates and organic compounds leading to smaller peak breadths and higher intensities

precise eclogitization ages deduced from rb sr mineral systematics the maksyutov complex southern urals russia abstract the maksyutov complex southern urals russia is a well preserved example of subduction related high pressure metamorphism one of its two litho tectonic units consists of rocks that experienced eclogite facies conditions published 40ar 39ar data on phengite u pb data on rutile and sm nd mineral data define a cluster of ages around 370 to 380 ma nevertheless no consensus exists as to the detailed interpretation of data and the exact age of eclogitization we present new high precision internal mineral rb sr isochrons for eclogite facies metabasites felsic eclogites and eclogite facies quartz veins nine isochrons mainly controlled by omphacite and white mica phases give concordant ages with an average value of 375 2 ma 2 microtextural features such as prograde growth zoning in eclogite facies phases suggest that the assemblages dated formed at a stage of prograde metamorphism sr isotopic equilibria among eclogite facies phases and among eclogite facies fluid veins and the host rocks indicate that our ages reflect crystallization ages related to the prograde metamorphic probably fluid mediated eclogitization reactions this interpretation is reinforced by data from fluid precipitated quartzitic eclogites whose modal composition together with intergrowth relationships conclusively imply closed system behavior after crystallization the possible occurrence of a pre 375 ma event of ultra high pressure metamorphism uhpm in the maksyutov complex is disproved by isotope systematics microtextures and mineral zoning patterns

40 ar 39 ar thermochronology west of the main uralian fault southern urals russia west of the main uralian fault the main suture in the southern urals 40ar 39ar apparent ages of amphibole muscovite and potassium feldspar are interpreted as cooling ages a fast exhumation of the metamorphic complex of kurtinsky during upper carboniferous time is indicated by the small age difference 15 ma between cogenetic amphibole and muscovite differentiated movement in the footwall of the main uralian fault along strike is indicated by the age difference of 70 ma between the metamorphic complexes of kurtinsky north and maksyutov south no upper paleozoic uralian medium to high temperature event is recorded in 40ar 39ar data from the metamorphic complex of beloretzk mcb an amphibole age of 718 5 ma and the occurrence of mafic intrusions might signal the break up of rodinia and therefore indicate the rifting period followed by the separate movement of the beloretzk terrane muscovite ages of approximately 550 5 ma the unique pre ordovician tectonometamorphic evolution of the mcb and the late vendian sedimentary history of the western bashkirian megaanticlinorium bma imply the existence of a neoproterozoic orogeny at the eastern margin of baltica this orogeny might have been initiated by the accretion of the beloretzk terrane the metamorphic grade of the overlain silurian shales and the k ar microcline ages from the beloretzk terrane give evidence for a new thermal event at approximately 370 ma a microcline age of 530 550 ma obtained for the vendian conglomerate in the western bma suggests that a maximum temperature of approximately 200 c was reached in cambrian or vendian times an orthoclase age 590 630 ma of the vendian zigan flysch deposits might be inherited from the eastern source area the cadomian orogen an orthoclase age 910 950 ma from the riphean zilmerdak conglomerate coincides with a documented decrease in the subsidence rate of the upper riphean basin

a cross section through the zilair nappe southern urals a structural transect in the zilair kugarchi area involves the western part of the suvanyak complex the zilair nappe and the eastern part of the foreland thrust and fold belt this section has been analyzed using field microstructural and seismic data the cross section shows the transition from the hinterland to the foreland in the footwall to the suture of the southern urals the rocks involved range from early palaeozoic to permian in age a characteristic of the zilair nappe is the dominance of a succession of volcanic greywackes and mudrocks of late devonian age zilair formation the metamorphic grade decreases from east to west from greenschist facies to diagenetic conditions the structure of the cross section mainly comprises west directed thrusts and thrust related folds with an associated cleavage fold vergence changes along the section depending on of the distance to the associated thrust and its geometry the zilair thrust which separates the zilair nappe from the foreland thrust and fold belt accommodated ca 10 km displacement and the characteristics of the deformation are similar on both sides of it the contact between the zilair nappe and suvanyak complex is a west dipping normal fault that does not represent a major tectonic boundary

structural framework of the bashkirian anticlinorium sw urals the bashkirian anticlinorium of the southwestern urals shows a much more complex structural architecture and tectonic evolution than previously known pre uralian proterozoic extensional and compressional structures controlled significantly the uralian tectonic convergence a long lasting proterozoic rift process created extensional basement structures and a riphean basin topography which influenced the formation of the western fold and thrust belt with inversion structures during the uralian deformation a complete orogenic cycle during cadomian times including terrane accretion at the eastern margin of the east european platform resulted in a high level cadomian basement complex which controlled the onset of uralian deformation and resulted in intense imbrication and tectonic stacking in the subjacent footwall of the main uralian fault the uralian orogenic evolution can be subdivided into three deformation stages with differently oriented stress regimes tectonic convergence started in the late devonian with ophiolite obduction tectonic accretion of basin and slope units and early flysch deposits zilair flysch the accretionary complex prograded from the se to the nw continuous nw se directed convergence resulted finally in the formation of an early orogenic wedge thrusting the cadomian basement complex onto the east european platform the main tectonic shortening was connected with these two stages and although not well constrained appears to be of late devonian to carboniferous age in the permian a final stage of e w compression is observed throughout the sw urals in the west the fold and thrust belt prograded to the west with reactivation of former extensional structures and minor shortening in the east this phase was related to intense back thrusting the east european platform was subducted beneath the magnitogorsk magmatic arc during the late paleozoic collision the thick and cold east european platform reacted as a stable rigid block which resulted in a narrow zone of intense crustal shortening tectonic stacking and high strain at its eastern margin whereas the first orogenic wedge is of thick skinned type with the involvement of crystalline basement even the later west directed wedge is not typically thin skinned as the depth of the basal detachment appears below 15 km and the involvement of archean basement can be assumed

geometric and kinematic evolution of the foreland thrust and fold belt in the southern urals the first balanced and restored cross section through the foreland thrust and fold belt of the southern urals along the belaya river of bashkortostan is presented this cross section is used to discuss the paleozoic structure and kinematic evolution of the area and to provide quantitative estimates of fault displacement and shortening the belaya river thrust stack can be divided into a late imbricate thrust system nygush thrust system the burzyan thrust sheet and an early duplex system timirovo thrust system overprinting relationships indicate two deformation events during which the foreland thrust and fold belt evolved by a forward propagating thrust sequence the first deformation event involved emplacement of the low metamorphic grade timirovo thrust system and the overlying zilair nappe during accretion of the magnitogorsk volcanic arc with the east european craton at the end of the devonian a deformational hiatus followed until the end of the carboniferous at which time a second deformation event related to final closure of the uralian ocean resulted in development of the nygush thrust system the calculated shortening in the belaya river area 16 7 km or 17 is significantly less than that in other foreland thrust and fold belts the basal thrust in the belaya river section is located within the basement and cuts continuously up section with a staircase like geometry instead of following an easy glide horizon

provenance and thermal history of the franciscan accretionary complex constraints from zircon fission track thermochronology the franciscan accretionary complex of california contains large belts of sediments that were subducted to depths of 10 to 30 km metamorphosed under high pressure and low temperature conditions and later returned to the surface reconnaissance zircon fission track ft data 21 samples place constraints on the sedimentary provenance thermal history and or exhumation history of various franciscan units in a transect across the northern coast ranges through mendocino pass metagraywacke samples from the valantine springs formation of the franciscan eastern belt experienced maximum temperatures tmax ranging from 250 to 310 c zircon ft and previously reported apatite ft data indicate that parts of the western eastern and eastern central belts cooled at about 100 70 ma from 300 c to 100 c considering the low paleogeothermal gradient of roughly 9 c km during franciscan subduction these rocks were apparently uplifted and exhumed from 30 to 10 km depth at this time one sample from the eyler mountain sequence in the northwestern diablo range similarly shows tmax 310 c and major cooling at 100 70 ma this uplift and exhumation may have reflected accelerated accretion at the base as well as the front of the franciscan wedge accompanied by extensional thinning at shallower levels as a result of massive sediment influx into the franciscan trench from the sierra nevada magmatic arc in the northern coast ranges the western part of the central belt and the coastal belt experienced lower tmax probably 200 c and retain source area detrital zircon ft ages burnt hills terrane samples in the diablo range also experienced tmax 230 c and retain detrital ages the detrital single grain age patterns from these areas are compatible with those expected from the sierra nevada magmatic arc and its country rocks this is consistent with derivation of franciscan sediments from arc terranes in california and provides no particular suggestion that these parts of the franciscan are highly allochthonous paleogene coastal belt sandstones also yield detrital ages compatible with derivation from the sierra nevada but also include early tertiary zircon populations compatible with reconstructions suggesting these sandstones were sourced partly from the idaho batholith

contrasting provenance signals in riphean and vendian sandstones in the sw urals russia constraints for a change from passive to active continental margin conditions in the neoproterozoic abstract two contrasting provenance areas for neoproterozoic sandstones can be distinguished in the southwestern urals by light and heavy mineral analyses as well as by mineral chemistry these reflect a dramatic change of geotectonic conditions at the eastern border of the baltica protocontinent at around 610 620 ma detritus from riphean and lower vendian sandstones representing about 1 ga of continuous sedimentation is characterised by a continental platform provenance reflecting its derivation from the proterozoic basement of the east european platform source rocks include mainly minerals and few lithic clasts from granitoids and high grade metamorphic rocks as well as reworked clastic sediments and silicic volcanic rocks the provenance signal changes abruptly with upper vendian detritus representing a recycled orogenic provenance this includes mineral and lithic clasts of low grade siliciclastic metasediments and mylonites containing phengites with a high pressure signature as well as clasts of bimodal volcanic rocks and reworked siliciclastic sediments the composition of phengites contrasts strongly with those of detrital white mica in the riphean rocks also the composition of tourmalines derived from a metapsammopelitic source indicates a mainly al poor metasediment provenance whereas riphean tourmalines were derived from mainly al rich metapsammopelites zircon morphology tourmaline zoning and a reduced heavy mineral spectrum provide evidence for polycyclic sedimentation during riphean and vendian upper vendian sedimentary rocks were deposited in a foreland basin derived from a proximal uplift to the east provenance characteristics of the upper vendian detritus are consistent with areas affected by a high pressure low temperature metamorphism during a pre uralian orogenic event most likely from the metamorphic complex of beloretsk which was emplaced and exhumed during the upper vendian the change of geotectonic conditions in the upper vendian reflects a change from a passive continental margin in the south urals throughout the entire riphean since at least 1350 ma to a convergent continental margin within a presumed transpressional setting

the isostatic state of the southern urals crust the uralide orogen in central russia is the focus of intense geoscientific investigations during recent years the international research is motivated by some unusual lithospheric features compared with other collisional belts including the preservation of a a collisional architecture with an orogenic root and a crustal thickness of 55 58 km and b large volumes of very low grade and non metamorphic oceanic crust and island arc rocks in the upper crust of a low relief mountain belt the latter cause anomalous gravity highs along the thickened crust and the isostatic equilibrium inside the uralides lithosphere as well as the overthrust high metamorphic rocks the integrated urseis 95 seismic experiment provides fundamentally new data revealing the lithospheric architecture of an intact paleozoic collisional orogen that allows the construction of density models in the urals lithosphere different velocity structures resolved by wide angle seismic experiments along both the urseis 95 and the troitsk profile they can be used to constrain lithospheric density models a first model consists of a deep subducted continental lower crust which has been highly eclogitized at depths of 60 90 km to a density of 3550 kg m3 the second model shows a slightly eclogitized lower crust underlying the uralide orogen with a crustal thickness of 60 km the eclogitized lower crust causes a too small impedance contrast to the lithospheric mantle resulting in a lack of reflectors in the area of the largest crustal thickness both models fit the measured gravity field analyzing the isostatic state of the southern urals lithosphere both density models are in isostatic equilibrium

basement influence on foreland thrust and fold belt development an example from the southern urals abstract the reactivation of two sets of pre existing basement faults provided strong control on the geometric and kinematic evolution of the paleozoic south urals foreland thrust and fold belt pre existing basement faults oriented subparallel to the uralide structural grain were related to several stages of precambrian deformation reactivation focused the deformation along these earlier faults resulting in the subsequent incorporation of crystalline basement thrust sheets in the thrust belt at an early stage of its evolution pre existing basement faults oriented subperpendicular to the developing thrust belt structural grain were related to aulacogens in the archean crystalline basement that were filled by variable thickness of riphean aged sediments these influenced the localisation and development of numerous structures in the thrust belt that caused along strike structural changes related to lateral ramps recognition of these features and their influence on the geometric and kinematic evolution of the south urals foreland thrust and fold belt are important for understanding seismic reflection fabrics in the south urals thrust belt and for potential field 3 d geological and kinematic modelling

the relationship of phyllosilicate orientation x ray diffraction intensity ratios and c b fissility ratios in metasedimentary rocks of the helvetic zone of the swiss alps and the caledonides of jamtland central western sweden phyllosilicate preferred orientations x ray diaraction intensity ratios and c b fissility ratios were determined from 23 metasedimentary rocks from the helvetic zone of the swiss alps and from the caledonides of jamtland sweden the relationships between these parameters of phyllosilicate orientation depend strongly on the lithology and the cleavage morphology diaerences in orientation direction and in degree of preferred orientation reflect both deformation intensities and lithologies whereas polyphase deformed fine grained samples generally have phyllosilicates that are oriented parallel to cleavage showing high orientation intensities phyllosilicates in less deformed and or coarse grained rocks are oriented parallel to bedding with low orientation intensities weak orientation intensities in samples with phyllosilicates that are oriented parallel to bedding reflect compaction strain the higher strain in samples with micas and chlorites that are parallel to cleavage is a combination of compaction and tectonic strain due to the development of crenulation cleavage 2000 elsevier science ltd all rights reserved

clay mineral formation in soils of two different chronosequences in the swiss alps two chronosequences of soils developed from postglacial tills at two different sites in the swiss alps were studied with respect to their soil mineralogy and chemistry the age of these soils ranged between 0 and 11 500 years the parent material for both chronosequences was similar but differences were found in the clay fraction within the considered time span podzols developed at both sites however at one site already after about 3000 years and at the other a few years later especially trioctahedral minerals were strongly weathered within the time span of about 11 000 years smectite and regularly interstratified dioctahedral mica smectite could be found in the most weathered horizons at one site the origin of smectite could be traced back to both chlorite and trioctahedral mica which supports the fact that smectite is the end product of chlorite alteration and regularly interstratified mica smectite or even smectite the end product of mica weathering in strongly leached and acidified horizons at the other site smectite was already present in the parent material most presumably due to hydrothermal formation during the first 500 years of soil formation a kind of retrograde podzolisation was observed leading to the elimination of this smectite within the same time increased amounts of dioctahedral minerals were formed and after 11 000 years a small proportion of pedogenic smectite was discernible again main clay mineral transformations occurred at both sites within the first 3000 years of soil development weathering and transformation reactions were most advanced in the e horizon being almost complete after 3000 years at one site the presence of significant amounts of chlorite and or a minimal content of mica of ca 5 seems however to be compulsory in order to detect low charge expandable minerals already after a 3000 year duration of soil formation in the alps otherwise smectite formation is retarded

preliminary fission track results from the southern urals sterlitamak to magnitogorsk abstract results are reported from a pilot fission track study of a west east traverse across the southern urals from sterlitamak through to the dzhabyk granite east of magnitogorsk which was undertaken in order to study the low temperature 300 c thermotectonic post uralian history of the mountain belt the transect crosses the major tectonic units including the main uralian fault the suture zone which separates the east european craton from palaeozoic oceanic island arc and continental terranes of asia zircon fission track ages range from 226 ma to 604 ma in the foreland thrust and fold belt with a single age of 262 ma in the magnitogorsk zone an age grouping of about 250 ma for zircons on either side of the main uralian fault suggests that there has been no differential movement identifiable through fission track analysis along this line since the triassic the similarity of apatite ages ranging from 180 to 210 ma further verifies little differential movement within the footwall to the suture since the jurassic in the central part of the magnitogorsk zone apatite ages are older they are slightly annealed crystallisation cooling ages but further confirm that there has been only little tectonic activity since the triassic except in the east uralian zone apatite fission track analysis reveals variable denudation rates the highest rates occurred during the permo triassic ending at about 210 ma just prior to the final development of the jurassic peneplain this was followed possibly by a period of burial before final cooling exhumation from approximately middle cretaceous onwards

geological partial annealing zone of zircon fission track system additional constrains from the deep drilling miti nishikubiki and miti mishima abstract fission track ft analysis of zircon from rhyolite and sandstone samples of ministry of international trade and industry miti nishikubiki and miti mishima boreholes has given additional constraints on the temperature range of the zircon partial annealing zone zpaz over a geological time scale the advantages of these samples are the following 1 they have been exposed to a stable temperature for 1 million years and 2 it is possible to obtain data at successive temperatures ages and confined track lengths were measured in samples from depths of 3 5 5 6 km with a current environmental temperature of 223 c at the deepest track lengths in samples below 200 c are still long and ft ages are compatible with their sedimentary ages showing no evidence of annealing for a heating duration of 1 million years samples at 205 c seem to yield shortened tracks as a result of annealing because of a low number of zircon crystals only four track lengths were measured for the deepest sample whose mean length was shortest among analysed samples these data are consistent with previous results from ultra deep boreholes

thermobarometric data from a fossil zircon partial annealing zone in high pressure low temperature rocks of eastern and central crete greece abstract a fossil partial annealing zone of fission tracks in zircon is described from high pressure low temperature hp lt rocks of the phyllite quartzite unit pq on the island of crete greece correlation of regional trends in fission track age populations with independent thermobarometric and microstructural data and with new experimental annealing results allows a calibration of this low temperature thermochronological method to a degree hitherto not available from other field examples the zircon fission track ft ages of samples from the pq across crete range from original detrital signature through reduced to completely reset the annealing is the result of a single heating period related to the hp lt metamorphism with near peak temperatures lasting for only a few million years some time between 24 1 and 20 1 ma in eastern crete where rocks have experienced temperatures of 300 50 c and pressures of 0 8 0 3 gpa zircon ft ages range from 414 24 to 145 10 ma ages above 300 ma occur mostly near the east coast of the island in rocks which have not been heated to above ca 280 c and probably represent a pre variscan source track lengths are already indicative of a substantial annealing at this temperature most of the zircon ft ages from eastern crete scatter within error around the stratigraphic age samples with apparent zircon ft ages significantly younger than the depositional age are only observed in areas where temperatures exceeded ca 320 c towards the west a sudden decrease to very young ages ranging from 17 2 to 18 1 ma reflects a complete resetting at ca 350 c short tracks however are still observed throughout the central and western part of the island ages are consistently below 22 ma thermobarometric data for this area indicate maximum temperatures of 400 50 c and pressures of 1 0 3 gpa only samples from western crete which have been exposed to 400 50 c show exclusively long tracks consequently the high temperature limit of the zircon partial annealing zone zpaz appears to be between 350 and 400 c a significant influence of elevated confining pressure on the stability of fission tracks in zircon is ruled out by the results of annealing experiments at 0 5 gpa and at different temperatures which fit the curves previously obtained by other authors at ambient pressure

natural long term annealing of the zircon fission track system around a granitic pluton we measured 24 ages and 14 length distributions of fission tracks in zircons separated from basement sandstones around a granitic pluton to investigate natural long term annealing behaviors of the zircon fission track zft system samples were collected from three cretaceous coherent units of the shimanto accretionary complex shikoku japan along an eastward traverse at distances of between 1 6 and 10 6 km from the intrusion contact of 15 ma takatsukiyama granite exposing about 5 km in diameter sampling was carried out around the expected position of the transition zone of track retention i e the fossil partial annealing zone fpaz based on previous regional zft age distributions approaching the contact original zft ages of 100 ma show a continuous reduction to 15 ma at 3 km distance their single grain age distributions accordingly change from widespread multimodal patterns reflecting provenance ages to unimodal ones characterizing the secondary heating by the granite intrusion mean and distributions of zft lengths also show notable variations within the fpaz as a result of mixing both preexistent tracks that were shortened by the miocene heating and unannealed ones having original long lengths that have been formed and accumulated after the cooling of the pluton these facts along with observed track segmentation and annealing anisotropy suggest that the shortening patterns of tracks in nature a heating duration of 105 106 years estimated from thermal modeling are indistinguishable from those previously demonstrated at laboratory timescales this basically validates the conventional approach of extrapolating laboratory based kinetic parameters to geologic timescales the observed fpaz and thermal modeling results in conjunction with laboratory heating data previously reported and recent constraints from an ultradeep borehole favor a relatively narrow temperature range for the partial annealing zone i e 230 to 330 c for a heating duration of 106 years

structure and evolution of the magnitogorsk forearc basin identifying upper crustal processes during arc continent collision in the southern urals the southern urals of russia contain a well preserved example of a paleozoic arc continent collision in which the intraoceanic magnitogorsk volcanic arc and its forearc basin sediments accreted to the east european craton during the devonian the magnitogorsk arc records the evolution from incipient intraoceanic subduction to a mature arc and by comparing its surface geological features with those in active arc continent collision settings it is possible to identify upper crustal processes that were active in the southern urals the arc edifice can be divided into western and eastern volcanic fronts that were active during different stages of arc evolution and for which two distinct phases of forearc basin development can be recognized the late lower to middle devonian aktau formation represents a remnant of the intraoceanic to collisional forearc basin to the irendyk volcanic front whereas the middle devonian to lower carboniferous ulutau koltubanian and zilair formations were deposited in a suture forearc basin to the east magnitogorsk volcanic front it was not until the late devonian that these two basins were joined structural mapping combined with reflection seismic profiling shows these basins to be affected by open nonlinear volcanic basement cored synsedimentary folds the karamalytash anticline appears to have the geometry of a growth fold that formed during deposition of sediments in the suture forearc basin the forearc region is affected by minor thrusting that involves the volcanic basement although it is not clear if these thrusts reactivate preexisting trench parallel faults synsedimentary deformation slumping and olistostrome development were common throughout the suture forearc basin history but were especially widespread during the late devonian when the full thickness of the continental crust is interpreted as having arrived at the subduction zone

spatial distribution patterns of calcareous nannofossils across the callovian oxfordian transition in the french subalpine basin abstract callovian oxfordian calcareous nannofossils are documented from four sections distributed along a proximal distal slope to central basin transect in the french subalpine basin south eastern france the sections were dated and correlated using integrated ammonite dinoflagellate and nannofossil biostratigraphies the nannofossil assemblages are constantly dominated by watznaueria britannica however significant spatial changes in nannofossil assemblage composition are recorded nannofossil assemblages recovered in slope and slope to basin transition sections are characterized by high abundances lowest diversities highest percentages of smallest sized morphotypes of w britannica subordinated w britannica manivitiae a morphotype described in this study and are indicative of turbulent unstable and or eutrophic conditions towards the central part of the basin as the nutrient content and turbulence declined and paleoenvironmental stability increased the nannofossil assemblages become more diverse and characterized by lower relative abundances of w britannica but higher contribution of larger morphotypes and higher relative abundances of w barnesiae fossacincta biscutum dubium and zeugrhabdotus erectus these latter small coccoliths markers of high surface waters fertility for the cretaceous were probably not competitive with respect to smaller sized w britannica in unstable and eutrophic surface waters for the jurassic an increase in the surface water productivity is recorded both in proximal and distal sections at the callovian oxfordian transition and is demonstrated both by an increase in nannofossil total abundances and in the relative abundances of taxa adapted to high trophic levels thermal minimum in surface waters as indicated by an increase in the percentages of the cool water nannofossil taxa is associated to increased productivity further studies will be necessary to demonstrate whether surface water productivity changes already recorded in the eastern paris basin were global

the main tectonic events depositional history and the palaeogeography of the southern urals during the riphean early palaeozoic abstract investigation of former and new sections in the classic riphean region of the bashkirian anticlinorium ba revealed that this palaeozoic segment of the passive margin of the east european platform eep during its proterozoic history was initially formed as an intracratonic aulacogen basin which developed as an inter cratonic half structure only after the early ordovician opening of the uralian palaeo ocean the originally opposite half structure of this riphean basin may have been located either on the afro european part of gondwana or along the margins of the siberian craton or elsewhere but definitely not along the conjugate permian collision suture with the kazakh block or the mugodzhary microcontinent the ca 1150 ma 1635 to 488 ma depositional history of the bashkirian basin was punctuated several times due to major tectonic events folding downfaulting uplift magmatic intrusions metamorphism which may have caused extended periods of erosion and non deposition furthermore numerous cyclothems of unknown regional extent are incorporated into the enormous time span involved in the evolution of the ca 12 15 km thick riphean sequence the riphean vendian sedimentary assemblages reflect alternating shallow marine to peritidal and continental fluviatile environments the regional distribution of which is illustrated in sets of palaeogeographic maps angular unconformities are seen at the base of the lower riphean ai formation dated at 1635 ma at the base of the middle riphean mashak formation dated at 1340 ma at the base of the upper riphean zilmerdak formation approx 1000 ma and below the middle ordovician quartzites containing shelly fossils which overlie steeply folded and slightly metamorphosed proterozoic suites along the southeastern margin of the bashkirian anticlinorium during the vendian to ordovician interval major eastern parts of the bashkirian anticlinorium as well as regions further north along the european margin of the urals were subjected to strong diastrophism probably related to the cadomian or baikalian orogeny later on during the ordovician the western half part of the bashkirian basin turned into a marginal basin of the east european platform and thus was modified by the early stages of the uralian oceanic development

deep structure of the continental lithosphere in an unextended orogen an explosive source seismic reflection profile in the urals urals seismic experiment and integrated studies urseis 1995 explosive source near vertical seismic reflection data from the urals seismic experiment and integrated studies urseis profile displays an image of orogenic lithosphere to depths of 225 km the reflective crustal section is characterized by dipping crustal scale shear zones and a pronounced crustal root that show no evidence of overprinting by extension and are preserved since late paleozoic collision toward the east the uralian crustal root is composed of a partially subducted volcanic arc while to the west it has affinity with the east european platform the reflection character of the moho varies across tectonic strike and implies that the moho 1 acted as a structural detachment beneath the trans uralian zone 2 forms a tectonic boundary between terranes beneath the east uralian zone 3 consists of a transitional zone from eclogitized lower crust to peridotitic upper mantle in the crustal root 4 is a 3 9 km thick reflective zone beneath the fold and thrust belt and 5 is a boundary 200 m thick in the west mantle reflections at 80 100 km depth 22 24 s may represent a continuation of the main uralian fault into the subcrustal lithosphere alternatively these reflectors may signify paleozoic or younger mantle shear zones or the top of a zone of partial melting in the upper mantle deeper mantle reflections at 140 160 km 35 45 s and 225 km 55 s may image mafic intrusions at the base of the lithosphere or along localized shear zones in the upper mantle

thermotectonic evolution of the western fold and thrust belt southern uralides russia as revealed by apatite fission track data abstract the uralides a linear n s trending palaeozoic fold belt reveals an intact well preserved orogen with a deep crustal root within a stable continental interior in the western fold and thrust belt of the southern uralides devonian to carboniferous siliciclastic and carbonate rocks overlay mesoproterozoic to neoproterozoic sedimentary rocks deformation in the devonian carboniferous and permian caused thick skinned tectonic features in the western and central parts of the western fold and thrust belt a stack of several nappes characterizes the deformation in the eastern part along the e w transect ac ts 96 that crosses the western fold and thrust belt apatite fission track data record various stages of the geodynamic evolution of the uralide orogeny such as basin evolution during the palaeozoic synorogenic movements along major thrusts synorogenic to postorogenic exhumation and a change in the regional stress field during the upper jurassic and lower cretaceous the palaeozoic sedimentary cover and the neoproterozoic basement of the ala tau anticlinorium never exceed the upper limit of the paz since the devonian a temperature gradient similar to the recent one 20 c km would account for the ft data reactivation of the neoproterozoic zilmerdak thrust was time equivalent to the onset of the devonian and carboniferous collision related deformation in the east west directed movement along the tashli thrust occurred in the lower permian the devonian and carboniferous exhumation path of the neoproterozoic siliciclastic units of the tirlyan synclinorium mirrors the onset of the uralian orogeny the emplacement of the tirlyan nappe and the continuous west directed compression the five main tectonic segments inzer synclinorium beloretzk terrane ala tau anticlinorium yamantau anticlinorium and zilair synclinorium were exhumed one after another to a stable position in the crust between 290 and 230 ma each segment has its own t t path but the exhumation rate was nearly the same final denudation of the western fold and thrust belt and exhumation to the present surface probably began in late tertiary in jurassic and cretaceous south directed movements along w e trending normal faults indicate a change in the tectonic regime in the southern uralides

soil development along primary succession sequences on moraines of hailuogou glacier gongga mountain sichuan china abstract soil properties related to soil development were measured in six profiles over approximately 180 years of soil development on recessional moraines of the hailuogou glacier sichuan of southwestern china it is hypothesized that soil development is strictly time dependent field and laboratory work indicate that as soil develops from initially coarse gravel outwash the properties undergo a progressive physical and chemical change such that there is a considerable profile differentiation between the youngest and the oldest soils the ph is also highly stratified it decreases with time from 8 5 to 4 2 in the upper mineral soil and increases with depth in all profiles accumulation of soil organic c and n increases with time but the rates of accumulation become slower with time within the investigated timespan soil c and n accumulated to a considerable level of 3 5 and 0 6 kg m2 respectively with mean annual rates of 28 g m2 for carbon and 3 5 g m2 for nitrogen the rapid accumulation of organic c and n accelerates the processes of soil formation but the content of organic c and n did not reach a steady state during the observed timespan the accumulation of soil organic matter results in increased acid production and in the chemical weathering of minerals that promote formation and translocation of the clay fraction and leaching of carbonate it is also directly responsible for development of soil properties such as cation exchange capacity cec and bulk density

crustal scale structure and evolution of an arc continent collision zone in the southern urals russia the outcropping geology of the southern urals contains a well preserved accretionary complex related to the paleozoic collision that took place between the magnitogorsk arc and the former east european craton the crustal scale structure of the accretionary complex has been determined from outcropping field geology that is integrated with three reflection seismic profiles the reflection profiles show the accretionary complex to be highly reflective allowing direct comparison of many reflections with surface geological features we interpret the accretionary complex to be a thrust stack that is composed of shallowly subducted continental shelf and rise material syncollisional sediments derived from the arc deeply subducted high pressure gneisses that are intercalated with eclogites and blueschist and at the highest structural level ophiolite complexes it is bound at the base by a thrust and at the rear by a highly deformed zone the main uralian fault adjacent to the backstop the magnitogorsk arc deposition of the late devonian volcaniclastic sediments of the zilair formation appears to be related to collision uplift and erosion of the arc possibly following the arrival of the full thickness of the east european craton continental crust at the subduction zone with the arrival of the continental crust at the subduction zone offscraping and underplating of paleozoic slope and platform material took place at the base of the accretionary complex uplift of the arc was followed by its collapse and the unconformable deposition of lower carboniferous shallow water carbonates on top of it a time lag of 10 15 myr occurred between the high pressure metamorphism and the subsequent arrival of the east european craton at the subduction zone

40ar 39ar u pb and sm nd constraints on the timing of metamorphic events in the maksyutov complex southern ural mountains new 40 ar 39 ar u pb and sm nd data from 13 metamorphic samples constrain the formation and exhumation of the high pressure maksyutov complex in the southern uralide orogen the maksyutov complex records the highest pressure metamorphism in the southern uralides and is part of the thrust stack that composes the footwall beneath the main ural fault the new isotopic data from eclogite in the lower unit of the maksyutov complex include 40 ar 39 ar data from phengite u pb data from rutile and apatite and sm nd data from garnet clinopyroxene rutile and apatite these data indicate that eclogite facies metamorphism occurred in the mid devonian epoch c 380 ma corresponding with eastward subduction of the east european craton beneath the magnitogorsk island arc after partial exhumation the lower unit was juxtaposed c 360 ma based on 40 ar 39 ar white mica data with the middle and upper units at mid crustal levels during the development of a d 3 shear zone within the subduction zone by the late carboniferous epoch the maksyutov complex was exhumed to upper crustal levels compatible with sedimentologic evidence that at this time the foreland thrust and fold belt began to form and material was shed off it into the foreland basin

soil development on moraines of mendenhall glacier southeast alaska 2 chemical transformations and soil micromorphology abstract soils on holocene age moraines of the mendenhall glacier in southeast alaska range from morphologically undeveloped to soils having field identified spodic horizons that are more strongly expressed with increasing soil age a soil chronosequence was sampled to study development of spodic features and to compare the expression of these features with chemical and micromorphological properties organic c accumulates rapidly in these soils with o horizons forming within 38 yr organic c is highly correlated with cation exchange capacity r2 0 92 variable charge r2 0 94 extractable acidity r2 0 83 and 1500 kpa water retention r2 0 97 the ph of the 10 yr old pedon is acidic with a soil ph h20 ranging from 5 0 to 6 4 the ph decreases with soil age with the lowest ph in horizons at the organic mineral contact increases in dithionite citrate sodium pyrophosphate and acid oxalate extractable fe feo are most evident in the 240 yr old soil depth trends for these measured properties within pedons are most distinctive for fe which increases from surface mineral horizons a or e to underlying horizons in all pedons the feo fed ratio increases with soil age in b horizons and in pedons 70 yr this ratio ranges from 0 3 to 0 5 in the e horizons and from 0 4 to 0 83 in b horizons immediately below these data indicate a greater proportion of poorly crystalline fe in illuvial horizons with increasing soil age allophane content is low 240 yr old pedon this chronosequence study indicates that spodic development is achieved within a relatively short period of time in soils of this region

strain related differences in the crystal growth of white mica and chlorite a tem and xrd study of the development of metapelitic microfabrics in the southern uplands thrust terrane scotland tem and xrd techniques were used to study crystal growth characteristics of the fabric forming phyllosilicates which developed in response to low grade metamorphism and tectonic imbrication in part of the southern uplands thrust terrane prograde regional metamorphism ranging from late diagenesis through the anchizone to the epizone was accompanied by the development of a slaty cleavage which is commonly bedding parallel tem measured mean thicknesses of white mica and chlorite crystallite populations increase with advancing grade and correlate with xrd measured crystallinity indices analytical tem data show that prograde changes in composition lead to a net loss of si ca and minor fe from the fabric forming phyllosilicates white micas are paragonite poor phengites with a mean b lattice parameter of 9 037 a and indicate an intermediate pressure series of metamorphism with a field gradient of 25 c km chlorite compositions evolved from diabantite with intergrown corrensite to ripidolite over an estimated temperature range of 150 320 c field gradient and temperature estimates suggest that crystal growth and fabric development occurred at burial depths ranging from 6 km to at least 13 km in the thrust terrane during late diagenesis crystal growth of white mica and chlorite was predominantly a consequence of polytypic and phase transitions and resulted in similar size distributions which resemble typical ostwald ripening curves under anchizonal and epizonal conditions white mica grew more rapidly than chlorite because of its greater ability to store strain energy and recover from subgrain development as a result crystal thickness distributions are not typical of ostwald ripening in contrast chlorite crystals which grew under these conditions developed subgrain boundaries at high strain rates which were only partially recovered at low strain rates these retained dislocations reduce the crystallite thicknesses detected by tem and xrd compared with those of white mica these differences in strain induced crystal growth indicate that white mica illite and chlorite crystallinity indices are likely to show significant differences where low grade metamorphism is closely associated with tectonic fabric development

the metamorphic complex of beloretzk sw urals russia â a terrane with a polyphase meso to neoproterozoic thermo dynamic evolution abstract an integrated geological study of the tectono metamorphic evolution of the metamorphic complex of beloretzk mcb which is part of the eastern bashkirian mega anticlinorium bma sw urals russia shows that the main lithological units are neoproterozoic riphean and vendian age siliciclastic to carbonate successions granitic syenitic and mafic intrusions together with subaerial equivalents comprise the neo and mesoproterozoic magmatic rocks the metamorphic grade ranges from diagenetic and very low grade in the western bma to high grade in the mcb the n s trending zuratkul fault marks the change in metamorphic grade and structural evolution between the central and eastern bma structural data pb pb single zircon ages 40 ar 39 ar cooling ages and the provenance signature of riphean and vendian siliciclastic rocks in the western bma give evidence of mesoproterozoic grenvillian rifting deformation and eclogite facies metamorphism in the mcb and a neoproterozoic cadomian orogenic event in the sw urals three pre ordovician deformation phases can be identified in the mcb the first sse vergent isoclinal folding phase d 1 is younger than the intrusion of mafic dykes pb pb single zircon 1350 ma and older than the eclogite facies metamorphism high p low t eclogite facies metamorphism is bracketed by d 1 and the intrusion of the achmerovo granite pb pb single zircon 970 ma an extensional sinistral top down to nw directed shearing d 2 is correlated with the first exhumation of the mcb e vergent folding and thrusting d 3 occurred at retrograde greenschist facies metamorphic conditions the tremolite 40 ar 39 ar cooling age 718 5 ma of amphibolitic eclogite and muscovite 40 ar 39 ar cooling ages about 550 ma of mica schists indicate that a maximum temperature of 500 50 c was not reached during the neoproterozoic orogeny the style and timing of the neoproterozoic orogeny show similarities to the cadomian aged timan range nw of the polar urals geochronological and thermochronological data together with the abrupt change in structural style and metamorphism east of the zuratkul fault suggest that the mcb is exotic with respect to the se margin of the east european platform thus the mcb is named the beloretzk terrane recognition of the beloretzk terrane and the neoproterozoic orogeny at the eastern margin of baltica has important implications for neoproterozoic plate reconstruction and suggests that the eastern margin of baltica might have lain close to the avalonian cadomian belt

interlaboratory standardization and calibration of day mineral crystallinity and crystallite size data clay mineral crystallinity and crystallite domain size data determined by x ray diffraction xrd are methods extensively used in the characterization of very low grade metamorphic conditions however the lack of sufficient interlaboratory standardization has made comparisons between different research groups unreliable due to significant variations in numerical results obtained a consequence of the different machine conditions measurement methods and sample preparations used during analysis a calibration approach to the standardization of data using rock chip standards is presented which allows data sets produced by different research groups to be directly and quantitatively compared a standardized scale the crystallinity index standard cis is proposed with illite crystallinity anchizonal boundary limits of 0 25d 2 and 0 42d 2 and equivalent illite crystallite sizes of 52 and 23 nm respectively determined by the warren averbach method calibrating both old and new data will enable more reliable comparisons between similar and contrasting geological environments and should improve the accuracy and reliability of correlations made between xrd data and other indicators of very low grade metamorphism hence increasing the value of such clay mineral studies

neoproterozoic metamorphism and deformation at the southeastern margin of the east european craton uralides russia the eastern margin of the east european craton eec has a long lasting geological record of precambrian age archaean and proterozoic strata are exposed in the western fold and thrust belt of the uralides and are known from drill cores and geophysical data below the palaeozoic cover in the uralides and its western foredeep in the southern uralides sedimentary metamorphic and magmatic rocks of riphean and vendian age occur in the bashkirian mega anticlinorium bma and the beloretzk terrane in the eastern part of the bma yamantau anticlinorium and the beloretzk terrane k ar ages of the 2 m size fraction of phyllites potassic white mica and slates illite give evidence for a complex pre uralian metamorphic and deformational history of the precambrian basement at the southeastern margin of the eec interpretation of the k ar ages considered the variation of secondary foliation and the diagenetic to metamorphic grade in the yamantau anticlinorium the greenschist facies metamorphism of the mesoproterozoic siliciclastic rocks is of early neoproterozoic origin about 970 ma and the s1 cleavage formation of late neoproterozoic about 550 ma the second wide spaced cleavage is of uralian origin in the central and western part of the bma the diagenetic to incipient metamorphic grade developed in late neoproterozoic time in post uralian time proterozoic siliciclastic rocks with a cleavage of uralian age have not been exhumed to the surface of the bma late neoproterozoic thrusts and faults within the eastern margin of the eec are reactivated during the uralian deformation

main uralian thrust and main uralian normal fault non extensional palaeozoic high p rock exhumation oblique collision and normal faulting in the southern urals the crustal architecture of the southern urals is dominated by an orogenic wedge thrusted westward upon the subducted east european continental margin the n s trending wedge constitutes an antiformal stack composed mainly of the high p maksyutov complex the overlying suvanyak complex and the allochthonous synformal zilair flysch further west these tectono metamorphic units are separated by tectonic contacts and record discontinously decreasing metamorphic conditions from bottom to top in the east the e dipping main uralian normal fault cross cuts the metamorphic footwall and juxtaposes the non metamorphic magnitogorsk island arc this syncollisional normal fault compensated crustal thickening and exhumation of the high p rocks orogenic shortening was accommodated by the main uralian thrust a w vergent crustal scale shear zone at the base of the wedge geological investigations and reflection seismics urseis 95 argue in favour of a geodynamic evolution integrating subduction and basal accretion of high p rocks during sinistral oblique thrusting along the main uralian thrust and coeval normal faulting along the main uralian normal fault

the structural architecture of the footwall to the main uralian fault southern urals abstract the uralide orogen is a linear collisional belt formed during the upper paleozoic as a result of convergence between the east european craton and outboard terranes and accretion of intervening island arcs and obduction of oceanic crust onto the east european craton this paper presents a new structural subdivision of the southern urals to the west of the main suture zone that puts this part of the mountain belt in a context similar to that of other collisional orogenic belts this subdivision consists of a west vergent thrust stack that is made up of an autochthonous to parautochthonous foreland basin and a parautochthonous foreland thrust and fold belt flanked to the east by a metamorphic thrust stack the latter units are structurally overlain by allochthonous rocks of an accretionary complex slope sediments oceanic crust and high grade eclogite blueschist bearing gneiss where possible these units are defined on the basis of their internal stratigraphy and structure and on the nature of their bounding faults

annealing kinetics of fission tracks in zircon an experimental study a series of laboratory annealing experiments on zircon fission tracks has been carried out under heating conditions of 350 750 c for 10 1 103 hr i e 4 5 min 40 days variation in the confined lengths of spontaneous fission tracks was determined using zircon grains from nisatai dacite the fading contours of normalized mean track length r on the arrhenius diagram showed as sets of straight lines we performed a series of model fittings called the parallel and fanning models in order to describe the decrease in r with increasing temperature or heating time the lowest temperature limit of the zircon partial annealing zone zpaz was defined as r 0 95 and the highest as r 0 4 which approximately corresponded to the total fading of surface tracks extrapolation of the results of the laboratory experiments to the geological timescale gives for a heating duration of 106 yr estimated values of the zpaz of 210 320 c 60 c 2 with the parallel model 190 350 c 50 c 2 with the fanning model critical temperature t0 and 170 390 c 50 c 2 with the fanning model t0 the temperatures of the zpaz decrease by 20 c for an annealing duration that is an order of magnitude longer because the estimated closure temperature of zircon fission track analysis approximately corresponds to the middle of the zpaz these results support the previously estimated closure temperature of 240 c by varying the etching time it was revealed that significant removal of radiation damage occurs at r 0 93

initial soil development and carbon accumulation on moraines of the rapidly retreating werenskiold glacier sw spitsbergen svalbard archipelago article i nfo the rapid retreat of the werenskiold glacier the svalbard archipelago high arctic is leading to an extensive broadening of the proglacial zone covered with recent moraine till on older glacigenic deposits or directly on bedrock schists to study the type and intensity of initial soil development under a harsh periglacial climate a chronosequence of six soils was established between the glacier front and its terminal moraine on 1 to about 80 year old moraines although the surface layer over the entire area of study is frost active the patterned features are not well developed the succession of vegetation mainly saxifraga sp and lichens starts 5 6 years after deglaciation successively covering up to 30 of the soil surface then stagnating present day soil forming processes within the uppermost soil layer comprise initial weathering of primary minerals chlorites and amphiboles carbonate dissolution and base cation leaching associated with ph lowering accumulation of organic matter and nitrogen and an increase in pedogenically derived fe soil development measures are time related and in general fit a logarithmic model the intensity of transformation including organic carbon and nitrogen accumulation started at high rates comparable to those reported in low arctic and alpine environments however in the fourth fifth decade after deglaciation it reached a quasi steady state low annual precipitation is probably a crucial factor that controls plant succession and leaching of carbonates thus limiting mineral weathering organic matter accumulation and soil development on the werenskiold moraines

chemical weathering in the foreland of a retreating glacier chemical denudation rates and strontium isotope ratios in streams vary substantially and systematically in the foreland of the retreating bench glacier in south central alaska to study weathering of young glacier sediments we sampled 12 streams draining a chronosequence of till and moraine soils derived from cretaceous metagraywacke metapelite bedrock both sediment age and vegetation cover increase with distance from the glacier cation denudation rates decline with increasing distance from the glacier whereas silica denudation rates increase carbonate dissolution and sulfide oxidation account for roughly 90 of the solute flux from the youngest sediments biotite alteration accounts for 5 11 of the solute flux its peak contribution is found in the glacier outlet stream silicate weathering is the dominant reaction only in the oldest sediments in a laboratory dissolution experiment using fresh glacial sediment carbonate dissolution dominated the solute flux during the first 700 hours paralleling the behavior of young sediments in the field in contrast to trends in the field the silica flux did not increase after the carbonate was exhausted from the reactor a possible reason for this difference is that establishment of vegetation causes an increase in silicate weathering the 87sr 86sr ratio in the glacier outlet stream is greater than that in proglacial streams and in bulk rock due to a greater contribution of biotite weathering in the outlet than in proglacial streams strontium isotope ratios decline with sediment exposure age in the proglacial streams and are consistent with a carbonate source because the dominant weathering reactions in the young sediments are of carbonate and sulfide rather than silicate minerals weathering at the glacier margin is not an important long term sink for atmospheric co2

the distinction between caledonian burial and regional metamorphism in metapelites from north wales an analysis of isocryst patterns in snowdonia and ll n three prograde stages in metapelites gwna group to wenlock are recognized stage i with white mica crystallinity values 0 43 2 stage ii 0 43 0 26 2 stage iii isocrysts at 0 03 2 intervals are drawn separately for pelites above and below the sub arenig unconformity approximately concordant isocryst patterns characterize the unconformity in the northwestern and southeastern limbs of the snowdonia syncline whereas discordant patterns are developed northwest of the aber dinlle fault and at the closure of the ynyscynhaiarn anticline the contrasting patterns are the result of a pre arenig burial metamorphism in post tremadoc pelites belts of steep metamorphic gradient coincide with belts of high strain and a broad area of higher grade caradoc pelites coincides with the core of the snowdonia syncline the later metamorphism is related to caledonian deformation rather than to burial pelite alteration adjacent to small intermediate to acid plutons suggests emplacement before the caledonian regional metamorphism a close correlation exists between metabasite zones and metapelite stages

formation rates of smectites derived from two holocene chronosequences in the swiss alps the formation rate of smectitic components in alpine soils is derived from two chronosequences in the swiss alps covering a time span of 11 500 years the soils developed on granitic parent material the lithologies between the two chronosequences investigation areas however showed some distinct differences with respect to the main mineralogy and to a lower extent to the chemistry the chronofunctions of smectitic phase formation g kgclay year were fitted to data using an exponential formation model extensive mineral weathering resulted in significant losses of chlorite and mica and the corresponding formation of smectite and regularly and irregularly interstratified mica smectite this formation is especially pronounced in the early stages of soil formation our investigations reveal that the greatest changes in soil clay mineralogy of alpine soils on granitic or gneiss host material occur within the first 1000 3000 years of soil development at both investigation sites the annual formation rates are in a similar order of magnitude with 0 1 g kg year or even higher at the start of soil formation and with values 0 01 g kg year after about 7000 years the pedogenetic smectites from the e or bs horizons included several populations with various interlayer charges this heterogeneity seems to be related to the nature of their precursors

diagenesis and incipient metamorphism in the western fold and thrust belt sw urals russia in the western fold and thrust belt of the southern urals the kubler and arkai indices determined on shales slates and phyllites record an increase from lower late diagenetic to epizonal grade from west to east the metamorphic grade varies strongly within the different tectonic segments which are separated by major thrusts the increase of diagenetic and incipient metamorphic grade from the footwall to the hanging wall of all major upper palaeozoic thrusts indicates a pre permo triassic origin west of the avzyan thrust zone the diagenetic to incipient metamorphic grade is related to the palaeozoic basin development and reached the final grades in late carboniferous to early permian times east of the first avzyan thrust in the yamantau anticlinorium the diagenetic to lower greenschist metamorphic grade is possibly of neoproterozoic origin and might be related to the development of the neoproterozoic basin at the eastern margin of the east european craton the eastern part of the yamantau anticlinorium was exhumed below 200 c in the late carboniferous or early permian the diagenetic grade of the autochthonous palaeozoic sedimentary units increases toward the stack of palaeozoic nappes and might partly be caused by the deformational process due to the emplacement of the palaeozoic nappes within the timirovo thrust sheet the decrease of metamorphic grade with stratigraphic age developed prior to the emplacement of the nappes the upper anchizonal metamorphic grade of the upper devonian slates of the zilair nappe results from the deformation process related to the lower carboniferous nappe emplacement

variations in weathering processes and rates with time in a chronosequence of soils from glen feshie scotland chemical and mineralogical characteristics have been determined for a chronosequence of six soil profiles ranging in age from 80 13 000 years bp developed on river terraces in the western cairngorms of scotland the c horizons are similar chemically and mineralogically and the soils have similar pedogenetic histories exchangeable ca and mg decrease with time and base saturation decreases exponentially from 24 6 in the ah horizon of the youngest profile to 2 8 in the comparable horizon of the 10 000 year old profile according to the chronofunction y 3 372 22 612 exp 0 0007365t long term weathering rates of base cations calculated from the loss of these cations relative to zr appear to decrease exponentially with time but this may be due to the method of calculation the magnitude of loss of base cations decreases in the sequence na k mg ca but when the relative mobilities of these elements are considered the loss is in the order mg na ca k this reflects the dissolution of chlorite and loss of mg and the more rapid weathering of plagioclase feldspar and loss of na and ca particularly in the coarse sand fraction than k feldspar the clay fractions although 2 of all horizons also show distinct patterns with age in that chlorite and mica are less abundant in older soils and vermiculite is more abundant the latter phase often having hydroxyaluminium polymers in the interlayer region the chemical and mineralogical trends in the soil sequence are closely associated and are induced by pedogenic weathering

preserved collisional crustal structure of the southern urals revealed by vibroseis profiling the vibroseis reflection profiling component of the urseis 95 experiment provides a high resolution crustal scale image of the unextended southern uralide orogen a marked lateral and vertical variation of reflectivity throughout the entire crust differentiates the former margin of the east european craton to the west from accreted terranes to the east between these regions is a less reflective zone corresponding to the magnitogorsk volcanic arc and the crustal root zone continuous reflections and reflective domains that correlate at the surface with major tectonic features define a bivergent orogen in which the paleozoic collisional structure has been largely preserved